Process for preparaing partially hydrogenated butadiene polymers
The present invention relates to a process for preparing a partially hydrogenated butadiene polymer 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 butadiene polymer comprising 1,2-butadiene recurring units (A) and 1,4-butadiene recurring units (B) is hydrogenated in the presence of hydrogen and a titanium-, zirconium- and/or hafnium-based metallocene compound as hydrogenation catalyst and a cocatalyst, characterized in that: a) 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, b) the cocatalyst is an alkali metal hydride, added as such or prepared in situ, and c) hydrogenation of the conjugated diene is carried out until at least 97% of recurring units (A) have been hydrogenated.
1. 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.
2. The process of claim 1 wherein the partially hydrogenated block copolymer has at least two styrene end blocks and at least one hydrogenated polybutadiene midblock.
3. The process of claim 2 wherein the partially hydrogenated block copolymer is a polystyrene-partially hydrogenated polybutadiene-polystyrene linear block copolymer.
4. The process of claim 1 wherein the block copolymer comprises from 10 to 90 wt. % of vinyl aromatic compounds prior to hydrogenation.
5. The process of claim 1 wherein the polybutadiene block comprises from about 25 to about 80% of the 1,2-structure.
6. The process of claim 1 , wherein the alkali metal hydride is lithium hydride.
7. The process of claim 1 , wherein the initial molar ratio of cocatalyst to hydrogenation catalyst is between 2 and 100.
8. The process of claim 8 , wherein M is titanium.
9. The process of claim 1 wherein the hydrogenation is conducted at a hydrogenation pressure between 1 and 70 kg/cm2 and a reaction temperature of between 20 and 150° C.