High-strength single-component moisture-curing polyurethane containing amido bonds and preparation method of high-strength single-component moisture-curing polyurethane

Abstract

The preparation method comprises the following steps: dissolving a lactone bond-containing monomer in an organic solvent, adding a monomer of which the molecular structure contains primary amine or simultaneously contains hydroxyl and primary amine, heating to 60-80 DEG C, condensing and refluxing, and removing the organic solvent to obtain an amido bond-containing chain extender; the preparation method comprises the following steps: washing an amido bond-containing chain extender by using a low-boiling-point solvent, reacting the amido bond-containing chain extender with polyether polyol, a catalyst and diisocyanate to obtain a single-component moisture-cured polyurethane prepolymer with the-NCO content of 2-6wt.%, and curing the prepolymer to obtain a target product. The amido bond in the molecular chain of the single-component moisture-cured polyurethane can increase the hydrogen bond density and interaction force between the hard segments and improve the bonding strength of the hard segments, so that the mechanical property of the material is remarkably improved, and good transmittance can be considered.

Description

Technical Field

[0001] The invention relates to polyurethane materials, in particular to a high-strength single-component moisture-curing polyurethane containing amide bonds and a preparation method thereof. Background Art

[0002] One-component moisture-curing polyurethane is a reaction-curing (water vapor curing) polyurethane material that relies on the reaction of the -NCO group in the prepolymer with the water vapor in the air or the substrate to cure. It has the characteristics of easy construction, low requirements for the moisture content of the substrate, excellent elasticity and high and low temperature resistance, etc. It is widely used as a base material for materials such as adhesives, sealants and coatings. However, due to the curing method, the one-component moisture-curing polyurethane has a low degree of microphase separation, a small polymer molecular weight, and poor mechanical properties, which limits its application scenarios to a certain extent. Therefore, improving the mechanical properties of one-component moisture-curing polyurethane is of great significance to broadening its application fields and scope of use.

[0003] The mechanical properties of single-component moisture-cured polyurethane are closely related to its microphase separation structure. The polarity and cohesive energy of the soft segment and hard segment in the polymer molecular weight are different. The hard segment in the molecular chain has a large polarity and high cohesive energy, and can form a tightly bound hard segment phase through hydrogen bond interaction. When subjected to external stress, the material can dissipate a large amount of external energy through the breakage and reorganization of hydrogen bonds between hard segments, thereby improving its mechanical properties.

[0004] 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, although the light transmittance of the one-component moisture-curing polyurethane material prepared in the application can reach a high level, the viscosity of the one-component moisture-curing polyurethane increases during the curing process, 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 to achieve a high level of mechanical properties and difficult to meet the application occasions with high requirements for mechanical properties.

[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 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] 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

[0008] In view of the fact that the single-component moisture-curing polyurethane in the prior art has a low molecular weight and its mechanical properties need to be improved, and it is difficult to achieve both mechanical properties and light transmittance in the coating produced using the single-component moisture-curing polyurethane, the purpose of the present invention is to provide a high-strength single-component moisture-curing polyurethane containing an amide bond and a preparation method thereof, which can significantly improve the mechanical properties of the single-component moisture-curing polyurethane while achieving good light transmittance.

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

[0010] A high-strength one-component moisture-curing polyurethane containing amide bonds has the following structural formula:

[0011]

[0012] Wherein m = 33-38, n = 25-30;

[0013] R 1 One of the following groups:

[0014]

[0015] R 2 One of the following groups:

[0016]

[0017] A method for preparing a high-strength one-component moisture-curing polyurethane containing an amide bond comprises the following steps:

[0018] (1) dissolving a lactone bond-containing monomer in an organic solvent, adding a monomer containing a primary amine or containing both a hydroxyl group and a primary amine in the molecular structure, 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 an amide bond-containing chain extender;

[0019] (2) washing the amide bond-containing chain extender with a low boiling point solvent, removing the low boiling point solvent, and obtaining the amide bond-containing chain extender;

[0020] (3) reacting the chain extender containing an amide bond with a polyether polyol, a catalyst and a diisocyanate to obtain a one-component moisture-curable polyurethane prepolymer having an -NCO content of 2-6 wt.%, and curing the one-component moisture-curable polyurethane prepolymer to obtain a high-strength one-component moisture-curable polyurethane containing an amide bond; the catalyst is one or more of dibutyltin dilaurate, triethylenediamine, stannous octoate, zinc isooctanoate and bismuth cyclohexanecarboxylate.

