7.2. Cationic Polymerization - 7 Ionic Polymerization

Chapter 7. Ionic Polymerization

7.2. Cationic Polymerization + + E + CH =CR CR

  → ECH

  2

  2

  2

  2

electrophile carbocation

7.2.1. Cationic Initiators 1) Protonic acids: H SO , H PO

  2

  4

  3

  4 2) Lewis acids : AlCl , BF , TiCl , SnCl

  3

  

3

  4

  4 (Coinitiator) + Proton donor or cation source : H O, alkyl chloride

  2 (Initiator)

• + - + BF H O HOBF H

  3

  2

  3

  3) Autoinitiation Lewis acid and cation source - +

  2 AlBr AlBr AlBr

  3

  4

  2 are the same 4) Ionizable compounds + - (C H ) C -Cl (C H ) C + Cl Stable carbocation

  6

  5

  3

  6

  5

  3 ∴

  Only useful with - Cl + + very reactive monomers Cl such as vinyl ethers Tropylium chloride 5) I

  2 In situ generation of HI + HI

  ICH CR

  2 ICH CIR

  CH CR I +

  2

  2

  2

  2

  2

• + -

  ICH CR

   I

  2

  2

  6) M + A → M• + + A• - N CH CH

  2 RNO

• + - + Electron transfer process Electron donor Electron acceptor Radical cation

  2 N CH CH

  2 RNO

  2 +

7.2.2. Mechanism, Kinetics, and Reactivity in Cationic Polymerization o Markovnikov’s rule Addition of electrophile to monomer The more stable carbocation intermediate is formed. When an unsymmetrical alkene undergoes addition with E-Nu , then the electrophile , E , adds to the carbon of the alkene that has the greater number of hydrogen substituents , and the nucleophile, Nu , to the carbon of the alkene with the fewer number of hydrogen substituents " o o 2 carbocation 1 carbocation More stable major

  X X Only isobutylene provides the requisite carbocation stability for cationic polymerization CH

  (CH

  3 )

  2 C=CH

  2 > CH

  3 CH=CH

  2 > CH

  2 =CH

  2 o Rate of addition to aliphatic monomers O

2 CH

  X Reactivity ( para -substituted) X: OCH

  3 > CH

  3 > H > Cl Electron-donating Electron-withdrawing Ortho substituents retard the addition ∵ Steric hindrance

  Vinyl ether : particularly reactive CH

• + +

  2 CH OR CH

  2 CH OR R' CH

  2 C OR R' R' + +

  o Propagation Two steps CR

  2 CH

  2 CR

  2 CH

  2 CH

  2 CR

  2 + + slow + fast + Covalent bond formation π-complex

  Rate-determining o Solvent effect As solvent polarity ↑

  , R i ↑

  ∵ R i : charged species is generated Polar solvent stabilizes the charged species

• - Degree of association between cationic chain end and anion (A ) + +
• + A

  A-

  A- + A-

  

covalent intimate ion pair solvent-separated solvated ions

ion pair = contact ion pair

  = free ions Small R p Large R p The more intimate the association, the lower the R . p In poorly solvating solvents

  ↑ As solvent polarity↑, R ∵ more separation p In solvating solvents (ether solvent )

  ↓ ∵ As solvent polarity↑, R less π-complex formation p Polar solvent stabilizes the initial state (monomer + ion pair)

  slow CR

  2 + CH CR

• + +

  2

2 CH

  2 Polar solvent stabilizes Charge is dispersed the initial state over a larger volume O O + O O

  o Chain transfer reactions M = styrene, I = H

  2 SO

  4 1) With monomer HSO ₄ + CH CH ₂ CH CH ₂

• + - 2) By ring alkylation Electrophilic substitution HSO
₄ + CH CH ₂ CH CH ₂

  HSO ₄

• + -
• + CH CH
CH 3 CH<
• - HSO
₄
• + CH CH
₂ CH CH 2<
• + - CH CH
2<
• + CH CH
₃

  

