Poly(aryl ether-benzoxazoles)

A general method for the preparation of poly(aryl ether-benzoxazoles) has been developed where the generation of an ether linkage is the polymer-forming reaction. We found that aryl fluorides para to a 2-benzoxazolyl group were activated toward nucleophilic aromatic substitution with phenoxides. Facile displacement occurred at this position since the benzoxazole ring can stabilize the negative charge developed in the transition state through a Meisenheimer complex, analogous to conventional activating groups (e.g. sulfone or carbonyl). Appropriately substituted dihalo bisbenzoxazoles, 2,2'-bis[2-(4-fluorophenyl)benzoxazol-6-yl]hexafluoropropane, 2,2'-bis(4-fluorophenyl)-6,6'-bibenzoxazole, and 2,2'-(4-fluorophenyl)-5,5'-bibenzoxazole, were prepared and polymerized with bisphenols in N-methyl-2-pyrroli-done in the presence of K2CO3. High molecular weight polymers were obtained, with glass transition temperatures ranging from 213 to 300°C. The resulting polymers were processable from solution or the melt and showed excellent thermal stability and mechanical properties. This synthetic route affords the poly-(benzoxazole) analogue of poly(ether-imide) and shows many of the same desirable characteristics. © 1990, American Chemical Society. All rights reserved.