POLYISOIMIDES - SYNTHESIS AND EVALUATION AS EFFICIENT PRECURSORS FOR POLYIMIDES

Polyisoimides have been evaluated as potential precursors for polyimid es since they are expected to be tractable and isomerized to polyimide s without producing water. Detailed studies on isoimides were carried out first with model compounds. Compared to N-phenyl- and N-benzylphth alisoimides, N-(benzyloxy)phthalisoimide proved to be superior in term s of ease of synthesis, hydrolytic stability, and quantitative isomeri zation to the imide. Polymerizations of p- and m-xylylenebis(oxyamine) s with tetracarboxylic dianhydrides such as pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, and 2,2-bis(3,4-dicarboxyphen yl)hexafluoropropane dianhydride proceeded efficiently in N-methyl-2-p yrrolidone, and the resulting poly(amic acid)s had inherent viscositie s up to 0.61 dL/g. The poly(amic acid)s were then converted into polyi soimides by chemical dehydration. Under appropriate conditions with N, N'-dicyclohexylcarbodiimide, isoimide formation was preferred to imide formation, and the isoimide contents of the polymers were about 90%. The polyisoimides obtained exhibited high solubility and low glass tra nsition temperatures unlike the corresponding polyimides. Furthermore, on heating or treating with a base catalyst, the polyisoimides were i somerized to polyimides quantitatively, indicating the high potential of the polyisoimides as precursors for polyimides.