Single-component moisture-curing polyurethane chain extender containing single dynamic boric acid ester bond and preparation method of single-component moisture-curing polyurethane chain extender

Abstract

The invention discloses a single-component moisture-curing polyurethane chain extender containing a single dynamic borate bond and a preparation method of the single-component moisture-curing polyurethane chain extender. The preparation method comprises the following steps: dissolving a boric acid monomer in an organic solvent, adding a monomer containing vicinal diol and primary alcohol and a water removal agent, heating to 60-80 DEG C, condensing and refluxing for 12-24 hours, cooling to 25-40 DEG C, and removing the water removal agent to obtain a mixed solution containing a boric acid ester chain extender; and heating the mixed solution containing the boric acid ester chain extender to 40-60 DEG C, removing the organic solvent to obtain the boric acid ester chain extender, washing with a low-boiling-point solvent, and filtering. The chain extender provided by the invention only contains a single boric acid ester bond, so that the single-component moisture-cured polyurethane prepared from the chain extender does not have the conditions of precipitation loss, mechanical property weakening and self-repairing property reduction of micromolecular boric acid monomers due to repeated repair in the use process, and the safety and reliability of the material can be improved.

Description

Technical Field

[0001] The invention relates to a single-component moisture-curing polyurethane chain extender, in particular to a single-component moisture-curing polyurethane chain extender containing a single dynamic 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, which is mainly prepared from polyols, diisocyanates and chain extenders. It is cured by the reaction of the -NCO group in the prepolymer with moisture in the air or substrate. It has the characteristics of easy construction, low VOC, no strict requirements on the moisture content of the base surface, excellent elasticity and high and low temperature resistance, etc. It is widely used in industrial fields such as adhesives, sealants and coatings.

[0003] During the use of 1C-MCPU, it will be affected by various factors, and microscopic defects or mechanical damage will occur inside or on its surface, affecting the safety and reliability of the material and shortening its service life. In addition, 1C-MCPU has stable chemical properties and is non-degradable in its natural state. Random abandonment will cause serious pollution to the environment and endanger environmental safety. Therefore, after the material fails, it needs to be scrapped and recycled in a centralized manner. The whole process consumes a lot of energy and is costly, which will cause a lot of waste of resources. Reversible dynamic bonds can break and reorganize under specific conditions, during which the polymer molecular chains diffuse and rearrange, thereby repairing the mechanical damage or internal defects of the material. Moreover, reversible dynamic bonds can give the material degradable properties, allowing the polymer material to degrade under specific conditions and reduce harm to the environment.

[0004] The prior art uses chain extenders containing reversible dynamic bonds to prepare a series of polymer materials, which enable them to achieve self-repair or degrade under specific conditions. For example, Chinese invention patent application CN116845351A uses a chain extender containing DA bonds to introduce reversible dynamic bonds into the polymer main chain, so that the polymer material can be heated at 70-90°C to repair mechanical damage and restore initial performance. Chinese invention patent application CN116003730A uses 2,4-diamino-6-hydroxypyrimidine as a chain extender to introduce multiple hydrogen bonds into the polymer main chain, so that the material can repair mechanical damage at 120°C. Chinese invention patent CN112409561B prepares a degradable polyurethane containing dynamic bonds, and the material can only begin to degrade in a solution with a sodium hydroxide concentration greater than 1 mol / L. Although the above-mentioned prior arts all use chain extenders containing reversible dynamic bonds to give the material self-repairing properties or degradable properties, the above-mentioned repair or degradation conditions are harsh and not conducive to practical applications. Therefore, it is very necessary to find a dynamic bond that can be broken and reorganized under mild conditions.

[0005] The borate bond has dynamic activity and can be hydrolyzed under mild conditions to form boric acid and vicinal diols, or dehydrated to reform the borate bond. The use of a chain extender containing a borate group to prepare 1C-MCPU can not only use its dynamic exchange characteristics to give the material self-healing properties, so that it can repair mechanical damage under mild conditions, but also use its easy hydrolysis characteristics to give the material degradable properties. By hydrolyzing the borate under mild conditions, the polymer main chain is broken and the molecular weight is reduced, so that degradation or recycling can be achieved. Chinese invention patent CN114752030B uses a chain extender containing a borate bond to prepare a self-healing polyurethane, so that the material can repair mechanical damage under room temperature aqueous conditions and achieve a high repair efficiency. However, the chain extender is prepared from 1,4-diphenylboronic acid, in which the boric acid groups are converted into borate bonds. During use, the hydrolysis of the borate bond will cause the 1,4-diphenylboronic acid to precipitate and lose, which will not only reduce the borate bond content and weaken the self-healing performance, but also reduce the molecular weight of the polymer and weaken its mechanical properties.

