Conductive shape memory fiber and method of making and using same

Abstract

The present application belongs to the technical field of shape memory fiber, and relates to a conductive shape memory fiber and a preparation method and application thereof.A shape memory polyurethane is prepared by the following method: S1.polytetrahydrofuran glycol and hexamethylene diisocyanate are subjected to a first-step polymerization reaction; S2.2,6-pyridine dimethyl alcohol and hexamethylene diisocyanate are added and subjected to a second-step polymerization reaction; S3.1,4-butanediol and hexamethylene diisocyanate are added and subjected to a third-step polymerization reaction.The present application discloses a shape memory polyurethane, which has a relatively high shape fixing rate and shape recovery rate, and excellent mechanical properties.The present application further discloses a conductive shape memory fiber, which has shape memory performance, high flexibility and stable conductive performance.

Description

Technical Field

[0001] This invention relates to the field of shape memory fiber technology, and more specifically, to a conductive shape memory fiber, its preparation method, and its application. Background Technology

[0002] Flexible smart fibers are key substrates for wearable electronics, smart drives and electromagnetic protection, and composite fibers with both shape memory and conductivity have become a research hotspot.

[0003] Shape memory polymers (SMPs) are a class of smart polymer materials that can recover from a temporary shape to a permanent shape under the action of external stimuli (heat, electricity, light, chemicals, magnetic fields, etc.) and can repeat this process.

[0004] The shape memory function of SMP mainly relies on the synergistic effect of soft and hard segments: hard segments form a physical or chemical cross-linked network with a high glass transition temperature or melting point, which remains stable during the shape memory process and determines the permanent shape of the material; soft segments, as a reversible phase, have a low glass transition temperature or melting point and undergo phase transformation (such as crystallization / melting, glass transition) when the temperature rises, and the molecular chains change from a frozen state to a free-moving state, enabling the material to recover to its permanent shape. When the temperature drops, the molecular chains freeze again, thus fixing the temporary shape.

[0005] The shape memory process of thermotropic SMP typically involves stretching the material to a target temporary shape at a temperature above the soft segment glass transition temperature (Tg) or melting point (Tm), maintaining the stretched state, and cooling it to a temperature below Tg or Tm. The molecular chains freeze, fixing the temporary shape. Reheating to a temperature above Tg or Tm allows the molecular chains to regain free movement, and the material returns to its permanent shape. A common thermotropic SMP is polyurethane (PU).

[0006] In the fields of wearable electronics, smart drives, and electromagnetic protection, shape memory polymers are required to have high shape fixation rate and shape recovery rate, as well as excellent mechanical properties.

[0007] Existing technology discloses a polyurethane / polyvinylidene fluoride coaxial fiber membrane, using self-healing polyurethane as the core layer and polyvinylidene fluoride (PVDF) as the shell layer. The core-shell structured fiber membrane material is prepared by coaxial electrospinning, and elemental silver is modified onto the fiber membrane surface. The preparation method of the self-healing polyurethane is as follows: isophorone diisocyanate (IPDI), polytetrahydrofuran (PTMEG), and the catalyst dibutyltin dilaurate are added to a round-bottom flask. The reaction apparatus is placed in a 75°C constant-temperature oil bath and stirred for 2 h to generate a prepolymer. Then, the chain extender bis(4-hydroxyphenyl)-disulfide is added, and the reaction is carried out in a 75°C constant-temperature oil bath for 4 h to obtain the self-healing polyurethane. Although this polyurethane also has a certain shape memory function, its mechanical properties and shape recovery properties are too poor. Summary of the Invention

[0008] The purpose of this invention is to overcome the defects and shortcomings of existing polyurethanes in terms of poor mechanical properties and shape recovery performance, and to provide a shape memory polyurethane with high shape recovery rate and excellent mechanical properties.

[0009] Another object of the present invention is to provide a conductive shape memory fiber.

[0010] The above-mentioned objective of the present invention is achieved through the following technical solution: A shape memory polyurethane is prepared by the following method: S1. In a protective atmosphere, using organotin as a catalyst, polytetrahydrofuran diol (PTMEG) and hexamethylene diisocyanate (HDI) in a molar ratio of 1:(1.2~2.0) are subjected to a first-step polymerization reaction. The polymerization reaction time is 1~2h and the polymerization reaction temperature is 70~90℃. S2. Add 2,6-pyridinediethanol (PDM) and hexamethylene diisocyanate (HDI) to the product of step S1 to carry out a second polymerization reaction for 0.5-1.5 h; wherein the molar ratio of 2,6-pyridinediethanol to polytetrahydrofuran glycol (PTMEG) in step S1 is (1.5-2.5):1; and the molar ratio of hexamethylene diisocyanate (HDI) to polytetrahydrofuran glycol (PTMEG) in step S1 is (1-1.5):1. S3. Add 1,4-butanediol (BDO) and hexamethylene diisocyanate (HDI) to the product of step S2 to carry out a third polymerization reaction for 3-5 hours; to obtain shape memory polyurethane; wherein the molar ratio of 1,4-butanediol (BDO) to polytetrahydrofurandiol (PTMEG) in step S1 is (1-2):1; the molar ratio of hexamethylene diisocyanate (HDI) to polytetrahydrofurandiol (PTMEG) in step S1 is (1-2.5):1; In the thermally responsive shape memory polyurethane of this invention, a composite chain extender system containing a pyridine structure is used to introduce additional hydrogen bonding sites and rigid units, thereby optimizing microphase separation and overall performance. Specifically, 2,6-pyridinediethanol (PDM) is introduced as a composite chain extender in the shape memory polyurethane of this invention. The N atoms on the pyridine ring can form a high-density, strong, and reversible hydrogen bond network, thereby giving the shape memory polyurethane of this invention high strength and high toughness, i.e., excellent mechanical properties.

