A boronate bond-based multi-crosslinking self-repairing epoxy-based glass elastomer, a preparation method and application thereof

Abstract

The application provides a borate bond-based multi-crosslinking self-repairing epoxy glass elastomer and a preparation method and application, and relates to the technical field of self-repairing epoxy glass elastomer materials. The preparation method comprises the following steps: dissolving trimethylolpropane triglycidyl ether, a crosslinking agent and a catalyst in a solvent to obtain a mixed solution, removing the organic solvent by heating at a certain temperature, and then performing solidification to obtain the borate bond-based multi-crosslinking self-repairing epoxy glass elastomer; wherein the crosslinking agent comprises 2,2'-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxolane and a low-molecular polyamide. By introducing multi-functional crosslinking units and borate dynamic bonds to cooperatively construct a multi-crosslinking network, high strength, rapid self-repairing and excellent environmental stability are achieved, and a novel design idea is provided for high-performance protective coatings and structure repairing materials.

Description

Technical Field

[0001] This invention relates to the field of self-healing epoxy glass elastomer materials, specifically to a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds, its preparation method, and its application. Background Technology

[0002] Epoxy resins are a widely used class of thermosetting polymers. Due to their excellent mechanical properties, chemical stability, electrical insulation properties, and good interfacial adhesion, they are extensively used in aerospace, electronic packaging, structural adhesives, and anti-corrosion coatings. However, traditional epoxy resins typically rely on irreversible three-dimensional covalent cross-linked network structures for curing. These networks are difficult to restructure effectively after formation. Once microcracks or macroscopic fractures occur during service, the damage cannot be repaired through the rearrangement or reconstruction of the network itself, leading to crack propagation, performance degradation, and even structural failure.

[0003] The aforementioned irreversible crosslinking characteristics make epoxy resins susceptible to fatigue loads, mechanical shocks, and environmental factors such as humidity, heat, and ultraviolet radiation during long-term use. This leads to a continuous decline in mechanical properties and reliability, severely restricting their further development in high-reliability and long-life applications. Therefore, endowing epoxy resin materials with self-healing capabilities has become an important research direction for improving their service safety and lifespan.

[0004] To address the aforementioned issues, researchers have recently attempted to introduce reversible interactions into epoxy resin systems, including dynamic non-covalent interactions and reversible covalent bonds, to construct cross-linked networks with self-healing capabilities. Among these, self-healing systems based on non-covalent interactions such as hydrogen bonds, metal coordination bonds, or π-π stacking can achieve molecular chain migration and crack healing under relatively mild conditions. However, due to the low binding energy of non-covalent interactions, the materials often struggle to maintain high mechanical strength while achieving self-healing. In contrast, self-healing systems constructed based on reversible covalent bonds such as Diels-Alder bonds, disulfide bonds, or imine bonds offer advantages in structural stability and mechanical properties. However, their dynamic bond exchange processes typically have high activation energies, often requiring high temperatures or specific catalytic conditions to occur, thus limiting their application range to some extent.

[0005] Among numerous dynamic covalent bonds, borate ester bonds have attracted widespread attention due to their excellent reversibility and environmental responsiveness. Borate ester bonds are typically formed by the condensation of boric acid and diol, and their bonding and dissociation processes can be rapidly and reversibly controlled under conditions of humidity, pH, or temperature changes. This dynamic equilibrium characteristic makes borate ester bonds significantly advantageous in constructing polymer networks with self-healing, remodelable, and stress-relaxation capabilities.

[0006] For example, Liu et al. reported a reconfigurable epoxy resin bonding system based on dynamic borate ester bonds. By introducing borate ester structural units into soybean oil-based epoxy resin, a crosslinked network with reversible bond exchange capability was constructed. This material can achieve reconfiguration of the fracture interface under relatively mild heating conditions (120 °C, 30 min), with a shear strength recovery rate of approximately 81% after repair, while also exhibiting good recyclability and reprocessing properties. Zeng et al. further proposed a rosin-based epoxy vitrimer system, introducing a borate ester-type dioxaborolane structure into its cured network. This dynamic crosslinked network can achieve more than 80% mechanical property recovery after heating at 170 °C for 30 min, and can be repeatedly hot-pressed and reshaped without significant reduction in strength. This research provides a useful exploration for the dynamic design of renewable resource-based epoxy resins. Zhang et al. constructed a plant oil-based epoxy resin system containing triple dynamic covalent bonds, achieving a self-healing efficiency of approximately 90% within 24 h at room temperature, with a maximum tensile strength of 43.2 MPa, and maintaining high mechanical properties even after multiple recycling. The results indicate that the dynamic bonds of borate esters play a crucial role in promoting rapid bond exchange and stress relaxation in this system.

