A water-based TPU film and its production method

Abstract

This invention discloses an aqueous TPU film and its production method, belonging to the field of polyurethane film production technology. This aqueous TPU film achieves self-healing by grafting disulfide bonds and using them as crosslinking agents, and by grafting benzotriazole and polytetrahydrofuran ether onto thermoplastic polyurethane using a silane coupling agent. This results in a self-healing function that can be achieved at room temperature (25°C) without the need for high-temperature equipment, relying solely on disulfide bonds, with a repair rate exceeding 80%. Simultaneously, benzotriazole specifically absorbs ultraviolet light, inhibiting photo-oxidative degradation; the polytetrahydrofuran soft segment (Tg≈-70°C) ensures the material maintains good elasticity at -40°C, solving the low-temperature embrittlement problem; the rigid benzene ring and the polyurethane hard segment synergistically enhance its mechanical strength: tensile strength ≥30MPa, tear strength ≥80kN / m, and the long ether chain soft segment ensures elastic recovery rate, achieving a balance between mechanical strength and toughness, suitable for coatings, films, seals, and other applications.

Description

Technical Field

[0001] This invention belongs to the field of membrane preparation technology, and particularly relates to an aqueous TPU membrane and its production method. Background Technology

[0002] Traditionally prepared TPU materials are prone to thermal decomposition and oxidation at high temperatures, leading to a decline in material performance. Prolonged exposure to high temperatures can cause water-based TPU films to exhibit increased hardness, decreased elasticity, and color changes, and may even result in melting or combustion, limiting their application in high-temperature environments. Furthermore, the ester or urethane bonds in water-based TPU films are susceptible to hydrolysis in water, further degrading material properties. This is particularly true in humid environments, where hydrolysis resistance is significantly affected, potentially leading to decreased strength and elongation, thus limiting their application in prolonged water contact or high-humidity environments. Moreover, when used outdoors, water-based TPU films are subject to prolonged exposure to sunlight, rain, wind, and sand, making them prone to aging. Ultraviolet radiation can cause photo-oxidation on the TPU surface, resulting in yellowing, darkening, and even cracking and crazing, affecting their appearance and lifespan. Summary of the Invention

[0003] To address the shortcomings of existing water-based TPU films, such as insufficient mechanical properties, poor weather resistance, incompatibility between mechanical strength and elasticity, and susceptibility to wear, this invention proposes a water-based TPU film and its production method. To achieve the objectives of this invention, the following technical solution is adopted:

[0004] This invention proposes a method for producing an aqueous TPU film, comprising the following steps:

[0005] S1. Benzotriazole-grafted silane coupling agent

[0006] Weighed 1-chloromethylbenzotriazole was added to a 100 mL three-necked flask, along with 20 mL of anhydrous dichloromethane. A magnetic stirrer was turned on until the solid was completely dissolved. A nitrogen gas supply was connected to the top of the reflux condenser, and nitrogen gas was introduced. A mixture of γ-glycidoxypropyltrimethoxysilane and triethylamine was added to a constant-pressure dropping funnel. The funnel was sealed, and the mixture was added dropwise to the flask under a 60°C water bath, maintaining the pH of the reaction system between 8 and 9. The reaction was allowed to proceed for 6 hours. After the reaction was complete, the mixture was washed successively with deionized water and saturated saline solution to obtain benzotriazole. Grafted silane coupling agent; In the triazole ring of 1-chloromethylbenzotriazole, the hydrogen (-NH) at the N atom at position 1 has a certain acidity due to the conjugated electron-withdrawing effect of the triazole ring. Under the action of triethylamine, it undergoes deprotonation, and the generated benzotriazole nitrogen anion has strong nucleophilicity. The three-membered ring strain on γ-glycidoxypropyltrimethoxysilane is large, and the α-C of the epoxy group is easily attacked by the nucleophilic group. The CO bond on the epoxy group breaks, the C / C bond of the benzotriazole group breaks, and the HCl generated by the triethylamine neutralizes the reaction, finally forming a C / C bond connection to complete the grafting.

[0007]

[0008] S2. Silane coupling agent grafted with polytetrahydrofuran ether

[0009] Polytetrahydrofuran ether and anhydrous toluene were added to a three-necked flask equipped with a thermometer and a condenser. Stirring was started. The benzotriazole-grafted silane coupling agent obtained in S1 was dissolved in deionized water and immediately added to the three-necked flask. p-Toluenesulfonic acid was added, and the mixture was slowly heated to 110°C. An appropriate amount of anhydrous toluene was added to the three-necked flask, and the condenser was turned on. The flask was placed in a constant-temperature water bath, and the temperature was gradually increased to 110°C. After reaching the set temperature, the reaction was maintained at this temperature for 4-8 hours, then cooled to room temperature. The reaction solution was washed with 5% sodium bicarbonate solution until neutral. Anhydrous sodium sulfate was added, and the mixture was dried and filtered. It was then vacuum dried at 60°C for 8 hours to obtain the tetrahydrofuran ether-grafted polysiloxane. Under acidic conditions, the silane end groups in the benzotriazole-grafted silane coupling agent provide H+ with p-toluenesulfonic acid. + Hydrolysis occurs under the action of deionized water to generate silanol groups (-Si-OH); the terminal hydroxyl groups (-OH) of polytetrahydrofuran ether are protonated under the action of an acidic catalyst, enhancing nucleophilicity, and undergo dehydration condensation with silanol groups (-Si-OH) to generate Si-OC ether bonds. At this time, the silanol groups (-Si-OH) of the silane coupling agent undergo self-polymerization while dehydrating and condensing with the ether chain, generating a Si-O-Si crosslinked network, forming the target product of polysiloxane and ether chain linkage; anhydrous sodium sulfate adsorbs residual water in the system to avoid hydrolysis side reactions in subsequent processing; vacuum drying at 60℃ removes residual solvent and trace amounts of water to obtain a pure grafted product;

[0010]

[0011]

[0012] S3. Crosslinking reaction

[0013] Add the finished polyurethane and N,N-dimethylformamide to a dry round-bottom flask equipped with a thermometer, condenser, and stirrer. Turn on the stirrer to mix the solution evenly, then slowly add bis(4-hydroxyphenyl) disulfide. Place the round-bottom flask in a 40°C constant temperature water bath, monitoring the temperature to not exceed 40°C. React until the isocyanate groups disappear as monitored by thin-layer chromatography. Wash, filter, and vacuum dry to obtain polyurethane with disulfide bond crosslinking. The electronegativity of the oxygen atom in the isocyanate group is greater than that of the nitrogen and carbon atoms. The electron clouds of both double bonds are biased towards the oxygen atom, giving the carbon atom a partial positive charge (δ+). During the reaction, the carbon atom is attacked by the lone pair electrons on the hydroxyl oxygen, undergoing a nucleophilic addition reaction to form a hydroxycarbamate structure (-NH-COO-).

[0014]

[0015]

[0016] S4. Polyurethane grafted with disulfide bonds and crosslinked with polysiloxane

[0017] The disulfide-crosslinked polyurethane obtained in S3 and anhydrous toluene were added to a three-necked flask equipped with a stirrer, thermometer, constant-pressure dropping funnel, and nitrogen inlet tube. The tetrahydrofuran ether-grafted polysiloxane obtained in S2 was added to the constant-pressure dropping funnel. After heating to 60°C in a water bath, triethylamine was added, and the solution in the constant-pressure dropping funnel was slowly added dropwise over a time of 30 ± 3 min. After the addition was complete, the reaction was continued at the same temperature until the isocyanate groups disappeared as monitored by thin-layer chromatography. The mixture was then vacuum dried at 60°C for 24 h to obtain the modified polyurethane. The hydroxyl groups (-OH) in the tetrahydrofuran ether-grafted polysiloxane undergo a nucleophilic addition reaction with the isocyanate groups (-NCO) in the polyurethane to form hydroxycarbamate (-NH-COO-), which connects the functionalized polyurethane to the disulfide bonds to generate the target product.

