Conjugated diene graft polymer, method for producing same, lubricating oil additive, viscosity index improver, friction-suppressing agent and oil composition

Abstract

Provided are: a novel polymer which has a high viscosity index and a favorable friction-reducing effect; a lubricating oil additive comprising said polymer; a viscosity index improver comprising said polymer; a friction-suppressing agent comprising said polymer; an oil composition containing said lubricating oil additive; an oil composition containing said viscosity index improver; and an oil composition containing said friction-suppressing agent.　A conjugated diene graft copolymer which includes a main chain (a) comprising a polymer containing a conjugated diene unit, and a side chain (b) comprising a polymer containing one or more monomer units selected from the group consisting of a conjugated diene unit and an aromatic vinyl compound unit, wherein the side chain (b) is bonded to an atom contained in the monomer unit forming the branched section belonging to the main chain (a), the number-average molecular weight of the main chain (a) is at least 5,000, and a hydroxyl group is bonded to the main chain (a).

Description

Conjugated diene graft polymer and its production method, lubricating oil additive, viscosity index improver, friction inhibitor, and oil composition

[0001] The present invention relates to a conjugated diene graft polymer having a high viscosity index and a good friction-reducing effect, a lubricating oil additive comprising the conjugated diene graft polymer, and an oil composition containing a base oil and the lubricating oil additive.

[0002] Lubricating oils used as engine oils and automatic transmission fluids often contain various lubricating oil additives to improve their performance. For example, lubricating oils may contain additives commonly referred to as viscosity index improvers to improve their viscosity characteristics. Viscosity index improvers are added to reduce the viscosity change of lubricating oils due to temperature. The higher the viscosity index, the smaller the viscosity change, resulting in improved fuel economy. Examples of viscosity index improvers include olefin copolymers, polymethacrylates, and styrene / hydrogenated diene block polymers. Viscosity index improvers are subject to high shear stresses in the operating environment, which can cause a decrease in viscosity due to molecular weight loss over long periods of use, resulting in a reduction in the required lubricating performance. In recent years, growing environmental awareness has led to a demand for viscosity index improvers with higher shear stability.

[0003] It is known that viscosity index improvers made of star polymers have better shear stability than linear polymers due to their molecular structure. For example, Patent Document 1 describes that viscosity index improvers made of star-shaped hydrogenated polyisoprene, in which living polyisoprene synthesized by anionic polymerization is coupled with divinylbenzene, have excellent shear stability. Furthermore, Patent Document 2, as an example of a graft polymer, describes a graft polymer synthesized by preparing a mixture of a polymer having two active ends, which will serve as a main chain component, and a polymer having one active end, which will serve as a side chain component, and then adding a coupling agent containing a silicon atom having three or more reactive sites to this mixture and reacting them. In this graft polymer, heteroatoms such as silicon atoms derived from the coupling agent are contained at the branch points connecting the main chain and the side chain.

[0004] Furthermore, lubricating oils may contain friction inhibitors, which are classified as extreme pressure agents, friction modifiers, anti-wear agents, etc., as lubricating oil additives, with the aim of improving fuel efficiency and extending the life of machinery by suppressing seizure and the like.

[0005] U.S. Patent No. 4,116,917 and U.S. Patent No. 5,089,007

[0006] Due to the recent tightening of environmental regulations, viscosity index improvers with higher viscosity indices are in demand. Furthermore, in order to improve fuel economy and extend the life of machinery, lubricating oil additives (friction inhibitors) that have the effect of further reducing metal-to-metal friction are in demand. The graft polymers described in the above patent documents have high shear stability, but there is room for improvement in terms of viscosity index. Furthermore, the graft polymers described in the above patent documents also have room for improvement in terms of friction-reducing effect.

[0007] The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide a new polymer having a high viscosity index and a good friction-reducing effect, a lubricating oil additive comprising said polymer, a viscosity index improver comprising said polymer, a friction inhibitor comprising said polymer, an oil composition containing said lubricating oil additive, an oil composition containing said viscosity index improver, and an oil composition containing said friction inhibitor.

[0008] As a result of intensive research, the present inventors have found that a viscosity index improver made from a conjugated diene graft polymer in which a main chain (a) made of a polymer containing conjugated diene units is bonded to a side chain (b) made of a polymer containing at least one monomer unit selected from the group consisting of conjugated diene units and aromatic vinyl compound units, the main chain (a) having a number average molecular weight that satisfies specific conditions and a hydroxyl group bonded to the main chain (a), has a high viscosity index. They have also found that a friction inhibitor made from the above conjugated diene graft polymer has a good friction-reducing effect. They have also found that a lubricating oil additive made from the above conjugated diene graft polymer is useful for lubricating oils because of these properties, and have thus completed the present invention.

[0009] That is, the present invention provides the following items [1] to

[17] . [1] A conjugated diene graft polymer comprising a main chain (a) made of a polymer containing a conjugated diene unit, and a side chain (b) made of a polymer containing at least one monomer unit selected from the group consisting of a conjugated diene unit and an aromatic vinyl compound unit, wherein the side chain (b) is bonded to an atom contained in a monomer unit that becomes a branching moiety contained in the main chain (a), the main chain (a) has a number average molecular weight of 5,000 or more, and a hydroxyl group is bonded to the main chain (a). [2] The conjugated diene graft polymer according to [1], wherein the hydroxyl groups bonded to the main chain (a) account for 3.0 mol % or more. [3] The conjugated diene graft polymer according to [1] or [2], wherein the main chain (a) has a number average molecular weight of 20,000 or more. [4] A conjugated diene graft polymer according to any one of [1] to [3], wherein at least a portion of the carbon-carbon double bonds contained in the conjugated diene units of the conjugated diene graft polymer are hydrogenated. [5] The conjugated diene graft polymer according to [4], wherein 50 mol % or more of the carbon-carbon double bonds contained in the conjugated diene units of the conjugated diene graft polymer are hydrogenated. [6] The conjugated diene graft polymer according to any one of [1] to [5], wherein the average number of side chains (b) per molecule of the conjugated diene graft polymer is 2 or more. [7] The conjugated diene graft polymer according to any one of [1] to [6], wherein an atom bonding to the side chain (b) contained in the monomer unit that becomes the branching moiety is not a heteroatom, and the linking moiety including an atom bonding to the side chain (b) contained in the monomer unit that becomes the branching moiety is not an aromatic group derived from an aromatic vinyl compound.[8] The method for producing a conjugated diene graft polymer according to any one of [1] to [7], comprising: (A-1) a step of reacting a polymer (M) containing conjugated diene units with an organolithium compound in the presence of a polar compound to lithiate anionic active sites contained in the polymer (M); (A-2) a step of adding a functionalizing agent to functionalize a portion of the lithiated anionic active sites; (B) a step of adding at least one monomer selected from the group consisting of a conjugated diene and an aromatic vinyl compound to polymerize the remaining lithiated anionic active sites in the polymer (M) to form side chains on the main chain of the polymer (M), thereby producing a conjugated diene graft polymer; and (D) a step of recovering the obtained conjugated diene graft polymer. [9] The method for producing a conjugated diene graft polymer according to [8], further comprising: (A-3) a step of adding a Lewis acid after step (A-2).

[10] The method for producing a conjugated diene graft polymer according to any one of [1] to [7], comprising: (E) a step of reacting an active terminal polymer represented by the following formula (I) with a functional group-modified conjugated diene polymer having an epoxy group, P-X (I) (in formula (I), P represents a polymer chain containing at least one monomer unit selected from the group consisting of a conjugated diene unit and an aromatic vinyl compound unit, and X represents an active terminal for anionic polymerization), to produce a conjugated diene graft polymer; and (D) a step of recovering the obtained conjugated diene graft polymer.

[11] The method for producing a conjugated diene graft polymer according to [8] or

[10] , further comprising: (C) a step of hydrogenating at least a portion of the carbon-carbon double bonds contained in the conjugated diene units in the conjugated diene graft polymer after step (B) or step (E) and before step (D).

[12] A lubricating oil additive comprising the conjugated diene graft polymer according to any one of [1] to [7].

[13] A viscosity index improver comprising the conjugated diene graft polymer according to any one of [1] to [7].

[14] A friction inhibitor comprising the conjugated diene graft polymer according to any one of [1] to [7].

[15] An oil composition comprising a base oil and the lubricating oil additive according to

[12] .

[16] An oil composition comprising a base oil and the viscosity index improver according to

[13] .

[17] An oil composition comprising a base oil and the friction inhibitor according to

[14] .

[0010] According to the present invention, there are provided a conjugated diene graft polymer having a high viscosity index and a good friction-reducing effect, a lubricating oil additive comprising the conjugated diene graft polymer, a viscosity index improver comprising the conjugated diene graft polymer, a friction inhibitor comprising the conjugated diene graft polymer, an oil composition containing the lubricating oil additive, an oil composition containing the viscosity index improver, and an oil composition containing the friction inhibitor.

[0011] The present invention will be described in detail below. The conjugated diene graft polymer of the present invention comprises a main chain (a) made of a polymer containing structural units derived from a conjugated diene (hereinafter also referred to as conjugated diene units), and side chains (b) made of a polymer containing structural units derived from at least one monomer selected from the group consisting of conjugated diene units and structural units derived from an aromatic vinyl compound (hereinafter also referred to as aromatic vinyl compound units), wherein the side chains (b) are bonded to atoms contained in monomer units that form branching moieties contained in the main chain (a), the number average molecular weight of the main chain (a) is 5,000 or more, and a hydroxyl group is bonded to the main chain (a). Note that, in the present invention, a graft polymer refers to a polymer having a main chain consisting of a polymer chain as a backbone and side chains consisting of polymer chains as branches, and the monomer units constituting the main polymer chain and the monomer units constituting the side polymer chains may be the same or different.

[0012] <Main Chain (a)> The conjugated diene graft polymer of the present invention has a main chain (a) made of a polymer containing a conjugated diene unit. The main chain contained in the conjugated diene graft polymer of the present invention refers to the entire polymer chain made of all monomer units including the conjugated diene unit that constitutes the main chain. For example, in the case of production by a method in which a conjugated diene polymer synthesized in advance, as described below, is reacted with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain, and then a monomer that becomes a structural unit of the side chain is polymerized, the main chain refers to the entire conjugated diene polymer portion synthesized in advance. For example, in the case of production by a method in which a structural unit derived from vinyl-bonded butadiene (butadiene unit) is polymerized in advance, the main chain (a) refers to the entire conjugated diene polymer portion synthesized in advance. n The main chain includes the -CH=CH2 portion bonded to the carbon atom in the alkyl group.

[0013] The main chain (a) contains a conjugated diene unit as a monomer unit constituting the polymer. Examples of conjugated dienes include butadiene, isoprene, farnesene, myrcene, 2,3-dimethylbutadiene, 2-phenylbutadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 1,3-octadiene, 1,3-cyclohexadiene, 2-methyl-1,3-octadiene, 1,3,7-octatriene, and chloroprene. Among these conjugated dienes, butadiene, isoprene, farnesene, and myrcene are preferred, butadiene and isoprene are more preferred, and butadiene is even more preferred. The conjugated dienes that form the conjugated diene units may be used alone or in combination of two or more.

[0014] In one preferred embodiment, the main chain (a) contains conjugated diene units in an amount of 40% by mass or more of all monomer units constituting the polymer. The total content of the conjugated diene units is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, based on all monomer units in the main chain (a).

[0015] In one preferred embodiment, the main chain (a) is composed of at least one monomer unit selected from the group consisting of butadiene units and structural units derived from isoprene (isoprene units), accounting for 40% by mass or more of all monomer units constituting the polymer. The total content of butadiene units and isoprene units is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, of all monomer units constituting the main chain (a).

[0016] Examples of other monomer units than the butadiene unit and the isoprene unit contained in the main chain (a) include the above-mentioned conjugated diene units other than the butadiene unit and the isoprene unit, and aromatic vinyl compound units.

[0017] Examples of aromatic vinyl compounds include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-t-butylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 2,4,6-trimethylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, vinylanthracene, N,N-diethyl-4-aminoethylstyrene, vinylpyridine, 4-methoxystyrene, monochlorostyrene, dichlorostyrene, and divinylbenzene. Among these aromatic vinyl compounds, styrene, 4-methylstyrene, and α-methylstyrene are preferred, and styrene and α-methylstyrene are more preferred. The aromatic vinyl compounds that form the aromatic vinyl compound units may be used alone or in combination of two or more.

[0018] The content of other monomer units other than butadiene units and isoprene units in the main chain (a) is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. For example, when the aromatic vinyl compound unit is within the above range or less, the shear stability of the lubricating oil additive (viscosity index improver, friction suppressant) made of the obtained conjugated diene graft polymer tends to be improved. In addition, the processability of the obtained conjugated diene graft polymer tends to be improved.

[0019] The number-average molecular weight (Mn) of the main chain (a) is 5,000 or more, preferably 6,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and particularly preferably 20,000 or more. It is also preferably 1,000,000 or less, more preferably 500,000 or less, and even more preferably 100,000 or less. In the present invention, the Mn of the main chain (a) is the Mn of a pre-synthesized conjugated diene polymer that serves as a structural unit of the main chain, for example, when the main chain is produced by a method in which a pre-synthesized conjugated diene polymer (described below) is reacted with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain, and then a monomer that will become a structural unit of the side chain is polymerized. When the Mn of the main chain (a) is within the above range, when a conjugated diene graft polymer is produced by the production method of the present invention, the processability during production tends to be excellent and the economy tends to be good. Furthermore, the viscosity index and friction-reducing effect of the conjugated diene graft polymer tend to be excellent. In the present invention, unless otherwise specified, Mn is a number average molecular weight calculated in terms of standard polystyrene as determined by gel permeation chromatography (GPC). The conjugated diene graft polymer used in the present invention may be a polymer hydrogenated by a method such as the hydrogenation step described below. In the case of a hydrogenated conjugated diene graft polymer, Mn of the main chain (a) means Mn in a state before hydrogenation.

[0020] In one embodiment, the vinyl content of the main chain (a) is preferably 90 mol% or less, more preferably 70 mol% or less, and even more preferably 60 mol% or less. The vinyl content of the main chain (a) is preferably 0.5 mol% or more, and more preferably 1 mol% or more. In the present invention, the "vinyl content" refers to the total mol% of conjugated diene units bonded via 1,2-bonds, 3,4-bonds (in the case of other than farnesene), and 3,13-bonds (in the case of farnesene) (conjugated diene units bonded via bonds other than 1,4-bonds (in the case of other than farnesene) and 1,13-bonds (in the case of farnesene)) out of a total of 100 mol% of conjugated diene units contained in the polymer. In the present invention, even in the case of a hydrogenated conjugated diene graft polymer, the vinyl content of the polymer is defined as the vinyl content determined from the bond form of the conjugated diene units contained in the polymer before hydrogenation. The vinyl content is 1 Using H-NMR, it is calculated from the area ratio of the peaks derived from conjugated diene units bonded via 1,2-bonds, 3,4-bonds (in the case of compounds other than farnesene), and 3,13-bonds (in the case of farnesene) to the peaks derived from conjugated diene units bonded via 1,4-bonds (in the case of compounds other than farnesene) and 1,13-bonds (in the case of farnesene).

[0021] The vinyl content of the main chain (a) can be designed depending on the purpose. For example, if the vinyl content is less than 50 mol%, the glass transition temperature (Tg) of the main chain (a), which will be described later, will be low, and the resulting conjugated diene graft polymer will tend to have excellent fluidity and low-temperature properties. Furthermore, if the vinyl content is 50 mol% or more, the resulting conjugated diene graft polymer will tend to have excellent reactivity. Furthermore, if the main chain (a) is a conjugated diene graft polymer composed only of butadiene units, in which at least a portion of the carbon-carbon double bonds contained in the butadiene units have been hydrogenated, and the Mn is relatively large (for example, if the Mn is about 10,000 or more), it is preferable to set the vinyl content to 25 mol% or more in order to prevent performance degradation due to crystallization after hydrogenation.

[0022] In addition, when the main chain (a) is produced by, for example, a method in which a conjugated diene polymer synthesized in advance, which will be described later, is reacted with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain, and then a monomer that will become a structural unit of the side chain is polymerized, the vinyl content of the main chain (a) can be adjusted to a desired value by controlling the type of solvent used in producing the conjugated diene polymer synthesized in advance, which will be a constituent element of the main chain (a), the polar compound used as needed, the polymerization temperature, etc.

