High-toughness semi-interpenetrating network liquid crystal elastomer with low phase transition temperature, and preparation method and application thereof
By constructing a semi-interpenetrating network liquid crystal elastomer, the problems of weak mechanical properties and high phase transition temperature of traditional liquid crystal elastomers are solved, achieving low phase transition temperature and high toughness, which is suitable for fields such as flexible actuators and artificial muscles.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- PEKING UNIV
- Filing Date
- 2026-04-21
- Publication Date
- 2026-06-09
AI Technical Summary
Traditional liquid crystal elastomers have weak mechanical properties, insufficient tensile strength and actuation stress, and excessively high phase change driving temperature, which limits their application in fields such as flexible actuators and artificial muscles.
By employing a semi-interpenetrating network structure and crosslinking linear liquid crystal polyurethane with a liquid crystal polymer network, the ratio of liquid crystal polymerizable monomers and the use of chain extenders and crosslinking agents are controlled to construct a "rigid-flexible" network structure, achieving low phase transition temperature and high toughness.
It achieves large-strain reversible deformation under low-temperature stimulation, possesses excellent mechanical robustness and tear resistance, and outputs stable actuation stress, making it suitable for applications such as flexible actuators and artificial muscles.
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Figure CN122168017A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of new energy and new materials technology, specifically to a high-toughness semi-interpenetrating network liquid crystal elastomer with low phase transition temperature, its preparation method, and its application. Background Technology
[0002] Liquid crystal elastomers (LCEs) are a class of intelligent polymer materials that combine the anisotropy of liquid crystals with the hyperelasticity of cross-linked networks. Under stimuli such as heat and light, the internal liquid crystal units undergo a phase transition, driving reversible deformation of the macroscopic network. Based on this property, liquid crystal elastomers have great application potential in fields such as soft robotics, flexible sensors, and artificial muscles.
[0003] However, the intrinsic mechanical properties of traditional single-network liquid crystal elastomers are relatively weak, and their low tensile strength and actuation stress are insufficient to meet the requirements of practical high-load applications. To overcome this deficiency, existing technologies often employ reinforcement strategies that construct interpenetrating polymer networks (IPNs). For example, a second crosslinked polyurethane network is introduced into the system to significantly increase the crosslinking density, thereby improving the high-temperature tensile strength of the material above the phase transition temperature.
[0004] While fully interpenetrating polymer networks (MIPFs) significantly improve the absolute strength of materials, they also introduce noticeable negative effects: First, extremely poor toughness. The highly cross-linked dual-network structure results in an extremely dense and rigid three-dimensional structure, restricting the movement of polymer chain segments. Under stress, the polymer chains cannot effectively dissipate mechanical energy through slippage, making them highly susceptible to stress concentration and brittle fracture, leading to extremely low fatigue resistance. Second, excessively high actuation temperature. The dense cross-linking nodes and strong intermolecular forces significantly increase the phase transition energy barrier, resulting in a persistently high phase transition actuation temperature (Tni). This not only greatly increases actuation energy consumption but also severely limits its application in flexible actuators, artificial muscles, and flexible sensors.
[0005] Therefore, there is an urgent need to develop a liquid crystal elastomer with low phase transition temperature and high toughness. Summary of the Invention
[0006] This invention proposes a high-toughness semi-interpenetrating network liquid crystal elastomer with low phase transition temperature, its preparation method, and its application. This liquid crystal elastomer exhibits superior comprehensive mechanical properties and a low phase transition temperature, solving the problems of poor mechanical properties and excessively high driving temperature of traditional liquid crystal elastomers.
