Reactive monomers containing the trifluorovinyloxy group may be copolymerized to form polymers useful as membranes, especially polymer electrolyte membranes for fuel cells. The monomers have the formula ((CF.sub.2CFO(R.sup.1).sub.p).sub.nArX.sub.2 wherein Ar is a trivalent, tetravalent or pentavalent, substituted or unsubstituted, aromatic or heteroaromatic, monocyclic or polycyclic group having from 5 to 50 carbon atoms; X is OH, SH, NR.sup.2aR.sup.2b, F or Br; p is 0 or 1; n is 1, 2 or 3; R.sup.1 is substituted or unsubstituted phenyl and R.sup.2a and R.sup.2b are independently H, C.sub.1-C.sub.8 alkyl or C.sub.1-C.sub.8 perfluoroalkyl.