CN109485837B - Main chain type liquid crystal elastomer with side group containing cinnamyl crosslinking monomer and preparation method thereof - Google Patents
Main chain type liquid crystal elastomer with side group containing cinnamyl crosslinking monomer and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a main chain type liquid crystal elastomer with a side group containing cinnamyl crosslinking monomers and a preparation method thereof. The liquid crystal elastomer is prepared by preparing liquid crystal copolyester by a high-temperature melt polycondensation method from a liquid crystal element, a photo-crosslinking monomer and a connecting group, then obtaining a film with uniform thickness by hot pressing, carrying out stretching orientation (single-domain orientation state) on the film in a liquid crystal state, and then fixing the single-domain orientation state of the liquid crystal by utilizing photochemical reaction of a cinnamon group on a molecular side group to prepare the multifunctional single-domain liquid crystal elastomer intelligent material. The preparation method does not need solvent and expensive catalyst, has no small molecular monomer residue, can realize clean production, and can realize industrial production by combining various polymer orientation processes such as spinning, film stretching and the like. The single-domain liquid crystal elastomer has very quick response actuation to heat, and can realize various response modes and response behaviors after special surface treatment.
Description
Technical Field
The invention relates to the field of thermoreversible deformable single-domain liquid crystal elastomers, in particular to a main chain type liquid crystal elastomer with a side group containing cinnamyl crosslinking monomers and a preparation method thereof.
Background
The monodomain liquid crystal elastomer combines the rubber elasticity (entropy elasticity) of a polymer network and the orientation order of a liquid crystal state, and can generate great shape change for a series of external stimuli (such as heat, light, an electric field, a magnetic field or pH and the like). The artificial muscle can imitate human muscle, can realize functions of reversible expansion, bending, tightening or expansion and the like under the action of external stimulation, and is always a hot point of domestic and foreign research. The french physicist p.g.de Gennes, well known as early as 1975, has predicted that liquid crystal elastomers can become a good choice for artificial muscle materials and can meet the performance indexes. Only the monodomain aligned liquid-crystalline elastomers have a spontaneously reversible contraction/expansion behaviour between the isotropic phase and the liquid-crystalline phase, the material appearing macroscopically to shrink at elevated temperatures; the material again macroscopically exhibits stretching or expansion when the temperature is reduced. Because the orientations of the mesogens in all the domains are consistent, the micro deformation generated in the reversible process can be expressed as large-scale contraction and expansion on the macro whole, and the characteristic provides a foundation for the development and application of various actuators, artificial muscles, micro robots and other devices.
To achieve this, it is most important to prepare a monodomain aligned liquid crystalline elastomer. According to the classification of chemical synthesis methods, there are two main methods for preparing single-domain liquid crystal elastomers, namely a two-step crosslinking method and a one-step synthesis method. Both have their advantages and uniqueness, but also have some limitations. The former is to prepare a liquid crystal polymer precursor and then to crosslink with a crosslinking agent, generally prepared by hydrosilylation reaction, and can prepare tail-joint type and waist-joint type liquid crystal elastomers and azo single-domain liquid crystal elastomers with photosensitivity through molecular design. But the biggest disadvantage is that the polymerization reaction can not be completely carried out, so that a small amount of monomer residues still exist in the prepared liquid crystal elastomer, and the small molecular monomers can migrate and phase separate with the passage of time, which influences the service performance and the service life of the final product; the one-step synthesis method is to directly form a cross-linked network structure, and the liquid crystal polymer and the cross-linking agent directly perform polymerization reaction, so that the micromolecular liquid crystal is easier to orient compared with macromolecules, and the method can be used for various preparation methods. However, the difficulty is that in order to satisfy the polymerization process and provide multiple functionalization to the small-molecule liquid