Boronic ester-based polyurethanes, methods for their preparation, renewable polyurethane materials comprising the same and applications

Abstract

The application discloses a borate-based polyurethane and a preparation method thereof, a renewable polyurethane material containing the borate-based polyurethane and application of the borate-based polyurethane, and a processable and renewable polyurethane with excellent hydrolysis / thermal stability is prepared. Due to the boron-nitrogen bidentate coordination in the borate compound M and the synergistic effect of the imine bond and the borate group, the renewable polyurethane material containing the borate group has high stability to thermal stimulation, water or a hydroxyl-containing compound, and the application range of the renewable polyurethane material is widened. The obtained renewable polyurethane material can be completely repaired and recycled under relatively mild conditions, so that an environment-friendly polymer material is obtained, the renewable polyurethane material is a re-upgrade of traditional polymers, and the continuous generation of plastic waste can be expected to be alleviated and curbed.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, and relates to a borate ester-based polyurethane and its preparation method, as well as renewable polyurethane materials containing the same and their applications. Background Technology

[0002] Polyurethane (PU) is a class of polymers characterized by urethane bonds as the main chain unit. Its unique and flexible molecular chain structure and aggregate structure make it one of the most widely used polymer materials. However, while the extremely stable urethane groups endow polyurethane materials with excellent properties, they also make them difficult to recycle, reprocess, and biodegrade. Large amounts of polyurethane waste cause serious environmental pollution and resource waste, becoming a problem that requires the joint efforts of all humankind. Therefore, it is necessary to develop novel polyurethane materials with reprocessability and repairability through chemical structure design.

[0003] To overcome the shortcomings of traditional thermosetting polyurethanes, introducing dynamic covalent bonds into the polymer crosslinking network has become an effective means of endowing thermosetting polyurethanes with renewability, reprocessability, and repairability. The efflux of borate ester bonds in transesterification endows polymer materials with renewable, processable, and repairable properties, and no catalyst is required during the formation of borate ester groups (CN108484939 A and CN108341944 A). Weng Qiumei et al. prepared a hybrid dynamic polymer using the dynamic reversibility of cyclic organic borate ester groups and supramolecular hydrogen bonds, giving the polymer self-healing and recyclability; details can be found in Chinese patent application publication number CN108341943A.

[0004] However, common borate esters are prone to hydrolysis and alcoholysis, making it difficult to obtain materials with high stability and strength. Therefore, improving the stability of borate esters to media (especially alcohols and water) and heat is key to expanding the application range of borate ester dynamic covalent bond materials. In the field of organic chemistry, the principle of stabilizing borate esters through nitrogen coordination has been applied to the protection and deprotection of organoboronic acid functional groups (Journal of the American Chemical Society, 2007, 129(21): 6716-6717). Polyurethane materials based on nitrogen-boron internally coordinated cyclic borate ester compounds synthesized using this principle have higher stability and mechanical properties, as shown in Chinese patent application CN109897148A. However, the improvement in material stability and heat resistance by a single dynamic covalent bond is ultimately limited. Combining two or more dynamic covalent bonds with complementary properties can effectively compensate for the shortcomings of single dynamic covalent bond crosslinked polymers. Imine bonds, due to their electron-rich N atoms, are one of the ideal candidates to form stable multiple covalent bonds with borate esters. Lin et al. reported the preparation of interpenetrating covalent adaptive materials using imine bonds and borate ester groups, focusing on the effects of various dynamic covalent bonds on the mechanical properties and reprocessing properties of the materials (Polymer Chemistry, 2021, 12(28):4052-4062). However, the tensile strength and Young's modulus of these interpenetrating networks with various dynamic covalent bonds cannot meet the requirements for certain mechanical strength and have poor thermal stability.

[0005] In summary, although N→B coordination has been shown to improve the stability of borate ester-based polyurethanes, synthesizing polyurethanes with high hydrolytic / thermal stability, good mechanical properties, and reprocessability remains a major challenge. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention aims to provide a borate ester-based polyurethane and its preparation method, a renewable polyurethane material containing the same and its application. The resulting renewable polyurethane material has excellent hydrolytic / thermal stability, high mechanical strength, and is repairable and remodelable, and can be recycled multiple times.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A borate ester-based polyurethane, with the following structural formula:

[0009]

[0010] Wherein, G is the same or different, and each is independently selected from substituted or unsubstituted alkylene groups with 1 to 10 carbon atoms, substituted or unsubstituted aryl groups with 6 to 18 carbon atoms, or substituted or unsubstituted cycloalkylene groups with 3 to 10 carbon atoms; m is the number of G, and m is selected from 1, 2 or 3.

[0011] The substituents of G may be the same or different, and each is independently selected from hydrogen, alkyl with 1 to 10 carbon atoms or aryl with 6 to 18 carbon atoms; n is selected from 1, 2, 3, 4 or 5;

[0012] in," "" indicates that the linker bond is connected to the rest of the compound molecule.

[0013] Furthermore, the (G)m is selected from any of the following structures:

[0014] , or ;in," " " represents a chemical bond.

[0015] The preparation method of borate ester-based polyurethane includes the following steps:

[0016] (1) Dissolve 100 parts by mass of diamine and 250-600 parts by mass of o-hydroxybenzaldehyde in an organic solvent. Slowly add the diamine solution to the o-hydroxybenzaldehyde solution and react at a preset temperature. After the reaction is completed, distill the mixture and cool it to precipitate the solid. Collect the solid product by filtration and recrystallize the obtained solid product to obtain Schiff base compound S.

[0017] (2) Dissolve 100 parts of the obtained Schiff base compound S and (100~150) hydroxymethylphenylboronic acid in an organic solvent by mass, stir thoroughly until a homogeneous solution is formed, and react at a preset temperature; after the reaction is completed, the solid product is obtained by distillation and then by filtration, and the obtained solid product is recrystallized to obtain the N→B bidentate coordinated borate ester compound M.

[0018] (3) Dissolve the obtained borate compound M and isocyanate compound in an organic solvent and stir thoroughly to form a homogeneous solution as a presol. The feeding ratio of borate compound M to isocyanate compound is determined according to the molar ratio of active hydroxyl hydrogen to isocyanate group of 1:(0.8~1.5). After the presol is subjected to molding treatment, borate-based polyurethane is obtained.