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

• - + CH CH CH CH CH HSO +
₂ ^{4 2} 2<
• - HSO
4<
• + CH C + CH CH
_{2 2} ^{2 CH} ₂ Chain branching

4) With solvent by electrophilic substitution - + HSO CH CH CH +

  _{2 4 CH + 2}

• - + HSO CH CH
³ 4<

• +

  CH CH
₂

  o Termination reactions Combination of chain end with counterion (i.e., change from ionic to covalent bonding) CH CH ₂

• - C CH
₂ O C O CF ₃ C C
• + O C O CF
₃

  2 CH

  3 + CH

  3 HOBCl

  3 - C CH

  2 CH

  3 + CH

  3 BCl

  2 OH Cl

  o Chain transfer to monomer is so common

Proton trap intercepts proton before it transfers to monomer.

Lower overall yield , higher mol. wt ., lower polydispersity index CR

  2 + + N CR

  2 CH + + N H Proton trap The bulky t-butyl groups prevent reaction with electrophiles larger than the proton .

2 CH

  o Telechelic polymers Inifer : ini tiator + chain trans fer agent CH _{3 CH} CH _{3 CH 3} ³

• + - Cl C C BCl Cl C C Cl BCl
₃ 4<
• + CH CH
_{3 3} CH CH _{3 3} Cocatalyst ini tiator

  CH CH _{3 CH 3} CH CH _{3 CH 3 3} ³

• + + Cl C C CH C
₂ Cl C C
• + CH
₂ CH CH _{3 3} CH ₃ CH CH _{3 3} CH ₃ CH CH CH _{3 CH 3 3 3 CH} CH ₃ 3<
• + + CH C Cl C C Cl CH C +

  Cl C C Cl ₂

• + ₂ CH CH CH
_{3 3 3} CH CH CH _{3 3 3}

  chain trans fer agent

  CH CH ₃ CH ₃ ^{3 CH} ₃ CH C C CH C Cl Cl C _{2 2}

  o Pseudocationic polymerization I = HClO , M = styrene, S = hydrocarbon solvent

4 R much slower compared with most cationic processes. p

  CH CH CH CH CH CH ^{2 OClO} CH OClO + ₃ CH ₂ ^{2 2} ₃ Covalently bonded

  Monomer is inserted perchlorate ester between C-O bonds

• + + -

  2 C CH

  3

  3 BCl

  3 BCl

  O C O CH

  3 C

  3 R

  3 CH

  3 CH

  3 CH

  

CH

  2 C

  CH

  o Living cationic polymerization M = isobutylene, I = tertiary ester + BCl

  3 C

  3 R

  O CH

  3 O C

  3 BCl

  O CH

  3 C O C

  2 R

  )

  3

  2 C(CH

  3 CH

  δ+ δ- Very tightly bound But still active ion pair

  M = vinyl ether , I = I

  2 /HI or

  I

  2 /ZnI

  2 CH ₂ CH

  I OR CH ₂ CH OR ZnI ₂ CH ₂ CH

  I OR CH ₂ CH OR ZnI ₂ Insertion of monomer into an activated C-I bond Low polydispersity ,

Block copolymers are formed upon addition of a second monomer

  [ ][ ] _{t i} k M I k

  Kinetics R i = k i [ I ] [ M ] R p = k p [M + ] [M] R t = k t [ M + ] R tr = k tr [ M + ] [ M ] Steady-state assumption R i = R t k i [I] [M] = k t [M + ] or [ ]

• ∴ [ ][ ] _t
² _{i p p} k

  M =

  

M

I k k R =
Table 7.2 Cationic Propagation Rate Constants , k

  p

Monomer Solvent Temperature(℃) Initiator k

_P (L/mol s)

