Self-repairing degradable single-component moisture-curing polyurethane containing single boric acid ester bond and preparation method of self-repairing degradable single-component moisture-curing polyurethane

Abstract

The preparation method comprises the following steps: dissolving a boric acid monomer in an organic solvent, adding monomers containing vicinal diol and primary alcohol at the same time, then adding a water removal agent, heating to 60-80 DEG C, and carrying out condensation reflux to obtain a mixed solution containing a boric acid ester chain extender; removing the organic solvent from the mixed solution containing the boric acid ester chain extender, and washing with a low-boiling-point solvent to obtain a chain extender containing a single boric acid ester bond; the preparation method comprises the following steps: reacting a chain extender containing a single boric acid ester bond, an organic metal or tertiary amine catalyst, polyether polyol and diisocyanate to obtain a single-component moisture-cured polyurethane prepolymer with the-NCO reservation amount of 4-8wt.%, and curing. The single-component moisture-curable polyurethane has excellent mechanical properties, the phenomena that the mechanical properties are reduced and the self-repairing efficiency is reduced after repeated damage-repairing are avoided, the safety and reliability of the material are greatly improved, and the service life is prolonged.

Description

Technical Field

[0001] The present invention relates to a one-component moisture-curing polyurethane, in particular to a self-healing and degradable one-component moisture-curing polyurethane containing a single borate ester bond and a preparation method thereof. Background Art

[0002] One-component moisture-curing polyurethane (1C-MCPU) is a reaction-curing (moisture-curing) polyurethane material that relies on the reaction of -NCO groups in the prepolymer with moisture in the air or on the substrate to cure. It has the characteristics of convenient construction, low VOC, not being overly demanding on the moisture content of the base surface, excellent elasticity and high and low temperature resistance, and is widely used in industrial fields such as adhesives, sealants, and coatings.

[0003] When 1C-MCPU is in use, it will be affected by various factors, resulting in microscopic defects or mechanical damage on its interior or surface, which affects the safety and reliability of the material and shortens its service life. In addition, 1C-MCPU has stable chemical properties and is not degradable under natural conditions. If discarded casually, it will cause serious pollution to the environment and endanger environmental safety. Therefore, after the material fails, it needs to be centrally scrapped and recycled, which consumes a large amount of energy, has a high cost, and will cause a large amount of resource waste. Reversible dynamic bonds can break and recombine under specific conditions. During this period, the polymer molecular chains break and recombine to repair mechanical damage or internal defects of the material. Moreover, its dynamic activity can also enable the material to degrade under certain conditions, reducing the harm to the environment. For example, Chinese Patent Application CN116845351A introduces a DA bond with reversible dynamic activity into the polymer main chain, enabling the polymer material to repair mechanical damage and restore its initial performance under heating conditions. Chinese Patent Application CN116003730A uses 2,4-diamino-6-hydroxypyrimidine as a chain extender to introduce multiple hydrogen bonds into the polymer main chain, enabling the material to achieve self-healing above 120°C. Although the above materials can repair mechanical damage, their repair conditions are harsh and not conducive to practical applications. Chinese Patent CN112409561B discloses a self-healing, anti-aging, and controllable degradation polyurethane and its preparation method and application, but the material can only start to degrade in a solution with a sodium hydroxide concentration greater than 1 mol / L, and its degradation conditions are harsh and not conducive to practical applications. Therefore, it is very necessary to find a dynamic bond that can break and recombine under mild conditions.

[0004] Borate ester bonds have dynamic activity and can hydrolyze under mild conditions to form boric acid and vicinal diols, or dehydrate to reform borate ester bonds. Introducing them into the polymer molecular chain can not only endow 1C-MCPU with self-healing performance through the dynamic exchange of borate ester bonds, enabling it to repair mechanical damage under mild conditions, but also endow 1C-MCPU with degradable performance by taking advantage of the characteristics of borate hydrolysis. Through borate hydrolysis, the polymer main chain breaks and the molecular weight decreases, achieving degradation and recycling. Chinese invention patent CN114752030A introduces dynamic borate ester bonds into the polymer main chain, enabling the material to achieve excellent self-healing performance under room temperature aqueous conditions. However, in this technology, the borate chain extender used is prepared from 1,4-diphenylboronic acid, and during use, 1,4-diphenylboronic acid will precipitate and flow out, resulting in a decrease in the content of borate ester bonds, a decline in self-healing performance, and also weakening of mechanical properties. Similar practices in the prior art, such as Chinese invention patent application CN112521583A and Chinese invention patent application CN117229472A, also use 1,4-diphenylboronic acid to prepare polymers containing double dynamic borate esters, and there are also problems with the performance degradation of the obtained materials due to the precipitation and outflow of 1,4-diphenylboronic acid during use. Summary of the Invention

[0005] In order to improve the mechanical properties of 1C-MCPU, extend the service life of the material, and alleviate the problem of environmental pollution caused by its non-degradability after failure and scrapping, starting from the perspective of polymer molecular structure design, the present invention proposes a 1C-MCPU prepared from a single borate chain extender. This polyurethane has excellent mechanical properties and can degrade or repair mechanical damage under mild conditions. In addition, after multiple damage-repair cycles, the material will not show a decline in mechanical properties or a reduction in self-healing efficiency, greatly improving the safety and reliability of the material and extending its service life.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A self-healing and degradable one-component moisture-curing polyurethane containing a single borate ester bond, characterized in that it has the following structural formula:

[0008]

[0009] where m = 33 - 38 and n = 25 - 30;

[0010] R1 is one of the following groups:

[0011] In R1, the oxygen (O) atom is connected to the carbon (C) atom in the carbonyl (C=O) through a single bond, and the other end (carbon atom) is connected to the carbon (C) atom on the benzene ring through a single bond.

