A method for preparing a covalent organic framework-polymer mechanically interlocked structure hydrogel

Abstract

The application discloses a preparation method of a covalent organic framework-polymer mechanical interlocking structure hydrogel. The method uniformly disperses COFs in a monomer solution, stirs, and then makes the monomer enter the COF channel, and then through a free radical polymerization method, the monomer is polymerized in the COF channel to form a mechanical interlocking structure COF and polymer hydrogel. The obtained hydrogel has the advantages that the introduction of the COF enhances the total dissipation energy of the hydrogel, the mechanical interlocking structure of the COF and the polymer increases the binding energy between molecules, reduces the energy dissipation of the sacrifice bond, and improves the tensile strength and elasticity of the hydrogel. The channel of the COF is beneficial to ion transmission, improves the ion conductivity, and compared with the polymer hydrogel alone, the tensile strength is improved by 2.2 times, and the conductivity is improved by 2.9 times.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel preparation technology, specifically relating to a method for preparing a hydrogel with a covalent organic framework (COFs) and a polymer mechanically interlocked structure. Background Technology

[0002] Hydrogels have attracted widespread attention in the field of wearable strain sensors due to their excellent biocompatibility, stretchability, and similarity to the modulus of skin tissue. High conductivity and excellent mechanical properties (elasticity and tensile strength, etc.) are key to achieving a long cycle 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, achieving a tensile strength of 0.251±0.05MPa and a resistivity of 86.68±6.97kΩ, thus achieving a significant performance improvement. However, due to the significant energy dissipation of sacrificial bonds, the elasticity of hydrogels is less than 60%, which greatly limits their application in wearable strain sensors. Designing and synthesizing hydrogel materials with strong intermolecular binding energy and reducing sacrificial bond energy dissipation are essential for improving conductivity and mechanical properties.

[0003] Covalent organic frameworks (COFs) are crystalline porous materials formed by covalent bonds. Due to their designable chemical structures, ordered pores, and high specific surface area, they show great promise for applications in strain sensing. The pores of COFs facilitate ion transport and improve ionic conductivity. Inserting polymer chains into the pores of COFs to form a mechanically interlocked structure, and allowing the abundant organic groups on the COF backbone to form dense intermolecular interactions with the polymer chains, reducing energy dissipation from sacrificial bonds, is an effective method to improve the tensile strength and elasticity of hydrogels. However, due to the significant modulus difference between the hard and soft polymer chains in COFs, and the insolubility of COFs in water, they tend to aggregate in polymer solutions, making uniform dispersion difficult. This severely affects the insertion of polymer chains into the COF pores, further impacting the mechanical properties and conductivity of the hydrogel. Designing and synthesizing novel hydrogel materials is crucial for improving their mechanical properties and conductivity.

[0004] Currently, there are relatively few hydrogels that utilize COFs and polymers to form mechanically interlocked structures for wearable strain sensors. Developing COFs and polymer composite hydrogels with high ionic conductivity, excellent mechanical properties, simple fabrication, and low cost is a crucial issue that needs to be addressed to expand their application in wearable strain sensors. Summary of the Invention

[0005] This invention addresses the problems existing in current wearable strain sensors by providing a method for preparing a covalent organic framework-polymer mechanically interlocked hydrogel. The method involves uniformly dispersing COFs in a monomer solution, stirring to allow the monomers to enter the COF channels, and then polymerizing the monomers within the COF channels via free radical polymerization to form a mechanically interlocked COF and polymer hydrogel. The hydrogel obtained by this invention exhibits enhanced total energy dissipation due to the introduction of COFs. The mechanically interlocked structure between the COFs and the polymer increases intermolecular binding energy, reduces energy dissipation from sacrificial bonds, and improves the tensile strength and elasticity of the hydrogel. The channels of the COFs facilitate ion transport, improving ionic conductivity. Compared to a standalone polymer hydrogel, the mechanically interlocked hydrogel obtained by this invention shows a 2.2-fold increase in tensile strength and a 1.3-fold increase in electrical conductivity.

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

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

[0008] COFs were added to deionized water and a eutectic solvent and stirred for 1–12 hours. Then, monomers and crosslinking agents were added and stirred for 1–24 hours. Finally, an initiator was added and stirred for 0.1–3 minutes to obtain a dispersion. The dispersion was poured into a polytetrafluoroethylene mold and free radical polymerization was carried out at room temperature for 0.01–4 hours to obtain a covalent organic framework-polymer hydrogel with a mechanically interlocked structure.

[0009] The COFs contain 0.1–50% of the monomer mass; each 1 mL of deionized water contains 0.5–20 g of eutectic solvent, 0.1–10 g of monomer, 0.001–5 g of crosslinking agent, and 0.001–0.5 g of initiator.

