Polymer hydrogenation process

An improved process for the selective hydrogenation of the carbon-carbon double bonds in a copolymer of a conjugated diene and one or more copolymerizable monomers which comprises hydrogenating said copolymer at a temperature of from about 40.degree. to about 170.degree. C. and at a pressure of hydrogen of from about 0.05 to about 7 MPa, the improvement being that said hydrogenation is carried out in the presence of (i) from about 0.05 to about 20 percent by weight of a catalyst which is a monovalent rhodium hydride complex of the general formula RhH(L.sub.1).sub.x in which x is 3 or 4 and L.sub.1 is a first ligand compound, (ii) from about 1 to about 25 percent by weight of a second ligand compound L.sub.2 and (iii) a solvent for said copolymer, said (i) and said (ii), the weights of said (i) and (ii) being based on the weight of said copolymer and the weight ratio of (ii):(i) being from about 0.1:1 to about 20:1, wherein L.sub.1 and L.sub.2 may be the same or different ligand compounds which when x is 4, are phosphorus compounds selected from 5-phenyl-5H-dibenzophosphole and compounds of the formula PR.sub.1 R.sub.2 R.sub.3 and when x is 3, are arsenic or antimony compounds of the formula MR.sub.1 R.sub.2 R.sub.3 wherein M is arsenic or antimony, and wherein R.sub.1, R.sub.2 and R.sub.3 may be the same or different and are selected from CH.sub.3, C.sub.2 H.sub.5, C.sub.6-10 aryl groups and C.sub.7-12 aralkyl groups.