A dendritic azobenzene molecular compound, a preparation method thereof and application thereof in a doped optical switching adhesive

Abstract

The present application provides a kind of dendritic azobenzene molecular compound, the dendritic azobenzene molecular compound has the structure shown in formula I.The dendritic azobenzene molecular compound has three branches, each branch contains azobenzene group and hydroxyl end cap.This dendritic azobenzene molecular compound is beneficial to improve the adhesion of adhesive performance.The photo switch small molecule containing azobenzene group can provide significant photo-thermal effect, is beneficial to promote the rapid melting of adhesive, so that the adhesive has excellent light switching performance.The dendritic azobenzene molecular compound of the present application is suitable as a doping component for a variety of common adhesive substrates, and the prepared adhesive can exhibit excellent adhesion and light switching performance on different substrates, and has wide application value and good production prospect.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to a dendritic azobenzene molecular compound, its preparation method, and its application in doped optical switching adhesives. Background Technology

[0002] Smart, switchable adhesives that can bond and peel off various surfaces on demand play a vital role in our daily lives and are widely used in emerging fields such as automotive, medical, robotics, labeling, and wearable devices. Many novel photo-switchable adhesives have been developed, such as those prepared by introducing azo groups to alter the physicochemical properties of the adhesive system or by introducing nano-ferric oxide to provide photothermal response. However, these photo-switchable adhesives still face some challenges. For example, introducing azobenzene and its derivatives into various polymer adhesives through chemical grafting or copolymerization requires complex synthesis, and the resulting adhesives often exhibit low bonding strength and poor switchability. There are also many reports on low molecular weight adhesives, which, while easy to synthesize and process and capable of forming adhesive layers in situ, suffer from low bonding strength due to a lack of sufficient intermolecular covalent interactions. Summary of the Invention

[0003] The primary objective of this invention is to overcome the shortcomings and deficiencies of existing switchable adhesive materials, which have poor adhesion and switchability and are difficult to meet application requirements. This invention provides a dendritic azobenzene molecular compound that, when doped into a base polymer, can significantly improve the adhesive strength and switchability of the adhesive.

[0004] A second objective of this invention is to provide a method for preparing a dendritic azobenzene molecular compound.

[0005] A third objective of this invention is to provide a doped optical switching adhesive.

[0006] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0007] A dendritic azobenzene molecule compound, with the structural formula shown in Formula I:

[0008]

[0009] This dendritic azobenzene molecular compound has three branches, each containing an azophenyl group and hydroxyl end caps. When incorporated into adhesives, it can improve adhesive performance and adhesive switching properties.

[0010] A method for preparing the above-mentioned dendritic azobenzene molecular compound, the method comprising the following steps:

[0011] S1. Preparation of compound II;

[0012] S2. The compound of formula II obtained in step S1 is condensed with 6-chlorohexanol to obtain the dendritic azobenzene molecular compound;

[0013] The structural formula of compound II is shown below:

[0014]

[0015] The preparation principle of the dendritic azobenzene molecule is as follows:

[0016]

[0017] Preferably, the preparation method of the dendritic azobenzene molecular compound in step S2 is as follows: adding compound of formula II, base, catalyst, 6-chlorohexanol and solvent to the reaction system, reacting fully under heating, and then purifying to obtain the dendritic azobenzene molecular compound.

[0018] Preferably, the molar ratio of the compound of formula II to 6-chlorohexanol in step S2 is 1:3 to 5.

[0019] More preferably, the molar ratio of the compound of formula II to 6-chlorohexanol in step S2 is 1:3.5.

[0020] Preferably, the molar ratio of the compound of formula II, the base, and the catalyst in step S2 is 1:3 to 5:7 to 10.

[0021] More preferably, the molar ratio of the compound of formula II to the base in step S2 is 1:4.

[0022] More preferably, the molar ratio of the compound of formula II to the catalyst in step S2 is 1:8.

