Self-repairing degradable bio-based polyurethane containing a single imine bond and preparation method thereof

Abstract

The present invention discloses a self-repairing, degradable bio-based polyurethane containing a single imine bond and a preparation method thereof: the preparation method first converts the phenolic hydroxyl group of vanillin into a glycidyl ether bond by epichlorohydrin; then, the vanillin glycidyl ether is modified using a substance containing both a secondary amine and a primary hydroxyl group and a substance containing both a primary amine and a primary hydroxyl group, respectively; finally, the modified bio-based chain extender is introduced into the polyurethane main chain to obtain a self-repairing, degradable bio-based polyurethane containing a single imine bond and an imine bond. The bio-based polyurethane of the present invention is connected to the main chain through hydroxyl groups at both ends, and contains only a single imine bond, which ensures that the polyurethane will not precipitate and lose small molecules during use, and the number of imine bonds will not decrease. The self-repairing polyurethane of the present invention has excellent repeatable repair performance. In a harsh working environment with high loss, it can achieve high safety, reliability and long service life through multiple self-repairs.

Description

Technical Field

[0001] The invention relates to a polyurethane material, in particular to a self-repairing degradable bio-based polyurethane containing a single imine bond and a preparation method thereof. Background Art

[0002] Due to its unique microphase separation structure, polyurethane has excellent mechanical properties and is widely used in various fields. Currently, most polyurethane raw materials are derived from petroleum resources, which are limited and non-renewable. As petroleum resources are depleted, the development of polyurethane will inevitably be restricted. To achieve the green and sustainable development of polyurethane, it is crucial to find a bio-based raw material that is widely available and low-cost. Vanillin, currently the second largest natural and renewable bio-based raw material, contains both highly active aldehyde groups and phenolic hydroxyl groups in its structure, and has the potential for widespread application.

[0003] During use, polyurethane is inevitably affected by various factors, resulting in defects such as microcracks. As microcracks continue to accumulate and expand, the performance of the material will be greatly reduced and its safety and reliability will be affected, which will greatly shorten the service life of the material and cause waste of resources. Reversible dynamic bonds can break and reorganize under certain conditions, thereby repairing defects such as microcracks and extending the service life of the material. For example, Chinese invention patent application CN115109225A introduces DA bonds with reversible dynamic properties into the polyurethane main chain, enabling the polyurethane material to repair mechanical damage and restore mechanical properties under heating conditions. Chinese invention patent application CN115260446A uses hydrogen bonds and dynamic thiurethane bonds to prepare a polyurethane film with high strength and high transparency that can achieve self-repairing function under heating conditions. Although the first two dynamic bonds have excellent self-repairing properties, the temperature required to repair the damage is relatively high, which is not conducive to the practical application of the material. Therefore, it is very necessary to find a dynamic bond that can achieve self-repairing function under mild conditions. Chinese invention patent application CN112979919A introduces highly dynamically active imine bonds into polyurethane, enabling the material to achieve a self-healing efficiency of up to 87% at 60°C. However, the bio-based chain extender prepared using this technology contains imine bonds at both ends. Because imine bonds are highly dynamically active, the difurfurylamine is gradually lost during daily use or during damage repair. This results in a decrease in polymer molecular weight and mechanical properties, while also reducing the imine bond content, weakening the material's self-healing properties.

[0004] As a polymer, polyurethane has a large molecular weight and stable chemical properties. It is difficult to degrade in its natural state. Therefore, it will produce a large number of microplastic particles in the natural environment, which has an immeasurable impact on the ecological environment. Therefore, the preparation of polyurethane with degradable functions is very important for alleviating environmental pollution. As a dynamic bond, the imine bond can be hydrolyzed under acidic conditions, thereby breaking the polymer molecular chain and achieving polymer degradation. Chinese invention patent application CN114015003A introduces an imine bond into the polyurethane backbone, enabling polyurethane to be rapidly degraded under mild conditions. However, the bio-based chain extender prepared by this technology also contains two imine bonds at both ends. During use, it will cause the precipitation and loss of vanillin dimer, which greatly affects the mechanical properties and self-healing properties of the material.