  Styrene None

  15 Radiation

  3.5 X 10 ⁶ α-Methylstyrene

  None Radiation

  4 X 10 ⁶ i

• -Butyl vinyl ether None

  30 Radiation

  3 X 10 ⁵ i

• -Butyl vinyl ether CH
₂ Cl ₂ C ₇ H ₇ ⁺ SbCl ₆ ^-

  5 X 10 ³ t

• -Butyl vinyl ether CH
₂ Cl ₂ C ₇ H ₇ ⁺ SbCl ₆ ^-

  3.5 X 10 ³ Methyl vinyl ether CH ₂ Cl ₂ C ₇ H ₇ ⁺ SbCl ₆ ^-

  1.4 X 10 ² 2-Chloroethyl vinyl ether CH ₂ Cl ₂ C ₇ H ₇ ⁺ SbCl ₆ ^-

  2 X 10 ²

  In the absence of any chain transfer

  [ ] [ ] ν = DP = = =

• R k M M k M _{p p [ ] p}
• R k M k _{t t [ ] t}

  If transfer is the predominant mechanism controlling chain growth

• R k M M k

  [ ] [ ] p p p DP

  ν = = = =

• R k M M k

  

[ ] [ ]

tr tr tr Free radical Cationic

  1

2 R ∝ I , M

  [ ] [ ] p

  2 R ∝ I , M [ ] [ ] p

  1 −

  2 ν ∝

  M , independen t of [I] [ ]

  ν ∝ [ ] [ ] I , M

  The difference arises from radical disproportionation and

combination reactions chacteristic of free radical termination.

  Ph Ph R Ph Ph Ph Ph R Ph Ph R Ph Ph Ph Ph R + +

  o Diene monomers Cationic polymerization only for copolymer synthesis o Nonconjugated dienes Cationic cyclopolymerization

• + +

7.2.3 Stereochemistry of Cationic Polymerization (1) Greater stereogularity at lower temperature (2) Degree of stereoregularity varies with initiator counterion (3) Degree and type of stereoregularity (isotactic or syndiotactic) vary with solvent polarity Ex CH CH Isotactic in nonpolar solvents

  2 Syndiotactic in polar solvents

  O t-Bu In polar solvents : both carbocation chain end and counterion are strongly solvated ∴ free carbocation Syndiotactic placement In nonpolar solvents : strong association between carbocation chain end and counterion

  Isotactic poly(vinyl ether) Several models have been proposed 1) Six-membered cyclic chain end Formed by coordination of the carbocation of the terminal carbon with the oxygen of the alkoxy group attached to the fifth carbon atom axial

  OR H RO H RO RO H H H C C H - + C

  CH CH C C

  X ² ₂ CH C CH CH _{2 2 2}

  bulkiest

• + R O CH
₂

  equatorial

  OR -

  X OR H

  equatorial

  H C C H RO H RO RO H H CH ₂ CH ₂ C C C

• + C
• - CH CH CH CH CH +
_{2 2 2 2} X R O CH ₂ O
• - X

  OR CH CHOR ₂ Attack of monomer atC from the backside causing inversion .

  1

• - 2) Strong carbocation chain end counterion association Insert monomer: alkoxy groups are anti to one another

  RO H RO RO H H RO H CH CHOR ₂ H

• + - +

  C C C

  X C CH C CH ₂ CH ² CH _{2 2} H H C

• - X RO RO H RO RO RO H RO

  H H H

• - H
• + C

  X C C C C CH CH CH CH C ² CH _{2 2} ^{2 2} H H

• + C -

  X RO

  As long as propagation proceeds faster than rotation about carbon-carbon bonds in the chain, a regular repeating isotactic polymer results.

  3) sp

  2 hybridization of the terminal chain carbon atom CH ₂ C CH ₂ C R R' R' R

  X + - + C C H H R R' C CH ₂ C CH ₂ C R' R R R'

  X + - CH ₂ R R'

Front

Back

  C CH ₂ C CH ₂ C R' R R R'

  X + - CH ₂ R R' C CH ₂ C CH ₂ C R R'

  R R'

  X + -

CH

₂ R R'

  In polar solvent syndiotactic isotactic In nonpolar solvent front back

  Poly(α-methylstyrene) Due to two bulky groups on the 3rd carbon, back-side attack is hindered .

  ∴ Syndiotactic placement is favored in both polar and nonpolar solvents .

