JP2008214484A - Conjugated diene star polymer and its preparation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a star polymer with a controlled molecular structure and a narrow dispersion, and a preparation method of the star polymer, capable of easily preparing the star polymer with a controlled molecular structure and a narrow dispersion. <P>SOLUTION: The star polymer has a structure of formula (I) (wherein B is a group comprising a conjugated diene polymer; R is a hydrogen atom or a 1-4C alkyl group; and n is an integer of ≥2) as arm parts. The star polymer can be prepared by reacting a compound having two or more ester groups and a conjugated diene polymer having an anionically polymerizable terminal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a narrowly dispersed star polymer having an arm portion made of a conjugated diene polymer and a method for producing the same.

Conventionally, as a method for producing a star polymer having a large number of arm chains,
(A) AB type and ABA type block polymers having different properties such as amphiphilic properties are micellized in a solvent, and this is used as it is, or the inner core is crosslinked by some method (for example, see Patent Document 1).
(B) A method of forming an arm from a core compound by a polymer polymerization method such as a living polymerization method (for example, see Non-Patent Document 1),
(C) A method using a dendrimer having many multi-branched chains (for example, see Patent Document 2), etc. are known.

  However, in the method using the block polymer (a), it is necessary to form micelles at the critical micelle concentration (CMC), and depending on the polymer composition, it may be difficult to form the micelles themselves. Even if it is formed, it may be difficult to internally crosslink. The method of forming an arm from the core compound (b) by a polymerization method requires advanced techniques and polymerization equipment in the polymerization. In the method using the dendrimer of (c), the dendrimer to be used is a compound having excellent multi-branching properties. However, similar to the method of (b), an advanced synthesis technique is required.

  On the other hand, methyl methacrylate, isobutyl methacrylate and t-butyl methacrylate were polymerized using diphenylhexyl lithium obtained by reacting 1,1-diphenylethylene and sec-butyllithium as a polymerization initiator, and then dicumyl alcohol dimethacrylate, Alternatively, it has been reported that a polymer having a star structure can be obtained by reacting 2,5-dimethyl-2,5-hexanediol dimethacrylate (see Non-Patent Document 2). However, the molecular weight distribution of the star polymer obtained by the conventional production method including this method is 1.5 or more, and it is difficult to form a star polymer having uniform arms.

JP-A-10-195152 JP-A-6-219966 Macromol.Chem., 189,2885-2889 (1998) J. Polymer Science, Part A, 2003, 3083

  An object of the present invention is to provide a narrowly dispersed star polymer having a controlled molecular structure and a method for producing a star polymer capable of easily producing a narrowly dispersed star polymer having a controlled molecular structure.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have reacted a compound (core part) having two or more ester groups with a conjugated diene polymer having an anion polymerization active terminal serving as an arm part. The conjugated diene-based polymer having an anionic polymerization active terminal has been found to be able to reliably attack the ester group of a compound having two or more ester groups and reliably form a desired arm. It has been found that a novel star polymer having a controlled structure and a narrow dispersion can be produced, and the present invention has been completed.

That is, the present invention
A star polymer characterized in that the structure represented by formula (I) is an arm part;

(In formula (I), B represents a group composed of a conjugated diene polymer, R represents a hydrogen atom or a C1-C4 alkyl group, and n represents an integer of 2 or more.)
(2) The star polymer according to (1), wherein the core part is a group having a benzene ring in the skeleton,
(3) The star polymer according to (1) or (2), which is represented by the formula (II):

(Wherein B, R and n are as defined above)
(4) The star polymer according to (1) or (2), which is represented by the formula (III):

(In the formula (III), D represents (CH ₂ ) _q or a p-phenylene group, q represents an integer of 0 to 3, and the sum of n ^{1 to} n ⁴ is n. B and R are as defined above. Same as)
(5) The star polymer according to any one of (1) to (4), wherein the conjugated diene polymer is a polymer of butadiene or isoprene or a copolymer thereof.
(6) The star polymer according to any one of (1) to (4), wherein the conjugated diene polymer is a copolymer of a conjugated diene monomer and a non-conjugated diene monomer.
(7) The star polymer according to (6), wherein the copolymer of a conjugated diene monomer and a non-conjugated diene monomer is a block copolymer,
(8) The star polymer according to (6) or (7), wherein the non-conjugated diene monomer is an aromatic vinyl monomer and / or a (meth) acrylate monomer,
(9) The star polymer according to any one of (5) to (8), wherein part or all of the olefin of the conjugated diene polymer is hydrogenated, and (10) the olefin of the conjugated diene polymer The star polymer according to any one of (5) to (8), wherein a part or all of is an oxidized oxirane ring.

