Inhibition of thermo-oxidative degradation of poly(methyl methacrylate) and polystyrene by C 60

Abstract

Investigations were made on the effects of C 60 on the degradation of poly(methyl methacrylate) (PMMA) and PSt in the stream of helium having 0.06% of oxygen and in dynamic oxygen by differential scanning calorimetry (DSC) method and under oxygen at 282 and 238°C for the case of PMMA and PSt, respectively, by thermogravimetric method. It was shown that C 60 retards the degradation of the polymers. By thermogravimetry it was demonstrated that in the presence of fullerene, induction periods on the curves of dependence of weight loss of polymers on time of degradation, rise substantially. By DSC method it was illustrated that C 60 considerably increases the temperatures of the onset of polymers degradation. The degradation of PMMA and PSt at elevated temperatures in the presence of small amounts of oxygen is assumed to be the purely thermal degradation initiated by decomposition of small quantities of formed polymeric hydroperoxides in addition. The suggestion was made that in this case, the retarding effect of C 60 is connected with its interaction with macroradicals R • with formation of less active compounds. The correlation between the rate of the depropagation reaction of R • and the rate of their interaction with oxygen was estimated in the PMMA degradation at different temperatures and concentrations of oxygen in the polymer. The retarding influence of oxygen on the PMMA depropagation rises with an increase in oxygen concentration in the polymer and with a decrease in the degradation temperature. It was supposed that in the thermo-oxidative degradation of PMMA at elevated temperatures, the inhibiting effect of C 60 is due to its interaction with R • and oxygen-containing radicals with formation of less active compounds. In the case of PSt retarding influence of fullerene is mainly connected with its reaction with oxygen-containing radicals, but the interaction of C 60 with R • must not be ruled out.