chap 9. chain-growth polymerization

Hanyang Univ.Hanyang Univ.

Spring 2008

Chap 9. Chain-growth Polymerization

Chain-Growth Polymerization (Addition) Processes

1. Free radical Initiation Processes

2. Cationically Initiated Processes

3. Anionically Initiated Processes

4. Group Transfer Polymerization

5. Coordination Polymerization


Spring 2008

Chain-Growth Polymerization

Step-Growth Polymerization1. Molecular weight increases steadily.

2.2. High molecular weight polymers are found at the end.High molecular weight polymers are found at the end.

3. Long reaction time needs to synthesize high conversion and high molecular weight.

1. Only growth reaction adds repeating units one at a time to the chain

2.2. Monomer concentration decreases steadily throughout the reactionMonomer concentration decreases steadily throughout the reaction

3. High Molecular weight polymer is formed at once; polymer molecular weight changes little throughout the reaction.

4. Long reaction times give high yields but affect molecular weight little.

5.5. Reaction mixture contains only monomer, high polymer, and about 10Reaction mixture contains only monomer, high polymer, and about 10 -8-8 part of growing chains.part of growing chains.


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(1) Initiation(1) Initiation

kkdd : I : Initiator decomposition rate constant

: 10: 10-4-4 ~ 10 ~ 10-6-6 L/mole sec L/mole sec

Unstable radicalUnstable radical

Chain Growth Polymerization

Heat (60ºC)Heat (60ºC)

UV UV kkdd

Primary radicalPrimary radicalAIBNAIBN

Bond EnergyBond Energy = 46 kcal/mole= 46 kcal/mole

IMkR ii


Spring 2008

(2) Propagation (2) Propagation

kkpp : 10 : 1022 ~ 10 ~ 1044 L/mole sec (much faster than step-growth polymerization) L/mole sec (much faster than step-growth polymerization)

(Repetition of similar reaction)


MMkR pp


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(3) Termination(3) Termination

(a) Coupling or combination(a) Coupling or combination



Spring 2008

(b) Disproportionation(b) Disproportionation

kktt=k=ktctc+k+ktdtd 101066 ~ 10 ~ 1088 L/mole sec L/mole sec

(3) Termination(3) Termination


2 MRMMkR tkt

tdk

tdk


Spring 2008

(4) Chain Transfer(4) Chain Transfer

Kinetic chain length

Monomer, Polymer, Solvent or Chain transfer agent

Physical chain length



Spring 2008


Kinetic Chain Length : kinetic chain length υ of a radical chain polymerization is defined as the average number of monomer molecules consumed (polymerized) per each radical, which initiates a polymer chain.

ex) Monomer # 4000 Disproportionation

υ =4,000/4 =1,000Determined by steps 1, 2, 3. (Initiation, propagation, and

termination)(No chain transfer)

Physical Chain Length :This condition contains Step 1, 2, 3, 4.

Radical

1,2,3,4


Spring 2008

Non-Polymerization Reaction

Peroxide induced Bromination of Toluene

1) Initiation

Two types of reaction

R-O-O-R 2RO• (1)

R-O• + Br2 ROBr + Br• (2)

R-O• + ФCH3 ROH + ФCH2• (3)

Two radicals and two kinetic chains are formed by decomposition of each ROOR molecules

Kinetic Chain Reaction


Spring 2008

2) Propagation

Br• + ФCH3 HBr + ФCH2 (4)

ФCH2• + Br2 ФCH2Br + Br • (5)

Two special features

The number of active species is fixed.

Same reactions are repeated during the kinetic chain reaction.



Spring 2008

3) Termination

2 Br• Br2

2ФCH2• ФCH2 CH2Ф

ФCH2• + Br • ФCH2Br + Br •

Net Effect of Kinetic Chain Reaction:

One ROOR molecule can cause formation of Br2, CH2CH2, CH2Br,HBr, .‥



Spring 2008

Time

Reaction

Rate

Induction period

Steady state

Chain reaction Ri = Rt

In proportion to the O2 concentration

Comparison between Chain Polymerization & Chain Reaction



Spring 2008

In the case of Chain reaction, there are induction periods, due to the existence of inhibitor.When an active center is formed, the reaction rate would be faster and then go to steady state. The whole reaction rate is reaching a plateau region.After that, reaction rate decreases due to a loss of monomers or initiators.

Linear Chain-Growth: Polymer of high DPn found easily in early reaction

Linear Step-Growth: high extent of reaction value required to obtain high DPn



Spring 2008

Comparison Free Radical Reaction & Ionic Reaction

- Ionic Initiation – multiple bond addition, ring opening polymerization

- Radical Initiation – Ring-opening polymerization is not initiated.

