WO2025169883A1 - Modified conjugated-diene-based polymer, production method therefor, polymer composition, crosslinked product, and tire - Google Patents

Abstract

This modified conjugated-diene-based polymer is produced by a method comprising: a step in which monomers including a conjugated diene compound are polymerized in the presence of an alkali metal compound (INI) to obtain a conjugated-diene-based polymer having an active terminal; and a step in which the conjugated-diene-based polymer having an active terminal is reacted with a terminal modifier. The alkali metal compound (INI) includes a compound having a nitrogen atom and an alkali metal element, and the terminal modifier includes a compound having a sulfur atom. Alternatively, the alkali metal compound (INI) includes a compound having a sulfur atom and an alkali metal element, and the terminal modifier includes a compound having a nitrogen atom.

Description

Modified conjugated diene polymer, method for producing the same, polymer composition, crosslinked product, and tire

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to Japanese Patent Application No. 2024-16701, filed February 6, 2024, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a modified conjugated diene-based polymer, a method for producing the same, a polymer composition, a crosslinked product, and a tire.

Conjugated diene polymers obtained by polymerization using conjugated diene compounds have excellent properties such as heat resistance, abrasion resistance, mechanical strength, and moldability, and are therefore widely used in various industrial products such as pneumatic tires, anti-vibration rubber, and hoses.

It is known that rubber compositions used in the treads and sidewalls of pneumatic tires are blended with fillers such as carbon black and silica along with conjugated diene polymers to improve product durability and abrasion resistance. Furthermore, to increase the affinity between conjugated diene polymers and fillers, it has been proposed to use modified conjugated diene polymers in which heteroatoms such as silicon, nitrogen, oxygen, sulfur, and phosphorus have been introduced into the conjugated diene polymers (see, for example, Patent Documents 1 to 3).

WO 2008/123164 Japanese Patent Application Publication No. 11-349632 International Publication No. 2017/221943

Amid the trend toward electrification and fuel efficiency in automobiles, rubber for automobile tires is required to have even lower rolling resistance than before, as well as high wear resistance and strength.

The present disclosure has been made in consideration of the above-mentioned problems, and one object of the present disclosure is to provide a modified conjugated diene polymer from which a crosslinked product having an improved and balanced rolling resistance, abrasion resistance, and strength can be obtained. Another object of the present disclosure is to provide a polymer composition from which a crosslinked product having an improved and balanced rolling resistance, abrasion resistance, and strength can be obtained. Yet another object of the present disclosure is to provide a crosslinked product or tire having an improved and balanced rolling resistance, abrasion resistance, and strength.

According to one aspect of the present disclosure, there is provided a method for producing a modified conjugated diene polymer, comprising the steps of: polymerizing a monomer containing a conjugated diene compound in the presence of an alkali metal compound (INI) to obtain a conjugated diene polymer having an active end; and reacting the conjugated diene polymer having an active end with a terminal end-modifying agent, wherein the alkali metal compound (INI) comprises a compound having a nitrogen atom and an alkali metal element, and the terminal end-modifying agent comprises a compound having a sulfur atom, or the alkali metal compound (INI) comprises a compound having a sulfur atom and an alkali metal element, and the terminal end-modifying agent comprises a compound having a nitrogen atom.

In another aspect, the present disclosure provides a modified conjugated diene polymer having polymer chains containing structural units derived from a conjugated diene compound, the polymer chains having a first functional group at one end and a second functional group at the other end, or having multiple polymer chains containing structural units derived from a conjugated diene compound and a partial structure derived from a compound having a first functional group, one end of each of the multiple polymer chains being bonded to the partial structure and the other end having a second functional group, one of the first functional group and the second functional group being a nitrogen-containing group and the other being a sulfur-containing group.

In another aspect, the present disclosure provides a modified conjugated diene polymer produced by the above-described production method, or a polymer composition containing the modified conjugated diene polymer and a filler. In another aspect, the present disclosure also provides a crosslinked body obtained by crosslinking the above-described polymer composition. Furthermore, the present disclosure also provides a tire in which one or both of the tread and sidewall are produced using the above-described polymer composition.

The manufacturing method disclosed herein makes it possible to produce a modified conjugated diene polymer that can yield a crosslinked product with a well-balanced improvement in rolling resistance, abrasion resistance, and strength. Furthermore, the modified conjugated diene polymer disclosed herein makes it possible to produce a crosslinked product with a well-balanced improvement in rolling resistance, abrasion resistance, and strength.

The following provides a detailed explanation of matters related to aspects of the present disclosure. It should be understood that the present invention is not limited to the embodiments described below, and includes various modifications that are implemented within the scope of the present invention. In this specification, a numerical range described as "X to Y" represents a numerical range that includes numerical value X as the lower limit and numerical value Y as the upper limit. The term "(meth)acrylic acid" is a concept that includes both "acrylic acid" and "methacrylic acid."

<Modified conjugated diene polymer and method for producing the same>
The modified conjugated diene polymer of the present disclosure (hereinafter also referred to as "modified conjugated diene polymer (P)") is a polymer having a polymer chain containing a structural unit derived from a conjugated diene compound, a first functional group, and a second functional group. The first functional group and the second functional group are functional groups introduced to modify the conjugated diene polymer. Specifically, one of the first functional group and the second functional group is a nitrogen-containing group, and the other is a sulfur-containing group. The modified conjugated diene polymer (P) may have one or more polymer chains.

Specifically, when the modified conjugated diene polymer (P) has one polymer chain, the modified conjugated diene polymer (P) has a first functional group at one end of the polymer chain and a second functional group at the other end. Furthermore, when the modified conjugated diene polymer (P) has two or more polymer chains, the modified conjugated diene polymer (P) has, along with the multiple polymer chains, a partial structure derived from a compound having a first functional group. When the modified conjugated diene polymer (P) has multiple polymer chains, one end of each of the multiple polymer chains is bonded to a partial structure derived from a compound having a first functional group, and the other end has a second functional group. The term "functional group" refers to a group having a specific structure (specifically, a structure containing a heteroatom) within the molecule of an organic compound, and refers to an atomic group or bonding pattern that characterizes the compound.

The modified conjugated diene polymer (P) can be produced by a method including the polymerization step and the modification step shown below, which method satisfies requirement 1 or requirement 2 shown below.
Polymerization step: A step of obtaining a conjugated diene polymer having an active end by polymerizing a monomer containing a conjugated diene compound in the presence of an alkali metal compound (INI). Modification step: A step of reacting a conjugated diene polymer having an active end with a terminal end-modifying agent. (Requirement 1) The alkali metal compound (INI) contains a compound having a nitrogen atom and an alkali metal element, and the terminal end-modifying agent contains a compound having a sulfur atom.
(Requirement 2) The alkali metal compound (INI) includes a compound having a sulfur atom and an alkali metal element, and the terminal modifying agent includes a compound having a nitrogen atom.
Below, a method that satisfies requirement 1 (hereinafter also referred to as the "first method") and a method that satisfies requirement 2 (hereinafter also referred to as the "second method") will be described in order.

<Regarding the first method>
(Polymerization process)
In the polymerization step of the first method, a compound having a nitrogen atom and an alkali metal element (hereinafter also referred to as a "first alkali metal compound") is used as the alkali metal compound (INI), and a monomer containing a conjugated diene compound is polymerized in the presence of the first alkali metal compound.

Examples of conjugated diene compounds include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 1,3-heptadiene, 2-phenyl-1,3-butadiene, 3-methyl-1,3-pentadiene, and 2-chloro-1,3-butadiene. Of these, 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene are preferred. One type of conjugated diene compound may be used alone, or two or more types may be used in combination.

The modified conjugated diene polymer (P) may be a homopolymer of a conjugated diene compound, or a copolymer of a conjugated diene compound and another compound. From the perspective of increasing the strength of the crosslinked product (i.e., rubber) obtained using the modified conjugated diene polymer (P), the modified conjugated diene polymer (P) is preferably a copolymer of a conjugated diene compound and an aromatic vinyl compound.

Aromatic vinyl compounds used in the polymerization include, for example, styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, vinylethylbenzene, divinylbenzene, trivinylbenzene, divinylnaphthalene, t-butoxystyrene, vinylbenzyldimethylamine, (4-vinylbenzyl)dimethylaminoethyl ether, N,N-dimethylaminoethylstyrene, N,N-dimethylaminomethylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 2-t-butylstyrene, 3-t-butylstyrene, vinylxylene, vinylnaphthalene, vinylpyridine, diphenylethylene, and tertiary amino group-containing diphenylethylenes (e.g., 1-(4-N,N-dimethylaminophenyl)-1-phenylethylene). The aromatic vinyl compound is preferably styrene or α-methylstyrene.

When the modified conjugated diene polymer (P) is a copolymer of a conjugated diene compound and an aromatic vinyl compound, it is preferably a copolymer containing 1,3-butadiene and styrene in its monomer composition, as this has high living properties in anionic polymerization. In terms of achieving a well-balanced improvement in hysteresis loss at low and high temperatures, the modified conjugated diene polymer (P) preferably has a random copolymerization portion in which the distribution of the conjugated diene compound and the aromatic vinyl compound is irregular. The modified conjugated diene polymer (P) may further have a block portion made of a conjugated diene compound or an aromatic vinyl compound. In the modified conjugated diene polymer (P), the proportion of the monomers constituting the random copolymerization portion is preferably 65% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more, based on the total amount of monomers used in the polymerization of the modified conjugated diene polymer (P).

When the modified conjugated diene polymer (P) is a copolymer of a conjugated diene compound and an aromatic vinyl compound, the proportion of the aromatic vinyl compound used is preferably 3 to 55 mass%, more preferably 5 to 50 mass%, based on the total amount of the conjugated diene compound and the aromatic vinyl compound used in the polymerization, from the viewpoint of achieving a good balance between the rolling resistance and the wet skid resistance of the resulting crosslinked product. The content of structural units derived from the aromatic vinyl compound in the polymer can be measured by ¹ H-NMR. One type of aromatic vinyl compound may be used alone, or two or more types may be used in combination.

In the above polymerization, compounds other than conjugated diene compounds and aromatic vinyl compounds (hereinafter also referred to as "other monomers") may be used as monomers. Examples of other monomers include acrylonitrile, methyl (meth)acrylate, and ethyl (meth)acrylate. The proportion of other monomers used is preferably 10% by mass or less, and more preferably 5% by mass or less, of the total amount of monomers used in the polymerization.

When producing the modified conjugated diene polymer (P), any of the following methods may be used to polymerize the monomers: solution polymerization, gas phase polymerization, bulk polymerization, etc. Solution polymerization is particularly preferred. Furthermore, either a batch or continuous polymerization method may be used. When using solution polymerization, one specific example of the polymerization method is to polymerize a monomer containing a conjugated diene compound in a solvent in the presence of an alkali metal compound and, if necessary, a vinyl content adjuster.

As the alkali metal compound (INI), at least a first alkali metal compound is used. In terms of ease of introducing a nitrogen-containing group into the initial end of the polymer, the first alkali metal compound is preferably a metal amide compound obtained by mixing a compound having an alkali metal element but no nitrogen atom (hereinafter also referred to as an "organic alkali metal") with a compound having a secondary amino group (hereinafter also referred to as a "first initial end modifier"), or a compound represented by the following formula (4):
(In formula (4), ^R10 is a nitrogen-containing group. ^Y1 is a hydrocarbylene group formed by polymerization of one or both of a conjugated diene compound and an aromatic vinyl compound. ^M1 is an alkali metal. n2 is an integer of 1 to 10.)

Regarding the metal amide compound, the organic alkali metal used to obtain the metal amide compound can be any compound commonly used as a polymerization initiator in the polymerization reaction of a conjugated diene compound. Specific examples of the organic alkali metal include compounds in which a hydrocarbon group is bonded to an alkali metal element. Examples of such organic alkali metals include methyl lithium, ethyl lithium, n-propyl lithium, n-butyl lithium, sec-butyl lithium, t-butyl lithium, 1,4-dilithiobutane, phenyl lithium, stilbene lithium, naphthyl lithium, 1,3-bis(1-lithio-1,3-dimethylpentyl)benzene, 1,3-phenylenebis(3-methyl-1-phenylpentylidene)dilithium, naphthyl sodium, and naphthyl potassium.

