The polymerization of pyromellitic dianhydride with diphenylmethane diisocyanate

A novel polyimide forming reaction is reported. Pyromellitic dianhydride undergoes a condensation polymerization with diphenylmethane diisocyanate in solution or under melt-fusion conditions to give polydiphenylmethanepyromellitimide (II) and carbon dioxide. Polymer II was characterized by inherent viscosity, infrared spectrum, and thermogravimetric analysis. An intermediate Polymer I was isolated which appeared to contain seven-membered rings in the backbone. It is postulated that these rings eliminate carbon dioxide to form polyimide II.