Conjugated diene-vinyl aromatic hydrocarbon copolymer and method for producing the same

Abstract

To achieve better overall performance among wet grip performance, wear resistance, and low rolling resistance, improved conjugated diene-vinyl aromatic hydrocarbon copolymers and methods for producing said copolymers are provided. [Solution] The copolymer of the present invention comprises a homopolymer segment composed of a conjugated diene and a copolymer segment composed of a conjugated diene and a vinyl aromatic hydrocarbon, bonded to the homopolymer segment. The copolymer has a first glass transition temperature of -10°C to -50°C and a second glass transition temperature of -45°C to -85°C, the first glass transition temperature being higher than the second glass transition temperature, and the content of vinyl aromatic hydrocarbon microblocks is 1.0% to 10.0% of the total content of vinyl aromatic hydrocarbons in the copolymer, where vinyl aromatic hydrocarbon microblocks refer to those having at least four consecutive vinyl aromatic hydrocarbon units.

Description

[[Technical Field]]

[0001] Cross-Reference to Related Applications This application is a non-provisional application claiming the priority and benefit of U.S. Provisional Patent Application No. 63 / 760,958, entitled "CONJUGATED DIENE-VINYL AROMATIC HYDROCARBON BLOCK COPOLYMER AND METHOD THEOF", filed on February 20, 2025, which is incorporated herein by reference.

[0002] Technical Field of the Invention The present invention relates to a conjugated diene-vinyl aromatic hydrocarbon copolymer, in particular to a conjugated diene-vinyl aromatic hydrocarbon copolymer comprising a homopolymer segment and a copolymer segment, and a method for producing the same. [[Background Art]]

[0003] Background of the Present Disclosure Solution polymerized styrene-butadiene rubber (SSBR) is a copolymer rubber material formed by polymerizing styrene and butadiene in an organic solvent. Compared with emulsion polymerized SBR, SSBR typically provides better control over molecular structure, such as adjustment of styrene content and butadiene microstructure. This allows further adjustment of the glass transition temperature (Tg) and viscoelastic behavior of the material, thereby improving dynamic mechanical properties. Based on these properties, SSBR is commonly used in tire-related applications, particularly in the formulation design of tire tread rubbers. [[Summary of the Invention]]

[0004] In recent years, the development of high-performance tire tread rubbers has required the simultaneous optimization of low rolling resistance (to reduce energy loss and improve fuel efficiency) and wet grip (to improve braking performance and handling safety on wet roads) while maintaining good wear resistance. Prior art such as U.S. Patent No. 4,843,120, Japanese Patent Application Publication No. 2008-231197A, and Chinese Patent No. 103958600B disclose SSBRs claiming various advantages. However, in practical applications, several issues still need to be addressed. [Problems that the invention aims to solve]

[0005] Problems that the invention aims to solve

[0006] The problems to be solved by the present invention are to simultaneously achieve the following requirements for tire tread rubber materials in order to meet the demands of energy saving and driving safety: (i) improving wet grip performance to improve braking performance and handling stability on wet and slippery road surfaces, (ii) reducing rolling resistance to reduce energy loss and improve fuel efficiency, and (iii) maintaining sufficient wear resistance to extend life. However, existing conjugated diene-vinyl aromatic hydrocarbon copolymers often have difficulty simultaneously meeting the above multiple performance requirements from the viewpoint of compounding or structural design, resulting in an insufficient balance of performance. Therefore, the present invention provides an improved conjugated diene-vinyl aromatic hydrocarbon copolymer to achieve better overall performance among wet grip performance, wear resistance, and low rolling resistance. [Means for solving the problem]

[0007] Means for solving the problem

[0008] In one embodiment, to improve the wet grip performance of tire tread rubber, the inventors of this application have carefully designed a conjugated diene-vinyl aromatic hydrocarbon copolymer having a double glass transition temperature (double Tg). The copolymer contains vinyl aromatic hydrocarbon microblocks, and such a specific structural arrangement significantly improves the wet grip performance. In another embodiment, the inventors of this application have further set and controlled the proportion (SB%) of vinyl aromatic hydrocarbon microblocks within the range of 1.0% to 10.0%. As a result, the copolymer can maintain good rolling resistance performance while improving wet grip performance. In yet another embodiment, for a conjugated diene-vinyl aromatic hydrocarbon copolymer having modified ends, the modified ends are directly bonded to the copolymer segment rather than the homopolymer segment, which is more advantageous for forming the double Tg property.