[0012] R2 is one of the following groups:

[0013]

[0014] In R2, the carbon (C) atom is connected to the carbon (C) atom on the borate ring by a single bond, and the oxygen (O) atom is connected to the carbon (C) atom in the carbonyl group (C=O) by a single bond.

[0015] The preparation method of a self-healing and degradable one-component moisture-curing polyurethane containing a single borate ester bond is characterized by including the following steps:

[0016] (1) Dissolve the boric acid monomer in an organic solvent, slowly dropwise add the mixture containing both the vicinal diol and the primary alcohol monomer, then add anhydrous magnesium sulfate. Heat the mixed dispersion to 60 - 80 °C and reflux for 12 - 24 h, then cool to 25 - 35 °C and filter to remove magnesium sulfate to obtain a clear mixed solution containing the borate ester chain extender.

[0017] (2) Heat the mixed solution to 40 - 60 °C and distill off the organic solvent under reduced pressure to obtain a white solid containing the borate ester chain extender. Then wash it with a low-boiling solvent to remove the unreacted raw materials, and the obtained white crystals are the chain extender containing the dynamic borate ester bond.

[0018] (3) React the chain extender containing the borate ester bond with polyether polyol, catalyst and diisocyanate to obtain a one-component moisture-curing polyurethane prepolymer with an -NCO reserve of 4 - 8 wt.%. Then cure it under specific temperature and humidity conditions for a certain time to obtain a self-healing and degradable one-component moisture-curing polyurethane containing a single borate ester bond.

[0019] To further achieve the object of the present invention, preferably, the boric acid monomer is one or more of 4-hydroxybenzeneboronic acid, 4-hydroxymethylbenzeneboronic acid, and (4-(3-hydroxypropyl)phenyl)boronic acid;

[0020] Preferably, the mixture containing both the vicinal diol and the primary alcohol monomer is one or more of glycerol, 1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,7-heptanetriol, and 1,2,8-octanetriol;

[0021] Preferably, the organic solvent is one or more of ethanol, isopropanol, tetrahydrofuran, and ethyl acetate;

[0022] Preferably, the low-boiling solvent is one or more of diethyl ether, petroleum ether, n-pentane, and isopentane;

[0023] Preferably, the mass ratio of the boric acid monomer to the organic solvent and the mass ratio of the monomer containing both vicinal diol and primary alcohol to the organic solvent are both 1:9 - 3:7, the mass ratio of anhydrous magnesium sulfate to the boric acid monomer is 1:2 - 3:2, and the molar ratio of the boric acid monomer to the monomer containing both vicinal diol and primary alcohol is 1:2 - 1:5;

[0024] Preferably, the mass ratio of the white solid containing the borate chain extender to the low-boiling solvent is 1:9 - 3:7, and the low-boiling solvent is removed after standing at 60 - 80 °C under negative pressure for 8 - 24 h;

[0025] Preferably, the molar ratio of the polyether polyol, the chain extender containing a single borate bond, the diisocyanate, and the catalyst in the preparation process of the prepolymer is 1:0.5:3.0:0.0001 - 1:1.5:4.5:0.0001, and the reserved -NCO is 4 - 8 wt.% of the resin;

[0026] Preferably, the catalyst is one or more of dibutyltin dilaurate, triethylenediamine, stannous octoate, zinc isooctanoate, bismuth naphthenate; the curing temperature of the -NCO terminated prepolymer is 25 °C, the curing humidity is 60%, and the curing time is 24 - 72 h.

[0027] The present invention has the following advantages compared with the prior art:

[0028] 1. The dynamic borate bond in the 1C-MCPU prepared by the present invention can endow the material with self-healing and degradable properties; since the chain extender used only contains a single borate bond, there will be no phenomenon that the loss of small molecules leads to the reduction of borate bonds, and the mechanical properties and self-healing efficiency of the material decline during the repeated repair process;

[0029] 2. The 1C-MCPU prepared in the present invention can quickly repair mechanical damage at 60 °C and can be degraded in a 0.1 mol / L hydrochloric acid solution. Its self-healing and degradation conditions are mild, and the whole process has low energy consumption and little pollution;

[0030] 3. The 1C-MCPU containing borate bonds in the present invention still has a high repair efficiency and maintains excellent mechanical properties after being damaged and repaired multiple times;

