A method for preparing a multifunctional crosslinking agent and a dynamic crosslinking thermoplastic elastomer based on the crosslinking agent and applications thereof

Abstract

The present application relates to the technical field of industrial material application, further relates to a multi-functionality crosslinking agent, a dynamic crosslinking thermoplastic elastomer and a preparation method and application. The present application first synthesizes a benzene boronic acid group-containing multi-functionality crosslinking agent which has a better crosslinking degree to rubber than a di-functionality crosslinking agent and a better dynamic exchange probability than the di-functionality crosslinking agent in a subsequent use process; then modifies the rubber to introduce a double hydroxyl structure into the rubber molecular chain to obtain a hydroxylated modified rubber; and then uses the benzene boronic acid group-containing multi-functionality crosslinking agent and the hydroxylated modified rubber to prepare a thermoplastic elastomer based on a reversible crosslinking system containing a borate ester bond. The dynamic crosslinking thermoplastic elastomer provided by the present application has the advantages of high tensile strength, excellent elongation at break, high crosslinking density, repeated processing, and small mechanical property attenuation after repeated processing.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial material applications. Further, it relates to a multifunctional crosslinking agent and a preparation method and application of a dynamically crosslinked thermoplastic elastomer constructed based on this crosslinking agent. Background Art

[0002] The rubber industry is a pillar industry of the national economy. Due to their unique mechanical properties (such as high resilience), rubber products not only provide daily-use, medical, and other light industrial rubber products that are indispensable in daily life. However, traditional rubber crosslinking systems use sulfur vulcanization or peroxide crosslinking methods to construct crosslinking networks, and the resulting rubber material products are insoluble and infusible, making it difficult to recycle and reuse, causing environmental pollution and resource waste. Currently, the rubber products consumed in China are as high as more than ten million tons, and about the same amount of rubber waste will be generated every year. However, the means of recycling rubber are limited and the recycling efficiency is very low. The waste rubber products cannot be effectively recycled and reused for a long time, not only occupying a large amount of land but also posing serious fire hazards. Since traditional crosslinking systems use many small molecule additives, the toxic components are complex and have strong anti-degradability, which will pollute the ecological environment such as soil and water sources on which people, animals, and plants depend for survival.

[0003] Reversible crosslinking is one of the important ways to achieve the recycling of rubber. Rubber products prepared by reversible crosslinking can not only be reused many times, solving the problems of rubber resource regeneration and recycling, but also have good physical and mechanical properties by using the reversible crosslinking method. However, there are also various problems with different types of dynamic bonds that have been studied more at present. For example, ion bond reversible crosslinked rubber has poor high-temperature resistance and poor compression set; hydrogen bond reversible crosslinked rubber has poor mechanical properties and poor high-temperature resistance. Due to the long molecular chains, when performing reversible crosslinking reactions, problems such as low reaction activity and poor reaction efficiency seriously limit the application of reversible crosslinking technology in the "green" rubber industry field.

[0004] In the current research on reversible cross-linked rubber, Patent CN109535626A introduced a method of constructing a dynamic cross-linking system based on DA reaction after grafting maleic anhydride, which provided a method for the dynamic cross-linking of rubber. However, the influence of side reactions of grafting maleic anhydride by free radicals was not reflected, and the recycling and processing performance of subsequent materials was not characterized. Patent CN117362786A constructed a β-hydroxyester bond dynamic cross-linking system through the epoxy group and carboxyl group of epoxidized natural rubber. This method was limited to the matrix of epoxidized natural rubber and had the problem of incomplete coverage of the rubber matrix. Patent CN109825022A provided a method for reversibly cross-linking ethylene-propylene-diene rubber through DA reaction. By modifying the molecular chain of rubber and synthesizing relevant cross-linking agents to construct a cross-linking system, there was a problem of complex experimental process flow. Secondly, after the rubber was modified, a bifunctional cross-linking agent was directly used for cross-linking. In this case, one end of the active site participated in the reaction, but the other end did not effectively react. This "hanging" state existed in the cross-linking network, resulting in less effective cross-linking and problems of low cross-linking degree and cross-linking density in the constructed cross-linking network, which affected the mechanical properties of the generated dynamic cross-linked thermoplastic elastomer. At the same time, multifunctional cross-linking agents can effectively increase the probability of dynamic bonds participating in the cross-linking network and improve the recycling and processing performance of materials. Summary of the Invention

[0005] To solve the technical problems of low cross-linking density, low cross-linking efficiency and poor dynamic performance of recycling and reprocessing caused by cross-linking with bifunctional cross-linking agents in the prior art, the present invention provides a multifunctional cross-linking agent and a preparation method of a dynamic cross-linked thermoplastic elastomer based on this cross-linking agent.

[0006] Compared with bifunctional cross-linking agents, multifunctional cross-linking agents can effectively improve the cross-linking density, cross-linking efficiency and recycling and processing performance of rubber. Then, the rubber is modified to introduce a dihydroxy structure on the rubber molecular chain to obtain hydroxylated modified rubber; and then a thermoplastic elastomer based on a reversible cross-linking system containing borate bonds is prepared by using a multifunctional cross-linking agent containing phenylboronic acid groups and hydroxylated modified rubber.

[0007] One of the purposes of the present invention is to provide a multifunctional cross-linking agent for constructing a dynamic cross-linked thermoplastic elastomer.

[0008] The structure of the multifunctional cross-linking agent is shown in Formula 1,

[0009]

[0010] wherein, derived from polyhydroxy compounds or polyamino compounds.