  Although isotacticity↑ as solvent polarity↓ Poly(vinyl ether) Being less hindered , exhibit a more pronounced preference for isotactic placement in nonpolar solvents As T↑, electroregularity ↓ Can be interpreted in terms of small difference in activation energy for front- and back-side attack as well as of the effect on conformational mobility of the growing chain.

  

Counterion-monomer interactions are assumed to be negligible ,

since both may be considered “ electron rich ”

7.2.4 Cationic Copolymerization Counterion effect

Table 7.3 Reactivity ratios Reactivity ratios vary with initiator type and solvent polarity . No apparent tendency for alternating copolymers to form.

  

Block copolymers or homopolymer blends are more likely .

• 100
• 103
78
• 92
• 78

  5.5 Styrene α-Methylstyrene p

  1.30

  0.32 Ethyl vinyl ether i -Butyl vinyl ether BF ₃ CH ₂ Cl ₂ -78

  0.32

  0.74

  1.0

  trans- β-Methyl- styrene SnCl ₄ SnCl ₄ CCl ₄ /PhNO ₂ (1:1) CCl ₄ /PhNO ₂ (1:1)

  0.10 P-Chlorostyrene cis - β

  1.74

  2.90

  1.80

  0.33

  0.05

  trans - β

  1.99

  0.17

  4.5

  0.4

  1.2

  9.02

  1.60

  0.60

  2.5

  43 115

  AlEtCl ₂ AlCl ₃ AlCl ₃ BF ₃ ·OEt

₂

SnCl ₄ AlCl ₃ TiCl ₄ CH ₃ Cl CH ₃ Cl CH ₃ Cl PhCH ₃ EtCl CH ₃ Cl PhCH ₃

  (℃) r ₁ r ₂ Isobutylene 1,3 Butadiene 1,3-Butadiene Isoprene Cyclopentadiene Styrene Styrene α-Methylstyrene

  Monomer 1 Monomer 2 Coinitiator solvent Temperature

Table 7.3 Cationic Reactivity ratios
• Methylstyrene
• 78
• Methyl- styrene SnCl
₄ SnCl ₄ SnCl ₄ EtCl CCl4 CH ₂ Cl 2<
• Methyl- styrene

  0.92

7.2.5 Isomerization CH

  2 CH CH CH

  3 CH

  3 X + CH

  

2

CH CH CH

  3 CH

  3 X + H - shift CH

  2 CH

  2 C CH

  3 CH

  3 X + Monomer CH

  2 CH

  2 C CH

  3 CH

  3 1,3-addition polymer More stable tert-carbocation R + R + R + terpene rearrangement Relieves strain in the bicyclic system

7.3 Anionic Polymerization

7.3.1 Anionic Initiators Initiation: nucleophilic addition to monomer CH

  CH

  2 CH - Nu R R R: -NO

2 CH Nu- +

  2

, -CN, -COOH , -CH=CH

  2 , e - -withdrawing group resonance where

  o Initiators Weak base initiator - For monomer with strong e withdrawing group Strong base initiator - For monomer with phenyl or weak e withdrawing group

CH

₃ CH ₃ KHCO ₃ CH C CH C _{2 2} NO ₂ NO ₂ CN CN H O ₂ CH C CH C _{2 2} CN

CN

  CN CN H O ₂ CH C CH C _{2 2} Super glue COOR COOR

1. Initiators that react by addition of a negative ion - -

  IM

  I M + Organometallic compounds of the alkali metals : e.g. butyllithium Organolithium compounds: low melting and soluble in inert organic solvents

2. Initiation by electron transfer 1) Free alkali metals In liquid ammonia, ether solvents 2) Complexes of alkali metals and unsaturated or aromatic compounds

  Electron transfer - + + M + M D D Metal Monomer Electron d onor

Addition complexes of alkali metals and naphthalene or stilbene

• + Na Na
• - +
• •

  D - + CH CH Ph Ph CH CH Na Ph +

  Ph Na Reaction with monomer - - + M + M D D Addition complexes (called ketyls ) of alkali metals and nonenolizable ketones, such as benzophenone O O - + Na + Na Ph C Ph Ph C Ph O ONa ONa

