Block copolymer, resin composition, and resin pellet

Abstract

Provided is a novel block copolymer that is rich in reactivity and easy to chemically modify.　The block copolymer includes a block A containing a vinyl aromatic monomer unit and a block B containing a conjugated diene monomer unit. In a kneading test by Labo Plastomill at 250°C, the torque value of the block copolymer at 30 minutes from the start of kneading is larger than the minimum torque value 1-10 minutes from the start of kneading. The content of the vinyl aromatic monomer unit in the block copolymer is preferably 50-95 mass% relative to the total amount of the block copolymer.

Description

Block copolymer, resin composition and resin pellets

[0001] The present disclosure relates to a block copolymer, a resin composition, and a resin pellet.

[0002] Block copolymers formed from aromatic vinyl compounds and conjugated dienes have blocks formed from the aromatic vinyl compounds that function as hard segments and blocks formed from the conjugated dienes that function as soft segments, thereby achieving both rubber elasticity at room temperature and fluidity at high temperatures. These copolymers have been used in a wide range of applications as resins with excellent mechanical properties and processability.

[0003] For example, Patent Document 1 describes a heat-shrinkable multilayer film obtained by stretching a co-extruded laminate in which inner and outer layers are composed of copolymer resin layers containing a styrene-butadiene block copolymer and polystyrene, and an intermediate layer between the inner and outer layers is composed of a polystyrene resin layer.

[0004] Japanese Patent Application Publication No. 9-272182

[0005] In recent years, the properties required of resins have become more diverse, and chemical modification may be required to enhance their functionality depending on the application.

[0006] The present disclosure aims to provide a novel block copolymer that is highly reactive and easily chemically modified, a resin composition containing the block copolymer, and resin pellets containing the block copolymer.

[0007] The present disclosure relates to, for example, the following items <1> to <6>. <1> A block copolymer comprising a block A containing vinyl aromatic monomer units and a block B containing conjugated diene monomer units, wherein, in a kneading test at 250°C using a Labo Plastomill, the torque value 30 minutes after the start of kneading is greater than the minimum torque value 1 to 10 minutes after the start of kneading. <2> The block copolymer according to <1>, wherein the content of the vinyl aromatic monomer units in the block copolymer is 50% by mass or more and 95% by mass or less, based on the total amount of the block copolymer. <3> The block copolymer according to <1> or <2>, wherein the content of the vinyl aromatic monomer units in the block A is 70% by mass or more, based on the total amount of the block A, and the content of the conjugated diene monomer units in the block B is 70% by mass or more, based on the total amount of the block B. <4> The block copolymer according to any one of <1> to <3>, wherein the vinyl aromatic monomer unit is a monomer unit derived from an aromatic vinyl compound selected from the group consisting of styrene, α-methylstyrene, and p-methylstyrene, and the conjugated diene monomer unit is a monomer unit derived from a conjugated diene selected from the group consisting of 1,3-butadiene and isoprene. <5> A resin composition comprising the block copolymer according to any one of <1> to <4>, and at least one selected from the group consisting of a radical initiator, a thermoplastic resin, and an elastomer. <6> Resin pellets comprising the block copolymer according to any one of <1> to <4>.

[0008] The present disclosure may also be embodied in the following aspects [1] to [5]. [1] A block copolymer comprising a block A containing vinyl aromatic monomer units and a block B containing conjugated diene monomer units, wherein the content of the vinyl aromatic monomer units in the block copolymer is 50% by mass or more and 95% by mass or less, based on the total amount of the block copolymer, and wherein, in a kneading test at 250°C using a Labo Plastomill, the torque value 30 minutes after the start of kneading is greater than the minimum torque value 1 to 10 minutes after the start of kneading. [2] The block copolymer according to [1], wherein the content of the vinyl aromatic monomer units in the block A is 70% by mass or more, based on the total amount of the block A, and the content of the conjugated diene monomer units in the block B is 70% by mass or more, based on the total amount of the block B. [3] The block copolymer according to [1] or [2], wherein the vinyl aromatic monomer unit is a monomer unit derived from an aromatic vinyl compound selected from the group consisting of styrene, α-methylstyrene, and p-methylstyrene, and the conjugated diene monomer unit is a monomer unit derived from a conjugated diene selected from the group consisting of 1,3-butadiene and isoprene. [4] A resin composition comprising the block copolymer according to any one of [1] to [3], and at least one selected from the group consisting of a radical initiator, a thermoplastic resin, and an elastomer. [5] Resin pellets comprising the block copolymer according to any one of [1] to [3].

[0009] The present disclosure provides a novel block copolymer that is highly reactive and easily chemically modified. The present disclosure also provides a resin composition containing the block copolymer and a resin pellet containing the block copolymer.

[0010] Fig. 1 is a diagram showing the results of a heat-kneading test of the block copolymer of Example 1. Fig. 2 is a diagram showing the results of a heat-kneading test of the block copolymer of Comparative Example 1.

[0011] Preferred embodiments of the present disclosure will be described in detail below.

[0012] (Block Copolymer) The block copolymer of this embodiment is a block copolymer including a block A containing a vinyl aromatic monomer unit and a block B containing a conjugated diene monomer unit. The block copolymer of this embodiment is characterized in that, in a kneading test at 250°C using a Labo Plastomill, the torque value 30 minutes after the start of kneading is greater than the minimum torque value 1 to 10 minutes after the start of kneading.

[0013] The block copolymer of the present embodiment may be a block copolymer including a block A containing a vinyl aromatic monomer unit and a block B containing a conjugated diene monomer unit, wherein the content of the vinyl aromatic monomer unit in the block copolymer is 50% by mass or more and 95% by mass or less based on the total amount of the block copolymer, and may be characterized in that, in a kneading test at 250°C using a Labo Plastomill, the torque value 30 minutes after the start of kneading is greater than the minimum torque value 1 to 10 minutes after the start of kneading.

[0014] In the above kneading test, typically, torque increases due to gelation within 5 to 7 minutes, followed by a decrease in torque due to molecular chain scission caused by shear, resulting in a small torque 30 minutes after the start of kneading. It is believed that the block copolymer of this embodiment inhibits torque decrease due to the progression of crosslinking reactions via carbon-carbon double bonds as molecular chains are scissioned. That is, the block copolymer of this embodiment can be said to have a large number of highly reactive carbon-carbon double bonds (specifically, 1,2-bonds or 3,4-bonds in conjugated diene monomer units) while comprising vinyl aromatic monomer units as the main structural units, and is therefore easily chemically modified.

