Star-type functionalized solution polymerized styrene-butadiene rubber and preparation method thereof

Abstract

The invention provides star-shaped functionalized solution polymerized styrene-butadiene rubber and a preparation method thereof, and the preparation method comprises the following steps: S10, in an inert atmosphere, in an organic solvent, taking a conjugated diene monomer as a polymeric monomer, taking a substance obtained by premixing lithium alkyl and a front-end modifier as a functionalized initiator, and carrying out solution polymerization to obtain a polymer precursor; s20, adding an active coupling agent into the polymer precursor to obtain a star polymer with an active star core and a polar functional group at the tail end of each star arm; and S30, adding a functionalization reagent into the star polymer to obtain the star functionalized solution polymerized styrene-butadiene rubber with both chain end functionalization and chain middle functionalization. The front-end modifier and the active coupling agent are introduced, so that an active center is reserved in a star core, and the functionalization reagent is introduced to modify in a chain and enhance the interface bonding force between white carbon black and butadiene styrene rubber, so that the hysteresis loss of tire rubber is reduced, and the tire rubber is endowed with wear resistance, fatigue resistance and wet skid-rolling resistance balance.

Description

Technical Field

[0001] The invention relates to the technical field of rubber, in particular to a star-shaped functionalized solution-polymerized styrene-butadiene rubber and a preparation method thereof. Background Art

[0002] Solution-polymerized styrene-butadiene rubber (SSBR) is a random copolymer of styrene and butadiene. Due to its advantages such as high monomer conversion, low polymerization additives, and low waste emissions, it has become a focus of research in the green tire field. Its narrow molecular weight distribution and controllable microstructure allow for the synthesis of rubber types with diverse properties tailored to specific application requirements, including high-styrene SSBR, high-, medium-, and low-vinyl SSBR, and end-functionalized SSBR, resulting in a rich variety of rubber types. The automotive industry is increasingly demanding energy-efficient tires. Research shows that energy loss from overcoming tire rolling resistance during vehicle operation accounts for approximately 30% of total energy consumption. To address this issue, the "SSBR + silica" system has become the standard for low-rolling-resistance tire tread compounds. Reinforcing SSBR with silica has become an industry consensus to address the "magic triangle" (i.e., the conflict between rolling resistance, wet skid performance, and wear resistance).

[0003] However, silica has a large number of silanol groups on its surface, resulting in poor dispersibility in styrene-butadiene rubber (SBR). Therefore, regulating the interfacial bonding between silica and SBR to achieve uniform dispersion of silica in the rubber matrix remains a key challenge. Currently, common approaches include adding silane coupling agents (such as bis(triethoxysilylpropane) tetrasulfide and γ-mercaptopropyltrimethoxysilane) during the rubber mixing process or surface modification of silica to improve its interfacial bonding with SBR. However, the use of silane coupling agents not only requires large amounts of addition but also leads to migration of the silane coupling agents into the final vulcanized product, degrading rubber properties. Furthermore, the improvement of the interfacial bonding between silica and SBR by silane coupling agents is limited, and the surface modification process is complex, resulting in poor results.

[0004] To improve the processing and dynamic properties of styrene-butadiene rubber (SBR), researchers have also employed techniques such as branched coupling and end-capping modification. For example, an amino-functionalized initiator is prepared by reacting cycloheximide with n-butyl lithium, which then initiates the random copolymerization of butadiene and styrene to prepare solution-polymerized SBR with amino functionalization at the chain end. Alkyl lithium initiators are used to initiate the copolymerization of butadiene and styrene, and various end-capping agents (such as triethoxysilyl compounds and tetraglycidyl compounds) are used to end-cap the SBR, ultimately introducing amino and / or siloxane groups at the rubber ends to improve its properties.

[0005] Although these technologies can introduce polar functional groups such as amino and siloxane groups into the molecular chain ends of styrene-butadiene rubber, due to the limited number of molecular chain ends, chain end modification techniques have a very limited effect on improving the interfacial bonding between fillers and polymers. Such methods generally face a series of problems: first, the chain end modifiers are complex, expensive, and highly toxic; second, the modifiers have low reactivity, require large addition amounts, and are prone to side reactions; and finally, the range of polar functional groups available is limited, typically tertiary amines and siloxanes. Summary of the Invention

[0006] To address the above-mentioned issues, the present invention proposes a star-shaped functionalized solution-polymerized styrene-butadiene rubber and a method for preparing the same. By combining a star-shaped branched structure design with chain-end functionalization technology, the invention aims to significantly reduce the rolling resistance of tire tread rubber and improve processing performance, while also taking into account the mechanical properties of the rubber. Furthermore, through "active coupling technology" and "in-chain functionalization technology," the number of polar functional groups in the solution-polymerized styrene-butadiene rubber is further increased, greatly improving the dispersibility of silica, thereby enhancing the overall performance of downstream tire products. In this way, the problems of poor filler dispersibility and limited performance improvement existing in the prior art can be effectively resolved, providing an effective solution for the development of green and energy-saving tires.

[0007] To achieve the above-mentioned objectives, the present invention provides a method for preparing a star-shaped functionalized solution-polymerized styrene-butadiene rubber, which comprises the following steps: S10, under inert atmosphere conditions, in an organic solvent, using a conjugated diene monomer as a polymerization monomer and a substance obtained by pre-mixing an alkyl lithium and a front-end modifier as a functionalized initiator, to carry out solution polymerization to obtain a polymer precursor; S20, adding an active coupling agent to the polymer precursor to react to obtain a star-shaped polymer having an active star core and a polar functional group at the end of each star arm; S30, adding a functionalizing agent to the star-shaped polymer to react to obtain a star-shaped functionalized solution-polymerized styrene-butadiene rubber having both chain end and chain functionalization; wherein the functionalizing agent comprises at least one of p-dimethylaminobenzophenone, diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; and the active coupling agent is a difunctional conjugated diene compound.

[0008] Furthermore, the conjugated diene monomer includes at least one of butadiene, isoprene, styrene, piperylene, 2,4-dimethyl-1,3-butadiene, and α-methylstyrene; and / or the alkyl lithium includes at least one of methyl lithium, ethyl lithium, isopropyl lithium, n-butyl lithium, tert-butyl lithium, and sec-butyl lithium.