[0006] The prior art also has a method of preparing a polymer material by preparing a chain extender containing two borate ester bonds from 1,4-diphenylboronic acid or its derivatives. For example, Chinese invention patent application CN112521583A and Chinese invention patent application CN117229472A both use a borate ester chain extender to impart degradation properties to the material. However, the chain extenders used therein all contain two borate ester bonds, and during use, there will be problems such as loss of boric acid monomers, breakage of molecular chains, and degradation of mechanical properties.

[0007] Chinese invention patent application CN115785390 discloses a photocurable polyurethane acrylate prepolymer based on nitrogen-carbon coordinated borate bonds. The polymer is obtained by reacting an isocyanate-terminated compound, a (meth) hydroxyalkyl acrylate and a chain extender containing a nitrogen-carbon coordinated borate bond. Although the preparation method of this technology is conventional polyurethane, the molecular weight can reach a high level, and the dynamic bond used is a NB coordination bond, its mechanical properties and degradation properties need to be improved, and high mechanical strength cannot be achieved. Summary of the invention

[0008] In order to improve the mechanical properties of 1C-MCPU, extend the service life of the material and alleviate the problem of its inability to degrade and pollute the environment after failure and scrapping, the present invention provides a single-component moisture-curing polyurethane chain extender containing a single dynamic borate bond, which can significantly improve the mechanical properties of the material while giving the material self-repair and degradability functions, and a preparation method thereof.

[0009] The purpose of the present invention can be achieved through the following technical solutions:

[0010] A one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond has the following structural formula:

[0011]

[0012] Wherein, R1 is one of the following groups:

[0013]

[0014] R2 is one of the following groups:

[0015]

[0016] The method for preparing the one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond comprises the following steps:

[0017] 1) dissolving a boric acid monomer in an organic solvent, adding a monomer containing both a vicinal diol and a primary alcohol and a dehydrating agent, heating to 60-80° C., condensing and refluxing for 12-24 hours, and then cooling to 25-40° C., removing the dehydrating agent, and obtaining a mixed solution containing a borate ester chain extender;

[0018] 2) heating the mixed solution containing the borate chain extender to 40-60° C., removing the organic solvent to obtain the borate chain extender, washing with a low boiling point solvent and filtering to obtain a single component moisture curing polyurethane chain extender with a single dynamic borate bond.

[0019] To further achieve the purpose of the present invention, preferably, the boronic acid monomer is one or more of 4-hydroxyphenylboric acid, 4-hydroxymethylphenylboric acid and (4-(3-hydroxypropyl)phenyl)boric acid.

[0020] Preferably, 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.

[0021] Preferably, the molar ratio of the boric acid monomer to the monomer containing both a vicinal diol and a primary alcohol is 1:2-1:5.

[0022] Preferably, the organic solvent is one or more of ethanol, isopropanol, tetrahydrofuran, and ethyl acetate; and the dehydrating agent is anhydrous magnesium sulfate.

[0023] Preferably, the mass ratio of the boric acid monomer to the organic solvent is 1:9-3:7; the mass ratio of the water scavenger to the boric acid monomer is 1:2-3:2.

[0024] Preferably, the low boiling point solvent is one or more of diethyl ether, petroleum ether, n-pentane and isopentane.

[0025] Preferably, the mass ratio of the borate ester chain extender to the low boiling point solvent is 1:9-3:7.

[0026] Preferably, the organic solvent is removed by distillation under reduced pressure.

[0027] The low boiling point solvent is removed after standing at 60-80° C. under negative pressure for 8-24 hours.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0029] 1. The chain extender containing a dynamic borate bond in the present invention contains only a single borate bond. When preparing 1C-MCPU, both ends of the chain extender are connected to the polymer main chain through carbamate bonds, and the borate bonds therein can achieve dynamic exchange through hydrolysis or dehydration condensation, giving 1C-MCPU self-repair and degradable properties; its structure contains only a single borate bond, and the 1C-MCPU prepared therefrom will not lose small molecules during use, resulting in a reduction in borate bonds, and a decrease in the mechanical properties and self-repair efficiency of the material;

[0030] 2. The 1C-MCPU prepared by the borate ester bond-containing chain extender of the present invention can quickly repair mechanical damage at 60°C and can be degraded in a 0.1 mol / L hydrochloric acid solution. The conditions required for self-repair and degradation of the material are mild, and the whole process has low energy consumption and little pollution.