[0007] Although the aforementioned research has made some progress in the field of borate ester-based self-healing epoxy glass elastomers, existing systems still have shortcomings: on the one hand, the distribution and crosslinking density of dynamic bonds in the crosslinked network are difficult to precisely control, making it difficult to simultaneously achieve a balance between the self-healing rate and mechanical properties; on the other hand, most systems still require external thermal stimulation or humidity regulation to activate the dynamic bond exchange process, which is insufficient to meet the practical needs for rapid and spontaneous repair under complex service environments. Therefore, developing a structurally balanced, highly efficient self-healing epoxy glass elastomer system with excellent mechanical properties, capable of achieving self-healing at room temperature, remains a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds and its preparation method. By introducing multifunctional crosslinking units and dynamic borate ester bonds to synergistically construct a multi-crosslinked network, high strength, rapid self-healing, and excellent environmental stability are achieved, providing a novel design approach for high-performance protective coatings and structural repair materials.

[0009] The first aspect of this invention provides a method for preparing a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds, the method comprising the following steps: Trimethylolpropane triglycidyl ether, a crosslinking agent, and a catalyst are dissolved in a solvent to obtain a mixed solution. The organic solvent is removed by heating at a certain temperature, and then the solution is cured to obtain a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds. The crosslinking agents include 2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane and low molecular weight polyamide.

[0010] Optionally, the total molar ratio of thiol and amino groups in the crosslinking agent to the molar ratio of epoxy groups in trimethylolpropane triglycidyl ether is 1:1.

[0011] Optionally, the molar ratio of 2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane to low molecular weight polyamide is (0.5-3):(0.5-3).

[0012] Optionally, the molar ratio of 2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane to low molecular weight polyamide is 0.5:1-3:1.

[0013] Optionally, the molar ratio of 2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane to low molecular weight polyamide is 1:1 to 2:1.

[0014] Optionally, the molar ratio of 2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane to low molecular weight polyamide is 1:1.

[0015] Optionally, the process of removing organic solvents by heating at a certain temperature includes: vacuum drying at 55-65℃ for 0.5-1 h.

[0016] Optionally, the curing temperature is 60-90℃.

[0017] Optionally, the low molecular weight polyamide is low molecular weight -650-polyamide. This application selects low molecular weight -650 polyamide, which has a moderate molecular chain length and a high content of terminal amino groups, allowing it to fully react with epoxy groups to form a uniform and stable cross-linked structure, thus improving the mechanical strength of the material. Polyamide segments within this molecular weight range have a certain degree of flexibility, providing the necessary chain segment movement capability for the system, which is beneficial for the exchange process of dynamic bonds in borate esters, thereby promoting self-healing behavior. When the molecular weight of the polyamide is too low, the cross-linking point density in the system is too high, and the network structure tends to be rigid, restricting chain segment movement and hindering the dynamic bond exchange and self-healing performance. When the molecular weight of the polyamide is too high, the content of active amino groups decreases, reducing the effective functional groups participating in the cross-linking reaction, easily leading to insufficient cross-linking density and a loose network structure, thereby reducing the mechanical properties and structural stability of the material.