[0009] Furthermore, the front-end modifier includes at least one of N,N-dimethylamine, diphenylamine, cycloheximide, and pyrrolidine; and / or the active coupling agent includes at least one of divinylbenzene and 1,4-diisopropenylbenzene.

[0010] Furthermore, S10 specifically includes: S11. Under a closed inert atmosphere, an organic solvent and a conjugated diene monomer are mixed in a mass ratio of (80-95): (5-20) to obtain a monomer solution; S12. Under a temperature condition of -78°C to 30°C, a dissociating agent and a front-end modifier are pre-mixed in a molar ratio of (1.0-1.5): 1 for 2 min-10 min, and then the front-end modifier and an alkyl lithium are pre-mixed in a molar ratio of 1: (1.0-1.3) for 2 min-200 min to obtain a functionalized initiator; S13. The functionalized initiator is added to the monomer solution at a temperature condition of 0°C to 60°C to initiate polymerization, and the reaction time is 10 min-200 min to obtain a polymer precursor.

[0011] Furthermore, after S11, the method further includes: adding a cyclohexane solution of alkyl lithium to the monomer solution at a temperature of 0° C. to 20° C.; wherein the mass ratio of alkyl lithium to cyclohexane is (10-20): (80-90).

[0012] Furthermore, S20 specifically includes: adding a cyclohexane solution of an active coupling agent to a polymer precursor, and stirring and mixing at a temperature of 0°C-60°C, with a reaction time of 5min-120min, to obtain a star-shaped polymer having an active star core and each star arm end having a polar functional group; wherein the mass ratio of the active coupling agent to cyclohexane is (1-3): (97-99).

[0013] Furthermore, the molar ratio of the functionalized initiator, the active coupling agent and the functionalized reagent is 1:(2.0-6.0):(0.8-1.6).

[0014] Furthermore, the preparation method further comprises: S40, adding an antioxidant to the star-shaped functionalized solution-polymerized styrene-butadiene rubber, concentrating the rubber, and then vacuum drying the rubber to obtain a finished product.

[0015] The invention provides a star-shaped functionalized solution-polymerized styrene-butadiene rubber. The star-shaped functionalized solution-polymerized styrene-butadiene rubber is prepared by adopting the above-mentioned preparation method.

[0016] Furthermore, the star-shaped functionalized solution-polymerized styrene-butadiene rubber uses butadiene and styrene as polymerization monomers, the mass fraction of the styrene monomer in the star-shaped functionalized solution-polymerized styrene-butadiene rubber is 5%-95%, and the mass fraction of the vinyl structural unit in the butadiene structural unit is 6%-90%; the Mooney viscosity of the star-shaped functionalized solution-polymerized styrene-butadiene rubber is 30-80, the glass transition temperature is -50°C to 0°C, and the modification rate of the polymer polar functional groups is >90%; the nitrogen content of the star-shaped functionalized solution-polymerized styrene-butadiene rubber is 2000-3500 mg / kg solution-polymerized styrene-butadiene rubber.

[0017] After adopting the technical solution of the present invention, the following technical effects can be achieved: (1) The present invention adopts an innovative combination of "functionalized initiator preparation technology" + "DVB active coupling technology" + "star-core chain functionalization technology". By introducing polar functional groups into the end groups and "star core" of each "star arm" of the star-shaped functionalized solution-polymerized styrene-butadiene rubber, the interfacial bonding force between silica and styrene-butadiene rubber can be significantly enhanced, thereby reducing the hysteresis loss of the final tire rubber product and giving it high wear resistance, fatigue resistance and excellent wet skid-rolling resistance balance; (2) The present invention utilizes the active groups of the functionalized reagents or their rigid cyclic skeletons and bifunctional properties to undergo coupling reactions with the active lithium sites at the ends of the solution-polymerized styrene-butadiene rubber chains. These reagents act as a "core" to connect multiple polymer chains, forming a unique cyclic multi-arm star structure. This unique star structure enhances the interaction between molecular chains through multi-arm cross-linking and reduces interfacial defects through the interaction between functional groups and fillers (such as white carbon black), thereby exhibiting higher tensile strength and better wear resistance. (3) The star-shaped functionalized solution-polymerized styrene-butadiene rubber of the present invention has a star-shaped branched structure, which can significantly improve the processing performance and dynamic performance while taking into account the physical and mechanical properties of the rubber; (4) In the present invention, the front-end modifier, back-end functionalization reagent, conjugated diene monomer, alkyl lithium initiator and DVB coupling agent used to prepare the star-shaped functionalized solution-polymerized styrene-butadiene rubber are all commonly used industrial chemicals, which have the advantages of being cheap, readily available and non-toxic. (5) The preparation principle of the functionalized initiator and the star-shaped functionalized polymer in the present invention is simple, the operation is simple, the reaction conditions are mild, there is no side reaction, and the product conversion rate is high; (6) The chemical structures of the front-end modifiers and back-end functionalization reagents used in the present invention and the diversification of the types of functional groups available for selection can achieve customized design of the polar groups and material properties of the star-shaped functionalized SSBR. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which: Figure 1 A reaction principle diagram of a star-shaped functionalized solution-polymerized styrene-butadiene rubber provided in an embodiment of the present invention; Figure 2 The present invention provides a chain functionalization mechanism of a star-shaped functionalized solution-polymerized styrene-butadiene rubber. DETAILED DESCRIPTION

[0019] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0020] Solution-polymerized styrene-butadiene rubber (SBR) is a random copolymer of styrene and butadiene. It boasts high monomer conversion, requires minimal polymerization aids, and produces minimal waste. The resulting rubber exhibits a narrow molecular weight distribution and a controllable microstructure. Based on diverse application requirements, SBR can be synthesized in a variety of formats, including high-styrene SSBR, high-, medium-, and low-vinyl SSBR, and end-functionalized SSBR. Due to its diverse range of rubber types, SBR has become a key focus of green tire research both domestically and internationally.