[0023] The glass transition temperature (Tg) of the main chain (a) may vary depending on the vinyl content of the conjugated diene units in the polymer chain that becomes the main chain (a), the type of conjugated diene units, the content of other monomer units than the conjugated diene units, etc., but is preferably −150 to 50° C., more preferably −130 to 50° C., and even more preferably −130 to 30° C. When the Tg is in the above range, for example, an increase in viscosity can be suppressed, making handling easier. In the present invention, Tg is the value of the peak top of differential scanning calorimetry (DSC) determined by DSC measurement.

[0024] <Side Chain (b)> The conjugated diene graft polymer of the present invention has a side chain (b) made of a polymer containing at least one monomer unit selected from the group consisting of a conjugated diene unit and an aromatic vinyl compound unit.

[0025] The side chain (b) contains, as a monomer unit constituting the polymer, at least one monomer unit selected from the group consisting of a conjugated diene unit and an aromatic vinyl compound unit.

[0026] Specific examples of conjugated dienes that can form the monomer units of the side chain (b) are the same as the specific examples of conjugated dienes that form the monomer units of the main chain (a). Among the conjugated dienes that form the conjugated diene units contained in the side chain (b), butadiene, isoprene, farnesene, and myrcene are preferred, and butadiene and isoprene are more preferred. The conjugated dienes that form the conjugated diene units may be used alone or in combination of two or more.

[0027] Specific examples of aromatic vinyl compounds that can form the monomer units of the side chain (b) are the same as the specific examples of aromatic vinyl compounds that can form the monomer units of the main chain (a). Among these aromatic vinyl compounds, styrene and α-methylstyrene are preferred. The aromatic vinyl compounds that form the aromatic vinyl compound units may be used alone or in combination of two or more.

[0028] The side chain (b) may be a homopolymer whose polymer chain skeleton is composed of only one conjugated diene unit or one aromatic vinyl compound unit, a copolymer composed of two or more monomer units selected from the group consisting of conjugated diene units and aromatic vinyl compound units, or a copolymer composed of structural units derived from one or more monomers selected from the group consisting of conjugated diene units and aromatic vinyl compound units and structural units derived from one or more vinyl monomers other than conjugated dienes and aromatic vinyl compounds. The polymer constituting the side chain (b) may be a single type, or two or more types having different structures.

[0029] The content of the conjugated diene units contained in the polymer constituting the side chain (b) is preferably 50% by mass or more, more preferably 70% by mass or more, particularly preferably 80% by mass or more, and may even be 100% by mass, based on the total monomer units of the side chain (b). When the content of the conjugated diene units is 50% by mass or more, when the resulting conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction suppressant), the shear stability of the lubricating oil additive (viscosity index improver, friction suppressant) tends to be improved.

[0030] The conjugated diene that can constitute the side chain (b) preferably includes at least one selected from the group consisting of butadiene and isoprene. The total content of butadiene units and isoprene units contained in the polymer that constitutes the side chain (b) is preferably 50% by mass or more, more preferably 70% by mass or more, particularly preferably 80% by mass or more, and may even be 100% by mass, of all monomer units that constitute the polymer. The mass ratio of butadiene units to isoprene units (butadiene units / isoprene units) contained in the side chain (b) is preferably in the range of 0 / 100 to 50 / 50, more preferably 0 / 100 to 30 / 70, and particularly preferably 0 / 100 to 20 / 80. When the total content of butadiene units and isoprene units in the side chain (b) and the mass ratio of butadiene units to isoprene units are within the above ranges, when the resulting conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction inhibitor), the lubricating oil additive (viscosity index improver, friction inhibitor) tends to have an excellent balance between the thickening effect and low-temperature properties.

[0031] The content of aromatic vinyl compound units contained in the polymer constituting the side chain (b) is preferably 50% by mass or less, more preferably 30% by mass or less, particularly preferably 20% by mass or less, and may even be 0% by mass, of all monomer units constituting the polymer. When the content of aromatic vinyl compound units is 50% by mass or less, when the resulting conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction suppressant), the shear stability of the lubricating oil additive (viscosity index improver, friction suppressant) tends to be improved.

[0032] In one preferred embodiment, the number average molecular weight (Mn) of the side chain (b) is from 500 to 300,000, more preferably from 1,000 to 200,000, and even more preferably from 1,000 to 150,000. In the present invention, when the side chain (b) is produced by, for example, reacting a previously synthesized conjugated diene polymer described below with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain and then polymerizing a monomer that will become a structural unit of the side chain (the macroinitiator method (MI method)), the Mn of the side chain (b) is calculated from the charge ratio of the organic alkali metal compound used in the lithiation reaction to the monomer that will become a structural unit of the side chain. When the Mn of the side chain (b) is within the above range, the processability during production tends to be excellent and the economy tends to be good. Furthermore, when the obtained conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction suppressant), the balance between the thickening effect of the lubricating oil additive (viscosity index improver, friction suppressant) and shear stability tends to be excellent. The conjugated diene graft polymer obtained in the present invention may be a polymer hydrogenated, for example, by a method such as the hydrogenation step described below. In the case of a hydrogenated conjugated diene graft polymer, the Mn of the side chain (b) is the Mn in the state before hydrogenation.

[0033] In one preferred embodiment, the vinyl content of the side chain (b) is 99 mol% or less, more preferably 90 mol% or less, and even more preferably 85 mol% or less. The vinyl content of the side chain (b) is preferably 0.5 mol% or more, more preferably 1 mol% or more. For example, when the side chain (b) is produced by a method in which a conjugated diene polymer synthesized in advance as described below is reacted with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain, and then a monomer that becomes a structural unit of the side chain is polymerized, the vinyl content of the side chain (b) is 1The vinyl content can be calculated from the vinyl content of the conjugated diene graft polymer calculated from H-NMR spectroscopy, the vinyl content of the main chain (a) described above, and the feed ratio of the monomers that serve as raw materials for the monomer units that constitute the main chain and side chain. When the vinyl content of the side chain (b) is within the above range, the resulting lubricating oil additive (viscosity index improver, friction suppressant) made from the conjugated diene graft polymer tends to have an excellent balance between the thickening effect and low-temperature properties. Furthermore, when the polymer that forms the side chain (b) is a conjugated diene graft polymer composed only of butadiene units, in which at least a portion of the carbon-carbon double bonds contained in the butadiene units have been hydrogenated, and the Mn is relatively large (for example, when the Mn is about 10,000 or more), it is preferable to set the vinyl content to 25 mol% or more to prevent performance degradation due to crystallization after hydrogenation.

[0034] In addition, when the vinyl content of the side chain (b) is produced by, for example, a method in which a conjugated diene polymer synthesized in advance as described below is reacted with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain, and then a monomer that becomes a structural unit of the side chain is polymerized, the vinyl content of the side chain (b) can be adjusted to a desired value by controlling the type of solvent used in polymerizing the side chain (b), the polar compound or Lewis acid used as needed, the polymerization temperature, etc.

[0035] The glass transition temperature (Tg) of the side chain (b) may vary depending on the vinyl content of the conjugated diene units in the polymer chain that becomes the side chain (b), the type of conjugated diene, the content of other monomer units than the conjugated diene units, etc., but is preferably −150 to 50° C., more preferably −130 to 50° C., and even more preferably −130 to 30° C. When the Tg is in the above range, for example, an increase in viscosity can be suppressed, making the polymer easier to handle.

[0036] The side chain (b) may be a block copolymer chain containing a polymer block (b1) containing an aromatic vinyl compound unit and a polymer block (b2) containing a conjugated diene unit.

[0037] The polymer block (b1) contains an aromatic vinyl compound unit. Specific examples and suitable examples of the aromatic vinyl compound unit are the same as the specific examples and suitable examples of the aromatic vinyl compound unit constituting the monomer unit of the side chain (b). From the viewpoint of improving the physical properties of the resulting oil composition containing the conjugated diene graft polymer, the content of the aromatic vinyl compound unit in the polymer block (b1) is preferably more than 70 mol%, more preferably 80 mol% or more, even more preferably 90 mol% or more, still more preferably 95 mol% or more, and particularly preferably substantially 100 mol%.

[0038] As long as the object and effect of the present invention are not hindered, the polymer block (b1) may contain structural units derived from unsaturated monomers other than aromatic vinyl compounds (hereinafter also referred to as "other unsaturated monomer units") in a proportion of 30 mol % or less in the polymer block (b1), but the proportion is preferably less than 20 mol %, more preferably less than 15 mol %, even more preferably less than 10 mol %, still more preferably less than 5 mol %, and particularly preferably 0 mol %.

[0039] Examples of the other unsaturated monomer include at least one selected from the group consisting of butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-pentadiene, 1,3-hexadiene, myrcene, farnesene, isobutylene, methyl methacrylate, methyl vinyl ether, β-pinene, 8,9-p-menthene, dipentene, methylenenorbornene, 2-methylenetetrahydrofuran, etc. When polymer block (b1) contains the other unsaturated monomer unit, the bonding form is not particularly limited and may be either random or tapered.

[0040] When the side chain (b) is the block copolymer chain, the Mn of the polymer block (b1) is not particularly limited, but the Mn of the polymer block (b1) is preferably 500 to 300,000, more preferably 1,000 to 200,000, and even more preferably 1,000 to 50,000. When the side chain (b) of the conjugated diene graft polymer has a polymer block (b1) having an Mn within the above range, the properties such as shear stability of the oil composition containing the conjugated diene graft polymer tend to be further improved.

[0041] The content of polymer block (b1) in the conjugated diene graft polymer is preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, and particularly preferably 40% by mass or less. When the content of polymer block (b1) is the above upper limit or less, the properties such as shear stability of the obtained oil composition containing the conjugated diene graft polymer tend to be further improved. Furthermore, the content of polymer block (b1) is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more. When the content of polymer block (b1) is the above lower limit or more, the production of the conjugated diene graft polymer tends to be easier. Note that the content of polymer block (b1) in the conjugated diene graft polymer is 1 It can be determined by H-NMR measurement.

[0042] When the side chain (b) is the block copolymer chain, it is sufficient that it contains at least one polymer block (b1). When the block copolymer chain contains two or more polymer blocks (b1), the polymer blocks (b1) may be the same or different. When different side chains (b) are also block copolymer chains, the polymer blocks (b1) contained in these two or more copolymer chains may be the same or different. In the present invention, "different polymer blocks" means that at least one of the monomer units constituting the polymer block, Mw, stereoregularity, and, when multiple monomer units are present, the ratio of each monomer unit and copolymerization form (random, gradient, block) is different.

[0043] When the side chain (b) is the block copolymer chain, the polymer block (b2) contains conjugated diene compound units. From the viewpoint of improving the properties of the resulting oil composition containing the conjugated diene graft polymer, the content of the conjugated diene units in the polymer block (b2) is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 90 mol % or more, and particularly preferably substantially 100 mol %.

[0044] The specific examples and preferred examples of the conjugated diene, and the contents and preferred ratios of each monomer are the same as the specific examples and preferred examples of the conjugated diene constituting the monomer unit of the side chain (b), and the contents and preferred ratios of each monomer.

[0045] When the side chain (b) is the block copolymer chain and contains two or more polymer blocks (b2), the polymer blocks (b2) may be the same or different. When the different side chains (b) are also the block copolymer chains, the polymer blocks (b2) contained in these two or more copolymer chains may be the same or different.

[0046] The vinyl content of the conjugated diene units of polymer block (b2) is preferably 1 to 60 mol%, more preferably 2 to 40 mol%, even more preferably 3 to 30 mol%, and particularly preferably 4 to 20 mol%. When a conjugated diene graft polymer is produced by anionic polymerization, as described below, the vinyl content of the polymer block or polymer chain can be adjusted to a desired value by controlling the type of solvent used, the polar compound used if necessary, the polymerization temperature, etc.

[0047] The polymer block (b2) may contain structural units derived from monomers other than the conjugated diene compound, as long as the purpose and effects of the present invention are not impaired. In this case, the content of structural units derived from monomers other than the conjugated diene compound in the polymer block (b2) is preferably less than 50 mol%, more preferably less than 30 mol%, even more preferably less than 20 mol%, still more preferably less than 10 mol%, and particularly preferably 0 mol%.

[0048] Preferred examples of the other monomer include aromatic vinyl compounds such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-t-butylstyrene, 2,4-dimethylstyrene, N-vinylcarbazole, vinylnaphthalene, and vinylanthracene, as well as at least one compound selected from the group consisting of methyl methacrylate, methyl vinyl ether, β-pinene, 8,9-p-menthene, dipentene, methylenenorbornene, 2-methylenetetrahydrofuran, 1,3-cyclopentadiene, 1,3-cyclohexadiene, 1,3-cycloheptadiene, and 1,3-cyclooctadiene.

[0049] When the side chain (b) is the block copolymer chain, the Mn of the polymer block (b2) is not particularly limited, but from the viewpoint of improving the physical properties of the resulting oil composition containing the conjugated diene graft polymer, the Mn of the polymer block (b2) is preferably 500 to 300,000, more preferably 1,000 to 200,000, and even more preferably 1,000 to 50,000.

[0050] When the side chain (b) is the block copolymer chain, it is sufficient that it has at least one polymer block (b2). When the block copolymer chain has two or more polymer blocks (b2), the polymer blocks (b2) may be the same or different. Furthermore, when the different side chains (b) are also block copolymer chains, the polymer blocks (b2) contained in these two or more copolymer chains may be the same or different.

[0051] When the side chain (b) is the block copolymer chain, the block copolymer chain may contain a polymer block composed of a monomer other than the polymer blocks (b1) and (b2), as long as the object and effect of the present invention are not impaired. When the side chain (b) contains the block copolymer chain, the total content of the polymer blocks (b1) and (b2) relative to the entire side chain (b) is preferably 90% by mass or more, more preferably 95% by mass or more, and particularly preferably substantially 100% by mass. When it is 90% by mass or more, the physical properties of the resulting oil composition containing the conjugated diene graft polymer tend to be improved.

[0052] When the side chain (b) is the block copolymer chain, the bonding form is not limited as long as the block copolymer chain contains the polymer block (b1) and the polymer block (b2), and may be linear, branched, radial, or a combination of two or more of these. Furthermore, these polymer blocks may be bonded directly to each other or indirectly via other polymer blocks. Among these, the bonding form between the polymer block (b1) and the polymer block (b2) is preferably a linear form in which these polymer blocks are directly bonded to each other. Examples of such bonding forms include, when polymer block (b1) is represented as b1, polymer block (b2) is represented as b2, and the polymer blocks are represented in order from closest to the branching portion, a diblock copolymer chain represented by b2-b1, a triblock copolymer chain represented by b2-b1-b2 or b1-b2-b1, a tetrablock copolymer chain represented by b2-b1-b2-b1 or b1-b2-b1-b2, and a pentablock copolymer chain represented by b2-b1-b2-b1-b2 or b1-b2-b1-b2-b1.

[0053] Among these, a diblock copolymer chain represented by b2-b1 when each polymer block is represented in order from the closest to the branching portion is preferred, because the physical properties of the resulting oil composition containing the conjugated diene graft polymer are more likely to be improved and production is easier.

[0054] <Conjugated Diene Graft Polymer> The conjugated diene graft polymer of the present invention comprises a main chain (a) made of a polymer containing a conjugated diene unit, and a side chain (b) made of a polymer containing at least one monomer unit selected from the group consisting of a conjugated diene unit and an aromatic vinyl compound unit, wherein the side chain (b) is bonded to an atom contained in a monomer unit that becomes a branching moiety contained in the main chain (a), the number average molecular weight of the main chain (a) is 5,000 or more, and a hydroxyl group is bonded to the main chain (a).

[0055] The main chain (a) of the conjugated diene graft polymer of the present invention contains a monomer unit that will become a branched portion. A side chain (b) is bonded to an atom contained in the branched portion of the main chain (a). The atom bonded to the side chain (b) contained in the branched portion is not a heteroatom. Here, "the atom bonded to the side chain (b) is not a heteroatom" means that the atom is not an atom other than a carbon atom or a hydrogen atom, i.e., the atom is a carbon atom or a hydrogen atom (the atom to which the side chain (b) is bonded is a branched point, and therefore is actually a carbon atom). If the branched point to which the side chain (b) is bonded is a heteroatom itself, this is undesirable because it tends to deteriorate shear stability and thermal stability. Note that "an atom contained in the monomer unit that will become the branched portion is bonded to the side chain (b)" means that one of the atoms (typically a carbon atom) constituting the monomer unit that will become the branched portion in the main chain is bonded to an atom constituting the side chain (b). Methods for bonding atoms contained in the monomer units that form the branching moieties to the side chains (b) will be described in detail below as examples of methods for producing conjugated diene-based graft polymers. Examples include a method of lithiating a moiety containing a carbon atom having anionic activity (hereinafter, the moiety containing a carbon atom having anionic activity is also referred to as an anionic active moiety) contained in a monomer unit that forms the branching moiety of the polymer that forms the main chain (a), and then addition-polymerizing a monomer starting from the lithiated moiety having anionic activity to form the side chains (MI method); and a method of reacting an epoxy group contained in a monomer unit that forms the branching moiety of the functional group-modified polymer that forms the main chain (a) with the active terminal of a polymer obtained by polymerizing a monomer that forms the structural unit of the side chain (coupling method (CP method)).

