Viscosity index enhancer composition, additive composition for lubricating oil, and lubricating oil composition

Abstract

The present invention addresses the problem of providing a viscosity index enhancer composition having an excellent viscosity index enhancing effect. This problem is solved by a viscosity index enhancer composition which comprises the poly(meth)acrylate (A) below and the poly(meth)acrylate (B), and which satisfies specific requirements. Poly(meth)acrylate (A): comprises a structural unit (Y) derived from a monomer (y) that has a diol functional group. Poly(meth)acrylate (B): comprises a structural unit (Z) derived from a monomer (z) that has a boronic acid ester.

Description

Viscosity index improver composition, lubricating oil additive composition, and lubricating oil composition

[0001] The present invention relates to a viscosity index improver composition, a lubricating oil additive composition, and a lubricating oil composition.

[0002] In recent years, various properties are required for lubricating oil compositions used as drive system oils such as automatic transmission fluids (ATF), continuously variable transmission fluids (CVTF), and shock absorber fluids (SAF), internal combustion engine oils, and equipment oils such as hydraulic fluids, depending on their respective applications. For example, with regard to fuel economy of automobiles, in addition to improvements in automobiles themselves, such as weight reduction and engine improvements, improvements in lubricating oils, such as reducing the viscosity of lubricating oil compositions to reduce viscous resistance and adding various lubricating oil additives, are also important. However, since lubricating oil compositions are used over a wide temperature range, simply lowering the viscosity can result in a thinner oil film at lubricated parts under high temperature conditions, causing problems such as increased wear and seizure due to contact between components. Therefore, it is desirable for the viscosity of the lubricating oil composition to remain as constant as possible over a wide temperature range. In other words, a lubricating oil composition with a high viscosity index is desirable. Therefore, for lubricating oil compositions used over a wide temperature range, from high to low temperatures, a method of adding a viscosity index improver to improve the temperature dependency of viscosity is generally used.

[0003] For example, Patent Document 1 describes a lubricating oil composition containing a composition (viscosity index improver composition) in which a copolymer containing a diol group and a compound containing a boronic acid ester functional group are mixed.

[0004] Special table 2017-508055 publication

[0005] However, the composition (viscosity index improver composition) described in Patent Document 1 does not have a sufficient viscosity index improving effect, and there is room for further improvement.

[0006] Therefore, an object of the present invention is to provide a viscosity index improver composition that has an excellent viscosity index improving effect, a lubricating oil additive composition containing the viscosity index improver composition, a lubricating oil composition containing the viscosity index improver composition, and a method for producing the lubricating oil composition.

[0007] According to the present invention, the following [1] to [4] are provided. [1] A viscosity index improver composition containing the following poly(meth)acrylate (A) and the following poly(meth)acrylate (B), and satisfying the following requirement (1) or (2): - Poly(meth)acrylate (A): Contains a structural unit (Y) derived from a monomer (y) having a diol-based functional group. - Poly(meth)acrylate (B): Contains a structural unit (Z) derived from a monomer (z) having a boronic acid ester. - Requirement (1): Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contain a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in its side chain. Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) may further contain a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain. Requirement (2): One of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in its side chain. At least the other of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain. [2] A lubricating oil additive composition containing the viscosity index improver composition according to [1] above. [3] A lubricating oil composition containing the viscosity index improver composition according to [1] above and a lubricating oil base oil. [4] A method for producing a lubricating oil composition, comprising the step of mixing a lubricating oil base oil with the following poly(meth)acrylate (A) and the following poly(meth)acrylate (B), and satisfying the following requirement (1) or (2): - Poly(meth)acrylate (A): Contains a constituent unit (Y) derived from a monomer (y) having a diol functional group.Poly(meth)acrylate (B): Contains a structural unit (Z) derived from a monomer (z) having a boronic acid ester. Requirement (1): Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contain a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain. Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) may further contain a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group with 10 to 23 carbon atoms in its side chain. Requirement (2): One of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain. At least the other of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group with 10 to 23 carbon atoms in its side chain.

[0008] According to the present invention, it is possible to provide a viscosity index improver composition that has an excellent viscosity index improving effect, a lubricating oil additive composition containing the viscosity index improver composition, a lubricating oil composition containing the viscosity index improver composition, and a method for producing the lubricating oil composition.

[0009] The upper and lower limit values ​​of the numerical ranges described in this specification can be combined in any way. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges "A to D" and "C to B" are also included in the scope of the present invention. Furthermore, the numerical range "lower limit to upper limit" described in this specification means that the range is equal to or greater than the lower limit and equal to or less than the upper limit, unless otherwise specified. Furthermore, in this specification, the numerical values ​​in the examples are numerical values ​​that can be used as upper or lower limit values.

[0010] As used herein, "(meth)acrylate" means acrylate or methacrylate, and similar meanings apply to other similar terms. For example, "poly(meth)acrylate" means polyacrylate or polymethacrylate.

[0011] [Aspects of Viscosity Index Improver Composition] The viscosity index improver composition of this embodiment contains the following poly(meth)acrylate (A) and poly(meth)acrylate (B), and satisfies the following requirement (1) or (2): Poly(meth)acrylate (A): Contains a structural unit (Y) derived from a monomer (y) having a diol-based functional group. Poly(meth)acrylate (B): Contains a structural unit (Z) derived from a monomer (z) having a boronic acid ester. Requirement (1): Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contain a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain. Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) may further contain a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain. Requirement (2): One of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in its side chain. At least the other of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain.

[0012] When the viscosity index improver composition of this embodiment satisfies requirement (1), the structural units (X1) contained in the poly(meth)acrylate (A) and the poly(meth)acrylate (B) may be the same or different. When the viscosity index improver composition of this embodiment satisfies requirement (1), the structural units (X3) contained in the poly(meth)acrylate (A) and the poly(meth)acrylate (B) may be the same or different. When the viscosity index improver composition of this embodiment contains the structural unit (X2) in both the poly(meth)acrylate (A) and the poly(meth)acrylate (B), these structural units may be the same or different.

[0013] The present inventors conducted extensive research to solve the above-mentioned problems. As a result, they found that a viscosity index improver composition containing the poly(meth)acrylate (A) and the poly(meth)acrylate (B) and satisfying the above-mentioned requirement (1) or (2) has an excellent viscosity index improving effect. The reasons why the viscosity index improver composition of this embodiment has an excellent viscosity index improving effect are presumed to be as follows (i) to (iii): (i) When a viscosity index improver composition containing the poly(meth)acrylate (A) and the poly(meth)acrylate (B) and satisfying the above-mentioned requirement (1) or (2) is blended into a lubricating base oil, the poly(meth)acrylate (A) and the poly(meth)acrylate (B) are unlikely to react at low temperatures and tend to remain separate and independent, and therefore the viscosity of the lubricating oil composition is unlikely to increase at low temperatures. On the other hand, at high temperatures, the boronic acid ester bond present in the side chain of the poly(meth)acrylate (B) undergoes a transesterification reaction with the diol group present in the side chain of the poly(meth)acrylate (A). Therefore, at high temperatures, the poly(meth)acrylate (B) and the poly(meth)acrylate (A) tend to associate, which tends to increase the viscosity of the lubricating oil composition at high temperatures. (ii) Poly(meth)acrylates containing the structural unit (X1) tend to shrink at low temperatures. Therefore, it is easy to keep the viscosity of the lubricating oil composition low at low temperatures. By satisfying the above requirement (1) or (2), the structural unit (X1) is contained in one or both of the poly(meth)acrylate (A) and the poly(meth)acrylate (B), which tends to keep the viscosity of the lubricating oil composition low at low temperatures. (iii) The combination of the "effect of increasing the viscosity of the lubricating oil composition at high temperatures" due to the above (i) and the "effect of keeping the viscosity of the lubricating oil composition low at low temperatures" due to the above (ii) results in an excellent viscosity index improving effect.

[0014] In the following description, "poly(meth)acrylate" may be abbreviated as "PMA." Below, the structural units that PMA (A) and PMA (B) contain or can contain will be described in detail, and then PMA (A) and PMA (B) will be described in detail.

[0015] (Structural Unit (X1)) The structural unit (X1) is a structural unit derived from a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain. When the viscosity index improver composition of this embodiment satisfies requirement (1), the structural unit (X1) is contained in both PMA (A) and PMA (B). When the viscosity index improver composition of this embodiment satisfies requirement (2), the structural unit (X1) is contained in one of PMA (A) and PMA (B). PMA containing the structural unit (X1) is prone to shrinkage at low temperatures. Therefore, by including the structural unit (X1) in one or both of PMA (A) and PMA (B), a viscosity index improver composition with excellent viscosity index improving effects can be obtained. When neither PMA (A) nor PMA (B) contains the structural unit (X1), the viscosity index improving effect is not fully exerted. From the viewpoint of making it easier to enhance the viscosity index improving effect, it is preferable that the structural unit (X1) is contained in both PMA (A) and PMA (B), as defined in requirement (1). Furthermore, when the viscosity index improver composition of the present embodiment satisfies requirement (2), it is preferable that the structural unit (X1) is contained in PMA (A), from the viewpoint of making it easier to enhance the viscosity index improving effect.

[0016] The alkyl group contained in the (meth)acrylate (x1) is preferably a methyl group or an ethyl group, more preferably a methyl group, from the viewpoint of more easily enhancing the viscosity index improving effect.

[0017] The (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain (hereinafter also referred to as "monomer (x1)") is preferably a (meth)acrylate represented by the following general formula (I-1): [In general formula (I-1), R １１ represents a hydrogen atom or a methyl group, and R １２ represents a linear or branched alkylene group having 2 to 4 carbon atoms; R １３ represents a linear alkyl group having 4 or less carbon atoms. n1 represents an integer of 0 to 20. When n1 is 2 or more, a plurality of R １２ may be the same or different.]

[0018] Preferred embodiments of each symbol in general formula (I-1) are shown below. １１ is preferably a methyl group from the viewpoint of making it easier to enhance the viscosity index improving effect. １２ Examples of the linear or branched alkylene group having 2 to 4 carbon atoms that can be selected as R include an ethylene group, a propane-1,2-diyl group, a propane-1,3-diyl group, a butane-1,2-diyl group, a butane-1,3-diyl group, a butane-1,4-diyl group, and a butane-2,2-diyl group, and among these, an ethylene group and a propane-1,2-diyl group are preferred. １３ Examples of linear alkyl groups having 4 or less carbon atoms that can be selected as n1 include a methyl group, an ethyl group, an n-propyl group, and an n-butyl group. Among these, from the viewpoint of making it easier to enhance the viscosity index improving effect, a methyl group or an ethyl group is preferred, and a methyl group is more preferred. From the viewpoint of the solubility in base oil of PMA (A) and PMA (B) that contain or can contain the structural unit (X1), n1 is preferably an integer of 0 to 5, more preferably an integer of 0 to 2, and even more preferably 0. Note that when n1 is 2 or more, multiple R １２ may be the same or different. １２ O-) ｎ１ The bonding between the moieties represented by the formula (I) may be random bonding or block bonding.

[0019] Specific examples of the (meth)acrylate represented by general formula (I-1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and n-butyl (meth)acrylate. Among these, methyl (meth)acrylate and ethyl (meth)acrylate are preferred, methyl (meth)acrylate is more preferred, and methyl methacrylate is even more preferred.

[0020] The monomer (x1) may be used alone or in combination of two or more.

[0021] (Structural Unit (X2)) The structural unit (X2) is a structural unit derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain. When the viscosity index improver composition of this embodiment satisfies requirement (1), the structural unit (X2) may be contained in one or both of PMA (A) and PMA (B). When the viscosity index improver composition of this embodiment satisfies requirement (2), the structural unit (X2) is contained in at least the other of PMA (A) and PMA (B). In other words, the structural unit (X2) is contained in PMA (A) or PMA (B) that does not contain the structural unit (X1) and the structural unit (X3). Furthermore, the structural unit (X2) may be contained in PMA (A) or PMA (B) that contains the structural unit (X1) and the structural unit (X3). In addition, when the viscosity index improver composition of this embodiment satisfies requirement (2), if the structural unit (X2) is not contained in at least the other of PMA (A) and PMA (B), the solubility of the other PMA in the base oil cannot be ensured. PMA containing the structural unit (X2) tends to have excellent solubility in the base oil. Therefore, when PMA (A) contains the structural unit (X2), the solubility of PMA (A) in the base oil tends to be improved. Similarly, when PMA (B) contains the structural unit (X2), the solubility of PMA (B) in the base oil tends to be improved. In addition, from the viewpoint of easily improving the solubility of the viscosity index improver composition of this embodiment in the base oil, it is preferable that both PMA (A) and PMA (B) contain the structural unit (X2). Furthermore, when both PMA (A) and PMA (B) contain the structural unit (X2), the structural units (X2) contained in PMA (A) and PMA (B) may be the same or different.

[0022] The number of carbon atoms in the linear or branched alkyl group contained in the structural unit (X2) is preferably 10 to 20, and more preferably 12 to 18, from the viewpoint of making it easier to improve the solubility of the viscosity index improver composition of this embodiment in the base oil and from the viewpoint of making it easier to exert the effects of the present invention.