[0031] 4. The preparation method of the 1C-MCPU containing borate bonds in the present invention is simple, the synthesis conditions are mild, and the solvent used in the preparation process can be reused, which is conducive to large-scale production. Description of the Drawings

[0032] Figure 1 1H NMR spectrum of the chain extender containing a single dynamic borate bond prepared in Example 1;

[0033] Figure 21H NMR spectrum of chain extender containing two dynamic borate ester bonds in the comparative example;

[0034] Figure 3 Stress-strain test curve of the one-component moisture-curing polyurethane in Example 1. Detailed implementation manners

[0035] To better understand the present invention, the present invention will be described below in conjunction with specific embodiments. However, the embodiments do not constitute a limitation on the protection scope of the claims of the present invention. Based on the embodiments, other embodiments obtained by those skilled in the art without creative labor all fall within the protection scope of the present invention.

[0036] From the existing technical measures, it can be seen that although introducing dynamic borate ester bonds into the main chain of 1C-MCPU can enable self-healing or degradation under mild conditions, the prior art generally uses monomers with a symmetric structure and containing double borate ester bonds to prepare polymer materials with self-healing and degradable functions. However, during the use of the polymer materials prepared by such monomers, boronic acid monomers will gradually precipitate and be lost, weakening the mechanical properties and self-healing properties of the materials, and causing the materials to gradually fail.

[0037] Therefore, a self-healing and degradable one-component moisture-curing polyurethane containing a single borate ester bond provided by the present invention has the following structural formula:

[0038]

[0039] where m = 33 - 38 and n = 25 - 30;

[0040] R1 is and one of them;

[0041] R2 is one of the following groups:

[0042]

[0043] The preparation method of the self-healing and degradable one-component moisture-curing polyurethane containing a single borate ester bond includes the following steps:

[0044] (1) Dissolve the boronic acid monomer in an organic solvent, add the mixture of the vicinal diol and the primary alcohol monomer, and then add a water scavenger. Heat the mixed dispersion to 60 - 80 °C and reflux for 12 - 24 h, then cool to 25 - 40 °C and filter to remove the water scavenger to obtain a mixed solution containing a borate ester chain extender;

[0045] (2) Heat the mixed solution containing the borate ester chain extender to 40 - 60 °C and distill off the organic solvent under reduced pressure to obtain a solid borate ester chain extender, and wash it with a low-boiling solvent to obtain a chain extender containing a single borate ester bond;

[0046] (3) React a chain extender containing a single borate bond, an organometallic or tertiary amine catalyst, a polyether polyol, and a diisocyanate to obtain a one-component moisture-curing polyurethane prepolymer with an -NCO reserve of 4-8 wt.%. Cure it at a temperature of 25-35 °C and a humidity of 60-80% for 24-72 h to obtain a self-healing and degradable one-component moisture-curing polyurethane containing a single borate bond.

[0047] In the above preparation method, a monomer containing a boronic acid group and a monomer containing both a vicinal diol and a primary alcohol are used as raw materials. Utilizing the characteristic that the boronic acid group can undergo dehydration condensation with the vicinal diol to form a borate bond, a chain extender containing a single dynamic borate bond is prepared. Using this chain extender as a raw material, the chain extender is incorporated into the polymer main chain. The prepared 1C-MCPU main chain contains a dynamic borate bond, which enables the material to repair mechanical damage or undergo degradation under mild conditions. During the preparation of 1C-MCPU, the borate-containing chain extender used is incorporated into the polymer main chain through a urethane bond, and its structure contains only a single borate bond. Therefore, during use, there will be no phenomenon of small molecules flowing out, resulting in a reduction in the number of borate bonds in the material, a weakening of mechanical properties, and a decrease in self-healing efficiency. Thus, it can increase the number of self-healing cycles of the damaged-repaired material, improve its safety and reliability, and extend its service life. Moreover, the one-component moisture-curing polyurethane in the present invention can achieve the repair of mechanical damage and degradation under mild conditions through the reversible hydrolysis cleavage and dehydration recombination of the borate bond.

[0048] In the above preparation method, the boronic acid monomer, the monomer containing both a vicinal diol and a primary alcohol, and the low-boiling solvent can be selected according to their names for such substances; preferably, the boronic acid monomer is one or more of 4-hydroxyphenylboronic acid, 4-hydroxymethylphenylboronic acid, and (4-(3-hydroxypropyl)phenyl)boronic acid; the monomer containing both a vicinal diol and a primary alcohol can be selected from one or more of glycerol, 1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,7-heptanetriol, and 1,2,8-octanetriol; the low-boiling solvent is preferably one or more of diethyl ether, petroleum ether, n-pentane, and isopentane according to its boiling point and solubility.

[0049] The polyether polyol, diisocyanate, and organic solvent in the present invention are common substances in the art. The organic solvent is selected from one or more of ethanol, isopropanol, tetrahydrofuran, and ethyl acetate according to the substance to be dissolved.

