An azobenzene polymer nanocomposite and application thereof

Abstract

The application discloses an azobenzene polymer nanocomposite and application thereof, wherein the azobenzene polymer nanocomposite is composed of two parts: an azobenzene small molecule matrix or an azobenzene polymer matrix and nano-silica particles with surface grafted azobenzene polymer. Azobenzene groups can reversibly undergo cis-trans isomerization under the irradiation of ultraviolet light and visible light; the composite material exhibits a solid state in the trans state, and due to the presence of nano-particles, the cohesive energy is improved, so that the composite material has strong adhesion and can bear a large load; the composite material exhibits a liquid state in the cis state, and the adhesion is greatly reduced, that is, photoisomerization can cause load reduction. The introduction of SiO2@PAzo solves the problems of insufficient bonding strength, low reversible efficiency and the like of conventional reversible adhesives.

Description

Technical Field

[0001] This invention belongs to the field of photoresponsive polymer materials technology, and particularly relates to a composite material of an azobenzene compound and inorganic nanoparticles and its applications. Background Technology

[0002] Adhesives are auxiliary materials that bond two separated surfaces together, and are widely used in production, daily life, biomedicine, and electronic devices. Based on the durability of the bond, adhesives can be divided into permanent adhesives and reversible adhesives. Permanent adhesives have strong adhesion, but are difficult to remove once applied. Common permanent adhesives include epoxy resins, polyurethanes, and cyanoacrylates. Reversible adhesives, on the other hand, can be detached as needed, but their bond strength is often low and cannot withstand large loads. Designing polymeric adhesives that simultaneously possess high adhesive strength and reversibility is theoretically very difficult. High strength means the polymer is solid, and its chain movement is frozen; good reversibility means the polymer chain movement is highly active, easily undergoing structural transformation. These two properties are contradictory. Therefore, designing adhesives that simultaneously possess high adhesive strength and reversible bonding properties is a challenging problem.

[0003] Currently, inorganic filler reinforcement is the most widely used and effective method for reinforcing polymer materials. However, due to compatibility issues between inorganic materials and polymers, inorganic fillers tend to aggregate within the material, leading to stress concentration and ultimately hindering further increases in material strength. Grafting polymers consistent with the matrix material onto the surface of inorganic nanoparticles is an effective method to enhance nanoparticle compatibility. However, there have been no reports on improving the mechanical strength of photoinduced reversible solid-liquid transition polymers through the preparation of polymer composites. Summary of the Invention

[0004] In view of this, the present invention aims to provide an adhesive that simultaneously possesses high adhesive strength and reversible adhesive properties, and its applications. This adhesive is an azobenzene polymer nanocomposite material that can undergo a photoinduced reversible solid-liquid transition at room temperature, exhibiting both high adhesive strength and reversible adhesive capability.

[0005] The azobenzene polymer nanocomposite material of the present invention is composed of two mixed parts: a small azobenzene matrix (Azo) or a high azobenzene polymer matrix (PAzo), and nano-silica particles (SiO2@PAzo) grafted with azobenzene polymer on the surface.

[0006] The structure of the azobenzene small molecule matrix is ​​shown in Formula I below:

[0007]

[0008] The structure of the azobenzene polymer matrix is ​​shown in Formula II below:

[0009]

[0010] The degree of polymerization n is 4-500, and the tail group R is butyl or decaalkyl.

[0011] The structure of the nano-silica particles with surface-grafted azobenzene polymer is shown in Formula III below:

[0012]

[0013] This invention effectively improves the compatibility between nanoparticles and the matrix by grafting polymers with the same structure as matrix molecules onto the surface of nanoparticles, preventing nanoparticle aggregation. By further adjusting parameters such as the degree of polymerization, surface grafting density, and molecular weight of the matrix molecules on the nanoparticle surface, the dispersion of nanoparticles in the system is improved. The presence of nanoparticles effectively enhances the cohesive strength of the composite material, increasing its adhesive strength while maintaining its photoinduced reversible solid-liquid transition properties, enabling photoinduced reversible solid-liquid transitions to be achieved in a relatively short time. The introduction of SiO2@PAzo can solve the problems of insufficient adhesive strength and low reversibility efficiency of conventional reversible adhesives.

[0014] The azobenzene polymer nanocomposite material of this invention is solid in the trans state, exhibiting strong adhesion and the ability to withstand large loads. Conversely, in the cis state, the composite material is liquid, with significantly reduced adhesion; that is, photoisomerization causes a decrease in load capacity. Irradiation of the trans polymer solid with ultraviolet light enables the separation of the substrate, while irradiation of the cis polymer liquid with visible light allows the substrate to re-bond, achieving reversible adhesion.

