Preparation method of star butyl rubber

Abstract

The invention relates to the field of polymer preparation, in particular to a preparation method of star butyl rubber, which comprises the following steps: firstly, initiating cationic polymerization of isobutene and isoprene to form a linear main chain with a cationic active terminal, then adding a silane end-capping agent to complete silanization end capping, and then adding an AlCl3 / Et2O composite catalyst in stages to obtain the star butyl rubber. The preparation method comprises the following steps: adding a silane group to selectively activate the silane group to form a grafting anchor point, and then adding a branching agent containing at least two olefin groups, so that double bonds of the branching agent and the grafting anchor point are subjected to cationic copolymerization, thereby forming a star-shaped branched structure. According to the invention, through silane end capping and gradient activation technologies, branching points are strictly positioned at the tail end of a main chain, random distribution is avoided, the uniformity of a product is remarkably improved, through the synergistic effect of staged catalyst addition and branching agent gradient feeding, the reaction process is effectively controlled, the gel content is reduced to an extremely low level (lt, 0.1%), and the processing stability is guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of polymer preparation, and particularly relates to a preparation method of star - shaped butyl rubber. Background Art

[0002] As a high - performance polymer material, star - shaped butyl rubber has a core structural feature of a star - shaped topological configuration with a linear butyl rubber as the main chain and multiple branches connected at the ends. Butyl rubber itself is a synthetic rubber made by cationic polymerization of isobutene and a small amount of isoprene (usually 1 - 3 mol%). Due to the unique combination of highly saturated isobutene units and isolated double bonds in its molecular chain, it has excellent airtightness, aging resistance and damping properties, and is widely used in fields such as inner tubes of tires, stoppers for medicine bottles, and damping materials. However, traditional linear butyl rubber exposes defects such as high internal friction and insufficient tear resistance in dynamic use scenarios. The introduction of a star - shaped structure can significantly improve its performance through molecular chain topology engineering: the physical entanglement effect generated by star - shaped branching can reduce the cold flow tendency of the polymer and improve the dimensional stability of the uncured rubber; the high - density double - bond distribution at the end of the branches can optimize the uniformity of the vulcanization network, increasing the fatigue resistance life of the vulcanized rubber by 2 - 3 times; at the same time, the relaxation time spectrum broadening effect of the star - shaped structure can effectively reduce the rolling resistance, which is of great significance for the energy - saving development of green tires.

[0003] The current mainstream preparation technology of star - shaped butyl rubber mainly focuses on the two - step process. Its core idea is to first synthesize a multi - armed core with active ends, and then generate a star - shaped structure through chain extension or coupling reactions. For example, in the prior art, tin tetrachloride (SnCl4) is used as a multifunctional initiator to initiate the polymerization of isobutene and isoprene at - 70 °C to form a multi - armed core, and then a styrene derivative is added as a chain transfer agent for arm - chain growth. The defect of this process is that SnCl4 is prone to hydrolysis side reactions with trace moisture in the monomer, resulting in fluctuations in the initiation efficiency, and the residual tin compounds will poison the subsequent vulcanization system. Another representative technology pre - polymerizes isoprene with butyllithium to form an active chain, and then couples it with an epoxide to generate a star - shaped structure. Although the molecular weight distribution of this method is relatively narrow (PDI≈1.2), its reaction needs to be carried out at an ultra - low temperature (-90 °C), the equipment energy consumption is extremely high, and the high proportion introduction of isoprene (>5 mol%) will seriously damage the airtightness advantage of butyl rubber. In addition, some researchers have tried to construct a star - shaped structure through a free - radical grafting method, such as using dicumyl peroxide (DCP) to initiate the graft copolymerization of butyl rubber and divinylbenzene. However, the randomness of the free - radical reaction leads to a serious uneven distribution of branching points (the fluctuation range of the number of branched arms is 2 - 8), and the residual peroxide will cause pre - crosslinking problems during storage.

[0004] In recent years, the academic and industrial communities have begun to explore one-step synthesis processes to simplify the production process. For example, the literature reports a synchronous polymerization-branching technique based on double metal cyanide (DMC) catalysts. Utilizing the dual active center characteristics of DMC catalysts, branching points are generated in situ during the polymerization of isobutene. Although this method avoids the complexity of multi-step reactions, DMC catalysts are extremely sensitive to impurities, making industrial implementation difficult. Moreover, the branching points are prone to appear inside the main chain (about 40% of the branching points are more than 5 monomer units away from the end), resulting in limited improvement in dynamic mechanical properties.

[0005] The common problems faced by the existing technologies can be summarized into three aspects: First is the problem of precise control of the branching structure. Since the chain transfer side reaction in the cationic polymerization of butyl rubber is difficult to completely suppress (especially at higher temperatures), the branching points are randomly distributed. Statistical data shows that only 55-65% of the branching points in star-shaped butyl rubber prepared by traditional methods are located at the ends of the main chain, and the remaining branching points are scattered in the middle of the chain segments, which will significantly weaken the performance advantages of the star-shaped structure. Second is the balance contradiction between the molecular weight distribution and the branching efficiency. To achieve a higher degree of branching (>3 arms / molecule), it is often necessary to increase the dosage of initiators or multi-functional reagents, but this will exacerbate the broadening of the molecular weight distribution (PDI>2.5), resulting in unstable processing performance of the product. Finally is the feasibility bottleneck of industrial production. Existing methods generally require multi-step reaction switching (such as initiator activation-chain growth-coupling) or extreme process conditions (such as -90°C low temperature, ultra-high vacuum dehydration). This not only increases the equipment investment cost but also leads to high energy consumption indicators. More seriously, gelation phenomena are difficult to avoid during the branching stage in most existing processes. Even with strict control of reaction conditions, the gel content still generally fluctuates within the range of 0.5-1.2%. These micro-crosslinked particles will form surface defects during extrusion molding, directly affecting the airtightness level of the product.

