JP7832007B2 - Method for producing branched conjugated diene polymers, branched conjugated diene polymers, rubber compositions, methods for producing rubber compositions, and tires - Google Patents

Description

This invention relates to a method for producing branched conjugated diene polymers, branched conjugated diene polymers, rubber compositions, methods for producing rubber compositions, and tires.

From an environmental perspective, there has been a growing demand for more fuel-efficient automobiles. In particular, for automobile tires, there is a need to improve the fuel efficiency of the materials used in the tread, which is in direct contact with the ground.
In recent years, there has been a growing demand for the development of materials with low rolling resistance, i.e., materials with low hysteresis loss.
Furthermore, there is a demand for lighter tires, which requires reducing the thickness of the tire tread and using highly wear-resistant materials for the tire tread.
On the other hand, the materials used in the tire tread are required to have excellent wet skid resistance and sufficient fracture characteristics for practical use, from a safety standpoint.

As a material that can meet the various requirements mentioned above, a rubber material containing a rubber-like polymer and reinforcing fillers such as carbon black and silica can be mentioned.
Using a rubber material containing silica can improve the balance between low hysteresis loss (an indicator of fuel efficiency) and wet skid resistance. Furthermore, by introducing functional groups with affinity or reactivity to silica at the molecular ends of a highly mobile rubber-like polymer, the dispersibility of silica in the rubber material can be improved. Additionally, by reducing the mobility of the molecular ends of the rubber-like polymer through bonding with silica particles, hysteresis loss can be reduced.
On the other hand, one method to improve wear resistance is to increase the molecular weight of the rubbery polymer. However, increasing the molecular weight of the rubbery polymer tends to worsen the processability when mixing the rubbery polymer with the reinforcing filler.
In light of these circumstances, attempts are being made to introduce branched structures into rubbery polymers in order to increase their molecular weight without impairing their processability.

For example, conventionally, resin compositions have been proposed in which a modified conjugated diene polymer, obtained by reacting an amino group-containing alkoxysilane with the active end of a conjugated diene polymer, is combined with silica.
Furthermore, modified conjugated diene polymers have been proposed that incorporate branched structures obtained by coupling the active ends of a polymer with a polyfunctional silane compound (see, for example, Patent Documents 1 and 2).
Furthermore, a technique has been proposed to utilize styrene derivatives as branching agents to introduce a branched structure into the main chain (see, for example, Patent Document 3).

International Publication No. 2007/114203 Pamphlet International Publication No. 2016/133154 Brochure International Publication No. 2020/070961 brochure

However, in the method of introducing a branched structure to a conjugated diene polymer by coupling the polymer active end with a polyfunctional silane compound, as disclosed in Patent Documents 1 and 2, the degree of branching of the resulting modified conjugated diene polymer depends largely on the number of reactive groups that the polyfunctional silane compound has with the polymer active end, and cannot exceed the number of reactive groups. From the viewpoint of synthesizability, there is a problem in that there is a limit to the number of reactive groups that can be attached to a single polyfunctional silane, and therefore there is a limit to the degree of branching of the resulting modified conjugated diene polymer.
Furthermore, the technique disclosed in Patent Document 3, which utilizes a styrene derivative as a branching agent to introduce a branched structure into the main chain, has the problem that the introduction of nitrogen atoms depends on the progress of the modification reaction, thus limiting the improvement of the modification rate of the resulting modified conjugated diene polymer, and that the position of introduction of nitrogen atoms cannot be freely adjusted.

Therefore, the present invention aims to provide a method for producing a branched conjugated diene polymer that offers a high degree of design flexibility. This method allows for the production of conjugated diene polymers with a higher degree of branching and nitrogen content than when a branched structure is introduced into a conjugated diene polymer using only a coupling agent, and achieves improved introduction of nitrogen atoms into the main chain and a higher modification rate compared to when a styrene derivative is used as a branching agent. The objective is to provide a method for producing a branched conjugated diene polymer with excellent fuel efficiency, wear resistance, wet skid resistance, and fracture strength.

As a result of diligent research and investigation to solve the problems of the prior art described above, the present inventors have discovered that a branched conjugated diene polymer that can solve the problems of the prior art can be obtained by reacting a conjugated diene polymer with a branching agent containing nitrogen atoms to simultaneously introduce branching points and nitrogen atoms into the main chain, thereby completing the present invention.
In other words, the present invention is as follows.

[1]
A polymerization step to obtain a conjugated diene polymer having an active end by polymerizing or copolymerizing a conjugated diene compound, or a conjugated diene compound and an aromatic vinyl compound, using an alkali metal compound or alkaline earth metal compound as a polymerization initiator,
A branching step is performed in which a nitrogen atom-containing branching agent, which is a compound represented by the following formula (1), is reacted with the active end of the conjugated diene polymer to introduce a branched structure.
A method for producing a branched conjugated diene polymer having the following characteristics.

(In formula (1), ^R1 to ^R8 each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, and ^R9 to ^R12 each independently represent an alkylene group having 1 to 20 carbon atoms.)
m, n, l, and o each independently represent integers between 1 and 3, and (m + n + l + o) represents an integer greater than or equal to 4. If multiple ^R1 through ^R8 exist, they are all independent.

[2]
A method for producing a branched conjugated diene polymer according to [1], further comprising the step of adding a conjugated diene compound and/or an aromatic vinyl compound to the reaction system during and/or thereafter the branching step.
[3]
A method for producing a branched conjugated diene polymer according to [1] or [2], further comprising a reaction step of reacting the active end of the branched conjugated diene polymer obtained in the branching step with a coupling agent or a polymerization inhibitor.
[4]
A method for producing a branched conjugated diene polymer according to [3], wherein the coupling agent has a nitrogen atom-containing group.
[5]
A method for producing a branched conjugated diene polymer according to [3], wherein the polymerization inhibitor has a nitrogen atom-containing group.
[6]
A method for producing a branched conjugated diene polymer according to any one of [3] to [5], wherein the polymerization inhibitor is an alkoxy compound having a nitrogen atom-containing group.
[7]
A branched conjugated diene polymer obtained by the method for producing a branched conjugated diene polymer described in any one of [1] to [6] above,
A branched conjugated diene polymer having a main chain branch structure derived from a nitrogen atom-containing branching agent, which is a compound represented by formula (1), in the polymer main chain.

[8]
A rubber component containing 10% by mass or more of the branched conjugated diene polymer described in [7] above,
A rubber composition containing 5.0 parts by mass or more and 150 parts by mass or less of a filler per 100 parts by mass of the rubber component.
[9]
A step of obtaining a branched conjugated diene polymer by the manufacturing method described in any one of the above [1] to [6],
A step to obtain a rubber component containing 10% by mass or more of the branched conjugated diene polymer,
A step of obtaining a rubber composition by adding 5.0 parts by mass or more and 150 parts by mass or less of a filler to 100 parts by mass of the rubber component,
A method for producing a rubber composition having the following characteristics.
[10]
A step of obtaining a rubber composition by the method for producing a rubber composition described in [9] above,
The process involves molding the rubber composition to obtain a tire,
A method for manufacturing tires, comprising:

According to the present invention, it is possible to produce branched conjugated diene polymers with high branching degree, high nitrogen content, and high modification rate. Furthermore, a method for producing branched conjugated diene polymers that can constitute rubber compositions with excellent performance in areas such as fuel efficiency, abrasion resistance, wet skid resistance, and fracture strength is obtained.

The embodiments for carrying out the present invention (hereinafter referred to as "this embodiment") will be described in detail below.
The following embodiments are illustrative examples for explaining the present invention, and the present invention is not limited to these embodiments. The present invention can be implemented by modifying it as appropriate within the scope of its gist.

[Method for producing branched conjugated diene polymers]
The method for producing the branched conjugated diene polymer of this embodiment is:
A polymerization step to obtain a conjugated diene polymer having an active end by polymerizing or copolymerizing a conjugated diene compound, or a conjugated diene compound and an aromatic vinyl compound, using an alkali metal compound or alkaline earth metal compound as a polymerization initiator,
A branching step is performed in which a nitrogen atom-containing branching agent, which is a compound represented by the following formula (1), is reacted with the active end of the conjugated diene polymer to introduce a branched structure.
It has.

(In formula (1), ^R1 to ^R8 each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, and ^R9 to ^R12 each independently represent an alkylene group having 1 to 20 carbon atoms.)
m, n, l, and o each independently represent integers between 1 and 3, and (m + n + l + o) represents an integer greater than or equal to 4. If multiple ^R1 through ^R8 exist, they are all independent.

The branched conjugated diene polymer obtained by the manufacturing method of this embodiment may be a homopolymer of a single conjugated diene compound, a polymer (i.e., copolymer) of different types of conjugated diene compounds, or a copolymer of a conjugated diene compound and an aromatic vinyl compound.
According to the method for producing branched conjugated diene polymers of this embodiment, by simultaneously introducing branching points and nitrogen atoms into the main chain, it is possible to produce branched conjugated diene polymers with a higher degree of branching and nitrogen content than when a branched structure is introduced into a conjugated diene polymer using only a coupling agent. Furthermore, the length of the main chain and side chains can be easily adjusted, increasing the degree of freedom in polymer design. Moreover, according to the present invention, it is possible to produce branched conjugated diene polymers that yield rubber compositions with excellent fuel efficiency, wear resistance, wet skid resistance, and fracture strength.

(Polymerization process)
In the method for producing branched conjugated diene polymers of this embodiment, the polymerization step involves using an alkali metal compound or an alkaline earth metal compound as a polymerization initiator to polymerize or copolymerize a conjugated diene compound, or a conjugated diene compound with an aromatic vinyl compound, to obtain a conjugated diene polymer having an active end.
In the polymerization process, polymerization is preferably carried out by a growth reaction using living anionic polymerization, thereby obtaining a conjugated diene polymer having an active end.

<Polymerization Initiator>
Alkali metal compounds or alkaline earth metal compounds are used as polymerization initiators.
As the alkali metal compound, organolithium compounds are preferred, and organomonolithium compounds are more preferred.
Examples of alkaline earth metal compounds include organomagnesium compounds, organocalcium compounds, and organostrontium compounds. Compounds of alkaline earth metals as alkoxides, sulfonates, carbonates, and amides are also examples.
Examples of organic monolithium compounds include, but are not limited to, low-molecular-weight compounds and solubilized oligomeric organic monolithium compounds.
Furthermore, in terms of the bonding mode between the organic group and its lithium, any of the following can be used for the organic monolithium compound: for example, a compound having a carbon-lithium bond, a compound having a nitrogen-lithium bond, or a compound having a tin-lithium bond.

The amount of polymerization initiator used is preferably determined by the molecular weight of the target conjugated diene polymer.
The amount of monomers such as conjugated diene compounds used relative to the amount of polymerization initiator used is related to the degree of polymerization of the target conjugated diene polymer. In other words, it tends to be related to the number-average molecular weight and/or weight-average molecular weight.
Therefore, to increase the molecular weight of a conjugated diene polymer, it is best to adjust the amount of polymerization initiator to decrease it, and to decrease the molecular weight, it is best to adjust the amount of polymerization initiator to increase it.

From the viewpoint of using organic monolithium compounds as a method for introducing nitrogen atoms into conjugated diene polymers, they are preferably alkyllithium compounds having a substituted amino group, or dialkylaminolithium compounds.
In this case, a conjugated diene polymer is obtained that has a nitrogen atom consisting of an amino group at the polymerization initiation end.

A substituted amino group is an amino group that either lacks active hydrogen or has a structure in which active hydrogen is protected.
Alkyl lithium compounds having an amino group that does not possess active hydrogen include, but are not limited to, 3-dimethylaminopropyllithium, 3-diethylaminopropyllithium, 4-(methylpropylamino)butyllithium, and 4-hexamethyleneiminobutyllithium.
Alkyllithium compounds having an amino group with a structure that protects active hydrogen include, but are not limited to, 3-bistrimethylsilylaminopropyllithium and 4-trimethylsilylmethylaminobutyllithium.

Examples of dialkylaminolithium include, but are not limited to, lithium dimethylamide, lithium diethylamide, lithium dipropylamide, lithium dibutylamide, lithium di-n-hexylamide, lithium diheptylamide, lithium diisopropylamide, lithium dioctylamide, lithium di-2-ethylhexylamide, lithium didecylamide, lithium ethylpropylamide, lithium ethylbutylamide, lithium ethylbenzylamide, lithium methylphenethylamide, lithium hexamethyleneimide, lithium pyrrolidide, lithium piperidide, lithium heptamethyleneimide, lithium morpholide, 1-lithiazacyclooctane, 6-lithio-1,3,3-trimethyl-6-azabicyclo[3.2.1]octane, and 1-lithio-1,2,3,6-tetrahydropyridine.

These organomonolithium compounds having substituted amino groups can also be used as oligomeric organomonolithium compounds solubilized in n-hexane or cyclohexane by reacting small amounts of polymerizable monomers, such as 1,3-butadiene, isoprene, or styrene.

From the viewpoint of ease of industrial availability and ease of control of the polymerization reaction, the organic monolithium compound is preferably an alkyllithium compound. In this case, a conjugated diene polymer having an alkyl group at the polymerization initiation end is obtained.
The alkyllithium compound is not limited to the following, but examples include n-butyllithium, sec-butyllithium, tert-butyllithium, n-hexyllithium, benzyllithium, phenyllithium, and stilbenithium.
As alkyllithium compounds, n-butyllithium and sec-butyllithium are preferred from the viewpoint of ease of industrial availability and ease of control of polymerization reactions.

These organic monolithium compounds may be used individually or in combination of two or more. They may also be used in combination with other organometallic compounds as polymerization initiators.
Other organometallic compounds include, for example, alkaline earth metal compounds, other alkali metal compounds, and other organometallic compounds.
Examples of alkaline earth metal compounds include, as mentioned above, organomagnesium compounds, organocalcium compounds, and organostrontium compounds. Compounds of alkaline earth metals as alkoxides, sulfonates, carbonates, and amides are also examples.
Examples of organomagnesium compounds include dibutylmagnesium and ethylbutylmagnesium.
Other organometallic compounds include, for example, organoaluminum compounds.

In the polymerization process, the polymerization reaction mode is not limited to the following, but examples include batch mode (also called "batch reaction") and continuous polymerization reaction mode.
In a continuous reactor, one or more connected reactors can be used. Continuous reactors include, for example, tank-type or tubular-type reactors equipped with stirrers. In a continuous reactor, preferably, monomers, an inert solvent, and a polymerization initiator are continuously fed into the reactor, a polymer solution containing the polymer is obtained within the reactor, and the polymer solution is continuously discharged.
Batch reactors, for example, are tank-type reactors equipped with stirrers. In a batch reactor, monomers, an inert solvent, and a polymerization initiator are preferably fed into the reactor, and monomers are added continuously or intermittently during polymerization as needed. A polymer solution containing the polymer is obtained within the reactor, and the polymer solution is discharged after polymerization is complete.
In the method for producing branched conjugated diene polymers of this embodiment, a continuous process is preferred in the polymerization step to obtain a conjugated diene polymer with a high proportion of active ends, which allows for the continuous discharge of the polymer and its rapid use in the next reaction. In a continuous process, the number of reactors is not particularly limited, and one or two or more connected reactors can be used. The reactors are preferably capable of allowing sufficient contact between the monomer and the polymerization initiator in solution, and tank-type, tubular-type, or other types equipped with stirrers are used. The number of reactors can be selected as appropriate, but one reactor is preferred from the viewpoint of saving space in the manufacturing equipment, and two or more reactors are preferred from the viewpoint of improving productivity. When using two or more reactors, it is more preferable to add the branching agent to the second reactor and subsequent reactors.

