(Thiocarbonyl-α-thio)carboxylic acid derivatives as transfer agents in reversible addition-fragmentation chain-transfer polymerizations

Ethyl S-(thiobenzoyl)thioacetate, ethyl S-thiobenzoyl-2-thiopropionate, and S-(thiobenzoyl)thioglycolic acid were used as chain-transfer agents for the reversible addition-fragmentation chain-transfer (RAFT) polymerizations of styrene, methyl methacrylate, and butyl acrylate. Of these polymerizations, only those of styrene and butyl acrylate with any of the transfer agents showed molecular weight control corresponding to controlled/living polymerizations. The best molecular weight control was observed for the polymerizations of styrene and butyl acrylate with ethyl (S)-thiobenzoyl-2-thiopropionate. Semiempirical PM3 calculations were performed for the investigation of the relative heats of reaction of the chain-transfer equilibria between the aforementioned chain-transfer agents and dimer radicals of the three monomers. The molecular weight control of the polymerizations correlated with the stability trend of the leaving-group radical of the chain-transfer agent. This relatively simple computational model offered some value in determining which transfer agents would show the best molecular weight control in RAFT polymerizations. (C) 2002 John Wiley Sons, Inc.