Photoresponsive Multimodal Deformation Polyurethane Liquid Crystal Elastomer Based on Helicene Molecular Motors, Preparation Method and Application

Abstract

A photo-responsive multi-mode deformable polyurethane liquid crystal elastomer based on a helicene molecular motor, its preparation method and application. The preparation method comprises the following steps: dissolving a liquid crystal monomer, an isocyanate monomer, a cross-linking agent, a thermal initiator and a helicene molecular motor in an ultra-dry solvent, heating and stirring for reaction to obtain a prepolymer solution; pouring the prepolymer solution into a mold with a thickness of 0.5-5 mm; putting the mold into a vacuum oven for gradient drying and thermal polymerization to obtain a polyurethane liquid crystal elastomer. The polyurethane liquid crystal elastomer of the present invention can generate variable-speed curling deformation, de-helix deformation and shrinkage energy release deformation under ultraviolet light irradiation, and can return to the initial shape due to the shape memory effect of the elastomer after removing the ultraviolet light. The deformation speed and deformation mode can be adjusted by the ultraviolet light intensity and the initial shape of the film, and it is expected to be used for preparing various intelligent devices.

Description

Technical Field

[0001] The present invention relates to the field of liquid crystal polymer materials, and particularly relates to a light-responsive multi-mode deformation polyurethane liquid crystal elastomer based on a helicene molecular motor, a preparation method thereof, and an application thereof. Background Art

[0002] The photo-induced deformation liquid crystal polymer material is a material that can move under light driving, and it can directly convert light energy into mechanical energy of the material. At the same time, light energy is a clean energy source, which has the advantages of being simple to obtain, non-contact remote control, etc., and is easy to control in terms of time and space, and is an ideal driving method.

[0003] Helicene molecules are a type of molecular machine that has emerged in recent years. It can undergo cis-trans isomerization under ultraviolet light irradiation, and the upper and lower parts of the molecule rotate relative to each other to become an unstable configuration. After removing the ultraviolet light irradiation, it can thermally return to the initial state. Due to its excellent molecular dynamics performance, such molecules are currently mainly used for surface modification of materials at the microscale and molecular self-assembly, etc. Chinese Patent Application No. 201711115349.X proposes a photo-induced deformation liquid crystal polymer film based on helicene molecules. The matrix system used is an acrylate system, and the synthesized helicene molecular motor needs to carry acrylate functional groups. Although polymers in the acrylate system have the advantages of easy polymerization reaction and relatively easy preparation of polymers, there are still some defects: First, the acrylate system is too rigid, resulting in a relatively slow deformation speed of the material; Second, the movement of the molecular motor is restricted by the polymer network, with a low movement rate and a small range of regulation of material properties; Third, the complex mode of deformation of the molecular motor liquid crystal polymer has not been achieved. Summary of the Invention

[0004] Based on this, the present invention provides a light-responsive multi-mode deformation polyurethane liquid crystal elastomer based on a helicene molecular motor, a preparation method thereof, and an application thereof. By introducing a hydroxyl-functionalized helicene molecular motor into the polyurethane liquid crystal elastomer network, the prepared elastomer has variable-speed light-responsive curling, uncoiling, and shrinking characteristics, and its deformation mode and deformation speed can be adjusted by the ultraviolet light intensity and the initial shape. The prepared polyurethane liquid crystal elastomer can realize the functions of various light-controlled driving devices without further processing. This material is expected to further improve the performance of light-controlled intelligent materials and has great research potential in the fields of sensors and light-controlled robots, etc.

[0005] To achieve the above object, the present invention provides a preparation method of a light-responsive multi-mode deformation polyurethane liquid crystal elastomer based on a helicene molecular motor, which includes the following steps:

[0006] 1) Dissolve liquid crystal monomers, isocyanate monomers, crosslinking agents, thermal initiators and helicene molecular motors in an ultra-dry solvent, heat and stir to react to obtain a prepolymer solution;

[0007] 2) Pour the prepolymer solution in step 1) into a mold with a thickness of 0.5 - 5 mm;

[0008] 3) Put the mold in step 2) into a vacuum oven for gradient drying and thermal polymerization to obtain a polyurethane liquid crystal elastomer;

[0009] Among them: the liquid crystal monomer contains a liquid crystal moiety, has a hydroxyl functional group at the end, and the whole molecule exhibits liquid crystal properties; the isocyanate monomer contains at least two isocyanate functional groups; the crosslinking agent is a monomer containing three hydroxyl groups or three isocyanate groups; the helicene molecular motor has a stator-rotor structure and has a hydroxyl substituent; the thermal initiator is used to initiate the polymerization reaction between the hydroxyl group and the isocyanate group.

