Process for selective hydrogenation of conjugated diene polymer

A process for selective hydrogenation of a conjugated diene polymer, the conjugated diene polymer being a homopolymer of a conjugated diene, a copolymer of two or more conjugated dienes or a copolymer of at least one conjugated diene and at least one vinyl aromatic hydrocarbon, said process comprising bringing the conjugated diene polymer in an inert organic solvent into contact with hydrogen in the presence of a hydrogenation catalyst combination to selectively hydrogenate the unsaturated double bonds in the conjugated diene units of the conjugated diene polymer,

• wherein the hydrogenation catalyst combination includes at least one catalyst (A) and at least one catalyst (B),
• wherein the catalyst (A) is an unsubstituted or substituted bis(cyclopentadienyl) Group VIII transition metal compound, which is represented by the following formula:
• (C.sub.5 R.sub.n R'.sub.5-n)(C.sub.5 R.sub.m R".sub.5-m)M
• wherein
• R, R' and R" are the same or different and are selected from the group consisting of hydrogen, C.sub.1 -C.sub.8 alkyl and alkoxy groups, C.sub.6 -C.sub.8 aryl and aryloxy groups, C.sub.6 -C.sub.8 cycloalkyl and cycloalkoxy groups, C.sub.1 -C.sub.5 hydroxyalkyl groups, aldehyde groups, carboxyl groups, silyl groups,
• m and n are integers independently from 0 to 5,
• C.sub.5 R.sub.n R'.sub.5-n and C.sub.5 R.sub.m R".sub.5-m are the same or different unsubstituted or substituted cyclopentadienyl groups,
• M is a Group VIII transition metal selected from the group consisting of cobalt, nickel, rhodium, palladium, platinum and iridium,
• wherein the catalyst (B) is an organic lithium compound having at least one lithium atom or is lithium hydride,
• wherein the organic lithium compound is selected from the group consisting of R"'Li and R"'Li.sub.2,
• wherein R"' is a C.sub.1 -C.sub.30 hydrocarbon moiety or a polymeric moiety,
• wherein the molar ratio of lithium atom to M atom is from 0.1 to 100.