7.3.2 Mechanism , Kinetics , and Reactivity Li compounds Covalent carbon-metal bonds Higher alkali metals More ionic bonds

  

In polar solvents , free solvated ions addition of anion to monomer

• - CH CH Nu CH

  2 Nu- + CH

2 R R In nonpolar solvents , close association between ions

  π-complex formation CHR' CH CH Li CH

  R ² R Li R Li CH ₂

• + CH
₂ R' R' π-complex formation

  Initiation by

  e- transfer - CH Na+ CH CH Na CH +

  2

2 R R - -

  Potassium amide-initiated polymerization in liquid ammonia - + + NH K

2 KNH

  2 - M H N

  2 slow

2 NH - + M

  − R = k NH M _{i i [ 2 ]} [ ]

  Propagation

• - -

  M + M M M M H N H N

  2

  2 n+1 n

  − =

  R k M M _{p p} [ ] [ ] Chain termination : transfer to solvent - -

  NH M M H + H N

  3

  2 + NH

  2 M M H N

  2 n n

  − R = k M NH _{tr tr} [ ] [ ] ₃ Steady-state assumption

  R = R i tr − k NH M

  − [ ] _{i 2} [ ]

  − − M =

  [ ] k NH M = k M NH

  [ ] [ ] _{i [ 2 ] tr} [ ] ₃ k NH _tr [ ] ₃

  − − ₂ R k M M k M _{p p [ ] p} [ ] [ ] k k NH M

  [ ] _{p i} [ ] ₂ ν = = = ^-

  R = _p R k M NH k NH

  [ ] [ ] [ ]

  o Chain transfer to monomer Initiation by the resultant vinyl anion Unsaturated end groups CH ₂ CH CN CH ₂ CH CN CH _{2 CH 2} CN CH ₂ C CN

• - + CH
₂ C C
• - +
• - CH
₂ CH CN o Termination mechanism in MMA polymerization Backbiting nucleophilic displacement of methoxide

by the enolate anion chain end to form a cyclohexanone ring.- CH ₂ CH C

• + CH
₂ C CN

  CH ₂ C C CH ₃ CH ₂ C CH ₃ C O OCH ₃ CH ₂ C H ₃ C OCH ₃ O CH ₂ C C CH ₃ CH ₂ C CH ₃ C O OCH ₃ CH ₂ C CH ₃ C OCH O

• -
• - + OCH
₃

  o Living anionic polymerization [ ] [ ] [ ]

  M I k dt M d _{o p} = −

  [ ] [ ] [ ]

  I k dt M M d _{o p} − =

  [ ] [ ] [ ]

  I k dt M M ln

− =

_{o p o} [ ] [ ]

  [ ] ^{dt I k} _{o o p} M e M

  − = where [I] o = initial concentration of initiator e.g., M = styrene, I = naphthalenesodium, T = -78 o C R i &gt;&gt; R p No termination or chain transfer reactions

  [ ] [ ] _o ^o

  I M

= ν

  [ ] [ ] [ ] _o ^o

  I M M − = ν

  M completely consumed For simple anionic initiator (e.g., BuLi) DP = ν

  For electron-transfer initiators

Table 7.4 k for polystyrene p In poorly solvating hydrocarbon solvents Li CH CH

  H C

  2

  2

2 Li CH C C

  2 Li R R R

  ↓ association R p + Larger alkali metal cations Weaker coordination than Li

  ↑ R p In a more polar solvating medium (e.g., ether) + Li the most strongly solvated of the alkali metal cations Li-based initiators the fastest R p

Table 7.4 k p for polystyrene Counterion Solvent

  k p (L/mol s) Na + Tetrahydrofuran

  80 Na + 1,2-Dimethoxyethane 3600 Li + Tetrahydrofuran 160 Li + Benzene

  10 -3 -10 -1 Li + Cyclohexane (5-100)X10 -5

  Solvating power 1,2-dimethoxyethane &gt; tetrafydrofuran &gt; benzene &gt; cyclohexane

