Preparation method of covalent organic framework-polymer mechanical interlocking structure hydrogel

Abstract

The invention relates to a preparation method of hydrogel with a covalent organic framework-polymer mechanical interlocking structure. The method comprises the following steps: uniformly dispersing COFs in a monomer solution, stirring to enable monomers to enter channels of the COFs, and polymerizing the monomers in the channels of the COFs through a free radical polymerization method to form the COFs with a mechanical interlocking structure and the polymer hydrogel. According to the hydrogel obtained by the invention, the introduction of the COFs enhances the total dissipation energy of the hydrogel, the COFs and the polymer form a mechanical interlocking structure to increase the binding energy between molecules, the energy dissipation of sacrificial bonds is reduced, and the tensile strength and elasticity of the hydrogel are improved. The pore channels of the COFs are beneficial to ion transmission, the ion conductivity is improved, and compared with single polymer hydrogel, the tensile strength is improved by 2.2 times, and the conductivity is improved by 2.9 times.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogel preparation, and specifically relates to a preparation method of a hydrogel with a covalent organic framework (COF) and a polymer mechanical interlocking structure. Background Art

[0002] Hydrogels have received extensive attention in the field of wearable strain sensors due to their good biocompatibility, stretchability, and similarity in modulus to skin tissue. High conductivity and excellent mechanical properties (such as elasticity and tensile strength) are the keys to achieving a long cycle service life of wearable sensors. Introducing conductive nanofillers into polymer hydrogels is a common method to simultaneously improve their mechanical properties and conductivity. Qin et al. (M. Qin, W. Yuan, X. Zhang, Y. Cheng, M. Xu, Y. Wei, W. Chen, D. Huang, Preparation of PAA / PAM / MXene / TA hydrogel with antioxidant, healable ability as strain sensor, Colloids Surf. B 2022, 214, 112482.) introduced conductive MXene into polyacrylamide hydrogels, with a tensile strength of 0.251 ± 0.05 MPa and a resistance of 86.68 ± 6.97 kΩ, achieving a significant improvement in performance. However, due to the large energy dissipation of sacrificial bonds, the elasticity of the hydrogel is <60%, which greatly limits their application in the field of wearable strain sensors. Designing and synthesizing hydrogel materials with strong intermolecular binding energy and reducing the energy dissipation of sacrificial bonds are necessary conditions for improving conductivity and mechanical properties.

[0003] Covalent organic frameworks (COFs) are crystalline porous materials formed by covalent bonding. Due to their advantages such as a designable chemical structure, regular and ordered pores, and a high specific surface area, they show great application prospects in strain sensing. The pores of COFs are conducive to ion transport and improve ionic conductivity. Threading polymer chains into the pores of COFs to form a mechanical interlocking structure, and the abundant organic groups on the main framework of COFs can form dense intermolecular interactions with polymer chains, reducing the energy dissipation of sacrificial bonds, which is an effective method to improve the tensile strength and elasticity of hydrogels. However, due to the large difference in modulus between the hard phase of COFs and the soft phase polymer chains, and the insolubility of COFs in water, they are prone to aggregation in polymer solutions, resulting in difficult uniform dispersion, seriously affecting the threading of polymer chains into the pores of COFs, and further affecting the mechanical properties and conductivity of hydrogels. Designing and synthesizing new hydrogel materials is the key to improving their mechanical properties and conductivity.

[0004] Currently, there are still few hydrogels formed by the composite of COFs and polymers with mechanical interlocking structures applied in the field of wearable strain sensors. Developing COF-polymer composite hydrogels with high ionic conductivity, excellent mechanical properties, simple preparation, and low cost has become an urgent problem to be solved for expanding their applications in wearable strain sensors. Summary of the Invention