[0023] Preferably, the amount of solvent used in step S2 is 2 to 5 times the volume of 6-chlorohexane.

[0024] More specifically, the alkali mentioned in step S2 is either potassium carbonate or sodium hydroxide.

[0025] More specifically, the catalyst is one of potassium iodide or 4-dimethylaminopyridine (DMAP).

[0026] More specifically, the solvent is one or more of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and acetone (ACE).

[0027] Preferably, the preparation method of compound II in step S1 is as follows: 1,3,5-tris(4-aminophenyl)benzene, solvent, and hydrochloric acid solution are added to the reaction system. The aqueous solution of nitrite undergoes a diazotization reaction to generate a diazonium salt. Then, a phenol solution pre-dissolved in an alkaline solution is added, and the reaction is carried out to a complete extent. The mixture is then purified to obtain compound II.

[0028] Preferably, the solvent in step S1 is one or more of tetrahydrofuran (THF), N,N-dimethylformamide, and dimethyl sulfoxide.

[0029] Preferably, the nitrite in step S1 is sodium nitrite.

[0030] In the diazotization reaction, hydrochloric acid is used to provide an acidic environment to generate nitrous acid and stabilize the formed diazonium salt. If the amount of hydrochloric acid is insufficient, the generated diazonium salt is prone to self-coupling with unreacted aromatic amines, affecting the subsequent reaction. However, if the acid concentration increases, the concentration of free amine decreases, which slows down the diazotization process. Excess nitrous acid is needed in the diazotization reaction to inhibit the self-coupling of 1,3,5-tris(4-aminophenyl)benzene, but excessive nitrous acid can lead to oxidative decomposition and nitrosation of 1,3,5-tris(4-aminophenyl)benzene, causing a series of side reactions that are detrimental to subsequent coupling.

[0031] Preferably, the molar ratio of 1,3,5-tris(4-aminophenyl)benzene, sodium nitrite, and phenol in step S1 is 1:3-5:3-5.

[0032] Preferably, the volume ratio of hydrochloric acid solution to solvent in step S1 is 1:1.5 to 3, and the mass fraction of hydrochloric acid solution is 10% to 37%.

[0033] Preferably, the sodium nitrite aqueous solution in step S1 has a mass fraction of 5% to 10%.

[0034] More preferably, in step S1, the molar ratio of 1,3,5-tris(4-aminophenyl)benzene, sodium nitrate and phenol is 1:3:3, the volume ratio of hydrochloric acid solution to solvent is 1:2, and the mass fraction of sodium nitrite aqueous solution is 8%.

[0035] pH has a significant impact on the rate of coupling reactions. For phenolic coupling components, increasing the pH value is beneficial for the generation of active phenol oxide anions, thereby increasing the coupling rate. When the pH value reaches a certain value, the coupling rate reaches its maximum value. If the pH value is further increased, the diazonium salt will be converted into sodium trans-diazoate salt with no coupling ability, which will affect the reaction yield.

[0036] Preferably, the pH range of the reaction system after adding the phenol solution pre-dissolved in the alkaline solution in step S1 is 7 to 12.

[0037] The above-mentioned dendritic azobenzene molecular compounds are used as additives to improve the light switching properties and / or adhesive properties of adhesives.

[0038] A doped optical switching adhesive, the doped optical switching adhesive comprising a base polymer and the aforementioned dendritic azobenzene compound.

[0039] Preferably, the dendritic azobenzene compound has a mass content of 2% to 28% in the doped optical switching adhesive.

[0040] More preferably, the dendritic azobenzene compound has a mass content of 10-20% in the doped optical switching adhesive, for example, 10%, 15% or 20%.

[0041] The optimal amount of dendritic azobenzene compound incorporated into the doped adhesive provides the best bonding and light-switching properties. The higher the amount of dendritic azobenzene compound incorporated, the more significant the improvement in adhesive performance. However, once the incorporation exceeds a certain value, further increases in the amount of dendritic azobenzene compound will cause a decrease in the adhesive performance.

