A high-performance self-healing epoxy resin and its preparation method

Abstract

This invention application belongs to the field of organic materials technology, specifically disclosing a high-performance self-healing epoxy resin, prepared from raw materials including a curing agent obtained by the Diels-Alder reaction of 3-substituted furan and bismaleimide, epoxy resin, and a chain extender. It also provides a method for preparing the high-performance self-healing epoxy resin, including mixing epoxy resin and chain extender, heating to obtain a prepolymer, uniformly mixing 3-substituted furan and bismaleimide, adding to the prepolymer to obtain a mixed system; degassing the mixed system in a vacuum oven, then casting it into a mold, and curing it in an oven in three stages. This method features mild reaction conditions, simple preparation, high conversion rate, and high product purity. It effectively solves the problems of low heat resistance and mechanical properties of self-healing epoxy resin polymers.

Description

Technical Field

[0001] This invention belongs to the field of organic materials technology, and specifically discloses a high-performance self-healing epoxy resin and its preparation method. Background Technology

[0002] Currently, self-healing polymers are mainly divided into two categories: extrinsic and intrinsic. Intrinsic self-healing relies on dynamic forces at the molecular level. One such dynamic force is the Diels-Alder reversible cycloaddition reaction. Currently, the most widely used self-healing epoxy resins are based on the Diels-Alder reaction between 2-substituted furans and maleimides.

[0003]

[0004] Since the first US patent report on this reaction in 1966, all research in this area has been based on this general reaction formula. However, a drawback of this type of reaction is that the reverse reaction temperature of the Diels-Alder reaction is relatively low. When the operating temperature of the self-healing polymer is too high (around 100°C), the reverse reaction will occur, leading to a decrease in the crosslinking density of the polymer, which in turn leads to a significant decrease in the mechanical properties of the polymer. Summary of the Invention

[0005] The purpose of this invention is to provide a high-performance self-healing epoxy resin and its preparation method, so as to solve the problem of low heat resistance and mechanical properties of self-healing epoxy resin polymers.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a high-performance self-healing epoxy resin, which is prepared from raw materials including a curing agent obtained by the Diels-Alder reaction of 3-substituted furan and bismaleimide, an epoxy resin and a chain extender.

[0007] The working principle of this technical solution is as follows:

[0008] A self-healing epoxy resin was prepared by utilizing the Diels-Alder reaction based on 3-substituted furan and bismaleimide, and using it as a curing agent for epoxy resin.

[0009]

[0010] The core of this invention lies in 3-substituted furans. Compared to traditional 2-substituted furans, 3-substituted furans exhibit higher temperatures in both the Diels-Alder reaction and the reverse Diels-Alder reaction with bismaleimide, with a forward reaction temperature of 110-140℃ and a reverse reaction temperature of 220-280℃. 3-substituted furans contain electron-withdrawing groups and possess either p or π electrons, enabling them to form a conjugated system with the double bonds formed in the Diels-Alder reaction. This improves the stability of the Diels-Alder adduct, increases the activation energy and temperature of the reverse reaction, and significantly enhances the heat resistance of the self-healing epoxy resin based on this reaction.

[0011] After high-temperature treatment, the self-healing epoxy resin undergoes a reverse Diels-Alder reaction, causing the 3-substituted furan and bismaleimide adduct to decompose and some crosslinking bonds to open. This significantly reduces the crosslinking density of the self-healing epoxy resin, resulting in some thermoplasticity. Upon low-temperature treatment, a forward Diels-Alder reaction occurs again, where the 3-substituted furan and bismaleimide recombine to form crosslinking bonds in the self-healing epoxy resin, restoring the crosslinking density and allowing the epoxy resin to exhibit the thermosetting properties of a three-dimensional crosslinked network.

