A polycaprolactone diol containing a maleimide group, and a preparation method and application thereof

Abstract

The application discloses a poly-caprolactone diol containing a maleimide group and a preparation method and application thereof, and the preparation method of the poly-caprolactone diol is as follows: N-(2,3-dihydroxypropyl) maleimide, caprolactone and a catalyst are added into a reaction container, and after high-temperature reaction for 12-18 hours, the poly-caprolactone diol containing the maleimide group is obtained by discharging after temperature reduction. The poly-caprolactone diol containing the maleimide group is used as a raw material to prepare a polyurethane prepolymer, so that the side chain of the prepolymer has the maleimide group, then a double-furan compound is introduced as a dynamic crosslinking agent to obtain a self-repairing polyurethane elastomer containing a Diels-Alder bond. The polyurethane elastomer can be remolded and recycled through the reversible Diels-Alder (D-A) reaction of the functional components, and has excellent and stable mechanical properties, self-repairing efficiency and repeated self-repairing capacity.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, specifically relating to a polycaprolactone diol containing maleimide groups, its preparation method, and its application in self-healing polyurethane elastomers containing Diels-Alder bonds. Background Technology

[0002] Polyurethane elastomers are a special type of elastomeric material with multiple urethane bonds (-NHCOO-) distributed in their molecular backbone. This unique interlocking structure of hard and soft segments endows polyurethane elastomers with extremely high structural and performance controllability. Thanks to their excellent mechanical properties, superior wear resistance, and excellent weather resistance, polyurethane elastomers are widely used in various fields such as building materials, machinery industry, and food industry. However, during processing, transportation, storage, and use, polyurethane elastomers are prone to localized damage and microcracks. This not only shortens the material's service life but also causes environmental pollution due to the non-recyclable nature of the polyurethane elastomers.

[0003] Dynamic networks based on reversible bonds endow elastomers with reprocessability, enabling them to be reshaped for self-healing. Among these, self-healing polymer materials based on reversible covalent bonds exhibit high self-healing efficiency and the ability to repeatedly repair damage. The Diels-Alder reaction is a thermally reversible reaction with advantages such as mild reaction conditions, fast reaction rate, no catalyst required, and few side reactions. It can be embedded as a reversible covalent bond in elastomer materials, giving them self-healing properties while exhibiting excellent temperature adaptability and mechanical properties. Because maleimide groups exhibit high reactivity in the Diels-Alder reaction, there has been considerable research on the Diels-Alder reaction between furan (diene) and maleimide (dieneophile). Previously, research on the application of the Diels-Alder reaction in the field of self-healing polyurethane elastomers mainly followed two approaches.

[0004] One approach involves using furan or maleimide-terminated isocyanates or prepolymers, reacting them with maleimide or furan compounds as chain extenders to form Diels-Alder bonds, thus preparing reversible polyurethane elastomers. This method is relatively simple to construct Diels-Alder bonds, and the resulting elastomers possess a certain degree of self-healing ability. However, it has significant drawbacks: after introducing Diels-Alder bonds, the elastomer's molecular chains maintain a linear structure. Once the Diels-Alder segments break or fail, the material's performance may deteriorate rapidly after only a few repair cycles. Furthermore, the chain growth is limited by the end-capping structure, ultimately leading to poor elasticity.

