JPS5950245B2 - Copolymer manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a copolymer suitable as a reinforcing agent for natural rubber and synthetic rubber. In the presence of an initiator formed by mixing a tertiary alkoxide, a conjugated diene and a vinyl aromatic compound are mixed at a specific composition,
Rubber reinforcing agent with excellent transparency and improved surface texture, hardness, tensile strength, abrasion resistance, compression set, and bending resistance when rolled out by polymerizing to have a specific structure. The present invention relates to a method for producing a random block copolymer of a conjugated diene and a vinyl aromatic compound, which is suitable for.

Conventionally, styrene-butadiene copolymer rubber containing about 50% by weight or more of bound styrene obtained by emulsion polymerization, so-called high styrene rubber, has been produced using natural rubber or styrene-butadiene containing about 25% by weight of bound styrene. When blended with rubber, it has a remarkable reinforcing effect, and exhibits high hardness and abrasion resistance, so it has been used in applications such as shoe soles, rubber rolls, and floor tiles.

However, these conventional emulsion polymerized high styrene rubbers have several drawbacks.

In other words, emulsion polymerized high styrene rubber undergoes intermolecular crosslinking and branching during the polymerization process, and because it is a high styrene content rubber, it is hard at room temperature.
When this is put on an open roll and mixed with other raw material rubbers, fillers, etc., the operability is extremely poor.

In addition, emulsion polymerized high styrene rubber is affected by emulsifiers and other additives during polymerization, or because many emulsion polymerized high styrene rubbers are non-uniform mixtures of high styrene resin and low styrene rubber. However, it was not possible to obtain a transparent rubber vulcanized product because the raw rubber became opaque.

Furthermore, the physical properties of the vulcanizate, bending resistance, and low-temperature properties are extremely poor. Attempts to overcome the drawbacks of such emulsion polymerized high styrene rubber have been studied so far in high styrene rubber produced by solution polymerization.

In particular, JP-A-52-78290 discloses that a lithium-based catalyst is used as an initiator, (hapolybutadiene or a butadiene-styrene random copolymer with a bound styrene content of 40% by weight or less, and (2) a bound styrene content). is 50-95
A copolymer in which % by weight of a butadiene-styrene random copolymer is bonded within the molecular chain, or a branched butadiene-styrene random copolymer obtained by treating the above copolymer with a polyfunctional treatment agent is disclosed. ing.

The solution-polymerized high-styrene rubber mentioned above has excellent surface texture and flow characteristics of the compound, and also has excellent compression set and bending resistance of the vulcanized product, improving various properties of conventional emulsion-polymerized high-styrene rubber. It is something.

However, in general, the most important properties required of high styrene rubber, considering its purpose and application, are good separation texture with a mixing roll or engraving roll in terms of processing, and high hardness in terms of physical properties. High styrene rubber has high strength and excellent bending resistance, compression set, abrasion resistance, and rebound elasticity.Furthermore, if the raw rubber has excellent transparency, it becomes possible to formulate a transparent product, and the uses of high styrene rubber. However, the above-mentioned high styrene rubber is still insufficient in these properties. Therefore, the present inventors conducted various studies to further improve the high styrene rubber disclosed in JP-A-52-78290, taking into account the important properties required of high styrene rubber. To the end,
A random block copolymer obtained by polymerizing a conjugated diene and a vinyl aromatic compound to have a specific structure with a specific composition is compared with the high styrene rubber of JP-A-52-78290. As a result, the present inventors discovered that the important properties of high styrene rubber, such as hardness, tensile strength, compression set, and bending resistance, can be further improved, leading to the completion of the present invention.