[0018] Optionally, the epoxy value of trimethylolpropane triglycidyl ether is 0.60-0.80 eq / 100g. Preferably, the epoxy value of trimethylolpropane triglycidyl ether is 0.70 eq / 100g. Within this range, the epoxy resin possesses moderate functionality and reactivity, enabling it to fully react with the thiol and amino groups in the crosslinking agent, thereby constructing a uniform three-dimensional network structure with moderate crosslinking density, resulting in materials exhibiting both good mechanical properties and self-healing properties. When the epoxy value is below the above range, the effective epoxy group content in the system is low, the number of functional groups participating in the crosslinking reaction decreases, easily leading to insufficient crosslinking density and a looser network structure, thus reducing the mechanical properties and structural stability of the material. When the epoxy value is above the above range, the crosslinking density in the system is too high, restricting chain segment movement and hindering the exchange and rearrangement of dynamic bonds in the borate ester, thereby affecting the self-healing properties of the material. More preferably, the epoxy value is about 0.70 eq / 100g, at which point the crosslinking density and chain segment mobility in the system reach a better balance, and the overall performance of the material is optimal.

[0019] Optionally, the catalyst is one or two of 4-dimethylaminopyridine, imidazole, tetrabutylammonium fluoride, zinc acetylacetonate, or 2-methylimidazolium.

[0020] Optionally, the amount of catalyst added is 1-3% of the mass of trimethylolpropane triglycidyl ether.

[0021] Optionally, the catalyst is 4-dimethylaminopyridine and imidazole, and the amount of 4-dimethylaminopyridine and imidazole added is 1 wt% and 1 wt% of the mass of trimethylolpropane triglycidyl ether, respectively.

[0022] Optionally, the solvent is tetrahydrofuran.

[0023] Optionally, the preparation method of 2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane includes the following steps: 1,4-Phenylated boric acid and 1-thioglycerol were dissolved in an organic solvent, and then anhydrous magnesium sulfate was added to carry out the reaction. After filtration, evaporation, impurity removal and drying, the borate ester crosslinking agent 2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane was obtained.

[0024] Optionally, the liquid product obtained by filtration can be subjected to rotary evaporation at 55-65℃ to remove the solvent and obtain a solid crude product.

[0025] Optionally, the obtained crude solid product is added to n-heptane and stirred and heated at 45-55°C to remove impurities. Then, it is filtered and dried under vacuum to obtain a white solid 2,2′-(1,4-phenylene)-bis[4-thiol 1,3,2-dioxapentane.

[0026] The third aspect of this invention provides an application of a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds in aerospace, electronic packaging, structural adhesives, or anti-corrosion coatings.

[0027] Compared with the prior art, the present invention achieves at least one of the following beneficial effects: (1) The present invention is based on the multi-crosslinked self-healing epoxy glass elastomer of borate ester bond. Through the synergistic effect of permanent crosslinking structure and dynamic covalent bond and hydrogen bond of borate ester bond, a multi-crosslinking network is constructed. While ensuring the mechanical strength and structural stability of epoxy glass elastomer, it endows the material with excellent self-healing ability, overcoming the problem that the performance of existing self-healing epoxy systems is difficult to balance.

[0028] (2) The dynamic covalent bonds of borate ester introduced in the multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds can undergo reversible breakage and recombination at low temperatures, so that the material can complete self-healing without high temperature or complex external stimulation, which significantly reduces repair energy consumption and improves the applicability of the material in actual service environment.

[0029] (3) The multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds of the present invention can effectively control the crosslinking density and dynamic bond content by adjusting the ratio of borate ester crosslinking agent to polyamide crosslinking agent, thereby achieving synergistic optimization of mechanical properties, self-healing efficiency and network stability, and is suitable for the performance requirements of different application scenarios.

[0030] (4) The preparation method of the present invention adopts conventional solution mixing, vacuum desolvation and thermosetting process. The reaction conditions are mild and the process route is clear. It has good repeatability and scalability and is suitable for industrial preparation and engineering application. Attached Figure Description

[0031] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 The synthesis route diagram of the crosslinking agent BDB provided by the present invention.

[0032] Figure 2 The synthesis route diagram of elastomer 1# provided by the present invention.

[0033] Figure 3Fourier transform infrared spectra of 1,4-phenylenediboric acid, 1-thioglycerol and BDB provided for this invention.

[0034] Figure 4 The proton NMR spectra of 1,4-phenylenediboric acid, 1-thioglycerol and BDB provided for this invention.

[0035] Figure 5 Fourier transform infrared spectra of BDB, LPA, and elastomer 1# provided for this invention.

