Aromatic diblock copolymers for lubricant and concentrate compositions and methods thereof

Abstract

A lubricant composition comprises (A) a major amount of an oil of lubricating viscosity and (B) a minor amount of a diblock copolymer comprising a poly(monovinyl aromatic hydrocarbon) block and a hydrogenated poly(conjugated diene) block where the diblock copolymer has a weight average molecular weight of 10,000 to 50,000 and a poly(monovinyl aromatic hydrocarbon) content of 5 to 45% by weight. A concentrate composition, a method for improving viscosity performance of a lubricant composition for an internal combustion engine, and a method for lubricating an internal combustion engine comprise the diblock copolymer which is especially useful for reducing soot-induced viscosity increase in a compression-ignited internal combustion engine equipped with an exhaust gas recirculation system.

1 . A lubricant composition, comprising; 
 (A) a major amount of an oil of lubricating viscosity; and    (B) a minor amount of a diblock copolymer comprising a poly(monovinyl aromatic hydrocarbon) block and a hydrogenated poly(conjugated diene) block wherein the diblock copolymer has a weight average molecular weight of 10,000 to 50,000 and a poly(monovinyl aromatic hydrocarbon) content of 5 to 45% by weight.    
   
   
       2 . The lubricant composition of  claim 1  wherein the monovinyl aromatic hydrocarbon is selected from the group consisting of styrene, an alkyl-substituted styrene, an alkoxy-substituted styrene, and a mixture thereof.  
   
   
       3 . The lubricant composition of  claim 1  wherein the conjugated diene is selected from the group consisting of 1,3-butadiene; isoprene; piperylene; and a mixture thereof.  
   
   
       4 . The lubricant composition of  claim 1  wherein the monovinyl aromatic hydrocarbon is styrene and the conjugated diene is isoprene or 1,3-butadiene.  
   
   
       5 . The lubricant composition of  claim 1  wherein the diblock copolymer has a weight average molecular weight of 12,000 to 47,000 and a poly(monovinyl aromatic hydrocarbon) content of 16 to 43% by weight.  
   
   
       6 . The lubricant composition of  claim 1 , further comprising: 
 (C) at least one other additive selected from the group consisting of a dispersant, an antiwear agent, an antioxidant, a detergent, a corrosion inhibitor, an antifoam agent, a pour point depressant, and a viscosity modifier that is different from component (B).    
   
   
       7 . The lubricant composition of  claim 6  wherein the lubricant composition is prepared by admixing the components.  
   
   
       8 . The lubricant composition of  claim 1  further comprising a dispersant wherein the dispersant comprises a reaction product of a hydrocarbyl-substituted succinic acylating agent and a polyethylenepolyamine wherein the hydrocarbyl substituent is derived from a polyisobutylene, and the dispersant reaction product has a nitrogen to carbonyl ratio that is greater than 1.  
   
   
       9 . The lubricant composition of  claim 1  further comprising an antiwear agent wherein the antiwear agent comprises a metal salt of a dialkyl dithiophosphate wherein the dialkyl dithiophosphate is derived from one or more secondary alcohols.  
   
   
       10 . The lubricant composition of  claim 1  further comprising an antioxidant wherein the antioxidant comprises at least one member selected from the group consisting of a hindered phenol, a diarylamine, and a sulfurized olefinic compound.  
   
   
       11 . The lubricant composition of  claim 1  further comprising a viscosity modifer wherein the viscosity modifier comprises an ethylene-propylene copolymer.  
   
   
       12 . The lubricant composition of  claim 1  wherein the lubricant composition has on a weight basis a sulfated ash content of 1.1% or less, a sulfur content of 0.5% or less, and a phosphorus content of 0.12% or less.  
   
   
       13 . A concentrate composition, comprising: 
 a concentrate-forming amount of an oil of lubricating viscosity; and    component (B) of  claim 1 .    
   
   
       14 . A method for improving the viscosity performance of a lubricant composition for an internal combustion engine, comprising: 
 incorporating into the lubricant composition a viscosity performance-improving amount of component (B) of  claim 1  wherein the lubricant composition comprises component (A).    
   
   
       15 . The method of  claim 14  wherein the engine is a compression-ignited internal combustion engine.  
   
   
       16 . The method of  claim 15  wherein the engine is equipped with an exhaust gas recirculation system.  
   
   
       17 . A method for lubricating an internal combustion engine, comprising; 
 supplying to the engine the lubricant composition of  claim 1 .    
   
   
       18 . The method of  claim 17  wherein the engine is a compression-ignited internal combustion engine.