Lubricating composition

Abstract

Use of a comb polymer for reducing the loss in viscosity of a lubricating composition for the crankcase of an internal combustion engine, wherein the internal combustion engine is fuelled by a fuel composition comprising a fatty acid alkyl ester.

1 . A method of operating an internal combustion engine comprising:
 lubricating a crankcase of the internal combustion engine with a lubricating composition comprising a comb polymer, and   using a fuel composition comprising a fatty acid alkyl ester to fuel the internal combustion engine.   
     
     
         2 . The method according to  claim 1  wherein the viscosity of the lubricating composition is the kinematic viscosity at 100° C. measured using ASTM D445. 
     
     
         3 . The method according to  claim 1  wherein the fatty acid alkyl ester is a fatty acid methyl ester. 
     
     
         4 . The method according to  claim 1  wherein the comb polymer comprises, in the main chain, at least one repeat unit which is obtained from at least one polyolefin-based macromonomer, and at least one repeat unit which is obtained from at least one low molecular weight monomer selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, alkyl (meth)acrylates having 1 to 10 carbon atoms in the alcohol group, vinyl esters having from 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumurates having 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having 1 to 10 carbon atoms in the alcohol group and mixtures thereof, where the molar degree of branching is in the range of 0.1 to 10 mol % and the comb polymer comprises a total of at least 80% by weight, based on the total weight of repeat units of the comb polymer, of the at least one repeat unit which is obtained from the at least one polyolefin-based macromonomer and the at least one repeat unit which is obtained from the at least one low molecular weight monomer. 
     
     
         5 . The method according to  claim 4  wherein the comb polymer has 11 to 26% by weight of the at least one repeat unit which is obtained from the at least one polyolefin-based macromonomer. 
     
     
         6 . The method according to  claim 4  wherein the at least one repeat unit which is obtained from the at least one polyolefin-based macromonomer has a number-average molecular weight in the range of 700 to 10000 g/mol. 
     
     
         7 . The method according to  claim 4  wherein the comb polymer comprises at least 90% by weight of repeat units which are obtained from at least one polyolefin-based macromonomer and from at least one low molecular weight monomer selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, alkyl (meth)acrylates having 1 to 10 carbon atoms in the alcohol group, vinyl esters having from 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumurates having 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having 1 to 10 carbon atoms in the alcohol group and mixtures thereof. 
     
     
         8 . The method according to  claim 4  wherein the polydispersity index Mw/Mn is in the range of from 1 to 5. 
     
     
         9 . The method according to  claim 4  wherein the molar degree of branching of the comb polymer is in the range of from 0.4% to 1.0%. 
     
     
         10 . The method according to  claim 4  wherein the at least one repeat unit obtained from the at least one polyolefin-based macromonomer comprises a group, preferably at a level of at least 80% by weight of the at least one repeat unit obtained from the at least one polyolefin-based macromonomer, which is obtained from monomers selected from the group consisting of C2-C10 alkenes and C4-C10 alkadienes. 
     
     
         11 . The method according to  claim 4  wherein the melting point of the at least one repeat unit obtained from the at least one polyolefin-based macromonomers is less than or equal to 10° C. 
     
     
         12 . The method according to  claim 4  wherein no melting point of the at least one repeat unit obtained from the at least one polyolefin-based macromonomer is measured. 
     
     
         13 . The method according to  claim 4  wherein the comb polymer has repeat units that are obtained from at least one or n butyl methacrylate and n butyl acrylate. 
     
     
         14 . The method according to  claim 4  wherein the comb polymer has repeat units which are obtained from styrene. 
     
     
         15 . The method according to  claim 4  wherein the comb polymer has a weight-average molecular weight in the range of 100,000 to 500,000 g/mol. 
     
     
         16 . The method according to  claim 4  wherein the comb polymer has repeat units which are obtained from alkyl (meth)acrylates having 11-30 carbon atoms in the alkyl radical. 
     
     
         17 . The method according to  claim 1  wherein the lubricating composition comprises from 0.1 wt % to 10 wt % of the comb polymer, by weight of the lubricating composition. 
     
     
         18 . The method according to  claim 1  wherein the lubricating composition comprises a base oil and one or more additives.