[0011] The ends of the multifunctional crosslinker are phenylboronic acid structures, which are obtained by reacting polyhydroxy compounds or polyamino compounds with functionalized phenylboronic acids.

[0012] The polyhydroxy compounds may be selected from one or more of polyether polyols (e.g., trihydroxy polypropylene oxide ether), polyester polyols, glycerol, trimethylolpropane, triethanolamine, xylitol, sorbitol, sucrose, pentaerythritol, cyclodextrin, cellulose, chitosan, and alginic acid.

[0013] The polyamino compounds may be selected from one or more of multifunctional polyetheramines, branched polyethyleneimine, and tris(2-aminoethyl)amine. The multifunctional polyetheramine refers to a polyetheramine with a functionality of greater than or equal to 3; for example, polyetheramine T403 and polyetheramine T5000.

[0014] The functionalized phenylboronic acids are selected from one or more of 4-carboxyphenylboronic acid, 3-carboxyphenylboronic acid, and 2-carboxyphenylboronic acid.

[0015] For the multifunctional crosslinker provided by the present invention, in the crosslinking network, the crosslinking reaction probability is higher than that of a bifunctional crosslinker; therefore, the multifunctional crosslinker can improve the effective crosslinking degree of the reversible crosslinked rubber. The improvement of the effective crosslinking degree of the reversible crosslinked rubber is reflected in the increase of its crosslinking density.

[0016] The multifunctional crosslinker provided by the present invention can also increase the probability of reversible dynamic bonds participating in the crosslinking network, thereby improving the recycling efficiency of the reversible crosslinked rubber.

[0017] In addition, the multifunctional crosslinker provided by the present invention also improves the mechanical properties of the crosslinked rubber, such as tensile strength, elongation at break, and hardness.

[0018] The second object of the present invention is to provide a preparation method of the multifunctional crosslinker described in the first object of the invention.

[0019] The multifunctional crosslinker is obtained by reacting a polyhydroxy compound or a polyamino compound with a functionalized phenylboronic acid. The synthetic route is schematically shown as follows: taking the reaction of the polyhydroxy compound and 4-carboxyphenylboronic acid to obtain the multifunctional crosslinker as an example,

[0020]

[0021] Among them, represents the polyhydroxy compound, represents the multifunctional crosslinker.

[0022] The synthetic route of the multifunctional crosslinker is schematically shown as follows: taking the reaction of the polyamino compound and 4-carboxyphenylboronic acid to obtain the multifunctional crosslinker as an example,

[0023]

[0024] Wherein, represents a polyamino compound, represents the polyfunctional crosslinking agent.

[0025] The preparation method includes two schemes, Scheme 1 or Scheme 2.

[0026] Scheme 1 includes: reacting a polyhydroxy compound or a polyamino compound with a functionalized phenylboronic acid in the presence of Solvent 1 and Catalyst 1 at 100-150°C for 5-9 h.

[0027] The Catalyst 1 is selected from one or more of strong acid catalysts, solid acid catalysts, and organometallic catalysts.

[0028] The Solvent 1 is selected from high-boiling polar solvents. The high boiling point means a boiling point of 100°C or higher. For example, DMF, dioxane, etc.

[0029] The molar ratio of the polyhydroxy compound or the polyamino compound to the functionalized phenylboronic acid and Catalyst 1 is preferably (1 / n - 2 / n):1:(0.05 - 0.1); wherein, n is the functionality of the polyhydroxy compound or the polyamino compound.

[0030] Scheme 2 includes: reacting a polyhydroxy compound or a polyamino compound with a functionalized phenylboronic acid in the presence of Solvent 2 and Catalyst 2 at -10-20°C for 12-16 h.

[0031] The Catalyst 2 is selected from N,N'-dicyclohexylcarbodiimide or 4-dimethylaminopyridine.

[0032] The Solvent 2 is selected from dichloromethane or tetrahydrofuran.

[0033] The molar ratio of the polyhydroxy compound or the polyamino compound to the functionalized phenylboronic acid and Catalyst 2 is preferably (1 / n - 5 / n):1:(1 - 3); wherein, n is the functionality of the polyhydroxy compound or the polyamino compound.

[0034] The third object of the present invention is to provide a dynamically crosslinked thermoplastic elastomer.

[0035] The structure of the dynamically crosslinked thermoplastic elastomer is shown in Formula 2,

[0036] [[ID=*43]]

[0037] Wherein is a rubber molecular chain.

[0038] The dynamic crosslinked thermoplastic elastomer is formed by dynamically crosslinking raw materials including hydroxylated modified rubber and polyfunctional crosslinking agent; the dynamic crosslinking preferably adopts a hot pressing process.

[0039] The polyfunctional crosslinking agent is: the polyfunctional crosslinking agent described in one of the invention purposes or the polyfunctional crosslinking agent prepared by the preparation method described in the second invention purpose.

[0040] The hydroxylated modified rubber can provide more active sites for subsequent reversible crosslinking compared with the existing rubber. The hydroxylated modified rubber is preferably obtained by catalytic hydrolysis ring-opening of epoxidized modified rubber.

