Fluorescent polyurethane material and its preparation method and application

Abstract

The present invention discloses a fluorescent polyurethane material, its preparation method, and its application. Due to the N→B bidentate coordination of the polymer M and the rich aromatic ring structure in the polymer, the prepared fluorescent polyurethane material (PMXT) exhibits high stability to thermal stimulation, water, or hydroxyl-containing compounds, broadening the industrial application range of PMXT materials. The polyurethane is processable, repairable, and renewable with excellent thermal stability, a tensile strength of up to 95 MPa, and a Young's modulus of up to 3.0 GPa. The electron-rich conjugated structure of the borate compound M imparts photoluminescence to the material, while the multiple dynamic covalent bond structures of M (including imine and borate bonds) enable self-healing and recycling capabilities, providing a low-cost approach to repairing polymer materials in industrial applications.

Description

Technical Field

[0001] The invention belongs to the technical field of new materials and relates to a fluorescent polyurethane material and a preparation method and application thereof. Background Art

[0002] Engineering polymers are widely used in the automotive, aerospace, and wind power sectors. These materials are susceptible to cracks and defects after long-term exposure to various insults, including mechanical shock, thermal radiation, and chemical corrosion. If these defects are allowed to develop, they will inevitably lead to a decrease in mechanical properties and a shortened service life, posing a serious safety hazard. However, the overhaul and replacement of these materials are costly and difficult to implement, resulting in significant energy consumption and the generation of plastic waste. Existing microscopic damage inspection technologies, such as ultrasound, X-ray, and thermal infrared imaging, require complex testing equipment and specialized personnel to analyze data, and have limited resolution (Progress in Materials Science, 2016, 83:536-573). Therefore, the design and development of polymer materials with autonomous damage detection and repair capabilities is of great significance.

[0003] Existing autonomous damage detection materials generally achieve the function of crack detection by giving the material photoluminescence properties, but they still cannot meet the industrial demand for the application of polymer materials in complex environments. Li Wenle et al. prepared a composite coating by encapsulating aggregation-induced emission compound (AIE) microcapsules. Cracks will cause the AIE capsules to rupture, and the fluorescence emitted from the cracks under ultraviolet light can clearly reflect the location and severity of the cracks (ACS Applied Materials & Interfaces, 2018, 10 (47): 40361-40365). Chen Jiucun et al. have achieved crack visualization under ultraviolet light by mixing a small amount of fluorescent luminescent material into the waterproof coating. For details, please refer to the Chinese patent application with publication number CN111205703 A. Sun Yinjie et al. mixed fluorescent powder into carbon / carbon composite materials and provided a low-cost method for observing microcracks and holes inside the composite material. For details, please refer to the Chinese patent application with publication number CN103529002 A. However, these fluorescent composite materials can only achieve one-time damage detection.

[0004] Unlike fluorescent composite materials that can only achieve one-time damage detection, intrinsically luminescent self-healing materials have the advantages of a stable luminescence mechanism, recyclability, and reprocessability. This not only ensures the accuracy of damage indication but also extends the service life of polymer materials, providing dual security guarantees for microcrack detection and self-healing tracking in structural materials. Meanwhile, 4,4'-difluoro-4-boron-3a,4a-diaza-s-indentriene (BODIPY), a classic luminescent compound containing an N→B-coordinated boron heterocyclic conjugated structure, is widely used in the synthesis of organic optical light-emitting devices due to its interesting optical properties, high thermal stability, and photochemical stability (Polymers, 2021, 13, 75). However, BODIPY cannot impart repairability, reprocessability, or improved mechanical properties to polymer materials. Therefore, constructing an intrinsically luminescent polymer material based on an N→B-coordinated boron heterocyclic conjugated structure with high stability, high mechanical strength, and repairability has great application potential and functionality, and is also a major challenge facing the low-cost implementation of autonomous damage detection. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the purpose of the present invention is to provide a fluorescent polyurethane material and its preparation method and application. The fluorescent material prepared is an intrinsically luminescent polyurethane material, which has the performance of realizing crack detection and repair, good thermal stability, extremely high mechanical strength, and the characteristics of being repairable and recyclable.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions.

