JP6164927B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a branched conjugated diene copolymer, a hydrogenated branched conjugated diene copolymer, a rubber composition comprising the copolymer, and a pneumatic tire produced using the rubber composition.

  High-performance tire treads are generally required to have both high grip performance and wear resistance. Conventionally, in order to obtain a rubber composition exhibiting high grip performance, for example, a rubber composition using a styrene-butadiene copolymer rubber (SBR) having a high glass transition temperature (Tg) as a rubber component, a process oil is highly softened. Equal amount substitution with point resin, rubber composition filled with rubber component, rubber composition highly filled with softener or carbon black, rubber composition using carbon black with small particle diameter, or SBR, high softening A rubber composition in which a point resin, the softener, or carbon black is combined is known.

  However, the rubber composition using SBR having a high Tg has a problem that the temperature dependency is increased and the performance change with respect to the temperature change is increased. Further, when the process oil is replaced with an equal amount of the high softening point resin, if the replacement amount is large, there is a problem that the temperature dependency becomes large due to the influence of the high softening point resin. Further, when carbon black having a small particle diameter or a large amount of softening agent is used, there is a problem that the dispersibility of carbon black is poor and wear resistance is lowered.

  In order to improve these problems, a rubber composition using a low molecular weight styrene-butadiene copolymer has been proposed (see Patent Document 1). There is a problem in that a part of the low molecular weight component forms a cross-link with the rubber component of the matrix and is taken into the matrix and the hysteresis cannot be sufficiently suppressed. In addition, in order to prevent low molecular weight components from being incorporated into the matrix due to cross-linking, when the double bond portion is saturated by hydrogenation, the compatibility with the matrix is significantly reduced. There are problems such as coming.

  In order to suppress bleeding of low molecular components, there is a method of increasing the styrene content in the low molecular styrene-butadiene copolymer to 40% or more, but as the styrene content increases, the hardness increases and handling becomes difficult. There is.

  In any case, a tire tread rubber composition that has solved the above-mentioned problems at a high level has not yet been obtained.

  Myrcene is a naturally occurring organic compound that is one of the olefins belonging to monoterpenes. Myrcene has two isomers, α-myrcene (2-methyl-6-methyleneocta-1,7-diene) and β-myrcene (7-methyl-3-methyleneocta-1,6-diene). Exists. Patent Document 2 discloses a myrcene polymer.

  Farnesene is one of the isoprenoid compounds chemically synthesized by oligomerization of isoprene or dehydration reaction of nerolidol, and is mainly used as a fragrance or a raw material thereof (Patent Document 3).

JP 63-101440 A JP-A 63-179908 JP 2008-156516 A

  The present invention is a novel branched conjugated diene copolymer useful for improving processability as a component of a rubber composition for tires, and particularly exhibits both excellent wear resistance and grip performance while exhibiting excellent properties in processability. A novel branched conjugated diene copolymer useful as a component of a tire rubber composition, which is improved to a level and further suppresses the occurrence of bleed, a tire rubber composition comprising the copolymer, and An object of the present invention is to provide a pneumatic tire produced using the rubber composition for tires.

  In addition, the present invention provides a novel hydrogenated branched conjugated diene copolymer useful for improving processability as a component of a rubber composition for tires, in particular, wear resistance and grip while exhibiting excellent properties in processability. A novel hydrogenated branched conjugated diene copolymer useful as a component of a tire rubber composition, which has improved performance to a high level and further suppressed the occurrence of bleeding, and the hydrogenated branched conjugated diene copolymer It is intended to provide a rubber composition for tires comprising, and a pneumatic tire produced using the rubber composition for tires.

  As a result of intensive studies to solve the above-mentioned problems, the use of branched conjugated diene having a multi-branched side chain as a conjugated diene compound in which butadiene, isoprene and the like are usually used contributes to improvement of workability and the like. The inventors have found that a new copolymer can be obtained, and have further studied to complete the present invention.

（式中、Ｒ¹は、炭素数６〜１１の脂肪族炭化水素を表す。）
で示される分枝共役ジエン化合物（１）と、一般式（２）

（式中、Ｒ²は、炭素数６〜１０の芳香族炭化水素基を表す。）
で示される芳香族ビニル化合物（２）とを含むモノマー成分を共重合させた分枝共役ジエン共重合体であって、
芳香族ビニル化合物（２）の共重合比（ｍ）が６０以上８０未満重量％である分枝共役ジエン共重合体に関する。 That is, the present invention relates to the general formula (1)

(In the formula, R ¹ represents an aliphatic hydrocarbon having 6 to 11 carbon atoms.)
A branched conjugated diene compound (1) represented by general formula (2):

(In the formula, R ² represents an aromatic hydrocarbon group having 6 to 10 carbon atoms.)
A branched conjugated diene copolymer obtained by copolymerizing a monomer component containing the aromatic vinyl compound (2) represented by
The present invention relates to a branched conjugated diene copolymer in which the copolymerization ratio (m) of the aromatic vinyl compound (2) is 60 or more and less than 80% by weight.

The branched conjugated diene copolymer comprises a branched conjugated diene compound (1) represented by the general formula (3)

CH ₂ C (R ³ ) CHCH ₂ (3)

(In the formula, R ³ represents a hydrogen atom or a methyl group.)
In comparison with the copolymer having the same weight average molecular weight replaced with the conjugated diene compound (3) represented by the formula, the Mooney viscosity ML _{1 + 4} (130 ° C.) of the rubber composition when blended with the rubber composition is It is preferable for improving workability, which shows a low value.

  The branched conjugated diene copolymer preferably has a weight average molecular weight of 2000 to 200,000.

  The branched conjugated diene copolymer is preferably such that the branched conjugated diene compound (1) is myrcene and / or farnesene.

  In the branched conjugated diene copolymer, the aromatic vinyl compound (2) is one or more selected from the group consisting of styrene, α-methylstyrene, α-vinylnaphthalene and β-vinylnaphthalene. Those are preferred.

  The present invention also relates to a rubber composition comprising the branched conjugated diene copolymer.

  Furthermore, this invention relates to the pneumatic tire produced using the said rubber composition.

