The mechanism of the depolymerization of polytetrafluoroethylene with pyrolytic and radiolytic initiation

T he rate of decom lJOsition of pol ytetraAuoroethylene, exposed to gamma radiation in a Aowing helium at mosp here, was studied in th e range of te mperatures 330 to 450 C, dose rates 0.1 to 7.6 MR/h, and sa mp le thi c kn esses 0.0006 to 0.01 e m. Rate meas ureme nts were made with a the rmal co nductivity ce ll in th e exit strea m, which recorded essentially th e diffe re nce between the thermal and radiation ind uced rate, in total molec ul es of volatiles per seco nd. At te mpe ratures below about 400 C, th e vo lati le products were a complex mixture. Above 400 C, tetraAuoroethylene was the major product, and the radiationinduced rate had a n activation e nergy' of 70 to 84 kJ / mol. The radiati on-indu ce d rate is proportional to square root of dose rate, after appropriate allowance for the thermal in itiat ion is mad e. Analysis of the res ult s s ugges ts that th e rate of th e the rmal initiation has a very hi gh preexpone ntial factor, 10'" to 10"0 s-' . Th e activation e ne rgy [or te rmination is large, E. > 155 kJ/ moJ. Diffus ion and reverse reaction appear to be minor fac tors above 400 C, but a surface reaction may be important. Th e th ermal decomposition mec hani sm see ms dearly to co ns ist" of rand om initiation, termination by bimol ec ular reco mbinati o n and a short kinetic c hain (13 at 480 C).