Abstract: What is disclosed is a concentrated polymer emulsion useful as a lubricating oil additive for improving the viscosity index thereof, said emulsion comprising:(1) a dispersed phase of an olefinic copolymer having a molecular weight complementary with respect to the thickening effect desired;(2) a dispersing phase of a polymer predominantly comprising at least one member selected from the group consisting of acrylate ester and methacrylate ester monomers;(3) a vehicle which is a good solvent for the esters in said dispersing phase and a substantially less good solvent for the olefinic copolymer by virtue of the esters dissolved in said vehicle; and(4) an emulsifier, stabilizing phase distribution, which is a member selected from the group consisting of graft copolymers and block copolymers formed from olefinic monomers and at least one member selected from the group consisting of acrylate ester and methacrylate ester monomers.

Abstract: What is disclosed is a method for making a lubricating oil additive which comprises a first step of graft copolymerizing an alkyl ester of acrylic acid or of methacrylic acid, alone or in combination with styrene, onto a backbone copolymer which is hydrogenated block copolymer of styrene and a conjugated diene having 4 to 6 carbon atoms to form a first graft copolymer, and a second step of graft copolymerizing a polymerizable heterocyclic monomer, alone or in combination with a hydrophobizing vinyl ester, onto said first graft copolymer to form a second graft copolymer, and the lubricating oil additive so made.