Poly(arylene ether ketone)s containing sulfonate groups were synthesized by aromatic nucleophilic polycondensation of 4,4'-difluorobenzophenone (DFK), sodium 2,5-dihydroxybenzensulfonate (SHQ) and bisphenols. Only low-molecular weight oligomer was obtained when hydroquinone (HQ) was employed as comonomer, while copolymerization of DFK, SHQ, and phenolphthalein (PL) proceeded quantitatively to high-molecular weight (reduced viscosities above 0.68 dL/g) in dimethylsulfoxide at 175 degrees C in presence of anhydrous potassium carbonate. The sulfonated polymers were soluble in dipolar aprotic solvents, such as N,N'-dimethylactamide and N-methyl-2-pyrrolidinone. Tough membranes cast from N,N-dimethylformamide solution with SHQ/DFK mole ratios <= 65:35 were obtained. Both glass transition temperatures and hydrophilicity of the copolymers increased with the content of sodium sulfonate groups. The materials are candidates as new polymeric electrolytes for proton exchange membranes. (c) 2006 Elsevier Ltd. All rights reserved.