[0056] In the conjugated diene graft polymer of the present invention, the atom bonded to the side chain (b) contained in the monomer unit that becomes the branching portion is not a heteroatom. In the conjugated diene graft copolymer, if the branching point where the main chain and the side chain are bonded is itself a heteroatom, this is not preferred because the shear stability and thermal stability tend to deteriorate.

[0057] For example, the graft polymer described in Patent Document 2 is synthesized by preparing a mixture of a polymer having two active ends, which will serve as a main chain component, and a polymer having one active end, which will serve as a side chain component, and then adding a silicon-containing coupling agent having three or more reactive sites to the mixture to cause a reaction. The heteroatom, such as a silicon atom, derived from this coupling agent serves as the branch point connecting the main chain and the side chain. Furthermore, prior to this application, the applicant of the present application filed a patent application relating to a method for synthesizing a graft polymer by modifying a previously synthesized main chain component polymer with a silicon-containing compound to form a functionally modified polymer, and then reacting this functionally modified polymer with the active end of a polymer obtained by polymerizing a monomer that will serve as a structural unit of the side chain. The heteroatom, such as a silicon atom, derived from this functionally modified polymer serves as the branch point connecting the main chain and the side chain. In the conjugated diene-based graft polymer of the present invention described below, the branch point of the main chain (a) is an atom that is not a heteroatom (typically a carbon atom), and the side chain (b) is directly bonded to this atom. Therefore, in the conjugated diene graft polymer of the present invention, unlike the above-mentioned polymer, the branching points (connecting points) where the main chain and the side chain are bonded are not heteroatoms.

[0058] In the conjugated diene graft polymer of the present invention, a preferred embodiment is that the linking moiety in the main chain (a) containing an atom bonding to the side chain (b) contained in the monomer unit that will become the branching moiety is not an aromatic group derived from an aromatic vinyl compound. The term "aromatic group" as used herein refers to a group containing an aromatic ring other than CH═CR (where R is hydrogen, an optionally substituted alkyl group, or an optionally substituted aryl group) contained in an aromatic vinyl compound. Here, "the linking moiety containing an atom bonding to the side chain (b) is not an aromatic group derived from an aromatic vinyl compound" means that the monomer unit that will become the branching moiety in the main chain itself is a structural unit derived from a monomer other than an aromatic vinyl compound (e.g., a conjugated diene), or that even if the monomer unit that will become the branching moiety in the main chain itself is an aromatic vinyl compound unit, the side chain (b) is not bonded to an atom in the aromatic group contained in the aromatic vinyl compound. This will be explained below using specific examples. When a graft polymer is synthesized by a method in which a moiety containing a carbon atom having anionic activity contained in a monomer unit that forms a branching portion of a polymer that becomes the main chain (a) described below is lithiated, and then the lithiated moiety having anionic activity is used as a starting point to add-polymerize a monomer to form a side chain (b), if the aromatic vinyl compound contained in the polymer that becomes the main chain (a) is, for example, 4-methylstyrene having a substituent with high anionic activity (high reactivity with organolithium compounds), the methyl group derived from 4-methylstyrene has high reactivity, and side chain (b) bonds to the carbon atom of this methyl group. On the other hand, in the case of an aromatic vinyl compound that does not have a substituent with high anionic activity in the aromatic group, such as styrene, side chain (b) bonds to the CH2 moiety adjacent to the CH to which the carbon atom of the benzene ring is bonded, which is contained in the (-CH2-CH-) portion of the styrene-derived structural unit (styrene unit) that forms the skeleton of the main chain (a). In this case, the side chain (b) is not bonded to the benzene ring derived from styrene, and the linking portion including the atom bonding to the side chain (b) in the branched portion contained in the main chain (a) is not an aromatic group derived from an aromatic vinyl compound.

[0059]

[0060] In the conjugated diene graft polymer of the present invention, as described above, it is preferable that the linking moiety in the main chain (a) including an atom bonding to the side chain (b) contained in the monomer unit that becomes the branching moiety is not an aromatic group derived from an aromatic vinyl compound. If the linking moiety is an aromatic group, the shear stability and thermal stability will be deteriorated.

[0061] For example, the graft polymer described in Journal of Polymer Science: Part A: Polymer Chemistry, 2007, 45, 3513 or Japanese Patent No. 5,508,066 is synthesized by a method of polymerizing a macromonomer (a macromonomer obtained by directly reacting an aromatic vinyl compound having a polymerizable functional group other than CH═C— bonded to an aromatic group at the active end of a polymer obtained by polymerizing a monomer that forms a structural unit of the side chain) with a monomer that forms a structural unit of the main chain. The linking moiety that is derived from this macromonomer and that is bonded to the side chain (b) contained in the branched portion of the main chain (a) is an aromatic group. In the graft polymer of the present invention, the linking moiety that is bonded to the side chain (b) contained in the branched portion of the main chain (a) is not an aromatic group, as is clear from, for example, an example of a method for producing the graft polymer described in detail below.

[0062] The average number of side chains (b) per molecule of the conjugated diene graft polymer is preferably 2 or more, more preferably 4 or more, and even more preferably 5 or more. For example, when the conjugated diene graft polymer is produced by reacting a previously synthesized conjugated diene polymer (described later) with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain, followed by polymerizing a monomer that will become the structural unit of the side chain, the average number of side chains (b) per molecule of the conjugated diene graft polymer is calculated from the charge ratio (molar ratio) of the organic alkali metal used in the lithiation reaction, the conjugated diene polymer that will become the structural unit of the main chain, and the functionalizing agent added as needed. If the average number of side chains (b) per molecule of the conjugated diene graft polymer is less than 2, the shear stability of the lubricating oil additive (viscosity index improver, friction suppressant) made from the resulting conjugated diene graft polymer tends to decrease, and the fluidity of the conjugated diene graft polymer tends to decrease, resulting in a poor balance between processability and mechanical properties.

[0063] In one embodiment of the conjugated diene graft polymer of the present invention, the side chain density of the side chain (b) is preferably 1.0 mol% or more, more preferably 2.0 mol% or more, even more preferably 3.0 mol% or more, and even more preferably 4.0 mol% or more. If the side chain density of the conjugated diene graft polymer is less than 1.0 mol%, when the resulting conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction suppressant), the shear stability of the lubricating oil additive (viscosity index improver, friction suppressant) tends to decrease, and the fluidity of the conjugated diene graft polymer tends to decrease, resulting in a poor balance between processability and mechanical properties.

[0064] In this specification, the side chain density of the side chains (b) is calculated from the average number of side chains (b) per molecule of the conjugated diene graft polymer and the number average molecular weight (Mn) of the main chain (a) in terms of standard polystyrene, using the following formula (1): Note that the side chain density refers to the ratio of the average number of side chains (b) per molecule of the conjugated diene graft polymer to the number of all monomer units, assuming that the main chain polymer is entirely composed of styrene units. (Side chain density)=(average number of side chains (b) per molecule of conjugated diene graft polymer) / [(number average molecular weight Mn of main chain (a)) / (molecular weight of styrene unit)]×100 (1) Note that, in the case of producing the main chain (a) by a method in which a conjugated diene polymer synthesized in advance, as described below, is reacted with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain, and then monomers that become structural units of the side chains are polymerized, the Mn of the main chain (a) is the Mn of the conjugated diene polymer synthesized in advance, which is a constituent element of the main chain, in terms of standard polystyrene.

[0065] In the conjugated diene graft polymer of the present invention, a hydroxyl group is bonded to the main chain (a). The hydroxyl group is bonded to the main chain (a) directly or through a linking chain. Here, "directly bonded to the main chain (a)" means that the hydroxyl group is bonded directly to a monomer unit constituting the main chain polymer. "Bonded to the main chain (a) through a linking chain" means that one end of the linking chain is bonded to a monomer unit constituting the main chain polymer, and a hydroxyl group is bonded directly to the other end of the linking chain. For example, when a hydroxyl group is bonded to a butadiene unit having a 1,2-bond, the case shown by formula (I-1) below is a case where the hydroxyl group is bonded directly to the main chain, and the case shown by formula (I-2) below is a case where the hydroxyl group is bonded to the main chain through a linking chain (the following formulas (I-1) and (I-2) below show structures when butadiene is hydrogenated).

[0066]

[0067] In the above formula (I-2), R 1 is the connecting chain. 1is a divalent organic group and is an alkylene group having no heteroatoms. When a heteroatom is contained in the linking chain, particularly when a hydroxyl group is directly bonded to the heteroatom, the shear stability and thermal stability of the conjugated diene graft polymer deteriorate.

[0068] The average number of hydroxyl groups bonded to the main chain (a) per molecule of the conjugated diene graft polymer is preferably at least 1, more preferably at least 2, and even more preferably at least 3. The average number of hydroxyl groups bonded to the main chain (a) per molecule of the conjugated diene graft polymer is determined from the following formula (2) using the hydroxyl value (mg KOH / g) of the conjugated diene graft polymer calculated in accordance with JIS K1557-1:2007 and the number average molecular weight (Mn) of the conjugated diene graft polymer in terms of standard polystyrene: (Average number of hydroxyl groups bonded to the main chain (a) per molecule of conjugated diene graft polymer)={(hydroxyl value of conjugated diene graft polymer) / [(molecular weight of potassium hydroxide)×1000]}×(number average molecular weight Mn of conjugated diene graft polymer)×[(average molecular weight of monomer units contained in conjugated diene graft polymer) / (molecular weight of styrene unit)] (2) When the average number of hydroxyl groups bonded to the main chain (a) per molecule of conjugated diene graft polymer is 1 or more, when the obtained conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction suppressant), the viscosity index and friction reducing effect of the lubricating oil additive (viscosity index improver, friction suppressant) tend to be excellent.

[0069] When hydroxyl groups are bonded to the main chain (a) of the conjugated diene graft polymer, the concentration of hydroxyl groups bonded to the main chain (a) is preferably 3.0 mol% or more, more preferably 3.5 mol% or more, and even more preferably 4.0 mol% or more. When the concentration of hydroxyl groups bonded to the main chain (a) is 3.0 mol% or more, the affinity with polar materials tends to be excellent. Furthermore, when the obtained conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction suppressant), the viscosity index and friction reducing effect of the lubricating oil additive (viscosity index improver, friction suppressant) tend to be excellent. Furthermore, the concentration of hydroxyl groups bonded to the main chain (a) is preferably 100 mol% or less, more preferably 80 mol% or less, and even more preferably 60 mol% or less. When the concentration of hydroxyl groups bonded to the main chain (a) is 100 mol% or less, the affinity with non-polar materials and the solubility in base oil tend to be excellent.

[0070] In this specification, the concentration of hydroxyl groups bonded to the main chain (a) is calculated from the average number of hydroxyl groups bonded to the main chain (a) per molecule of the conjugated diene graft polymer and the number average molecular weight (Mn) of the main chain (a) in terms of standard polystyrene, using the following formula (3): The hydroxyl group concentration means the ratio of the average number of hydroxyl groups bonded to the main chain (a) per molecule of the conjugated diene graft polymer to the number of all monomer units, assuming that the main chain polymer is entirely made of styrene units. (Hydroxyl group concentration)=(average number of hydroxyl groups bonded to main chain (a) per molecule of conjugated diene graft polymer) / [(number average molecular weight Mn of main chain (a)) / (molecular weight of styrene unit)]×100 (3) Note that, in the case of producing the main chain (a) by a method in which a conjugated diene polymer synthesized in advance, as described below, is reacted with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain, and then monomers that become structural units of side chains are polymerized, the Mn of the main chain (a) is the Mn of the conjugated diene polymer synthesized in advance, which is a constituent element of the main chain, in terms of standard polystyrene.

[0071] The combination of the polymer that forms the main chain (a) and the polymer that forms the side chain (b) contained in the conjugated diene graft polymer is not particularly limited and may be the same or different, and can be designed according to the purpose. The phrase "the polymer that forms the main chain (a) and the polymer that forms the side chain (b) are different" means that they differ in at least one of the following (i) to (iv): (i) the molecular weight of the polymer that forms the main chain (a) is different from the molecular weight of the polymer that forms the side chain (b); (ii) the type or combination of types of monomer units of the polymer that forms the main chain (a) is different from the type or combination of types of monomer units of the polymer that forms the side chain (b); and (iii) when the main chain (a) and the side chain (b) each contain a plurality of monomer units of the same type, the compositional ratio of the monomer units of the polymer that forms the main chain (a) is different from the compositional ratio of the monomer units of the polymer that forms the side chain (b). (iv) When the main chain (a) and the side chain (b) each contain a conjugated diene unit, the vinyl content of the conjugated diene unit of the polymer that becomes the main chain (a) is different from the vinyl content of the conjugated diene unit of the polymer that becomes the side chain (b).

[0072] In one preferred embodiment of the conjugated diene graft polymer of the present invention, at least 50 mass% of all monomer units constituting the polymer are at least one monomer unit selected from the group consisting of butadiene units and isoprene units. The total content of butadiene units and isoprene units is more preferably 60 to 100 mass%, and even more preferably 70 to 100 mass%, of the total monomer units of the conjugated diene graft polymer.

[0073] In the conjugated diene graft polymer of the present invention, the content of other monomer units than butadiene units and isoprene units is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. For example, if the aromatic vinyl compound unit is within the above range or less, when the obtained conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction suppressant), the shear stability of the lubricating oil additive (viscosity index improver, friction suppressant) tends to be improved, and the processability of the conjugated diene graft polymer also tends to be improved.

[0074] The conjugated diene graft polymer used in the present invention may have at least a portion of the carbon-carbon double bonds contained in the conjugated diene units of the polymer hydrogenated, or may not have any hydrogenated state. From the viewpoints of heat resistance and weather resistance, a preferred embodiment of the conjugated diene graft polymer used in the present invention is a conjugated diene graft polymer in which at least a portion of the carbon-carbon double bonds contained in the conjugated diene units of the polymer are hydrogenated. Preferably, 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more of the carbon-carbon double bonds contained in the conjugated diene units of the conjugated diene graft polymer are hydrogenated. The hydrogenation rate is usually 100 mol % or less. Furthermore, the hydrogenation rate (hydrogenation rate) may be substantially 100 mol % (i.e., substantially completely hydrogenated). When the hydrogenation rate is 50 mol % or more, the thermal stability and shear stability of the lubricating oil additive (viscosity index improver, friction suppressant) made of the conjugated diene graft polymer tend to be improved. 1 The content of carbon-carbon double bonds contained in the conjugated diene units in the polymer was calculated using H-NMR before and after hydrogenation, and the value was determined from these contents.

[0075] In one preferred embodiment, the weight average molecular weight (Mw) of the conjugated diene graft polymer of the present invention is 5,000 to 2,000,000, preferably 10,000 to 1,500,000, and more preferably 15,000 to 1,000,000. When the Mw of the conjugated diene graft polymer is within the above range, when the resulting conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction suppressant), the lubricating oil additive (viscosity index improver, friction suppressant) tends to have an excellent balance between the thickening effect and shear stability, and also tends to have excellent processability during production and be economical.

[0076] The molecular weight distribution (Mw / Mn) of the conjugated diene graft polymer of the present invention is preferably 1.0 to 20.0, more preferably 1.0 to 10.0, even more preferably 1.0 to 5.0, and particularly preferably 1.0 to 2.0. When Mw / Mn is within the above range, the viscosity of the conjugated diene graft polymer is less varied, which is more preferable. In the present invention, Mn refers to the number average molecular weight, and Mn is the number average molecular weight calculated in terms of standard polystyrene obtained by GPC measurement. Furthermore, the molecular weight distribution (Mw / Mn) refers to the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) calculated in terms of standard polystyrene obtained by GPC measurement.

