Cyclic polythioether cross-linking agent, preparation method and application thereof, and hydrogel prepared from cyclic polythioether cross-linking agent

Abstract

The invention discloses a cyclic polythioether cross-linking agent, a preparation method and application thereof, and hydrogel prepared by using the cyclic polythioether cross-linking agent. 2, 4-thiazolidinedione is used as an initiator to carry out ring opening polymerization on 1-allyloxy-2, 3-epithiopropane to obtain cyclic polythioether containing a vinyl side chain; the preparation method comprises the following steps: carrying out a click chemical reaction on a part of vinyl in cyclic polythioether by using mercaptocarboxylic acid, introducing carboxyl into cyclic polythioether with a vinyl side chain, and changing part of carboxyl into carboxylate by using an inorganic base to improve the hydrophilic ability of the cyclic polythioether so as to obtain a water-soluble cyclic polythioether cross-linking agent; when the polythioether is used as a cross-linking agent for hydrogel preparation, the polythioether part is affected by a hydrophobic unit and is in a curled state, energy is dissipated through chain extension under the action of external force, the hydrogel has good tensile property and good anti-fatigue performance, and the polythioether has good application prospects in the fields of soft brakes, skin sensors and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer material synthesis, and particularly relates to a cyclic polysulfide crosslinking agent, a preparation method and application thereof, and a hydrogel prepared therefrom. Background Art

[0002] A hydrogel is a special gel that forms a three-dimensional network structure with water as the dispersion medium. With its unique flexibility, biocompatibility and light weight characteristics, it shows important application value in the field of flexible electronic devices. The network structure formed by physical / chemical crosslinking can maintain the morphological stability under high water content. This characteristic enables the flexible strain sensor based on the hydrogel to closely adhere to the human body, convert mechanical signals into electrical signals, and capture large-scale and small-scale movements of the human body. Therefore, hydrogels have a wide range of applications in drug delivery, wearable devices, sensors and other fields. Existing crosslinking agents have a relatively simple structure, resulting in hydrogels with low strength and slow response speed, which greatly limits the application of hydrogels.

[0003] Compared with small molecule crosslinking agents, polymer crosslinking agents usually have better biocompatibility and can enhance the mechanical properties of hydrogels, giving them higher elastic modulus and mechanical strength, thus showing better durability and stability in various applications. In addition, polymer crosslinking points are more stable and not easily damaged, so the overall structure of the hydrogel is more stable and can maintain its performance in complex environments.

[0004] Traditional methods of forming networks, namely direct crosslinking of linear polymer precursors, or monomer radical copolymerization including a small amount of crosslinking agents or difunctional monomer species, such as a method for preparing a composite hydrogel using a silver nanowire-loaded composite crosslinking agent disclosed in Chinese Patent CN 113501998 A, are prone to structural defects in the polymer network, such as uncrosslinked hanging chain ends, which will damage the elastic and mechanical strength properties of the hydrogel; and the crosslinking agent disclosed in this patent requires composite silver nanowires, with a relatively high cost. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a cyclic polysulfide crosslinking agent, a preparation method and application thereof. The carboxyl groups, carboxylates and vinyl groups in the cyclic polysulfide crosslinking agent have good hydrophilicity and can be used as a crosslinking agent for hydrogels; there is a relatively high intramolecular repulsive force between the cyclic polymer segments, which will not only lead to a higher excluded volume effect and greater equilibrium swelling, but also generate a higher steric repulsive force inside the gel, improving the mechanical properties and rheological properties of the hydrogel.

[0006] The present invention also provides a hydrogel, which is prepared by using the cyclic polysulfide crosslinking agent provided by the present invention as a crosslinking agent and has good tensile properties and fatigue resistance.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a cyclic polysulfide crosslinking agent, and the structural formula of the cyclic polysulfide crosslinking agent is:

[0009]

[0010] Wherein, x and y are 0.1n and 0.9n respectively, n is 20-200; z is 1-12; A is Na or K.