[0023] The (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain (hereinafter also referred to as "monomer (x2)") preferably includes a (meth)acrylate represented by the following general formula (I-2): [In general formula (I-2), R ２１ represents a hydrogen atom or a methyl group, and R ２２ represents a linear or branched alkylene group having 2 to 4 carbon atoms; R ２３ represents a linear or branched alkyl group having 10 to 23 carbon atoms. n2 represents an integer of 0 to 20. When n2 is 2 or more, a plurality of R ２２ may be the same or different.]

[0024] Preferred embodiments of each symbol in general formula (I-2) are shown below. ２１ is preferably a methyl group, from the viewpoint of making it easier to enhance the viscosity index improving effect. ２２ Examples of the linear or branched alkylene group having 2 to 4 carbon atoms that can be selected as R １２ The same groups as those listed as R １２ It is the same as R ２３ Examples of the linear or branched alkyl group having 10 to 23 carbon atoms that can be selected as R include a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a heneicosyl group, a docosyl group, and a tricosyl group. ２３ When R is a branched alkyl group, the branching position is not particularly limited. ２３ The number of carbon atoms in the alkyl group that can be selected as the structural unit (X2) is preferably 10 to 20, more preferably 12 to 18. From the viewpoint of the solubility of PMA (A) and PMA (B) containing the structural unit (X2) in the base oil, n2 is preferably an integer of 0 to 5, more preferably an integer of 0 to 2, and even more preferably 0. When n2 is 2 or greater, multiple R ２２ may be the same or different. In addition, -(R ２２ O-) ｎ２The bonding between the moieties represented by the formula (I) may be random bonding or block bonding.

[0025] Specific examples of the (meth)acrylate represented by general formula (I-2) include n-decyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-pentadecyl (meth)acrylate, n-hexadecyl (meth)acrylate, n-heptadecyl (meth)acrylate, n-octadecyl (meth)acrylate, n-nonadecyl (meth)acrylate, n-icosyl (meth)acrylate, n-henicosyl (meth)acrylate, n-docosyl (meth)acrylate, n-tricosyl (meth)acrylate, and isostearyl (methacrylate). Among these, n-decyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, n-pentadecyl (meth)acrylate, n-hexadecyl (meth)acrylate, n-heptadecyl (meth)acrylate, n-octadecyl (meth)acrylate, n-nonadecyl (meth)acrylate Of these, n-dodecyl(meth)acrylate, n-tridecyl(meth)acrylate, n-tetradecyl(meth)acrylate, n-pentadecyl(meth)acrylate, n-hexadecyl(meth)acrylate, n-heptadecyl(meth)acrylate, and n-octadecyl(meth)acrylate are more preferred, and n-dodecyl(meth)acrylate is even more preferred.

[0026] The monomer (x2) may be used alone or in combination of two or more.

[0027] (Structural Unit (X3)) The structural unit (X3) is a structural unit derived from a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in its side chain. When the viscosity index improver composition of this embodiment satisfies requirement (1), the structural unit (X3) is contained in both PMA (A) and PMA (B). When the viscosity index improver composition of this embodiment satisfies requirement (2), the structural unit (X3) is contained in the PMA that contains the structural unit (X1) out of PMA (A) and PMA (B). A PMA that contains the structural unit (X1) has reduced solubility in base oil. For this reason, the viscosity index improver composition of this embodiment ensures the solubility of the PMA in base oil by incorporating the structural unit (X3) together with the structural unit (X1) into the PMA. Here, as described above, from the viewpoint of making it easier to enhance the viscosity index improving effect of the viscosity index improver composition of this embodiment, it is preferable that the structural unit (X1) be contained in both PMA (A) and PMA (B). Therefore, it is preferable that the structural unit (X3) is also contained in both PMA (A) and PMA (B). Furthermore, as described above, when the viscosity index improver composition of this embodiment satisfies requirement (2), it is preferable that the structural unit (X1) is contained in PMA (A), from the viewpoint of making it easier to enhance the viscosity index improving effect. Therefore, it is preferable that the structural unit (X3) is also contained in PMA (A).

[0028] From the viewpoint of making it easier to enhance the viscosity index improving effect of the viscosity index improver composition of this embodiment, the number of carbon atoms in the branched alkyl group contained in the structural unit (X3) is preferably 24 to 32, more preferably 28 to 32, and even more preferably 32.

[0029] The (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in its side chain (hereinafter also referred to as "monomer (x3)") preferably includes a (meth)acrylate represented by the following general formula (I-3): [In general formula (I-3), R ３１ represents a hydrogen atom or a methyl group, and R ３２ represents a linear or branched alkylene group having 2 to 4 carbon atoms; R ３３ and R ３４R each independently represents a linear or branched alkyl group. ３３ and R ３４ The total number of carbon atoms in the alkyl groups that can be selected as R is 22 to 36. n3 represents an integer of 0 to 20. When n3 is 2 or more, a plurality of R ３２ may be the same or different.]

[0030] Preferred embodiments of each symbol in general formula (I-3) are shown below. ３１ R preferably represents a methyl group, from the viewpoint of more easily enhancing the viscosity index improving effect. ３２ Examples of the linear or branched alkylene group having 2 to 4 carbon atoms that can be selected as R １２ The same groups as those listed as R １２ From the viewpoint of the solubility in base oil of PMA (A) and PMA (B) which contain or can contain the structural unit (X3), n3 is preferably an integer of 0 to 5, more preferably an integer of 0 to 2, and even more preferably 0. When n3 is 2 or greater, multiple R ３２ may be the same or different. ３２ O-) ｎ３ The bonding between the moieties represented by the formula (I) may be random bonding or block bonding.

[0031] R ３３ and R ３４ The total number of carbon atoms in the alkyl groups that can be selected as R is preferably 22 to 30, more preferably 26 to 30, and even more preferably 30. ３３ and R ３４ The alkyl group that can be selected as R may be either a linear or branched alkyl group, but is preferably a linear alkyl group. ３３ and R ３４ may be the same or different, but are preferably different. In addition, an example of a suitable embodiment of the (meth)acrylate represented by general formula (I-3) is, for example, R ３３ and R ３４ are different from each other, for example, R ３３is preferably an alkyl group having 10 to 18 carbon atoms, more preferably an alkyl group having 12 to 16 carbon atoms. ３４ represents an alkyl group preferably having 12 to 18 carbon atoms, more preferably an alkyl group having 14 to 18 carbon atoms.

[0032] Specific examples of the (meth)acrylate represented by general formula (I-3) include 2-hexyldecyl methacrylate, 2-decyltetradecyl methacrylate, 2-dodecylhexadecyl methacrylate, and 2-tetradecyloctadecyl methacrylate. Among these, 2-decyltetradecyl methacrylate, 2-dodecylhexadecyl methacrylate, or 2-tetradecyloctadecyl methacrylate is preferred, 2-decyltetradecyl methacrylate or 2-tetradecyloctadecyl methacrylate is more preferred, and 2-tetradecyloctadecyl methacrylate is even more preferred.

[0033] The monomer (x3) may be used alone or in combination of two or more.

[0034] (Structural Unit (Y)) The structural unit (Y) is a structural unit derived from a monomer (y) having a diol-based functional group, and is contained in PMA (A). Preferred examples of the monomer (y) having a diol-based functional group include compounds represented by the following general formula (II): In the general formula (II), R ４１ represents a hydrogen atom or a methyl group, preferably a methyl group.

[0035] p represents an integer of 2 to 18. p is preferably 3 to 8, and more preferably 4.

[0036] q is 0 or 1. q is preferably 0.

[0037] R ４２ and R ４３ each independently represents a hydrogen atom, a tetrahydropyranyl group, a methyloxymethyl group, a tert-butyl group, a benzyl group, a trimethylsilyl group, or a tert-butyldimethylsilyl group.

[0038] Or, R４２ and R ４３ may form a bridge represented by the following general formula (IIa) together with an oxygen atom. In the general formula (IIa), * indicates the bonding position to the oxygen atom. ４４ and R ４５ Each independently represents a hydrogen atom or an alkyl group having 1 to 11 carbon atoms. ４４ and R ４５ is an alkyl group having 1 to 11 carbon atoms, the alkyl group may be linear or branched, but is preferably a linear alkyl group. Specifically, the linear alkyl group is preferably a methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, or n-undecyl group. A methyl group is more preferred.

[0039] Or, R ４２ and R ４３ may form a boronic acid ester represented by the following general formula (IIb) together with an oxygen atom: In the general formula (IIb), * indicates the bonding position to the oxygen atom. ４６ is an aryl group having 6 to 18 carbon atoms, an aralkyl group having 7 to 18 carbon atoms, or an alkyl group having 2 to 18 carbon atoms. The "aryl group having 6 to 18 carbon atoms" may be monocyclic or polycyclic. Examples of the aryl group having 6 to 18 carbon atoms include a phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, and a tetracenyl group. The "aralkyl group having 7 to 18 carbon atoms" refers to a group in which at least one hydrogen atom of the aryl group is substituted with a linear or branched alkyl group, and the total number of carbon atoms in the aryl group and the alkyl group is 7 to 18. Examples of the aralkyl group having 7 to 18 carbon atoms include a benzyl group, a tolyl group, and a xylyl group. The "alkyl group having 2 to 18 carbon atoms" may be linear or branched. R ４６ Among the above, an aryl group having 6 to 18 carbon atoms is preferable, and a phenyl group is more preferable.４６ When is an alkyl group having 2 to 18 carbon atoms, the alkyl group is preferably a linear alkyl group.

[0040] Among the monomers represented by the above general formula (II), a preferred embodiment is a monomer represented by the following general formula (II-A).

[0041] In the general formula (II-A), R ４１ , p, and q are as explained in the above general formula (II), and the preferred ranges are also as explained in the above general formula (II).

[0042] Among the monomers represented by the general formula (II) above, another preferred embodiment is a monomer represented by the following general formula (II-B):

[0043] In the general formula (II-A), R ４１ , p, and q are as described above in the general formula (II), and the preferred ranges are also as described above in the general formula (II). １ and Q ２ each independently represents a tetrahydropyranyl group, a methyloxymethyl group, a tert-butyl group, a benzyl group, a trimethylsilyl group, or a tert-butyldimethylsilyl group.

[0044] Or, Q １ and Q ２ forms a bridge represented by the above general formula (IIa) together with the oxygen atom.

[0045] Or, Q １ and Q ２ forms a boronic acid ester represented by the above general formula (IIb) together with the oxygen atom.

[0046] The monomer (y) may be used singly or in combination of two or more. From the viewpoint of the effects of the present invention, the monomer (y) preferably contains a monomer represented by the general formula (II-A) (i.e., a monomer having a diol group). The content of the monomer represented by the general formula (II-A) is preferably 50 mol% to 100 mol%, more preferably 60 mol% to 100 mol%, even more preferably 70 mol% to 100 mol%, still more preferably 80 mol% to 100 mol%, and even more preferably 90 mol% to 100 mol%, based on the total amount (100 mol%) of the monomer (y).

[0047] (Preparation of Monomer (y) Having a Diol-Based Functional Group) The monomer represented by the general formula (II-A) (monomer having a diol group) can be prepared by reacting -OQ of the monomer represented by the general formula (II-B) according to the following reaction formula (1): １ and -OQ ２ is obtained by deprotection of

[0048] -OQ of the monomer represented by the above general formula (II-B) １ and -OQ ２ The deprotection reaction of the protecting group Q １ and Q ２ The reaction conditions can be appropriately selected depending on the properties of the compound.

[0049] The monomer represented by the general formula (II-B) above can be obtained by reacting an alcohol compound represented by the following general formula (II-b) with a compound represented by the following general formula (II-c) (reaction formula 2).

[0050] R in the above general formula (II-b) and the above general formula (II-c) ４１ , p, and q are as described in the above general formula (II), and the preferred ranges are also as described in the above general formula (II). １ and Q ２ In the general formula (II-c), Q is as explained in the general formula (II-B). ３is a halogen atom (chlorine, bromine, fluorine, and iodine), preferably chlorine.

[0051] The compound of the above general formula (II-c) is available from suppliers such as, for example, Sigma-Aldrich® and Alfa Aesar®.

[0052] The alcohol compound of the general formula (II-b) can be obtained from the general formula (II-a) by protecting the diol group according to the following reaction scheme 3.

[0053] The protection reaction of the diol group of the monomer represented by the general formula (II-a) is carried out by the reaction of the protecting group Q １ and Q ２ The reaction conditions can be appropriately selected depending on the properties of the compound.

[0054] The compound of the above general formula (II-a) is available from suppliers such as, for example, Sigma-Aldrich® and Alfa Aesar®.

[0055] (Structural Unit (Z)) The structural unit (Z) is a structural unit derived from a monomer (z) having a boronic acid ester, and is contained in PMA (B). Preferred examples of the monomer (z) having a boronic acid ester include compounds represented by the following general formula (III):

[0056] In the general formula (III), t represents 0 or 1. t is preferably 0.

[0057] u represents 0 or 1. u is preferably 1.

