A room temperature self-repairing thermosetting polymer material and preparation method thereof

Abstract

The present invention discloses a room temperature self-healing thermosetting polymer material and a preparation method thereof, wherein the raw materials include: 2-amino-4-hydroxy-6-methylpyrimidine, hexamethylene diisocyanate, polyethyleneimine, and 1,2-cyclohexanedicarboxylic acid diglycidyl ester. The present invention uses a dual dynamic cross-linking strategy, i.e., covalent cross-linking ensures the high strength, high stiffness and high solvent resistance of the thermosetting polymer, and non-covalent cross-linking improves the toughness of the material and gives it room temperature self-healing properties. An epoxy curing agent UNP with highly mobile side chains and the ability to form high-density hydrogen bonds is designed and synthesized; an epoxy monomer DCN containing an ester structure is cured and cross-linked to obtain a glassy thermosetting polymer material UNP-DCN with room temperature self-healing function. The material has a glass transition temperature (T g1 =16℃, T g2 =106℃), showing a high room temperature self-healing ability.

Description

Technical Field

[0001] The present invention belongs to the technical field of self-repairing polymer materials, and in particular relates to a room temperature self-repairing thermosetting polymer material and a preparation method thereof. Background Art

[0002] Polymer materials are widely used in transportation, architectural decoration, electronics, and other fields due to their diverse variety, designability, low cost, and ease of processing. However, due to factors such as heat, force, and chemical reactions, microcracks inevitably develop within or on the surface of materials during use or processing. These microcracks do not immediately lead to structural failure, but can deteriorate other functional properties of the material, such as electrical, acoustic, optical, and thermal performance. Inspired by the self-healing phenomena of skin and bone, researchers proposed the concept of self-repairing materials in the 1980s to ensure the performance and extend the service life of aerospace composites. Polymer self-healing mechanisms can be categorized as either assisted self-healing or intrinsic self-healing. Assisted self-healing is a one-time, irreversible process that cannot repeatedly repair microcracks, thus having limited effectiveness in extending the material's service life. Intrinsic self-healing, on the other hand, relies on the dynamic exchange and recombination of reversible chemical bonds within polymer materials under the influence of certain external stimuli (such as temperature and pH), completing the healing and repair process of microcracks. Its reversibility allows for cyclic repair of microcracks, significantly extending the material's service life. However, most dynamic covalent bond exchange requires high temperatures, making it difficult to achieve room-temperature self-healing in polymer materials. Reported room-temperature self-healing glassy polymers all fall into the category of thermoplastic polymers, which suffer from poor solvent resistance, weak mechanical strength, complex preparation processes, and difficulty in directly using them as resin matrices for composite materials. Summary of the Invention

[0003] The present invention aims to provide a room-temperature self-healing thermosetting polymer material and its preparation method. The present invention synthesizes a functional curing agent with quadruple hydrogen bonds and cross-links it with an epoxy monomer to produce a room-temperature self-healing thermosetting polymer material.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] One aspect of the present invention provides a room-temperature self-healing thermosetting polymer material. According to an embodiment of the present invention, the raw materials for preparing the room-temperature self-healing thermosetting polymer material include: 2-amino-4-hydroxy-6-methylpyrimidine (MIC), hexamethylene diisocyanate (HDI), polyethyleneimine (PEI), and diglycidyl 1,2-cyclohexanedicarboxylate (DCN).

[0006] The prepared room temperature self-healing thermosetting polymer material can be represented by UNP-DCN. The structural formula of the room temperature self-healing thermosetting polymer material is as follows:

[0007]

[0008] The present invention introduces hexamethylene diisocyanate containing an isocyanate bond and reacts with 2-amino-4-hydroxy-6-methylpyrimidine to synthesize a monomer UPy-NCO capable of forming a quadruple hydrogen bond. The synthesis route is as follows:

[0009]

[0010] Furthermore, based on branched polyethyleneimine, a urea-pyrimidone side chain (UPy-NCO) capable of forming a quadruple hydrogen bond was introduced into its molecular structure to synthesize a new functional curing agent UNP. The synthesis route is as follows:

