Preparation method of supramolecular aggregation-induced emission self-repairing waterborne polyurethane

Abstract

The invention discloses a preparation method of supramolecular aggregation-induced emission self-repairing waterborne polyurethane, which comprises the following steps of: polymerizing isocyanate serving as a hard segment and polytetramethylene glycol serving as a soft segment under the action of a catalyst to obtain a prepolymer, adding a molecular ligand into the prepolymer, and reacting to obtain the supramolecular aggregation-induced emission self-repairing waterborne polyurethane. And carrying out a stirring induced reaction to obtain the waterborne polyurethane with both luminescence property and self-repairing function. The preparation method is simple, the process is easy to control, the prepared waterborne polyurethane has excellent mechanical properties, the tensile strength reaches up to 72.6 MPa, and the elongation at break is 689.6%; under excitation of ultraviolet light of 260-400 nm, the material can emit blue fluorescence, and shows reversible optical response under external stimulation of acid, alkali and the like. In addition, after the material is repaired for 24 hours under the condition of 60 DEG C, the repair rate reaches 100%, and excellent self-repair capability is shown.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer composite materials and relates to a preparation method of a supramolecular aggregation-induced emission self-repairing waterborne polyurethane. BACKGROUND

[0002] In nature, the natural tissues of animals, such as muscles and skins, can always repair wounds by themselves. In order to greatly improve the service life, firmness and safety of materials, researchers are currently studying synthetic materials that can imitate self-healing tissues for wearable electronic devices, tires and the like. At the same time, luminescent materials are widely concerned due to their various applications in the fields of flexible electronics, intelligent batteries, information encryption and anti-counterfeiting materials, but still face the challenges of how to simultaneously experiment high toughness, excellent tensile properties, fast self-repairing ability and photoluminescence, and improve the overall mechanical properties of the materials. It is of important practical significance to prepare photoluminescent film materials with self-healing ability for multiple applications.

[0003] However, the current research and development of waterborne polyurethane materials still faces significant bottlenecks: not only do most studies focus on the realization of single function, which is difficult to meet the composite needs in multiple scenarios, but there is also a prominent contradiction between the function given and the core performance, which ultimately leads to the difficulty of expanding the application boundary of the material due to the lack of key performance. For example, patent publication CN119798599A discloses a self-repairing waterborne polyurethane and its preparation method and application. The invention introduces dynamic reversible covalent bonds and non-covalent bonds by compounding specific amino-containing compounds and thiourea, and prepares a self-repairing waterborne polyurethane. The waterborne polyurethane material has a repair rate of about 95% after 8 h of self-repairing at 40 DEG C. However, it does not have luminescent properties and is limited in application in the field of intelligent sensing. Patent publication CN119931478A discloses a biomimetic patterned biomass-based photoluminescent polyurethane coating for leather. The mechanical property of the waterborne polyurethane is only about 25%, which limits its application in aspects such as bearing external force, dynamic deformation, high-frequency contact or long-term durability.

[0004] Based on this, the present application aims to provide a waterborne polyurethane with good self-repairing performance and luminescence. The prepared polyurethane can be applied to various industries and has excellent mechanical properties, optical response characteristics and environmental adaptability. SUMMARY

[0005] To solve the above technical problems, the present application aims to provide a preparation method of supramolecular aggregation-induced emission self-healing waterborne polyurethane, which comprises the following steps: adding a molecular ligand to a prepolymer obtained by polymerization of isocyanate as hard segment and polybutylene glycol as soft segment under the action of a catalyst, and then stirring and inducing reaction to obtain a waterborne polyurethane with both luminescent performance and self-healing function. The preparation method is simple and easy to control, and the prepared waterborne polyurethane has excellent mechanical properties, with a tensile strength of up to 72.6 MPa and an elongation at break of 689.6%. Under the excitation of 260-400 nm ultraviolet light, the material can emit blue fluorescence and exhibit reversible optical response under external stimuli such as acid and alkali. In addition, the material has an excellent self-healing ability, with a self-healing rate of 100% after 24 h of self-healing at 60℃.