CH3

CH3

CH2

R CH3

CH3

CH2H

CH2

CH3

CH2

CH2

CH3

CH2

+ +

For the cationic initiation, it will not be free radical.

Ex)

Because of resonance stability


isobutylene


Spring 2008

Ionic Free Radical Anionic Cationic

Ring opening + - - End-groups Generally, combine with counter-ion or gegenion

E.g. R+ AlCl4―

Degree of association depends on below Solvent-system polarity Stability of end group Type & size of scounter-ion Temp. Degree of association influences: Reaction rates Termination rate Stereospecificity

Truly Free Radical (no association)

Termination Depend on monomer consumption, Living polymer or Block copolymer

unimolecular Combination or disproportionation reaction

Bimolecular combination or disproportionation

Comparison between Free Radical Reaction & Ionic Reaction



Spring 2008

A) Free Radical Termination

CH2 CH

X

CH CH2

X

CH2 CH CH CH2

X X

CH CH

X

CHCH2X

CH CH

X

CH CH2

X

H

H

unsaturated group.

. . ....

ktc (coupling or combination)

ktd (disproportionation)

+

Comparison between Free Radical Reaction & Termination Step of Ionic Reaction

Two molecules involved = bimolecular reaction



Spring 2008

B) Cationic Termination

Anionic capture is similar to combination of free radical reaction.

But, this reaction can’t include increasing of MW because of unimolecular reaction

CH2 CH

R

CH2 CH

R

X

AlCl4

AlCl3

[XY]

+ Y

EX) ÀÌ °æ¿ì

X= Cl Y=

+ -

-

-



Spring 2008

C) Anionic Termination

Termination is rare but can occur by loss of a hydride ion

Unimolecular type termination occurs

CH2 CH

R

M-

-H-

+

CH CH

R

+ HM

CH

R

H

R[XY]

+ -

proton release+

..

+ HY + Y

The proton release is similar to disproportination of free radical.. But, one chain joins in the reaction unimolecular reaction

C) Anionic Termination



Spring 2008

Anionic Cationic Termination Termination

Free Radical Termination

Reaction rate Unimolecular High concentration of growing chains 10-2~10-3molar Rates 104~105 times higher than free radical

Bimolecular Relativity low concentration 10-8~10-9

molar occurs at high Rates

E Activation Energies Similar Chain Transfer Negligible + + Disadvantage Rigorous Purity or precautions Polymer System Solution or Bulk Wide variety of

polymer systems, Gas, Solid, Solution, Bulk, Precipitation, Suspension, Emulsion



Spring 2008

Free Radical Initiated Polymerization of Unsaturated monomers

Kinetic Scheme

InitiationTwo step sequence-Both enter into overall rate1. Initiator decomposition

I2 2I

2. Addition of Initiator fragment to the monomer, Initiation of Chain growth.

I+M IM

The efficiency of Initiator - Determined by competition of desired reaction and side reaction

Primary radical species

Generally, 0.5 << f << 1

kd

ki



Spring 2008

A.Cage Effect –primary recombinationInitiator fragments surrounded by restricting cage of solvent

Ex)

(acetyl peroxide)

CH3 C O O C CH3

OO


O

O CH3

CH3

O

O


Spring 2008

I) Recombination possible I2 2I

II) If elimination reaction occurs while the free radical in-cage,

Formation of stable molecules due to Radical combination.And formation of Inactive Species.

C H 3 C

O

O

.

C H 3

. + C O 2

C H 3 + C H 3

. . C H 3 C H 3

CH 3 + O

C C H 3

O .

. C H 3

O C H 3 C

O



Spring 2008

B. Induced Decomposition –Secondary combination

I) Through Radical attack on peroxide molecules

R + R-O-O-R RH + ROOR R=O + RO

Finally, R + ROOR ROR+ RO

Total number of radical does not change, but among them half molecules were wasted.

II) Chain Transfer to Solvent

(In this case, since just one radical was obtained half molecules were wasted.)

I . + SH IH S.

S. + I2 SI + I .



Spring 2008

III) Reaction with Chain Radical

Since not all Molecules participate in the initiation → Efficiency factor

f: Initiator Efficiency= mole fraction of initiator fragments that actually initiate polymer chains.

0.5 < f < 1.0


I + M . IMn .

IMn . + I2 IMnI + I .


Spring 2008

C. Reaction Rate

If [M] is representative for the concentration of chain radical,

That is , M = IM or = I [M]

f 1 Ri is unrelated with [M] f=[M]

f < 1 Ri is related with [M]

[M] , f [I2] , f due to induced decomposition

by convention, two radical formation.

