A series of aromatic copolyethers containing 1,3,4-oxadiazole rings and fluorene groups was prepared by nucleophilic substitution polymerization technique of 9,9-bis(4-hydroxyphenyl)fluorene, 1, or of different amounts of 1 and an aromatic bisphenol, such as 4,4'-isopropylidenediphenol or phenolphthalein, with 2,5'-bis(p-fluorophenyl)1,3,4-oxadiazole. The polymers were easily soluble in polar solvents like N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and chloroform and can be cast from solutions into thin flexible films. They showed high thermal stability, with decomposition temperature being above 425 degrees C. The polymers exhibited a glass-transition temperature in the range of 195-295 degrees C, with a reasonable interval between glass-transition and decomposition temperature. Electrical insulating properties of some polymer films were evaluated on the basis of dielectric constant and dielectric loss ad their variation with frequency and temperature. The values of dielectric constant at 19 kHz and 20 degrees C were in the range of 3.16-3.25. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 383-391, 2009