[0006] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows: The present application provides a preparation method of supramolecular aggregation-induced emission self-healing waterborne polyurethane, which comprises the following steps in sequence: S1, preparing [2,2'-dipyridyl]-4,4-dihydrazine molecular ligand S11, adding [2,2-dipyridyl]-4,4-dicarboxylic acid into a flask, then adding methanol into the flask, stirring uniformly, and then condensing and refluxing at 60℃ for 6-10 h, during which 5 mL of concentrated sulfuric acid is slowly added into the reaction system; S12, after the reaction is completed, adjusting the pH of the system to 7 using saturated sodium hydroxide solution, then adding 100 mL of chloroform and 30 mL of deionized water for extraction, drying the obtained organic phase with 5 g of anhydrous sodium sulfate, and then filtering and rotary evaporating under reduced pressure to obtain [2,2'-dipyridyl]-4,4'-dimethyl ester; S13, adding [2,2'-dipyridyl]-4,4'-dimethyl ester, methanol and hydrazine hydrate into a flask, stirring uniformly, and then condensing and refluxing at 80℃ for 8-12 h to obtain white precipitate; washing the white precipitate with 50 mL of dichloromethane, and then drying it in an oven at 80℃ for 20 min to obtain [2,2'-dipyridyl]-4,4-dihydrazine (BDs) molecular ligand; S2, preparing supramolecular aggregation-induced emission self-healing waterborne polyurethane S21, adding polybutylene glycol (PTMG with a weight average molecular weight of 600-5000) and isocyanate into a three-necked flask, and then adding dibutyltin dilaurate at 80℃ and a stirring rate of 220 rpm, wherein the addition amount of dibutyltin dilaurate is 0.03 wt.% of the total mass of polybutylene glycol and isocyanate, and then stirring and reacting for 1.2 h to obtain a prepolymer; S22, 2,2-dimethylol butyric acid (DMBA) and butyl tin dilaureate are added into the prepolymer, the addition amount of butyl tin dilaureate is 0.015 wt.% of the total mass of polybutylene glycol and isocyanate, after stirring for 1.5 h, the temperature of the reaction system is increased to 85℃, [2,2'-bipyridine]-4,4-dihydrazide molecular ligand is added, and stirring is carried out for 5 h; then the temperature of the reaction system is decreased to 35℃, 0.6 g of triethylamine is added, after reaction for 35 min, the rotation speed is increased to 1000 rpm, 50 mL of deionized water is added into the reaction system, and stirring reaction is carried out for 30 min, to obtain a polymer emulsion; S23, the polymer emulsion is poured into a polytetrafluoroethylene mold, dried at room temperature for 24 h, and then aged in an oven at 60℃ for 12 h, to obtain a supramolecular aggregation induced emission self-healing waterborne polyurethane.

[0007] As a limitation of the application, in step S11, the molar ratio of [2,2-bipyridine]-4,4-dicarboxylic acid to methanol is 1:100.

[0008] As another limitation of the application, in step S13, the molar ratio of [2,2'-bipyridine]-4,4'-dimethyl formate to methanol, hydrazine hydrate is 2:1000:5.

[0009] As a third limitation of the application, in step S21, the isocyanate is one of hexamethylene diisocyanate, isophorone diisocyanate, methylcyclohexyl diisocyanate, dicyclohexylmethylene diisocyanate, phenylene diisocyanate, 2,2,4-trimethylhexane diisocyanate or dimer acid diisocyanate.

[0010] As a fourth limitation of the application, in step S21, the molar ratio of polybutylene glycol to isocyanate is 1:3.

[0011] As a fifth limitation of the application, in step S22, the molar ratio among polybutylene glycol, 2,2-dimethylol butyric acid, [2,2'-bipyridine]-4,4-dihydrazine molecular ligand is 5:6:4.

[0012] In the present application, the molar ratio between polybutylene glycol and 2,2-dimethylol butyric acid, [2,2'-bipyridine]-4,4-dihydrazine molecular ligand will affect the water dispersibility, mechanical properties, self-repair efficiency and luminescence properties of the waterborne polyurethane. When the molar ratio is as such, the hydrogen bond density is moderate, the self-repair efficiency is high, and the aggregation-induced emission effect is significant, so that the effects of "water dispersion stability, high mechanical strength, high-efficiency self-repair and strong luminescence" can be achieved. If the molar ratio is greater than this, the ligand molecules will be excessively aggregated, resulting in luminescence quenching and excessive hydrogen bonds to increase the rigidity of the chain segments, thus reducing the flexibility of the waterborne polyurethane, so that the purposes of high toughness, excellent tensile properties, rapid self-repair ability and photoluminescence cannot be achieved. If the molar ratio is less than this, the ligand molecules are insufficiently introduced, the hydrogen bond crosslinking density is reduced, the intermolecular chain interaction is weakened, the self-repair efficiency is reduced, the aggregation-induced emission effect is not significant, and the mechanical properties and luminescence properties of the material are not ideal.

[0013] The above technical solutions of the present application are closely related and influence each other as a whole, which jointly determine the morphology characteristics and performance of the product. The supermolecular aggregation-induced emission self-repairing waterborne polyurethane prepared by the present application has high tensile property, excellent elasticity, self-repairing ability, optical response characteristics and environmental adaptability.

[0014] In the synthesis process of the waterborne polyurethane, the synthesis route of the molecular ligand BDs is as follows: .

