Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic...

61
Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization

Transcript of Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic...

Page 1: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

Chapter 7. Ionic polymerization

7.1 Introduction

7.2 Cationic polymerization

7.3 Anionic polymerization

7.4 Group transfer polymerization

Page 2: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.1 Introduction

Presence of counterions (= gegenions)

Influence of counterions

• Solvation effect

ex)

Cl C

CH3

CH3

C

CH3

CH3

Cl + BCl3 Cl C

CH3

CH3

C+

CH3

CH3

BCl4-

counterion

more complex than free radical polymerizations

but more versatile

Page 3: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.1 Introduction

Application : in ring-opening polymerizations of cyclic ethers , lactams , lactones and in the polymerization of aldehydes , ketones

Commercial processes (Table 7.1) far fewer in number reflect a much narrower choice of monomers

O O

O

NH

O

C

O (CH2)m

O

RCR

O

'

RC

O

H

monomers must contain substituent groups

capable of stabilizing carbocations or carbanions

the necessity for solution polymerzation

Page 4: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

TABLE 7.1. Commercially Important Polymers Prepared by Ionic Polymerization

Polymer or CopolymerCationica

Polyisobutylene and polybuteneb

(low and high molecular weight) Isobutylene-isoprene copolymerc

(“butyl rubber”)

Isobutylene-cyclopentadiene copolymer Hydrocarbond and polyterpene resins Coumarone-indene resinse

Poly(vinyl ether)s

Anionicf

cis-1,4-Polybutadiene cis-1,4-Polisoprene Styrene-butadiene rubber (SBR)g

Styrene-butadiene block and star copolymers ABA block copolymers (A= styrene, B=butadiene or isoprene) polycyanoacrylateh

Major Uses

Adhesives, sealants, insulating oils, lubricating oil and grease additives, moisture barriersInner tubes, engine mounts and springs, chemical tank linings, protective clothing, hoses, gaskets, electrical insulationOzone-resistant rubber

Inks, varnishes, paints, adhesives, sealantsFlooring, coatings, adhesivesPolymer modifiers, tackifiers, adhesives

TiresTires, footware, adhesives, coated fabricsTire treads, belting, hose, shoe soles, flooring, coated fabricsFlooring, shoe soles, artificial leather, wire and cable insulationThermoplastic elastomers

AdhesivesaAlCl3 and BF3 most frequently used coinitiators.b”Polybutenes” are copolymers based on C4 alkenes and lesser amounts of propylene and C5 and higher alkenes fromrefinery streams.cTerpolymers of isobutylene, isoprene, and divinylbenzene are also used in sealant and adhesive formulations.dAliphatic and aromatic refinery products.eCoumarone (benzofuran) and indene (benzocyclopentadiene) are products of coal tar.fn-Butyllithium most common initiator.gContains higher cis content than SBR prepared by free radical polymerization.hMonomer polymerized by adventitious water.

Page 5: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.2.1 Cationic initiators

7.2.2 Mechanism, kinetics, and reactivity in cationic polymerization

7.2.3 Stereochemistry of cationic polymerization

7.2.4.Cationic copolymerization

7.2.5 Isomerization in cationic polymerization

7.2 Cationic polymerization

Page 6: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.2.1 Cationic Initiators

The propagating species : carbocation

Initiation

E CH2 CR2 ECH2CR2++ + (7.1)

Initiator mineral acid : H2SO4, H3PO4

lewis acid : AlCl3, BF3, TiCl4, SnCl4

Coinitiator BF3 + H2O HOBF3-H+

AlCl3+ RCl AlCl4-R+

Page 7: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

(C6H5)3CCl (C6H5)3C + Cl

Cl + Cl

(7.5)

(7.6)

(7.7)

(7.8)

Very active Lewis acid autoionization

2AlBr3 AlBr4-AlBr2

+

Other initiators

I2 + CH2 CR2 ICH2CIR2

ICH CR2 + HI

ICH2CR2I -+

7.2.1 Cationic Initiators

Page 8: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

N

CH CH2

+ RNO2

N

CH CH

+ RNO

2

2

· ·

+

-

(7.9)

(7.10)

M + A M+

+ A -

Other initiators

7.2.1 Cationic Initiators

Page 9: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

A. Carbocationic Initiation.

addition of the electrophilic species – the more stable carbocation

(Markovnikov’s rule) intermediate is formed.

