Conventional and catalytic chain transfer in the free-radical polymerization of 2-phenoxyethyl methacrylate

Abstract

A comparative study was conducted on chain transfer mechanisms in the free radical polymerization of a viscous methacrylate, viz. 2-phenoxyethyl methacrylate. Two chain transfer agents were subjected to investigation: n-dodecanethiol (DDM) and bis[(difluoroboryl)diphenylglyoximato]cobalt (II) (COPhBF). The chain transfer constant ( C S) for DDM was found to be 0.7 (at 60°C); a value comparable with the C S value obtained for a low viscosity methacrylate, methyl methacrylate, under similar conditions. In contrast, the C S value for COPhBF was found to be 2×10 3 (at 60°C) which is one order of magnitude lower than the C S value published for methyl methacrylate. This result is explained in terms of the different chain transfer mechanisms operating in the two polymerizing systems. Radical reactions with DDM involve a chemically controlled hydrogen transfer event, whereas experimental results obtained for the reaction of methacrylate radicals with COPhBF indicate a diffusion-controlled, rate determining step in the hydrogen transfer process. Thus in the reaction of COPhBF with 2-phenoxyethyl methacrylate radicals, the high viscosity reaction medium (monomer) has a significant influence on the transfer rate.