Ionic dithioester-based RAFT agents derived from N-heterocyclic carbenes

The syntheses of two new dithioester-based reversible addition- fragmentation chain transfer (RAFT) agents containing imidazolium Z groups and their potential in controlling free radical polymerizations of styrene are discussed. Starting with commercial available 1,3-dimesitylimidazolylidene, these agents were synthesized in two or three high yielding steps that required no chromatography, distillation, or other elaborate purification procedures. The products were isolated using straightforward filtration techniques. These agents were found to be effective for preparing well-defined polystyrenes at relatively low chain transfer agents (CTA):initiator ratios. The synthesis approach can be significant in facilitating access of RAFT agents that are highly functionalized or exhibit tunable activities through judicious N-substitution, electronic modulation of N-heterocyclic carbene component, or variation of the counteranion.