Self-repairing waterborne polyurethane based on double dynamic bond synergy and preparation method of self-repairing waterborne polyurethane

Abstract

The invention discloses self-repairing waterborne polyurethane based on double dynamic bond synergy and a preparation method thereof.The method comprises the following steps that 1, in the nitrogen atmosphere, after isophorone diisocyanate, polytetrahydrofuran diol and dimethylolpropionic acid react for a period of time, a catalyst is added for continuous reaction, and a prepolymer is synthesized; (2) adding N, N-di-tert-butyl ethylenediamine into the prepolymer, and carrying out chain extension reaction; (3) adding dithiothreitol into the solution after the reaction in the step (2) to carry out cross-linking reaction; and (4) adding triethylamine into the solution obtained after the reaction in the step (3), and carrying out a salt forming reaction to obtain the self-repairing waterborne polyurethane emulsion based on double dynamic bond synergy. High self-healing efficiency and mechanical performance are achieved by introducing dynamic covalent bonds with double thermal responses, and reprocessing and recycling are achieved at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of polyurethanes, and in particular to a self-repairing waterborne polyurethane based on the synergy of double dynamic bonds and a preparation method thereof. Background Art

[0002] Waterborne polyurethane (WPU) is an environmentally friendly polymer material obtained by emulsifying polyurethane and dispersing it in water. Its molecular backbone consists of oligomeric polyols as soft segments and isocyanates and small molecule chain extenders as hard segments. Compared to traditional solvent-based polyurethanes, WPU not only retains the latter's characteristics of wide performance tunability, high mechanical strength, excellent wear resistance, and superior adhesion, but also offers significant environmental advantages, such as its water-based dispersion medium, lack of organic solvents, and low volatile organic compound (VOC) content. Therefore, WPU has become a key area of ​​development for polyurethane materials. Currently, WPU is widely used in a variety of applications, including industrial coatings, composite adhesives, printing inks, and artificial leather. However, in actual use, WPU products are susceptible to mechanical damage and surface wear, which severely restricts the material's service life and limits its further application.

[0003] In recent years, researchers have endowed WPU with self-healing capabilities by introducing dynamic bonds into it. Under the action of light, heat, or catalysts, damage repair is achieved through the reversible dissociation-association or exchange-recombination reaction of dynamic covalent bonds. Depending on the nature of the bond, these dynamic bonds are mainly divided into two categories: one is dynamic covalent bonds, including Diels-Alder bonds, disulfide bonds, boron ester bonds, thiocarbamate bonds, and hindered urea bonds; the other is non-covalent interactions, such as ionic bonds, hydrogen bonds, metal coordination, and host-guest interactions. However, the self-healing ability of the material depends not only on the characteristics of its dynamic bonds themselves, but is also affected by environmental factors such as molecular chain mobility. However, high chain mobility is usually inconsistent with mechanical strength, resulting in the high self-healing efficiency of the material often at the expense of mechanical properties. Therefore, how to achieve efficient self-healing while maintaining excellent mechanical properties remains an important scientific challenge and technical difficulty currently faced. Summary of the Invention

[0004] The purpose of the present invention is to provide a self-healing waterborne polyurethane based on the synergy of dual dynamic bonds and a preparation method thereof, which achieves higher self-healing efficiency and mechanical properties by introducing dynamic covalent bonds with dual thermal responses, while realizing reprocessing and recycling.

[0005] In one aspect of the present invention, a method for preparing a self-healing waterborne polyurethane based on the synergy of dual dynamic bonds is proposed. According to an embodiment of the present invention, the method comprises the following steps:

[0006] (1) Under nitrogen atmosphere, isophorone diisocyanate (IPDI), polytetramethylene glycol (PTMEG), and dimethylol propionic acid (DMPA) are reacted for a period of time, and then a catalyst is added to continue the reaction to synthesize a prepolymer;

[0007] The structural formula of the prepolymer is as follows:

[0008]

[0009] (2) Adding N,N-di-tert-butylethylenediamine (HUB) to the prepolymer to carry out chain extension reaction;