[0005] It can be seen that although biomass vanillin can be used as a raw material, by introducing imine bonds into polyurethane, the material can be given self-healing and degradable properties, thereby extending its service life and reducing its impact on the environment. However, vanillin has an asymmetric structure with a phenolic hydroxyl group at one end and an aldehyde group at the other end. Current research generally derives vanillin to prepare chain extenders with a symmetrical structure and imine bonds at both ends, thereby giving polyurethane materials self-healing and degradable properties. However, since the imine bond has high dynamic activity, and the chain extender contains a structure with imine bonds at both ends, the small molecule will gradually be lost during use and affect the mechanical properties and self-healing properties of the material, causing the material to fail. Summary of the Invention

[0006] In response to the problems existing in the prior art, the purpose of the present invention is to provide a self-healing polyurethane that can achieve multiple damage-repair cycles without significantly changing its performance. This is very beneficial for improving the safety and reliability of the material in various harsh environments, and can also greatly extend the service life of the material and reduce resource waste. It contains a self-healing biodegradable bio-based polyurethane containing a single imine bond and a preparation method thereof.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A self-healing, biodegradable bio-based polyurethane containing a single imine bond has the following structural formula:

[0009]

[0010] Wherein, m is 10-18, n is 12-15;

[0011] R1 is one of the following groups:

[0012]

[0013] R2 is one of the following groups:

[0014]

[0015] wherein R1 is derived from a group formed by the reaction of one of 2-(methylamino)ethanol, ethylhydroxyethylamine, 2-(isopropylamino)ethanol, 2-(propylamino)ethanol, and 2-(octadecylamino)ethanol with an epoxy group and an isocyanate group, respectively;

[0016] R2 is derived from a group generated by the reaction of one of ethanolamine, 2-amino-1-propanol, 1-amino-2-propanol, 2-amino-1-butanol, and 4-amino-1-butanol with an aldehyde group and an isocyanate group.

[0017] The method for preparing the self-repairing degradable bio-based polyurethane containing a single imine bond comprises the following steps:

[0018] (1) Vanillin, epichlorohydrin, and a phase transfer catalyst are mixed and reacted at 80–100°C for 2–4 hours, then cooled to 20–40°C, a strong base solution is added, and the mixture is diluted with a solvent, washed, and filtered to obtain vanillin glycidyl ether;

[0019] (2) mixing the vanillin glycidyl ether with a substance containing both a secondary amine and a primary hydroxyl group, reacting at 25-60° C. for 1-8 hours, and then removing excess solvent and the raw material to obtain an epoxy-ring-opened vanillin derivative containing a primary hydroxyl group;

[0020] (3) dissolving the epoxy-ring-opened vanillin derivative containing primary hydroxyl groups and a substance containing both primary amines and primary hydroxyl groups in a solvent; reacting at 25-50° C. for 0.5-4 hours, then removing excess raw materials and solvent to obtain a bio-based polyurethane chain extender containing an imine bond;

[0021] (4) reacting the obtained bio-based polyurethane chain extender containing an imine bond with a polyether polyol, a catalyst, and a diisocyanate, and removing the solvent after the reaction to obtain a self-repairing biodegradable bio-based polyurethane containing a single imine bond.

[0022] To further achieve the purpose of the present invention, preferably, the molar ratio of vanillin to epichlorohydrin in step (1) is 1:5-1:10; the molar ratio of vanillin glycidyl ether to the substance containing both a secondary amine and a primary hydroxyl group in step (2) is 1:1-1:10; and the molar ratio of the epoxy-ring-opened vanillin derivative containing primary hydroxyl groups to the substance containing both a primary amine and a primary hydroxyl group in step (3) is 1:1–1:2.

[0023] Preferably, the substance containing both secondary amine and primary hydroxyl groups is one or more of 2-(methylamino)ethanol, ethylhydroxyethylamine, 2-(isopropylamino)ethanol, 2-(propylamino)ethanol, and 2-(octadecylamino)ethanol.

[0024] Preferably, the substance containing both primary amine and primary hydroxyl group is one or more of ethanolamine, 2-amino-1-propanol, 1-amino-2-propanol, 2-amino-1-butanol, and 4-amino-1-butanol.

[0025] Preferably, the strong base is one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide; and the phase transfer catalyst is one or more of tetrabutylammonium bromide, tetraethylammonium bromide, triethylbenzylammonium chloride, and trimethylbenzylammonium chloride.

[0026] Preferably, the molar ratio of the polyether polyol, diisocyanate, imine-bonded bio-based polyurethane chain extender and catalyst in step (4) is 1:2:1:0.001-1:5:4:0.001.

[0027] Preferably, the catalyst described in step (4) is one or more of dibutyltin dilaurate, triethylenediamine, stannous octoate, zinc isooctanoate, and bismuth cyclohexane; and the solvent described in steps (1) to (4) is one or more of water, ethanol, n-propanol, isopropanol, N,N-dimethylformamide, tetrahydrofuran, acetone, and dimethyl sulfoxide.

[0028] Preferably, the excess raw materials and solvent can be removed by standing at 40-70° C. under negative pressure for 8-24 hours.

[0029] Preferably, the washing in step (1) is performed with deionized water.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] 1. The self-healing and degradable bio-based polyurethane containing a single imine bond prepared by the present invention contains an imine bond in the polymer chain. Due to the dynamic nature of the imine bond, it can impart self-healing and degradation properties to the material. In addition, due to its unique asymmetric structure, there will be no loss of small molecules during use, resulting in a reduction in the number of imine bonds and affecting the mechanical properties and self-healing properties of the material.

