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Kinetic Study of Stable Free Radical Polymerization
in Miniernulsion
BY
Jodi Smith
A thesis submitted to the Department of Chernical Engineering
in confonnity with the requirements for
the degree Master of Science (Eng.)
Queen's University
Kingston, Ontario, Canada
September, 200 1
Copyright O Jodi Smith, 200 1
Acquisitions et IC Setvices senriCBS bibiiographiques
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Abstract
Traditionally, well-defined rnacromolecular architectures and advanced
polymeric materials have only bein mainable through methods such as living ionic
polyrnerizations. The dificulties associated with these processes, including the
rigorous purification of reagents and monomers, complicate industrial scale synthesis.
Stable fiee radical polymerization (SFRP) provides a potential pathway for
controlling the macromolecular structure under less demanding reaction conditions.
The key to SFRP is the reversible exchange reaction between a propagating radical
and the nitroxide, which significantly reduces termination in the system and allows
for a controlled polymerization.
The primary objective of this work was to develop a better kinetic
understanding of SFRP in miniemulsion. Unimolecular initiators that dissociate to
provide both the initiating radical and nitroxide were investigated for potential
application in miniemulsion SFRP using BST and hydroxy-BST. BST and hydroxy-
BST are benzoylstyrl radicals terminated by 2,2,6,6- tetramethylpiperidinyloxy
(TEMPO) and 4-hydroxy-2,2,6,6- tetramethylpiperidinyloxy (4-hydroxy-TEMPO)
respectively. The influence of unimer concentration, system heterogeneity and
additives was specifically addressed using these alkoxyamines- In addition, TEMPO-
tenninated oligomers of polystyrene (TTOPS) were utilized as macroinitiators and the
SFRP of butyl acrylate was explored.
Conversions reaching 95 % were obtained for TTOPS initiated styrene
poIyrnerizations in 1.5 hours at high Ievels of surfactant. In addition, TTOPS
polymerizations could be performed in the absence of a costabilizer with faster
reaction rates and no change in the colloida[ stability of the emulsion.
The alkoxyamine concentration and differing partitioning characteristics of
the nitroxides did not greatly influence the kinetics of SFRP in miniemulsion. The
polymenzation rate in both bulk and miniemulsion was determined to be largely
dependent on the thermal polymerization rate of styrene. Larger polymerization rates
and greater deviation between experimental and theoretical molecular weights were
obtained in bulk. The source(s) of these differences is currently not established.
A small improvement in the rate of SFRP in miniemulsion was observed with
both camphorsulfonic acid (CSA) and acetic anhydride. L-ascorbic acid
demonstrated the greatest potential for rate enhancement however, uncontrolled
polyrnerizations resulted. Rate improvements were also significantly smaller than
observed in bulk systems. which is thought to result tiom partitioning ofthe additives
to the aqueous phase.
SFRP in miniemulsion with butyl acrylate was relatively unsuccesstùl due to
the buildup of nitroxide in the system and the absence of any significant thermal
polymerization. Polymerization rates were dramatically improved with the use of 4-
oxo-TEMPO and benzoyl peroxide (BPO) as the bimolecular initiation system.
We anticipate that the results tiom this investigation will aid in the kinetic
understanding of SFRP in miniemulsion using unimolecular initiators. In addition,
this study has already assisted in the deveIopment of mathematical models for
alkoxyamine-initiated styrene polymenzations in miniemulsion.
Acknowledgments
I would like to thank my supervisor, Dr. M.F. Cunningham, whose enthusiasm
sparked my interest in this work His direction, support and advice throughout this
project is greatly appreciated.
John Ma, Trish Witfy and Karine Tortosa deserve a big thank you for their
support and help in lab. I would tike to especially thank Karine, who took a special
interest in this project and contributed greatly to my work. Also, 1 rnust extend special
thanks to John for aiding me with the lab technical problems and providing me with
valuable guidance and advice
1 would also Iike to extend my thanks to Dr. Mchael K. Georges and Barkev
Keoshkerian at the Xerox Research Centre of Canada, who taught me to prepare BST,
provided valuable advice and kept me entertained. 1 would tùrther like to thank those at
Xerox who helped with the anaiysis in my work.
Steve Hodgson, Martin York and Shelley Timmons also deserve thanks for their
technical support. Without their assistance my experimental work and thesis wouid not
have been possible.
Finall y, 1 must thank my famiiy, Eiiends, fellow gradoate students and the
Department of Chemica! Engineering for their support dong the way.
Table o f Contents
Chapter 1
1. Introduction
Chapter 2
2. Literaiure Review 2.1 Miniemuision Polymerization
2.1.1 OveMew of Emuision Polperization 2.1.2 O v e ~ e w of Miniemulsion Polymehtion 2.1.3 Kinetics
2.2 Stable Free Radid Polymerization (SFRP) 2.2.1 Process OveNiew 2.2.2 Rate Enhancement 2.2.3 Unimolecular [Ntiatols 2.2.4 Kinetics 2,2.5 Acrylate Monomers 2.2.6 Stable Free Radical Polymerization in ErnuIsion
Chapter 3
3. Erperimenlal 3.1 Materials
3.1.1 Monomer Pltrification 3.2 Initiators and Nitrozrides
3.2.1 BST Synthesis 3.2.2 Hydrosy-BST Sqnthesis 3.2.3 ROPS Repasauon
3.3 Experimental Apparatus 3.4 Miniernuision Polymerizations
3.4.1 Preparation 3.4.2 Additives 3.4.3 PolymerUatian
3.5 Bulk Polyrnerizations 3 .S. 1 Pceparation 3.5.2 Polymerization
3.6 Repmducibility
Chapter 4
4. Analytical Procedures 4.1 Gravirneaic Analysis 4.2 Ge1 Permeation Chromatography (GPC)
4.2.1 Equipment 4.2.2 Calibralion Cume 4.2.3 SampIe Preparation
4.3 Particle Size Distributions 4.3.1 Equipment and Theory of Operation 4-32 Stamiard ûpaüng nocedure [SOP) 4.3.3 Sampie Analysis 4.3.4 Monomer Droplet Stability
4.4 Influence of Hydm.uy-BST Purification Rocdure 4.4. L Influence of Purification on Polymerimtion Rate and Molecular Weight
Chapter 5
Unimolecular Initiators in Miniemulsron 5.1 Experimental 5.2 Polymerization Results 5.3 BST Polymerization Results
5.3.1 Fractional Conversion 5.3.2 Number Average Molecular Weight 5.3.3 Particle Size and Particle Size Distribution
5.4 Kydro.xy-BST Polymerization Results 5.4.1 Fractional Conversion 5.4.2 Number Average Molecular Weight 5.4.3 Particle Size and Particle Size Distribution
5.5 Comparison of BST and Hydro.xy-BST Systems 5.5.1 Polymerization Results 5.5.2 Fractional Convenion 5.5.3 Number Average Molecular Weight
5.6 Conclusions
Chapter 6
6. Unjmoleailar Initiators in Bulk SFRP 6. I Evperimental 6.2 Polymerization Results
6.2.1 Fractional Conversion 6.2.2 Number Average Molecular Weight
6.3 Cotnparison of BST and Hydroy-BST Systems in Buk 6.3.1 Fractionai Conversion 6.3.2 Number Average Molecular Weight
6.4 Comparison of Bulk and Miniernuision SFRP 6.4.1 Fractional Conversion 6.4.2 Number Average Molecular Weight
6.5 Influence of He.xadecane Dilution in Buk 6.5.1 Fractional Conversion 6.5.2 Number Average Molecuiar Weight
6.6 Conclusions
Chapter 7
7. Use ofAdditives in Minietmilsion SFRP 7.1 Experimentai 7.2 CSA Results
7.2.1 Fractional Convenion 7.2.2 Number Average Molecular Weight and MoIecular Weight
Distriaution 7.2.3 Paxticle S k and Particle Size Distribution
7.3 Muence of Acetic Anhydride 7.3.1 Fractionai Conversion
7.3.2 Number Average Molecular Weight and Molecular Weight Dism3ution
7.3.3 Particle Size and Particle Size Disaibution 7.4 Muence of L-Ascorbic Acid
7.41 Fractionai Conversion
7.4.2 Number Average Molecular Weight and Molecular Weight Dimibution 7.4.3 Particle Size and Particle Size Distribution
7.5 Conclusions
Chapter 8
8. ?TOPS in Miniemilsion 8.1 E?cperimental 8.2 Polymerizrition Resulu 8.3 Mluence of T O P S Initiator and Heudecane
8.1.1 Fractional Conversion 8.1.2 Number Average Molecuiar Weight 8.1.3 Pamcle Size and Particle Size Distibution
8.4 infiuence of Surfactant Concentration 8.4.1 Fractional Conversion 8.4.2 Number Average Molecular Weight 8.4.3 Pamcle Size and Pasticle Size Distribution
8.5 inîiuence of Hexadecane and Surfactant Conceniraiion in BST Synem 8.5.1 Fractional Convenion 8.5.2 Number Average Molecular Weight 8.5.3 PYticle Size and Particle Size Disuibution
8.6 Conclusions
Chapter 9
9. Bzrtyi Acwlate SFRP 9.1 Evperimentai 9.2 Polymerization Results
9.2.1 4-0x0-TEMPO Nitmide 9.3 ûther Polymerizations
Chapter 10
10 Conclusions
98 99
LOO
LOO
Chapter 11
11 Recommendations
References
Appendù A: Typical NMR Spctra
B. Additional Polymerizaiions B. 1. Polymerizations with 44x0-TEMPO
B. 1.1 Styrene Polymerizations B. 1.2. Butyl Acrylate Polymerizations
8.2. Polymerizations with Unimoldar Initiators B.2.1 Additional Styrene Polymerizations with Unimolecular Initiators B.2.2 Butyl Acrylate Polymerizations with Unimolecular Initiators
0.3 Polymerizaiions with CSA 8.3.1 Butyl Acrylate Polymcrizations
834 Polymerizations with Varied D1W:Styrene Ratio B.4.1 Styrene Polymerizations B.J.2 Buel Acrylate Polymerizations
6.5 Autopolymentation Study B.5.1 Styrene Autopolymerization 8.5.2 ButyI Acrylate Aut~polyneri~on
9.6. Cornpartmentaiization Shi@ 8.7 pH Adjustrnent in Miniernulsion Systetns using KPS 8.8 Additional Runs with Ascorbic Acid
Appendix C C. Addirional Particle Site Disnibutions
List of Tables
Table 2.1 : Changes in Kinetic Variables during Miniemulsion Polymetization
Table 3.1 : List of Materiais Used in Polymerizations
Table 3.2: Lists of Solvents and other Matenals Used in Shidy
Tabte 3.3: Standard Miniemulsion Formulations for 300 ml and t .O t Reacton
Table 4.1 : Separation Range of CoIumns used in GPC
Tabte 4.2: Standard Operating Procedure Settings
Table 4.3: Miniemulsion Formulation for Droplet Stabiiity Study in 1 .O L Reactor
Table 4.4: Volume Weighted Mean Diameters of SampIes in Droplet Stability Experiment
Table 5.1 : Summary of Run Conditions for Unimer Study in Miniernulsion
Table 5.2: Summary of Unimer Miniernulsion Polymerization Results
Table 5.3 : Summary of Thermally Generated Chains and Corrected F,,
Table 5.4: Summary of Volume Weighted Mean Diameters for BST Polymerizations
Table 5.5: Summary of Volume Weighted Mean Diameters for Hydroxy-BST Polymerizations
Table 6.1 : Summary of Run Conditions for Unimer Study in Buik
Table 6.2: Summary of Unimer Bulk Polymerization Results
Tabie 6.3: Summary of Results for Buik Run with Hexadecane
Table 7.1: Surnmary of Run Conditions for Unimer Study with Additives
Table 7.2: Summary of Results for Unimer Study with CSA
Table 7.3: Summary of Volume Weighted Mean Diameters for CSA Study
Table 7.4: Summary of FinaI Resuks for BST Polymerization Using Acetic Anhydride
Table 8.1: Summary of TTOPS Run Conditions
Table 8.2 : Summary of Final TTOPS Polymerization Results
Table 8.3: Summary of Volume Weighted Mean Diameters for TTOPS Polymerizations (E-iexadecane Study)
Table 8.4: Summary of Volume Weighted Mean Diameters For TTOPS Polymerizations (SDBS Study)
Table 9.1 : Run Conditions for Butyl Acry late Polymerizations
Table 9.2: Summary of Resutts for Butyl Acrylate Polymerizations using Bimolecular Initiation
Table B 1: Surnmary of Run Conditions for Styrene Polymerizations using 4-0x0-TEMPO
Table B2: Surnmary of Final Resuits for Styrene Polyrnerizations using 4-0x0-TEMPO
Table B3: Summary of Run Conditions for Butyl Acrylate Polymerizations using 4-0x0-TEMPO and BPO
Table 84: Summary of Final Results for Brityi Acrylate Polymerizations using 4-0x0-TEMPO and BPO
Table BS: Sumrnary of Run Conditions for Styrene Polymerizations using Unirners
Table B6: Summary of Final Results for Styrene Polymerizations using Unimers
Table B7: Summary of Run Conditions for But$ Acrylate Polymerizations using Unimers
Table B8: Summary of Final Results for Butyl Acrylate Polymerizations using Unimers
Table B9: Summary of Run Conditions for ButyI Acrylate Polymerizations using CSA
Table B 10: Summary of Results from Butyl Acrylate Polymerizations using CSA
Table B 1 1: Summary of Run Conditions for Styrene Polymerizations with Varied Amounts of D W
Table B 12: Summary of Final ResuIts for Styrene Polymerizations with Varied Amounts of DiW
Table B 13: Surnmary of Run Conditions for Butyl Acrylate Polymerizations using Varied Arnounts of DiW
Table B 14: Summary of Results 6om Butyi AcryIate Polymerizations using Varied Arnounts of DiW
Table B 15: Summary of Styrene Autopolymerization Results B7
Table B 16: Surnmary of Run Conditions for Compartmentalization B9 Study
Table B 17: Summary of FinaI Results for Companmentalization B9 Study
Table B 18: Summary of Run Conditions for Buffered KPSJTEMPO System
Table B 19: Summary of Buffered Polymerization Results for KPS/TEMPO System
Table B20: Summary of Run Conditions for BuEFered KPS/Hydroxy-TEMPO System
Table B2 1 : Sumrnary of Buffered Polymerization Results for KPSMydroxy-TEMPO S ystem
Table B22: Summary of Experimentd Conditions for AdditionaI B 12 Runs with L-Ascorbic Acid
Table 823: Summary of ResuIt. for AdditionaI Runs with L-Ascorbic Acid B 12
List of Figures Figure 2.1: Chernical Structure of Benzyl-TEMPO Derivative Sîudied by Hawker et al. ( 1996)
Figure 2.2: Chemical Structure of a-Phenyl-a-Isopropyl Derivative
Figure 3.1 : Diagrarn of 300 ml Reactor
Figure 3.2: Diagram of 1 .O L Reactor
Figure 4.1 : Droplet Size Distributions for Droplet Stability Study (a) Zero sample taken directly after microfluidization (b) Sample taken at 3 hours
Figure 4.2: Influence of DIW Extraction on Hydroxy-BST Conversion
Figure 4.3: Influence of DIW Extraction of Hydroxy-BST on Mn
Figure 5.1 : Influence of BST Concentration on Conversion in Minemulsion
Figure 5.2: Influence of BST Concentration on Mn in Miniernulsion
Figure 5.3: Particle Size Distributions for SFRMP-74 (a) Zero Sample (b) 3 Hours (c) 6 Hours (d) Overlay
Figure 5.4: Influence of Hydroxy-BST Concentration on Conversion in Miniernulsion
Figure 5.5: influence of Hydroxy-BST Concentration on Mn in Miniemulsion
Figure 5.6: Particle Size Distributions for SFRMP-8 1 (a) Zero Sample (b) 3 Hours (c) 6 Hours (d) Overlay
Figure 5.7: Influence of Unimer on Polymerization Rate in Miniemulsion (a) 0.007 M (b) 0.014 M (c) 0.020 M
Figure 5.8: Influence of Unimer on Mn in Miniernuision (a) 0.007 M (b) 0.0 14 M (c) 0.020 M
Figure 5.9: Influence of Unimer on Number of Chains in Miniemulsion (a) 0.007 M (b) 0.014 M (c) 0.020 M
Figure 6.1 : Influence of BST Concentration on Conversion in Bulk
Figure 6.2: Influence of Hydroxy-BST Concentration on Conversion
Figure 6.3: Influence of BST Concentration on Mn in Buik
Figure 6.4: Influence of Hydroxy-BST Concentration on M, in Bulk
Figure 6.5: lnfluence of Unimer on Bulk Polymerization Rate (a) 0.007 M (b) 0.0 14 M (c) 0.020 M
Figure 6.6: Influence of Unimer on Mn in Bulk (a) 0.007 M (b) 0.014 M (c) 0.020 M
Figure 6.7: Intluence of Poly rnenzation System on Conversion (a) 0.007 M BST (b) 0.014 M BST (c) 0.020 M BST
Figure 6.8: lntluence of Poiymerization System on Conversion (a) 0.007 M Hydro~y-BST (b) 0.014 M Hydroxy-BST (c) 0.020 M Hydroxy-BST
Figure 6.9: Influence of Polymerization System on Mn-Conversion Profile for SST
Figure 6.10: [nfluence of Polymerization System on Mn-Conversion Profile for Hydroxy-BST
Figure 6.1 1 : Influence of Hexadecane Dilution on Conversion in Bulk
Figure 6.1 1 : Influence of Hexadecane Dilution on Mn in Bulk
Figure 7. i : Influence of CSA on Polyrnerization Rate in BST S ystem
Figure 7.2: Influence of CSA on Polymerization Rate in Hydroxy-BST System
Figure 7.3: Influence of CSA on Mn in BST System
Figure 7.4: Influence of CSA on Mn in Hydroxy-BST System
Figure 7.5: influence of CSA on Polydispersity in BST System
Figure 7.6: Muence of CSA on Polydispersity in Hydroxy-B ST Sy stem
Figure 7.7: Particte Size Distribution for SFRMP-99 (a) Time zero (b) 3 hours (c) 6 hours (d) overlay
Figure 7.8: Particle Size Distribution for SFRMP- 100 (a) Time zero (b) 3 hours (c) 6 hours (d) overlay
Figure 7.9: Influence of Acetic Anhydride on Polymerization Rate in BST System
Figure 7. IO: Influence of Acetic Anhydride on Mn in BST System
Figure 7.1 1: Influence of .\cetic Anhydride on Polydispersity in BST System
Figure 7.12: Particle Size Distribution for SFRMP-105 (a) Time zero (b) 3 hours (c) 6 hours (d) overlay
Figure 7.13: Influence of Additives on Polymerization Rate In BST System
Figure 7-14: Molecular Weight Distribution for SFRMP-IO8
Figure 7.15: Particle Size Distribution for SFRMP- IO8 (a) Time zero (b) 3 hours (c) 6 hours (d) overlay
Figure 8. i : Influence of Hexadecane on Conversion in TTOPS Polymerizations
Figure 8.2: Influence of Hexadecane on Mn in TTOPS Polymerizations
Figure 8.3: Particle Size Distributions for SFRMP-I 14 (a) zero sample (b) 3 hours (c) 6 hours (d) overlay
Figure 8.4: lnfluence of SDBS Concentration on Conversion Using Macroinitiator (B)
Figure 8.5: Influence of SDBS Concentration on Conversion using Macroinitiator (A)
Figure 8.6: Mluence of SDBS Concentration on Mn for Macroinitiator (B)
Figure 8.7: infiuence of SDBS Concentration on Mn for Macroinitiator (A)
Figure 8.8: Particle Size Distributions for SFRMP-122 (a) zero sample (b) 3 hours (c) 6 hours (d) oveday
Figure 8.9: Influence of Hexadecane and Sudictant Concentration on BST Conversion
Figure 8.10: Influence of Hexadecane and Surfactant Concentration on BST Mn
Figure 8.1 1: Particle Size Distributions for SFRMP-124 (a) zero sample (b) 3 hours (c) 6 hours (d) 24 hours (e) overIay
Figure 9.1 : Influence of Initiaior on Conversion in Butyl Acrylate Polyrnerizations using 4-0x0-TEMPO
Figure 9.2: Influence of initiator on hZ, in Butyl Acrylate Polymerizations using 4-0x0-TEMPO
Figure C 1 : Particle Size Distributions for SFRMP-74 (a) 1.5 hours (b) 4.5 hours (c) 12 hours
Figure C2: Particle Size Distributions for SFRMP-75 (a) Zero Sample (b) 1.5 hours (c) 3 hours (d) 4.5 hours (e) 6 hours ( f ) 12 hours
Figure C3: Particle Size Distributions for SFRMP-78 (a) Zero Sarnple (b) 1.5 hours (c) 3 hours (d) 4.5 hours (e) 6 hours (f) 24 hours
Figure C4: Particle Site Distributions for SFRMP-79 (a) Zero Sarnple (b) 1.5 hours (c) 3 hours (d) 4.5 hours (e) 6 hours (f) 24 hours
Figure CS: Particle Size Distributions for SFRMP-8 L (a) 1.5 hours (b) 4.5 hours (c) 12 hours
Figure C6: ParticIe Size Distributions for SFRMP-82 (a) 1.5 hours (b) 3 hours (c) 4.5 hours (d) 6 hours (e) t 2 h o m
Figure C7: Particle Size Distributions for SFRMP-96 (a) Zero Sample (b) 1.5 hours (c) 3 hours (d) 4.5 hours (e) 6 hours [ f ) 24 hours
CIO
Figure CS: Particle Size Distributions for SFRMP-99 (a) 1.5 hours (b) 4.5 hours (c) 8 hours
Figure C9: Particle Size Distributions for SFRMP-100 (a) 1.5 hours (b) 4.5 hours (c) 8 hours (d) 24 hours
Figure C 10: Particle Size Distributions for SFRMP-IO5 (a) 1.5 hours (b) 4.5 hours (c) 24 hours
Figure C t 1: Particle Size Distributions for SFRMP-108 (a) 1.5 hours (b) 4.5 hours (c) 22 hours
Figure C 12: Panicle Size Distributions for SFRMP-113 (a) zero sample (c) 1.5 hours (c) 3 hours (d) 4.5 hours (e) 6 hours
Figure C 13: Particle Size Distributions for SFRMP-114 (a) 1.5 hours (b) 4.5 hours (c) 24 hours
Figure C 14: Panicle Size Distributions for SFRMP-I 19 (a) zero sampte (d) 1.5 hours (c) 3 hours (d) 4.5 hours (e) 6 hours
Figure C 15: Panicle Size Distributions for SFRMP-120 (a) zero sample (e) 1.5 hours (c) 3 hours (d) 4.5 hours (e) 6 hours
Figure C 16: Panicle Size Distributions for SFRMP-122 (a) 1.5 hours (f) 4.5 hours
Figure C17: Panicle Size Distributions for SFRMP-124 (a) 1.5 hours (b) 4.5 hours
Nomenclature
BPO- Benzoyl Peroxide
BST- Benzoylstyrl RadicaI Terminated by 2,2,6,&tmamethyIpipendinyloxy
CSA- CamphorsuIfonic Acid
D, - Volume Weighted MW Diameter
DIW- Deionized Water
Fa,, - Apparent Initiator Eficiency
F,,,,,,,d - Corrected Initiator Eniciency
HBST - Benzoylstyrl Radical Terminated by 4-hydroxy-2,2,6,6- tetramethylpiperidinyloxy
1 - Initiator
j - TEMPO, CHydroxy-TEMPO
KPS- Potassium Persulfate
[j],,, - Concentration of j in the Organic Phase
lilas - Concentration of j in the Aqueous Phase
kd - Rate Constant for Initiator Dissociation (f ')
ki - Rate Constant for Monomer Addition to Prirnary Radical (~mol-'<l)
kt - Rate Constant for Deactivation Reaction (LMOI-' S-')
k-t - Rate Constant for Activation Reaction (s")
Kt - EquiIibrium Constant for Deactivation/Activation Reaction &morl)
- Rate Constant for Propagation Reaction (&mol-'i')
b, ktd - Rate Constants for Termination by Combination and Disproponionation respectively (mol-'sa')
kt - Rate Constant for Termination (Lm&-')
xvi
ka - Rate Constant of Thennal Polymerization ~ ~ m o l ~ ~ s - '
Li - Dormant PoIymer Chain
M - Monomer
[Ml - Monomer Concentration
MI' - Styrene Monorneric Radical
Mi - Styrene DimeRc Radical
Mn - Number Average Molecular Weight
Mn ,, - Experimental Number Average Molecular Weight
Mn - Theoretical Number Average Molecular Weight
IM], - Monomer Concentration in the Polymer Particles
M,JMn - Polydispersity
MW, - Molecular Weight of Monomer
n - Average Number of Radicals per PanicIe
N, - Avogadros Number
Pl' , PiS* Pis, Pi-,' - Gmwing PoIyrner Chains
Pi+, Pi, Pj - Dead PoIymer Chains
C p l - Total Concentration of Propagating Polymer Chains
Pj - Partition Coefficient for Species j between Styrene and Water
P-TI- Concentration of Dormant AIkoxyamine
F-T], - Initial Concentration of Alkoxyarnine
R' - Prirnary Radical
Ri - Overall Rate of Thermd andtor Conventional Initiation (rnoIL"s-')
- Rate of Polymerkation (molL"~-~)
SDBS - Sodium Dodecyl Benzenesulfonate
SFRP - Stable Free Radical Polymerization or "Living" Radical Polymerization
SFRMP - Stable Free Radical Miniemulsion Polymerization
t - tirne
T' - Stable Free Radical
[Tl - Concentration o f Stable Free Radical
TEMPO - 2,2,6,6-tetramethylpiperidinyloxy TTOPS - TEMPO Teminated Oligomers o f Polystyrene
x - Conversion
Chapter 1
1. Introduction
Traditionally, accurate control over macromolecuiar structure was only attainable
through living ionic polymerizations. While offering a high degree of control these
methods are limited by demanding reaction conditions, including the rigorous
puritkation of monomers and other reagents. In addition, the chain ends in these
polymerizations are incompatible with a wide variety of tlnctional groups. Radical
polymerization on the other hand, is a synthetically Iess demanding process.