[0010] The structural formula of the product of the chain extension reaction is as follows:

[0011]

[0012] (3) adding dithiothreitol (DTT) to the solution after the reaction in step (2) to carry out a cross-linking reaction to prevent the reaction from being too intense to be dispersed;

[0013] The structural formula of the cross-linking reaction product is as follows:

[0014]

[0015] (4) adding triethylamine to the solution after the reaction in step (3) to carry out a salt-forming reaction, protonating the carboxyl group by triethylamine to increase the hydrophilicity of the polymer, and obtaining an aqueous polyurethane emulsion, and then removing the solvent (rotary evaporation method can be used) to obtain the self-healing aqueous polyurethane based on the synergy of double dynamic bonds.

[0016] The final product has the following structural formula:

[0017]

[0018] In addition, the method for preparing a self-healing waterborne polyurethane based on dual dynamic bond synergy according to the above embodiment of the present invention may also have the following additional technical features:

[0019] In some embodiments of the present invention, in step (1), water is removed from the polytetrahydrofuran diol before the reaction; and the catalyst is dibutyltin dilaurate.

[0020] In some embodiments of the present invention, the molecular weight of the polytetrahydrofuran diol is 500-3000 g / mol, and the molecular weight of the polytetrahydrofuran diol is 500-3000 g / mol. o C and vacuum dried to remove moisture and prevent the influence of water on the reaction system.

[0021] In some embodiments of the present invention, in step (1), the reaction temperature is 60-120 oC, the reaction time before adding the catalyst is 0.5-3 h, and the reaction time after adding the catalyst is 0.5-3 h.

[0022] The synthesis route of the prepolymer in step (1) is as follows:

[0023] .

[0024] In some embodiments of the present invention, in step (2), the viscosity of the reaction system is diluted by adding acetone. During the reaction process, due to the rapid reaction of the HUB, the viscosity of the system increases, and there will be a climbing phenomenon. An appropriate amount of acetone is added to reduce the viscosity of the system.

[0025] In some embodiments of the present invention, in step (2), the temperature of the chain extension reaction is 10-50 o C, reaction time is 2-4 h.

[0026] The chain extension reaction synthesis route in step (2) is as follows:

[0027] .

[0028] In some embodiments of the present invention, in step (3), the temperature of the cross-linking reaction is 30-70 o C, reaction time is 2-4 h.

[0029] The cross-linking reaction synthesis route in step (3) is as follows:

[0030]

[0031] In some embodiments of the present invention, in step (4), the reaction temperature is 20-50 o C. During the reaction, stir the mixture for 0.2-2 h, then add deionized water and stir vigorously for 2-6 h.

[0032] The synthesis route of the salt formation reaction in step (4) is as follows:

[0033]

[0034] In some embodiments of the present invention, the molar ratio of polytetramethylene glycol, isophorone diisocyanate, dimethylolpropionic acid, N,N-di-tert-butylethylenediamine, dithiothreitol and triethylamine is 1-2:1-3:0.1-1:0.1-1:0.5-2:0.1-1.

[0035] In another aspect of the present invention, the present invention provides a self-repairing waterborne polyurethane emulsion based on double dynamic bond synergy prepared based on the preparation method.

[0036] In another aspect of the present invention, a self-repairing waterborne polyurethane film based on dual dynamic bond synergy is proposed. In an embodiment of the present invention, the self-repairing waterborne polyurethane film based on dual dynamic bond synergy is obtained by drying the self-repairing waterborne polyurethane emulsion based on dual dynamic bond synergy. Specifically, the self-repairing waterborne polyurethane emulsion based on dual dynamic bond synergy is evenly spread in a mold and dried for 10-30 minutes. o C for 3-5 days, then heat to 50-90 o C dry for 1-3 days.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1) This invention utilizes tetrafunctional dithiothreitol (DTT) to react with difunctional isocyanate, creating a crosslinked network while simultaneously introducing dynamic, thermoresponsive thiocarbamate bonds. These dynamic bonds, when heated, promote reversible exchange and rearrangement of the molecular chains through enhanced molecular chain mobility, thereby endowing the material with excellent self-healing and recyclable properties. This imparts self-healing and recyclability to the crosslinked system. As the temperature rises, the increased mobility of the molecular chains allows for rapid exchange and rearrangement of the thiocarbamate bonds, conferring self-healing capabilities. To further optimize the material's performance, this invention innovatively introduces thermoresponsive, dynamically hindered urea bonds, which synergize with the thiocarbamate bonds to significantly enhance the system's dynamic exchange efficiency, further improving the material's self-healing and recyclable capabilities.