[0006] Against this background, developing a method for preparing star-shaped butyl rubber with precisely positioned branching points, controllable molecular weight distribution, and suitable for industrial scale-up has become a technical problem that urgently needs to be broken through in this field. In particular, it is necessary to design a new type of end-capping agent system and activation mechanism to achieve end-selective branching reactions while ensuring the integrity of the main chain structure, and at the same time avoid the generation of initiator residues and gel by-products. This requires innovating the functional group combination of the end-capping agent at the molecular design level and breaking through the dilemma that it is difficult to have both high branching efficiency and product homogeneity in the existing technology through the coordinated regulation of process parameters. Summary of the Invention

[0007] To overcome the deficiencies in the existing star-shaped butyl rubber during preparation, such as the inability to precisely control the branching structure, the inability to balance the contradiction between the molecular weight distribution and the branching efficiency, and the high cost and complex process, this application provides a method for preparing star-shaped butyl rubber to overcome the above deficiencies.

[0008] To achieve the above-mentioned invention object, the present invention is realized through the following technical solutions: In a first aspect, the present invention first provides a preparation method of star-shaped butyl rubber, comprising the following steps: (a) In an inert solvent, through cationic polymerization of isobutene and isoprene, a linear main chain with a cationic active end is formed; (b) A silane capping agent is added, and it causes a nucleophilic substitution reaction to occur at the cationic active end, thereby completing silanization capping; The silane capping agent has the following general formula: Cl-CH2-SiR1R2R3; Wherein, R1, R2, and R3 are independently selected from C1-C4 alkyl groups or phenyl groups; (c) The temperature of the reaction system is raised, and an AlCl3 / Et2O composite catalyst is added in stages to selectively activate the silyl group to form a grafting anchor point; (d) A branching agent containing at least two olefin groups is added, and the double bond of the branching agent undergoes cationic copolymerization with the grafting anchor point, thereby forming a star-shaped branched structure.

[0009] As described in the background art, the preparation method of star-shaped butyl rubber, as an important branch of the functional modification of butyl rubber, its core challenge lies in how to achieve precise positioning of the branching points and coordinated control of the molecular weight distribution. In the traditional technical route, whether it is the "core-first and arms-later" strategy based on multi-functional initiators or the end-crosslinking of linear chains through coupling agents, both face the dilemma of difficult to balance the branching efficiency and structural uniformity. Existing methods often improve the degree of branching by increasing the functionality of the initiator or the concentration of the coupling agent, but this directly leads to an increase in chain transfer side reactions during the molecular chain growth process, an increase in initiator residues, and the branching points in the final product are randomly distributed at different positions (even inside the main chain) of the main chain, and the molecular weight distribution index (PDI) is generally higher than 2.0. This structural defect is manifested as large fluctuations in the mechanical properties of vulcanized rubber and significant cold flow tendency of unvulcanized rubber in the application scenario. Especially in fields such as tire inner liners where strict requirements are imposed on the material uniformity, the batch stability of traditional star-shaped butyl rubber is difficult to meet the industrial demand. In addition, multi-functional initiators widely used in existing processes (such as tin tetrachloride, multi-epoxy compounds, etc.) are difficult to be completely consumed after chain initiation. The residual active components will not only interfere with subsequent vulcanization reactions but also cause pre-crosslinking phenomena during storage, resulting in an increase in gel content (usually > 0.5%), directly affecting the processing performance of the product. These problems essentially stem from the extensive control of the branching reaction path in traditional technologies - the branching process and the main chain synthesis cannot be effectively separated in the space-time dimension, resulting in multiple competing paths such as chain growth, chain transfer, and branching crosslinking in the reaction system, and the topological structure of the final product shows uncontrollable statistical distribution characteristics.

[0010] The creative breakthrough of this preparation method is aimed at the above-mentioned technical pain points. The core design logic lies in decoupling the physicochemical conditions of two key steps: the synthesis of the linear main chain and the star-shaped branching. First, a linear main chain with active ends is prepared by cationic polymerization, and then a silane capping agent with a specific structure (Cl-CH2-SiR1R2R3) is introduced to selectively passivate the active ends. The ingenuity of this step is that the chlorine atom in the silane capping agent, as a highly reactive leaving group, can quickly undergo a nucleophilic substitution reaction with the cationic active ends, efficiently terminating the chain growth at extremely low temperatures (e.g., -80 °C) (capping efficiency > 98%), thus avoiding the broadening of the molecular weight distribution caused by chain transfer side reactions in traditional methods. At the same time, the three-dimensional structure of the silyl group (SiR1R2R3) not only plays a steric hindrance role to prevent unexpected reactions at the main chain ends in subsequent steps, but more importantly, its special electronic properties through the silicon atom reserve controllable activation sites for subsequent branching reactions. This "dynamic capping" mechanism is an innovation not disclosed in the prior art. Traditional capping agents (such as methanol, tert-butylamine, etc.) can only achieve the function of chain termination, while the silane capping agent in this solution has the dual functions of capping protection and anchoring potential reaction sites, laying a molecular foundation for the site-directed triggering of subsequent branching reactions.

[0011] After completing the main chain capping, the preparation method realizes the selective activation of the silyl group through a synergistic strategy of temperature regulation and staged addition of the catalyst. Specifically, during the process of increasing the system temperature, the AlCl3 / Et2O composite catalyst is introduced in stages: in the first stage, the addition of a small amount of catalyst preferentially activates the Si-C bond in the silyl group to generate a highly reactive siloxane-aluminum complex intermediate (such as ≡Si-O-AlCl2 + ), while the C-Si bond inside the main chain remains inert due to the differences in steric hindrance and electron cloud distribution; in the second stage, the addition of the catalyst is supplemented to further strengthen this activation process, ensuring the formation of a high density of grafting anchor points. This gradient catalytic mechanism effectively solves the problem of non-selective attack of the activator on the main chain structure in traditional methods, restricting the branching reaction strictly to the end region of the main chain. In the prior art, whether using a single catalyst (such as BF3·Et2O) or homogeneous catalysis at a constant temperature, it is impossible to avoid the migration of the branching point into the main chain interior. However, in this solution, through the fine regulation of the addition timing and concentration of the catalyst, combined with the directional intervention of temperature on the reaction kinetics, the positioning accuracy of the branching point is successfully improved to within 3 monomer units at the end, and the deviation of the branching point distribution is controlled within ±8%.

