Fabrication of one-component epoxy resin systems using maleic acid modified imidazole derivatives

A series of maleic acid modified imidazole derivatives (IM-MA, 2MI-MA and 2EI-MA) were synthesized via the Michael addition reaction of maleic acid (MA) with imidazole (IM), 2-methylimidazole (2-MI) and 2-ethylimidazole (2-EI), respectively. 1H nuclear magnetic resonance (NMR), Fourier Transform Infrared (FTIR) spectra and Elemental analysis (EA) were used to verify the structure of maleic acid modified imidazole derivatives. The maleic acid modified imidazole derivatives were used as latent curing agents for epoxy resin (EP). Differential scanning calorimeter (DSC) under dynamic and isothermal condition was used to study the curing behavior of the prepared EP systems. The curing reactivity of maleic acid modified imidazole derivatives were significantly suppressed, compared with the common imidazole compounds. The EP systems containing maleic acid modified imidazole derivatives possessed excellent storage stability of at room temperature, due to the electron-withdrawing effect of carboxyl reduced the nucleophilicity of imidazole ring and the intermolecular hydrogen bond formed between carboxyl and 3-position nitrogen atom further restrained the nucleophilicity of imidazole ring. What's more, the maleic acid modified imidazole derivatives regained fast curing ability towards EP under heating condition. Taking advantage of these characteristics, the maleic acid modified imidazole derivatives were suitable for preparing one-component EP systems.