| 摘要 |
Provided is a viscosity index improver which exhibits high viscosity index improving effect and thus can inhibit a lubricating oil composition from suffering viscosity increase at low temperatures. The present invention is a viscosity index improver that contains a (co)polymer (A) which is prepared by using a monomer (a) represented by general formula (1) as the essential constituent monomer and which has a solubility parameter of 8.4 to 9.7. In general formula (1), R1 is a hydrogen atom or methyl; X1 is -O- or -NH-; Y is C3-15 branched alkyl; A1 is C2-4 alkylene; m is a number of 0 to 20; and when m is 2 or more, the A1 groups may be the same or different, and the units constituting the (A1O)m moiety may be added at random or in blocks. |