[0058] R ５０ and R ５１ each independently represents a hydrogen atom or a hydrocarbon-containing chain having 1 to 24 carbon atoms. A "hydrocarbon-containing chain having 1 to 24 carbon atoms" means a linear or branched chain alkyl group having 1 to 24 carbon atoms, or a linear or branched chain alkenyl group having 1 to 24 carbon atoms. The number of carbon atoms in the hydrocarbon-containing chain is preferably 4 to 18, more preferably 6 to 12. R ５０ and R ５１may be the same or different.

[0059] R ５２ and R ５３ each independently represents an arylene group having 6 to 18 carbon atoms, an aralkylene group having 7 to 24 carbon atoms, or an alkylene group having 2 to 24 carbon atoms. The "arylene group having 6 to 18 carbon atoms" may be monocyclic or polycyclic. Examples of the arylene group having 6 to 18 carbon atoms include a phenylene group, a naphthylene group, an anthracenylene group, a phenanthrenylene group, and a tetracenylene group. The "aralkylene group having 7 to 24 carbon atoms" is a divalent group obtained by removing one hydrogen atom from an aralkyl group having 7 to 24 carbon atoms. Examples of the aralkylene group having 7 to 24 carbon atoms include a divalent group obtained by removing one hydrogen atom from a benzyl group, a divalent group obtained by removing one hydrogen atom from a tolyl group, and a divalent group obtained by removing one hydrogen atom from a xylyl group. The "alkylene group having 2 to 24 carbon atoms" may be linear or branched. The number of carbon atoms in the alkylene group is preferably 6 to 16. R ５２ is preferably an arylene group having 6 to 18 carbon atoms, and more preferably a phenylene group. ５３ is preferably an aralkylene group having 7 to 24 carbon atoms, and more preferably a divalent group obtained by removing one hydrogen atom from a benzyl group. ５２ and R ５３ may be the same or different.

[0060] M is -O-C(O)-, -C(O)-O-, -C(O)-N(H)-, -N(H)-C(O)-, -S-, -N(H)-, -N(R ａ )- or -O-. ａ is a hydrocarbon-containing chain having 1 to 15 carbon atoms. The "hydrocarbon-containing chain having 1 to 15 carbon atoms" means a linear or branched chain alkyl group having 1 to 15 carbon atoms, or a linear or branched chain alkenyl group having 1 to 15 carbon atoms. A linear alkyl group is preferred. The number of carbon atoms is also preferably 1 to 8. M is preferably -C(O)-O-.

[0061] R５４ represents a hydrogen atom or a methyl group. ５４ is preferably a methyl group.

[0062] The monomer (z) may be used alone or in combination of two or more.

[0063] (Preparation of Monomer (z) Having Boronic Acid Ester) The monomer (z) having a boronic acid ester can be obtained, for example, by a preparation process including at least one step of condensation of a compound of the following general formula (III-a) with a compound of the following general formula (III-b) according to the following reaction formula 4:

[0064] R in the above general formula (III-a), the above general formula (III-b), and the above general formula (III) ５０ , R ５１ , R ５２ , R ５３ , R ５４ , M, t, and u are as described above for general formula (III), and their preferred ranges are also as described above for general formula (III). Monomer (z) of general formula (III) is obtained by condensation of the boronic acid group in the compound of general formula (III-a) with the diol group in the compound of general formula (III-b). This step is carried out by a method well known to those skilled in the art. The compound of general formula (III-a) is dissolved in a polar solvent such as acetone in the presence of water. The condensation reaction is carried out in the presence of a dehydrating agent such as magnesium sulfate.

[0065] Compounds of the above general formula (III-b) are available from suppliers such as, for example, Sigma-Aldrich®, Alfa Aesar®, and TCI®.

[0066] The compound of the general formula (III-a) can be obtained directly from the compound of the general formula (III-a1) by hydrolysis according to the following reaction formula 5.

[0067] In the above general formula (III-a1), v is 0 or 1. ５５ is a hydrogen atom, a methyl group, or an ethyl group. ５２, R ５３ , R ５４ , M, and u are as explained in the above general formula (III), and the preferred ranges are also as explained in the above general formula (III).

[0068] The compound of general formula (III-a1) can be obtained by condensation reaction of a compound of general formula (III-a11) and a compound of general formula (III-a12) according to the following reaction formula 6.

[0069] In the general formula (III-a11), the general formula (III-a12), and the general formula (III-a1), R ５２ , R ５３ , R ５４ , R ５５ , and u are as explained in the above general formula (III), and the preferred ranges are also as explained in the above general formula (III). v is as explained in the above general formula (III-a1). When M represents —O—C(O)—, Y ４ is an alcohol functional group —OH or a halogen atom (preferably chlorine or bromine), and Y ５ is a carboxylic acid functional group -C(O)-OH. When M represents -C(O)-O-, Y ４ is a carboxylic acid functional group —C(O)—OH, and Y ５ is an alcohol functional group -OH or a halogen atom (preferably chlorine or bromine). When M represents -C(O)-N(H)-, Y ４ is a carboxylic acid functional group —C(O)—OH or a —C(O)-halogen group, and Y ５ is an amine functional group -NH ２ When M represents —N(H)—C(O)—, Y ４ is an amine functional group -NH ２ and Y ５ is a carboxylic acid functional group -C(O)-OH or a -C(O)-halogen group. When M represents -S-, Y ４ is a halogen atom, and Y ５ is a mercapto functional group -SH, or Y ４ is a mercapto functional group -SH, and Y ５is a halogen atom. When M represents —N(H)—, Y ４ is a halogen atom, and Y ５ is an amine functional group -NH ２ or Y ４ is an amine functional group -NH ２ and Y ５ is a halogen atom. ａ )-, Y ４ is a halogen atom, and Y ５ is an amine functional group -N(H)(R ａ ) or Y ４ is an amine functional group -N(H)(R ａ ) and Y ５ is a halogen atom. When M represents —O—, Y ４ is a halogen atom, and Y ５ is an alcohol functional group —OH, or Y ４ is an alcohol functional group —OH, and Y ５ is a halogen atom.

[0070] These esterification, etherification, thioetherification, alkylation or condensation reactions (reactions between an amine functional group and a carboxylic acid functional group) are well known to those skilled in the art. Therefore, those skilled in the art will be able to easily understand the reaction of Y ４ and Y ５ The reaction conditions can be selected depending on the chemical nature of the group.

[0071] The compound of the above general formula (III-a12) is available from suppliers such as, for example, Sigma-Aldrich® and TCI®.

[0072] The compound of general formula (III-a11) can be obtained by a condensation reaction between a boronic acid of general formula (III-a11-1) and at least one diol compound of general formula (III-a11-2) shown below, according to reaction formula 7 shown below.

[0073] In the above general formula (III-a11-1) and the above general formula (III-a11-2), R ５２ , R ５５ , Y４ and v are as explained in the above general formula (III), the above general formula (III-a1), and the above general formula (III-a11). ５５ is a methyl group and v=0.

[0074] Compounds of general formula (III-a11-1) and general formula (III-a11-2) are available from suppliers such as Sigma-Aldrich®, Alfa Aesar®, and TCI®.

[0075] <PMA (A)> PMA (A) contains a structural unit (Y) derived from a monomer (y) having a diol functional group. When requirement (1) is satisfied, PMA (A) contains structural units (X1) and (X3) in addition to the structural unit (Y) derived from the monomer (y) having a diol functional group. PMA (A) may further contain a structural unit (X2). When requirement (2) is satisfied, if PMA (B) contains structural units (X1) and (X3), PMA (A) does not contain structural units (X1) and (X3). However, in this case, PMA (A) contains a structural unit (X2). When requirement (2) is satisfied, if PMA (B) does not contain structural units (X1) and (X3), PMA (A) contains structural units (X1) and (X3). In this case, PMA (A) may further contain a structural unit (X2). When requirement (2) is satisfied, if PMA (B) does not contain structural units (X1) and (X3), PMA (A) contains structural units (X1) and (X3). In this case, PMA (A) may further contain a structural unit (X2).

[0076] (Content of Structural Unit (Y) in PMA (A)) From the viewpoint of ensuring appropriate reactivity with PMA (B) at high temperatures, the content of the structural unit (Y) derived from the monomer (y) having a diol functional group is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on all structural units (100% by mass) of PMA (A). It is also preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 1% by mass to 20% by mass, more preferably 3% by mass to 15% by mass, and even more preferably 5% by mass to 12% by mass. From the viewpoint of ensuring appropriate reactivity with PMA (B) at high temperatures, the content of the structural unit (Y) derived from the monomer (y) having a diol functional group is preferably 1 mol% or more, more preferably 3 mol% or more, and even more preferably 5 mol% or more, based on all structural units (100% by mass) of PMA (A). The content is preferably 20 mol% or less, more preferably 15 mol% or less, and even more preferably 12 mol% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, the content is preferably 1 mol% to 20 mol%, more preferably 3 mol% to 15 mol%, and even more preferably 5 mol% to 12 mol%.

[0077] (Content of Structural Unit (X2) in PMA (A)) When PMA (A) contains structural units (X1) and (X3), the content of the structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, based on all structural units (100% by mass) of PMA (A), in order to facilitate improving the solubility of PMA (A) in base oil. It is also preferably 30% by mass or less, more preferably 27% by mass or less, and even more preferably 25% by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 5% by mass to 30% by mass, more preferably 8% by mass to 27% by mass, and even more preferably 10% by mass to 25% by mass. Furthermore, when PMA (A) contains structural units (X1) and (X3), the content of the structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain is preferably 4 mol% or more, more preferably 6 mol% or more, and even more preferably 7.0 mol% or more, based on all structural units (100 mol%) of PMA (A), from the viewpoint of further improving the solubility of PMA (A) in base oil. It is also preferably 21 mol% or less, more preferably 19 mol% or less, and even more preferably 18 mol% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 4 mol% to 21 mol%, more preferably 6 mol% to 19 mol%, and even more preferably 7 mol% to 18 mol%.

[0078] When PMA (A) does not contain the structural units (X1) and (X3), the content of the structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 88% by mass or more, based on all structural units (100% by mass) of PMA (A), in order to further improve the solubility of PMA (A) in the base oil. It is also preferably 99% by mass or less, more preferably 97% by mass or less, and even more preferably 95% by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 80% by mass to 99% by mass, more preferably 85% by mass to 97% by mass, and even more preferably 88% by mass to 95% by mass. Furthermore, when PMA (A) does not contain the structural units (X1) and (X3), the content of the structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain is preferably 80 mol% or more, more preferably 85 mol% or more, and even more preferably 88 mol% or more, based on all structural units (100 mol%) of PMA (A), from the viewpoint of further improving the solubility of PMA (A) in base oil. It is also preferably 99 mol% or less, more preferably 97 mol% or less, and even more preferably 95 mol% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 80 mol% to 99 mol%, more preferably 85 mol% to 97 mol%, and even more preferably 88 mol% to 95 mol%.

[0079] (Content of Structural Unit (X1) in PMA (A)) When PMA (A) contains the structural unit (X1), the content of the structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain is, from the viewpoint of further enhancing the viscosity index improving effect, preferably 25% by mass or more, more preferably 29% by mass or more, and even more preferably 32% by mass or more, based on all structural units (100% by mass) of PMA (A). It is also preferably 47% by mass or less, more preferably 45% by mass or less, and even more preferably 43% by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 25% by mass to 47% by mass, more preferably 29% by mass to 45% by mass, and even more preferably 32% by mass to 43% by mass. Furthermore, when PMA (A) contains the structural unit (X1), the content of the structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain is preferably 44 mol% or more, more preferably 50 mol% or more, and even more preferably 56 mol% or more, based on all structural units (100 mol%) of PMA (A), from the viewpoint of further enhancing the viscosity index improving effect. It is also preferably 82 mol% or less, more preferably 78 mol% or less, and even more preferably 75 mol% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 44 mol% to 82 mol%, more preferably 50 mol% to 78 mol%, and even more preferably 56 mol% to 75 mol%.

[0080] (Content of Structural Unit (X3) in PMA (A)) When PMA (A) contains the structural unit (X3), the content of the structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in its side chain is preferably 25% by mass or more, more preferably 29% by mass or more, and even more preferably 31% by mass or more, based on all structural units (100% by mass) of PMA (A), from the viewpoint of further enhancing the viscosity index improving effect and enhancing the solubility of PMA (A) in the base oil. It is also preferably 47% by mass or less, more preferably 44% by mass or less, and even more preferably 42% by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 25% by mass to 47% by mass, more preferably 29% by mass to 44% by mass, and even more preferably 31% by mass to 42% by mass. Furthermore, when PMA (A) contains the structural unit (X3), the content of the structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in the side chain is preferably 8.5 mol% or more, more preferably 10 mol% or more, and even more preferably 11 mol% or more, based on all structural units (100 mol%) of PMA (A), from the viewpoint of further enhancing the viscosity index improving effect and enhancing the solubility of PMA (A) in the base oil. It is also preferably 16 mol% or less, more preferably 15 mol% or less, and even more preferably 14 mol% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 8.5 mol% to 16 mol%, more preferably 10 mol% to 15 mol%, and even more preferably 11 mol% to 14 mol%.