[0005] Another approach involves introducing furan or maleimide groups into the molecular chains of macromolecular polyols or small-molecule chain extenders, and then forming Diels-Alder bonds with maleimide or furan compounds acting as crosslinking agents to prepare reversible polyurethane elastomers. The Diels-Alder bonds constructed in this way exhibit a strong ability to repeatedly repair damage. However, the mechanical properties of the material often require the introduction of composite polyols to ensure their performance. Different polyols have compatibility issues, and their reactivity with isocyanates varies. This can negatively impact the microphase separation structure of the elastomer and the reaction uniformity of the entire system, leading to regional imbalances and instability in the material's mechanical properties, heat resistance, and hydrolysis resistance. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention provides a maleimide-containing polycaprolactone diol, its preparation method, and its application in self-healing polyurethane elastomers containing Diels-Alder bonds. The preparation method of this maleimide-containing polycaprolactone diol produces no byproducts, and the degree of polymerization and molecular weight of the prepared polycaprolactone diol can be controlled according to the ratio of caprolactone monomer to maleimide ring-opening agent. Furthermore, using this maleimide-containing polycaprolactone diol, isocyanate, and furan compound as raw materials to prepare self-healing polyurethane elastomers, the crosslinking density of the elastomer material can be directly and linearly controlled by changing the content of maleimide groups embedded in the polycaprolactone diol and the type of crosslinking agent furan compound, resulting in stable and excellent self-healing efficiency, repeated self-healing ability, and mechanical properties.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] The polycaprolactone diol containing maleimide groups described in this invention has the following structural formula:

[0009]

[0010] 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.

[0011] The preparation method of polycaprolactone diol containing maleimide groups according to the present invention comprises the following steps:

[0012] A ring-opening agent containing maleimide groups, caprolactone monomer, and catalyst are added to a reaction vessel and mixed. The reaction vessel is evacuated and purged with nitrogen. The mixture is stirred under nitrogen atmosphere and heated to 140-160°C for reaction. After reacting for 12-18 hours, the vessel is evacuated for 0.5-1 hours to remove unreacted monomers. The mixture is then cooled and discharged to obtain the polycaprolactone diol containing maleimide groups.

[0013] The ring-opening agent containing the maleimide group is N-(2,3-dihydroxypropyl)maleimide, with the following specific structural formula:

[0014]

[0015] In the above method, the molar ratio of the ring-opening agent containing maleimide groups 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.

[0016] In the above method, the catalyst is an organotin or organotitanium catalyst.

[0017] In the above method, the organotin catalyst is selected from one or more of stannous octoate, dibutyltin oxide, and dibutyltin dilaurate; the organotitanium catalyst is selected from one or more of tetrabutyl titanate and tetrapropyl titanate.

[0018] The application of a maleimide-containing polycaprolactone diol in a self-healing polyurethane elastomer containing Diels-Alder bonds, wherein the maleimide-containing polycaprolactone diol is used as a raw material for preparing a self-healing polyurethane elastomer containing Diels-Alder bonds, as described above.

[0019] A further improvement is made to the self-healing polyurethane elastomer containing Diels-Alder bonds, whose structural formula is as follows:

[0020]

[0021] ,

[0022] ;

[0023] .

[0024] A further improvement is made to the preparation method of the self-healing polyurethane elastomer containing Diels-Alder bonds, comprising the following steps:

[0025] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0026] Diisocyanate, the maleimide-containing polycaprolactone diol, and solvent were added to a three-necked flask under a nitrogen atmosphere. The mixture was heated to 80-90°C and stirred for 2-4 hours to obtain an isocyanate-terminated polyurethane prepolymer solution. Subsequently, the polyurethane prepolymer solution was cooled to 70-80°C, and a small molecule chain extender was added. The mixture was then stirred and reacted at 70-80°C under a nitrogen atmosphere for 4-6 hours to obtain a polyurethane solution with maleimide-containing side chains.

[0027] (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds

[0028] 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 vacuum dried at 50-80°C for 24-48 hours to obtain a self-healing polyurethane elastomer containing Diels-Alder bonds.

[0029] In the above method, the mass ratio of the maleimide-containing polycaprolactone diol, diisocyanate and solvent in step (1) is (30-90): (16-27): (150-300).

[0030] In a further improvement, the diisocyanate in step (1) is selected from one of isophorone diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, and dicyclohexylmethane diisocyanate; and the solvent is one of N,N-dimethylformamide, N-methylpyrrolidone, toluene, and xylene.

[0031] In the above method, the amount of the small molecule chain extender in step (1) is measured as the ratio of the total molar amount of the -OH or -NH2 groups contained in the polycaprolactone diol containing maleimide groups and the small molecule chain extender to the molar amount of the -NCO groups contained in the diisocyanate is 1:(1.0-1.05).

