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Advanced Polymer Synthesis
Tutorial on Macromolecular Engineering
Axel MllerMakromolekulare Chemie II
www.MCII.de
ENB Elite Study Program Macromolecular Science Lecture on August 28, 2007
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Tutorial on Macromolecular Engineering
A. Mechanisms of Living Polymerization
B. Synthesis and Properties of Block Copolymers
-
LiteratureMechanisms:G. Odian: "Principles of Polymerization", 4th Ed., Wiley, New York 2004Mark-Bikales-Overberger-Menges, Eds.: "Encyclopedia of Polymer Science and Engineering", 2nd Ed., Vol 1-
17+ Suppl. , Wiley, New York, 1985-89. Contains numerous review articles from "Anionic Polymerization" (Vol. 2, p. 1) via "Living Polymer Systems" (Suppl. Vol., p. 380) to "Zwitterionic Polymerization" (Vol. 17, p. 1028).
G. Allen, J.C. Bevington, Eds.: "Comprehensive Polymer Science", Vol. 3+4: Chain Polymerization, Pergamon Press, Oxford 1989 (very detailed review articles on mechanisms and properties)
Macromolecular Engineering in general:G. Allen, J.C. Bevington, Eds.: "Comprehensive Polymer Science", Pergamon Press, Oxford 1989; Vol. 6,
chapters 8-13 (p. 227-436), Vol. 7, chapter 1, Suppl. Vol. 1 (1992); p. 83-106H.L. Hsieh, R.P. Quirk: "Anionic Polymerization: Principles and Practical Applications",
Marcel Dekker, New York 1996Y. Gnanou: "Design and Synthesis of New Model Polymers", J. Macromol. Sci.-Rev. Macromol. Chem. Phys.,
C36, 77 (1996)J. C. Salamone (Ed.): Polymeric Materials Encyclopedia, CRC Press, Boca Raton (1996) K. Hatada, T. Kitayama, Eds.: "Macromolecular Design of Polymeric Materials", M. Dekker, New. York, 1997K. M. Stridsberg, M. Ryner, A.C. Albertsson: Controlled Ring-Opening Polymerization: Polymers with
Designed Macromolecular Architecture Adv. Polym. Sci. 157, 42 (2002)
Block copolymers:I.W. Hamley, The Physics of Block Copolymers, Oxford University Press 1998M. Pitsikalis, S. Pispas, J.W. Mays, N. Hadjichristidis, "Nonlinear Block Copolymer Architectures, Adv. Polym.
Sci. 134, 1 (1998)N. Hadjichristidis, S. Pispas, G. A. Floudas, Block Copolymers: Synthetic Strategies, Physical Properties,
and Applications; Wiley-Interscience, 2003
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Polymer Architecture
Topology Composition Molecular weightdistribution
Functionality
Microstructure
R R R R R R R R R
R
R
R
R
R
R
R
R
R
X
XX
X XX X
XX
X
XX
XXX
Polymer Properties
X X X X X X X X X
X
-
Part A:
Mechanisms of Living Polymerization
Anionic Polymerization
Cationic Polymerization
Ring-Opening Polymerization (anionic, cationic)
Living/Controlled Radical Polymerization
-
Basic Principles of Living Polymerization
When termination and transfer are absent
(Rt, Rtr
-
Conditions for a Living Polymerization (1)1. No Termination: kt = 0The number of active chain-ends [P*] is constant:Evidence:First-order kinetics with respect to monomer concentration:
[ ]
renders nIntegratio
bygivenistionpolymeriza ofrateThe
*]P][M[M pp kdtdR ==
[ ][ ] tktk appp == *]P[MM
ln 0
-
Conditions for a Living Polymerization (2)
Pn
[ ][ ]
[ ][ ]0
00
IM
PM
chainspolymer ofnumber monomers dpolymerize ofnumber
pp
n
xx
P
==
=
2. No Transfer: ktr = 0
There are no new chains formed,
the total number of polymer chains, [P], (including the terminated ones!)