crystal monomer, the structure of the liquid crystal monomer is relatively complex, and multiple steps of organic synthesis are required to obtain the corresponding monomer. In addition, the limitations of the above methods limit the large-area preparation and industrial production of single-domain liquid crystal elastomers, and therefore, it is necessary to develop a more simple and feasible preparation method. Based on the comparison of the advantages and disadvantages of the above methods and previous related studies, we have inspired in many review articles: the smectic liquid crystal polymer is firstly oriented and stretched in a liquid crystal state, and then the oriented structure is fixed by covalent bond in a cross-linking way, so that the single domain liquid crystal elastomer can be prepared.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: provides a main chain type liquid crystal elastomer (also called single domain liquid crystal elastomer) with a side group containing cinnamyl crosslinking monomer and a preparation method thereof, aiming at solving the limitations and the defects existing in two traditional preparation methods of single domain liquid crystal elastomers. Wherein the polymerization reaction of the two-step crosslinking method is incomplete, and the prepared liquid crystal elastomer has monomer residues; the difficulty of the one-step synthesis method is that the synthesis steps are complicated. These disadvantages and shortcomings limit the large-area preparation and industrial production of single-domain liquid-crystalline elastomers. The applicant of the invention researches and explores a novel simple and easy preparation method and a clean preparation process, and designs and successfully prepares a novel single-domain liquid crystal elastomer intelligent material, namely a main chain type liquid crystal elastomer with a side group containing a cinnamyl crosslinking monomer.
The technical scheme adopted by the invention is as follows: a side group contains the main chain type liquid crystal elastomer of the cinnamyl crosslinking monomer, the said main chain type liquid crystal elastomer is a thermoplastic backbone smectic liquid crystal elastomer (PBDPS) that the applicant of the invention utilizes the physical crosslinking function formed by piling up benzene ring in the previous research, have introduced the asymmetric benzene ring side group on the flexible molecular chain of this liquid crystal elastomer, the molecular chain arranges in the way of folding chain, the side group benzene ring piles up through the dislocation parallel to form the strong pi-pi interaction, play the function of the physical crosslinking point. The multifunctional single-domain liquid crystal elastomer intelligent material with rapid thermal actuation and multiple response behaviors can be prepared by introducing a photo-crosslinking monomer containing a cinnamon group into a molecular chain side group of PBDPS through molecular design, orienting the photo-crosslinking monomer in a liquid crystal state, and then fixing the liquid crystal single-domain oriented state through photochemical reaction of the cinnamon group.
The specific technical scheme is as follows:
a main chain type liquid crystal copolyester with a side group containing a cinnamyl crosslinking monomer has the following specific structural formula:
a main chain type liquid crystal elastomer with side group containing cinnamyl crosslinking monomer is prepared through orienting the liquid crystal copolyester in liquid crystal state, and then cross-linking and fixing the oriented state of liquid crystal monodomain by photochemical reaction.
Further, the liquid crystal copolyester is composed of the following structural units [ I ] liquid crystal elementary biphenyl dioxyhexanol, [ II ] photo-crosslinking monomer 2,2' - (cinnamoyl azoalkane diyl) diethyl diacetate and [ III ] connecting group phenyl succinic acid randomly:
wherein, the molar part of [ I ] accounts for 50% of all structural units, the molar part of [ II ] accounts for 10-50% of all structural units, and the balance is [ III ].
The preparation method of the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer specifically comprises the following steps:
(1) heating and stirring liquid crystal element biphenyl dioxyhexanol (BHHBP), a photo-crosslinking monomer 2,2' - (cinnamoyl azoalkanediyl) diethyl Diacetate (DCA) and a connecting group Phenyl Succinic Acid (PSA) for reacting for 2-4 h at 170-220 ℃ under the action of a catalyst and the protection of nitrogen; and then the reacted system continues to react under the vacuum condition, and the liquid crystal copolyester is obtained after the reaction is finished and the cooling is carried out. The catalyst can be any one of zinc acetate, antimony trioxide, stannous octoate, dialkyl tin oxide or ethylene glycol antimony.