[0011]

[0012] Furthermore, a new functional curing agent UNP was used to cure and cross-link the epoxy monomer DCN containing an ester structure to prepare a thermosetting polymer UNP-DCN with room temperature self-healing function. The synthesis route is as follows:

[0013]

[0014] In addition, the present invention provides a method for preparing a room temperature self-healing thermosetting polymer material. According to an embodiment of the present invention, the method comprises:

[0015] (1) Under inert gas protection, 2-amino-4-hydroxy-6-methylpyrimidine and hexamethylene diisocyanate were reacted with magnetic stirring at 100°C for 24 h. The reaction suspension was washed three times with n-hexane and dried in a vacuum oven at 50°C to obtain a white powder of UPy-NCO capable of forming quadruple hydrogen bonds.

[0016] (2) Under inert gas protection, UPy-NCO synthesized in step (1) was added to polyethyleneimine, and the mixture was stirred under magnetic stirring at 100° C. for 6 h to generate a functional curing agent, a light yellow viscous liquid UNP;

[0017] (3) adding the UNP synthesized in step (2) as a curing agent to the epoxy monomer 1,2-cyclohexanedicarboxylic acid diglycidyl ester and stirring until the mixture is uniformly mixed;

[0018] (4) Pour the mixed liquid obtained in step (3) into a mold and place it in a vacuum oven at 50°C for 30 minutes to completely remove bubbles;

[0019] (5) The sample was placed in an oven and heated to 100°C for curing for 2 h, then the oven temperature was increased to 150°C and accelerated curing was performed for 2 h to obtain the target sample UNP-DCN.

[0020] According to the method for preparing the room-temperature self-healing thermosetting polymer material of the present invention, the prepared polymer material UNP-DCN has a dual dynamic cross-linking network, that is, covalent cross-linking ensures the high strength, high stiffness and high solvent resistance of the thermosetting polymer, and non-covalent cross-linking can improve the toughness of the material and give it room-temperature self-healing properties. Because the main chain of the cross-linking network exists in the form of covalent cross-linking and contains highly mobile side chains and a large number of groups that can form quadruple hydrogen bonds, the material has two glass transition temperatures (T g1 =16℃, T g2 =106°C), demonstrating high room-temperature self-healing capabilities. After manually compressing the fractured surface for a few seconds at room temperature, the two broken halves of the rectangular sample reconnected and could easily lift heavy objects. A carbon fiber-reinforced composite based on this material recovered nearly its original strength after 24 hours of repair at room temperature under atmospheric pressure.

[0021] In some embodiments of the present invention, in step (1), the molar ratio of 2-amino-4-hydroxy-6-methylpyrimidine to hexamethylene diisocyanate is 0.147, and isocyanate is slightly excessive to ensure that each 2-amino-4-hydroxy-6-methylpyrimidine molecule is grafted with an isocyanate structure.

[0022] In some embodiments of the present invention, in step (2), the amount of UPy-NCO added is 15% of the total mass of the reaction system.

[0023] In some embodiments of the present invention, in step (3), the curing agent UNP and the epoxy monomer are cross-linked in a mass ratio of 1:1.

[0024] In some embodiments of the present invention, in step (4), the vacuum degassing is carried out at a temperature of 50° C. for 10 to 30 minutes.

[0025] In some embodiments of the present invention, in step (4), the vacuum degree of the vacuum degassing is not higher than 40Pa.

[0026] In some embodiments of the present invention, in step (5), the pre-curing temperature is 100° C. for 2 hours, and the post-curing temperature is 150° C. for 2 hours. In this way, the sample can be cured in stages until the target sample is obtained.

