Synthesis and characterization of polyimides and polyamide‐imides containing azomethine linkages

Polyimides and polyamide‐imides containing azomethine linkages in the polymer backbone have been synthesized from 4,4′‐bis(4‐isocyanatobenzylidene)‐diaminodiphenylether (ODAI), 4,4′‐bis(4‐isocyanatobenzylidene)‐diaminodiphenyl‐methane (MADI), 4,4′‐bis(4‐isocyanatobenzylidene)‐diaminodiphenylsulphone (SDAI), pyromellitic dianhydride (PMDA), 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA), and trimellitic anhydride (TMA), by a one‐step process. The diisocyanates ODAI, MDAI and SDAI were prepared from the corresponding diacids, namely, 4,4′‐bis(4‐carboxybenzylidene)‐diaminodiphenylether (ODAA), 4,4′‐bis(4‐carboxybenzylidene)‐diaminodiphenylmethane (MDAA) and 4,4′‐bis‐(4‐carboxybenzylidene)‐diaminodiphenylsulphone (SDAA) by a Weinstock‐modified Curtius rearrangement method. All the polycondensation reactions were conducted in N ‐methyl‐2‐pyrrolidone (NMP) under identical conditions and the polymers obtained were characterized by IR spectroscopy, solution viscosity, elemental analysis, thermogravimetric analysis, differential scanning calorimetry and X‐ray diffraction.