A sunlight-excitable self-healing polyurethane capable of repairing internal cracks, its preparation method and application

Abstract

The present invention discloses a self-healing polyurethane capable of repairing internal cracks by sunlight excitation, its preparation method and application, which relate to the field of self-repairing materials. The self-healing polyurethane comprises: a dynamic reversible diamine monomer containing a dithiocarbamate structure, a polyester or polyether diol monomer, a diisocyanate monomer, a common diamine monomer, a catalyst, and a polyamine crosslinking agent. The polyurethane provided by the present invention contains characteristic ultraviolet light-excited dynamic reversible dithiocarbamate bond units. Due to its unique free radical exchange and transfer mechanism, the polyurethane has the properties of sunlight-induced reversible self-healing and solid-state crushing and recycling, and can achieve the repair of internal cracks. At the same time, the mechanical strength of the material is improved, thereby greatly enhancing the use stability and service life of the material, meeting the energy-saving and clean low-carbon economic development concept, and being easy to scale up and promote.

Description

Technical Field

[0001] The present invention relates to the field of self - healing materials, and in particular to a self - healing polyurethane that can repair internal cracks under sunlight excitation, its preparation method and application. Background Art

[0002] During the processing and use of polymer materials, their performance often deteriorates and service life is affected due to internal micro - cracks and local damages. Self - healing polymer materials imitate the principle of biological damage healing and can self - heal through certain mechanisms. They are a type of polymer intelligent material with wide application requirements. The self - healing system includes intrinsic self - healing and non - intrinsic self - healing. Intrinsic self - healing polymer materials are generally prepared by introducing dynamic reversible bonds. The dynamic reversible bonds used to construct self - healing polymer materials are usually divided into dynamic reversible non - covalent bonds and covalent bonds.

[0003] Currently, the reported non - covalent bond systems mainly include hydrogen bonds, host - guest interactions, π - π stacking interactions, electrostatic interactions, etc. The covalent bond systems mainly include: (1) a thermally reversible system based on the Diels - Alder reaction; (2) a dynamic thermally reversible reaction system based on the C - ON bond; (3) other reversible covalent bonds such as disulfide bonds, acylhydrazone bonds, large - steric - hindrance urea bonds, thiourea bonds, etc. To trigger the dynamic reversible properties of these functional groups, external stimuli need to be provided, typically including thermal stimuli, chemical stimuli, light stimuli, etc. Among them, light - induced self - healing has some special advantages: (1) The repair conditions are mild and environmentally friendly, and self - healing can be completed at room temperature without a catalyst; (2) The repair controllability is strong, with wavelength selectivity, and self - healing can be performed on specific parts; (3) The repair speed is fast. Therefore, light - induced self - healing has attracted the attention of many scientific researchers. Common reversible [2 + 2] or [4 + 4] cycloaddition reactions, the exchange reaction of Se - Se bonds under visible light, and the isomerization of azobenzene excited by ultraviolet light have all been applied to photo - repair polymer materials. In addition, in reversible addition - fragmentation chain transfer polymerization (RAFT), the dynamic reversibility of chain - transfer reagents with ultraviolet - light response has also been applied to the construction of self - healing polymer materials.

[0004] However, currently, the main light sources for self - healing of these light - induced self - healing polymers are ultraviolet light and visible light. The penetration depth of ultraviolet light is in the range of dozens to hundreds of micrometers, making it difficult to repair internal cracks in materials. Moreover, its relatively high energy often accelerates the aging of materials, while visible - light repair easily leads to continuous stress relaxation behavior of materials and it is difficult to maintain structural stability in normal use environments. Summary of the Invention

[0005] The present invention provides a sunlight-excitable self-healing polyurethane capable of repairing internal cracks, and a preparation method and application thereof, so as to provide a sunlight-excitable self-healing polyurethane capable of repairing internal cracks and overcoming the deficiency in the prior art that photo-excitable self-healing materials can only repair surface cracks.

[0006] In order to solve the above technical problems, one of the objectives of the present invention is to provide a sunlight-excitable self-healing polyurethane capable of repairing internal cracks, comprising the following components in parts by weight:

[0007] A dynamic reversible diamine monomer containing a dithiocarbamate structure: 2 parts - 10 parts;

[0008] A polyester or polyether diol monomer: 1.7 parts - 30 parts;

[0009] A diisocyanate monomer: 4 parts - 12 parts;

[0010] An ordinary diamine monomer: 0 parts - 3.5 parts;

[0011] A catalyst: 0.001 parts - 0.01 parts;

[0012] A polyamine crosslinking agent: 0.1 parts - 1.4 parts;

[0013] The general structural formula of the dynamic reversible diamine monomer containing a dithiocarbamate structure is wherein, R 1 or R 2 is a group capable of forming a P-Π conjugate with the N atom, and R 1 , R 2 are alkyl groups, heterocyclic rings, aromatic rings or an aromatic conjugate structure jointly formed by R 1 and R 2 , and the probability that R 1 and R 2 are both alkyl groups at the same time is 0; R is any one of tert-butyl, benzyl, phenyl, benzyl connected with an ester group or a cyano group or a methyl group, alkyl connected with an electron-withdrawing ester group or a cyano group.

