JP2009149874A - Viscosity index-improver and lubricating oil composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a viscosity index-improver which is excellent in viscosity reduction effect at a low temperature and also excellent in viscosity index-improvement effect and shear stability. <P>SOLUTION: The viscosity index-improver for a lubricating oil consists of an oil-soluble copolymer (A) which comprises a constituent unit (a) consisting of a (meth)acrylate monomer having a specified branched alkyl group and one or more kinds of constituent units (b) selected from the group consisting of a phosphate group-containing constituent unit (b1), a phosphono group-containing constituent unit (b2), an amino group-containing constituent unit (b3), and a thiol group-containing constituent unit (b4). Based on the weight of the copolymer (A), the content of the constituent unit (a) is 5-90 wt.% and that of the constituent units (b) is 0.5-50 wt.%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In recent years, the trend of protecting the global environment has been increasing, and the fuel efficiency of automobiles has been further demanded. Therefore, the performance required for the lubricating oil has become higher. In particular, lowering the viscosity of a lubricating oil is one of the effective means for reducing fuel consumption by reducing viscous resistance. To reduce the viscosity of the lubricating oil, it is an effective method to use a low-viscosity base oil. However, simply reducing the viscosity causes problems such as liquid leakage and image sticking. In order to solve this problem, it is generally necessary to increase the viscosity index. Conventionally, viscosity index improvers composed of various polymethacrylate copolymers have been proposed (see, for example, Patent Documents 1 to 3). ). However, conventional polymethacrylate viscosity index improvers have problems that the viscosity index improving effect is not sufficient, the viscosity at low temperature is high, the viscosity resistance at the start of the vehicle is high, and the fuel consumption is deteriorated. It was.

JP-A-7-62372 Japanese Patent No. 2732187 Japanese Patent No. 2941392

  The subject of this invention is providing the viscosity index improver which was excellent in the viscosity reduction effect at the time of low temperature, and was excellent also in the viscosity index improvement effect and shear stability.

As a result of intensive studies, the present inventors have found that a copolymer composed of a specific structural unit is excellent in viscosity index improving ability and shear stability and has a low viscosity at a low temperature, and has led to the present invention.
That is, the present invention relates to the structural unit (a) comprising the monomer represented by the general formula (1), the phosphate group-containing structural unit (b1), the phosphono group-containing structural unit (b2), the amino group-containing structural unit ( b3) and a viscosity index improver for lubricating oil comprising an oil-soluble copolymer (A) containing one or more structural units (b) selected from the group consisting of thiol group-containing structural units (b4), Viscosity index for lubricating oil containing 5 to 90% by weight of the structural unit (a) and 0.5 to 50% by weight of the structural unit (b) based on the weight of the copolymer (A) An improver; a viscosity index improver composition for lubricants comprising 20 to 90% by weight of the viscosity index improver for lubricants and 10 to 80% by weight of a diluent; and a base oil and the viscosity index improver for lubricants Containing a viscosity index improver for lubricating oils. A lubricating oil composition containing 0.01 to 45% by weight, based on.
^{_{CH 2 = C (R 1)}} -COO (A 1 -O) n-R 2 (1)
In the formula, R ¹ is a hydrogen atom or a methyl group, A ¹ is an alkylene group having 2 to 4 carbon atoms, and R ² is a branched alkyl group having 16 to 36 carbon atoms. The number is 16 or less, and n is an integer of 0-20.

  The viscosity index improver of the present invention is superior to the conventional polymethacrylate viscosity index improver in reducing the viscosity at low temperatures when used in a lubricating oil composition, and is also effective in improving the viscosity index and shear stability. Excellent.

Of the structural units of the oil-soluble copolymer (A) in the present invention, the structural unit (a) is introduced by copolymerizing the monomer represented by the general formula (1) as one of the copolymerization components. can do. In the general formula (1), n is preferably 10 or less, more preferably 5 or less, and particularly preferably 0 from the viewpoints of viscosity index and low temperature viscosity. A ¹ in the general formula (1) is an alkylene group having 2 to 4 carbon atoms (C _{2-4 in the} case of representing 2 to 4 carbon atoms, and the same expression is used hereinafter), specifically an ethylene group. 1,2- or 1,3-propylene group, 1,2-, 1,3- or 1,4-butylene group. Of these, ethylene groups, 1,2-propylene groups, and combinations thereof are preferable from the viewpoint of viscosity index. R ¹ is preferably a methyl group. The number of carbon atoms of the branched alkyl group R ² is preferably 20 to 32, more preferably 20 to 28, particularly preferably 20 to 24, and most preferably 24 from the viewpoint of viscosity index and low temperature viscosity. R ² usually has a polymethylene group of 14 or less, preferably 2 to 14, more preferably 4 to 14, particularly preferably 6 to 14, and most preferably 10 to 12, from the viewpoints of viscosity index and low temperature viscosity. The carbon number in the polymethylene group includes the carbon atom of the terminal methyl group. R ² usually has 1 to 17, preferably 1 to 12, especially 1 to 6, especially 1 branch. Preferable R ² is a group represented by the general formula (2).

In the formula (2), p is an integer of 0 to 15, and R ′ and R ″ are the same or different C _1-12 linear alkyl groups and C _3-34 branched alkyl groups.

Specific examples of R ² include the following groups.
(1) A group having a C _15-16 polymethylene group:
For example, 1-C _1-18 alkyl-hexadecyl group (for example, 1-octylhexadecyl group) and 2-C _1-16 alkyl-octadecyl group (for example, 2-ethyloctadecyl, 2-tetradecyloctadecyl and 2-hexadecyloctadecyl groups) );
(2) a group having a C _13-14 polymethylene group:
For example 1-C _1-20 alkyl-tetradecyl groups (eg 1-hexyl tetradecyl, 1-decyl tetradecyl and 1-undecyl tridecyl groups) and 2-C _1-18 alkyl-hexadecyl groups (eg 2-ethylhexa Decyl and 2-dodecyl hexadecyl groups);
(3) Group having C _10-12 polymethylene group:
For example, 1-C _1-22 alkyl-dodecyl group (eg 1-octyldodecyl group), 2-C _1-22 alkyl-dodecyl group (eg 2-hexyldecyl and 2-octyldodecyl group) and 2-C _1-20 Alkyl-tetradecyl groups (eg 2-hexyltetradecyl and 2-decyltetradecyl groups);
(4) Group having C _6-9 polymethylene group:
For example 2-C _1-24 alkyl-decyl group (eg 2-octyldecyl group) and 2,4-diC _1-23 alkyl-decyl group (eg 2-ethyl-4-butyl-decyl group);
(5) a group having a C _1-5 polymethylene group:
For example 2- (3-methylhexyl) -7-methyl-decyl and 2- (1,4,4-trimethylbutyl) -5,7,7-trimethyl-octyl groups;
(6) A mixture of two or more branched alkyl groups:
For example, propylene oligomer (hexamer to 11mer), ethylene / propylene oligomer (molar ratio 16/1 to 1/11), isobutene oligomer (5 to 8mer) and _C5-17 α-olefin oligomer (2 Alkyl residues of oxo alcohols corresponding to ˜hexamers) and the like. 2-isooctylisododecyl group (residue excluding the hydroxyl group of “Nissan Chemical Industry: Fine Oxocol 2000”), 2-isoundecylisopentadecyl group (“Nissan Chemical Industry: Fine Oxocol 2600”) Residues excluding hydroxyl groups).

