A Simple and Efficient Synthesis of RAFT Chain Transfer Agents via Atom Transfer Radical Addition-Fragmentation

A simple, versatile, and one-step atom transfer radical addition-fragmentation (ATRAF) technique is reported for the synthesis of chain transfer agents (CTA) containing dithio groups (dithiobenzoate, dithiocarbamate, and xanthate), with various alkyl substituents, in the presence of copper catalyst, alkyl halide, and bis(thiocarbonyl) disulfide. The ATRAF procedure is efficient and selective, leading to almost quantitative conversion of alkyl halide initiators and formation of CTAs in high isolated yield under stoichiometric conditions as well as in the presence of catalytic amounts of copper(l) species. The CTAs synthesized by this process were used for reversible addition-fragmentation chain transfer (RAFT) polymerizations of styrene and methyl methacrylate without any further column purification, producing well-controlled polymers with low polydispersity, thereby demonstrating the effectiveness of ATRAF Moreover, a simple one-pot, two-step RAFT polymerization was successful, starting from CTA synthesized in situ via ATRAF, followed directly by the addition of a monomer.