[0019] Furthermore, the diamine is one of methyldiamine, ethylenediamine, propylenediamine, butyldiamine, and pentanediamine;

[0020] The hydroxymethylphenylboronic acid is one or more mixtures of 2-hydroxymethylphenylboronic acid, 3-hydroxymethylphenylboronic acid and 4-hydroxymethylphenylboronic acid;

[0021] The isocyanate compound in step (3) is one or a mixture of hexamethylene diisocyanate trimer, toluene diisocyanate trimer and isophorone diisocyanate trimer.

[0022] Furthermore, in step (1), the dissolution temperature of the diamine and o-hydroxybenzaldehyde is 30~60℃; the temperature at which they precipitate is -20~20℃; and the reaction conditions at the preset temperature are: reacting at 0~60℃ for 1~10 h.

[0023] The reaction conditions in step (2) at the preset temperature include: reacting at 80~160℃ for 1~10 h.

[0024] A renewable polyurethane material comprising, as described above, borate-based polyurethane, or comprising borate-based polyurethane prepared by the method described above; the renewable polyurethane material is a renewable polyurethane plastic or a renewable polyurethane coating.

[0025] Furthermore, it also includes performance additives; said performance additives include defoamers, antioxidants, or color masterbatches.

[0026] Furthermore, the method for molding and processing the renewable polyurethane plastic is as follows:

[0027] First, the pre-solution described above is gelled at 60~100℃ for 1~20 h, and then vacuumed to obtain a sample; the obtained sample is crushed to obtain renewable polyurethane plastic powder.

[0028] The vacuuming process includes: first heating to 120~180℃, holding at that temperature for 5~10 hours, then stopping heating and cooling down to below 60℃, and finally stopping the vacuuming process.

[0029] The renewable polyurethane plastic is recycled through compression molding and solid crushing.

[0030] Furthermore, the method for molding the renewable polyurethane coating is as follows:

[0031] First, the presol as described in any one of claims 3 to 5 is reacted at 60 to 80°C for 20 to 60 min to obtain a uniform and transparent solution; the obtained uniform and transparent solution is coated on a substrate and kept at 60 to 100°C for 7 to 14 days to obtain a renewable polyurethane coating.

[0032] The regenerable polyurethane coating achieves self-healing by being kept at 150~200℃ for 5~24 hours.

[0033] Applications of renewable polyurethane materials as heat-resistant and fire-resistant materials or repairable coatings.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The borate-based polyurethane of the present invention is a processable and renewable polyurethane with excellent hydrolytic / thermal stability. Due to the bidentate coordination of boron and nitrogen in the borate compound M and the synergistic effect of the imine bond and the borate group, the renewable polyurethane material containing the borate group has high stability against thermal stimulation, water or hydroxyl-containing compounds, thus broadening the application range of renewable polyurethane materials.

[0036] (2) The renewable polyurethane material prepared by the present invention also exhibits good mechanical properties comparable to those of traditional polyurethane, with tensile strength reaching 34.7~40.1 MPa or above and Young's modulus reaching 1.04~1.21 GPa or above.

[0037] (3) Due to the high hydrolytic and thermal stability of borate compound M, the borate compound M in this invention does not require the use of a catalyst or timely removal of water generated in the system during preparation, which can reduce the complexity of the synthesis process and provide convenience for the production of renewable polyurethane materials with high stability and good mechanical properties.

[0038] (4) Renewable polyurethane materials can be fully repaired and recycled under relatively mild conditions, thus obtaining environmentally friendly polymer materials. This is a further upgrade of traditional polymer development and is expected to alleviate and curb the continuous generation of plastic waste. Attached Figure Description

[0039] Figure 1. M as described in Embodiment 1 of the present invention 1 H NMR spectrum;

[0040] Figure 2. FTIR spectrum of the m-PU plastic powder described in Example 1 of the present invention;

[0041] Figure 3. Schematic diagram of the crushing-molding process of m-PU plastic powder as described in Embodiment 1 of the present invention;

[0042] Figure 4 shows the thermogravimetric curve of the m-PU plastic powder described in Embodiment 1 of the present invention;

[0043] Figure 5 shows the stress-strain curve of the m-PU plastic block described in Embodiment 1 of the present invention after being immersed in water for 48 hours. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0045] The borate ester compound M prepared by this invention can also be introduced into thermosetting resin systems such as epoxy resin, phenolic resin, benzoxazine resin, and bismaleimide resin, giving traditional thermosetting resins the properties of being reprocessable and recyclable.

[0046] A first aspect of the present invention provides a borate-based polyurethane, which is a renewable polyurethane based on dynamic covalent crosslinking of stable borate groups containing N→B bidentate coordination, wherein the dynamic covalent crosslinking is achieved by a highly stable borate compound; the structural formula of the borate-based polyurethane is:

[0047] ;

[0048] Wherein, G may be the same or different, and each is independently selected from substituted or unsubstituted alkylene groups having 1 to 10 carbon atoms, substituted or unsubstituted aryl groups having 6 to 18 carbon atoms, or substituted or unsubstituted cycloalkylene groups having 3 to 10 carbon atoms; m is the number of Gs, and m is selected from 1, 2, or 3; the substituents of G may be the same or different, and each is independently selected from hydrogen, alkyl groups having 1 to 10 carbon atoms, or aryl groups having 6 to 18 carbon atoms.

[0049] Where n is selected from 1, 2, 3, 4 or 5.

[0050] in," "" indicates that the linker bond is connected to the rest of the compound molecule.

[0051] In this invention, the descriptive terms “each…independently is”, “…independently is”, and “…independently selected” are interchangeable and should be interpreted broadly. They can mean that the specific options expressed by the same symbols in different groups do not affect each other, or that the specific options expressed by the same symbols in the same group do not affect each other.

[0052] In this invention, the term "substituted or unsubstituted" means that a functional group may or may not have substituents. A "substituted" functional group may be substituted by one or more substituents; when two substituents are attached to the same atom, the two substituents may exist independently or be connected to each other to form a ring with said atom; when two adjacent substituents are present on a functional group, the two adjacent substituents may exist independently or fuse with the functional group to which they are attached to form a ring.

