Reactivity ratio(竞聚率) The ratio of rate constant of 1三 k2k 2 homopolymerization to copolymerization copolymerizaiton homopolymerizaiton Special cases: T=0 and r2=0 Each comonomer prefers to react with the other Perfectly alternating copolymer 1 andr>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 ka k Random incorporation of comonomers: Ideal copolymerization 16
16 Reactivity ratio （竞聚率） Special cases: • r 1=0 and r2=0 • Each comonomer prefers to react with the other. • Perfectly alternating copolymer. • r 1 > 1 and r2 > 1 • Each comonomer prefers to react with others of its own kind. • Tendency to form block copolymers. • r 1 * r2=1 • There is no preference due to the chain ends. • Random incorporation of comonomers; “Ideal” copolymerization. 12 11 1 k k r = 21 22 2 k k r = The ratio of rate constant of homopolymerization to copolymerization 1 copolymerizaiton homopolymerizaiton r 22 21 12 11 k k k k =
Examples r,=003 r2=0.03 Neither monomer homopolymerize very well Forms almost perfectly alternating copolymer of high MW Alternating copolymerization is common in free radical reactions when one monomer has electron withdrawing groups and the other has electron donating groups
17 Examples • Neither monomer homopolymerizes very well. • Forms almost perfectly alternating copolymer of high MW. • Alternating copolymerization is common in free radical reactions when one monomer has electron withdrawing groups and the other has electron donating groups
nflunece of polymerization mechanism on r St(M1-MMA(M2) Radical r1=0.52, I2=0.46; Cationic r2=0.1 Ionic 18
18 Influnece of polymerization mechanism on r St(M1 )-MMA(M2 ) Radical ： r1=0.52, r2=0.46; Cationic： r1=10, r2=0.1; Ionic: r1=0.1, r2=6;
Copolymer equation in terms of mole fraction [M1] M2]2M2]+[M1 Jf [M1]+[M f2 [M1]+[M2 F1=+M/2 1f1+2ff2+12f2 Copolymer composition depends on not only the monomer feed but the reactivity ratio as well
19 Copolymer equation in terms of mole fraction [ ] [ ] [ ] 1 2 1 1 M M M f + = [ ] [ ] [ ] 1 2 2 2 M M M f + = 2 2 1 1 1 2 2 1 2 1 r M M r M M M M F F + + = 2 1 2 2 2 2 1 1 1 2 2 1 1 1 r f 2 f f r f r f f f F + + + = Copolymer composition depends on not only the monomer feed, but the reactivity ratio as well
2.2 Copolymer composition curve Variation of reactivity ratio r1=0ork1=0 r <l or ku<k12 r>l or kuki II-cc or k1>>k 11 12 tend to co-than tend to homo only only copolymn homopolymn than copolymn. homopolymn 0 F is the function of both r and f 20
20 0 1 r1 r1>1 or k11>k12 tend to homothan copolymn. r1<1 or k11<k12 tend to co- than homopolymn. r1= 0 or k11= 0 only copolymn. Variation of reactivity ratio F is the function of both r and f 2.2 Copolymer composition curve r1= or k11>>k12 only homopolymn