A bio-based polyurethane chain extender containing a single imine bond and its preparation method

Abstract

The present invention discloses a bio-based polyurethane chain extender containing a single imine bond and a preparation method thereof: in this preparation method, vanillin, epichlorohydrin and a strong base are used as raw materials to convert the phenolic hydroxyl group of vanillin into a glycidyl ether bond, obtaining vanillin-based glycidyl ether; substances containing only secondary amines and substances containing both primary amines and primary hydroxyl groups are respectively used to modify vanillin glycidyl ether; finally, a bio-based chain extender containing a dynamic imine bond is obtained. The bio-based polyurethane chain extender of the present invention contains an imine bond, which can enable the material to achieve self-repair of defects such as microcracks under certain conditions and extend the service life of the material; at the same time, the presence of the imine bond endows the material with good degradability; moreover, only a single imine bond is contained in the structure of this bio-based chain extender, and there will be no phenomenon that small molecules in the structure are lost due to the strong dynamics of the imine bond, resulting in a reduction in the number of imine bonds and affecting the mechanical properties and repeated self-repair performance of the final material.

Description

Technical Field

[0001] The present invention relates to a polyurethane chain extender, and particularly to a bio-based polyurethane chain extender containing a single imine bond and a preparation method thereof. Background Art

[0002] Polyurethane is generally polymerized from oligomeric diols, diisocyanates and chain extenders. Among them, oligomeric diols serve as soft segments, and diisocyanates and chain extenders serve as hard segments. The cohesive energies of the soft and hard segments are different, and their compatibility is poor, so a microphase separation structure will be formed. It is precisely due to the existence of the microphase separation structure that polyurethane has both the strength of plastic and the elasticity of rubber. Polyurethane is widely used in various fields such as medical treatment, construction, aerospace, etc. due to its excellent strength, toughness and wear resistance.

[0003] At present, most of the raw materials of polyurethane are derived from non-renewable fossil energy. Fossil energy is limited and non-renewable. As fossil energy is continuously consumed, the raw material cost will continue to rise, thus restricting the development of polyurethane materials. In addition, as a polymer, polyurethane has a large molecular weight and stable chemical properties, and it is difficult to degrade in the natural state, and a large number of microplastic particles will be continuously generated. On the one hand, these microplastic particles will continuously pollute the ecological environment and cause inestimable impacts; on the other hand, they will also continuously accumulate in the food chain through the ecological cycle, thus affecting the life and health of various animals, plants and even humans.

[0004] Preparing bio-based degradable polyurethane can effectively reduce the dependence of polyurethane on fossil energy and alleviate environmental pollution problems. A common method is to introduce ester bonds into the polyurethane main chain and utilize the principle of ester bond hydrolysis to achieve the degradation of the polymer. For example, Chinese Patent Application CN202211234604.3 uses degradable polylactic acid diol and bio-based polyol to prepare polyurethane. The material is given degradable properties by introducing ester bonds into the main chain. Chinese Patent Application CN202211104812.1 discloses a biodegradable slow-rebound polyurethane foam and a preparation method thereof. By introducing L-lysine into the polyurethane main chain, the polyurethane is given degradable properties by using the ester bonds therein. Chinese Patent Application CN202210960377.6 discloses a preparation method of a polysorbate-modified polylactic acid-based polyurethane. The polysorbate-modified polylactic acid-based polyurethane uses all-natural raw materials and has the characteristics of green degradability. Although the ester bonds in the above-mentioned prior art can endow polyurethane with degradable properties, their characteristic of being easily broken will also greatly reduce the performance of polyurethane during use and cannot meet the long-term actual use requirements of the material.

[0005] Therefore, in addition to introducing ester bonds into the main chain, introducing dynamic covalent bonds into polyurethane can also endow the material with degradable properties. Moreover, polyurethane materials with dynamic covalent bonds can repair material defects through the breakage and recombination of dynamic bonds under specific conditions, thereby extending the service life of the material and reducing waste of resources. For example, Chinese Patent Application CN202010951771.4 uses a degradable biological raw material, castor oil, as a cross-linking agent and prepares a bio-based degradable polyurethane with self-healing function by introducing disulfide bonds.