[0050] The function of the water scavenger in the present invention is to effectively absorb the water in the reaction system, thereby preventing the interference of water on the reaction and promoting the smooth progress of the reaction. The presence of water causes the hydrolysis reaction of the borate ester, reducing the yield or affecting the reaction selectivity. Therefore, by using a water scavenger, the efficiency of borate ester synthesis and the purity of the product can be improved. For the above purposes, the present invention preferably uses anhydrous magnesium sulfate as the water scavenger.

[0051] For the present invention, the relevant dosages of boric acid monomer, monomer containing both vicinal diol and primary alcohol, low-boiling solvent, polyether polyol, diisocyanate and organic solvent can be obtained through testing for the purpose of the present invention. Preferably, the molar ratio of boric acid monomer to the monomer containing both vicinal diol and primary alcohol is 1:2 - 1:5; the mass ratio of boric acid monomer to organic solvent is preferably 1:9 - 3:7; the mass ratio of water scavenger to boric acid monomer is preferably 1:2 - 3:2, and the mass ratio of the boric acid ester chain extender solid to low-boiling solvent is preferably 1:9 - 3:7. The molar ratio of polyether polyol, chain extender containing a single boric acid ester bond, diisocyanate, organometallic or tertiary amine catalyst is preferably 1:0.5:3.0:0.0001 - 1:1.5:4.5:0.0001.

[0052] In the present invention, the low-boiling solvent needs to be removed, and the low-boiling solvent can be removed by standing still for 8 - 24 h under negative pressure at 60 - 80 °C.

[0053] The organometallic or tertiary amine catalyst in the present invention is a conventional selection in the art, and is preferably one or more of dibutyltin dilaurate, triethylenediamine, stannous octoate, zinc isooctoate, bismuth naphthenate.

[0054] In the present invention, the one-component moisture-curing polyurethane prepolymer with an -NCO reserve of 4 - 8 wt.% means that the mass fraction of the isocyanate group (-NCO) in the one-component moisture-curing polyurethane prepolymer is 4 - 8 wt.%. The -NCO reserve is controlled by the addition amount of the boric acid ester chain extender. The more boric acid ester chain extender is added, the lower the -NCO reserve.

[0055] The relevant test methods in the examples of the present invention are as follows:

[0056] For the mechanical property test, a universal material testing machine is used to characterize the tensile properties of the original sample and the repaired sample. The sample film with a thickness of 0.5 - 0.8 mm is cut into type 3 dumbbell-shaped specimens according to GB / T 528 - 2009, with dimensions of 4 × 75 mm, a gauge length of 16 mm, a tensile rate of 500 mm / min, a test temperature of 25 ± 2 °C, and a humidity of 60 ± 10%. Each sample is repeated at least 3 times, and the average value is taken.

[0057] For the self-healing property test, type 3 dumbbell-shaped specimens are cut according to the national standard GB / T 528 - 2009. After the specimens are cut in the middle, they are placed in an oven at 60 °C for 4 h under the condition that the cut surfaces are in contact to obtain the corresponding repaired samples. The tensile strength of the specimen before repair is denoted as σ1, the tensile strength of the specimen after repair is denoted as σ2, and the self-healing efficiency is denoted as η, where η = σ2 / σ1 × 100%. (Reference can be made to the invention patent CN112979919A)

[0058] Degradation performance test: Take 2.0 - 2.5 g of polyurethane sample film with a thickness less than 2 mm, and record its mass as m1. Place the sample in 0.1 mol / L hydrochloric acid solution, and let it stand for 24 h at 25 °C and then take it out. Let it stand in an oven at 60 °C for 24 h and weigh it, and record it as m2. The degradation rate is δ = (m1 - m2) / m1 × 100%.

[0059] Example 1

[0060] A preparation method of self-healing and degradable 1C-MCPU containing a single dynamic borate bond, comprising the following steps:

[0061] Synthesis of borate chain extender: Dissolve 13.8 g of 4-hydroxybenzeneboronic acid (0.1 mol) in 55.2 g of tetrahydrofuran, then slowly add 26.8 g of 1,2,6-hexanetriol (0.2 mol) and then add 18 g of anhydrous magnesium sulfate. Heat the mixed dispersion to 60 °C and reflux for 24 h, then cool to 25 °C and filter to remove magnesium sulfate to obtain a clear mixed solution containing the borate chain extender.

[0062] Purification of borate chain extender: Heat the mixed solution to 60 °C and distill off tetrahydrofuran under reduced pressure to obtain a white solid containing the borate chain extender. Mix it with ether in a mass ratio of 3:7 and wash it ultrasonically three times. Place the filtered solid in a vacuum oven at 80 °C under negative pressure for 18 h to remove ether, and finally obtain 22.9 g of 1C-MCPU chain extender containing a single borate bond, with a yield of 96.8%.