[0011] The present invention also provides a preparation method of the cyclic polysulfide crosslinking agent, and the preparation method includes the following steps:

[0012] (1) Mix 2,4-thiazolidinedione, 1-allyloxy-2,3-epithiopropane, a catalyst and a solvent, and carry out a heating polymerization reaction under anhydrous and anaerobic conditions. After post-treatment and drying, a cyclic polysulfide P1 with vinyl groups as side chains is obtained;

[0013] The structural formula of the cyclic polysulfide P1 with vinyl groups as side chains is: n = x + y, n is 20-200;

[0014] (2) Dissolve the cyclic polysulfide P1 with vinyl groups as side chains, a photoinitiator, and mercapto carboxylic acid in a solvent, carry out ultraviolet light irradiation under anaerobic conditions, then add an inorganic base to adjust the pH of the system to neutral, and after dialysis and drying, the cyclic polysulfide crosslinking agent is obtained.

[0015] In step (1), the conditions of the heating polymerization reaction are: stirring reaction at 60-100 °C for 10-48 h, preferably stirring reaction at 70-80 °C for 20-30 h, and more preferably stirring reaction at 75 °C for 24 h.

[0016] In step (1), the catalyst is a quaternary ammonium salt or a quaternary phosphonium salt; preferably tetrabutylammonium chloride.

[0017] In step (1), the solvent is any one or more of N-methylpyrrolidone, tetrahydrofuran, N,N-dimethylformamide, and N-ethylpyrrolidone; preferably N-methylpyrrolidone.

[0018] In step (1), the molar ratio of 2,4-thiazolidinedione, 1-allyloxy-2,3-epithiopropane, and the catalyst is 1:1-1000:0.01-1.2, preferably 1:20-200:1.0-1.2, and more preferably 1:100:1.

[0019] In step (1), the mass ratio of 2,4-thiazolidinedione, 1-allyloxy-2,3-epithiopropane, and the catalyst is 1:20 - 220:2 - 12, preferably 1:110 - 140:2 - 6.

[0020] In step (1), the concentration of 1-allyloxy-2,3-epithiopropane in the solvent is 1.0 - 4.0 M; preferably 1.5 M.

[0021] In step (2), the molar ratio of the cyclic polysulfide P1 with vinyl side groups, the photoinitiator, and the mercapto carboxylic acid is 1:1 - 10:70 - 90, preferably 1:3 - 7:90, and more preferably 1:5:90.

[0022] In step (2), the mass ratio of the cyclic polysulfide P1 with vinyl side groups, the photoinitiator, and the mercapto carboxylic acid is 1:0.05 - 0.2:0.73.

[0023] In step (2), the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone.

[0024] In step (2), the mercapto carboxylic acid is a mercapto carboxylic acid with less than twelve carbons; preferably any one of mercaptoformic acid, mercaptoacetic acid, mercaptopropionic acid, mercaptobutyric acid, mercaptovaleric acid, mercaptohexanoic acid, mercaptooctanoic acid, mercaptoundecanoic acid, mercaptododecanoic acid; more preferably 3-mercaptopropionic acid.

[0025] In step (2), the inorganic base is any one or more of sodium bicarbonate, potassium carbonate, sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide; preferably sodium bicarbonate.

[0026] In step (2), the conditions of ultraviolet light irradiation are irradiation under a 365 nm ultraviolet lamp for 1 - 24 h, preferably irradiation under a 365 nm ultraviolet lamp for 3 - 5 h, and more preferably irradiation under a 365 nm ultraviolet lamp for 4 h.

[0027] The present invention provides the application of the described cyclic polysulfide crosslinking agent in the preparation of hydrogels.

[0028] The present invention provides a hydrogel, which is prepared by using the described cyclic polysulfide crosslinking agent as a crosslinking agent.

[0029] The preparation method of the hydrogel includes the following steps: adding an acrylamide monomer, an initiator, and the cyclic polysulfide crosslinking agent of the present invention into deionized water, stirring and mixing evenly, injecting into a polytetrafluoroethylene mold, and then standing and reacting under anaerobic and heating conditions to obtain the hydrogel.

