Viscosity index improver, method for producing same, and oil composition

Abstract

The present invention provides a viscosity index improver that is excellent in an effect of improving a viscosity index and a high-temperature high-shear viscosity of oils, etc. The viscosity index improver of the present invention includes a hydrogenated product of a copolymer containing a constitutional unit (a) derived from an aromatic vinyl compound and a constitutional unit (b) derived from a conjugated diene, a content of a constitutional unit (b 1 ) derived from farnesene in a whole amount of the constitutional unit (b) derived from the conjugated diene being from 1 to 100% by mass, and a content of a constitutional unit (b 2 ) derived from a conjugated diene other than farnesene in a whole amount of the constitutional unit (b) derived from the conjugated diene being from 0 to 99% by mass, and 50 mol % or more of carbon-carbon double bonds in the constitutional unit (b) derived from the conjugated diene being hydrogenated.

1 . A viscosity index improver consisting of a hydrogenated product of a copolymer containing a constitutional unit (a) derived from an aromatic vinyl compound and a constitutional unit (b) derived from a conjugated diene,
 a content of a constitutional unit (b1) derived from farnesene in a whole amount of the constitutional unit (b) derived from the conjugated diene being from 1 to 100% by mass, and a content of a constitutional unit (b2) derived from a conjugated diene other than farnesene in a whole amount of the constitutional unit (b) derived from the conjugated diene being from 0 to 99% by mass, and   50 mol % or more of carbon-carbon double bonds in the constitutional unit (b) derived from the conjugated diene being hydrogenated.   
     
     
         2 . The viscosity index improver according to  claim 1 , wherein a mass ratio of a whole amount of the constitutional unit (a) derived from the aromatic vinyl compound and a whole amount of the constitutional unit (b) derived from the conjugated diene [(a)/(b)] is from 1/99 to 99/1. 
     
     
         3 . The viscosity index improver according to  claim 1 , wherein the farnesene is β-farnesene. 
     
     
         4 . The viscosity index improver according to  claim 1 , wherein a peak top molecular weight (Mp) of the viscosity index is from 4,000 to 1,500,000. 
     
     
         5 . The viscosity index improver according to  claim 4 , wherein a molecular weight distribution (Mw/Mn) of the viscosity index improver is from 1 to 4. 
     
     
         6 . The viscosity index improver according to  claim 1 , wherein the aromatic vinyl compound is styrene. 
     
     
         7 . The viscosity index improver according to  claim 1 , wherein the conjugated diene other than farnesene is at least one compound selected from the group consisting of isoprene, butadiene and myrcene. 
     
     
         8 . The viscosity index improver according to  claim 1 , wherein the viscosity index improver consists of a hydrogenated product of a block copolymer comprising a polymer block (A) containing the constitutional unit (a) derived from the aromatic vinyl compound as a main component and a polymer block (B) containing the constitutional unit (b) derived from the conjugated diene as a main component. 
     
     
         9 . The viscosity index improver according to  claim 8 , wherein 50 mol % or more of carbon-carbon double bonds in the polymer block (B) are hydrogenated. 
     
     
         10 . An oil composition comprising a base oil and the viscosity index improver as claimed in  claim 1 . 
     
     
         11 . A process for producing the viscosity index improver as claimed in  claim 1 , comprising:
 a polymerization step of obtaining the copolymer containing the constitutional unit (a) derived from the aromatic vinyl compound and the constitutional unit (b) derived from the conjugated diene by anionic polymerization; and   a hydrogenation step of hydrogenating 50 mol % or more of carbon-carbon double bonds in the constitutional unit (b) derived from the conjugated diene.   
     
     
         12 . A process for producing the viscosity index improver according to  claim 11 , comprising:
 a polymerization step of obtaining the block copolymer comprising the polymer block (A) containing the constitutional unit (a) derived from the aromatic vinyl compound as a main component and the polymer block (B) containing the constitutional unit (b) derived from the conjugated diene as a main component by anionic polymerization; and   a hydrogenation step of hydrogenating 50 mol % or more of carbon-carbon double bonds in the constitutional unit (b) derived from the conjugated diene.