[0039] 2) The hindered urea bond not only has temperature-responsive properties, but the rich -NH- groups in its molecular structure can form a multiple hydrogen bond cross-linking network with the carbonyl groups in the system. This physical cross-linking structure not only greatly improves the mechanical strength of the material, but also gives it excellent damage resistance. When defects or cracks appear on the surface of the material, the dynamic fracture and reorganization of the hydrogen bond network can effectively dissipate stress energy, thereby preventing crack development. At the same time, crack development also needs to overcome hydrogen bond interactions and increase the energy threshold required for material destruction. This innovative design strategy based on hydrogen bond network enhancement not only improves the mechanical properties of the material, but also significantly enhances its reliability and durability, providing new ideas for the development of high-performance polymer films.

[0040] 3) The dual dynamic bond synergistic mechanism proposed in this invention provides an innovative solution for the molecular design of waterborne polyurethane materials. By precisely controlling the synergistic effects of dynamic covalent bonds and physical crosslinking networks, this technology achieves multi-dimensional optimization of material properties. This technology demonstrates broad application prospects and significant industrial value in high-tech fields such as flexible electronics, intelligent responsive coatings, and advanced packaging materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1It is the reaction route of the self-healing waterborne polyurethane based on the synergy of dual dynamic bonds in Examples 1-5 of the present invention;

[0042] Figure 2 is a particle size diagram of the self-repairing waterborne polyurethane emulsion based on dual dynamic bond synergy in Examples 1-5 of the present invention;

[0043] Figure 3 is the Zeta potential diagram of the self-repairing aqueous polyurethane emulsion based on double dynamic bond synergy in Examples 1-5 of the present invention;

[0044] Figure 4 Transmission electron microscopy (TEM) images of the self-healing waterborne polyurethane emulsion based on dual dynamic bond synergy in Examples 1-5 of the present invention;

[0045] Figure 5 This is the infrared spectrum of the self-healing waterborne polyurethane film based on the synergy of dual dynamic bonds in the application example of the present invention;

[0046] Figure 6 WPU-H in the application example of the present invention 0.8 D 0.2 X-ray photoelectron spectroscopy (XPS) of thin films;

[0047] Figure 7 This is the ultraviolet-visible light absorption (UV-Vis) graph of the self-healing waterborne polyurethane film based on dual dynamic bonds in the application example of the present invention;

[0048] Figure 8 This is a thermogravimetric analysis (TGA) graph of a self-healing waterborne polyurethane film based on dual dynamic bonds prepared in an application example of the present invention;

[0049] Figure 9 This is a DSC curve diagram of the self-healing waterborne polyurethane film based on dual dynamic bonds prepared in an application example of the present invention;

[0050] Figure 10 This is a stress-strain curve of a waterborne polyurethane film based on dual dynamic bond synergistic self-healing prepared in an application example of the present invention;

[0051] Figure 11 WPU-H in the application example of the present invention 0.8 D 0.2 Stress-strain curves of films with different notch depths;

[0052] Figure 12 This is a graph showing the storage modulus (G') and loss modulus (G'') of the self-healing waterborne polyurethane film based on dual dynamic bonds prepared in an application example of the present invention as a function of temperature;

[0053] Figure 13 WPU-H in the application example of the present invention0.8 D 0.2 Stress relaxation curve of the film;

[0054] Figure 14 The figure is a schematic diagram of the dynamic exchange of hindered urea bonds (a) and thiocarbamate bonds (b) in the application examples of the present invention;

[0055] Figure 15 WPU-H in the application example of the present invention 0.8 D 0.2 Stress-strain curves of the film before and after self-healing;

