JP2014141577A - Viscosity index improver and lubricating oil composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a viscosity index improver which exhibits a high viscosity index improving effect and hardly increases the low-temperature viscosity of a lubricating oil composition.SOLUTION: There is provided a viscosity index improver which contains a (co)polymer containing a monomer (a) represented by the following general formula (1) as an essential component monomer. [Ris a hydrogen atom or a methyl group; Xis a group represented by -O- or -NH-; Ris an alkylene group having 2 to 4 carbon atoms; Ris an alkyl group having 2 to 24 carbon atoms; m is an integer of 0 to 20, when m is 2 or more, Rmay be the same or different; the part of (RO)may be a random bond or a block bond; and n is a number of 0 to 20.]

Description

  The present invention relates to a lubricating oil composition containing a viscosity index improver and a viscosity index improver.

Lubricating oils and hydraulic oils used in automobiles and the like have a lower viscosity as the temperature increases, but in practice, it is desirable that the viscosity does not change as much as possible over a wide range from a low temperature to a high temperature. Therefore, a method for improving the temperature dependence of viscosity by adding a viscosity index improver to lubricating oil is widely used. As such a viscosity index improver, a methacrylic acid ester copolymer (Patent Documents 1 to 3), an olefin copolymer (Patent Document 4) and the like are known.
However, the above-described viscosity index improver is not yet sufficiently effective in improving the viscosity index, and when added to the lubricating oil composition, there is a problem that the viscosity at a low temperature of the lubricating oil composition increases.

Japanese Patent No. 2732187 JP-A-8-53683 JP 2004-307551 A JP 2005-200454 A

  An object of the present invention is to provide a viscosity index improver that has a high effect of improving the viscosity index and hardly increases the low temperature viscosity of the lubricating oil composition.

  As a result of intensive studies, the present inventors have arrived at the present invention. That is, the present invention provides a viscosity index improver containing a (co) polymer (A) having the monomer (a) represented by the following general formula (1) as an essential constituent monomer; A lubricating oil composition comprising a base oil.

［Ｒ^１は水素原子又はメチル基；Ｘ^１は−Ｏ−または−ＮＨ−で表される基；Ｒ^２は炭素数２〜４のアルキレン基；Ｒ^３は炭素数２〜２４のアルキル基；ｍは０〜２０の数であり、ｍが２以上の場合のＲ^２は同一でも異なっていてもよく、（Ｒ^２Ｏ）_ｍ部分はランダム結合でもブロック結合でもよい。；ｎは０〜２０の数である。］

[R ¹ is a hydrogen atom or a methyl group; X ¹ is a group represented by —O— or —NH—; R ² is an alkylene group having 2 to 4 carbon atoms; R ³ is an alkyl group having 2 to 24 carbon atoms; m is a number from 0 to 20, and R ² when m is 2 or more may be the same or different, and the (R ² O) _m moiety may be a random bond or a block bond. N is a number from 0 to 20. ]

  The lubricating oil composition containing the viscosity index improver of the present invention has a high viscosity index improving effect and exhibits an effect that it is difficult to increase the low temperature viscosity of the lubricating oil composition.

  The viscosity index improver of the present invention is a viscosity index improver containing a (co) polymer (A) having the monomer (a) represented by the general formula (1) as an essential constituent monomer. “(Co) polymerization” means polymerization or copolymerization.

R ¹ in the general formula (1) is a hydrogen atom or a methyl group. Among these, a methyl group is preferable from the viewpoint of improving the viscosity index.

R ² in the general formula (1) is an alkylene group having 2 to 4 carbon atoms. Among these, an ethylene group having 2 carbon atoms is preferred from the viewpoint of the effect of improving the viscosity index.

M in the general formula (1) is a number of 0 to 20, and preferably a number of 0 to 10 from the viewpoint of improving the viscosity index. When m is 2 or more, R ² may be the same or different, and the (R ² O) _m moiety may be a random bond or a block bond.

R ³ in the general formula (1) is an alkyl group having 2 to 24 carbon atoms.
Examples of the alkyl group having 2 to 24 carbon atoms include a linear alkyl group having 2 to 24 carbon atoms and a branched alkyl group having 3 to 24 carbon atoms.
Examples of the linear alkyl group having 2 to 24 carbon atoms include ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group and n-nonyl group. N-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group , N-eicosyl group, n-heneicosyl group, n-docosyl group, n-tricosyl group and n-tetracosyl group.
Examples of the branched alkyl group having 3 to 24 carbon atoms include isopropyl group, isobutyl group, t-butyl group, isopentyl group, neopentyl group, isohexyl group, isooctyl group, 2-ethylhexyl group, isononyl group, 3,5,5-trimethyl. Hexyl group, 2,4,6-trimethylheptyl group, 2-methylnonyl group, isodecyl group, 2-ethylnonyl group, isoundecyl group, isododecyl group, 2-ethyldodecyl group, 2-ethyltridecyl group, 2-methyltetradecyl group Group, isohexadecyl group, 2-octylnonyl group, 2-hexylundecyl group, 2-ethylpentadecyl group, 2- (3-methylhexyl) -7-methyl-nonyl group, isooctadecyl group, 1-hexyl Tridecyl group, 2-ethylheptadecyl group, isoicosyl group, 1-octylpentadecyl Group, and 2-decyl tetradecyl group and the like.
Among R ³ , an alkyl group having 2 to 20 carbon atoms is preferable from the viewpoint of the effect of improving the viscosity index and low temperature viscosity, more preferably an alkyl group having 2 to 18 carbon atoms, and particularly preferably 2 carbon atoms. ˜16 alkyl groups.

  N in the general formula (1) is a number from 0 to 20, and from the viewpoint of the effect of improving the viscosity index and the low-temperature viscosity, a number from 1 to 18 is preferable, and a number from 2 to 16 is particularly preferable. Is a number from 4 to 14.

X ¹ in the general formula (1) is independently a group represented by —O— or —NH—. Among these, a group represented by -O- is preferable from the viewpoint of the effect of improving the viscosity index.