The present invention also provides:
(11) A compound having two or more ester groups is reacted with a conjugated diene polymer having an anionic polymerization active terminal, and a compound having two or more ester groups is used as a core part, and a conjugated diene system having an anionic polymerization active terminal The present invention relates to a method for producing a star polymer according to (1), wherein a polymer having a polymer arm portion is produced.

  The star polymer of the present invention is a narrowly dispersed star polymer having a controlled molecular structure. For example, as an epoxy resin modifier, an adhesive, a paint, a casting material, a composite material (glass fiber, carbon fiber, aramid fiber) Etc.), and used for electronic and electrical materials, semiconductor encapsulants, light-emitting diode encapsulants, printed wiring boards and the like. Moreover, as liquid rubber, it is used for varnish, rubber plasticizer, adhesive plasticizer, tackifier, sealing agent, lubricating oil, and the like. In addition, it can be used for photoresists, films and tapes for semiconductor processing and display parts.

  The star polymer of the present invention has a structure represented by formula (I) as an arm portion, wherein B represents a group composed of a conjugated diene polymer, and R represents a hydrogen atom or a C1-C4 alkyl group. N represents an integer of 2 or more. Where n is the following equation that binds to the core part

The number of arms represented by That is, when n = 2, the number of structures represented by the above formula is two, and the number of conjugated diene polymers represented by B is four.

(Core part)
The core part in the star polymer of the present invention is not particularly limited as long as it is a group capable of forming a star polymer having two or more bonds and having the structure represented by the formula (I) as an arm part. , A linear or cyclic aliphatic hydrocarbon group, an aromatic hydrocarbon group, a heterocyclic group, and the like. Among these, a group having a benzene ring in the skeleton such as an aromatic hydrocarbon group is preferable.
Examples of the chain aliphatic hydrocarbon group include a methylene group, an ethylene group, a propylene group, an optionally branched butylene group, a hexylene group, and an octylene group.
Examples of the cycloaliphatic group include the following.

As a particularly preferred star polymer of the present invention in which the core part is a group having a benzene ring in the skeleton, a star polymer represented by the formula (II) or the formula (III) can be mentioned. Wherein (III), D represents _{(CH 2) q} or p- phenylene, q represents an integer of 0 to ^3, the sum of n 1 ~n ⁴ is n.

  Other examples of the group having a benzene ring constituting the core in the skeleton include those described in J. Am. Chem. Soc., Vol. 118, No. 37, 8647, 1996, and the following. be able to.

(Arm part)
The star polymer of the present invention is not particularly limited as long as it is a star polymer having the structure represented by formula (I) as an arm part, B represents a group composed of a conjugated diene polymer, and R represents hydrogen. An atom or a C1-C4 alkyl group is represented, n represents an integer greater than or equal to 2, and it is preferable that it is 4-8.
Specific examples of R include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and a t-butyl group.

  The conjugated diene-based polymer represented by B is a homopolymer composed of one kind of linear or cyclic conjugated diene-based monomers having 4 to 15 carbon atoms, preferably 4 to 10 carbon atoms, or a copolymer composed of two or more kinds. The conjugated diene-based polymer also includes a copolymer with a non-conjugated diene monomer. Copolymers include random copolymers, partial block copolymers, and full block copolymers. Furthermore, the conjugated diene polymer of the present invention includes a conjugated diene polymer in which part or all of the olefin is hydrogenated and a conjugated diene polymer in which part or all of the olefin is oxidized to form an oxirane ring. To do.

  Specific examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2-ethyl-1,3-butadiene, 2-t-butyl-1,3-butadiene, 2-phenyl-1,3- Butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 1,3-hexadiene, 2-methyl- 1,3-octadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, 1,3-cyclopentadiene, 1,3-cyclohexadiene, 1,3-cyclooctadiene, 1,3-tricyclodecadiene, myrcene, chloroprene and the like can be mentioned, and these can be used alone or in admixture of two or more.

  Examples of the hydrogenated conjugated diene polymer or conjugated diene polymer forming an oxirane ring include 1,2-polybutadiene, 1,4-polybutadiene, 1,2-polyisoprene, 3,4-polyisoprene, 1, 4-polyisoprene etc. are mentioned. Two or more kinds of microstructures may be included, and these copolymers may be used.