[0021] The automotive industry's energy-saving requirements for tires are gradually increasing. Studies have shown that the energy consumption generated by overcoming the rolling resistance of tires during vehicle driving accounts for 30% of the total energy consumption. In order to reduce tire energy loss, the "SSBR+silica gel" system has become the standard for low rolling resistance tread rubber. It has become an industry consensus to use silica gel to enhance SSBR to prepare tread rubber to solve the "magic triangle" problem. However, due to the large number of silanol groups on the surface of silica gel, its dispersion in styrene-butadiene rubber is poor. How to regulate the interfacial bonding force between silica gel and styrene-butadiene rubber so that polar silica can be evenly dispersed in the rubber matrix remains a key problem that needs to be overcome.

[0022] During the rubber mixing process, silane coupling agents (such as bis(triethoxysilylpropane) tetrasulfide and γ-mercaptopropyltrimethoxysilane) can be added, or silica surface modified using these agents. This can modulate the interfacial properties of silica and achieve good interfacial bonding between silica and styrene-butadiene rubber (SBR). However, adding silane coupling agents during mixing not only requires large amounts of them but also easily leads to agent "migration" in the vulcanized product, resulting in a decrease in rubber properties. Furthermore, this method does not significantly improve the interfacial bonding between silica and SBR. Furthermore, the pretreatment process for surface modification of silica with silane coupling agents is complex, resulting in poor modification results and limited improvement in interfacial bonding.

[0023] In addition, technologies such as branched coupling and end-capping modification are also common methods for improving the processing and dynamic properties of styrene-butadiene rubber. LG Chem Co., Ltd. of South Korea describes two methods in its patent CN107810209B: one involves reacting cycloheximide with n-butyl lithium and then immediately reacting it with a conjugated diene (such as butadiene) to prepare an amino-functionalized initiator, which is used to initiate the random copolymerization of butadiene and styrene, thereby producing chain-end amino-functionalized solution-polymerized styrene-butadiene rubber; the other involves reacting a vinyl-N,N-dimethylbenzylamine compound with butyl lithium to prepare an amino-functionalized anionic initiator, which can also be used to prepare chain-end amino-functionalized solution-polymerized styrene-butadiene rubber.

[0024] Asahi Chemical of Japan introduced a method in its patent CN105175582B: using an alkyl lithium initiator to initiate the random copolymerization of butadiene and styrene, followed by the addition of 1-[3-(triethoxysilyl)propyl]-4-methylpiperazine, 1-[3-(triethoxysilyl)propyl]-4-(trimethylsilyl)piperazine, tetraglycidyl-1,3-bisaminomethylcyclohexane, 2-[3-(trimethoxysilyl)propyl]-1,3-dimethylimidazolidine, [3-(dimethylamino)propyl]trimethoxysilane, 1,3-dimethyl-2-imidazolidinone, etc. as end-capping agents. These end-capping agents can introduce amino and / or siloxane groups to the ends of styrene-butadiene rubber, and the end-capping modification rate can reach over 80%.

[0025] CN105777946B discloses a double-end modified star-shaped solution-polymerized styrene-butadiene rubber (SPBR), a preparation method thereof, a vulcanized rubber thereof, and its application. The double-end modified star-shaped SPBR is formed by initiating with an organic lithium initiator, coupling with a coupling agent such as DVB, and capping with silane. In this invention, the initiator introduces only silane hydrocarbon chains, and functional groups such as silane are introduced through end-capping.

[0026] In addition, CN102482359A also uses a piperazine compound containing a siloxane substituent as a capping agent for styrene-butadiene rubber; CN107250172B and CN109476778B use a silazane compound as a capping agent for styrene-butadiene rubber; CN107835752A uses 3-isocyanate propyltrimethoxysilane to react with terminal hydroxyl polybutadiene to prepare silane-modified polybutadiene rubber for tire components.

[0027] The above methods can all introduce polar functional groups such as amino groups and siloxane groups into the molecular chain ends of solution-polymerized styrene-butadiene rubber, with a capping rate of over 80%, thus achieving chain-end modification of solution-polymerized styrene-butadiene rubber. However, the above methods can only introduce polar functional groups into the molecular chain ends. Since the number of macromolecular chain ends of solution-polymerized styrene-butadiene rubber is very limited, the effect of chain-end modification technology on improving the interfacial bonding strength between filler and polymer is also very limited. In addition, the above-mentioned capping agents have the following problems: (1) complex structure and difficulty in obtaining; (2) high price; (3) very obvious odor and strong toxicity; (4) low reaction activity, large addition amount, and many side reactions; (5) a small range of polar functional groups available, generally mainly tertiary amino groups and siloxane groups.

[0028] In addition, common or functionalized grades of solution-polymerized styrene-butadiene rubber (SBR) are mostly linear molecular chains with high molecular weights, making compounding and processing difficult and requiring oil extension. However, oil extension can reduce performance, so some SBRs incorporate star-branched structures to improve processing while maintaining the rubber's excellent properties. Furthermore, the number of free ends can be reduced, lowering the rolling resistance of downstream tire tread compounds.

[0029] Therefore, we considered developing a star polymer functionalization modification technology for solution-polymerized styrene-butadiene rubber. On the one hand, we combined the star-branched structure design with the chain-end functionalization technology to significantly reduce the rolling resistance of the downstream tire tread rubber, improve the processing performance while taking into account excellent mechanical properties; on the other hand, we combined the "active coupling technology" and "chain functionalization technology" to further increase the number of polar functional groups in the solution-polymerized styrene-butadiene rubber, greatly improve the dispersibility of silica, and fully improve the overall performance of downstream tire products.

[0030] An embodiment of the present invention provides a method for preparing a star-shaped functionalized solution-polymerized styrene-butadiene rubber, which comprises the following steps: S10, under inert atmosphere conditions, in an organic solvent, using a conjugated diene monomer as a polymerization monomer and a substance obtained by pre-mixing an alkyl lithium and a front-end modifier as a functionalized initiator, to carry out solution polymerization to obtain a polymer precursor; S20, adding an active coupling agent to the polymer precursor, and reacting to obtain a star-shaped polymer having an active star core and a polar functional group at the end of each star arm; S30, adding a functionalizing agent to the star-shaped polymer, and reacting to obtain a star-shaped functionalized solution-polymerized styrene-butadiene rubber having both chain-end and chain functionalization; wherein the functionalizing agent comprises at least one of p-dimethylaminobenzophenone, diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; and the active coupling agent is a difunctional conjugated diene compound.

