A grafted
polyolefin containing one or more of N-vinylimidazole, 4-vinylpyridine, or other ethylenically-unsaturated
nitrogen-containing or
oxygen-containing graftable monomers grafted to a
polyolefin copolymer is disclosed. The grafted
polyolefin preferably has a weight average molecular weight of from about 20,000 to about 500,000, a polydispersity of less than about 10, and an ADT value of at least about 8. The grafted polyolefin can be defined as containing more than about 1.2% by weight of grafted
monomer on a polyolefin, or as containing at least about 13 moles of graftable monomers per mole of polyolefin, or as having an
asphaltene dispersancy test (ADT) value of at least about 8. 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-vinyl-
imidazole or other ethylenically unsaturated
nitrogen-containing and / or
oxygen-containing graftable monomers and a graftable polyolefin are reacted with enough of an initiator to graft the
monomer to the polyolefin. The initiator and / or graftable
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. The N-vinylimidazole and the initiator each can be added at a uniform, relatively
slow rate during the reaction.