[0015] <Block A> Block A is a block containing a vinyl aromatic monomer unit.

[0016] The vinyl aromatic monomer unit is a monomer unit derived from an aromatic vinyl compound. Note that the term "monomer unit derived from a compound" refers to a structural unit formed from the compound in a polymerization reaction using the compound as a monomer.

[0017] The aromatic vinyl compound may be, for example, a compound having an aromatic ring and a vinyl group or vinylidene group bonded to the aromatic ring.

[0018] Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, and a pyrene ring, and these aromatic rings may have a substituent. Examples of the substituent that the aromatic ring may have include an alkyl group, an alkoxy group, a halogeno group (e.g., a fluoro group, a chloro group, a bromo group, or an iodo group, preferably a fluoro group), an aryl group, a dialkylamino group, a trialkylsilyl group, and a trialkoxysilyl group.

[0019] The vinyl group is -CH=CH ２ The vinylidene group bonded to the aromatic ring is, for example, a group represented by -CR=CH ２ (R represents an alkyl group). The number of carbon atoms in the alkyl group for R may be, for example, 1 to 10, 1 to 4, or even 1. R may be, for example, a methyl group.

[0020] Examples of aromatic vinyl compounds include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, 2,3-dimethylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 2,6-dimethylstyrene, p-tert-butylstyrene, 4-methoxystyrene, 4-trimethylsilylstyrene, vinylnaphthalene, vinylanthracene, and vinylpyrene.

[0021] As the aromatic vinyl compound, an aromatic vinyl compound selected from the group consisting of styrene, α-methylstyrene, and p-methylstyrene is preferred from the viewpoints of easy availability and easily achieving both good mechanical properties and good fluidity when melted.

[0022] The vinyl aromatic monomer unit may be, for example, a structural unit represented by the following formula (A-1).

[0023]

[0024] In formula (A-1), R １ represents a hydrogen atom or an alkyl group, and Ar１ represents an aryl group.

[0025] R １ The number of carbon atoms in the alkyl group in R may be, for example, 1 to 20, 1 to 10, or 1. １ may be, for example, a methyl group.

[0026] Ar １ Examples of the aryl group in the formula (I) include a phenyl group which may have a substituent, a naphthyl group which may have a substituent, an anthracenyl group which may have a substituent, a pyrenyl group which may have a substituent, etc. Examples of the substituent include an alkyl group, an alkoxy group, a halogeno group (e.g., a fluoro group, a chloro group, a bromo group, or an iodo group, preferably a fluoro group), an aryl group, a dialkylamino group, a trialkylsilyl group, a trialkoxysilyl group, etc.

[0027] Ar １ may be, for example, a phenyl group which may have a substituent, such as a phenyl group, a 4-methylphenyl group, a 2,3-dimethylphenyl group, a 2,4-dimethylphenyl group, a 2,5-dimethylphenyl group, a 2,6-dimethylphenyl group, a 4-tert-butylphenyl group, a 4-methoxyphenyl group, or a 4-trimethylsilylphenyl group, or may be a phenyl group or a 4-methylphenyl group.

[0028] Block A may be a block containing vinyl aromatic monomer units as a main component. The content of vinyl aromatic monomer units in block A may be, for example, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 99% by mass or more, or even 100% by mass, based on the total amount of block A.

[0029] Block A may further contain conjugated diene monomer units in addition to vinyl aromatic monomer units.

[0030] The content of the conjugated diene monomer units in block A may be, for example, 30% by mass or less, 20% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less, or may be 0% by mass, based on the total amount of block A.

[0031] The block copolymer of the present embodiment may have one block A or two or more blocks A.

[0032] The size of one block A is not particularly limited. The amount of one block A relative to the total amount of the block copolymer may be, for example, 1% by mass or more, 3% by mass or more, or 5% by mass or more. Furthermore, the amount of one block A relative to the total amount of the block copolymer may be, for example, 95% by mass or less, 90% by mass or less, 85% by mass or less, or 80% by mass or less. In one embodiment, the amount of one block A relative to the total amount of the block copolymer may be 1% by mass or more and 90% by mass or less, 3% by mass or more and 85% by mass or less, or 5% by mass or more and 80% by mass or less.

[0033] Among the blocks A in the block copolymer, the amount of the largest block A (hereinafter referred to as block A-1) may be, for example, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, relative to the total amount of the block copolymer. The amount of block A-1 relative to the total amount of the block copolymer may be, for example, 95% by mass or less, 90% by mass or less, 85% by mass or less, or 80% by mass or less. In one embodiment, the amount of block A-1 may be 30% by mass or more and 95% by mass or less, 40% by mass or more and 90% by mass or less, 50% by mass or more and 85% by mass or less, or 60% by mass or more and 80% by mass or less, relative to the total amount of the block copolymer.

[0034] The total amount of block A in the block copolymer of this embodiment may be, for example, 50% by mass or more, 60% by mass or more, or 70% by mass or more, based on the total amount of the block copolymer. Furthermore, the total amount of block A in the block copolymer of this embodiment may be, for example, 95% by mass or less, 90% by mass or less, or 85% by mass or less, based on the total amount of the block copolymer. In one embodiment, the total amount of block A in the block copolymer may be 50% by mass or more and 95% by mass or less, 60% by mass or more and 90% by mass or less, 70% by mass or more and 90% by mass or less, or 70% by mass or more and 85% by mass or less, based on the total amount of the block copolymer.

[0035] <Block B> Block B is a block containing conjugated diene monomer units.

[0036] The conjugated diene monomer unit is a monomer unit derived from a conjugated diene. A conjugated diene can be defined as a compound having two carbon-carbon double bonds connected by a single bond.

[0037] Examples of conjugated dienes include 1,3-butadiene, isoprene, 2-tert-butyl-1,3-butadiene, β-myrcene, β-farnesene, etc. From the viewpoint of availability, the conjugated diene is preferably a conjugated diene selected from the group consisting of butadiene and isoprene.