[0031] This invention introduces a front-end modifier before initiating the reaction and uses an active coupling agent to connect the polymerization-active SSBR active chains. After coupling, the active center is retained at the center of the star-shaped molecular chain (i.e., the core). Finally, a functionalizing agent is introduced for mid-chain modification. This innovative combination of "functionalized initiator preparation technology," "DVB active coupling technology," and "core-in-chain functionalization technology" introduces polar functional groups at the end groups and core of each "arm" of the star-shaped functionalized solution-polymerized styrene-butadiene rubber. This significantly enhances the interfacial bonding between silica and styrene-butadiene rubber, thereby reducing hysteresis loss in the final tire rubber product and imparting high wear and fatigue resistance, as well as an excellent wet skid-rolling resistance balance.

[0032] A difunctional conjugated diene compound, such as DVB, which is an active coupling agent, is added to a polymer precursor solution. The active coupling agent undergoes an active coupling reaction with the active chain end of the polymer precursor. The star core of the resulting star-shaped polymer still has a carbon anion active center that can react with the functionalization reagent, and each star arm end has a polar functional group.

[0033] The end-blocking modifiers used in the prior art are typically siloxane-based, which can cause molecular weight jumps and even crosslinking during production and storage, negatively impacting product processing and performance. The functionalizing agents used in the present invention include at least one of p-dimethylaminobenzophenone, diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate. After these functionalizing agents react with the active centers at the core of the molecular chain, there are no side reactions such as molecular weight growth or even crosslinking during subsequent production and storage.

[0034] The star polymer preparation process is carried out under a nitrogen atmosphere with a purity level of 99.999% or above. The star polymer is polymerized by initiating polymerization of conjugated diene monomers in cyclohexane solvent using a functionalized initiator prepared by pre-mixing alkyl lithium with a front-end modifier. The polymer is then coupled with divinyl aromatic hydrocarbons and reacted with an equivalent amount of a chain functionalizing agent.

[0035] In some embodiments of the present application, the conjugated diene monomer includes at least one of butadiene, isoprene, styrene, piperylene, 2,4-dimethyl-1,3-butadiene, and α-methylstyrene; and / or the alkyl lithium includes at least one of methyl lithium, ethyl lithium, isopropyl lithium, n-butyl lithium, tert-butyl lithium, and sec-butyl lithium.

[0036] Olefin monomers with conjugated structures can react with other monomers during polymerization to form polymers with specific properties, and they have important applications in synthetic rubber. Different conjugated diene monomers have varying structures and reactivities, and the selection of different monomers can control the properties and performance of the polymer. In the present invention, alkyl lithium typically acts as an initiator, driving the polymerization reaction of the conjugated diene monomers. Different types of alkyl lithium (such as methyl lithium and ethyl lithium) exhibit varying activity and selectivity in the reaction, thus affecting the properties of the final polymer.

[0037] In some embodiments of the present application, the front-end modifier includes at least one of N,N-dimethylamine, diphenylamine, cycloheximide, and pyrrolidine; and / or the active coupling agent includes at least one of divinylbenzene and 1,4-diisopropenylbenzene; and / or the functionalizing agent includes at least one of p-dimethylaminobenzophenone, diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

[0038] Front-end modifiers chemically modify the ends of polymer chains, providing reactive groups for subsequent functionalization reactions. N,N-dimethylamine, diphenylamine, cycloheximide, and pyrrolidine can be used as front-end modifiers to introduce nitrogen or aromatic ring groups. These groups can effectively influence the final properties of the polymer, such as increasing polarity, improving solubility, or improving compatibility with other materials.

[0039] Active coupling agents are used to promote crosslinking reactions between polymer chains or facilitate the bonding of polymers to other materials. Compounds such as divinylbenzene and 1,4-diisopropenylbenzene possess double bonds or multiple olefin structures, which can trigger crosslinking or coupling reactions under appropriate conditions. This allows for the connection of different polymer chains or the interaction of multiple polymers, improving the overall performance and structural strength of the material. Preferably, divinylbenzenes include o-, m-, and p-divinylbenzene and o-, m-, and p-diisopropenylbenzene.

[0040] Functionalizing agents are mainly used to further modify the middle part of the polymer chain and give it specific functional groups. Specifically, the listed functionalizing agents, such as p-dimethylaminobenzophenone, diphenylmethane diisocyanate, toluene diisocyanate, etc., have active groups such as isocyanate and amino groups, which can be used for further reaction modification to make the polymer more functional and improve its performance in specific applications.

[0041] In some embodiments of the present application, S10 specifically includes: S11. Under a closed inert atmosphere, an organic solvent and a conjugated diene monomer are mixed in a mass ratio of (80-95): (5-20) to obtain a monomer solution; S12. Under a temperature of -78°C to 30°C, a dissociating agent and a front-end modifier are pre-mixed in a molar ratio of (1.0-1.5): 1 for 2 min-10 min, and then the front-end modifier and an alkyl lithium are pre-mixed in a molar ratio of 1: (1.0-1.3) for 2 min-200 min to obtain a functionalized initiator; S13. The functionalized initiator is added to the monomer solution at a temperature of 0°C to 60°C to initiate polymerization, and the reaction time is 10 min-200 min to obtain a polymer precursor.

[0042] Preferably, the dissociating agent can be selected as tetrahydrofuran.

[0043] In some embodiments of the present application, after S11, the step further includes: adding a cyclohexane solution of alkyl lithium to the monomer solution at a temperature of 0°C-20°C; wherein the mass ratio of alkyl lithium to cyclohexane is (10-20): (80-90).

[0044] Adding an alkyllithium solution at low temperatures can reduce the impact of impurities while maintaining the desired reaction stability. During polymerization, impurities (such as moisture, oxygen from the air, residual reactants or byproducts) can interfere with the reaction or affect the quality of the final product. The purpose of adding an alkyllithium solution is to react with these impurities, removing or converting them, thereby ensuring the purity of the reaction system and smooth reaction progress.

