Polycaprolactone dihydric alcohol containing maleimide group as well as preparation method and application of polycaprolactone dihydric alcohol

Abstract

The invention discloses polycaprolactone dihydric alcohol containing maleimide groups and a preparation method and application thereof, and the preparation method of the polycaprolactone dihydric alcohol comprises the following steps: adding N-(2, 3-dihydroxy propyl) maleimide, caprolactone and a catalyst into a reaction container, carrying out high-temperature reaction for 12-18 hours, filtering, washing, and drying to obtain the polycaprolactone dihydric alcohol containing the maleimide groups. And cooling and discharging to obtain the polycaprolactone diol containing the maleimide group. The polycaprolactone diol containing the maleimide group is used as a raw material to prepare a polyurethane prepolymer, so that the side chain of the prepolymer is provided with the maleimide group, and then a difuran compound is introduced as a dynamic cross-linking agent to obtain the self-repairing polyurethane elastomer containing the Diels-Alder bond. Through the reversible Diels-Alder (D-A) reaction effect of the functional components, the polyurethane elastomer can be remodeled and recycled, and the polyurethane elastomer has excellent and stable mechanical properties, self-repairing efficiency and repeated self-repairing capability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high polymer materials, and particularly relates to a poly-caprolactone diol containing a maleimide group, a preparation method thereof and application thereof in a Diels-Alder bond-containing self-repairing polyurethane elastomer. BACKGROUND

[0002] Polyurethane elastomer is a special elastomer material, and a plurality of urethane bonds (-NHCOO-) are distributed in a molecular main chain of the polyurethane elastomer. A unique soft-hard segment mosaic structure endows the polyurethane elastomer with strong structure and performance controllability. Owing to excellent mechanical properties, outstanding wear resistance and excellent weather resistance, the polyurethane elastomer is widely applied in many fields such as building materials, mechanical industry, food industry and the like. However, during processing, transportation, storage and use, the polyurethane elastomer is prone to local damage and micro-cracks, which not only shortens the service life of the material, but also causes pollution to the environment due to the unrecoverable polyurethane elastomer.

[0003] A dynamic network based on reversible bonds endows the elastomer with reworkability, so that the elastomer can be reshaped to complete self-repair. Among them, the self-repairing polymer material based on reversible covalent bonds has high self-repairing efficiency and the ability to repeatedly repair damage. Diels-Alder reaction is a thermally reversible reaction, which has the advantages of mild reaction conditions, fast reaction rate, no catalyst and less side reactions, and can be embedded in elastomer material as a reversible covalent bond, so that the elastomer has self-repairing property, and also exhibits excellent temperature adaptability and mechanical properties. Since the maleimide group exhibits high reactivity in the Diels-Alder reaction, the Diels-Alder reaction between furan (dien) and maleimide (dienophile) has been studied more. Previously, there are two ways for the application research of Diels-Alder reaction in the field of self-repairing polyurethane elastomer.

[0004] One way is to use isocyanate or prepolymer terminated by furan or maleimide group, so that it reacts with maleimide or furan compound as a chain extender, and a reversible polyurethane elastomer is prepared by forming Diels-Alder bond. This method is relatively simple in operation for constructing Diels-Alder bond, and the prepared elastomer also has certain self-repairing ability. However, it has obvious defects: after introducing Diels-Alder bond, the molecular chain of the elastomer still maintains linear structure, and once the Diels-Alder segment is broken and fails, the performance of the material may rapidly decline after a few repair cycles; in addition, due to the restriction of the terminal structure, the chain structure of the material is limited, which finally leads to poor elasticity of the material.

[0005] Another approach is to introduce furan or maleimide groups into the molecular chain of macromolecular polyols or small molecule chain extenders, and then form Diels-Alder bonds with maleimide or furan compounds as crosslinking agents to prepare reversible polyurethane elastomers. The Diels-Alder bonds constructed in this way exhibit strong ability to repeatedly repair damage. However, the mechanical properties of the material often need to be guaranteed by introducing composite polyols, but there are compatibility problems between different polyols, and there are differences in the reactivity of each polyol with isocyanate, which easily affects the microphase separation structure of the elastomer and the reaction uniformity of the entire system, thereby leading to regional imbalance and instability in the mechanical properties, heat resistance and hydrolysis resistance of the material. SUMMARY

[0006] In order to overcome the deficiencies of the prior art, the present application provides a maleimide group-containing polycaprolactone diol, a preparation method thereof and an application thereof in a Diels-Alder bond-containing self-repairing polyurethane elastomer. The preparation method of the maleimide group-containing polycaprolactone diol has no by-products, and the polymerization degree and molecular weight of the polycaprolactone diol can be adjusted according to the ratio of caprolactone monomers to maleimide ring-opening agents. Further, using the maleimide group-containing polycaprolactone diol, isocyanate and furan compound as raw materials to prepare a self-repairing polyurethane elastomer, by changing the content of the maleimide group embedded in the polycaprolactone diol and the type of the crosslinking agent furan compound, the crosslinking density of the elastomer material can be directly and linearly adjusted, so that the elastomer material has stable and excellent self-repairing efficiency, repeated self-repairing ability and mechanical properties.

