Table 6. 1 Commercially Important Vinyl Polymers

Chapter 6.

Free Radical Polymerization

Table 6. 1 Commercially Important Vinyl Polymers

6.1. Introduction

6. 2 Free Radical Initiators

Four types

Peroxides and hydroperoxides

6.2.1. Peroxides and Hydroperoxides ( ROOR ) ( ROOH )

Thermal homolysis

C O O C O

Ph O

Ph

∆ C O

O Ph

2

Decomposition

C O

O

Ph _{Ph + CO2}

Radical combination _{∵ Cage effect}

(confining effect of solvent molecules) Wastage reaction

Ph Ph Ph

2

C O O

Ph Ph _{C O}

O

Ph Ph

+

Induced decomposition

C O O C

O

Ph O

Ph _{Ph C O O C}

O

Ph O

Ph

Ph +

O C

O

Ph

C O

O

Ph _Ph +

Radical stability

Ph C CH₃

CH₃

O CH₃ C

CH₃

CH₃

O _{C O}

O

Ph C O

O CH₃

> > >

Unstable radical More wastage reaction Stable radical

Less wastage reaction

Half-lifes

BPO (Benzoyl peroxide)

CH₃ C CH₃

CH₃

O O C CH₃

CH₃ CH₃

C O O C

O

Ph O

Ph

1.4 h at 85o_C

1.38 h at 145o_C

Ph C CH₃

CH₃

O O H

C O O C O

CH₃ O

CH₃

Promoters

C O O C

O

Ph O

Ph

CH₃ Ph N

CH₃ +

+ CH₃

Ph N

CH₃

O C

O

Ph +

O O

Ph C

-CH₃

Ph N

CH₃

O C

O

Ph +

+

No initiation of polymerization

∵ No N in polymers

6.2.2. Azo Compounds

C(CH₃)₂ N N

CN CN

(CH₃)₂C

CN

(CH₃)₂C

2 + N2

AIBN (Azobisiso(butyronitrile))

Radical combination

CN

C(CH₃)₂ CN

(CH₃)₂C CN

(CH₃)₂C 2

C N C(CH₃)₂ CN

(CH₃)₂C

(CH₃)₂C

C N

(CH₃)₂C

6.2.3. Redox Initiators

Production of free radicals by one–electron transfer reactions. Useful in low–temp polymerization and emulsion polymerization

C(CH3)2 OOH

Ph _Fe2+

O

Ph C(CH₃)₂ + OH + Fe3+

+

-HOOH Fe2+ + OH Fe

3+

+ HO - +

O

₃

SOOSO

₃

-

+

S

₂

O

₃2-

+

SO

₄2-

+

-

SO

-

-4

S

₂

O

₃

6.2.4. Photoinitiators

RSSR

hν

2 RS

C O

CH Ph

OH

Ph

O

C Ph

OH

Ph CH

+ hν

C O

Ph C

O

Ph C

O

Ph hν

2

The major advantages of photoinitiation:

The reaction is essentially independent of temp

Polymerization may be conducted even at very low temperatures

Better control of the polymerization reaction

6.2.5. Thermal Polymerization

Ph H

Ph +

2

∆ CH

CH₂

CH CH₂

CH CH₃

Diels-Alder dimer

Transfer of H atom to monomer Molecule-induced homolysis

6.2.6. Electrochemical Polymerization

RCH

CH

2

+

e

-

RCH

CH

₂

_

RCH

CH

₂

RCH

CH

2

+

e

-+

Radical ions : initiate free radical or ionic polymerization or both

6. 3 Techniques of Free Radical Polymerization Techniques

Method Advantages Disadvantages

Bulk Simple Rxn exotherm difficult to control No contaminants added High viscosity

Suspension Heat readily dispersed Washing and drying required Low viscosity Agglomeration may occur Obtained in granular form Contamination by stabilizer

Solution Heat readily dispersed Added cost of solvent

Low viscosity Solvent difficult to remove

Used directly as solution Possible chain transfer with solvent Possible environmental pollution

Emulsion Heat readily dispersed Contamination by emulsifier

Low viscosity Chain transfer agents often needed High MW obtainable Washing and drying necessary Used directly as emulsion.