[0031] 3. The present invention can change the structure of the borate ester bond-containing chain extender by changing the type of monomer used in preparing the chain extender, thereby adjusting the aggregation state of the polymer molecular chain and the microphase separation structure of the material, thereby changing the mechanical properties of 1C-MCPU to meet the use requirements in different scenarios;

[0032] 4. The 1C-MCPU prepared by the chain extender of the present invention can still have a high repair efficiency and maintain excellent mechanical properties after multiple damage-repairs, which is beneficial to improving the safety and reliability of the material and extending its service life;

[0033] 5. The chain extender containing a single borate ester bond in the present invention is simple to prepare, the synthesis conditions are mild, and the solvent used in the preparation process can be reused, which is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a hydrogen nuclear magnetic resonance spectrum of the chain extender containing a single dynamic borate ester bond prepared in Example 1;

[0035] Figure 2 is the hydrogen nuclear magnetic resonance spectrum of the chain extender containing two dynamic borate ester bonds in the comparative example;

[0036] Figure 3 This is the stress-strain test curve of C-MCPU in Application Example 1. DETAILED DESCRIPTION

[0037] In order to better understand the present invention, the present invention is explained below in conjunction with specific embodiments, but the embodiments do not constitute a limitation on the scope of protection of the claims of the present invention. Based on the embodiments, other embodiments obtained by those skilled in the art without making any creative work all fall within the scope of protection of the present invention.

[0038] From the perspective of molecular structure design, the present invention proposes a 1C-MCPU chain extender containing a single dynamic borate bond. The goal is first to enable the application of the chain extender to improve the mechanical properties of the material, while allowing the material to have self-repair and degradable properties; secondly, the 1C-MCPU prepared by the chain extender will not have small molecule loss during use, resulting in weakened mechanical properties of the material and reduced self-repair efficiency, so that it can achieve multiple damage-repair cycles, greatly improving the safety and reliability of the material. The core goal is that the borate chain extender prepared by the present invention can achieve the improvement of mechanical properties while giving the material self-repair and degradable functions.

[0039] To this end, the present invention uses phenylboronic acid derivatives and monomers containing both vicinal diols and primary alcohols as raw materials, and utilizes the characteristics that the boric acid group can dehydrate and condense with the vicinal diol to form a borate bond, to prepare a chain extender containing a single dynamic borate bond, which can give 1C-MCPU excellent self-repair performance and degradable performance. In the preparation process of 1C-MCPU, both ends of the chain extender are connected to the polymer main chain, and its structure contains only a single borate bond. Therefore, during use, there will be no loss of small molecules, resulting in a decrease in the number of borate bonds, weakened mechanical properties, and reduced self-repair efficiency, thereby increasing the number of self-repair cycles of material damage-repair, improving safety and reliability, and extending service life.

[0040] Therefore, the present invention provides a one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond, having the following structural formula:

[0041]

[0042] Wherein, R1 is one of the following groups:

[0043]

[0044] R2 is one of the following groups:

[0045]

[0046] The method for preparing the one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond comprises the following steps:

[0047] 1) dissolving a boric acid monomer in an organic solvent, adding a monomer containing both a vicinal diol and a primary alcohol and a dehydrating agent, heating to 60-80° C., condensing and refluxing for 12-24 hours, and then cooling to 25-40° C., removing the dehydrating agent, and obtaining a mixed solution containing a borate ester chain extender;

[0048] 2) heating the mixed solution containing the borate chain extender to 40-60° C., removing the organic solvent to obtain the borate chain extender, washing with a low boiling point solvent and filtering to obtain a single component moisture curing polyurethane chain extender with a single dynamic borate bond.