[0006] Chinese Patent Application CN202111369673.0 uses vanillin as a raw material and endows the material with degradable properties by introducing dynamic imine bonds into the main chain, enabling the material to degrade in a diethylamine solution. However, both ends of the vanillin dimer in the structure of the bio-based chain extender prepared by this technology are imine bonds. Due to the high cohesive energy of the vanillin dimer, during use, as the imine bonds break and reform, the vanillin dimer will gradually aggregate and crystallize out, reducing the number of imine bonds in the material and resulting in a decrease in the mechanical properties of the material and a weakening of the repeated repair performance. Summary of the Invention

[0007] In order to reduce the dependence on fossil resources in the preparation of polyurethane and alleviate the problem of environmental pollution caused by the non-degradability of conventional polyurethane, from the perspective of sustainable development, the present invention provides a bio-based polyurethane chain extender containing a single imine bond prepared from vanillin, which can endow the chain-extended material with self-healing performance and degradable properties, while ensuring that there is no loss of small molecules during use, resulting in a decrease in the mechanical properties of the material and a weakening of the self-healing performance, enabling the material to achieve multiple damaged-repaired cycles, greatly improving the safety and reliability of the material in high-loss environments and extending the service life of the material, as well as its preparation method.

[0008] The object of the present invention can be achieved by the following technical solutions:

[0009] A bio-based polyurethane chain extender containing a single imine bond has the following structural formula:

[0010]

[0011] Wherein, R1 is one of the following groups:

[0012]

[0013] R2 is one of the following groups:

[0014]

[0015] The preparation method of the bio-based polyurethane chain extender containing a single imine bond includes the following steps:

[0016] (1) Mix vanillin, epichlorohydrin and a phase transfer catalyst, heat up to 70 - 90 °C and react for 2 - 4 h, then cool down to 20 - 40 °C. Then add a strong base to convert the phenolic hydroxyl group of vanillin into a glycidyl ether bond, obtaining vanillin-based glycidyl ether.

[0017] (2) Add vanillin-based glycidyl ether and a secondary amine-containing substance into a solvent system and react at room temperature for 1 - 8 h to obtain a vanillin derivative after epoxy ring-opening.

[0018] (3) React the vanillin derivative after epoxy ring-opening with a substance containing both primary amine and secondary hydroxyl group in a solvent at room temperature for 0.5 - 4 h, then remove the solvent and excessive raw materials to obtain a bio-based polyurethane chain extender containing a single imine bond.

[0019] To further achieve the object of the present invention, preferably, the molar ratio of vanillin to epichlorohydrin is 1:5 - 1:10.

[0020] Preferably, 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.

[0021] Preferably, the secondary amine-containing substance is one or more of dimethylamine, N-ethylmethylamine, N-ethylpropylamine, N-ethylisopropylamine, diethylamine, dipropylamine, and di-sec-butylamine.

[0022] Preferably, the molar ratio of vanillin-based glycidyl ether to the secondary amine-containing substance is 1:1 - 1:10.

[0023] Preferably, the substance containing both primary amine and primary hydroxyl group is one or more of ethanolamine, propanolamine, 2-amino-1-propanol, 1-amino-2-propanol, 2-amino-1-butanol, and 4-amino-1-butanol.

[0024] Preferably, the molar ratio of the vanillin derivative after epoxy ring-opening to the substance containing both primary amine and primary hydroxyl group is 1:1 – 1:2.

[0025] Preferably, the solvent is one or more of water, ethanol, n-propanol, isopropanol, N,N-dimethylformamide, tetrahydrofuran, acetone, and dimethyl sulfoxide.

[0026] Preferably, the solvent is removed after standing at 40 - 70 °C under negative pressure for 8 - 24 h.