In the polymerization process of conjugated diene polymers, polymerization is preferably carried out in an inert solvent.
Examples of inert solvents include hydrocarbon solvents such as saturated hydrocarbons and aromatic hydrocarbons. Specific examples of hydrocarbon solvents include, but are not limited to, aliphatic hydrocarbons such as butane, pentane, hexane, and heptane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane, and methylcyclohexane; and hydrocarbons consisting of aromatic hydrocarbons such as benzene, toluene, and xylene, and mixtures thereof.
Treating the impurities, such as allenes and acetylenes, with organometallic compounds before the polymerization reaction tends to yield conjugated diene polymers with high concentrations of active ends, and is preferable because it tends to yield modified conjugated diene polymers with a high degree of modification.

In the polymerization process, polar compounds (polar substances) may be added. This allows for random copolymerization of aromatic vinyl compounds with conjugated diene compounds. Furthermore, polar compounds tend to be used as vinylizing agents to control the microstructure of the conjugated diene moiety. They also tend to be effective in accelerating the polymerization reaction.
Polar compounds include, but are not limited to, ethers such as tetrahydrofuran, diethyl ether, dioxane, ethylene glycol dimethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, dimethoxybenzene, and 2,2-bis(2-oxolanyl)propane; tertiary amine compounds such as tetramethylethylenediamine, dipiperidinoethane, trimethylamine, triethylamine, pyridine, and quinuclidine; alkali metal alkoxide compounds such as potassium-tert-amylate, potassium-tert-butyrate, sodium-tert-butyrate, and sodium amylate; and phosphine compounds such as triphenylphosphine.
These polar compounds may be used individually or in combination of two or more.

The amount of polar compound used is not particularly limited and can be selected according to the purpose, but it is preferably 0.01 moles or more and 100 moles or less per mole of polymerization initiator.
Such polar compounds also function as vinylizing agents and can be used in appropriate amounts, depending on the desired amount of vinyl bonding, as modifiers for the microstructure of the conjugated diene moiety in conjugated diene polymers.
Many polar compounds simultaneously exhibit an effective randomization effect in copolymerization of conjugated diene compounds and aromatic vinyl compounds, and tend to be used as agents for adjusting the distribution of aromatic vinyl monomer units and the amount of styrene block.
As a method for randomizing the conjugated diene compound and aromatic vinyl compound, for example, as described in Japanese Patent Publication No. 59-140211, a copolymerization reaction may be initiated with the entire amount of styrene and a portion of 1,3-butadiene, and the remaining 1,3-butadiene may be added intermittently during the copolymerization reaction.

The polymerization temperature in the polymerization process is preferably the temperature at which living anionic polymerization proceeds, and from the viewpoint of productivity, it is more preferably 0°C to 120°C.
Within this range, it tends to be possible to ensure sufficient reaction amounts of branching agents and coupling agents, described later, to the active ends of the conjugated diene polymer after the polymerization process is complete. More preferably, the temperature is between 50°C and 100°C.

The conjugated diene polymers obtained through the polymerization process are polymers of conjugated diene compounds, or copolymers of conjugated diene compounds and aromatic vinyl compounds.

<Conjugated diene compounds>
The conjugated diene compound is not particularly limited and can be any polymerizable monomer, and is not limited to the following, but examples include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 3-methyl-1,3-pentadiene, 1,3-heptadiene, and 1,3-hexadiene. Among these, 1,3-butadiene and isoprene are preferred from the viewpoint of ease of industrial availability. These may be used individually or in combination of two or more.

<Aromatic vinyl compounds>
The aromatic vinyl compound can be any monomer copolymerizable with a conjugated diene compound and is not particularly limited, but examples include styrene, p-methylstyrene, α-methylstyrene, vinylethylbenzene, vinylxylene, vinylnaphthalene, and diphenylethylene. Among these, styrene is preferred from the viewpoint of ease of industrial availability. These may be used individually or in combination of two or more.

(Branching process)
In the method for producing branched conjugated diene polymers of this embodiment, a branching step is performed in which a nitrogen atom-containing branching agent, which is a compound represented by the following formula (1), is reacted with the active end of the conjugated diene polymer obtained in the polymerization step as a branching agent.
The branching agent maintains its polymerization activity and polymerizes with the monomer, while the active ends of other polymer chains react with the functional groups of the branching agent, thereby forming a branched structure in the polymer.
It is also possible to further polymerize and react a conjugated diene polymer with a branched structure with monomers and branching agents to form an even more branched structure. Furthermore, as will be described later, it is possible to react it with a modifying agent having a functional group to form a modified conjugated diene polymer, or to further extend the polymer chain by coupling.
In this embodiment, a branched conjugated diene polymer is produced using a branching agent, and the branched conjugated diene polymer has a portion derived from the compound represented by formula (1).
In this specification, the "part derived from the compound represented by formula (1)" refers to a skeleton in which a nitrogen atom is linked to a diphenylethylene skeleton and which has multiple alkoxysilyl groups.

<Branching agent>
The nitrogen atom-containing branching agent used in the branching process preferably has a main skeleton in which only one active end remains at the branching site after the branching reaction, from the viewpoint of the continuity of polymerization and the prevention of gelation, and further preferably has reactivity that reacts sufficiently with the polymerization active end during the branching reaction.
In other words, the branching agent reacts to incorporate the nitrogen atom-containing branching agent into the main chain while maintaining polymerization activity, and further monomers polymerize on the active ends, extending the polymer chain further. Additionally, the active ends of other polymer chains react with the functional groups of the incorporated nitrogen atom-containing branching agent, forming bonds and creating a branched structure. Repeated occurrences of this reaction increase the branching of the polymer chain, resulting in a more complex polymer structure and a larger molecular weight.
From the standpoint of ensuring the continuity of polymerization and the controllability of the polymer structure, it is also necessary that the functional groups that are eliminated after reacting with the active end of another polymer chain have little inhibitory effect on polymerization. Here, "little inhibitory effect on polymerization" means that there are few side reactions of anionic polymerization, such as chain transfer reactions, deactivation during polymerization, and decreased activity due to increased degree of polymer association.
The functional groups of a nitrogen atom-containing branching agent must not excessively enhance polymerization activity, nor must they deactivate it. When polymerizing polymers by living anionic polymerization, it is important that the functional groups that do not deactivate the active ends do not contain hydrogen atoms and are hard bases as defined by Pearson's HASB rule; more specifically, alkoxy groups are examples. From among these, the structure of the nitrogen atom-containing branching agent used in the manufacturing method of this embodiment can be selected from among them, in addition to reactivity with the active ends, from the viewpoint that the detached functional groups do not inhibit polymerization.
More specifically, using the following formula (1) as a nitrogen atom-containing branching agent is preferable from the viewpoint of suppressing chain transfer reactions, suppressing deactivation of active ends, and preventing gelation.

(In formula (1), ^R1 to ^R8 each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, and ^R9 to ^R12 each independently represent an alkylene group having 1 to 20 carbon atoms.)
m, n, l, and o each independently represent integers between 1 and 3, and (m + n + l + o) represents an integer greater than or equal to 4. If multiple ^R1 through ^R8 exist, they are all independent.

The nitrogen atom-containing branching agent represented by formula (1) is not limited to the following, but examples include compounds represented by formulas (M-1) to (M-6) below.
Furthermore, the nitrogen atom-containing branching agent may be used individually or in combination of two or more types.

<Examples of nitrogen atom-containing branching agents used in the branching process>
Specific examples of nitrogen atom-containing branching agents are shown in the following formulas (M-1) to (M-6).
In the formula, Me represents a methyl group and Et represents an ethyl group.

The timing for adding the nitrogen atom-containing branching agent is not particularly limited and can be selected according to the purpose, etc. However, from the viewpoint of improving the absolute molecular weight of the conjugated diene polymer and improving the coupling rate, it is preferable to add the nitrogen atom-containing branching agent when the raw material conversion rate is 20% or more, more preferably 40% or more, even more preferably 50% or more, even more preferably 65% or more, and even more preferably 75% or more.
Furthermore, during and/or after the branching process, additional monomers, which are desired raw materials, may be added, and the polymerization process may be continued after the branching process, or the above-described contents may be repeated.
Here, "after the branching process" refers to the period after the addition of a nitrogen atom-containing branching agent.
The monomer to be added is not particularly limited, but is preferably a conjugated diene compound and/or an aromatic vinyl compound. In particular, when the monomer is added during the branching step, from the viewpoint of improving the modification rate by mitigating steric hindrance at the branching points of the conjugated diene polymer, it is preferably 5% or more of the total amount of conjugated diene monomers used in the polymerization step, for example, the total amount of butadiene, more preferably 10% or more, even more preferably 15% or more, even more preferably 20% or more, and even more preferably 25% or more. In such cases, it is particularly preferable from the viewpoint of improving the modification rate to use a continuous polymerization process and add the monomer during the branching step in an amount equal to or greater than the total amount of conjugated diene monomers used in the polymerization step, for example, the total amount of butadiene.
Because the length of the main chain and side chains can be adjusted by changing the timing of the addition of branching agents and the amount of monomers added, polymer design offers a high degree of flexibility.

In the branching step of the method for producing branched conjugated diene polymers of this embodiment, the branched structure of the branched conjugated diene polymer obtained is preferably 3 to 24 branches, more preferably 4 to 20 branches, and even more preferably 5 to 18 branches.
By limiting the number of branches to 24 or fewer, it tends to be easier to react with a functional modifier to form a modified conjugated diene polymer, or to further extend the polymer chain through a coupling reaction. By limiting the number of branches to 3 or more, the resulting branched conjugated diene polymer tends to have excellent processability and wear resistance.

The amount of branching agent added in the branching process is not particularly limited, and the amount can be selected according to the purpose, etc. However, from the viewpoint of improving the end-termination reaction rate of the conjugated diene polymer, improving the coupling rate, and ensuring the continuity of polymerization after branching, the molar ratio of the branching agent to the amount of active polymerization initiator is preferably 1/2 or less and 1/100 or more, more preferably 1/3 or less and 1/50 or more, even more preferably 1/4 or less and 1/30 or more, even more preferably 1/6 or less and 1/25 or more, and even more preferably 1/8 or less and 1/12 or more.

Furthermore, as described above, monomers may be added during and/or after the branching process, and the polymerization process may be continued after branching, or the branching agent may be added after the addition of monomers, and the process of adding monomers may be repeated.
By adding monomers, steric hindrance around the branching point is alleviated, resulting in improved polymerization continuity, coupling rate, and modification rate. This allows for increasing the molecular weight of the polymer while forming branches at desired locations.
The added monomers may be aromatic vinyl compounds such as styrene, conjugated diene compounds such as butadiene, or mixtures thereof. The type and ratio of the monomers initially polymerized may be the same as or different from those used initially, but conjugated diene compounds are preferred from the viewpoint of sustained polymerization. Furthermore, adding aromatic vinyl compounds is preferable from the viewpoint of improving the heat resistance of the polymer.

The branched conjugated diene polymer containing nitrogen atoms with a branched structure, obtained in the branching step of the manufacturing method of this embodiment, preferably has a Mooney viscosity of 10 to 150, more preferably 15 to 140, even more preferably 20 to 130, and even more preferably 30 to 100, as measured at 110°C.
When the Mooney viscosity is within the aforementioned range, the branched conjugated diene polymer obtained by the manufacturing method of this embodiment tends to have excellent processability and wear resistance.

The weight-average molecular weight of the branched conjugated diene polymer containing a branched nitrogen atom, obtained in the branching step of the manufacturing method of this embodiment, is preferably 10,000 to 1,500,000, more preferably 100,000 to 1,000,000, and even more preferably 200,000 to 900,000.
When the weight-average molecular weight is within the aforementioned range, the branched conjugated diene polymer obtained by the manufacturing method of this embodiment tends to have excellent processability, wear resistance, and balance of these properties.
When producing branched conjugated diene polymers with added modifying agents, in order to reliably achieve a weight-average molecular weight range of 100,000 to 1,000,000 after modification, it is necessary to control the amount of nitrogen atom-containing branching agent added within a range of molar ratio of 1/3 or less and 1/50 or more relative to the polymerization initiator, thereby preventing the polymerization initiator from being completely consumed before the coupling step while forming branches, and ensuring that the coupling agent has two or more functional groups. In order to achieve a weight-average molecular weight range of 200,000 to 900,000, it is necessary to control the amount of nitrogen atom-containing branching agent added within a range of molar ratio of 1/3 or less and 1/50 or more relative to the polymerization initiator, while ensuring that the coupling agent has three or more functional groups.

The branched conjugated diene polymer obtained by the manufacturing method of this embodiment may be a polymer of a conjugated diene compound and a nitrogen atom-containing branching agent, or a polymer of an aromatic vinyl compound, a conjugated diene compound and a nitrogen atom-containing branching agent, or a copolymer of these with other monomers.
For example, when a conjugated diene compound is butadiene or isoprene, and it is polymerized with a nitrogen atom-containing branching agent that includes an aromatic vinyl portion, the polymer chain becomes so-called polybutadiene or polyisoprene, and the branched portion contains a structure derived from aromatic vinyl. Having such a structure allows for improved linearity per polymer chain and improved crosslinking density after vulcanization, resulting in improved wear resistance of the polymer. Therefore, it is suitable for applications such as tires, resin modification, automotive interior and exterior parts, vibration-damping rubber, and footwear.
When branched conjugated diene polymers are used for tire tread applications, copolymers of a conjugated diene compound, an aromatic vinyl compound, and a nitrogen atom-containing branching agent are preferred. In copolymers for this application, the amount of bonded conjugated diene is preferably 40% by mass or more and 100% by mass or less, and more preferably 55% by mass or more and 80% by mass or less.
Furthermore, the amount of bonded aromatic vinyl in the branched conjugated diene polymer obtained by the manufacturing method of this embodiment is not particularly limited, but is preferably 0% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 45% by mass or less.
When the amount of bonded conjugated diene and bonded aromatic vinyl is within the above range, the resulting vulcanized product tends to have a better balance of low hysteresis loss and wet skid resistance, as well as superior abrasion resistance and fracture characteristics.
Here, the amount of bonded aromatic vinyl can be measured by ultraviolet absorbance of the phenyl group, and from this, the amount of bonded conjugated diene can also be determined. Specifically, it can be measured according to the method described in the examples below.

In the branched conjugated diene polymer obtained by the manufacturing method of this embodiment, the amount of vinyl bond in the conjugated diene bond unit is not particularly limited, but is preferably 10 mol% or more and 75 mol% or less, and more preferably 20 mol% or more and 65 mol% or less.
When the amount of vinyl bonding is within the above range, the resulting vulcanized product tends to have a better balance of low hysteresis loss and wet skid resistance, as well as superior abrasion resistance and fracture strength.
Here, if the conjugated diene polymer is a copolymer of butadiene and styrene, the amount of vinyl bonds (1,2-bonds) in the butadiene bond unit can be determined by Hampton's method (R.R. Hampton, Analytical Chemistry, 21, 923 (1949)). Specifically, it can be measured by the method described in the examples below.

Regarding the microstructure of the conjugated diene polymer, when the amount of vinyl bonds, the amount of bonded aromatic vinyl, and the amount of bonded conjugated diene in the branched conjugated diene polymer obtained by the manufacturing method of this embodiment are within the above-mentioned numerical range, and furthermore, when the glass transition temperature of the conjugated diene polymer is in the range of -80°C to -15°C, it is possible to obtain a vulcanized product with an even better balance of low hysteresis loss and wet skid resistance.
The glass transition temperature is determined according to ISO 22768:2006, by recording the DSC curve while increasing the temperature within a specified range, and the peak top (influence point) of the DSC differential curve is defined as the glass transition temperature.