(2) Hot-pressing and cutting the liquid crystal copolyester obtained in the step (1), preparing a thin strip-shaped film sample strip which is required regularly according to needs, stretching and orienting the sample strip at a certain temperature, and then carrying out ultraviolet irradiation crosslinking to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
The temperature of a heating table for ultraviolet light crosslinking is 25-55 ℃, the wavelength of the ultraviolet light is 280-365 nm, and the uniform crosslinking time of two surfaces of the film sample strip is 1-3 h.
Wherein, the thickness of the pressed uniform film can be 0.2mm, the width of the cut sample strip can be 4mm, the water bath stretching temperature can be 30-60 ℃, and the stretching multiplying power can be 200-500%.
Combining the preparation method, the specific mode of heating and stirring at 170-220 ℃ for reaction for 2-4 h in the step (1) is controlled as follows: reacting at 170-200 ℃ for 1h, and then raising the temperature to 190-220 ℃ for reacting for 1-3h in half an hour; the mode of continuing the reaction under vacuum condition was controlled as follows: controlling the vacuum degree to be less than 30Pa, the reaction temperature of heating and stirring to be 190-220 ℃, and the reaction time to be 1-4 h. Therefore, the side reaction caused by monomer decomposition can be effectively avoided, and the residual micromolecules in the liquid crystal copolyester can be effectively avoided.
The beneficial technical effects obtained by the invention are as follows:
1) the invention solves the defects and limitations of the traditional preparation method of the single-domain liquid crystal elastomer, explores a novel and simple preparation method and a clean preparation process, and designs and successfully prepares a novel single-domain liquid crystal elastomer intelligent material with rapid thermal response.
2) The invention provides a main chain type liquid crystal elastomer with a side group containing cinnamyl crosslinking monomers and a preparation method thereof. Compared with the prior thermotropic response single-domain liquid crystal elastomer and the preparation technology and process thereof, the invention has the following advantages: the preparation method of the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer overcomes the defects and limitations of incomplete polymerization reaction, complex and fussy synthesis steps and the like in the traditional preparation method, simultaneously does not need solvents and expensive catalysts, does not leave small molecular monomers in polymers, is simple and easy to implement, and can realize industrial production by combining various high molecular processing technologies.
3) Asymmetric benzene ring side groups are introduced into a flexible molecular chain of the liquid crystal elastomer, the molecular chain is arranged in a folding chain mode, and benzene rings of the side groups are staggered and stacked in parallel to form a strong pi-pi interaction to play a role of a physical crosslinking point. The special structure endows the fabric with good physical and mechanical properties, film forming property, spinnability and excellent shape memory function. In addition, cinnamon groups DCA introduced into a molecular chain undergo a [2+2] cycloaddition reaction under the irradiation of ultraviolet light with a certain wavelength to form a large number of covalent cross-linked networks in a polymer, so that the oriented cross-linked structure of the single-domain liquid crystal elastomer can be fixed, and the multiple-cycle reversible response to the temperature is realized.
Drawings
FIG. 1 is a nuclear magnetic spectrum of the liquid crystal copolyester of example 6.
Detailed Description
To determine the effect of the content of the photo-crosslinking monomer DCA on the degree of stimulus response and the crosslinking density of the main-chain liquid crystalline elastomer having a pendant cinnamyl-containing crosslinking monomer, we reflected by the reversible degree of actuation and the gel content, respectively. Oriented crosslinked, main chain, liquid crystalline elastomer films containing pendant cinnamyl crosslinking monomers slowly shrink during phase heating to the isotropic state and stretch during cooling to the LC phase, the magnitude of actuation generated during this time being defined as the degree of Reversible Actuation (RAD). The mass fraction of the undissolved portion after sufficiently soaking the crosslinked liquid-crystal elastomer sample in a solvent was defined as the gel content (GF).
The above-described aspects of the present invention will be described and illustrated in more detail by specific examples in order to better explain the objects, technical problems, technical solutions and advantages of the present invention.