[0010] As a further preferred technical solution of the present invention, the thermal initiator added in step 1) is dibutyltin dilaurate, but is not limited to this material, and all materials that can initiate the polymerization of the hydroxyl group and the isocyanate group under heating conditions are included; based on the total mass percentage of the thermal initiator, the monomer containing a hydroxyl functional group and the monomer containing an isocyanate functional group being 100%, the mass percentage of the thermal initiator is 0.1% - 0.5%.

[0011] As a further preferred technical solution of the present invention, the mold containing the prepolymer solution is subjected to gradient drying in a vacuum oven to achieve thermal polymerization, the temperature range is 50 - 100 °C, and the polymerization time is 1 - 48 h.

[0012] As a further preferred technical solution of the present invention, the helicene molecular motor in step 1) is selected from one or more of the compounds shown in the following formula (1):

[0013]

[0014] Among them, R1 - R8 are independently selected from H or any one of the groups in formula (2) - (12), and at least one of R1 - R8 is selected from any one of the groups in formula (9) - (12), and n in formula (2) - (12) is an integer between 0 and 20; X is selected from any one of the groups in formula (13) - (16); y is 0 or 1; m is 0 or 1.

[0015] As a further preferred technical solution of the present invention, the liquid crystal monomers used in step 1) include both single-hydroxyl functional group monomers and double-hydroxyl functional group monomers. The following formula (17) - (22) are the liquid crystal monomers listed in the present invention, but are not limited to these materials:

[0016]

[0017] Among them, R is selected from any one of the groups represented by formulas (23)-(26), and n is a positive integer from 1 to 12:

[0018]

[0019] As a further preferred technical solution of the present invention, the isocyanate monomer used in step 1) is the isocyanate monomer listed in the following formulas (27)-(31) in the present invention, but is not limited to these materials, and includes all monomers containing at least two isocyanate functional groups. According to previous studies, polyurethane refers to a class of polymers with a main chain containing -NHCOO- repeating structural units, which are polymerized from isocyanates (monomers) and hydroxyl compounds. The synthesis reaction formula of polyurethane is: -N=C=O + HO- → -NH-COO-. Polyols with end groups (such as polyesters, polyethers, and other polyols) react with polyisocyanates to form polyurethane polymers, which is the most basic reaction for synthesizing polyurethanes. Therefore, in addition to the several isocyanate-containing monomers listed below in the present invention, all monomers containing isocyanate functional groups meet the preparation requirements of polyurethane materials.

[0020]

[0021] As a further preferred technical solution of the present invention, the crosslinking agent used in step 1) is a monomer containing three isocyanate functional groups or three hydroxyl functional groups. The following formulas (32)-(37) are the crosslinking agents listed in the present invention, but are not limited to these materials. According to the general reaction formula for synthesizing polyurethane, all monomers containing three isocyanate functional groups or three hydroxyl functional groups can be used as the crosslinking agent in the present invention:

[0022]

[0023] As a further preferred technical solution of the present invention, a chain extender is further added in step 1). The chain extender is PEG400, which is used to provide flexibility for the polyurethane liquid crystal elastomer.