[0038] Examples of conjugated diene monomer units include 1,4-bonds, 1,2-bonds, and 3,4-bonds. 1,4-bonds are formed by polymerization such that the carbon atoms at the 1st and 4th positions of a conjugated diene skeleton are bonded to adjacent monomer units, and have a carbon-carbon double bond in the main chain. In contrast, 1,2-bonds (or 3,4-bonds) are formed by polymerization such that the carbon atoms at the 1st and 2nd positions (or 3rd and 4th positions) of a conjugated diene skeleton are bonded to adjacent monomer units, and have a carbon-carbon double bond in the side chain.

[0039] The conjugated diene monomer unit may be, for example, a structural unit represented by the following formula (B-1), formula (B-2), or formula (B-3). The structural unit represented by formula (B-1) is a 1,4-bonded compound, the structural unit represented by formula (B-2) is a 1,2-bonded compound, and the structural unit represented by formula (B-3) is a 3,4-bonded compound.

[0040]

[0041] In formula (B-1), formula (B-2) and formula (B-3), R ２ represents a hydrogen atom or an alkyl group. ２ When is a hydrogen atom, formula (B-2) and formula (B-3) represent the same structural unit.

[0042] R ２ The number of carbon atoms in the alkyl group in R may be, for example, 1 to 15, 1 to 4, or 1. １ may be, for example, a methyl group.

[0043] Block B may be a block containing conjugated diene monomer units as a main component. The content of the conjugated diene monomer units in block B may be, for example, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 99% by mass or more, or even 100% by mass, based on the total amount of block B.

[0044] Block B may further contain an aromatic vinyl monomer unit in addition to the conjugated diene monomer unit.

[0045] The content of aromatic vinyl monomer units in block B may be, for example, 30% by mass or less, 20% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less, or even 0% by mass, based on the total amount of block B.

[0046] The block copolymer of the present embodiment may have one block B or two or more blocks B.

[0047] The size of one block B is not particularly limited. The amount of one block B relative to the total amount of the block copolymer may be, for example, 1% by mass or more, 3% by mass or more, or 5% by mass or more. Furthermore, the amount of one block B relative to the total amount of the block copolymer may be, for example, 50% by mass or less, 40% by mass or less, or 30% by mass or less. In one embodiment, the amount of one block B relative to the total amount of the block copolymer may be 1% by mass or more and 50% by mass or less, 3% by mass or more and 40% by mass or less, or 5% by mass or more and 50% by mass or less.

[0048] Among the blocks B in the block copolymer, the amount of the largest block B (hereinafter referred to as block B-1) may be, for example, 3% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more, relative to the total amount of the block copolymer. The amount of block B-1 relative to the total amount of the block copolymer may be, for example, 50% by mass or less, 40% by mass or less, or 30% by mass or less. In one embodiment, the amount of one block B-1 relative to the total amount of the block copolymer may be 3% by mass or more and 50% by mass or less, 5% by mass or more and 40% by mass or less, 10% by mass or more and 40% by mass or less, or 15% by mass or more and 30% by mass or less.

[0049] In each block B, the total content of 1,2-bonds and 3,4-bonds in the conjugated diene monomer units in block B (i.e., the total content of 1,2-bonds and 3,4-bonds based on the total amount of conjugated diene monomer units in block B) may be, for example, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, or 75% or more. Also, the total content of 1,2-bonds and 3,4-bonds in the conjugated diene monomer units in block B (i.e., the total content of 1,2-bonds and 3,4-bonds based on the total amount of conjugated diene monomer units in block B) may be, for example, 99% or less, 97% or less, 95% or less, or 93% or less. In one embodiment, the total content of 1,2-bonds and 3,4-bonds, based on the total amount of conjugated diene monomer units in block B, may be 30% or more and 99% or less, 40% or more and 97% or less, 50% or more and 95% or less, 60% or more and 93% or less, 70% or more and 93% or less, or 75% or more and 93% or less.

[0050] The total amount of block B in the block copolymer of this embodiment may be, for example, 5% by mass or more, 10% by mass or more, or 15% by mass or more, based on the total amount of the block copolymer. Furthermore, the total amount of block B in the block copolymer of this embodiment may be, for example, 50% by mass or less, 40% by mass or less, or 30% by mass or less, based on the total amount of the block copolymer. In one embodiment, the total amount of block B in the block copolymer may be 5% by mass or more and 50% by mass or less, 10% by mass or more and 40% by mass or less, or 15% by mass or more and 30% by mass or less, based on the total amount of the block copolymer.

[0051] The block copolymer of this embodiment has a vinyl aromatic monomer unit and a conjugated diene monomer unit. The block copolymer of this embodiment may contain a vinyl aromatic monomer unit in a portion other than block A, and may contain a conjugated diene monomer unit in a portion other than block B.

[0052] In the block copolymer of this embodiment, the content of the vinyl aromatic monomer unit may be, for example, 50% by mass or more, 60% by mass or more, or 70% by mass or more, based on the total amount of the block copolymer. Furthermore, the content of the vinyl aromatic monomer unit may be, for example, 95% by mass or less, 90% by mass or less, or 85% by mass or less, based on the total amount of the block copolymer. In one embodiment, the content of the vinyl aromatic monomer unit may be 50% by mass or more and 95% by mass or less, 60% by mass or more and 90% by mass or less, or 70% by mass or more and 85% by mass or less, based on the total amount of the block copolymer.

[0053] In the block copolymer of this embodiment, the content of the conjugated diene monomer units may be, for example, 5% by mass or more, 10% by mass or more, or 15% by mass or more, based on the total amount of the block copolymer. Furthermore, the content of the conjugated diene monomer units may be, for example, 50% by mass or less, 40% by mass or less, or 30% by mass or less, based on the total amount of the block copolymer. In one embodiment, the content of the conjugated diene monomer units may be 5% by mass or more and 50% by mass or less, 10% by mass or more and 40% by mass or less, or 15% by mass or more and 30% by mass or less, based on the total amount of the block copolymer.

