A crosslinked epoxy resin which can be reprocessed at temperatures below the glass transition temperature, and a process for its preparation and use

Abstract

The application provides a crosslinked epoxy resin which can be reprocessed under conditions below the glass transition temperature, and a preparation method and application thereof, and belongs to the technical field of frontier new materials. The application introduces imine bonds and VU dynamic covalent bonds into epoxy resins and curing agents with specific structures respectively, and obtains an epoxy resin glass polymer material with a crosslinked structure. The lowest relaxation temperature of the glass polymer material is significantly reduced, the relaxation time is significantly shortened, and the glass polymer material can be reprocessed under conditions below the glass transition temperature. The application has good application prospects in the fields of improving material repairability, material reprocessing, material recycling and utilization, and the like.

Description

Technical Field

[0001] This invention belongs to the field of cutting-edge new materials technology, specifically relating to a cross-linked epoxy resin that can be reprocessed under conditions below the glass transition temperature, its preparation method, and its uses. Background Technology

[0002] Epoxy resin is an important thermosetting resin widely used in industry and daily life. It possesses excellent dimensional stability, thermal stability, mechanical strength, creep resistance, electrical insulation, and chemical resistance. However, due to its infusible nature, epoxy resin is difficult to reprocess, recycle, and remodel, resulting in aged, damaged, and discarded epoxy resin being disposed of only through incineration or landfill, causing environmental pollution and resource waste.

[0003] Vitrimers are polymers with reversible covalent cross-linked networks, capable of reconstructing the cross-linked network while maintaining the cross-linked structure, combining the advantages of both thermosetting and thermoplastic polymers. This material not only inherits the good mechanical properties and solvent resistance of traditional thermosetting resins such as epoxy resins, but also exhibits flowability and reprocessing performance similar to thermoplastic resins, providing an effective way to recycle and reuse cross-linked resins. Epoxy resin vitrimers combine thermoplasticity and thermosetting properties; they exhibit properties similar to traditional thermosetting epoxy at low temperatures, while showing good thermoplasticity at high temperatures, allowing for multiple remolding, welding, and recycling. However, the repair temperature of traditional epoxy resin vitrimers is much higher than the glass transition temperature; excessively high reprocessing temperatures can lead to segmental degradation of the material to some extent, and the harsh repair conditions limit the application areas of the material. Patent application CN116333268A discloses an epoxy resin obtained by compounding a curing agent containing VU dynamic covalent bonds with E51 type epoxy resin, but its minimum relaxation temperature is 140°C, and the relaxation time at 140°C exceeds 1000s, making it impossible to reprocess under conditions below the glass transition temperature.

[0004] Therefore, choosing appropriate methods to lower the temperature barrier for material reprocessing or self-healing / repairable materials, enabling them to be reprocessed below the glass transition temperature, is of great significance for expanding the material properties and application areas. Summary of the Invention

[0005] The purpose of this invention is to provide a cross-linked epoxy resin that can be reprocessed at temperatures below the glass transition temperature, as well as its preparation method and uses.

[0006] This invention provides an epoxy resin-based glass polymer material, prepared from an epoxy resin containing imine dynamic bonds and a curing agent containing VU dynamic covalent bonds as raw materials; the mass ratio of the epoxy resin containing imine dynamic bonds to the curing agent containing VU dynamic covalent bonds is 1:0.5-5; the imine dynamic bonds are... The VU dynamic covalent bond is

[0007] Furthermore, the epoxy resin is selected from glycidyl ether type epoxy resin, glycidyl ester type epoxy resin, glycidyl amine type epoxy resin, alicyclic epoxide, aromatic epoxy resin, linear aliphatic epoxide, bisphenol A type epoxy resin, phenolic epoxy resin, and polyol glycidyl ether type epoxy resin.

[0008] The mass ratio of the epoxy resin containing imine dynamic bonds to the curing agent containing VU dynamic covalent bonds is 1:1 to 1.2.