[0032] 2. The self-healing, biodegradable polyurethane containing a single imine bond can be rapidly repaired at 60°C and degraded in 0.1 mol / L acidic conditions. The self-healing and degradation conditions are mild, energy-efficient, and minimally polluting.

[0033] 3. The self-healing, biodegradable polyurethane containing a single imine bond of the present invention has high self-healing efficiency and excellent repeated self-healing performance, and can maintain excellent mechanical properties after multiple damage repairs;

[0034] 4. The raw material cost for preparing the self-repairing biodegradable polyurethane containing a single imine bond in the present invention is low, sustainable, and conducive to mass production;

[0035] 5. The self-repairing and degradable bio-based polyurethane containing a single imine bond of the present invention has the characteristics of simple preparation method and mild synthesis conditions, and can use a green and environmentally friendly solvent system, which is easy to achieve large-scale production and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the H NMR spectrum of vanillin glycidyl ether in Example 1.

[0037] Figure 2 This is the H-NMR spectrum of the vanillin derivative after epoxy ring opening of vanillin in Example 1.

[0038] Figure 3 This is the H-NMR spectrum of the bio-based polyurethane chain extender in Example 1. DETAILED DESCRIPTION

[0039] In order to better understand the present invention, the present invention is described below in conjunction with specific embodiments, but the embodiments do not constitute a limitation on the scope of protection of the claims of the present invention. Based on the embodiments, other embodiments obtained by those skilled in the art without making any creative work shall fall within the scope of protection of the present invention.

[0040] The present invention is to epoxidize biomass vanillin to obtain vanillin glycidyl ether, then use a substance containing both a secondary amine and a primary alcohol to open the epoxy ring in a mixed solvent, and use a substance containing both a primary amine and a primary hydroxyl group to react with the aldehyde group. The obtained chain extender is used as a raw material to prepare polyurethane to obtain a self-repairing and degradable bio-based polyurethane containing a single imine bond. By introducing an imine structure into the polyurethane main chain, the material is given self-repairing and degradation properties. The conditions required for the material to achieve self-repair and degradation are mild, and mechanical damage can be easily repaired and the material can be degraded. In addition, the bio-based chain extender is connected to the polyurethane main chain through a carbamate bond, and its structure only contains a single imine bond. Therefore, during the use of the polyurethane, the precipitation and loss of small molecular substances will not occur, resulting in a decrease in mechanical properties. The polyurethane prepared by the present invention can achieve multiple damage-repair cycles while ensuring mechanical properties in a variety of application environments, thereby greatly improving the safety and reliability of the material, extending the service life of the material, and reducing resource waste.

[0041] Therefore, according to the above mechanism, the present invention uses biomass vanillin as a raw material to prepare a self-repairing polyurethane that can achieve multiple damage-repair cycles without significantly changing its performance. This is very beneficial for improving the safety and reliability of the material in various harsh environments, and can also greatly extend the service life of the material and reduce resource waste. In order to extend the service life of the material and solve the problem that the degradation performance of polyurethane materials is poor and large-scale use will cause environmental pollution, the present invention uses biomass vanillin as a raw material to prepare an asymmetric chain extender containing a single imine bond to synthesize a polyurethane material. During use, the polyurethane will not precipitate and lose small molecules, which will affect the mechanical properties and self-repair properties of the material. Moreover, due to its unique structure, the polyurethane can achieve multiple damage-repair cycles in a high-loss environment without significantly changing its mechanical properties, which greatly improves the safety and reliability of the material and extends its service life, reducing resource waste.

[0042] The relevant testing methods in the embodiments of the present invention are as follows:

[0043] Mechanical properties test: A universal material testing machine was used to characterize the tensile properties of the original and repaired samples. The sample film with a thickness of 0.5-0.8 mm was cut into type 3 dumbbell-shaped specimens according to GB / T 528-2009, with a size of 4×75 mm and a gauge length of 16 mm. The tensile rate was 500 mm / min, the test temperature was 25±2°C, and the humidity was 60±10%. Each sample was repeated at least 3 times and the average value was taken.

[0044] Self-healing performance testing was performed using dumbbell-shaped splines of type 3, cut according to the national standard GB / T 528-2009. The splines were then cut in the middle, kept in contact, and placed in a 60°C oven for 4 hours to produce the corresponding repaired samples. The tensile strength of the spline before repair was denoted as σ1, and the tensile strength after repair was denoted as σ2. The self-healing efficiency was denoted as η, where η = σ2 / σ1 × 100%. (See invention patent CN112979919A for reference.)

[0045] Degradation performance test: Take 2.0-2.5g of polyurethane film sample (less than 2mm thick), record its mass as m1. Place the sample in a 0.1mol / L hydrochloric acid solution and let it sit at 25°C for 24 hours. Remove the sample and place it in a 60°C oven for 24 hours. Weigh it and record it as m2. Degradation rate δ = (m1 - m2) / m1 × 100%.