[0027] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0029] Figure 1 The infrared spectra of UPy-NCO, UNP, and UNP-DCN and the nuclear magnetic resonance hydrogen spectrum of UPy-NCO prepared from room temperature self-healing materials according to an embodiment of the present invention are shown;

[0030] Figure 2 is a sample diagram of UNP-DCN according to an embodiment of the present invention;

[0031] Figure 3 1. The differential scanning calorimetry and dynamic mechanical analysis diagrams of UNP-DCN according to an embodiment of the present invention;

[0032] Figure 4 2. It is a repair effect diagram of UNP-DCN according to an embodiment of the present invention;

[0033] Figure 5 is a polarizing microscope repair image of a carbon fiber composite material UNP-DCN according to an embodiment of the present invention;

[0034] Figure 6 3. The bending stress-strain curves of carbon fiber composite materials according to Example UNP-DCN of the present invention and Comparative Example EP;

[0035] Figure 7 3 is a graph showing the self-repair efficiency of the carbon fiber composite material according to Example UNP-DCN of the present invention and Comparative Example EP. DETAILED DESCRIPTION

[0036] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0037] The present invention discloses a room-temperature self-healing thermosetting polymer material and a preparation method thereof, wherein the preparation raw materials include: 2-amino-4-hydroxy-6-methylpyrimidine (MIC), hexamethylene diisocyanate (HDI), polyethyleneimine (PEI), and 1,2-cyclohexanedicarboxylic acid diglycidyl ester (DCN).

[0038] The inventors discovered that the polymer material UNP-DCN prepared in this application has a dual dynamic cross-linked network, namely, covalent cross-linking ensures the high strength, high stiffness and high solvent resistance of the thermosetting polymer, while non-covalent cross-linking improves the toughness of the material and gives it room temperature self-healing properties. Because the main chain of the cross-linked network exists in the form of covalent cross-links and contains highly mobile side chains and a large number of groups that can form quadruple hydrogen bonds, the material has two glass transition temperatures (T g1 =16℃, T g2 =106°C), demonstrating high room-temperature self-healing capabilities. After manually compressing the fractured surface for a few seconds at room temperature, the two broken halves of the rectangular sample reconnected and could easily lift heavy objects. A carbon fiber-reinforced composite based on this material recovered nearly its original strength after 24 hours of repair at room temperature under atmospheric pressure.

[0039] The following embodiments of the present invention are described in detail. It should be noted that the following embodiments are illustrative and are intended only to explain the present invention and are not to be construed as limiting the present invention. In addition, unless otherwise expressly stated, all reagents used in the following embodiments are commercially available or can be synthesized according to methods described herein or known methods. Reaction conditions not listed are also readily available to those skilled in the art.

[0040] The raw materials and auxiliary agents used in the examples of the present invention are as follows:

[0041]

[0042]

[0043] Example

[0044] The preparation method of room temperature self-healing thermosetting polymer material comprises the following steps:

[0045] (1) 2-Amino-4-hydroxy-6-methylpyrimidine (MIC) (2.5 g, 0.02 mol) and hexamethylene diisocyanate (HDI) (23 ml, 0.136 mol) were added to a three-necked flask (50 ml). The mixture was stirred under magnetic stirring in an oil bath at 100 °C for 24 h under nitrogen protection. The suspension was washed with n-hexane three times and dried in a vacuum oven at 50 °C to obtain a white powder of UPy-NCO capable of forming quadruple hydrogen bonds.

[0046] (2) UPy-NCO (3 g) and polyethyleneimine (PEI) (17 g) synthesized in step (1) were placed in a three-necked flask, nitrogen was introduced, and the mixture was stirred in an oil bath at 100°C for 6 hours to obtain a light yellow viscous liquid UNP.

[0047] (3) At room temperature, the UNP synthesized in step (2) and the epoxy monomer 1,2-cyclohexanedicarboxylic acid diglycidyl ester were mixed uniformly in an aluminum weighing dish (mass ratio of 1:1).

[0048] (4) The mixed liquid in step (3) was placed in a vacuum oven at 50°C for 30 minutes to completely remove bubbles.

[0049] (5) The sample was placed in an oven and heated to 100°C for curing for 2 h, then the oven temperature was increased to 150°C and accelerated curing was performed for 2 h to obtain the target sample UNP-DCN.

[0050] Comparative Example

[0051] The preparation method of conventional epoxy resin samples includes the following steps:

[0052] (1) First weigh 8 g of 4,4'-4,4'-diaminodiphenylmethane into a plastic cup and place it in an oven at 105°C to melt. Set aside.