[0009] Furthermore, the epoxy resin containing imine dynamic bonds has the following structure:

[0010]

[0011] Furthermore, the epoxy resin containing imine dynamic bonds is prepared from vanillin, p-aminophenol, epichlorohydrin and a phase transfer catalyst as raw materials; the mass ratio of vanillin, p-aminophenol, epichlorohydrin and phase transfer catalyst is 1:0.2-1.5:10-20:0.01-0.15;

[0012] The mass ratio of vanillin, p-aminophenol, epichlorohydrin, and phase transfer catalyst is 1:0.5-0.9:14-17:0.06-0.1;

[0013] The phase transfer catalyst is tetrabutylammonium bromide;

[0014] The curing agent containing VU dynamic covalent bonds is prepared from difunctional amines, tris(2-aminoethyl)amine and EGAA as raw materials;

[0015] The molar ratio of the difunctional amine, tris(2-aminoethyl)amine, and EGAA is 1–5:0.1–0.5:1;

[0016] The structure of the EGAA is as follows:

[0017] Furthermore, the molar ratio of the difunctional amine, tris(2-aminoethyl)amine, and EGAA is 1–2:0.4–0.5:1;

[0018] The difunctional amine is selected from isophorone diamine, m-phenylenediamine, or bis(4-amino-3-methylcyclohexyl)methane;

[0019] The preparation method of the EGAA includes the following steps: ethylene glycol and tert-butyl acetoacetate are mixed evenly and then heated to react, and the EGAA is obtained; the molar ratio of ethylene glycol and tert-butyl acetoacetate is 1:1 to 5.

[0020] Furthermore, the preparation method of the EGAA includes the following steps: mixing ethylene glycol and tert-butyl acetoacetate evenly and then heating to react, thereby obtaining the EGAA; the molar ratio of ethylene glycol and tert-butyl acetoacetate is 1:1 to 5.

[0021] Preferably, the molar ratio of ethylene glycol to tert-butyl acetoacetate is 1:2.3;

[0022] And / or, the temperature of the heating reaction is 120–130°C, and the reaction time is 1–5 h;

[0023] And / or, the product is purified by vacuum extraction after the reaction.

[0024] Furthermore, the preparation method of the epoxy resin containing imine dynamic bonds includes the following steps:

[0025] (1) Vanillin and p-aminophenol were mixed and reacted to obtain an intermediate containing an imine dynamic bond;

[0026] (2) After mixing the intermediate, epichlorohydrin and phase transfer catalyst, the first reaction is carried out, followed by a second reaction with alkali, to obtain an epoxy resin containing imine dynamic bonds.

[0027] Furthermore, the preparation method of the curing agent containing VU dynamic covalent bonds includes the following steps:

[0028] (i) Mixing a difunctional amine with tris(2-aminoethyl)amine;

[0029] (ii) Add EGAA to the mixture from step (i) to react and obtain a curing agent containing VU dynamic covalent bonds.

[0030] Furthermore, in step (1), the solvent for the reaction is an inorganic solvent; the reaction temperature is 10–40°C, and the reaction time is 2–6 hours.

[0031] In step (2), the base is an organic base or an inorganic base; the temperature of the first reaction is 50-100℃ and the time is 2-6 hours; the conditions for the second reaction are to react at 50-100℃ for 0.5-2 hours first, and then at 10-40℃ for 0.5-2 hours.

[0032] Furthermore, in step (1), the solvent for the reaction is water; the reaction temperature is 20-30°C, and the reaction time is 4 hours;

[0033] In step (2), the alkali is sodium hydroxide; the temperature of the first reaction is 80°C and the time is 4 hours; the conditions for the second reaction are to react at 80°C for 1 hour first, and then at 20-30°C for 1 hour.

[0034] Further, in step (i), the difunctional amine and tris(2-aminoethyl)amine are mixed and preheated at 70-90°C for 1-5 minutes;

[0035] And / or, in step (ii), stirring is performed when EGAA is added;

[0036] And / or, in step (ii), after adding EGAA and reacting, the reactants are dried.

[0037] Furthermore, the difunctional amine and tris(2-aminoethyl)amine are mixed and preheated at 80°C for 3 minutes.

[0038] The present invention also provides a method for preparing the above-mentioned epoxy resin-based glass polymer material, the method comprising the following steps: mixing an epoxy resin containing imine dynamic bonds and a curing agent containing VU dynamic covalent bonds, and then carrying out a curing reaction to obtain the product.

[0039] Furthermore, the curing reaction is carried out under the following conditions: first, the reaction is carried out at 1-10 MPa and 50-100°C for 1-4 hours, and then at 1-10 MPa and 100-140°C for 1-4 hours.