[0027] Compared with the prior art, the present invention has the following advantages and effects:

[0028] 1. The preparation of the bio - based polyurethane chain extender containing a single imine bond of the present invention uses biomass vanillin as a raw material. Through molecular design, a bio - based polyurethane chain extender with only a single imine bond in its structure is developed. Due to its structural characteristics, the polyurethane prepared from this chain extender will not have the situation that small molecules are lost and the number of imine bonds is reduced during use, which affects the performance of the material, ensuring the repeated self - healing performance and degradation performance of the material.

[0029] 2. The polyurethane material prepared from the bio - based polyurethane chain extender containing a single imine bond of the present invention can be rapidly repaired at 60 °C and can be degraded under the condition of 0.1 mol / L acidic condition. The conditions required for its self - healing and degradation are mild, with low energy consumption and little pollution.

[0030] 3. By changing the amine substances used in the preparation of the bio - based chain extender of the present invention, the molecular structure of the polymer molecular chain can be appropriately adjusted. Different amine substances have different steric hindrances, which will affect the movement ability and crystallization ability of the microscopic polymer molecular chain, thereby realizing the regulation of the macroscopic mechanical properties of the material to meet the usage requirements under different environmental conditions.

[0031] 4. The synthesis process of the bio - based polyurethane chain extender containing a single imine bond of the present invention is simple, the conditions are mild, the raw materials are easy to obtain, the cost is low, and a green and environmentally friendly solvent system can be selected, which is easy to realize large - scale production and use.

[0032] 5. Compared with related self - healing polyurethanes, the polyurethane prepared from this chain extender has excellent repeatable repair performance, enabling the material to achieve multiple damage - repair cycles. Using this chain extender to prepare materials in a high - loss working environment can greatly improve the safety reliability and service life of the materials. Description of the Drawings

[0033] Figure 1 It is the nuclear magnetic hydrogen spectrum of vanillin glycidyl ether in Example 1.

[0034] Figure 2 It is the nuclear magnetic hydrogen spectrum of the vanillin derivative after epoxy ring - opening of vanillin in Example 1.

[0035] Figure 3 It is the nuclear magnetic hydrogen spectrum of the bio - based polyurethane chain extender in Example 1. Detailed Embodiments

[0036] To better understand the present invention, the present invention is described below in conjunction with specific embodiments. However, the embodiments do not constitute a limitation on the protection scope of the claims of the present invention. Based on the embodiments, other embodiments obtained by those skilled in the art without creative labor all fall within the protection scope of the present invention.

[0037] The present invention epoxidizes biomass vanillin to obtain vanillin-based glycidyl ether, then uses a substance containing secondary amine to ring-open the epoxy group in a mixed solvent, and uses a substance containing both primary amine and primary hydroxyl group to react with the aldehyde group. After that, the solvent is removed by standing still under vacuum conditions at 40 - 70 °C for 8 - 24 h, and a bio-based polyurethane chain extender containing dynamic imine bonds is prepared. Since the chain extender contains dynamic imine bonds, excellent self-healing performance and degradation performance can be imparted to the polyurethane material. The bio-based polyurethane chain extender contains only a single imine bond in its structure, and after being incorporated into the polyurethane main chain, there will be no phenomenon of small molecule loss causing a reduction in the number of imine bonds and a decrease in mechanical properties. The application of this chain extender can effectively increase the number of repeated self-healing cycles of the damaged-repaired material, so that the material can still have sufficient safety and reliability in harsh and complex working environments such as high loss, and has a long service life.

[0038] The relevant test methods in the examples of the present invention are as follows:

[0039] For the mechanical property test, a universal material testing machine is used to characterize the tensile properties of the original sample and the repaired sample. The sample film with a thickness of 0.5 - 0.8 mm is cut into type 3 dumbbell-shaped specimens according to GB / T 528 - 2009, with a size of 4 × 75 mm, a gauge length of 16 mm, a tensile rate of 500 mm / min, a test temperature of 25 ± 2 °C, and a humidity of 60 ± 10%. Each sample is repeated at least 3 times, and the average value is taken.

