Lubricating Composition Containing Viscosity Modifier Combination

Abstract

The present invention relates to a lubricating composition containing (a) an oil of lubricating viscosity, (b) a star polymer and (c) a substantially linear polymer with a weight average molecular weight of 45,000 or less. The invention further provides a method of lubricating a mechanical device, typically a manual transmission with the lubricating composition. The invention further provides for the use of the lubricating composition to provide a number of benefits including lower operating temperatures and fuel economy.

What is claimed is: 
     
         1 . A lubricating composition comprising (a) an oil of lubricating viscosity, (b) a star polymer, and (c) a substantially linear polymer with a weight average molecular weight of 45,000 or less, wherein the substantially linear polymer is a copolymer comprising units derived from monomers (i) an α-olefin and (ii) an ethylenically unsaturated carboxylic acid or derivatives thereof esterified with a primary alcohol branched at the β- or higher position. 
     
     
         2 . The lubricating composition of  claim 1 , wherein the substantially linear polymer has a weight average molecular weight of 8000 to 25,000. 
     
     
         3 . The lubricating composition of  claim 1 , wherein the substantially linear polymer has a weight average molecular weight of 12,000 to 20,000. 
     
     
         4 . The lubricating composition of  claim 1 , wherein the substantially linear polymer is a copolymer derived from monomers (i) an α-olefin and (ii) an ethylenically unsaturated carboxylic acid or derivatives thereof,
 wherein 0.1 to 99.89 percent of the carboxylic acid units are esterified with a primary alcohol branched at the β- or higher position, 
 wherein 0.1 to 99.89 percent of the carboxylic acid units are esterified with a linear alcohol or an alpha-branched alcohol, 
 wherein 0.01 to 10% of the carboxylic acid units has at least one of an amino-, amido- and/or imido-group, and 
 wherein the copolymer has a reduced specific viscosity of up to 0.08. 
 
     
     
         5 . The lubricating composition of  claim 1 , wherein the copolymer, prior to esterification has a reduced specific viscosity of up to 0.15. 
     
     
         6 . The lubricating composition of  claim 5 , wherein the substantially linear polymer prior to esterification has a reduced specific viscosity of 0.02 to 0.07. 
     
     
         7 . The lubricating composition of  claim 5 , wherein the substantially linear polymer prior to esterification has a reduced specific viscosity of 0.04 to 0.06. 
     
     
         8 . The lubricating composition of  claim 1 , wherein the substantially linear polymer is present at 5 wt % to 30 wt % of the lubricating composition. 
     
     
         9 . The lubricating composition of  claim 1 , wherein the substantially linear polymer is a copolymer comprising units derived from monomers (i) an α-olefin and (ii) an ethylenically unsaturated carboxylic acid or derivatives thereof esterified with a primary alcohol branched at the β- or higher position; and wherein the substantially linear polymer is present at 5 wt % to 30 wt % of the lubricating composition. 
     
     
         10 . The lubricating composition of  claim 1 , wherein the ethylenically unsaturated carboxylic acid or derivatives thereof is at least one of maleic anhydride or maleic acid. 
     
     
         11 . The lubricating composition of  claim 1 , wherein the star polymer is a poly(meth)acrylate, and wherein the star polymer is derived from a monomer composition comprising:
 (a) 50 wt % to 100 wt % of an alkyl (meth)acrylate, wherein the alkyl group of the (meth)acrylate has 10 to 20 carbon atoms, or mixtures thereof;   (b) 0 wt % to 40 wt % of an alkyl (meth)acrylate, wherein the alkyl group of the (meth)acrylate has 1 to 9 carbon atoms, or mixtures thereof; and   (c) 0 wt % to 10 wt % of a nitrogen-containing monomer.   
     
     
         12 . The lubricating composition of  claim 1 , wherein the star polymer is a poly(meth)acrylate, and wherein the star polymer is derived from a monomer composition comprising:
 (a) 65 wt % to 95 wt % of an alkyl (meth)acrylate, wherein the alkyl group of the (meth)acrylate has 12 to 18 carbon atoms, or mixtures thereof;   (b) 5 wt % to 30 wt % of an alkyl (meth)acrylate, wherein the alkyl group of the (meth)acrylate has 1 to 9, carbon atoms, or mixtures thereof; and   (c) 0 wt % to 5 wt % of a nitrogen-containing monomer.   
     
     
         13 . The lubricating composition of  claim 1 , wherein the star polymer is a polymethacrylate and is present at 2 wt % to 30 wt % of the lubricating composition 
     
     
         14 . The lubricating composition of  claim 1 , wherein the star polymer is a polymethacrylate and present at 5 wt % to 20 wt %, of the lubricating composition. 
     
     
         15 . The lubricating composition of  claim 1 , wherein the star polymer is a polymethacrylate and is present at 0.5 to 10 wt % of the lubricating composition. 
     
     
         16 . The lubricating composition of  claim 1 , wherein the lubricating composition contains 0.3 wt % to 15 wt % of star polymer and 1 wt % to 35 wt % of the substantially linear polymer. 
     
     
         17 . The lubricating composition of  claim 1 , wherein the lubricating composition contains 0.45 wt % to 5 wt % of star polymer and 2 wt % to 25 wt % of the substantially linear polymer. 
     
     
         18 . A method of lubricating a mechanical device comprising supplying to the device lubricating composition of  claim 1 . 
     
     
         19 . The method of  claim 18 , wherein the mechanical device is a manual transmission. 
     
     
         20 . The method of  claim 18 , wherein the mechanical device is an automatic transmission.