[0007] A fluorescent polyurethane material, the structural formula of which is:

[0008]

[0009] wherein x:y=0.05-1.0, and n is selected from 2 or 3;

[0010] Indicates that this link is connected to the rest of the polyurethane material.

[0011] The preparation method of the fluorescent polyurethane material comprises the following steps:

[0012] (1) dissolving 100 parts by mass of a diamine, 320-420 parts by mass of o-hydroxybenzaldehyde, and 400-510 parts by mass of hydroxymethylphenylboric acid in an organic solvent, first slowly dropping the diamine solution into the o-hydroxybenzaldehyde solution, and then adding the hydroxymethylphenylboric acid solution; reacting at a preset temperature; after the reaction is completed, removing the solvent and collecting a solid product, and recrystallizing the obtained solid product to obtain a borate ester compound M;

[0013] (2) The obtained borate compound M, xylene diisocyanate and tris(2-hydroxyethyl)isocyanurate are reacted to prepare a prefabricated liquid, wherein the reaction amounts of the borate compound M, xylene diisocyanate and tris(2-hydroxyethyl)isocyanurate are determined according to a molar ratio of hydroxyl active hydrogen to isocyanate group of 1:(0.8-1.5), and a molar ratio of the borate compound M to tris(2-hydroxyethyl)isocyanurate is 0.05-1.00; the prefabricated liquid is subjected to a molding process to prepare a fluorescent polyurethane material.

[0014] Furthermore, the reaction is carried out at a preset temperature at 110 to 160° C. for 5 to 10 hours.

[0015] Furthermore, the operation of the molding process in step (2) is as follows:

[0016] The prefabricated liquid is subjected to a gel reaction, and the obtained gel is vacuum-treated to obtain a sample; the obtained sample is crushed to obtain a fluorescent polyurethane plastic;

[0017] The gelation reaction conditions are as follows: maintaining at 60-100°C for 30 minutes to 20 hours;

[0018] The vacuum treatment process includes: under vacuum conditions, first heating to 120-180°C, keeping warm for 5-10 hours, then stopping heating and cooling to below 60°C, and stopping vacuuming.

[0019] Furthermore, the fluorescent polyurethane plastic is recycled and recyclable through compression molding and solid crushing.

[0020] Furthermore, the operation of the molding process in step (2) is as follows:

[0021] The prefabricated liquid is reacted to a uniform transparent solution state; the obtained uniform transparent solution is coated on a substrate, and kept at 70 to 100° C. for 7 to 14 days to obtain a fluorescent polyurethane coating;

[0022] The reaction conditions are: reaction at 60-80°C for 30-90 minutes.

[0023] Furthermore, the fluorescent polyurethane coating is self-repaired by being kept at 180-220° C. for 2-15 hours.

[0024] A fluorescent polyurethane material is used as an engineering material or a repairable protective coating.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The fluorescent polyurethane material (PMXT) prepared in this invention is a processable, repairable, and renewable polyurethane with excellent thermal stability. Due to the N→B bidentate coordination of the polymer M and the rich aromatic ring structure in the polymer, the PMXT material is highly stable to thermal stimulation, water, and hydroxyl-containing compounds, broadening the industrial application range of PMXT materials.

[0027] (2) By adjusting the feed ratio, the PMXT material prepared by the present invention can selectively design the specific structural proportions of the material, thereby exhibiting excellent mechanical properties that surpass traditional polyurethanes, with a tensile strength of up to 95 MPa and a Young's modulus of up to 3.0 GPa.

[0028] (3) The PMXT material prepared by the present invention can realize the use function of micro crack detection and self-healing tracking under a portable ultraviolet lamp. The reason is that the electron-rich conjugated structure of the borate compound M gives the material the characteristics of photoluminescence, and at the same time, the multiple dynamic covalent bond structure of M (including imine bonds and borate bonds) gives the material the function of self-healing and recycling. This can not only ensure the accuracy of crack detection, but also extend the service life of polymer materials. Crack detection and self-healing tracking that can be achieved under a portable ultraviolet lamp provide dual safety protection for structural materials, and also provide a low-cost way to repair polymer materials in industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the 13C NMR spectrum of M described in Example 1 of the present invention;

[0030] Figure 2 FTIR spectrum of PMXT described in Example 1 of the present invention;