  Examples of non-conjugated diene monomers include (meth) acrylic acid monomers, aromatic vinyl monomers, acrylonitrile, and cyclic siloxanes.

  Examples of (meth) acrylic acid monomers include (meth) acrylic acid; methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, (meth ) N-butyl acrylate, i-butyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, glycidyl (meth) acrylate, (meta ) (Meth) acrylate compounds such as cyclohexyl acrylate, 2-ethylhexyl (meth) acrylate, 1-ethylcyclohexyl (meth) acrylate, benzyl (meth) acrylate; 2-methoxyethyl (meth) acrylate , Methoxypolyethylene glycol (meth) acrylate (the number of ethylene glycol units is 2 to 100), Butoxy polyethylene glycol (meth) acrylate, can be mentioned phenoxy polyethylene glycol (meth) acrylate and the like, these are mixed singly, or two or more can be used.

  Examples of the aromatic vinyl monomer include styrene, o-methylstyrene, p-methylstyrene, pt-butylstyrene, α-methylstyrene, pt-butoxystyrene, mt-butoxystyrene, p- (1 -Ethoxyethoxy) styrene, 2,4-dimethylstyrene, vinylaniline, vinylbenzoic acid, vinylnaphthalene, vinylanthracene, 2-vinylpyridine, 4-vinylpyridine, 2-vinylquinoline, 4-vinylquinoline, 2-vinylthiophene And heteroaryl compounds such as 4-vinylthiophene, and the like. These can be used alone or in admixture of two or more.

  The number average molecular weight of the polymer chain constituting the arm portion of the star polymer of the present invention is not particularly limited, but is 5,000 to 1,000,000 by gel permeation chromatography using a polystyrene standard, and the mass average molecular weight. Those having a ratio (Mw / Mn) (molecular weight distribution) of (Mw) to number average molecular weight (Mn) of 1.01 to 1.30 can be obtained.

  Further, the number average molecular weight (Mn) of the entire star polymer of the present invention is not particularly limited, but the number average molecular weight (Mn) is 1,000,000 or less, the weight average molecular weight (Mw) and the number average. Those having a molecular weight (Mn) ratio (Mw / Mn) (molecular weight distribution) of 1.01 to 1.30 can be obtained.

(Production method)
As a method for producing a star polymer of the present invention, a compound having two or more ester groups is reacted with a conjugated diene polymer having an anionic polymerization active terminal, and a compound having two or more ester groups is used as a core part, It is not particularly limited as long as it is a method for producing a star polymer having a conjugated diene polymer having a polymerization active terminal as an arm part. According to the production method of the present invention, a narrowly dispersed star polymer can be easily and reliably produced. Obtainable. Moreover, according to the manufacturing method of this invention, the star polymer of the said invention can be manufactured suitably.

  Examples of the compound having two or more ester groups include chain-like or cyclic aliphatic hydrocarbons, aromatic hydrocarbons, heterocyclic compounds, etc., but are not particularly limited, such as aromatic hydrocarbons A compound having a benzene ring in the skeleton is preferred. The compound having a benzene ring in the skeleton may be a compound having two or more benzene rings in the skeleton.

  Compounds having a benzene ring in the skeleton include those represented by formula (VII)

(Wherein R ¹ represents a C1 to C6 alkyl group and t represents an integer of 2 to 6), or a group represented by Formula (VIII)

(Wherein R ^{2 to} R ⁵ each independently represents a C1 to C6 alkyl group, p ^{2 to} p ⁵ each independently represents an integer of 1 to 5, and D represents (CH ₂ ) represents a _q or p-phenylene group, and q represents an integer of 0 to 3). In the formula (VII), R ¹ represents a C1-C6 alkyl group, for example, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, t-butyl group, n-pentyl. Group and n-hexyl group. t represents an integer of 2 to 6, and is preferably an integer of 2 to 4. In formula (VIII), R ^{2 to} R ⁵ each independently represent a C ^{1 to} C ⁶ alkyl group, and specific examples thereof include the above. p < ² > -p < ⁵ > represents the integer of 1-5 each independently, and it is preferable that it is 1-2. D represents _{(CH 2) q} or p- phenylene, q is an integer of 0 to 3.

  The polymer having an anionic polymerization active terminal (arm polymer) is the conjugated diene-based polymer, specifically, a polymer composed of the above-described monomers.