[0045] In some embodiments of the present application, S20 specifically includes: adding a cyclohexane solution of an active coupling agent to a polymer precursor, stirring and mixing at a temperature of 0°C-60°C, and reacting for 5min-120min to obtain a star-shaped polymer having an active star core and each star arm end having a polar functional group; wherein the mass ratio of the active coupling agent to cyclohexane is (1-3): (97-99).

[0046] In this step, a reactive coupling agent is used to further modify the molecular structure of the polymer precursor, imparting a star-shaped structure and introducing polar functional groups at the termini. Dissolving the coupling agent in cyclohexane improves its solubility and promotes uniformity in the reaction. An appropriate concentration of the reactive coupling agent effectively promotes polymerization while avoiding excessive amounts that could trigger unwanted side reactions.

[0047] In some embodiments of the present application, the molar ratio of the functionalized initiator, the active coupling agent, and the functionalizing agent is 1:(2.0-6.0):(0.8-1.6).

[0048] In some embodiments of the present application, the preparation method further includes: S40, adding an antioxidant to the star-shaped functionalized solution-polymerized styrene-butadiene rubber, concentrating, and then vacuum drying to obtain a finished rubber.

[0049] An embodiment of the present invention provides a star-shaped functionalized solution-polymerized styrene-butadiene rubber. The star-shaped functionalized solution-polymerized styrene-butadiene rubber is prepared by the preparation method described above.

[0050] In some embodiments of the present application, the star-shaped functionalized solution-polymerized styrene-butadiene rubber uses butadiene and styrene as polymerization monomers, the mass fraction of the styrene monomer in the star-shaped functionalized solution-polymerized styrene-butadiene rubber is 5%-95%, and the mass fraction of the vinyl structural unit in the butadiene structural unit is 6%-90%; the Mooney viscosity of the star-shaped functionalized solution-polymerized styrene-butadiene rubber is 30-80, the glass transition temperature is -50°C to 0°C, and the modification rate of the polymer polar functional groups is >90%; the nitrogen content of the star-shaped functionalized solution-polymerized styrene-butadiene rubber is 2000-3500 mg / kg solution-polymerized styrene-butadiene rubber.

[0051] Specifically, the product structure of the star-shaped functionalized solution-polymerized styrene-butadiene rubber polymer is designed as follows (chain end functionalization in the starfish-shaped chain): the star-shaped functionalized solution-polymerized styrene-butadiene rubber is a random copolymer of butadiene and styrene, and also has a unique cyclic multi-star arm structure. The active center is retained at the center of the star-shaped molecular chain (i.e., the star core), and chain functionalization can be achieved through functionalization reagents; after coupling, the end group of each star arm of the star-shaped functionalized solution-polymerized styrene-butadiene rubber carries polar functional groups, and these polar functional groups come from the front-end modifier, including N,N-dimethylamine and diphenylamine compounds.

[0052] The mass fraction of styrene monomer in the star-shaped functionalized solution-polymerized styrene-butadiene rubber is 5-95%, preferably 30%. The proportion of vinyl units in the total butadiene structural units is 6-90%, preferably 13-60%, and most preferably 40%. The Mooney viscosity is 30-80, preferably 55-65, and most preferably 65. The glass transition temperature is -50-0°C, preferably -40-15°C, and most preferably -30°C. The polar functional group modification rate of the polymer is >90%, preferably 97%. The nitrogen content is 2000-3500 mg / kg of solution-polymerized styrene-butadiene rubber, preferably 2500-3200 mg / kg of solution-polymerized styrene-butadiene rubber.

[0053] The molecular weight distribution spectrum obtained by GPC analysis generally shows a three-peak distribution. The number average molecular weight of the first polymer peak is 80,000-150,000 g / mol, preferably 90,000-120,000 g / mol, and most preferably 100,000 g / mol; the molecular weight distribution of the first polymer peak is 1.0-1.5, preferably 1.05-1.1. The number average molecular weight of the second polymer peak is 240,000-450,000 g / mol, and most preferably 300,000 g / mol; the molecular weight distribution of the second polymer peak is 1.0-1.5, preferably 1.1-1.3; the peak area ratio of the second polymer peak is 20-40%, preferably 35%. The number average molecular weight of the third polymer peak is 480,000-900,000 g / mol, and most preferably 600,000 g / mol; the molecular weight distribution of the third polymer peak is 1.0-1.5, preferably 1.1-1.3; the peak area ratio of the third polymer peak is 40-60%, preferably 55%.

[0054] The chain functionalization reagents of the star-shaped functionalized solution-polymerized styrene-butadiene rubber include: p-dimethylaminobenzophenone, diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

[0055] An embodiment of the present invention provides a method for preparing a star-shaped functionalized solution-polymerized styrene-butadiene rubber, comprising the following steps: S1: Prepare a clean, dry glass bottle and purge it with nitrogen to exclude oxygen. Under a sealed inert atmosphere, add 900g of cyclohexane, 30g of styrene, 70g of butadiene, and 5ml of a 10g / L THF solution in cyclohexane. Then, add 0.6ml of a 0.5mol / L n-butyllithium solution in cyclohexane at below 20°C to remove impurities. Next, in another clean, dry, nitrogen-purged glass bottle, premix 2.0ml of 0.5mol / L n-butyllithium and 2.1ml-2.4ml of a 0.5mol / L cycloheximide (or other front-end modifier) solution at -78°C-30°C for 2-200 minutes to produce the functionalized initiator. Subsequently, add the monomer solution at 60°C and stir to allow polymerization to proceed for 10-200 minutes. Continue stirring before proceeding to the next coupling reaction.

[0056] S2: Add 2.4 ml to 21 ml of 0.5 mol / L DVB coupling agent solution to the reaction system, and rapidly stir and react at 60° C. for 5 min to 120 min to generate a star-shaped polymer having an active star core and polar functional groups at the end of each star arm.

[0057] S3: Add 2.2 ml to 10.5 ml of a 0.5 mol / L mid-chain functionalization reagent to form a multifunctional star polymer with chain end and mid-chain functionalization.

[0058] S4: Add an antioxidant solution (1520 / 1076, 1 / 1, by mass) to the polymer solution at 0.6% of the dry resin content. After removing 80% of the solvent using a rotary evaporator, place the concentrated solution in an enamel tray and vacuum dry it in a 70°C vacuum oven for 24 hours to obtain a colorless, transparent sample.

