A supramolecular nanocomposite self-healing hydrogel prepared by using oligomeric silsesquioxane

Abstract

The application provides a preparation method of a supramolecular nanocomposite self-repairing hydrogel, and belongs to the technical field of supramolecular materials. The spatial structure of the hydrogel material is: or wherein B is an oligomeric silsesquioxane crosslinking agent, the general structure of which is R n Si n O 1.5n , wherein n=8, 10 or 12; A is a polymer network of the supramolecular hydrogel, the general structure of which is: ; and C is a multiple hydrogen bond interaction between the polymer network and the oligomeric silsesquioxane crosslinking agent. The application further provides a synthesis method of the oligomeric silsesquioxane crosslinking agent, which provides a brand-new strategy for preparing the hydrogel with excellent mechanical properties. The hydrogel material constructed by the application has the advantages of simple operation, mild conditions, high yield and good selectivity of the synthesis product, easy purification of the product, simple post-treatment, excellent mechanical properties of the obtained material, self-healing and shape memory functions.

Description

Technical Field

[0001] This invention belongs to the field of supramolecular materials technology, specifically relating to the preparation of a supramolecular nanocomposite hydrogel and the synthesis of an oligomeric silsesquioxane crosslinking agent. The prepared hydrogel has self-healing and shape memory functions, as well as outstanding mechanical strength, toughness, puncture resistance and fatigue resistance. Background Technology

[0002] Hydrogels, as soft materials, are widely used in many fields such as biomedical engineering, soft robotics, and environmental research due to their softness and water content. However, one of the main obstacles to their practical application is their relatively low mechanical strength and toughness, precisely because of their softness. Therefore, many strategies for reinforcing and toughening hydrogels have been developed in the past. Among these, self-healing hydrogels, which aim to endow specific functions of repairing mechanical failures to improve the durability, reliability, and service life of hydrogels, have attracted attention. However, self-healing hydrogels typically possess either mechanical robustness or rapid self-healing properties, rather than both. Therefore, the development of a mechanically robust hydrogel material with autonomous self-healing capabilities on a timescale of seconds has not yet been fully realized. Simultaneously, the long-term mechanical stability of hydrogels, i.e., their resistance to cyclic fatigue and self-reinforcing properties, is also crucial for their suitability as load-bearing materials. Overall, while significant breakthroughs have been achieved in the design of mechanically strong and tough hydrogels, some challenges remain in basic science and engineering. From a basic science perspective, hydrogels with dynamic bonds exhibit a strong strain rate dependence. Furthermore, hydrogels with relatively strong dynamic bonds exhibit loading history dependence, leading to richer and more complex mechanical behaviors. Existing fracture mechanics theories can no longer explain the phenomena exhibited by newly developed materials, requiring new theoretical and experimental methods to understand the toughening and fatigue resistance mechanisms associated with this nonlinear viscoelastic effect. From an engineering perspective, developing hydrogels with comprehensive mechanical properties that match specific biological tissues is essential. Currently, loading-induced softening, significant stress relaxation, and large hysteresis loops are the main mechanical characteristics of tough hydrogels. Enabling hydrogels to possess rapid hysteresis recovery properties remains a challenge for future breakthroughs.

[0003] New technologies rely on the development of new materials, which may simply be innovative combinations of known components. The structural combination of polymer hydrogel networks and nanoparticles promises to provide superior functionality for composite materials and applications across a variety of fields. This hybridization of hydrogels and nanoparticles may lead to synergistic enhancements in the properties of each component, and these mutually beneficial and related potential applications have attracted considerable interest from multidisciplinary research groups in recent years. Compared to the unique synergistic properties lacking in single-component hydrogels, these composite materials always possess multifunctionality and stimulus-responsive properties, making them ideal for "smart" materials. This approach to preparing composite hydrogel materials provides a feasible strategy for overcoming some inherent limitations of hydrogel materials in the future. Summary of the Invention

