Synthesis of Photoreactive Imidazole Derivatives and Thermal Curing Reaction of Epoxy Resins Catalyzed by Photo-Generated Imidazole

Abstract

Photoreactive blocked imidazoles such as N-(2-nitrobenzyloxycarbonyl)imidazole (2-NBCI), N-(3-nitrobenzyloxycarbonyl)imidazole (3-NBCI), N-(4-nitrobenzyloxycarbonyl)imidazole (4-NBCI), N-(4-chloro-2-nitrobenzyloxycarbonyl)imidazole (CNBCI), N-(5-methyl-2-nitrobenzyloxycarbonyl)imidazole (MNBCI), and N-(4,5-dimethoxy-2-nitrobenzyloxycarbonyl)imidazole (DNBCI) were synthesized in good yields by reactions of N,N′-carbonyldiimidazole (CDI) with corresponding benzyl alcohols. The prepared 2-NBCI decomposed smoothly to produce imidazole by UV-irradiation in tetrahydrofuran (THF) solution or poly(methyl methacrylate) (PMMA) film. Rates of photolysis of DNBCI, MNBCI and CNBCI were higher than that of 2-NBCI in PMMA film, although the rates of 3-NBCI and 4-NBCI were slower than that of 2-NBCI in PMMA film under the same conditions. Thermal curing reactions of epoxy resins and poly(glycidyl methacrylate-co-methyl methacrylate) [P(GMA55-MMA45)] using photo-generated imidazole were examined at 100–160°C. The ring opening reaction of epoxide groups, confirmed by IR spectra, in epoxy resins and P(GMA55-MMA45) proceeded smoothly by catalysis of the photo-generated imidazole.