[0014] By adopting the above scheme, the cross-linked polyurethane material prepared by the present invention has better advantages in application compared with uncross-linked polyurethane. Uncross-linked polyurethane has defects such as poor solvent resistance, thermal stability and creep resistance, which affect its application range. At the same time, the provided structure containing dithiocarbamate generates free radicals when irradiated by ultraviolet light, and the S-C bond breaks. The free radicals then add to the C═S bond, and the R group breaks away, thus realizing the process of exchange transfer, enabling the molecular chains at the damaged part to exchange and recombine; one of R1 and R2 is a group that can stabilize the lone pair electrons of the N atom or a group that forms a P-Π conjugation with the N atom, which is beneficial to activating the C═S bond, and R is a stable and easily leaving group, which is beneficial to the better addition, fracture and transfer of free radicals. The two work together to achieve the free radical transfer and exchange in the application. Therefore, the polymer containing the dithiocarbamate structure has excellent self-healing performance excited by sunlight, enabling the internal cracks of the polymer to self-heal. The present invention introduces a dithiocarbamate structure with sunlight-excited dynamic reversibility into the polymer material, endowing the polymer material with the properties of sunlight-reversible self-healing and solid-state recyclability, while improving the mechanical strength of the material and enhancing the use stability and service life of the material.

[0015] If the polymer is crushed, covalent bond recombination will also occur between the fragments, thus endowing the polymer with sunlight-excited solid-state recycling and cyclic application. The recycling process is to collect and crush the waste polyurethane, apply pressure, and irradiate it under sunlight for a certain period of time, and a polymer with mechanical properties equivalent to those of the original sample can be obtained, which has the characteristics of simple operation, solvent-free, environmental protection, energy saving, and is easy to be popularized on a large scale.

[0016] As a preferred scheme, the binary amine monomer containing a dynamically reversible dithiocarbamate bond is prepared by the following method: A secondary amine derivative containing a tert-butoxycarbonyl-protected amino group is mixed with a base and CS 2 and reacted in a dimethyl sulfoxide solution for 0.5 - 8 h at a reaction temperature of 25 - 45 °C. Then, a dibromo compound or an aromatic bromide containing a tert-butoxycarbonyl-protected amino group is added and reacted for 1 - 5 days at a reaction temperature of 25 - 45 °C. After that, the tert-butoxycarbonyl group is removed in trifluoroacetic acid / dichloromethane.

[0017] As a preferred scheme, the preparation method of the binary amine monomer containing a dynamically reversible dithiocarbamate bond includes the following components in parts by weight:

[0018] Secondary amine derivative containing a tert-butoxycarbonyl-protected amino group: 0.5 part - 4 parts;

[0019] Base: 0 part - 2 parts;

[0020] CS 2 : 0.2 part - 5.2 parts;

[0021] Dimethyl sulfoxide solution: 4 parts - 48.1 parts;

[0022] Dibromo compound or aromatic bromide containing a tert-butoxycarbonyl-protected amino group: 0.2 parts - 3 parts;

[0023] Trifluoroacetic acid / dichloromethane: 3.4 parts - 27 parts.

[0024] As a preferred embodiment, the secondary amine derivative containing a tert-butoxycarbonyl-protected amino group is prepared by the following method (1) or (2):

[0025] (1) React the secondary amine derivative containing a primary amino group with di-tert-butyl dicarbonate in a saturated dioxane base solution for 1 - 12 h at a reaction temperature of 25 - 80 °C to obtain a secondary amine derivative containing a tert-butoxycarbonyl-protected amino group;

[0026] (2) Dissolve the secondary amine derivative containing a primary amino group or the secondary amine derivative containing a hydroxyl group and the bromide containing a tert-butoxycarbonyl-protected amino group in N,N-dimethylformamide, and react for 2 - 24 h under the catalysis of anhydrous potassium carbonate at a reaction temperature of 25 - 100 °C to obtain a secondary amine derivative containing a tert-butoxycarbonyl-protected amino group.

[0027] As a preferred embodiment, the preparation method (1) of the secondary amine derivative containing a tert-butoxycarbonyl-protected amino group includes the following components in parts by weight:

[0028] Secondary amine derivative containing a primary amino group: 0.5 parts - 5.5 parts;

[0029] Di-tert-butyl dicarbonate: 1 part - 11 parts;

[0030] Saturated dioxane base solution: 10 parts - 47 parts.

