TECHNOLOGY FOCUS - POLYMERS - Preparation (claimed): The (a+b) mol of bisphenol monomer having carboxyl group on its side chain, a mol of fluoro-terminated monomer and b mol of sulfonated fluoro-terminated monomer are added in a flask equipped with stirrer, guide tube, water diverter and condensing tube. Then, 1.5-2.0(a+b) mol of potassium carbonate as salt, dimethyl sulfoxide, N,N-dimethyl formamide, dimethyl acetamide, N-methyl pyrrolidone or sulfolane as solvent and toluene as water carrier are added, such that the solid content of reaction system is 20-40 wt.%. The reaction system is heated at 130-140 degrees C, water carrying reaction is performed for 2-4 hours, toluene is distilled, and further heated at 160-220 degrees C for 4-6 hours. The resultant product is added to mixed solution of hydrochloric acid and ethanol, to obtain white stick-like material. The ratio of content of hydrochloric acid and content of mixture of ethanol and hydrochloric acid is 20-40%. The content of hydrochloric acid is 30-40 mass% and content of ethanol is 95-100 mass%. The obtained material is crushed, pumped by Buchner funnel, boiled with acetone, again pumped for 5-8 times, boiled 3-5 times with water, again pumped for 5-8 times and dried at 100-150 degrees C, to obtain sulfonated poly(arylene ether ketone) polymer having carboxyl group. Preferred Compounds: The fluoro-terminated monomer is 4,4-difluoro-diphenyl-ketone, 4,4-di(4-fluoro-benzoyl)benzene, 4,4-difluoro-diphenyl sulfone or 1,3-di(4-fluoro-benzoyl)benzene. The sulfonated fluoro-terminated monomer is 3,3-sodium-disulfonate-4,4-difluoro-diphenyl-ketone, 1,4-di(3-sodium-sulfonate-4-fluoro-benzoyl)benzene, 3,3-sodium-disulfonate-4,4-difluoro-diphenyl sulfone or 1,3-di(3-sodium sulfonate-4-fluoro-benzoyl)benzene. The bisphenol monomer is 2-(bis(4-hydroyphenyl)methyl)benzoic acid, diphenolic acid, 4-(2,5-dihydroxyl-benzyl)benzoic acid, 5,5-methylene-di(2-hydroxyl)benzoic acid or 2,5-dihydroxyl-diphenyl acetic acid. Preferred Process: A c mol of sulfonated poly(arylene ether ketone) polymer having carboxyl group, (0.95-1.05) c mol of o-phenylene-triamine and (18-22) c mol of lithium chloride are added into flask. Then, N,N-dimethyl formamide as solvent and triphenyl phosphate as water absorber are added, reacted at 90-110 degrees C for 2-4 hours, and again heated at 145-155 degrees C for 10-12 hours. The obtained reaction fluid is added into ethanol solution, precipitate is separated, filtered, collected and dried at 100-150 degrees C for 10-24 hours. Thus, sulfonated poly(arylene ether ketone) polymer having carboxyl group on its side chain is obtained.