The invention provides a composition comprising: (a) a star polymer comprising: (i) a core portion comprising a polyvalent (meth)acrylic monomer, oligomer or polymer thereof or a polyvalent divinyl non-acrylic monomer, oligomer or polymer thereof; and (ii) at least two arms of polymerized alkyl(meth)acrylate ester; and (b) an oil of lubricating viscosity, wherein the core portion further comprises a functional group of formula (I): —CH2—C(R1)(C(═O)A)-Y—  (I) wherein R1 is hydrogen, a linear or branched alkyl group containing 1 to 5 carbon atoms; A is nitrogen or oxygen; and Y is a free radical leaving group selected from the group consisting of one or more atoms or groups of atoms which may be transferred by a radical mechanism under the polymerization conditions, a halogen, an —O—N═ group and an —S—C(═S)— group. The invention further provides the use of the composition in an oil of lubricating viscosity as a dispersant, a viscosity modifier or a precursor to a dispersant viscosity modifier.