[0031] As a preferred embodiment, the preparation method (2) of the secondary amine derivative containing a tert-butoxycarbonyl-protected amino group includes the following components in parts by weight:

[0032] Secondary amine derivative containing a primary amino group or secondary amine derivative containing a hydroxyl group: 0.5 parts - 5.5 parts;

[0033] Bromide containing a tert-butoxycarbonyl-protected amino group: 2 parts - 12 parts;

[0034] N,N-dimethylformamide: 7.9 parts - 47.2 parts;

[0035] Anhydrous potassium carbonate: 1.2 parts - 10.0 parts.

[0036] As a preferred embodiment, the structural formula of the secondary amine derivative containing a primary amino group is:

[0037]

[0038] one or more of the above.

[0039] As a preferred embodiment, the structural formula of the secondary amine derivative containing a hydroxyl group is:

[0040]

[0041] one or more of the above.

[0042] As a preferred embodiment, the dibromo compound is one or more of the substances with the following structural formula:

[0043]

[0044] one or more of the above.

[0045] As a preferred embodiment, the structural formula of the bromide containing a tert-butoxycarbonyl-protected amino group is:

[0046] one or more of the above.

[0047] As a preferred embodiment, the structural formula of the polyester or polyether diol monomer is:

[0048] one or more of the above.

[0049] As a preferred embodiment, the structural formula of the diisocyanate monomer is:

[0050] one or more of the above.

[0051] As a preferred embodiment, the structural formula of the ordinary diamine monomer is:

[0052] one or more of the above.

[0053] As a preferred embodiment, the structural formula of the polyamine crosslinking agent is: one or more of them, wherein R' is H or dimer acid.

[0054] As a preferred embodiment, the dynamic reversible diamine monomer containing a dithiocarbamate structure is one or more of 1,4-phenylenebis(methylenebis(3-(2-aminoethyl)-1H-indole-1-carbodithioate)), 4-(2-aminoethoxy)-9H-carbazole-9-methylsulfate benzyl ester, 4-(aminomethyl)benzyl 3-(2-aminoethyl)-1H-indole-1-carbodithioate.

[0055] As a preferred embodiment, the polyester or polyether diol monomer is one or more of polytetrahydrofuran diol, polycaprolactone diol, polyethylene glycol.

[0056] As a preferred embodiment, the polyester or polyether diol monomer is polytetrahydrofuran diol and / or polycaprolactone diol.

[0057] As a preferred embodiment, the diisocyanate monomer is one or more of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4-diisocyanate.

[0058] As a preferred embodiment, the diisocyanate monomer is dicyclohexylmethane 4,4-diisocyanate.

[0059] As a preferred embodiment, the ordinary diamine monomer is 1,2-bis(2-aminoethoxy)ethane and / or adipic dihydrazide.

[0060] As a preferred embodiment, the polyamine crosslinking agent is tris(2-aminoethyl)amine and / or amino-capped trimethylolpropane tripropylene glycol ether.

[0061] As a preferred embodiment, the catalyst is a polyurethane catalyst.

[0062] As a preferred embodiment, the catalyst is dibutyltin dilaurate and / or stannous octoate.

[0063] To solve the above technical problems, the second object of the present invention provides a preparation method of a self-healing polyurethane that can be repaired by sunlight excitation for internal cracks, including the following steps: After melting and drying the polyester or polyether diol monomer, add the diisocyanate monomer and the catalyst and react for 3-10 h, then add the dynamic reversible diamine monomer containing a dithiocarbamate structure and react for 3-10 h, then add the ordinary diamine monomer and react for 3-10 h, and finally add the polyamine crosslinking agent and continue to react for 3-10 h. After drying and curing, the polyurethane is obtained.

[0064] By adopting the above-mentioned scheme, the present invention first introduces a tert-butoxycarbonyl group to protect the amino group on a secondary amine derivative containing a primary amino group or a hydroxyl group. Then, the secondary amine is reacted with potassium hydroxide, carbon disulfide, and a dibromo compound or an aromatic bromide containing a tert-butoxycarbonyl-protected amino group. Finally, the protection of the tert-butoxycarbonyl group is removed to obtain a diamine monomer containing a dithiocarbamate structure. Furthermore, the diamine monomer is reacted with a polyether or polyester diol monomer, a diisocyanate monomer, and a polyamine crosslinking agent to prepare a crosslinked polyurethane material, which has the characteristics of simple preparation, self-healing ability, and solid-state recycling.

[0065] To solve the above technical problems, a third object of the present invention is to provide an application of a self-healing polyurethane that can repair internal cracks under sunlight excitation in a self-healing or recyclable polymer material under sunlight.

