A high-toughness low-hysteresis polyurethane composite film with self-repairing function and a preparation method and application thereof

Abstract

The application discloses a high-toughness low-hysteresis polyurethane composite film with a self-repairing function and a preparation method and application thereof, and the method comprises the following steps: (1) carrying out prepolymerization on polybutadiene, isophorone diisocyanate and dibutyl tin dilaurate to prepare a prepolymer solution; (2) dissolving VPSB and 1,4-butanediol, and then adding into the prepolymer solution to carry out chain extension reaction under a nitrogen atmosphere, and an HTPU-VPSB solution is prepared, wherein, the structural formula of the VPSB is as follows: (3) pouring the HTPU-VPSB solution into a mold, and drying to obtain an HTPU-VPSB film. The film prepared by the application can be efficiently and quickly repaired after being damaged, the film after being repaired still maintains good mechanical properties, and the service life of the material is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of functional application materials, specifically to a high-toughness, low-hysteresis polyurethane composite film with self-healing function, its preparation method, and its application. Background Technology

[0002] With the rapid development of wearable electronics and biomimetic robotics, higher demands are being placed on the response fidelity and signal stability of flexible sensing materials. The mechanical hysteresis effect of materials directly leads to sensor signal drift, response delay, and measurement distortion. Therefore, developing elastomer substrates with low hysteresis characteristics has become one of the core challenges in improving the reliability and accuracy of flexible devices.

[0003] Traditional elastomer materials, such as silicone rubber or some thermoplastic elastomers, exhibit strong permanent physical entanglement between molecular chain segments or filler-matrix interfacial friction. During cyclic deformation, this leads to significant viscoelastic dissipation, resulting in large hysteresis loops and irreversible deformation accumulation. In contrast, polyurethane (PU), with its unique microphase separation structure, provides an ideal molecular structure for achieving low hysteresis performance.

[0004] The self-healing function of polyurethane films is achieved by constructing a dynamic network composed of reversible chemical bonds and physical interactions within the material. By introducing dynamic covalent bonds such as disulfide bonds, diselenylene bonds, and DA bonds, as well as dynamic non-covalent bonds such as hydrogen bonds and metal coordination bonds, intelligent polyurethane materials with high strength and multifunctionality can achieve rapid repair under various conditions, including photothermal conditions. Wear resistance is typically increased by altering the ratio of isocyanate to polyol in the polyurethane and changing its degree of crosslinking. Physical interactions such as hydrogen bonds between polyurethane molecules effectively dissipate frictional energy and improve the material's cohesive strength and toughness, indirectly enhancing wear resistance.

[0005] Traditional polyurethane soft segments are typically polyethers (such as PTMEG) or polyesters (such as PBA). These molecular chains contain polar groups (such as ether bonds and ester bonds). These polar groups create strong attraction between the soft segment molecular chains and between the soft and hard segments. When the material is stretched, it must overcome significant internal friction, converting this energy into heat. Many polyether or polyester soft segments also undergo strain during stretching, inducing crystallization. The originally disordered molecular chains are straightened and aligned neatly under external force, forming tiny crystalline regions. This process itself absorbs energy (hysteresis loop area increases), and when the external force is removed and the crystals melt, the energy release is asynchronous with the absorption, further exacerbating energy loss. Because the soft segments are polar, they attract the equally polar hard segments, leading to incomplete microphase separation and the formation of a blurred interface layer. When the material deforms, the hard and soft segments become entangled at the interface layer, and a large amount of energy is dissipated as heat.

[0006] Polyurethane films inevitably suffer mechanical damage such as scratches and microcracks during use, leading to material performance degradation and even structural failure. Traditional damage repair relies on manual intervention or component replacement, which is not only costly but also wasteful of resources. Therefore, a self-healing mechanism is needed to endow materials with the ability to autonomously repair damage, thereby extending service life and reducing maintenance costs.

[0007] Current research on self-healing polyurethanes mainly falls into two categories: exogenous and intrinsic. Exogenous self-healing relies on carriers such as microcapsules and hollow fibers to encapsulate the repair agent. When the material is damaged, the carrier ruptures, releasing the repair agent to fill the crack. However, this strategy faces insurmountable bottlenecks: limited repair agent reserves restrict the number of repairs, interfacial compatibility between the carrier and the matrix affects repair reliability, and the secondary repair capability is essentially lost after the repair agent is released. In contrast, intrinsic self-healing materials introduce dynamic covalent bonds (such as disulfide bonds, diselenide bonds, and Diels-Alder bonds) or dynamic non-covalent bonds (such as hydrogen bonds and metal coordination bonds), utilizing the reversible breakage and recombination of dynamic bonds to achieve damage repair, theoretically allowing for multiple repeated repairs.

[0008] Despite the significant advantages of intrinsic self-healing strategies, current research still faces key challenges. First, it is difficult to balance mechanical properties with self-healing efficiency. Second, single dynamic bond systems have inherent limitations. While disulfide-based self-healing systems offer high repair efficiency, aromatic disulfide monomers are expensive, and excessive introduction can disrupt the material's performance balance. Although diselenate bonds have lower bond energies (approximately 172 kJ / mol) and visible light responsiveness, the potential environmental and health risks of selenium limit their application. The Diels-Alder system, while achieving repair rates exceeding 90%, requires a high temperature (130°C) to trigger the reaction, contradicting the application requirement of rapid room-temperature repair. While dynamic non-covalent bonds can achieve room-temperature repair, their weak interaction strength makes it difficult to restore the material's original properties. Summary of the Invention

[0009] The purpose of this invention is to provide a high-toughness, low-hysteresis polyurethane composite film with self-healing function, its preparation method and application, which solves the drawbacks of intrinsic self-healing polyurethane.

