the unsaturated monomer the proportion of fluoropolymer is advantageously by weight from 90 to 99 9 per 0 1 to 10 of unsaturated monomer respectively preferably the proportion of fluoropolymer is from 95 to 99 9 per 0 1 to 5 of unsaturated monomer respectively after the blending step it is found that the blend of the fluoropolymer and the unsaturated monomer has lost about 10 to 50 of the unsaturated monomer that had been introduced at the start of the blending step this proportion depends on the volatility and the nature of the unsaturated monomer in fact the monomer was vented in the extruder or the blender and it was recovered from the venting circuits as regards the grafting step proper the products recovered after the blending step are advantageously packaged in polyethylene bags the air is expelled and the bags then sealed as regards the method of irradiation it is possible to use without distinction electron irradiation more commonly known as u03b2 irradiation and photon irradiation more commonly known as u03b3 irradiation advantageously the dose is between 2 and 6 mrad and preferably between 3 and 5 mrad with regard to the step of removing the non grafted unsaturated monomer and the residues liberated by the grafting it is possible to use any technique known to those skilled in the art the proportion of radiation grafted monomer relative to the amount of monomer present at the start of the blending step is between 50 and 100 the product may be washed with solvents that are inert to the fluoropolymer and to the radiation grafted functional groups for example when grafting with maleic anhydride the product may be washed with chlorobenzene it is.