[0015] The preparation method of the azobenzene polymer nanocomposite material of the present invention includes the following steps:

[0016] Step 1: 4-(4-Butylphenylazo)phenol, represented by Formula Ia, reacts with a haloalcohol, represented by Formula Ib, to obtain the compound represented by Formula Ic.

[0017] Step 2: The compound shown in Formula Ic undergoes an acylation reaction with methacryloyl chloride to obtain the azobenzene small molecule shown in Formula I;

[0018] Step 3: The azobenzene small molecule shown in Formula I undergoes an atom transfer radical polymerization reaction to obtain the polymer shown in Formula II;

[0019] Step 4: The compound shown in Formula III-a undergoes an acylation reaction with 2-bromoisobutyryl bromide shown in Formula III-b to give the compound shown in Formula III-c;

[0020] Step 5: The compound shown in Formula III-c reacts with the triethoxysilane shown in Formula III-d under the catalysis of a caster catalyst to give Formula III-e;

[0021] Step 6: The siloxane initiator shown in Formula III-e reacts with the hydroxyl groups on the surface of nano-silica to obtain Formula III-f;

[0022] Step 7: The silica surface initiator shown in Formula III-f initiates the surface atom transfer radical polymerization of the azobenzene small molecule shown in Formula I to obtain nano silica (SiO2@PAzo) with surface grafted azobenzene polymer shown in Formula III;

[0023] Step 8: Weigh out the azobenzene small molecule shown in Formula I or the polymer shown in Formula II and the nano-silica with surface-grafted azobenzene polymer shown in Formula III in proportion and put them into the same container. Add a good solvent (polar solvent) to completely dissolve the compound. After sonicating to mix evenly, evaporate the solvent by rotary evaporation and continue drying in a vacuum oven for 24 hours to obtain the composite material.

[0024]

[0025]

[0026] The matrix polymer has a degree of polymerization n(P) of 4-500 and a tailing group R of butyl or decaalkyl; the surface graft polymer has a degree of polymerization (N) of 4-500; the nano-silica particles have a particle size of 10 nm-120 nm; and the surface grafting density is 0.05 chains / nm. 2 -1 chain / nm 2 The ratio (1 / α) of the molecular weight of the matrix molecule to the molecular weight of the surface-grafted polymer is 0.01-10. The volume percentage of SiO2@PAzo in the composite material is 0%-99.99%, preferably 10-90%, and more preferably 50-90%.

[0027] In some specific embodiments of the present invention, the polymerization reaction in step 3 uses ethyl 2-bromoisobutyrate as an initiator.

[0028] The application of the azobenzene polymer nanocomposite material of this invention is as a light-controlled reversible adhesive. Compared with pure polymer without blended nanoparticles, its adhesion performance is improved.

[0029] Specifically, the method for achieving photo-controlled reversible adhesion using the aforementioned azobenzene polymer nanocomposite material includes the following steps:

[0030] a) Molten azobenzene polymer nanocomposite material is used as a bonding medium, which is then bonded to the substrate to be bonded and cured under visible light to achieve bonding of the substrate;

[0031] b) When the bonding area is irradiated with ultraviolet light, the azobenzene polymer nanocomposite material changes to a cis configuration, undergoes a solid-liquid transition, and achieves separation from the substrate;

[0032] c) Repeat steps a) and b) above to achieve reversible bonding.

[0033] Preferably, the ultraviolet light wavelength is 365nm; in some specific embodiments of the present invention, an LED light source with a wavelength of 365nm is used.

[0034] Preferably, the visible light wavelength is 530nm; in some specific embodiments of the present invention, an LED light source with a wavelength of 530nm is used.

[0035] Compared with existing technologies, this invention provides an azobenzene polymer nanocomposite material with photo-controlled reversible adhesive properties. In its trans state, it is a solid. Due to the presence of nanoparticles, its cohesive energy is increased, giving it strong adhesive ability and the capacity to withstand large loads. Simultaneously, when the azobenzene groups in the composite material are isomerized to the cis state, it macroscopically exhibits a liquid state, with a significantly reduced adhesive ability; that is, photoisomerization can cause a decrease in load. The introduction of SiO2@PAzo addresses the problems of insufficient adhesive strength and low reversibility efficiency found in conventional reversible adhesives. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a composite material structure based on azobenzene polymer;

[0037] Figure 2 This is a schematic diagram of a composite material structure based on azobenzene small molecules;

[0038] Figure 3 The 1H NMR spectrum of azobenzene small molecules;

[0039] Figure 4 The image shows the 1H NMR spectrum of the azobenzene polymer (PAzo-4).