[0053] In this invention, the number of carbon atoms in a substituted or unsubstituted functional group refers to the total number of carbon atoms. For example, if G is selected from an arylene with 7 substituted carbon atoms, then the total number of carbon atoms in the arylene and its substituents is 7.

[0054] In this invention, The structure illustrates that chemical bonds can be attached to any position on the benzene ring, as shown below:

[0055] In this invention, a non-positioned connecting key refers to a single bond extending from a ring system. The term "" indicates that one end of the linker bond can connect to any position in the ring system that the bond penetrates, while the other end connects to the rest of the compound molecule.

[0056] In specific embodiments of the present invention, the substituted or unsubstituted alkyl group having 1 to 10 carbon atoms can be a straight-chain alkyl group having 1 to 10 carbon atoms, or a branched alkyl group having 3 to 10 carbon atoms. Specific examples of substituted or unsubstituted alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, n-hexyl, heptyl, n-octyl, nonyl, decyl, etc.

[0057] In a specific embodiment of the present invention, the alkylene group referred to refers to a divalent group formed by the further loss of a hydrogen atom from an alkyl group.

[0058] In specific embodiments of the present invention, substituted or unsubstituted aryl groups having 6 to 18 carbon atoms are included, but are not limited to, phenyl, naphthyl, biphenyl, terphenyl, etc.

[0059] In a specific embodiment of the present invention, the aryl group refers to a divalent group formed by the further loss of a hydrogen atom from an aryl group.

[0060] In specific embodiments of the present invention, substituted or unsubstituted cycloalkyl groups having 3 to 10 carbon atoms are used, including but not limited to cyclopropane, cyclopentane, and cyclohexane.

[0061] In a specific embodiment of the present invention, the cycloalkylene group refers to a divalent group formed by the further loss of a hydrogen atom from an aryl group.

[0062] In this invention, (G) m Choose any one of the following structures:

[0063] , or .

[0064] In a specific embodiment of the present invention, the borate-based polyurethane may be selected from the group consisting of the following compounds:

[0065]

[0066] or

[0067]

[0068] or

[0069]

[0070] or

[0071]

[0072] or

[0073]

[0074] or

[0075]

[0076] or

[0077] ;

[0078] in," "" indicates that the linker bond is connected to the rest of the compound molecule.

[0079] The borate ester-based polyurethane of the present invention is prepared by the following method:

[0080] (1) Synthesis of Schiff base compound S

[0081] First, a highly stable bidentate ligand Schiff base compound S was synthesized. The synthetic method is as follows:

[0082] By mass, 100 parts of diamine and 250-600 parts of o-hydroxybenzaldehyde were dissolved in an organic solvent at 30-60℃. The diamine solution was slowly added dropwise to the o-hydroxybenzaldehyde solution and stirred thoroughly. The reaction was carried out completely at a preset temperature. Most of the solvent was removed by distillation. The temperature was lowered to -20 to 20℃. After the solid precipitated, the solid product was obtained by filtration and recrystallization to obtain Schiff base compound S.

[0083] In a specific embodiment of the present invention, the chemical structural formula of Schiff base compound S is as follows:

[0084] ; where n is selected from 1, 2, 3, 4 or 5.

[0085] The diamine is one of methyldiamine, ethylenediamine, propylenediamine, butyldiamine, and pentanediamine.

[0086] The organic solvent is one or a mixture of methanol, ethanol, acetone or tetrahydrofuran.

[0087] Specifically, the complete reaction at the preset temperature includes reacting at 0~60℃ for 1~10 h.

[0088] (2) Synthesis of borate ester compound M

[0089] By mass, 100 parts of S and 100-150 parts of hydroxymethylphenylboronic acid are dissolved together in an organic solvent and stirred thoroughly to form a homogeneous solution. The reaction is carried out completely at a preset temperature. Most of the solvent is removed by distillation, and the solid product is obtained by filtration. The N→B bidentate coordinated borate ester compound M is obtained by recrystallization.

[0090] The hydroxymethylphenylboronic acid is one or more mixtures of 2-hydroxymethylphenylboronic acid, 3-hydroxymethylphenylboronic acid and 4-hydroxymethylphenylboronic acid.

[0091] The organic solvent used is one or a mixture of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, and acetonitrile.

[0092] Complete reaction at the preset temperature specifically includes reacting at 80~160℃ for 1~10 h.

[0093] In a specific embodiment of the present invention, when hydroxymethylphenylboronic acid is 4-hydroxymethylphenylboronic acid, the chemical structural formula of the borate ester compound M containing N→B bidentate coordination is:

[0094]

[0095] In a specific embodiment of the present invention, when hydroxymethylphenylboronic acid is 3-hydroxymethylphenylboronic acid, the chemical structural formula of the borate ester compound M containing N→B bidentate coordination is:

[0096]

[0097] In a specific embodiment of the present invention, when hydroxymethylphenylboronic acid is 2-hydroxymethylphenylboronic acid, the chemical structural formula of the borate ester compound M containing N→B bidentate coordination is:

[0098]

[0099] (3) Preparation of borate ester-based polyurethane

[0100] According to the molar ratio of hydroxyl active hydrogen to isocyanate group of 1:(0.8~1.5), borate compound M and isocyanate compound are dissolved in organic solvent and stirred thoroughly to form a homogeneous solution as a presol. After the presol is subjected to molding treatment, borate-based polyurethane is obtained.

[0101] The isocyanate compounds used here are one or more of the trifunctional isocyanate compounds, such as hexamethylene diisocyanate trimer, toluene diisocyanate trimer, or isophorone diisocyanate trimer.

[0102] The organic solvent used is one or a mixture of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, and acetonitrile.

[0103] A second aspect of the present invention provides a renewable polyurethane material comprising the above-described borate ester-based polyurethane:

[0104] Specifically, the renewable polyurethane material is renewable polyurethane (m-PU) plastic.