[0042] The dendritic azobenzene molecular compound of the present invention is applicable to a variety of common adhesive substrates. The substrate raw material polymer is readily available, and the dendritic azobenzene molecular compound has good versatility as a dopant in adhesive preparation, and has broad application value.

[0043] Preferably, the base polymer is one or more of polycaprolactone, ethylene-vinyl acetate copolymer, polyurethane, and ethylene-acrylic acid copolymer.

[0044] Preferably, the preparation method of the doped optical switching adhesive is as follows: dissolving the base polymer in a solvent to obtain a base polymer solution, adding a dendritic azobenzene molecular compound, mixing evenly to obtain a mixed polymer solution, dropping the mixed polymer solution onto the surface of the substrate to form an adhesive film, hot-pressing the substrate covered with the adhesive film and cooling it to room temperature to obtain the adhesive material;

[0045] The solvent of the substrate polymer solution is one or more of tetrahydrofuran, N,N-dimethylformamide, and dimethyl sulfoxide;

[0046] The concentration of the substrate polymer solution is 0.02–0.1 g / mL;

[0047] The substrates include acrylic sheets (PMMA), aluminum sheets (Al), copper sheets (Cu), stainless steel (SS), polyethylene terephthalate (PET), polystyrene (PS), epoxy resin sheets (EP), etc.

[0048] The doped light-switching adhesive of the present invention can achieve light switching under the condition of using ultraviolet flashlight irradiation;

[0049] Preferably, the power of the ultraviolet flashlight is 30–80 mW / cm. 2 .

[0050] Compared with the prior art, the beneficial effects of the present invention are:

[0051] (1) The dendritic azobenzene molecular compound of the present invention has a multi-branched structure, with multiple branches containing azophenyl groups and hydroxyl groups at the ends. This multi-branched structure can physically entangle with the polymer chains of the substrate polymer. At the same time, the hydroxyl groups at the ends of the branches form a rich hydrogen bond network with the functional groups on the substrate polymer through non-covalent interactions, thereby adjusting the chain structure of the substrate polymer. The benzene rings and dendritic structures of the doped small molecules help to increase the rigidity of the doped system and enhance the intermolecular and intramolecular crosslinking, which is beneficial to the enhancement of polymer cohesion. Meanwhile, the terminal hydroxyl groups of the dendritic azobenzene molecule increase the interaction between the adhesive and the substrate, which is beneficial to the improvement of interfacial adhesion, thereby improving the adhesive performance. In addition, the photo-switching small molecules containing azobenzene provide a significant photothermal effect, which is beneficial to promoting the rapid melting of the adhesive and giving the adhesive excellent photo-switching performance.

[0052] (2) The doped switchable adhesive of the present invention employs a doping strategy to dope dendritic azobenzene molecules into a polymer substrate to obtain a light-switching adhesive. The preparation process is simple, and with a small amount of doping, the adhesive can exhibit excellent adhesion and light-switching properties on different substrates. In addition, the dendritic azobenzene molecule compound of the present invention is suitable as a dopant for a variety of common adhesive substrates, showing good versatility in adhesive preparation. The prepared adhesive can be switched by ultraviolet light irradiation, making it convenient to use and possessing broad application value and good production prospects. Attached Figure Description

[0053] Figure 1 This is the 1H NMR spectrum of compound II.

[0054] Figure 2 This is the carbon NMR spectrum of compound II.

[0055] Figure 3 This is the 1H NMR spectrum of compound I.

[0056] Figure 4 This is the carbon NMR spectrum of compound I.

[0057] Figure 5 The figures show the overlap shear test results of the polymer solutions of Example 1 and Comparative Example 1 coated on different types of substrates.

[0058] Figure 6 The figures show the lap shear test results of Examples 2-4 and Comparative Examples 2-4 coated on acrylic sheet (PMMA) substrates.

