Self-healing polyurethane as well as preparation method and application thereof

Abstract

The invention provides self-healing polyurethane as well as a preparation method and application thereof, and relates to the technical field of polyurethane materials. The self-healing polyurethane provided by the invention simultaneously contains a high-density dynamic hydrogen bond and a dynamic disulfide bond; the disulfide bond and the hydrogen bond both have the advantage of ideal low activation energy, fracture or recombination of an S-S bond or an H-H bond can occur at room temperature, the room-temperature quick-response polyurethane three-dimensional network based on the two high-density dynamic bonds can achieve the characteristic of room-temperature quick self-healing through topological structure recombination, the surface scratch self-healing degree is close to 100%, and the surface scratch self-healing degree is close to 100%. After cutting off, the mechanical self-healing efficiency is up to 70% or above, and rapid self-healing can be achieved within 30 min at room temperature without the help of external conditions such as heating or illumination.

Description

Technical Field

[0001] This invention relates to the field of polyurethane materials technology, specifically to a self-healing polyurethane, its preparation method, and its application. Background Technology

[0002] Thermosetting polyurethane resins possess a permanent three-dimensional cross-linked network structure, resulting in high costs and energy consumption for degradation and recycling. Therefore, developing novel three-dimensional polyurethane networks with rapid recycling and regeneration capabilities is of great significance. Self-healing materials have attracted considerable attention due to their ability to repeatedly repair physical damage and defects, prevent material failure, and extend service life. Compared to supramolecular interactions, self-healing materials dynamically cross-linked via reversible covalent bonds not only ensure mechanical strength, dimensional stability, and heat resistance but also facilitate the development of high-toughness materials that combine self-healing capabilities with ductility. Existing self-healing polyurethane materials possess self-healing, recyclability, and plasticity. Their self-healing property is achieved through topological restructuring based on exchange interactions. These characteristics mainly depend on the initiation temperature of the dynamic cross-linking exchange reaction and the glass transition temperature (Tg). When the temperature is below Tg, the exchange reaction cannot occur due to restricted molecular chain segment movement, resulting in a frozen state of topological restructuring. This makes it difficult to achieve rapid self-healing, recycling, and plastic processing at room temperature (25~35℃), requiring additional light or heating to assist self-healing. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a self-healing polyurethane, its preparation method, and its application. The self-healing polyurethane provided by this invention can achieve rapid self-healing within 30 minutes at room temperature without additional light or heating.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a self-healing polyurethane, which is obtained by crosslinking an isocyanate-based end-capping curing agent and a triol; the raw materials for preparing the isocyanate-based end-capping curing agent include 2,2'-dithiodiacetic acid and a difunctional isocyanate.

[0005] Preferably, the difunctional isocyanate includes hexamethylene diisocyanate, isophorone diisocyanate, or diphenylmethane diisocyanate; The molar ratio of the difunctional isocyanate to 2,2'-dithiodiacetic acid is 1.1:0.95~1.05.

[0006] Preferably, the triol comprises one or more of castor oil, glycerin, and trimethylolpropane; The molar ratio of isocyanate groups in the isocyanate-based end-capping curing agent to hydroxyl groups in the triol is 1:1 to 1.1.

[0007] This invention provides a method for preparing the self-healing polyurethane described in the above technical solution, comprising the following steps: The isocyanate-based end-capping curing agent, triol, and crosslinking catalyst are mixed and subjected to a crosslinking reaction to obtain a self-healing polyurethane.

[0008] Preferably, the preparation method of the isocyanate-based end-capping curing agent includes the following steps: 2,2'-dithiodiacetic acid, difunctional isocyanate, and addition catalyst are mixed and subjected to an addition reaction to obtain an isocyanate-based end-capping curing agent.

[0009] Preferably, the addition catalyst comprises dibutyltin dilaurate; The molar ratio of 2,2'-dithiodiacetic acid to the mass of the addition catalyst is 1 mol: 0.6~0.8 g; The addition reaction is carried out at a temperature of 75-85°C for 3.5-4.5 hours.

[0010] Preferably, the crosslinking catalyst comprises dibutyltin dilaurate.

[0011] Preferably, the molar ratio of the triol to the mass of the crosslinking catalyst is 1 mol: 0.25~0.3 g.

[0012] Preferably, the crosslinking reaction is carried out at a temperature of 75~85℃ for 3.5~4.5h.

[0013] The present invention also provides the application of the self-healing polyurethane described in the above technical solution or the self-healing polyurethane prepared by the preparation method described in the above technical solution in adhesives, soft robots, coatings or clothing.