[0021] To further achieve the purpose of the present invention, preferably, the lactone-containing monomer is one or more of ε-caprolactone, γ-valerolactone, γ-caprolactone, δ-caprolactone and β-propiolactone.

[0022] Preferably, the molecular structure contains primary amine (-NH 2 ) or the monomer containing both a hydroxyl group (-OH) and a primary amine is one or more of hydrazine, ethylenediamine, 1,4-diaminobutane, ethanolamine and 4-amino-1-butanol.

[0023] Preferably, the molar ratio of the lactone monomer to the monomer containing a primary amine or a hydroxyl group and a primary amine in the molecular structure in the mixed solution is 1:1-1:10.

[0024] Preferably, the organic solvent is one or more of ethanol, isopropanol, tetrahydrofuran, ethyl acetate and N,N-dimethylformamide; and the mass ratio of the lactone-containing monomer to the organic solvent is 1:9-5:5.

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

[0026] Preferably, the mass ratio of the amide bond-containing chain extender to the low boiling point solvent is 1:9-3:7; the removal of the low boiling point solvent is to control the temperature of the product obtained by washing the amide bond-containing chain extender with the low boiling point solvent at 60-80°C and let it stand under negative pressure for 8-24 hours.

[0027] Preferably, in step (3), the molar ratio of polyether polyol, diisocyanate and catalyst in the prepolymer preparation process is 1:3.0:0.0001-1:4.5:0.0001.

[0028] Preferably, the curing temperature is 10-40° C., the relative humidity is 40-80%, and the curing time is 48-72 hours.

[0029] Compared with the prior art, the present invention has the following advantages and effects:

[0030] 1) The present invention uses a monomer containing a lactone bond and a monomer containing a primary amine or containing both a hydroxyl group and a primary amine group as raw materials to synthesize a chain extender containing an amide bond, and uses it to prepare a single-component moisture-cured polyurethane. The amide bond in the molecular chain can increase the hydrogen bond density and interaction force between hard segments, improve the strength of the hard segment combination, and significantly improve the mechanical properties of the material.

[0031] The amide bond between molecular chains can increase the hydrogen bond density between hard segments of single-component moisture-curing polyurethane, increase the hydrogen bond force between hard segments, improve the microphase separation structure, and thus improve the mechanical properties of single-component moisture-curing polyurethane;

[0032] 2) The amide bond-containing chain extender prepared by the present invention 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 therefrom has the characteristics of low viscosity and convenient construction. In particular, the polyurethane coating has excellent transparency and mechanical properties after curing, which solves the difficulty of balancing transparency and mechanical properties in the prior art.

[0033] 3) The tensile strength of the polyurethane coating prepared by using the chain extender of the present invention is tested to be above 20 MPa, and the elongation at break is above 2000%. In addition, the prepared polyurethane is colorless, transparent, single-component, moisture-cured polyurethane, and the transmittance is above 90%.

[0034] 4) The single-component moisture-curing polyurethane containing amide bonds in 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

[0035] Figure 1 is the hydrogen nuclear magnetic resonance spectrum of the amide bond-containing chain extender in Example 1;

[0036] Figure 2 is the stress-strain test curve of the comparative sample;

[0037] Figure 3 This is the stress-strain test curve of the sample in Example 1;

[0038] Figure 4 This is the Maldi-tof mass spectrum of the sample in Example 1. DETAILED DESCRIPTION

[0039] 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.

[0040] Conventional polyurethane is prepared by prepolymerization and chain extension in solution. After the preparation is completed, the product is a high molecular weight polymer with a molecular weight of generally 20,000-80,000 g / mol. Therefore, a large amount of solvent dilution is required to obtain a suitable viscosity. It is generally supplied in the form of 30-50wt% solid content. The mechanical strength of this conventional polyurethane can reach 30-50Mpa, and the elongation can reach 1000%-2000%. The moisture-curable polyurethane of the present invention exists in the form of an oligomer with isocyanate groups retained at the end, with a molecular weight of 2,000-6,000 g / mol (such as Figure 4 As shown in the mass spectrum of the invention, the viscosity is low and not much solvent is required to dissolve the polyurethane. The solid content is generally 90-100wt%. This type of polyurethane has obvious cost advantages in the construction field and is safer and more environmentally friendly to use.

