Imidazole derivatives as latent curing agents for epoxy thermosetting resins

We have developed novel liquid-type thermal latent curing agents to generate imidazoles in epoxy resins. The latent curing agents were synthesized using a Michael addition reaction of fumarate with imidazoles in 14–53% yields. The latent curing agent, having a thermally labile bulky long-chain alkyl succinate group at the nitrogen atom of the imidazole ring, underwent a thermal decomposition reaction in the temperature range from 200 to 280°C, which generated the corresponding imidazole by a retro-Michael addition reaction. The curing reaction of epoxy resins by thermally generated free imidazoles proceeded at 150°C. Furthermore, it was demonstrated that a mixture of the latent curing agent with epoxy resins has long storage stability at room temperature, which was not accomplished with the imidazoles themselves. [Display omitted] •We have developed a novel liquid-type thermal latent curing agent to form imidazoles.•The latent curing agent thermally decomposed to form the corresponding imidazoles.•We achieved thermal curing of epoxy resins containing the latent curing agents.•A mixture of the latent curing agents with epoxy resins had long storage stability.