The present invention is directed to an oil-soluble lubricating oil additive comprising at least one terminally unsaturated ethylene alpha-olefin polymer of 300 to 10,000 number average molecular weight substituted with thiocarboxylic acid producing moieties (preferably acid or anhydride moieties), wherein the terminal unsaturation comprises ethenylidene unsaturation. The thiocarboxylic acid or anhydride substituted polymers of this invention are useful per se as additives to lubricating oils, and can also be reacted with a nucleophilic reagent, such as amines, alcohols, amino alcohols and metal compounds, to form products which are also useful lubricating oil additives, e.g., as dispersants.