[0014] The self-healing polyurethane provided by this invention is obtained by crosslinking an isocyanate-based end-capping curing agent with a triol. The isocyanate-based end-capping curing agent is prepared from 2,2'-dithiodiacetic acid and a difunctional isocyanate. The 2,2'-dithiodiacetic acid contains highly reactive disulfide bonds, giving the isocyanate-based end-capping curing agent a high density of dynamic disulfide bonds. After the isocyanate-based end-capping curing agent and the triol undergo a crosslinking reaction, the isocyanate groups add to the hydroxyl groups in the triol to form urethane bonds. Hydrogen bonds can form both internally and intermolecularly, resulting in a self-healing polyurethane that simultaneously... It contains high-density dynamic hydrogen bonds and dynamic disulfide bonds; both disulfide bonds and hydrogen bonds have the advantage of ideal low activation energy, and SS bonds or HH bonds can break or recombine at room temperature. Based on the two types of high-density dynamic bonds, the room temperature fast-response polyurethane three-dimensional network can achieve room temperature fast self-healing through topological restructuring. The self-healing degree of surface scratches is close to 100%, and the mechanical self-healing efficiency after cutting (mechanical self-healing efficiency = mechanical strength of the repaired specimen / mechanical strength of the original specimen) is as high as 70% or more. It can achieve rapid self-healing within 30 minutes at room temperature without the need for external conditions such as heating or light.

[0015] Furthermore, the triol used in this invention is bio-based castor oil, which is green and environmentally friendly with minimal pollution.

[0016] The method for preparing self-healing polyurethane provided by this invention is simple to operate, produces little environmental pollution, and is suitable for industrial production. Attached Figure Description

[0017] Figure 1 A schematic diagram of the three-dimensional network structure of self-healing polyurethane; Figure 2 The image shows the scratches on the self-healing polyurethane obtained in Example 1 before repair after cutting. Figure 3 The image shows the scratches repaired by the self-healing polyurethane obtained in Example 1 after cutting. Figure 4 This is a comparison of the mechanical properties of the self-healing polyurethane prepared in Example 1 before and after repair after cutting. Detailed Implementation

[0018] This invention provides a self-healing polyurethane, which is obtained by crosslinking an isocyanate-based end-capping curing agent and a triol; the raw materials for preparing the isocyanate-based end-capping curing agent include 2,2'-dithiodiacetic acid and a difunctional isocyanate.

[0019] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0020] In this invention, the difunctional isocyanate may include hexamethylene diisocyanate, isophorone diisocyanate, or diphenylmethane diisocyanate; the molar ratio of the difunctional isocyanate to 2,2'-dithiodiacetic acid may be 1.1:0.95~1.05, specifically 1.1:0.95, 1.1:0.98, 1.1:1, 1.1:1.03, or 1.1:1.05.

[0021] In this invention, the triol may include one or more of castor oil, glycerin, and trimethylolpropane; the molar ratio of the isocyanate group in the isocyanate-terminated curing agent to the hydroxyl group in the triol may be 1:1 to 1.1, specifically 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, or 1:1.1.

[0022] The present invention provides a method for preparing the self-healing polyurethane described in the above technical solution, comprising the following steps: mixing the isocyanate-based end-capping curing agent, triol and crosslinking catalyst, and carrying out a crosslinking reaction to obtain the self-healing polyurethane.

[0023] In this invention, the crosslinking catalyst can be dibutyltin dilaurate; the molar ratio of the triol to the crosslinking catalyst can be 1 mol: 0.25~0.3 g, specifically 1 mol: 0.25 g, 1 mol: 0.26 g, 1 mol: 0.27 g, 1 mol: 0.28 g, 1 mol: 0.29 g, or 1 mol: 0.3 g. In this invention, the type of triol and the molar ratio of isocyanate groups in the isocyanate-terminated curing agent to hydroxyl groups in the triol are the same as described above, and will not be repeated here.

[0024] In this invention, the temperature of the crosslinking reaction can be 75~85℃, specifically 75℃, 78℃, 80℃, 82℃ or 85℃; the time of the crosslinking reaction is 3.5~4.5h, specifically 3.5h, 3.8h, 4h, 4.3h or 4.5h.

[0025] In this invention, the preparation method of the isocyanate-based end-capping curing agent may include the following steps: mixing 2,2'-dithiodiacetic acid, difunctional isocyanate and addition catalyst, and carrying out an addition reaction to obtain the isocyanate-based end-capping curing agent.

