A grafted polyolefin containing at least about 13 moles of N-vinylimidazole or other ethylenically-unsaturated nitrogen-containing and/or oxygen-containing monomers per mole of a grafted polyolefin backbone is disclosed. The graft polyolefin has a weight average molecular weight of from about 20,000 to about 500,000 and a polydispersity of less than about 10. The grafted polyolefin can alternatively be defined as containing more than about 1.2% by weight of grafted monomer on a polyolefin. Also described is a lubricating oil comprising a lubricant base oil and a grafted polyolefin as described above. Also described is a method of making a dispersant-viscosity index improver. N-vinylimidazole or other ethylenically unsaturated nitrogen-containing and/or oxygen-containingmonomers and a graftable polyolefin are reacted with enough of an initiator to graft at least about 13 moles of the monomer to each mole of the polyolefin. The initiator and/or monomer is added to the other ingredients, maintained at the reaction temperature, over a period of time. The reaction temperature is maintained at a level high enough to give acceptable reaction times. In one embodiment, the N-vinylimidazole and the initiator are each added at a uniform, relatively slow rate during the reaction.