[0040] Furthermore, the curing reaction is carried out under the following conditions: first, the reaction is carried out at 5 MPa and 80°C for 2 hours, and then at 5 MPa and 120°C for 2 hours.

[0041] The present invention also provides the use of the above-mentioned epoxy resin-based glass polymer materials in the preparation of self-healing materials for aerospace applications.

[0042] The present invention also provides the use of the above-mentioned epoxy resin-based glass polymer materials in the field of heavy processing.

[0043] In this invention, a difunctional amine refers to a small molecule that simultaneously possesses two amino (-NH2) functional groups.

[0044] Experimental results show that this invention uses self-synthesized epoxy resin and introduces imine bonds and VU dynamic covalent bonds into the epoxy resin and curing agent structures, respectively, to prepare epoxy resin-based glass polymer materials. The minimum relaxation temperature of these glass polymer materials is significantly reduced, and the relaxation time is significantly shortened. They can be reprocessed at temperatures below the glass transition temperature, and have good application prospects in the preparation of self-healing materials for aerospace applications.

[0045] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0046] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following embodiments. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0047] Figure 1 A schematic diagram of the synthesis of EDT curing agent containing VU dynamic covalent bonds (a), chemical shift characterization of EGAA (b), and infrared spectral changes of EGAA and EDT (c).

[0048] Figure 2 The DSC curves of DDEM at different heating rates are shown in (a), and the fitting results of the onset temperature, peak temperature and termination temperature of the peak curves at different heating rates are shown in (b).

[0049] Figure 3 Stress relaxation test curves of resin system (E51-100) containing single dynamic exchange bonds (a) and resin system (b) containing double dynamic exchange bonds, and structural schematic diagrams of GE-VAN-AP and E51 (c).

[0050] Figure 4 The DMA test results are for a resin system containing two dynamic exchange bonds before and after reprocessing.

[0051] Figure 5 The infrared spectral changes of the original sample and the first and second reprocessing of the resin system containing double dynamic exchange bonds.

[0052] Figure 6 The tensile strength curves are for the original sample of the resin system containing double dynamic exchange bonds and after two reprocessing cycles. Detailed Implementation

[0053] The raw materials and equipment used in this invention are all known products, obtained by purchasing commercially available products.

[0054] The "room temperature" condition of this invention is 25±5℃.

[0055] Example 1: Preparation of an epoxy resin system containing dual dynamic exchange bonds

[0056] 1. Preparation of imine-containing dynamic bond intermediates

[0057] 6.08 g (40 mmol) of vanillin and 4.36 g (40 mmol) of p-aminophenol were mixed and added to a round-bottom flask, followed by 125 mL of water. The mixture was stirred at room temperature for 4 hours. After filtration, a yellow powder was collected, washed with water, and dried in a desiccator to obtain a pale yellow powder (9.32 g), which was named VAN-AP powder. The NMR data of VAN-AP are as follows: 1 H NMR(DMSO-d6,400MHz)δ:9.69(s,1H,-OH),9.44(s,1H,-OH),8.43(s,1H,-CH=N-),7.49(d,1H,Ar-H),7.2 7(dd,1H,Ar-H),7.10-7.13(m,2H,Ar-H),6.86(d,1H,Ar-H),6.75-6.79(m,2H,Ar-H),3.84(s,3H,-OCH3).