[0036] Figure 6 Fourier transform infrared spectra of BLTTE elastomers with different crosslinking agent ratios provided by the present invention.

[0037] Figure 7 Stress-strain diagrams of BLTTE elastomers with different crosslinking agent ratios provided by the present invention.

[0038] Figure 8 Stress-strain diagram of the elastomer BLTTE1# after multiple fracture repairs provided by the present invention.

[0039] Figure 9 Self-healing micrographs of BLTTE elastomers with different crosslinking agent ratios provided by this invention at room temperature (25°C).

[0040] Figure 10 The repair photograph and mechanism diagram of elastomer 1# provided by the present invention.

[0041] Figure 11 This is a diagram illustrating the self-healing mechanism of the cross-linking structure of the elastomer 1# coating provided by the present invention. Detailed Implementation

[0042] To more clearly illustrate the overall concept of the present invention, a detailed description will be provided below with reference to the accompanying drawings and examples.

[0043] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0044] All the raw materials required for this invention can be purchased through commercial channels.

[0045] Example 1 In an exemplary embodiment of the present invention, 3.0 g of 1,4-phenylenediboric acid and 4.01 g of 1-thioglycerol were dissolved in a mixed solvent of 80 mL tetrahydrofuran and 0.1 mL water, and then 5.0 g of anhydrous magnesium sulfate was added. The reaction system was stirred at room temperature for 24 h, and the precipitate was filtered off to obtain a mixed liquid. The mixed liquid was rotary evaporated at 60 °C. The obtained solid was added to n-heptane, and impurities were removed by stirring and heating in an oil bath at 50 °C for 3 h. Finally, the mixture was filtered and vacuum dried to obtain a white solid target compound, the crosslinking agent BDB2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane. The synthetic route of 2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane is referenced. Figure 1 As shown.

[0046] Example 2 Multi-crosslinked self-healing epoxy glass elastomer #1 In an exemplary embodiment of the present invention, the method for preparing a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds includes the following steps: Under the premise of an epoxy system (epoxy / (thiol + amino) molar ratio of 1), 2g of trimethylolpropane triglycidyl ether (TTE, trimethylolpropane triglycidyl ether epoxy value of 0.70 eq / 100g), 2,2′-(1,4-phenylene)-bis[4-thiol 1,3,2-dioxapentane (BDB) and low molecular weight -650-polyamide (LPA) prepared in Example 1 (molar ratio of 1:1), and catalysts 4-dimethylaminopyridine (DMAP) and imidazole (IM) were used. (DMAP and IM were added at 1 wt% and 1 wt% of TTE, respectively) and dissolved together in 20 mL of tetrahydrofuran. After mixing evenly, the mixture was heated to 60 °C in an oil bath and stirred to concentrate. When the solution became viscous, the mixture was placed in a polytetrafluoroethylene dumbbell-shaped mold plate and vacuum dried in a 60 °C oven for 0.5 h to allow the solvent to evaporate completely. The completely evaporated mixture was then placed in a drying oven and heated to 80 °C overnight to allow the reaction to proceed fully and the epoxy resin to cure completely, resulting in a yellow film material. This material is a multi-crosslinked self-healing epoxy glass elastomer material based on borate ester bonds, denoted as BLTTE (1:1).

[0047] Multi-crosslinked self-healing epoxy glass elastomer #2 In an exemplary embodiment of the present invention, the method for preparing a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds includes the following steps: Under the premise of an epoxy system (epoxy / (thiol + amino) molar ratio of 1), 2g of trimethylolpropane triglycidyl ether (TTE, trimethylolpropane triglycidyl ether epoxy value of 0.70 eq / 100g), 2,2′-(1,4-phenylene)-bis[4-thiol 1,3,2-dioxapentane and low molecular weight -650-polyamide (molar ratio of 1:3), and catalysts 4-dimethylaminopyridine (DMAP) and imidazole (IM) were prepared in Example 1. (DMAP and IM were added at 1 wt% and 1 wt% of TTE, respectively) and dissolved together in 20 mL of tetrahydrofuran. After mixing evenly, the mixture was heated to 60 °C in an oil bath and stirred to concentrate. When the solution became viscous, the mixture was placed in a polytetrafluoroethylene dumbbell-shaped mold plate and vacuum dried in an oven at 55 °C for 1 h to allow the solvent to evaporate completely. The completely evaporated mixture was then placed in a drying oven and heated to 60 °C overnight to allow the reaction to proceed fully and the epoxy resin to completely cure, resulting in a yellow film material. This material is a multi-crosslinked self-healing epoxy glass elastomer material based on borate ester bonds, denoted as BLTTE (1:3).

