Preparation method of liquid crystal elastomer film containing dynamic acylhydrazone bonds and product thereof

Abstract

The invention discloses a preparation method of a liquid crystal elastomer film containing dynamic acylhydrazone bonds and a product thereof. The dynamic acylhydrazone bond is introduced into the liquid crystal elastomer through a thiol-Michael addition reaction, and the liquid crystal elastomer film containing the dynamic acylhydrazone bond is prepared. The liquid crystal elastomer film material has excellent mechanical properties, also has programming, self-repairing and recycling properties, can be applied to the fields of artificial muscles, flexible actuators, biomedical engineering and the like, and has a good market application prospect.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and in particular relates to a preparation method of a liquid crystal elastomer film containing dynamic acylhydrazone bonds and a product thereof. Background Art

[0002] Liquid crystal elastomers (LCEs) combine the elasticity of elastomers with the orientational response of liquid crystal molecules. They can undergo significant reversible deformation in response to external stimuli such as light and heat, making them ideal materials for flexible actuators. To achieve macroscopic deformation, the mesogens must be aligned to form a single-domain structure through two-step crosslinking or in situ polymerization. However, the permanent covalent crosslinked networks formed by these traditional methods are irreversible, making the materials difficult to reprocess or recycle. To overcome these limitations, researchers have proposed introducing dynamic covalent bonds (such as ester bonds, disulfide bonds, and borate ester bonds) into the crosslinked networks to construct reconfigurable LCE systems. Dynamic exchange reactions of these dynamic bonds can reconfigure the network under stimuli such as heat and light, endowing the LCEs with programmable properties. However, the mechanical properties of DN-LCEs often fall short of meeting the requirements of practical applications. Inspired by the dual network (DN) strategy commonly used to enhance the mechanical properties of LCEs, constructing a dual network structure holds promise for addressing the mechanical limitations of DN-LCEs. However, traditional methods for preparing DN-LCEs (DN-LCEs) often require multiple polymerization steps, resulting in a complex and costly synthesis process. Therefore, it is of great significance to develop an exchangeable liquid crystal elastomer that can form a double network structure through a simple process and a preparation method thereof. Summary of the Invention

[0003] Purpose of the invention: The present invention provides a method for preparing a liquid crystal elastomer film containing dynamic acylhydrazone bonds with simple preparation process and excellent mechanical properties, and its product.

[0004] Technical solution: In order to solve the above technical problems, the present invention provides a method for preparing a liquid crystal elastomer film containing dynamic acylhydrazone bonds, comprising the following steps:

[0005] (1) 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (RM82), ((1E,1'E)-(adipoylbis(hydrazino-2-yl-1-ylidene))bis(methaneylidene))bis(4,1-phenylene) diacrylate (7HB), pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), 3,6-dioxa-1,8-octanedithiol (EDDT), and 2,2-dimethoxyphenylacetophenone (DMPA) were added to an organic solvent and heated until completely dissolved. The mixture was ultrasonically treated using an ultrasonic cleaning machine to uniformly mix the mixture to obtain a mixed reaction solution.

[0006] (2) Pour the mixed reaction liquid into a polytetrafluoroethylene mold and cure it using ultraviolet light.

[0007] (3) The mold is placed in an oven and heated until the organic solvent evaporates, thereby obtaining a liquid crystal elastomer film containing dynamic acylhydrazone bonds.

[0008] The mass ratio of the 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, ((1E,1'E)-(adipoylbis(hydrazino-2-yl-1-ylidene))bis(methaneylidene))bis(4,1-phenylene) diacrylate, pentaerythritol tetrakis(3-mercaptopropionate), 3,6-dioxa-1,8-octanedithiol and 2,2-dimethoxy-phenylacetophenone is 186-278:22-87:73:13:1.

[0009] The mass volume ratio of the 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene to the organic solvent is 186-278:1 mg / ml.

[0010] Wherein, the organic solvent in step (1) is N,N-dimethylformamide.

[0011] Wherein, the temperature of heating and dissolving in step (1) is 80-90°C.

[0012] Wherein, the ultrasonic treatment time in step (1) is 3-5 minutes.