[0007] To solve the above technical problems, the technical scheme adopted by the present application is: The maleimide group-containing polycaprolactone diol has the following structural formula:

[0008] The number average molecular weight of the maleimide group-containing polycaprolactone diol is 1767-2451 g / mol, and m and n are both integers greater than 0; 14≤m+n≤20.

[0009] The preparation method of the maleimide group-containing polycaprolactone diol comprises the following steps: The ring-opening agent containing a maleimide group, caprolactone monomers and a catalyst are added to a reaction container and mixed; the reaction container is vacuumed and purged with nitrogen, the mixture is stirred under a nitrogen atmosphere and heated to 140-160℃ for reaction, after reaction for 12-18h, the unreacted monomers are removed by vacuuming for 0.5-1h, and the temperature is lowered to discharge the material to obtain the maleimide group-containing polycaprolactone diol.

[0010] wherein the ring-opening agent containing maleimide group is N-(2,3-dihydroxypropyl) maleimide, and the specific structural formula is as follows:

[0011] In the above method, the molar ratio of the ring-opening agent containing maleimide group to the caprolactone monomer is 1: (14.3-20.3), and the mass ratio of the catalyst to the caprolactone monomer is (0.0692-0.0798): 13.3.

[0012] In the above method, the catalyst is an organic tin-based or organic titanium-based catalyst.

[0013] In the above method, the organic tin-based catalyst is selected from one or more of stannous octoate, dibutyltin oxide, and dibutyltin dilaurate; and the organic titanium-based catalyst is selected from one or more of tetrabutyl titanate and tetrapropyl titanate.

[0014] Application of a poly (caprolactone diol) containing a maleimide group in a self-repairing polyurethane elastomer containing a Diels-Alder bond, wherein the poly (caprolactone diol) containing a maleimide group is as described above, and is used as a raw material for preparing the self-repairing polyurethane elastomer containing a Diels-Alder bond.

[0015] Further improvement, the self-repairing polyurethane elastomer containing a Diels-Alder bond has the following structural formula:

[0016] 、 ; .

[0017] Further improvement, the method for preparing the self-repairing polyurethane elastomer containing a Diels-Alder bond comprises the following steps: (1) preparing a polyurethane solution containing a maleimide group in the side chain The diisocyanate, the poly (caprolactone diol) containing a maleimide group, and a solvent are added into a three-necked flask under the protection of nitrogen atmosphere, and the mixture is stirred at a temperature of 80-90°C for 2-4h to obtain an isocyanate-terminated polyurethane prepolymer solution; then the polyurethane prepolymer solution is cooled to a temperature of 70-80°C, and a small molecule chain extender is added, and the mixture is continuously stirred at a temperature of 70-80°C for 4-6h under the protection of nitrogen atmosphere to obtain a polyurethane solution containing a maleimide group in the side chain; (2) preparing a self-repairing polyurethane elastomer containing a Diels-Alder bond The polyurethane prepolymer solution containing maleimide group side chain is mixed with furan compound, poured into a polytetrafluoroethylene mold, dried at room temperature for 24-48h, and then dried at 50-80℃ in vacuum for 24-48h to obtain a self-repairing polyurethane elastomer containing Diels-Alder bond.

[0018] In the above method, the mass ratio of the maleimide group-containing polycaprolactone diol, diisocyanate and solvent in step (1) is (30-90):(16-27):(150-300).

[0019] Further improvement, the diisocyanate in step (1) is selected from one of isophorone diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, diphenyl methane diisocyanate, dicyclohexyl methane diisocyanate; and the solvent is one of N,N-dimethylformamide, N-methyl pyrrolidone, toluene, xylene.

[0020] In the above method, the amount of the small molecule chain extender in step (1) is calculated according to the ratio of the total molar amount of -OH or -NH2 groups contained in the maleimide group-containing polycaprolactone diol and the small molecule chain extender to the molar amount of -NCO groups contained in the diisocyanate, which is 1:(1.0-1.05).

[0021] Further improvement, the small molecule chain extender is one of 1,4-butanediol, ethylene glycol, 1,6-hexanediol, 1,6-hexanediamine, 4,4'-diaminodicyclohexyl methane.

[0022] In the above method, the amount of the furan compound in step (2) is calculated according to the molar ratio of maleimide functional groups to furan functional groups, which is (1-3):1.

[0023] Further improvement, the furan compound in step (2) is: 、 .

[0024] The beneficial effects of the present application are: (1) The ring-opening polymerization process of the maleimide group-containing polycaprolactone diol of the present application is bulk polymerization, without by-products. The chain length and molecular weight of the polycaprolactone diol can be adjusted according to the ratio of caprolactone monomer to ring-opening agent.