（式中、Ｒ¹は、炭素数６〜１１の脂肪族炭化水素を表す。）
で示される分枝共役ジエン化合物（１）と、一般式（２）

（式中、Ｒ²は、炭素数６〜１０の芳香族炭化水素基を表す。）
で示される芳香族ビニル化合物（２）とを含むモノマー成分を共重合させた後、該共重合体を水素添加して得られる水添分枝共役ジエン共重合体であって、
芳香族ビニル化合物（２）の共重合比（ｍ）が６０以上８０未満重量％である水添分枝共役ジエン共重合体に関する。 In addition, the present invention provides a general formula (1)

(In the formula, R ¹ represents an aliphatic hydrocarbon having 6 to 11 carbon atoms.)
A branched conjugated diene compound (1) represented by general formula (2):

(In the formula, R ² represents an aromatic hydrocarbon group having 6 to 10 carbon atoms.)
A hydrogenated branched conjugated diene copolymer obtained by copolymerizing a monomer component containing the aromatic vinyl compound (2) represented by formula (2) and then hydrogenating the copolymer,
The present invention relates to a hydrogenated branched conjugated diene copolymer in which the copolymerization ratio (m) of the aromatic vinyl compound (2) is 60 to less than 80% by weight.

The hydrogenated branched conjugated diene copolymer is obtained by converting the branched conjugated diene compound (1) to the general formula (3).

CH ₂ C (R ³ ) CHCH ₂ (3)

(In the formula, R ³ represents a hydrogen atom or a methyl group.)
In comparison with the copolymer having the same weight average molecular weight replaced with the conjugated diene compound (3) represented by the formula, the Mooney viscosity ML _{1 + 4} (130 ° C.) of the rubber composition when blended with the rubber composition is It is preferable for improving workability, which shows a low value.

  The hydrogenated branched conjugated diene copolymer preferably has a weight average molecular weight of 2000 to 200,000.

  In the hydrogenated branched conjugated diene copolymer, the branched conjugated diene compound (1) is preferably myrcene and / or farnesene.

  In the hydrogenated branched conjugated diene copolymer, the aromatic vinyl compound (2) is one or more selected from the group consisting of styrene, α-methylstyrene, α-vinylnaphthalene and β-vinylnaphthalene. It is preferable that

  The hydrogenated branched conjugated diene copolymer preferably has a hydrogenation rate of 10 to 100%.

  The present invention also relates to a rubber composition comprising the hydrogenated branched conjugated diene copolymer.

  Furthermore, this invention relates to the pneumatic tire produced using the said rubber composition.

  According to the present invention, a novel branched conjugated diene copolymer and a novel hydrogenated branched conjugated diene copolymer useful for improving processability as components of a rubber composition for tires, particularly excellent in improving processability. These copolymers useful as a component of a rubber composition for tires, which can improve wear resistance and grip performance to a high level while suppressing the occurrence of bleeding, while exhibiting excellent characteristics. The rubber composition for tires which comprises can be provided. Such a rubber composition for tires of the present invention is useful as a rubber for tire treads and the like, and is particularly useful as a rubber composition for tire treads for competition (race etc.) vehicles. Furthermore, according to this invention, the pneumatic tire produced using this rubber composition for tires can be provided.

  In particular, in the present invention, a branched conjugated diene copolymer or a hydrogenated branched conjugated diene copolymer having a low molecular weight (a weight average molecular weight of about 2000 to about 200,000) has good compatibility with a rubber component. The branched conjugated diene compound (1) is used as the conjugated diene compound even when the styrene content is high (for example, the styrene content in the copolymer is 60% by weight or more) in order to maintain the bleed and suppress the occurrence of bleeding. By using this, it is possible to improve processability and to prevent a decrease in handling performance due to the hardness of the rubber becoming too hard.

  Such a rubber composition for tires of the present invention includes various rubbers for tire treads, side rubbers, rubbers for case members, etc., such as ordinary passenger cars, truck buses, light trucks, small trucks, motorcycles, motorbikes, and industrial vehicles. Although useful as a composition, it is particularly useful as a rubber composition for tire treads for competition vehicles.

<Branched conjugated diene copolymer>
The hydrogenated branched conjugated diene copolymer of the present invention refers to one obtained by copolymerizing monomer components containing a branched conjugated diene compound (1) and an aromatic vinyl compound (2).

  If the weight average molecular weight (Mw) of the branched conjugated diene copolymer of this invention is 1000 or more, there will be no limitation in particular, Preferably it is 2000 or more. If Mw is less than 1000, it tends to be a liquid polymer with high fluidity. On the other hand, Mw is not particularly limited as long as it is 3 million or less. When Mw exceeds 3 million, it tends to be a solid having no rubber elasticity.

  From the viewpoint of achieving both grip performance and wear resistance, Mw is preferably 2000 or more, and more preferably 5000 or more. When Mw is less than 2000, there is a tendency that sufficient wear resistance cannot be obtained. On the other hand, Mw is preferably 200,000 or less, and more preferably 100,000 or less. When Mw exceeds 200,000, there is a tendency that sufficient grip performance cannot be obtained.

  In the branched conjugated diene copolymer, the preferable range of Mw / Mn is 20.0 or less, more preferably 10.0 or less. When Mw / Mn is more than 20.0, there is a tendency that the processability is not deteriorated due to a decrease in the hardness of the rubber composition. On the other hand, the lower limit value of Mw / Mn is not particularly limited, and there is no particular problem at 1.0 or more.

  The glass transition temperature (Tg) of the branched conjugated diene copolymer is usually in the range of 40 to 150 ° C, more preferably 60 to 150 ° C. If it is less than 40 ° C., the fluidity of the compounded rubber tends to be too high during processing, whereas if it exceeds 150 ° C., the fluidity of the compounded rubber tends to be too low, which is disadvantageous in the kneading process.

The Mooney viscosity ML _{1 + 4} (130 ° C.) of the branched conjugated diene copolymer is the same molecular weight as that obtained by replacing the branched conjugated diene compound (1) constituting the copolymer with the conjugated diene compound (3). In the comparison with coalescence, as long as it shows a low value, the effect of the present invention of improving the workability can be obtained, so there is no particular limitation, but generally it is preferably 25 or more, more preferably 30. That's it. If the Mooney viscosity is less than 25, it tends to have fluidity. On the other hand, the Mooney viscosity is preferably 160 or less, more preferably 150 or less, more preferably 140 or less, and still more preferably 100 or less. If the Mooney viscosity is more than 160, a large amount of softening agent or processing aid tends to be required during processing.

