Amido-bond-containing chain extender for single-component moisture-curing polyurethane coating and preparation method of amido-bond-containing chain extender

Abstract

The preparation method comprises the following steps: dissolving a lactone bond-containing monomer in an organic solvent, adding a monomer containing primary amine and hydroxyl / primary amine at the same time, heating the obtained mixed solution to 60-80 DEG C, condensing and refluxing for 12-24 hours, cooling to 20-50 DEG C, and removing the organic solvent, thereby obtaining the amido bond-containing chain extender for the single-component moisture-curing polyurethane coating. And washing the white solid containing the amide chain extender by using a low-boiling-point solvent, removing residual reactants, and removing the low-boiling-point solvent, so as to obtain the amido bond-containing chain extender for the single-component moisture-curing polyurethane coating. The prepared amido-bond-containing chain extender is high in organic solvent solubility and good in compatibility with polymer molecular chains, the interaction force between the molecular chains can be increased, a single-component moisture-curing polyurethane coating prepared from the amido-bond-containing chain extender has the advantages of being low in viscosity and convenient to construct, and a cured material has excellent transparency and mechanical performance at the same time.

Description

Technical Field

[0001] The invention relates to a polyurethane chain extender for a single-component moisture-curing polyurethane coating, in particular to an amide bond-containing chain extender for a single-component moisture-curing polyurethane coating and a preparation method thereof. Background Art

[0002] One-component moisture-curing polyurethane coating is a reaction-curing (moisture-curing) polyurethane coating that relies on the reaction of the -NCO group in the prepolymer with moisture in the air or substrate to cure. It has the characteristics of less solvent and low VOC, convenient construction, no harsh requirements on the moisture content of the construction surface, excellent elasticity and high and low temperature resistance. However, the one-component moisture-curing polyurethane prepolymer has a high viscosity, low molecular weight and poor mechanical properties after curing, which severely limits its application field. In addition, certain specific usage scenarios require a higher light transmittance, so there are higher requirements for the transparency of the coating. Therefore, the development of a one-component moisture-curing polyurethane coating with excellent mechanical properties and high light transmittance is of great significance to broadening its application range.

[0003] To solve the above problems, there are currently several main ways, such as reducing the microscopic defects formed by carbon dioxide inside the material, increasing the cross-linking density of the coating, and improving the microphase separation structure inside the material. See the following examples for details:

[0004] Chinese invention patent application CN110387187A discloses a one-component polyurethane waterproof coating prepared using a latent curing agent. Compared with the NCO group, the latent curing agent has higher reactivity. The primary amine or secondary amine generated by the reaction with water will react with NCO to generate a high-polarity urea bond. This process does not produce carbon dioxide, which can effectively reduce the internal microscopic defects of the coating and is conducive to improving the mechanical properties of the material. However, the high reactivity of the latent curing agent with water and the generated high-polarity groups will cause the viscosity of the prepolymer to rise rapidly, which is not conducive to the movement of the molecular chain and makes it difficult for the molecular weight to continue to rise. At the same time, when the latent curing agent reacts with water to generate molecules containing primary or secondary amines, it will also produce ketone small molecules that do not participate in the reaction. Such molecules will act as plasticizers to destroy the interaction between molecular chains. Under the combined action of multiple effects, the use of latent curing agents will not significantly improve the final mechanical properties of the material.

[0005] Chinese invention patent application CN116496691A discloses an environmentally friendly solvent-free high-strength one-component moisture-curing polyurethane waterproof coating with modified montmorillonite as a functional filler and a preparation method thereof. A large number of amino groups on the surface of polydopamine-modified montmorillonite can react with NCO to form urea bonds. The filler can significantly improve the mechanical strength of the one-component moisture-curing polyurethane by increasing the internal cross-linking density of the material. However, the montmorillonite modified by polydopamine is black, and the one-component moisture-curing polyurethane coating prepared from it is dark in color and opaque, which makes it difficult to meet some usage scenarios that require transparency, such as building exterior walls that need to show the color of the substrate.

[0006] Chinese invention patent application CN113444439B discloses a silicone-fluorine modified one-component polyurethane waterproof coating and its preparation method. This technology uses a silane modifier to convert the chain end NCO into a silane group. Compared with the NCO group, silane has a higher reactivity with water. After hydrolysis, covalent cross-linking points will be formed to increase the cross-linking density, and no carbon dioxide will be produced, which can improve the mechanical properties of the one-component moisture-curing polyurethane. The silane modifier is colorless and transparent, and the one-component moisture-curing polyurethane coating prepared therefrom has excellent light transmittance. However, the reactivity of silane with water is too high, and the cross-linking network formed by hydrolysis is dense. Although the tensile strength can be improved, the elongation at break is low, resulting in poor toughness of the material, which is difficult to meet the demand for high-toughness coatings in buildings.