[0077] In one embodiment, the vinyl content of the conjugated diene graft polymer of the present invention is preferably 99 mol% or less, more preferably 90 mol% or less, and even more preferably 85 mol% or less. The vinyl content of the conjugated diene graft polymer is preferably 0.5 mol% or more, more preferably 1 mol% or more. When the vinyl content of the conjugated diene graft polymer is within the above range, when the obtained conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction suppressant), the lubricating oil additive (viscosity index improver, friction suppressant) tends to have an excellent balance between the thickening effect and low-temperature properties. Furthermore, when the conjugated diene graft polymer is composed only of butadiene units, at least a portion of the carbon-carbon double bonds contained in the butadiene units are hydrogenated, and the Mw is relatively large (for example, when the Mn of at least one of the main chain (a) or the side chain (b) is about 10,000 or more), it is preferable to set the vinyl content to 25 mol% or more in order to prevent performance degradation due to crystallization after hydrogenation.

[0078] The glass transition temperature (Tg) of the conjugated diene graft polymer may vary depending on the vinyl content of butadiene units, isoprene units, and conjugated diene units other than isoprene units, the type of conjugated diene units, the content of other monomer units other than conjugated diene units, etc., but is preferably −150 to 50° C., more preferably −130 to 50° C., and even more preferably −130 to 30° C. When the Tg is within the above range, for example, an increase in viscosity can be suppressed, making the polymer easier to handle.

[0079] The mass ratio of the main chain to the side chain in the conjugated diene graft polymer of the present invention is preferably in the range of 1 / 99 to 90 / 10, more preferably in the range of 3 / 97 to 80 / 20, and even more preferably in the range of 5 / 95 to 70 / 30. When the mass ratio of the main chain to the side chain is in the above range, the processability of the conjugated diene graft polymer tends to be improved.

[0080] The conjugated diene graft polymer used in the present invention preferably has a total catalyst residue amount, derived from the polymerization catalyst, hydrogenation catalyst (hydrogenation catalyst), and the like, used in its production, in the range of 0 to 500 ppm in terms of metal. For example, when an organic alkali metal, such as an organolithium compound described below, is used as the polymerization catalyst for producing the conjugated diene graft polymer, an alkali metal such as lithium is contained. Furthermore, when a hydrogenated conjugated diene graft polymer is used as the conjugated diene graft polymer, nickel or aluminum is contained when a Ziegler catalyst described below is used as the catalyst in the hydrogenation reaction. Having the catalyst residue amount within the above range prevents a decrease in tack during processing, etc., and improves the heat resistance of the conjugated diene graft polymer obtained by the present invention. The total amount of catalyst residue in the conjugated diene graft polymer, in terms of metal, is more preferably 0 to 300 ppm in total, and even more preferably 0 to 200 ppm. The amount of catalyst residue can be measured using, for example, an inductively coupled plasma mass spectrometer (ICP-MS) or a polarized Zeeman atomic absorption spectrophotometer.

[0081] Examples of methods for adjusting the catalyst residue content of the conjugated diene graft polymer to such a specific amount include purifying the conjugated diene graft polymer and thoroughly removing the catalyst residue. Preferred purification methods include washing with water or hot water, an acidic aqueous solution, or an organic solvent such as methanol or acetone, or washing with supercritical fluid carbon dioxide. The use of an acidic aqueous solution for washing can further enhance the washing efficiency. Preferred acids to be used include, for example, strong monovalent or polyvalent acids such as hydrochloric acid, nitric acid, and sulfuric acid; monovalent or polyvalent carboxylic acids such as acetic acid, propionic acid, succinic acid, and citric acid; and weak monovalent or polyvalent acids such as carbonic acid and phosphoric acid. From an economical standpoint, the number of washes is preferably 1 to 20, and more preferably 1 to 10. The washing temperature is preferably 20 to 100°C, and more preferably 40 to 90°C. Furthermore, impurities that may inhibit the polymerization may be removed by distillation or using an adsorbent before the polymerization reaction, and the purity of the monomer may be increased before the polymerization reaction. This also reduces the amount of polymerization catalyst required, thereby enabling the amount of catalyst residue to be reduced.

[0082] <Method for Producing Conjugated Diene Graft Polymer> From the viewpoint of synthesizing a conjugated diene graft polymer having a suitable structure, the method for producing the conjugated diene graft polymer of the present invention is preferably a method in which a previously synthesized conjugated diene polymer is reacted with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain, and then a functionalizing agent is added to add hydroxyl groups to some of the lithiation points, and then a monomer that will become a structural unit of the side chain is polymerized (hereinafter referred to as a macroinitiator method in this specification), or a method in which an epoxy group contained in a monomer unit that will become a branched portion of the functional group-modified polymer that will become the main chain (a) is reacted with an active terminal of a polymer obtained by polymerizing a monomer that will become a structural unit of the side chain (hereinafter referred to as a coupling method in this specification).

[0083] <Macroinitiator Method (MI Method)> As a preferred embodiment of the method for producing the conjugated diene-based graft polymer of the present invention, a production method by the macroinitiator method (MI method) including the following steps (A-1), (A-2), (B), and (D) is used.

[0084] (A-1) a step of reacting a polymer (M) containing conjugated diene units with an organolithium compound in the presence of a polar compound to lithiate anion-active sites contained in the polymer (M); (A-2) a step of adding a functionalizing agent to functionalize a portion of the lithiated sites having anion activity; (B) a step of adding at least one monomer selected from the group consisting of conjugated dienes and aromatic vinyl compounds to polymerize the remaining lithiated sites having anion activity in the polymer (M) to form side chains on the polymer (M) that serves as the main chain, thereby producing a conjugated diene graft polymer; and (D) a step of recovering the obtained conjugated diene graft polymer.

[0085] [Step (A-1)] The method for producing the polymer (M) containing conjugated diene units, which is a constituent element of the main chain in the step (A-1), is preferably, for example, an emulsion polymerization method or a solution polymerization method, and from the viewpoint of the molecular weight distribution of the obtained polymer, a solution polymerization method is more preferred. The polymer (M) containing conjugated diene units becomes the main chain (a) of the conjugated diene graft polymer of the present invention.

[0086] Specific examples, preferred examples, and preferred contents of the conjugated diene that serves as the monomer unit constituting the polymer (M) containing a conjugated diene unit are the same as those described for the main chain (a) of the conjugated diene graft polymer.

[0087] Examples of the monomer other than the conjugated diene that serves as the monomer unit constituting the polymer (M) containing a conjugated diene unit include aromatic vinyl compounds.

[0088] Examples of aromatic vinyl compounds include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-t-butylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 2,4,6-trimethylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, vinylanthracene, N,N-diethyl-4-aminoethylstyrene, vinylpyridine, 4-methoxystyrene, monochlorostyrene, dichlorostyrene, and divinylbenzene. Among these aromatic vinyl compounds, styrene and α-methylstyrene are preferred. The aromatic vinyl compounds that form the aromatic vinyl compound units may be used alone or in combination of two or more.

[0089] In the polymer (M) containing conjugated diene units, the content of other monomer units than butadiene units and isoprene units is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.For example, when the aromatic vinyl compound unit is less than the above range, when the obtained conjugated diene graft polymer is used as, for example, a lubricating oil additive (viscosity index improver, friction suppressant), the shear stability of the lubricating oil additive (viscosity index improver, friction suppressant) tends to be improved.In addition, the processability of the obtained conjugated diene graft polymer tends to be improved.

[0090] The preferred embodiments of the number average molecular weight (Mn), vinyl content, and Tg of the polymer (M) containing a conjugated diene unit are the same as those of the main chain (a) of the conjugated diene graft polymer.

[0091] The emulsion polymerization method, which is one example of a method for producing the polymer (M) containing a conjugated diene unit, can be a known method or a method equivalent to a known method, for example, by emulsifying and dispersing a predetermined amount of a monomer containing a conjugated diene in a dispersion medium in the presence of an emulsifier, and then emulsion-polymerizing the resulting mixture with a radical polymerization initiator.

[0092] Examples of emulsifiers include salts of long-chain fatty acids having 10 or more carbon atoms, rosinate salts, etc. Examples of long-chain fatty acid salts include potassium salts or sodium salts of fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, and stearic acid.

[0093] The dispersion medium is usually water, but may contain a water-soluble organic solvent such as methanol or ethanol, as long as the stability during polymerization is not impaired.

[0094] Examples of the radical polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate, organic peroxides, and hydrogen peroxide.

[0095] A chain transfer agent may be used to adjust the molecular weight of the resulting polymer (M) containing conjugated diene units. Examples of the chain transfer agent include mercaptans such as t-dodecyl mercaptan and n-dodecyl mercaptan; carbon tetrachloride, thioglycolic acid, diterpenes, terpinolene, γ-terpinene, and α-methylstyrene dimer.

[0096] The temperature of the emulsion polymerization can be appropriately set depending on the type of radical polymerization initiator used, but is usually in the range of 0 to 100° C., preferably 0 to 60° C. The polymerization method may be either continuous polymerization or batch polymerization.

[0097] The polymerization reaction can be terminated by adding a polymerization terminator, such as an amine compound such as isopropylhydroxylamine, diethylhydroxylamine, or hydroxylamine, a quinone compound such as hydroquinone or benzoquinone, or sodium nitrite.

[0098] After the polymerization reaction is terminated, an antioxidant may be added as needed. After the polymerization reaction is terminated, unreacted monomers are removed from the obtained latex as needed. Next, the polymer (M) containing conjugated diene units is coagulated using a salt such as sodium chloride, calcium chloride, or potassium chloride as a coagulant, and an acid such as nitric acid or sulfuric acid is added as needed to adjust the pH of the coagulation system to a predetermined value, and the dispersion medium is then separated to recover the polymer. Next, the polymer is washed with water, dehydrated, and dried to obtain the polymer (M) containing conjugated diene units. Note that during the coagulation, the latex and an extender oil previously prepared as an emulsified dispersion may be mixed as needed, and the oil-extended polymer (M) containing conjugated diene units may be recovered.

[0099] As the solution polymerization method, which is one example of a method for producing the polymer (M) containing a conjugated diene unit, a known method or a method equivalent to a known method can be applied. For example, a monomer containing a conjugated diene is polymerized in a solvent using a Ziegler catalyst, a metallocene catalyst, or an anionically polymerizable active metal or active metal compound as an initiator, optionally in the presence of a polar compound.

[0100] Examples of the solvent include aliphatic hydrocarbons such as n-butane, n-pentane, isopentane, n-hexane, n-heptane, and isooctane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclopentane; and aromatic hydrocarbons such as benzene, toluene, and xylene.

[0101] The initiator is preferably an anionically polymerizable active metal or active metal compound, more preferably an anionically polymerizable active metal compound.

[0102] Examples of the active metal capable of anion polymerization include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; and lanthanoid rare earth metals such as lanthanum and neodymium. Among these, alkali metals and alkaline earth metals are preferred, and alkali metals are more preferred.

[0103] The anionically polymerizable active metal compound is preferably an organic alkali metal compound. Examples of the organic alkali metal compound include organic monolithium compounds such as methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium, and stilbenelithium; polyfunctional organic lithium compounds such as dilithiomethane, dilithionaphthalene, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, and 1,3,5-trilithiobenzene; sodium naphthalene, potassium naphthalene, and the like. Among these organic alkali metal compounds, organic lithium compounds are preferred, and organic monolithium compounds are more preferred.

[0104] The amount of the initiator used can be appropriately set depending on the melt viscosity, molecular weight, etc. of the polymer (M) containing a conjugated diene unit, but it is usually used in an amount of 0.01 to 3 parts by mass per 100 parts by mass of all monomers including the conjugated diene.

[0105] When an organic alkali metal compound is used as an initiator, the organic alkali metal compound can be reacted with a secondary amine such as dibutylamine, dihexylamine, or dibenzylamine to be used as an organic alkali metal amide.

[0106] In anionic polymerization, polar compounds are usually used to adjust the microstructure (vinyl content) of the conjugated diene units without deactivating the reaction. Examples of polar compounds include ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether; tertiary amines such as tetramethylethylenediamine and trimethylamine; alkali metal alkoxides; and phosphine compounds. The polar compound is usually used in an amount of 0.01 to 1,000 moles per mole of the organic alkali metal compound.

[0107] The temperature for solution polymerization is usually in the range of −80 to 150° C., preferably in the range of 0 to 100° C., and more preferably in the range of 10 to 90° C. The polymerization may be carried out in either a batch or continuous manner.

[0108] The polymerization reaction of the solution polymerization can be terminated by adding a polymerization terminator. Examples of the polymerization terminator include alcohols such as methanol and isopropanol. The polymer (M) containing conjugated diene units can be isolated by pouring the obtained polymerization reaction solution into a poor solvent such as methanol to precipitate the polymer (M) containing conjugated diene units, or by washing the polymerization reaction solution with water, separating it, and then drying it. Note that the polymerization reaction solution after polymerization termination may be used directly in the lithiation reaction, as long as it does not affect the lithiation reaction. Furthermore, if necessary, the solvent may be partially removed or a solvent may be added to dilute the polymerization reaction solution.

[0109] The polymer (M) containing conjugated diene units obtained in this manner may be used in the lithiation reaction as it is, but the conjugated diene polymer may be modified after at least a portion of the carbon-carbon double bonds contained in the conjugated diene units is hydrogenated by a hydrogenation method described below.

[0110] In step (A-1), the anion-active sites contained in the polymer (M) containing conjugated diene units obtained as described above are lithiated by reacting with an organolithium compound in the presence of a polar compound. Lithiation under these conditions results in lithiation of the anion-active sites, particularly the carbon-carbon double bond moieties contained in the vinyl-bond type conjugated diene units contained in the polymer (M). Furthermore, the aromatic vinyl compound units contained in the polymer (M) that do not have a substituent in the aromatic group that is highly reactive with anions, such as the CH moiety adjacent to the CH bonded to the benzene ring contained in the (—CH—CH—) moiety that forms the backbone of the main chain (a) of the styrene unit, are lithiated. Therefore, in the graft polymer obtained by this production method, the linking moiety containing the atom bonding to the side chain (b) contained in the monomer unit that forms the branching moiety is not an aromatic group derived from an aromatic vinyl compound. In order to more reliably lithiate the conjugated diene unit containing a moiety having anionic activity, when the polymer (M) contains an aromatic vinyl compound unit, it is desirable that the aromatic vinyl compound unit does not contain a functional group with high anionic activity (a functional group highly reactive with an organolithium compound) in the aromatic group. Examples of styrenes having an aromatic group containing such a functional group include 4-methylstyrene and 4-propylstyrene.

[0111] Examples of the organolithium compound used in the lithiation of polymer (M) in step (A-1) include organomonolithium compounds such as methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium, and stilbenelithium; and polyfunctional organolithium compounds such as dilithiomethane, dilithionaphthalene, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, and 1,3,5-trilithiobenzene. Among these organolithium compounds, organomonolithium compounds are preferred, with n-butyllithium and sec-butyllithium being more preferred, and sec-butyllithium being particularly preferred.

[0112] The amount of the organolithium compound used can be appropriately set depending on the average number of side chains (b) of the conjugated diene graft polymer and the average number of hydroxyl groups bonded to the main chain (a). For example, when the ratio of (charge amount (number of moles) of organolithium compound) / (charge amount (number of moles) of functionalizing agent used in the functionalization reaction) / (charge amount (number of moles) of polymer (M) containing conjugated diene units) is 10 / 4 / 1, the average number of side chains (b) is 6. In addition, the average number of hydroxyl groups can be designed to be 4.

[0113] As described above, the side chain density is calculated by the following formula (1): (Side chain density)=(Average number of side chains (b) per molecule of conjugated diene graft polymer) / [(Number average molecular weight Mn of main chain (a)) / (Molecular weight of styrene unit)]×100 (1) In other words, the amount of the organolithium compound used can be determined automatically by designing the number average molecular weight Mn of the main chain (a), the average number of side chains (b) per molecule of the conjugated diene graft polymer, and the average number of hydroxyl groups bonded to the main chain (a) so as to achieve the desired side chain density and hydroxyl group concentration.

[0114] The polar compound used in the lithiation of the polymer (M) in step (A-1) above is used to promote the lithiation reaction. Examples of polar compounds include ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether; tertiary amines such as tetramethylethylenediamine and trimethylamine; alkali metal alkoxides; and phosphine compounds. Among these polar compounds, tertiary amines are preferred, and tetramethylethylenediamine is particularly preferred. The amount of polar compound used is preferably 0.01 mol or more, more preferably 0.05 mol or more, and particularly preferably 0.1 mol or more, per mol of the organic alkali metal compound. The amount of polar compound used is preferably 100 mol or less, more preferably 50 mol or less, and particularly preferably 10 mol or less, per mol of the organic alkali metal compound. When the amount of polar compound used is less than 0.01 mol per mol of the organic alkali metal compound, the reaction rate tends to be poor, and when it exceeds 100 mol, the cost efficiency tends to be poor.

