Visible Light Photoiniferter Polymerization for Dispersity Control in High Molecular Weight Polymers.

Synthesis of polymers with high molecular weights, controlled sequence and tunable dispersities remains a challenge. A simple and effective visible-light controlled photoiniferter reversible addition-fragmentation chain transfer (RAFT) polymerization is reported here to realize this goal. Key to this strategy is the use of switchable RAFT agents (SRAs) to tune polymerization activities coupled with the inherent high livingness of photoiniferter RAFT polymerization. The polymerization activities of SRAs were in situ adjusted by addition of acid. In addition to switchable chain transfer coefficient, photolysis and polymerization kinetic studies revealed that neutral and protonated SRAs showed different photolysis and polymerization rates, which is unique to photoiniferter RAFT polymerization in dispersity control. This strategy features no catalyst, no exogenous radical source, temporal regulation by visible light, and tunable dispersities in the unprecedented high molecular weight regime (up to ~500 kg mol-1). Pentablock copolymers with three different dispersity combinations were also synthesized, highlighting that high livingness was maintained even for blocks with large dispersities. Tg was lowered for high-dispersity polymers of similar MWs due to the existence of more low-MW polymers. This strategy holds great potential in synthesis of advanced materials with controlled molecular weight, dispersity and sequence.