Star branching agents, methods of making the same, and star branched butyl rubber, methods of making the same

Abstract

This application relates to the field of butyl rubber technology, and provides a star-shaped branching agent, its preparation method, and star-branched butyl rubber, as well as the preparation method thereof. The preparation method of the star-shaped branching agent includes the following steps: under the action of a catalyst, pentaerythritol and an unsaturated fatty acid monomer containing a sterically hindered group undergo an esterification reaction to obtain the star-shaped branching agent; the sterically hindered group includes one or more of isopropyl, tert-butyl, and isobutyl. The star-shaped branching agent provided in this application regulates the branching reaction activity during the polymerization of butyl rubber by introducing sterically hindered groups, achieving controllable adjustment of the degree of branching. Simultaneously, it improves the compatibility between the branching agent and the reactant monomer. Based on effective control of the branching reaction activity, it simplifies the process steps, making industrial production feasible, environmentally friendly, and potentially leading to higher economic benefits.

Description

Technical Field

[0001] This application relates to the field of butyl rubber technology, and more particularly to star-shaped branching agents, their preparation methods, and star-shaped branched butyl rubber, and their preparation methods. Background Technology

[0002] Butyl rubber is a synthetic rubber prepared by cationic polymerization of isobutylene and a small amount of isoprene. Due to its extremely high airtightness, excellent aging resistance, and damping properties, it is widely used in tire liners, medical bottle stoppers, and sealing materials. However, traditional linear butyl rubber has a tightly packed molecular chain, resulting in poor processing performance, slow stress relaxation, and poor compatibility with reinforcing fillers. Furthermore, its non-polar structure leads to poor resistance to oil and organic solvents, and it is prone to swelling in non-polar media, limiting its application in high-end fields.

[0003] To address the aforementioned problems of butyl rubber, existing technologies often employ branching modification to prepare star-branched butyl rubber. This involves introducing a branching agent to create a star-branched butyl rubber structure. While maintaining the basic properties of butyl rubber, this reduces entanglement between molecular chains, resulting in superior processing flowability, lower Mooney viscosity, and improved processing performance, thus enabling the manufacture of complex rubber products. For example, the following patents provide several types of star-branched butyl rubber:

[0004] Chinese Patent Publication No. CN121319354A discloses a structurally tunable hyperbranched polyether branching agent, its preparation method, and its application: using 3-buten-1-ol as an initiator, a hyperbranched polyether skeleton is constructed by anionic ring-opening polymerization with diglycidyl ether, followed by anhydride esterification to end-cap, forming a hyperbranched polyether with vinyl double bonds and a tunable ester group structure at the ends; the molecular weight, polarity, and number of functional groups of the branching agent can be controlled by selecting different diepoxides and anhydrides. Chinese Patent Publication No. CN118255951A discloses a star-shaped branched butyl rubber and its preparation method: first, PS blocks are synthesized by anionic polymerization, then a four-armed star structure is formed by coupling with silicon tetrachloride, and finally, IR blocks are introduced. The branching agent is added during the cationic polymerization of butyl rubber for graft modification. Chinese Patent Publication No. CN116143821A discloses a star-shaped branched butyl rubber and its preparation method: tetra(dimethylsilyl)siloxane is synthesized from tetramethoxysilane and dimethylchlorosilane. p-Nitrophenol, a reduced amino group, and maleic anhydride are introduced sequentially, followed by condensation to obtain a branching agent containing imide and double bonds. This improves the high and low temperature resistance of butyl rubber and its compatibility with reinforcing agents. Chinese Patent Publication No. CN112011018A discloses a slurry method for preparing bimodal star-shaped branched butyl rubber: poly(styrene-conjugated diene) is synthesized by anionic polymerization, and then coupled with silicon tetrachloride to obtain a four-armed star polymer. HCl gas is introduced at low temperature to carry out a hydrohalogenation reaction, introducing chlorine. This branching agent is used in the slurry method for butyl rubber synthesis to obtain bimodal star-shaped branched butyl rubber.

[0005] The macromolecular branching agents provided in the above patents have the following problems: 1) The synthesis steps are complicated and the molecular weight distribution is wide, which affects the branching efficiency; 2) There are too many active sites in the branching agent, which can easily lead to over-branching or even gelation during cationic polymerization; 3) The compatibility between the branching agent and the butyl rubber matrix needs to be improved, and phase separation is likely to occur during long-term storage. Summary of the Invention

[0006] The technical problem solved by this application is to provide a star-shaped branching agent that can precisely control the degree of branching, improve the stability of the star-shaped structure of branched butyl rubber, and at the same time, the branching agent has good compatibility with the reactive monomers, ultimately resulting in branched butyl rubber with a higher degree of branching and a lower Mooney viscosity, thus enabling branched butyl rubber to exhibit excellent mechanical properties.

