Electric heating material with high adhesive force to PET (polyethylene terephthalate) base material as well as preparation method and application of electric heating material

Abstract

The invention discloses an electric heating material with high adhesive force to a PET (polyethylene terephthalate) base material and a preparation method and application thereof, and the electric heating material takes a carbon material as a conducting medium, small organic molecules as a resin monomer, water as a solvent and a small amount of acid as a catalyst; the electrothermal material with high adhesive force to a polyethylene glycol terephthalate (PET) base material can be prepared after heating and curing, and belongs to the technical field of new materials. The invention also discloses a preparation method and an application of the composite material, the components are mixed and then printed on a polyethylene glycol terephthalate base material in a silk-screen printing mode, after heating and curing, the adhesive force can be effectively improved, and the composite material is very suitable for being used as a heating element of electric heating products such as electric heating carpets, electric heating cushions, electric heating gloves and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new materials, more particularly to an electrothermal material with high adhesion to a PET substrate and a preparation method and application thereof. BACKGROUND

[0002] Graphene is an emerging electrothermal material that is widely used in heating products such as electric floor heating, anti-fog film, and electric heating carpet due to its high electrothermal efficiency, silence, and long service life. Compared with resistance wire heating bodies, graphene materials have a larger heating area, more uniform heating, and faster heating rate. Moreover, graphene heating elements have an independent carrier and can be easily removed from the product. For products that need to be cleaned, such as electric heating carpets and electric heating clothing, graphene heating elements have a great advantage.

[0003] Polyethylene terephthalate is a commonly used substrate in graphene electrothermal products. Adhesion is a crucial indicator when evaluating the performance of graphene materials. Despite the fact that numerous patents use polyethylene terephthalate as the substrate for graphene electrothermal films, this field still faces many challenges and problems. For example, patent CN 110149738 A not only uses organic solvents but also uses a large amount of acidic ferrous chloride as a key raw material, both of which pose a threat to the environment. Similar environmental problems are also found in other patents, such as the use of strong acid in CN 112509729 B, the use of organic solvents in CN 110167216 A, and the use of highly toxic isocyanate compounds in CN 109618433 A. In addition, many patents, including CN 111726899 A and CN 114957761 A, do not test the adhesion between the electrothermal material and the substrate. Currently, only two patents, CN 111683420 A and CN 106229081 A, have tested graphene materials and polyethylene terephthalate, but these patents still cannot completely escape the problem of environmental protection. SUMMARY

[0004] Therefore, in order to solve the problems encountered by graphene materials, simplify the formula while ensuring performance, and realize the concept of green environmental protection, the present application provides an electrothermal material. The material has a simple formula, a green process, and can be substituted for or even surpass graphene materials in performance. The material uses carbon fibers as the conductive medium, organic small molecules as the resin monomer, water as the solvent, and a small amount of acid as the catalyst. After heating and curing, an electrothermal material with high adhesion to a polyethylene terephthalate substrate can be prepared. After mixing the above components and printing them on a polyethylene terephthalate substrate using silk-screen printing, the adhesion can be effectively improved after heating and curing, making it very suitable as a heating element for electric heating products such as electric heating carpets, electric heating cushions, and electric heating gloves.

[0005] To achieve the above object, the application adopts the following technical scheme: The high-adhesion electrocaloric material to PET substrate is a reticular polymer structure, and its structural formula is: .

[0006] The application further provides a preparation method of the high-adhesion electrocaloric material to PET substrate, comprising the following steps: S1. The monomer A is dispersed in water at room temperature, and is stirred for 20 min at a rotating speed of 600-880 rpm of the dispersing machine; after the rotating speed of the dispersing machine is adjusted to 600-1000 rpm, carbon material is added in three times according to a mass ratio of 1:1:1 in a stirring state; after all the carbon material is added, the rotating speed of the dispersing machine is adjusted to 1100-1500 rpm, and the slurry is stirred for 1 h until the surface of the slurry is uniform and free of granular substances; S2. The acid is added, and the stirring is continued for 5 min, so that a viscous slurry is obtained, which is a precursor of the high-adhesion electrocaloric material to PET substrate; S3. The electrocaloric material precursor is subjected to heat treatment, so that the high-adhesion electrocaloric material is obtained; The structural formula of the monomer A is: .