[0030] Further, the initiator is any one of potassium persulfate, ammonium persulfate, and sodium persulfate, and preferably potassium persulfate. The temperature of the static reaction is 0 - 90°C, and the time is 3 - 8 hours; preferably 65°C for 6 hours. The mass concentration of the acrylamide monomer relative to deionized water is 15% - 35%, and preferably 30%. The molar amount of the crosslinking agent is 0.02 - 0.1% of the molar amount of the acrylamide monomer, and preferably 0.08%. The degree of polymerization of the cyclic polysulfide is 20 - 200, and preferably 100.

[0031] In the preparation method of the cyclic polysulfide crosslinking agent provided by the present invention, 1-allyloxy-2,3-epithiopropane is subjected to ring-opening polymerization with 2,4-thiazolidinedione as the initiator to obtain a cyclic polysulfide containing vinyl side chains. Then, a click chemical reaction is carried out between mercapto carboxylic acid and a part of the vinyl groups in the cyclic polysulfide to introduce carboxyl groups into the cyclic polysulfide with vinyl side chains. Then, an inorganic base is used to convert part of the carboxyl groups into carboxylates to improve the hydrophilic ability of the cyclic polysulfide and obtain a water-soluble cyclic polysulfide crosslinking agent.

[0032] When the cyclic polysulfide crosslinking agent provided by the present invention is used as a crosslinking agent for preparing hydrogels, its polysulfide part is in a curled state under the influence of hydrophobic units. When subjected to external forces, it dissipates energy through chain stretching and endows the hydrogel with good tensile properties and better fatigue resistance, and has good application prospects in fields such as soft brakes and skin sensors.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The cyclic polysulfide crosslinking agent provided by the present invention uses cyclic polymer chains as basic structural units, and more than two crosslinking points are constructed on each polymer chain, and it can form a perfect network without hanging chain ends. Moreover, there is a relatively high intramolecular effective repulsive force between polymer chain segments. After forming the polymer network, this characteristic will not only lead to a higher excluded volume effect and greater equilibrium swelling, but also generate a higher steric repulsive force inside the gel, improving its mechanical properties and rheological properties. This cannot be achieved by linear polymer crosslinking agents. Description of the Drawings

[0035] Figure 1 Synthesis route diagram of the water-soluble cyclic polysulfide P2-Na in Example 1;

[0036] Figure 2 1H NMR spectrum of the cyclic polysulfide P1 with vinyl side groups prepared in Example 1;

[0037] Figure 3 GPC diagram of the cyclic polysulfide P1 with vinyl side groups prepared in Examples 1 - 5;

[0038] Figure 4 Infrared spectra of cyclic polysulfide P1 with vinyl side groups and water-soluble cyclic polysulfide P2-Na prepared in Example 1;

[0039] Figure 5 Synthesis route diagram of cyclic polymer brush P5 in Experimental Example 1;

[0040] Figure 6 AFM diagram of cyclic polymer brush P5 in Experimental Example 1;

[0041] Figure 7 Mass spectrum of water-soluble cyclic polysulfide-P1 prepared in Example 2;

[0042] Figure 8 Synthesis route diagram of water-soluble linear polysulfide P4-Na in Comparative Example 1;

[0043] Figure 9 1H NMR spectrum of S-(p-tolyl) p-toluenethiocarbamate prepared in Comparative Example 1;

[0044] Figure 10 1H NMR spectrum of linear polysulfide P3 with vinyl side groups prepared in Example 1;

[0045] Figure 11 GPC diagram of linear polysulfide P3 with vinyl side groups prepared in Comparative Example 1;

[0046] Figure 12 DSC diagrams of cyclic polysulfide P1 with vinyl side groups and linear polysulfide P3 with vinyl side groups;

[0047] Figure 13 Infrared spectra of linear polysulfide P3 with vinyl side groups and water-soluble linear polysulfide P4-Na prepared in Comparative Example 1;

[0048] Figure 14 SEM diagram of the hydrogel prepared in Application Example 1;

[0049] Figure 15 SEM diagram of the hydrogel prepared in Comparative Application Example 1;