6. 4 Kinetics and Mechanism of Polymerization

Formation of the initiator radical

Addition of the initiator radical to monomer Initiation

Initiator R

R CH₂ CH

Y

+ R CH2 CH

Y

Propagation

CH CH₂

Y

CH CH₂

Y

+ CH2 CH

Y

CH CH₂

Y

Termination CH CH₂

Y

HC H₂C

Y +

Coupling or combination

Disproportionation

CH CH₂

Y

HC H₂C Y

CH CH

Y

H₂C H₂C Y

Coupling almost exclusively at low temp _Polystyrene

CH

CH₂ + HC H₂C CH2 CH HC H2C

C CH₂

C

+ O OCH3 CH3

C H₂C C

O

OCH₃ CH₃

C CH

C

+ O OCH₃ CH₃

HC H₂C C

O

OCH3 CH3 Disproportionation

PMMA

∵

Steric repulsion

Electrostatic repulsion

Initiator

k

d

R

R

+ M

k

_i

M

₁ Initiation

Propagation

+ M

k_p

M₂ M₁

+ M

k_p

M₃ M₂

+ M

k_p

M_(x+1) M_x

Termination

+ M_y

k_tc

M_(x+y)

M_x Coupling

+ M_y

k_td

Initiation rate (R_i)

[ ]

[ ]

I

fk

2

dt

M

d

R

_i

=

•

=

_d

where

[M•] = total conc of chain radicals

[I] = molar conc of initiator

f = initiator efficiency = 0.3 ~ 0.8

Termination rate (R_t)

[ ]

[ ]

2 t

t

2

k

M

dt

M

d

R

=

−

•

=

•

Steady-state assumption R_i = R_t

[ ]

[ ]

2

t

d

I

2

k

M

fk

2

=

•

[ ]

[ ]

t d

k

I

fk

M

•

=

[ ]

[ ][ ]

[ ]

[ ]

t d p

p p

k

I

fk

M

k

M

M

k

dt

M

d

R

=

−

=

•

=

Propagation rate (R_p)

Average kinetic chain length ( )

ν

= Average # of monomer units polymerized per chain initiated

[ ][ ]

[ ]

[ ]

[ ]

(

[ ]

[ ]

)

₂1 d

t p

t p 2

t p

t p

i p

I

k

fk

2

M

k

M

k

2

M

k

M

k

2

M

M

k

R

R

R

R

=

•

=

•

•

=

=

=

ν

ν

=

DP

ν

2

Coupling

•

Gel effect, Trommsdorff effect, Norris-Smith effect

Occurs in bulk or concentrated solution polymerizations

η↑ _{Chain mobility}↓ _{R [M•] ↑}

t↓

R_p↑ _{Release of more heat R}

i↑ Rp↑

Polymerization of MMA in benzene 50°C benzoylperoxide

•

Chain transfer reactions

Transfer of reactivity from the growing polymer chain

to another species

Chain-end radical abstract a H atom from a chain

Chain branching

2) Backbiting : intramolecular chain transfer

3) C.T. to Initiator or Monomer

Important with monomers containing allylic hydrogen, such as propylene

Reactive radical

Resonance-stabilized radical

∴ _{High-mol-wt polypropylene cannot be prepared}

CH₂ C CH₃

COOCH3

CH₂ C CH₃

COOCH₃

+ allylic hydrogen

C.T. to monomer

Propagation

CH₂ CH CH₃

COOCH3

CH₂ C CH₂

COOCH₃ +

CH₂ C CH₂

COOCH₃

Resonance-stabilized radical CH2 C

CH₃

COOCH3

CH₂ C

CH₃

C

O

OCH₃

CH₂ C CH₃

COOCH₃

CH₂ C

CH₃

C

O

OCH₃

Resonance-stabilized radical

4) C.T. to Solvent or Chain transfer agents

CCl₄

Transfer reaction rate

[ ][ ]

M

T

k

R

_tr

=

_tr

•

where _{T = transfer agent} Kinetic chain length

[ ]

[ ]

