Method for improving thermal-oxidative stability and elastomer compatibility

A lubricating oil comprising a lubricating oil base stock;

• wherein the lubricating oil base stock comprises a di-alkylated aromatic base stock of the formula:
• (R1)—(R2)—(R1)
• wherein each R1 is the same or different and represents a C10-C30 alkyl group;
• R2 represents an aromatic moiety;
• wherein branching characteristics of the alkyl groups have a total methyl number (“TMN”) determined by C13 NMR spectroscopy of from 1.0 to 2.1 or have a branching index (“BI”) of from −1.0 to 0.1, wherein TMN is calculated by dividing the sum of integrated areas for all methyl groups by the total integration area for all aliphatic carbons and multiplying the result by the averaged chain length carbon number, and wherein BI is TMN minus 2 (two terminal methyl carbons);
• wherein the di-alkylated aromatic base stock comprises at least 44 wt % dialkylate product;
• and wherein thermo-oxidative stability and elastomer compatibility are improved as compared to thermo-oxidative stability and elastomer compatibility achieved using a lubricating oil base stock other than the di-alkylated aromatic base stock.

A di-alkylated aromatic base stock of the formula:

• (R1)—(R2)—(R1)
• wherein each R1 is the same or different and represents a C10-C30 alkyl group;
• R2 represents an aromatic moiety;
• wherein branching characteristics of the alkyl groups have a total methyl number (“TMN”) determined by C13 NMR spectroscopy of from 1.0 to 2.1 or have a branching index (“BI”) of from −1.0 to 0.1, wherein TMN is calculated by dividing the sum of integrated areas for all methyl groups by the total integration area for all aliphatic carbons and multiplying the result by the averaged chain length carbon number, wherein the di-alkylated aromatic base stock comprises at least 44 wt % dialkylate product;
• and wherein BI is TMN minus 2 (two terminal methyl carbons);
• and wherein thermo-oxidative stability and elastomer compatibility are improved as compared to thermo-oxidative stability and elastomer compatibility achieved using a lubricating oil base stock other than the di-alkylated aromatic base stock.