That is, the present invention is an A-B type random block copolymer having random blocks A and B composed of a conjugated diene and a vinyl aromatic compound, wherein the vinyl aromatic compound content in the copolymer is 35 to 90%. Weight%, viscosity (
ML5+4,100℃'y/) {30 to 120, the difference in vinyl aromatic compound content between random blocks B and A is 45
In the production method of A-B type random block copolymer having a concentration of % by weight or more, 1) a mixture of an organolithium compound and an alkali metal tertiary alkoxide is used as a polymerization initiator ~ 2) a) First of all. conjugated diene monomer, or 40
A conjugated diene polymer or a conjugated diene is produced by polymerizing 10 to 50 parts by weight of a monomer mixture of a conjugated diene and a vinyl aromatic compound containing up to % by weight of a vinyl aromatic compound and substantially completing the polymerization. -Vinyl aromatic compound random copolymer (these are referred to as random block A)
and then polymerizing 90 to 50 parts by weight of a monomer mixture of a conjugated diene and a vinyl aromatic compound containing 50 to 95% by weight of a vinyl aromatic compound to substantially complete the polymerization, Conjugated diene-vinyl aromatic compound random copolymer (these are referred to as random block B)
or b) first forming a random block B and then additionally forming a random block A, and during polymerization, 3) the block vinyl aromatic compound forms an A-B type random If it is formed at the end of the entire proc copolymer chain, the proc vinyl aromatic compound content is 100 parts by weight of the total copolymer.
5 parts by weight or less, and if the block vinyl aromatic compound content is formed in a region other than the terminal end of the entire A-B type random block copolymer chain, the block vinyl aromatic compound content should be 30 parts by weight or less. This is a method for producing an A-B type random block copolymer, which is characterized in that the ratio of the organolithium compound and the alkali metal tertiary alkoxide is adjusted so that the ratio of the organolithium compound to the alkali metal tertiary alkoxide is equal to or less than 1%.

The manufacturing method of the present invention differs from the manufacturing method of JP-A-52-78290 in the following three points.

1) The entire A-B type random block copolymer was
The composition and structure are limited so that when expressed as parts by weight, random block A with a low content of vinyl aromatic compounds is 10 to 50 parts by weight, and random block B with a high content of vinyl aromatic compounds is 90 to 50 parts by weight. What I did.

2) Use a mixture of an organolithium compound and an alkali metal tertiary alkoxide as a polymerization initiator.

An excellent copolymer can be obtained by combining the use of this initiator with the above-mentioned compositional and structural limitations.

3) Even though Random Blocks A and B are each random copolymers, the permissible amounts of block vinyl aromatic compounds may vary depending on the position along the entire A-B block copolymer chain. make it clear that the
so that the tolerance is limited depending on each position,
Adjusting the ratio of organolithium compound and alkali metal tertiary alkoxide.

As described above, the specific copolymer achieved for the first time by the method of the present invention has the following characteristics compared to conventional copolymers.

1) Compared to emulsion polymerized high styrene rubber, it has excellent transparency, roll separation texture and flow characteristics in terms of processing, and physical properties such as hardness, tensile strength, compression set, and abrasion resistance. , excellent bending resistance.

2) Compared with the solution polymerized high styrene rubber produced by the method of JP-A-52-78290, the vulcanizate is particularly excellent in hardness, tensile strength, compression set, and bending resistance.

As already mentioned, these properties are all important properties in view of the purpose and application of general high styrene rubber, and the present invention is of great significance.

The present invention will be explained in detail below.

The conjugated dienes used in the present invention include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, and 1,3-butadiene.
Examples include pentadiene and 1,3-hexadiene, with 1,3-butadiene being particularly preferred.

These may be used alone or as a mixture of two or more. Furthermore, examples of the vinyl aromatic compound used in the present invention include styrene, O-methylstyrene, P-methylstyrene, P-Tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene,
Examples include vinylanthracene, and styrene is particularly preferred.

These may be used alone or as a mixture of two or more. The vinyl aromatic compound content of the A-B type random block copolymer obtained by the method of the present invention is 35 to 90.
% by weight, preferably 50-70% by weight. If it is less than 35% by weight, the hardness is too low to be used as a reinforcing agent for various rubbers, and if it exceeds 90% by weight, the compression set and bending resistance of the vulcanizate will change significantly.

Furthermore, the Mooney viscosity (ML, f4lOO℃) of the A-B type random block copolymer obtained by the method of the present invention is
, using a large rotor, heating 5 molecules at 100°C, and the Mooney viscosity after 4 minutes of rotation) must be in the range of 30-120.

If it is less than 30, the tensile strength of the vulcanizate decreases;
If this occurs, not only will processability such as the ability to wrap around open rolls deteriorate, but also the mixability with other rubbers and fillers will deteriorate.

The random block A of the present invention can be obtained by polymerizing a conjugated diene monomer or a monomer mixture of a conjugated diene and a vinyl aromatic daughter compound having a vinyl aromatic compound content of 40% by weight or more. A monomer mixture of a conjugated diene and a vinyl aromatic compound preferably has a vinyl aromatic compound content of 5 to 35% by weight.

