Thermoresponsive adhesive hydrogel and method of making same

Abstract

The application discloses a temperature-controllable adhesive hydrogel and a preparation method thereof. The temperature-controllable adhesive hydrogel is prepared by polymerization of AAm, AA, QCA, a free radical polymerization initiator, an antioxidant and ultrapure water as raw materials. The temperature-controllable adhesive hydrogel does not contain a chemical crosslinking agent, is crosslinked by weak physical interactions such as hydrogen bonds and electrostatic interactions, and is composed of a physical crosslinking network system of acrylic acid, acrylamide, QCA, 2,2-azobis(2-methylpropylimid) dihydrochloride and water, so that the degree of free movement of the polymer chain is relatively high, and the polymer chain can quickly respond to temperature changes.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of functional polymer materials, and particularly relates to a temperature-controlled adhesive hydrogel and a preparation method thereof. BACKGROUND

[0002] Intelligent hydrogels are mainly constructed through non-covalent interactions involved in the hydrogel network, including electrostatic interactions (ionic bonds, hydrogen bonds and halogen bonds), van der Waals forces (dipole-dipole, dipole-induced dipole and dispersion forces), π effects (π-π, cation-π, anion-π and polarity-π interactions) and hydrophobic interactions. Due to these dynamic properties, the structure, properties and shape of the material itself can be changed under the influence of environmental stimuli such as light, electricity, magnetism, temperature, stress and oxidation-reduction. Since temperature is a common and easy-to-control environmental stimulus, temperature-sensitive hydrogels are the most typical and widely studied intelligent hydrogels. They can sense temperature changes and make corresponding changes in volume, color, gel state, etc. in a timely manner. In most cases, temperature-sensitive hydrogel materials can easily achieve reversible and large deformation, but the slow response and low mechanical strength of these hydrogels limit their practical application fields.

[0003] In recent years, the preparation of temperature-controlled adhesive hydrogels that can respond to changes in external temperature to achieve on-demand adhesion / detachment conversion has been widely studied. Shi et al. (Xiaofang Shi and Peiyi Wu. A Smart Patch with On-Demand Detachable Adhesion for Bioelectronics. Small. 2021) constructed a thermal response behavior by in-situ polymerization of acrylic acid in a quaternized chitosan aqueous solution, achieving temperature-controlled adjustment of the mechanical properties, adhesion, and optical effects of the hydrogel; Jiang et al. (Yanan Jiang, Xin Zhang, et al. Infant Skin Friendly Adhesive Hydrogel Patch Activated at Body Temperature for Bioelectronics Securing and Diabetic Wound Healing. ACS Nano. 2022) complexed gallic acid with a methacryl gelatin network, enabling the methacryl gelatin network to respond to thermal stimuli, resulting in temperature-induced hydrogel adhesion and detachment.

[0004] For the adhesive hydrogel material, the most important factor affecting its surface adhesion performance is the balance between cohesion and adhesion. If the cohesion of the hydrogel is too large, the number of surface adhesive molecules will be correspondingly reduced, thereby reducing the adhesion. If the adhesion is sufficient and the cohesion is insufficient, internal tearing often occurs during the peeling of the hydrogel. The existing temperature-responsive adhesive hydrogel is difficult to achieve the balance between high adhesion strength and high tensile strength. SUMMARY

[0005] The present application aims to overcome the deficiencies of the prior art and provide a temperature-controlled adhesive hydrogel.

[0006] Another object of the present application is to provide a preparation method of the temperature-controlled adhesive hydrogel.

[0007] The technical scheme of the present application is as follows:

[0008] A temperature-controlled adhesive hydrogel is prepared by polymerization of AAm, AA (acrylic acid), QCA, a free radical polymerization initiator, an antioxidant and ultrapure water, wherein the structural formula of the QCA is

[0009]

[0010] In a preferred embodiment of the present application, the free radical polymerization initiator is AIBA.

[0011] In a preferred embodiment of the present application, the antioxidant is sodium citrate.

[0012] In a preferred embodiment of the present application, the synthetic route of the QCA is as follows:

[0013]

[0014] Further preferably, the preparation method of the QCA comprises: dissolving 2-chloro-3', 4'-dihydroxyacetophenone in ethyl acetate at room temperature, adding dimethylaminoethyl methacrylate, passing nitrogen for 25-35 min, reacting at 65-75°C for 40-50 h to obtain a precipitate, and then sequentially dissolving the precipitate in methanol, precipitating with diethyl ether and vacuum drying to obtain the QCA.