The Mooney viscosity can also be compared as the Mooney viscosity of a rubber composition obtained by blending a branched conjugated diene copolymer in a rubber composition. That is, when the branched conjugated diene copolymer is added to a rubber composition in comparison with a polymer having the same weight average molecular weight obtained by replacing the branched conjugated diene compound (1) with the conjugated diene compound (3). The rubber composition has a low Mooney viscosity ML _{1 + 4} (130 ° C.). The preferred Mooney viscosity in this case is the same as that for the copolymer.

<Hydrogenated branched conjugated diene copolymer>
The branched conjugated diene copolymer of the present invention itself has excellent effects on processability, abrasion resistance, grip performance and bleed generation suppression. Furthermore, the hydrogenated branched conjugated diene copolymer is also excellent in workability, wear resistance, grip performance and bleed generation suppression by being subjected to a hydrogenation reaction. The description of the branched conjugated diene copolymer is applicable to the hydrogenated branched conjugated diene copolymer of the present invention as long as there is no obvious contradiction.

  In the hydrogenated branched conjugated diene copolymer, the hydrogenation rate is not particularly limited and may be in the range of more than 0 to 100%, preferably 10 to 100%, more preferably 30 to 100%. .

<About monomer>
In the copolymer of the present invention, the copolymerization ratio of the branched conjugated diene compound (1) and the aromatic vinyl compound (2), which are monomers, will be described.

  The copolymerization ratio (1) of the branched conjugated diene compound (1) is not particularly limited as long as it is 1 to 40% by weight, but the lower limit is preferably 2.5% by weight or more, and more preferably 5% by weight or more. More preferably, 10% by weight or more is more preferable, 20% by weight or more is more preferable, and 25% by weight or more is more preferable. If it is less than 1%, the effect of blending the branched conjugated diene compound (1) to improve processability tends to be insufficient. On the other hand, as an upper limit, it is 40 weight% or less, and 35 weight% or less is preferable.

  The lower limit of the preferable range of the polymerization ratio (m) (60 to less than 80% by weight) of the aromatic vinyl compound (2) is 61% by weight or more, more preferably 62% by weight or more, more preferably 63% by weight or more, More preferably, it is 64 weight% or more, More preferably, it is 65 weight% or more. When m is less than 60% by weight, the fluidity of the compounded rubber becomes too low and tends to be disadvantageous in the kneading process. The upper limit of the preferable range is 79% by weight or less, preferably 78% by weight or less, more preferably 77% by weight or less, more preferably 76% by weight or less, and further preferably 75% by weight or less. If it is 80% by weight or more, the wear resistance tends to be somewhat lowered.

  The branched conjugated diene copolymer or hydrogenated branched conjugated diene copolymer of the present invention is preferably composed only of the branched conjugated diene compound (1) and the aromatic vinyl compound (2). In this case, since the total polymerization ratio of the monomers in the branched conjugated diene copolymer or the hydrogenated branched conjugated diene copolymer is 100% by weight, the total of (l) and (m) is 100% by weight. is there. Therefore, if any one of the polymerization ratios is selected from the description of the preferable range of (l) or (m), the remaining polymerization ratio is determined automatically.

<Branched conjugated diene compound (1)>
In the branched conjugated diene compound (1), examples of the aliphatic hydrocarbon group having 6 to 11 carbon atoms include those having a normal structure such as hexyl group, heptyl group, octyl group, nonyl group, decyl group, and undecyl group, These isomers and / or unsaturated compounds, and derivatives thereof (for example, halides, hydroxylates, etc.) can be mentioned. Preferable examples include 4-methyl-3-pentenyl group, 4,8-dimethyl-nona-3,7-dienyl group, and derivatives thereof.

  Specific examples of the branched conjugated diene compound (1) include, for example, myrcene and farnesene.

  In the present invention, “myrcene” includes both α-myrcene (2-methyl-6-methyleneocta-1,7-diene) and β-myrcene, and among these, β having the following structure: -Myrcene (7-methyl-3-methyleneocta-1,6-diene) is preferred.

  On the other hand, “farnesene” includes any isomers such as α-farnesene ((3E, 7E) -3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene. Of these, (E) -β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene) having the following structure is preferred.

  As the branched conjugated diene compound (1), one or more compounds can be used.

<About the aromatic vinyl compound (2)>
In the aromatic vinyl compound (2), examples of the aromatic hydrocarbon group having 6 to 10 carbon atoms include phenyl group, benzyl group, phenethyl group, tolyl group, xylyl group, and naphthyl group. . However, the substitution position of the methyl group on the benzene ring in the tolyl group includes any position of ortho-, meta- or para-, and the substitution position of the methyl group in the xylyl group is any of the arbitrary substitution positions. Is also included. Of these, a phenyl group, a tolyl group, and a naphthyl group are preferable. As specific examples of the vinyl compound (3), styrene, α-methylstyrene, α-vinylnaphthalene or β-vinylnaphthalene is preferable. As the vinyl compound (2), one type or two or more types can be used.

<Production method>
The method for producing a copolymer according to the present invention will be described. In the present invention, the copolymerization of the monomer component containing the branched conjugated diene compound (1) and the vinyl compound (2) is not particularly limited in the order of copolymerization as long as each monomer component is copolymerized. For example, all monomers may be randomly copolymerized at once, or a part of a specific monomer may be copolymerized in advance and then the remaining monomer may be added for copolymerization. The copolymer may be block copolymerized. Under the polymerization reaction conditions where the polymerization conversion rate (“dry weight of target product” / “charge amount”) is almost 100%, the copolymerization ratio of each monomer is a percentage value (% by weight) according to the charge amount. A branched conjugated diene copolymer can be obtained.

  Such copolymerization can be carried out by a conventional method, for example, by anionic polymerization reaction, coordination polymerization or the like.

  The polymerization method is not particularly limited, and any of a solution polymerization method, an emulsion polymerization method, a gas phase polymerization method, and a bulk polymerization method can be used. Among these, the solution polymerization method is preferable. Further, the polymerization format may be either a batch type or a continuous type.