[0010] In one aspect of the present invention, a method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function is provided. According to an embodiment of the present invention, the method includes the following steps:

[0011] (1) A prepolymer solution was prepared by prepolymerizing polybutadiene (HTPB), isoflurane diisocyanate (IPDI) and dibutyltin dilaurate (DBTDL);

[0012] (2) VPSB is dissolved in 1,4-butanediol (BDO) and then added to the prepolymer solution. A chain extension reaction is carried out under a nitrogen atmosphere to prepare an HTPU-VPSB solution. The structural formula of the VPSB is as follows:

[0013] ;

[0014] (3) Pour the HTPU-VPSB solution into a mold and dry it to obtain an HTPU-VPSB film.

[0015] In addition, the method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function according to the above embodiments of the present invention may also have the following additional technical features:

[0016] In some embodiments of the present invention, in step (1), the molar ratio of polybutadiene (HTPB), isoflurane diisocyanate (IPDI), and dibutyltin dilaurate (DBTDL) is 1 : (1.2-1.6) : (0.001-0.003).

[0017] In this invention, the reasons for selecting hydroxyl-terminated polybutadiene (HTPB) as the soft segment raw material in step (1) are as follows: a. HTPB molecular chains are flexible and have a low glass transition temperature (about -80°C), which endows the elastomer with excellent flexibility and wear resistance; b. HTPB is a smooth, amorphous, nonpolar chain with very low resistance to chain segment movement, which can significantly reduce frictional heat generation; c. HTPB has good thermal stability, and its molecular motion is stable in a wide temperature range, and its hysteresis performance is not easily deteriorated with temperature changes; d. The hydroxyl-terminated structure can react directly with isocyanates, which facilitates polyurethane prepolymerization, and its compatibility with IPDI is moderate, which is conducive to the formation of an ideal microphase separation structure.

[0018] The reasons for choosing isophorone diisocyanate (IPDI) as the hard segment monomer in step (1) are as follows: a. IPDI is an alicyclic diisocyanate that does not contain aromatic rings. Polyurethane synthesized from it has excellent resistance to yellowing and weathering, and is not easily discolored or degraded by ultraviolet radiation; b. The two isocyanate groups in IPDI have different reactivity (one of which is affected by the steric hindrance of the cyclic structure), which facilitates selective control of the reaction in the prepolymerization stage and is conducive to the formation of prepolymers with regular structure and controllable molecular weight; c. The nonpolar part of IPDI is compatible with the soft segment of HTPB, which is conducive to the formation of a stable microphase separation structure, thereby improving the mechanical properties and wear resistance of the elastomer; d. IPDI has a stable structure and is not prone to side reactions under high temperature or dynamic use conditions, which helps to maintain the hysteresis performance and thermal stability of the elastomer.

[0019] The reasons for choosing dibutyltin dilaurate (DBTDL) as a catalyst in step (1) are as follows: a. DBTDL has high catalytic activity for the reaction of hydroxyl groups with isocyanates and can significantly accelerate the prepolymerization reaction at a low dosage (0.001-0.003 molar ratio); b. The reaction is mild and controllable, with good synergistic effect at 55-60℃, and is not prone to initiating isocyanate self-polymerization or side reactions; c. It has good compatibility with HTPB and IPDI systems, does not introduce harmful impurities, and does not affect the mechanical properties and thermal stability of the final elastomer.

[0020] In step (1), the principle of the prepolymerization reaction is as follows: the hydroxyl group (-OH) at the end of HTPB and the isocyanate group (-NCO) in IPDI undergo a stepwise addition polymerization reaction under the catalysis of DBTDL to generate a prepolymer containing urethane bonds (-NH-COO-). The essence of this reaction is the nucleophilic addition of hydroxyl groups to isocyanate groups. Step (1) provides active sites for subsequent chain extension reactions by forming isocyanate-terminated prepolymers; controls the ratio and distribution of soft and hard segments to construct an ideal microphase separation structure for the final elastomer; and removes residual moisture in the system during the prepolymerization stage to avoid later foaming or side reactions.

[0021] In some embodiments of the present invention, in step (1), the temperature of the prepolymerization reaction is 55-60°C, and the reaction time is 2-3 hours. The reasons for choosing this temperature range are as follows: a. The reaction rate is moderate at this temperature: the reaction is slow below 50°C, requiring a longer reaction time; above 60°C, isocyanate is prone to react with trace amounts of water in the system to form urea compounds, or to undergo dimerization or trimerization; 55-60°C is the optimal temperature window that balances reaction activity and selectivity. b. Within this temperature range, the catalytic activity of the catalyst dibutyltin dilaurate (DBTDL) is fully released, the reaction can be completed within 2-3 hours, and the resulting prepolymer has a narrow molecular weight distribution and controllable viscosity and structure. c. HTPB does not undergo thermal degradation or cross-linking side reactions within this temperature range, and its amorphous and low-motion-resistance characteristics are maintained.

[0022] The specific operation of step (1) is as follows: a certain amount of polybutadiene is added to a three-necked flask, and the water is removed by vacuum pump (the oil bath temperature for removing water from HTPB using vacuum pump is 130°C and the time is 2h). Then, isoflurane diisocyanate is added to the three-necked flask, and dibutyltin dilaurate is added for catalysis. The prepolymer solution is prepared by stirring with polytetrafluoroethylene (PTFE) stirring paddle.

[0023] The synthetic route in step (1) is as follows:

[0024] .

[0025] In some embodiments of the present invention, step (2) of the preparation method of VPSB includes the following steps: mixing dissolved p-phenylenediamine (PPD) with vanillin, refluxing and stirring the mixture under a nitrogen atmosphere, evaporating the solvent after the reaction is complete, redissolving the dried product, centrifuging and removing the supernatant, and drying to obtain VPSB. Specifically, both p-phenylenediamine (PPD) and vanillin are dissolved in anhydrous ethanol; the solvent is evaporated using a rotary evaporator.

[0026] In some embodiments of the present invention, the molar ratio of p-phenylenediamine to vanillin is (2.1-2.3):1, the reaction temperature is 45-50°C, and the reaction time is 2-3 hours.