When the branched conjugated diene polymer obtained by the manufacturing method of this embodiment is a conjugated diene-aromatic vinyl copolymer, it is preferable that the branched conjugated diene polymer has a small number of blocks in which 30 or more aromatic vinyl units are linked together, or that such blocks have no such blocks. More specifically, when the branched conjugated diene polymer obtained by the manufacturing method of this embodiment is a butadiene-styrene copolymer, in a known method of decomposing the polymer by Kolthoff's method (as described in I.M. KOLTHOFF, et al., J. Polym. Sci. 1,429 (1946)) and analyzing the amount of methanol-insoluble polystyrene, it is preferable that the number of blocks in which 30 or more aromatic vinyl units are linked together is 5.0% by mass or less, more preferably 3.0% by mass or less, relative to the total amount of the branched conjugated diene polymer.

From the viewpoint of improving fuel efficiency, it is preferable that the branched conjugated diene polymer obtained by the manufacturing method of this embodiment has a high proportion of aromatic vinyl units present individually.
Specifically, when the branched conjugated diene polymer obtained by the manufacturing method of this embodiment is a butadiene-styrene copolymer, it is preferable that the conjugated diene polymer is decomposed by an ozonolysis method known as the method of Tanaka et al. (Polymer, 22, 1721 (1981)), and the styrene chain distribution is analyzed by GPC, and that the amount of isolated styrene is 40% by mass or more relative to the amount of total bound styrene, and that the amount of chained styrene structures with 8 or more styrene chains is 5.0% by mass or less.
In this case, the resulting vulcanized rubber tends to exhibit superior performance, particularly low hysteresis loss.

(Reaction process)
In the method for producing branched conjugated diene polymers according to this embodiment, it is preferable to perform a coupling step using a coupling agent, for example, a reactive compound with three or more functions, to the active ends of the branched conjugated diene polymer obtained through the polymerization step and branching step described above, or to perform a polymerization inhibitor, for example, a reactive compound with two or fewer functions, to the active ends of the branched conjugated diene polymer.
Hereinafter, the process of reacting with a coupling agent (coupling process) or the process of stopping polymerization (polymerization stopping process) will be collectively referred to as the reaction process.
In the reaction step, one end of the active end of the branched conjugated diene polymer is reacted with a coupling agent or polymerization inhibitor.

<Process for reacting with the coupling agent>
In the method for producing branched conjugated diene polymers according to this embodiment, it is preferable to have a coupling step as a reaction step in which the branched conjugated diene polymer obtained through the polymerization step and branching step described above is coupled with a coupling agent.
The coupling process allows for the efficient lengthening of molecular chains, and by employing a coupling agent with three or more functions, branching can be introduced into the polymer. While the function of introducing branching is common to the process using branching agents, performing it in the coupling process is preferable from the viewpoint that it is possible to form branches while introducing desired elements such as nitrogen, sulfur, and silicon using known coupling agents.
The coupling process is preferably one in which a reactive compound with three or more functionalities is applied to the active end of a branched conjugated diene polymer, or a coupling agent having a nitrogen atom-containing group (hereinafter collectively referred to as "coupling agent").

In the coupling process, for example, a branched conjugated diene polymer can be obtained by coupling one end of the active end of the conjugated diene polymer with a trifunctional or more reactive compound, or a coupling agent having a nitrogen atom-containing group.

[Reactive compounds with three or more functionalities]
In the method for producing branched conjugated diene polymers according to this embodiment, the reactive compound with three or more functions used in the coupling step is preferably a reactive compound with three or more functions having silicon atoms.

Examples of reactive compounds with three or more functions containing silicon atoms include, but are not limited to, halogenated silane compounds, epoxidized silane compounds, vinylinated silane compounds, alkoxysilane compounds, and alkoxysilane compounds containing nitrogen groups.

Examples of halogenated silane compounds used as coupling agents include, but are not limited to, methyltrichlorosilane, tetrachlorosilane, tris(trimethylsiloxy)chlorosilane, tris(dimethylamino)chlorosilane, hexachlorodisilane, bis(trichlorosilyl)methane, 1,2-bis(trichlorosilyl)ethane, 1,2-bis(methyldichlorosilyl)ethane, 1,4-bis(trichlorosilyl)butane, and 1,4-bis(methyldichlorosilyl)butane.

Examples of epoxidized silane compounds used as coupling agents include, but are not limited to, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and epoxy-modified silicones.

Examples of vinylated silane compounds used as coupling agents include, but are not limited to, vinyltrimethoxysilane and vinyltriethoxysilane.

Examples of alkoxysilane compounds used as coupling agents include, but are not limited to, tetramethoxysilane, tetraethoxysilane, triphenoxymethylsilane, 1,2-bis(triethoxysilyl)ethane, and methoxy-substituted polyorganosiloxanes.

[Coupling agent containing nitrogen atom groups]
Examples of coupling agents having a nitrogen atom-containing group include, but are not limited to, isocyanate compounds, isothiocyanate compounds, isocyanuric acid derivatives, carbonyl compounds having a nitrogen atom-containing group, vinyl compounds having a nitrogen atom-containing group, epoxy compounds having a nitrogen atom-containing group, alkoxysilane compounds having a nitrogen atom-containing group, and protected amine compounds having a nitrogen atom-containing group and capable of forming a primary or secondary amine.

In coupling agents having a nitrogen atom-containing group, the nitrogen atom-containing group is preferably a functional group derived from an amine compound that does not have active hydrogen. Examples of such amine compounds include tertiary amine compounds and protected amine compounds in which the active hydrogen is substituted with a protecting group. Other compounds that can form a nitrogen atom-containing group include imine compounds represented by the general formula -N=C, and alkoxysilane compounds bonded to the nitrogen atom-containing group.

Examples of isocyanate compounds that are coupling agents containing nitrogen atom groups include, but are not limited to, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, polymeric type diphenylmethane diisocyanate (C-MDI), phenyl isocyanate, isophorone diisocyanate, hexamethylene diisocyanate, butyl isocyanate, and 1,3,5-benzene triisocyanate.

Examples of isocyanuric acid derivatives that are coupling agents containing nitrogen atom groups include, but are not limited to, 1,3,5-tris(3-trimethoxysilylpropyl) isocyanurate, 1,3,5-tris(3-triethoxysilylpropyl) isocyanurate, 1,3,5-tri(oxiran-2-yl)-1,3,5-triazinan-2,4,6-trione, 1,3,5-tris(isocyanatomethyl)-1,3,5-triazinan-2,4,6-trione, and 1,3,5-trivinyl-1,3,5-triazinan-2,4,6-trione.

Carbonyl compounds that are coupling agents having a nitrogen atom-containing group are not limited to the following, but include, for example, 1,3-dimethyl-2-imidazolidinone, 1-methyl-3-ethyl-2-imidazolidinone, 1-methyl-3-(2-methoxyethyl)-2-imidazolidinone, N-methyl-2-pyrrolidone, N-methyl-2-piperidone, N-methyl-2-quinolone, 4,4'-bis(diethylamino)benzophenone, 4,4'-bis(dimethylamino)benzophenone, Examples include ethyl-2-pyridylketone, methyl-4-pyridylketone, propyl-2-pyridylketone, di-4-pyridylketone, 2-benzoylpyridine, N,N,N',N'-tetramethylurea, N,N-dimethyl-N',N'-diphenylurea, N,N-diethylcarbamate methyl, N,N-diethylacetamide, N,N-dimethyl-N',N'-dimethylaminoacetamide, N,N-dimethylpicolinamide, and N,N-dimethylisonicotinamide.

Examples of vinyl compounds that act as coupling agents containing nitrogen atoms include, but are not limited to, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N-methylmaleimide, N-methylphthalimide, N,N-bistrimethylsilylacrylamide, morpholinocrylamide, 3-(2-dimethylaminoethyl)styrene, (dimethylamino)dimethyl-4-vinylphenylsilane, 4,4'-vinylidenebis(N,N-dimethylaniline), 4,4'-vinylidenebis(N,N-diethylaniline), 1,1-bis(4-morpholinophenyl)ethylene, and 1-phenyl-1-(4-N,N-dimethylaminophenyl)ethylene.

Examples of epoxy compounds that act as coupling agents containing nitrogen atom-containing groups include, but are not limited to, epoxy group-containing hydrocarbon compounds bonded to an amino group, and epoxy group-containing hydrocarbon compounds bonded to an ether group. Examples of such epoxy compounds, but are not limited to, include epoxy compounds represented by general formula (i).

In formula (i) above, R is a divalent or greater organic group having at least one polar group selected from the group consisting of a divalent or greater hydrocarbon group, or a polar group having oxygen such as an ether, epoxy, or ketone; a polar group having sulfur such as a thioether or thioketone; or a polar group having nitrogen such as a tertiary amino group or imino group.

The hydrocarbon group with two or more valent values is a hydrocarbon group that may be saturated or unsaturated, linear, branched, or cyclic, and includes alkylene groups, alkenylene groups, phenylene groups, etc. Preferably, it is a hydrocarbon group having 1 to 20 carbon atoms. Examples include methylene, ethylene, butylene, cyclohexylene, 1,3-bis(methylene)-cyclohexane, 1,3-bis(ethylene)-cyclohexane, o-,m-,p-phenylene, m-,p-xylene, bis(phenylene)-methane, etc.

In formula (i) above, ^R1 and ^R4 are hydrocarbon groups having 1 to 10 carbon atoms, and ^R1 and ^R4 may be the same or different from each other.
In formula (i) above, ^R2 and ^R5 are hydrogen or a hydrocarbon group having 1 to 10 carbon atoms, and ^R2 and ^R5 may be the same or different from each other.
In formula (i) above, ^R3 is a hydrocarbon group having 1 to 10 carbon atoms, or the structure of formula (ii) below.
^R1 , ^R2 , and ^R3 may be linked to each other in a cyclic structure.
Furthermore, if ^R3 is a hydrocarbon group, it may be a cyclic structure bonded to R. In the case of the aforementioned cyclic structure, the N bonded to ^R3 and R may be directly bonded to each other.
In the above formula (i), n is an integer of 1 or more, and m is 0 or an integer of 1 or more.

In equation (ii) above, ^R1 and ^R2 are defined in the same way as ^R1 and ^R2 in equation (i) above, and ^R1 and ^R2 may be the same or different from each other.

The epoxy compound used as a coupling agent containing a nitrogen atom is preferably one having an epoxy group-containing hydrocarbon group, and more preferably one having a glycidyl group-containing hydrocarbon group.

The epoxy group-containing hydrocarbon group bonded to the amino group or ether group is not limited to the following, but examples include a glycidylamino group, a diglycidylamino group, or a glycididoxy group. A more preferred molecular structure is an epoxy group-containing compound having a glycidylamino group or a diglycidylamino group and a glycididoxy group, respectively, and examples include compounds represented by the following general formula (iii).

In formula (iii) above, R is defined in the same way as R in formula (i) above, and ^R6 is a hydrocarbon group having 1 to 10 carbon atoms or the structure of formula (iv) below.
If ^R6 is a hydrocarbon group, it may be bonded to R in a cyclic structure, and in that case, the N bonded to ^R6 and R may be directly bonded.
In equation (iii), n is an integer greater than or equal to 1, and m is an integer greater than or equal to 0 or 1.

As an epoxy compound that acts as a coupling agent containing a nitrogen atom, particularly preferred is a compound having one or more diglycidylamino groups and one or more glycidoxy groups in its molecule.

The epoxy compounds that act as coupling agents having nitrogen atom-containing groups are not limited to the following, but include, for example, N,N-diglycidyl-4-glycidoxyaniline, 1-N,N-diglycidylaminomethyl-4-glycidoxycyclohexane, 4-(4-glycidoxyphenyl)-(N,N-diglycidyl)aniline, 4-(4-glycidoxyphenoxy)-(N,N-diglycidyl)aniline, 4-(4-glycidoxybenzyl)-(N,N-diglycidyl)aniline, 4-(N,N'-diglycidyl-2-piperazinyl)-glycidoxybenzene, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m- Examples include xylenediamine, 4,4-methylene-bis(N,N-diglycidylaniline), 1,4-bis(N,N-diglycidylamino)cyclohexane, N,N,N',N'-tetraglycidyl-p-phenylenediamine, 4,4'-bis(diglycidylamino)benzophenone, 4-(4-glycidylpiperazinyl)-(N,N-diglycidyl)aniline, 2-[2-(N,N-diglycidylamino)ethyl]-1-glycidylpyrrolidine, N,N-diglycidylaniline, 4,4'-diglycidyl-dibenzylmethylamine, N,N-diglycidylaniline, N,N-diglycidylorthotoluidine, and N,N-diglycidylaminomethylcyclohexane. Among these, particularly preferred are N,N-diglycidyl-4-glycidoxyaniline and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

The alkoxysilane compounds that are coupling agents having a nitrogen atom-containing group are not limited to the following, but include, for example, 3-dimethylaminopropyltrimethoxysilane, 3-dimethylaminopropylmethyldimethoxysilane, 3-diethylaminopropyltriethoxysilane, 3-morpholinopropyltrimethoxysilane, 3-piperidinopropyltriethoxysilane, 3-hexamethyleneiminopropylmethyldiethoxysilane, 3-(4-methyl-1-piperazino)propyltriethoxysilane, and 1-[3-(triethoxysilyl)-propyl]-3-methylhexapropyl Dropyrimidine, 3-(4-trimethylsilyl-1-piperazino)propyltriethoxysilane, 3-(3-triethylsilyl-1-imidazolidinyl)propylmethyldiethoxysilane, 3-(3-trimethylsilyl-1-hexahydropyrimidinyl)propyltrimethoxysilane, 3-dimethylamino-2-(dimethylaminomethyl)propyltrimethoxysilane, bis(3-dimethoxymethylsilylpropyl)-N-methylamine, bis(3-trimethoxysilylpropyl)-N-methylamine, bis(3-triethoxysilylpropyl)methylamine, tris(t (Dimethoxysilyl)amine, Tris(3-trimethoxysilylpropyl)amine, N,N,N',N'-Tetra(3-trimethoxysilylpropyl)ethylenediamine, 3-Isocyanatopropyltrimethoxysilane, 3-Cyanopropyltrimethoxysilane, 2,2-Dimethoxy-1-(3-trimethoxysilylpropyl)-1-Aza-2-Silacyclopentane, 2,2-Diethoxy-1-(3-triethoxysilylpropyl)-1-Aza-2-Silacyclopentane, 2,2-Dimethoxy-1-(4-trimethoxysilylbutyl)-1-Aza-2-Silacyclohexane Examples include 2,2-dimethoxy-1-(3-dimethoxymethylsilylpropyl)-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-phenyl-1-aza-2-silacyclopentane, 2,2-diethoxy-1-butyl-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-methyl-1-aza-2-silacyclopentane, 2,2-dimethoxy-8-(4-methylpiperazinyl)methyl-1,6-dioxa-2-silacyclooctane, and 2,2-dimethoxy-8-(N,N-diethylamino)methyl-1,6-dioxa-2-silacyclooctane.

A coupling agent having a nitrogen atom-containing group, a protected amine compound capable of forming a primary or secondary amine, and a compound having an unsaturated bond and a protected amine in its molecule, is not limited to the following, but includes, for example, 4,4'-vinylidenebis[N,N-bis(trimethylsilyl)aniline], 4,4'-vinylidenebis[N,N-bis(triethylsilyl)aniline], 4,4'-vinylidenebis[N,N-bis(t-butyldimethylsilyl)aniline], 4,4'-vinylidenebis[N-methyl-N-(trimethylsilyl)aniline], 4,4'-vinylidenebis[N-ethyl-N-(trimethylsilyl)aniline], 4,4' Examples include -vinylidenebis[N-methyl-N-(triethylsilyl)aniline], 4,4'-vinylidenebis[N-ethyl-N-(triethylsilyl)aniline], 4,4'-vinylidenebis[N-methyl-N-(t-butyldimethylsilyl)aniline], 4,4'-vinylidenebis[N-ethyl-N-(t-butyldimethylsilyl)aniline], 1-[4-N,N-bis(trimethylsilyl)aminophenyl]-1-[4-N-methyl-N-(trimethylsilyl)aminophenyl]ethylene, and 1-[4-N,N-bis(trimethylsilyl)aminophenyl]-1-[4-N,N-dimethylaminophenyl]ethylene.