[0031] Figure 3 Schematic diagram of the solid crushing-compression molding of PMXT resin described in Example 1 of the present invention;

[0032] Figure 4 Schematic diagram of PMXT resin microcrack detection and self-healing tracking described in Example 1 of the present invention;

[0033] Figure 5 Stress-strain curve of the PMXT resin block described in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0035] The first aspect of the present invention provides a fluorescent polyurethane material (PMXT), which is synthesized by reacting o-hydroxybenzaldehyde, a diamine and hydroxymethylphenylboronic acid to obtain an active monomer M with an N→B bidentate coordination structure. The active monomer M reacts with xylylene diisocyanate (XDI) and tris(2-hydroxyethyl)isocyanurate (THC) to obtain a polymer material that can emit fluorescence and realize microcrack detection and repair. The polymer material has good stability, mechanical properties, reprocessability and intrinsic luminescence characteristics.

[0036] The structural formula of the fluorescent polyurethane material is:

[0037]

[0038] in, Indicates that this link is connected to the rest of the polyurethane material.

[0039] wherein n is selected from 2 or 3.

[0040] Among them, x:y=0.05~1.0.

[0041] In the present invention, What the structure shows means that the chemical bond can be attached to any position on the benzene ring, as shown below: Non-positional connecting bonds are single bonds extending from the ring system It means that one end of the connecting bond can be connected to any position in the ring system that the bond passes through, and the other end is connected to the rest of the compound molecule.

[0042] The second aspect of the present invention provides a method for preparing the above-mentioned fluorescent polyurethane material (PMXT), which is as follows:

[0043] (1) Synthesis of borate compound M

[0044] 100 parts of a diamine, 320-420 parts of o-hydroxybenzaldehyde, and 400-510 parts of hydroxymethylphenylboric acid are respectively dissolved in an organic solvent, the diamine solution is slowly dripped into the o-hydroxybenzaldehyde solution and stirred thoroughly, and then the hydroxymethylphenylboric acid solution is added; after the reaction solution is stirred thoroughly, the reaction is completed at a preset temperature, most of the solvent is removed by distillation, and a solid product is obtained by filtration, which is recrystallized to obtain the N→B bidentate coordinated borate compound M.

[0045] Wherein, the diamine is ethylenediamine or propylenediamine.

[0046] The hydroxymethylphenylboric acid is a mixture of one or more of 2-hydroxymethylphenylboric acid, 3-hydroxymethylphenylboric acid and 4-hydroxymethylphenylboric acid.

[0047] The organic solvent used is a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone and dimethyl sulfoxide.

[0048] The complete reaction at the preset temperature specifically includes: reacting at 110-160° C. for 5-10 hours.

[0049] In a specific embodiment of the present invention, when the hydroxymethylphenylboronic acid is 4-hydroxymethylphenylboronic acid, the chemical structural formula of the borate compound M is:

[0050] Wherein, n=2 or 3.

[0051] In a specific embodiment of the present invention, when the hydroxymethylphenylboronic acid is 3-hydroxymethylphenylboronic acid, the chemical structural formula of the borate compound M containing N→B bidentate coordination is:

[0052] Wherein, n=2 or 3.

[0053] In a specific embodiment of the present invention, when the hydroxymethylphenylboronic acid is 2-hydroxymethylphenylboronic acid, the chemical structural formula of the borate compound M containing N→B bidentate coordination is:

[0054] Wherein, n=2 or 3.

[0055] (2) Preparation of fluorescent polyurethane material (PMXT)

[0056] According to the molar ratio of hydroxyl active hydrogen to isocyanate group of 1: (0.8-1.5), a borate compound M, xylylene diisocyanate (XDI) and tris (2-hydroxyethyl) isocyanurate (THC) were dissolved in an organic solvent and stirred thoroughly to form a homogeneous solution, wherein the molar ratio of the borate compound M to THC was between 0.05 and 1.00; the homogeneous solution was used as a prefabricated liquid, and the prefabricated liquid was subjected to a molding process to prepare a fluorescent polyurethane material (PMXT).

