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.