[0027] In this invention, the reasons for selecting p-phenylenediamine (PPD) and vanillin as raw materials for VPSB synthesis in step (2) are as follows: a. PPD contains two primary amine groups (-NH2), and vanillin contains one aldehyde group (-CHO). The two can be condensed through Schiff base reaction to form a bis-Schiff base structure, providing a basis for the subsequent introduction of dynamic covalent bonds. b. Vanillin is derived from biomass and contains phenolic hydroxyl and methoxy groups, which can introduce polar groups into VPSB, enhancing compatibility with the polyurethane matrix and hydrogen bonding. c. The aromatic amine structure of PPD is relatively rigid, which can improve the thermal stability of VPSB; the molar ratio of feed is controlled at (2.1-2.3):1 (PPD in excess) to ensure that the aldehyde group of vanillin reacts completely and to avoid residual aldehyde groups interfering with subsequent polymerization.

[0028] The reaction principle of VPSB synthesis is as follows: the two primary amino groups of p-phenylenediamine undergo nucleophilic addition-elimination reactions with the aldehyde groups of two molecules of vanillin, respectively, to generate a Schiff base containing two carbon-nitrogen double bonds (-CH=N-), while simultaneously removing two molecules of water. Applications: a. It yields Schiff base compounds (VPSB) with phenolic hydroxyl groups at both ends, which can be introduced into polyurethane systems as dynamic crosslinking agents or chain extenders; b. The carbon-nitrogen double bonds exhibit reversibility under specific conditions (such as acid, heat, and light), providing elastomers with self-healing or reprocessing capabilities; c. The phenolic hydroxyl groups can participate in hydrogen bonding or react with isocyanates, enhancing the mechanical properties and interfacial compatibility of materials; d. The reaction temperature is 45-50℃, and the time is 2-3 hours, providing mild conditions that avoid aldehyde oxidation or amino side reactions, resulting in a high Schiff base yield.

[0029] The synthetic route for VPSB is as follows:

[0030] .

[0031] In some embodiments of the present invention, in step (2), the molar ratio of VPSB to 1,4-butanediol is 1:(0.8-1.2). The reasons for choosing this range are as follows: a. To balance the difference in reactivity between phenolic hydroxyl groups (VPSB) and alcoholic hydroxyl groups (BDO), avoiding excessively fast or slow local reactions and forming a uniform network. b. To balance self-healing properties (VPSB provides reversible Schiff base bonds) and mechanical strength (BDO provides a rigid structure). c. To match the total amount of NCO in the prepolymer, ensuring sufficient chain extension and no residual active groups.

[0032] In this invention, the reasons for choosing VPSB as a chain extender in step (2) are as follows: a. VPSB contains phenolic hydroxyl groups at both ends, which can react with the NCO groups in the prepolymer to introduce reversible Schiff base bonds (-CH=N-) into the polyurethane backbone, giving the elastomer self-healing and reprocessing capabilities. b. VPSB contains aromatic rings and polar groups (phenolic hydroxyl, methoxy), which can enhance compatibility with HTPB soft segments and promote microphase separation stability.

[0033] The reasons for choosing BDO as a chain extender in step (2) are as follows: a. BDO is a small molecule diol with high reactivity of hydroxyl groups, which can react quickly with NCO groups to form regular hard segments, thereby improving the mechanical strength and modulus of the elastomer. b. BDO has short chain segments and a regular structure, which helps to build dense hard segment regions and work with VPSB to regulate crosslinking density, ensuring the basic mechanical properties of the material.

[0034] In step (2), the chain extension reaction follows this principle: the isocyanate groups (-NCO) at the end of the prepolymer undergo a stepwise addition polymerization reaction with the chain extenders (phenolic hydroxyl groups of VPSB and alcoholic hydroxyl groups of BDO) to generate urethane bonds (-NH-COO-), thus extending the molecular chain and forming a high molecular weight polyurethane elastomer. The reaction has the following effects: a. It completes the chain growth of the polymer, obtaining the target molecular weight and mechanical properties; b. It introduces reversible Schiff base bonds through VPSB, endowing the material with self-healing ability; c. It regulates the hard segment content and microphase separation structure, optimizing the overall performance of the elastomer.

[0035] In some embodiments of the present invention, in step (2), the chain extension reaction temperature is 45-50°C and the time is 20-24h. The reasons for choosing a chain extension reaction temperature of 45°C-50°C are as follows: a. At this temperature, both the prepolymer and the chain extender can dissolve well in the reaction medium (such as THF), the system viscosity is moderate, and it is easy to stir and transfer heat. b. When the temperature is below 45°C, the phenolic hydroxyl group of VPSB has low reactivity, the chain extension reaction is too slow, and the reaction time needs to be greatly extended or even the reaction may be incomplete. c. When the temperature is above 50°C, isocyanate is prone to side reactions with water or solvent in the system (such as the formation of urethane), and may also destroy the Schiff base bond (-CH=N-) in VPSB, affecting the self-repair function. 45-50°C can ensure the reaction rate while avoiding side reactions and protecting the dynamic covalent bonds.

[0036] The reasons for choosing a chain extension reaction time of 20-24h in step (2) are as follows: a. The phenolic hydroxyl activity of VPSB is lower than that of BDO's alcoholic hydroxyl activity, and VPSB molecules are larger and diffuse more slowly, requiring sufficient time to ensure that the NCO at the end of the prepolymer reacts fully with the chain extender to achieve a higher conversion rate. b. Experimental verification of 20-24h shows that the molecular weight distribution of the product is narrowest within this time range, and the mechanical properties and self-healing efficiency reach the best balance. Too short a time (<20h) will lead to incomplete chain extension, and residual -NCO will affect subsequent processing and stability; too long a time (>24h) may cause side reactions or increase energy consumption due to prolonged heating, and the performance improvement is not significant. c. Compared with the prepolymerization reaction (2-3h), the chain extension reaction requires a longer time to balance low-temperature activity and macromolecular diffusion, and 20h-24h is the empirically preferred range.

