WO2024090556A1

WO2024090556A1 - Polymer composition and tire

Info

Publication number: WO2024090556A1
Application number: PCT/JP2023/038891
Authority: WO
Inventors: 拓哉佐野; 寛文千賀; 龍源中濱; 天斗福本; 法由大野
Original assignee: 株式会社Ｅｎｅｏｓマテリアル
Priority date: 2022-10-28
Filing date: 2023-10-27
Publication date: 2024-05-02

Abstract

A polymer composition comprising a first polymer, which comprises aromatic vinyl units and butadiene units and satisfies requirements (x) and (y), and a second polymer, which comprises aromatic vinyl units and butadiene units, satisfies requirements (x) and (y), and has a lower aromatic-vinyl-unit content than the first polymer, wherein the difference in β between the first polymer and the second polymer is 0.10 or less and the difference in aromatic-vinyl-unit content between the first polymer and the second polymer is 10-30 mass%. Requirement (x): α is 0.60-0.97 inclusive. Requirement (y): β is 0.10-0.40 inclusive.　(i) α=(p+(0.5×r))/(p+q+(0.5×r)+s) (ii) β=(p+q)/(p+q+(0.5×r)+s)

Description

Polymer composition and tire

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to Japanese Patent Application No. 2022-173391, filed on October 28, 2022, the entire contents of which are incorporated herein by reference.
The present disclosure relates to polymer compositions and tires.

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 polymer compositions used in the manufacture of pneumatic tire treads, sidewalls, etc., contain inorganic fillers such as carbon black and silica as reinforcing agents along with conjugated diene polymers in order to improve the durability and abrasion resistance of the products. Also, conjugated diene polymers modified with silicon- or nitrogen-containing compounds have been used in the past to increase the affinity between the conjugated diene polymers and reinforcing agents (see, for example, Patent Documents 1 to 3).

In recent years, it has been proposed to obtain vulcanized rubber with high strength and excellent abrasion resistance by using hydrogenated conjugated diene polymers (see, for example, Patent Documents 4 and 5).

International Publication No. 2008/123164 Japanese Patent Application Laid-Open No. 11-349632 International Publication No. 2017/221943 International Publication No. 2014/133097 JP 2020-045388 A

Due to recent environmental circumstances, growing awareness of resource and energy conservation, and rising consumer needs for safety, rubber for automobile tires is expected to have better performance than ever before, such as grip on ice and low-temperature grip performance, which is a requirement for winter tires or all-season tires, in addition to mechanical strength and ozone resistance.

　Generally, several different rubber compositions are often used in tire manufacturing, and therefore rubber for automobile tires is required to have excellent vulcanization adhesion.

The present disclosure has been made in consideration of the above problems, and has as its main objective the provision of a polymer composition that can produce a crosslinked product with high strength, excellent low-temperature grip performance, and ozone resistance, and that also has excellent vulcanization adhesion.

The present disclosure provides the following polymer composition and tire.

[1] A polymer composition comprising: a first polymer containing a structural unit derived from an aromatic vinyl compound and a structural unit derived from butadiene and satisfying the following conditions (x) and (y); and a second polymer containing a structural unit derived from an aromatic vinyl compound and a structural unit derived from butadiene and satisfying the following conditions (x) and (y), wherein the difference between the β of the first polymer and the β of the second polymer is 0.10 or less, and the difference between the content ratio of the structural unit derived from the aromatic vinyl compound in the first polymer and the content ratio of the structural unit derived from the aromatic vinyl compound in the second polymer is 10 to 30 mass %.
Condition (x): α is 0.60 or more and 0.97 or less. Condition (y): β is 0.10 or more and 0.40 or less. α = (p + (0.5 × r)) / (p + q + (0.5 × r) + s).
... (i)
β = (p + q) / (p + q + (0.5 × r) + s) ... (ii)

[2] A tire in which either or both of the cap tread and sidewall are made of the cured product of the polymer composition of [1] above.

According to the present disclosure, by including a first polymer and a second polymer in which α represented by the above formula (i) is 0.60 or more and 0.97 or less, β represented by the above formula (ii) is 0.10 or more and 0.40 or less, the difference in β is within a specified range, and the difference in the content ratio of structural units derived from aromatic vinyl compounds is within a specified range, a crosslinked body having high strength and excellent low-temperature grip performance and ozone resistance can be obtained. In addition, the polymer composition of the present disclosure has excellent vulcanization adhesion.

　Below, matters related to the implementation of this disclosure are explained in detail. In this specification, a numerical range described using "~" indicates a range that includes the numerical values described before and after "~" as the lower and upper limits. This disclosure is not limited to the embodiments described below, and should be understood to include various modified examples that are implemented within the scope that does not change the gist of this disclosure.

In this specification, the term "(modified) conjugated diene polymer" includes unmodified conjugated diene polymers and modified conjugated diene polymers (i.e. modified conjugated diene polymers). In the following description, when simply referring to a "conjugated diene polymer," the "conjugated diene polymer" may be a modified conjugated diene polymer or an unmodified conjugated diene polymer, unless otherwise specified that it is unmodified.

Polymer Composition
The polymer composition of the present disclosure (hereinafter also referred to as "the composition") contains a first polymer and a second polymer, which are polymers containing a structural unit derived from an aromatic vinyl compound and a structural unit derived from butadiene, and have different content ratios of the structural unit derived from an aromatic vinyl compound. In the following, the first polymer and the second polymer are also referred to as "polymer [P]". In the following, the content described by polymer [P] describes the respective configurations of the first polymer and the second polymer. Hereinafter, the components contained in the composition and the components that are optionally blended will be described in detail.

<Polymer [P]>
Examples of aromatic vinyl compounds constituting the polymer [P] (i.e., each of the first polymer and the second polymer) include 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)dimethylaminoethylether, 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 diphenylethylene (e.g., 1-(4-N,N-dimethylaminophenyl)-1-phenylethylene). Among these, the aromatic vinyl compound is preferably styrene or α-methylstyrene. The aromatic vinyl compounds constituting the polymer [P] may be used alone or in combination of two or more kinds.

Each of the first polymer and the second polymer is a highly saturated copolymer containing a structural unit derived from an aromatic vinyl compound and a structural unit derived from butadiene. Specifically, when the constituent ratios (molar ratios) in the polymer of the structural unit represented by the following formula (1), the structural unit represented by the following formula (2), the structural unit represented by the following formula (3), and the structural unit represented by the following formula (4) are respectively p, q, r, and s, the polymer [P] is represented by the following mathematical formula (i):
α=(p+(0.5×r))/(p+q+(0.5×r)+s)
... (i)
(i.e., α) is 0.60 or more and 0.97 or less (this is referred to as condition (x)).

If the α of each of the first polymer and the second polymer is less than 0.60, the strength, abrasion resistance, and ozone resistance of the crosslinked body tend to be insufficient. If the α of each of the polymers exceeds 0.97, crosslinking cannot be sufficiently advanced, and the strength and viscoelastic properties of the crosslinked body tend to be reduced. In addition, in a laminated crosslinked body obtained by laminating the present composition with a conjugated diene material sheet or the like and vulcanizing it, it tends to be difficult to ensure adhesion to the conjugated diene material sheet or the like. From these viewpoints, the α of each of the first polymer and the second polymer is preferably 0.65 or more, more preferably 0.70 or more, even more preferably 0.75 or more, and particularly preferably 0.80 or more. In addition, the α of each polymer is preferably 0.96 or less.

The weight average molecular weight (Mw) of each of the first polymer and the second polymer, measured by gel permeation chromatography (GPC) in terms of polystyrene, is preferably in the range of 0.5×10 ⁵ or more and 2.0×10 ⁶ or less, from the viewpoint of obtaining a crosslinked body having high strength and excellent abrasion resistance. The Mw of each polymer is more preferably 0.7×10 ⁵ or more, and even more preferably 1.0×10 ⁵ or more. The Mw of each polymer is more preferably 1.6×10 ⁶ or less, and even more preferably 1.4×10 ⁶ or less. The weight average molecular weight (Mw) of the polymer [P] represents the weight average molecular weight (total weight average molecular weight) based on all peaks of the GPC curve measured by GPC before hydrogenation.

Furthermore, for each of the first polymer and the second polymer, the molecular weight distribution (Mw/Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by GPC, is preferably 4.0 or less, and more preferably 3.5 or less.

For each of the first polymer and the second polymer, the peak top molecular weight of the peak with the smallest molecular weight measured by GPC (hereinafter also referred to as "1st peak average molecular weight") is preferably in the range of 0.5 x 10 ⁵ or more and 1.0 x 10 ⁶ or less. When the 1st peak average molecular weight is 0.5 x 10 ⁵ or more, the strength and abrasion resistance of the obtained crosslinked body can be sufficiently increased while the viscoelastic properties and processability can be improved. The 1st peak average molecular weight of each polymer is more preferably 0.7 x 10 ⁵ or more, and even more preferably 1.0 x 10 ⁵ or more. In addition, from the viewpoint of making the viscoelastic properties and processability more excellent, the 1st peak average molecular weight of each polymer is more preferably 8.0 x 10 ⁵ or less, and even more preferably 5.0 x 10 ⁵ or less. The 1st peak average molecular weight is a value obtained from a GPC curve measured by GPC before hydrogenation.

The ratio of the structural units derived from the aromatic vinyl compound in each of the first polymer and the second polymer is preferably greater than 0% by mass and less than 45% by mass, based on the total structural units constituting each polymer. By setting the ratio within the above range, a crosslinked body having high strength and excellent abrasion resistance can be obtained while maintaining good processability of the polymer composition. From these viewpoints, the ratio of the structural units derived from the aromatic vinyl compound is more preferably 2% by mass or more, and even more preferably 5% by mass or more, based on the total structural units constituting each of the first polymer and the second polymer. Moreover, the ratio of the structural units derived from the aromatic vinyl compound is more preferably 40% by mass or less, more preferably 38% by mass or less, and even more preferably 36% by mass or less, based on the total structural units constituting each polymer. The content ratio of the structural units derived from the aromatic vinyl compound in the polymer is a value measured by ¹ H-NMR.

