Poly(meth)acrylate-based viscosity index improver, lubricant additive and lubricant composition containing viscosity index improver
The present invention provides a poly(meth)acrylate-based viscosity index improver comprising a core portion and three or more arm portions, wherein each of the arm portions consists of a polymer chain comprising a structural unit represented by the following formula (1), and one end of the polymer chain is bonded to the core portion, and wherein a weight-average molecular weight Mw is 100000 or more, and a ratio of the weight-average molecular weight Mw to a number average molecular weight Mn, Mw/Mn, is 1.6 or less. [R 1 represents hydrogen or a methyl group, and R 2 represents a C1 to C36 alkyl group.]
1. A lubricating oil composition comprising:
a lubricating base oil; and
a poly(meth)acrylate-based viscosity index improver comprising:
a core portion derived from a compound having three or more functional groups that react with a carbon-carbon double bond of an acryloyl group chosen from the group consisting of 1,1,1-tris(2-bromoisobutyloxymethylene)ethane, pentaerythritoltetrakis(2-bromoisobutyrate), and dipentaerythritolhexakis(2-bromoisobutyrate); and
three or more arm portions,
wherein each of the arm portions consists of a polymer chain consisting of structural units represented by formula (1) shown below, and one end of the polymer chain is bonded to the core portion,
wherein R 1 represents a hydrogen or a methyl group, and R 2 represents a C1 to C36 alkyl group,
wherein the polymer chain comprises 20 to 45 mass % of the structural unit wherein R 2 is a methyl group and 20 mass % or more of the structural unit wherein R 2 is an alkyl group having 18 or more carbon atoms, based on the total amount of the structural units contained in the polymer chain, and
wherein the ratio of the weight-average molecular weight Mw to the number average molecular weight Mn of the poly(meth)acrylate-based viscosity index improver, Mw/Mn, is 1.6 or less.
2. The lubricating oil composition according to claim 1 , wherein the weight-average molecular weight, Mw, of the poly(meth)acrylate-based viscosity index improver is 100000 or more.
3. The lubricating oil composition according to claim 1 , wherein the weight-average molecular weight, Mw, of the poly(meth)acrylate-based viscosity index improver is less than 100000.