Polyimides based on pyrazinetetracarboxylic dianhydride and some related model compounds

Abstract A study was made of polyimides based on pyrazinetetracarboxylic dianhydride (PTDA) plus heterocyclic diamines different from the one previously reported by Hirsch. It was postulated that thermal properties might be improved if the diamine portion did not contain the N–N linkage. The results indicate that these heterocyclic‐based polyimides are in fact of lower thermal stability and of less molecular weight buildup than their corresponding polypyromellitimides. Thermal failure, outlined by their TGA curves, is shown not to be due to an inherent lack of stability for such polymers, but rather, to synthesis problems arising from both the anhydride and amine precursors. The synthetic problems are twofold: (1) the heterocyclic diamines used in this study display low reactivity; (2) pyrazinecarboxylic acids readily decarboxylate. These conclusions were drawn from a correlation of the relative basicity values of the diamines of consideration and from study of a series of model compounds prepared from an appropriate amine or diamine with PDTA, pyrazinedicarboxylic anhydride, phthalic anhydride, or pyromellitic dianhydride. An accumulation of infrared and mass spectra data for these models relate that the proposed pyrazine polyimides are not of complete polyimide structure, but rather resemble recurring amide‐imide units.