Thesis (Ph.D.)--Chulalongkorn University, 2004

The structure of natural rubber (NR) 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 normally utilized to enhance the resistance of polymers to thermal and oxidative degradation by reducing the amount of unsaturation in various diene polymers. The purpose of the present work is to study the hydrogenation of NR in the presence of OsHClCO(CO)(O[subscript 2])(PCy[subscript 3])[subscript 2] or [Ir(cod)(PCy[subscript 3])(py)]PF[subscript 6] as a catalyst. The level of hydrogenation was determined via a [superscript 1]H-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 NR catalyzed by both catalysts 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. The apparent activation energy for NR hydrogenation catalyzed by OsHClCO(CO)(O[subscript 2])(PCy[subscript 3])[subscript 2] and [Ir(cod)(PCy[subscript 3])(py)]PF[subscript 6] were 122.8 and 75.6 kJ/mol, respectively. Mechanistic aspects of NR hydrogenation were derived from the kinetic results. The addition of some acids and certain nitrogen containing materials exhibited an effect on the hydrogenation rate. The thermal stability of NR was improved by hydrogenation without affecting its glass transition temperature. The molecular weight and molecular weight distribution of hydrogenated NR were not changed during hydrogenation. In addition, a study of mechanical properties and ozone resistance of hydrogenated NR after vulcanization process was also investigated