Star-branched butyl rubber and a method for preparing the same

Abstract

This invention provides a method for preparing star-shaped branched butyl rubber, comprising the following steps: A) Styrene and its derivatives, a nitrogen-lithium initiator, a polarity modifier, and a solvent are mixed and reacted, and then butadiene is added to continue the reaction to obtain an SBS branching agent; B) SBS is catalytically hydrogenated, controlling the degree of hydrogenation to 20%~70%, to obtain a partially hydrogenated SBS branching agent; C) The partially hydrogenated SBS branching agent is dissolved in a solvent, mixed with isobutylene and isoprene, and an initiator is added to carry out a polymerization reaction to obtain the desired product. This invention uses living anionic polymerization technology to prepare block copolymers of styrene and its derivatives with butadiene, and partially hydrogenates them through catalytic hydrogenation. By controlling the catalyst / polarity modifier ratio, a branching agent with a specific degree of hydrogenation is synthesized. Then, the branching agent is dissolved in dichloromethane for the preparation of butyl rubber, resulting in star-shaped branched butyl rubber with a bimodal broad molecular weight distribution.

Description

Technical Field

[0001] This invention relates to the field of butyl rubber preparation technology, and in particular to a star-shaped branched butyl rubber and its preparation method. Background Technology

[0002] Butyl rubber is a linear polymer formed by cationic polymerization of isobutylene and a small amount of isoprene. Due to its excellent airtightness, ozone resistance, and chemical corrosion resistance, it is widely used in tires and the pharmaceutical industry. Although butyl rubber has many advantages, it also has disadvantages such as slow vulcanization speed, poor adhesion, and poor compatibility with other general-purpose rubbers. Because butyl rubber is prone to excessive flow and deformation during processing, star-branched butyl rubber has been developed.

[0003] Commercially available star-branched butyl rubber is a polymer with a bimodal molecular weight distribution, consisting of a high-molecular-weight grafted structure and a low-molecular-weight linear component. This results in a unique three-dimensional network structure and excellent viscoelastic properties, along with high raw rubber strength and a fast stress relaxation rate, giving butyl rubber superior processing performance. Because star-branched polymers can achieve high molecular weight polymers while maintaining low melt and solution viscosity, thus unifying physical and mechanical properties with processing performance, they have become a research hotspot in polymer chemistry in recent years.

[0004] Existing branching agent / grafting agent methods for preparing star-shaped branched butyl rubber typically use polymers containing unsaturated double bonds (such as polybutadiene, styrene-butadiene-styrene copolymer SBS, etc.) as branching agents to introduce branches during cationic polymerization.

[0005] Branching agents such as US4358560A only play a physical role and cannot construct a star-shaped branched structure. US4474924A clearly reveals that when the degree of hydrogenation of SBS-type branching agents reaches more than 85%, their chemical branching activity is basically lost, and they can only act as physical stabilizers, and cannot fundamentally change the intrinsic properties of butyl rubber (such as stress relaxation and processability).

[0006] Therefore, to address the binary dilemma of easy gelation when using unhydrogenated branching agents and lack of branching effect when using high-hydrogenated copolymers, it is essential to provide a star-branched butyl rubber with stable polymerization process, controllable product structure, and excellent processing and physical-mechanical properties, as well as its preparation method. Summary of the Invention

[0007] In view of this, the preparation method provided by the present invention has a stable polymerization process, controllable product structure, and excellent processing performance and physical and mechanical properties.

[0008] The present invention provides a method for preparing star-branched butyl rubber, comprising the following steps:

[0009] A) Styrene and its derivatives, nitrogen-lithium initiator, polarity modifier and solvent are mixed and reacted, and then butadiene is added to continue the reaction to obtain linear active SB copolymer; then a coupling agent is added to carry out a coupling reaction to obtain star-shaped SBS branching agent;

[0010] B) Catalytically hydrogenate SBS, controlling the degree of hydrogenation to be 20%~70%, to obtain a partially hydrogenated SBS branching agent;

[0011] C) Dissolve the partially hydrogenated SBS branching agent in a solvent, mix it with isobutylene and isoprene, add an initiator, and carry out a polymerization reaction to obtain the product.

[0012] In some specific embodiments, the content of residual 1,2-butadiene units in the branching agent is 5~15 mol.

[0013] In some specific embodiments, the preparation method of the nitrogen-lithium initiator includes:

[0014] Hexamethyleneimine is reacted with n-butyllithium, butadiene is added, and the reaction is continued to obtain a hexamethyleneimine-based alkyllithium initiator; the degree of polymerization of butadiene on the initiator chain is 4-10.

[0015] The molar ratio of hexamethyleneimine to n-butyllithium is 0.1~1.2; the reaction temperature is 20~25℃; and the reaction time is 10~40min.

