On the kinetics and mechanism of thermal degradation of poly(p-methylstyrene)

The thermal behavior of polydisperse poly(p-methylstyrene) (PPMS) samples with M?_w's of 99200 and 356000 g/mol was investigated under oxygen-free conditions at temperatures between 220 and 345°C. The reaction products were analysed by gel permeation chromatography (GPC), gas chromatography (GC) and swelling measurements. In the initial stage of the reaction crosslinking occurs; at higher temperatures the gel decomposes to polymers with a low degree of polymerization and to volatile products with molecular weights in the range up to trimers. A radical chain mechanism is proposed for degradation which explains the experimental results. On this basis a model is evaluated for gel formation, which is discussed in detail. The results of the present investigation are compared with the thermal degradation of polystyrene (PS) which is chemically similar but does not crosslink.