The organic alkali metal used to obtain the metal amide compound is preferably a lithium compound, more preferably at least one selected from the group consisting of alkyllithiums and aryllithiums, with alkyllithiums (methyllithium, ethyllithium, n-propyllithium, n-butyllithium, sec-butyllithium, t-butyllithium, etc.) being particularly preferred. One organic alkali metal may be used alone, or two or more may be used in combination.

The first initiating end modifier is not particularly limited as long as it has one or more secondary amino groups. When the first initiating end modifier has a secondary amino group, the hydrogen atoms of the secondary amino group become reaction sites with the organic alkali metal, and the hydrogen atoms are replaced by alkali metal elements, allowing for efficient production of a metal amide compound. From the perspective of efficiently producing a metal amide compound by mixing the first initiating end modifier with the organic alkali metal, the secondary amino group of the first initiating end modifier preferably constitutes part of a ring skeleton, and more preferably constitutes part of a nitrogen-containing aliphatic ring.

Preferred specific examples of the first initiating end-modifying agent include a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (3).
(In formulas (1) and (2), R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently a hydrocarbylene group having 1 to 10 carbon atoms. ^{X 1} is a hydrocarbylene group or —N(A ³ )—. ^{A 1} , A ² and A ³ are each independently a trihydrocarbylsilyl group or a hydrocarbyl group having 1 to 20 carbon atoms.)
(In formula (3), ^A4 is an (i+k)-valent hydrocarbon group having 1 to 20 carbon atoms, or an (i+k)-valent group having 1 to 20 carbon atoms which has a nitrogen atom, no active hydrogen, and is bonded to each of the silicon atom and the nitrogen atom in the formula via a carbon atom. ^R6 and ^R7 are each independently a hydrocarbyl group having 1 to 20 carbon atoms. n1 is an integer of 0 to 2. ^R8 and ^R9 are each independently a hydrocarbylene group having 1 to 10 carbon atoms. i and k are each independently an integer of 1 to 6, provided that i+k≦10 is satisfied. In the formula, when a plurality of ^R6s are present, the plurality of R6s may be the same or different; when ^a plurality of ^R7s are present, the plurality of ^R7s may be the same or different; when a plurality of ^R8s are present, the plurality of ^R8s may be the same or different; and when a plurality of ^R9s are present, the plurality of ^R9s may be the same or different.)

Compounds Represented by the Above Formula (1) or (2) In the above formulas (1) and (2), examples of the hydrocarbyl group having 1 to 20 carbon atoms represented by A ¹ , A ² or A ³ include a linear or branched alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, and an aralkyl group having 7 to 20 carbon atoms. The number of carbon atoms in the hydrocarbyl group is preferably 1 to 12, and more preferably 3 to 10.

Examples of the trihydrocarbylsilyl group represented by A ¹ , A ² or A ³ include a trimethylsilyl group, a triethylsilyl group, an ethyldimethylsilyl group, a tert-butyldimethylsilyl group, a triisopropylsilyl group and a tert-butyldiphenylsilyl group.
A ¹ , A ² and A ³ are preferably trihydrocarbylsilyl groups, in that the effect of reducing the rolling resistance of the crosslinked body obtained using the modified conjugated diene polymer (P) can be enhanced.

The hydrocarbylene groups represented by R ¹ to R ⁵ are preferably linear or branched alkanediyl groups. The hydrocarbylene groups preferably have 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms.

Specific examples of the compound represented by formula (1) or (2) above include pyrrolidine, piperidine, hexamethyleneimine, heptamethyleneimine, dodecamethyleneimine, N-(trimethylsilyl)piperazine, N-(triethylsilyl)piperazine, N-(tert-butyldimethylsilyl)piperazine, 1-n-propylpiperazine, 1-n-hexylpiperazine, 1,3-ditrimethylsilyl-1,3,5-triazinane, 1,3-(tert-butyldimethylsilyl)-1,3,5-triazinane, and the compounds represented by the following formulae (L1-1) to (L1-3).

Compounds represented by the above formula (3) In the above formula (3), examples of when ^A4 is an (i+k)-valent hydrocarbyl group include groups obtained by removing (i+k) hydrogen atoms from a chain hydrocarbon having 1 to 20 carbon atoms, an alicyclic hydrocarbon having 3 to 20 carbon atoms, or an aromatic hydrocarbon having 6 to 20 carbon atoms. When ^A4 is an (i+k)-valent hydrocarbyl group, ^A4 is preferably a group obtained by removing (i+k) hydrogen atoms from a chain hydrocarbon, and more preferably a group obtained by removing (i+k) hydrogen atoms from a saturated chain hydrocarbon.

Specific examples of ^A4 being an (i+k)-valent group having 1 to 20 carbon atoms and containing a nitrogen atom but no active hydrogen include an (i+k)-valent nitrogen-containing heterocyclic group and an (i+k)-valent group having a tertiary amine structure. The nitrogen-containing heterocyclic group is preferably a conjugated system, and examples thereof include a monocyclic or fused ring such as pyridine, pyrimidine, pyrazine, quinoline, or naphthalidine, or a group in which (i+k) hydrogen atoms have been removed from the ring portion of a structure in which a plurality of such monocyclic or fused rings are linked together.

(i+k) is an integer of 2 to 10. From the viewpoint of improving processability, (i+k) is preferably 2 to 6. ^A4 is bonded to each of the silicon atom and the nitrogen atom in formula (3) via a carbon atom. It is preferable that ^A4 is bonded to each of the silicon atom and the nitrogen atom in formula (3) via the same or different carbon atoms constituting the hydrocarbylene group.

Examples of the hydrocarbyl group having 1 to 20 carbon atoms represented by ^R6 or ^R7 include an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, and an aryl group having 6 to 20 carbon atoms. ^R6 or ^R7 is preferably a linear or branched alkyl group having 1 to 20 carbon atoms, and more preferably a linear or branched alkyl group having 1 to 12 carbon atoms.

The hydrocarbylene group having 1 to 10 carbon atoms represented by R ⁸ or R ⁹ is preferably a linear or branched alkanediyl group having 1 to 10 carbon atoms, more preferably a methylene group or an ethylene group.

Specific examples of the compound represented by formula (3) include compounds represented by the following formulas (M1-1) to (M1-35): As the compound represented by formula (3), one type may be used alone, or two or more types may be used in combination.

Methods of polymerization in the presence of a metal amide compound include a method in which an organic alkali metal and a first initiating end-modifier are mixed in advance to generate a metal amide compound outside the system, and the resulting metal amide compound is mixed with a monomer to perform polymerization (this method will be referred to as Method A); and a method in which a first initiating end-modifier and an organic alkali metal are mixed in a reactor containing a monomer to generate a metal amide compound inside the system, and then polymerization is performed (this method will be referred to as Method B). Both of these methods are included in the embodiment of "polymerizing a monomer containing a conjugated diene compound in the presence of a metal amide compound obtained by mixing an organic alkali metal and a first initiating end-modifier." From the perspective of simplifying the operation, Method B is preferred, and from the perspective of sufficiently reducing the rolling resistance of the resulting crosslinked body and improving fuel economy, Method A is preferred.

When Method A is used as a method for polymerizing in the presence of a metal amide compound, the first initiating end-modifying agent and the organic alkali metal may be mixed in an organic solvent. The organic solvent used to produce the metal amide compound may be any organic solvent that is inert to the first initiating end-modifying agent and the organic alkali metal. Specific examples include aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons. In Method A, the temperature at which the first initiating end-modifying agent and the polymerization initiator are mixed is preferably -20°C to 150°C, and more preferably 0°C to 120°C.

When the metal amide compound obtained by premixing the first initiation end modifier and the organic alkali metal is added to a reactor containing monomers, the method for adding the metal amide compound to the reactor is not particularly limited. Examples include adding the metal amide compound all at once, adding it in portions, or adding it continuously. Adding the metal amide compound all at once to the reactor is advantageous in that it narrows the molecular weight distribution of the resulting modified conjugated diene polymer (P). Adding the metal amide compound in portions to the reactor tends to increase the efficiency of introducing the first initiation end modifier into the polymerization terminals while improving the processability of the resulting modified conjugated diene polymer (P).

When the metal amide compound is added to the reactor in portions, the second and subsequent additions of the metal amide compound may be made before or after the initiation of monomer polymerization. From the perspective of increasing the efficiency of introducing the first initiation end modifier into the polymerization ends, it is preferable to make the second and subsequent additions of the metal amide compound after the initiation of monomer polymerization, i.e., to add the metal amide compound to the reactor after initiating polymerization with the initial addition of the metal amide compound. When the metal amide compound is added in portions, the mass ratio of the amount added the first time to the total amount added the second and subsequent times is preferably 9:1 to 1:1.

The amount of the first initiation end modifier used relative to the polymerization initiator can be appropriately set depending on the type of polymerization initiator. For example, when a lithium compound is used as the organic alkali metal, the amount of the first initiation end modifier used is preferably in the range of 0.1 to 1.8 mol per mol of the lithium compound used in the polymerization. From the viewpoint of suppressing a decrease in processability when a rubber composition containing the modified conjugated diene polymer (P) is prepared, the amount of the first initiation end modifier used is preferably less than 1 mol per mol of the lithium compound used in the polymerization, more preferably 0.98 mol or less, and even more preferably 0.95 mol or less. Furthermore, from the viewpoint of obtaining a sufficient effect of reducing rolling resistance, the amount of the first initiation end modifier used is preferably 0.2 mol or more, more preferably 0.3 mol or more, per mol of the lithium compound used in the polymerization.

Regarding the compound represented by formula (4): In the above formula (4), the nitrogen-containing group represented by R ¹⁰ is preferably a tertiary amino group. Specific examples thereof include groups represented by the group "-NR ¹¹ R ¹² " (wherein R ¹¹ and R ¹² are each independently a hydrocarbyl group having 1 to 10 carbon atoms).
Examples of the hydrocarbyl group having 1 to 10 carbon atoms represented by R ¹¹ or R ¹² include an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, and an aryl group having 6 to 10 carbon atoms.

With regard to ^Y1 , examples of the conjugated diene compound and aromatic vinyl compound include the same compounds as those exemplified as the monomers that can be used in the polymerization. ^Y1 is preferably a hydrocarbylene group obtained by polymerization of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, or styrene, and more preferably a hydrocarbylene group obtained by polymerization of isoprene. The degree of polymerization of ^Y1 is preferably 2 to 10, more preferably 2 to 4. Examples of ^M1 include lithium, sodium, and potassium. ^M1 is preferably lithium.

Specific examples of compounds represented by formula (4) above include ((2E,6E)-11-(dimethylamino)-3,7-dimethylundeca-2,6-dien-1-yl)lithium. Also commercially available products include the reaction product of 3-(dimethylamino)propyllithium and isoprene, manufactured by FMC Corporation.

In the polymerization, the amount of alkali metal compound used is preferably 0.01 to 20 mmol, and more preferably 0.05 to 15 mmol, per 100 g of monomer used to synthesize the modified conjugated diene polymer (P).

In the first method, the total amount of the metal amide compound and the compound represented by formula (4) used is preferably 50 mol % or more, more preferably 70 mol % or more, and even more preferably 80 mol % or more, based on the total amount of alkali metal compounds used in the polymerization of the monomer.

Using a compound having a hydrocarbyloxysilyl group in addition to a nitrogen atom and an alkali metal element as the alkali metal compound (INI) is preferred in that it can enhance the effects of improving the rolling resistance, wear resistance, and strength of the crosslinked body obtained using the modified conjugated diene polymer (P). As the compound having a nitrogen atom, a hydrocarbyloxysilyl group, and an alkali metal element, a metal amide compound obtained by mixing an organic alkali metal with a compound represented by the above formula (3) can be preferably used.

In this specification, the term "hydrocarbyloxysilyl group" refers to a group in which at least one hydrocarbyloxy group is bonded to a silicon atom. Specific examples of the hydrocarbyloxysilyl group include a group represented by the following formula (5) and a group represented by the following formula (5A).
(In formula (5), R ²⁰ and R ²¹ are each independently a hydrocarbyl group. y is an integer of 0 to 2. When y is 2, multiple R ^20s in the formula are the same or different. When y is 0 or 1, multiple R ^21s in the formula are the same or different. "*" represents a bond.)
(In formula (5A), R ²⁰ and R ²¹ are each independently a hydrocarbyl group. y1 is 0 or 1. When y1 is 0, multiple R ²¹ in the formula are the same or different. "*" represents a bond.)

