Searching for Stars: Selective Desulfurization and Fluorescence Spectroscopy as New Tools in the Search for Cross Termination Side-products in RAFT Polymerization

Abstract

We present a novel approach to the examination of the ‘controversial’ three-armed stars that are argued to exist in rate-retarded reversible addition–fragmentation chain transfer (RAFT) polymerizations by using a fluorescent carbazole-containing RAFT agent that exhibits classical signs of retardation, and provides a route to polymer-RAFT agent cross termination. We also pioneer the use of an existing desulfurization technique for the purification of polymers by removal of the coloured RAFT derived moiety, with the added benefit of potentially isolating and identifying the presence of cross termination side-products. Our findings suggest that the rate retardation is either due to the RAFT intermediate being sufficiently stable that it does not cross terminate, or that most of cross termination events occur between the intermediate and short radicals. Our findings are consistent with a model proposed earlier by this group for rate retardation in RAFT systems, which assumed a slow rate for long-chain cross termination, and a fast short chain cross termination rate.