[0066] As a preferred scheme, the self-healing method is to place the self-healing polyurethane with mechanical damage or internal cracks under sunlight for repair; the recyclable method is to crush the self-healing polyurethane and then apply pressure and irradiate it under sunlight to form a shape, so as to realize the recycling of the polymer material.

[0067] As a preferred scheme, the irradiation time for repair under sunlight is 0.5 - 20 h to achieve self-healing.

[0068] As a preferred scheme, the solid recycling method is as follows: under sunlight and the pressure of a clip, the self-healing polyurethane is used to form the polymer powder for 1 - 20 h, and a block material with a tensile strength similar to that of the original sample can be prepared.

[0069] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0070] 1. Under the irradiation of ultraviolet light, the S-C bond in the dithiocarbamate structure provided by the present invention breaks to generate free radicals. The free radicals then add to the C=S bond, causing the R group to break and leave, thus realizing the process of exchange and transfer. This enables the molecular chains at the damaged site to exchange and recombine. R 1 and R 2 form a conjugated structure, which is beneficial to activating the C=S bond. The R group is a stable and easily leaving group, which is beneficial to the better addition, fracture, and transfer of free radicals, enabling the internal cracks of the polymer to self-heal. At the same time, the mechanical strength of the material is improved, and the service stability and service life of the material are enhanced.

[0071] 2. The present invention endows polymers with solid-state recycling and cyclic applications under sunlight excitation. The recycling process involves collecting and pulverizing waste polyurethane, applying pressure, and irradiating it under sunlight for a certain period of time. Covalent bond recombination also occurs between the fragments, and polymers with mechanical properties equivalent to those of the original sample can be prepared. The repair time is short, and the material does not depolymerize during the repair process. It has the characteristics of simple operation, solvent-free, environmental protection, energy conservation, and is easy to promote on a large scale. Description of the Drawings

[0072] Figure 1 : 1H NMR spectrum of a diamine monomer containing a dithiocarbamate structure in Preparation Example 1 of the present invention;

[0073] Figure 2 : Photos of a self-healing polyurethane with internally crack-repairable properties before and after crack repair under sunlight excitation in Example 1 of the present invention (Note: 1 is the original crack made for the first time; 2 is the sample after 1 h of repair; 3 is the crack made again; 4 is the sample after 1 h of repair again). Detailed Embodiments

[0074] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0075] The present invention proposes to introduce dithiocarbamate bonds with high ultraviolet light activity into polymers. Due to their unique free radical transfer mechanism, the dynamically photo-reversible dithiocarbamate bonds can achieve a self-healing polymer with high mechanical strength and internally crack-repairable properties. The excellent ultraviolet light activity of the dithiocarbamate bonds makes sunlight containing a small amount of ultraviolet light (3 - 5%) a suitable stimulus source, and can maintain the integrity of its structure, preparing a self-healing polymer material with both high mechanical strength and the ability to repair internal cracks.

[0076] Preparation Example 1

[0077] A dynamically reversible diamine monomer containing a dithiocarbamate structure, including the following preparation steps:

[0078] (1) React 4 g of tryptamine with 10 g of di-tert-butyl dicarbonate in 35 g of an anhydrous potassium carbonate solution in saturated dioxane (weight ratio of dioxane to anhydrous potassium carbonate is 2:1) for 8 h at a reaction temperature of 30 °C; after the reaction is completed, pour the mixed solution into distilled water, extract it 3 times with ethyl acetate, then dry the collected organic layer with anhydrous sodium sulfate overnight, rotary evaporate and wash with petroleum ether to obtain tert-butoxycarbonyl (Boc)-protected tryptamine ((2-(1H-indol-3-yl)ethyl)carbamic acid tert-butyl ester), and its molecular structural formula is

[0079]

[0080] (2) First, mix 2.5 g of Boc-protected tryptamine with 1 g of potassium hydroxide and 27 g of dimethyl sulfoxide solution, react at room temperature for 1 h, then slowly add dropwise 1.5 g of CS 2 , and continue the reaction for 4 h; then add 1.5 g of p-dibromobenzyl and react at 30 °C for 2 days. Pour the reacted mixed solution into a large amount of distilled water to precipitate, filter and wash to obtain a yellow solid containing a dithiocarbamate structure with a Boc-protected amino group. Remove the Boc of the yellow solid in 5 g of trifluoroacetic acid / dichloromethane at a reaction temperature of 25 °C, filter, wash and dry to obtain 1,4-phenylenebis(methylenebis(3-(2-aminoethyl)-1H-indole-1-carbodithioate)), and its molecular structural formula is The nuclear magnetic resonance hydrogen spectrum of this product is shown in Figure 1 as follows.

