Chain-length dependent termination in pulsed-laser polymerization, 4. The influence of the type of mean involved in the bimolecular termination step

Abstract

The chain-length distribution (cld) of living and dead chains and their moments have been calculated by an iterative simulation procedure for pseudostationary laser-induced polymerization (without chain-transfer) assuming various types of means between the lenghts of the two chains involved in the termination process. The overall appearance of the cld is dramactically influenced by the type of mean: the stronger the influence of the shorter of the two chains the more prominent are the “extra-peaks” of the cld and the smaller the rate of polymerization. The different types of means are subject to different short-chain effects; in the long-chain limit, however, the correct exponent of the power law governing the chain-length dependence of kt is correctly recovered in all cases. The estimation of kt(1,1) works the better the less prominent is the role of the smaller chain. Because of its close proximity to the “diffusion mean” the geometric mean approximation – although unphysical – is proved to give an excellent qualitative and quantitative description of all effects associated with chain-length dependent termination.