is constant: [P] = [P*] + [Pdead] = [I]0Evidence:the number-average degree of polymerization,
,is a linear function of monomer conversion, xp:
-
Molecular Weight Distribution (MWD)Ideally, a very narrow MWD is expected, the Poisson distribution(Flory, 1940).The polydispersity index is given by
MM
PP P
w
n
n
n n
= +
+ 11
11
12
Factors leading to broader MWD'sNon-living Processes: termination Mw/Mn 2 (important for anionic polymerization of (meth)acrylates) transfer Mw/Mn 2 (important in cationic polymerization of isobutylene)
Living Processes: inadequate mixing:
tmix > t1/2 Mw/Mn can be very high slow initiation:
ki < kp Mw/Mn 1.33 reversible polymerization ("scrambling"):
Mw/Mn 2 slow equilibria between species of different activity:
Rex < Rp Mw/Mn can be very high (important for many "new" living/controlled processes)
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Controlled Polymerization
[ ][ ]
[ ][ ]00
0
IM
IM
== pnx
P
nw MM /
is a synthetic method to obtain polymers where: the number-average degree of polymerization is given by ratio of monomer over initiator:
MWD is narrow:
all chains can be functionalized: Pi* + X Pi-X
< 1.1 or 1.2
This is obtained if: the rate of initiation and rate of exchange reactions between various active species
are fast compared to propagation (Rex, Ri > Rp).
chain-breaking reactions (termination or transfer) are not too strong (Rt, Rtr
-
Anionic Polymerization
~~~~~C + C=C ~~~~~C-C-C
R R R R
M. Szwarc, 1956:Living Polymers
Nature 178, 1168 (1956)
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Important Monomers1. Non-polar vinyl compounds (with strong delocalization): styrene, -methyl styrene o-, m-,p-alkyl styrenes vinyl naphthalene dienes (butadiene, isoprene, )
2. Polar electrophilic vinyl compounds (with electron attracting substiuents): vinyl pyridine (meth)acrylates N,N-dialkyl acrylamides (meth)acrylonitrile
3. Cyclic Ethers, Esters, Siloxanes, ...:Ring-Opening Polymerization
-
Protected MonomersMonomers with acidic hydrogens need to be protected:
2-hydroxyethyl methacrylate (HEMA)
solketal methacrylate
methacrylic acidAS tert-BUTYL ESTER:
-
Initiators1. Organometallic bases (monofunctional):
- organolithium: n-BuLi, s-BuLi, t-BuLi - alcoholates (t-BuO-Li, t-BuO-K, ...)- alkali salts of aromatic hydrocarbons: benzyl-Na, cumyl-K, ...
2. Electron transfer agents (bifunctional):- alkali metals (heterogeneous):
- radical anions: naphthalene sodium (homogeneous):
-
Special Considerations for Experimental WorkDue to the high nucleophilicity of the initiators (and propagating chain ends) it is absolutely necessary to avoid oxygen, water and protic impurities:This implies
- aprotic solvents:polar: THF, ...non-polar: toluene, cyclohexane, hexane, ...
- rigorous purification of reagents- handling of reagents in vacuum or under inert gas.
Due to the absence of termination, the concentration of active species can be much higher than in radical polymerization. Thus, the rates sometimes can be very high(e.g., t1/2 < 1 s for MMA in THF at room temperature).
In order to control the polymerization it may be necessary to - use specially designed reactors (fast mixing: flow tube)- add monomer slowly (vapour phase)- work at low temperatures (-78 C)
-
First-Order Plot of Kinetics kapp = kp[P*]is the slope of the first-order plot
Linear plot (constant slope)[P*] = const. no terminationfast initiation
Polymerization of styrene with Na+ counterion in THF
Anionic Polymerizaton of Non-Polar Monomers
G.V. Schulz et al., Makromol. Chem. 71, 198 (1964)
(+) T = 24 C(o) T = -28 C
-
Molecular Weight vs. Conversion
Linear plot (constant slope)the number of all chains, [P], is constant
no transferfast initiation
Mw/Mn < 1.02
-
Cationic Polymerization
~~~~~C + C=C ~~~~~C-C-C
R R R R
M. Sawamoto, T. Higashimura, 1979
-
Monomers
: isobutylene ( low Tg rubber, low permeability)
: PS-b-PIB-b-PS: excellent thermoplastic elastomer
: poly(methyl vinyl ether) is water-soluble
-
Initiators
Protic Acids: HClO4, CF3SO3H, ...
Stable cations
Photoinitiatorsh
Lewis Acids: AlCl3, BF3, : H2O + BF3 H+(OH)BF3-
-
Living Polymerization Initiators
2,4,4-Trimethylpentyl-2-chloride(TMP-Cl)
monofunctional
1,3-Di(2-chloro-2-propyl)-5-tert.-butylbenzene (tBu-DiCum-Cl)
bifunctional
In situ generation of halides from HI and vinyl ethers:
Catalyst necessary to generate cations!
-
Living Polymerization of Isobutylene
Termination by Protons:
K
-
Conclusions: Cationic Polymerization
Living cationic polymerization depends on a catalyzeddynamic equilibrium between dormant (inactive, covalent) and active species (ion pairs, free cations)
The rate of polymerization is determined by the position of the dissociation and aggregation equilibria.