[0026] In this invention, the addition catalyst may include dibutyltin dilaurate; the molar ratio of 2,2'-dithiodiacetic acid to the mass of the addition catalyst may be 1 mol: 0.6~0.8 g, specifically 1 mol: 0.6 g, 1 mol: 0.65 g, 1 mol: 0.7 g, 1 mol: 0.75 g, or 1 mol: 0.8 g. In this invention, the solvent for the addition reaction may be one or more of ethyl acetate, toluene, and tetrahydrofuran; the molar ratio of 2,2'-dithiodiacetic acid to the volume of the solvent may be 1 mol: 200~250 mL, specifically 1 mol: 200 mL, 1 mol: 210 mL, 1 mol: 220 mL, 1 mol: 230 mL, 1 mol: 240 mL, or 1 mol: 250 mL. In this invention, the temperature of the addition reaction can be 75~85℃, specifically 75℃, 78℃, 80℃, 82℃ or 85℃; the time of the addition reaction can be 3.5~4.5h, specifically 3.5h, 3.8h, 4h, 4.3h or 4.5h.

[0027] After the addition reaction is completed, the present invention may further include desolventizing the addition reaction solution obtained from the addition reaction. In the present invention, the desolventizing method may be rotary evaporation. The present invention does not have a particular limitation on the rotary evaporation method, as long as it can completely remove the solvent.

[0028] In this invention, the preparation method of 2,2'-dithiodiacetic acid may include the following steps: mixing 2-mercaptoacetic acid, an oxidant and an oxidation catalyst, performing a catalytic oxidation reaction and then quenching it to obtain 2,2'-dithiodiacetic acid.

[0029] In this invention, the oxidant may include hydrogen peroxide; the hydrogen peroxide may be used in the form of an aqueous solution of hydrogen peroxide; the mass percentage of hydrogen peroxide in the aqueous solution may be 30-35%, specifically 30%, 31%, 32%, 33%, 34%, or 35%; the molar ratio of 2-mercaptoacetic acid to the oxidant may be 2:1-1.1, specifically 2:1, 2:1.02, 2:1.04, 2:1.06, 2:1.08, or 2:1.1. In this invention, the oxidation catalyst may include potassium iodide; the mass ratio of 2-mercaptoacetic acid to the oxidation catalyst may be 3.5-4.02 mol:0.9 g, specifically 3.5 mol:0.9 g, 3.7 mol:0.9 g, 3.9 mol:0.9 g, 4 mol:0.9 g, or 4.02 mol:0.9 g.

[0030] In this invention, the solvent for catalytic oxidation can be ethyl acetate; the molar ratio of 2-mercaptoacetic acid to solvent volume can be 1.34~1.75 mol:500 mL, specifically 1.34 mol:500 mL, 1.4 mol:500 mL, 1.5 mol:500 mL, 1.65 mol:500 mL, or 1.75 mol:500 mL. In this invention, mixing 2-mercaptoacetic acid, the oxidant, and the oxidation catalyst can specifically involve: first mixing the 2-mercaptoacetic acid, the oxidation catalyst, and the solvent, and then second mixing with the oxidant. In this invention, the second mixing can be achieved by adding the oxidant dropwise to the mixture obtained from the first mixing. In this invention, the temperature of the catalytic oxidation can be 25~30℃, specifically 25℃, 26℃, 27℃, 28℃, 29℃ or 30℃; the time of the catalytic oxidation can be 2~2.5h, specifically 2h, 2.1h, 2.2h, 2.3h, 2.4h or 2.5h.

[0031] In this invention, the quenching agent used can be a saturated sodium sulfate aqueous solution; the volume ratio of the catalytic oxidation reaction solution to the saturated sodium sulfate aqueous solution can be 1:0.9~1.1, specifically 1:0.9, 1:0.95, 1:1, 1:1.05, or 1:1.1. This invention, by quenching the catalytic oxidation reaction solution, can reduce and consume the remaining oxidant in the catalytic oxidation reaction solution, preventing the obtained 2,2'-dithiodiacetic acid from being over-oxidized.

[0032] After quenching, the present invention further includes extracting the suspension obtained from the quenching, drying and concentrating the resulting organic phase to obtain the 2,2'-dithiodiacetic acid. In this invention, the extractant used for extraction can be ethyl acetate and / or toluene; the number of extractions can be 3-4 times; the volume ratio of the suspension to the extractant used in each extraction can be 1:3-4, specifically 1:3, 1:3.2, 1:3.4, 1:3.6, 1:3.8, or 1:4. In this invention, the drying agent used for drying can be anhydrous ethanol; the concentration can be vacuum concentration. The present invention does not specifically limit the concentration conditions, as long as the solvent in the organic phase is completely removed.

