Liquid crystal oligomer and preparation method thereof, and liquid crystal elastomer and preparation method thereof

Abstract

The invention discloses a liquid crystal oligomer and a preparation method thereof, and a liquid crystal elastomer and a preparation method thereof, and the end group structure of the main chain of the liquid crystal oligomer is as shown in the formula I. Through molecular structure design, a thiocarbamate structure and a double-bond end-capped structure are introduced, the double-bond end-capped liquid crystal oligomer containing the thiocarbamate structure is provided, combination of ultraviolet light induced rapid curing and thermal reversible reconstruction of a network is achieved, and the stability of the liquid crystal oligomer containing the thiocarbamate structure is improved. The method can be used for constructing a photocuring liquid crystal elastomer with a reversible cross-linked network structure. Therefore, the liquid crystal elastomer provided by the invention not only has rapid processing and forming capability, but also has excellent dynamic performance, and reversible reconstruction and reprocessing can be realized through dynamic key exchange. Meanwhile, the energy dissipation capacity is remarkably improved through the introduction of the liquid crystal domain and the cooperation of a polythionocarbamate structure, so that the liquid crystal elastomer shows excellent performance in the application of impact protection and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of liquid crystal elastomers, and particularly relates to a liquid crystal oligomer and a preparation method thereof, and a liquid crystal elastomer and a preparation method thereof. BACKGROUND

[0002] Liquid crystal elastomers (LCEs) are a kind of intelligent response polymer materials with both liquid crystal order and rubber elasticity, which can produce large reversible deformation under external stimuli (such as heat, light, electricity, etc.), and are widely used in soft robots, intelligent actuators, artificial muscles and other frontier fields.

[0003] At present, the existing liquid crystal elastomers have deficiencies in rapid forming ability, dynamic adjustment performance, reworkability and impact protection performance, thereby limiting their practical application in the fields of flexible protection, wearable devices and intelligent structural materials in extreme environments. SUMMARY

[0004] The present application aims to at least solve one of the technical problems in the related art. To this end, the present application aims to provide a liquid crystal oligomer and a preparation method thereof, and a liquid crystal elastomer and a preparation method thereof. Through molecular structure design, the thio urethane structure and the double bond end-capping structure in the liquid crystal oligomer make the liquid crystal oligomer can be quickly cured and processed into a shape under the condition of ultraviolet light irradiation, and at the same time, a cross-linked network with thermal reversibility reworkability can be constructed, which can be applied to produce photo-curable liquid crystal elastomers. Thus, the liquid crystal elastomer provided by the present application not only has the ability of rapid processing and forming, but also has excellent thermal reversibility reworkability and impact protection performance.

[0005] The first aspect of the present application provides a liquid crystal oligomer. According to the embodiments of the present application, the end group structure of the main chain of the liquid crystal oligomer is shown as formula I;

[0006] The formula I is:

[0007] The liquid crystal oligomer of the above-mentioned embodiments of the present application, through molecular structure design, the thio urethane structure and the double bond end-capping structure in the liquid crystal oligomer make the liquid crystal oligomer can be quickly cured and processed into a shape under the condition of ultraviolet light irradiation, and at the same time, a cross-linked network with thermal reversibility reworkability can be constructed, which can be applied to produce photo-curable liquid crystal elastomers. Thus, the liquid crystal elastomer provided by the present application not only has the ability of rapid processing and forming, but also has excellent thermal reversibility reworkability and impact protection performance.

[0008] In addition, the liquid crystal oligomer according to the above-mentioned embodiments of the present application can also have the following additional technical features:

[0009] In some embodiments of the present application, the physicochemical property parameter of the liquid crystal oligomer includes: a number average molecular weight of 1350-17500 g / mol.

[0010] In some embodiments of the present application, the structural general formula of the liquid crystal oligomer is as follows:

[0011]

[0012] wherein R1 is a liquid crystal monomer with double-end acrylate double bonds, R2 is a chain extender with double-end mercapto groups, R3 is an alkyl structure, and R4 is -H or -CH3.

[0013] Alternatively, the chemical structural formula of the liquid crystal oligomer is as follows:

[0014]

[0015] wherein Ra:

[0016] Rb:

[0017] The second aspect of the present application provides a preparation method of the liquid crystal oligomer of the first aspect. According to an embodiment of the present application, the preparation method of the liquid crystal oligomer includes the following steps:

[0018] reacting the mercapto-terminated liquid crystal oligomer with a first compound to obtain the liquid crystal oligomer;

[0019] wherein the first compound contains a carbon-carbon double bond and an isocyanate group.

[0020] The preparation method of the liquid crystal oligomer according to the above embodiments of the present application introduces a thiocarbamic acid ester structure and a double bond end-capping structure by reacting a mercapto-terminated liquid crystal oligomer with a first compound that has both a carbon-carbon double bond and an isocyanate group, to obtain a double bond end-capped liquid crystal oligomer containing a thiocarbamic acid ester structure.

