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SynopsisVacuum pyrolysw of thin samples of polytetrafluoroethylene follows firsborder kinetics wit,h monomer aa the only important decomposition product in the temperature range 360-510°C. The rate constant for vacuum pyrolysis is independent of both the melt viscosity and the type of polymer and is characterized by an activation enthalpy of 83.0 kcal./mole and a frequency factor of 3 X lo1$ set.-'. The molecular weight is found to decrease during pyrolysis. A plausible reaction mechanism consistent with these facts involves random chain cleavage, depropagation with short kinetic chain length, and termination by disproportionation. For thick samples the rate of vacuum pyrolysis is controlled by diffusion of monomer. The course of pyrolysis is changed by the presence of monomer or gaseous pyrolysis products. Accumulation of monomer reduces the rate of pyrolysis as measured by the weight loss and resultr, in formation of a waxy product consisting of low molecular weight fluorocarbons.

Improved methods for measuring weight‐ and number‐average molecular weight of polymers soluble only at elevated temperatures are applied to selcted samples of polyethylene. For two samples of essentially linear polyethylene, number‐average molecular weights by cryoscopy are 11,500 and 13,000, and weight‐average molecular weights by light scattering are 144,000 and 175,000. For samples of branched Fawcett‐type polyethylene, number‐average molecular weights are in the range 10,000–19,000 and weight‐average molecular weights are between 300,000 and 700,000. For one sample each of branched and essentially linear polyethylene it is demonstrated that light scattering measurement in three solvents gives the same molecular weight: no evidence is found for the “association” of these samples of polyethylene in thermodynamically poor solvents. It is thus demonstrated that association is not observed for all samples of polyethylene in dilute solution in α‐chloronaphthalene.