C

H3C

H3C

CH2 + HCl C

H3C

H3C

CH3+

(CH3)2C CH2 > CH3CH CH2 > CH2 CH2

Stability of carbocation

Page 10: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

A. Carbocationic Initiation.

For a series of para-substituted styrenes, the reactivity for substituent group

OCH3 > CH3 > H > Cl

Vinyl ethers

(7.11)CH2 CHORR'+

R'CH2 CH OR+

R'CH2 CH OR+

X CH2 CH

X

(Because of steric hindrance)

Page 11: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

B. Propagation Step

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

Two Step

① -complex of chain end and approaching monomer

② formation of covalent bond

① ②

(7.12)+ + CH2 CR2slow

CH2

CR2

+ fast CH2CR2+

Page 12: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

C. Influences polymerization rate

A + A- + A- + + A-

Covalent Intimateion pair

Solvent-separatedion pair

Solvated ions

(7.13)

① Solvent polarity

(polarity

② Degree of association between the cationic chain end and counterion (A-)

favors the initiation step)

Page 13: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

D. Chain transfer reaction

1. With monomer :

2. By ring alkylation

CH2CH+HSO-4 + CH2 CH + CH3CH+HSO4CH CH

(7.14)

CH2 CH CH2 CH+HSO-4 + CH2 CH

CH2 + CH3 CH+HSO-4

(7.15)

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

Page 14: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

D. Chain transfer reaction

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

3. By hydride abstraction from the chain to form a more stable ion :

4. With solvent-for example, benzene-by electrophilic substitution :

CH2CH+HSO-4 + CH2CHCH2 CH2CH2 + CH2CCH2

HSO-4+

(7.16)

CH2CH+HSO-4 + + CH2 CH

CH2CH + CH3CH+HSO-4

(7.17)

Page 15: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

E. Termination reaction

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

Termination are the combination of chain end with counterion.

CH2CH+ -OCCF3

O

CH2CHOCCF3

O

CH2C+

CH3

CH3

BCl3OH-CH2C

CH3

Cl

CH3

+ BCl2OH

(7.18)

(7.19)

① styrene + CF3COOHinitiator

② Isobutylene + BCl3/H2o

Page 16: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

F. Proton trap

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

It intercepts the proton before it transfers to monomer.

The result lower overall yield

higher molecular weight

lower polydispersity index.

(7.20)CH2CR2+

+

NCH CR2 +

N+

H

A:proton trap··B:monomer··

A

B

Page 17: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

G. Telechelic Polymer

Cl C

CH3

CH3

C

CH3

CH3

Cl + BCl3 Cl C

CH3

CH3

C+

CH3

CH3

BCl4-

C

CH3

CH3

C+

CH3

CH3

Cl + CH2 C

CH3

CH3

Cl C

CH3

CH3

C

CH3

CH3

CH2C+

CH3

CH3

(7.21)

(7.22)

(7.23)

inifer

(bifunctionalcompound)

Cl C

CH3

CH3

C

CH3

CH3

C

CH3

CH3

C

CH3

CH3

Cl

CH2C+

CH3

CH3

+ C

CH3

CH3

C

CH3

CH3

ClCl

CH2C

CH3

CH3

Cl + C

CH3

CH3

C

CH3

CH3

Cl+

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

Page 18: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

H. Pseudocationic Polymerization

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

(7.24)CH2CH OClO3

Ph

+ CH2 CH

Ph

CH2CHCH2CH

Ph Ph

OClO3

The reaction proceeds at a much slower compared with most cationic processes.