Each of the first polymer and the second polymer has the following formula (ii):
β = (p + q) / (p + q + (0.5 × r) + s) ... (ii)
The value represented by (i.e., β) is 0.10 or more and 0.40 or less (this is referred to as condition (y)). If the β of each polymer is less than 0.10, the flexibility of the resulting crosslinked body is insufficient, and sufficient strength cannot be ensured, or good low-temperature grip performance tends not to be obtained. Furthermore, if the β of each polymer exceeds 0.40, the strength and wear resistance of the crosslinked body tend to be insufficient. From these viewpoints, the β of each of the first polymer and the second polymer is preferably 0.15 or more, more preferably 0.20 or more. Furthermore, the β of each of the first polymer and the second polymer is preferably 0.39 or less, more preferably 0.37 or less.

The composition contains, as the polymer [P], a first polymer and a second polymer that contains a smaller proportion of structural units derived from an aromatic vinyl compound than the first polymer. According to the composition, by containing the first polymer and the second polymer that have different microstructures, it is possible to obtain a crosslinked product that has a good balance of improved strength, low-temperature grip performance, ozone resistance, and vulcanization adhesion compared to when only one of the two polymers is contained.

In the first polymer and the second polymer, the difference between the content ratio of structural units derived from aromatic vinyl compounds in the first polymer and the content ratio of structural units derived from aromatic vinyl compounds in the second polymer (hereinafter also referred to as the "aromatic vinyl content difference") is 10 to 30% by mass. If the aromatic vinyl content difference is less than 10% by mass, the difference in the microstructure of the first polymer and the second polymer is small, and the effect of improving the strength, low-temperature grip performance, ozone resistance, and vulcanization adhesion of the crosslinked body in a well-balanced manner cannot be fully obtained. Furthermore, if the aromatic vinyl content difference is greater than 30% by mass, the strength of the crosslinked body is insufficient and the low-temperature grip performance is inferior. From these viewpoints, the aromatic vinyl content difference is preferably 11% by mass or more, and more preferably 12% by mass or more. Furthermore, the aromatic vinyl content difference is preferably 28% by mass or less, and more preferably 27% by mass or less.

In the first polymer and the second polymer, the difference between the β of the first polymer and the β of the second polymer (hereinafter also referred to as "Δβ") is 0.10 or less. If Δβ exceeds 0.10, the strength and low-temperature grip performance of the obtained crosslinked body tend to be insufficient. From these viewpoints, Δβ is preferably 0.08 or less, more preferably 0.07 or less, and even more preferably 0.06 or less. Furthermore, from the viewpoint of improving the strength, low-temperature grip performance, ozone resistance, and vulcanization adhesion of the crosslinked body in a well-balanced manner, it is preferable that the β of the first polymer is different from the β of the second polymer. Δβ is preferably greater than 0, and more preferably 0.01 or more.

When the β of the first polymer is different from the β of the second polymer, the β of either the first polymer or the second polymer may be larger. From the viewpoint of obtaining a polymer composition with good balance between improving the strength, low-temperature grip performance, and ozone resistance of the crosslinked body and having excellent vulcanization adhesion, it is preferable that the β of the second polymer is larger than the β of the first polymer.

The first polymer and the second polymer may be modified polymers (hereinafter, also referred to as "modified polymers") or unmodified polymers. In this specification, "modification" refers to providing an unmodified conjugated diene polymer consisting of structural units derived from hydrocarbons with a partial structure containing a heteroatom such as nitrogen, oxygen, sulfur, or silicon. When at least one of the first polymer and the second polymer is a modified polymer, the modified polymer may be a polymer obtained by terminal modification in which a partial structure containing a heteroatom is introduced into the polymerization initiation end or polymerization termination end of the conjugated diene polymer using a modifying agent, or a polymer obtained by main chain modification in which a monomer having a heteroatom is copolymerized or a conjugated diene polymer is reacted with a modifying agent to introduce a partial structure containing a heteroatom into the main chain of the polymer. Note that when a partial structure containing a heteroatom is introduced into the main chain of the polymer by reacting a conjugated diene polymer with a modifying agent, the partial structure containing a heteroatom is introduced into the side chain of the polymer and exists in the side chain. The "modifying agent" refers to a chemical agent that causes modification.

It is preferable that one or both of the first polymer and the second polymer have a functional group (hereinafter also referred to as a "specific functional group") that contains at least one element selected from the group consisting of nitrogen, oxygen, silicon, and phosphorus. By having at least one of the first polymer and the second polymer have a specific functional group, various physical properties (specifically, strength, viscoelasticity, and fuel efficiency) of the crosslinked body obtained using this composition can be further improved.

In the first polymer and the second polymer having a specific functional group (hereinafter also referred to as a "specific group-containing polymer"), the position of the specific functional group in the polymer is not particularly limited. That is, the specific group-containing polymer may have a specific functional group at the end of the molecular chain, or may have a specific functional group on the side chain of the polymer. In addition, in a polymer having a specific functional group at the end of the molecular chain, the specific group-containing polymer may have the specific functional group at the polymerization initiation end, the polymerization termination end, or both the polymerization initiation end and the polymerization termination end. In terms of being able to enhance the effect of improving various physical properties of the crosslinked body obtained using this composition, it is preferable that the specific group-containing polymer has a specific functional group at one end or both ends of the molecular chain.

Specific functional groups include, for example, primary amino groups, secondary amino groups, tertiary amino groups, nitrogen-containing groups in which two hydrogen atoms of a primary amino group are protected, nitrogen-containing groups in which one hydrogen atom of a secondary amino group is protected, tertiary amino groups, imino groups, phosphorus-containing groups in which two hydrogen atoms of a primary phosphino group are protected, phosphorus-containing groups in which one hydrogen atom of a secondary phosphino group is protected, tertiary phosphino groups, cyclic ether groups, hydroxyl groups, oxygen-containing groups in which the hydrogen atom of a hydroxyl group is protected, nitrogen-containing heterocyclic groups (e.g., groups having heterocyclic rings such as pyridine rings and imide rings), hydrocarbyloxysilyl groups, hydrocarbyloxycarbonyl groups, ether bonds, etc. Among these, from the viewpoint of further enhancing the effect of improving various physical properties of the crosslinked body, it is preferable that one or both of the first polymer and the second polymer have at least one specific functional group selected from the group consisting of nitrogen-containing groups and hydrocarbyloxysilyl groups.

The specific group-containing polymer is preferably a reaction product between a conjugated diene polymer having an active end and a compound having a specific functional group and a reactive site with the active end of the conjugated diene polymer. The compound may have one reactive site with the active end, or two or more reactive sites.

When one of the first polymer and the second polymer is a specific group-containing polymer, the first polymer may be a specific group-containing polymer, and the second polymer may be a specific group-containing polymer. From the viewpoint of further enhancing the effect of improving various physical properties of the crosslinked body obtained by using this composition, it is preferable that at least one of the first polymer and the second polymer is a specific group-containing polymer, and it is more preferable that both the first polymer and the second polymer are specific group-containing polymers.

The blending ratio of the first polymer to the second polymer in this composition is preferably in the range of 10:90 to 90:10 by mass ratio (first polymer:second polymer). When the blending ratio of the first polymer to the second polymer is in the above range, the effect of improving the strength, low-temperature grip performance, and ozone resistance of the obtained crosslinked body, as well as the vulcanization adhesion of the polymer composition in a well-balanced manner can be sufficiently obtained. The blending ratio of the first polymer to the second polymer is more preferably in the range of 15:85 to 85:15 (first polymer:second polymer), and even more preferably in the range of 20:80 to 80:20 (first polymer:second polymer).

<Production method of polymer [P]>
The polymer [P] can be produced by a method including the following polymerization step and hydrogenation step. The polymer [P] may also be produced by a method including the following modification step in addition to the polymerization step and hydrogenation step.

(Polymerization process)
The polymerization step is a step of polymerizing a monomer containing 1,3-butadiene and an aromatic vinyl compound to obtain a conjugated diene polymer having an active terminal. Specific and preferred examples of the aromatic vinyl compound used in the polymerization step include the same compounds as the above-mentioned illustrative and preferred examples of the aromatic vinyl compound.

When producing the polymer [P], a conjugated diene compound other than 1,3-butadiene may be used together with the aromatic vinyl compound. Specific examples of the conjugated diene compound include 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, the conjugated diene compound used in combination with 1,3-butadiene is preferably isoprene or 2,3-dimethyl-1,3-butadiene. The proportion of the conjugated diene compound used in combination with 1,3-butadiene is preferably 30% by mass or less, and more preferably 20% by mass or less, based on the total amount of the conjugated diene compound used in the polymerization.

The monomers used in the polymerization reaction to obtain the polymer [P] may contain compounds other than conjugated diene compounds and aromatic vinyl compounds (hereinafter also referred to as "other 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, based on the total amount of monomers used in the polymerization.

In order to improve the dispersibility of the inorganic filler when the composition contains an inorganic filler, and thereby improve various physical properties (e.g., strength, abrasion resistance, viscoelastic properties, etc.) of the crosslinked body obtained using the composition, it is preferable that the polymer [P] has a random copolymerization portion in which the distribution of the conjugated diene compound and the aromatic vinyl compound is irregular. When the polymer [P] has a random copolymerization portion of a conjugated diene compound and an aromatic vinyl compound, the polymer [P] may further have a block portion made of a conjugated diene compound or an aromatic vinyl compound. In terms of high living property in anionic polymerization, the polymer [P] is preferably a copolymer containing 1,3-butadiene and styrene in the monomer composition.

