Star polymer and lubricating composition thereof

Abstract

The present invention relates to a lubricating composition containing an oil of lubricating viscosity and a star polymer that has at least two inner blocks, at least one of which is in turn bonded to one or more outer blocks. The invention further relates to methods of lubricating a mechanical device with the lubricating composition.

What is claimed is: 
     
         1 . A lubricating composition comprising an oil of lubricating viscosity and a star polymer, wherein the star polymer comprises a core bonded to at least two inner blocks, at least one of which in turn is bonded to one or more outer blocks,
 wherein at least one inner block comprises:
 (a) 20 wt % to 90 wt % of a C 1-4 -alkyl (meth)acrylate-derived unit, 
 (b) 10 wt % to 80 wt % of a C 4-18 -alkyl (meth)acrylate-derived unit different from (a), 
   wherein the (meth)acrylate alkyl group of the inner block has a number average number of carbons of 1.5 to 8; and
 (c) 0 wt % to 5 wt % of a vinyl aromatic derived unit; 
 (d) 0 wt % to 5 wt % of a dispersant unit derived from a dispersant monomer, 
   wherein at least one outer block comprises:
 (a) 50 to 95 wt % of a C 10-16 -alkyl (meth)acrylate-derived unit, and 
 (b) 5 wt % to 50 wt % of a C 1-20 -alkyl methacrylate-derived unit different from (a) and wherein the outer block is different from the inner block, and 
 (c) 0 wt % to 5 wt % of a dispersant unit, wherein the dispersant unit is derived from a dispersant monomer, 
   wherein the (meth)acrylate alkyl group of the outer block has a number average number of carbons of greater than 7, and
 (d) 0 wt % to 5 wt % of a vinyl aromatic derived unit; and 
   wherein the difference in the number average number of carbon atoms between the alkyl groups of the inner block and the alkyl groups of the outer block is at least 0.8 (the difference in the number average number of carbon atoms between the inner block and outer block may be at least 1.2;   wherein the number average number of carbon atoms in the alkyl groups of the inner block is less than the average number of carbon atoms in the alkyl groups of the outer block, and   wherein the star the ratio of the inner block to the outer block is 20:80 to 80:20 by weight.   
     
     
         2 . The lubricating composition of  claim 1 , wherein the (meth)acrylate-derived units are methacrylate-derived units, or mixtures thereof. 
     
     
         3 . The lubricating composition of  claim 1 , wherein the star polymer comprises 0 wt % to 2 wt % of a dispersant unit and 0 wt % to 2 wt % of a vinyl aromatic unit. 
     
     
         4 . The lubricating composition of  claim 1 , wherein the star polymer comprises 0 wt % of a dispersant unit and 0 wt % of a vinyl aromatic derived unit. 
     
     
         5 . The lubricating composition of  claim 1 , wherein the inner block comprises:
 (a) 20 wt % to 90 wt % of a C 1-4 -alkyl (meth)acrylate-derived unit,   (b) 10 wt % to 80 wt % of a C 5-18 -alkyl (meth)acrylate-derived unit,   
       wherein the (meth)acrylate alkyl group of the inner block has a number average number of carbons of 1.5 to 8; and
 (c) 0 wt % of a vinyl aromatic derived unit; 
 (d) 0 wt % of a dispersant unit dispersant unit derived from a dispersant monomer, 
 
       wherein at least one outer block comprises:
 (a) 50 to 95 wt % of a C 1-16 -alkyl (meth)acrylate-derived unit, and 
 (b) 5 wt % to 50 wt % of a C 1-20 -alkyl methacrylate-derived unit different from (a) and different from the inner block, and 
 (c) 0 wt % of a dispersant unit, wherein the dispersant unit is derived from a dispersant monomer, 
 
       wherein the (meth)acrylate alkyl group of the outer block has a number average number of carbons of greater than 7, and
 (d) 0 wt % of a vinyl aromatic derived unit from a monomer; and 
 
       wherein the difference in the number average number of carbon atoms in the alkyl groups of the inner block and the number average number of carbon atoms in the alkyl groups of the outer block is 0.8 to 8; 
       and wherein the number average number of carbon atoms in the alkyl groups of the inner block is less than the number average number of carbon atoms in the alkyl groups of the outer block. 
     
     
         6 . The lubricating composition of  claim 1 , wherein the difference in the number average number of carbon atoms of the alkyl groups of the alkyl (meth)acrylate-derived units between the inner block and outer block is 0.8 to 8. 
     
     
         7 . The lubricating composition of  claim 1 , wherein the inner block C 1-4 -alkyl (meth)acrylate-derived units comprise methyl methacrylate. 
     
     
         8 . The lubricating composition of  claim 1 , wherein the star polymer is derivable from a free radical polymerisation or a controlled free radical polymerisation. 
     
     
         9 . The lubricating composition of  claim 8 , wherein the controlled free radical polymerisation includes RAFT, or ATRP, or nitroxide-mediated polymerisation. 
     
     
         10 . The lubricating composition of  claim 1  further comprising at least one of a dispersant, an antiwear agent, a dispersant viscosity modifier, a friction modifier, a viscosity modifier, an antioxidant, an overbased detergent, an extreme pressure agent, or mixtures thereof. 
     
     
         11 . The lubricating composition of  claim 1  further comprising at least one of a polyisobutylene succinimide dispersant, an antiwear agent, a dispersant viscosity modifier, a friction modifier, a viscosity modifier, an antioxidant, an overbased detergent, an extreme pressure agent, or mixtures thereof. 
     
     
         12 . The lubricating composition of  claim 1  further comprising an overbased detergent, a dispersant, and an antiwear agent. 
     
     
         13 . The lubricating composition of  claim 1  further comprising an antiwear agent and a corrosion inhibitor. 
     
     
         14 . The lubricating composition of  claim 1  further comprising a phosphorus-containing acid, salt, or ester, and a dispersant. 
     
     
         15 . The lubricating composition of  claim 1  further comprising a phosphorus-containing acid, salt, or ester, and an extreme pressure agent other than a phosphorus-containing acid, salt, or ester. 
     
     
         16 . The lubricating composition of  claim 1 , wherein the star polymer comprises at least 25% of the polymer arms having at least one inner block bonded to at least one outer block. 
     
     
         17 . The lubricating composition of  claim 1 , wherein the star the ratio of the inner block to the outer block is 75:25 to 50:50 by weight. 
     
     
         18 . A method of lubricating a mechanical device comprising supplying to the mechanical device a lubricating composition of  claim 1 , wherein the mechanical device is an internal combustion engine, a hydraulic device, a manual or automatic transmission, an industrial gear, an automotive gear or axle, or a farm tractor.