  Specific examples of the monomer (a) include 1-methylpropyl (meth) acrylate, 1-methylbutyl (meth) acrylate, 2-methylbutyl (meth) acrylate, 1-methylpentyl (meth) acrylate, (Meth) acrylic acid 2-methylpentyl, ethylene glycol mono-2-methylbutyl ether and (meth) acrylic acid ester, (meth) acrylic acid 3-methylpentyl, (meth) acrylic acid 1-methylhexyl, (meta ) 2-methylhexyl acrylate, 3-methylhexyl (meth) acrylate, 4-methylhexyl (meth) acrylate, 1-methylheptyl (meth) acrylate, N- (1-methylheptyl) (meth) acrylamide , 2-methylheptyl (meth) acrylate, 3-methylheptyl (meth) acrylate, (meth) acrylic 4-methylheptyl acid, 5-methylheptyl (meth) acrylate, 1-methyloctyl (meth) acrylate, 2-methyloctyl (meth) acrylate, 3-methyloctyl (meth) acrylate, (meth) acrylic 4-methyloctyl acid, 5-methyloctyl (meth) acrylate, 6-methyloctyl (meth) acrylate, 1-methylnonyl (meth) acrylate, 2-methylnonyl (meth) acrylate, diethylene glycol mono-2-methyl Esters of nonyl ether and (meth) acrylic acid, 3-methylnonyl (meth) acrylate, 4-methylnonyl (meth) acrylate, 5-methylnonyl (meth) acrylate, 6-methylnonyl (meth) acrylate, (meth ) 7-methylnonyl acrylate, 1-methyldecyl (meth) acrylate, (meth ) 2-methyldecyl acrylate, 3-methyldecyl (meth) acrylate, 4-methyldecyl (meth) acrylate, 5-methyldecyl (meth) acrylate, 6-methyldecyl (meth) acrylate, 7- (meth) acrylic acid Methyl decyl, 8-methyl decyl (meth) acrylate, 1-methyl tridecyl (meth) acrylate, 2-methyl tridecyl (meth) acrylate, 3-methyl tridecyl (meth) acrylate, (meth) acrylic acid 4 -Methyltridecyl, 5-methyltridecyl (meth) acrylate, 6-methyltridecyl (meth) acrylate, 7-methyltridecyl (meth) acrylate, 8-methyltridecyl (meth) acrylate, ( 9-methyltridecyl (meth) acrylate, 10-methyltridecyl (meth) acrylate, (meth) acrylic acid 11-methyltridecyl, 1-methylheptadecyl (meth) acrylate, 2-methylheptadecyl (meth) acrylate, 3-methylheptadecyl (meth) acrylate, 4-methylheptadecyl (meth) acrylate, 5-methylheptadecyl (meth) acrylate, 6-methylheptadecyl (meth) acrylate, 7-methylheptadecyl (meth) acrylate, 8-methylheptadecyl (meth) acrylate, (meth) acrylic acid 9 -Methylheptadecyl, 10-methylheptadecyl (meth) acrylate, 11-methylheptadecyl (meth) acrylate, 12-methylheptadecyl (meth) acrylate, 13-methylheptadecyl (meth) acrylate, ( 14-methylheptadecyl (meth) acrylate, 15-methylheptadecyl (meth) acrylate, (Meth) acrylic acid 1-methylheneicosyl, (meth) acrylic acid 2-methylheneicosyl, (meth) acrylic acid 3-methylheneicosyl, (meth) acrylic acid 4-methylheneicosyl, (meth) 5-methylheneicosyl acrylate, 6-methylheneicosyl (meth) acrylate, 7-methylheneicosyl (meth) acrylate, 8-methylheneicosyl (meth) acrylate, (meth) acrylic acid 9-methylheneicosyl, (meth) acrylic acid 10-methylheneicosyl, (meth) acrylic acid 11-methylheneicosyl, (meth) acrylic acid 12-methylheneicosyl, (meth) acrylic acid 13- Methylhenecosyl, 14-methylheneicosyl (meth) acrylate, 15-methylheneico (meth) acrylate , 17-methylhenecosyl (meth) acrylate, 19-methylheneicosyl (meth) acrylate, 1-methyltricosyl (meth) acrylate, 3-methyltricosyl (meth) acrylate, (meth ) 5-methyltricosyl acrylate, 7-methyltricosyl (meth) acrylate, 9-methyltricosyl (meth) acrylate, 11-methyltricosyl (meth) acrylate, 13-methyl (meth) acrylate Tricosyl, 15-methyltricosyl (meth) acrylate, 17-methyltricosyl (meth) acrylate, 19-methyltricosyl (meth) acrylate, 21-methyltricosyl (meth) acrylate, (meth) 1-methylhentriacontyl acrylate, 10-methylhentriacontyl (meth) acrylate, (meth) acrylic acid 1 8-methylhentriacontyl, (meth) acrylic acid 25-methylhentriacontyl, (meth) acrylic acid 29-methylhentriacontyl, (meth) acrylic acid 1-methylpentatetracontyl, (meth) acrylic acid 15 -Methylpentatetracontyl, (meth) acrylic acid 29-methylpentatetracontyl, (meth) acrylic acid 43-methylpentatetracontyl, etc., (meth) acrylic acid 1,2-dimethylpropyl, (meth) acrylic 1,2-dimethylbutyl acid, 1,3-dimethylbutyl (meth) acrylate, 1,2-dimethylhexyl (meth) acrylate, 1,5-dimethylhexyl (meth) acrylate, (meth) acrylic acid 1 , 2-dimethyldecyl, 1,5-dimethyldecyl (meth) acrylate, 5,9-di (meth) acrylic acid Tildecyl, 1,8-dimethylhexadecyl (meth) acrylate, 5,10-dimethylhexadecyl (meth) acrylate, 8,15-dimethylhexadecyl (meth) acrylate, 1,2- (meth) acrylic acid 1,2- Examples thereof include dimethyleicosyl, 5,10-dimethyleicosyl (meth) acrylate, 9,19-dimethyleicosyl (meth) acrylate, and 1,9,19-trimethyleicosyl (meth) acrylate.

  In addition to the monomer (a), the (co) polymer (A) in the present invention has a (meth) acrylic acid alkyl ester (b) having a linear alkyl group having 1 to 4 carbon atoms and / or 8 carbon atoms. It is preferable from a viewpoint of a viscosity index improvement effect that it is a copolymer which uses the (meth) acrylic-acid alkylester (c) which has -36 linear alkyl group as a structural monomer.