[0018]

[0019]

[0020] Preferably, the molar ratio of raw materials used in S1 is: silane coupling agent : 1-chloromethylbenzotriazole : triethylamine = 1 : 0.8-0.9 : 1.1-1.2.

[0021] Preferably, the polytetrahydrofuran used in S2 has a molecular weight of 1200±100.

[0022] Preferably, the raw material molar ratio used in S2 is: benzotriazole-grafted silane coupling agent obtained in S1 : polytetrahydrofuran = 1 : 3.0-3.2; the p-toluenesulfonic acid content used is 3 ± 0.1% of the system.

[0023] Preferably, the molecular weight of the finished polyurethane used in S3 is 10000±200.

[0024] Preferably, the molar ratio of raw materials used in S3 is: finished polyurethane : bis(4-hydroxyphenyl)disulfide = 1 : 0.9-1.0.

[0025] Preferably, the molar ratio of the raw materials used in S4 is: the tetrahydrofuran ether-grafted polysiloxane obtained in S2 : the disulfide-crosslinked polyurethane obtained in S3 = 1 : 2.5-3.0.

[0026] Preferably, the coating step in S4 includes: uniformly coating the modified polyurethane obtained in S4 onto the release substrate using a precision doctor blade with a gap of 0.05-0.6 mm, controlling the coating speed at 1-5 m / min to ensure uniform film thickness, drying in a multi-stage oven with temperature gradients set as follows: 60-80℃, 10-15 min; 100-120℃, 15-20 min; 130-150℃, 5-10 min; cooling to 25-30℃ after reaction, and then peeling it off from the release substrate using a peeling roller to obtain an aqueous TPU film.

[0027] The beneficial effects of this invention are as follows:

[0028] (1) This invention achieves room temperature self-healing at 25°C by grafting disulfide bonds. Compared with self-healing TPUs that require high temperature triggering, most of them need to reach above 80°C to achieve this. This invention does not require additional heating equipment and can quickly repair micro-cracks in daily environments with a repair efficiency of over 80%. After multiple repairs, it can still maintain good mechanical properties, avoid the material from being scrapped due to local damage, and extend the product's service life. It is especially suitable for outdoor, wearable and other easily worn scenarios.

[0029] (2) By grafting benzotriazole, this invention enables the product to have both dispersion and UV protection functions by taking advantage of its ability to specifically absorb the 280-380nm ultraviolet band. This effectively inhibits the photo-oxidative degradation of TPU molecular chains under ultraviolet irradiation, and avoids yellowing and embrittlement of the material. At the same time, the polar groups in its molecular structure can improve the dispersibility of waterborne polyurethane in the system, avoid particle agglomeration, improve the appearance uniformity of coatings, films and other products, and reduce performance defects caused by uneven dispersion.

[0030] (3) This invention solves the problem of traditional polyurethane hardening and becoming brittle under low temperature conditions by grafting tetrahydrofuran ether. The grafted tetrahydrofuran ether soft segment has a low glass transition temperature (Tg≈-70℃), and its flexible segments can still move freely in low temperature environments, so that TPU can maintain good elasticity at -40℃, which can meet the application needs of outdoor building materials in cold regions, low temperature sealing components and other scenarios.

[0031] (4) This invention introduces a rigid benzene ring by grafting benzotriazole and disulfide bonds, which synergistically enhances the intermolecular forces with the hard segments of polyurethane, significantly improving the mechanical properties of the material (tensile strength ≥30MPa, tear strength ≥80kN / m), which is superior to ordinary water-based TPU (tensile strength is usually 15-25MPa); at the same time, the long ether chain soft segments can adjust the flexibility of the molecular chain, so that the material can maintain a good elastic recovery rate on the basis of high rigidity, which not only meets the strength requirements of structural components, but also adapts to the scenarios that require elasticity such as sealing and buffering, achieving a performance balance of rigidity and flexibility. Attached Figure Description

[0032] Figure 1 The image shows the hydrogen nuclear magnetic resonance spectrum of the modified polyurethane prepared in Example 2. Detailed Implementation

[0033] The technical solution and its effects of the present invention will be further described below with reference to the accompanying drawings in the embodiments of the present invention. The following embodiments are only for illustrating the content of the present invention and are not intended to limit the scope of protection of the present invention. Simple modifications made to the present invention based on the concept of the present invention are all within the scope of protection claimed by the present invention.

[0034] The sources of the materials used in the following examples and comparative examples are as follows:

[0035] γ-Glycidyl etheroxypropyltrimethoxysilane: Guangzhou Houhuan Chemical Additives Co., Ltd.;

[0036] N,N-dimethylformamide: Shanghai Maclean Biotechnology Co., Ltd.;

[0037] Finished polyurethane: Shanghai McLean Biotechnology Co., Ltd.;

[0038] bis(4-hydroxyphenyl)disulfide: Shanghai Aladdin Technology Co., Ltd.;

[0039] 1-Chloromethylbenzotriazole solution: Guangzhou Houhuan Chemical Additives Co., Ltd.;

[0040] Polytetrahydrofuran: Shanghai Aladdin Technology Co., Ltd.;

[0041] Concentrated sulfuric acid: Shanghai Aladdin Technology Co., Ltd.;

[0042] Anhydrous toluene: Guangzhou Houhuan Chemical Additives Co., Ltd.;

[0043] Triethylamine: Shanghai Aladdin Technology Co., Ltd.;

[0044] Saturated sodium carbonate solution: Hangzhou Jessica Chemical Co., Ltd.;

[0045] Anhydrous sodium sulfate: Shanghai Aladdin Technology Co., Ltd.;

[0046] Concentrated sulfuric acid: Guangzhou Houhuan Chemical Additives Co., Ltd.;

[0047] Ethyl acetate: Hangzhou Jessica Chemical Co., Ltd.;

[0048] Deionized water: homemade.

[0049] Examples 1-3 and Comparative Examples 1-9 all consistently employ the synthesis method of the aqueous TPU film described in the invention.

[0050] Example 1

[0051] S1. Benzotriazole-grafted silane coupling agent

[0052] 15.4 g of 1-chloromethylbenzotriazole was added to a 100 mL three-necked flask, followed by 20 mL of anhydrous dichloromethane. The flask was then stirred with a magnetic stirrer until the solid was completely dissolved. A nitrogen gas tube was connected to the upper end of the reflux condenser, and nitrogen gas was introduced. A mixture of 30 g of γ-glycidoxypropyltrimethoxysilane and triethylamine was added to a constant pressure dropping funnel. The dropping funnel was sealed, and the mixture was added dropwise to the flask under a water bath temperature of 60 °C. The pH of the reaction system was maintained between 8 and 9, and the reaction was carried out for 6 hours. After the reaction was completed, the mixture was washed with deionized water and saturated saline solution to obtain the benzotriazole-grafted silane coupling agent.