• = ν M k 2 M k t p

[ ][ ]

[ ]

• +

∑

[ ][ ]

• =

[ ]

• +

[ ]

∑

[ ]

• = + = ν T k M k 2 M k T M k M k 2 M M k R R R tr t p tr 2 t p tr t p tr

w/o transfer agent

with transfer agent

[ ]

[ ]

[ ]

[ ]

[ ]

[ ]

M

[ ]

T C 1 M k T k 1 M k T k M k 2 1 T p tr p tr t tr

∑

∑

∑

₊ ν = + ν = + • = ν T p tr

C

k

k

=

Chain transfer constant

[ ]

[ ]

M

Table 6.5 C_Tfor St and MMA

Strong C-H bond

Benzene Low C_T

Toluene Benzylic H _{Higher C}

T

Weak S-H bond Large C_T CCl₃• Resonance stabilization

CHCl₃

CCl₄ C_T↑

CBr₃•

CBr4 RSH

Very-low-mol-wt polymer

Telomerization

When [T] is high, k_tr >> k_p ⇒

Telomer

CH₃ CH₂ CH₂ CH₂ CH₂

- H

C Cl Cl

Cl C Cl

Cl

Cl C Cl

Cl

Cl C _Cl

ο Inhibitors

Added to monomers to prevent polymerization

during shipment or storage

Must be removed by distillation of monomer or extraction

Alkylated Phenol

R' . +

OH R R

R

R'H + R R

R

R R

R O

R R

R

R

R R

R

. _{O O}

.

R .

R' . OR' R R

R

R R

R

R R

R O

R

R R

R

O

+ 'R +

% Polymerization

Time 0

No inhibitor

Inhibitor

More inhibitor

Induction period

Induction periods are common even with purified monomer

o Atom Transfer Radical Polymerization (ATRP)

ο Living free radical Polymerization

No chain termination or chain transfer

CH₃CHCl

Ph

+ Cu(I)(bpy) _CH3CH Ph

. + Cu(II)(bpy)Cl

H₂C CH Ph

CH₃CHCH₂CHCl

Ph Ph

+ Cu(I)(bpy) CH3CHCH2CH Ph Ph

.

+ Cu(II)(bpy)Cl

bpy = bipyridyl =

N N

Polymerization of styrene

Transfer of Halogen atom

propagation

Preventing radical termination

o Addition of a Stable Free Radical

CH₂CH Ph

. +

N

H₃C CH3

H₃C

CH₃ O

.

CH₂CH Ph

N

H₃C CH3

H₃C

CH₃ O

TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy) Too stale to initiate polymerization

Promotes decomposition of BPO to benzoyloxy radicals

Propagation Prevent termination

[ ]

[ ]

o o I M DP =

All the chains are initiated at about the same time. No chain termination or transfer reactions.

ο Emulsion Polymerization

Smith-Ewart kinetics

[ ]

⎟

⎠

⎞

⎜

⎝

⎛

=

2

N

M

k

R

_{p p}

where [M] = concentration of monomer in the polymer particle

Rate of radical entry into the particle

[ ]

[ ]

[ ]

[ ]

I

fk

2

N

M

k

N

R

M

k

M

k

d p i p

p

=

=

ρ

=

ν

Average kinetic chain length

ν

=

DP

N R_i = ρ

[ ]

(

)

0.6

s 4 . 0

i _{a E}

R k N ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ µ =

k = constant (0.37~0.53)

µ = rate of increase in the volume of a polymer particle [E] = concentration of micellar emulsifier

a_s = interfacial area occupied by an emulsifier molecule in the micelles

where

[ ] [ ]

0.4 0.6

E

,

I

6.5. Stereochemistry of Polymerization

Steric and electrostatic interactions are responsible for stereochemistry of free radical polymerization

1) Interaction between Terminal unit & Monomer

Mirror approach

CH₂C CH₂C Y

X Y _{X .}

C C Y X H

H

CH₂C CH₂C Y _X

CH₂ Y X

C Y

X .

etc

Isotactic polymer

Nonmirror approach

CH₂C CH₂C X

Y Y _{X .}

C C Y X H

H

CH₂C CH₂C Y _X

CH₂ X Y

C Y

X .

