Degradation of natural rubber during hydrogenation using RuCl2(PPh3)3

Abstract

Natural rubber with high degree of unsaturation is prone to be thermally and oxidatively unstable. Hydrogenation is one of the practical reactions used to change chemical structure in order to improve both thermal and oxidative properties. In this study, the nature rubber was hydrogenated using RuCI₂(PPh₃)₃ as a homogeneous catalyst. The effects of reaction parameters on the level of hydrogenation i.e., temperature, hydrogen pressure, reaction time, and catalyst amount were investigated. The reaction products were identified by FT-IR and NMR spectroscopy. The percentage of hydrogenation of natural rubber was determinated by NMR spectroscopic analysis. It was found that the extent of hydrogenation increased with increasing temperature, hydrogen pressure, reaction time, and catalyst amount. The optimum condition for hydrogenating 0.5 g natural rubber in toluene 50 ml was found to be 100 ℃ with the hydrogen pressure of 30 bar for 24 hours by using 0.09 g RuCI₂(PPh₃)₃. Hydrogenation of natural rubber as high as 63% was achieved. Molecular weight and molecular weight distribution of hydrogenated products were measured by using GPC. After hydrogenation, its molecular weight decreased and its molecular weight distribution became narrow than those of pre-treated natural rubber. These indicated that chain cleavage occurred during the hydrogenation. From DSC measurement, T(subscript g) of the hydrogenated natural rubber increased about 1-2℃ from the original natural rubber. The thermal stability of hydrogenated natural rubber was improved as shown by TGA.