[0024] As a further preferred technical solution of the present invention, the specific operations in step 1) include:

[0025] First, dissolve liquid crystal monomers, crosslinking agents, and helicene molecular motors in an ultra-dry N,N-dimethylformamide solvent, heat and stir under nitrogen protection, where the mass percentage of helicene molecular motors in the monomers containing hydroxyl functional groups is 1%-5%; then add isocyanate monomers and thermal initiators, where the mass percentage of monomers containing hydroxyl functional groups and monomers containing isocyanate functional groups is 50.5% / 49.5% - 50.1% / 49.9%, with the total mass fraction of the thermal initiator, monomers containing hydroxyl functional groups, and monomers containing isocyanate functional groups being 100%. The monomers containing hydroxyl functional groups refer to the monomers containing three hydroxyl groups in the liquid crystal monomers and crosslinking agents, and the monomers containing isocyanate functional groups refer to the monomers containing three isocyanate groups in the isocyanate monomers and crosslinking agents.

[0026] According to another aspect of the present invention, the present invention also provides a photo-responsive multi-mode deformation polyurethane liquid crystal elastomer based on helicene molecular motors, which is prepared by the preparation method of the photo-responsive multi-mode deformation polyurethane liquid crystal elastomer based on helicene molecular motors described above.

[0027] According to another aspect of the present invention, the present invention also provides an application of a photo-responsive multi-mode deformation polyurethane liquid crystal elastomer based on helicene molecular motors, preparing the polyurethane liquid crystal elastomer into a photo-induced deformation device, such as a biomimetic dehelicization motion device, a robotic gripper, or an artificial muscle.

[0028] In the present invention, a hydroxyl-functionalized helicene molecular motor with photo-responsive characteristics is introduced into the polyurethane liquid crystal polymer system to form a liquid crystal polymer film that can undergo photo-controlled deformation. The added helicene molecular motor can undergo cis-trans isomerization under ultraviolet light excitation and return to the initial configuration after the ultraviolet light is removed. The hydroxyl functional groups introduced on the molecule enable it to participate in the polymerization reaction and become crosslinking points in the polyurethane liquid crystal polymer. The dynamic isomerization of the helicene molecular motor makes the polymer chain segments move more easily, thereby reducing the glass transition temperature of the material and causing a decrease in the elastic modulus. At the same time, the material has an uneven density gradient in the thickness direction. Therefore, the weak photothermal effect, combined with the significant reduction in modulus caused by the isomerization of the molecular motor, causes the material to deform and bend towards the side with a lower elastic modulus. This mechanism can explain different modes of deformation. At low light intensities, the modulus reduction and photothermal effect are not significant, and at high light intensities, the modulus reduction and photothermal effect are significant. Therefore, devices with different deformation amplitudes and speeds can be prepared.

[0029] The present invention synthesizes a photo-responsive multi-mode deformation polyurethane liquid crystal elastomer based on a helicene molecular motor, which is expected to prepare a photo-driven material with excellent performance. It is beneficial to combine the advantages of helicene molecules such as rapid photo-response, large deformation, and non-toxicity with the existing photo-induced deformation polyurethane liquid crystal materials. The prepared polyurethane liquid crystal polymer film has the characteristics of multi-model deformation under ultraviolet light irradiation. Its deformation characteristics include bending, helical unwinding motion, and shrinkage energy release. The deformation mode and deformation speed can be determined by the ultraviolet light irradiation intensity and the initial state of the film. The initial state of the film also depends on the intrinsic shape memory characteristics of the polyurethane system. The prepared polyurethane liquid crystal elastomer has broad application prospects in the research and development of new intelligent materials and the manufacture of artificial muscles, etc.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1) The present invention utilizes the advantages of helicene molecules being non-toxic and having a relatively large deformation. The photo-responsive multi-mode deformation polyurethane liquid crystal elastomer based on helicene molecular motors requires a lower doping concentration to achieve a large-scale curling deformation compared to the current azobenzene photo-induced deformation liquid crystal polymer materials. Therefore, it has less impact on the properties of the liquid crystal polymer material itself, such as strength and toughness.

[0032] 2) The present invention utilizes the characteristic of helicene molecules having chiral inversion, which can achieve the change between left-handed and right-handed under ultraviolet light excitation. Therefore, the prepared polyurethane liquid crystal elastomer not only has photo-induced deformation characteristics but also can play an important role in the fields of selective reflection, broadband reflection, and photochromism of cholesteric liquid crystals.