[0041] The reaction temperature of the catalytic hydrolysis ring-opening is preferably 20-60°C. The catalyst for the catalytic hydrolysis ring-opening is preferably selected from one or more of proton acids (including but not limited to sulfuric acid, perchloric acid, fluorosulfuric acid, hydrochloric acid, etc.), Lewis acids (including but not limited to tin tetrachloride, boron trifluoride, trifluoromethanesulfonate, zirconium tetrachloride, aluminum trichloride, iron bromide, etc.), and metal oxides (including but not limited to calcium oxide, magnesium oxide, aluminum oxide, zirconium oxide, etc.).

[0042] The epoxidized modified rubber is obtained by epoxidizing the matrix rubber. The matrix rubber is selected from one or more of rubbers containing double bonds in the molecular chain, preferably selected from one or more of natural rubber (NR), styrene-butadiene rubber (SBR), cis-butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), butyl rubber (IIR), nitrile rubber (NBR), ethylene propylene diene monomer rubber (EPDM).

[0043] One of the methods for epoxidizing the matrix rubber includes: dissolving the matrix rubber in an organic solvent, adding an acid, a surfactant and a peroxide, reacting at 40-60°C for 6-12 h, and drying to obtain the epoxidized modified rubber. The organic solvent can be selected from substances that can dissolve the matrix modified rubber, for example, tetrahydrofuran (THF) can be selected.

[0044] In the present invention, by modifying the matrix rubber, a structure with dihydroxy groups is introduced into the molecular chain to obtain hydroxylated modified rubber. The route of epoxidizing and hydroxylating the matrix rubber is shown as follows:

[0045]

[0046] Taking ethylene propylene diene monomer rubber (EPDM) as an example, the method for preparing the hydroxylated modified rubber from the matrix rubber includes: dissolving EPDM in the organic solvent n-hexane, adding formic acid and Tween 80 at a temperature of 50 °C, stirring evenly, adding hydrogen peroxide, reacting for 8 h, and then flocculating and drying to obtain epoxidized ethylene propylene diene monomer rubber (e-EPDM); dissolving e-EPDM in the organic solvent tetrahydrofuran, adding water and the catalyst zirconium tetrachloride, reacting at room temperature for 3 h, and then flocculating and drying to obtain hydroxylated ethylene propylene diene monomer rubber (EPDM-OH).

[0047] The fourth object of the present invention is to provide a preparation method of the dynamically crosslinked thermoplastic elastomer described in the third object of the invention purpose.

[0048] The preparation method includes: mixing the hydroxylated modified rubber with a multifunctional crosslinking agent and then hot pressing and molding.

[0049] The dynamic crosslinking process of the hydroxylated modified rubber and the multifunctional crosslinking agent is schematically shown as follows:

[0050]

[0051] Among them, represents the hydroxylated modified rubber, represents the multifunctional crosslinking agent, represents the dynamically crosslinked thermoplastic elastomer.

[0052] The ratio of the molar amount of dihydroxy groups of the hydroxylated modified rubber to the molar amount of phenylboronic acid groups of the multifunctional crosslinking agent is 1:(0.5 - 1.5). For example, 1:(0.5 - 0.75), 1:(0.75 - 1.0), 1:(1.0 - 1.25), 1:(1.25 - 1.5). Compared with other molar ratios, when the ratio of the molar amount of dihydroxy groups of the hydroxylated modified rubber to the molar amount of phenylboronic acid groups of the multifunctional crosslinking agent is 1:(0.9 - 1.1), the tensile strength and elongation at break of the prepared dynamically crosslinked thermoplastic elastomer are better. Therefore, as a preferred scheme, the ratio of the molar amount of dihydroxy groups of the hydroxylated modified rubber to the molar amount of phenylboronic acid groups of the multifunctional crosslinking agent is 1:(0.9 - 1.1).

[0053] As a preferred scheme, the hydroxylated modified rubber and the multifunctional crosslinking agent are mixed in a solvent, the solvent is removed, and then hot pressing and molding are carried out. The solvent can be selected as a substance that can dissolve the hydroxylated modified rubber. For example, tetrahydrofuran (THF) can be selected.

[0054] As a preferred scheme, the temperature of the hot pressing and molding is 150 - 180 °C, the pressure is 10 - 20 MPa, and the time is 30 - 90 min.

[0055] As a preferred solution, the hydroxylated modified rubber and the multifunctional crosslinking agent are uniformly mixed by an open mill.

[0056] The preparation method, one of the schemes includes: uniformly mixing the hydroxylated modified rubber and multifunctional crosslinking agents with different molar amounts by an open mill, and under the conditions of 150-160 °C and 16-18 MPa, hot pressing for 50-60 min to obtain a dynamically crosslinked thermoplastic elastomer.

[0057] The dynamically crosslinked thermoplastic elastomer provided by the present invention is a reversibly crosslinked elastomer material with excellent repeated processing performance. Compared with traditional sulfur vulcanization crosslinking, the dynamically crosslinked thermoplastic elastomer has the advantages of high tensile strength, excellent elongation at break, high crosslinking density, and repeatable processing. Compared with the existing dynamically reversible crosslinked elastomers, due to the role of the multifunctional crosslinking agent in the crosslinking network, the dynamically crosslinked thermoplastic elastomer has excellent dynamic performance and small attenuation of mechanical properties after repeated processing.

[0058] The fifth object of the present invention is to provide an application of the dynamically crosslinked thermoplastic elastomer prepared by the preparation method described in the fourth object of the invention in the rubber field. Especially in promoting the application of dynamic chemical crosslinking technology in the rubber field, improving the comprehensive performance of rubber materials, providing new ideas for the development of low-cost and high-performance rubber materials, and leading the technological innovation and development in the synthetic rubber industry.

