New perfluorinated vinyl ethers containing a secondary hydrogen atom in the molecule of the formula I ##STR1## in which n is 0-5, preferably 0-3 and particularly 0-2, are useful intermediate products (particularly for the preparation of polymeric intermediates and of perfluorinated cation exchangers containing carboxyl groups) and are prepared by(a) reacting 3-H-perfluorobutyryl fluoride IIFOC--CF.sub.2 --CHF--CF.sub.3 (II)with hexafluoropropene epoxide III ##STR2## to give the acid fluoride IV ##STR3## in which n has the same meaning as in formula I, (b) pyrolyzing the acid fluoride IV, as such or after conversion into the corresponding alkali metal carboxylate, at elevated temperature and(c) isolating the vinyl ether I formed in the pyrolysis.