[0063] Preparation of 1C-MCPU containing borate bond: Mix 25 g of polypropylene glycol and 20 g of polytetrahydrofuran diol (-OH in total 0.045 mol) with 15.0 g of isophorone diisocyanate (-NCO in total 0.135 mol), add 0.06 g of dibutyltin dilaurate (1×10 -4 mol), then heat to 75 °C and react for 3 h. After the prepolymerization is completed, add 5 mL of DMF solution containing 3.6 g of borate bond chain extender to make the chain extension complete, and leave 4 wt.% of -NCO in the 1C-MCPU prepolymer. Pour the prepolymer into a mold and cure it at 25 °C and a relative humidity of 60% for 72 h to obtain self-healing and degradable 1C-MCPU containing a single dynamic borate bond.

[0064] The borate chain extender in Example 1 was tested by nuclear magnetic resonance hydrogen spectrum with deuterated DMSO as the solvent, as Figure 1Shown as follows: 9.80 (s, H), 7.52 (s, 2H), 6.78 (s, 2H), 4.51 (m, H), 4.35 (m, 2H), 3.85 (q, H), 3.41 (q, 2H), 1.59 (m, 2H), 1.45 (m, 4H). Additionally, the signal peaks at chemical shifts of 3.33 ppm and 2.50 ppm are the absorption peaks of a small amount of water and the solvent DMSO respectively. There are no other impurity peaks besides this, and the test results are completely matched with the molecular structure.

[0065] Example 2

[0066] A preparation method of a self-healing and degradable 1C-MCPU containing a single dynamic borate ester bond, comprising the following steps:

[0067] Synthesis of the borate ester chain extender: Dissolve 13.8 g of 4-hydroxybenzeneboronic acid (0.1 mol) in 124.2 g of ethanol, then slowly add 18.6 g of glycerol (0.2 mol) and then add 10 g of anhydrous magnesium sulfate. The mixed dispersion is heated to 60 °C and refluxed for 12 h, and then cooled to 25 °C. After filtering off the magnesium sulfate, a clear mixed solution containing the borate ester chain extender is obtained.

[0068] Purification of the borate ester chain extender: The mixed solution is heated to 40 °C and the organic solvent is removed by vacuum distillation to obtain a white solid containing the borate ester chain extender. It is mixed with diethyl ether in a mass ratio of 1:9 and ultrasonically washed three times. The solid obtained by filtration is placed in a vacuum oven at 60 °C under negative pressure conditions for 19 h to remove diethyl ether. Finally, 16.8 g of a 1C-MCPU chain extender containing a single borate ester bond is obtained, and the yield is 86.7%.

[0069] Preparation of 1C-MCPU containing a borate ester bond: Mix 25 g of polypropylene glycol and 20 g of polytetrahydrofuran diol (-OH in total 0.045 mol) with 22.5 g of isophorone diisocyanate (-NCO in total 0.2025 mol), add 0.06 g of dibutyltin dilaurate (1×10 -4 mol), and then heat to 75 °C and continuously react for 3 h. After the prepolymerization is completed, add 5 mL of a DMF solution containing 4 g of the borate ester bond-containing chain extender. After complete chain extension, 7 wt.% of -NCO is reserved in the 1C-MCPU prepolymer. The prepolymer is poured into a mold and cured at 25 °C and a relative humidity of 60% for 72 h to obtain a self-healing and degradable 1C-MCPU containing a single dynamic borate ester bond.

[0070] Example 3

[0071] A preparation method of a self-healing and degradable 1C-MCPU containing a single dynamic borate ester bond, comprising the following steps:

[0072] Synthesis of borate chain extender: Dissolve 15.2 g of 4-hydroxymethylphenylboronic acid (0.1 mol) in 35.5 g of isopropanol. Then slowly add dropwise 53.1 g of 1,2,4-butanetriol (0.5 mol), and then add 20 g of anhydrous magnesium sulfate. Heat the mixed dispersion to 80 °C and reflux under condensation for 24 h. Then cool to 25 °C, filter to remove magnesium sulfate, and obtain a clear mixed solution containing the borate chain extender.

[0073] Purification of borate chain extender: Heat the mixed solution to 60 °C and distill off isopropanol under reduced pressure to obtain a white solid containing the borate chain extender. Mix it with petroleum ether at a mass ratio of 3:7 and wash it ultrasonically three times. Place the solid obtained by filtration in a vacuum oven at 80 °C under negative pressure for 24 h to remove petroleum ether. Finally, 20.5 g of 1C-MCPU chain extender containing a single borate bond is obtained, and the yield is 92.4%.

[0074] Preparation of 1C-MCPU containing borate bond: Mix 25 g of polypropylene glycol and 20 g of polytetrahydrofuran diol (-OH in total 0.045 mol) with 15.0 g of isophorone diisocyanate (-NCO in total 0.135 mol), add 0.003 g of triethylenediamine (3×10 -5 mol), then heat to 75 °C and react continuously for 3 h. After the prepolymerization is completed, add 5 mL of a DMF solution containing 3.3 g of the borate bond chain extender to make the chain extension complete, and leave -NCO = 4 wt.% in the 1C-MCPU prepolymer. Pour the prepolymer into a mold and cure it at 25 °C and a relative humidity of 60% for 24 h to obtain a self-healing and degradable 1C-MCPU containing a single dynamic borate bond.