[0033] This invention also provides the application of the self-healing polyurethane described in the above-described technical solutions or the self-healing polyurethane prepared by the above-described preparation methods in adhesives, soft robots, coatings, or clothing. The self-healing polyurethane provided by this invention exhibits a near 100% self-healing rate for surface scratches and a mechanical self-healing efficiency of over 70% after cutting. It achieves rapid self-healing within 30 minutes at room temperature without the need for external conditions such as heating or light exposure, demonstrating promising application prospects in adhesives, soft robots, coatings, or clothing.

[0034] To further illustrate the present invention, the solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0035] Example 1 2-Mercaptoacetic acid, potassium iodide, and ethyl acetate were mixed to obtain a mixed solution. A 30% (w / w) aqueous solution of hydrogen peroxide was added dropwise to the mixed solution, and the reaction was carried out at 25°C for 2 hours to obtain a catalytic oxidation reaction solution. The mass ratio of 2-mercaptoacetic acid to potassium iodide was 1.34 mol:0.3 g, the volume ratio of 2-mercaptoacetic acid to ethyl acetate was 1.34 mol:500 mL, and the molar ratio of hydrogen peroxide to 2-mercaptoacetic acid in the aqueous hydrogen peroxide solution was 0.34:0.67.

[0036] The obtained catalytic oxidation reaction solution was quenched with a saturated sodium sulfate aqueous solution. The resulting suspension was extracted three times with ethyl acetate. The combined organic layers were dried over anhydrous ethanol and concentrated under reduced pressure to obtain a white solid product, 2,2'-dithiodiacetic acid, with a yield of 96%. The volume ratio of the catalytic oxidation reaction solution to the saturated sodium sulfate aqueous solution was 1:1, and the volume ratio of the suspension to the extractant used in each extraction was 1:3.

[0037] The obtained 2,2'-dithiodiacetic acid was mixed with hexamethylene diisocyanate, dibutyltin dilaurate, and ethyl acetate, and the mixture was subjected to an addition reaction at 80°C for 4 hours to obtain an addition reaction solution. The solvent was removed from the obtained addition reaction solution by rotary evaporation to obtain an isocyanate-based end-capping curing agent with a yield of 95%. The molar ratio of hexamethylene diisocyanate to 2,2'-dithiodiacetic acid was 1.1:1, the mass ratio of 2,2'-dithiodiacetic acid to dibutyltin dilaurate was 1 mol:0.6 g, and the volume ratio of 2,2'-dithiodiacetic acid to ethyl acetate was 1 mol:250 mL.

[0038] Castor oil was mixed with isocyanate end-capping curing agent and dibutyltin dilaurate, and the mixture was crosslinked at 80°C for 4 hours to obtain self-healing polyurethane. The molar ratio of castor oil to isocyanate end-capping curing agent was 1:1.5; the molar ratio of castor oil to dibutyltin dilaurate could be 1 mol:0.25 g.

[0039] Figure 1 This is a schematic diagram of the three-dimensional network structure of self-healing polyurethane, where blue dots represent disulfide groups and green dots represent urethane groups. Figure 1 It can be seen that the self-healing polyurethane provided by the present invention forms a three-dimensional network structure.

[0040] Figure 2 The image shows the scratches on the self-healing polyurethane obtained in Example 1 before repair after cutting. Figure 3 This image shows the scratches repaired by the self-healing polyurethane obtained in Example 1 after cutting. Figure 2 and Figure 3 It can be seen that the self-healing polyurethane provided by the present invention has a self-healing degree of nearly 100% for surface scratches after cutting, and the self-healing polyurethane has excellent self-healing performance.

[0041] Figure 4 This is a comparison of the mechanical properties of the self-healing polyurethane prepared in Example 1 before and after repair after cutting. The horizontal axis represents elongation at break, and the vertical axis represents tensile strength. Figure 4 It is known that the self-healing polyurethane provided by the present invention can restore the mechanical properties of the repaired (repaired sample) to more than 70% of the original sample before cutting after cutting.

