Fluoropolymers comprising at least one repeat unit of formula (I): ##STR00001## wherein: groups X and Y, identical or different, represent H or F; group Z represents F or a perfluorinated alkyl group; group W represents CH.sub.2O or CF.sub.2O or CO.sub.2; group Ar represents a divalent group including at least one optionally substituted carbon-containing aromatic cycle; group Q represents a single bond, (CF.sub.2).sub.n with 1.ltoreq.n.ltoreq.10, or C.sub.2F.sub.4OC.sub.2F.sub.4; group G represents a cation exchanging group, preferably selected among: SO.sub.2R.sub.1, with R.sub.1 representing OH, F or Cl; or P(.dbd.O) (OR.sub.2).sub.2 with R.sub.2 representing H or an optionally substituted alkyl group; or CO.sub.2H and having ion exchange capacity not less than 0.5 meq/g polymer are provided. Methods of synthesis, membranes obtained using these polymers and fuel cell systems containing such membranes are also provided.