Improvement of the thermal latency for epoxy-phenolic resins by novel amphiphatic imidazole catalysts

Abstract

Novel amphiphatic imidazole compounds were evaluated as thermal latent catalysts for the polymerization of diglycidyl ether of bisphenol A (DGEBA). Amphiphatic compounds 5–9, two commercially available catalysts 1 and 2, and compounds 3 and 4 were used to cure epoxy resin systems for an investigation of their thermal latency and storage stability. The results from the cure activation energy and viscosity-storage time of the catalysts, the order of thermally latent activity was 3-phenylpropanoic acid (4) > 2-amino-3-phenylpropinoic acid (5) > 2-amino-3-(imidazole-4-yl)-propionic acid (H-His-OH, 8) > N-tert-butoxycarbonyl-histidine (9) > imidazole-4-acrylic acid (6) > 3-(imidazole-4-yl)propionic acid (7) > 1-cyanoethyl-2-ethyl-4-methyl-imidazole (2) > 2-ethyl-4-methylimidazole (1) > histamine (3). From the results, the amphiphatic imidazole catalysts 5–9 showed better thermal latency than commercialized catalysts 1 and 2, basic catalyst 3 and acidic catalyst 4. Concerning the glass transition temperature (Tg), the use of amphiphatic imidazole catalysts 5–9 provided complete or near complete curing systems at temperatures ranging from 152–163 °C, which were similar to two commercially available catalysts (151–152 °C, 1 and 2) and histamine (159 °C, 3). On the other hand, the Tg for compounds 4 and 5 could not be detected at 30–300 °C from the temperature scans because of their weak nucleophilicity and low cross-linking reactivity.