[0040] For the self-healing performance test, the specimens are cut into type 3 dumbbell-shaped specimens according to the national standard GB / T 528 - 2009. After the specimens are cut in half, they are placed in an oven at 60 °C for 4 h under the condition of keeping the cut surfaces in contact to obtain the corresponding repaired specimens. The tensile strength of the specimen before repair is denoted as σ1, the tensile strength of the specimen after repair is denoted as σ2, and the self-healing efficiency is denoted as η, where η = σ2 / σ1 × 100%; reference can be made to Chinese Patent Application CN112979919A.

[0041] For the degradation performance test, 2.0 - 2.5 g of polyurethane sample film with a thickness less than 2 mm is taken, and its mass is denoted as m1. The sample is placed in a 0.1 mol / L hydrochloric acid solution and left standing at 25 °C for 24 h, then taken out. It is left standing in an oven at 60 °C for 24 h and weighed, denoted as m2. The degradation rate is δ = (m1 - m2) / m1 × 100%.

[0042] Example 1

[0043] A preparation method of a bio-based polyurethane chain extender containing a single imine bond includes the following steps:

[0044] (1) Synthesis of vanillin-based glycidyl ether: 60.86 g of vanillin (0.40 mol), 185.04 g of epichlorohydrin (2.00 mol) and 2.27 g of triethylbenzylammonium chloride (0.01 mol) were mixed and heated to 70 °C for reaction for 4 h. Subsequently, the temperature was lowered to 20 °C and 100.00 g of 40 wt% aqueous sodium hydroxide solution (1.00 mol) was added dropwise within 0.5 h. After the addition was completed, 100.00 g of ethanol was added for dilution, and the reaction continued for 1 h after dilution. After the reaction was completed, the product was washed 3 times with deionized water. Finally, 60.35 g of vanillin-based glycidyl ether was obtained, and the yield was about 73.51%. The 1H NMR spectrum of vanillin-based glycidyl ether is as shown in Figure 1 . It can be seen that the absorption peak representing the phenolic hydroxyl hydrogen in the figure has disappeared, and at the same time, the characteristic absorption peak representing the epoxy group has appeared, proving that the epoxy group has been successfully grafted.

[0045] (2) Synthesis of vanillin derivative after epoxy ring opening: 8.32 g of vanillin-based glycidyl ether (0.04 mol) was dissolved in 100 g of 1.83 wt% aqueous dimethylamine solution (0.04 mol). After reacting at 30 °C for 1 h, water and the remaining raw materials were removed under vacuum, and the vanillin derivative after epoxy ring opening was obtained. The 1H NMR spectrum of the vanillin derivative after epoxy ring opening is as shown in Figure 2 . It can be seen in the figure that the characteristic peak of the epoxy group has disappeared, and at the same time, the absorption peak representing the dimethylamine methyl group has appeared, proving that dimethylamine has successfully opened the epoxy group.

[0046] (3) Preparation method of bio-based polyurethane chain extender: 10.13 g of vanillin derivative after epoxy ring opening (0.04 mol) was dissolved in ethanol. After the solution was homogeneous and clear, 2.44 g of ethanolamine (0.04 mol) was added and stirred at 30 °C for 0.5 h. After the reaction was completed, the solvent and the remaining raw materials were removed under vacuum at 70 °C for 8 h, and finally a bio-based chain extender that can enable polyurethane to achieve self-repair and degradation was obtained. Its 1H NMR spectrum is as shown in Figure 3 . It can be seen that the absorption peak representing the aldehyde group hydrogen has basically disappeared, and at the same time, the characteristic absorption peak of ethanolamine has appeared, proving that ethanolamine has been successfully grafted, and the bio-based polyurethane chain extender containing a single imine bond has been successfully synthesized.

[0047] The 1H NMR spectra of vanillin glycidyl ether, the intermediate after vanillin epoxy ring opening, and the bio-based polyurethane chain extender in the following examples are basically similar to Figures 1 - 3 and will not be provided one by one.