Among R ² , a group represented by the general formula (2) is preferable, in particular, p is 0 or 1 (especially 1), and R ′ and R ″ are linear C _6-14 (particularly C _8-14 ) Alkyl groups and branched C _6-14 (especially C _8-14 ) alkyl groups are preferred. Most preferably, p is 1 and R ′ and R ″ are straight chain C _8-14 alkyl. Particularly preferably, from the viewpoint of low temperature viscosity and viscosity index, p is 1, R ′ and R ″ are a combination of a linear C _8-10 alkyl group and a linear C _10-12 alkyl group, and R ² is 2-linear C _8-10 alkyl-linear C _12-14 alkyl group.

  Specific examples of the monomer represented by the general formula (1) include 2-octyldodecyl methacrylate (hereinafter abbreviated as O-DM), 2-decyltetradecyl methacrylate (hereinafter abbreviated as D-TM); 1-octyldodecyl. 2-hexyldecyl, 2-hexyltetradecyl, 1-hexyltetradecyl, 1-decyltetradecyl, 1-undecyltridecyl, 2-ethylhexadecyl, 2-dodecylhexadecyl, 2-octyldodecyloxyethyl and 2-decyltetradecyloxyethyl methacrylate; and acrylates corresponding thereto (for example, 2-octyldodecyl acrylate and 2-decyltetradecyl acrylate).

  Of these, 2-octyldodecyl and 2-decyltetradecyl acrylate, O-DM and D-TM, more preferably O-DM and D-TM, particularly preferably, from the viewpoint of low temperature viscosity and viscosity index. Is D-TM.

  Among the constituent units of the oil-soluble copolymer (A) in the present invention, the phosphate ester group-containing constituent unit (b1) or the phosphono group-containing constituent unit (b2) is a phosphate ester group-containing monomer or phosphono group-containing unit. The monomer can be introduced by copolymerizing as one of the copolymerization components.

Examples of the phosphate ester group-containing monomer include a phosphate ester group-containing (meth) acrylic acid ester represented by the following general formula (3) and a C _2-12 phosphate ester group-containing alkene.

In the formula, Q ¹ is a (meth) acryloyl group or a C _2-12 radical polymerizable alkenyl group, A ² is a C _2-4 alkylene group, m is an integer of 0 to 50, and Q ¹ is (meta In the case of acryloyl group, m is 1-50.

_Examples of the C _2-12 alkenyl group include a vinyl group, an allyl group, a methallyl group, a propenyl group, an isopropenyl group, a butenyl group, an octenyl group, and an undecenyl group. The vinyl group and allyl group are preferred from the viewpoint of the viscosity index. It is a group. Preferred among Q ¹ is a (meth) acryloyl group. In addition, examples of A ² include the same groups as those described above for A ^1, and preferred examples are also the same. m is preferably an integer of 0 to 20, more preferably an integer of 0 to 4, particularly preferably 0 or 1, from the viewpoints of viscosity index and low temperature viscosity.
When m is 2 or more, A ² may be one kind or a combination of two or more kinds, and the (O-A ² ) m part may be random or block.

  Examples of the phosphono group-containing monomer include phosphono group-containing (meth) acrylic acid esters and phosphono group-containing alkenes represented by the following general formula (4).

In the formula, Q ² , A ³ and k are the same as Q ¹ , A ² and m in the general formula (3).

The phosphate group-containing monomer or phosphono group-containing monomer may be a salt of the compound represented by the general formula (3) or (4). Examples of the salt include one in which one acidic hydrogen atom is a salt or two in a salt. Examples of the cation constituting the salt include alkali metal (for example, sodium, potassium and lithium) cation, alkaline earth metal (for example, calcium, magnesium and barium) cation, organic amine cation (for example, aliphatic amine, alicyclic amine, and heterocyclic ring). Amines or alkanolamines or their alkylene oxide adducts) and quaternary ammonium cations (eg tetraalkylammonium cations having a C _1-12 alkyl group, C _4-12 cycloalkyl groups and C _1-6 alkyls) Cycloalkyldialkylammonium cation having a group, a trihydroxyalkylalkylammonium cation having a C _2-8 hydroxyalkyl group and a C _1-6 alkyl group, and the like.

Specific examples of the phosphate group-containing monomer include (meth) acryloyloxyalkyl (C _2-4 ) phosphate [(meth) acryloyloxyethyl phosphate and (meth) acryloyloxyisopropyl phosphate] and alkenyl phosphate. Esters [vinyl phosphate, allyl phosphate, propenyl phosphate, isopropenyl phosphate, butenyl phosphate, pentenyl phosphate, octenyl phosphate, decenyl phosphate, dodecenyl phosphate, and the like].

Specific examples of the phosphono group-containing monomer include (meth) acryloyloxyalkyl (C _2-4 ) phosphonic acid [(meth) acryloyloxyethylphosphonic acid etc.] and alkenyl (C _2-12 ) phosphonic acid [vinyl phosphone]. Acid, allyl phosphonic acid, octenyl phosphonic acid and the like].

Among the phosphate ester group-containing monomers and phosphono group-containing monomers, preferred are phosphate ester group-containing monomers from the viewpoint of viscosity index, and more preferred are (meth) acryloyloxyalkyl (C _2-4 ) Phosphoric acid ester, particularly preferred is (meth) acryloyloxyethyl phosphate.