[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a high-toughness semi-interpenetrating network liquid crystal elastomer with a low phase transition temperature. The raw materials for preparing the semi-interpenetrating network liquid crystal elastomer include a liquid crystal polymer network system (System 1) and a linear liquid crystal polyurethane system (System 2), wherein: The liquid crystal polymer network system comprises: liquid crystal polymerizable monomers, dithiols, polythiols, photoinitiator benzoin dimethyl ether, and thermal catalyst dipropylamine; The linear liquid crystal polyurethane system comprises: 4,4-methylenebis(phenyl isocyanate), hydroxyl-containing liquid crystal monomer, polycaprolactone diol 2000 and catalyst dibutyltin dilaurate; The method for preparing this semi-interpenetrating network liquid crystal elastomer includes the following steps: Step 1: Polycaprolactone diol, 4,4-methylenebis(phenyl isocyanate), and dibutyl dilaurate catalyst are added to a reaction vessel and stirred at 50-70°C under an inert atmosphere to obtain a prepolymer; then, a hydroxyl-containing liquid crystal monomer is added to the prepolymer, and an appropriate amount of anhydrous liquid crystal monomer is used. N,N - Dimethylformamide (DMF) was completely dissolved and reacted under an inert atmosphere at 70-90°C with stirring to obtain a viscous mixture; the viscous mixture was precipitated with excess ice-cold methanol, the precipitated polymer solid was collected, washed, and vacuum dried to obtain pure linear liquid crystal polyurethane. Step 2: Using a mass ratio of linear liquid crystal polyurethane system to liquid crystal polymer network system of (0.2-2):1, combine the above-mentioned linear liquid crystal polyurethane with liquid crystal polymerizable monomers, dithiols, polythiols, photoinitiator benzoin dimethyl ether, and thermal catalyst dipropylamine. N,N Dimethylformamide (DMF) is fully dissolved and thoroughly stirred under light-protected conditions to obtain a uniform and transparent semi-interpenetrating network precursor solution. Step 3: Pour the above semi-interpenetrating network precursor solution into a mold, defoam it, and then dry it in a vacuum oven at 60-90℃ to obtain a thermally cross-linked polymer film. Step 4: Remove the polymer film from the mold, cut it into strips, stretch it to 1.5 to 3.5 times its original length on a constant temperature stretching device, and finally irradiate the polymer film with ultraviolet light while maintaining the tensile stress to obtain a semi-interpenetrating network liquid crystal elastomer with an oriented structure. The liquid crystal polymerizable monomer includes one or both of a first polymerizable monomer and a second polymerizable monomer; The first polymeric monomer possesses the chemical structure shown in formula (Ⅰ):
[0008] Equation (I) In equation (I), R1 and R2 are selected independently from each other. , , and One of the following structures, where m is any integer from 2 to 8 and n is any integer from 2 to 8; the ring X is independently selected from the following structures: , , ; The second polymeric monomer possesses the chemical structure shown in formula (Ⅱ):
[0009] Formula (II) In equation (II), R1 and R2 are selected independently from each other. , , and One of the following structures, where m is any integer from 2 to 8 and n is any integer from 2 to 8; the ring X is independently selected from the following structures: , ; The hydroxyl-containing liquid crystal monomer has the structure shown in formula (Ⅲ):
[0010] Formula (III) In equation (Ⅲ), m is any integer from 2 to 8, and n is any integer from 2 to 8; the ring X is independently selected from the following structures: , , , .
[0011] It should be noted that the wavy lines in the above structure represent the connecting bonds of the substituents.
[0012] In this invention, the ratio of the first polymerizable monomer and the second polymerizable monomer in system 1 is controlled, which effectively reduces the intrinsic energy barrier of the liquid crystal phase to isotropic phase transition. This is the core reason why the material of this invention undergoes macroscopic deformation at a low phase transition temperature (e.g., 40°C). Preferably, the molar ratio of the first polymerizable monomer and the second polymerizable monomer is 1:(0-4), for example, the molar ratio can be 1:0, 1:1, 1:2, 1:3, 1:4, etc., without limitation.
[0013] In this invention, dithiol acts as a chain extender, increasing the chain length of the polymer network through an addition reaction with the liquid crystal monomer, thereby increasing the tensile properties and flexibility of the polymer material.
[0014] In this invention, polythiols act as crosslinking agents, increasing the number of reaction sites to transform the polymer network from a linear network to a three-dimensional crosslinked network.
[0015] In this invention, the linear liquid crystal polyurethane in System 2 plays a crucial toughening role. In the semi-interpenetrating network, linear flexible polyurethane polymer chains are interwoven within the main network formed by System 1. When the material is subjected to external tensile forces or cyclic loading, these polymer chains can effectively dissipate mechanical energy through slippage and deentanglement, thereby significantly alleviating stress concentration and endowing the material with extremely high fracture toughness.
