Structure and properties of hydrogenated natural rubber latex using OsHCI(CO)(O[subscript 2])(PCy[subscript 3])[subscript 2] as a catalyst and dimide reduction

Abstract

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 in the polymer backbone. Hydrogenation is a useful method, which has been used to improve oxidative, and thermal degradation resistance of dience based polymers. The purpose of the present work is to study the hydrogenation of NRL via three systems: homogenous catalytic hydrogenation, noncatalytic hydrogenation and diimide hydrogenation. The level of hydrogenation was determined via a [superscript 1]H-NMR spectroscopic technique. For homogeneous catalytic hydrogenation, 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 OsHCICO(CO)(O[subscript 2]) (PCy[subscript 3])[subscript 2] and [Ir(cod)(PCy[subscript 3])(py)]PF[subscript 6] exhibited a first-order behavior with respect to catalyst concentration and an inverse behavior dependence on rubber concentration due to impurities present in the rubber. Noncatalytic hydrogenation using p-TSH as reducing agent was also very effective method and it was also found that the degree of hydrogenation increased with increasing ratio of p-TSH /C=C. For diimide hydrogenation, the HNR product was in liquid form and the degree of hydrogenation was increased with increasing effective diimide amount. From TEM micrograph, diimide hydrogenated rubber particle exhibited a layer model for hydrogenation. The thermal stability of NR was improved by hydrogenation. The molecular weight and molecular weight distribution of hydrogenated NR were not changed during hydrogenation. In addition, the mechanical properties and ozone resistance of vulcanized HNR blends were also investigated.