[0012] The selection and introduction method of the branching agent further reflects the technological innovation of this solution. By using a branching agent containing at least two olefin groups (such as 1,5 - hexadiene, 1,3 - butadiene, etc.), the double bonds undergo cationic copolymerization under the action of the activated siloxane - aluminum complex to form a star - shaped branched structure starting from the end of the main chain. Different from the random cross - linking of traditional coupling agents (such as divinylbenzene), the double bonds of the branching agent in this solution first undergo a directional reaction with the grafting anchor points, and then form regular branched chains through chain growth. This process realizes the controllable growth of the branched structure at the molecular level. It is particularly worth noting that the gradient addition strategy of the branching agent (controlling the addition rate and temperature in stages) effectively inhibits the gelation tendency caused by excessive local concentration. When adding the branching agent by the traditional one - step method, due to the sudden increase in the concentration of the branching agent at the initial stage of the reaction, multiple branching agent molecules are likely to attack the same grafting anchor point simultaneously, forming over - cross - linked microgel particles (with a diameter of about 50 - 200 nm). However, in this solution, by controlling the addition rate in stages, the branching agent molecules diffuse evenly in the system, and the grafting reaction shows a progressive characteristic. Finally, the gel content can be controlled below 0.1%, which is reduced by an order of magnitude compared with the traditional method.

[0013] Finally, evaluated from the dimension of technical effects, this preparation method realizes the comprehensive improvement of the structural properties of star - shaped butyl rubber. First, the terminal positioning accuracy and distribution uniformity of the branching points are significantly improved, which maximizes the physical entanglement effect of the star - shaped structure. Through dynamic mechanical analysis, it shows that compared with the star - shaped butyl rubber prepared by the traditional method, the Payne effect of the product of this solution is reduced by about 40%, indicating a significant improvement in filler dispersion. Secondly, the molecular weight distribution index (PDI) can be stably controlled below 1.5, far lower than the range of 2.0 - 3.0 in the existing technology, which directly translates into better processing stability, and the die - swell ratio during extrusion molding decreases by about 25%. Finally, the combination of the efficient consumption of the silane end - capping agent and the gradient activation strategy reduces the residual amount of the initiator to less than 1 / 5 of the traditional method, completely solving the problem of the interference of the residual initiator on the vulcanization network, and the compression set value of the vulcanizate (ASTM D395 test) is reduced by 15% - 20%. Particularly importantly, the entire preparation process does not require extreme low temperature (> - 80°C) or ultra - high vacuum conditions, and the reaction equipment is compatible with the conventional butyl rubber production line, and the feasibility of industrial scale - up is significantly better than the existing technology. The synergistic effect of these technical advantages not only breaks through the long - standing problem of structural control in the preparation of star - shaped butyl rubber, but also achieves the optimal balance between industrialization cost and product performance, providing a new technical path for the development of high - performance rubber materials.

[0014] Preferably, the silane end - capping agent is selected from any one of the following: Any one of chloromethyltrimethylsilane, chloromethyltriethylsilane, and chloromethylphenyldimethylsilane.

[0015] Preferably, the specific operation of adding the AlCl3 / Et2O composite catalyst in stages in step (c) is as follows: In the first stage, a complex with a molar ratio of AlCl3 to Et2O of 1:1.2 - 1.5 is added, and the addition amount is 10 - 20% of the total catalyst amount; in the second stage, the remaining AlCl3 is added to control the total catalyst concentration to 0.05 - 0.3 mol / L.

[0016] The staged catalyst addition mechanism in this application achieves precise activation control through a gradient initiation strategy: in the first stage, a highly selective complex is formed with a specific ratio (AlCl3 / Et2O = 1:1.2 - 1.5), preferentially activating the Si - C bond at the silane - capped end to generate grafting anchor points, while suppressing the non - specific attack of the branching agent on the interior of the main chain; in the second stage, AlCl3 is accurately added to maintain the catalytic activity concentration, which not only avoids the chain - transfer side reaction caused by excessive initiator but also ensures the orderly grafting of the branching agent through a slow - release catalytic effect. Under the synergistic effect, the distribution of branching points is narrowed and the grafting density is effectively increased, while reducing the gel content, achieving the synergistic optimization of the efficient construction of the star structure and the stability of industrial production.

[0017] Preferably, in step (c), the temperature of the reaction system is raised to - 40°C to - 10°C, the activation time is controlled within 5 - 20 minutes, and the growth rate of the system viscosity ≤ 3% / min.

[0018] The inventors of this application found that within the temperature window of - 40°C to - 10°C, moderate temperature increase can improve the migration rate of the catalyst without destroying the stability of the silane capping. Combining with short - time activation of 5 - 20 minutes, the formation rate of grafting anchor points and the diffusion of the branching agent reach a dynamic balance, effectively suppressing the branching cross - linking caused by chain entanglement, thereby realizing the construction of high - density and uniformly distributed active sites.

[0019] Preferably, in step (d), the branching agent is a polyolefin containing 3 - 6 double bonds, and its structural general formula is: CH2 = CH-(CH2)n - CH = CH2, where n = 0 - 4; and, The molar ratio of the branching agent to the end of the main chain is 1:3 to 1:6.

[0020] Preferably, the branching agent is selected from any one of 1,3 - butadiene, 1,5 - hexadiene, and 1,7 - octadiene.