[0040] Figure 5 The 1H NMR spectrum of the siloxane initiator;

[0041] Figure 6 Transmission electron microscope image of SiO2 with surface-grafted polymer (magnification 400,000x);

[0042] Figure 7 The sample is a solid composite of trans-AZo and SiO2@PAzo, with SiO2@PAzo comprising 30% by mass. Its properties under ultraviolet light (365 nm, 6.7 mW / cm²) are analyzed. 2Liquefaction occurred under irradiation, and the cis-composite sample was subjected to visible light (530 nm, 8.2 mW / cm²). 2 Microscopic images of the solidified material after irradiation (scale bar is 500 μm);

[0043] Figure 8 The adhesion strength of the cis-trans configuration azobenzene polymer nanocomposite material to the silicon wafer surface, as measured by a universal testing machine;

[0044] Figure 9 A 3D bar chart showing the change in the adhesive strength of matrix molecules as the proportion of doped nanoparticles changes.

[0045] Figure 10 This describes the photocontrolled deadhesion process of azobenzene nanocomposites. Detailed Implementation

[0046] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, describes the azobenzene polymer-inorganic nanoparticle composite material with photo-controlled reversible adhesion, its preparation method, and its applications.

[0047] Example 1: Synthesis of small azobenzene molecules (Azo)

[0048] 1. Dissolve 9.16 g (0.036 mol) of 4-(4-butylphenylazo)phenol in 40 mL of N,N-dimethylformamide, then add potassium carbonate (4.98 g, 0.036 mol) and stir at 30 °C for 30 minutes. Add potassium iodide (2.77 g, 0.09 mol) and 6-chloro-1-hexanol (5.20 mL, 0.039 mol) to the system and react at 110 °C for 24 hours. Cool the reaction solution to room temperature, extract three times with dichloromethane and water, collect the organic phase and dry it with magnesium sulfate. Remove the solvent by rotary evaporation to obtain the crude product, and recrystallize from methanol to give the final product 6-[4-(4-methylphenyl)azophenoxy]-1-hexanol.

[0049] 2. The final product from step 2 (0.016 mol) and triethylamine (2.22 mL, 0.016 mol) were dissolved in 50 mL of anhydrous dichloromethane. Methacrylamide chloride (1.84 mL, 0.019 mol) was mixed with 10 mL of anhydrous dichloromethane, and the mixture was added dropwise to the above solution under an ice-water bath. The reaction was carried out at room temperature for 20 hours. The reaction solution was concentrated by rotary evaporation and washed with dilute hydrochloric acid, saturated sodium bicarbonate solution, and sodium chloride solution, respectively. The oil phase was collected, and the solvent was removed by rotary evaporation to obtain the crude product. Purification was achieved by silica gel column chromatography using dichloromethane as the eluent, yielding a small molecule containing azobenzene: 6-[4-(4-methylbenzene)azophenoxy]n-hexyl methacrylate. Its 1H NMR spectrum is shown below. Figure 3 As shown.

[0050] Example 2: Synthesis of azobenzene polymer (PAzo-4)

[0051] The polymer was obtained via atom transfer radical polymerization. The final product of Example 1 (3 g, 7.11 mmol) was added to a polymerization tube, and ethyl 2-bromo-2-methylpropionate (9.75 μL, 0.07 mmol), cuprous bromide (20.08 mg, 0.14 mmol), and pentamethyldiethylenetriamine (58.46 μL, 0.28 mmol) were added to a glove box and dissolved in 5 mL of anhydrous anisole. The reaction system was polymerized in an oil bath at 75 °C for 48 hours. After the reaction was complete, the lid was opened, and the polymerization reaction was quenched by air. The reaction solution was added dropwise to 40 mL of ethanol, centrifuged to obtain a precipitate, dissolved in tetrahydrofuran, and then precipitated again with ethanol. This process was repeated three times to remove unreacted monomers. The precipitate was collected and dried in a vacuum drying oven at 40 °C for 24 hours to obtain the final azobenzene polymer. Its 1H NMR spectrum is shown below. Figure 4 As shown.

