VISCOSITY INDEX IMPROVER AND LUBRICATING OIL COMPOSITION COMPRISING THE SAME

摘要

PROBLEM TO BE SOLVED: To obtain a viscosity index improver which, when added to a mineral oil or a synthetic oil, can provide a lubricating oil having high viscosity index and excellent shear stability. SOLUTION: This viscosity index improver comprises a branched polymer prepd. by copolymerizing a radical polymerizable macromonomer, comprising a vinyl polymer composed mainly of an alkyl methacrylate monomer unit having a 12-30C alkyl group, with a radical polymerizable monomer composed mainly of an alkyl methacrylate. The objective lubricating oil compsn. comprises a mineral oil and/or a synthetic oil contg. the viscosity index improver.