[0054] The total content of 1,2-bonds and 3,4-bonds in the conjugated diene monomer units in the block copolymer (i.e., the total content of 1,2-bonds and 3,4-bonds based on the total amount of conjugated diene monomer units) may be, for example, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, or 75% or more. Such block copolymers are highly reactive and have a high content of 1,2-bonds and 3,4-bonds that easily form crosslinked structures, making them more likely to satisfy the torque characteristics described above. Furthermore, the total content of 1,2-bonds and 3,4-bonds in the conjugated diene monomer units in the block copolymer (i.e., the total content of 1,2-bonds and 3,4-bonds based on the total amount of conjugated diene monomer units) may be, for example, 95% or less, 90% or less, 85% or less, or 80% or less. In one embodiment, the total content of 1,2-bonds and 3,4-bonds based on the total amount of conjugated diene monomer units may be 30% or more and 95% or less, 40% or more and 90% or less, 50% or more and 85% or less, 60% or more and 80% or less, 70% or more and 80% or less, or 75% or more and 80% or less.

[0055] The block copolymer of this embodiment may have one block A or may have two or more blocks A. The number of blocks A in the block copolymer of this embodiment may be, for example, 1 to 4, or may be 1 or 2. The block copolymer of this embodiment may have one block B or may have two or more blocks B. The number of blocks B in the block copolymer of this embodiment may be, for example, 1 to 4, or may be 1 or 2.

[0056] In the block copolymer of this embodiment, it is preferable that the block A is bonded to the block B. The block copolymer of this embodiment may be, for example, an A-B copolymer in which the block A is bonded to the block B, an A-B-A copolymer in which the first block A, the block B, and the second block B are bonded to each other, or a B-A-B copolymer in which the first block B, the block A, and the second block B are bonded to each other.

[0057] The weight average molecular weight (Mw) of the block copolymer of this embodiment may be, for example, 40,000 or more, and from the viewpoint of the strength of molded products such as pellets and films, may be 60,000 or more, 80,000 or more, or 100,000 or more. The weight average molecular weight (Mw) of the block copolymer of this embodiment may be, for example, 300,000 or less, and from the viewpoint of reducing shear heat generation in the devolatilizing extrusion step, may be 200,000 or less or 150,000 or less. In one embodiment, the weight average molecular weight (Mw) of the block copolymer may be 40,000 or more and 300,000 or less, 40,000 or more and 200,000 or less, 60,000 or more and 200,000 or less, or 80,000 or more and 150,000 or less.

[0058] The molecular weight distribution (Mw / Mn) of the block copolymer of this embodiment may be, for example, 2 or less, 1.9 or less, 1.7 or less, or 1.5 or less.

[0059] The block copolymer of this embodiment exhibits a characteristic change in torque over time in a kneading test using a Labo Plastomill at 250° C. The kneading test is carried out under the following conditions.

[0060] <Kneading test> (i) Measuring device Device: Labo Plastomill 4C150 heat kneading tester (manufactured by Toyo Seiki) Blade shape: Roller mixer R60 (ii) Measuring conditions Sample amount: 48 g Rotation speed: 100 rpm Kneading temperature: 250°C Kneading time: 30 minutes

[0061] The kneading test is applicable to resins that are solid at room temperature (e.g., 23° C.), and the block copolymer of the present embodiment that satisfies the criteria based on the kneading test is solid at room temperature (e.g., 23° C.). Therefore, it can be said that the block copolymer of the present embodiment can be suitably used as a solid thermoplastic resin and can be easily molded into various shapes, such as pellets or films, by known molding methods such as extrusion molding.

[0062] In the above-mentioned kneading test, the torque usually decreases as the sample melts, and after 5 to 7 minutes, the torque increases due to gelation, followed by a decrease in torque due to molecular chain scission caused by shear. The block copolymer of this embodiment suppresses the decrease in torque, and the torque value 30 minutes after the start of kneading is greater than the minimum torque value 1 to 10 minutes after the start of kneading. In such a block copolymer of this embodiment, the crosslinking reaction proceeds to the same extent as or even more than the molecular chain scission caused by shear, and it can be said that the block copolymer has many highly reactive crosslinking points and is easily chemically modified.

[0063] In the above kneading test, the minimum torque (T ｍｉｎ ) is an index showing the fluidity when melted. ｍｉｎ may be, for example, 4 Nm or more, 6 Nm or more, or 8 Nm or more. ｍｉｎ may be, for example, 17 Nm or less, 16 Nm or less, or 15 Nm or less.

[0064] In the above kneading test, the maximum value of the torque (T ｍａｘ ) is an index showing the crosslinking reactivity of a polymer material. ｍａｘ may be, for example, 8 Nm or more, 9 Nm or more, or 10 Nm or more. ｍａｘ may be, for example, 20 Nm or less, 18 Nm or less, or 15 Nm or less.

[0065] In the kneading test, the T ｍａｘ and the torque value T 30 minutes after the start of kneading ３０ The difference between (T ｍａｘ -T ３０ ) may be, for example, 4 Nm or less, 3 Nm or less, or 2 Nm or less. A small difference indicates that the block copolymer of this embodiment has more reactive crosslinking points and is easier to chemically modify.

[0066] The block copolymer may contain a biomass-derived component. For example, some or all of the monomer units contained in the block copolymer may be biomass-derived components. Furthermore, some or all of the monomer units contained in the block copolymer may be chemically recycled components.

[0067] The block copolymer of this embodiment can be produced, for example, by the following method.

[0068] (Method for Producing Block Copolymer) The method for producing a block copolymer of this embodiment is a method for producing the above-mentioned block copolymer by anionic polymerization. In the production method of this embodiment, the formation of block B is carried out in a reaction solution to which a chelating agent and an alkali metal alkoxide have been added.

[0069] According to this production method, a block copolymer satisfying the torque characteristics described above can be easily obtained.

[0070] The anionic polymerization of the block copolymer may be carried out in a reaction solution to which an anionic polymerization initiator has been added.

[0071] The anionic polymerization initiator may be, for example, an organolithium compound. As the organolithium compound, alkyllithium compounds (e.g., n-butyllithium, sec-butyllithium, tert-butyllithium, isobutyllithium, methyllithium, ethyllithium, n-propyllithium, isopropyllithium, etc.) can be suitably used.

[0072] The amount of the anionic polymerization initiator to be added is not particularly limited, and may be adjusted appropriately so that the concentration of polymerization active species (also called active sites) in the reaction liquid falls within the range described below.