[0009] The present invention further includes other embodiments and various models for solving other problems. In combination with the above embodiments, such other embodiments are disclosed in detail in the embodiments. [Modes for carrying out the invention]

[0010] Detailed description of exemplary embodiments To ensure a full understanding of the present invention and its claims, preferred embodiments of the invention are illustrated below. To avoid obscuring the scope of the invention, known components, related materials, and related processing techniques are omitted in the following description.

[0011] Analysis method

[0012] Vinyl aromatic hydrocarbon microblock content: As used in this invention, vinyl aromatic hydrocarbon microblocks are defined as microblocks having at least four consecutive vinyl aromatic hydrocarbon units. The analytical method is illustrated using styrene: 20 mg of the sample is dissolved in 2.0 mL of CDCl3 and analyzed using a Bruker 500 MHz NMR spectrometer.1 Perform an H NMR scan; 1 In the 1H NMR spectrum, if we define the integral value at 6.2–7.0 ppm as a, and the value obtained by subtracting the integral value of CDCl3 from the integral value at 7.0–7.8 ppm as b, then the styrene microblock content based on the total styrene content of the copolymer to which the sample belongs is calculated as [a / (a+b)] × 100%.

[0013] Rolling Resistance (RR): The loss tangent tanδ at 60°C is used as an index to evaluate the rolling resistance (RR) of copolymer rubber compounds after they have been made into rubber (tread rubber). The test is performed using a TA Instruments ARES-G2 rheometer to measure the storage modulus G' and loss modulus G'' of the specimen under strain sweep conditions, and the tanδ value is calculated according to tanδ = G'' / G'. During scanning, the sample temperature is 60°C, the strain sweep range is 0.1% to 10%, and the tanδ value is taken at 5.0% strain.

[0014] Wet Grip (WG): The loss tangent tanδ at 0°C is used as an index to evaluate the wet grip performance (Wet Grip, WG) of copolymer rubber compounds after they have been made into rubber (tread rubber). The test is performed using a TA Instruments ARES-G2 rheometer to measure the storage modulus G' and loss modulus G'' of the test specimen under strain sweep conditions, and the tanδ value is calculated according to tanδ = G'' / G'. During scanning, the sample temperature is 0°C, the strain sweep range is 0.1% to 10%, and the tanδ value at 5.0% strain is used as an index to evaluate wet grip performance.

[0015] Abrasion test (DIN): Measurements are performed using the GT-7012-DN model in accordance with ASTM D5963.

[0016] Glass transition temperature (Tg, °C): Main method: Tg measurement is performed using dynamic mechanical analysis (DMA). A cut strip neat polymer sample is tested according to ASTM E1640, and the glass transition temperature is determined using a rheometer (TA Instruments, trade name "RSA-G2"). During the test, an air-cooling system (TA Instruments, trade name "ACS-3") is used, and the temperature is increased from -85°C at a rate of 2°C / min under conditions of flowing nitrogen gas at 50 mL / min, and the changes in storage modulus E' and loss modulus E'' are recorded. The peak temperature of the loss tangent tanδ (tanδ = E'' / E') is defined as Tg. Special notes: The embodiments and comparative examples of the present invention all measure the glass transition temperature by this method, and this method is preferred. However, if two glass transition temperatures are too close to be clearly distinguishable by this method, the following secondary method can be used.

[0017] Glass transition temperature (Tg, °C): Secondary method: Measurement is performed using differential scanning calorimetry (DSC) (Model Q200, TA Instruments) in reference to ASTM E1356. The specific test conditions are as follows: Under a nitrogen gas flow environment of 50 mL / min, the temperature is increased from -90 °C to 100 °C at a heating rate of 20 °C / min, and the heat flow curve is recorded. The glass transition temperature (Tg) is defined as the characteristic peak corresponding to the peak of the first derivative of the heat flow curve with respect to temperature. By analyzing the characteristic peak of the first derivative curve, the glass transition point with a relatively weak signal intensity in the original heat flow curve can be effectively identified, thereby determining the glass transition temperature of the material in a multiphase structure.

[0018] The content of bonded vinyl aromatic hydrocarbons and vinyl content of copolymers were measured using the relevant measurement method described in Chinese Patent CN103476815B. The NMR was a Bruker AV-500 model (500 MHz), the probe was a 5 mm dual probe with an automatic frequency tuning device, the NMR operating software was TOPSPIN, and the solvent used was deuterated chloroform / tetramethylsilane (CDCl3 / TMS).

