Polyimides from diisocyanates, dianhydrides, and tetracarboxylic acids

Abstract High molecular weight polyimide resins have been prepared by the reaction of diisocyanates and a mixture of dianhydrides and their acids in the presence of a tertiary amine catalyst. The polyimides thus formed can be made into tough flexible films similar to those polyimides prepared by the conventional method of reacting a dianhydride with a diamine. The preparation of high molecular weight polymer is affected by the purity of reagents, the anhydride‐acid ratio, temperature, and moisture. Evidence from model compound studies is presented regarding the nature of the reaction mechanism.