[0016] In some specific embodiments, the coupling agent mentioned in step A) is a multifunctional coupling agent selected from one or more of silicon tetrachloride, dichlorodimethylsilane, and divinylbenzene, preferably silicon tetrachloride; the molar ratio of the coupling agent to the initiator is 0.1~1.0, preferably 0.3~0.8; the coupling reaction temperature is 50~110℃, and the coupling reaction time is 10~60min.

[0017] In some specific embodiments, the molar ratio of styrene and its derivatives to butadiene in step A) is 40:60 to 50:50;

[0018] In some specific embodiments, in the butadiene block described in step A), the initial content of the 1,2-structure is controlled to be 15~25 mol% (percentage of butadiene), and the content of the 1,4-structure is 75~85 mol%.

[0019] In some specific embodiments, the molar ratio of the polarity modifier and the nitrogen-lithium initiator in step A) is 1~20; the reaction temperature is 45~65℃, butadiene is added after reacting for 30~60 min, and the reaction continues for 40~80 min; the temperature for continuing the reaction is 55~75℃.

[0020] In some specific embodiments, the solvent in step C) is dichloromethane, the main catalyst in the initiator is a Lewis acid, and the co-initiator is a proton donor.

[0021] In some specific embodiments, step C) involves a reaction temperature of -80 to -98°C and a reaction time of 1 to 10 minutes.

[0022] In some specific embodiments, the number-average molecular weight Mn of the SBS branching agent is 5 × 10⁻⁶. 4 ~ 2.0×10 5 g / mol;

[0023] The star-branched butyl rubber has a bimodal molecular weight distribution, and the ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is greater than 4.0.

[0024] This invention provides a star-shaped branched butyl rubber, which is prepared by any one of the preparation methods described in the above technical solutions.

[0025] Compared with existing technologies, this invention provides a method for preparing star-shaped branched butyl rubber, comprising the following steps: A) Styrene and its derivatives, a nitrogen-lithium initiator, a polarity modifier, and a solvent are mixed and reacted, and then butadiene is added to continue the reaction to obtain an SBS branching agent; B) SBS is catalytically hydrogenated, controlling the degree of hydrogenation to 20%~70%, to obtain a partially hydrogenated SBS branching agent; C) The partially hydrogenated SBS branching agent is dissolved in a solvent, mixed with isobutylene and isoprene, and an initiator is added to carry out a polymerization reaction to obtain the desired product. This invention uses living anionic polymerization technology to prepare block copolymers of styrene and its derivatives with butadiene, and partially hydrogenates them through catalytic hydrogenation. By controlling the ratio of catalyst / polarity modifier, a branching agent with a specific degree of hydrogenation is synthesized. Then, the branching agent is dissolved in dichloromethane for the preparation of butyl rubber to obtain star-shaped branched butyl rubber with a bimodal broad molecular weight distribution. Attached Figure Description

[0026] Figure 1A schematic diagram of the relationship between "hydrogenation degree - branching efficiency / gel content" based on experimental data from US4474924A and this invention; the diagram clearly shows: the low hydrogenation degree gel region (<20%), the "effective range" (20-70%), the "preferred range" (30-60%) defined by this invention, the branching efficiency decrease region (70-85%), and the high hydrogenation degree failure region (>85%);

[0027] Figure 2 The comparison of the GPC spectra of the embodiments of the present invention with those of the comparative examples shows the difference between bimodal and unimodal distributions. Detailed Implementation

[0028] This invention provides a star-branched butyl rubber and its preparation method. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of protection of this invention. The method and application of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the method and application described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0029] This invention aims to solve the binary dilemma in the prior art, where the use of unhydrogenated branching agents results in easy gelation, and the use of highly hydrogenated copolymers results in no branching effect. It provides a star-branched butyl rubber with a stable polymerization process, controllable product structure, and excellent processing and physical-mechanical properties, as well as its preparation method.

[0030] The inventors have provided the following scientific basis:

[0031] The key active site for branching reaction is the 1,2-structure double bond: According to the cationic polymerization mechanism, the vinyl group of the side chain (1,2-structure) has a higher electron cloud density and smaller steric hindrance than the inner double bond of the main chain (1,4-structure), and therefore is the main active site for branching reaction.

[0032] The hydrogenation process is selective; during hydrogenation, the highly reactive 1,2-structure double bonds are preferentially saturated, while the 1,4-structure double bonds are relatively preserved.

[0033] This invention is the first to discover and define the “effective range” (20% ~ 70%) and the “preferred range” (30% ~ 60%) of hydrogenation degree. Within this range, the branching agent can retain a sufficient amount of highly active 1,2-structure double bonds to achieve efficient branching, and can also improve compatibility and process controllability through appropriate hydrogenation, thereby achieving synergistic optimization of branching efficiency and polymerization stability.