[0041] The present invention starts from the perspective of polymer molecular design, and introduces amide bonds that can form hydrogen bonds and increase the interaction force between hard segments into the polymer molecular chain. Specifically, there is an acylhydrazine containing an amide bond in the chain extender structure, which can react with -NCO to generate an acylaminourea group that can generate multiple hydrogen bonds; the groups can increase the interaction force between hard segments through multiple hydrogen bonds, improve the microphase separation structure, and help improve the mechanical strength of the material. The amide bond-containing chain extender prepared by the present invention 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 present invention has the characteristics of low viscosity and convenient construction. In particular, the material after the polyurethane coating is cured has excellent transparency and mechanical properties, 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%, and the prepared colorless and transparent single-component moisture-curing polyurethane has a transmittance of above 90%.

[0042] Based on the above mechanism, the present invention provides a high-strength one-component moisture-curing polyurethane containing an amide bond, which has the following structural formula:

[0043]

[0044] Wherein m = 33-38, n = 25-30;

[0045] R 1 One of the following groups:

[0046]

[0047] R 2 One of the following groups:

[0048]

[0049] The present invention provides a method for preparing a high-strength single-component moisture-curing polyurethane containing an amide bond, comprising the following steps:

[0050] (1) dissolving a lactone bond-containing monomer in an organic solvent, adding a monomer containing a primary amine or containing both a hydroxyl group and a primary amine in the molecular structure, 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 bond chain extender;

[0051] (2) washing the white solid containing the amide bond chain extender with a low boiling point solvent to remove the unreacted ester monomer and the monomer containing the primary amine or containing both the hydroxyl group and the primary amine, and removing the low boiling point solvent to obtain the amide bond chain extender for the one-component moisture-curing polyurethane coating;

[0052] (3) reacting the chain extender containing an amide bond with a polyether polyol, a catalyst and a diisocyanate to obtain a one-component moisture-curable polyurethane prepolymer having an -NCO content of 2-6 wt.%, and curing the one-component moisture-curable polyurethane prepolymer to obtain a high-strength one-component moisture-curable polyurethane containing an amide bond; the catalyst is one or more of dibutyltin dilaurate, triethylenediamine, stannous octoate, zinc isooctanoate and bismuth cyclohexanecarboxylate.

[0053] After the construction of the high-strength single-component moisture-curing polyurethane containing amide bonds of the present invention is completed, the isocyanate group at the end of the oligomer can react with water vapor in the air to carry out autonomous chain extension to become a high molecular weight polymer. However, during the water vapor chain extension process, due to the high solid content of the material, the movement of the polymer chain is more difficult than in the solution, resulting in its chain extension effect and mechanical properties being far inferior to the polyurethane prepared in the solution. But in fact, in the field of building waterproofing, more attention is paid to cost and the release of VOCs, so appropriately low mechanical strength is acceptable. In the national standard GBT 19250-2013, the strength of Type I moisture-curing polyurethane is only required to be 2MPa, and the mechanical strength of conventional market products is also generally the same.

[0054] The usage amount of chain extender in the formula of the present invention accounts for a very small proportion, so the present invention can obtain extremely significant mechanical property improvement under the condition of slightly increasing the cost. The mechanical strength (30MPa) close to that of conventional solution-type polyurethane can expand the application scope of this high-solid content, low-viscosity moisture-curing polyurethane to the application field of conventional solution-type polyurethane, replacing solvent-type polyurethane products, and has obvious advantages in VOCs emission relative to solvent-type products. Therefore, the present invention has great application value in structural adhesives, battery pack bonding, automotive interior fitting, optical component packaging, etc. in the field of construction. The moisture-curing polyurethane that takes into account both mechanical properties and transparency can be used in high value-added fields such as automotive dashboard and lamp bonding, LED packaging, etc., breaking through the limitation that the original single-component moisture-curing polyurethane is only suitable for use in the application field of building waterproofing due to its poor appearance and low strength.