[0081] Preparation Example 2

[0082] A dynamic reversible diamine monomer containing a dithiocarbamate structure, comprising the following preparation steps:

[0083] (1) React 4.6 g of 4-hydroxycarbazole with 5 g of anhydrous potassium carbonate in 47 g of N,N-dimethylformamide for 2 h at a reaction temperature of 30 °C; then add dropwise 6.7 g of N-Boc-bromoethylamine and continue the reaction for 8 h; after the reaction is completed, pour the mixed solution into distilled water, extract it 3 times with ethyl acetate, then dry the collected organic layer with anhydrous sodium sulfate overnight, rotary evaporate and precipitate and wash with petroleum ether to obtain tert-butoxycarbonyl-protected 4-hydroxycarbazole ((2-(9H-carbazol-1-yloxy)ethyl)carbamic acid tert-butyl ester), and its molecular structural formula is

[0084] (2) First, mix 3 g of Boc-protected 4-hydroxycarbazole with 1 g of potassium hydroxide and 27 g of dimethyl sulfoxide solution, react at room temperature for 1 h, then slowly add dropwise 1.5 g of CS 2, continue the reaction for 4 h; then add 2.8 g of tert-butyl 4-(bromomethyl)benzylcarbamate and react at 30 °C for 24 h. Pour the reaction mixture into a large amount of distilled water to precipitate. After suction filtration and washing, a yellow solid with a dithiocarbamate structure protected by Boc is obtained. The yellow solid is deprotected by Boc in 5 g of trifluoroacetic acid / dichloromethane at a reaction temperature of 25 °C. After suction filtration, washing, and drying, 4-(2-aminoethoxy)-9H-carbazole-9-methylbenzylsulfate is obtained, and its molecular structural formula is

[0085] Preparation Example 3

[0086] Preparation steps of a dynamic reversible diamine monomer containing a dithiocarbamate structure:

[0087] First, mix 2.5 g of tert-butyl 2-(1H-indol-3-yl)ethylcarbamate in Preparation Example 1 with 1 g of potassium hydroxide and 27 g of dimethyl sulfoxide solution, react at room temperature for 1 h, and then slowly add 1.5 g of CS 2 , continue the reaction for 4 h; then add 2.8 g of tert-butyl 4-(bromomethyl)benzylcarbamate and react at 30 °C for 24 h. Pour the reaction mixture into a large amount of distilled water to precipitate. After suction filtration and washing, a yellow solid with a dithiocarbamate structure protected by Boc is obtained. The yellow solid is deprotected by Boc in 5 g of trifluoroacetic acid / dichloromethane at a reaction temperature of 25 °C. After suction filtration, washing, and drying, 4-(aminomethyl)benzyl 3-(2-aminoethyl)-1H-indole-1-carbodithioate is obtained, and its molecular structural formula is

[0088]

[0089] Preparation Example 4

[0090] Preparation steps of a common diamine monomer containing a dithiocarbamate structure:

[0091] First, mix 3.0 g of tert-butyl (2-bromoethyl)carbamate with 2.5 g of CS 2 , 27 g of dimethyl sulfoxide solution, and then slowly add 3.5 g of tert-butyl 2-(methylamino)ethylcarbamate and react at 30 °C for 24 h; then pour the reaction mixture into a large amount of distilled water to precipitate. After suction filtration and washing, a light yellow solid with a dithiocarbamate structure protected by Boc is obtained. The light yellow solid is deprotected by Boc in 5 g of trifluoroacetic acid / dichloromethane at a reaction temperature of 25 °C. After suction filtration, washing, and drying, 2-aminoethyl (2-aminoethyl)(methyl)aminodithiocarbonate is obtained, and its molecular structural formula is

[0092]

[0093] Example 1

[0094] A self-healing polyurethane that can be excited by sunlight to repair internal cracks includes the following preparation steps:

[0095] (1) Under an argon atmosphere, 11 g of polytetrahydrofuran diol PTMEG2000 (number-average molecular weight of 2000) was added to a 250 ml three-necked flask. After heating to 120 °C to melt PTMEG2000, continuous ventilation was carried out for 2 h to remove trace water vapor in the reaction system;

[0096] (2) Then, the temperature was lowered to 80 °C, 7.9 g of dicyclohexylmethane 4,4-diisocyanate and 0.005 g of dibutyltin dilaurate catalyst were added, and the reaction was continued for 4 h. After the temperature was lowered to 50 °C again, 4 g of 1,4-phenylenebis(methylene)bis(3-(2-aminoethyl)-1H-indole-1-carbodithioate) obtained in Preparation Example 1 was added. After reacting for 6 h, 1.25 g of 1,2-bis(2-aminoethoxy)ethane was slowly added dropwise. After the above system reacted for 6 h, it was crosslinked with 0.25 g of tris(2-aminoethyl)amine for 6 h, and then poured into a mold and cured at 60 °C for 16 h to obtain a self-healing polyurethane.