[0011] Furthermore, the lone pair electrons of the N atom in the pyridine ring of the pyridine structure of this invention can form intermolecular or intramolecular hydrogen bonds with the N-H and C=O groups of the urethane ester in the polyurethane molecular chain, superimposing a large number of reversible hydrogen bond crosslinking points on the basis of the original urethane bonds, making the hard segment aggregation region form a denser and more stable physical crosslinking network. As the stationary phase of the shape memory system, this network can effectively lock the permanent morphology of the material, while providing sufficient molecular rebound driving force for deformation recovery, thereby improving the shape recovery rate.

[0012] In a specific implementation, the protective atmosphere can be a nitrogen atmosphere or an inert gas atmosphere.

[0013] Preferably, the organotin is dibutyltin dilaurate.

[0014] Preferably, in step S3, the molar ratio of 1,4-butanediol (BDO) to polytetrahydrofurandiol (PTMEG) is (1.5~2):1; and the molar ratio of hexamethylene diisocyanate (HDI) to polytetrahydrofurandiol (PTMEG) is (1.5~2.5):1.

[0015] Preferably, the molecular weight of polytetrahydrofuran diol is 1000~5000 g / mol.

[0016] This invention also protects a conductive shape memory fiber, which is prepared by the following method: S1. Dissolve the shape memory polyurethane described in any of the above items in a solvent to prepare a core solution, dissolve PVDF in a solvent to prepare a shell solution, and coaxially electrospin to obtain a core-shell structured composite fiber; S2. Silver powder is loaded onto the surface of the core-shell composite fiber to obtain conductive shape memory fiber.

[0017] Preferably, in step S1, during coaxial electrospinning, the injection speed of the core solution is 0.01~0.1 mm / min, the injection speed of the shell solution is 0.05~0.15 mm / min, the spinning voltage is 14~20 kV, and the receiving distance is controlled at 10~20 cm.

[0018] In a specific implementation, the ratio of the injection rate of the shell solution to the injection rate of the core solution is 2:1, which can make the core-shell structure more uniformly encapsulated.

[0019] In a specific embodiment, the solvent can be N,N-dimethylformamide (DFM).

[0020] In a specific embodiment, the mass concentration of the core solution is 10-20%, and the mass concentration of the shell solution is 10-20%.

[0021] In a specific embodiment, the viscosity of the core solution is 900~1200 mPa·s, and the viscosity of the shell solution is 2500~3000 mPa·s.

[0022] In a specific implementation, the needle for the nucleus solution is 23g, and the needle for the shell solution is 16g.

[0023] In a specific implementation, the spinning environment temperature is set to 60±2℃ and the relative humidity to 30%~40% to avoid the influence of ambient temperature and humidity on the viscosity of the spinning solution and fiber formation.

[0024] Preferably, in step S1, the molecular weight of PVDF is 200,000 to 600,000 g / mol.

[0025] Preferably, in step S2, the method for preparing the silver powder includes the following steps: placing a silver nitrate solution in a sodium citrate solution, stirring at 200~500 r / min for 15~40 min, adding hydrazine hydrate solution for reduction reaction, and preparing silver powder.

[0026] The concentration of silver nitrate solution was 0.4–0.6 mol / L. The concentration of sodium citrate solution was 0.2–0.3 mol / L. The concentration of hydrazine hydrate solution was 0.4–0.6 mol / L, and the pH of the hydrazine hydrate solution was 10. The reaction temperature was 20–30℃.

[0027] Hydrazine hydrate is used as a reducing agent, and the molar ratio of hydrazine hydrate to silver nitrate is greater than 1. Sodium citrate is used as a stabilizer, and the molar ratio of sodium citrate to silver nitrate is greater than 0.5:1.

[0028] Preferably, in step S2, silver powder is loaded onto the core-shell composite fiber membrane by negative pressure filtration. Specifically, silver powder is first ultrasonically dispersed in an ethanol solution to obtain a silver powder dispersion. This dispersion is then placed on the core-shell composite fiber membrane, and the silver powder is loaded onto the membrane by filtration under a negative pressure of -0.02 to -0.05 MPa.

[0029] Preferably, the silver powder loading is 0.5~2 mg / cm³. 2 .

[0030] This invention also protects the application of the conductive shape memory fibers described in any of the above claims in flexible sensing, intelligent actuation, and electromagnetic protection.

[0031] This invention constructs a core-shell structure of shape memory polyurethane SMP@PVDF using coaxial electrospinning. The inner shape memory polyurethane SMP layer imparts excellent shape memory driving properties to the material, while the outer PVDF layer provides good mechanical flexibility and coating protection, improving the problems of poor interfacial bonding and mechanical-electrical imbalance. Furthermore, a green vacuum filtration method is used to physically load silver powder onto the fiber surface, avoiding the corrosive damage to the fiber structure caused by chemical plating and improving the uniformity and bonding stability of silver particles. This preparation route achieves a highly efficient synergy of shape memory performance, high flexibility, and stable conductivity. Without damaging the intrinsic properties of the substrate, it significantly enhances the bonding force of the silver layer and the conductivity stability during deformation. This provides a systematic experimental basis and technical reference for the green, low-consumption, and controllable preparation of high-performance flexible conductive shape memory fiber materials, promoting the engineering application of intelligent flexible composite materials in wearable sensing, intelligent actuators, and electromagnetic protection.

[0032] Compared with the prior art, the beneficial effects of the present invention are: the present invention discloses a shape memory polyurethane with a high shape fixation rate and shape recovery rate, as well as excellent mechanical properties.

[0033] The present invention also discloses a conductive shape memory fiber, which has shape memory properties, high flexibility and stable conductivity. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of shape memory polyurethane in Example 1.

[0035] Figure 2 The images show actual photos of the shape memory polyurethane film, the shape memory polyurethane SMP polymer spinning solution, the core-shell structure composite fiber, and the conductive shape memory fiber from Example 1.

[0036] Figure 3 The images are FTIR images of shape memory polyurethanes from Examples 1-3.