Vinyl content adjusters (also called randomizers) are used to adjust the vinyl group content (hereinafter also referred to as "vinyl group content") in a polymer. Examples of vinyl content adjusters include ether compounds and tertiary amine compounds. Specific examples of vinyl content adjusters include dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, 2,2-di(2-tetrahydrofuryl)propane, 2-(2-ethoxyethoxy)-2-methylpropane, triethylamine, pyridine, N-methylmorpholine, and tetramethylethylenediamine. Vinyl content adjusters can be used alone or in combination of two or more.

The solvent used in the polymerization (hereinafter also referred to as the "polymerization solvent") may be any solvent inert to the reaction. Organic solvents are preferably used as the polymerization solvent. Examples of organic solvents include linear or cyclic aliphatic hydrocarbons and aromatic hydrocarbons. Among these, hydrocarbons having 3 to 8 carbon atoms are preferred, and specific examples include propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, propene, 1-butene, isobutene, trans-2-butene, cis-2-butene, 1-hexene, 2-hexene, benzene, toluene, xylene, ethylbenzene, heptane, cyclopentane, methylcyclopentane, methylcyclohexane, 1-pentene, 2-pentene, and cyclohexene. Polymerization solvents can be used alone or in combination of two or more.

When solution polymerization is used, the monomer concentration in the reaction solvent is preferably 5 to 50% by mass, and more preferably 10 to 30% by mass, from the perspective of maintaining a balance between productivity and ease of polymerization control. The polymerization reaction temperature is preferably -20°C to 150°C, and more preferably 0 to 120°C. The polymerization reaction is preferably carried out under pressure sufficient to maintain the monomers substantially in a liquid phase. This polymerization reaction can produce a conjugated diene polymer having an active end. In this specification, "active end" refers to the portion at the end of the polymer chain other than the structure derived from the monomer having a carbon-carbon double bond (more specifically, the alkali metal end).

(Modification step)
In the modification step of the first method, a compound having a sulfur atom (hereinafter also referred to as "first terminal modifier") is used as a terminal end modifier, and the conjugated diene polymer obtained in the polymerization step (i.e., a conjugated diene polymer having an active end) is reacted with the first terminal end modifier. By reacting the polymer having an active end with the first terminal end modifier, a polymer chain containing a monomer unit derived from a conjugated diene compound is bonded to the first terminal end modifier, thereby producing a conjugated diene polymer having a sulfur-containing group at a polymerization terminal end.

The first terminal end modifier is not particularly limited as long as it has a sulfur atom and is capable of reacting with the active terminal of the conjugated diene polymer. Furthermore, the number of sites in the first terminal end modifier that can react with the active terminal of the conjugated diene polymer is also not particularly limited. For example, if the first terminal end modifier has one site for reaction with the active terminal, it is possible to obtain a modified conjugated diene polymer (P) having a nitrogen-containing group at one end of the polymer chain and a sulfur-containing group at the other end. Furthermore, if the first terminal end modifier has two or more sites for reaction with the active terminal, it is possible to obtain a modified conjugated diene polymer (P) having multiple polymer chains, one end of each of which is bonded to a partial structure derived from the first terminal end modifier and a nitrogen-containing group at the other end.

As the first terminal modifier, at least one selected from the group consisting of the following modifiers (N1) and (N2) can be preferably used because of its high reactivity with the active terminals of the conjugated diene polymer.
Modifier (N1): A compound having one or more groups (hereinafter also referred to as "reactive group W 1 ") selected from the group consisting of a vinylthio group (CH ₂ ═CH—S—), a thioester group (—C(═O)—S—), a thioepoxy group, a thienyl group, and —C( ^═S )—. Modifier (N2): A compound having a sulfur atom and a hydrocarbyloxysilyl group.

Regarding the modifier (N1), the number of reactive groups ^W1 contained in one molecule of the modifier (N1) may be one or two or more. By using a compound having two or more reactive groups ^W1 in one molecule as the modifier (N1), two or more polymer chains are bonded to the modifier (N1), thereby obtaining a modified conjugated diene polymer (P) having sulfur atoms at the branched portions of the polymer chains. The molecular weight of the modifier (N1) is preferably 1,000 or less, more preferably 800 or less. It is preferable that the modifier (N1) does not contain a hydrocarbyloxysilyl group.

When the reactive group ^W1 is —C(═S)—, the modifying agent (N1) may have a functional group containing —C(═S)—, thereby having —C(═S)— as the reactive group ^W1 . Examples of functional groups containing -C(=S)- include a thionoester group (-C(=S)-O-), a dithioester group (-C(=S)-S-), a thiocarbamide group (-NR ⁵⁰ -C(=S)-NR ⁵¹ -), a xanthate group (-O-C(=S)-S-), a trithiocarbonate group (-S-C(=S)-S-), a dithiocarbamate group (-NR ⁵⁰ -C(=S)-S-), a thioaldehyde group (-C(=S)-H), an isothiocyanate group (-N=C=S), and the like (wherein R ⁵⁰ and R ⁵¹ are each independently a hydrocarbyl group having 1 to 20 carbon atoms).

Specific examples of the first terminal modifying agent include ethylene sulfide, propylene sulfide, vinyl phenyl sulfide, cumyl dithiobenzoate (2-phenylpropan-2-yl benzodithioate), 4,4'-bis(dimethylamino)thiobenzophenone, di-tert-butyl-thioketone, 2-phenylpropan-2-yl benzodithioate, carbon disulfide, 2-propyl dithiobenzoate, S-ethyl thioacetate, S-furfuryl thiopropionate, S,S-dibenzyl trithiocarbonate, methyl thionobenzoate, 2-bromothiophene, 2-thiophenecarboxaldehyde, sulforaphane, and allyl isocyanate.

Regarding the Modifier (N2), the modifier (N2) is not particularly limited as long as it has a sulfur atom and a hydrocarbyloxysilyl group. The modifier (N2) may have only one hydrocarbyloxysilyl group (preferably a group represented by the above formula (5)) in one molecule, or may have two or more hydrocarbyloxysilyl groups.

Specific examples of the modifying agent (N2) include a compound represented by the following formula (N2-1) and a compound represented by the following formula (N2-2).
(In formula (N2-1), R ²² , R ²³ and R ²⁴ are each independently a hydrocarbyl group. A ⁵ is a hydrocarbylene group. n2 is an integer of 0 to 2. When n2 is 2, multiple R ^22s in the formula are the same or different. When n2 is 0 or 1, multiple R ^23s in the formula are the same or different.)
(In formula (N2-2), R ²⁵ , R ²⁶ and R ²⁷ are each independently a hydrocarbyl group. ^{A 6} is a hydrocarbylene group. ^{B 1} is a silicon atom or a tin atom. ^{X 1} is a halogen atom or a hydrocarbyloxy group. n3 is an integer of 0 to 2. k2 is an integer of 2 or greater. k3 and k4 are each independently an integer of 0 to 2, provided that k2 + k3 + k4 = 4 is satisfied. Multiple R ^25s in the formula may be the same or different, and multiple R ^26s in the formula may be the same or different. When k3 is 2, multiple R ^27s in the formula may be the same or different. When k4 is 2, multiple X ^1s in the formula may be the same or different.)

In the above formulas (N2-1) and (N2-2), examples of the hydrocarbyl group represented by R ²² , R ²³ , R ²⁴ , R ²⁵ , R ²⁶ or R ²⁷ , or the hydrocarbyl group in the hydrocarbyloxy group represented by X ¹ , include alkyl groups having 1 to 10 carbon atoms, cycloalkyl groups having 3 to 10 carbon atoms, and aryl groups having 6 to 10 carbon atoms.
Examples of the hydrocarbylene group represented by ^A5 or ^A6 include an alkanediyl group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 10 carbon atoms, an arylene group having 6 to 10 carbon atoms, and an aralkylene group having 7 to 10 carbon atoms.
The halogen atom represented by ^X1 is preferably a chlorine atom or a bromine atom.

Specific examples of the compound represented by formula (N2-1) above include compounds represented by the following formulas (n2-1-1) to (n2-1-8), and compounds in which one or more alkyl groups in these compounds are replaced with alkyl groups having 2 to 6 carbon atoms.

Specific examples of the compound represented by formula (N2-2) above include compounds represented by formulas (n2-2-1) to (n2-2-8) below, and compounds in which one or more alkyl groups in these compounds have been replaced with alkyl groups having 2 to 6 carbon atoms.

In the method for producing the modified conjugated diene polymer (P), it is preferable that the alkali metal compound (INI) or the terminal modifier further contains a hydrocarbyloxysilyl group. This is preferable in that the effect of improving the rolling resistance, wear resistance, and strength of the crosslinked body obtained using the modified conjugated diene polymer (P) can be further enhanced. Specific examples of the first method include a method in which a compound having a nitrogen atom, an alkali metal element, and a hydrocarbyloxysilyl group is used as the first alkali metal compound, and a modifier (N1) is used as the second terminal modifier; and a method in which a compound having a nitrogen atom and an alkali metal element but no hydrocarbyloxysilyl group is used as the first alkali metal compound, and a modifier (N2) is used as the second terminal modifier.

The reaction between a conjugated diene polymer having an active end and a terminal end-modifier can be carried out, for example, as a solution reaction. This solution reaction may be carried out using a solution containing unreacted monomers after the polymerization reaction has been completed, or the conjugated diene polymer contained in the solution may be isolated and dissolved in an appropriate solvent such as cyclohexane before being carried out. The reaction may be carried out batchwise or continuously. In this case, the method of adding the terminal end-modifier is not particularly limited, and examples include adding it all at once, adding it in portions, or adding it continuously.

The amount of terminal end modifier used can be set appropriately depending on the type of compound used in the reaction. The amount of terminal end modifier used is preferably 0.1 mol equivalent or more, more preferably 0.3 to 1.5 mol equivalents, relative to the metal element contained in the polymerization initiator that participates in the polymerization reaction. The reaction temperature is usually the same as the polymerization reaction temperature, preferably -20 to 150°C, and more preferably 0 to 120°C. If the modification reaction temperature is low, the viscosity of the polymer solution tends to increase. Furthermore, if the modification reaction temperature is high, the active polymerization terminals are more likely to be deactivated. The reaction time is preferably 1 minute to 5 hours, and more preferably 2 minutes to 1 hour.

In the modification step, a compound different from the first end-modifier may be used as the end-terminal modifier together with the first end-terminal modifier. Such a compound is not particularly limited as long as it is capable of reacting with the active terminals of the conjugated diene polymer obtained by the polymerization. For example, compounds known as modifiers for conjugated diene polymers (e.g., nitrogen-containing alkoxysilane compounds, glycidyl group-containing polysiloxanes, etc.) can be used. When a compound different from the first end-terminal modifier is used as the end-terminal modifier, its proportion is preferably 5 mol % or less, and more preferably 1 mol % or less, based on the total amount of end-terminal modifier used in the reaction. Furthermore, in the modification step, a coupling agent such as tin tetrachloride, tin tetrabromide, or silicon tetrachloride may be used in combination with the end-terminal modifier. Furthermore, in the modification step, after the reaction of the conjugated diene polymer having an active terminal with the first end-terminal modifier, a sulfur-containing group (e.g., a thiol group) introduced by this reaction may serve as a reaction site for reaction with another end-terminal modifier.

The modified conjugated diene polymer contained in the reaction solution can be isolated by known solvent removal methods such as steam stripping and drying procedures such as heat treatment.

<Regarding the second method>
Next, a second method for obtaining a modified conjugated diene polymer (P) will be described. In the first method, a compound having a nitrogen atom and an alkali metal element is used as the alkali metal compound (INI), and a compound having a sulfur atom is used as the terminal end modifier to polymerize a monomer. In contrast, in the second method, a compound having a sulfur atom and an alkali metal element is used as the alkali metal compound (INI), and a compound having a nitrogen atom is used as the terminal end modifier to polymerize a monomer. Note that the second method is basically the same as the first method, except that the alkali metal compound (INI) and terminal end modifier used are different. Therefore, the following describes a compound having a sulfur atom and an alkali metal element (hereinafter also referred to as a "second alkali metal compound") and a compound having a nitrogen atom as the terminal end modifier.