[0007] In view of this, this application provides a star-shaped branching agent as shown in formula (I),

[0008] (I);

[0009] Wherein, R is a group having 8 to 20 carbon atoms, and simultaneously contains sterically hindered groups and unsaturated bonds;

[0010] The steric hindrance group includes one or more of isopropyl, tert-butyl, and isobutyl.

[0011] In some specific embodiments, R is selected from (t-Bu)2(HO)C6H2-CH=CH-, Ph-CH2-CH(t-Bu)-, CH2=CH-CH(i-Pr)-, 4-i-BuO-C6H4-CH=CH- or (CH3)2CH-CH=CH-.

[0012] This application also provides a method for preparing the aforementioned star-shaped branching agent, comprising the following steps:

[0013] Under the action of a catalyst, pentaerythritol and sterically hindered unsaturated fatty acid monomers are esterified to obtain a star-shaped branching agent.

[0014] The steric hindrance group includes one or more of isopropyl, tert-butyl, and isobutyl.

[0015] In some specific embodiments, the molar ratio of pentaerythritol to the unsaturated fatty acid monomer is 1:(4.0~5.0); and / or, the catalyst is 0.5~2% of the total mass of the pentaerythritol and the unsaturated fatty acid monomer; and / or, the temperature of the esterification reaction is 120~150℃, and the time of the esterification reaction is 4~8h.

[0016] In some specific embodiments, the unsaturated fatty acid monomer includes one or more of 3,5-di-tert-butyl-4-hydroxycinnamic acid, α-(tert-butyl)hydrocinnamic acid, 2-isopropyl-3-butenoic acid, 3-(4-isobutoxyphenyl)acrylic acid, 1-buten-1-isopropylcarboxylic acid, and 3-isopropylbut-3-enoic acid; and / or, the catalyst includes p-toluenesulfonic acid or sulfuric acid.

[0017] This application also provides a method for preparing star-branched butyl rubber, comprising the following steps:

[0018] The main initiator, co-initiator, isobutylene monomer, isoprene monomer and branching agent are reacted in a solvent, and then a terminating agent is added to terminate the reaction to obtain star-branched butyl rubber.

[0019] The branching agent is the star-shaped branching agent described in the above scheme or the branching agent prepared by the preparation method described in the above scheme.

[0020] In some specific embodiments, the main initiator includes one of water, 2-chloro-2,4,4-trimethylpentane, cumyl chloride, tert-butyl chloride, and hydrogen chloride; and / or, the co-initiator includes one or two of aluminum trichloride, dichloroethylaluminum, and trichlorotriethylaluminum complex; and / or, the molar ratio of the main initiator to the co-initiator is (5~10):1.

[0021] In some specific embodiments, the main initiator, co-initiator, isobutylene monomer, isoprene monomer, branching agent, and solvent constitute a polymer system; the mass concentration of the isobutylene monomer in the polymerization system is 10-25 wt%; and / or, the molar ratio of the isoprene monomer to the isobutylene monomer is (0.01-0.05):1; and / or, the branching agent is 0.3-1.2 wt% of the total mass of the isobutylene monomer and the isoprene monomer; and / or, the reaction temperature is -80 to -90°C.

[0022] In some specific embodiments, the terminating agent is a mixed solution of an alcohol compound and sodium hydroxide in a mass ratio of (100~150):1.

[0023] This application also provides a star-branched butyl rubber prepared by the preparation method described above, with the structural formula shown in formula (II):

[0024] (II);

[0025] Wherein, R is a group having 8 to 20 carbon atoms, and simultaneously contains sterically hindered groups and unsaturated bonds;

[0026] The steric hindrance group includes one or more of isopropyl, tert-butyl, and isobutyl.

[0027] This application provides a star-shaped branching agent with pentaerythritol as the core skeleton. Through a branching reaction, unsaturated fatty acid ester chains containing sterically hindered groups are introduced to construct a star-shaped branched core. This effectively inhibits chain transfer and cross-linking side reactions during the polymerization of branched butyl rubber, precisely controls the degree of branching, and improves the stability of the star-shaped structure of butyl rubber. Simultaneously, by introducing sterically hindered groups to regulate the branching reaction activity, the degree of branching of the branching agent is controllable. The introduction of sterically hindered groups also improves the compatibility of the branching agent with isobutylene and isoprene monomers. Based on effective control of the branching reaction activity, the process steps are simplified, and the branched butyl rubber exhibits a higher degree of branching and a lower Mooney viscosity, resulting in excellent mechanical properties. Experimental results show that the star-shaped branched butyl rubber prepared in this application has a reasonable molecular weight distribution, with a number average molecular weight of 170,000~300,000 g / mol, a molecular weight distribution of 2.0~2.9, a branching degree of 3.2~4.5, and a Mooney viscosity (ML). 1+8(125℃) is 45~60. Attached Figure Description

[0028] Figure 1 The FTIR spectrum of the star-shaped branching agent prepared in Example 1 of this application;

[0029] Figure 2 The star-branched butyl rubber prepared in Example 1 of this application 1 H NMR spectrum (H). Detailed Implementation

[0030] To further understand this application, preferred embodiments of this application are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of this application, and not for limiting the claims of this application.

