A novel kind of Sm(Ⅲ) complex with 2-mercaptobenzimidazole was prepared.The antioxidative properties and mechanism of the Sm(Ⅲ) complex in the natural rubber (NR) vulcanizates was investigated by attenuated total-reflectance Fourier transform infrared (FTIR-ATR) spectroscopy and thermogravimetric analysis.The thermo-oxidative stability of the NR vulcanizates was found to be improved markedly by the addition of the Sm(Ⅲ) complex.The FTIR-ATR results showed that the Sm(Ⅲ) complex retarded aging and allowed the oxidation products to increase more slowly.The Sm(Ⅲ) complex had no effect on the thermal decomposition of the NR vulcanizate

but it improved the thermo-oxidative stability significantly.The antioxidant effect of the Sm(Ⅲ) complex was superior to that of antioxidant MB and antioxidant 4010NA.It could be attributed to the thioether bonds which can decompose the hydroperoxide and the Sm(Ⅲ) ions which can capture and inactivate the oxy radicals.The apparent thermo-oxidation activation energy (E) of the NR vulcanizates was calculated by the Kissinger and Flynn-Wall-Ozawa methods

respectively.The results showed that the NR vulcanizate with the Sm(Ⅲ) complex had higher thermo-oxidation activation energy than that of the samples with antioxidant MB and antioxidant 4010NA.