[0056] Figure 16 WPU-H in the application example of the present invention 0.8 D 0.2 Photos of the film before and after recycling (a) and stress-strain curves of multiple recycling (b). DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0058] Example 1

[0059] A method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy, comprising the following steps:

[0060] (1) Preparation of prepolymer

[0061] First, 20 g of polytetrahydrofuran (PTMEG-2000) with a molecular weight of 2000 g / mol was passed through 85 o C and vacuum drying was used to fully remove water. 6.67 g of isophorone diisocyanate (IPDI) was added to a three-necked flask with stirring, followed by PTMEG-2000 and thorough stirring, followed by 0.94 g of 2,2-dimethylolpropionic acid (DMPA). During this process, nitrogen was introduced. After 1 h of reaction, 0.1 wt% of catalyst butyltin dilaurate (DBTBL) was added and the reaction was continued with stirring for 2 h. The reaction temperature was controlled at 85°C throughout the reaction. o C.

[0062] (2) Chain extension reaction

[0063] Lower the reaction temperature to 25 oC, add a small amount of acetone to reduce the reaction viscosity, then slowly add 1.21g N,N-di-tert-butylethylenediamine (HUB), 25 o C for 3 h.

[0064] (3) Cross-linking reaction

[0065] Dissolve 1.07 g of dithiothreitol (DTT) in 5 ml of acetone and raise the reaction temperature to 60 o C, DTT was slowly added into the three-necked flask and reacted for 3 h.

[0066] (4) Salt formation and emulsification reaction

[0067] The reaction temperature was reduced to 25 o After C, 0.71 g of triethylamine (TEA) was added and the mixture was salted for 2 h. Subsequently, 120 g of water was added and stirred vigorously for 4 h to fully disperse the mixture. The solvent was then removed by rotary evaporation to obtain a self-healing waterborne polyurethane emulsion based on the synergy of dual dynamic bonds, which was designated as WPU-H. 0.7 D 0.3 .

[0068] Example 2

[0069] A method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy, comprising the following steps:

[0070] (1) Preparation of prepolymer

[0071] First, 20g of polytetrahydrofuran (PTMEG-2000) with a molecular weight of 2000 g / mol was passed through 85 o C and vacuum drying was used to fully remove water. 6.67 g of isophorone diisocyanate (IPDI) was added to a three-necked flask with stirring, followed by PTMEG-2000 and thorough stirring, followed by 1.01 g of 2,2-dimethylolpropionic acid (DMPA). During this process, nitrogen was introduced. After 1 h of reaction, 0.1 wt% of catalyst butyltin dilaurate (DBTBL) was added and the reaction was continued with stirring for 2 h. The reaction temperature was controlled at 85°C throughout the reaction. o C.

[0072] (2) Chain extension reaction

[0073] Lower the reaction temperature to 25 o C, add a small amount of acetone to reduce the reaction viscosity, then slowly add 1.29g N,N-di-tert-butylethylenediamine (HUB), 25 o C for 3 h.

[0074] (3) Cross-linking reaction

[0075] Dissolve 1.14 g of dithiothreitol (DTT) in 5 ml of acetone and raise the reaction temperature to 60 o C, DTT was slowly added into the three-necked flask and reacted for 3 h.

[0076] (4) Salt formation and emulsification reaction

[0077] The reaction temperature was reduced to 25 o After C, 0.76 g of triethylamine (TEA) was added and the mixture was salted for 2 h. Subsequently, 120 g of water was added and stirred vigorously for 4 h to fully disperse the mixture. The solvent was then removed by rotary evaporation to obtain a self-healing waterborne polyurethane emulsion based on the synergy of dual dynamic bonds, which was designated as WPU-H. 0.75 D 0.25 .

