Viscosity index improver, refrigerator oil, and working fluid composition for refrigerators

Abstract

The present invention relates to a viscosity index improver containing a copolymer (A) that contains, as essential constituent monomers, a fluorine atom-containing monomer (a) represented by the following formula (1) and a monomer (b) represented by the following formula (2), wherein the copolymer (A) has a solubility parameter of 8.1 to 10.0 (cal/cm), and a mass ratio (b/a) of the monomer (b) to the monomer (a) in the monomers constituting the copolymer (A) is 0.01 to 42: wherein Rrepresents a hydrogen atom or a methyl group; Ris a C2-C4 alkylene group; p is an integer of 0 or 1; q is an integer from 0 to 20, each Rmay be the same as or different from each other when q is 2 or greater; and Y is a monovalent group in which one or more or all of hydrogen atoms in a C1-C40 hydrocarbon group are replaced by fluorine atoms, and wherein Rrepresents a hydrogen atom or a methyl group; —X— is a group represented by —O— or —NH—; Ris a C2-C4 alkylene group; r is an integer of 0 or 1; s is an integer from 0 to 20, and each Rmay be the same as or different from each other when s is 2 or greater; and Ris a C1-C40 hydrocarbon group.