[0019] Copolymers of conjugated dienes and vinyl aromatic hydrocarbons

[0020] The present invention provides a copolymer of a conjugated diene and a vinyl aromatic hydrocarbon, comprising a homopolymer segment composed of the conjugated diene and a copolymer segment of the conjugated diene and a vinyl aromatic hydrocarbon, wherein the copolymer segment is bonded to the homopolymer segment. The copolymer has two glass transition temperatures (Tg), a first glass transition temperature between -10°C and -50°C, and a second glass transition temperature between -45°C and -85°C, where the first glass transition temperature is higher than the second glass transition temperature, and the content of vinyl aromatic hydrocarbon microblocks in the copolymer is 1.0% to 10.0% of the total content of vinyl aromatic hydrocarbons in the copolymer. In a preferred embodiment, the first glass transition temperature is between -12°C and -40°C, and the second glass transition temperature is between -50°C and -60°C. In a preferred embodiment, the content of vinyl aromatic hydrocarbon microblocks in the copolymer is 1.0% to 8.0% of the total content of vinyl aromatic hydrocarbons in the copolymer. In a preferred embodiment, the content of conjugated dienes in the homopolymer segment is 60% by weight or more, preferably 60% to 90% by weight, and more preferably 65% ​​to 73% by weight, relative to the total content of the copolymer. In a preferred embodiment, the content of bonded vinyl aromatic hydrocarbons in the copolymer is 10% to 20% by weight, preferably 12% to 16% by weight. In a preferred embodiment, the vinyl content of the copolymer (based on the total content of conjugated dienes) is 30% to 40% by weight, preferably 31% to 36% by weight. In a preferred embodiment, the copolymer has no other glass transition temperatures in addition to the first and second glass transition temperatures described above. In a preferred embodiment, the copolymer further has modified ends, which are connected to the copolymer segment such that the copolymer segment is positioned between the homopolymer segment and the modified ends. In a preferred embodiment, the modified ends contain silicon. In a preferred embodiment, the copolymer is non-hydrogenated.

[0021] The conjugated diene monomers applicable to the present invention are conjugated dienes having 4 to 12 carbon atoms, and specific examples include 1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 1,3-heptadiene, 2-methyl-1,3-butadiene (isoprene), 2-methyl-1,3-pentadiene, 2-hexyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 2-phenyl-1,3-pentadiene, 2-p-tolyl-1,3-butadiene, 2-benzyl-1,3-butadiene, and 3-methyl-1 Examples include ,3-pentadiene, 3-methyl-1,3-hexadiene, 3-butyl-1,3-octadiene, 3-phenyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 1,4-diphenyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2,3-dimethyl-1,3-pentadiene, 2,3-dibenzyl-1,3-butadiene, 4,5-diethyl-1,3-octadiene, myrcene, and any combination thereof, with 1,3-butadiene being a preferred choice. In this specification, "butadiene" refers entirely to 1,3-butadiene.

[0022] Specific examples of vinyl aromatic hydrocarbon monomers applicable to the present invention include styrene, methylstyrene and all isomers thereof, ethylstyrene and all isomers thereof, tert-butylstyrene and all isomers thereof, dimethylstyrene and all isomers thereof, methoxystyrene and all isomers thereof, cyclohexylstyrene and all isomers thereof, vinylbiphenyl, 1-vinyl-5-hexylnaphthalene, vinylnaphthalene, vinylanthracene, 2,4-diisopropylstyrene, 5-tert-butyl-2-methylstyrene, divinylbenzene, trivinylbenzene, divinylnaphthalene, tert-butoxystyrene, 4-propylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl)styrene, N-4-vinylphenyl-N,N-dimethylamine, (4-vinylphenyl)dimethylaminoethyl ether, N,N-dimethylaminomethylstyrene, N,N-dimethylaminoethylstyrene, N,N-diethylaminomethylstyrene, N,N-diethylaminoethylstyrene, vinylxylene, vinylpyridine, diphenylethylene, 2,4,6-trimethylstyrene, α-methyl-2,6-dimethylstyrene, α-methyl-2,4-dimethylstyrene, β-methyl-2,6-dimethylstyrene, β-methyl-2,4-dimethylstyrene, indene, diphenylethylene containing a tertiary amino group such as 1-(4-N,N-dimethylaminophenyl)-1-phenylethylene, and any combination of the foregoing, with styrene being a preferred option.