[0012] The beneficial effects of this technical solution are as follows:

[0013] The prepared epoxy resin exhibits high self-healing properties, with mild reaction conditions, simple preparation, high conversion rate, and high product purity. The curing agent involved in this invention possesses p or π electrons, enabling it to form a conjugated system with the double bonds formed in the Diels-Alder reaction, thereby improving the stability of the Diels-Alder adduct. Compared to traditional 2-substituted furans, the Diels-Alder reaction and reverse Diels-Alder reaction of the 3-substituted furan with bismaleimide in this technical solution both have higher temperatures. The forward reaction temperature can reach 110-140℃, and the reverse reaction temperature can reach 220-280℃, greatly improving the heat resistance of the self-healing epoxy resin based on this reaction.

[0014] Furthermore, 3-substituted furans include furan-3-carboxamide and furan-3-carboxylic acid; bismaleimides include all small molecules with two maleimide groups; epoxy resins include all resins containing diepoxy groups; and chain extenders include all small molecule amine compounds with two active NH bonds. The purpose of chain extenders is to increase the chain length of epoxy resins without increasing crosslinking density, improve toughness, and introduce tertiary amines as catalysts. Chain extenders include all small molecule amine compounds with two active NH bonds, such as aliphatic monoprimary amine compounds like methylamine, ethylamine, propylamine, isopropylamine, benzylamine, and phenethylamine, as well as aromatic primary amines like o-methylaniline, p-methylaniline, and naphthylamine, and disecondary amine compounds like N,N'-dimethylethylenediamine, N,N'-dimethylhexanediamine, N,N'-dimethylp-phenylenediamine, piperazine, and dimethylpiperazine. Bismaleimides include all small molecules containing two maleimide groups, including but not limited to diphenylmethane bismaleimide, 1,6-bismaleimide hexane, and diphenyl ether bismaleimide. Epoxy resins include all resins containing two epoxy groups, including but not limited to bisphenol A epoxy resin, bisphenol F epoxy resin, and bisphenol S epoxy resin.

[0015] Furthermore, the molar ratio of 3-substituted furan to bismaleimide is 1.5-2.5:1.

[0016] Furthermore, the molar ratio of epoxy resin to chain extender is 3:1-10:1.

[0017] Furthermore, the molar ratio of epoxy resin to 3-substituted furan is 0.5-3:1.

[0018] Furthermore, a method for preparing a high-performance self-healing epoxy resin includes the following steps:

[0019] (1) Mix epoxy resin and chain extender evenly, heat for 5 min-5 h to prepolymerize, and react fully to obtain prepolymer;

[0020] (2) Mix 3-substituted furan and bismaleimide evenly, add them to the prepolymer obtained in step (1), and stir evenly to obtain a mixed system;

[0021] (3) Degas the mixture obtained in step (2) in a vacuum oven and then cast it into a mold;

[0022] (4) The epoxy resin is cured in three stages in an oven. The first stage is cured at 110-140℃ for 1-4 hours, the second stage is cured at 160-240℃ for 4-10 hours, and the third stage is cured at 110-140℃ for 2-8 hours, thus obtaining an epoxy resin with high self-healing properties. Setting the prepolymerization time from 5 minutes to 8 hours is beneficial for the reaction between chain extenders with different reactivity and epoxy resin to be complete, and the active NH bonds are completely consumed, avoiding affecting the subsequent Diels-Alder reaction. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the self-healing mechanism of an epoxy resin with high self-healing properties according to the present invention.

[0024] Figure 2 The infrared spectrum curves of the sample in Example 1 as the treatment time at 120°C increased are shown.

[0025] Figure 3 The infrared spectrum curves of the sample in Example 1 as the treatment time at 200℃ increased are shown.

[0026] Figure 4 These are the DMA test results of the self-healing epoxy resin cured product in Example 1;

[0027] Figure 5 This is the thermogravimetric curve of the self-healing epoxy resin cured product in Example 1;

[0028] Figure 6 This is the bending stress-strain curve of the self-healing epoxy resin casting in Example 1;

[0029] Figure 7 This is a schematic diagram of the crushing and repair process in Example 1;

[0030] Figure 8 This is a comparison of the bending strength and elastic modulus of the intact sample and the repaired sample in Example 1. Detailed Implementation

[0031] The following detailed description illustrates the specific implementation method:

[0032] A method for preparing a high-performance self-healing epoxy resin includes the following steps:

[0033] (1) Mix epoxy resin and chain extender in a molar ratio of 3:1-10:1, heat for 5 min-5 h to prepolymerize, and react fully to obtain prepolymer.