[0021] In addition, the preparation method of the liquid crystal oligomer according to the above embodiments of the present application can also have the following additional technical features:

[0022] In some embodiments of the present application, the molar ratio of the mercapto-terminated liquid crystal oligomer to the first compound is (0.5-1):(1-2);

[0023] And / or, the temperature of the first reaction is 25-35°C;

[0024] And / or, the time of the first reaction is 12-48 h.

[0025] In some embodiments of the present application, a catalyst is added to catalyze the first reaction, the catalyst includes at least one of tetramethylguanidine, 1,8-diazobis-spiro[5.4.0]undec-7-ene and 1,5-diazabicyclo[4.3.0]non-5-ene, and the catalyst is added in an amount of 0.05-0.2 wt% based on the total weight of the thiol-terminated liquid crystal oligomer and the first compound.

[0026] In some embodiments of the present application, the method for preparing the thiol-terminated liquid crystal oligomer includes the following steps:

[0027] carrying out a second reaction of the liquid crystal monomer and a second compound containing a thiol group to obtain the thiol-terminated liquid crystal oligomer; wherein the liquid crystal monomer includes a liquid crystal monomer terminated by an acrylate double bond structure, the second compound includes at least one of 2,2'-(1,2-ethanediyldioxy)bisethanethiol, ethylene glycol dimercaptoacetate, di(mercaptoacetic acid)-1,4-butanediol ester and bis(2-mercaptoethyl) ether, and the second reaction is carried out under conditions including a temperature of 25-40°C and a time of 18-36 h;

[0028] And / or, the first compound includes at least one of isocyanatoethyl methacrylate and isocyanate acrylate.

[0029] A third aspect of the present application provides a liquid crystal elastomer. According to embodiments of the present application, the liquid crystal elastomer contains a reversibly cross-linked network structure, the reversibly cross-linked network structure includes the liquid crystal oligomer of any one of the first aspect, and / or the liquid crystal oligomer prepared by the preparation method of any one of the second aspect.

[0030] The liquid crystal elastomer of the above embodiments of the present application. The liquid crystal elastomer is a photocurable polythiourethane liquid crystal elastomer, which contains a reversibly cross-linked network structure, the reversibly cross-linked network structure includes the liquid crystal oligomer of any one of the first aspect, and / or the liquid crystal oligomer prepared by the preparation method of any one of the second aspect. Thus, the liquid crystal elastomer provided by the present application not only has the ability of rapid processing and molding, but also has excellent thermal reversible reprocessing characteristics and impact protection performance.

[0031] A fourth aspect of the present application provides a preparation method of the liquid crystal elastomer of the above third aspect. According to embodiments of the present application, the preparation method of the liquid crystal elastomer includes:

[0032] carrying out a photocuring cross-linking reaction of the liquid crystal oligomer to obtain the liquid crystal elastomer.

[0033] The preparation method of the liquid crystal elastomer of the above embodiments of the present application. The preparation method is to perform a photocuring cross-linking reaction on the above-mentioned double bond-terminated liquid crystal oligomer containing a thiourethane structure. Not only the forming speed of the liquid crystal elastomer is fast, but also a liquid crystal elastomer with excellent thermal reversibility and reprocessing ability and excellent impact protection performance is successfully constructed, which can meet the practical application of the liquid crystal elastomer in the fields of flexible protection, wearable devices and intelligent structural materials in extreme environments.

[0034] In some embodiments of the present application, the weight addition amount of the photoinitiator is 0.5-1.5wt% of the weight of the liquid crystal oligomer;

[0035] And / or, the weight addition amount of the solvent is 1-5 times of the weight of the liquid crystal oligomer.

[0036] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter in the description of the application. BRIEF DESCRIPTION OF DRAWINGS

[0037] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the description of the embodiments, taken in conjunction with the following drawings in which:

[0038] Figure 1 The chemical structure schematic diagram of the main chain of the double bond-terminated liquid crystal oligomer containing a thiourethane structure in the present application;

[0039] Figure 2 The chemical structure schematic diagram of the main chain of the mercapto-terminated liquid crystal oligomer in the present application;

[0040] Figure 3 The synthetic route diagram of the preparation of the liquid crystal oligomer in Example 1 of the present application;

[0041] Figure 4 The synthetic route diagram of the preparation of the liquid crystal elastomer in Example 7 of the present application;

[0042] Figure 5 The nuclear magnetic resonance hydrogen spectrum obtained in Test Example 1 of the present application;

[0043] Figure 6 The thermal compression reprocessing experimental result diagram of the liquid crystal elastomer obtained in Example 7 of Test Example 2 of the present application;

[0044] Figure 7 The impact experimental result diagram of the liquid crystal elastomer obtained in Example 7 of Test Example 3 of the present application. DETAILED DESCRIPTION