  The polymerization reaction for synthesizing the arm polymer is performed by either a method of dropping an anionic polymerization initiator into a monomer (mixed) solution or a method of dropping a monomer (mixed) solution into a solution containing an anionic polymerization initiator. However, since the molecular weight and molecular weight distribution can be controlled, a method in which a monomer (mixed) solution is dropped into a solution containing an anionic polymerization initiator is preferable. This arm polymer synthesis reaction is usually carried out in an organic solvent under an inert gas atmosphere such as nitrogen or argon at a temperature in the range of −100 to 80 ° C., preferably 0 to 50 ° C.

  Examples of the anionic polymerization initiator used in producing the arm polymer can include alkali metals or organic alkali metals. Examples of the alkali metals include lithium, sodium, potassium, cesium, and the like. Examples of the metal include alkylated products, allylated products, arylated products and the like of the above alkali metals. Specifically, ethyl lithium, n-butyl lithium, sec-butyl lithium, tert-butyl lithium, ethyl sodium, Examples include lithium biphenyl, lithium naphthalene, lithium triphenyl, sodium naphthalene, potassium naphthalene, α-methylstyrene sodium dianion, 1,1-diphenylhexyl lithium, 1,1-diphenyl-3-methylpentyl lithium, and the like. Kill.

  Examples of the organic solvent used in producing the arm polymer include aliphatic hydrocarbons such as n-hexane and n-heptane, alicyclic hydrocarbons such as cyclohexane and cyclopentane, and aromatic hydrocarbons such as benzene and toluene. In addition to ethers such as diethyl ether, tetrahydrofuran (THF) and dioxane, organic solvents usually used in anionic polymerization such as anisole and hexamethylphosphoramide can be mentioned. It can be used as the above mixed solvent. Among these, from the viewpoints of polarity and solubility, a mixed solvent of benzene, cyclohexane, hexane or one or more of these and THF and THF can be preferably exemplified.

  Examples of the polymerized form of the arm polymer include a homopolymer composed of a single component (monomer) and a copolymer composed of two or more components (monomers). Examples of the copolymer include a random copolymer, a partial block copolymer, and a complete block copolymer. Each of these can be synthesized by selecting a method for adding the monomer to be used.

  In the reaction to produce a star polymer using the arm polymer thus obtained as a branched polymer chain, after completion of the arm polymer synthesis reaction, a compound having two or more ester groups that become the core part is further added to the reaction solution. Can be performed. In addition, the synthesized arm polymer can be added to a solution of a compound having two or more ester groups serving as a core part. This reaction is usually carried out in an inert gas atmosphere such as nitrogen or argon in an organic solvent at a temperature of −100 ° C. to 80 ° C., preferably −10 ° C. to 40 ° C., more preferably 0 ° C. to 20 ° C. By performing the above, a polymer having a controlled structure and a narrow molecular weight distribution can be obtained. In addition, the star polymer formation reaction can be performed continuously in the solvent used to form the arm polymer, the composition is changed by adding a solvent, or the solvent is replaced with another solvent. It can also be done. As such a solvent, the same solvent as that used in the arm polymer synthesis reaction can be used.

  In the method for producing a star polymer of the present invention, the addition ratio of the compound having two or more ester groups and the conjugated diene polymer having an anionic polymerization active terminal is the active terminal of the conjugated diene polymer having an anionic polymerization active terminal (D ) May be calculated and added in advance so as to be twice the molar amount (P) of the number of ester groups (P) of the compound having two or more ester groups, and (D) is twice the molar amount of (P). You may add so that it may become the excess amount exceeding the quantity.

  The number of arms of the star polymer can form two arms for one ester group because the anionic polymerization active terminal attacks twice for one ester group. According to the production method of the present invention, a low molecular weight and narrowly dispersed star polymer can be obtained. For example, the number average molecular weight (Mn) is 1,000,000 or less, the mass average molecular weight (Mw) and the number average molecular weight. Those having a ratio (Mw / Mn) (molecular weight distribution) of (Mn) of 1.01 to 1.30 can be obtained.

OH groups formed by reacting the conjugated diene polymer with a compound having a anionic polymerization active end having two or more ester groups may be converted to alkoxy C ₁ -C ₄ by a conventional method. Further, after reacting a compound having two or more ester groups with a conjugated diene polymer having an anionic polymerization active terminal, the corresponding alkoxy group is armed by reacting with a C ₁ -C ₄ hydrocarbon halide. Can be introduced into the department.

EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, the technical scope of this invention is not limited to these illustrations.

Example 1 Synthesis of a star polymer whose arm is a homopolymer of isoprene To a nitrogen-substituted 500 mL three-necked flask, 172.2 g of dehydrated cyclohexane and 29.9 g (438.9 mmol) of isoprene were added, and the mixture was stirred and mixed. Warmed to. To this was added 5.4 g (8.8 mmol) of a 10.59% sec-butyllithium-cyclohexane solution. The mixture was stirred at 40 ° C. for 1.5 hours, and it was confirmed by gas chromatography that no isoprene monomer remained in the system. The polyisoprene produced at this time was Mn = 3700, Mw = 3900, Mw / Mn = 1.048 (GPC-RI analysis, polyisoprene standard). The reaction solution was cooled to 0 ° C., and 0.6 g (1.0 mmol) of 1,1,2,2-tetrakis- (4-ethoxycarbonylphenyl) ethane dissolved in 14.5 g of dehydrated THF was added thereto. Stir at ° C. After 30 minutes, 5 ml of methanol was added to stop the reaction. This reaction crude liquid was washed three times with distilled water, and the solvent was distilled off from the polymer-containing organic layer. This was dissolved in THF, and then methanol was added for liquid separation. The lower layer was taken out and dried under vacuum at 50 ° C. for 15 hours to obtain 25.9 g of a star polymer. The obtained star polymer was colorless and transparent and was viscous at room temperature. As a result of 1H-NMR analysis at the stage where all of the isoprene polymer was consumed, the microstructure of the polyisoprene in the arm portion was cis-1,4: 3,4-vinyl = 94%: 6%. The molecular weight of the arm portion calculated from the proton integral ratio of the terminal butyl group derived from the initiator and the polyisoprene was 3630, which was in good agreement with the molecular weight of the polyisoprene measured by sampling in the middle. Moreover, the molecular weight and molecular weight distribution of the star polymer measured by GPC-MALLS analysis were Mn = 32,500, Mw = 32,700, and Mw / Mn = 1.005. The number of arms of the star polymer was calculated from the molecular weight of the polyisoprene in the arm portion calculated from 1H-NMR analysis and the molecular weight of the star polymer measured from GPC-MALLS analysis.

Example 2 Synthesis of a star polymer whose arm is a block copolymer of isoprene and styrene To a nitrogen-substituted 200 ml three-necked flask, 113.9 g of dehydrated cyclohexane and 8.1 g (118.5 mmol) of isoprene were added, and the mixture was stirred and mixed. Warmed to 40 ° C. To this was added 3.3 g (5.5 mmol) of a 10.59% sec-butyllithium-cyclohexane solution. The mixture was stirred at 40 degrees for 1 hour, and after confirming that no isoprene monomer remained in the system by gas chromatography, the mixture was cooled to 0 ° C. To this was added 12.1 g (116.4 mmol) of styrene mixed with 12.7 g of dehydrated THF. After stirring at 0 ° C. for 30 minutes, it was confirmed by gas chromatography that no styrene monomer remained in the system, and then 1,1,2,2-tetrakis- (4-ethoxy) dissolved in dehydrated THF 8.3 g. Carbonylphenyl) ethane (0.3 g, 0.5 mmol) was added, and the mixture was stirred at 0 ° C. After 2 hours, 3 ml of methanol was added to stop the reaction. This reaction crude liquid was washed three times with distilled water, and the solvent was distilled off from the polymer-containing organic layer. This was dissolved in THF, and then methanol was added thereto for liquid separation. The lower layer was taken out, diluted with THF, and then methanol was added to separate the layers. The lower layer was taken out and dried under vacuum at 50 ° C. for 15 hours to obtain 12.5 g of a star polymer.

The obtained star polymer was colorless and transparent and viscous at room temperature.
As a result of 1H-NMR analysis, the composition ratio of polyisoprene and polystyrene in the arm portion was polyisoprene: polystyrene = 50.5: 49.5 (mol%). The molecular weight and molecular weight distribution of the star polymer measured by GPC-MALLS analysis were Mn = 29,300, MW = 29,300, and Mw / Mn = 1.003.