[0007] Preferably, the components are in parts by weight, and the monomer A is 100 parts, the carbon material is 5-41 parts, the acid is 0.4-2.7 parts, and the water is 53-76 parts.

[0008] Preferably, the content of the impurity 4- (oxirane-2-yl) benzoic acid in the monomer A is less than 0.1%.

[0009] Preferably, the carbon material is carbon fiber, and the carbon material provides good electrical conductivity for the electrocaloric material in the application. The acid is any one or several of boron trifluoride, aluminum trichloride or ferric trichloride, and the Lewis acids can be hydrolyzed in water to generate hydrogen ions. On the one hand, the hydrogen ions can reduce the bond energy of the C-O bond in the epoxy group, so that the epoxy group is more easily attacked by the carboxyl anion; on the other hand, the acidic environment promotes the protonation of the carboxyl group, increases the stability of the carboxyl anion, and improves the reaction efficiency.

[0010] Preferably, the heat treatment temperature in step S3 is 65 ℃.

[0011] The application further protects the application of the high-adhesion electrocaloric material to PET substrate in the preparation of a PET-based electrocaloric heating element, comprising the following steps: The electrothermal material with high adhesion to the PET substrate is attached to the surface layer of the PET substrate.

[0012] Preferably, the attachment method is that the electrothermal material precursor is printed on the surface of the PET substrate by silk screen printing using a 100 mesh screen plate, and then baked at 65 DEG C for 0.6-2 hours to form, and cooled to room temperature.

[0013] Preferably, the PET substrate is subjected to a corona treatment before use, and specifically, the surface of the PET substrate is subjected to a corona treatment by using a rotating Plasma surface treatment device, and the treatment is performed at a power of 500 W and a speed of 1 second per square decimeter.

[0014] In addition, the application also provides a synthesis method of the monomer A, comprising the following steps: 3-vinylbenzaldehyde is poured into tetrahydrofuran, the mixture is stirred uniformly, and then the temperature of the mixture is reduced to -10 DEG C, and lithium aluminum hydride is added to the mixture in three equal portions, wherein the molar ratio of lithium aluminum hydride to 3-vinylbenzaldehyde is 1.2:1, after the addition is completed, the stirring is continued at -10 DEG C until the 3-vinylbenzaldehyde is completely reacted, after the reaction is completed, the mixture is extracted with ethyl acetate three times, and the organic phase is combined and rotary evaporated to obtain a crude product 1; The crude product 1 and m-chloroperbenzoic acid are added to diethyl ether, wherein the molar ratio of the crude product 1 to m-chloroperbenzoic acid is 1:1.4, the mixture is stirred at room temperature for 24 hours, after the reaction is completed, the mixture is extracted with ethyl acetate three times, and the organic phase is combined and rotary evaporated to obtain a crude product 2; The crude product 2 is added to tetrahydrofuran, the mixture is cooled to 0 DEG C, and potassium permanganate is added to the mixture, wherein the molar ratio of the crude product 2 to potassium permanganate is 1:1.1, the stirring is continued until the crude product 2 is completely reacted, the mixture is extracted with ethyl acetate three times, and then the crude product is purified by silica gel column chromatography to obtain the monomer A.

[0015] Preferably, in the process of purification by silica gel column chromatography, the volume ratio of PE to EtOAc is 1:1.

[0016] According to the technical solution, compared with the prior art, the application provides an electrothermal material with high adhesion to a PET substrate, a preparation method and application thereof, and has the following beneficial effects: The structure of the monomer A and the polymer has the following characteristics: 1) Each monomer A molecule is connected with one epoxy group and one carboxyl group, each epoxy group can form an ester bond with two carboxyl groups, and finally a space network structure is formed; 2) A large number of active hydroxyl groups exist at the end of the polymer molecule, and the O atom and the H atom on the hydroxyl group form a hydrogen bond with the ester group on the surface of the polyethylene terephthalate substrate, thereby improving the adhesion. 3) The main structure of the polymer is polybenzoate, which is similar to the structure of polyethylene terephthalate, and the polarity of the two is very close, which makes the molecules on the surface of the polymer closely adhere to the surface of the substrate to increase the adhesion; 4) The epoxy group on the monomer molecule will hydrolyze two hydroxyl groups in acidic aqueous solution, and both hydroxyl and carboxyl groups are hydrophilic groups, so the monomer molecule has good solubility in water, which is convenient for adjusting the viscosity of the carbon material and convenient for screen printing.