etc

2) Interaction between Terminal unit & Penultimate unit

C

C

P CH3

CO₂CH₃ H

H

C

CO₂CH₃ CH₃ CH_{2 C}

CH₃

CO₂CH₃

C

C

P CH3

CO₂CH₃ H

H

C

CO₂CH₃ CH₃ CH₂ C

CH₃

CO₂CH₃

P: bulkiest group

If terminal carbon has sp2 _{planar structure,}

Interaction between terminal unit & monomer is dominant factor

If terminal carbon has sp3 _{hybridization,}

Interaction between penultimate unit & terminal unit is dominant factor

Stereoregularity ↑ as T

↓

Free radical polymerization of MMA at T < 0 o_C

Crystalline polymer

Syndiotactic

(Expect) As size of substituent groups ↑, stereoregularity ↑

(Experiment) bulkier substituent

Less syndiotactic than PMMA under the same conditions

CH₂ C CH₃

6.6 Polymerization of Dienes

6.6.1. Isolated Dienes

Crosslinked polymer

Cooperative addition of one double bond to the other of the monomer

Independent reaction

Cyclic polymer

5- or 6-membered ring

Cyclopolymerization:

Cyclopolymerization of divinylformal

.

R +

O O O O

R

O O R

O O R

. .

O O R

O O R

.

head-to-tail mode six-membered ring

head-to-tail mode _{five-membered ring}

Head-to-tail mode

Head-to-head mode

Six-membered ring

Highly crosslinked polymers Diallyl monomer

C

C O

O O

O

Used for manufacturing

electrical or electronics items (circuit boards, insulators,

television components, etc)

preimpregnating glass cloth or fiber for

fiber-reinforced plastics

Diallyl phthalate

O O

O O

2

Used for applications requiring good optical clarity

(eyeware lenses, camera filters,

panel covers, and the like)

6.6.2. Conjugated Dienes

H₂C CH HC CH₂ RH2C CH2

H

C CH₂ .

RH₂C HC CH CH₂ .

.

R

CH₂CH CH CH₂

CH₂

C C

CH₂

H H

CH₂

C C H

H CH2

Pendant vinyl groups unsaturation in the chain

cis trans

1,3-butadiene

1,4-addition 1,2-addition

CH₂ C CH CH₃

CH₂

CH₂CH CH CH₂

CH₃

CH₂CH C CH₂

CH₃

CH₃

CH₂

C C

CH₂

H H

CH₂

C C H

H CH2

cis trans

1,2-addition 3,4-addition cis-1,4-addition trans-1,4-addition Isoprene (2-methyl-1,3-butadiene)

Natural rubber

(Hevea) _Predominant

10%

trans-1,4 s-trans

s-cis cis-1,4 As T↑ , cis-1,4 ↑

CH₂ C CH CH₂

Sn(n-C₄H₁₀)₃

cis-1,4 s-cis

Table 6.6 Structures of Free Radical-Initiated Diene Polymers

percent

Monomer

Polymerization

Temperature(℃) cis-1,4 trans-1,4 1,2 3,4

k_p:

6.7 Monomer Reactivity

-C6H5 < -CN < -COOCH3 < -Cl < -OCOCH3 o Three factors in monomer reactivity

1) Resonance stabilization of free radicals: k_p↓

-C₆H₅ > -CN > -COOCH₃ > -Cl > -OCOCH₃

Reactive monomer Stable monomer

Reactive radical Stable radical

Inverse relationship between monomer reactivity and k_p Radical reactivity is the major factor.

R +

R R R R

2) Polarization of double bond by substituents: k_p↓

Extreme polarization prevents free radical polymerization

e.g.

