2,6-Diphenoxybenzonitrile (DPOBN) was synthesized by reaction of phenol with 2,6-difluorobenzonitrile in N-methyl-2-pyrrolidone in the presence of KOH and K2CO3. Poly(aryl ether ketone ketone)/poly(aryl ether ether ketone ketone) copolymers with pendant cyano groups were prepared by the Friedel-Crafts electrophilic substitution reaction of terephthaloyl chloride with varying mole proportions of diphenyl ether and DPOBN using 1,2-dichloroethane as solvent and N-methyl-2-pyrrolidone as Lewis base in the presence of anhydrous AlCl3. The resulting polymers were characterized by various analytical techniques, such as FT-IR, differential scanning calorimeter, thermal gravimetric analysis, and wide-angle X-ray diffraction. The crystallinity and melting temperature of the polymers were found to decrease with increase in concentration of the DPOBN units in the polymer. Thermogravimetric studies showed that all the polymers were stable up to 514 degrees C in N-2 atmosphere. The glass transition temperature was found to increase with increase in concentration of the DPOBN units in the polymer when the molar ratios of DPOBN to DPE ranged from 10/90 to 30/70. The copolymers containing 30-40 mol% of the DPOBN units exhibit excellent thermostability at (350 +/- 10)degrees C and have good resistance to acidity, alkali, and organic solvents. (c) 2007 Wiley Periodicals, Inc.