[0078] Example 3

[0079] A method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy, comprising the following steps:

[0080] (1) Preparation of prepolymer

[0081] First, 20 g of polytetrahydrofuran (PTMEG-2000) with a molecular weight of 2000 g / mol was passed through 85 o C and vacuum drying was used to fully remove water. 6.67 g of isophorone diisocyanate (IPDI) was added to a three-necked flask with stirring, followed by PTMEG-2000 and thorough stirring, followed by 1.07 g of 2,2-dimethylolpropionic acid (DMPA). During this process, nitrogen was introduced. After 1 h of reaction, 0.1 wt% of catalyst butyltin dilaurate (DBTBL) was added and the reaction was continued with stirring for 2 h. The reaction temperature was controlled at 85°C throughout the reaction. o C.

[0082] (2) Chain extension reaction

[0083] Lower the reaction temperature to 25 o C, add a small amount of acetone to reduce the reaction viscosity, then slowly add 1.38g N,N-di-tert-butylethylenediamine (HUB), 25 o C for 3 h.

[0084] (3) Cross-linking reaction

[0085] Dissolve 1.14 g of dithiothreitol (DTT) in 5 ml of acetone and raise the reaction temperature to 60 o C, DTT was slowly added into the three-necked flask and reacted for 3 h.

[0086] (4) Salt formation and emulsification reaction

[0087] The reaction temperature was reduced to 25 o After C, 0.81 g of triethylamine (TEA) was added and the mixture was salted for 2 h. Subsequently, 120 g of water was added and stirred vigorously for 4 h to fully disperse the mixture. The solvent was then removed by rotary evaporation to obtain a self-healing waterborne polyurethane emulsion based on the synergy of dual dynamic bonds, which was designated as WPU-H. 0.8 D 0.2 .

[0088] Example 4

[0089] A method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy, comprising the following steps:

[0090] (1) Preparation of prepolymer

[0091] First, 20 g of polytetrahydrofuran (PTMEG-2000) with a molecular weight of 2000 g / mol was passed through 85 o C and vacuum drying were used to remove water. 6.67 g of isophorone diisocyanate (IPDI) was added to a three-necked flask with stirring, followed by PTMEG-2000 and thorough stirring, followed by 1.14 g of 2,2-dimethylolpropionic acid (DMPA). During this process, nitrogen was introduced. After 1 h of reaction, 0.1 wt% of catalyst butyltin dilaurate (DBTBL) was added and the reaction was continued with stirring for 2 h. The reaction temperature was controlled at 85°C throughout the reaction. o C.

[0092] (2) Chain extension reaction

[0093] Lower the reaction temperature to 25 o C, add a small amount of acetone to reduce the reaction viscosity, then slowly add 1.46g N,N-di-tert-butylethylenediamine (HUB), 25 o C for 3 h.

[0094] (3) Cross-linking reaction

[0095] Dissolve 1.29 g of dithiothreitol (DTT) in 5 ml of acetone and raise the reaction temperature to 60 o C, DTT was slowly added into the three-necked flask and reacted for 3 h.

[0096] (4) Salt formation and emulsification reaction

[0097] The reaction temperature was reduced to 25 o After C, 0.86 g of triethylamine (TEA) was added and the mixture was salted for 2 h. Subsequently, 120 g of water was added and stirred vigorously for 4 h to fully disperse the mixture. The solvent was then removed by rotary evaporation to obtain a self-healing waterborne polyurethane emulsion based on the synergy of dual dynamic bonds, which was designated as WPU-H. 0.85 D0.15 .

[0098] Example 5

[0099] A method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy, comprising the following steps:

[0100] (1) Preparation of prepolymer

[0101] First, 20 g of polytetrahydrofuran (PTMEG-2000) with a molecular weight of 2000 g / mol was passed through 85 o C and vacuum drying was used to fully remove water. 6.67 g of isophorone diisocyanate (IPDI) was added to a three-necked flask with stirring, followed by PTMEG-2000 and thorough stirring, followed by 1.21 g of 2,2-dimethylolpropionic acid (DMPA). During this process, nitrogen was introduced. After 1 h of reaction, 0.1 wt% of the catalyst butyltin dilaurate (DBTBL) was added and the reaction was continued with stirring for 2 h. The reaction temperature was controlled at 85°C throughout the reaction. o C.