[0033] 3) The polyurethane liquid crystal elastomer of the present invention has a unique photo-induced curling behavior. The prepared liquid crystal polymer film can realize the functions of various light-controlled driving devices without further processing and has great research potential in the fields of intelligent materials and light-controlled robots, etc.

[0034] 4) The film formed by stretching and orientation of the polyurethane liquid crystal elastomer of the present invention has a good shape memory effect. The initial shape is not only a long strip, but also the initial shape of the film can be controlled to be a spiral, a rectangle, or an arch shape, etc. Furthermore, under light driving, the device containing this film can not only achieve bending motion, but also achieve helical unwinding motion and rapid shrinkage energy release motion, that is, a complex motion mode of the molecular motor liquid crystal polymer is realized.

[0035] 5) The film formed by stretching and orientation of the polyurethane liquid crystal elastomer of the present invention has a deformable rate that can be regulated. By controlling the ultraviolet light intensity, the device containing this film can deform slowly or rapidly, and the deformation amplitude of the material can also be controlled, truly realizing the complex and adjustable multi-mode deformation of the molecular motor liquid crystal polymer. Description of the Drawings

[0036] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0037] Figure 1 For the bending deformation of the stretched and oriented film under ultraviolet light irradiation of 11 mW / cm². -2

[0038] Figure 2 For the bending deformation of the stretched and oriented film under ultraviolet light irradiation of 100 mW / cm². -2

[0039] Figure 3 For the process of the helical film undergoing a de - helical motion under ultraviolet light irradiation.

[0040] Figure 4 The energy release motion of the film under ultraviolet light control.

[0041] The realization of the object, functional features, and advantages of the present invention will be further described in conjunction with the embodiments with reference to the accompanying drawings. Specific Embodiments

[0042] The following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining and illustrating the present invention, and are not used to limit the present invention.

[0043] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0044] Example 1

[0045] This example presents a synthesis method for a liquid crystal monomer (M1) containing a hydroxyl functional group with the following structural formula:

[0046]

[0047] Dissolve 4 - hydroxybenzoic acid 4 - hydroxyphenyl ester (5 g, 21.72 mmol), hexabromohexanol (7.96 g, 44 mmol), potassium carbonate (27 g, 195.48 mmol), and potassium iodide (0.6 g, 0.724 mmol) in acetone. The turbid solution is heated and stirred to 60 °C under a nitrogen atmosphere and stirred for eight hours. After the reaction is completed, the mixture is filtered under reduced pressure, and the filtrate is rotary evaporated. The crude product is purified by column chromatography separation. The eluent ratio is petroleum ether:ethyl acetate = 2:1. The obtained crude M1 product is a white powder with a yield of approximately 48.4%.

[0048] Example 2

[0049] This example presents a synthesis method of a hydroxyl-containing crosslinkable molecular motor (MM-OH) with the following structural formula:

[0050]

[0051] Step 1: Dissolve 10 g of monomethoxynaphthalene in 200 ml of polyphosphoric acid in a flask, heat to 50 °C and stir mechanically. Gradually add 10 g of methacrylic acid and stir mechanically for 8 h. Then cool the reaction solution to room temperature with ice cubes, extract with dichloromethane, wash twice with saturated sodium bicarbonate aqueous solution and deionized water respectively, separate the aqueous layer by liquid separation, absorb the residual water with anhydrous magnesium sulfate, distill off the solvent under reduced pressure, and then purify by column chromatography. The eluent is a mixed solvent of ethyl acetate and petroleum ether at a ratio of 1:5. Rotate and evaporate under reduced pressure to remove the solvent to obtain 7.2 g of white powder with a yield of 67%.

[0052] Step 2: Dissolve the product from Step 1 (5 g, 22.095 mmol) in toluene solvent, heat to 90 °C, add AlCl3 (4.4 g, 22 mmol), and continue the reaction for five hours. Add water to the reactant, extract with ethyl acetate, wash the organic layer three times with 0.5 M hydrochloric acid solution and aqueous solution, and then dry the solution with anhydrous magnesium sulfate. Rotate and evaporate to remove the solvent, and purify the crude product by column chromatography with silica gel. Petroleum ether:ethyl acetate = 2:1 to obtain an orange-yellow solid (1.2 g, 51% yield).

