Aromatic polypyromellitimides from aromatic polyamic acids

Aromatic diamines react with pyromellitic dianhydride in solvents such as dimethyl‐acetamide to form solutions of high molecular weight polyamic acids. These soluble polymers can be converted to insoluble aromatic polyimides. The aromatic polyimides exhibit zero strength temperatures above 700°C. and possess excellent thermal and oxidative stability. The stability characteristics of films and the relation of chemical structure to thermal and hydrolytic stability and to polymer properties such as crystallinity are described.