[0037] Figure 4 The images are XRD patterns of shape memory polyurethanes from Examples 1-3.

[0038] Figure 5 Thermogravimetric analysis (TGA) diagrams of shape memory polyurethane in Examples 1-3 are shown.

[0039] Figure 6 The following are DSC diagrams of shape memory polyurethane in Examples 1-3.

[0040] Figure 7The stress-strain curves of shape memory polyurethane in Examples 1-3 are shown.

[0041] Figure 8 The shape memory diagram is shown for the shape memory polyurethane in Example 3.

[0042] Figure 9 The images shown are SEM images of the core-shell composite fiber membranes of Examples 3-6.

[0043] Figure 10 This is a SEM-EDS image of the core-shell structured composite fiber membrane of Example 3.

[0044] Figure 11 This is a SEM image of the silver powder prepared in Example 1.

[0045] Figure 12 The graphs show the flexible electronic performance of the conductive shape memory fiber membranes in Examples 1 and 7.

[0046] Figure 13 This is a demonstration diagram of the flexible electronic testing performance of the conductive shape memory fiber membrane in Example 1. Detailed Implementation

[0047] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0048] Polytetrahydrofuran (PTMEG), Mn=3000g / mol, manufactured by Adamas-beta.

[0049] Polyvinylidene fluoride (PVDF), Mw≈400000g / mol, manufactured by Aladdin.

[0050] Dibutyltin dilaurate, abbreviated as DBTDL.

[0051] Example 1 A shape memory polyurethane, the preparation method of which includes the following steps: S1. In a nitrogen atmosphere, weigh 5g PTMEG (0.00166mol, 1 equivalent) and 10ml DMF, place them in a three-necked flask, turn on the stirrer (mechanical stirring, speed 250 rpm), place it in a constant temperature oil bath, set the temperature to 60℃, and seal the other two necks with rubber stoppers to prevent solvent evaporation and air entry.

[0052] After the temperature is raised to 60℃ and PTMEG is completely dissolved, 0.1 mL of DBTDL is added as a catalyst. At this time, the temperature is set to 80℃. After the temperature is raised to 80℃, 0.40 mL of HDI (0.00249 mol, 1.5 equivalents) is added to make the molar ratio of polytetrahydrofuran diol (PTMEG) and hexamethylene diisocyanate (HDI) 1:1.5. The stirring speed is adjusted to about 350 rpm, and the reaction is carried out at 80℃ for 1.5 h.

[0053] S2. Weigh 0.464 g of PDM (0.0033 mol, 2 equivalents) into a three-necked flask, i.e., the molar ratio of 2,6-pyridinediethanol to polytetrahydrofurandiol (PTMEG) is 2:1; then add 0.27 mL of HDI (0.00168 mol, 1.0125 equivalents) (PDM is in powder form, and the residual PDM on the flask wall can be washed off with HDI or DMF), i.e., the molar ratio of hexamethylene diisocyanate (HDI) to polytetrahydrofurandiol (PTMEG) is 1.0125:1; react for 1 h.

[0054] S3. Add 0.15 g BDO (0.00166 mol, 1 equivalent) and 0.27 mL HDI (0.00168 mol, 1.0125 equivalent) to a three-necked flask, i.e., the molar ratio of 1,4-butanediol (BDO) to polytetrahydrofurandiol (PTMEG) is 1:1, and the molar ratio of hexamethylene diisocyanate (HDI) to polytetrahydrofurandiol (PTMEG) is 1.0125:1; react for 3.5 h.

[0055] The reaction ended, and the result was as follows: Figure 1 The structure shown is a shape memory polyurethane (SMP), abbreviated as P1.

[0056] A conductive shape memory fiber is prepared by the following method: S1. Prepare a 15% (w / w) SMP polymer spinning solution as the core solution by adding the above-mentioned shape memory polyurethane (SMP) to DMF solvent. Figure 2 As shown in (b) above. A 15% mass concentration PVDF spinning solution was prepared as the shell solution. The viscosity of the SMP polymer spinning solution was 1082 mPa·s, and the viscosity of the PVDF spinning solution was 2805 mPa·s. Coaxial electrospinning was performed using a 20 mL syringe with 16G (shell) and 23G (core) needles. The injection speed of the core solution was 0.03 mm / min, the injection speed of the shell solution was 0.07 mm / min, the spinning voltage was 18 kV, and the receiving distance was controlled at 15~20 cm.

[0057] The spun fibers are collected on a receiving plate covered with aluminum foil, and spinning continues for a certain period of time (set according to experimental needs). After collection, the fiber sample is placed in a fume hood and dried for 6-8 hours to completely remove residual DMF solvent, yielding core-shell structured composite fibers. These fibers are then sealed and stored for subsequent performance testing. Figure 2 As shown in (c) in the figure.

[0058] S2. Cut the fiber membrane formed by the core-shell composite fiber on the receiving plate into three 50mm×50mm square films, and load 50mg of silver powder through physical filtration, as follows: Preparation of silver powder: a) Reagent pretreatment: Prepare 0.48 mol / L silver nitrate solution, 0.48 mol / L hydrazine hydrate solution and 0.24 mol / L sodium citrate solution in advance; adjust the pH of the hydrazine hydrate solution to 10.0 using 2% dilute nitric acid, and set aside. b) Take 200 mL of the pre-prepared 0.24 mol / L sodium citrate solution and place it in a beaker. Install the mechanical stirrer, start the stirrer and adjust the speed to 350 r / min, and keep the stirring state stable. c) Using a two-tube peristaltic pump, 200 mL of 0.48 mol / L silver nitrate solution was vertically added to sodium citrate solution at a speed of 10 rpm. The stirring rate was kept constant during the addition process to ensure that the system was mixed evenly.

[0059] d) After the silver nitrate solution has been added, continue stirring at a speed of 350 r / min for 30 min to allow the system to react completely.