The propagating chain end is a covalently bonded perchlorate ester

Page 19: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

I. To prepare living polymers under cationic conditions.

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

Tertiary ester + BCl3 / Isobutylene polymerization ① formation of tertiary carbocation-initiating species.

② Polymerization to yield polyisobutylene terminated

R3COCCH3

O

+ BCl3 R3C+ -OCCH3

O BCl3

(7.27)

–… (7.26)CH2 C(CH3)2

R3C CH2C

CH3

CH3

CH2C

CH3

CH3

OCCH3

O BCl3

: appearance of a very tightly bound – but still active – ion pair

(Termination or chain transfer reaction 없이 중합반응이 종결되는 예 )

ex1)

Page 20: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

I. To prepare living polymers under cationic conditions.

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

I2 / HI or I2 / ZnI2 : vinyl ether propagation

CH2CH

OR

ICH2CH

OR

ZnI2

CH2CH

OR

CH2CH

I ZnI2

OR

(7.27)

Living Polymer

Termination 이 전체적으로 멈춘 곳에서 chain end 가 여전히 active 한 성질을 가지고 있는 polymer

Monomer 첨가 시 분자량이 증가하며 starting monomer 와 다를 경우 block copolymer 형성 매우 길고 anionic polymerization 에 많이 이용 대부분의 living polymer 는 낮은 온도에서 합성 Living polymer 란 용어는 정지 반응이 일어나지 않는 이온 중합에 이용

ex2)

(Termination or chain transfer reaction 없이 중합반응이 종결되는 예 )

Page 21: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

J. Kinetics

Expression of general initiation, propagation, termination, and transfer rates

]][[

][

]][[

]][[

MMkR

MkR

MMkR

MIkR

trtr

tt

pp

ii

][

][

][

M

M

I : molar concentration of initiation

: molar concentration of monomer

: molar concentration of cationic chain end

As with free radical polymerization approximation to a steady state for the growing chain end.

ti RR

][]][[ MkMIk tit

i

k

MIkM

]][[][ or

thus

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

Page 22: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

TABLE 7.2. Representative Cationic propagation Rate Constants,a

PR

Monomer

Styrene-Methylstyrenei-Butyl vinyl etheri-Butyl vinyl etheri-Butyl vinyl etherMethyl vinyl ether2-Chloroethyl vinyl ether

Solvent

NoneNoneNoneCH2Cl2

CH2Cl2

CH2Cl2

CH2Cl2

Temperature (oC)

150300000

Initiator

RadiationRadiationRadiationC7H7

+SbCl6-

C7H7+SbCl6

-

C7H7+SbCl6

-

C7H7+SbCl6

-

kp (L/mol s)

3.5 106

4 106

3 105

5 103

3.5 103

1.4 102

2 102

aData from Ledwith and Sherrington.19

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

Page 23: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

Substituting for ][ M in pR , one obtains

In the absence of any chain transfer, (the kinetic chain length = )

If transfer is the predominant mechanism controlling chain growth,

DP =

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

Page 24: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

K. Difference between free radical and cationic processes.

free radical process cationic process

propagation rate (Rp)

DP ()

proportional to the square root of initiator concentration

dependent of initiator concentration

first-order dependence

independent of initiator concentration

Rp = dt-d[M] = kp[M]

t

d

k

Ifk ][Rp = dt

-d[M] = kp[M]t

d

k

Ifk ][Rp = dt

-d[M] = kp[M]t

d

k

Ifk ][Rp = dt

-d[M] = kp[M]t

d

k

Ifk ][

tr

p

tr

p

tr

p

t

p

t

p

t

p

t

ipp

t

i

ti

ti

k

k

MMk

MMk

R

RDP

k

Mk

Mk

MMk

R

RDP

k

MIkkR

k

MIkM

MkMIk

RR

M

M

I

]][[

]][[

][

][

]][[

]][[

]][[][

][]][[

][

][

][

2

tr

p

tr

p

tr

p

t

p

t

p

t

p

t

ipp

t

i

ti

ti

k

k

MMk

MMk

R

RDP

k

Mk

Mk

MMk

R

RDP

k

MIkkR

k

MIkM

MkMIk

RR

M

M

I

]][[

]][[

][

][

]][[

]][[

]][[][

][]][[

][

][

][

2

=

2kt[M·]2

kp[M][M·]=

2kt[M·]kp[M]