[0031] In view of the problems of branching degree control and compatibility with butyl rubber matrix in the prior art, this application provides a star-shaped branching agent and its preparation method. By introducing sterically hindered groups to regulate the branching reaction activity, the degree of branching can be controlled and adjusted. Simultaneously, the compatibility between the branching agent and the reactant monomer is improved. Based on effective control of the branching reaction activity, the process steps are simplified. Furthermore, the branched butyl rubber has a star-shaped core with a sterically hindered branching agent and isobutylene-isoprene copolymer as the branches, resulting in a uniform star structure and a reasonable molecular weight distribution. Ultimately, the star-shaped branched butyl rubber possesses excellent processing performance and mechanical properties, making it suitable for high-end applications with high requirements for comprehensive rubber performance. Specifically, this application discloses a star-shaped branching agent as shown in formula (Ⅰ).

[0032] (I);

[0033] Wherein, R is a group having 8 to 20 carbon atoms, and simultaneously contains sterically hindered groups and unsaturated bonds;

[0034] The steric hindrance group includes one or more of isopropyl, tert-butyl, and isobutyl.

[0035] In the star-shaped branching agent provided in this application, R needs to contain both a sterically hindered group and an unsaturated bond. Specifically, the sterically hindered group is selected from one or more of isopropyl, tert-butyl, and isobutyl, as described above. In some specific embodiments, the sterically hindered group is selected from two or three of isopropyl, tert-butyl, and isobutyl. The unsaturated bond can be a carbon-carbon double bond. The number of unsaturated double bonds in R is not particularly limited. For example, the number of unsaturated double bonds is 1 to 5. In some specific embodiments, R may include 1 carbon-carbon double bond, 2 carbon-carbon double bonds, or 3 carbon-carbon double bonds.

[0036] Furthermore, in some specific embodiments, R is selected from (t-Bu)2(HO)C6H2-CH=CH-, Ph-CH2-CH(t-Bu)-, CH2=CH-CH(i-Pr)-, 4-i-BuO-C6H4-CH=CH- or (CH3)2CH-CH=CH-.

[0037] This application also provides a method for preparing the above-mentioned star-shaped branching agent, including the following steps:

[0038] Under the action of a catalyst, pentaerythritol and sterically hindered unsaturated fatty acid monomers are esterified to obtain a star-shaped branching agent.

[0039] The steric hindrance group includes one or more of isopropyl, tert-butyl, and isobutyl.

[0040] In the preparation of the star-shaped branching agent, pentaerythritol serves as the core framework. The steric hindrance groups in the unsaturated fatty acid monomers are selected from one or more of isopropyl, tert-butyl, and isobutyl. Specifically, the unsaturated fatty acid monomers include one or more of 3,5-di-tert-butyl-4-hydroxycinnamic acid, α-(tert-butyl)hydrocinnamic acid, 2-isopropyl-3-butenoic acid, 3-(4-isobutoxyphenyl)acrylic acid, 1-buten-1-isopropylcarboxylic acid, and 3-isopropylbut-3-enoic acid. In some specific embodiments, the unsaturated fatty acid monomers are selected from 3,5-di-tert-butyl-4-hydroxycinnamic acid, α-(tert-butyl)hydrocinnamic acid, 2-isopropyl-3-butenoic acid, 3-(4-isobutoxyphenyl)acrylic acid, 1-buten-1-isopropylcarboxylic acid, and 3-isopropylbut-3-butenoic acid. The unsaturated fatty acid monomer is selected from one or more of tert-butyl-4-hydroxycinnamic acid, α-(tert-butyl)hydrocinnamic acid, 2-isopropyl-3-butenoic acid, 3-(4-isobutoxyphenyl)acrylic acid, 1-buten-1-isopropylcarboxylic acid, and 3-isopropylbut-3-enoic acid. In some specific embodiments, the unsaturated fatty acid monomer is selected from one or two of 3,5-di-tert-butyl-4-hydroxycinnamic acid, α-(tert-butyl)hydrocinnamic acid, 2-isopropyl-3-butenoic acid, 3-(4-isobutoxyphenyl)acrylic acid, 1-buten-1-isopropylcarboxylic acid, and 3-isopropylbut-3-enoic acid. The catalyst includes p-toluenesulfonic acid or sulfuric acid; in some specific embodiments, the catalyst is selected from p-toluenesulfonic acid or sulfuric acid.