Polymerization methods that can be used include solution polymerization, gas phase polymerization, bulk polymerization, and the like. Of these, solution polymerization is particularly preferred. The polymerization form may be either batch or continuous. When using solution polymerization, a specific example of the polymerization method is a method in which monomers including a conjugated diene compound and an aromatic vinyl compound are polymerized in a solvent (preferably an organic solvent) in the presence of a polymerization initiator and, if necessary, a vinyl content regulator (hereinafter, also referred to as a "randomizer").

As the polymerization initiator, a metal compound containing an alkali metal or an alkaline earth metal can be used. Of these, a compound containing an alkali metal is preferred. Specific examples of metal compounds include alkyl lithium such as methyl lithium, ethyl lithium, n-propyl lithium, n-butyl lithium, sec-butyl lithium, and 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, naphthyl potassium, and ethoxy potassium. Of these, lithium compounds are preferred.

The metal compound used as the polymerization initiator may be a metal amide compound having an alkali metal or an alkaline earth metal. By carrying out the polymerization to obtain the polymer [P] in the presence of a metal amide compound, an amino group (preferably a secondary amino group or a tertiary amino group) can be introduced to the polymerization initiation terminal of the conjugated diene polymer. The polymer [P] obtained by polymerizing the monomers in the presence of a metal amide compound is preferable in that it can increase the strength of the crosslinked body and can increase the effect of improving the fuel efficiency of the crosslinked body when used for tires.

The metal amide compound is preferably a compound obtained by mixing a lithium compound (e.g., alkyl lithium, etc.) with a compound having a nitrogen atom (hereinafter also referred to as the "initial end modifier"). The initial end modifier is preferably a secondary amine compound. Specific examples thereof include dimethylamine, diethylamine, dipropylamine, dibutylamine, dodecamethyleneimine, N,N'-dimethyl-N'-trimethylsilyl-1,6-diaminohexane, piperidine, pyrrolidine, hexamethyleneimine, heptamethyleneimine, dicyclohexylamine, N-methylbenzylamine, di-(2-ethylhexyl)amine, diallylamine, morpholine, N-(trimethylsilyl)piperazine, N-(tert-butyldimethylsilyl)-4-piperazine, 1,3-ditrimethylsilyl-1,3,5-triazinane, etc.

When polymerization is carried out in the presence of a metal amide compound, a lithium compound and an initiating end modifier may be mixed in advance to prepare a metal amide compound, and the prepared metal amide compound may be added to the polymerization system to carry out polymerization. Alternatively, a lithium compound and an initiating end modifier may be added to the polymerization system, and the two may be mixed in the polymerization system to prepare a metal amide compound, and polymerization may be carried out. The amount of polymerization initiator used in polymerization is preferably 0.01 to 20 mmol, and more preferably 0.05 to 15 mmol, per 100 g of monomer used to synthesize the polymer.

The randomizer can be used for the purpose of adjusting the vinyl bond content, which indicates the content of vinyl bonds in a polymer. Examples of randomizers include dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, 2,2-di(tetrahydrofuryl)propane, 2-(2-ethoxyethoxy)-2-methylpropane, triethylamine, pyridine, N-methylmorpholine, tetramethylethylenediamine, potassium dodecylbenzenesulfonate, etc. The randomizer can be used alone or in combination of two or more types.

As the organic solvent used in the polymerization, an organic solvent that does not participate in the polymerization reaction can be preferably used. Specific examples of the organic solvent used in the polymerization include, for example, chain or cyclic aliphatic hydrocarbons, aromatic hydrocarbons, etc. Among these, hydrocarbons having 3 to 8 carbon atoms are preferred, and specific examples thereof include, for example, 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, cyclohexene, etc. The organic solvent can be used alone or in combination of two or more kinds.

When solution polymerization is used, the monomer concentration in the reaction solvent is preferably 5 to 50% by mass, more preferably 10 to 30% by mass, from the viewpoint of maintaining a balance between productivity and ease of polymerization control. The temperature of the polymerization reaction is preferably -20°C to 150°C, more preferably 0 to 120°C. The polymerization reaction is preferably carried out under a pressure sufficient to substantially keep the monomer in a liquid phase. Such a pressure can be obtained by a method such as pressurizing the inside of the reactor with a gas that is not involved in the polymerization reaction. By such a polymerization reaction, a conjugated diene polymer having an active end can be obtained. In this specification, the term "active end" refers to the portion (more specifically, the metal end) other than the structure derived from the monomer having a carbon-carbon double bond that is present at the end of the molecular chain.

The vinyl bond content of the conjugated diene polymer obtained by the polymerization is preferably 10 to 40 mol%. The vinyl bond content is preferably 15 mol% or more, more preferably 20 mol% or more. The vinyl bond content of the conjugated diene polymer is preferably 39 mol% or less, more preferably 37 mol% or less. In this specification, the "vinyl bond content" is a value indicating the content ratio of structural units having vinyl bonds (1,2-bonds) to all structural units derived from 1,3-butadiene contained in the conjugated diene polymer before hydrogenation. The vinyl bond content is a value measured by a ¹ H-NMR device. Note that β represented by the above formula (ii) corresponds to the vinyl bond content of the conjugated diene polymer before hydrogenation. For example, when the β of a polymer is 0.10, the vinyl bond content of the polymer before hydrogenation is 10%.

The polymerization can be terminated by reacting the conjugated diene polymer having an active end with an alcohol or hydrogen. Alternatively, the conjugated diene polymer having an active end may be reacted with a modifier by the modification process described below.

<Modification step>
In the modification step, a compound having a functional group that is covalently bonded or interacts with the inorganic filler and can react with the active end of the polymer is preferably used as a modifying agent, and the modifying agent is reacted with the conjugated diene polymer having an active end. The modifying agent may be a compound having one reactive site with the active end of the polymer (hereinafter also referred to as a "terminal end modifying agent"), or a polyfunctional compound having two or more reactive sites with the active end of the polymer (hereinafter also referred to as a "specific coupling agent").

The end-terminal modifier is not particularly limited, and can be appropriately selected from compounds known as modifiers for conjugated diene polymers. As the end-terminal modifier, a compound having at least one element selected from the group consisting of nitrogen, oxygen, silicon, and phosphorus, and having no active hydrogen bonded to the element, can be preferably used. As the end-terminal modifier, a compound having at least one specific functional group selected from the group consisting of an amino group, a group having a carbon-nitrogen double bond, a nitrogen-containing heterocyclic group, a phosphino group, a cyclic ether group, a protected hydroxyl group, and a hydrocarbyloxysilyl group, and capable of reacting with a polymerization active terminal, can be preferably used. The amino group is preferably a protected primary amino group, a protected secondary amino group, or a tertiary amino group. Such a compound is not particularly limited, but for example, one or more of the compounds described in JP-A-2003-171418 and WO2021/112167 can be preferably used.

A preferred specific example of the terminal modifying agent is at least one selected from the group consisting of compounds represented by the following formula (5) and compounds represented by the following formula (6).

(In formula (5), A ¹¹ is a monovalent functional group having at least one element selected from the group consisting of nitrogen, sulfur, phosphorus, and oxygen, having no active hydrogen, and bonded to R ³⁵ via nitrogen, sulfur, phosphorus, oxygen, or a carbon atom contained in a carbonyl group, or is an epoxy group. R ³³ and R ³⁴ are each independently a hydrocarbyl group. R ³⁵ is a hydrocarbylene group. t is an integer of 0 to 2. However, when t is 2, multiple R ^33s in the formula are the same as or different from each other. When t is 0 or 1, multiple R ^34s in the formula are the same as or different from each other.)

(In formula (6), A ¹² is a monovalent functional group having at least one element selected from the group consisting of nitrogen, sulfur, phosphorus, and oxygen, having no active hydrogen, and bonded to R ³⁹ via nitrogen, sulfur, phosphorus, or oxygen, or a hydrocarbyl group having 1 to 20 carbon atoms. R ³⁶ and R ³⁷ are each independently a hydrocarbyl group. R ³⁸ is a hydrocarbylene group. ^{R 39} is a single bond or a hydrocarbylene group. u is 0 or 1. However, when u is 0, multiple R ³⁷ in the formula are the same or different from each other.)

In the above formulas (5) and (6), with respect to R ³³ , R ³⁴ , R ³⁶ , R ³⁷ , and A ¹² when it is a hydrocarbyl group, the hydrocarbyl group is preferably a linear or branched alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms.
The hydrocarbylene group represented by R ³⁵ and R ³⁹ is preferably a linear or branched alkanediyl group having 1 to 20 carbon atoms, a cycloalkylene group having 3 to 20 carbon atoms, or an arylene group having 6 to 20 carbon atoms. The hydrocarbylene group represented by R ³⁸ is preferably a linear or branched alkanediyl group having 1 to 20 carbon atoms.
t is preferably 0 or 1.

When A ¹¹ is the monovalent functional group, at least one element selected from the group consisting of nitrogen, sulfur, phosphorus, and oxygen possessed by A ¹¹ , and when A ¹² is the monovalent functional group, at least one element selected from the group consisting of nitrogen, sulfur, phosphorus, and oxygen possessed by A ¹² may be protected, for example, by a tri-substituted hydrocarbylsilyl group, etc. In this specification, active hydrogen refers to a hydrogen atom bonded to an atom other than a carbon atom, and preferably refers to one having a bond energy lower than that of the carbon-hydrogen bond of polymethylene.

