A synthetic method of side chain uniformly distributed SEBS

Abstract

This invention discloses a method for synthesizing SEBS with uniformly distributed side chains. The method employs anionic polymerization to obtain SBS solution through a three-stage polymerization process, followed by hydrogenation to obtain SEBS. The improvement lies in the following: during the second-stage polymerization reaction, 80-90% of the theoretical molar amount of structure modifier is added at once, with the remaining 10-20% added according to the temperature rise. The addition of the structure modifier begins when the temperature of the second-stage polymerization reaction starts to rise and ends when the temperature reaches its maximum. This method not only achieves a more uniform distribution of SEBS side chains but also allows for higher polymerization temperatures and fully utilizes the heat of polymerization to meet the initial temperature requirements of the hydrogenation reaction, thus contributing to energy conservation, reduced consumption, and improved production efficiency.

Description

Technical Field

[0001] This invention relates to a method for synthesizing SEBS, and more particularly to a method for synthesizing SEBS with uniformly distributed side chains, belonging to the field of styrene-based thermoplastic elastomer synthesis technology. Background Technology

[0002] SEBS is a linear triblock copolymer with polystyrene as the terminal block and hydrogenated polybutadiene as the intermediate elastic block. Because it does not contain unsaturated double bonds, this type of polymer has good light aging resistance and stability. It can be blended with filler oils, polypropylene, additives and inorganic fillers and is widely used for tool handle coating, shoe materials, headphone wires, wires and cables, medical infusion equipment, etc.

[0003] The structure of polymer materials determines their properties. The main influencing factor on the structure of SEBS block copolymers is the content and distribution of side chain structures. Theoretical calculations and experimental data show that 20 methylene sequences can produce polyethylene-like crystals at room temperature. Crystallization reduces the volume of amorphous regions in the polymer, increasing the tensile strength of the elastomer; therefore, the content of side chain structures cannot be too low. When the content of 1,2-structured polybutadiene in SBS reaches 50%, crystallization is essentially suppressed after hydrogenation, but the glass transition temperature (Tg) increases significantly, and resilience decreases. Therefore, to prevent the methylene sequences in SEBS from growing to a sufficiently crystallized degree while ensuring sufficient E content in the EB segment to maintain elasticity, the content of 1,2-structured polybutadiene must be controlled and have good uniformity. Experiments show that when the 1,2-structure in polybutadiene has good uniformity and a content of around 38%, a good balance can be achieved between the increase in crystallization and the rise in Tg, resulting in ideal performance, such as that of Kraton's best-selling SEBS product G1651.

[0004] The main influencing factors on the 1,2 structure content in polybutadiene segments are the amount of structure modifier added and the polymerization temperature of butadiene. Numerous studies have shown that the higher the amount of structure modifier added, the higher the 1,2 structure content in the polybutadiene segments; conversely, with the same amount of structure modifier added, the higher the polymerization temperature, the lower the 1,2 structure content in the polybutadiene segments. Furthermore, as the polymerization temperature increases, the 1,2-addition rate of butadiene gradually decreases, while the corresponding 1,4-addition rate of butadiene gradually increases. The 1,2-structure content in the polybutadiene segments of the synthesized SBS exhibits a gradually decreasing distribution. The hydrogenated SEBS molecular chain contains a certain amount of slightly longer polyethylene segments, which have no adsorption capacity or compatibility with mineral oils (such as white oil, naphthenic oil, paraffin oil, etc.). When this SEBS is filled with mineral oil to make products, the mineral oil in the products will slowly migrate out of the products over time, and at the same time, the oil will separate out of the products, causing a significant decline in product performance. Currently, most domestic manufacturers use this control method, resulting in a large gap in product quality compared with foreign competitors. Some manufacturers have used forced cooling to narrow the control temperature of butadiene addition, changing it from 60℃~90℃ to 63℃~73℃, in order to improve the uniformity of the 1,2 structure content in the butadiene chain. However, the difference between the two at low and high temperatures is still 3%~5%, which does not achieve the expected effect. Moreover, the temperature of the polymer solution obtained by this method will be lower than 70℃, while the starting temperature of the subsequent hydrogenation reaction is higher than 70℃. This means that the solution needs to be heated by a heat source, which is not conducive to energy saving. If the polymerization temperature is further narrowed, the only way is to extend the feeding time by 30min~60min, which will seriously affect the production efficiency.