Examples of the (meth) acrylic acid alkyl ester (b) having a linear alkyl group having 1 to 4 carbon atoms include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and (meth) ) N-butyl acrylate.
Of these, (b) is preferably a (meth) acrylic acid ester having a linear alkyl group having 1 to 3 carbon atoms, more preferably methyl (meth) acrylate and ethyl (meth) acrylate, Particularly preferred is methyl (meth) acrylate.

Examples of the (meth) acrylic acid alkyl ester (c) having a linear alkyl group having 8 to 36 carbon atoms include n-octyl (meth) acrylate, n-nonyl (meth) acrylate, and n- (meth) acrylate. Decyl, n-dodecyl (meth) acrylate, n-tridecyl (meth) acrylate, n-tetradecyl (meth) acrylate, n-pentadecyl (meth) acrylate, n-hexadecyl (meth) acrylate, (meth) Examples include n-octadecyl acrylate, n-icosyl (meth) acrylate, n-tetracosyl (meth) acrylate, n-triacontyl (meth) acrylate, and n-hexatriacontyl (meth) acrylate.
Among (c), (meth) acrylic acid alkyl ester having a linear alkyl group having 12 to 32 carbon atoms is preferred, and (meth) having a linear alkyl group having 16 to 30 carbon atoms is more preferred. Acrylic acid esters, particularly preferred are (meth) acrylic acid esters having a linear alkyl group having 18 to 28 carbon atoms.

  The (co) polymer (A) in the present invention is a copolymer having a monomer (d) represented by the following general formula (2) as a constituent monomer in addition to (a). It is preferable from the viewpoint of the effect of improving the viscosity index.

［Ｒ^４は水素原子又はメチル基；Ｒ^５は炭素数２〜４のアルキレン基；Ｒ^６は、一般式（１）における−（ＣＨ_２）_ｎ−ＣＨ（ＣＨ_３）−Ｒ^３で表されるアルキル基を除いた、炭素数１６〜６０の分岐アルキル基；Ｘ^２は−Ｏ−又は−ＮＨ−で表される基；ｐは０〜２０の数であり、ｐが２以上の場合のＲ^５は同一でも異なっていてもよく、（Ｒ^５Ｏ）_ｐ部分はランダム結合でもブロック結合でもよい。］

[R ⁴ is a hydrogen atom or a methyl group; R ⁵ is an alkylene group having 2 to 4 carbon atoms; R ⁶ is represented by — (CH ₂ ) _n —CH (CH ₃ ) —R ³ in the general formula (1). A branched alkyl group having 16 to 60 carbon atoms excluding the alkyl group; X ² is a group represented by —O— or —NH—; p is a number of 0 to 20, and p is 2 or more. R ⁵ may be the same or different, and the (R ⁵ O) _p moiety may be a random bond or a block bond. ]

R ⁴ in the general formula (2) is a hydrogen atom or a methyl group. Among these, a methyl group is preferable from the viewpoint of improving the viscosity index.

X ² in the general formula (2) is a group represented by —O— or —NH—. Among these, the group represented by —O— is preferable from the viewpoint of the effect of improving the viscosity index.

R ⁵ in the general formula (2) is an alkylene group having 2 to 4 carbon atoms. Examples of the alkylene group having 2 to 4 carbon atoms include an ethylene group, 1,2- or 1,3-propylene group, and 1,2-, 1,3- or 1,4-butylene group. Among these, the ethylene group and the 1,2-propylene group are preferable from the viewpoint of the effect of improving the viscosity index.

P in the general formula (2) is a number from 0 to 20, preferably from 0 to 5, more preferably from 0 to 2 from the viewpoint of the effect of improving the viscosity index and low temperature viscosity.
When p is 2 or more, R ⁵ may be the same or different, and the (R ⁵ O) _p portion may be a random bond or a block bond.

R ⁶ in the general formula (2) is a branched alkyl group having 16 to 60 carbon atoms, excluding the alkyl group represented by — (CH ₂ ) _n —CH (CH ₃ ) —R ³ in the general formula (1). Specifically, 2-octylnonyl group, 2-hexylundecyl group, 2-ethylpentadecyl group, 2- (3-methylhexyl) -7-methyl-nonyl group, 1-hexyltridecyl group 2-ethylheptadecyl group, 2-octylundecyl group, 1-undecyldodecyl group, 1-octylpentadecyl group, 2-decyltridecyl group, 2-decyltetradecyl group, 2- (1,4,4- Trimethylbutyl) -5,7,7-trimethyl-heptyl group, 2-dodecylpentadecyl group, 2-tetradecylheptadecyl group, 2-hexadecylheptadecyl group, 1-heptyltriconti Group, 2-heptadecylicosyl group, 1-octadecylicosyl group, 2-hexadecyldocosyl group, 2- (1,4,4-trimethylbutyl) -5,7,7-trimethyl-tricontyl group, 2 -Icosyl docosyl group, 1-icosyl tetracosyl group, 2-ethyl-4-butyl-tetracontyl group, 2-tetracosyl hexacosyl group, 2-tetradecyl tetracontyl group, 2-dodecyl hexatetracontyl group Group, 2- (3-methylhexyl) -7-ethyl-pentacontyl group, 1-octacosyltricontyl group, 1-icosyltetracontyl group, 2-decylpentacontyl group and olefin [for example, isobutene oligomer (10 ˜15-mer) and the like], and the like, and the like.
Of the branched alkyl groups having 16 to 60 carbon atoms, preferred are branched alkyl groups having 16 to 50 carbon atoms, and more preferred are branched alkyl groups having 16 to 44 carbon atoms, particularly from the viewpoint of improving the viscosity index. A branched alkyl group having 20 to 40 carbon atoms is preferred.

  Specific examples of the monomer (d) include 2-octylnonyl (meth) acrylate, an ester of ethylene glycol mono-2-ethylpentadecyl ether and (meth) acrylic acid, and 1-hexyl (meth) acrylate. Tridecyl, 2-ethylheptadecyl (meth) acrylate, 1-octylpentadecyl (meth) acrylate, 2-decyltetradecyl (meth) acrylate, 2-dodecylpentadecyl (meth) acrylate, (meth) 2-tetradecylheptadecyl acrylate, 2-hexadecylheptadecyl (meth) acrylate, 2-heptadecylicosyl (meth) acrylate, 2-hexadecyldocosyl (meth) acrylate, (meth) acrylic acid 2-eicosyl docosyl, (meth) acrylic acid 2-tetracosyl hexacosyl, (meth) acrylic acid 2- An oxoalcohol obtained from tradecyltetracontyl, (meth) acrylate 2-dodecylhexatetracontyl, (meth) acrylate 1-octacosyltricontyl, and isobutene oligomer (10-15mer) and (meta ) An ester with acrylic acid.