[0005] The present invention mainly aims at the problems existing in current wearable strain sensors and provides a preparation method for a covalent organic framework-polymer mechanically interlocked structure hydrogel. In this method, COFs are uniformly dispersed in a monomer solution. After stirring, the monomers enter the pores of the COFs, and then through free radical polymerization, the monomers polymerize in the pores of the COFs to form a mechanically interlocked structure of COFs and polymer hydrogel. For the hydrogel obtained in the present invention, the introduction of COFs enhances the total dissipation energy of the hydrogel. The formation of a mechanical interlocking structure between COFs and polymers increases the binding energy between molecules, reduces the energy dissipation of sacrificial bonds, and improves the tensile strength and elasticity of the hydrogel. The pores of COFs are beneficial to ion transport and improve ionic conductivity. Compared with a single polymer hydrogel, the tensile strength of the mechanically interlocked structure hydrogel obtained in the present invention is increased by 2.2 times, and the conductivity is increased by 1.3 times.

[0006] The technical solution of the present invention is as follows:

[0007] A preparation method for a covalent organic framework-polymer mechanically interlocked structure hydrogel, the method comprising the following steps:

[0008] Add COFs to deionized water and a deep eutectic solvent, stir for 1 to 12 hours, then add monomers and a crosslinking agent, stir for 1 to 24 hours, then add an initiator, and finally stir for 0.1 to 3 minutes to obtain a dispersion. Pour the dispersion into a polytetrafluoroethylene mold, and at room temperature, free radical polymerization occurs for 0.01 to 4 hours to obtain a covalent organic framework-polymer hydrogel with a mechanically interlocked structure;

[0009] Wherein, the mass of COFs is 0.1 to 50% of the mass of the monomers; each 1 mL of deionized water contains 0.5 to 20 g of the deep eutectic solvent, 0.1 to 10 g of the monomers, 0.001 to 5 g of the crosslinking agent, and 0.001 to 0.5 g of the initiator;

[0010] The monomers are one or more of acrylamide, acrylic acid, 2-hydroxyethyl methacrylate, n-butyl acrylate, and methyl methacrylate;

[0011] The crosslinking agent is N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, or α,ω-diacrylate-based polyethylene glycol;

[0012] The initiator described above is ammonium persulfate or potassium persulfate;

[0013] The preparation method of the COFs described above includes the following steps:

[0014] Add COFs precursors, organic solvents and acid solutions into a Schlenk tube, ultrasonically treat the obtained mixture for 1 to 60 minutes, place it in a microwave reactor, and react at 80 to 200 °C for 0.5 to 12 hours; wash the generated solid powder and dry it under vacuum to obtain COFs;

[0015] Among them, 0.001 to 0.5 mmol of COFs precursors and 0.01 to 20 mL of acid solutions are added to every 1 mL of organic solvent;

[0016] The COFs precursors described above are one or more of aromatic aldehyde compounds, aromatic amine compounds, aromatic hydrazide compounds, aromatic anhydride compounds, and aromatic nitrile compounds.

[0017] The aromatic aldehyde compounds are phloroglucinol trialdehyde, 2,2'-bipyridine-5,5'-dicarboxaldehyde or 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraphenylbenzaldehyde; the aromatic amine compounds are 1,4-phenylenediamine, 2,5-dichloro-1,4-phenylenediamine or 1,3,5-tris(4-aminophenyl)benzene; the aromatic hydrazide compounds are 2,5-dihydrazino-1,3,4-thiadiazole, 2,5-dimethoxyterephthalohydrazide, isophthalohydrazide or p-aminobenzohydrazide; the aromatic anhydride compounds are 1,4,5,8-naphthalenetetracarboxylic dianhydride, pyromellitic dianhydride or benzenehexacarboxylic trianhydride; the aromatic nitrile compounds are 1,4-dicyanobenzene or 2,4,6-trimethylbenzene-1,3,5-tricarbonitrile;

[0018] The organic solvents described above are any one or more of mesitylene, 1,4-dioxane, o-dichlorobenzene, n-butanol, N,N-dimethylformamide, toluene and N-methylpyrrolidone;

[0019] The acid solution is hydrochloric acid, acetic acid or aqueous nitric acid, with a concentration of 1 to 10 mol / L -1 。

[0020] The preparation method of the deep eutectic solvent described above includes the following steps:

[0021] Mix the hydrogen bond donor and the hydrogen bond acceptor, and heat at 25 to 100 °C for 0.5 to 2 hours to obtain the deep eutectic solvent;

[0022] The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor therein is 1:0.1 to 3;

[0023] The hydrogen bond donor is any one of glycerol, ethylene glycol, 1,4-butanediol, urea, and lactic acid;

[0024] The hydrogen bond acceptor is choline chloride or tetramethylammonium chloride.