[0048] Example 2

[0049] A preparation method of a bio-based polyurethane chain extender containing a single imine bond, comprising the following steps:

[0050] (1) Synthesis of vanillin - based glycidyl ether: 60.86 g of vanillin (0.40 mol), 370.80 g of epichlorohydrin (4.00 mol) and 1.85 g of trimethylbenzylammonium chloride (0.01 mol) were mixed and heated to 90 °C for reaction for 2 h. Subsequently, the temperature was lowered to 40 °C and 100.00 g of 40 wt% aqueous potassium hydroxide solution (0.71 mol) was added dropwise within 0.5 h. After the addition was completed, 100.00 g of ethanol was added for dilution, and the reaction continued for 1 h after dilution. After the reaction was completed, the product was washed 3 times with deionized water. Finally, 63.51 g of vanillin - based glycidyl ether was obtained, and the yield was approximately 77.36%.

[0051] (2) Synthesis of vanillin derivative after epoxy ring - opening: 8.32 g of vanillin - based glycidyl ether (0.04 mol) was dissolved in n - propanol, then 29.52 g of diethylamine (0.4 mol) was added, and after reacting at 50 °C for 8 h, water was removed under vacuum to obtain the vanillin derivative after epoxy ring - opening.

[0052] (3) Preparation method of bio - based polyurethane chain extender: 10.13 g of vanillin derivative after epoxy ring - opening (0.04 mol) was dissolved in n - propanol. After the solution was homogeneous and clear, 6.00 g of propanolamine (0.08 mol) was added and stirred at 50 °C for 4 h. After the reaction was completed, the solvent and excessive propanolamine were removed under vacuum at 40 °C for 24 h to finally obtain a bio - based polyurethane chain extender containing a single imine bond that can enable the polyurethane to achieve self - repair and degradation.

[0053] Example 3

[0054] A preparation method of a bio - based polyurethane chain extender containing a single imine bond, comprising the following steps:

[0055] (1) Synthesis of vanillin - based 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 and heated to 85 °C for reaction for 2.5 h. Subsequently, the temperature was lowered to 25 °C and 100.00 g of 40 wt% aqueous calcium hydroxide solution (0.54 mol) was added dropwise within 0.5 h. After the addition was completed, 100.00 g of ethanol was added for dilution, and the reaction continued for 1 h after dilution. After the reaction was completed, the product was washed 3 times with deionized water. Finally, 62.39 g of vanillin - based glycidyl ether was obtained, and the yield was approximately 75.99%.

[0056] (2) Synthesis of vanillin derivative after epoxy ring - opening: 8.32 g of vanillin - based glycidyl ether (0.04 mol) was dissolved in tetrahydrofuran, then 29.52 g of diethylamine (0.4 mol) was added, and after reacting at 50 °C for 8 h, tetrahydrofuran was removed under vacuum to obtain the vanillin derivative after epoxy ring - opening.

[0057] (3) Preparation method of bio-based polyurethane chain extender: Dissolve 10.13 g of the vanillin derivative after epoxy ring-opening (0.04 mol) in tetrahydrofuran. After the solution becomes homogeneous and clear, add 7.13 g of 2-aminobutanol (0.08 mol) and stir at 50 °C for 4 h. After the reaction is completed, vacuum for 12 h at 50 °C to remove excessive tetrahydrofuran, and finally obtain a bio-based polyurethane chain extender containing a single imine bond that can enable the polyurethane to achieve self-healing and degradation.

[0058] Example 4

[0059] A preparation method of a bio-based polyurethane chain extender containing a single imine bond, comprising the following steps:

[0060] (1) Synthesis of vanillin-based glycidyl ether: Mix 60.86 g of vanillin (0.40 mol), 227.56 g of epichlorohydrin (3.00 mol) and 2.11 g of tetraethylammonium bromide (0.01 mol), and heat up to 85 °C for reaction for 2.5 h. Subsequently, cool down to 25 °C and dropwise add 100.00 g of 40 wt% sodium hydroxide aqueous solution (1.00 mol) within 0.5 h. After the dropping is completed, add 100.00 g of ethanol for dilution, and continue the reaction for 1 h after dilution is completed. After the reaction is completed, wash the product 3 times with deionized water. Finally, 66.76 g of vanillin-based glycidyl ether is obtained, and the yield is about 81.32%.