[0046] Example 1

[0047] (1) Synthesis of vanillin glycidyl ether: 60.86g of vanillin (0.40mol), 185.04g of epichlorohydrin (2.00mol) and 2.27g (0.01mol) of triethylbenzylammonium chloride were mixed, heated to 80℃ and reacted for 4h. Then the temperature was lowered to 20℃ and 100.00g of 40wt% sodium hydroxide aqueous solution (1.00mol) was added dropwise within 0.5h. After the addition was completed, 100.00g of ethanol was added for dilution, and the reaction was continued for 1h after the dilution was completed. After the reaction was completed, the product was washed 3 times with deionized water and filtered. Finally, 62.72g of vanillin glycidyl ether was obtained with a yield of about 75.31%. The nuclear magnetic hydrogen spectrum of vanillin glycidyl ether is shown as follows Figure 1 As shown in the figure, the hydrogen of the vanillin phenolic hydroxyl group has disappeared, replaced by the characteristic peak of the epoxy group substituent, proving that the epoxy group grafting was successful.

[0048] (2) Synthesis of epoxy-ring-opened vanillin derivatives: 8.32 g of vanillin glycidyl ether (0.04 mol) was dissolved in tetrahydrofuran, 3.00 g of 2-(methylamino)ethanol (0.04 mol) was added, and the mixture was reacted at 25°C for 8 h, and then the solvent was removed at 40°C under negative pressure for 24 h to obtain epoxy-ring-opened vanillin derivatives. The NMR spectrum of the epoxy-ring-opened vanillin derivative is shown in FIG. Figure 2 As shown. Figure 1 The comparison shows that the characteristic peaks of the epoxy group have disappeared, while the characteristic peaks of methylethanolamine appear in the H-NMR spectrum, proving that the epoxy group ring-opened successfully and methylethanolamine was successfully grafted onto vanillin glycidyl ether.

[0049] (3) Preparation method of bio-based polyurethane chain extender: 11.33g of vanillin derivative (0.04mol) after epoxy ring opening was dissolved in tetrahydrofuran, and after the solution was homogeneously clarified, 2.44g of ethanolamine (0.04mol) was added and reacted at 25℃ for 4h. After the reaction was completed, the solvent was removed at 40℃ under negative pressure for 24h to obtain a bio-based polyurethane chain extender. Its H NMR spectrum is shown as follows Figure 3 As shown. Figure 2 By comparison, it can be seen that the characteristic absorption peak of aldehyde hydrogen has disappeared, while there is an obvious characteristic absorption peak of ethanolamine, which proves that the amino group and the aldehyde group react completely and the bio-based chain extender containing an imine bond is successfully synthesized.

[0050] (4) Preparation method of self-healing and degradable bio-based polyurethane containing a single imine bond: 20 g of polytetrahydrofuran (0.02 mol) with an average molecular weight of 1000 was dissolved in tetrahydrofuran and 10.49 g of 4,4'-dicyclohexylmethane diisocyanate (0.04 mol), 6.53 g of the bio-based polyurethane chain extender (0.02 mol) synthesized in the previous step and 0.013 g of dibutyltin dilaurate were added thereto. The mixture was reacted at 60 °C under nitrogen protection for 6 h. After that, the product was poured into a mold and kept warm at 70 °C under negative pressure for 8 h to remove the solvent, and finally a self-healing and degradable bio-based polyurethane containing a single imine bond was obtained.

[0051] The following examples are related to the H NMR spectra of vanillin glycidyl ether, the intermediate after the epoxy ring opening of vanillin and the bio-based polyurethane chain extender. Figure 1-3 Basically similar, not provided one by one.

[0052] Example 2

[0053] A method for preparing a self-repairing and degradable bio-based polyurethane containing a single imine bond comprises the following steps:

[0054] (1) Synthesis of vanillin glycidyl ether: 60.86 g of vanillin (0.40 mol), 370.80 g of epichlorohydrin (4.00 mol) and 1.85 g (0.01 mol) of trimethylbenzylammonium chloride were mixed and heated to 100°C for 2 h. The temperature was then lowered to 40°C and 100.00 g of a 40 wt% aqueous potassium hydroxide solution (0.71 mol) was added dropwise over 0.5 h. After the addition was complete, 100.00 g of n-propanol was added for dilution, and the reaction was continued for 1 h. After the reaction was complete, the product was washed three times with deionized water and filtered. Finally, 69.33 g of vanillin glycidyl ether was obtained with a yield of approximately 83.25%.