[0105] The molding process of the above-mentioned renewable polyurethane (m-PU) plastic of the present invention is as follows:

[0106] The pre-solution was kept at 60~100℃ for 1~20 h, and the system gelled. The gel was transferred to a polytetrafluoroethylene tank and then placed in a vacuum oven. Vacuum was drawn (-0.10~-0.06 MPa), the temperature was raised to 120~180℃, and then kept at that temperature for 5~10 h before heating was stopped. When the material temperature dropped below 60℃, the vacuum was stopped, the vacuum oven was restored to normal pressure, the sample was taken out and crushed to obtain renewable polyurethane (m-PU) plastic powder.

[0107] Preferably, the curing and molding process of m-PU resin is carried out in a vacuum oven.

[0108] The above-mentioned renewable polyurethane (m-PU) plastic of the present invention has processability, repairability, and renewability: m-PU plastic powder is placed in a mold and then molded into m-PU resin blocks. After long-term practical use, the m-PU resin blocks can be repaired and recycled by crushing them and then performing a "molding-solid crushing" method.

[0109] Preferably, during the compression molding process, the compression temperature is 150~230℃, the compression time is 30~120 min, and the compression pressure is 10~50 MPa.

[0110] Preferably, when recycling using the "molding-solid crushing" method, the molding temperature is 150~230℃, the molding pressure is 10~100 MPa, and the molding time is 5~300 min, thereby achieving recyclable treatment.

[0111] Specifically, the renewable polyurethane material is a renewable polyurethane (m-PU) coating.

[0112] The curing and molding method for the above-mentioned renewable polyurethane (m-PU) coating of the present invention is as follows:

[0113] The above presol was reacted at 60-80℃ for 20-60 min to obtain a uniform and transparent m-PU solution. The m-PU solution was then scraped, spin-coated or sprayed onto a glass plate or tinplate. The glass plate or tinplate was then placed in a forced-air oven and heated to 60-100℃. After holding at this temperature for 7-14 days, heating was stopped to obtain a renewable polyurethane (m-PU) coating.

[0114] The above-mentioned renewable polyurethane (m-PU) coating of the present invention is repairable: when scratches appear on the surface of the m-PU coating, the m-PU coating can be transferred to a forced-air drying oven, the oven temperature is raised to 150~200℃, and the temperature is kept for 5~24 hours to achieve coating repair.

[0115] For the borate ester-based polyurethane and the renewable polyurethane material containing it described in this invention, relevant additives can be added during the application and construction process according to the performance of the target product. The additives that can be used in conjunction include defoamers, antioxidants, etc.

[0116] The borate-based polyurethane and the renewable polyurethane materials containing it described in this invention can be applied to structural components or protective coatings in the automotive, aerospace, and wind power industries. Specifically, the borate-based polyurethane and the renewable polyurethane materials containing it described in this invention can be used in the preparation and application of heat-resistant, fire-resistant materials or repairable coatings in the automotive, aerospace, and other fields.

[0117] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings:

[0118] Example 1

[0119] Synthesis of S: At 30°C, 9 g of ethylenediamine and 37 g of o-hydroxybenzaldehyde were placed in a 250 mL beaker, and 100 mL of ethanol was added and mixed thoroughly. The mixture was stirred at 30°C for 3 h. After removing most of the solvent by rotary evaporation (60°C, -0.06 MPa), the mixture was cooled to 20°C, filtered through a Buchner funnel, and washed several times with anhydrous ethanol to obtain the crude product. The crude product was added to a certain amount of toluene, heated to 100°C to dissolve it completely, slowly cooled to room temperature, and then cooled in an ice-water bath for 2 h. The mixture was then filtered through a Buchner funnel, and the resulting product was washed three times with dichloromethane and dried under vacuum at 40°C for 5 h to obtain a bright yellow crystalline product with a yield of 90%. 1H NMR (400 MHz, DMSO-d6, δ): 13.35 (s,1H), 8.55 (s, 2H), 7.38 (dd, J = 7.7, 1.7 Hz, 2H), 7.28 (ddd, J = 8.8, 7.5,1.8 Hz, 2H), 6.89-6.79 (m, 4H), 3.88 (s, 4H).

[0120] Synthesis of M: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 10 g of S, 12 g of 4-hydroxymethylphenylboronic acid, and 100 mL of anhydrous N,N-dimethylformamide were added sequentially under a nitrogen atmosphere. The mixture was stirred at 110 °C until the solution became clear and then maintained at this temperature for 6 h. After removing most of the solvent by rotary evaporation (100 °C, -0.06 MPa vacuum), the product was filtered through a Buchner funnel and washed multiple times with dichloromethane to obtain a crude product. The crude product was added to a certain amount of N,N-dimethylformamide and heated to 150 °C to dissolve it completely. After slowly cooling to room temperature, the mixture was cooled in an ice-water bath for 2 h and then filtered through a Buchner funnel. The resulting product was washed three times with dichloromethane and dried under vacuum at 100 °C for 5 h to obtain a pale yellow crystalline product with a yield of 89%. Figure 1 The structure of M and its 1H NMR (400 MHz, DMSO-d6) spectrum are presented, showing that M has been successfully synthesized.

[0121] Preparation of borate-based polyurethane: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 11 g of M and 100 mL of N,N-dimethylformamide were added under a nitrogen atmosphere and stirred at 150 °C until fully dissolved. The solution was cooled to room temperature, and then 7 g of hexamethylene diisocyanate trimer was added. After thorough stirring until a homogeneous solution was formed, borate-based polyurethane was obtained. Its structural formula is:

[0122]

[0123] Synthesis of m-PU: Without using a catalyst, borate ester polyurethane was reacted at 90℃ for 1 h to obtain m-PU gel. The product was then vacuum dried at 150℃ for 5 h and pulverized to obtain m-PU plastic powder.

[0124] Figure 2 The infrared spectrum of the renewable polyurethane (m-PU) plastic powder prepared in this embodiment is shown. It can be seen that the characteristic absorption peak of -NCO at 2276 cm⁻¹ has disappeared, indicating that the m-PU has been completely cured. The characteristic absorption peak at 1676 cm⁻¹ corresponds to the C=O stretching vibration peak in the urethane bond, indicating that the experiment successfully synthesized m-PU.

