THE INFLUENCE OF TEMPERATURE AND CATALYST RESIDUES ON THE DEGRADATION OF UNSTABILIZED POLYPROPYLENE

The influence of temperature and of residues of a TiCl3-based polymerization catalyst on the oxidation rate of polypropylene was determined. The plots of the logarithm of the induction period versus the reciprocal temperature (Arrhenius plot) are curved. The influence of the concentration of the polymerization catalyst on the stability depends on the degradation temperature. At 50-degrees-C polymers containing less than 2 or 8 ppm of a killed Ti polymerization catalyst show a longer induction period than polymers containing 64 and 180 ppm Ti. At 130-degrees-C there is almost no difference in the stability of these four different polymers. The different influences for the different polymers at high and low temperatures as well as the curvature of the Arrhenius plots can be explained assuming a change in the hydroperoxide decomposition mechanism. The hydroperoxide decomposition is probably thermal at high temperature and Ti-catalysed at low temperature.