Gelation Suppression in RAFT Polymerization

In this article, we extend the understanding of gelation suppression in reversible addition–fragmentation chain-transfer (RAFT) polymerization in systems with long primary chains and high crosslinker content, regimes which have been mostly overlooked to date. Using a model methacrylate system, the gel point, apparent propagation rate constants, and polymer architectures are seen to vary in a systematic fashion. By combining our experimental data with several related studies, we introduce a new phenomenological parameter, the “crosslinking tendency,” that incorporates monomer concentration and excess functionality to universally describe the gelation suppression in both RAFT- and atom-transfer radical polymerization (ATRP)-controlled radical polymerization systems. The ability of the crosslinking tendency to quantitatively account for a broad range of RAFT and ATRP systems suggests that factors such as monomer architecture and details of activation/deactivation mechanisms may play only a secondary role in gel-point suppression.