[0053] Step 3: Dissolve the product from Step 2 (2 g, 9.45 mmol) and K2CO3 (1.46 g, 10.5 mmol) in N,N-dimethylformamide, heat to 50 °C, add tert-butyl chloroacetate, then raise the temperature to 80 °C and react for 5 hours. Cool the reaction solution to room temperature, then rotate and evaporate to extract the crude product, and purify it by column chromatography. The ratio of petroleum ether:ethyl acetate is 5:2, and the product is a yellow solid (3.1 g, 82%).

[0054] Step 4: Dissolve the product from Step 3 (50 mg, 0.15 mmol) in tetrahydrofuran solvent, add Lawesson's reagent, heat the reactant to 50 °C and react for 5 h. Rotate and evaporate, take the crude product, and purify it by column chromatography with silica gel. Petroleum ether:ethyl acetate = 10:1, and the product is a purple-red solid (40 mg, 78%).

[0055] Step 5: Dissolve the product from Step 4 (540 mg, 1.58 mmol) in toluene solution, then add azide compound and triphenylphosphine. The solvent is stirred at room temperature for 3 h, and then heated to reflux for 13 h. The reaction intermediate is rotary evaporated under reduced pressure and then redissolved in diethyl ether solvent (25 ml). Add methyl iodide (0.3 ml) and stir at room temperature for 12 h to produce a white precipitate. Filter the reactant by suction and rotary evaporate to concentrate. Purify the crude product by column chromatography. The eluent ratio is petroleum ether:ethyl acetate = 2:1. The product is a yellow solid with a yield of 52%.

[0056] Step 6: Dissolve the product from Step 5 (1 g, 2 mmol) in tetrahydrofuran solvent. Place the reaction device in an ice-water bath and slowly add LiAlH4 (700 mg, 18.4 mmol). Stir at 0 °C for 5 h. After the reaction is completed, quench the reaction solution with excessive Na2SO4·10H2O. Then place the reactant at room temperature, filter off the solid by suction, and rinse it several times with ethyl acetate solvent. Take the filtrate and rotary evaporate under reduced pressure. Purify the obtained concentrate by column chromatography. The eluent ratio is petroleum ether:ethyl acetate = 2:1. The product MM-OH is a yellow solid with a yield of 58.8%.

[0057] Example 3

[0058] This example presents a preparation method of a photo-responsive multi-mode deformable polyurethane liquid crystal elastomer based on a helicene molecular motor. The materials used to prepare the polyurethane liquid crystal elastomer are as follows:

[0059]

[0060] Among them, M1 is a liquid crystal monomer containing a hydroxyl functional group, MDI is an isocyanate monomer containing an isocyanate functional group, PEG400 is a chain extender, TMP is a crosslinking agent, MM-OH is a helicene molecular motor, and DBTL is a thermal initiator.

[0061] The specific preparation process of the polyurethane liquid crystal elastomer is as follows: Dissolve the liquid crystal monomer M1 (735 mg, 1.70 mmol), PEG400 (400 mg, 0.67 mmol), crosslinking agent TMP (6.7 mg, 0.05 mmol) and helicene molecular motor MM-OH (26 mg, 0.05 mmol) in 3 ml of ultra-dry N,N-dimethylformamide solvent, heat to 80 °C and stir under a nitrogen atmosphere. Subsequently, add the isocyanate monomer MDI (738 mg, 1.70 mmol) and thermal initiator DBTL (9.4 mg, 15 mmol), and continue heating and stirring for 5 h. After the reaction is completed, pour the mixture into a polytetrafluoroethylene mold with a thickness of 2 mm, place it in a vacuum oven at 60 °C and dry for 5 h, then raise the temperature to 100 °C and dry for 20 h. Finally, a thin film of the polyurethane liquid crystal elastomer is obtained.

[0062] Example 4

[0063] This example presents the application of the thin film of the polyurethane liquid crystal elastomer prepared according to Example 3.