[0050] Figure 16 Tensile test curve diagrams of the hydrogels prepared in Application Examples 1 to 5;

[0051] Figure 17 Tensile test curve diagrams of the hydrogels prepared in Application Examples 1, 6 to 9;

[0052] Figure 18 Tensile test curve diagrams of the hydrogels prepared in Application Examples 1, 10 to 13;

[0053] Figure 19 To compare the tensile test curves of the hydrogels prepared in Application Examples 1 to 5;

[0054] Figure 20 To compare the tensile test curves of the hydrogels prepared in Application Examples 1, 6 to 9;

[0055] Figure 21 To compare the compressive test curves of the hydrogels prepared in Application Example 1 and Comparative Application Example 1;

[0056] Figure 22 To compare the cyclic tensile curve of the hydrogel prepared in Application Example 1;

[0057] Figure 23 To compare the cyclic tensile curve of the hydrogel prepared in Comparative Application Example 1;

[0058] Figure 24 To compare the frequency sweep of the hydrogel prepared in Application Example 1;

[0059] Figure 25 To compare the frequency sweep of the hydrogel prepared in Comparative Application Example 1;

[0060] Figure 26 To compare the frequency sweep of the hydrogels prepared in Application Example 1 and Comparative Application Example 1;

[0061] Figure 27 To compare the tensile test curves of the hydrogels prepared in Application Example 1 and Comparative Application Example 10. Detailed implementation mode

[0062] The present invention will be described in detail below in conjunction with the embodiments.

[0063] The preparation method of 1-allyloxy-2,3-epithiopropane is prepared by referring to the method disclosed in Chinese Patent CN113501998A.

[0064] Example 1

[0065] A cyclic polysulfide crosslinking agent, the structural formula of the cyclic polysulfide crosslinking agent is:

[0066]

[0067] Among them, x = 10, y = 90.

[0068] The synthesis route of the cyclic polysulfide crosslinking agent is as Figure 1 shown.

[0069] The preparation method of the cyclic polysulfide crosslinking agent includes the following steps:

[0070] (1) Preparation of cyclic polysulfide P1 with vinyl side groups: Weigh 17.6 mg of 2,4-thiazolidinedione, 1.95 g of 1-allyloxy-2,3-epithiopropane, 41.7 mg of tetrabutylammonium chloride, and 15 mL of N-methylpyrrolidone, place them in a 100 mL Schlenk tube and seal it. By subjecting the Schlenk tube to 3 cycles of freezing-freeze pumping-thawing under liquid nitrogen, heating to 75 °C for reaction for 24 h, after cooling to room temperature, the product is precipitated with 200 mL of methanol, and after vacuum drying, a viscous product P1 is obtained. Its 1H NMR spectrum is as shown in Figure 2 shown. It can be proved from the figure that it is a cyclic polysulfide with vinyl side groups. Its GPC spectrum is as shown in Figure 3 shown; its DSC diagram is as shown in Figure 12 shown.

[0071] The structural formula of P1 is: where n = 100;

[0072] (2) Preparation of cyclic polysulfide P2 with some carboxyl-containing side groups: Weigh 0.80 g of cyclic polysulfide P1 with vinyl side groups, 0.10 g of 2,2-dimethoxy-2-phenylacetophenone, and 0.61 g of 3-mercaptopropionic acid, dissolve them in 4 mL of N-methylpyrrolidone, then bubble nitrogen through the solution for 30 min to remove oxygen in the system. Subsequently, the solution is irradiated with ultraviolet light at 365 nm for 4 h to obtain cyclic polysulfide P2 with some carboxyl-containing side groups;

[0073] (3) Preparation of water-soluble cyclic polysulfide crosslinker P2-Na: Add an aqueous solution of NaHCO3 with a mass concentration of 8.76 wt% to step (2) to adjust the pH value to 7, so that the side-chain carboxylic acid is converted into carboxylate sodium. The obtained mixture is filled into a dialysis bag with a molecular weight cut-off of 2000 and dialyzed in deionized water for 2 days, during which the water is changed every 6 hours. Finally, a pale yellow solid P2-Na is obtained through freeze-drying. The remaining double bond content is obtained as 0.45 mmol / g by bromine titration.