[0015] More preferably, the ratio of the 2-chloro-3', 4'-dihydroxyacetophenone, ethyl acetate and dimethylaminoethyl methacrylate is 4-5 g: 50 mL: 3-4 mL.

[0016] In a preferred embodiment of the present application, the ratio of the AAm, AA, QCA, free radical polymerization initiator, antioxidant and ultrapure water is 0.25-0.27 g: 0.85-1.00 g: 0.04-0.17 g: 0.01-0.03 g: 0.01-0.03 g: 3 mL.

[0017] Further preferably, the proportions of the AAm, AA, QCA, radical polymerization initiator, antioxidant, and ultrapure water are 0.26 g: 0.88-0.99 g: 0.05-0.16 g: 0.02 g: 0.02 g: 3 mL.

[0018] The preparation method of the temperature-controlled adhesive hydrogel described above comprises the following steps:

[0019] (1) Dissolve the AAm, AA, QCA, radical polymerization initiator, and antioxidant in ultrapure water, and ultrasonically disperse to obtain a prepolymer solution;

[0020] (2) Centrifuge the prepolymer solution described above to remove air bubbles;

[0021] (3) Pour the material obtained in step (2) into a mold, and perform a polymerization reaction under the protection of a nitrogen atmosphere at 55°C for 2 h, and then cool to room temperature.

[0022] In a preferred embodiment of the present application, the protective atmosphere of the polymerization reaction is a nitrogen atmosphere, the temperature is 55°C, and the time is 2 h.

[0023] The present application has the following beneficial effects:

[0024] 1. The temperature-controlled adhesive hydrogel of the present application does not contain a chemical crosslinking agent, is crosslinked by weak physical interactions such as hydrogen bonds and electrostatic interactions, and is a physical crosslinking network system composed of acrylic acid (AA), acrylamide (AAm), a quaternary ammonium salt type catechol-based polymerizable monomer (QCA), 2,2-azobis(2-methylpropylimide) dihydrochloride (AIBA), and water, so that the degree of free movement of the polymer chains is relatively high and the polymer can quickly respond to changes in temperature.

[0025] 2. The temperature-controlled adhesive hydrogel of the present application is sensitive to pH, and as the pH of the system increases, the phase transition temperature of the hydrogel increases; sodium citrate in the system is both an antioxidant and a pH regulator; when the pH increases, the degree of ionization of AA increases, forming a strong electrostatic interaction with the quaternary ammonium cation in QCA, increasing the intermolecular force of the polymer, and increasing the phase transition temperature of the system.

[0026] 3. As shown in the formula (I), the present application introduces catechol groups into the hydrogel system by a free radical random copolymerization method, which can interact with the surfaces of various materials, improve the adhesion strength of the hydrogel, and adjust the adhesion of the hydrogel by adjusting the content of the catechol monomer in the system, thereby endowing the hydrogel with excellent adhesion strength. The addition of acrylamide monomers can significantly improve the mechanical properties of the hydrogel. Figure 1

[0027] ​4. The temperature-controlled adhesive hydrogel of the present invention is an amphoteric polyelectrolyte containing carboxylic acid anions and quaternary ammonium cations on the polymer side chains, so that the hydrogel has a maximum critical transition temperature (UCST).

[0028] 5. If Figure 7 As shown, the present invention can adjust the phase transition temperature of the hydrogel by changing the pH value of the system, thereby changing the application range of the hydrogel's adhesion / debonding: when the temperature is lower than the phase transition temperature, the interaction between the polymer chains in the temperature-controlled adhesive hydrogel of the present invention is greater than the interaction between the polymer and water, causing the polymer chains to curl and entangle together, scattering incident light, making the hydrogel opaque, and the catechol groups wrapped inside the polymer, making the hydrogel non-sticky; when the temperature is higher than the phase transition temperature, the physical interaction between the polymers is destroyed, the interaction between the polymer and water is enhanced, a solvation effect occurs, the hydrogel becomes transparent, the catechol groups are exposed, and the adhesion is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The synthetic route of the temperature-controlled adhesive hydrogel of the present invention is shown in FIG.

[0030] Figure 2 IR spectra of the temperature-controlled adhesive hydrogels prepared in Examples 1 to 3 of the present invention.

[0031] Figure 3 The UV spectra of the temperature-controlled adhesive hydrogels prepared in Examples 1 to 3 of the present invention are shown.

[0032] Figure 4 Graphs showing stress-strain curves of the temperature-controlled adhesive hydrogels prepared in Examples 1 to 3 of the present invention above and below the upper critical transition temperature (UCST) are shown.