[0016] It should be noted that during the preparation process, the monomers in System 1 first undergo a thiol-Michael addition reaction with the thiol to form a preliminary elastomer network. During this process, the linear liquid crystal polyurethane in System 2 is in situ embedded, constructing a semi-interpenetrating network structure that combines rigidity and flexibility. Subsequently, after being mechanically stretched and oriented, ultraviolet light is used to initiate a further self-polymerization reaction of the remaining polymerizable double bonds in System 1. This orthogonal two-step crosslinking reaction synergistically optimizes the rigid constraint caused by the high density of traditional interpenetrating networks (IPNs).
[0017] As a further preferred embodiment of the present invention, the molar ratio of isocyanate in 4,4'-methylenebis(phenyl isocyanate) to the molar ratio of hydroxyl-containing liquid crystal monomer and hydroxyl groups in polycaprolactone diol 2000 is 1:1.
[0018] As a further preferred embodiment of the present invention, the dithiol is one or more of ethylenedithiol, di(mercaptoacetic acid)-1,4-butanediol, 2,2-(1,2-ethylenedioxy)bis(ethanediol), and ethylene glycol dimercaptoacetate; and / or, the polythiol is pentaerythritol tetra-3-mercaptopropionate or trimethylolpropane tris(3-mercaptopropionate).
[0019] As a further preferred embodiment of the present invention, the amount of photoinitiator is 0.1%-2% of the total mass of the liquid crystal polymerizable monomers; and / or, the amount of thermal catalyst is 1%-5% of the total mass of the liquid crystal polymerizable monomers.
[0020] As a further preferred embodiment of the present invention, the structure of the hydroxyl-containing liquid crystal monomer is shown in formula M1 below:
[0021] M1.
[0022] As a further preferred embodiment of the present invention, the amount of the catalyst dibutyltin dilaurate is 0.1%-1% of the total mass of 4,4-methylenebis(phenyl isocyanate), hydroxyl-containing liquid crystal monomer and polycaprolactone diol 2000.
[0023] According to a second aspect of the present invention, a semi-interpenetrating network liquid crystal elastomer is also provided, which is prepared by the above-described preparation method. The resulting elastomer has the ability to achieve large strain reversible deformation at a relatively low thermal stimulation temperature, while also possessing extremely high mechanical robustness and tear resistance.
[0024] According to a third aspect of the present invention, an application of a semi-interpenetrating network liquid crystal elastomer in flexible actuators, artificial muscles, and flexible sensors is also provided. Due to the low driving energy consumption and excellent workability of the semi-interpenetrating network liquid crystal elastomer, it can output stable, continuous actuating stress with high load-bearing capacity.
[0025] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) The semi-interpenetrating network liquid crystal elastomer prepared by the present invention has excellent strain capacity, exhibits excellent work capacity under thermal triggering, and can effectively dissipate mechanical energy under stress, exhibiting excellent toughness.
[0026] (2) The semi-interpenetrating network liquid crystal elastomer prepared by the present invention has a low phase transition temperature, which enables the material to undergo significant and reversible macroscopic anisotropic deformation at a low thermal stimulation temperature.
[0027] (3) The semi-interpenetrating network liquid crystal elastomer prepared by the present invention can output stable and continuous actuation stress, and has extremely high practical application value in cutting-edge fields such as flexible actuators, artificial muscles, and smart wearable devices. Attached Figure Description
[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0029] Figure 1 The Fourier transform infrared spectrum is shown for the low phase transition temperature, high toughness semi-interpenetrating network liquid crystal elastomer (SIPN1) prepared in this invention.
[0030] Figure 2 The tensile stress-strain comparison curves at room temperature are shown for the liquid crystal elastomers prepared in Example 1 (SIPN1), Example 3 (SIPN3) and Comparative Example 1 (pure LCE) of the present invention. Figure 3 Differential scanning calorimetry (DSC) curves of the low phase transition temperature, high toughness semi-interpenetrating network liquid crystal elastomer prepared in Example 1 (SIPN1) of the present invention; Figure 4 Differential scanning calorimetry (DSC) curves of the semi-interpenetrating network liquid crystal elastomer with altered liquid crystal monomer ratio prepared in Example 2 (SIPN2) of the present invention.
[0031] Figure 5This diagram illustrates the application of the low phase transition temperature, high toughness semi-interpenetrating network liquid crystal elastomer prepared in this invention in flexible actuators and biomimetic artificial muscles.
[0032] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0033] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.
[0034] 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 this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.
