A perfluorinated nitrosoalkane (RNO) and hexafluoropropylene are copolymerized at at least 50 DEG C. and 30 atmospheres absolute to yield a copolymer having repeating units of the structure where R is a perfluoroalkyl group and X is F and Y is CF, or vice versa. It is preferred to use equimolar proportions of the monomers, which proportion is found in the product regardless of the initial proportions of the reactants. In the specific example trifluoronitrosomethane is used. The copolymer products range from oils to waxes and elastomeric gels and are insoluble in water and common organic solvents. They may be used as coolants, heat transfer media, coating and sealing compositions, flexible hosing and lubricants, especially under chemically corrosive conditions.ALSO:Polymers comprising structural units of the formula where R is a perfluoroalkyl group and X is F and Y is CF3 or vice versa are obtained by heating hexafluoropropylene with a perfluoronitrosoalkane under pressure. To obtain high polymers (see Group IV(a)) the minimum pressure is 30 atmospheres absolute. At pressures up to 60 atmospheres a temperature of 100 DEG C. is needed; above 60 atmospheres the minimum temperature is 50 DEG C.