Mechanistic approach to a photochemical/thermal dual-cure initiating system based on pyrylium salt-hydroperoxide for epoxide cationic polymerization

Dual-cure initiating systems have emerged as promising alternatives to perform fast and on-demand curing of thick polymers. In this paper, a system based on pyrylium salt/hydroperoxide is reported to be efficient in the polymerization of epoxide resins. The chemical mechanisms involved are studied by ESR, laser flash photolysis and fluorimetry. It is found that the interaction between pyrylium salts and hydroperoxide releases a proton that could initiate the polymerization reaction at room temperature as well as under UV light. The combination of both methods allows the polymerization of a thick sample by photoinduced thermal polymerization.