[0032] In a further improvement, the small molecule chain extender is one of 1,4-butanediol, ethylene glycol, 1,6-hexanediol, 1,6-hexanediamine, and 4,4'-diaminodicyclohexylmethane.

[0033] In the above method, the amount of furan compound in step (2) is measured in a molar ratio of maleimide functional group to furan functional group of (1-3):1.

[0034] A further improvement is made to the furan compound mentioned in step (2):

[0035] ,

[0036] .

[0037] The beneficial effects of this invention are as follows:

[0038] (1) The ring-opening polymerization process of the polycaprolactone diol containing maleimide groups of the present invention is a bulk polymerization with no byproducts. The chain length and molecular weight of the polycaprolactone diol can be controlled according to the ratio of caprolactone monomer to ring-opening agent.

[0039] (2) The self-healing polyurethane elastomer containing Diels-Alder bonds described in this invention possesses thermally reversible Diels-Alder covalent bonds. At lower temperatures (40℃ < T < 80℃), the formation of Diels-Alder bonds gives the elastomer a three-dimensional network structure; while at higher temperatures (100℃ < T < 160℃), the Diels-Alder bonds break, destroying the three-dimensional network structure, making the elastomer a linear structure. Therefore, the crosslinked elastomer can be reshaped and recycled by breaking the Diels-Alder covalent bonds at high temperatures.

[0040] (3) The self-healing polyurethane elastomer containing Diels-Alder bonds described in this invention has a distinct soft and hard segment microphase separation structure. After cross-linking by Diels-Alder covalent bonds, a three-dimensional network structure is formed. The synergistic effect of cross-linking and hard segment microregions further enhances the strength and modulus of the elastomer. At the same time, the soft segment is a single polycaprolactone chain segment microregion, which endows the elastomer with stable overall mechanical properties and other properties.

[0041] (4) The self-healing polyurethane elastomer containing Diels-Alder bonds described in this invention has a dynamic crosslinking network constructed through a Diels-Alder reaction between maleimide groups on the side chains of the soft segment polycaprolactone and furan groups in the crosslinking agent. The dynamic crosslinking points exist in the soft phase region, and the high fluidity of the soft segment provides the necessary free volume and mobility for the breaking and recombination of the dynamic Diels-Alder bonds, enabling the elastomer to have excellent self-healing efficiency and the ability to repeatedly self-heal.

[0042] (5) The self-healing polyurethane elastomer containing Diels-Alder bonds described in this invention has dynamic crosslinking points distributed in the side chain region of the soft segment. In the process of constructing the main polyurethane molecular chain, conventional small molecule chain extenders are still used to enable the molecular chain structure to grow normally without restriction, thereby ensuring the good elasticity of the elastomer. Attached Figure Description

[0043] Figure 1 The infrared spectrum of polycaprolactone diol containing maleimide groups prepared in Example 1.

[0044] Figure 2This is a stress-strain comparison diagram of the self-healing polyurethane elastomer containing Diels-Alder bonds prepared in Example 6, and its first and third repair samples after damage, compared with the linear polyurethane elastomer with furan functional groups in the side chain prepared in Comparative Example 6. In the diagram, "Example 6" is the self-healing polyurethane elastomer containing Diels-Alder bonds prepared in Example 6, "Comparative Sample 4" is the linear polyurethane elastomer with maleimide groups in the side chain prepared in Comparative Example 4, "Repaired Sample 6" is the sample of "Example 6" repaired after being damaged once, and "Repaired Sample f" is the sample of "Example 6" repaired after being damaged three times. Detailed Implementation

[0045] Example 1

[0046] In this embodiment, polycaprolactone diol containing maleimide groups was prepared according to the following steps:

[0047] 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.

[0048] This embodiment prepares a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps:

[0049] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0050] 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.

[0051] (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds

[0052] 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.

[0053] The furan compound 1 used is .

[0054] Example 2

[0055] In this embodiment, polycaprolactone diol containing maleimide groups was prepared according to the following steps:

[0056] 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.