[0037] Step (2) is as follows: Dissolve VPSB and 1,4-butanediol separately in ultra-dry tetrahydrofuran and add them to a three-necked flask. Under a nitrogen atmosphere, stir with a polytetrafluoroethylene stirrer to carry out the chain extension reaction until the solution becomes a relatively viscous yellow solution, thus preparing the HTPU-VPSB solution.

[0038] The synthetic route in step (2) is as follows:

[0039] .

[0040] This invention prepares polyurethane (HTPU-VPSB) by polymerizing VPSB containing a Schiff base in its main chain with hydroxyl-terminated polybutadiene (Mn = 3000), isophorone diisocyanate, and 1,4-butanediol. In HTPB-based polyurethane, the soft and hard phases separate cleanly and distinctly, resulting in a clear interface and efficient energy transfer. The hard segments, acting as physical crosslinking points, can stably bear stress and rebound rapidly, avoiding energy dissipation due to friction at ambiguous interfaces.

[0041] In some embodiments of the present invention, in step (3), the drying temperature is 50°C-80°C, and the drying time is 48-72 hours. The reasons for choosing the drying temperature of 50-80°C are as follows: a. The boiling point of ultra-dry tetrahydrofuran (THF) is 66°C, and 50-80°C covers the range below, close to, and slightly above the boiling point. At a temperature of 50-66°C, THF mainly evaporates, the film surface is smooth, and boiling and bubble generation are avoided; at a temperature of 66-80°C, internal solvent diffusion can be accelerated, but the heating rate needs to be controlled to prevent film cracking. b. At a temperature below 50°C, THF evaporates too slowly, the drying time is significantly prolonged, and residual solvent is easily left, affecting the elastomer properties. c. At a temperature above 80°C, THF boils violently, leading to the formation of pores or surface defects in the film, and may also trigger thermal oxidation of polyurethane or decomposition of Schiff base bonds. 50-80°C can effectively remove solvent while ensuring film quality.

[0042] In another aspect of the present invention, the present invention provides a method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function, thereby obtaining a high-toughness, low-hysteresis polyurethane composite film with self-healing function.

[0043] In another aspect, the present invention proposes an application of a high-toughness, low-hysteresis polyurethane composite film with self-healing capabilities. According to embodiments of the present invention, the polyurethane composite film is used to fabricate flexible sensing and wearable electronic devices.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] 1) This invention introduces dynamic Schiff bases into aromatic compounds to generate VPSB with a conjugated aromatic Schiff base structure. When applied to polyurethane, this results in high-performance self-healing materials, and the mechanical strength is further enhanced by the π-π conjugated structure formed by the Schiff base reaction and aromatic ring reaction. This invention uses VPSB containing dynamic Schiff base bonds (-CH=N-) in combination with the conventional small-molecule chain extender BDO. The phenolic hydroxyl groups at both ends of VPSB react with the -NCO groups in the prepolymer, introducing reversible dynamic covalent bonds into the polyurethane backbone, endowing the material with photothermal responsive self-healing capabilities. Simultaneously, the aromatic rings and conjugated structures in the VPSB molecule can form π-π stacking, enhancing the cohesive strength of the hard segment microregions. BDO, as a highly reactive chain extender, can rapidly form regular hard segments, providing basic mechanical support. The synergistic effect of these two agents allows the material to maintain a tensile strength of approximately 4 MPa while achieving an elongation at break of 800%, achieving a balance between high toughness and efficient self-healing.

[0046] 2) This invention firstly introduces hydroxyl-terminated polybutadiene as a soft segment into the polyurethane main chain, effectively avoiding the internal friction and strain-induced crystallization phenomena present in traditional polyurethanes. This reduces energy dissipation during cyclic tensile testing and exhibits extremely low mechanical hysteresis. The polyurethane prepared from block Schiff bases using hydroxyl-terminated polybutadiene can achieve an elongation at break of up to 800%; while the tensile strength can be maintained at 4 MPa without excessive strength loss, demonstrating extremely high toughness.

[0047] 3) To address the mechanical hysteresis problem caused by the presence of polar groups in traditional polyether or polyester soft segments, this invention selects hydroxyl-terminated polybutadiene (HTPB) as the soft segment. HTPB is a smooth, amorphous, nonpolar chain with a glass transition temperature as low as approximately -80°C, exhibiting minimal resistance to chain segment movement and avoiding the internal friction caused by polar groups in traditional soft segments. Simultaneously, HTPB does not undergo strain-induced crystallization during stretching, eliminating energy dissipation during crystallization / melting. The microphase separation between the soft and hard segments (IPDI-based) is clear, the interface is clean, and energy can be transferred efficiently. The hard segments act as physical crosslinking points, stabilizing stress and rapidly rebounding. Therefore, the material exhibits excellent elastic recovery after cyclic loading and unloading (no significant hysteresis after 100 cycles).

[0048] 4) The VPSB containing dynamic Schiff base bonds introduced in this invention endows the material with photothermal response self-healing ability. The dynamic covalent bonds (C=O) in VPSB can undergo reversible breakage and recombination under light irradiation or heating conditions, enabling the material to repair itself efficiently and quickly after damage. Experiments show that the repaired film still maintains good mechanical properties, greatly improving the service life of the material. To address the inherent drawbacks of single dynamic bond systems (such as the high cost of disulfide monomers, environmental and health risks associated with diselenylene bonds, the need for high-temperature triggering of Diels-Alder bonds, and weak dynamic non-covalent interactions), the Schiff base bond (-CH=N-) used in this invention offers the following advantages: mild synthesis conditions (45-50℃, ambient pressure), and the raw material vanillin derived from biomass, resulting in low cost and environmental friendliness; the Schiff base bond can undergo reversible breakage and recombination under visible light (e.g., xenon lamp, 500 W / m²) or heating conditions, without the need for high temperatures or special chemical stimulation, thus meeting the requirement for rapid repair at room temperature; through the electron-donating effect of the methoxy (-OCH3) and phenolic hydroxyl (-OH) groups in VPSB, the absorption wavelength of the Schiff base is red-shifted to 468 nm, enhancing the utilization efficiency of visible light and improving the practicality of photo-induced self-repair.