[0075] Example 4

[0076] A preparation method of a self-healing and degradable 1C-MCPU containing a single dynamic borate bond, comprising the following steps:

[0077] Synthesis of borate chain extender: Dissolve 18.0 g of (4-(3-hydroxypropyl)phenyl)boronic acid (0.1 mol) in 72.0 g of tetrahydrofuran. Then slowly add dropwise 40.3 g of 1,2,6-hexanetriol (0.3 mol), and then add 15 g of anhydrous magnesium sulfate. Heat the mixed dispersion to 70 °C and reflux under condensation for 18 h. Then cool to 25 °C, filter to remove magnesium sulfate, and obtain a clear mixed solution containing the borate chain extender.

[0078] Purification of borate chain extender: The mixed solution was heated to 60 °C and distilled under reduced pressure to remove tetrahydrofuran, obtaining a white solid containing the borate chain extender. It was mixed with n-pentane at a mass ratio of 2:8 and ultrasonically washed three times. The solid obtained by filtration was placed in a vacuum oven at 80 °C under negative pressure conditions and kept warm for 24 h to remove n-pentane. Finally, 25.3 g of 1C-MCPU chain extender containing a single borate bond was obtained, with a yield of 90.8%.

[0079] Preparation of 1C-MCPU containing borate bond: 25 g of polypropylene glycol and 20 g of polytetrahydrofuran diol (-OH in total 0.045 mol) were mixed with 17.5 g of isophorone diisocyanate (-NCO in total 0.1575 mol), and 0.02 g of dibutyltin dilaurate (3×10 -5 mol) was added. Then the temperature was raised to 75 °C and the reaction continued for 3 h. After the prepolymerization was completed, 5 mL of DMF solution containing 2.7 g of borate bond chain extender was added. After complete chain extension, 6 wt.% of -NCO was reserved in the 1C-MCPU prepolymer. The prepolymer was poured into a mold and cured at 25 °C and a relative humidity of 60% for 48 h to obtain self-healing and degradable 1C-MCPU containing a single dynamic borate bond.

[0080] Example 5

[0081] A preparation method of self-healing and degradable 1C-MCPU containing a single dynamic borate bond, comprising the following steps:

[0082] Synthesis of borate chain extender: 13.8 g of 4-hydroxybenzeneboronic acid (0.1 mol) was dissolved in 55.2 g of ethyl acetate. Then, 59.3 g of 1,2,7-heptanetriol (0.4 mol) was slowly added dropwise, and 18 g of anhydrous magnesium sulfate was added. The mixed dispersion was heated to 60 °C and refluxed under condensation for 24 h. Then it was cooled to 25 °C and filtered to remove magnesium sulfate, obtaining a clear mixed solution containing the borate chain extender.

[0083] Purification of borate chain extender: The mixed solution was heated to 60 °C and distilled under reduced pressure to remove ethyl acetate, obtaining a white solid containing the borate chain extender. It was mixed with isopentane at a mass ratio of 3:7 and ultrasonically washed three times. The solid obtained by filtration was placed in a vacuum oven at 80 °C under negative pressure conditions and kept warm for 18 h to remove isopentane. Finally, 22.4 g of 1C-MCPU chain extender containing a single borate bond was obtained, with a yield of 89.4%.

[0084] Preparation of 1C-MCPU containing borate bond: 25 g of polypropylene glycol and 20 g of polytetrahydrofuran diol (-OH in total 0.045 mol) were mixed with 15.0 g of isophorone diisocyanate (-NCO in total 0.135 mol), and 0.06 g of dibutyltin dilaurate (1×10 -4After (0.1 mol), the temperature was raised to 75 °C and the reaction was continued for 3 h. After the prepolymerization was completed, 5 mL of a DMF solution containing 3.8 g of a chain extender with a borate ester bond was added. After the chain extension was complete, 4 wt.% of -NCO was reserved in the 1C-MCPU prepolymer. The prepolymer was poured into a mold and cured at 25 °C and a relative humidity of 60% for 72 h to obtain a self-healing and degradable 1C-MCPU containing a single dynamic borate ester bond.

[0085] Comparative example

[0086] A preparation method of a self-healing and degradable 1C-MCPU containing a dual dynamic borate ester bond, comprising the following steps:

[0087] Synthesis of the borate ester chain extender: 16.6 g of 1,4-diphenylboronic acid (0.1 mol) was dissolved in 55.2 g of tetrahydrofuran. Thereafter, 23.7 g of 1,2,6-hexanetriol (0.4 mol) was slowly added dropwise, and then 18 g of anhydrous magnesium sulfate was added. The mixed dispersion was heated to 60 °C and refluxed under condensation for 24 h. Thereafter, it was cooled to 25 °C and filtered to remove magnesium sulfate to obtain a clear mixed solution containing the borate ester chain extender.