[0004] For existing nanocomposite-reinforced hydrogels, the common understanding is that the incorporation of nanoparticles increases the interfacial bonding between the polymer network and the nanoparticles, thereby increasing stiffness and improving energy dissipation. Simultaneously, the nanoparticles act as physical cross-linking bonds in the hydrogel network, hindering crack propagation and improving the strength and toughness of the hydrogel. However, the mechanical strength of the hydrogel decreases with the aggregation of nanoparticles. Therefore, reducing nanoparticle aggregation while improving the uniformity of nanoparticle dispersion is a significant challenge that must be overcome when using nanocomposite strategies to reinforce hydrogels. This invention prepares a supramolecular hydrogel with "hexagonal" properties. A low-polymer silsesquioxane cross-linking agent with multiple hydrogen bonds forms dynamic physical cross-linking bonds with the hydrogel polymer network. By controlling the number of multiple hydrogen bonds, the mechanical properties of the hydrogel are improved. This not only enhances the uniformity of nanoparticle dispersion in the hydrogel but also endows the hydrogel with self-healing and shape memory functions.

[0005] This invention provides a supramolecular nanocomposite self-healing hydrogel, characterized in that its spatial structure is as follows: , or B is an oligomeric silsesquioxane crosslinking agent with the general structural formula R. n Si n O 1.5n Where n = 8, 10, or 12; A is the polymer network of the supramolecular hydrogel, with the general structural formula: C represents the multiple hydrogen bond interactions between the polymer network and the oligomeric silsesquioxane crosslinking agent.

[0006] Further, X is selected from: , , , , Y is selected from: , , , , , , , , , .

[0007] n=1, 2, 3; m=1, 2, 3;

[0008] R1 is selected from: H, CH3;

[0009] R2 is selected from: CH3, C 13 H 27 CF3, C6H5, p-NO2-C6H5 , ;

[0010] R3 is selected from: CH3, C2H5, C3H7, C4H9, C5H 11 C6H 13 ;

[0011] 1. The present invention also provides an oligomeric silsesquioxane crosslinking agent, wherein the crosslinking agent has the general structural formula R. n Si n O 1.5 Where n = 8, 10, or 12. Each oligomeric silsesquioxane cage has 1 to 12 (not 1) flexible arms radiating from Si atoms with multiple hydrogen bond interactions. The flexible arms are R4, and their ends are chemically bonded to the Si atoms of the cage and physically bonded to the hydrogel polymer network. R4 is selected from: , , , , , , , , , .

[0012] n = 1, 2, 3;

[0013] R2 is selected from: CH3, C 13 H 27 CF3, C6H5, p-NO2-C6H5 , ;

[0014] R3 is selected from: CH3, C2H5, C3H7, C4H9, C5H 11 C6H 13 ;

[0015] Furthermore, the oligomeric silsesquioxane crosslinking agent is compound I-1, I-2, I-3, I-4, I-5, I-6, I-7, I-8, I-9, or I-10.

[0016] This invention also provides a method for preparing the above-mentioned supramolecular nanocomposite self-healing hydrogel. The preparation method involves one-pot free radical random copolymerization of monomers X and Y with an oligomeric silsesquioxane crosslinking agent. Specifically, it includes the following steps:

[0017] (1) Add monomers X and Y and oligomeric silsesquioxane crosslinking agent to the aqueous solution according to the required ratio, stir under ice bath, then add a small amount of sodium hydroxide solution to adjust the pH of the prepolymer solution to 10. After the monomers and oligomeric silsesquioxane crosslinking agent are completely dissolved, add the initiator ammonium persulfate (APS) and the catalyst tetramethylethylenediamine (TEMED). Stir under ice bath for 5 minutes and then pour the solution into a polytetrafluoroethylene mold.

