Viscosity index improver composition and lubricating oil composition

Abstract

A viscosity index improver composition for a lubricating oil composition containing a phosphate ester (C), the viscosity index improver composition including a (co)polymer (A) containing a monomer (a) represented by the following formula (1) as an essential constituent monomer; and a chain aliphatic alcohol (B) having an HLB value of 2.5 to 7.0, the (co)polymer (A) having a solubility parameter of 9.00 to 9.80 (cal/cm3)1/2, wherein R1 is a hydrogen atom or a methyl group; —X1— is a group represented by —O— or —NH—; R2 is an alkylene group having 2 to 4 carbon atoms; R3 is a linear or branched alkyl group having 1 to 17 carbon atoms; p is an integer of 0 to 20, and when p is 2 or more, each R2 may be the same or different.

Dependencies are inferred from the claim text.