[0017] After mixing the above components and printing on a polyethylene terephthalate substrate by screen printing, after heating and curing, the adhesion can be effectively improved, and it is very suitable for use as a heating element for electric heating products such as electric heating carpets, electric heating cushions, electric heating gloves, etc. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed in the embodiment or prior art description will be briefly introduced below. Obviously, the drawings described below are only some of the embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without creative labor.

[0019] Figure 1 It is the appearance photo of Example 1; Figure 2 It is the appearance photo of Example 2; Figure 3 It is the adhesion test photo of Comparative Example 1. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0021] In the following examples, the mass of each raw material is 10 grams, and the printing equipment is TX-5080SF-P type screen printing machine of Hangzhou Taoxing Printing Equipment Co., Ltd. Unless otherwise specified, the reagents, methods, instruments and equipment used in the present application are conventional reagents, methods, instruments and equipment in the art. (The synthesis raw materials of monomer A are also commercially available), and the synthesis process of monomer A is as follows:

[0022] S1: Synthesis of (3-vinylphenyl)methanol (1): The 3-vinylbenzaldehyde was poured into tetrahydrofuran, and the mixture was stirred uniformly, then the temperature of the mixture was reduced to -10 ℃, and the lithium aluminum hydride was added into the mixture in three times (the molar ratio of lithium aluminum hydride: 3-vinylbenzaldehyde = 1.2:1). After the addition was completed, the stirring was continued at -10 ℃ until the 3-vinylbenzaldehyde was completely reacted. After the reaction was completed, the extraction was performed three times with ethyl acetate (100 mL x 3), and the organic phase was combined and spin-dried to obtain the crude product 1.

[0023] S2: Synthesis of (3-(oxirane-2-yl)phenyl)methanol (2): The crude product 1 and meta-chloro peroxide benzoic acid were added into ethyl ether (the molar ratio of crude product 1: meta-chloro peroxide benzoic acid = 1:1.4). The stirring was performed at room temperature for 24 hours, and after the reaction was completed, the extraction was performed three times with ethyl acetate (100 mL x 3), and the organic phase was combined and spin-dried to obtain the crude product 2.

[0024] S3: Synthesis of 3-(oxirane-2-yl)benzoic acid (A): The crude product 2 was added into tetrahydrofuran, and the mixture was cooled to 0 ℃. The potassium permanganate was added into the mixture (the molar ratio of crude product 2: potassium permanganate = 1:1.1), and the stirring was continued until the crude product 2 was completely reacted. The extraction was performed three times with ethyl acetate (100 mL x 3), and then the crude product was purified by silica gel column chromatography (PE / EtOAc = 1:1) to obtain the monomer A.

[0025] The nuclear magnetic resonance data of the monomer A are as follows: 1 H (200 MHz, CDCl3) δ 2.85 (dd, J = 5.4, 2.6 Hz, 1H), 3.2 (dd, J =5.2, 4.1 Hz, 1H), 3.9 (dd, J = 4.1, 2.6 Hz, 1H), 7.5-7.6 (m, 2H), 8.1-8.2 (m,2H); 13 C (75.5 MHz, CDCl3) δ 51.4, 52.0, 127.6, 128.6, 130, 130.8, 134.7,138.5, 171.3.

[0026] Example 1 According to the weight proportion of each component raw material: 100 parts of monomer A, 11 parts of carbon fiber, 0.7 parts of aluminum chloride, and 66 parts of water.