[0055] The relevant testing methods in the embodiments of the present invention are as follows:

[0056] Mechanical property test, using a universal material testing machine to characterize the tensile properties of the original sample and the repaired sample, 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, a gauge length of 16mm, a tensile rate of 500mm / min, a test temperature of 25±2℃, and a humidity of 60±10%. Each sample was repeated at least 3 times and the average value was taken. The sample film refers to the solid sheet material obtained by pouring the reacted polyurethane reaction liquid into the polypropylene mold box and peeling it off from the mold box after a certain period of wet curing, which is the cured polyurethane material.

[0057] 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 single-component moisture-cured polyurethane on a glass substrate. First, select the transmittance mode, select a scanning wavelength of 300nm to 800nm, a scanning speed of 200nm / min, barium sulfate as the standard white board, blank glass as the baseline, and then put in the test sample to get the transmittance data.

[0058] Molecular weight test, the test method is derived from the relevant literature (Acta Polymerica, 1998, 49 (06): 272-293): Use MALDI-TOF mass spectrometer (Shimadzu MALDI-8020) to characterize the molecular weight of the synthesized polyurethane material. First, the cured single-component moisture-cured polyurethane sample is dissolved in 80-110°C N, N-dimethylformamide, and the dissolved solution is gently tapped onto the test target plate through a capillary. After drying and evaporating the solvent, it is sent to the mass spectrometer, and "Mass Spectrum Acquisition" is selected in the instrument operation page. Wait for the data acquisition to complete to obtain the Maldi-tof mass spectrum of the sample.

[0059] Example 1

[0060] Synthesis of amide bond-containing chain extender: Dissolve 64.1g of 50% aqueous solution of hydrazine hydrate (hydrazine content 1.0mol) in 64.1g of tetrahydrofuran, dissolve 11.4g of ε-caprolactone (0.1mol) in 102.6g of tetrahydrofuran and slowly drip into the hydrazine hydrate tetrahydrofuran solution. Heat the mixed solution to 60°C and condense and reflux for 12h, then cool to 20°C and distill under reduced pressure to obtain a white solid containing amide bond chain extender;

[0061] Purification of the chain extender containing an amide bond: The obtained white solid was mixed with ether in a mass ratio of 1:9 and ultrasonically washed three times. The filtered solid was placed in a vacuum oven at 60°C under negative pressure conditions for 8 hours, and then the ether was removed to obtain 13.8 g of 6-hydroxyhexanoylhydrazide chain extender containing an amide bond, with a yield of 94.8%.

[0062] Preparation of one-component moisture-curing polyurethane: 25 g polypropylene glycol and 20 g polytetrahydrofuran diol (-OH total 0.045 mol) were mixed with 15.0 g isophorone diisocyanate (-NCO total 0.135 mol) and 0.02 g dibutyltin dilaurate (3 × 10 -5 mol) and then heated to 75°C for 3 hours. After the prepolymerization is completed, 5 mL of DMF solution containing a specific amount of hydrazide chain extender is added to make the reserved -NCO content of the one-component moisture-curable polyurethane prepolymer after the chain extension is complete to be 4 wt.%. The prepolymer is poured into a mold and cured for 72 hours at 25°C and a relative humidity of 60% to obtain a high-strength one-component moisture-curable polyurethane containing amide bonds.

[0063] Example 2

[0064] Synthesis of amide bond-containing chain extender: 6.0 g of ethylenediamine (0.1 mol) was dissolved in 54.0 g of ethanol, 10.0 g of γ-valerolactone (0.1 mol) was dissolved in 10.0 g of ethanol and slowly added to the ethylenediamine-ethanol solution. The mixed solution was heated to 80°C and refluxed for 24 hours, then cooled to 50°C and distilled under reduced pressure to obtain a white solid containing amide bond chain extender.

[0065] Purification of the amide bond-containing chain extender: The obtained white solid was mixed with petroleum ether in a mass ratio of 3:7 and ultrasonically washed three times. The filtered solid was placed in a vacuum oven at 70°C under negative pressure conditions for 18 hours, and then the petroleum ether was removed to obtain 14.9 g of an amide bond-containing chain extender with a yield of 93.2%.

[0066] Preparation of one-component moisture-curing polyurethane: 25 g of polypropylene glycol and 20 g of polytetrahydrofuran diol (-OH total 0.045 mol) were mixed with 22.5 g of isophorone diisocyanate (-NCO total 0.2025 mol) and 0.01 g of triethylene diamine (1×10 -4 mol) and then heated to 75°C for 3 hours. After the prepolymerization is completed, 5 mL of DMF solution containing a specific amount of hydrazide chain extender is added to make the reserved -NCO content of the one-component moisture-curable polyurethane prepolymer after the chain extension is complete to be 4 wt.%. The prepolymer is poured into a mold and cured for 24 hours at 25°C and a relative humidity of 60% to obtain a high-strength one-component moisture-curable polyurethane containing amide bonds.

