高分子化学浙江大学polymer3FreeRadicalCopolymerization

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1 Introduction
2
1.1 Concept
• Homopolymerization —— polymerization of one kind of monomer;
• Copolymerization (addition polymerization) —— polymerization of more than one kind of monomer;
reactivity • no side reactions, such as depropagation, monomer
partitioning, and various forms of complex formation
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Reactions in copolymerization
R + M1
Ethylene-vinyl acetate copolymer
vinyl acetate % 10 ~ 20 30 ~ 40 50
property plastic adhesive rubber
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Possible propagation sequences in free-radical copolymerization
Sequence distributionห้องสมุดไป่ตู้
the way in which these monomer units are arranged within a polymer chain; AA or AB
2. Copolymer composition
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Essential Point
The composition of a copolymer does not necessarily match the composition of the comonomers used in the reaction ( feed ratio 投料比).
ki,1
M1
R + M2
ki,2
M2
M1 + M1 M1 + M2 M2 + M2
kt,11 kt,12 kt,22
k11
M1 + M1
M1
k12
M1 + M2
M2
k21
M2 + M1
M1
k22
M2 + M2
M2
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2.1 Copolymer composition equation
The overall rates of consumption of monomers [M1],[M2] then follow these expressions:
2
F 1
1
0.4
0.5
r1<1
0.2
0.2
0.1
0.0
0.0
0.2
0.4
0.6
0.8
1.0
f
1
butadiene r1 = 1.39, styrene r2 = 0.78
F F1 2M M1 2rr1 2M M 12 M M 21
F1 F2
r1
M1 M2
F1r1f12r1f212f1ff21f2r2f22
copolymerizaiton homopolymerizaiton
r
1
Special cases:
• r1=0 and r2=0 • Each comonomer prefers to react with the other.
• Perfectly alternating copolymer.
poly(ethylene-co-propylene) poly(ethylene-r-propylene) poly(ethylene-b-propylene) poly(ethylene-g-propylene) poly(ethylene-a-styrene)
乙烯-丙烯共聚物 乙烯-丙烯无规共聚物 乙烯-丙烯嵌段共聚物 乙烯-丙烯接枝共聚物 乙烯-苯乙烯交替共聚物
Radical ： Cationic： Ionic:
r1=0.52, r1=10, r1=0.1,
r2=0.46; r2=0.1; r2=6;
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Copolymer equation in terms of mole fraction
f1
[M1] [M1][M2]
f2
[M2] [M1][M2]
F F1 2M M1 2rr1 2M M 12 M M 21
0
1
r1
F is the function of both r and f
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Typical copolymer composition curves
1. Ideal copolymerization (r1*r2=1)
r1>1
1.0
k11 k 21
k12 k 22
r10.r82 1 10
5
0.6
Key topics in copolymerization
-ABABBAABABBAAABABA-
Composition distribution
the relative amounts of each monomer unit incorporated into the copolymer, A% or B%
New kinds of copolymer can be synthesized by copolymerization of different combination of various monomers. Copolymer generated from same monomers can have different compositions and topologies.
r1 = 1.0, r2 = 1.0 r1 = 1.0, r2 = 1.0 r1 = 1.07, r2 = 1.08
B. r1<1, r2>1
F1 F2
M1 M 2
F1 f1
C. r1>1, r2<1
F1r1f12r1f212f1ff21f2r2f22
Copolymer composition depends on not only the monomer feed, but the reactivity ratio as well.
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2.2 Copolymer composition curve
k 1M 2 1 • M 2 k 2M 1 2 • M 1 M M12••kk1221M M21
F F 1 2 d d M M 1 2 k k 1 1M M 2 1 1 1 • • M M 2 1 k k 2 2M M 2 12 2 • • M M 1 2
F F 1 2k k 1 12 M M 11 1• • //M M 2 2• • M M 2 1 k k2 2M 2 1 M 1 2 F F 1 2k k1 12 M M 12 1k k k k1 1 2 22 2 M M M M 1 12 1 2 1 k k2 2M 2 1 M 1 2k k1 1k k 2 1 2 22 M M 11 22 2 k k1 1k k 2 2 2 2M 1 M 11 1M M 2 2
• r1 > 1 and r2 > 1 • Each comonomer prefers to react with others of its own kind.
• Tendency to form block copolymers.
• r1 * r2=1 • There is no preference due to the chain ends.
molar fraction of M1
molar fraction of M2
F F 1 2 d d M M 1 2 k k 1 1M M 2 1 1 1 • • M M 2 1 k k 2 2M M 2 12 2 • • M M 1 2
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Steady-state assumption
d d M 1 tR 1 1 R 2 1 k 1 M 1 1 • M 1 k 2 M 1 2 • M 1
ignore the initiation
d d M 2 tR 1 2 R 2 2 k 1 M 2 1 • M 2 k 2 M 2 2 • M 2
The expression for instantaneous copolymer composition (F1/F2)
Maleic anhydride Styrene + maleic anhydride
O
No polymer SMA
O
O
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1.2 Type of copolymer
Normally prepared by other methods
also obtained by other methods
1.2 Nomenclature of copolymer
k11 k 21 k12 k 22
• Random incorporation of comonomers; “Ideal” copolymerization.
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Examples
• Neither monomer homopolymerizes very well. • Forms almost perfectly alternating copolymer of high MW. • Alternating copolymerization is common in free radical
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assumptions in copolymerization
• the rate of the propagation be chain-length-independent. • only the terminal unit of the polymer radical can affect its
F1
r1
r1 f1 f1＋f2
A. r1=r2=1
F1 F2
r1
M1 M2
F1 F2
M1 M 2
F1
r1
r1 f1 f1＋f2
F1 f1
azeotropic copolymerization 恒比共聚
copolymer composition equals to monomer feed
VDC (偏氯乙烯)- MMA, Acrylamide(丙烯酰胺)-丙烯酸甘油酯, Ethylene-VAc
dR • 0
dt
dM1 • 0
dt
dM2 • 0
dt
k11
M1 + M1
M1
k12
M1 + M2
M2
k21
M2 + M1
M1
k22
M2 + M2
M2
d M d 1• t k 1M 21• M 2 k 2M 12• M 1 d M d 2• t k 2M 12• M 1 k 1M 21• M 2
Examples
Styrene Styrene + Acrylonitrile Styrene + Butadiene Styrene + Acrylonitrile+ Butadiene
PS SAN SBR ABS
Brittle, transparent, poor solvent toleration High impact, good solvent toleration High elasticity Engineering plastics
Variation of reactivity ratio
r1= 0 or k11= 0
only copolymn.
r1<1 or k11<k12 tend to co- than homopolymn.
r1>1 or k11>k12 r1= or k11>>k12 tend to homo- only than copolymn. homopolymn.
F1 F2
M1 M2
k11 k12
M1
M2
k22 k21
M2
M1
F F1 2M M1 2rr1 2M M 12 M M 21
Mayo-Lewis Equation
Reactivity ratio （竞聚率）
r1
k 11 k 12
r2
k 22 k 21
The ratio of rate coefficient of homopolymerization to copolymerization
reactions when one monomer has electron withdrawing groups and the other has electron donating groups.
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Influnece of Polymerization mechanism on r
St(M1)-MMA(M2)