Catalytic hydrogenation of methyl methacrylate-g-natural rubber (MMA-g-NR) in the presence of OsHCl(CO)(O2)(PCy3)2 Original Research Article

The graft copolymerization of methyl methacrylate onto natural rubber (NR) was carried out by using cumene hydroperoxide as redox initiator. The monomer conversion, grafting efficiency, and graft copolymer composition were examined. The purified graft copolymer was then hydrogenated by using a homogeneous osmium catalyst, OsHCl(CO)(O2)(PCy3)2. The purified graft copolymer and hydrogenated graft copolymer samples were characterized by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. A detailed kinetic investigation of the hydrogenation was carried out by monitoring the amount of hydrogen consumption using a gas-uptake apparatus. The kinetic results for the hydrogenation of graft natural rubber indicated that the rate of hydrogenation exhibited a first-order dependence on the catalyst concentration. The hydrogenation exhibited a first-order dependence on hydrogen pressure which then decreased toward a zero-order dependence at higher hydrogen pressure. The addition of a small amount of acid provided a beneficial effect on the hydrogenation of grafted natural rubber. The hydrogenation rate was dependent on the reaction temperature and the apparent activation energy over the range of 120–160 °C was found to be 70.3 kJ/mol. The mechanistic aspects of these catalytic processes are discussed based on the observed kinetic results. Thermal properties of the grafted copolymer and hydrogenated grafted copolymer were also determined.