[0034] (2) Mix 3-substituted furan and bismaleimide uniformly at a molar ratio of 1.5-2.5:1, and add epoxy resin and 3-substituted furan to the prepolymer obtained in step (1) at a molar ratio of 0.5-3:1, and stir evenly to obtain a mixed system.

[0035] (3) Degas the mixture obtained in step (2) in a vacuum oven and then cast it into a mold;

[0036] (4) Curing is carried out in three stages in an oven. The first stage is cured at 110-140℃ for 1-4 hours, the second stage is cured at 160-240℃ for 4-10 hours, and the third stage is cured at 110-140℃ for 2-8 hours, thus obtaining epoxy resin with high self-healing properties.

[0037] Combination Figure 1 As shown, after treatment at 240℃, a Diels-Alder reverse reaction occurs in the self-healing epoxy resin, the 3-substituted furan and bismaleimide adduct decomposes, some crosslinking bonds open, and the crosslinking density of the self-healing epoxy resin decreases significantly, exhibiting a certain degree of thermoplasticity. After treatment at 120℃, a Diels-Alder forward reaction occurs again, and the 3-substituted furan and bismaleimide combine again to form crosslinking bonds in the self-healing epoxy resin, thereby restoring the crosslinking density and the epoxy resin exhibiting the thermosetting properties of a three-dimensional crosslinked network.

[0038] The specific implementation process is as follows:

[0039] Example 1

[0040] Furan-3-carboxamide (labeled as FCA in Example 1) was selected as the 3-substituted furan, diphenylmethane bismaleimide (labeled as BMI in Example 1) was selected, E-51 epoxy resin (labeled as E-51 in Example 1) was selected, and benzylamine (labeled as BA in Example 1) was selected as the chain extender.

[0041] E-51 and BA were mixed evenly at a molar ratio of 3:1 and prepolymerized at 120℃ for 30 minutes to obtain a prepolymer. FCA and BMI powders were mixed evenly at a molar ratio of 2:1. The mixed powder was then added to the prepolymer at a molar ratio of E-51 to FCA of 1.5:1 and stirred evenly to obtain a mixed system. The mixed system was degassed in a vacuum oven at 120℃ for 10 minutes and then cast into a mold. The system was cured in three stages: the first stage was cured at 120℃ for 4 hours, the second stage was cured at 200℃ for 8 hours, and the third stage was cured at 120℃ for 8 hours to obtain an epoxy resin with high self-healing properties.

[0042] Infrared spectroscopy was performed on the samples, which were prepared using the clip method. The wavenumber range for acquisition was 4000–500 cm⁻¹. -1 The absorbance data were obtained. After the initial sample was tested, it was placed in an oven for high-temperature treatment, and tested at regular intervals to obtain a series of infrared test data. Combined with... Figure 2 As shown, with increasing processing time, the CH characteristic peak connected to C=C in BMI reaches 691 cm⁻¹. -1 And CNC characteristic peak 1152cm -1 Gradually disappearing, and the characteristic peak of the furan ring at 961 cm⁻¹ in FCA. -1 and 604cm -1 Gradually disappearing, at 1775cm -1 and 1559cm -1 New characteristic absorption peaks were generated, corresponding to the C—C single bonds and C=C double bonds formed in the Diels-Alder reaction, respectively, proving the occurrence of the Diels-Alder forward reaction. Combined with... Figure 3 As shown, after the sample was heated at 200℃ for 6 hours, the characteristic absorption peak of the epoxy group completely disappeared, indicating that it had been completely cured.