[0023] As a modifier used for terminal modification applicable to the present invention, organosilane compounds are preferable. Preferred organosilane compounds include compounds represented by the following Formula 1:

[0024] Formula 1 JPEG2026139598000001.jpg2739

[0025] R 1 and R 2R3 is a C1-C12 alkyl, C6-C18 aromatic group, or allyl group; R4 is a C1-C12 alkyl or C6-C18 aromatic group; R4 is a C1-C12 alkoxy, C1-C12 alkyl, C6-C18 aromatic group, or allyl group; Y is a functional group containing O and / or N atoms and / or P atoms, preferably Y is an epoxyalkyl group, a tertiary amino group, a secondary or primary amine group, an ester group, an aldehyde group, a ketone group, an acrylic acid group, an acrylate group, an imidazoline group, a morpholine group, or any combination of the above. Preferred organosilane compounds are 4-{3-[dimethoxy(methyl)silyl]propyl}morpholine, 3-(trimethoxysilyl)-N,N-dimethylpropane-1-amine, or diethyl[2-(triethoxysilyl)ethyl]phosphonate.

[0026] Method for preparing conjugated diene-vinyl aromatic hydrocarbon copolymers

[0027] The copolymer of the present invention may be produced by various suitable methods. In a preferred embodiment, the production method of the present invention includes: (1) providing an initiator; (2) polymerizing by anionic polymerization using the initiator in the presence of a cyclic ether and a diether compound to form a homopolymer segment composed of a conjugated diene; and (3) after step (2) forming a copolymer segment composed of a conjugated diene and a vinyl aromatic hydrocarbon bonded to the homopolymer segment, wherein in step (3) the vinyl aromatic hydrocarbon and the conjugated diene are added simultaneously to the polymerization reactor, and the rate of addition of the vinyl aromatic hydrocarbon is different from the rate of addition of the conjugated diene. In a preferred embodiment, the above method further includes: (4) after step (3) forming a modified end bonded to the copolymer segment, wherein the copolymer segment is located between the homopolymer segment and the modified end.

[0028] Initiator

[0029] The term "anionic polymerization" refers to a polymerization method in which an initiator forms an activated carbon anion, and after the addition of a monomer, an addition polymerization reaction occurs between the monomer and the activated carbon anion to form a polymer having negatively charged molecular chain ends. In a preferred embodiment, the present invention uses an organoalkali metal as the initiator for anionic polymerization. In a preferred embodiment, the present invention uses a polyfunctional initiator as the initiator for anionic polymerization. In a preferred embodiment, the polyfunctional initiator is obtained by reacting a divinylarene compound with an organoalkali metal.

[0030] Preferred divinylarene compounds include compounds represented by the following formula (2).

[0031] Formula (2) JPEG2026139598000002.jpg2649

[0032] A and B are C n H 2n+1or an aromatic ring, where n is 0 to 5. A and B may be the same or different; Q is an aromatic ring. In the divinylarene compound, substituents A, B and / or Q may be aromatic rings containing substituted or unsubstituted monocyclic, polycyclic, or fused polycyclic rings, independently selected from the group consisting of substituted or unsubstituted benzene, naphthalene, anthracene, phenanthrene, fluorene, tetracene, pyrene, biphenyl, terphenyl, quaterphenyl, chrysene, triphenylene, perylene, indene, and any combination thereof or combination of fused rings. Preferably, the aromatic ring is benzene. Divinylarene compounds include, for example, m-divinylbenzene, p-divinylbenzene, 1,2-diisopropenylbenzene, 1,3-diisopropenylbenzene, 1,4-diisopropenylbenzene, 1,3-divinylnaphthalene, 1,8-divinylnaphthalene, 1,4-divinylnaphthalene, 1,5-divinylnaphthalene, 2,3-divinylnaphthalene, 2,7-divinylnaphthalene, 2,6-vinylnaphthalene, and 4,4'-divinylbiphenyl Divinylarene compounds can be independently selected from the group consisting of 4,3'-divinylbiphenyl, 4,2'-divinylbiphenyl, 3,2'-divinylbiphenyl, 3,3'-divinylbiphenyl, 2,2'-divinylbiphenyl, 2,4-divinylbiphenyl, 1,2-divinyl-3,4-dimethylbenzene, 1,3-divinyl-4,5,8-tributylnaphthalene, 2,2'-divinyl-4-ethyl-4'-propylbiphenyl, and any combination thereof. Preferably, the divinylarene compound is 1,3-diisopropenylbenzene (wherein used herein, "diisopropenylbenzene" refers to 1,3-diisopropenylbenzene).