[0034] The "effective range" and "preferred range" for the degree of hydrogenation are defined:

[0035] Hydrogenation degree < 20%: Too many residual 1,2-structure double bonds, high reactivity, and easy gel formation during polymerization.

[0036] Hydrogenation degree 20% ~ 70%: The branching agent retains an appropriate amount of highly active 1,2-structure double bonds, ensuring the branching effect while significantly improving the compatibility with the butyl rubber matrix and the controllability of the reaction through hydrogenation. The polymerization process is stable and gel-free. This is the "effective range" of the present invention.

[0037] A hydrogenation degree of 30% to 60% results in the optimal synergistic effect between branching efficiency and polymerization stability, leading to the best overall product performance. This is the "preferred range" of this invention.

[0038] Hydrogenation degree > 70%: The 1,2-structure double bond remains too little, and the branching efficiency decreases significantly; when the hydrogenation degree exceeds 85%, it basically loses its chemical branching ability and only plays a physical stabilizing role.

[0039] The technical effect of this invention is "dual-effect in one agent"—it inhibits gelation (polymerization stabilization) through partial hydrogenation, and achieves efficient chemical branching by retaining the 1,2-structure. This invention achieves a unity of both within the 20-70% hydrogenation range for the first time, which is an unexpected technical effect.

[0040] The present invention provides a method for preparing star-branched butyl rubber, comprising the following steps:

[0041] A) Styrene and its derivatives, nitrogen-lithium initiator, polarity modifier and solvent are mixed and reacted, and then butadiene is added to continue the reaction to obtain linear active SB copolymer; then a coupling agent is added to carry out a coupling reaction to obtain star-shaped SBS branching agent; B) SBS is catalytically hydrogenated, and the degree of hydrogenation is controlled at 20%~70% to obtain partially hydrogenated SBS branching agent.

[0042] C) Dissolve the partially hydrogenated SBS branching agent in a solvent, mix it with isobutylene and isoprene, add an initiator, and carry out a polymerization reaction to obtain the product.

[0043] The present invention first prepares a nitrogen-lithium initiator.

[0044] In some specific embodiments, the preparation method of the nitrogen-lithium initiator includes:

[0045] Hexamethyleneimine is reacted with n-butyllithium, butadiene is added, and the reaction is continued to obtain a hexamethyleneimine-based alkyllithium initiator; the degree of polymerization of butadiene on the initiator chain is 4-10.

[0046] The molar ratio of hexamethyleneimine to n-butyllithium in this invention is 0.1 to 1.2; specifically, it can be 0.2, 0.5, 0.8 or 1.0. Those skilled in the art can select a suitable ratio within this range according to actual needs.

[0047] The reaction temperature is 20~25℃, specifically 21℃, 22℃, 23℃ or 24℃. Those skilled in the art can select a suitable reaction temperature within this range according to the actual reaction process. The reaction time is controlled within 10~40 minutes, specifically 15 minutes, 20 minutes, 25 minutes or 30 minutes. Those skilled in the art can select a suitable reaction time within this range according to the actual reaction process.

[0048] To improve the initiation activity of LHMI, a small amount of butadiene is added for activation. The amount of butadiene added for activation in this invention is determined according to the degree of polymerization of butadiene on the target initiator chain (4~10) and the molar amount of nitrogen-lithium initiator. Specifically, the ratio of the amount (molar) of butadiene added to the molar amount of LHMI in the nitrogen-lithium initiator is 4:1 to 10:1.

[0049] Prepare a hexamethyleneimine-based alkyl lithium initiator, controlling the degree of polymerization of butadiene on the initiator chain to be 4-10; preferably 5-8.

[0050] Styrene and its derivatives, nitrogen-lithium initiators, polar modifiers and solvents are mixed and reacted.

[0051] The present invention relates to styrene and its derivatives, including styrene, α-methylstyrene, etc. Those skilled in the art can select the specific monomer type according to the molecular weight requirements of the product.

[0052] The polarity modifier of the present invention includes one or more of tetrahydrofuran (THF), diethylene glycol dimethyl ether (2G), and tetramethylethylenediamine (TMEDA), preferably THF.

[0053] The above reaction was carried out in an anhydrous and oxygen-free environment, and the solvent was cyclohexane.

[0054] In some specific embodiments, the molar ratio of styrene and its derivatives to butadiene in step A) is 40:60 to 50:50; specifically, it can be 40:60, 42:58, 45:55, 48:52 or 50:50; particularly preferred is 45:55.

[0055] In the butadiene block, the initial content of the 1,2-structure is controlled at 15-25 mol% (percentage of butadiene), and the content of the 1,4-structure is 75-85 mol%.

