Synthesis of Hyperbranched Polymers with High Molecular Weight in the Homopolymerization of Polymerizable Trithiocarbonate Transfer Agent without Thermal Initiator

This article presents the first synthesis of high-molecular-weight hyperbranched polymers (over half a million) in the homopolymerization of a polymerizable trithiocarbonate chain transfer agent (i.e., transmer). Traditional reversible additionfragmentation chain transfer (RAFT) homopolymerization of transmers that used thermal initiator as radical source has been reported to only produce hyperbranched polymers with relatively low molecular weights (<= 10(4)). The first part of this study extensively varied the experimental parameters in RAFT polymerization but could only marginally improve the polymer molecular weights. It was found that the vinyl focal groups were gradually consumed during the polymerization and the radical termination reactions were mainly happening between propagating radicals and primary radicals from the thermal initiator, which failed to increase the polymer molecular weight. In the second part, a new strategy was explored that used copper catalyst to activate the alkyl trithiocarbonate to generate radicals without the use of thermal initiator. This new initiation system eliminated the presence of primary radicals and ensured radical termination reactions only happening between propagating radicals, resulting in the production of hyperbranched polymers with very high molecular weight. When a small amount of atom transfer radical polymerization (ATRP) inimer was added, the concurrent ATRP/RAFT homopolymerization of transmer achieved faster polymerization rate and produced hyperbranched polymers with both high molecular weight and high degree of branching.