=kp[M]

][(2 Ikfk dt

=2kt[M·]2

kp[M][M·]=

2kt[M·]kp[M]

=kp[M]

][(2 Ikfk dt

tr

p

tr

p

tr

p

t

p

t

p

t

p

t

ipp

t

i

ti

ti

k

k

MMk

MMk

R

RDP

k

Mk

Mk

MMk

R

RDP

k

MIkkR

k

MIkM

MkMIk

RR

M

M

I

]][[

]][[

][

][

]][[

]][[

]][[][

][]][[

][

][

][

2

Page 25: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

L. Nonconjugation diene – Cationic cyclopolymerization

C6H5 C6H5

R+R

C6H5 C6H5

+

R

C6H5C6H5

+monomer

R

C6H5 C6H5

(7.28)

7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization

Page 26: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

Cationic Polymerization lead to stereoregular structures.

ex) vinyl ether - methylstyrene

Vinyl ether observation resulting

(1) greater stereoregularity is achieved at lower temperatures

(2) the degree of stereoregularity can vary with initiator

(3) the degree and type of stereoregularity (isotactic or syndiotactic)

vary with solvent polarity.

7.2.3 Stereochemistry of Cationic Polymerization

R O CH CH2

CH2 C CH3

Page 27: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

EX) t-butyl vinyl ether forms isotactic polymer in nonpolar solvents. forms mainly syndiotactic polymer in polar solvents.

( cationic chain end and the counterion are associated )

7.2.3 Stereochemistry of Cationic Polymerization

Solvent effect

Page 28: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

In polar solvents both ions 1) be strongly solvated 2) the chain end – exist as a free carbocation surrounded by solvent molecules

In nonpolar solvents 1) association between carbocation chain end and counterion would be strong 2) counterion could influence the course of steric control.

7.2.3 Stereochemistry of Cationic Polymerization

Solvent effect

Page 29: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

CCH2

RO HC

CH2

RO H

CH2C+

RO H

6 45 3

21 X

-CH2

C

H

CH2

C

OR

H

CH2C

H

ORR O

X-

65

43

1 2

+

(7.29)

CCH2

RO HC

CH2

RO H

CH2C

HRO

CH2CH+

OR

X-

CH2C

H

CH2

C

OR

H

CH2C

H

ORR O

X-+

ROCH CH2

(7.30)

Models proposed for vinyl ether polymerization

Page 30: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

X-

CCH2

RO HC+

RO H

CH2 CH2 CHORC

CH2

RO HC+

RO H

CH2C

HOR

C

HH

-X

CCH2

RO H

CH2C

RO H

X-

ORH

CCH2

+

CCH2

RO HC+

RO H

CH2-

XC

RO H

CH2

(7.31)

CH2C

CH2C

R R' RR'

+ X-

+ C

H

HC

R'

R

front

(syndiotactic)

X-CH2

CCH2

C

R' R R'R

C

R R'

CH2+

back sideback(isotactic)

CH2C

R R'

CH2C

R'R

CH2 CR

R'

X-+

CH2C

CH2C

R R'RR'

C

R R'

CH2X-

+

(7.32)

(7.33)

front side

Page 31: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.2.4 Cationic Copolymerization

A. Copolymerization equation - the situation is complication by counterion effects.

B. Reactivity ratios vary with initiator type and solvent polarity.

C. Temperature – unpredictable effect

D. Steric effects (Table 7.3)

E. commercial cationic copolymers – butyl rubber (prepared from isobutylene and isoprene.)

protective clothing tire inner tubes

Page 32: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

TABLE 7.3. Representative Cationic Reactivity Rations (r)a

Monomer 1 Monomer 2 Coinitiatorb SolventbTemperature

(oC) r1 r2

1,3-Butadiene1,3-ButadieneIsopreneCyclopentadieneStyreneStyrene-Methylstyrene-Methylstyrenep-Methylstyrenetrans--Methyl- styrenecis--Methyl- styrenetrans--Methyl- styrenei-Butyl vinyl ether-Methylstyrene