[0045] Embodiments of the present application are described below in detail with reference to the accompanying drawings, examples of which are shown in the drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0046] The first aspect of the present application provides a liquid crystal oligomer. According to embodiments of the present application, the end group structure of the main chain of the liquid crystal oligomer is shown as formula I;

[0047] The formula I is:

[0048] At present, with the increasing demand for rapid prototyping and structural complexity, photopolymerization technology has gradually become an important means for building liquid crystal elastomers due to its high spatial resolution, fast response characteristics and good adaptability to complex structures. However, most of the existing photopolymerization liquid crystal elastomer systems adopt permanent crosslinking structure, which is difficult to realize reversible processing, structure reconstruction or damage repair after solidification and molding, which limits its application range to some extent.

[0049] In addition, polythiourethane liquid crystal elastomers, as a new type of material with unique properties, show great application potential in many fields. However, due to the particularity of the molecular structure, chemical properties and liquid crystal phase of polythiourethane liquid crystal elastomers, it is difficult to process them by photopolymerization technology.

[0050] The liquid crystal oligomer of the above-mentioned embodiments of the present application, the liquid crystal oligomer of the above-mentioned embodiments of the present application, through the design of the molecular structure, the thiourethane structure and the double bond end-capping structure in the liquid crystal oligomer, the liquid crystal oligomer can be quickly solidified and molded under the condition of ultraviolet light irradiation, and at the same time, it can also realize the construction of a crosslinking network with thermal reversibility and reprocessing characteristics, and can be applied to the production of photopolymerization type liquid crystal elastomers. Therefore, the liquid crystal elastomer provided by the present application not only has the ability of rapid processing and molding, but also has excellent thermal reversibility and reprocessing characteristics and impact protection performance.

[0051] Further, based on the above-mentioned liquid crystal oligomer, the present application develops a liquid crystal elastomer system with both photopolymerization rapid prototyping ability and polythiourethane dynamic adjustment ability, that is, by using the above-mentioned liquid crystal oligomer for photopolymerization crosslinking, a photopolymerization type liquid crystal elastomer with reversible crosslinking network structure is constructed. The liquid crystal elastomer not only has the ability of rapid processing and molding, but also can realize reversible reconstruction and reprocessing through the exchange of thiourethane dynamic bonds. At the same time, the introduction of liquid crystal domains and polythiourethane structure cooperatively significantly improves the energy dissipation capacity, so that the liquid crystal elastomer shows excellent performance in impact protection and other applications.

[0052] In the embodiments of the present application, oligomer refers to an oligomer formed by 2-20 repeating units connected by covalent bonds. Thus, liquid crystal oligomer refers to an oligomer containing mesogenic units (or liquid crystal units, such as including biphenyl or phenyl benzoate structures, etc.) in the main chain, which are structural units capable of promoting the formation of a liquid crystal state in the molecular structure, and can spontaneously form a liquid crystal phase under suitable external conditions. These mesogenic units can be rigid rod-like; can be discotic or disc-like; or more complex two-dimensional or even three-dimensional shapes, etc. Specifically, the chemical structure of the main chain of the above-mentioned liquid crystal oligomer of the present application can be as shown in Figure 1 The end groups at both ends of the main chain of the liquid crystal oligomer are structures shown in formula I, and the middle part of the end groups is a repeating unit segment, which includes mesogenic units (i.e. Figure 1 The middle blue oval part).

[0053] In the embodiments of the present application, in the above formula I, represents that the chemical bond on the end group of the liquid crystal oligomer is broken from here to the middle part "repeating unit segment" or the chemical bond on the end group of the liquid crystal oligomer is connected from here to the middle part "repeating unit segment".

[0054] In the embodiments of the present application, the above-mentioned thiourethane structure refers to "-NH-C(=O)-S-" in the end group; and the double bond end-capping structure refers to "-C=C-" in the end group.

[0055] In the embodiments of the present application, the above-mentioned "thermal reversible reprocessing property" refers to the property that the internal crosslinking network of the liquid crystal elastomer can realize network structure reorganization through reversible breaking-recombination of the thiourethane dynamic bond, without the need to destroy the integrity of the overall network.

[0056] In the embodiments of the present application, the above-mentioned "polythiourethane dynamic adjustment ability" can be understood as the reversible breaking and recombination of the thiourethane bond (-NH-C(=O)-S-) in the liquid crystal elastomer, such as when heated, etc. Through this dynamic covalent crosslinking (thiourethane bond), the material has the ability to be arbitrarily shaped when heated, to absorb energy and buffer when hit, and to recover after damage when heated.

[0057] In the embodiments of the present application, the above-mentioned "liquid crystal domain" refers to a region of liquid crystal molecules with the same arrangement structure.