In the case where the oil-soluble copolymer (A) is an oil-soluble copolymer containing an amino group-containing structural unit (b3), the following two methods are exemplified as the amino group introduction method.
(1) A method of copolymerizing an amino group-containing monomer.
(2) A method of converting the functional group in the precursor copolymer having a functional group that can be converted into an amino group into an amino group.

  Examples of the amino group-containing monomer in the method (1) include the following monomers having a primary, secondary, or tertiary amino group. Of these, primary and secondary amino group-containing monomers are preferred from the viewpoint of viscosity index.

Primary amino group-containing monomer:
Aminoalkyl (C _1-8 ) (meth) acrylate or (meth) acrylamide [aminoethyl (meth) acrylate, aminopropyl (meth) acrylate and N-aminoethyl (meth) acrylamide etc.] and monoalkenylamine [monoallylamine etc. ].
Secondary amino group-containing monomer:
Monoalkyl (C _1-6 ) aminoalkyl (C _2-6 ) (meth) acrylate [monomethylaminoethyl (meth) acrylate, monoethylaminoethyl (meth) acrylate, t-butylaminoethyl methacrylate, etc.], heterocyclic amino Examples thereof include group-containing vinyl monomers [morpholinoethyl (meth) acrylate, 4-vinylpyridine, 2-vinylpyridine, vinylimidazole, N-vinylpyrrole, etc.] and diallylamine.

Tertiary amino group-containing monomer dialkyl (C _1-8 ) aminoalkyl (C _2-6 ) (meth) acrylate or (meth) acrylamide [dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate etc.] Can be mentioned.

  The method (2) is a method that is particularly preferably used when the amino group is a primary amino group. Specific examples of the case where the amino group is a primary amino group include a method of converting a copolymer having a ketimine group as a functional group into an amino group-containing copolymer.

  A copolymer having a ketimine group as a functional group is usually obtained by copolymerizing a ketimine group-containing monomer as one of the copolymerization components. The ketimine group-containing monomer is preferably used because it is relatively hydrophobic and has high stability even in the copolymerization step and hardly causes side reactions.

  Examples of the ketimine-containing monomer include monomers represented by the following general formula (5). When the monomer is used, the obtained copolymer is hydrolyzed with alkali or neutrality. The ketimine group can be converted to a primary amino group.

In the formula, R ³ is a hydrogen atom or a methyl group, Q ³ is a carbonyl group or a C _1-8 alkylene group, Z is —O— or —NH—, A ⁴ is a C _2-4 alkylene group, and h is 0 it is an integer of 50, when Q ³ is a carbonyl group, h is an integer of 1 to 50. R ⁴ and R ⁵ are hydrogen atom, an alkyl group, or R ⁴ and R ⁵ of C _1-8 is cycloalkylene group C _4-12 bound to one another, R ⁴ and R ⁵ is a hydrogen atom at the same time There is nothing.

Among the monomers represented by the general formula (5), examples of the method for producing a monomer in which Q ³ is a carbonyl group and Z is —O— include the following methods. For example, with primary amino group-containing alcohols (eg 2-aminoethanol, 2-aminopropanol, 3-aminopropanol, 2-aminobutanol, 3-aminobutanol, 4-aminobutanol and 2- (2-aminoethoxy) ethanol) A solvent (such as cyclopentanone, cyclohexanone, acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, diisopropyl ketone and diisobutyl ketone) or an aldehyde (such as benzaldehyde and methoxybenzaldehyde) azeotropically with water as necessary ( Toluene, benzene, xylene, etc.) were used to distill water at a temperature of 100 ° C. or higher to obtain a ketiminated alcohol, and the resulting ketiminated alcohol and (meth) a Acrylic acid, the monomer is synthesized which is represented by (meth) acrylate or (meth) dehydration of ethyl acrylate esterification reaction or transesterification reaction is allowed to general formula (5).

Among the monomers represented by the general formula (5), when Q ³ is an alkylene group, (meth) allylamine, aminoethyl (meth) allyl ether, aminoethoxyethyl (meth) allyl ether, etc. Obtained by reaction with ketones (such as acetone and methyl isobutyl ketone).

  Specific examples of the monomer represented by the general formula (5) include esters of (meth) acrylic acid and N-isopropylidene-2-hydroxyethylamine, (meth) acrylic acid and N- (1-methylisopenty Ridene) -2-hydroxyethylamine ester, (meth) acrylic acid and N-1-isobutylisopentylidene-2- (2-hydroxyethoxy) ethylamine ester, (meth) acrylic acid and N-isopropylidene- Examples include amides with 2-aminoethylamine and amides of (meth) acrylic acid with N-1-methylisopentylidene-2-aminoethylamine.

As the method for introducing a thiol group when the oil-soluble copolymer (A) is an oil-soluble copolymer containing a thiol group-containing structural unit (b4), the following two methods are exemplified.
(1) A method of copolymerizing a thiol group-containing monomer.
(2) A method in which the functional group in the precursor copolymer having a functional group that can be derived to a thiol group is derived to a thiol group.
Of the methods (1) and (2), the method (2) is preferable from the viewpoint of stability during the production process.

  Examples of the thiol group-containing monomer in the method (1) include allyl mercaptan and 2-mercaptoethyl (meth) acrylate.

  Examples of the functional group that can be derived from the thiol group in the method (2) include a primary amino group, a hydroxyl group, and a carboxyl group. Of the functional groups, a primary amino group and a hydroxyl group, particularly a primary amino group, are preferable from the viewpoint of reactivity. The precursor copolymer in the method (2) is a method of copolymerizing a monomer containing a primary amino group-containing monomer, a hydroxyl group-containing monomer or a carboxyl group-containing monomer, or 1 In the case of a primary amino group, it is obtained by a method of hydrolyzing the ketimine group of the aforementioned ketimine group-containing copolymer. Then, the oil-soluble copolymer containing the target thiol group-containing structural unit is reacted with a compound that reacts with the primary amino group, hydroxyl group or carboxyl group in the obtained copolymer to form a thiol group. Coalescence is obtained.