[0005] Chinese patent CN109206568A discloses a butadiene block containing uniformly distributed 1,2-structure butadiene segments, its hydride SEBS, and methods for preparation and application. The SBS preparation process involves a first-stage polymerization of styrene with an initiator under the action of an activator. The second-stage polymerization involves dissolving a 1,2-structure modifier in butadiene and uniformly adding it to the polymerization reactor over 16-18 minutes. After addition, the reaction continues for another 8-12 minutes. This method considers that an increase in butadiene polymerization temperature will cause a decrease in the 1,2-structure content. However, in the second-stage addition of the mixture of 1,2-structure modifier and butadiene, the initial addition of the modifier is too low, resulting in a much lower initial 1,2-structure content in the butadiene segments than designed. As more mixture is added, the structure content tends to normalize. After the mixture is fully added, there is still a 5-10°C temperature rise, which also causes a decrease in structure content, making it difficult to achieve a truly ideal random distribution. Chinese patent CN100497406C adopts a method of adding the main regulator and the auxiliary regulator in batches. The main regulator is added in the first stage, and the auxiliary regulator is added continuously after the butadiene in the second stage to compensate for the decrease in the content of 1,2 structure segments caused by the temperature rise. The auxiliary regulator is added at 15 minutes, and the reaction time in the second stage is 35 minutes. This method does not correspond the addition rate of the auxiliary regulator to the temperature rise. There is a situation where the reaction temperature has not reached the high temperature after the auxiliary regulator is added. In this case, the amount of structure regulator in the reaction system remains unchanged, but the polymerization temperature is constantly rising, which may cause the content of 1,2 structure segments of polybutadiene to decrease and the distribution to be uneven. Summary of the Invention

[0006] To address the technical problem of existing technologies failing to achieve a uniform distribution of 1,2-structure content in polybutadiene segments during SEBS base adhesive synthesis, resulting in uneven distribution of SEBS side chains, the present invention aims to provide a method for synthesizing SEBS with uniform side chain distribution. This method utilizes the characteristic that the regulating ability of structure modifiers decreases with increasing polymerization temperature. By adding structure modifiers in batches or continuously according to the variation law of polymerization temperature, a more uniform distribution of SEBS side chains can be achieved. This method can eliminate the influence of the continuous decrease in the 1,2-structure content of polybutadiene due to the increase in polymerization temperature during the polymerization process. At the same time, it allows the polymerization temperature to rise to higher temperatures and makes full use of the heat of polymerization to meet the starting temperature requirements of the hydrogenation reaction, which is beneficial for energy saving, consumption reduction, and improved production efficiency.

[0007] To achieve the above technical objectives, this invention provides a method for synthesizing SEBS with uniformly distributed side chains. This method involves adding styrene monomer, an activator, and an initiator to an anionic polymerization solution system to initiate a first-stage polymerization reaction. After the first-stage polymerization is completed, a structure modifier is added, and simultaneously, butadiene monomer is continuously and uniformly added to initiate a second-stage polymerization reaction. After the second-stage polymerization is completed, styrene monomer is added to initiate a third-stage polymerization reaction. After the third-stage polymerization is completed, an SBS solution is obtained. The SBS solution is then subjected to a hydrogenation reaction to obtain SEBS with uniformly distributed side chains. The improvement lies in the method of adding the structure modifier: 80-90% of the theoretical molar amount of the structure modifier is added at once, with the remaining 10-20% added according to the temperature rise. The addition of the structure modifier begins when the temperature of the second-stage polymerization reaction begins to rise and ends when the temperature reaches its highest point.

[0008] This invention is based on extensive experimental research on the homopolymerization process of butadiene. Studies have shown that the homopolymerization of butadiene is an exothermic reaction, and the activity of structure modifiers regulating the 1,2-polymerization of butadiene is highly sensitive to polymerization temperature. Generally, the higher the temperature, the lower the activity. The optimal dosage of structure modifier at different polymerization temperatures is determined by analyzing its activity, thereby ensuring a stable 1,2-polymerization ratio throughout the butadiene block polymerization process. This results in a uniform distribution of the 1,2-polymerization units of polybutadiene within the butadiene blocks. In this invention, during the butadiene polymerization process, the dosage of structure modifier is controlled at the initial polymerization temperature to correspond to the designed 1,2-polymer content. Subsequently, a certain amount of structure modifier is added intermittently or continuously based on temperature rise to compensate for the decrease in 1,2-polymerization activity caused by the increase in polymerization temperature, thus maintaining a relatively uniform level of polybutadiene segments.

