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

C-60 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 C-60 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 C-60 acts as an antioxidant for cis-1,4- polyisoprene, provided that the heating rate of the samples is slow (5 degrees /min). At higher heating rates (20 degreesC/min) C-60 does not show any antioxidant effect.