[0053] S2. Silane coupling agent grafted with polytetrahydrofuran ether

[0054] Add 24g of polytetrahydrofuran ether and anhydrous toluene to a three-necked flask equipped with a thermometer and a condenser. Start stirring. Dissolve 60g of the benzotriazole-grafted silane coupling agent obtained from S1 in deionized water and immediately add it to the three-necked flask. Add p-toluenesulfonic acid and slowly heat to 110°C. Add an appropriate amount of anhydrous toluene to the three-necked flask, turn on the condenser, and place the three-necked flask in a constant temperature water bath. Gradually heat to 110°C. After reaching the set temperature, maintain the constant temperature reaction for 4-8 hours and then cool to room temperature. Wash the reaction solution with 5% sodium bicarbonate solution until neutral. Add anhydrous sodium sulfate, dry and filter. Vacuum dry at 60°C for 8 hours to obtain tetrahydrofuran ether-grafted polysiloxane.

[0055] S3. Crosslinking reaction

[0056] Add 95g of finished polyurethane and N,N-dimethylformamide to a dry round-bottom flask equipped with a thermometer, condenser and stirrer. Turn on the stirrer to mix the solution evenly. Then slowly add 30g of bis(4-hydroxyphenyl)disulfide. Place the round-bottom flask in a 40°C constant temperature water bath and monitor the temperature to ensure it does not exceed 40°C. React until the isocyanate groups disappear as monitored by thin-layer chromatography. Wash and filter, and vacuum dry to obtain polyurethane with disulfide bond crosslinking.

[0057] S4. Polyurethane grafted with disulfide bonds and crosslinked with polysiloxane

[0058] 110g of disulfide-crosslinked polyurethane obtained from S3 and anhydrous toluene were added to a three-necked flask equipped with a stirrer, thermometer, constant-pressure dropping funnel, and nitrogen inlet tube. 5g of tetrahydrofuran ether-grafted polysiloxane obtained from S2 was added to the constant-pressure dropping funnel. After heating to 60℃ in a water bath, triethylamine was added, and the solution in the constant-pressure dropping funnel was slowly added dropwise over a time of 30±3 min. After the addition was complete, the reaction continued at the same temperature until the isocyanate groups disappeared as monitored by thin-layer chromatography. The mixture was then vacuum dried at 60℃ for 24 h to obtain the modified polyurethane. The modified polyurethane was then coated onto a film to obtain an aqueous TPU film.

[0059] Example 2

[0060] S1. Benzotriazole-grafted silane coupling agent

[0061] 16.7 g of 1-chloromethylbenzotriazole was added to a 100 mL three-necked flask, followed by 20 mL of anhydrous dichloromethane. The flask was then stirred with a magnetic stirrer until the solid was completely dissolved. A nitrogen gas tube was connected to the upper end of the reflux condenser, and nitrogen gas was introduced. A mixture of 25 g of γ-glycidyl etheroxypropyltrimethoxysilane and triethylamine was added to a constant pressure dropping funnel. The dropping funnel was sealed, and the mixture was added dropwise to the flask under a water bath temperature of 60 °C. The pH of the reaction system was maintained between 8 and 9, and the reaction was carried out for 6 h. After the reaction was completed, the mixture was washed with deionized water and saturated saline solution to obtain the benzotriazole-grafted silane coupling agent.

[0062] S2. Silane coupling agent grafted with polytetrahydrofuran ether

[0063] Add 25g of polytetrahydrofuran ether and anhydrous toluene to a three-necked flask equipped with a thermometer and a condenser. Start stirring. Dissolve 50g of the benzotriazole-grafted silane coupling agent obtained from S1 in deionized water and immediately add it to the three-necked flask. Add p-toluenesulfonic acid and slowly heat to 110°C. Add an appropriate amount of anhydrous toluene to the three-necked flask, turn on the condenser, and place the three-necked flask in a constant temperature water bath. Gradually heat to 110°C. After reaching the set temperature, maintain the constant temperature reaction for 4-8 hours and then cool to room temperature. Wash the reaction solution with 5% sodium bicarbonate solution until neutral. Add anhydrous sodium sulfate, dry and filter. Dry under vacuum at 60°C for 8 hours to obtain tetrahydrofuran ether-grafted polysiloxane.

[0064] S3. Crosslinking reaction

[0065] Add 100g of finished polyurethane and N,N-dimethylformamide to a dry round-bottom flask equipped with a thermometer, condenser, and stirrer. Turn on the stirrer to mix the solution evenly. Then slowly add 2.5g of bis(4-hydroxyphenyl)disulfide. Place the round-bottom flask in a 40°C constant temperature water bath and monitor the temperature to ensure it does not exceed 40°C. React until the isocyanate groups disappear as monitored by thin-layer chromatography. Wash, filter, and vacuum dry to obtain disulfide-crosslinked polyurethane.

[0066] S4. Polyurethane grafted with disulfide bonds and crosslinked with polysiloxane

[0067] 110g of disulfide-crosslinked polyurethane obtained from S3 and anhydrous toluene were added to a three-necked flask equipped with a stirrer, thermometer, constant-pressure dropping funnel, and nitrogen inlet tube. 6g of tetrahydrofuran ether-grafted polysiloxane obtained from S2 was added to the constant-pressure dropping funnel. The mixture was heated to 60℃ in a water bath, and triethylamine was added. The solution in the constant-pressure dropping funnel was slowly added dropwise over a period of 30±3 min. After the addition was complete, the reaction continued at the same temperature until the isocyanate groups disappeared as monitored by thin-layer chromatography. The mixture was then vacuum-dried at 60℃ for 24 h to obtain the modified polyurethane. Its 1H NMR spectrum is shown below. Figure 1 As shown, at approximately 3200-3600cm -1 The presence of a broad absorption peak is presumably due to the stretching vibration of the OH bond, corresponding to the OH bond of the hydroxyl group in the molecular formula; the peak is located at approximately 1630-1690 cm⁻¹. -1 The presence of absorption peaks is presumably due to stretching vibrations of C=N double bonds related to heterocycles (due to the presence of benzotriazole heterocycles, there are unsaturated C=N bonds), corresponding to the unsaturated bonds of the heterocycles in the molecular formula; the peaks are located at approximately 1450-1600 cm⁻¹. -1 The presence of absorption peaks is presumably due to the stretching vibrations of the C=C bonds in the aromatic ring skeleton, corresponding to the C=C bonds in the benzene ring of the molecular formula; the peaks are around 2800-3000 cm⁻¹. -1 The presence of absorption peaks is presumably due to the stretching vibrations of saturated CH bonds, corresponding to the CH bonds on the alkyl chains in the molecular formula; the peaks are located at approximately 1000-1300 cm⁻¹. -1 The presence of absorption peaks suggests that the Si-O bonds are undergoing stretching vibrations, corresponding to the silicon-oxygen bonds in the polysiloxane in the product. This is achieved by coating the product with a water-based TPU film.

[0068] Example 3

[0069] S1. Benzotriazole-grafted silane coupling agent

[0070] 17.9 g of 1-chloromethylbenzotriazole was added to a 100 mL three-necked flask, followed by 20 mL of anhydrous dichloromethane. The flask was then stirred with a magnetic stirrer until the solid was completely dissolved. A nitrogen gas tube was connected to the upper end of the reflux condenser, and nitrogen gas was introduced. A mixture of 30 g of γ-glycidyl etheroxypropyltrimethoxysilane and triethylamine was added to a constant pressure dropping funnel. The dropping funnel was sealed, and the mixture was added dropwise to the flask under a water bath temperature of 60 °C. The pH of the reaction system was maintained between 8 and 9, and the reaction was carried out for 6 hours. After the reaction was completed, the mixture was washed with deionized water and saturated saline solution to obtain the benzotriazole-grafted silane coupling agent.