[0052] Example 3: Synthesis of surface-grafted azobenzene polymer nanoparticles (SiO2@PAzo)

[0053] 1. Dissolve 10-undecen-1-ol (1.1 mL, 5.49 mmol) in anhydrous dichloromethane (15 mL). Add 2-bromoisobutyryl bromide (525 μL, 6.49 mmol) and 10 mL of anhydrous dichloromethane solution dropwise under an ice-water bath. After the addition of the 2-bromoisobutyryl bromide solution, react at room temperature for 12 hours. After the reaction, filter off the solid. Transfer the filtrate to a separating funnel and wash twice with HCl aqueous solution, twice with sodium carbonate solution, and finally twice with pure water. Collect the organic phase and dry it with magnesium sulfate. Remove the solvent by rotary evaporation to obtain the crude product, which is then purified by silica gel column chromatography using a 25:1 mixture of hexane and ethyl acetate as the eluent. The result is a colorless oily compound, 2-bromo-2-methylpropionic acid-10-undecenyl ester.

[0054] 2. Under a nitrogen atmosphere, the final product of step (1) (0.56 g, 1.74 mmol), triethoxysilane (2.7 mL, 14.63 mmol), and Karl Fischer catalyst (100 μL) were added. The reaction was carried out at 40 °C for 12 hours. After the reaction was completed, excess triethoxysilane was removed by vacuum distillation. A pale yellow transparent oil was obtained. It was purified by silica gel column chromatography using a 100:1 mixture of hexane and ethyl acetate as the eluent. Finally, a colorless oil, 2-bromo-2-methylpropionic acid (3-trimethoxysilyl) undecyl ester, was obtained. Its 1H NMR spectrum is shown below. Figure 5 As shown;

[0055] 3. Weigh 4g of SiO2 colloid (EAC-ST, provided by Nissan Chemical Company), add dropwise anhydrous toluene solution of the final product (4g, 8.32mmol) from step (2), and finally react at 95℃ for 24 hours under N2 atmosphere, followed by reflux. After cooling, add hexamethyldisilazane to the system, react at 35℃ for 12 hours, and centrifuge to remove the precipitate after 12 hours. Remove the solvent from the supernatant by rotary evaporation to obtain a pale yellow viscous fluid. Add it dropwise to n-hexane to form a pale yellow flocculent precipitate. After centrifugation, dissolve the precipitate in tetrahydrofuran, add n-hexane to settle it. Repeat the above steps multiple times until there is no siloxane initiator in the supernatant. After drying the precipitate in a vacuum oven, a pale yellow powder is obtained, which is the nano-silica surface initiator.

[0056] 4. 6-[4-(4-methylbenzene)azophenoxy]n-hexyl methacrylate (6 g, 14.22 mmol) was added to a polymerization tube. In a glove box, nano-silica surface initiator (727 mg), cuprous bromide (77.50 mg, 0.54 mmol), and pentamethyldiethylenetriamine (226 μL, 1.08 mmol) were dissolved in 9 mL of anhydrous anisole. The reaction system was incubated at 55 °C for 12 hours. After the reaction, the lid was opened, and the polymerization reaction was quenched by air. The reaction solution was added dropwise to 100 mL of methanol. The precipitate was dissolved in tetrahydrofuran and then precipitated again with methanol. This process was repeated three times to remove unreacted monomers. The precipitate was collected and dried in a vacuum drying oven at 40 °C for 24 hours. This yielded nano-silica with azobenzene polymer grafted onto its surface. Transmission electron microscopy revealed that the nanoparticles were clearly and uniformly dispersed. Figure 6 As shown.

[0057] Example 4: Synthesis of azobenzene polymer nanocomposites

[0058] Weigh 40 mg of surface-grafted azobenzene polymer nanofiber silica, and then weigh 60 mg of azobenzene small molecules or azobenzene polymer. Pour them into a glass sample bottle, and add tetrahydrofuran solvent until both parts are completely dissolved. Seal the sample bottle and sonicate it in an ultrasonic instrument for 1 hour. After evaporating the solvent using a rotary evaporator, place it in an oven and continue drying for 24 hours to ensure complete solvent removal, thus obtaining the azobenzene polymer nanocomposite material.

[0059] Example 5: Photoinduced solid-liquid transition of azobenzene polymer nanocomposites at the micrometer scale

[0060] At room temperature, a small amount of solid azobenzene polymer nanocomposite material (Example 4) was placed on a smooth, clean glass slide. The slide was then placed on the stage of a microscope and exposed to ultraviolet light (365 nm, 6.7 mW / cm²). 2The surface of a solid sample is irradiated to induce photoisomerization, and after 10 minutes of irradiation, a complete solid-liquid transition is achieved. Figure 7 The trans solid sample was shown to liquefy under ultraviolet light irradiation.