[0033] Specific examples of organoalkali metals include methyllithium, ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, isobutyllithium, n-pentyllithium, n-hexyllithium, benzyllithium, phenyllithium, tolyllithium and all their isomers, as well as monoorganolithium compounds such as naphthyllithium and stilbenilithium. These polymerization initiators may be used alone or in combination of two or more, but lithium compounds are preferred. Preferably, the organolithium compound is n-butyllithium.

[0034] To adjust the vinyl content of the copolymer, it is preferable to add a polar modifier during the reaction to improve the solvent polarity. In specific examples, cyclic ether compounds and / or diether compounds may be added. The cyclic ether compound may be a monocyclic ether compound or a bicyclic ether compound. For example, monocyclic ether compounds can be independently selected from the group consisting of tetrahydrofuran, furan, tetrahydropyran, 2-methyltetrahydropyran, 3-methyltetrahydropyran, crown ethers (e.g., 12-crown-4-ether, 15-crown-5-ether, or 18-crown-6-ether), 1,4-dioxane, and any combination thereof. The bicyclic ether compound may be 2,2-bis(2-tetrahydrofuranyl)propane. The diether compound can be independently selected from the group consisting of diethyl ether, di-n-propyl ether, di-n-butyl ether, ethylene glycol dibutyl ether, ethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, methyl n-propyl ether, diisopropyl ether, tert-amyl ethyl ether, methyl tert-butyl ether, ethyl tert-butyl ether, and any combination thereof. Among these, tetrahydrofuran and ethylene glycol diethyl ether are preferred.

[0035] Formation of copolymer segments

[0036] In step (3), the distribution of vinyl aromatic hydrocarbon microblocks within the copolymer segment can be adjusted by controlling the difference in monomer addition rates. To achieve a balance between various properties of the rubber composition, such as DIN wear, rolling resistance (RR), and wet grip (WG), a preferred distribution of vinyl aromatic hydrocarbon microblocks is such that the content of vinyl aromatic hydrocarbon microblocks accounts for 1.0% to 10.0% of the total vinyl aromatic hydrocarbon content of the copolymer. Specifically, when forming the copolymer segment, vinyl aromatic hydrocarbons and conjugated dienes are added simultaneously to the polymerization reactor, and the addition rates of the vinyl aromatic hydrocarbons and the conjugated dienes are made to differ from each other. For example, in terms of mass flow rate, the addition rate of vinyl aromatic hydrocarbons may be controlled to 70 g / min, and the addition rate of conjugated dienes may be controlled to 11 to 18 g / min. As a result, the ratio of their addition rates (vinyl aromatic hydrocarbons / conjugated dienes) is controlled to 3.8 to 6.4, thereby achieving the above control of the vinyl aromatic hydrocarbon microblock distribution.

[0037] Applications of conjugated diene-vinyl aromatic hydrocarbon copolymers

[0038] The conjugated diene-vinyl aromatic hydrocarbon copolymer of the present invention may be mixed with other components to form a rubber composition. Specific examples of other components include natural rubber, other conjugated diene polymers different from the copolymer of the present invention, ethylene-propylene copolymer, ethylene-octene copolymer, and the like. Furthermore, the above rubber composition may further contain additives. Specific examples of additives include vulcanizing agents such as sulfur powder; vulcanizing accelerators such as sulfenamide-based vulcanizing accelerators and diphenylguanidine (DPG) secondary accelerators; vulcanizing activators such as stearic acid and zinc oxide; reinforcing agents such as silica and carbon black; fillers such as calcium carbonate and talc; silane coupling agents; drawstring oils; processing aids; antioxidants; and lubricants.

[0039] The rubber composition of the present invention can be compounded by kneading each component using a known kneader such as a roll mixer, Banbury mixer, or internal mixer. When compounding additives other than vulcanizing agents or vulcanization accelerators, fillers, silica, and / or other reinforcing agents, the compounding temperature is usually 50°C to 200°C, preferably 80°C to 150°C. When mixing with a vulcanizing agent or vulcanization accelerator, the compounding temperature is usually 100°C or lower, preferably room temperature to 90°C.

