Patent ID: 7186783

Claim:
A process for preparing a partially hydrogenated block copolymer having at least one partially hydrogenated polybutadiene block, the entire block copolymer comprising no more than 3 mol % 1,2-butadiene recurring units (A) and no more than 3 mol % ethylene recurring units (D), calculated on the total content mol/mol of recurring units, wherein a block copolymer comprising 1,2-butadiene recurring units (A) and 1,4-butadiene recurring units (B) is hydrogenated in the presence of hydrogen, a metal based metallocene compound as hydrogenation catalyst represented by the general formula: L 2 MX 2 wherein M represents the metal selected from the group consisting of titanium, zirconium and hafniu; each X independently is selected from hydrogen, C 1 –C 12 hydrocarbon groups, C 1 –C 12 hydrocarbonoxy groups, C 1 –C 12 hydrocarbonylsilyl groups, halogens and carbonyl groups; and wherein each L is selected from the group consisting of pentamethylcyclopentadienyl, 1-trimethylsilylindenyl, 2-methylindenyl; 1,2-dimethylindenyl; 2-phenylindenyl; 1,3-dimethylindenyl; 1,3-di(tert-butyl)indenyl; 2-tertbutylindenyl; and 1,2,3-trimethylindenyl, and a cocatalyst, wherein the hydrogenation catalyst has a reaction rate ratio of r1/r2 greater than 5, wherein r1 and r2 are the hydrogenation rates of recurring units (A) and (B) respectively at the same reaction conditions, the cocatalyst is an alkali metal hydride, and hydrogenation of the butadiene is carried out until at least 97% of recurring units (A) have been hydrogenated.