[0049] Regarding the above-mentioned one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond and the preparation method, the present invention is characterized in that the borate ester bond in the one-component moisture-curable polyurethane prepared by using the one-component moisture-curable polyurethane chain extender containing a dynamic borate ester bond can react with water under acidic conditions to break the bond to generate boric acid and vicinal diols, interrupt the polymer molecular chain, and reduce the polymer molecular weight, thereby achieving the one-component moisture-curable polyurethane being degradable under weak acid and aqueous conditions.

[0050] At the same time, the molecular structure of the one-component moisture-curing polyurethane chain extender containing a dynamic borate bond of the present invention contains a rigid structure, and the other end has a longer carbon chain, which is conducive to stacking to form a dense hard segment phase, improve the microphase separation structure, and increase the density of physical cross-linking points, ultimately enabling the one-component moisture-curing polyurethane to achieve excellent mechanical properties.

[0051] The chain extender of the present invention introduces a dynamic borate bond into the polymer molecular chain. When the material is discarded, the characteristics of the borate bond breaking and reorganization can be used to degrade the polymer under specific conditions, and the degradation products can be recycled and reused to prepare new materials. In addition, the borate bond degradation conditions are mild, and degradation can be achieved under weak acid aqueous conditions without causing harm to the environment. These two factors together give the material environmentally friendly characteristics.

[0052] Based on the above characteristics, for the preparation method, the main measure is that the boric acid monomer reacts with the monomer containing both the vicinal diol and the primary alcohol in the presence of an organic solvent and a dehydrating agent to obtain a mixed solution containing a borate ester chain extender. Under this goal, the specific boric acid monomer and the monomer containing both the vicinal diol and the primary alcohol can be obtained by selecting according to the reaction mechanism. The preferred boric acid monomer of the present invention is one or more of 4-hydroxyphenylboric acid, 4-hydroxymethylphenylboric acid and (4-(3-hydroxypropyl)phenyl)boric acid. The monomer containing both the vicinal diol and the 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 molar ratio of the boric acid monomer to the monomer containing both the vicinal diol and the primary alcohol is 1:2-1:5. As for the selection of the organic solvent and the dehydrating agent, it can be obtained from the purpose of the invention in combination with the reaction mechanism. The preferred organic solvent is one or more of ethanol, isopropanol, tetrahydrofuran and ethyl acetate; the dehydrating agent is anhydrous magnesium sulfate. The dosage of the organic solvent and the water removing agent can be obtained through experiments. The low boiling point solvent and the removal process after use and the purification process are all conventional practices in the art.

[0053] The relevant testing methods in the embodiments of the present invention are as follows:

[0054] Mechanical properties test: a universal material testing machine was used to characterize the tensile properties of the original and repaired samples. The sample films with a thickness of 0.5-0.8 mm were cut into 3 types of dumbbell-shaped specimens according to GB / T 528-2009, with a size 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 was repeated at least 3 times and the average value was taken.

[0055] Self-repair performance test, according to the national standard GB / T 528-2009, cut into 3 types of dumbbell-shaped splines, cut the splines from the middle, keep the cross section moist and in contact with each other, and place them in a 60℃ oven for 4 hours to obtain the corresponding repaired samples. The tensile strength of the spline before repair is recorded as σ1, the tensile strength of the spline after repair is recorded as σ2, and the self-repair efficiency is recorded as η, where η=σ2 / σ1×100%. (Refer to invention patent CN112979919A)

[0056] Degradation performance test, take 2.0-2.5g of polyurethane sample film with a thickness of less than 2mm, and record its mass as m1. Place the sample in a 0.1mol / L hydrochloric acid solution, let it stand for 24h at 25℃ and take it out. Let it stand in a 60℃ oven for 24h and weigh it as m2. The degradation rate is δ=(m1-m2) / m1×100%. This degradation performance test is a common method in this field, see Chen Dongxiang. Preparation and performance study of self-healing and degradable dual-functional polymer materials [D]. Beijing University of Chemical Technology, 2023.

[0057] Example 1

[0058] A method for preparing a 1C-MCPU chain extender containing a single dynamic borate ester bond comprises the following steps:

[0059] Synthesis of borate chain extender: 13.8 g of 4-hydroxyphenylboric acid (0.1 mol) was dissolved in 55.2 g of tetrahydrofuran, and then 26.8 g of 1,2,6-hexanetriol (0.2 mol) was slowly added dropwise, followed by 18 g of anhydrous magnesium sulfate. The mixed dispersion was heated to 60°C and refluxed for 24 h, then cooled to 25°C and filtered to remove magnesium sulfate to obtain a clear mixed solution containing borate chain extender.

