| Abstract: | Hydrogenation is an important method of chemical modification, which improves the physical, chemical, and thermal properties of diene elastomers. Natural rubber latex (NRL) can be quantitatively hydrogenated to provide a strictly alternating ethylene–propylene copolymer using a homogeneous osmium catalyst OsHCl(CO)(O2)(PCy3)2. A detailed kinetic investigation was carried out by monitoring the amount of hydrogen consumption during the reaction using a gas‐uptake apparatus. The kinetic results of NRL hydrogenation indicated that this system had a second‐order dependence of the hydrogenation rate on hydrogen pressure and then decreased toward a zero‐order dependence for hydrogen pressures above 13.8 bar. The hydrogenation was also observed to be first‐order with respect to catalyst concentration and inverse first‐order on rubber concentration due to impurities present in the rubber latex. Additions of a controlled amount of acid demonstrated a beneficial effect on the hydrogenation rate of NRL. The temperature dependence of the hydrogenation rate was investigated and an apparent activation energy (over the range of 120–160°C) was calculated as 57.6 kJ/mol. Mechanistic aspects of this catalytic process are discussed on the basis of kinetic results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 640–655, 2006 |