[0061] (2) Synthesis of vanillin derivative after epoxy ring-opening: Dissolve 8.32 g of vanillin-based glycidyl ether (0.04 mol) in tetrahydrofuran, then add 25.85 g of diethylamine (0.2 mol), react at 40 °C for 8 h, and then remove tetrahydrofuran under vacuum to obtain the vanillin derivative after epoxy ring-opening.

[0062] (3) Preparation method of bio-based polyurethane chain extender: Dissolve 10.13 g of the vanillin derivative after epoxy ring-opening (0.04 mol) in tetrahydrofuran. After the solution becomes homogeneous and clear, add 7.13 g of 2-aminobutanol (0.08 mol) and stir at 40 °C for 2 h. After the reaction is completed, remove the solvent, excessive tetrahydrofuran and raw materials under vacuum, and finally obtain a bio-based polyurethane chain extender containing a single imine bond that can enable the polyurethane to achieve self-healing and degradation.

[0063] Example 5

[0064] A preparation method of a bio-based polyurethane chain extender containing a single imine bond, comprising the following steps:

[0065] (1) Synthesis of vanillin - based 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 the temperature was raised to 85 °C for reaction for 2.5 h. Subsequently, the temperature was lowered to 25 °C and 100.00 g of 40 wt% aqueous sodium hydroxide solution (1.00 mol) was added dropwise within 0.5 h. After the addition was completed, 100.00 g of ethanol was added for dilution, and the reaction continued for 1 h after dilution. After the reaction was completed, the product was washed 3 times with deionized water. Finally, 59.21 g of vanillin - based glycidyl ether was obtained, and the yield was about 72.12%.

[0066] (2) Synthesis of vanillin derivative after epoxy ring - opening: 8.32 g of vanillin - based glycidyl ether (0.04 mol) was dissolved in acetone, and then 25.85 g of diethylamine (0.2 mol) was added. After reacting at 30 °C for 8 h, acetone was removed under vacuum, and the vanillin derivative after epoxy ring - opening could be obtained.

[0067] (3) Preparation method of bio - based polyurethane chain extender: 10.13 g of vanillin derivative after epoxy ring - opening (0.04 mol) was dissolved in acetone. After the solution was homogeneous and clear, 5.35 g of 2 - aminobutanol (0.06 mol) was added and stirred at 40 °C for 2 h. After the reaction was completed, the solvent, excessive acetone and raw materials were removed under vacuum. Finally, a bio - based polyurethane chain extender containing a single imine bond that can enable polyurethane to achieve self - repair and degradation was obtained.

[0068] Application Example

[0069] A preparation method of bio - based polyurethane

[0070] 20 g of polytetrahydrofuran with an average molecular weight of 1000 (0.02 mol) was dehydrated under vacuum at 120 °C for 2 h and then cooled to 60 °C. After cooling, 15.74 g of 4,4'-dicyclohexylmethane diisocyanate (0.06 mol) and 25 μL of dibutyltin dilaurate solution with a solvent of N,N - dimethylformamide and a concentration of 0.1 g / mL were added. During the stirring reaction under N2 protection, the NCO content was monitored by titration. After the prepolymerization was completed, 11.85 g of the bio - based polyurethane chain extender prepared in Example 1 (0.04 mol) and 500 μL of the prepared dibutyltin dilaurate catalyst solution were added and the temperature was raised to 75 °C and continuously stirred for 4 h. Finally, 50 mL of N,N - dimethylformamide was added to reduce the viscosity. The prepared polyurethane solution was poured into a polypropylene mold and dried in a forced - air oven at 70 °C for 24 h, and then continued to be dried in a vacuum oven at 70 °C for 24 h. Finally, a transparent polyurethane film sample was obtained.

