Dual-cure Photo-thermal Initiating System for Cationic Polymerization of Epoxy under LED Visible Light

The development of new initiating systems for epoxy resin curing remains a highly interesting topic, especially for composites and coatings applications. Among all the possibilities existing to cure an epoxy resin, recent works have highlighted novel photo-thermal cationic initiators based on pyrylium salts. Interestingly, absorption spectra of trisubstituted pyrylium salts extend up to the visible region, a feature that was not exploited yet. In this paper, the pyrylium salts absorption spectra were predicted using Density Functional Theory. It is shown that accurate prediction of UV-Vis spectra can be made at relatively moderate level of theory. Then, visible photopolymerization of epoxy resin was performed under mercury lamp and 395 nm LED. Finally, a photoinduced thermal frontal polymerization of a thick sample of epoxy resin was performed by prompting the reaction at 395 nm. This work opens new opportunity in the polymerization of thick materials such as for composites.