Novel aromatic poly(ether ketones) containing bulky lateral groups were synthesized via nucleophilic substitution reactions of 4,4'-biphenol and (4-chloro-3-trifluoromethyl)phenylhydroquinone (CF-PH) with 1,4-bis(p-fluorobenzoyl)benzene. The copolymers were characterized by differential scanning calorimetry (DSC), wide-angle X-ray diffraction, and polarized light microscopy observation. Thermotropic liquid-crystalline behavior was observed in the copolymers containing 40, 50, 60, and 70 mol % CF-PH. The crystalline-liquid-crystalline transition [melting temperature (T-m)] and the liquid-crystalline-isotropic phase transition appeared in the DSC thermograms, whereas the biphenol-based homopolymer had only a melting transition. The novel poly(aryl ether ketones) had glass-transition temperatures that ranged from 143 to 151degreesC and lower T-m's that ranged from 279 to 291degreesC, due to the copolymerization. The polymers showed high thermal stability, and some exhibited a large range in mesophase stability. (C) 2003 Wiley Periodicals, Inc.