[0040] The conjugated diene-vinyl aromatic hydrocarbon copolymer and its rubber composition according to the present invention can be used in applications such as tires, shoe soles, flooring materials, and vibration damping materials, and is particularly suitable for tires. When applied to tire treads, it can reduce rolling resistance and improve wet skid performance, thereby improving handling stability and reliability on wet surfaces, creating a good balance between the wet grip, wear resistance, and rolling resistance of the tire, and further contributing to improved fuel efficiency.

[0041] Various examples of conjugated diene-vinyl aromatic hydrocarbon copolymers

[0042] Example 1: To a solution of 5525g of cyclohexane containing 8.3g of cyclic ether and 0.5g of a diether compound, 4.9mmol of n-butyllithium and 1g of diisopropenylbenzene were added and mixed, and the mixture was reacted at 50°C for 30 minutes. Then, 1,3-butadiene (65% by weight of the total copolymer) was added to carry out the first step of polymerization, and after reaching the highest temperature of the first step, the reaction was maintained at that temperature for 10 minutes. Next, the remaining butadiene and styrene (35% by weight in total of the total copolymer) were added to carry out the second step of polymerization. Here, the styrene microblock content was controlled by adjusting the ratio of the addition rates, with styrene and butadiene being added simultaneously but at different rates. After reaching the highest temperature of the second step, the reaction was continued for another 15 minutes. Then, 4.2g of 4-{3-[dimethoxy(methyl)silyl]propyl}morpholine was added, and the reaction was maintained at the same temperature for 20 minutes, and finally methanol was added to stop the reaction.

[0043] The preparation methods for Examples 2 to 7 can be carried out by referring to Example 1, except that in Example 5 only 4.9 mmol of n-butyllithium was added and diisopropenylbenzene was not added. The remaining different conditions are shown in Table 1.

[0044] Comparative Example 1: To a 5525g solution of cyclohexane containing 8.3g of cyclic ether and 0.5g of a diether compound, 4.9mmol of n-butyllithium and 1g of diisopropenylbenzene were added and mixed, and the mixture was reacted at 50°C for 30 minutes. Then, 1,3-butadiene and styrene (totaling 65% by weight of the total copolymer) were added to carry out the first step of polymerization. Styrene and butadiene were added simultaneously at different rates, and after reaching the highest temperature of the first step, the reaction was maintained at that temperature for 10 minutes. Next, the remaining butadiene (35% by weight of the total copolymer) was added to carry out the second step of polymerization, and after reaching the highest temperature of the second step, the reaction was continued for another 15 minutes. Then, 4.2g of 4-{3-[dimethoxy(methyl)silyl]propyl}morpholine was added, and the reaction was maintained at the same temperature for 20 minutes, and finally methanol was added to stop the reaction. The difference between Comparative Example 1 and the Example is that Comparative Example 1 first formed copolymer segments and then homopolymer segments, and the butadiene content of the homopolymer segments was 35% by weight based on the total copolymer.

[0045] The manufacturing method for Comparative Example 2 can be carried out by referring to Comparative Example 1, with the differences being shown in Table 1. The difference between Comparative Example 2 and the Examples is that Comparative Example 2 first formed the copolymer segment, and then the homopolymer segment.

[0046] Comparative Example 3: To a 5525g solution of cyclohexane containing 8.3g of cyclic ether and 0.5g of a diether compound, 4.9 mmol of n-butyllithium was added, and 1,3-butadiene (65% by weight of the total copolymer) was added to carry out the first step of polymerization. After reaching the maximum temperature of the first step, the reaction was maintained at that temperature for 10 minutes. Then, the remaining butadiene and styrene (35% by weight in total of the total copolymer) were added to carry out the second step of polymerization. Here, styrene and butadiene were added simultaneously, but at different rates. After reaching the maximum temperature of the second step, the reaction was continued for another 15 minutes. Then, 4.2g of 4-{3-[dimethoxy(methyl)silyl]propyl}morpholine was added, the reaction was maintained at the same temperature for 20 minutes, and finally methanol was added to stop the reaction. The main difference between Comparative Example 3 and the Examples is that Comparative Example 3 used a lower rate of butadiene addition in the second step of polymerization.