[0060] Purification of borate chain extender: The mixed solution was heated to 60°C and distilled under reduced pressure to remove tetrahydrofuran to obtain a white solid containing the borate chain extender. The white solid was mixed with ether in a mass ratio of 3:7 and ultrasonically washed three times before filtration. The filtered solid was placed in a vacuum oven at 80°C under negative pressure for 18 hours to remove the ether. Finally, 22.9 g of 1C-MCPU chain extender containing a single borate bond was obtained with a yield of 96.8%.

[0061] The borate chain extender in Example 1 was tested by H NMR using deuterated DMSO as solvent. Figure 1 As shown: 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). In addition, the signal peaks at the chemical shifts of 3.33ppm and 2.50ppm are the absorption peaks of a small amount of water and solvent DMSO, respectively. There are no other impurity peaks. The test results are completely consistent with the molecular structure.

[0062] Example 2

[0063] A method for preparing a 1C-MCPU chain extender containing a single dynamic borate ester bond comprises the following steps:

[0064] Synthesis of borate chain extender: 13.8 g of 4-hydroxyphenylboric acid (0.1 mol) was dissolved in 124.2 g of ethanol, and then 18.6 g of glycerol (0.2 mol) was slowly added dropwise, followed by 10 g of anhydrous magnesium sulfate. The mixed dispersion was heated to 60°C and refluxed for 12 h, then cooled to 25°C and filtered to remove magnesium sulfate to obtain a clear mixed solution containing borate chain extender.

[0065] Purification of borate chain extender: The mixed solution was heated to 40°C and the organic solvent ethanol was distilled off under reduced pressure to obtain a white solid containing the borate chain extender. The obtained white solid was mixed with ether in a mass ratio of 1:9 and ultrasonically washed three times before filtration. The filtered solid was placed in a vacuum oven at 60°C under negative pressure conditions and kept warm for 19 hours to remove the ether. Finally, 16.8 g of 1C-MCPU chain extender containing a single dynamic borate bond was obtained with a yield of 86.7%.

[0066] Example 3

[0067] A method for preparing a 1C-MCPU chain extender containing a single dynamic borate ester bond comprises the following steps:

[0068] Synthesis of borate chain extender: 15.2 g of 4-hydroxymethylphenylboronic acid (0.1 mol) was dissolved in 35.5 g of isopropanol, and then 53.1 g of 1,2,4-butanetriol (0.5 mol) was slowly added dropwise, followed by 20 g of anhydrous magnesium sulfate. The mixed dispersion was heated to 80°C and refluxed for 24 h, then cooled to 25°C and filtered to remove magnesium sulfate to obtain a clear mixed solution containing borate chain extender.

[0069] Purification of borate chain extender: The mixed solution was heated to 60°C and distilled under reduced pressure to remove isopropanol to obtain a white solid containing borate chain extender, which was mixed with petroleum ether in a mass ratio of 3:7 and ultrasonically washed three times before filtration. The filtered solid was placed in a vacuum oven at 80°C under negative pressure for 24 hours to remove the petroleum ether, and finally 20.5 g of 1C-MCPU chain extender containing a single borate bond was obtained with a yield of 92.4%.

[0070] Example 4

[0071] A method for preparing a 1C-MCPU chain extender containing a single dynamic borate ester bond comprises the following steps:

[0072] Synthesis of borate chain extender: 18.0 g (4-(3-hydroxypropyl)phenyl)boric acid (0.1 mol) was dissolved in 72.0 g tetrahydrofuran, and then 40.3 g 1,2,6-hexanetriol (0.3 mol) was slowly added dropwise, followed by 15 g anhydrous magnesium sulfate. The mixed dispersion was heated to 70°C, condensed and refluxed for 18 h, and then cooled to 25°C, filtered to remove magnesium sulfate, and a clear mixed solution containing borate chain extender was obtained.

[0073] Purification of borate chain extender: The mixed solution was heated to 60°C and distilled under reduced pressure to remove tetrahydrofuran to obtain a white solid containing borate chain extender, which was mixed with n-pentane in a mass ratio of 2:8 and ultrasonically washed three times before filtration. The filtered solid was placed in a vacuum oven at 80°C under negative pressure for 24 hours to remove n-pentane, and finally 25.3 g of 1C-MCPU chain extender containing a single borate bond was obtained with a yield of 90.8%.