[0088] Purification of the borate ester chain extender: The mixed solution was heated to 60 °C and the tetrahydrofuran was removed by vacuum distillation to obtain a white solid containing the borate ester chain extender. It was mixed with ether in a mass ratio of 3:7 and ultrasonically washed three times. The solid obtained by filtration was placed in a vacuum oven at 80 °C under negative pressure conditions and kept warm for 18 h to remove ether. Finally, 29.9 g of a 1C-MCPU chain extender containing two borate ester bonds was obtained, and the yield was 82.6%.

[0089] Preparation of 1C-MCPU containing a borate ester bond: 25 g of polypropylene glycol and 20 g of polytetrahydrofuran diol (-OH in total 0.045 mol) were mixed with 15.0 g of isophorone diisocyanate (-NCO in total 0.135 mol), and 0.06 g of dibutyltin dilaurate (1×10 -4 mol) was added. Then the temperature was raised to 75 °C and the reaction was continued for 3 h. After the prepolymerization was completed, 5 mL of a DMF solution containing 5.1 g of a chain extender with a dual borate ester bond was added. After the chain extension was complete, 4 wt.% of -NCO was reserved in the 1C-MCPU prepolymer. The prepolymer was poured into a mold and cured at 25 °C and a relative humidity of 60% for 72 h to obtain a self-healing and degradable 1C-MCPU containing a single dynamic borate ester bond.

[0090] Table 1 shows the test results of various properties of Examples 1-5 and the comparative example.

[0091] Table 1

[0092]

[0093] In Example 1, the chain extender used for preparing 1C-MCPU was prepared from 4-hydroxybenzeneboronic acid and 1,2,6-hexanetriol, and its structure contains only a single dynamic borate ester bond; the chain extender used in the comparative example was prepared from 1,4-diphenylboronic acid and 1,2,6-hexanetriol, and its structure contains two dynamic borate ester bonds. The proportions of polyether polyol, isocyanate and borate ester chain extender used for preparing 1C-MCPU in Example 1 and the comparative example were the same, and the -NCO content of the prepolymer and the curing method were also the same. As can be seen from Table 1, the tensile strengths of the two 1C-MCPUs were basically the same with no obvious difference, indicating that the number of borate ester bonds in the chain extender has no obvious effect on the mechanical properties of the material.

[0094] After cutting the samples with a blade, under the condition of a wet cross-section at 60 °C, the samples of Example 1 and the comparative example could both repair mechanical damage within 4 h. This is because the borate ester on the material cross-section can be hydrolyzed to form boric acid and re-dehydrated to form borate ester bonds during the drying process. During the borate ester exchange process, the polymer molecular chains re-diffuse and arrange to repair mechanical damage. The mechanical property test results show that both samples can achieve a high self-healing efficiency after the first damage repair. The self-healing efficiencies of the polyurethanes in Example 1 and the comparative example were 97.4% and 98.7% respectively, indicating that the material can reach a high repair efficiency under mild conditions, and the mechanical properties after repair can still meet the use requirements of the original scenario.

[0095] When the two samples were placed in a 0.1 mol / L hydrochloric acid solution, the borate ester bonds in the polymer main chain were hydrolyzed and broken under acidic conditions, and the polymer molecular weight decreased, enabling the material to achieve a degradation rate of more than 85% after 24 h. The test results show that 1C-MCPU containing borate ester can achieve a high degradation rate under mild conditions, which is beneficial to reducing the environmental pollution caused by damaged and discarded materials.

[0096] During the preparation of 1C-MCPU, the molar amounts of the borate chain extender used in Example 1 and the comparative example were basically the same. The borate chain extender used in the comparative example contained two borate bonds, while the borate chain extender used in Example 1 contained only a single borate bond, indicating that the content of borate bonds in the one-component moisture-curing polyurethane of Example 1 was only half that of the comparative example. The test results showed that there was no significant difference in the repair efficiency and degradation rate after the first damage of the two samples, indicating that 1C-MCPU prepared with a single borate chain extender could still maintain excellent self-healing and degradation properties. Moreover, the amount of 1,2,6-hexanetriol used in Example 1 for preparing the chain extender was only half that of the comparative example, which was beneficial to reducing the preparation cost. However, as the number of damage-repair cycles of 1C-MCPU increased and the samples underwent multiple wet-dry processes, the self-healing efficiency of the comparative example sample decreased significantly, only reaching 41.6%; in contrast, the self-healing efficiency of the sample in the application example did not decrease significantly and remained at a relatively high level, reaching 90.4%. In Comparative Example 1, the chain extender used for C-MCPU was prepared from 1,4-diphenylboric acid and 1,2,6-hexanetriol, and all the boric acid groups in 1,4-diphenylboric acid were converted into borate bonds with dynamic activity. During the repeated self-healing process, as the material underwent multiple wet-dry processes and the borate bonds in the molecular chain broke and reorganized, 1,4-diphenylboric acid with high polarity and good water solubility would precipitate from the polymer main chain and dissolve in water, reducing the borate bonds in the molecular chain and lowering the molecular weight, resulting in a significant reduction in the mechanical properties and self-healing efficiency of the material. On the contrary, in Example 1, both ends of the borate chain extender were incorporated into the polymer main chain, and its structure contained only a single borate bond. During the wet-dry self-healing process, there would be no loss of small molecule monomers, which would reduce the number of borate bonds and lead to a decrease in mechanical properties and self-healing efficiency. Therefore, it could greatly increase the number of times the material could be reused, extend its service life, and reduce resource waste.