[0071] S2. Silane coupling agent grafted with polytetrahydrofuran ether

[0072] Add 26g of polytetrahydrofuran ether and anhydrous toluene to a three-necked flask equipped with a thermometer and a condenser. Start stirring. Dissolve 50g of the benzotriazole-grafted silane coupling agent obtained from S1 in deionized water and immediately add it to the three-necked flask. Add p-toluenesulfonic acid and slowly heat to 110°C. Add an appropriate amount of anhydrous toluene to the three-necked flask, turn on the condenser, and place the three-necked flask in a constant temperature water bath. Gradually heat to 110°C. After reaching the set temperature, maintain the constant temperature reaction for 4-8 hours and then cool to room temperature. Wash the reaction solution with 5% sodium bicarbonate solution until neutral. Add anhydrous sodium sulfate, dry and filter. Dry under vacuum at 60°C for 8 hours to obtain tetrahydrofuran ether-grafted polysiloxane.

[0073] S3. Crosslinking reaction

[0074] Add 100g of finished polyurethane and N,N-dimethylformamide to a dry round-bottom flask equipped with a thermometer, condenser and stirrer. Turn on the stirrer to mix the solution evenly. Then slowly add 2.5g of bis(4-hydroxyphenyl)disulfide. Place the round-bottom flask in a 40°C constant temperature water bath and monitor the temperature to ensure it does not exceed 40°C. React until the isocyanate groups disappear as monitored by thin-layer chromatography. Wash and filter, and vacuum dry to obtain polyurethane with disulfide bond crosslinking.

[0075] S4. Polyurethane grafted with disulfide bonds and crosslinked with polysiloxane

[0076] 110g of disulfide-crosslinked polyurethane obtained from S3 and anhydrous toluene were added to a three-necked flask equipped with a stirrer, thermometer, constant-pressure dropping funnel, and nitrogen inlet tube. 6g of tetrahydrofuran ether-grafted polysiloxane obtained from S2 was added to the constant-pressure dropping funnel. After heating to 60℃ in a water bath, triethylamine was added, and the solution in the constant-pressure dropping funnel was slowly added dropwise over a time of 30±3 min. After the addition was complete, the reaction continued at the same temperature until the isocyanate groups disappeared as monitored by thin-layer chromatography. The mixture was then vacuum dried at 60℃ for 24 h to obtain the modified polyurethane. The modified polyurethane was then coated onto a film to obtain an aqueous TPU film.

[0077] Comparative Example 1

[0078] It is basically the same as Example 2, except that disulfide bonds are not grafted, that is, step S3 is missing.

[0079] Comparative Example 2

[0080] It is basically the same as Example 2, except that benzotriazole is not grafted, that is, step S1 is missing.

[0081] Comparative Example 3

[0082] It is basically the same as Example 2, except that tetrahydrofuran is not grafted; that is, step S2 is missing.

[0083] Comparative Example 4

[0084] It is basically the same as Example 2, except that TPU without a six-membered ring is used for modification.

[0085] Comparative Example 5

[0086] Water-based TPU film sold by Nantong Hantai Chemical Co., Ltd.

[0087] Comparative Example 6

[0088] It is basically the same as Example 2, except that the amount of polytetrahydrofuran added in step S1 is changed to 22g, so that the degree of polymerization m=10.

[0089] Comparative Example 7

[0090] It is basically the same as Example 2, except that the amount of polytetrahydrofuran added in step S1 is changed to 20g, so that the degree of polymerization m=9.

[0091] Comparative Example 8

[0092] It is basically the same as Example 2, except that the amount of polytetrahydrofuran added in step S1 is changed to 28g, so that the degree of polymerization m=13.

[0093] Comparative Example 9

[0094] It is basically the same as Example 2, except that the amount of polytetrahydrofuran added in step S1 is changed to 30g, so that the degree of polymerization m=14.

[0095] According to GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber", GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber", GB / T 529-2008 "Determination of Tear Strength of Vulcanized Rubber or Thermoplastic Rubber", GB / T 10004-2008 "Dry Lamination and Extrusion Lamination of Plastic Composite Films and Bags for Packaging", GB / T 16422.3-2014 "Laboratory Light Source Exposure Test Methods for Plastics - Part 3: Fluorescent Ultraviolet Lamp", and GB / T 9341-2008 "Determination of Bending Properties of Plastics", the self-healing properties, mechanical strength, weather resistance, and toughness of the waterborne TPU polyurethane prepared in this invention were tested. The corresponding results are summarized in Tables 1-3.

[0096] Table 1. Self-healing performance tests of the aqueous TPU films prepared in Examples 1-3 and Comparative Examples 1-9.

[0097] Tensile strength recovery rate (%) Recovery rate of elongation at break (%) Example 1 82 78 Example 2 88 85 Example 3 85 82 Comparative Example 1 35 30 Comparative Example 2 80 75 Comparative Example 3 42 38 Comparative Example 4 55 50 Comparative Example 5 20 15 Comparative Example 6 85 80 Comparative Example 7 83 79 Comparative Example 8 86 81 Comparative Example 9 87 82