[0115] The lithiation in the step (A-1) is usually carried out in a state in which the polymer (M) is dissolved in a solvent. Examples of the solvent include aliphatic hydrocarbons such as n-butane, n-pentane, isopentane, n-hexane, n-heptane, and isooctane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclopentane; aromatic hydrocarbons such as benzene, toluene, and xylene; and ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether.

[0116] The reaction temperature for the lithiation in step (A-1) is preferably 0° C. or higher, more preferably 10° C. or higher, and particularly preferably 20° C. or higher. The reaction temperature is preferably 100° C. or lower, more preferably 80° C. or lower, and particularly preferably 60° C. or lower. If the temperature is lower than 0° C., the reaction rate tends to be poor, and if the temperature is higher than 100° C., side reactions such as decomposition tend to increase.

[0117] The reaction time for the lithiation in the above step (A-1) can be appropriately set depending on the progress of the reaction, but is preferably 0.01 to 100 hours, more preferably 0.1 to 50 hours, and particularly preferably 0.2 to 20 hours.

[0118] Polymer (M) after lithiation in step (A-1) 1 In H-NMR measurement, when the peak area in the range of 4.0 to 5.7 ppm is taken as 100, the peak area in the range of 5.7 to 6.4 ppm is preferably in the range of 0.1 to 10, more preferably in the range of 0.3 to 5, and particularly preferably in the range of 0.5 to 4. When the peak area is in this range, it can be said that the lithiation reaction is proceeding appropriately, and the average number of side chains (b) in the obtained conjugated diene graft polymer is in an appropriate range.

[0119] [Step (A-2)] In step (A-2) using the MI method, a portion of the lithiated anionic active sites obtained in step (A-1) is reacted with a functionalizing agent to form hydroxyl groups that are bonded to the main chain (a) of the finally obtained conjugated diene graft polymer. When hydroxyl groups are formed by this synthesis method, the hydroxyl groups are bonded to the main chain (a) through linking chains.

[0120] Examples of functionalizing agents used in the functionalization reaction of the lithiated anionic active site in step (A-2) include aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, valeraldehyde, isovaleraldehyde, n-octylaldehyde, 2-ethylhexylaldehyde, decylaldehyde, dodecylaldehyde, and benzaldehyde; and epoxides such as ethylene oxide and propylene oxide. Among these functionalizing agents, aldehydes such as n-butyraldehyde, isobutyraldehyde, valeraldehyde, isovaleraldehyde, n-octylaldehyde, 2-ethylhexylaldehyde, decylaldehyde, dodecylaldehyde, and benzaldehyde are preferred, with 2-ethylhexylaldehyde and benzaldehyde being particularly preferred.

[0121] The amount of the functionalizing agent used can be appropriately set depending on the average number of hydroxyl groups bonded to the main chain (a). For example, when the ratio of (charge amount (number of moles) of the organolithium compound) / (charge amount (number of moles) of the functionalizing agent used in the functionalization reaction) / (charge amount (number of moles) of the polymer (M) containing conjugated diene units) is 10 / 4 / 1, the average number of side chains (b) is 6. In addition, the average number of hydroxyl groups can be designed to be 4.

[0122] As described above, the hydroxyl group concentration is calculated by the following formula (3): (Hydroxyl group concentration)=(average number of hydroxyl groups bonded to the main chain (a) per molecule of conjugated diene graft polymer) / [(number average molecular weight Mn of the main chain (a)) / (molecular weight of styrene unit)]×100 (3) In other words, the amount of the functionalizing agent used can be determined automatically by designing the number average molecular weight Mn of the main chain (a) and the average number of hydroxyl groups bonded to the main chain (a) per molecule of conjugated diene graft polymer so as to achieve a desired hydroxyl group concentration.

[0123] The solvents that can be used in the step (A-2) are the same as the preferred examples of the solvents in the step (A-1). If necessary, a solvent may be further added at any timing after the step (A-1).

[0124] The reaction temperature for functionalization in step (A-2) is preferably 0° C. or higher, more preferably 10° C. or higher, and particularly preferably 20° C. or higher. The reaction temperature is preferably 100° C. or lower, more preferably 80° C. or lower, and particularly preferably 60° C. or lower. If the temperature is lower than 0° C., the reaction rate tends to be poor, and if the temperature is higher than 100° C., side reactions such as decomposition tend to increase.

[0125] The reaction time for functionalization in the step (A-2) can be appropriately set depending on the progress of the reaction, but is preferably 0.01 to 100 hours, more preferably 0.05 to 50 hours, and particularly preferably 0.1 to 20 hours.

[0126] [Step (A-3)] In one preferred embodiment, the method for producing a conjugated diene graft polymer by the MI method includes, after step (A-1) or step (A-2), a step (A-3) of adding a Lewis acid in order to adjust the vinyl content of the side chain (b) within a desired range.

[0127] The Lewis acid is added to reduce the effect of the polar compound added to promote the lithiation reaction and to adjust the vinyl content of the side chains to the desired range in step (B), which will be described later. As the Lewis acid, an alkyl metal compound that does not deactivate the lithiation site generated in step (A-1) is preferred. Examples include alkyl aluminum compounds such as trimethyl aluminum, tri-n-propyl aluminum, tri-n-butyl aluminum, triisobutyl aluminum, tri-n-hexyl aluminum, and trioctyl aluminum; alkyl magnesium compounds such as butylethyl magnesium, di-n-butyl magnesium, and di-n-hexyl magnesium; and alkyl zinc compounds such as dimethyl zinc, diethyl zinc, di-n-propyl zinc, diisobutyl zinc, and di-n-butyl zinc. Among these alkyl metal compounds, alkyl aluminum compounds or alkyl zinc compounds are preferred, alkyl aluminum compounds are more preferred, and triisobutyl aluminum is particularly preferred.

[0128] The amount of the Lewis acid used can be adjusted appropriately depending on the vinyl content of the desired side chain (b). For example, it is preferably 0.01 mol or more, more preferably 0.05 mol or more, and particularly preferably 0.1 mol or more, relative to 1 mol of the organic alkali metal compound used in step (A-1). The amount of the Lewis acid used is preferably 10 mol or less, more preferably 5 mol or less, and particularly preferably 1 mol or less, relative to 1 mol of the organic alkali metal compound. If the amount of the Lewis acid used per mol of the organic alkali metal compound is less than 0.01 mol, the effect of adding the Lewis acid is poor, making it difficult to adjust the desired vinylation degree. If the amount is more than 10 mol, the polymerization rate of the side chain polymerization tends to decrease and the process tends to be less economical. The amount of the Lewis acid used is preferably 0.02 mol or more, more preferably 0.1 mol or more, and particularly preferably 0.2 mol or more, relative to 1 mol of the polar compound used in step (A-1). The amount of the Lewis acid used is preferably 20 moles or less, more preferably 10 moles or less, and particularly preferably 2 moles or less, relative to 1 mole of the polar compound. If the amount of the Lewis acid used relative to 1 mole of the polar compound is less than 0.02 moles, the effect of adding the Lewis acid is poor and it is difficult to adjust the vinylation degree to the desired level. If the amount of the Lewis acid used relative to 1 mole of the polar compound is more than 20 moles, the polymerization rate of the side chain polymerization tends to decrease and the cost efficiency tends to be poor.

[0129] The timing of adding the Lewis acid may be before the step (B) described below, or at any timing during the step (B), as long as it is after the step (A-1), and can be selected arbitrarily depending on the desired vinyl content of the side chain (b).

[0130] [Step (B)] A method for producing a conjugated diene graft polymer by the MI method includes the following step: (B) adding at least one monomer selected from the group consisting of a conjugated diene and an aromatic vinyl compound, and polymerizing the monomer from the lithiated anionic active site remaining in the polymer (M) to form a side chain on the main chain of the polymer (M), thereby preparing a conjugated diene graft polymer. The monomer polymerized in step (B) becomes the side chain (b) of the conjugated diene graft polymer of the present invention. Specific examples, preferred examples, and preferred contents of the conjugated diene that serves as a monomer unit constituting the polymer polymerized in step (B), as well as specific examples, preferred examples, and preferred contents of other monomers (such as aromatic vinyl compounds) other than the conjugated diene, are the same as those described for the side chain (b) of the conjugated diene graft polymer. The preferred embodiments of the weight average molecular weight (Mn), vinyl content, and Tg of the polymer polymerized in step (B) are the same as those of the side chain (b) of the conjugated diene graft polymer.

[0131] In the step (B), a polar compound may be further added to adjust the vinyl content of the side chain (b) to a desired range. Also, a Lewis acid may be added as described above to adjust the vinyl content to a desired range.

[0132] The solvents that can be used in the step (B) are the same as the preferred examples of the solvents in the step (A-1). If necessary, a solvent may be further added at any timing after the step (A-1).

[0133] The polymerization temperature in step (B) is preferably 0° C. or higher, more preferably 10° C. or higher, and particularly preferably 20° C. or higher. The polymerization temperature is preferably 100° C. or lower, more preferably 80° C. or lower, and particularly preferably 60° C. or lower. If the polymerization temperature is lower than 0° C., the polymerization rate tends to be low, and if it exceeds 100° C., side reactions such as decomposition tend to increase.

[0134] The polymerization time in the step (B) can be appropriately set depending on the progress of the reaction, but is preferably 0.01 to 100 hours, more preferably 0.1 to 50 hours, and particularly preferably 0.2 to 20 hours.

[0135] The polymerization reaction in step (B) can be terminated by adding a polymerization terminator, such as an alcohol such as methanol or isopropanol.

[0136] The conjugated diene graft polymer obtained by the production method including steps (A-1), (B), and (D) but not including step (C) described in detail below is a non-hydrogenated conjugated diene graft polymer.

[0137] [Step (C)] In one preferred embodiment, the method for producing a conjugated diene graft polymer by the MI method includes, before step (D), (C) a step of hydrogenating at least a portion of the carbon-carbon double bonds contained in the conjugated diene units in the conjugated diene graft polymer.

[0138] The conjugated diene graft polymer obtained by the above method can be subjected to a hydrogenation step to obtain a hydrogenated conjugated diene graft polymer. There are no particular limitations on the hydrogenation method, and for example, a known method can be used. The above step (B) and the hydrogenation may be carried out consecutively, or the unhydrogenated conjugated diene graft polymer may be isolated first and then hydrogenated. The method for isolating the unhydrogenated conjugated diene graft polymer is the same as the recovery step (D) described below.

[0139] As the catalyst used in the hydrogenation reaction of step (C), a catalyst capable of hydrogenating the carbon-carbon double bond contained in an olefin compound, etc. Examples of such a catalyst include heterogeneous catalysts and homogeneous catalysts.

[0140] The heterogeneous catalyst is not particularly limited, and specific examples thereof include sponge metal catalysts such as sponge nickel, sponge cobalt, and sponge copper; and supported metal catalysts such as nickel silica, nickel alumina, nickel zeolite, nickel diatomaceous earth, palladium silica, palladium alumina, palladium zeolite, palladium diatomaceous earth, palladium carbon, palladium calcium carbonate, platinum silica, platinum alumina, platinum zeolite, platinum diatomaceous earth, platinum carbon, platinum calcium carbonate, ruthenium silica, ruthenium alumina, ruthenium zeolite, ruthenium diatomaceous earth, ruthenium carbon, ruthenium calcium carbonate, iridium silica, iridium alumina, iridium zeolite, iridium diatomaceous earth, iridium carbon, iridium calcium carbonate, cobalt silica, cobalt alumina, cobalt zeolite, cobalt diatomaceous earth, cobalt carbon, and cobalt calcium carbonate. These heterogeneous catalysts may be modified with iron, molybdenum, magnesium, etc. for the purpose of improving activity, selectivity, and stability. These heterogeneous catalysts may be used alone or in combination of two or more.

[0141] The homogeneous catalyst is not particularly limited, but specific examples include Ziegler catalysts composed of a transition metal compound and an alkylaluminum or alkyllithium; and metallocene catalysts. Specific examples of transition metal compounds used in Ziegler catalysts include nickel salts such as nickel acetate, nickel octylate, and nickel acetylacetonate; cobalt salts such as cobalt acetate, cobalt octylate, and cobalt acetylacetonate; titanocene dichloride, and zirconocene dichloride. Specific examples of alkylaluminums used in Ziegler catalysts include trimethylaluminum, triethylaluminum, triisobutylaluminum, and trioctylaluminum. Specific examples of alkyllithiums used in Ziegler catalysts include methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, and t-butyllithium. These homogeneous catalysts may be used alone or in combination. Furthermore, homogeneous catalysts may be used in combination with heterogeneous catalysts.

[0142] In the hydrogenation reaction of step (C), since a polymer is hydrogenated, the reaction activity for low molecular weight compounds is generally low. Therefore, relatively high temperature and pressure conditions are often preferred as reaction conditions, and it is preferable to carry out the reaction using a heterogeneous catalyst with high thermal stability. In terms of hydrogenation activity, it is preferable to use nickel or palladium as a metal having hydrogenation activity. Furthermore, in order to suppress undesirable side reactions during the hydrogenation reaction, it is preferable to use calcium carbonate or a carbon support as a support, and it is more preferable to use a carbon support.

[0143] The hydrogenation reaction is usually carried out in an organic solvent. The organic solvent is not particularly limited, and examples thereof include the solvents exemplified in the above step (B) or the step (E) described below.

[0144] The hydrogenation reaction may be carried out, for example, in a state in which the unhydrogenated conjugated diene graft polymer is present in the solvent used in the step (B) without any particular treatment of the organic solvent, or may be carried out in the remaining solvent after removing a portion of the solvent by a method such as distillation, or may be carried out in a solvent after diluting with a separate organic solvent. Alternatively, after completion of the step (B), the unhydrogenated conjugated diene graft polymer may be temporarily removed and then introduced into an organic solvent, and the hydrogenation reaction may be carried out in the solvent.

[0145] When the hydrogenation reaction is carried out in an organic solvent, the amount of organic solvent used is preferably an amount that results in a concentration of the unhydrogenated conjugated diene graft polymer in the reaction solution of 1% by mass or more and 30% by mass or less. If the concentration is less than 1% by mass, productivity may be significantly reduced, while if it exceeds 30% by mass, viscosity may be significantly increased, resulting in a reduction in mixing efficiency.

[0146] The reaction pressure for the hydrogenation reaction may be appropriately set depending on the catalyst used and the like, but is usually 0.1 MPa to 20 MPa, preferably 0.5 MPa to 15 MPa, more preferably 0.5 MPa to 5 MPa in terms of total pressure.

[0147] The hydrogenation reaction is carried out in the presence of hydrogen gas, but may also be carried out in the presence of a gas mixture containing a gas other than hydrogen gas that is inert to the hydrogenation reaction. Specific examples of gases inert to the hydrogenation reaction include nitrogen, helium, argon, and carbon dioxide. Depending on the reaction conditions, the solvent used in the reaction may have a significant partial pressure as a gas component, but as long as the hydrogenation reaction proceeds, such a situation is usually not a problem.

[0148] The reaction temperature of the hydrogenation reaction may be appropriately set depending on the catalyst used, but is usually 20°C to 250°C, preferably 50°C to 180°C, and more preferably 70°C to 180°C. In general, it may be desirable to carry out the reaction at a higher temperature with a heterogeneous catalyst than with a homogeneous catalyst. The reaction time of the hydrogenation reaction may be appropriately set depending on the type of catalyst used, the amount of catalyst, and the reaction temperature, but is usually 0.1 to 100 hours, preferably 1 to 50 hours. If the reaction time is too short, the desired hydrogenation rate may not be obtained. On the other hand, if the reaction time is too long, undesired side reactions may progress significantly, and a hydrogenated conjugated diene graft polymer with the desired physical properties may not be obtained.