Example 1
(1) 3.8652g (1X 10) of biphenyldioxyhexanol-2mol) and diethyl 2,2' - (cinnamoylazanediyl) diacetate 3.19g (1X 10)-2mol) is added into a three-neck reaction bottle, 0.0353g of zinc acetate catalyst is additionally added, the mixture is stirred and reacted for 1 hour at the temperature of 170 ℃ under the protection of nitrogen atmosphere, and then the temperature is raised to 190 ℃ for continuous reaction for 1 hour.
(2) Introducing a high vacuum condition within 30Pa into the system reacted in the step (1), continuously heating and stirring at 190 ℃ for reacting for 4h, and cooling after the reaction is finished to obtain the liquid crystal copolyester with the number average molecular weight of 50000.
(3) And (3) hot-pressing the liquid crystal copolyester obtained in the step (2) at 110 ℃ to form a uniform film with the thickness of 0.2mm, cutting the uniform film into a standard sample strip with the length of 20mm and the width of 4mm, and stretching and orienting the sample strip in a water bath at 60 ℃ along the length direction, wherein the stretching ratio is 500%.
(4) And (4) carrying out double-sided uniform ultraviolet irradiation crosslinking on the stretched and oriented film sample strip in the step (3) at 55 ℃ under the irradiation of ultraviolet light with the wavelength of 280nm for 3 hours in total to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
Reversible Actuation Degree (RAD) of the main chain type liquid crystal elastomer film sample strip with the side group containing the cinnamyl crosslinking monomer prepared in the embodiment is measured between 20 ℃ (liquid crystal state) and 80 ℃ (isotropic state); the gel content (GF) was measured after swelling in chloroform for 24h and vacuum drying for 24 h. As shown in table 1.
Example 2
(1) 3.8652g (1X 10) of biphenyldioxyhexanol-2mol), 2.871g (9.0X 10) of diethyl 2,2' - (cinnamoylazanediyl) diacetate-3mol) and 0.1942g (1.0X 10 g) of phenylsuccinic acid-3mol) is added into a three-neck reaction bottle, 0.0347g of catalyst antimony trioxide is additionally added, stirring reaction is carried out for 1h at 170 ℃ under the protection of nitrogen atmosphere, and then the temperature is raised to 190 ℃ for continuous reaction for 1.5 h.
(2) Introducing a high vacuum condition within 30Pa into the system reacted in the step (1), continuously heating and stirring at 190 ℃ for reaction for 3.5h, and cooling after the reaction is finished to obtain the liquid crystal copolyester with the number average molecular weight of 46500.
(3) Preparing a standard sample strip from the liquid crystal copolyester obtained in the step (2) according to the example 1, and carrying out stretching orientation on the sample strip in a water bath at 55 ℃, wherein the stretching magnification is 500%.
(4) And (4) carrying out double-sided uniform crosslinking on the stretched and oriented film sample strip in the step (3) at 50 ℃ under the irradiation of ultraviolet light with the wavelength of 313nm for 3 hours in total to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
The main chain type liquid crystal elastomer having a pendant cinnamyl-containing crosslinking monomer prepared in this example was subjected to relative tests for reversible degree of actuation (RAD) and gel content (GF) with reference to the relative procedures of example 1, as shown in table 1.
Example 3
(1) 3.8652g (1X 10) of biphenyldioxyhexanol-2mol), 2.7115g (8.5X 10) of diethyl 2,2' - (cinnamoylazanediyl) diacetate-3mol) and 0.2913g (1.5X 10) of phenylsuccinic acid-3mol) is added into a three-neck reaction bottle, 0.0343g of catalyst stannous octoate is additionally added, the mixture is stirred and reacted for 1 hour at 180 ℃ under the protection of nitrogen atmosphere, and then the temperature is raised to 190 ℃ for continuous reaction for 1.5 hours.
(2) Introducing a high vacuum condition within 30Pa into the system reacted in the step (1), continuously heating and stirring at 190 ℃ for reaction for 3.5h, and cooling after the reaction is finished to obtain the liquid crystal copolyester with the number average molecular weight of 43600.
(3) Preparing a standard sample strip from the liquid crystal copolyester obtained in the step (2) according to the example 1, and stretching and orienting the sample strip in a water bath at 55 ℃ along the length direction, wherein the stretching ratio is 450%.