Conventional radical polymerizations however. cannot be employed to control
macromolecular structure because of the high degree of termination reactions. Recent
advances in the area of stable fiee radical polymerization (SFRP), or "living" tiee r a d i d
polymerization, have allowed the preparation of narrow polydispersity polymers with
accurate control over molecular weight and macromolecular structure. Early work in this
area was generally restricted to buIk systerns, which are not easily applicable to large-
scale production. The commercial importance ofemulsion polymerization makes it a
more attractive system for SFRP development. Emulsion polymerizations maintain a
lower viscosity, improved heat uansfer and a lower amount of chain termination than
their homogeneous counterparts. Utilizing a miniemdsion polymerization improves the
stabiiity and simplifies the kinetics of particle nucleation over traditional emulsion
systems.
In this investigation, SFRP is employed in miniemulsion. Aithough a good
understanding of bulk SFRMP has been developed, the mechanisms and kinetics in
miniernuision are not yet well documented. Complications such as nitroxide partitionhg
and cornpartmentalization are also introduced in heterogeneous systerns. The main
objective of this study was to irnprove the kinetic understanding of SFRP in
miniemulsion. In panicular, improving monomer conversion in shoner reaction times,
while maintaining accurate control over molecular weight and namw polydispersities
were major goals of this work. Several areas were explored in order to gain a better
appreciation for the influence of systern heterogeneity on the characteristics of SFRP and
included the following:
i Implernentation of Unirnolecular lnitiators (Unimers) including :
Effect of varying unimer level
Comparison of BST and hydroxy-BST unimers
Comparison of miniernulsion systems with bulk systems
influence of rate-enhancing additives
Use of TEMPO-terminated oligorners of polystyrene (TTOPS) as
initiating systems
Stable fiee radical polymerization of butyl acrylate in miniemulsion
The results of these experiments may aid in the kinetic understanding of SFRP in
miniemulsion. In addition, the data acquired could be usefiil for system modetng. The
number average molecular weight (Mn), polydispersity, conversion and particle size
distribution were used as the response variables to changes applied to the system.
Chapter 2
2. Literature Review
2.1. Miniernulsion Polymerization
2.1.1 Ovewiew of Emulsion Polymerization
Emulsion polymerization is commercially attractive as it offers several
advantages over homogeneous polyrnerizations, including lower viscosity, improved heat
transfer and a lower degree of chain termination resulting kom the separation of
propagating radicals (compartmentalization). In addition, this process is environmentaliy
safe and allows for fast reaction rates and the production of high molecular weight
polymers. The basic elements of a conventional emulsion system include monomer,
water. surfactant and a fiee radical source. Typically, a water-soluble initiator is
employed although oil-soluble initiators have also been successfully used. Mixing of the
monomer. water and surfactant above the critical micelle concentration (CMC) results in
an emulsion consisting of monomer swollen micelles, surfactant stabilized monomer
droplets and some monomer dissolved in the aqueous phase. Pnor to the onset of
polymerization approximately 99 % of the monomer is Iocated in the monomer droplets
(Gilbert, 1995). typicaily on the order of 1-10 pm with number densities between 10'-
10" dmJ. The swolIen micelles cornrnoniy have diameters between 50-150 A with much
higher number densities ( 1 0 ~ ' - 1 0 ~ ~ than the monomer dmplets (El-Aasser et al.,
1997).
Using a water-soluble initiator. fiee radicals are generated in the aqueous phase.
Particle nucleation can then proceed by micellar, homogeneous, or droplet nucleation. In
theory al1 three mechanisms may be operative however, their relative contributions
depend on the surfactant concentration, monorner solubility in the aqueous phase and the
size of the monorner droplets (El-Aasser et ai.. 1997).
Primary radicals generated fiom the decomposition of the initiator in the aqueous
phase are ionic and thus do not directly enter the hydrophobic environment of the
monomer droplets or micelles. Instead these radicals will propagate by adding monomer
solubilized in the aqueous phase until a critical chain length for entry is achieved. At this
chain length, the radical is suficiently hydrophobic to enter the micelles andlor droplets.
Entry into a micelle or droplet is known as micellar nucleation and dropiet nucleation
respectively. Once inside polymeritation commences rapidly and poiymer particles are
formed. in both modes of nucleation, additional monomer is supplied by diffision from
the monomer droplets. Generally, droplet nucleation is considered insigniticant as the
total surface area of the droplets is small compared to that of the micelles. One in every
100-1000 micelles is entered by an oligoradical and succeeds in becoming a polymer
particle. Unnucleated micelles supply additional surfactant required to stabilize the
growing panicles (El-Aasser et ai., 1997).
Altematively, radicals propagating in the aqueous phase may continue to add
more monomer units until they are no longer soluble and precipitate out of solution to
f om primary particles. These primary particles are stabilized by surfactant molecules
and monorner is again supplied by the monomer droplets (El-Aasser et al., 1997).
2.1.2 Overview of Miniernulsion Polymerization
Miniemulsions differ fiom conventional emulsions in the size of the monomer
droplets, typically on the order of 50-500 nm. This is achieved by addition of a
costabilizer, which is generally a Iong chah aikane or alcohol with low molar mass and
low water-solubility. The low water-solubility hinders Ostwald ripening, the diffusion of
monomer fiom small monomer droplets to larger ones. In the case of alcohols, the
costabilizer can further serve to prevent droplet coalescence by creating a barrier at the
water-oil boundary (Sudol et al., 1997).
In contrast to conventional emulsion systems, the small size of the monomer
droplets in miniemulsion provides a large surface area for radical capture. The monomer
droplets thus serve as the primary locus of particle nucleation. Initial droplet size and
distribution play a major role in the polymerization kinetics and final particle size
distributions (Tang et al., 199 1).
2.1.3 Kinetics
The kinetics of emulsion polymeritations are complicated by the partitioning of
species between the aqueous and organic phases. The kinetics of miniemulsion
polymerizations can be described by an extension of the theory derived for conventional
emulsion systems. Traditional emulsion systems are most ofien described by three
intervals. Interva1 I is the particle nucleation stage, which is characterïzed by an
increasing rate of polymerization and an increase in the number of particles. All polymer
particles are created dunng this interval and typically 10-15 % of d l monomer is
consumed. The disappearance of micelles eom the system signifies the onset of interval
II. Sufficient monomer is present in the system during this interval to ensure the
concentration of monomer in the particles is constant and thus a constant rate of
polymerization is observed. The number of particles is also ideally constant in this
interval. The transition to interval iIi occurs at approximately 30-40 % conversion when
normally al1 of the monomer droplets have disappeared. This last interva1 starts with a
decreasing rate of polymerization resulting fiom a steady decrease in the concentration of
monorner in the particles. An increase in the polymenzation rate may also be observed
due to the gel effect. This interval persists until complete monomer conversion or when
the reaction terminates (Gilbert, 1995).
Recently the kinetics of miniemulsion polymerizations have been investigated by
Bechthold et al. (2000) using calorimetry. A styrene miniemulsion was prepared using
hexadecane. sodium dodecyl sulfate (SDS) and potassium persulfate (KPS) as the water-
soluble initiator, The calorimetric curves obtained fiom the miniemulsion
polyrnerizations showed three distinct intervals (1. üi, W), similar to the intervals
developed for conventional emulsion systems. The general characteristics of these
intervals are summarized in Table 2.1 on the next page.
In Interval1 of miniemulsion polymerization, the radical concentration within the
droplets is continually changing. This stage persists until a steady radical concentration
is achieved. In comparison to classical emulsion systems, the particle nucleation stage
was found to be shoner in miniemulsion. It was conchded fiom these results that a
criticai chain length for radical entry was required for droplet nucleation otherwise this
stage would not be observed. The slow rate of radical entry was believed to stem &om
the Iow monomer concentration in the aqueous phase (Bechthold et al., 2000).
Table 2.1. Changes in Kinetic Variables during Miniernulsion Polymerization (Bschthold et al.r2000)
-
- Region n Conversion
Where: % = the polymerization rate Np= monomer concentration in the polymer particles
n = average nurnber of radicals per particle
Unlike classical emulsion polymerization, interval iI. characterized by a constant
rate of polymerization, was not observed in this miniemulsion system. The absence of
this interval indicated monomer difision to the polymer particles was not involved in the
system kinetics (Bechthold et d., 2000). This observation was supported by previous
studies including investigations by MiIIer et al. (1995) and Choi et al. (1985), who also
did not report a region of constant reaction rate. Chamberlain et al. (1982) however,
observed a constant polymerization rate in hterval il in a miniemulsion system
compriseci of styrene, water, SDS and a dodecan-1-01 costabilizer.
interval III was analogous to a normal emukon systern and wss characterized by
a decrease in the rate of polymerization, resulting ffom a steady dedine in the monomer
concentration in the droplets. As indicated in Table 2.1, the number of free radicals per
particle was determined to be constant at 0.5 in this intervd. In region IV for the system
under study the rate was initially observed to increase followed by a decrease. The
increase in rate was explaineci by the onset of the gel effect, which leads to a decrease in
bimolecular termination and increase in the average number of fiee radicals per particte.
At higher conversion the rate decreased again because of monomer depletion in the
system (Bechthold et ai., 2000).
The kinetics of miniemulsion polymerizations were further investigated by
Bechthold et al. (2000) by examining the influence of particle size on the polymerization
rate. In miniemulsion, the monomer droplet size and hence particle size can be changed
by changing the concentration of surfactant. Employing this technique, the group found
the length of Interval 1 was relatively constant regardless of the particle size. This
provided support for the requirement of a critical chain length for radical entry. Evidence
for the droplet nucleation method was confirmed by the dependence of polymerization
rate on droplet size, with smaller sizes resulting in shorter reaction times (Bechthold et
al., 2000).
This group also studied the inff uence of initiator concentration at a constant
particle size. Particle nucleation (Interval 1) required a slightly longer time at Iower
Ievels of initiator. The length of the interval however, could only be shortened to some
extent before the level of initiator had no influence. This again supported the theory that
Interval 1 is governed by monomer addition to the primary radicals in the aqueous phase,
rather than the total concentration of chains produced. The kinetics of Interval iU were
unaffected by the amount of initiator employed and showed an average radical
concentration per radical to be constant at 0.5. The major influence of increasing the
initiator level was seen in Interva1 IV, where the gel effect was observed to begin at Iower
conversions and result in a decrease in reaction time. The amount of nucleated droplets
was aIso detennined to be independent of initiator concentration (Bechthold et al., 2000).
Miniernulsion simplifies the kinetics of emulsion significantly as particle
nucleation occurs mainly in the monomer droplets. The size and distribution of the
droplets can thus be used to manipulate the polymerization characteristics. Studies in
minemulsion are thus easier to anaIyze than conventional emulsions.
2.2. Stable Free Radical Polymerization (SFRP)
2.2.1 Process Overview
Radical polymerization is a synthetically robust process that is compatible with a
wide variety of monomers. Conventional radical polymerizations however, cannot be
employed to control macromolecular structure because of the high degree of temination
reactions. which result in broad polydisperisties and uncontrolled molecular weights.
Recent advances in the area of stable fiee radical polymerization, or "living" radical
polymerization have allowed the preparation of narrow polydispersity polymers with
accurate control over molecular weight and polymer structure.
The basic mechanism of fiee radical polymerization is outlined in Reactions 2.1
to 2.6 given on the next page.
4 Initiation I + 2R
Propagation P, -+A4 P l , @.3)
k tc
Termination P ,- +P, + PI., (2.4)
kP Transfer P ; +M + Pu + M - (2.6)
w here :
P, , P, -, P, -, P,+, . = Growing polymer chains
P,+, . P, , PI P,, = Dead polymer chains
M. = Monomeric Radid M = Munomer I = Initiator R = Primary radical
k, = Rate constant For initiator dissociation (s" )
k, = Rateconstant for monomer addition to prirnary radical (Lmol-'s-' )
k, = Rate constant for propagation reaction (Lmol-'s-' )
k, = Rate constant for transfer reaction (Lmol-' s-' ) k, , k ,, = Rate constants for termination by combinatio n
and disproportionation respectively (Lmol" S.' )
The key to control in "livingw radicai systems is the ability of the propagating
polyrneric radicaI to react reversibty with a stable Eee radical, typically a nitroxide, to
f o m a dormant alkoxyamine species as shown in Equation 2.7.
P-T , ' P W + T * (2.7)
k~
where:
P = Growing polyrner chain
T g = Stable fiee radical(nitroxide)
P- T = Dormant polymerchain
k, = Rate constant for deactivat~n reaction(L.mot's-' ) k, = Rate constant for activation reaction(s-')
K, = Equilibrium rate constant(L.motl)
At ternperatures above 100 OC, the C-ON bond of the dormant species is unstable
and can dissociate to reproduce an active poIymeric radical and a nitroxide molecule.
The polymer radical can then add more rnonomer units according to Equation 2.3 before
it is again deactivated by the nitroxide. The equilibrium shown in Equation 2.7 favors the
donnant polymer form (Kt = 2 . ~ ~ 1 0 " ' m o n at 125 O C . Fuhda et al., 2000). resulting in
a low concentration of propagating chains and a significant reduction in the Iikelihood of
termination in the system. The lack of premature temination, cornbined with the fast
exchange between dormant and propagating polymer forms and the inability of the
nitroxide to initiate new chains, gives the polymerization its living character. A narrow,
fairly constant polydispersity, typically below 1.5 (the theoretical lower lirnit for
conventional radical polymerization) and an incremental increase in molecular weight
with conversion characterize the living nature of the potymerization. The control
afforded by this technique aIlows for control over molecular weight, chain ends and
macromoIecular structure.
The rate of the polymerization is governed by Equation 2.8 show below.
where :
R, = Rate of polymerization (molL's")
Fr] = Concentration of monomer (rnolL' )
According to the rate equation above, the SFRP reaction rate should increase as
the concentration of fiee nitroxide decreases. A large deficiency in the nitroxide
concentration however, leads to a decrease in the level of control and may result in a
conventional radical polymerization. This is because at low levels of nitroxide the
presence of more radicals leads to rapid termination.
The influence of nitroxide IeveI was tirst observed in the early work conducted
by Georges et al. (1993). Bulk systems empioying styrene monomer, a benzoyl peroxide
(BPO) initiator, and 2,2,6,6-tetramethyl-L -piperidinyIoxy (TEMPO) as the nitroxide were
investigated. These initial polymerizations produced molecuiar weights up to 150,000
with narrow polydispersities (1.3 or less) that remained constant during the reaction. As
expected fiom Equation 2.7. the rate was observed to depend on the ratio of
TEMP0:BPO. Slower rates of polyrnerization and lower polydispersities and molecular
weights were obtained at higher ratios (Georges et al., 1993). These results indicated that
although slower reaction rates are observed at higher nitroxide levels, better control of the
polymerization rnay be gained. SimiIar results were demonstrated by MacLeod et al.
(1997) who also observed that the conversion and polydispersity could be infiuenced by
varying the initiatocnitroXide ratio. Buk polymerizations conducted using BPO,
TEMPO and styrene showed that at Iaw molar ratios (0.5: 1, TEMF0:BPO) insuficient
nitroxide was present, resuiting in low molecular weight dead potymer and a broadening
of the polydispersity.
2.2.2 Rate Enhancement
Autopolymerization is known to occur at the elevated temperatures required for
SFRP. Georges et al. (1995) showed that thermal initiation occurs even in the presence
of TEMPO. Thermally initiated radicals could result in a Iarger degree of bimolecular
termination and lead to a broadening of the polydispersity and a loss of livingness.
Shortening the reaction time decreases the amount of radicals generated by
autopolymerization and thus rate enhancement has received significant attention. In
addition, SFRP is also complicated by the buildup of excess nitroxide from termination
reactions, or low initiator efficiencies. This buildup shifis the equilibriurn reaction in
Equation 2.7 towards the dormant polymer fonn and uitimately decreases the rate of
polymerization. Removal of excess nitroxide fiom the system is therefore an effective
route for increasing the polymerization rate.
Early styrene bulk polymerizations using TEMPO and BPO required 70 hours to
reach conversions above 85 % (Georges et ai.. 1993). Addition of camp horsulfonic acid
(CSA) to this system (0.027 M) resulted in significant improvement in the pdymerization
rate with conversions reaching 92 % in 5.5 hours. The moIecular weight, conversion, and
poIydispersities were al1 observed to increase with the concentration of acid added
(Georges et al., 1994).
The mechanism of rate enhancement using strong organic acids, specificaiIy
CSA, was investigated by Veregin et al. (1996) in the polymerization of styrene using
TEMPO and BPO. ESR studies indicated that the concentration of TEMPO declined
dramatically after the addition of CSA compared to the same system without acid. The
main influence of CSA was thus determined to be the direct consumption of TEMPO. As
shown by Equation 2.7, decreasing the TEMPO concentration shifis the equilibrium
towards the propagating polymer fami and increases the rate of polymerization.
A less significant effect noted in the work of Veregin et al. (1996). was a -30%
increase in the ratio of k,,KL with the addition of CSA, This effect could be attributed to
either an increase in the rate of the activation reaction (kt), or a decrease in the rate of
chain deactivation by TEMPO (kt) (Veregin et al., 1996).
In addition to these findings. the presence of acid is also thought to decrease the
influence of autopolymerization. An investigation of the autopolymerization of styrene
in the presence of acids was undertaken by Buzanowski et al. (1992). Thermal
polymerization was shown to decrease significantly in the presence of CSA. This
decrease in rate was amibuted to a reduction of the amount of dimer in the proposed
Mayo mechanism of autopolymerization (Buzanowski et al., 1992).
CSA has also recently been shown to improve the rate of styrene polymerization
in emulsion. Tortosa et al. (unpublished), studied the influence of CSA in miniernulsion
employing a BPO initiator and either TEMPO or Chydroxy TEMPO as the nitroxide. [n
both nitroxide systems. the induction period observed in poIymerizations without CSA
disappears with the addition of acid to the systern. The concentration of CSA was also
varied between 0.028 M-0.085 M in the TEMPO system, while keeping the molar ratio of
TEMP0:BPO constant. The fina[ conversion and molecular weight both increased with
increasing CSA concentration. At the high concentration of CSA, more than 80 %
conversion was reached in 6 hours with the polydispersity increasing frorn 1.12 in the
system without CSA to 1.28 in the presence of acid. The relationship between average
number rnolecular weight and conversion showed some curvature at -35% conversion for
CSA concentrations above 0.028 M. This may indicate some loss of control in the
polyrnerization at high acid concentrations (Tortosa et al., unpublished). The results
presented in this work indicate that CSA may also provide some rate enhancement in
heterogeneous systems without significantly broadening the poiydispersity.
Other routes besides strong acid addition have also been explored to increase the
reaction rate in SFRP systems. Malmstrom et al. (1997) have reported an increase in the
rate of SFRP in the presence of acetic anhydride. They proposed that acetic anhydride
increased the polymerization rate either by promoting the activations reaction in Equation
2.7, or by decreasing the free nitroxide concentration.
Keoshkerian et al. (1998) have also investigated rate enhancement of acrylate and
diene bulk polymerizations. SFRP of these monomers is often dificult as the rate of
polyrnerization is extremely slow and has been known to even stop with time due to the
buildup of nitroxide. In addition. the deactivation reaction shown in Equation 2.7 is
faster in acrylate systems than styrene systems, resulting in an enhanced sensitivity to
excess nitroxide. Polymerkation of butyl acrylate at 145 "C using BPO and TEMPO was
found to essentially stop in 1-2 hours (-5 % conversion). Addition oFglucose as a
reducing sugar was show to dramatically influence the polymerization rate of this
system, increasing the conversion to over 60 % in 6.5 hours. ESR measurements
indicated that the level of &ee nitroxide decreased in the presence of the reducing agent
(Keoshkerian et al., 1998).
2.2.3 Unimolecular Initiators
Improved structural control of chah ends, molecular weight and macromolecular
architecture has been obtained with the use of unimolecular initiators in living radical
polymerizations. The unimer is based on an alkoxyamine structure, which dissociates to
produce both the initiating radical and the nitroxide species at temperatures above 100 O C
(Malmstrom et al.. 1998). The dissociation of BST (1). a well studied unimer. to
produce the initiating radical (2) and TEMPO (3) is shown in Equation 2.9.
90th chah ends of polymers produced in the presence of unimers arise fiom the
alkoxyamine stmcture. The one to one stoichiometry provided by these initiators also
ensures no significant excess of nitroxide is initially present in the system, eliminating
induction periods. The motecular weight of the resulting polymer is also controlled by
the molar ratio of monomer(s) to the unimer. These systems have shown close agreement
between theoretical and observed molecuiar weights below molecular weights of 30,000.
In addition, the ability of alkoxyamines to be easiiy fùnctionalized allows for synthesis of
novel initiators that cm be used to create cornpiex macromolecular architectures
(Malmstrom et ai., 1998).
