wherein r 1 represents a covalent bond or a perfluoroalkenyl radical having 1 to 20 carbon atoms r 2 is a radical of the formula u2014 o u2014 cf 2 cf r 3 u2014 o m n u2014 cf 2 cf 2 u2014 wherein m 0 or 1 n 0 1 or 2 and r 3 is f or a perfluoroalkyl radical having 1 10 carbons and x is f or the radical represented by the formula wherein y is c or n m is an alkali metal r 4 is a perfluoroalkyl radical having 1 10 carbons optionally substituted with one or more ether oxygens and p 1 or 2 with the proviso that p 1 when y is n and p 2 when y is c preferably r 1 is a bond or u2014 cf 2 u2014 r 3 is a perfluoroalkyl radical having 1 4 carbons m 1 n 0 or 1 and x is f most preferably r 1 is a bond r 3 is u2014 cf 3 and n 1 the grafting reaction is carried out by contacting the perfluorovinyl compound which is usually a liquid at the reaction temperature with the polymer in the presence of the solvent the polymer can be dissolved in a solvent or just swollen by the solvent higher incorporation of the monomers is achieved when the polymer is completely dissolved in the solvent suitable solvents include aromatic hydrocarbons such as chlorobenzene and dichlorobenzene halogenated hydrocarbons and polar aprotic solvents such as dimethyl acetamide and dimethyl formamide chlorobenzene is preferred in.