[0057] (a) In a specific embodiment of the present invention, the specific steps of the above-mentioned molding process are as follows:

[0058] The prefabricated liquid is kept at a preset temperature for 30 minutes to 20 hours to allow the system to gel; the gel is transferred to a polytetrafluoroethylene tank, then placed in a vacuum oven, evacuated (-0.10 to -0.06 MPa), heated to 120 to 180°C, and kept warm for 5 to 10 hours before stopping heating; when the material temperature drops below 60°C, the vacuum is stopped, the vacuum oven is restored to normal pressure, the sample is taken out and crushed to obtain fluorescent polyurethane plastic powder.

[0059] The organic solvent used here is a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, and acetonitrile.

[0060] The preset temperature is 60~100℃.

[0061] Preferably, curing of PMXT is performed in a vacuum oven.

[0062] The fluorescent polyurethane plastic of the present invention is processable, repairable, and recyclable. The PMXT plastic powder is placed in a mold and compression-molded to produce a PMXT resin block. After long-term use, the PMXT resin block can be crushed and then repaired and recycled using a compression-molding-solid crushing process.

[0063] Preferably, during the compression molding process, the compression temperature is 170-220° C., the compression time is 30-120 min, and the compression pressure is 10-50 MPa.

[0064] Preferably, when recycling by the "compression molding-solid crushing" method, the compression temperature is 170-220°C, the compression pressure is 10-100 MPa, and the compression time is 5-300 min; thereby achieving renewable recycling treatment.

[0065] (b) In a specific embodiment of the present invention, the specific steps of the above-mentioned molding process are as follows:

[0066] The preformed liquid is reacted at 60-80° C. for 30-90 minutes to obtain a uniform and transparent PMXT solution. The PMXT solution is then applied by knife coating, spin coating, or spraying on a glass plate or a tinplate sheet. The glass plate or the tinplate sheet is then placed in a forced air oven, heated to 70-100° C., maintained at this temperature for 7-14 days, and then heating is stopped to obtain a fluorescent polyurethane PMXT coating.

[0067] The PMXT coating of the present invention is repairable: if scratches appear on the surface of the PMXT coating, the coating can be repaired by transferring the PMXT coating to a forced air oven, heating the oven to 180-220°C, and keeping the oven warm for 2-15 hours.

[0068] The organic solvent used is a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone and dimethyl sulfoxide.

[0069] The fluorescent polyurethane material (PMXT) of the present invention can be used to manufacture engineering materials such as wind turbine blades, adhesives for automotive structural parts, or repairable protective coatings and repairable paints.

[0070] The present invention is further described in detail below with reference to specific embodiments and accompanying drawings:

[0071] Example 1

[0072] Synthesis of M: 9 g of ethylenediamine was dissolved in 15 mL of N,N-dimethylformamide (DMF) and slowly added dropwise to a solution of 36 g of o-hydroxybenzaldehyde in 50 mL of DMF. After thorough mixing, a solution of 45 g of 4-hydroxymethylphenylboronic acid in 100 mL of DMF was added. The reaction solution was stirred at 120°C under a nitrogen atmosphere for 6 h. Most of the solvent was removed by rotary evaporation (100°C, vacuum -0.06 MPa), followed by filtration using a Buchner funnel and multiple washings with dichloromethane to obtain a crude product. The crude product was added to a predetermined amount of DMF, heated to 150°C to fully dissolve, and then slowly cooled to room temperature. After crystallization, the product was filtered using a Buchner funnel, washed three times with dichloromethane, and dried under vacuum at 100°C for 5 h to obtain pale yellow crystals with a yield of 93%. Figure 1 The structure of M and its 13C NMR spectrum are given, indicating that M has been successfully synthesized.

[0073] Synthesis of PMXT: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 5 g of M and 50 mL of DMF were added under a nitrogen atmosphere and stirred at 150°C until fully dissolved. After cooling the solution to room temperature, 29 g of XDI and 25 g of THC were added and stirred thoroughly until a homogeneous solution formed. The reaction was then carried out at 80°C for 1 hour to obtain PMXT gel. The product was vacuum-dried at 150°C for 5 hours and then pulverized using a grinder to obtain PMXT plastic powder.

[0074] In the PMXT prepared in this example, x:y=0.1.

