Synthesis of poly[oxy-(2,3,5,6-tetrafluoro-1,4-phenylene)-(1,3,4-oxadiazol-2-yl)-1,4-phenylene] (F-PEOz) was examined by nucleophilic aromatic substitution reaction of 2-(4-hydroxyphenyl)-5-pentafluorophenyl-1,3,4-oxadiazole (HPOz). Only low molecular weight F-PEOz or crosslinked insoluble polymers were obtained by the solution polymerization with bases. In contrast, thermally induced solid-state polymerization of HPOz potassium salts at 180 degrees C for 1 h gave fully soluble F-PEOz with the yield of 84% and its reduced viscosity was 0.66 dL The longer polymerization time gave insoluble polymers due to the crosslinking reaction even in solid state. The solid-state polymerization did not undergo topochemically and it proceeded in an amorphous state. The crosslinking reaction was slightly inhibited by the solid-state polymerization. F-PEOz exhibited excellent solubility, high T-g of 246 degrees C and good thermal stability. (c) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 91-98, 2010