Samples of a series of fluorine-containing copolymers have been studied by pyrolytic gas chromatography. In the volatile products of pyrolysis of polymers containing ethylene and hexafluoropropylene units at least three “hybrid” fluorine-containing compounds are present-vinylidene fluoride, tetrafluoropropylene and 1-trifluoro-methyl-1,2,2,-triflurocyclobutane. The basic scheme of rupture of the main C - C bonds on pyrolysis of these polymers is proposed. The optically transparent terpolymer of tetrafluoroethylene, ethylene and hexafluoropropylene constitutes a regularly alternating terpolymer in which the perfluorinated tetrafluoroethylene or hexafluoropropylene units are between the ethylene units.