[0048] Multi-crosslinked self-healing epoxy glass elastomer #3 In an exemplary embodiment of the present invention, the method for preparing a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds includes the following steps: Under the premise of an epoxy system (epoxy / (thiol + amino) molar ratio of 1), 2g of trimethylolpropane triglycidyl ether (TTE, the epoxy value of trimethylolpropane triglycidyl ether is 0.70 eq / 100g), 2,2′-(1,4-phenylene)-bis[4-thiol 1,3,2-dioxapentane and low molecular weight -650-polyamide (molar ratio of 3:1), and catalysts 4-dimethylaminopyridine (DMAP) and imidazole (IM) were prepared in Example 1. (DMAP and IM were added at 1 wt% and 1 wt% of TTE, respectively) and dissolved together in 20 mL of tetrahydrofuran. After mixing evenly, the mixture was heated to 60 °C in an oil bath and stirred to concentrate. When the solution became viscous, the mixture was placed in a polytetrafluoroethylene dumbbell-shaped mold plate and vacuum dried in an oven at 65 °C for 1 h to allow the solvent to evaporate completely. The completely evaporated mixture was then placed in a drying oven and heated to 90 °C overnight to allow the reaction to proceed fully and the epoxy resin to completely cure, resulting in a yellow film material. This material is a multi-crosslinked self-healing epoxy glass elastomer material based on borate ester bonds, denoted as BLTTE (3:1).

[0049] Multi-crosslinked self-healing epoxy glass elastomer #4 In an exemplary embodiment of the present invention, the method for preparing a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds includes the following steps: Under the premise of an epoxy system (epoxy / (thiol + amino) molar ratio of 1), 2g of trimethylolpropane triglycidyl ether (TTE, the epoxy value of trimethylolpropane triglycidyl ether is 0.70 eq / 100g), 2,2′-(1,4-phenylene)-bis[4-thiol 1,3,2-dioxapentane and low molecular weight -650-polyamide (molar ratio of 0:1), and catalysts 4-dimethylaminopyridine (DMAP) and imidazole (IM) were used. (DMAP and IM were added at 1 wt% and 1 wt% of TTE, respectively) and dissolved together in 20 mL of tetrahydrofuran. After mixing evenly, the mixture was heated to 60 °C in an oil bath and stirred to concentrate. When the solution became viscous, the mixture was placed in a polytetrafluoroethylene dumbbell-shaped mold plate and vacuum dried in an oven at 55 °C for 1 h to allow the solvent to evaporate completely. The completely evaporated mixture was then placed in a drying oven and heated to 60 °C overnight to allow the reaction to proceed fully and the epoxy resin to cure completely, resulting in a yellow film material. This material is a multi-crosslinked self-healing epoxy glass elastomer material based on borate ester bonds, denoted as BLTTE (0:1).

[0050] Multi-crosslinked self-healing epoxy glass elastomer #5 In an exemplary embodiment of the present invention, the method for preparing a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds includes the following steps: Under the premise of an epoxy system (epoxy / (thiol + amino) molar ratio of 1), 2g of trimethylolpropane triglycidyl ether (TTE, trimethylolpropane triglycidyl ether epoxy value of 0.60 eq / 100g), 2,2′-(1,4-phenylene)-bis[4-thiol 1,3,2-dioxapentane (BDB) and low molecular weight -650-polyamide (LPA) prepared in Example 1 (molar ratio of 1:1), and catalysts 4-dimethylaminopyridine (DMAP) and imidazole (IM) were used. (DMAP and IM are each added at 1 wt% of TTE) and dissolved together in 20 mL of tetrahydrofuran; after mixing evenly, the mixture is heated to 60 °C in an oil bath and stirred to concentrate. When the solution becomes thick, the mixture is placed in a polytetrafluoroethylene dumbbell-shaped mold plate and vacuum dried in a 60 °C oven for 0.5 h to allow the solvent to completely evaporate. The completely evaporated mixture is then placed in a drying oven and heated to 80 °C overnight to allow the reaction to proceed fully and the epoxy resin to completely cure, resulting in a yellow film material, which is a multi-crosslinked self-healing epoxy glass elastomer material based on borate ester bonds.