<Anionic polymerization>
The anionic polymerization can be carried out in a suitable solvent in the presence of an anionic polymerization initiator. Any conventional anionic polymerization initiator can be suitably used. Examples of such an anionic polymerization initiator include a general formula RLix (where R represents one or more carbon atoms). An organic lithium compound having an aliphatic, aromatic or alicyclic group, and x is an integer of 1 to 20. Suitable organolithium compounds include methyllithium, ethyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, phenyllithium and naphthyllithium. Preferred organolithium compounds are n-butyllithium and sec-butyllithium. An anionic polymerization initiator can be used individually or in mixture of 2 or more types. When the amount of the polymerization initiator used is less than 0.05 mmol, the copolymer tends to be resinous rather than rubbery, and when it exceeds 35 mmol, the copolymer is soft and has a branched conjugated diene for workability. There exists a tendency for the effect by copolymerizing a compound (1) to become small.

  Moreover, as a solvent used for anionic polymerization, any solvent can be used suitably as long as it does not deactivate the anionic polymerization initiator or stop the polymerization reaction. Either a polar solvent or a nonpolar solvent can be used. Can be used. Examples of the polar solvent include ether solvents such as tetrahydrofuran, and examples of the nonpolar solvent include chain hydrocarbons such as hexane, heptane, octane and pentane, cyclic hydrocarbons such as cyclohexane, benzene and toluene. And aromatic hydrocarbons such as xylene. These solvents can be used alone or in admixture of two or more.

  Anionic polymerization is preferably carried out in the presence of a polar compound. Examples of polar compounds include dimethyl ether, diethyl ether, ethyl methyl ether, ethyl propyl ether, tetrahydrofuran, dioxane, diphenyl ether, tripropylamine, tributylamine, trimethylamine, triethylamine, N, N, N ′, N′-tetramethylethylenediamine. (TMEDA). A polar compound can be used individually or in mixture of 2 or more types. This polar compound is useful for reducing the content of 1,2-structure in terms of controlling the microstructure of the butadiene moiety. The amount of the polar compound used varies depending on the type of the polar compound and the polymerization conditions, but is preferably 0.1 or more as the molar ratio (polar compound / anionic polymerization initiator) to the anionic polymerization initiator. If the molar ratio with the anionic polymerization initiator (polar compound / anionic polymerization initiator) is less than 0.1, the effect of the polar substance on controlling the microstructure tends to be insufficient.

  The reaction temperature during the anionic polymerization is not particularly limited as long as the reaction proceeds suitably, but it is usually preferably −10 ° C. to 100 ° C., more preferably 25 ° C. to 70 ° C. Moreover, although reaction time changes with preparation amounts, reaction temperature, and other conditions, it is sufficient to carry out for about 3 hours normally, for example.

  The anionic polymerization can be stopped by adding a reaction terminator usually used in this field. Examples of such a reaction terminator include polar solvents having active protons such as alcohols such as methanol, ethanol and isopropanol or acetic acid and mixtures thereof, or polar solvents and nonpolar solvents such as hexane and cyclohexane. A mixed solution is mentioned. The amount of the reaction terminator added is usually about the same molar amount or twice the molar amount relative to the anionic polymerization initiator.

  After the termination of the polymerization reaction, the branched conjugated diene copolymer can be obtained by removing the solvent from the polymerization solution by a conventional method or by pouring the polymerization solution into one or more times the amount of alcohol to obtain the branched conjugated diene copolymer. It can be easily isolated by precipitation.

<Coordination polymerization>
The coordination polymerization can be carried out by using a coordination polymerization initiator instead of the anionic polymerization initiator in the anionic polymerization. As the coordination polymerization initiator, any conventional one can be suitably used. Examples of such coordination polymerization initiator include transition metals such as lanthanoid compounds, titanium compounds, cobalt compounds, and nickel compounds. The catalyst which is a compound is mentioned. Further, if desired, an aluminum compound or a boron compound can be further used as a promoter.

  The lanthanoid compound is not particularly limited as long as it contains any of the elements of atomic numbers 57 to 71 (lanthanoid), but among these lanthanoids, neodymium is particularly preferable. Examples of lanthanoid compounds include carboxylates, β-diketone complexes, alkoxides, phosphates or phosphites, halides, and the like of these elements. Of these, carboxylates, alkoxides, and β-diketone complexes are preferred because of easy handling. Examples of the titanium compound include a cyclopentadienyl group, an indenyl group, a substituted cyclopentadienyl group or a substituted indenyl group, and 1 to 3 substituents selected from a halogen, an alkoxysilyl group, and an alkyl group. Examples of the titanium-containing compound include compounds having one alkoxysilyl group from the viewpoint of catalyst performance. Examples of the cobalt compound include cobalt halides, carboxylates, β-diketone complexes, organic base complexes, and organic phosphine complexes. Examples of the nickel compound include nickel halides, carboxylates, β-diketone complexes, and organic base complexes. The catalyst used as the coordination polymerization initiator can be used alone or in combination of two or more.

  Examples of the aluminum compound used as a cocatalyst include organic aluminoxanes, halogenated organoaluminum compounds, organoaluminum compounds, and hydrogenated organoaluminum compounds. Examples of organic aluminoxanes include alkylaluminoxanes (such as methylaluminoxane, ethylaluminoxane, propylaluminoxane, butylaluminoxane, isobutylaluminoxane, octylaluminoxane, hexylaluminoxane), and examples of halogenated organoaluminum compounds include alkyl halides. Aluminum compounds (dimethylaluminum chloride, diethylaluminum chloride, methylaluminum dichloride, ethylaluminum dichloride) are organic aluminum compounds. For example, alkylaluminum compounds (trimethylaluminum, triethylaluminum, triisopropylaluminum, triisobutylaluminum) are hydrogenated. An organoaluminum compound Is, for example, hydride alkylaluminum compound (diethyl aluminum hydride, diisobutyl aluminum hydride) and the like. Examples of the boron compound include compounds containing anionic species such as tetraphenylborate, tetrakis (pentafluorophenyl) borate, and (3,5-bistrifluoromethylphenyl) borate. These promoters can also be used alone or in combination of two or more.

  Regarding the coordination polymerization, as the solvent and the polar compound, those described in the anionic polymerization can be used in the same manner. The reaction time and reaction temperature are also the same as those described in the anionic polymerization. Termination of the polymerization reaction and isolation of the branched conjugated diene copolymer can be performed in the same manner as in the case of anionic polymerization.