[0021] Preferably, the addition method of the branching agent in step (d) is staged gradient addition, specifically including: In the first stage, 60 - 80% of the total amount of the branching agent is added at a rate of 0.5 - 2.0 mL / min, and the system temperature is maintained at - 30°C to - 10°C; In the second stage, the remaining branching agent is added at a rate of 0.1 - 0.5 mL / min, while the temperature is raised to 0°C to 10°C; and, the interval time between the two stages is 3 - 8 minutes, and the total addition time is controlled not to exceed 30 minutes.

[0022] In this application, the step-by-step adaptation of kinetics and thermodynamics is achieved through the strategy of gradient addition of the branching agent, enabling the orderly growth of the branched structure: First, when the main branching agent is rapidly introduced in the first stage, the low-temperature environment (-30°C to -10°C) inhibits the overreaction of active sites, forcing the branching agent molecules to preferentially graft in a directional manner along the ends of the main chain to form primary nucleation points; Second, the coupling of temperature increase (0 - 10°C) and rate reduction and supplementary addition in the second stage activates the secondary activity of the pre-grafted nucleation points to initiate the progressive insertion of the remaining branching agent, forming an independent three-dimensional radial branched chain network. An interval of 3 - 8 minutes stabilizes the primary nucleation points, avoiding chain entanglement competition during batch addition, ensuring that each branching anchor point independently completes space occupation before starting chain extension, thus breaking through the original two-dimensional plane crosslinking mode and fundamentally avoiding the formation of gel microdomains.

[0023] Preferably, in step (a), the addition amount of isoprene is 0.8 - 2.0% of the molar amount of isobutene, and the number-average molecular weight of the main chain is controlled at 150,000 - 400,000.

[0024] Preferably, the inert solvent in step (a) is a mixed solvent with a volume ratio of halogenated hydrocarbon to aliphatic hydrocarbon of 3:1 to 5:1; Among them, the halogenated hydrocarbon is selected from any one of chloromethane, dichloromethane, or chloroethane; the aliphatic hydrocarbon is selected from any one of n-pentane or cyclohexane.

[0025] Preferably, it further includes step (e): adding a terminator containing an amino group to quench the reaction; the terminator is selected from any one of diethylamine, N-methylpyrrolidone, or triethylenediamine; and, the molar ratio of the terminator to the catalyst AlCl3 is 1.5:1 to 3:1.

[0026] Therefore, this application has the following beneficial effects: (1) Through the silane capping and gradient activation technologies, this application realizes that the branching points are strictly located at the ends of the main chain, avoiding random distribution and significantly improving the product homogeneity; (2) Through the synergistic effect of staged catalyst addition and gradient feeding of the branching agent, the reaction process is effectively controlled, and the gel content is reduced to an extremely low level (<0.1%), ensuring processing stability; (3) The rapid termination characteristic of silane capping reduces the side reaction of chain transfer. With the dynamic regulation of temperature - catalyst, the molecular weight distribution index (PDI) is significantly better than the traditional method; (4) No cryogenic temperature or complex equipment is required, and the reaction conditions are highly compatible with the conventional butyl rubber production line, reducing the industrialization transformation cost; (5) The obtained star-shaped butyl rubber has excellent airtightness, high tear resistance and low rolling resistance, meeting the stringent requirements for material properties in high-end fields such as tires and seals. Detailed implementation mode

[0027] The present invention will be further described below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are usually only a part of the embodiments of the present invention, rather than all the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the scope of protection of the present invention.

[0028] Example 1 A preparation method of star-shaped butyl rubber, which comprises the following steps: Step (a): Synthesis of linear main chain: In a dry 5L stainless steel reactor, add 3L of a mixed solvent (chloromethane: n-hexane = 4:1 volume ratio), and purge with high-purity nitrogen three times until the oxygen content < 5 ppm. Cool the system to -80 °C, and successively add 500 g (8.93 mol) of isobutene and isoprene (4.3 g, 0.06 mol), and stir for 10 minutes to mix evenly. Inject the initiator solution (0.45 g of AlCl3 dissolved in 50 mL of chloromethane, concentration 0.01 mol / L) to initiate the cationic polymerization reaction. Maintain the temperature at -80 °C ± 1 °C. After reacting for 60 minutes, the number-average molecular weight (Mn) of the main chain measured by GPC is 152,000, the molecular weight distribution index (PDI = 1.28), and the double bond content of the isoprene unit is 1.8 mol%. At this time, the conversion rate of the main chain reaches 90%, and the end is an active cation (-C + (CH3)2).

[0029] Step (b): Silylation end-capping: Keep the temperature at -80 °C, and slowly add to the reactor a chloromethane solution of chloromethyltrimethylsilane (Cl-CH2-Si(CH3)3) (12.5 g dissolved in 100 mL). After reacting for 15 minutes, online FTIR monitoring shows that the characteristic peak of the Si-Cl bond (580 cm -1 ) completely disappears, indicating that the end-capping efficiency > 99%.

[0030] Step (c): Activation of silyl groups: Heat up to -40 °C at a rate of 5 °C / min, and add the AlCl3 / Et2O composite catalyst in two stages: The first stage: Add a premixed AlCl3 / Et2O (molar ratio 1:1.3) solution, with an addition amount of 15% of the total catalyst, and stir for 10 minutes.

[0031] The second stage: Supplement the remaining AlCl3 / Et2O to make the total catalyst concentration 0.12 mol / L, continue to heat up to -10 °C, and maintain for 20 minutes.

[0032] Step (d): Branching reaction: Stabilize the reaction system at -10 °C, and add 1,3-butadiene (branching agent) in two stages: The first stage: Add 80% of the total amount (24 g, 0.29 mol) at a rate of 1.2 mL / min, maintain the temperature at -10 °C ± 1 °C, and stir for 15 minutes.