[0033] Figure 5 Graphs showing the adhesion performance of the temperature-controlled adhesive hydrogels prepared in Examples 1 to 3 of the present invention.

[0034] Figure 6 1 is a comparison chart of the adhesion strength of the temperature-controlled adhesion hydrogels prepared in Examples 1 to 3 of the present invention on a glass surface above and below the upper critical transition temperature (UCST).

[0035] Figure 7 Schematic diagram of high-temperature adhesion and low-temperature debonding of the temperature-controlled adhesive hydrogel of the present invention.

[0036] Figure 8 This is an infrared spectrum of QCA prepared in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further illustrated and described below through specific implementation methods in conjunction with the accompanying drawings.

[0038] The synthetic route of QCA used in the following Examples 1 to 3 is as follows:

[0039]

[0040] Specifically, 4.2 g of 2-chloro-3',4'-dihydroxyacetophenone was dissolved in 50 mL of ethyl acetate at room temperature, 3.8 mL of dimethylaminoethyl methacrylate was added, nitrogen was passed for 30 min, and the reaction was carried out at 70°C for 48 h. The precipitate was dissolved in 42 mL of methanol, precipitated with 500 mL of diethyl ether, and dried in vacuum for 24 h to obtain the quaternary ammonium salt type pyrocatechol-based polymerizable monomer QCA (2-(3,4-dihydroxyphenyl)-N-(2-(methacryloyloxy)ethyl)-N,N-dimethyl-2-oxoethanol-1-ammonium chloride) as shown in Figure 8 .

[0041] Example 1

[0042] (1) 0.26 g of AAm, 0.99 g of AA, 0.05 g of QCA, 0.02 g of AIBA and 0.02 g of sodium citrate were dissolved in 3 mL of ultrapure water, and ultrasonic dispersion was carried out for 1 min to obtain a prepolymer solution;

[0043] (2) The prepolymer solution was centrifuged at 8000 r / min for 5 min to remove bubbles; (3) The material obtained in step (2) was poured into a glass mold, and the polymerization reaction was carried out at 55°C for 2 h under the protection of nitrogen atmosphere to obtain a light yellow transparent hydrogel, and a white opaque temperature-sensitive adhesive hydrogel as shown in Figure 2 was obtained after cooling to room temperature.

[0044] As shown in Figure 3 , 4 and 6, the phase transition temperature of the temperature-sensitive adhesive hydrogel prepared in this example was 42.07°C; the breaking strength of the temperature-sensitive adhesive hydrogel was 25.47 kPa and the elongation at break was 637% at a stretching rate of 100 mm / min under the condition that the ambient temperature was higher than 49°C, the breaking strength was 26.67 kPa and the elongation at break was 1837% at room temperature; the adhesive strength on glass as the adhesive test substrate was 4.40 kPa at 25°C and 22.85 kPa at 55°C.

[0045] As shown in Figure 5 , the temperature-sensitive adhesive hydrogel prepared in this example adhered to the substrate when the temperature of the substrate was higher than the upper critical solution temperature (UCST) of the hydrogel, and the hydrogel was debonded when the temperature of the substrate was lower than the upper critical solution temperature (UCST) of the hydrogel.

[0046] Example 2

[0047] (1) 0.26 g AAm, 0.94 g AA, 0.1 g QCA, 0.02 g AIBA and 0.02 g sodium citrate were dissolved in 3 mL ultrapure water, ultrasonic dispersion for 1 min to obtain a prepolymer solution; (2) the prepolymer solution was centrifuged at 8000 r / min for 5 min to remove bubbles; (3) the material obtained in step (2) was poured into a glass mold, and the polymerization reaction was carried out at 55°C for 2 h under the protection of nitrogen atmosphere, to obtain a light yellow brown transparent hydrogel, which was cooled to room temperature to obtain a white opaque temperature-sensitive adhesive hydrogel as shown in Figure 2 .

[0048] As shown in Figure 3 , 4 and 6, the phase transition temperature of the temperature-sensitive adhesive hydrogel prepared in this embodiment was 49.02°C; the breaking strength of the temperature-sensitive adhesive hydrogel was 30.45 kPa and the elongation at break was 817% at a stretching rate of 100 mm / min when the ambient temperature was higher than 49°C, the breaking strength was 32.33 kPa and the elongation at break was 1316% at room temperature; the adhesive strength was 3.14 kPa at 25°C and the adhesive strength was 29.37 kPa at 55°C when glass was used as the adhesive test substrate.

