Amine reactivity changes in imide formation from heterocyclic bases

The inclusion of aza-heterocyclic di- or tri-amines in aromatic polyimide formulations can hinder the formation of high molecular weight products. Model studies using the reactions of pyridine, pyrimidine and triazine polyamines with phthalic anhydride and substituted phthalic anhydrides have shown that the combined deactivating effects of multiple ate-substitution and successive imidization of the amino groups can be sufficient to seriously impede or even prevent the formation of fully imidized derivatives. Model co-polyimides incorporating 2,4,6-triaminopyrimidine were found to have lowered molecular weights and to contain persistent free amino groups. Other polyimides containing these amines could be expected to have similar non-ideal structures (defects), which could extend into the structures of products formed from these resins, thereby potentially lessening the extent of any beneficial effects arising from use of the heterocyclic amines.