New investigation of 1-substituted imidazole derivatives as thermal latent catalysts for epoxy-phenolic resins

Novel 1-substituted imidazole derivatives (4-10) were synthesized by imidazole and the corresponding substituted reagents (chloromethylpivalate, diphenylphosphinicchloride, di-tert-butyldicarbonate, 1,1'-oxalylchloride, pyrazine, phneylisocyanat, and p-toluensulfonylchloride). Polymerization of diglycidyl ether of bisphenol A (DGEBA) with 1-substituted imidazole derivatives, two commercial available catalysts (imidazole and 1-cyanoethyl-2-ethyl-4-methylimidazole) and N-benzylpyrazinium hexafluoroantimonate were investigated as model reactions of epoxy resin systems with respect to the thermal latency and storage stability of the catalysts. The catalytic activity of I-substituted imidazole derivatives 4-10 depended on the steric and withdrawing electronic effect of the substitution groups. To characterize the cure activation energy and the viscosity-storage time, the order of thermally latent activity is 1-tosylimidazole (6) > 1,1'-oxalyldiimidazole (8) > N-benzylpyrazinium hexafluoroantimonate (BPH, 3) > 1-tritylimidazole (9) > N-phenyl-imidazole-1-carboxamide (5) > 3-(diphenylphosphinoyl)imidazole (7) > tert-butyl-1H-imidazole-1-carboxylate (4) > 1-cyanoethyl-2-ethyl-4-methylimidazole (2E4MZ, 2) > 1-[(pivalyloxy)methyl]imidazol (10) > imidazole (1). In comparison with commercially available catalysts imidazole (1) and 1-cyanoethyl-2-ethyl-4-methylimidazole (2) and a cationic latent catalyst N-benzylpyrazinium hexafluoroantimonate (BPH, 3) as the standard compounds, in addition to 1-[(pivalyloxy)methyl]imidazole (10), the I-substituted imidazole derivatives (4-9) revealed better thermal latency. (c) 2007 Wiley Periodicals, Inc.