The thermal stability ofthe C-ON bond has been observed to exert considerable
influence in the level of control attained in polyrnerizations ernpioying a unirnolecuIar
initiator. Hawker et ai. (1996) have show if the activation reaction is slow compared to
rnonomer addition nonliving behavior characterized by broad polydispersities may result.
In an investigation conducted by Moad et ai. (1995), the homolysis rate was found to
depend on a combination of polar, steric, and eiectronic factors.
Considerable insight into the improvernent of SFRP polymerizations with unimers
was demonstrated by Hawker et al. (1996). In this work, a styrene poIymerization
ernploying a unirner was cornpared with a sirnilar birnolecular system ernploying BPO
and TEMPO ( I : t -3 molar mixture of BP0:TEMPO). Close agreement between
experimental and theoretical molecular weight was observed below molecular weights of
30,000 for the unimer system, with the deviation still within 10 % at rnolecular weights
above 100,000. The theoretical rnolecular weight for the bimolecular systern on the other
hand, cannot be easily calculated without reliable knowledge of the initiator eficiency
and therefore a cornparison with experirnental molecular weight cannot be made. The
bimolecular system also showed a broadening of the polydispersity with increasing
rnolecular weight and generally demonstrated broader polydispersities than the
unimolecular system (Hawker et al., 1996). Moad et al. (1982) have previously shown
that bimoIecuIar initiation with a BPOiTEMPO system is complicated by a vanety of side
reactions, leading to a decrease in the "livingness* of the polymerization. These results
indicated that a higher degree of control of both molecular weight and polydispersity can
be achieved by ernploying a unirnolecular initiator.
The alkoxyamine structure has been shown to be of extreme importance in
determining the polymerization characteristics. Hawker et al. (1996) investigated the
influence of structural variation of the atkoxyarnine (41, shown in Figure 2.1 on SFRP.
Figure 2.1: Chemical Structure of BenzyI-TEMPO Denvative Studied by Hawker et al. ( 1996)
In the absence of an a-methyl group on the benzyl-TEMPO derivative (4). a
significant increase in the reaction rate was observeci, in addition to broad
polydispersities (2.2-2.3) and a leveling of the moIecular weight to constant value above
30 % conversion. These results suggested that enhancing the stability of the initiating
radical improves the degree ofcontrol in the system. On the other hand, is was found
that a variety of different ftnctional groups could be substituted on the phenyl ring. B-
carbon, or aromatic ring without influencing the ability of the unimer to control the
polymerization (Hawker et al.. 1996).
Similady, the structure of the nitroide aIso demonstrates considerable influence
on the polymerization. Puis et al. (1996)- have shown an increase in reaction rate results
if two of the rnethyl groups of TEMPO are replaced with phenyl groups to give 2.5-
dimethyl-2,Ediphenyl-piperidinyt- 1-oxy.
Recent efforts have been focused on the development of a universal aikoxyamine
for polymerization of a variety of monomers. Benoit et al. (1999) explored the possibility
of such a unirner by examining a wide range of structurally different alkoxyarnines. In
their initial polyrnerizations, vanous alkolcyamines were studied in the bulk
hornopolymerizations of styrene and acryiates A 2.5-dimethyl-2,s-diphenylpyrrolidin- 1 -
oxy derivative and a-phenyl-a-isopropyl derivatives gave the fastest reaction rates and
narrowest polydispersities in the styrene polymerizations. The a-phenyl-a-isopropyl
derivatives, such as (5) shown in Figure 2.2 were the only unimers employed that could
control the poiyrnerization of acrylates. Other unimers investigated gave uncontrolled
experirnental molecular weights and broad polydispersities of 1.75 or greater. This group
detennined that the a-pheny1-a-isopropyl derivatives were suitable for use as universal
initiators for nitroxide mediated polyrnerizations. This family of unimers was able to
homopolymerize a variety of monomer systems including acrylates, acrylamides and
acryIonitri1e based monorners with a significant degree of control. In addition, randorn
and block copolymers, including those containing reactive monorner units were also
dernonstrated using these unirners (Benoit et al., 1999).
Figure 2.2: Chernical Structure of a a-PhenyI-a-Isopropyl Derivative
2.2.4 Kinetics
Numerous papers have been published on the kinetics of SFRP. Fukuda et al.
(2000) have described living radical palymerization in tenns of a stationary state, where
the rates of initiation and tenination are balanceci. The kinetic equations were derived
based on a system with a purifieci unimolecular initiator and no additional nitroxide. [n
systems utilizing conventional initiation (systems with thermal initiation andior a radical
generator such as BPO), the concentration of growing chains ([P.]) at the stationary state
was detemined solely frorn initiation and termination reactions. The concentration of
nitroxide ([Tm]) on the other hand, was found to be governed by the exchange reaction
shown in Equation 2.7 and thus depends on the constant KL and the concentration of the
aikoxyamine ([P-Tl) and p.] at the stationary state. Using this devetopment the rate of
the polymerization was derived and is shown in Equation 2.10 (Fukuda et al.. 2000).
where:
R,= Overall Rate of Thermat and/or Conventional Initiation
kt = Rate constant for termination ( L ~ o I " ~ ' )
According to this kinetic development the rate ofpropagation is independent of
the concentration of alkoxyamine. This phenornenon has been experirnentaily
demonstrateci by CataIa et al. (1995) and was used as support for this analysis. This rate
law predicts that at Iow conversions the rate of reaction for a nitroxide-mediated
polymerization shouId be the same as the rate of conventional radical polymerization. To
fiirther support this analysis the group observeci that by increasing the concentration of a
conventional initiator (in this case t-butyihydroperoxide) resulted in an increase in the
rate of polymerization, as would be expected for an uncontrolled radical polymerization
(Fukuda et al., 2000).
The analysis provided by Fukuda et al. (2000) has been the subject of some
debate. Veregin and coworkers (1997) have argued that BPO initiated SFRP of styrene
does not agree with a steady-state mechanism. Their main point of disagreement with
this kinetic mechanism is in the assumption that the rates of termination and initiation are
equal. This group also argued that [PO] and [TOI are not constant during the
poIyrnenzation, which is required for a steady state approximation to be valid.
Furthemore, the rate law devejoped by Fukuda et al. (2000) does not include a
dependence on the nitroxide concentration. Previously, the apparent rate constant of
polymerization has been show to change in agreement with [T'] (Veregin et al. 1997).
Alternatively, Fischer (1997) has explained the kinetics of SFRP in tems of a
persistent radical effect. In this development, the nitroxide species is described as a
persistent radical and the initiating and propagating moieties are defined as transient
radicals. Unlike the transient species, which can decrease in concentration by termination
reactions, the persistent radical is assumed not to self-terminate. In contrast to the work
by Fukuda et al. (2000) this anaIysis does not involve the assumption of a steady-state
except at inftnite times, where the concentration of persistent radicals reaches the initia1
alkoxyamine concentration (P-TJo) and p.] is fully converted to dead species (Fischer,
1997).
According to this work, as an alkoxyamine thermally dissociates initially the
concentrations of both radicals increases until the Ievel oftransient radicals is suficient
for termination reactions to occur. At this tirne the concentration of transient radicals
decreases due to termination, while the persistent radical species continues to increase.
The increasing concentration of the persistent radical species shifls the equilibrium
shown in Equation 2.7 to the dormant polymer form and decreases the probability of
termination. Eventually, an intermediate quasi-equilibrium is reached, where the radical
concentrations are slightly dependent on time and there is a Iarge excess of fiee nitroxide.
Using these concepts Souaille and coworkers (2000) developed a rate equation for the
quasi-equilibrium stage shown below in Equation 2. L 1.
where:
~ - T ] o = Initial concentration of alkoxyamine
t= tirne
The rate equation developed by Souaille et al. (2000) includes a term to account
for the concentration of alkoxyamine and time dependence in contrast to the work of
Fukuda et al. (2000). It is important to note that both developments are for ideal systems
and do not take into account important side reactions that can significantly influence the
kinetics of these systems.
Souaille et ai. (2000) aiso provided a set of necessary conditions required to
achieve a living radical polymerization. FirstIy, they stated al1 monomer consumption
must occur in the quasi-equilibrium stage- SecondIy, a large rate constant for the
activation reaction (kL) is required to ensure a fast initiation of c h a h so that narrow
polydispersites can be obtained. Finally, the k, of the monomer dictates the ideal rate
constants for the activation and deactivation reactions in Equation 2.6. A fast k, can lead
to non-living behavior if the deactivation reaction is not suitably fast (Souaille et al.,
2000).
2.2.5 Acrylate Monomers
Despite the success achieved with styrenic SFRP, the polymerization of
acrylates and methacrylates has been troublesome. Steenbock et al. (1996) attempted to
homopolymerize methyl methacrylate (MMA) in the presence of TEMPO. These
polymerizations were unsuccesstùl with no polymer formed afler 72 hours. Addition of
CSA to the reaction resulted in 40 % conversion in 2 hours, with no fùrther monomer
consumption afler this point. Attempts to vary the level of CSA resulted in no polymer
formation or uncontrolled polymerizations. Hydrogen transfer reactions to the nitroxide
were thought to be responsible for the Iack of polymerization (Steenbock et al., 1996).
Although transfer may lead to the generation of a significant amount of dead chains it is
likely not the only reason for the Iack of polymerization. The deactivation reaction
shown in Equation 2.6 is much faster for acrylates compared to styrene, which promotes
greater formation of the dormant species (Keoshkerian et al., 1998). The creation of dead
chains and buildup of nitroxide wouId fiirther shifi this equilibrium to the deactivated
polymer fonn. The presence of a large pottion of inactive species may slow down the
rate of polymerization so that Iittle or no monomer addition occurs.
Listigovers et al. (1996), obtained better success polymerizing butyl acrylate
using 40x0-TEMPO at 155 OC. In 9 hours a butyi acrylate polymer was obtained with
an average number molecular weight of 10,504 and a polydispersity of 1.53. Molecular
weights up to 37,000 could be obtained and the polymer could be successfùlly chain
extended with styrene. In addition, synthesis of mixed acrylate di- and tri-block
copolymers and acry1ateJstyrene diblock copolymers were demonstrated (Listigovers et
al., 1996)- The high reaction temperatures required for this polymerization however,
restrict its commercial application.
The application of unimers has shown considerably more success in acrylate
hornopolymerizations. Benoit et al. (1999) have shown using (5 ) , that n-butyl acrylate
can be polymerized to a molecular weight of 26.500 with a polydispersity of 1.44 at
125 O C . The reaction rate was considerably improved by addition of acetic anhydride and
0.01 equivalents of nitroxide (to initiator) to the system, resulting in 95 % conversion in
16 hours while still retaining a low polydispersity (1.25). These results indicate the
ability to successtùlly apply SFRP to acrylate systems using unirners.
The results previously discussed indicate the sensitivity of acrylates to a buildup
of nitroxide. A buildup of nitroxide in the system can effectively slow d o m or halt the
addition of monomer to the growing chains. The success of "living" radical
polymerizations depends on balancing the amount of propagating chains and the level of
fiee nitroxide.
2.2.6 Stable Free Radical Polymerkation in Ernulsion
StabIe radical polymerization in emulsion is complicated by partitioning of
species to the aqueous phase. Recently, Ma et al. (200 1) have measured the partition
coefficients between 25-135 "C for severai nitroxides in miniernulsion with various
degrees of water sohbility. The partition coefficient was defined as shown in Equation
2.12.
Where:
j = ïEW0,4 -Hydroxy -TEMPO, 4 - amino -TEMPO P, = the partition coefficient for species j between styrene and water
Ci], = the concentration of j ÛI the organic phase
Ij], = the concentration of j in the aqueous phase
The partition coefficients (moI%/moI%) for TEMPO, Chydroxy-TEMPO and 4-
amino-TEMPO between styrene and water were found to be 652.2, 14.3 and 43.9
respectively at 135 "C (Ma et al., 2001). The large difference in the partitiming behaviors
of various nitroxides could significantly impact the resulting kinetics in heterogeneous
systems.
A pteliminary study on the application of SFRP in emulsion was conducted by
Bon et al. (1997). A I-tert-butoxy-2-phenyl-(1-oxy-2,2,6,&tetramethylpiperdinyl) ethane
akoxyamine and additional TEMPO were used as the nitroxides in a seeded ernulsion
polymehtion of styrene at 125 O C . In 36 hours, a conversion exceeding 99 % was
achieved wÏth an average number molecuIar weight of?,900 and a polydispersity of 1.54.
Cornparison of these SFRP results in emulsion with a bulk system showed strong
similarities. The emu1sion system however, dispIayed a broadening in polydispersity to
lower mofecufar weights, with more chains in the system than predicted theoretically.
These observations were attributed to a greater degree of termination and transfer
reactions in heterogeneous systems (Bon et al., 1997). This investigation demonstrated
the feasibility of applying SFRP to emulsions.
Nitroxide mediated SFRP of styrene in emulsion was also studied by Marestin et
al. (1998). This group employed a miniemdsion using SDS and hexadecanol as the
surfactant and cosurfactant respectively. SeveraI TEMPO derivatives were studied in
order to gain an appreciation for the influence of the nitroxide on the polyrnerization. in
their system. TEMPO, CHydroxy TEMPO and 4-carboxy-TEMPO resulted in less than
I % conversion before latex coagulation was obsewed. 4-amino TEMPO however,
atlowed for a controlled polymerization without coagulation to yield a polystyrene
product with a molecular weight of 8,700 and a narrow polydispersity ( 1 27). The
success of this nitroxide was thaught to be the result of an optimized degree of
partitioning between the aqueous and otganic phases. It was reasoned that optimal
partitioning altowed for both conuolled particle growth and control of radicals generated
in the aqueous phase fiom i~t ia tor decomposition (Marestin et al.. 1998). These early
results indicated that nitroxide parti'tioning could exert considerabIy influence on the
polymerization characteristics. SuEcient nitroxide in the organic phase is required to
effectively control the polyrnerization. Further study is needed to discem the influence of
nitroxide in the aqueous phase.
More recently SFRP has been appIied to miniernulsion poIymerizations ofstyrene
by Pan et al. (200 1). TEMPO-temhated oligomers of polystyrene (TTOPS) were
applied as macroinitiators at concentrations of 5 % and 20 %. The rate of polymerization
was found to be very similar at both concentrations with close agreement to bulk
polymerizations conducted by Fukuda et al. (1996). Both TTOPS concentrations also
showed possible leveling at higher conversions, which may be explained by irreversible
termination reactions andlor a increase in the level of dormant species (Pan et al., 2001).
A linear average number molecular weight-conversion profite was demonstrated
at both TTOPS concentrations up to conversions of 75 %. The polydispersity in these
systems was observed to broaden with conversion, which was attributed to short chain
generation by autopolymerization ancilor termination reactions. The poiydispersities at
the 20 % TTOPS concentration were lower than at the 5 % concentration up to 65 %
conversion. The larger amount of TTOPS and hence greater level of nitroxide seems to
provide a more controlled polymerization (Pan et al, 200 1). This investigation suggests
the possibility of gaining better control of the polymerization by preventing short chah
generation, which may lead to a broadening of the polydispersity and deviation between
experimental and theoretical molecular weights. Suppression of autopolyrnerization may
be promising in this regard.
The advantages of emulsion systems combined with the control and versatility of
SFRP rnake their combined potential application commercially significant. The
mechanism of SFRP in miniemulsion is stili not weil understood and requires many
refinements. This study focuses on obtaining a better understanding of the SFRP process
with particular interest in the use of unimoIecular initiators, rate enhancement and the use
of a butyl acrylate monomer in place of the conventional styrene monomer.
Chapter 3
3. Experimental
The following sections describe the experimental procedures, materials and
apparatus utilized in this investigation.
3.1 Materials
Polymerizations were conducted employing different nitroxides, monomers.
initiators and unimers. Table 3. I lists the materials used dut-ing the polymerizations.
including additives. Table 3.2 lists solvents and additional materials that were employed
dunng the course of this study. Ail materials were used as received unless indicated.
Table 3.1 : List of Materials Used in Polymerizations
1 n-Butyl Acrylate 1 99+% ( Aldrich, columned to 1
SupplierKomments
Aldrich, washed and distilled
- Material
S tyrene
I 1
n-Hexadecane I 1 Sigma
~ u n t y
99%
TEMPO 4-Hydroxy-TEMPO 4-0x0-TEMPO Benzoyl Peroxide @PO) Potassium Persulfate (KPS)
98%
97% 99.6%
Sodium Dodecyl Benzenesulfonate (SDBS) Camp horsul fonic Acid
remove inhibitor Aidrich Aldrich Aldrich Aldrich Fisher Scientific
(CS A) Sodium Bicarbonate
98%
Fisher Scientific, A C 5
L-Ascorbic Acid
Aldrich, AC.S. certified
Aldrich
Acetic Anhydride
Min 99%
1 Fisher Scientifk
certified Sigma
l
Table 3.2: List of Solvents and Other Materiais Used in Study
Material
Tetrahydrofùran (THF)
1 1 certified
Nonane Toluene
Dichioromethane \ 1 Fisher Scientific, A.C.S.
~ u n t y
99+%
Supplier/Comments
Aldrich, A.C.S. certified 99%
Calcium Chloride I 1 Aldrich, -4-30 mesh
Aidrich Fisher Scientific, A.C.S.
Isopropanol Hexanes Methanol
Sodium Hydroxide
Nitrogen ( IR[P 1 Praxair
3.1.1 Monomer Purification
99.5% 98.5%
97%
The styrene monomer was inhibited with 10-15 ppm of Ctert butyicatechol. The
inhibitor was removed by washing the styrene three times with an equal volume o f a
2 wt % solution of NaOH. The monorner was washed three times with deionized water
(DIW) to remove any remaining NaOH and then dried with calcium chloride overnight in
the refigerator. The dried styrene was distillai under vacuum and kept refngerated prior
to use.
The butyl acrylate monomer was inhibited with 10-55 ppm of monomethyl ether
hydroquinone (MEHQ). The inhibitor was removed by passing the monomer drop-wise
through a MEHQ removaI coIumn from Aldrich. The punfied monomer was kept
reffigerated.
certified Aldrich, A.C.S. certified Aldrich, A.C.S. certified Fisher Scientific, AC.S. certified Aldrich, A.C.S. certified, oellets
3.2 Initiators and Nitronides
Unimolecular and bimolecular methods of initiation were employed in this study.
In the bimolecular systems, TENPO. Chydroxy-TEMPO, or 4-oxo-TEMPO nitroxides
were used with either KPS or BPO as the initiator. The unimolecular systems utilized
BST, hydroxy-BST, or TEMPO-terminated oligomers of polystyrene (TTOPS). The
synthesis of these unimers is discussed in the sections that follow.
3.2.1 BST Synthesis
In order to synthesize BST, BPO (28 g, O. LI6 mol) was dissolved with stirring in
150 ml of styrene. TEMPO (24 g O. 154 mol) dissolved in the rernainder of styrene ( 150
ml) was then added and mixed into the BPO solution. The solution was then added to the
1 .O L reactor and purged with nitrogen (40 psi) for 30 minutes (6 times). M e r the last
purge, the reactor was heated to 135 "C. The reaction progress was monitored using thin
layer chromatography (TLC) on samples taken from the reactor. These samples were
diluted in dichlorornethane and sported on a TLC plate aIong with separate samples of
BPO, TEMPO and punfied BST also dissolved in dichloromethane. Dichloromethane
was then used to separate the components and the presence of BST in the reaction
samples was determined by observing the plate under a W Iamp. The typical reaction
time was between 20-30 minutes.
A brown, sticky residue was obtained d e r the excess monomer was removed.
The cnide pmduct was then putifid by hexane extraction. Afier solvent removal, the
resulting materia1 was dissolved in dichioromethane and passed through a column
containhg silica gel 60 (mesh 35-70, particle size 0.5-0.5 mm) using dichloromethane as
the eluent. Fractions fiom the column were analyzed for BST using TLC. The solvent
was evaporated and the resulting BST was recrystallized twice using isopropanol to yield
a white crystalline product (yield < 20 %). Conformation of the desired product was
done by proton NMR analysis in CDCL at room temperature. A sample NMR is provided
in Appendix A. 'H NMR (CDCb) G 0.75, L.07, 1.21. 1.37 (s, CH3 ), 1.38-1.52 (m. CHI),
4.53 (q, I H . CHH),4.83 (q, lH, 0 , 5.06 (t, IH, CH), 7.25-7.56 (rn Ar H), 7.91 (m.
2H, Am.
3.2.2 Hydroxy-BST Synthesis
Hydroxy-BST (6) was prepared through an exchange reaction using BST (1) and
hydroxy-TEMPO (5). The reaction scheme is shown in Equations 3.1 and 3.2.
0 (1) O L
L OH
='O?. + -wN OHp - N -H (3.2) 1 1 , -
--C -Tc i l I
BST (1 .O g, 2.6~10;' moles) was dissolved in nonane (200 ml) with stirring. A
five moIar excess of 4-hydroxy TEMPO (2.3 g, 1 . 3 ~ IO-' moles) was then added. The
solution was gentIy heated with stimng to dissolve the nitroxide (-60-70 "C) and then
added to the 300 mi reactor. The system was purged with nitrogen 6 times at 40 psi (30
minute penod) and then heated to 135 OC. A 1 hour time period for exchange was
allotted before cooling. A beige-orange product precipitated fiom solution ovemight
and was vacuum ftltered. The product was then washed three tirnes with DIW water to
remove excess nitroxide. Hydroxy-BST was obtained as an off-white powder (55-6 1%).
Conformation of the desired product was confirrned using proton NMR in CDCI? at room
temperature. A sarnple NMR is provided in Appendix A. 'H NMR (CDC13) 6 0.75. 1.15,
1.27, 1.45 (CH3), 1.5-1.9 (CHZ), 3.95 (lH,CH(OH)). 4.53 (LH, Cm. 4.85 (1H. CHH),
5.05 (lH, CH), 7.25-7.6 (ArH), 7.95 (2H, ArH).
3 -2.3 TTOPS Preparation
A polyrner produced from a 1.5 hour bulk poiyrnenzation of styrene using BST
was isolated by precipitation in methanol. The polymer was then vacuum filtered and
dried under vacuum at 70 O C for two days. The purified polymer was then used as a
unimolecular initiator (A). The Mn and polydispersity of the prepared 'ITOPS was
18,900 and 1.24 respectively.
A second batch of TTOPS (B) was also prepared according to the procedures
documented by Keoshkerian et ai. (200 1) in a 1 hour bulk polymerization using TEMPO
and BPO. The resulting polymer was not isolated but used directly in subsequent
miniemutsion pofymerizations. This macroinitiator had a M, of 1, 284 and a
polydispersity of 1.25.
3.3 Experimental Apparatus
The poIymerizations were performed in either a 300 ml stainless steel autoclave
reactor (Autoclave Engineers) or a 1.0 L stainiess steel Bpper-clave reactor (Autoclave
Engineers). A schematic diagram of the 300 ml and 1 .O L reactors is provided in Figures
3.1 and 3.2 respectively. Both reactors were equipped with venting, sarnpling, vacuum
and nitrogen sparging lines and variable-speed motors.
