Hydrogenation of natural rubber in the presence of OsHCL(CO)(O₂)(PCY₃)₂: Kinetics and mechanism

Abstract

ABSTRACT:The homogeneous catalyst precursor, OsHCl-(CO)(O 2 )(PCy 3 ) 2 , was utilized for the hydrogenation of natural rubber to convert the unsaturated structure to a saturated form, providing an alternating ethylene-propylene copolymer. A detailed kinetic investigation was carried out by monitoring the amount of hydrogen consumption during the reaction using a gas-uptake apparatus.1 H NMR spectroscopy was used to determine the final olefin conversion to the hydrogenated product. Kinetic data, collected according to a statistical design framework, defined the influence of catalyst and polymer concentration, hydrogen pressure, and reaction temperature on the catalytic activity. The kinetic results indicated that the hydrogenation rate exhibited a first-shifted to zero-order dependence on hydrogen at lower hydrogen pressure, which then decreased toward an inverse behavior at pressures higher than 41.4 bar. The hydrogenation was also observed to be first-order with respect to catalyst concentration, and an apparent inverse dependence on rubber concentration was observed due to the impurities in the rubber. The hydrogenation rate was dependent on reaction temperature, and the apparent activation energy over the temperature range of 125-145°C was found to be 122.76 kJ/mol. Mechanistic aspects of the hydrogenation of natural rubber in the presence of OsHCl(CO)(O 2 )(PCy 3 ) 2 were proposed on the basis of the observed kinetic results. The addition of some acids and certain nitrogen containing materials showed an effect on the hydrogenation rate. The thermal properties of hydrogenated natural rubber indicated that the thermal stability increased with increasing % hydrogenation of the rubber.

Improving thermal and ozone stability of skim natural rubber by diimide reduction

“…Thus, the two glass transition temperatures observed for HSNR confirmed the layer model morphology for the hydrogenation as discussed in the previous section regarding the TEM study. Compared with the complete HNR produced from hydrogenation in the presence of OsHCl(CO)(O 2 )(PCy 3 ) 2 , all DSC thermograms of 99% HNR samples indicated the one step base-line shift at À61.8 C [17] and À59.6 C [18]. This implies that the HNR prepared from catalytic hydrogenation has a single glass transition temperature.…”

“…[15][16][17][18][19], the extent of hydrogenation increased with increasing rubber concentration up to 0.55 M and then decreased. At high rubber concentration, the diimide species may self-decompose during the hydrogenation process resulting in a low degree of hydrogenation.…”

Synthesis of polybutadiene-silica nanoparticles via differential microemulsion polymerization and their hydrogenated nanoparticles by diimide reduction

“…The C]C of the rubber are sensitive to oxygen, ozone and heat resulting in rubber degradation and the reduction of mechanical and thermal properties. Hydrogenation of diene-based rubbers is an important process to obtain hydrogenated rubber and improve their thermal properties and oxidative stability while maintaining their elastomeric properties [12]. NR latex was hydrogenated by diimide reduction, using hydrazine and hydrogen peroxide with copper sulfate as catalyst.…”

Hydrogenated natural rubber blends: Aspect on thermal stability and oxidative behavior

“…11,15 A specific amount of NR (ca. 612.7 mM) dissolved in 1,200 mL of toluene with a small amount of 3-CPA (5 mM) was hydrogenated in a 2-L Parr reactor.…”

“…[9][10][11][12] It has been shown that the structure of NR is changed from cis-1,4-polyisoprene to an alternating ethylene-propylene copolymer upon hydrogenation, which has higher thermal stability without affecting the inherent glass transition temperature of NR. [11][12][13] Although the kinetics of NR hydrogenation and thermal properties of hydrogenated NR (HNR) have been investigated, there are few literature reports on the measurement of any technological properties of HNR vulcanizates and rubber blends containing HNR. Inoue and Nishio 14 studied NR hydrogenation catalyzed by RhCl(PPh 3 ) 3 at 70-80 C and 100% hydrogenation was achieved within 96 h. For their HNR materials, the mechanical properties of the HNR vulcanizates after aging were higher than NR and EPDM vulcanizates.…”