[0053] (2) Place a beaker containing 40 g of bisphenol A diglycidyl ether on a magnetic stirrer, heat to 70°C and stir, slowly add the melted 4,4'-diaminodiphenylmethane solution into the beaker and stir until a homogeneous solution is obtained.

[0054] (3) Preheat the standard mold at 120°C, then pour the stirred epoxy resin solution into the mold and vacuum degas at 105°C for 10 minutes.

[0055] (4) Finally, the mold containing the resin sample was placed in a 120°C oven for heating and curing for 6 h, and finally heated in a 150°C oven for curing for 3 h to obtain the final sample, named EP.

[0056] Test example

[0057] The beneficial effects of the present invention are demonstrated below through specific test examples. The performance tests and characterizations of the room temperature self-healing thermosetting polymer material of the embodiment and the epoxy resin of the comparative example are as follows:

[0058] (1) UPy-NCO, UNP, and UNP-DCN were analyzed using a Fourier transform infrared spectrometer in attenuated total reflection mode at 500–4500 cm -1 32 scans were collected within the range to obtain the infrared (FTIR) spectrum.

[0059] (2) The structure of the synthesized product was characterized by measuring 1H NMR using a nuclear magnetic resonance analyzer. The solvent used in the test was deuterated chloroform and the ambient temperature was room temperature, and a hydrogen nuclear magnetic resonance spectrum was obtained.

[0060] (3) The thermodynamic parameters of the UNP-DCN thermosetting epoxy resin were measured using a differential scanning calorimeter. Under a nitrogen atmosphere, the sample was heated and cooled at a heating / cooling rate of 20°C / min between -30°C and 120°C, with a holding time of 3 min at both -30°C and 120°C. Two heating / cooling cycles were performed.

[0061] (4) UNP-DCN thermosetting epoxy resin was analyzed using a dynamic mechanical analyzer. Using a single cantilever mode, the temperature was increased at a rate of 3°C / min from -30°C to 120°C, with a frequency of 1 Hz and an amplitude of 10 μm.

[0062] (5) A three-point bending test was performed on the UNP-DCN carbon fiber composite material using a mechanical testing machine to obtain a bending stress-strain curve.

[0063] The performance test results and conclusions of the room temperature self-healing thermosetting polymer material of the present invention are as follows:

[0064] like Figure 1 As shown in the figure, the -NH2 group (3324 cm -1 ) disappeared, and -NH-(3216cm -1 ,3147cm -1 ), C=O(1167cm -1 ,1587cm -1 ) characteristic peak, in addition at 2286cm -1 A very obvious -NCO characteristic peak appeared nearby, indicating that UPy-NCO was successfully synthesized. To further determine the chemical structure of the UPy-NCO monomer, the synthesized white solid powder was dissolved in deuterated chloroform solvent, and its liquid phase H NMR spectrum was measured as shown in (b). The attribution of the various absorption peaks of UPy-NCO is as follows:

[0065] 1HNMR (600 MHz, CDCl3) δ13.11 (s, 1H), 11.86 (s, 1H), 10.18 (d, J = 5.7 Hz, 1H), 5.82 (d, J = 1.6 Hz, 1H), 3.39-3.19 (m, 4H), 2.23 (s, 3H), 1.76-1.37 (m, 10H). The peak with a chemical shift of 13.11 ppm is the peak of hydrogen on the secondary amino group (-NH-) in the pyrimidine structure; the peaks with chemical shifts of 11.86 ppm and 10.18 ppm are the peaks of hydrogen on the two secondary amino groups in the newly formed urea group; the methylene hydrogen and methyl hydrogen in the pyrimidine structure correspond to the peaks at 5.82 ppm and 2.23 ppm, respectively; in the cyanate structure, the peaks corresponding to the hydrogen on the methylene group have chemical shifts of 3.39-3.19 and 1.76-1.37 ppm, respectively. The above hydrogen signal peak position and integrated area are basically consistent with those reported in the literature. Combined with the infrared spectrum data, it is proved that the white powder is indeed UPy-NCO.

