Hydrogenation of unsaturated rubbers using diimide as a reducing agent

The hydrogenation of natural rubber (NR) and various epoxidized natural rubbers (ENR) was investigated by using diimide generated in situ from the thermal decomposition of p-toluenesulfonylhydrazide (TSH) in o-xylene solution at 135°C. ¹H-NMR analysis indicated that approximately 85-95% of hydrogenation was performed with a twofold excess of TSH. FT-IR and Raman spectroscopy were employed to confirm the microstructure characteristics of the hydrogenated rubbers. The cis-trans isomerization was also observed by ¹H- and ¹³C-NMR. The signal in ¹H-NMR of the epoxide group of the ENR disappears after hydrogenation while the signal of the opened epoxide ring product was detected. This may be due to the epoxide ring opening reaction caused by the p-toluenesulfinic acid by-product. The high temperature of the reaction condition leads to chain degradation in both NR and ENR. Thermal behaviors of the hydrogenated rubbers characterized by differential scanning calorimetry showed that the glass transition temperatures of the hydrogenated rubbers were increased about 10-20°C compared with the starting rubbers.