[0027] In the normal temperature environment, monomer A is added into water, stirring for 20 minutes at the speed of 660 rpm of the disperser; carbon fiber is added into the solution in batches, dispersing at the speed of 830 rpm of the disperser; after all the carbon fiber is added, the speed of the disperser is increased to 1210 rpm, stirring for 1 hour until the surface of the slurry is uniform without granular material; aluminum chloride is added, continuing to stir for 5 minutes; the obtained viscous slurry is the precursor of the electrothermal material with high adhesion to the polyethylene terephthalate substrate; The application step is: before printing, the protective layer material precursor needs to be stirred uniformly in the dark, then it is printed on the polyethylene terephthalate substrate by the way of silk screen printing, after printing, it is baked in the air oven at 65 ℃ for 1.4 hours, the polyethylene terephthalate is taken out and cooled to room temperature; The silver paste is printed on both ends of the electrothermal material by the way of silk screen printing, then it is baked in the air oven at 40 ℃ for 0.5 hours, the polyethylene terephthalate is taken out and cooled to room temperature, thus the heating sheet with electrothermal effect of example 1 is obtained.

[0028] Example 2 According to the weight proportion, the raw materials of each component are: monomer A 100 parts, carbon fiber 35 parts, boron trifluoride 2 parts, water 69 parts.

[0029] In the normal temperature environment, monomer A is added into water, stirring for 20 minutes at the speed of 640 rpm of the disperser; carbon fiber is added into the solution in batches, dispersing at the speed of 920 rpm of the disperser; after all the carbon fiber is added, the speed of the disperser is increased to 1350 rpm, stirring for 1 hour until the surface of the slurry is uniform without granular material; boron trifluoride is added, continuing to stir for 5 minutes; the obtained viscous slurry is the precursor of the electrothermal material with high adhesion to the polyethylene terephthalate substrate; The application step is: before printing, the protective layer material precursor needs to be stirred uniformly in the dark, then it is printed on the polyethylene terephthalate substrate by the way of silk screen printing, after printing, it is baked in the air oven at 65 ℃ for 0.8 hours, the polyethylene terephthalate is taken out and cooled to room temperature; The silver paste is printed on both ends of the electrothermal material by the way of silk screen printing, then it is baked in the air oven at 40 ℃ for 0.5 hours, the polyethylene terephthalate is taken out and cooled to room temperature, thus the heating sheet with electrothermal effect of example 2 is obtained.

[0030] Example 3 According to the weight proportion, the raw materials of each component are: monomer A 100 parts, carbon fiber 38 parts, aluminum chloride 2.1 parts, water 57 parts.

[0031] In the normal temperature environment, monomer A is added into water, stirring for 20 minutes at the speed of 670 rpm of the disperser; carbon fiber is added into the solution in batches, dispersing at the speed of 940 rpm of the disperser; after all the carbon fiber is added, the speed of the disperser is increased to 1400 rpm, stirring for 1 hour until the surface of the slurry is uniform without granular material; aluminum chloride is added, continuing to stir for 5 minutes; the obtained viscous slurry is the precursor of the electrothermal material with high adhesion to the polyethylene terephthalate substrate; The application step is: before printing, the protective layer material precursor needs to be stirred uniformly in the dark, and then it is printed on the polyethylene terephthalate substrate by means of silk screen printing; after printing, the polyethylene terephthalate is taken out and cooled to room temperature after being baked in a blast oven at 65 ℃ for 1.5 hours; Silver paste is printed on both ends of the electrothermal material by means of silk screen printing, and then the polyethylene terephthalate is taken out and cooled to room temperature after being baked in a blast oven at 40 ℃ for 0.5 hours, so that the heating sheet with electrothermal effect of Example 3 is obtained.

[0032] Example 4 According to the weight proportion of each component raw material: monomer A 100 parts, carbon fiber 40 parts, ferric chloride 0.9 parts, water 55 parts.