[0041] In this application, the molar ratio of pentaerythritol to the unsaturated fatty acid monomer is 1:(4.0~5.0). In some specific embodiments, the molar ratio of pentaerythritol to the unsaturated fatty acid monomer is 1:4.1, 1:4.2, 1:4.3, 1:4.4, 1:4.5, 1:4.6, 1:4.7, 1:4.8, or 1:4.9. In this application, the unsaturated fatty acid monomer needs to be in excess to ensure that the reaction proceeds completely and to prevent hydroxyl residues from causing subsequent polymerization and crosslinking. The catalyst is 0.5-2% of the total mass of the pentaerythritol and the unsaturated fatty acid monomers. In some specific embodiments, the catalyst is 0.8-1.6% of the total mass of the pentaerythritol and the unsaturated fatty acid monomers; in other specific embodiments, the catalyst is 1.0-1.4% of the total mass of the pentaerythritol and the unsaturated fatty acid monomers. For example, in this application, the catalyst is 0.6%, 0.7%, 0.9%, 1.1%, 1.2%, 1.3%, 1.5%, 1.7%, 1.8%, or 1.9% of the total mass of the pentaerythritol and the unsaturated fatty acid monomers. Using too little catalyst will result in low catalytic efficiency, while using too much will cause unsaturated bond polymerization or corrosion of the equipment.

[0042] In the above esterification reaction, the temperature is 120-150℃ and the reaction time is 4-8 hours; in some specific embodiments, the temperature is 130-145℃ and the reaction time is 5-7 hours; in some specific embodiments, the temperature is 135-140℃ and the reaction time is 6-6.5 hours. If the esterification temperature is too low, the reaction rate is slow and the conversion rate is low; if the temperature is too high, unsaturated bond polymerization or fatty acid oxidation is likely to occur. If the reaction time is too short, the esterification reaction will be incomplete; if the reaction time is too long, side reactions will occur.

[0043] Furthermore, this application also provides a method for preparing star-branched butyl rubber, comprising the following steps:

[0044] The main initiator, co-initiator, isobutylene monomer, isoprene monomer and branching agent are reacted in a solvent, and then a terminating agent is added to terminate the reaction to obtain star-branched butyl rubber.

[0045] The branching agent is the star-shaped branching agent described in the above scheme.

[0046] In the preparation of star-branched butyl rubber, a low-temperature cationic slurry polymerization process is employed. The main initiator includes one of water, 2-chloro-2,4,4-trimethylpentane, cumyl chloride, tert-butyl chloride, and hydrogen chloride. In some specific embodiments, the main initiator is selected from one of water, 2-chloro-2,4,4-trimethylpentane, cumyl chloride, tert-butyl chloride, and hydrogen chloride; in other specific embodiments, the main initiator is selected from water. The main initiator determines the initiation rate and active center stability of the carbocation polymerization, affecting the molecular weight and molecular weight distribution of the star-branched butyl rubber. The co-initiator includes one or two of aluminum trichloride, dichloroethylaluminum, and trichlorotriethylaluminum complex. In some specific embodiments, the co-initiator is selected from one or two of aluminum trichloride, dichloroethylaluminum, and trichlorotriethylaluminum complex; in other specific embodiments, the co-initiator is selected from dichloroethylaluminum. The molar ratio of the main initiator to the co-initiator is (5~10):1. In some specific embodiments, the molar ratio of the main initiator to the co-initiator is (5~7):1. The co-initiator forms an active center complex with the main initiator, and the acidity and amount of the co-initiator directly affect the polymerization rate and polymer molecular weight.

[0047] In this application, the polymer system is composed of the main initiator, co-initiator, isobutylene monomer, isoprene monomer, branching agent, and solvent. The mass concentration of the isobutylene monomer in the polymerization system is 10-25 wt%. In some specific embodiments, the mass concentration of the isobutylene monomer in the polymerization system is 12-22 wt%. In some specific embodiments, the mass concentration of the isobutylene monomer in the polymerization system is 15-20 wt%. In some specific embodiments, the mass concentration of the isobutylene monomer in the polymerization system is 16-18 wt%. The concentration of the isobutylene monomer affects the polymerization reaction rate. If the concentration is too high, it can easily lead to uneven heat dissipation. The molar ratio of the isoprene monomer to the isobutylene monomer is (0.01~0.05):1. In some specific embodiments, the molar ratio of the isoprene monomer to the isobutylene monomer is (0.02~0.04):1. In some specific embodiments, the molar ratio of the isoprene monomer to the isobutylene monomer is 0.03:1. The molar ratio of the isoprene monomer to the isobutylene monomer determines the degree of unsaturation (double bond content) of the butyl rubber, which directly affects the vulcanization rate and crosslinking density. The branching agent is 0.3-1.2 wt% of the total mass of the isobutylene monomer and the isoprene monomer. In some specific embodiments, the branching agent is 0.4-1.0 wt% of the total mass of the isobutylene monomer and the isoprene monomer. In other specific embodiments, the branching agent is 0.5-0.8 wt% of the total mass of the isobutylene monomer and the isoprene monomer. The branching agent directly determines the degree of branching of the branched butyl rubber, thereby affecting the Mooney viscosity, processing fluidity, and mechanical properties of the butyl rubber. If the amount added is too low, the branching effect will be insignificant; if it is too high, it will lead to over-branching or gel formation. The reaction temperature is -80 to -90°C. In some specific embodiments, the reaction temperature is -90°C.