[0060] e) Slowly pour in 200 mL of hydrazine hydrate solution with pH adjusted to 10.0 beforehand to carry out the reduction reaction. The reaction time is controlled at 15 min, and the system is gently stirred during the process.

[0061] f) After the reduction reaction is complete, stop stirring, let the reaction product stand to precipitate, and after the precipitation is complete, discard the supernatant.

[0062] g) Wash the precipitate repeatedly with deionized water. After each wash, let it stand and discard the supernatant. Repeat the washing operation 6 times to remove impurities and unreacted reagents from the system.

[0063] h) After washing, freeze-dry the target silver powder sample, affix a sample label (indicating sample name, preparation date, reagent concentration, etc.), and place it in a dry place for later use.

[0064] The specific steps of S2 are as follows: a) The fiber membrane formed by the cut core-shell composite fiber is placed in a plasma cleaner for 60 seconds to improve the surface hydrophilic wettability; then it is laid flat and sealed on the filter membrane of the sand core filter device, without wrinkles or damage, and the edges are pressed to prevent leakage and uneven load. b) Accurately weigh 50 mg of silver powder into a sample bottle, add anhydrous ethanol-deionized water and ultrasonically disperse to obtain a uniform and stable silver powder dispersion. c) Pour the silver powder dispersion into the device and filter it under a constant negative pressure of -0.04MPa. The silver particles are trapped and accumulated by the fiber membrane to build a continuous pre-conductive network. After the dispersion is dried, maintain the negative pressure to make the silver particles embed into the fiber pores, enhance the interfacial bonding force, and avoid the silver layer from falling off and failing during use. d) Remove the composite membrane and vacuum dry it to evaporate any residual solvent, such as... Figure 2 As shown in (d) in the figure.

[0065] The test results showed that the silver powder loading in the conductive shape memory fiber membrane was 1 mg / cm³. 2 .

[0066] Example 2 A shape memory polyurethane, the preparation method of which differs from that of Example 1 is as follows: S1. The molar ratio of polytetrahydrofuran diol and hexamethylene diisocyanate is 1:1.3, and the reaction is carried out at 70°C for 2 hours; The molar ratio of S2,2,6-pyridinediethanol to polytetrahydrofurandiol was 1.5:1; the molar ratio of hexamethylene diisocyanate to polytetrahydrofurandiol was 1.5:1, and the reaction time was 0.5 h. S3. After reacting for 1 hour, add 0.225 g BDO (0.0025 mol, 1.5 equivalent) and 0.4 mL HDI (0.00249 mol, 1.5 equivalent) to a three-necked flask and react for 3-4 hours.

[0067] The molar ratio of 1,4-butanediol (BDO) to polytetrahydrofurandiol (PTMEG) is 1.5:1; the molar ratio of hexamethylene diisocyanate (HDI) to polytetrahydrofurandiol (PTMEG) is 1.5:1.

[0068] Shape memory polyurethane (SMP), abbreviated as P2, is obtained.

[0069] A conductive shape memory fiber, prepared using the same method as in Example 1.

[0070] Example 3 A shape memory polyurethane, the preparation method of which differs from that of Example 1 is as follows: S1. The molar ratio of polytetrahydrofuran diol and hexamethylene diisocyanate is 1:1.9, and the reaction is carried out at 90°C for 1 h. The molar ratio of S2,2,6-pyridinediethanol to polytetrahydrofurandiol was 2.5:1; the molar ratio of hexamethylene diisocyanate to polytetrahydrofurandiol was 1:1, and the reaction was carried out for 1.5 h. S3. After reacting for 1 hour, add 0.3 g BDO (0.0033 mol, 2 equivalents) and 0.54 mL HDI (0.00336 mol, 2.025 equivalents) to a three-necked flask and react for 3-4 hours.

[0071] The molar ratio of 1,4-butanediol (BDO) to polytetrahydrofurandiol (PTMEG) is 2:1; the molar ratio of hexamethylene diisocyanate (HDI) to polytetrahydrofurandiol (PTMEG) is 2.025:1.

[0072] Shape memory polyurethane (SMP), abbreviated as P3, is obtained.

[0073] A conductive shape memory fiber, prepared using the same method as in Example 1.

[0074] Example 4 A conductive shape memory fiber, the preparation method of which differs from that in Example 3 is as follows: The spinning voltage is adjusted to 14kV.

[0075] Example 5 A conductive shape memory fiber, the preparation method of which differs from that in Example 3 is as follows: The spinning voltage is adjusted to 16kV.

[0076] Example 6 A conductive shape memory fiber, the preparation method of which differs from that in Example 3 is as follows: The spinning voltage is adjusted to 20kV.

[0077] Example 7 A conductive shape memory fiber, the preparation method of which differs from that in Example 3 is as follows: S2. Cut the fiber membrane formed by the core-shell composite fiber on the receiving plate into three 50mm×50mm square films, and load 25mg of silver powder through physical filtration.

[0078] The test results showed that the silver powder loading in the conductive shape memory fiber membrane was 0.5 mg / cm³. 2 .

[0079] Comparative Example 1 A polyurethane, differing from Example 1 in its preparation method: (1) Preparation of prepolymer: 15 mL of DMF and 4.0000 g (0.0040 mol) of polytetrahydrofuran diol (PTMEG) were added to a round-bottom flask. Then, 2.6678 g (0.0120 mol) of isoflurane diisocyanate (IPDI) was slowly added dropwise to the flask at a rate of 0.5 g / min. Next, dibutyltin dilaurate was added at a mass of 0.1% of the reactants. Finally, the mixture was sealed and reacted in an oil bath at a constant temperature of 75 °C for 2 h.

[0080] (2) Add 1.8525 g (0.0074 mol) of chain extender bis(4-hydroxyphenyl)-disulfide to the flask, then add 10 mL of DMF to adjust the viscosity of the reaction solution, and finally react in an oil bath at a constant temperature of 75 °C for 4 h.

