Poly(aryl ether oxadiazoles)

Abstract

A general method for the preparation of poly(aryl ether oxadiazoles) has been developed where the generation of an aryl ether linkage was the polymer-forming reaction. Two synthetic approaches were investigated based on either an oxadiazole-activated halo displacement with phenoxides or a hydrazide-activated halo-displacement with phenoxides. The hydrazide may be subsequently thermally cyclodehydrated to the oxadiazole heterocyclic. In each case, the negative charge developed in the transition state could be stabilized through a Meisenheimer Complex, analogous to conventional activating groups (e.g., sulfone and ketone), and the electron affinity, as judged by 1H NMR, was comparable to that of other activating groups. An appropriately substituted diarylfluoro oxadiazole was prepared and polymerized with various bisphenols in an NMP/CHP solvent mixture in the presence of K2CO3. High molecular weight poly(aryl ether oxadiazoles) were synthesized with viscosities ranging from 0.44 to 0.76 dL/g and Tg's in the 200°C range. Conversely, the hydrazide activated halo-displacement as a means of preparing poly(aryl ether hydrazides) was not as successful, since it appears that the hydrazide was of sufficient acidity to form a salt with K2CO3 preventing solubility and polymerization.