[0059] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0060] (1) The idea and scheme for synthesizing the multifunctional crosslinking agent are proposed. The reaction reagents and drugs used for synthesizing the multifunctional crosslinking agent are economical in price, the experimental process is simple, and the operation difficulty is low.

[0061] (2) For the matrix rubber, epoxidation modification is first carried out, and then hydroxylation modification is carried out to obtain the hydroxylated modified rubber. For the first step of epoxidation modification, there are already mature large-scale production processes for some rubber matrices, and the subsequent experimental process of hydroxylation modification is simple, easy to operate, and easy to realize large-scale production preparation.

[0062] (3) A dynamically crosslinked thermoplastic elastomer is prepared by using a multifunctional crosslinking agent and a hydroxylated modified rubber. The dynamically crosslinked thermoplastic elastomer is a reversibly crosslinked rubber material, which has the advantages of excellent tensile strength, high elongation at break, high crosslinking density, good dynamic performance, repeatable processing, small attenuation of mechanical properties after repeated processing, and high recovery rate. Its各项性能优于传统硫磺硫化体系交联的产品。 Brief Description of the Drawings

[0063] Figure 1It is a schematic diagram of the synthesis technical route for preparing dynamically crosslinked thermoplastic elastomers in Examples 1 - 8;

[0064] Figure 2 It is the NMR characterization diagram of the multifunctional crosslinking agent (PEA - 3BA) prepared in Example 2;

[0065] Figure 3 It is the infrared characterization diagram of the multifunctional crosslinking agent (PEA - 3BA) prepared in Example 2;

[0066] Figure 4 It is the stress - strain curve of the dynamically crosslinked thermoplastic elastomers with different dosages of the multifunctional crosslinking agent PEA - 3BA prepared in Example 2. Specific Embodiments

[0067] The present invention will be specifically described below in conjunction with specific drawings and examples. It is necessary to point out here that the following examples are only for further illustration of the present invention and cannot be construed as limiting the protection scope of the present invention. Some non - essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0068] The raw materials used in the following examples and comparative examples are all commercially available products.

[0069] The ethylene - propylene - diene monomer rubber comes from 6950C of LANXESS in Germany; the styrene - butadiene rubber grade is SBS1301; the cis - 1,4 - polybutadiene rubber grade is BR1550; the butyl rubber grade is IIR1751.

[0070] Example 1

[0071] Step 1: Preparation of hydroxylated ethylene - propylene - diene monomer rubber (EPDM - OH): First, weigh 60 g of ethylene - propylene - diene monomer rubber (EPDM) and dissolve it in 1 L of n - hexane solvent. At a temperature of 50 °C, add 1 g of formic acid and 3 g of emulsifier Tween 80. After stirring evenly, add 10 g of hydrogen peroxide. After reacting for 8 h, add flocculant ethanol, and the flocculated product is flocculated and dried to obtain epoxidized ethylene - propylene - diene monomer rubber (e - EPDM). Dissolve 60 g of epoxidized ethylene - propylene - diene monomer rubber (e - EPDM) in 1.5 L of tetrahydrofuran (THF), add 22 g of water and 1 g of zirconium tetrachloride, react at room temperature for 3 h, add flocculant ethanol, and the flocculated product is flocculated and dried to obtain hydroxylated ethylene - propylene - diene monomer rubber (EPDM - OH).

[0072] Step 2: Preparation of multifunctional crosslinker (PPG-3BA): Dissolve 3 g of trihydroxy polyoxypropylene ether (Mw = 3000 g / mol, PPG) in 150 mL of dichloromethane, add 2.5 g of 4-carboxyphenylboronic acid and 1.4 g of catalyst (the catalyst is composed of 1,3-diisopropylcarbodiimide (DIC) and 4-dimethylaminopyridine (DMAP) in a mass ratio of 1:1.05), react under ice bath conditions at 0 °C for 12 h, remove the solvent dichloromethane in a well-ventilated place at room temperature, and use a regenerated cellulose dialysis bag (model 1000) to remove the excessive 4-carboxyphenylboronic acid and catalyst in the system to obtain the multifunctional crosslinker PPG-3BA.

[0073] Step 3: Preparation of dynamically crosslinked thermoplastic elastomer: Dissolve 5 g of hydroxylated ethylene propylene rubber (EPDM-OH) in THF to obtain a glue solution, add 2.5 g of multifunctional crosslinker (PPG-3BA) to the glue solution and mix evenly. After the solvent is volatilized in a vacuum oven at 50 °C, hot press at 160 °C and 15 MPa for 1 hour to obtain the dynamically crosslinked thermoplastic elastomer.

[0074] Example 2

[0075] Step 1: Preparation of hydroxylated ethylene propylene rubber (EPDM-OH): First, weigh 60 g of ethylene propylene diene monomer (EPDM) and dissolve it in 1 L of n-hexane solvent. At a temperature of 50 °C, add 1 g of formic acid and 3 g of emulsifier Tween 80, stir evenly, then add 10 g of hydrogen peroxide, react for 8 h, add the flocculant ethanol, and dry the floccules to obtain epoxidized ethylene propylene rubber (e-EPDM). Dissolve 50 g of epoxidized ethylene propylene rubber (e-EPDM) in 1.5 L of tetrahydrofuran (THF), add 20 g of water and 1.7 g of boron trifluoride, react at room temperature for 3.5 h, add the flocculant ethanol, and flocculate and dry the floccules to obtain hydroxylated ethylene propylene rubber (EPDM-OH).

