Thermal oxidation of isotactic polypropylene synthesized with a metallocene catalyst

The mechanism and kinetics of thermal oxidation of metallocene PP are investigated. It is shown that the rate of oxidation of the samples synthesized at a high temperature (40–70°C) is higher than that of the samples synthesized at a low temperature (20 and 30°C). The composition of oxidation products of PP samples; the kinetics of the accumulation of these products; and changes in structural, thermal, and thermophysical parameters during oxidation are analyzed in detail. Our data indicate that the oxidation of low-temperature samples and the oxidation of high-temperature samples obey different mechanisms. The oxidation of low-temperature samples corresponds to the radical-chain process, in which the intramolecular transfer of kinetic chains prevails. High-temperature samples are characterized by the intermolecular transfer of oxidation kinetic chains, which leads to the degradation of macromolecules. It is inferred that the rate and mechanism of thermal oxidation are determined by the microstructure of polymer chains.