[0047] Comparative Example 4: To a 5525g solution of cyclohexane containing 8.3g of cyclic ether and 0.5g of a diether compound, 4.9mmol of n-butyllithium and 1g of diisopropenylbenzene were added and mixed, and the mixture was reacted at 50°C for 30 minutes. Then, 1,3-butadiene (65% by weight of the total copolymer) was added to carry out the first stage of polymerization, and after reaching the maximum temperature of the first stage, the reaction was maintained at that temperature for 10 minutes. Next, the remaining butadiene and styrene (totaling 35% by weight of the total copolymer) were added to carry out the second stage of polymerization. In this step, styrene was added first, and then butadiene was added 30 seconds later. Some of the styrene formed blocks first, and the addition rates of both styrene and butadiene were 70g / min. After reaching the maximum temperature of the second stage, the reaction was continued for another 15 minutes. Then, 4.2g of 4-{3-[dimethoxy(methyl)silyl]propyl}morpholine was added, and the reaction was maintained at the same temperature for 20 minutes, and finally methanol was added to stop the reaction. The difference between Comparative Example 4 and the Example is that, during the second-step polymerization of butadiene and styrene, the two monomers were not added simultaneously; instead, styrene was added for a certain period of time before the addition of butadiene, so that the addition rates of styrene and butadiene were the same.

[0048] Comparative Example 5: The preparation method for Comparative Example 5 can be carried out by referring to Comparative Example 4, except that styrene was added first during the second polymerization step, and the addition of butadiene was started 1 minute later.

[0049] [Table 1] Note: "Y" means used, and "N" means unused. *: The interval between each supply start point between SM and BD2 was longer than in Comparative Example 4.

[0050] The copolymers obtained in the above examples and comparative examples (collectively referred to as solution-polymerized styrene-butadiene rubber, SSBR) were compounded into rubber compositions according to the formulations shown in Table 2, and measurements of each item shown in Tables 3 and 4 were performed. An internal mixer was used to knead each component in preparing the formulations in Table 2. During compounding of the masterbatch formulation, the rotor speed was controlled to 55 rpm and the temperature to 150°C. During compounding of the final formulation, the rotor speed was controlled to 45 rpm and the temperature to 100°C.

[0051] [Table 2]

[0052] [Table 3] The DIN, RR, and WG values ​​shown in Table 3 are normalized and are relative values, not absolute values.

[0053] [Table 4] The DIN, RR, and WG values ​​shown in Table 4 are normalized and are relative values, not absolute values.

[0054] Comparative Example 1 was formed by first forming a copolymer segment, followed by the formation of a homopolymer segment, with the butadiene homopolymer segment present at 35% by weight of the total copolymer. As can be seen from the data in Tables 3 and 4, Comparative Example 1 exhibited a single Tg phase, and its wet grip performance was inferior to that of the example which exhibited a double Tg phase.

[0055] Comparative Example 2 involved forming a copolymer segment first, followed by a homopolymer segment. As can be seen from the data in Tables 3 and 4, Comparative Example 2 not only exhibited a single Tg phase but also had zero styrene microblock content; therefore, its wet grip performance was significantly lower than that of the Examples (even worse than that of Comparative Example 1).

[0056] The copolymer of Comparative Example 2 is structurally similar to the copolymers of Examples 1-7, with the main difference being the polymerization sequence of the copolymer and homopolymer segments. In Comparative Example 2, the copolymer segment is formed in the first stage of polymerization. Since no polymerization reaction is underway in the reactor, the reactor environment gradually rises from a relatively low temperature as polymerization begins in the first stage. That is, the copolymer segment of Comparative Example 2 begins polymerization in a relatively low temperature environment, making the distribution of styrene units in the chain more random, resulting in a near-zero proportion of styrene microblocks. This structural characteristic also affects its glass transition behavior, resulting in the observation of only a single glass transition temperature (Tg) in viscoelastic rheological analysis. In contrast, in Examples 1-7, the copolymer segment is formed in the second stage of polymerization. After the first stage of polymerization, the reactor is already at a high temperature; that is, the copolymer segments of Examples 1-7 are polymerized in a relatively high temperature environment favorable for the formation of styrene microblocks, thereby forming polymers with two glass transition temperatures (double Tg).

[0057] Comparative Example 3 differs from the Example in that the rate of butadiene addition in the second polymerization step was slower. As can be seen from the data in Tables 3 and 4, Comparative Example 3 has a relatively low styrene microblock content despite exhibiting a double Tg phase, and therefore its wet grip performance is still inferior to that of the Example.

[0058] In Comparative Examples 4 and 5, styrene was added first, followed by butadiene, during the formation of the copolymer segment. As can be seen from the data in Tables 3 and 4, both Comparative Examples 4 and 5 exhibit a single Tg phase and have an excessively high styrene microblock content. Therefore, while they provide good wet grip performance, their rolling resistance is significantly reduced.