[0018] (1) Place the mold in a nitrogen-protected drying oven at 60 °C for 3-5 hours to polymerize until the hydrogel is fully formed, thus obtaining a supramolecular nanocomposite self-healing hydrogel. Attached Figure Description

[0019] Figure 1 This is a magnified SEM image of the three-dimensional network structure of the supramolecular nanocomposite self-healing hydrogel in Example 11.

[0020] Figure 2 This is a mapping diagram of the three-dimensional network structure of the supramolecular nanocomposite self-healing hydrogel in Example 11.

[0021] Figure 3 The image shows the three-dimensional network structure of the supramolecular nanocomposite self-healing hydrogel in Example 11.

[0022] Figure 4 The diagram shows the rotational rheological curve of the supramolecular nanocomposite self-healing hydrogel in Example 11.

[0023] Figure 5 This is a bar chart of Young's modulus for the supramolecular nanocomposite self-healing hydrogel of Example 11.

[0024] Figure 6 The bar chart shows the fracture toughness of the supramolecular nanocomposite self-healing hydrogel in Example 11.

[0025] Figure 7 The stress-strain curves for the compression test of the supramolecular nanocomposite self-healing hydrogel in Example 11 are shown.

[0026] Figure 8 The fatigue test curve of the supramolecular nanocomposite self-healing hydrogel in Example 11 is shown.

[0027] Figure 9 The puncture resistance test curve is shown for the supramolecular nanocomposite self-healing hydrogel of Example 11.

[0028] Figure 10 The tensile stress-strain test curves of the supramolecular nanocomposite self-healing hydrogel before and after healing in Example 11 are shown.

[0029] Figure 11 The temperature-time curve for shape memory recovery of the supramolecular nanocomposite self-healing hydrogel in Example 11 is shown. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The present invention provides certain specific embodiments of oligomeric silsesquioxane crosslinking agents, including compounds I-1 to I-10 shown in Table 1 below.

[0031] Table 1. Structural formulas of compounds I-1 to I-10

[0032]

[0033] Example 1: Synthesis of Compound I-1

[0034]

[0035] The synthesis of compound I-1 includes the following steps:

[0036] 1) Synthesis of compound a: Guanidine hydrochloride (0.500 g, 0.0052 mol) was neutralized in anhydrous ethanol with sodium hydroxide (0.249 g, 0.0062 mol), and the resulting NaCl solid was removed. Then, ethyl acetoacetate (0.681 g, 0.0052 mol) was added dropwise. The reaction mixture was stirred at room temperature (25 °C) for 3-4 h. The mother liquor was filtered to obtain a white solid, 2-amino-4-hydroxy-6-methylpyrimidine, which was dried in a vacuum drying oven. The obtained 2-amino-4-hydroxy-6-methylpyrimidine (0.500 g, 0.0040 mol) was refluxed with N',N-dimethylimidazole (0.842 g, 0.0052 mol) in anhydrous tetrahydrofuran at 70 °C for 12 h. After the reaction was completed, the reaction solution was cooled to 25 °C and filtered again. The obtained solid was washed twice with acetone and dried under vacuum to obtain compound a. This product was used in subsequent steps and did not require further purification.

[0037] 2) Synthesis of compound I-1: A mixture of product a (0.149 g, 0.0046 mol), octaaminoPOSS (0.100 g, 0.000085 mol), and N,N-diisopropylethylamine (0.589 g, 0.0046 mol) was stirred in anhydrous dimethyl sulfoxide at 80 °C for 12 h to form a transparent orange solution. The mother liquor was concentrated by rotary evaporation, cooled to room temperature, and a large amount of diethyl ether was poured in to precipitate the solid. After centrifugation, the supernatant was removed, and the solid was dried in a vacuum drying oven to finally obtain compound I-1.

