Polymers and copolymers of one or more fluorinated dienes of structure CFX.sup.1 .dbd.CX.sup.2 --O--CX.sup.3 X.sup.4 --O--CX.sup.2 .dbd.CX.sup.1 F, wherein X.sup.1 and X.sup.2 are F, Cl or H, and X.sup.3 and X.sup.4 are F or CF.sub.3, wherein said dienes essentially form cyclic repetitive units, the comonomers used for preparing copolymers being ethylene unsaturated fluorinated compounds. Processes for preparing the fluorinated dienes having said structure which comprise the reaction in solution between one halogenated olefin and one hypofluorite CX.sup.3 X.sup.4 (OF).sub.2, wherein X.sup.3 and X.sup.4 are F or CF.sub.3, and the dehalogenation or dehydrohalogenation of the linear adduct between one hypofluorite molecule and two olefin molecules. The polymers and copolymers of the invention are particularly suitable for preparing coatings for applications at high temperatures.