[0076] Step 2: Preparation of multifunctional crosslinker (PEA-3BA): Dissolve 4.4 g of polyetheramine T403 and 5.2 g of 4-carboxyphenylboronic acid in 150 mL of dimethylformamide (DMF), add 1 drop of phosphoric acid, react at 130 °C for 6 h, and then remove the reaction solvent DMF by vacuum distillation to obtain the multifunctional crosslinker (PEA-3BA).

[0077] Perform NMR testing on the multifunctional crosslinker PEA-3BA prepared in Step 2 to obtain Figure 2 Perform IR testing on the multifunctional crosslinker PEA-3BA prepared in Step 2 to obtain Figure 3 . Figure 2 、 Figure 3 The signal peaks shown correspond to the target product, proving the successful synthesis of the multifunctional crosslinker.

[0078] Step 3: Preparation of dynamically crosslinked thermoplastic elastomer. 40g of hydroxylated ethylene propylene rubber (EPDM-OH) and multifunctional crosslinking agent (PEA-3BA) of different molar amounts were mixed evenly in a two-roll mill and hot-pressed at 160℃ and 15MPa for 50min to obtain dynamically crosslinked thermoplastic elastomer.

[0079] Tensile tests were conducted on the dynamically cross-linked thermoplastic elastomers with different formulations prepared in step 3. The tensile tests were performed using a CMT5105 electronic universal testing machine from Shenzhen Sansi Testing Equipment Co., Ltd. The samples were cut into dumbbell-shaped specimens using a cutter, and the tests were conducted according to the experimental protocol specified in national standard GB / T528-2009. The initial control method was displacement control, the speed was 500.0 mm / min, and the constant force decay rate was 40.0%. The test results are as follows: Figure 4 As shown.

[0080] Figure 4 In the text, PEA-3BA-0.5, PEA-3BA-0.75, PEA-3BA-1, and PEA-3BA-1.25 refer to dynamically crosslinked thermoplastic elastomers with a molar ratio of 0.5, 0.75, 1, and 1.25 of the multifunctional crosslinking agent (PEA-3BA) to the molar ratio of the dihydroxyl groups in hydroxylated ethylene propylene rubber (EPDM-OH).

[0081] Figure 4 Note: The mechanical properties of dynamically crosslinked thermoplastic elastomers differ when the molar ratio of the multifunctional crosslinking agent (PEA-3BA) to the molar ratio of the dihydroxyl groups in hydroxylated ethylene propylene rubber (EPDM-OH) is 0.5, 0.75, 1, or 1.25. The change in the molar amount of the multifunctional crosslinking agent relative to the hydroxyl content on the rubber molecular chain has a certain impact on the mechanical properties of dynamically crosslinked thermoplastic elastomers.

[0082] Example 3

[0083] Step 1: Preparation of hydroxylated ethylene propylene rubber (EPDM-OH): First, weigh 60g of EPDM and dissolve it in 1L of n-hexane solvent. At 50℃, add 1g of formic acid and 3g of emulsifier Tween 80, stir evenly, then add 10g of hydrogen peroxide. After reacting for 8 hours, add flocculant ethanol, and dry the flocculant to obtain epoxidized ethylene propylene rubber (e-EPDM). Dissolve 50g of epoxidized ethylene propylene rubber (e-EPDM) in 1.5L of tetrahydrofuran (THF), add 20g of water and 1.2g of trifluoromethanesulfonate, react at room temperature for 4 hours, add flocculant ethanol, and dry the flocculant to obtain hydroxylated ethylene propylene rubber (EPDM-OH).

[0084] Step 2: Preparation of multifunctional crosslinking agent (GLY-3BA): Dissolve 9.2g of glycerol and 5.5g of 4-carboxyphenylboronic acid in 150mL of dimethylformamide (DMF), add 1 drop of dibutyl dicitrin, react at 115℃ for 4.5h, and then remove the reaction solvent DMF by vacuum distillation to obtain the multifunctional crosslinking agent (GLY-3BA).

[0085] Step 3: Preparation of dynamically crosslinked thermoplastic elastomer: 35g of hydroxylated ethylene propylene rubber (EPDM-OH) and 3.57g of multifunctional crosslinking agent (GLY-3BA) were mixed evenly in a two-roll mill and hot-pressed at 160℃ and 15MPa for 55min to obtain the dynamically crosslinked thermoplastic elastomer.

[0086] Example 4

[0087] Step 1: Preparation of hydroxylated ethylene propylene rubber (EPDM-OH): First, weigh 60g of EPDM and dissolve it in 1L of n-hexane solvent. At 50℃, add 1g of formic acid and 3g of emulsifier Tween 80, stir evenly, then add 10g of hydrogen peroxide. After reacting for 8 hours, add flocculant ethanol, and dry the flocculant to obtain epoxidized ethylene propylene rubber (e-EPDM). Dissolve 40g of epoxidized ethylene propylene rubber (e-EPDM) in 1.5L of tetrahydrofuran (THF), add 20g of water and 2g of zirconium oxide, react at room temperature for 3 hours, add flocculant ethanol, and dry the flocculant to obtain hydroxylated ethylene propylene rubber (EPDM-OH).

[0088] Step 2: Preparation of multifunctional crosslinking agent (DETA-3BA): 14.6g of tris(2-aminoethyl)amine and 5.5g of 4-carboxyphenylboronic acid were dissolved in 150mL of dimethylformamide (DMF), 1 drop of concentrated sulfuric acid was added, and the reaction was carried out at 120℃ for 5h. The reaction solvent DMF was removed by vacuum distillation to obtain the multifunctional crosslinking agent (DETA-3BA).