[0049] 5) The soft polyurethane segment HTPB, with its low surface binding energy and non-polarity, combined with the unique microphase separation structure of the hard polyurethane segment, gives the material surface excellent anti-friction properties. Addressing the insufficient wear resistance of traditional polyurethane films, the non-polar and low surface energy characteristics of the HTPB soft segment endow the material surface with superior anti-friction properties. Combined with the microphase separation structure of the hard polyurethane segment, the hard segment acts as a wear-resistant skeleton during friction, while the soft segment provides a tough buffer. In the Martindale abrasion test (12 kPa load, friction against a standard wool abrasive Lissara trajectory), the total wear rate after 10,000 cycles was only 0.0184%, and the swelling rates after immersion in strong acid (pH=1) and strong alkali (pH=14) for 24 h were only 1.14% and 1.36%, respectively, demonstrating excellent wear resistance and solvent stability.

[0050] In summary, the HTPU-VPSB polyurethane film prepared by this invention has low hysteresis, self-healing, and high toughness, and can be widely used in high-precision and high-requirement electronic device fields such as flexible sensing and wearable electronic devices, showing good application prospects. Attached Figure Description

[0051] Figure 1 The 1H NMR spectrum of VPSB obtained in Example 1 of this invention;

[0052] Figure 2 The ultraviolet-visible spectra of different concentrations of VPSB were obtained in Example 1 of this invention;

[0053] Figure 3 The infrared contrast spectrum of vanillin prepared in Example 1 of this invention;

[0054] Figure 4 The infrared contrast spectrum of VPSB obtained in Example 1 of this invention;

[0055] Figure 5 The hydrogen nuclear magnetic resonance spectrum of VPSB under a xenon lamp was obtained in Example 1 of this invention;

[0056] Figure 6 The hydrogen nuclear magnetic resonance spectrum of VPSB obtained in Example 1 of this invention under light-shielded conditions;

[0057] Figure 7 The 1H NMR spectrum of VPSB obtained at high temperature in Example 1 of this invention;

[0058] Figure 8 The infrared spectra of IPDI and HTPU2-VPSB obtained in Example 1 of this invention;

[0059] Figure 9 HTPU prepared in Examples 1-4 of this invention n-VPSB (n=1-4) glass transition temperature;

[0060] Figure 10 The hydrogen nuclear magnetic resonance spectrum of HTPU2-VPSB obtained in Example 2 of this invention;

[0061] Figure 11 HTPU prepared in Examples 1-4 of this invention n Stress-strain curves of -VPSB (n=1-4);

[0062] Figure 12 This is a tensile stress-strain curve of HTPU2-VPSB after 100 consecutive loading-unloading cycles, obtained in Example 2 of the present invention.

[0063] Figure 13 The mechanical properties of HTPU2-VPSB obtained in Example 2 of this invention after solvent immersion are shown in the figure.

[0064] Figure 14 Thermogravimetric curves of HTPUn-VPSB (n=1-4) obtained in Examples 1-4 of this invention;

[0065] Figure 15 The HTPU2-VPSB prepared in Example 2 of this invention is at 500W / m 2 Stress-strain curve after self-repair under xenon lamp irradiation. Detailed Implementation

[0066] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0067] Example 1

[0068] A method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function includes the following steps:

[0069] (1) Synthesis of VPSB: 4.3256 g (40 mol) of p-phenylenediamine was dissolved in 70 mL of anhydrous ethanol. 12.1718 g (80 mol) of vanillin was dissolved in 250 mL of anhydrous ethanol at 50 °C. o C, then stir until dissolved to prepare the product. Subsequently, the p-phenylenediamine solution is slowly added dropwise to the vanillin solution, and the reaction is carried out under nitrogen protection at 50°C. oC. Reflux and stir for 3 hours. After the reaction is complete, the solvent is evaporated using a rotary evaporator. The precipitate is cooled, collected, filtered and washed with anhydrous ethanol, and dried to obtain a yellow powder. Figure 1 The image shows the 1H NMR spectrum of VPSB. The successful synthesis of VPSB was confirmed by the appearance of peaks (δ=8.5ppm) of newly formed dynamic covalent aromatic imine bonds in the deuterated dimethyl sulfoxide (DMSO-d6) NMR spectrum.

[0070] Figure 2 To obtain the UV-Vis spectrum of VPSB, accurately weigh 3.76 g of VPSB (relative molecular mass 376.4, corresponding to 0.01 mol), dissolve it in anhydrous ethanol, transfer it to a 100 mL volumetric flask, dilute to the mark, and mix well to obtain a concentration of 10. -1 The mother liquor was diluted 10-fold with anhydrous ethanol to obtain 10 mol / L solutions. -2 mol / L, 10 -3 mol / L, 10 -4 mol / L and 10 -5 A series of mol / L solutions were prepared. All solutions were stored in the dark for UV-Vis absorption spectroscopy. The spectral responsiveness to visible light confirmed that the absorption peak range was between 400 and 800 nm, originating from the absorption of specific ASB groups. Notably, the maximum absorption wavelength of the current ASB is 468 nm, a 30–40 nm redshift compared to other reported ASB compounds. This difference is due to the presence of methoxy (–OCH3) and phenolic hydroxyl (–OH) groups in the vanillin structure. These groups are strong electron-donating substituents, and the conjugation effect increases the electron cloud density, reduces the energy required for electron transitions, and shifts the absorption wavelength towards longer wavelengths. This gives them better visible light utilization, which is beneficial for their application under practical lighting conditions.

[0071] Figure 3 , 4 Infrared contrast spectra of vanillin and VPSB. 1621 cm⁻¹ -1 The new absorption peak at the position corresponds to the stretching vibration of the imine bond (C=N), which is a characteristic peak of Schiff base, indicating that the synthesis of VPSB was successful.