[0056] The molar ratio of the polarity modifier to the nitrogen-lithium initiator in this invention is 1 to 20; specifically, it can be any value from 1, 3, 4, 5, 8, 10, 12, 15, 18, to 20, or fall within the range formed by any two of the above values. A ratio of 4 to 10 is particularly preferred.

[0057] The ratio of styrene to nitrogen-lithium initiator is determined based on the molecular weight of the target branching agent by Mn≈total monomer mass / molar number of initiator; the molar ratio of polarity modifier to nitrogen-lithium initiator is 1~20; specifically, it can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20.

[0058] In some specific embodiments, the reaction temperature in step A) is 45~65℃, preferably 55~60℃; specifically, it can be 45℃, 48℃, 50℃, 53℃, 55℃, 58℃, 60℃, 62℃, or 65℃, or fall within the range formed by any two of the above values. The reaction time is 30~60min, specifically 30min, 35min, 40min, 45min, 50min, 55min, or 60min, or fall within the range formed by any two of the above values, preferably 30~45min. Butadiene is added after 30~60min of reaction, and the reaction continues for 40~80min; the temperature of the continued reaction is 55~75℃.

[0059] After the butadiene reaction is complete, a coupling agent is added to the reaction system to carry out a coupling reaction, yielding a star-shaped SBS branching agent. The coupling agent is a multifunctional coupling agent, preferably silicon tetrachloride (SiCl4), but other conventional coupling agents such as dichlorodimethylsilane and divinylbenzene can also be selected according to actual reaction requirements. The coupling reaction mechanism is as follows: multiple reaction sites in the coupling agent undergo nucleophilic substitution reactions with the chain ends of the linear active SB copolymer, forming a star-shaped structure with multiple SB arms extending radially from the coupling agent residues at the center.

[0060] The process parameters for the coupling reaction are as follows: the molar ratio of coupling agent to initiator is 0.1~1.0, preferably 0.3~0.8; the coupling reaction temperature is 50~110℃, preferably 60~90℃; and the coupling reaction time is 10~60 min, preferably 20~40 min. After the coupling reaction is completed, anhydrous ethanol is added to terminate the reaction, yielding a star-shaped SBS branching agent.

[0061] In some specific embodiments, the number-average molecular weight Mn of the SBS branching agent is 5 × 10⁻⁶. 4 ~ 2.0×10 5 g / mol;

[0062] SBS is catalytically hydrogenated, with the degree of hydrogenation controlled at 20%–70%, to obtain a partially hydrogenated SBS branched agent. Preferably, the degree of hydrogenation is 30%–60%. Within this range, the difference in hydrogenation activity between the 1,2- and 1,4- structures is utilized.

[0063] The highly reactive 1,2-structure double bonds are preferentially saturated. According to the inventors' experimental data, when the degree of hydrogenation is controlled at 20-70%, the content of the residual 1,2-structure after hydrogenation is approximately 5-15 mol%. These residual 1,2-structures can serve as active sites for subsequent cationic polymerization of butyl rubber, ensuring that the branching agent chemically bonds with the butyl rubber backbone to construct a star-shaped branched structure. After the reaction is complete, anhydrous ethanol is used to terminate flocculation, and the mixture is dried in a vacuum oven to constant weight for later use.

[0064] The partially hydrogenated SBS branching agent is dissolved in a solvent, namely dichloromethane; it is then mixed with isobutylene and isoprene, and an initiator is added to carry out a polymerization reaction, thus obtaining the product. The main catalyst in the initiator is a Lewis acid, preferably aluminum trichloride, but other conventional Lewis acids such as dichloroethylaluminum and titanium tetrachloride can also be selected according to actual reaction requirements. The co-initiator is a proton donor. Specifically, it can be any one of HCl gas, water, and phenol, or a mixture of two or more of the above substances in any proportion. In this embodiment, the proton donor is HCl gas with a purity ≥99.9% and which has undergone drying pretreatment.

[0065] In some specific embodiments, step C) involves a reaction temperature of -80 to -98°C; specifically, it can be -85°C, -90°C, or -95°C; and a reaction time of 1 to 10 minutes; specifically, it can be 3 minutes, 5 minutes, or 8 minutes. Anhydrous ethanol is added to terminate the reaction, and the sample is vacuum dried to obtain a bimodal star-branched butyl rubber. After reacting according to the above proportions and process parameters, a star-branched butyl rubber product is obtained. Its structure and properties are characterized, and the weight-average molecular weight of the obtained product is measured to be 4.5 × 10⁻⁶ Mw. 5 ~ 5.5×10 5 g / mol, star structure content 15%-25%, Mooney viscosity 47-55.

[0066] Compared to linear butyl rubber of the same molecular weight, the product obtained in this embodiment has superior processing performance and lower extrusion shrinkage, meeting the requirements for higher performance processing. The star-branched butyl rubber has a bimodal molecular weight distribution, with a weight-average molecular weight to number-average molecular weight ratio (Mw / Mn) greater than 4.0.