A- 300 ml R e ~ t a r 1 B- Thrcc Blade h a 1 Row kripdcr
C- Band &&en (2 x 340 watts) D- Thamocoupic (K type) E Tcmpetaauc Connaücr F- Pressure Clliagt G- Vmraig VaIve H- Vacuum Lmt Valve 1- Zhret-way Bali Vdve J - Stanttss Sted Sampiing Tube K- Naogen Mct
A
Figure 3.1: Diagram of 300 ml Reactor (Xie. 2000)
A- 1.0 L Zippcrciave Ekactor B- 4 Btdc Aauai Dawn impekr C- Naogen Spugms ime D-Sampfins Lmt E- ThcrmowcIL F- Coofme Codïabh 114' sohoid mhtt (nor shown) G- Viton O-mg K- Samplmg vahic 1- Soaless steel Sampbg Lnc J- N*rogm Inlet K- v* L- vea~g Vdvc M- Pressure Guqe N- vacuum V k O- Nrpogm Sparsnig V h P- Beit DIIVCU -e -or Q- Clamp on Hermig Jacket
Figure 3 -2: Diagram of 1 .O L Reactor
3.4. Miniemulsion Polymerizations
3.4.1 Preparation
Sodium dodecyl benzenesulfonate (SDBS) and hexadecane were used as the
surfactant and cosurfactant respectively in the miniemulsion polymerizations. The
miniemulsion was prepared by first dissolving the SDBS in DiW to form the aqueous
phase. The organic phase was made by dissolving the nitroxide or unimer in the
monomer and hexadecane. The aqueous and organic phases were then mixed and
homogenized (2 passes) on the Microfluidizer-1 10s (Microfluidics International
Corporation) to fonn the miniemulsion. An inlet pressure of 40 psi was used on the
microfluidizer. The standard miniemulsion formulation for both the 300 ml and I .O L
reactors is given in Table 3.3. The entire formulation was doubled when the I.0 L reactor
was employed to aflow for adequate sampling.
Table 3.3: Standard Miniemulsion Formulation for 300 ml and 1 .O L Reactors
3 -4.2 Additives
Several rate-enhancing additives were ernployed in the course of this
investigation. Depending on the additive's solubility in styrene, the addition was made to
either the organic or aqueous phase ptïor to mixing of the two phases. In mns using
CSA or L-ascorbic acid, the acid was added to the aqueous phase. Acetic anhydride on
the other hanci, was added directly to the organic phase.
Material DIW (ml) SDBS (g) Distilled Styrene (mi) Hexadecane
300 ml Reactor 120
0.88 3 3
4.37
1.0 L Reactor 240 1.76 66
8.74
3 -4.3 Polyrnerization
The rniniemulsion was transferred to the reactor after hornogenization and 3 zero
sample of approximately 5 ml was taken. An initiator (KPS or BPO) was added to
systems not employing a unimer. The reactor was then sealed and purged six times with
nitrogen at 40 psi to rernove oxygen, which is known to inhibit free radical
polymenzations. The purging was done over a 1.5 hours or a half hour time period for
the 1 .O L and 300 ml reactor respectively. The reactor was heated to the desired
temperature (typically 135 O C ) after the sixth purge, which was estimated to take
between 15-20 minutes. Sarnples of approximately 10 ml were removed periodically
during the course of the reaction. Some of the reaction mixture was discarded prior to
sampling to prevent contamination (-5 ml for 300 ml reactor and - 10 ml for 1 .O L
reactor). Nitrogen was also used to clear the sarnpling line after sampling. Samples were
analyzed for conversion, molecular weight and polydispersity. The particle site
distribution was also measured when possible.
3.5 Bulk Polymerizations
3 S. 1 Preparation
Buk polymerizations using either BST or hydroxy-BST were conducted for
cornparison with miniernulsion systems containing the sarne organic phase unirner
concentration. The reaction mixture was produced by dissolving the unimer in styrene.
The poIymerizations were conducted so there was at Ieast 120 ml of rnonomer in the
reactor. This was done to ensure adequate sampling during the course of the
polymerization.
3.5.2 Polyrnerization
B u k conditions were conducted in the same manner as miniemulsion
polymerizations. Smaller sampies (-5 ml) were however, taken during the course of the
reaction, Bulk polymerizations were also conducted for shorter reaction tirnes due to
difficulties in controlling the reaction temperature at high conversions. Toluene was
added via the vacuum line at the end of the reaction to facilitate removal of the viscous
polymer melt. Samptes were analyzed for conversion, molecular weight and
polydispersity.
3.6 Reproducibility
The reproducibility of the fiactional conversion calculations was determined by
repeating the gravimetnc analysis for the 12 hour sarnple of SFRMP-82 five times. The
sample standard deviation was calculated to be 3 fiom these results. Previous work in this
lab has also dernonstrated the repeatability of both molecular weight and fiactional
conversion (Smith, 2000).
Chapter 4
4. Analytical Procedures
4.1 Gravimetric Analysis
In order to determine the fiactional conversion, gravimetric analysis was
performed on al1 samples taken fiom the reactor. A latex sample (typically between 5-10
g) was added to a 15 ml glass via1 of known mass and weighed by difference. The
sample was then dried by gentle blowing of compressed air overnight in the hme hood.
M e r air drying, the samples were placed in a vacuum oven dessicator under -30 in Hg at
70 O C for two days. The samples were then weighed and the mass of dried poiymer was
used to determine the fractional conversion.
4.2 Gel Permeation Chromatography (GPC)
4.2.1 Equipment
The molecular weights and polydispersities of the samples were determined on
the Waters 2960 Separations Module, which contains a Waters 4 10 Differential
Refiactometer and an on-line degasser. StyrageI columns, HRS.0, HR3 .O, HR 1 .O and
HR0.5 were employed in the analysis. The separation range of each column is Iisted
below in Table 4.1.
Table 4.1 : Separation Range of Columns used in GPC Colamn
HR0.5 HRI -0 HR3.0 HR5.0
6
Molecular Weigbt Range
@Pitons) 0-1000
100-5000 500-3x 105
2000-4x 10'
4.2.2 Caiibration Curve
The molecular weights and polydispersities of the experimental samples were
determined using a calibration curve. The calibration cuwe was generated using 10 or
more, narrow polydispersity polystyrene standards over a large range of molecular
weights. The standards were analyzed using the Millennium GPC software and fitted to a
fourth order polynomial. The calibration curve was then used to determine the molecular
weights and polydispersities of experimental samples.
4.2.3 Sample Preparation
The dried polymer obtained after gravimetnc analysis was used to perform GPC
measurements. Approximately 5-12 mg of polymer was dissolved in 10 ml of filtered
THF. The solution was then added to a glass synnge and passed through a nylon filter (2
pm pore size) to remove any particdates. Samples were directfy filtered into Waters
GPC sample vials and mn on the GPC. Millennium software was used to obtain and
process the sample data.
4.3 Particle Size Distributions
4.3.1 Equipment and Theory of Operation
Particle size measurements were made on the Malvern Mastersizer 2000 equipped
with a Hydro 2000s optical unit. The optical unit is composed of a detector array that
allows the scattering pattern of particles to be measured. This array is composed of many
separate daectors, each of which collects light fiam a certain range of angles. The
particle size can then be calculated based on the interaction of light with the particIes.
The measurement principle used, predicts particle size for spherical particles and requires
the input of specific particle information into a standard operating procedure.
4.3.2 Standard Operating Procedure (SOP)
To anaiyze sampks, a standard operating procedure (SOP) was fist defined.
Once the SOP is created, the Malvern automatically runs through the specified
measurement procedure. The settings employed in the SOP used in this study are show
in Table 4.2. These settings were based on previous experimental findings on this
machine (Witty, 2001). The SOP included a sample sonification prior to analysis in
addition to a cleaning procedure &er each measurement. Micro 90 solution was added
to the optical unit and circulated at approximately 1500 rpm when the Malvem was not in
use.
Table 4.2: Standard Operating Procedure Settings
1 Water Dispersant Refractive Index / 1.33 I
- -
Variable
Polystyrene Latex Refractive Index
1 Measurement Time 1 12 s 1
Setting
1.59
I Number of Snaps During Measurement Measurement Delay
13,000
IO s 1
Background Measurement Time
Number of Snaps During Bac k+ground Measurernent Agitation Speed
12 s
t 2.000
1500 rpm
4.3.3 Sample Analysis
The sarnples taken fiom the reactor during the course of the polyrnerization were
directly added to the optical unit of the Maivern. Styrene-saturated DiW was used as the
dispersant. This was done to rninimize the possibility of styrene diffision Eom the
polymer particles and allowed measurement of the monomer-swoilen particle size. The
sample was added until the Mastersizer software obscuration bar indicated the
concentration was in the required range. Witty (2001) detennined that sarnples should be
added quickly in a non-dropwise manner. Care was taken to ensure that the samples were
added in this manner. The data fiom the Malvern was then analyzed on a volume basis.
4.3.4 Monomer Droplet Stability
The stability ofthe monomer droplets with time was a concem in the particle size
measurements, as these are the sites of polymerization in miniemulsion. The droplet size
distribution thus provides valuable information about particle growth. To address this, a
miniemulsion with the formulation shown in Table 4.3 was prepared. Undistilled
styrene inhibited with 4-tert-butylcatechol was used as the monomer with no added
initiator or nitroxide. Additional Ctert-butylcatechol was dso supplied to the organic
phase to suppress any autopolymerization and allow the droplet size distribution in the
absence of particle growth to be detemineci.
Table 4.3: Miniernulsion Formulation for Droplet Stability Study in 1 .O L reactor
1 Material Quantity
SDBS
D W
1.77 g
240 ml
Hexadecane
The miniemulsion was prepared as described in Chapter 3 and the reaction was
conducted at 135 OC for 6 hours. Samples were taken every 20 minutes for the first hour
and every hour thereafler. Additional samples were also taken directly aller
microfluidization and once the set-point was reached. SampIes were then analyzed on the
Malvern Mastersizer 2000. Table 4.4 gives the volume weighted mean diameters (D,) of
the samples taken. The D, for each of the 3 distributions in the tirne zero sample at 25°C
are provided.
8.75 g l
TabIe 4.4: Volume Weighted Mean Diameters of Samples in Droplet Stability
Styrene 66 ml
Experiment Sample Time
Time zero (25°C) Time zero (1 35°C) 20 minutes 40 minutes
DV ( ~ m )
0.222, 7.149, 156.617 0.248 0.156 O. 172
1 hour 2 hours 3 hours
O. 176 O. 176 0.181
4 hours 5 hours
O. 179 0.176
6 hours O. 189
As indicated in Table 4.4, the monomer droplet size was very consistent after the
miniernulsion was heated to 135 O C . The zero sampIe taken &er rnicrofluidization had
broad shouldws of large diameter droplets as indicted in Figure 4.1. The major
distrilution bas a similar Dv to the samples taken later in the polyrnerization. The droplet
size distribution at 3 hours, du, s h o w in Figure 4.1, shows a srnall shodder o f largar
diameter tiroplets This droplet size distribution wu very similar to aii otha samples
1 Partide S i e (mi) 1
I Particle Sie (p) . -
@) --
Figure 4.1: Droplet S-m Distniutions for Droplet Stability Study (a) Zero sampletaken diiedly after microfluidiation @) Sample taken at 3 hours
The results obtained from this experiment indicate that the size distribution of
monomer droplets is relatively constant after heating. The sample taken directly after
microfluidization shows a mmodal droplet size distribution. This seems to indicate the
droplet distribution may be initially broad but seems to equilibrate with time.
4.4 Influence of Hyd roxy-BST Purification Procedure
This work documents to our knowledge the first attempt to prepare hydroxy-BST
via the exchange reactions shown in Equations 3.1 and 3.2. To ensure Our final product
was fiee of excess nitroxide, the hydroxy-BST was washed three times with DIW. In this
procedure the product was observed to change fiom a slightly orange color to an off-
white color. The orange color is characteristic of the TEMPO and hydroxy-TEMPO
nitroxides and its disappearance seemed to indicate the success of this purification. Two
miniemulsion polymerizations were conducted using both the purified and unpurified
hydroxy-BST to determine if any residual nitroxide was present after the DiW extraction.
Both poIymerizations used the 300 ml reactor standard miniemulsion formulation
presented in Chapter 3 and 0.22 g of hydroxy-BST. SFRMP-5 1 and SFRMP-38 refer to
the runs with and without purification of the hydroxy-BST respectively.
4.4.1 Muence of Purification on Polymerization Rate and Moiecular Weight
The conversion versus time relationships for SFRMP-38 and SFRMP-5 1 are
shown in Figure 4.2. The conversion (x) has been piotted as the -In(I-x) to remove the
dependence of the polymenzation rate on monomer concentration. The polymerization
utilizing the unpurified hydroxy-BST shows an induction period of approximately 1.5
hours, which is absent in the polymerization with purified unimer. This induction period
is indicative of an excess of nitroxide, which suppresses the concentration of growing
radical by shifting the equilibrium shown in Equation 2.7 to the dormant polymer form.
The -In(l-x) versus time relationship is linear for both polymerizations once started,
indicating a constant number of polymerizing chains during the reaction as would be
expected in a "living" system.
Time (hours)
/ 4 Unpurifieci Hydroxy EST : ! A P u M Hvdmxv BST : 1
Figure 4.2: Influence of DIW Extraction of Hydroxy-BST Conversion
The influence of D W purification on the relationship between average number
molecular weight (Mn) and conversion is given in Figure 4.3. In both cases, a linear
relationship is observed indicating the "livingnessn of the system. In addition, at a given
conversion the molecular weight is very similar in both systems as would be expected for
at the same Ievel of initiator. This indicates that the two systems have a comparable
number of growing chains
Conversion (Oh)
Figure 4.3: Influence of DIW Extraction of Hydroxy-BST on Mn
1
I
1 Unpunfied Hydmxy 1 1 EST I
A Punlied Hydmxy EST-2 1
, I
30000 - 25000 -
20000 -
8 15000 -
10000 *
5000 .
The results obtained from these polymerizations and 'H NMR indicates the DIW
extraction does successfully remove excess nitroxide. This washing procedure was used
to puri& all subsequent hydroxy-BST samples.
0.00 20.00 40.00 60.00
4 A
a
A
0 O C
Chapter 5
S. Unimolecular Initiators in Miniernulsion
Unimers in SFRP allow for greater control of molecular weight, chain ends and
macromolecular structure because the initiai number of chains is specified by the
arnount of alkoxyamine added to the systern. On the other hand, in bimolecular
initiation unknown initiator efficiencies make it difficult to accurately predict
molecular weight. In addition, the i : 1 stoichiometry of the nitr0xide:initiating
radical in the unimer ensures little excess nitroxide is initially present in the system
and eliminates induction periods. Nitroxide partitioning in heterogeneous systems
however, could dismpt this 1: 1 stoichiometric balance.
Two unimers, BST and hydroxy-BST were investigated for their potential in
SFRP of styrene in miniemulsion. The fotlowing sections of this report summarize
the results of these poiymerizations.
5.1 Experimental
The reactions were canied out in the 300 ml autoclave reactor at 135 "C. using
the standard miniemulsion formulation presented in Chapter 3. Three runs at unimer
concentrations of 0.007 M, 0.0 14 M and 0.020 M were performed for each
aikoxyamine. A summary of the run conditions is provided in Table 5.1.
Experiments employing the 0.014 M unimer concentration were run for 24 hours to
determine the polymerization characteristics at Ionger time penods.
5.2 Polymerizatioo Results
Table 5.1: Summary of Run Conditions for Unimer Srudy in Miniernulsion
A summary of the final conversions (x), number average molecular weights
(Mn). polydispersities (Mm,), nurnber of poiymer chains and apparent initiator
Reaction Time (hours)
12 12
Run
SFRMP-74 S M - 7 5
eficiencies (Fa,) for both systems is provided in Table 5.2. The number of polymer
chains was calculated according to Equation 5.1 show below, where NA represents
SFRMP-78 S M - 7 9 SFRMP-8 1
: S M - 8 2
Unimer
BST BST
Avogadros number. The average chain Iength and moles of styrene reacted required
Unimer Concentration in
Organic Phase (moles/L) 0,007 0.020
for this caldation were found by Equations 5.2 and 5.3 respectively, where MW, is
BST Hydroxy-BST Hydroxy-BST Hydtoxy-BST
the molecular weight of the monomer. F,, was then caIcuIated fiom Equation 5.4.
moles OC styene reacted # of Polymer Chains =
average chah Iength 1
0.0 14 0.0 14 0.007 0.020
Mm Average Chain Lengîh = - (WC,
24 24 12 12
( rnass of styrene initiaily present ) ( conversion ) moles of styrene reacted = (5.3)
(MW),
The final polydispersities ranged h m 1.28- 1.43 and remained below the
lower theoretical limit for conventional fiee radicaI polymerization (1.5). In both
systems, the polydispersities were narrowest at the highest level of unimer and
broadened as the unimer concentration was decreased. This suggests that better
control in the polymerization is achieved at higher unimer concentrations, where the
nitroxide concentration is effectively increased. At higher nitroxide levels, the
probability of propagating radicals reacting with the nitroxide is substantially greater
than termination, resulting in a higher degree of Iivingness.
Table 5.2 also shows that high initiator eficiencies are achieved in al1 of the
mns. This indicates the majority of radicals generated fiom the thermal dissociation
of the alkoxyamine succeed in becoming polymer chains. Initiator efficiencies above
one are the result of chains generated From the autopolymenzation of styrene. Lower
initiator eficiencies at higher nitroxide levels couId result frorn a reaction of the
nitroxide with the Diels-Alder dimer produced From styrene autopolymerization
(Boutevin et al., 1999). This could decrease the number of radicals generated fiom
thermal polymerization.
To acwunt for the thermal generation of chains, a corrected Fa, was
calculated using Equation 5.5 below. The number of thermally generated chains used
in this calculation was supplied by PREDICI Q simulations (Ma, unpublished) and
represents between 5-13 % of the total number of radicds. The number of thermally
generated chains and the corrected apparent initiator efficiencies at the finai reaction
times are provided in Table 5.3.
- #polymer chains- thermally generated chahs FappQiI1Cded - # radicals generated from initiaîor
Table 5.2: Summary of Unimer Miniemulsion Polymerization ResuIts
Table 5.3
5.3 BST Polymerization Results
,
5.3.1 Fractional Conversion
The conversion data is presented in Figure 5. t, which indicates the
polymerization rate is not strongly dependent on the concentration of BST. In
addition, the final conversions with the exception of SFRMP-78, are approximately
the same.
F~PP
1.26 1.18 1.13 1.10 1.38 0.92
Run
SFRMP-74 S N - 7 5 SFRMP-78 SFRMP-79 SFRMP-8 1 SFRMP-82
I (%)
60 63 5 5 73 66 65
# Polymer Chains iL Organic
Phase (1 r oz')
4.68 12.86 8.21 8.04 4.86 9.83
Ma
52,998 19,996 27,377 37,255 56,065 26,957
M a n
1.42 1.34 1.38 1.40 1.43 1.28
At higher unimer concentrations more radicals are produced, which in
conventional radical polymerizations increases the polymerization rate. However, in
SFRP the polymerization rate is also highly dependent on the concentration of
nitroxide in the system as shown in Equation 2.8.
O 10 20 30 1 1 fime (hours)
Figure 5.1 : Influence of BST Concentration on Conversion in Miniernulsion
Thermal initiation, termination reactions and the equilibrium reaction
provided in Equation 2.7 dictate the concentration of growing chains in the system.
Thermal initiation produces a styrene monomeric radical (Mtw) and a styrene dimeric
radical (M2*) according to Equation 5.6 below, where M refers to a monomer
moiecule and Iih is the rate constant of thermal polymerization (Hui et al., 1972).
Using Equations 5.6,2.7 and considering only termination by combination
(Equation 2.4) the kinetic relationship for the concentration of growing chains can be
developed. This relationship is shown in Equation 5.7, where the variables have been
previously described and typical values for the rate constants are provided,
4 1 k -L= 4.0~10 s' (Fukuda et al., 2000) kt=8 xlo7 L m o ~ ' s" (Greszta et al., 1996)
IO 2 b= 4 . 3 7 ~ 10- L rnof"s-' (Hui et al., 1972) k=5xlog mor' s" (Beuemann et ai., 2001)
As the unimer dissociates the concentration of nitroxide is initially balanced
by the amount of growing radicafs. According to the persistent radical effect
however, irreversible termination reactions lead to a buildup of nitroxide in the
system, resulting in the rnajority of chains existing in the dormant form. Regardless
of the initial level of unimer empioyed comparable values for [P.] and [Tg] are
attained. which has ben demonstrated in the PREDICI Q simulations of Greszta et
al. (19%). A typical unirner concentration ir ~o*'M and values on the order of 1 0 ~
mol L-' and 10" mol L-' for p] and [Tq respectively are comrnonlÿ reported
(Greszta et al., 1996). The large d u e for the deactivation rate constant (kt) coupled
with the large excess of nitroxide result in very few propagating chains in the systern.
The generation of radicals by thermal polyrnerïzation can thus be seen to dominate
Equation 5.7, with the concentration of unimer exerting M e influence on the
concentration of propagating radicals in the system. The polymenzation rate is
therefore governed by the rate of thermal radical generation, which is the same in al1
of the systems investigated.
It is also evident from Figure 5.1 that substantial curvature in the conversion-
tirne profile may exist. This leveling effect is thought to stem fiom a buiidup of
nitroxide in the system, which would shift the equiIibriurn in Equation 2.7 to the
dormant polymer f o m and decrease the rate of polymehtion. Since there is
initially no excess nitroxide present in the BST system, this buildup could onIy result
fiom unavoidable chain temination reactions. In addition, the decrease in
polyrnerization rate could also result if there is a significant amount of dead chains,
which woutd decrease the amount of propagating chains in the system. PREDICI Q
simulations by Ma et aI. (unpublished, 200 1) for this system have shown that the
population of dead chains increases throughout the poiymenzation, with almost half
of the polymer chains predicted to be dead by 60 % conversion.
5.3.2 Number Average MolecuIar Weight
The number average mo[ecular weight is s h o w as a hnction of conversion in
Figure 5.2 for al1 three EST concentrations. A "livingn radicai poIymerization is
chatacterized by a linear relationship between molecular weight and conversion,
which indicates a constant nurnber of propagating chains. Conventional radical
polymen'zations on the other hand, do not exhibit a linear relationship between Mn
and conversion.
in the BST systems, a fiirly linear relationship is observed indicating
a cuntrolled polyrnerization is achieved. This linearity suggests that the influence of
autopolymerization and/or termination reactions to the total amount of propagating
chains is relatively small. At higher BST concentrations, lower molecular weight
polystyrenes are obtained. This is because mare radicals are generated at higher
levels of unimer, thus decreasing the average chah length at a given conversion.
The alkoxyamine therefore acts to control the molecular weight of the resulting
polymer.
O 20 40 60 80
Conversion (% )
Figure 5.2: Influence of BST Concentration on Mn in Miniemulsion
The molecular weight of the potystyrenes produced in these experiments
should theoretically be controlled by the molar ratio of styrene to BST. Commonly,
the experimental rnolecular weight of polystyrene produced from unimers has show
close agreement with the calculated theoretical rnolecular weight. To examine this
relationship in miniemulsion, the theoretical molecular weights were calculated
according to Equation 5.8, which assumes that every TEMPO molecule caps one
polymer chain.
moles of styrene reacted M*& = [ moles of TEMW
In the above expression Mnth represents the theoretical molecular weight. The
calculated values of M~ are compared to the experimental Mn in Figure 5.2 for each
unimer concentration. At low conversions there is close agreement between the
experimental and theoretical molecular weights. Above approximateky 20%
conversion. greater deviation between the values is observed. This deviation is likely
due to the increasing influence of thermal polymerization, which generates more
radicals and hence lowers the average chain length. The data aiso suggests that less
discrepancy between experimental and thecretical Mn is achieved at higher unimer
concentrations, where the corresponding nitroxide level is also higher.