[0049] As shown in Figure 5 , the temperature-sensitive adhesive hydrogel prepared in this embodiment adheres to the substrate when the temperature of the substrate is higher than the upper critical solution temperature (UCST), and the hydrogel is debonded when the temperature drops below the upper critical solution temperature (UCST).

[0050] Example 3

[0051] (1) 0.26 g AAm, 0.88 g AA, 0.16 g QCA, 0.02 g AIBA, 0.02 g sodium citrate were dissolved in 3 mL ultrapure water, ultrasonic dispersion for 1 min to obtain a prepolymer solution; (2) the prepolymer solution was centrifuged at 8000 r / min for 5 min to remove bubbles;

[0052] (3) the material obtained in step (2) was poured into a glass mold, and the polymerization reaction was carried out at 55°C for 2 h under the protection of nitrogen atmosphere, to obtain a light yellow brown transparent hydrogel, which was cooled to room temperature to obtain a white opaque temperature-sensitive adhesive hydrogel as shown in Figure 2 .

[0053] As shown in Figure 3 , 4As shown in Figures 6 and 7, the phase transition temperature of the temperature-controlled adhesive hydrogel prepared in this embodiment is 44.45°C. At a tensile rate of 100 mm / min, the temperature-controlled adhesive hydrogel has a breaking strength of 31.733 kPa and an elongation at break of 530% at an ambient temperature above 44°C, and a breaking strength of 39.13 kPa and an elongation at break of 1214% at room temperature. Using glass as the adhesion test substrate, the adhesion strength at 25°C is 3.28 kPa, and the adhesion strength at 55°C is 26.61 kPa.

[0054] like Figure 5 As shown, the temperature-controlled adhesive hydrogel prepared in this embodiment adheres to the substrate when the substrate temperature is higher than its upper critical transition temperature (UCST), and the hydrogel debonds when the temperature drops below the upper critical transition temperature (UCST).

[0055] The above description is merely a preferred embodiment of the present invention and therefore cannot be used to limit the scope of the present invention. In other words, equivalent changes and modifications made within the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A temperature-controlled adhesive hydrogel, characterized in that: It is prepared by polymerization of acrylamide, acrylic acid, QCA, free radical polymerization initiator, antioxidant and ultrapure water. The structural formula of the above QCA is The free radical polymerization initiator is AIBA, The antioxidant is sodium citrate.

2. The temperature-controlled adhesive hydrogel according to claim 1, wherein: The synthetic route of the QCA is:

3. The temperature-controlled adhesive hydrogel according to claim 2, wherein: The preparation method of QCA comprises: dissolving 2-chloro-3′,4′-dihydroxyacetophenone in ethyl acetate at room temperature, adding dimethylaminoethyl methacrylate, passing nitrogen for 25-35 minutes, reacting at 65-75° C. for 40-50 hours to obtain a precipitate, and then dissolving the precipitate in methanol, precipitating with ether, and vacuum drying to obtain the QCA.

4. The temperature-controlled adhesive hydrogel according to claim 3, wherein: The ratio of the 2-chloro-3',4'-dihydroxyacetophenone, ethyl acetate and dimethylaminoethyl methacrylate is 4-5 g:50 mL:3-4 mL.

5. The temperature-controlled adhesive hydrogel according to any one of claims 1 to 4, characterized in that: The ratio of acrylamide, acrylic acid, QCA, free radical polymerization initiator, antioxidant and ultrapure water is 0.25-0.27 g: 0.85-1.00 g: 0.04-0.17 g: 0.01-0.03 g: 0.01-0.03 g: 3 mL.

6. The temperature-controlled adhesive hydrogel according to claim 5, characterized in that: The ratio of acrylamide, acrylic acid, QCA, free radical polymerization initiator, antioxidant and ultrapure water is 0.26g:0.88-0.99g:0.05-0.16g:0.02g:0.02g:3mL.

7. The method for preparing the temperature-controlled adhesive hydrogel according to any one of claims 1 to 6, characterized in that: The steps include: (1) dissolving acrylamide, acrylic acid, QCA, a free radical polymerization initiator, and an antioxidant in ultrapure water, and ultrasonically dispersing the mixture to obtain a prepolymer solution; (2) centrifuging the prepolymer solution to remove air bubbles; (3) Pour the material obtained in step (2) into a mold, carry out polymerization reaction at 55° C. under nitrogen atmosphere for 2 h, and then cool to room temperature to obtain the product.

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