Hydrogenation of synthetic rubber cid-1-4-polyisoprene and nutural rubber catalyzed by ruthenium (II) complex

Abstract

Hydrogenation is a useful method, which has been used to improve oxidative, and thermal degradation resistance of diene based polymers. A detailed study of the homogeneous hydrogenation of cis-1,4-polyisoprene (CPIP), natural rubber (NR) and natural rubber latex (NRL) using Ru(CH=CH(Ph))CI(CO)(PCy₃)₂ as catalyst was carried out by monitoring the amount of of hydrogen consumed during reaction. The hydrogenation rate of CPIP, NR and NRL followed pseudo first order kinetics in double bond concentration up to high conversions of double bond, under all sets of studied conditions. The kinetic results suggested a first-order behavior with respect to total catalyst concentration as well as with respect to hydrogen pressure. An inverse first order dependence on added PCy₃ was observed in hydrogenation of CPIP and NR. The addition of a small amount of p-toluenesulfonic acid to the reaction system led to a substantial increase in the reaction rate. However, the presence of impurities in natural polymer seems to decrease the catalyst activity of the Ru complexes. Mechanistic aspects of the catalytic process are discussed. A numerical analysis of a continuous process for CPIP hydrogenation is also presented. Infrared and ¹H-NMR spectroscopic measurements confirmed the final degree of hydrogenation. The composition of hydrogenated product was characterized by ¹³C-NMR spectroscopy. The quantitative hydrogenation of polyisoprene leads to an alternating ethylene-propylene copolymer. The thermal properties of the hydrogenated polymer were characterized. The results show that the hydrogenation can increase thermal stability of rubber without affecting its glass transition temperature.