A ¹¹ may be a group that can be turned into an onium ion by an onium salt generating agent. The end-end modifying agent has such a group (A ¹¹ ), and thus can impart excellent shape retention to the polymer. Specific examples of A ¹¹ include a nitrogen-containing group in which two hydrogen atoms of a primary amino group are protected, a nitrogen-containing group in which one hydrogen atom of a secondary amino group is protected, a tertiary amino group, an imino group, a nitrogen-containing heterocyclic group (e.g., a group having a heterocyclic ring such as a pyridine ring or an imide ring), a phosphorus-containing group in which two hydrogen atoms of a primary phosphino group are protected, a phosphorus-containing group in which one hydrogen atom of a secondary phosphino group is protected, a tertiary phosphino group, an epoxy group, an oxygen-containing group in which the hydrogen atom of a hydroxyl group is protected, a sulfur-containing group in which the hydrogen atom of a thiol group is substituted with a protecting group, and a hydrocarbyloxycarbonyl group.

Among these, a group having a nitrogen atom is preferred because of its good affinity with silica, and a nitrogen-containing group or an imino group in which two hydrogen atoms of a tertiary amino group or a primary amino group are protected is more preferred. The protected group is a group in which A ¹¹ and A ¹² are converted into functional groups that do not react with the polymerization active terminal. The onium salt generating agent is a Bronsted acid or a compound that generates a Bronsted acid when contacted with water.

Specific examples of end-terminal modifying agents include compounds represented by formula (5), such as N,N-bis(trimethylsilyl)aminopropyltrimethoxysilane, N,N-dimethylaminopropyltriethoxysilane, 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-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-(trimethylsilylmercapto)propyltrimethoxysilane, and 3-(diphenylphosphino)propylmethyldiethoxysilane.

Specific examples of compounds represented by formula (6) include, for example, 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1,2-azasilolidine, 2,2-diethoxy-1-(3-trimethoxysilylpropyl)-1,2-azasilolidine, 2,2-dimethoxy-1-phenyl-1,2-azasilolidine, 1-trimethylsilyl-2,2-dimethoxy-1-aza-2-silacyclopentane, 2-(2,2-dimethoxy-1,2-azasilolidine-1-yl)-N,N-diethylethane-1-amine, 2-(2,2-dimethoxy-1,2-azasilolidine-1-yl)-N,N-dimethylethane-1-amine, and 3-(2,2-dimethoxy-1,2-azasilolidine-1-yl)-N,N-diethylpropane-1-amine. The terminal modifying agent may be used alone or in combination of two or more.

Specific examples of the polyfunctional compound having either or both of nitrogen and oxygen among the specific coupling agents include tetraglycidyl-1,3-bisaminomethylcyclohexane, N,N,N',N'-tetra(3-trimethoxysilylpropyl)ethylenediamine, N,N,N',N'-tetra(3-triethoxysilylpropyl)ethylenediamine, N,N,N'-tris(3-trimethoxysilylpropyl)-N'-methyl-ethylenediamine, N,N,N',N'-tetra(3-trimethoxysilylpropyl)-1,3-propanediamine, N,N,N',N'-tetra(3-trimethoxysilylpropyl)-1,4-butanediamine, bis(3-trimethoxysilylpropyl)-[2-(dimethylamino)ethyl]amine, bis(3-trimethoxysilylpropyl)-[2-(2,2-dimethoxy-1-aza-2-silanediamine], and the like. cyclopentane)ethyl]amine, bis(3-triethoxysilylpropyl)-[2-(2,2-diethoxy-1-aza-2-silacyclopentane)ethyl]amine, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine, bis(3-trimethoxysilylpropyl)-[2-(2,2-dimethoxy-1-aza-2-silacyclohexane)ethyl]amine, bis(3-trimethoxysilylpropyl)-[2-(2,2-dimethoxy-1-aza-2-silacyclooctane)ethyl]amine, N,N-bis(3-trimethoxysilylpropyl)-3-imidazolylpropylamine, bis(3-trimethoxysilylpropyl)-(3-dimethylaminopropyl)amine, and compounds represented by each of the following formulas (M-1) to (M-4).

(In formula (M-1), R ²⁰ represents a hydrogen atom or an alkyl group. n1 represents an integer of 1 to 8.)

Specific examples of polyfunctional compounds containing silicon or phosphorus include dibutyldichlorosilicon, methyltrichlorosilicon, methyldichlorosilicon, tetrachlorosilicon (silicon tetrachloride), silicon tetrabromide, silicon tetraiodide, trichloromethoxysilane, tribromomethoxysilane, trimethoxysilane, tetramethoxysilane, trichlorophosphine, etc.

In the reaction to obtain the polymer [P], a multifunctional compound other than the specific coupling agent may be used as a coupling agent to react with the polymer having an active end. Examples of such multifunctional compounds include tetrachlorotin (tin tetrachloride), tetrabromotin, trichlorobutyltin, trichloromethyltin, trichloroethyltin, trichlorophenyltin, trichlorooctyltin, divinylbenzene, and trichloropropane.

The reaction between the conjugated diene polymer having an active end and the 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 is completed, or the conjugated diene polymer contained in the solution may be isolated and dissolved in a suitable solvent such as cyclohexane before the reaction. The reaction may be carried out either batchwise or continuously. In this case, the method of adding the modifier is not particularly limited, and examples include a method of adding the modifier all at once, a method of adding the modifier in portions, and a method of adding the modifier continuously.

The amount of modifier to be reacted with the conjugated diene polymer having an active end may be appropriately set according to the type of compound used in the reaction. The amount of modifier used is preferably 0.1 mol equivalent or more, more preferably 0.3 to 1.5 mol equivalent, relative to the metal element involved in the polymerization reaction of the polymerization initiator. 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. Also, if the modification reaction temperature is high, the polymerization active end is easily deactivated. The reaction time is preferably 1 minute to 5 hours, more preferably 2 minutes to 1 hour.

<Hydrogenation process>
In the hydrogenation step, the conjugated diene polymer obtained by the polymerization step or modification step is hydrogenated (hereinafter also referred to as "hydrogenation"). Any method and conditions for the hydrogenation reaction can be used as long as a conjugated diene polymer with a desired hydrogenation rate can be obtained. Examples of such hydrogenation methods include a method using a catalyst mainly composed of an organometallic compound of titanium as a hydrogenation catalyst; a method using a catalyst composed of an organometallic compound of iron, nickel, or cobalt and an organometallic compound such as alkylaluminum; a method using an organic complex of an organometallic compound such as ruthenium or rhodium; and a method using a catalyst in which a metal such as palladium, platinum, ruthenium, cobalt, or nickel is supported on a carrier such as carbon, silica, or alumina. Among various methods, a method in which hydrogenation is carried out under mild conditions of low pressure and low temperature using a homogeneous catalyst consisting of an organometallic compound of titanium alone or an organometallic compound of titanium and an organometallic compound of lithium, magnesium or aluminum (for example, the catalysts described in JP-B-63-4841 and JP-B-1-37970) is preferred from an industrial viewpoint, and is also suitable because of its high hydrogenation selectivity to the double bonds of butadiene.

Hydrogenation of the conjugated diene polymer is preferably carried out using a solvent that does not react with the catalyst and dissolves the conjugated diene polymer. Preferred solvents include chain aliphatic hydrocarbons such as n-pentane, n-hexane, and n-octane; cyclic aliphatic hydrocarbons such as cyclohexane and cycloheptane; aromatic hydrocarbons such as benzene and toluene; and ethers such as diethyl ether and tetrahydrofuran. The solvent used for hydrogenation may be one of the above compounds, or a mixture containing the above compounds as the main components.

The hydrogenation reaction is generally carried out by maintaining the conjugated diene polymer at a prescribed temperature in a hydrogen or inert atmosphere, adding a hydrogenation catalyst with or without stirring, and then introducing hydrogen gas to pressurize to a prescribed pressure. An inert atmosphere means an atmosphere that does not react with the substances involved in the hydrogenation reaction, such as an atmosphere of helium, neon, or argon. Air and oxygen are not preferred as they oxidize the catalyst and cause it to become inactive. Nitrogen is also not preferred as it acts as a catalyst poison during the hydrogenation reaction and reduces the hydrogenation activity. In particular, it is preferable that the hydrogenation reactor be an atmosphere of hydrogen gas alone.

The hydrogenation reaction process can be a batch process, a continuous process, or a combination of both. When a titanocene diaryl compound is used as the hydrogenation catalyst, it can be added to the reaction solution either alone or as a solution in an inert organic solvent. When the catalyst is used as a solution, various solvents that do not react with the substances involved in the hydrogenation reaction can be used as the inert organic solvent. The same solvent as that used in the hydrogenation reaction is preferably used. The preferred amount of catalyst to be added is 0.02 to 20 mmol per 100 g of the conjugated diene polymer before hydrogenation.

The hydrogenated conjugated diene polymer (hereinafter also referred to as "hydrogenated conjugated diene polymer") has a hydrogenation rate of 60% or more and 97% or less. The hydrogenation rate of the polymer [P] is preferably 65% or more, more preferably 70% or more, even more preferably 75% or more, and particularly preferably 80% or more. The hydrogenation rate of the polymer [P] is preferably 96% or less. In addition, α represented by the above mathematical formula (i) corresponds to the hydrogenation rate of the hydrogenated conjugated diene polymer. For example, when α of a polymer is 0.60, the hydrogenation rate of the polymer is 60%. In this specification, the hydrogenation rate is a value measured by a ¹ H-NMR device. The hydrogenation rate of the hydrogenated conjugated diene polymer can be adjusted by adjusting the hydrogenation reaction time or controlling the cumulative supply amount of hydrogen.

The preferred method for obtaining polymer [P] is to solution polymerize monomers containing 1,3-butadiene and styrene in the presence of a polymerization initiator, add a compound (polymerization termination end, specific coupling agent) that contains at least one element selected from the group consisting of nitrogen, oxygen, silicon, and phosphorus and that can react with the active end of the conjugated diene polymer to the obtained polymer solution to carry out a modification reaction, and then subject the solution to a hydrogenation step. This method is preferred in that it can obtain a crosslinked product that is excellent in various physical properties (strength, wet grip performance, etc.), and is also industrially useful.

