Hydrogenation of natural rubber latex in the presence of [Ir(cod)(PCy3)(py)]PF6

Natural rubber latex (NRL) is comprised of cis-1.4-polyisoprene as the major component which has poor resistance to oxidation and degradation by ozone and long-term heating due to the presence of carbon-carbon double bonds in the polymer backbone. Hydrogenation is a useful method, for improving the oxidative and thermal degradation resistance of diene-based polymers. Hydrogenation of NRL was carried out and the degree of hydrogenation was determined via a H-1 NMR spectroscopic technique. Kinetic data were collected using a computer controlled gas-uptake apparatus in terms of hydrogen consumption as a function of time. The kinetic results indicated that the hydrogenation of NRL catalyzed by [Ir(cod)(PCy3)(py)]PF6 exhibited a first-order dependence on hydrogen pressure and first-order dependence with respect to catalyst concentration and an apparent inverse behavior with respect to rubber concentration due to the effect of impurities present in the NRL. Acid addition helped to suppress the poisoning of the catalyst by impurities. The apparent activation energy of the hydrogenation of NRL was calculated to be 31.8 kJ/mol. A mechanism for the hydrogenation of the NRL was also proposed. (C) 2008 Elsevier B.V. All rights reserved.