[0007] Chinese invention patent application CN107325709A discloses a one-component moisture-curing polyurethane waterproof coating, which optimizes the internal microphase separation structure of the material by adjusting the ratio of difunctional and trifunctional chain extenders to improve the mechanical properties of the one-component moisture-curing polyurethane coating. Since no inorganic filler is used, the light transmittance of the one-component moisture-curing polyurethane material prepared by this method can reach a relatively high level. However, during the curing process of the one-component moisture-curing polyurethane, the viscosity increases, and the difficulty of molecular chain movement increases. The effect of changing the microphase separation structure only by adjusting the ratio of difunctional and trifunctional chain extenders is limited, making it difficult for the material's mechanical properties to reach a relatively high level, and it is difficult to meet the requirements of some scenarios for high-performance coatings.

[0008] The one-component moisture-curing polyurethane coating prepared by the above-mentioned prior art is difficult to take into account both mechanical properties and light transmittance, and cannot meet the use requirements of the scenarios where both are often required. Therefore, it is very important to ensure that the material has excellent light transmittance while improving the mechanical properties of the one-component moisture-curing polyurethane coating. Summary of the invention

[0009] In view of the problems existing in the prior art, the purpose of the present invention is to provide an amide bond-containing chain extender for single-component moisture-curing polyurethane coatings and a preparation method thereof, which can take into account both mechanical properties and light transmittance, has mild preparation conditions, and uses readily available and renewable raw materials. The solvents and raw materials used during material preparation can be recycled and reused, and have a low overall cost, which is conducive to large-scale production and application.

[0010] The purpose of the invention can be achieved through the following technical solutions:

[0011] An amide bond-containing chain extender for one-component moisture-curing polyurethane coatings having the following structural formula:

[0012]

[0013] Wherein, R1 is one of the following groups:

[0014]

[0015] R2 is one of the following groups:

[0016]

[0017] The method for preparing the amide bond-containing chain extender for a one-component moisture-curing polyurethane coating comprises the following steps:

[0018] (1) dissolving a lactone bond-containing monomer in an organic solvent, adding a monomer containing both a primary amine and a hydroxyl / primary amine, heating the resulting mixed solution to 60-80° C., condensing and refluxing for 12-24 hours, cooling to 20-50° C., and removing the organic solvent to obtain a white solid containing an amide chain extender;

[0019] (2) washing the white solid containing the amide chain extender with a low boiling point solvent to remove the unreacted ester monomers and the monomers containing both primary amine and hydroxyl / primary amine, and removing the low boiling point solvent to obtain an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating.

[0020] To further achieve the purpose of the present invention, preferably, the lactone bond-containing monomer is one or more of ε-caprolactone, γ-valerolactone, γ-caprolactone, δ-caprolactone, β-butyrolactone and β-propiolactone.

[0021] Preferably, the monomer containing both primary amine and hydroxyl / primary amine is one or more of hydrazine, ethanolamine, isopropanolamine, 2-amino-1-propanol and 4-amino-1-butanol.

[0022] Preferably, the organic solvent is one or more of ethanol, isopropanol, tetrahydrofuran and ethyl acetate.

[0023] Preferably, the organic solvent is removed by distillation under reduced pressure.

[0024] Preferably, the mass ratio of the lactone-containing monomer to the organic solvent is 1:9-5:5, and the molar ratio of the lactone-containing monomer to the monomer containing both primary amine and hydroxyl / primary amine is 1:1-1:10.

[0025] Preferably, the low boiling point solvent is one or more of diethyl ether, petroleum ether, n-pentane and isopentane.

[0026] Preferably, in step (2), the mass ratio of the white solid containing the amide chain extender to the low boiling point solvent is 1:9-3:7.

[0027] Preferably, the removal of the low boiling point solvent is performed by leaving the low boiling point solvent to stand at 60-80° C. under negative pressure for 8-24 hours before removing it.

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

[0029] 1. The amide bond in the molecular structure of the amide bond-containing chain extender used for the one-component moisture-curing polyurethane coating of the present invention can effectively increase the hydrogen bond density between the hard segments of the one-component moisture-curing polyurethane, increase the hydrogen bond force between the hard segments, and improve the mechanical properties of the material.