[0074] Its infrared spectrum is as shown in Figure 4 shown. It can be seen from the figure that compared with the polysulfide P1 with vinyl side groups, the water-soluble cyclic polysulfide P2-Na prepared in this example shows a characteristic peak of carboxylate sodium at 1570 cm -1 −1, proving that the water-soluble cyclic polysulfide crosslinker is obtained.

[0075] Experimental Example 1

[0076] To confirm that the product prepared in Example 1 has a cyclic structure, the following experiments were carried out:

[0077] Dissolve 0.3 g of cyclic polysulfide P2 with carboxyl groups on some side chains, 3.65 g of PEG2000, and 0.6 g of EDCI in 40 mL of DMF solvent, and stir at room temperature for 24 h under a nitrogen atmosphere. Subsequently, transfer it to a dialysis bag with a molecular weight of 3000 and dialyze with deionized water for 2 days, changing the water every 6 hours. Lyophilize the obtained solution to obtain a white solid P5. The synthesis route is as Figure 5 shown. P5 is a cyclic polymer brush, and its cyclic structure can be further proven by AFM characterization. The results are as Figure 6 shown. By grafting polymer brushes, the flexibility of the cyclic polymer can be reduced, the local steric hindrance of the cyclic molecules can be increased, and the aggregation of the rings can be avoided, thereby maintaining the stability of the cyclic topological structure during AFM imaging. As can be seen from Figure 6 , the polymer brush formed by connecting PEG2000 to the cyclic polysulfide P2 with carboxyl groups on some side chains is a cyclic structure, thus proving that the cyclic polysulfide P2 with carboxyl groups on some side chains prepared in Example 1 and the water-soluble polysulfide P2-Na are also cyclic structures.

[0078] Example 2

[0079] Other conditions are the same as in Example 1, except that the addition amount of 1-allyloxy-2,3-epithiopropane in step (1) is changed to 0.39 g.

[0080] The mass spectrum of the water-soluble cyclic polysulfide P1 prepared in this example is as Figure 7 shown. There is an isotope peak with a molecular weight of 2756.85, proving that it is a cyclic polysulfide with a degree of polymerization of 20.

[0081] Example 3

[0082] Other conditions are the same as in Example 1, except that the addition amount of 1-allyloxy-2,3-epithiopropane in step (1) is changed to 0.96 g.

[0083] Example 4

[0084] Other conditions are the same as in Example 1, except that the addition amount of 1-allyloxy-2,3-epithiopropane in step (1) is changed to 2.9 g.

[0085] Example 5

[0086] Other conditions are the same as in Example 1, except that the addition amount of 1-allyloxy-2,3-epithiopropane in step (1) is changed to 3.9 g.

[0087] Comparative Example 1

[0088] A linear polysulfide crosslinking agent, and the structural formula of the linear polysulfide crosslinking agent is:

[0089]

[0090] Among them, x = 10 and y = 90.

[0091] The synthesis route diagram of the linear polysulfide crosslinking agent is as Figure 8 shown.

[0092] The preparation method of the linear polysulfide crosslinking agent includes the following steps:

[0093] (1) Mix 1.33 g of p-tolyl isocyanate, 1.24 g of p-thiocresol and 10 mL of dichloromethane, then add 1.01 g of triethylamine to the mixture. After stirring the obtained solution at room temperature for 30 min, pour the solution into a large amount of n-hexane to precipitate a white solid. The crude product is purified by rapid silica gel column chromatography, and the eluent is a mixed solution composed of PE and EA in a volume ratio of 10:1 to obtain 1.85 g of white solid, which is the initiator S-(p-tolyl) p-tolylthiocarbamate. Its 1H NMR spectrum is as Figure 9 shown. It can be proved from the figure that it is S-(p-tolyl) p-tolylthiocarbamate.