[0081] (3) Add 10 mL of acetone before the reaction ends to reduce the concentration in the 18% solution, reduce the adhesion of polyurethane to the inner wall of the flask when pouring, and improve the yield.

[0082] (4) Pour the well-reacted solution into a polytetrafluoroethylene mold and dry it in an oven at 80 °C for 48 h to fully evaporate the solvent. Then, react it in a vacuum drying oven at 40 °C for 4 h to remove bubbles from the film and finally obtain a polyurethane film.

[0083] Comparative Example 2 A conductive shape memory fiber, the preparation method of which differs from that in Example 3 is as follows: S2. Cut the fiber membrane formed by the core-shell composite fiber on the receiving plate into three 50mm×50mm square films, and load 5mg of silver powder through physical filtration.

[0084] The test results showed that the silver powder loading in the conductive shape memory fiber membrane was 0.1 mg / cm³. 2 .

[0085] Performance testing The polyurethanes of Examples 1-3 and Comparative Example 1 were poured into a mold preheated to 80°C to form films. An image of the polyurethane film of Example 1 is shown below. Figure 2 As shown in (a) of the diagram, the following test was performed.

[0086] (1) Fourier Transform Infrared Spectroscopy (FT-IR) Test: Infrared tests were performed on the shape memory polyurethanes of Examples 1-3, and the test results are as follows: Figure 3 As shown.

[0087] from Figure 3 It can be seen that at 3320 cm -1A stretching vibration peak of NH bonds appeared nearby, and the peak intensity increased and the peak shape broadened with increasing BDO equivalent, indicating that the hydrogen bonding effect in the system is enhanced with increasing hard segment content; in the range of 2500 ~ 1900 cm⁻¹ -1 No absorption peak for -N=C=O was observed nearby, suggesting that the -OH group reacted completely with the -N=C=O group in HDI, indicating successful synthesis of polyurethane; absorption peaks were observed in the 1700~1720 cm⁻¹ range. -1 The nearby carbonyl absorption peak exhibits a bimodal characteristic: 1720 cm⁻¹ -1 The point is a free state C=O stretching vibration, 1700 cm. -1 The peak at position 1 represents the hydrogen-bonded C=O stretching vibration. With increasing BDO content, the relative intensity of the hydrogen-bonded C=O peak significantly increases, further confirming that increased hard segment content promotes the formation of the hydrogen bond network. Furthermore, characteristic peaks of pyridine ring backbone vibrations were also observed, verifying the successful introduction of PDM into the polymer backbone. In summary, the FTIR results confirm the successful synthesis of pyridine-containing polyurethanes, and that adjusting the BDO content can effectively enhance hydrogen bonding within the system.

[0088] (2) X-ray diffraction (XRD) test: X-ray diffraction (XRD) tests were performed on the shape memory polyurethanes of Examples 1-3, and the results are as follows. Figure 4 As shown. Figure 4 It can be observed that at 2θ ≈ 20°, all shape memory polyurethane (SMP) samples have a broad and diffuse diffraction peak. This peak is attributed to the weak crystalline / amorphous superposition signal of PTMEG soft segments, indicating that the material as a whole is dominated by an amorphous structure with only a small number of soft segment microcrystals.

[0089] As the BDO equivalent increases, the intensity of the diffraction peaks gradually increases and the peak shape becomes sharper, indicating that the crystallinity of the material increases with the increase of BDO content. This phenomenon is due to the fact that the increased BDO content enhances the hydrogen bonding and aggregation ability between hard segments, promotes the microphase separation of hard and soft segments, reduces the restriction of hard segments on the movement of soft segment chains, and enables soft segments to be arranged more fully to form ordered crystalline regions.

[0090] The absence of sharp crystalline peaks in the spectrum indicates that the hard segment phase, composed of HDI, PDM, and BDO, mainly exists in an amorphous or microcrystalline state, forming a physical cross-linked network through hydrogen bonding.

[0091] In summary, the XRD results confirmed the amorphous / weakly crystalline aggregated structure of polyurethane under different BDO equivalents, and the crystallinity and microphase separation of the material can be effectively adjusted by controlling the amount of BDO, providing a structural basis for understanding the shape memory behavior and mechanical properties of the material.

[0092] (3) Thermogravimetric analysis (TG): Thermogravimetric analysis was performed on the shape memory polyurethanes of Examples 1-3. The test results are as follows: Figure 5 As shown. Figure 5 (a) in the figure is the TG curve; Figure 5 (b) DTG curve. The thermogravimetric data are shown in Table 1.

[0093] Table 1

[0094] from Figure 5 As shown in Table 1, the first stage of weight loss corresponds to the decomposition of urethane bonds and pyridine rings in the hard segment, while the main decomposition stage at 350–450 °C is attributed to the thermal degradation of the PTMEG soft segment backbone. With the gradual increase of BDO equivalent and the rise in hard segment content, the hydrogen bonding and physical cross-linking network of the system are enhanced, and the 5% weight loss temperature (Td) of the sample increases from approximately 270 °C to 280 °C. The main decomposition peak of the DTG curve also shifts synchronously towards higher temperatures, indicating that the thermal stability of the material increases with the increase of hard segment content.

[0095] Furthermore, the char residue gradually decreased with increasing BDO content, consistent with the compositional change pattern of decreasing soft segment proportion and increasing nitrogen-containing hard segment proportion. Overall, the initial decomposition temperature of this series of SMPs is above 270 ℃, significantly higher than their shape memory response temperature and subsequent electrospinning processing temperature, thus meeting the temperature requirements for material processing and application.

[0096] (4) Differential scanning calorimetry (DSC) The thermal transformation behavior of the shape memory polyurethane in Examples 1-3 was characterized using differential scanning calorimetry (DSC). The cooling and heating curves are shown below. Figure 6 As shown in (a) and (b) in the figure.