[0059] The data from Examples 1-7 demonstrate that the conjugated diene-vinyl aromatic hydrocarbon copolymer of the present invention can significantly improve wet grip performance (WG) by having two glass transition temperatures (a first Tg of -10 to -50°C; and a second Tg of -45 to -85°C) and a specific structural design in which the styrene microblock content (SB%) is controlled to 1.0% to 10.0%. As shown in Examples 1-7 in Table 3 and expressed as normalized relative values, the wet grip (WG) can reach a magnitude of 167, which is clearly superior to copolymers having only a single Tg (e.g., Comparative Example 2). On the other hand, the present invention can maintain the rolling resistance (RR) at a relative value level of 98-103, thereby avoiding a significant drop to a relative value of 81 due to an excessively high styrene microblock content (e.g., 22% in Comparative Example 5). Furthermore, the DIN wear index of the present invention can also be stably maintained at a relative value of approximately 100-110.

[0060] The foregoing description relates only to preferred embodiments of the present invention and does not limit the scope of the claims of the present invention. Any equivalent changes or modifications made without departing from the spirit of the invention disclosed herein shall fall within the scope of the appended claims.

Claims

1. A copolymer of a conjugated diene and a vinyl aromatic hydrocarbon, comprising a homopolymer segment composed of a conjugated diene and a copolymer segment composed of a conjugated diene and a vinyl aromatic hydrocarbon, wherein the copolymer segment is bonded to the homopolymer segment, and the copolymer has a first glass transition temperature of -10°C to -50°C and a second glass transition temperature of -45°C to -85°C, the first glass transition temperature being higher than the second glass transition temperature, and the copolymer has a vinyl aromatic hydrocarbon microblock content of 1.0% to 10.0% of the total vinyl aromatic hydrocarbon content of the copolymer, where the vinyl aromatic hydrocarbon microblock refers to a unit having at least four consecutive vinyl aromatic hydrocarbon units.

2. The copolymer according to claim 1, wherein the conjugated diene content of the homopolymer segment is 60% to 90% by weight relative to the total content of the copolymer.

3. The copolymer according to claim 2, wherein the conjugated diene content of the homopolymer segment is 65% to 73% by weight relative to the total content of the copolymer.

4. The copolymer according to claim 1, wherein the vinyl aromatic hydrocarbon is styrene and the conjugated diene is 1,3-butadiene.

5. The copolymer according to claim 1, wherein the copolymer has a bonded vinyl aromatic hydrocarbon content of 10% to 20% by weight.

6. The copolymer according to claim 1, wherein the vinyl content of the copolymer is 30% to 40% by weight relative to the total conjugated diene content of the copolymer.

7. The copolymer according to claim 1, which does not have any other glass transition temperatures.

8. The copolymer according to claim 1, further comprising a modified end bonded to the copolymer segment, wherein the copolymer segment is located between the homopolymer segment and the modified end.

9. The copolymer according to claim 8, wherein the modified end contains silicon.

10. A method for producing the copolymer according to any one of claims 1 to 7, including the following: The process includes (1) providing an initiator; (2) polymerizing by anionic polymerization using the initiator under conditions in which a cyclic ether compound and a diether compound are present to form a homopolymer segment composed of the conjugated diene; and (3) forming a copolymer segment composed of the conjugated diene and the vinyl aromatic hydrocarbon after step (2) and bonding it with the homopolymer segment, wherein in step (3), the vinyl aromatic hydrocarbon and the conjugated diene are added to the polymerization reactor simultaneously, and the rate of addition of the vinyl aromatic hydrocarbon is different from the rate of addition of the conjugated diene.

11. The method according to claim 10, wherein the initiator is a polyfunctional initiator produced by reacting a divinylarene compound with an organoalkali metal.

12. The method according to claim 10, wherein the cyclic ether compound and the diether compound are tetrahydrofuran and ethylene glycol diethyl ether, respectively.

13. The method according to claim 10, wherein in step (3), the ratio of the rate of addition of the vinyl aromatic hydrocarbon to the rate of addition of the conjugated diene is 3.8 to 6.

4.

14. The method according to claim 10, further comprising the step (4) of forming a modified end bonded to the copolymer segment after the step (3), wherein the copolymer segment is located between the homopolymer segment and the modified end.

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