Polymeric Phosphorus Esters for Lubricant Applications

Abstract

A lubricant composition of an oil of lubricating viscosity and a polymeric phosphorus ester comprising the condensation product of a monomeric phosphorus acid or an ester thereof with a diol having two hydroxy groups separated by a chain of 4 to about 100 atoms exhibits good volatility, corrosion, wear, and/or seal performance in lubrication of a transmission.

What is claimed is: 
     
         1 . A method for lubricating a drivetrain component, comprising supplying thereto a lubricant composition comprising:
 (a) an oil of lubricating viscosity and   (b) a polymeric phosphorus ester other than a zinc salt, comprising the condensation product of (i) a monomeric phosphorus acid or an ester thereof with (ii) an alkylene diol wherein the two hydroxy groups of said alkylene diol are separated by a chain of 4 to about 20 carbon atoms, said polymeric phosphorus ester containing at least three phosphorus-containing monomer units.   
     
     
         2 . The method of  claim 1  wherein said diol is selected from the group consisting of butanediol and hexanediol. 
     
     
         3 . The method of  claim 1  wherein the alkylene diol comprises hexanediol. 
     
     
         4 . The method of  claim 1  wherein the monomeric phosphorus acid or ester thereof comprises a dialkyl phosphite. 
     
     
         5 . The method of  claim 4  wherein the alkyl groups of the dialkyl phosphite each independently contain 1 to about 6 carbon atoms. 
     
     
         6 . The method of  claim 5  wherein the alkyl groups are methyl groups. 
     
     
         7 . The method of  claim 1  wherein the ratio of the moles of monomeric phosphorus acid or ester to the moles of alkylene diol is about 0.9:1 to about 1.1:1. 
     
     
         8 . The method of  claim 1  wherein the monomeric phosphorus acid or ester thereof comprises a trialkyl phosphite. 
     
     
         9 . The method of  claim 1  wherein the monomeric phosphorus acid or ester thereof comprises a trialkyl phosphite and wherein the ratio of the moles of trialkyl phosphite to the moles of diol is greater than about 1.25:1. 
     
     
         10 . The method of  claim 8  wherein the alkyl groups of the trialkyl phosphite each independently contain 1 to about 6 carbon atoms. 
     
     
         11 . The method  claim 1  wherein the monomeric phosphorus acid or ester thereof comprises a dialkyl phosphite and a trialkyl phosphite. 
     
     
         12 . The method  claim 1  wherein the polymeric phosphorus ester comprises molecules containing 5 to about 500 phosphorus-containing monomer units. 
     
     
         13 . The method of  claim 1  wherein the polymeric phosphorus ester comprises molecules containing 5 to about 15 phosphorus-containing monomer units. 
     
     
         14 . The method of  claim 1  wherein the polymeric phosphorus ester further comprises (iii) at least one monomer unit of a polycarboxylic acid. 
     
     
         15 . The method of  claim 14  wherein said polycarboxylic acid comprises tartaric acid or citric acid and wherein at least a portion of said tartaric acid or citric acid is present as an end unit of the polymer, being condensed through an ester linkage with an OH group of an alkylene diol. 
     
     
         16 . The method of  claim 1  wherein the amount of the polymeric phosphorus ester is an amount to provide about 0.01 to about 0.3 weight percent phosphorus to the composition. 
     
     
         17 . The method of  claim 1  wherein the amount of the polymeric phosphorus ester is about 0.06 to about 2.0 weight percent of the composition. 
     
     
         18 . The method of  claim 1  wherein the lubricant composition further comprises at least one dispersant, viscosity modifier, or antioxidant. 
     
     
         19 . The method of  claim 1  wherein said drivetrain component is a transmission. 
     
     
         20 . The method of  claim 1  wherein said drivetrain component is an automatic transmission.