[0051] Multi-crosslinked self-healing epoxy glass elastomer #6 In an exemplary embodiment of the present invention, the method for preparing a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds includes the following steps: Under the premise of an epoxy system (epoxy / (thiol + amino) molar ratio of 1), 2g of trimethylolpropane triglycidyl ether (TTE, trimethylolpropane triglycidyl ether epoxy value of 0.80 eq / 100g), 2,2′-(1,4-phenylene)-bis[4-thiol 1,3,2-dioxapentane (BDB) and low molecular weight -650-polyamide (LPA) prepared in Example 1 (molar ratio of 1:1), and catalysts 4-dimethylaminopyridine (DMAP) and imidazole (IM) were used. (DMAP and IM are each added at 1 wt% of TTE) and dissolved together in 20 mL of tetrahydrofuran; after mixing evenly, heat to 60 °C in an oil bath and stir to concentrate. When the solution becomes viscous, place the mixture in a polytetrafluoroethylene dumbbell-shaped mold plate and vacuum dry in a 60 °C oven for 0.5 h to allow the solvent to evaporate completely. Place the completely evaporated mixture in a drying oven and heat to cure overnight at 80 °C to allow the reaction to proceed fully and the epoxy resin to cure completely, resulting in a yellow film material, which is a multi-crosslinked self-healing epoxy glass elastomer material based on borate ester bonds.

[0052] Multi-crosslinked self-healing epoxy glass elastomer #7 In an exemplary embodiment of the present invention, the method for preparing a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds includes the following steps: Under the premise of an epoxy system (epoxy group / (thiol + amino) molar ratio of 1), 2g of trimethylolpropane triglycidyl ether (TTE, trimethylolpropane triglycidyl ether epoxy value of 0.70 eq / 100g), 2,2′-(1,4-phenylene)-bis[4-thiol 1,3,2-dioxapentane (BDB) and polymer-1000-polyamide (HPA) prepared in Example 1 (molar ratio of 1:1), and catalysts 4-dimethylaminopyridine (DMAP) and imidazole (IM) were used. (DMAP and IM are each added at 1 wt% of TTE) and dissolved together in 20 mL of tetrahydrofuran; after mixing evenly, heat to 60 °C in an oil bath and stir to concentrate. When the solution becomes viscous, place the mixture in a polytetrafluoroethylene dumbbell-shaped mold plate and vacuum dry in a 60 °C oven for 0.5 h to allow the solvent to evaporate completely. Place the completely evaporated mixture in a drying oven and heat to cure overnight at 80 °C to allow the reaction to proceed fully and the epoxy resin to cure completely, resulting in a yellow film material, which is a multi-crosslinked self-healing epoxy glass elastomer material based on borate ester bonds.

[0053] Elastomer D1 Based on the multi-crosslinked self-healing epoxy glass elastomer 1#, the main difference is that trimethylolpropane triglycidyl ether is replaced with bisphenol A diglycidyl ether.

[0054] The other steps are the same as those for multi-crosslinked self-healing epoxy glass elastomer #1.