[0035] Example 1 This example provides a method for preparing a high-toughness semi-interpenetrating network liquid crystal elastomer SIPN1 with a low phase transition temperature. The raw materials for preparing the semi-interpenetrating network liquid crystal elastomer include a liquid crystal polymer network system and a linear liquid crystal polyurethane system. The liquid crystal polymer network system (system 1) comprises: a liquid crystal polymerizable monomer, a dithiol EDDET, a polythiol PETMP, a photoinitiator benzoin dimethyl ether, and a thermal catalyst dipropylamine; The linear liquid crystal polyurethane system (system 2) comprises: 4,4-methylenebis(phenyl isocyanate), hydroxyl-containing liquid crystal monomer, polycaprolactone diol 2000 and catalyst dibutyltin dilaurate; The specific preparation method is as follows: S101: Polycaprolactone diol (PCL-2000, 6.0 g, 3.0 mmol), 4,4'-methylenebis(phenyl isocyanate) (MDI, 3.0 g, 12.0 mmol), and dibutyl dilaurate catalyst were added sequentially to a flask. The mixture was evacuated and purged three times with high-purity nitrogen, maintaining a continuous nitrogen purging to preserve the inert atmosphere inside the flask. The reaction mixture was stirred at 50°C for 2.5 hours to obtain a prepolymer. Subsequently, the hydroxyl-containing liquid crystal monomer 4-((6-(acryloyloxy)hexyl)oxy)phenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate (3.89 g, 9.0 mmol) was added and completely dissolved in an appropriate amount of anhydrous N,N-dimethylformamide (DMF). The system temperature was then raised to 70°C under nitrogen purging, and the reaction was continued with constant temperature stirring for 4 hours. After 1 hour, a viscous mixture was obtained; the viscous mixture after reaction was slowly poured into an excess of ice-cold methanol for precipitation, the precipitated polymer solid was taken out, washed several times with pure water and methanol, and then placed in a vacuum drying oven at 80°C to dry to constant weight, to obtain pure linear liquid crystal polyurethane (LLCPU) for later use.
[0036] S102: The polymerizable liquid crystal monomer RM257 and C6BAPE were mixed according to the molar ratio in Table 1, wherein RM257 (353 mg, 0.6 mmol) and C6BAPE (323 mg, 0.6 mmol) were added, followed by the crosslinking agent pentaerythritol tetrakis(3-mercaptopropionic acid) (PETMP) (48 mg, 0.1 mmol), the chain extender 2,2'-(1,2-ethylenedioxydioxo)diethylthiol (EDDET) (145 mg, 0.8 mmol), and the photoinitiator Irgacure 651 (added at 1.0 wt% of the total monomer mass), dissolved in 10 ml. A solution was prepared in DMF, and the total molar ratio of thiol groups to acrylate double bonds in the system was controlled to be 1:1.2. Then, 0.86g of the prepared LLCPU was added to the solution (the mass ratio of the linear liquid crystal polyurethane system to the liquid crystal polymer network system was 1:1), and the mixture was stirred thoroughly at 25°C in the dark to obtain a uniform and transparent semi-interpenetrating network precursor solution. S103: Slowly pour the above precursor solution into the mold, place it on a horizontal operating table and wait for the air bubbles to disappear. Then, put it in a vacuum oven at 70°C and dry it for 24 hours to allow the LLCPU to be inserted in situ into the formed polymer network to form a polymer film. S104: Carefully remove the above thermally cross-linked polymer film from the mold, cut it into strips 30 mm long and 8 mm wide using a cutter, stretch it to 3.5 times its original length on a constant temperature stretching device, and then irradiate it with a 365 nm light source for 30 min while maintaining the stretching state to initiate the polymerization of the remaining double bond free radicals, completely lock the liquid crystal orientation, and obtain the target elastomer SIPN1 film.
[0037] Table 1. Formulations for preparing SIPN1 liquid crystal polymerizable monomers
[0038] Example 2 This example provides a method for preparing SIPN2, a high-toughness semi-interpenetrating network liquid crystal elastomer with a low phase transition temperature, including the following steps: S201: Same as step S101 in Example 1, to prepare a pure linear liquid crystal polyurethane for later use. S202: The only difference from Example 1 is that the polymerizable liquid crystal monomers are selected as RM82 and C6BAPE and mixed according to the molar ratio in Table 2. Then, in the same step as S102 in Example 1, the components of the linear liquid crystal polyurethane and liquid crystal polymer network system are fully dissolved and stirred in DMF to form a uniform and transparent semi-interpenetrating network precursor solution.