[0097] Example 2

[0098] A self-healing polyurethane that can be excited by sunlight to repair internal cracks, the steps in its preparation steps and the reagents and process parameters used in each step are the same as those in Example 1. The difference is that in step (1), 11 g of polytetrahydrofuran diol PTMEG2000 is replaced by 14 g of polycaprolactone diol PCLD2000 (number-average molecular weight of 2000).

[0099] Example 3

[0100] A self-healing polyurethane that can be excited by sunlight to repair internal cracks, the steps in its preparation steps and the reagents and process parameters used in each step are the same as those in Example 1. The difference is that in step (1), polytetrahydrofuran diol PTMEG2000 is replaced by an equal amount of polyethylene glycol PEG2000 (number-average molecular weight of 2000).

[0101] Example 4

[0102] A self-healing polyurethane that can be excited by sunlight to repair internal cracks, the steps in its preparation steps and the reagents and process parameters used in each step are the same as those in Example 1. The difference is that in step (2), 7.9 g of dicyclohexylmethane 4,4-diisocyanate is replaced by 6.7 g of isophorone diisocyanate monomer.

[0103] Example 5

[0104] A self-healing polyurethane that can be excited by sunlight to repair internal cracks. The steps in its preparation process, the reagents used in each step, and the process parameters are all the same as those in Example 1. The difference is that in step (2), 7.9 g of dicyclohexylmethane 4,4-diisocyanate is replaced with 5 g of hexamethylene diisocyanate.

[0105] Example 6

[0106] A self-healing polyurethane that can be excited by sunlight to repair internal cracks. The steps in its preparation process, the reagents used in each step, and the process parameters are all the same as those in Example 1. The difference is that in step (2), 4 g of 1,4-phenylenebis(methylene)bis(3-(2-aminoethyl)-1H-indole-1-carbodithioate) obtained in Preparation Example 1 is replaced with 2.9 g of benzyl 4-(2-aminoethoxy)-9H-carbazole-9-methanesulfonate obtained in Preparation Example 2.

[0107] Example 7

[0108] A self-healing polyurethane that can be excited by sunlight to repair internal cracks. The steps in its preparation process, the reagents used in each step, and the process parameters are all the same as those in Example 1. The difference is that in step (2), 4 g of 1,4-phenylenebis(methylene)bis(3-(2-aminoethyl)-1H-indole-1-carbodithioate) obtained in Preparation Example 1 is replaced with 2.5 g of benzyl 4-(aminomethyl)-3-(2-aminoethyl)-1H-indole-1-carbodithioate obtained in Preparation Example 3.

[0109] Example 8

[0110] A self-healing polyurethane that can be excited by sunlight to repair internal cracks. The steps in its preparation process, the reagents used in each step, and the process parameters are all the same as those in Example 1. The difference is that in step (2), 1.25 g of 1,2-bis(2-aminoethoxy)ethane is replaced with 2.41 g of adipic dihydrazide.

[0111] Example 9

[0112] A self-healing polyurethane that can be excited by sunlight to repair internal cracks. The steps in its preparation process, the reagents used in each step, and the process parameters are all the same as those in Example 1. The difference is that in step (2), 0.25 g of tris(2-aminoethyl)amine is replaced with 1.12 g of amino-terminated trimethylolpropane tripropyleneglycol ether.

[0113] Example 10

[0114] A self-healing polyurethane that can be excited by sunlight to repair internal cracks, and the steps, reagents used in each step, and process parameters in its preparation steps are all the same as those in Example 1. The difference is that in step (2), the addition amount of 1,2-bis(2-aminoethoxy)ethane is 0.

[0115] Comparative Example 1

[0116] A self-healing polyurethane that can be excited by sunlight to repair internal cracks, and the steps, reagents used in each step, and process parameters in its preparation steps are all the same as those in Example 1. The difference is that in step (2), after cooling to 50 °C again, the addition amount of 1,4-phenylenebis(methylene)bis(3-(2-aminoethyl)-1H-indole-1-carbodithioate) obtained in Preparation Example 1 is 0, and 1.25 g of 1,2-bis(2-aminoethoxy)ethane is directly added dropwise slowly.

[0117] Comparative Example 2

[0118] A self-healing polyurethane that can be excited by sunlight to repair internal cracks, and the steps, reagents used in each step, and process parameters in its preparation steps are all the same as those in Example 1. The difference is that in step (2), 4 g of 1,4-phenylenebis(methylene)bis(3-(2-aminoethyl)-1H-indole-1-carbodithioate) obtained in Preparation Example 1 is replaced by 2 g of 2-aminoethyl(2-aminoethyl)(methyl)carbamodithioate obtained in Preparation Example 4.