[0030] 2. The amide bond-containing chain extender used for the one-component moisture-curing polyurethane coating of the present invention has low polarity and high solubility in organic solvents. The one-component moisture-curing polyurethane coating prepared therefrom has not only excellent mechanical properties but also excellent transmittance;

[0031] 3. The amide bond-containing chain extender for single-component moisture-curing polyurethane coatings of the present invention has a simple preparation method, mild preparation conditions, and readily available and renewable raw materials. The solvents and raw materials used during material preparation can be recycled and reused, and the overall cost is low, which is conducive to large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the amide group-containing chain extender prepared in Example 1;

[0033] Figure 2 The infrared absorption spectra of the amide group-containing chain extender and ε-caprolactone prepared in Example 1;

[0034] Figure 3 This is a Maldi-tof test diagram of an application example of the present invention;

[0035] Figure 4 This is the stress-strain test curve of the single-component moisture-curing polyurethane of Comparative Example 1;

[0036] Figure 5 It is the stress-strain test curve of the one-component moisture-curing polyurethane of the application example. 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 protection scope 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 protection scope of the present invention.

[0038] In order to solve the problem of low molecular weight and poor mechanical properties of single-component moisture-curing polyurethane coatings after curing, the present invention designs and prepares a chain extender containing amide bonds from the perspective of molecular structure. Multiple hydrogen bonds can be formed between the hard segments generated by the chain extender, which can improve the microphase separation structure of the single-component moisture-curing polyurethane and enhance the mechanical properties of the material.

[0039] The design idea of ​​the present invention is mainly to use monomers containing lactone bonds and both primary amines and hydroxyl / primary amine groups as raw materials, and synthesize an amide bond-containing chain extender that can be used for one-component moisture-curing polyurethane according to the characteristics that the active hydrogen in the primary amine can undergo a ring-opening reaction with the lactone bond to generate an amide group. Therefore, the amide bond-containing chain extender for one-component moisture-curing polyurethane coatings of the present invention has the following structural formula:

[0040]

[0041] Wherein, R1 is one of the following groups:

[0042]

[0043] R2 is one of the following groups:

[0044]

[0045] The method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating of the present invention comprises the following steps:

[0046] (1) dissolving a lactone bond-containing monomer in an organic solvent, adding a monomer containing both a primary amine and a hydroxyl / primary amine, heating the resulting mixed solution to 60-80° C., condensing and refluxing for 12-24 hours, cooling to 20-50° C., and removing the organic solvent to obtain a white solid containing an amide chain extender;

[0047] (2) washing the white solid containing the amide chain extender with a low boiling point solvent to remove the unreacted ester monomers and the monomers containing both primary amine and hydroxyl / primary amine, and removing the low boiling point solvent to obtain an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating.

[0048] Based on the above technical measures, monomers containing lactone bonds and monomers containing both primary amines and hydroxyl / primary amines can be selected according to the specified characteristics; organic solvents can be selected according to the solubility requirements; the appropriate ratios of monomers containing lactone bonds, monomers containing both primary amines and hydroxyl / primary amines and organic solvents can be determined according to the purpose of the invention and the above principles and through experiments.

[0049] Preferably, the lactone bond-containing monomer is one or more of ε-caprolactone, γ-valerolactone, γ-caprolactone, δ-caprolactone, β-butyrolactone and β-propiolactone. The monomer containing both primary amine and hydroxyl / primary amine is one or more of hydrazine, ethanolamine, isopropanolamine, 2-amino-1-propanol and 4-amino-1-butanol. The organic solvent is one or more of ethanol, isopropanol, tetrahydrofuran and ethyl acetate. The mass ratio of the lactone bond-containing monomer to the organic solvent is 1:9-5:5, and the molar ratio of the lactone-containing monomer to the monomer containing both primary amine and hydroxyl / primary amine is 1:1-1:10.

[0050] The characteristics of the amide bond-containing chain extender prepared by the present invention are that the chain extender has high solubility in organic solvents, good compatibility with polymer molecular chains, and can increase the interaction force between molecular chains. The single-component moisture-curing polyurethane coating prepared by the chain extender has the characteristics of low viscosity and convenient construction. In particular, the material has excellent transparency and mechanical properties after the polyurethane coating is cured, which solves the difficulty of taking both transparency and mechanical properties into account in the prior art. The tensile strength of the polyurethane coating prepared by the chain extender of the present invention is tested to be above 20MPa, and the elongation at break is above 2000%. In addition, the prepared colorless and transparent single-component moisture-curing polyurethane has a transmittance of above 90%.

[0051] The relevant testing methods in the embodiments of the present invention are as follows:

[0052] Mechanical properties test, the tensile properties of the original sample and the repaired sample were characterized by a universal material testing machine, and the sample film with a thickness of 0.5-0.8mm was cut into 3 types of dumbbell-shaped specimens according to GB / T 528-2009, with a size of 4×75mm and a gauge length of 16mm. The test method is derived from the relevant literature (Polymer 222 (2021) 123674): the tensile rate is 500mm / min, the test temperature is 25±2℃, the humidity is 60±20%, and each sample is repeated at least 3 times to take the average value.