[0125] Figure 3 This is a schematic diagram of m-PU resin crushing and molding. The m-PU plastic powder is evenly spread in the mold cavity of a steel mold and molded at 190℃ / 10 MPa for 1 h. The resulting sample is uniform and transparent, indicating that this material has repairable and reprocessable properties.

[0126] Figure 4 Thermogravimetric analysis (TGA) curves of the renewable polyurethane (m-PU) plastic powder prepared in this embodiment are presented. The thermal decomposition temperature of the material is defined as the temperature at which 5% weight is lost in the TGA curve. The test method is thermogravimetric analysis performed on a NETZSCH TG 209C-TASC 414 / 4 instrument (Germany). The sample mass is 5–10 mg; the nitrogen flow rate is 60 mL·min⁻¹; the heating rate is 10 °C·min⁻¹; and the temperature range is 30–800 °C. The thermal decomposition temperature (T⁵%) of the m-PU plastic powder is 268 °C, which is higher than the decomposition temperature of most conventional polyurethanes, demonstrating the excellent thermal stability of m-PU.

[0127] Figure 5 Stress-strain curves of the renewable polyurethane (m-PU) plastic block prepared in this embodiment and the m-PU plastic block after immersion in water for 48 h are presented. Tensile strength, elongation at break, and Young's modulus of the material were obtained according to ASTM D638. The original m-PU plastic block achieved a tensile strength of 36.6 MPa, an elongation at break of 4.1%, and a Young's modulus of 1.04 GPa. After immersion in water for 48 h, the tensile strength of the original m-PU plastic block increased to 40.1 MPa, the elongation at break increased to 4.7%, and the Young's modulus reached 1.21 GPa. This demonstrates that m-PU possesses good mechanical properties and excellent hydrolytic stability.

[0128] Table 1 shows the changes in mechanical properties of the recyclable polyurethane (m-PU) plastic block prepared in this embodiment after undergoing three "molding-solid crushing" reprocessing processes, proving that m-PU material can be reshaped, repaired and recycled multiple times, and that the mechanical properties of m-PU material after multiple reshaping processes do not decrease significantly.

[0129] Table 1. Changes in the mechanical properties of the m-PU resin block described in Example 1 of this invention after undergoing three reprocessing steps of "compression molding-solid crushing".

[0130]

[0131] Example 2

[0132] Synthesis of S: At 30°C, 10 g of methyldiamine and 60 g of o-hydroxybenzaldehyde were placed in a 500 mL beaker, and 250 mL of acetone were added and mixed thoroughly. The mixture was stirred and kept at 0°C for 10 h. After removing most of the solvent by rotary evaporation (40°C), the mixture was cooled to 10°C, filtered through a Buchner funnel, and washed several times with anhydrous acetone to obtain the crude product. The crude product was added to a certain amount of dichloromethane, heated to 35°C to dissolve it completely, slowly cooled to room temperature, and then cooled in an ice-water bath for 2 h. The mixture was filtered through a Buchner funnel, and the resulting product was washed three times with dichloromethane and dried under vacuum at 30°C for 10 h to obtain a bright yellow crystalline product with a yield of 93%.

[0133] Synthesis of M: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 20 g of S, 30 g of 3-hydroxymethylphenylboronic acid, and 150 mL of anhydrous dimethyl sulfoxide were added sequentially under a nitrogen atmosphere. The mixture was stirred at 160 °C until the solution became clear and then maintained at this temperature for 1 h. After removing most of the solvent by rotary evaporation (150 °C), the solution was filtered through a Buchner funnel and washed several times with dichloromethane to obtain the crude product. The crude product was added to a certain amount of dimethyl sulfoxide and heated to 150 °C to dissolve it completely. After slowly cooling to room temperature, the solution was cooled in an ice-water bath for 2 h and then filtered through a Buchner funnel. The resulting product was washed three times with dichloromethane and dried under vacuum at 100 °C for 5 h to obtain a pale yellow crystalline product with a yield of 91%.

[0134] Preparation of borate-based polyurethane: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 40 g of M and 200 mL of dimethyl sulfoxide were added under a nitrogen atmosphere and stirred at 170 °C until fully dissolved. The solution was cooled to room temperature, and then 41 g of toluene diisocyanate trimer was added. After thorough stirring until a homogeneous solution was formed, borate-based polyurethane was obtained. Its structural formula is:

[0135]

[0136] Synthesis of m-PU: Without using a catalyst, borate ester polyurethane was reacted at 60°C for 20 h to obtain m-PU gel. The product was then vacuum dried at 120°C for 10 h and pulverized to obtain m-PU plastic powder.

[0137] 20 g of m-PU powder was evenly spread in the cavity of a steel mold and molded at 160℃ / 50 MPa for 2 h to obtain m-PU blocks.

[0138] Example 3

[0139] Synthesis of S: At 50°C, 5 g of propylenediamine and 19 g of o-hydroxybenzaldehyde were placed in a 250 mL beaker, and 100 mL of methanol was added and mixed thoroughly. The mixture was stirred and kept at 50°C for 8 h. After removing most of the solvent by rotary evaporation (40°C), the mixture was cooled to 0°C, filtered through a Buchner funnel, and washed several times with anhydrous methanol to obtain the crude product. The crude product was added to a certain amount of dichloromethane, heated to 35°C to dissolve it completely, slowly cooled to room temperature, and then cooled in an ice-water bath for 5 h. The mixture was filtered through a Buchner funnel, and the resulting product was washed three times with dichloromethane and dried under vacuum at 30°C for 10 h to obtain a yellow liquid product with a yield of 90%.

[0140] Synthesis of M: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 10 g of S, 10 g of 2-hydroxymethylphenylboronic acid, and 100 mL of anhydrous N,N-dimethylacetamide were added sequentially under a nitrogen atmosphere. The mixture was stirred at 80 °C until the solution became clear and then maintained at this temperature for 10 h. After removing most of the solvent by rotary evaporation (140 °C), the solution was filtered through a Buchner funnel and washed several times with dichloromethane to obtain a crude product. The crude product was added to a certain amount of N,N-dimethylformamide and heated to 150 °C to dissolve it completely. After slowly cooling to room temperature, the solution was cooled in an ice-water bath for 2 h and then filtered through a Buchner funnel. The product was washed three times with dichloromethane and dried under vacuum at 120 °C for 10 h to obtain a white crystalline product with a yield of 95%.

