| abstract |
PROBLEM TO BE SOLVED: To provide a viscosity index improver excellent in shear stability and a lubricating oil composition containing the same. SOLUTION: When polymerizing a vinyl monomer (a), an initiator (b) selected from the group consisting of an azo initiator, a peroxide initiator, a redox initiator and an organic halogen compound initiator, It contains a complex compound (c) of a metal element (c1) and a ligand of an anion or neutral molecule (c2) and a vinyl polymer (A) obtained by performing polymerization in the presence of an oil or an organic solvent. A viscosity index improver characterized by the following. |