[0015] The BDs are composed of two hydrazides and a bipyridine, the multi-layer hydrogen bond cross-linking (strong hydrogen bonds: bipyridine, carbonyl, weak hydrogen bonds: -NH-, urea bond) introduced by the BDs and the ionic interaction between the tertiary amine groups provided by the BDs and the carboxyl groups provided by the aqueous emulsifier DMBA synergize to provide the aqueous polyurethane with excellent mechanical properties and self-repairing ability. In the dynamic supramolecular polymer network, the strong cross-linking hydrogen bonds mainly endow the elastomer with robustness and elasticity, while the weak hydrogen bonds dissipate strain energy through effective reversible bond breaking and reorganization, and the dynamic hydrogen bond network collectively promotes the self-healing characteristics. Moreover, the BDs have intramolecular restricted rotation (RIM) and rich conjugated structure, which can meet the conditions required by the aggregation-induced emission, that is, the bipyridine groups in the molecular ligand BDs provide the π-conjugated skeleton, the π-π interaction between the pyridine rings promotes molecular aggregation, and the pyridine ring is a strong hydrogen bond site to form a strong hydrogen bond with the carbonyl in the aqueous polyurethane, thereby enhancing the degree of molecular chain entanglement and restricting intramolecular rotation. The -NH- in the hydrazide group in the BDs forms a weak hydrogen bond with the urea bond in the aqueous polyurethane, strengthens the supramolecular aggregation, and restricts the free rotation of the molecular ligand. The ionic interaction between the tertiary amine groups and the carboxyl groups provided by the DMBA in the aqueous polyurethane system enhances the binding force of the BDs and the aqueous polyurethane network, promotes the formation of stable aggregates, and strengthens the restriction of intramolecular rotation (RIM) on the emission induction. These binding sites enable the aqueous polyurethane to break and reconfigure, and have high tensile strength, high extensibility and toughness.

[0016] The above technical solution has the following advantages or beneficial effects: 1. The aqueous polyurethane prepared by the present application has excellent mechanical properties, with a tensile strength of up to 72.6 MPa and an elongation at break of 689.6%; under 260-400 nm ultraviolet light excitation, the material can emit blue fluorescence and exhibit reversible optical response under external stimuli such as acid and base; and after 24 h of repair at 60℃, the repair rate reaches 100%, showing excellent self-repairing ability. 2. The aqueous polyurethane material prepared by the present application can be widely used in various repair self-healing and optical sensing, has good compatibility, is widely applicable, and has good popularization and application value. 3. The preparation method of the present application is simple, the process is easy to control, and can be mass-produced industrially.

[0017] The present application is suitable for preparing supramolecular aggregation-induced emission self-repairing aqueous polyurethane.

[0018] The technical solution of the present application will be further described in detail below in combination with the drawings and specific embodiments in the specification. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1Structure characterization diagram of [2,2'-bipyridine]-4,4-dihydrazide molecular ligand prepared in Example 1 of the present application, wherein: (a) is a nuclear magnetic resonance hydrogen spectrum, (b) is a Fourier infrared spectrum; Figure 2 Infrared spectrum of the waterborne polyurethane prepared in Example 1 and Comparative Examples 1-4 of the present application; Figure 3 Mechanical property test diagram of the waterborne polyurethane prepared in Example 1 and Comparative Examples 1-4 of the present application; Figure 4 Self-repairing schematic diagram and mechanical property characterization diagram within 4-24 h of self-healing of the waterborne polyurethane prepared in Example 1 of the present application, wherein: (a) is a self-repairing schematic diagram, (b) is a mechanical property characterization diagram within 4-24 h of self-healing; Figure 5 Fluorescence spectrum of the waterborne polyurethane prepared in the present application, wherein: (a) is a fluorescence spectrum under normal conditions of Example 1 and Comparative Examples 1-2 and Comparative Example 4, (b) is a fluorescence spectrum under different recovery times after acid stimulus response of the waterborne polyurethane prepared in Example 1, (c) is a fluorescence spectrum under different recovery times after base stimulus response of the waterborne polyurethane prepared in Example 1. DETAILED DESCRIPTION

[0020] The following examples are only a part of the embodiments of the present application, rather than all the embodiments. Therefore, the detailed description of the embodiments of the present application provided below is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0021] In the present application, all the equipment and raw materials, etc. can be purchased from the market or commonly used in the industry, unless otherwise specified. The methods in the following examples are all conventional methods in the art, unless otherwise specified. Example 1