[0053] Transmittance test, the test method comes from the relevant literature (Polym.Chem., 2020, 11, 2585): Use a solid UV spectrophotometer (U3900) to characterize the transmittance of the emulsion film formed on the glass substrate. First, select the transmittance mode, select the scanning wavelength of 300nm~800nm, the scanning speed of 200nm / min, barium sulfate as the standard white board, blank glass measurement baseline, and then put in the test sample to get the transmittance data.

[0054] Example 1

[0055] A method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating comprises the following steps:

[0056] Synthesis of amide-containing chain extender: First, 11.4 g of ε-caprolactone (0.1 mol) was dissolved in 102.6 g of ethanol, and then 64.1 g of 50% aqueous solution of hydrated hydrazine (hydrazine content was 1.0 mol) was slowly added dropwise. The mixed solution was heated to 60°C and refluxed for 12 hours, then cooled to 20°C and distilled under reduced pressure to obtain a white solid of amide-containing chain extender;

[0057] Purification of amide chain extender: The obtained white solid was mixed with ether at a mass ratio of 1:9 and ultrasonically washed three times, then filtered and the obtained solid was placed in a vacuum oven at 60°C under negative pressure for 8 hours to remove the ether, and finally 14.2g of 6-hydroxyhexanoyl hydrazide chain extender containing amide group was obtained, with a yield of 97.3%. The H NMR spectrum of the product is as follows Figure 1 shown. Figure 1 The hydrogen nuclear magnetic resonance spectrum test results of the chain extender using deuterated water as the solvent are: 4.70 (s D2O), 3.52 (t, 2H), 2.15 (t, 2H), 1.53 (m, 4H), 1.26 (m, 2H). The solvent is deuterated water. The hydroxyl hydrogen atoms and the hydrogen atoms in the hydrazide will be ionized, and no dipole moment will appear. No signal peak will appear in the nuclear magnetic resonance, and there are no other impurity peaks. Figure 2 In the absorption spectrum of ε-caprolactone, 2927 cm -1 The two nearby absorption peaks represent the stretching vibration of the CH bond in the methylene group of caprolactone. -1 The absorption peak at 1255 cm represents the stretching vibration of C=O. -1 The absorption peak at 3300cm is generated by the stretching vibration of the CO bond, and the two prove the existence of the ester bond. -1 The absorption peak at 3196cm is the symmetric stretching vibration peak of NH in hydrazide (NH2). -1 The absorption peak at 1630 cm represents the NH stretching vibration in hydrazide (NH). -1The absorption peak at 1531 cm is the C=O stretching vibration peak in hydrazide. -1 With 1034cm -1 The absorption peaks at 3121cm -1 With 1055cm -1 The absorption peaks at 1722 cm-1 are OH and CO stretching vibration peaks. -1 The absorption peak of ester bond completely disappeared. The results of H NMR spectrum and IR absorption spectrum showed that 6-hydroxyhexanoyl hydrazide was successfully synthesized.

[0058] Example 2

[0059] A method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating comprises the following steps:

[0060] Synthesis of amide-containing chain extender: First, 10.0 g of γ-valerolactone (0.1 mol) was dissolved in 10 g of tetrahydrofuran, and then 6.1 g of ethanolamine (0.1 mol) was slowly added dropwise. The mixed solution was heated to 80 ° C and refluxed for 24 h, then cooled to 50 ° C and distilled under reduced pressure to obtain a white solid of amide-containing chain extender;

[0061] Purification of amide chain extender: The obtained white solid was mixed with petroleum ether in a mass ratio of 3:7 and ultrasonically washed three times. After that, the obtained solid was filtered and placed in a vacuum oven at 80°C under negative pressure conditions for 24 hours to remove the petroleum ether, and finally 14.9g of polyurethane chain extender containing amide group was obtained with a yield of 92.5%.

[0062] Example 3

[0063] A method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating comprises the following steps:

[0064] Synthesis of amide group-containing chain extender: First, 11.4 g of γ-caprolactone (0.1 mol) was dissolved in 45.6 g of isopropanol, and then 52.6 g of isopropanolamine (0.7 mol) was slowly added dropwise. The mixed solution was heated to 70°C and refluxed for 18 h, then cooled to 40°C and distilled under reduced pressure to obtain a white solid of amide group-containing chain extender;

[0065] Purification of the amide group-containing chain extender: The obtained white solid was mixed with petroleum ether in a mass ratio of 2:8 and ultrasonically washed three times. The obtained solid was then filtered and placed in a vacuum oven at 70°C under negative pressure for 18 hours to remove the petroleum ether. Finally, 16.94 g of a polyurethane chain extender containing an amide group was obtained with a yield of 96.8%.