[0038] Example 2 Synthesis of Compound I-2

[0039] The synthesis of compound I-2 includes the following steps:

[0040] 2,4-Diamino-6-hydroxypyrimidine was condensed with 1,1,3,3-tetraethoxypropane in a mildly acidic aqueous solution (pH=4) with the addition of sodium bisulfite. The mixture was heated under reflux overnight. After the reaction was complete, solid impurities were removed by filtration, and the crude product was purified by silica gel column chromatography. The sample was dissolved in an acidic aqueous solution at pH=4, loaded onto the sample, eluted with water, and finally freeze-dried to obtain a white solid. The obtained white solid was used to replace compound 2-amino-4-hydroxy-6-methylpyrimidine in Example 1. The remaining reagents and preparation methods were the same as steps 1 and 2 of Example 1, and compound I-2 was finally prepared.

[0041] Example 3 Synthesis of Compound I-3

[0042]

[0043] The synthesis of compound I-3 includes the following steps:

[0044] 4-Nitrophenylacetic acid ester was reacted with 2,4-diamino-6-methyl-1,3,5-triazine in anhydrous dimethyl sulfoxide at 80°C for 48 h. After cooling, the reaction mixture was poured into 200 ml of water containing crushed ice. The mixture was filtered to obtain a solid product, which was then dried in a vacuum drying oven at 50°C for 24 h. The obtained solid intermediate product was used to replace compound 2-amino-4-hydroxy-6-methylpyrimidine in Example 1. The other required reagents and preparation methods were the same as steps 1 and 2 of Example 1, and compound I-3 was finally prepared.

[0045] Example 4 Synthesis of Compound I-4

[0046]

[0047]

[0048] The synthesis of compound I-4 includes the following steps:

[0049] 1,8-Naphthyl-2,7-diamine and N',N-dimethylimidazole were refluxed in anhydrous tetrahydrofuran at 70°C for 12 h. After the reaction, the reaction solution was cooled to 25°C and then filtered. The obtained solid was washed twice with acetone and dried under vacuum to obtain compound b. This product was used in subsequent steps and did not require further purification. Compound b was used instead of compound a in Example 1, and the other required reagents and preparation methods were the same as steps 1 and 2 of Example 1, finally yielding compound I-4.

[0050] Example 5: Synthesis of Compound I-5

[0051]

[0052] The synthesis of compound I-5 includes the following steps:

[0053] 1) 2-Methoxy-5-nitrobenzoic acid was dissolved in 100 ml of dichloromethane, and excess methylamine hydrochloride solution was added dropwise for neutralization. Triethylamine was then added, and the mixture was stirred overnight in an ice bath at 0-5°C. After the reaction was complete, the solvent was removed by filtration. The solid was washed with dilute hydrochloric acid solution, saturated sodium bicarbonate solution, and aqueous solution, and dried before proceeding to the next reaction step. Using Pd-C (10%) as a catalyst, the solid product from the previous step was catalytically hydrogenated in methanol at room temperature for 1 h. The crude product was purified by flash column chromatography (silica gel) using dichloromethane as the eluent to obtain the first intermediate product.

[0054] 2) Dissolve 2-methoxy-5-nitrobenzoic acid in 700 ml of dichloromethane, then add excess methylamine hydrochloride solution for neutralization. Add glycine ethyl ester hydrochloride, followed by triethylamine. Stir overnight in an ice bath, then filter to remove the solvent. Wash the solid with dilute hydrochloric acid solution, saturated sodium bicarbonate solution, and water. Hydrolyze the solid product with NaOH in a 10:1 mixture of methanol and water. After refluxing overnight, rotary evaporate the mother liquor and concentrate it to a small volume (~60 ml), then acidify with concentrated hydrochloric acid solution. Collect the precipitated solid, wash with water, and recrystallize in water to obtain the second intermediate product.

