Star polymers and compositions thereof

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 polymerisation 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.