ON THE REACTIVITY OF C60 FULLERENE WITH DIENE RUBBER MACRORADICALS. I. THE CASE OF NATURAL AND SYNTHETIC CIS-1,4-POLYISOPRENE UNDER ANAEROBIC AND THERMOOXIDATIVE DEGRADATION CONDITIONS

C60 fullerene has been studied as thermal stabilizer and as antioxidant of both natural rubber (cis-1,4-polyisoprene) and synthetic cis-1,4-polyisoprene. The study has been conducted respectively under nitrogen flow and under air flow by simultaneous thermogravimetric analysis and differential thermal analysis (TGA-DTA) on rubber samples containing known quantities of fullerene in comparison to a “blank” of pure rubber. The results show that C60 fullerene (in absence of oxygen) is a thermal stabilizer of cis-1,4-polyisoprene because it reacts with the polyisoprene macroradicals formed by the thermally-induced chain scission reaction slowing down the degradation reaction. Conversely, under thermo-oxidative degradation conditions (in air flow) fullerene C60 acts as an antioxidant for cis-1,4-polyisoprene, provided that the heating rate of the samples is slow (5°/min). At higher heating rates (20°C/min) C60 does not show any antioxidant effect.