[0074] Example 5

[0075] A method for preparing a 1C-MCPU chain extender containing a single dynamic borate ester bond comprises the following steps:

[0076] Synthesis of borate chain extender: 13.8 g of 4-hydroxyphenylboric acid (0.1 mol) was dissolved in 55.2 g of ethyl acetate, and then 59.3 g of 1,2,7-heptanetriol (0.4 mol) was slowly added dropwise, followed by 18 g of anhydrous magnesium sulfate. The mixed dispersion was heated to 60°C and refluxed for 24 h, then cooled to 25°C and filtered to remove magnesium sulfate to obtain a clear mixed solution containing borate chain extender.

[0077] Purification of borate chain extender: The mixed solution was heated to 60°C and distilled under reduced pressure to remove ethyl acetate to obtain a white solid containing borate chain extender, which was mixed with isopentane in a mass ratio of 3:7 and ultrasonically washed twice before filtration. The filtered solid was placed in a vacuum oven at 80°C under negative pressure and kept warm for 18 hours to remove n-pentane, ultimately obtaining 22.4 g of 1C-MCPU chain extender containing a single borate bond with a yield of 89.4%.

[0078] Application Examples

[0079] 25 g of polypropylene glycol with a difunctional average molecular weight of 2000 and 20 g of polytetrahydrofuran diol with a difunctional average molecular weight of 2000 (-OH total 0.045 mol) were mixed and dehydrated under vacuum at 120 °C for 2 h and then cooled to 40 °C. Then 15.0 g of isophorone diisocyanate (-NCO total 0.135 mol) and 100 μL of 0.1 g mL -1 The N,N-dimethylformamide solution of dibutyltin dilaurate was heated to 70°C. During the reaction, the degree of reaction was determined by titrating the residual -NCO. When the residual -NCO reached the theoretical expectation, the prepolymerization was completed. 3.5 g of the bio-based amide chain extender prepared in Example 5 was dissolved in 10 mL of DMF and added to the prepolymerization system after the prepolymerization was completed. At the same time, 100 μL of 0.1 g·mL -1 The DBTDL-DMF solution was heated to 80°C and continued to react. The residual -NCO was titrated continuously during the chain extension stage. When the chain extender was completely consumed and the residual -NCO was 4wt.%, the chain extension was completed to obtain a high-solid-content -NCO-terminated 1C-MCPU prepolymer. It was poured into a polytetrafluoroethylene mold to ensure that the film thickness was about 1mm, and placed at 25°C and a relative humidity of 60% to cure to obtain a colorless and transparent 1C-MCPU.

[0080] Figure 3This is the stress-strain test curve of C-MCPU in Application Example 1. As shown in the figure, the tensile strength of the sample obtained in the Example reached 35.9 MPa, and the elongation at break reached 1702.1%, and both the tensile strength and the elongation at break were at a relatively high level.

[0081] Comparative Example

[0082] A method for preparing a one-component moisture-curable polyurethane chain extender containing two dynamic borate ester bonds comprises the following steps:

[0083] Synthesis of borate chain extender: 16.6 g of 1,4-diphenylboric acid (0.1 mol) was dissolved in 55.2 g of tetrahydrofuran, and then 23.7 g of 1,2,6-hexanetriol (0.4 mol) was slowly added dropwise, followed by 18 g of anhydrous magnesium sulfate. The mixed dispersion was heated to 60°C and refluxed for 24 h, then cooled to 25°C and filtered to remove magnesium sulfate to obtain a clear mixed solution containing borate chain extender.

[0084] Purification of borate chain extender: The mixed solution was heated to 60°C and distilled under reduced pressure to remove tetrahydrofuran to obtain a white solid containing the borate chain extender. The white solid was mixed with ether in a mass ratio of 3:7 and ultrasonically washed three times before filtration. The filtered solid was placed in a vacuum oven at 80°C under negative pressure for 18 hours to remove the ether. Finally, 29.9 g of 1C-MCPU chain extender containing two borate bonds was obtained with a yield of 82.6%.