[0039] S203-S204: The steps are the same as those in S103-S104 of Example 1, and thermal crosslinking, cutting, 3.5 times stretching and ultraviolet irradiation are performed in sequence to obtain the elastomer SIPN2 film.
[0040] Table 2 Formulations for preparing SIPN2 liquid crystal polymerizable monomers
[0041] Example 3 This example provides a method for preparing SIPN3, a high-toughness semi-interpenetrating network liquid crystal elastomer with a low phase transition temperature, comprising the following steps: S301: Same as step S101 in Example 1, to prepare a pure linear liquid crystal polyurethane for later use. S302: Based on the same step as S102 in Example 1, the components of the linear liquid crystal polyurethane and liquid crystal polymer network system are fully dissolved in DMF and stirred to form a uniform and transparent semi-interpenetrating network precursor solution; the only difference in this step is that the mass doping ratio of the linear liquid crystal polyurethane system to the liquid crystal polymer network system is changed to 2:1. S303-S304: The steps are the same as those in S103-S104 of Example 1, and thermal crosslinking, cutting, 3.5 times stretching and ultraviolet irradiation are performed in sequence to obtain the elastomer SIPN3 film.
[0042] Comparative Example 1 This comparative example provides a method for preparing a pure liquid crystal elastomer (LCE) without a linear polyurethane system, comprising the following steps: S401: Without adding linear liquid crystal polyurethane, polymerizable liquid crystal monomer RM257 and C6BAPE are directly mixed according to the molar ratio in Table 1: RM257 (353 mg, 0.6 mmol) and C6BAPE (323 mg, 0.6 mmol). Then, the crosslinking agent pentaerythritol tetrakis(3-mercaptopropionic acid) ester (PETMP) (48 mg, 0.1 mmol), the chain extender 2,2'-(1,2-ethylenedioxydioxo)diethylthiol (EDDET) (145 mg, 0.8 mmol), and the photoinitiator Irgacure 651 (added at 1.0 wt% of the total monomer mass) are added and dissolved in DMF to prepare a liquid crystal polymer network system solution. The solution is mixed in the dark to obtain a pure liquid crystal polymer precursor solution. S402: Slowly pour the above precursor solution into a petri dish, place it on a horizontal operating table and wait for the air bubbles to disappear, then place it in a vacuum oven at 70°C for 24 hours to dry and form a pre-crosslinked film with certain mechanical properties. S403: Carefully remove the pre-crosslinked polymer film from the mold, cut it into strips 30 mm long and 8 mm wide using a cutter, stretch it to 3.5 times its original length on a constant temperature stretching device, and then irradiate it with a 365 nm light source for 30 min while maintaining the stretching state to initiate the polymerization of the remaining double bond free radicals, completely lock the liquid crystal orientation, and obtain the target elastomer film.
[0043] To fully illustrate the technical effects of the present invention, the thermomechanical properties and thermodynamic phase transition behavior of the thin films prepared in the embodiments and comparative examples are analyzed in conjunction with the accompanying drawings: according to Figure 1 Fourier transform infrared (FTIR) spectroscopy confirmed the successful construction of the SIPN1 crosslinking network. The monomer M before the reaction (containing the hydroxyl-containing liquid crystal monomer M1-OH, approximately 3530 cm⁻¹) was [missing information]. - ¹), RM257 (-C=C-, approximately 1643 cm) - ¹) and MDI (-N=C=O, approximately 2274 cm⁻¹) - The characteristic absorption peaks of ¹) completely disappeared after polymerization to form an interpenetrating liquid crystal elastomer, and a new peak NH (approximately 3430 cm⁻¹) appeared. -¹). This result confirms that the relevant monomers in the system have reacted completely and the cross-linked network has been successfully constructed.
[0044] according to Figure 2 The tensile stress-strain comparison curves show that, under tensile stress, the linear polyurethane flexible polymer chains interwoven in the main network can effectively dissipate mechanical energy through slippage and deentanglement. Example 1 (SIPN1) exhibits extremely high elongation at break and fracture strength, with a curve integral area (fracture toughness) as high as 76.5 MJ / m³. Comparative Example 1 (pure LCE), lacking the interpenetration and toughening effect of linear liquid crystal polyurethane, exhibits obvious intrinsic brittleness, fractures at minimal tensile strain, and has extremely low fracture toughness. Example 3 (SIPN3), while keeping the liquid crystal monomer types unchanged, altered the mass doping ratio of System 2 to System 1 (to 2:1), and its tensile curve shows a further increase in mechanical strength. This intuitively and powerfully demonstrates that the linear polyurethane network plays a decisive role in mechanical energy dissipation, and adjusting the interpenetration ratio allows for independent control of the material's toughness and strength.
