NOVELTY - Preparing ion-conducting membrane, comprises e.g. (a) reacting trifluoro-vinyloxy-benzene derivatives (I) with a polymer comprising perfluoro-cyclobutyl groups-containing unit (II) to obtain a copolymer comprising (II) and phenoxy units (III), and (b) molding the copolymer to obtain the ion-conducting membrane, or (a3) reacting (I) with 4-trifluorovinyloxy-biphenyl polymers (VI) to obtain a copolymer comprising biphenyl units (VII), (b3) sulfonating the copolymer, and (c3) molding the copolymer to obtain the ion-conducting membrane.    USE - The membrane is useful in fuel cell.    DETAILED DESCRIPTION - Preparing ion-conducting membrane (12), comprises (a1) reacting trifluoro-vinyloxy-benzene derivatives of formula (I) with a polymer comprising perfluoro-cyclobutyl groups-containing of formula (II) to obtain a copolymer comprising (II) and phenoxy units of formula (III), and (b1) molding the copolymer to obtain the ion-conducting membrane, or (a2) reacting (I) with 1,2,2-trifluoro-ethenol polymers of formula (IV) to obtain a copolymer comprising phenoxy units of formula (V), and (b2) molding the copolymer to obtain the ion-conducting membrane, or (a3) reacting (I) with 4-trifluorovinyloxy-biphenyl polymers of formula (VI) to obtain a copolymer comprising biphenyl units of formula (VII), (b3) sulfonating the copolymer, and (c3) molding the copolymer to obtain the ion-conducting membrane.    Z = 6-80C aliphatic group, polyether group or perfluoropolyether group;    Y1 = O, NH, S, or carbamoyloxy moieties of formula (Ia);    E = hydrocarbyl;    Q1 = perfluoro-cyclobutyl;    P1, P2 = -O-, -S-, -SO-, -CO-, -SO2-, -NH-, NR2- or -R3-;    R2 = 1-25C alkyl, 1-25C aryl or 1-25C arylene;    R3 = 1-25C alkylene, 1-25C perfluoroalkylene, perfluoroalkylether, alkyl ether or 1-25C arylene;    n = 5-60; and    E1 = aromatic group.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of the fuel cell comprising the ion-conducting membrane.    Proton exchange membrane fuel cell (10)    Ion-conducting membrane (12)    Cathode catalyst layer (14)    Anode catalyst layer (16)    Flow field plate (20)