[0009] As a preferred embodiment, the remaining 10-20% of the theoretical molar amount of structure modifier is divided into N units according to the temperature rise during the two-stage polymerization reaction, where N = M / (t1 - t2), in mol / ℃; where M is the remaining 10-20% of the theoretical molar amount, in mol; t1 is the highest temperature during the two-stage polymerization reaction, in ℃; and t2 is the initial temperature during the two-stage polymerization reaction (i.e., the temperature of the polymerization system before the polymerization temperature begins to rise), in ℃. The remaining 10-20% of the theoretical molar amount of structure modifier is added once for every 1-3℃ increase in temperature, with each addition being (1-3)N. Alternatively, the remaining 10-20% of the theoretical molar amount of structure modifier is continuously and uniformly added within the time range from the start of the temperature rise during the two-stage polymerization reaction to the time range when the temperature reaches its highest point. The amount of structure modifier must be strictly determined according to the relationship between temperature change and structure modifier activity during butadiene homopolymerization. If too much or too little structure modifier is added, it will be difficult to stabilize the activity of the structure modifier in the polymerization system, resulting in uneven distribution of 1,2 structural units.

[0010] The theoretical molar amount of the structure modifier of the present invention is determined based on the molecular weight of the designed SBS polymer and the 1,2 structure content of the butadiene block contained therein. If the molecular weight of the designed SBS polymer and the 1,2 structure ratio of the butadiene block are determined, then the molar amount of the corresponding specific structure modifier is determined. This correspondence is well known in the industry.

[0011] As a preferred embodiment, the structure modifier includes at least one selected from ethylene glycol dimethyl ether, bis(tetrahydrofurfuryl)propane, ethylene glycol diethyl ether, tetrahydrofurfuryl ethyl ether, tetramethylethylenediamine, and hexamethylphosphoric triamine. These structure modifiers are commonly used in the prior art to regulate the 1,2-polymerization activity of butadiene. These preferred structure modifiers all exhibit a trend where the modulating activity decreases with increasing temperature.

[0012] As a preferred embodiment, the butadiene monomer is added within 40–80 minutes. If the butadiene monomer is added rapidly all at once, the polymerization system will heat up too quickly, causing the reaction to polymerize rapidly, forming a large amount of gel and resulting in reactor blockage.

[0013] As a preferred embodiment, the initial temperature of the two-stage polymerization reaction is controlled at 62-65°C, the maximum temperature is controlled at 70-85°C, and the total reaction time is controlled at 30-80 minutes.

[0014] As a preferred embodiment, the activator comprises tetrahydrofuran.

[0015] As a preferred embodiment, the initiator includes at least one selected from n-butyllithium, sec-butyllithium, and isobutyllithium. These are all conventional anionic polymerization initiators, with n-butyllithium being the most preferred.

[0016] As a preferred embodiment, the temperature of the polymerization reaction is 50℃~70℃ and the time is 20~50min.

[0017] As a preferred embodiment, the hydrogenation reaction is carried out under the following conditions: a titanoceramsite-benzoate composite catalytic system is used, with an initial temperature of 72–80°C, a hydrogen pressure of 1.2–1.4 MPa, and a reaction time of 2–3 hours. This type of catalyst has relatively low cost and good reactivity, achieving a degree of hydrogenation of over 97% in a short time.

[0018] As a preferred embodiment, the titanium-benzoate composite catalytic system includes at least one main catalyst selected from bis(cyclopentadienyl)titanium chloride, bis(cyclopentadienyl)titanium dibromide, bis(cyclopentadienyl)titanium diiodide, bis(cyclopentadienyl)titanium difluoride, bis(cyclopentadienyl)dicarbonyltitanium, bis(cyclopentadienyl)dimethyltitanium, bis(cyclopentadienyl)diethyltitanium, and bis(cyclopentadienyl)dibutyltitanium, and at least one co-catalyst selected from C1-C5 alkyl benzoate and C1-C5 alkyl phthalate.