When the vinyl aromatic compound content exceeds 40% by weight, the hardness, compression set, bending resistance, etc. of the finally obtained A-B type random block copolymer generally decrease. Also,
Random block B has a vinyl aromatic compound content of 50~
It is obtained by polymerizing a monomer mixture of 95% by weight, preferably 70 to 90% by weight, of a vinyl aromatic compound and a conjugated diene.

If the vinyl aromatic compound content is less than 50% by weight, the hardness of the final vulcanizate of the A-B type random block copolymer will be too low, the effect as a reinforcing material will be insufficient, and 95% by weight. %, the compression set becomes low, which is undesirable. In the A-B type random block copolymer obtained by the method of the present invention, random blocks A and B contained in the copolymer must be linked by a molecular chain.

This is extremely important; for example, a mere blend of Random Block A and Random Block B would result in extremely poor mill shrinkage or roll separation, which is undesirable. In this case, the A-B type of the A-B type random block copolymer does not mean the polymerization order of random block A and random block B; instead, random block A is polymerized first, This method includes both a method in which random block B is then polymerized, and a method in which random block B is first polymerized and then random block A is polymerized. In the present invention, the monomers are mixed so that the difference in vinyl aromatic compound content between random block B (!I and A) of the finally obtained copolymer is 45% by weight or more, preferably 50% by weight or more. The composition must be adjusted and polymerized.

If the difference in vinyl aromatic compound content is less than 45% by weight, the hardness and tensile strength of the finally obtained copolymer will deteriorate.
In the present invention, when the entire A-B type random block copolymer finally obtained is 100 parts by weight, the random block A is 0 to 50 parts by weight, preferably 20 to 50 parts by weight.
40 parts by weight, 90 to 50 parts by weight of random block B,
It is necessary to adjust the monomer composition during polymerization so that it is preferably 60 to 80 parts by weight, and this is an important requirement for achieving the object of the present invention.

If random block A is less than 10 parts by weight and random block B is 90 parts by weight, compression set and bending resistance will deteriorate; When B is less than 50 parts by weight, hardness and tensile strength deteriorate. In this way, random block A (5
One of the important requirements for distinguishing the present invention from the invention of JP-A-52-78290 is that B is polymerized to have a specific composition and groove structure; The following may be considered.

That is, in the A-B type random block copolymer obtained by the present invention, when viewed morphologically, random block A is a polymer with a low vinyl aromatic compound content, and random block B is a polymer with a low vinyl aromatic compound content. Since the polymer has a high vinyl aromatic compound content and the difference in the vinyl aromatic compound content is 45% by weight or more, random procs A and B are non-uniformly dispersed and are mutually incompatible. On the other hand,
By limiting the composition and purchase of random blocks A and B as described above, it is possible to create a non-uniform structure in which random block A forms a discontinuous phase or continuous phase, and random block B forms a continuous phase. It is thought that it is a copolymer with a structure. In the invention of JP-A-52-78290, as shown in Example 2, it is true that polymer block A with a low styrene content and polymer block B with a high styrene content are mutually incompatible. Same as the invention, but with 60 parts by weight of polymer block A and 40 parts by weight of polymer block B.
It is considered that the case of parts by weight, that is, the case where polymer block B is a discontinuous phase, is also included, and this point is different from the method of the present invention.

Another important requirement in the method for producing the A-B type random block copolymer of the present invention is to use a catalyst made of a mixture of an organolithium compound and an alkali metal tertiary alkoxide as a polymerization initiator. .

Alkali metal tertiary alkoxides are already known as randomizers in the copolymerization of butadiene and styrene.
For example, J. Polymer. Sci, A-1, v01
．． 7,449 (1960)], but the present inventors
It has been discovered that this catalyst is particularly effective in producing a conjugated diene-vinyl aromatic compound copolymer having a limited composition/purchase as in the present invention, and is disclosed in JP-A No. 5
2-78290, such as tetrahydrofuran, cannot produce the effects of the present invention.

Examples of the alkali metal tertiary alkoxide include alkali metal tertiary alkoxides other than lithium such as sodium and potassium, potassium tert-butoxide, sodium tert-amyl oxide, rubidium tert-
-butoxide, cesium tert-butoxide, potassium isopentyl oxide, and the like.