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

The total proportion of the first polymer and the second polymer in the composition is preferably 50 to 100 mass% of the total amount of the rubber component contained in the composition. By setting the total proportion of the first polymer and the second polymer in the above range, it is possible to obtain a polymer composition that is highly effective in improving the strength and ozone resistance of the crosslinked body and has excellent abrasion resistance. From these viewpoints, the total proportion of the first polymer and the second polymer is preferably 60 mass% or more, and more preferably 70 mass% or more, of the total amount of the rubber component contained in the composition.

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

<Other ingredients>
In addition to the First Polymer and the Second Polymer, the composition may further contain the following components.

(Component (B): Inorganic Filler)
The composition may contain an inorganic filler. Examples of the inorganic filler include silica and carbon black, and fillers other than silica and carbon black (hereinafter, also referred to as "other fillers"). The inorganic filler blended in the composition preferably contains one or both of silica and carbon black.

Component (B-1): Silica The present composition may contain silica. The amount of silica is preferably in the range of 20 to 120 parts by mass, more preferably in the range of 30 to 100 parts by mass, per 100 parts by mass of the rubber component containing the 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, and when it is 120 parts by mass or less, the processability of the polymer composition can be sufficiently improved.

The silica is not particularly limited, and examples thereof include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. Among these, wet silica is preferred. As the silica, one type may be used alone, or two or more types may be used in combination. The BET specific surface area of the silica (a value measured in accordance with ISO 5794/1) is preferably in the range of 10 to 350 m ² /g, more preferably in the range of 20 to 300 m ² /g, and particularly preferably in the range of 30 to 250 m ² /g. Silica having a BET specific surface area in this range has the advantage of being able to achieve both rubber reinforcing properties and dispersibility in the modified diene polymer (A). Examples of such silica that can be used include commercially available products such as "Nipsil AQ" (BET specific surface area = 205 ^m2 /g) and "Nipsil KQ" manufactured by Tosoh Silica Corporation, and "Ultrasil VN3" (BET specific surface area = 175 ^m2 /g) manufactured by Degussa.

The silica to be blended in the present composition may be a combination of two or more 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.

The composition may contain 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. By using such a first silica and a second silica in combination, it becomes possible to disperse the first silica, which has a small average primary particle size but a relatively large aggregate size, well in the rubber component. This improves the dispersibility of the silica, and provides excellent 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 190 m ² /g or more, the breaking strength and abrasion resistance of the crosslinked body obtained by the polymer composition tend to be sufficiently improved. The CTAB specific surface area of the first silica 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, the silica is less likely to aggregate, and the physical properties tend to be improved.

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 190 m ² /g or more, the breaking strength and abrasion resistance of the crosslinked body obtained from the polymer composition tend to be sufficiently improved. The BET specific surface area of the first silica 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, the silica is less likely to aggregate, and the physical properties tend to be improved. The BET specific surface area of the 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. By having such an aggregate size, it is possible to provide excellent fuel efficiency and wear resistance while having good dispersibility (processability). The aggregate size of silica can be measured by 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. The lower limit of the average primary particle diameter is not particularly limited, but is preferably 3 nm or more, more preferably 5 nm or more, and even more preferably 7 nm or more. Although it has such a small average primary particle diameter, the dispersibility (processability) of the silica can be further improved by a carbon black-like structure having the above aggregate size, and the fuel efficiency and wear resistance can be further improved. 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 particles of silica observed within the field of view, and averaging the measured particle 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. If the CTAB specific surface area is less than 10 m ² /g, the reinforcing property is low, and it may be difficult to sufficiently secure the mechanical strength and abrasion resistance required for the polymer composition for tire production. 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. If the CTAB specific surface area exceeds 95 m ² /g, the dispersibility of the silica may be poor, and it may be difficult to improve the 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 of the second silica is 10 m ² /g or more, it has sufficient reinforcing properties and tends to easily ensure the mechanical strength and abrasion resistance required for a polymer composition for obtaining rubber for tires. The BET specific surface area of the second silica 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 of the second silica is 85 m ² /g or less, the silica is sufficiently dispersed, and it tends to easily improve the rubber fracture 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. There is no particular upper limit to the average primary particle diameter, but it 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. By having such an average primary particle diameter, it is possible to sufficiently ensure fracture strength and abrasion resistance.

Component (B-2): Carbon Black The present composition may contain carbon black 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. The nitrogen adsorption specific surface area (N ₂ SA) is the value obtained by measuring the amount of nitrogen adsorbed on the carbon black surface according to JIS K6217-2:2001 "Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method". Carbon black may be used alone or in combination of two or more types. The amount of carbon black in the composition is preferably in the range of 1 to 150 parts by mass, and more preferably in the range of 5 to 120 parts by mass, per 100 parts by mass of the rubber component containing the polymer [P].

Component (B-3): Other Fillers The present composition may contain other fillers in addition to silica and carbon black as inorganic fillers. 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 ], magnesium aluminum 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], zirconium carbonate [Zr(CO ₃ ) ₂ ], crystalline aluminosilicates containing hydrogen, alkali metals or alkaline earth metals to compensate for the charge, such as various zeolites, and the like.

In the present composition, the amount of inorganic filler containing silica and carbon black is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, per 100 parts by mass of the rubber component containing the polymer [P]. The amount of inorganic filler is preferably 350 parts by mass or less, more preferably 200 parts by mass or less, per 100 parts by mass of the rubber component containing the polymer [P]. If the amount of inorganic filler in the present composition is within the above range, when the present composition is applied to a tire tread, the tire can have a high level of balance and goodness in terms of low rolling resistance, braking performance on wet road surfaces, handling performance on dry road surfaces, and abrasion resistance.

(Component (C): Other rubber components)
The present composition may contain only the polymer [P] as a rubber component, but may also contain a rubber component different from the polymer [P] (hereinafter, also referred to as "other rubber component") in addition to the polymer [P], within a range that does not impair the effects of the present disclosure. As the other rubber component, for example, at least one type of rubber selected from natural rubber, a conjugated diene-based polymer different from the first polymer and the second polymer (for example, isoprene rubber, butadiene rubber, emulsion-polymerized or solution-polymerized styrene-butadiene rubber, hydrogenated styrene-butadiene rubber), butyl rubber, halogenated butyl rubber, and ethylene-propylene rubber can be used. Among these, the other rubber component is preferably at least one type selected from the group consisting of a conjugated diene-based polymer different from the first polymer and the second polymer and natural rubber, and more preferably at least one type selected from the group consisting of natural rubber, butadiene rubber, and styrene-butadiene rubber.

When mixing the other rubber components with the polymer [P], the manner in which they are mixed is not particularly limited. For example, the other rubber components may be mixed with the polymer [P] during kneading using a Banbury mixer or rolls, which is normally performed, or the other rubber components may be mixed with a polymer solution containing the polymer [P] after polymerization, and then a desolvation and drying process may be performed.

The amount of the other rubber components is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total amount of the rubber components (first polymer, second polymer, and other rubber components) contained in the polymer composition.

In this composition, liquid rubber can be used as part 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. In this specification, the weight average molecular weight of the liquid rubber refers to the weight average molecular weight in terms of polystyrene analyzed by gel permeation chromatography (GPC). The liquid rubber used in this composition refers to one that has fluidity at 23°C.

(Component (D): Resin Component)
The composition may further contain a resin component. The resin component may be a thermoplastic resin or a thermosetting resin. From the viewpoint of obtaining a crosslinked body having excellent properties such as strength, abrasion resistance, and crack growth resistance, the resin component is preferably at least one selected from the group consisting of styrene-based resins, polyethylene, C5-based resins, C9-based resins, C5/C9-based resins, dicyclopentadiene-based resins, alkylphenol-based resins, and terpene-based resins. As the resin component, one type may be used alone, or two or more types may be used in combination.

Here, the styrene-based resin is a polymer obtained using a styrene-based monomer, and in particular, it is preferable for the polymer to have structural units derived from styrene-based monomers in an amount of 20 mass% or more relative to the total amount of monomer units possessed by the styrene-based resin. Examples of styrene-based monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, etc. Of these, it is preferable for the styrene-based monomer to be at least one of styrene and α-methylstyrene.

The styrene resin may be a homopolymer obtained by polymerizing one type of styrene monomer, or a copolymer obtained by copolymerizing two or more types of styrene monomer. The styrene resin may also be a copolymer obtained by using a styrene monomer and another monomer that can be copolymerized with the styrene monomer. Examples of other monomers include unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylics and methacrylic acid; unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate; dienes such as chloroprene, butadiene, and isoprene; olefins such as 1-butene and 1-pentene; α,β-unsaturated carboxylic acids such as maleic anhydride or their acid anhydrides, etc.

The softening point of the styrene resin is preferably 30°C or higher, more preferably 60°C or higher, and even more preferably 80°C or higher. When the softening point is 30°C or higher, the crosslinked body tends to have an improved crack growth resistance. The softening point of the styrene resin is preferably 160°C or lower, more preferably 130°C or lower, and even more preferably 100°C or lower. When the softening point is 160°C or lower, the resin has good dispersibility, and crack growth resistance, abrasion resistance, and breaking strength tend to be improved. In this disclosure, the softening point of the styrene resin is a value measured using a ring and ball softening point measuring device according to the method specified in JIS K 6220-1:2015, and is the temperature when the sample softens and the ball placed on the sample falls onto the bottom plate.

As the styrene-based resin, a block polymer (thermoplastic elastomer) having a conjugated diene polymer block as a soft segment and a polystyrene block as a hard segment can also be used. When such a block polymer is used, the effect of improving crack growth resistance can be further enhanced, which is preferable. Note that the conjugated diene polymer block of the block polymer may have some of the carbon-carbon double bonds in the structural unit derived from the conjugated diene compound hydrogenated.