[0013] The wavelength of the ultraviolet light in step (2) is 365 nm, and the optical power density is about 50-100 mW / cm 2 , the irradiation time is 15-25min.

[0014] Wherein, the heating temperature in step (3) is 75-85° C., and the heating time is 10-14 h.

[0015] The present invention also provides a liquid crystal elastomer film containing dynamic acylhydrazone bonds prepared by the preparation method.

[0016] In the preparation of an exchangeable liquid crystal elastomer with a dual-network structure, the present invention chooses to introduce a dynamic acylhydrazone bond into the liquid crystal elastomer, mainly based on the following considerations: the acylhydrazone bond (-CO-NH-N=CH-) is a dynamic covalent bond (DCB) formed by the reaction of a hydrazide group and an aldehyde group. Structurally, the acylhydrazone bond can be divided into two parts: an amide group (-CO-NH-) and an imine bond (-C=N-). Its dynamic covalent exchange properties originate from the imine bond, while the amide group can serve as an active site, interacting through hydrogen bonds formed by C=O and NH groups to increase the crosslinking degree of the polymer, thereby improving the mechanical strength of the material. This acylhydrazone bond, which combines dynamic properties with mechanical reinforcement effects, has advantages in preparing exchangeable liquid crystal elastomers with a chemical / physical dual crosslinking network.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) Simple preparation process: The preparation of the present invention adopts the thiol-Michael addition reaction, which has the characteristics of high reaction efficiency, high selectivity and few side reactions, and the entire preparation process is mild, with few process steps and simple operation. (2) Excellent mechanical properties of the material: By introducing a dynamic acylhydrazone bond, the liquid crystal elastomer film containing a dynamic acylhydrazone bond prepared by the present invention greatly improves the mechanical properties of the material. (3) The liquid crystal elastomer film containing a dynamic acylhydrazone bond prepared by the present invention has the characteristics of reversible deformation by heating and cooling, self-repairability, and recyclability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the synthetic route of 7HB;

[0019] Figure 2 is the H NMR spectrum of intermediate 1;

[0020] Figure 3 is the H NMR spectrum of 7HB;

[0021] Figure 4 A structural diagram of the monomers used to prepare liquid crystal elastomer films;

[0022] Figure 5 Thermogravimetric curves of liquid crystal elastomer films with different acylhydrazone bond contents;

[0023] Figure 6 is the differential scanning calorimetry curve of liquid crystal elastomer films with different acylhydrazone bond contents;

[0024] Figure 7 is the stress-strain curve of liquid crystal elastomer films with different acylhydrazone bond contents;

[0025] Figure 8 is the stress relaxation curve of liquid crystal elastomer films with different acylhydrazone bond contents;

[0026] Figure 9 is the stress relaxation curve of LCE-7HB-40 film at different temperatures;

[0027] Figure 10 Programming of multi-domain LCE-7HB-40 films by heating and reversible deformation of single-domain LCE-7HB-40 films upon heating and cooling;

[0028] Figure 11 Images of LCE-7HB-40 film before and after self-repair;

[0029] Figure 12 Schematic diagram of solution recovery of LCE-7HB-40 film;

[0030] Figure 13 Fourier transform infrared spectra of the original LCE-7HB-40 film and the recycled film. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0032] Example 1

[0033] The synthetic route of dynamic acylhydrazone monomer 7HB is as follows: Figure 1 shown.

[0034] (1) Synthesis of intermediate 1: Add p-hydroxybenzaldehyde (4.00 g, 32.75 mmol), triethylamine (9.34 g, 92.30 mmol) and tetrahydrofuran (100 mL) to a 250 mL three-necked flask. Then slowly add acryloyl chloride (3.59 g, 39.70 mmol) under ice-water bath conditions. The above reaction mixture is stirred at room temperature for 12 h. Add a few drops of distilled water to the reaction solution to quench it and wash it three times with saturated sodium bicarbonate solution, and collect the organic phase. The crude product is purified by silica gel chromatography (eluent: ethyl acetate / petroleum ether, volume ratio: 1 / 8) to obtain intermediate 1 (4.00 g, yield: 68%), which is a colorless oily liquid. The hydrogen nuclear magnetic resonance spectrum of intermediate 1 is as follows Figure 2 shown. 1 H NMR (600MHz, C2D6SO): δ10.02(s,1H),8.12-7.89(dt,J=8.4,2.4Hz,2H),7.60-7.29(dt,J=8.4,2.4 Hz, 2H), 6.58 (dd, J=17.3, 1.2Hz, 1H), 6.44 (dd, J=17.3, 10.4Hz, 1H), 6.19 (dd, J=10.4, 1.2Hz, 1H).

