Teflon and tetrafluoroethylene photopolymers, on pyrolysis in a vacuum at 423.5° to 513.0° C, yield almost 100 percent of monomer. The rate of formation of monomer at any given temperature follows a first-order reaction and is independent of the method of preparation of polymer or its initial average molecular weight. The activation energy was determined by a pressure method and a weight method, and a value of 80.5 kcal was found by both methods. A preliminary heating of Teflon in air at 400° to 470° C did not change appreciably its rate of degradation into monomer when it was subsequently heated in a vacuum. Polyvinyl fluoride, 1, 1-polyvinylidene fluoride, and polytrifluoroethylene were pyrolized in the range 372° to 500° C. The volatiles consisted in all cases of HF and a wax-like material consisting of chain fragments of low volatility. Polyvinyl fluoride and polytrifluoroethylene degrade to complete volatilization, whereas 1,1-polyvinylidene fluoride becomes stabilized at about 70-percent loss of weight. The rate-of-volatilization curves indicate a first-order reaction for polyvinyl fluoride, a zero-order reaction for trifluoroethylene, and an undetermined order for 1, 1-polyvinylidene fluoride. The order of thermal stability for these polymers, as compared with polymethylene, is as follows: Polyvinyl fluorideÉ46polymethyleneÉ46polytrifluoroethyleneÉ461,1-poly vinylidene fluorideÉ46polytetrafluoroethylene.