[0022] In this embodiment, a supramolecular aggregation-induced emission self-repairing waterborne polyurethane is prepared, and the preparation process and steps are as follows: S1, Preparation of [2,2'-bipyridine]-4,4-dihydrazine molecular ligand S11, flame dry the glass flask under vacuum condition, and flush with nitrogen for several times, then add 5 mmol [2,2-bipyridine]-4,4-dicarboxylic acid into the flask, add 20 mL of methanol into the flask, stir uniformly, and then condense and reflux at 60℃ for 6 h. Slowly add 5 mL of concentrated sulfuric acid into the reaction system during condensation and reflux; S12, after the reaction, the pH of the system is adjusted to 7 using saturated sodium hydroxide solution, then 30 mL of deionized water and 100 mL of chloroform are added to separate the organic phase, and the obtained organic phase is dried with 5 g of anhydrous sodium sulfate, and after filtration and rotary evaporation under reduced pressure, [2,2'-bipyridine]-4,4'-dimethyl methanesulfonate is obtained; S13, 4 mmol of [2,2'-bipyridine]-4,4'-dimethyl methanesulfonate, 80 mL of methanol and 10 mmol of hydrazine hydrate are added to a flask, stirred uniformly, then condensed and refluxed at 80°C for 8 h to obtain a white precipitate; the white precipitate is washed with 50 mL of dichloromethane, and then placed in an oven and dried at 80°C for 20 min to obtain a [2,2'-bipyridine]-4,4-dihydrazide molecular ligand; S2, preparation of a supramolecular aggregation-induced emission self-repairing waterborne polyurethane S21, 5 mmol of polybutylene glycol and 15 mmol of isophorone diisocyanate are added to a three-necked flask, and butyltin dilaurate is added dropwise, the amount of butyltin dilaurate added is 0.03 wt.% of the total mass of polybutylene glycol and isocyanate, and the reaction is stirred at 80°C and 220 rpm for 1.2 h to obtain a prepolymer; S22, 0.88 g of 2,2-dimethylol butyric acid is dissolved in 5 mL of acetone and added to the above prepolymer together with butyltin dilaurate, the amount of butyltin dilaurate added is 0.015 wt.% of the total mass of polybutylene glycol and isocyanate, and the reaction is stirred at 220 rpm for 1.5 h, then the temperature of the reaction system is increased to 85°C, 1.088 g of [2,2'-bipyridine]-4,4-dihydrazide molecular ligand is dissolved in 5 mL of acetone and added to the system, and the reaction is stirred at 220 rpm for 5 h; then the temperature of the reaction system is reduced to 35°C, 0.6 g of triethylamine is added, and after 35 min of reaction, the stirring speed is increased to 1000 rpm, 50 mL of deionized water is added to the reaction system, and the reaction is stirred for 30 min to obtain a polymer emulsion; S23, the polymer emulsion is poured into a polytetrafluoroethylene mold, dried at room temperature for 24 h, and then aged in an oven at 60°C for 12 h to obtain a supramolecular aggregation-induced emission self-repairing waterborne polyurethane. Example 2

[0023] In this example, a supramolecular aggregation-induced emission self-repairing waterborne polyurethane is prepared, and the preparation process and steps are as follows: S1, preparation of [2,2'-bipyridine]-4,4-dihydrazine molecular ligand S11, flame dry the glass flask under vacuum condition, and flush with nitrogen for several times, then add 5 mmol [2,2-bipyridine]-4,4-dicarboxylic acid into the flask, add 20 mL of methanol into the flask, stir uniformly, and then condense and reflux at 60 ℃ for 8 h, slowly add 5 mL of concentrated sulfuric acid into the reaction system during condensation and reflux; S12, after the reaction is completed, adjust the pH of the system to 7 using saturated sodium hydroxide solution, then add 100 mL of chloroform and 30 mL of deionized water for extraction, dry the obtained organic phase with 5 g of anhydrous sodium sulfate, and then filter and rotary evaporate under reduced pressure to obtain [2,2'-bipyridine]-4,4'-dimethyl carboxylate; S13, add 4 mmol of [2,2'-bipyridine]-4,4'-dimethyl carboxylate, 80 mL of methanol and 10 mmol of hydrazine hydrate into the flask, stir uniformly, and then condense and reflux at 80 ℃ for 12 h to obtain a white precipitate; wash the white precipitate with 50 mL of dichloromethane, and then place it in an oven and dry at 80 ℃ for 20 min to obtain a [2,2'-bipyridine]-4,4-dihydrazide molecular ligand; S2, preparation of a supramolecular aggregation-induced emission self-healing waterborne polyurethane S21, add 5 mmol of polybutylene glycol and 15 mmol of hexamethylene diisocyanate into a three-necked flask, and drop butyltin dilaurate, the drop amount of butyltin dilaurate being 0.03 wt.% of the total mass of polybutylene glycol and isocyanate, stir and react at 80 ℃ and a speed of 220 rpm for 1.2 h to obtain a prepolymer; S22, dissolve 0.88 g of 2,2-dimethylol butyric acid in 5 mL of acetone, and add butyltin dilaurate and the above prepolymer together, the addition amount of butyltin dilaurate being 0.015 wt.% of the total mass of polybutylene glycol and isocyanate, stir and react at a speed of 220 rpm for 1.5 h, then increase the temperature of the reaction system to 85 ℃, dissolve 1.088 g of [2,2'-bipyridine]-4,4-dihydrazide molecular ligand in 5 mL of acetone, and add it into the system, stir and react at a speed of 220 rpm for 5 h, then reduce the temperature of the reaction system to 35 ℃, add 0.6 g of triethylamine, react for 35 min, increase the speed to 1000 rpm, add 50 mL of deionized water into the reaction system, stir and react for 30 min to obtain a polymer emulsion; S23, pour the polymer emulsion into a polytetrafluoroethylene mold, dry at room temperature for 24 h, and then age in an oven at 60 ℃ for 12 h to obtain a supramolecular aggregation-induced emission self-healing waterborne polyurethane. Example 3