[0010] The monomer is one or more selected from acrylamide, acrylic acid, 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 is ammonium persulfate or potassium persulfate;

[0013] The method for preparing the COFs includes the following steps:

[0014] COFs precursors, organic solvents, and acid solutions are added to a Schlenk tube. The resulting mixture is sonicated for 1–60 minutes, placed in a microwave reactor, and reacted at 80–200°C for 0.5–12 hours. The resulting solid powder is washed and vacuum dried to obtain COFs.

[0015] In this process, 0.001–0.5 mmol of COFs precursor and 0.01–20 mL of acid solution are added to each 1 mL of organic solvent.

[0016] The COFs precursors are one or more of aromatic aldehydes, aromatic amines, aromatic hydrazines, aromatic anhydrides, and aromatic nitriles.

[0017] The aromatic aldehydes are 2,4,6-tricarboxyloylphloroglucinol, 2,2'-bipyridine-5,5'-dicarboxaldehyde, or 4,4',4”,4”'-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde; the aromatic amines are 1,4-phenylenediamine, 2,5-dichloro-1,4-phenylenediamine, or 1,3,5-tris(4-aminophenyl)benzene; the aromatic hydrazides are 2,5-diahydrazyl-1,3,4-thiadiazole, 2,5-dimethoxyterephthaloylhydrazide, isophthaloylhydrazide, or p-aminobenzoylhydrazide; the aromatic anhydrides are 1,4,5,8-naphthalenetetracarboxylic anhydride, pyromellitic dianhydride, or phenylhexacarboxylic trihydride; and the aromatic nitriles are 1,4-dicyanobenzene or 2,4,6-trimethylbenzene-1,3,5-tricarboxynitrile.

[0018] The organic solvent is any one or more selected from mesitylene, 1,4-dioxane, o-dichlorobenzene, n-butanol, N,N-dimethylformamide, toluene, and N-methylpyrrolidone;

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

[0020] The method for preparing the eutectic solvent includes the following steps:

[0021] A eutectic solvent is obtained by mixing hydrogen bond donors and hydrogen bond acceptors and heating at 25–100 °C for 0.5–2 hours.

[0022] The molar ratio of hydrogen bond donor to hydrogen bond acceptor 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 covalent organic framework-polymer mechanically interlocked hydrogel obtained by the method is used as an intermediate layer in a strain sensor. The specific steps are as follows:

[0026] A covalent organic framework-polymer mechanically interlocked hydrogel was used as the intermediate layer of a strain sensor and encapsulated between two pressure-sensitive tapes to assemble the strain sensor.

[0027] The essential features of this invention are:

[0028] This invention uniformly disperses COFs in a monomer solution, and then uses free radical polymerization to polymerize the monomers in situ within the pores of the COFs, forming a mechanically interlocked COFs and polymer hydrogel. The hydrogel obtained by this invention exhibits enhanced total energy dissipation due to the introduction of COFs. The mechanically interlocked structure between the COFs and the polymer increases the binding energy between molecules, reduces energy dissipation from sacrificial bonds, and improves the tensile strength and elasticity of the hydrogel. Furthermore, the pores of the COFs facilitate ion transport and improve conductivity, resulting in superior performance compared to many existing hydrogel strain sensors.

[0029] The beneficial effects of this invention are as follows:

[0030] (1) This invention provides a method for preparing mechanically interlocked hydrogels by compositing COFs with polymers. The well-defined structure of COFs and polymers provides an ideal platform for understanding the relationship between hydrogel structure and strain sensing properties.

[0031] (2) The mechanically interlocked hydrogel prepared by combining COFs and polymers provided by the present invention has a tensile strength of 0.41 MPa due to the mechanical interlocking structure. Compared with the polymer hydrogel alone (0.186 MPa), the tensile strength of the mechanically interlocked hydrogel is increased by 2.2 times.

[0032] (3) The mechanically interlocked hydrogel prepared by combining COFs and polymers 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 polymer hydrogel alone has an elastic recovery rate of only 90% after the sixth stretching cycle and breaks during the unloading process of the seventh stretching cycle.

[0033] (4) The mechanically interlocked hydrogel prepared by combining COFs and polymers provided in this invention has an electrical conductivity of 1.27 Sm. -1 Compared to polymer hydrogels alone (0.44S m)-1 The conductivity of the mechanically interlocked hydrogel was increased by 2.9 times.

[0034] (5) The mechanically interlocked hydrogel prepared by combining COFs and polymers provided by the present invention, after being assembled into a strain sensor, still maintains a stable relative current change after being cyclically stretched 250 times under a strain of 50%. Attached Figure Description

[0035] Figure 1 This 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 The tensile stress-strain curves of the mechanically interlocked hydrogel and polymer hydrogel obtained in Example 1 and Comparative Example 1 are shown.