[0035] (2) Synthesis of 7HB: 1,4-Butanediamine (4.00 g, 22.96 mmol) was dissolved in 200 mL of methanol, and then intermediate 1 (8.08 g, 45.92 mmol) was added dropwise. The reaction mixture was stirred at room temperature for 12 h, and a large amount of white precipitate was precipitated in the reaction solution. The residue was collected by suction filtration using a Buchner funnel, and then washed with methanol several times. Finally, it was vacuum dried at 45 ° C to obtain 7HB (5.17 g, yield 73%), which was a white solid. The hydrogen nuclear magnetic resonance spectrum of 7HB is as follows Figure 3 shown. 1H NMR (600MHz, C2D6SO): δ11.34(m,2H),8.18(s,1H),7.99(d,J=4.7Hz,1H),7.88-7.51(m,4H),7.36-6.87(m, 4H),6.55(m,2H),6.49-6.23(m,2H),6.17(m,2H),2.70-2.63(m,2H),2.34-2.07(m,2H),1.75-1.54(m,4H).

[0036] Example 2:

[0037] (1) Add 0.278 mg of RM82, 0.022 mg of 7HB, 0.013 mg of PETMP, 0.073 mg of EDDT, and 0.001 mg of DMPA to 1 ml of N,N-dimethylformamide and heat at 85°C until completely dissolved. Ultrasonicate the mixture for 4 min in an ultrasonic cleaner to uniformly mix the mixture to obtain a mixed reaction solution.

[0038] (2) The mixed reaction solution was poured into a polytetrafluoroethylene mold and heated at room temperature using a 365 nm, 75 mW / cm 2 Irradiate with UV light for 20 min until a thin film is formed.

[0039] (3) The mold was placed in an oven and heated at 80 °C for 12 h until the organic solvent evaporated to obtain the LCE-7HB-10 film.

[0040] Example 3:

[0041] (1) Add 0.248 mg of RM82, 0.044 mg of 7HB, 0.013 mg of PETMP, 0.073 mg of EDDT, and 0.001 mg of DMPA to 1 ml of N,N-dimethylformamide and heat at 85°C until completely dissolved. Ultrasonicate the mixture for 4 min in an ultrasonic cleaner to uniformly mix the mixture to obtain a mixed reaction solution.

[0042] (2) The mixed reaction solution was poured into a polytetrafluoroethylene mold and irradiated with ultraviolet light at room temperature for 20 minutes until a thin film was formed.

[0043] (3) The mold was placed in an oven and heated at 80°C for 12 h until the organic solvent evaporated to obtain the LCE-7HB-20 film.

[0044] Example 4:

[0045] (1) Add 0.216 mg of RM82, 0.066 mg of 7HB, 0.013 mg of PETMP, 0.073 mg of EDDT, and 0.001 mg of DMPA to 1 ml of N,N-dimethylformamide and heat at 85°C until completely dissolved. Ultrasonicate the mixture for 4 min in an ultrasonic cleaner to uniformly mix the mixture to obtain a mixed reaction solution.

[0046] (2) The mixed reaction solution was poured into a polytetrafluoroethylene mold and irradiated with ultraviolet light at room temperature for 20 minutes until a thin film was formed.

[0047] (3) The mold was placed in an oven and heated at 80 °C for 12 h until the organic solvent evaporated to obtain the LCE-7HB-30 film.

[0048] Example 5:

[0049] (1) Add 0.186 mg of RM82, 0.087 mg of 7HB, 0.013 mg of PETMP, 0.073 mg of EDDT, and 0.001 mg of DMPA to 1 ml of N,N-dimethylformamide and heat at 85°C until completely dissolved. Ultrasonicate the mixture for 4 min in an ultrasonic cleaner to uniformly mix the mixture to obtain a mixed reaction solution.