[0048] After a certain reaction time, a terminator is added to terminate the reaction, yielding star-branched butyl rubber. The terminator is a mixed solution of an alcohol compound and sodium hydroxide in a mass ratio of (100-150):1. In some specific embodiments, the mass ratio of the alcohol compound to sodium hydroxide is (110-140):1, and in other specific embodiments, it is (120-130):1. In this application, the alcohol compound is selected from ethanol. The terminator can both rapidly terminate the polymerization reaction and neutralize any initiator residues in the system.

[0049] This application constructs a well-defined star-shaped branching agent core by designing an unsaturated fatty acid ester chain containing a specific hindered group. Specifically, pentaerythritol undergoes an esterification reaction with the unsaturated fatty acid containing the hindered group, successfully preparing a high-purity four-arm star-shaped branching agent. This branching agent serves as the core in low-temperature cationic polymerization, copolymerizing with isobutylene and isoprene to form star-shaped branched butyl rubber. The monomer conversion rate of the polymerization reaction can reach over 95%, and the branching agent participation rate exceeds 90%. Compared with linear butyl rubber, the star-shaped branched butyl rubber prepared in this application exhibits higher branching degree and lower Mooney viscosity, demonstrating excellent processing performance and physical and mechanical properties, improving mixing efficiency and extrusion rate, while maintaining good airtightness and aging resistance.

[0050] Furthermore, this application also provides a star-branched butyl rubber prepared by the above preparation method, with the structural formula shown in formula (II):

[0051] (II);

[0052] Wherein, R is a group having 8 to 20 carbon atoms, and simultaneously contains sterically hindered groups and unsaturated bonds;

[0053] The steric hindrance group includes one or more of isopropyl, tert-butyl, and isobutyl.

[0054] The branching agent provided in this application uses pentaerythritol as the core skeleton and introduces unsaturated fatty acid ester chains containing sterically hindered groups such as isopropyl and tert-butyl through esterification to construct a star-shaped branched core for butyl rubber. This branching agent can effectively inhibit chain transfer and cross-linking side reactions during polymerization, precisely control the degree of branching, and improve the stability of the star structure. The star-shaped branched butyl rubber prepared in this application has a star-shaped core with a branching agent containing steric hindrance effect and isobutylene-isoprene copolymer as branches. It has a uniform star structure, a reasonable molecular weight distribution, a number average molecular weight of 170,000~300,000 g / mol, a molecular weight distribution of 2.0~2.9, a degree of branching of 3.2~4.5, and a Mooney viscosity (ML). 1+8 The temperature range (at 125℃) is 45~60°C. Furthermore, the star-branched butyl rubber prepared in this application possesses excellent processing performance, mechanical properties, and oil resistance, making it suitable for high-end applications requiring high overall rubber performance, thus expanding the application scope of butyl rubber.

[0055] To further understand this application, the following detailed description, in conjunction with embodiments, provides the star-shaped branching agent, its preparation method, and star-shaped branched butyl rubber, its preparation method. The scope of protection of this application is not limited by the following embodiments.

[0056] In the examples below, the number-average molecular weight and molecular weight distribution of the polymers were determined by gel permeation chromatography (GPC), the degree of branching was determined by GPC-multi-angle laser scattering, and the Mooney viscosity was determined at 125°C according to GB / T 1232 standard (ML). 1+8 (125℃), tensile strength was tested according to GB / T 528 standard.

[0057] Example 1

[0058] Preparation of a sterically hindered branching agent: 1 mol pentaerythritol and 4.5 mol 3,5-di-tert-butyl-4-hydroxycinnamic acid were added to a reaction vessel, along with 0.8% (based on the total mass of pentaerythritol and 3,5-di-tert-butyl-4-hydroxycinnamic acid) of p-toluenesulfonic acid as a catalyst. Nitrogen gas was introduced to purge air, and the mixture was heated to 135°C and reacted for 6 hours to obtain a crude product. The crude product was then subjected to vacuum distillation to remove unreacted raw materials and byproducts, followed by recrystallization from ethanol for purification, yielding a sterically hindered branching agent, such as... Figure 1 As shown, Figure 1 The image shows the FTIR spectrum of the branching agent.