[0024] The present embodiment prepares a supramolecular aggregation-induced emission self-repairing waterborne polyurethane, the preparation process and steps are as follows: S1, preparing [2,2'-bipyridine]-4,4-dihydrazine molecular ligand S11, flame drying the glass flask under vacuum conditions, and flushing with nitrogen several times, then adding 5 mmol [2,2-bipyridine]-4,4-dicarboxylic acid into the flask, then adding 20 mL of methanol into the flask, stirring uniformly, and then condensing and refluxing at 60°C for 10 h, and slowly adding 5 mL of concentrated sulfuric acid into the reaction system during condensing and refluxing; S12, after the reaction is completed, the pH of the system is adjusted to 7 using saturated sodium hydroxide solution, then 100 mL of chloroform and 30 mL of deionized water are added for extraction, the obtained organic phase is dried with 5 g of anhydrous sodium sulfate, and after filtration and rotary evaporation under reduced pressure, [2,2'-bipyridine]-4,4'-dimethyl dicarboxylate is obtained; S13, adding 4 mmol [2,2'-bipyridine]-4,4'-dimethyl dicarboxylate, 80 mL of methanol and 10 mmol of hydrazine hydrate into the flask, stirring uniformly, and then condensing and refluxing at 80°C for 10 h to obtain a white precipitate; the white precipitate is washed with 50 mL of dichloromethane, and then placed in an oven and dried at 80°C for 20 min to obtain [2,2'-bipyridine]-4,4-dihydrazine molecular ligand; S2, preparing a supramolecular aggregation-induced emission self-repairing waterborne polyurethane S21, adding 5 mmol of polybutylene glycol and 15 mmol of hexamethylene diisocyanate into a three-necked flask, and adding dibutyltin dilaurate dropwise, the amount of dibutyltin dilaurate added is 0.03 wt.% of the total mass of polybutylene glycol and isocyanate, stirring at 80°C and 220 rpm for 1.2 h to obtain a prepolymer; S22, dissolving 0.88 g of 2,2-dimethylol butyric acid in 5 mL of acetone and adding it into the above prepolymer together with dibutyltin dilaurate, the amount of dibutyltin dilaurate added is 0.015 wt.% of the total mass of polybutylene glycol and isocyanate, stirring at a speed of 220 rpm for 1.5 h, then increasing the temperature of the reaction system to 85°C, dissolving 1.088 g of [2,2'-bipyridine]-4,4-dihydrazine molecular ligand in 5 mL of acetone and adding it into the system, stirring at 220 rpm for 5 h, then reducing the temperature of the reaction system to 35°C, adding 0.6 g of triethylamine, reacting for 35 min, then increasing the speed to 1000 rpm, adding 50 mL of deionized water into the reaction system, stirring for 30 min to obtain a polymer emulsion; S23, pour the polymer emulsion into a polytetrafluoroethylene mold, dry at room temperature for 24 h, then mature in an oven at 60℃ for 12 h, to obtain a supramolecular aggregation-induced emission self-healing waterborne polyurethane. Comparative Example

[0025] In order to explore the influence of different reactants and different parameters in the preparation process of the present application on the performance of the product, the following comparative experiments were carried out, and different waterborne polyurethanes were prepared in the following comparative examples: Comparative Example 1 A waterborne polyurethane was prepared in this comparative example, and the preparation process was similar to that of Example 1, except that in step S22, the mass of the added [2,2'-bipyridine]-4,4-dihydrazide molecular ligand was different, and 1,4-butanediol was additionally added, as follows: 0.88 g of 2,2-dimethylol butyric acid was dissolved in 5 mL of acetone and added to the above prepolymer together with butyl tin dilaurate. The amount of butyl tin dilaurate added was 0.015 wt.% of the total mass of polybutylene glycol and isocyanate. After stirring at a rate of 220 rpm for 1.5 h, the temperature of the reaction system was increased to 85℃. 0.816 g of [2,2'-bipyridine]-4,4-dihydrazide molecular ligand and 0.09 g of 1,4-butanediol were dissolved in 5 mL of acetone respectively and added to the system. The reaction was stirred at 220 rpm for 5 h. Then the temperature of the reaction system was reduced to 35℃, 0.6 g of triethylamine was added, and the reaction was carried out for 35 min. Then the stirring speed was increased to 1000 rpm, 50 mL of deionized water was added to the reaction system, and the reaction was stirred for 30 min to obtain a polymer emulsion.