[0075] Figure 2 The infrared spectrum of the PMXT plastic prepared in this example is given. It can be seen that the characteristic absorption peak at 1695 cm-1 corresponds to the C=O stretching vibration peak in the carbamate bond, indicating that PMXT was successfully synthesized in the experiment.

[0076] Figure 3 This is a schematic diagram of the crushing and compression molding of the PMXT plastic prepared in this example. PMXT powder was evenly spread in the cavity of a steel mold. After compression molding at 180°C / 10 MPa for 1 hour, the resulting sample was uniform and transparent, demonstrating the reprocessability of this material.

[0077] Figure 4A schematic diagram shows how the PMXT plastic prepared in this example can be used to detect microcracks and track self-healing. Cracks in the PMXT material become more pronounced under irradiation with a portable UV lamp (365 nm) and can self-heal after treatment at 200°C for 6 hours.

[0078] Figure 5 This is a stress-strain curve for a PMXT plastic block prepared in an embodiment of the present invention. The tensile strength, elongation at break, and Young's modulus of the material were determined according to ASTM D638. The material in this embodiment exhibited a tensile strength of 93.2 MPa, an elongation at break of 6.8%, and a Young's modulus of 1.86 GPa, demonstrating superior mechanical properties exceeding those of conventional polyurethanes.

[0079] Example 2

[0080] Synthesis of M: Dissolve 10 g of propylenediamine in 20 mL of dimethyl sulfoxide (DMSO) and slowly add dropwise to a solution of 32 g of o-hydroxybenzaldehyde in 45 mL of DMSO. After mixing thoroughly, add a solution of 40 g of 2-hydroxymethylphenylboronic acid in 120 mL of DMF. Under a nitrogen atmosphere, incubate the reaction solution at 160°C with stirring for 5 h. Remove most of the solvent using a rotary evaporator (120°C, vacuum -0.05 MPa), filter with suction using a Buchner funnel, and rinse several times with dichloromethane to obtain a crude product. Add the crude product to a sufficient amount of DMSO, heat to 160°C to fully dissolve it, and slowly cool to room temperature. After crystallization, filter with suction using a Buchner funnel. Wash the resulting product three times with dichloromethane and dry it under vacuum at 150°C for 6 h to obtain pale yellow crystals with a yield of 95%.

[0081] Synthesis of PMXT: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 3 g of M and 80 mL of N,N-dimethylacetamide were added under a nitrogen atmosphere and stirred at 150°C until fully dissolved. After cooling the solution to room temperature, 34 g of XDI and 29.5 g of THC were added and stirred thoroughly until a homogeneous solution was formed. The reaction was then carried out at 60°C for 20 h to obtain PMXT gel. The product was vacuum-dried at 180°C for 6 h and then pulverized using a grinder to obtain PMXT plastic powder.

[0082] 25 g of PMXT powder was evenly spread in the mold cavity of a steel mold and pressed at 220°C / 50 MPa for 2 h to obtain PMXT blocks.

[0083] In the PMXT prepared in this example, x:y=0.05.

[0084] Example 3

[0085] Synthesis of M: 8 g of ethylenediamine was dissolved in 10 mL of N-ethylpyrrolidone and slowly added dropwise to a solution of 28 g of o-hydroxybenzaldehyde in 50 mL of N-ethylpyrrolidone. After mixing thoroughly, 36 g of 4-hydroxymethylphenylboronic acid in 80 mL of N-ethylpyrrolidone was added. The reaction solution was stirred at 120°C under a nitrogen atmosphere for 8 h. Most of the solvent was removed by distillation using a rotary evaporator (temperature 120°C, vacuum degree -0.05 MPa), and the crude product was filtered using a Buchner funnel and rinsed multiple times with dichloromethane. The crude product was added to a certain amount of N-methylpyrrolidone, heated to 150°C to fully dissolve, and then slowly cooled to room temperature. After the product crystallized, it was filtered using a Buchner funnel and washed three times with dichloromethane. The product was dried under vacuum at 160°C for 5 h to obtain pale yellow crystals with a yield of 95%.