[0055] Elastomer D2 The preparation method of multi-crosslinked self-healing epoxy glass elastomers based on borate ester bonds includes the following steps: Under the premise of an epoxy system (epoxy / (thiol + amino) molar ratio of 1), 2g of trimethylolpropane triglycidyl ether (TTE, the epoxy value of trimethylolpropane triglycidyl ether is 0.70 eq / 100g), 2,2′-(1,4-phenylene)-bis[4-thiol 1,3,2-dioxapentane and low molecular weight -650-polyamide (molar ratio of 1:0), and catalysts 4-dimethylaminopyridine (DMAP) and imidazole (IM) were prepared in Example 1. (DMAP and IM are each added at 1 wt% of TTE) and dissolved together in 20 mL of tetrahydrofuran; after mixing evenly, heat to 60 °C in an oil bath and stir to concentrate. When the solution becomes viscous, place the mixture in a polytetrafluoroethylene dumbbell-shaped mold plate and vacuum dry in an oven at 55 °C for 1 h to allow the solvent to evaporate completely. Place the completely evaporated mixture in a drying oven and heat to cure overnight at 60 °C to allow the reaction to proceed fully and the epoxy resin to cure completely, resulting in a yellow film material, which is a multi-crosslinked self-healing epoxy glass elastomer material based on borate ester bonds.

[0056] Test case Table 1

[0057] Referring to Table 1, the elastomer prepared by this invention can complete self-repair without high temperature or complex external stimuli, and the self-repair time is <100 min. Preferably, the self-repair time is no more than 30 min.

[0058] In elastomer D2, when LPA is 0, the system lacks sufficient permanent cross-linking structures, resulting in cross-linking failure.

[0059] Figure 1 The synthesis route diagram of the crosslinking agent BDB provided by the present invention.

[0060] Figure 2 The synthesis route diagram of elastomer 1# provided by the present invention.

[0061] Figure 3 Fourier transform infrared spectra of 1,4-phenylenediboric acid, 1-thioglycerol and BDB provided for this invention.

[0062] Figure 4 The proton NMR spectra of 1,4-phenylenediboric acid, 1-thioglycerol and BDB provided for this invention.

[0063] Figure 5Fourier transform infrared spectra of BDB, LPA, and elastomer 1# provided for this invention.

[0064] Figure 6 Fourier transform infrared spectra of BLTTE elastomers with different crosslinking agent ratios provided by the present invention.

[0065] Figure 7 Stress-strain diagrams of BLTTE elastomers with different crosslinking agent ratios provided by this invention are shown. It can be seen that different BDB to LPA ratios have a significant impact on the mechanical properties of the material. When the proportion of LPA in the crosslinking agent is high (such as BLTTE (0:1) and BLTTE (1:3)), the material exhibits high tensile strength, with the maximum stress of BLTTE (1:3) reaching over 16 MPa. However, its elongation at break is relatively low, exhibiting certain brittle characteristics. When the molar ratio of BDB to LPA is 1:1 (BLTTE (1:1)), the material exhibits moderate strength and high elongation at break, indicating that the system achieves a good balance between strength and toughness. When the proportion of BDB is further increased (such as BLTTE (3:1)), the elongation at break of the material increases significantly, but its tensile strength decreases significantly, indicating that the increased content of dynamic borate ester bonds is beneficial to chain segment movement but reduces network rigidity. By adjusting the ratio of BDB to LPA, the mechanical properties of the material can be effectively controlled, with the 1:1 ratio exhibiting superior comprehensive performance in terms of strength and ductility.

[0066] Figure 8 Stress-strain diagrams of the multi-crosslinked self-healing epoxy glass elastomer 1#BLTTE (1:1) provided by this invention after multiple fracture repairs are shown. It can be seen that the material can still recover high mechanical properties after multiple fractures and repairs. Compared with the original sample, the sample after the first repair only slightly decreased in maximum stress and elongation at break, with the maximum stress still reaching approximately 6 MPa or higher, indicating that the material has high initial self-healing efficiency. As the number of repairs increases, the maximum stress and elongation at break gradually decrease, but still maintain a certain level of mechanical properties, indicating that the system has good multiple repair capabilities. The above results show that the multi-crosslinked network constructed in this invention can maintain structural integrity during repeated fractures and repairs, and the reversible exchange of the borate ester dynamic bonds can effectively promote the reconnection of the fracture interface, thereby achieving the recovery of the material's mechanical properties.