[0067] This invention provides a star-shaped branched butyl rubber, which is prepared by any one of the preparation methods described in the above technical solutions.

[0068] The method of the present invention has been described in detail above, and will not be repeated here.

[0069] This invention passivates the highly reactive 1,2-structure double bonds through partial hydrogenation, avoiding excessive cross-linking. Compared with unhydrogenated SBS branching agents, the embodiments of this invention do not produce significant gelation during polymerization, the polymerization system is stable, the reactor is free of glue buildup and blockage, and the equipment operating cycle is extended.

[0070] The retained 1,2-double bonds serve as active sites in cationic polymerization, chemically bonding the branching agent to the butyl rubber backbone. A star-shaped branched structure was successfully constructed, resulting in a significantly broadened molecular weight distribution and greatly improved processing performance. Compared to linear IIR polymerization, the GPC products of this invention exhibit a typical bimodal distribution, with a molecular weight distribution index (Mw / Mn) of 4.8-5.2, a stress relaxation rate (t80) decreasing from 12.8 s to approximately 6 s, reduced Mooney viscosity, and significantly improved processing performance.

[0071] The preferred hydrogenation range (30-60%) of this invention achieves an optimal balance between branching efficiency and polymerization stability. The star-branched butyl rubber prepared by this invention maintains excellent physical and mechanical properties (tensile strength ≥19MPa) while also possessing excellent processing performance with low Mooney viscosity and fast stress relaxation rate, meeting the requirements of high-end applications such as high-performance tire airtight layers and vulcanizing bladders.

[0072] The branching agent prepared in this invention employs mature anionic polymerization and catalytic hydrogenation processes. The butyl rubber polymerization section is fully compatible with existing industrial equipment. No large-scale equipment modifications are required, the process flow is simple, and it is easy to achieve industrial-scale production, resulting in significant economic benefits.

[0073] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0074] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0075] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0076] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items.

[0077] It should be understood that the order of the steps or the order in which certain actions are performed is not important as long as the invention remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0078] The use of any and all instances or exemplary language such as “e.g.” or “including” in this document is merely intended to better illustrate the invention and is not intended to limit the scope of the invention unless the claims are made. No language in this specification should be construed as indicating that any unclaimed element is essential to the practice of the invention.

[0079] Furthermore, the numerical ranges and parameters used to define the present invention are approximate values, and the relevant values ​​in the specific embodiments have been presented as precisely as possible. However, any value inevitably contains standard deviations due to individual test methods. Therefore, unless explicitly stated otherwise, it should be understood that all ranges, quantities, values, and percentages used in this disclosure are modified with the word "approximately". Here, "approximately" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific value or range.

[0080] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0081] The embodiments and comparative examples of this invention describe some examples, in which the embodiments illustrate certain implementations of the invention. However, this does not mean that the effects of the invention can only be achieved in these examples.

[0082] Raw material description:

[0083] Isobutylene, isoprene, styrene, butadiene: Polymer grade, purified and dried before use.

[0084] Chloromethane and cyclohexane: Polymerization grade, dried by molecular sieve before use.

[0085] n-Butyllithium: 1.6 mol / L cyclohexane solution.

[0086] Hexamethyleneimine, tetrahydrofuran (THF), silicon tetrachloride (SiCl4) (new addition): analytical grade, dried before use.

[0087] Dichloroethylaluminum: 20wt% n-hexane solution.

[0088] HCl gas: purity ≥ 99.9%, dry before use.

[0089] SBS base resin: Star-shaped SBS prepared by living anionic polymerization. Styrene molar ratio 45%, butadiene molar ratio 55%. In the butadiene blocks, the initial content of 1,2-structure is 20 mol%, and the content of 1,4-structure is 80 mol%. Mn = 120,000, PDI < 1.2.

[0090] Partially hydrogenated SBS branching agent: prepared by catalytic hydrogenation of the above-mentioned SBS under different conditions.

[0091] Analysis and testing methods:

[0092] Molecular weight and distribution: determined by gel permeation chromatography (GPC) with tetrahydrofuran as the mobile phase.

[0093] Mooney viscosity: measured in ml (1+8) at 125°C according to GB / T 1232.1 standard.

