A light-responsive reversible adhesive and its preparation method and application

Abstract

The present invention belongs to the fields of adhesives and stimuli-responsive materials, and particularly relates to a photo-responsive reversible adhesive and its preparation method and application. The azobenzene-based hyperbranched polymer reversible adhesive provided by the present invention introduces a large number of hydrogen bonds into the system through the selection of monomers, improving the adhesion of the azobenzene-based adhesive. Its shear adhesion strength on a glass substrate can reach 8.07 MPa. In addition, for the azobenzene-based hyperbranched polymer reversible adhesive provided by the present invention, by grafting azobenzene at the end of the hyperbranched polymer, the drawback of the easy entanglement of the main chain in common linear side-chain azobenzene polymers is avoided. Through the conformational transformation of azobenzene, relative movement is more likely to occur between hyperbranched polymer molecules, increasing the switching ratio of the adhesion strength during adhesion and debonding of the adhesive (up to 53.80), making it easier to peel off the adhered substrate.

Description

Technical Field

[0001] The present invention belongs to the fields of adhesives and stimulus-responsive materials, and particularly relates to a photo-responsive reversible adhesive and its preparation method and application. Background Art

[0002] An adhesive is a functional substance that connects two or more identical or different materials together through actions such as interfacial adhesion and cohesion of substances. Depending on the application scenario and the substrate, adhesives must meet various requirements, and their categories include everything from tapes to permanent "super glues" to structural adhesives with high load-bearing capacity.

[0003] With the development of technology and the needs of commercial applications, traditional adhesives have limitations in their applications in cutting-edge technology fields such as electronic skin, semiconductor packaging, and simulation robots due to defects such as difficulty in debonding and recycling. Therefore, adhesives that can achieve reversible adhesion have received extensive attention. Reversible adhesives can be adjusted by their response to external stimuli (such as temperature, light, electricity, pH, etc.) to adhere and debond on demand and can be reused multiple times, which is both environmentally friendly and economical. Among them, photo-responsive debonding has become an emerging technology field in recent years. It can achieve efficient and contactless remote stimulation, and parameters such as irradiation wavelength, intensity, area, and time are easy to adjust. Azobenzene and its derivatives, as a common photo-responsive material, can undergo conformational transitions between cis and trans forms under irradiation with light of different wavelengths, and then undergo a transition in melting point or glass transition temperature macroscopically, resulting in a solid-liquid transition of the material. Its trans structure is solid macroscopically and can firmly adhere the substrates together; while its cis structure is liquid macroscopically and loses the adhesion effect between the substrates. Therefore, it can be used to prepare photo-responsive reversible adhesives.

[0004] Currently, the adhesion strength of common small-molecule azobenzene-based reversible adhesives is relatively low. For example, the highest adhesion strength of the small-molecule azo derivatives prepared by Huang et al. in recent years is only 1.58 MPa (Xianhui Huang, Zhichun Shangguan, Zhao-Yang Zhang, et al. Visible-Light-Induced Reversible Photochemical Crystal−Liquid Transitions of Azo-Switches for Smart and Robust Adhesives[J]. Chemistry of Materials, 2022, 34, 2636−2644.). Although the adhesion strength of azobenzene-based polymer adhesives is relatively high, since common azobenzene-based polymers are mostly linear side-chain azobenzene polymers, there is a problem of easy entanglement of the main chain, resulting in a relatively low switching of the adhesion strength during adhesion and debonding, which affects the peeling effect. For example, Ito et al. synthesized an ABA-type triblock copolymer composed of a methacrylate copolymer containing an azobenzene group side chain (A segment) and a 2-ethylhexyl side chain (B segment) for photo-controlled adhesion, but its switching ratio is only 4.17 (Shotaro Ito, Haruhisa Akiyama, Reiko Sekizawa, et al. Light-Induced Reworkable Adhesives Based on ABA-type Triblock Copolymers with Azopolymer Termini[J]. ACS Applied Materials & Interfaces, 2018, 10, 32649−32658.). Hyperbranched polymers have the advantages of difficult intermolecular entanglement and high terminal functional group density. Therefore, after introducing azobenzene at their terminals, a relatively high switching ratio can be achieved. At the same time, by selecting monomers, hydrogen bonds can be introduced into hyperbranched polymers, which improves the adhesion strength. The adhesion strength of the azobenzene-based hyperbranched polymer prepared in Comparative Patent CN114133547A is only 2.02 MPa. Through the photoisomerization of azobenzene, the hydrogen bonds can be regulated, thereby realizing the adhesion / debonding cycle of the hyperbranched polymer reversible adhesive.

[0005] CN114410252B and CN115058217B disclose photo-responsive reversible adhesives. The prepared reversible adhesive polymers are all linear side-chain azobenzene copolymers with a linear main chain and azobenzene or other functional groups as side chains. One characteristic of such polymers is that the main chain is prone to entanglement, resulting in poor liquefaction effect after ultraviolet light irradiation, and further affecting the switching ratio of the adhesion strength during adhesion and debonding. The specific values of the adhesion strength and switching ratio after the adhesive liquefies under ultraviolet light irradiation are not mentioned in the examples of these two patents. The reversible adhesive prepared in the present invention is a hyperbranched polymer, which inherently has the characteristics of difficult intermolecular entanglement and easy movement. Therefore, the adhesion strength is very low after liquefaction and debonding under ultraviolet light irradiation, and has a very high switching ratio. Secondly, the polymerization methods used in the preparation of adhesives in these two prior arts both require the use of a double-tube to evacuate and introduce nitrogen to create an anhydrous and anaerobic environment, and the implementation conditions are relatively harsh. The present invention uses Michael addition reaction in the preparation of hyperbranched polymer adhesives, without considering the influence of water and oxygen environment, and the implementation conditions are simple and convenient.

[0006] The literature "Photochromic dendrimers for photoswitched solid-to-liquid transitions and solar thermal fuels" also uses a hyperbranched polymer core grafted with azobenzene monomers, but the structure of the hyperbranched polymer core prepared by it is different from that in the present application, and the maximum adhesion strength of the adhesive prepared in the present application is higher than the adhesion strength of this literature (8.07 MPa in the present application and 1.62 NPa in the literature). Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the present invention provides a photo-responsive reversible adhesive, its preparation method and application.

[0008] The technical solution of the present invention is as follows: A reversible adhesive of azobenzene-based hyperbranched polymer is prepared by Michael addition reaction of azobenzene-based acrylate monomer, N, N-methylenebisacrylamide and diamine monomer, and the molar ratio of the azobenzene-based acrylate monomer, N, N-methylenebisacrylamide and diamine monomer is (0.2~0.8):0.9:1.