[0064] Place the thin film above the glass transition temperature point and stretch it to 150% of its original length, so that the thin film has orientation along the stretching direction. Irradiate the upper surface of the thin film with ultraviolet light of 11 mW cm -2 . It is found that the thin film bends away from the light source; when the ultraviolet light irradiates the lower surface of the thin film, the thin film bends towards the light source, with a smaller bending amplitude and a longer time taken for deformation. The bending process is as Figure 1 shown. Further, increase the intensity of ultraviolet light irradiation to 100 mW cm -2 , and irradiate the upper and lower surfaces of the thin film respectively. It is found that the thin film can undergo a large degree of bending deformation in a shorter time. The deformation is as Figure 2 shown. Further, stretch the thin film at a high temperature and fix it on a circular metal rod in a spiral shape under an external force. Keep the external force and lower the temperature to room temperature. The thin film presents a spiral shape. Continuously irradiate the edge part of the thin film with ultraviolet light. The thin film undergoes a de-spiraling movement. The thin film wound around the metal rod in a spiral shape gradually unwinds and finally falls off the metal rod, as Figure 3 shown. Further explore the instantaneous energy release movement of the thin film. When the thin film is in a stretched state, energy is stored inside the thin film. It can undergo rapid contraction and bending movements within 0.4 s under ultraviolet light irradiation to achieve energy release, as Figure 4 shown. In such a process of controlling the energy release of the thin film by ultraviolet light, by controlling the intensity of ultraviolet light, the device containing this thin film can deform slowly or quickly, and the deformation amplitude of the material is also controllable. Thus, it is expected to apply such thin films in artificial muscles, such as forming robotic grippers or artificial muscles.

[0065] Example 5

[0066] The same preparation method as in Example 3 is adopted, and the only difference lies in the different structural combinations of the materials. The specific materials are as follows:

[0067]

[0068] The film of the polyurethane liquid crystal elastomer prepared by using the above material combination is made into a practical device, and its performance is tested. The effects are as follows:

[0069] The film is placed above the glass transition temperature point and stretched to 150%-200% of its original length. The film has an orientation along the stretching direction. The upper surface of the film is irradiated with ultraviolet light of 11 mW / cm -2 . It is found that the film bends away from the light source; when the lower surface of the film is irradiated with ultraviolet light, the film tends to bend towards the light source, with a smaller bending amplitude and a longer time taken for deformation, realizing a slow and small-amplitude deformation of the film. When the intensity of the ultraviolet light irradiation is increased to 100 mW / cm -2 and above, and the upper and lower surfaces of the film are irradiated respectively, it is found that the film can quickly undergo a large degree of bending deformation. The film is stretched at a high temperature and fixed in a spiral shape on a circular metal rod under an external force. Keeping the external force, the temperature is lowered to room temperature. The film presents a spiral shape. When the edge part of the film is continuously irradiated with ultraviolet light, the film undergoes a de-spiraling movement, and the film wound around the metal rod in a spiral shape gradually unwinds and finally falls off the metal rod. Further, the instantaneous energy release movement of the film is explored. When the film is in a stretched state, energy is stored inside the film, and it can undergo a rapid contraction and bending movement within 0.7 s under ultraviolet light irradiation, realizing the release of energy. Such a process of controlling the energy release of the film by ultraviolet light is expected to be applied to such films in artificial muscles.

[0070] Example 6

[0071] The same preparation method as in Example 3 is adopted, and the only difference lies in the different structural combinations of the materials. The specific materials are as follows:

[0072]

[0073] The film of the polyurethane liquid crystal elastomer prepared by using the above material combination is made into a practical device, and similar deformation effects to those in Examples 4 and 5 above can be obtained. The film is stretched to 150%-200% of its original length, so that the film has an orientation along the stretching direction. The upper / lower surface of the film is irradiated with ultraviolet light of 11 mW / cm -2 . It is found that the film bends away from / towards the light source. In this case, the film deforms slowly with a smaller deformation amplitude. When the intensity of the ultraviolet light irradiation is increased to 100 mW / cm-2 When irradiating the upper and lower surfaces of the film respectively at and above a certain intensity, it is found that the film can quickly undergo a large degree of bending deformation. Utilizing the shape memory effect of the film, the film is stretched and fixed in a helical shape at a high temperature. When the film wound around a metal rod is continuously irradiated with ultraviolet light, the film can undergo a dehelicization motion, gradually unwind and finally fall off the metal rod. Continuing to explore the instantaneous energy release motion of the film, when the film is in a stretched state, energy is accumulated inside the film, and it can achieve a rapid contraction and bending motion within just 0.9 s under ultraviolet light irradiation, realizing the release of energy.

