The Catalytic Degradation Reaction of Polypropylene with Silica–Alumina

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Abstract
A detailed analysis was carried out on the catalytic degradation of polypropylene with silica–alumina, using a glass tube reactor (25φ×150 mm) at 180 to 300 °C and a N2 flow rate of 120 ml min−1 over a period of 5 to 120 minutes. The ratio of C/S was from 0.1 to 6.0. The molecular weight of PP decreased slightly at about 160 °C by cationic degradation, but the decrease started at about 200 °C by radical degradation (without catalyst). The main chain of PP was remarkable weakened by the catalytic degradation with silica–alumina. Analysis of degradation products by 13C NMR, FD-MS and variation in chain scission number clearly indicated the catalytic degradation of PP to occur in two stages. The first stage at low temperature is initiated by the addition of a proton released from the catalyst to weak links in the main chain. The second stage at high temperature occurs by attack a low-molecular-weight carbonium ion of the saturated degraded oligomer. These ions are closely involved in the production of irregular structural oligomers and their redegradation.