[0094] Stress relaxation test: Immediately after the Mooney viscosity test (GB / T 1232.1, 125℃), stop the rotor rotation and record the torque decay curve over time. Using the torque at rotor stop as the initial value (100%), record the time required for the torque to decay to 20%, denoted as t80 (s). t80, as a parameter characterizing the stress relaxation rate of rubber, has been widely used in evaluating processing performance. The national standard GB / T 1232.4-2017, "Determination of Unvulcanized Rubber by Disk Shear Viscometer - Part 4: Determination of Mooney Stress Relaxation Rate," clearly stipulates that the Mooney stress relaxation test can obtain the elastic response characteristics of materials in addition to viscous response, and is a standard method for evaluating the processing performance of raw rubber or unvulcanized compound rubber. Studies have shown that there is an intrinsic relationship between stress relaxation parameters and the degree of branching of rubber molecular chains, viscoelastic properties, and product processing behavior, and it can be used to semi-quantitatively characterize and predict processing behavior. In practical applications, the Mooney stress relaxation test has been used in various scenarios such as rubber incoming inspection, tread extrusion porosity control, and calender roll sticking problem diagnosis. It is an effective means of controlling rubber compound quality due to its simple sample preparation and short analysis time. A smaller t80 value indicates faster stress relaxation and better processing performance.

[0095] Tensile strength: tested according to GB / T 528 standard.

[0096] Gel content: determined by toluene extraction method.

[0097] Microstructure and degree of hydrogenation: determined by ¹H-NMR.

[0098] To further illustrate the present invention, the following detailed description of a star-shaped branched butyl rubber and its preparation method provided by the present invention is provided in conjunction with embodiments.

[0099] Example 1: Application of SBS branching agents with partially hydrogenated hydrogenation within the preferred range (hydrogenation degree 45%)

[0100] Preparation of nitrogen-lithium initiator: Following a well-known method in the field of anionic polymerization, 15.6 g of cyclohexane, 5 ml of 1.6 mol / L n-butyllithium, and 0.8 g of hexamethyleneimine were added to an anhydrous and oxygen-free reaction flask. After reacting at room temperature for 20 min, 1.3 g of butadiene was added, and the reaction was carried out at 40 °C for 40 min to obtain a hexamethyleneimine-based alkyllithium initiator (abbreviated as N-Li) with a molar concentration of 0.32 mol / L. The initiator was sealed and stored in a refrigerator for later use.

[0101] Preparation of partially hydrogenated SBS branching agent: In an anhydrous and oxygen-free reaction flask, 195 g cyclohexane, 14.5 g styrene (0.14 mol), 0.033 g THF, and 1.4 ml N-Li initiator (approximately 0.45 mmol) were added. After reacting at 60 °C for 40 min, 21.75 g butadiene (0.4 mol) was added, and the reaction was continued at 70 °C for 60 min to obtain a linear active SB copolymer. Then, silicon tetrachloride (SiCl4) was added as a coupling agent, with a SiCl4 to Li molar ratio of 0.3–0.5. The reaction was continued at 70 °C for 30 min to obtain star-shaped SBS. ¹H-NMR analysis showed that the styrene molar ratio was 45%, and the initial 1,2-structure content in the butadiene block was 20%. The above SBS was then catalytically hydrogenated, with the hydrogenation degree controlled to reach 45%. ¹H-NMR analysis showed that the residual 1,2-structure content after hydrogenation was 9.2 mol. Anhydrous ethanol was used to terminate flocculation, and the mixture was then vacuum-dried to constant weight for later use.

[0102] Preparation of star-shaped branched butyl rubber: In an anhydrous and oxygen-free environment, at -95°C, 110.5 g of monochloromethane, 0.2 g of the partially hydrogenated SBS branching agent, 19.5 g of isobutylene, and 0.6 g of isoprene were added to a reaction flask and mixed thoroughly. 0.22 g of a 20% dichloroethylaluminum n-hexane solution was mixed with 2 g of a water-saturated dichloromethane solution, with a main catalyst to co-catalyst molar ratio of 1:10. After aging at -95°C for 30 min, the mixture was added to the above mixture, reacted for 3 min, and then terminated by adding anhydrous ethanol. The mixture was then vacuum dried.

[0103] The branching agent Mn was found to be 7.8 × 10⁻⁶. 4 Mw is 9.3 × 10 4 The molecular weight distribution is 1.20; the star-branched butyl rubber exhibits a bimodal distribution with a molecular weight of 5.3 × 10⁻⁶. 5 The Mw / Mn ratio is 5.2, the gel content is <0.1%, the Mooney viscosity is 47, the t80 is 5.8s, and the tensile strength is 19.0MPa.

[0104] Example 2: Application of SBS branching agents partially hydrogenated at the lower limit of the effective range (hydrogenation degree 25%)

[0105] Except for controlling the hydrogenation conditions to achieve a hydrogenation degree of 25% (approximately 13.5 mol% of the 1,2-structure remains after hydrogenation), the other conditions were the same as in Example 1.

[0106] The star-branched butyl rubber obtained exhibits a bimodal distribution with a Mw of 5.1 × 10⁻⁶. 5 The Mw / Mn ratio is 5.0, the gel content is 0.3%, the Mooney viscosity is 49, the t80 is 6.5s, and the tensile strength is 18.5MPa.