[0033] The second stage: Add the remaining 20% (6 g) at a rate of 0.3 mL / min, while heating up to 5 °C, and continue the reaction for 10 minutes. The formation of the branched structure is monitored by online GPC throughout the process. The number-average molecular weight Mn of the final product is 623,000, and PDI = 1.41.

[0034] After the reaction is completed, inject diethylamine (molar ratio to AlCl3 is 2:1) to terminate the reaction. Pour the colloidal solution into excessive ethanol for precipitation, and dry it in a vacuum at 60 °C for 24 hours to obtain the finished product of star-shaped butyl rubber.

[0035] Example 2 A preparation method of star-shaped butyl rubber, which comprises the following steps: Step (a): Synthesis of linear main chain: In a dry 5 L stainless steel reaction kettle, add 3 L of mixed solvent (chloromethane:n-hexane = 4:1 volume ratio), and purge with high-purity nitrogen three times until the oxygen content < 5 ppm. Cool the system to -80 °C, and successively add 480 g (8.57 mol) of isobutene and 6.0 g (0.09 mol) of isoprene, and stir for 10 minutes to mix evenly. Inject the initiator solution (0.45 g of AlCl3 dissolved in 50 mL of chloromethane, concentration 0.01 mol / L) to initiate the cationic polymerization reaction. Maintain the temperature at -80 °C ± 1 °C. After reacting for 60 minutes, take a sample and test it by GPC. The number-average molecular weight (Mn) of the main chain is 321,000, the molecular weight distribution index (PDI = 1.38), and the double bond content of the isoprene unit is 1.16 mol%. At this time, the conversion rate of the main chain reaches 90%, and the end is an active cation (-C + (CH3)2).

[0036] Step (b): Silylation capping: Keep the temperature at -85 °C, and slowly add a chloroform solution of chloromethyltriethylsilane (Cl-CH2-Si(C2H5)3) (12.5 g dissolved in 100 mL) to the reaction kettle. After reacting for 8 minutes, online FTIR monitoring shows that the characteristic peak of the Si-Cl bond (580 cm -1 ) completely disappears, indicating that the capping efficiency > 99%.

[0037] Step (c): Activation of silyl groups: Heat up to -10 °C at a rate of 5 °C / min, and add the AlCl3 / Et2O composite catalyst in two stages: First stage: Add a premixed solution of AlCl3 / Et2O (molar ratio 1:1.5), and the addition amount is 20% of the total catalyst, and stir for 10 minutes.

[0038] Second stage: Supplement the remaining AlCl3 / Et2O to make the total catalyst concentration 0.2 mol / L, and continue to maintain at -10 °C for 20 minutes.

[0039] Step (d): Branching reaction: Stabilize the reaction system at -10 °C, and add 1,7-octadiene (n = 4) (branching agent) in two stages: First stage: Add 80% of the total amount (0.128 mol) at a rate of 0.8 mL / min, maintain the temperature at -10 °C ± 1 °C, and stir for 15 minutes.

[0040] Second stage: Add the remaining 20% (0.032 nol) at a rate of 0.25 mL / min, and at the same time heat up to 5 °C, and continue to react for 10 minutes.

[0041] After the reaction is completed, inject diethylamine (molar ratio to AlCl3 is 2:1) to terminate the reaction, pour the glue solution into excessive ethanol for precipitation, and dry it in vacuum at 60 °C for 24 hours to obtain the finished product of star-shaped butyl rubber.

[0042] Example 3 A preparation method of star-shaped butyl rubber, which comprises the following steps: Step (a): Synthesis of the linear backbone: In a dry 5 L stainless steel reactor, 3 L of a mixed solvent (chloroethane / n-pentane = 5:1 by volume) was added, and the system was purged with high-purity nitrogen three times until the oxygen content was < 5 ppm. The system was cooled to -80 °C, and 510 g (9.11 mol) of isobutene and 7.5 g (0.11 mol) of isoprene were added successively. The mixture was stirred for 10 minutes to ensure uniform mixing. An initiator solution (0.6 g of AlCl3 dissolved in 50 mL of chloromethane, concentration 0.01 mol / L) was injected to initiate the cationic polymerization reaction. The temperature was maintained at -80 °C ± 1 °C. After 60 minutes of reaction, a sample was taken and tested by GPC, showing that the number-average molecular weight (Mn) of the backbone was 400,000, the molecular weight distribution index (PDI = 1.38), and the double bond content of the isoprene unit was 1.16 mol%. At this time, the conversion rate of the backbone reached 90%, and the end was an active cation (-C + (CH3)2).

[0043] Step (b): Silylation capping: Maintaining the temperature at -85 °C, a solution of chloromethylphenyldimethylsilane (Cl-CH2-Si(CH3)2Ph) in chloromethane (18.8 g dissolved in 100 mL) was slowly added to the reactor. After 20 minutes of reaction, online FTIR monitoring showed that the characteristic peak of the Si-Cl bond (580 cm -1 ) completely disappeared, indicating that the capping efficiency was > 99%.

[0044] Step (c): Activation of the silyl group: The temperature was raised to -25 °C at a rate of 5 °C / min, and an AlCl3 / Et2O composite catalyst was added in two stages: First stage: A premixed solution of AlCl3 / Et2O (molar ratio 1:1.35) was added, and the addition amount was 18% of the total catalyst. The mixture was stirred for 10 minutes.

[0045] Second stage: The remaining AlCl3 / Et2O was added to make the total catalyst concentration 0.3 mol / L, and the reaction was continued at -10 °C for 20 minutes.

[0046] Step (d): Branching reaction: The reaction system was stabilized at -25 °C, and 1,5-hexadiene (n = 2) (branching agent) was added in two stages: First stage: 80% of the total amount (24 g, 0.29 mol) was added at a rate of 2.0 mL / min, and the temperature was maintained at -10 °C ± 1 °C. The mixture was stirred for 15 minutes.