CH₂ C

CN

CN CH2 CH

OCH3 No radical polymerization

C C C C

C C

Homolytic fission Heterolytic fission

Anionic Cationic polymerization

3) Steric hindrance: k_p↓

CH₂ CH

X

CH₂ C

Y

X _{CH CH CH CH}

Y X

k_p: MMA < MA

CH₂ C

COOCH3

C

H H

H CH2 C

COOCH₃ H

MA MMA

∵ _{Resonance stabilization of the radical by hyperconjugation and} steric hindrance

o Free energy of polymerization

∆G_p = ∆H_p - T∆S_p

∆H < 0 : exothermic, π-bond in monomer → σ-bond in polymer ∆S < 0 : monomer → covalently bonded chain structure

∴ _{Degree of freedom (randomness)} ↓

favorable

unfavorable

(1) The higher the resonance stabilization of monomer, l∆Hl ↓ (2) Steric strain in polymer, l∆Hl ↓

(3) Decrease in H-bonding or dipole interaction on polymerization, l∆Hl ↓

Monomer Polymer

energy

π-bond σ-bond

Resonance Stabilization

of monomer ∆H Steric strain

Decrease in

Table 6.7 ∆H and ∆S of Polymerization

Monomer

-△H (kJ/mol)

-△S

(J/mol)

Acylonitrile 77 109

1,3-Butadiene 78 89

Ethylene 109 155

Isoprene 75 101

Methyl methacrylate 65 117

Propylene 84 116

Styrene 70 104

Tetrafluoroethylene 163

-Vinyl acetate 90

-o P-olymerizati-on-dep-olymerizati-on Equilibrium

M_x + M M_(x+1) k_p

k_dp

where

k_dp = depropagation rate constant

T_{c T}

k_dp

k_p [M]

k_p [M] - k_dp

At T_c

[ ][ ]

M• M = k

[ ]

M•

k_{p dp}

Equilibrium constant

[ ]

[ ][ ]

_e

[ ]

_e k_dpp k M

1 M

M M

K = =

• • =

where [M]_e = equilibrium monomer concentration

∆G = ∆Go _{+ RT ln K}

where ∆Go= ∆G in standard state

(pure monomer or 1-M solution monomer,

pure polymer or 1-M repeating units of polymer) At equilibrium

∆G = 0

∆Go ₌ ∆_Ho _{- T}

c∆So = - RTc ln K = RTc ln [M]e

[ ]

_e o

o c

M ln R S

H T

+ ∆

∆

=

[ ]

R S RT

H M

ln

o

c o

e

∆ − ∆

=

R

S

o

∆

−

[

]

R

S

RT

H

M

ln

o

c

o

e

∆

−

∆

=

R

H

o

∆

[

]

e

M

ln

1

c

T

Table 6.8 T_c of Pure Liquid Monomers Monomer T_c(℃)

1,3-Butadiene 585

Ethylene 610

Isobutylene 175

Isoprene 466

Methyl methacrylate 198

α-Methylstyrene 66

Styrene 395

Tetrafluoroethylene 1100

[ ]

e o

o c

M ln R S

H T

+ ∆

∆ =

CH₂ C

CH₃

CH₂ C

CH₃

-△H = 35 kJ/mol

T_c = 66 o_C

6.8 Copolymerization

Reaction Rate

k₁₁

M₁

•

+ M_{1 M1}

•

k₁₁ [M₁•] [M₁] k₁₂

M₁

•

+ M_{2 M2}

•

k₁₂ [M₁•] [M₂] k₂₁

M₂

•

_M

1

•

+ M _k

21 [M2•] [M1] 1

k₂₂

M₂

•

+ M_{2 M2}

•

k₂₂ [M₂•] [M₂]

o Steady-state assumption for [M₁•] and [M₂•] k₁₂ [M₁•] [M₂] = k₂₁ [M₂•] [M₁]

o Rate of consumption of M₁ and M₂

[ ]

[

][ ]

[

][ ]

1 2 21 1 1 11 1 M M k M M k dt M d • + • = −

[ ]

[

][ ]

[

][ ]

2 2 22 2 1 12 2 M M k M M k dt M

d _{= • + •}

−

[ ]

[ ]

o Instant composition of copolymer

[ ]

[ ]

[

[

]

]

[

[

]

]

⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ • + • • + • = 2 22 1 12 2 21 1 11 2 1 2 1 M k M k M k M k M M M d M d

[

]

[ ][

[ ]

]