[0059] Figure 1 A schematic diagram of the reaction principle of a star-shaped polymer provided in an embodiment of the present invention; Figure 2 The in-chain functionalization mechanism of the star polymer provided in the embodiments of the present invention.

[0060] 1. Analysis and detection methods Mooney viscosity test: A sample weighing 15 g or more was preheated for 1 minute and then measured at 100° C. for 4 minutes using MV-2000 manufactured by ALPHA Technologies.

[0061] Molecular weight (number average molecular weight, weight average molecular weight, polydispersity index): Measured by gel permeation chromatography (GPC) at 40°C. Monodisperse polystyrene standards were used as the standard for molecular weight calculations. THF was used as the mobile phase at a flow rate of 1 ml / min.

[0062] Modification Rate Analysis Method: Using a mid-chain modified styrene butadiene rubber sample, the content of the mid-chain modified styrene butadiene rubber component is determined by exploiting its adsorption to a GPC column filled with silica gel. The amount of the mid-chain modified styrene butadiene rubber component adsorbed on the silica column is determined by the difference in chromatograms (the difference between the chromatograms obtained by measuring a sample solution containing the sample and a low molecular weight internal standard polystyrene using a polystyrene gel column and the chromatograms obtained by measuring a solution using a silica column). GPC Analysis Sample Preparation Method: Dissolve 10 mg of sample and 5 mg of a low molecular weight polystyrene internal standard in 20 mL of tetrahydrofuran. GPC Measurement Conditions for the polystyrene column: Use THF as the eluent, and inject 200 μL of the sample into the instrument for measurement. A guard column: "TSK guard column HHR-H" (trade name, manufactured by Tosoh Corporation) and three columns: "TSKgelSuper Multipore HZ-H" (trade name, manufactured by Tosoh Corporation) are used in series. The chromatogram was obtained using an RI detector (HLC8020, manufactured by Tosoh Corporation) at a column oven temperature of 40°C and a THF flow rate of 1.0 mL / min. Silica column GPC measurement conditions: THF was used as the eluent, and 200 μL of sample was injected into the instrument for measurement. Three silica columns, Zorbax PSM-1000S, PSM-300S, and PSM-60S, were connected and used, with a DIOL 4.6×12.5 mm 5 micron column connected upstream as a guard column. The chromatogram was obtained using an RI detector (HLC8020, manufactured by Tosoh Corporation) at a column oven temperature of 40°C and a THF flow rate of 0.5 mL / min. Calculation method for the modification rate (content of modified styrene-butadiene rubber in the chain): Assume that the peak area of the chromatogram using a polystyrene column is 100, the peak area of the sample is P1, and the peak area of the standard polystyrene is P2; assume that the peak area of the chromatogram using a silica column is 100, the area of the sample is P3, and the peak area of the standard polystyrene is P4, and calculate the modification rate (%) using the following formula: Modification rate (%) = [1-(P2×P3) / (P1×P4)]×100 (where P1+P2=P3+P4=100) Definition of polymer modification rate: The polymer modification rate index indicates the mass fraction of molecular chains carrying polar functional groups at the end groups or cores of the molecular chains among all polymer molecular chains.

[0063] NMR analysis: The sample microstructure was analyzed using a Brucker 600 MHz superconducting Fourier transform nuclear magnetic resonance spectrometer. 1H spectra were observed at 600 MHz, and 13C spectra were observed at 150.9 MHz. The solvent was CDCl3, TMS was used as the internal standard, and the test temperature was 20°C. This method can be used to analyze the styrene and vinyl content of styrene-butadiene rubber.

[0064] DSC thermal performance analysis: Samples are taken in the 15-20mg range, and the temperature range is -120°C to 120°C. Thermal history is eliminated before testing. The heating and cooling rates are 10°C / min, and the dwell times at the highest and lowest temperatures are 5 minutes. This method can be used to analyze the glass transition temperature of styrene-butadiene rubber.

[0065] Conversion rate test method: Use a special cylindrical container to remove a small amount of glue from the reactor, then measure the total weight of the cylindrical container containing the polymer solution (A), then transfer the polymer solution in the cylindrical container to an aluminum tray, and measure the weight of the cylindrical container after removing the polymer solution (B). Dry the aluminum tray containing the polymer solution in a vacuum oven at 100°C for more than 180 minutes until the polymer is completely dry and transparent. Finally, measure the weight of the dry polymer (C) and calculate the polymer conversion rate according to the following mathematical formula: Nitrogen Content Analysis Method: Nitrogen content was measured using the NSX analytical method using a trace nitrogen quantitative analyzer (NSX-2100H). Specifically, the trace nitrogen quantitative analyzer (autosampler, horizontal furnace, PMT & Nitrogen detector) was turned on, with carrier gas flows set to 250 ml / min for Ar, 350 ml / min for O, and 300 ml / min for the ozone generator. The heater was set to 800°C, and the analyzer was left to stabilize for approximately 3 hours. After the analyzer stabilized, a calibration curve was created using a nitrogen standard (AccuStandard S-22750-01, 5 ml) with concentrations of 5 ppm, 10 ppm, 50 ppm, 100 ppm, and 500 ppm. The area corresponding to each concentration was calculated. A ceramic boat containing 20 mg of sample was then placed in the analyzer's autosampler and measured to obtain the area. The nitrogen content was calculated using the sample area obtained and the calibration curve.

[0066] Silicon content analysis: Silicon content was measured using inductively coupled plasma optical emission spectrometry (ICP-OES: Optima 7300DV) using ICP analysis. Specifically, approximately 0.7 g of sample was placed in a platinum crucible, to which approximately 1 ml of concentrated sulfuric acid (98% by mass, electronic grade) was added. The sample was heated at 300°C for 3 h and then burned in an electric furnace (Thermo Scientific, Lindberg Blue M) using the following procedure: Step 1: initial temperature 0°C, rate (temperature / hour) 180°C / hour, temperature (holding time) 180°C (1 hour); Step 2: initial temperature 180°C, rate (temperature / hour) 85°C / hour, temperature (holding time) 370°C (2 hours); Step 3: initial temperature 370°C, rate (temperature / hour) 47°C / hour, temperature (holding time) 510°C (3 hours); Add 1 ml of concentrated nitric acid (48% mass fraction) and 20 μL of concentrated hydrofluoric acid (50% mass fraction) to the residue, seal the platinum crucible and shake for more than 30 minutes, add 1 ml of boric acid to the sample, store at 0°C for more than 2 hours, dilute with 30 ml of ultrapure water, and incinerate.