[0085] 25 g of polypropylene glycol with a difunctional average molecular weight of 2000 and 20 g of polytetrahydrofuran diol with a difunctional average molecular weight of 2000 (-OH total 0.045 mol) were mixed and dehydrated under vacuum at 120 °C for 2 h and then cooled to 40 °C. Then 15.0 g of isophorone diisocyanate (-NCO total 0.135 mol) and 100 μL of 0.1 g mL -1 The N,N-dimethylformamide solution of dibutyltin dilaurate was heated to 70°C. The degree of reaction was determined by titrating the residual -NCO during the reaction. The prepolymerization was completed when the residual -NCO reached the theoretical expectation. 5.1 g of chain extender 10 mL of DMF containing two dynamic borate bonds was added to the prepolymerization system after the prepolymerization was completed. At the same time, 100 μL of 0.1 g mL -1 The DBTDL-DMF solution was heated to 80°C and continued to react. The residual -NCO was titrated continuously during the chain extension stage. When the chain extender was completely consumed and the residual -NCO was 4wt.%, the chain extension was completed to obtain a high-solid-content -NCO-terminated 1C-MCPU prepolymer. It was poured into a polytetrafluoroethylene mold to ensure that the film thickness was about 1mm, and placed at 25°C and a relative humidity of 60% to cure to obtain a colorless and transparent 1C-MCPU.

[0086] Figure 2 It is the hydrogen nuclear magnetic resonance spectrum of the chain extender containing two dynamic borate ester bonds in the comparative example. Figure 2 The chain extender structure contains two dynamic borate bonds. During the preparation of single-component moisture-cured polyurethane, the two ends of the chain extender are fixed in the polymer molecular chain. However, when the dynamic borate and water undergo dynamic exchange, the two borate bonds in the chain extender are disconnected, which may cause the loss of diphenylboronic acid monomers, making it impossible to form borate bonds again, resulting in the breakage of polymer molecular chains and a decrease in molecular weight. The macroscopic manifestation is a weakening of mechanical properties, which in turn creates safety hazards. Figure 1 The chain extender structure contains only a single borate group. During the single-component moisture-curing polyurethane process, both ends of the chain extender will be fixed in the molecular chain by covalent bonds. Even if dynamic exchange occurs, there will be no loss of small molecules. Therefore, the borate bond can be formed again, so that the polymer molecular weight can still reach a high level, and there will be no problem of mechanical property degradation.

[0087] Table 1 shows the performance test results of the application examples and comparative examples.

[0088] Table 1

[0089]

[0090] The chain extender used in the application example is prepared from 4-hydroxyphenylboronic acid and 1,2,6-hexanetriol, and its structure contains only a single dynamic borate bond; the chain extender used in the comparative example is prepared from 1,4-diphenylboronic acid and 1,2,6-hexanetriol, and its structure contains two dynamic borate bonds. The proportions of polyether polyols, isocyanates and borate chain extenders used in the preparation process of 1C-MCPU in the application example and the comparative example are the same, and the prepolymer-NCO content and curing method are also the same. It can be seen from Table 1 that the mechanical strengths of the two 1C-MCPUs are basically the same, with no obvious difference. After the sample was cut with a blade, under the condition of 60°C cross-section wet conditions, the sample strips could repair mechanical damage within 4 hours. This is because the borate in the material absorbs water and breaks to form boric acid, and dehydrates again during the drying process to form borate bonds. During the borate exchange process, the polymer molecular chains diffuse and arrange again to repair mechanical damage. The results of mechanical properties tests show that the self-repair efficiency of both 1C-MCPUs can reach a high level, 96.5% and 94.3% respectively, indicating that the material can achieve self-repair under mild conditions, and the mechanical properties after repair can still meet most usage requirements.

[0091] When the sample was placed in a 0.1 mol / L hydrochloric acid solution, the boric acid ester in the molecular chain absorbed water and broke under acidic conditions, allowing the material to achieve a degradation rate of more than 85% within 24 hours. This shows that the material can also achieve a high degradation rate under mild conditions, which is helpful to alleviate the pollution caused by 1C-MCPU to the environment after it is discarded.

