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

The curing mechanisms and kinetics of diglycidyl ether of bisphenol A using 1-methylimidazole (1-MI), 2-methylimidazole (2-MI), 2-phenylimidazole (2-P hI) and 1,2-dimethylimidazole (1,2-DMI) as the curing agents were studied u sing scanning and isothermal differential scanning calorimetry (DSC). Both scanning and isothermal DSC studies indicated that only 1-MI was an effecti ve 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 p eak was observed for the 1-MI curing system. These peaks were assigned to a dduct formation, etherification (via the alkoxide anion) and to the process of imidazole regeneration. In the isothermal DSC studies, two peaks were o bserved for all curing systems being attributed to adduct formation and eth erification. The differences in curing behaviour of the three imidazole cur ing agents was discussed in terms of steric versus inductive effects caused by the substituent attached to the imidazole ring located at the 2-positio n, and of differences in their initiation mechanism. The curing mechanisms and kinetics of the 1-MI curing system was also inves tigated in the presence of a salt, tetramethylammonium chloride, hydrochlor ic acid and water, and were discussed in terms of their effects on adduct f ormation and on the stability of the propagating alkoxide anion. (C) 2000 E lsevier Science Ltd. All rights reserved.