The Application of Model Reactions to the Oxidation of Polyolefins

Abstract

Abstract Initial attempts have been made using computational techniques to apply model compound reactions quantitatively to the oxidation of ethylenepropylene copolymers by molecular oxygen at 100° C. The oxidations of n-butane, isobutane, and isopentane (the simplest model of a polypropylene repeat unit) were chosen as models and applied to the prediction of rates and products in the low conversion oxidations of squalane and a series of ethylenepropylene copolymers of differing composition at 100°. For simplicity, these initial calculations were done for a low viscosity fluid phase. For externally initiated reactions, where calculated and experimental rates (mostly amorphous, solid phase) could be compared, agreement was usually within a factor of 3–5, with the calculated rates generally too fast. Our results on both self- and externally initiated systems suggest that the effect of phase change, from liquid to amorphous solid, on the overall oxidation rate is not large, except in a few cases where effects such as chemically induced crystallization may be significant in the solid phase. Calculations for externally initiated oxidations predict that the rate of chain scission is proportional to the rate of radical production in excellent agreement with experimental results. Our initial results indicate that small alkane molecule reactions can be applied usefully, at present with limited accuracy, to the oxidation of hydrocarbon polymers.