[0025] The application of the covalent organic framework-polymer mechanically interlocked structure hydrogel obtained by the method is used as an intermediate layer of a strain sensor, and the specific steps are as follows:

[0026] The covalent organic framework-polymer mechanically interlocked structure hydrogel is used as an intermediate layer of a strain sensor and is assembled into a strain sensor by encapsulating it between two pieces of pressure-sensitive tape.

[0027] The substantial features of the present invention are:

[0028] In the present invention, COFs are uniformly dispersed in a monomer solution, and through a free radical polymerization method, the monomers are in-situ polymerized in the pores of COFs to form a mechanically interlocked structure of COFs and a polymer hydrogel. For the hydrogel obtained in the present invention, the introduction of COFs enhances the total dissipation energy of the hydrogel. The formation of a mechanically interlocked structure between COFs and the polymer increases the binding energy between molecules, reduces the energy dissipation of sacrificial bonds, and improves the tensile strength and elasticity of the hydrogel; the pores of COFs are conducive to ion transport, improving the conductivity, which is superior to many existing hydrogel strain sensors.

[0029] The beneficial effects of the present invention are:

[0030] (1) The present invention provides a method for preparing a mechanically interlocked structure hydrogel by compounding COFs and a polymer. The clear structures of COFs and the polymer provide an ideal platform for the relationship between the hydrogel structure and strain sensing performance.

[0031] (2) The mechanically interlocked structure hydrogel prepared by compounding COFs and a polymer provided by the present invention, benefiting from the mechanically interlocked structure, has a tensile strength of 0.41 MPa. Compared with a single polymer hydrogel (0.186 MPa), the tensile strength of the mechanically interlocked structure hydrogel is increased by 2.2 times.

[0032] (3) The mechanically interlocked structure hydrogel prepared by compounding COFs and a polymer provided by the present invention has an elastic recovery rate of 99% after the first stretching cycle and 96% after the ninth stretching cycle; the elastic recovery rate of a single polymer hydrogel is only 90% after the sixth stretching cycle and breaks during the unloading process of the seventh stretching cycle.

[0033] (4) The mechanically interlocked structure hydrogel prepared by compounding COFs and a polymer provided by the present invention has a conductivity of 1.27 S / m -1 , compared with a single polymer hydrogel (0.44 S / m-1 ) The conductivity of the mechanically interlocked structure hydrogel is increased by 2.9 times.

[0034] (5) After the mechanically interlocked structure hydrogel prepared by the composite of COFs and polymers provided by the present invention is assembled into a strain sensor, at 50% strain, after 250 cycles of cyclic stretching, it still maintains a stable relative current change. Description of the Drawings

[0035] Figure 1 It is a schematic diagram of a covalent organic framework-polymer hydrogel with a mechanically interlocked structure, where 1-COFs and 2-polymer.

[0036] Figure 2 It is the stress-strain curve of the tensile of the mechanically interlocked structure hydrogel and the polymer hydrogel obtained in Example 1 and Comparative Example 1.

[0037] Figure 3 It is the cyclic tensile stress-strain curve of the mechanically interlocked structure hydrogel obtained in Example 1.

[0038] Figure 4 It is the cyclic tensile stress-strain curve of the polymer hydrogel obtained in Comparative Example 1.

[0039] Figure 5 It is the ionic conductivity of the mechanically interlocked structure hydrogel and the polymer hydrogel obtained in Example 1 and Comparative Example 1.

[0040] Figure 6 It is the relative current change curve graph of the mechanically interlocked structure hydrogel sensor obtained in Example 1 after 250 cycles of cyclic stretching at 50% strain. Detailed Embodiments

[0041] For a further understanding of the method of the present invention, specific descriptions are made in the form of examples with reference to the drawings. The following examples are only for the specific preparation methods of the present invention and do not limit the scope of the present invention.