A coupling agent having a nitrogen atom-containing group, a protected amine compound capable of forming a primary or secondary amine, and a compound having an alkoxysilane and a protected amine in its molecule, is not limited to the following, but includes, for example, N,N-bis(trimethylsilyl)aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, N,N-bis(trimethylsilyl)aminopropyltriethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, N,N-bis(trimethylsilyl)aminoethyltrimethoxysilane, N,N-bis(trimethylsilyl)aminoethyl Tyldiethoxysilane, N,N-bis(triethylsilyl)aminopropylmethyldiethoxysilane, 3-(4-trimethylsilyl-1-piperazino)propyltriethoxysilane, 3-(3-triethylsilyl-1-imidazolidinyl)propylmethyldiethoxysilane, 3-(3-trimethylsilyl-1-hexahydropyrimidinyl)propyltrimethoxysilane, 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane, 2,2-diethoxy-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-(4-trimethoxysilylbutyl )-1-aza-2-silacyclohexane, 2,2-dimethoxy-1-(3-dimethoxymethylsilylpropyl)-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-phenyl-1-aza-2-silacyclopentane, 2,2-diethoxy-1-butyl-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-methyl-1-aza-2-silacyclopentane, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, N-(1-methylethylidene)-3-(triethoxysilyl)-1-propanamine, N-ethylidene-3-(triethoxysilyl)-1-propanamine, N-(1-methylethylidene)-3-(triethoxysilyl)-1-propanamine, N-(1-methylethylidene)-3-(triethoxysilyl)-1-propanamine Examples include N-(1-methylpropylidene)-3-(triethoxysilyl)-1-propanamine, N-(4-N,N-dimethylaminobenzylidene)-3-(triethoxysilyl)-1-propanamine, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, 3-(benzylideneamino)propyltrimethoxysilane, 3-(benzylideneamino)propyltrimethoxysilane, 3-(benzylideneamino)propyltriethoxysilane, 3-(benzylideneamino)propyltripropylsisilane, etc.

Particularly preferred alkoxysilane compounds that are coupling agents having nitrogen atom-containing groups include, but are not limited to, tris(3-trimethoxysilylpropyl)amine, tris(3-triethoxysilylpropyl)amine, tris(3-tripropoxysilylpropyl)amine, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-methyl-1-sila-2-azacyclopentane)propyl]-1, 3-propanediamine, bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, tetrakis(3-trimethoxysilylpropyl)-1,6-hexamethylenediamine, pentakis(3-trimethoxysilylpropyl)-diethylenetriamine, tris(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine, tetrakis[3-(2,2 [3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)silane, tris[3-(2,2-dimethoxy-1-aza-2-silacyclo [Pentane)propyl]-[3-(1-Methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]silane, 3-Tris[2-(2,2-dimethoxy-1-aza-2-silacyclopentane)ethoxy]silyl-1-trimethoxysilylpropane, 1-[3-(1-Methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-3,4,5-Tris(3-trimethoxy Examples include silylpropyl)-cyclohexane, 1-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-3,4,5-tris(3-trimethoxysilylpropyl)-cyclohexane, 3,4,5-tris(3-trimethoxysilylpropyl)-cyclohexyl-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl] ether, (3-trimethoxysilylpropyl) phosphate, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl] phosphate, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl) phosphate, and tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl] phosphate.

<Branched conjugated diene polymers obtained through polymerization, branching, and reaction processes>
In the method for producing branched conjugated diene polymers of this embodiment, the branched conjugated diene polymer obtained through the above-described reaction steps, particularly the step of reacting with a coupling agent, preferably contains a structure derived from a compound having a nitrogen atom-containing group, represented by the following general formula (i) or any of (A) to (C).

In formula (i) above, R is a divalent or greater organic group having at least one polar group selected from a divalent or greater hydrocarbon group, or a polar group having oxygen such as an ether, epoxy, or ketone; a polar group having sulfur such as a thioether or thioketone; or a polar group having nitrogen such as a tertiary amino group or imino group.

The hydrocarbon group with two or more valent values is a hydrocarbon group that may be saturated or unsaturated, linear, branched, or cyclic, and includes alkylene groups, alkenylene groups, phenylene groups, etc. Preferably, it is a hydrocarbon group having 1 to 20 carbon atoms. Examples include methylene, ethylene, butylene, cyclohexylene, 1,3-bis(methylene)-cyclohexane, 1,3-bis(ethylene)-cyclohexane, o-,m-,p-phenylene, m-,p-xylene, bis(phenylene)-methane, etc.

In formula (i) above, ^R1 and ^R4 are hydrocarbon groups having 1 to 10 carbon atoms, and ^R1 and ^R4 may be the same or different from each other.
In formula (i) above, ^R2 and ^R5 are hydrogen or a hydrocarbon group having 1 to 10 carbon atoms, and ^R2 and ^R5 may be the same or different from each other.
In formula (i) above, ^R3 is a hydrocarbon group having 1 to 10 carbon atoms, or the structure of formula (ii) below.
^R1 , ^R2 , and ^R3 may be linked to each other in a cyclic structure.
Furthermore, if ^R3 is a hydrocarbon group, it may be a cyclic structure bonded to R. In the case of the aforementioned cyclic structure, the N bonded to ^R3 and R may be directly bonded to each other.
In the above formula (i), n is an integer of 1 or more, and m is 0 or an integer of 1 or more.

In equation (ii) above, ^R1 and ^R2 are defined in the same way as ^R1 and ^R2 in equation (i) above, and ^R1 and ^R2 may be the same or different from each other.

(In formula (A), ^R1 to ^R4 each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, ^R5 represents an alkylene group having 1 to 10 carbon atoms, and ^R6 represents an alkylene group having 1 to 20 carbon atoms.)
m represents an integer of 1 or 2, n represents an integer of 2 or 3, and (m + n) represents an integer of 4 or greater. If there are multiple ^R1 to ^R4 , they are each independent.

(In formula (B), ^R1 to ^R6 each independently represent an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, and ^R7 to ^R9 each independently represent an alkylene group having 1 to 20 carbon atoms.)
m, n, and l each independently represent integers between 1 and 3, and (m + n + l) represents an integer greater than or equal to 4. If multiple ^R1 through ^R6 exist, they are all independent of each other.

(In formula (C), R ¹² to R ¹⁴ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms, R ¹⁵ to R ¹⁸ and R ²⁰ each independently represent an alkyl group having 1 to 20 carbon atoms, R ¹⁹ and R ²² each independently represent an alkylene group having 1 to 20 carbon atoms, and R ²¹ represents an alkyl group having 1 to 20 carbon atoms or a trialkylsilyl group.
m represents an integer between 1 and 3, and p represents 1 or 2.
When multiple ^R12 to ^R22 , m, and p exist, they are all independent and may be the same or different.
i represents an integer from 0 to 6, j represents an integer from 0 to 6, k represents an integer from 0 to 6, and (i + j + k) is an integer from 4 to 10.
A represents a hydrocarbon group having 1 to 20 carbon atoms, or an organic group having at least one atom selected from the group consisting of oxygen, nitrogen, silicon, sulfur, and phosphorus atoms, and lacking active hydrogen.

The coupling agent having a nitrogen atom-containing group represented by formula (A) is not limited to the following, but examples include 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane, 2,2-diethoxy-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane, 2,2-dimethoxy-1-(4-trimethoxysilylbutyl)-1-aza-2-silacyclohexane, 2,2-dimethoxy-1-(5-trimethoxysilylpentyl)-1-aza-2-silacycloheptane, and 2,2-dimethoxy-1-(3-dimethoxymethylsilylpropyl)-1-aza- Examples include 2-silacyclopentane, 2,2-diethoxy-1-(3-diethoxyethylsilylpropyl)-1-aza-2-silacyclopentane, 2-methoxy-2-methyl-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane, 2-ethoxy-2-ethyl-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane, 2-methoxy-2-methyl-1-(3-dimethoxymethylsilylpropyl)-1-aza-2-silacyclopentane, and 2-ethoxy-2-ethyl-1-(3-diethoxyethylsilylpropyl)-1-aza-2-silacyclopentane.

Among these, those in which m is 2 and n is 3 are preferred from the viewpoint of reactivity and interaction between the functional group of the coupling agent having a nitrogen atom-containing group and inorganic fillers such as silica, as well as from the viewpoint of processability. Specifically, 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane and 2,2-diethoxy-1-(3-triethoxysilylpropyl)-1-aza-2-silacyclopentane are preferred.

The reaction temperature and reaction time when reacting the coupling agent having a nitrogen atom-containing group represented by formula (A) with the polymerization active end are not particularly limited, but it is preferable to react at a temperature of 0°C to 120°C for 30 seconds or more.

The total number of moles of alkoxy groups bonded to the silyl groups in the coupling agent compound having the nitrogen atom-containing group represented by formula (A) is preferably in the range of 0.6 to 3.0 times the number of moles of the alkali metal compound and/or alkaline earth metal compound added as the polymerization initiator, more preferably in the range of 0.8 to 2.5 times, and even more preferably in the range of 0.8 to 2.0 times. From the viewpoint of obtaining a sufficient modification rate, molecular weight, and branched structure in the resulting branched conjugated diene polymer, it is preferable to have a ratio of 0.6 times or more. Furthermore, in addition to the preference for coupling the polymer ends to improve processability and obtain branched conjugated diene polymer components, it is preferable to have a ratio of 3.0 times or less from the viewpoint of coupling agent cost.

The number of moles of the polymerization initiator is preferably 3.0 times or more, more preferably 4.0 times or more, the number of moles of the coupling agent having a nitrogen atom-containing group represented by formula (A).

The coupling agent having a nitrogen atom-containing group represented by formula (B) is not limited to the following, but examples include tris(3-trimethoxysilylpropyl)amine, tris(3-methyldimethoxysilylpropyl)amine, tris(3-triethoxysilylpropyl)amine, tris(3-methyldiethoxysilylpropyl)amine, tris(trimethoxysilylmethyl)amine, tris(2-trimethoxysilylethyl)amine, and tris(4-trimethoxysilylbutyl)amine.

Among these, from the viewpoint of reactivity and interaction between the functional group of the coupling agent and inorganic fillers such as silica, as well as processability, it is preferable that in formula (B), n, m, and l all represent 3. Preferred specific examples include tris(3-trimethoxysilylpropyl)amine and tris(3-triethoxysilylpropyl)amine.

The reaction temperature and reaction time when reacting the coupling agent having a nitrogen atom-containing group represented by formula (B) with the active end of the branched conjugated diene polymer obtained in the branching step are not particularly limited, but it is preferable to react at 0°C to 120°C for 30 seconds or more.

The total number of moles of alkoxy groups bonded to the silyl groups in the coupling agent compound represented by formula (B) is preferably in the range of 0.6 to 3.0 times the number of moles of lithium constituting the polymerization initiator described above, more preferably in the range of 0.8 to 2.5 times, and even more preferably in the range of 0.8 to 2.0 times. From the viewpoint of obtaining a sufficient modification rate, molecular weight, and branched structure in the branched conjugated diene polymer obtained by the manufacturing method of this embodiment, it is preferable to have a total number of moles of 0.6 or more. Furthermore, in addition to the preference for coupling the polymer ends to improve processability and obtain branched conjugated diene polymer components, it is preferable to have a total number of moles of 3.0 or less from the viewpoint of coupling agent cost.

The number of moles of the polymerization initiator is preferably 4.0 times or more, more preferably 5.0 times or more, the number of moles of the coupling agent having a nitrogen atom-containing group represented by formula (B).

In formula (C) above, A is preferably represented by one of the following general formulas (II) to (V).

(In formula (II), ^B1 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer from 1 to 10. If there are multiple ^B1s , each is independent.)

(In formula (III), ^B2 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, ^B3 represents an alkyl group having 1 to 20 carbon atoms, and a represents an integer from 1 to 10. When multiple ^B2 and ^B3 are present, they are considered independent of each other.)

(In formula (IV), ^B4 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer from 1 to 10. If there are multiple ^B4s , each is independent.)

(In formula (V), ^B5 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer from 1 to 10. If there are multiple ^B5s , each is independent.)

In formula (C), the coupling agent having a nitrogen atom-containing group when A is represented by formula (II) is not limited to the following, but includes, for example, tris(3-trimethoxysilylpropyl)amine, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)amine, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine, tris(3-ethoxysilylpropyl)amine, bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]amine, Bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)amine, Tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]amine, Tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, Tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, Bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, Tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilyl (3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl)-1,3-propanediamine, tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-[3-(1-methylsilylpropyl)- Examples include [Toxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, Tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, Tetrakis(3-triethoxysilylpropyl)-1,3-propanediamine, Tris(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, and Bis(3-triethoxysilylpropyl)-bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine.

Also, tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-1,3-propanediamine, tetrakis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tris(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3 -(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine, tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-propanediamine Tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, Tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, Bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, Tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-1,3-bis- Minomethylcyclohexane, tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tris(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethyl Cyclohexane, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, tetrakis(3-triethoxysilylpropyl)-1,3-propanedi Amine, Tris(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, Bis(3-triethoxysilylpropyl)-bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, Tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-1,3-propanediamine, Tetrakis[3-(2,2-diethoxy-1-aza-2-silacyclopentane) [Propyl]-1,3-propanediamine, tris(3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, bis(3-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-( Examples include 3-triethoxysilylpropyl)-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, tris[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-[3-(1-ethoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-1,3-bisaminomethylcyclohexane, tetrakis(3-trimethoxysilylpropyl)-1,6-hexamethylenediamine, and pentakis(3-trimethoxysilylpropyl)-diethylenetriamine.

In formula (C), the coupling agent having a nitrogen atom-containing group when A is represented by formula (III) is not limited to the following, but examples include tris(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine, bis(2-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-methyl-1,3-propanediamine, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3- Trimethoxysilylpropyl)-methyl-1,3-propanediamine, Tris(3-triethoxysilylpropyl)-methyl-1,3-propanediamine, Bis(2-triethoxysilylpropyl)-[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-methyl-1,3-propanediamine, Bis[3-(2,2-diethoxy-1-aza-2-silacyclopentane)propyl]-(3-triethoxysilylpropyl)-methyl-1,3-propanediamine, N ^{Examples include 1} , ^N1 '-(propane-1,3-diyl)bis( ^N1 -methyl- ^N3 , ^N3 -bis(3-(trimethoxysilyl)propyl)-1,3-propanediamine), and ^N1- (3-(bis(3-(trimethoxysilyl)propyl)amino)propyl)-N1-methyl-N3-(3-(methyl(3-(trimethoxysilyl)propyl)amino)propyl)-N3-(3-(trimethoxysilyl)propyl)-1,3-propanediamine.

In formula (C) above, the coupling agent having a nitrogen atom-containing group when A is represented by formula (IV) is not limited to the following, but examples include tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trimethoxysilylpropyl)silane, tris[3-(2,2-dimethoxy-1-aza-2-silacyclopentane) [3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]silane, bis(3-trimethoxysilylpropyl)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, (3-trimethoxysilyl)-[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane) [Tan)propyl]silane, bis[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)-bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, bis(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-silacyclopentane)propyl]silane, bis(3-trimethoxysilylpropyl)-[3-(1-methoxy-2-trimethylsilyl-1-silacyclopentane) Examples include [la-2-azacyclopentane)propyl]-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]silane, bis[3-(1-methoxy-2-trimethylsilyl-1-sila-2-azacyclopentane)propyl]-bis(3-trimethoxysilylpropyl)silane, and bis(3-trimethoxysilylpropyl)-bis[3-(1-methoxy-2-methyl-1-sila-2-azacyclopentane)propyl]silane.