[0086] Synthesis of PMXT: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 6 g of M and 30 mL of N-ethylpyrrolidone were added under a nitrogen atmosphere and stirred at 150°C until fully dissolved. After cooling the solution to room temperature, 13.1 g of XDI and 10.1 g of THC were added and stirred thoroughly until a homogeneous solution formed. The reaction was then carried out at 70°C for 6 h to obtain PMXT gel. The product was vacuum-dried at 130°C for 10 h and then pulverized using a grinder to obtain PMXT plastic powder.

[0087] 20 g of PMXT powder was evenly spread in the cavity of a steel mold and pressed at 190°C / 30 MPa for 1.5 h to obtain PMXT blocks.

[0088] In the PMXT prepared in this example, x:y=0.3.

[0089] Example 4

[0090] Synthesis of M: 8 g of ethylenediamine was dissolved in 10 mL of N-methylpyrrolidone and slowly added dropwise to a solution of 33.6 g of o-hydroxybenzaldehyde in 60 mL of N-methylpyrrolidone. After mixing thoroughly, a solution of 40.8 g of 3-hydroxymethylphenylboronic acid in 100 mL of N-methylpyrrolidone was added. The reaction solution was stirred at 110°C under a nitrogen atmosphere for 10 h. Most of the solvent was removed by distillation using a rotary evaporator (temperature 100°C, vacuum degree -0.05 MPa), and the crude product was filtered using a Buchner funnel and rinsed multiple times with dichloromethane to obtain a crude product. The crude product was added to a certain amount of N-methylpyrrolidone, heated to 150°C to fully dissolve, and then slowly cooled to room temperature. After the product crystallized, it was filtered using a Buchner funnel and washed three times with dichloromethane. The product was dried under vacuum at 120°C for 15 h to obtain pale yellow crystals with a yield of 90%.

[0091] Synthesis of PMXT: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 9 g of M and 20 mL of DMSO were added under a nitrogen atmosphere and stirred at 150°C until fully dissolved. After cooling the solution to room temperature, 12.2 g of XDI and 4.5 g of THC were added and stirred thoroughly until a homogeneous solution formed. The mixture was then reacted at 100°C for 30 minutes to obtain a PMXT gel. The product was then vacuum-dried at 120°C for 10 hours and pulverized using a grinder to obtain PMXT plastic powder.

[0092] 15 g of PMXT powder was evenly spread in the cavity of a steel mold and pressed at 170°C / 10 MPa for 30 min to obtain PMXT blocks.

[0093] In the PMXT prepared in this example, x:y=1.0.

[0094] Example 5

[0095] Synthesis of M: Dissolve 5g of ethylenediamine in 10mL of DMF and slowly add dropwise to a solution of 16g ​​of o-hydroxybenzaldehyde in 10mL of DMF. After mixing thoroughly, add a solution of 20g of 3-hydroxymethylphenylboronic acid in 60mL of DMF. Under a nitrogen atmosphere, incubate the reaction solution at 140°C with stirring for 7 hours. Remove most of the solvent using a rotary evaporator (110°C, vacuum -0.06MPa), filter with suction using a Buchner funnel, and rinse several times with dichloromethane to obtain a crude product. Add the crude product to a sufficient amount of DMF, heat to 150°C to fully dissolve it, and slowly cool to room temperature. After crystallization, filter with suction using a Buchner funnel. Wash the resulting product three times with dichloromethane and dry it under vacuum at 120°C for 10 hours to obtain pale yellow crystals with a yield of 92%.

[0096] Synthesis of PMXT coating: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 2 g of M and 50 mL of DMSO were added under a nitrogen atmosphere and stirred at 150°C until fully dissolved. After cooling the solution to room temperature, 18 g of XDI and 20.1 g of THC were added and stirred thoroughly until a homogeneous solution was formed. The mixture was then reacted at 60°C for 90 minutes to obtain a uniform, transparent PMXT solution. The PMXT solution was sprayed onto a 1 × 1 m² glass plate and placed in a forced-air oven at 100°C for drying for 7 days before heating was stopped to obtain a fluorescent polyurethane PMXT coating.

[0097] In the PMXT prepared in this example, x:y=0.05.

