POLY(ARYL ETHER OXADIAZOLES)

A general method for the preparation of poly(aryl ether oxadiazoles) has been developed based on an oxadiazole-activated halo or nitro displacement with phenoxides. The oxadiazole heterocycle was found to be sufficiently electron withdrawing to activate halo and nitro substituents toward nucleophilic aromatic substitution analogous to other heterocycles and conventional activating groups (i.e., sulfone, ketone, etc.). Model reactions demonstrated that the oxadiazole-activated displacement occurred with high selectively in near quantitative yield and was judged suitable as a polymer-forming reaction. Appropriately halo- or nitro-substituted 2,5-diphenyloxadiazoles were prepared and subjected to displacement polymerizations with bis(phenoxides) in an N-methyl-2-pyrrolidone (NMP)/N-cyclohexyl-2-pyrrolidone (CHP) solvent mixture. High molecular weight polymers with glass transition temperatures in the 200-degrees-C range were obtained by each synthetic route. The thermal stability for the resulting polymers was good with decomposition temperatures in the 450-degrees-C range, just below the temperature range of other heterocycle-containing polymers. The poly(aryl ether oxadiazoles) showed limited solubility in common organic solvents, but films could be readily fabricated from the melt.