(A) is a copolymer further comprising a nitrogen atom-containing monomer (e), a hydroxyl group-containing monomer (f) and / or a phosphate group-containing monomer (g) as a constituent monomer. Is preferable from the viewpoint of the effect of improving the viscosity index.
Examples of the nitrogen atom-containing monomer (e) include the following monomers (e1) to (e4) excluding the monomer (a).

Amide group-containing monomer (e1):
(Meth) acrylamide, monoalkyl (meth) acrylamide [one having an alkyl group having 1 to 4 carbon atoms bonded to a nitrogen atom; for example, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-isopropyl (Meth) acrylamide and Nn- or isobutyl (meth) acrylamide etc.], N- (N′-monoalkylaminoalkyl) (meth) acrylamide [one alkyl group having 1 to 4 carbon atoms bound to the nitrogen atom. Those having an aminoalkyl group (2 to 6 carbon atoms); for example, N- (N′-methylaminoethyl) (meth) acrylamide, N- (N′-ethylaminoethyl) (meth) acrylamide, N- (N ′ -Isopropylamino-n-butyl) (meth) acrylamide and N- (N'-n- or isobutylamino-n-butyl) ) (Meth) acrylamide etc.], dialkyl (meth) acrylamide [nitrogen atom having two C1-C4 alkyl groups bonded; for example, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meta ) Acrylamide, N, N-diisopropyl (meth) acrylamide and N, N-di-n-butyl (meth) acrylamide etc.], N- (N ′, N′-dialkylaminoalkyl) (meth) acrylamide [aminoalkyl group Having an aminoalkyl group (2 to 6 carbon atoms) in which two alkyl groups having 1 to 4 carbon atoms are bonded to the nitrogen atom of, for example, N- (N ′, N′-dimethylaminoethyl) (meth) acrylamide, N- (N ′, N′-diethylaminoethyl) (meth) acrylamide, N- (N ′, N′-dimethylaminopropyl) (meth) acrylic And N- (N ′, N′-di-n-butylaminobutyl) (meth) acrylamide etc.]; N-vinylcarboxylic acid amide [N-vinylformamide, N-vinylacetamide, N-vinyl-n- or Isopropionic acid amide, N-vinylhydroxyacetamide and the like] and the like.

Nitro group-containing monomer (e2):
4-nitrostyrene etc. are mentioned.

Primary to tertiary amino group-containing monomer (e3):
Primary amino group-containing monomer {C3-C6 alkenylamine [(meth) allylamine, crotylamine, etc.], Aminoalkyl (C2-C6) (meth) acrylate [Aminoethyl (meth) acrylate, etc.}} Secondary amino group-containing monomer {monoalkylaminoalkyl (meth) acrylate [having an aminoalkyl group (2 to 6 carbon atoms) in which one alkyl group having 1 to 6 carbon atoms is bonded to a nitrogen atom; Nt-butylaminoethyl (meth) acrylate and N-methylaminoethyl (meth) acrylate, etc.], C6-C12 dialkenylamine [di (meth) allylamine, etc.]}; tertiary amino group-containing single amount Body {dialkylaminoalkyl (meth) acrylate [an aminoalkyl group in which two alkyl groups having 1 to 6 carbon atoms are bonded to a nitrogen atom (carbon Having 2 to 6); for example, N, N-dimethylaminoethyl (meth) acrylate and N, N-diethylaminoethyl (meth) acrylate, etc.], alicyclic (meth) acrylate having a nitrogen atom [morpholinoethyl ( Meth) acrylates, etc.], aromatic monomers [N- (N ′, N′-diphenylaminoethyl) (meth) acrylamide, N, N-dimethylaminostyrene, 4-vinylpyridine, 2-vinylpyridine, N -Vinyl pyrrole, N-vinyl pyrrolidone, N-vinyl thiopyrrolidone, etc.]} and their hydrochlorides, sulfates, phosphates or lower alkyl (C1-8) monocarboxylic acids (such as acetic acid and propionic acid) Examples include salts.

Nitrile group-containing monomer (e4):
Examples include (meth) acrylonitrile.

  Among (e), preferred are (e1) and (e3), and more preferred are N- (N ′, N′-diphenylaminoethyl) (meth) acrylamide, N- (N ′, N ′). -Dimethylaminoethyl) (meth) acrylamide, N- (N ', N'-diethylaminoethyl) (meth) acrylamide, N- (N', N'-dimethylaminopropyl) (meth) acrylamide, N, N-dimethyl Aminoethyl (meth) acrylate and N, N-diethylaminoethyl (meth) acrylate.

Hydroxyl group-containing monomer (f):
Hydroxyl group-containing aromatic monomer (p-hydroxystyrene and the like), hydroxyalkyl (2 to 6 carbon atoms) (meth) acrylate [2-hydroxyethyl (meth) acrylate, and 2- or 3-hydroxypropyl (meth) acrylate Etc.], mono- or bis-hydroxyalkyl (C1-C4) substituted (meth) acrylamide [N, N-bis (hydroxymethyl) (meth) acrylamide, N, N-bis (hydroxypropyl) (meth) acrylamide N, N-bis (2-hydroxybutyl) (meth) acrylamide etc.], vinyl alcohol, alkenol having 3 to 12 carbon atoms [(meth) allyl alcohol, crotyl alcohol, isocrotyl alcohol, 1-octenol and 1 -Undecenol and the like], an alkene monool having 4 to 12 carbon atoms, or Lucenediol [1-buten-3-ol, 2-buten-1-ol, 2-butene-1,4-diol, etc.], hydroxyalkyl (C1-6) alkenyl (C3-10) ether (2 -Hydroxyethylpropenyl ether, etc.), polyvalent (3-8 valent) alcohols (glycerin, pentaerythritol, sorbitol, sorbitan, diglycerin, saccharides, sucrose, etc.) alkenyl (3 to 10 carbon atoms) ether or (meth) acrylate [Sucrose (meth) allyl ether etc.] etc .;
Polyoxyalkylene glycol (alkylene group having 2 to 4 carbon atoms, polymerization degree 2 to 50), polyoxyalkylene polyol [polyoxyalkylene ether of 3 to 8 valent alcohol (alkylene group having 2 to 4 carbon atoms, polymerization degree) 2-100)], mono (meth) acrylates of polyoxyalkylene glycol or polyoxyalkylene polyol alkyl (carbon number 1-4) ether [polyethylene glycol (Mn: 100-300) mono (meth) acrylate, polypropylene glycol ( Mn: 130-500) mono (meth) acrylate, methoxypolyethylene glycol (Mn: 110-310) (meth) acrylate, lauryl alcohol ethylene oxide adduct (2-30 mol) (meth) acrylate and mono (meth) acryl Polyoxyethylene (Mn: 150 to 230), sorbitan, etc.] or the like; and the like.