[0094] (2) The other steps are the same as step (1) in Example 1, except that 2,4-thiazolidinedione is replaced with 38.5 mg of S-(p-tolyl) p-tolylthiocarbamate to prepare a linear polysulfide P3 with vinyl side groups. Its 1H NMR spectrum is as Figure 10 shown. It can be proved from the figure that it is a linear polysulfide with vinyl side groups. Its GPC spectrum is as Figure 11 shown. Its DSC diagram is as Figure 12 shown. From the comparison of the glass transition temperatures of the cyclic polysulfide P1 with vinyl side groups and the linear polysulfide P3 with vinyl side groups in Figure 12 , it can be seen that the glass transition temperature of the cyclic polysulfide P1 with vinyl side groups is higher. This is because cyclic polymers have lower conformational freedom and are more compact than linear analogues, which will lead to a higher glass transition temperature. This also proves that the cyclic polysulfide P1 with vinyl side groups prepared in Example 1 has a cyclic topological structure.

[0095] (3) The other steps are the same as step (2) in Example 1, except that the cyclic polysulfide P1 with vinyl side groups is replaced with the linear polysulfide P3 with vinyl side groups to prepare a linear polysulfide P4 with some side groups carrying carboxyl groups. The remaining double bond content is obtained by bromine titration to be 0.44 mmol / g.

[0096] (4) The same as step (3) in Example 1 to prepare a water-soluble linear polysulfide crosslinking agent P4-Na. Its infrared spectrum is as Figure 13As shown, it can be seen from the figure that compared with the linear polysulfide P3 with vinyl side groups, the water-soluble linear polysulfide crosslinker P4-Na prepared in this step shows a characteristic peak of sodium carboxylate at 1400 cm -1 , proving that the water-soluble polysulfide crosslinker is obtained.

[0097] Application Example 1

[0098] Using the water-soluble cyclic polysulfide crosslinker P2-Na prepared in Example 1 as a crosslinker to prepare a hydrogel, the preparation method includes the following steps:

[0099] Weigh 178 mg of the water-soluble cyclic polysulfide crosslinker P2-Na prepared in Example 1, add 7.1 g of acrylamide, 0.54 g of potassium persulfate, and 16 g of water, continue to stir for 2 h, purge nitrogen for 1 min to remove oxygen in the mixed solution, and let it stand at 65 °C for 6 hours to obtain a cyclic polysulfide crosslinked hydrogel. Its SEM image is as Figure 14 shown. It can be seen from the figure that the hydrogel obtained with the P2-Na crosslinker has a loose and porous structure with uniform pores.

[0100] Application Example 2

[0101] Other conditions are the same as those in Application Example 1, except that the amount of water used is 12.5 g.

[0102] Application Example 3

[0103] Other conditions are the same as those in Application Example 1, except that the amount of water used is 20.6 g.

[0104] Application Example 4

[0105] Other conditions are the same as those in Application Example 1, except that the amount of water used is 27.7 g.

[0106] Application Example 5

[0107] Other conditions are the same as those in Application Example 1, except that the amount of water used is 39.5 g.

[0108] Application Example 6

[0109] Other conditions are the same as those in Application Example 1, except that the amount of the water-soluble cyclic polysulfide crosslinker P2-Na used is 45 mg.

[0110] Application Example 7

[0111] Other conditions are the same as those in Application Example 1, except that the content of the water-soluble cyclic polysulfide crosslinker P2-Na used is 89 mg.

[0112] Application Example 8

[0113] Others are the same as Application Example 1, except that the content of the water-soluble cyclic polysulfide cross-linking agent P2-Na used is 133 mg.

[0114] Application Example 9

[0115] Others are the same as Application Example 1, except that the content of the water-soluble cyclic polysulfide cross-linking agent P2-Na used is 222 mg.

[0116] Application Example 10

[0117] Others are the same as Application Example 1, except that the water-soluble cyclic polysulfide cross-linking agent P2-Na prepared in Example 2 is used.

[0118] Application Example 11

[0119] Others are the same as Application Example 1, except that the water-soluble cyclic polysulfide cross-linking agent P2-Na prepared in Example 3 is used.

[0120] Application Example 12

[0121] Others are the same as Application Example 1, except that the water-soluble cyclic polysulfide cross-linking agent P2-Na prepared in Example 4 is used.

