RAFT Polymerization under Microwave Irradiation: Toward Mechanistic Understanding

The mechanism for the rate enhancement in reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene under microwave irradiation has been investigated by means of modeling and simulations. quantitative analysis of previously published data [Chem. Commun. 2007, 2145-2147] has revealed that the high propagating radical concentration that can be inferred from the polymerization rate would (based on classical kinetics of radical polymerization) lead to a bimolecular termination rate inconsistent with the radical generation rate and the control/livingness observed experimentally. The data were modeled based on (i) an increase in temperature caused by microwave irradiation, (ii) microwave-enhanced propagation (k(p)) and addition to RAFT moiety (k(add)), and (iii) microwave-induced radical generation from monomer. It was found that only model ii can be invoked to explain the experimental data, which are consistent with the microwave irradiation resulting in an increase in k(p) and k(add) by similar to 1 order of magnitude in this particular case.