  Examples of the phosphate group-containing monomer (g) include the following monomers (g1) to (g2).

Phosphoric ester group-containing monomer (g1):
(Meth) acryloyloxyalkyl (2 to 4 carbon atoms) phosphoric acid ester [(meth) acryloyloxyethyl phosphate and (meth) acryloyloxyisopropyl phosphate] and phosphoric acid alkenyl ester [vinyl phosphate, allyl phosphate, Propenyl phosphate, isopropenyl phosphate, butenyl phosphate, pentenyl phosphate, octenyl phosphate, decenyl phosphate, dodecenyl phosphate, etc.]. “(Meth) acryloyloxy” means acryloyloxy or methacryloyloxy.

Phosphono group-containing monomer (g2):
(Meth) acryloyloxyalkyl (2 to 4 carbon atoms) phosphonic acid [(meth) acryloyloxyethyl phosphonic acid etc.] and alkenyl (2 to 12 carbon atoms) phosphonic acid [vinyl phosphonic acid, allyl phosphonic acid and octenyl Phosphonic acid, etc.].

  Of these, (g1) is preferable among (g), (meth) acryloyloxyalkyl (2 to 4 carbon atoms) phosphate is more preferable, and (meth) acryloyloxyethyl phosphate is particularly preferable. It is.

  In addition to the monomers (a) to (g), (A) may use the following monomers (h) to (n) as constituent monomers.

Aliphatic hydrocarbon monomer (h):
Alkenes having 2 to 20 carbon atoms (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.) and alkadienes having 4 to 12 carbon atoms (butadiene, isoprene, 1,4-pentadiene, 1 , 6-heptadiene and 1,7-octadiene).

Alicyclic hydrocarbon monomer (i):
Examples include cyclohexene, (di) cyclopentadiene, pinene, limonene, vinylcyclohexene, and ethylidenebicycloheptene.

Aromatic hydrocarbon monomer (j):
Styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, 4-ethylstyrene, 4-isopropylstyrene, 4-butylstyrene, 4-phenylstyrene, 4-cyclohexylstyrene, 4-benzylstyrene, 4-chloro Examples include tilbenzene, indene, and 2-vinylnaphthalene.

Vinyl esters, vinyl ethers, vinyl ketones (k):
Vinyl esters of saturated fatty acids having 2 to 12 carbon atoms (such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl octoate), alkyl, aryl or alkoxyalkyl vinyl ethers having 1 to 12 carbon atoms (methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether) Butyl vinyl ether, 2-ethylhexyl vinyl ether, phenyl vinyl ether, vinyl-2-methoxyethyl ether and vinyl-2-butoxyethyl ether) and alkyl or aryl vinyl ketones having 1 to 8 carbon atoms (methyl vinyl ketone, ethyl vinyl ketone and Phenyl vinyl ketone, etc.).

Epoxy group-containing monomer (l):
Examples thereof include glycidyl (meth) acrylate and glycidyl (meth) allyl ether.

Halogen element-containing monomer (m):
Examples thereof include vinyl chloride, vinyl bromide, vinylidene chloride, (meth) allyl chloride and halogenated styrene (dichlorostyrene and the like).

Unsaturated polycarboxylic acid ester (n):
Alkyl, cycloalkyl or aralkyl ester of unsaturated polycarboxylic acid [alkyl diester having 1 to 8 carbon atoms of unsaturated dicarboxylic acid (such as maleic acid, fumaric acid and itaconic acid) (dimethyl maleate, dimethyl fumarate, diethyl maleate) And dioctyl maleate)] and the like.

The proportion of (a) constituting (A) is preferably 5 to 80% by weight, more preferably, based on the weight of (A), from the viewpoint of the effect of improving the viscosity index and the low temperature viscosity of the lubricating oil composition. Is 5 to 65% by weight, particularly preferably 10 to 50% by weight.
The proportion of (b) constituting (A) is preferably 5 to 60% by weight, more preferably, based on the weight of (A), from the viewpoint of the viscosity index improving effect and the low temperature viscosity of the lubricating oil composition. Is 10 to 55% by weight, particularly preferably 20 to 50% by weight.
The proportion of (c) constituting (A) is preferably 0.1 to 40% by weight based on the weight of (A), from the viewpoint of the viscosity index improving effect and the low temperature viscosity of the lubricating oil composition. More preferably, it is 1-35 weight%, Most preferably, it is 2-30 weight%.
The proportion of (d) constituting (A) is preferably 0.1 to 40% by weight based on the weight of (A) from the viewpoint of the effect of improving the viscosity index and the low temperature viscosity of the lubricating oil composition, More preferably, it is 1-35 weight%, Most preferably, it is 2-30 weight%.
The ratio of (e) to (g) constituting (A) is preferably 0 to 15% by weight, based on the weight of (A), from the viewpoint of the effect of improving the viscosity index and the low temperature viscosity of the lubricating oil composition. More preferably 1 to 12% by weight, particularly preferably 2 to 10% by weight.
The proportion of (h) to (n) constituting (A) is preferably 0 to 10% by weight based on the weight of (A) from the viewpoint of the effect of improving the viscosity index and the low temperature viscosity of the lubricating oil composition. More preferably 1 to 7% by weight, particularly preferably 2 to 5% by weight.