[0037] Figure 3 The image shows the cyclic tensile stress-strain curve of the mechanically interlocked hydrogel obtained in Example 1.

[0038] Figure 4 The cyclic tensile stress-strain curves of the polymer hydrogel obtained in Comparative Example 1 are shown.

[0039] Figure 5 The ionic conductivity is the mechanical interlocking structure hydrogel and polymer hydrogel obtained in Example 1 and Comparative Example 1.

[0040] Figure 6 The graph shows the relative current change of the mechanically interlocked hydrogel sensor obtained in Example 1 after 250 cycles of cyclic stretching at 50% strain. Detailed Implementation

[0041] To further illustrate the method of the present invention, specific embodiments are described below with reference to the accompanying drawings. The following embodiments are merely specific preparation methods of the present invention and do not limit the scope of the 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 eutectic solvent;

[0044] Acrylamide (2.25 g) and N,N'-methylenebisacrylamide (0.025 g) were added to a eutectic solvent (7.5 g) and deionized water (2.5 mL), and stirred for 5 minutes. Ammonium persulfate (0.02 g) was added, and the mixture was 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] Add 2,5-dihydrazino-1,3,4-thiadiazole (60 mg, 0.2 mmol), 4,4',4”,4”'-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde (61.8 mg, 0.1 mmol), o-dichlorobenzene (3 mL), n-butanol (3 mL), and acetic acid (6 mol / L) to a Schlenk tube. -1 The mixture was ultrasonicated for 2 minutes, then placed in a microwave reactor and reacted at 120°C for 5 hours. The resulting solid powder was washed and vacuum dried 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 eutectic solvent;

[0048] COFs (0.0225 g) were added to deionized water (2.5 mL) and a eutectic solvent (7.5 g). After stirring for 1 hour, acrylamide (2.25 g) and N,N'-methylenebisacrylamide (0.025 g) were added, and the mixture was stirred for 12 hours. Then, ammonium persulfate (0.02 g) was added, and the mixture was 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 mechanically interlocked covalent organic framework-polymer hydrogel, as shown in the schematic diagram. Figure 1 As shown, 1 represents COFs and 2 represents the polymer. Monomers form polymers through free radicals within the channels of COFs, thus creating a mechanically interlocked structure.

[0049] Figure 2 In this study, the stress-strain curves of the mechanically interlocked hydrogel and the polymer hydrogel in Comparative Example 1 were obtained using a material tensile testing machine (CMT 6104). The maximum stress on the tensile stress-strain curve was the tensile strength. The tensile strength of the mechanically interlocked hydrogel was 0.41 MPa, which was 2.2 times higher than that of the polymer hydrogel alone (0.186 MPa).

[0050] Figure 3In this study, cyclic tensile stress-strain curves of mechanically interlocked hydrogels at 100% strain were obtained using a material tensile testing machine (CMT 6104). The intersection of the cyclic stress-strain curves with the horizontal axis during unloading represents the residual strain. Based on the formula: Elastic recovery rate = (100% - Residual strain) / 100%, the elastic recovery rate of the mechanically interlocked hydrogel after the first tensile cycle was 99%, and after the ninth tensile cycle, it was 96%. Due to the good elasticity of the mechanically interlocked hydrogel, the cyclic curves from the first to the ninth cycle overlapped.

[0051] Figure 4 In Comparative Example 1, the polymer hydrogel obtained had an elastic recovery rate of only 90% after the 6th stretching cycle and fractured during the unloading process of the 7th stretching cycle.

[0052] Figure 5 In this study, the ionic conductivity of the mechanically interlocked hydrogel and the polymer hydrogel in Comparative Example 1 were measured using an electrochemical workstation (CHI 760E) via electrochemical impedance spectroscopy. The conductivity of the mechanically interlocked hydrogel was 1.27 S m. -1 Compared to polymer hydrogels alone (0.44S m) -1 The conductivity of the mechanically interlocked hydrogel was increased by 2.9 times.

[0053] Figure 6 In this study, a covalent organic framework-polymer mechanically interlocked hydrogel was used as the intermediate layer of a strain sensor, encapsulated between two pressure-sensitive adhesive tapes. Copper wires were connected to both ends of the mechanically interlocked hydrogel, and these wires were then connected to an electrochemical workstation (CHI 760E). Simultaneously, the two ends of the strain sensor were connected to a tensile testing machine (CMT 6104). By controlling the deformation applied by the tensile testing machine, the electrochemical workstation measured the corresponding current in real time, calculated the relative current change, and plotted a curve of relative current change versus strain and time. The relative current change of the mechanically interlocked hydrogel sensor remained stable after 250 cyclic stretching cycles at 50% strain.