[0072] Figure 5 , 6 7 is VPSB at 500W / m 2The 1H NMR spectra were obtained after irradiation under a xenon lamp for 1 hour, light-shielded treatment for 1 hour, and high-temperature treatment (120℃) for 1 hour. The imine bonds and their integral ratios at different chemical shifts reveal the dynamic exchange characteristics between aromatic Schiff base bonds under photothermal stimulation. Under light-shielded conditions, the peak generated by imine bond exchange was significantly weaker than in the other two cases. This indicates that under photothermal conditions, the imine bonds in Schiff bases undergo dynamic exchange.

[0073] (2) Prepolymer solution: First, 15.0 g of hydroxyl-terminated polybutadiene (Mn = 3000) was added to a 500 ml three-necked flask. A certain amount of polybutadiene was then added to the flask, and the mixture was evacuated using a vacuum pump to remove water (the oil bath temperature for HTPB dehydration was 130°C for 2 hours). After the temperature was lowered to 50°C, 2.5 g of isoflurane diisocyanate (IPDI) was added to the flask, followed by the addition of dibutyltin dilaurate for catalysis. The mixture was reacted at 50°C for 3 hours under a nitrogen atmosphere. After the reaction, an isocyanate-terminated prepolymer solution was successfully obtained.

[0074] (3) HTPU1-VPSB solution: 0.94 g Schiff base VPSB and 0.23 g 1,4-butanediol (BDO) were mixed at 60 °C. o Dissolved in 30 mL of ultra-dry tetrahydrofuran (THF) at C, then added to the prepolymer solution. Under a nitrogen atmosphere at 50 °C... o The reaction was carried out at C for 24 hours, and the chain extension reaction was completed, thus preparing HTPU1-VPSB solution.

[0075] (4) Preparation of HTPU1-VPSB film: The HTPU1-VPSB solution was poured into a polytetrafluoroethylene (PTFE) mold. At 50°C... o Dry at C for 12 hours, then raise the temperature to 80°C. o After vacuum drying at C for 48 hours (gradient drying to prevent bubbles), the HTPU1-VPSB membrane was successfully obtained.

[0076] Example 2

[0077] A method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function includes the following steps:

[0078] (1) Prepolymer solution: First, add 15.0 g of hydroxyl-terminated polybutadiene to a 500 ml three-necked flask. Then, add a certain amount of polybutadiene to the three-necked flask and use a vacuum pump to remove moisture (the oil bath temperature for dehydrating HTPB using a vacuum pump is 130°C, and the time is 2 hours). Reduce the temperature to 50°C. o After step C, 3.0 g of isoflurone diisocyanate (IPDI) was added to a three-necked flask, followed by the addition of dibutyltin dilaurate for catalysis. The mixture was then incubated at 50°C under a nitrogen atmosphere. oThe reaction was carried out at C for 3 h. After the reaction, an isocyanate-terminated prepolymer solution was successfully obtained.

[0079] (2) HTPU2-VPSB solution: 1.41 g of VPSB prepared in step (1) of Example 1 and 0.34 g of 1,4-butanediol (BDO) were heated at 60 °C. o Dissolved in 30 ml of ultra-dry tetrahydrofuran (THF) at C, then added to the prepolymer solution. Under a nitrogen atmosphere at 50 °C... o The reaction was carried out at C for 24 hours, and the chain extension reaction was completed, thus preparing HTPU2-VPSB solution.

[0080] (3) Preparation of HTPU2-VPSB film: The HTPU2-VPSB solution was poured into a polytetrafluoroethylene (PTFE) mold. At 50°C... o Dry at C for 12 hours, then at 80°C o After vacuum drying at C for 48 h, the HTPU2-VPSB membrane was successfully obtained.

[0081] Example 3

[0082] A method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function includes the following steps:

[0083] (1) Prepolymer solution: First, add 15.0 g of hydroxyl-terminated polybutadiene to a 500 ml three-necked flask. Then, add a certain amount of polybutadiene to the three-necked flask and use a vacuum pump to remove water (the oil bath temperature for removing water from HTPB using a vacuum pump is 130°C, and the time is 2 hours). Reduce the temperature to 40-60°C. o After step C, 3.5 g of isoflurone diisocyanate (IPDI) was added to a three-necked flask, followed by the addition of dibutyltin dilaurate for catalysis. The mixture was then incubated at 50°C under a nitrogen atmosphere. o The reaction was carried out at C for 3 h. After the reaction, an isocyanate-terminated prepolymer solution was successfully obtained.

[0084] (2) HTPU3-VPSB solution: 1.88g of VPSB prepared in step (1) of Example 1 and 0.45g of 1,4-butanediol (BDO) were heated at 60°C. o The solution was dissolved in 30 ml of ultra-dry tetrahydrofuran (THF) at temperature C, and then added to the prepolymer solution. The reaction was carried out at 50°C for 24 h under a nitrogen atmosphere until the chain extension reaction was completed, thus preparing the HTPU3-VPSB solution.

[0085] (3) Preparation of HTPU3-VPSB film: The HTPU3-VPSB solution was poured into a polytetrafluoroethylene (PTFE) mold. At 50°C... oAfter drying at 12°C and then under vacuum at 80°C for 48 hours, the HTPU3-VPSB membrane was successfully obtained.

[0086] Example 4

[0087] A method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function includes the following steps:

[0088] (1) Prepolymer solution: First, add 15.0 g of hydroxyl-terminated polybutadiene to a 500 ml three-necked flask. Then, add a certain amount of polybutadiene to the three-necked flask and use a vacuum pump to remove water (the oil bath temperature for removing water from HTPB using a vacuum pump is 130°C, and the time is 2 hours). Reduce the temperature to 50°C. o After step C, 4.0 g of isoflurane diisocyanate (IPDI) was added to a three-necked flask, followed by the addition of dibutyltin dilaurate for catalysis. The mixture was then incubated at 50°C under a nitrogen atmosphere. o The reaction was carried out at C for 3 h. After the reaction, an isocyanate-terminated prepolymer solution was successfully obtained.