Conjugated diene compounds constituting the above-mentioned conjugated diene polymer block include, for example, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, etc. The conjugated diene compounds may be used alone or in combination of two or more. Among these, the conjugated diene compound is preferably at least one of 1,3-butadiene and isoprene. The content of the conjugated diene units in the block polymer is preferably 20% by mass or more, and more preferably 30% by mass or more. The content of the conjugated diene units is preferably 80% by mass or less, and more preferably 70% by mass or less.

The content of the polystyrene block in the block polymer is preferably 20% by mass or more in terms of increasing the breaking strength. The content of the polystyrene block is preferably 80% by mass or less, and more preferably 70% by mass or less. The content ratios of the polystyrene block, the conjugated diene polymer block, and the conjugated diene unit in the block polymer can be calculated from the integral ratio of ¹ H-NMR spectrum.

Specific examples of the block polymer include styrene-butadiene block copolymers, styrene-isoprene block copolymers, epoxidized products of styrene-butadiene block copolymers, and block copolymers in which a part of the conjugated diene polymer block of a styrene-butadiene block copolymer or a styrene-isoprene block copolymer has been hydrogenated. More specifically, examples include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene-butylene-styrene block copolymer (SBBS), and epoxidized products of styrene-butadiene-styrene block copolymers, as well as hydrogenated products of these copolymers. As the block polymer, from the viewpoint of being easily crosslinked, it is preferable to use SBS or SIS having a conjugated diene polymer block in which the soft segment is not hydrogenated, or an epoxidized product of a styrene-butadiene-styrene block copolymer.

Examples of polyethylene include low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), etc. C5 resin is a solid polymer (C5 synthetic petroleum resin) obtained by polymerizing a C5 fraction using a Friedel-Crafts type catalyst ( _AlCl3 , _BF3 , etc.). Specific examples of C5 resin include copolymers mainly composed of isoprene, cyclopentadiene, 1,3-pentadiene, 1-pentene, etc., copolymers of 2-pentene and dicyclopentadiene, polymers mainly composed of 1,3-pentadiene, etc.

The C9 resin is a solid polymer (C9 synthetic petroleum resin) obtained by polymerizing the C9 fraction using a Friedel-Crafts catalyst (AlCl ₃ , BF ₃ , etc.). Specific examples of the C9 resin include copolymers mainly composed of indene, methylindene, vinyltoluene, etc. The C5/C9 resin is a solid polymer (C5/C9 synthetic petroleum resin) obtained by polymerizing the C5 to C9 fraction using a Friedel-Crafts catalyst (AlCl ₃ , BF ₃ , etc.). Specific examples of the C5/C9 resin include copolymers mainly composed of vinyltoluene, indene, etc. The C5/C9 resin is preferably a resin with a small amount of C9 or more components from the viewpoint of compatibility with the rubber component. Specifically, the C5/C9 resin is preferably a resin with a C9 or more component in the total amount of the resin less than 50 mass%, more preferably 40 mass% or less.

Dicyclopentadiene resins are petroleum resins that use dicyclopentadiene from the C5 fraction as the main raw material. Specific examples of dicyclopentadiene resins include Maruzen Petrochemical Co., Ltd.'s "Marukaretzu M" series (M-890A, M-845A, M-990A, etc.). Examples of alkylphenol resins include alkylphenol-acetylene resins such as p-tert-butylphenol-acetylene resin, and low-polymerization alkylphenol-formaldehyde resins.

Terpene resins are solid resins obtained by blending turpentine oil, which is obtained at the same time as rosin is obtained from pine trees, or polymerization components separated from this, and polymerizing them using a Friedel-Crafts catalyst, and examples of such resins include β-pinene resin and α-pinene resin. Commercially available terpene resins can be used, such as the "YS Resin" series (PX-1250, TR-105, etc.) manufactured by Yasuhara Chemical Co., Ltd. and the "Picolite" series (A115, S115, etc.) manufactured by Hercules.

A representative example of a terpene-aromatic compound resin is terpene-phenol resin. This terpene-phenol resin can be obtained by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing them with formalin. There are no particular restrictions on the terpenes used as raw materials, and monoterpene hydrocarbons such as α-pinene and limonene are preferred, and those containing α-pinene are more preferred, with α-pinene being particularly preferred. Furthermore, as the terpene-phenol resin, a terpene-phenol resin with a low ratio of phenol components is preferred. Here, "low ratio of phenol components" refers to a phenol component content of less than 50 mass%, preferably 40 mass% or less in the total amount of resin. In addition, if a terpene-aromatic compound resin, particularly a terpene-phenol resin, is used as the thermoplastic resin, the handling performance can be further improved. As the terpene-aromatic compound resin, commercially available products can be used. Examples of commercially available products include those sold under the trade names "Tamanol 803L" and "Tamanol 901" (manufactured by Arakawa Chemical Industries, Ltd.), and the "YS Polystar (registered trademark)" series (manufactured by Yasuhara Chemical Co., Ltd.).

The blending ratio of the resin component is preferably 1 part by mass or more per 100 parts by mass of the rubber component contained in the composition. By blending 1 part by mass or more of the resin component, the effect of improving the abrasion resistance, breaking strength, and crack growth resistance by adding the resin component can be sufficiently increased in the crosslinked body obtained using the composition, which is preferable. The blending ratio of the resin component is more preferably 3 parts by mass or more per 100 parts by mass of the rubber component, and even more preferably 7 parts by mass or more. In addition, from the viewpoint of maintaining various performances of the composition well, the blending ratio of the resin component is preferably 50 parts by mass or less per 100 parts by mass of the rubber component contained in the composition, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less. As the resin component, one type may be used alone, or two or more types may be used in combination.

(Component (E): Silane Coupling Agent)
In the present composition, a silane coupling agent may be blended to further increase the dispersibility of silica. There is no particular limitation on the silane coupling agent used. As the silane coupling agent, a sulfur-containing silane coupling agent is preferable, and examples thereof include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthiopropyltriethoxysilane.

The amount of the silane coupling agent is preferably 1 to 20 parts by mass per 100 parts by mass of silica contained in the composition. If the amount of the silane coupling agent is less than 1 part by mass, there is a concern that the effect of improving the dispersibility of the silica will be reduced due to the small amount. On the other hand, if the amount of the silane coupling agent is more than 20 parts by mass, the processability of the polymer composition and the breaking elongation of the crosslinked body may decrease. It is more preferable that the amount of the silane coupling agent is 5 to 15 parts by mass per 100 parts by mass of silica contained in the composition.

(Component (F): Crosslinking Agent)
The composition may contain a crosslinking agent. When the composition contains a crosslinking agent, a crosslinked product having improved strength and abrasion resistance can be obtained. Examples of the crosslinking agent include sulfur, halogenated sulfur, organic peroxides, quinone dioximes, organic polyamine compounds, and alkylphenol resins having methylol groups, and sulfur is usually used. The amount of the crosslinking agent is preferably 0.1 to 5 parts by mass, more preferably 0.5 to 3 parts by mass, based on 100 parts by mass of the total amount of the rubber components contained in the composition.

(Component (G): Extending oil)
The composition may contain a process oil that is generally used to extend elastomers. The method of adding the process oil is not particularly limited. For example, the process oil may be developed in the conjugated diene polymer solution after polymerization and then desolvated to form an oil-extended rubber, or the process oil may be directly added during kneading to obtain a rubber compound (compounded rubber) to be added to the polymer composition. Preferred process oils include various oils known in the art, such as aromatic oils, paraffinic oils, naphthenic oils, vegetable oils (sunflower oil, soybean oil, etc.), and oils with low polycyclic aromatic compound content (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 Catenex SNR (heavy paraffin obtained by dewaxing distillate oil with a solvent) manufactured by Shell as MES, Vivatec 500 manufactured by H&R Wasag AG as TDAE, and NC140 manufactured by Japan Energy Corp. as SRAE. The amount of the process oil to be blended is preferably 10 to 100 parts by mass based on 100 parts by mass of the total amount of the polymer components contained in the polymer composition.

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

The composition may be in the form of solid particles (crumbs), or may be a rubber veil obtained by compression molding the crumbs into a desired shape (e.g., a rectangular parallelepiped shape). The rubber veil as the composition may contain an extender oil together with the first polymer and the second polymer. When the composition is a rubber veil, the total proportion of the first polymer, the second polymer, and the extender oil in the composition is preferably 90 to 100% by mass, and more preferably 95 to 100% by mass, when the entire composition is taken as 100% by mass.

Another embodiment of the present composition is a blended composition obtained by blending the various components described above (components (B) to (G), etc.) with the first polymer and the second polymer as necessary. The blended composition can be obtained by mixing the first polymer and the second polymer with various additives (components (B) to (G), etc.) that are optionally used in the polymer composition for obtaining vulcanized rubber, and kneading them using a kneading machine such as an open kneader (e.g., a roll) or an internal kneader (e.g., a Banbury mixer). The blended rubber thus obtained is crosslinked (vulcanized) after molding and processing to obtain a crosslinked body (i.e., vulcanized rubber).

The crosslinked body obtained using the polymer composition of the present disclosure, which contains the first polymer and the second polymer, can be applied to various rubber products. Specifically, the crosslinked body obtained using the present composition can be applied to applications such as tire applications such as tire treads, undertreads, carcasses, sidewalls, and bead parts; sealing materials such as packings, gaskets, weather strips, and O-rings; interior and exterior skin materials for various vehicles such as automobiles, ships, aircraft, and railways; building materials; vibration-proof rubbers 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 electric wires; and other industrial products.

The present composition containing the first polymer and the second polymer can provide a crosslinked product with a good balance of various physical properties required for tire applications, such as mechanical strength, low-temperature grip performance, and ozone resistance. Therefore, the polymer composition containing the first polymer and the second polymer can be particularly suitably used as a material for the cap tread, sidewall, or both of tires.