[0107] Example 3: Application of SBS branching agents partially hydrogenated at the upper limit of the effective range (hydrogenation degree 65%)

[0108] Except for controlling the hydrogenation conditions to achieve a hydrogenation degree of 65% (approximately 5.5 mol% of the 1,2-structure remains after hydrogenation), the other conditions were the same as in Example 1.

[0109] The star-branched butyl rubber obtained exhibits a bimodal distribution with a Mw of 5.0 × 10⁻⁶. 5 The Mw / Mn ratio is 4.8, the gel content is <0.1%, the Mooney viscosity is 48, the t80 is 6.3s, and the tensile strength is 18.8MPa.

[0110] Comparative Example 1: Unbranched agent (linear IIR)

[0111] Except for the absence of any branching agent, the other conditions are the same as in Example 1.

[0112] The butyl rubber was found to have a unimodal distribution with a Mw of 4.5 × 10⁻⁶.5 The Mw / Mn ratio is 2.5, the Mooney viscosity is 55, the t80 is 12.8s, and the tensile strength is 17.5MPa.

[0113] Comparative Example 2: Unhydrogenated SBS branching agent (0% hydrogenation)

[0114] Except for using unhydrogenated SBS (0% hydrogenation) as the branching agent, the other conditions were the same as in Example 1.

[0115] The viscosity increased dramatically during the polymerization process, the product had a gel content of 5.2%, a Mooney viscosity of 51, a t80 of 7.8s, and a tensile strength of 17.5 MPa.

[0116] Comparative Example 3: Partially hydrogenated SBS branching agent with high hydrogenation degree (hydrogenation degree 85%)

[0117] Except for controlling the hydrogenation conditions to achieve a hydrogenation degree of 85% (0 mol% of 1,2-structure remains after hydrogenation), the other conditions were the same as in Example 1.

[0118] The polymerization process was stable and gel-free. The product GPC exhibited a unimodal distribution with a Mw of 3.8 × 10⁻⁶. 5 The Mw / Mn ratio is 3.4, the Mooney viscosity is 53, the t80 is 11.2 s, and the tensile strength is 17.8 MPa. These results are in complete agreement with the teachings of US4474924A, demonstrating that when the hydrogenation is too high (85%), the 1,2-structure is completely saturated, and the branching agent loses its chemical branching ability.

[0119] Comparative Example 4: Fully hydrogenated and partially hydrogenated SBS branching agent (degree of hydrogenation > 98%)

[0120] Except for controlling the hydrogenation conditions to achieve a hydrogenation degree of >98%, the other conditions are the same as in Example 1.

[0121] The polymerization process was stable and gel-free. The product GPC exhibited a unimodal distribution with a Mw of 3.6 × 10⁻⁶. 5 The Mw / Mn ratio is 3.3, Mooney viscosity is 54, t80 is 12.0 s, and tensile strength is 17.8 MPa. This further demonstrates that excessive hydrogenation leads to the complete loss of branching function.

[0122] Comparative Example 5: Partially hydrogenated SBS branching agent with high styrene content

[0123] Except for using SBS base resin with a styrene molar ratio of 62%, a butadiene molar ratio of 38%, and an initial 1,2-structure content of 12% in butadiene, and controlling the degree of hydrogenation to reach 45%, the other conditions are the same as in Example 1.

[0124] The star-branched butyl rubber obtained exhibits a bimodal distribution, but with a low content in the high molecular weight region, a Mw / Mn ratio of 3.8, a t80 of 8.5s, and a tensile strength of 18.2 MPa. The results indicate that when the styrene content is too high and the initial 1,2- content is too low, even with a hydrogenation degree controlled at 45%, the branching effect is significantly inferior to the preferred embodiment of this invention.

[0125]

[0126] Note: t80 is the time required for the torque to decrease by 80% from its initial value in the Mooney stress relaxation test, characterizing the stress relaxation rate of the rubber. A smaller t80 value indicates faster stress relaxation and better processability. The test method follows GB / T 1232.1 and is performed after the Mooney viscosity determination.

[0127] Discussion of Results:

[0128] From the above examples and comparative examples, we can conclude that:

[0129] The effective range for hydrogenation degree is 20-70%: The products of Examples 1-3 (hydrogenation degree 25-65%) all showed bimodal distribution, low gel content and excellent processing performance, which proved the scientific validity of the "20-70% effective range".

[0130] The preferred range for hydrogenation degree is 30-60%. Example 1 (45%) showed the best performance in polymerization stability (gel <0.1%), branching efficiency (Mw / Mn=5.2) and overall performance (t80=5.8s, tensile strength 19.0MPa), representing the preferred range.

[0131] 85% is the critical point of failure: In Comparative Example 3 (85%), the product becomes a single-peak distribution and the branching effect disappears, perfectly confirming the discovery of US4474924A, and also verifying that the definition of the effective range of hydrogenation degree in this invention is reasonable.