[0059] Preparation of star-branched butyl rubber: A low-temperature polymerization reactor was used. After baking, vacuuming, and purging with nitrogen, the temperature was cooled to -90°C. A chloromethane solvent was added, followed by distilled isobutylene, vacuum-distilled isoprene, the prepared branching agent, and the initiator. The isobutylene concentration in the polymerization system was 15 wt%, the molar ratio of isoprene to isobutylene was 0.03:1, the branching agent was added at 0.8 wt% of the total mass of isobutylene and isoprene, and the initiator consisted of water (molar ratio 5:1) as the main initiator and dichloroethylaluminum as the co-initiator. After the reaction, an ethanol-water solution containing sodium hydroxide (ethanol to sodium hydroxide mass ratio 120:1) was added to the polymerization solution to terminate the polymerization. The polymerization product was washed with water until neutral and then vacuum-dried at 70°C for 10 h to obtain star-branched butyl rubber. Figure 2 As shown, Figure 2 For star-branched butyl rubber 1 H NMR spectrum (H).

[0060] Example 2

[0061] Preparation of a branching agent with steric hindrance effect: 1 mol pentaerythritol and 4.5 mol 2-isopropyl-3-butenoic acid were added to a reaction vessel, and 0.8% (based on the total mass of pentaerythritol and 2-isopropyl-3-butenoic acid) of p-toluenesulfonic acid was added as a catalyst. Nitrogen gas was introduced to purge air, the temperature was raised to 135℃, and the reaction was carried out for 6 h to obtain a crude product. The crude product was subjected to vacuum distillation to remove unreacted raw materials and by-products, and then purified by recrystallization with ethanol to obtain a branching agent with steric hindrance effect.

[0062] Preparation of star-branched butyl rubber: A low-temperature polymerization reactor was used. After baking, vacuuming, and purging with nitrogen, the temperature was cooled to -90°C. A chloromethane solvent was added, followed by distilled isobutylene, vacuum-distilled isoprene, the prepared branching agent, and the initiator. The isobutylene concentration in the polymerization system was 15 wt%, the molar ratio of isoprene to isobutylene was 0.03:1, the branching agent was added at 0.8 wt% of the total mass of isobutylene and isoprene, and the initiator consisted of water (molar ratio 5:1) as the main initiator and dichloroethylaluminum as the co-initiator. After the reaction was complete, an ethanol-water solution containing sodium hydroxide (ethanol to sodium hydroxide mass ratio 120:1) was added to the polymerization solution to terminate the polymerization. The polymerization product was washed with water until neutral and then vacuum-dried at 70°C for 10 h to obtain star-branched butyl rubber.

[0063] Example 3

[0064] Preparation of a branching agent with steric hindrance effect: 1 mol pentaerythritol and 4.5 mol 3,5-di-tert-butyl-4-hydroxycinnamic acid were added to a reaction vessel, and 0.8% (based on the total mass of pentaerythritol and 3,5-di-tert-butyl-4-hydroxycinnamic acid) of p-toluenesulfonic acid was added as a catalyst. Nitrogen gas was introduced to purge air, the temperature was raised to 135℃, and the reaction was carried out for 6 hours to obtain a crude product. The crude product was subjected to vacuum distillation to remove unreacted raw materials and by-products, and then purified by recrystallization with ethanol to obtain a branching agent with steric hindrance effect.

[0065] Preparation of star-branched butyl rubber: A low-temperature polymerization reactor was used. After baking, vacuuming, and purging with nitrogen, the temperature was cooled to -90°C. A chloromethane solvent was added, followed by distilled isobutylene, vacuum-distilled isoprene, the branching agent prepared above, and the initiator. The isobutylene mass concentration in the polymerization system was 15 wt%, the molar ratio of isoprene to isobutylene was 0.03:1, the branching agent was added at 0.4 wt% of the total mass of isobutylene and isoprene, and the initiator consisted of water (molar ratio 5:1) as the main initiator and dichloroethylaluminum as the co-initiator. After the reaction was complete, an ethanol-water solution containing sodium hydroxide (ethanol to sodium hydroxide mass ratio 120:1) was added to the polymerization solution to terminate the polymerization. The polymerization product was washed with water until neutral and then vacuum-dried at 70°C for 10 h to obtain star-branched butyl rubber.