[0073] In the anionic polymerization of a block copolymer, the concentration of the polymerization active species in the reaction solution may be, for example, 0.001 mol / L or more, and from the viewpoint of further improving the reaction rate, may be 0.002 mol / L or more or 0.003 mol / L or more. In the anionic polymerization of a block copolymer, the concentration of the polymerization active species in the reaction solution may be, for example, 0.015 mol / L or less, and from the viewpoint of facilitating reaction control and making it easier to obtain a block copolymer with a higher molecular weight, may be 0.01 mol / L or less or 0.005 mol / L or less.

[0074] In the anionic polymerization of the block copolymer, the reaction solution may contain a solvent, as long as the solvent is capable of dissolving the monomer components (a) and (b) described below and does not inhibit the anionic polymerization.

[0075] Examples of the solvent include hydrocarbon solvents such as aliphatic hydrocarbons (e.g., pentane, isopentane, hexane, heptane, octane, isooctane, etc.), alicyclic hydrocarbons (e.g., cyclohexane, cyclopentane, methylcyclopentane, methylcyclohexane, ethylcyclohexane, etc.), and aromatic hydrocarbons (e.g., benzene, toluene, ethylbenzene, xylene, etc.).

[0076] The amount of solvent used is not particularly limited, and may be adjusted appropriately so that the concentration of the polymerization active species in the reaction liquid falls within the above-mentioned range.

[0077] In the anionic polymerization of a block copolymer, an aprotic polar additive may be added to the reaction solution as a Lewis base. The addition of the Lewis base may improve the reactivity of the anionic polymerization initiator, facilitating the polymerization reaction.

[0078] Examples of Lewis bases include ether solvent compounds (eg, tetrahydrofuran, diethyl ether, tetrahydropyran, crown ether, etc.), amine compounds (eg, triethylamine, N,N-dimethylaniline, pyridine, etc.), and the like.

[0079] In the anionic polymerization of a block copolymer, a chelating agent and an alkali metal alkoxide may be added to the reaction solution. In a reaction solution to which a chelating agent and an alkali metal alkoxide have been added, the stability and reactivity of the polymerization active species are improved, making it easier to obtain a block copolymer with a high molecular weight. Furthermore, in a reaction solution to which a chelating agent and an alkali metal alkoxide have been added, the polymerization rate is increased and the polymerization reaction proceeds even at room temperature (e.g., 23°C). This eliminates the need to heat the reaction solution, and the reaction can be carried out using only a cooling means for cooling the reaction solution. Furthermore, in a reaction solution to which a chelating agent and an alkali metal alkoxide have been added, 1,2-bonds (or 3,4-bonds) are easily formed from conjugated dienes.

[0080] The chelating agent may be any chelating agent that can coordinate with a cation (e.g., lithium cation) derived from the anionic polymerization initiator, and may be appropriately selected from known chelating agents.

[0081] Examples of chelating agents include compounds having a linear molecular skeleton and nitrogen atoms bonded to both ends of the molecular skeleton. The chelating agent may be, for example, a compound represented by the following formula (1-1):

[0082]

[0083] In formula (1-1), n １ and n ２ each independently represents an integer of 0 or more, R ３ represents a single bond, —O—, or —NR ５ - indicates R ４ and R ５ each independently represents an alkyl group.

[0084] n １ and n ２ may be, for example, 0 to 1, and is preferably 0 or 1.

[0085] R ４ The number of carbon atoms in the alkyl group in R may be, for example, 1 to 5, 1 to 2, or 1. ４ may be, for example, a methyl group.

[0086] R５ The number of carbon atoms in the alkyl group in R may be, for example, 1 to 5, 1 to 2, or 1. ５ may be, for example, a methyl group.

[0087] Examples of the chelating agent include N,N,N',N'-tetramethylethylenediamine, N,N,N',N'',N''-pentamethyldiethylenetriamine, and bis(2-dimethylaminoethyl) ether.

[0088] The alkali metal alkoxide is, for example, M １ (OR １１ ) can be expressed as M １ is an alkali metal, and R １１ is an alkyl group.

[0089] M １ is preferably sodium. That is, the alkali metal alkoxide is preferably sodium alkoxide.

[0090] R １１ The number of carbon atoms in the alkyl group in R may be, for example, 1 or more, 2 or more, 3 or more, or 4 or more. １１ The number of carbon atoms in the alkyl group may be, for example, 10 or less, 9 or less, 8 or less, or 6 or less.

[0091] The amount of the chelating agent added may be, for example, 1 equivalent or more, or 2 equivalents or more, relative to the polymerization active species in the reaction solution, and may be, for example, 4 equivalents or less, or 3 equivalents or less, relative to the polymerization active species in the reaction solution.

[0092] The amount of alkali metal alkoxide added may be, for example, 0.1 equivalents or more, 0.2 equivalents or more, 0.4 equivalents or more, or 0.5 equivalents or more relative to the polymerization active species in the reaction solution, and may be, for example, 1 equivalent or less, 0.9 equivalents or less, 0.8 equivalents or less, or 0.7 equivalents or less relative to the polymerization active species in the reaction solution.

[0093] The chelating agent and the alkali metal alkoxide may be added to the reaction solution from the early stage of the polymerization reaction of the block copolymer, or may be added to the reaction solution during the polymerization reaction of the block copolymer (for example, after the formation of block A and before the formation of block B).

[0094] In the anionic polymerization of a block copolymer, the formation of block A and the formation of block B may each be carried out once or multiple times depending on the desired block configuration.

[0095] In the production method of this embodiment, block A may be formed by anionic polymerization of a monomer component (a) containing an aromatic vinyl compound.

[0096] The composition of the monomer component (a) may be selected depending on the composition of the block A. The content of the aromatic vinyl compound in the monomer component (a) may be, for example, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 99% by mass or more, or even 100% by mass, based on the total amount of the monomer component (a).

[0097] The anionic polymerization of the monomer component (a) may be carried out in the reaction liquid described above.

[0098] In the anionic polymerization of the monomer component (a), a chelating agent and an alkali metal alkoxide are preferably added to the reaction solution. That is, the anionic polymerization of the monomer component (a) may be carried out in a reaction solution to which a chelating agent and an alkali metal alkoxide have been added. In the reaction solution to which a chelating agent and an alkali metal alkoxide have been added, the reactivity of the polymerization active species is improved, facilitating the formation of a block A having a large molecular weight.