[0057] This embodiment prepares a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps:

[0058] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0059] 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.

[0060] (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds

[0061] 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.

[0062] The furan compound 1 used is .

[0063] Example 3

[0064] In this embodiment, polycaprolactone diol containing maleimide groups was prepared according to the following steps:

[0065] 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.

[0066] This embodiment prepares a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps:

[0067] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0068] 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.

[0069] (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds

[0070] 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.

[0071] The furan compound 1 used is .

[0072] Example 4

[0073] In this embodiment, polycaprolactone diol containing maleimide groups was prepared according to the following steps:

[0074] 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.

[0075] This embodiment prepares a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps:

[0076] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0077] 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.

[0078] (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds

[0079] 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.

[0080] The furan compound 1 used is .

[0081] Example 5

[0082] In this embodiment, polycaprolactone diol containing maleimide groups was prepared according to the following steps:

[0083] 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.

[0084] This embodiment prepares a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps:

[0085] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0086] 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.

[0087] (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds

[0088] 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.

[0089] The furan compound 2 used is .

[0090] Example 6

[0091] In this embodiment, polycaprolactone diol containing maleimide groups was prepared according to the following steps:

[0092] 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.

[0093] This embodiment prepares a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps:

[0094] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0095] 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.

[0096] (2) Preparation of self-healing polyurethane elastomers containing Diels-Alder bonds

[0097] 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.

[0098] The furan compound 3 used is .

[0099] Comparative Example 1

[0100] This comparative example prepared polycaprolactone diol containing maleimide groups according to the following steps:

[0101] 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.

[0102] This comparative example prepared a linear polyurethane elastomer with maleimide side chains according to the following steps:

[0103] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0104] 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.

[0105] (2) Preparation of linear polyurethane elastomers with maleimide groups in the side chains

[0106] 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.

[0107] Comparative Example 2

[0108] This comparative example prepared polycaprolactone diol containing maleimide groups according to the following steps:

[0109] 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.

[0110] This comparative example prepared a linear polyurethane elastomer with maleimide side chains according to the following steps:

[0111] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0112] 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.

[0113] (2) Preparation of linear polyurethane elastomers with maleimide groups in the side chains

[0114] 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.

[0115] Comparative Example 3

[0116] This comparative example prepared polycaprolactone diol containing maleimide groups according to the following steps:

[0117] 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.

[0118] This comparative example prepared a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps:

[0119] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0120] 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.

[0121] (2) Preparation of linear polyurethane elastomers with maleimide groups in the side chains

[0122] 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.

[0123] Comparative Example 4

[0124] This comparative example prepared polycaprolactone diol containing maleimide groups according to the following steps:

[0125] 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.

[0126] This comparative example prepared a self-healing polyurethane elastomer containing Diels-Alder bonds according to the following steps:

[0127] (1) Preparation of polyurethane solutions with maleimide groups in the side chains

[0128] 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.

[0129] (2) Preparation of linear polyurethane elastomers with maleimide groups in the side chains

[0130] 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.

[0131] Performance testing

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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 .

[0138] Table 1: Tensile properties of test specimen 1, repair specimen, and comparison specimen 1, and repair efficiency of test specimen 1.

[0139]

[0140] Table 2: Tensile properties of test specimen 2, repair specimen, and comparison specimen 2, and repair efficiency of test specimen 2.

[0141]

[0142] Table 3: Tensile properties of test specimen 3, repair specimen, and comparison specimen 3, and repair efficiency of test specimen 3.

[0143]

[0144] Table 4: Tensile properties of test specimen 4, repair specimen, and control specimen 4, and repair efficiency of test specimen 4.

[0145]

[0146] Table 5: Tensile properties of test specimen 5, repaired specimen, and control specimen 4, and repair efficiency of test specimen 5.

[0147]

[0148] Table 6: Tensile properties of test specimen 6, repaired specimen, and control specimen 4, and repair efficiency of test specimen 6.

[0149]

[0150] 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.

[0151] 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.