The second alkali metal compound used as the alkali metal compound (INI) is preferably a compound (SCI) obtained by mixing a compound containing an alkali metal element but no sulfur atom with a compound containing a sulfur atom and capable of reacting with an alkali metal (hereinafter referred to as the "second initiation end modifier"), as this makes it easier to introduce a sulfur-containing group into the initiation end of the polymer.

Regarding compound (SCI), the above-mentioned organic alkali metals are preferably used as the alkali metal compound not having a sulfur atom. Examples and preferred examples of the organic alkali metals used to produce compound (SCI) are the same as those exemplified in the first method.

Examples of the second initiating end modifier include compounds having a thioacetal structure and sulfur-containing aromatic heterocyclic compounds. Specific examples of the second initiating end modifier include 1,3-dithiane, 2-methyl-1,3-dithiane, 1,3-dithiolane, and thiophene. Compounds having a cyclic thioacetal structure are preferably used as the second initiating end modifier, since the compound (SCI) can be efficiently produced by mixing the second initiating end modifier with an organic alkali metal.

Regarding the compound having a nitrogen atom, the compound having a nitrogen atom used as the terminal modifier (hereinafter also referred to as the "second terminal modifier") is preferably a compound having one or more nitrogen-containing groups and one or more hydrocarbyloxysilyl groups per molecule. By using such a compound as the terminal modifier, the rolling resistance of the crosslinked product can be improved.

Specifically, the second terminal modifying agent is preferably at least one selected from the group consisting of a compound represented by the following formula (6), a compound represented by the following formula (7), a compound represented by the following formula (8), and a compound represented by the following formula (9).
(In formula (6), ^A7 is a monovalent functional group which has a nitrogen atom but does not have active hydrogen and which is bonded to ^R32 via the nitrogen atom. ^R30 and ^R31 are each independently a hydrocarbyl group, ^R32 is a hydrocarbylene group, and r1 is an integer of 0 to 2. When r1 is 2, multiple ^R30s in the formula may be the same or different, and when r1 is 0 or 1, multiple ^R31s in the formula may be the same or different.)
(In formula (7), ^A8 is a monovalent functional group which has a nitrogen atom but does not have active hydrogen and which is bonded to ^R33 via the nitrogen atom, or a hydrocarbyloxysilyl group, or a hydrocarbyl group having 1 to 20 carbon atoms. ^R33 is a single bond or a hydrocarbylene group, ^R34 and ^R35 are each independently a hydrocarbyl group, ^R36 is a hydrocarbylene group, and r2 is 0 or 1. However, when r2 is 0, multiple ^R35 in the formula may be the same or different.)
(In formula (8), R ³⁷ is a hydrocarbylene group having 1 to 20 carbon atoms, R ³⁸ and R ³⁹ are each independently a hydrocarbyl group having 1 to 20 carbon atoms, and A ⁹ is a group *-C(R ⁴¹ )=N- or a group *-N=C(R ⁴¹ )- (wherein R ⁴¹ is a hydrogen atom or a hydrocarbyl group, and * represents a bond to R ⁴⁰ ). R ⁴⁰ is an m-valent hydrocarbon group having 1 to 20 carbon atoms, or an m-valent group having a nitrogen atom and no active hydrogen and having 1 to 20 carbon atoms. r3 is an integer of 0 to 2, and m is an integer of 2 to 10. When the same symbol appears multiple times in the formula for each of R ³⁷ to R ⁴¹ and A ⁹ , the groups represented by those symbols are the same or different. Multiple r3s in the formula are the same or different.)
In formula (9), R ⁴⁴ , R ⁴⁵ and R ⁴⁶ are each independently an alkanediyl group having 1 to 12 carbon atoms, and R ⁴² , R ⁴³ , R ⁴⁷ and R ⁴⁸ are each independently a hydrocarbyl group having 1 to 20 carbon atoms. ^{A 10} is a nitrogen-containing heterocyclic group or a group represented by the following formula (a4):
(In formula (a4), R ⁴⁹ and R ⁵⁰ are each independently a hydrocarbyl group having 1 to 20 carbon atoms. a is an integer of 0 to 2. When the same symbol occurs multiple times in the formula, the groups represented by the symbols are the same or different. "*" represents a bond.)
c and d are each independently an integer of 0 to 2, and b is an integer of 1 to 10. When the same symbol is present multiple times in the formula, the groups represented by those symbols may be the same or different.

In the above formulas (6) and (7), the hydrocarbyl groups represented by R ³⁰ , R ³¹ , R ³⁴ , and R ³⁵ are preferably linear or branched alkyl groups having 1 to 20 carbon atoms, cycloalkyl groups having 3 to 20 carbon atoms, or aryl groups having 6 to 20 carbon atoms. ^{R 32} and R ³³ are preferably linear or branched alkanediyl groups having 1 to 20 carbon atoms, cycloalkylene groups having 3 to 20 carbon atoms, or arylene groups having 6 to 20 carbon atoms. R ³⁶ is preferably a linear or branched alkanediyl group having 1 to 20 carbon atoms.

^A7 is a nitrogen-containing group and may have a chain structure or a cyclic structure. The nitrogen contained in ^A7 is not bound to an active hydrogen and may be protected by a protecting group (e.g., a tri-substituted hydrocarbylsilyl group). ^A7 may also be a group that can be converted into an onium ion by an onium salt generating agent.

Specific examples of ^A7 include a nitrogen-containing group in which two hydrogen atoms of a primary amino group are substituted with two protecting groups, a nitrogen-containing group in which one hydrogen atom of a secondary amino group is substituted with one protecting group, a tertiary amino group, an imino group, a pyridyl group, etc. Among these, ^A7 preferably has at least one selected from the group consisting of a tertiary amino group, a group in which one hydrogen atom of a secondary amino group is substituted with one protecting group, a group in which two hydrogen atoms of a primary amino group are substituted with two protecting groups, and an imino group. In this specification, the term "protecting group" refers to a functional group that converts ^A7 into a functional group that is inactive against the polymerization active terminal. The nitrogen-containing group in which one hydrogen atom of a secondary amino group is substituted with one protecting group and the tertiary amino group may be linear or cyclic.

When ^A8 is a monovalent functional group having a nitrogen atom but no active hydrogen and bonding to ^R33 via the nitrogen atom, the nitrogen atom of ^A8 is not bonded to an active hydrogen and may be protected by a protecting group (e.g., a tri-substituted hydrocarbylsilyl group, etc.). ^A8 may be a group that can be converted into an onium ion by an onium salt generating agent.
When ^A8 is a hydrocarbyloxysilyl group, ^A8 is preferably a group represented by the above formula (5). Examples of ^R20 and ^R21 in the above formula (5) include an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, and an aryl group having 6 to 10 carbon atoms. ^R20 and ^R21 are preferably an alkyl group having 1 to 10 carbon atoms.

Specific examples of ^A8 include a nitrogen-containing group in which two hydrogen atoms of a primary amino group are substituted with two protecting groups, a nitrogen-containing group in which one hydrogen atom of a secondary amino group is substituted with one protecting group, a tertiary amino group, an imino group, a pyridyl group, a trihydrocarbyloxysilyl group, a hydrocarbyldihydrocarbyloxysilyl group, a dihydrocarbylhydrocarbyloxysilyl group, etc. Specific examples of the trihydrocarbyloxysilyl group, hydrocarbyldihydrocarbyloxysilyl group, or dihydrocarbylhydrocarbyloxysilyl group include a trimethoxysilyl group, a methyldimethoxysilyl group, a dimethylmethoxysilyl group, and groups in which the methyl group in each of these groups is replaced with an alkyl group having 2 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 12 carbon atoms.

In the above formula (8), examples of the hydrocarbylene group for R ³⁷ include an alkanediyl group having 1 to 12 carbon atoms, a cycloalkylene group having 3 to 12 carbon atoms, and an arylene group having 6 to 12 carbon atoms. Examples of the hydrocarbyl group for ^{R 38} and R ³⁹ include an alkyl group having 1 to 20 carbon atoms, an allyl group, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 20 carbon atoms.
The m-valent hydrocarbon group represented by R ⁴⁰ is a group obtained by removing m hydrogen atoms from a hydrocarbon. The m-valent hydrocarbon group represented by ^{R 40} is preferably a group obtained by removing m hydrogen atoms from the ring portion of an aromatic hydrocarbon (an m-valent aromatic ring group). Specific examples of the aromatic hydrocarbon include a single ring or condensed ring such as a benzene ring, a naphthalene ring, or an anthracene ring, and a structure in which two or more of these rings are bonded by a single bond.

When R ⁴⁰ is an m-valent group having 1 to 20 carbon atoms and containing a nitrogen atom but no active hydrogen, specific examples thereof include an m-valent nitrogen-containing heterocyclic group and an m-valent group having a tertiary amine structure. The nitrogen-containing heterocyclic group is preferably a conjugated system, and examples thereof include a single ring or condensed ring such as pyridine, pyrimidine, pyrazine, quinoline, or naphthalidine, or a group in which m hydrogen atoms have been removed from the ring portion of a structure in which multiple rings are linked together. m is preferably 2 to 6 from the viewpoint of improving the processability of the modified conjugated diene polymer (P).

In the above formula (9) and formula ( ^a4 ), the alkanediyl groups of R ^to R are preferably linear. Examples of the hydrocarbyl groups of ^R , R, ^and R ^to R include alkyl groups having 1 to ²⁰ carbon atoms, allyl groups, cycloalkyl groups having 3 to 20 carbon atoms, and aryl groups having 6 to 20 carbon atoms.
When ^A10 is a nitrogen-containing heterocyclic group, the nitrogen-containing heterocyclic group is preferably a group derived from a conjugated heterocycle. Examples of the nitrogen-containing heterocyclic group include groups in which one hydrogen atom has been removed from a nitrogen-containing heterocycle such as pyrrole, imidazole, pyridine, pyrimidine, pyrazine, quinoline, naphthalidine, or benzimidazole. b is preferably 1 to 5, and more preferably 1 to 3.

Specific examples of the second terminal modifier include compounds represented by the above formula (6), such as N,N-bis(trimethylsilyl)aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, 1-phenyl-N-(3-(triethoxysilyl)propyl)methanimine, N,N',N'-tris(trimethylsilyl)-N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-(4-trimethylsilyl-1-piperazino)propylmethyldimethoxysilane, 3-(trimethylsilylmercapto)propyltrimethoxysilane, and 3-(diphenylphosphino)propylmethyldiethoxysilane.

Examples of compounds represented by formula (7) above include 1-trimethylsilyl-2,2-dimethoxy-1-aza-2-silacyclopentane, 1-triethylsilyl-2,2-diethoxy-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1,2-azasilolidine, 2,2-dimethoxy-1-phenyl-1,2-azasilolidine, 2-(2,2-dimethoxy-1,2-azasilolidine-1-yl)-N,N-diethylethan-1-amine, and compounds in which the alkyl groups and alkanediyl groups in these compounds are replaced with alkyl groups having 1 to 6 carbon atoms and alkanediyl groups having 1 to 6 carbon atoms, respectively.

Examples of the compound represented by formula (8) above include compounds represented by the following formulas (m-1-1) to (m-1-6), and compounds in which the alkyl group and alkanediyl group in the compounds are replaced with alkyl groups having 1 to 6 carbon atoms and alkanediyl groups having 1 to 6 carbon atoms, respectively.

Examples of compounds represented by the above formula (9) include tris(2-triethoxysilylethyl)amine, tris(3-triethoxysilylpropyl)amine, tris(5-triethoxysilylpentyl)amine, N,N,N',N'-tetra(2-triethoxysilylethyl)-1,2-diaminoethane, N,N,N',N'-tetra(3-triethoxysilylpropyl)-1,3-diaminopropane, N-(3-(1H-imidazole-1 Examples of such compounds include N-(3-(1H-imidazol-1-yl)propyl)-3-(trimethoxysilyl)-N-(3-(trimethoxysilyl))propyl)propan-1-amine, N-(3-(1H-imidazol-1-yl)propyl)-N,N-bis(3-(trimethoxysilyl))propyl)propanamine, and compounds in which the alkyl group and alkanediyl group in these compounds are replaced with an alkyl group having 1 to 6 carbon atoms and an alkanediyl group having 1 to 6 carbon atoms, respectively.

