Acceleration of the Epoxy Resin-Dicyandiamide Cure Cycle by Trisubstituted Ureas

摘要

The addition of accelerators such as Monuron, N-(4-chlorophenyl)-N',N'-dimethylurea, or Diuron, N-(3,4-dichlorophenyl)-N',N'-dimethylurea, to epoxy resin-dicyandiamide mixtures significantly decreases the hardening temperature of these systems. These trisubstituted urea accelerators are believed to serve mainly as a latent source of dimethylamine. This amine is believed to play a very important role in the cure cycle. One pathway to dimethylamine is a low-temperature cyclocondensation reaction between the trisubstituted urea and the epoxy functionality to form a 2-oxazoli-done; this reaction partially hardens the resin. The significance of this source of dimethylamine in the overall mechanism of epoxy hardening was illustrated by differential scanning calorimetry. Several epoxy formulations were examined at various heating rates. Arrhenius plots of the data indicated that the slope of a two-component mixture consisting of resin and Monuron was approximately the same as that of a three-component system composed of resin, dicyandiamide, and Monuron. In contrast, the slope of a two-component resin-dicyandiamide system was found to be considerably larger. Thus the reaction of Monuron with the resin is an important factor that must be considered in any explanation of the acceleration of the hardening process of dicyandiamide-containing resins. (Author)