[0009] Among them, N, N-methylenebisacrylamide and diamine monomers introduce a variety of hydrogen bonds (such as Figure 1 ) in the reversible adhesive, which improves the adhesion strength of the adhesive; the azobenzene-based acrylate monomer endows the adhesive with photo-responsive characteristics, realizing its reversible adhesion effect.

[0010] In some embodiments, the azobenzene acrylate monomer is selected from one of 6-(4-(phenyldiazenyl)phenoxy)-hexyl acrylate and 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate.

[0011] In some embodiments, the diamine monomer is selected from one of polyetheramine D-230, 1,4-butanediamine, 1,6-hexanediamine, and 1,8-octanediamine, and preferably 1,8-octanediamine.

[0012] The present invention provides a method for preparing the azobenzene-based hyperbranched polymer reversible adhesive, comprising the following steps:

[0013] 1) Preparation of azobenzene acrylate monomer (AZOn): React 4-phenylazophenol with a haloalcohol, and then react the obtained product with acryloyl chloride to obtain the azobenzene acrylate monomer.

[0014] 2) Preparation of hyperbranched polymer core (HBP): Perform a Michael addition reaction between N,N-methylenebisacrylamide (MBA) and the diamine monomer to obtain a random hyperbranched polymer core (HBP).

[0015] 3) Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Perform a Michael addition reaction between the azobenzene acrylate monomer and the amino group at the end of HBP to obtain the azobenzene-based hyperbranched polymer reversible adhesive HBP-AZOn.

[0016] In some embodiments, the haloalcohol in step 1) is selected from 6-chloro-1-hexanol or 9-chloro-1-nonanol.

[0017] The present invention provides the application of the above azobenzene-based hyperbranched polymer reversible adhesive in the preparation of reversible adhesion and stimulus-responsive materials.

[0018] Advantages of the present invention: 1) Through the selection of monomers, a large number of hydrogen bonds are introduced into the system in the hyperbranched polymer reversible adhesive provided by the present invention, enhancing the adhesion of the azobenzene-based adhesive, and its shear adhesion strength on a glass substrate can reach 8.07 MPa.

[0019] In the hyperbranched polymer reversible adhesive provided by the present invention, by grafting azobenzene at the end of the hyperbranched polymer, the drawback of the easy entanglement of the main chain in common linear side-chain azobenzene polymers is avoided. Through the conformational transformation of azobenzene, relative movement between hyperbranched polymer molecules is more likely to occur, increasing the switching ratio of the adhesion strength during adhesion and debonding of the adhesive (up to 53.80), making it easier to peel off the adhered substrate. Description of the Drawings

[0020] Figure 1Hydrogen bonds existing in the azobenzene-based hyperbranched polymer reversible adhesive

[0021] Figure 2 Preparation process of the azobenzene-based hyperbranched polymer reversible adhesive

[0022] Figure 3 Photo-responsive properties of the azobenzene-based hyperbranched polymer reversible adhesive prepared in Example 6

[0023] Figure 4 Adhesion strength curve graph of the azobenzene-based hyperbranched polymer reversible adhesive prepared in Example 6

[0024] Figure 5 Adhesion cyclic test of the azobenzene-based hyperbranched polymer reversible adhesive prepared in Example 6

[0025] Figure 6 Schematic diagram of the azobenzene-based hyperbranched polymer reversible adhesive prepared in Example 6 capable of lifting a 24.20 kg heavy object Specific implementation manners

[0026] The following examples can enable those skilled in the art of this specialty to understand the present invention more comprehensively, but do not limit the present invention to the scope of the described examples. Examples

[0027] Preparation of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol: Dissolve 7.1 g of 4-phenylazophenol in 40 mL of N,N-dimethylformamide, and then add 4.9 g of potassium carbonate. The solution is stirred at 30 °C for 30 min. Then, add 0.015 g of potassium iodide and 5.335 g of 6-chloro-1-hexanol to the solution. The reaction mixture is then stirred at 110 °C for 24 h. After the reaction is completed, the system is naturally cooled to room temperature and poured into 900 g of ice-water mixture, producing a brown-red flocculent precipitate. The precipitate is filtered out and vacuum dried overnight at 45 °C. The obtained crude product is further purified by recrystallization with ethanol, and then vacuum dried at 45 °C for 24 h to obtain the final product, which is a red-brown solid.

[0028] Preparation of 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate: Weigh 4.768 g of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine, which is Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane, which is Component 2. Under an ice-water bath condition, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution, and saturated sodium chloride solution. Collect the organic layer and remove the solvent using a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is vacuum dried at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0029] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate, N,N-methylenebisacrylamide, and polyetheramine D-230 according to a molar ratio of 0.2:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add polyetheramine D-230 and stir at 60 °C for 24 h. Then add 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate to the system and continue to stir at 60 °C for 24 h. After the reaction is completed, naturally cool the system to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water multiple times, and vacuum dry it at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0030] Photoresponse performance of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the conformational transformation of azobenzene groups from trans conformation to cis conformation, the glass transition temperature of the polymer decreases, and thus a solid-liquid conversion phenomenon occurs. After irradiating for 3 - 5 min, the polymer starts to liquefy and the color turns orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible light lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon does not show obvious attenuation.

[0031] Reversible Adhesion Performance of the Azobenzene-based Hyperbranched Polymer Reversible Adhesive Prepared in the Example: Two pieces of glass with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. Take 20 mg of the adhesive in the trans conformation and place it on a glass substrate. Irradiate it with a 365 nm ultraviolet lamp for 15 min until it is completely liquefied. Then, place another glass substrate on the liquefied adhesive. The adhesion area is 10 mm × 25 mm, and the thickness of the adhesion layer is 0.1 mm. After that, irradiate the adhesion area with a 530 nm visible light lamp for 20 min to cure the adhesive to bond the two glass substrates together. Fix the adhered glass substrates on a universal material testing machine and stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the trans conformation is 2.63 MPa. Then, fix the adhered glass substrates on a universal material testing machine and irradiate the adhesion area with a 365 nm ultraviolet lamp for 15 min. Then, stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the cis conformation is 0.07 MPa. Divide the adhesion strength in the trans conformation by the adhesion strength in the cis conformation to obtain a switching ratio of 37.57. Example

[0032] Preparation of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol: Dissolve 7.1 g of 4-phenylazophenol in 40 mL of N,N-dimethylformamide, and then add 4.9 g of potassium carbonate. Stir the solution at 30 °C for 30 min. Then, add 0.015 g of potassium iodide and 5.335 g of 6-chloro-1-hexanol to the solution. The reaction mixture is then stirred and reacted at 110 °C for 24 h. After the reaction is completed, cool the system to room temperature naturally and pour it into 900 g of ice-water mixture to produce a brownish-red flocculent precipitate. Filter out the precipitate and dry it under vacuum at 45 °C overnight. The obtained crude product is further purified by recrystallization from ethanol, and then dried under vacuum at 45 °C for 24 h to obtain the final product, which is a reddish-brown solid.