On the other hand, examples of organic lithium compounds include methyllithium,
Ethyllithium, propyllithium, n-butyllithium, Sec-butyllithium, hexyllithium, 2-
Examples include monolithium compounds such as ethylhexyllithium and phenyllithium, and dilithium compounds such as pentamethyllithium, 1,5-dilithionaphthalene, and 1,2-dilithiostilbene.

The amount of the organolithium compound and alkali metal tertiary alkoxide to be used varies depending on the monomer composition, polymerization temperature, etc., but the amount of the organolithium compound to be used is usually 10% of the monomer.
The molar ratio of organolithium compound/alkali metal alkoxide is usually 5.
/1 to 500/1.

In the force method of the present invention, the molar ratio of the organolithium compound and the alkali metal alkoxide has a great influence on the properties of the A-B type random block copolymer that is finally obtained, as well as the composition of the monomer. By selecting an appropriate molar ratio, it is possible to obtain a well-balanced product with excellent physical properties such as roll processability, roll separation skin, hardness, tensile strength, compression set, and abrasion resistance. It will be done.

That is, the molar ratio between the organolithium compound and the alkali metal alkoxide is yet another important requirement of the present invention. This has the function of adjusting the AB type random block copolymer obtained by the present invention to contain a specific block vinyl aromatic compound. Although the A-B type random block copolymer obtained by the present invention is composed of random copolymer blocks A and B each having a different vinyl aromatic compound content, it contains some block vinyl aromatic compounds. .

The lower the content of procvinyl aromatic compounds is, the more desirable it is, but the permissible content is that procvinyl aromatic compounds
-Type B Random Block Copolymer The relationship between the permissible content of the block vinyl aromatic compound and its position is extremely important in achieving the present invention. It has a meaning. When the block vinyl aromatic compound is polymerized so as to be formed at the end along the entire A-B type random block copolymer chain finally obtained (this is called the terminal block type), The molar ratio of the organolithium compound and the alkali metal alkoxide must be adjusted so that the content of the block vinyl aromatic compound is 15 parts by weight or less in 100 parts by weight of the total copolymer.

In addition, when the block vinyl aromatic compound is polymerized so as to be formed along the entire A-B type random block copolymer chain other than at the terminal end (this is called a center block type). ), the molar ratio of the organolithium compound and the alkali metal alkoxide must be adjusted so that the content of the blocked vinyl aromatic compound is not less than 30% by weight.

When polymerized to contain a blocked vinyl aromatic compound outside the above range, roll processability, hardness, compression set, and abrasion resistance deteriorate, making it impossible to obtain a well-balanced product.

The molar ratio of organolithium compound/alkali metal alkoxide is usually 5/1 to 500/1, but generally speaking, as this ratio increases, the content of protoxvinyl aromatic compounds in the resulting copolymer increases. However, as this ratio decreases, it decreases.

In the present invention, random block A and random block B were polymerized and bonded in any order.

In addition to finally obtaining a linear A-B type random block copolymer, after polymerizing the linear copolymer,
Furthermore, it is also possible to obtain a branched copolymer by adding a polyfunctional processing agent. In more detail,
For example, after polymerizing a linear copolymer by the method described above, the copolymer solution contains a polyfunctional polymer containing at least three functional groups that can react with the lithium-carbon bond in the copolymer. It is manufactured by adding a processing agent and bonding the copolymer in a branched manner. As a polyfunctional processing agent,
Silicon tetrachloride, methyltrichlorosilane, halides such as carbon tetrachloride, diesters such as diethyl adipate, etc. [For example, JournalOfpOlym. Sc
i. Part A, vOl3, 93-103 (1965)
, British Patent No. 1223079, etc.) are used.

Furthermore, in the present invention, in addition to polymerizing random block A and random block B in any order to finally obtain a bonded linear AB type random block copolymer, A-B-A, B-A-B, A-B-A-
It is also possible to obtain linear random block copolymers such as Type B. The A-B type random block copolymer of a conjugated diene and a vinyl aromatic compound obtained by the present invention can be used alone or in combination with natural rubber or other synthetic rubber, blended with various compounding agents, etc. After mixing and vulcanization, the product is put to practical use. In addition to such uses, the A-B type random block copolymer of the present invention can be blended with other plastics as a raw rubber without vulcanization to make sheets, films, and injection molded products. It can also be used for plastic applications such as. The present invention will now be described with reference to Examples, but these Examples are not intended to limit the present invention.

Example A-B type random block copolymer of Example Λ was obtained using the method and charge ratio shown in Example 1.