[0152] 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 structure is as follows: ； The number average molecular weight of the poly-caprolactone diol containing a maleimide group is 1767-2451 g / mol, and m and n are both integers greater than 0; 14≤m+n≤20.

2. A process for the preparation of a maleimide group containing polycaprolactone diol as claimed in claim 1, characterized by The steps are as follows: The open ring agent containing a maleimide group, caprolactone monomer and catalyst are mixed in a reaction container to form a mixture; the reaction container is vacuumed and purged with nitrogen, the mixture is stirred and heated to 140-160 DEG C for reaction, after reaction for 12-18 h, vacuum is applied for 1-1.5 h to remove unreacted monomers, and the temperature is lowered to discharge the material to obtain the poly-caprolactone diol containing a maleimide group; The open ring agent containing a maleimide group is N-(2,3-dihydroxypropyl) maleimide, and the specific structure is as follows: 。 3. The method of claim 2, wherein the maleimide group-containing polycaprolactone diol is prepared by the reaction of a polycaprolactone diol and maleic anhydride. The molar ratio of the open ring agent containing a 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.

4. Process for the preparation of a poly(caprolactone) diol containing a maleimide group according to claim 2 or 3, characterized in that, The catalyst is an organic tin or organic titanium catalyst; wherein the organic tin catalyst includes one or more of stannous octoate, dibutyltin oxide and dibutyltin dilaurate; and the organic titanium catalyst includes one or more of tetrabutyl titanate and tetrapropyl titanate.

5. Use of a polycaprolactone diol containing a maleimide group, characterized in that, The poly-caprolactone diol containing a maleimide group has the following structure: ； The number average molecular weight of the poly-caprolactone diol containing a maleimide group is 1767-2451 g / mol, and m and n are both integers greater than 0; 14≤m+n≤20; The poly-caprolactone diol containing a maleimide group is used as a raw material for preparing a self-repairing polyurethane elastomer containing a Diels-Alder bond.

6. Use of a poly (caprolactone) diol containing a maleimide group according to claim 5, characterized in that, The steps for preparing the self-repairing polyurethane elastomer containing a Diels-Alder bond are as follows: (1) Preparation of 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 to a container under nitrogen atmosphere protection, heated to 80-90 DEG C and stirred for 2-4 h to obtain an isocyanate-terminated polyurethane prepolymer solution; then the polyurethane prepolymer solution is cooled to 70-80 DEG C, and a small molecule chain extender is added, and the stirring is continued at 70-80 DEG C under nitrogen atmosphere for 4-6 h to obtain a polyurethane solution containing a maleimide group in the side chain; (2) Preparation of a self-repairing polyurethane elastomer containing a Diels-Alder bond The polyurethane prepolymer solution containing a maleimide group in the side chain is mixed uniformly with a furan compound, poured into a polytetrafluoroethylene mold, dried at room temperature for 24-48 h, and then dried at 50-80 DEG C under vacuum for 24-48 h to obtain a self-repairing polyurethane elastomer containing a Diels-Alder bond.

7. Use of a poly (caprolactone) diol containing a maleimide group according to claim 6, characterized in that, The mass ratio of the poly-caprolactone diol containing a maleimide group, the diisocyanate and the solvent is 30-90:16-27:150-300. The amount of the small molecule chain extender is calculated according to the ratio of the total moles of the -OH groups contained in the maleimide group-containing polycaprolactone diol and the small molecule chain extender to the moles of the -NCO groups contained in the diisocyanate, which is 1:1.0-1.05; The amount of the furan compound is calculated according to the ratio of the moles of the maleimide functional groups to the moles of the furan functional groups, which is 1-3:

1.

8. Use of a poly-caprolactone diol containing a maleimide group 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. Use of a poly-caprolactone diol containing a maleimide group according to claim 8, characterized in that, The furan compound is: 、 。 10. The use of the poly (caprolactone) diol containing a maleimide group according to claim 5, characterized by, The structure of the self-repairing polyurethane elastomer containing a Diels-Alder bond is: 、 、 ； ； m and n are both integers greater than 0; 14≤m+n≤20.

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