Morphological and phase behavior studies of uniquely derived epoxy/polyimide semi‐IPNS

Abstract Interpenetrating networks (IPNs) of polyimide (PI) and epoxy were made by reaction of epoxy (EGEBA) with a polyamic acid (PAA). In addition, epoxy was cured with both a monomeric hardener, pyromellitic dianhydride (PMDA) and PAA to see changes in the morphology and glass transitions caused by the monomeric hardener. Due to “molecular interlock” of the individual polyimide molecules that was brought about by the PAA‐epoxy reaction, systems cured with only PAA did not phase separate and showed a significant increase in T g when compared to PMDA cured epoxy. All PMDA cured systems phase separated By dynamic mechanical analysis (DMA), it was confirmed that all systems containing over 20% PAA had two glass transitions. The extent of miscibility of the polyimide into the epoxy was relatively constant. PAA cured epoxy systems showed phase miscibility over all compositions and cure regimes