[0097] As can be observed from the cooling curves (Figure a), all samples exhibited significant exothermic peaks in the range of -18 to -15℃, corresponding to the non-isothermal crystallization process of the PTMEG soft segments. As the BDO equivalent increased from P1 to P3, the peak temperature gradually increased from -18℃ to -15℃, indicating that the crystallization ability of the soft segments increased with the increase of BDO content, and the chain segments were more likely to form ordered crystalline regions.

[0098] In the secondary heating curve (Figure b), an endothermic peak corresponding to the melting of the PTMEG crystallization region appears in the 20~30℃ range, and the intensity of the peak and the enthalpy of melting increase with the increase of BDO dosage, further confirming the improvement of the crystallinity of the soft segment.

[0099] In addition, all samples showed endothermic peaks at ~177 °C corresponding to the melting of the hard segment aggregation region, and the peak positions remained basically unchanged, indicating that the hard domains have excellent thermal stability and are not affected by the amount of BDO.

[0100] Based on the analysis of the microphase separation mechanism, the increased BDO dosage promoted hydrogen bonding and aggregation between hard segments, improved the order of hard domains, enhanced the phase separation from soft segments, reduced the restriction of hard segments on the movement of soft segment chains, and thus enabled soft segments to be more fully arranged to form perfect crystal regions, with crystallinity and crystallization temperature increasing simultaneously.

[0101] (5) Mechanical properties of polyurethane The mechanical properties of shape memory polyurethanes prepared with different BDO equivalents (P1~P3) in Examples 1-3 were characterized by room temperature uniaxial tensile tests. The stress-strain curves are shown below. Figure 7 As shown in the figure. The test results are shown in Table 2.

[0102] Table 2

[0103] Depend on Figure 7 As shown in Table 2, the shape memory polyurethanes of Examples 1-3 all exhibit typical thermoplastic elastomer tensile behavior, possessing both high tensile strength and elongation at break. The tensile strength reaches 15.8-25.2 MPa, the elongation at break reaches 850-1180%, and the elastic modulus reaches 2.8-3.8 MPa. In contrast, the polyurethane of Comparative Example 1 has significantly lower tensile strength, elongation at break, and elastic modulus than that of this invention, resulting in poor mechanical properties. This may be because 2,6-pyridinediethanol (PDM) is introduced as a composite chain extender in the shape memory polyurethane of this invention. The N atoms on the pyridine ring can form a high-density, strong, and reversible hydrogen bond network, thereby giving the shape memory polyurethane of this invention high strength and high toughness, i.e., excellent mechanical properties.

[0104] The shape memory polyurethane of Example 3 exhibits the best overall mechanical properties, possessing both high strength and high toughness. Analysis of the structural and thermal performance characterization results shows that the improved mechanical properties of Example 3 compared to Example 1 are mainly attributed to the following two aspects: First, the increased BDO content leads to a higher hard segment content, denser hard domain aggregation, and increased physical crosslinking point density, significantly improving the material's modulus and tensile strength. Second, the enhanced separation of the hard and soft segments reduces the restriction of hard segments on the movement of soft segment chains, allowing the soft segments to fully orient and slide during stretching, thus achieving a simultaneous increase in elongation at break. Simultaneously, XRD and DSC results show that the soft segments of the shape memory polyurethane of Example 3 have higher crystallinity. The crystalline regions can serve as additional physical crosslinking points, further enhancing the material's mechanical properties and optimizing both strength and toughness.

[0105] In summary, the mechanical properties of materials can be effectively improved by adjusting the amount of BDO. The shape memory polyurethane in Example 3 has both high tensile strength and high elongation at break, providing a reliable mechanical basis for it to withstand repeated deformation in shape memory applications.

[0106] (6) Shape memory performance: The testing method is as follows: a) The shape memory polyurethane film sample from Example 3 was cut into a flower shape using a mold, such as... Figure 8 Figure a in the middle; b) After softening the sample by heating it to 35 °C, shape it. Following Example 3, at room temperature, use tweezers to carefully fold the cut flower-shaped sample until it finally forms a shape similar to... Figure 8 The flower bud shape shown in b is as follows.

[0107] c) Finally, the temporary shape of Example 3 is placed on a heating platform and gradually heated from room temperature. The petal-shaped sample made of the material of Example 3 will slowly open and eventually fully recover to its original initial shape.

[0108] The specific recovery process is shown in the diagram as the temperature gradually rises. Figure 8 As shown in c ~ f: Experimental results show that Example 3 exhibits excellent thermo-induced shape fixation and recovery properties. To verify its cyclic stability, Example 3 underwent five repeated shape memory tests. The results indicate that after five cycles, Example 3 still maintains stable and consistent shape fixation and recovery behavior. Overall test results confirm that this shape memory polymer can undergo controllable deformation under thermal stimulation and effectively recover to its initial morphology after the thermal stimulation is removed, demonstrating good thermo-responsive shape memory cyclic stability.

[0109] (7) Cut the shape memory polyurethane films of Examples 1 to 3 into dumbbell shapes with a width of 2 mm and an initial length L0 of 14 mm. Stretch them at room temperature with a strain of 200%, and test the length L1 after stretching. Then remove the stretching force, heat to 100°C, and allow the samples to recover on their own. Measure the recovery length L2. f Taking 100% as an example, calculate the shape recovery rate R. r , The calculation formula is R r = (L1-L2) / (L1-L0) The obtained data is shown in Table 3 below: Table 3

[0110] As shown in Table 3, the shape recovery rate increases significantly with the increase of BDO equivalent, which is directly related to the increase of hard segment content: higher hard segment content forms a more complete physical cross-linking network, which can more effectively drive the soft segment to recover to the initial conformation after heating, thus exhibiting better shape memory performance.