[0025] (2) The self-repairing polyurethane elastomer containing Diels-Alder bond has a thermoreversible Diels-Alder covalent bond. At a lower temperature (40℃ < T < 80℃), the Diels-Alder bond forms to make the elastomer present a three-dimensional network structure; and at a high temperature (100℃ < T < 160℃), the Diels-Alder bond breaks to destroy the three-dimensional network structure, so that the elastomer becomes a linear structure. Therefore, the Diels-Alder covalent bond can be broken by high temperature to reshape and recycle the crosslinked elastomer.

[0026] (3) The self-repairing polyurethane elastomer containing Diels-Alder bond has a clear soft-hard segment microphase separation structure, and forms a three-dimensional network structure after crosslinking by the Diels-Alder covalent bond. The synergistic effect of crosslinking and hard segment microzone further improves the strength and modulus of the elastomer. Meanwhile, the soft segment is a single polycaprolactone segment microzone, which gives the elastomer overall stable mechanical properties and other properties.

[0027] (4) The self-repairing polyurethane elastomer containing Diels-Alder bond constructs a dynamic crosslinking network by Diels-Alder reaction between maleimide groups on the side chain of the soft segment polycaprolactone segment and furan groups in the crosslinking agent. The dynamic crosslinking points exist in the soft phase zone, and the high fluidity of the soft segment chain segment provides the necessary free volume and movement ability for the breakage and recombination of the dynamic Diels-Alder bond, so that the elastomer has excellent self-repairing efficiency and the ability of repeated self-repairing.

[0028] (5) The self-repairing polyurethane elastomer containing Diels-Alder bond has dynamic crosslinking points distributed in the side chain region of the soft segment. In the construction process of the polyurethane main molecular chain, a conventional small molecule chain extender is still used, so that the molecular chain structure can grow normally without limitation, thereby ensuring good elasticity of the elastomer. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The infrared spectrum of the polycaprolactone diol containing maleimide groups prepared in Example 1.

[0030] Figure 2The stress-strain comparison chart of the self-repairing polyurethane elastomer containing Diels-Alder bond prepared in Example 6 and its once, three times repaired samples after being damaged and the linear polyurethane elastomer containing furan functional groups prepared in Comparative Example 6. In the chart, "Example 6" is the self-repairing polyurethane elastomer containing Diels-Alder bond prepared in Example 6, "Comparative Example 4" is the linear polyurethane elastomer containing maleimide groups prepared in Comparative Example 4, "Repairing sample 6" is the sample of "Example 6" repaired once after being damaged, and "Repairing sample f" is the sample of "Example 6" repaired three times after being damaged. DETAILED DESCRIPTION

[0031] Example 1 This example prepared the poly (caprolactone) diol containing maleimide groups according to the following steps: 8.56 g (50 mmol) of N- (2, 3-dihydroxypropyl) maleimide, 81.51 g (715 mmol) of caprolactone monomer and 0.456 g of stannous octoate were mixed in a reaction container, the reaction container was vacuumed and purged with nitrogen, the mixture was stirred and heated to 140 ℃ under nitrogen atmosphere, and reacted for 16 h. After the reaction, the unreacted monomers were removed by vacuuming for 1.5 h, and the poly (caprolactone) diol containing maleimide groups was obtained by cooling and discharging. The Mn thereof was tested to be 1767.

[0032] This example prepared the self-repairing polyurethane elastomer containing Diels-Alder bond according to the following steps: (1) Preparation of polyurethane solution containing maleimide groups in side chains 25.03 g (100 mmol) of diphenylmethane diisocyanate (MDI), 70.68 g (40 mmol) of the poly (caprolactone) diol containing maleimide groups (Mn is 1767) and 200 g of toluene were added into a three-necked flask under the protection of nitrogen atmosphere, heated to 80 ℃ and stirred for 4 h to obtain an isocyanate-terminated polyurethane prepolymer solution. Then, 4.97 g (55.2 mmol) of BDO was added into the polyurethane prepolymer solution cooled to 80 ℃, and the stirring reaction was continued at 70 ℃ under nitrogen atmosphere for 6 h to obtain the polyurethane solution containing maleimide groups in side chains. (2) Preparation of self-repairing polyurethane elastomer containing Diels-Alder bond The polyurethane solution containing maleimide groups in side chains and furan compound 1 were mixed uniformly according to the molar ratio of maleimide functional groups to furan functional groups of 2:1, poured into a polytetrafluoroethylene mold, dried at room temperature for 48 h, and then dried in a vacuum oven at 75 ℃ for 48 h to obtain the self-repairing polyurethane elastomer containing Diels-Alder bond.

[0033] The furan compound 1 used is .

[0034] Example 2 The maleimide group-containing polycaprolactone diol was prepared according to the following steps: 8.56 g (50 mmol) of N-(2,3-dihydroxypropyl) maleimide, 115.71 g (1015 mmol) of caprolactone monomer and 0.671 g of dibutyltin dilaurate were added into a reaction container and mixed, the reaction container was vacuumed and purged with nitrogen, the mixture was stirred and heated to 140°C for reaction, after 14 h of reaction, the unreacted monomer was removed by vacuuming for 1.5 h, and the maleimide group-containing polycaprolactone diol was obtained by cooling and discharging, and the Mn thereof was tested to be 2451.