[0102] (2) Chain extension reaction

[0103] Lower the reaction temperature to 25 o C, add a small amount of acetone to reduce the reaction viscosity, then slowly add 1.55g N,N-di-tert-butylethylenediamine (HUB), 25 o C for 3 h.

[0104] (3) Cross-linking reaction

[0105] Dissolve 1.37 g of dithiothreitol (DTT) in 5 ml of acetone and raise the reaction temperature to 60 o C, DTT was slowly added into the three-necked flask and reacted for 3 h.

[0106] (4) Salt formation and emulsification reaction

[0107] The reaction temperature was reduced to 25 o After C, 0.91 g of triethylamine (TEA) was added and the mixture was salted for 2 h. Subsequently, 120 g of water was added and stirred vigorously for 4 h to fully disperse the mixture. The solvent was then removed by rotary evaporation to obtain a self-healing waterborne polyurethane emulsion based on the synergy of dual dynamic bonds, which was designated as WPU-H. 0.90 D 0.1 .

[0108] The following is the feeding ratio of Examples 1-5:

[0109] Table 1 Feed ratio of Examples 1-5

[0110]

[0111] The self-repairing waterborne polyurethane emulsions based on dual dynamic bond synergy prepared in Examples 1-5 were subjected to performance tests:

[0112] (1) The emulsion was diluted to a concentration of 1 / 500 with water and sonicated for 2 h. Dynamic light scattering (DLS) measurements were performed on a Nano-Zetasizer 90 from Malvern Instruments (UK). Figure 2 As shown, the prepared aqueous polyurethane emulsion has a narrow particle size distribution and is monodisperse, which proves that the aqueous polyurethane emulsion is well dispersed.

[0113] (2) The emulsion was diluted to 1 / 500 with deionized water and sonicated for 2 h. Zeta potential measurements were performed on a Nano-Zetasizer 90 from Malvern Instruments (UK). Figure 3 As shown in the figure, the absolute value of the ZETA potential of the self-healing waterborne polyurethane based on the synergy of double dynamic bonds is greater than 40, which proves that it has good storage stability.

[0114] (3) Transmission electron microscopy (TEM) observations were performed on a JEM-2100F electron microscope with an accelerating voltage of 100 kV. The emulsion was diluted to 1 / 100 with deionized water, and the diluted emulsion was dropped onto a 200-mesh copper grid. After natural drying, the test was performed at room temperature. Figure 4 As shown, it can be observed that the particles of the self-healing waterborne polyurethane emulsion based on the synergy of double dynamic bonds are uniform in size and evenly dispersed, proving that the emulsion has good dispersibility and stable micron morphology.

[0115] Application Examples

[0116] A method for preparing a self-repairing waterborne polyurethane film based on dual dynamic bond synergy, comprising the following steps:

[0117] The self-repairing waterborne polyurethane emulsions based on the synergistic dual dynamic bonds prepared in Examples 1-5 were evenly spread in a tetrafluoroethylene mold and o C for 3-5 days, then heat to 50-900 o C for 1-3 days to obtain WPU-H with a thickness of 0.1 mm. 0.7 D 0.3 、WPU-H 0.75 D 0.25 、WPU-H 0.8 D 0.2 、WPU-H 0.85 D 0.15 、WPU-H 0.9 D 0.1 film.

[0118] The five films prepared were subjected to performance tests:

[0119] (1) The film was tested by infrared spectroscopy at room temperature using an ATR-FTIR spectrometer (Nicol iS 50) using the reflection method. Figure 5 As shown, at 3307 cm -1 The broad absorption peaks at 1097 and 1037 cm are attributed to the stretching vibration of NH in the carbamate and hindered urea groups. -1 The stretching vibration peaks of CO and CS were observed at 1620 cm -1 The absorption peak at 1717 cm is the C=O in the hindered urea group. -1 The peak at 2265 cm-1 is attributed to the C=O in the carbamate and thiocarbamate groups. -1 The complete disappearance of the characteristic absorption peak of NCO groups at φ 100 nm confirmed the complete consumption of isocyanate groups during the polymerization.

