Efficient unimolecular photoinitiators for simultaneous hybrid thiol–yne–epoxy photopolymerization under visible LED light irradiation

Simultaneous thiol-based hybrid photopolymerization is an efficient and versatile tool to prepare interpenetrating polymeric networks. A highly active photoinitiator is essential for an efficient simultaneous hybrid reaction. In this paper, several unimolecular photoinitiators, which contain thioxanthone derivatives as chromophores as well as free radical generators, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a latent alkaline species, were straightforwardly prepared in two steps. The photolysis study indicated that under 405 nm LED light irradiation, the photoinitiators can produce free radicals and a strong base simultaneously via a photodecarboxylation mechanism. The generated active species are highly efficient in catalyzing thiol–yne–epoxy hybrid polymerization without post-exposure baking and the properties of the hybrid network can be tailored by adjusting the compositional ratios of the formulations. The photocured materials using unimolecular photoinitiators exhibit superior thermal and mechanical properties compared to those prepared using a bimolecular initiation system from the literature. The presented strategy to realize simultaneous thiol–yne–epoxy hybrid photopolymerization shows potential for the fabrication of optical devices with enhanced refractive index and improved mechanical properties.