Polymers from ortho aromatic tetraamines and aromatic dianhydrides

Aromatic heteropolymers were synthesized from aromatic tetraamines and dianhydrides; some of the polymers had a ladder‐type structure. The properties and thermal stability of the polymer were studied. The experimental conditions yielding the imidazolone structure were determined on model compounds. Polymers containing mixed aromatic units in the chain were prepared from pyromellitic anhydride or 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride, and 3,3′‐diaminobenzidine, 3,3′,4,4′‐tetraaminodiphenyl ether, 1,4,5,8‐tetraaminonaphthalene, or 1,2,4,5‐tetraaminobenzene. The polycondensations were carried out in melt and in solution (in melted phenol, pyridine, dimethylacetamide, 116% polyphosphoric acid). The inherent viscosities of a number of polymers synthesized by melt condensation were in the range of approximately 0.2–0.7; the higher polymers were obtained by carrying out the polycondensations in solution in 116% polyphosphoric acid; in this case, the intrinsic viscosities ranged from 1.1 to 1.8. Most of the polymers do not melt at 350°C. and are soluble in the usual organic solvents, but the ladder‐type structure polymers were soluble only in concentrated sulfuric acid.