[0120] (2) Application of WPU-H 0.8 D 0.2 The X-ray photoelectron spectroscopy (XPS) data of the films were obtained at room temperature using an ESCALAB 250Xi (Thermo Fisher Scientific) instrument. Figure 6 As shown, characteristic absorption peaks of C1s, O1s, N1s and S2p can be observed, proving the successful preparation of polyurethane.

[0121] (3) The ultraviolet-visible spectra (UV-Vis) of the films were recorded at ambient temperature using an Agilent (USA) CARY 5000 UV-Vis-NIR instrument in the wavelength range of 400–800 nm. Figure 7 As shown, it is proved that the self-healing waterborne polyurethane based on the synergy of dual dynamic bonds has good transparency and can be well applied in various daily life scenarios.

[0122] (4) The dried film samples were subjected to thermogravimetric analysis (TGA) on a TGA8000 thermogravimetric analyzer at temperatures ranging from room temperature to 800 o C, the heating rate under nitrogen flow was 10 o C / min. Figure 8 As shown, the temperature of 5% thermal weight loss is 200 o C and above, the complete decomposition temperature is 430 o C, which proves that it has good thermal stability.

[0123] (5) Differential scanning calorimetry (DSC) measurements were performed on a TA DSC Q2000 thermal analysis system in the temperature range of -80 to 120 oC. The heating and cooling rates were set to 10 o C / min, and the nitrogen flow rate was set to 40 mL / min. Glass transition temperature (T g ) is determined based on the midpoint of the transition recorded during the second heating process. Figure 9 As shown, T g It shows a trend of first decreasing and then increasing. This is because the cross-linking degree decreases and the polymer chain activity increases, resulting in its T g However, more hydrogen bonds are added later to form physical cross-links, which weakens the activity of the molecular chain. g Increase.

[0124] (6) The tensile stress-strain curves of the WPU films were obtained at room temperature using a universal testing machine (CMT 4104, NSS (Shenzhen) Laboratory Equipment Co., Ltd.). Figure 10 As shown in the figure, as the degree of cross-linking decreases, the stress gradually decreases and the strain gradually increases. The rigid structure of the polymer decreases and the flexibility of the molecular chain increases, so there is a trend of increasing strain and decreasing stress. However, as the hydrogen bond content increases, physical cross-linking is formed, resulting in an increase in stress and a decrease in strain.

[0125] (7) Using a universal testing machine (CMT 4104, Nss (Shenzhen) Laboratory Equipment Co., Ltd.) at room temperature, a 10 mm wide WPU-H 0.8 D 0.2 The film specimens were cut vertically with 1-3 mm notches along the width direction and stretched under a tensile testing machine to obtain the stress-strain curves, as shown in Figure 11 As shown in the figure, due to the chemical cross-linking and physical hydrogen bond cross-linking of the polymer network, the stress can be effectively dispersed throughout the polymer network during the stretching process, which can effectively prevent the propagation of notch cracks, dissipate the stress at the notch, and have excellent damage tolerance.

[0126] (8) Rheological tests were performed using a TA HR10 rheometer (USA). o C / min, controlled strain 0.55%. Rheological test results show that the storage modulus and loss modulus are as follows: Figure 12 As shown in the figure, initially, the storage modulus is higher than the loss modulus, and the waterborne polyurethane film is elastic. When the two intersect, a viscoelastic transition occurs, and the viscoelastic transition temperature shows a pattern of first decreasing and then increasing. 0.8 -P 0.2 It has the lowest viscoelastic transition temperature, so it has faster dynamic exchange and self-healing capabilities.

[0127] (9) Stress relaxation test was performed using a TA HR10 rheometer (USA). The temperature was controlled at 70 o C and 3% strain. Figure 13 As shown, it was found that WPU-H 0.8 D 0.2 The time taken for stress relaxation to 1 / e is the shortest, which proves that its dynamic structure has rapid exchange and good self-healing performance.

[0128] (10) Figure 14 As shown in the figure, the exchange mechanism of two dynamic bonds (hindered urea bond (a) and thiocarbamate bond (b)) occurs. In waterborne polyurethane, hindered urea bond and thiocarbamate bond will undergo dynamic exchange, so the prepared waterborne polyurethane has excellent self-healing ability.

