Lubricating oil additives

A method for making a lubricating oil additive which comprises a first step of free-radically graft copolymerizing an alkyl ester of acrylic acid or of methacrylic acid, alone or in combination with styrene in a weight ratio of styrene to esters of 1:15 to 1:9, onto a backbone copolymer which is a hydrogenated block copolymer of styrene and a conjugated diene having 4 to 6 carbon atoms and a residual content of olefinic double bonds of less than 15 percent, in a medium suitable for use as a lubricant, to form a first graft copolymer, and a second step of free-radically graft copolymerizing at least one N-heterocyclic monomer selected from the group consisting of N-vinyl-pyrrolidone-2 and N-vinyl-imidazole, alone or in combination with a hydrophobizing vinyl ester in a weight ratio of ester to said N-heterocyclic monomer of 1:0.1 to 1:3, onto said first graft copolymer, in a medium suitable for use as a lubricant, to form a second graft copolymer comprising 5 to 50 percent by weight of said hydrogenated block copolymer, from 49.5 to 85 percent by weight of monomers graft copolymerized in said first step, and from 0.5 to 10 percent by weight of monomers graft copolymerized in said second step.