[0058] In the embodiments of the present application, the "energy dissipation" refers to the process that the material converts mechanical energy into irreversible heat energy under the action of external force. Its essence is that the energy consumption units (such as molecular chain segment movement, bond rupture or phase transition) inside the material consume energy through viscous resistance or internal friction, reducing the transmission of energy to crack propagation. In the context of the present application, the approaches to improve "energy dissipation" include liquid crystal domain orientation dissipation (specifically, under the action of external force, the rod-shaped liquid crystal unit (such as biphenyl ester unit) rotates and deflects, breaks the smectic / nematic ordered phase, and consumes energy) and thioamino acid ester dynamic covalent bond sacrifice dissipation (specifically, under the action of external force, the thioamino acid ester bond breaks / recombines, and consumes energy).

[0059] According to still some specific embodiments of the present application, the liquid crystal oligomer according to the above embodiments of the present application can also have the following additional technical features:

[0060] In some embodiments of the present application, the physicochemical property parameters of the liquid crystal oligomer include: a number average molecular weight of 1350-17500 g / mol, for example, 1350 g / mol, 2200 g / mol, 3058 g / mol, 3912 g / mol, 5623 g / mol, 6478 g / mol, 7333 g / mol, 8188 g / mol, 9043 g / mol, 9898 g / mol, 10753 g / mol, 11609 g / mol, etc. The inventors have found that if the number average molecular weight of the liquid crystal oligomer is too small, the adverse effect is that the material is too hard and is not conducive to energy dissipation, and if the number average molecular weight is too large, the adverse effect is that the network structure integrity is reduced.

[0061] According to still some specific embodiments of the present application, the structure general formula of the liquid crystal oligomer is as follows:

[0062]

[0063] wherein R1 is a liquid crystal monomer with double-end acrylate double bond, R2 is a chain extender with double-end mercapto group, R3 is an alkyl structure, and R4 is -H or -CH3;

[0064] Alternatively, the chemical structure formula of the liquid crystal oligomer is as follows:

[0065]

[0066] wherein Ra:

[0067] Rb:

[0068] The second aspect of the present application provides a preparation method of the liquid crystal oligomer according to the first aspect. According to an embodiment of the present application, the preparation method of the liquid crystal oligomer comprises the following steps:

[0069] reacting the thiol-terminated liquid crystal oligomer with a first compound to obtain the liquid crystal oligomer;

[0070] wherein the first compound contains a carbon-carbon double bond and an isocyanate group.

[0071] The preparation method of the liquid crystal oligomer according to the above embodiment of the present application introduces a thiocarbamate structure and a double bond end-capping structure by reacting a thiol-terminated liquid crystal oligomer with a first compound which has both a carbon-carbon double bond and an isocyanate group, to obtain a double bond end-capped liquid crystal oligomer containing a thiocarbamate structure.

[0072] In the embodiments of the present application, with reference to the above Figure 1 For the liquid crystal oligomer provided by the present application, the above-mentioned thiol-terminated liquid crystal oligomer refers to a type of liquid crystal oligomer obtained by adaptively replacing the end group shown in Formula I Figure 1 with a thiol group (-SH). Figure 2

[0073] In the embodiments of the present application, the above-mentioned first compound refers to a type of multifunctional compound which has both a carbon-carbon double bond (-C=C-) and an isocyanate group (-NCO).

[0074] In the embodiments of the present application, the above-mentioned first reaction specifically comprises a thiol-isocyanate addition reaction (or called thiocarbamoylation reaction) between the thiol group (-SH) on the thiol-terminated liquid crystal oligomer and the isocyanate group (-NCO) on the first compound, to obtain a double bond end-capped liquid crystal oligomer containing a thiocarbamate structure.

[0075] In the embodiments of the present application, in order to obtain a liquid crystal oligomer with higher purity, the preparation method of the liquid crystal oligomer can further comprise steps of washing and drying the obtained product after the reaction according to the conventional methods disclosed in the organic chemical synthesis in the art, such as repeatedly precipitating and dissolving the product in a methanol solution for 3 times, and further drying at a temperature of 40°C for 48 hours, etc.

[0076] According to still some specific embodiments of the present application, the preparation method of the liquid crystal oligomer according to the above embodiments of the present application can further have the following additional technical features:

[0077] ​According to some embodiments of the present application, the molar ratio of the thiol-terminated liquid crystalline oligomer and the first compound is (0.5-1):(1-2), for example, it can be 0.5:1, 0.5:1.2, 0.5:1.5, 0.5:2, etc. The inventors have found that by limiting the molar ratio of the thiol-terminated liquid crystalline oligomer and the first compound to the above range, it is beneficial to form the double bond-terminated oligomer.

[0078] And / or, the temperature of the first reaction is 25-35°C, for example, it can be 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, etc.

[0079] And / or, the time of the first reaction is 12-48h, for example, it can be 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, 25h, 26h, 27h, 28h, 29h, 30h, 31h, 32h, 33h, 34h, 35h, 36h, 37h, 38h, 39h, 40h, 41h, 42h, 43h, 44h, 45h, 46h, 47h, 48h, etc.