5.3.3 Particle Size and Particle Size Distribution
Particle size measurements were made on the Malvern Mastersizer 2000.
Particle size is an important variable in understanding the colloidal properties and
stability of miniernulsion polymerizations. Table 5.4 below provides the results of
the volume weighted mean diameters (D,) for the time zero and 6 hour latex sampies.
Values are reported at 6 hours due to the different reaction times employed in this
Table 5.4: Summary of Volume Weighted Mean Diameters for BST Polymerizations
As shown in Table 5.4, the volume weighted mean diameter at ail unimer
Run 1 Zero Sample Dv (pm)
leveIs are comparable at 6 hours. The zero samples volume weighted mean diameters
6 Hour Sample Dv (pm)
include only the main particle size distribution peak. A very srnail fraction of Iarger
diameter particies were present in these sarnples, which is believed to be the result of
some droplet inMbüity. These l u g a particles disappured in the subsequent
samples.
F i p 5.3 shows the variation in particle diiniution at t h e zero, 3 houn and
12 hours for SFRMP-74. SFRMP-75 and SFRMP-78 produced similas results
although a smd shoulder of larger diameter partictes was observeci in SRIMP-78
after 1.5 hours. At 1 5 houn SFRMP-75 dso displayed a s d distniution of
particles between 1-10 )im Partide size distniutions for aU sampla taken during
these mns are provided in Appendii C.
As displayed in Rgure 5.3, the particle s k distniution was fairly constant
thmughout the polymdtion. These results indicate that the little or no additional
particle nudeation is o m n i n g in the system during the polyrneihtion. Larger
diarneta particles were obsemd in dl ofthe m samples. It is unclear if this
shoulder relates to possible dmplet waiescence or the meanirement produre.
Regardles of the rPason, after the onset ofpolyrnerintion the system appears to
equüiirate and these particles disappear.
Particle Sue (pm)
--
[ Partide Size (w)
Fi@re 53: Pdde Size Distributions for SFRMP-74 (a) zero ample @) 3 houn (c) 6 hours (d) overiay
5.4 Hydroxy-BST Polymerization Results
5.4.1 Fractional Conversion
The fiactional conversion of the hydroxy-BST mns as a tiinction of time is
displayed in Figure 5.4. As seen in the BST system, the concentration of hydroxy-
BST has little effect on either the polymerization rate or final conversion and
indicates the polymerization rate is again controlied by the thermal polymerization
rate. Possible leveling in the conversion-time relationship is also apparent. The
likely sources of this curvature are a buildup oFexcess nitroxide and/or dead polyrner
in the system.
Figure 5.4: Influence- of Hydroxy-BST Concentration on Conversion in Miniemulsion
5.4.2 Number Average Molecular Weight
Figure 5.5 shows a nearly linear relationship between average number
moIecular weight and conversion at each of the 3 tevels of hydroxy-BST investigated.
As expected, the higher the unimer concentration the lower the average number
molecular weight at a given conversion. This is attributed to the greater amount of
radicals produced at higher unimer concentrations. The nearly linear relationship
again verifies the minor effect of termination and thermal polymerization on the
number of propagating chahs in the system.
O 20 40 60 80
Conversion (% ) I
Figure 5.5: Influence of Hydroxy-BST Concentration on Mn in Miniemulsion
The relationship between experimentai and theoretical moIecular weights for
the hydroxy-BST system are alw shown in Figure 5.5. As illustrated in the plot,
excellent agreement between theoretical and experimental Mn is achieved. At
concentrations of 0.0014 M and 0.020 M the deviation is Iess than 10 % at
conversions above 60 %. At greater concentrations of unimer, there appears to be
better agreement between theoretid and experirnental molecular weights. The
deviation between theoreticid and experirnental values can again be likely attributed
to radical generation from autopolymerization. In addition, better molecular weight
control appears to be obtained with the hydroxy-BST system. Partitioning of the
hydroxy-BST unimer to the aqueous phase could potentially decrease the number of
chains in the system. As a resuIt, chains generated thermally may not influence the
molecular weight as significantly in the BST system. Furthemore, fewer low
molecutar weight dead chains in the hydroxy-BST systems coutd also account for the
closer agreement between experimental and theoretical molecular weight.
5.4.3 Particla Size and Particle Size Distribution
Table 5.5 provides the volume weighted mean diameters for the time zero and
6 haur samples. Both the zero samples and 6 hour sarnples show fairly good
agreement at al1 unimer Ievels. In contrast to the BST system, the time zero samples
didn't indicate the presence otany large diameter particles.
Figure 5.6 shows the particle size distribution for SFRMP-8 1 at tirne zero. 3
houn and 12 hours. Al1 other particle size distributions are provided in Appendix C.
The distribution is fairIy similar at al1 poIymerization times and comparable results
were obtained for SFRMP-79 and SFRMP-82. A maIl shoulder of larger particles
appeared during the course of the polymerization at 12 hours for SFRMP-8 1. Similar
shoutders were observed in SFRMP-79 and SFRMP-82 at 1.5 and 3 hours
respectively. This is thought to be the result of some minor latex instability in the
system.
Table 5.5: Summary of Volume Weighted Mean Diameters for Hydroxy-BST Polymerizations
Run 1 Zero Sample Dv (pm) 1 6 Hour Sample Dv (pm) 1
PaRicte Size (pm) I I
Figure 5.6: Particle SLe Distributions for SFRMP-8 1 (a) Zero Sample @) 3 hours (c) 6 hours (d) Overlay
5.5 Cornparison of BST and Hydroxy-BST Systems
It was thought that the differing water solubilities of the nitroxide moieties
composing the unimers would exert considerable influence on SFRP in miniernuision.
Dissociation of BST and hydroxy-BST produces TEMPO and hydroxy-TEMPO
respectively as the nitroxide species. It was expected that a higher degree of
partitioning of hydroxy-TEMPO could decrease the amount of nitroxide in the
particles thereby increasing the polymerization rate compared to the system
employing BST.
Using the standard minemuIsion formulation the proportion of fie nitroxide
(TEMPO or hydroxy-TEMPO) residing in the organic phase was calculated. The
partition coefficients for TEMPO and hydroxy-TEMPO at 135 O C have been reported
as 98.8 M/M and 2.2 M/M respectiveIy (Ma et al., 2001). At the reaction temperature
of 135 O C , the volume of the organic (hexadecane + styrene) and aqueous phases is
approximately 44 ml and 130 ml respectivety. Assuming 0.0001 moles of ndroxide
in the aqueous phase the percentage of TEMPO/hydroxy-TEMPO in the organic
phase is determined fiom the partition coefficients and Equation 2.12. These
calculations are shown below for the TEMPO system.
[nitroxide in aqueous phase] = 0.000 1 moies / 0.130 L = 7.69 x 1 O-' M
[TEMPO]oec = (98.8 MIM) x (7.69 x lo4 M) = 7.60 x M
(moles = (7.60 x 1 O-' M) x (0.044 L) = 3.34 x 1 O-'
Total moles TEMPO = 3.34 x 105 + 0.000 1 moles = 3.44 x 10''
% TEMPO in Organic Phase = (3.34 x 1 u3)/ (3.44 x 10") x 100 = 97??
Similarly, the percentage of hydroxy-TEMPO in the organic phase was calculated to
be 43 %.
5.5.1 Polymenzation Results
Table 5.1 shown previously, displays the final results for both systerns. The
polydispersities in the hydroxy-BST systems were siightly broader than their BST
counterparts. This is thought to indicate a slightly greater degree of termination in the
hydroxy-BST systern. A possible explanation for ths phenomenon may be the
partitioning of hydroxy-BST to the aqueous phase, wkch results in a lower nitroxide
concentration in the polymer particles. Further cornparison of these two systerns will
be made in the following sections.
5.5.2 Fractional Conversion
The m i o n a l conversion as a fùnction of time is compared for the BST and
hydroxy-BST systems in Figure 5.7 (a)-(c) for each unimer concentration. The
polymerization rates are very similar for both unimer systems at al1 of the
concentrations employed. This indicates varying the water solubility of the nitroxide
does not intiuence the polymerization rate significantly. This result is not completely
unexpected given that equilibrium show in Equation 2.7 has relativety Little
influence on the concentration of propagating radicals in the system. The
polyrnerization rates of both BST and hydroxy-BST systems are largely controlled by
the rate of thermal polyrnerization and therefore the influence of nitroxide
partitioning has relatively insignificant effect on the observed rate. In general,
higher final conversions were reached with the hydroxy-BST system. This indicates
that the role of partitioning might increase at longer reaction tirnes (higher
conversions) when the role of thermal polyrnerization is less significant. Greater
partitioning to the aqueous phase would result in a lower hydroxy-BST concentration
in the polyrner particles and hence a faster rate of monomer addition.
l -
1 Time (hours)
H B S T , m BST !
i Time (houn)
l O 5 10 15 I lime ( ~ o u ~ s )
HBST1 ' a BST
( 4 Figure 5.7: Influence of Unimer on Polymerization Rate in Miniernulsion (a) 0.007 M (b) 0.0 14 M (c) 0.020 M
Figure 5.7 also indicates that the polymerization rate for the BST
polymerization may be slightly greater than in the hydroxy-BST system. The
partitioning characteristics of BST and hydroxy-BST unimers in this system is
currentiy unknown. Given the nature of hydroxy-TEMPO to partition to the aqueous
phase, it is likely that hydroxy-BST also partitions to a much greater extent than BST.
A loss of unimer to the aqueous phase results in fewer propagating chahs in the
particles and accounts for a slightIy Iower polyrnerization rate in the hydroxy-BST
system.
5.5.3 Number Average Molecular Weight
The Mn-conversion profile for both systems at al1 unimer concentrations is
displayed in Figure 5.8 (a)-(c).
Conversion (%)
I
Conversion (%)
O P 40 60
Conversion (X)
(cl Figure 5.8: Influence of Unimer on Mn in Miniemulsion (a) 0.007 M (b)0.0 14 M (C) 0.020 M
Figure 5.8 shows that at al1 unimer concentrations the Mn at a given
conversion is lower for the BST system after approximately 20% conversion. This
indicates that there are fewer propagating chains in the hydroxy-BST system.
resulting in a greater chain fength at a given conversion. Theoretically, at the same
unirner concentration an qua i amount of radicals and hence polyrner chains should
be generated. The Iower amount of c h a h in the hydroxy-BST system is thought to
indicate a loss of unimer to the aqueous phase. In addition, a Ioss of unimer to the
aqueous phase also decreases the concentration of nitroxide at the polymerization
sites possibly resulting in more termination reactions. A slightly higher rate of
termination, as supported by the somewhat broader polydispersities in the hydroxy
BST system, can also account for the lower concentration of propagating chains.
Figure 5.9 (a)-(c) compares the number of chains in BST and hydroxy-BST
systems at each unimer concentration directly. As expected fiom the molecular
weight data the number of chains in the hydroxy-BST system is generaily Iower at a
given conversion than in the BST system. The reason for this discrepancy is again
believed to be a larger degree of partitioning of hydroxy-BST to the aqueous phase.
O 20 40 60 80
Conversion (% )
/ 4 0.007 M HBS' i 8 0.007 M BST
1 4 0.014 M HBST l
I H 0.014 M BST
O 20 40 60 80
Conversion (%)
Conversion (% )
1 0.020 M HBST / / / 0.020 M BST i j
(c) Figure 5.9: Influence of Unimer on Number of Chains in Miniernulsion (a) 0.007 M (b) 0.014 M (c) 0.020 M
5.6 Conclusions
"Living" Radical polymerizations conducted with BST and hydroxy-BST
indicate the polymerization rate is dominated largely by the rate of
autopolymerization. Nitroxide partitioning to the aqueous phase does not influence
the kinetics of SFRP in minernulsion as shown by the similarity of the rate profiles
for the two alkoxyamines. Furthemore, the concentration of unimer also exerts little
influence on the polymerization rate. Leveling in the rate protiles is believed to
result from a buildup of excess nitroxide andor the accumulation of dead chains in
the systern.
The principle role of the akoxyarnine is to conml the molecular weight and
polydispersity of the systern. It is thought that partitioning of hydroxy-BST rnay aIso
decrease the amount of propagating chains compared to systems using BST. This
phenomenon may lead to better moiecular weight controi with hydroxy-BST unimers.
Chapter 6
6. Unimolecular Initiators in Bulk SFRP
Although SFRP has been studied extensively in bulk, considerably less work has
been done in heterogeneous systems. Currentiy, there is an increasing interest in
conducting SFRP in emulsion systems, where process scale-up could be more easily
accomplished. This chapter outlines the results obtained fiorn styrene bulk
polymerizations employing BST and hydroxy-BST. Bulk and miniemulsion systems
employing the same concentration of unimers are compared directly in order to gain a
better understanding of SFRP in miniemulsion.
6.1 Experimental
Bulk polymerizations were conducted in the 300 mi autoclave reactor at 13 5 OC.
using the standard miniemulsion formulation and procedures outlined in Chapter 3.
Three nins were conducted for both BST and hydroxy-BST at the same organic phase
concentrations as utilized in the miniemulsions discussed in Chapter 5 . Run conditions
are outlined in Table 6.1 below.
Table 6.1: Summary of Run Conditions for Unirner Study in Bulk
Rua
SFRMP-83 SFRMP-84 SFRMP-85 SFRMP-90 SFRMP-9 1 SFRMP-97
Unimer
BST BST BST
Hydroxy-BST Hydro~y-BST
Unimer Concentration (molcsk)
0.007 0.0 14 0.020 0.007 0.014
Reaction Time (hours)
8 8 8 8 8
Hydroxy-BST 1 0.020 8
6.2 Polymerization Results
A summary of the final conversions (x), number average moIecular weights (Mn),
polydispersities (Ma,,), number of polyrner chains and apparent initiator efficiencies
(F,,) for both unimer systems is provided in Table 6.2. The number of chains and
apparent initiator efficiencies were calculated using the equations presented in Chapter 5.
The polydispersities at 8 hours ranged from 1.46-1.62. These somewhat broad
polydispersities indicate irreversible termination reactions andor short chain generation
by thermal polyrnerization may broaden the molecdar weight distribution of buIk
systems considerably.
lnitiator efficiencies well above one were obtained in ati of the bulk
polymerizations, illustrating the high success rate of radicats produced from unimer
dissociation in becoming propagating chains. In addition, these initiator eficiencies
veri@ that thermal polymerization is significant in these systerns.
Table 6.2: Summary of Unimer Bulk Polymerization Results
Run
SFRMP-83
r (?A)
8 1
M n
50,967
M&ln
1.60
# Polymer Chainsk Organic
Phase (x 1 or')
7.71
Fa,,
2.06
6.2.1 Fractionai Conversion
The fiactional conversion data for BST and hydroxy-BST at al1 unirner
concentrations is depicted in Figures 6.1 and 6.2 respectively. As previously seen in
miniernulsion, the reaction rates are relatively independent of the concentration of
alkoxyamine employed. The initial 1: 1 stochiometry of the unimer and the buitdup of
nitroxide according to the persistent radical efEect, strongIy favors the deactivation
reaction shown in Equation 2.7. The dominance ofthis reaction results in most radicals
existing in the dormant form. ThermaI radical generation acts to consume nitroxide
molecules in the system and promote the activation reaction (Equation 2.7). The rate of
poIymenzation is therefore largely governed by the thermal initiation rate and is not
greatly infiuenced by the unimer concentration.
in both the BST and hydroxy-BST systerns, lower final conversions are obtained at
the Iowest unimer concentration (0.007 M). The reason for this difference is believed to
stem from a lower amount of propagating chains in the system, which results in a greater
sensitivity to the buildup of nitroxide.
i
T i m (hours)
Figure 6.1 : Influence of BST Concentration on Conversion in BuIk
Q 50 100
Conversion (% )
Figure 6.3: Influence of BST Concentration on M, in Bulk
O 50 1 00
Conversion (% )
Figure 6.4: Influence of Hydroxy-BST Concentration on Mn in Buik
As shown above, similar values for experimental and theoretical molecular
weights are obtained at Iow conversions (-20 %). Above this limit, the deviation
increases substantially with the expenmental molecular weight lower than theoretically
predicted. At 8 hours this deviation is greater than 40 % for both unimer systems. The
lower experimental molecular weight at a given conversion illustrates that
a significantly greater amount of propagaring chains exists in the system than
theoretically expected. The source of this discrepancy can be attributed to thermaliy
generated polymer chains, which influence molecular weight more significantly at higher
conversions. As indicated by the high initiator eficiencies, autopolyrnerization is
substantial in these systems.
6.3 Comparison of BST and Hydroxy-BST Systems in Bulk
The bulk polyrnerkations employing BST and hydroxy-BST are compared in the
following sections. Similar polymerization characteristics were expected since the same
concentrations of unimer were employed in a homogeneous system.
6.3.1 Fractional Conversion
Figure 6.5 (a)-(c) compares the bulk polymerization rates for the BST and
hydroxy-BST systems. At the same tevel of unimer, the polymerization rates are very
similar for the two alkoxyamines. This result is expected since at a given unimer
concentration and in the absence of partitioning, the two systems should theoretically
have the same amount of nitroxide and propagating radicals. In addition, the rate of
polymerization is governed by the thermal polymerization rate and neither the unimer or
its concentration significantly influences the reaction rate.
l l O 5 10 l I Time (hours) 1 I
2.00 I
LI 1.50 - rn
Y 4 1 ; 4 EST / 1 C 1.00 - m 1 l
BST 1 i Hydroxy-BST i
C I
0.50 -
Figure 6.5: Influence of Unimer on Bulk PoIymerization Rate (a) 0.007 M (b) 0.0 i4 M (c) 0.020 M
0.00 O 5 10
0.07
Time (hours)
8
a'
1 i ~ ~ d r o x y 4 ~ 7 j ~ 1
6.3.2 Number Average Molecular Weight
The &-conversion profile for both systerns is presented in Figure 6.6 (a)-(c). At
unimer concentrations of 0.014 M and 0.020 M, the BST and hydroxy-BST systerns have
very similar Mn d u e s at a aven conversion. This indicates a comparable amount of
propagating chains exists in the system regardless of the unirner employed. Previously in
the miniemulsion system discussed in Chapter 5. higher molecular weights at a given
conversion were achieved when hydroxy-BST was utilized. The similarity of the Mn-
conversion profiles in the bulk systerns supports the belief that unimer partitioning in
miniemulsion may influence the amount of propagating chains. The differences observed
in the Mn-conversion profile at the unimer concentration of 0.007 M is currently unclear
and requires furcher investigation to detemine if this difference is significant.
4 BST . . Hydroxy-BST I ;
! 0.00 50.00 100.00 I I Conversion (% ) I
/ 4 BST 1 1 : ~ i y d m ~ - ~ ~ ~ j /
i Conversion (%)
Conversion (016)
: 4 BST
(cl Figure 6.6: Influence of Unimer on M,, in Bulk (a) 0.007 M (b) 0.014 M (c) 0.020 M
6.4 Cornparison of Bulk and Miniernulsion SFRP
The foliowing sections directly compare the results obtained from bulk and
miniernulsion polymerizations using BST and hydroxy-BST unimers.
6.4.1 Fractional Conversion
A comparison of the conversion-time profiles for the various unimer
concentrations is presented in Figure 6.7 (a)-(c) and Figure 6.8 (a)-(c) for the BST and
hydroxy-BST systems respectively.
-
O 5 1 O 15
tirne (hours)
I ; + Bulk l 1 1 i j ; l i i Miniemulsion i !
+ Bulk I
l Miniemulsion 1 1
1 1 l O 5 10 15 I i Time (hours)
Time (hours)
(cl Figure 6.7 : influence of Polymerization System on Conversion (a) 0.007 M BST (b) 0.014 M BST (c) 0.020 M BST
1
J i Miniernulsion i i
I
3.00
I
2.50 -
p 2.00 - t 1 SO - c 7 1.00 -
0.50 -
Time (hours)
I
8 . . 4
1
0.00
, l
1.6 - i 1.4 - 1
I 1.2 - LI 1 -
i Y 6
1 = 0.8 - i 1 4 0.6 - i
I 0.4 - i
' l 0.2 - i 0 8
O 10 20 30
Time (hours)
1 Bulk Miniemulsion ,
I
: Bulk I
I
' I , i Miniernulsion 1 1
2.5 - j 2 -
i 8 1 . 5 - i 1 % 1 Î 1 - I
I I
i
*mm
l 0 - 8 4,
/ 4 Bulk 1
/ 1 1 I I 1 i Miniernulsion i !
(cl Figure 6.8: Influence of Polymerization Systern on Conversion (a) 0.007 M Hydroxy- BST (b) 0.0 14 M Hydroxy-BST (c) 0.020 M Hydroxy-BST
As shown in Figures 6.7 and 6.8, the rate profiles are significantly different in
buik and rniniemulsion for both unimer systems. The reaction rate in bulk is initialty
sirnilar to the rate observed in miniemulsion, but shows a substantially faster rate at
langer reaction tirnes. The source of this large deviation in reaction rate can be attributed
to several possible sources. Although the systems are compared at the sarne organic
concentration of unimer, the presence of hexadecane in the miniemulsion system results
in a lower rnonomer concentration than the conesponding bulk system. As shown
previously in Equation 5.5, the thermai rate of initiation has a third order dependence on
the monomer concentration. Thermal polymerization is therefore about 1.5 times greater
in the bulk systems because the monorner concentration is approximately 20 % higher
than in miniemulsion. The difference in autopolymerization between the two systems
may contibute to a bulk reaction rate that is significantly greater. This conclusion is
fiirther supported by examining the apparent initiator eEciencies shown in Tables 5.2
and 6.2 for the miniemulsion and bulk systems respectively. Significantly higher
efficiencies are obtained in the bulk systern (1.69-2.06) compared to miniernulsion (0.92-
1-38), which could result fiom the differing contributions of thennally generated radicals.
It is also possible that partitioning of the monomer between the polymer particles and
hexadecane may occur and also contribute to a reduced monomer concentration in the
miniemulsion system.
In addition, the absence of hexadecane in the bulk system increases the system
viscosity and may decrease the termination rate especially at high conversions. This may
result in a greater number of propagating chains in the bulk system and hence a faster
polyrnerization rate. Similarly, a loss of radicals, to the aqueous phase in rniniemulsion
could also reduce the nurnber of propagating chains compared to the bulk system.
Finally, the nature of this difference might also be attributed to the viscous nature of the
homogeneous system, which resulted in difftculty in maintaining the reaction temperature
at longer time periods. Higher temperatures at later stages in the reaction may also
increase the thermal polymerization rate in bulk systems.
The differences in the number of propagating chains may also explain the absence
of leveling in the rate profiles for the bulk system. The greater arnount of propagating
chains in bulk enhances the activation reaction (Equation 2.6). A significantly greater
amount of propagating chains makes these systems Iess sensitive to the buildup of
nitroxide and possibly eliminateddecreases the leveling observed in miniernulsion.
6.4.2 Number Average Molecular Weight
Figures 6.9 and 6.10 compare the bulk and miniernulsion relationships between
M,, and conversion for BST and hydroxy- BST respectively. As demonstrated in the
figures, at a given conversion the average number molecuIar weight is approxirnately the
same regardless of the poIymerization system. The dilution effect of hexadecane results
in differing unimermonomer ratios in the corresponding bulk and miniemulsion systems.