[0067] Example 3

[0068] Synthesis of amide bond-containing chain extender: 35.3 g of 1,4-diaminobutane (0.4 mol) was dissolved in 82.4 g of isopropanol, and 11.4 g of γ-caprolactone (0.1 mol) was dissolved in 26.6 g of isopropanol and slowly dripped into the 1,4-diaminobutane solution. The mixed solution was heated to 70°C and refluxed for 18 hours, then cooled to 30°C and distilled under reduced pressure to obtain a white solid containing an amide bond chain extender.

[0069] Purification of the chain extender containing an amide bond: The obtained white solid was mixed with n-pentane in a mass ratio of 2:8 and ultrasonically washed three times. The filtered solid was placed in a vacuum oven at 70°C under negative pressure conditions for 18 hours, and then the petroleum ether was removed to obtain 18.3 g of a chain extender containing an amide bond, with a yield of 90.7%.

[0070] Preparation of one-component moisture-curing polyurethane: 25 g of polypropylene glycol and 20 g of polytetrahydrofuran diol (-OH total 0.045 mol) were mixed with 17.5 g of isophorone diisocyanate (-NCO total 0.2025 mol) and 0.06 g of dibutyltin dilaurate (1×10 -4 mol) and then heated to 75°C for 3 hours. After the prepolymerization is completed, 5 mL of DMF solution containing a specific amount of hydrazide chain extender is added to make the reserved -NCO content of the one-component moisture-curable polyurethane prepolymer after the chain extension is complete to be 4 wt.%. The prepolymer is poured into a mold and cured for 72 hours at 25°C and a relative humidity of 60% to obtain a high-strength one-component moisture-curable polyurethane containing amide bonds.

[0071] Example 4

[0072] Synthesis of amide bond-containing chain extender: Dissolve 30.5 g of ethanolamine (0.1 mol) in 122 g of ethyl acetate, dissolve 11.4 g of δ-caprolactone (0.1 mol) in 45.6 g of ethyl acetate and slowly drip into the ethanolamine solution, slowly heat to 80 ° C and condense and reflux for 12 hours, then cool to 20 ° C and distill under reduced pressure to obtain a white solid containing an amide bond chain extender.

[0073] Purification of the amide bond-containing chain extender: The obtained white solid was mixed with isopentane in a mass ratio of 1:9 and ultrasonically washed three times. The filtered solid was placed in a vacuum oven at 80°C under negative pressure conditions for 24 hours, and then the isopentane was removed to obtain 16.9 g of an amide bond-containing chain extender with a yield of 96.8%.

[0074] Preparation of one-component moisture-curing polyurethane: 25 g polypropylene glycol and 20 g polytetrahydrofuran diol (-OH total 0.045 mol) were mixed with 15.0 g isophorone diisocyanate (-NCO total 0.135 mol) and 0.06 g dibutyltin dilaurate (1×10 -4 mol) and then heated to 75°C for 3 hours. After the prepolymerization is completed, 5 mL of DMF solution containing a specific amount of hydrazide chain extender is added to make the reserved -NCO content of the one-component moisture-curable polyurethane prepolymer after the chain extension is complete to be 4 wt.%. The prepolymer is poured into a mold and cured for 72 hours at 25°C and a relative humidity of 60% to obtain a high-strength one-component moisture-curable polyurethane containing amide bonds.

[0075] Example 5

[0076] Synthesis of amide bond-containing chain extender: 13.4 g of 4-amino-1-butanol (0.15 mol) was dissolved in 20.1 g of tetrahydrofuran, 7.2 g (0.1 mol) of β-propiolactone was dissolved in 10.8 g of tetrahydrofuran and slowly added to the 4-amino-1-butanol solution. The mixed solution was heated to 70°C and refluxed for 24 hours, then cooled to 30°C and distilled under reduced pressure to obtain a white solid containing an amide bond chain extender.