[0059] Figure 7 The image shows the overlap shear test results of Example 1 before and after ultraviolet light irradiation. Detailed Implementation

[0060] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0061] Example 1: Preparation of dendritic azobenzene molecular compounds

[0062] A dendritic azobenzene molecular compound, the structural formula of which is shown in Formula I:

[0063]

[0064] Its preparation method includes the following steps:

[0065] S1. Add 1.00 g (2.8 mmol) of 1,3,5-tris(4-aminophenyl)benzene, 8 mL of THF, 2 g of ice water, and 4 mL of 37% hydrochloric acid solution to a round-bottom flask. While stirring, add 0.69 g (10 mmol) of sodium nitrite solution dissolved in 4 g of ice water. After stirring thoroughly, add 0.93 g (10 mmol) of phenol solution pre-dissolved in 14 mL (4 mol / L) of sodium hydroxide. Adjust the pH to 9 and react for 2 hours. After the reaction is complete, purify to obtain compound II.

[0066] S2. In a round-bottom flask, add 1.00 g (1.5 mmol) of product 1, 0.72 g (5.25 mmol) of potassium carbonate, and 10 mL of DMF. After stirring until homogeneous, add 2 g (12 mmol) of potassium iodide and 0.71 g (5.25 mmol) of 6-chlorohexanol. Stir at 110 °C for 24 hours. After the reaction is complete, purify to obtain the dendritic azobenzene molecule, i.e., compound I.

[0067] The structures of the above-mentioned compound II and the finally obtained dendritic azobenzene molecule (compound I) were characterized by proton and carbon nuclear magnetic resonance spectroscopy, as follows: Figures 1-4 As shown.

[0068] in Figure 1 and Figure 2 The images show the proton and carbon NMR spectra of the compound of formula II, respectively. Figure 3 and Figure 4 The images show the hydrogen NMR spectrum and carbon NMR spectrum of the dendritic azobenzene molecule (compound of formula I), respectively.

[0069] Examples 2-8 describe the preparation of doped optical switching adhesive solutions.

[0070] Example 2

[0071] Weigh 1g of the base polymer polycaprolactone (PCL) and dissolve it in 20mL of THF solution to obtain a PCL solution with a concentration of 0.05g / mL. Add 0.25g of dendritic azobenzene molecular compound (doping amount of 20%) and mix well to obtain a doped optical switching adhesive solution.

[0072] Example 3

[0073] This embodiment provides a doped optical switching adhesive solution, the preparation process of which is basically the same as that of Example 1, except that the base polymer is an ethylene-vinyl acetate copolymer solution (EVA).

[0074] Example 4

[0075] This embodiment provides a doped optical switching adhesive solution, the preparation process of which is basically the same as that in Example 1, except that the base polymer is ethylene-acrylic acid copolymer (EAA).

[0076] Example 5

[0077] This embodiment provides a doped optical switching adhesive solution, the preparation process of which is basically the same as that of Example 1, except that the base polymer is polyurethane (TPU).

[0078] Example 6

[0079] This embodiment provides a doped optical switching adhesive solution, the preparation process of which is basically the same as that of Example 1, except that the mass of the added dendritic azobenzene molecule compound is 0.0425g (doping amount is 4%).

[0080] Example 7

[0081] This embodiment provides a doped optical switching adhesive solution, the preparation process of which is basically the same as that of Example 1, except that the mass of the added dendritic azobenzene molecule compound is 0.136g (doping amount is 12%).

[0082] Example 8

[0083] This embodiment provides a doped optical switching adhesive solution, the preparation process of which is basically the same as that of Example 1, except that the mass of the added dendritic azobenzene molecule compound is 0.335g (doping amount is 25%).

[0084] Comparative Example 1

[0085] Weigh 1g of the base polymer polycaprolactone (PCL) and dissolve it in 20mL of THF solution to obtain a polymer solution with a concentration of 0.05g / mL.