(4) And (3) carrying out double-sided uniform ultraviolet irradiation crosslinking on the stretched and oriented film sample strip in the step (3) at 50 ℃ under the irradiation of ultraviolet light with the wavelength of 365nm for 2.5 hours to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
The main chain type liquid crystal elastomer having a pendant cinnamyl-containing crosslinking monomer prepared in this example was subjected to relative tests for reversible degree of actuation (RAD) and gel content (GF) with reference to the relative procedures of example 1, as shown in table 1.
Example 4
(1) 3.8652g (1X 10) of biphenyldioxyhexanol-2mol), 2.3925g (7.5X 10) of diethyl 2,2' - (cinnamoylazanediyl) diacetate-3mol) and 0.4855g (2.5X 10) of phenylsuccinic acid-3mol) is added into a three-neck reaction bottle, 0.0337g of catalyst antimony trioxide is additionally added, stirring reaction is carried out for 1h at 180 ℃ under the protection of nitrogen atmosphere, and then the temperature is raised to 200 ℃ for continuous reaction for 2 h.
(2) Introducing a high vacuum condition within 30Pa into the system reacted in the step (1), continuously heating and stirring at 200 ℃ for reaction for 3h, and cooling after the reaction is finished to obtain the liquid crystal copolyester with the number average molecular weight of 39000.
(3) Preparing a standard sample strip from the liquid crystal copolyester obtained in the step (2) according to the example 1, and carrying out stretching orientation on the sample strip along the length direction in a water bath at 50 ℃, wherein the stretching ratio is 450%.
(4) And (3) carrying out double-sided uniform ultraviolet irradiation crosslinking on the stretched and oriented film sample strip in the step (3) at 45 ℃ under the irradiation of ultraviolet light with the wavelength of 313nm for 2.5 hours to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
The main chain type liquid crystal elastomer having a pendant cinnamyl-containing crosslinking monomer prepared in this example was subjected to relative tests for reversible degree of actuation (RAD) and gel content (GF) with reference to the relative procedures of example 1, as shown in table 1.
Example 5
(1) 3.8652g (1X 10) of biphenyldioxyhexanol-2mol), 1.914g (6.0X 10) of diethyl 2,2' - (cinnamoylazanediyl) diacetate-3mol) and 0.7767g (4.0X 10 g) of phenylsuccinic acid-3mol) is added into a three-neck reaction bottle, in addition, 0.0328g of catalyst stannous octoate is added, the mixture is stirred and reacted for 1h at 190 ℃ under the protection of nitrogen atmosphere, and then the temperature is raised to 200 ℃ for continuous reaction for 2 h.
(2) Introducing a high vacuum condition within 30Pa into the system reacted in the step (1), continuously heating and stirring at 200 ℃ for reaction for 3h, and cooling after the reaction is finished to obtain the liquid crystal copolyester with the number average molecular weight of 34300.
(3) Preparing a standard sample strip from the liquid crystal copolyester obtained in the step (2) according to the example 1, and carrying out stretching orientation on the sample strip along the length direction in a water bath at the temperature of 45 ℃, wherein the stretching magnification is 400%.
(4) And (3) carrying out double-sided uniform ultraviolet irradiation crosslinking on the stretched and oriented film sample strip in the step (3) at 40 ℃ under the irradiation of ultraviolet light with the wavelength of 365nm for 2 hours in total to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
The main chain type liquid crystal elastomer having a pendant cinnamyl-containing crosslinking monomer prepared in this example was subjected to relative tests for reversible degree of actuation (RAD) and gel content (GF) with reference to the relative procedures of example 1, as shown in table 1.
Example 6
(1) 3.8652g (1X 10) of biphenyldioxyhexanol-2mol), 1.595g (5.0X 10) of diethyl 2,2' - (cinnamoylazanediyl) diacetate-3mol) and 0.9709g (5.0X 10 g) of phenylsuccinic acid-3mol) is added into a three-neck reaction bottle, 0.0322g of catalyst dialkyl tin oxide is additionally added, the mixture is stirred and reacted for 1h at 190 ℃ under the protection of nitrogen atmosphere, and then the temperature is raised to 200 ℃ for further reaction for 2.5 h.