[0080] According to still some embodiments of the present application, a catalyst is added to catalyze the first reaction, the catalyst includes at least one of tetramethylguanidine, 1,8-diazabicyclo[5.4.0]undec-7-ene and 1,5-diazabicyclo[4.3.0]non-5-ene, the weight addition amount of the catalyst is 0.05-0.2wt% of the total weight of the thiol-terminated liquid crystalline oligomer and the first compound, for example, it can be 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.10wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt%, 0.20wt%, etc.

[0081] According to still some embodiments of the present application, the preparation method of the thiol-terminated liquid crystalline oligomer includes the following steps:

[0082] reacting a liquid crystal monomer with a second compound containing a thiol group to obtain the thiol-terminated liquid crystal oligomer; wherein the liquid crystal monomer comprises at least one of an acrylate double bond structure-terminated liquid crystal monomer, such as 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, 2-methyl-1,4-phenylene bis(4-(4-(acryloyloxy)butoxy)benzoate), 2-methyl-1,4-phenylene bis(4-(4-(acryloyloxy)butoxy)benzoate), and (3R,3AR,6S,6AR)-hexahydrofuro[3,2-B]furan-3,6-diyl bis(4-((acryloyloxy)butoxy)carbonyl)oxy)benzoyl)oxy)benzoate); the second compound comprises at least one of 2,2'-(1,2-ethanediylbis(oxy))bis-ethanethiol, ethylene glycol dimercaptoacetate, di(mercaptoacetic acid)-1,4-butanediyl ester, and bis(2-mercaptoethyl)ether, and the second reaction has a temperature of 25-40 °C, such as 25 °C, 26 °C, 27 °C, 28 °C, 29 °C, 30 °C, 31 °C, 32 °C, 33 °C, 34 °C, 35 °C, 36 °C, 37 °C, 38 °C, 39 °C, 40 °C, and the like, and a time of 18-36 h, such as 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h, 25 h, 26 h, 27 h, 28 h, 29 h, 30 h, 31 h, 32 h, 33 h, 34 h, 35 h, 36 h, and the like.

[0083] and / or the first compound comprises at least one of isocyanatoethyl methacrylate and isocyanatoethyl acrylate.

[0084] A third aspect of the present application provides a liquid crystal elastomer. According to embodiments of the present application, the liquid crystal elastomer contains a reversibly cross-linked network structure, the reversibly cross-linked network structure comprising the liquid crystal oligomer of any one of the first aspect, and / or the liquid crystal oligomer prepared by the method of any one of the second aspect.

[0085] The liquid crystal elastomer of the above embodiments of the present application. The liquid crystal elastomer is a photocurable polythiourethane liquid crystal elastomer, which contains a reversibly cross-linked network structure, the reversibly cross-linked network structure comprising the liquid crystal oligomer of any one of the first aspect, and / or the liquid crystal oligomer prepared by the method of any one of the second aspect. Thus, the liquid crystal elastomer provided by the present application not only has the ability to be quickly processed and molded, but also has excellent thermal reversible reprocessing properties and impact protection performance.

[0086] In the embodiments of the present application, reversible crosslinking refers to a crosslinking mode in which chemical bonds can be broken / recombined under suitable conditions (such as heat, light stimulation, etc.) to realize reconstruction of the crosslinking structure without destroying the overall structural performance characteristics. For example, after the liquid crystal elastomer in the present application is completely formed and is cut into pieces, the pieces are placed in a flat hot press mold and hot pressed under conditions such as 120°C and 10 MPa for a period of time, and then cooled and demolded, and based on the reversible crosslinking characteristics, a liquid crystal elastomer with a complete structure and high density can be obtained again.

[0087] The fourth aspect of the present application provides a preparation method of the liquid crystal elastomer of the third aspect described above. According to the embodiments of the present application, the preparation method of the liquid crystal elastomer comprises:

[0088] The liquid crystal oligomer is subjected to a photocuring crosslinking reaction to obtain the liquid crystal elastomer.

[0089] The preparation method of the liquid crystal elastomer of the above embodiments of the present application. The preparation method is to subject the above double bond-terminated liquid crystal oligomer containing a thiourethane structure to a photocuring crosslinking reaction, which not only has a fast molding speed of the liquid crystal elastomer, but also successfully constructs a liquid crystal elastomer with excellent thermal reversibility and reworkability as well as excellent impact protection performance, which can meet the practical application in the fields of flexible protection, wearable devices and intelligent structural materials in extreme environments.

[0090] In the embodiments of the present application, the above photocuring crosslinking reaction process comprises further initiating the reaction of the photoactive groups such as carbon-carbon double bonds in the oligomer under ultraviolet light (UV) or visible light irradiation through a photoinitiator to form a three-dimensional network structure through covalent bonds between molecular chains.