[0033] In the normal temperature environment, monomer A is added into water, stirring for 20 minutes at the speed of 760 rpm of the disperser; carbon fiber is added into the solution in batches, dispersing at the speed of 680 rpm of the disperser; after all the carbon fiber is added, the speed of the disperser is increased to 1170 rpm, stirring for 1 hour until the surface of the slurry is uniform without granular material; ferric chloride is added, continuing to stir for 5 minutes; the obtained viscous slurry is the precursor of the electrothermal material with high adhesion to the polyethylene terephthalate substrate; The application step is: before printing, the protective layer material precursor needs to be stirred uniformly in the dark, and then it is printed on the polyethylene terephthalate substrate by means of silk screen printing; after printing, the polyethylene terephthalate is taken out and cooled to room temperature after being baked in a blast oven at 65 ℃ for 1.9 hours; Silver paste is printed on both ends of the electrothermal material by means of silk screen printing, and then the polyethylene terephthalate is taken out and cooled to room temperature after being baked in a blast oven at 40 ℃ for 0.5 hours, so that the heating sheet with electrothermal effect of Example 4 is obtained.

[0034] Example 5 According to the weight proportion of each component raw material: monomer A 100 parts, carbon fiber 20 parts, ferric chloride 2.3 parts, water 74 parts.

[0035] In the normal temperature environment, monomer A is added into water, stirred for 20 minutes at the speed of 830 rpm of the disperser; carbon fiber is added into the solution in batches, dispersed at the speed of 940 rpm of the disperser; after all the carbon fiber is added, the speed of the disperser is increased to 1280 rpm, and stirred for 1 hour until the surface of the slurry is uniform without granular material; ferric chloride is added, and stirred for 5 minutes; the obtained viscous slurry is an electrothermal material precursor with high adhesion to polyethylene terephthalate substrate; The application step is as follows: before printing, the protective layer material precursor is uniformly stirred in the dark, and then is printed on the polyethylene terephthalate substrate by means of silk screen printing; after printing, the polyethylene terephthalate is taken out and cooled to room temperature after being baked at 65 ℃ for 2 hours by using a blast oven. Silver paste is printed on both ends of the electrothermal material by means of silk screen printing, and then the polyethylene terephthalate is taken out and cooled to room temperature after being baked at 40 ℃ for 0.5 hours by using a blast oven, so that a heating sheet with electrothermal effect of Example 5 is obtained.

[0036] In Examples 1-5, the chemical reaction equation of monomer A after heat treatment is as follows:

[0037] The final network polymer molecular structure formula obtained on the PET surface is as follows:

[0038] Comparative Example 1 The raw material formula and preparation steps are the same as those of Example 1, except that no acid is added.

[0039] The application step is as follows: before printing, the electrothermal material precursor is uniformly stirred, and then is printed on the polyethylene terephthalate substrate by means of 100-mesh silk screen printing; the polyethylene terephthalate is taken out and cooled to room temperature after being baked at 65 ℃ for 1.4 hours by using a blast oven. Silver paste is printed on both ends of the electrothermal material by means of silk screen printing, and then the polyethylene terephthalate is taken out and cooled to room temperature after being baked at 40 ℃ for 0.5 hours by using a blast oven, so that a heating sheet with electrothermal effect of Comparative Example 1 is obtained.

[0040] Comparative Example 2 The raw material formula and preparation steps are the same as those of Example 2, except that the amount of carbon fiber is 80 parts.

[0041] The application steps are as follows: the electrothermal material precursor is stirred uniformly before printing, and is printed on the polyethylene terephthalate substrate by 100-mesh screen printing, and is baked in a blast oven at 65°C for 0.8 h, and the polyethylene terephthalate is taken out and cooled to room temperature; Silver paste is printed on both ends of the electrothermal material by screen printing, and then the polyethylene terephthalate is baked in a blast oven at 40°C for 0.5 h, and is cooled to room temperature, to obtain the heating sheet of Comparative Example 2 having an electrothermal effect.

[0042] Experimental Examples Examples 1-5 and Comparative Examples 1-2 are tested according to the standards in Table 1, and the test results are shown in Table 2.

[0043] Table 1 Test content

[0044] Table 2 Test results

[0045] From the above results, it can be seen that Examples 1-5 can meet the requirements of appearance, adhesion and flexibility, and the resistance decreases with the increase of carbon material, and in addition, the trend of resistance decrease gradually slows down with the increase of carbon material. Comparative Example 1 lacks acid, so the reaction is incomplete, and the monomer molecules cannot be polymerized. On the one hand, the carbon material agglomerates cannot pass through the screen, resulting in an increase in the printed coating resistance; on the other hand, the conductive material precursor with too small viscosity has an overflow phenomenon. In Comparative Example 2, the carbon material is too much, and the viscosity of the conductive material precursor is very large, so it cannot be printed through the screen at all, and will be adhered to the screen.

