Polyimide films from linear and network precursors

Pyromellitic anhydride-4,4'-diaminodiphenyl ether (PMDA-DDE) polyimide precursor was blended with mellitic acid hexamethyl ester-4,4'-diaminodiphenyl (MAHE-DDE) precursor to obtain polyimide films. The films from blends required higher temperatures for complete imidisation than those necessary for either of the pure constituents. Storage moduli and secondary glass transition temperatures improved with increase of imidisation temperature and amount of the network constituent, indicating that the latter provided some reinforcement to the mixed films. Differential thermal analysis (DTA) of the blends and the changes in morphology with composition observed by scanning electron microscopy suggested that the two constituents may be cross-linked.