[0097] As can be seen from the above, the present invention prepared a self-healing and degradable 1C-MCPU containing a single borate bond. The cured one-component moisture-curing polyurethane had excellent mechanical properties and could degrade or repair mechanical damage under mild conditions. Moreover, the 1C-MCPU prepared in the present invention had excellent repeated self-healing function and could still maintain a relatively high self-healing efficiency and mechanical strength after multiple damage-repair cycles, which was beneficial to improving the safety and reliability of the material and extending its service life, while reducing environmental pollution after the material was discarded.

[0098] The implementation manners of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement manners and are all included in the protection scope of the present invention.

Claims

1. A self-repairing, degradable, one-component, moisture-curable polyurethane containing a single borate ester bond, characterized in that: Has the following structural formula: Wherein m = 33-38, n = 25-30; R1 is One of the following: In R1, the oxygen atom is connected to the carbon atom in the carbonyl group by a single bond; R2 is one of the following groups: The carbon atom in R2 is connected to the carbon atom on the borane ring through a single bond.

2. The method for preparing a self-repairing, degradable, one-component moisture-curing polyurethane containing a single borate ester bond according to claim 1, characterized in that The steps include: (1) dissolving a boric acid monomer in an organic solvent, adding a monomer containing both a vicinal diol and a primary alcohol, and then adding a dehydrating agent, heating the mixed dispersion to 60-80° C., condensing and refluxing for 12-24 hours, cooling to 25-40° C., filtering and removing the dehydrating agent, and obtaining a mixed solution containing a borate ester chain extender; (2) heating the mixed solution containing the borate chain extender to 40-60° C. and removing the organic solvent by distillation under reduced pressure to obtain a borate chain extender solid, and washing it with a low boiling point solvent to obtain a chain extender containing a single borate bond; (3) reacting a chain extender containing a single borate bond, an organic metal or tertiary amine catalyst, a polyether polyol and a diisocyanate to obtain a one-component moisture-curable polyurethane prepolymer having an -NCO reserve of 4-8 wt.%; curing the prepolymer at a temperature of 25-35°C and a humidity of 60-80% for 24-72 hours to obtain a self-healing, degradable one-component moisture-curable polyurethane containing a single borate bond.

3. The method for preparing a self-repairing, degradable, single-component moisture-curing polyurethane containing a single borate ester bond according to claim 2, characterized in that: The boric acid monomer is one or more of 4-hydroxyphenylboric acid, 4-hydroxymethylphenylboric acid and (4-(3-hydroxypropyl)phenyl)boric acid.

4. The method for preparing a self-repairing, degradable, single-component moisture-curing polyurethane containing a single borate ester bond according to claim 2, characterized in that: The monomer containing both vicinal diol and primary alcohol is one or more of propylene glycol, 1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,7-heptanetriol and 1,2,8-octantriol; The dehydrating agent is anhydrous magnesium sulfate.

5. A method for preparing a self-repairing, degradable, one-component moisture-curing polyurethane containing a single borate ester bond according to claim 2, 3 or 4, characterized in that: The molar ratio of the boric acid-containing monomer to the monomer containing both vicinal diol and primary alcohol is 1:2-1:5; the mass ratio of the boric acid monomer to the organic solvent is 1:9-3:7; the mass ratio of the water remover to the boric acid monomer is 1:2-3:2;.

6. The method for preparing a self-repairing, degradable, single-component moisture-curing polyurethane containing a single borate ester bond according to claim 2, characterized in that: The organic solvent is one or more of ethanol, isopropanol, tetrahydrofuran and ethyl acetate.

7. The method for preparing a self-repairing, degradable, one-component moisture-curing polyurethane containing a single borate ester bond according to claim 2, characterized in that: The low boiling point solvent is one or more of ether, petroleum ether, n-pentane and isopentane.

8. A method for preparing a self-repairing, degradable, one-component moisture-curing polyurethane containing a single borate ester bond according to claim 2 or 7, characterized in that: The mass ratio of the borate chain extender solid to the low boiling point solvent is 1:9-3:7; the low boiling point solvent is removed after standing for 8-24 hours under negative pressure at 60-80°C.

9. The method for preparing a self-repairing, degradable, single-component moisture-curing polyurethane containing a single borate ester bond according to claim 2, characterized in that: The molar ratio of the polyether polyol, the chain extender containing a single borate ester bond, the diisocyanate, and the organic metal or tertiary amine catalyst is 1:0.5:3.0:0.0001-1:1.5:4.5:0.0001.

10. The method for preparing a self-repairing, degradable, one-component moisture-curing polyurethane containing a single borate bond according to claim 2, characterized in that: The organic metal or tertiary amine catalyst is one or more of dibutyltin dilaurate, triethylenediamine, stannous octoate, zinc isooctanoate, and bismuth cyclohexaneate.

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