The modified conjugated diene polymer (P) is preferably produced by the first method, since it allows for the production of a crosslinked product with higher strength. Specific preferred examples of the method for producing the modified conjugated diene polymer (P) include the following:

(Aspect 1) A method of polymerizing a monomer containing a conjugated diene compound in the presence of a metal amide compound obtained by mixing at least one selected from the group consisting of compounds represented by the above formula (1) and compounds represented by formula (2) with an organic alkali metal to obtain a conjugated diene polymer having an active end, and then reacting the conjugated diene polymer having an active end with a first terminal-modifying agent.
(Embodiment 2) A method in which a conjugated diene polymer having an active end is obtained by polymerizing a monomer containing a conjugated diene compound in the presence of a metal amide compound having a hydrocarbyloxysilyl group, and then the conjugated diene polymer having an active end is reacted with a first terminal-modifying agent.
(Aspect 3) A method in which a conjugated diene-based polymer having an active end is obtained by polymerizing a monomer containing a conjugated diene compound in the presence of a metal amide compound obtained by mixing a compound represented by the above formula (3) with an organic alkali metal, and then the conjugated diene-based polymer having an active end is reacted with a first terminal-modifying agent.
(Aspect 4) A method of polymerizing a monomer containing a conjugated diene compound in the presence of a compound represented by formula (4) to obtain a conjugated diene polymer having an active end, and then reacting the conjugated diene polymer having an active end with a first terminal-modifying agent.
The third aspect is one of the specific aspects of the second aspect.

The modified conjugated diene polymer (P) is preferably produced by a method in which the alkali metal compound (INI) or the terminal modifier further contains a hydrocarbyloxysilyl group, since this allows for the production of a crosslinked product with highly improved and well-balanced rolling resistance, abrasion resistance, and strength. Specifically, in Aspects 1 and 4, a compound containing a hydrocarbyloxysilyl group (e.g., modifier (N2)) can be preferably used as the first terminal modifier. In Aspects 2 and 3, a compound not containing a hydrocarbyloxysilyl group (preferably modifier (N1)) can be preferably used as the first terminal modifier.

<Physical Properties of Modified Conjugated Diene Polymer (P)>
The weight average molecular weight (Mw) of the modified conjugated diene polymer (P) measured by GPC in terms of polystyrene is preferably 50,000 to 2,000,000, from the viewpoint of obtaining a crosslinked product having high strength, excellent abrasion resistance, and sufficiently low rolling resistance. The Mw of the modified conjugated diene polymer (P) is more preferably 100,000 or more, and even more preferably 150,000 or more. The Mw of the modified conjugated diene polymer (P) is more preferably 1,500,000 or less, and even more preferably 1,200,000 or less. The weight average molecular weight of the modified conjugated diene polymer referred to here refers to the weight average molecular weight (total weight average molecular weight) based on all peaks of the GPC curve measured by GPC.

The molecular weight distribution (Mw/Mn) of the modified conjugated diene polymer (P), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured using GPC, is preferably 4.0 or less, more preferably 3.0 or less, and even more preferably 2.3 or less. Furthermore, the molecular weight distribution (Mw/Mn) may be 1.0 or more.

The vinyl group content of the modified conjugated diene polymer (P) is preferably 15 to 70% by mass. A vinyl group content of 15% by mass or more is preferable in that it can improve grip properties, and a vinyl group content of 70% by mass or less is preferable in that it can suppress a decrease in the abrasion resistance of the resulting vulcanized rubber. The vinyl group content is more preferably 20% by mass or more, and even more preferably 30% by mass or more. Furthermore, the vinyl group content is preferably 70% by mass or less, and more preferably 65% by mass or less. In this specification, the "vinyl group content" is a value indicating the content ratio of structural units having 1,2-bonds to all structural units of butadiene in the modified conjugated diene polymer, and is a value measured by ^1H -NMR.

The modified conjugated diene polymer (P) has nitrogen atoms derived from the first alkali metal compound or the second terminal modifier. The nitrogen atom content (hereinafter also referred to as "nitrogen content") in the modified conjugated diene polymer (P) is preferably 60 ppm or more and 600 ppm or less, in order to fully achieve the effects of improving the rolling resistance, wear resistance, and strength of the crosslinked body obtained using the modified conjugated diene polymer (P). The nitrogen content of the modified conjugated diene polymer (P) is more preferably 70 ppm or more, and even more preferably 80 ppm or more. The nitrogen content of the modified conjugated diene polymer (P) is more preferably 500 ppm or less, and even more preferably 400 ppm or less. In this specification, the nitrogen content of the polymer is a value measured using a trace total nitrogen analyzer in accordance with JIS-2609:1998.

The modified conjugated diene polymer (P) also contains sulfur atoms derived from the first terminal modifier or the second alkali metal compound. The sulfur atom content in the modified conjugated diene polymer (P) (hereinafter also referred to as "sulfur content") is preferably 50 ppm or more and 800 ppm or less, in order to fully achieve the effects of improving the rolling resistance, wear resistance, and strength of the crosslinked product obtained using the modified conjugated diene polymer (P). The sulfur content of the modified conjugated diene polymer (P) is more preferably 60 ppm or more, even more preferably 80 ppm or more, and even more preferably 100 ppm or more. The sulfur content of the modified conjugated diene polymer (P) is more preferably 600 ppm or less, even more preferably 500 ppm or less. In this specification, the sulfur content of the polymer is a value measured by combustion ion chromatography (IC).

Specific embodiments of the modified conjugated diene polymer (P) include the following.
- A modified conjugated diene polymer having a nitrogen-containing group at one end of the polymer chain and a sulfur-containing group at the other end. - A modified conjugated diene polymer having a sulfur-containing group at one end of the polymer chain and a nitrogen-containing group at the other end. - A modified conjugated diene polymer having a plurality of polymer chains and a partial structure derived from a first terminal modifier, wherein one end of each of the plurality of polymer chains is bonded to the partial structure derived from the first terminal modifier and the other end has a nitrogen-containing group. - A modified conjugated diene polymer having a plurality of polymer chains and a partial structure derived from a second terminal modifier, wherein one end of each of the plurality of polymer chains is bonded to the partial structure derived from the second terminal modifier and the other end has a sulfur-containing group.

In the above embodiment, examples of the nitrogen-containing group possessed by the modified conjugated diene polymer (P) include a primary amino group, a protected primary amino group, a secondary amino group, a protected secondary amino group, a tertiary amino group, a nitrogen-containing heterocyclic group, and an imino group. Specifically, the modified conjugated diene polymer (P) preferably has a partial structure derived from at least one selected from the group consisting of a compound represented by the above formula (1), a compound represented by the above formula (2), a compound represented by the above formula (3), and a compound represented by the above formula (4).

Furthermore, examples of the sulfur-containing group contained in the modified conjugated diene polymer (P) include monovalent groups such as a thiol group (-SH), a protected thiol group, a hydrocarbylthio group, a thioepoxy group, a thioaldehyde group (-C(=S)-H), an isothiocyanate group (-N=C=S), and a thienyl group; a thioether group (-S-), a vinylthio group (CH ₂ =CH-S-), a thioester group (-C(=O)-S-), a thionoester group (-C(=S)-O-), a dithioester group (-C(=S)-S-), a thiocarbamide group (-NR ⁵⁰ -C(=S)-NR ⁵¹ -), a xanthate group (-O-C(=S)-S-), a trithiocarbonate group (-S-C(=S)-S-), a dithiocarbamate group (-NR ⁵⁰ and divalent groups such as -C(=S)-S-, -C(=S)-, etc. (R ⁵⁰ and R ⁵¹ are defined as above).

<Polymer Composition>
The polymer composition of the present disclosure contains the modified conjugated diene-based polymer (P) and a filler, such as silica, carbon black, or other fillers.

Filler [B] Silica The polymer composition of the present disclosure can contain silica as a filler. The amount of silica is preferably 20 to 160 parts by mass, more preferably 30 to 120 parts by mass, per 100 parts by mass of the rubber component containing the modified conjugated diene polymer (P). When the amount of silica is 20 parts by mass or more per 100 parts by mass of the rubber component, the low hysteresis loss, fracture properties, and abrasion resistance of the polymer composition can be sufficiently improved. When the amount of silica is 160 parts by mass or less, the processability of the polymer composition can be sufficiently improved.

In this specification, the "rubber component" contained in the polymer composition refers to a polymer that can be cured to yield a cured product that exhibits rubber elasticity. This cured product exhibits the property of undergoing large deformation with a small force at room temperature (for example, stretching to more than twice its original size when stretched at room temperature), and rapidly returning to nearly its original shape when the force is removed.

The silica is not particularly limited, and examples thereof include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among these, wet silica is preferred. Silica may be used alone or in combination of two or more types. The BET specific surface area of the silica (measured in accordance with ISO 5794/1) is preferably in the range of 40 to 350 ^{m 2} /g, more preferably in the range of 80 to 300 ^{m 2} /g, and particularly preferably in the range of 120 to 250 m ² /g. Silica with a BET specific surface area in this range has the advantage of being able to achieve both dispersibility in modified conjugated diene polymers and rubber reinforcement properties. As such silica, commercially available products such as "Nipsil AQ" (BET specific surface area = 205 m ² /g) and "Nipsil KQ" manufactured by Tosoh Silica Corporation, and "Ultrasil VN3" (BET specific surface area = 175 m ² /g) manufactured by Degussa can be used.

The polymer composition may contain two or more types of silica having different specific surface areas. Specifically, a first silica having a CTAB (cetyltrimethylammonium bromide) specific surface area of 180 m ² /g or more, a BET specific surface area of 185 m ² /g or more, and an aggregate size of 45 nm or more may be used in combination with a second silica having a CTAB specific surface area of 95 m ² /g or less and a BET specific surface area of 100 m ² /g or less. The CTAB specific surface area of the silica is measured in accordance with ASTM D3765-92.

One embodiment of the polymer composition contains a first silica having a CTAB specific surface area of 180 m ² /g or more, a BET specific surface area of 185 m ² /g or more, and an aggregate size of 45 nm or more, and a second silica having a CTAB specific surface area of 95 m ² /g or less and a BET specific surface area of 100 m ² /g or less. The combined use of such first and second silicas enables the first silica, which has a small average primary particle size but a relatively large aggregate size, to be well dispersed in the rubber component. This improves the dispersibility of the silica, resulting in excellent rubber fracture strength, abrasion resistance, fuel economy, and processability.

The CTAB specific surface area of the first silica is preferably 190 m ² /g or more, more preferably 195 m ² /g or more, and even more preferably 197 ^{m 2} /g or more. When the CTAB specific surface area is 180 m ² /g or more, rubber breaking strength and abrasion resistance tend to be sufficiently improved. The CTAB specific surface area is preferably 350 m ² /g or less, more preferably 300 m ² /g or less, and even more preferably 250 ^{m 2} /g or less. When the CTAB specific surface area is 350 ^{m 2} /g or less, dispersibility is good and aggregation is difficult, so deterioration of physical properties tends to be suppressed.

The BET specific surface area of the first silica is preferably 190 m ² /g or more, more preferably 195 m ² /g or more, and even more preferably 210 m ² /g or more. When the BET specific surface area is 185 ^{m 2} /g or more, rubber breaking strength and abrasion resistance tend to be sufficiently improved. The BET specific surface area is preferably 350 m ² /g or less, more preferably 300 ^{m 2} /g or less, and even more preferably 260 ^{m 2} /g or less. When the BET specific surface area is 350 ^{m 2} /g or less, dispersibility is good and aggregation is unlikely, so deterioration of physical properties tends to be suppressed. The BET specific surface area of silica is measured in accordance with ASTM D3037-81.

The aggregate size of the first silica is 45 nm or more, preferably 50 nm or more, more preferably 55 nm or more, and even more preferably 60 nm or more. The aggregate size is preferably 100 nm or less, more preferably 80 nm or less, even more preferably 70 nm or less, and particularly preferably 67 nm or less. Having such an aggregate size provides excellent fuel economy and abrasion resistance while maintaining good dispersibility (processability). The aggregate size of silica can be measured using the method described in JP 2011-140613 A.