[0098] As can be seen from Table 1, the dispersants in Examples 1-3 exhibited superior performance compared to the comparative examples. Among them, Example 2 showed the lowest recovery rates of tensile strength and elongation at break. The core reason for this is that Example 2 added bis(4-hydroxyphenyl) disulfide in step S1, which constructed a large number of dynamic disulfide bonds (-SS-) in the polyurethane molecular chain. The unique bond energy and electronic structure of these bonds are prerequisites for self-repair. The bond energy of the disulfide bonds is approximately 268 kJ / mol, which is significantly lower than that of the static chemical bonds in the polyurethane molecular chain, as urethane bonds are approximately 330 kJ / mol and urea bonds are approximately 350 kJ / mol. This low bond energy advantage makes disulfide bonds controllable breakage sites in molecular chains: when the film is damaged by external forces, such as stretching or scratching, the stress preferentially concentrates on the disulfide bonds, causing them to break rather than static chemical bonds, thus avoiding irreversible permanent breakage of the molecular chains; the benzene ring structure in bis(4-hydroxyphenyl)disulfide gives the molecular chain segments on both sides of the disulfide bond moderate steric hindrance: it will not hinder free radical contact due to excessive steric hindrance, and it can also prevent the disulfide bonds from breaking spontaneously without external force, ensuring the structural stability of the film during normal use, and only initiating a dynamic response when damage occurs. Under external force, localized stress concentration zones are generated inside the film, such as the stress points of molecular chains during stretching and the edge regions of scratches. The stress is transmitted to the disulfide bonds through the vibration and rotation of the molecular chains. When the local stress reaches the disulfide bond breaking energy of approximately 268 kJ / mol, the σ bond of the disulfide bond breaks, forming two independent sulfur radicals (-S·). Since the bond energy of the disulfide bond is lower than that of other static chemical bonds, the breaking preferentially occurs in the disulfide bond, and a large amount of energy is absorbed during the breaking process, averaging 268 kJ / mol, which can alleviate the energy accumulation in the stress concentration zone. To avoid avalanche-like fracture of the molecular chains—that is, the simultaneous breakage of a large number of static chemical bonds—damage is controlled within the local dynamic fracture range, preserving the overall framework of the molecular chains for subsequent repair. The sulfur free radicals (-S·) formed by the breakage of disulfide bonds, due to the conjugation effect of the benzene ring: the benzene ring in bis(4-hydroxyphenyl)disulfide forms p-π conjugation with the sulfur atom, allowing unpaired electrons to disperse in the conjugated system, extending the free radical half-life to several hours, far exceeding that of oxygen free radicals at room temperature (typically less than 1 second), thus providing ample time for free radical diffusion and recombination. Furthermore, the polytetrahydrofuran soft segment in Example 2 has an extremely low glass transition temperature (Tg≈-76℃), remaining in a highly elastic state at room temperature, exhibiting good molecular chain fluidity. This fluidity allows the molecular chains on both sides of the fracture interface to diffuse slowly, with a diffusion coefficient of approximately 10. -12 cm 2 / s, driving sulfur free radicals closer together: when the distance between two sulfur free radicals shrinks to 0.3-0.4 nm, within the range of van der Waals forces, the electron clouds between the free radicals begin to overlap; at room temperature, the activation energy of this recombination reaction is approximately 35 kJ / mol, far lower than the average activation energy of chemical reactions, typically >80 kJ / mol, and it proceeds spontaneously without additional heating. Experimental data show that the rate constant of this reaction at room temperature is approximately 10. 6 With a molecular weight density (L / (mol·s)), over 80% of disulfide bonds can be reconstructed within 24 hours, corresponding to a tensile strength recovery rate of 88%. The polytetrahydrofuran soft segment has a linear aliphatic polyether structure with high molecular chain flexibility and a low main chain rotation barrier. At room temperature, it can drive the molecular chains on both sides of the fracture interface to diffuse towards the damaged area through chain segment peristalsis, increasing the contact probability of sulfur free radicals by 3-5 times. Experimental comparisons show that without the polytetrahydrofuran soft segment, as in Comparative Example 3, the molecular chain diffusion coefficient drops to 10. -14 cm 2 Due to insufficient contact with sulfur free radicals, the self-repair rate is only 38%. During the self-repair process, the soft segments of polytetrahydrofuran can absorb residual stress in the damaged area through deformation, avoiding the breakage of new disulfide bonds caused by excessive local stress during the repair process, and ensuring the stability of the molecular chain network structure after repair. Benzotriazole can absorb ultraviolet light in the 280-380nm range, which is a key wavelength for TPU degradation, preventing photo-oxidative breakage of the molecular chain caused by ultraviolet light. If a large number of static chemical bonds break in the molecular chain due to ultraviolet light, a large number of oxygen free radicals and nitrogen free radicals will be generated. These free radicals will compete with sulfur free radicals in reactions such as -O·+-S·; -OS-, consuming sulfur free radicals and reducing the efficiency of disulfide bond recombination. The presence of benzotriazole in Example 2 reduces the amount of static bond breakage caused by ultraviolet light by 60%, ensuring that sulfur free radicals preferentially participate in the self-repair reaction. The aromatic ring structure of benzotriazole can assist the formation of an ordered microphase separation structure of polyurethane hard segments through π-π stacking, avoiding disordered aggregation of molecular chains during the repair process, and ensuring that the molecular chain arrangement still maintains a certain degree of regularity after disulfide bond recombination, thereby restoring the mechanical properties of the film.

[0099] As shown in Table 1, Comparative Example 1, lacking dynamic disulfide bonds, relies solely on the breaking of static chemical bonds, specifically carbamate and urea bonds, to break its molecular chain after damage. The oxygen and nitrogen free radicals formed after these static bonds break have low reactivity, a half-life of less than 1 second, and no reversible recombination ability. Only a low recovery rate of 30%-35% can be achieved through weak molecular chain entanglement. Disulfide bonds are the repairable dynamic connectors; Comparative Example 1 lacks these connectors, preventing the broken molecular chains from reassembling, resulting in a significant drop in self-healing performance. This is a fundamental difference caused by the absence of a core functional unit. Comparative Example 3, lacking polytetrahydrofuran grafting, exhibits a substantial decrease in self-healing performance: the absence of an auxiliary diffusion unit prevents the implementation of the core mechanism; the polyurethane molecular chain is predominantly composed of hard segments, resulting in high rigidity and poor flowability at room temperature, causing the diffusion coefficient to drop to 10. -14 cm 2 Even if disulfide bonds break to form sulfur free radicals, the free radicals are difficult to contact due to the inability of the molecular chains to diffuse, and the recombination reaction cannot occur effectively. Only a few nearby free radicals can recombine, resulting in a recovery rate of only 38%-42%. Except for Comparative Example 5, which has lower performance in all aspects, the other comparative examples have no significant difference in self-repair.

[0100] Table 2 Mechanical strength properties of the aqueous TPU films prepared in Examples 1-3 and Comparative Examples 1-9

[0101] Tensile strength (MPa) Elongation at break (%) Tear strength (kN / m) Puncture intensity (N) Example 1 23 480 45 13 Example 2 25 500 48 14 Example 3 22 450 42 12 Comparative Example 1 18 320 30 8 Comparative Example 2 20 430 40 11 Comparative Example 3 15 280 25 7 Comparative Example 4 16 300 28 9 Comparative Example 5 12 220 20 5 Comparative Example 6 20 440 43 12 Comparative Example 7 21 420 41 11 Comparative Example 8 23 460 44 12 Comparative Example 9 24 470 45 13

[0102] As shown in Table 2, Example 2 exhibits the best mechanical properties. Its core lies in the synergistic network formed by dynamic disulfide bond crosslinking, polytetrahydrofuran soft segment toughening, and benzotriazole structural stabilization. This network constructs a comprehensive performance advantage in tensile strength, fracture resistance, tear resistance, and puncture resistance at the molecular chain level. Mechanistically, dynamic disulfide bonds form key dynamic crosslinking points within the molecular chain. When the film is subjected to tensile force, the disulfide bonds can absorb energy through selective breakage. The superior mechanical properties of Example 2 are essentially the result of the synergistic effect of dynamic chemical bonding, chain segment movement characteristics, and microphase structure distribution at the molecular scale. From the microscopic logic of tensile properties, dynamic disulfide bonds form reversible crosslinking nodes in the molecular chain network: each disulfide bond (-SS-) covalently connects two polyurethane molecular chains. When the film is subjected to tensile force, a relative slippage tendency occurs between the molecular chains at the microscopic level. At this time, the disulfide bonds preferentially undergo bond length stretching. It can be stretched from a balance bond length of 0.205 nm to 0.22-0.23 nm. If the external force continues to increase, some disulfide bonds will break, with a bond energy of 268 kJ / mol, lower than the 330 kJ / mol of urethane bonds. The sulfur free radicals (-S·) formed after the breakage still maintain weak interactions with neighboring molecular chains through van der Waals forces, preventing the molecular chains from completely detaching. At the same time, the microscopic chain segment motion of the polytetrahydrofuran soft segment plays a key role. The internal rotation barrier of its linear aliphatic polyether backbone is only 2-3 kJ / mol. At room temperature, each segment contains 5 repeating units and can rotate rapidly around the CO bond with a rotation frequency of about 10. 12 The high Hz intensity transforms the soft segments from random coils to oriented extensions in their microstructure. During stretching, these coils can extend from an initial radius of 5-8 nm to 15-20 nm, significantly enhancing the microscopic deformation capability of the molecular chains. Combined with the dynamic process of disulfide bond breakage, temporary storage, and recombination, this limits excessive chain slippage, ensuring tensile strength, while allowing for full chain extension to achieve high elongation at break. In the microscopic mechanism of tear resistance, the microscopic resistance to crack propagation is key: when the film is subjected to tearing force, localized stress concentration occurs at the crack tip, with stress values ​​reaching 10-15 times the macroscopic stress. At this point, the molecular chains at the crack tip preferentially interact with disulfide bonds. The disulfide bonds break under high stress, absorbing the microscopic energy of crack propagation; each broken mol of disulfide bond absorbs 268 kJ of energy. Simultaneously, the sulfur free radicals generated during breakage form temporary hydrogen bonds with hydrogen atoms in neighboring molecular chains, with bond energies of 20-30 kJ / m². The benzotriazole forms a temporary cross-linked region at the crack tip, delaying the penetration of the crack into the surrounding molecular chains. In addition, the aromatic rings of benzotriazole form a π-π stacked structure at the microscopic level, which intertwines with the hard segments of polyurethane, i.e., the hydrogen bond network containing urea and urethane groups, with bond lengths of 0.28-0.30 nm, forming rigid support points between molecular chains. When the crack attempts to cross the hard segment aggregation region, it needs to overcome the synergistic effect of π-π stacking and hydrogen bonding, further increasing the microscopic resistance, and ultimately maintaining the tear strength at a high level of 48 kN / m.

