Hydrogenated lithiated copolymers grafted with organic nitrogen compounds as viscosity index improvers having dispersant properties

Shear-stable, mineral oil-based compositions comprising a major amount of a mineral base oil, and a minor effective viscosity improving amount of an oil-soluble organonitrogen compound grafted hydrogenated conjugated diene/monovinylarene copolymer dissolved therein, said copolymer having a polymerized monovinylarene content of about 20 to 70 weight percent with the proviso that when said copolymer contains a random block, the block polymonovinylarene content is in the range of about 15 to 35 weight percent, a number average molecular weight suitable for oil solubility, the extent of hydrogenation of said copolymer such that about at least 95 weight percent of olefinic double bonds having been saturated and less than about 5 weight percent of aromatic double bonds having been saturated, said copolymer characterized as having been prepared by the process which comprises metalating a hydrogenated conjugated diene hydrocarbon/monovinylarene hydrocarbon copolymer, and reacting the resulting metalated hydrogenated copolymer with effective amounts of at least one nitrogen-containing organic compound represented by the general formulae X--Q--(NR.sub.2.sup.3).sub.n or Y›Q--(NR.sub.2.sup.3).sub.n !.sub.m wherein each R.sup.3 is the same or different alkyl, cycloalkyl, aryl, or combination radical, Q is a hydrocarbon radical having a valence of n+1 and is a saturated aliphatic, saturated cycloaliphatic, aromatic or combination radical, X is a functional group capable of reaction on a one-to-one basis with one equivalent of polymer metal, Y is or contains a functional group capable of reacting on a one-to-one basis with one equivalent of polymer metal, n is at least one, and m is 2 or 3, thereby preparing said grafted copolymer.