  CH ₂ CH ₂ OCH ₃ OCH ₃ O

  Reactivity of monomer CH ₂ CH CH

2 CH CN CH

  2 resonance CH

  ₂ C COOCH ₃ CH ₃ &gt; &gt; &gt; e - -withdrawing

  R p ↓

  Methyl substitution on the α-carbon CH

  2 CH CH CH

  3 CH

  3 CH

  2 C CN CH

  3 CH

  2 CH COOCH

  3 &gt; &gt; CH

  2 CH CN &gt; ∵ induction destabilization of the carbanion and steric interference

  2 C COOCH

7.3.3 Stereochemistry of Anionic Polymerization Polar solvents : favor syndiotactic placement Nonpolar solvents : favor isotactic placement o Six-membered cyclic chain end

  C CH ₂ C CH ₃ C OCH ₃ O CH ₃ C O CH ₃ O Li C CH ₃ C CH ₂ C O C O CH ₃ O OCH ₃ CH ₃ Li

• + - C CH
₃ C CH ₂ C O C O CH ₃ O OCH ₃ CH ₃ Li CH ₂ C CH ₃ C OCH ₃ O C CH ₂ C CH ₂ C CH ₃ C OCH _{3 O} C C CH ₃ CH ₃ O CH ₃ O O CH ₃
• + -
• + - Isotactic placement

  Li + -

  ↓ as Solvent polarity

  ↑

  o Ion pairing Counterion - monomer coordination isotactic In nonpolar solvents Counterion - solvent coordination syndiotactic In polar solvents

  C C CH ₃ C OCH ₃ O H H Li CH ₂ C CH ₂ CH C O OR R R C RO O O O C C CH ₃ C CH ₃ O O

  Li CH ₂ C CH ₂ C C O OR R R C RO O H H

  o Diene Polymerization: isoprene, 1,3-butadiene cis-1,4 polymerization ↑

  By Li-based initiators In nonpolar solvents e.g., Almost entirely cis-1,4 isoprene = “ synthetic natural rubber ” BuLi initiator in pentane or hexane 1) s-cis conformation by π-complexation CH

  2 Li CH

  2 C CH

  3 CH CH

  2 CH

  2 Li C C H CH

  2 CH

  3 CH

  2 +

2) Cis configuration by forming a six-membered ring transition state

• + - + CH
₂ CH C CH ₃ CH ₂ CH ₂ CH Li CH ₂ CH ₂ C CH ₃ CH ₂

  CH ₂ C H C CH ₃ CH ₂ Li

  Cis-1,4-poly(1,3-butadiene) configuration Somewhat lower stereospecificity BD ∵ Favors s-trans conformation isoprene Favors s-cis conformation C C CH

  C CH

  CH

  2 H

  C C CH

  2 H

  CH

  2 H

  3 C

  2 H

  2 CH

  CH

  2 H

  C CH

  3 C

  2 CH

  CH

  2 H

7.3.4 Anionic copolymerization

Table 7.5 Anionic Reactivity Ratios

  ● Solvent effect r r

  1

  2 o 0.03 &lt;

  12.5 M = St M = BD I = n-BuLi S = hexane T = 25 C

  1

  2 o 4.0 &gt; 0.3 M = St M = BD I = n-BuLi S = THF T = 25 C

  1

2 In homopolymerization, St is more reactive than BD Polystyryl anion exhibits preference towards BD in hexane CH CH CH CH

  _{2 2 2 2} H H H H C C C C CHLi CHLi CH Li CH Li _{2 2} C C CH CH

CH CH

_{2 3 2 3}
Table 7.5 Anionic Reactivity Ratios Monomer 1 Monomer 2 Initiator Solvent Temperature (℃) r

