Spectroscopic Study of Di-Imide Hydrogenation of Natural Rubber

The diimide hydrogenation of natural rubber (NR) was studied by using p-toluenesulfonylhydrazide (TSH) as a diimide-releasing agent. The microstructure and the percentage of hydrogenation were studied by Raman, ¹H-NMR and ¹³C-NMR spectroscopic techniques. Quantitative measurements on fraction of hydrogenated part gave the results in good agreement by using these techniques. The results indicated that percent hydrogenation increased with increasing of reaction time and about 80-85 % hydrogenation was achieved when a two-fold excess of TSH was used. The vibrational characteristic of C=C bond of NR is strongly Raman active and noted at 1663 cm⁻¹. The decrease of this signal was clearly observed during the progress of hydrogenation but the vibrational frequency of the cis and trans structures of the trisubstituted olefin unit of NR can not be differentiated by this technique. While ¹H- and ¹³C-NMR analysis showed that cis-trans isomerization of carbon-carbon unsaturation of NR occurred during hydrogenation.