The molar ratio of unimer:monomer determines the molecular weight of the resulting
polymer, with lower ratios resulting in higher molecular weights. In the absence of
thermal polymerization, higher molecular weight polyrners at a given conversion (fewer
chains) would thus be expected in the bulk system where the unimer:monomer ratio is
lower. In the bulk system, there is a larger amount of polymer chains resulting from
several possible sources as previously discussed. This coincidently seems to result in
simiiar Mn values at a given conversion for both systems at a given unimer
concentration.
0.007 M -Bulk, 1
0.014 M -Bulk / l
A 0.020 M -Bulk ' ; 0.007 M-ME '
x 0.014 M -ME 0.020 M -ME 1
1
I
0.00 50.00 100.00
Conversion (%)
Figure 6.9: Influence of Polymerization System on &-Conversion Profile for BST
j r 0.007M-Bulk ( ! 8
i .0.007 M- ME 1 A 0.020 M- Buk 1 1 +0.020 M-ME i /
1 j x 0.014 M-Bulkjj ia0.014M-ME , !
l O 50 100 I j i Conversion (% ) 1
Figure 6.10: Influence of Polymerization System on Mn-Conversion Profile for Hydroxy- BST
In addition, the significant differences between the two systems can be obtained
by exarnining the relationship between experimental and theoretical molecular weight in
Figures 5.2, 5.5,6.3 and 6.4. The difference between the experimental and theoretical
values is substantially greater in the bulk system at al1 unimer concentrations, This larger
deviation can again be expiained by a larger amount of growing c h a h in the bulk
sy stem.
6.5 Influence of Hexadecane Dilution in B d k
To determine the influence of hexadecane dilution on the polymerization rate, a
bulk polymenzation with hexadecane was perforrned (SFRMP- 12 1). The organic phase
concentration of BST was 0.014 M so that a direct cornparison could be made with
SFRMP-84. The final results for this run are provided in Tabie 8.3.
6.5.1 Fractional Conversion
Table 6.3: Summary of Results for Bulk Run with Hexadecane
The conversion-time profiles for both runs are show in Figure 6.1 1. As shown in
the plot, the addition of hexadecane has a very rninor influence on the polymerization
rate. The substantial rate enhancement in bulk is therefore not entirely dependent on the
thermal polymerization rate or viscosity effects.
6 No hexadecane ! !
Run
SFRMP-121
i Hexadecane : ;
x (%)
87
M n
3 1,26 1
Figure 6.1 1 : Influence of Hexadecane Dilution on Conversion in Bulk
6.5.2 Number Average Molecular Weight
The M,,-conversion profiles for buik runs SFRMP-84 and SFRMP-121 are dispiayed
in Figure 6.12. The similarity in the profiIes suggests that a larger thermal
M J M n
1.25
# Polymer Chains /L Organic
Phase (x ion) 1.15
F,,,
1.59
poIymerizations rate in the absence of hexadecane dilution does not significantly
contribute to the total number of propagating chains in the systern.
O 50 100
Conversion (% )
Figure 6.12: Influence of Hexadecane Dilution on Mn in Bulk
6.6 Conclusions
As seen in the miniemulsion systems of Chapter 5, neither the unimer concentration
nor the actual unimer employed significantly influenced the polymerization rate. The
reaction rate in bulk systems is primarily determined by the thermal polymerization rate,
which acts to consume excess nitroxide in the system. Ln addition, the slope of the
conversion-time profile in bulk is significantly steeper than the corresponding
miniemulsion system. The source of this deviation is currently unknown and requires
hrther investigation. The Iarger amount of chains may ultimately lead to broad
polydispersities at high conversions and dificulties in obtaining a weII controlled bulk
polymerization.
Chapter 7
7. Use of Additives in Miniernulsion SFRP
Successtùl application of SFRP to miniernulsion requires 100 % rnonorner
conversion within relatively short reaction times. The resuits presented in Chapter 5
show the maximum conversion in miniemulsion with unirners is less than 75 % in 12
hours. Additives such as CSA, have shown considerable rate enhancernent in
birnolecular bulk polyrnerizations. The influence of additives on the polymerization rate
in miniemulsion was therefore of interest in this study. CSA, acetic anhydride and L-
ascorbic acid were investigated for their potential in rate enhancernent of SFRP in
miniernulsion using unimolecular initiators. The influence of additives in these systems
is of particular interest due to the inherent 1 : 1 stochiometry of initiating radica1s:nitroxide
initiatly present in the systern.
7.1 Experimental
Ai1 miniemulsion poIymerizations were conducted in the 300 ml reactor using the
formulation and procedures reported previously in Chapter 3. Run conditions are
specified in Table 7.1. Additional nins with L-ascorbic acid are provided in Appendix
B.
Table 7.1: Summary of Run Conditions for Unimer Study with Additives
1 Run [ Unimer (g) 1 Additive 1 Molar ratio 1 Reaction Time 1 SFRMP-96 S m - 9 9 SFRMP- 100
SFRMP-105
7.2 CSA Results
CSA has been shown to influence nitroxide-mediated polymerizations by directly
SFRMP-108
reducing the fiee TEMPO concentration. The results of runs employing CSA in
BST, 0.20 g BST, 0.20 g Hydroxy- BST, 0.21 g BST, 0.20 g
miniernulsion with unimolecular initiators are provided in Table 7.2.
BST, 0.20 g
CSA CSA CSA
Acetic
7.2.1 Fractional Conversion
Anhydride L-Ascorbic
Acid
Table 7.2: Summary of Results for Unimer Study with CSA
The conversion-time profiles for the runs with added CSA are shown in Figures
7.1 and 7.2 for the BST and hydroxy-BST systems respectively. The relationship
between conversion and time has also been plotted for the same nins without acid for
Unimer:Additive 1:OS 1:l 1: 1
1:l
Run
S m - 9 6
SFRMP-99
SFRMP- 1 O0
(hours) 24 8 8
8
1 :0.05 22
x (Yo)
76
75
74
M A I , ,
1.37
1.34
1.48
Mm
37,374
32,877
34,205
# Polymer Chainsl L Organic Phase
(XI O") 8.30
9.32
8.83
F,,,
1.15
1.28
1.21
cornparison. In both systems, a small rate enhancement is observed with the addition of
CSA in the BST system, the rate enhancement appears to be significantly larger at 8
hours for the highest BST:CSA ratio. At 24 hours the low ratio of BST:CSA (1 : O S ) still
shows a substantially higher final conversion than the polymerization without added
acid. The increase in rate is thought to result 6om a decrease in the Level of fiee
nitroxide in the system, thereby promoting the activation reaction shown in Equation 2.7.
The main influence of CSA seems to be a reduction in the leveling of the polymerization
rate previously observed in the mns without acid in Chapter S. This is thought to indicate
the sensitivity of these systems to the buildup of nitroxide.
These prelirninary experiments indicate that wme rate enhancement in
miniernulsion systems may be gained with the addition of CSA. The rate improvement
in miniernulsion is however, not as dramatic as results in bulk polyrnerizations obtained
by Georges et al. (1994). CSA residing in the aqueous phase iikely reduces its
effectiveness in decreasing the free nitroxide concentration in the polymer particies.
Figure 7.1: Muence of CSA on PoIymerization Rate in BST System
O 10 20 30
Time (hours)
j 8 NO CSA i 1
Figure 7.2: Influence of CSA on Polymerization Rate in Kydroxy-BST System
7.2.2 Number Average Molecular Weight and Polydispersity
Figures 7.3 and 7.4 present the relationship between Mn and conversion for the
BST and hydroxy-BST systems respectively. The conesponding runs without CSA have
again been shown for comparison. As required for a living system, the molecular weight
increases linearly with conversion. In the BST system, larger molecular weights at a
given conversion occur at the high level ofCSA. It is possible some suppression of
thermal initiation andfor increased chain termination in the presence of CSA may be
responsible for this behavior. On the other hanci, the Mn-conversion profile in the
hydroxy-BST system appears relativeIy unaffected by the presence of CSA, indicating a
similar number of chains in both systems. This suggests that suppression of thema1
poIymerization in the BST system is not IikeIy responsible for the greater moIecuIar
weight at a given conversion. in addition, both the BST and hydroxy-BST system may
show some leveling d e r -50 % conversion, which may denote some Ioss of Iivingness in
the systern. Further investigation is required to determine if CSA significantly influences
the molecular weight of the resulting polymer.
i O 50 100 1 Conversion (% ) I
Figure 7.3: Influence of CSA on Mn in BST System
I
Conversion (%)
1 + 1:l HBST:CSA 1 ' m No CSA
l !
Figure 7.4: Influence of CSA on Mn in Hydroxy-BST Systern
The influence of CSA on the polydispersity of these systems was also of interest.
Figures 7.5 and 7.6 display the reiationship becween conversion and polydispersity for the
BST and hydroxy-BST systems. In g e n e d the systems with CSA show broader
molecuiar weight distribution as might be expected with less nitroxide to control the
polymerization, Acid addition however, still resulted in polydispersities below the lower
theoretical limit for conventional radical polymerization (1 S).
Conversion (% )
/ & M C S A l i I
: m 1:1 BSTCSA
Figure 7.5: Influence of CSA on Polydispersity in BST System
I 1 1 6 - I I 1.55 - 1 1.5 - ; 1.45-
m I r : i Hydmxy BSTCSA 1 . 4 B No CSA I
m . g 1.25 -
l I l -
! Conversion (%) ; 1 1
Figure 7.6: Influence of CSA on Polydispenity in Hydroxy-BST System
7.2.3 Particle Size and Particle Size Distribution
The volume weighted mean diameters 0,) for the time zero and 6 hour samples
are provide in Table 7.3. Srnail and relativety insignificant secondary peaks were
observed in al1 zero samples and were not used in the calculation of Dv. A bimodal
distribution was measured at 6 hours for SFRMP-96 and 99 and both partide
distributions have been inctuded in Table 7.3.
Table 7.3: Surnrnary of Volume Weighted Mean Diameters for CSA Study
I Run 1 Zero Sample Dv (pm) 1 6 Hour Sample Dv (pm) 1
A comparison of SFRMP-96 and SFRMP-99 with the results fiom run SFRMP-78
(no CSA) shows substantial differences. The BST mns employing CSA exhibit a
significant distribution of large diameter particles at 6 hours. Figure 7.7 (a)-(c) shows the
variation in particle size distribution at time zero, 3 hours and 6 hours for SFRMP-99.
These large particles may illustrate some reduced stability in emulsions containing CSA.
The results fiom SFRMP-IO0 shown in Table 7.3 show better agreement with the
run without added CSA (SFRMP-82, Table 5.5). A small shoulder of large diameter
particles is present as depicted in Figure 7.8 (a)-(c).
I Particle Ske (um)
I Particle Size m)
3-01 0.1 I Partide Size hm)
(4 l I Figure 7.7: Pa&&'& Disinbution for SFRMP-() The Zero @J 3 houn (c) 6 hours (ci) overlay
Partiçle Size (w) \ 3 H o m 6 H o m
I&re 7.8: Particle Size Distribution for SFMRP-100 (a) Time Zero (b) 3 hours (c) 6 hours (d) Overlay
7.3 Influence of Acetic Anhydride
Acetic anhydride has previously been show to improve the rate of SFRP of
styrene in bulk (Miilmstom et al., 1997). A prelirninary run to determine the influence of
acetic anhydride in the miniemulsion polymerization of styrene using BST was
conducted. The final resuIts for this run are provided in Table 7.4.
7.3.2 Fractionai Conversion
The conversion data for SFRMP-105 is compared to the systern without acetic
anhydride (SFRMP-78) in Figure 7.9 below. Acetic anhydride provides a rnodest
increase in polyrnerization rate very sirnilar to that obsenred with CSA The difference in
fiadona1 conversion is most apparent at 24 hours. The ongin of this rate enhancernent is
Table 7.4: Sumrnary of Final Results for BST Polymenzation Using Acetic Anydride F ~ P P
1.20
Run
S M - 1 0 5
r (%)
74
Mmm
1.39
Mm
35,046
# Polymer Chains / L
organic hase !Il (x 10
8.70
believed to be a reduction of the fiee nitroxide level by reaction with acetic anhydride.
The presence of water in the miniernulsion rapidly converts acetic anhydride to acetic
acid. Partitionhg of acetic acid to the aqueous phase likely reduces its effectiveness in
reducing the nitroxide level in the organic phase.
-~ -
Figure 7.9: influence of Acetic Anhydride on Polymerization Rate in BST System
7.3.2 Average Number Molecular Weight and PoIydispersity
The evolution of molecular tveight with conversion in the system follows a
tinear trend in the presence of acetic anhydride as shown in Figure 7.10. [n addition,
acetic anhydride appears to exert no significant influence on the number of propagating
chains as illustrated by the similarity of the Mn-conversion profiles.
Conversion ("rd )
4 No Acetic Anhydride
, ! 1:1 EsTacetic anhydride / /
l
Figure 7.10: Influence of Acetic Anhydride on M,, in BST System
Figure 7.1 1 depicts the change in potydispersity as a tiinction of conversion.
Initially, the polydispersity is significantly broader in the system employing acetic
anhydride. However, the polydispersity in S M - 1 0 5 decreases over the course of the
polymerization and shows no significant difference Fiom S M - 7 8 at 8 houn.
: No Acetic , Anhydride
' l:1 8 ~ f : ~ c e t i c i : Anhydride
O 20 40 60 80
Convarsion (%)
Figure 7.1 1 : Muence of Acetic Anhydride on Polydispersity in BST System
73.3 Particle Size and Particle Sue Distribution
The Dv àt t h e zero and 6 hours was measured to 0.137 pn and 0.153 -p
respdivcly. The volume weighted mean diameten at 6 hours for run SFRMP-105 and
the nrn without acetic anhydride (SFRMP-78, Table 5.4) are very simüar, with both
particle sire distriiutions displaying a maIl shoulder of larger diameter particles. At
t h e zero the Dv is sEghtly smaller for the system with acetic anhydride,
The particle size distributions at zero, 3 houn and 6 hours for SFRMP-105 are shown
in Figure 7.12 (a)-(d). As depicted in the figure, the particle size distriiution is consistent
-oughout the polymerization.
PartFe Sie @m) .
Figure 7.12: Particle Site Distn'butian for SFMRP-IO5 (a) T i e Zero @) 3 hours (c) 6 hours (d) Overlay
7.4 Influence of L-Ascorbic Acid
Thé use of L-ascorbic acid as a rate enhancirrg additive has not yet been reported. L-
ascorbic acid is however, believed to be capable of decreasing the level of fiee nitroxide
considerably in SFRP (Georges, 2000). To explore this possibiiity, L-ascorbic acid was
added to a minimernulsion poIymerization with a BST unimer (SFRMP-108).
SFRMP-IO8 employed a 1:0.05 molar ratio ofBST:ascorbic acid and reached a final
conversion of 68 % in 22 hours. Results of this poIymerization will be discussed further
in the following sections.
7.4.1 Fractional Conversion
The conversion-time profile for SFRMP- 1 O8 is provided in Figure 7.13. The rate
profiles for SFRMP-96, SFRMP-99 and SFRMP-105 have been included so the rate
enhancement of the different additives can be directly compared. As shown in the figure,
ascorbic acid most effectively increases the reaction rate eady on in the polymerization
even at a very low level. At longer reaction times the final conversion is better for
systems empIoying acetic anhydride or CSA but at much higher additive concentrations.
no acid
i
i 1 :O.Os B S T : ~ S C O ~ ~ ~ C I ~ acid
A 1 : O S 0ST:CSA
' 4 1 :1 BST:Acetic / Anhydride ' 1 :1 BST:CSA
O 10 20 30 I
Tirne (hours)
Figure 7.13: Influence of Additives on Polymerization Rate in BST System
7.4.2 Number Average Molecular Weight and Polydispersity
A meaningful measure of molecular weight and moIecular weight distribution
could not be obtained for SFRMP-108. A bimodai distribution, signaling a poorly
controlled polymerization was obtaiaed h r ail samples. The GPC traces for the 3,6 a d
22 hour simples are shown in Figure 7.14. Th Iower moiecular peak is observed to shift
to higher moIecuIar weights during the course of the polymerizatioa. nie very broad
higher molecular weight peak remab rdativeIy unchanged with t h e and may indiate
figure 7,
Elution Time (minutes) ' . .
1: ~decular ~ a @ t ~ i s t r i b u t i o n for SFRh@-108
7.4.4 Particle Size and Particle S i Distriiution
The volume weighted mean diameters for the t h e zero and 6 hour sarnples were
0.1 12 and 0.134 pn rq&y. Ai bah siunpling times the Dv was slightly d e r
thk the rame experiment without ~scorbi i acid (SFRMP-78). As indicated in Figure
7.15 (a)-@), the particle sizc distn"bution is relaiively stable throughout the
polymerization
1 Particie Size @m)
Particle Sie @III) \ Zero Hom 6 Hom
\'-1 - -
Figure 7.15: Particle Size Disttr'bution for SFMRP-108 (a) T i e Zero @) 3 hours (c) 6 hours (d) Overlay
7.5 Conclusions
CSA, acetic anhydride and L-ascorbic acid provided a small improvement in the
polymerization rate of SFRP in miniemulsion with unimers. In al1 cases, the mechanism
of rate enhancement was thought to result fiom a reduction in the level of fiee nitroxide.
L-ascrobic acid displayed the most rate enhancing potential, although though the degree
ofcontrol in the system was dramatically reduced. Partitioning to the aqueous phase is
also thought to decrease the influence of additives in miniemulsion.
Chapter 8
8. TTOPS in Miniernulsion
TEMPO-terminated oligomers of polystyrene were utilized as macroinitiators
to fùrther the kinetic understanding of SFRP in miniemulsion. In addition to the
benefits of unimolecular initiation previously discussed, macroinitiators have
essentially no water-solubility. The insolubility of TTOPS initiators prevents
partitioning to the aqueous phase and makes them a potentiai costabiiizer for
miniemulsion systems.
The influence of hexadecane and the surfactant concentration were specifically
addressed in this study. The results of these polymerizations are discussed in the
sections that follow. In addition, a BST polymerization was conducted bas4 on the
results From the TTOPS experirnents and is also discussed.
8.1 Experimental
The polymerizations were conducted at 135 O C in the 300 ml reactor. The
ïTOPS initiaton were prepared as described in Chapter 3. A summary of the run
conditions is provided in Table 8.1, where (A) (Mn=18,900, M&= 1.24) and (B)
(Mn=1,284, MJl&=1.25) denote the specific rnacroinitiator utilized. The comment
section indicates ifthe macroinitiator was purified and isolated before use.
Table 8.1: Sumrnary of TTOPS Run Conditions
Run
SFRMP-113
SFRMP-114
SFRMP-Il9
8.2 Polymerization Results
The final results for the TTOPS polymerizations are presented in Table 8.2 and
are discussed in the sections that follow. Results for SFRMP-122 are reported at 6
TTOPS (g)
6.60
SFRMP-120
SFRMP-122
hours due to an inconsistent conversion believed to be the result of a
6.60
1.37
nonhomogeneous sample at 24 hours.
Ecxadecane (g)
4.37
1.37
6.60
O
O
SDBS Concentration
0.02 1
O
O
Table 8.2: Summary of Final TTOPS Polymerization Results
0.021
0.089
Reaction Time
(hours) 24
0.02 1
0.089
Run
SFRMP-113
SFRMP-II4
S W - 1 1 9
SFRMP- 120
SFRMP-122
Comments
Isolated (A)
24
6
M,/M,
1.54
L .46
L .3 5
1 .27
1.49
Isolated (A)
Non-Isolated
6
24
x (%)
4 1
58
89
72
96
(B) Non-Isolated
(B) Isolated (A)
# Polymer Chahs/ L Orgnnic
Phase (xi$')
3.85
6.08
26.60
2 1-60
7.55
M.
43,26 1
46,759
16,022
15,896
62,232
F~PP
0.8 1
1 .O7
1.12
0.9 1
1 .O2
8.3 Influence of TTOPS Initiator and Hexadecane
Stable minemulsions have been prepared using polystyrene in place of a
traditional hydrophobe such as hexadecane. The low water-solubility of the polymer
also serves to prevent OstwaId ripening and stabilizes the miniernulsion droplets
(Bechthold et al., 2000). The ability to obtain stable latexes without a costabilizer is
important fiom an industrial scale-up perspective, as removal of the hydrophobe is
otlen dificult and economically unattractive.
To determine the influence of a TTOPS initiator cornpared to the tow molecular
weight unimers previously discussed, miniemulsion polymerizations with
macrointiators were conducted. The effect of hexadecane in miniemulsion SFRP
with TTOPS was explored in runs SFRMP-113 and SFRMP-114. The polydispersity
was observed to increase during the course of the polymerization for both systems
and ranged between 1.39- 1.54 and 1.35-1.46 for SFRMP-113 and S F M - 1 14
respectively. The results for both runs are compared in the following sections.
8.3. t Fractional Conversion
Figure 8.1 shows the monomer conversion as a tiinction of time for SFRMP-
113 and SFRMP-114. As indicated in the plot, both polymerizations show an initial
rapid increase in conversion foIIowed by a substantial leveling after approximately
4.5 hours. As before, this leveling may result fiom a buildup of nitroxide in the
systern andfor the presence of dead polymer chains. In both runs, the macroinitiators
were purifieci and thus ody a smaII equilibrium arnount of excess TEMPO should be
present at the start of the polymerization. irreversible termination reactions must
therefore be accountable for any excess nitroxide. It is also apparent fiom these
results that macroinitiators do not improve the reaction rate of SFRP in miniernulsion
over the unimers discussed in Chapter 5.
Figure 8.1 : Influence of Hexadecane on Conversion in TTOPS Polymerizations
Figure 8.1 also shows the polymerization rate is significantly faster in the
system without hexadecane. The higher viscosity in the absence of the costablizer
may contribute to the observed rate enhancement. In more viscous systems chain
termination by combination is decreased due to difision limitations. In addition, the
monomer concentration is lower in SFRMP-1 13 because the organic phase is diluted
with hexadecane. The rate of thermal initiation has a third order dependence on
monomer concentration as indicated in Equation 5.6. The polymerization rate is
therefore faster in SFRMP-Il4 because the monomer concentration is approximately
20 % higher than in SFRMP-113. This is supported by the larger amount of potyrner
chains and greater initiator efficiencies found for SFRMP-114 (Table 8.1).
8.3.2 Number Average Molecular Weight
The &-conversion profile is provided in Figure 8.2 and displays a relativeiy
linear relationship. The polymenzation without hexadecane has a slightly lower Mn
at a given conversion, indicating a greater number of propagating chains. The greater
rate of thermal polymerïzation in SFRMP-I 14 accounts for the deviation in the
number of chains between the two runs. In addition, SFRMP-113 may have a more
substantial rate of termination because of the Iower viscosity in the presencc of
hexadecane, which may also decrease the amount of propagating chains. A Iarger
rate of termination in SFRMP-113 is further supported by broader polydispersities
compared to SFRMP- 1 14.
O 20 40 60 80
Conversion (% ) L
Figure 8.2: Influence of Hexadecane on M, in TTOPS Polymerizations
Figure 8.2 aiso shows the expenmental molecular weights at agiven
conversion are lower than theoretically predicted. The generation of chains by
thermal poiymerization andfor the presence of low molecular weight dead polymer
chains are not incorporated into the theoreticai molecular weight calculation and
account for this difference.