][2

]][[

][

2Ifk

MIkdtMd

R

d

i

i



Spring 2008

D. Initiator

- containing compounds.

O O S S N N

OO

O

CCH3

O

CH3C

OO

O

C

O

C

OOC

CH3

CH3

C

CH3

CH3


Acetyl peroxide 80~100C

Benzoyl peroxide 80~100C

Cumyl peroxide 120~140C


Spring 2008

NNC

CH3

CN

C

CN

CH3

CH3CH3 C

CH3

CN

CH3

. + N2250~70C

AIBN 2,2 azobisisobutyronitrile


CH3 O O CH3

CH3

CH3

CH3

CH3

CH3 O OH

CH3

CH3

Hydroperoxides, cumyl or t-butyl80~100C

t-butyl peroxide


Spring 2008

Propagation

Termination

n

k

k

pp

IM

IMMI

MMkdt

MdR

p

p

2

]][[][

By conventionSince 2 radical elimination

2])[ (2][

Mkkdt

MdR tdtct

M . M.

ktc ktd



Spring 2008

Overall Rate of Polymerzation

Radical concentration

• Difficulty of measurement, low concentration. (~10-8molar)

• Thus, it is impractical using this therm.

• [M] elimination is desirable.

]][[~

]][[]][[

MMkRR

MMkMIkR

ppo

pio

(# of propagation step >>> # of initiation step)



Spring 2008

[M] elimination methods

Steady-State Assumption

Radical concentration increases at the start, comes to steady state simultaneously and then reaction rate change becomes 0. (active centers created and destroyed at the same time) Ri = Rt

2

1

2

1

22

1

22

]2

[

][)(][

])[(2][2

t

i

tdtc

d

tdtcd

R

Ror

Ikk

fkM

MkkIfk

2

1

2

1

2 )(]][[

]][[][

tdtc

d

kkfk

IMk

MMkdtMd

R



Spring 2008

Mostly in case of f<1 system → [I2]1/2 (Square Root Dependence of [I2])

※ Odian Fig. 3-4 MMA using BPO

Vinyl Acetate using AIBN

Rp

[I2]1/2

OO

O

C

O

C

O

C O

NNC

CH3

CN

C

CN

CH3

CH3CH3 C

CH3

CN

CH3.2

BPO

-CO22

300C

+ N2

Azobisisobutyronitrile


H

.


Spring 2008

+ BPO + system

In case f < 1, but SRD is not applicable,

][][ 2

1

2 MIRp

2

3

2

1

2 ][][ MIRp

Because f is ‘dependent’ on [M]

Why? Due to induced decomposition of toluene + [I2]


+ BPO + CH3


Spring 2008

At S-S assumption

(1) Disproportionation

Knowing that

Kinetic Chain Length (KCL)

)(

chain)polymer a initiates( radicaleach

ed)(polymeriz consumed moleculesmonomer ofnumber average the

it

p

RR

R

KCL

dt

MdRRR tctdt

][

(2) Coupling or combination

termtc

tc

dt

MdR

k

][

chains)polymer 2 fromproduct polymer 1(2

1const. rate the


Spring 2008

(3) Both (1)+(2)


)1(

22

2

1

t

tdt

p

tdtctd

p

tctd

p

t

p

RR

R

R

RRR

R

RR

R

R

RKCL

)1(

2 case, in this

:

yR

RKCL

ionationdisproportbycausednterminatiooffractionR

Rydefine

t

p

t

td


Spring 2008

The more concentration of monomer, The less concentration of initiator,

(1) Dispropotionation

(2) Coupling

Degree of Polymerization


nDP

2nDP

dtPolymerd

dtMdDPn /][

/][

Monomer consumption rate

polymer formation rate

nDP

nDP


Spring 2008

)3(][2

)2(][][

1

2

)1()1(

2

2

1

2

1

2

2

1

2

IfkRR

MIfk

kkRthatknowing

yDP

R

Rywhere

yR

R

RR

RDP

R

RRPolymer

dit

t

dpp

n

t

td

t

p

tctd

pn

p

tctd

소비속도모노머

생성속도

(3) Dispropotionation & Coupling

Polymer formation rate

Monomer consumption rate



Spring 2008

From (1),(2),(3)

In case of no Chain transfer, and valid S-S assumption

)4(

][)1(

][

2

1

2

Ifkk

ky

MkDP

t

dt

pn

)5()1(

][ 22

pt

pn Rky

MkDPor



Spring 2008

M + XY MX + Y Chain transfer agent

If Chain transfer occurs Rp is unchangable but has an effect on DPn

( Since∵ Since∵ [Y] instead of Rp=kp[M][M] )

ex)

(1) Chain transfer occurs by solvents or additives In this case, High chain transfer coefficient.