In formula (C), the coupling agent having a nitrogen atom-containing group when A is represented by formula (V) is not limited to the following, but examples include 3-tris[2-(2,2-dimethoxy-1-aza-2-silacyclopentane)ethoxy]silyl-1-(2,2-dimethoxy-1-aza-2-silacyclopentane)propane and 3-tris[2-(2,2-dimethoxy-1-aza-2-silacyclopentane)ethoxy]silyl-1-trimethoxysilylpropane.

In formula (C) above, A is preferably represented by formula (II) or formula (III), and k represents 0.

Such coupling agents having a nitrogen atom-containing group with the structure represented by formula (C) tend to be readily available, and the branched conjugated diene polymer obtained by the manufacturing method of this embodiment tends to have superior wear resistance and low hysteresis loss performance when used as a vulcanized product. Such coupling agents having a nitrogen atom-containing group are not limited to the following, but include, for example, bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine, tris(3-trimethoxysilylpropyl)amine, tris(3-triethoxysilylpropyl)amine, tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetrakis[3-(2,2-dimethoxysilylpropyl] Examples include toxic-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, tris(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine, and bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trismethoxysilylpropyl)-methyl-1,3-propanediamine.

In formula (C), A is more preferably represented by formula (II) or formula (III), where k is 0, and in formula (II) or formula (III), a is an integer from 2 to 10.
As a result, branched conjugated diene polymers tend to exhibit superior abrasion resistance and low hysteresis loss performance when vulcanized.
Such coupling agents having nitrogen atom-containing groups include, but are not limited to, tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, and _N1- (3-(bis(3-(trimethoxysilyl)propyl)amino)propyl) _-N1 -methyl-N3-(3-(methyl( _3- (trimethoxysilyl)propyl)amino)propyl) _-N3- (3-(trimethoxysilyl)propyl)-1,3-propanediamine.

The amount of the compound represented by formula (C) added as a coupling agent containing a nitrogen atom can be adjusted so that the number of moles of the branched conjugated diene polymer before the coupling reaction is in the desired stoichiometric ratio to the number of moles of the coupling agent, thereby tending to achieve the desired star-shaped highly branched structure.

The number of moles of the polymerization initiator is preferably 5.0 times or more, more preferably 6.0 times or more, than the number of moles of the coupling agent having a nitrogen atom-containing group represented by formula (C).

In this case, in formula (C), the number of functional groups of the coupling agent ((m-1) × i + p × j + k) is preferably an integer between 5 and 10, and more preferably an integer between 6 and 10.

The branched conjugated diene polymer obtained by the manufacturing method of this embodiment has a nitrogen atom-containing polymer ratio, which is expressed as the modification rate.
The rate of modification is preferably 60% by mass or more, more preferably 65% by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, even more preferably 80% by mass or more, and particularly preferably 82% by mass or more.
By setting the modification rate to 60% by mass or more, the processability when forming a vulcanized product is excellent, and the wear resistance and low hysteresis loss performance of the vulcanized product tend to be superior.

<Steps involving reaction with polymerization inhibitor>
In the method for producing branched conjugated diene polymers of this embodiment, a reaction step can be carried out in which the active ends of the branched conjugated diene polymer obtained through the polymerization step and branching step described above are reacted with the coupling agent or polymerization inhibitor described above.
As a polymerization termination step, for example, a polymerization termination step performed using a bifunctional reactive compound on the active end of a branched conjugated diene polymer, or a polymerization termination step performed using a polymerization termination agent having a nitrogen atom-containing group (hereinafter, these may collectively be referred to as "polymerization termination agent") is preferred.

In the polymerization termination step, for example, the active end of the branched conjugated diene polymer obtained in the branching step described above can be terminated with a bifunctional reactive compound or a polymerization termination agent having a nitrogen atom-containing group to obtain the desired branched conjugated diene polymer.

[Bifunctional reactive compounds]
In the method for producing branched conjugated diene polymers of this embodiment, the bifunctional reactive compound used in the polymerization termination step may have any structure, but it is preferably a bifunctional reactive compound having a silicon atom.
Examples of difunctional reactive compounds containing silicon atoms include, but are not limited to, tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, and dimethyldiethoxysilane.

[Polymerization inhibitor containing nitrogen atom groups]
In the method for producing branched conjugated diene polymers of this embodiment, the polymerization arrester having a nitrogen atom-containing group used in the polymerization termination step may have any structure, but it is preferable that it has a functional group that reacts with the branched conjugated diene polymer after the branching step.

As the polymerization inhibitor having the nitrogen atom-containing group, an alkoxy compound having the nitrogen atom-containing group is preferred from the viewpoint of improving fuel efficiency.
Polymerization inhibitors having nitrogen atom-containing groups are not limited to the following, but examples include 3-(N,N-dimethylaminopropyl)dimethoxymethylsilane, 3-(N,N-diethylaminopropyl)dimethoxymethylsilane, 3-(N,N-dipropylaminopropyl)dimethoxymethylsilane, 3-(N,N-dimethylaminopropyl)diethoxymethylsilane, 3-(N,N-diethylaminopropyl)diethoxymethylsilane, 3-(N,N-dipropylaminopropyl)diethoxymethylsilane, 3-(N,N-dimethylaminopropyl)dimethoxyethylsilane, 3-(N,N-diethylaminopropyl)dimethoxyethylsilane, 3-(N,N-dipropylaminopropyl)dimethoxyethylsilane, 3-(N,N-dimethylaminopropyl)diethoxyethylsilane, 3-(N,N-diethylaminopropyl)diethoxyethylsilane, and 3-(N,N-dipropylaminopropyl)diethoxyethylsilane.

In the manufacturing method of this embodiment, the branched conjugated diene polymer obtained through the polymerization step, branching step, and reaction step described above preferably has 8 to 36 branches, more preferably 10 to 24 branches, and even more preferably 12 to 20 branches.
The total number of branching points in the branched conjugated diene polymer obtained by the manufacturing method of this embodiment is preferably two or more, more preferably three or more, even more preferably four or more, and even more preferably five or more.
When the branching structure and the total number of branching points are within the range described above, there is a tendency for superior machinability, fuel efficiency, and wear resistance.
For branched conjugated diene polymers with a branched structure of 8 to 36 branches, and in the case of branched conjugated diene polymers to which a modifying agent has been added, in order to construct a polymer with a total number of branching points of 2 to 15, the molar ratio of the branching agent must be 1/2 or less and 1/100 or more of the polymerization initiator, and the coupling agent must have three or more functional groups. In the case of polymers that do not require modification, one or more branching points are acceptable.
In order to construct a branched structure with 8 to 36 branches and a total of 3 to 12 branching points, it is preferable to use a branching agent whose molar ratio is 1/3 or less and 1/50 or more of the polymerization initiator, and a coupling agent with 4 or more functional groups.
In order to construct a branched structure with 10 to 24 branches and a total of 4 to 10 branching points, it is preferable to use a branching agent whose molar ratio is 1/6 or less and 1/25 or more of the polymerization initiator, and a coupling agent with 5 or more functional groups.
In order to construct a branched structure with 12 to 20 branches and a total of 5 to 9 branching points, it is preferable to use a branching agent whose molar ratio is 1/8 or less and 1/12 or more of the polymerization initiator, and a coupling agent with 6 or more functional groups.

(Condensation reaction process)
In the method for producing branched conjugated diene polymers according to this embodiment, a condensation reaction step may be performed after or before the coupling step described above, in which a condensation reaction is carried out in the presence of a condensation accelerator.

(Hydrogenation process)
In the method for producing branched conjugated diene polymers according to this embodiment, a hydrogenation step may be performed to hydrogenate the conjugated diene portion.
The method for hydrogenating the conjugated diene portion of a branched conjugated diene polymer is not particularly limited, and known methods can be used.
A suitable hydrogenation method involves blowing gaseous hydrogen into a polymer solution in the presence of a catalyst.
The catalyst is not particularly limited, but examples include heterogeneous catalysts such as catalysts in which noble metals are supported on porous inorganic materials; homogeneous catalysts such as catalysts obtained by solubilizing salts of nickel, cobalt, etc., and reacting them with organoaluminum, etc., and catalysts using metallocenes such as titanocene. Among these, titanocene catalysts are preferred from the viewpoint of being able to select mild hydrogenation conditions. Furthermore, hydrogenation of aromatic groups can be carried out by using a catalyst supported on a noble metal.

Examples of hydrogenation catalysts include, but are not limited to, (1) supported heterogeneous hydrogenation catalysts in which metals such as Ni, Pt, Pd, and Ru are supported on carbon, silica, alumina, diatomaceous earth, etc.; (2) so-called Ziegler-type hydrogenation catalysts using organic acid salts of Ni, Co, Fe, Cr, etc. or transition metal salts such as acetylacetone salts and reducing agents such as organoaluminum; and (3) so-called organometallic complexes such as organometallic compounds of Ti, Ru, Rh, and Zr. Furthermore, although not particularly limited, known hydrogenation catalysts described in Japanese Patent Publication No. 42-8704, Japanese Patent Publication No. 43-6636, Japanese Patent Publication No. 63-4841, Japanese Patent Publication No. 1-37970, Japanese Patent Publication No. 1-53851, Japanese Patent Publication No. 2-9041, and Japanese Patent Application Publication No. 8-109219 are also examples. A preferred hydrogenation catalyst is a reaction mixture of a titanocene compound and a reducing organometallic compound.

(Addition of deactivating agent and neutralizing agent)
In the method for producing branched conjugated diene polymers according to this embodiment, after the coupling step described above, a deactivator, neutralizing agent, etc. may be added to the polymer solution as needed.
Inactivators are not limited to the following, but examples include water; and alcohols such as methanol, ethanol, and isopropanol.
Examples of neutralizing agents include, but are not limited to, carboxylic acids such as stearic acid, oleic acid, and versatic acid (a highly branched mixture of carboxylic acids with 9 to 11 carbon atoms, mainly 10); aqueous solutions of inorganic acids; and carbon dioxide.

(Addition process for rubber stabilizers)
In the method for producing branched conjugated diene polymers according to this embodiment, it is preferable to add a rubber stabilizer from the viewpoint of preventing gel formation after polymerization and improving stability during processing.
The rubber stabilizers are not limited to those listed below, but any known ones can be used. For example, antioxidants such as 2,6-di-tert-butyl-4-hydroxytoluene (hereinafter also referred to as "BHT"), n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenol)propinate, and 2-methyl-4,6-bis[(octylthio)methyl]phenol are preferred.

(Addition process for rubber softener)
In the method for producing the branched conjugated diene polymer of this embodiment, a rubber softener may be added as needed, from the viewpoint of further improving the productivity of the branched conjugated diene polymer and the processability when it is compounded with fillers and the like to form a rubber composition.
Rubber softeners are not particularly limited, but examples include stretching oils, liquid rubber, and resins.
While not limited to the following, a preferred method for adding a rubber softener to a branched conjugated diene polymer is to add the rubber softener to the branched conjugated diene polymer solution, mix it, obtain a polymer solution containing the rubber softener, and then desolvate the resulting solution.

Preferred spreading oils include, for example, aromatic oils, naphthenic oils, and paraffinic oils. Among these, from the viewpoint of environmental safety, as well as preventing oil bleeding and improving wet grip characteristics, aromatic substitute oils containing 3% by mass or less of polycyclic aromatic (PCA) components according to the IP346 method are preferred. Examples of aromatic substitute oils include TDAE (Treated Distillate Aromatic Extracts) and MES (Mild Extraction Solvate) as described in Kautschuk Gumi Kunststoffe 52(12)799(1999), as well as RAE (Residual Aromatic Extracts).

Preferred liquid rubbers include, but are not limited to, liquid polybutadiene, liquid styrene-butazine rubber, and the like.
The effects of adding liquid rubber include improving the processability of resin compositions that combine branched conjugated diene polymers and fillers, and shifting the glass transition temperature of the resin composition to a lower temperature, which tends to improve the wear resistance, low hysteresis loss, and low-temperature properties of the vulcanized product.
Examples of resins used as rubber softeners include, but are not limited to, aromatic petroleum resins, coumarone-indene resins, terpene resins, rosin derivatives (including tung oil resins), tall oil, tall oil derivatives, rosin ester resins, natural and synthetic terpene resins, aliphatic hydrocarbon resins, aromatic hydrocarbon resins, mixed aliphatic-aromatic hydrocarbon resins, coumarin-indene resins, phenol resins, p-tert-butylphenol-acetylene resins, phenol-formaldehyde resins, xylene-formaldehyde resins, monoolefin oligomers, diolefin oligomers, hydrogenated aromatic hydrocarbon resins, cyclic aliphatic hydrocarbon resins, hydrogenated hydrocarbon resins, hydrocarbon resins, hydrogenated tung oil resins, hydrogenated oil resins, and esters of hydrogenated oil resins with monofunctional or polyfunctional alcohols. These resins may be used individually or in combination of two or more. When hydrogenating, all unsaturated groups may be hydrogenated, or some may be left intact.
The effects of adding resin as a rubber softener include improving the processability of resin compositions that combine conjugated diene polymers and fillers, improving the fracture strength of vulcanized products, and improving wet skid resistance by shifting the glass transition temperature of the resin composition to a higher temperature.

The amount of rubber softener added, such as a stretching oil, liquid rubber, or resin, is not particularly limited, but is preferably 1 to 60 parts by mass, more preferably 5 to 50 parts by mass, and even more preferably 10 to 37.5 parts by mass, per 100 parts by mass of the branched conjugated diene polymer obtained by the manufacturing method of this embodiment.
When a rubber softener is added within the aforementioned range, the processability of the resin composition obtained by the manufacturing method of this embodiment, which is a blend of the branched conjugated diene polymer and fillers, tends to be good, and the fracture strength and abrasion resistance of the vulcanized product tend to be good.

(Desolvation process)
In the method for producing branched conjugated diene polymers of this embodiment, known methods can be used to obtain the obtained branched conjugated diene polymer from the polymer solution. The method is not particularly limited, but examples include a method in which the solvent is separated by steam stripping or the like, the polymer is filtered off, and then dehydrated and dried to obtain the polymer; a method in which the solution is concentrated in a flushing tank and then defolalated using a vent extruder or the like; and a method in which the solution is directly defolarated using a drum dryer or the like.

[Branched conjugated diene polymers]
The branched conjugated diene polymer of this embodiment is a branched conjugated diene polymer obtained by the method for producing the branched conjugated diene polymer of this embodiment described above, and the polymer main chain has a main chain branched structure derived from a nitrogen atom-containing branching agent which is a compound represented by the following formula (1).

[Rubber composition, and method for manufacturing the rubber composition]
The rubber composition of this embodiment contains a rubber component comprising 10% by mass or more of the branched conjugated diene polymer of this embodiment, manufactured by the manufacturing method of this embodiment described above, and a filler in an amount of 5.0 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the rubber component.
The method for producing the rubber composition of this embodiment includes the steps of: obtaining a branched conjugated diene polymer by the production method described above; obtaining a rubber component containing 10% by mass or more of the branched conjugated diene polymer; and adding 5.0 parts by mass or more and 150 parts by mass or less of a filler per 100 parts by mass of the rubber component.
Furthermore, by including 10% by mass of the branched conjugated diene polymer obtained by the manufacturing method of this embodiment in the rubber component, excellent fuel efficiency, processability, and improved wear resistance can be obtained.

The filler preferably contains a silica-based inorganic filler.
Rubber compositions, when filled with silica-based inorganic fillers, tend to exhibit superior processability when vulcanized, and tend to have a better balance of abrasion resistance, fracture strength, low hysteresis loss, and wet skid resistance in the vulcanized product.
When the rubber composition is used for applications such as tires, vibration-damping rubber for automobile parts, and vulcanized rubber for shoes, it is preferable to include a silica-based inorganic filler.