[0033] Preparation of 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate: Weigh 4.768 g of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine to obtain Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane to obtain Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution, and saturated sodium chloride solution. Collect the organic layer and remove the solvent using a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is dried in vacuo at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0034] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate, N,N-methylenebisacrylamide, and 1,4-butanediamine according to a molar ratio of 0.2:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,4-butanediamine and stir at 60 °C for 24 h. Then add 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate to the system and continue to stir at 60 °C for 24 h. After the reaction is completed, let the system cool naturally to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water several times, and dry it in vacuo at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0035] Photoresponse properties of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the conformational transition of the azobenzene group from the trans conformation to the cis conformation, the glass transition temperature of the polymer decreases, resulting in a solid-liquid conversion phenomenon. After irradiating for 3 - 5 min, the polymer begins to liquefy and the color changes to orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon does not show obvious attenuation.

[0036] Reversible Adhesion Performance of the Azobenzene-based Hyperbranched Polymer Reversible Adhesive Prepared in the Example: Two glass pieces with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. 20 mg of the adhesive in the trans conformation was placed on one glass substrate and irradiated with a 365 nm ultraviolet lamp for 15 min until it was completely liquefied. Then, another glass substrate was placed on the liquefied adhesive, with the adhesion area being 10 mm × 25 mm and the adhesion layer thickness being 0.1 mm. After that, the adhesion area was irradiated with a 530 nm visible light lamp for 20 min to cure the adhesive and bond the two glass substrates together. The bonded glass substrates were fixed on a universal material testing machine and stretched at a tensile rate of 5 mm / min until the adhesion area was completely damaged. Five tensile tests were repeated and the average value was taken. The adhesion strength in the trans conformation was measured to be 3.27 MPa. Then, the bonded glass substrates were fixed on the universal material testing machine and the adhesion area was irradiated with a 365 nm ultraviolet lamp for 15 min. After that, it was stretched at a tensile rate of 5 mm / min until the adhesion area was completely damaged. Five tensile tests were repeated and the average value was taken. The adhesion strength in the cis conformation was measured to be 0.12 MPa. The switching ratio was obtained by dividing the adhesion strength in the trans conformation by the adhesion strength in the cis conformation, which was 27.52. Example

[0037] Preparation of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol: 7.1 g of 4-phenylazophenol was dissolved in 40 mL of N,N-dimethylformamide, and then 4.9 g of potassium carbonate was added. The solution was stirred at 30 °C for 30 min. Then, 0.015 g of potassium iodide and 5.335 g of 6-chloro-1-hexanol were added to the solution. The reaction mixture was then stirred at 110 °C for 24 h. After the reaction was completed, the system was naturally cooled to room temperature and poured into 900 g of an ice-water mixture, resulting in a brownish-red flocculent precipitate. The precipitate was filtered out and vacuum-dried overnight at 45 °C. The obtained crude product was further purified by recrystallization from ethanol and then vacuum-dried at 45 °C for 24 h to obtain the final product, which was a reddish-brown solid.

[0038] Preparation of 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate: Weigh 4.768 g of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine, which is Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane, which is Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution, and saturated sodium chloride solution. Collect the organic layer and remove the solvent using a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is dried in vacuo at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0039] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate, N,N-methylenebisacrylamide, and 1,6-hexanediamine according to a molar ratio of 0.2:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,6-hexanediamine and stir at 60 °C for 24 h. Then add 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate to the system and continue to stir at 60 °C for 24 h. After the reaction is completed, let the system cool naturally to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water multiple times, and dry it in vacuo at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0040] Photo-responsive properties of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the conformational transformation of azobenzene groups from trans to cis, the glass transition temperature of the polymer decreases, resulting in a solid-liquid conversion phenomenon. After irradiating for 3 - 5 min, the polymer begins to liquefy, and the color changes to orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon does not show obvious attenuation.

[0041] Reversible adhesion performance of the azobenzene-based hyperbranched polymer reversible adhesive prepared in the example: Two pieces of glass with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. Take 20 mg of the adhesive in the trans conformation and place it on a glass substrate. Irradiate it with a 365 nm ultraviolet lamp for 15 min until it is completely liquefied. Then, place another glass substrate on the liquefied adhesive. The adhesion area is 10 mm × 25 mm, and the thickness of the adhesion layer is 0.1 mm. After that, irradiate the adhesion area with a 530 nm visible light lamp for 20 min to cure the adhesive to bond the two glass substrates together. Fix the adhered glass substrates on a universal material testing machine and stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the tensile test five times and take the average value. The measured adhesion strength in the trans conformation is 6.43 MPa. Then, fix the adhered glass substrates on a universal material testing machine and irradiate the adhesion area with a 365 nm ultraviolet lamp for 15 min. Then, stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the tensile test five times and take the average value. The measured adhesion strength in the cis conformation is 0.20 MPa. Divide the adhesion strength in the trans conformation by the adhesion strength in the cis conformation to obtain a switching ratio of 32.15. Example

[0042] Preparation of 6-(4-(phenyldiazeneyl)phenoxy)-1-hexanol: Dissolve 7.1 g of 4-phenylazophenol in 40 mL of N,N-dimethylformamide, and then add 4.9 g of potassium carbonate. Stir the solution at 30 °C for 30 min. Then, add 0.015 g of potassium iodide and 5.335 g of 6-chloro-1-hexanol to the solution. The reaction mixture is then stirred at 110 °C for 24 h. After the reaction is completed, cool the system to room temperature naturally and pour it into 900 g of ice-water mixture to produce a brown-red flocculent precipitate. Filter out the precipitate and dry it under vacuum at 45 °C overnight. The obtained crude product is further purified by recrystallization from ethanol, and then dried under vacuum at 45 °C for 24 h to obtain the final product, which is a red-brown solid.