[0099] In the anionic polymerization of the monomer component (a), the monomer component (a) may be added to the reaction solution all at once or in multiple portions. Adding the monomer component (a) in multiple portions can prevent a rapid increase in the internal temperature, which may make it easier to satisfy the preferred temperature range described below.

[0100] In the production method of this embodiment, the block B may be formed by anionic polymerization of a monomer component (b) containing a conjugated diene.

[0101] The composition of the monomer component (b) may be selected depending on the composition of the block B. The content of the conjugated diene in the monomer component (b) may be, for example, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 99% by mass or more, or even 100% by mass, based on the total amount of the monomer component (b).

[0102] The anionic polymerization of the monomer component (b) may be carried out in the reaction liquid described above.

[0103] During the anionic polymerization of the monomer component (b), a chelating agent and an alkali metal alkoxide are preferably added to the reaction solution. That is, the anionic polymerization of the monomer component (b) may be carried out in a reaction solution to which a chelating agent and an alkali metal alkoxide have been added. In the reaction solution to which a chelating agent and an alkali metal alkoxide have been added, 1,2-bonds (or 3,4-bonds) are selectively formed from the conjugated diene, making it easier to obtain a block copolymer that satisfies the torque characteristics described above.

[0104] In the anionic polymerization of the monomer component (b), the monomer component (b) may be added to the reaction solution all at once or in multiple portions. Adding the monomer component (b) in multiple portions can prevent a rapid increase in the internal temperature, which may make it easier to satisfy the preferred temperature range described below.

[0105] In the production method of this embodiment, the temperature of the reaction solution may be controlled by the amount of monomer added and by cooling means. The cooling means is not particularly limited, and may be, for example, water cooling.

[0106] The temperature of the reaction solution may be controlled to, for example, 90° C. or lower, or 80° C. or lower, 70° C. or lower, or 60° C. or lower. The lower limit of the temperature of the reaction solution does not need to be controlled, and may be, for example, room temperature or higher, or 20° C. or higher, 30° C. or higher, or 40° C. or higher.

[0107] The production method of this embodiment may be carried out using a reaction apparatus including a reactor and a cooling means for cooling the reactor.

[0108] In the production method of this embodiment, the use of a chelating agent and an alkali metal alkoxide allows the reaction to be initiated at room temperature (e.g., 20 to 30°C), and the temperature of the reaction solution can be easily controlled by portionwise addition of the monomer and cooling means, making it easy to scale up the process. Therefore, the capacity of the reactor may be, for example, 100 L or more, or even 1000 L or more. The amount of the reaction solution in the reactor may be, for example, 100 L or more, or even 1000 L or more.

[0109] A preferred embodiment of this embodiment will be described below.

[0110] The production method of this embodiment includes a first step of adding a first monomer component to a reaction liquid (i) to which an anionic polymerization initiator, a chelating agent, and an alkali metal alkoxide have been added, to obtain a reaction liquid (ii) containing a first block having an active site at its terminal; and a second step of adding a second monomer component to the reaction liquid (ii) to bond with the first block to obtain a reaction liquid (iii) containing a second block having an active site at its terminal.

[0111] The production method of this embodiment may further include a third step in which a first monomer component is added to reaction solution (iii) to bond with the second block to obtain reaction solution (iv) containing a third block having an active site at its terminal. This allows for the formation of a block copolymer having three blocks. Furthermore, by alternately performing the second step and the third step, block copolymers having four or more blocks can also be easily produced.

[0112] One of the first and second monomer components is the above-mentioned monomer component (a), and the other is the above-mentioned monomer component (b).

[0113] For example, when the first monomer component is monomer component (a) and the second monomer component is monomer component (b), the first block and the third block are block A, and the second block is block B. Also, when the first monomer component is monomer component (b) and the second monomer component is monomer component (a), the first block and the third block are block B, and the second block is block A.

[0114] After the desired block structure is formed through the first and second steps (and, if necessary, the third step), the active sites can be inactivated by adding a deactivator to obtain a block copolymer.

[0115] The deactivator is not particularly limited as long as it is a component that can deactivate the active sites, and may be, for example, water, alcohol, phenol, an epoxide compound, an alkyl halide, carbon dioxide, or the like.

[0116] (Uses of Block Copolymer) The block copolymer of this embodiment is solid at room temperature and melts at high temperatures (for example, 200 to 230° C.), and therefore can be easily molded to form a molded article.

[0117] The method for molding the block copolymer is not particularly limited, and may be appropriately selected from known molding methods for molding thermoplastic resins, for example.

[0118] The method for molding the block copolymer may be, for example, extrusion molding, and from the viewpoint of being able to remove the solvent and unreacted monomers while molding, devolatilizing extrusion may also be used.

[0119] The molded article may be, for example, a resin pellet, a film, a sheet, a plate, or the like.

[0120] The block copolymer of the present embodiment may be chemically modified and then molded into a molded article. That is, the molded article of the present embodiment may be a molded article containing the block copolymer or a molded article containing a chemically modified version of the block copolymer.

[0121] The block copolymer of the present embodiment may be used as a resin composition by mixing it with other components, such as a radical initiator, a thermoplastic resin (a thermoplastic resin other than the above-described block copolymer), an elastomer, etc.

[0122] Examples of radical initiators include peroxide initiators such as benzoyl peroxide, diisopropylbenzene hydroperoxide, tert-butyl hydroperoxide, cumene hydroperoxide, di-tert-butyl peroxide, dicumyl peroxide, and tert-butylcumyl peroxide, and azo initiators such as 2,2'-azobisisobutyronitrile, 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis(2,4,4-trimethylpentane). The block copolymer of the present embodiment contains many highly reactive crosslinking points, and therefore can easily form a crosslinked structure by mixing it with a radical initiator.

[0123] Examples of thermoplastic resins include polystyrene resin (PS), styrene-butadiene copolymer resin (SBC), and polyphenylene ether resin (PPE).

[0124] Examples of elastomers include styrene-butadiene copolymer rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), styrene-based thermoplastic elastomer (SBS), and hydrogenated styrene-based thermoplastic elastomer (SEBS).

[0125] The block copolymer of the present embodiment may be chemically modified and then mixed with other components to form a resin composition. That is, the resin composition of the present embodiment may be a resin composition containing the block copolymer, or may be a resin composition containing a chemically modified version of the block copolymer.