[0019] As a preferred embodiment, the molar ratio of the main catalyst to the co-catalyst is 2–5:1. The hydrogenation catalyst is measured as 0.01%–0.05% of the total mass of the polymerization monomers (including butadiene and styrene) by the main catalyst.

[0020] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0021] 1) The technical solution of the present invention can achieve a more uniform distribution of SEBS side chains.

[0022] 2) The technical solution of the present invention allows the polymerization temperature to rise to a higher temperature and makes full use of the polymerization heat to meet the starting temperature requirements of the hydrogenation reaction, which is conducive to energy saving, consumption reduction and production efficiency improvement. Attached Figure Description

[0023] Figure 1 The image shows the 1H NMR spectrum of the SEBS base adhesive prepared in Example 1. Detailed Implementation

[0024] The following embodiments are intended to further illustrate the content of the present invention and do not constitute a limitation on the scope of protection of the claims or the implementation methods of the present invention.

[0025] It should be noted that: in the following examples, gel permeation chromatography (mobile phase: tetrahydrofuran) was used to test the number average molecular weight (Mn) of the gel solution; 1,2 structure content of polybutadiene segments was analyzed by 1H-NMR. The attached figure is a typical 1H NMR spectrum of the basic SEBS polymerized gel. The peaks with shifts of 5.3-5.6 ppm are hydrogen peaks on the double bonds of the 1,4 structure of polybutadiene and single hydrogen peaks on the double bonds of the 1,2 structure side chains, with peak area A. The peaks with shifts around 4.96 ppm are two hydrogen peaks on the double bonds of the 1,2 structure side chains of polybutadiene, with peak area B. The formula for calculating the polybutadiene 1,2 structure content is: 2B / (2A+B)*100%. Before performing the analysis of the polybutadiene 1,2 structure content by sampling, the gel solution needs to be dried to remove unreacted butadiene and solvent.

[0026] The following example illustrates the synthesis of SEBS-YH-503 (a commercial product) using conventional methods, used to determine the relationship between temperature and the activity of the structure modifier. The specific operation is the same as in Example 1, except that the structure modifier is added only once during the two-stage butadiene polymerization reaction. NMR samples were taken at different temperatures, dried, and analyzed. The data are shown in Table 1.

[0027] Table 1. NMR analysis data of samples taken during butadiene polymerization in the synthesis of SEBS-YH-503.

[0028]

[0029] The data in Table 1 shows that, according to conventional control methods, the polymerization temperature during butadiene polymerization is controlled between 61 and 75℃, and the 1,2 structure content of polybutadiene segments ranges from 35.2% to 42.2%, with a 7% difference between the low and high values, indicating a very uneven distribution of 1,2 structure content on the polybutadiene molecular chain segments. If a structure modifier is added before the second-stage reaction to control the required 1,2 structure content at the initial temperature, and then a certain amount of structure modifier is added intermittently or continuously according to the temperature rise, the decrease in the 1,2 structure content of butadiene segments caused by the increase in polymerization temperature can theoretically maintain a more uniform level of polybutadiene segments. Taking Table 1 as an example: at 61℃, the 1,2 structure content is 42.2%, and the temperature is still rising. Therefore, if a certain amount of structure modifier is added at 61℃, then at 63℃, the 1,2 structure content should be closer to 42.2%, possibly reaching 42%.

[0030] Example 1

[0031] SEBS with a number-average molecular weight (Mn) of 6 ± 10,000 was synthesized using an anionic polymerization method known in the industry. The design required that the content of polybutadiene segments 1,2 was 38%. Theoretically, the concentration of the structure modifier tetramethylethylenediamine in the solvent should be 93.5 mg / Kg. In a polymerization reactor purged with a dry protective gas (e.g., nitrogen), 40 tons of cyclohexane, 12 kg of tetrahydrofuran, and 66 mol of butyllithium were added. The reactor temperature was maintained at 65°C and the pressure at 0.3 MPa. First, 600 kg of styrene monomer was added for a first-stage reaction, which lasted 30 min. After the reaction, the polymerization temperature was lowered to 63°C, and 3.2 kg of tetramethylethylenediamine was added. Then, 2800 kg of butadiene monomer was continuously added until the temperature rose significantly. Tetramethylethylenediamine was added in batches: 0.06 kg of tetramethylethylenediamine was added at 65°C, and another 0.06 kg of tetramethylethylenediamine was added at 67°C, i.e., 0.06 kg of tetramethylethylenediamine was added for every 2°C increase, until the reaction reached a high temperature of 81°C (the time from the significant temperature rise to the high temperature was 35 min). After entering the second-stage reaction, samples were taken every 2 minutes for NMR analysis. After reaching the high temperature, the reaction was allowed to proceed to the third-stage reaction, where 600 kg of styrene monomer was added and the reaction lasted 30 min. The prepared polymer solution was poured into a hydrogenation reactor, and 1000g of dicyclopentadiene titanium dichloride and 273g of methyl benzoate were added. The initial reaction temperature was controlled at 75℃, and hydrogen gas was introduced to make the pressure inside the reactor 1.2MPa. The reaction time was 3h to obtain the SEBS solution.