[0066] Example 4

[0067] A method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating comprises the following steps:

[0068] Synthesis of amide-containing chain extender: First, 11.4 g of δ-caprolactone (0.1 mol) was dissolved in 17.1 g of ethyl acetate, and then 37.6 g of 2-amino-1-propanol (0.5 mol) was slowly added dropwise. The mixed solution was heated to 80°C and refluxed for 24 h, then cooled to 35°C and distilled under reduced pressure to obtain a white solid of amide-containing chain extender;

[0069] Purification of amide chain extender: The obtained white solid was mixed with petroleum ether in a mass ratio of 1:9 and ultrasonically washed three times. After that, the obtained solid was filtered and placed in a vacuum oven at 80°C under negative pressure conditions for 18 hours to remove the petroleum ether, and finally 16.4g of polyurethane chain extender containing amide group was obtained with a yield of 93.6%.

[0070] Application Examples

[0071] 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 (DMF) solution of dibutyltin dilaurate was heated to 70°C. During the reaction, the degree of reaction was determined by titrating the residual -NCO. The prepolymerization was completed when the residual -NCO reached the theoretical expectation. 2.1 g of the amide group-containing chain extender prepared in Example 1 was dissolved in 5 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 -NCO concentration was continuously titrated during the chain extension stage. When the chain extender was completely consumed and the -NCO remaining amount was 4wt.%, the chain extension was completed to obtain a high-solid-content -NCO-terminated one-component moisture-curable polyurethane prepolymer. Thereafter, the one-component moisture-curable polyurethane prepolymer was poured into a polytetrafluoroethylene mold to ensure that the film thickness was about 1mm, and was placed at 25°C and a relative humidity of 60% for curing to obtain a colorless and transparent one-component moisture-curable polyurethane.

[0072] The following are conventional chain extenders commonly used in the one-component moisture-curing polyurethane industry in the art and representative chain extenders used in the preparation of one-component moisture-curing polyurethane containing multiple hydrogen bonds reported in prior art literature as comparative examples.

[0073] Comparative Example 1: Using 1,6-hexanediol as a chain extender

[0074] 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 (DMF) solution of dibutyltin dilaurate was heated to 70° C. The degree of reaction was determined by titrating the residual -NCO during the reaction, and the prepolymerization was completed when the residual -NCO reached the theoretical expectation.

[0075] Then, 1.71 g of 1,6-hexanediol and 100 μL of 0.1 g mL -1 The DBTDL-DMF solution was heated to 80°C for continuous reaction. The -NCO concentration was continuously titrated during the chain extension stage. When the chain extender was completely consumed and the -NCO remaining amount was 4wt.%, the chain extension was completed to obtain a high-solid-content -NCO-terminated one-component moisture-curable polyurethane prepolymer. Thereafter, the one-component moisture-curable polyurethane prepolymer was poured into a polytetrafluoroethylene mold to ensure that the film thickness was about 1mm, and was placed at 25°C and a relative humidity of 60% for curing to obtain a colorless and transparent one-component moisture-curable polyurethane.

[0076] Comparative Example 2: Using 1,6-hexanediamine as a chain extender

[0077] 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 (DMF) solution of dibutyltin dilaurate was heated to 70° C. The degree of reaction was determined by titrating the residual -NCO during the reaction, and the prepolymerization was completed when the residual -NCO reached the theoretical expectation.

[0078] Then, 1.65 g of 1,6-hexanediol and 100 μL of 0.1 g mL -1The DBTDL-DMF solution was heated to 80°C for continuous reaction. The -NCO concentration was continuously titrated during the chain extension stage. When the chain extender was completely consumed and the -NCO remaining amount was 4wt.%, the chain extension was completed to obtain a high-solid-content -NCO-terminated one-component moisture-curable polyurethane prepolymer. Thereafter, the one-component moisture-curable polyurethane prepolymer was poured into a polytetrafluoroethylene mold to ensure that the film thickness was about 1mm, and was placed at 25°C and a relative humidity of 60% for curing to obtain a colorless and transparent one-component moisture-curable polyurethane.

[0079] Comparative Example 3: Using 2-hydroxymethyl-1,3-propanediol as a crosslinking agent

[0080] 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 (DMF) solution of dibutyltin dilaurate was heated to 70° C. The degree of reaction was determined by titrating the residual -NCO during the reaction, and the prepolymerization was completed when the residual -NCO reached the theoretical expectation.

[0081] Then, 1.05 g of 2-hydroxymethyl-1,3-propanediol and 100 μL of 0.1 g mL -1 The DBTDL-DMF solution was heated to 80°C for continuous reaction. The -NCO concentration was continuously titrated during the chain extension stage. When the chain extender was completely consumed and the -NCO remaining amount was 4wt.%, the chain extension was completed to obtain a high-solid-content -NCO-terminated one-component moisture-curable polyurethane prepolymer. Thereafter, the one-component moisture-curable polyurethane prepolymer was poured into a polytetrafluoroethylene mold to ensure that the film thickness was about 1mm, and was placed at 25°C and a relative humidity of 60% for curing to obtain a colorless and transparent one-component moisture-curable polyurethane.