[0026] Comparative Example 2 A waterborne polyurethane was prepared in this comparative example, and the preparation process was similar to that of Example 1, except that in step S22, the molar ratio between the polybutylene glycol and 2,2-dimethylol butyric acid, [2,2'-bipyridine]-4,4-dihydrazide molecular ligand was 5:5:5.

[0027] Comparative Example 3 A waterborne polyurethane was prepared in this comparative example, and the preparation process was similar to that of Example 1, except that in step S22, the [2,2'-bipyridine]-4,4-dihydrazide molecular ligand was replaced by 1,4-butanediol.

[0028] Comparative Example 4 A waterborne polyurethane was prepared in this comparative example, and the preparation process was similar to that of Example 1, except that in step S22, 2,2-dimethylol butyric acid was not added. Performance Test

[0029] The waterborne polyurethanes prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to a series of performance tests, as detailed below: like Figure 1 The image shows the structural characterization of the [2,2'-bipyridine]-4,4-diacylhydrazide ligand prepared in Example 1 of this invention. Data can be obtained from (a) the 1H NMR spectrum: 1 H-NMR (400MHz, DMSO): δ=10.25 (s, 2H, NH), 8.87 (d, 2H, Ar-H), 8.85 (d, 2H, Ar-H), 7.83 (d, 2H, Ar-H), 4.71 (s, 4H, NH2). 13 C-NMR (100 MHz, DMSO): δ = 163.7 (2C), 155.5 (2C), 150 (2C), 141.7 (2C), 121.4 (2C), 118.2 (2C). In molecular ligands BDs... 1 In H-NMR, the peaks at 8.87 ppm, 8.85 ppm, and 7.83 ppm correspond to H atoms in the pyridine ring, the peak at 10.25 ppm corresponds to H atoms in -NH-, and the peak at 4.71 ppm corresponds to H atoms in -NH2-. In BDs... 13 In C-NMR, the peaks at 155.5 ppm, 150 ppm, 141.7 ppm, 121.4 ppm, and 118.2 ppm correspond to the C atoms (Ar-H) on the pyridine ring, and the peak at 163.7 ppm corresponds to the C atoms of the C=O bond. The NMR chemical shifts (δ) of BDs indicate that the ligands BDs have been successfully synthesized. From the Fourier transform infrared spectrum in (b), it can be seen that at 3302 cm⁻¹... -1 The characteristic peak at 1614 cm⁻¹ is attributed to the stretching vibration of the NH bond. -1 The characteristic peak at 3068 cm⁻¹ belongs to the stretching vibration of C=O. -1 1519 cm -1 and 1320cm -1 The peaks at these points correspond to the stretching vibrations of CH, C=C, and CN within the pyridine ring, respectively. In summary... 1 H-NMR, 13 The results of C-NMR and FT-IR tests confirm that the compound BDs was successfully synthesized.

[0030] like Figure 2 The figures show the infrared spectra of the waterborne polyurethanes prepared in Example 1 and Comparative Examples 1-4 of this invention, with the 3200-3400 cm⁻¹ range shown. -1The broad absorption bands within the range are due to the -OH groups in PTMG, DMBA, and BDO. As the polycondensation reaction proceeds, the 2258 cm⁻¹ band corresponds to the -NCO group in isophorone diisocyanate (IPDI). -1 The characteristic absorption peak at 1713 cm⁻¹ gradually disappears. Meanwhile, at 1713 cm⁻¹... -1 A new absorption peak appeared at 2796 cm⁻¹, indicating the formation of the C=O group. This confirms that the -NCO group in IPDI has completely reacted with the -OH groups of PTMG, DMBA, and BDO. -1 2856 cm -1 2930 cm -1 and 3300 cm -1 The absorption peaks at these locations represent the stretching vibrations of the CH and NH bonds, respectively, indicating that the chain extension reaction of the waterborne polyurethane has been completed.