[0032] Example 2

[0033] Unlike Example 1, this is a two-stage reaction. All other process controls remain the same, except the structure modifier is changed from being added in batches to being added continuously. In the second stage, the polymerization temperature is lowered to 63°C, 3.2 kg of tetramethylethylenediamine is added, and then butadiene monomer is continuously added until the temperature rises significantly. Tetramethylethylenediamine is then continuously added at a rate of 0.925 kg / h until the reaction reaches its high temperature.

[0034] Comparative Example 1

[0035] Unlike Example 1, the second-stage reaction was carried out, while all other process controls remained the same, except that the structure modifier was added all at once. That is, after the first-stage reaction was completed, the polymerization temperature was lowered to 63°C, and 3.74 kg of tetramethylethylenediamine was added until the reaction reached a high temperature of 73°C. After entering the second-stage reaction, samples were taken every 2 minutes for NMR analysis. After reaching the high temperature, the reaction was allowed to proceed for 5 minutes before entering the third-stage reaction.

[0036] Example 3

[0037] SEBS with a number-average molecular weight (Mn) of 10 ± 10,000 was synthesized using an internationally recognized anionic polymerization method. The design required a polybutadiene segment 1,2 structure content of 38%, and theoretically, the amount of structure modifier ethylene glycol diethyl ether in the solvent should be 70 mg / kg. In a polymerization reactor purged with a dry protective gas (e.g., nitrogen), 40 tons of cyclohexane, 12 kg of tetrahydrofuran, and 40 mol of butyllithium were added. The reactor temperature was maintained at 65°C and the pressure at 0.3 MPa. First, 600 kg of styrene monomer was added for a first-stage reaction lasting 30 min. After the reaction, the polymerization temperature was lowered to 63°C, and 2.4 kg of ethylene glycol diethyl ether was added. Then, 2800 kg of butadiene monomer was continuously added until the temperature rose significantly. Finally, ethylene glycol diethyl ether was added in batches. Ethyl ether was added at 65°C with 0.045 kg of ethylene glycol diethyl ether, and then at 67°C with another 0.045 kg of ethylene glycol diethyl ether, i.e., 0.045 kg of ethylene glycol diethyl ether was added for every 2°C increase in temperature, until the reaction reached a high temperature of approximately 81°C (the time from a significant temperature rise to the high temperature was 35 min). After entering the second stage of reaction, samples were taken every 2 minutes for NMR analysis. After reaching the high temperature, the reaction was allowed to proceed to the third stage of reaction after 5 min. In the third stage of reaction, 600 kg of styrene monomer was added, and the reaction was allowed to proceed for 30 min. The resulting polymer solution was poured into a hydrogenation reactor, and 1000 g of dicyclopentadiene titanium dibromide and 300 g of ethyl benzoate were added. The initial reaction temperature was controlled at 73°C, and hydrogen gas was introduced to maintain the pressure inside the reactor at 1.3 MPa. The reaction time was 2.5 h to obtain the SEBS solution.

[0038] Example 4

[0039] The process differs from Example 3 in that it involves a two-stage reaction. All other process controls remain the same, except that the structure modifier is added continuously instead of in batches. In the second stage, the polymerization temperature is lowered to 63°C, 2.4 kg of ethylene glycol diethyl ether is added, and then butadiene monomer is continuously added until the temperature rises significantly. Tetrahydrofurfuryl ethyl ether is then continuously added at a rate of 0.694 kg / h until the reaction reaches its high temperature.

