DSC studies of the curing mechanisms and kinetics of DGEBA using imidazole curing agents

Abstract

The curing mechanisms and kinetics of diglycidyl ether of bisphenol A using 1-methylimidazole (1-MI), 2-methylimidazole (2-MI), 2-phenylimidazole (2-PhI) and 1,2-dimethylimidazole (1,2-DMI) as the curing agents were studied using scanning and isothermal differential scanning calorimetry (DSC). Both scanning and isothermal DSC studies indicated that only 1-MI was an effective curing agent, resulting in a high degree of conversion and high T g, at relatively low concentrations. In the scanning DSC studies, multiple peaks were observed for the 2-MI and 2-PhI curing systems whereas only a single peak was observed for the 1-MI curing system. These peaks were assigned to adduct formation, etherification (via the alkoxide anion) and to the process of imidazole regeneration. In the isothermal DSC studies, two peaks were observed for all curing systems being attributed to adduct formation and etherification. The differences in curing behaviour of the three imidazole curing agents was discussed in terms of steric versus inductive effects caused by the substituent attached to the imidazole ring located at the 2-position, and of differences in their initiation mechanism. The curing mechanisms and kinetics of the 1-MI curing system was also investigated in the presence of a salt, tetramethylammonium chloride, hydrochloric acid and water, and were discussed in terms of their effects on adduct formation and on the stability of the propagating alkoxide anion.