The solubility parameter (hereinafter abbreviated as SP value) of (A) is 7.3 to 9.7 (cal / cm ³ ) ^1/2 , and the viewpoint of improving the viscosity index and the low temperature viscosity of the lubricating oil composition Therefore, it is preferably 9.0 to 9.6 (cal / cm ³ ) ^1/2 , and more preferably 9.1 to 9.5 (cal / cm ³ ) ^1/2 .
The SP value of (A) is a value obtained by calculating the SP value of each monomer constituting (A) and averaging the SP value of each monomer based on the mole fraction of the constituent monomer units. It is.
The SP value of (A) can be adjusted to 7.3 to 9.5 (cal / cm ³ ) ^1/2 by appropriately adjusting the SP value and molar fraction of the monomer used.
The SP value in the present invention is a value calculated by the method described in the Fedors method (Polymer Engineering and Science, February, 1974, Vol. 14, No. 2 P. 147 to 154).

The absolute value of the difference between the SP value of (A) and the SP value of the base oil is preferably 0.5 to 1.8 (cal / cm ³ ) from the viewpoint of the effect of improving the viscosity index and the low temperature viscosity of the lubricating oil composition. It is ^1/2 , More preferably, it is 1.0-1.8 (cal / cm < ³ >) < ^1/2 >.

The weight average molecular weight (hereinafter abbreviated as Mw) of (A) is preferably 5,000 to 2,000,000 from the viewpoint of the effect of improving the viscosity index and the low temperature viscosity of the lubricating oil composition, and a more preferable range is Depends on the use of the lubricating oil composition, and is in the range shown in Table 1.
Mw of (A) can be measured under the following conditions by gel permeation chromatography (GPC).
<GPC measurement conditions>
Apparatus: “HLC-802A” [manufactured by Tosoh Corporation]
Column: Two “TSK gel GMH6” [manufactured by Tosoh Corporation] Measurement temperature: 40 ° C.
Sample solution: 0.5 wt% tetrahydrofuran solution Solution injection amount: 200 μl
Detection device: Refractive index detector Reference material: Standard polystyrene (TSK standard POLYSTYRENE) 12 points (molecular weight: 500, 1,050, 2,800, 5,970, 9,100, 18,100, 37,900, 96,400) , 190,000, 355,000, 1,090,000, 2,890,000) [manufactured by Tosoh Corporation]

* ：オートマチックトランスミッション油
** ：ベルト−コンティニュアスリーバリュアブルトランスミッション油
*** ：マニュアルトランスミッション油

*: Automatic transmission oil
**: Belt-Continuously variable transmission oil
***: Manual transmission oil

The crystallization temperature of (A) is preferably −30 ° C. or less, more preferably −40 ° C. or less, and particularly preferably −50 ° C. or less from the viewpoint of the low temperature viscosity of the lubricating oil composition.
The crystallization temperature of (A) was measured using a differential scanning calorimeter “UNIX (registered trademark) DSC7” (manufactured by PERKIN-ELMER) at a constant rate of 10 ° C./min with 5 mg as a sample. It is the crystallization temperature observed when cooling from 100 ° C to -70 ° C.

(A) can be obtained by a known production method, and specifically includes a method obtained by solution polymerization of the above monomer in a solvent in the presence of a polymerization catalyst.
Examples of the solvent include toluene, xylene, alkylbenzene having 9 to 10 carbon atoms, methyl ethyl ketone, and mineral oil.
Examples of the polymerization catalyst include azo catalysts (2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), etc.), peroxide catalysts (benzoylper Oxide, cumyl peroxide, lauryl peroxide, etc.) and redox catalysts (a mixture of benzoyl peroxide and tertiary amine, etc.). Furthermore, if necessary, a known chain transfer agent (such as an alkyl mercaptan having 2 to 20 carbon atoms) can also be used.
The polymerization temperature is preferably 25 to 140 ° C, more preferably 50 to 120 ° C. In addition to the above solution polymerization, (A) can be obtained by bulk polymerization, emulsion polymerization or suspension polymerization.
When (A) is a copolymer, the polymerization form may be either a random addition polymer or an alternating copolymer, and may be either a graft copolymer or a block copolymer.

The viscosity index improver of the present invention may be used in combination with (A) and an alkyl (meth) acrylate (co) polymer (B) other than (A).
(B) is not particularly limited as long as it is an alkyl (meth) acrylic acid ester (co) polymer other than (A), but a (meth) acrylic acid alkyl ester having a linear alkyl group having 1 to 18 carbon atoms. Examples include (co) polymers.
Specific examples of (B) include n-octadecyl methacrylate / n-dodecyl methacrylate (molar ratio 10-30 / 90-70) copolymer, n-tetradecyl methacrylate / n-dodecyl methacrylate (molar ratio 10). -30 / 90-70) Copolymer, n-hexadecyl methacrylate / n-dodecyl methacrylate / methyl methacrylate (molar ratio 20-40 / 55-75 / 0-10) copolymer and n-dodecyl acrylate / N-dodecyl methacrylate (molar ratio 10 to 40/90 to 60) copolymer and the like, and these may be used alone or in combination of two or more.

  When (A) and (B) are used in combination, the amount of (B) used is preferably 0.01 to 30% by weight based on the weight of (A) from the viewpoint of the low temperature viscosity of the lubricating oil composition. More preferably, the content is 0.01 to 20% by weight, and particularly preferably 0.01 to 10% by weight.

  The lubricating oil composition of the present invention comprises the viscosity index improver of the present invention and a base oil. Base oils include mineral oils (solvent refined oils, paraffin oils, high viscosity index oils containing isoparaffins, high viscosity index oils obtained by hydrocracking isoparaffins, naphthenic oils, etc.), synthetic lubricating oils (hydrocarbon synthetic lubricating oils) (Poly α-olefin-based synthetic lubricating oil, etc.) and ester-based synthetic lubricating oil, etc.] and mixtures thereof. Of these, mineral oil is preferred.

(Measured by JIS-K2283) kinematic viscosity at 100 ° C. of the base oil is preferably from the viewpoint of the viscosity index improving effect is 1 to 15 mm ² / s, more preferably from 2 to 5 mm ² / s.
The viscosity index (measured according to JIS-K2283) of the base oil is preferably 110 or more from the viewpoint of the effect of improving the viscosity index.

  The cloud point (measured according to JIS-K2269) of the base oil is preferably −5 ° C. or lower, more preferably −15 ° C. or lower. When the cloud point of the base oil is within this range, the low temperature viscosity of the lubricating oil composition is good.

