TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The blocks with sulfonic acid groups may have the sulfonic acid groups directly bonded to the aromatic rings. The blocks with sulfonic acid groups are an epoxy resin or compounds with the formulae (I), (II) or (III), all of which have sulfonic acid groups that have been introducedwhere less thanMARmore than X = -O-, -S-, -NH- or direct bond, preferably -O-, R1 = 1-6C alkyl or alkoxyl group or phenyl group, a = 0-3. Ar1 = (IIa) or (IIb),R2, = 1-6C alkyl or alkoxy group or phenyl or phenoxy group, b = 0-4, c = 0-6. Ar2 = (IIIa), (IIIb), (IIIc), (IIId) or (IIIe),where R3 = 1-6C alkyl or alkoxyl group or phenyl group, d = 0-3, e = 0-2, Y = -O-, -S-, 1-20C alkylene or alkylenedioxy group or 1-10C halogenated alkylene. When a plurality of R1, R2, R3 or Y are present, they may be the same or different. less thanMARmore than The block with no sulfonic acid groups is formula (IV),where less thanMARmore than R4 = 1-6C alkyl, f = 0-4, Z = -CO- or SO2-, preferably -SO2-. When a plurality of R4s are present, they may be the same or different. less thanMARmore than The blocks with no sulfonic acid groups accounts for 60-95% by weight of block copolymer.Preferred Process: Sulfonation is achieved with sulfuric acid of 90% or more. EXAMPLE - A hydroxy group-ended polyether sulfone (3.0g) and poly(2-phenylene ether) (0.78g) with potassium carbonate (0.04g), N,N-dimethylacetamide (15 ml) and toluene (3.0ml) were heated with stirring under azeotropic conditions. 4,4'-difluorobenzene (0.05g) was added and stirred at 160 oC for 5 h. The mixture was added to acidic methanol to precipitate the polymer, that was purified and dried. The product was stirred with 98% sulfuric acid at room temperature to obtain a homogeneous solution and stirred for a further 2 h. The product was added to ice water to obtain the sulfonated block copolymer. Polymers obtained by this method had superior proton conductivity, suppressed water absorption and superior water resistance compared with randomly sulfonated comparative examples.