VISCOSITY INDEX IMPROVER, PROCESS FOR PREPARING THE SAME AND LUBRICATING OIL COMPOSITION

摘要

A viscosity index improver for addition to lubricating oil or the like, which comprises a graft copolymer having structural units of an oil-soluble polymer (a) comprising an olefin polymer and sttructural units of a copolymer (b) of a monomer having a peroxide bond with a (meth)acrylate or the like or a copolymer (c) of a monomer having a peroxide bond with 2-hydroxyethyl (meth)acrylate or the like. The improver is excellent in the effect of improving the viscosity index, the thickening effect, the fluidity at low temperatures and the shear stability, and has no fear of causing phase separation in lubricating oil.