RAFT Kinetics Revisited: Revival of the RAFT Debate

Abstract

Recently, two electron spin resonance (ESR)-based methods for the determination of addition and fragmentation rate coefficients in dithiobenzoate-mediated reversible addition fragmentation transfer (RAFT) polymerization were introduced, one being based on a spin-trapping method and the other on single-laser pulse initiation in conjunction with ESR detection at microsecond time resolution. For the RAFT-intermediate radical fragmentation rate, coefficient data differing by six orders of magnitude were obtained, which cannot be explained by the usual model dependencies, that is the so-called cross-termination versus stable intermediate model. Even under consideration of fast cross-termination in both cases, the large difference persists. Both the experimental designs are thus critically reviewed to identify potential error sources and to explain the vast difference in the individual results. Both techniques appear to be robust and only small interferences could be identified. Finally, recommendations for the refinement of the individual techniques are given to achieve a consistent kinetic picture of the underpinning reaction equilibria. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49:4154-4163,2011