[0055] (2) Synthesis of epoxy-ring-opened vanillin derivatives: 8.32 g of vanillin glycidyl ether (0.04 mol) was dissolved in acetone, and 35.65 g of ethylhydroxyethylamine (0.4 mol) was added. The mixture was reacted at 60°C for 1 h, and then the solvent and excess raw materials were removed at 70°C under reduced pressure for 8 h to obtain epoxy-ring-opened vanillin derivatives.

[0056] (3) Preparation method of bio-based polyurethane chain extender: 11.89 g of vanillin derivative (0.04 mol) after epoxy ring opening was dissolved in acetone. After the solution was clarified, 6.00 g of 1-amino-2-propanol (0.08 mol) was added and reacted at 50°C for 0.5 h. After the reaction was completed, the solvent and excess raw materials were removed at 70°C under negative pressure for 8 h to obtain a bio-based polyurethane chain extender.

[0057] (4) Preparation method of self-healing and degradable bio-based polyurethane containing a single imine bond: 20 g of polytetrahydrofuran (0.02 mol) with an average molecular weight of 1000 was dissolved in acetone and 15.74 g of 4,4'-dicyclohexylmethane diisocyanate (0.06 mol), 13.62 g of the bio-based polyurethane chain extender synthesized in the previous step (0.04 mol) and 0.022 g of triethylenediamine were added thereto. The mixture was reacted at 75 °C under nitrogen protection for 3 h. After that, the product was poured into a mold and kept warm at 40 °C under negative pressure for 24 h to remove the solvent, and finally a self-healing and degradable bio-based polyurethane containing a single imine bond was obtained.

[0058] Example 3

[0059] A method for preparing a self-repairing and degradable bio-based polyurethane containing a single imine bond comprises the following steps:

[0060] (1) Synthesis of vanillin glycidyl ether: 60.86 g of vanillin (0.40 mol), 227.56 g of epichlorohydrin (3.00 mol) and 3.22 g of tetrabutylammonium bromide (0.01 mol) were mixed, heated to 85°C and reacted for 2.5 h. The temperature was then lowered to 25°C and 100.00 g of a 40 wt% aqueous solution of calcium hydroxide (0.54 mol) was added dropwise over 0.5 h. After the addition was complete, 100.00 g of ethanol was added for dilution, and the reaction was continued for 1 h. After the reaction was complete, the product was washed three times with deionized water and filtered. Finally, 67.83 g of vanillin glycidyl ether was obtained with a yield of approximately 81.45%.

[0061] (2) Synthesis of epoxy-ring-opened vanillin derivatives: 8.32 g of vanillin glycidyl ether (0.04 mol) was dissolved in n-propanol, and 20.63 g of 2-(propylamino)ethanol (0.2 mol) was added. The mixture was reacted at 45°C for 4 h, and then the solvent and excess raw materials were removed at 60°C under reduced pressure for 18 h to obtain epoxy-ring-opened vanillin derivatives.

[0062] (3) Preparation method of bio-based polyurethane chain extender: 14.18 g of vanillin derivative (0.04 mol) after epoxy ring opening was dissolved in n-propanol. After the solution was clarified, 5.35 g of 2-amino-1-butanol (0.06 mol) was added and reacted at 45 °C for 2 h. After the reaction was completed, the solvent and excess raw materials were removed at 60 °C under negative pressure for 18 h to obtain a bio-based polyurethane chain extender.

[0063] (4) Preparation method of self-healing and degradable bio-based polyurethane containing a single imine bond: 20 g of polytetrahydrofuran (0.02 mol) with an average molecular weight of 1000 was dissolved in n-propanol and 26.23 g of 4,4'-dicyclohexylmethane diisocyanate (0.10 mol), 30.60 g of the bio-based polyurethane chain extender synthesized in the previous step (0.08 mol) and 0.081 g of stannous octoate were added thereto, and the mixture was reacted at 65 °C under nitrogen protection for 4 h. After that, the product was poured into a mold and kept warm at 60 °C under negative pressure for 18 h to remove the solvent, and finally a self-healing and degradable bio-based polyurethane containing a single imine bond was obtained.

[0064] Example 4

[0065] A method for preparing a self-repairing and degradable bio-based polyurethane containing a single imine bond comprises the following steps:

[0066] (1) Synthesis of vanillin glycidyl ether: 60.86 g of vanillin (0.40 mol), 227.56 g of epichlorohydrin (3.00 mol) and 3.00 g of triethylbenzylammonium chloride (0.01 mol) were mixed and heated to 85°C for 2.5 h. The temperature was then lowered to 25°C and 100.00 g of a 40 wt% aqueous sodium hydroxide solution (1.00 mol) was added dropwise over 0.5 h. After the addition was complete, 100.00 g of isopropanol was added for dilution, and the reaction was continued for 1 h. After the reaction was complete, the product was washed three times with deionized water and filtered. Finally, 65.99 g of vanillin glycidyl ether was obtained with a yield of approximately 79.25%.