[0058] 2. Preparation of epoxy resins containing imine dynamic bonds

[0059] 9.8 g (40 mmol) of VAN-AP powder was mixed with 100 g (1081 mmol) of epichlorohydrin and added to a round-bottom flask. Then, 0.5 g (1.7 mmol) of tetrabutylammonium bromide was added as a phase transfer catalyst. The flask was heated at 80 °C and stirred for 4 hours. Then, 12.5 g of 50% NaOH aqueous solution was added, and the reaction was continued for 1 hour, followed by 1 hour at room temperature. Excess ethyl acetate was added, and the resulting NaCl solid particles were removed by filtration. The mixture was washed three times with deionized water, concentrated, and transferred to a vacuum oven for overnight dehydration at 60 °C. The final product was an imine-containing epoxy resin, a pale yellow solid, which was named GE-VAN-AP resin. The NMR data of GE-VAN-AP resin are as follows: 1H NMR(DMSO-d6,400MHz)δ:8.52(s,1H,-CH=N-),7.56(d,1H,Ar-H),7.39-7.41(dd, 1H,Ar-H),7.26-7.24(m,2H,Ar-H),7.08-7.10(d,1H,Ar-H),6.99-7.01(m,2H,Ar -H),4.37-4.40(dd,1H,Ar-H),4.33-4.37(dd,1H,Ar-H),3.87-3.92(dd,1H,-O-C H2-),3.86(s,3H,-OCH3),3.83-3.87(dd,1H,-O-CH2-),3.34-3.39(m,2H,-CH-in oxirane),2.85-2.86(m,2H,-CH2-in oxirane),2.71-2.73(m,2H,-CH2-in oxirane).

[0060] 3. Preparation of ethylene glycol diacetate

[0061] First, ethylene glycol and tert-butyl acetoacetate were mixed thoroughly at a molar ratio of 1:2.3 and heated to 125°C for 1 hour. Next, a circulating water vacuum pump was used to perform vacuum extraction at 0.03 MPa for 3 hours to remove the tert-butanol produced in the reaction and promote the forward reaction. Subsequently, the vacuum level was reduced to 0.09 MPa and maintained for 1 hour to remove unreacted ethylene glycol and tert-butyl acetoacetate, ensuring the purity of the product. The final product, a pale orange color, was obtained, which is ethylene glycol diacetoacetate (EGAA).

[0062] 4. Preparation of curing agents containing VU dynamic covalent bonds

[0063] Weigh 12.93 g (0.0761 mol) of isophorone diamine and 3.17 g (0.0217 mol) of tris(2-aminoethyl)amine into a round-bottom flask, mix thoroughly, and then heat in an oil bath to 80°C for 3 minutes. Next, under magnetic stirring, slowly add 10 g (0.04347 mol) of EGAA dropwise into the flask over 8 minutes. Over time, the transparent amine solution gradually turns pale yellow. After the addition is complete, continue stirring for 5 minutes to ensure the amine and EGAA react completely and are thoroughly mixed, obtaining a mixture containing m-ethyleneamine ester groups. This curing agent is named EDT curing agent. The mixture is then poured into a 200 mm diameter petri dish and transferred to a vacuum oven. It is then heated at 65°C under a vacuum of 0.1 MPa for 24 hours to remove the water produced during the reaction. After water removal, the curing agent containing VU dynamic bonds is frozen to prevent oxidation. Calculations show that the primary amine content in the curing agent is 0.005311 mol / g.

[0064] 5. Preparation of epoxy resin systems containing double dynamic exchange bonds

[0065] Take 10g of GE-VAN-AP resin and 11.65g of EDT curing agent, stir and mix them at 80℃, then transfer them to a vacuum oven to remove air bubbles. Then transfer the mixed sample to a flat vulcanizing machine, pour it into a steel plate mold, heat it to 80℃ under 5MPa pressure, hold it for two hours, then heat it to 120℃ and hold it for two hours. Demold the obtained sample at high temperature, then anneal and cool it in a forced-air oven to obtain a sheet sample, which is named the Dual dynamic exchange mechanism resin system (DDEM resin).

[0066] The following is the preparation method of the control example.

[0067] Comparative Example 1: Preparation of an epoxy resin system containing a single dynamic exchange bond

[0068] Referring to the method of Example 1, the only difference is that the GE-VAN-AP resin in step 5 is replaced with commercial E51 type epoxy resin (epoxy value 0.51), and a sheet sample is prepared together with EDT curing agent, which is named a resin system containing single dynamic exchange bonds, abbreviated as E51-100.

[0069] The following experimental examples demonstrate the beneficial effects of the present invention.

[0070] Experimental Example 1: Performance Testing of Epoxy Resins Containing Double Dynamic Exchange Bonds at Temperatures Below Glass Transition Temperature

[0071] 1. Experimental Methods

[0072] (1) Dynamic thermomechanical property test (DMA): The Q800 dynamic thermomechanical analyzer manufactured by TA Company of the United States was used. Tensile fixture was selected for testing. The test frequency was 1Hz, the amplitude was 15um, the heating rate was 3℃ / min, and the test temperature range was 0℃~200℃.