[0132] Compared to the KR series structure of US4474924A, the styrene content (40-50%) and initial 1,2- content (15-25%) design of this invention are superior: Comparative Example 5 shows that even with the same hydrogenation degree controlled at 45%, the branching effect (Mw / Mn=3.8, t80=8.5s) of the KR series SBS with high styrene content (62%) and low initial 1,2- content (12%) is significantly worse than that of Example 1 of this invention (Mw / Mn=5.2, t80=5.8s). This indicates that the microstructure parameters selected in this invention have a synergistic optimization effect with the hydrogenation degree range, which is not taught in the prior art.

[0133] The fundamental difference in their mechanisms of action is as follows: In this invention, the partially hydrogenated SBS acts as a chemical branching agent, chemically bonding with the butyl rubber backbone through the residual 1,2-double bonds to construct a star-shaped branched structure; while in US4474924A, the hydrogenated product acts only as a physical stabilizer, preventing particle aggregation through adsorption. Comparative Examples 3 and 4 further demonstrate that when the hydrogenation concentration is too high (above 85%), the 1,2-structure is completely saturated, and the branching agent loses its chemical branching ability, only playing a physical stabilizing role, which is completely contrary to the technical concept of this invention.

[0134] The star-branched butyl rubber prepared by this invention maintains excellent physical and mechanical properties (tensile strength ≥19MPa) while significantly improving processing performance. Compared with linear IIR (Comparative Example 1, t80=12.8s), the stress relaxation rate t80 of Example 1 is shortened to 5.8s, indicating faster stress relaxation and reduced processing energy consumption, which is consistent with the characteristics of the star-branched structure.

[0135] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing star-branched butyl rubber, characterized in that, Includes the following steps: A) Styrene and its derivatives, nitrogen-lithium initiator, polarity modifier and solvent are mixed and reacted, and then butadiene is added to continue the reaction to obtain linear active SB copolymer; then a coupling agent is added to carry out a coupling reaction to obtain star-shaped SBS branching agent; B) Catalytically hydrogenate SBS, controlling the degree of hydrogenation to be 20%~70%, to obtain a partially hydrogenated SBS branching agent; C) Dissolve the partially hydrogenated SBS branching agent in a solvent, mix it with isobutylene and isoprene, add an initiator, and carry out a polymerization reaction to obtain the product.

2. The preparation method according to claim 1, characterized in that, The content of residual 1,2-butadiene units in the branching agent is 5~15 mol.

3. The preparation method according to claim 1, characterized in that, The preparation method of the nitrogen-lithium initiator includes: Hexamethyleneimine is reacted with n-butyllithium, butadiene is added, and the reaction is continued to obtain a hexamethyleneimine-based alkyllithium initiator; the degree of polymerization of butadiene on the initiator chain is 4-10. The molar ratio of hexamethyleneimine to n-butyllithium is 0.1~1.2; the reaction temperature is 20~25℃; and the reaction time is 10~40min.

4. The preparation method according to claim 1, characterized in that, The coupling agent mentioned in step A) is a multifunctional coupling agent selected from one or more of silicon tetrachloride, dichlorodimethylsilane, and divinylbenzene, preferably silicon tetrachloride; the molar ratio of the coupling agent to the initiator is 0.1~1.0, preferably 0.3~0.8; the coupling reaction temperature is 50~110℃, and the coupling reaction time is 10~60min.

5. The preparation method according to claim 1, characterized in that, In step A), the molar ratio of styrene and its derivatives to butadiene is 40:60 to 50:50; in the butadiene block, the initial content of the 1,2-structure is controlled at 15 to 25 mol% (percentage of butadiene), and the content of the 1,4-structure is 75 to 85 mol%.

6. The preparation method according to claim 1, characterized in that, In step A), the molar ratio of the polarity modifier to the nitrogen-lithium initiator is 1-20; the reaction temperature is 45-65°C; butadiene is added after 30-60 minutes of reaction, and the reaction continues for 40-80 minutes; the temperature for the continued reaction is 55-75°C.

7. The preparation method according to claim 1, characterized in that, In step C), the solvent is dichloromethane, the main catalyst in the initiator is a Lewis acid, and the co-initiator is a proton donor.

8. The preparation method according to claim 1, characterized in that, Step C) The reaction temperature is -80~-98℃; the reaction time is 1~10min.

9. The preparation method according to claim 1, characterized in that, The number-average molecular weight Mn of the SBS branching agent is 5 × 10⁻⁶. 4 ~ 2.0×10 5 g / mol; The star-branched butyl rubber has a bimodal molecular weight distribution, and the ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn) is greater than 4.

0.

10. A star-branched butyl rubber, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

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