Poly(aroylene-bisbenzimidazoles) and Polyimides Based on Aromatized Adducts of Bisf urans with Maleic Anhydride

A synthesis procedure has been developed for dianhydrides of the aromatic tetracarboxylic acids which are the starting compounds for producing poly(aroylene-bisbenzimidazoles) (PAB) and polyimides (PI). The procedure involves Diels-Alder reaction between maleic anhydride and bisfurans-Schiff bases of furfurol or 5-phenylfurfurol with aromatic diamines, bis(α-furyl)arylenes, cyclic acetals of furfurol and pentaerythritol, or other tetramethylol derivatives and bisfurfuryl esters of the aromatic dicarboxylic acids. The diene synthesis results in bisadducts; two water molecules are split out under the action of acidic reactants, resulting in dianhydrides of aromatic tetracids. The latter are used for synthesis of PAB and PI, either with isolation of the prepoly-mer or in one step in polyphosphoric acid. All the polymers produced are soluble in concentrated acids, and the PAB based on the dianhydrides with phenyl substituents are soluble also in organic solvents. The polymers possess high thermoxi-dation and ablation resistance.