[0067] 2. Experimental Data Summary Table 1 Data results of Examples 1-2 and Comparative Examples 1-5 The star-shaped functionalized solution-polymerized styrene-butadiene rubber of this embodiment has the following advantages: 1. The modification rate of the star-shaped functionalized solution-polymerized styrene-butadiene rubber is higher. It can be seen that the combination of the "functionalized initiator preparation technology" and the "star-core chain modification technology" of the present invention significantly improves the molecular chain polarity of the solution-polymerized styrene-butadiene rubber and can significantly improve the interfacial bonding force between SSBR and silica.

[0068] 2. From the higher nitrogen content of the star-shaped functionalized solution-polymerized styrene-butadiene rubber, it can be seen that the functionalization technology of the present invention can give SSBR a higher degree of functionalization, thereby significantly improving the interfacial bonding strength between SSBR and silica.

[0069] 3. The combination of the coupling technology and the functionalization technology of the present invention significantly increases the molecular weight and Mooney viscosity of the star-shaped functionalized solution styrene-butadiene rubber, which can significantly improve the strength of the rubber product.

[0070] 3. Vulcanized rubber mixing formula and manufacturing conditions The mixing formula of the vulcanized rubber is shown in Table 2 (the raw material amounts in Table 2 are expressed in parts by weight based on 100 parts by weight of styrene-butadiene rubber): Table 2 Mixing formula of vulcanized rubber Vulcanized rubber is prepared through a first-stage mixing process and a second-stage mixing process. In the first-stage mixing process, rubber, silica, an organosilane coupling agent (X50S, Evonik), a process oil (TDAE), zinc oxide (zinc white), stearic acid, an antioxidant (TMQ(RD)) (2,2,4-trimethyl-1,2-dihydroquinoline polymer), an anti-aging agent (6PPD (dimethylbutyl-N-phenyl-phenylenediamine)), and microcrystalline wax) are mixed in a Banbury mixer equipped with a temperature control system. The initial mixing temperature is controlled at 70°C, and the first rubber mix is obtained at a discharge temperature of 145°C after the mixing is completed. In the second mixing stage, the first rubber mix was cooled to room temperature. The first rubber mix, sulfur, a rubber accelerator (DPD (diphenylguanidine)), and a vulcanization accelerator (CZ (N-cyclohexyl-2-benzothiazolylsulfenamide)) were added to a mixer and mixed at a temperature below 100°C to produce a second rubber mix. Finally, vulcanized rubber samples were prepared by cross-linking in a flat-plate vulcanizer at 160°C for 20 minutes.

[0071] 4. Evaluation Method of Application Performance of Vulcanized Rubber 1. Vulcanized Rubber Tensile Test: The tensile strength of the cut test specimens and the tensile stress at 300% elongation (300% modulus) were measured according to the tensile test method of ASTM 412. For this purpose, a Universal Test Machine 4204 manufactured by Instron was used, and the tensile strength, modulus, and elongation were measured at room temperature at a tensile rate of 50 cm / min.

[0072] 2. Dynamic Mechanical Properties of Vulcanized Rubber: A dynamic mechanical analyzer manufactured by TA was used. The loss factor, Tanδ, was measured for each sample while deforming under conditions of a 10 Hz frequency in the deformation mode and a measurement temperature ranging from -60°C to 80°C. The Payne effect is represented by the difference between the minimum and maximum values in the deformation range of 0.28% to 40%. The lower the Payne effect, the higher the filler dispersion. As the loss factor at 0°C increases, wet skid resistance improves, and as the loss factor at 60°C decreases, hysteresis loss decreases, rolling resistance decreases, and fuel economy improves. As the loss modulus at 60°C decreases, internal heat generation in the rubber decreases, hysteresis loss decreases, and dynamic performance improves.

[0073] 3. DIN abrasion resistance test of vulcanized rubber: For each vulcanized rubber sample, a DIN abrasion test is performed based on ASTM D5963 and displayed by the DIN loss index (volume index: ARIA (Abrasion Resistance Index, Method A)).

[0074] Table 3 Evaluation results of application performance of vulcanized rubber (analytical values) From the comparison of the Mooney viscosity of the rubber mix, the Mooney viscosity of all the rubber mixes has increased compared to the raw rubber, but the Mooney viscosity of the rubber mix of Comparative Examples 2-4 is not significantly increased compared to the raw rubber, and is much lower than that of Examples 1-2. This shows that the innovative combination of "functionalized initiator technology" + "DVB active coupling technology" + "rear-end functionalized chain modification technology" of the present invention has significantly improved the mixing processability of solution-polymerized styrene-butadiene rubber, and the mixing and dispersibility of rubber and filler are the best, and it is easy to eat the material. The heat generation in the mixing process is not high, so the pre-vulcanization degree of its rubber mix is the lowest. The data characteristics embodied are exactly: the Mooney viscosity of the rubber mix is not significantly increased compared to the raw rubber Mooney.

[0075] The 300% modulus, elongation at break and tensile strength of Example 1-2 are significantly higher than those of Comparative Example 1-3, which is related to the molecular weight and Mooney viscosity.

[0076] The elongation at break and tensile strength of Examples 1-2 were higher than those of Comparative Examples 4-5 due to the higher degree of molecular chain functionalization in Examples 1-2. The star-functionalized solution-polymerized styrene-butadiene rubber exhibited optimal mixing and dispersion properties with fillers, resulting in a vulcanized rubber with the most complete filler-polymer network and the best mechanical properties. This demonstrates the advantages of the star-functionalized modification technology of the present invention.

[0077] The higher the wear resistance index, the better the wear resistance of the vulcanized rubber. The wear resistance index of Examples 1-2 is significantly higher than that of Comparative Examples 1-5, indicating that the star polymer functionalization modification technology improves the wear resistance of SSBR.