Example 3 Synthesis of a star polymer whose arm is a block copolymer of styrene and isoprene To a nitrogen-substituted 200 ml three-necked flask, 113.9 g of dehydrated cyclohexane and 12.1 g (116.4 mmol) of styrene were added, stirred and mixed. Warmed to 40 ° C. To this was added 3.5 g (5.7 mmol) of a 10.59% sec-butyllithium-cyclohexane solution. After stirring at 40 degrees for 30 minutes and confirming that no styrene monomer remained in the system by gas chromatography, 7.8 g (114.4 mmol) of isoprene was added. After stirring at 40 ° C. for 30 minutes, the mixture was cooled to 0 ° C. To this, 0.4 g (0.6 mmol) of 1,1,2,2-tetrakis- (4-ethoxycarbonylphenyl) ethane dissolved in 8.3 g of dehydrated THF was added and stirred at 0 ° C. After 30 minutes, 3 ml of methanol was added to stop the reaction. This reaction crude liquid was washed three times with distilled water, and the solvent was distilled off from the polymer-containing organic layer. This was dissolved in THF, and then methanol was added thereto for liquid separation. The lower layer was taken out, diluted with THF, and then methanol was added to separate the layers. The lower layer was taken out and dried under vacuum at 50 ° C. for 15 hours to obtain 13.1 g of a star polymer.
The obtained star polymer was colorless and transparent and viscous at room temperature. As a result of 1H-NMR analysis, the composition ratio of polystyrene and polyisoprene in the arm portion was polystyrene: polyisoprene = 50.5: 49.5 (mol%). The molecular weight and molecular weight distribution of the star polymer measured by GPC-MALLS analysis were Mn = 28,800, MW = 28,800, and Mw / Mn = 1.002.

Example 4 Epoxy curing-imidazole catalyst 1.0 g of the star polymer synthesized in Example 1, 9.0 g of bisphenol A type epoxy resin (Tohto Kasei, YD-128) and 0.4 g of 2-ethyl-4-methylimidazole Mix and stir at 40 ° C. until 2-ethyl-4-methylimidazole is dissolved. When 3.0 g of this mixture was transferred to an aluminum dish and heated in an oven set at 140 ° C. for 1 hour, a cured resin product was obtained.

Example 5 Epoxy curing-cationic polymerization catalyst 1.0 g of the star polymer synthesized in Example 1, 9.0 g of bisphenol A type epoxy resin (Toto Kasei, YD-128) and indanylmethylphenylsulfonium hexafluoroantimonate Was mixed with 0.2 g of 50% γ-butyrolactone solution and stirred until uniform. When 7.0 g of this mixture was transferred to an aluminum dish and heated in an oven set at 130 ° C. for 30 minutes, a cured resin having a sticky surface was obtained.

Claims (11)

A star polymer characterized in that the structure represented by formula (I) is an arm portion.

(In formula (I), B represents a group composed of a conjugated diene polymer, R represents a hydrogen atom or a C1-C4 alkyl group, and n represents an integer of 2 or more.)   The star polymer according to claim 1, wherein the core part is a group having a benzene ring in the skeleton. The star polymer according to claim 1 or 2, which is represented by the formula (II).

(Wherein B, R and n are as defined above) The star polymer according to claim 1 or 2, which is represented by the formula (III).

(In the formula (III), D represents (CH ₂ ) _q or a p-phenylene group, q represents an integer of 0 to 3, and the sum of n ^{1 to} n ⁴ is n. B and R are as defined above. Same as)   The star polymer according to any one of claims 1 to 4, wherein the conjugated diene polymer is a polymer of butadiene or isoprene or a copolymer thereof.   5. The star polymer according to claim 1, wherein the conjugated diene polymer is a copolymer of a conjugated diene monomer and a non-conjugated diene monomer.   The star polymer according to claim 6, wherein the copolymer of the conjugated diene monomer and the non-conjugated diene monomer is a block copolymer.   The star polymer according to claim 6 or 7, wherein the non-conjugated diene monomer is an aromatic vinyl monomer and / or a (meth) acrylate monomer.   The star polymer according to any one of claims 5 to 8, wherein a part or all of the olefin of the conjugated diene polymer is hydrogenated.   The star polymer according to any one of claims 5 to 8, wherein a part or all of the olefin of the conjugated diene polymer is an oxidized oxirane ring.   A compound having two or more ester groups is reacted with a conjugated diene polymer having an anionic polymerization active terminal, and a compound having two or more ester groups is used as a core part, and a conjugated diene polymer having an anionic polymerization active terminal is armed. The method for producing a star polymer according to claim 1, wherein the polymer is produced as a part.