[0089] (2) HTPU4-VPSB solution: 2.35g of VPSB prepared in step (1) of Example 1 and 0.56g of 1,4-butanediol (BDO) were heated at 60°C. o Dissolved in 30 ml of ultra-dry N,N-dimethylformamide (DMF) at C, then added to the prepolymer solution. Incubated at 50 °C under a nitrogen atmosphere. o The reaction was carried out at C for 24 hours, and the chain extension reaction was completed, thus preparing HTPU4-VPSB solution.

[0090] (3) Preparation of HTPU4-VPSB film: Pour the HTPU4-VPSB solution into a polytetrafluoroethylene (PTFE) mold. At 60-80°C... o After drying at 60-80°C for 12-36 h and then vacuum drying at 60-80°C for 24-48 h, the HTPU4-VPSB membrane was successfully obtained.

[0091] HTPU prepared in Examples 1-4 n The performance of -VPSB (n=1-4) was tested as follows:

[0092] (1) Figure 8Infrared spectra of HTPU2-VPSB prepared by IPDI and Example 2 of this invention are shown. A Fourier transform infrared spectrometer (FTIR, Nicolet 6700) equipped with an attenuated total reflectance (ATR) accessory was used. Test conditions: wavenumber range 4000 cm⁻¹~400 cm⁻¹, resolution 4 cm⁻¹, 32 scans, spectra acquired at room temperature. Air was used as a reference for background subtraction. The sample was placed directly on the ATR crystal, uniformly compacted, and then scanned. The results were obtained at 2250 cm⁻¹. -1 The strong characteristic peak corresponds to the isocyanate group (-NCO), and the -NCO on the HTPU2-VPSB line has basically disappeared, indicating that the isocyanate group is fully involved in the reaction.

[0093] (2) Figure 9 HTPU prepared in Examples 1-4 of this invention n The glass transition temperature of -VPSB (n=1-4) was determined. A differential scanning calorimeter (DSC, such as TA Q200) was used under a nitrogen atmosphere at a flow rate of 50 mL / min. 10 mg of sample was weighed and sealed in an aluminum crucible. The test procedure was as follows: the temperature was first increased from room temperature to 100 °C at a rate of 10 °C / min and held for 3 min to eliminate thermal history; then the temperature was decreased to -80 °C at a rate of 20 °C / min and held for 3 min; finally, the temperature was increased to 100 °C at a rate of 10 °C / min, and the secondary heating curve was recorded. The glass transition temperature (Tg) was taken as the midpoint of the curve step. HTPU1-VPSB, HTPU2-VPSB, HTPU3-VPSB, and HTPU4-VPSB correspond to the final polyurethane elastomer films prepared in Examples 1, 2, 3, and 4 of this invention, respectively. The molar ratio of VPSB to BDO decreased sequentially in each example (see the example description for specific ratios). As the content of hard segment VPSB increases, the rigidity of HTPU-VPSB is enhanced. Therefore, as the VPSB content decreases, the chain segments move more easily, and the glass transition temperature of HTPU-VPSB also decreases continuously.

[0094] (3) Figure 10 The infrared spectrum of the HTPU2-VPSB of this invention is shown. A Fourier transform infrared spectrometer (FTIR, Nicolet 6700) equipped with an attenuated total reflectance (ATR) accessory was used. Test conditions: wavenumber range 4000 cm⁻¹~400 cm⁻¹, resolution 4 cm⁻¹, 32 scans, spectra acquired at room temperature. The sample was a dried elastomer film, placed directly on an ATR crystal, uniformly compacted, and then scanned. Background subtraction was performed using air. The sample was the HTPU2-VPSB elastomer film prepared in Example 2. The wavelength range was 1500-1600 cm⁻¹. -1 and 1650 - 1750cm -1The characteristic peaks are -NO and -C=O, which indicates that VPSB is introduced into HTPU2-VPSB.

[0095] (4) Figure 11 The HTPU of this invention n - Stress-strain curves of VPSB (n=1-4). According to GB / T 528-2009 standard, the elastomer membrane was cut into dumbbell-shaped specimens (ISO 37 Type 2, gauge length 20 mm). A universal testing machine (computer-controlled electronic universal testing machine CMT4304) was used, and uniaxial tension was applied at room temperature at a tensile rate of 50 mm / min until the specimen fractured. Stress-strain curves were recorded, with at least 5 parallel samples tested in each group, and representative curves were taken. The graph shows that the stress decreases continuously with increasing VPSB content because VPSB is a rigid structure that can damage the strength of the hard segment micro-regions; simultaneously, the dynamic imine bonds in VPSB undergo reversible fracture and slippage under stress.

[0096] (5) Figure 12 This image shows the tensile stress-strain curve of the HTPU2-VPSB elastomer membrane prepared in Example 2 of this invention after 100 consecutive loading-unloading cycles. The same universal testing machine and dumbbell-shaped specimens were used. A cyclic tensile program was set: stretching at a rate of 50 mm / min to 50% of the maximum strain (or a preset strain), then unloading at the same rate to zero stress, repeating this 100 times. The stress-strain curve for each loading-unloading cycle was recorded, and elastic recovery and hysteresis changes were observed. The test was conducted at room temperature. The sample was the HTPU2-VPSB elastomer membrane prepared in Example 2. The image shows that the HTPU2-VPSB elastomer membrane exhibits excellent elastic recovery after 100 consecutive loading-unloading cycles.

[0097] (6) Table 1 shows the solvent resistance parameters of HTPU2-VPSB of the present invention. The swelling effect was obtained after soaking in 12 kinds of solvents for 24 hours, indicating that HTPU2-VPSB is resistant to strong acids, strong alkalis and salts as well as some organic solvents, and has good solvent resistance.