[0055] 3) The two intermediate products obtained in steps 1 and 2 were added to DMF (50 ml) at room temperature in proportion, followed by EDC and methylamine. After stirring overnight at room temperature, the mixture was reduced with sulfur to remove the solvent. The solid was washed with dilute hydrochloric acid solution, saturated sodium hydroxide solution, and water, and recrystallized in water. The obtained solid product was catalytically hydrogenated and reduced in methanol at room temperature using Pd-C as a catalyst to obtain a pure solid product. The pure solid product was refluxed with N'N-dimethylimidazole in anhydrous tetrahydrofuran at 70°C for 12 h. After the reaction was completed, the reaction solution was cooled to room temperature and then filtered. The obtained solid was washed twice with acetone and dried under vacuum to obtain e. This product was used in subsequent steps and did not require further purification. Compound e was used instead of compound a in Example 1. The other required reagents and preparation methods were the same as in steps 1 and 2 of Example 1 to finally prepare compound I-5.

[0056] Example 6 Synthesis of Compound I-6

[0057]

[0058] The synthesis of compound I-6 includes the following steps:

[0059] 1,6-Hexanediamine and N',N-dimethylimidazole were refluxed in tetrahydrofuran for 12 h. The mixture was cooled to 25 °C, filtered, and the solid was washed with acetone (2 × 20 mL) and dried under vacuum to obtain a white solid. This product was used in subsequent steps and did not require further purification. The solid obtained in the previous step was reacted with 2-amino-4-hydroxy-6-methylpyrimidine using the same procedure to obtain product f. Compound f was used instead of compound a in Example 1, and the remaining reagents and preparation methods were the same as in steps 1 and 2 of Example 1, ultimately yielding compound I-5.

[0060] Example 7 Synthesis of Compound I-7

[0061]

[0062] The synthesis of compound I-7 includes the following steps:

[0063] Using the same reagents and preparation method as in Example 6, 2-amino-4-hydroxy-6-methylpyrimidine was replaced with 2,4-diamino-6-hydroxypyrimidine to finally prepare compound I-7.

[0064] Example 8: Synthesis of Compound I-8

[0065]

[0066] The synthesis of compound I-8 includes the following steps:

[0067] Using the same reagents and preparation method as in Example 6, 2-amino-4-hydroxy-6-methylpyrimidine was replaced with the solid intermediate product in Example 3 to finally prepare compound I-8.

[0068] Example 9 Synthesis of Compound I-9

[0069]

[0070] The synthesis of compound I-9 includes the following steps:

[0071] Using the same reagents and preparation method as in Example 6, 2-amino-4-hydroxy-6-methylpyrimidine was replaced with 2,4-diamino-6-hydroxypyrimidine to finally prepare compound I-7.

[0072] Example 10 Synthesis of Compound I-10

[0073]

[0074] The synthesis of compound I-10 includes the following steps:

[0075] Using the same reagents and preparation method as in Example 6, but replacing N'N-dimethylimidazole with compound e, compound I-10 was finally prepared.

[0076] Example 11 Hydrogel P8U 14 Preparation

[0077] The specific steps include: adding 3.8 ml of N'N-dimethylacrylamide, 600 mg of UpyMA, and 365 mg of I-1 to 7.2 ml of H2O, followed by the addition of a small amount of sodium hydroxide solution to adjust the pH of the mixture to 10. After the solid has completely dissolved, adding 196.8 mg of ammonium persulfate and 10.8 μl of tetramethylethylenediamine under an ice bath and stirring for 5 min, then pouring the solution into a polytetrafluoroethylene mold. The mold is then placed in a nitrogen-protected drying oven at 60 °C for polymerization for 3-5 h until the hydrogel is fully formed, thus obtaining the supramolecular nanocomposite self-healing hydrogel P8U. 14 Its structure is as follows:

[0078]

[0079] The supramolecular nanocomposite self-healing hydrogel P8U prepared in Example 11 14 I-1 was added to the hydrogel as a nanoparticle crosslinking agent, with... Figure 1 and attached Figure 2The results demonstrate that the added nanoparticles are uniformly dispersed in the hydrogel matrix. The multiple hydrogen bonds inherent in I-1 increase the interfacial bonding with the polymer network, thereby increasing the stiffness and energy dissipation of the hydrogel. Simultaneously, the nanoparticles act as physical cross-linking bonds in the hydrogel network, hindering crack propagation and improving the strength and toughness of the hydrogel, as shown in the attached figure. Figure 5 and Figure 6 As shown in the figure. The reinforcement and toughening effect of nanoparticles also improves the puncture resistance of the hydrogel material, as illustrated in the attached figure. Figure 9 As shown.

