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

The 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 highly living nature of photoiniferter RAFT polymerization. The polymerization activities of SRAs were in situ adjusted by the addition of acid. In addition to a 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 terms of 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 the highly living nature 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 for the synthesis of advanced materials with controlled molecular weight, dispersity and sequence. Photoiniferter RAFT polymerization was used to tune the dispersity in high-molecular-weight polymers (up to ca. 500 kg mol-1) as well as in multiblock copolymers. This strategy features no catalyst, no exogeneous radical source, visible-light regulation, and high end-group fidelity and holds great potential for the synthesis of pre-designed materials with controlled molecular weight, dispersity and sequence.image

Automated summary

Visible-light controlled photoiniferter reversible addition-fragmentation chain transfer (RAFT) polymerization enables the synthesis of polymers with high molecular weights, controlled sequence, and tunable dispersities, offering great potential for the synthesis of advanced materials.