[0043] Preparation of 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate: Weigh 4.768 g of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine, which is Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane, which is Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution, and saturated sodium chloride solution. Collect the organic layer and remove the solvent using a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is vacuum dried at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0044] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate, N,N-methylenebisacrylamide, and 1,8-octanediamine according to a molar ratio of 0.2:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,8-octanediamine and stir at 60 °C for 24 h. Then add 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate to the system and continue to stir at 60 °C for 24 h. After the reaction is completed, let the system cool naturally to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water multiple times, and vacuum dry it at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0045] Photoresponse properties of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the transformation of the azobenzene group from the trans conformation to the cis conformation, the glass transition temperature of the polymer decreases, so a solid-liquid conversion phenomenon will occur. After irradiating for 3 - 5 min, the polymer begins to liquefy, and the color changes to orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible light lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon does not show obvious attenuation.

[0046] Reversible adhesion performance of the azobenzene-based hyperbranched polymer reversible adhesive prepared in the example: Two pieces of glass with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. Take 20 mg of the adhesive in the trans conformation and place it on a glass substrate. Irradiate it with a 365 nm ultraviolet lamp for 15 min until it is completely liquefied, and then place another glass substrate on the liquefied adhesive. The adhesion area is 10 mm × 25 mm, and the thickness of the adhesion layer is 0.1 mm. Then, irradiate the adhesion area with a 530 nm visible light lamp for 20 min to cure the adhesive to bond the two glass substrates together. Fix the adhered glass substrates on a universal material testing machine and stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the trans conformation is 6.57 MPa. Then, fix the adhered glass substrates on a universal material testing machine and irradiate the adhesion area with a 365 nm ultraviolet lamp for 15 min. Then, stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the cis conformation is 0.14 MPa. Divide the adhesion strength in the trans conformation by the adhesion strength in the cis conformation to obtain a switching ratio of 46.93. Example

[0047] Preparation of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol: Dissolve 7.1 g of 4-phenylazophenol in 40 mL of N,N-dimethylformamide, and then add 4.9 g of potassium carbonate. Stir the solution at 30 °C for 30 min. Then, add 0.015 g of potassium iodide and 5.335 g of 6-chloro-1-hexanol to the solution. The reaction mixture was then stirred at 110 °C for 24 h. After the reaction, the system was naturally cooled to room temperature and poured into 900 g of an ice-water mixture to produce a brownish-red flocculent precipitate. Filter out the precipitate and dry it under vacuum at 45 °C overnight. The obtained crude product was further purified by recrystallization from ethanol, and then dried under vacuum at 45 °C for 24 h to obtain the final product, which is a reddish-brown solid.

[0048] Preparation of 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate: Weigh 4.768 g of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine, which is Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane, which is Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution, and saturated sodium chloride solution. Collect the organic layer and remove the solvent using a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is dried in vacuo at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0049] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate, N,N'-methylenebisacrylamide, and 1,8-octanediamine according to a molar ratio of 0.4:0.9:1. First, add N,N'-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,8-octanediamine and stir the reaction at 60 °C for 24 h. Then add 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate to the system and continue to stir the reaction at 60 °C for 24 h. After the reaction is completed, let the system cool naturally to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it repeatedly with ether and deionized water alternately, and dry it in vacuo at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0050] Photoresponsive properties of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the transformation of the azobenzene group from the trans conformation to the cis conformation, the glass transition temperature of the polymer decreases, and thus a solid-liquid conversion phenomenon occurs. After irradiating for 3 - 5 min, the polymer begins to liquefy, and the color changes to orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible light lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon shows no obvious attenuation.

[0051] Reversible adhesion performance of the azobenzene-based hyperbranched polymer reversible adhesive prepared in the example: Two pieces of glass with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. Take 20 mg of the adhesive in the trans conformation and place it on a glass substrate. Irradiate it with a 365 nm ultraviolet lamp for 15 min until it is completely liquefied. Then place another glass substrate on the liquefied adhesive. The adhesion area is 10 mm × 25 mm, and the thickness of the adhesion layer is 0.1 mm. After that, irradiate the adhesion area with a 530 nm visible light lamp for 20 min to cure the adhesive to bond the two glass substrates together. Fix the adhered glass substrates on a universal material testing machine and stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the trans conformation is 7.10 MPa. Then fix the adhered glass substrates on a universal material testing machine and irradiate the adhesion area with a 365 nm ultraviolet lamp for 15 min. Then stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the cis conformation is 0.18 MPa. Divide the adhesion strength in the trans conformation by the adhesion strength in the cis conformation to obtain a switching ratio of 39.44. Example

[0052] Preparation of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol: Dissolve 7.1 g of 4-phenylazophenol in 40 mL of N,N-dimethylformamide, and then add 4.9 g of potassium carbonate. The solution was stirred at 30 °C for 30 min. Then, add 0.015 g of potassium iodide and 5.335 g of 6-chloro-1-hexanol to the solution. The reaction mixture was then stirred at 110 °C for 24 h. After the reaction, the system was naturally cooled to room temperature and poured into 900 g of ice-water mixture, resulting in a brownish-red flocculent precipitate. Filter out the precipitate and dry it under vacuum at 45 °C overnight. The obtained crude product was further purified by recrystallization from ethanol, and then dried under vacuum at 45 °C for 24 h to obtain the final product, which is a reddish-brown solid.

[0053] Preparation of 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate: Weigh 4.768 g of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine, which is Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane, which is Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution, and saturated sodium chloride solution. Collect the organic layer and remove the solvent using a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is vacuum dried at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0054] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate, N,N-methylenebisacrylamide, and 1,8-octanediamine according to a molar ratio of 0.6:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,8-octanediamine and stir at 60 °C for 24 h. Then add 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate to the system and continue to stir at 60 °C for 24 h. After the reaction is completed, let the system cool naturally to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water multiple times, and vacuum dry it at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0055] Photoresponse properties of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the conformational transformation of the azobenzene group from the trans conformation to the cis conformation, the glass transition temperature of the polymer decreases, and thus a solid-liquid conversion phenomenon occurs. After irradiating for 3 - 5 min, the polymer begins to liquefy, and the color changes to orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible light lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon shows no obvious attenuation.