[0040] Comparative Example 2

[0041] Unlike Example 1, the second-stage reaction is the same, except that the structure modifier is added all at once. Specifically, after the first-stage reaction, the polymerization temperature is lowered to 63°C, and 2.8 kg of ethylene glycol diethyl ether is added until the reaction reaches a high temperature of 73°C. After entering the second-stage reaction, samples are taken every 2 minutes for NMR analysis. After reaching the high temperature, the reaction is held for 5 minutes before entering the third-stage reaction.

[0042] Example 5

[0043] SEBS with a number-average molecular weight (Mn) of 20 ± 10,000 was synthesized using an anionic polymerization method known in the industry. The design required the content of polybutadiene segments 1,2 to be 38%, and theoretically, the amount of hexamethylphosphoric triamine, a structure modifier, in the solvent should be 47 mg / Kg. In a polymerization reactor purged with a dry protective gas (e.g., nitrogen), 40 tons of cyclohexane, 12 kg of tetrahydrofuran, and 40 mol of butyllithium were added. The reactor temperature was maintained at 65°C and the pressure at 0.3 MPa. First, 600 kg of styrene monomer was added for a first-stage reaction, which lasted 30 min. After the reaction, the polymerization temperature was lowered to 63°C, and 1.6 kg of hexamethylphosphoric triamine was added. Then, 2800 kg of butadiene monomer was continuously added until the temperature rose significantly. Hexamethylphosphoric triamine was added in batches: 0.03 kg of hexamethylphosphoric triamine was added at 65°C, and another 0.03 kg at 67°C, i.e., 0.03 kg of hexamethylphosphoric triamine was added for every 2°C increase, until the reaction reached a high temperature of approximately 81°C (the time from the significant temperature rise to the high temperature was 35 min). After entering the second-stage reaction, samples were taken every 2 minutes for NMR analysis. After reaching the high temperature, the reaction was allowed to proceed to the third-stage reaction after a 5-minute pause. In the third-stage reaction, 600 kg of styrene monomer was added, and the reaction lasted 30 min. The prepared polymer solution was poured into a hydrogenation reactor, and 1000g of dicyclopentadiene titanium dibromide and 273g of methyl benzoate were added. The initial reaction temperature was controlled at 73℃, and hydrogen gas was introduced to make the pressure inside the reactor 1.4MPa. The reaction time was 2h to obtain the SEBS solution.

[0044] Example 6

[0045] The process differs from Example 5 in that it involves a two-stage reaction. All other process controls remain the same, except that the structure modifier is added continuously instead of in batches. In the second stage, the polymerization temperature is lowered to 63°C, 1.6 kg of hexamethylphosphoric triamine is added, and then butadiene monomer is continuously added until the temperature rises significantly. Hexamethylphosphoric triamine is then continuously added at a rate of 0.462 kg / h until the reaction reaches its high temperature.

[0046] Comparative Example 3

[0047] Unlike Example 5, the second-stage reaction was carried out, while all other process controls remained the same, except that the structure modifier was added all at once. That is, after the first-stage reaction was completed, the polymerization temperature was lowered to 63°C, and 1.87 kg of hexamethylphosphoric triamine was added until the reaction reached a high temperature of 73°C. After entering the second-stage reaction, samples were taken every 2 minutes for NMR analysis. After reaching the high temperature, the reaction was allowed to proceed for 5 minutes before entering the third-stage reaction.

[0048] Table 2. Test results after adopting the new process.

[0049]

[0050]

[0051] As shown in Table 2, although the content of polybutadiene 1,2 structure in the final product can be controlled at around 38% using conventional methods (i.e., Comparative Examples 1, 2, and 3), the NMR analysis results of process sampling show that the distribution of polybutadiene 1,2 structure in the molecular chain is very uneven, with the difference between the maximum and minimum values ​​exceeding 6%. However, regardless of whether the structure modifier is added in batches or continuously, the distribution of 1,2 structure content in the polybutadiene chain segments is more uniform compared to before the process adjustment, achieving the expected results. In addition, within the designed number-average molecular weight range of 5 to 200,000, by adjusting the one-time addition and subsequent replenishment of the structure modifier, the content of polybutadiene 1,2 structure can be controlled at around 38%, and the polybutadiene 1,2 structure in the molecular chain shows a relatively uniform distribution, with the difference between the maximum and minimum values ​​within 1%.