  50

  0.3

  0.4

  1.6

  16.6

  12.5

  0.01 Butadiene Isoprene n-BuLi Hexane

  3.38

  12.5

  0.47 MMA Acrylonitrile Vinyl acetate NaNH

₂

RLi NaNH

₂

NH ₃ None NH ₃

  0.25

  0.34

  3.2

  7.9

  6.7

  11.8

  11.2

  ₁ r ₂ Styrene MMA Butadiene Isoprene Acrylonitrile Vinyl acetate Na n-BuLi n-BuLi n-BuLi n-BuLi n-BuLi n-BuLi EtNa n-BuLi RLi Na NH ₃ None

  0.12

  None Hexane Hexane THF THF Benzene Cyclohexane None NH ₃

  25

  25

  50

  25 -78

  40

  0.04

  6.4

  0.03

  0.04

  4.0

  11.0

  0.96 0.046

  0.12

  0.01

  0.4

  ● T effect M

  1 = St M

  2 = BD I = n-BuLi S = hexane T =

  25 o C T =

  50 o C S = THF T =

  25 o C T = - 78 o C r

  1

  0.03

  0.04

  4.0

  11.0 r

  2

  12.5

  11.8

  0.3

  0.4 Not to any appreciable extent in hexane Solvation is felt more strongly at lower T in THF

  ● Homogeneous and heterogeneous processes M = St M = MMA I = Na S = NH r = 0.12 r = 6.4

  1

  2

  3

  1

  2 ∞

  M = St M = MMA I = n-BuLi S = none r = 0 r =

  1

  2

  1

  2 No detectable styrene in polymer Homogeneous Soluble n-BuLi only PMMA is formed ∵

  MMA is more reactive than St Heterogeneous

Insoluble metallic lithium or MeLi Block copolymer

  ∵ Initial St polymerization on the initiator surface Detachment Initiation of MMA by detached polystyryl anion

  ● Nucleophilic displacement of aliphatic dihalides by the dianion Formed by electron transfer initiation Li CH CH ₂ CH ₂ CH

  X X Li Cl R Cl CH CH ₂ CH ₂ CH

  X X R + + - - +

  3 CH

  3 CH

  2 C COOCH

  2 CH CH

• - m-1

  If MMA was polymerized first, the copolymer would not form.

  X CH

  2 CH

  2 CH CH

  3 CH

  ● Block copolymers by living polymerization method Polystyrene -block- poly(methyl methacrylate) CH

  2 C COOCH

  

3

CH

  3 CH

  2 C

COOCH

  2 CH CH

  2 CH R CH

  3 n - n-1 - n

  ● St-BD-St (SBS) triblock polymer B B SSSSSBBBBBBBBBBSSSSS S

• - - 50,000~70,000 10,000~15,000 SiCl
• - - -

  BB B BBBBBBBBBB initiator combination - -

• - 4 +

  4 Si

  ● Star-block (radial) copolymer Living block copolymer

7.4 Group Transfer Polymerization (GTP) Living polymers at room temp or above

  ● Initiators : -SiMe compound Transfer to carbonyl oxygen

  3

• - - + H

  O R N Li - ₂ O CH O ³ C C CH C C ₃ CH C C ₃ CH OCH OCH ₃ ^{3 3} OCH ₃ CH ₃ CH ₃

  

strong base anion

ester

  O Si(CH ) _{3 3} CH ₃ (CH ) SiCl _{3 3} C C CH OCH _{3 3} O

  RS Si(CH ) (CH ) Si CN ArS Si(CH )

  3

  3

  3

  3

  3

  3 (CH ) Si CH C

  3

  3

2 OCH

  3 ●

  Catalysts : Anion or Lewis acid - - - - HF , CN , N , CH SiF ZnX , R AlCl, (R Al) O

  2

  3

  3

  2

  2

  2

  2

  2

TABLE 7.6 Compounds used in Group Transfer Polymerization

  monomers initiators catalysts solvent CH ₂ =CH CO ₂ R Me OMe Me ₂ C=C O SiMe ₃ Anionic HF ₂ ^- CN

• ^- N
₃ ^- Me ₃ SiF ₂ Acetonitrile 1,2-Dichloroethane