Syntheses of polyanhydrides. XII. Crystalline and high melting polyamidepolyanhydride of methylenebis(p‐carboxyphenyl)amide

The acid‐catalyzed condensation of formaldehyde and aromatic nitrile has been investigated. Methylenebis( p ‐carboxyphenyl)amide was synthesized in 90% yield by the interaction of p ‐cyanobenzoic acid with formaldehyde under the influence of conc. sulfuric acid. Polycondensation of methylenebis( p ‐carboxyphenyl)‐amide was carried out with acetic anhydride at 260–365°C. under vacuum and under a N 2 atmosphere. The linear crystalline polyamidepolyanhydride thus obtained has a melting point at 325–330°C. and exhibits excellent stability towards thermal and hydrolytic degradation. It was confirmed from the experimental evidence that the introduction of the amide linkage in the main chain of the polymer increases the melting temperature of crystallite owing to the formation of intermolecular hydrogen bonds within the molecule of polyanhydride repeating unit. The molecular structure was inferred on the basis of infrared spectra and the x‐ray diffraction pattern of the polyamidepolyanhydride. The correlation between cohesion energy per chain unit and crystalline melting temperature of various aromatic and aliphatic polyanhydrides is discussed in detail.