AQUEOUS-PHASE HYDROGENATION OF NANOSIZED POLYISOPRENE EMULSION AND NATURAL RUBBER LATEX USING RHODIUM CATALYSTS

A water-soluble rhodium catalyst is an efficient catalyst for hydrogenation of unsaturated polymers in the absence of organic solvent. Natural rubber (NR) latex and nanosized polyisoprene (PIP) emulsion were hydrogenated using rhodium complexes (RhCl3/PPh3, RhCl3/TPPTS and RhCl3/TPPMS) as a catalyst precursor. A high hydrogenation degree (HD) (85.8% for NR, 96.0% for PIP) was achieved by using RhCl3/TPPMS. The catalytic behavior could be well explained by the Hartley ionic spherical micelle model. The HD increased with increasing catalyst amount, reaction temperature and H2 pressure. The catalyst activity in NR hydrogenation was found to be lower than that in PIP hydrogenation for all conditions due to impurities in the latex, including protein. Kinetic experiments for PIP hydrogenation indicate that the hydrogenation rate is first order with respect to catalyst and carbon– carbon double bond concentration. The rate constant 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 117.0 kJ/mol. The hydrogenated NR (HNR) and PIP (HPIP) has high thermal stability with a maximum decomposition temperature of 466 and 462ºC, respectively. In addition, HNR and HPIP had a maximum storage modulus due to the saturated carbon domains in the polymer chains. For vulcanized NR, the thermal and ozone resistance of NR could be improved by using HPIP as filler.