Abstract: Disclosed are isomeric polyisobutenyl butyrolactones and lactams thereof useful as dispersants in lubricant oils and having the formulas: ##STR1## wherein R is a hydrocarbyl group having from 12 to 300 carbon atoms; X is O or >N--R', where R' is an alkyl or alkylamino group having from 1 to 20 carbon atoms and from 0 to 10 nitrogen atoms. The butyrolactones are made by mild reduction of the corresponding cyclic anhydrides and the lactams are prepared by reacting the intermediate butyrolactones with at least a molar equivalent of a primary amine, optionally, in the presence of a base or an acid.

Abstract: Disclosed are the preparation and use of thioureas derived from hydrocarbyl succinimides which have the formula: ##STR1## wherein R is a hydrocarbyl succinimide residue or hydrogen, with the proviso that only one R can be hydrogen. These thioureas offer superior performance over their parent succinimides in the areas of gasoline and diesel engine dispersancy, oxidation stability and friction modification.