(2) Introducing a high vacuum condition within 30Pa into the system reacted in the step (1), continuously heating and stirring at 200 ℃ for reacting for 2.5h, and cooling after the reaction is finished to obtain the liquid crystal copolyester with the number average molecular weight of 28500.
(3) Preparing a standard sample strip from the liquid crystal copolyester obtained in the step (2) according to the example 1, and carrying out stretching orientation on the sample strip along the length direction in a water bath at the temperature of 45 ℃, wherein the stretching ratio is 350%.
(4) And (3) carrying out double-sided uniform ultraviolet irradiation crosslinking on the stretched and oriented film sample strip in the step (3) at 40 ℃ under the irradiation of ultraviolet light with the wavelength of 313nm for 2 hours in total to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
The main chain type liquid crystal elastomer having a pendant cinnamyl-containing crosslinking monomer prepared in this example was subjected to relative tests for reversible degree of actuation (RAD) and gel content (GF) with reference to the relative procedures of example 1, as shown in table 1.
Example 7
(1) 3.8652g (1X 10) of biphenyldioxyhexanol-2mol), diethyl 2,2' - (cinnamoylazanediyl) diacetate 1.276g (4.0X 10)-3mol) and 1.1651g (6.0X 10 g) of phenylsuccinic acid-3mol) is added into a three-neck reaction bottle, 0.0315g of zinc acetate catalyst is additionally added, the mixture is stirred and reacted for 1h at 190 ℃ under the protection of nitrogen atmosphere, and then the temperature is raised to 210 ℃ for continuous reaction for 2.5 h.
(2) Introducing a high vacuum condition within 30Pa into the system reacted in the step (1), continuously heating and stirring at 210 ℃ for reacting for 2.5h, and cooling after the reaction is finished to obtain the liquid crystal copolyester with the number average molecular weight of 22300.
(3) Preparing a standard sample strip from the liquid crystal copolyester obtained in the step (2) according to the example 1, and stretching and orienting the sample strip along the length direction in a water bath at 40 ℃ with the stretching ratio of 300%.
(4) And (3) carrying out double-sided uniform crosslinking on the stretched and oriented film sample strip in the step (3) at 35 ℃ under the irradiation of ultraviolet light with the wavelength of 313nm for 1.5h to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
The main chain type liquid crystal elastomer having a pendant cinnamyl-containing crosslinking monomer prepared in this example was subjected to relative tests for reversible degree of actuation (RAD) and gel content (GF) with reference to the relative procedures of example 1, as shown in table 1.
Example 8
(1) 3.8652g (1X 10) of biphenyldioxyhexanol-2mol), 1.1165g (3.5X 10) of diethyl 2,2' - (cinnamoylazanediyl) diacetate-3mol) and 1.2622g (6.5X 10) of phenylsuccinic acid-3mol) is added into a three-neck reaction bottle, 0.0312g of catalyst antimony trioxide is additionally added, the mixture is stirred and reacted for 1h at 190 ℃ under the protection of nitrogen atmosphere, and then the temperature is raised to 210 ℃ for continuous reaction for 3 h.
(2) Introducing a high vacuum condition within 30Pa into the system reacted in the step (1), continuously heating and stirring at 210 ℃ for reaction for 2h, and cooling after the reaction is finished to obtain the liquid crystal copolyester with the number average molecular weight of 15700.
(3) The liquid crystal copolyester obtained in the step (2) is used for preparing a standard sample strip according to the example 1, and the sample strip is subjected to stretching orientation along the length direction in a water bath at the temperature of 40 ℃, wherein the stretching magnification is 250%.