<Hydrogenation>
The branched conjugated diene copolymer obtained above can be made into a hydrogenated branched conjugated diene copolymer by further subjecting it to a hydrogenation reaction. In this case, the hydrogenation reaction can be carried out by a conventional method, and any of a method of catalytic hydrogenation using a metal catalyst, a method using hydrazine, etc. can be preferably used (Japanese Patent Laid-Open No. 59-161415, etc.) . For example, catalytic hydrogenation with a metal catalyst can be carried out by adding hydrogen under pressure in the presence of a metal catalyst in an organic solvent. As the organic solvent, any of tetrahydrofuran, methanol, ethanol, etc. is suitable. Can be used for These organic solvents can be used individually by 1 type or in mixture of 2 or more types. In addition, as the metal catalyst, for example, palladium, platinum, rhodium, ruthenium, nickel and the like can be preferably used. These metal catalysts can be used alone or in combination of two or more. . As a pressure at the time of pressurizing, it is preferable that it is 1-300 kgf / cm < ² >, for example.

  The weight average molecular weight (Mw) of the branched conjugated diene copolymer or hydrogenated branched conjugated diene copolymer according to the present invention can be controlled by a conventional method. For example, each monomer charged at the time of polymerization with respect to the catalyst It can be controlled by adjusting the amount. For example, if the total monomer / anion polymerization catalyst ratio or the total monomer / coordination polymerization catalyst ratio is increased, Mw can be increased, and conversely, if it is decreased, Mw can be decreased. The same applies to the number average molecular weight (Mn) of the branched conjugated diene copolymer.

  The Tg of the branched conjugated diene copolymer or hydrogenated branched conjugated diene copolymer according to the present invention can be controlled by a conventional method. For example, the amount of the branched conjugated diene compound (1) monomer is increased. By making it, it can be made relatively low, while it can be made relatively high by increasing the amount of the aromatic vinyl compound (2) charged.

  The Mooney viscosity of the branched conjugated diene copolymer or hydrogenated branched conjugated diene copolymer according to the present invention can be controlled by a conventional method. For example, the branched conjugated diene compound (1) monomer charged at the time of polymerization is used. It can be controlled by adjusting the amount. For example, if the amount of the branched conjugated diene compound (1) monomer is decreased, the Mooney viscosity increases. Conversely, if the amount of the branched conjugated diene compound (1) monomer is increased, the Mooney viscosity decreases.

<Rubber composition using branched conjugated diene copolymer or hydrogenated branched conjugated diene copolymer>
The thus obtained branched conjugated diene copolymer or hydrogenated branched conjugated diene copolymer of the present invention is made into a rubber composition for tires by appropriately blending other components usually used in the field of rubber industry. be able to. Examples of other components to be blended in the rubber composition of the present invention include rubber components, fillers, silane coupling agents, and the like.

  In the tire rubber composition of the present invention, the amount of the branched conjugated diene copolymer or hydrogenated branched conjugated diene copolymer is about 3% by weight or more, preferably about 5% by weight or more, more preferably. Is 30% by weight or more, more preferably 50% by weight or more. If the blending amount is less than 3% by weight, the effect of blending the hydrogenated branched conjugated diene copolymer with respect to processability tends to be small. On the other hand, there is no restriction | limiting in particular about the upper limit of a compounding quantity, and 100 weight% may be sufficient.

  In the present invention, examples of the rubber component used together with the branched conjugated diene copolymer or hydrogenated branched conjugated diene copolymer according to the present invention include natural rubber (NR), isoprene rubber (IR), butadiene rubber ( BR), styrene butadiene rubber (SBR), styrene isoprene (SIR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), butyl rubber (IIR) And diene rubbers. These diene rubbers may be used alone or in combination of two or more. Among them, it is preferable to use NR, BR and SBR because the grip performance and wear resistance in combination with the branched conjugated diene copolymer can be obtained in a well-balanced manner, and the reason that particularly high grip performance is exhibited. Therefore, SBR is preferable.

  Alternatively, the branched conjugated diene copolymer or the hydrogenated branched conjugated diene copolymer according to the present invention can be blended in the rubber composition as a component other than the rubber component, when it is liquid. In this case, the amount of the hydrogenated branched conjugated diene copolymer is 10 to 100 parts by weight, preferably 20 to 80 parts by weight, more preferably 30 to 70 parts by weight, based on 100 parts by weight of the rubber component. It is. If it is less than 10 parts by weight, the effect of blending the hydrogenated branched conjugated diene copolymer with respect to processability tends to be small. On the other hand, if it exceeds 100 parts by weight, the effect of blending the hydrogenated branched conjugated diene copolymer with respect to the balance of grip performance and wear resistance tends to be small.

  Examples of the filler include fillers usually used in this field such as carbon black and silica.

As carbon black, those generally used in tire production can be used, for example, SAF, ISAF, HAF, FF, FEF, GPF, etc., and these carbon blacks can be used alone, Two or more kinds may be used in combination. The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is about 80 m ² / g or more, preferably about 110 m ² / g or more. When N ₂ SA is less than 80, both grip performance and wear resistance tend to be poor, and when it is less than 110 m ² / g, the effect of using a branched conjugated diene copolymer tends to be small for improving processability. . On the other hand, the N ₂ SA of carbon black is about 270 m ² / g or less, preferably about 260 m ² / g or less. When N ₂ SA of carbon black is larger than 270, the dispersion of carbon black tends to deteriorate.

  The compounding amount of the carbon black is about 1 part by weight or more and preferably about 3 parts by weight or more with respect to 100 parts by weight of the rubber component. If the blending amount of carbon black is less than 1 part by weight, the wear resistance tends to decrease. On the other hand, the compounding amount of carbon black is about 200 parts by weight or less, and more preferably 150 parts by weight or less. When the blending amount of carbon black exceeds 200 parts by weight, processability tends to deteriorate.

Examples of the silica include silica prepared by a dry method (anhydrous silicic acid), silica prepared by a wet method (hydrous silicic acid), and the like. Of these, silica prepared by a wet method is preferred because of the large number of silanol groups on the surface and many reactive sites with the silane coupling agent. The N ₂ SA of the silica is about 50 m ² / g or more, preferably about 80 m ² / g or more. If N ₂ SA is less than 50, the reinforcing effect is small and the wear resistance tends to be lowered. On the other hand, the N ₂ SA of silica is about 300 m ² / g or less, preferably about 250 m ² / g or less. When N ₂ SA is larger than 300 m ² / g, the dispersion tends to decrease and the workability tends to decrease.

