Structural transformations in the oxidation of isotactic polypropylene

Abstract

Structural rearrangements accompanying the thermal oxidation of isotactic PP with different molecular masses and molecular mass distributions were studied. The structure of virgin and oxidized PP specimens was examined using X-ray diffraction, DSC, and IR spectroscopy. It was shown that the thermal oxidation of the polymers results in the annealing of crystals and conformational reorganization of interlamellar tie chains in amorphous regions. The contribution of both processes depends on the initial molecular structure and is associated with the kinetics of oxygen uptake and buildup of polymer oxidation products. The PP sample in which conformational G --> T transitions in interlamellar tie chains prevail and the chains are enriched in stretched conformers is oxidized at a lower rate than the sample with a prevalent annealing of crystallites. In turn, the thermooxidative degradation of tie chains facilitates the annealing and thickening of crystallites