[0035] The Diels-Alder bond-containing self-repairing polyurethane elastomer was prepared according to the following steps: (1) Preparation of a maleimide group-containing polyurethane solution 25.03 g (100 mmol) of diphenylmethane diisocyanate (MDI), 98.04 g (40 mmol) of the maleimide group-containing polycaprolactone diol (Mn is 2451) described above, and 200 g of toluene were added into a three-necked flask under the protection of nitrogen atmosphere, and heated to 80°C for stirring reaction for 4 h to obtain an isocyanate-terminated polyurethane prepolymer solution; then 4.97 g (55.2 mmol) of BDO was added into the polyurethane prepolymer solution cooled to 80°C, and the stirring reaction was continued at 70°C for 6 h under the nitrogen atmosphere to obtain a maleimide group-containing polyurethane solution; (2) Preparation of a Diels-Alder bond-containing self-repairing polyurethane elastomer The maleimide group-containing polyurethane solution and the furan compound 1 were uniformly mixed according to a molar ratio of 2:1 of the maleimide functional group to the furan functional group, poured into a polytetrafluoroethylene mold, dried at room temperature for 48 h, and then dried in a vacuum oven at 75°C for 48 h to obtain a Diels-Alder bond-containing self-repairing polyurethane elastomer.

[0036] The furan compound 1 used is .

[0037] Example 3 The maleimide group-containing polycaprolactone diol was prepared according to the following steps: 8.56 g (50 mmol) N-(2,3-dihydroxypropyl)maleimide, 92.91 g (815 mmol) caprolactone monomer and 0.52 g dibutyltin dilaurate were added to a reaction vessel and mixed. The reaction vessel was evacuated and purged with nitrogen. The mixture was stirred under nitrogen atmosphere and heated to 140 °C for reaction. After reacting for 16 h, the vessel was evacuated for 1.5 h to remove unreacted monomers. The mixture was then cooled and discharged to obtain polycaprolactone diol containing maleimide groups. Its Mn was determined to be 1995.

[0038] This embodiment prepares a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps: (1) Preparation of polyurethane solutions with maleimide groups in the side chains 25.03 g (100 mmol) of diphenylmethane diisocyanate (MDI), 79.8 g (40 mmol) of the above-mentioned maleimide-containing polycaprolactone diol (Mn 1995), and 200 g of toluene were added to a three-necked flask under a nitrogen atmosphere. The mixture was heated to 80 °C and stirred for 4 h to obtain an isocyanate-terminated polyurethane prepolymer solution. Subsequently, the polyurethane prepolymer solution was cooled to 80 °C and 4.97 g (55.2 mmol) of BDO was added. The mixture was stirred at 70 °C under a nitrogen atmosphere for 6 h to obtain a polyurethane solution with maleimide-containing side chains. (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds A polyurethane solution containing maleimide groups on the side chain was mixed with furan compound 1 at a molar ratio of maleimide functional group to furan functional group of 2:1. The mixture was poured into a polytetrafluoroethylene mold and dried at room temperature for 48 h. Then it was dried in a vacuum oven at 75 °C for 48 h to obtain a self-healing polyurethane elastomer containing Diels-Alder bonds.

[0039] The furan compound 1 used is .

[0040] Example 4 In this embodiment, polycaprolactone diol containing maleimide groups was prepared according to the following steps: 8.56 g (50 mmol) N-(2,3-dihydroxypropyl)maleimide, 92.91 g (815 mmol) caprolactone monomer and 0.557 g tetrabutyl titanate were added to a reaction vessel and mixed. The reaction vessel was evacuated and purged with nitrogen. The mixture was stirred under nitrogen atmosphere and heated to 140 °C for reaction. After reacting for 12 h, the mixture was evacuated for 1.5 h to remove unreacted monomers. The mixture was then cooled and discharged to obtain polycaprolactone diol containing maleimide groups. Its Mn was determined to be 1995.

[0041] This embodiment prepares a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps: (1) Preparation of polyurethane solutions with maleimide groups in the side chains 22.23 g (100 mmol) of isophorone diisocyanate (IPDI), 79.8 g (40 mmol) of the above-mentioned maleimide-containing polycaprolactone diol (Mn 1995), and 200 g of toluene were added to a three-necked flask under nitrogen atmosphere. The mixture was heated to 90 °C and stirred for 4 h to obtain an isocyanate-terminated polyurethane prepolymer solution. Subsequently, the polyurethane prepolymer solution was cooled to 80 °C and 11.61 g (55.2 mmol) of 4,4'-diaminodicyclohexylmethane was added. The mixture was stirred at 80 °C under nitrogen atmosphere for another 6 h to obtain a polyurethane solution with maleimide side chains. (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds A polyurethane solution containing maleimide groups on the side chain was mixed with furan compound 1 at a molar ratio of maleimide functional group to furan functional group of 2:1. The mixture was poured into a polytetrafluoroethylene mold and dried at room temperature for 48 h. Then it was dried in a vacuum oven at 75 °C for 48 h to obtain a self-healing polyurethane elastomer containing Diels-Alder bonds.