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

According to the present disclosure described above in detail, the following means are provided.
[Means 1] A polymer composition comprising: a first polymer containing a structural unit derived from an aromatic vinyl compound and a structural unit derived from butadiene and satisfying the following conditions (x) and (y); and a second polymer containing a structural unit derived from an aromatic vinyl compound and a structural unit derived from butadiene and satisfying the following conditions (x) and (y), wherein the difference between the β of the first polymer and the β of the second polymer is 0.10 or less, and the difference between the content ratio of the structural unit derived from an aromatic vinyl compound in the first polymer and the content ratio of the structural unit derived from an aromatic vinyl compound in the second polymer is 10 to 30 mass %.
Condition (x) α is 0.60 or more and 0.97 or less. Condition (y) β is 0.10 or more and 0.40 or less. α = (p + (0.5 × r)) / (p + q + (0.5 × r) + s).
... (i)
β = (p + q) / (p + q + (0.5 × r) + s) ... (ii)
[Means 2] The polymer composition according to [Means 1], wherein β of the first polymer is different from β of the second polymer.
[Means 3] The polymer composition according to [Means 2], wherein β of the second polymer is larger than β of the first polymer.
[Means 4] The polymer composition according to any one of [Means 1] to [Means 3], wherein one or both of the first polymer and the second polymer have a functional group containing at least one element selected from the group consisting of nitrogen, oxygen, silicon, and phosphorus.
[Means 5] The polymer composition according to any one of [Means 1] to [Means 4], wherein the first polymer and the second polymer have a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography of 0.5 × 10 ⁵ or more and 2.0 × 10 ⁶ or less.
[Means 6] The polymer composition according to any one of [Means 1] to [Means 5], wherein a ratio of the first polymer to the second polymer, in terms of mass ratio, of the first polymer:the second polymer is in a range of 10:90 to 90:10.
[Means 7] The polymer composition according to any one of [Means 1] to [Means 6], further comprising at least one selected from the group consisting of a conjugated diene-based polymer different from the first polymer and the second polymer, and a natural rubber.
[Means 8] The polymer composition according to any one of [Means 1] to [Means 7], wherein a total ratio of the first polymer and the second polymer is 50 to 100 mass% of a total amount of a rubber component contained in the polymer composition.
[Means 9] The polymer composition according to any one of [Means 1] to [Means 8], further comprising an inorganic filler.
[Means 10] The polymer composition according to any one of [Means 1] to [Means 9], further comprising a silane coupling agent.
[Means 11] The polymer composition according to any one of [Means 1] to [Means 10], further comprising a resin component.
[Means 12] The polymer composition according to any one of [Means 1] to [Means 8], further comprising an extender oil.
[Means 13] The polymer composition according to [Means 12], wherein a total content ratio of the first polymer, the second polymer, and the extender oil is 90 to 100% by mass when the entire composition is taken as 100% by mass.
[Means 14] A tire having a cap tread and/or a sidewall constituted by a cured product of the polymer composition according to any one of [Means 1] to [Means 11].

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

[Evaluation of polymer properties]
Vinyl bond content (mol %) and β: Measured by 400 MHz ¹ H-NMR for the polymer before hydrogenation.
Bound styrene content (%): Measured by 400 MHz ¹ H-NMR for the polymer before hydrogenation.
First peak average molecular weight: For the polymer before hydrogenation, a chart based on the molecular weight converted into polystyrene was obtained using a gel permeation chromatograph (GPC, product name: HLC-8020, manufactured by Tosoh Corporation), and the first peak average molecular weight was determined from the retention time of the peak having the longest retention time in the obtained GPC curve. The specific measurement conditions are as follows:
(Measurement condition)
Column: Two GMH-HR-H columns (manufactured by Tosoh Corporation) were 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
Total weight average molecular weight: For the polymer before hydrogenation, it was determined in terms of polystyrene from all peaks of a GPC curve obtained using GPC (product name: HLC-8020, manufactured by Tosoh Corporation). The measurement conditions were the same as above.
Hydrogenation rate (%) and α: Calculated from ¹ H-NMR spectrum measured with a 100 MHz apparatus using ethylene tetrachloride as a solvent.

<Production of (hydrogenated) conjugated diene polymer>
[Production Example 1: Synthesis and Properties of Hydrogenated Conjugated Diene Polymer P1]
Into a nitrogen-substituted autoclave reactor having an internal volume of 50 liters, 25,800 g of cyclohexane, 39 g of tetrahydrofuran, 1,505 g of styrene, and 2,666 g of 1,3-butadiene were charged. After adjusting the temperature of the reactor contents to 40°C, a cyclohexane solution containing n-butyllithium (48 mmol) was added to initiate polymerization. The polymerization was carried out under adiabatic conditions. After confirming that the polymerization conversion rate had reached 99%, 129 g of 1,3-butadiene was added (additional butadiene), and polymerization was continued for another 3 minutes to obtain a reaction liquid containing a polymer. 2 mmol of silicon tetrachloride was added to the obtained reaction liquid and reacted for 5 minutes, and further 24 mmol of [N,N-bis(trimethylsilyl)aminopropyl]methyldiethoxysilane was added and reacted for 15 minutes.
Next, the reaction solution was heated to 80°C or higher, hydrogen was introduced into the system, and the reaction was carried out for 1 hour. A small amount of the polymer solution was extracted from the reaction vessel to obtain a conjugated diene polymer before hydrogenation for analysis. Thereafter, 28 mmol of diethylaluminum chloride, 9 mmol of bis(η5-cyclopentadienyl)titanium(furfuryloxy)chloride, and 19 mmol of n-butyllithium were added, and the hydrogenation reaction was carried out while maintaining the hydrogen pressure at 1.0 MPa. After the reaction, hydrogen was supplied until a predetermined hydrogen accumulation value was reached while maintaining the hydrogen pressure at 0.7 MPa or higher, and the reaction solution was returned to room temperature and pressure and extracted from the reaction vessel to obtain a polymer solution containing a hydrogenated conjugated diene polymer P1. A small amount of the obtained polymer solution was extracted, the solvent was removed by steam stripping, and the solution was dried by a hot roll adjusted to 130°C to obtain a hydrogenated conjugated diene polymer P1. Table 1 shows the polymerization recipe for the hydrogenated conjugated diene polymer P1, and Table 2 shows various physical properties of the hydrogenated conjugated diene polymer P1.

[Production Examples 2 to 8, Production Example 10: Production of Hydrogenated Conjugated Diene Polymers P2 to P8, and P10 and Their Physical Properties]
Polymer solutions containing hydrogenated conjugated diene polymers P2 to P8 and P10 were obtained in the same manner as in Production Example 1, except that the polymerization recipe was changed as shown in Table 1 and the hydrogenation rate was changed as shown in Table 2. Various physical property values of the hydrogenated conjugated diene polymers P2 to P8 and P10 are shown in Table 2.

[Production Examples 9 and 11: Production of Conjugated Diene Polymers P9 and P11 and Their Physical Properties]
Polymer solutions containing conjugated diene polymers P9 and P11 were obtained in the same manner as in Production Example 1, except that the polymerization recipe was changed as shown in Table 1 and that the hydrogenation reaction was not carried out. Various physical property values of the conjugated diene polymers P9 and P11 are shown in Table 2.

In Table 1, "-" means that the compound in the corresponding column was not used (the same applies to the rubber component columns in Tables 4, 5 and 7). Details of the compounds are as follows.
Compound A: [N,N-bis(trimethylsilyl)aminopropyl]methyldiethoxysilane Compound B: silicon tetrachloride Ti compound: [bis(η5-cyclopentadienyl)titanium(furfuryloxy)chloride]
Al compound: diethylaluminum chloride Li compound: n-butyllithium

<Production of polymer composition and crosslinked product>
[Examples 1 to 9, Comparative Examples 1 to 12]
Using the (hydrogenated) conjugated diene polymers P1 to P11, butadiene rubber (BR), and natural rubber (NR) produced above, each component was blended according to the blending recipe shown in Table 3, and the blended mixture was kneaded to produce a polymer composition. Kneading was performed in the following manner. Using a plastomill (capacity: 250 mL) equipped with a temperature control device, the rubber components ((hydrogenated) conjugated diene polymers P1 to P11, BR, NR), carbon black, silica, a silane coupling agent, a softener (extender oil), zinc oxide, stearic acid, and an antioxidant were blended and kneaded under conditions of a filling rate of 72% and a rotation speed of 60 rpm in the first stage of kneading to obtain a blend. The types and blending ratios of the rubber components used in each example were as shown in Tables 4 and 5. In Tables 4 and 5, the numerical values of the rubber components indicate the blending ratios (parts by mass) of each polymer relative to 100 parts by mass of the rubber components used in the preparation of the blend.
Next, in the second stage of kneading, the obtained compound was cooled to room temperature, and then a vulcanization accelerator and sulfur were added and kneaded. The kneaded composition was molded and vulcanized at 160°C for a predetermined time in a vulcanization press to obtain a crosslinked product (vulcanized rubber). In addition, the tensile strength, low-temperature grip performance, ozone resistance, and vulcanization adhesion were evaluated as follows. The results are shown in Tables 4 and 5.