[0078] A higher 0°C loss factor indicates greater wet skid resistance and grip of the vulcanized rubber. The 0°C loss factors of Examples 1-2 are all greater than 0.3, higher than those of Comparative Examples 1-5. Therefore, the star-functionalized SSBR of the present invention exhibits excellent grip and wet skid resistance on icy surfaces.

[0079] The lower the 60°C loss factor, the lower the rolling resistance of the vulcanized rubber, and its use as a tire can improve the fuel economy of a car. The 60°C loss factors of Examples 1-2 are all lower than 0.1000, significantly lower than those of Comparative Examples 1-2, and not much different from Comparative Examples 3-5. This shows that the star-shaped functionalization modification technology of the present invention, compared with traditional chain end functionalization technology and star-shaped branching technology, mainly improves the 0°C loss factor, but has a relatively insignificant effect on the 60°C loss factor. The star-shaped functionalization modification technology of the present invention significantly reduces the hysteresis loss of SSBR and has excellent dynamic performance.

[0080] A lower 60°C loss modulus indicates lower internal heat buildup in the vulcanized rubber, better dynamic performance, and improved fatigue resistance when used in tires. The 60°C loss moduli of Examples 1-2 are all lower than those of Comparative Examples 1-5, demonstrating that the star-functionalized solution-polymerized styrene-butadiene rubber of the present invention has lower internal heat buildup and better fatigue resistance. Similarly, the 60°C loss modulus of Comparative Examples 3-5 is all lower than that of Comparative Example 1, indicating that chain-end modification with tertiary amine and siloxane groups can also improve the dynamic performance and fatigue resistance of SSBR, but the improvement is slightly less than that achieved by the star-functionalized modification technology of the present invention.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a star-shaped functionalized solution-polymerized styrene-butadiene rubber, characterized in that: The preparation method comprises the following steps: S10, under inert atmosphere conditions, in an organic solvent, using a conjugated diene monomer as a polymerization monomer and a premixed substance obtained by mixing an alkyl lithium and a front-end modifier as a functionalized initiator, to carry out solution polymerization to obtain a polymer precursor; S20, adding an active coupling agent to the polymer precursor to react to obtain a star-shaped polymer having an active star core and each star arm end having a polar functional group; S30, adding a functionalizing agent to the star-shaped polymer to react to obtain the star-shaped functionalized solution-polymerized styrene-butadiene rubber having both chain end and chain functionalization; Wherein, the functionalizing agent includes at least one of p-dimethylaminobenzophenone, diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; The active coupling agent is a difunctional conjugated diene compound.

2. The preparation method according to claim 1, characterized in that The conjugated diene monomer includes at least one of butadiene, isoprene, styrene, piperylene, 2,4-dimethyl-1,3-butadiene, and α-methylstyrene; and / or The alkyl lithium includes at least one of methyl lithium, ethyl lithium, isopropyl lithium, n-butyl lithium, tert-butyl lithium, and sec-butyl lithium.

3. The preparation method according to claim 1, characterized in that The front-end modifier includes at least one of N,N-dimethylamine, diphenylamine, cycloheximide, and pyrrolidine; and / or The active coupling agent includes at least one of divinylbenzene and 1,4-diisopropenylbenzene.

4. The preparation method according to claim 1, characterized in that The S10 specifically includes: S11, under a closed inert atmosphere, mixing the organic solvent and the conjugated diene monomer in a mass ratio of (80-95): (5-20) to obtain a monomer solution; S12. Under a temperature condition of -78°C to 30°C, premix the dissociating agent and the front-end modifier in a molar ratio of (1.0-1.5):1 for 2 minutes to 10 minutes, and then premix the front-end modifier and the alkyl lithium in a molar ratio of 1:(1.0-1.3) for 2 minutes to 200 minutes to obtain the functionalized initiator; S13, adding the functionalized initiator to the monomer solution at a temperature of 0° C. to 60° C. to initiate polymerization for a reaction time of 10 min to 200 min to obtain the polymer precursor.

5. The preparation method according to claim 4, characterized in that After S11, the method further includes: adding the cyclohexane solution of the alkyl lithium to the monomer solution at a temperature of 0° C. to 20° C.; Wherein, the mass ratio of the alkyl lithium to the cyclohexane is (10-20): (80-90).

6. The preparation method according to claim 1, characterized in that The S20 specifically includes: Adding the cyclohexane solution of the active coupling agent to the polymer precursor, stirring and mixing at a temperature of 0° C. to 60° C. for a reaction time of 5 min to 120 min, to obtain the star-shaped polymer having an active star core and polar functional groups at the end of each star arm; Wherein, the mass ratio of the active coupling agent to the cyclohexane is (1-3): (97-99).

7. The preparation method according to claim 1, characterized in that The molar ratio of the functionalized initiator, the active coupling agent and the functionalized reagent is 1:(2.0-6.0):(0.8-1.6).

8. The preparation method according to claim 1, characterized in that The preparation method further comprises: S40, adding an antioxidant to the star-shaped functionalized solution-polymerized styrene-butadiene rubber, concentrating the solution, and then vacuum drying to obtain a finished rubber.

9. A star-shaped functionalized solution-polymerized styrene-butadiene rubber, characterized in that: The star-shaped functionalized solution-polymerized styrene-butadiene rubber is prepared by the preparation method according to any one of claims 1 to 8.

10. The star-shaped functionalized solution-polymerized styrene-butadiene rubber according to claim 9, characterized in that: The star-shaped functionalized solution-polymerized styrene-butadiene rubber uses butadiene and styrene as polymerization monomers, the mass fraction of the styrene monomer in the star-shaped functionalized solution-polymerized styrene-butadiene rubber is 5%-95%, and the mass fraction of the vinyl structural unit in the butadiene structural unit is 6%-90%; The star-shaped functionalized solution-polymerized styrene-butadiene rubber has a Mooney viscosity of 30-80, a glass transition temperature of -50°C to 0°C, and a polymer polar functional group modification rate of >90%; The nitrogen content of the star-shaped functionalized solution-polymerized styrene-butadiene rubber is 2000-3500 mg / kg of the solution-polymerized styrene-butadiene rubber.

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