[0073] (2) Differential Scanning Calorimetry (DSC) Testing: For uncured samples, a differential scanning calorimeter (Mettler-Toledo, Switzerland) was used to investigate the curing temperature of the curing agent and resin. The test atmosphere was N2, and the test temperature range was 30–200℃, with heating rates of 5 K / min, 10 K / min, 15 K / min, and 20 K / min, respectively. For cured samples, a temperature range of 30–200℃ and a heating rate of 10 K / min were selected to characterize the curing process and glass transition temperature of the material.

[0074] (3) Mechanical property test: The tensile properties were tested using an Instron universal testing machine in accordance with the GB / T1040-2006 standard. The test size used a 5B type tensile specimen, and the tensile speed was 1 mm / min.

[0075] (4) Reprocessing Experiment: 20 grams of the cured sample from Example 1 were placed in a crusher and continuously crushed for 10 seconds. The crushed particles were then evenly placed into a hot press mold and hot-pressed at 120°C and 5MPa for 30 minutes. After natural cooling, the mold was opened. The reprocessed hot-pressed repaired sample was cut into target strips using a cutter. The repair efficiency was calculated using the following formula:

[0076]

[0077] (5) Stress relaxation test: An Anton Paar rheometer was used to conduct stress relaxation test, with a constant shear strain of 1% and a normal force of 5N.

[0078] 2. Experimental Results

[0079] Experimental results ( Figure 1 (ac) indicates that this study successfully synthesized EGAA and EDT containing VU dynamic covalent bonds, wherein the structure of the VU dynamic covalent bonds is as follows: Figure 1 As shown in Figure a, the chemical shift characterization of EGAA and the infrared spectral changes of EGAA and EDT are respectively as follows: Figure 1 As shown in b and c.

[0080] (1) Study on the curing process of resin systems containing double dynamic exchange bonds

[0081] Figure 2Figure a shows the DSC curves at different heating rates. It can be seen that the position and peak height of the curves change significantly with different heating rates; as the heating rate increases, the DSC exothermic peak generally shifts to higher temperatures. Then, the onset temperature, peak temperature, and termination temperature of the peak curves at different heating rates are used for fitting. The fitting results are shown in [Figure 1]. Figure 2 b. The extrapolated intercept of the fitted linear lines for the three curing temperatures represents the reaction temperature during isothermal curing at a heating rate of 0. Table 1 shows the statistics of the fitted curing temperatures. The initial curing temperature of the resin system containing double dynamic exchange bonds is approximately 43.08℃, the peak temperature is 83.69℃, and the exothermic curing termination temperature is 115.77℃. Therefore, to ensure complete curing, the final curing process was determined to be a constant temperature of 80℃ for two hours, followed by a constant temperature of 120℃ for two hours.

[0082] Table 1. Curing temperature fitting table for resins containing double dynamic exchange bonds

[0083]

[0084] (2) Stress relaxation study of resin systems containing different dynamic exchange bonds

[0085] Figure 3 Stress relaxation test curves are shown for resin systems containing single dynamic exchange bonds (E51-100) and resin systems containing double dynamic exchange bonds. Figure 3 As shown in Figure a, with increasing temperature, the relaxation curve gradually shifts to the left, and the relaxation time gradually decreases. The relaxation rate of the E51-100 system gradually increases with increasing temperature, and its relaxation time at 140℃ exceeds 1000s. Compared to E51-100, the relaxation rate of the resin containing double dynamic exchange bonds is significantly increased, and the relaxation time is significantly shortened, with relaxation times less than 400s at temperatures ranging from 120℃ to 140℃. Figure 3 (b) In the E51-100 system, E51 is a common commercial epoxy resin that is not cured together with the VU dynamic bond curing agent and cannot be subjected to stress relaxation testing alone. In the resin system containing dual dynamic exchange bonds, GE-VAN-AP is a self-synthesized epoxy resin. The structural difference between GE-VAN-AP and E51 is that the GE-VAN-AP structure has an imine bond in the middle, while the E51 structure has a C-C bond in the middle. Figure 3 c). Therefore, it can be demonstrated that the introduction of imine bonds can achieve a faster stress relaxation rate and enable repair at 120°C.