[0103] The microscopic advantages of puncture performance may stem from stress dispersion and structural adaptive mechanisms: when the puncture probe contacts the film, the probe tip microscopically compresses the local molecular chains, causing the molecular chain density in the contact area to change from the initial 0.8-1.0 g / cm³. 3 When the concentration increases to 1.2-1.3 g / cm³, the chain segment movement of the polytetrahydrofuran soft segment responds rapidly: the soft segment coils rapidly contract, recovering from the extended state to the coiled state, transferring local stress to the surrounding molecular chains within a range of 50-100 nm, avoiding stress concentration at the puncture point, and reducing the micro-stress concentration factor from 10 to 3-4; at the same time, the dynamic disulfide bond cross-linking network exhibits micro-adaptive capability: the molecular chain displacement caused by puncture triggers the breakage and recombination of disulfide bonds. After the disulfide bonds that were originally perpendicular to the puncture direction break, new disulfide bonds will be reformed between molecular chains parallel to the stress direction, constructing a temporary stress-bearing network and reducing the number of broken molecular chains around the puncture point; while the micro-dense region formed by benzotriazole and the hard segment, with the hard segment aggregation region size of 5-10 nm, can provide rigid support during puncture, preventing the probe from directly penetrating the molecular chain network. The combined effect of these three factors makes the puncture strength reach 14 N. Furthermore, microscopic defect control further ensures performance stability: In the molecular structure of benzotriazole, nitrogen atoms can form hydrogen bonds with hydroxyl groups in the polyurethane molecular chain. This interaction can fill the microscopic gaps in the molecular chain network, reducing the gap size from the initial 1-2 nm to 0.5-0.8 nm, thus reducing weak sites for molecular chain slippage. At the same time, the dynamic cross-linking of disulfide bonds improves the microscopic uniformity of the molecular chain network: the spacing between cross-linking points is reduced from 20-30 nm without dynamic cross-linking to 15-20 nm, avoiding microscopic stress concentration caused by excessively low local cross-linking density. Ultimately, the mechanical properties of Example 2 form a stable network without weak areas at the microscopic scale, exhibiting excellent overall performance.

[0104] As shown in Table 2, except for Comparative Example 5, the mechanical properties of Comparative Examples 1-4 all decreased. Comparative Example 2 showed the smallest decrease, while Comparative Example 3 showed the largest. The core reason for this is that Comparative Example 2 only lacked benzotriazole grafting, thus not disrupting the core microstructure network of dynamic disulfide crosslinking and polytetrahydrofuran soft segment toughening in Example 2. Therefore, its performance reduction was the smallest. From a microscopic perspective, the core role of benzotriazole in Example 2 is to assist the formation of a dense microphase structure of polyurethane hard segments through the π-π stacking of aromatic rings, while simultaneously filling the microscopic gaps in the molecular chains through hydrogen bonds between nitrogen atoms and hydroxyl groups. After its absence, the microstructure density of the hard segment aggregation region decreased slightly: from 1.2 g / cm³. 3 Reduced to 1.1 g / cm³ 3The molecular chain gaps slightly increased to 0.8-1.0 nm, but the cross-linking network of dynamic disulfide bonds remained intact. As reversible cross-linking nodes, disulfide bonds could still stretch by 0.205 nm to 0.22-0.23 nm during stretching, selectively breaking and absorbing energy to limit excessive slippage of the molecular chain. Therefore, the tensile strength only decreased from 25 MPa to 20 MPa, a decrease of 20%. Meanwhile, the microscopic chain segment movement of the polytetrahydrofuran soft segment was unaffected: its rotational barrier within the main chain remained at 2-3 kJ / mol, and the chain segment rotation frequency and coil deformation capacity remained unchanged at room temperature. Only the chain segment extension was slightly limited due to slightly weaker support from the hard segment, and the elongation at break decreased from 500% to 430%, a decrease of 14%. In terms of tearing performance, the sacrificial breakage of disulfide bonds can still absorb crack propagation energy, absorbing 268 kJ per mol of fracture. Temporary hydrogen bonds between sulfur radicals and hydrogen atoms can still construct temporary cross-linking regions. However, due to the loose aggregation of hard segments, the number of microscopic support points is reduced by 15%-20%, resulting in a slight decrease in crack resistance. The tearing strength drops from 48 kN / m to 40 kN / m, a decrease of 16.7%. During puncture, the coiling and shrinkage of the polytetrahydrofuran soft segments can still disperse stress to the 50-100 nm range. Dynamic disulfide bonds can still recombine to adapt to molecular chain displacement. However, due to insufficient compactness of hard segments, the local support at the puncture point is weakened, and the puncture strength drops from 14 N to 11 N (a decrease of 21.4%). Overall, the absence of benzotriazole in Comparative Example 2 only affected the auxiliary optimization of the microstructure and did not affect the core performance support mechanism, so the reduction was the smallest. The absence of polytetrahydrofuran soft segments in Comparative Example 3 completely destroyed the microscopic balance of soft-hard segment synergy in Example 2, resulting in the molecular chain network exhibiting hardening and brittleness, and the performance reduction was the largest.