[0149] The reaction format of the hydrogenation reaction is not particularly limited and may be appropriately selected depending on the type of catalyst used in the reaction. Examples of the reaction format include a batch reaction format, a semi-continuous reaction format (semi-batch reaction format), and a continuous reaction format. Suitable continuous reaction formats include a plug flow reactor (PFR) and a continuous stirred tank (CSTR). When a heterogeneous catalyst is used, the hydrogenation reaction can be carried out using a fixed-bed reactor. When the hydrogenation reaction is carried out under active mixing conditions, mixing methods include a mixing method using stirring and a mixing method in which the reaction liquid is circulated in a loop. When a heterogeneous catalyst is used under mixed conditions, the reaction takes place using a suspension bed, resulting in a gas-liquid-solid reaction field. Furthermore, when a homogeneous catalyst is used under mixed conditions, the reaction field takes place in a gas-liquid two-phase system. The hydrogenation reaction may also be carried out in a reaction format in which the hydrogenation reaction in the reaction vessel is temporarily terminated, the reaction liquid is withdrawn, and at least a portion of the withdrawn reaction liquid is introduced into the same or a different reaction vessel for further hydrogenation. By carrying out the hydrogenation reaction in such a reaction format, it is possible to avoid localized heat generation accompanying the hydrogenation reaction, and the hydrogenation rate may be improved. The hydrogenation reaction may be carried out using a single reaction format, or may be carried out by combining two or more reaction formats, which may be the same or different. When a higher hydrogenation rate is desired, a hydrogenation reaction step including a step of carrying out the reaction in a plug flow format using a fixed-bed reactor may be desirable.

[0150] The amount of catalyst used in the hydrogenation reaction may be appropriately set depending on the type of catalyst used, the concentration of the unhydrogenated conjugated diene graft polymer, the reaction format, etc. When the hydrogenation reaction is carried out using a heterogeneous catalyst in a suspension bed, the amount of catalyst used per 100 parts by mass of the reaction solution containing the unhydrogenated conjugated diene graft polymer is usually 0.01 to 20 parts by mass, preferably 0.05 to 15 parts by mass, and more preferably 0.1 to 10 parts by mass. If the amount of catalyst used is too small, the hydrogenation reaction may require a long time, and if the amount of catalyst used is too large, more power may be required to mix the heterogeneous catalyst. Furthermore, when the hydrogenation reaction is carried out in a fixed bed, it is difficult to specify the amount of catalyst used per reaction solution containing the unhydrogenated conjugated diene graft polymer, and the amount may be appropriately set depending on the type of reaction vessel used, etc. When a Ziegler catalyst or a metallocene catalyst is used as the homogeneous catalyst, the concentration of the transition metal compound in the reaction solution containing the unhydrogenated conjugated diene graft polymer is usually 0.001 mmol / L to 100 mmol / L, preferably 0.01 mmol / L to 10 mmol / L.

[0151] The catalyst used in the hydrogenation reaction may be separated from the liquid containing the hydrogenated conjugated diene graft polymer after the hydrogenation reaction is completed, if necessary. The separation method is not particularly limited as long as it allows for the separation of the catalyst. When a heterogeneous catalyst is used, the catalyst can be separated, for example, by continuous or batch filtration, centrifugation, settling by standing, and decantation. When a homogeneous catalyst is used, the catalyst can be separated, for example, by coagulation-sedimentation, adsorption, washing, and aqueous phase extraction. Even if the used catalyst is separated by these separation methods, trace amounts of metal components derived from the catalyst may remain in the liquid containing the hydrogenated conjugated diene graft polymer. In this case, the metal components will remain in the liquid, and the remaining metal components can be separated by separation methods such as coagulation-sedimentation, adsorption, washing, and aqueous phase extraction, as described above. The catalyst recovered by separation can be reused in the hydrogenation reaction after partial removal or addition of new catalyst, if necessary.

[0152] [Step (D)] The method for producing a conjugated diene graft polymer by the MI method includes: (D) a step of recovering the obtained conjugated diene graft polymer.

[0153] In step (D), the obtained conjugated diene graft polymer of the present invention is recovered. There are no particular limitations on the method for recovering the conjugated diene graft polymer. For example, before carrying out step (D), the conjugated diene graft polymer is converted into a solution containing the polymer, and the solution containing the conjugated diene graft polymer is poured into a poor solvent such as methanol to precipitate the conjugated diene graft polymer; alternatively, the polymerization reaction solution is poured into hot water together with steam to remove the solvent by azeotropy (steam stripping), followed by drying; or the polymerization reaction solution is washed with water, separated, and then dried to isolate and recover the conjugated diene graft polymer. When the conjugated diene graft polymer has already been obtained as a solution containing the conjugated diene graft polymer before carrying out step (D), step (D) may be carried out as is or after concentrating or diluting the solution by the method described above.

[0154] An antioxidant may be added to the conjugated diene graft polymer of the present invention, if necessary, in any of the above-mentioned steps. For example, it may be added after step (B), or after or at any stage during step (C), or after or at any stage during step (D). Preferred antioxidants for use in this case include, for example, 2,6-di-t-butyl-4-methylphenol (BHT), 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol) (AO-40), 3,9-bis[1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyl] ... pionyloxy]ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane (AO-80), 2,4-bis[(octylthio)methyl]-6-methylphenol (Irganox 1520L), 2,4-bis[(dodecylthio)methyl]-6-methylphenol (Irganox 1726), 2-[1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenyl acrylate (Sumilizer GS), 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (Sumilizer GM), 6-t-butyl-4-[3-(2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]dioxaphosphepin-6-yloxy)propyl]-2-methylphenol (Sumilizer GP), tris(2,4-di-t-butylphenyl) phosphite (Irgafos 168), di Examples of antioxidants include octadecyl 3,3'-dithiobispropionate, hydroquinone, p-methoxyphenol, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (Nocrac 6C), bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (LA-77Y), N,N-dioctadecylhydroxylamine (Irgastab FS042), bis(4-t-octylphenyl)amine (Irganox 5057), etc. The antioxidants may be used alone or in combination of two or more.

[0155] <Coupling Method (CP Method)> As a method for producing the conjugated diene graft polymer of the present invention, a preferred embodiment is a production method by a coupling method (CP method) including the following steps (E) and (D).

[0156] (E) A step of reacting an active terminal polymer represented by the following formula (I) with a functional group-modified conjugated diene polymer having an epoxy group (hereinafter, this polymer is also referred to as functional group-modified conjugated diene polymer (F)) to prepare a conjugated diene graft polymer:

[0157] P-X (I) (in formula (I), P represents a polymer chain containing at least one monomer unit selected from the group consisting of a conjugated diene unit and an aromatic vinyl compound unit, and X represents an active end of anionic polymerization); and (D) a step of recovering the obtained conjugated diene graft polymer.

[0158] [Step (E)] The active terminal polymer (I) used in the above step (E) can be produced by a known polymerization method. For example, the active terminal polymer (I) can be obtained by anionically polymerizing a monomer in a solvent inert to the polymerization terminals using an anionically polymerizable active metal or active metal compound as an initiator, optionally in the presence of a polar compound. P in this active terminal polymer (I) becomes the side chain (b) of the conjugated diene graft polymer obtained in the present invention.

[0159] The explanation of specific examples and preferred embodiments of the monomers that become the monomer units constituting the active terminal polymer (I), and the explanation of specific examples and preferred embodiments of the monomer units contained in the active terminal polymer (I) are the same as the explanation of the side chain (b) of the conjugated diene graft polymer.

[0160] The anionically polymerizable active metal or active metal compound is preferably an organic alkali metal compound, more preferably an organic lithium compound, such as methyl lithium, ethyl lithium, n-butyl lithium, sec-butyl lithium, tert-butyl lithium, or pentyl lithium.

[0161] Examples of the solvent include aliphatic hydrocarbons such as n-butane, n-pentane, isopentane, n-hexane, n-heptane, and isooctane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclopentane; aromatic hydrocarbons such as benzene, toluene, and xylene; and ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether.

[0162] A polar compound may be added during the anionic polymerization. In anionic polymerization, the polar compound is typically used to adjust the microstructure (vinyl content) of the conjugated diene units without deactivating the reaction. Examples of polar compounds include ether compounds such as dibutyl ether, tetrahydrofuran, and ethylene glycol diethyl ether; tertiary amines such as tetramethylethylenediamine and trimethylamine; alkali metal alkoxides; and phosphine compounds. The polar compound is typically used in an amount of 0.01 to 1,000 moles per mole of the organic alkali metal compound.

[0163] The temperature for the anionic polymerization is usually in the range of −80 to 150° C., preferably in the range of 0 to 100° C., and more preferably in the range of 10 to 90° C. The polymerization may be carried out in either a batch or continuous manner.

[0164] P in the active terminal polymer (I) ultimately becomes the side chain (b) of the conjugated diene graft polymer of the present invention. The preferred embodiments of the number average molecular weight (Mn), vinyl content, and Tg of P in the active terminal polymer (I) are the same as those for the side chain (b) of the conjugated diene graft polymer of the present invention.

[0165] In the step (E), the functional group-modified conjugated diene polymer (F) can be obtained, for example, by modifying an unmodified conjugated diene polymer (F') with a functional group in a modification step described below. The method for producing the unmodified conjugated diene polymer (F') is not particularly limited, and the same method for producing the polymer (M) containing a conjugated diene unit as described above can be applied. The portion of the functional group-modified conjugated diene polymer (F) other than the portion modified with the functional group becomes the main chain (a) of the conjugated diene graft polymer of the present invention.

[0166] Specific examples, preferred examples, and preferred contents of the conjugated diene that constitutes the monomer unit constituting the unmodified conjugated diene polymer (F'), as well as specific examples, preferred examples, and preferred contents of other monomers (such as aromatic vinyl compounds) other than the conjugated diene, are the same as those described for the main chain (a) of the conjugated diene graft polymer. Furthermore, preferred embodiments of the number average molecular weight (Mn), vinyl content, and Tg of the unmodified conjugated diene polymer (F') are the same as those described for the main chain (a) of the conjugated diene graft polymer. When the functional group-modified conjugated diene polymer (F) that constitutes the main chain (a) is produced by the CP method, the aromatic vinyl compound unit contained in the polymer may contain a 4-methylstyrene unit. This is because, when the conjugated diene graft polymer is produced by the CP method, the side chain (b) is not bound to the aromatic group contained in the 4-methylstyrene unit.

[0167] The method for producing the functional group-modified conjugated diene polymer (F) having an epoxy group by modifying the unmodified conjugated diene polymer (F') with a functional group is not particularly limited, and a conventionally known method can be used. For example, the functional group-modified conjugated diene polymer (F) having an epoxy group can be produced by epoxidizing the unmodified conjugated diene polymer (F') using an epoxidizing agent such as a hydroperoxide or an organic peracid. Examples of hydroperoxides include hydrogen peroxide, t-butyl hydroperoxide, and cumene hydroperoxide. Examples of organic peracids include performic acid, peracetic acid, perbenzoic acid, trifluoroperacetic acid, and m-chloroperbenzoic acid. The organic peracid may be an equilibrium peracid obtained by using hydrogen peroxide and an organic acid.

[0168] A catalyst may be used in the epoxidation reaction, if necessary. Examples of combinations of epoxidizing agents and catalysts include, when the epoxidizing agent is a hydroperoxide, a combination of hydrogen peroxide with a mixture of tungstic acid and caustic soda, a combination of hydrogen peroxide with an organic acid, or a combination of t-butyl hydroperoxide with molybdenum hexacarbonyl. When the epoxidizing agent is an organic peracid, a combination of an organic peracid with an alkali such as sodium carbonate or an acid such as sulfuric acid may be used. Another example of an epoxidation reaction involves epoxidation with hydrogen peroxide in a two-phase system consisting of an aqueous phase and an organic phase in the presence of a phase-transfer heteropolyacid prepared from a tungsten- or molybdenum-containing heteropolyacid (particularly, 12-tungstophosphoric acid) and a surfactant (particularly, a quaternary ammonium halide). The amounts of epoxidizing agent and catalyst used are not particularly limited and can be appropriately determined depending on the type of polymer to be epoxidized, the type of epoxidizing agent, the degree of epoxidation of the polymer to be epoxidized, and other factors.

[0169] The epoxidation reaction can be carried out in the absence of a solvent, or in the presence of a solvent inert to the epoxidizing agent, etc. Solvents that can be used in carrying out the epoxidation reaction include aliphatic hydrocarbons such as hexane and heptane, esters such as ethyl acetate, aromatic hydrocarbons such as benzene and xylene, and halogenated hydrocarbons such as chloroform and carbon tetrachloride.

[0170] The reaction temperature of the above epoxidation reaction is generally in the range of 0 to 140°C, preferably 0 to 80°C, and more preferably 10 to 40°C, from the viewpoints of reaction rate, reaction selectivity, safety, etc. If the reaction temperature is too low, the reaction rate tends to decrease, and conversely, if the reaction temperature is too high, side reactions such as ring-opening reactions of the epoxy group tend to occur. From the viewpoint of safety, the reaction is preferably carried out in an inert gas atmosphere such as nitrogen or argon. The reaction time can be appropriately set depending on the desired epoxidation rate and is, for example, 1 to 48 hours, preferably 4 to 36 hours, and more preferably 8 to 36 hours.

[0171] The average number of epoxy groups per molecule of the functional group-modified conjugated diene polymer (F) is preferably 2 to 150, more preferably 3 to 90, and even more preferably 4 to 70.

[0172] The average number of epoxy groups per molecule of the functional group-modified conjugated diene polymer (F) is calculated from the following formula (4) using the epoxy equivalent (g / eq) contained in the functional group-modified conjugated diene polymer (F) and the number average molecular weight (Mn) of the functional group-modified conjugated diene polymer (F) converted into standard polystyrene: (average number of epoxy groups per molecule of the functional group-modified conjugated diene polymer (F)) = [(number average molecular weight Mn of the functional group-modified conjugated diene polymer (F)) / (molecular weight of styrene unit) × (average molecular weight of the conjugated diene unit and other monomer units other than the conjugated diene contained as needed in the functional group-modified conjugated diene polymer (F)] / (epoxy equivalent) (4)

[0173] The epoxy equivalent of the epoxy group contained in the functional group-modified conjugated diene polymer (F) means the mass of the conjugated diene bonded to one epoxy group and the mass of other monomers other than the conjugated diene that are contained as needed. 1 It is calculated from the area ratio of the peak derived from the epoxy group and the peak derived from the polymer main chain using H-NMR.

[0174] The preferred embodiments of the number average molecular weight (Mn), vinyl content, Tg, etc. of the functional group-modified conjugated diene polymer (F) are the same as those of the unmodified conjugated diene polymer (F').

[0175] The melt viscosity of the functional group-modified conjugated diene polymer (F) measured at 38° C. is preferably 0.01 to 2,000 Pa s, more preferably 0.05 to 1,500 Pa s, and even more preferably 0.1 to 1,000 Pa s. When the melt viscosity of the functional group-modified conjugated diene polymer (F) is within the above range, the processability during production tends to be excellent, and the economic efficiency tends to be good.

[0176] In step (E), the active terminal polymer (I) is reacted with the functional group-modified conjugated diene polymer (F), whereby the epoxy groups in the functional group-modified conjugated diene polymer (F) react with the active terminal polymer (I), forming a conjugated diene graft polymer in which the active terminal polymer (I) serving as a side chain is bonded to the main chain (a) (hereinafter, this reaction is referred to as a coupling reaction). An example of the coupling reaction when an epoxy-modified polybutadiene is used as the functional group-modified conjugated diene polymer (F) is shown in the following formula (II).

[0177] (In formula (II), P represents a polymer chain containing at least one monomer unit selected from the group consisting of a conjugated diene unit and an aromatic vinyl compound unit.)

[0178] In the coupling reaction or the hydrogenation or washing step described below, the epoxy group in the functional group-modified conjugated diene polymer (F) undergoes ring-opening, thereby forming a hydroxyl group bonded to the main chain (a) of the conjugated diene graft polymer. When a hydroxyl group is formed by this synthesis method, the hydroxyl group is directly bonded to an atom (typically a carbon atom) constituting the main chain (a) other than the atom bonded to the side chain (b).

[0179] The average number of epoxy groups per molecule of the functional group-modified conjugated diene polymer (F) can be appropriately set depending on the average number of hydroxyl groups bonded to the main chain (a). For example, when the average number of epoxy groups per molecule of the functional group-modified conjugated diene polymer (F) is 4, the average number of hydroxyl groups bonded to the main chain (a) per molecule of the finally obtained conjugated diene graft polymer can be designed to be 4.

[0180] The average number of side chains (b) per molecule of the conjugated diene graft polymer can be adjusted to a desired range by adjusting the ratio of the amounts of the active terminal polymer (I) and the functional group-modified conjugated diene polymer (F) charged in the coupling reaction. For example, when (the amount (moles) of the active terminal polymer (I) charged) / (the amount (moles) of the functional group-modified conjugated diene polymer (F) charged)=4 / 1, the average number of side chains (b) is 4. However, the upper limit of the average number of side chains (b) is the number of epoxy groups per molecule of the functional group-modified conjugated diene polymer (F).