AlEtCl2

AlCl3

AlCl3

BF3·OEt2

SnCl4

AlCl3

TiCl4

SnCl4

SnCl4

SnCl4

SnCl4

SnCl4

BF3

BF3

CH3ClCH3ClCH3ClPhCH3

EtClCH3ClPhCH3

EtClCCl4

CH2Cl2

CCl4/PhNO2(1:1)

CCl4/PhNO2(1:1)

CH2Cl2

CH2Cl2

-100-103-103-780

-92-780

-780

0

0

-78

-23

431152.5

0.601.609.021.2

0.050.331.80

1.0

0.74

1.30

6.02

00

0.44.5

1.171.995.5

2.901.741.10

0.32

0.32

0.92

0.42

Isobutylene

Styrene

p-Chlorostyrene

Ethyl vinyl ether

2-Chloroethyl vinyl ether

aData from Kennedy and Marechal.5

bEt = C2H5, Ph = phenyl.

Page 33: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.2.5 Isomerization in Cationic Polymerization

XCH2 CH2 C+

CH3

CH3

monomer CH2 CH2 C

CH3

CH3

CH2 CH CH

CH3

CH3X+

XCH2 CH CH

CH3

CH3

H:shift

(7.34)

R+

R R

+

+ (7.35)

Page 34: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.3 Anionic Polymerization

7.3.1 Anionic initiators

7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization

7.3.3 Stereochemistry of anionic polymerization

7.3.4 Anionic copolymerization

Page 35: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

Nu- + CH2 CHR NuCH2 CH-

R(7.36)

Propagating chain - carbanion

Examples – nitro, cyano, carboxyl, vinyl, and phenyl.

Monomers having substituent group – stabilizing a carbanion

resonance or induction

7.3.1 Anionic Initiators

Page 36: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

CH2 C

CH3

NO2

KHCO3 CH2 C

CH3

NO2

(7.37)

CH2 C

CN

CN

H2O CH2 C

CN

CN

(7.38)

The strength of the base necessary to initiate polymerization depends in large measure on monomer structure

cyanoacrylate adhesives

high reactivity

7.3.1 Anionic Initiators

Page 37: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

Two basic types

that react by addition of a negative ion

that undergo electron transfer.

① The most common initiators that react by addition of a negative ion

simple organometallic compounds of the alkali metals

For example : butyllithium

Character of organolithium compounds - low melting - soluble in inert organic solvents.

Organometallic compounds of the higher alkali metals - more ionic character - generally insoluble

7.3.1 Anionic Initiators

Page 38: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.3.1 Anionic Initiators

② Electron transfer (charge transfer)

by free alkali metal : solutions in liquid ammonia or ether solvents suspensions in inert solvents

by addition complex of alkali metal and unsaturated or aromatic compounds.

Electron transfer processes (involving metal donor D· , monomer M)

D + M D+ + M_

Na + Na+

Na + Ph CH CH Ph [Ph CH CH Ph] Na+

D + M D + M__

Na + PhCPh

O

PhCPh

O

Na+

2 PhCPh

O

Na+ Ph2C

O

CPh2

Na ONa

Page 39: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization

A. Mechanism 을 변화시킬 수 있는 요인a. solvent polarity

R metal R-Me+ R- Me+ R- + Me+

ion pair solvent separatedion pair

solvated ion

Degree of association of ioncounterion 의 역할

polar solvent : solvated ion 우세

X- + CH2 CH R XCH2 CH R-

non polar solvent : 이온들간의 association 우세 - complex 형성

R Li + CH2 CH

R'