[0071] Comparative Example

[0072] Take 30.43 g of vanillin (0.20 mol) and 10.00 g of sodium hydroxide (0.25 mol), dissolve them in 200 mL of absolute ethanol, add 15 mL of 1,2-dibromoethane and 2.49 g of potassium iodide (0.15 mol) as a phase transfer catalyst. React at 60 °C for 24 h to obtain vanillin dimer. Dissolve 12.21 g of ethanolamine (0.30 mol) and 34.43 g of vanillin dimer (0.10 mol) in 200 mL of ethanol, react at 60 °C for 4 h, and then wash 5 times with deionized water to obtain a bio-based chain extender.

[0073] Under the condition of 120 °C, dehydrate 20 g of polytetrahydrofuran with an average molecular weight of 1000 (0.02 mol) in vacuum for 2 h, and then cool down to 60 °C. After the cooling is completed, add 15.74 g of 4,4'-dicyclohexylmethane diisocyanate (0.06 mol) and 25 μL of a dibutyltin dilaurate solution with a solvent of N,N-dimethylformamide and a concentration of 0.1 g / mL. Monitor the NCO content by titration during the stirring reaction under N2 protection. After the prepolymerization is completed, add 12.24 g of the bio-based polyurethane chain extender prepared in the previous step (0.04 mol) and 500 μL of the prepared dibutyltin dilaurate catalyst solution, and raise the temperature to 75 °C and continue to stir and react for 4 h. Finally, add 50 mL of N,N-dimethylformamide to reduce the viscosity. Pour the prepared polyurethane solution into a polypropylene mold, dry it in a forced-air oven at 70 °C for 24 h, and then continue to dry it in a vacuum oven at 70 °C for 24 h to finally obtain a transparent polyurethane film sample.

[0074] Table 1 shows the test results of various properties of Comparative Example 1 and Comparative Example 2.

[0075] Table 1

[0076]

[0077] The polyurethane in the application example is prepared using the bio-based polyurethane chain extender prepared in Example 1 of the present invention. This bio-based polyurethane chain extender contains only a single imine bond. In the comparative example, the polyurethane uses biomass vanillin as the raw material. First, vanillin dimer is prepared, and then the chain extender is prepared by reacting with ethanolamine. Both ends of the vanillin dimer in this chain extender are imine bonds. The ratio of polyether polyol, isocyanate, and bio-based chain extender used in the preparation of the two polyurethanes in the application example and the comparative example is the same. As can be seen from Table 1, the mechanical strengths of the two polyurethanes are not very different and are basically the same. At the same time, after cutting the splines of the two polyurethane materials with a blade, the samples can complete self-repair within 4 hours at 60°C. Tests found that the self-repair efficiencies of the two materials can reach relatively high levels, 94.68% and 95.74% respectively. It is proved that the material can achieve self-repair under mild conditions and can meet most usage requirements.

[0078] In addition, when the material is statically placed in a 0.1 mol / L hydrochloric acid solution, most of the samples can be degraded after 24 hours, and the degradation rate of the samples can reach 83.56%. It shows that the degradation conditions of the surface material are mild, and the degradation rate can also reach a relatively high level. Thus, it can greatly reduce the degree of environmental pollution after the material is discarded.

[0079] Generally speaking, the imine bond content in the polyurethane of the application example is only half of that of the comparative example, but its self-repair efficiency degradation rate after the first damage is equivalent to that of the comparative example. It is proved that the polyurethane prepared using the chain extender of the present invention can maintain excellent self-repair performance and degradation performance. However, as the number of repair times increases, when the damage is repaired ten times, the strength of the polyurethane prepared in the comparative example is only 48.67% compared with the initial strength, and its self-repair efficiency drops significantly. While the self-repair efficiency of the polyurethane prepared in the application example is still at a relatively high level, reaching 88.46%. This is because during the multiple damage repair process, since both ends of the vanillin dimer in the comparative example are imine bonds, and it itself has a relatively strong cohesive energy, it gradually crystallizes and precipitates during the breaking and recombination of the imine bonds, resulting in the loss of imine bonds, thus greatly reducing the self-repair efficiency. In the application example of the present invention, since its chain extender structure contains only a single imine bond, there will be no loss of small molecules during the repair process, which will reduce the imine bonds and affect the self-repair efficiency. Therefore, the number of repeated repairs of the material can be greatly increased, thereby further extending the service life of the material. Moreover, this chain extender uses biomass vanillin as the raw material, can be prepared at a relatively low temperature, and the raw materials and various solvents used can be recycled, which can greatly reduce costs and the degree of environmental pollution, and has the potential for large-scale production.