[0081] (Total Content of Structural Units (X1) and (X3) in PMA (A)) When PMA (A) contains structural units (X1) and (X3), the total content of the structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain and the structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain is, from the perspective of making it easier to enhance the viscosity index improving effect and making it easier to increase the solubility of PMA (A) in base oil, preferably 50% by mass or more, more preferably 58% by mass or more, and even more preferably 63% by mass or more, based on all structural units (100% by mass) of PMA (A). It is also preferably 90% by mass or less, more preferably 87% by mass or less, and even more preferably 85% by mass or less. The upper and lower limits of these numerical ranges can be combined arbitrarily. Specifically, it is preferably 50% by mass to 90% by mass, more preferably 58% by mass to 87% by mass, and even more preferably 63% by mass to 85% by mass. Furthermore, when PMA (A) contains structural units (X1) and (X3), the total content of the structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain and the structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain is, from the viewpoint of more easily enhancing the viscosity index improving effect and from the viewpoint of more easily increasing the solubility of PMA (A) in the base oil, preferably 54 mol% or more, more preferably 63 mol% or more, and even more preferably 68 mol% or more, based on all structural units (100 mol%) of PMA (A). Furthermore, it is preferably 97 mol% or less, more preferably 96 mol% or less, and even more preferably 92 mol% or less. The upper and lower limits of these numerical ranges can be combined arbitrarily. Specifically, it is preferably 54 mol % to 97 mol %, more preferably 63 mol % to 96 mol %, and even more preferably 68 mol % to 92 mol %.

[0082] (Ratio of Content of the Structural Unit (X1) and the Structural Unit (X3) in PMA (A) [(X1) / (X3)]) When PMA (A) contains the structural units (X1) and (X3), the ratio of content of the structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group of 4 or less carbon atoms in its side chain to the structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group of 24 to 38 carbon atoms in its side chain [(X1) / (X3)] is preferably from 1 / 5 to 5 / 1, more preferably from 1 / 3 to 3 / 1, and even more preferably from 1 / 2 to 2 / 1, in terms of a mass ratio, from the viewpoint of making it easier to enhance the viscosity index improving effect and from the viewpoint of making it easier to increase the solubility of PMA (A) in the base oil.

[0083] (Other Structural Units in PMA (A)) In addition to the structural units (X1), (X2), (X3), and (Y), PMA (A) may contain structural units derived from other monomers, as long as the effects of the present invention are not impaired. Examples of such other monomers include functional group-containing monomers other than the monomers (x1), (x2), (x3), and (y). However, from the viewpoint of making it easier to achieve the effects of the present invention, the total content of the structural units (X1), (X2), (X3), and (Y) in PMA (A) is preferably 80% by mass to 100% by mass, more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, based on the total amount of PMA (A).

[0084] (Physical Properties of PMA (A)) The mass average molecular weight (Mw) of PMA (A) is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 25,000 or more, from the viewpoint of more easily enhancing the viscosity index improving effect. Furthermore, from the viewpoint of more easily improving the shear stability of PMA (A), it is preferably 70,000 or less, more preferably 60,000 or less, and even more preferably 55,000 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 10,000 to 70,000, more preferably 20,000 to 60,000, and even more preferably 25,000 to 55,000.

[0085] The molecular weight distribution (Mw / Mn) of PMA (A) is preferably 3.0 or less, more preferably 2.5 or less, even more preferably 2.0 or less, and still more preferably 1.8 or less. The lower limit of the molecular weight distribution (Mw / Mn) of PMA (A) is not particularly limited, but is preferably 1.01 or more.

[0086] The mass average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of PMA (A) are values ​​measured by the method described in the examples below.

[0087] (Polymerization Mode of PMA (A)) The polymerization mode of PMA (A) is not particularly limited, and may be any of block copolymerization, random copolymerization, and block / random copolymerization, with random copolymerization being preferred.

[0088] <PMA (B)> PMA (B) contains a structural unit (Z) derived from a monomer (z) having a boronic acid ester. When requirement (1) is satisfied, PMA (B) contains structural units (X1) and (X3) in addition to the structural unit (Z) derived from the monomer (z) having a boronic acid ester. PMA (B) may further contain a structural unit (X2). When requirement (2) is satisfied, if PMA (A) contains structural units (X1) and (X3), PMA (B) does not contain structural units (X1) and (X3). However, in this case, PMA (B) contains a structural unit (X2). When requirement (2) is satisfied, if PMA (A) does not contain structural units (X1) and (X3), PMA (B) contains structural units (X1) and (X3). In this case, PMA (B) may further contain a structural unit (X2).

[0089] (Content of Structural Unit (Z) in PMA (B)) From the viewpoint of making it easier to achieve appropriate reactivity with PMA (A) at high temperatures, the content of the structural unit (Z) derived from the monomer (z) having a boronic acid ester is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on all structural units (100% by mass) of PMA (B). It is also preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 1% by mass to 20% by mass, more preferably 3% by mass to 15% by mass, and even more preferably 5% by mass to 12% by mass. Furthermore, from the viewpoint of making it easier to achieve appropriate reactivity with PMA (A) at high temperatures, the content of the structural unit (Z) derived from the monomer (z) having a boronic acid ester is preferably 0.5 mol% or more, more preferably 2 mol% or more, and even more preferably 3 mol% or more, based on all structural units (100% by mass) of PMA (B). The content is preferably 12 mol% or less, more preferably 9 mol% or less, and even more preferably 7 mol% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, the content is preferably 0.6 mol% to 12 mol%, more preferably 2 mol% to 9 mol%, and even more preferably 3 mol% to 7 mol%.

[0090] (Content of Structural Unit (X2) in PMA (B)) When PMA (B) contains structural units (X1) and (X3), the content of the structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, based on all structural units (100% by mass) of PMA (B), in order to facilitate improving the solubility of PMA (B) in the base oil. It is also preferably 30% by mass or less, more preferably 27% by mass or less, and even more preferably 25% by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 5% by mass to 30% by mass, more preferably 8% by mass to 27% by mass, and even more preferably 10% by mass to 25% by mass. Furthermore, when PMA (B) contains structural units (X1) and (X3), the content of the structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain is preferably 4 mol% or more, more preferably 6 mol% or more, and even more preferably 7 mol% or more, based on all structural units (100 mol%) of PMA (B), from the viewpoint of further improving the solubility of PMA (B) in the base oil. It is also preferably 21 mol% or less, more preferably 19 mol% or less, and even more preferably 18 mol% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 4 mol% to 21 mol%, more preferably 6 mol% to 19 mol%, and even more preferably 7 mol% to 18 mol%.

[0091] When PMA (B) does not contain the structural units (X1) and (X3), the content of the structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 88% by mass or more, based on all structural units (100% by mass) of PMA (B), in order to further improve the solubility of PMA (B) in the base oil. It is also preferably 99% by mass or less, more preferably 97% by mass or less, and even more preferably 95% by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 80% by mass to 99% by mass, more preferably 85% by mass to 97% by mass, and even more preferably 88% by mass to 95% by mass. Furthermore, when PMA (B) does not contain the structural units (X1) and (X3), the content of the structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain is preferably 81 mol% or more, more preferably 86 mol% or more, and even more preferably 89 mol% or more, based on all structural units (100 mol%) of PMA (B), from the viewpoint of further improving the solubility of PMA (B) in the base oil. It is also preferably 99 mol% or less, more preferably 98 mol% or less, and even more preferably 96 mol% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 81 mol% to 99 mol%, more preferably 86 mol% to 98 mol%, and even more preferably 89 mol% to 96 mol%.

[0092] (Content of Structural Unit (X1) in PMA (B)) When PMA (B) contains the structural unit (X1), the content of the structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain is, from the viewpoint of further enhancing the viscosity index improving effect, preferably 25% by mass or more, more preferably 29% by mass or more, and even more preferably 32% by mass or more, based on all structural units (100% by mass) of PMA (B). It is also preferably 47% by mass or less, more preferably 45% by mass or less, and even more preferably 43% by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 25% by mass to 47% by mass, more preferably 29% by mass to 45% by mass, and even more preferably 32% by mass to 43% by mass. Furthermore, when PMA (B) contains the structural unit (X1), the content of the structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain is preferably 45 mol% or more, more preferably 52 mol% or more, and even more preferably 58 mol% or more, based on all structural units (100 mol%) of PMA (B), from the viewpoint of further enhancing the viscosity index improving effect. It is also preferably 85 mol% or less, more preferably 81 mol% or less, and even more preferably 77 mol% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 45 mol% to 85 mol%, more preferably 52 mol% to 81 mol%, and even more preferably 58 mol% to 77 mol%.

[0093] (Content of Structural Unit (X3) in PMA (B)) When PMA (B) contains the structural unit (X3), the content of the structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in its side chain is preferably 25% by mass or more, more preferably 29% by mass or more, and even more preferably 31% by mass or more, based on all structural units (100% by mass) of PMA (B), from the viewpoint of further enhancing the viscosity index improving effect and further improving the solubility of PMA (B) in the base oil. It is also preferably 47% by mass or less, more preferably 44% by mass or less, and even more preferably 42% by mass or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 25% by mass to 47% by mass, more preferably 29% by mass to 44% by mass, and even more preferably 31% by mass to 42% by mass. Furthermore, when PMA (B) contains the structural unit (X3), the content of the structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in its side chain is preferably 8.5 mol% or more, more preferably 10 mol% or more, and even more preferably 11 mol% or more, based on all structural units (100 mol%) of PMA (B), from the viewpoint of further enhancing the viscosity index improving effect and enhancing the solubility of PMA (B) in the base oil. It is also preferably 16 mol% or less, more preferably 15 mol% or less, and even more preferably 14 mol% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 8.5 mol% to 16 mol%, more preferably 10 mol% to 15 mol%, and even more preferably 11 mol% to 14 mol%.

[0094] (Total Content of Structural Units (X1) and (X3) in PMA (B)) When PMA (B) contains structural units (X1) and (X3), the total content of the structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain and the structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain is, from the perspective of making it easier to enhance the viscosity index improving effect and making it easier to improve the solubility of PMA (B) in the base oil, preferably 50% by mass or more, more preferably 58% by mass or more, and even more preferably 63% by mass or more, based on all structural units (100% by mass) of PMA (B). It is also preferably 90% by mass or less, more preferably 87% by mass or less, and even more preferably 85% by mass or less. The upper and lower limits of these numerical ranges can be combined arbitrarily. Specifically, it is preferably 50% by mass to 90% by mass, more preferably 58% by mass to 87% by mass, and even more preferably 63% by mass to 85% by mass. Furthermore, when PMA (B) contains structural units (X1) and (X3), the total content of the structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain and the structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain is, from the viewpoint of more easily enhancing the viscosity index improving effect and more easily improving the solubility of PMA (B) in the base oil, preferably 54 mol% or more, more preferably 63 mol% or more, and even more preferably 68 mol% or more, based on all structural units (100 mol%) of PMA (B). Furthermore, it is preferably 97 mol% or less, more preferably 96 mol% or less, and even more preferably 92 mol% or less. The upper and lower limits of these numerical ranges can be combined arbitrarily. Specifically, it is preferably 54 mol % to 97 mol %, more preferably 63 mol % to 96 mol %, and even more preferably 68 mol % to 92 mol %.

[0095] (Ratio of Content of the Structural Unit (X1) and the Structural Unit (X3) in PMA (B) [(X1) / (X3)]) When PMA (B) contains the structural units (X1) and (X3), the ratio of content of the structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group of 4 or less carbon atoms in its side chain to the structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group of 24 to 38 carbon atoms in its side chain [(X1) / (X3)] is preferably from 1 / 5 to 5 / 1, more preferably from 1 / 3 to 3 / 1, and even more preferably from 1 / 2 to 2 / 1, in terms of a mass ratio, from the viewpoint of making it easier to enhance the viscosity index improving effect and from the viewpoint of making it easier to improve the solubility of PMA (B) in the base oil.

[0096] (Other Structural Units in PMA (B)) In addition to the structural units (X1), (X2), (X3), and (Z), PMA (B) may contain structural units derived from other monomers, as long as the effects of the present invention are not impaired. Examples of such other monomers include functional group-containing monomers other than the monomers (x1), (x2), (x3), and (z). However, from the viewpoint of making it easier to achieve the effects of the present invention, the total content of the structural units (X1), (X2), (X3), and (Z) in PMA (B) is preferably 80% by mass to 100% by mass, more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass.

[0097] (Physical Properties of PMA (B)) The mass average molecular weight (Mw) of PMA (B) is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 25,000 or more, from the viewpoint of more easily enhancing the viscosity index improving effect. Furthermore, from the viewpoint of more easily improving the shear stability of PMA (A), it is preferably 70,000 or less, more preferably 60,000 or less, and even more preferably 55,000 or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 10,000 to 70,000, more preferably 20,000 to 60,000, and even more preferably 25,000 to 55,000.

[0098] The molecular weight distribution (Mw / Mn) of PMA (B) is preferably 3.0 or less, more preferably 2.5 or less, even more preferably 2.0 or less, and still more preferably 1.8 or less. The lower limit of the molecular weight distribution (Mw / Mn) of PMA (B) is not particularly limited, but is preferably 1.01 or more.