Claims

1. A method for synthesizing SEBS with uniformly distributed side chains, comprising: adding styrene monomer, activator, and initiator to an anionic polymerization solution system to initiate and carry out a first-stage polymerization reaction; after the first-stage polymerization reaction is completed, adding a structure modifier and simultaneously and continuously and uniformly adding butadiene monomer to carry out a second-stage polymerization reaction; after the second-stage polymerization reaction is completed, adding styrene monomer to carry out a third-stage polymerization reaction; after the third-stage polymerization reaction is completed, an SBS adhesive is obtained, wherein the SBS adhesive is subjected to a hydrogenation reaction to obtain SEBS; characterized in that: The structure modifier is added as follows: 80-90% of the theoretical molar amount of the structure modifier is added at once, based on a 100% measurement of the theoretical molar amount; then the remaining 10-20% of the theoretical molar amount of the structure modifier is added according to the temperature rise. The addition of the structure modifier begins when the temperature of the second-stage polymerization reaction begins to rise, and ends when the temperature reaches its highest point. The remaining 10-20% of the theoretical molar amount of structure modifier is divided into N units according to the temperature rise during the two-stage polymerization reaction, where N = M / (t1 - t2), in mol / ℃; where M is the remaining 10-20% of the theoretical molar amount, in mol; t1 is the highest temperature during the two-stage polymerization reaction, in ℃; and t2 is the initial temperature during the two-stage polymerization reaction, in ℃. The remaining 10-20% of the theoretical molar amount of structure modifier is added once for every 1-3℃ increase in temperature, with each addition being (1-3)N. or, The remaining 10-20% of the theoretical molar amount of structure modifier is continuously and uniformly added during the time range from the start of the two-stage polymerization reaction to the time range when the temperature rises to its highest point.

2. The method for synthesizing SEBS with uniformly distributed side chains according to claim 1, characterized in that: The structure modifier includes at least one of ethylene glycol dimethyl ether, bis(tetrahydrofurfuryl)propane, ethylene glycol diethyl ether, tetrahydrofurfuryl ethyl ether, tetramethylethylenediamine, and hexamethylphosphoric triamine.

3. The method for synthesizing SEBS with uniformly distributed side chains according to claim 1, characterized in that: The total time for the continuous and uniform addition of the butadiene monomer is 40-60 minutes.

4. A method for synthesizing SEBS with uniformly distributed side chains according to claim 1 or 3, characterized in that: The initial temperature of the two-stage polymerization reaction is controlled at 62~65℃, the maximum temperature is 70~85℃, and the total reaction time is in the range of 30~80 min.

5. The method for synthesizing SEBS with uniformly distributed side chains according to claim 1, characterized in that: The activator includes tetrahydrofuran; The initiator includes at least one of n-butyllithium, sec-butyllithium, and isobutyllithium.

6. The method for synthesizing SEBS with uniformly distributed side chains according to claim 1 or 5, characterized in that: The polymerization reaction is carried out at a temperature of 50℃~70℃ for 20~50 minutes.

7. A method for synthesizing SEBS with uniformly distributed side chains according to claim 1 or 5, characterized in that: The conditions for the hydrogenation reaction are as follows: a titanium-benzoate composite catalytic system is used, the initial temperature is 72~80℃, the hydrogen pressure is 1.2~1.4MPa, and the time is 2h~3h.

8. The method for synthesizing SEBS with uniformly distributed side chains according to claim 7, characterized in that: The titanium-benzoate composite catalytic system includes at least one main catalyst selected from bis(cyclopentadienyl)titanium chloride, bis(cyclopentadienyl)titanium dibromide, bis(cyclopentadienyl)titanium diiodide, bis(cyclopentadienyl)titanium difluoride, bis(cyclopentadienyl)dicarbonyltitanium, bis(cyclopentadienyl)dimethyltitanium, bis(cyclopentadienyl)diethyltitanium, and bis(cyclopentadienyl)dibutyltitanium, and at least one co-catalyst selected from C1-C5 alkyl benzoate and C1-C5 alkyl phthalate.

9. The method for synthesizing SEBS with uniformly distributed side chains according to claim 8, characterized in that: The molar ratio of the main catalyst to the co-catalyst is 2~5:1.

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