[0050] (2) The mixed reaction solution was poured into a polytetrafluoroethylene mold and irradiated with ultraviolet light at room temperature for 20 minutes until a thin film was formed.

[0051] (3) The mold was placed in an oven and heated at 80°C for 12 h until the organic solvent evaporated to obtain the LCE-7HB-40 film.

[0052] Comparative Example

[0053] (1) Add 0.309 mg RM82, 0.013 mg PETMP, 0.073 mg EDDT, and 0.001 mg DMPA to 1 ml N,N-dimethylformamide and heat at 85°C until completely dissolved. Ultrasonicate for 4 minutes using an ultrasonic cleaner to uniformly mix the mixture to obtain a mixed reaction solution. The structures of the monomers RM82, PETMP, EDDT, and DMPA used to prepare the liquid crystal elastomer film are shown in FIG. Figure 4 shown.

[0054] (2) The mixed reaction solution was poured into a polytetrafluoroethylene mold and heated at room temperature using a 365 nm, 75 mW / cm 2 Irradiate with UV light for 20 min until a thin film is formed.

[0055] (3) The mold was placed in an oven and heated at 80 °C for 12 h until the organic solvent evaporated to obtain the LCE-7HB-0 film.

[0056] The LCE-7HB-10, LCE-7HB-20, LCE-7HB-30, and LCE-7HB-40 films prepared in Examples 2-5 and the LCE-7HB-0 prepared in the comparative example were tested.

[0057] Figure 5 Thermogravimetric curves of liquid crystal elastomer films with varying acylhydrazone bond contents are shown below. As can be seen, the temperatures at which 5% decomposition occurs for LCE-7HB-0, LCE-7HB-10, LCE-7HB-20, LCE-7HB-30, and LCE-7HB-40 films are 330.9°C, 325.5°C, 315.7°C, 308.2°C, and 310.4°C, respectively. However, all films exhibit less than 5% weight loss upon heating to 300°C, demonstrating the excellent thermal stability of these films.

[0058] Figure 6 The differential scanning calorimetry curves of liquid crystal elastomer films with different acylhydrazone bond contents are shown in Figure 2. As can be seen from the figure, with the increase of acylhydrazone bond content, the glass transition temperature (T g ) and the transition temperature between the liquid crystal phase and the isotropic phase (T i ) gradually increased, and the glass transition temperatures (T g ) are 1.5℃, 2.9℃, 5.1℃, 6.2℃, 14.6℃, respectively, and the liquid crystal phase-isotropic phase transition temperature (T i ) were 95.6℃, 101.8℃, 102.9℃, 108.2℃ and 110.1℃ respectively.

[0059] Figure 7 The stress-strain curves of liquid crystal elastomer films with varying acylhydrazone content are shown in Figure 1. As can be seen, the breaking strength and elongation at break of the liquid crystal elastomer films increase with increasing acylhydrazone content. The breaking strengths of the multidomain LCE-7HB-0, LCE-7HB-10, LCE-7HB-20, LCE-7HB-30, and LCE-7HB-40 films are 3.3 MPa, 6.3 MPa, 11.5 MPa, 20.6 MPa, and 33.1 MPa, respectively, and the elongations at break are 198.2%, 221.8%, 244.1%, 264.6%, and 292.5%, respectively, demonstrating the excellent mechanical properties of the liquid crystal elastomer films.

[0060] Figure 8 The following graph shows the stress relaxation curves of liquid crystal elastomer films with varying acylhydrazone content. As can be seen from the graph, at 60°C, the stress relaxation rate of the liquid crystal elastomer films increases with increasing acylhydrazone content. Typically, the stress relaxation time τ* is defined as the time required for the normalized stress to reach 1 / e. At 60°C, only the LCE-7HB-40 film exhibits a stress relaxation time τ* less than 60 minutes. Considering the mechanical properties and network rearrangement capabilities of liquid crystal elastomer films, the LCE-7HB-40 film was selected as the primary subject of this study.