[0066] Example 4

[0067] Preparation of a branching agent with steric hindrance effect: 1 mol pentaerythritol and 4.5 mol 3,5-di-tert-butyl-4-hydroxycinnamic acid were added to a reaction vessel, and 0.8% (based on the total mass of pentaerythritol and 3,5-di-tert-butyl-4-hydroxycinnamic acid) of p-toluenesulfonic acid was added as a catalyst. Nitrogen gas was introduced to purge air, the temperature was raised to 135℃, and the reaction was carried out for 6 hours to obtain a crude product. The crude product was subjected to vacuum distillation to remove unreacted raw materials and by-products, and then purified by recrystallization with ethanol to obtain a branching agent with steric hindrance effect.

[0068] Preparation of star-branched butyl rubber: A low-temperature polymerization reactor was used. After baking, vacuuming, and purging with nitrogen, the temperature was cooled to -90°C. A chloromethane solvent was added, followed by the treatment of isobutylene, isoprene, a branching agent, and an initiator. The isobutylene mass concentration in the polymerization system was 15 wt%, the molar ratio of isoprene to isobutylene was 0.03:1, the amount of branching agent added was 1.2 wt% of the total mass of isobutylene and isoprene, and the initiator consisted of water (main initiator) and dichloroethylaluminum (co-initiator) in a 5:1 ratio. After the reaction was completed, an ethanol-water solution containing sodium hydroxide (ethanol to sodium hydroxide mass ratio of 120:1) was added to the polymerization liquid to terminate the polymerization. The polymerization product was washed with water until neutral and then vacuum dried at 70°C for 10 h to obtain star-branched butyl rubber.

[0069] Comparative Example 1

[0070] Preparation of a branching agent with steric hindrance effect: 1 mol pentaerythritol and 4.5 mol 3,5-di-tert-butyl-4-hydroxycinnamic acid were added to a reaction vessel, and 0.8% p-toluenesulfonic acid was added as a catalyst. Nitrogen gas was introduced to purge air, the temperature was raised to 135℃, and the reaction was carried out for 6 hours to obtain a crude product. The crude product was subjected to vacuum distillation to remove unreacted raw materials and by-products, and then purified by recrystallization with ethanol to obtain a branching agent with steric hindrance effect.

[0071] Preparation of star-branched butyl rubber: A low-temperature polymerization reactor was used. After baking, vacuuming, and nitrogen purging, the temperature was cooled to -90°C. A chloromethane solvent was added, followed by the treatment of isobutylene, isoprene, a branching agent, and an initiator. The isobutylene mass concentration in the polymerization system was 15 wt%, the molar ratio of isoprene to isobutylene was 0.03:1, the branching agent was added at 2.0 wt% of the total mass of isobutylene and isoprene, and the initiator consisted of water (molar ratio 5:1) as the main initiator and dichloroethylaluminum as the co-initiator. After the reaction was completed, an ethanol-water solution containing sodium hydroxide (ethanol to sodium hydroxide mass ratio 120:1) was added to the polymerization solution to terminate the polymerization. The polymerization product was washed with water until neutral and then vacuum dried at 70°C for 10 h to obtain star-branched butyl rubber.

[0072] Comparative Example 2

[0073] Preparation of a branching agent with steric hindrance effect: 1 mol pentaerythritol and 4.5 mol 3,5-di-tert-butyl-4-hydroxycinnamic acid were added to a reaction vessel, and 0.8% p-toluenesulfonic acid was added as a catalyst. Nitrogen gas was introduced to purge air, the temperature was raised to 135℃, and the reaction was carried out for 6 hours to obtain a crude product. The crude product was subjected to vacuum distillation to remove unreacted raw materials and by-products, and then purified by recrystallization with ethanol to obtain a branching agent with steric hindrance effect.

[0074] Preparation of star-branched butyl rubber: A low-temperature polymerization reactor was used. After baking, vacuuming, and nitrogen purging, the temperature was cooled to -70°C. A chloromethane solvent was added, followed by the treatment of isobutylene, isoprene, a branching agent, and an initiator. The isobutylene mass concentration in the polymerization system was 15 wt%, the molar ratio of isoprene to isobutylene was 0.03:1, the amount of branching agent added was 0.8 wt% of the total mass of isobutylene and isoprene, and the initiator consisted of water (molar ratio 5:1) as the main initiator and dichloroethylaluminum as the co-initiator. After the reaction was completed, an ethanol-water solution containing sodium hydroxide (with a mass ratio of ethanol to sodium hydroxide of 120:1) was added to the polymerization solution to terminate the polymerization. The polymerization product was washed with water until neutral and then vacuum dried at 70°C for 10 h to obtain star-branched butyl rubber.