[0089] Step 3: Preparation of dynamically crosslinked thermoplastic elastomer: 40g of hydroxylated ethylene propylene rubber (EPDM-OH) and 3.73g of multifunctional crosslinking agent (DETA-3BA) were mixed evenly in a two-roll mill and hot-pressed at 160℃ and 15MPa for 1h to obtain the dynamically crosslinked thermoplastic elastomer.

[0090] Example 5

[0091] Step 1: Preparation of hydroxylated styrene-butadiene rubber (SBR-OH): First, weigh 50g of SBR and dissolve it in 1L of n-hexane solvent. At 50℃, add 1.8g of formic acid and 5g of emulsifier Tween 80, stir evenly, then add 18g of hydrogen peroxide. After reacting for 9 hours, add flocculant ethanol, and dry the flocculant to obtain epoxidized styrene-butadiene rubber (e-SBR). Dissolve 40g of epoxidized styrene-butadiene rubber (e-SBR) in 1L of tetrahydrofuran (THF), add 25g of water and 2g of zirconium oxide, react at room temperature for 4 hours, add flocculant ethanol, and dry the flocculant to obtain hydroxylated styrene-butadiene rubber (SBR-OH).

[0092] Step 2: Preparation of multifunctional crosslinking agent (XYL-3BA): Dissolve 18.9g xylitol and 7.5g 4-carboxyphenylboronic acid in 150mL dimethylformamide (DMF), add 2 drops of p-toluenesulfonic acid, react at 125℃ for 4.5h, and then remove the reaction solvent DMF by vacuum distillation to obtain multifunctional crosslinking agent (XYL-3BA).

[0093] Step 3: Preparation of dynamically crosslinked thermoplastic elastomer: 45g of hydroxylated styrene-butadiene rubber (SBR-OH) and 3.4g of multifunctional crosslinking agent (XYL-3BA) were mixed evenly using a two-roll mill and hot-pressed at 170℃ and 15MPa for 55min to obtain the dynamically crosslinked thermoplastic elastomer.

[0094] Example 6

[0095] Step 1: Preparation of hydroxylated cis-butadiene rubber (BR-OH): First, weigh 50g of BR and dissolve it in 800mL of n-hexane solvent. At 60℃, add 1g of formic acid and 2.5g of emulsifier Tween 80, stir evenly, then add 10g of hydrogen peroxide. After reacting for 6 hours, add flocculant ethanol, and dry the flocculant to obtain epoxidized cis-butadiene rubber (e-BR). Dissolve 60g of epoxidized cis-butadiene rubber (e-BR) in 1L of tetrahydrofuran (THF), add 15g of water and 2.3g of zirconium oxide, react at room temperature for 3.5 hours, add flocculant ethanol, and dry the flocculant to obtain hydroxylated cis-butadiene rubber (BR-OH).

[0096] Step 2: Preparation of multifunctional crosslinking agent (PEI-3BA): Dissolve 30g of branched polyethyleneimine and 4g of 4-carboxyphenylboronic acid in 150mL of dimethylformamide (DMF), add 1 drop of concentrated sulfuric acid, react at 130℃ for 4h, and then remove the reaction solvent DMF by vacuum distillation to obtain multifunctional crosslinking agent (PEI-3BA).

[0097] Step 3: Preparation of dynamically crosslinked thermoplastic elastomer: 40g of hydroxylated cis-butadiene rubber (BR-OH) and 2.84g of multifunctional crosslinking agent (PEI-3BA) were mixed with a solvent. After the solvent was evaporated, the mixture was hot-pressed at 170℃ and 15MPa for 1h to obtain the dynamically crosslinked thermoplastic elastomer.

[0098] Example 7

[0099] Step 1: Preparation of hydroxylated butyl rubber (IIR-OH): First, weigh 50g of IIR and dissolve it in 1.2L of n-hexane solvent. At 55℃, add 1.6g of formic acid and 3.5g of emulsifier Tween 80, stir evenly, add 15g of hydrogen peroxide, and react for 9h. Then, add flocculant ethanol, and dry the flocculant to obtain epoxidized cis-butadiene rubber (e-IIR). Dissolve 50g of epoxidized cis-butadiene rubber (e-IIR) in 1L of tetrahydrofuran (THF), add 18g of water and 2.3g of zirconium chloride, react at room temperature for 5.5h, add flocculant ethanol, and dry the flocculant to obtain hydroxylated butyl rubber (IIR-OH).

[0100] Step 2: Preparation of multifunctional crosslinking agent (TEA-3BA): 1.5g of triethanolamine and 5.2g of 4-carboxyphenylboronic acid were dissolved in 50mL of dichloromethane, and 2.3g of N,N'-dicyclohexylcarbodiimide (DCC) was added. After reacting for 16h under ice bath conditions, the reaction solvent was evaporated, and the mixture was dissolved in methanol. Excess 4-carboxyphenylboronic acid and catalyst in the system were removed using a regenerated cellulose dialysis bag (model 1000) to prepare the multifunctional crosslinking agent (TEA-3BA).

[0101] Step 3: Preparation of dynamically crosslinked thermoplastic elastomer: 40g of hydroxylated butyl rubber (IIR-OH) and 4.22g of multifunctional crosslinking agent (TEA-3BA) were mixed evenly by a two-roll mill and hot-pressed at 160℃ and 15MPa for 1h to obtain the dynamically crosslinked thermoplastic elastomer.