[0141] Preparation of borate-based polyurethane: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 10 g of M and 100 mL of N,N-dimethylformamide were added under a nitrogen atmosphere and stirred at 150 °C until fully dissolved. The solution was cooled to room temperature, and then 7 g of isophorone diisocyanate trimer was added. After thorough stirring until a homogeneous solution was formed, borate-based polyurethane was obtained. Its structural formula is:

[0142]

[0143] Synthesis of m-PU coating: Without using a catalyst, borate ester-based polyurethane was reacted at 60℃ for 60 min to obtain a uniform and transparent m-PU solution. The m-PU solution was sprayed onto a 1×1 m2 glass plate and placed in an 80℃ forced-air drying oven. After drying for 10 days, heating was stopped to obtain a regenerable polyurethane m-PU coating.

[0144] Example 4

[0145] Synthesis of S: At 60°C, 5 g of pentanediamine and 12.5 g of o-hydroxybenzaldehyde were placed in a 250 mL beaker, and 100 mL of ethanol was added and mixed thoroughly. The mixture was stirred and kept at 60°C for 1 h. After removing most of the solvent by rotary evaporation (60°C), the mixture was cooled to -20°C, filtered through a Buchner funnel, and washed repeatedly with anhydrous ethanol to obtain the crude product. The crude product was added to a certain amount of tetrahydrofuran, heated to 60°C to dissolve completely, slowly cooled to room temperature, and then cooled in an ice-water bath for 5 h. The mixture was filtered through a Buchner funnel, and the resulting product was washed three times with tetrahydrofuran and dried under vacuum at 40°C for 10 h to obtain a yellow liquid product with a yield of 95%.

[0146] Synthesis of M: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 10 g of S, 5 g of 4-hydroxymethylphenylboronic acid, 5 g of 3-hydroxymethylphenylboronic acid, and 100 mL of anhydrous N,N-dimethylformamide were added sequentially under a nitrogen atmosphere. The mixture was stirred at 140 °C until the solution became clear and then maintained at this temperature for 8 h. After removing most of the solvent by rotary evaporation (140 °C), the solution was filtered through a Buchner funnel and washed several times with dichloromethane to obtain a crude product. The crude product was added to a certain amount of anhydrous dimethyl sulfoxide and heated to 150 °C to dissolve it completely. After slowly cooling to room temperature, the solution was cooled in an ice-water bath for 5 h and then filtered through a Buchner funnel. The product was washed three times with dichloromethane and dried under vacuum at 100 °C for 10 h to obtain a pale yellow solid product with a yield of 92%.

[0147] Preparation of borate-based polyurethane: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 5 g of M and 50 mL of N,N-dimethylacetamide were added under a nitrogen atmosphere and stirred at 150 °C until fully dissolved. The solution was cooled to room temperature, and then 5 g of hexamethylene diisocyanate trimer was added to the solution. After stirring thoroughly until a homogeneous solution was formed, borate-based polyurethane was obtained.

[0148] Synthesis of m-PU coating: Without using a catalyst, borate ester-based polyurethane was reacted at 80℃ for 20 min to obtain a uniform and transparent m-PU solution. The m-PU solution was scraped onto a 0.5×0.5 m2 tinplate sheet and placed in a 100℃ forced-air drying oven. After drying for 7 days, heating was stopped to obtain a regenerable polyurethane m-PU coating.

[0149] In this embodiment, a mixture of 4-hydroxymethylphenylboronic acid and 3-hydroxymethylphenylboronic acid was used for the feeding reaction, and the resulting M structure contained the following three structures:

[0150] .

[0151] Example 5

[0152] Synthesis of S: At 40°C, 10 g of pentanediamine and 25 g of o-hydroxybenzaldehyde were placed in a 500 mL beaker, and 250 mL of acetone were added and mixed thoroughly. The mixture was stirred at 60°C for 5 h. After removing most of the solvent by rotary evaporation (40°C), the mixture was cooled to -10°C, filtered through a Buchner funnel, and washed several times with anhydrous acetone to obtain the crude product. The crude product was added to a certain amount of tetrahydrofuran, heated to 60°C to dissolve it completely, slowly cooled to room temperature, and then cooled in an ice-water bath for 5 h. The mixture was filtered through a Buchner funnel, and the resulting product was washed three times with dichloromethane and dried under vacuum at 40°C for 10 h to obtain a yellow liquid product with a yield of 93%.

[0153] Synthesis of M: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 10 g of S, 11 g of 2-hydroxymethylphenylboronic acid, and 200 mL of anhydrous N,N-dimethylformamide were added sequentially under a nitrogen atmosphere. The mixture was stirred at 150 °C until the solution became clear, and the reaction was maintained at this temperature with stirring for 2 h. After removing most of the solvent by rotary evaporation (120 °C), the product was filtered through a Buchner funnel and washed several times with dichloromethane to obtain a crude product. The crude product was added to a certain amount of N,N-dimethylformamide and heated to 150 °C to dissolve it completely. After slowly cooling to room temperature, the mixture was cooled in an ice-water bath for 5 h and then filtered through a Buchner funnel. The resulting product was washed three times with dichloromethane and dried under vacuum at 100 °C for 8 h to obtain a pale yellow crystalline product with a yield of 90%.

[0154] Preparation of borate-based polyurethane: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 15 g of M and 200 mL of N,N-dimethylacetamide were added under a nitrogen atmosphere and stirred at 150 °C until fully dissolved. The solution was cooled to room temperature, and then 9 g of toluene diisocyanate trimer was added. After thorough stirring until a homogeneous solution was formed, borate-based polyurethane was obtained. Its structural formula is:

[0155]

[0156] Synthesis of m-PU: Without using a catalyst, borate ester polyurethane was reacted at 100℃ for 2 h to obtain m-PU gel. The product was then vacuum dried at 180℃ for 6 h and pulverized to obtain m-PU plastic powder.

[0157] 20 g of m-PU powder was evenly spread in the cavity of a steel mold and molded at 200℃ / 20 MPa for 2 h to obtain m-PU blocks.