Transfer" (spontaneous and to monomer) is the main sidereaction; it can be minimized by using larger counterions
and highly polar solvents.
-
Ring-Opening Polymerization (ROP)
X-Y~~~~~~X-Y~~~~~~
R or R
Anionic ROP (AROP)
Cationic ROP (CROP)
Ring-Opening Metathesis Polymerization (ROMP)
-
Anionic Ring-Opening Polymerization (AROP)Monomers (1):
Nucleophilic Substitution linear anionic chain end
Ethylene Oxide, Propylene Oxide
Propylene Sulfide
O
-
Monomers (2)
lactide -caprolactam N-carboxyanhydrides
polypeptides
small cycles alkyl split
larger cycles acyl split
(initiation with RLi, ROLi)
Nylon 6
silicones
-
Cationic Ring-Opening Polymerization (CROP)Some monomers
THF
azridines oxazolines
1,3-dioxolane + trioxane POM
phosphazenes
-
Mechanism of Living CROP of THF
Equilibrium polymerization!
-
Living CROP of Oxazolines
Methyl oxazoline (MeOX)
Hor
OH
Linear poly(ethylene imine)
polyMeOX: water-soluble
polyBuOX: hydrophobic
-
Controlled/Living Radical Polymerization
Nitroxide-Mediated Polymerization (NMP)E. Rizzardo, M. Georges 1992
Atom Transfer Radical Polymerization (ATRP)K. Matyjaszewski, M. Sawamoto 1994
Reversible Addition-Fragmentation Chain Transfer (RAFT)E. Rizzardo, G. Moad, S. Thang 1996
~~~~~C + C=C ~~~~~C-C-C
R R R R
-
Controlled/Living Radical Polymerization
>5,000 papers on CRP(>3,000 ATRP since 95)
>600 patents on CRP(>400 ATRP since 95)
Anticipated market:>20$billion/yearBob Matheson (DuPont)
Applications:coatings, adhesives,surfactants, dispersants,lubricants, gels, additives,thermoplastic elastomers,electronics, biomaterials, Specialties
SciFinder Scholar: September 14, 2005
0
1 0 0
2 0 0
3 0 0
4 0 0
5 0 0
6 0 0
7 0 0
8 0 0
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
C R P & L R P
A T R P o n ly
S F R P & N M P
R A F T & D T & C C T
Y e a r
Num
ber o
f Pub
licat
ions
/Yea
r
-
Polymerizability of Monomers
Radical Polymerization works for the largest number of monomers!
Very many monomer pairs can be copolymerized
Undemanding reaction conditions (just remove oxygen)
-
Problems of Conventional Radical Polymerization1. Termination via fast bimolecular radical-radical reactions:- Recombination: ~~~Pn + Pm~~~ ~~~Pn+m~~~- Disproportionation:
~~~CH2-CH + CH-CH2~~~ ~~~CH=CH + CH2-CH2~~~X X X X
Radical lifetime is in the range of milliseconds!
2. Transfer to monomer, polymer, solvent, :- Generates new chains: ~~~CH2-CH + Y ~~~CH=CH + H-Y
X X
Decreasing Termination by Dilution of Chain Ends:
-
1. Reversible Deactivation of Chain Ends
Dynamic equilibrium between active and dormant species
propag-ation
Solution:reversible
deactivation(endcapping)
Bob Gilbert
+ R
+ M
+X
+ MX = persistent radical:
X = nitroxide, e.g., TEMPO NMP, SFRP
X = transition metal halide, e.g. CuBr2 ATRP
Problem:Termination by
Recombination or Disproportionation
-
Nitroxide-Mediated Polymerization (NMP)
alkoxyamine radical persistent radical
Advantages: Simple, many (functional) nitroxides available Radicals can be formed by classical initiators or from alkoxyamines works well in emulsion and miniemulsion Mw/Mn < 1.2 possible
Disadvantages: slow, high temperatures needed (> 100 C) works for few monomers only (styrene, acrylates)
M. Georges, 1994
-
Partial library of alkoxyamine structures evaluated as initiators for the living radical polymerization of styrene and n-butyl acrylate.