[0080] The present invention uses biomass vanillin as a raw material to prepare a bio-based chain extender containing an imine bond, which can enable the material to achieve multiple repeated self-repairs, and the self-repair performance will not decrease with the number of damage-repair cycles. For improving the safety reliability and service life of materials in a high-loss environment, the application of bio-based raw materials and their degradable properties can also reduce the dependence on fossil raw materials and alleviate environmental pollution problems.

[0081] Therefore, the bio-based polyurethane chain extender prepared by the present invention can not only enable the material to be degraded, but also endow the material with the performance of multiple self-repairs and extend the service life of the material.

Claims

1. A bio-based polyurethane chain extender containing a single imine bond, characterized in that, It has the following structural formula: Among them, R1 is one of the following groups: R2 is one of the following groups:

2. The preparation method of a bio-based polyurethane chain extender containing a single imine bond according to claim 1, characterized in that It includes the following steps: (1) Mix vanillin, epichlorohydrin and a phase transfer catalyst, heat up to 70 - 90 °C and react for 2 - 4 h, then cool down to 20 - 40 °C, and then add a strong base to convert the phenolic hydroxyl group of vanillin into a glycidyl ether bond to obtain vanillin-based glycidyl ether; (2) Add vanillin-based glycidyl ether and a substance containing secondary amine into a solvent system, and react at room temperature for 1 - 8 h to obtain a vanillin derivative after ring-opening of the epoxy group; (3) React the vanillin derivative after ring-opening of the epoxy group with a substance containing both primary amine and secondary hydroxyl group in a solvent at room temperature for 0.5 - 4 h, and then remove the solvent and excess raw materials to obtain a bio-based polyurethane chain extender containing a single imine bond.

3. The preparation method of a bio-based polyurethane chain extender containing a single imine bond according to claim 2, characterized in that: The molar ratio of vanillin to epichlorohydrin is 1:5 - 1:

10.

4. The preparation method of a bio-based polyurethane chain extender 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.

5. The preparation method of a bio-based polyurethane chain extender containing a single imine bond according to claim 2, characterized in that: The substance containing secondary amine is one or more of dimethylamine, N-ethylmethylamine, N-ethylpropylamine, N-ethylisopropylamine, diethylamine, dipropylamine and di-sec-butylamine.

6. The preparation method of a bio-based polyurethane chain extender containing a single imine bond according to claim 2, characterized in that: The molar ratio of vanillin-based glycidyl ether to the substance containing secondary amine is 1:1 - 1:

10.

7. The preparation method of a bio-based polyurethane chain extender containing a single imine bond according to claim 2, wherein: The substance containing both primary amine and primary hydroxyl group is one or more of ethanolamine, propanolamine, 2-amino-1-propanol, 1-amino-2-propanol, 2-amino-1-butanol and 4-amino-1-butanol.

8. The preparation method of a bio-based polyurethane chain extender containing a single imine bond according to claim 2, characterized in that: The molar ratio of the vanillin derivative after ring-opening of the epoxy group to the substance containing both primary amine and primary hydroxyl group is 1:1 - 1:

2.

9. The preparation method of a bio-based polyurethane chain extender containing a single imine bond according to claim 2, characterized in that: The solvent is one or more of water, ethanol, n-propanol, isopropanol, N,N-dimethylformamide, tetrahydrofuran, acetone and dimethyl sulfoxide.

10. The preparation method of a bio-based polyurethane chain extender containing a single imine bond according to claim 2, characterized in that: The solvent is removed after standing at 40 - 70 °C under negative pressure for 8 - 24 h.

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