Star-polymer synthesis via radical reversible addition-fragmentation chain-transfer polymerization

Polystyrene stars were synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization using hexakis(thiobenzoylthiomethyl)benzene (I) as a hexafunctional RAFT agent at 80, 100, and 120°C. The polymerizations conformed to pseudo-first-order kinetic behavior. The molecular weight distributions displayed characteristics consistent with a living radical process. A number of salient features were observed in the molecular weight distributions with the star distribution accompanied by a linear polymer-chain distribution and shoulders on the distributions that can be attributed to radical-radical-termination events. The evidence suggests that high temperatures are required to activate all the RAFT active sites on I, and a hypothesis proposes that there is significant steric hindrance in the initial stages of the RAFT process with I.