[0054] Example 2

[0055] Add isophthalyl hydrazide (77.6 mg, 0.4 mmol), 4,4',4”,4”'-(pyrene-1,3,6,8-tetramethyl)tetrabenzaldehyde (123.6 mg, 0.2 mmol), o-dichlorobenzene (6 mL), n-butanol (6 mL), and acetic acid (6 mol / L) to a Schlenk tube. -1The mixture was ultrasonicated for 4 minutes, then placed in a microwave reactor and reacted at 120°C for 5 hours. The resulting solid powder was washed and vacuum dried 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 hours to obtain a eutectic solvent;

[0057] COFs (0.25 g) were added to deionized water (5 mL) and eutectic solvent (5 g). After stirring for 6 hours, acrylic acid (2.25 g) and α,ω-diacrylate-based 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 was carried out at room temperature for 0.01 hours to obtain a covalent organic framework-polymer hydrogel with a mechanically interlocked structure.

[0058] Example 3

[0059] In Schlenk tubes, 1,4-phenylenediamine (77.6 mg, 0.7 mmol) and 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) were added. -1 The mixture was ultrasonicated for 10 minutes, then placed in a microwave reactor and reacted at 150°C for 3 hours. The resulting solid powder was washed and vacuum dried 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 eutectic solvent;

[0061] COFs (0.5 g) were added to deionized water (2.5 mL) and eutectic solvent (7.5 g). After stirring for 12 hours, 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 was carried out at room temperature for 0.01 hours to obtain a covalent organic framework-polymer hydrogel with a mechanically interlocked structure.

[0062] Matters not covered in this invention are common knowledge.

Claims

1. A method of preparing a covalent organic framework-polymer mechanically interlocked structure hydrogel, characterized by, The method comprises the following steps: The COFs are added into deionized water and a eutectic solvent, after stirring for 1-12 hours, monomers and a crosslinking agent are added, stirring for 1-24 hours, then an initiator is added, and finally stirring for 0.1-3 minutes to obtain a dispersion liquid, the dispersion liquid is poured into a polytetrafluoroethylene mold, at room temperature, free radical polymerization occurs within 0.01-4 hours, and a covalent organic framework-polymer hydrogel with a mechanical interlocking structure is obtained; The mass of the COFs is 0.1-50% of the mass of the monomers; 0.5-20 g of the eutectic solvent, 0.1-10 g of the monomers, 0.001-5 g of the crosslinking agent and 0.001-0.5 g of the initiator are contained in 1 mL of the deionized water; The monomers are one or more of acrylamide, acrylic acid, hydroxyethyl methacrylate, n-butyl acrylate and methyl methacrylate; The crosslinking agent is N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate or α,ω-diacrylate-based polyethylene glycol; The initiator is ammonium persulfate or potassium persulfate; The preparation method of the COFs comprises the following steps: The COFs precursor, an organic solvent and an acid solution are added into a Schlenk tube, the obtained mixture is ultrasonically treated for 1-60 minutes, and is placed in a microwave reactor and reacted at 80-200 ℃ for 0.5-12 hours; the generated solid powder is washed and vacuum dried to obtain the COFs; 0.001-0.5 mmol of the COFs precursor and 0.01-20 mL of the acid solution are added into 1 mL of the 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; The preparation method of the eutectic solvent comprises the following steps: The hydrogen bond donor and the hydrogen bond acceptor are mixed and heated at 25-100 ℃ for 0.5-2 hours to obtain the eutectic solvent; The molar ratio of the hydrogen bond donor to the 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.

2. The method of claim 1, wherein the covalent organic framework-polymer mechanically interlocked structure hydrogel is prepared by, The aromatic aldehyde compound is 2,4,6-triformylphloroglucinol, 2,2'-bipyridine-5,5'-diformyl or 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl) tetrakisbenzaldehyde; the aromatic amine compound is 1,4-phenylenediamine, 2,5-dichloro-1,4-phenylenediamine or 1,3,5-tris(4-aminophenyl)benzene; the aromatic hydrazine compound is 2,5-dihydrazino-1,3,4-thiadiazole, 2,5-dimethoxyterephthalic dihydrazide, isophthalic dihydrazide or p-aminobenzoyl hydrazine; the aromatic anhydride compound is 1,4,5,8-naphthalenetetracarboxylic anhydride, pyromellitic dianhydride or benzenehexacarboxylic anhydride; and the aromatic nitrile compound is 1,4-dicyanobenzene or 2,4,6-trimethylbenzene-1,3,5-triazine. 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 an aqueous solution of hydrochloric acid, acetic acid or nitric acid, having a concentration of 1 to 10 mol L -1 .

3. Use of the covalent organic framework-polymer mechanically interlocked structure hydrogel obtained by the method of claim 1, characterized in that, The intermediate layer for use as a strain sensor.

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