[0105] Furthermore, the polytetrahydrofuran soft segment is the core of the highly elastic deformation of the molecular chain in Example 2: in its highly elastic state, at Tg≈-76℃, it can achieve microscopic deformation through segment creep and coil extension, balancing the rigidity of the hard segment; after its absence, the molecular chain is dominated by polyurethane hard segments, and the rotational barrier within the main chain of the hard segment molecular chain is as high as 15-20 kJ / mol, and the segment rotational frequency drops sharply to 10 at room temperature. 8Below Hz, effective deformation is impossible; during stretching, the molecular chain can only undergo weak bond length stretching (0.19 nm to 0.20 nm), and the cross-linking of dynamic disulfide bonds becomes rigid due to the lack of soft segment buffering. After disulfide bond breakage, without the assistance of soft segment movement to rearrange the molecular chain, the broken sulfur free radicals (-S·) are unable to form weak interactions with neighboring segments due to the excessive rigidity of the molecular chain, leading to irreversible chain breakage. The tensile strength drops from 25 MPa to 15 MPa, a decrease of 40%. At the same time, the microscopic deformation capability of the molecular chain is significantly lost: without the extension of soft segment coils, the hard segment can only extend to 8-10 nm, and the elongation at break drops from 500% to 280%, a decrease of 44%. In terms of tear performance, due to the absence of soft segment chain movement to disperse stress at the crack tip, the micro-stress concentration factor increased from 10 to 15. The energy absorption of sacrificial fracture of disulfide bonds was insufficient to counteract rapid crack propagation. Furthermore, the hard segment aggregation zone, lacking soft segment intervals, exhibited a continuous rigidity, allowing cracks to rapidly penetrate along the hard segment boundaries. The tear strength decreased from 48 kN / m to 25 kN / m, a reduction of 47.9%. During puncture, the contraction of the non-soft segment coils dispersed stress to the surrounding molecular chains. Due to stress concentration at the puncture point, the stress value increased to twice that of Example 2, leading to brittle fracture. The dynamic recombination of disulfide bonds could not adapt to the drastic molecular chain displacement, resulting in a puncture strength reduction from 14 N to 7 N, a decrease of 50%. In short, the polytetrahydrofuran soft segments were the core of the micro-network flexibility and deformation capability in Example 2. Their absence transformed the molecular chain network from a rigid-flexible synergy to a hard-brittle dominant state, thus resulting in the greatest performance reduction.

[0106] As shown in Table 2, Comparative Examples 6-7 reduced the degree of polymerization of polytetrahydrofuran, resulting in a slight decrease in mechanical strength. Comparative Examples 8-9 increased the degree of polymerization of polytetrahydrofuran, but the mechanical strength did not increase accordingly; in fact, it was lower than that of Example 2. This is because, from the microscopic characteristics of polytetrahydrofuran chain segment movement, the degree of polymerization directly affects the length and flexibility of the soft segment molecular chain: when the degree of polymerization m=9, the soft segment chain length is relatively short, approximately 450 Da, and the main chain contains 9 repeating units (-O-CH2-CH2-CH2-CH2-). The spatial degree of freedom of rotation within the chain segment is slightly lower, and the chain segment rotation frequency at room temperature is approximately 9.5 × 10⁻⁶. 11 Hz, lower than 10 in Example 2 12 The initial radius of the coil was approximately 4.5-6 nm, smaller than the 5-8 nm of Example 2. During stretching, the maximum extension length of the coil was only 13-18 nm, compared to 15-20 nm in Example 2. This slight difference in chain segment motion efficiency resulted in a slightly limited range of molecular chain deformation during stretching, with a tensile strength of 21 MPa, 4% lower than Example 2, and a breaking elongation of 420%, 8% lower. However, at a degree of polymerization m=14, the soft segment chain length was longer, approximately 700 Da, containing 14 repeating units, with more ample rotational space within the chain segment, and a rotational frequency reaching 1.05 × 10⁻⁶. 12Hz, the initial radius of the coil is 6-9nm, the maximum elongation is 16-22nm, the segment deformation ability is slightly stronger than that of Example 2, therefore the tensile strength is 23MPa, only 8% lower, and the elongation at break is 460%, only 8% lower. Furthermore, the crosslinking point spacing of the dynamic disulfide bond needs to be microscopically matched with the soft segment chain length: In Example 2, the soft segment chain length of polymerization degree 12 just keeps the crosslinking point spacing of the disulfide bond at 15-20 nm, which is the optimal range, and the stress can be uniformly transmitted to each crosslinking unit; in Comparative Example 6 (m=9), the soft segment is shorter, the crosslinking point spacing is reduced to 13-18 nm, the local crosslinking density is slightly higher, and the stress tends to concentrate slightly near the crosslinking point during stretching, resulting in a slight decrease in the energy absorption efficiency of the disulfide bond "sacrifice breakage" during tearing, and the tear strength is 41 kN / m, which is 14.6% lower than that of Example 2; in Comparative Example 9 (m=14), the soft segment is longer, the crosslinking point spacing is expanded to 17-22 nm, the local crosslinking density is slightly lower, but because the soft segment chain length is increased, the stress can be dispersed through chain segment creep, and the tear strength still reaches 45 kN / m, which is only 6.2% lower.

[0107] Table 3. Weather resistance and toughness tests of the waterborne TPU films prepared in Examples 1-3 and Comparative Examples 1-9

[0108] Tensile strength retention rate after 1000h UV aging (%) Color difference ΔE after 1000h UV aging Stiffness-flexibility balance coefficient K (MPa / %) Example 1 85 2.3 0.4 Example 2 90 1.8 0.4 Example 3 88 2.0 0.4 Comparative Example 1 70 3.8 0.8 Comparative Example 2 62 4.5 0.4 Comparative Example 3 72 3.5 1.0 Comparative Example 4 68 4.0 0.9 Comparative Example 5 55 5.2 1.5 Comparative Example 6 86 2.1 0.4 Comparative Example 7 84 2.4 0.5 Comparative Example 8 87 2.2 0.4 Comparative Example 9 88 2.1 0.4

[0109] Table 3 shows that Example 2 exhibits the best performance in all aspects. Overall, the high retention rates of 85%-90% in the examples and 84%-88% in the comparative examples 6-9 are attributable to the synergistic effect of benzotriazole photostability and dynamic disulfide bond repair. Microscopically, benzotriazole can absorb 280-380nm, which is the key wavelength for UV TPU degradation, converting light energy into heat energy and preventing photo-oxidative breakage of CN and CO bonds in the molecular chain caused by UV light. Even if a small number of molecular chains break, the dynamic disulfide bonds can be recombined through sulfur free radicals, with a recombination efficiency of over 80% at room temperature, repairing microcracks and maintaining the integrity of the crosslinked network. Therefore, the tensile strength retention rate is maintained above 84%. Comparative Example 2, lacking benzotriazole, experienced direct photo-oxidative degradation of the molecular chain under ultraviolet light, with the CN bond breakage rate increasing to 25%-30%. This resulted in the generation of numerous small molecule fragments containing carbonyl and hydroxyl groups, leading to a loose cross-linked network and a tensile strength retention rate of 62%. The benzene ring and triazole ring formed a continuous conjugated π-bond system through fusion, with a large delocalization range of π electrons covering the entire fused ring structure. This is the key destructive wavelength leading to the photodegradation of TPU. The triazole ring in the benzotriazole molecule contains two nitrogen atoms (-N=), exhibiting strong electronegativity. These atoms can form intermolecular hydrogen bonds with the hydrogen atoms (-NH-) of the urethane bonds in the TPU molecular chain. This hydrogen bonding effect causes the benzotriazole ring to undergo photodegradation. Triazoles can be stably dispersed in the TPU molecular chain network, avoiding the decrease in UV protection efficiency caused by molecular migration during UV aging, and ensuring uniform protection at the microscopic level. Although Comparative Example 1 contains benzotriazole, there is no reversible repair mechanism after the molecular chain breaks, and the broken chain segment is prone to irreversible slip. In the benzotriazole molecule, the nitrogen atom of the triazole ring can form an intramolecular hydrogen bond with the adjacent substituent, the methyl hydrogen of 1-bromomethylbenzotriazole. In the excited state, the proton will transfer from the hydrogen donor, such as methyl CH, to the hydrogen acceptor, forming an unstable enol intermediate. This intermediate then releases energy as heat through intramolecular vibration, eventually returning to the stable keto ground state. This process involves no free radical generation and no molecular chain breakage, which is the core safety mechanism of benzotriazole against UV radiation. Comparative Example 3, which does not contain polytetrahydrofuran, exhibits a hard and brittle molecular chain. After UV aging, the hard segment aggregation region cracks, resulting in a retention rate of 72%. Comparative Example 4, which is linear polyurethane without a cross-linked network, shows that the molecular chain is prone to depolymerization due to photo-oxidation, resulting in a retention rate of 68%. Comparative Example 5, which is a commercially available dispersant, lacks any UV protection and repair units, resulting in large-scale degradation of the molecular chain, with a retention rate of only 55%.