[0067] (2) Synthesis of epoxy-ring-opened vanillin derivatives: 8.32 g of vanillin glycidyl ether (0.04 mol) was dissolved in n-propanol, and 4.13 g of 2-(propylamino)ethanol (0.04 mol) was added. The mixture was reacted at 45°C for 4 h, and then the solvent and excess raw materials were removed at 60°C under reduced pressure for 18 h to obtain epoxy-ring-opened vanillin derivatives.

[0068] (3) Preparation method of bio-based polyurethane chain extender: 14.18 g of vanillin derivative (0.04 mol) after epoxy ring opening was dissolved in n-propanol. After the solution was clarified, 3.57 g of 2-amino-1-butanol (0.04 mol) was added and reacted at 45°C for 2 h. After the reaction was completed, the solvent and excess raw materials were removed at 60°C under negative pressure for 18 h to obtain a bio-based polyurethane chain extender.

[0069] (4) Preparation method of bio-based polyurethane: 20 g of polytetrahydrofuran (0.02 mol) with an average molecular weight of 1000 was dissolved in N,N-dimethylformamide and 10.45 g of toluene diisocyanate (0.06 mol), 15.30 g of the bio-based polyurethane chain extender (0.04 mol) synthesized in the previous step and 0.0071 g of zinc isooctanoate were added thereto. The mixture was reacted at 65 °C under nitrogen protection for 4 h. After that, the product was poured into a mold and kept warm at 60 °C under negative pressure for 18 h to remove the solvent. Finally, a self-healing and degradable bio-based polyurethane containing a single imine bond was obtained.

[0070] Example 5

[0071] A method for preparing a self-repairing and degradable bio-based polyurethane containing a single imine bond comprises the following steps:

[0072] (1) Synthesis of vanillin glycidyl ether: 60.86 g of vanillin (0.40 mol), 370.80 g of epichlorohydrin (4.00 mol) and 2.27 g (0.01 mol) of triethylbenzylammonium chloride were mixed and heated to 100°C for 2 h. The temperature was then lowered to 25°C and 100.00 g of a 40 wt% aqueous sodium hydroxide solution (1.00 mol) was added dropwise over 0.5 h. After the addition was complete, 100.00 g of ethanol was added for dilution, and the reaction was continued for 1 h. After the reaction was complete, the product was washed three times with deionized water and filtered. Finally, 69.33 g of vanillin glycidyl ether was obtained with a yield of approximately 83.25%.

[0073] (2) Synthesis of epoxy-ring-opened vanillin derivatives: 8.32 g of vanillin glycidyl ether (0.04 mol) was dissolved in acetone, and 35.65 g of ethylhydroxyethylamine (0.4 mol) was added. The mixture was reacted at 60°C for 1 h, and then the solvent and excess raw materials were removed at 70°C under reduced pressure for 8 h to obtain epoxy-ring-opened vanillin derivatives.

[0074] (3) Preparation method of bio-based polyurethane chain extender: 11.89 g of vanillin derivative (0.04 mol) after epoxy ring opening was dissolved in acetone. After the solution was clarified, 4.89 g of ethanolamine (0.08 mol) was added and reacted at 50°C for 0.5 h. After the reaction was completed, the solvent and excess raw materials were removed under negative pressure at 70°C for 8 h to obtain a bio-based polyurethane chain extender.

[0075] (4) Preparation method of self-healing and degradable bio-based polyurethane containing a single imine bond: 20 g of polytetrahydrofuran (0.02 mol) with an average molecular weight of 1000 was dissolved in acetone and 10.49 g of 4,4'-dicyclohexylmethane diisocyanate (0.04 mol), 6.81 g of the bio-based polyurethane chain extender synthesized in the previous step (0.02 mol) and 0.013 g of dibutyltin dilaurate were added thereto. The mixture was reacted at 75 °C under nitrogen protection for 3 h. After that, the product was poured into a mold and kept warm at 40 °C under negative pressure for 24 h to remove the solvent, and finally a self-healing and degradable bio-based polyurethane containing a single imine bond was obtained.

[0076] Example 6

[0077] A method for preparing a self-repairing and degradable bio-based polyurethane containing a single imine bond comprises the following steps:

[0078] (1) Synthesis of vanillin glycidyl ether: 60.86 g of vanillin (0.40 mol), 185.04 g of epichlorohydrin (2.00 mol) and 2.27 g (0.01 mol) of triethylbenzylammonium chloride were mixed and heated to 80°C for 4 h. The temperature was then lowered to 25°C and 100.00 g of a 40 wt% aqueous sodium hydroxide solution (1.00 mol) was added dropwise over 0.5 h. After the addition was complete, 100.00 g of ethanol was added for dilution, and the reaction was continued for 1 h. After the reaction was complete, the product was washed three times with deionized water. Finally, 62.72 g of vanillin glycidyl ether was obtained with a yield of approximately 75.31%.