The rubber composition of this embodiment is obtained by mixing a rubber component containing 10% by mass or more of a branched conjugated diene polymer obtained by the manufacturing method described above with the filler.
The rubber component may also contain rubbery polymers other than the branched conjugated diene polymers described above (hereinafter simply referred to as "rubbery polymers").
Examples of such rubbery polymers include, but are not limited to, conjugated diene polymers or their hydrogenated derivatives, random copolymers of conjugated diene compounds and aromatic vinyl compounds or their hydrogenated derivatives, and block copolymers of conjugated diene compounds and aromatic vinyl compounds or their hydrogenated derivatives. Other examples include non-diene polymers and natural rubber.

Examples of rubbery polymers include, but are not limited to, but styrene-based elastomers such as butadiene rubber or its hydrogenated derivatives, isoprene rubber or its hydrogenated derivatives, styrene-butadiene rubber or its hydrogenated derivatives, styrene-butadiene block copolymer or its hydrogenated derivatives, styrene-isoprene block copolymer or its hydrogenated derivatives, and acrylonitrile-butadiene rubber or its hydrogenated derivatives.

Examples of non-diene polymers include, but are not limited to, olefin-based elastomers such as ethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-butene-diene rubber, ethylene-butene rubber, ethylene-hexene rubber, and ethylene-octene rubber; butyl rubber, brominated butyl rubber, acrylic rubber, fluororubber, silicone rubber, chlorinated polyethylene rubber, epichlorohydrin rubber, α,β-unsaturated nitrile-acrylic acid ester-conjugated diene copolymer rubber, urethane rubber, and polysulfide rubber.

Examples of natural rubber include, but are not limited to, smoked sheets such as RSS 3-5, SMR, and epoxidized natural rubber.

The various rubbery polymers described above may be modified rubbers to which polar functional groups such as hydroxyl groups and amino groups have been added. For use in tires, butadiene rubber, isoprene rubber, styrene-butadiene rubber, natural rubber, and butyl rubber are preferably used.

The weight-average molecular weight of the rubbery polymer is preferably 2,000 to 2,000,000, and more preferably 5,000 to 1,500,000, from the viewpoint of balancing the various performance characteristics and processing properties of the rubber composition of this embodiment. Alternatively, a low molecular weight rubbery polymer, so-called liquid rubber, can also be used.
These rubbery polymers may be used individually or in combination of two or more types.

When the rubber composition using the branched conjugated diene polymer of this embodiment is a rubber composition containing the above-mentioned rubbery polymer, the content ratio (mass ratio) of the branched conjugated diene polymer to the rubbery polymer is preferably 10/90 or more and 100/0 or less, more preferably 20/80 or more and 90/10 or less, and even more preferably 50/50 or more and 80/20 or less, as (branched conjugated diene polymer/rubbery polymer).
Therefore, the rubber component preferably contains 10% to 100% by mass, more preferably 20% to 90% by mass, and even more preferably 50% to 80% by mass, of the above-mentioned branched conjugated diene polymer based on the total amount (100% by mass) of the rubber component.

When the content ratio of (branched conjugated diene polymer/rubber-like polymer) is within the above range, the vulcanized product tends to exhibit excellent abrasion resistance and fracture strength, as well as a good balance between low hysteresis loss and wet skid resistance.

The fillers included in the rubber composition of this embodiment are not limited to the following, but include, for example, carbon black, metal oxides, and metal hydroxides, in addition to the silica-based inorganic filler. Among these, the silica-based inorganic filler is preferred.
The filler may be used alone or in combination of two or more types.
The filler content in the rubber composition is 5.0 parts by mass to 150 parts by mass, preferably 20 parts by mass to 100 parts by mass, and more preferably 30 parts by mass to 90 parts by mass, per 100 parts by mass of the rubber component containing the branched conjugated diene polymer described above.
In the rubber composition, the filler content is 5.0 parts by mass or more per 100 parts by mass of rubber components, from the viewpoint of exhibiting the effect of the filler addition, and 150 parts by mass or less per 100 parts by mass of rubber components, from the viewpoint of sufficiently dispersing the filler and making the processability and mechanical strength of the rubber composition practically sufficient.

The silica-based inorganic filler is not particularly limited, and known fillers can be used, but solid particles containing _SiO₂ or _Si₃Al as constituent units are preferred, and solid particles containing _SiO₂ or _Si₃Al as the main component of the constituent units are more preferred. Here, the main component refers to a component that is contained in the silica-based inorganic filler at a concentration of 50% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more.

Examples of silica-based inorganic fillers include, but are not limited to, silica, clay, talc, mica, diatomaceous earth, wollastonite, montmorillonite, zeolite, glass fibers, and other inorganic fibrous materials. Other examples include silica-based inorganic fillers with hydrophobic surfaces and mixtures of silica-based inorganic fillers and non-silica-based inorganic fillers.
Among these, silica and glass fiber are preferred from the viewpoint of strength and abrasion resistance, with silica being more preferred.
Examples of silica include dry silica, wet silica, and synthetic silicate silica. Among these silicas, wet silica is preferred because it offers an excellent balance between improving fracture strength and wet skid resistance.

From the viewpoint of obtaining practically good abrasion resistance and fracture strength in a rubber composition, the nitrogen adsorption specific surface area obtained by the BET adsorption method of silica-based inorganic fillers is preferably 100 ^m² /g or more and 300 ^m² /g or less, and more preferably 170 ^m² /g or more and 250 ^m² /g or less.
Furthermore, if necessary, a combination of silica-based inorganic fillers with a relatively small specific surface area (for example, less than 200 ^m² /g) and silica-based inorganic fillers with a relatively large specific surface area (for example, 200 ^m² /g or more) can be used.
In particular, when using silica-based inorganic fillers with a relatively large specific surface area (for example, 200 ^m² /g or more), rubber compositions containing the aforementioned branched conjugated diene polymers improve the dispersibility of silica, are especially effective in improving abrasion resistance, and tend to achieve a high degree of balance between good fracture strength and low hysteresis loss.

The content of silica-based inorganic filler in the rubber composition is preferably 5.0 parts by mass or more and 150 parts by mass, and more preferably 20 parts by mass or more and 100 parts by mass, per 100 parts by mass of the rubber component containing the branched conjugated diene polymer obtained by the manufacturing method of this embodiment. In the rubber composition, the content of silica-based inorganic filler is preferably 5.0 parts by mass or more per 100 parts by mass of the rubber component, from the viewpoint of exhibiting the additive effect of the silica-based inorganic filler. From the viewpoint of sufficiently dispersing the silica-based inorganic filler and ensuring that the processability and mechanical strength of the rubber composition are practically sufficient, it is preferably 150 parts by mass or less per 100 parts by mass of the rubber component.

Carbon black is not limited to the following, but examples include carbon blacks of various classes such as SRF, FEF, HAF, ISAF, and SAF. Among these, carbon black with a nitrogen adsorption specific surface area of 50 ^m² /g or more and a dibutyl phthalate (DBP) oil absorption amount of 80 mL/100 g or less is preferred.

The carbon black content in the rubber composition is preferably 0.5 parts by mass or more and 100 parts by mass or less, more preferably 3.0 parts by mass or more and 100 parts by mass or less, and even more preferably 5.0 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the rubber component containing the branched conjugated diene polymer obtained by the manufacturing method of this embodiment. In the rubber composition, the carbon black content is preferably 0.5 parts by mass or more per 100 parts by mass of the rubber component from the viewpoint of exhibiting performance required for applications such as tires, such as dry grip performance and conductivity, and preferably 100 parts by mass or less per 100 parts by mass of the rubber component from the viewpoint of dispersibility.

Metal oxides are solid particles whose main constituent unit is the chemical formula MxOy (where M represents a metal atom, and x and y independently represent integers from 1 to 6).

Examples of metal oxides, though not limited to those listed below, include alumina, titanium oxide, magnesium oxide, and zinc oxide.

Examples of metal hydroxides include, but are not limited to, aluminum hydroxide, magnesium hydroxide, and zirconium hydroxide.

The rubber composition of this embodiment may contain a silane coupling agent.
Silane coupling agents have the function of strengthening the interaction between rubber components and inorganic fillers. Specifically, compounds that have groups that have affinity or binding properties to both rubber components and silica-based inorganic fillers, and that contain a sulfur bond portion and an alkoxysilyl group or silanol group portion in a single molecule are preferred.
Examples of such compounds, though not particularly limited, include bis-[3-(triethoxysilyl)-propyl]tetrasulfide, bis-[3-(triethoxysilyl)-propyl]-disulfide, and bis-[2-(triethoxysilyl)-ethyl]tetrasulfide.

In the rubber composition, the content of the silane coupling agent is preferably 0.1 parts by mass or more and 30 parts by mass or less, more preferably 0.5 parts by mass or more and 20 parts by mass or less, and even more preferably 1.0 part by mass or more and 15 parts by mass or less, per 100 parts by mass of the inorganic filler described above. When the content of the silane coupling agent is within the above range, the additive effect of the silane coupling agent tends to be made even more pronounced.

The rubber composition of this embodiment may contain a rubber softener from the viewpoint of improving its processability.
The amount of rubber softener added is expressed as the total amount of rubber softener added when manufacturing the rubber composition, plus the amount of rubber softener already contained in the branched conjugated diene polymer or other rubbery polymers, per 100 parts by mass of the rubber component containing the branched conjugated diene polymer obtained by the manufacturing method of this embodiment described above.
Suitable rubber softeners include mineral oil or liquid or low molecular weight synthetic softeners.
Process oils or extender oils, which are mineral oil-based rubber softeners used to soften, increase the volume of, and improve the processability of rubber, are mixtures of aromatic rings, naphthenic rings, and paraffinic chains. Those in which the number of carbon atoms in the paraffinic chain accounts for 50% or more of the total carbon are called paraffinic, those in which the number of carbon atoms in the naphthenic ring accounts for 30% to 45% of the total carbon are called naphthenic, and those in which the number of carbon atoms in the aromatic ring accounts for more than 30% of the total carbon are called aromatic.
When the branched conjugated diene polymer of this embodiment contains a conjugated diene compound and an aromatic vinyl compound as polymerization monomers, a rubber softener with an appropriate aromatic content is preferred because it tends to blend well with the branched conjugated diene copolymer.
In the rubber composition, the content of the rubber softener is preferably 0 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the rubber component, more preferably 10 parts by mass or more and 90 parts by mass or less, and even more preferably 30 parts by mass or more and 90 parts by mass or less. When the content of the rubber softener is 100 parts by mass or less per 100 parts by mass of the rubber component, bleed-out is suppressed and stickiness on the surface of the rubber composition tends to be suppressed.

The method for mixing the branched conjugated diene polymer obtained by the manufacturing method of this embodiment with other rubbery polymers, silica-based inorganic fillers, carbon black and other fillers, silane coupling agents, rubber softeners, and other additives is not limited to the following, but examples include a melt-kneading method using a general mixer such as an open roll, Banbury mixer, kneader, single-screw extruder, twin-screw extruder, or multi-screw extruder, and a method in which the solvent is removed by heating after dissolving and mixing each component.
Of these methods, melt-kneading methods using rolls, Banbury mixers, kneaders, and extruders are preferred from the viewpoint of productivity and good kneading performance. Furthermore, both methods of kneading the rubber components with other fillers, silane coupling agents, and additives in a single step, or methods of mixing in multiple steps, are applicable.

The rubber composition of this embodiment may be a vulcanized composition that has been vulcanized with a vulcanizing agent. The vulcanizing agent is not limited to the following, but examples include radical generators such as organic peroxides and azo compounds, oxime compounds, nitroso compounds, polyamine compounds, sulfur, and sulfur compounds. Sulfur compounds include sulfur monochloride, sulfur dichloride, disulfide compounds, high molecular weight polysulfur compounds, etc.
In the rubber composition of this embodiment, the content of the vulcanizing agent is preferably 0.01 parts by mass or more and 20 parts by mass or less, and more preferably 0.1 parts by mass or more and 15 parts by mass or less, per 100 parts by mass of the rubber component. A conventionally known method can be applied as the vulcanization method, and the vulcanization temperature is preferably 120°C or more and 200°C or less, and more preferably 140°C or more and 180°C or less.

During vulcanization, a vulcanization accelerator may be used as needed.
Conventional known materials can be used as vulcanization accelerators, and are not limited to the following, but examples include sulfenamide-based, guanidine-based, thiuram-based, aldehyde-amine-based, aldehyde-ammonia-based, thiazole-based, thiourea-based, and dithiocarbamate-based vulcanization accelerators.
Furthermore, while not limited to the following, examples of vulcanization aids include zinc oxide and stearic acid.
The content of the vulcanization accelerator is preferably 0.01 parts by mass or more and 20 parts by mass or less, and more preferably 0.1 parts by mass or more and 15 parts by mass or less, per 100 parts by mass of the rubber component.

The rubber composition of this embodiment may also contain various additives other than those described above, such as softeners and fillers, heat stabilizers, antistatic agents, weather stabilizers, anti-aging agents, colorants, and lubricants, as long as they do not impair the purpose of this embodiment.
Other known softening agents can be used.
Other fillers, while not particularly limited, include, for example, calcium carbonate, magnesium carbonate, aluminum sulfate, and barium sulfate. Known materials can be used as the heat stabilizer, antistatic agent, weather stabilizer, anti-aging agent, colorant, and lubricant.

[Tires and methods for manufacturing tires]
The tire of this embodiment contains the rubber composition of this embodiment described above.
The tire manufacturing method of this embodiment comprises the steps of obtaining a branched conjugated diene polymer by the manufacturing method of this embodiment, obtaining a rubber composition containing the branched conjugated diene polymer, and molding the rubber composition.
The rubber composition containing the branched conjugated diene polymer obtained by the manufacturing method of this embodiment described above is suitably used as a rubber composition for tires.

The rubber composition for tires is not limited to the following, but can be used in various tire components such as the tread, carcass, sidewall, and bead, including fuel-efficient tires, all-season tires, high-performance tires, and studless tires. In particular, the rubber composition for tires exhibits excellent balance between wear resistance, fracture strength, low hysteresis loss, and wet skid resistance when vulcanized, making it suitable for use in the treads of fuel-efficient and high-performance tires.

The embodiment will be described in more detail below with reference to specific examples and comparative examples, but this embodiment is not limited in any way to the following examples and comparative examples.
The various physical properties in the examples and comparative examples were measured by the methods described below.
In the following, conjugated diene polymers coupled with a coupling agent will be referred to as "coupled conjugated diene polymers."
Furthermore, conjugated diene polymers having a branched structure derived from a nitrogen atom-containing branching agent are described as "modified branched conjugated diene polymers."
Furthermore, the term "conjugated diene polymer" is sometimes used as a general term for coupling conjugated diene polymers, modified branched conjugated diene polymers, and conjugated diene polymers that do not have a branched structure derived from nitrogen atom-containing branching agents.
In the examples described later, a conjugated diene polymer having a branched structure derived from a nitrogen atom-containing branching agent will be referred to as a "modified branched conjugated diene polymer," but this notation does not in any way limit the branched conjugated diene polymer produced by the method for producing branched conjugated diene polymers of the present invention.

The various physical properties in the examples and comparative examples were measured by the methods described below.

(Physical Properties 1) Polymer Mooney Viscosity Various conjugated diene polymers were used as samples, and the Mooney viscosity was measured using a Mooney viscometer (product name "VR1132" manufactured by Ueshima Seisakusho Co., Ltd.) in accordance with ISO 289 and with an L-shaped rotor.
The measurement temperature was set to 110°C when the sample was a modified branched conjugated diene polymer or a conjugated diene polymer that did not use a nitrogen atom-containing branching agent, and to 100°C when the sample was a coupling conjugated diene polymer.
First, the sample was preheated to the test temperature for 1 minute, then the rotor was rotated at 2 rpm, and the torque after 4 minutes was measured to determine the Mooney viscosity (ML ₍₁₊₄₎ ).