2 12 2 1 21 1 M k M M k

M • = •

o Monomer reactivity ratio

1 12 11 r k k = ₂ 21 22 _r k k =

o Copolymer (composition) equation

o Instantaneous composition of feed and polymer

[ ]

[ ] [ ]

1 2

1 2 1 M M M f 1 f + = − =

f₁ = mole fraction of M₁ in the feed f₂ = mole fraction of M₂ in the feed

[ ]

[ ] [ ]

1 2

1 2 1 M d M d M d F 1 F + = − =

F₁ = mole fraction of M₁ in the copolymer F₂ = mole fraction of M₂ in the copolymer

[ ]

[ ]

1

1 2 1 F 1 F M d M d − =

[ ]

[ ]

2 1 2 1 f f M M =

[ ]

[ ]

[ ]

[ ]

[ ] [ ]

[ ] [ ]

⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ + + = 2 2 1 2 1 1 2 1 2 1 M r M M M r M M M d M d ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ + + = − = − 2 1 1 2 2 1 1 2 1 1 1 f f r f r f f f 1 F 1 F F 1 ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ + + =

− _{1 2 2}

2 1 1 2 1 1 1 f r f f f r f f F 1 F 2 1 2 1 1 2 2 2 2 1 2 1 1 2 1 1 2 2 1 1 2

1 r f f f

[ ]

[ ]

₂1

2 1 M d M d F F

F = =

[ ]

[ ]

2 1 2 1 M M f f f = =

[ ]

[ ]

[ ]

[ ]

[ ] [ ]

[ ] [ ]

⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ + + = 2 2 1 2 1 1 2 1 2 1 M r M M M r M M M d M d 2 2 1 2 1 r f f f r r f 1 f r f F + + = ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ + + =

f

f

r

F

r

fF

+

2

=

₁ 2

+

(

)

1 2 2 r F f r F F 1 f ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − = −

Finemann and Rose Equation

(

)

F

F

1

f

−

1 - r₁

r₂

2 2 2 2

1 2

1 1

2 1 2

1 1 1

f

r

f

f

2

f

r

f

f

f

r

F

+

+

+

=

1) r₁ = r₂ = 1

No preference for homopolymerization or copolymerization Random copolymer

F₁ = f₁ e.g. _M

1 = ethylene M2 = vinyl acetate r₁ = 0.97 r₂ = 1.02

2) r₁ = r₂ = 0

Alternating copolymer

F₁ = 0.5 e.g. _M

1 = styrene r₁ = 0.041

3) 0 < r₁, r₂ < 1

More common e.g. _M

1 = styrene r₁ = 0.52

M₂ = methyl methacrylate r₂ = 0.46

Azeotropic copolymerization

[ ]

[ ]

[ ]

[ ]

2 1 2 1 M M M d M

d ₌

[ ]

[ ]

[ ]

[ ]

[ ] [ ]

[ ] [ ]

⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ + + = 2 2 1 2 1 1 2 1 2 1 M r M M M r M M M d M d

[ ] [ ]

[ ] [ ]

M r M 1

M M r 2 2 1 2 1 1 = + +

[ ]

[ ]

1

4) 1 << r₁ and r₂ << 1

e.g. _M

1 = styrene M2 = vinyl acetate r₁ = 55 r₂ = 0.01

M₁ = styrene M₂ = vinyl chloride r₁ = 17 r₂ = 0.02

Essentially homopolymer

5) r₁

•

r₂ = 1

e.g. _M

1 = MMA

r₁ = 10 r₂ = 0.1

M₂ = vinyl chloride Ideal copolymerization

r₁

=

r₂ = 1 Real random copolymerization The more r₁ and r₂ diverge, the less random

2 2 2 2 1 2 1 1 2 1 2 1 1 1 f r f f 2 f r f f f r F + + + =

(

)

(

)

1 1 2

Table 6.9 Reactivity Ratios

M₁ M₂ r₁ r₂ Temperature(℃)