[0042] Comparative Example 1

[0043] Glycerol (4.29 g, 0.047 mol) and choline chloride (3.21 g, 0.023 mol) were stirred at 80 °C for 1 hour to obtain a deep eutectic solvent;

[0044] Acrylamide (2.25 g) and N,N'-methylenebisacrylamide (0.025 g) were added to a deep eutectic solvent (7.5 g) and deionized water (2.5 mL), stirred for 5 minutes, ammonium persulfate (0.02 g) was added, and stirred for 0.5 minutes to obtain a solution. The solution was poured into a polytetrafluoroethylene mold, and free radical polymerization occurred at room temperature for 0.01 hours to obtain a polymer hydrogel.

[0045] Example 1

[0046] 2,5-Dihydrazino-1,3,4-thiadiazole (60 mg, 0.2 mmol), 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetrabenzaldehyde (61.8 mg, 0.1 mmol), o-dichlorobenzene (3 mL), n-butanol (3 mL) and acetic acid (6 mol L -1 , 0.6 mL) were added to a Schlenk tube. The resulting mixture was sonicated for 2 minutes and placed in a microwave reactor and reacted at 120 °C for 5 hours. The resulting solid powder was washed and dried under vacuum to obtain COFs;

[0047] Glycerol (4.29 g, 0.047 mol) and choline chloride (3.21 g, 0.023 mol) were stirred at 80 °C for 1 hour to obtain a deep eutectic solvent;

[0048] COFs (0.0225 g) were added to deionized water (2.5 mL) and a deep eutectic solvent (7.5 g). After stirring for 1 hour, acrylamide (2.25 g) and N,N'-methylenebisacrylamide (0.025 g) were added and stirred for 12 hours. Then ammonium persulfate (0.02 g) was added and stirred for 0.5 minutes to obtain a dispersion. The dispersion was poured into a polytetrafluoroethylene mold, and free radical polymerization occurred at room temperature for 0.01 hours to obtain a covalent organic framework-polymer hydrogel with a mechanically interlocked structure. The schematic diagram is as Figure 1 shown, where 1 is COFs and 2 is the polymer. The monomer forms a polymer through free radicals in the pores of COFs, thus forming a mechanically interlocked structure.

[0049] Figure 2 In, a material tensile testing machine (CMT 6104) was used to obtain the stress-strain curves of the tensile of the mechanically interlocked structure hydrogel and the polymer hydrogel in Comparative Example 1. The maximum stress of the stress-strain curve of the tensile is the tensile strength. The tensile strength of the mechanically interlocked structure hydrogel is 0.41 MPa. Compared with the separate polymer hydrogel (0.186 MPa), the tensile strength of the mechanically interlocked structure hydrogel is increased by 2.2 times.

[0050] Figure 3Among them, a cyclic tensile stress-strain curve of the mechanically interlocked structure hydrogel at 100% strain was obtained using a material tensile testing machine (CMT 6104). The intersection point of the cyclic stress-strain curve with the horizontal axis during the unloading process at 100% strain is the residual strain. According to the formula: elastic recovery rate = (100% - residual strain) / 100%, the elastic recovery rate of the mechanically interlocked structure hydrogel after the first tensile cycle is 99%, and the elastic recovery rate after the ninth tensile cycle is 96%. Due to the good elasticity of the mechanically interlocked structure hydrogel, the cyclic curves from the first to the ninth cycles overlap.

[0051] Figure 4 Among them, the elastic recovery rate of the polymer hydrogel obtained in Comparative Example 1 was only 90% after the sixth tensile cycle, and it fractured during the unloading process of the seventh tensile cycle.

[0052] Figure 5 Among them, an electrochemical workstation (CHI 760E) was used to measure the ionic conductivity of the mechanically interlocked structure hydrogel and the polymer hydrogel in Comparative Example 1 by electrochemical impedance spectroscopy. The conductivity of the mechanically interlocked structure hydrogel is 1.27 S m -1 , compared with the pure polymer hydrogel (0.44 S m -1 ), the conductivity of the mechanically interlocked structure hydrogel increased by 2.9 times.