R LiCHR'

CH2

RCH2CHLi

R'

Page 40: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

b. Type of cation (counterion)

c. Temperature

B. The rate of initiation - initiator 와 monomer 의 structure 에 의존

C. Initiation by electron transfer dianion 생성

2 CH2 C

R

Na+Na+CHCH2CH2CHNa+

R R

Na + CH2 CH

R

CH2 CH

R

Na+

(7.46)

(7.47)

7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization

Page 41: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

D. Kinetic

7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization

KNH2 K+ + NH2-

NH2-

+ M H2N M-

H2N(M)n- + NH3 H2N(M)nMH + NH2

-

]][[ 2 MNHkR ii

]][[ MMkR pp

]][[ 3NHMkR trtr

DPBecause the second step is slow relative to the first,

Chain termination is known to result primarily by transfer to solvent:

Rate expressions for propagation and transfer may be written in the conventional way:

Page 42: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

][

][

]][[

]][[

33 NHk

Mk

NHMk

MMk

R

R

tr

p

tr

p

tr

p

][

]][[

3

22

NHk

MNHkkR

tr

ipp

Substituting in Rp we obtain

The average kinetic chain length, is expressed as

tri RR

]][[]][[ 32 NHMkMNHk tri

][

]][[][

3

2

NHk

MNHkM

tr

i

Assuming a steady state whereby

and

D. Kinetic

7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization

Page 43: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

E. Other types of transfer reactions

CH2CH

CN

+ CH2 CH

CN

CH2CH2

CN

+ CH2 C

CN

CH2 C

CN

+ CH2 CH

CN

CH2 C

CN

CH2CH

CN

CH2 C

CH3

C

CH2 C

CH3

CH2

CO2CH3

O

OCH3

OCH3

H3C

O

H2C

C

CH3

CH2

C CH2

O

H3C CO2CH3

CO2CH3

CH3

+ OCH3

_

7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization

Page 44: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization

living anionic polymers can be made

When impurities are rigorously excluded

When the polymerization temperature is kept low

pi RR In Living PolymerizationF.

][][][

MIkdt

Mdop

tIko eMM ][][][

o

o

I

MM

][

][][

o

o

I

M

][

][

all chains begin to grow simultaneously.

No termination, no chain transfer reaction.

as monomer is completely consumed.

DP

electron transfer initiators

2DP

Page 45: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization

G. Important factor in propagation rate.

a. Association between counterion and terminal carbanion

2 CH2CHLi

R

CH2CH

R

Li

Li

CHCH2

R

(7.54)

TABLE 7.4. Representative Anionic PropagationRate Constants, kp, for Polystyrenea

Counterion Solvent kp (L/mol s)b

Na+

Na+

Li+

Li+

Li+

Tetrahydrofuran1,2-DimethoxyethaneTetrahydrofuranBenzeneCyclohexane

803600160

10-3-10-1c

(5-100)10-5c

aData from Morton.30

Bat 25oC unless otherwise noted.cVariable temperature.

Page 46: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization

G. Important factor in propagation rate.

b. Monomer structure

CH2 CHCN CH2 CCO2CH3

CH3

CH2 CH CH CH2CH2 CHC6H5> >>

CH2 CHCN > CH2 CCN

CH3

> CH2 CHCO2CH3 > CH2 CCO2CH3

CH3

steric effect

inductive destabilization of the carbanion

Page 47: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.3.3 Stereochemistry of anionic polymerization

A. Stereochemical of nondiene vinyl monomer

With soluble anionic initiators (homogeneous conditions) at low temperatures,

polar solvents favor syndiotactic placement

nonpolar solvents favor isotactic placement.