[0119] Performance detection test

[0120] 1. In the present invention, the repair effect of the material is qualitatively evaluated by multiple repairs of microcracks. As Figure 2 shown, where 1) is the original crack made for the first time, 2) is the sample after 1 h of repair, 3) is the crack made again, and 4) is the sample after 1 h of re-repair.

[0121] 2. The polymer spline is made into a dumbbell-shaped spline (l = 35 mm; b = 2 mm; h = 0.5 mm) for repair testing. That is, when the spline is cut in the middle with a cutting thickness of 0.5 mm, then the cross-sections of the spline are combined, and after irradiating in sunlight for 12 h, the tensile strength of the polymer is tested. The tensile strength is calculated as follows: σ = F / (b·h), where: F is the maximum load at which the specimen is stretched and broken; b is the width of the joint surface of the specimen; h is the thickness of the specimen; the formula for the elongation at break is as follows: ε = (l a -l 0 ) / l 0 , where ε is the elongation at break, l 0 is the original length of the specimen within the gauge length, and l a is the length of the specimen when it is broken.

[0122] The repair efficiency is defined as the ratio of the tensile strength or elongation at break of the repaired specimen to that of the original specimen: η = σ recycled / σ virgin or η = ε recycled / ε virgin , and the test results are shown in Table 1 below.

[0123] 3. The repair efficiency of internal cracks in the material is evaluated by the tensile test method: The polyurethane materials prepared in the examples and comparative examples are made into rectangular splines (l = 35 mm; b = 8.0 mm; h = 1.0 mm). A 1.0-mm incision is made in the middle of one end of the wide surface (8.0 mm), and there is still a width of 7.0 mm that is not cut. After obtaining the mechanical strength of the specimen with the incision through the tensile test, the polymer sample is then wrapped in white electrical tape, leaving only the other end of the wide surface (8.0 × 1 mm 2 ) exposed to sunlight for 12 h for repair, and then the tensile test is carried out. The repair efficiency of the internal cracks is defined as the ratio of the tensile strength or elongation at break of the repaired specimen to that of the original specimen, and the test results are shown in Table 2 below.

[0124] 4. The recycling efficiency of the material is evaluated by the tensile test method: After obtaining the original mechanical strength by the tensile test of the polyurethane materials prepared in the examples or comparative examples, the polymer materials are then pulverized under liquid nitrogen quenching, and the obtained polymer powder is pressed under sunlight for 12 h to obtain the recycled specimen (a disc with a diameter of 40 - 50 mm). After cutting it into a dumbbell shape and carrying out the tensile test, the recycling efficiency is defined as the ratio of the tensile strength or elongation at break of the recycled specimen to that of the original specimen, and the test results are shown in Table 3 below.

[0125] Table 1 - Repair test results of polyurethane in the examples and comparative examples of this application

[0126]

[0127]

[0128] Table 2 - Internal crack repair test results of polyurethane in the examples and comparative examples of this application

[0129]

[0130]

[0131] Table 3 - Repair test results after solid-state recycling of polyurethane in the examples and comparative examples of this application

[0132]

[0133] According to the performance test results of Example 1 and Comparative Examples 1-2 in Table 1-3, after the characteristic ultraviolet-excited dynamic reversible dithiocarbamate bond unit is introduced into the embodiment of the present application, the polymer can achieve a tensile strength and elongation at break greater than 80% repair for internal or external damage of the material after being cut and irradiated with sunlight for a period of time. However, the polymer containing no dithiocarbamate structure in Comparative Example 1 and the polymer containing ordinary dithiocarbamate structure in Comparative Example 2 (R1 and R2 are both alkyl groups and cannot form P-II conjugation with N atoms, and R is also an ordinary alkyl group, which is not easy to leave) can only be repaired very little for tensile strength and elongation at break even after the same repair conditions, and the external repair efficiency is less than 43.3%, and the internal repair efficiency is less than 38%. This part of the recovery mainly comes from the hydrogen bonds in the polyurethane urea bond structure, proving that the unique free radical addition fracture transfer mechanism of the ultraviolet-excited dynamic reversible dithiocarbamate structure designed in the present application is an intrinsic mechanism for realizing the sunlight repair of internal and external cracks in polyurethane materials.

[0134] Combined with the performance test results of Examples 1-5 in Tables 1-3, it can be seen that compared with the results of Examples 1-3, the tensile strength of the polyurethane material after adding PTMEG or PCLD is superior to that of PEG, and compared with the results of Examples 1 and 4-5, rigid diisocyanates such as dicyclohexylmethane 4,4-diisocyanate are more conducive to enhancing the tensile strength of the material than isophorone diisocyanate monomer or hexamethylene diisocyanate.