[0080] Furthermore, the complex three-dimensional network crosslinking structure formed between the oligomeric silsesquioxane crosslinking agent I-1 and the polymer chains through multiple hydrogen bonds gives the material excellent fatigue resistance in compression tests. This improves the hydrogel's shape retention after cyclic stress, allowing it to withstand 100 compression cycles without damage, as shown in the attached figure. Figure 7 and Figure 8 As shown in the attached figure, the hydrogel material also possesses self-healing properties through a completely physical cross-linking strategy. After the hydrogel was cut and healed at room temperature for 24 hours, the tensile properties of the repaired hydrogel were tested. The hydrogel's properties recovered to over 90%, as shown in the attached figure. Figure 10 As shown.

[0081] This hydrogel material also exhibits shape memory properties, with varying recovery times at different temperatures, as shown in the attached figure. Figure 11 As shown, the higher the temperature, the shorter the recovery time, indicating good temperature responsiveness. It can be applied to different occasions as needed.

[0082] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, alterations, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A supramolecular nanocomposite self-healing hydrogel prepared from an oligomeric silsesquioxane crosslinking agent, characterized in that its spatial structure is as follows: , or B is an oligomeric silsesquioxane crosslinking agent with the general structural formula R. n Si n O 1.5n Where n = 8, 10, or 12; A is the polymer network of the supramolecular hydrogel, with the general structural formula: C represents the multiple hydrogen bond interactions between the polymer network and the oligomeric silsesquioxane crosslinking agent; the polymer side chains of the hydrogel have supramolecular hydrogen bond interaction groups, where X is selected from: , , , , Y is selected from: , , , , , , , , , ; n=1, 2, 3; m=1, 2, 3; R1 is selected from: H, CH3; R2 is selected from: CH3, C 13 H 27 CF3, C6H5 p -NO2-C6H4、 , ; R3 is selected from: CH3, C2H5, C3H7, C4H9, C5H 11 C6H 13 ; Each oligomeric silsesquioxane cage has 1 to 12, and not just one, flexible arms radiating from Si atoms with multiple hydrogen bond interactions. These flexible arms are designated R4. The two ends of each flexible arm are chemically bonded to the Si atoms of the cage and physically bonded to the hydrogel polymer network. R4 is selected from: , , , , , , , , , ; n=1、2、3； R2 is selected from: CH3, C 13 H 27 CF3, C6H5 p -NO2-C6H4、 , ; R3 is selected from: CH3, C2H5, C3H7, C4H9, C5H 11 C6H 13。 2. A method for preparing the supramolecular nanocomposite self-healing hydrogel according to claim 1, characterized in that: The hydrogel is prepared by one-pot free radical random copolymerization of monomers containing an X structure, monomers containing a Y structure, and oligomeric silsesquioxane crosslinking agent, including the following steps: adding monomers and oligomeric silsesquioxane crosslinking agent into an aqueous solution according to the required ratio, stirring under an ice bath, then adding a small amount of sodium hydroxide solution to adjust the pH of the prepolymer solution to 10, and adding ammonium persulfate (APS) initiator and tetramethylethylenediamine (TEMED) catalyst after the monomers and oligomeric silsesquioxane crosslinking agent are completely dissolved. After stirring under an ice bath for 5 minutes, the solution is poured into a polytetrafluoroethylene mold; the mold is placed in a nitrogen-protected drying oven at 60 °C for polymerization for 3-5 hours until the hydrogel is completely formed, thus obtaining a supramolecular nanocomposite self-healing hydrogel.

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