[0061] Figure 9 The following graph shows the stress relaxation curves of the LCE-7HB-40 film at different temperatures. As can be seen from the figure, at 40°C, the stress relaxation process of the LCE-7HB-40 film is relatively slow, with stress relaxation still less than 50% after 60 minutes. As the temperature increases, the stress relaxation rate of the LCE-7HB-40 film accelerates. At 120°C, the LCE-7HB-40 film releases over 80% of its stress within 3 minutes.

[0062] Figure 10 The figure shows the reversible deformation of the multi-domain LCE-7HB-40 film during heating and cooling. As can be seen from the figure, the multi-domain LCE-7HB-40 film after stretching and shape editing is programmed into a spiral shape when heated at 120℃ for 6h. i When the temperature is above 110℃, the film unwinds. When the temperature returns to room temperature, the film returns to its original shape. Subsequently, the spiral-shaped film can be reprogrammed to a curled form by heating at 120℃ for 6h. i When the temperature is above 110℃, the film unfolds. As the temperature drops to room temperature, the film returns to its original shape.

[0063] Figure 11 Images of the LCE-7HB-40 film before and after self-healing (scale: 100μm). A scratch was created on the surface of the LCE-7HB-40 film prepared in Example 5 using a blade. The film was then heated in a 120°C oven to promote dynamic exchange reactions at the scratch. After heating for 6 hours, partial self-healing of the scratch on the film surface was observed. The left image shows the image before heating, and the right image shows the image after self-healing.

[0064] Figure 12Schematic diagram of the solution recovery process for LCE-7HB-40 films. Several LCE-7HB-40 films prepared in Example 5 were placed in a glass bottle. 1 ml of DMF solvent was added. After heating and stirring at 140°C for 24 hours, the solution became homogeneous, indicating that the network was decrosslinked. Subsequently, solution casting was performed to obtain a complete film free of visible cracks and defects.

[0065] Figure 13 Fourier transform infrared spectra of the original LCE-7HB-40 film and the recovered film prepared in Example 5. As can be seen from the figure, there is no significant difference between the infrared spectra of the recovered film and the original LCE-7HB-40 film, indicating that the chemical structure of the film remains stable.

Claims

1. A method for preparing a liquid crystal elastomer film containing dynamic acylhydrazone bonds, characterized in that: The method comprises the following steps: adding 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, ((1E,1'E)-(adipoylbis(hydrazine-2-yl-1-ylidene))bis(methaneylidene))bis(4,1-phenylene) diacrylate, pentaerythritol tetrakis(3-mercaptopropionate), 3,6-dioxa-1,8-octanedithiol and 2,2-dimethoxy-phenylacetophenone into an organic solvent, heating until completely dissolved, ultrasonically treating the mixture to uniformly mix the mixture, curing with ultraviolet light, and heating until the organic solvent volatilizes, thereby obtaining the liquid crystal elastomer film containing dynamic acylhydrazone bonds.

2. The preparation method according to claim 1, characterized in that The mass ratio of the 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, ((1E,1'E)-(adipoylbis(hydrazino-2-yl-1-ylidene))bis(methaneylidene))bis(4,1-phenylene) diacrylate, pentaerythritol tetrakis(3-mercaptopropionate), 3,6-dioxa-1,8-octanedithiol and 2,2-dimethoxy-phenylacetophenone is 186-278:22-87:73:13:

1.

3. The preparation method according to claim 1, characterized in that: The organic solvent includes N,N-dimethylformamide.

4. The preparation method according to claim 1, characterized in that The mass volume ratio of the 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene to the organic solvent is 186-278:1 mg / ml.

5. The preparation method according to claim 1, characterized in that: The temperature of the heating and dissolving is 80-90°C.

6. The preparation method according to claim 1, characterized in that: The ultrasonic treatment time is 3-5 minutes.

7. The preparation method according to claim 1, characterized in that: The light power density of the UV lamp is about 50-100 mW / cm 2 , the irradiation time is 15-25min.

8. The preparation method according to claim 1, characterized in that: The temperature is heated to 75-85°C when the organic solvent evaporates, and the time is 10-14 hours.

9. A liquid crystal elastomer film containing dynamic acylhydrazone bonds prepared by the preparation method according to any one of claims 1 to 8.

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