[0135] Combining the performance test results of Examples 1 and 10 in Tables 1-3, it can be seen that the ordinary diamine monomer structure is not as rigid as the dithiocarbamate structure. Therefore, adding the polymer is beneficial to improving the elongation at break, which can meet the tensile strength and elongation at break of the original polyurethane material to reach a better standard, and the overall performance is excellent.

[0136] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A self-healing polyurethane that can be repaired for internal cracks by sunlight excitation, characterized in that, it comprises the following components in parts by weight: Dynamic reversible diamine monomer containing dithiocarbamate structure: 2 parts - 10 parts; Polyester or polyether diol monomer: 1.7 parts - 30 parts; Diisocyanate monomer: 4 parts - 12 parts; Ordinary diamine monomer: 0 parts - 3.5 parts; Catalyst: 0.001 parts - 0.01 parts; Polyamine crosslinking agent: 0.1 parts - 1.4 parts; The dynamic reversible diamine monomer containing a dithiocarbamate bond is prepared by the following method: A secondary amine derivative containing a tert-butoxycarbonyl-protected amino group is mixed with a base and CS 2 and reacted in a dimethyl sulfoxide solution for 0.5 - 8 h at a reaction temperature of 25 - 45 °C. Then, a dibromo compound or an aromatic bromide containing a tert-butoxycarbonyl-protected amino group is added and reacted for 1 - 5 days at a reaction temperature of 25 - 45 °C. After that, the tert-butoxycarbonyl group is removed in trifluoroacetic acid / dichloromethane; The secondary amine derivative containing tert-butoxycarbonyl-protected amino group is prepared by the following method (1) or (2): (1) React the secondary amine derivative containing primary amino group with di-tert-butyl dicarbonate and saturated dioxane base solution for 1 - 12 h, and the reaction temperature is 25 - 80 °C to obtain the secondary amine derivative containing tert-butoxycarbonyl-protected amino group; (2) Dissolve the secondary amine derivative containing hydroxyl group and the bromide containing tert-butoxycarbonyl-protected amino group in N,N-dimethylformamide, and react for 2 - 24 h under the catalysis of anhydrous potassium carbonate, and the reaction temperature is 25 - 100 °C to obtain the secondary amine derivative containing tert-butoxycarbonyl-protected amino group; The structural formula of the secondary amine derivative containing a primary amino group is as follows: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , or one or more of them; The structural formula of the hydroxyl-containing secondary amine derivative is as follows: and and and and and and and and and and and and and and and and and and and and and and and or more of them.

2. A self-healing polyurethane that can be repaired for internal cracks by sunlight excitation according to claim 1, characterized in that, The dibromo compound is one or more of the substances with the following structural formulas: , , , , , , , , , , , , , , , , , one or more of; The structural formula of the bromide containing a tert-butoxycarbonyl-protected amino group is as follows: , , , , , , , , , , , or one or more of them.

3. A self-healing polyurethane that can be repaired for internal cracks by sunlight excitation according to claim 1, characterized in that, The structural formula of the diisocyanate monomer is as follows: , , , , , , , , , , , , , , or one or more of them; The structural formula of the ordinary diamine monomer is as follows: , , , , , , , , one or more of; The structural formula of the polyamine crosslinking agent is as follows: , , , , , , One or more of them, where R' is H or dimer acid.

4. A self-healing polyurethane that can be repaired for internal cracks by sunlight excitation according to claim 1, characterized in that, The dynamic reversible diamine monomer containing a dithiocarbamate structure is , , one or more of the above.

5. A self-healing polyurethane that can be repaired for internal cracks by sunlight excitation according to claim 1, characterized in that, The polyester or polyether diol monomer is one or more of polytetrahydrofuran diol, polycaprolactone diol, polyethylene glycol; the diisocyanate monomer is one or more of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane 4,4-diisocyanate; the ordinary diamine monomer is 1,2-bis(2-aminoethoxy)ethane and / or adipic dihydrazide; the polyamine crosslinking agent is tris(2-aminoethyl)amine and / or amino-terminated trimethylolpropane tripropyleneglycol ether.

6. A preparation method of a self-healing polyurethane that can be repaired for internal cracks by sunlight excitation based on any one of claims 1 - 5, characterized in that, it comprises the following steps: After melting and drying the polyester or polyether diol monomer, add the diisocyanate monomer and the catalyst and react for 3 - 10 h, then add the dynamic reversible diamine monomer containing dithiocarbamate structure and react for 3 - 10 h, then add the ordinary diamine monomer and react for 3 - 10 h, and finally add the polyamine crosslinking agent and continue to react for 3 - 10 h, and obtain the polyurethane after drying and curing.

7. An application of a self-healing polyurethane that can be repaired for internal cracks by sunlight excitation based on any one of claims 1 - 5 in sunlight self-healing or recyclable polymer materials.

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