[0031] like Figure 3The mechanical property test chart of the waterborne polyurethane prepared in Example 1 and Comparative Examples 1-4 of the present application is shown in the figure. As can be seen from the figure, in Comparative Example 3, Comparative Example 1 and Example 1, the tensile strength of the waterborne polyurethane is significantly improved with the increase of the content of ligand BDs, from 0.3 MPa in Comparative Example 3 to 72.6 MPa in Example 1, which is 241 times higher than that in Comparative Example 3. Although the content of ligand in Comparative Example 2 is higher than that in Example 1, the density of hydrogen bond crosslinking points in the system is too high, which seriously limits the activity of the polymer chain segment, and the molecular chain is difficult to disperse external stress through slippage and rearrangement, so the mechanical property is reduced. The mechanical property of Comparative Example 4 is decreased due to the lack of carboxyl groups provided by DMBA, so that the ionic bond formed between the tertiary amine groups in BDs and the carboxyl groups no longer exists. Relying only on the hydrogen bond of BDs, it is not possible to construct a dynamic supramolecular network that is strong and stable enough, resulting in low material strength. In Comparative Example 3, Comparative Example 1, Example 1 and Comparative Example 2, the elongation at break shows a trend of first decreasing, then increasing and then decreasing again. This phenomenon can be attributed to the dual effect caused by the introduction of BDs molecules: initially, with the increase of the content of BDs, a large number of hydrogen bonds are formed between the supramolecular crosslinking agent and the polyurethane chain segment, significantly enhancing the interaction between the molecular chains and the crosslinking density, limiting the slippage and movement of the chain segment, resulting in increased material rigidity and decreased plastic deformation capacity, thus the elongation at break decreases; later, when the content of BDs increases to the optimal proportion, the density of dynamic reversible hydrogen bonds reaches a critical point, forming a dense and reversible supramolecular network. When stressed, a large number of weak hydrogen bonds can undergo "breakage-reconstruction" to effectively dissipate energy, avoiding stress concentration, and instead giving the material higher toughness, thus the elongation at break increases again. When the content of BDs continues to increase, the hydrogen bond crosslinking points will be too dense, resulting in a decrease in the reversibility of dynamic hydrogen bonds. The high crosslinking density will seriously inhibit the movement and energy dissipation process of the polymer chain segment, and the material will become hard and brittle. At this time, there is no effective energy dissipation path when stressed, and brittle fracture will occur quickly, resulting in a decrease in the elongation at break. In Comparative Example 4, although the molar amount of BDs is the same as that in Example 1, it lacks DMBA, so it cannot form ionic bonds with BDs, resulting in an incomplete cooperative dynamic network. The lack of key "sacrificial bonds" in the network makes it unable to effectively dissipate energy when stressed, resulting in brittle fracture, so the elongation at break is reduced.

[0032] The waterborne polyurethane prepared in Example 1 of the present application was cut into two parts using a blade, and immediately spliced together. The healing process was observed under an optical microscope, as shown in Figure 4shown. As can be seen from (a), the waterborne polyurethane crack interface is almost completely healed after 24 h of repair at 60°C, indicating that it has good self-healing ability. To further quantify the self-repairing efficiency, the waterborne polyurethane under different repair times was subjected to tensile testing, and the test results are shown in Table 1. Figure 4 As shown in (b), the self-repairing efficiency of the waterborne polyurethane after being cut and placed at 60°C for 4 h, 8 h, 12 h, 18 h and 24 h was 18%, 53%, 72%, 87% and 100%, respectively. Notably, the waterborne polyurethane after 24 h of repair, the breaking point in the tensile process is located outside the original damage point, indicating that the repair interface has been restored to the mechanical strength close to the original material, confirming its high-efficiency self-repairing ability under mild conditions.

[0033] As shown in (b), the self-repairing efficiency of the waterborne polyurethane after being cut and placed at 60°C for 4 h, 8 h, 12 h, 18 h and 24 h was 18%, 53%, 72%, 87% and 100%, respectively. Notably, the waterborne polyurethane after 24 h of repair, the breaking point in the tensile process is located outside the original damage point, indicating that the repair interface has been restored to the mechanical strength close to the original material, confirming its high-efficiency self-repairing ability under mild conditions. Figure 5 As shown in (b), the self-repairing efficiency of the waterborne polyurethane after being cut and placed at 60°C for 4 h, 8 h, 12 h, 18 h and 24 h was 18%, 53%, 72%, 87% and 100%, respectively. Notably, the waterborne polyurethane after 24 h of repair, the breaking point in the tensile process is located outside the original damage point, indicating that the repair interface has been restored to the mechanical strength close to the original material, confirming its high-efficiency self-repairing ability under mild conditions.

[0034] As shown in (b), the self-repairing efficiency of the waterborne polyurethane after being cut and placed at 60°C for 4 h, 8 h, 12 h, 18 h and 24 h was 18%, 53%, 72%, 87% and 100%, respectively. Notably, the waterborne polyurethane after 24 h of repair, the breaking point in the tensile process is located outside the original damage point, indicating that the repair interface has been restored to the mechanical strength close to the original material, confirming its high-efficiency self-repairing ability under mild conditions. Figure 5It can be seen from (b) that under acidic conditions, the emission color of the aqueous polyurethane changes from blue to yellow, while the fluorescence intensity decreases significantly. However, the fluorescence gradually recovers after washing with water for 3 s, and recovers 85% of the initial emission intensity within 60 min. Figure (b) also characterizes the movement of the emission peak during the process of the aqueous polyurethane fluorescence changing from yellow to blue. This phenomenon can be attributed to the protonation-deprotonation effect, i.e. the acidic environment protonates the light-emitting centers (such as pyridine, carbonyl), reduces the LUMO level, and causes red shift of fluorescence; at the same time, the acid destroys the hydrogen-bonded crosslinked network inside the material, weakens the intermolecular interaction and destroys the rigid light-emitting structure, so that the movement ability of the molecular chain is enhanced, the non-radiative transition is increased, and thus the fluorescence intensity decreases. After leaving the acidic environment, the aqueous polyurethane restores the electronic structure of the molecule by deprotonation, and the hydrogen-bonded crosslinked network gradually restructures, the molecular aggregation structure returns to the initial state, the non-radiative transition decreases, and finally the fluorescence intensity recovers and re-emits blue light.