The average primary particle diameter of the first silica is preferably 25 nm or less, more preferably 22 nm or less, even more preferably 17 nm or less, and particularly preferably 14 nm or less. There is no particular lower limit to the average primary particle diameter, but it is preferably 3 nm or more, more preferably 5 nm or more, and even more preferably 7 nm or more. Despite having such a small average primary particle diameter, the dispersibility (processability) of the silica can be further improved due to the carbon black-like structure with the above aggregate size, thereby further improving fuel economy and abrasion resistance. The average primary particle diameter of the silica can be determined by observing the silica with a transmission or scanning electron microscope, measuring the particle diameters of 400 or more primary silica particles observed within the field of view, and averaging the measured diameters.

The CTAB specific surface area of the second silica is preferably 10 m ² /g or more, more preferably 20 m ² /g or more, and even more preferably 30 m ² /g or more. When the CTAB specific surface area is 10 m ² /g or more, the effect of improving reinforcing properties is high, and it tends to be easier to ensure the mechanical strength and abrasion resistance required for a polymer composition for obtaining tire rubber. The CTAB specific surface area is preferably 80 m ² /g or less, more preferably 60 m ² /g or less, and even more preferably 50 m ² /g or less. When the CTAB specific surface area is 95 m ² /g or less, it is possible to ensure the dispersibility of the silica, and it tends to be easier to improve the rubber breaking strength and abrasion resistance.

The BET specific surface area of the second silica is preferably 10 m ² /g or more, more preferably 20 m ² /g or more, and even more preferably 30 m ² /g or more. When the BET specific surface area is 10 m ² /g or more, the effect of improving reinforcing properties is high, and it tends to be easier to ensure the mechanical strength and abrasion resistance required for a polymer composition for obtaining tire rubber. The BET specific surface area is preferably 85 m ² /g or less, more preferably 60 m ² /g or less, and even more preferably 50 m ² /g or less. When the BET specific surface area is 100 m ² /g or less, it is possible to ensure the dispersibility of the silica, and it tends to be easier to improve the rubber breaking strength and abrasion resistance.

The average primary particle diameter of the second silica is preferably 20 nm or more, more preferably 25 nm or more, even more preferably 30 nm or more, particularly preferably 35 nm or more, and most preferably 55 nm or more. Furthermore, the average primary particle diameter is preferably 500 nm or less, more preferably 200 nm or less, even more preferably 100 nm or less, and particularly preferably 70 nm or less. Having such an average primary particle diameter can enhance the effect of improving rubber fracture strength and abrasion resistance.

[C] Carbon Black The polymer composition of the present disclosure preferably contains carbon black as a filler from the viewpoint of the fracture properties and abrasion resistance of the polymer composition. The carbon black is not particularly limited, and examples thereof include GPF, FEF, HAF, ISAF, and SAF grade carbon black. The nitrogen adsorption specific surface area (N ₂ SA) of the carbon black is not particularly limited, but is preferably 50 to 200 ^{m 2} /g, and more preferably 70 to 150 m ² /g, because this provides superior effects of the present disclosure. The nitrogen adsorption specific surface area (N ₂ SA) is the value obtained by measuring the amount of nitrogen adsorbed to the carbon black surface in accordance with JIS K6217-2:2001 "Part 2: Determination of Specific Surface Area - Nitrogen Adsorption Method - Single Point Method." These carbon blacks may be used alone or in combination of two or more types. The amount of carbon black added is preferably in the range of 1 to 150 parts by mass, more preferably 3 to 120 parts by mass, per 100 parts by mass of the rubber component containing the modified conjugated diene polymer (P).

[Other fillers]
The polymer composition of the present disclosure may contain other fillers in addition to the silica (B) and carbon black (C). Such other fillers include alumina (Al ₂ O ₃ ) such as γ-alumina and α-alumina, alumina monohydrate (Al ₂ O _{3.H 2} O) such as boehmite and diaspore, aluminum hydroxide [Al(OH) ₃ ] such as gibbsite and bayerite, aluminum carbonate [Al ₂ (CO ₃ ) ₃ ], magnesium hydroxide [Mg(OH) ₂ ], magnesium oxide (MgO), magnesium carbonate (MgCO ₃ ), talc (3MgO.4SiO _{2.H 2 O} ), attapulgite (5MgO.8SiO _{2.9H 2} O), titanium white (TiO ₂ ), titanium black (TiO _2n-1 ), calcium oxide (CaO), calcium hydroxide [Ca(OH) ₂ ], aluminum magnesium oxide (MgO.Al ₂ O ₃ ), clay (Al ₂ O ₃ ·2SiO ₂ ), kaolin (Al ₂ O ₃ ·2SiO ₂ ·2H ₂ O), pyrophyllite (Al ₂ O ₃ ·4SiO ₂ ·H ₂ O), bentonite (Al ₂ O ₃ ·4SiO ₂ ·2H ₂ O), aluminum silicate (Al ₂ SiO ₅ , Al ₄ ·3SiO ₄ ·5H ₂ O, etc.), magnesium silicate (Mg ₂ SiO ₄ , MgSiO ₃ , etc.), calcium silicate (Ca ₂ SiO ₄ , etc.), aluminum calcium silicate (Al ₂ O ₃ ·CaO·2SiO ₂ , etc.), magnesium calcium silicate (CaMgSiO ₄ ), calcium carbonate (CaCO ₃ ), zirconium oxide (ZrO ₂ ), zirconium hydroxide [ZrO(OH) ₂ ·nH _{2 O].} O], zirconium carbonate [Zr(CO ₃ ) ₂ ], and crystalline aluminosilicates containing hydrogen, alkali metals, or alkaline earth metals to compensate for the charge, such as various zeolites.

In the polymer composition of the present disclosure, the blending amount of the filler containing [B] silica and [C] carbon black is preferably 30 parts by mass or more, and more preferably 40 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the blending amount of the filler containing [B] silica and [C] carbon black is preferably 160 parts by mass or less, and more preferably 120 parts by mass or less. When the blending amount of the filler in the polymer composition is within the above range, applying the polymer composition to a tire tread can achieve an even higher level of compatibility between tire rolling resistance, braking performance on wet roads, handling performance on dry roads, and abrasion resistance.

In addition to the modified conjugated diene polymer (P) and the filler, the polymer composition of the present disclosure may further contain the various components listed below.

[D] Other Rubber Components In the present disclosure, as the rubber component other than the modified conjugated diene polymer (P), for example, at least one diene rubber selected from natural rubber, isoprene rubber, butadiene rubber, emulsion-polymerized styrene-butadiene rubber, solution-polymerized styrene-butadiene rubber, butyl rubber, halogenated butyl rubber, and ethylene-propylene rubber can be used. Among these, it is preferable to include at least one of natural rubber, butadiene rubber, and styrene-butadiene rubber. When mixing the other rubber components with the modified conjugated diene polymer (P), they may be mixed during the usual kneading process using a Banbury mixer, roll, or the like, or they may be mixed in advance in the solution state after polymerization and dried before use.

The ratio of the modified conjugated diene polymer (P) to the other rubber components is preferably 5 to 95 parts by mass of the modified conjugated diene polymer (P) and 5 to 95 parts by mass of the component [D], and more preferably 20 to 90 parts by mass of the modified conjugated diene polymer (P) and 10 to 80 parts by mass of the other rubber components, per 100 parts by mass of the combined total of the modified conjugated diene polymer (P) and the other rubber components. A ratio of 35 to 85 parts by mass of the modified conjugated diene polymer (P) and 15 to 65 parts by mass of the other rubber components is particularly suitable as a polymer composition for producing rubber for tires.

When producing the polymer composition of the present disclosure, liquid rubber can also be used for some or all of the other rubber components in order to further improve dry grip performance, wet grip performance, and blowout resistance.

Liquid rubbers include liquid polyisoprene (liquid IR), liquid polybutadiene (liquid BR), liquid styrene-butadiene copolymer (liquid SBR), and liquid ethylene-propylene copolymer (liquid EP). For example, liquid SBR with a weight-average molecular weight of 1,000 to 100,000, preferably 2,000 to 80,000, can be used. Note that the weight-average molecular weight refers to the weight-average molecular weight in terms of polystyrene as analyzed by gel permeation chromatography (GPC). Liquid rubber refers to rubber that has fluidity at 23°C.

[E] Thermoplastic/Thermosetting Resin The polymer composition of the present disclosure may contain a thermoplastic/thermosetting resin (hereinafter, also simply referred to as "resin [E]"). From the viewpoint of obtaining a crosslinked product with excellent properties such as strength, abrasion resistance, and crack growth resistance, the resin [E] is preferably at least one selected from the group consisting of styrene-based resins, polyethylene, C5-based resins, hydrogenated C5-based resins, C9-based resins, hydrogenated C9 resins, C5/C9-based resins, hydrogenated C5/C9-based resins, dicyclopentadiene-based resins, hydrogenated dicyclopentadiene-based resins, alkylphenol-based resins, coumarone-indene resins, terpene-based resins, and hydrogenated terpene-based resins. As the resin [E], one type may be used alone, or two or more types may be used in combination.

When the [E] resin is blended into the polymer composition, the blending ratio of the [E] resin is preferably 1 part by mass or more per 100 parts by mass of the rubber component contained in the polymer composition. Blending 1 part by mass or more of the [E] resin is preferable because it sufficiently enhances the effects of improving the abrasion resistance, breaking strength, and crack growth resistance of the crosslinked product obtained using the polymer composition. When the [E] resin is blended into the polymer composition, the blending ratio of the [E] resin is more preferably 3 parts by mass or more, and even more preferably 7 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of maintaining the various performance properties of the rubber composition, the blending ratio of the [E] resin is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less, per 100 parts by mass of the rubber component contained in the polymer composition. Note that one type of [E] resin may be used alone, or two or more types may be used in combination.

[F] Silane Coupling Agent In the present disclosure, the dispersibility of silica can be further improved by blending a silane coupling agent. The silane coupling agent used is not particularly limited, but sulfur-containing silane coupling agents are preferred. Examples of sulfur-containing silane coupling agents include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, 3-[ethoxybis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silyl]propane-1-thiol (e.g., Evonik, trade name "Si363"), and mercapto-based silane compounds such as NXT and NXT-Z manufactured by Momentive.

The amount of silane coupling agent is preferably 1 to 20 parts by mass per 100 parts by mass of silica. If the amount of silane coupling agent is less than 1 part by mass, the amount may be too small and the effect of improving the dispersibility of the silica may not be fully achieved. On the other hand, if the amount of silane coupling agent is more than 20 parts by mass, processability and elongation at break may decrease. The amount of silane coupling agent is more preferably 5 to 15 parts by mass per 100 parts by mass of silica. One type of silane coupling agent may be used alone, or two or more types may be used in combination.

[G] Crosslinking Agent The polymer composition of the present disclosure may contain a crosslinking agent. By containing a crosslinking agent in the polymer composition of the present disclosure, a crosslinked product with improved strength and abrasion resistance can be obtained. Examples of crosslinking agents include sulfur, sulfur halides, organic peroxides, quinone dioximes, organic polyamine compounds, and alkylphenol resins having methylol groups, with sulfur typically being used. The amount of crosslinking agent blended is preferably 0.1 to 5 parts by mass, more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the total amount of rubber components contained in the polymer composition.

The polymer composition may contain a process oil commonly used to extend elastomers as an oil for oil extension. The process oil is incorporated into the polymer composition, for example, by directly adding the oil during rubber compounding. Preferred process oils include various oils known in the art, such as aromatic oils, paraffinic oils, naphthenic oils, vegetable oils (soybean oil, sunflower oil, etc.), and oils with a low content of polycyclic aromatic compounds (low PCA oils), such as mild extraction solvates (MES), treated distillate aromatic extracts (TDAE), special residual aromatic extracts (SRAE), and heavy naphthenic oils. Examples of commercially available MES, TDAE, and SRAE include Shell's Catenex SNR (heavy paraffin obtained by dewaxing distillate oil with a solvent) as an MES, H&R Wasag AG's Vivatec 500 as a TDAE, and Japan Energy Corp.'s NC140 as an SRAE. The amount of process oil blended is preferably 10 to 100 parts by mass per 100 parts by mass of the total amount of polymer components contained in the polymer composition.

