Syntheses and properties of new aromatic‐aliphatic copolyimides

Aromatic aliphatic copolyimides (19a–m) containing pyromellitdiimide and glutar‐ or succinimide rings in the main chain were synthesized by a two‐step reaction of specified dianhydrides (5a, b) with primary diamines (11a–h). In the first step, poly(amic acid)s (17/18) having pyromellitdiimide rings were prepared by the reaction of 2,2′‐pyromellitdiimido‐diglutaric or disuccinic anhydride (5b, 5a) with 11a–h in polar solvents. In the second step, the conversion of 17/18 to the copolyimides 19a–m was carried out either thermally or by chemical means. 5b and 5a were synthesized by the reaction of pyromellitic anhydride with glutamic or aspartic acid, respectively. No gelation was observed during a long period of storage of the poly(imidoamic acid)s 17/18 in polar solvents at room temperature. For their conversion to copolyimides, a dehydrating agent such as acetic anhydride and a catalyst such as pyridine were applied successfully. The copolyimides gave clear, tough and flexible films from DMSO solution. They show excellent stabilities at high temperatures and against oxidative degradation. IR spectra, solubilities, TG analyses and the formation of the new copolyimides were studied and compared with those of corresponding model compounds.