  The amount of silica is about 1 part by weight or more and preferably about 10 parts by weight or more with respect to 100 parts by weight of the rubber component. If the amount of silica is less than 1 part by weight, the wear resistance tends to be insufficient. On the other hand, the compounding quantity of a silica is about 150 weight part or less, and it is more preferable that it is 100 or less. If the amount of silica exceeds 150 parts by weight, the dispersibility of silica tends to deteriorate and the processability tends to deteriorate.

  The rubber composition preferably contains a silane coupling agent. As the silane coupling agent, a conventionally known silane coupling agent can be used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4- Triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilylbutyl) tetrasulfide, bis (3-triethoxy Silylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (2-trimethoxysilylethyl) ) Sulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3 -Trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxy Ethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N, N-dimethylthioca Sulfide systems such as vamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-trimethoxysilylpropyl methacrylate monosulfide; 3-mercaptopropyltrimethoxysilane Mercapto type such as 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; Vinyl type such as vinyltriethoxysilane, vinyltrimethoxysilane; 3-aminopropyltriethoxysilane 3-aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane Amino systems such as orchid; glycidoxy systems such as γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane Nitro compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2-chloroethyltri Chloro type such as ethoxysilane; and the like. These silane coupling agents may be used alone or in combination of two or more. Of these, bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide are preferably contained from the viewpoint of good processability.

  When the silane coupling agent is contained, the blending amount is preferably 1 part by weight or more, and more preferably 2 parts by weight or more with respect to 100 parts by weight of silica. When the content of the silane coupling agent is less than 1 part by weight, effects such as improvement in dispersibility tend not to be obtained sufficiently. Further, the content of the silane coupling agent is preferably 20 parts by weight or less, and more preferably 15 parts by weight or less. When the content of the silane coupling agent exceeds 20 parts by weight, a sufficient coupling effect cannot be obtained and the reinforcing property tends to be lowered.

  In addition to the above-mentioned components, the rubber composition of the present invention includes compounding agents conventionally used in the rubber industry, such as other reinforcing fillers, anti-aging agents, vulcanizing agents such as oils, waxes, sulfur, etc. Sulfur accelerators, vulcanization accelerators and the like can be appropriately blended.

  The rubber composition of the present invention thus obtained can be used suitably as a tire tread, particularly as a tire tread for a racing vehicle tire, because both the wear resistance and grip performance can be improved to a high level. Can do.

  The rubber composition of the present invention is used for manufacturing a tire and can be made into a tire by a usual method. That is, if necessary, a mixture containing the above ingredients is kneaded, extruded in accordance with the shape of each member of the tire at an unvulcanized stage, and molded on a tire molding machine by a normal method. Thus, an unvulcanized tire is formed. A tire can be obtained by heating and pressurizing the unvulcanized tire in a vulcanizer, and air can be put into the tire to obtain a pneumatic tire.

In this specification, Mw and Mn are measured using a gel permeation chromatograph (GPC) and converted from standard polystyrene.
The hydrogenation (hydrogenation) rate (%) is obtained according to the following calculation formula by calculating the iodine value (iodine g / 100 g of sample) using the iodine value method.
Hydrogenation rate (%) = {[(iodine value before hydrogenation) − (iodine value after hydrogenation)] / (iodine value before hydrogenation)} × 100
The glass transition temperature (Tg) is measured by a differential scanning calorimeter (DSC).
Mooney viscosity is measured according to JIS K 6300.
Simply “1-99 wt%” includes values at both ends.

  The present invention will be described based on examples, but the present invention is not limited to the examples.

  Below, the synthesis | combination of the copolymer of an Example and a comparative example and the various chemical | medical agent used for manufacture of a rubber composition are shown collectively. Various chemicals were purified according to conventional methods as needed.

<Various chemicals used for copolymer synthesis>
Hexane: anhydrous hexane isopropanol manufactured by Kanto Chemical Co., Ltd .: isopropanol THF manufactured by Kanto Chemical Co., Ltd .: tetrahydrofuran myrcene (branched conjugated diene compound) manufactured by Kanto Chemical Co., Ltd .: β- of Wako Pure Chemical Industries, Ltd. Myrcene farnesene (branched conjugated diene compound): (E) -β-farnesene (reagent) of Nippon Terpene Chemical Co., Ltd.
Isoprene (conjugated diene compound): Isoprene butadiene (conjugated diene compound) from Wako Pure Chemical Industries, Ltd .: 1,3-butadiene styrene (aromatic vinyl compound) manufactured by Takachiho Chemical Co., Ltd .: from Wako Pure Chemical Industries, Ltd. styrene

<Various chemicals used in the production of rubber composition>
Copolymer: synthesized according to the description of the present specification SBR: Toughden 4850 manufactured by Asahi Kasei Chemicals Co., Ltd. (S-SBR; contains 50% oil based on 100 g of SBR solid content; styrene content 39% by mass )
Carbon Black: Show Black N220 (nitrogen adsorption specific surface area (N ² SA): 125 m ² / g) manufactured by Cabot Japan
Anti-aging agent: NOCRACK 6C (N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Stearic acid: Zinc stearate manufactured by NOF Corporation: Zinc Hua No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Ouchi Shinsei Chemical Industry Co., Ltd. Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide)

1. Copolymer Synthesis and Production Example 1-1 (Synthesis of Copolymer 1)
To a 3 L pressure-resistant stainless steel container that has been dried and purged with nitrogen, 2000 ml of hexane, 105 g of butadiene, and 0.22 mmol of TMEDA are added together with 195 g of styrene, and 60 mmol of n-butyllithium (n-BuLi) is added, followed by polymerization at 50 ° C. for 5 hours. Reaction was performed. After 5 hours, 60 ml of 1M isopropanol / hexane solution was added dropwise to complete the reaction. After cooling, the reaction solution was air-dried overnight and further dried under reduced pressure for 2 days to obtain 300 g of copolymer 1. The polymerization conversion rate (“dry weight / charge amount”) was almost 100%.

Production Example 2-1 (Synthesis of Copolymer 2)
To a 1 L pressure-resistant stainless steel container, 200 g of the copolymer 1 obtained above, 300 g of THF, 10 g of 10% palladium carbon were added, and the atmosphere was replaced with nitrogen, followed by replacement with hydrogen so that the pressure was 5.0 kgf / cm ² . The reaction was carried out at 80 ° C. for 4 hours. After completion of the reaction, the reaction solution was filtered to remove palladium carbon, and then the filtrate was air-dried overnight and further dried under reduced pressure for 2 days to obtain 200 g of copolymer 2. The hydrogenation rate was 100%.

