Tuning the Mechanical Properties of Multiblock Copolymers Generated by Polyfunctional RAFT Agents

Abstract

When employing polyfunctional reversible addition–fragmentation chain transfer (RAFT) agents (e.g., polytrithiocarbonates) in a reversible-deactivation radical polymerization, a redistribution of the RAFT groups being connected to polymer segments occurs, which leads to a characteristic distribution of blocks in the polymer. The authors show that by adding bifunctional RAFT agents to such a system, the average number of blocks and their distribution may be tailored, proving that in principle any RAFT agent may be combined with a polyfunctional RAFT agent to tailor its topology. The authors thus add star-shaped RAFT agents and develop multiblock copolymers of styrene and n-butyl acrylate having incorporated star-shaped topological features and investigate the materials via tensile testing. Using this novel mixing approach, the material toughness is substantially increased compared to multiblock copolymers obtained from pure polyfunctional RAFT agent, and stress whitening is prevented. Importantly, the approach yields copolymers with a significantly higher toughness compared to conventional blends of star and multiblock copolymers.