[0061] Example 6: A method for achieving reversible adhesives using azobenzene polymer nanocomposites

[0062] The inverse composite material firmly bonds the two substrates together. The composite material between the quartz plates exhibits excellent adhesion under ultraviolet light (365nm, 22.39mW / cm²). 2 Under irradiation, a photoinduced solid-liquid transition occurs, causing a decrease in the adhesive strength and separation of the two substrates. The adhesive strength was tested using a tensile testing machine (UTM5017 universal testing machine from Sansi Zongheng Technology Co., Ltd.) to perform lap shear tests on both cis and anti-cissor specimens. The tensile strength curves are shown below. Figure 8 As shown, compared to matrix molecules without nanoparticles, the adhesive strength of the composite material is significantly improved. Figure 9 As shown.

[0063] The reversibility properties of the composite material were tested by exposing the substrate with adhesion failure in the above experiment to ultraviolet light (365nm, 22.39mW / cm²). 2 The material was liquefied by irradiation, and then the two pieces were bonded and fixed together, followed by irradiation with visible light (530nm, 20.75mW / cm²). 2 The adhesive is then cured to improve its viscosity, resulting in a reversibly bonded sample. The adhesion strength of the reversibly bonded sample is tested using a tensile testing machine. Experimental results show that the small molecule (Azo) incorporated into the SiO2@PAzo composite exhibits the best reversibility, while the liquefaction performance of the polymer with four carbon tails (PAzo-4) incorporated into the SiO2@PAzo composite decreases. This is because the addition of SiO2@PAzo increases the entanglement points between molecular chains in the system, restricting the movement of molecular chain segments and thus reducing liquefaction capacity. When the matrix polymer is replaced with a polymer with more than 10 carbon tails (19kPAzo-10), the difference lies in the fact that polymers with longer tails have larger free volumes, stronger molecular chain segment mobility, and enhanced liquefaction performance, thus ensuring reversibility.

[0064] Table 1 Comparison of reversible properties of composite materials

[0065]

[0066] Example 7: Photocontrolled deadhesion of azobenzene nanocomposites

[0067] A 2 kg bell was continuously suspended using a substrate bonded with composite materials. The bonded area was then subjected to ultraviolet light (365 nm, 26.75 mW / cm²). 2Irradiation with ultraviolet light weakened the adhesion of the composite material, and the adhered substrate slid off after 16 seconds. Figure 10 The process of the adhesive load test is shown.

[0068] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An azobenzene polymer nanocomposite material, characterized in that: The azobenzene polymer nanocomposite material is composed of two parts: a small molecule azobenzene matrix or a high molecule azobenzene matrix, and nano-silica particles SiO2@PAzo grafted with azobenzene polymer on the surface. The structure of the azobenzene small molecule matrix is ​​shown in Formula I below: ； The structure of the azobenzene polymer matrix is ​​shown in Formula II below: ； The degree of polymerization n of the azobenzene polymer matrix is ​​4-500, and the tail group R is butyl or decaalkyl; The structure of the nano-silica particles with surface-grafted azobenzene polymer is shown in Formula III below: ； The degree of polymerization of the surface-grafted azobenzene polymer in the nano-silica particles is 4-500.

2. The azobenzene polymer nanocomposite material according to claim 1, characterized in that: The nano-silica particles in the surface-grafted azobenzene polymer have a particle size of 10 nm-120 nm.

3. The azobenzene polymer nanocomposite material according to claim 1, characterized in that: The surface grafting density of the surface-grafted azobenzene polymer in the nano-silica particles is 0.05 chains / nm. 2 -1 chain / nm 2 .

4. The azobenzene polymer nanocomposite material according to claim 1, characterized in that: The ratio of the molecular weight of the azobenzene polymer matrix to the molecular weight of the surface-grafted polymer in the nano-silica particles grafted with azobenzene polymer is 0.01-10.

5. The azobenzene polymer nanocomposite material according to claim 1, characterized in that: The volume percentage of SiO2@PAzo in the azobenzene polymer nanocomposite is 10-90%.

6. The application of the azobenzene polymer nanocomposite material according to any one of claims 1-5, characterized in that: The azobenzene polymer nanocomposite material is used as a light-controlled reversible adhesive.

7. The application according to claim 6, characterized in that: The method for achieving photo-controlled reversible bonding using the aforementioned azobenzene polymer nanocomposite material includes the following steps: a) Molten azobenzene polymer nanocomposite material is used as a bonding medium, which is then bonded to the substrate to be bonded and cured under visible light to achieve bonding of the substrate; b) When the bonding area is irradiated with ultraviolet light, the azobenzene polymer nanocomposite material changes to a cis configuration, undergoes a solid-liquid transition, and achieves separation from the substrate; c) Repeat steps a) and b) above to achieve reversible bonding.

8. The application according to claim 7, characterized in that: The ultraviolet light wavelength is 365nm.

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