The content of the viscosity index improver in the lubricating oil composition of the present invention is preferably 1 to 30% by weight in terms of the weight of (A) in the viscosity index improver based on the weight of the base oil. .
When the lubricating oil composition is used as an engine oil, a base oil having a kinematic viscosity at 100 ° C. of 4 to 10 mm ² / s and containing 2 to 10% by weight of (A) is preferable.
When the lubricating oil composition is used as a gear oil, a base oil having a kinematic viscosity at 100 ° C. of ² to 10 mm ² / s and containing 3 to 30% by weight of (A) is preferable.
When the lubricating oil composition is used as an automatic transmission oil (such as ATF and belt-CVTF), a base oil having a kinematic viscosity at 100 ° C. of ² to 6 mm ² / s and 3 to 25% by weight of (A) What is contained is preferable.
When the lubricating oil composition is used as a traction oil, a base oil having a kinematic viscosity at 100 ° C. of 1 to 5 mm ² / s and containing (A) of 0.5 to 10% by weight is preferable. .

The lubricating oil composition of the present invention may contain various additives. The following are mentioned as an additive.
(1) Detergent:
Basic, overbased or neutral metal salts [overbased or alkaline earth metal salts of sulfonates (such as petroleum sulfonates, alkylbenzene sulfonates and alkylnaphthalene sulfonates)], salicylates, phenates, naphthenates , Carbonates, phosphonates and mixtures thereof;
(2) Dispersant:
Succinimides (bis- or mono-polybutenyl succinimides), Mannich condensation products, borates and the like;
(3) Antioxidant:
Hindered phenols and aromatic secondary amines, etc .;
(4) Oiliness improver:
Long chain fatty acids and their esters (such as oleic acid and oleic acid esters), long chain amines and their amides (such as oleylamine and oleylamide), etc .;
(5) Friction and wear modifier:
Molybdenum and zinc compounds (such as molybdenum dithiophosphate, molybdenum dithiocarbamate and zinc dialkyldithiophosphate);
(6) Extreme pressure agent:
Sulfur compounds (mono or disulfides, sulfoxides and sulfur phosphide compounds), phosphide compounds and chlorinated compounds (chlorinated paraffins, etc.);
(7) Antifoaming agent:
Silicon oil, metal soap, fatty acid ester and phosphate compound, etc .;
(8) Demulsifier:
Quaternary ammonium salts (tetraalkylammonium salts, etc.), sulfated oils and phosphates (polyoxyethylene-containing nonionic surfactant phosphates, etc.);
(9) Corrosion inhibitor:
Nitrogen atom-containing compounds (such as benzotriazole and 1,3,4-thiodiazolyl-2,5-bisdialkyldithiocarbamate) and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

<Examples 1-6, Comparative Examples 1-4>
In a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a nitrogen introducing tube, base oil A (SP value: 8.3 (cal / cm ³ ) ^1/2 , kinematic viscosity at 100 ° C .: 4.2 mm ² / S, viscosity index: 128) 400 parts by weight, 100 parts by weight of the monomer composition described in Table 2, 0.5 part by weight of 2,2′-azobis (2,4-dimethylvaleronitrile) and 2,2 After 0.2 parts by weight of '-azobis (2-methylbutyronitrile) was added and nitrogen substitution (gas phase oxygen concentration 100 ppm) was performed, the temperature was raised to 76 ° C. with stirring in a sealed state. The polymerization reaction was performed for 4 hours. After raising the temperature to 120 to 130 ° C., the unreacted monomer is removed under reduced pressure (0.027 to 0.040 MPa) at the same temperature over 2 hours, and the copolymers (A1) to (A6), (H1 Viscosity index improvers (R1) to (R6) and (S1) to (S4) containing (H4) to (H4). The SP values of the obtained copolymers (A1) to (A6) and (H1) to (H4) were calculated by the above method, and Mw and the crystallization temperature were measured by the above method. Moreover, the base oil solubility of the copolymer was evaluated by the following method. The results are shown in Table 2.

<Examples 7-8, Comparative Examples 5-6>
In a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, a dropping funnel, a nitrogen introduction tube and a decompression device, base oil B [SP value: 8.3 (cal / cm ³ ) ^1/2 , 100 ° C. Viscosity: 2.4 mm ² / s, Viscosity index: 96] 100 parts by weight were charged, and in another glass beaker, 100 parts by weight of the monomers listed in Table 2 and 1.0 part by weight of dodecyl mercaptan as a chain transfer agent Part, 0.5 part by weight of 2,2′-azobis (2,4-dimethylvaleronitrile) and 0.2 part by weight of 2,2′-azobis (2-methylbutyronitrile) are added and stirred at 20 ° C. The monomer solution was prepared by mixing, and charged into the dropping funnel. After carrying out nitrogen substitution of the gas phase part of the reaction vessel, the monomer solution was dropped over 2 hours while maintaining the temperature in the system under sealed at 70 to 85 ° C., and ripened at 85 ° C. for 2 hours from the end of dropping. Then, after raising the temperature to 120 to 130 ° C., the unreacted monomer is removed under reduced pressure (0.027 to 0.040 MPa) at the same temperature over 2 hours, and the copolymers (A7) to (A8) Viscosity index improvers (R7) to (R8) and (S5) to (S6) containing (H5) to (H6). The SP values of the obtained copolymers (A7) to (A8) and (H5) to (H6) were calculated by the above method, and Mw and crystallization temperature were measured by the above method. Moreover, the base oil solubility of the copolymer was evaluated by the following method. The results are shown in Table 2.

<Evaluation method of base oil solubility of copolymer>
The appearance of the viscosity index improvers (R1) to (R8) and (S1) to (S6) was visually observed, and the base oil solubility was evaluated according to the following evaluation criteria.
[Evaluation criteria]
○: Appearance is uniform and there is no insoluble matter in the copolymer ×: Appearance is inhomogeneous and insoluble matter in the copolymer is observed

The compositions of the monomers (a) to (g) described in Table 2 are as described below.
(A-1): Methyl tridecyl methacrylate (mixture of 30% by weight of 2-methyl tridecyl methacrylate and 70% by weight of 5-methyl tridecyl methacrylate)
(A-2): methyl heptadecyl methacrylate (mixture of 50% by weight of 5-methylheptadecyl methacrylate and 50% by weight of 13-methylheptadecyl methacrylate)
(A-3): Methyl heneicosyl methacrylate (mixture of 30% by weight of 4-methyl heneicosyl methacrylate, 40% by weight of 10-methyl heneicosyl methacrylate, 30% by weight of 18-methyl heneicosyl methacrylate) )
(B-1): methyl methacrylate (c-1): n-tetradecyl methacrylate (c-2): n-hexadecyl methacrylate (c-3): n-octadecyl methacrylate (d-1): methacrylic acid 2-n-decyltetradecyl (e-1): N, N-dimethylaminoethyl methacrylate (f-1): hydroxyethyl methacrylate (g-1): methacryloyloxyethyl phosphate