[0122] Application Example 13

[0123] Others are the same as Application Example 1, except that the water-soluble cyclic polysulfide cross-linking agent P2-Na prepared in Example 5 is used.

[0124] Comparative Application Example 1

[0125] Others are the same as Application Example 1, except that the water-soluble linear polysulfide cross-linking agent P4-Na prepared in Comparative Example 1 is used. The SEM image of the hydrogel prepared in this comparative application example is as Figure 15 shown. It can be seen from the figure that the hydrogel obtained with P4-Na as the cross-linking agent has a loose and porous structure, but its pore structure is sparse and non-uniform.

[0126] Comparative Application Example 2

[0127] Others are the same as Comparative Application Example 1, except that the amount of water used is 12.5 g.

[0128] Comparative Application Example 3

[0129] Others are the same as Comparative Application Example 1, except that the amount of water used is 20.6 g.

[0130] Comparative Application Example 4

[0131] Others are the same as Comparative Application Example 1, except that the amount of water used is 27.7 g.

[0132] Comparative Application Example 5

[0133] Others are the same as Comparative Application Example 1, except that the amount of water used is 39.5 g.

[0134] Comparative Application Example 6

[0135] Others are the same as Comparative Application Example 1, except that the amount of the water-soluble linear polysulfide crosslinking agent P4-Na used is 45 mg.

[0136] Comparative Application Example 7

[0137] Others are the same as Comparative Application Example 1, except that the content of the water-soluble linear polysulfide crosslinking agent P4-Na used is 91 mg.

[0138] Comparative Application Example 8

[0139] Others are the same as Comparative Application Example 1, except that the content of the water-soluble linear polysulfide crosslinking agent P4-Na used is 136 mg.

[0140] Comparative Application Example 9

[0141] Others are the same as Comparative Application Example 1, except that the content of the water-soluble linear polysulfide crosslinking agent P4-Na used is 227 mg.

[0142] Comparative Application Example 10

[0143] Others are the same as Application Example 1, except that the crosslinking agent used is a water-soluble linear polysulfide (PPEMT-COONa) prepared by the method in Example 1 of Chinese Patent CN113501998A.

[0144] Test Example 1

[0145] Inject the deoxygenated mixed solutions in the above-mentioned application examples and comparative application examples into a 50 mm × 4 mm dumbbell-shaped mold, and let it stand in a 65 °C environment for 6 hours to obtain the tensile specimens of the hydrogels in the corresponding application examples and comparative application examples. Use a universal tensile machine to test each tensile specimen respectively, and the tensile rate is 50 mm / min.

[0146] The test results are as Figures 16 - 20As shown, it can be seen from the figure that the hydrogel prepared with the cyclic polysulfide crosslinking agent has better mechanical properties than the hydrogel prepared with the linear polysulfide crosslinking agent, and the hydrogel in Application Example 1 has better tensile properties than the hydrogels in other application examples. It can be seen that the water-soluble cyclic polysulfide crosslinking agent prepared by the present invention can significantly improve the tensile properties of the hydrogel.

[0147] Test Example 2

[0148] The deoxygenated mixed solutions in Application Example 1 and Comparative Application Example 1 above were respectively injected into the molds of 10 mm×10 mm cylindrical compression specimens and left standing in an environment of 65 °C for 6 hours to obtain the compression specimens of the hydrogels in Application Example 1 and Comparative Application Examples 1-2. The splines of different examples were respectively tested using a universal tensile machine at a compression rate of 5 mm / min.

[0149] The test results are as Figure 21 shown. It can be seen from the figure that the hydrogel prepared using the cyclic polysulfide in the present invention as a crosslinking agent has good toughness.

[0150] Test Example 3

[0151] The tensile specimens prepared in Application Example 1 and Comparative Application Examples 1-2 above were placed in a universal testing machine, and the fatigue resistance of the hydrogel was tested by multiple loading-unloading within 100% deformation at a tensile rate of 50 mm / min. The test results are as Figure 22 、 23 shown, indicating good fatigue resistance.