[0042] The furan compound 1 used is .

[0043] Example 5 In this embodiment, polycaprolactone diol containing maleimide groups was prepared according to the following steps: 8.56 g (50 mmol) N-(2,3-dihydroxypropyl)maleimide, 92.91 g (815 mmol) caprolactone monomer and 0.557 g tetrabutyl titanate were added to a reaction vessel and mixed. The reaction vessel was evacuated and purged with nitrogen. The mixture was stirred under nitrogen atmosphere and heated to 140 °C for reaction. After reacting for 12 h, the mixture was evacuated for 1.5 h to remove unreacted monomers. The mixture was then cooled and discharged to obtain polycaprolactone diol containing maleimide groups. Its Mn was determined to be 1995.

[0044] This embodiment prepares a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps: (1) Preparation of polyurethane solutions with maleimide groups in the side chains 22.23 g (100 mmol) of isophorone diisocyanate (IPDI), 79.8 g (40 mmol) of the above-mentioned maleimide-containing polycaprolactone diol (Mn 1995), and 200 g of toluene were added to a three-necked flask under nitrogen atmosphere. The mixture was heated to 90 °C and stirred for 4 h to obtain an isocyanate-terminated polyurethane prepolymer solution. Subsequently, the polyurethane prepolymer solution was cooled to 80 °C and 11.61 g (55.2 mmol) of 4,4'-diaminodicyclohexylmethane was added. The mixture was stirred at 80 °C under nitrogen atmosphere for another 6 h to obtain a polyurethane solution with maleimide side chains. (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds A polyurethane solution containing maleimide groups on the side chain was mixed with furan compound 2 at a molar ratio of maleimide functional group to furan functional group of 2:1. The mixture was poured into a polytetrafluoroethylene mold and dried at room temperature for 48 h. Then it was dried in a vacuum oven at 75 °C for 48 h to obtain a self-healing polyurethane elastomer containing Diels-Alder bonds.

[0045] The furan compound 2 used is .

[0046] Example 6 In this embodiment, polycaprolactone diol containing maleimide groups was prepared according to the following steps: 8.56 g (50 mmol) N-(2,3-dihydroxypropyl)maleimide, 92.91 g (815 mmol) caprolactone monomer and 0.557 g tetrabutyl titanate were added to a reaction vessel and mixed. The reaction vessel was evacuated and purged with nitrogen. The mixture was stirred under nitrogen atmosphere and heated to 140 °C for reaction. After reacting for 12 h, the mixture was evacuated for 1.5 h to remove unreacted monomers. The mixture was then cooled and discharged to obtain polycaprolactone diol containing maleimide groups. Its Mn was determined to be 1995.

[0047] This embodiment prepares a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps: (1) Preparation of polyurethane solutions with maleimide groups in the side chains 22.23 g (100 mmol) of isophorone diisocyanate (IPDI), 79.8 g (40 mmol) of the above-mentioned maleimide-containing polycaprolactone diol (Mn 1995), and 200 g of toluene were added to a three-necked flask under nitrogen atmosphere. The mixture was heated to 90 °C and stirred for 4 h to obtain an isocyanate-terminated polyurethane prepolymer solution. Subsequently, the polyurethane prepolymer solution was cooled to 80 °C and 11.61 g (55.2 mmol) of 4,4'-diaminodicyclohexylmethane was added. The mixture was stirred at 80 °C under nitrogen atmosphere for another 6 h to obtain a polyurethane solution with maleimide side chains. (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds A polyurethane solution containing maleimide groups in the side chain was mixed with furan compound 3 at a molar ratio of maleimide functional group to furan functional group of 2:1. The mixture was poured into a polytetrafluoroethylene mold and dried at room temperature for 48 h. Then it was dried in a vacuum oven at 75 °C for 48 h to obtain a self-healing polyurethane elastomer containing Diels-Alder bonds.

[0048] The furan compound 3 used is .

[0049] Comparative Example 1 This comparative example prepared polycaprolactone diol containing maleimide groups according to the following steps: 8.56 g (50 mmol) N-(2,3-dihydroxypropyl)maleimide, 81.51 g (715 mmol) caprolactone monomer and 0.456 g stannous octoate were added to a reaction vessel and mixed. The reaction vessel was evacuated and purged with nitrogen. The mixture was stirred under nitrogen atmosphere and heated to 140 °C for reaction. After 16 h of reaction, the mixture was evacuated for 1.5 h to remove unreacted monomers. The mixture was then cooled and discharged to obtain polycaprolactone diol containing maleimide groups. Its Mn was measured to be 1767.