(Physical Properties 2) Mooney Relaxation Rate Using a coupling-conjugated diene polymer as a sample, the Mooney viscosity was measured using a Mooney viscometer (product name "VR1132" manufactured by Ueshima Seisakusho Co., Ltd.) in accordance with ISO 289, using an L-shaped rotor. Immediately after measuring the Mooney viscosity, the rotor rotation was stopped, and the torque was recorded in Mooney units at 0.1-second intervals from 1.6 seconds to 5 seconds after stopping. The slope of the line when torque and time (seconds) were plotted on a log-log scale was determined, and its absolute value was defined as the Mooney relaxation rate (MSR).

(Physical property 3) Degree of branching (Bn)
The degree of branching (Bn) of coupling-conjugated diene polymers was measured as follows using GPC-light scattering with a viscosity detector.
Using coupling-conjugated diene polymers as samples, measurements were performed using a gel permeation chromatography (GPC) analyzer (Malvern product name "GPCmax VE-2001") with three columns packed with polystyrene gel. The three detectors were connected in the following order: a light scattering detector, an RI detector, and a viscometer (Malvern product name "TDA305"). Based on standard polystyrene, the absolute molecular weight was determined from the measurement results of the light scattering detector and the RI detector, and the intrinsic viscosity was determined from the measurement results of the RI detector and the viscometer.
Linear polymers were assumed to follow an intrinsic viscosity [η] = ^{10⁻³⁸³⁰ M⁻⁰}
Subsequently, the degree of branching (Bn), defined as g' = 6Bn / [(Bn+1)(Bn+2)], was calculated using the obtained contraction factor (g').
The eluent used was tetrahydrofuran containing 5 mmol/L triethylamine (hereinafter also referred to as "THF").
The columns used were TSKgel G4000HXL, TSKgel G5000HXL, and TSKgel G6000HXL, all manufactured by Tosoh Corporation, connected together.
20 mg of the sample for measurement was dissolved in 10 mL of THF to prepare the measurement solution. 100 μL of the measurement solution was injected into a GPC measuring device, and measurements were taken under the conditions of an oven temperature of 40°C and a THF flow rate of 1 mL/min.

(Physical property 4) Molecular weight <Measurement conditions 1>:
Using various conjugated diene polymers as samples, chromatograms were measured using a GPC analyzer (Tosoh Corporation, product name "HLC-8320GPC") consisting of three columns packed with polystyrene gel, and an RI detector (Tosoh Corporation, product name "HLC8020"). Based on a calibration curve obtained using standard polystyrene, the weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution (Mw/Mn) were determined.
The eluent used was 5 mmol/L triethylamine-containing THF (tetrahydrofuran). Three TSKgel SuperMultiporeHZ-H columns, manufactured by Tosoh Corporation, were connected together, and a TSKguardcolumn SuperMP(HZ)-H column, also manufactured by Tosoh Corporation, was connected before them as a guard column.
10 mg of the sample for measurement was dissolved in 10 mL of THF to prepare the measurement solution. 10 μL of the measurement solution was injected into the GPC measuring device, and measurements were taken under the conditions of an oven temperature of 40°C and a THF flow rate of 0.35 mL/min.
Among the various samples measured under measurement condition 1 described above, those with a molecular weight distribution (Mw/Mn) value of less than 1.6 were measured again under measurement condition 2 described below. Samples measured under measurement condition 1 with a molecular weight distribution value of 1.6 or higher were measured under measurement condition 1 again.
<Measurement Condition 2>:
Various conjugated diene polymers were used as samples, and chromatograms were measured using a GPC analyzer with three columns packed with polystyrene gel. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) were determined based on a calibration curve using standard polystyrene.
The eluent used was THF containing 5 mmol/L triethylamine. The columns used were: Guard column: "TSKguardcolumn SuperH-H" manufactured by Tosoh Corporation; Columns: "TSKgel SuperH5000", "TSKgel SuperH6000", and "TSKgel SuperH7000" manufactured by Tosoh Corporation.
An RI detector (Tosoh Corporation product name "HLC8020") was used under conditions of an oven temperature of 40°C and a THF flow rate of 0.6 mL/min. 10 mg of the sample for measurement was dissolved in 20 mL of THF to prepare the measurement solution, and 20 μL of the measurement solution was injected into the GPC analyzer for measurement.
For samples measured under measurement condition 1, if the molecular weight distribution value was less than 1.6, measurement was performed under measurement condition 2.

(Physical Properties 5) Modification Rate The modification rates of modified branched conjugated diene polymers and coupling conjugated diene polymers were measured by column adsorption GPC as follows.
Modified branched conjugated diene polymers and coupling conjugated diene polymers were used as samples, and measurements were performed by applying the property of adsorption of modified basic polymer components to a GPC column packed with silica gel.
The amount of adsorption onto the silica column was determined by comparing the chromatograms obtained using a polystyrene column with the chromatograms obtained using a silica column for a sample solution containing the sample and a low molecular weight internal standard polystyrene, and the denaturation rate was then calculated.
Specifically, it is as follows:
Furthermore, for samples measured under measurement condition 1 of (Physical Property 4) above, and whose molecular weight distribution value was 1.6 or higher, the samples were measured under measurement condition 3 below, and the measured values were adopted. For samples measured under measurement condition 1 of (Physical Property 4) above, and whose molecular weight distribution value was less than 1.6, the samples were measured under measurement condition 4 below, and the measured values were adopted.

<Preparation of sample solution>:
10 mg of the sample and 5 mg of standard polystyrene were dissolved in 20 mL of THF to prepare the sample solution.
<Measurement Condition 3>:
GPC measurement conditions using polystyrene columns:
Using the "HLC-8320GPC" product manufactured by Tosoh Corporation, 10 μL of the sample solution was injected into the apparatus with 5 mmol/L of triethylamine-containing THF as the eluent. A chromatogram was obtained using an RI detector under the conditions of a column oven temperature of 40°C and a THF flow rate of 0.35 mL/min.
The column consisted of three "TSKgel SuperMultiporeHZ-H" columns manufactured by Tosoh Corporation, with a "TSKguardcolumn SuperMP(HZ)-H" column, also manufactured by Tosoh Corporation, connected before them as a guard column.

<Measurement Condition 4>:
THF containing 5 mmol/L triethylamine was used as the eluent, and 20 μL of the sample solution was injected into the instrument for measurement.
The columns used were: guard column: "TSKguardcolumn SuperH-H" manufactured by Tosoh Corporation; columns: "TSKgel SuperH5000", "TSKgel SuperH6000", and "TSKgel SuperH7000" manufactured by Tosoh Corporation. Chromatograms were obtained by measuring under conditions of a column oven temperature of 40°C and a THF flow rate of 0.6 mL/min using an RI detector (Tosoh Corporation HLC8020).

GPC measurement conditions using silica-based columns:
Using a Tosoh Corporation product name "HLC-8320GPC," 50 μL of sample solution was injected into the apparatus with THF as the eluent. A chromatogram was obtained using an RI detector under the conditions of a column oven temperature of 40°C and a THF flow rate of 0.5 ml/min. The columns used were "Zorbax PSM-1000S,""PSM-300S," and "PSM-60S," with a "DIOL 4.6 × 12.5 mm 5 micron" column connected before them as a guard column.

Method for calculating the rate of degeneration:
The denaturation rate (%) was calculated using the following formula, with the total peak area of the chromatogram using a polystyrene column set to 100, the peak area of the sample being P1, and the peak area of standard polystyrene being P2. The total peak area of the chromatogram using a silica column was also set to 100, with the peak area of the sample being P3 and the peak area of standard polystyrene being P4.
Degeneration rate (%) = [1 - (P2 × P3) / (P1 × P4)] × 100
(However, P1 + P2 = P3 + P4 = 100)

(Physical property 6) Amount of bound styrene A coupling conjugated diene polymer that does not contain rubber softener was used as the sample. 100 mg of the sample was made up to 100 mL with chloroform and dissolved to prepare the measurement sample.
The amount of bound styrene (mass%) relative to 100% by mass of the coupling-conjugated diene polymer sample was measured by the amount of ultraviolet absorption at the phenyl group of styrene (around 254 nm) (measurement device: Shimadzu UV-2450 spectrophotometer).

(Physical property 7) Microstructure of the butadiene portion (amount of 1,2-vinyl bonds)
A coupling-conjugated diene polymer that does not contain rubber softeners was used as the sample. 50 mg of the sample was dissolved in 10 mL of carbon disulfide to prepare the measurement sample.
Using a solution cell, the infrared spectrum was measured in the range of 600 to 1000 ^cm⁻¹ , and the microstructure of the butadiene portion, i.e., the amount of 1,2-vinyl bonds (also referred to as 1,2-bond amount in the table) (mol%) was determined according to the calculation formula of Hampton's method (R.R. Hampton, Analytical Chemistry 21, 923 (1949)) based on the absorbance at a predetermined wavenumber (measuring device: Fourier transform infrared spectrophotometer "FT-IR230" manufactured by JASCO Corporation).

(Physical property 8) Molecular weight (absolute molecular weight) measured by GPC-light scattering method
Using coupling-conjugated diene polymers as samples, chromatograms were measured using a GPC-light scattering analyzer with three columns packed with polystyrene gel. The weight-average molecular weight (Mw-i) was determined based on solution viscosity and light scattering (also known as "absolute molecular weight").
The eluent used was a mixed solution of tetrahydrofuran and triethylamine (THF in TEA: prepared by mixing 5 mL of triethylamine with 1 L of tetrahydrofuran).
The columns used were a combination of a guard column (product name "TSKguardcolumn HHR-H" manufactured by Tosoh Corporation) and columns (product names "TSKgel G6000HHR", "TSKgel G5000HHR", and "TSKgel G4000HHR" manufactured by Tosoh Corporation).
Under oven temperature of 40°C and THF flow rate of 1.0 mL/min, a GPC-light scattering analyzer (Malvern Corporation product name "Viscotec TDAmax") was used.
10 mg of the sample for measurement was dissolved in 20 mL of THF to prepare the measurement solution, and 200 μL of the measurement solution was injected into a GPC analyzer for measurement.

[Conjugated diene polymers]
( Reference Example 1) Coupling-conjugated diene polymer (Sample 1)
Two tank-type pressure vessels, each with an internal volume of 10 L, an internal height (L) to diameter (D) ratio (L/D) of 4.0, an inlet at the bottom and an outlet at the top, and equipped with a stirrer and a jacket for temperature control, were connected together as polymerization reactors.
1,3-butadiene, from which water had been removed beforehand, was mixed at a rate of 18.6 g/min, styrene at 10.0 g/min, and n-hexane at 175.2 g/min. In a static mixer installed in the middle of the piping supplying this mixed solution to the reactor inlet, n-butyllithium for inactivating residual impurities was added at a rate of 0.103 mmol/min, mixed, and then continuously supplied to the bottom of the first reactor, which was being vigorously mixed with a stirrer. Furthermore, 2,2-bis(2-oxolanil)propane was supplied at a rate of 0.081 mmol/min as a polar substance, and n-butyllithium was supplied at a rate of 0.143 mmol/min as a polymerization initiator, to the bottom of the first reactor, which was being vigorously mixed with a stirrer, and the reactor temperature was maintained at 67°C.
The polymer solution was continuously withdrawn from the top of the first reactor and continuously supplied to the bottom of the second reactor, where the reaction was continued at 70°C. The solution was then supplied to a static mixer from the top of the second reactor. Once the polymerization was sufficiently stable, compound M-1 (abbreviated as "M-1" in the table) was added at a rate of 0.0080 mmol/min from the bottom of the second reactor as a nitrogen atom-containing branching agent while copolymerizing 1,3-butadiene and styrene. A polymerization and branching reaction was carried out to obtain a modified branched conjugated diene polymer having a main chain branched structure.
Furthermore, once the polymerization and branching reactions were stable, a small amount of the modified branched conjugated diene polymer was extracted before the addition of the coupling agent. An antioxidant (BHT) was added at a rate of 0.2 g per 100 g of polymer, and then the solvent was removed. The Mooney viscosity at 110°C and various molecular weights were measured. The physical properties are shown in Table 1.
Next, tetraethoxysilane (abbreviated as "A" in the table) was continuously added at a rate of 0.0480 mmol/min as a coupling agent to the polymer solution that flowed out of the reactor outlet, and the mixture was mixed using a static mixer to carry out the coupling reaction. At this time, the time until the coupling agent was added to the polymer solution flowing out of the reactor outlet was 4.8 minutes, and the temperature was 68°C. The difference between the temperature during the polymerization process and the temperature until the coupling agent was added was 2°C. A small amount of the conjugated diene polymer solution after the coupling reaction was withdrawn, and an antioxidant (BHT) was added at a rate of 0.2 g per 100 g of polymer, followed by removal of the solvent. The amount of bound styrene (physical property 6) and the microstructure of the butadiene portion (amount of 1,2-vinyl bonds: physical property 7) were measured. The measurement results are shown in Table 1.
Next, an antioxidant (BHT) was continuously added to the polymer solution after the coupling reaction at a rate of 0.055 g/min (n-hexane solution) so that the BHT amounted to 0.2 g per 100 g of polymer, and the coupling reaction was terminated. Simultaneously with the antioxidant, SRAE oil (JOMO Process NC140, manufactured by JX Nippon Oil & Energy Corporation) was continuously added as a rubber softener at a rate of 25.0 g per 100 g of polymer, and the mixture was mixed using a static mixer. The solvent was removed by steam stripping to obtain a coupling-conjugated diene polymer (Sample 1) having a branched structure derived from a nitrogen atom-containing branching agent (hereinafter also referred to as "branching agent structure (1)"), which is a compound represented by the following formula (M-1), in part of the main chain, and a three-branched star polymer structure derived from the coupling agent.
The physical properties of sample 1 are shown in Table 1.
Furthermore, the structure of the coupling-conjugated diene polymer was identified by comparing the molecular weight measured by GPC with the degree of branching measured by GPC with a viscometer for the polymer before the addition of the nitrogen atom-containing branching agent, the polymer after the addition of the nitrogen atom-containing branching agent, and the polymer at each step after the addition of the coupling agent. The structure of each sample was identified in the same manner below.

In formula (M-1), Me represents a methyl group.

( Reference Example 2) Coupling-conjugated diene polymer (Sample 2)
Except for changing the coupling agent from tetraethoxysilane to 1,2-bis(triethoxysilyl)ethane (abbreviated as "B" in the table) and changing the amount added to 0.0360 mmol/min, a coupling-conjugated diene polymer ( Sample 2) was obtained in the same manner as in Reference Example 1, having an octave branched structure derived from the branching agent structure (1) in part of the main chain and a tetrabranched star polymer structure derived from the coupling agent. The physical properties of Sample 2 are shown in Table 1.

(Example 3) Coupling-conjugated diene polymer (Sample 3)
Except for changing the coupling agent from tetraethoxysilane to 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (abbreviated as "C" in the table) and changing the amount added to 0.0360 mmol/min, a coupling-conjugated diene polymer (Sample 3) was obtained in the same manner as in Reference Example 1, having an octave branched structure derived from the branching agent structure (1) in part of the main chain and a tetrabranched star polymer structure derived from the coupling agent. The physical properties of Sample 3 are shown in Table 1.

(Example 4) Coupling-conjugated diene polymer (Sample 4)
Except for changing the coupling agent from tetraethoxysilane to 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane (abbreviated as "D" in the table) and changing the amount added to 0.0360 mmol/min, a coupling-conjugated diene polymer (Sample 4) was obtained in the same manner as in Reference Example 1, having a 4-branched structure derived from the branching agent structure (1) in part of the main chain and an 8-branched star-shaped polymer structure derived from the coupling agent. The physical properties of Sample 4 are shown in Table 1.