[0086] Comparative Example 2

[0087] This comparative example provides a polymer solution whose preparation process is basically the same as that of comparative example 1, except that the base polymer is an ethylene-vinyl acetate copolymer solution (EVA).

[0088] Comparative Example 3

[0089] This comparative example provides a polymer solution whose preparation process is basically the same as that of comparative example 1, except that the base polymer is an ethylene-acrylic acid copolymer (EAA).

[0090] Comparative Example 4

[0091] This comparative example provides a polymer solution whose preparation process is basically the same as that of comparative example 1, except that the base polymer is polyurethane (TPU).

[0092] Performance testing

[0093] (I) Testing Methods

[0094] 1. Overlap shear test:

[0095] Referring to the standard ASTM F2255-05 (2015), and with appropriate modifications, an lap shear test was performed. The specific procedure was as follows: A substrate sample measuring 10mm × 40mm × 2mm was cut. 25μL of doped adhesive solution or undoped polymer solution was dropped onto the substrate, covering an area of ​​10mm × 5mm. After the solvent evaporated, the coated area was heated to 70℃ until it reached a molten state. Then, it was hot-pressed with another substrate of the same type and cooled to room temperature to obtain the test sample. Subsequently, the test sample was subjected to an lap shear test using a tensile testing machine at a rate of 1.3mm / min until the two bonded substrate pieces broke at the bond joint. The maximum load Fmax during this process was recorded. Each sample was repeated three times.

[0096] Calculation of lap shear strength: τ=Fmax / S

[0097] Where τ is the lap shear strength (MPa), Fmax is the maximum load (N), and S is the bonded area (mm²). 2 ).

[0098] (1) The doped adhesive solution of Example 2 and the polymer solution of Comparative Example 1 were coated onto different types of substrates and subjected to overlap shear tests, as shown in Table 1. Figure 5 The test results are shown.

[0099] Among them, the different types of substrates mentioned above are acrylic sheet (PMMA), aluminum sheet (Al), copper sheet (Cu), stainless steel (SS), polyethylene terephthalate (PET), polystyrene (PS), and epoxy resin sheet (EP).

[0100] (2) Examples 3-5 and Comparative Examples 2-4 were coated onto acrylic sheet (PMMA) substrates and subjected to overlap shear tests, as shown in Table 2. Figure 6 The test results are shown.

[0101] (3) Examples 6-8 were coated on acrylic sheet (PMMA) substrates and lap shear tests were performed to obtain the test results shown in Table 3.

[0102] 2. Switchability test:

[0103] The doped adhesive solution prepared in Example 1 was coated onto an acrylic sheet (PMMA) substrate using the method described in the lap shear test to prepare the test sample. The adhesive joint was irradiated with a UV flashlight for 30 seconds. The substrate coated with adhesive was then subjected to an lap shear test using a tensile testing machine at a rate of 1.3 mm / min until the two bonded substrates broke at the adhesive joint. The maximum load Fmax during this process was recorded, as shown in Table 4. Figure 7 The test results are shown.

[0104] (II) Performance Test Results

[0105] 1. Overlap shear test:

[0106] (1) The overlap shear test results of the doped adhesive solution of Example 2 and the PCL polymer solution of Comparative Example 1 coated on different substrates are shown in Table 1 and Figure 3 As shown:

[0107] Table 1

[0108]

[0109] From Table 1 and Figure 3 It can be seen that the shear strength of the doped adhesive solution (Formula I-PCL) of Example 2 and the PCL polymer solution (blank PCL) of Comparative Example 1 coated on different substrates are different. The adhesive prepared by incorporating dendritic azobenzene molecular compounds has improved shear strength on different substrates compared with pure PCL polymer solution. Among them, Formula I-PCL has the best shear strength on PMMA substrate, with an overlap shear strength of 6.7 MPa, which has excellent adhesive properties.