[0098] Example 6

[0099] Synthesis of M: Dissolve 7g of propylenediamine in 15mL of N-methylpyrrolidone and slowly add dropwise to a solution of 29.4g of o-hydroxybenzaldehyde in 10mL of N-methylpyrrolidone. Mix thoroughly, then add a solution of 35.7g of 4-hydroxymethylphenylboronic acid in 60mL of DMSO. Under a nitrogen atmosphere, incubate the reaction solution at 120°C with stirring for 8 hours. Remove most of the solvent using a rotary evaporator (140°C, vacuum -0.06MPa), filter with suction using a Buchner funnel, and rinse several times with dichloromethane to obtain a crude product. Add the crude product to a predetermined amount of DMSO, heat to 150°C to fully dissolve it, then slowly cool to room temperature. Once the product crystallizes, filter with suction using a Buchner funnel, wash three times with dichloromethane, and dry under vacuum at 100°C for 15 hours to obtain pale yellow crystals with a yield of 91%.

[0100] Synthesis of PMXT coating: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 12 g of M and 60 mL of N-methylpyrrolidone were added under a nitrogen atmosphere and stirred at 150°C until fully dissolved. After cooling the solution to room temperature, 15.9 g of XDI and 5.9 g of THC were added and stirred thoroughly until a homogeneous solution was formed. The mixture was then reacted at 80°C for 30 minutes to obtain a uniform, transparent PMXT solution. The PMXT solution was then knife-coated onto a 1 x 1 m² tinplate sheet and placed in a forced-air oven at 70°C for drying for 14 days before heating was stopped to obtain a fluorescent polyurethane PMXT coating.

[0101] In the PMXT prepared in this example, x:y=1.00.

[0102] Example 7

[0103] Synthesis of M: 5 g of ethylenediamine was dissolved in 8 mL of N,N-dimethylacetamide and slowly added dropwise to a solution of 19 g of o-hydroxybenzaldehyde in 20 mL of N,N-dimethylacetamide. After thorough mixing, a solution of 24 g of 2-hydroxymethylphenylboronic acid in 40 mL of N,N-dimethylacetamide was added. The reaction solution was stirred at 150°C under a nitrogen atmosphere for 7 h. Most of the solvent was removed by rotary evaporation (110°C, vacuum -0.06 MPa), followed by filtration using a Büchner funnel and multiple washings with dichloromethane to obtain a crude product. The crude product was added to a predetermined amount of N,N-dimethylacetamide, heated to 150°C to fully dissolve, and then slowly cooled to room temperature. After crystallization, the product was filtered using a Büchner funnel and washed three times with dichloromethane. The product was dried under vacuum at 110°C for 10 h to obtain pale yellow crystals with a yield of 94%.

[0104] Synthesis of PMXT coating: In a three-necked flask equipped with a stirrer, thermometer, and condenser, 9 g of M and 50 mL of N-ethylpyrrolidone were added under a nitrogen atmosphere and stirred at 150°C until fully dissolved. After cooling the solution to room temperature, 13.8 g of XDI and 7.6 g of THC were added and stirred thoroughly until a homogeneous solution was formed. The mixture was then reacted at 70°C for 60 minutes to obtain a uniform, transparent PMXT solution. The PMXT solution was spin-coated onto a 1 × 1 m² tinplate sheet and placed in an 80°C forced air oven for drying for 10 days before heating was stopped to obtain a fluorescent polyurethane PMXT coating.

[0105] In the PMXT prepared in this example, x:y=0.6.

[0106] Comparative Example 1

[0107] Synthesis of M-free polyurethane (PXT): In a three-necked flask equipped with a stirrer, thermometer, and condenser under a nitrogen atmosphere, 6.8 g of XDI and 14.1 g of THC were added to 40 mL of DMF. The mixture was stirred thoroughly until a homogeneous solution was formed. The mixture was reacted at 80°C for 30 minutes, then poured into the cavity of a steel mold. The mixture was placed in an 80°C forced air oven and dried for 14 days before heating was stopped to obtain a M-free polyurethane PXT block. The PXT prepared in this comparative example had x:y = 0. The PXT structure is as follows:

[0108]

[0109] Mechanical properties and thermal stability tests were conducted on Example 1, Example 2, Example 3, Example 4, and Comparative Example 1. According to ASTM D638, the tensile strength, elongation at break, and Young's modulus of the material were obtained; the thermal stability of the material was reflected by the charring rate, which was the mass fraction remaining after thermogravimetric analysis. The test method was to conduct thermogravimetric analysis on a TG 209C-TASC 414 / 4 instrument from NETZSCH, Germany. The material 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.