[0067] Figure 9Self-healing micrographs of BLTTE elastomers with different crosslinking agent ratios provided by this invention at room temperature (25°C). It can be seen that different BDB to LPA ratios have a significant impact on the self-healing behavior of the material. For systems with high LPA content (such as BLTTE (0:1) and BLTTE (1:3)), scratches or cracks heal slowly at room temperature, and obvious traces remain at the interface after repair, indicating that the chain segment movement in the system is restricted and the self-healing ability is weak. When the molar ratio of BDB to LPA is 1:1 (BLTTE (1:1)), the material can achieve relatively obvious crack healing at room temperature. As time goes on, the scratches gradually become shallower until they basically disappear, showing excellent self-healing ability. When the BDB content is further increased (such as BLTTE (3:1)), the crack healing speed of the material is further improved and the interface recovery is more obvious, indicating that the increase of dynamic borate ester bond content in the system is conducive to promoting chain segment rearrangement and interface repair. By adjusting the ratio of BDB to LPA, the self-healing performance of the material at room temperature can be effectively controlled. Among them, the system containing an appropriate amount of dynamic borate ester bonds shows better self-healing effect.

[0068] Figure 10 The images and mechanism diagrams of the repair process of elastomer 1# provided by this invention are shown. It can be seen that the fractured sample can effectively heal after re-contact at room temperature, and the repaired sample as a whole recovers its continuous structure, indicating that the material has good self-healing ability. The dynamic covalent bonds of borate esters introduced in this invention can undergo reversible breakage and recombination under external conditions. When the material breaks, the original borate ester bonds dissociate; after re-contact at the fracture interface, the molecular chains rearrange under certain chain segment movements, and the borate ester bonds undergo exchange reactions and reform, thereby achieving interface healing and structural reconstruction. The permanent cross-linking network formed by the reaction of epoxy groups with thiol and amino groups plays a role in maintaining the overall structural stability during the repair process, while the dynamic borate ester bonds endow the system with the necessary reversibility and chain segment rearrangement ability. The synergistic effect of these two factors enables the material to achieve self-healing function while maintaining its mechanical properties. This invention achieves spontaneous repair of the material at room temperature by constructing a multi-cross-linking structure with the synergistic effect of a "permanent cross-linking network + dynamic borate ester bonds".

[0069] Figure 11 The diagram shows the self-healing mechanism of the coating crosslinking structure of elastomer 1# provided by the present invention.

[0070] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds, characterized in that, The preparation method includes the following steps: Trimethylolpropane triglycidyl ether, a crosslinking agent, and a catalyst are dissolved in a solvent to obtain a mixed solution. The organic solvent is removed by heating at a certain temperature, and then the solution is cured to obtain a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds. The crosslinking agents include 2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane and low molecular weight polyamide.

2. The preparation method according to claim 1, characterized in that, The total molar ratio of thiol and amino groups in the crosslinking agent to the molar ratio of epoxy groups in trimethylolpropane triglycidyl ether is 1:

1.

3. The preparation method according to claim 1, characterized in that, The molar ratio of 2,2′-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxapentane to low molecular weight polyamide is 0.5:1-3:

1.

4. The preparation method according to claim 3, characterized in that, The molar ratio of 2,2′-(1,4-phenylene)-bis[4-thiol 1,3,2-dioxapentane to low molecular weight polyamide is 1:1-2:

1.

5. The preparation method according to claim 1, characterized in that, The process of removing organic solvents by heating at a certain temperature includes: vacuum drying at 55-65℃ for 0.5-1 h; And / or the curing temperature is 60-90℃.

6. The preparation method according to claim 1, characterized in that, The low molecular weight polyamide is low molecular weight -650-polyamide.

7. The preparation method according to claim 1, characterized in that, The epoxy value of trimethylolpropane triglycidyl ether is 0.60-0.80 eq / 100g.

8. The preparation method according to claim 1, characterized in that, The catalyst is one or two of 4-dimethylaminopyridine, imidazole, tetrabutylammonium fluoride, zinc acetylacetonate, or 2-methylimidazolium.

9. A multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds, prepared by any one of the preparation methods of claims 1-8.

10. The application of a multi-crosslinked self-healing epoxy glass elastomer based on borate ester bonds as described in claim 9 in aerospace, electronic packaging, structural adhesives, or anti-corrosion coatings.

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