[0092] During the preparation of 1C-MCPU, the molar amount of the borate chain extender used in the application example and the comparative example is basically the same, but the borate chain extender used in the application example of the present invention contains only a single borate bond, indicating that the borate bond content in the application example 1C-MCPU is only half of that in the comparative example. The test found that the repair efficiency and degradation rate after the first damage of the application example were similar to those of the comparative example, indicating that the 1C-MCPU prepared by the present invention containing a single borate chain extender can also maintain excellent self-repair and degradation properties. Moreover, the alcohol monomers used in the preparation of the chain extender of the present invention are relatively small, which is conducive to reducing costs. It should be emphasized that with the increase in the number of damage-repair cycles, the sample undergoes multiple wetting-drying, and the self-repair efficiency of 1C-MCPU in the comparative example drops significantly, only 43.6%; in contrast, the self-repair efficiency of the material in the application example does not drop significantly, and is still at a high level, reaching 89.4%. In the comparative example, the chain extender is prepared from 1,4-diphenylboric acid and 1,2,6-hexanetriol, and the boric acid in 1,4-diphenylboric acid is converted into a borate bond with dynamic activity. During the self-repair process of multiple wet-drying, the borate bond breaks and reorganizes, and the 1,4-diphenylboric acid with higher polarity and better water solubility during the period will precipitate from the polyurethane and dissolve in water, resulting in a reduction in borate bonds in the polymer main chain, a decrease in polymer molecular weight, and a significant reduction in mechanical properties and self-repair efficiency. On the contrary, Application Example 1C-MCPU is prepared from a borate bond chain extender in the present invention, and both ends of the chain extender are connected to the polymer main chain, and its structure contains only a single borate bond. In the self-repair process of wet-drying, there will be no loss of small molecules, resulting in a reduction in the number of borate bonds, and a decrease in mechanical properties and self-repair efficiency, thereby increasing the number of times the material can be reused, extending the service life and reducing resource waste.

[0093] The present invention prepares a 1C-MCPU chain extender containing a single borate ester bond, and the single-component moisture-curing polyurethane prepared by the chain extender can degrade or repair mechanical damage under mild conditions. In addition, the chain extender can give the material an excellent cyclic self-repairing function, so that it can still maintain a high self-repairing efficiency and mechanical strength after multiple damage-repair cycles, which is beneficial to improving the safety and reliability of the material and extending its service life, and reducing the pollution to the environment after disposal.

[0094] The single-component moisture-curing polyurethane molecular chain prepared by the present invention is a linear structure, and the material degradation can be achieved by the rupture of the borate ester bond, and the material recycling and reprocessing can also be achieved by the formation of the borate ester bond, thereby reducing the consumption and waste of resources.

[0095] The implementation methods of the present invention are not limited to the above-mentioned embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond, characterized in that It has the following structural formula: Wherein, R1 is one of the following groups: R2 is one of the following groups:

2. The method for preparing a one-component moisture-curable polyurethane chain extender containing a single dynamic 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 a dehydrating agent, heating to 60-80° C., condensing and refluxing for 12-24 hours, and then cooling to 25-40° C., 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., removing the organic solvent to obtain the borate chain extender, washing with a low boiling point solvent and filtering to obtain a single component moisture curing polyurethane chain extender with a single dynamic borate bond.

3. The method for preparing a one-component moisture-curable polyurethane chain extender containing a single dynamic 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 one-component moisture-curable polyurethane chain extender containing a single dynamic 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.

5. The method for preparing a one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond according to claim 2, 3 or 4, characterized in that: The molar ratio of the boric acid monomer to the monomer containing both vicinal diol and primary alcohol is 1:5-1:

2.

6. The method for preparing a one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond according to claim 2, characterized in that: The organic solvent is one or more of ethanol, isopropanol, tetrahydrofuran and ethyl acetate; and the dehydrating agent is anhydrous magnesium sulfate.

7. The method for preparing a one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond according to claim 2 or 6, characterized in that: The mass ratio of the boric acid monomer to the organic solvent is 1:9-3:7; the mass ratio of the water removing agent to the boric acid monomer is 1:2-3:

2.

8. The method for preparing a one-component moisture-curable polyurethane chain extender containing a single dynamic 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.

9. The method for preparing a one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond according to claim 2 or 8, characterized in that: The mass ratio of the borate-containing chain extender to the low-boiling-point solvent is 1:9-3:

7.

10. The method for preparing a one-component moisture-curable polyurethane chain extender containing a single dynamic borate ester bond according to claim 2, characterized in that: The organic solvent is removed by distillation under reduced pressure; After filtration, the low boiling point solvent is removed after standing at 60-80° C. under negative pressure for 8-24 hours.

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