(2) Transfer occurs by monomer or polymer

Chain Transfer

C C

H

X

H

H

R . + C C l 4

C C

H

X

H

H

R C l + C C l 3 .


Spring 2008

Inhibitor When Y take part in chain opening reaction, polymer moves from one site to another. In this case, hydroquinone etc. are used as inhibitor.

Retarder When the reactivity of Y is low, controlling the MW of the monomer including these two materials, Mercaptan etc. are used as Retarder.

Chain Transfer

Inhibitor and Retarder

2

1

2

2

]}[{][

][)1]([

][

]][[2)1(][2

]][[2

2)1(

2

][

2

1][

Ik

fkMthatKnowing

XYkyMk

Mk

XYMkyMk

MMk

RyR

R

dtPolymerd

RDP

RRRdt

Polymerd

t

d

trt

p

trt

p

trt

ppn

trtctd

Like this, when chain transfer condition arises


Spring 2008

][

][

][

][11

][

][

][

][11

][

][][

][

)1(1

][][)1(

][

0,

,,

0,

2

1

2

2

1

2

M

TC

M

SC

DPDP

Mk

Tk

Mk

Sk

DPDP

Mk

XYkIf

k

k

Mk

yk

DP

XYkIfk

kyk

MkDP

TS

nn

p

ttr

p

str

nn

p

tr

t

d

p

t

n

trt

dt

pn

From the slope of a graphChain transfer coefficient ‘Cs’

See Odian P.235

1

[5]/[M]

DPn

Chain Transfer


Spring 2008

Assume : no chain transfer

Temperature Dependence of Rp and DPn

molekcal Eekk

molekcal Eekk

molekcal Eekk

(1) Ifk

kkMR

MIfk

kkR

tRTE

tt

dRTE

dd

pRTE

pp

t

dpp

t

dpp

t

d

/5~2

/30

/8~5

]][ln[ln]ln[ln

][][

/

/

/

2

1

2

2

1

2

1

2


Spring 2008

slope of lnRp/T is ( + )

as T lnRp

but Rate of Increase as d lnRp/dT


0152722

]ln[ln

.,][],[),1(

22

2

1

2

RTRT

EEE

dT

kk

kd

dT

Rd

ToftindependenfconstMIassumeandEqFrom

dtp

t

dp

p


Spring 2008


n

np

n

dtp

i

p

t

p

t

pn

DPT

DPbutRI

DPTas

RTRT

EEE

dT

d

R

R

R

R

yR

RDP

][

ln,

0152722ln

,)1(

2

22


Spring 2008

ㆍㆍ Ceiling TemperatureCeiling Temperature

Polymerization and Depolymerization are in equilibrium

ΔGΔGpp = ΔH = ΔHpp – TΔS – TΔSpp

ΔHΔHpp : : HeatHeat of polymerizationof polymerization

ΔSΔSpp : : Molecular arrangement changes between monomer andMolecular arrangement changes between monomer and polymerpolymer

At eq. State ΔGAt eq. State ΔGpp=0=0

Monomers can no longer be persuaded to form polymers by chain polymerization aabove a certain temperature. ceiling Temperature(Tceiling Temperature(Tcc))

Ceiling Temperature Polymer-Depolymerization Equilibria


Spring 2008

Rate Eq. of Polymerization Reactions at Depolymerization prominent Temperature

If,If,

M TM Tcc


Spring 2008

ksec-1 kdp

kp[M]

kp[M]- kdp

300 400 500 Tc

Tc

: No reaction above Tc

Stable blow Tc



Spring 2008

Monomer -H kcal/g mole Tc C (bulk)

St 16 235

MMA 13 164

Ethylene 26 407

Propylene 21 300

-methyl St. 7 6

※Odian Fig 3-18

Entropy changes for all polymers are not so different.

Sp= Sp- Sm (–) value of Sp is higherHp= Hp- Hm if (–) , exothermic.



Spring 2008

Trommsdorff Effect or Gel Effect

restricted mobility of polymer radical restricted mobility of polymer radical

kkpp ( relative to [M] )( relative to [M] )

( k∵( k∵ pp const. in reaction progress, k const. in reaction progress, ktt drop off in reaction progressdrop off in reaction progress

))

→ → Autoaccerelation effectAutoaccerelation effect

The increasing viscosity limits the rate of termination because of diffusional limitations


Spring 2008

t

80%

60%

40%

10% autoacceleratioan

as [M0] drastic in .

Trommsdorff Effect or Gel Effect

kte 1 one would expect ξ as t But ξ as [[M0]

chap 9. chain-growth polymerization

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