[0082] Comparative Example 4

[0083] Referring to the method for preparing high-strength polyurethane in the prior art literature (Zhu X, Zhang W, Lu G, et al. Ultrahigh mechanical strength and robust room-temperature self-healing properties of a polyurethane–graphene oxide network resulting from multiple dynamic bonds [J]. Acs Nano, 2022, 16 (10): 16724-16735.), this comparative example uses adipic acid dihydrazide containing two hydrazide groups to prepare a one-component moisture-curing polyurethane.

[0084] 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 (DMF) solution of dibutyltin dilaurate was heated to 70° C. The degree of reaction was determined by titrating the residual -NCO during the reaction, and the prepolymerization was completed when the residual -NCO reached the theoretical expectation.

[0085] 2.4 g of adipic acid dihydrazide chain extender containing two hydrazide groups was dissolved in 5 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 reacted for 2 hours to obtain a high solid content -NCO-terminated one-component moisture-curable polyurethane prepolymer. Thereafter, the one-component moisture-curable polyurethane prepolymer was poured into a polytetrafluoroethylene mold to ensure that the film thickness was about 1 mm, and was placed at 25°C and a relative humidity of 60% for curing.

[0086] Comparative Example 5

[0087] Referring to the method for preparing high-strength polyurethane in the prior art literature (Liu C, Yin Q, Yuan Q, et al. A wear-resistant, self-healing and recyclable multifunctional waterborne polyurethane coating with mechanical tunability based on hydrogen bonding and an aromatic disulfide structure [J]. Polymer Chemistry, 2022, 13 (39): 5647-5658.), this comparative example uses a chain extender that can form multiple hydrogen bonds to prepare a single-component moisture-curing polyurethane.

[0088] 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 (DMF) solution of dibutyltin dilaurate was heated to 70° C. The degree of reaction was determined by titrating the residual -NCO during the reaction, and the prepolymerization was completed when the residual -NCO reached the theoretical expectation.

[0089] 2.33 g of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil chain extender capable of forming quadruple hydrogen bonds was dissolved in 5 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 reacted for 2 hours to obtain a high solid content -NCO-terminated one-component moisture-curable polyurethane prepolymer. Thereafter, the one-component moisture-curable polyurethane prepolymer was poured into a polytetrafluoroethylene mold to ensure that the film thickness was about 1 mm, and was placed at 25°C and a relative humidity of 60% for curing.

[0090] Table 1 shows the performance test results of the application examples and comparative examples.

[0091] Table 1

[0092]

[0093] Comparative Examples 1-3 (using aliphatic diol, aliphatic diamine and trimethylolpropane as chain extenders or crosslinkers) are conventional chain extenders used in the industrial preparation of one-component moisture-curing polyurethanes, and Comparative Examples 4 and 5 are chain extenders used in the preparation of one-component moisture-curing polyurethanes containing multiple hydrogen bonds reported in recent literature. As can be seen from Table 1, although the quality and type of the polyether polyol and diisocyanate used are the same, the performance of the one-component moisture-curing polyurethane coatings prepared in different ways is significantly different. The one-component moisture-curing polyurethane coating in the application example is prepared using the chain extender containing an amide group prepared in Example 1 of the present invention. The chain extender has a hydroxyl group at one end and an amide group-containing hydrazide at the other end. The prepared sample has a tensile strength of 20.43 MPa and an elongation at break of 2071.57%, and its mechanical properties are far superior to those of other comparative examples.

[0094] In Comparative Example 1, the single-component moisture-curing polyurethane coating is prepared using 1,6-hexanediol having hydroxyl groups at both ends as a chain extender. The sample has a tensile strength of 2.46 MPa and an elongation at break of 1593.44%, and has relatively weak mechanical properties.

[0095] In Comparative Example 2, 1,6-hexanediamine was used as a chain extender to prepare a single-component moisture-cured polyurethane. The sample had a tensile strength of 4.58 MPa and an elongation at break of 1275.92%, and the mechanical properties were slightly improved compared to those in Comparative Example 1.

[0096] In Comparative Example 3, trifunctional 2-hydroxymethyl-1,3-propanediol was used as a crosslinker to prepare a one-component moisture-cured polyurethane. The sample had a tensile strength of 6.94 MPa and an elongation at break of 430.35%. The mechanical properties were further improved, but the elongation at break was significantly reduced.