[0079] (2) Synthesis of epoxy-ring-opened vanillin derivatives: 8.32 g of vanillin glycidyl ether (0.04 mol) was dissolved in tetrahydrofuran, and 3.00 g of 2-(methylamino)ethanol (0.04 mol) was added. The mixture was reacted at 25°C for 8 h, and then the solvent was removed at 40°C under reduced pressure for 24 h to obtain epoxy-ring-opened vanillin derivatives.

[0080] (3) Preparation method of bio-based polyurethane chain extender: 11.33 g of epoxy ring-opened vanillin derivative (0.04 mol) was dissolved in tetrahydrofuran. After the solution was clarified, 3.00 g of 1-amino-2-propanol (0.04 mol) was added and reacted at 25°C for 4 h. After the reaction was completed, the solvent was removed at 40°C under negative pressure for 24 h to obtain a bio-based polyurethane chain extender.

[0081] (4) Preparation method of self-healing and degradable bio-based polyurethane containing a single imine bond: 20 g of polytetrahydrofuran (0.02 mol) with an average molecular weight of 1000 was dissolved in tetrahydrofuran and 15.74 g of 4,4'-dicyclohexylmethane diisocyanate (0.06 mol), 13.06 g of the bio-based polyurethane chain extender synthesized in the previous step (0.04 mol) and 0.013 g of dibutyltin dilaurate were added thereto. The mixture was reacted at 60 °C under nitrogen protection for 6 h. After that, the product was poured into a mold and kept warm at 70 °C under negative pressure for 8 h to remove the solvent, and finally a self-healing and degradable bio-based polyurethane chain extender containing a single imine bond was obtained.

[0082] Comparative Example 1

[0083] 60.86g of vanillin (0.40mol) and 20.00g of sodium hydroxide (0.50mol) were dissolved in 300mL of anhydrous ethanol. 25mL of 1,2-dibromoethane and 4.98g of potassium iodide (0.03mol) were added as a phase transfer catalyst. The mixture was reacted at 60°C for 24h to obtain vanillin dimer. 12.21g of ethanolamine (0.30mol) and 34.43g of vanillin dimer (0.10mol) were dissolved in 200mL of ethanol, reacted at 60°C for 4h, and then washed five times with deionized water to obtain a bio-based chain extender. 20 g of polytetrahydrofuran (0.02 mol) with a molecular weight of 1000 was dissolved in N,N-dimethylformamide, and 10.494 g of 4,4'-dicyclohexylmethane diisocyanate (0.04 mol), 8.16 g of the bio-based chain extender synthesized in the previous step (0.04 mol) and 0.013 g of dibutyltin dilaurate were added thereto. The mixture was reacted under nitrogen protection at 60 ° C for 6 h. After that, the product was poured into a mold and kept warm at 70 ° C under negative pressure for 8 h to remove the solvent to finally obtain the product.

[0084] Table 1 shows the performance test results of Example 1 and Comparative Example 1 of the present invention.

[0085] Table 1

[0086]

[0087] In Example 1, the bio-based chain extender prepared using vanillin as the raw material was incorporated into the polyurethane backbone via a carbamate bond and contained only a single imine bond. In Comparative Example 1, a bio-based chain extender was also prepared using vanillin as the raw material. This chain extender was incorporated into the polyurethane backbone via a carbamate bond, but the vanillin dimer contained imine bonds at both ends. The ratios of polyether polyol, isocyanate, and bio-based chain extender used in the preparation of both polyurethanes were identical. Therefore, the mechanical strength of the polyurethanes in Example 1 and Comparative Example 1 was not significantly different. After cutting strips of both materials with a blade, the samples self-healed within 4 hours at 60°C. Testing revealed that both materials achieved high self-healing efficiencies of 94.68% and 95.74%, respectively. This demonstrates that the materials can achieve self-healing under mild conditions and meet most application requirements. Furthermore, after 24 hours of exposure to a 0.1 mol / L hydrochloric acid solution, the majority of the samples degraded, reaching a degradation rate of 83.56%. The surface material degradation conditions are mild, and the degradation rate can reach a high level. This significantly reduces the environmental pollution caused by the discarded material. Although the imine bond content in the bio-based chain extender in Example 1 is only half that of the polyurethane in Comparative Example 1, the self-repair efficiency of the two polyurethanes after the first damage is similar. This demonstrates that the self-repair performance of the polyurethane prepared in this invention is similar to that of polyurethanes previously studied and lacks significant defects. However, as the number of damage repairs increases, after ten repairs, the repair efficiency of Example 1 remains high at 88.39%, while the repair efficiency of Comparative Example 1 decreases significantly, reaching only 53.24%, far lower than that of Example 1. This may be because the vanillin dimer in Comparative Example 1 contains imine bonds at both ends. While imine bonds break and recombine during the repair process, the vanillin dimer has a high cohesive energy, which causes it to gradually aggregate, crystallize, and precipitate during multiple repairs. This reduces the molecular weight of the polyurethane and the number of imine bonds. This significantly reduces the mechanical properties of the material and significantly weakens its self-repair performance, making it unable to meet the requirements of long-term use. At the same time, the polyurethane prepared in Example 1 also exhibits excellent degradation properties.