[0098] Table 1 Solvent Resistance Parameters of HTPU2-VPSB

[0099]

[0100] (7) Figure 13The mechanical properties of HTPU2-VPSB after solvent immersion in the present invention are described. The elastomer membrane was cut into dumbbell-shaped specimens (ISO 37 Type 2, gauge length 20 mm) according to GB / T 528-2009 standard. Uniaxial tensile testing was performed at room temperature and a tensile rate of 50 mm / min using a universal testing machine (computer-controlled electronic universal testing machine CMT4304) until the specimen fractured. Stress-strain curves were recorded, with at least 5 parallel samples tested in each group, and representative curves were taken. The fracture strain remained at 800%~1200% after immersion in ethanol, acetone, and methanol, indicating that low swelling has little impact on mechanical properties.

[0101] (8) Table 2 shows the wear resistance parameters of HTPU2-VPSB of the present invention. The wear resistance of the fibers was tested using a Martindale abrasion tester (YG401E) according to GB / T 21196 standard. The elastomer film prepared in step (3) of Examples 1-4 of the present invention was cut into circular samples with a diameter of 38 mm, and three parallel samples were taken for each example. After weighing the initial mass, the samples were clamped in the sample holder and rubbed with standard wool abrasive along a Lissajous trajectory under a load of 12 kPa. The total number of friction cycles and the wear rate were recorded. After 10,000 wear cycles, the total wear rate was only 0.0184%, which shows that HTPU2-VPSB has an extremely low wear rate and excellent wear resistance.

[0102] Table 2 Abrasion Resistance Parameters of HTPU2-VPSB

[0103]

[0104] (9) Figure 14 The HTPU of this invention n Thermogravimetric curves of VPSB (n=1-4). A thermogravimetric analyzer (TAQ500) was used under a nitrogen atmosphere at a flow rate of 60 mL / min. 10 mg of sample was weighed and placed in a platinum crucible, heated from room temperature to 800 °C at a heating rate of 10 °C / min, and the mass change curve with temperature was recorded. The samples were HTPU1-VPSB, HTPU2-VPSB, HTPU3-VPSB, and HTPU4-VPSB elastomer films prepared in Examples 1-4 of this invention. HTPU-VPSB with different VPSB contents showed good thermal stability and no significant mass loss below 300 °C.

[0105] (10) Figure 15 The HTPU2-VPSB prepared for Example 2 of this invention is at 500 W / m 2Stress-strain curves after self-healing under xenon lamp irradiation. Self-healing treatment: The HTPU2-VPSB elastomer film prepared in step (3) of Example 2 of this invention was cut into dumbbell-shaped samples (same as GB / T 528-2009), and cut in the middle with a blade. The cut sample cross-sections were then joined together and placed in a xenon lamp aging chamber with an irradiation intensity of 500 W / m. 2 At a temperature of 25℃, four specimens were irradiated for 1, 2, 3, and 4 hours respectively to allow the fracture surfaces to reform. Tensile testing: The repaired specimens were tested using the aforementioned stress-strain testing method (same as above). Figure 11 The sample was subjected to uniaxial tension at a tensile rate of 50 mm / min until fracture, and the tensile strength after repair was recorded. Simultaneously, the tensile strength of the uncut original sample was tested, and the repair efficiency was calculated: Repair efficiency (%) = (Repaired strength / Original strength) × 100%. Figure 15 The results show that the strength of the repaired specimen recovered to approximately 30% of its original strength. The tensile strength of the repaired specimen recovered to approximately 30% of its original strength, confirming that visible light irradiation can drive the dynamic rearrangement of Schiff base bonds and interfacial reorganization, thereby endowing the material with intrinsic self-healing capabilities.

[0106] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function, characterized in that, Includes the following steps: (1) A prepolymer solution was prepared by prepolymerizing polybutadiene, isoflurone diisocyanate and dibutyltin dilaurate. (2) VPSB is dissolved in 1,4-butanediol and then added to the prepolymer solution. A chain extension reaction is carried out under a nitrogen atmosphere to prepare an HTPU-VPSB solution. The structural formula of the VPSB is as follows: ； (3) Pour the HTPU-VPSB solution into a mold and dry it to obtain an HTPU-VPSB film.

2. The method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function according to claim 1, characterized in that: In step (1), the molar ratio of polybutadiene, isoflurane diisocyanate, and dibutyltin dilaurate is 1 : (1.2~1.6) : (0.001~0.003).

3. The method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function according to claim 1, characterized in that: In step (1), the temperature of the prepolymerization reaction is 55-60℃ and the reaction time is 2-3h.

4. The method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function according to claim 1, characterized in that, In step (2), the preparation method of VPSB includes the following steps: mixing the dissolved p-phenylenediamine with vanillin, stirring under reflux in a nitrogen atmosphere, evaporating the solvent after the reaction is completed, redissolving the dried product, removing the supernatant after centrifugation, and drying to obtain VPSB.

5. The method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function according to claim 4, characterized in that: The molar ratio of p-phenylenediamine to vanillin is (2.1-2.3):1, the reaction temperature is 45-50℃, and the reaction time is 3-5h.

6. The method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function according to claim 1, characterized in that: In step (2), the molar ratio of VPSB to 1,4-butanediol is 1:(0.8-1.2).

7. The method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function according to claim 1, characterized in that: In step (2), the chain extension reaction temperature is 45-50°C and the time is 20-24h.

8. The method for preparing a high-toughness, low-hysteresis polyurethane composite film with self-healing function according to claim 1, characterized in that: In step (3), the drying temperature is 50-80°C and the drying time is 48-72h.

9. A high-toughness, low-hysteresis polyurethane composite film with self-healing function prepared by a method according to any one of claims 1-8.

10. The application of the high-toughness, low-hysteresis polyurethane composite film with self-healing function as described in claim 9, characterized in that: The polyurethane composite film is used to prepare flexible sensing and wearable electronic devices.

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