[0056] Reversible Adhesion Performance of the Azobenzene-based Hyperbranched Polymer Reversible Adhesive Prepared in the Example: Two glass pieces with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. 20 mg of the adhesive in the trans conformation was placed on one glass substrate and irradiated with a 365 nm ultraviolet lamp for 15 min until it was completely liquefied. Then, another glass substrate was placed on the liquefied adhesive, with the adhesion area being 10 mm × 25 mm and the adhesion layer thickness being 0.1 mm. After that, the adhesion area was irradiated with a 530 nm visible light lamp for 20 min to cure the adhesive and bond the two glass substrates together. The bonded glass substrates were fixed on a universal material testing machine and stretched at a tensile rate of 5 mm / min until the adhesion area was completely damaged. Five tensile tests were repeated and the average value was taken. The adhesion strength in the trans conformation was measured to be 8.07 MPa. Then, the bonded glass substrates were fixed on the universal material testing machine and the adhesion area was irradiated with a 365 nm ultraviolet lamp for 15 min. After that, it was stretched at a tensile rate of 5 mm / min until the adhesion area was completely damaged. Five tensile tests were repeated and the average value was taken. The adhesion strength in the cis conformation was measured to be 0.15 MPa. The switching ratio was obtained by dividing the adhesion strength in the trans conformation by the adhesion strength in the cis conformation, which was 53.80. Example

[0057] Preparation of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol: 7.1 g of 4-phenylazophenol was dissolved in 40 mL of N,N-dimethylformamide, and then 4.9 g of potassium carbonate was added. The solution was stirred at 30 °C for 30 min. Then, 0.015 g of potassium iodide and 5.335 g of 6-chloro-1-hexanol were added to the solution. The reaction mixture was then stirred at 110 °C for 24 h. After the reaction was completed, the system was naturally cooled to room temperature and poured into 900 g of an ice-water mixture, resulting in a brownish-red flocculent precipitate. The precipitate was filtered out and vacuum dried overnight at 45 °C. The obtained crude product was further purified by recrystallization from ethanol and then vacuum dried at 45 °C for 24 h to obtain the final product, which was a reddish-brown solid.

[0058] Preparation of 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate: Weigh 4.768 g of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine, which is Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane, which is Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution, and saturated sodium chloride solution. Collect the organic layer and remove the solvent using a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is vacuum dried at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0059] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate, N,N-methylenebisacrylamide, and 1,8-octanediamine according to a molar ratio of 0.8:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,8-octanediamine and stir and react at 60 °C for 24 h. Then add 6-(4-(phenyldiazenyl)phenoxy)hexyl acrylate to the system and continue to stir and react at 60 °C for 24 h. After the reaction is completed, let the system cool naturally to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water multiple times, and vacuum dry it at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0060] Photoresponse properties of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the transformation of the azobenzene group from the trans conformation to the cis conformation, the glass transition temperature of the polymer decreases, so a solid-liquid conversion phenomenon will occur. After irradiating for 3 - 5 min, the polymer begins to liquefy, and the color turns orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible light lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon does not show obvious attenuation.

[0061] Reversible adhesion performance of the azobenzene-based hyperbranched polymer reversible adhesive prepared in the example: Two pieces of glass with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. Take 20 mg of the adhesive in the trans conformation and place it on one glass substrate. Irradiate it with a 365 nm ultraviolet lamp for 15 min until it is completely liquefied. Then, place another glass substrate on the liquefied adhesive. The adhesion area is 10 mm × 25 mm, and the thickness of the adhesion layer is 0.1 mm. After that, irradiate the adhesion area with a 530 nm visible light lamp for 20 min to cure the adhesive to bond the two glass substrates together. Fix the bonded glass substrates on a universal material testing machine and stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the trans conformation is 7.89 MPa. Then, fix the bonded glass substrates on a universal material testing machine and irradiate the adhesion area with a 365 nm ultraviolet lamp for 15 min. Then, stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the cis conformation is 0.18 MPa. Divide the adhesion strength in the trans conformation by the adhesion strength in the cis conformation to obtain a switching ratio of 43.83. Example

[0062] Preparation of 9-(4-(phenyldiazeneyl)phenoxy)-1-nonanol: Dissolve 7.1 g of 4-phenylazophenol in 40 mL of N,N-dimethylformamide, and then add 4.9 g of potassium carbonate. Stir the solution at 30 °C for 30 min. Then, add 0.015 g of potassium iodide and 6.962 g of 9-chloro-1-nonanol to the solution. The reaction mixture was then stirred at 110 °C for 24 h. After the reaction, cool the system to room temperature naturally and pour it into 900 g of ice-water mixture to produce a brownish-red flocculent precipitate. Filter out the precipitate and dry it under vacuum at 45 °C overnight. The obtained crude product was further purified by recrystallization from ethanol and then dried under vacuum at 45 °C for 24 h to obtain the final product, which is a red-brown solid.

[0063] Preparation of 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate: Weigh 5.44 g of 9-(4-(phenyldiazenyl)phenoxy)-1-nonanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine, which is Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane, which is Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution and saturated sodium chloride solution. Collect the organic layer and remove the solvent with a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is dried under vacuum at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0064] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate, N,N-methylenebisacrylamide and 1,8-octanediamine according to a molar ratio of 0.4:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,8-octanediamine and stir at 60 °C for 24 h. Then add 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate to the system and continue to stir at 60 °C for 24 h. After the reaction is completed, let the system cool naturally to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water for several times, and dry it under vacuum at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0065] Photo-responsive properties of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the transformation of azobenzene groups from the trans conformation to the cis conformation, the glass transition temperature of the polymer decreases, so a solid-liquid conversion phenomenon will occur. After irradiating for 3 - 5 min, the polymer begins to liquefy and the color changes to orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon does not show obvious attenuation.

[0066] Reversible Adhesion Performance of the Azo-based Hyperbranched Polymer Reversible Adhesive Prepared in the Example: Two glass pieces with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. 20 mg of the adhesive in the trans conformation was placed on one glass substrate and irradiated with a 365 nm ultraviolet lamp for 15 min until it was completely liquefied. Then, another glass substrate was placed on the liquefied adhesive, with the adhesion area being 10 mm × 25 mm and the adhesion layer thickness being 0.1 mm. After that, the adhesion area was irradiated with a 530 nm visible light lamp for 20 min to cure the adhesive and bond the two glass substrates together. The bonded glass substrates were fixed on a universal material testing machine and stretched at a stretching rate of 5 mm / min until the adhesion area was completely damaged. Five tensile tests were repeated and the average value was taken. The adhesion strength in the trans conformation was measured to be 2.91 MPa. Then, the bonded glass substrates were fixed on the universal material testing machine and the adhesion area was irradiated with a 365 nm ultraviolet lamp for 15 min. After that, it was stretched at a stretching rate of 5 mm / min until the adhesion area was completely damaged. Five tensile tests were repeated and the average value was taken. The adhesion strength in the cis conformation was measured to be 0.21 MPa. The switching ratio was obtained by dividing the adhesion strength in the trans conformation by the adhesion strength in the cis conformation, which was 13.86. Example

[0067] Preparation of 9-(4-(phenyldiazenyl)phenoxy)-1-nonanol: 7.1 g of 4-phenylazophenol was dissolved in 40 mL of N,N-dimethylformamide, and then 4.9 g of potassium carbonate was added. The solution was stirred at 30 °C for 30 min. Then, 0.015 g of potassium iodide and 6.962 g of 9-chloro-1-nonanol were added to the solution. The reaction mixture was then stirred and reacted at 110 °C for 24 h. After the reaction was completed, the system was naturally cooled to room temperature and poured into 900 g of an ice-water mixture, resulting in a brownish-red flocculent precipitate. The precipitate was filtered out and vacuum dried overnight at 45 °C. The obtained crude product was further purified by ethanol recrystallization and then vacuum dried at 45 °C for 24 h to obtain the final product, which was a reddish-brown solid.

