Autoxidation of poly‐4‐methylpentene‐1. I. The role of diffusion in autoxidation kinetics

An apparatus is described for the measurement of oxygen uptake into a polymer sample at constant oxygen pressures in the range 20–1000 mm Hg. Measurements of the rate of oxygen uptake into poly‐4‐methylpentene‐1 show that the rate is accurately first‐order in oxygen pressure over the range 50–800 mm pressure for temperatures ranging from 122 to 154°C and film thickness in the range 0.001–0.025 cm. A theoretical treatment of the kinetics of a reaction in which oxygen diffuses into both faces of a thin film, in which it is consumed by a first‐order reaction shows that the oxidation rate ρ per unit area of film surface is given by ρ = ρ∞ tanh ßL/2 where ρ∞ is the limiting oxidation rate for a thick film, L is the film thickness, and ß = (k/D)1/2, k being the oxidation rate constant and D the diffusion constant. Values of D and the activation energy for diffusion calculated from autoxidation data are in good agreement with values determined directly.