Preparation of a polyimide foam

Abstract The reaction of phenyl isocyanate with phthalic anhydride to form N‐phenylphthalimide is strongly solvent dependent and catalyzed by tertiary amines. Water and alcohol promote imide formation, but Lewis acids and organometallic compounds are ineffective. In DMSO solvent, benzophenone tetracarboxylic dianhydride (BTDA) and polymethylene polyphenol isocyanate (PAPI) polymerize with the evolution of carbon dioxide to yield a foamed polyimide. The solvent‐freed open‐celled foams exhibit exceptional fire resistance and thermal stability.