[0050] This comparative example prepared a linear polyurethane elastomer with maleimide side chains according to the following steps: (1) Preparation of polyurethane solutions with maleimide groups in the side chains 25.03 g (100 mmol) of diphenylmethane diisocyanate (MDI), 70.68 g (40 mmol) of the above-mentioned maleimide-containing polycaprolactone diol (Mn 1767), and 200 g of toluene were added to a three-necked flask under nitrogen atmosphere. The mixture was heated to 80 °C and stirred for 4 h to obtain an isocyanate-terminated polyurethane prepolymer solution. Subsequently, the polyurethane prepolymer solution was cooled to 80 °C and 4.97 g (55.2 mmol) of BDO was added. The mixture was stirred at 70 °C for 6 h under nitrogen atmosphere to obtain a polyurethane solution with maleimide side chains. (2) Preparation of linear polyurethane elastomers with maleimide groups in the side chains A polyurethane solution containing maleimide groups in the side chain was poured into a polytetrafluoroethylene mold and dried at room temperature for 48 hours, and then dried in a vacuum oven at 75°C for 48 hours to obtain a linear polyurethane elastomer containing maleimide groups in the side chain.

[0051] Comparative Example 2 This comparative example prepared polycaprolactone diol containing maleimide groups according to the following steps: 8.56 g (50 mmol) N-(2,3-dihydroxypropyl)maleimide, 115.71 g (1015 mmol) caprolactone monomer and 0.671 g dibutyltin dilaurate were added to a reaction vessel and mixed. The reaction vessel was evacuated and purged with nitrogen. The mixture was stirred under nitrogen atmosphere and heated to 140 °C for reaction. After reacting for 14 h, the mixture was evacuated for 1.5 h to remove unreacted monomers. The mixture was then cooled and discharged to obtain polycaprolactone diol containing maleimide groups. Its Mn was tested to be 2451.

[0052] This comparative example prepared a linear polyurethane elastomer with maleimide side chains according to the following steps: (1) Preparation of polyurethane solutions with maleimide groups in the side chains 25.03 g (100 mmol) of diphenylmethane diisocyanate (MDI), 98.04 g (40 mmol) of the above-mentioned maleimide-containing polycaprolactone diol (Mn 2451), and 200 g of toluene were added to a three-necked flask under nitrogen atmosphere. The mixture was heated to 80 °C and stirred for 4 h to obtain an isocyanate-terminated polyurethane prepolymer solution. Subsequently, the polyurethane prepolymer solution was cooled to 80 °C and 4.97 g (55.2 mmol) of BDO was added. The mixture was stirred at 70 °C for 6 h under nitrogen atmosphere to obtain a polyurethane solution with maleimide-containing side chains. (2) Preparation of linear polyurethane elastomers with maleimide groups in the side chains A polyurethane solution containing maleimide groups in the side chain was poured into a polytetrafluoroethylene mold and dried at room temperature for 48 hours, and then dried in a vacuum oven at 75°C for 48 hours to obtain a linear polyurethane elastomer containing maleimide groups in the side chain.

[0053] Comparative Example 3 This comparative example prepared polycaprolactone diol containing maleimide groups according to the following steps: 8.56 g (50 mmol) N-(2,3-dihydroxypropyl)maleimide, 92.91 g (815 mmol) caprolactone monomer and 0.52 g dibutyltin dilaurate were added to a reaction vessel and mixed. The reaction vessel was evacuated and purged with nitrogen. The mixture was stirred under nitrogen atmosphere and heated to 140 °C for reaction. After reacting for 16 h, the vessel was evacuated for 1.5 h to remove unreacted monomers. The mixture was then cooled and discharged to obtain polycaprolactone diol containing maleimide groups. Its Mn was determined to be 1995.

[0054] This comparative example prepared a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps: (1) Preparation of polyurethane solutions with maleimide groups in the side chains 25.03 g (100 mmol) of diphenylmethane diisocyanate (MDI), 79.8 g (40 mmol) of the above-mentioned maleimide-containing polycaprolactone diol (Mn 1995), and 200 g of toluene were added to a three-necked flask under a nitrogen atmosphere. The mixture was heated to 80 °C and stirred for 4 h to obtain an isocyanate-terminated polyurethane prepolymer solution. Subsequently, the polyurethane prepolymer solution was cooled to 80 °C and 4.97 g (55.2 mmol) of BDO was added. The mixture was stirred at 70 °C under a nitrogen atmosphere for 6 h to obtain a polyurethane solution with maleimide-containing side chains. (2) Preparation of linear polyurethane elastomers with maleimide groups in the side chains A polyurethane solution containing maleimide groups in the side chain was poured into a polytetrafluoroethylene mold and dried at room temperature for 48 hours, and then dried in a vacuum oven at 75°C for 48 hours to obtain a linear polyurethane elastomer containing maleimide groups in the side chain.