In addition to the components described above, the polymer composition may contain various additives commonly used in polymer compositions for producing rubber for tires, such as antioxidants, zinc oxide, stearic acid, softeners, vulcanization accelerators, compatibilizers, vulcanization aids, processing aids, and scorch inhibitors. The blending ratios of these additives may be selected appropriately depending on the various components, as long as they do not impair the effects of the present disclosure.

The polymer composition of the present disclosure can be applied to various rubber products as a crosslinked product by kneading the polymer components, filler, and other optional components using a kneader such as an open kneader (e.g., a roll) or an internal kneader (e.g., a Banbury mixer), molding the composition, and then crosslinking (vulcanizing) the resulting composition. Specifically, the crosslinked product of the present disclosure can be used in tire applications such as tire treads, undertreads, carcasses, sidewalls, and bead portions; sealing materials such as packings, gaskets, weatherstrips, and O-rings; interior and exterior skin materials for various vehicles such as automobiles, ships, aircraft, and railways; building materials; vibration-proof rubber for industrial machinery and equipment; various hoses and hose covers such as diaphragms, rolls, radiator hoses, and air hoses; belts such as power transmission belts; linings; dust boots; medical equipment materials; fenders; insulating materials for electrical wires; and other industrial products.

The manufacturing method disclosed herein can produce a modified conjugated diene polymer that can be used to obtain a crosslinked product with excellent physical properties required for tire applications, such as rolling resistance (fuel economy), strength, and abrasion resistance. Therefore, the polymer composition containing the modified conjugated diene polymer obtained according to the present disclosure can be particularly suitably used as a material for tire treads, sidewalls, or both.

Tires can be manufactured using conventional methods. For example, the polymer composition is mixed in a kneader, formed into a sheet, and then placed in a predetermined position (for example, on the outside of the carcass in the case of a sidewall) using conventional methods and vulcanized to form the tread rubber or sidewall rubber, resulting in a pneumatic tire.

According to the present disclosure described above in detail, the following means are provided.
[Means 1] A method for producing a modified conjugated diene polymer, comprising: a step of polymerizing a monomer containing a conjugated diene compound in the presence of an alkali metal compound (INI) to obtain a conjugated diene polymer having an active end; and a step of reacting the conjugated diene polymer having an active end with a terminal end-modifying agent, wherein the alkali metal compound (INI) comprises a compound having a nitrogen atom and an alkali metal element, and the terminal end-modifying agent comprises a compound having a sulfur atom, or the alkali metal compound (INI) comprises a compound having a sulfur atom and an alkali metal element, and the terminal end-modifying agent comprises a compound having a nitrogen atom.
[Means 2] The method for producing a modified conjugated diene polymer according to [Means 1], wherein the alkali metal compound (INI) comprises a metal amide compound obtained by mixing, as a compound having a nitrogen atom and an alkali metal element, a compound having an alkali metal element but no nitrogen atom and a compound having a secondary amino group.
[Means 3] The method for producing a modified conjugated diene-based polymer according to [Means 2], wherein the compound having a secondary amino group includes at least one selected from the group consisting of compounds represented by the above formula (1) and compounds represented by the above formula (2).
[Means 4] The method for producing a modified conjugated diene polymer according to [Means 2] or [Means 3], wherein the compound having a secondary amino group includes a compound represented by the above formula (3).
[Means 5] The method for producing a modified conjugated diene polymer according to any one of [Means 1] to [Means 4], wherein the alkali metal compound (INI) contains a compound represented by the above formula (4) as a compound having a nitrogen atom and an alkali metal element.
[Means 6] The method for producing a modified conjugated diene polymer according to any one of [Means 1] to [Means 5], wherein the alkali metal compound (INI) or the terminal end-modifying agent further has a hydrocarbyloxysilyl group.
[Means 7] The method for producing a modified conjugated diene polymer according to any one of [Means 1] to [Means 6], wherein the terminal-modifying agent contains a compound having one or more groups selected from the group consisting of a vinylthio group, a thioester group, a thioepoxy group, a thienyl group, and -C(=S)-.
[Means 8] The method for producing a modified conjugated diene-based polymer according to [Means 1], wherein the alkali metal compound (INI) comprises a compound having a sulfur atom and an alkali metal element, and the terminal-modifying agent comprises a compound having a nitrogen atom and a hydrocarbyloxysilyl group.
[Means 9] A modified conjugated diene-based polymer having a polymer chain containing a structural unit derived from a conjugated diene compound, the polymer chain having a first functional group at one end and a second functional group at the other end, or having a plurality of polymer chains containing a structural unit derived from a conjugated diene compound and a partial structure derived from a compound having a first functional group, one end of each of the plurality of polymer chains being bonded to the partial structure and having a second functional group at the other end, one of the first functional group and the second functional group being a nitrogen-containing group and the other being a sulfur-containing group.
[Means 10] The modified conjugated diene polymer according to [Means 9], having at its terminal a partial structure derived from at least one selected from the group consisting of the compound represented by the formula (1), the compound represented by the formula (2), the compound represented by the formula (3), and the compound represented by the formula (4).
[Means 11] The modified conjugated diene polymer of [Means 9] or [Means 10], having a sulfur content of 50 ppm or more and 800 ppm or less.
[Means 12] The modified conjugated diene polymer according to any one of [Means 9] to [Means 11], having a weight average molecular weight of 50,000 to 2,000,000.
[Means 13] A polymer composition containing a modified conjugated diene polymer produced by the method for producing a modified conjugated diene polymer according to any one of [Means 1] to [Means 8] or a modified conjugated diene polymer according to any one of [Means 9] to [Means 12], and a filler.
[Means 14] A crosslinked product obtained by crosslinking the polymer composition of [Means 13].
[Means 15] A tire in which one or both of the tread and the sidewall are made using the polymer composition of [Means 13].

The following provides a more detailed explanation based on examples, but the present invention is not limited to these examples. Note that "parts" and "%" in the following synthesis examples, examples, and comparative examples are by mass unless otherwise specified. The methods for measuring various physical properties of the polymer are shown below.

Bound styrene content (%): Calculated by 400 MHz ¹ H-NMR measurement using deuterated chloroform as a solvent.
Vinyl group content (%): Calculated by 400 MHz ¹ H-NMR measurement.
Weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of polymer: A chart (GPC curve) based on the molecular weight converted to polystyrene was obtained by gel permeation chromatography (GPC), and the weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of polymer were determined based on the chart. The specific measurement conditions for GPC are as follows:
(GPC measurement conditions)
Measuring instrument: HLC-8020 (manufactured by Tosoh Corporation)
Column: GMH-HR-H (manufactured by Tosoh Corporation), two columns connected in series Detector: Differential refractometer RI-8020 (manufactured by Tosoh Corporation)
Eluent: tetrahydrofuran Column temperature: 40°C
Flow rate: 1.0 mL/min Sample concentration: 10 mg/20 mL

Nitrogen content (ppm) of polymer: Measured using a trace total nitrogen analyzer in accordance with the "chemiluminescence method" of JIS K-2609:1998 "Crude petroleum and petroleum products - Testing method for nitrogen content." The measurement method involved thermally decomposing a sample in a flow of argon gas, then burning and oxidizing it with oxygen gas, causing the resulting nitric oxide to react with ozone gas under dehydrating conditions, measuring the luminescence intensity detected in the range of 590 to 2500 nm, and determining the nitrogen content from the area value of the luminescence intensity.
(Measurement conditions for trace total nitrogen analyzer)
Measuring instrument: TN-2100H (Mitsubishi Chemical Analytech Co., Ltd.)
Sulfur content (ppm) of polymer: Measured by combustion ion chromatography (combustion IC) under the following conditions.
(Combustion IC measurement conditions)
Measuring instrument: AQF-2100H (manufactured by Nitto Seiko Analytech Co., Ltd.)
Combustion temperature: inlet temperature: 900°C, outlet temperature: 1000°C
Gas flow rate: argon 200 mL/min, oxygen 400 mL/min Humidification amount: 0.23 mL/min, internal standard substance (PO ₄ ): 20 mg/kg
Absorption solution (hydrogen peroxide solution): 900 mg/kg, volume of absorption solution: 5 mL, final diluted volume of absorption solution: 10 mL
Column: Ionpack AS18 (manufactured by Thermo Fisher Scientific)
Eluent: 30.5 mM KOH aqueous solution Flow rate: 1 mL/min Detector: Suppressed Conductivity Detector, SRS
Current: 76mA
Sample amount: 30 mg of the modified conjugated diene polymer was weighed out and placed in a sample boat, and a combustion improver (WO ₃ ) was added.

1. Production of modified conjugated diene polymer <Comparative Example 1>
A 5-liter autoclave reactor purged with nitrogen was charged with 2,500 g of cyclohexane, 0.8644 mmol of 2,2-di(tetrahydrofurfuryl)propane as a vinyl content adjuster (randomizer), 4.331 mmol of piperidine as an initiation terminal modifier, and 50 g of styrene and 400 g of 1,3-butadiene as monomers. After adjusting the temperature of the reactor contents to 20°C, 5.62 mmol of n-butyllithium was added as a polymerization initiator to initiate polymerization. The polymerization temperature was raised from room temperature to 75°C over 25 minutes.
After the polymerization conversion rate reached 99% (25 minutes after the start of polymerization), 50 g of 1,3-butadiene was added over 5 minutes, followed by the addition of 4.322 mmol of N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane (also referred to as "N-Si-1"), and the reaction was carried out for 15 minutes.
To the resulting polymer solution, 4.40 g of 2,6-di-tert-butyl-p-cresol was added, followed by steam stripping to remove the solvent, and drying with a heated roll adjusted to 110°C to obtain a modified conjugated diene polymer A-1.

<Comparative Examples 2 to 5, Examples 1 to 17, Example 19, Example 20>
Modified conjugated diene polymers A-2 to A-5, A-9 to A-25, A-27, and A-28 were obtained by performing polymerization, desolvation, and drying in the same manner as in Comparative Example 1, except that the types and amounts of reagents used were as shown in Table 1.

<Comparative Example 6>
Ethylene sulfide was added and reacted for 15 minutes, and then polymerization, desolvation, and drying were carried out in the same manner as in Comparative Example 4, except that before adding 4.40 g of 2,6-di-tert-butyl-p-cresol, 4.322 mmol of n-octanoyl chloride was added and reacted for 10 minutes, thereby obtaining a modified conjugated diene polymer A-6.

Comparative Example 7
Polymerization, desolvation, and drying were performed in the same manner as in Comparative Example 1, except that 4.331 mmol of 1-(3-(dimethyl(tert-butoxy)silyl)propyl)piperazine (also referred to as "Si-N-1") was used instead of piperidine and 2.161 mmol of divinylbenzene was used instead of N-Si-1, thereby obtaining a modified conjugated diene polymer A-7.

<Comparative Example 8>
A 5-liter autoclave reactor purged with nitrogen was charged with 2,500 g of cyclohexane, 0.8644 mmol of 2,2-di(tetrahydrofurfuryl)propane as a vinyl content adjuster (randomizer), and 50 g of styrene and 400 g of 1,3-butadiene as monomers. The temperature of the reactor contents was adjusted to 20°C. A 100 mL pressure bottle previously purged with nitrogen was used to separately prepare an initiator solution by reacting 11.24 mmol of n-butyllithium and 5.62 mmol of divinylbenzene in 50 g of cyclohexane. This initiator solution was added to the autoclave reactor to initiate polymerization. The polymerization temperature was raised from room temperature to 75°C over 25 minutes.
After the polymerization conversion rate reached 99% (25 minutes after the start of polymerization), 50 g of 1,3-butadiene was added over 5 minutes, and then 8.644 mmol of ethylene sulfide was added, and the reaction was carried out for 15 minutes.
To the resulting polymer solution, 4.40 g of 2,6-di-tert-butyl-p-cresol was added, followed by steam stripping to remove the solvent, and drying with a heated roll adjusted to 110°C to obtain a modified conjugated diene polymer A-8.