Under a nitrogen atmosphere, 1,3-butadiene and styrene were added in a weight ratio of 1 to 700 parts by weight of toluene in a polymerization vessel with a volume of 101.
Charge 70 parts by weight of a 5:85 monomer mixture, then add 0.0041 parts by weight of potassium-tert-butoxide and n
A mixture of 0.07 parts by weight of -butyllithium (that is, a molar ratio of n-butyllithium/potassium-tert-butoxide of 30) was added, and the mixture was polymerized at 70'C for 3 hours to obtain random block B.

When the polymerization conversion rate of this polymerization solution was measured, it was found that the polymerization was substantially completed, and the styrene content in the produced polymer was 84.6% by weight, and the pro-styrene content was 12.6% by weight.
It was hot. Thereafter, 30 parts by weight of a monomer mixture of 1,3-butadiene and styrene in a weight ratio of 82:18 was added and polymerization was continued for 4 hours to additionally form random block A, random block B, and then random block B. An AB type random block copolymer polymerized in the order of block A was obtained. Add 1 part by weight of 2,6-di-Ter to this copolymer solution.
t-Butyl-4-methylphenol was added as a stabilizer, and then the solvent was removed by heating to isolate the copolymer.

The thus obtained copolymer of Example A had a styrene content of 64.7% by weight and a viscosity of 64.7% by weight (ML5+4,
100°C) was 61.

The styrene content of random block A is calculated from this styrene content and the styrene content of the first random block B, and is approximately 18% by weight. In addition, the protuxtyrene content of the final copolymer was 8.6% by weight, and this figure was calculated from the protuxtyrene content of the initial random block B. Since the formula is 12.6% by weight x 0.78.8% by weight, the random block A has a block styrene content of almost O, and therefore Example A is a center block type. I understand that. Next, for comparison, a butadiene-styrene copolymer (Comparative Example B) described in JP-A-52-78290 was obtained using the method and charge ratio shown below.

First, in the polymerization vessel used earlier, add 700 parts by weight of toluene to a heavy blue ratio of 1,3-butadiene and styrene of 15:85.
Then, 2.1 parts by weight of tetrahydrofuran and 0.07 parts by weight of n-butyllithium were added, and polymerization was carried out at 70°C for 3 hours to obtain polymer block B. The polymerization conversion rate of this polymerization solution was substantially completed, and the styrene content in the produced polymer was 84.7% by weight, and the protoxtyrene content was 13.8% by weight. After that, the weight ratio of 1,3-butadiene and styrene is 8
30 parts by weight of a 2:18 monomer mixture was added and the polymerization was continued for 4 hours to additionally form polymer block A, polymer block B, and then polymer block A to obtain a copolymer. . To this copolymer solution, 1 part by weight of 2,6-di-tert-butyl-4-methylphenol was added as a stabilizer, and then the solvent was removed by heating to isolate the copolymer.

The thus obtained copolymer of Comparative Example B had a styrene content of 64.8% by weight and a pro-styrene content of 9.

5% by weight, and the viscosity (ML, +4,100°C
) was 60.

When the styrene content and the amount of pro-styrene of polymer pro-styrene constituting this copolymer were calculated in the same manner as in Example 1, the styrene content was approximately 18% by weight, and the pro-styrene content was approximately O. . Therefore, it can be seen that Comparative Example B is a center block type. In addition to the above Example A and Comparative Example B, a commercially available high styrene rubber, Nipole 2057SS, was prepared as Comparative Example C. Using these three types of high styrene combs, the formulations shown in Table 1-1 were mixed on an 8-inch open roll, and the processability and physical properties of the resulting formulations were measured. 1-
Shown in 2. The amount of proxtyrene was measured as follows.

Dissolve 2 parts by weight of the copolymer in 100 parts by weight of carbon tetrachloride,
Add 50 parts by weight of di-tert-butyl hydroperoxide, and further add 0.0 parts of osmium tetraoxide.
02 parts by weight of the copolymer was added and heated at 100°C for 30 minutes to completely cleave the double bonds in the copolymer. Protuxtyrene is obtained by precipitating the solution thus obtained in a large amount of methanol. Moreover, the styrene content was calculated from the absorption based on styrene at 262 mμ by ultraviolet absorption spectroscopy.

The following can be seen from Table 1-2.

