Abstract
Rhodium catalysts are effective catalysts for catalytic hydrogenation of unsaturated polymers in aqueous media under optimum conditions. Hydrogenation of a nanosized polyisoprene (PIP) emulsion was carried out in a Parr reactor. Rhodium trichloride (RhCl3⋅3H2O) and different ligand types, triphenylphosphine (PPh3), trisulfonated triphenylphosphine (TPPTS) and monosulfonated triphenylphosphine (TPPMS) were used as a catalyst precursor. The hydrogenated PIP (HPIP) was characterized by proton nuclear magnetic resonance spectroscopy (1H NMR). Low conversions of CC were observed when RhCl3/PPh3 or RhCl3/TPPTS was used as catalyst precursors, however, 96.0% hydrogenation (HD) was achieved when using RhCl3/TPPMS. The Hartley ionic spherical micelle model was proposed to explain the catalytic behavior. The process variables did not affect PIP particle size after hydrogenation. Mechanistic aspects of the hydrogenation of PIP in the presence of RhCl3/TPPMS were proposed on the basis of the observed kinetic results. Kinetic experiments for PIP hydrogenation in aqueous media indicate that the hydrogenation rate is first order with respect to catalyst and carbon–carbon double bond concentration. The hydrogenation rate was dependent on catalyst concentration, temperature and hydrogen pressure, and PIP particle size. The apparent activation energy over the temperature range of 120–140°C was found to be 117.0kJ/mol. HPIP (96%HD) has high thermal stability with a maximum decomposition temperature of 462°C and a glass transition temperature of −49°C. Dynamic mechanical analysis indicated that HPIP had a maximum storage modulus due to the saturated carbon domains of the ethylene segments in the polymer chains.
Published Version
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