[0046] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts of each embodiment can be referred to each other. The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrocaloric material having high adhesion to a PET substrate, characterized in that, The electrocaloric material is a reticular polymer structure, and its structural formula is: 。 2. The electrocaloric material having high adhesion to a PET substrate according to claim 1, characterized in that, The method comprises the following steps: S1. At room temperature, the monomer A is dispersed in water, and stirred at a rotational speed of 600-880 rpm of the dispersing machine for 20 min; after adjusting the rotational speed of the dispersing machine to 600-1000 rpm, carbon materials are added in three times at a mass ratio of 1:1:1 under stirring; after all the carbon materials are added, the rotational speed of the dispersing machine is adjusted to 1100-1500 rpm, and stirring is performed for 1 h until the surface of the slurry is uniform and free of granular substances; S2. Acid is added, and stirring is continuously performed for 5 min, so that a viscous slurry, which is an electrocaloric material precursor with high adhesion to a PET substrate, is obtained; S3. The electrocaloric material precursor is subjected to heat treatment, so that an electrocaloric material with high adhesion is obtained; The structural formula of the monomer A is: 。 3. The method of claim 2, wherein the electrocaloric material has a high adhesion to the PET substrate. The monomer A is 100 parts, the carbon material is 5-41 parts, the acid is 0.4-2.7 parts, and the water is 53-76 parts in terms of weight parts.

4. The method of claim 2 or 3, wherein the method is characterized by, The carbon material is carbon fiber, and the acid is any one or several of boron trifluoride, aluminum trichloride or iron trichloride.

5. The method of claim 2, wherein the electrocaloric material has a high adhesion to the PET substrate. The heat treatment temperature in step S3 is 65 ℃.

6. Use of the electrocaloric material having high adhesion to PET substrate according to claim 1 for the production of PET-based electrocaloric heating elements, characterized by the fact that, The method comprises the following steps: The electrocaloric material with high adhesion to the PET substrate is attached to the surface layer of the PET substrate.

7. Use according to claim 6, characterized in that, The attachment method is that the electrocaloric material precursor is printed on the surface of the PET substrate in the form of silk screen printing by using a 100-mesh screen plate, and then is baked at 65 ℃ for 0.6-2 h to form a shape, and is cooled to room temperature.

8. Use according to claim 6, characterized in that, The PET substrate is subjected to corona treatment before use.

9. A method of synthesizing monomer A according to claim 2, characterized in that, The method comprises the following steps: 3-Vinylbenzaldehyde is poured into tetrahydrofuran, and after stirring, the temperature of the mixture is reduced to -10 ℃; tetrahydroaluminum lithium is added into the mixture in three equal portions, and the molar ratio of tetrahydroaluminum lithium to 3-vinylbenzaldehyde is 1.2:1; after the addition is completed, stirring is continuously performed at -10 ℃ until 3-vinylbenzaldehyde is completely reacted; after the reaction is completed, 3-vinylbenzaldehyde is extracted with ethyl acetate for three times; the organic phases are combined and rotary evaporated to obtain a crude product 1; The crude product 1 and meta-chloro peroxi benzoic acid are added into ethyl ether, and the molar ratio of the crude product 1 to meta-chloro peroxi benzoic acid is 1:1.4; stirring is performed at room temperature for 24 h; after the reaction is completed, the crude product 2 is extracted with ethyl acetate for three times; the organic phases are combined and rotary evaporated to obtain a crude product 2; The crude product 2 is added into tetrahydrofuran, and the mixture is cooled to 0 ℃; potassium permanganate is added into the mixture, and the molar ratio of the crude product 2 to potassium permanganate is 1:1.1; stirring is continuously performed until the crude product 2 is completely reacted; the crude product is extracted with ethyl acetate for three times, and then is purified by silica gel column chromatography, so that the monomer A is obtained.

10. The method of synthesis of claim 9, wherein, In the purification process by silica gel column chromatography, the volume ratio of PE to EtOAc is 1:1.

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