[0152] Test Example 4

[0153] The deoxygenated mixed solutions in Application Example 1, Comparative Application Example 1, and Comparative Application Example 2 above were injected into a cylindrical mold with a diameter of 20 mm and left standing in an environment of 65 °C for 6 hours to obtain the corresponding hydrogel specimens. The splines of the examples were tested using a TA rheometer, and frequency scanning was performed at a strain of 0.1% within a frequency range of 0.1-600 rad / s. The test results are as Figure 24 、 25 shown in 26 and 27. It can be seen from the figure that the hydrogel prepared using the cyclic polysulfide in the present invention as a crosslinking agent has good viscoelasticity, and the storage modulus of the hydrogel prepared with the cyclic polysulfide crosslinking agent is significantly higher than that of the hydrogel prepared with the linear polysulfide crosslinking agent, indicating that the hydrogel synthesized with the cyclic polysulfide crosslinking agent has higher rigidity and greater hardness compared to its linear counterpart.

[0154] The above detailed description of a cyclic polysulfide crosslinking agent, its preparation method and application, and the hydrogel prepared therefrom with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be enumerated within the defined scope. Therefore, changes and modifications without departing from the general concept of the present invention shall fall within the protection scope of the present invention.

Claims

1. A cyclic polysulfide crosslinking agent, characterized in that, The structural formula of the cyclic polysulfide crosslinking agent is as follows: Wherein, x and y are 0.1n and 0.9n respectively, n is 20 - 200; z is 1 - 12; A is Na or K.

2. The preparation method of the cyclic polysulfide crosslinking agent according to claim 1, wherein The preparation method includes the following steps: (1) Mix 2,4-thiazolidinedione, 1-allyloxy-2,3-epithiopropane, a catalyst and a solvent, and carry out a heating polymerization reaction under anhydrous and anaerobic conditions. After post-treatment and drying, a cyclic polysulfide P1 with vinyl groups as side chains is obtained; The structural formula of the cyclic polysulfide P1 with vinyl as the side group is as follows: (2) Dissolve the cyclic polysulfide P1 with vinyl groups as side chains, a photoinitiator, and mercapto carboxylic acid in a solvent, carry out ultraviolet light irradiation under anaerobic conditions, then add an inorganic base to adjust the pH of the system to neutral, and obtain the cyclic polysulfide crosslinking agent after dialysis and drying.

3. The preparation method according to claim 2, characterized in that, In step (1), the conditions of the heating polymerization reaction are: stirring reaction at 60 - 100 °C for 10 - 48 h.

4. The preparation method according to claim 2, characterized in that, In step (1), the catalyst is a quaternary ammonium salt or a quaternary phosphonium salt; the solvent is any one or more of N-methylpyrrolidone, tetrahydrofuran, N,N-dimethylformamide, and N-ethylpyrrolidone.

5. The preparation method according to claim 2, characterized in that, In step (1), the molar ratio of 2,4-thiazolidinedione, 1-allyloxy-2,3-epithiopropane, and the catalyst is 1:1 - 1000:0.01 - 1.

2.

6. The preparation method according to claim 2, wherein In step (2), the molar ratio of the cyclic polysulfide P1 with vinyl groups as side chains, the photoinitiator, and mercapto carboxylic acid is 1:1 - 10:

90.

7. The preparation method according to claim 2 or 6, characterized in that, In step (2), the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone; the mercapto carboxylic acid is a mercapto carboxylic acid with less than twelve carbon atoms; the inorganic base is any one or more of sodium bicarbonate, potassium carbonate, sodium carbonate, sodium bicarbonate, sodium hydroxide, and potassium hydroxide.

8. The preparation method according to claim 2, wherein In step (2), the conditions of the ultraviolet light irradiation are irradiation under a 365 nm ultraviolet lamp for 1 - 24 h.

9. Use of the cyclic polysulfide crosslinking agent according to claim 1 in the preparation of a hydrogel.

10. A hydrogel, characterized in that, Prepared using the cyclic polysulfide crosslinking agent according to claim 1 as a crosslinking agent.

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