(1) Tensile strength: A tensile test was performed in accordance with JIS K6251:2017 using vulcanized rubber as a measurement sample. Here, a dumbbell-shaped No. 3 was used as a test sample, and the stress at break (TB) and elongation at break (EB) were measured at room temperature. The larger the TB and EB values, the higher the breaking strength and the higher and better the mechanical strength of the material. Evaluation was performed based on the TB value, and was evaluated as an index based on Comparative Example 1. The higher the value, the higher the tensile strength and the better the strength. From the obtained tensile strength value, the tensile strength was judged as A to D according to the following criteria.
A (very good): 110 or more B (good): 100 or more and less than 110 C (acceptable level): 80 or more and less than 100 D (poor): less than 80

(2) Low-temperature grip performance (0°C-G ^* ): Using vulcanized rubber as a measurement sample, the complex modulus (0°C-G ^* ) was measured using an ARES-RDA (manufactured by TA Instruments) under conditions of shear strain of 0.14%, angular velocity of 100 radians per second, and 0°C. The measurement results were evaluated using an index based on Comparative Example 1. The larger the value, the better the low-temperature grip performance. From the obtained index, the low-temperature grip performance was judged from A to D according to the following criteria.
A: 200 or more B: 150 or more but less than 200 C: 100 or more but less than 150 D: Less than 100

(3) Ozone resistance test: Vulcanized rubber was used as a measurement sample, and a test piece (length 60 mm × width 10 mm × thickness 2.0 mm) was attached to an elongation jig and given a tensile strain of 20%, and left for 48 hours in an ozone concentration of 0.5 ppm to perform a static ozone deterioration test (ambient temperature 40° C.) in accordance with JIS K6259-1:2015. The sample was observed after the test and evaluated as follows.
<Evaluation based on crack size>
A: No cracks B: Cracks invisible to the naked eye but visible under magnification C: Very small cracks of 0.5 mm or less visible to the naked eye D: Cracks larger than 0.5 mm

(4) Vulcanization Adhesion A pre-vulcanization sheet prepared by forming the pre-vulcanization polymer composition of each of the Examples and Comparative Examples into a sheet form and a pre-vulcanization sheet mainly composed of natural rubber were laminated with a PET film sandwiched between the ends, and vulcanized under conditions of a temperature of 170°C and a time of 15 minutes, to obtain a laminated vulcanizate in which the portions not sandwiched by the PET film were vulcanized and bonded.
From the laminated vulcanizate, a rectangular sample piece was taken from the part where PET was sandwiched to the part where it was not sandwiched so that the adhesive strength at a width of 15 mm could be measured, and the PET film was removed to prepare a test piece. On one side of an autograph tester equipped with a thermostatic chamber, a vulcanized sheet formed from the polymer composition of the Examples and Comparative Examples was placed, and on the other side, a vulcanized sheet of natural rubber was placed and chucked from above and below, and a peel test was performed at a speed of 50 mm/min in an atmosphere of 70°C to measure the adhesive strength. From the obtained adhesive strength value, an index was evaluated based on Comparative Example 1. It can be said that the larger the value, the higher the adhesive strength and the better the vulcanization adhesiveness (co-crosslinking property). From the obtained index, the vulcanization adhesiveness was judged from A to D according to the following judgment criteria.
A: 140 or more B: 110 or more but less than 140 C: 90 or more but less than 110 D: Less than 90

Details of each component in Table 3 are as follows (same for Table 6).
*1: Seast 3 manufactured by Tokai Carbon Co., Ltd.
*2: ZEOSIL 1165MP manufactured by Rhodia
*3: Evonik Si75
*4: Diana Process Oil NS manufactured by Idemitsu Kosan Co., Ltd.
*5: Zinc oxide type 2 manufactured by Seido Chemical Industry Co., Ltd. *6: Lunac S-98 manufactured by Kao Chemical Co., Ltd.
*7: Ozonone 6C manufactured by Seiko Chemical Co., Ltd.
*8: Noccela CZ manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
*9: Noccela D manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
*10: Precipitated sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

Details of the rubber component are as follows:
BR: ENEOS Materials BR01
NR: RSS #3

<Production of polymer composition and crosslinked product>
[Examples 10 to 14, Comparative Examples 13 to 21]
Each component was blended according to the blending recipe shown in Table 6, and the resulting mixture was kneaded to produce a polymer composition. Kneading was performed by the following method. Using a plastomill (capacity: 250 mL) equipped with a temperature control device, the rubber component ((hydrogenated) conjugated diene polymers P1 to P11), carbon black, silica, a silane coupling agent, a softener (extender oil), zinc oxide, and stearic acid were blended and kneaded at a filling rate of 72% and a rotation speed of 60 rpm in the first stage of kneading to obtain a blend. The type and blending ratio of the rubber component used in each example were as shown in Table 7. In Table 7, the numerical value of the rubber component indicates the blending ratio (parts by mass) of each polymer relative to 100 parts by mass of the rubber component used in the preparation of the blend.
Next, in the second stage of kneading, the obtained compound was cooled to room temperature, and then a vulcanization accelerator and sulfur were added and kneaded. The kneaded composition was molded and vulcanized at 160°C for a predetermined time in a vulcanization press to obtain a crosslinked product (vulcanized rubber). The tensile strength, low-temperature grip performance, ozone resistance, and vulcanization adhesion were evaluated as follows. The results are shown in Table 7.

As shown in Tables 4 and 7, the polymer compositions of Examples 1 to 12 were all rated A or B for vulcanization adhesion, and rated A to C for the tensile strength, low-temperature grip performance, and ozone resistance of the crosslinked product, showing that the various properties could be improved in a well-balanced manner. Among these, the polymer compositions of Examples 1 to 7, 10, 11, 13, and 14, in which the entire rubber component was hydrogenated conjugated diene polymers P1 to P5, were particularly excellent, with three or more A or B evaluation results. In addition, looking at Examples 1 to 7, Examples 1 to 4, 6, and 7, which had sufficiently small Δβ, were rated A or B in all evaluation items, and were particularly excellent. In addition, comparing Examples 2 and 3, and Examples 10 and 11, which had sufficiently small Δβ and used the same type of rubber component, respectively, Examples 2 and 10, which contained a large amount of polymer with a higher hydrogenation rate, showed a high improvement effect on tensile strength and ozone resistance.

In contrast, as shown in Table 5, among the examples containing only one type of polymer as the rubber component, the polymer compositions of Comparative Example 1 and Comparative Example 13 were rated D for low-temperature grip performance and vulcanization adhesion. The polymer compositions of Comparative Example 2 and Comparative Example 14 were rated B for low-temperature grip performance and vulcanization adhesion, and C for tensile strength and ozone resistance, and were inferior to Examples 2 and 3, which also contained hydrogenated conjugated diene polymer P4. The polymer compositions of Comparative Examples 7, 8, 16, and 17, which contained only an unhydrogenated conjugated diene polymer or a hydrogenated conjugated diene copolymer with an α value of less than 0.6, were rated D for strength and ozone resistance.

Comparative examples 3 to 5 and 15, which contain two types of hydrogenated conjugated diene polymers but in which the β value of one of the hydrogenated conjugated diene polymers is outside the range of 0.10 to 0.40, received one or more ratings of D. The polymer composition of comparative example 6, which uses an unhydrogenated conjugated diene polymer and butadiene, received a rating of D for tensile strength and ozone resistance. The polymer compositions of comparative examples 9 to 12 and 18 to 21, in which one of the two conjugated diene polymers is an unhydrogenated conjugated diene polymer or a hydrogenated conjugated diene copolymer with an α value of less than 0.6, received a rating of D for strength and ozone resistance.

These results demonstrate that the polymer composition disclosed herein can produce a crosslinked product that is high in strength and has excellent low-temperature grip performance and ozone resistance, and also has excellent vulcanization adhesion.

Claims

When the constituent ratios (molar ratios) of the structural unit represented by the following formula (1), the structural unit represented by the following formula (2), the structural unit represented by the following formula (3), and the structural unit represented by the following formula (4) in the polymer are p, q, r, and s, respectively, the value represented by the following mathematical formula (i) is α, and the value represented by the following mathematical formula (ii) is β,
A first polymer containing a structural unit derived from an aromatic vinyl compound and a structural unit derived from butadiene and satisfying the following conditions (x) and (y):
a second polymer which contains a structural unit derived from an aromatic vinyl compound and a structural unit derived from butadiene, satisfies the following condition (x) and condition (y), and has a lower content of the structural unit derived from the aromatic vinyl compound than the first polymer,
The difference between the β of the first polymer and the β of the second polymer is 0.10 or less, and
a difference between a content ratio of structural units derived from an aromatic vinyl compound in the first polymer and a content ratio of structural units derived from an aromatic vinyl compound in the second polymer is 10 to 30 mass %.
Condition (x): α is 0.60 or more and 0.97 or less. Condition (y): β is 0.10 or more and 0.40 or less. α = (p + (0.5 × r)) / (p + q + (0.5 × r) + s).
... (i)
β = (p + q) / (p + q + (0.5 × r) + s) ... (ii)
The polymer composition according to claim 1, wherein the β of the first polymer is different from the β of the second polymer.
The polymer composition according to claim 2, wherein the β of the second polymer is greater than the β of the first polymer.
The polymer composition according to claim 1, wherein one or both of the first polymer and the second polymer have a functional group containing at least one element selected from the group consisting of nitrogen, oxygen, silicon, and phosphorus.
The polymer composition according to claim 1 , wherein the first polymer and the second polymer have a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography of 0.5×10 5 or more and 2.0×10 6 or less.
The polymer composition according to claim 1, wherein the ratio of the first polymer to the second polymer is in the range of 10:90 to 90:10 by mass ratio of the first polymer:the second polymer.
The polymer composition according to claim 1, further comprising at least one selected from the group consisting of conjugated diene polymers different from the first polymer and the second polymer, and natural rubber.
The polymer composition according to claim 1, wherein the total proportion of the first polymer and the second polymer is 50 to 100 mass % of the total amount of the rubber component contained in the polymer composition.
The polymer composition according to claim 1, further comprising an inorganic filler.
The polymer composition according to claim 1, further comprising a silane coupling agent.
The polymer composition according to claim 1, further comprising a resin component.
The polymer composition according to claim 1, further comprising an extender oil.
The polymer composition according to claim 12, wherein the total ratio of the first polymer, the second polymer, and the extender oil is 90 to 100% by mass when the entire composition is taken as 100% by mass.
A tire in which one or both of the cap tread and the sidewall are made of a cured product of the polymer composition according to any one of claims 1 to 11.