[0126] The resin composition may be molded into a molded article by, for example, a known molding method for molding a thermoplastic resin. That is, the molded article of the present embodiment may be a molded article containing the resin composition.

[0127] Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments.

[0128] For example, one aspect of the present disclosure is a method for measuring the minimum torque (T ｍｉｎ ) and the torque value (T３０ Another aspect of the present disclosure may relate to an evaluation method for evaluating a block copolymer or a method for producing a block copolymer based on the above T ｍｉｎ and T ３０ The present invention may relate to a screening method for screening a block copolymer or a method for producing a block copolymer based on the above.

[0129] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0130] Example 1 Under a nitrogen atmosphere, 374 kg of cyclohexane, 428 g of N,N,N',N'-tetramethylethylenediamine (TMEDA), and 68 g of sodium tert-amylate (NaOAm) were placed in a reaction vessel. Next, 1900 mL of an n-butyllithium / cyclohexane solution (concentration: 10% by mass) was added as a polymerization initiator, and the internal temperature was maintained at 30°C.

[0131] Next, while the reaction vessel was water-cooled, 64.0 kg of styrene was added to the reaction vessel, and a polymerization reaction was carried out. At this time, the internal temperature rose to a maximum of 64°C. Next, after the styrene was completely consumed, the internal temperature of the reaction vessel was lowered to 50°C, and an additional 56.0 kg of styrene was added, and a polymerization reaction was carried out. At this time, the internal temperature rose to a maximum of 76°C. Next, after the styrene was completely consumed, the internal temperature of the reaction vessel was lowered to 50°C, and 32.0 kg of butadiene was added, and a polymerization reaction was carried out. At this time, the internal temperature rose to a maximum of 77°C. Next, after the butadiene was completely consumed, 8.0 kg of styrene was added, and a polymerization reaction was carried out. Thereafter, the active polymerization species were deactivated with water, and a polymerization liquid containing a block copolymer was obtained. The obtained polymerization liquid was devolatilized and granulated in an extruder, to obtain a block copolymer having a polystyrene block-polybutadiene block-polystyrene block.

[0132] The weight-average molecular weight and molecular weight distribution of the obtained block copolymer were measured by the following method, and the weight-average molecular weight was 124,000 and the molecular weight distribution was 1.37. In addition, a kneading test was carried out by the following method using a Labo Plastomill. The minimum torque (T ｍｉｎ ) is 5 Nm, and the maximum value of the torque (T ｍａｘ ) was 10 Nm, and the torque value (T ３０ ) was 9 Nm.

[0133] <Measurement of Weight-Average Molecular Weight and Molecular Weight Distribution> The weight-average molecular weight and molecular weight distribution were measured by GPC measurement under the following conditions: Apparatus: HLC-8220GPC (manufactured by Tosoh Corporation) Column: Four Shodex GPCKF-404 (manufactured by Showa Denko K.K.) connected in series Temperature: 40°C Detection: UV-visible spectroscopy (254 nm) Solvent: Tetrahydrofuran Concentration: 2% by mass Calibration curve: Prepared using standard polystyrene (manufactured by VARIAN).

[0134] <Kneading test> (i) Measuring device Device: Labo Plastomill 4C150 heat kneading tester (manufactured by Toyo Seiki) Blade shape: Roller mixer R60 (ii) Measuring conditions Sample amount: 48 g Rotation speed: 100 rpm Kneading temperature: 250°C Kneading time: 30 minutes

[0135] Fig. 1 shows the results of the heat-kneading test of the block copolymer of Example 1. In Fig. 1, the horizontal axis represents time (minutes) and the vertical axis represents torque (Nm).

[0136] Next, the block copolymer of Example 1 was subjected to structural analysis by the following method. As a result, the content of styrene units was 83 mass% based on the total mass of the block copolymer, and the proportion of 1,2-bonds in the butadiene units was 76%.

[0137] <Structural Analysis of Block Copolymer> The content of vinyl aromatic monomer units in the block copolymer and the microstructure of the conjugated diene monomer units (proportions of 1,2-bonds and 3,4-bonds in the conjugated diene monomer units) were calculated from the results of nuclear magnetic resonance (NMR) measurements under the following conditions. Observation nuclei: １ H Observation frequency: 500.13 MHz Pulse waiting time: 3.0 seconds Number of accumulations: 64 Solvent: deuterated chloroform (CDCl ３ )

[0138] From the above results, the above T ｍｉｎ From the above T ３０ It was confirmed that the block copolymer of Example 1, which has a large value, contains a large amount of highly reactive 1,2-bonds as conjugated diene monomer units.

[0139] Example 2 Under a nitrogen atmosphere, 408 kg of cyclohexane, 311 g of N,N,N',N'-tetramethylethylenediamine (TMEDA), and 48.6 g of sodium tert-amylate (NaOAm) were placed in a reaction vessel. Next, 742 mL of an n-butyllithium / cyclohexane solution (concentration: 10% by mass) was added as a polymerization initiator, and the internal temperature was maintained at 30°C.

[0140] Next, while the reaction vessel was cooled with water, 50 kg of styrene was added to the reaction vessel, and a polymerization reaction was carried out. At this time, the internal temperature rose to a maximum of 55°C. Next, after the styrene was completely consumed, the internal temperature of the reaction vessel was lowered to 40°C, and 21.4 kg of isoprene was added, and a polymerization reaction was carried out. At this time, the internal temperature rose to a maximum of 48°C. Thereafter, the reaction solution was removed from the reaction vessel, and a small amount of methanol was added to terminate the polymerization reaction. Next, the reaction solution was poured into methanol, and the precipitate was collected, thereby obtaining a block copolymer having a polystyrene block-polyisoprene block.

[0141] The weight-average molecular weight and molecular weight distribution of the obtained block copolymer were measured and a kneading test was carried out in the same manner as in Example 1. As a result, the weight-average molecular weight was 125,000 and the molecular weight distribution was 1.15. In addition, the minimum torque (T ｍｉｎ) is 3 Nm, and the maximum value of the torque (T ｍａｘ ) was 7 Nm, and the torque value (T ３０ ) was 4 Nm.

[0142] Next, the block copolymer of Example 2 was subjected to structural analysis in the same manner as in Example 1. As a result, the content of styrene units was 74 mass% based on the total mass of the block copolymer, and the proportions of 1,2-bonds and 3,4-bonds in the isoprene units were 91%.