[0097] The single-component moisture-curing polyurethane coating of Comparative Example 4 refers to high-strength polyurethane (ACS Nano 2022, 16, 16724-16735), and is prepared using diacyl adipic acid with hydrazide groups at both ends as a chain extender. The tensile strength is 5.44 MPa and the elongation at break is 862.71%. Although the tensile strength has increased, it is far lower than the mechanical strength in the relevant references.

[0098] Comparative Example 5 refers to high-strength polyurethane (Polym.Chem., 2022, 13, 5647-5658) and uses 5-(2-hydroxyethyl)-6-methyl-2-aminouracil that can form multiple hydrogen bonds as a chain extender to prepare 1C-MCU. The tensile strength of the sample is 3.95 MPa and the elongation at break is 438.13%, which is also much lower than the mechanical strength in the reference.

[0099] The single-component moisture-curing polyurethane prepolymer has less solvent and higher solid content. During the curing process, the viscosity of the system increases, and the activity of the molecular chain decreases, which makes it more difficult for the chain end groups to react, making it difficult to further increase the molecular weight, and it only stays at a low level. In addition, the molecular chains are difficult to arrange regularly to form an excellent microphase separation structure, so that the final mechanical properties of the material are poor. The single-component moisture-curing polyurethane coating in Comparative Example 1 uses 1,6-hexanediol. 1,6-Hexanediol is a transparent liquid and has excellent compatibility with the prepolymer. The light transmittance of the coating prepared therefrom can reach a high level of 89.1%. However, in its structure, only a single hydrogen bond can be generated between the carbamate groups generated by the reaction of the hydroxyl groups at both ends with the NCO, and the hydrogen bond density between the molecular chains is low, making it difficult to improve the mechanical properties of the single-component moisture-curing polyurethane with a low molecular weight after curing. The stress-strain curve of the material is shown in FIG. Figure 4 The tensile strength of the sample is 2.46MPa, the elongation at break is 1593.44%, and the overall mechanical properties are weak.

[0100] Comparative Example 2 uses 1,6-hexanediamine as a chain extender, in which the amino group at the chain end can react with the NCO group to form a urea bond. Compared with the carbamate group, double hydrogen bonds can be formed between urea bonds, which can increase the interaction between molecular chains and help improve the mechanical properties of the material. However, since the system contains a large number of urea bonds that can form double hydrogen bonds, the viscosity of the prepolymer is high, which is not conducive to the diffusion of water vapor and carbon dioxide, resulting in a longer curing time of the material. The carbon dioxide generated during this period will form bubbles inside the material, reducing the light transmittance and mechanical properties of the material.

[0101] The application of trifunctional 2-hydroxymethyl-1,3-propylene glycol in Comparative Example 3 converts the linear network in the prepolymer into a cross-linked network, significantly increasing the cross-linking density of the system. Due to the increase in cross-linking density, the tensile strength of the material is significantly improved, which is at a higher level compared to other comparative examples, but its elongation at break is still low and cannot meet the national standard requirements. In addition, due to the increase in the cross-linking density of the system, the viscosity of the prepolymer increases significantly, which is not conducive to the diffusion of carbon dioxide during the curing process, causing the material to contain a large number of carbon dioxide bubbles, thereby weakening the light transmittance of the material and making it difficult to further improve the mechanical properties of the material.

[0102] Comparative Example 4 uses adipic acid dihydrazide as a chain extender, in which the hydrazide groups can react with the NCO groups to form multiple hydrogen bonds between the acyl semicarbazide groups, which can greatly increase the hydrogen bond density between the molecular chains and help improve the mechanical properties of the material. However, both ends of adipic acid dihydrazide are hydrazide groups, with high polarity and poor solubility in organic solvents. The single-component moisture-curing polyurethane has a low solvent content and poor compatibility with adipic acid dihydrazide. The solvent used is difficult to completely dissolve the required ADH, making it difficult for the adipic acid dihydrazide used to completely participate in the reaction and be introduced into the polymer molecular chain. Slightly soluble ADH powder or nanoparticles dispersed in the material will weaken the mechanical properties of the material as a microscopic defect, and will also reduce the transmittance of the coating, which only reaches 63.2%.

[0103] Comparative Example 5 uses 5-(2-hydroxyethyl)-6-methyl-2-aminouracil which can form multiple hydrogen bonds as a chain extender. The chain extender has a high polarity and can form quadruple hydrogen bonds between groups. Its solubility in organic solvents is also poor. Therefore, it encounters the same problem as Comparative Example 4. 5-(2-hydroxyethyl)-6-methyl-2-aminouracil is also difficult to completely dissolve into organic solvents, resulting in a low level of mechanical properties and transmittance of the material.