(4) And (4) carrying out double-sided uniform crosslinking on the film sample strip subjected to stretching orientation in the step (3) at 35 ℃ under the irradiation of ultraviolet light with the wavelength of 280nm for 1.5h to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
The main chain type liquid crystal elastomer having a pendant cinnamyl-containing crosslinking monomer prepared in this example was subjected to relative tests for reversible degree of actuation (RAD) and gel content (GF) with reference to the relative procedures of example 1, as shown in table 1.
Example 9
(1) 3.8652g (1X 10) of biphenyldioxyhexanol-2mol), 0.7975g (2.5X 10) of diethyl 2,2' - (cinnamoylazanediyl) diacetate-3mol) and 1.4564g (7.5X 10) of phenylsuccinic acid-3mol) is added into a three-neck reaction bottle, 0.0306g of catalyst dialkyl tin oxide is additionally added, the mixture is stirred and reacted for 1h at 200 ℃ under the protection of nitrogen atmosphere, and then the temperature is raised to 220 ℃ for continuous reaction for 3 h.
(2) Introducing a high vacuum condition within 30Pa into the system reacted in the step (1), continuously heating and stirring at 220 ℃ for reacting for 1.5h, and cooling after the reaction is finished to obtain the liquid crystal copolyester with the number average molecular weight of 9900.
(3) The liquid crystal copolyester obtained in the step (2) is used for preparing a standard sample strip according to the example 1, and the sample strip is subjected to stretching orientation along the length direction in a water bath at the temperature of 35 ℃, wherein the stretching magnification is 250%.
(4) And (3) carrying out double-sided uniform crosslinking on the stretched and oriented film sample strip in the step (3) at 30 ℃ under the irradiation of ultraviolet light with the wavelength of 313nm for 1 hour in total to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
The main chain type liquid crystal elastomer having a pendant cinnamyl-containing crosslinking monomer prepared in this example was subjected to relative tests for reversible degree of actuation (RAD) and gel content (GF) with reference to the relative procedures of example 1, as shown in table 1.
Example 10
(1) 3.8652g (1X 10) of biphenyldioxyhexanol-2mol), diethyl 2,2' - (cinnamoylazanediyl) diacetate 0.638g (2.0X 10)-3mol) andphenylsuccinic acid 1.5534g (8.0X 10)-3mol) is added into a three-neck reaction bottle, 0.0303g of catalyst ethylene glycol antimony is additionally added, the mixture is stirred and reacted for 1h at 200 ℃ under the protection of nitrogen atmosphere, then the temperature is raised to 220 ℃ for continuous reaction for 3h,
(2) introducing a high vacuum condition within 30Pa into the system reacted in the step (1), continuously heating and stirring at 220 ℃ for reaction for 1h, and cooling after the reaction is finished to obtain the liquid crystal copolyester with the number average molecular weight of 5000.
(3) Preparing a standard sample strip from the liquid crystal copolyester obtained in the step (2) according to the example 1, and stretching and orienting the sample strip in the length direction in a water bath at the temperature of 30 ℃, wherein the stretching ratio is 200%.
(4) And (3) carrying out double-sided uniform crosslinking on the stretched and oriented film sample strip in the step (3) at 25 ℃ under the irradiation of ultraviolet light with the wavelength of 313nm for 1 hour in total to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
The main chain type liquid crystal elastomer having a pendant cinnamyl-containing crosslinking monomer prepared in this example was subjected to relative tests for reversible degree of actuation (RAD) and gel content (GF) with reference to the relative procedures of example 1, as shown in table 1.
From the reversible actuation degree and the gel content measured in table 1, comparative analysis can find that the content of the photo-crosslinking monomer DCA has a significant influence on the reversible deformation and the crosslinking degree of the liquid crystal elastomer. The reversible actuation degree RAD of the liquid crystal elastomer is slowly reduced along with the increase of the content of DCA, and is reduced from 54% to 25%; the crosslinking density increases continuously and the gel content GF rises gradually from 42% to 91%.