[0068] Preparation of 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate: Weigh 5.44 g of 9-(4-(phenyldiazenyl)phenoxy)-1-nonanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine, which is Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane, which is Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution, and saturated sodium chloride solution. Collect the organic layer and remove the solvent using a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is vacuum dried at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0069] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate, N,N-methylenebisacrylamide, and 1,8-octanediamine according to a molar ratio of 0.6:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,8-octanediamine and stir the reaction at 60 °C for 24 h. Then add 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate to the system and continue to stir the reaction at 60 °C for 24 h. After the reaction is completed, let the system cool naturally to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water multiple times, and vacuum dry it at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0070] Photoresponse performance of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the conformational transformation of azobenzene groups from trans conformation to cis conformation, the glass transition temperature of the polymer decreases, resulting in a solid-liquid conversion phenomenon. After irradiating for 3 - 5 min, the polymer begins to liquefy, and the color changes to orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible light lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon shows no obvious attenuation.

[0071] Reversible adhesion performance of the azobenzene-based hyperbranched polymer reversible adhesive prepared in the example: Two pieces of glass with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. 20 mg of the adhesive in the trans conformation was placed on one glass substrate and irradiated with a 365 nm ultraviolet lamp for 15 min until it was completely liquefied. Then, another glass substrate was placed on the liquefied adhesive, and the adhesion area was 10 mm × 25 mm, and the thickness of the adhesion layer was 0.1 mm. After that, the adhesion area was irradiated with a 530 nm visible light lamp for 20 min to cure the adhesive to bond the two glass substrates together. The adhered glass substrates were fixed on a universal material testing machine and stretched at a stretching rate of 5 mm / min until the adhesion area was completely damaged. Five tensile tests were repeated and the average value was taken. The adhesion strength in the trans conformation was measured to be 3.67 MPa. Then, the adhered glass substrates were fixed on a universal material testing machine and irradiated with a 365 nm ultraviolet lamp for 15 min for the adhesion area. Then, it was stretched at a stretching rate of 5 mm / min until the adhesion area was completely damaged. Five tensile tests were repeated and the average value was taken. The adhesion strength in the cis conformation was measured to be 0.19 MPa. The switching ratio was obtained by dividing the adhesion strength in the trans conformation by the adhesion strength in the cis conformation, and the switching ratio was 19.31. Example

[0072] Preparation of 9-(4-(phenyldiazenyl)phenoxy)-1-nonanol: 7.1 g of 4-phenylazophenol was dissolved in 40 mL of N,N-dimethylformamide, and then 4.9 g of potassium carbonate was added. The solution was stirred at 30 °C for 30 min. Then, 0.015 g of potassium iodide and 6.962 g of 9-chloro-1-nonanol were added to the solution. The reaction mixture was then stirred at 110 °C for 24 h. After the reaction was completed, the system was naturally cooled to room temperature and poured into 900 g of an ice-water mixture, producing a brownish-red flocculent precipitate. The precipitate was filtered out and vacuum dried at 45 °C overnight. The obtained crude product was further purified by recrystallization from ethanol and then vacuum dried at 45 °C for 24 h to obtain the final product, which was a reddish-brown solid.

[0073] Preparation of 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate: Weigh 5.44 g of 9-(4-(phenyldiazenyl)phenoxy)-1-nonanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine, which is Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane, which is Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution and saturated sodium chloride solution. Collect the organic layer and remove the solvent with a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is vacuum dried at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0074] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate, N,N-methylenebisacrylamide and 1,8-octanediamine according to a molar ratio of 0.8:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,8-octanediamine and stir at 60 °C for 24 h. Then add 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate to the system and continue to stir at 60 °C for 24 h. After the reaction is completed, let the system cool naturally to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water for several times, and vacuum dry it at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0075] Photoresponsive properties of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the conformational transformation of azobenzene groups from trans to cis, the glass transition temperature of the polymer decreases, resulting in a solid-liquid conversion phenomenon. After irradiating for 3 - 5 min, the polymer begins to liquefy and the color changes to orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible light lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon does not show obvious attenuation.

[0076] Reversible adhesion performance of the azobenzene-based hyperbranched polymer reversible adhesive prepared in the example: Two pieces of glass with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. Take 20 mg of the adhesive in the trans conformation and place it on a glass substrate. Irradiate it with a 365 nm ultraviolet lamp for 15 min until it is completely liquefied. Then, place another glass substrate on the liquefied adhesive. The adhesion area is 10 mm × 25 mm, and the thickness of the adhesion layer is 0.1 mm. After that, irradiate the adhesion area with a 530 nm visible light lamp for 20 min to cure the adhesive to bond the two glass substrates together. Fix the bonded glass substrates on a universal material testing machine and stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the trans conformation is 3.27 MPa. Then, fix the bonded glass substrates on a universal material testing machine and irradiate the adhesion area with a 365 nm ultraviolet lamp for 15 min. After that, stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the cis conformation is 0.17 MPa. Divide the adhesion strength in the trans conformation by the adhesion strength in the cis conformation to obtain a switching ratio of 19.24.

[0077] Preparation of 6-(4-(phenyldiazeneyl)phenoxy)-1-hexanol: Dissolve 7.1 g of 4-phenylazophenol in 40 mL of N,N-dimethylformamide, and then add 4.9 g of potassium carbonate. Stir the solution at 30 °C for 30 min. Then, add 0.015 g of potassium iodide and 5.335 g of 6-chloro-1-hexanol to the solution. The reaction mixture is then stirred at 110 °C for 24 h. After the reaction is completed, cool the system to room temperature naturally and pour it into 900 g of ice-water mixture to produce a brown-red flocculent precipitate. Filter out the precipitate and dry it under vacuum at 45 °C overnight. The obtained crude product is further purified by recrystallization from ethanol, and then dried under vacuum at 45 °C for 24 h to obtain the final product, which is a red-brown solid.

