Visible Light-Activatable Organoboron Complexes Featuring Salicylaldehyde Azine Ligands for Rapid Cationic Polymerization and Mechanism Studies

Rapid polymerization controlled by visible light holds great potential for advancing 3D printing technologies. However, a significant challenge limiting the implementation of visible-light-activated polymerizations is its low efficiency compared to UV light driven processes. To address this, we developed a series of visible-light-activatable organoboron (BOSHY) complexes featuring salicylaldehyde azine ligands for rapid cationic polymerization. These BOSHYs featuring different brominated BOSHY catalyze the polymerization of epoxides under 405 nm LED light in three-component systems with iodonium salt and amine, achieving a 78% epoxy conversion in just 52 s at low intensity irradiation of 50 mW cm^-2. Additionally, the mechanism of photopolymerization involves the formation of cations by EDB, which initiates the polymerization process. The triplet state lifetime (15.4-23.5 μs) indicates effective intersystem crossing, enabling efficient energy and electron transfer reactions. Experiments confirm nearly 100% electron transfer due to the extended triplet state lifetime. This study not only introduces novel BOSHY derivatives for cationic polymerization but also elucidates the reaction kinetics analysis of the photopolymerization, significantly expanding the use of visible light LEDs as an alternative to UV light in photopolymerization.