Styrene Methyl methacrylate 0.52 0.46 60

Styrene Acrylonitrile 0.40 0.04 60

Styrene Vinyl acetate 55 0.01 60

Styrene Maleic anhydride 0.041 0.01 60

Styrene Vinyl chloride 17 0.02 60

Styrene 1,3-Butadiene 0.58 1.35 50

Styrene Isoprene 0.54 1.92 80

Methyl methacylate Vinyl chloride 10 0.1 68

Methyl methacylate Vinyl acetate 20 0.015 60

Methyl methacylate Acrylonitrile 1.20 0.15 60

Methyl methacylate 1,3-Butadiene 0.25 0.75 90

Ethylene Tetrafluoroethylene 0.38 0.1 25

Ethylene Acrylonitrile 0 7 20

r₁ = r₂ = 1 r₁ = r₂ = 0

0 < r₁, r₂ < 1 1 << r₁ and r₂ << 1

r₁

•

r₂ = 1 r₁ =10, r₂ = 0.1

Azeotropic composition

2 1

2 1

r r 2

r 1 f

− −

Q-e Scheme (Alfrey-Price Treatment)

k₁₂ = P₁Q₂ exp (- e₁e₂)

P₁ = reactivity of radical M₁

•

Q₂ = reactivity of monomer M₂ e₁ = polarity of monomer M₁ e₂ = polarity of monomer M₂ where

(

)

(

)

[

1

(

1 2

)

]

2 1 2 1 2 1 1 1 1 1 12 11

1 exp e e e

Q Q e e exp Q P e e exp Q P k k

r _⎟⎟ − −

⎠ ⎞ ⎜⎜ ⎝ ⎛ = − − = =

(

)

[

_{2 2 1}

]

1 2

2 exp e e e

Q Q

r _⎟⎟ − −

⎠ ⎞ ⎜⎜ ⎝ ⎛ =

Styrene: standard

Q = 1.00 e = - 0.80

Resonance factor ( + steric factor)

Polarity factor

+ : electron-withdrawing group

Table 6.10 Reactivity (Q) and Polarity (e) of Monomer

Monomer Q e

1-vinylnaphthalene 1.94 -1.12

p-Nitrostyrene 1.63 0.39

p-Methoxystyrene 1.36 -1.11

Styrene 1.00 -0.80

Methyl methacrylate 0.74 0.40

Acrylonitrile 0.60 1.20

Methyl acrylate 0.42 0.60

Vinyl chloride 0.044 0.20

CH₂ CH ₊ CH₂ CH

O C CH₃ O

CH₂ CH

O C CH₃ O

Little tendency

No resonance-stabilization

Resonance-stabilization

M₁ = Styrene M₂ = Vinyl acetate r₁ = 55 r₂ = 0.01

Styrene Q = 1.00 e = - 0.80 Vinyl acetate Q = 0.026 e = - 0.22

M₁ = Styrene M₂ = MMA

Styrene Q = 1.00 e = - 0.80

r₁ = 0.52 r2 = 0.46

MMA Q = 0.74 e = 0.40

H₃

CH₂ C C CH₃

O

OCH3 + CH2 C

CH₃

C O

OC CH₂ CH

Each radical has about twice as much tendency to react with its opposite monomer

Copolymerization of styrene and maleic anhydride

Strong tendency toward alternation (r₁ and r₂ = ~ 0) 1) Polar effects in the transition state

Electron transfer

Electron transfer

2) Formation of Charge-transfer complexes between comonomers Homopolymerization of charge-transfer complex

~ (DA)_n D+_..A- _{+ D}+_..A- _{~ (DA)}

n+1 D+..A -charge-transfer complex

<Evidence>

(1) R_p maximum when monomer composition ratio = 1:1 maximum conc. of donor-acceptor complex (2) Alternation is independent of monomer feed ratios,

and other reactive monomers included with the feed fail to react while alternating copolymer is forming

(3) R_p is enhanced by addition of Lewis acids,

which increase the acceptor properties of one of the monomers (4) Chain transfer agents have little effect on the mol. wt.

Other compounds that undergo free radical-initiated copolymerization with vinyl monomers are CO and SO₂

CH_{2 CH} R CH_{2 CH}

R

CO

SO₂

CH₂ CH R

C O

CH₂ CH R

SO₂ polyketones