[0181] The molar ratio of (charge amount of active terminal polymer (I)) / (charge amount of functional group-modified conjugated diene polymer (F)) may be appropriately set so that the average number of side chains (b) per molecule of the conjugated diene graft polymer is a desired value, and is, for example, preferably 2 to 200, more preferably 4 to 100, and even more preferably 5 to 50. If the molar ratio of (charge amount of active terminal polymer (I)) / (charge amount of functional group-modified conjugated diene polymer (F)) is less than 2, the number of side chains that can be introduced decreases, and if it is more than 200, the coupling rate, which will be described later, tends to decrease.

[0182] The coupling reaction is typically carried out at a temperature ranging from 0 to 100°C for 0.5 to 50 hours. The functional group-modified conjugated diene polymer (F) may be diluted before use. The dilution solvent is not particularly limited as long as it is inert to the active terminals and does not adversely affect the reaction. Examples of the dilution solvent include saturated aliphatic hydrocarbons or aromatic hydrocarbons such as hexane, cyclohexane, heptane, octane, decane, toluene, benzene, and xylene. A Lewis base may also be added as an additive during the coupling reaction. Examples of Lewis bases include ethers such as dimethyl ether, diethyl ether, and tetrahydrofuran; glycol ethers such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether; and amines such as triethylamine, N,N,N',N'-tetramethylethylenediamine, and N-methylmorpholine. These Lewis bases may be used alone or in combination.

[0183] In the coupling reaction, the functional group-modified conjugated diene polymer (F) may be added to the reaction system in which the active terminal polymer (I) has been synthesized, or conversely, the active terminal polymer (I) may be added to a system containing the functional group-modified conjugated diene polymer (F). As described above, both the active terminal polymer (I) and the functional group-modified conjugated diene polymer (F) may be diluted with a solvent as necessary. The active terminal polymer (I) may be used alone or in combination of two or more types, and the functional group-modified conjugated diene polymer (F) may be used alone or in combination of two or more types.

[0184] The coupling rate in the coupling reaction is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. A coupling rate of less than 40% is not preferred because the mechanical properties of the resulting conjugated diene graft polymer will be reduced. The coupling rate is calculated from the peak area of ​​the component derived from the active terminal polymer (I) that has not undergone coupling reaction and the sum of all peak areas obtained by GPC measurement using the following formula (4): (Coupling rate (%)) = [{(Sum of all peak areas) - (Peak area of ​​the component derived from the active terminal polymer (I))} / (Sum of all peak areas)] × 100 (4)

[0185] The coupling rate can be increased by increasing the amount of functional group-modified conjugated diene polymer (F) added relative to the active terminal polymer (I), increasing the amount of Lewis base added relative to the active terminal polymer (I), increasing the reaction temperature, or extending the reaction time. The coupling reaction can be carried out until the coupling rate reaches the desired range. Thereafter, the coupling reaction can be terminated by adding a polymerization terminator such as methanol or isopropanol.

[0186] The conjugated diene graft polymer obtained by the production method including steps (E) and (D) but not including step (C) described in detail below is a non-hydrogenated conjugated diene graft polymer.

[0187] [Step (C)] In one preferred embodiment, the method for producing a conjugated diene graft polymer of the present invention includes, before step (D), (C) a step of hydrogenating at least a portion of the carbon-carbon double bonds contained in the conjugated diene units in the conjugated diene graft polymer.

[0188] The unhydrogenated conjugated diene graft polymer obtained by the above method can be subjected to a hydrogenation step to obtain a hydrogenated conjugated diene graft polymer. There are no particular limitations on the method for hydrogenating the conjugated diene graft polymer, and a method similar to the method for hydrogenating the conjugated diene graft polymer described as step (C) of the above-mentioned MI method can be applied.

[0189] [Step (D)] The method for producing a conjugated diene graft polymer of the present invention includes: (D) a step of recovering the obtained conjugated diene graft polymer.

[0190] In step (D), the obtained conjugated diene graft polymer used in the present invention is recovered. There are no particular limitations on the method for recovering the conjugated diene graft polymer, and the same method as the method for recovering the conjugated diene graft polymer described as step (D) of the above-mentioned MI method can be applied.

[0191] An antioxidant may be added to the conjugated diene graft polymer of the present invention, if necessary, in any of the above-mentioned steps. For example, it may be added after step (E), or after step (C) or at any stage therebetween, or after step (D) or at any stage therebetween. Preferred antioxidants to be used in this case are the same as those exemplified in the steps of the MI method described above.

[0192] [Lubricating oil additive] The conjugated diene graft polymer of the present invention can be suitably used as a lubricating oil additive. Preferred embodiments of the conjugated diene graft polymer of the present invention when used as a lubricating oil additive are the same as the preferred embodiments of the conjugated diene graft polymer. Examples of lubricating oil additives include viscosity index improvers and friction inhibitors, which will be described later.

[0193] [Viscosity index improver] The conjugated diene graft polymer of the present invention can be suitably used as a viscosity index improver. Preferred embodiments when using the conjugated diene graft polymer of the present invention as a viscosity index improver are the same as the preferred embodiments of the conjugated diene graft polymer described above.

[0194] [Friction Inhibitor] The conjugated diene graft polymer of the present invention can be suitably used as a friction inhibitor. Preferred embodiments of the conjugated diene graft polymer of the present invention when used as a friction inhibitor are the same as the preferred embodiments of the conjugated diene graft polymer described above.

[0195] [Oil Composition] The oil composition of the present invention comprises a base oil and a lubricating oil additive (preferably a viscosity index improver or a friction inhibitor) comprising the conjugated diene graft polymer of the present invention.

[0196] [Base Oil] The base oil is not particularly limited, and known base oils can be used, for example. Examples of base oils include fuel oils such as middle distillate fuels, synthetic and natural lubricating oils, unrefined oils, and industrial oils. The base oil may be at least one of paraffinic base oils, naphthenic base oils, and aromatic base oils, or at least one of natural oils and synthetically prepared oils. The base oil may be any of Groups I to V of the API (American Petroleum Institute) classification, but from an economical standpoint, Groups I to III are preferred. Examples of base oils that can be used in the oil composition of the present invention include the base oils described in Japanese Patent No. 5,933,263 and Japanese Patent Application Laid-Open No. 2005-23320.

[0197] [Lubricant Additive (Viscosity Index Improver, Friction Repressor) Content] The oil composition of the present invention contains a lubricant additive (viscosity index improver, friction suppressor) comprising the conjugated diene graft polymer of the present invention. The content of the lubricant additive (viscosity index improver, friction suppressor) in the oil composition can be adjusted as appropriate so that the viscosity, viscosity index, or friction characteristics of the lubricant fall within the desired range, but is preferably 0.1 to 20 mass%, more preferably 0.5 to 15 mass%, and particularly preferably 0.5 to 10 mass%. When the content of the lubricant additive (viscosity index improver, friction suppressor) is within the above range, the lubricant tends to have an excellent balance between performance and economy.

[0198] [Other Additives] The oil composition of the present invention may contain additives such as rust inhibitors, antioxidants, surfactants, pour point depressants, detergents and dispersants, metal deactivators, antifoaming agents, friction modifiers, extreme pressure agents, etc. These additives may be used alone or in combination of two or more.

[0199] [Method for Producing Oil Composition] The method for producing the oil composition of the present invention is not particularly limited as long as it is possible to produce the oil composition. For example, the oil composition can be produced by mixing the above-mentioned base oil with the above-mentioned lubricating oil additives (viscosity index improver, friction inhibitor). Mixing can be carried out using, for example, a known mixing device. Mixing is preferably carried out while heating. The heating temperature is preferably 80 to 180°C.

[0200] When the oil composition of the present invention is used as an engine oil, automatic transmission fluid, gear lubricant, hydraulic oil, etc., its kinematic viscosity at 40°C is 20 to 300 mm 2 / sec is preferable, and 25 to 150 mm 2 From the same viewpoint, the kinematic viscosity at 100°C is preferably in the range of 3 to 30 mm / sec. 2 / sec is preferable, and 4 to 20 mm 2 When the kinematic viscosity is within this range, the fuel consumption of a vehicle can be reduced when the composition is used for the above-mentioned purposes. In the present invention, the kinematic viscosity is a value measured in accordance with JIS K2283:2000.

[0201] When the oil composition of the present invention is used as an engine oil, automatic transmission fluid, gear lubricant, hydraulic oil, etc., its shear stability is preferably in the range of 0 to 20%, more preferably in the range of 0 to 10%, and particularly preferably in the range of 0 to 4%. In the present invention, the shear stability is determined by the kinematic viscosity at 100°C of 6.9 to 9.3 mm 2 / sec, and the rate of decrease in kinematic viscosity at 100°C was measured in accordance with JPI-5S-29-2006.

[0202] The conjugated diene graft polymer obtained by the present invention can be mixed with the base oil to form an oil composition. The oil composition containing the conjugated diene graft polymer and the base oil can be used, for example, in cosmetic compositions that constitute cosmetic products. Examples of cosmetic products include hair makeup products such as shampoo, hair setting gel or lotion, blow-drying lotion, and fixing and styling agents; skin makeup products such as foundation, eye shadow, blusher, concealer, compact powder, and makeup base; lip makeup products such as lipstick, liquid lipstick, and lip gloss; cleansing products such as facial cleansers and makeup removers; and cream products such as petrolatum cream, hand cream, and ultrasound diagnostic cream. The oil composition can also be used in asphalt modifiers, adhesives, pressure-sensitive adhesives, resin modifiers, compatibilizers, sealants, coating materials, molded articles, fibers and nonwoven fabrics, drilling fluids, and internal buffering agents for cables such as optical fiber cables and electric wire cables.

[0203] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following examples and comparative examples, the physical properties of the conjugated diene graft polymers were evaluated by the following methods.

[0204] (1) Weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of the conjugated diene graft polymer and the polymer at each stage of its production were determined in terms of standard polystyrene by gel permeation chromatography (GPC). Apparatus: GPC apparatus "HLC-8220" manufactured by Tosoh Corporation Separation column: "TSKgel SuperMultiporeHZ-M (column diameter = 4.6 mm, column length = 15 cm)" manufactured by Tosoh Corporation (two columns connected in series) Eluent: tetrahydrofuran Eluent flow rate: 0.35 mL / min Column temperature: 40°C Detection method: differential refractive index (RI) Injection volume: 10 μl Concentration: 1 mg / 1 cc (conjugated diene graft polymer / THF)

[0205] (2) Vinyl content, styrene unit (structural unit derived from styrene) content, hydrogenation rate 1 The vinyl content, styrene unit content, and hydrogenation rate of the conjugated diene graft polymer and the polymer at each stage of its production were calculated by H-NMR. The vinyl content was calculated from the area ratio of the peak of the double bond derived from the vinylated conjugated diene unit to the peak of the double bond derived from the non-vinylated conjugated diene unit in the obtained spectrum, and the styrene unit content was calculated from the area ratio of the peak of the aromatic ring derived from the styrene unit to the peak of the double bond derived from the conjugated diene unit. The vinyl content and styrene unit content were calculated from the area ratio of the peak of the aromatic ring derived from the styrene unit to the peak of the double bond derived from the conjugated diene unit of the conjugated diene graft polymer before hydrogenation. 1 The hydrogenation rate was determined using H-NMR. The hydrogenation rate was calculated from the ratio of the peaks of double bonds derived from conjugated diene units in the conjugated diene graft polymer before hydrogenation and the conjugated diene graft polymer after hydrogenation. Apparatus: Nuclear magnetic resonance apparatus "JNM-ECX400" manufactured by JEOL Ltd. Solvent: deuterated chloroform Measurement temperature: 50°C Number of accumulations: 1024

[0206] (3) Average Number of Side Chains (b) Per Molecule of Conjugated Diene Graft Polymer The average number of side chains (b) per molecule of conjugated diene graft polymer was calculated from the charge ratio of the organic alkali metal used in the lithiation reaction, the conjugated diene polymer that forms the structural unit of the main chain, and the functionalizing agent added as needed, when the conjugated diene graft polymer was produced by a method in which a previously synthesized conjugated diene polymer described below was reacted with an organic alkali metal compound in the presence of tetramethylethylenediamine to lithiate the main chain, and then a monomer that forms the structural unit of the side chain was polymerized. Also, when the conjugated diene graft polymer was produced by a method in which an epoxy group contained in a monomer unit that forms the branching portion of a functionally modified polymer that forms the main chain (a) described below reacts with an active terminal of a polymer obtained by polymerizing a monomer that forms the structural unit of the side chain, the average number of side chains (b) per molecule was calculated from the charge ratio of the active terminal polymer that forms the component of the side chain (b) in the coupling reaction to the functionally modified conjugated diene polymer.

[0207] (4) Side Chain Density of Side Chain (b) The side chain density of the side chain (b) was calculated from the average number of side chains (b) per molecule of the conjugated diene graft polymer and the number average molecular weight (Mn) of the main chain (a) in terms of standard polystyrene, according to the following formula (1): (Side Chain Density) = (Average Number of Side Chains (b) per Molecule of the Conjugated Diene Graft Polymer) / [(Number Average Molecular Weight Mn of the Main Chain (a)) / (Molecular Weight of Styrene Unit)] × 100 (1)

[0208] (5) Average Number of Hydroxyl Groups Bonded to the Main Chain (a) Per Molecule of Conjugated Diene Graft Polymer As described above, the average number of hydroxyl groups bonded to the main chain (a) per molecule of conjugated diene graft polymer is determined from the following formula (2) using the hydroxyl value (mg KOH / g) of the conjugated diene graft polymer calculated in accordance with JIS K1557-1:2007 and the number average molecular weight (Mn) of the conjugated diene graft polymer in terms of standard polystyrene. (Average Number of Hydroxyl Groups Bonded to the Main Chain (a) Per Molecule of Conjugated Diene Graft Polymer)={(Hydroxyl Value of Conjugated Diene Graft Polymer) / [(Molecular Weight of Potassium Hydroxide)×1000]}×(Number Average Molecular Weight Mn of Conjugated Diene Graft Polymer)×[(Average Molecular Weight of Monomer Units Contained in Conjugated Diene Graft Polymer) / (Molecular Weight of Styrene Unit)] (2)

[0209] (6) Hydroxyl Group Concentration The concentration of hydroxyl groups bonded to the main chain (a) is calculated from the average number of hydroxyl groups bonded to the main chain (a) per molecule of the conjugated diene graft polymer and the number average molecular weight (Mn) of the main chain (a) in terms of standard polystyrene, using the following formula (3): (Hydroxyl Group Concentration) = (Average Number of hydroxyl groups bonded to the main chain (a) per molecule of the conjugated diene graft polymer) / [(Number Average Molecular Weight Mn of the Main Chain (a)) / (Molecular Weight of Styrene Unit)] × 100 (3)

[0210] (7) Viscosity index: SK Lubricants Group III base oil "YUBASE 4" is used as the base oil, and the kinematic viscosity at 100 ° C is 6.9 to 9.3 mm 2 The viscosity index of an oil composition consisting of a base oil / conjugated diene graft polymer adjusted to have a viscosity of 1 / sec was measured in accordance with JIS K2283:2000.

[0211] (8) Friction coefficient (relative value) SK Lubricants Group III base oil "YUBASE4" was used as the base oil, and the kinematic viscosity at 100 ° C. was 6.0 mm 2 An oil composition consisting of a base oil / conjugated diene graft polymer was prepared so that the friction coefficient was 1 / sec. The absolute value of the friction coefficient of the obtained oil composition was measured under the following conditions using an MTM mini-traction tester manufactured by PCS Instruments. Furthermore, as a reference oil not containing a conjugated diene graft polymer, Group III base oils "YUBASE 4" and "YUBASE 6" manufactured by SK Lubricants Co., Ltd., having a kinematic viscosity of 6.0 mm at 100°C, were used. 2 The friction coefficient was measured in the same manner for oil compositions mixed so that the friction coefficient was 1 / sec. The friction-reducing effect of the conjugated diene graft polymer was evaluated based on the relative value when the friction coefficient of the reference oil was set to 100. <Measurement conditions> Temperature: 100°C Load: 40 N Peripheral speed: 50 mm / s Slide ratio: 50% Materials: steel ball, steel disc

[0212] Example 1 (Step (1)) A thoroughly dried 5 L autoclave was purged with nitrogen, and 1,430 g of cyclohexane, 223 g of sec-butyllithium (10.5 mass % cyclohexane solution), and 15 g of tetrahydrofuran were charged. The autoclave was then heated to 50°C, and 1,350 g of butadiene was gradually added thereto while stirring and controlling the polymerization temperature to 50°C, allowing polymerization for 1 hour. Thereafter, 13 g of methanol was added to terminate the polymerization reaction, thereby obtaining a polymer solution. Water was added to the obtained polymer solution, and the mixture was stirred. The polymer solution was washed with water. After stirring was stopped, it was confirmed that the polymer solution phase and the aqueous phase had separated, and then the water was separated. The polymer solution after washing was vacuum dried at 70°C for 24 hours to obtain an unmodified conjugated diene-based polymer (F'-1).