Braslau, Hawker
SG1(diethylphosphonate)
Tordo, Gnanou
-
Atom Transfer Radical Polymerization (ATRP)(Transition Metal Mediated Polymerization)
K. Matyjaszewski, M. Sawamoto, 1995
Advantages: Simple; many metal ions (Fe, Ni, ) and ligands available works for most monomers (not acrylic acid, ) No conventional initiator needed Mw/Mn < 1.2 possibleDisadvantages: removal of catalyst on large scale difficult does not work for monomers that complex the Mt ion (acrylic acid, )
NNCuN N
Br CuN
NPn Br
NNPn+ +
ka ~ 1 M-1.s-1
kd ~ 107 M-1.s-1
+ M
3 1 1
Chemistry
-
Note: Values (M-1s-1) are measured with EtBriB/Cu(I)Br in AN at 35 C. N2: red, N3: green, N4: blue; Amine/imine: solid, Pyridine: open, Mixed: left-half solid; Linear: , Branched: , Cyclic: .
Some Ligands
-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3-3 -2 -1 0 1 2 3
log(ka)Extrapolated Values
N N
NN
N[2,3,2] (1.2 10-3)
N N
N[3,2,3] (5 10-3)
N N
N N
N
N[2,2,3] (0.23)
NN N
NN
N[2,2,2] (HMTETA) (0.14)
N
N N
N[2,3] (9.2 10-3)
N
NR
NPPMI: R=C3H7 NOPMI: R=C8H17(2.4 10-3)
N
NN
PMDETA (N[2,2]) (2.7)N
N
N
N
TPMA (62.4)
N N
N N
Cyclam (Nick) (708.7)
N
N
N
N
Me4Cyclam (0.67)N
N N
N
PyNMeNMePy (4.5)
N Nbpy (0.092)
N N
dNbpy (0.6)
NNN
N
O
nBu
O
O
BunO
OBun
OnBu
OnBu
O
nBu
O
O
O
O
BA6TREN (4.09)
NNN
N
O
O
OO
OO
O
O
O
O
O
O
MA6TREN (1.23)
NNN
N
Me6TREN (455.6)
NNN
N
Et6TREN (0.044)
NNN
N
CN
NC
NC CN
CN
CN
AN6TREN (0.012)
N N
TMEDA (0.042)
Active
-
Some Initiators
S
CH3O
ClO
O
-
Bulk ATRP of Styrene
-
2. Reversible TransferDegenerative Transfer between active and dormant chains:
~~~Pm-I + Pn~~~ ~~~Pm + I-Pn~~~ where [P-I] >> [P ]
-
Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization
Rizzardo, Moad 1998
Addition / fragmentation:
Equilibration:
Propagation:
dormant dormantdormant activeactive
Initiation: initiator + monomer Pm
PnMonomer
Rki
Re-inintiation: Pn+1Monomer
Pnkp
Z
S S PnPm
Z
SS Pn+
Pm S S
Z
+PmPn
M M(2)
k
k
k-
k-
chain transfer agent
dormantdormant
Z
SS R+
Z
S S RPmPm
Pm S S
ZR+
k-,1k,1
k,1k-,1
-
are thiocarbonylthio compounds:
Z CS
SR Z = alkyl, aryl, N ...
R = alkyl, aryl
R' CS
SR R'S CS
SR
R' O CS
SR SRR'R''N CS
dithioester trithiocarbonate
xanthateMADIX
(Rhodia 1999)
dithiocarbamate
Chain Transfer Agents (CTAs)
, RO-, RS- (stabilizes radical)
(leaving group): reinitiates polymerization,can carry functional groups
-
RAFT of N-isopropylacrylamide (NIPAAm)Synthesis of polyNIPAAm via RAFT with
dithiocarbamates as chain transfer agents
benzyl 1-pyrrolecarbodithioate cumyl 1-pyrrolecarbodithioate
Chain transfer agents used:
CH2 CH
NHiPrO
CH2 CH
NHiPrO
R SS
Zn
CTA, AIBN
60 C, dioxane
N
SS CH2Ph
N
SS CCH3
CH3Ph
-
Conclusions: Controlled Radical Polymerization
Controlled Radical Polymerization proceeds either by
Reversible Deactivation (NMR, ATRP) or by
Reversible Transfer (Degenrative Transfer, RAFT).
The rate of polymerization depends on the position of the
activation equilibrium.
The MWD depends on the dynamics of the activation
equilibrium.
Termination cannot be completely avoided.
Transfer is not affected by CRP.
