TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The ionic liquid contains a proton donor. The polymeric electrolyte film consists of ionic liquid (in wt.pts) (0.5-200) and sulfonic acid group-containing polyarylene-type copolymer (100). Preferred Component: The proton donor is chosen from trifluoro methanesulfonic acid, bis(trifluoro methylsulfonyl)imido acid and/or tris(trifluoro methylsulfonyl)methide acid.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The sulfonic acid group-containing polyarylene-type copolymer contains structural unit of formula (1) and structural unit of formula (2).A=divalent electron withdrawing group;B=divalent electron donating or direct bond;Ar=aromatic group having substituent of formula: -SO3H;m,n=0-10;k=1-4;R1-R8=H, F, alkyl, fluoroalkyl, allyl, aryl or cyano;W=divalent electron withdrawing group or single bond;T=single bond or divalent organic group;andp=0 or positive integer. EXAMPLE - 4-(4-(2,5-dichloro benzoyl)phenoxy) benzenesulfonic acid neopentyl (in g) (39.58), oligomer (15.23) of formula (6), nickel salt (Ni(PPh3)2Cl2), dry PPh3 (10.49), sodium iodide (0.45), zinc dust (15.69) and N-methyl-2-pyrrolidone (390 ml), were stirred under nitrogen atmosphere. The resulting mixture was heat-reacted at 75degreesC for 3 hours. The reaction liquid was diluted with tetrahydrofuran (250 ml) and stirred. The resulting solution was filtered. The resulting filtrate was solidified with methanol (1500 ml). The solidified substance was filter-collected and air-dried. The resulting product was further dissolved in mixed solvent of tetrahydrofran (200 ml) and N-methyl-2-pyrrolidone (300 ml), and solidification-precipitation was carried out with methanol (1500 ml), to obtain a copolymer (47) having number average molecular weight of 47600 and weight average molecular weight of 159000. The obtained copolymer was dissolved in N-methyl-2-pyrrolidone (60 ml) and heated at 90degreesC. Mixture containing methanol (50 ml) and concentrated hydrochloric acid (800) was added to the reaction liquid, and reacted for 10 hours. Excess methanol was distilled from the reaction liquid, to obtain light green transparent liquid. The resulting solution was washed with liquid mixture containing water and methanol in weight ratio of 1:1, and solidified, to obtain sulfonic acid group-containing polyarylene-type copolymer having number average molecular weight of 53200 and weight average molecular weight of 185000. The obtained sulfonated polymer was washed with water until pH became 4-6, and dried. The resulting product was dissolved in mixed solvent of tetrahydrofuran and water, and titrated with standard solution of sodium hydroxide using phenolphthalein as indicator, to obtain sulfonated polymer having ion exchange capacity of 1.9 meq/g. The obtained sulfonated polymer (10) and N-ethyl imidazole-bis(trifluoro methyl sulfonyl imide) (1), were dissolved in N-methyl-2-pyrrolidone (100 ml). The resulting solution was flow-spread on glass plate and dried at 80degreesC for 1 hour and 140degreesC for 60 minutes, to obtain a film having thickness of 40 microns. The obtained film was clamped between pair of electrode catalyst layer, to obtain a membrane-electrode structure. The obtained membrane-electrode structure has high proton conductivity at low temperature and humidity conditions, and provided polymer electrolyte fuel cell with excellent electric power generation capability.