[0091] Further, the specific operation process of the preparation method is not particularly limited, for example, the oligomer, a photoinitiator such as dimethyl anisole (DMPA), and a solvent such as toluene can be dissolved to obtain a mixture; the obtained mixture is subjected to ultraviolet light irradiation crosslinking molding in a mold to obtain a liquid crystal elastomer. At the same time, the addition amount of the photoinitiator and the solvent in the above specific operation process is also not particularly limited, for example, the weight addition amount of the photoinitiator can account for 0.5-1.5 wt% of the weight of the oligomer, specifically 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, etc.; for example, the weight addition amount of the solvent can account for 1-5 times of the weight of the oligomer, specifically 1 times, 2 times, 3 times, 4 times, 5 times, etc. Moreover, in order to obtain a liquid crystal oligomer with higher purity, the liquid crystal elastomer after the above ultraviolet light irradiation crosslinking molding can be subjected to a drying treatment to remove the solvent.

[0092] The embodiments of the present application are described in detail below, it should be noted that the embodiments described below are exemplary, only for explaining the present application, and can not be understood as limiting the present application. In addition, if not specifically stated, all reagents used in the following examples are commercially available, or can be synthesized according to the methods described herein or known methods, and the reaction conditions not listed are also readily available to those skilled in the art.

[0093] Example 1

[0094] The present embodiment provides a liquid crystal oligomer, the end group structure of the main chain of the liquid crystal oligomer is shown as formula I, and the number average molecular weight thereof is 5600 g / mol;

[0095] The formula I is as follows:

[0096] The structural formula of the liquid crystal oligomer is as follows:

[0097]

[0098] Ra:

[0099] Rb:

[0100] As shown in Figure 3 The preparation method of the above liquid crystal oligomer comprises the following steps:

[0101] Dissolve the liquid crystal monomer (1,4-bis-[4-(6-acryloyloxyhexyloxy) benzoyloxy]-2-methylbenzene, RM82, 70 mmol, 47.1 g) and the second compound containing thiol group (2,2'-(1,2-ethylenediylbis oxy) bis ethanethiol, EDDET, 80 mmol, 14.6 g) in toluene (150% of the total mass of the liquid crystal monomer and the second compound, 92.5 g), add the catalyst triethylamine (1.5 wt% of the total mass of the liquid crystal monomer and the second compound, 1.27 mL), and react at 30°C for 24 hours to obtain the thiol-terminated liquid crystal oligomer;

[0102] The thiol-terminated liquid crystal oligomer obtained above (10 mmol, 61.7 g) was added with a first compound having both carbon-carbon double bond and isocyanate group (isocyanatoethyl methacrylate, 25 mmol, 3.88 g), and a catalyst tetramethyl guanidine (0.1 wt% of the total mass of the thiol-terminated liquid crystal oligomer and the first compound, 72 μL) was added to catalyze the reaction between thiol and isocyanate group, and the reaction was carried out at 30 °C for 24 hours to form a liquid crystal oligomer containing thiourethane structure in the main chain and having double bond at the end; the crude product was repeatedly precipitated and dissolved in methanol solution for 3 times, and dried at 40 °C for 48 hours to obtain the target product, the liquid crystal oligomer containing thiourethane structure and terminated with double bond.

[0103] Example 2

[0104] This example provides a liquid crystal oligomer and a preparation method thereof, which is only different from Example 1 in that:

[0105] (1) the number average molecular weight of the liquid crystal oligomer is 3058 g / mol;

[0106] (2) the molar amount of the liquid crystal monomer is adjusted to 30 mmol and the molar amount of the first compound is adjusted to 40 mmol in the preparation method of the liquid crystal oligomer.

[0107] Example 3

[0108] This example provides a liquid crystal oligomer and a preparation method thereof, which is only different from Example 1 in that:

[0109] (1) the number average molecular weight of the liquid crystal oligomer is 10753 g / mol;

[0110] (2) the molar amount of the liquid crystal monomer is adjusted to 120 mmol and the molar amount of the first compound is adjusted to 130 mmol in the preparation method of the liquid crystal oligomer.

[0111] Example 4

[0112] This example provides a liquid crystal oligomer and a preparation method thereof, which is only different from Example 1 in that:

[0113] (1) the number average molecular weight of the liquid crystal oligomer is 17500 g / mol;

[0114] (2) the molar amount of the liquid crystal monomer is adjusted to 20 mmol and the amount of the second compound containing thiol is adjusted to 21 mmol in the preparation method of the liquid crystal oligomer.

[0115] Example 5

[0116] This example provides a liquid crystal oligomer and a preparation method thereof, which is only different from Example 1 in that:

[0117] (1) the number average molecular weight of the liquid crystal oligomer is 5082 g / mol;

[0118] (2) the liquid crystal monomer in the preparation method of the liquid crystal oligomer is adjusted to 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257, CAS: 174063-87-7).