[0099] The mass average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of PMA (B) are values ​​measured by the method described in the examples below.

[0100] (Polymerization Mode of PMA (B)) The polymerization mode of PMA (B) is not particularly limited, and may be any of block copolymerization, random copolymerization, and block / random copolymerization, with random copolymerization being preferred.

[0101] <Method for producing PMA (A) and PMA (B)> PMA (A) and PMA (B) can be produced by polymerizing the above-mentioned monomers in a polymerization solvent. When PMA (A) and PMA (B) are produced by solution polymerization, they can be obtained by polymerizing the above-mentioned monomers, and if necessary, other monomers, in a polymerization solvent using a polymerization initiator.

[0102] The polymerization initiator may be one or more selected from the group consisting of an azo initiator, a peroxide initiator, a redox initiator, and an organic halogen compound initiator. The polymerization initiator used for the polymerization of PMA (A) and PMA (B) is preferably one or more selected from an azo initiator and a peroxide initiator, more preferably one or more selected from an azo initiator and an organic peroxide, and even more preferably an azo initiator. Examples of the azo polymerization initiator include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 4,4'-azobis(4-cyanovaleric acid) and salts thereof (for example, hydrochloride salts), dimethyl 2,2'-azobisisobutyrate, 2,2'-azobis(2-amidinopropane) hydrochloride, and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide].

[0103] Examples of peroxide initiators include inorganic peroxides and organic peroxides. Examples of inorganic peroxides include hydrogen peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate. Examples of organic peroxides include benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, succinic acid peroxide, di(2-ethoxyethyl)peroxydicarbonate, tert-butyl peroxypivalate, tert-hexyl peroxypivalate, tert-butyl peroxyneoheptanoate, tert-butyl peroxyneodecanoate, tert-butyl peroxy 2-ethylhexanoate, tert-butyl peroxyisobutyrate, tert-amyl peroxy 2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxy 2-ethylhexanoate, dibutyl peroxytrimethyladipate, and lauryl peroxide.

[0104] Examples of redox initiators include those comprising a combination of a reducing agent such as an alkali metal sulfite or bisulfite (e.g., ammonium sulfite, ammonium bisulfite, etc.), ferrous chloride, ferrous sulfate, ascorbic acid, etc., and an oxidizing agent such as an alkali metal persulfate, ammonium persulfate, hydrogen peroxide, organic peroxide, etc. Furthermore, as described above, if the conversion rate of the constituent monomers during polymerization of PMA (A) and PMA (B) does not reach 98%, the conversion rate can be increased to the above conversion rate, for example, by further adding additional polymerization initiator to the polymerization system.

[0105] During polymerization, a known chain transfer agent may be used as needed, for example, for the purpose of adjusting the physical properties of the copolymer, such as molecular weight. Examples of chain transfer agents include mercaptans, thiocarboxylic acids, secondary alcohols such as isopropanol, amines such as dibutylamine, hypophosphites such as sodium hypophosphite, chlorine-containing compounds, and alkylbenzene compounds. Examples of mercaptans include alkyl mercaptan compounds having an alkyl group having 2 to 20 carbon atoms, such as n-butyl mercaptan, isobutyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, sec-butyl mercaptan, tert-butyl mercaptan, and tert-dodecyl mercaptan; and hydroxyl group-containing mercaptan compounds such as mercaptoethanol and mercaptopropanol. Examples of thiocarboxylic acids include thioglycolic acid and thiomalic acid. The amounts of the polymerization initiator and the chain transfer agent used can be appropriately selected in consideration of the desired physical properties of the copolymer (for example, adjustment of the molecular weight, etc.).

[0106] Methods for controlling polymerization include adiabatic polymerization and temperature-controlled polymerization. The reaction temperature during polymerization is preferably 30 to 140°C, more preferably 50 to 130°C, and even more preferably 70 to 120°C. In addition to the method of initiating polymerization by heat, a method of initiating polymerization by irradiation with radiation, electron beams, ultraviolet rays, or the like can also be employed. A preferred method is a temperature-controlled solution polymerization method. The mode of copolymerization may be any of block copolymerization, random copolymerization, and block / random copolymerization, with random copolymerization being preferred.

[0107] In addition, when producing PMA (A), a monomer in which the diol group is protected with a protecting group, such as that represented by the above general formula (II-B), may be used as the monomer (y). In this case, deprotection may be carried out before or after the initiation of polymerization.

[0108] <Total content of PMA (A) and PMA (B) in viscosity index improver composition> The viscosity index improver composition of this embodiment may or may not contain viscosity index improvers other than PMA (A) and PMA (B) as long as the effects of the present invention are not significantly impaired. However, from the viewpoint of making it easier to exhibit the effects of the present invention when added to a lubricating base oil, the total content of PMA (A) and PMA (B) is preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 70 mass% or more, even more preferably 80 mass% or more, even more preferably 90 mass% or more, and even more preferably 95 mass% or more, based on the total amount of the viscosity index improver composition. In addition, considering the purity of PMA (A) and PMA (B), the total content of PMA (A) and PMA (B) is usually less than 100 mass% based on the total amount of the viscosity index improver composition. Note that the viscosity index improver composition of this embodiment may be diluted with a diluting solvent from the viewpoint of ease of handling. The total content of PMA (A) and PMA (B) in the viscosity index improver composition refers to the content based on the total amount of the active ingredients (resin components) in the viscosity index improver composition excluding the dilution solvent. As the dilution solvent, it is preferable to use the same solvent as the polymerization solvent.

[0109] <Content Ratio of PMA (A) and PMA (B) in Viscosity Index Improver Composition> In the viscosity index improver composition of the present embodiment, the content ratio of PMA (A) and PMA (B) [PMA (A) / PMA (B)] is preferably 1 / 5 to 5 / 1, more preferably 1 / 3 to 3 / 1, and even more preferably 1 / 2 to 2 / 1, in molar ratio.

[0110] <Lubricating Oil Additive Composition> The viscosity index improver composition of this embodiment may be provided as a lubricating oil additive composition (e.g., an additive package for a lubricating oil composition) containing one or more additives selected from the group consisting of metal detergents, antiwear agents, ashless dispersants, extreme pressure agents, pour point depressants, antioxidants, antifoaming agents, surfactants, demulsifiers, friction modifiers, oiliness improvers, rust inhibitors, and metal deactivators. Details of the one or more additives selected from the group consisting of metal detergents, antiwear agents, ashless dispersants, extreme pressure agents, pour point depressants, antioxidants, antifoaming agents, surfactants, demulsifiers, friction modifiers, oiliness improvers, rust inhibitors, and metal deactivators will be described later.

[0111] [Lubricating Oil Composition] The lubricating oil composition of this embodiment contains the viscosity index improver composition of this embodiment and a lubricating base oil. From the viewpoint of more easily achieving the viscosity index improving effect, the content of the viscosity index improver composition (equivalent to the resin content) is preferably 1 mass% or more, more preferably 2 mass% or more, and even more preferably 3 mass% or more, based on the total amount (100 mass%) of the lubricating oil composition. Furthermore, from the viewpoint of lowering the viscosity of the lubricating oil composition, it is preferably 20 mass% or less, more preferably 15 mass% or less, and even more preferably 12 mass% or less. The upper and lower limits of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 1 mass% to 20 mass%, more preferably 2 mass% to 15 mass%, and even more preferably 3 mass% to 12 mass%.

[0112] <Lubricant base oil> The lubricant base oil may be any general base oil used in lubricant compositions without any particular limitations. Specific examples include one or more types selected from the group consisting of mineral oils and synthetic oils. The kinematic viscosity of the lubricant base oil at 100°C is 1 mm ２ / s ~ 50 mm ２ / s, and preferably in the range of 2 mm ２ / s ~ 30 mm ２ / s, and more preferably in the range of 3 mm ２ / s ~ 20 mm ２ / s. The viscosity index of the lubricating base oil is preferably 80 or more, more preferably 90 or more, and even more preferably 100 or more. The kinematic viscosity and viscosity index of the lubricating base oil are values ​​measured or calculated in accordance with JIS K2283:2000.

[0113] Specific examples of lubricating base oils are listed below. Examples of mineral oils include distillates obtained by atmospheric and / or vacuum distillation of paraffin-based crude oil, intermediate-based crude oil, or naphthene-based crude oil; and refined oils obtained by refining the distillates according to conventional methods. Examples of refining methods for obtaining refined oils include solvent dewaxing, hydroisomerization, hydrofinishing, and clay treatment. Examples of synthetic oils include hydrocarbon oils, aromatic oils, ester oils, and ether oils. Furthermore, synthetic oils may include GTL (Gas to Liquids) obtained by isomerizing wax (GTL wax, Gas to Liquids wax) produced from natural gas by the Fischer-Tropsch process or the like. From the viewpoint of further enhancing the viscosity index improving effect of the viscosity index improver composition of this embodiment, it is preferable that the lubricating base oil contains an ester oil. When the lubricating base oil contains an ester oil, the content of the ester oil in the lubricating base oil is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, and even more preferably 90% by mass to 100% by mass, based on the total amount of the lubricating base oil.

[0114] <Additives Other Than Viscosity Index Improver Composition> The lubricating oil composition of this embodiment may further contain one or more additives (hereinafter also referred to as "other additives") selected from the group consisting of metal-based detergents, antiwear agents, ashless dispersants, extreme pressure agents, pour point depressants, antioxidants, antifoaming agents, surfactants, demulsifiers, friction modifiers, oiliness improvers, rust inhibitors, and metal deactivators, to the extent that the effects of the viscosity index improver composition of this embodiment are not impaired. When the lubricating oil composition of this embodiment contains other additives, the content of each of the other additives is, for example, preferably 0.001 to 15 mass%, more preferably 0.005 to 10 mass%, and even more preferably 0.01 to 8 mass%, based on the total amount (100 mass%) of the lubricating oil composition. Furthermore, when the lubricating oil composition of this embodiment contains other additives, the total content of the other additives is preferably more than 0 mass % and not more than 30 mass %, more preferably 0.001 to 25 mass %, even more preferably 0.001 to 20 mass %, and still more preferably 0.001 to 15 mass %, based on the total amount (100 mass %) of the lubricating oil composition. Note that the lubricating oil composition of this embodiment may contain the viscosity index improver composition of this embodiment and the other additives by containing the above-mentioned lubricating oil additive composition (lubricating oil package) and a lubricating base oil.

[0115] (Metallic Detergents) Examples of metallic detergents include organic acid metal salt compounds containing a metal atom selected from alkali metals and alkaline earth metals. Specific examples include metal salicylates, metal phenates, and metal sulfonates containing a metal atom selected from alkali metals and alkaline earth metals. In this specification, "alkali metals" refers to lithium, sodium, potassium, rubidium, cesium, and francium. Furthermore, "alkaline earth metals" refers to beryllium, magnesium, calcium, strontium, and barium. As the metal atom contained in the metallic detergent, sodium, calcium, magnesium, or barium is preferred, and calcium is more preferred, from the viewpoint of improving detergency at high temperatures.

[0116] Among the metallic detergents, one or more selected from calcium salicylate, calcium phenate, and calcium sulfonate are preferred from the viewpoints of improving detergency at high temperatures and solubility in the base oil.

[0117] The metallic detergent may be any of a neutral salt, a basic salt, an overbased salt, and a mixture thereof. The total base number of the metallic detergent is preferably 0 to 600 mgKOH / g. When the metallic detergent is a basic salt or an overbased salt, the total base number of the metallic detergent is preferably 10 to 600 mgKOH / g, more preferably 20 to 500 mgKOH / g. In this specification, the term "base number" refers to the base number measured by the perchloric acid method in accordance with JIS K2501:2003 "Petroleum products and lubricants - Test method for neutralization number".

[0118] When the lubricating oil composition of this embodiment contains a metallic detergent as an additional additive, the content of the metallic detergent is preferably 0.01 to 10 mass % based on the total amount (100 mass %) of the lubricating oil composition. The metallic detergents may be used alone or in combination of two or more.

[0119] (Anti-wear Agents) Examples of anti-wear agents include sulfur-containing compounds such as zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphites, phosphate esters, phosphonate esters, and their amine salts or metal salts; and sulfur- and phosphorus-containing anti-wear agents such as thiophosphites, thiophosphate esters, thiophosphonate esters, and their amine salts or metal salts. Among these, zinc dialkyldithiophosphate (ZnDTP) is preferred. When the lubricating oil composition of this embodiment contains an anti-wear agent as an additional additive, the content of the anti-wear agent is preferably 0.05 to 5.0 mass% based on the total amount (100 mass%) of the lubricating oil composition. Note that one type of anti-wear agent may be used alone, or two or more types may be used in combination.

[0120] (Ashless Dispersant) Examples of ashless dispersants include succinimide, benzylamine, succinic acid esters, and boron-modified versions of these, with alkenyl succinimide and boron-modified alkenyl succinimide being preferred.

