PREPARATION OF POLYIMIDE-EPOXY COMPOSITES

The formation of a three dimensional network of crosslinked epoxy lead s all unmodified epoxies to have inherent brittleness and relatively l ow degradation temperatures. Polyimides, on the other hand, are widely used for applications that require high degrees of flexibility and th ermal resistance. Here, we have focused on the preparation of epoxy sy stems cured with polyamic acids instead of traditional amino-group-con taining hardening agents. The cure behavior and potential reaction mec hanisms of EPON 828 resin and polyamic acid mixtures were evaluated by DSC and TGA. Thermal analysis showed a complex reaction sequence taki ng place in the mixture and also determined the extent of reaction of the polyamic acid with itself and the competitive reaction of the poly amic acid with the epoxy. The compositions of the mixtures were varied to see the dependence of the cure behavior on component concentration s. Solutions of the two components did not phase separate and also pha se separation was not apparent either optically or microscopically in the cured samples. This phase behavior was attributed to a unique in s itu reaction. A novel solvent system for the polyamic acid precursor w as also used.