[0102] Example 8

[0103] Step 1: Same as Step 1 in Example 4.

[0104] Step 2: Same as step 2 in Example 2.

[0105] Step 3: Preparation of dynamically crosslinked thermoplastic elastomer: 40g of hydroxylated ethylene propylene rubber (EPDM-OH) and 3.52g of multifunctional crosslinking agent (PEA-3BA) were mixed evenly in a two-roll mill and hot-pressed at 170℃ and 15MPa for 1h to obtain the dynamically crosslinked thermoplastic elastomer.

[0106] The preparation flowcharts for Examples 1-8 are as follows: Figure 1As shown.

[0107] Comparative Example 1

[0108] A difunctional crosslinking agent was prepared to compare its crosslinking effect with that of multifunctional crosslinking agents.

[0109] Step 1: Same as Step 1 in Example 2

[0110] Step 2: Preparation of difunctional crosslinking agent (PEA-2BA): Dissolve 4g of polyetheramine D400 and 3.5g of 4-carboxyphenylboronic acid in 150mL of dimethylformamide (DMF), add 1 drop of p-toluenesulfonic acid, react at 130℃ for 6h, and then remove the reaction solvent DMF by vacuum distillation to obtain the difunctional crosslinking agent (PEA-2BA).

[0111] Step 3: Preparation of dynamically crosslinked thermoplastic elastomer. 35g of hydroxylated ethylene propylene rubber (EPDM-OH) and 4.38g of difunctional crosslinking agent (PEA-2BA) were mixed evenly in a two-roll mill and hot-pressed at 160℃ and 15MPa for 40min to obtain the dynamically crosslinked thermoplastic elastomer.

[0112] Comparative Example 2

[0113] Preparation of sulfur-cured crosslinked EPDM: 100g of ethylene propylene diene monomer (EPDM), 3g of zinc oxide, 1g of stearic acid, 1g of accelerator CZ, and 1.2g of sulfur were mixed at room temperature for 8-10 minutes, allowed to stand for 12 hours, and then vulcanized at 160℃ and 15MPa for 37 minutes (the optimal vulcanization time was determined to be 37 minutes through vulcanization curves) to obtain sulfur-cured crosslinked EPDM.

[0114] Performance testing

[0115] The tensile strength, elongation at break, hardness, and crosslinking density of the dynamically crosslinked thermoplastic elastomers prepared in Examples 1-8, Comparative Example 1, and the vulcanized crosslinked EPDM prepared in Comparative Example 2 were tested, and the recovery rate was calculated. The test results are shown in Table 1.

[0116] Tensile strength and elongation at break were obtained through tensile testing. The tensile tests were conducted using a CMT5105 electronic universal testing machine from Shenzhen Sansi Testing Equipment Co., Ltd. Samples were cut into dumbbell shapes using a cutter and tested according to the experimental protocol specified in national standard GB / T528-2009. The initial control method was displacement control, with a speed of 500.0 mm / min and a constant force decay rate of 40.0%.

[0117] The hardness was tested using the Shore A test method according to GB_T2411-2008, and the indentation hardness (Shore hardness) was determined using a hardness tester.

[0118] The swelling method was used to measure the crosslinking density.

[0119] Recovery rate: The dynamically cross-linked thermoplastic elastomer samples prepared in Examples 1-8 and Comparative Example 1 were cut into small pieces, hot-pressed at 180°C and 15 MPa for 1 hour, re-processed and shaped, and then subjected to tensile tests. The recovery rate of the samples can be obtained by comparing the tensile curves.

[0120] The EPDM crosslinked by sulfur in Comparative Example 2 was crosslinked by sulfur using traditional sulfur crosslinking, which is irreversible and cannot be repeatedly processed, so the recycling efficiency was 0%.

[0121] Table 1

[0122]

[0123]

[0124] Table 1 shows that the recovery rates of Examples 1-8 are above 70%, with a maximum of over 90%; while the recovery rate of Comparative Example 2 is 0%. Examples 1-8 are the dynamically cross-linked thermoplastic elastomers provided by this invention, while Comparative Example 2 is a product cross-linked using a traditional sulfur vulcanization system. This indicates that products cross-linked using a traditional sulfur vulcanization system cannot be repeatedly processed; however, the dynamically cross-linked thermoplastic elastomer provided by this invention has excellent dynamic properties, can be repeatedly processed, and exhibits minimal degradation in mechanical properties after repeated processing.

[0125] The tensile strength, elongation at break, hardness, and crosslinking density of Examples 1-8 are all higher than those of Comparative Example 2. This indicates that the dynamically crosslinked thermoplastic elastomer provided by the present invention not only possesses excellent dynamic properties, but also exhibits superior mechanical properties such as tensile strength, elongation at break, and hardness compared to products crosslinked using traditional sulfur vulcanization systems.