[0129] (11) Choose WPU-H 0.8 -D 0.2 As a self-healing sample, the original film sample (70 mm × 10 mm × 1.2 mm) was cut into two pieces. After that, both ends were fully contacted by adding ethanol. o The self-healing properties of the samples were tested by heating them in a vacuum oven for different times at a tensile rate of 50 mm / min, and the test was repeated three times for each sample. Figure 15 (a) is a photo of the sample being stretched on a tensile testing machine after the fracture surfaces are fully contacted. The self-repair efficiency (η) is the tensile strength after repair (σ t ) divided by the original tensile strength (σ0). Figure 15 (b) shows that the data proves that at 90 o C, the healing efficiency gradually increased with time and was almost saturated after 12 h, reaching 93%.

[0130]

[0131] (12) Figure 16 As shown in a, WPU-H 0.8 -D 0.2 The film samples were cut into slices and grinded at 80 o C, after hot pressing at 10 MPa for 30 min, the mechanical properties of the samples were tested at a tensile rate of 50 mm / min. Figure 16 As shown in b, after 3 cycles of hot pressing, its mechanical properties can still reach 80% of the original mechanical properties.

[0132] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a self-repairing waterborne polyurethane based on the synergy of dual dynamic bonds, characterized in that: The following steps are involved: (1) Under nitrogen atmosphere, isophorone diisocyanate, polytetramethylene glycol, and dimethylol propionic acid are reacted for a period of time, and then a catalyst is added to continue the reaction to synthesize a prepolymer; (2) adding N,N-di-tert-butylethylenediamine to the prepolymer described in step (1) to carry out a chain extension reaction; (3) adding dithiothreitol to the solution after the reaction in step (2) to carry out a cross-linking reaction; (4) Adding triethylamine to the solution after the reaction in step (3) to carry out a salt-forming reaction to obtain an aqueous polyurethane emulsion.

2. The method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy according to claim 1, characterized in that: In step (1), water is removed from the polytetrahydrofuran diol before the reaction; and the catalyst is dibutyltin dilaurate.

3. The method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy according to claim 2, characterized in that: The molecular weight of the polytetrahydrofuran diol is 500-3000 g / mol, and the molecular weight of the polytetrahydrofuran diol is 500-3000 g / mol. o C and vacuum dried to remove moisture.

4. The method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy according to claim 1, characterized in that: In step (1), the reaction temperature is 60-120 o C, the reaction time before adding the catalyst is 0.5-3 h, and the reaction time after adding the catalyst is 0.5-3 h.

5. The method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy according to claim 1, characterized in that: In step (2), the viscosity of the reaction system is diluted by adding acetone; the temperature of the chain extension reaction is 10-50 o C, reaction time is 2-4 h.

6. The method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy according to claim 1, characterized in that: In step (3), the temperature of the cross-linking reaction is 30-70 o C, reaction time is 1-4 h.

7. The method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy according to claim 1, characterized in that: In step (4), the temperature of the salt-forming reaction is 20-50 o C. During the reaction, stir the mixture for 0.5-2 h, then add deionized water and stir vigorously for 2-6 h.

8. The method for preparing a self-repairing waterborne polyurethane based on dual dynamic bond synergy according to claim 1, characterized in that: The molar ratio of the polytetramethylene glycol, isophorone diisocyanate, dimethylol propionic acid, N,N-di-tert-butylethylenediamine, dithiothreitol and triethylamine is 1-2:1-3:0.1-1:0.1-1:0.5-2:0.1-1.

9. A self-repairing waterborne polyurethane emulsion based on double dynamic bond synergy prepared by the preparation method of the self-repairing waterborne polyurethane based on double dynamic bond synergy according to any one of claims 1 to 8.

10. A self-healing waterborne polyurethane film based on dual dynamic bond synergy, characterized by: Obtained by drying the self-repairing aqueous polyurethane emulsion based on double dynamic bond synergy as described in claim 9.

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