[0055] Comparative Example 4 This comparative example prepared polycaprolactone diol containing maleimide groups according to the following steps: 8.56 g (50 mmol) N-(2,3-dihydroxypropyl)maleimide, 92.91 g (815 mmol) caprolactone monomer and 0.557 g tetrabutyl titanate were added to a reaction vessel and mixed. The reaction vessel was evacuated and purged with nitrogen. The mixture was stirred under nitrogen atmosphere and heated to 140 °C for reaction. After reacting for 12 h, the mixture was evacuated for 1.5 h to remove unreacted monomers. The mixture was then cooled and discharged to obtain polycaprolactone diol containing maleimide groups. Its Mn was determined to be 1995.

[0056] This comparative example prepared a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps: (1) Preparation of polyurethane solutions with maleimide groups in the side chains 22.23 g (100 mmol) of isophorone diisocyanate (IPDI), 79.8 g (40 mmol) of the above-mentioned maleimide-containing polycaprolactone diol (Mn 1995), and 200 g of toluene were added to a three-necked flask under nitrogen atmosphere. The mixture was heated to 90 °C and stirred for 4 h to obtain an isocyanate-terminated polyurethane prepolymer solution. Subsequently, the polyurethane prepolymer solution was cooled to 80 °C and 11.61 g (55.2 mmol) of 4,4'-diaminodicyclohexylmethane was added. The mixture was stirred at 80 °C under nitrogen atmosphere for another 6 h to obtain a polyurethane solution with maleimide side chains. (2) Preparation of linear polyurethane elastomers with maleimide groups in the side chains A polyurethane solution containing maleimide groups in the side chain was poured into a polytetrafluoroethylene mold and dried at room temperature for 48 hours, and then dried in a vacuum oven at 75°C for 48 hours to obtain a linear polyurethane elastomer containing maleimide groups in the side chain.

[0057] Performance testing According to GB / T 528-2009 standard, the self-healing polyurethane elastomers containing Diels-Alder bonds prepared in Examples 1-6 were cut into tensile strips and recorded as implementation samples 1-6 respectively. The linear polyurethane elastomers with maleimide groups in the side chains prepared in Comparative Examples 1-4 were cut into tensile strips and labeled as Comparative Samples 1-4 respectively. Another batch of specimens from Examples 1-6 were prepared by cutting the specimens in the middle of the specimens with a knife in a direction perpendicular to the tensile axis. Then, the cross-sections of the two cut specimens were brought into contact with each other and bonded together. They were placed in an oven at 140°C for about 1 hour, and then kept at 75°C for 24 hours to obtain the repaired specimens, which were designated as repaired specimens 1-6. Another batch of specimens from Examples 1-6 was prepared by cutting the specimens at the middle of the specimens with a knife in a direction perpendicular to the tensile axis. Then, the cross-sections of the two cut specimens were brought into contact and bonded together. They were placed in an oven at 140°C for approximately 1 hour, followed by incubation at 75°C for 24 hours to obtain a first-repair specimen. The above steps of cutting and repairing the specimens were repeated twice more, resulting in a third-repair specimen, denoted as repair specimen af.

[0058] According to the testing standard GB / T 528-2009, the tensile properties of the above-mentioned implementation specimens 1-6, their repaired specimens, and control specimens 1-4 were tested using a universal tensile testing machine. The results are shown in Tables 1-6. In addition, [the following is attached...] Figure 2 The stress-strain curves of specimen 6, control specimen 4, repaired specimen 6, and repaired specimen f were obtained.

[0059] Define the repair efficiency of the test specimen. To repair the tensile strength of the specimen Tensile strength of the test specimen The ratio, that is .

[0060] Table 1: Tensile properties of test specimen 1, repair specimen, and comparison specimen 1, and repair efficiency of test specimen 1.

[0061] Table 2: Tensile properties of test specimen 2, repair specimen, and comparison specimen 2, and repair efficiency of test specimen 2.

[0062] Table 3: Tensile properties of test specimen 3, repair specimen, and comparison specimen 3, and repair efficiency of test specimen 3.

[0063] Table 4: Tensile properties of test specimen 4, repair specimen, and control specimen 4, and repair efficiency of test specimen 4.

[0064] Table 5: Tensile properties of test specimen 5, repaired specimen, and control specimen 4, and repair efficiency of test specimen 5.

[0065] Table 6: Tensile properties of test specimen 6, repaired specimen, and control specimen 4, and repair efficiency of test specimen 6.

[0066] The tensile strength test data of the test specimens, control specimens, and repair specimens show that the introduction of the dynamic cross-linking network Diels-Alder bonds significantly enhances the mechanical properties of polyurethane elastomers and gives them excellent self-healing efficiency and repeated self-healing ability.

[0067] Compared to other test specimens, test specimens 5 and 6 exhibited superior tensile strength and self-healing ability. This is attributed to the presence of urethane and urea groups in the furan compounds 2 and 3 used in the preparation of these two elastomers. The introduction of these groups significantly increases the number of hydrogen bonds within the elastomer. Hydrogen bonds, as reversible non-covalent bonds, can significantly improve the mechanical properties of the elastomer by enhancing intermolecular forces, while also endowing it with stronger dynamic characteristics.

