Epoxy resins are important thermosetting resins widely employed in industrial fields. Although the epoxy-imidazole curing system has attracted attention because of its reactivity, solidification of a liquid epoxy resin containing imidazoles proceeds gradually even at room temperature. This makes it difficult to use them for one-component epoxy resin materials. Though powder-type latent curing agents have been used for one-component epoxy resin materials, they are difficult to apply for fabrication of fine industrial products due to their poor miscibility. To overcome this situation and to improve the shelf life of epoxy-imidazole compositions, we have developed a liquid-type thermal latent curing agent 1, generating an imidazole with a thermal trigger via a retro-Michael addition reaction. The latent curing agent 1 has superior miscibility toward epoxy resins; in addition, it was confirmed that the epoxy resin composition has both high reactivity at 150 degrees C, and long-term storage stability at room temperature. (C) 2016 Wiley Periodicals, Inc.