Compared to Comparative Example C, Example A of the present invention has excellent transparency of the polymer itself, excellent roll separation texture during processing, high hardness of the vulcanizate, and high tensile strength and compression set. , wear resistance,
It can be seen that the bending resistance etc. are excellent.

Furthermore, it can be seen that Example A of the present invention has higher hardness and is superior in tensile strength, compression set, bending resistance, etc., as compared to Comparative Example B.

Example 2 In the same manner as in Example A, random block B was polymerized and then random block A was polymerized to obtain various center block type A-B random block copolymers. .

The difference in vinyl aromatic compound content between random block B and random block A was 50% by weight. The polymerization conditions for these copolymers, the characteristics and physical properties of the obtained copolymers are shown in Tables 2-1, 2-2 and 2-3.

As is clear from Table 2-3, in Comparative Example D, Example E
, F, and G are inferior in compression set and bending resistance, while Comparative Example H is inferior in hardness and tensile strength.

Example 3 In the same manner as in Example A, various center block types A with different block rates were prepared by changing the ratio of n-butyllithium and potassium-tert-butoxide.
-B type copolymer and terminal block type A-B type copolymer were obtained.

The polymerization conditions and basic properties of the center block type A-B type copolymer are shown in Table 3-1, and the polymerization conditions and basic properties of the end block type A-B type copolymer are shown in Table 3-2.

Further, Table 3-3 shows the physical properties of both. As shown in Table 3-3, in the center block type copolymer,
Compared with Examples A1 and H, Comparative Example 1 is inferior in roll workability, hardness, compression set, and abrasion resistance.

Claims (1)

[Scope of Claims] 1. A-B type random block copolymer having random blocks A and B consisting of a conjugated diene and a vinyl aromatic compound, wherein the content of the vinyl aromatic compound in the copolymer is 35 to 90. Weight%, Mooney viscosity (ML_5_+_
4100℃) is 30 to 120, random blocks B and A
In the method for producing an A-B type random block copolymer in which the difference in vinyl aromatic compound content is 45% by weight or more, 1) a mixture of an organolithium compound and an alkali metal tertiary alkoxide is used as a polymerization initiator; use, 2) a)
First, 10 to 50 parts by weight of a conjugated diene monomer or a monomer mixture of a conjugated diene and a vinyl aromatic compound containing 40% by weight or less of a vinyl aromatic compound are polymerized,
Forming a conjugated diene polymer or a conjugated diene-vinyl aromatic compound random copolymer (these are referred to as random blocks A) by substantially completing the polymerization,
A monomer mixture of a conjugated diene and a vinyl aromatic compound containing 50 to 95% by weight of a vinyl aromatic compound is then added.
a step of additionally forming a conjugated diene-vinyl aromatic compound random copolymer (these are referred to as random blocks B) by polymerizing 50 parts by weight and substantially completing the polymerization; or b) First of all, random block B
and then additionally forming a random block A, and during polymerization, 3) when the block vinyl aromatic compound is formed at the end of the entire A-B type random block copolymer chain, The content of the block vinyl aromatic compound is 15 parts by weight or less in 100 parts by weight of the total copolymer, and the block vinyl aromatic compound is
When the A-B type random block copolymer is formed at a location other than the terminal end of the entire chain, an organic lithium compound and an alkali metal tertiary alkoxide are added, respectively, so that the block vinyl aromatic compound content is 30 parts by weight or less. A method for producing an A-B random block copolymer, which comprises adjusting the ratio. 2. The manufacturing method according to claim 1, wherein the conjugated diene is 1,3-butadiene. 3. The manufacturing method according to claim 1, wherein the vinyl aromatic compound is styrene. 4. The manufacturing method according to claim 1, wherein the vinyl aromatic compound content of the A-B random block copolymer is 50 to 70% by weight. 5. Claim 1, wherein the monomer mixture for polymerizing random block A is 20 to 40 parts by weight, and the monomer mixture for polymerizing random block B is 80 to 60 parts by weight. manufacturing method. 6 Difference between the vinyl aromatic compound content (wt%) in the monomer mixture for polymerizing random block B and the vinyl aromatic compound content (wt%) in the monomer mixture for polymerizing random block A is 50% by weight or more, the manufacturing method according to claim 1. 7 The vinyl aromatic compound content in the monomer mixture for polymerizing random block A is 15 to 35% by weight, and the vinyl aromatic compound content in the monomer mixture for polymerizing random block B is 70% by weight. The manufacturing method according to claim 6, wherein the content is 90% by weight.