[0047] Second stage: The remaining 20% (6 g) was added at a rate of 0.3 mL / min, and the temperature was raised to 8 °C at the same time. The reaction was continued for 10 minutes.

[0048] After the reaction was completed, diethylamine (molar ratio to AlCl3 of 2:1) was injected to terminate the reaction. The colloidal solution was poured into excessive ethanol for precipitation and dried in vacuum at 60 °C for 24 hours to obtain the finished star-shaped butyl rubber.

[0049] Example 4 A preparation method of star-shaped butyl rubber, which comprises the following steps: Step (a): Synthesis of linear main chain: In a dry 5 L stainless steel reactor, 3 L of a mixed solvent (chloromethane / cyclohexane = 3:1 by volume) was added, and high-purity nitrogen was introduced to displace three times until the oxygen content < 5 ppm. The system was cooled to -80 °C, and 470 g (8.39 mol) of isobutene and 5.0 g (0.07 mol) of isoprene were added in sequence, and stirred for 10 minutes to make the mixture uniform. An initiator solution (0.5 g of AlCl3 dissolved in 50 mL of chloromethane, concentration 0.01 mol / L) was injected to initiate a cationic polymerization reaction. The temperature was maintained at -80 °C ± 1 °C. After reacting for 60 minutes, sampling and GPC testing showed that the number-average molecular weight (Mn) of the main chain was 150,000, the molecular weight distribution index (PDI = 1.25), and the double bond content of the isoprene unit was 1.0 mol%. At this time, the conversion rate of the main chain reached 90%, and the end was an active cation (-C + (CH3)2).

[0050] Step (b): Silylation end-capping: Keeping the temperature at -85 °C, a chloromethane solution of chloromethyltrimethylsilane (14.6 g dissolved in 100 mL) was slowly added to the reactor. After reacting for 20 minutes, online FTIR monitoring showed that the characteristic peak of the Si-Cl bond (580 cm -1 ) completely disappeared, indicating that the end-capping efficiency > 99%.

[0051] Step (c): Activation of silyl groups: The temperature was raised to -35 °C at a rate of 5 °C / min, and an AlCl3 / Et2O composite catalyst was added in two stages: The first stage: Add a premixed AlCl3 / Et2O (molar ratio 1:1.25) solution, and the addition amount is 10% of the total catalyst, and stir for 10 minutes.

[0052] The second stage: Supplement the remaining AlCl3 / Et2O to make the total catalyst concentration 0.05 mol / L, and continue to maintain at -10 °C for 20 minutes.

[0053] Step (d): Branching reaction: The reaction system was stabilized at -25 °C, and 1,5-hexadiene (n = 2) (branching agent) was added in two stages: The first stage: Add 80% of the total amount (11.2 g, 0.135 mol) at a rate of 0.5 mL / min, maintain the temperature at -20 °C ± 1 °C, and stir for 8 minutes.

[0054] The second stage: Add the remaining 25% at a rate of 0.1 mL / min, while heating up to 5 °C and continue the reaction for 22 minutes.

[0055] After the reaction is completed, inject diethylamine (molar ratio to AlCl3 is 2:1) to terminate the reaction. Pour the colloidal solution into excessive ethanol for precipitation, and dry it under vacuum at 60 °C for 24 hours to obtain the finished star-shaped butyl rubber.

[0056] Example 5 A preparation method of star-shaped butyl rubber, which comprises the following steps: Step (a): Synthesis of linear main chain: In a dry 5 L stainless steel reactor, add 3 L of mixed solvent (volume ratio of dichloromethane / n-pentane = 5:1), and purge with high-purity nitrogen three times until the oxygen content < 5 ppm. Cool the system to -80 °C, and successively add 520 g (9.29 mol) of isobutene and 8.9 g (0.13 mol) of isoprene, and stir for 15 minutes to mix evenly. Inject the initiator solution (0.5 g of AlCl3 dissolved in 50 mL of chloromethane, concentration 0.01 mol / L) to initiate the cationic polymerization reaction. Maintain the temperature at -80 °C ± 1 °C. After reacting for 60 minutes, sampling and testing by GPC show that the number-average molecular weight (Mn) of the main chain is 400,000, the molecular weight distribution index (PDI = 1.48), and the end is an active cation (-C + (CH3)2).

[0057] Step (b): Silylation end-capping: Keep the temperature at -85 °C, and slowly add the chloromethane solution of chloromethyltriethylsilane (14.6 g dissolved in 100 mL) to the reactor. After reacting for 20 minutes, online FTIR monitoring shows that the characteristic peak of the Si-Cl bond (580 cm -1 ) completely disappears, indicating that the end-capping efficiency > 99%.

[0058] Step (c): Activation of silyl groups: Heat up to -15 °C at a rate of 5 °C / min, and add the AlCl3 / Et2O composite catalyst in two stages: The first stage: Add the premixed AlCl3 / Et2O (molar ratio 1:1.5) solution, and the addition amount is 17% of the total catalyst, and stir for 10 minutes.

[0059] The second stage: Supplement the remaining AlCl3 / Et2O to make the total catalyst concentration 0.25 mol / L, and continue to maintain at -10 °C for 20 minutes.

[0060] Step (d): Branching reaction: Stabilize the reaction system at -25 °C, and add 1,5-hexadiene (n = 2) (branching agent) in two stages: The first stage: Add a total of 75% (11.2 g, 0.135 mol) at a rate of 2 mL / min, maintain the temperature at -20°C ± 1°C, and stir for 8 minutes.

[0061] The second stage: Add the remaining 25% at a rate of 0.5 mL / min, and at the same time raise the temperature to 5°C, and continue the reaction for 22 minutes.

[0062] After the reaction is completed, inject triethylenediamine (molar ratio to AlCl3 is 3:1) to terminate the reaction. Pour the colloidal solution into excessive ethanol for precipitation, and dry it in vacuum at 60°C for 24 hours to obtain the finished product of star-shaped butyl rubber.