[0158] Example 6

[0159] Synthesis of S: At 30°C, 5 g of butanediamine and 21 g of o-hydroxybenzaldehyde were placed in a 500 mL beaker, and 250 mL of ethanol was added and mixed thoroughly. The mixture was stirred and kept at 20°C for 10 h. After removing most of the solvent by rotary evaporation (60°C), the mixture was cooled to -15°C, filtered through a Buchner funnel, and washed several times with anhydrous ethanol to obtain the crude product. The crude product was added to a certain amount of dichloromethane, heated to 35°C to dissolve it completely, slowly cooled to room temperature, and then cooled in an ice-water bath for 5 h. The mixture was filtered through a Buchner funnel, and the resulting product was washed three times with dichloromethane and dried under vacuum at 40°C for 8 h to obtain a bright yellow crystalline product with a yield of 94%.

[0160] Synthesis of M: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 10 g of S, 12 g of 2-hydroxymethylphenylboronic acid, and 200 mL of anhydrous dimethyl sulfoxide were added sequentially under a nitrogen atmosphere. The mixture was stirred at 100 °C until the solution became clear and then maintained at this temperature for 5 h. After removing most of the solvent by rotary evaporation (150 °C), the solution was filtered through a Buchner funnel and washed several times with dichloromethane to obtain a crude product. The crude product was added to a certain amount of dimethyl sulfoxide and heated to 150 °C to dissolve it completely. After slowly cooling to room temperature, the solution was cooled in an ice-water bath for 5 h and then filtered through a Buchner funnel. The resulting product was washed three times with dichloromethane and dried under vacuum at 100 °C for 10 h to obtain a pale yellow crystalline product with a yield of 90%.

[0161] Preparation of borate-based polyurethane: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 10 g of M and 200 mL of N,N-dimethylacetamide were added under a nitrogen atmosphere and stirred at 150 °C until fully dissolved. The solution was cooled to room temperature, and then 10 g of isophorone diisocyanate trimer was added. After thorough stirring until a homogeneous solution was formed, borate-based polyurethane was obtained. Its structural formula is:

[0162]

[0163] Synthesis of m-PU: Without using a catalyst, borate ester polyurethane was reacted at 70°C for 10 h to obtain m-PU gel. The product was then vacuum dried at 130°C for 8 h and pulverized to obtain m-PU plastic powder.

[0164] 20 g of m-PU powder was evenly spread in the cavity of a steel mold and molded at 210℃ / 30 MPa for 1 h to obtain m-PU blocks.

[0165] Example 7

[0166] Synthesis of S: At 30°C, 10 g of methyldiamine and 55 g of o-hydroxybenzaldehyde were placed in a 500 mL beaker, and 250 mL of acetone were added and mixed thoroughly. The mixture was stirred and kept at 0°C for 10 h. After removing most of the solvent by rotary evaporation (40°C), the mixture was cooled to 18°C, filtered through a Buchner funnel, and washed several times with anhydrous acetone to obtain the crude product. The crude product was added to a certain amount of dichloromethane, heated to 35°C to dissolve it completely, slowly cooled to room temperature, and then cooled in an ice-water bath for 2 h. The mixture was filtered through a Buchner funnel, and the resulting product was washed three times with dichloromethane and dried under vacuum at 30°C for 10 h to obtain a bright yellow crystalline product with a yield of 93%.

[0167] Synthesis of M: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 20 g of S, 28 g of 3-hydroxymethylphenylboronic acid, and 150 mL of anhydrous dimethyl sulfoxide were added sequentially under a nitrogen atmosphere. The mixture was stirred at 120 °C until the solution became clear and then maintained at this temperature for 4 h. After removing most of the solvent by rotary evaporation (150 °C), the solution was filtered through a Buchner funnel and washed several times with dichloromethane to obtain a crude product. The crude product was added to a certain amount of dimethyl sulfoxide and heated to 150 °C to dissolve it completely. After slowly cooling to room temperature, the solution was cooled in an ice-water bath for 2 h and then filtered through a Buchner funnel. The resulting product was washed three times with dichloromethane and dried under vacuum at 100 °C for 5 h to obtain a pale yellow crystalline product with a yield of 91%.

[0168] Preparation of borate-based polyurethane: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 40 g of M and 200 mL of dimethyl sulfoxide were added under a nitrogen atmosphere and stirred at 170 °C until fully dissolved. The solution was cooled to room temperature, and then 32 g of toluene diisocyanate trimer was added. After thorough stirring until a homogeneous solution was formed, borate-based polyurethane was obtained. Its structural formula is:

[0169]

[0170] Synthesis of m-PU coating: Without using a catalyst, borate ester-based polyurethane was reacted at 70℃ for 40 min to obtain a uniform and transparent m-PU solution. The m-PU solution was then coated onto a 0.5×0.5 m2 tinplate sheet and placed in a 60℃ forced-air oven for drying for 14 days before heating was stopped to obtain a regenerable polyurethane m-PU coating.

[0171] Comparative Example 1

[0172] The selected imine-containing monomer S and trifunctional isocyanate (hexamethylene diisocyanate trimer) are the same as those in Example 1.

[0173] Preparation of a single-dynamic covalent polyurethane: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 12 g of toluene and 100 mL of toluene were added under a nitrogen atmosphere and stirred at 50°C until fully dissolved. The solution was cooled to room temperature, and then 15 g of hexamethylene diisocyanate trimer was added. The mixture was stirred thoroughly until a homogeneous solution was formed, thus obtaining a single-dynamic covalent polyurethane. Its structural formula is as follows:

[0174]

[0175] Synthesis of renewable single dynamic covalent polyurethane (s-PU): Without using a catalyst, single dynamic covalent polyurethane was reacted at 80℃ for 30 min to obtain s-PU gel. The product was then vacuum dried at 150℃ for 5 h and pulverized to obtain s-PU plastic powder.

[0176] 20 g of s-PU powder was evenly spread in the cavity of a steel mold and molded at 150℃ / 20 MPa for 1 h to obtain s-PU blocks.

