Is the rate constant of chain propagation k(p) in radical polymerization really chain-length independent?

摘要

A careful investigation of the k(p) data obtained from pulsed- laser polymerization at different pulse separations t(o) in a lot of systems has revealed that k(p) exhibits a slight but significant decrease when t(o) is increased, corresponding to an about 20% decrease of k(p) extending over several hundreds in degree of polymerization. Transformation of this integral effect to individual chain-lengths reduces this range, of course, but still shows more than one hundred propagation steps to be concerned. This is interpreted in terms of a decrease of the monomer concentration at the site of propagation caused by the segments already added to the growing chain. [References: 33]