[0074] To further prove that the qualified materials in the present invention can all meet the technical problems of the present invention application, the structures of the qualified materials are listed as follows. Since there are relatively many structures corresponding to each material and it is impossible to list them one by one, and according to the reaction general formula for synthesizing polyurethane materials, -N=C=O + HO- → -NH-COO-, polyols with end groups (such as polyesters, polyethers, and other polyols) react with polyisocyanates to form polyurethane polymers. The materials for preparing polyurethane liquid crystal elastomers need to meet the following principles:

[0075] The choice of liquid crystal monomer is that it contains a liquid crystal unit in the middle and a hydroxyl functional group at the end, and the whole molecule exhibits liquid crystal properties; the helicene molecular motor has a typical stator-rotor structure, with a hydroxyl substituent, can be cross-linked into the polyurethane system, and at least one of the groups R1-R8 in its structural formula is selected from any one of formulas (9)-(12); the isocyanate monomer needs to contain at least two isocyanate functional groups; the cross-linking agent is a monomer containing three hydroxyl groups or three isocyanate groups. According to the reaction general formula for synthesizing polyurethane, it can be polymerized only by isocyanate monomers or hydroxyl-containing compounds, so monomers containing three isocyanate functional groups or three hydroxyl functional groups can both be used as cross-linking agents.

[0076] It should be noted here that when a monomer containing three isocyanate groups is selected, this monomer can be used both as an isocyanate monomer and as a cross-linking agent. That is to say, when selecting materials, a cross-linking agent containing three isocyanate groups can also be used to replace the isocyanate monomer. Therefore, in actual material selection, only the dosage of the monomer needs to be determined according to the following principle. Taking the total mass fraction of the thermal initiator, the monomer containing a hydroxyl functional group, and the monomer containing an isocyanate functional group as 100%, the mass percentages of the monomer containing a hydroxyl functional group and the monomer containing an isocyanate functional group are 50.5% / 49.5% - 50.1% / 49.9%.

[0077] Example 7

[0078] On the basis of Example 6, the same preparation method is adopted, with the only difference being the different structures of the helicene molecular motors. At least one of the groups in R1-R8 of the helicene molecular motors is selected from any one of the groups in Formula (9)-(12). The film of the polyurethane liquid crystal elastomer prepared using this material combination is made into a practical device, and a deformation effect similar to that of Examples 4, 5, and 6 above can be obtained. Specifically, the prepared polyurethane liquid crystal elastomer is stretched and oriented above the glass transition temperature to form a film oriented along the stretching direction. The film is irradiated with ultraviolet light at 365 nm, and the film can produce local deformation and accumulate into a bending deformation. When the upper surface or the lower surface of the film is irradiated with ultraviolet light respectively, the bending direction of the film always faces the lower surface side. By changing the intensity of the ultraviolet light irradiation, due to different photothermal effects generated, the amplitude and speed of the bending deformation of the film can be adjusted. With the aid of the shape memory effect of the polyurethane system, films with different initial shapes can be prepared, enabling the realization of the biomimetic film's dehelicization movement, and with the aid of the significant photothermal effect of the film, the instantaneous energy release of the film under ultraviolet light control can be achieved.

[0079] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only examples, and various changes or modifications can be made to this embodiment without departing from the principles and essence of the present invention. The protection scope of the present invention is only defined by the appended claims.