[0110] (2) The overlap shear test results of Examples 3-5 and Comparative Examples 2-4 coated on acrylic sheet (PMMA) substrates are shown in Table 2 and... Figure 6 As shown:

[0111] Table 2

[0112]

[0113]

[0114] From Table 2 and Figure 6 It can be seen that the adhesives obtained by doping dendritic azobenzene molecules into different polymer matrices have certain differences in adhesive ability, but all of them have stronger adhesive ability than pure polymer matrices. This shows that dendritic azobenzene molecular compounds are suitable as dopants for a variety of common adhesive substrates and have good universality in adhesive preparation.

[0115] (3) The overlap shear test results of the acrylic sheet (PMMA) substrates coated in Examples 6-8 are shown in Table 3:

[0116] Table 3

[0117]

[0118] Table 3 shows that the higher the amount of dendritic azobenzene compound incorporated, the more significant the improvement in adhesive performance. However, once the incorporation exceeds a certain value, further increases in the amount of dendritic azobenzene compound will decrease the adhesive performance. Controlling the amount of dendritic azobenzene compound incorporated into the doped adhesive can achieve optimal adhesive performance.

[0119] 2. Switchability test:

[0120] The results of the overlap shear test before and after ultraviolet irradiation in Example 2 are shown in Table 4 and Figure 7 As shown:

[0121] Table 4

[0122] sample <![CDATA[F max / N]]> τ / MPa UV light exposure 335 6.7 After ultraviolet light exposure 0 0

[0123] From Table 3 and Figure 7 It is known that the adhesive prepared by doping with dendritic azobenzene molecules has high shear strength and excellent adhesive performance. After ultraviolet light irradiation, the shear strength drops to 0, showing excellent light switching properties.

[0124] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A dendritic azobenzene molecular compound, characterized by, The structural formula is shown as Formula I: 。 2. A method for producing the dendritic azobenzene molecular compound according to claim 1, characterized by, The preparation method comprises the following steps: S1. preparing a compound of Formula II; S2. condensing the compound of Formula II prepared in step S1 with 6-chlorohexanol to obtain the dendritic azobenzene molecular compound; The structural formula of the compound of Formula II is shown as follows: 。 3. The preparation method according to claim 2, characterized in that, The preparation method of the dendritic azobenzene molecular compound in step S2 is as follows: the compound of Formula II, a base, a catalyst, 6-chlorohexanol and a solvent are added into a reaction system, and the reaction is carried out under heating conditions, and the dendritic azobenzene molecular compound is obtained after purification.

4. The preparation method according to claim 3, characterized in that, The molar ratio of the compound of Formula II to 6-chlorohexanol in step S2 is 1:3-5.

5. The preparation method according to claim 3, characterized in that, The molar ratio of the compound of Formula II, the base and the catalyst in step S2 is 1:3-5:7-10.

6. The preparation method according to claim 2, characterized in that, The preparation method of the compound of Formula II in step S1 is as follows: 1,3,5-tris(4-aminophenyl)benzene, a solvent and a hydrochloric acid solution are added into a reaction system, diazotization reaction is carried out between the nitrite aqueous solution to generate diazonium salt, and then a phenol solution dissolved in a base solution in advance is added, and the reaction is carried out sufficiently, and the compound of Formula II is obtained after purification.

7. Application of the dendritic azobenzene molecular compound of claim 1 as an additive for improving the light switching performance and / or the bonding performance of an adhesive; the adhesive is a doped light switching adhesive, and the adhesive comprises a base polymer; the base polymer is one or more of polycaprolactone, ethylene-vinyl acetate copolymer, polyurethane and ethylene-acrylic acid copolymer.

8. A doped optical switching adhesive, characterized by, The adhesive comprises a base polymer and the dendritic azobenzene molecular compound of claim 1; The base polymer is one or more of polycaprolactone, ethylene-vinyl acetate copolymer, polyurethane and ethylene-acrylic acid copolymer; The mass content of the dendritic azobenzene molecular compound in the doped light switching adhesive is 4%-25%.

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