Example 18
Ethylene sulfide was added and reacted for 15 minutes, and then polymerization, desolvation, and drying were carried out in the same manner as in Example 1, except that before adding 4.40 g of 2,6-di-tert-butyl-p-cresol, 4.322 mmol of n-octanoyl chloride was added and reacted for 10 minutes, thereby obtaining a modified conjugated diene polymer A-26.

The physical properties of the modified conjugated diene polymers A-1 to A-28 obtained by removing the solvent are shown in Tables 1 and 2.

Details of the compounds in Tables 1 and 2 are as follows:
Initiating end-modifying agent: Si-N-1: 1-(3-(dimethyl(tert-butoxy)silyl)propyl)piperazine; AI-200CE2: Reaction product of 3-(dimethylamino)propyllithium and isoprene [reaction ratio: isoprene/3-(dimethylamino)propyllithium = 2/1 (molar ratio)], manufactured by FMC Corporation; Ending end-modifying agent: N-Si-1: N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane; S-Si-1: Compound represented by the following formula (S-Si-1):

Example 21
A nitrogen-purged autoclave reactor (first reactor) having an internal volume of 50 L was continuously charged with 26.6 g/min of 1,3-butadiene and 2.95 g/min of styrene as monomers, 180.2 g/min of cyclohexane as a solvent, 0.4 g/min of tetrahydrofuran as a vinyl group content adjuster (randomizer), and a mixture of n-butyllithium as a polymerization initiator and Si-N-1 as an initiation terminal modifier (1/1, molar ratio) at a rate of 0.25 mmol/min, and the temperature inside the reactor was controlled at 75°C.
The polymer solution was continuously decharged from the first reactor at a rate of 210.2 g/min, and ethylene sulfide was added to the decharged polymer solution at a rate of 0.20 mmol/min, followed by continuous introduction into the second reactor to carry out the reaction. At the outlet of the second reactor, di-tert-butyl-p-cresol was added in an amount of 0.88 parts by mass per 100 parts by mass of the polymer. The solvent was removed from the resulting polymer solution by steam stripping, and the polymer was dried using a heated roll adjusted to 110°C, yielding a modified conjugated diene polymer A-29. The various physical property values of the modified conjugated diene polymer A-29 were as follows.
Bound styrene content: 10%, vinyl group content: 39%, Mw: 960,000, Mw/Mn: 1.6, nitrogen content: 68 ppm, sulfur content: 133 ppm

2. Production of polymer compositions and crosslinked products <Comparative Examples 1 to 8, Examples 1 to 21>
Polymer compositions were produced by blending the components according to the formulations shown in Tables 3 and 4 and melt-kneading the blended components. The kneading was carried out in the following manner.
A batch mixer equipped with a temperature control device (manufactured by Toyo Seiki Seisaku-Sho, Ltd.; trade name: Labo Plastomill) was used to knead the modified conjugated diene polymer, polybutadiene rubber (BR), extender oil, silica, carbon black, silane coupling agent, stearic acid, antioxidant, and zinc oxide in the first stage of kneading under conditions of a set temperature of 100°C, a rotation speed of 60 rpm, and a kneading time of 4 minutes.
Next, in the second stage of kneading, the kneaded material obtained in the first stage of kneading was cooled to room temperature, and then a vulcanization accelerator and sulfur were added to the mixer. The set temperature was adjusted to 70°C, and the kneading was continued under conditions of 60 rpm rotation and 1.5 minutes of kneading time, thereby obtaining polymer compositions (Q-1 to Q-29). The temperature of the kneaded material discharged from the mixer was 100°C or lower when discharged. Next, each of the obtained compositions was vulcanized and molded in a vulcanization press at 160°C for a predetermined time, thereby obtaining vulcanized rubber (crosslinked product). The obtained vulcanized rubber was evaluated for the following physical properties. The results are shown in Tables 3 and 4.

[Method for evaluating compound properties]
・Rolling resistance (3% tan δ @ 50℃)
Using the vulcanized rubber as a measurement sample, the ratio of the loss modulus G" to the storage modulus G' (50°C tan δ) was measured using a shear-type dynamic spectrometer (manufactured by TA Instruments) under conditions of an angular velocity of 100 radians per second, a temperature of 50°C, and a shear strain of 3%. The ratio is expressed as an index, with Comparative Example 1 being set at 100, and a larger index indicates lower rolling resistance, better rolling resistance, and better fuel economy.

・Strength ((TB×EB)/2)
Tensile tests were conducted in accordance with JIS K6251:2010 using vulcanized rubber as the measurement sample. Here, a dumbbell No. 3 was used as the test sample, and the stress at break (TB, MPa) and elongation at break (EB, %) were measured at room temperature. Strength was calculated from half the tensile product (= (TB x EB)). The measurement results are expressed as an index, with Comparative Example 1 set to 100. A larger value indicates higher strength.

- Abrasion resistance (DIN abrasion)
Using vulcanized rubber as a measurement sample, measurements were carried out in accordance with JIS K6264 using a DIN abrasion tester (manufactured by Toyo Seiki Co., Ltd.) under a load of 10 N at 25°C. The measurement results are expressed as an index, with Comparative Example 1 being set at 100. A larger index value indicates better abrasion resistance.

In Tables 3 and 4, the details of each component are as follows:
*1) Manufactured by ENEOS Materials, product name "BR01"
*2) Solvay, product name "ZEOSIL 1165MP"
*3) Mitsubishi Chemical Corporation, product name "Diablack N330"
*4) Evonik, product name "Si75"
*5) ENEOS process oil, product name "T-DAE"
*6) Ozonone 6C manufactured by Seiko Chemical Co., Ltd.
*7) Product name "Noccela D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
*8) Product name "Noccela CZ-G" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

As shown in Tables 1 to 4, it was found that the modified conjugated diene polymers obtained in Examples 1 to 21 could produce crosslinked products with a good balance of improved rolling resistance, abrasion resistance, and strength.

Claims (15)

a step of polymerizing a monomer containing a conjugated diene compound in the presence of an alkali metal compound (INI) to obtain a conjugated diene polymer having an active terminal;
a step of reacting the conjugated diene polymer having an active terminal with a terminal-modifying agent;
Including,
The method for producing a modified conjugated diene-based polymer, wherein the alkali metal compound (INI) comprises a compound having a nitrogen atom and an alkali metal element, and the terminal end-modifier comprises a compound having a sulfur atom, or the alkali metal compound (INI) comprises a compound having a sulfur atom and an alkali metal element, and the terminal end-modifier comprises a compound having a nitrogen atom. The method for producing a modified conjugated diene polymer according to claim 1, wherein the alkali metal compound (INI) includes a metal amide compound obtained by mixing, as a compound having a nitrogen atom and an alkali metal element, a compound having an alkali metal element but no nitrogen atom with a compound having a secondary amino group. The method for producing a modified conjugated diene polymer according to claim 2, wherein the compound having a secondary amino group includes at least one selected from the group consisting of a compound represented by the following formula (1) and a compound represented by the following formula (2):
(In formulas (1) and (2), R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently a hydrocarbylene group having 1 to 10 carbon atoms. ^{X 1} is a hydrocarbylene group or —N(A ³ )—. ^{A 1} , A ² and A ³ are each independently a trihydrocarbylsilyl group or a hydrocarbyl group having 1 to 20 carbon atoms.) The method for producing a modified conjugated diene polymer according to claim 2 , wherein the compound having a secondary amino group includes a compound represented by the following formula (3):
(In formula (3), ^A4 is an (i+k)-valent hydrocarbon group having 1 to 20 carbon atoms, or an (i+k)-valent group having 1 to 20 carbon atoms which has a nitrogen atom, no active hydrogen, and is bonded to each of the silicon atom and the nitrogen atom in the formula via a carbon atom. ^R6 and ^R7 are each independently a hydrocarbyl group having 1 to 20 carbon atoms. n1 is an integer of 0 to 2. ^R8 and ^R9 are each independently a hydrocarbylene group having 1 to 10 carbon atoms. i and k are each independently an integer of 1 to 6, provided that i+k≦10 is satisfied. In the formula, when a plurality of ^R6s are present, the plurality of R6s may be the same or different; when ^a plurality of ^R7s are present, the plurality of ^R7s may be the same or different; when a plurality of ^R8s are present, the plurality of ^R8s may be the same or different; and when a plurality of ^R9s are present, the plurality of ^R9s may be the same or different.) 2. The method for producing a modified conjugated diene polymer according to claim 1, wherein the alkali metal compound (INI) contains a compound represented by the following formula (4) as a compound having a nitrogen atom and an alkali metal element:
(In formula (4), ^R10 is a nitrogen-containing group. ^Y1 is a hydrocarbylene group formed by polymerization of one or both of a conjugated diene compound and an aromatic vinyl compound. ^M1 is an alkali metal. n2 is an integer of 1 to 10.) The method for producing a modified conjugated diene polymer according to claim 1 or 2, wherein the alkali metal compound (INI) or the terminal end-modifying agent further has a hydrocarbyloxysilyl group. The method for producing a modified conjugated diene polymer according to claim 1 or 2, wherein the terminal-modifying agent includes a compound having one or more groups selected from the group consisting of a vinylthio group, a thioester group, a thioepoxy group, a thienyl group, and -C(=S)-. the alkali metal compound (INI) includes a compound having the sulfur atom and an alkali metal element,
The method for producing a modified conjugated diene polymer according to claim 1 , wherein the terminal-modifying agent comprises a compound having a nitrogen atom and a hydrocarbyloxysilyl group. a polymer chain containing a structural unit derived from a conjugated diene compound, the polymer chain having a first functional group at one end and a second functional group at the other end, or
a polymer chain including a structural unit derived from a conjugated diene compound and a partial structure derived from a compound having a first functional group, wherein one end of each of the plurality of polymer chains is bonded to the partial structure and the other end has a second functional group;
One of the first functional group and the second functional group is a nitrogen-containing group, and the other is a sulfur-containing group. The modified conjugated diene-based polymer according to claim 9, having at its terminal a partial structure derived from at least one selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2), a compound represented by the following formula (3), and a compound represented by the following formula (4):
(In formulas (1) and (2), R ¹ , R ² , R ³ , R ⁴ and R ⁵ are each independently a hydrocarbylene group having 1 to 10 carbon atoms. ^{X 1} is a hydrocarbylene group or —N(A ³ )—. ^{A 1} , A ² and A ³ are each independently a trihydrocarbylsilyl group or a hydrocarbyl group having 1 to 20 carbon atoms.)
(In formula (3), ^A4 is an (i+k)-valent hydrocarbon group having 1 to 20 carbon atoms, or an (i+k)-valent group having 1 to 20 carbon atoms which has a nitrogen atom, no active hydrogen, and is bonded to each of the silicon atom and the nitrogen atom in the formula via a carbon atom. ^R6 and ^R7 are each independently a hydrocarbyl group having 1 to 20 carbon atoms. n1 is an integer of 0 to 2. ^R8 and ^R9 are each independently a hydrocarbylene group having 1 to 10 carbon atoms. i and k are each independently an integer of 1 to 6, provided that i+k≦10 is satisfied. In the formula, when a plurality of ^R6s are present, the plurality of R6s may be the same or different; when ^a plurality of ^R7s are present, the plurality of ^R7s may be the same or different; when a plurality of ^R8s are present, the plurality of ^R8s may be the same or different; and when a plurality of ^R9s are present, the plurality of ^R9s may be the same or different.)
(In formula (4), ^R10 is a nitrogen-containing group. ^Y1 is a hydrocarbylene group formed by polymerization of one or both of a conjugated diene compound and an aromatic vinyl compound. ^M1 is an alkali metal. n2 is an integer of 1 to 10.) The modified conjugated diene polymer according to claim 9 or 10, having a sulfur content of 50 ppm or more and 800 ppm or less. The modified conjugated diene polymer according to claim 9 or 10, having a weight-average molecular weight of 50,000 to 2,000,000. A polymer composition containing a modified conjugated diene polymer produced by the method for producing a modified conjugated diene polymer described in claim 1 or 2, or the modified conjugated diene polymer described in claim 9 or 10, and a filler. A crosslinked body obtained by crosslinking the polymer composition described in claim 13. A tire having a tread, a sidewall, or both made using the polymer composition described in claim 13.