[0111] As can be seen from the examples and Comparative Example 1, the polyurethane in Comparative Example 1 does not include the pyridine structure. The shape recovery performance of the polyurethane in Comparative Example 1 is significantly lower than that of the embodiments of the present invention. This is because the lone pair electrons of the N atom of the pyridine ring in the pyridine structure can form intermolecular / intramolecular hydrogen bonds with the N-H and C=O groups of the urethane in the polyurethane molecular chain, superimposing a large number of reversible hydrogen bond crosslinking points on the basis of the original urethane bonds, making the hard segment aggregation region form a denser and more stable physical crosslinking network. This network, as the stationary phase of the shape memory system, can effectively lock the permanent morphology of the material, while providing sufficient molecular springback driving force for deformation recovery, thereby improving the shape recovery rate.

[0112] (8) Micromorphological analysis of SMP@PVDF coaxial electrospun core-shell structure composite fiber membrane The microstructure of the SMP nanofiber membranes prepared under different spinning voltages in Examples 3-6 was characterized by scanning electron microscopy (SEM), and the results are as follows: Figure 9 As shown, Figure 9 In the above, a) 14kV; b) 16kV; c) 18kV; d) 20kV.

[0113] From an overall morphological perspective, all samples exhibited a typical nonwoven fiber network structure, with fibers randomly stacked to form a three-dimensional network with a porous structure, a typical characteristic of electrospinning. As the spinning voltage gradually increased from 14 kV to 20 kV, the fiber morphology showed a clear changing pattern: From an overall morphological perspective, all samples exhibited a typical three-dimensional porous fiber network structure resembling nonwoven fabric, typical of electrospun fibers. As the spinning voltage increased from 14 kV to 20 kV, the fiber morphology changed significantly: at 14–16 kV, the fibers were uneven in thickness, exhibiting defects such as beading, localized coarsening, and adhesion. In contrast, the fiber morphology was optimal at 18–20 kV, with uniform diameter, smooth surface, no obvious defects, and uniform pore distribution.

[0114] (9) The elemental distribution of the SMP@PVDF core-shell fiber membrane prepared by coaxial electrospinning in Example 3 was characterized by SEM-EDS surface scanning. The results are as follows: Figure 10 As shown. Figure 10(a) Scanning electron microscopy (SEM) morphology of the core-shell structured fiber membrane; (b) Energy dispersive spectroscopy (EDS); (cf) Elemental distribution maps of C, O, N, and F, respectively. SEM results show that the coaxial electrospun fibers have smooth surfaces and uniform diameters, forming a continuous three-dimensional network structure. EDS surface scanning indicates that N, F, C, and O elements are uniformly distributed within the fibers: N (from the SMP core polyurethane segments) is uniformly distributed in a dotted pattern, F (from the PVDF shell) is continuously distributed throughout the fiber cross-section, and C and O are shared by both components and are uniformly distributed. These results confirm that the composite fiber membrane contains both SMP and PVDF components, providing a reliable structural basis for subsequent functional applications.

[0115] (10) The silver powder prepared in Example 1 was characterized using field emission scanning electron microscopy (FE-SEM, Regulus). The morphology results at different magnifications (×10.0 k, ×25.0 k, ×50.0 k) are shown below. Figure 11 As shown. Figure 11 (a) in the image represents the original silver powder; Figure 11 (b) 10k times; Figure 11 (c) 25k times; Figure 11 (d) 50k times.

[0116] As can be seen from the image, the product exhibits a one-dimensional linear / fibrous silver structure, with numerous silver lines intertwined and entangled without obvious directional arrangement, forming a network-like distribution. The surface of the silver lines is generally smooth with clear edges, without obvious dendrites or rough protrusions, indicating that sodium citrate effectively plays a role in morphology regulation during the reaction process, inhibiting the random aggregation and secondary growth of silver particles.

[0117] (11) Conductivity test: Conductivity tests were conducted on the conductive shape memory fiber membranes of Example 1, Example 7 and Comparative Example 2 respectively. The dispersion formed by the reaction was filtered and dried to obtain composite fiber membrane materials with a diameter of 40 mm × 40 mm. The conductivity data are shown in Table 4 below: Table 4 Conductivity data of SPA fiber membranes with different silver powder contents

[0118] As shown in Table 4, in Comparative Example 2, due to the low silver content, a continuous conductive path could not be constructed inside the fiber membrane, resulting in no conductivity. When the silver loading was increased to 0.5 mg / cm³ in Example 7... 2At this point, the resistivity of the fiber membrane had dropped to as low as 1.7Ω, exhibiting excellent conductivity. Its loading was only half that of Sample Example 1 (resistance 0.6Ω), indicating that the present invention can achieve high-efficiency conductivity with a low silver loading, significantly reducing the amount and cost of conductive filler. Furthermore, the present invention employs a room-temperature aqueous phase synthesis of silver powder combined with vacuum filtration, eliminating the need for high-temperature, high-pressure, or complex post-processing steps. The process is simple to operate and can be scaled up, possessing significant advantages for industrial application.

[0119] In summary, the silver loading per unit area is the key factor determining the conductivity of SPA fiber membranes, with 0.5 mg / cm² in Example 7 being a significant indicator. 2 The silver loading can be used to construct a continuous conductive network and achieve excellent conductivity, providing a feasible preparation strategy for the development of low-cost, high-performance conductive fiber membranes.

[0120] (12) Flexible electronics testing performance: The conductive shape memory fiber membranes of Examples 1 and 7 were cut into rectangular strips of uniform size and placed on a flexible electronics testing instrument for tensile and bending tests. The parameters were set as follows: 1000 tensile cycles and tensile speed of 5 mm / s. The obtained data are as follows: Figure 12 As shown. By Figure 12 As can be seen, the initial resistance of Example 1 was approximately 2Ω. During 1000 cycles of stretching, the resistance remained stable within a narrow range of 1~5Ω, with no significant baseline drift or irreversible increase throughout the process. In the middle and later stages of stretching, the resistance rebound recovery was consistent and the hysteresis was small. After the cyclic test, no macroscopic defects such as silver layer peeling, flaking, or cracks appeared on the sample surface. The interface integrity between the conductive layer and the substrate remained good, demonstrating excellent synergistic performance of mechanical fatigue resistance and conductive stability. It can be adapted to flexible electronic applications such as high-stability flexible sensing and long-term dynamic service.