[0053] Figure 6 Among them, the covalent organic framework-polymer mechanically interlocked structure hydrogel was used as the intermediate layer of a strain sensor, encapsulated between two pieces of pressure-sensitive tape to form a strain sensor. Among them, copper wires were connected to both ends of the mechanically interlocked structure hydrogel, and then the copper wires at both ends were connected to an electrochemical workstation (CHI 760E). At the same time, both ends of the strain sensor were connected to a material tensile testing machine (CMT 6104). By controlling the material tensile testing machine to apply deformation, the electrochemical workstation measured the corresponding current in real time, calculated the relative current change, and drew a graph of the relative current change with strain and time. The relative current change of the mechanically interlocked structure hydrogel sensor remained stable after 250 cyclic tensile tests at 50% strain.

[0054] Example 2

[0055] Add isophthalohydrazide (77.6 mg, 0.4 mmol), 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraphenylaldehyde (123.6 mg, 0.2 mmol), o-dichlorobenzene (6 mL), n-butanol (6 mL) and acetic acid (6 mol L -1, (1.2 mL), the obtained mixture was ultrasonically treated for 4 minutes, placed in a microwave reactor, and reacted at 120 °C for 5 hours. The resulting solid powder was washed and dried under vacuum to obtain COFs;

[0056] Ethylene glycol (4.29 g, 0.069 mol) and tetramethylammonium chloride (3.21 g, 0.029 mol) were stirred at 90 °C for 0.5 hour to obtain a deep eutectic solvent;

[0057] COFs (0.25 g) were added to deionized water (5 mL) and the deep eutectic solvent (5 g). After stirring for 6 hours, acrylic acid (2.25 g) and α,ω-diacrylate polyethylene glycol (0.025 g) were added, and stirred for 12 hours. Then ammonium persulfate (0.04 g) was added and stirred for 0.3 minutes to obtain a dispersion. The dispersion was poured into a polytetrafluoroethylene mold, and free radical polymerization occurred at room temperature for 0.01 hour to obtain a covalent organic framework-polymer hydrogel with a mechanically interlocked structure.

[0058] Example 3

[0059] In a Schlenk tube, 1,4-phenylenediamine (77.6 mg, 0.7 mmol), 2,2'-bipyridine-5,5'-dicarboxaldehyde (148.54 mg, 0.7 mmol), o-dichlorobenzene (6 mL), 1,4-dioxane (6 mL) and acetic acid (3 mol L -1 , (1.2 mL), the obtained mixture was ultrasonically treated for 10 minutes, placed in a microwave reactor, and reacted at 150 °C for 3 hours. The resulting solid powder was washed and dried under vacuum to obtain COFs;

[0060] Urea (4.29 g, 0.072 mol) and tetramethylammonium chloride (9.63 g, 0.087 mol) were stirred at 60 °C for 1.5 hours to obtain a deep eutectic solvent;

[0061] COFs (0.5 g) were added to deionized water (2.5 mL) and the deep eutectic solvent (7.5 g). After stirring for 12 hours, 2-hydroxyethyl methacrylate (5 g) and ethylene glycol dimethacrylate (0.025 g) were added, and stirred for 24 hours. Then potassium persulfate (0.04 g) was added and stirred for 0.5 minutes to obtain a dispersion. The dispersion was poured into a polytetrafluoroethylene mold, and free radical polymerization occurred at room temperature for 0.01 hour to obtain a covalent organic framework-polymer hydrogel with a mechanically interlocked structure.

[0062] Matters not covered by the present invention are well-known techniques.

