CURE BEHAVIOR OF AN EPOXY-ANHYDRIDE-IMIDAZOLE SYSTEM

The cure behavior of an epoxy-anhydride system with one of imidazole d erivatives as an accelerator was investigated for both stoichiometric and epoxy-rich formulations. The mixtures were isothermally cured for different times at various temperatures, and the glass transition temp erature (T-g) was determined by differential scanning calorimetry (DSC ). There was a considerable increase in the T-g during curing, and mas ter curves were formed by shifting and superposing the T-g vs. cure ti me curves. The activation energies obtained by the shift were 15.2 kca l mol(-1) and 16.5 kcal mol(-1) for the stoichiometric and epoxy-rich systems, respectively. For the epoxy-rich one, plateaus were observed on the T-g vs. cure time curves, and two exothermic peaks appeared on DSC curves in the early stage of cure and became one thereafter. This phenomenon is related to the competitive reactions between esterificat ion and etherification reactions. We found that the maximum T(g)s were 80 degrees C for esterification and 125 degrees C for etherification in the excess epoxy system.