[0121] Examples of alkenyl succinimides include alkenyl succinic acid monoimides represented by the following general formula (i) and alkenyl succinic acid bisimides represented by the following general formula (ii). The alkenyl succinimides may be modified alkenyl succinimides obtained by reacting a compound represented by the following general formula (i) or (ii) with one or more selected from alcohols, aldehydes, ketones, alkylphenols, cyclic carbonates, epoxy compounds, and organic acids. Examples of boron-modified alkenyl succinimides include boron-modified compounds represented by the following general formula (i) or (ii).

[0122]

[0123] In the general formulas (i) and (ii), R Ａ , R Ａ１ and R Ａ２ are each independently an alkenyl group having a mass average molecular weight (Mw) of 500 to 3,000 (preferably 1,000 to 3,000), and are preferably a polybutenyl group or a polyisobutenyl group. Ｂ , R Ｂ１ and R Ｂ２ are each independently an alkylene group having 2 to 5 carbon atoms. x1 is an integer of 1 to 10, preferably an integer of 2 to 5, and more preferably 3 or 4. x2 is an integer of 0 to 10, preferably an integer of 1 to 4, and more preferably 2 or 3.

[0124] From the viewpoint of improving detergency, the ratio of boron atoms to nitrogen atoms [B / N] constituting the boron-modified alkenyl succinimide is preferably 0.5 or more, more preferably 0.6 or more, even more preferably 0.8 or more, and even more preferably 0.9 or more. When the lubricating oil composition of this embodiment contains an ashless dispersant as an additional additive, the content of the ashless dispersant is preferably 0.1 to 20 mass% based on the total amount (100 mass%) of the lubricating oil composition. The ashless dispersants may be used alone or in combination of two or more.

[0125] (Extreme Pressure Agents) Examples of extreme pressure agents include sulfur-based extreme pressure agents such as sulfides, sulfoxides, sulfones, and thiophosphinates; halogen-based extreme pressure agents such as chlorinated hydrocarbons; and organometallic extreme pressure agents. Furthermore, among the above-mentioned antiwear agents, compounds that function as extreme pressure agents can also be used. When the lubricating oil composition of this embodiment contains an extreme pressure agent as an additional additive, the content of the extreme pressure agent is preferably 0.1 to 10 mass% based on the total amount (100 mass%) of the lubricating oil composition. One type of extreme pressure agent may be used alone, or two or more types may be used in combination.

[0126] (Antioxidant) The antioxidant can be appropriately selected from known antioxidants conventionally used as antioxidants for lubricating oils, and examples thereof include amine-based antioxidants, phenol-based antioxidants, molybdenum-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, etc. Examples of the amine-based antioxidant include diphenylamine-based antioxidants such as diphenylamine and alkylated diphenylamines having an alkyl group with 3 to 20 carbon atoms; naphthylamine-based antioxidants such as α-naphthylamine, phenyl-α-naphthylamine, and substituted phenyl-α-naphthylamines having an alkyl group with 3 to 20 carbon atoms; and the like. Examples of phenolic antioxidants include monophenolic antioxidants such as 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; diphenolic antioxidants such as 4,4'-methylenebis(2,6-di-tert-butylphenol) and 2,2'-methylenebis(4-ethyl-6-tert-butylphenol); hindered phenolic antioxidants; and the like. Examples of molybdenum-based antioxidants include molybdenum amine complexes obtained by reacting molybdenum trioxide and / or molybdic acid with an amine compound. Examples of sulfur-based antioxidants include dilauryl-3,3'-thiodipropionate. Examples of phosphorus-based antioxidants include phosphites. When using a phosphorus-based antioxidant, it is preferable to use an amount that satisfies the suitable phosphorus atom content of the lubricating oil composition described below. In this embodiment, these antioxidants can be contained alone or in any combination of two or more, and it is preferable to contain a phenol-based antioxidant and / or an amine-based antioxidant.When the lubricating oil composition of this embodiment contains an antioxidant as an additional additive, the content of the antioxidant is preferably 0.05 to 7 mass % based on the total amount (100 mass %) of the lubricating oil composition.

[0127] (Pour Point Depressant) Examples of pour point depressants include ethylene-vinyl acetate copolymers, condensates of chlorinated paraffin and naphthalene, condensates of chlorinated paraffin and phenol, polymethacrylates (PMA-based; polyalkyl(meth)acrylates, etc.), polyvinyl acetate, polybutene, polyalkylstyrene, etc., with polymethacrylates being preferred. When the lubricating oil composition of this embodiment contains a pour point depressant as an additional additive, the content of the pour point depressant is preferably 0.01 to 10 mass% based on the total amount (100 mass%) of the lubricating oil composition. Note that one type of pour point depressant may be used alone, or two or more types may be used in combination.

[0128] (Antifoaming Agent) Examples of antifoaming agents include silicone oils such as dimethylpolysiloxane, fluorosilicone oils, and fluoroalkyl ethers. When the lubricating oil composition of this embodiment contains an antifoaming agent as an additional additive, the content of the antifoaming agent is preferably 0.05 to 5 mass% based on the total amount (100 mass%) of the lubricating oil composition. One type of antifoaming agent may be used alone, or two or more types may be used in combination.

[0129] (Surfactant or Emulsifier) ​​Examples of surfactants or demulsifiers include polyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and polyoxyethylene alkyl naphthyl ethers. When the lubricating oil composition of this embodiment contains a surfactant or demulsifier as an additional additive, the content of the surfactant or demulsifier is preferably 0.01 to 3 mass% based on the total amount (100 mass%) of the lubricating oil composition. These surfactants or demulsifiers may be used alone or in combination of two or more.

[0130] (Friction Modifiers) Examples of friction modifiers include molybdenum-based friction modifiers such as molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and amine salts of molybdenum acid; ashless friction modifiers such as aliphatic amines, fatty acid esters, fatty acid amides, fatty acids, fatty alcohols, and aliphatic ethers, each having at least one alkyl or alkenyl group having 6 to 30 carbon atoms in the molecule; and fats and oils, amines, amides, sulfurized esters, phosphate esters, phosphites, and phosphate ester amine salts. When the lubricating oil composition of this embodiment contains a friction modifier as an additional additive, the content of the friction modifier is preferably 0.05 to 4 mass% based on the total amount (100 mass%) of the lubricating oil composition. Note that one type of friction modifier may be used alone, or two or more types may be used in combination.

[0131] (Oilability Improver) Examples of oiliness improvers include saturated or unsaturated aliphatic monocarboxylic acids such as stearic acid and oleic acid; polymerized fatty acids such as dimer acid and hydrogenated dimer acid; hydroxy fatty acids such as ricinoleic acid and 12-hydroxystearic acid; saturated or unsaturated aliphatic monoalcohols such as lauryl alcohol and oleyl alcohol; saturated or unsaturated aliphatic monoamines such as stearylamine and oleylamine; saturated or unsaturated aliphatic monocarboxylic acid amides such as lauric acid amide and oleic acid amide; partial esters of polyhydric alcohols such as glycerin and sorbitol with saturated or unsaturated aliphatic monocarboxylic acids; and the like. When the lubricating oil composition of this embodiment contains an oiliness improver as an additional additive, the content of the oiliness improver is preferably 0.01 to 5 mass% based on the total amount (100 mass%) of the lubricating oil composition. One type of oiliness improver may be used alone, or two or more types may be used in combination.

[0132] (Rust inhibitor) Examples of rust inhibitors include fatty acids, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, oxidized paraffins, and alkyl polyoxyethylene ethers. When the lubricating oil composition of this embodiment contains a rust inhibitor as an additional additive, the content of the rust inhibitor is preferably 0.01 to 3 mass% based on the total amount (100 mass%) of the lubricating oil composition. Note that one type of rust inhibitor may be used alone, or two or more types may be used in combination.

[0133] (Metal Deactivator) Examples of metal deactivators include benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, and pyrimidine-based compounds. When the lubricating oil composition of this embodiment contains a metal deactivator as an additional additive, the content of the metal deactivator is preferably 0.01 to 5 mass% based on the total amount (100 mass%) of the lubricating oil composition. Note that one type of metal deactivator may be used alone, or two or more types may be used in combination.

[0134] <Physical Properties of Lubricating Oil Composition> (Kinematic Viscosity, Viscosity Index) The kinematic viscosity at 100°C of the lubricating oil composition of this embodiment is preferably 1.0 mm ２ / s ~ 50 mm ２ / s, more preferably 2.0 mm ２ / s ~ 30 mm ２ / s, more preferably 3.0 mm ２ / s ~ 20 mm ２ The viscosity index of the lubricating oil composition of this embodiment is preferably 220 or more, more preferably 230 or more, even more preferably 240 or more, and still more preferably 250 or more. The kinematic viscosity and viscosity index of the lubricating oil composition are values ​​measured or calculated in accordance with JIS K2283:2000.

[0135] [Uses of Lubricating Oil Composition] The lubricating oil composition of this embodiment contains the viscosity index improver composition of this embodiment, and therefore has an excellent viscosity index. Therefore, the lubricating oil composition of this embodiment can be suitably used in a variety of applications, including drive system oils such as gear oils (manual transmission oil, differential oil, etc.), automatic transmission oils (automatic transmission oil, etc.), continuously variable transmission oils (belt CVT oil, toroidal CVT oil, etc.), power steering oil, shock absorber oil, and electric motor oil; internal combustion engine (engine) oils for gasoline engines, diesel engines, and gas engines; equipment oils such as hydraulic oils, turbine oils, and compressor oils; fluid bearing oils; rolling bearing oils; refrigeration oils, etc.

[0136] [Method for Producing Lubricating Oil Composition] The method for producing the lubricating oil composition of this embodiment is not particularly limited, but examples include a method for producing a lubricating oil composition that includes a step of mixing a lubricating base oil, the PMA (A), and the PMA (B), and satisfies the above requirement (1) or (2).

[0137] In the above process, the lubricating base oil, the PMA (A), and the PMA (B) are not limited to being mixed all at once. The PMA (A) may be blended and mixed with the lubricating base oil, and then the PMA (B) may be blended and mixed, or the PMA (B) may be blended and mixed with the lubricating base oil, and then the PMA (A) may be blended and mixed. Of course, the PMA (A) and the PMA (B) may be blended and mixed simultaneously with the lubricating base oil. When the PMA (A) and the PMA (B) are blended and mixed simultaneously with the lubricating base oil, it is preferable to blend the viscosity index improver composition of this embodiment with the lubricating base oil and mix it. Note that the PMA (A) and the PMA (B) may be blended after being made into a solution (dispersion) by adding a diluent oil or the like. Alternatively, they may be blended in the form of a dispersion in the polymerization solvent without removing the polymerization solvent used during polymerization.

[0138] The method for producing a lubricating oil composition of this embodiment may or may not further include a step of blending additives other than the viscosity index improver composition of this embodiment into a lubricating base oil, as described above. When blending the additive into a lubricating base oil, the additive may be blended after being made into a solution (dispersion) by adding a diluent oil or the like. Alternatively, the lubricating oil additive composition of this embodiment may be blended into a lubricating base oil, and the viscosity index improver composition of this embodiment and additives other than the viscosity index improver composition may be blended together. In the method for producing a lubricating oil composition of this embodiment, preferred aspects of the lubricating base oil and preferred aspects of PMA (A) and PMA (B) are as described above.

[0139] [Lubrication Method Using Lubricating Oil Composition] A lubrication method using the lubricating oil composition of this embodiment includes filling the lubricating oil composition of this embodiment into equipment used for each of the above-mentioned applications and lubricating the components of each of the equipment.

[0140] [One Aspect of the Present Invention Provided] According to one aspect of the present invention, the following [1] to

[15] are provided. [1] A viscosity index improver composition containing the following poly(meth)acrylate (A) and the following poly(meth)acrylate (B), and satisfying the following requirement (1) or (2): - Poly(meth)acrylate (A): Contains a structural unit (Y) derived from a monomer (y) having a diol-based functional group. - Poly(meth)acrylate (B): Contains a structural unit (Z) derived from a monomer (z) having a boronic acid ester. - Requirement (1): Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contain a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in its side chain. Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) may further contain a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain. Requirement (2): One of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in its side chain. At least the other of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in its side chain. [2] The viscosity index improver composition according to [1], wherein the poly(meth)acrylate (A) has a mass average molecular weight (Mw) of 10,000 to 70,000. [3] The viscosity index improver composition according to [1] or [2], wherein the poly(meth)acrylate (B) has a mass average molecular weight (Mw) of 10,000 to 70,000.[4] The viscosity index improver composition according to any one of [1] to [3], wherein, when the poly(meth)acrylate (A) contains the structural unit (X1) and the structural unit (X3), the total content of the structural unit (X1) and the structural unit (X3) is 50 mass% or more, based on all structural units of the poly(meth)acrylate (A). [5] The viscosity index improver composition according to any one of [1] to [4], wherein, when the poly(meth)acrylate (A) contains the structural unit (X1) and the structural unit (X3), the content ratio of the structural unit (X1) to the structural unit (X3), [(X1) / (X3)], in mass ratio, is 1 / 5 to 5 / 1. [6] The viscosity index improver composition according to any one of [1] to [5], wherein, when the poly(meth)acrylate (B) contains the structural unit (X1) and the structural unit (X3), the total content of the structural unit (X1) and the structural unit (X3) is 50 mass% or more based on all structural units of the poly(meth)acrylate (B). [7] The viscosity index improver composition according to any one of [1] to [6], wherein, when the poly(meth)acrylate (B) contains the structural unit (X1) and the structural unit (X3), the content ratio of the structural unit (X1) to the structural unit (X3), [(X1) / (X3)], in mass ratio, is 1 / 5 to 5 / 1. [8] The viscosity index improver composition according to any one of [1] to [5], which satisfies the requirement (1). [9] The viscosity index improver composition according to any one of [1] to [8], wherein the alkyl group in the (meth)acrylate (x1) is a methyl group.