[0119] Example 6

[0120] The present example provides a liquid crystal elastomer containing a reversible crosslinked network structure, the reversible crosslinked network structure comprising interconnected oligomers, the oligomers being the liquid crystal oligomers obtained in Example 1.

[0121] As shown in Figure 4 , the preparation method of the above liquid crystal elastomer comprises the following steps:

[0122] The oligomers (60 g) and a photoinitiator (DMPA, 0.06 g, 1 wt% of the mass of the oligomers) are added to a flask and an equal mass of toluene (60 g) is added for uniform dissolution to obtain a mixture; the mixture is crosslinked and formed in a mold (specifically a 4*4 cm polytetrafluoroethylene mold) by ultraviolet light irradiation, the specific parameters of the ultraviolet light irradiation including: 20 mW / cm 2 , 365 nm, for 8 min, to form a reversible crosslinked network structure; after the crosslinking is completed, the sample is dried at 40°C for 48 hours to remove the solvent to obtain a liquid crystal elastomer.

[0123] Example 7

[0124] The present example provides a liquid crystal elastomer and a preparation method thereof, which is only different from Example 6 in that:

[0125] (1) the oligomers are the liquid crystal oligomers obtained in Example 2.

[0126] Example 8

[0127] The present example provides a liquid crystal elastomer and a preparation method thereof, which is only different from Example 6 in that:

[0128] (1) the oligomers are the liquid crystal oligomers obtained in Example 3.

[0129] Example 9

[0130] The present example provides a liquid crystal elastomer and a preparation method thereof, which is only different from Example 6 in that:

[0131] (1) the oligomers are the liquid crystal oligomers obtained in Example 4.

[0132] Example 10

[0133] This example provides a liquid crystal elastomer and a method for preparing the same, which is only different from Example 6 in that:

[0134] (1) the oligomer is the liquid crystal oligomer obtained in Example 5.

[0135] Comparative Example 1

[0136] This comparative example provides a liquid crystal elastomer not containing a thiourethane dynamic bond, and a method for preparing the same, which comprises the following steps:

[0137] The liquid crystal monomer (1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, RM82, 80 mmol, 53.8 g) and the second compound containing a mercapto group (2,2'-(1,2-ethanediyldioxy)bisethanethiol, EDDET, 70 mmol, 12.8 g) are dissolved in toluene (150% of the total mass of the liquid crystal monomer and the second compound, 99.9 g), a catalyst triethylamine (1.5 wt% of the total mass of the liquid crystal monomer and the second compound, 1.37 mL) is added, and the reaction is carried out at 30°C for 24 hours to obtain a mercapto-terminated liquid crystal oligomer;

[0138] The mercapto-terminated liquid crystal oligomer obtained above (10 mmol, 66.6 g) and a photoinitiator (DMPA, 0.06 g, 1 wt% of the mass of the oligomer) are added to a flask and dissolved uniformly by adding an equal mass of toluene (66.6 g) to obtain a mixture; the mixture is crosslinked and formed into a shape by ultraviolet light irradiation in a mold (specifically a 4*4 cm polytetrafluoroethylene mold), and the specific parameters of the ultraviolet light irradiation include: 20 mW / cm 2 , 365 nm, 8 min; a reversible crosslinked network structure is formed; after the crosslinking is completed, the sample is dried at 40°C for 48 hours to remove the solvent to obtain a liquid crystal elastomer.

[0139] Test Example 1

[0140] This test example characterizes the mercapto-terminated liquid crystal oligomer and the double bond-terminated liquid crystal oligomer containing a thiourethane structure in Example 1, and the obtained nuclear magnetic resonance hydrogen spectrum is as shown in Figure 5 .

[0141] It can be seen from Figure 5 that the nuclear magnetic resonance hydrogen spectrum shows that the double bond-terminated liquid crystal oligomer containing a thiourethane structure is successfully prepared, Figure 5 and the red box in the middle is the characteristic peak of the carbon-carbon double bond.

[0142] Test Example 2

[0143] The thermal reprocessing properties of the liquid crystal elastomers obtained in Example 6 to Example 10 and Comparative Example 1 were tested, and the test results are shown in Table 1; the test method conditions include: the sample was cut into pieces and placed in a stainless steel mold, and was thermally pressed at 120°C in a flat plate heating chamber under a pressure of 4 MPa for 1 hour.

[0144] Table 1

[0145] Test sample Hot press reworkability Example 6 Can be hot press reworked Example 7 Can be hot press reworked Example 8 Can be hot press reworked Example 9 Can be hot press reworked Example 10 Can be hot press reworked Comparative Example 1 Cannot be hot press reworked

[0146] As shown in Table 1, the liquid crystal elastomer containing the thio urethane dynamic bond can be recycled by thermal pressing after being broken, while the liquid crystal elastomer without the thio urethane dynamic bond cannot be recycled by thermal pressing. This shows that the thio urethane dynamic bond can undergo dynamic exchange under thermal stimulation, and endows the network with dynamic properties.