[0045] The endothermic peak in differential scanning calorimetry (DSC) directly reflects the thermodynamic process of the transformation of liquid crystal units within the material from a nematic phase to an isotropic phase (Tni). According to... Figure 3 It can be seen that Example 1 (SIPN1) exhibits a significant phase transition endothermic peak in an extremely low temperature range, with a phase transition driving temperature (Tni) of 32°C. This demonstrates that this material overcomes the problem of excessively high driving temperatures in traditional high-strength liquid crystal elastomers, achieving mild thermal actuation within a safe physiological temperature range. According to... Figure 4 It can be seen that in Example 2 (SIPN2), after changing the polymerizable liquid crystal monomer, the phase transition endothermic peak on its DSC curve underwent a significant shift, and the phase transition temperature changed to 70°C. (Comparison) Figure 3 and Figure 4 The DSC test results prove that by precisely controlling the type and proportion of polymerizable liquid crystal monomers in system 1, the relative proportion of rigid units and flexible segments in the system can be effectively changed, thereby directly changing the intrinsic energy barrier of phase transition and realizing independent and precise control of the phase transition driving temperature.
[0046] Example 4 This example provides a test application of a high-toughness semi-interpenetrating network liquid crystal elastomer with a low phase transition temperature in flexible actuators and biomimetic artificial muscles.
[0047] The semi-interpenetrating network liquid crystal elastomer (SIPN1) film prepared in Example 1 was cut into strip-shaped samples (sample mass 7 mg). The upper end of the film sample was fixed, and a 105 g weight was suspended from the lower end. When thermal stimulation (heating) was applied to the film, the liquid crystal units inside the film underwent a phase transition, driving significant contraction of the macroscopic film, thereby overcoming gravity and lifting the weight. When the thermal stimulation was removed (cooling), the film reversibly returned to its initial length, and the weight subsequently decreased (see [link to relevant documentation]). Figure 5 (As shown).
[0048] according to Figure 5 As shown, a composite film with a mass of only 7 mg can stably and reversibly lift a load of up to 105 g using low-thermal stimulation triggering, achieving a load-to-weight ratio as high as 15,000 times. Calculations show that its maximum work capacity reaches 588 kJ / m³. This application example fully demonstrates that the semi-interpenetrating network liquid crystal elastomer prepared by this invention not only possesses excellent mechanical properties but also has extremely high energy density mechanical output capability, fully capable of meeting the actuation requirements under high loads, and has definite industrial application value in fields such as flexible actuators and artificial muscles.
[0049] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.
Claims
1. A method for preparing a high-toughness semi-interpenetrating network liquid crystal elastomer with a low phase transition temperature, characterized in that, The raw materials for preparing this semi-interpenetrating network liquid crystal elastomer include a liquid crystal polymer network system and a linear liquid crystal polyurethane system; The liquid crystal polymer network system comprises: a liquid crystal polymerizable monomer, a dithiol, a polythiol, a photoinitiator benzoin dimethyl ether, and a thermal catalyst dipropylamine; The linear liquid crystal polyurethane system comprises: 4,4-methylenebis(phenyl isocyanate), hydroxyl-containing liquid crystal monomer, polycaprolactone diol 2000 and catalyst dibutyltin dilaurate. The method for preparing this semi-interpenetrating network liquid crystal elastomer includes the following steps: Step 1: Polycaprolactone diol, 4,4-methylenebis(phenyl isocyanate), and dibutyl dilaurate catalyst are added to a reaction vessel and stirred at 50-70°C under an inert atmosphere to obtain a prepolymer; then, a hydroxyl-containing liquid crystal monomer is added to the prepolymer, and an appropriate amount of anhydrous liquid crystal monomer is used. N,N - Dimethylformamide (DMF) was completely dissolved and reacted under an inert atmosphere at 70-90°C with stirring to obtain a viscous mixture; the viscous mixture was precipitated with excess ice-cold methanol, the precipitated polymer solid was collected, washed, and vacuum dried to obtain pure linear liquid crystal polyurethane. Step 2: Using a mass ratio of linear liquid crystal polyurethane system to liquid crystal polymer network system of (0.2-2):1, combine the above-mentioned linear liquid crystal polyurethane with liquid crystal polymerizable monomers, dithiols, polythiols, photoinitiator benzoin dimethyl ether, and thermal catalyst dipropylamine. N,N Dimethylformamide (DMF) is fully dissolved and thoroughly stirred under light-protected conditions to obtain a uniform and transparent semi-interpenetrating network precursor solution. Step 3: Pour the above semi-interpenetrating network precursor solution into a mold, defoam it, and then dry it in a vacuum oven at 60-90℃ to obtain a thermally cross-linked polymer film. Step 4: Remove the polymer film from the mold, cut it into strips, stretch it to 1.5 to 3.5 times its original length on a constant temperature stretching device, and finally irradiate the polymer film with ultraviolet light while maintaining the tensile stress to obtain a semi-interpenetrating network liquid crystal elastomer with an oriented structure. The liquid crystal polymerizable monomer includes one or both of a first polymerizable monomer and a second polymerizable monomer; The first polymeric monomer possesses the chemical structure shown in formula (Ⅰ): Equation (I) In equation (I), R1 and R2 are selected independently from each other. , , and One of the following structures, where m is any integer from 2 to 8 and n is any integer from 2 to 8; the ring X is independently selected from the following structures: , , ； The second polymeric monomer possesses the chemical structure shown in formula (Ⅱ): Formula (II) In equation (II), R1 and R2 are selected independently from each other. , , and One of the following structures, where m is any integer from 2 to 8 and n is any integer from 2 to 8; the ring X is independently selected from the following structures: , ； The hydroxyl-containing liquid crystal monomer has the structure shown in formula (Ⅲ): Formula (III) In equation (Ⅲ), m is any integer from 2 to 8, and n is any integer from 2 to 8; the ring X is independently selected from the following structures: , ， , 。 2. The method for preparing a high-toughness semi-interpenetrating network liquid crystal elastomer with low phase transition temperature according to claim 1, characterized in that, The molar ratio of isocyanate in the 4,4'-methylenebis(phenyl isocyanate) to the molar ratio of hydroxyl-containing liquid crystal monomer and hydroxyl group in polycaprolactone diol 2000 is 1:
1.
3. The method for preparing a high-toughness semi-interpenetrating network liquid crystal elastomer with low phase transition temperature according to claim 1, characterized in that, The dithiol is one or more of ethylenedithiol, di(mercaptoacetic acid)-1,4-butanediol, 2,2-(1,2-ethylenedioxy)bis(ethanediol), and ethylene glycol dimercaptoacetate.
4. The method for preparing a high-toughness semi-interpenetrating network liquid crystal elastomer with low phase transition temperature according to claim 1, characterized in that, The polythiol is pentaerythritol tetra-3-mercaptopropionate or trimethylolpropane tri(3-mercaptopropionate).
5. The method for preparing a high-toughness semi-interpenetrating network liquid crystal elastomer with low phase transition temperature according to claim 1, characterized in that, The amount of photoinitiator used is 0.1%-2% of the total mass of the liquid crystal polymerizable monomer.
6. The method for preparing a high-toughness semi-interpenetrating network liquid crystal elastomer with low phase transition temperature according to claim 1, characterized in that, The amount of the thermal catalyst used is 1%-5% of the total mass of the liquid crystal polymerizable monomers.
7. The method for preparing a high-toughness semi-interpenetrating network liquid crystal elastomer with low phase transition temperature according to claim 1, characterized in that, The structure of the hydroxyl-containing liquid crystal monomer is shown below: 。 8. The method for preparing a high-toughness semi-interpenetrating network liquid crystal elastomer with low phase transition temperature according to claim 1, characterized in that, The catalyst, dibutyltin dilaurate, is used in an amount of 0.1%-1% of the total mass of 4,4'-methylenebis(phenyl isocyanate), hydroxyl-containing liquid crystal monomer, and polycaprolactone diol 2000.
9. A semi-interpenetrating network liquid crystal elastomer, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.
10. The application of the semi-interpenetrating network liquid crystal elastomer of claim 9 in flexible actuators, artificial muscles, and flexible sensors.