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Relationship between kinetic chain length and radical polymerization rate

1976; Wiley; Volume: 14; Issue: 7 Linguagem: Inglês

10.1002/pol.1976.170140716

1542-9369

Katsukiyo Ito,

Inorganic and Organometallic Chemistry

Abstract In the copolymerization of monomers M 1 and M 2 which form polymer radicals of chain length n of N 1 n with electron on a M 1 type and N 2 n with one on a M 2 type, it is assumed that the specific rates of termination between N 1 n and N 1 n and N 1 s , N 1 n and N 2 s , and N 2 n and N 2 s are k α ( ns ) −a , k β ( ns ) −a , and k γ ( ns ) −a , respectively, where k α , k β , and k γ are the rate constants of reaction between segment radicals in the respective termination, and a is constant. The relation between kinetic chain length n̄ and polymerization rate R p is derived as: 1/ n̄ = 1/ n̄ 0 + const. ( R p ) A(a) , where n̄ 0 is the kinetic chain length of the polymer formed by transfer and A ( a ) is unity (predominance of transfer) and 1/(1–2 a ) (no transfer). In the copolymerization between methyl methacrylate (M 1 ) and styrene (M 2 ) at 60°C, when R p → 0, k r 12 / k 12 + k r 21 / k 21 = 5.9× 10 −5 is obtained, where k r 12 and k r 21 are the rate constants of transfer of N 1 to M 2 and N 2 to M 1 , and k 12 and k 21 are the rate constants of propagation of N 1 to M 2 and N 2 to M 1 . In the absence of transfer, the a value is found to be 0.065 ± 0.008, from the relation between n̄ and R p , regardless of the monomer composition. Such a value is also estimated by setting b = 0.72 in a = 0.153 (2 b –1), where b is the constant in the Mark‐Houwink equation. Further, the value of k β is found to be 1.18 × 10 9 l./mole‐sec, which is comparable with the diffusion‐controlled rate of reaction between small molecules. The rate of reaction between segment radicals is fivefold larger than the polymer‐polymer termination when transfer predominates.