TECHNOLOGY FOCUS - POLYMERS - Preferred Polymer: The structural unit of formula (5) is obtained using 3-(2,5-dichloro-benzoyl)-benzenesulfonic acid 2,2-dimethyl-propyl ester. Aromatic monomer of formula (6 or 7) and halogenated monomers of formulae (8-a to 8-c, 9) are condensed. The obtained compound is reacted with sulfonic acid compound of formula (10), and the sulfonic acid ester group is hydrolyzed or transesterified to obtain structural unit containing sulfonic acid group.Ar'=aromatic group having substituent chosen from -SO3R, -O(CH2)pSO3R or -O(CF2)pSO3R;p=1-12;X=halo, preferably fluoro;X'=fluoro, chloro, bromo or iodo;R=4-12C alkyl;andB'=-OH or -SH. EXAMPLE - (In g) 2,2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane (97.6), 4,4'-dichlorobenzophenone (73.9), 2,4,4'-trichlorobenzophenone (4.4), and potassium carbonate (52.2) were taken in a flask. N,N-dimethylacetamide (436 mL) and toluene (218 mL) were added and stirred after nitrogen substitution. The reaction liquid was heated and refluxed at 130 degrees C. Water and toluene were removed, and the reaction temperature was raised to 190 degrees C. Tetrahydrofuran (300 mL) was added and diluted after cooling the reaction liquid. Insoluble mineral salt was filtered, the filtrate was poured into methanol (3 L), and a product was precipitated. The product was dissolved in tetrahydrofuran (600 mL) after filtration and drying, and poured into methanol (2 L) and reprecipitated. The precipitated white powder was filtered and dried, to obtain a polyarylene polymer with (145) having number average molecular weight of 12000. Neopentyl 3-(2,5-dichlorobenzoyl)-benzenesulfonic acid (51.4), polyarylene polymer (22.5), bis(triphenylphosphine)nickel dichloride (3.4), sodium iodide (0.58), triphenylphosphine (13.64), and zinc (20.4) were stirred for 3 hours. N,N-dimethylacetamide (265 mL) was added, and the reaction mixture was reacted at 80 degrees C. N,N-dimethylacetamide (480 mL) was added and diluted, and insoluble matter was filtered. The obtained solution was heat-stirred at 115 degrees C, and lithium bromide (31) was added. After stirring for 7 hours, the reaction liquid was poured into ion-exchange water (7 L). The precipitated product was washed with acetone, hydrochloric acid and pure water, and dried to obtain branched polyarylene copolymer having weight average molecular weight of 218000 and ion-exchange capacity of 2.3 meq/g. Distilled water (0.88), 15% water-1,2-dimethoxyethane solution of the obtained copolymer (3.23) and 1,2-dimethoxyethane (13.97) were mixed with zirconia balls (25) and platinum supported carbon particles (1.51) to obtain paste with viscosity of 50 cp. The obtained paste was used for forming membrane electrode assembly. The fuel cell produced using the membrane electrode assembly had favorable electric power generation characteristics, high durability and swelling resistance.