TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (Disclosed): Preparation of (I) comprises: (i) synthesizing the segment containing a sulfonic acid group, which contains a diphenyl sulfonic acid constituent unit of formula (S2), and/or a constituent unit which is to be a precursor of the constituent unit (S2), and has both ends with hydroxyl group; (ii) synthesizing the segment not containing a sulfonic acid group, which contains a tetraphenyl constituent unit of formula (P1), and/or a constituent unit which is to be a precursor of the constituent unit (P1) and has a both ends with hydroxyl group; (iii) introducing a linker site into both ends with hydroxyl group of the segment containing a sulfonic acid group or the segment not containing a sulfonic acid group; and (iv) making a block copolymer and a block copolymer precursor by polymerizing a both ends linker site of the segment synthesized, and a both ends hydroxyl group of the other segment. Preferred Components: The polymer has a 5-(3,5-disulfo-benzoyl)-2-(4-(4-hydroxy-benzoyl)-phenoxy)-benzene-1,3-disulfonic acid structure of formula (S3). The segments not containing a sulfonic acid group (B2) has (4-(4-(4-hydroxy-benzoyl)-phenoxy)-phenyl)-phenyl-methanone structure of formula (P2), where (P1) is optionally substituted, but does not contain a sulfonic acid group. The sulfonic acid group-containing polymer contains one or more linker sites linking the segments.Ar1 = divalent group of formula (q1) or (q2);M1 = H, metal cation, ammonium cation or 1-20C hydrocarbyl;X3 = electron withdrawing group; andZ3 = electron withdrawing group, O or S. EXAMPLE - Potassium carbonate (5.5 g), 2,2-bis(4-hydroxyphenyl)-1,3-dioxane mixture (5.2 g), 4,4'-difluorobenzophenone (2.2 g) tetrasodium 3,5,3',5'-tetrasulfonate-4,4'-difluorobenzophenone (6.3 g) and 18-crown-6-ether (2.6 g) were added to a 3-neck flask (500 ml) equipped with a stirrer, a nitrogen introducing tube and a Dean-Stark trap, dehydration was performed at 180 degrees C in N-methylpyrrolidone (50 ml)/toluene (40 ml), then the temperature was raised to remove the toluene, and polymerization was performed at 240 degrees C for 3 hours. Purification was performed by re-precipitation with a large amount of water to obtain a precursor polymer having a ketal group. A N-methylpyrrolidone (25 wt.%) solution in which the resulting precursor polymer had been dissolved was casting-coated on a glass substrate, and this was dried at 100 degrees C for 4 hours, and heat-treated at 150 degrees C for 30 minutes under nitrogen to obtain a membrane. After the membrane was immersed in a 10 wt.% of aqueous sulfuric acid solution at 25 degrees C for 24 hours to perform proton substitution and a deprotection reaction, this was immersed in a largely excessive amount of pure water for 24 hours to sufficiently wash the membrane, and a polymer electrolyte membrane including a sulfonic acid group-containing polymer of formula (A) was obtained.