[0143] From the above results, the above T ｍｉｎ From the above T ３０ It was confirmed that the block copolymer of Example 2, which has a large value, contains many highly reactive 1,2-bonds and 3,4-bonds as conjugated diene monomer units.

[0144] Comparative Example 1: Under a nitrogen atmosphere, 467 kg of cyclohexane was added to a reaction vessel, followed by the addition of 1,470 mL of an n-butyllithium / cyclohexane solution (concentration: 10% by mass) as a polymerization initiator, and the internal temperature was maintained at 30°C.

[0145] Next, while the reaction vessel was water-cooled, 75.2 kg of styrene was added to the reaction vessel, and a polymerization reaction was carried out. At this time, the internal temperature rose to a maximum of 58°C. Next, the internal temperature of the reaction vessel was allowed to drop to 50°C, and an additional 75.2 kg of styrene was added, and a polymerization reaction was carried out. At this time, the internal temperature rose to 78°C. Next, after the styrene was completely consumed, the internal temperature of the reaction vessel was allowed to drop to 50°C, and 39.6 kg of butadiene was added, and a polymerization reaction was carried out. At this time, the internal temperature rose to 78°C. Next, after the butadiene was completely consumed, 10.0 kg of styrene was added and a polymerization reaction was carried out when the internal temperature dropped to 60°C. Thereafter, the active polymerization species were deactivated with water, and a polymerization liquid containing a block copolymer was obtained. The obtained polymerization liquid was devolatilized and granulated in an extruder, and a block copolymer having a polystyrene block-polybutadiene block-polystyrene block was obtained.

[0146] The weight-average molecular weight and molecular weight distribution of the obtained block copolymer were measured and a kneading test was carried out in the same manner as in Example 1. As a result, the weight-average molecular weight was 168,000 and the molecular weight distribution was 1.09. In addition, the minimum torque (T ｍｉｎ ) is 12 Nm, and the maximum value of the torque (T ｍａｘ ) was 18 Nm, and the torque value (T ３０ ) was 8 Nm.

[0147] Fig. 2 is a diagram showing the results of the heat-kneading test of the block copolymer of Comparative Example 1. In Fig. 2, the horizontal axis represents time (minutes) and the vertical axis represents torque (Nm).

[0148] Next, the block copolymer of Comparative Example 1 was subjected to structural analysis in the same manner as in Example 1. As a result, the content of styrene units was 80 mass% based on the total mass of the block copolymer, and the proportion of 1,2-bonds in the butadiene units was 10%.

[0149] From the above results, the above T ｍｉｎ From the above T ３０ It was confirmed that the block copolymer of Comparative Example 1, which had a small value, contained a large amount of 1,4-bonds, which have poor reactivity, as conjugated diene monomer units.

[0150] Comparative Example 2: Under a nitrogen atmosphere, 408 kg of cyclohexane was placed in a reaction vessel, followed by the addition of 742 mL of an n-butyllithium / cyclohexane solution (concentration: 10% by mass) as a polymerization initiator, and the internal temperature was maintained at 30°C.

[0151] Next, 50 kg of styrene was added to the reaction vessel, and the internal temperature of the reaction vessel was raised to 60°C to carry out the reaction. Next, after the styrene was completely consumed, the internal temperature of the reaction vessel was allowed to drop to 40°C, and then 21.4 kg of isoprene was added, and the internal temperature was raised to 60°C to carry out the reaction. Thereafter, the polymerization liquid was removed, and a small amount of methanol was added to terminate the polymerization reaction, thereby obtaining a polymerization liquid containing a block copolymer. The obtained polymerization liquid was poured into methanol, and the precipitate was collected to obtain a block copolymer having a polystyrene block-polyisoprene block.

[0152] The weight-average molecular weight and molecular weight distribution of the obtained block copolymer were measured and a kneading test was carried out in the same manner as in Example 1. As a result, the weight-average molecular weight was 287,000 and the molecular weight distribution was 1.30. In addition, the minimum torque (T ｍｉｎ ) is 2 Nm, and the maximum value of the torque (T ｍａｘ ) was 13 Nm, and the torque value (T ３０ ) was 1 Nm.

[0153] Next, the block copolymer of Comparative Example 2 was subjected to structural analysis in the same manner as in Example 1. As a result, the content of styrene units was 75 mass% based on the total mass of the block copolymer, and the proportions of 1,2-bonds and 3,4-bonds in the isoprene units were 9.8%.

[0154] From the above results, the above T ｍｉｎ From the above T ３０ It was confirmed that the block copolymer of Comparative Example 2, which had a small value, contained a large amount of 1,4-bonds, which have poor reactivity, as conjugated diene monomer units.

[0155] The block copolymer according to the present embodiment is a novel block copolymer that is highly reactive and easily chemically modified, and therefore can be molded into resin pellets, films, sheets, plates, etc. and used for various applications.

Claims

1. A block copolymer comprising a block A containing vinyl aromatic monomer units and a block B containing conjugated diene monomer units, wherein in a kneading test at 250°C using a Labo Plastomill, the torque value 30 minutes after the start of kneading is greater than the minimum torque value 1 to 10 minutes after the start of kneading.

2. The block copolymer according to claim 1, wherein the content of the vinyl aromatic monomer units in the block copolymer is 50% by mass or more and 95% by mass or less based on the total mass of the block copolymer.

3. The block copolymer according to claim 1, wherein the content of the vinyl aromatic monomer units in the block A is 70% by mass or more based on the total amount of the block A, and the content of the conjugated diene monomer units in the block B is 70% by mass or more based on the total amount of the block B.

4. The block copolymer according to claim 1, wherein the vinyl aromatic monomer units are monomer units derived from an aromatic vinyl compound selected from the group consisting of styrene, α-methylstyrene, and p-methylstyrene, and the conjugated diene monomer units are monomer units derived from a conjugated diene selected from the group consisting of 1,3-butadiene and isoprene.

5. A resin composition comprising the block copolymer according to any one of claims 1 to 4 and at least one member selected from the group consisting of a radical initiator, a thermoplastic resin, and an elastomer.

6. Resin pellets containing the block copolymer according to any one of claims 1 to 4.

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