Addition-fragmentation chain transfer to polymer in the free radical ring-opening polymerization of an eight-membered cyclic allylic sulfide monomer

摘要

A detailed investigation of chain transfer to polymer during free radical ring-opening polymerization of the eight-membered disulfide monomer 2-methyl-7-methylene-1,5-dithiacyclooctane (MDTO) is presented. It has been shown that extensive chain transfer to polymer occurs involving both poly(MDTO) radicals and cyanoisopropyl radicals. Significant decreases in molecular weight were observed when cyanoisopropyl radicals were generated in the presence of poly(MDTO) in the absence of monomer. The molecular weight distribution (MWD) obtained from polymerization of MDTO in the presence of pre-added poly(MDTO) was markedly different from that obtained without pre-added polymer. A kinetic model was constructed in an attempt to quantitatively describe the chain transfer to polymer process based on the addition fragmentation chain transfer mechanism. It was found however that the simulated MWDs were considerably broker than the experimental MWDs, which were similar to the Schutz-Flory distribution.