(stereochemistry depends in large measure on the degree of association with counterion, as it does in cationic polymerization)

(7.55)

Page 48: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.3.3 Stereochemistry of anionic polymerization

A. Stereochemical of nondiene vinyl monomer

CH3

CCH2

C

CCH3

COCH3O

OH3C

O Li+

_ CH2 C

CH3

COCH3

O

C

CH2

C

CH2

C

CH3

C

O OCH3_Li+

CH3CH3

CO2 CH

3

CO2 CH

3

(7.56)

level of isotactic placement decreases –as the solvent polarity is increased or as lithium is replaced with the less strongly coordinating higher alkali metal ions.

level of isotactic placement decreases –as the solvent polarity is increased or as lithium is replaced with the less strongly coordinating higher alkali metal ions.

Page 49: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.3.3 Stereochemistry of anionic polymerization

A. Stereochemical of nondiene vinyl monomer

RO

R R

COR

O

CO

Li

OC

RO

HH

R

R R

C

OORC

RO O

LiO O

RH

HC

OOR

(a) (b)SCHEME 7.1. (a) Isotactic approach of methyl methacrylate in a nonpolar solvent(b) Syndiotactic approach of methyl methacrylate in tetrahydrofuran.(Circles represent backbone or incipient backbone carbons: R=methyl. Backbone hydrogens omitted.)

Effect of solvent

Page 50: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

B. Stereochemical of Dienes

H2C C

CH3

HC CH2

H2C CHHC CH2

7.3.3 Stereochemistry of anionic polymerization

catalyst, solvent 의 영향

isoprene 1,3-butadiene

Li-based initiator/nonpolar solventscis-1,4 polymer 의 생성이 증가

ex) Isoprene/BuLi/pentane or hexane cis-1,4 polyisoprene

Page 51: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

(7.57)CH2Li + CH2 C

CH3

CH CH2CH2Li

C

CCH2 CH3

CH2H

formation of cis-polyisoprene – lithium’s ability

CH2C

HC

CH2

CH3

+ CH2 CH C CH2

CH3

CH2C C

H

CH2

CH3

LiCH2

CCHCH2

CH3

Li+-

(7.58)

forming a six-membered ring transition state – “lock” the isoprene into a cis-configuration

s-cis comformation by pi complexation – hold isoprene

CH

CCH2

CH2

CH3

CH

C

CH2

CH2CH3

(7.59)steric effect

7.3.3 Stereochemistry of anionic polymerization

Page 52: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.3.4 Anionic Copolymerization

Complicating factors of counterion.

① solvating polar of the solvent

② temperature effect

③ electron transfer initiator 사용

Table 7.5

④ contrasts between homogeneous and heterogeneous polymerization systems.

relatively few reactivity ratios

free radical polymerizationAnionic polymerization

competition

Li+CHCH2CH2CHLi+ + Cl R Cl CHCH2CH2CH R

X X

- -

X X(7.60)

Page 53: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

TABLE 7.5. Representative Anionic Reactivity Ratios (r)a

Monomer 1 Monomer 2 Initiatorb Solventc Temperatured

(oC)r1 r2

Nan-BuLin-BuLin-BuLin-BuLin-BuLin-BuLiEtNan-BuLiRLiNan-BuLiNaNH2

RLiNaNH2

NH3

NoneNoneHexaneHexaneTHFTHFBenzeneCyclohexaneNoneNH3

HexaneNH3

NoneNH3

25255025-78

40

50

0.12e

0.040.030.044.0

11.00.96

0.0460.120.013.380.250.343.2

6.4e

11.212.511.80.30.41.6

16.612.50.010.477.96.70.4

Methyl methacrylate

Butadiene

IsopreneAcrylonitrileVinyl acetateIsopreneAcrylonitrile

Vinyl acetate

Styrene

ButadieneMethyl methacrylate

aData from Morton.30

bBu=butyl, Et=ethyl, R=alkyl.cTHF=tetrahydrofuran.dTemperature cot specified in some instances.eNo detectable styrene in polymer.

Page 54: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

(7.61)

7.3.4 Anionic Copolymerization

formation of block copolymers by the living polymer method.