[10] The viscosity index improver composition according to any one of [1] to [9], wherein the (meth)acrylate (x3) is a compound represented by the following general formula (I-3): [In the general formula (I-3), R ３１ represents a hydrogen atom or a methyl group, and R ３２ represents a linear or branched alkylene group having 2 to 4 carbon atoms; R ３３ and R ３４ R each independently represents a linear or branched alkyl group. ３３ and R ３４ The total number of carbon atoms in the alkyl groups that can be selected as R is 22 to 36. n3 represents an integer of 0 to 20. When n3 is 2 or more, a plurality of R３２ may be the same or different.]

[11] The viscosity index improver composition according to any one of [1] to

[10] , wherein the monomer (y) having a diol functional group is a compound represented by the following general formula (II): [In the general formula (II), R ４１ represents a hydrogen atom or a methyl group, p represents an integer of 2 to 18, and q is 0 or 1. R ４２ and R ４３ each independently represents hydrogen, a tetrahydropyranyl group, a methyloxymethyl group, a tert-butyl group, a benzyl group, a trimethylsilyl group, or a tert-butyldimethylsilyl group. ４２ and R ４３ forms a bridge represented by the following general formula (IIa) together with an oxygen atom. In the general formula (IIa), * indicates the bonding position to the oxygen atom. ４４ and R ４５ each independently represents a hydrogen atom or an alkyl group having 1 to 11 carbon atoms. ４２ and R ４３ forms a boronic acid ester represented by the following general formula (IIb) together with an oxygen atom. In the general formula (IIb), * indicates the bonding position to the oxygen atom. ４６ is an aryl group having 6 to 18 carbon atoms, an aralkyl group having 7 to 18 carbon atoms, or an alkyl group having 2 to 18 carbon atoms.]

[12] The viscosity index improver composition according to any one of [1] to

[11] , wherein the monomer (z) having a boronic acid ester is a compound represented by the following general formula (III): [In the general formula (III), t represents 0 or 1, and u represents 0 or 1. ５０ and R ５１ R each independently represents a hydrogen atom or a hydrocarbon-containing chain having 1 to 24 carbon atoms. ５２ and R ５３ each independently represents an arylene group having 6 to 18 carbon atoms, an aralkylene group having 7 to 24 carbon atoms, or an alkylene group having 2 to 24 carbon atoms. M represents -O-C(O)-, -C(O)-O-, -C(O)-N(H)-, -N(H)-C(O)-, -S-, -N(H)-, -N(Rａ ) - or -O- (wherein R ａ is a hydrocarbon-containing chain having 1 to 15 carbon atoms). ５４represents a hydrogen atom or a methyl group.]

[13] A lubricating oil additive composition comprising the viscosity index improver composition according to any one of [1] to

[12] and one or more additives selected from the group consisting of metal-based detergents, antiwear agents, ashless dispersants, extreme pressure agents, pour point depressants, antioxidants, antifoaming agents, surfactants, demulsifiers, friction modifiers, oiliness improvers, rust inhibitors, and metal deactivators.

[14] A lubricating oil composition comprising the viscosity index improver composition according to any one of [1] to

[12] and a lubricating oil base oil.

[15] A method for producing a lubricating oil composition comprising a step of mixing a lubricating oil base oil with the following poly(meth)acrylate (A) and the following poly(meth)acrylate (B), wherein the method satisfies the following requirement (1) or (2): - Poly(meth)acrylate (A): Contains a constituent unit (Y) derived from a monomer (y) having a diol-based functional group. Poly(meth)acrylate (B): Contains a structural unit (Z) derived from a monomer (z) having a boronic acid ester. Requirement (1): Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contain a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain. Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) may further contain a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group with 10 to 23 carbon atoms in its side chain. Requirement (2): One of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain. At least the other of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group with 10 to 23 carbon atoms in its side chain.

[0141] The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0142] [Methods for Measuring Various Physical Properties] Measurements of the various properties of the raw materials used in each Example and Comparative Example and the lubricating oil compositions of each Example and Comparative Example were carried out according to the procedures set out below.

[0143] (1) Kinematic Viscosity and Viscosity Index The 100°C kinematic viscosity and viscosity index of the base oil and lubricating oil composition were measured or calculated in accordance with JIS K2283:2000.

[0144] (2) Mass-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) One column, "TSKguard column Super HZ-L" and two columns, "TSKSuper Multipore HZ-M," manufactured by Tosoh Corporation, were attached to a "1515 Isocratic HPLC Pump" and a "2414 Differential Refractive Index (RI) Detector" manufactured by Waters Corporation in this order from the upstream side. Measurement was carried out under the conditions of a measurement temperature of 40°C, a mobile phase of tetrahydrofuran, a flow rate of 0.35 mL / min, and a sample concentration of 1.0 mg / mL, and the values ​​were calculated in terms of standard polystyrene.

[0145] [Production of PMA (A), PMA (B), and PMA (C) (Comparative PMAs)] PMA (A), PMA (B), and PMA (C) (Comparative PMAs) were produced by Production Examples 1 to 4 and Comparative Production Example 1 described below.

[0146] In the following description and in Table 1, the abbreviations of the components represent the following compounds.

[0147] "C1MA": methyl methacrylate Methyl methacrylate is a compound represented by the general formula (I-1) above, where R １１ is a methyl group, and R １３ is a methyl group, and n1 = 0. Methyl methacrylate corresponds to a (meth)acrylate (x1) having a linear alkyl group having 4 or less carbon atoms in the side chain.

[0148] "C12MA": n-dodecyl methacrylate n-Dodecyl methacrylate is a compound represented by the general formula (I-2) above, where R ２１ is a methyl group, and R２３ is an n-dodecyl group, and n2 = 0. n-Dodecyl methacrylate corresponds to a (meth)acrylate (x2) having a linear or branched alkyl group having 10 to 23 carbon atoms in the side chain.

[0149] "C32MA": 2-tetradecyl octadecyl methacrylate 2-tetradecyl octadecyl methacrylate is a compound represented by the general formula (I-3) above, where R ３３ is an n-tetradecyl group, and R ３４ is an n-hexadecyl group, and n3 = 0. 2-Tetradecyl octadecyl methacrylate corresponds to a (meth)acrylate (x3) having a branched alkyl group having 24 to 38 carbon atoms in the side chain.

[0150] "Monomer having a diol group": The compound is represented by the general formula (II) R ４１ is a methyl group, p=4, q=0, and R ４２ and R ４３ is a hydrogen atom.

[0151] The diol group-containing monomer was prepared by the following method (three-step process).

[0152] (First step: protection of the diol group in the triol compound) 21.1 g (157 mmol) of 1,2,6-hexanetriol were introduced into a 0.5 L flask. 2.0 g of molecular sieves (4 Å) were then added successively to 200 mL of acetone. 1.0 g (5.2 mmol) of p-toluenesulfonic acid was then added slowly. The reaction medium was stirred for 12 hours at ambient temperature. 2.0 g (23.7 mmol) of NaHCO ３ The reaction medium was stirred at ambient temperature for 3 hours before being filtered. The filtrate was then concentrated under reduced pressure on a rotary evaporator until a white crystalline suspension was obtained. 200 mL of water was then added to this suspension. The solution thus obtained was extracted three times with 200 mL of dichloromethane. The organic phases from each extraction were combined and MgSO ４The solvent was then completely evaporated under reduced pressure at 25°C using a rotary evaporator.

[0153] (Step 2: Introduction of Methacryloyl Group) The product obtained in Step 1 was introduced into a 0.5 L flask equipped with a dropping funnel. 500 mL of dichloromethane was added to the flask, followed by 17.9 g (182 mmol) of triethylamine. A solution of 18.0 g (172 mmol) of methacryloyl chloride and 20 mL of dichloromethane was added to the dropping funnel. The flask was then placed in an ice bath to lower the temperature of the reaction medium to around 0°C, and the methacryloyl chloride solution was added dropwise under vigorous stirring. After the addition of methacryloyl chloride was complete, the reaction medium was stirred at 0°C for 1 hour and then at ambient temperature for 6 hours. The reaction medium was then transferred to a 2 L Erlenmeyer flask, and 0.5 L of dichloromethane was added. The organic phase was then washed twice with 0.5 M hydrochloric acid and 150 mL of NaHCO . ３ The organic phase was washed twice with saturated aqueous solution and twice with 150 mL of saturated brine. ４ The mixture was dried at 75°C, filtered, and concentrated under reduced pressure using a rotary evaporator to produce 30.0 g (78.2% yield) of a whitish-yellow liquid diol monomer protected in a ketal form. The structural formula of the diol monomer protected in a ketal form is shown below.

[0154] (Step 3: Deprotection) Next, 30.0 g (124.0 mmol) of the product obtained in Step 2 was placed in a 1 L round-bottom flask. Subsequently, 120 mL of water and 120 mL of acetonitrile were placed in the flask, followed by 30.0 mL (80.7 mmol) of acetic acid. The flask was then stirred at 35°C for 24 hours while gently bubbling nitrogen gas through the flask to remove acetone from the reaction system. The solution thus obtained was extracted with 3 x 50 mL of ethyl acetate. The organic phase was washed successively with 3 x 50 mL of 0.5 M aqueous NaOH solution, followed by 50 mL of saturated aqueous saline. Furthermore, MgSO ４ The organic phase was dried through a filtration tank, filtered, and concentrated under vacuum using a rotary evaporator to give 20.2 g (80.6% yield) of a pale yellow liquid.

[0155] ・"Boronate ester monomer": The compound is represented by the general formula (III) where t=0, u=1, and R ５０ and R ５１ one of which is a hydrogen atom and the other is a linear alkyl group having 10 carbon atoms, and R ５２ is a phenylene group, and R ５３ is a divalent group obtained by removing one hydrogen atom from a benzyl group, M is —C(O)—O—, and R ５４ is a methyl group.

[0156] The boronic ester monomers were prepared by the following method (two-step process).

[0157] (Step 1) 4-carboxyphenylboronic acid (CPBA) (5.01 g; 30.2 mmol) was introduced into a 1 L beaker, followed by 350 mL of acetone. The reaction medium was stirred, and 7.90 mL (439 mmol) of water was added dropwise until the 4-carboxyphenylboronic acid was completely dissolved. 1,2-propanediol (2.78 g; 36.6 mmol) was then slowly added, followed by an excess of magnesium sulfate to capture the water initially introduced and that released by the condensation between CPBA and 1,2-propanediol. The reaction medium was stirred for 1 hour at 25°C before being filtered. The solvent was then removed by rotary evaporation. The obtained product and 85 mL of dimethyl sulfoxide (DMSO) were introduced into a 250 mL flask. The reaction medium was stirred, and after complete homogenization of the reaction medium, 8.33 g (60.3 mmol) of K ２ CO ３ was added. 4-Chloromethylstyrene (3.34 g; 21.9 mmol) was then slowly introduced into the flask. The reaction medium was then left under stirring at 50°C for 12 hours. The reaction medium was transferred to a 2 L Erlenmeyer flask and 900 mL of water was added. The aqueous phase was extracted 8 times with 150 mL of ethyl acetate. The organic phases from each extraction were mixed and then extracted 3 times with 250 mL of water. The organic phase was diluted with MgSO ４The filtrate was dried by rotary evaporation and filtered to produce a white powder of boronic acid monomer (5.70 g; 92.2% yield).

[0158] (Step 2) The boronic acid monomer (5.7 g; 20.2 mmol) obtained in Step 1 and 500 mL of acetone were introduced into a 1 L Erlenmeyer flask. The reaction medium was stirred, and 2.6 mL (144 mmol) of water was added dropwise until the boronic acid monomer was completely dissolved. A solution of 1,2-dodecanediol (5.32 g; 26.3 mmol) in 50 mL of acetone was slowly added to the reaction medium, followed by the addition of an excess amount of magnesium sulfate to capture the water initially introduced and the water released by the condensation between the boronic acid monomer and 1,2-dodecanediol. After stirring for 3 hours at ambient temperature, the reaction medium was filtered. The solvent was then removed from the filtrate using a rotary evaporator, producing 10.2 g of a white-yellow solid mixture of boronic acid ester monomer and 1,2-dodecanediol.