[0213] (Step (2)) Subsequently, 200 g of the unmodified conjugated diene polymer (F′-1) obtained in step (1), 3,800 g of chloroform, 12-tungstophosphoric acid hydrate (HPW 12 O 40 60 g of hexadecylpyridinium chloride (30H2O), 60 g of hexadecylpyridinium chloride, and 51 g of 35 wt% hydrogen peroxide were charged and stirred at room temperature for 15 hours under a nitrogen atmosphere. After the reaction, water was added and stirred. The aqueous phase was removed and washed with a 10 wt% aqueous solution of sodium hydrogen sulfite. Silica gel (manufactured by Wako Pure Chemical Industries, Ltd., trade name "C-200") was added to the separated organic phase, and the mixture was stirred for 1 hour and then filtered. The filtrate was vacuum dried at 70°C for 24 hours to obtain a functional group-modified conjugated diene polymer (F-1). The number average molecular weight and vinyl content of the main chain (a) of the conjugated diene graft polymer (G-1), which will be described later, can be determined by analyzing the obtained functional group-modified conjugated diene polymer (F-1). The resulting functional group-modified conjugated diene polymer (F-1) had a number average molecular weight of 7,000, a vinyl content of 50 mol%, and the average number of epoxy groups per molecule of the functional group-modified conjugated diene polymer (F-1) was 3. 720 g of toluene was added to 180 g of the resulting functional group-modified conjugated diene polymer (F-1) to dilute it to a concentration of 20 mass %, thereby obtaining a diluted solution of the functional group-modified conjugated diene polymer (F-1) to be used in the coupling reaction described below.

[0214] (Step (3)) A thoroughly dried 5 L autoclave was purged with nitrogen, and 1,670 g of toluene and 80 g of sec-butyllithium (10.5 mass % cyclohexane solution) were charged. The temperature was raised to 50°C, and then 440 g of isoprene was gradually added under stirring conditions while controlling the polymerization temperature to 50°C. Polymerization was carried out for 1 hour to obtain an active terminal polymer (I-1). By sampling and analyzing the polymer solution in step (3), the number average molecular weight, vinyl content, and styrene unit content of the side chain (b) of the conjugated diene graft polymer (G-1) described below can be determined. The number average molecular weight of the obtained active terminal polymer (I-1) was 5,000, the vinyl content was 10 mol%, and the styrene unit content was 0 mass%.

[0215] (Step (4)) Subsequently, 810 g of the diluted solution of the functional group-modified conjugated diene polymer (F-1) obtained in step (2) was added to the solution containing the active terminal polymer (I-1) obtained in step (3), and a coupling reaction was carried out for 2 hours at 50° C. Thereafter, 8.7 g of methanol was added to terminate the reaction, and a polymer solution was obtained.

[0216] (Step (5)) To the obtained polymer solution, 450 mL of a Ziegler hydrogenation catalyst (0.095 mmol / L cyclohexane solution) formed from nickel octylate and trimethylaluminum was added, and the mixture was reacted for 10 hours under conditions of a hydrogen pressure of 1 MPa and 80°C to obtain a solution containing a conjugated diene graft polymer (G-1).

[0217] (Step (6)) Water was added to the obtained polymer solution and stirred, and the polymer solution was washed with water. After stirring was stopped and it was confirmed that the polymer solution phase and the aqueous phase had separated, the water was separated. After washing was completed, the polymer solution was vacuum dried at 70°C for 24 hours to recover a conjugated diene graft polymer (G-1). The obtained conjugated diene graft polymer (G-1) had a weight average molecular weight of 22,000, an Mw / Mn of 1.5, a content of structural units derived from styrene of 0% by mass, a hydrogenation rate of 85 mol%, an average number of hydroxyl groups bonded to the main chain per polymer molecule of 3, a hydroxyl group concentration of 4.5 mol%, an average number of side chains (b) per polymer molecule of 3, and a side chain density of 4.5 mol%. Furthermore, the atom bonded to the side chain (b) contained in the monomer unit that becomes the branched portion is not a heteroatom, and the linking portion including the atom bonded to the side chain (b) is not an aromatic group derived from an aromatic vinyl compound. The molecular specifications and physical properties of the obtained conjugated diene graft polymer (G-1) are shown in Table 3.

[0218] Examples 2 to 4 Conjugated diene graft polymers (G-2) to (G-4) were obtained in the same manner as in Example 1, except that the types and amounts of the reagents used in steps (1) to (5) were changed as shown in Table 1. The molecular specifications and physical properties of the obtained conjugated diene graft polymers (G-2) to (G-4) are shown in Table 3.

[0219] Example 5 (Step (1)) A thoroughly dried 5 L autoclave was purged with nitrogen, and 1,470 g of cyclohexane and 177 g of sec-butyllithium (10.5 mass % cyclohexane solution) were charged. The temperature was raised to 50°C, and then 1,350 g of isoprene was gradually added under stirring conditions while controlling the polymerization temperature to 50°C, and polymerization was carried out for 1 hour. Thereafter, 10 g of methanol was added to terminate the polymerization reaction, thereby obtaining a polymer solution. Water was added to the obtained polymer solution, and the mixture was stirred. The polymer solution was washed with water. After stirring was stopped, separation of the polymer solution phase and the aqueous phase was confirmed, and then the water was separated. The polymer solution after washing was vacuum dried at 70°C for 24 hours to obtain a conjugated diene polymer (M-1). The obtained conjugated diene polymer (M-1) can be analyzed to determine the number average molecular weight and vinyl content of the main chain (a) of the conjugated diene graft polymer (G-5) described below. The resulting conjugated diene polymer (M-1) had a number average molecular weight of 7,000 and a vinyl content of 10 mol %.

[0220] (Step (2)) Subsequently, 111 g of the conjugated diene polymer (M-1) obtained in step (1) was charged into a thoroughly dried 5 L autoclave, and the polymer was degassed with nitrogen and the air inside the autoclave was replaced with nitrogen while stirring at 60° C. for 3 hours. 1,230 g of cyclohexane was charged, and the temperature was raised to 40° C., after which 87 g of sec-butyllithium (10.5 mass % cyclohexane solution) and 9.2 g of N,N,N′,N′-tetramethylethylenediamine were successively added, and a lithiation reaction was carried out at 40° C. for 1 hour.

[0221] (Step (3)) Subsequently, 1,370 g of cyclohexane was added to dilute the reaction solution, and the temperature was again raised to 40° C. Thereafter, 9.3 g of 2-ethylhexylaldehyde was added, and the mixture was stirred at 40° C. for 1 hour to functionalize a portion of the lithiated anion active sites.

[0222] (Step (4)) While controlling the polymerization temperature to 40°C, 190 g of butadiene was gradually added, and polymerization was carried out for 2 hours. Thereafter, 7.0 g of methanol was added to terminate the polymerization reaction, yielding a polymer solution. From the amounts of reagents charged in step (3) and analysis of the polymer solution in step (3), the number average molecular weight, vinyl content, and styrene unit content of the side chain (b) of the conjugated diene graft polymer (G-5), which will be described later, can be determined. The number average molecular weight of the side chain (b) of the conjugated diene graft polymer (G-1) was 5,000, the vinyl content was 75 mol%, and the styrene unit content was 0 mass%.

[0223] (Step (5)) To the obtained polymer solution, 450 mL of a Ziegler hydrogenation catalyst (0.095 mmol / L cyclohexane solution) formed from nickel octylate and trimethylaluminum was added, and the mixture was reacted for 10 hours under conditions of a hydrogen pressure of 1 MPa and 80°C, thereby obtaining a solution containing a conjugated diene graft polymer (G-5).

[0224] (Step (6)) Water was added to the obtained polymer solution and stirred, and the polymer solution was washed with water. After stirring was stopped and it was confirmed that the polymer solution phase and the aqueous phase had separated, the water was separated. After washing was completed, the polymer solution was vacuum dried at 70°C for 24 hours to recover a conjugated diene graft polymer (G-5). The obtained conjugated diene graft polymer (G-5) had a weight average molecular weight of 22,000, an Mw / Mn of 1.5, a content of structural units derived from styrene of 0% by mass, a hydrogenation rate of 85 mol%, an average number of hydroxyl groups bonded to the main chain per polymer molecule of 3, a hydroxyl group concentration of 4.5 mol%, an average number of side chains (b) per polymer molecule of 3, and a side chain density of 4.5 mol%. Furthermore, the atom bonded to the side chain (b) contained in the monomer unit that becomes the branched portion is not a heteroatom, and the linking portion including the atom bonded to the side chain (b) is not an aromatic group derived from an aromatic vinyl compound. The molecular specifications and physical properties of the obtained conjugated diene graft polymer (G-5) are shown in Table 3.

[0225] Examples 6 to 10 Conjugated diene graft polymers (G-6) to (G-8) and (G-11) to (G-12) were obtained by the same method as in Example 5, except that the types and amounts of each reagent used in steps (1) to (5) were changed as shown in Table 2. In Examples 9 to 10, TMEDA (polar compound) used in step (1) was added immediately before the addition of butadiene after cyclohexane and sec-butyllithium were charged into a 5 L autoclave. The molecular specifications and physical properties of the obtained conjugated diene graft polymers (G-6) to (G-8) and (G-11) to (G-12) are shown in Table 3.

[0226] Comparative Example 1 A conjugated diene graft polymer (G-9) was obtained in the same manner as in Example 1, except that the types and amounts of the reagents used in steps (1) to (5) were changed as shown in Table 1. The molecular specifications and physical properties of the obtained conjugated diene graft polymer (G-9) are shown in Table 3.

[0227] Comparative Examples 2 to 3 Conjugated diene graft polymers (G-10) and (G-13) not having hydroxyl groups bonded to the main chain were obtained by the same method as in Example 5, except that the types and amounts of the reagents used in steps (1), (2), (4), and (5) were changed as shown in Table 2 and the functionalization reaction in step (3) was not performed. In Comparative Example 3, TMEDA (polar compound) used in step (1) was added immediately before the addition of butadiene after cyclohexane and sec-butyllithium were charged into a 5 L autoclave. The molecular specifications and physical properties of the obtained conjugated diene graft polymers (G-10) and (G-13) are shown in Table 3.

[0228] The types and amounts of the reagents used in steps (1) to (5) in Examples 1 to 10 and Comparative Examples 1 to 3 are shown in Tables 1 and 2 below, and the molecular specifications and physical properties of the conjugated diene graft polymers obtained in Examples 1 to 10 and Comparative Examples 1 to 3 are shown in Table 3.

[0229]

[0230] In Table 1, the abbreviations have the following meanings: SBL: sec-butyllithium (10.5 mass % cyclohexane solution) THF: tetrahydrofuran HPC: hexadecylpyridinium chloride Bd: butadiene Ip: isoprene

[0231]

[0232] In Table 2, the abbreviations have the following meanings: SBL: sec-butyllithium (10.5 mass % cyclohexane solution) TMEDA: N,N,N',N'-tetramethylethylenediamine 2-EHA: 2-ethylhexylaldehyde BzA: benzaldehyde Bd: butadiene Ip: isoprene

[0233]

[0234] It can be seen from Table 3 that the lubricating oil additives (viscosity index improvers) composed of the conjugated diene graft polymers of Examples 1 to 10 have a superior viscosity index than the lubricating oil additives (viscosity index improvers) composed of the conjugated diene graft polymers of Comparative Examples 1 to 3. It can also be seen that the lubricating oil additives (friction inhibitors) composed of the conjugated diene graft polymers of Examples 8 to 10 have a superior friction-reducing effect than the lubricating oil additives (friction inhibitors) composed of the conjugated diene graft polymers of Comparative Examples 1 and 3.

[0235] When the conjugated diene graft polymer of the present invention is used as a viscosity index improver, the viscosity index improver has a high viscosity index. Furthermore, when the conjugated diene graft polymer of the present invention is used as a friction inhibitor, the friction inhibitor has a good friction-reducing effect. Therefore, the conjugated diene graft polymer of the present invention is useful as a lubricating oil additive, for example, a viscosity index improver or a friction inhibitor, for lubricating oils used in engine oils and automatic transmission fluids.

Claims

1. A conjugated diene graft polymer comprising: a main chain (a) made of a polymer containing a conjugated diene unit; and a side chain (b) made of a polymer containing at least one monomer unit selected from the group consisting of a conjugated diene unit and an aromatic vinyl compound unit, the side chain (b) is bonded to an atom contained in a monomer unit that becomes a branched portion contained in the main chain (a), The number average molecular weight of the main chain (a) is 5,000 or more, A conjugated diene graft polymer having a hydroxyl group bonded to the main chain (a).

2. 2. The conjugated diene graft polymer according to claim 1, wherein the main chain (a) contains 3.0 mol % or more of hydroxyl groups.

3. 2. The conjugated diene graft polymer according to claim 1, wherein the main chain (a) has a number average molecular weight of 20,000 or more.

4. 2. The conjugated diene graft polymer according to claim 1, wherein at least a portion of the carbon-carbon double bonds contained in the conjugated diene units in the conjugated diene graft polymer are hydrogenated.

5. 5. The conjugated diene graft polymer according to claim 4, wherein 50 mol % or more of the carbon-carbon double bonds contained in the conjugated diene units in the conjugated diene graft polymer are hydrogenated.

6. The conjugated diene graft polymer according to claim 1 , wherein the average number of the side chains (b) per molecule of the conjugated diene graft polymer is 2 or more.

7. the atom bonded to the side chain (b) contained in the monomer unit that becomes the branched portion is not a heteroatom, The conjugated diene graft polymer according to claim 1, wherein a linking moiety including an atom bonded to the side chain (b) contained in the monomer unit that becomes the branching moiety is not an aromatic group derived from an aromatic vinyl compound.

8. (A-1) a step of reacting a polymer (M) containing a conjugated diene unit with an organolithium compound in the presence of a polar compound to lithiate an anion active site contained in the polymer (M); (A-2) adding a functionalizing agent to functionalize a portion of the lithiated anion active sites; (B) adding at least one monomer selected from the group consisting of conjugated dienes and aromatic vinyl compounds to polymerize the remaining lithiated anion active sites in the polymer (M) to form side chains on the main chain of the polymer (M), thereby preparing a conjugated diene-based graft polymer; and (D) a step of recovering the obtained conjugated diene graft polymer; The method for producing the conjugated diene graft polymer according to any one of claims 1 to 7, comprising:

9. Furthermore, after step (A-2), (A-3) adding a Lewis acid; The method for producing the conjugated diene graft polymer according to claim 8, comprising:

10. (E) an active terminal polymer represented by the following formula (I); P-X (I) (In formula (I), P represents a polymer chain containing at least one monomer unit selected from the group consisting of a conjugated diene unit and an aromatic vinyl compound unit, and X represents an active end of anionic polymerization.) A step of reacting a functional group-modified conjugated diene polymer having an epoxy group to prepare a conjugated diene graft polymer; and (D) a step of recovering the obtained conjugated diene graft polymer; The method for producing the conjugated diene graft polymer according to any one of claims 1 to 7, comprising:

11. Furthermore, after step (B) or step (E) and before step (D), (C) A step of hydrogenating at least a portion of the carbon-carbon double bonds contained in the conjugated diene units in the conjugated diene graft polymer. The method for producing the conjugated diene graft polymer according to claim 8, comprising:

12. Further, after the step (B) or the step (E) and before the step (D), (C) A step of hydrogenating at least a portion of the carbon-carbon double bonds contained in the conjugated diene units in the conjugated diene graft polymer. The method for producing the conjugated diene graft polymer according to claim 10, comprising:

13. A lubricating oil additive comprising the conjugated diene graft polymer according to any one of claims 1 to 7.

14. A viscosity index improver comprising the conjugated diene graft polymer according to any one of claims 1 to 7.

15. A friction suppressant comprising the conjugated diene graft polymer according to any one of claims 1 to 7.

16. 14. An oil composition comprising a base oil and the lubricating oil additive of claim 13.

17. An oil composition comprising a base oil and the viscosity index improver of claim 14.

18. 16. An oil composition comprising a base oil and the friction inhibitor of claim 15.