[0088] There is no significant difference in the performance of the materials prepared in other examples compared to Example 1, and they will not be analyzed one by one.

[0089] Therefore, the self-repairing and degradable bio-based polyurethane containing a single imine bond prepared by the present invention can have excellent repeated self-repairing and degradation properties while maintaining certain mechanical properties.

Claims

1. A self-repairing biodegradable polyurethane containing a single imine bond, characterized in that: It has the following structural formula: Wherein, m is 10-18, n is 12-15; R1 is one of the following groups: R2 is one of the following groups:

2. The method for preparing the self-repairing degradable bio-based polyurethane containing a single imine bond according to claim 1, characterized in that The following steps are involved: (1) Vanillin, epichlorohydrin, and a phase transfer catalyst are mixed and reacted at 80-100°C for 2-4 hours, then cooled to 20-40°C, a strong base solution is added, diluted with a solvent, washed, and filtered to obtain vanillin glycidyl ether; (2) mixing the vanillin glycidyl ether with a substance containing both a secondary amine and a primary hydroxyl group, reacting at 25-60° C. for 1-8 hours, and then removing excess solvent and the raw material to obtain an epoxy-ring-opened vanillin derivative containing a primary hydroxyl group; (3) dissolving the epoxy-ring-opened vanillin derivative containing primary hydroxyl groups and a substance containing both primary amines and primary hydroxyl groups in a solvent; reacting at 25-50° C. for 0.5-4 hours, then removing excess raw materials and solvent to obtain a bio-based polyurethane chain extender containing an imine bond; (4) reacting the obtained bio-based polyurethane chain extender containing an imine bond with a polyether polyol, a catalyst, and a diisocyanate, and removing the solvent after the reaction to obtain a self-repairing biodegradable bio-based polyurethane containing a single imine bond.

3. The method for preparing a self-repairing biodegradable polyurethane containing a single imine bond according to claim 2, characterized in that: The molar ratio of vanillin to epichlorohydrin in step (1) is 1:5-1:10; the molar ratio of vanillin glycidyl ether to the substance containing both a secondary amine and a primary hydroxyl group in step (2) is 1:1-1:10; the molar ratio of the epoxy-ring-opened vanillin derivative containing primary hydroxyl groups to the substance containing both a primary amine and a primary hydroxyl group in step (3) is 1:1-1:

2.

4. The method for preparing a self-repairing biodegradable polyurethane containing a single imine bond according to claim 2, wherein: The substance containing both secondary amine and primary hydroxyl group is one or more of 2-(methylamino)ethanol, ethylhydroxyethylamine, 2-(isopropylamino)ethanol, and 2-(propylamino)ethanol.

5. The method for preparing a self-repairing biodegradable polyurethane containing a single imine bond according to claim 2, characterized in that: The substance containing both primary amine and primary hydroxyl group is one or more of ethanolamine, 2-amino-1-propanol, 1-amino-2-propanol, 2-amino-1-butanol, and 4-amino-1-butanol.

6. The method for preparing a self-repairing biodegradable polyurethane containing a single imine bond according to claim 2, characterized in that: The strong base is one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide; the phase transfer catalyst is one or more of tetrabutylammonium bromide, tetraethylammonium bromide, triethylbenzylammonium chloride, and trimethylbenzylammonium chloride.

7. The method for preparing a self-repairing biodegradable polyurethane containing a single imine bond according to claim 2, characterized in that: The molar ratio of the polyether polyol, diisocyanate, imide-bonded bio-based polyurethane chain extender and catalyst in step (4) is 1:2:1:0.001-1:5:4:0.

001.

8. The method for preparing a self-repairing biodegradable polyurethane containing a single imine bond according to claim 2, wherein: The catalyst described in step (4) is one or more of dibutyltin dilaurate, triethylenediamine, stannous octoate, zinc isooctanoate, and bismuth cyclohexane; and the solvent described in steps (1) to (4) is one or more of N,N-dimethylformamide, tetrahydrofuran, acetone, and dimethyl sulfoxide.

9. The method for preparing a self-repairing biodegradable polyurethane containing a single imine bond according to claim 2, wherein: The excess raw materials and solvent can be removed by standing the mixture at 40-70° C. under negative pressure for 8-24 hours.

10. The method for preparing a self-repairing biodegradable polyurethane containing a single imine bond according to claim 2, characterized in that: The washing in step (1) is washing with deionized water.

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