[0078] Preparation of 6-(4-(phenyldiazenyl)phenoxy)-hexyl acrylate: Weigh 4.768 g of 6-(4-(phenyldiazenyl)phenoxy)-1-hexanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine to obtain Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane to obtain Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution, and saturated sodium chloride solution. Collect the organic layer and remove the solvent using a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is dried in vacuo at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0079] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 6-(4-(phenyldiazenyl)phenoxy)-hexyl acrylate, N,N-methylenebisacrylamide, and 1,8-octanediamine in a molar ratio of 0.1:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,8-octanediamine and stir the reaction at 60 °C for 24 h. Then add 6-(4-(phenyldiazenyl)phenoxy)-hexyl acrylate to the system and continue to stir the reaction at 60 °C for 24 h. After the reaction is completed, naturally cool the system to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water multiple times, and dry it in vacuo at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0080] Photoresponsive properties of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, due to the conformational transformation of azobenzene groups from trans conformation to cis conformation, the glass transition temperature of the polymer decreases, resulting in a solid-liquid conversion phenomenon. After irradiating for 3 - 5 min, the polymer begins to liquefy and the color changes to orange-red. As the irradiation time prolongs, the degree of liquefaction deepens, and it can be completely liquefied when irradiated for more than 15 min. Then irradiate with a 530 nm visible light lamp for 20 min to restore to the solid state. After repeating the above operation five times, this reversible phenomenon shows no obvious attenuation.

[0081] Reversible adhesion performance of the azobenzene-based hyperbranched polymer reversible adhesive prepared in the example: Two pieces of glass with dimensions of 55 mm × 25 mm × 1 mm were alternately cleaned with acetone and ethanol. Take 20 mg of the adhesive in the trans conformation and place it on a glass substrate. Irradiate it with a 365 nm ultraviolet lamp for 15 min until it is completely liquefied, and then place another glass substrate on the liquefied adhesive. The adhesion area is 10 mm × 25 mm, and the thickness of the adhesion layer is 0.1 mm. Then, irradiate the adhesion area with a 530 nm visible light lamp for 20 min to cure the adhesive to bond the two glass substrates together. Fix the adhered glass substrates on a universal material testing machine and stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the trans conformation is 1.44 MPa. Then, fix the adhered glass substrates on a universal material testing machine and irradiate the adhesion area with a 365 nm ultraviolet lamp for 15 min. Then, stretch them at a stretching rate of 5 mm / min until the adhesion area is completely damaged. Repeat the stretching test five times and take the average value. The measured adhesion strength in the cis conformation is 0.28 MPa. Divide the adhesion strength in the trans conformation by the adhesion strength in the cis conformation to obtain a switching ratio of 5.14.

[0082] Preparation of 3-(4-(phenyldiazeneyl)phenoxy)-1-propanol: Dissolve 7.1 g of 4-phenylazophenol in 40 mL of N,N-dimethylformamide, and then add 4.9 g of potassium carbonate. Stir the solution at 30 °C for 30 min. Then, add 0.015 g of potassium iodide and 3.686 g of 3-chloro-1-propanol to the solution. The reaction mixture was then stirred at 110 °C for 24 h. After the reaction, the system was naturally cooled to room temperature and poured into 900 g of an ice-water mixture to produce a brownish-red flocculent precipitate. Filter out the precipitate and dry it under vacuum at 45 °C overnight. The obtained crude product was further purified by recrystallization from ethanol and then dried under vacuum at 45 °C for 24 h to obtain the final product, which is a red-brown solid.

[0083] Preparation of 3-(4-(phenyldiazeneyl)phenoxy)-propyl acrylate: Weigh 4.096 g of 3-(4-(phenyldiazeneyl)phenoxy)-1-propanol and dissolve it in 50 mL of dry dichloromethane. Add 1.624 g of triethylamine, which is Component 1. Dissolve 1.743 g of acryloyl chloride in 10 mL of dry dichloromethane, which is Component 2. Under the condition of an ice-water bath, slowly add Component 2 dropwise to Component 1, and then stir the mixture at room temperature for 20 h. After the reaction is completed, the mixture is concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution, and saturated sodium chloride solution. Collect the organic layer and remove the solvent using a rotary evaporator. The crude product is purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it is dried under vacuum at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0084] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Weigh 3-(4-(phenyldiazeneyl)phenoxy)-propyl acrylate, N,N-methylenebisacrylamide, and 1,8-octanediamine according to a molar ratio of 0.6:0.9:1. First, add N,N-methylenebisacrylamide to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stir at 30 °C until completely dissolved. Then add 1,8-octanediamine and stir and react at 60 °C for 24 h. Then add 3-(4-(phenyldiazeneyl)phenoxy)-propyl acrylate to the system and continue to stir and react at 60 °C for 24 h. After the reaction is completed, naturally cool the system to room temperature. After cooling, the crude product precipitates as an orange-yellow flocculent precipitate. Filter out the crude product, wash it alternately with ether and deionized water multiple times, and dry it under vacuum at 45 °C for 24 h to obtain the final product, which is an orange-yellow solid.

[0085] Photoresponse performance of azobenzene-based hyperbranched polymer reversible adhesive: When irradiating the polymer with a 365 nm ultraviolet lamp, after irradiating for 3 - 5 min, the color of the polymer changes to orange-red, but no liquefaction phenomenon occurs. As the irradiation time prolongs, its morphology does not change either, so it cannot be used as a photoresponse reversible adhesive.

[0086] Preparation of 12-(4-(phenyldiazenyl)phenoxy)-1-dodecanol: 7.1 g of 4-phenylazophenol was dissolved in 40 mL of N,N-dimethylformamide, and then 4.9 g of potassium carbonate was added. The solution was stirred at 30 °C for 30 min. Then, 0.015 g of potassium iodide and 8.6 g of 12-chloro-1-dodecanol were added to the solution. The reaction mixture was then stirred at 110 °C for 24 h. After the reaction was completed, the system was naturally cooled to room temperature and poured into 900 g of ice-water mixture, resulting in a brownish-red flocculent precipitate. The precipitate was filtered out and vacuum dried at 45 °C overnight. The obtained crude product was further purified by recrystallization from ethanol and then vacuum dried at 45 °C for 24 h to obtain the final product, which was a red-brown solid.

