Kinetic investigation of photoiniferter-RAFT polymerization in continuous flow using inline NMR analysis

Abstract

Photo reversible deactivation radical polymerization and, in particular, photoiniferter-reversible addition–fragmentation chain transfer (PI-RAFT) polymerization have become popular approaches to polymer synthesis in recent years. There is, however, a lack of fundamental investigations concerning the mechanism and kinetics of such reactions. Herein, we apply an automated continuous flow platform featuring inline NMR analysis that allows for rapid kinetic screening via transient timesweep experiments for detailed investigation of the PI-RAFT of two model monomers with different propagation rates and radical stabilities—methyl acrylate (MA) and methyl methacrylate (MMA). The effect of the structure of the RAFT agent on polymerization kinetics is studied. For the polymerization of MA, RAFT agents with a more stabilised R group lead to an induction period whose extent can be tuned by varying the light intensity. Faster polymerization of MA with xanthates than with trithiocarbonates suggests the important role of reversible termination in the PI-RAFT mechanism. The slower apparent rate of propagation for the polymerization of acrylates compared to polymerization of methacrylates, when mediated by trithiocarbonate RAFT agents, indicates that polymerization of MA is retarded due to the lower radical stability of the propagating radical compared to methacrylic radicals.