[0063] Example 6 A preparation method of star-shaped butyl rubber, which comprises the following steps: Step (a): Synthesis of the linear main chain: In a dry 5 L stainless steel reaction kettle, add 3 L of a mixed solvent (chloromethane / n-pentane = 3:1 volume ratio), and purge with high-purity nitrogen three times until the oxygen content < 5 ppm. Cool the system to -80°C, and successively add 490 g (8.75 mol) of isobutene and 6.7 g (0.10 mol) of isoprene, and stir for 15 minutes to mix evenly. Inject the initiator solution (0.5 g of AlCl3 dissolved in 50 mL of chloromethane, concentration 0.01 mol / L) to initiate the cationic polymerization reaction. Maintain the temperature at -80°C ± 1°C. After reacting for 60 minutes, sampling and testing by GPC show that the number-average molecular weight (Mn) of the main chain is 253,000, the molecular weight distribution index (PDI = 1.33), and the end is an active cation (-C + (CH3)2).

[0064] Step (b): Silylation end-capping: Keep the temperature at -85°C, and slowly add chloromethylphenyldimethylsilane (14.6 g dissolved in 100 mL) to the reaction kettle. After reacting for 20 minutes, online FTIR monitoring shows that the characteristic peak of the Si-Cl bond (580 cm -1 ) completely disappears, indicating that the end-capping efficiency > 99%.

[0065] Step (c): Activation of the silyl group: Raise the temperature to -40°C at a rate of 5°C / min, and add the AlCl3 / Et2O composite catalyst in two stages: The first stage: Add the premixed AlCl3 / Et2O (molar ratio 1:1.3) solution, and the addition amount is 10% of the total catalyst, and stir for 10 minutes.

[0066] The second stage: Supplement the remaining AlCl3 / Et2O to make the total catalyst concentration 0.08 mol / L, and continue to maintain at -10°C for 20 minutes.

[0067] Step (d): Branching reaction: The reaction system was stabilized at -30°C, and 1,7-octadiene (branching agent) was added in two stages, with a total amount of 0.19 mol: First stage: add 60% of the total amount at a rate of 0.8 mL / min and stir for 3 minutes.

[0068] The second stage: the remaining 40% was added at a rate of 0.3 mL / min, while the temperature was raised to 5°C, and the reaction was continued for 22 minutes.

[0069] After the reaction is completed, triethylenediamine (with a molar ratio of 3:1 to AlCl3) is injected to terminate the reaction, the rubber solution is poured into excess ethanol for precipitation, and vacuum dried at 60°C for 24 hours to obtain a star-shaped butyl rubber product.

[0070] Comparative Example 1 Steps (a) to (d) are the same as in Example 1, except that the end-capping agent in step (b) is replaced with tert-butyl chloride ((CH3)3CCl).

[0071] Comparative Example 2 Steps (a) to (d) are the same as in Example 1, except that in step (c) only AlCl3 (without Et2O coordination) is used, and 0.3 mol / L of Comparative Example 3 is added at one time. Steps (a) to (d) are the same as in Example 3, but the temperature is maintained at -80°C (no temperature gradient) throughout the process.

[0072] Comparative Example 4 Steps (a) to (d) are the same as in Example 1, but in step (d) the branching agent is added at a time at 2 mL / min.

[0073] Comparative Example 5 Steps (a) to (d) are the same as in Example 5, except that the end-capping agent in step (b) is changed to propylene oxide.

[0074] Performance test: The star-shaped butyl rubber prepared in Examples 1-6 and Comparative Examples 1-5 was tested, and the test method was as follows: Determination of branch point number Determination of branch point number Test method: Gel permeation chromatography-multi-angle laser light scattering (GPC-MALLS) Principle: GPC is used to separate components of different molecular weights, and MALLS is used to detect the scattered light intensity to calculate the absolute molecular weight and branching factor (g' = η branching / η linear).

[0075] Standard: ASTM D6474, using THF as mobile phase (1.0 mL / min), Wyatt DAWN HELEOS II detector.

[0076] Data processing: by the formula g' = (Mw branched / Mw linear) 0.5 , calculate the degree of branching, and use the Mark-Houwink equation to estimate the number of branching points.

[0077] Gel content determination Test method: Toluene extraction method step: Weigh 1 g of sample (accurate to 0.1 mg) and wrap it in a 120-mesh stainless steel mesh bag; Reflux in boiling toluene for 24 hours to dissolve the soluble part; The residual gel was dried under vacuum at 60°C to constant weight, and the gel content was calculated: Gel content (%) = W residual / W initial × 100; Standard: ASTM D2765, repeat the test 3 times and take the average value.

[0078] Mooney viscosity (ML 1+4) test Test method: Mooney Viscometer condition: Temperature: 125℃±0.3℃ Warm-up time: 1 minute Test time: 4 minutes Rotor type: Large rotor (MV 2000) Standard: ASTM D1646, record Mooney viscosity value (ML1+4 125℃).

[0079] Molecular weight distribution (PDI) determination Test method: Gel Permeation Chromatography (GPC) Instrument: Agilent 1260 Infinity II system, PLgel Mixed-C column; Standard sample: polystyrene standard (molecular weight range 500-2,000,000Da); Conditions: THF mobile phase (1.0 mL / min, 35 °C), RI detector; Calculation: The number average molecular weight (Mn) and weight average molecular weight (Mw) were calculated by software, PDI = Mw / Mn.

[0080] Vulcanized rubber tensile strength test Test method: Universal material testing machine Sample preparation: Curing conditions: 160℃×15min (compression molding according to ASTM D3182); Cut into dumbbell-shaped specimens (Type C, ASTM D412).

[0081] Test parameters: Tensile rate: 500 mm / min; Clamp spacing: 25mm; Ambient temperature: 23℃±2℃.

