Switchable RAFT Polymerization Employing Photoresponsive HABI as a Mediator

Recently, considerable interest has been devoted to developing switchable reversible addition fragmentation chain transfer (RAFT) polymerizations via photoactivation methods. Herein, a photo-deactivation strategy is introduced to regulate RAFT polymerization using photoresponsive hexaarylbiimidozole (HABI) as a mediator, which leads to switchable RAFT polymerization by repeated ON/OFF experiments. In comparison with well-known PET-RAFT polymerization, photo-deactivation RAFT (PD-RAFT) polymerization can be temporally stopped with UV light ON, where photoresponsive HABI can reversibly quench propagating radicals, resulting in switchable RAFT polymerization. The proposed mechanism of PD-RAFT polymerization in the presence of HABI involving radical quenching is based on ESR, NMR, GPC, MALDI-TOF-MS, and kinetics studies.