[0075] Table 1. Reaction conditions and data for the Examples and Comparative Examples

[0076]

[0077] Table 1. Reaction conditions and data for the examples and comparative examples (continued)

[0078]

[0079] As shown in Table 1, the star-shaped branched butyl rubber prepared using the sterically hindered branching agent of this application has a weight-average molecular weight that can be controlled within the range of 17,000 to 30,000, a narrow molecular weight distribution of 2.0 to 2.9, a branching degree of 3.2 to 4.5, and a moderate Mooney viscosity. With the increase of the amount of branching agent, the molecular weight generally shows an upward trend, but the branching degree decreases after exceeding the optimal amount. Excessive amount will lead to cross-linking and gelation, making it impossible to obtain an effective product. For example, in Comparative Example 1, the amount of branching agent was too high, resulting in severe cross-linking and gel formation during polymerization, making it impossible to obtain an effective rubber product. Lowering the polymerization temperature is beneficial to increasing the molecular weight and branching degree, while reducing the molecular weight distribution and improving mechanical properties. In Comparative Example 2, the polymerization temperature was too high, leading to increased side reactions, resulting in a wider molecular weight distribution, a lower branching degree, and decreased performance.

[0080] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

[0081] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A star-shaped branching agent as shown in formula (Ⅰ), （Ⅰ）； in, R is a group with 8 to 20 carbon atoms, and contains both sterically hindered groups and unsaturated bonds; The steric hindrance group includes one or more of isopropyl, tert-butyl, and isobutyl.

2. The star-shaped branching agent according to claim 1, characterized in that, The R is selected from (t-Bu)2(HO)C6H2-CH=CH-, Ph-CH2-CH(t-Bu)-, CH2=CH-CH(i-Pr)-, 4-i-BuO-C6H4-CH=CH- or (CH3)2CH-CH=CH-.

3. The method for preparing the star-shaped branching agent according to claim 1, comprising the following steps: Under the action of a catalyst, pentaerythritol and sterically hindered unsaturated fatty acid monomers are esterified to obtain a star-shaped branching agent. The steric hindrance group includes one or more of isopropyl, tert-butyl, and isobutyl.

4. The preparation method according to claim 3, characterized in that, The molar ratio of the pentaerythritol to the unsaturated fatty acid monomer is 1:(4.0~5.0); and / or, the catalyst is 0.5~2% of the total mass of the pentaerythritol and the unsaturated fatty acid monomer; and / or, the temperature of the esterification reaction is 120~150℃, and the time of the esterification reaction is 4~8h.

5. The preparation method according to claim 3 or 4, characterized in that, The unsaturated fatty acid monomers include one or more of 3,5-di-tert-butyl-4-hydroxycinnamic acid, α-(tert-butyl)hydrocinnamic acid, 2-isopropyl-3-butenoic acid, 3-(4-isobutoxyphenyl)acrylic acid, 1-buten-1-isopropylcarboxylic acid, and 3-isopropylbut-3-enoic acid; and / or, the catalyst includes p-toluenesulfonic acid or sulfuric acid.

6. A method for preparing star-branched butyl rubber, comprising the following steps: The main initiator, co-initiator, isobutylene monomer, isoprene monomer and branching agent are reacted in a solvent, and then a terminating agent is added to terminate the reaction to obtain star-branched butyl rubber. The branching agent is the star-shaped branching agent according to any one of claims 1 to 2 or the branching agent prepared by the preparation method according to any one of claims 3 to 5.

7. The preparation method according to claim 6, characterized in that, The primary initiator includes one of water, 2-chloro-2,4,4-trimethylpentane, cumyl chloride, tert-butyl chloride, and hydrogen chloride; and / or, the co-initiator includes one or two of aluminum trichloride, dichloroethylaluminum, and trichlorotriethylaluminum complex; and / or, the molar ratio of the primary initiator to the co-initiator is (5~10):

1.

8. The preparation method according to claim 6 or 7, characterized in that, The main initiator, co-initiator, isobutylene monomer, isoprene monomer, branching agent, and solvent constitute a polymer system. The mass concentration of the isobutylene monomer in the polymerization system is 10~25wt%, and / or the molar ratio of the isoprene monomer to the isobutylene monomer is (0.01~0.05):1, and / or the branching agent is 0.3~1.2wt% of the total mass of the isobutylene monomer and the isoprene monomer, and / or the reaction temperature is -80~-90℃.

9. The preparation method according to claim 6, characterized in that, The terminating agent is a mixed solution of an alcohol compound and sodium hydroxide in a mass ratio of (100~150):

1.

10. The star-branched butyl rubber prepared by the preparation method according to claim 6 has the structural formula shown in formula (II): （Ⅱ）； in, R is a group with 8 to 20 carbon atoms, and contains both sterically hindered groups and unsaturated bonds; The steric hindrance group includes one or more of isopropyl, tert-butyl, and isobutyl.

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