[0126] The tensile strength, elongation at break, hardness, crosslinking density, and recovery rate of Examples 1-8 are all higher than those of Comparative Example 1. Specifically, the recovery rate of Examples 1-8 is increased by 13-36% compared to Comparative Example 1. Examples 1-8 represent the dynamically crosslinked thermoplastic elastomers provided by this invention, while Comparative Example 1 is a dynamically crosslinked thermoplastic elastomer prepared using a difunctional crosslinking agent. This illustrates that although dynamically crosslinked thermoplastic elastomers with dynamic properties can also be prepared using difunctional crosslinking agents, their crosslinking properties are poor, their recovery rate is low, and their dynamic properties are also poor. Compared to dynamically crosslinked thermoplastic elastomers with dynamic properties that can also be prepared using difunctional crosslinking agents, the dynamically crosslinked thermoplastic elastomers prepared by this invention show significantly improved crosslinking density, recovery rate, and dynamic properties, as well as significantly improved tensile strength, elongation at break, and hardness.

Claims

1. A multifunctional crosslinking agent, characterized in that, The structure of the multifunctional crosslinking agent is shown in Formula 1. in, Derived from polyhydroxy compounds or polyamine compounds.

2. The multifunctional crosslinking agent as described in claim 1, characterized in that, The multifunctional crosslinking agent is obtained by reacting a polyhydroxy compound or a polyamine compound with functionalized phenylboronic acid; preferably, The polyhydroxy compound is selected from one or more of the following: polyether polyols, polyester polyols, glycerol, trimethylolpropane, triethanolamine, xylitol, sorbitol, sucrose, pentaerythritol, cyclodextrin, cellulose, chitosan, and alginate; or / and, The polyamine compound is selected from one or more of the following: polyfunctional polyetheramines, branched polyethyleneimine, and tris(2-aminoethyl)amine; or / and, The functionalized phenylboronic acid is selected from one or more of 4-carboxyphenylboronic acid, 3-carboxyphenylboronic acid, and 2-carboxyphenylboronic acid.

3. A method for preparing a multifunctional crosslinking agent as described in claim 1 or 2, characterized in that, The preparation method includes: A polyhydroxy or polyamine compound reacts with functionalized phenylboronic acid in the presence of solvent 1 and catalyst 1 at 100–150 °C for 5–9 h; or, Polyhydroxy or polyamine compounds are reacted with functionalized phenylboronic acid in the presence of solvent 2 and catalyst 2 at -10 to 20°C for 12 to 16 hours.

4. The preparation method according to claim 3, characterized in that, The catalyst 1 is selected from one or more of strong acid catalysts, solid acid catalysts, and organometallic catalysts; or / and, Solvent 1 is selected from high-boiling-point polar solvents; or / and, The molar ratio of the polyhydroxy compound or polyamine compound to the functionalized phenylboronic acid and catalyst 1 is (1 / n to 2 / n): 1: (0.05 to 0.1); where n is the functionality of the polyhydroxy compound or polyamine compound; or / and, The catalyst 2 is selected from N,N'-dicyclohexylcarbodiimide or 4-dimethylaminopyridine; or / and, Solvent 2 is selected from dichloromethane or tetrahydrofuran; or / and, The molar ratio of the polyhydroxy compound or polyamine compound to the functionalized phenylboronic acid and catalyst 2 is (1 / n~5 / n):1:(1~3); where n is the degree of functionality of the polyhydroxy compound or polyamine compound.

5. A dynamically crosslinked thermoplastic elastomer, characterized in that, The structure of the dynamically cross-linked thermoplastic elastomer is shown in Formula 2. in It consists of rubber molecular chains.

6. The dynamically crosslinked thermoplastic elastomer as described in claim 5, characterized in that, The dynamically crosslinked thermoplastic elastomer is dynamically crosslinked from raw materials including hydroxylated modified rubber and a multifunctional crosslinking agent; the multifunctional crosslinking agent is: The multifunctional crosslinking agent as described in claim 1 or 2, or the multifunctional crosslinking agent prepared by the preparation method as described in claim 3 or 4; preferably, The ratio of the molar amount of dihydroxyl groups in the hydroxylated modified rubber to the molar amount of phenylboronic acid groups in the multifunctional crosslinking agent is 1:(0.5-1.5), more preferably 1:(0.9-1.1).

7. The dynamically crosslinked thermoplastic elastomer as described in claim 6, characterized in that, The hydroxylated modified rubber is obtained by catalytic hydrolysis and ring-opening of epoxidized modified rubber; preferably, The reaction temperature for catalytic hydrolysis and ring-opening is 20–60 °C; or / and, The catalyst for catalytic hydrolysis ring opening is selected from one or more of protic acids, Lewis acids, and metal oxides.

8. The dynamically crosslinked thermoplastic elastomer as described in claim 7, characterized in that, The epoxidized modified rubber is obtained by epoxidizing the base rubber; preferably, The base rubber is selected from one or more rubbers containing double bonds in the molecular chain, preferably one or more of natural rubber, styrene-butadiene rubber, cis-butadiene rubber, isoprene rubber, chloroprene rubber, butyl rubber, nitrile rubber, and ethylene propylene diene monomer (EPDM) rubber.

9. A method for preparing a dynamically crosslinked thermoplastic elastomer as described in any one of claims 5-8, characterized in that, The preparation method includes: mixing the hydroxylated modified rubber with a multifunctional crosslinking agent and then hot-pressing it; preferably, The basic modified rubber is mixed with a multifunctional crosslinking agent in a solvent, the solvent is removed, and the mixture is hot-pressed; or / and, The hot pressing process is carried out at a temperature of 150–180°C, a pressure of 10–20 MPa, and a time of 30–90 min.

10. The application of a dynamically crosslinked thermoplastic elastomer as described in any one of claims 5-8 or a dynamically crosslinked thermoplastic elastomer prepared by the preparation method as described in claim 9 in the field of rubber.

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