[0082] Standard: ASTM D412, record the maximum stress at break (MPa).

[0083] The test results are shown in Table 1 below: Table 1

[0084] It can be seen from the data in the above table that the performance difference between Examples 1-6 and Comparative Examples 1-5 is due to the synergistic optimization of key process parameters by the patented technology: the patented examples efficiently terminate the active ends of the main chain at low temperature (-80°C) (capping efficiency > 98%) through the precise design of the silane capping agent, and the three-dimensional steric hindrance effect of the silane group blocks the non-terminal reaction, while the AlCl3 / Et2O composite catalyst (molar ratio 1:1.2-1.5) added in stages selectively activates the terminal silane group to generate [Si-O-AlCl2] by gradient heating (-40°C → 10°C). + Intermediates ensure that the double bonds of the branching agent (such as 1,5-hexadiene) only undergo cationic copolymerization with the terminal anchor point, and cooperate with the phased gradient addition of the branching agent (rate 0.5-2.0mL / min) to effectively inhibit gelation caused by excessive local concentration (gel content <0.1%). In contrast, the comparative examples fail due to the lack of the above-mentioned synergistic mechanism: Comparative Example 1 uses traditional tert-butyl chloride end-capping, which cannot form controllable activation sites, resulting in random branching (end branching rate 52%); Comparative Example 2 uses a single AlCl3 catalyst to non-selectively activate the main chain C-Si bond, causing internal branching (40% branching points deviate from the end); Comparative Example 3 constant low temperature (-80°C) leads to a low silane activation rate and incomplete branching reaction; Comparative Example 4 branching agent is added at one time to cause local cross-linking (gel content 0.6%); Comparative Example 5 uses propylene oxide end-capping, lacks the dynamic activation function of silane, and the branching discreteness is >60%. In summary, the present application systematically solves the contradictions among branching positioning, molecular weight distribution and gel control through deep coupling of molecular design and process logic, while the deviation of a single parameter in the contrast ratio destroys the synergistic system and leads to overall performance degradation.

[0085] The examples of the present invention are merely illustrative of the technical solutions of the present invention. Any modifications, supplements or equivalent substitutions made by technicians in the field of the present invention on the basis of the examples are within the scope of protection required by the claims of the present invention.

Claims

1. A preparation method of star-shaped butyl rubber, characterized in that, It includes the following steps: (a) In an inert solvent, through the cationic polymerization of isobutene and isoprene, a linear main chain with a cationic active end is formed; (b) A silane capping agent is added, and it causes a nucleophilic substitution reaction at the cationic active end, thereby completing the silanization capping; The silane capping agent has the following general formula: Cl-CH2-SiR1R2R3; Wherein, R1, R2, and R3 are independently selected from C1-C4 alkyl groups or phenyl groups; (c) Raise the temperature of the reaction system, and add the AlCl3 / Et2O composite catalyst in stages, thereby selectively activating the silyl group to form a grafting anchor point; (d) Add a branching agent containing at least two olefin groups, and cause the double bond of the branching agent to undergo cationic copolymerization with the grafting anchor point, thereby forming a star-shaped branched structure.

2. The method according to claim 1, wherein: The silane capping agent is selected from any one of the following: Any one of chloromethyltrimethylsilane, chloromethyltriethylsilane, and chloromethylphenyldimethylsilane.

3. The method according to claim 1, wherein: The specific operation of adding the AlCl3 / Et2O composite catalyst in stages in step (c) is: In the first stage, add a complex with a molar ratio of AlCl3 to Et2O of 1:1.2 - 1.5, and the addition amount is 10 - 20% of the total catalyst amount; In the second stage, supplement the remaining AlCl3, and control the total catalyst concentration to be 0.05 - 0.3 mol / L.

4. The method according to claim 1, wherein: In step (c), the temperature of the reaction system is raised to -40°C to -10°C, and the activation time is controlled within 5 - 20 minutes.

5. The method according to claim 1, wherein: In step (d), the branching agent is a polyolefin containing 3 - 6 double bonds, and its structural general formula is: CH2=CH-(CH2)n-CH=CH2, where n = 0 - 4; and, The molar ratio of the branching agent to the main chain end is 1:3 to 1:

6.

6. The method according to claim 5, wherein: The branching agent is selected from any one of 1,3-butadiene, 1,5-hexadiene, and 1,7-octadiene.

7. The method according to claim 1 or 5 or 6, wherein: The addition method of the branching agent in step (d) is to add it in stages and gradients, specifically including: In the first stage, add 60 - 80% of the total amount of the branching agent at a rate of 0.5 - 2.0 mL / min, and maintain the system temperature at -30°C to -10°C; In the second stage, add the remaining branching agent at a rate of 0.1 - 0.5 mL / min, and at the same time raise the temperature to 0°C to 10°C; and, the interval time between the two stages is 3 - 8 minutes, and the total addition time is controlled not to exceed 30 minutes.

8. The method according to claim 1, wherein: In step (a), the addition amount of isoprene is 0.8 - 2.0% of the molar amount of isobutene, and the number-average molecular weight of the main chain is controlled at 150,000 - 400,000.

9. The method according to claim 1 or 8, wherein: The inert solvent described in step (a) is a mixed solvent with a volume ratio of halogenated hydrocarbon to aliphatic hydrocarbon of 3:1 to 5:1; wherein, the halogenated hydrocarbon is selected from any one of methyl chloride, dichloromethane or chloroethane; the aliphatic hydrocarbon is selected from any one of n-pentane or cyclohexane.

10. According to the method described in claim 1, characterized in that: it further includes step (e): adding a terminator containing an amino group to quench the reaction; the terminator is selected from any one of diethylamine, N-methylpyrrolidone or triethylenediamine; and, the molar ratio of the terminator to the catalyst AlCl3 is 1.5:1 to 3:1.

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