Additives and lubricating oil compositions containing same
Para-alkylated substituted diphenylamines are made by catalytically alkylating diphenylamine with a branched-chain alkene, such as propene, oligomer mixture in which the oligomer present in the greatest percentage has 15-24 carbon atoms. The alkylated diphenylamines are useful crankcase lubricant additives such as for reducing piston deposits and engine sludge.
1. A method of preparing a para-alkyl-substituted diphenylamine comprising catalytically alkylating diphenylamine with an alkylating agent in the form of a mixture of branched-chain propene oligomers, wherein greater than 50% of the oligomer that is present is C 15 oligomer, and oligomers having 9 or fewer carbon atoms and oligomers having from 24 or more carbon atoms constitute 10% or less of the mixture, all percentages being area/area as measured chromatographically; and wherein the mole ratio of alkylating agent to diphenylamine is in the range of 1:3 to 1.5:1.
2. A method as claimed in claim 1 wherein said mixture of branched-chain alkene-oligomers is a mixture of propene oligomers.