Claims

1. A preparation method of a light-responsive multi-mode deformation polyurethane liquid crystal elastomer based on a helicene molecular motor, characterized in that, It includes the following steps: 1) Mix and dissolve liquid crystal monomers, isocyanate monomers, crosslinking agents, thermal initiators and helicene molecular motors in an ultra-dry solvent, and heat and stir for reaction to obtain a prepolymer solution; 2) Pour the prepolymer solution obtained in step 1) into a mold with a thickness of 0.5 - 5 mm; 3) Place the mold obtained in step 2) into a vacuum oven for gradient drying and thermal polymerization to obtain a polyurethane liquid crystal elastomer; Wherein: the liquid crystal monomer contains a liquid crystal unit, has a hydroxyl functional group at the end, and the whole molecule exhibits liquid crystal properties; the isocyanate monomer contains at least two isocyanate functional groups; the crosslinking agent is a monomer containing three hydroxyl groups or three isocyanate groups; the helicene molecular motor has a stator-rotor structure and has a hydroxyl substituent; the thermal initiator is used to initiate the polymerization reaction between the hydroxyl group and the isocyanate group; The helicene molecular motor is selected from one or more of the compounds shown in the following formula (1): ； ； Wherein, R1 - R8 are independently selected from H or any one of the groups in formula (2) - (12), and at least one of R1 - R8 is selected from any one of the groups in formula (9) - (12), and n in formula (2) - (12) is an integer between 0 - 20; X is selected from any one of the groups in formula (13) - (16); y is 0 or 1; m is 0 or 1.

2. The preparation method of the photo-responsive multi-mode deformation polyurethane liquid crystal elastomer based on helicene molecular motor according to claim 1, wherein, The liquid crystal monomer in step 1) is selected from one or more of the compounds shown in the following formula (17) - (22): ； Wherein, R is selected from any one of the groups shown in formula (23) - (26), and n is a positive integer from 1 to 12: 。 3. The preparation method of the photo-responsive multi-mode deformable polyurethane liquid crystal elastomer based on hexahelicene molecular motor according to claim 1, characterized in that, The isocyanate monomer in step 1) is selected from one or more of the compounds shown in the following formula (27) - (31): 。 4. The preparation method of the photo-responsive multi-mode deformable polyurethane liquid crystal elastomer based on heliene molecular motor according to claim 1, wherein, The crosslinking agent in step 1) is selected from one or more of the compounds shown in the following formula (32) - (37): 。 5. The preparation method of the photo-responsive multi-mode deformable polyurethane liquid crystal elastomer based on the helicene-based molecular motor according to claim 1, characterized in that, The thermal initiator in step 1) is dibutyltin dilaurate.

6. The preparation method of the photo-responsive multi-mode deformable polyurethane liquid crystal elastomer based on helicene molecular motor according to claim 1, wherein, A chain extender is also added in step 1), and the chain extender is PEG 400.

7. The preparation method of the photo-responsive multi-mode deformable polyurethane liquid crystal elastomer based on heliene molecular motor according to any one of claims 1-6, characterized in that, Step 1) specifically includes: Dissolve the liquid crystal monomer, crosslinking agent and helicene molecular motor in an ultra-dry N,N-dimethylformamide solvent, heat and stir under nitrogen protection, wherein the mass percentage of the helicene molecular motor in the monomers containing hydroxyl functional groups is 1% - 5%; then add the monomers containing isocyanate functional groups and the thermal initiator, wherein based on the total mass fraction of the thermal initiator, monomers containing hydroxyl functional groups, and monomers containing isocyanate functional groups being 100%, the mass percentage of the monomers containing hydroxyl functional groups and the monomers containing isocyanate functional groups is 50.5% / 49.5% - 50.1% / 49.9%; the monomers containing hydroxyl functional groups refer to the liquid crystal monomer and the monomer containing three hydroxyl groups in the crosslinking agent, and the monomers containing isocyanate functional groups refer to the isocyanate monomer and the monomer containing three isocyanate groups in the crosslinking agent.

8. A photo-responsive multi-mode deformable polyurethane liquid crystal elastomer based on a helicene-based molecular motor, characterized in that, It is prepared by the preparation method of the photo-responsive multi-mode deformation polyurethane liquid crystal elastomer based on helicene molecular motor according to any one of claims 1 - 7.

9. Use of the photo-responsive multi-mode deformation polyurethane liquid crystal elastomer based on helicene molecular motor according to claim 8, characterized in that, Prepare the polyurethane liquid crystal elastomer into a photo-induced deformation device.

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