[0066] (c) -NCO (2286cm -1 ) characteristic peak completely disappeared, indicating that -NCO has been completely reacted. 906cm in (d) -1 The nearby epoxy groups completely disappeared, indicating that the epoxy groups were fully cured. In addition, the FTIR spectrum clearly shows that the -NH-, -OH, and C=O moieties in the thermosetting UNP-DCN network have abundant hydrogen bonds. Due to the unique branched structure of PEI, adjacent main chains can be loosely stacked, while the -NH-, -OH, and C=O on the mobile side chains with mobility can assemble within the network to form quadruple hydrogen bonds. The reversible dynamic interaction between these dense hydrogen bonds gives the material room temperature self-healing properties, and the rigid six-atom ring of DCN contributes to the excellent mechanical rigidity of the UNP-DCN polymer.

[0067] like Figure 2 As shown, the example sample UNP-DCN has good transparency and mechanical robustness, exhibits a glassy state at room temperature, and can easily lift heavy objects without any bending in the single cantilever beam state.

[0068] like Figure 3 As shown in the figure, after two heating and cooling cycles, the second DSC heating curve of the example sample UNP-DCN measured T g The temperature of the material is 8.3℃, which is much lower than room temperature. However, the material does not show a rubbery state at room temperature, but a rigid glassy state. Combining the trends of the two curves in the range of 80℃-120℃, it seems that there is another high temperature range T gTherefore, the dynamic thermomechanical properties of UNP-DCN polymer were further studied by dynamic thermomechanical analyzer (DMA). Two Tanδ peaks appeared in the temperature range of -50℃-200℃. The first peak was located in the low temperature region. g The second peak is the main peak, located in the high temperature area, and the measured T g It is 106°C, which is much higher than room temperature. When the temperature is around room temperature, the side chains of the polymer are non-covalently cross-linked through quadruple hydrogen bonds, and the thermal mobility is high, and the storage modulus of the polymer decreases compared to that at low temperatures. However, the polymer still has a storage modulus of 543.5MPa at 25°C, indicating good rigidity at room temperature. The rubbery state transition only occurs when the temperature is raised to around 100°C, and a stable storage modulus stage related to the rubbery state can be observed before 200°C. This shows that the main chain of the UNP-DCN polymer has a covalent cross-linked network, which makes the thermosetting polymer UNP-DCN insoluble and infusible at high temperatures.

[0069] like Figure 4 As shown, after manually compressing the fracture surface of the example UNP-DCN at room temperature for a few seconds, the two broken parts of the rectangular sample can be reconnected and can easily lift heavy objects.

[0070] like Figure 5 As shown in the image, the carbon fiber composite material of Example UNP-DCN exhibited significant cracking and delamination between the polymer material and the carbon fiber cloth after a three-point bending test. After repair, the delaminated sample healed, with virtually no cracks visible in the image.

[0071] like Figure 6 As shown, the curves of the carbon fiber composites EP-1 and EP-2 samples from the comparative example EP show a significant difference between the two tests, with the maximum bending stress values ​​losing almost half. The curves of samples EP-3 and EP-4, which were repaired at room temperature at 10 MPa for 24 hours, are similar to those of EP-1 and EP-2, showing no self-healing effect. This is because traditional thermosetting polymers only have irreversible covalent crosslinks, and the polymer segments cannot reconnect after the material breaks or delaminates. Compared with the EP samples, the bending stress-strain curves of the four groups of UNP-DCN samples from the example UNP-DCN carbon fiber composites show little difference between the two tests, indicating self-healing capabilities.

