ISSN:
0360-6376
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
In the copolymerization of monomers M1 and M2 which form polymer radicals of chain length n of N1n with electron on a M1 type and N2n with one on a M2 type, it is assumed that the specific rates of termination between N1n and N1n and N1s, N1n and N2s, and N2n and N2s are kα(ns)-a, kβ(ns)-a, and kγ(ns)-a, respectively, where kα, kβ, and kγ 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 Rp is derived as: 1/n̄ = 1/n̄0 + const. (Rp)A(a), where n̄0 is the kinetic chain length of the polymer formed by transfer and A (a) is unity (predominance of transfer) and 1/(1-2a) (no transfer). In the copolymerization between methyl methacrylate (M1) and styrene (M2) at 60°C, when Rp → 0, kr12/k12 + kr21/k21 = 5.9× 10-5 is obtained, where kr12 and kr21 are the rate constants of transfer of N1 to M2 and N2 to M1, and k12 and k21 are the rate constants of propagation of N1 to M2 and N2 to M1. In the absence of transfer, the a value is found to be 0.065 ± 0.008, from the relation between n̄ and Rp, regardless of the monomer composition. Such a value is also estimated by setting b = 0.72 in a = 0.153 (2b-1), where b is the constant in the Mark-Houwink equation. Further, the value of kβ is found to be 1.18 × 109l./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.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1976.170140716
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