[0121] For the sample of Example 7: its initial resistance was approximately 5~6Ω. During 1000 cycles of stretching, the resistance remained stable within the range of 4~7Ω without any complete open-circuit failure, which meets the requirements for basic flexible conductive applications. However, compared to Example 1, its initial resistance was significantly higher, the intrinsic connectivity density of the conductive network was insufficient, and the resistance fluctuation was slightly greater than that of the high-load sample, indicating that its long-term dynamic service performance needs to be improved.

[0122] Comprehensive comparative analysis shows that: Example 1 had a silver loading of 1.0 mg / cm³. 2 The conductive shape memory fiber membrane can construct a highly redundant and stable three-dimensional conductive network, exhibiting optimal deformation adaptability with the SMP@PVDF flexible memory substrate. It demonstrates outstanding synergy in maintaining its mechanical structure and conductive function under thousands of dynamic service cycles. Example 7, however, has a silver loading of 0.5 mg / cm³. 2The load capacity of conductive shape memory fiber membranes is limited by the sparse conductive network and weak interfacial bonding strength, resulting in insufficient long-term flexible service performance.

[0123] (13) Demonstration of Flexible Electronics Testing Performance: A conductive shape memory fiber membrane with a silver powder loading of 50 mg from Example 1 was selected and used for LED bulb lighting tests to demonstrate its conductivity. A power supply, several wires, and a green LED bulb were used... Figure 13 (a) Flat; (b) Twisted; (c) Bending; (e) Stretched. It can be seen that the conductive shape memory fiber membrane can support the long-term illumination of LED lights, indicating its stable conductivity and application value. Testing the brightness of LED lights on the conductive shape memory fiber membrane flexible substrate under flat and bent conditions reveals that the brightness of the LED lights remains almost unchanged. This indicates that the conductive pathway constructed by the conductive silver particles is not interrupted even under bending conditions, demonstrating that the SPA fiber membrane exhibits good flexibility and conductive stability.

[0124] In summary, the shape memory polyurethane of the present invention contains a pyridine structure and has excellent shape memory recovery performance and mechanical properties.

[0125] The cyclic tensile test results of the conductive shape memory composite fiber membrane of the present invention show that the resistance of the composite membrane remains stable throughout 1000 consecutive bending cycles, without any obvious jumps or open circuits, demonstrating excellent flexible conductive durability and mechanical-conductive synergistic stability. The LED lighting experiment also verifies its application potential in flexible electronics, wearable sensing and other fields.

[0126] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A shape memory polyurethane, characterized in that, It is prepared by the following method: S1. In a protective atmosphere, using organotin as a catalyst, polytetrahydrofuran glycol and hexamethylene diisocyanate in a molar ratio of 1:(1.2~2.0) are subjected to a first-step polymerization reaction. The polymerization reaction time is 1~2h and the polymerization reaction temperature is 70~90℃. S2. Add 2,6-pyridinediethanol and hexamethylene diisocyanate to the product of step S1 to carry out a second polymerization reaction. The polymerization reaction time is 0.5~1.5h. The molar ratio of 2,6-pyridinediethanol to polytetrahydrofurandiol in step S1 is (1.5~2.5):

1. The molar ratio of hexamethylene diisocyanate to polytetrahydrofurandiol in step S1 is (1~1.5):

1. S3. Add 1,4-butanediol and hexamethylene diisocyanate to the product of step S2 to carry out a third polymerization reaction for 3-5 hours to obtain shape memory polyurethane; wherein the molar ratio of 1,4-butanediol to polytetrahydrofurandiol in step S1 is (1-2):1; and the molar ratio of hexamethylene diisocyanate to polytetrahydrofurandiol in step S1 is (1-2.5):

1.

2. The shape memory polyurethane according to claim 1, characterized in that, In step S3, the molar ratio of 1,4-butanediol to polytetrahydrofurandiol in step S1 is (1.5~2):1; the molar ratio of hexamethylene diisocyanate to polytetrahydrofurandiol in step S1 is (1.5~2.5):

1.

3. The shape memory polyurethane according to claim 1, characterized in that, The molecular weight of polytetrahydrofuran diol is 1000~5000 g / mol.

4. A conductive shape memory fiber, characterized in that, It is prepared by the following method: S1. Dissolve the shape memory polyurethane according to any one of claims 1 to 3 in a solvent to prepare a core solution, dissolve PVDF in a solvent to prepare a shell solution, and coaxially electrospin to obtain a core-shell structured composite fiber; S2. Silver powder is loaded onto the surface of the core-shell composite fiber to obtain conductive shape memory fiber.

5. The conductive shape memory fiber according to claim 4, characterized in that, In step S1, during coaxial electrospinning, the injection speed of the core solution is 0.01~0.1 mm / min, the injection speed of the shell solution is 0.05~0.15 mm / min, the spinning voltage is 14~20 kV, and the receiving distance is 10~20 cm.

6. The conductive shape memory fiber according to claim 4, characterized in that, In step S1, the molecular weight of PVDF is 200,000~600,000 g / mol.

7. The conductive shape memory fiber according to claim 4, characterized in that, In step S2, the method for preparing the silver powder includes the following steps: placing a silver nitrate solution in a sodium citrate solution, adding a hydrazine hydrate solution for reduction reaction, and preparing silver powder.

8. The conductive shape memory fiber according to claim 4, characterized in that, In step S2, silver powder is loaded onto the core-shell composite fiber by negative pressure filtration.

9. The conductive shape memory fiber according to claim 4, characterized in that, The silver powder loading is 0.5 ~ 2 mg / cm³. 2 .

10. The application of the conductive shape memory fiber according to any one of claims 4 to 9 in flexible sensing, intelligent driving and electromagnetic protection.

Images