[0035] From Figure 5 It can be seen from (c) that in the alkaline environment, the fluorescence of the aqueous polyurethane is completely extinguished. However, the fluorescence gradually recovers after washing with water for 3 s, and recovers completely within 180 min. Unlike the acidic response, the emission color of the aqueous polyurethane fluorescence remains unchanged, and only the brightness gradually increases. This phenomenon is due to the fact that the alkaline environment destroys the hydrogen-bonded crosslinked network, enhances the movement ability of the molecular chain, and increases the non-radiative transition, thereby leading to fluorescence quenching. After water washing, the hydrogen-bonded crosslinked network gradually reorganizes, reduces the non-radiative transition, and enables the fluorescence to recover.

[0036] Finally, it should be noted that the above description is only for the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the claims of the present application.

Claims

1. A method for preparing a supramolecular aggregation-induced emission- switching self-healing waterborne polyurethane, characterized in that, The following steps are carried out in sequence: S1, preparation of [2,2'-dipyridyl]-4,4-dihydrazide molecular ligand S11, [2,2-dipyridyl]-4,4-dicarboxylic acid is added to a flask, and methanol is added to the flask, stirred uniformly, and then condensed and refluxed at 60°C for 6-10 h. When condensing and refluxing, 5 mL of concentrated sulfuric acid is slowly added to the reaction system; S12, after the reaction is completed, the system pH is adjusted to 7 using a saturated sodium hydroxide solution, and then 100 mL of chloroform and 30 mL of deionized water are added for extraction. The obtained organic phase is dried with 5 g of anhydrous sodium sulfate, filtered and rotary evaporated under reduced pressure to obtain [2,2'-dipyridyl]-4,4'-dimethyl carboxylate; S13, [2,2'-dipyridyl]-4,4'-dimethyl carboxylate, methanol and hydrazine hydrate are added to a flask, stirred uniformly, and then condensed and refluxed at 80°C for 8-12 h to obtain a white precipitate. The white precipitate is washed with 50 mL of dichloromethane, and then placed in an oven and dried at 80°C for 20 min to obtain [2,2'-dipyridyl]-4,4-dihydrazine molecular ligand; S2, preparation of a supramolecular aggregation-induced emission self-healing waterborne polyurethane S21, polybutylene glycol and isocyanate are added to a three-necked flask, and butyltin dilaurylate is added dropwise at 80°C and a stirring rate of 220 rpm. The addition amount of butyltin dilauryl is 0.03 wt.% of the total mass of polybutylene glycol and isocyanate. The stirring reaction is carried out for 1.2 h to obtain a prepolymer; S22, 2,2-dimethylol butyric acid and butyltin dilauryl are added to the prepolymer. The addition amount of butyltin dilauryl is 0.015 wt.% of the total mass of polybutylene glycol and isocyanate. After stirring for 1.5 h, the temperature of the reaction system is increased to 85°C, and [2,2'-dipyridyl]-4,4-dihydrazine molecular ligand is added. The stirring is carried out for 5 h. Then the temperature of the reaction system is reduced to 35°C, 0.6 g of triethylamine is added, and the reaction is carried out for 35 min. The stirring speed is increased to 1000 rpm, 50 mL of deionized water is added to the reaction system, and the stirring reaction is carried out for 30 min to obtain a polymer emulsion; S23, the polymer emulsion is poured into a polytetrafluoroethylene mold, dried at room temperature for 24 h, and then aged in an oven at 60°C for 12 h to obtain a supramolecular aggregation-induced emission self-healing waterborne polyurethane.

2. The method of claim 1, wherein the method is characterized by, In step S11, the molar ratio of [2,2-dipyridyl]-4,4-dicarboxylic acid to methanol is 1:

100.

3. The method of claim 1, wherein the method is characterized by, In step S13, the molar ratio of [2,2'-dipyridyl]-4,4'-dimethyl carboxylate to methanol and hydrazine hydrate is 2:1000:

5.

4. The method of claim 1, wherein the method is characterized by, In step S21, the isocyanate is one of hexamethylene diisocyanate, isophorone diisocyanate, methylcyclohexyl diisocyanate, dicyclohexylmethylene diisocyanate, phenylene diisocyanate, 2,2,4-trimethylhexane diisocyanate or diisocyanate of dimer acid.

5. The method of claim 1, wherein the method is characterized by, In step S21, the molar ratio of polybutylene glycol to isocyanate is 1:

3.

6. The method of claim 1, wherein the method is characterized by, In step S22, the molar ratio of the polybutylene glycol to 2,2-dimethylol butanoic acid to [2,2'-bipyridine]-4,4-dihydrazide molecular ligand is 5:6:4.

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