8.3.3 Particle Size and Particle Site Distribution
The influence of hexadecane on latex stability was an important consideration
in this investigation. Table 8.3 provides the vofume weighted mean diameters at time
zero and 6 hours. The mean diameters are similx at both sampling times and for both
runs. indicating a high degree of colloidal stability even without hexadecane. The
stability of SFRMP-114 is further illustrated in Figure 8.3, which displays the particle
size distributions at time zero, 3 houn and 6 hours. Replicate measurements of the
same samples also produced consistent distributions and volume average weighted
diameters except in the case of the time zero sarnple. Results for the remainder of
samples are provided in Appendix C.
Table 8.3: Summary of Volume Weighted Mean Diameters for ïTOPS merizations (Hexadecane Study)
Run 1 Zem Simple Dy (pm) 1 6 Baur Sample h /
Particle Size (pm)
Particle Sire (pm)
Particle Size luml
&un 8.3: Piutide Size Distn'butions for SFRMP-114 (a) zero sample (b) 3 hours (c) 6 hours (d) Overlay
8.4 Influence of Surfactant Concentration
TTOPS polymerizations with macroinitiator (A) achieved a maximum
conversion of only 58 % in 24 hours. Recently, Keoshkerian et al. (2001) have
reported TTOPS polymerizations in miniernulsion with conversions up to -99.5 % in
6 hours (Kwshkerian et al., 2001). The SDBS concentration was a major diaence
in the formulation used by the Xerox group and that employed previously in this
work. The possible influence of SDBS concentration on SFRP kinetics was
investigated by repeating the initial experiment wnduded by Keoshkarian et al.
(2001) at 0.089 M SDBS, with another nrn at our 0.021 M SDBS coucentdon - .* .
(SERMP-120). The influence of surfactant concentration was fùrther exploreci by
repeating SFRMP-114 at the high IeveI of SDBS. The resuIts of these
polymerizations are discussed in the sections that foUow.
8.4.1 Fractional Conversion
The influence of surfactant concentration on the conversion-time profile is
shown in Figures 8.4 and 8.5 for rnacroinitiators (B) and (A) respectively, As
indicated in the plots, the level of SDBS appears to have a very significant influence
on the polymerization rate. In both TTOPS systerns, increasing the surfactant
concentration results in substantially higher reaction rates. In the case of
macroinitiator (A), conversions above 95 % were reached in only 1 .S hours. which
shows an even faster reaction rate than reported by the Xerox group. Several
possible explanations can be proposeci to expiain this relationship. In minemulsion,
increasing the amount of surfactant can potentially decrease the size of the monomer
droplets. As the monorner size is decreased compartmentalization effects (increased
radical segregation) become more significant, resuiting in the ability to achieve high
reaction rates. In addition, it was aIso thougfit that higher SDBS concentrations rnight
allow for micellar and/or homogeneous nucleation, resuiting in a greater number of
polyrner particles and an enhanced polymerization rate. As will be discussed in the
section 8-43, the similarity in the particle size distributions at difEerent SDBS
concentrations appears to rule out al1 of these possibilities.
The enhanced polymerization rate is currently thought to be the influence of
impurities in the SDBS, which may be acting to consume fiee nitroxide in the system.
As shown in Equation 2.7, decreasing the level of nitroxide promotes the activation
reaction and improves the polymetization rate.
I 1 a 0.021 M SDBS'I
I Time (hours)
Figure 8.4: Influence o f SDBS Concentration on Conversion for Macroinitiator (B) -
ïime (hours)
Figure 8.5: Influence o f SDBS Concentration on Conversion for Macroinitiator (A)
0.021 M SDBS, I i 0,089 M 1
l
4.00 1 3.50 -
3.00
, 7 2so 2.00
! + 1 5 0 - 1 1 00 - l 0.50 - I
0.00
8.4.2 Number Average MolecuIar Weight
. 8
4 4
The influence of SDBS on the relationship between Mn and conversion is
provided in Figures 8.6 and 8.7.
20000 iaooo 1 A
16000 - 8 .
14000 - ,#' 12000 - /- g 10000 - ic' 8000 -
6000 -
Conversion (% ) 1
Figure 8.6: Influence of SDBS Concentration on Mn for Macroinitiator (B)
1 Conversion (% )
Figure 8.7: Influence of SDBS Concentration on Mn for Macroinitiator (A)
As shown by the above plots, the Iinear relationship between conversion and
Mn indicates the polymerizations proceeds in a controiled manner. At the 0.089 M
SDBS concentration for macroinitiator (A), the reiationship between conversion and
Mn is not established because very M e change in the conversion occurred aller 1.5
hours. The polydispersities measured however, do not indicate an uncontrolled
conventional radical polymerization.
For both TTOPS initiators, the experimental M, is lower than the theoretical
value at the high level of SDBS. The difference is very small for TTOPS (B) and
much greater for TTOPS (A). In both TTOPS systems, low molecular weight dead
polymer andor thermal polymerization may increase the number of propagating
chains and decrease the experimental Mn. At the 0.021 M SDBS concentration for
(A). the experimental molecular weight-conversion profite nearly coincides with the
theoretical profile, indicating excellent molecular weight control. The larger
difference obtained with TTOPS (B) at both SDBS concentrations requires tùrther
study but may be the result of a significant amount of high molecular weight dead
polymer in the purified macroinitiator. The presence of these dead chains may inflate
both the theoretical molecular weight and the Mn of the living chains which are used
subsequent TTOPS polymerizations. The theoretical molecular weight may therefore
actually be lower than the calculateci value and doser to what is observed
experimentally.
8.4.3 Particle Size and Particle Size Distributions
The average volume weighted mean diameters for these mns are provided in
Table 8.4. Results are reported at 1.5 hours due to very broad distributions (often
covering the entire range between 0.02-2000 pm) and dificuity in obtaining
consistent values for the time zero samples of SFRMP- 1 19 and SFRMP- 120. The
d u e s for SFRMP- 1 14 have been reported previously in Table 8.3.
As shown in Tables 8.4 and 8.3, the D, at both sampling times is relatively
Table 8.4: Summary of Volume Weighted Mean Diameters for TTOPS Polymerizations (SDBS Study)
consistent at both SDBS concentrations. The particle size distributions for SFRMP-
122 at time zero, 3 hours and 6 hours is provided in Figure 8.8. As shown, the
6 Hour Sample D v (pm) O. 116
Run
SFRMP-119
particle size distributions are also comparabte throughout the polymerization,
1.5 Hour Sample D v (pm) O. t08
indicating a high degree of colloida1 stability. A shoulder of lower diarneter particles
is not observed as might be expected if a significant amount of homogeneous ancilor
micellar nucleation was occumng In addition, comparison of the distributions in
Figure 8.8 with those in Figure 8.3 show the two runs produce nearly coincidental
distributions. CompartrnentaIization effects may be apparent at the 0.089 M SDBS
concentration if significantly smaller particle sites were obtained. These results
indicate that neither enhanced homogeneous nucleation, micellar nucleation or
compartmentalization effects seem to be responsible for the enhanced polymerization
rates at the higher SDBS Ievel. ïhe same conclusions were developed by examining
the panicle size distributions for SFRMP- 1 19 and t20, which are provided in
Appendix C.
Parücle Size (pm) (4
Particle Size (pm)
Particle Size (ph) --.
;
Figure 8.8: Particle SUe Didniutiom for SFRMP-122 (a) zero sample @) 3 hours (c) 6 hours (d) overlay
8.5 Influence of Hexadecane and Surfactant Concentration in BST System
The stability of the monomer droplets without hexadecane in S M - 1 14,
prompted fùrther investigation towards an emulsion based SFRP systern. To explore
this possibility, BST was polymerized according to run SFRMP-78 but without
hexadecane and at the higher IeveI of surfactant.
8-51 Fractional Conversion
A conversion of 8 1 % was achieved in 1.5 hours, which shows a substantial
increase in the polymenzation rate fiom the BST nrns discussed in Chapter 5 . As
shown in Figure 8.9, the polymerization was aiso essentiaily complete afîer 1.5 hours
and displays a much faster reaction rate than SFRMP-78. At 12 hours a slightIy
lower conversion was calculated. This is thought to stem tiom stability problems in
the emulsion, resulting in non-homogenous sarnpting.
- ..
Figure 8.9: influence of Hexadecane and Surfactant Concentration on BST Conversion
8.5.2 Number Average Molecular Weight
The Mn-conversion proflie is provided in Figure 8.10. The relationship
between Mn and conversion cannot be detemined from the data obtained as the
polymerization was essentially finished by 3 hours. Comparkon with SFRMP-78
seems to indicate more chains are present in the system without hexadecane. This
may again be attributed to a greater thermal polymerization rate and possibly less
termination due in the absence of hexadecane.
Conversion (% )
Figure 8. IO: infiuence of Hexadecane and Surfactant Concentration on BST Mn
1
I MI exp SFRMP-124 / 1
1-Mth 1 , & M exp SïRMP-78 , ,
i l
l
60000 - 50000 -
40000 - 30000 -
20000 -
10000 -
O
O 50 100
0 v
: eo
A
A
, &'- .Y.
&
8.5.3 Particle S k and Particle Sie Diiiution
The volume weighted mean diameters at t h e zero and 6 hours were rneasured
to be 3.262 pn and 1.003 jm respectively- The large diameter particies obtained
indicate the absence of costabilizer has a dramatic influence on the colloida1
properties of the emulsion. Phase separation of the emulsion during the
polymerization also supports this conclusion.
Particle size distributions ofsamples taken during the course of the
polymerization are shown in Figure 8.11. As shown, the distn'butions were bmad and
varie. considerably d u ~ g the course of the polymerization. The size of the
monomer droplets at time zero is consistent with those typidy observed in a
conventional emulsion. Bknodal distributions were obtained at 1.5,3,4,5 and 12
houn, These distributions may indicate additionai nucleation mechanisms
(hornogeneous and micellar) in the systen The coiioidai stability of the potymer
partides in the absence of hexadecane for the BST rystem appean signifioidly
Parficle Size (pm) * -.
1 PaWe Size (pm)
h
2 5
Zero-
Figure 8.11: Particle Sue distributions for SFRMP-124 (a) zero sample @) 3 houn (c) 6 hours (d) 12 hours (e) overlay
8.6 Conclusions
The results presented in this chapter indicate that stable TTOPS
miniemulsions cm be forrned without the presence of a costablilizer. Faster
polymerization rates are also achieved in the absence of hexadecane because of lower
chah termination and a greater rate of theFrna1 potymerization
The concentration of surfactant employed in lTOPS poIymerizations was
found to dramatically influence the reaction rate with conversions over 95 %
attainable in 1.5 hours. The source of the rate enhancement at higher surfktant
concentrations is currentIy thought to be a reduction in the ftee nitroxide Ievels by
impurities present in SDBS,
S p with BST at a high concentration of sudactant and without hexadecane
substantially hproved the polymerization rate. Reduced coiIoidal stabiiity was
however, observed in the absence of the wstabiir.
Chapter 9
9. Butyl Acrylate SFRP
There have ben few documented reports on stable fiee radical polymenzations of
acrylate monomers in heterogeneous systems. As previously mentioned, successtiil
acrylate polymerization is complicated by the sensitivity of these systems to the buildup
of nitroxide. It was thought that the partitioning of nitroxide to the aqueous phase in
miniemulsion could be beneficial by reducing the nitroxide Ievel in the organic phase.
Decreasing the amount of nitroxide at the polymerization sites would shifl the
equilibrium shown in Equation 2.6 to the active polymer form and increase the rate of
polymerization.
9.1 Experimental
Miniernulsion polymerizations of butyl acrylate were peîformed using various
nitroxiddinitiator systems. The standard miniemulsion formulations for the 300 ml and
1 .O L reactors discussed in Chapter 3 were employed.
A water-soluble initiator (KPS) and an organic-soluble initiator @PO) were
utilized to determine the influence of initiation in the aqueous and organic phases
respectively. TEMPO. hydroxy-TEMPO and 4-0x0-EMPO were investigated as
possibIe nitroxides. PotentiaIly, the different partitioning behaviors of these nitroxides
could be used to controI the concentration of nitroxide in the organic and aqueous phases,
thus conceivably influencing the molecular weight, polydispersity, reaction rate and other
polymerization characteristics. The initiator:nitroxide molar ratio was 1 :2 to ensure 1
molecule of ~ t roxide for every radical generated. The temperature was increased above
135 O C where indicated, in an attempt to promote dissociation of the dormant species.
The run conditions are outline in Table 9.1.
1 S M - ( 9 1 0.46 (TEMPO) 1 0.40 (KPS) 1 150 6 ]
Table 9.1: Run Conditions for Butyl Acrylate Polymerization Run
S M - 1 4
1 SFRMP-22. 1 0.25 (Hydroxy-TEMPO) 1 0.18 (BPO) 1 135 1 6 1 SFRMP-20
I
SFRMP-23 1 0.46 (TEMPO) 1 0.36 (BPO) / 150 6 1
Run Time (hours)
L 2
Nitroxide (g)
0.46 (TEMPO)
0.50 (Hydroxy-TEMPO)
i I I 1
SFRMP-28 1 0.50 (40x0-TEMPO) 1 0.40 (KPS) 1 150 6
I l I I
* lndicates reaction performed in 300 ml reactor
tnitiator (g)
0.40 (KPS)
0.40 (KPS)
SFRMP-26' 1 0.50 (Hydroxy-TEMPO) 1 0.36 (BPO) 1 150
9.2 Polymerization Results
Temperature ( O C )
135
6
The final conversions, average number molecular weights, polydispersities,
theoretical molecular weights and apparent initiator eficiencies of the runs employing
bimolecular initiation are provided in Table 9.2 on the next page. The apparent initiator
eficiencies and theoretical molecular weights were caiculated as s h o w previously in
Chapter 5.
Table 9.2 indicates (with the exception of SFRMP-29) that very Little butyl
acrylate polymerized in the bimolecular systems investigated. The polydispersities were
al1 fairly dose to 1.5, the theoreticai Iower limit for radical polymerization. In ail runs
150 6 1
the initiator eficiencies were extremely low, indicating that very few radicals generated
tiom the initiator succeeded in becoming polymer chains. The low initiator eficiencies
result in experimentally higher molecular weights than theoretically expected. In
addition, this means the number of polymeric radicals in the system is much lower than
the number of TEMPO molecules. Nitroxide may also accumulate in the system due to
termination and hydrogen transfer reactions. Furthermore, acrylates do not thermally
polymerize as significantly as styrene. The low amount of thermally generated radicals
may therefore also contribute to the buildup of nitroxide in acrylate systems. Excess
nitroxide coupled with the fast deactivation reaction may lead to the slow rates of
polymerization observed here,
Hydroxy-TEMPO has a larger water solubility than TEMPO and thus a Iower
concentration of this nitroxide was expected at the polymerization sites. However, no
significant improvement was gained by changing the nitroxide fiom TEMPO to hydroxy-
Table 9.2: Summary of Results for Butyl Acrylate Polymerizations f&
0.15
O. 10
0.11
0.09 * *
0.09 * *
0.03
0.32
Run
SFRMF-14
SFRMP-15
SFRMP-19
SFRMP-20
S W - 2 2
S M - 2 3
SFRMP-26
S M - 2 8
SFRMP-29
* Indicates no polymer detected by GPC ** Results could not be caiculated
Run Time (hours)
12
12
6
6
6
6
6
6
6
x(%)
9
5
10
6
0.8
5
4
4
49
Mn
1 1,648
10,477
18,563
12,397 *
12,355 *
23,537
29,793
Mna
1,713
1,048
2,029
1 , I 14 * *
1,068 **
866
9,865
Mwmn
1.49
1.37
1.77
1.57 *
2.1 *
1.46
1.74
TEMPO with either initiator. In addition, little if any improvement was gained by
increasing the temperature. Some success was achieved when 4-0x0-TEMPO and BPO
were employed as the nitroxide and initiator respectively. These results are discussed in
the next section.
9.2.1 4-0x0-TEMPO Nitroxide
As show in Table 9.2, the best bimolecular system utilized a 40x0-TEMPO
nitroxide. Figure 9. L shows the rates of polymerization for a system with 4-0x0-TEMPO
and KPS or BPO as the initiator (SFRMP-28 and SFRMP-29 respectively).
Figure 9.1 : Influence of initiator on Conversion in Butyl Acrylate Polymerizations using 4-0x0-TEMPO
The rate of polymerization is significantly increased in the Coxo-TEMPO system
employing a BPO initiator over systems utiIizing TEMPO or hydroxy-TEMPO with
either initiator. In addition, Figure 9.1 shows that the rate of polymerization is only
improved in the 4-0x0-TEMPO system if BPO is used as the initiator. Recently, Stenzel
et ai. (1999) have found similar results using 44x0-TEMPO and BPO in styrene bulk
polymerizations. They found in contrast to polymerizations employing TEMPO, no
induction period was observed if styrene was polymerired using 40x0-TEMPO and
BPO. It was believed that side reactions of 4-0x0-TEMPO with BPO andior independent
decomposition reactions of 4-0x0-TEMPO were responsible for this behavior. 4-0x0-
TEMPO is thought to have a lower stability than other nitroxides such as TEMPO as a
result of the carbonyl group. A proposed decomposition reaction of Coxo-TEMPO to
produce an unsaturated nitroso compound and a hydroxylamine is shown in Equation 9.1
(Stenzel et al., 1999). Dewmposition in this manner may effectively reduce the nitroxide
concentration and allow for monomer addition to occur at an improved rate compared to
the TEMPO or hydroxy-TEMPO systerns.
In addition, Stenzel et al. (1999) suggested that BPO could abstract hydrogen
fiom Coxo-TEMPO (Equation 9.2) to fom bentoic acid. This possibility may be
responsible for the observed improvement in the polymerization rate in the 4-0x0-
TEMPO system employing BPO. Since no reaI rate improvement is experimentally
observed with KPS, the side reactions of BPO and 44x0-TEMPO may be the dominant
factor in the observed rate enhancement.
Figure 9.2 shows the relationships between conversion and Mn for the 4-0x0-
TEMPO nitroxide with both KPS and BPO initiators. The polymerization initiated with
BPO shows a linear relationship characteristic of a contmlled polymerization. On the
other hand, there is virtually no change in molecular weight atler 1.5 hours for the K P S
initiated system. This behaviour might be expected if a large excess of nitroxide
essentially stopped monomer addition. The lower amount of nitroxide in the BPO
polymerization does however. resuit in a broadening of the polydispersity compared to
the KPS system. These results indicate some improvement in polymerization rate may be
attained if 4-0x0-TEMPO and BPO are used as the nitroxide and initiator respectively.
Figure 9.2: influence of Initiator on M, in Butyi Acrylate Polymerizations using 40x0- TEMPO
' 4 KPS SFRMP-28 1
i BPO SFRMP-29
-
O 20 40 60
Conversion (%) !
4 . . 0
4 . .* -4'
U'
8-
9.3 Other Polymerizations
In addition to the previously discussed experiments, several other nitroxide-
mediated polyrnerizations of butyl acrylate were attempted. Emphasis was placed on
decreasing the level of nitroxide during the polymerizations in an attempt to enhance the
reaction rate. The applications of unimers, addition of CSA and fiirther polymerizations
with 4-oxo-TEMPO and BPO were explored in this respect. The results of these
experiments and others are summarized in Appendix B. Further studies are required to
h l ly interpret these results.
Chapter 10
10. Conclusions
A vanety of nitroxide-mediated polymerizations were conducted in order
to develop a better understanding of SFRP in miniemulsion. BST and hydroxy-BST
unirnolecular initiators were utilized and the influence of using a heterogeneous
system. unirner concentration and additives was addressed. TEMPO-terminated
oligomers of polystyrene (T'TOPS) were also used as initiating systems. In addition,
the use of butyl acrylate in living radical miniemulsion polymerization was explored.
Molecular weight, polydispersity, conversion, and particle size distribution were the
response variables, which were measured by GPC, gravimetry and the Malvem
Mastersizer 2000. The data acquired from these results ted to the following
conclusions:
i In both miniemulsion and bulk systems the concentration of unimer has an
insignificant eft'ect on the polyrnerization rate. The reaction rate in these systems
is deterrnined by the thermal polymerization. The role of the unimer is to control
the molecular weight and polydispersity of the resulting polymer by the
activatioddeactivation reaction s h o w in Equation 2.6.
i The different partitionhg characteristics of nitroxides in unirnolecular initiators
does not greatIy influence the kinetics of SFRP in miniernulsion.
> Leveling tvas observed in the conversion-time profiles for afl alkoxyamines
studied in miniemulsion. The source of this curvature is thought to be a buildup
of excess nitroxide andor the presence of a signiftcant amount of dead chains.
h Polymerization rates for both unimers were faster in bulk systerns. The source of
this rate enhancement has not yet been determined. Accurate molecular weight
control is also complicated in bulk systems by the larger arnount of propagating
chains.
i Moderate rate enhancement was obtained using both CSA and acetic anhydride in
miniemulsion SFRP with unimolecular initiators. The observed rate
enhancement in miniemulsion is thought to be less dramatic than observed in bulk
due to additive partitioning. L-ascorbic acid has greater rate enhancement
capabilities than either CSA or acetic anhydride but results in a uncontrolled
polymerization.
i Butyl Acrylate SFRP is complicated by the buildup of nitroxide in the system
resulting tiom termination reactions and the absence of a significant amount of
thermal polymerization. These features lead to very slow polymerization rates,
which may be improved upon by ernploying BPO and 4-oxo-TEMPO as the
initiator and nitroxide respectively
i T'TOPS polymerizations conducted without hexadecane resulted in faster
polymerization rates and no change in the colloidal stability of the emulsion
i High levels of surfactant with a TïOPS macroinitiator achieved a conversion of
- 95 % conversion in 1.5 hours. Consumption of excess TEMPO by impurities
in the surfactant is currentiy thought to be responsible for this behavior.
Chapter I I
1 1. Recommendations
The results Eom this investigation have provided valuable information on SFRP
in miniernulsion. Based on these results the following recornmendations have been
identified for future work in this area:
A quantitative measure of the degree of Iivingness is rquired to better understand
the kinetics of SFRP in miniernulsion. In addition, reinitiation of the polymer
chahs should be attempted to demonstrate the feasibility of bIock copolyrners and
other more complex macromolecular structures.
> Rate enhancement is required in alkoxyarnine miniernulsion polymerizations to
achieve hiyh conversions and narrow molecular weights. Further investigation
into possible additives in these systems is required. Continuous addition of
additives. or addition at a Jater point in the polymerization might be investigated
as a means to enhance reaction rate.
> Investigation of SFRP rnediated by nitroxides with potential decomposition
pathways may allow for improved polymerization rates of styrenelacrylates by
decreasiny the kee nitroxide concentration.
> The source($ of the observed rate enhancement in buik systems requires fiirther
study.
i Additional investigation into the possible sources of rate enhancement in TTOPS
polymerizations is warranted. Further studies with TTOPS should include:
Influence of polymer isoiation/purification on SFRP characteristics
> Measurement of TEMPO concentration with time in the presence of SDBS to
determine if the nitroxide level is reduced in the presence of this surfactant
> Assessment of the influence of initiation (unimolecular/bimolecular initiation)
and system (buIWminiemulsion) utilized in TTOPS preparation on
polymerization characteristics.
> Determination of the maximum molecular weight attainable by SFRP with
TTOPS while still retaining a high degree of "livingness".
i Future TTOPS polymerizations should be conducted without hexadecane as scale-
up possibilities would be limited in the presence of this CO-stabilizer.
> Possible rate enhancement of acrylate rniniemulsion polymerizations via
addition of a slow decomposing initiator should be explored to possibly assume
the role of autopolymerization (Goto et al., 1999).