[0147] In addition, the impact test results of the liquid crystal elastomer obtained in Example 6 in this test example are shown in Table 2. Figure 6

[0148] Test Example 3

[0149] In this test example, the liquid crystal elastomer obtained in Example 6 was formed into a 4 mm thick liquid crystal elastomer sample by the thermal reprocessing method described in the above test example, and a ball drop impact test (ball drop height: 40 cm, ball mass: 265 g) was performed, and a rubber (rubber sample thickness: 4 mm) was used as a control to investigate the impact protection performance and energy dissipation capacity of the liquid crystal elastomer. The test results are shown in Table 2.

[0150] Table 2

[0151] Test sample Impact force (N) Blank (no protection) 2289 Example 6 1097 Rubber 1642

[0152] As shown in Table 2, the liquid crystal elastomer obtained in Example 6 has good energy absorption effect, and can better convert impact potential energy into heat energy dissipation compared with rubber materials.

[0153] In addition, the impact test results of the liquid crystal elastomer obtained in Example 6 in this test example are shown in Table 2. Figure 6

[0154] ​​In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0155] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A liquid crystal oligomer, characterized in that The end group structure of the main chain of the liquid crystal oligomer is shown in Formula I; The formula I:

2. The liquid crystal oligomer according to claim 1, wherein The physical and chemical property parameters of the liquid crystal oligomer include: a number average molecular weight of 1350 to 17500 g / mol.

3. The liquid crystal oligomer according to claim 1 or 2, characterized in that The general structural formula of the liquid crystal oligomer is shown below: Wherein, R1 is a liquid crystal monomer with a double-terminal acrylate double bond, R2 is a chain extender with a double-terminal thiol group, R3 is an alkyl structure, and R4 is -H or -CH3; Alternatively, the chemical structural formula of the liquid crystal oligomer is as follows: Where Ra: Rb:

4. A method for preparing a liquid crystal oligomer according to any one of claims 1 to 3, characterized in that: The preparation method of the liquid crystal oligomer comprises the following steps: performing a first reaction between the mercapto-terminated liquid crystal oligomer and the first compound to obtain the liquid crystal oligomer; Wherein, the first compound contains a carbon-carbon double bond and an isocyanate group.

5. The method for preparing a liquid crystal oligomer according to claim 4, wherein: The molar ratio of the mercapto-terminated liquid crystal oligomer to the first compound is (0.5-1):(1-2); and / or, the temperature of the first reaction is 25-35°C; And / or, the first reaction time is 12 to 48 hours.

6. The method for preparing a liquid crystal oligomer according to claim 4, wherein: A catalyst is added to catalyze the first reaction, wherein the catalyst includes at least one of tetramethylguanidine, 1,8-diazobispiro[5.4.0]undec-7-ene and 1,5-diazabicyclo[4.3.0]non-5-ene, and the weight addition amount of the catalyst accounts for 0.05 to 0.2 wt% of the total weight of the thiol-terminated liquid crystal oligomer and the first compound.

7. The method for preparing a liquid crystal oligomer according to any one of claims 4 to 6, wherein: The preparation method of the mercapto-terminated liquid crystal oligomer comprises the following steps: Performing a second reaction between a liquid crystal monomer and a second compound containing a thiol group to obtain the thiol-terminated liquid crystal oligomer; wherein the liquid crystal monomer includes a liquid crystal monomer terminated with an acrylate double bond structure, the second compound includes at least one of 2,2'-(1,2-ethylenedioxy)bis(thioglycolate)diethanethiol, ethylene glycol bis(thioglycolate), 1,4-butylene di(thioglycolate), and bis(2-mercaptoethyl) ether; and the conditions of the second reaction include: a temperature of 25 to 40° C. and a time of 18 to 36 hours. And / or, the first compound includes at least one of isocyanoethyl methacrylate and isocyanate ethyl acrylate.

8. A liquid crystal elastomer, characterized in that: The liquid crystal elastomer contains a reversibly cross-linked network structure, which includes the liquid crystal oligomers according to any one of claims 1 to 3 that are interconnected, and / or the liquid crystal oligomers prepared by the preparation method according to any one of claims 4 to 7.

9. A method for preparing the liquid crystal elastomer according to claim 8, characterized in that: The preparation method of the liquid crystal elastomer comprises: The liquid crystal oligomer is subjected to a photocuring cross-linking reaction to obtain the liquid crystal elastomer.

10. The method for preparing a liquid crystal elastomer according to claim 9, wherein: The weight of the photoinitiator added accounts for 0.5 to 1.5 wt% of the weight of the liquid crystal oligomer; And / or, the weight amount of the solvent added is 1 to 5 times the weight of the liquid crystal oligomer.

Images