[0068] Furthermore, the hydrogen bonds formed by the urethane groups are medium-strong hydrogen bonds, while the hydrogen bonds formed by the urea groups are strong hydrogen bonds. It is this difference that makes the mechanical properties of sample 6 more outstanding compared to sample 5.

Claims

1. A polycaprolactone diol containing a maleimide group, characterized in that, The structural formula is: ； The number-average molecular weight of the polycaprolactone diol containing maleimide groups is 1767-2451 g / mol, where m and n are both integers greater than 0; 14 ≤ m + n ≤ 20.

2. A method for preparing the polycaprolactone diol containing maleimide groups as described in claim 1, characterized in that... The steps are as follows: A ring-opening agent containing maleimide groups, caprolactone monomer, and catalyst are added to a reaction vessel and mixed to form a mixture. The reaction vessel is evacuated and purged with nitrogen. The mixture is stirred and heated to 140-160°C under a nitrogen atmosphere for 12-18 hours. After the reaction, the mixture is evacuated for 1-1.5 hours to remove unreacted monomers. The mixture is then cooled and discharged to obtain the polycaprolactone diol containing maleimide groups. The ring-opening agent containing the maleimide group is N-(2,3-dihydroxypropyl)maleimide, with the following specific structural formula: 。 3. The method for preparing polycaprolactone diol containing maleimide groups according to claim 2, characterized in that, The molar ratio of the maleimide-containing ring-opening agent to the caprolactone monomer is 1:14.3-20.3, and the mass ratio of the catalyst to the caprolactone monomer is 0.0692-0.0798:13.

3.

4. The method for preparing polycaprolactone diol containing maleimide groups according to claim 2 or 3, characterized in that, The catalyst is an organotin or organotitanium catalyst; wherein the organotin catalyst includes one or more of stannous octoate, dibutyltin oxide, and dibutyltin dilaurate; and the organotitanium catalyst includes one or more of tetrabutyl titanate and tetrapropyl titanate.

5. The application of a polycaprolactone diol containing a maleimide group, characterized in that, The structural formula of the polycaprolactone diol containing maleimide groups is as follows: ； The number-average molecular weight of polycaprolactone diols containing maleimide groups is 1767-2451 g / mol, where m and n are both integers greater than 0; 14≤m+n≤20; The polycaprolactone diol containing maleimide groups is used as a raw material for preparing self-healing polyurethane elastomers containing Diels-Alder bonds.

6. The application of the polycaprolactone diol containing maleimide groups according to claim 5, characterized in that, The steps for preparing a self-healing polyurethane elastomer containing Diels-Alder bonds are as follows: (1) Preparation of polyurethane solutions with maleimide groups in the side chains Diisocyanate, the maleimide-containing polycaprolactone diol, and solvent are added to a container under nitrogen atmosphere protection. The mixture is heated to 80-90°C and stirred for 2-4 hours to obtain an isocyanate-terminated polyurethane prepolymer solution. Subsequently, the polyurethane prepolymer solution is cooled to 70-80°C, and a small molecule chain extender is added. The mixture is then stirred and reacted at 70-80°C under nitrogen atmosphere for 4-6 hours to obtain a polyurethane solution with maleimide-containing side chains. (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds A polyurethane prepolymer solution with maleimide side chains was mixed evenly with a furan compound, poured into a polytetrafluoroethylene mold, dried at room temperature for 24-48 hours, and then dried under vacuum at 50-80°C for 24-48 hours to obtain a self-healing polyurethane elastomer containing Diels-Alder bonds.

7. The application of the polycaprolactone diol containing maleimide groups according to claim 6, characterized in that, The mass ratio of the maleimide-containing polycaprolactone diol, diisocyanate, and solvent is 30-90:16-27:150-300. The amount of the small molecule chain extender is measured as a ratio of 1:1.0-1.05 between the total molar amount of -OH groups contained in the polycaprolactone diol containing maleimide groups and the small molecule chain extender and the molar amount of -NCO groups contained in the diisocyanate. The amount of the furan compound used is measured in a molar ratio of maleimide functional group to furan functional group of 1-3:

1.

8. The application of the polycaprolactone diol containing maleimide groups according to claim 6 or 7, characterized in that, The diisocyanate is one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate; The solvent is one of N,N-dimethylformamide, N-methylpyrrolidone, toluene, and xylene; The small molecule chain extender is one of 1,4-butanediol, ethylene glycol, 1,6-hexanediol, 1,6-hexanediamine, and 4,4'-diaminodicyclohexylmethane.

9. The application of the polycaprolactone diol containing maleimide groups according to claim 8, characterized in that, The furan compound is: 、 。 10. The application of the polycaprolactone diol containing maleimide groups according to claim 5, characterized in that, The structural formula of the self-healing polyurethane elastomer containing Diels-Alder bonds is as follows: 、 、 ； 。

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