-
Comparison of Living Mechanisms
Pro ConRadical Low purity requirements (cheap)
Convenient temperatures (cheap)Large variety of monomersBlock copolymersRandom copolymersGradient copolymers
Expensive nitroxides, CTAsRemoval of metals difficultVery few cyclic monomers for ROPSome terminationNo control of transfer low MWLittle control of microstructure
Ionic No (little) termination or transfer Block copolymersHigh MWROP possibleSome control of microstructure
Termination or transfer (some cases)High purity, low T (expensive)Choice of monomers restrictedRandom copolymers difficult
-
Part B
Synthesis and Properties of Block Copolymers
-
Synthesis of linear block copolymers
Sequential monomer addition
Polymer-polymer coupling
AB
ABC
2 x AB
ABA
ABA
Problem: low coupling efficiencies
+
-
Sequential monomer addition
I- I~~~~MA-MB
Good blocking efficiency when the reactivityof the first block is higher or comparable tothat of the second block.
MAI~~~~~~~~~MB-
Attenuation of the reactivity of the first blockmay be necessary in order to avoid sidereactions in the cross-over step.
PS- + DPE PS-DPE-
MMA
PS-PMMA
MCI~~~~~~~~~~~~~~MC-
macroinitiator
-
Special Case: RAFT
R CH2 CH CH2
OHO
CH
NHiPrO
SS
Zm n
CH2 CH
OHO
SSNC
NO
m
NIPAAm, AIBN
MeOH, 60 C
Macro-chain transfer agent
-
Bifunctional initiation
-I-I- + MB -MB~~~~~~I-I~~~~~~MB-
MA
~~~~~~~~~~~~~~~~~~~~~I-I~~~~~~~~~~~~~~~~~~~~~
Problem:
Most important properties:
Most important applications:
Bifunctional initiators are not well soluble in hydrocarbon solvents (due to aggregation)
Microphase separation in bulkMicelle formation in solution
SBS, thermoplastic elastomers (Kraton)PPO-PEO-PPO, amphiphilic copolymers (Pluronics)
-
Anionic bifunctional initiators for non-polar solvents
-
Phase diagram and topology of diblock copolymers in bulk
Hexagonal cylinders(H)
BCC spheres(QIm3m)
_
Gyroid(QIa3d)
_
-
PS-PB-PS cubic (spherical) morphologyPS-b-PI lamellar morphology
TEM
OsO4
SAXS
-
Morphologies of triblock terpolymers(found with S-B-M)
knitting pattern
R. Stadler et al.
S-EP-M
-
hard (high Tg)
PS, PMMA
hard
Thermoplastic elastomers based on ABA bock copolymers
PB, PIB, PnBA
soft (low Tg) microphase
separation
physical cross-linking
reversible!
-
Superstructures of Amphiphilic Diblock Copolymers
star micelle
Crew-cut micelle vesicle
incorporation of OmpF
cylinder vesicle(nanotube)
-
Cryo-TEM of micelles at high pH
100 nm
Collapsed core surrounded by an extended corona
Rcore ~ 5 nmRmicelle ~ 30 - 50 nm (?)Rh ~ 50 nm (DLS)Lcontour (PAA) = 75 nm
PnBA90-b-PAA300
Advanced Polymer Synthesis Tutorial on Macromolecular EngineeringLiteraturePolymer ArchitectureFoliennummer 5Basic Principles of Living PolymerizationConditions for a Living Polymerization (1)Conditions for a Living Polymerization (2)Molecular Weight Distribution (MWD)Controlled PolymerizationAnionic PolymerizationImportant MonomersProtected MonomersInitiatorsSpecial Considerations for Experimental WorkFirst-Order Plot of KineticsMolecular Weight vs. ConversionCationic PolymerizationMonomersInitiatorsLiving Polymerization InitiatorsLiving Polymerization of IsobutyleneConclusions: Cationic PolymerizationFoliennummer 24Anionic Ring-Opening Polymerization (AROP)Monomers (2)Foliennummer 27Mechanism of Living CROP of THFLiving CROP of OxazolinesControlled/Living Radical PolymerizationControlled/Living Radical PolymerizationPolymerizability of MonomersProblems of Conventional Radical Polymerization1. Reversible Deactivation of Chain EndsNitroxide-Mediated Polymerization (NMP)Foliennummer 36Atom Transfer Radical Polymerization (ATRP)(Transition Metal Mediated Polymerization)Some LigandsFoliennummer 39Bulk ATRP of Styrene2. Reversible TransferFoliennummer 42Foliennummer 43Foliennummer 44Conclusions: Controlled Radical PolymerizationComparison of Living MechanismsFoliennummer 47Foliennummer 48Foliennummer 49Foliennummer 50Foliennummer 51Foliennummer 52Phase diagram and topology of diblock copolymers in bulkFoliennummer 54Morphologies of triblock terpolymers(found with S-B-M)Foliennummer 56Foliennummer 57Foliennummer 58
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