[0086] (3) Comparison of various properties of resin before and after reprocessing

[0087] Figure 4 The DMA test results for a resin containing dual dynamic exchange bonds before and after two reprocessing steps are presented. Figure 4 As shown, the storage modulus differences before and after the original sample, one reprocessing (Recycle 1), and two reprocessing (Recycle 2) are small, all around 4000 MPa, indicating that the recycled material retains a certain degree of rigidity and forms a cohesive whole. The Tanδ peak temperature represents the glass transition temperature of the material, and the glass transition temperatures of the original sample, one reprocessing, and two reprocessing are 125.87℃, 131.65℃, and 128.63℃, respectively, with small differences between them, all within the range of 125-135℃. Simultaneously, it can be seen that with the increase in the number of reprocessing times, the Tanδ peak value gradually decreases while the peak width gradually widens, indicating that the internal friction of the system gradually decreases and the flexibility distribution of molecular chain segments becomes wider. The DMA test results show that the sample after multiple reprocessings maintains the same storage modulus and glass transition temperature as the original sample, demonstrating the sample's good reprocessing capability.

[0088] Figure 5 The figures show the changes in infrared spectroscopy and DSC analysis of the original sample, and the samples recovered from the initial and secondary reprocessing of the resin containing double dynamic exchange bonds. Figure 5 As shown, the original sample was at 1650 cm⁻¹ -1 The peak at 915 cm⁻¹ is a characteristic peak of the generated imine bond (CN). -1 The absence of significant peaks at and around the 1500 cm⁻¹ indicates that the unopened epoxy groups in the system have completely reacted. -1 The peak at 3000 cm⁻¹ is a significant characteristic peak of aromatic rings. -1 The above are characteristic peaks of the -OH group formed by the ring opening of epoxy resin and the NH band caused by the incompletely reacted -NH2 group, at 2850 cm⁻¹. -1 up to 2900cm -1 The peak at this point is a characteristic peak of the -CH2- chain segment. The original sample with the above groups is not significantly different from the samples obtained after one or two reprocessing and recovery processes, indicating that the groups did not change significantly before and after multiple reprocessing processes.

[0089] Figure 6 The tensile strength curves of the original resin sample containing double dynamic exchange bonds and after two reprocessing steps are shown. Figure 6As shown, all the tensile fracture modes of the spline were brittle fractures with no obvious yield point; Table 2 shows the comparison of different mechanical properties of the spline under tensile conditions. The tensile strength of the original sample was approximately 100 MPa, which is significantly higher than that of ordinary commercial epoxy resins (40–70 MPa). After hot pressing, the cured epoxy resin particles were able to re-fuse into a uniform whole. After the first reprocessing, the tensile strength decreased to 91.77 MPa, which is 91.47% of the initial tensile strength. After the second reprocessing, the tensile strength decreased to 75.78 MPa, which is 75.54% of the initial tensile strength. With the increase of reprocessing times, both tensile strength and elongation at break showed a significant decreasing trend, while the tensile modulus showed a gradual increasing trend. This is mainly because with repeated crushing-reprocessing and hot pressing processes, more defects exist in the epoxy resin structure. Furthermore, due to the high temperature maintained in the air, it gradually accumulates thermo-oxidative aging, leading to a gradual decrease in tensile strength and elongation. At the same time, hot pressing can also be regarded as a post-curing process, which may lead to an increase in crosslinking density, thus resulting in an increasing modulus. However, even after two reprocessing cycles, the resin still achieves a tensile strength of 75.78 MPa, comparable to that of ordinary commercial epoxy resins. This indicates that the material achieves excellent reprocessing capability under the dual dynamic exchange mechanism; and the mechanical property enhancement effect brought by the imine bonds is very significant; achieving a simultaneous improvement in both the material's mechanical strength and dynamic exchange capability.

[0090] Table 2. Comparison of tensile strength and other mechanical properties of different samples

[0091]

[0092] The experimental results above show that the lowest relaxation temperature of the resin system (E51-100) containing a single dynamic exchange bond in Comparative Example 1 is 140°C, and the relaxation time at 140°C exceeds 1000s. Compared to E51-100, the lowest relaxation temperature of the resin containing a double dynamic exchange bond, which introduces imine bonds and VU dynamic covalent bonds in Example 1 of the present invention, is 95°C, and the relaxation time at temperatures from 95°C to 120°C is less than 10s. In other words, compared with the resin system containing a single dynamic exchange bond in Comparative Example 1, the lowest relaxation temperature of the resin system containing a double dynamic exchange bond in the present invention is significantly reduced, and the relaxation time is significantly shortened.