[0177] Mechanical properties and thermal stability were tested for Examples 1, 2, 5, 6, and Comparative Example 1. Tensile strength, elongation at break, and Young's modulus were obtained according to ASTM D638. The thermal decomposition temperature was defined as the temperature at which 5% weight loss occurred in the thermogravimetric analysis (TGA) curve. The test method was thermogravimetric analysis performed on a NETZSCH TG 209 C-TASC414 / 4 instrument (Germany). The sample mass was 5–10 mg; the nitrogen flow rate was 60 mL·min⁻¹; the heating rate was 10 °C·min⁻¹; and the temperature range was 30–800 °C. The data are shown in the table below.

[0178]

[0179] Thermal stability tests were conducted on Examples 3, 4, and 7. The thermal decomposition temperature of the coating was the temperature at which 5% weight loss occurred in the thermogravimetric curve. The test method was the same as in Example 1, and the data are shown in the table below.

[0180]

[0181] As can be seen from the above embodiments, the present invention is highly feasible. The resulting borate-based polyurethane and the renewable polyurethane materials containing it (renewable polyurethane (m-PU) plastics and renewable polyurethane (m-PU) coatings) are simple to synthesize, economical, and environmentally friendly, and possess high hydrolytic / thermal stability and good mechanical properties. Furthermore, the m-PU materials can be reshaped, repaired, and recycled multiple times, and the mechanical properties of the m-PU materials after multiple reshaping processes do not show a significant decrease. Therefore, the borate-based polyurethane of the present invention, and the renewable polyurethane materials based on this borate-based polyurethane, can be used as renewable polyurethane plastics and coatings, possessing excellent hydrolytic / thermal stability, high mechanical strength, repairability, and reshaping properties, and can be recycled multiple times.

Claims

1. A boronate-based polyurethane, characterized by The structural formula is: Wherein, G is the same or different, and each is independently selected from substituted or unsubstituted alkylene group of carbon atoms 1~10, substituted or unsubstituted aryl group of carbon atoms 6~18 or substituted or unsubstituted cycloalkyl group of carbon atoms 3~10; m is the number of G, m is selected from 1, 2 or 3; The substituent group of G is the same or different, and each is independently selected from hydrogen, alkyl group of carbon atoms 1~10 or aryl group of carbon atoms 6~18; n is selected from 1, 2, 3, 4 or 5; wherein, represents a bond connecting to the rest of the molecule of the compound.

2. The boronate-based polyurethane of claim 1, wherein: The G is selected from any one of the following structures: , or ; wherein, represents a chemical bond.

3. The method of claim 1, wherein the boronate-based polyurethane is prepared by the reaction of a polyisocyanate and a borate compound. The method comprises the following steps: (1) 100 parts of a binary amine and 250~600 parts of o-hydroxybenzaldehyde are respectively dissolved in an organic solvent according to mass parts, the binary amine solution is slowly dropped into the o-hydroxybenzaldehyde solution, and the reaction is carried out at a preset temperature; after the reaction is completed and treated by distillation, the solid is precipitated by cooling, the solid product is collected by suction filtration, and the obtained solid product is treated by recrystallization to obtain a Schiff base compound S; (2) 100 parts of the obtained Schiff base compound S and (100~150) parts of hydroxymethyl phenyl boronic acid are dissolved in an organic solvent according to mass parts, and fully stirred to form a uniform solution, and the reaction is carried out at a preset temperature; after the reaction is completed, the solid product is obtained by distillation treatment and suction filtration, and the obtained solid product is treated by recrystallization to obtain a N→B bidentate boronate compound M; (3) the obtained boronate compound M and isocyanate compound are dissolved in an organic solvent, fully stirred to form a uniform solution as a pre-solution, and the feeding ratio of the boronate compound M and the isocyanate compound is determined according to the molar ratio of hydroxyl active hydrogen to isocyanate group being 1:(0.8~1.5); after the pre-solution is treated by molding, a boronate-based polyurethane is prepared.

4. The method for preparing borate ester-based polyurethane as described in claim 3, characterized in that: The binary amine is one of methylenediamine, ethylenediamine, propylenediamine, butylenediamine and pentanediamine; The hydroxymethyl phenyl boronic acid is one or a mixture of more than one of 2-hydroxymethyl phenyl boronic acid, 3-hydroxymethyl phenyl boronic acid and 4-hydroxymethyl phenyl boronic acid; The isocyanate compound in step (3) is one or a mixture of more than one of hexamethylene diisocyanate trimer, toluene diisocyanate trimer and isophorone diisocyanate trimer.

5. The method of preparing a borate-based polyurethane according to claim 3, characterized by: In step (1), the dissolution temperature of the binary amine and o-hydroxybenzaldehyde is 30~60℃; the temperature for precipitating the solid is-20~20℃; and the reaction condition at the preset temperature is that the reaction is carried out at 0~60℃ for 1~10 h. In step (2), the reaction condition at the preset temperature includes that the reaction is carried out at 80~160℃ for 1~10 h.

6. A renewable polyurethane material characterized by: The renewable polyurethane material is renewable polyurethane plastic or renewable polyurethane coating.

7. The renewable polyurethane material of claim 6, wherein: The performance aid includes defoaming agent, antioxidant or color masterbatch.

8. The renewable polyurethane material of claim 6, wherein: The molding treatment method of the renewable polyurethane plastic is as follows: The pre-solution described in any one of claims 3-5 is subjected to gel reaction at 60-100℃ for 1-20 hours, and then vacuum treatment to obtain a sample; the sample is crushed to obtain a renewable polyurethane plastic powder; The vacuum treatment process comprises: first heating to 120-180℃, holding for 5-10 hours, then stopping heating and cooling to below 60℃, and stopping vacuum treatment; The renewable polyurethane plastic is recycled by mold forming-solid crushing.

9. A renewable polyurethane material as in claim 6, wherein, The renewable polyurethane coating forming treatment method is as follows: The pre-solution described in any one of claims 3-5 is subjected to reaction at 60-80℃ for 20-60 minutes to obtain a uniform transparent solution; the uniform transparent solution is coated on a substrate, and held at 60-100℃ for 7-14 days to obtain a renewable polyurethane coating; The renewable polyurethane coating is self-repaired by holding at 150-200℃ for 5-24 hours.

10. Use of the renewable polyurethane material described in any one of claims 6-9 as a heat-resistant and fire-resistant material or a repairable coating.

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