TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The carbonyl group-containing structural unit (II) is preferably of formula (III). The ionic group is sulfonic acid group. The molar ratio of segment (A1) containing ionic group and segment (A2) which does not contain ionic group is 0.2-5. The carbonyl group-containing structural unit (I) is preferably of formula (IV). The linker moiety is of formula (V)-(XI). The linker compound is chosen from 1-chloro-4-((4-chloro-3-nitrobenzene)sulfonyl)-2-nitrobenzene, 1-fluoro-4-((4-fluoro-3-nitrobenzene)sulfonyl)-2-nitrobenzene, 1-fluoro-4-((4-fluorobenzene)sulfonyl)benzene, bis(4-chloro-3-nitrophenyl)methanone, bis(4-fluoro-3-nitrophenyl)methanone, 2,4-dichloro-6-methoxy-1,3,5-triazine, 2,4-difluorobenzonitrile, 2,5-difluorobenzene-1,4-dicarbonitrile or 2,6-difluorobenzonitrile.M1,M2=H, metal cation, and ammonium cation;X=H, NO2, CN, CF3, Cl, Br or I;Y'=NO2, CN, CF3, Cl, Br or I;Z=electron-attractive group chosen from NO2, CN, CF3, Cl, Br or I;R=organic group;E=O or S;andAr'=arylene.Preferred Property: The number average molecular weight of segment (A1) and segment (A2) is 0.5-50000.    TECHNOLOGY FOCUS - POLYMERS - Preparation (claimed): Ionic group-containing segment (A1) containing structural unit (I) or its precursor, segment (A2) containing carbonyl group-containing structural unit of formula: -Ar5-C(=O)-Ar6-O-Ar7-C(=O)-Ar8-O- (II) or its precursor, and linker compound containing group (-OM) on both terminals, are reacted to obtain block copolymer.Ar5-Ar8=bivalent arylene;andM=H, metal cation or ammonium cation.Preferred Properties: The block copolymer has ion exchange capacity of 1.5-3.5 m equivalent/g. EXAMPLE - Potassium carbonate (16.59 g), 2,2-bis(4-hydroxyphenol)-1,3-dioxolone (25.8 g), 4,4'-difluoro benzophenone (20.3 g), N-methylpyrrolidone (300 ml), and toluene (100 ml) were subjected to spin-dehydration process at 160 degrees C, heated and polymerized at 180 degrees C for 1 hour. The resultant mixture was purified by reprecipitating with large amount of methanol, to obtain an oligomer (a1) which does not contain ionic group and containing terminal group (OM). The obtained oligomer (a1), potassium carbonate (1.1 g), N-methyl pyrrolidone (100 ml) and cyclohexane (30 ml) were spin-dehydrated, and decafluoro biphenyl (4 g) was added, and reacted to obtain oligomer of formula (XII) having terminal fluoro group and not containing ionic group.    m=positive integer;and    A=group of formula (a).