[0104] It can be seen from Comparative Examples 1-5 that it is difficult to simultaneously achieve high mechanical and light transmittance properties of a single-component moisture-curing polyurethane coating with the prior art, and it is of great significance to prepare a single-component moisture-curing polyurethane coating with excellent mechanical and light transmittance properties.

[0105] The molecular weight of the sample after curing of the prepolymer was characterized by Maldi-Tof. The test results are as follows: Figure 3 As shown. Although the one-component moisture-curing polyurethane prepolymer has been fully cured, its molecular weight is still at a relatively low level, mainly distributed around 2000 and 3300 m / z, which is much lower than that of traditional polyurethane. The molecular chain with a molecular weight of about 2000 m / z contains only one segment of polyether as a soft segment; the molecular weight of the longest polymer molecular chain is around 3300 m / z, and contains only two or three segments of polyether as soft segments. When the one-component moisture-curing polyurethane prepolymer is cured, the viscosity increases, the activity of the molecular chain decreases, the difficulty of the chain end amino group to react with NCO increases, and the molecular weight is difficult to continue to increase, resulting in the polymer molecular chain containing only two or three polyether molecular chain soft segments, and the overall molecular weight is at a relatively low level.

[0106] Compared with adipic acid dihydrazide, the chain extender of the present invention has low polarity and excellent organic solvent solubility. It can be completely dissolved in fewer solvents, thereby reacting with NCO in the system and connecting to the polymer molecular chain. The single-component moisture-curing polyurethane coating prepared therefrom has excellent light transmittance after curing, and the transmittance can reach 92.4%. The prepolymer relies on the reaction of NCO with water in the air for curing, wherein the solvent is high-boiling point DMF, the curing speed is moderate, and the open time is long, which is not only convenient for construction, but also conducive to the diffusion of carbon dioxide and the reduction of internal microscopic defects. The acylaminourea groups generated by the hydrazide groups in the chain extender can form multiple hydrogen bonds with NCO, which can greatly increase the hydrogen bond density between polymer molecular chains. The hard segment composed of acylaminourea groups has high polarity and strong cohesive energy, and can form a hard segment phase that is tightly bonded inside the material and can serve as a physical crosslinking point. When the material is subjected to stress, a large amount of energy will be dissipated in the process of breaking and reorganizing the hydrogen bonds between the hard segments, which can significantly improve the mechanical properties of the material. The stress-strain curve of the material is shown in Figure 5 The tensile strength of the sample is as high as 20.8MPa, and the elongation at break can reach more than 2000%. The strength is 4-6 times that of the moisture-curing polyurethane prepared by the current conventional technology, and the elongation is about 2 times. It has significant performance advantages and can greatly increase the service life and environmental stress resistance in waterproof coating applications.

Claims

1. An amide bond-containing chain extender for a one-component moisture-curing polyurethane coating, 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 an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating according to claim 1, characterized in that The steps include: (1) dissolving a lactone bond-containing monomer in an organic solvent, adding a monomer containing both a primary amine and a hydroxyl / primary amine, heating the resulting mixed solution to 60-80° C., condensing and refluxing for 12-24 hours, cooling to 20-50° C., and removing the organic solvent to obtain a white solid containing an amide chain extender; (2) washing the white solid containing the amide chain extender with a low boiling point solvent to remove the unreacted ester monomers and the monomers containing both primary amine and hydroxyl / primary amine, and removing the low boiling point solvent to obtain an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating.

3. The method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating according to claim 2, characterized in that: The lactone bond-containing monomer is one or more of ε-caprolactone, γ-valerolactone, γ-caprolactone, δ-caprolactone, β-butyrolactone and β-propiolactone.

4. The method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating according to claim 2, characterized in that: The monomer containing both primary amine and hydroxyl / primary amine is one or more of hydrazine, ethanolamine, isopropanolamine, 2-amino-1-propanol and 4-amino-1-butanol.

5. The method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating according to claim 2, characterized in that: The organic solvent is one or more of ethanol, isopropanol, tetrahydrofuran and ethyl acetate.

6. The method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating according to claim 2, characterized in that: The organic solvent is removed by distillation under reduced pressure.

7. The method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating according to claim 2, characterized in that: The mass ratio of the lactone-bond-containing monomer to the organic solvent is 1:9-5:5, and the molar ratio of the lactone-containing monomer to the monomer containing both primary amine and hydroxyl / primary amine is 1:1-1:

10.

8. The method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating 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 an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating according to claim 9, characterized in that: In step (2), the mass ratio of the white solid containing the amide chain extender to the low boiling point solvent is 1:9-3:

7.

10. The method for preparing an amide bond-containing chain extender for a one-component moisture-curing polyurethane coating according to claim 2, characterized in that: The removal of the low boiling point solvent is to remove the low boiling point solvent after standing at 60-80° C. under negative pressure for 8-24 hours.

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