TABLE 1 reversible deformation and degree of crosslinking of Main chain liquid Crystal Elastomers with pendant groups containing a cinnamyl Cross-linking monomer with varying DCA content
In the above table, the Reversible Actuation Degree (RAD) is calculated by the following formula:
RAD＝(LLC-Liso)/Liso×100％，
wherein L isisoThe length of the liquid crystal elastomer sample at high temperature (80 ℃),
LLCthe length of the liquid crystal elastomer sample at low temperature (20 ℃ C.).
The gel content (GF) was calculated by the following formula:
GF＝m1/m0×100％，
wherein m is0Is the initial mass of the liquid crystal elastomer spline,
m1the mass of the liquid crystal elastomer sample after being placed in chloroform for 24 hours and dried under vacuum condition at 45 ℃ for 24 hours.
Claims (5)
1. A main chain type liquid crystal copolyester with a side group containing a cinnamyl crosslinking monomer is characterized in that: the specific structural formula of the liquid crystal copolyester is as follows:
the liquid crystal copolyester comprises a structural unit derived from liquid crystal elementary biphenyl dioxyhexanol shown in the formula [ I ], a structural unit derived from a photo-crosslinking monomer 2,2' - (cinnamoyl azoalkanediyl) diethyl diacetate shown in the formula [ II ], and a structural unit derived from a connecting group phenyl succinic acid shown in the formula [ III ]; wherein the mole fraction of the structural unit derived from the liquid crystal element biphenyl dioxyhexanol shown in the formula [ I ] accounts for 50% of all the structural units, the mole fraction of the structural unit derived from the photo-crosslinking monomer 2,2' - (cinnamoyl azoalkanediyl) diethyl diacetate shown in the formula [ II ] accounts for 10-50% of all the structural units, and the balance is a connecting group derived from phenylsuccinic acid;
2. a main chain type liquid crystal elastomer with a side group containing cinnamyl crosslinking monomer is characterized in that: the main chain type liquid crystal elastomer is prepared by the following steps of aligning the liquid crystal copolyester in a liquid crystal state according to claim 1, and crosslinking and fixing the aligned state of a liquid crystal single domain through photochemical reaction.
3. A process for the preparation of a main chain liquid crystalline elastomer having pendant cinnamyl crosslinking monomers as claimed in claim 2, wherein: the preparation method of the liquid crystal elastomer comprises the following steps:
(1) heating and stirring liquid crystal element biphenyl dioxyhexanol, a photo-crosslinking monomer 2,2' - (cinnamoyl azoalkanediyl) diethyl diacetate and a connecting group phenyl succinic acid for reaction for 2-4 h at 170-220 ℃ under the action of a catalyst and the protection of nitrogen; then the reacted system continues to react under the vacuum condition, and the liquid crystal copolyester is obtained after the reaction is finished and is cooled;
(2) hot-pressing and cutting the liquid crystal copolyester obtained in the step (1), preparing a regular thin strip-shaped film sample strip as required, stretching and orienting the sample strip at a certain temperature, and then crosslinking by ultraviolet illumination at 25-55 ℃, wherein the wavelength of ultraviolet light is 280-365 nm, and the crosslinking time of two surfaces of the film sample strip is 1-3h, so as to obtain the main chain type liquid crystal elastomer with the side group containing the cinnamyl crosslinking monomer.
4. A process for the preparation of a main chain liquid crystalline elastomer having pendant cinnamyl crosslinking monomers as claimed in claim 3, wherein: the specific way of heating and stirring at 170-220 ℃ for reaction for 2-4 h in the step (1) is as follows: reacting at 170-200 ℃ for 1h, and then raising the temperature to 190-220 ℃ for reacting for 1-3h in half an hour; the reaction was continued under vacuum in the following manner: controlling the vacuum degree to be less than 30Pa, the reaction temperature of heating and stirring to be 190-220 ℃, and the reaction time to be 1-4 h.
5. A process for the preparation of a main chain liquid crystalline elastomer having pendant cinnamyl crosslinking monomers as claimed in claim 4, wherein: the catalyst in the step (1) is any one of zinc acetate, antimony trioxide, stannous octoate, dialkyl tin oxide or ethylene glycol antimony.
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