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Ma, J. W., Smith. J. A., and Cunningham, M.F. (200 1). Stable Free-Radical Polymerization of Styrene in Miniemulsion Part 1- Mode1 Studies of Alko~yamine- tnitiated Systerns. To be published, 200 1.
Ma, J.W.. Unpublished Simulation Results.
MacLeod, P.J., Veregin, R.P.N., OdeIl, P.G., and Georges, M.K. (1997). Stable Free Radical Polymerization of Styrene: Controlling the Process with Low Leveis of Nitroxide, Macromolecrrlrs, 30. 2207-2208.
Malrnstrom. E.. Miller. R.D., and Hawker, C.J. (1997). Development of a New Class of Rate-Accelerating Additives for Nitroxide-Mediated 'Living' Free Radical Polyrnerization. T~.rruheJron. 53. 15225- 15236.
Malrnstrom, E.E., and Hawker. C.J. (1998). Macrornolecular Engineering via 'Living' Free Radical Polymerizations. Macromoi. C'hem. Phys. ., 199,923 -93 5.
Marestin, C., Noel. C., Guyot, A., and Claverie, J. (1998). Nitroxide Mediated Living Radical Polymerization of Styrene in Ernulsion. Mucromoirrrrles, 3 1,4041- 4044.
Miller, C.M., Sudol, E.D., Silebi, C.A., and El-Aasser, M.S. (1995). Miniemulsion Polymerization of Styrene: Evolution of the Particle Site Distribution. Jut~n~uf of Polymrr Scierrce: P m A: Poiymer ('hrmistry, 3 3, 139 1 - 1408.
Moad. G., Rizzardo, E., and Solomon. D.H. (1982). Mcrcromolectlrs. 15.909.
Moad, G., and Rizzardo, E. (1995). Alkoxyamine-Initiated Living Radical Polymerization: Factors Affecting Alkoxyamine Hornolysis Rates. Macromolrmles, 28,8722-8728.
Pan, G.. Sudol, E.D.. Dirnonie, V.L., and El-Aasser, M.S. (2001). Nitmxide- Mediated Living Free Radical Miniemulsion Polymerization of Styrene. M~cromnizc~~lcs. 34.48 1-488.
Puts, RD., and Sogak D. Y. (1996). Macromofcc~~~ies~ 29, 3323.
Smith. J.A. (2000). Undergraduate Thesis, Queen's University.
Souaille, and M.. Fischer. H. (2000). Kinetic Conditions for Living and Conuolled Free Radical Polymerizations Mediated by Reversible Combination of Transient
Propagating and Persistent Radicals: The Ideal Mechanism. Macrornolec~ifes, 33, 7378-7394.
Steenbock, M., Klapper, M., Muilen, K., Pinhal, N., and Hubrich, M. (1996). Synthesis of Block Copolymers by Nitroxyl-Controlled RadicaI Polymerization. Acta Pofymer, 47,276-279.
Stenzel, M., and Schmidt-Naake. G. (1999). High Conversion Study of "Living" Radical Polymerization of Styrene using DSC. Atrgavmrdte Makromolrkzilare ('hernie, 265,4246.
Sudol, E.D., and El-Aasser, M.S. Miniemulsion Polymerizations, in Etntrlsioti Pulyrnerizati~~t~ trtrd Emrrlsiori Polymers ( P.A Lovell and M.S. El-Aasser, Eds.), John Wiley and Sons Ltd., Toronto. 1997, Chapter 20.
Tang, P.L., Sudol, E.D.. Silebi, C.A., and El-Aasser, M.S. (1991) Miniemulsion Polymerization-A Comparative Study of Preparative Variables. Jcrrirrral of Applird Pofymrr Scirtrcr. 43. 1059- 1066.
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Appendix A: Typical NMR Spectra
Figure Al: Typical 'H NMR of BST
Figure A2: Typical 'HNMK o f ~ ~ d r o x ~ BST
Appendix B
B. Additional Polymerizations
B. I Polymerizations with 4-Oxo-TEMPO
B. 1.1 Styrene PoIymerizations
A series of runs were conducted using styrene, 4-oxo-EWO and either BPO or
KPS as the initiator. The initiator level and mass ratio of nitr0xide:initiator were varied
as s h o w in Table B 1, with al1 other ingredients kept constant at the standard
miniemuIsion formulation. Reactions were perfomed at 135 O C in the t .O L reactor
unless otherwise indicated. Final results at 6 hours are shown in Table B2-
able B I : Summary of Run Conditions for Polymerizations usinp; 4-Oxo-TEMPO Run ] Initiator 1 4-oxo-TEMPO ( Mass ratio
S M - 5 8
SFRMP-59
Comments
SFRMP-60
(g)
0.2 (BPO) 0.10
S M - 6 1
(BPO) 0. 10
SFRMP-64
(8)
0.22
0.1 1
@PO) 0.30
( B W
SFRMP-67
@PO) 0.20
SFRMP-69
4-0x0- TEMP0:initiator
1.1
1.1 300 ml reactor
LHH I
0.33
@PO) O. IO
SFRMP-7 1
LLH 150 O C
LLH
0.23
0.34
(KPS) 0.30 W S )
2.3
2.3
0.11
(KPS) 0.20
HLH
: -7
0.33
MMH
1.1
0.34
LLH
1.1 HLH
1.7 MMH
B. 1.2 Butyl Acrylate Polymerizations
Table B2: Summary of Final Results for Styrene Polymerizations using 4-0x0-TEMPO
Additional butyl acrylate poIymerizations were also conducted with 4-0x0-
Run 1 x (Yo) 1 Mm
TEMPO and BPO. As before, the initiator level and nitr0xide:initiator ratio were varied.
Mn& 1 M w m 1 F~PP
The run conditions and final results at 6 hours are provided in Tables 8 3 and B4
respectively. The standard 1 .O L miniemulsion formulation was employed and reactions
were conducted at 150 OC.
ible 83: Summary of Run Conditions for Butyl Acrylate Polymerizations using 4-0x0- SMPO and BPO
Run 1 BPO 1 hxo-TEMPO ( Mass ratio 1 Cornmenti 1 I ( 9 ) 1 ( 1 1 kxo-TEMPO: BPO 1 I 1 1
SFRMP-44 1 0.20 1 0.22 1 1 I 1
I 1 1 I SFRMP-47 I 0.40 1 0.68 1.7 MMM
SFRMP-45 1 0.20 1 0.46 1 1 1 1
1.1
SFRMP-46 1 0.60 1 0.66
LLH
1 2.3
SFRMP-50
LHH
t.1 HLH
0.30 049 2.3 HHH
Table B4: Summary of Final Results for Butyl Acrylate Polymerizations using 40x0- TEMPO and BPO
Run 1 s(%) 1 Mn Mmui 1 MJMn 1 Fapp 1
SFRNP-40 was also conducted to determine if the polymerization continued past
6 hours. The run conditions are identical to those for SFRMP-29, except a 24 hour
reaction time was used. Final results are not provided. as the experiment appears to have
been unsuccessful.
B.2 Polymerizations with Unimolecular initiators
B.2.1 Additional Styrene Polymerizations with Unirnolecular Initiators
Additional styrene polyrnerizations not discussed in the previous chapters were
also performed. Table B5 and B6 summarize the run conditions and final results at 6
hours for these runs. Reactions were canied out in the 300 ml reactor at L35 OC.
1 1
t SFRMP-4 1 1 0.22 (hydr@ST) 1 Mer DIW extraction
Table B5: Summary of Run Conditions for Styrene Polymerizations using Unimers
I 1 t S M - 5 7 O. 19 (BST)
Comments Run Unimer (g)
Table B6: Summary of Final Results for Styrene Polymerizations using Unimers Mmib
22,245
Mn
29,838
Run
SFRMP41
x (%)
42
WMn
1.25 Fipp 0.75
B.2.2 Butyl Acrylate Polymerizations wit h Unirnolecular Initiators
Unimolecular initiators were also studied in butyl acrylate miniemulsion
polymerizations. Two unimers, BST and hydroxy-BST, were utilized in these
experiments. Upon thermal dissociation hydroxy-BST forms hydroxy-TEMPO, which is
known to partition to the aqueous phase to a much greater extent than TEMPO. It was
initially thought that ernploying hydroxy- BST may irnprove the rate of polymerization
over BST systems by decreasing the amount of nitroxide in the organic phase. All
experiments were conducted in the 300 ml reactor for 6 houn using the previously
described miniernulsion formulation. The mn conditions and results are shown in Tables
B7 and B8 respectively.
Table B7: Sumrnary of Run Conditions for Butyl Acrylate Polyrnerizations using
1 SFRMP-21 1 O.L4(BST) ( 145 "C ( Sampling 1
Unimers
(Hydroxy BST) [
Run SFRMP-16
B.3 Polymerizations with CSA
Unimer (g) 0.20 PST)
Table BS: Sumrnary of Final Results for Butyl Acryiate Polymerizations using Unimers
B.3.1 Butyl Acrylate Polymerizations
In order to improve the extremely slow reaction rates observed with TEMPO in
the SFRP of butyl acrylate, CSA was added to the system. Molar ratios above 1 : 1.5 of
TEMP0:CSA codd not be performed without influencing the stability of the
miniernulsion. The run conditions and results are provided in the tables that follow.
Temperature ( O C )
135 O C
Fm,, 0.83
0.93
1.14
Run
SFRMP- 16
SFRMP-2 1
SFRMP-56
Comments
x (%)
3 9
3 2
15
&/Mn
1.54
1.81
1.22
Mm 26,376
27,566
7,506
M,u
2 1,903
25.73 1
8,532
Reactions were perfonned in the 1 .O L reactor for 6 hours at 135 O C using the standard
miniernulsion formutation.
Tabl
P
-
e B9: Sumrnary of Run Conditions for Butyl Acrylate Polyrnerizations using CSA Run
SFRMP-17
L I
SFRMP-49 1 0.46 (JXMPOO 1 0.40 (KPS) 1 1:1.5 1 Emulsion / SFRMP-48
0.46 (TEMPO)
1 with Sodium ( bicarbonate
Nitroxide (g)
@Iydroxy- TEMPO) 0.46 (TEMPO)
SFRMP-52 S m - 5 3 SFRMP-55
Molar Ratio TEMPO:
tnitiator mass (g)
0.40 fKPS)
SFRMP-48 was mn using the same formulation as run SFRMP-17 except a
Comments
CSA 1: 1
0.40 (KPS)
0.46 (TEMPO) 0.46 (TEMPO) 0.46 (TEMPO)
Table B IO: Sumrnary of Results from Butyl Acrylate Polymerizations using CSA
poiymerization time of 24 hours was used. Results are not reported as the emuIsion was
not stable.
1: 1
0.40 (KPS) 0.36 (BPO) 0.40 (KPS)
F~PP O. 18
0.08
Run
SFRMP- 17
SFRMP- 18
Run time 24 hours
1:0.5 1:l 1:l
unstable
Buffered
x (%)
62
22
M n th
12,358
4,465
Mn
67,99 1
53,555
M J M n
1.39
1.66
B.4 Poiymerizatioas with Varied DIWStyrene Ratio
It was originally thought that the hetemgeneous nature ofemulsion could reduce
the buildup of nitroxide in both styrene and butyl acrylate systems. Varying the amount
of water in the emulsion might influence the degree of nitroxide partitioning and hence
possibly strongly influence the polymerization characteristics. To test this theory a series
of polymerizations were perfonned in which the arnount of DiW was varied.
B.4.1. Styrene Polymerizations
A summary of the run conditions and final results for the styrene polymerizations
is provided in Tables BI 1 and B 12 respectively. PoIymerizations were performed at
135 O C for 6 hours.
Table B 12: Summary of Final Results for Styrene Polymerizations with Varied Amounts of Dtw
Table B 1 1: Summary of Run Conditions for Styrene Polymerizations with Varied Amounts of DlW
DIW (ml)
480
720
480
720
480
Run
SFRMP-32
SFRMP-33
SFRMP-34
SFRMP-36
S W - 3 7
Nitro ride (g)
0.72 (Hydroxy-TEMPO)
0.72 (Hydroxy TEMPO)
0.66 (TEMPO)
0.66 (TEMPO)
0.69 (TEMPO)
initiator (g)
0.40 (KPS)
0.40 (KPS)
0.40 ( U S )
0.40 (Ki's)
0.40 @PO)
GPC measurements were not performed for SFRMP-36 as the study was
abandoned.
B.4.2 Butyl Acrylate Polymerizations
Nitroxide, initiator and water levels for butyl acrylate polymerizations with varied
amounts of DlW are shown in Table BI3 and were run at 150 OC. The results at 6 hours
are provided in Table B 14.
Table B 13: Summary of Run Conditions for Butyl Acrylate Polymerizations using Varied Amounts of D W
Run
SFRMP-24
Table B L4: Summary of Results fiom Butyl Acrylate Polymerizations using Varied Amounts of D W
SFRMP-25
Eydrosy TEMPO (g) 0.50
B.5 Autopolymerizatioo Study
0.50
Run SFRMP-24 SFRMP-25
B.5.1 Styrene Autopolyermization
Initiator mass (g)
0.40 (KPS)
Thermal polymerization of styrene in the absence of initiator and nitroxide was
studied in run SFRMP-42. The teaction was conducted at 135 OC for 7.5 hours using the
standard 300 ml reactor miniemutsion formulation. Final results are summarized in
Table B t 5 below.
DCW (ml)
240
0.40 g KPS
L (%) 10 1
720
Mn 40,455 14,639
Table B 15: Summary of Styrene Autopolymerization Results
1.36 1.39
M & f n
2.48
Mt, 26 1,967
Run
SFRMP-42
r (94)
64
B.5.2. Butyl Acrylate Autopolymerization
To determine the role of autopolymerization, two runs were performed in the
absence of nitroxide and initiator using the 300 mi reactor miniemulsion formulation
(SFRMP-62 and SFRMP-66). SFRMP-62 used 1.5 hour sample times for 6 hours, while
in SFRMP-66 samples were taken every 10 minutes for the first hour and every 1.5 hours
thereatler. These reactions were both conducted at 135 O C . An additional run without
initiator but in the presence of TEMPO (0.23 g) was also conducted ( S M - 6 5 ) . No
polymer was detected after 6 hours in this mn.
B.6 Compartmentalization Study
Radical polymerization in emuision differs from polymerizations in homogeneous
systems in that the propagating radicals are isolated from each other and thus are less
likely to terminate. This characteristic. known as compartmentalization. allows the
formation of high molecular weight polymers with fast reaction rates. in rniniemulsion
very high molecular weights and polymerization rates could be achieved if the number of
polymer chains per droplet is very Iow.
A series of nitroxide mediated polymerizations were conducted using a hydroxy-
TEMPO terminated polystyrene oligomer obtained fiom the Xerox Research Centre of
Canada. The macroinitiator dissolved in a but$ acrylate or styrene solution (0.24 g/L)
was added directly to the organic phase of the miniemulsion. The reactions were run for
6 hours at 135 "C using the 1 .O L reactor standard formulation unless otherwise indicated.
Miniemulsions polyrnerizations using both styrene and butyl acrylate monomers were
attempted. Run conditions and final results at 6 hours (unless otherwise indicated) are
given in Table B 15 and B 16 respectively. Benzoic acid was added to reduce the
influence of autopolymerization where indicated.
Table B 16: Summary of Run Conditions for Compartmentalization Study
1 S M - 3 5 1 lr05 1 Styrene 1 -300 ml reactor
SFRMP-30 SFRMP-3 1
Run Monomer TEMPO terminated Polystyrene
from XRCC (ml) 2.10 1.71
--
*Results reported at 4.5 hours
Commenîs
SFRMP-43 * S m - 5 4
B7. pH Adjustment in Miniernulsion Systems using KPS
Styrene Styrene
Styrene 2.10
The influence of HSOJ' produced in the decomposition of KPS was thus thought
to be a possible source of rate enhancement in the system studied by Xie (2000). To
investigate this possibility, several of these mns were repeated using a buffered system.
The DiW used to prepare the miniemulsion was buffered to a pH of -8 using sodium
bicarbonate. Reaction conditions for the buffered system were conducted as done
previously, which included varying the initiator concentration and nitroxideinitiator
ratio. The high and Iow levels for the initiator were 0.30 g and 0.10 g respectivety and
2.3 : 1 and 1.1 : 1 were the high and low nitroxide:initiator ratios. The polymerizations were
performed in the 300 ml reactor at 135 "C for six hours using the conditions outlined in
Table B 18. High (H) and low (L) Ievels for the initiator and nitr0xide:initiator ratio have
been indicated in the comment section. A summary of the final resuhs for these nins is
given in Table B 19 below.
-Assumed Dv=160 nm -Assumed Dv= 1 70 nm
-0.18 g Benzoic acid -2.00 g Benzoic acid
2.10 ButyI Acrylate
Table B 18: Summary of Run Conditions for BufKered KPSITEMPO System 1 Run 1 Kps (g) 1 TEMPO (g) 1 TEMP0:KPS 1 Comments 1
Table B 19: Summary of Buffered Polymerization Results for KPS/TEMPO System
A series of 4 mns were also performed using a KPS initiator and hydroxy-
TEMPO as the nitroxide. The DiW was again buffered to a pH of -8 and the reactions
were conducted at 135 "C for 7.5 hours. The run conditions are surnmarized in Table
B20. The final results at 7.5 hours for these mns are surnmarized in Table 82 i
Table B20: Summary of Run Conditions for Buffered KPS/Hydroxy-TEMPO System Commcnts Rua Eydrory-
TEMP0:KPS KI'S (g) Bydroxy-
TEMPO(g)
Table B2 1 : Summary of Buffered Polymerization Results for KPSMydroxy-TEMPO Svstem
B8. Additional Runs with Ascorbic Acid
-
Several additional runs with ascorbic acid were performed during the course of
this study. Ascorbic acid was added to systems displaying substantial curvature in the
reaction rate in an attempt to reinitiate these polymerizations. SFRMP- 102 and SFRMP-
1 10 were replicate trials of SFRMP-74 (0.007 M BST) and SFRMP-78 (0.0 14 M BST)
respectiveiy. These runs were performed without sampling so that a large amount of
latex could be obtained. Reaction times for these runs were 12 hours (SFRMP-102) and
22 hours (SFRMP-1 IO). Ascorbic acid was added to the final latex in the molar ratios
specifted in TabIe B22 in runs SFRMP-103 and SFRMP- 1 1 1 for SFRMP- t 02 and
SFRMP-110 respectively. Ascorbic acid was also added directly to the final latex of
SFRMP-74 and SFRMP-75 in runs SFW-109 and SFRMP-106 respectively to
determine if the system could be polymerized further.
In addition, SFRMP-10 1 and SFRMP-112 were also performed with ascorbic acid
added directly at the start of the run. SFRMP-1 12 utilized the same conditions as
SFRMP-IO8 but was conducted at a reaction temperature of 120 O C . Run conditions for
al1 additional ascorbic acid nins are summarized in Table 822 and were conducted at 13 5
OC in the 300 ml reactor.
-. .
Run
SFRMP-89
SFRMP-92
SFRMP-93
SFRMP-94
x (96)
3 5
59
42
13
Mn
19,077
44,920
20,473
4,879
M,/M,
1.40
1.37
1.42
1.22
#Cbains
( ~ 1 0 ~ " )
3.30
2.36
3.70
4.98
F~PP
0.67
0.5 1
0.28
0.37
Table 822: Summary of Experimental Conditions for Additional Runs with L-Ascorbic Acid
Runs SFRMP-103 through SFRMP-1 I l did not show any significant changes in
conversion or molecular weight with the addition of ascorbic acid. The conversion
results for SFRMP-101 and S M - L 12 are provided in Table B23. GPC analysis of
SFRMP- 1 O t
SFRMP- 103
these nins showed a bimodal distribution for ail simples.
Reaction Time (hours)
Run BST:Ascorbic Acid (molar
ratio) l:i
I:0.2
6.5
24
Table 823: Summary of Results for Additional runs with L-Ascorbic Acid
I Run x (%)
Appendir C
C. Additional P idcb Si Diskibutions
I Particle Sue (Inil
Particle Sue @) --- .
(4 Figure Cl: Particle S k Distcibutions for SFRMP-74 (a) 1.5 hours @) 4.5 hous (c) 12 hours
Parücle Sie (pm)
Parücle Size (m)
I Parücle Sue (pm) -
Pattiife Sie (pn)
Figure Q: P&k Size Distriautions for SFRMP-75 (a) Zero Sample @) 1.5 homs (c) 3 ho- (ii) 4.5 buts (e) 6 burs If) 12 hm
Particle Size (un)
ParÜcie Sie (Cm)
Particle Sue (riml
\-J
Figure C3: Paitict S b DistriWonr fbr SFRMP-78 (a) Zero SampIe @) 15 hous (c) 3 hem (ci) 4.5 hm (e) 6 hm (f) 24 hom
Particle Size (Cm)
Particle Sie (mil
I Panicie size (cmi)
1 Particle Sire (Cm)
LAI Figure C4: Partide Sip Distriauthom fot SFRMP-79 (a) Zao SampIe @) 1.5 burs (c) 3 hours (d) 45 hm (e) 6 houn (f) 24 hem
1 Particle Sue (p)
(4 Figure C5: P h l e Size DistnIbrrtions for SFRMP-81 (a) 1.5 ho- @) 4 5 hours (c) 12 hom
Parücle Ske (m)
PaRide Size (um) I
(el Figure C6: Particle Size Distriibutions for SFRMP-82 (a) 1.5 hours (b) 3 hours (c) 4.5
Particle Sie @n)
CIO
I Particle Size (Cm)
l Particle Sie (pn)
Partide Sie (p) -
(0
r
, - Figure CI: Particle S é c Disbn'butions for SFRMP-96 (a) ocre sample @) 1.5 hoürs (c) 3 hours (d) 4.5 homs (e) 6 hoim (f) 24 hours
Parücie Size (Cm)
I Particle Size Qm)
(4 1 Fgure C8: Particle S k DistrrMom 6x SFRMP-99 (a) 1.5 hom @) 4.5 hm (c) 8 burs
Particle Ske (Cm)
Particle Size (pm)
Particle Sue
(4 I Figure Cg: PatticIe Si Disûi'butions for SFRMP-1ûû (a) 1.5 hours @) 4 5 houn (c) 8 hours (d) 24 hotus
Parücie Sie (p) - L
(4 Figure CIO: Paaicle Sia D i s t n i n s for SFRMP-LOS (a) 15 ho= @) 4.5 hous (c) 24 hom
Particle S ie (Cm) - -
Parücle Size (pn)
Figure CH: Particle S h Disûihdiom for SFRMP-108 (a) 1.5 hoira @) 4.5 homs (c) 22 hours
Particle Sue 6m)
l Particle Size (Cm)
Particle Size &un) I
(el I Figure C12: Paaicle Size Disûiiutions for SFRMP-113 (a) zero sample @) 1.5 hom (c) 3 hours (d) 4.5 hours (e) 6 hours
Particle Ske (pn)
Particle Size (um)
Particle Size (pn)
(cl Figure C13: Parücle Size Dismaiti011~ fbr SFRMP-114 (a). 1.5 horn @) 4 5 hours (c) 24 hours
Parücle Size Uni) i
Particle Size (Un)
Particle Size
Particle Size (Irm)
0.1 1 I O 100
Particle Size (pn)
(b) Figure CL6: ParOele Si ze D O t n i n s for SFRMP-122 (a) LS houn @) 4.5 hom
Parücle Sie
(b) 1 Figure C17: Paaicle Sia Distrihtions for SFRMP-124 (a) 1 J hours @) 4.5 hom