[0087] Preparation of 12-(4-(phenyldiazenyl)phenoxy)-dodecyl-acrylate: 6.112 g of 3-(4-(phenyldiazenyl)phenoxy)-1-propanol was weighed and dissolved in 50 mL of dry dichloromethane, and 1.624 g of triethylamine was added, which was designated as Component 1. 1.743 g of acryloyl chloride was dissolved in 10 mL of dry dichloromethane, which was designated as Component 2. Under the condition of an ice-water bath, Component 2 was slowly added dropwise to Component 1, and then the mixture was stirred at room temperature for 20 h. After the reaction was completed, the mixture was concentrated by rotary evaporation and then washed with dilute hydrochloric acid (1 mmol / L), saturated sodium bicarbonate solution and saturated sodium chloride solution. The organic layer was collected and the solvent was removed using a rotary evaporator. The crude product was purified by eluting with dichloromethane on a silica gel column. After removing the solvent, it was vacuum dried at 45 °C for 24 h to obtain the final product, which was an orange-yellow solid.

[0088] Preparation of azobenzene-based hyperbranched polymer reversible adhesive: 12-(4-(phenyldiazenyl)phenoxy)-dodecyl-acrylate, N,N-methylenebisacrylamide and 1,8-octanediamine were weighed according to a molar ratio of 0.6:0.9:1. First, N,N-methylenebisacrylamide was added to a mixed solvent of 30 mL of methanol and 15 mL of deionized water and stirred at 30 °C until completely dissolved. Then 1,8-octanediamine was added and the reaction was stirred at 60 °C for 24 h. Then 12-(4-(phenyldiazenyl)phenoxy)-dodecyl-acrylate was added to the system and the reaction was continued to stir at 60 °C for 24 h. After the reaction was completed, the system was naturally cooled to room temperature. After cooling, the crude product precipitated as an orange-yellow flocculent precipitate. The crude product was filtered out, washed alternately with ether and deionized water for several times, and vacuum dried at 45 °C for 24 h to obtain the final product, which was an orange-yellow solid.

[0089] Photoresponse performance of azobenzene-based hyperbranched polymer reversible adhesives: When the polymer was irradiated with a 365 nm ultraviolet lamp, after irradiation for 3 - 5 minutes, the color of the polymer changed to orange-red, but no liquefaction occurred. As the irradiation time was extended, its morphology did not change either, so it could not be used as a photoresponsive reversible adhesive.

[0090] Table 1 Comparison of the performance of the examples and comparative examples

[0091] Photoresponse performance Adhesion strength before UV irradiation (MPa) Adhesion strength after UV irradiation (MPa) Adhesion strength switching ratio Example 1 Yes 2.63 0.07 37.57 Example 2 Yes 3.27 0.12 27.52 Example 3 Yes 6.43 0.20 32.15 Example 4 Yes 6.57 0.14 46.93 Example 5 Yes 7.10 0.18 39.44 Example 6 Yes 8.07 0.15 53.80 Example 7 Yes 7.89 0.18 43.83 Example 8 Yes 2.91 0.21 13.86 Example 9 Yes 3.67 0.19 19.31 Example 10 Yes 3.27 0.17 19.24 Comparative Example 1 Yes 1.44 0.28 5.14 Comparative Example 2 No \ \ \ Comparative Example 3 No \ \ \

[0092] By comparing Example 4 with Examples 1 - 3, it can be seen that when the diamine monomer selected is 1,8-octanediamine under the same component ratios of each group, the adhesion strength of the prepared reversible adhesive is the highest, reaching 6.57 MPa, and the adhesion strength switching ratio before and after ultraviolet light irradiation is also the highest, being 46.93.

[0093] By comparing Examples 4 - 7, it can be seen that when the component ratios of each monomer are within the range selected in the present invention, the prepared reversible adhesives all have relatively high adhesion strength and switching ratio, with the maximum values being 8.07 MPa and 53.80 respectively.

[0094] By comparing Examples 5 - 7 with Examples 8 - 10, it can be seen that when the haloalcohol selected for synthesizing the azobenzene monomer is 6-chloro-1-hexanol under the same component ratios of each group, the prepared reversible adhesive has relatively high adhesion strength and switching ratio.

[0095] By comparing Examples 4 - 7 with Comparative Example 1, it can be seen that when the ratio of the selected azobenzene monomer is less than the range selected in the present invention, the adhesion strength and switching ratio of the prepared reversible adhesive are both poor.

[0096] By comparing Example 6, Example 9 with Comparative Examples 2 - 3, it can be seen that when the type of haloalcohol selected for synthesizing the azobenzene monomer is not within the range selected in the present invention, the prepared hyperbranched polymer does not have the solid-liquid conversion phenomenon of photoresponse, so it cannot be used as a photoresponsive reversible adhesive.

Claims

1. A reversible adhesive of azobenzene-based hyperbranched polymer, characterized in that, It is prepared by Michael addition reaction of azobenzene-based acrylate monomer, N, N-methylenebisacrylamide and diamine monomer, and the molar ratio of the azobenzene-based acrylate monomer, N, N-methylenebisacrylamide and diamine monomer is (0.2~0.8):0.9:1; The azobenzene-based acrylate monomer is selected from one of 6-(4-(phenyldiazenyl)phenoxy)-hexyl acrylate and 9-(4-(phenyldiazenyl)phenoxy)-nonyl acrylate.

2. The reversible adhesive according to claim 1, characterized in that, The diamine monomer is selected from one of polyetheramine D-230, 1,4-butanediamine, 1,6-hexanediamine and 1,8-octanediamine.

3. The preparation method of the azobenzene-based hyperbranched polymer reversible adhesive according to claim 1, comprising the following steps: 1) Preparation of azobenzene-based acrylate monomer AZOn: React 4-phenylazophenol with haloalcohol, and react the obtained product with acryloyl chloride to obtain azobenzene-based acrylate monomer; 2) Preparation of hyperbranched polymer core HBP: Michael addition reaction of N, N-methylenebisacrylamide MBA and diamine monomer to obtain random hyperbranched polymer core HBP; 3) Preparation of azobenzene-based hyperbranched polymer reversible adhesive: Michael addition reaction of azobenzene-based acrylate monomer with the amino group at the end of HBP to obtain azobenzene-based hyperbranched polymer reversible adhesive HBP-AZOn.

4. The preparation method according to claim 3, characterized in that, The haloalcohol in the step 1) is selected from 6-chloro-1-hexanol or 9-chloro-1-nonanol.

5. The application of the azobenzene-based hyperbranched polymer reversible adhesive according to claim 1 in the preparation of reversible adhesion and stimulus-responsive materials.

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