[0042] Example 2 2-Mercaptoacetic acid, potassium iodide, and ethyl acetate were mixed to obtain a mixed solution. A 30% (w / w) aqueous solution of hydrogen peroxide was added dropwise to the mixed solution, and the reaction was carried out at 25°C for 2 hours to obtain a catalytic oxidation reaction solution. The mass ratio of 2-mercaptoacetic acid to potassium iodide was 0.35 mol:0.9 g, the volume ratio of 2-mercaptoacetic acid to ethyl acetate was 1.75 mol:500 mL, and the molar ratio of hydrogen peroxide to 2-mercaptoacetic acid in the aqueous hydrogen peroxide solution was 0.9:1.75.

[0043] The obtained catalytic oxidation reaction solution was quenched with a saturated sodium sulfate aqueous solution. The resulting suspension was extracted three times with ethyl acetate. The combined organic layers were dried over anhydrous ethanol and concentrated under reduced pressure to obtain a white solid product, 2,2'-dithiodiacetic acid, with a yield of 96%. The volume ratio of the catalytic oxidation reaction solution to the saturated sodium sulfate aqueous solution was 1:1, and the volume ratio of the suspension to the extractant used in each extraction was 1:3.

[0044] The obtained 2,2'-dithiodiacetic acid was mixed with diphenylmethane diisocyanate, dibutyltin dilaurate, and ethyl acetate, and the mixture was subjected to an addition reaction at 80°C for 4 hours to obtain an addition reaction solution. The solvent was removed from the obtained addition reaction solution by rotary evaporation to obtain an isocyanate-based end-capping curing agent with a yield of 95%. The molar ratio of hexamethylene diisocyanate to 2,2'-dithiodiacetic acid was 1.1:1, the mass ratio of 2,2'-dithiodiacetic acid to dibutyltin dilaurate was 1 mol:0.6 g, and the volume ratio of 2,2'-dithiodiacetic acid to ethyl acetate was 1 mol:250 mL.

[0045] Castor oil was mixed with isocyanate end-capping curing agent and dibutyltin dilaurate, and crosslinked at 80°C for 4 hours to obtain self-healing polyurethane. The molar ratio of castor oil to isocyanate end-capping curing agent was 1:1.5, and the molar ratio of castor oil to dibutyltin dilaurate could be 1 mol:0.3 g.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A self-healing polyurethane, characterized in that, It is obtained by crosslinking an isocyanate-based end-capping curing agent and a triol; the raw materials for preparing the isocyanate-based end-capping curing agent include 2,2'-dithiodiacetic acid and difunctional isocyanate.

2. The self-healing polyurethane according to claim 1, characterized in that, The difunctional isocyanate includes hexamethylene diisocyanate, isophorone diisocyanate or diphenylmethane diisocyanate; The molar ratio of the difunctional isocyanate to 2,2'-dithiodiacetic acid is 1.1:0.95~1.

05.

3. The self-healing polyurethane according to claim 1, characterized in that, The triol includes one or more of castor oil, glycerin, and trimethylolpropane; The molar ratio of isocyanate groups in the isocyanate-based end-capping curing agent to hydroxyl groups in the triol is 1:1 to 1.

1.

4. The method for preparing the self-healing polyurethane according to any one of claims 1 to 3, characterized in that, Includes the following steps: The isocyanate-based end-capping curing agent, triol, and crosslinking catalyst are mixed and subjected to a crosslinking reaction to obtain a self-healing polyurethane.

5. The preparation method according to claim 4, characterized in that, The preparation method of the isocyanate-based end-capping curing agent includes the following steps: 2,2'-dithiodiacetic acid, difunctional isocyanate, and addition catalyst are mixed and subjected to an addition reaction to obtain an isocyanate-based end-capping curing agent.

6. The preparation method according to claim 5, characterized in that, The addition catalyst includes dibutyltin dilaurate; The molar ratio of 2,2'-dithiodiacetic acid to the mass of the addition catalyst is 1 mol: 0.6~0.8 g; The addition reaction is carried out at a temperature of 75-85°C for 3.5-4.5 hours.

7. The preparation method according to claim 4, characterized in that, The crosslinking catalyst includes dibutyltin dilaurate.

8. The preparation method according to claim 4, characterized in that, The molar ratio of the triol to the mass of the crosslinking catalyst is 1 mol: 0.25~0.3 g.

9. The preparation method according to claim 4, 7 or 8, characterized in that, The cross-linking reaction is carried out at a temperature of 75~85℃ for 3.5~4.5h.

10. The use of the self-healing polyurethane according to any one of claims 1 to 3 or the self-healing polyurethane prepared by the preparation method according to any one of claims 4 to 9 in adhesives, soft robots, coatings or clothing.

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