[0110]

[0111] Thermal stability tests were conducted on Examples 5, 6, and 7. The thermal stability of the coating is reflected by the charring rate, which is the mass fraction remaining after thermogravimetric analysis. The test method is the same as that of Example 1, and the data are shown in the table below.

[0112]

[0113] Combined with the above examples, it can be seen that the technology of the present invention is highly feasible. The resulting fluorescent polyurethane material (PMXT) can be further prepared into fluorescent polyurethane plastics or fluorescent polyurethane coatings. The preparation method of PMXT is simple, economical, and environmentally friendly, which is conducive to industrial mass production and promotion. At the same time, the fluorescent polyurethane material (PMXT) has excellent thermal stability, mechanical properties, reprocessability, and intrinsic luminescence properties. Moreover, the PMXT materials provided by the present invention can be reshaped, repaired, and recycled multiple times. The intrinsic luminescence properties of the PMXT material can realize the functions of microcrack detection and self-healing tracking.

Claims

1. A fluorescent polyurethane material, characterized in that Its structural formula is: wherein x:y=0.05-1.0, and n is selected from 2 or 3; Indicates that this link is connected to the rest of the polyurethane material.

2. The method for preparing the fluorescent polyurethane material according to claim 1, wherein The following steps are involved: (1) dissolving 100 parts by mass of a diamine, 320-420 parts by mass of o-hydroxybenzaldehyde, and 400-510 parts by mass of hydroxymethylphenylboric acid in an organic solvent, first slowly dropping the diamine solution into the o-hydroxybenzaldehyde solution, and then adding the hydroxymethylphenylboric acid solution; reacting at a preset temperature; after the reaction is completed, removing the solvent and collecting a solid product, and recrystallizing the obtained solid product to obtain a borate ester compound M; (2) The obtained borate compound M, xylene diisocyanate and tris(2-hydroxyethyl)isocyanurate are reacted to prepare a prefabricated liquid, wherein the reaction amounts of the borate compound M, xylene diisocyanate and tris(2-hydroxyethyl)isocyanurate are determined according to a molar ratio of hydroxyl active hydrogen to isocyanate group of 1:(0.8-1.5), and a molar ratio of the borate compound M to tris(2-hydroxyethyl)isocyanurate is 0.05-1.00; the prefabricated liquid is subjected to a molding process to prepare a fluorescent polyurethane material.

3. The method for preparing the fluorescent polyurethane material according to claim 2, wherein: The reaction conditions at the preset temperature are 110-160° C. for 5-10 hours.

4. The method for preparing the fluorescent polyurethane material according to claim 2, wherein: The operation of the molding process in step (2) is as follows: The prefabricated liquid is subjected to a gel reaction, and the obtained gel is vacuum-treated to obtain a sample; the obtained sample is crushed to obtain a fluorescent polyurethane plastic; The gelation reaction conditions are as follows: maintaining at 60-100°C for 30 minutes to 20 hours; The vacuum treatment process includes: under vacuum conditions, first heating to 120-180°C, keeping warm for 5-10 hours, then stopping heating and cooling to below 60°C, and stopping vacuuming.

5. The method for preparing the fluorescent polyurethane material according to claim 4, wherein: The fluorescent polyurethane plastic is recycled and recyclable through compression molding and solid crushing.

6. The method for preparing a fluorescent polyurethane material according to claim 2, wherein: The operation of the molding process in step (2) is as follows: The prefabricated liquid is reacted to a uniform transparent solution state; the obtained uniform transparent solution is coated on a substrate, and kept at 70 to 100° C. for 7 to 14 days to obtain a fluorescent polyurethane coating; The reaction conditions are: reaction at 60-80°C for 30-90 minutes.

7. The method for preparing a fluorescent polyurethane material according to claim 6, wherein: The fluorescent polyurethane coating is self-repaired by being kept at 180-220° C. for 2-15 hours.

8. Use of the fluorescent polyurethane material according to claim 1 or the fluorescent polyurethane material prepared by the preparation method according to any one of claims 2 to 7 as an engineering material or a repairable protective coating.

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