Production Example 3-1 (Synthesis of Copolymer 3)
After adding 500 ml of hexane, 46 g of THF, and 60 mmol of n-butyllithium (n-BuLi) to a 1 L glass container that has been dried and purged with nitrogen, a mixture of 100 ml of hexane, 105 g of isoprene, and 195 g of styrene is added to the reaction container over 2 hours. The polymerization reaction was carried out while dropping. Immediately after the dropping, 60 ml of 2M isopropanol / hexane solution was dropped to complete the reaction. After cooling, the reaction solution was air-dried overnight and further dried under reduced pressure for 2 days to obtain 300 g of copolymer 3. The polymerization conversion was almost 100%.

Production Example 4-1 (Synthesis of Copolymer 4)
200 g of copolymer 3 was treated in the same manner as in Production Example 2-1, to obtain 200 g of copolymer 4.

Production Example 5-1 (Synthesis of Copolymer 5)
After adding 500 ml of hexane, 46 g of THF, and 60 mmol of n-butyllithium (n-BuLi) to a 1 L glass container that has been dried and purged with nitrogen, a mixture of 100 ml of hexane, 105 g of myrcene, and 195 g of styrene is added to the reaction container over 2 hours. The polymerization reaction was carried out while dropping. Immediately after completion of the dropping, 10 ml of 2M isopropanol / hexane solution was dropped to complete the reaction. After cooling, the reaction solution was air-dried overnight and further dried under reduced pressure for 2 days to obtain 300 g of copolymer 5. The polymerization conversion was almost 100%.

Production Example 6-1 (Synthesis of Copolymer 6)
200 g of copolymer 5 was processed in the same manner as in Production Example 2-1, to obtain 200 g of copolymer 6.

Production Example 7-1 (Synthesis of Copolymer 7)
After adding 500 ml of hexane, 46 g of THF and 60 mmol of n-butyllithium (n-BuLi) to a 1 L pressure-resistant stainless steel container which has been dried and purged with nitrogen, a mixture of 100 ml of hexane, 105 g of farnesene and 195 g of styrene is added to the reaction container over 2 hours. The polymerization reaction was carried out while dropping. After completion of the dropwise addition, 60 ml of 2M isopropanol / hexane solution was dropped to complete the reaction. The reaction solution was air-dried overnight and further dried under reduced pressure for 2 days to obtain 300 g of copolymer 7. The polymerization conversion was almost 100%.

Production Example 8-1 (Synthesis of Copolymer 8)
200 g of copolymer 7 was treated in the same manner as in Production Example 2-1, to obtain 200 g of copolymer 8.

Production Example 9-1 (Synthesis of Copolymer 9)
A copolymer 10 300 g was obtained in the same manner as in Production Example 1-1 except that 75 g of butadiene was used and 225 g of styrene was used instead of 195 g. The polymerization conversion was almost 100%.

Production Example 10-1 (Synthesis of Copolymer 10)
200 g of copolymer 9 was treated in the same manner as in Production Example 2-1, to obtain 200 g of copolymer 10.

Production Example 11-1 (Synthesis of Copolymer 11)
A copolymer 11 (300 g) was obtained in the same manner as in Production Example 3-1, except that 75 g of isoprene was used instead of 105 g and 225 g of styrene was used instead of 195 g. The polymerization conversion was almost 100%.

Production Example 12-1 (Synthesis of Copolymer 12)
200 g of copolymer 11 was processed in the same manner as in Production Example 2-1, to obtain 200 g of copolymer 12.

Production Example 13-1 (Synthesis of Copolymer 13)
The same process as in Production Example 5-1, except that 75 g was used instead of 105 g and 225 g of styrene was used instead of 195 g, to obtain 300 g of copolymer 13. The polymerization conversion was almost 100%.

Production Example 14-1 (Synthesis of Copolymer 14)
200 g of copolymer 13 was treated in the same manner as in Production Example 2-1, to obtain 200 g of copolymer 14.

Production Example 15-1 (Synthesis of Copolymer 15)
A copolymer 15 300 g was obtained in the same manner as in Production Example 7-1 except that 75 g of farnesene was used instead of 105 g and 225 g of styrene was used instead of 195 g. The polymerization conversion was almost 100%.

Production Example 16-1 (Synthesis of Copolymer 16)
200 g of copolymer 15 was treated in the same manner as in Production Example 2-1, to obtain 200 g of copolymer 16.

2. Production and production example 1-2 of rubber composition and tire
(1) In accordance with the formulation shown in Table 3, copolymer 1 obtained above and various chemicals for producing the rubber composition (excluding sulfur and vulcanization accelerator) were mixed at 150 ° C. with a Banbury mixer. Kneading was performed for a minute to obtain a kneaded product. To the obtained kneaded product, sulfur and a vulcanization accelerator were added and kneaded for 12 minutes at 170 ° C. using an open roll to obtain an unvulcanized rubber composition 1.

(2) The unvulcanized rubber composition obtained in (1) above is extruded according to the shape of the tire tread, and molded with other members on a tire molding machine to form an unvulcanized tire did. This unvulcanized tire was press vulcanized at 170 ° C. for 20 minutes in a vulcanizer to obtain a tire. Air was introduced into the tire to obtain a pneumatic tire 1.

Production Example 2-2 to Production Example 16-2
In accordance with the formulations shown in Table 3 and Table 4, the corresponding raw material compounds were treated in the same manner as in Production Example 1-2 to obtain unvulcanized rubber compositions 2-16 and pneumatic tires 2-16, respectively.

3. Result <Copolymer>
About the copolymers 1-16 obtained above, the weight average molecular weight Mw, the number average molecular weight Mn, the glass transition temperature Tg, the Mooney viscosity, and the copolymerization ratio (l) were measured in accordance with the following method. The results are shown in Tables 1 and 2.

(Measurement of weight average molecular weight Mw, number average molecular weight Mn)
Mw and Mn were measured using a differential refractometer as a GPC-8000 series device and detector manufactured by Tosoh Corporation, and calibrated with standard polystyrene.

(Measurement of glass transition temperature (Tg))
For each copolymer, a differential scanning calorimeter (DSC) was used to measure Tg from a starting temperature of −150 ° C. to a final temperature of 150 ° C. at a heating rate of 10 ° C./min.