[0159] <Production Example 1: Production of PMA(A)-1> 22 g (91 mmol) of dodecyl methacrylate, 2 g (10 mmol) of a monomer having a diol group, and 24 g of 2-ethylhexyl sebacate as a solvent were charged into a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a nitrogen inlet tube. The atmosphere inside the reaction vessel was then purged with nitrogen, and 0.1 g (0.4 mmol) of 2,2'-azobis(2,4-dimethylvaleronitrile) as an initiator and 0.08 g (0.4 mmol) of n-dodecyl mercaptan were added. The temperature was then slowly raised with stirring, and the reaction was carried out at a temperature of 75 to 85°C for 6 hours. After completion of the reaction, unreacted monomer was distilled off under reduced pressure to obtain PMA(A)-1.

[0160] Preparation Example 2: Preparation of PMA(A)-2 A reaction vessel equipped with a stirrer, heater / cooler, thermometer, and nitrogen inlet tube was charged with 4 g (17 mmol) of dodecyl methacrylate, 2 g (10 mmol) of a monomer having a diol group, 8 g (15 mmol) of 2-tetradecyl octadecyl methacrylate, 9 g (90 mmol) of methyl methacrylate, and 28 g of 2-ethylhexyl sebacate as a solvent. The atmosphere in the reaction vessel was then purged with nitrogen, and 0.1 g (0.4 mmol) of 2,2'-azobis(2,4-dimethylvaleronitrile) as an initiator and 0.08 g (0.4 mmol) of n-dodecyl mercaptan were added. The mixture was then slowly heated with stirring and reacted at 75-85°C for 6 hours. After completion of the reaction, unreacted monomer was removed by distillation under reduced pressure to obtain PMA(A)-2.

[0161] <Production Example 3: Production of PMA(B)-1> 22 g (91 mmol) of dodecyl methacrylate, 2 g of a boronic acid ester monomer, and 24 g of 2-ethylhexyl sebacate as a solvent were charged into a reaction vessel equipped with a stirrer, a heating / cooling device, a thermometer, and a nitrogen inlet tube. The atmosphere inside the reaction vessel was then purged with nitrogen, and 0.1 g (0.4 mmol) of 2,2'-azobis(2,4-dimethylvaleronitrile) as an initiator and 0.08 g (0.4 mmol) of n-dodecyl mercaptan were added. The temperature was then slowly raised with stirring, and the reaction was carried out at a temperature of 75 to 85°C for 6 hours. After completion of the reaction, unreacted monomer was distilled off under reduced pressure to obtain PMA(B)-1.

[0162] Preparation Example 4: Preparation of PMA(B)-2 A reaction vessel equipped with a stirrer, heater / cooler, thermometer, and nitrogen inlet tube was charged with 4 g (17 mmol) of dodecyl methacrylate, 2 g of a boronic acid ester monomer, 8 g (15 mmol) of 2-tetradecyloctadecyl methacrylate, 9 g (90 mmol) of methyl methacrylate, and 28 g of 2-ethylhexyl sebacate as a solvent. The atmosphere in the reaction vessel was then purged with nitrogen, and 0.1 g (0.4 mmol) of 2,2'-azobis(2,4-dimethylvaleronitrile) as an initiator and 0.08 g (0.4 mmol) of n-dodecyl mercaptan were added. The mixture was then slowly heated with stirring and reacted at 75-85°C for 6 hours. After completion of the reaction, unreacted monomer was removed by distillation under reduced pressure to obtain PMA(B)-2.

[0163] Comparative Production Example 1: Production of PMA(C)-1 A reaction vessel equipped with a stirrer, heater / cooler, thermometer, and nitrogen inlet tube was charged with 9 g (90 mmol) of methyl methacrylate, 11 g (21 mmol) of 2-tetradecyl octadecyl methacrylate, and 20 g of hydrocarbon GrII base oil (40°C, KV: 7.1 mm2 / s, VI: 109) as a solvent. The atmosphere inside the reaction vessel was then purged with nitrogen, and 0.1 g (0.4 mmol) of 2,2'-azobis(2,4-dimethylvaleronitrile) as an initiator and 0.08 g (0.4 mmol) of n-dodecyl mercaptan were added. The mixture was then slowly heated with stirring and reacted at a temperature of 75-85°C for 6 hours. After completion of the reaction, unreacted monomer was removed by distillation under reduced pressure to obtain PMA(C)-1.

[0164] Table 1 shows the blending ratio (mass%) of each monomer in Production Examples 1 to 4 and Comparative Production Example 1, the physical properties of the polymers (number average molecular weight, mass average molecular weight, molecular weight distribution), the composition of the viscosity index improver composition, and the appearance of the polymer in the viscosity index improver composition at room temperature (25°C) (results of visual observation).

[0165]

[0166] [Examples 1 to 3, Comparative Examples 1 to 6] The lubricating oil base oil (mineral oil) and each of the viscosity index improver compositions produced in Production Examples 1 to 4 and Comparative Production Example 1 were blended and thoroughly mixed in the proportions shown in Table 2 to prepare the lubricating oil compositions of Examples 1 to 3 and Comparative Examples 1 to 6. The blending proportions shown in Table 2 were determined based on the lubricating oil composition having a kinematic viscosity of 7 mm at 100°C. ２ / s.

[0167] Mineral oil has a kinematic viscosity of 4.2 mm at 100°C. ２ / s, a viscosity index of 122, and an API classification of Group II.

[0168] The results are shown in Table 2. The blending amount of the viscosity index improver composition in Table 2 includes the blending amount of the polymerization diluent.

[0169]

[0170] The following can be seen from Table 2. It can be seen that the lubricating oil compositions of Examples 1 to 3 have higher viscosity indexes than the lubricating oil compositions of Comparative Examples 1 to 6. Therefore, the results shown in Table 2 show that the effect of improving the viscosity index is achieved by having one or both of PMA (A) and PMA (B) further contain a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain.

[0171] [Examples 4 to 6, Comparative Examples 7 to 12] The lubricating oil base oil (ester oil) and each of the viscosity index improver compositions produced in Production Examples 1 to 4 and Comparative Production Example 1 were blended in the proportions shown in Table 3 and thoroughly mixed to prepare the lubricating oil compositions of Examples 4 to 6 and Comparative Examples 7 to 12, respectively.

[0172] The ester oil is 2-ethylhexyl sebacic acid (100°C kinematic viscosity: 3.2 mm ２ / s, viscosity index: 153).

[0173] The results are shown in Table 3. The blending amount of the viscosity index improver composition in Table 3 includes the blending amount of the polymerization diluent.

[0174]

[0175] The following can be seen from Table 3. It can be seen that the lubricating oil compositions of Examples 4 to 6 had higher viscosity indexes than the lubricating oil compositions of Comparative Examples 7 to 12. Therefore, also from the results shown in Table 3, it can be seen that the effect of improving the viscosity index is achieved by having one or both of PMA (A) and PMA (B) further contain a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain.

Claims

1. A viscosity index improver composition comprising the following poly(meth)acrylate (A) and the following poly(meth)acrylate (B), and satisfying the following requirement (1) or (2): Poly(meth)acrylate (A): Contains a structural unit (Y) derived from a monomer (y) having a diol-based functional group. Poly(meth)acrylate (B): Contains a structural unit (Z) derived from a monomer (z) having a boronic acid ester. Requirement (1): Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contain a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain. Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) may further contain a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group with 10 to 23 carbon atoms in its side chain. Requirement (2): One of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain. At least the other of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group with 10 to 23 carbon atoms in its side chain.

2. 2. The viscosity index improver composition according to claim 1, wherein the poly(meth)acrylate (A) has a mass average molecular weight (Mw) of 10,000 to 70,000.

3. 3. The viscosity index improver composition according to claim 1, wherein the poly(meth)acrylate (B) has a mass average molecular weight (Mw) of 10,000 to 70,000.

4. 3. The viscosity index improver composition according to claim 1, wherein when the poly(meth)acrylate (A) contains the structural unit (X1) and the structural unit (X3), the total content of the structural unit (X1) and the structural unit (X3) is 50 mass% or more based on all structural units of the poly(meth)acrylate (A).

5. 3. The viscosity index improver composition according to claim 1, wherein when the poly(meth)acrylate (A) comprises the structural unit (X1) and the structural unit (X3), the content ratio of the structural unit (X1) to the structural unit (X3), [(X1) / (X3)], is 1 / 5 to 5 / 1, in mass ratio.

6. 3. The viscosity index improver composition according to claim 1, wherein when the poly(meth)acrylate (B) contains the structural unit (X1) and the structural unit (X3), the total content of the structural unit (X1) and the structural unit (X3) is 50 mass% or more based on all structural units of the poly(meth)acrylate (B).

7. 3. The viscosity index improver composition according to claim 1, wherein when the poly(meth)acrylate (B) comprises the structural unit (X1) and the structural unit (X3), the content ratio of the structural unit (X1) to the structural unit (X3), [(X1) / (X3)], is 1 / 5 to 5 / 1, in mass ratio.

8. The viscosity index improver composition according to claim 1 or 2, which satisfies the requirement (1).

9. The viscosity index improver composition according to claim 1 or 2, wherein the alkyl group in the (meth)acrylate (x1) is a methyl group.

10. The viscosity index improver composition according to claim 1 or 2, wherein the (meth)acrylate (x3) is a compound represented by the following general formula (I-3): 【Chemical 1】 [In the general formula (I-3), R ３１ represents a hydrogen atom or a methyl group, and R ３２ represents a linear or branched alkylene group having 2 to 4 carbon atoms; R ３３ and R ３４ R each independently represents a linear or branched alkyl group. ３３ and R ３４ The total number of carbon atoms in the alkyl groups that can be selected as R is 22 to 36. n3 represents an integer of 0 to 20. When n3 is 2 or more, a plurality of R ３２ may be the same or different.]

11. 3. The viscosity index improver composition according to claim 1, wherein the monomer (y) having a diol functional group is a compound represented by the following general formula (II): 【Chemistry 2】 [In the general formula (II), R ４１ represents a hydrogen atom or a methyl group, p represents an integer of 2 to 18, and q is 0 or 1. R ４２ and R ４３ each independently represents a hydrogen atom, a tetrahydropyranyl group, a methyloxymethyl group, a tert-butyl group, a benzyl group, a trimethylsilyl group, or a tert-butyldimethylsilyl group. Or, R ４２ and R ４３ forms a bridge represented by the following general formula (IIa) together with an oxygen atom. 【Chemistry 3】 In the general formula (IIa), * indicates the bonding position to the oxygen atom. ４４ and R ４５ each independently represents a hydrogen atom or an alkyl group having 1 to 11 carbon atoms. Or, R ４２ and R ４３ forms a boronic acid ester represented by the following general formula (IIb) together with an oxygen atom. 【Chemistry 4】 In the general formula (IIb), * indicates the bonding position to the oxygen atom. ４６ is an aryl group having 6 to 18 carbon atoms, an aralkyl group having 7 to 18 carbon atoms, or an alkyl group having 2 to 18 carbon atoms.]

12. 3. The viscosity index improver composition according to claim 1, wherein the boronic acid ester-containing monomer (z) is a compound represented by the following general formula (III): 【Chemistry 5】 [In the general formula (III), t represents 0 or 1, and u represents 0 or 1. R ５０ and R ５１ R each independently represents a hydrogen atom or a hydrocarbon-containing chain having 1 to 24 carbon atoms. ５２ and R ５３ each independently represents an arylene group having 6 to 18 carbon atoms, an aralkylene group having 7 to 24 carbon atoms, or an alkylene group having 2 to 24 carbon atoms. M represents -O-C(O)-, -C(O)-O-, -C(O)-N(H)-, -N(H)-C(O)-, -S-, -N(H)-, -N(R ａ ) - or -O- (wherein R ａ is a hydrocarbon-containing chain having 1 to 15 carbon atoms). ５４ represents a hydrogen atom or a methyl group.

13. 3. A lubricating oil additive composition comprising the viscosity index improver composition according to claim 1 or 2 and one or more additives selected from the group consisting of metal-based detergents, antiwear agents, ashless dispersants, extreme pressure agents, pour point depressants, antioxidants, antifoaming agents, surfactants, demulsifiers, friction modifiers, oiliness improvers, rust inhibitors, and metal deactivators.

14. A lubricating oil composition comprising the viscosity index improver composition according to claim 1 or 2 and a lubricating base oil.

15. A method for producing a lubricating oil composition, comprising a step of mixing a lubricating base oil with the following poly(meth)acrylate (A) and the following poly(meth)acrylate (B), wherein the method satisfies the following requirement (1) or (2): Poly(meth)acrylate (A): Contains a structural unit (Y) derived from a monomer (y) having a diol-based functional group. Poly(meth)acrylate (B): Contains a structural unit (Z) derived from a monomer (z) having a boronic acid ester. Requirement (1): Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contain a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain. Both the poly(meth)acrylate (A) and the poly(meth)acrylate (B) may further contain a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group with 10 to 23 carbon atoms in its side chain. Requirement (2): One of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X1) derived from a (meth)acrylate (x1) having a linear alkyl group with 4 or less carbon atoms in its side chain, and a structural unit (X3) derived from a (meth)acrylate (x3) having a branched alkyl group with 24 to 38 carbon atoms in its side chain. At least the other of the poly(meth)acrylate (A) and the poly(meth)acrylate (B) contains a structural unit (X2) derived from a (meth)acrylate (x2) having a linear or branched alkyl group with 10 to 23 carbon atoms in its side chain.

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