(Example 5) Coupling-conjugated diene polymer (Sample 5)
Except for changing the coupling agent from tetraethoxysilane to tris(3-trimethoxysilylpropyl)amine (abbreviated as "E" in the table) and changing the amount added to 0.0250 mmol/min, a coupling-conjugated diene polymer (Sample 5) was obtained in the same manner as in Reference Example 1, having an octave branched structure derived from the branching agent structure (1) in part of the main chain and a hexabraded star polymer structure derived from the coupling agent. The physical properties of Sample 5 are shown in Table 1.

(Example 6) Coupling-conjugated diene polymer (Sample 6)
Except for changing the coupling agent from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table) and changing the amount added to 0.0190 mmol/min, a coupling-conjugated diene polymer (Sample 6) was obtained in the same manner as in Reference Example 1, having an octave branched structure derived from the branching agent structure (1) in part of the main chain and an octave branched star polymer structure derived from the coupling agent. The physical properties of Sample 6 are shown in Table 1.

(Example 7) Coupling-conjugated diene polymer (Sample 7)
Except for changing the coupling agent from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table) and changing the amount added to 0.0160 mmol/min, a coupling-conjugated diene polymer (Sample 7) was obtained in the same manner as in Reference Example 1, having a 4-branched structure derived from the branching agent structure (1) in part of the main chain and an 8-branched star polymer structure derived from the coupling agent. The physical properties of Sample 7 are shown in Table 1.

(Example 8) Coupling-conjugated diene polymer (Sample 8)
Except for changing the addition rate of 1,3-butadiene from 18.6 g/min to 24.3 g/min and the addition rate of styrene from 10.0 g/min to 4.3 g/min, and further changing the addition rate of 2,2-bis(2-oxolanil)propane as a polar substance from 0.081 mmol/min to 0.044 mmol/min, and changing the coupling agent from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table) and changing the amount added to 0.0160 mmol/min, a coupling-conjugated diene polymer (Sample 8) was obtained in the same manner as in Reference Example 1, having a 4-branched structure derived from the branching agent structure (1) in part of the main chain and an 8-branched star polymer structure derived from the coupling agent. The physical properties of Sample 8 are shown in Table 1.

(Example 9) Coupling-conjugated diene polymer (Sample 9)
Except for changing the addition rate of 1,3-butadiene from 18.6 g/min to 17.1 g/min and the addition rate of styrene from 10.0 g/min to 11.5 g/min, and further changing the addition rate of 2,2-bis(2-oxolanil)propane as a polar substance from 0.081 mmol/min to 0.089 mmol/min, and changing the coupling agent from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table) and changing the amount added to 0.0160 mmol/min, a coupling-conjugated diene polymer (sample 9) was obtained in the same manner as in Reference Example 1, having a 4-branched structure derived from the branching agent structure (1) in part of the main chain and an 8-branched star polymer structure derived from the coupling agent. The physical properties of sample 9 are shown in Table 1.

(Example 10) Coupling-conjugated diene polymer (Sample 10)
Except for changing the addition rate of the polar substance 2,2-bis(2-oxolanil)propane from 0.081 mmol/min to 0.200 mmol/min, and changing the coupling agent from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table) and the amount added to 0.0160 mmol/min, a coupling-conjugated diene polymer (Sample 10) was obtained in the same manner as in Reference Example 1, having a tetrabranched structure derived from the branching agent structure (1) in part of the main chain and an octave-branched star polymer structure derived from the coupling agent. The physical properties of Sample 10 are shown in Table 1.

(Comparative Example 1) Coupling-conjugated diene polymer (Sample 11)
Two tank-type pressure vessels, each with an internal volume of 10 L, an internal height (L) to diameter (D) ratio (L/D) of 4.0, an inlet at the bottom and an outlet at the top, and equipped with a stirrer and a jacket for temperature control, were connected together as polymerization reactors.
A mixture of 1,3-butadiene (from which water had been removed beforehand), styrene (10.0 g/min), and n-hexane (175.2 g/min) was prepared. This mixed solution was then added at a rate of 0.103 mmol/min to a static mixer installed in the piping supplying it to the reactor inlet. After mixing, the mixture was continuously supplied to the bottom of the reactor. Furthermore, 2,2-bis(2-oxolanil)propane was added at a rate of 0.081 mmol/min as a polar substance, and n-butyllithium was added at a rate of 0.143 mmol/min as a polymerization initiator. These were then vigorously mixed at the bottom of the first reactor with a stirrer, maintaining the reactor temperature at 67°C.
The polymer solution was continuously withdrawn from the top of the first reactor and continuously supplied to the bottom of the second reactor, where the reaction was continued at 70°C. The solution was then supplied to a static mixer from the top of the second reactor. Once the polymerization was sufficiently stable, a small amount of the polymer solution before the coupling agent was added was withdrawn. An antioxidant (BHT) was added at a rate of 0.2 g per 100 g of polymer, and the solvent was removed. The Mooney viscosity at 110°C and various molecular weights were then measured. This polymer before the coupling agent was defined as a conjugated diene polymer, and its properties are shown in Table 2.
Next, tetraethoxysilane (abbreviated as "A" in the table) was continuously added at a rate of 0.0480 mmol/min as a coupling agent to the polymer solution that flowed out of the reactor outlet, and the mixture was mixed using a static mixer to carry out the coupling reaction. At this time, the time until the coupling agent was added to the polymer solution flowing out of the reactor outlet was 4.8 minutes, and the temperature was 68°C. The difference between the temperature during the polymerization process and the temperature until the coupling agent was added was 2°C. A small amount of the conjugated diene polymer solution after the coupling reaction was withdrawn, and an antioxidant (BHT) was added at a rate of 0.2 g per 100 g of polymer, followed by removal of the solvent. The amount of bonded styrene (physical property 6) and the microstructure of the butadiene portion (amount of 1,2-vinyl bond: physical property 7) were measured. The measurement results are shown in Table 2.
Next, an antioxidant (BHT) was continuously added to the polymer solution after the coupling reaction at a rate of 0.055 g/min (n-hexane solution) so that the BHT amounted to 0.2 g per 100 g of polymer, and the coupling reaction was terminated. Simultaneously with the antioxidant, SRAE oil (JOMO Process NC140, manufactured by JX Nippon Oil & Energy Corporation) was continuously added as a rubber softener at a rate of 25.0 g per 100 g of polymer, and the mixture was mixed using a static mixer. The solvent was removed by steam stripping to obtain a coupling-conjugated diene polymer (Sample 11) that lacked main chain branching derived from the branching agent and possessed a three-branched star polymer structure derived from the coupling agent. The physical properties of Sample 11 are shown in Table 2.

(Comparative Example 2) Coupling-conjugated diene polymer (Sample 12)
Except for changing the coupling agent from tetraethoxysilane to 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane (abbreviated as "D" in the table) and changing the amount added to 0.0360 mmol/min, a coupling-conjugated diene polymer (Sample 12) was obtained in the same manner as in Comparative Example 1, having no main chain branching derived from the nitrogen atom-containing branching agent and having a tetrabranched star polymer structure derived from the coupling agent.
The physical properties of sample 12 are shown in Table 2.

(Comparative Example 3) Coupling-conjugated diene polymer (Sample 13)
Except for changing the coupling agent from tetraethoxysilane to tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine (abbreviated as "F" in the table) and changing the amount added to 0.0190 mmol/min, a coupling-conjugated diene polymer (Sample 13) was obtained in the same manner as in Comparative Example 1, having no main chain branching derived from the branching agent and an octave-branched star polymer structure derived from the coupling agent. The physical properties of Sample 13 are shown in Table 2.

(Comparative Example 4) Coupling-conjugated diene polymer (Sample 14)
Except for replacing the nitrogen atom-containing branching agent with the non-nitrogen atom-containing branching agent trimethoxy(4-vinylphenyl)silane (indicated as BS-1 in the table) and changing its addition amount to 0.0190 mmol/min, and replacing the coupling agent with 2,2-dimethoxy-1-(3-trimethoxysilylpropyl)-1-aza-2-silacyclopentane (abbreviated as "D" in the table) and changing its addition amount to 0.0360 mmol/min, a coupling-conjugated diene polymer ( Sample 14) having a main chain branching derived from the branching agent and a tetrabranched star polymer structure derived from the coupling agent was obtained in the same manner as in Reference Example 1. The physical properties of Sample 14 are shown in Table 2.
In this Comparative Example 4, since no branching agent containing nitrogen atoms was used as the branching agent, it is described as "conjugated diene polymer" in the table, rather than "modified branched conjugated diene polymer," and is distinguished from the above-mentioned Reference Examples 1-2 and Examples 3-10.

( Reference Examples 11-12, Examples 13-20), (Comparative Examples 5-8)
Using samples 1 to 14 shown in Tables 1 to 2 as raw material rubbers, rubber compositions containing each raw material rubber were obtained according to the formulations shown below.

(Rubber component)
• Coupling-conjugated diene polymers (Samples 1-14)
: 80 parts by mass (parts by mass excluding rubber softener)
- High-cis polybutadiene (product name "UBEPOL BR150" manufactured by Ube Industries, Ltd.)
:20 parts by mass

(Combination conditions)
The amount of each compounding agent added is shown as parts by mass per 100 parts by mass of rubber component excluding rubber softeners.
- Silica 1 (product name "Ultrasil 7000GR" manufactured by Evonik Degussa)
Nitrogen adsorption specific surface area (170 m²/g): 50.0 parts by mass; Silica 2 (product name "Zeosil Premium 200MP" manufactured by Rhodia Corporation)
Nitrogen adsorption specific surface area (220 m²/g): 25.0 parts by mass • Carbon black (product name "Seas KH (N339)" manufactured by Tokai Carbon Co., Ltd.)
: 5.0 parts by mass • Silane coupling agent (product name "Si75" manufactured by Evonik Degussa, bis(triethoxysilylpropyl) disulfide): 6.0 parts by mass • SRAE oil (product name "Process NC140" manufactured by JX Nippon Oil & Energy Corporation)
: 42.0 parts by mass (including the amount previously added as a rubber softener contained in samples 1 to 40)
• Zinc oxide: 2.5 parts by mass • Stearic acid: 1.0 part by mass • Anti-aging agent (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine): 2.0 parts by mass • Sulfur: 2.2 parts by mass • Vulcanization accelerator 1 (N-cyclohexyl-2-benzothiadylsulfinamide)
: 1.7 parts by mass • Vulcanization accelerator 2 (diphenylguanidine): 2.0 parts by mass • Total: 239.4 parts by mass

(Mixing method)
The above-mentioned materials were kneaded by the following method to obtain a rubber composition.
Using a sealed kneader (capacity 0.3 L) equipped with a temperature control device, the first stage of kneading involved mixing raw rubber (samples 1-14), fillers (silica 1, silica 2, carbon black), silane coupling agent, SRAE oil, zinc oxide, and stearic acid under conditions of a filling rate of 65% and a rotor rotation speed of 30-50 rpm. During this process, the temperature of the sealed mixer was controlled, and each rubber composition (compound) was obtained at a discharge temperature of 155-160°C.
Next, in the second stage of mixing, the mixture obtained above was cooled to room temperature, an antioxidant was added, and the mixture was kneaded again to improve the dispersion of silica. In this case as well, the discharge temperature of the mixture was adjusted to 155-160°C by controlling the temperature of the mixer.
After cooling, the third stage of mixing involved adding sulfur and vulcanization accelerators 1 and 2 and mixing them in an open roll oven set to 70°C.
Afterward, the material was molded and vulcanized in a vulcanizing press at 160°C for 20 minutes.
The rubber composition before vulcanization and the rubber composition after vulcanization were evaluated. Specifically, the evaluation was performed using the method described below. The results are shown in Tables 3 and 4.

[Evaluation of characteristics]
(Evaluation 1) Mooney viscosity of the compound The compound obtained above after the second stage of kneading and before the third stage of kneading was used as a sample, and the viscosity was measured using a Mooney viscometer after preheating at 130°C for 1 minute in accordance with ISO 289, and then rotating the rotor at 2 revolutions per minute for 4 minutes.
The results of Comparative Example 5 were indexed with a value of 100.
A smaller index indicates better processability.

(Evaluation 2) Tensile strength and tensile elongation Tensile strength and tensile elongation were measured in accordance with the tensile test method of JIS K6251, and the results of Comparative Example 5 were indexed with 100.
A higher index indicates better tensile strength and tensile elongation (breaking strength).

(Evaluation 3) Abrasion Resistance Using an Akron abrasion tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.), the amount of abrasion was measured at a load of 44.4 N and 1000 rotations in accordance with JIS K6264-2, and the result of Comparative Example 5 was indexed with 100.
A higher index indicates better wear resistance.

(Evaluation 4) Viscoelastic Parameters Viscoelastic parameters were measured in torsion mode using the "ARES" viscoelasticity tester manufactured by Rheometrics Scientific. Each measured value was indexed with the result for the rubber composition of Comparative Example 5 set to 100.
The tanδ, measured at 0°C with a frequency of 10 Hz and a strain of 1%, was used as an indicator of wet skid performance. A larger index indicates better wet skid performance.
Furthermore, tanδ, measured at 50°C, a frequency of 10 Hz, and a strain of 3%, was used as an indicator of fuel efficiency. A smaller index indicates better fuel efficiency.
Furthermore, the elastic modulus (G'), measured at 50°C, a frequency of 10 Hz, and a strain of 3%, was used as an indicator of handling stability. A higher index indicates better handling stability.

As shown in Tables 3 and 4, Reference Examples 11-12 and Examples 13-20 exhibited lower Mooney viscosity and better processability when vulcanized compared to Comparative Examples 5-8. They also demonstrated superior wear resistance, handling stability, and fracture strength in the vulcanized form, and were found to have an excellent balance between low hysteresis loss and wet skid resistance.

The branched conjugated diene polymers obtained by the manufacturing method of the present invention have industrial potential applications in fields such as tire treads, automotive interior and exterior parts, vibration-damping rubber, belts, footwear, foams, and various industrial products.

Claims (6)

A polymerization step to obtain a conjugated diene polymer having an active end by polymerizing or copolymerizing a conjugated diene compound, or a conjugated diene compound and an aromatic vinyl compound, using an alkali metal compound or alkaline earth metal compound as a polymerization initiator,
A branching step is performed in which a nitrogen atom-containing branching agent, which is a compound represented by (M-1) below , is reacted with the active end of the aforementioned conjugated diene polymer to introduce a branched structure.
A reaction step is performed in which a coupling agent is reacted with the active end of the branched conjugated diene polymer obtained in the branching step,
It has,
The coupling agent has a nitrogen atom-containing group.
A method for producing branched conjugated diene polymers.
(In formula (M-1), Me represents a methyl group.) The reaction further comprises adding a conjugated diene compound and/or an aromatic vinyl compound to the reaction system during and/or thereafter the branching step,
A method for producing a branched conjugated diene polymer according to claim 1. A branched conjugated diene polymer obtained by the method for producing a branched conjugated diene polymer according to claim 1 or 2 ,
The polymer main chain has a main chain branching structure derived from a nitrogen atom-containing branching agent, which is the (M-1) compound described below .
Branched conjugated diene polymers.
(In formula (M-1), Me represents a methyl group.) A rubber component comprising 10% by mass or more of the branched conjugated diene polymer described in claim 3 ,
A rubber composition containing 5.0 parts by mass or more and 150 parts by mass or less of a filler per 100 parts by mass of the rubber component. A step of obtaining a branched conjugated diene polymer by the manufacturing method described in claim 1 or 2 ,
A step to obtain a rubber component containing 10% by mass or more of the branched conjugated diene polymer,
A step of obtaining a rubber composition by adding 5.0 parts by mass or more and 150 parts by mass or less of a filler to 100 parts by mass of the rubber component,
A method for producing a rubber composition having the following characteristics. A step of obtaining a rubber composition by the method for producing a rubber composition described in claim 5 ,
The process involves molding the rubber composition to obtain a tire,
A method for manufacturing tires, comprising: