INTRAMOLECULAR CYCLIZATION OF PENDANT PHENYLETHYNYL GROUPS AS A ROUTE TO SOLVENT RESISTANCE IN POLYPHENYLQUINOXALINES

Biphenyl-based bisbenzil monomers which contain pendant phenylethynyl groups in the 2,2'-positions were condensed with 3,3'-diaminobenzidine to make polyphenylquinoxalines (PPQs) of high molecular weight. Thermal cure of these polymers at 193-degrees-C caused an intramolecular cyclization (IMC) of the phenylethynyl groups to give the rigid 9-phenyldibenzanthracene system in the backbone of the polymer. The initial, uncured polymers formed tough films which were soluble in m-cresol and chlorinated solvents, but after thermal cure the films became insoluble in all common organic solvents and acids while maintaining their toughness. DSC scans of the cured materials showed small residual exotherms indicating that after vitrification even the intramolecular rotation required for the IMC reaction became restricted.