Examples of the primary amino group-containing monomer include the aforementioned monomers.
As the hydroxyl group-containing monomer, C _5-8 (meth) acrylate containing one hydroxyl group [for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) Acrylate and 2-hydroxyethoxyethyl (meth) acrylate]; (meth) acrylate containing 2 to 8 hydroxyl groups [for example, glycerin, trimethylolpropane, pentaerythritol, sorbitol, sorbitan, diglycerin, sucrose and methylglucoside (meta Acrylates]; C _2-6 alkenols [eg vinyl alcohol (formed by hydrolysis of vinyl acetate units), (meth) allyl alcohol, (iso) propenyl alcohol and polyvalents containing 3-8 hydroxyl groups of alcohol C _3-6 alkenyl Ethers {trimethylolpropane mono- - or di - (meth) allyl ether}]; hydroxyl group-containing aromatic monomers (o-, m-or p- hydroxystyrene); and C ₂ of the hydroxyl group-containing monomer _-4 alkylene oxide adduct (addition mole number 1-20).

Examples of the carboxyl group-containing monomer include unsaturated monocarboxylic acids [methacrylic acid, acrylic acid, (iso) crotonic acid, cinnamic acid, etc.], unsaturated dicarboxylic acids (maleic acid, itaconic acid, citraconic acid, mesaconic acid, etc.) ) And mono-C _1-8 alkyl esters of unsaturated dicarboxylic acids (such as monoalkyl malates, monoalkyl fumarate and monoalkyl itaconates).

  Examples of the compound that reacts with a primary amino group, a hydroxyl group, or a carboxyl group to generate a thiol group include, for example, thiol group-containing carboxylic acids (such as thioglycolic acid and 3-mercaptopropionic acid), thiol group-containing carboxylic acid esters (thioglycols). And cyclic compounds having a dithioester group or a trithioester group represented by the general formula (6) (for example, ethylene dithiocarbonate, ethylene trithiocarbonate, C3-C22) Intramolecular cyclic ester of mercaptocarboxylic acid and intramolecular cyclic ester of mercaptothione carboxylic acid having 3 to 22 carbon atoms), and from the viewpoint of difficulty in side reactions, a dithioester group or a trithioester group is preferable. It is a cyclic compound having.

In the formula, R ⁶ is a linear or branched alkylene group having 1 to 20 carbon atoms, a linear or branched alkoxy alkylene group having 2 to 20 carbon atoms, X is O = or S =, and Y is -S- or A methylene group.

  The oil-soluble copolymer (A) in the present invention may further contain one or more other structural units in addition to the structural unit (a) and the structural unit (b). Examples of other structural units include structural units (c), (d) and (e) obtained by copolymerizing the following monomers (c1), (d1) and (e1). Of these structural units, (c) and (d) are preferred.

Monomer (c1): an alkyl (meth) acrylate having a C _1-4 alkyl group;
Mention may be made of methyl, ethyl, n- or isopropyl and n-, iso-, sec- or t-butyl (meth) acrylate. Of these, methyl methacrylate (hereinafter abbreviated as MMA) is preferable.

Monomer (d1): an alkyl (meth) acrylate having a C _8-17 alkyl group and an alkyl (meth) acrylate having a C _18-24 linear alkyl group;

_Examples of the alkyl (meth) acrylate having a C _8-17 alkyl group include linear C _8-17 alkyl (meth) acrylate, branched C _8-17 alkyl (meth) acrylate, and mixtures thereof.

As linear C _8-17 alkyl (meth) acrylate, n-dodecyl, n-tetradecyl, n-hexadecyl or n-octadecyl methacrylate (hereinafter abbreviated as DDM, TDM, HDM and ODM) and n-octyl, n -Nonyl, n-decyl, n-tridecyl or n-pentadecyl methacrylate, and the corresponding acrylates such as n-dodecyl acrylate (hereinafter abbreviated as DDA) and C _8-17 Ziegler alcohol (meta ) Acrylate and the like.

Examples of branched C _8-17 alkyl (meth) acrylates include isooctyl, 2-ethylhexyl, isononyl, isodecyl, isododecyl, 2-methylundecyl, isotridecyl, 2-methyldodecyl, isotetradecyl, 2-methyltridecyl, isopenta Examples include decyl and 2-methyltetradecyl (meth) acrylate.

The mixture of linear C _8-17 alkyl (meth) acrylate and branched C _8-17 alkyl (meth) acrylate includes, for example, (meth) acrylate of oxo alcohol, and examples of oxo alcohol include “Neodol 23” and “ Neodol 45 "(manufactured by Shell Chemical Co., Ltd.)," Dovanol 23 "and" Dovanol 45 "(manufactured by Mitsubishi Chemical Corporation)," Oxocol 1213 "and" Oxocol 1415 "(manufactured by Nissan Chemical Co., Ltd.)

Among the alkyl (meth) acrylates having a C _8-17 alkyl group, C _12-17 (further C _12-15 ) alkyl (meth) acrylates, particularly linear _chains are preferred from the viewpoint of viscosity index and low temperature viscosity. C _12-17 (further C _12-15 ) alkyl (meth) acrylate.

Examples of the alkyl (meth) acrylate having a C _18-24 linear alkyl group include n-octadecyl (meth) acrylate, n-nonadecyl (meth) acrylate, n-eicosyl methacrylate (hereinafter abbreviated as ESM), n -Eicosyl acrylate, n-docosyl (meth) acrylate and n-tetracosyl (meth) acrylate. Of the alkyl (meth) acrylates having a C _18-24 linear alkyl group, n-octadecyl (meth) acrylate is preferred from the viewpoint of viscosity index and low temperature viscosity.

Other monomers (e1) include unsaturated C _2-20 hydrocarbons [ethylene, propylene, isobutene, butene, diisobutylene, butadiene, isoprene, 1,4-pentadiene, cyclopentadiene, dicyclopentadiene, ethylidene norbornene. And styrene etc.], C _1-10 alkyl or C _6-8 aryl vinyl ketone [methyl vinyl ketone, ethyl vinyl ketone, phenyl vinyl ketone, etc.], epoxy group-containing unsaturated monomers [glycidyl (meth) acrylate and glycidyl ( Meth) allyl ether, etc.], halogen atom-containing unsaturated monomers [vinyl chloride, vinylidene chloride, etc.], alkyl alkenyl ether [C _1-10 alkyl C _2-10 alkenyl ether {alkyl vinyl ether (methyl vinyl ether, n-propyl vinyl ether) And ethyl bi Nyl ether etc.), alkyl (meth) allyl ether (methyl allyl ether and ethyl allyl ether etc.) and (iso) propenyl ether etc.], alkenyl carboxylate [C _2-10 alkenyl C _1-20 carboxylate {vinyl acetate, propion Non-containing nitrogen atoms other than vinyl acid, vinyl butyrate, vinyl hexanoate, vinyl heptanoate, vinyl 2-ethylhexanoate and vinyl n-octanoate (preferably vinyl acetate and vinyl propionate)}, etc. Saturated monomers [quaternary ammonium base-containing monomers {quaternary ammonium salts obtained by quaternization of the amino group-containing monomer (b3)} and nitrile or nitro group-containing monomers {( Meth) acrylonitrile and nitrostyrene}] and unsaturated dicarboxylic acid dialkyl ester [ Unsaturated dicarboxylic acid (maleic acid, fumaric acid, itaconic acid, citraconic acid, etc.) diC _1-40 (preferably C _1-20 ) hydrocarbyl (alkyl, cycloalkyl and aralkyl) ester {dimethyl, diethyl or dioctylma Rate and corresponding fumarate and itaconate etc.} and the like.

  The oil-soluble copolymer (A) contains the structural units in% by weight shown in Table 1 below based on the weight of (A) from the viewpoint of viscosity index, shear stability, and low temperature viscosity. In the following, “%” represents “% by weight” unless otherwise specified.

  The copolymer (A) is usually dissolved in at least 0.5 parts by weight, preferably at least 2 parts by weight, more preferably at least 30 parts by weight, particularly preferably at least 70 parts by weight in 100 parts by weight of mineral oil at 25 ° C. .

  The weight average molecular weight (hereinafter abbreviated as Mw) of (A) is preferably 3,000 to 1,000,000 from the viewpoints of viscosity index and shear stability. Mw is measured by gel permeation chromatography (GPC) using polystyrene as a standard. Although the preferable range of Mw of (A) changes with uses of a lubricating oil composition, from the viewpoint of shear stability, it is preferably the range described in Table 2 below. Mw of (A) can be adjusted by temperature at the time of polymerization, monomer concentration (solvent concentration), catalyst amount, chain transfer agent amount, or the like.

*: Automatic transmission oil
**: Belt-Continuously Variable Transmission Oil
***: Manual transmission oil

  (A) is usually 8.6 to 11, preferably has a SP value of 9.2 to 10.5, more preferably 9.4 to 9.8 from the viewpoint of solubility in base oil and an effect of improving the viscosity index. . The SP value is calculated by the method of Fedors [Polym. Eng. Sci. 14 (2) 152, (1974)]. The SP value of (A) can be adjusted by calculating the SP value of each structural unit and adopting the monomer type and molar ratio so as to obtain the target SP value. For example, in the case of (meth) acrylic acid alkyl ester, the SP value can be adjusted by the length of the alkyl group.

  (A) preferably has an HLB of 0.5 to 7, more preferably 1 to 6.5, and particularly 1.5 to 6 from the viewpoint of demulsibility. The HLB in the present invention is an HLB of the Oda method and is defined based on the concept of organic and inorganic properties of organic compounds ("Introduction to New Surfactants" written by Takehiko Fujimoto, published by Sanyo Chemical Industries, p197-201). It is what is done.

  (A) can be obtained by a known production method. For example, it can be obtained by radical polymerization of the above monomer in a solvent in the presence of a polymerization catalyst.

Examples of the solvent include aromatic solvents such as toluene, xylene or C _9-10 alkylbenzene, aliphatic C _6-18 hydrocarbons such as hexane, heptane, cyclohexane and octane, 2-propanol, 1-butanol or 2-butanol. C _3-8 alcohol solvents such as, ketone solvents such as methyl ethyl ketone, and mineral oils can be used. From the viewpoint of solubility, an alcohol solvent is preferable, and 2-propanol is more preferable.

Examples of the polymerization catalyst include azo catalysts [for example, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 2,2′-azobis (2,4-dimethylvalero]. Nitrile) (hereinafter abbreviated as ADVN) and dimethyl 2,2-azobisisobutyrate, etc.], peroxide-based catalysts [eg t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butyl per Oxyneoheptanoate, t-butylperoxyneodecanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-amylperoxy-2-ethylhexanoate, 1 , 1,3,3-Tetramethylbutylperoxy 2-ethylhexanoate, dibutylperoxytrimethyladipate, benzoylperoxy , Cumyl peroxide and lauryl peroxide and the like] can be used. Furthermore, a chain transfer agent [for example, a C _2-20 alkyl mercaptan, etc.] can be used if necessary.

  The reaction temperature is usually 50 to 140 ° C, preferably 60 to 120 ° C. In addition to the above solution polymerization, it can also be obtained by bulk polymerization, emulsion polymerization or suspension polymerization. Furthermore, the polymerization mode of the copolymer may be either random addition polymerization or alternating copolymerization, and may be either graft copolymerization or block copolymerization.

  The viscosity index improver of the present invention usually comprises only the oil-soluble copolymer (A).

  The viscosity index improver composition of the present invention contains 20 to 90% viscosity index improver and 10 to 80% diluent. Rather than adding the viscosity index improver as it is to the base oil, it is preferable to add the viscosity index improver composition because it is easier to dissolve in the base oil. Examples of the viscosity index improver composition include a solution obtained by producing the copolymer (A) by solution polymerization, and a solution obtained by dissolving the copolymer (A) in a diluent. It is done.

Diluents include aliphatic solvents [C _6-18 aliphatic hydrocarbons (hexane, heptane, cyclohexane, octane, decalin, kerosene, etc.)], aromatic solvents [eg C _7-15 aromatic solvents {toluene, Xylene, ethylbenzene, C ₉ aromatic mixed solvent (mixture of trimethylbenzene, ethyl toluene, etc. and C _10-11 aromatic mixed solvent, etc.)], mineral oil [for example, solvent refined oil, paraffin oil, isoparaffin High viscosity index oil, high viscosity index oil by hydrocracking and naphthenic oil] and synthetic lubricating oil [hydrocarbon synthetic lubricating oil (poly α-olefin synthetic lubricating oil, etc.) and ester synthetic lubricating oil, etc.] It is done. Of these, preferred are mineral oils and synthetic lubricating oils, and more preferred are mineral oils.

  In the viscosity index improver composition, the proportion of (A) is preferably 20 to 90%, more preferably 30 to 85%, particularly preferably 40 based on the weight of the viscosity index improver composition from the viewpoint of handling properties. The proportion of the diluent is preferably 10 to 80%, more preferably 15 to 70%, particularly preferably 20 to 60% from the viewpoint of handling properties, based on the weight of the viscosity index improver composition. It is.

  The lubricating oil composition of the present invention contains a base oil and the viscosity index improver, and usually contains 0.01 to 45% of the viscosity index improver based on the weight of the lubricating oil composition.

  Base oils include mineral oils [solvent refined oils, paraffin oils, high viscosity index oils containing isoparaffins, high viscosity index oils and naphthenic oils by hydrocracking], synthetic lubricants [hydrocarbon synthetic lubricants (poly α -Olefin synthetic lubricating oil etc.) and ester synthetic lubricating oil etc.] and mixtures thereof. Of these, mineral oil is preferred.

The kinematic viscosity at 100 ° C. of the base oil is preferably 1 to 18 mm ² / s, more preferably ² to 15 mm ² / s. When the kinematic viscosity is 1 mm ² / s or more, liquid leakage and seizure hardly occur, and when it is 18 mm ² / s or less, the viscous resistance is reduced, leading to fuel saving. The viscosity index of the base oil is preferably 60 or more, more preferably 100 or more, particularly preferably 105 or more, preferably 180 or less, more preferably 175 or less, and particularly preferably 170 or less. The lubricating oil composition in which the viscosity index improver of the present invention is blended with such a base oil has a higher viscosity index and good fuel economy.

  Moreover, the pour point (JIS K2269-1993) of the base oil is preferably −5 ° C. or lower, more preferably −10 ° C. to −70 ° C. When the pour point of the base oil is within this range, the amount of wax precipitated is small and the low temperature viscosity becomes better.

  The lubricating oil composition of the present invention includes gear oils such as differential oil and industrial gear oil, manual transmission oil (hereinafter abbreviated as MTF), automatic transmission oil (hereinafter abbreviated as ATF), and belt-CVTF oil. It is suitably used for traction oils such as machine oils, toroidal-CVT oils, shock absorber oils, power steering oils, hydraulic oils for construction machinery, industrial hydraulic oils, and engine oils. Of these, differential oil, ATF, belt-CVT oil, engine oil and MTF are preferred. More preferred are differential oil, ATF, belt-CVT oil and MTF.

  The preferred content of the viscosity index improver in the lubricating oil composition based on the use of the lubricating oil composition and the kinematic viscosity of the base oil is in the range of Table 3 below.

  The lubricating oil composition of the present invention may further contain an alkyl (meth) acrylate (co) polymer (B) other than the above (A). (B) is obtained by polymerizing a monomer represented by the general formula (1) and one or more monomers selected from the group consisting of alkyl (meth) acrylates in (c1) and (d1). (Co) polymers that can be used.

  (B) preferably contains 60 to 100%, more preferably 65 to 100% of the structural unit (d). The alkyl group of the alkyl (meth) acrylate constituting (B) preferably has an average carbon number of 12 to 16 (hereinafter abbreviated as Cav). (B) mainly contains linear alkyl (meth) acrylate units and preferably has 0 to 30% branched alkyl (meth) acrylate units.

  Specific examples of (B) include DDM / ODM (60 to 90% / 10 to 40%, Cav = 12.5 to 14.0), DDM / HDM (50 to 90% / 10 to 50%, Cav = 12.3-13.8), DDM / TDM (30-90% / 10-70%, Cav = 12.2-13.4) and DDA / DDM (10-40% / 90-60%, Cav = 12) and a copolymer of DDM / TDM / HDM / MMA (20-45% / 20-45% / 0-20% / 0.2-20%, Cav = 8.1-13.5) A polymer etc. are mentioned.

  Mw of (B) is preferably 10,000 to 500,000, more preferably 15,000 to 370,000, from the viewpoints of viscosity index improving ability and shear stability.

  (B) can be produced by the same method as (A), and can be used in the form of the same composition (diluted with a diluent) as (A).

  (A) and (B) may be added separately to the base oil, or may be added as a mixture thereof.

  The lubricating oil composition of the present invention can contain 0.8 to 45% in total of (A) and (B). The preferable range of the sum of (A) and (B) is 0.8 to 18% when the lubricating oil is engine oil and traction oil, 2.5 to 45% when the lubricating oil is MTF, MTF, ATF, belt- In the case of CVTF oil, it is 2.5 to 40%, and in the case of hydraulic oil, it is 0.8 to 28%.

  The weight ratio [(A) / (B)] of (A) and (B) is preferably 70/30 to 99.9 / 0.1, more preferably 80/20, from the viewpoint of low temperature viscosity. The weight ratio is ˜99.9 / 0.1.

  The lubricating oil composition containing (A) or (A) and (B) in the present invention can further contain any one or more additives.

The following can be used 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- and 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 (such as tetraalkylammonium salts), sulfated oil, phosphates (such as phosphates of polyoxyethylene-containing nonionic surfactants);
(9) Corrosion inhibitor:
Nitrogen atom-containing compounds (such as benzotriazole and 1,3,4-thiodiazolyl-2,5-bisdialkyldithiocarbamate) and the like.

  These additives (1) to (9) can be used in the amounts shown in Table 4 below based on the weight of the lubricating oil composition.

  The lubricating oil composition of the present invention has good shear stability. Shear stability can be evaluated by the rate of decrease in viscosity of the lubricating oil composition when the test time is 20 hours according to the method defined in CEC L45-45-A-99. The viscosity reduction rate of the lubricating oil composition of the present invention is preferably 20% or less, more preferably 15% or less, particularly preferably 10% or less, and most preferably 5% or less.

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In the following, parts represent parts by weight.
(Method for measuring weight average molecular weight by GPC)
Apparatus: HLC-802A manufactured by Toyo Soda
Column: TSK gel GMH6 2 Measurement temperature: 40 ° C
Sample solution: 0.5% THF solution Solution injection amount: 200 μl
Detector: Refractive index detector Standard: Polystyrene * (When the sample contains a primary amine, the sample was mixed with the same part by weight of salicylaldehyde and treated at room temperature for 1 hour as a measurement sample.)

(Test method for low temperature viscosity)
The viscosity at −40 ° C. was measured by the method of JPI-5S-26-85.

(Test method for viscosity index)
It was carried out by the method of JIS-K-2283.

(Shear stability test method)
The test time was 20 hours according to the method of CEC L45-45-A-99.

<Example 1>
In a reaction vessel equipped with a stirrer, heating / cooling device, thermometer, dropping funnel, nitrogen blowing tube and decompression device, 25 parts of 2-propanol was charged, and in another glass beaker, monomer (D-TM 90 parts, And 10 parts of methacryloyloxyethyl phosphate), 1.7 parts of dodecyl mercaptan as a chain transfer agent, 0.5 parts of ADVN as a radical polymerization initiator and 6 parts of 2-propanol, and stirred and mixed at 20 ° C. A monomer solution was prepared and charged into a 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 keeping the system temperature at 70 to 85 ° C. under sealing, and aged at 85 ° C. for 2 hours after completion of the dropping. Then, 2-propanol was distilled off under reduced pressure at a reduced pressure of 6 mmHg over 3 hours at 85 to 120 ° C. to obtain a viscosity index improver (A1). Table 5 shows the content (% by weight) of each structural unit in (A1), the Mw, SP value, and HLB of (A1).

<Example 2>
A viscosity index improver (A2) was obtained in the same manner as in Example 1 except that 10 parts of methacryloyloxyethyl phosphate was replaced with 10 parts of methacryloyloxyethylphosphonic acid. Table 5 shows the content (% by weight) of each structural unit in (A2), the Mw, SP value, and HLB of (A2).

<Example 3>
In the same reaction vessel as in Example 1, 90 parts of toluene, 200 parts of diisobutyl ketone and 50 parts of 2- (2-aminoethoxy) ethanol were reacted at 130 ° C. for 4 hours while refluxing, and then at a reduced pressure of 6 mmHg. Toluene and unreacted isobutyl ketone were removed. After cooling to 30 ° C., 75 parts of methyl methacrylate, 2.0 parts of sodium methoxide, 2.5 parts of phenothiazine and 200 parts of toluene were charged and reacted at 80 ° C. for 6 hours while refluxing at a reduced pressure of 500 mmHg. Toluene and methyl methacrylate were removed at a reduced pressure of 6 mmHg, and an ester of methacrylic acid and N-1-isobutylisopentylidene-2- (2-hydroxyethoxy) ethylamine having the following structural formula (hereinafter abbreviated as IPEAMA) was obtained. Obtained.

  In a reaction vessel similar to Example 1, 25 parts of toluene was charged, and in another glass beaker, monomer (80 parts of D-TM and 20 parts of IPEAMA), chain transfer agent (1.7 parts of dodecyl mercaptan), start An agent (ADVN 0.5 part) and 8 parts of toluene were charged, stirred and mixed at 20 ° C. to prepare a monomer solution, and charged into a dropping funnel. After carrying out nitrogen substitution of the gas phase part of the reaction vessel, the monomer solution was added dropwise over 2 hours while keeping the system temperature at 75 to 85 ° C. in a sealed state. Aged. Thereafter, 20 parts of water was added and hydrolyzed by heating and stirring at 85 ° C. for 2 hours. Next, the temperature was raised to 120 ° C., water and toluene were distilled off under reduced pressure at a reduced pressure of 6 mmHg, the resulting polymer was reprecipitated with 500 parts of methanol, washed twice with 200 parts of methanol, and then at 100 ° C. for 4 hours. And dried under reduced pressure at a reduced pressure of 6 mmHg to obtain a viscosity index improver (A3). Table 5 shows the content (% by weight) of each structural unit in (A3), the Mw, SP value, and HLB of (A3).

<Example 4>
In a reaction vessel similar to Example 1, 100 parts of (A3) produced in Example 3, 20 parts of ethylene trithiocarbonate and 500 parts of THF were charged, and the mixture was heated and stirred while refluxing at 85 ° C. for 2 hours. A ring reaction was performed. Thereafter, THF was removed at 85 ° C. and a reduced pressure of 6 mmHg. Next, it was reprecipitated with 500 parts of methanol, washed twice with 200 parts of methanol, and dried under reduced pressure at 100 ° C. for 4 hours at a reduced pressure of 6 mmHg to obtain a viscosity index improver (A4). Table 5 shows the content (% by weight) of each structural unit in (A4), the Mw, SP value, and HLB of (A4).

<Example 5>
A viscosity index improver (A5) was obtained in the same manner as in Example 1 except that 90 parts of D-TM was replaced with 90 parts of 2-octyldodecyloxyethyl methacrylate. Table 5 shows the content (% by weight) of each structural unit in (A5), the Mw, SP value, and HLB of (A5).

<Example 6>
Viscosity index improver (A6) in the same manner as in Example 1 except that 90 parts of D-TM is replaced with 90 parts of 2-octyldodecyloxyethyl methacrylate and 10 parts of methacryloyloxyethyl phosphate are replaced with 10 parts of methacryloyloxyethylphosphonic acid. Got. Table 5 shows the content (% by weight) of each structural unit in (A6), the Mw, SP value, and HLB of (A6).

<Comparative Example 1>
In a reaction vessel equipped with a stirrer, heating / cooling device, thermometer, dropping funnel nitrogen blowing tube and decompression device, 25 parts of 2-propanol was charged, and another glass beaker was charged with monomer (methacryloyloxyethyl phosphate 10 parts). , 63 parts of HDM and 27 parts of ODM), 1.5 parts of dodecyl mercaptan as a chain transfer agent, 0.5 parts of ADVN as a radical polymerization initiator and 6 parts of 2-propanol, stirred and mixed at 20 ° C. A body solution was prepared and charged into a 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 keeping the system temperature at 70 to 85 ° C. under sealing, and aged at 85 ° C. for 2 hours after completion of the dropping. Then, 2-propanol was distilled off under reduced pressure at a reduced pressure of 6 mmHg over 3 hours at 85 to 120 ° C. to obtain a comparative viscosity index improver (H1). Table 5 shows the content (% by weight) of each structural unit in (H1), the Mw, SP value, and HLB of (H1).

<Comparative example 2>
A comparative viscosity index improver (H2) was obtained in the same manner as in Example 3 except that 80 parts of D-TM was replaced with 56 parts of HDM and 24 parts of ODM. Table 5 shows the content (% by weight) of each structural unit in (H2), the Mw, SP value, and HLB of (H2).

<Comparative Example 3>
A comparative viscosity index improver (H3) was obtained in the same manner as in Example 4 except that (A2) was replaced with (H2). Table 5 shows the content (% by weight) of each structural unit in (H3), the Mw, SP value, and HLB of (H3).

<Comparative example 4>
A comparative viscosity index improver (H4) was prepared in the same manner as in Comparative Example 1 except that 10 parts of methacryloyloxyethyl phosphate was replaced with 20 parts of MMA, 63 parts of HDM were replaced with 56 parts, and 27 parts of ODM were replaced with 24 parts. Obtained. Table 5 shows the content (% by weight) of each structural unit in (H4), the Mw, SP value, and HLB of (H4).

<Comparative Example 5>
Comparative viscosity index improver (H5) as in Comparative Example 1 except that 10 parts of methacryloyloxyethyl phosphate are replaced with 80 parts of D-TM, 63 parts of HDM are replaced with 14 parts, and 27 parts of ODM are replaced with 6 parts. ) Table 5 shows the content (% by weight) of each structural unit in (H5), the Mw, SP value, and HLB of (H5).

Each structural unit of (a)-(d) of Table 5 is as follows.
(A1): 2-decyltetradecyl methacrylate (D-TM)
(A2): 2-octyldodecyloxyethyl methacrylate (b1): methacryloyloxyethyl phosphate (b2): methacryloyloxyethylphosphonic acid (b3): 2- (2-aminoethoxy) ethyl methacrylate (b4): 2- (2 -Mercaptoethoxy) ethyl methacrylate (c1): methyl methacrylate (MMA)
(D1): n-hexadecyl methacrylate (HDM)
(D2): n-octadecyl methacrylate (ODM)

Examples 7 to 12 and Comparative Examples 6 to 10 (Production and evaluation of viscosity index improver composition and lubricating oil composition)
Viscosity index is improved by mixing and dissolving 65 parts of (A1) to (A6) and (H1) to (H5) at 120 ° C. in 35 parts of mineral oil (dynamic viscosity 2.3 mm ² / s at 100 ° C.) Agent compositions (CA1) to (CA6) and comparative viscosity index improver compositions (CH1) to (CH5) were obtained.
In a stainless steel container equipped with a stirring and mixing device, the resulting lubricating oil composition has a kinematic viscosity at 100 ° C. of 14.3 ± 0.2 (mm ² / s) and a total of 100 parts of the lubricating oil composition. Base oil (high viscosity index oil; kinematic viscosity at 100 ° C. = 4.6 mm ² / s, viscosity index = 118, pour point = −17.5 ° C.) and (CA1) to (CA6) and (CH1) ) To (CH5) were added and mixed to obtain a lubricating oil composition.
Table 6 shows the measurement results of 100 ° C kinematic viscosity, viscosity index, viscosity at -40 ° C, and shear stability of the obtained lubricating oil composition.

  The lubricating oil composition using the viscosity index improver of the present invention can improve the viscosity index as compared with a lubricating oil composition using a conventional polymethacrylate viscosity index improver, and also has improved shear stability and low temperature viscosity. Because of its superiority, it is possible to produce manual transmission gear oil compatible with future fuel economy and SAE J306 without using expensive synthetic lubricant. Therefore, drive system lubricating oil (manual transmission oil, differential gear oil, automatic transmission oil and belt-CVTF oil, etc.), hydraulic oil (machine hydraulic oil, power steering oil, shock absorber oil, etc.), engine oil (for gasoline and For diesel) and traction oil.

Claims (7)

The structural unit (a) comprising the monomer represented by the general formula (1), the phosphate group-containing structural unit (b1), the phosphono group-containing structural unit (b2), the amino group-containing structural unit (b3), and the thiol group A viscosity index improver for a lubricating oil comprising an oil-soluble copolymer (A) containing at least one structural unit (b) selected from the group consisting of the containing structural unit (b4), wherein the copolymer (A The viscosity index improver for lubricating oils containing 5 to 90% by weight of the structural unit (a) and 0.5 to 50% by weight of the structural unit (b) based on the weight of
^{_{CH 2 = C (R 1)}} -COO (A 1 -O) n-R 2 (1)
Wherein R ¹ is a hydrogen atom or a methyl group, A ¹ is an alkylene group having 2 to 4 carbon atoms, R ² is a branched alkyl group having 16 to 36 carbon atoms, and a continuous methylene group in the branched alkyl group Is 16 or less, and n is an integer of 0-20. ]   The oil-soluble copolymer (A) is an oil-soluble copolymer and / or thiol group obtained by converting the functional group in the precursor copolymer having a functional group that can be converted into an amino group into an amino group. The viscosity index improver for lubricating oils according to claim 1, which is an oil-soluble copolymer obtained by derivatizing the functional group in the precursor copolymer having a functional group capable of being derived into a thiol group.   The oil-soluble copolymer (A) is a structural unit (c) further comprising an alkyl (meth) acrylate having an alkyl group having 1 to 4 carbon atoms, and an alkyl (meth) acrylate having an alkyl group having 8 to 17 carbon atoms. And one or more structural units (d) selected from the group consisting of structural units composed of alkyl (meth) acrylates having a linear alkyl group having 18 to 24 carbon atoms, and the copolymer ( Based on the weight of A), the structural unit (a) is 10 to 60% by weight, the structural unit (b) is 1 to 30% by weight, the structural unit (c) is 5 to 30% by weight and the structural unit. The viscosity index improver for lubricating oils according to claim 1 or 2, which contains 10 to 60% by weight of (d). The viscosity index improver for lubricating oil according to any one of claims 1 to 3, wherein R ² in the general formula (1) is a group represented by the general formula (2).

[Wherein, R ′ and R ″ are groups independently selected from a linear alkyl group having 1 to 16 carbon atoms and a branched alkyl group having 3 to 34 carbon atoms, and p is an integer of 0 to 15] is there. ]   A viscosity index improver composition for lubricating oil comprising 20 to 90% by weight of the viscosity index improver for lubricating oil according to any one of claims 1 to 4 and a diluent of 10 to 80% by weight.   A base oil and the viscosity index improver for lubricating oil according to any one of claims 1 to 4 are contained, and the viscosity index improver for lubricating oil is contained in an amount of 0.01 to 45% by weight based on the weight of the lubricating oil composition. Lubricating oil composition.   The lubricating oil composition according to claim 6, which is used for gear oil, transmission oil, traction oil, hydraulic oil or engine oil.