Page 55: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

B initiator B:- combination -:BB:- B -:BBBBBBBBBB:- S

-:SSSSSBBBBBBBBBBSSSSS:-(7.62)

ABA triblock polymers – Greatest commercial successex) styrene-butadiene-styrene

star-block (radial) – much lower melt viscosities, even at very high molecular weights

ex) silicon tetrachloride

Commercial block copolymers

4 + SiCl4 Si:- (7.63)

7.3.4 Anionic Copolymerization

Page 56: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.4 Group Transfer Polymerization (GTP)

(In the 1980s a new method for polymerizing acrylic-type monomers)

GTP 의 특성

① Anionic polymerization 에서 흔히 사용되는 monomer 를 사용 Living polymer 로 전환

② Propagating chain Covalent character

③ Organosilicon 이 개시제로 사용

C COR

OSiR3

R

R+ CH2 C

CH3

CO2CH3

HF2-

RO2C C

R

R

CH2C

CH3

COSiR3

OCH3

(R CH3)

n CH2 C

CH3

CO2CH3

RO2C C

R

R

CH2C

CH3

CO2CH3

CH2C

CH3

COSiR3

OCH3n

(7.64)

living polyme

rOrganosilicon 에서 SiR3 가 transfer되어 중합을 형성 (GTP)

Page 57: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

TABLE 7.6. Representative Compounds Used in Group Transfer Polymerization

Monomersa Initiatorsa Catalystsa Solvents

HF2-

CN-

N3-

Me3SiF2

Lewis acidc

ZnX2

R2AlCl

(R2Al)2O

CH2 CHCO2R

CH2 CCO2R

Me

CH2 CHCONR2

CH2 CHCN

CH2 CCN

Me

CH2 CHCR

O

Me2C COMe

OSiMe3

Me3SiCH2CO2Me

Me3SiCN

RSSiMe3

ArSSiMe3

Anionicb Acetonitrile1,2-Dichloroethaned

Dichloromethaned

N,N-DimethylacetamideN,N-DimethylformamideEthyl acetatePropylene carbonateTetrahydrofuranToluened

aR=alkyl, Ar=aryl, Me=methyl, X=halogen.b0.1 mol% relative to initiator.c10-20 mol% relative to monomer.dPreferred with Lewis acid catalysts.

Page 58: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.4 Group Transfer Polymerization (GTP)

R2CHCO2RR'2N-Li+

R2CCO2R R2C CO-

OR

R3SiClR2C C

OSiR3

OR

* Synthesis of initiator

CH2SSiMe3

CH2SSiMe3+ CH2 CHCO2R

ZnI2CH2S

CH2S

CH2CH

CO2R

CH2CH C

OSiMe3

OR

CH2CH

CO2R

CH2CH C

OSiMe3

OR(7.65)

두 개의 작용기를 갖는 개시제 사용 사슬의 양끝에서 성장

Page 59: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.4 Group Transfer Polymerization (GTP)

CH2C

CH3

COCH3

OSiR3

CH3OH

C6H5CH2Br

CH2CH

CH3

CO2CH3

CH2CCH2C6H5

CH3

CO2CH3

(7.66)

(7.67)

Speciality

① Once the monomer is consumed, a different monomer may be added

② chain can be terminated by removal of catalyst.

③ chain can be terminated by removal by protonation or alkylation.

Page 60: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.4 Group Transfer Polymerization (GTP)

C COR

OSiR3

R

R

Nu-

CR

R

CH2

C C

O

COR

O SiR3

Nu

OCH3CH3

-

R

CR COR

OCH2 C

CH3

COSiR3

OCH3

(7.68)

GPT mecahanism

Page 61: Chapter 7. Ionic polymerization 7.1 Introduction 7.2 Cationic polymerization 7.3 Anionic polymerization 7.4 Group transfer polymerization.

7.4 Group Transfer Polymerization (GTP)

CH2C C

OSiR3

CH3 OCH3+ C C

CH2

CH3

-O

CH3O

CH2C C

O Si (R3) O

CH3 OCH3

C C

CH3O CH3

CH2

(7.69)

Chain transfer of GPT