[0093] The glass transition temperature of the resin system containing dual dynamic exchange bonds of the present invention is 125.87°C. This resin system can be reprocessed at temperatures below the glass transition temperature, and the reprocessed sample still retains good mechanical properties.

[0094] In summary, this invention provides a cross-linked epoxy resin that can be reprocessed below its glass transition temperature, its preparation method, and its applications. This invention introduces imine bonds and VU dynamic covalent bonds into an epoxy resin with a specific structure and a curing agent, respectively, to prepare a cross-linked epoxy resin-based glass polymer material. This type of glass polymer material exhibits a significantly lower minimum relaxation temperature and a significantly shorter relaxation time, allowing for reprocessing below its glass transition temperature. It shows great promise for applications in improving material repairability, material reprocessing, and material recycling.

Claims

1. An epoxy resin-based glass polymer material, characterized in that, It is prepared from epoxy resin containing imine dynamic bonds and curing agent containing VU dynamic covalent bonds as raw materials; the mass ratio of the epoxy resin containing imine dynamic bonds to the curing agent containing VU dynamic covalent bonds is 1:0.5~5; the imine dynamic bonds are... The VU dynamic covalent bond is .

2. The epoxy resin-based glass polymer material according to claim 1, characterized in that, The epoxy resin containing imine dynamic bonds is prepared from vanillin, p-aminophenol, epichlorohydrin and a phase transfer catalyst as raw materials; The mass ratio of the epoxy resin containing imine dynamic bonds to the curing agent containing VU dynamic covalent bonds is 1:1 to 1.

2.

3. The epoxy resin-based glass polymer material according to claim 1, characterized in that, The epoxy resin containing imine dynamic bonds has the following structure: ； The curing agent containing VU dynamic covalent bonds is prepared from difunctional amines, tris(2-aminoethyl)amine and EGAA as raw materials; The molar ratio of the difunctional amine, tris(2-aminoethyl)amine, and EGAA is 1–5:0.1–0.5:1; The structure of the EGAA is as follows: .

4. The epoxy resin-based glass polymer material according to claim 3, characterized in that, The molar ratio of the difunctional amine, tris(2-aminoethyl)amine, and EGAA is 1–2:0.4–0.5:1; The difunctional amine is selected from isophorone diamine, m-phenylenediamine, or bis(4-amino-3-methylcyclohexyl)methane.

5. The epoxy resin-based glass polymer material according to claim 1, characterized in that, The preparation method of the curing agent containing VU dynamic covalent bonds includes the following steps: (i) Mixing a difunctional amine and tris(2-aminoethyl)amine; (ii) Add EGAA to the mixture from step (i) to react and obtain a curing agent containing VU dynamic covalent bonds.

6. The epoxy resin-based glass polymer material according to claim 5, characterized in that, In step (i), the difunctional amine and tris(2-aminoethyl)amine are mixed and preheated at 70-90°C for 1-5 minutes.

7. The epoxy resin-based glass polymer material according to claim 5, characterized in that, In step (ii), stir when adding EGAA.

8. The epoxy resin-based glass polymer material according to claim 5, characterized in that, In step (ii), after adding EGAA and reacting, the reactants are dried.

9. A method for preparing the epoxy resin-based glass polymer material according to any one of claims 1-8, characterized in that, The method includes the following steps: mixing an epoxy resin containing imine dynamic bonds and a curing agent containing VU dynamic covalent bonds, and then carrying out a curing reaction to obtain the product.

10. The method according to claim 9, characterized in that, The curing reaction conditions are as follows: first, react at 1-10 MPa and 50-100°C for 1-4 hours, and then react at 1-10 MPa and 100-140°C for 1-4 hours.

11. Use of the epoxy resin-based glass polymer material according to any one of claims 1-8 in the preparation of self-healing materials for aerospace applications.

12. Use of the epoxy resin-based glass polymer material according to any one of claims 1-8 in the field of reprocessing.

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