TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The at least one block (A1) is composed of the repeating units of formulae (I)-(III) into which sulfonic acid have been introduced. At least one block (A2) is an aromatic polyether having a repeating unit of formula (IV). The number of repeating units composition at least one of the blocks into which sulfonic acid groups have been introduced in 5-50. The at least one of the blocks (A1) has a structure where the sulfonic acid groups are directly bonded to the aromatic rings. The block (A1) or (A2) is a block having aromatic rings in the main chain.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The block copolymer comprises the block (A2) (60-95 wt.%). Preferred Method: The method involves sulfonating the block copolymer with sulfuric acid having a concentration of greater than or equal to 90%. Preferred Definitions:    X1=O.    EXAMPLE - A flask was charged with Sumika Excel PES5003P (RTM: hydroxyl group-ended polyether sulfone) (3 g), PE1 (0.75 g), potassium carbonate (0.04 g), N,N-dimethylacetamide (DMAc) (15 ml) and toluene (3 ml). The mixture was heated and the solution was dehydrated under azeotropic condition of toluene and water and then toluene was distilled off. To this was added 4,4-difluorosbenzophenone (0.05 g) and the mixture was stirred while heating at 160degrees C for 5 hours. The reaction solution was added dropwise to a large amount of acidic methanol containing HCl, the resultant precipitate was recovered and dried under reduced pressure at 80degrees C to obtain a block copolymer (3.8 g). The resultant block copolymer (2 g) was stirred together with 98% sulfuric acid (20 ml) at room temperature to obtain a uniform solution and stirred for 2 hours. The resultant solution was added into a large amount of ice water dropwise and the resultant precipitate was recovered. A mixer washing with ion exchange water was repeated until the washing solution became neutral and the polymer was dried at 40degrees C under reduced pressure to obtain a sulfonated block copolymer (B1). For a comparison, 4,4'-dihydroxydiphenylsulofone, 4,4'-dihydroxybiphenyl and 4,4'-dichlorophenylsulfone were polycondensed at a molar ratio of 7:3:10 at a temperature of 200-290degrees C using diphenylsulfone as a solvent in the co-existence of potassium carbonate. The resultant polymer was sulfonated with concentrated sulfuric acid to synthesize a random copolymer in which a sulfonic acid group had been introduced into a biphenyl unit. The test/comparative block copolymer were dissolved in a concentration of 5-20% into DMAc and cast on glass substrates to form films which were dried to obtain films. The proton conductivity of the film was measured according to an alternating method at a temperature of 80degrees C and humidity of 95%. The dried film was immersed in de-ionized water at 100degrees C for 2 hours and the increase in the film weight was measured based on the weight in dry condition to give water absorption of the film. The results showed proton conductivity (S/cm) and water absorption (%) of 1x10-1/1.3x10-2 and 79/24 respectively.