[0072] like Figure 7As shown, among the carbon fiber composites of the comparative example EP, the flexural strength of the control EP composites (EP-1 and EP-2) placed in a vacuum desiccator at room temperature was reduced by about half. The flexural strength of the control EP composites (EP-3 and EP-4) repaired at room temperature for 24 hours at 10 MPa pressure was almost the same as that of the previous group. The compression applied at room temperature for 24 hours helped to close the delamination. Although no chemical bonding occurred, some physical entanglement may have occurred. Among the carbon fiber composites of the example UNP-DCN, the flexural strength of the UNP-DCN composites (UNP-DCN-3 and UNP-DCN-4) repaired at room temperature for 24 hours at 10 MPa pressure recovered to about 90% of the original strength, a significant difference compared to the control group, which proves that UNP-DCN has excellent self-healing ability. It is worth noting that the flexural strength of the UNP-DCN composites (UNP-DCN-1 and UNP-DCN-2) placed in a vacuum desiccator at room temperature for 24 hours without applying 10 MPa pressure even exceeded the initial strength. Therefore, we can see that UNP-DCN thermosetting polymer composites have excellent room temperature self-healing ability, and their strength can almost be restored to their initial strength only under a certain atmospheric pressure.

[0073] In summary, the present invention provides a room temperature self-healing thermosetting polymer material and its preparation method. The prepared polymer material UNP-DCN has a dual dynamic cross-linking network, namely, covalent cross-linking ensures the high strength, high stiffness and high solvent resistance of the thermosetting polymer, and non-covalent cross-linking can improve the toughness of the material and give it room temperature self-healing properties. Because the main chain of the cross-linking network exists in the form of covalent cross-linking and contains highly mobile side chains and a large number of groups that can form quadruple hydrogen bonds, the material has two glass transition temperatures (T g1 =16℃, T g2 =106°C), demonstrating high room-temperature self-healing capabilities. After manually compressing the fractured surface for a few seconds at room temperature, the two broken halves of the rectangular sample reconnected and could easily lift heavy objects. A carbon fiber-reinforced composite based on this material recovered nearly its original strength after 24 hours of repair at room temperature under atmospheric pressure.

[0074] In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. In the absence of mutual contradiction, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples. Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and are not to be construed as limiting the present invention. Those skilled in the art may change, modify, replace, and modify the above embodiments within the scope of the present invention.

Claims

1. A room temperature self-healing thermosetting polymer material, characterized in that: The structural formula of the room temperature self-healing thermosetting polymer material is as follows:

2. A method for preparing the room temperature self-healing thermosetting polymer material according to claim 1, characterized in that: include: (1) Under inert gas protection, 2-amino-4-hydroxy-6-methylpyrimidine and hexamethylene diisocyanate were reacted at 100°C for 24 hours. The reaction suspension was filtered with n-hexane and vacuum dried to obtain a white powder of UPy-NCO capable of forming a quadruple hydrogen bond. (2) Under inert gas protection, UPy-NCO synthesized in step (1) was added to polyethyleneimine, and the mixture was stirred at 100° C. for 6 h to generate a functional curing agent, a light yellow viscous liquid UNP; (3) adding the UNP synthesized in step (2) as a curing agent to the epoxy monomer 1,2-cyclohexanedicarboxylic acid diglycidyl ester and stirring until the mixture is uniform; (4) pouring the mixed liquid obtained in step (3) into a mold and placing it in a vacuum oven for degassing for 30 minutes to completely remove bubbles; (5) The sample is cross-linked and cured according to the pre-curing and post-curing stages to obtain the room temperature self-healing thermosetting polymer material.

3. The method according to claim 2, characterized in that In step (1), the molar ratio of the 2-amino-4-hydroxy-6-methylpyrimidine to the hexamethylene diisocyanate is 0.

147.

4. The method according to claim 2, characterized in that In step (2), the amount of UPy-NCO added is 15% of the total mass of the reaction system.

5. The method according to claim 2, characterized in that In step (3), the curing agent UNP and the epoxy monomer are cross-linked in a mass ratio of 1:

1.

6. The method according to claim 2, characterized in that In step (4), the temperature of vacuum degassing is 50° C., the time is 10 to 30 minutes, and the vacuum degree of vacuum degassing does not exceed 40 Pa.

7. The method according to claim 2, characterized in that In step (5), the pre-curing temperature is 100° C. and the time is 2 hours, and the post-curing temperature is 150° C. and the time is 2 hours.

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