[0043] The glass transition temperature of the cured material was tested using a dynamic thermomechanical analyzer (DMA) in single cantilever beam mode. The test temperature range was 25-200℃, and the heating rate was 5℃ / min. Storage modulus and loss tangent data were collected, combined with... Figure 4 As shown, the temperature corresponding to the maximum value of the loss tangent is taken as the glass transition temperature (T). g From the results, the T value of the self-healing epoxy resin cured product can be obtained. g The temperature was 105℃. The results showed that the self-healing epoxy resin prepared in the examples had a lower T-value than traditional engineering epoxy resins. g Comparable to, and higher than, similar self-healing epoxy resins based on the Diels-Alder reaction in terms of T. g (40-90℃).

[0044] Thermogravimetric analysis (TGA) was performed on 10-15 mg samples of cured epoxy resin samples. The test temperature range was 25–600 °C, the heating rate was 10 °C / min, and the test was conducted in air. Figure 5 As shown, the thermal decomposition temperature T is taken as 5%. d5％ As its thermal decomposition temperature, the results show that T d5％ The temperature was 346℃, which is comparable to the thermal decomposition temperature of commonly used epoxy resins. This indicates that the self-healing epoxy resin prepared in the examples has excellent heat resistance, and the thermal decomposition temperature decreases due to the introduction of the self-healing reaction.

[0045] The mechanical properties of self-healing epoxy resin castings were characterized by flexural performance testing. The testing standard followed ISO 178, with sample dimensions of 65mm × 10mm × 3mm and a test span of 50mm. Five replicate tests were performed on the same set of samples. Figure 6 As shown, the self-healing epoxy resin exhibits an average flexural strength of 141.1 MPa and an elastic modulus of 4.29 GPa. Both strength and modulus are comparable to commonly used engineering epoxy resins, demonstrating significant application potential. Furthermore, they far exceed the strength and modulus (0.5-3 GPa) of other self-healing epoxy resins based on the Diels-Alder reaction of 2-substituted furans and maleimide, fully demonstrating the superior mechanical properties of the self-healing epoxy resin prepared in this example, while also possessing a certain degree of toughness.

[0046] The intact self-healing epoxy resin casting was crushed using a crusher to obtain powdered cured epoxy resin, which was then weighed and poured into a mold. Figure 7 As shown, a pressure of 5 MPa is first applied, and the mixture is kept at 240°C for 1 hour to induce a Diels-Alder reverse reaction, releasing furan groups from FCA and maleimide groups from BMI. Then, the pressure is removed, and the mixture is kept at 120°C for 8 hours to allow a full Diels-Alder forward reaction, re-crosslinking FCA and BMI. The mixture is then demolded to obtain a complete self-healing epoxy resin cured product.

[0047] The repaired and cured material was then subjected to another bending performance test, combined with... Figure 8 As shown, the flexural strength of the repaired sample recovered to 52.7% of that of the intact sample, demonstrating a certain degree of repair effect. The elastic modulus of the repaired sample recovered to 111.6% of that of the intact sample, exceeding the elastic modulus of the intact sample.

[0048] Example 2

[0049] Furan-3-carboxamide (labeled as FCA in Example 2) was selected as the 3-substituted furan, diphenylmethane bismaleimide (labeled as BMI in Example 2) was selected, E-51 epoxy resin (labeled as E-51 in Example 2) was selected, and benzylamine (labeled as BA in Example 2) was selected as the chain extender.

[0050] E-51 and BA were mixed evenly at a molar ratio of 3:1 and prepolymerized at 120℃ for 30 minutes to obtain a prepolymer. FCA and BMI powders were mixed evenly at a molar ratio of 2:0.8. The mixed powder was then added to the prepolymer at a molar ratio of E-51 to FCA of 1.5:1 and stirred evenly to obtain a mixed system. The mixed system was degassed in a vacuum oven at 120℃ for 10 minutes and then cast into a mold. The system was cured in three stages: the first stage was cured at 120℃ for 4 hours, the second stage was cured at 200℃ for 8 hours, and the third stage was cured at 120℃ for 8 hours to obtain an epoxy resin with high self-healing properties.