Claims

1. A method for preparing a covalent organic framework-polymer mechanical interlocking structure hydrogel, characterized in that: The method comprises the following steps: COFs are added to deionized water and a low eutectic solvent, stirred for 1 to 12 hours, monomers and crosslinking agents are added, stirred for 1 to 24 hours, and then an initiator is added, and finally stirred for 0.1 to 3 minutes to obtain a dispersion, and the dispersion is poured into a polytetrafluoroethylene mold, and free radical polymerization occurs at room temperature for 0.01 to 4 hours to obtain a covalent organic framework-polymer hydrogel with a mechanical interlocking structure; The mass of COFs is 0.1 to 50% of the mass of the monomer; each 1 mL of deionized water contains 0.5 to 20 g of a low eutectic solvent, 0.1 to 10 g of a monomer, 0.001 to 5 g of a cross-linking agent, and 0.001 to 0.5 g of an initiator; The monomer is one or more of acrylamide, acrylic acid, hydroxyethyl methacrylate, n-butyl acrylate and methyl methacrylate.

2. The method for preparing the covalent organic framework-polymer mechanical interlocking structure hydrogel according to claim 1, characterized in that: The cross-linking agent is N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate or α,ω-diacrylate-based polyethylene glycol; The initiator is ammonium persulfate or potassium persulfate.

3. The method for preparing the covalent organic framework-polymer mechanical interlocking structure hydrogel according to claim 1, characterized in that: The preparation method of COFs comprises the following steps: Adding COFs precursor, organic solvent and acid solution into a Schlenk tube, subjecting the obtained mixture to ultrasonic treatment for 1 to 60 minutes, placing it in a microwave reactor, and reacting it at 80 to 200° C. for 0.5 to 12 hours; washing the generated solid powder, and vacuum drying it to obtain COFs; Wherein, 0.001-0.5 mmol of COFs precursor and 0.01-20 mL of acid solution are added to every 1 mL of organic solvent; The COFs precursor is one or more of aromatic aldehyde compounds, aromatic amine compounds, aromatic hydrazine compounds, aromatic anhydride compounds, and aromatic nitrile compounds.

4. The method for preparing the covalent organic framework-polymer mechanical interlocking structure hydrogel according to claim 3, characterized in that: The aromatic aldehyde compound is 2,4,6-triformylphloroglucinol, 2,2'-bipyridine-5,5'-dicarboxaldehyde or 4,4',4",4"'-(pyrene-1,3,6,8-tetrayl)tetrabenzaldehyde; the aromatic amine compound is 1,4-phenylenediamine, 2,5-dichloro-1,4-phenylenediamine or 1,3,5-tri(4-aminophenyl)benzene; the aromatic hydrazine compound is 2,5-dihydrazine-1,3,4-thiadiazole, 2,5-dimethoxyterephthaloylhydrazide, isophthaloylhydrazide or p-aminobenzoylhydrazide; the aromatic anhydride compound is 1,4,5,8-naphthalenetetracarboxylic anhydride, pyromellitic dianhydride or mellitic trianhydride; the aromatic nitrile compound is 1,4-dicyanobenzene or 2,4,6-trimethylbenzene-1,3,5-tricarboxynitrile; The organic solvent is any one or more of mesitylene, 1,4-dioxane, o-dichlorobenzene, n-butanol, N,N-dimethylformamide, toluene and N-methylpyrrolidone; The acid solution is hydrochloric acid, acetic acid or nitric acid aqueous solution with a concentration of 1 to 10 mol L -1 .

5. The method for preparing the covalent organic framework-polymer mechanical interlocking structure hydrogel according to claim 1, characterized in that: The method for preparing the deep eutectic solvent comprises the following steps: The hydrogen bond donor and the hydrogen bond acceptor are mixed and heated at 25 to 100° C. for 0.5 to 2 hours to obtain a deep eutectic solvent; The molar ratio of hydrogen bond donor to hydrogen bond acceptor is 1:0.1-3; The hydrogen bond donor is any one of glycerol, ethylene glycol, 1,4-butanediol, urea, and lactic acid; The hydrogen bond acceptor is choline chloride or tetramethylammonium chloride.

6. Application of the covalent organic framework-polymer mechanical interlocking structure hydrogel obtained by the method as claimed in claim 1, characterized in that: Used as an intermediate layer for strain sensors.

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