Novel process strategy for tandem hydrogenation of nitrile butadiene rubber: Simultaneous nitrile and olefin reduction with mitigated gelation

This study presents the successful tandem hydrogenation of nitrile (C≡N) and olefinic (C═C) groups in acrylonitrile butadiene rubber using a rhodium hydrido complex, RhH[P(i-Pr)₃]₃, under mild conditions (60°C, 500 psig H₂). A novel catalytic system was established to achieve the simultaneous reduction of both functional groups in a macromolecular polymer for the first time. The nitrile content was reduced from 40% to below 10%, while olefinic groups were hydrogenated to over 95% conversion within 5 h. Fourier transform infrared spectroscopy analyses confirmed selective conversion of nitriles to primary amines without forming secondary amine byproducts. Gel formation, a critical challenge in polymer hydrogenation, was mitigated using triphenylphosphine, which selectively terminated nitrile hydrogenation while allowing olefin reduction to proceed, thereby suppressing cross-linking. A proposed reaction mechanism highlights the dual functionality of the catalyst, involving sequential hydrogen activation and substrate interaction. This work provides a novel, efficient route for modifying nitrile butadiene rubber to enhance thermal and chemical resistance while retaining processability, and holds potential for applications in high-performance elastomer industries.