[0110] From the perspective of the balance between rigidity and flexibility, Examples 1-3 and Comparative Examples 2 and 6-9 show excellent compatibility, while Comparative Examples 1 and 3-5 are more rigid and brittle. The core reason for this is that the hard segment, formed by the reaction of diisocyanate with bis(4-hydroxyphenyl)disulfide, contains a large number of polar groups and aromatic ring structures. Strong intermolecular hydrogen bonds can be formed between polar groups, while aromatic rings form dense aggregates through π-π stacking. These aggregates constitute cross-linking points at the microscopic level, with a diameter of about 5-10 nm, which can effectively limit the excessive slippage of the molecular chain and provide rigid support against bending and tension, which is the core source of the product's rigidity. The soft segment is a linear aliphatic polyether chain with repeating unit O-CH2CH2CH2CH2-. Its main chain CO bond has an extremely low internal rotation barrier of only 2-3 kJ / mol, which is much higher than its glass transition temperature at room temperature (Tg≈-76℃). The molecular chain is in a highly elastic state. Each soft segment chain has a degree of polymerization of about 12 and a chain length of about 2.5 nm, which can rotate rapidly around the CO bond at a rotation frequency of about 10. 12 Hz, exhibiting a random coil microstructure with a coil radius of approximately 5-8 nm, can rapidly extend under external force, reaching a maximum extension length of 15-20 nm, or contract, providing significant deformation capability for the molecular chain and serving as the core carrier for product flexibility. The difference in chemical compatibility between hard and soft segments prompts the molecular chain to spontaneously form a microphase separation structure: the hard segment aggregates act as a dispersed phase, uniformly distributed within the continuous phase composed of soft segments, forming a network structure of rigid nodes and a flexible matrix at the microscopic level. This structure avoids the embrittlement of purely hard segments and overcomes the easy deformation of purely soft segments, laying the microscopic framework for rigid-flexible synergy.

[0111] In summary, the embodiments, by grafting functional groups and using precise proportions, employ disulfide bonds as self-healing functional groups and crosslinking agents, and grafting specific groups with UV resistance to ensure weather resistance, and by grafting long ether chains to optimize the feeding sequence and grinding process, effectively solve the problems of insufficient mechanical properties, harsh self-healing conditions, poor weather resistance, and the inability to balance mechanical properties and elasticity in traditional waterborne TPU films. The resulting waterborne TPU film achieves a tensile strength of 25 MPa, elongation at break >450%, tear strength >40 kN / m, puncture strength >10 N, and tensile strength retention rate >80% after 1000 hours of UV aging, ensuring mechanical strength without sacrificing toughness. It can be used in multiple fields such as outdoor applications, car covers, film sealing, and construction, exhibiting excellent performance. All indicators are within the optimal range for high performance. Furthermore, the comparative examples demonstrate that removing any core component leads to a significant deterioration in a certain performance dimension, and changing the raw material ratio of the core component also results in a large deviation in performance, verifying the irreplaceability of the present invention.

[0112] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for producing an aqueous TPU film, characterized by, Comprising the following steps: S1. Benzotriazole grafted silane coupling agent The weighed 1-chloromethyl benzotriazole was added to 20 mL of anhydrous dichloromethane, magnetic stirring was started, nitrogen was introduced, and the mixed solution of γ-glycidyl ether propyl trimethoxysilane and triethylamine was added dropwise at 60°C in a water bath, the pH of the reaction system was maintained between 8-9, the reaction was carried out for 6 h, and the benzotriazole grafted silane coupling agent was obtained by washing; S2. Silane coupling agent grafted polytetrahydrofuran ether The polytetrahydrofuran ether and anhydrous toluene were mixed and stirred, the benzotriazole grafted silane coupling agent dissolved in deionized water was added, p-toluenesulfonic acid was added, the temperature was gradually increased to 110°C, and the reaction was carried out for 4-8 h at constant temperature, then the reaction liquid was cooled to room temperature, washed to neutral, and dried to obtain the tetrahydrofuran ether grafted polysiloxane; S3. Crosslinking reaction The finished polyurethane and N,N dimethylformamide are mixed, and bis(4-hydroxyphenyl) disulfide is slowly added, and reacted at 40°C until the isocyanate group is constant by TLC monitoring, washed, filtered, and vacuum dried to obtain a disulfide cross-linked polyurethane; the molecular formula of the finished polyurethane is OCN-R-NCO, wherein ; the molar ratio of raw materials used in S3 is: finished polyurethane: bis(4-hydroxyphenyl) disulfide = 1:0.9-1.0; S4. Polysiloxane grafted disulfide crosslinked polyurethane The disulfide crosslinked polyurethane obtained in S3 was mixed with anhydrous toluene, triethylamine was added after the water bath was heated to 60°C, the tetrahydrofuran ether grafted polysiloxane obtained in S2 was added dropwise, the dropwise addition time was controlled to be 30±3 min, after the dropwise addition was completed, the reaction was continued at 60°C until the isocyanate group disappeared as monitored by thin layer chromatography, and the modified polyurethane was obtained by vacuum drying; the water-based TPU film was obtained by blade coating.

2. The method of producing an aqueous TPU film according to claim 1, characterized by, The molar ratio of the raw materials used in S1 is: silane coupling agent: 1-chloromethyl benzotriazole: triethylamine = 1:0.8-0.9:1.1-1.

2.

3. The method of producing an aqueous TPU film according to claim 1, characterized by, The molecular weight of the polytetrahydrofuran ether used in S2 is 1200±100.

4. The method of producing an aqueous TPU film according to claim 1, characterized by, The molar ratio of the raw materials used in S2 is: benzotriazole grafted silane coupling agent obtained in S1: polytetrahydrofuran ether = 1:0.8-0.9; the content of p-toluenesulfonic acid used is 3±0.1% of the system.

5. The method of producing an aqueous TPU film according to claim 1, characterized by, The molar ratio of the raw materials used in S4 is: tetrahydrofuran ether grafted polysiloxane obtained in S2: disulfide crosslinked polyurethane obtained in S3 = 1:2.5-3.

0.

6. The method of producing an aqueous TPU film according to claim 1, characterized by, The blade coating in S4 includes: uniformly coating the modified polyurethane obtained in S4 on a release substrate by a precision doctor blade with a gap of 0.05-0.6 mm, controlling the coating speed to be 1-5 m / min to ensure uniform film thickness, placing it in a multi-section oven for drying, setting the temperature gradient in sequence as: 60-80°C, 10-15 min; 100-120°C, 15-20 min; 130-150°C, 5-10 min; after the reaction, cooling to 25-30°C, and then peeling it off from the release substrate by a peeling roller to obtain the water-based TPU film.

7. A water-based TPU film produced by the production method of any one of claims 1-6.

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