<Examples 9-14, Comparative Examples 7-10 (Evaluation of Lubricating Oil Composition for Engine Oil)>
Base oil A (SP value: 8.3 (cal / cm ³ ) ^1/2 , kinematic viscosity at 100 ° C .: 4.2 mm ² / s, viscosity index: 128) is put into a stainless steel container equipped with a stirrer. Viscosity index improvers (R1) to (R6) and (S1) to respectively have an HTHS viscosity at 150 ° C. of 2.60 ± 0.05 (mm ² / s). (S4) was added to obtain lubricating oil compositions (V1) to (V6) and (W1) to (W4).
The viscosity index, HTHS viscosity (80 ° C.), and low temperature viscosity (−40 ° C.) of the lubricating oil compositions (V1) to (V6) and (W1) to (W4) were measured by the following methods. The results are shown in Table 3.

<Examples 15-16, Comparative Examples 11-12 (Evaluation of Lubricating Oil Composition for Gear Oil)>
Base oil B (SP value: 8.3 (cal / cm ³ ) ^1/2 , kinematic viscosity at 100 ° C .: 2.4 mm ² / s, viscosity index: 96) is put into a stainless steel container equipped with a stirrer. Viscosity index improvers (R7) to (R8) and (S5) to (S5) so that the resulting lubricant composition has a kinematic viscosity at 100 ° C. of 4.50 ± 0.02 (mm ² / s). S6) was added to obtain lubricating oil compositions (V7) to (V8) and (W5) to (W6).
The viscosity index, kinematic viscosity at 40 ° C., HTHS viscosity and low temperature viscosity (−40 ° C.) of the lubricating oil compositions (V7) to (V8) and (W5) to (W6) were measured by the following methods. The results are shown in Table 4.

<Measuring method of viscosity index of lubricating oil composition and kinematic viscosity at 40 ° C.>
It measured by the method of JIS-K2283.

<Method for Measuring HTHS Viscosity of Lubricating Oil Composition>
The measurement was performed at 80 ° C. by the method of ASTM D 5481.

<Method for measuring low temperature viscosity of lubricating oil composition>
The viscosity at −40 ° C. was measured by the method of JPI-5S-42-2004.

  As apparent from the results of Tables 3 and 4, the lubricating oil compositions (Examples 9 to 16) containing the viscosity index improver of the present invention were compared with the lubricating oil compositions of Comparative Examples 7 to 12. Thus, the viscosity index improving effect is high and the low temperature viscosity is low.

  The lubricating oil composition containing the viscosity index improver of the present invention includes a drive system lubricating oil (MTF, differential gear oil, ATF, belt-CVTF, etc.), hydraulic oil (mechanical hydraulic oil, power steering oil, and shock). Absorber oil etc.), engine oil (gasoline and diesel etc.) and traction oil are suitable.

Claims (12)

A viscosity index improver containing a (co) polymer (A) having a monomer (a) represented by the following general formula (1) as an essential constituent monomer.

[R ¹ is a hydrogen atom or a methyl group; X ¹ is a group represented by —O— or —NH—; R ² is an alkylene group having 2 to 4 carbon atoms; R ³ is an alkyl group having 2 to 24 carbon atoms; m is a number from 0 to 20, and R ² when m is 2 or more may be the same or different, and the (R ² O) _m moiety may be a random bond or a block bond. N is a number from 0 to 20. ]   The viscosity index improver according to claim 1, wherein the absolute value of the difference between the solubility parameter of (A) and the solubility parameter of the base oil is 0.5 to 1.8.   The viscosity index improver according to claim 1 or 2, wherein (a) is a (meth) acrylic acid ester.   (A) is a (meth) acrylic acid alkyl ester (b) having a linear alkyl group having 1 to 4 carbon atoms and / or a linear alkyl group having 8 to 36 carbon atoms as a constituent monomer of (A). The viscosity index improver according to any one of claims 1 to 3, which is a copolymer comprising (meth) acrylic acid alkyl ester (c). (A) is a copolymer having the monomer (d) represented by the general formula (2) as a constituent monomer as the constituent monomer of (A). The viscosity index improver described in 1.

[R ⁴ is a hydrogen atom or a methyl group; X ² is a group represented by —O— or —NH—; R ⁵ is an alkylene group having 2 to 4 carbon atoms; R ⁶ is a branched alkyl group having 16 to ⁶⁰ carbon atoms; P is a number from 0 to 20, and when p is 2 or more, R ^{5 s} may be the same or different, and the (R ⁵ O) _p moiety may be a random bond or a block bond. ]   (A) is a constituent monomer of (A) further comprising a nitrogen atom-containing monomer (e), a hydroxyl group-containing monomer (f) and / or a phosphate group-containing monomer (g). The viscosity index improver according to any one of claims 1 to 5, wherein the viscosity index improver is a copolymer. (A) is 5 to 80% by weight of (a) based on the weight of (A) as a constituent monomer, (b)
The viscosity index improver according to claim 5 or 6, which is a copolymer containing 5 to 60% by weight, 0.1 to 40% by weight of (c) and 0.1 to 40% by weight of (d).   The viscosity index improver according to any one of claims 1 to 7, wherein (A) has a weight average molecular weight of 5,000 to 2,000,000.   Furthermore, the (co) polymer (B) other than (A) is contained in an amount of 0.01 to 30% by weight based on the weight of (A), improving the viscosity index according to any one of claims 1 to 8. Agent.   A lubricating oil composition comprising the viscosity index improver according to claim 1 and a base oil.   Furthermore, it contains at least one additive selected from the group consisting of detergents, dispersants, antioxidants, oiliness improvers, friction wear modifiers, extreme pressure agents, antifoaming agents, anti-emulsifiers and corrosion inhibitors. The lubricating oil composition according to claim 10. The lubricating oil composition according to claim 10 or 11, wherein the base oil has a kinematic viscosity at 100 ° C of 1 to 15 mm ² / s, and the base oil has a viscosity index of 110 or more.