Dependence of tacticity distribution in thermal oxidative degradation of polypropylene

Thermal oxidative degradation behavior of two kinds of polypropylene (PP) with different tacticity distribution was investigated based on the data obtained by NMR, temperature rising elution fractionation (TREF) and thermogravimetric analysis (TGA). Although these PPs have similar molecular weights and tacticity, the behavior of degradation was considerably different. The differences were found to be due to the tacticity distribution by TREF measurement. In order to investigate the effect of tacticity distribution on the degradation in more detail, the more stable PP having a broad tacticity distribution was divided into four kinds of tacticity fraction by TREF, and each of degradation behavior was investigated by TGA. The results indicated that the rate of degradation systematically depended on the tacticity. The higher stability of PP with the broader tacticity distribution would be originated from the abstraction reaction of tertiary hydrogen, which was the rate-determining step in PP degradation reaction.