(Processability)
For each copolymer, a large rotor was rotated at a temperature of 130 ° C. heated by preheating for 1 minute using a Mooney viscosity tester in accordance with JIS K 6300 “Testing method for unvulcanized rubber”. The Mooney viscosity ML _{1 + 4} (130 ° C.) after 4 minutes was measured. In addition, it has shown that it is excellent in workability, so that Mooney viscosity is small.

(Copolymerization ratio of branched conjugated diene compound (1) (l))
The copolymerization ratio (l) (% by weight) was measured by a conventional method using pyrolysis gas chromatography (PGC). That is, a calibration curve for the purified branched conjugated diene compound (1) was prepared, and the branched conjugated diene in the copolymer was determined from the area ratio of the thermal decomposition product derived from the branched conjugated diene compound (1) obtained by PGC. The weight percent of compound (1) was calculated. Pyrolysis chromatography used a system comprising a gas chromatograph mass spectrometer GCMS-QP5050A manufactured by Shimadzu Corporation and a thermal decomposition apparatus JHP-330 manufactured by Nihon Analytical Industries.

<Rubber composition and tire>
The following tests were conducted using the unvulcanized rubber compositions 1-16 and pneumatic tires 1-16 obtained above. The results are shown in Table 3 and Table 4.

(Processability)
Test pieces of a predetermined size were prepared from each unvulcanized rubber composition and heated by preheating for 1 minute using a Mooney viscosity tester according to JIS K 6300 “Testing method for unvulcanized rubber”. The large rotor was rotated under a temperature condition of 130 ° C., and the Mooney viscosity ML _{1 + 4} (130 ° C.) was measured after 4 minutes. In addition, it has shown that it is excellent in workability, so that Mooney viscosity is small.

(Grip performance)
Using the pneumatic tires obtained above, an actual vehicle was run on an asphalt road test course. The test driver evaluated the control stability during steering at that time in 10 stages. The larger the value, the better the grip performance.

(Abrasion resistance)
The test course was run 20 laps using each pneumatic tire, the depth of the groove before and after running was measured, and the case where the pneumatic tire 1 was used was indicated as 100 as an index. The larger the value, the greater the wear resistance.

(Bleed resistance)
The surface of each pneumatic tire was observed, and the degree of bleed of the oily one was visually determined.
○: No bleed △: Slightly bleed ×: Severe bleed

  As shown in Tables 3 and 4, Production Examples 5 to 8 and Production Examples 13 to 16 in which a branched conjugated diene copolymer or a hydrogenated branched conjugated diene copolymer is blended have low Mooney viscosity and processability. Has been improved. Moreover, it is shown that the grip performance, wear resistance and bleed resistance are also excellent.

  According to the present invention, a novel branched conjugated diene copolymer or hydrogenated branched conjugated diene copolymer useful for improving processability can be provided as a component of a tire rubber composition. By using the coalescence, it is possible to provide a tire rubber composition in which both wear resistance, grip performance and bleed resistance are improved to a high level while exhibiting excellent characteristics in improving processability.

Claims (11)

General formula (1)

(In the formula, R ¹ represents an aliphatic hydrocarbon having 6 to 11 carbon atoms.)
In the branched conjugated diene compound represented (1) as one general formula (2)

(In the formula, R ² represents an aromatic hydrocarbon group having 6 to 10 carbon atoms.)
A pneumatic tire having a tire tread produced using a rubber composition comprising a branched conjugated diene copolymer obtained by copolymerizing a monomer component consisting only of the aromatic vinyl compound (2) represented by ,
A pneumatic tire in which the copolymerization ratio (m) of the aromatic vinyl compound (2) is 60 to less than 80% by weight. The branched conjugated diene compound (1) is represented by the general formula (3)

CH ₂ C (R ³ ) CHCH ₂ (3)

(In the formula, R ³ represents a hydrogen atom or a methyl group.)
In comparison with the copolymer having the same weight average molecular weight replaced with the conjugated diene compound (3) represented by the formula, the Mooney viscosity ML _{1 + 4} (130 ° C.) of the rubber composition when blended with the rubber composition is The pneumatic tire according to claim 1, which exhibits a low value, for improving workability. The pneumatic tire according to claim 1 or 2, wherein the branched conjugated diene copolymer has a weight average molecular weight of 2000 to 200,000. The pneumatic tire according to any one of claims 1 to 3, wherein the branched conjugated diene compound (1) is myrcene and / or farnesene. The aromatic vinyl compound (2) is one or two or more selected from the group consisting of styrene, α-methylstyrene, α-vinylnaphthalene and β-vinylnaphthalene. Pneumatic tire described in 2. General formula (1)

(In the formula, R ¹ represents an aliphatic hydrocarbon having 6 to 11 carbon atoms.)
In the branched conjugated diene compound represented (1) as one general formula (2)

(In the formula, R ² represents an aromatic hydrocarbon group having 6 to 10 carbon atoms.)
A rubber composition comprising a hydrogenated branched conjugated diene copolymer obtained by copolymerizing a monomer component comprising only the aromatic vinyl compound (2) represented by formula (2) and then hydrogenating the copolymer. A pneumatic tire having a tire tread produced using
A pneumatic tire in which the copolymerization ratio (m) of the aromatic vinyl compound (2) is 60 to less than 80% by weight. The branched conjugated diene compound (1) is represented by the general formula (3)

CH ₂ C (R ³ ) CHCH ₂ (3)

(In the formula, R ³ represents a hydrogen atom or a methyl group.)
In comparison with the copolymer having the same weight average molecular weight replaced with the conjugated diene compound (3) represented by the formula, the Mooney viscosity ML _{1 + 4} (130 ° C.) of the rubber composition when blended with the rubber composition is The pneumatic tire according to claim 6 for improving workability, which exhibits a low value. The pneumatic tire according to claim 6 or 7 , wherein the hydrogenated branched conjugated diene copolymer has a weight average molecular weight of 2000 to 200,000. The pneumatic tire according to any one of claims 6 to 8 , wherein the branched conjugated diene compound (1) is myrcene and / or farnesene. Aromatic vinyl compound (2) is styrene, alpha-methyl styrene, alpha-vinyl naphthalene and one or more in which any one of claims 6-9 selected from the group consisting of β- vinylnaphthalene Pneumatic tire described in 2. The pneumatic tire according to any one of claims 6 to 10 , wherein a hydrogenation rate of the hydrogenated branched conjugated diene copolymer is 10 to 100%.