[0051] Example 3

[0052] Furan-3-carboxamide (labeled FCA in Example 3) was selected as the 3-substituted furan, diphenylmethane bismaleimide (labeled BMI in Example 3) was selected, E-51 epoxy resin (labeled E-51 in Example 3) was selected, and benzylamine (labeled BA in Example 3) was selected as the chain extender.

[0053] E-51 and BA were mixed evenly at a molar ratio of 3:1 and prepolymerized at 120℃ for 30 minutes to obtain a prepolymer. FCA and BMI powders were mixed evenly at a molar ratio of 2:1.2. The mixed powder was then added to the prepolymer at a molar ratio of E-51 to FCA of 1.5:1 and stirred evenly to obtain a mixed system. The mixed system was degassed in a vacuum oven at 120℃ for 10 minutes and then cast into a mold. The system was cured in three stages: the first stage was cured at 120℃ for 4 hours, the second stage was cured at 200℃ for 8 hours, and the third stage was cured at 120℃ for 8 hours to obtain an epoxy resin with high self-healing properties.

[0054] Example 4

[0055] Furan-3-carboxamide (labeled FCA in Example 4) was selected as the 3-substituted furan, diphenylmethane bismaleimide (labeled BMI in Example 4) was selected, E-51 epoxy resin (labeled E-51 in Example 4) was selected as the epoxy resin, and dimethylpiperazine (labeled DMPZ in Example 4) was selected as the chain extender.

[0056] E-51 and DMPZ were mixed evenly at a molar ratio of 3:1 and prepolymerized at 120℃ for 30 minutes to obtain a prepolymer. FCA and BMI powders were mixed evenly at a molar ratio of 2:1. The mixed powder was then added to the prepolymer at a molar ratio of E-51 to FCA of 1.5:1 and stirred evenly to obtain a mixed system. The mixed system was degassed in a vacuum oven at 120℃ for 10 minutes and then cast into a mold. The system was cured in three stages: the first stage was cured at 120℃ for 4 hours, the second stage was cured at 200℃ for 8 hours, and the third stage was cured at 120℃ for 8 hours to obtain an epoxy resin with high self-healing properties.

[0057] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics in the solutions is not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A high-performance self-healing epoxy resin, characterized in that, It is prepared from raw materials containing 3-substituted furan, bismaleimide, epoxy resin, and chain extender; The 3-substituted furan is selected from one or a combination of furan-3-carboxamide and furan-3-carboxylic acid; The bismaleimide is selected from small molecule compounds with two maleimide groups; The epoxy resin is selected from resins containing diepoxy groups; The chain extender is selected from small molecule amine compounds with two active NH bonds.

2. The high-performance self-healing epoxy resin according to claim 1, characterized in that, The molar ratio of 3-substituted furan to bismaleimide is 1.5-2.5:

1.

3. The high-performance self-healing epoxy resin according to claim 1, characterized in that, The molar ratio of epoxy resin to chain extender is 3:1 to 10:

1.

4. The high-performance self-healing epoxy resin according to claim 1, characterized in that, The molar ratio of epoxy resin to 3-substituted furan is 0.5-3:

1.

5. The method for preparing a high-performance self-healing epoxy resin according to claim 1, characterized in that, Includes the following steps: (1) Mix epoxy resin and chain extender evenly, heat for 5 min-5 h to prepolymerize, and react fully to obtain prepolymer; (2) Mix 3-substituted furan and bismaleimide evenly, add them to the prepolymer obtained in step (1), and stir evenly to obtain a mixed system; (3) Degas the mixture obtained in step (2) in a vacuum oven and then cast it into a mold; (4) The prepolymer is cured in three stages: the first stage is cured at 110-140℃ for 1-4 hours. During this stage, 3-substituted furan and maleimide undergo Diels-Alder reaction, and the prepolymer is pre-cured at the same time; the second stage is cured at 160-240℃ for 4-10 hours; the third stage is cured at 110-140℃ for 2-8 hours, and the high-performance self-healing epoxy resin is obtained.

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