[0077] Purification of the chain extender containing an amide bond: The obtained white solid was mixed with ether in a mass ratio of 2:8 and ultrasonically washed three times. The filtered solid was placed in a vacuum oven at 80°C under negative pressure conditions and kept warm for 12 hours. The ether was removed and 15.1 g of the chain extender containing an amide bond was obtained with a yield of 93.7%.

[0078] Preparation of one-component moisture-curing polyurethane: 25 g polypropylene glycol and 20 g polytetrahydrofuran diol (-OH total 0.045 mol) were mixed with 15.0 g isophorone diisocyanate (-NCO total 0.135 mol) and 0.06 g dibutyltin dilaurate (1×10 -4 mol) and then heated to 75°C for 3 hours. After the prepolymerization is completed, 5 mL of DMF solution containing a specific amount of hydrazide chain extender is added to make the reserved -NCO content of the one-component moisture-curable polyurethane prepolymer after the chain extension is complete to be 4 wt.%. The prepolymer is poured into a mold and cured for 72 hours at 25°C and a relative humidity of 60% to obtain a high-strength one-component moisture-curable polyurethane containing amide bonds.

[0079] Comparative Example

[0080] 25g of polypropylene glycol and 20g of polytetrahydrofuran diol (-OH total 0.045mol) were mixed and dehydrated under vacuum at 120℃ for 2h and then cooled to 40℃. Thereafter, 15.0g of isophorone diisocyanate (-NCO total 0.135mol) and 0.02g of dibutyltin dilaurate were added and the temperature was raised to 75℃ for continuous reaction for 3h. After the prepolymerization was completed, 1,4-butanediol was added for chain extension, so that the reserved -NCO in the one-component moisture-curing polyurethane prepolymer obtained after the chain extension was complete was 4wt.%. The prepolymer was poured into a mold and cured for 72h at 25℃ and a relative humidity of 60% to obtain a one-component moisture-curing polyurethane.

[0081] Figure 1 The results of the nuclear magnetic resonance hydrogen spectrum test of the amide bond-containing chain extender used in the preparation process of the single-component moisture-curing polyurethane in Example 1 are 4.70 (s D2O), 3.52 (t, 2H), 2.15 (t, 2H), 1.53 (m, 4H), 1.26 (m, 2H), wherein the solvent used is deuterated water. During the dissolution process, the hydroxyl hydrogen atom and the hydrazide hydrogen atom will be ionized, and no dipole moment will appear, so no absorption peak will appear during the test process, and there are no other miscellaneous peaks, proving that the structure of the chain extender is the same as expected, with a hydroxyl group at one end and a hydrazide group at the other end.

[0082] The amide bond-containing chain extender used in Example 1 has a hydroxyl group at one end and a hydrazide at the other end. The chain extender used in the comparative example is 1,4-butanediol, which has hydroxyl groups at both ends. Figure 2 and Figure 3 They are stress-strain curves of Example 1 and Comparative Example samples during stretching, Figure 2 and Figure 3The curve mainly presents the two parameters of tensile strength and elongation at break of Example 1 and the comparative example. These tests are summarized in Table 1 for intuitive comparison of the data. The sample is a sheet-like polyurethane film peeled off from the mold box of Example 1 and the comparative example. The amounts of polyether polyol, isocyanate and chain extender used in the comparative example and Example 1 are basically the same. It can be seen from Table 1 that the mechanical properties of the two single-component moisture-curing polyurethanes are significantly different. The tensile strength and elongation at break of the comparative example are 1.72MPa and 527.27% respectively, and its toughness is 7.36MJ·m -3 The mechanical strength of the sample in Example 1 increased significantly, with a tensile strength and elongation at break of 26.45 MPa and 1621.97% respectively, and a toughness of 148.18 MJ·m -3 , and its tensile strength and toughness are 20 times that of the comparative example. The test results of Examples 2-5 are also summarized in Table 1, which are basically at the same order of magnitude as the test results of Example 1, so Example 1 is compared with the comparative example for explanation.

[0083] Table 1 shows the performance test results of application examples 1-5 and comparative examples.

[0084] Table 1

[0085]

[0086] The molecular weight of the sample after curing of the prepolymer in Example 1 was characterized by Maldi-tof. The test results are as follows: Figure 4 Although the prepolymer has been fully cured, the test results show that its molecular weight is less than 3500m / z, which is still at a low level, far lower than conventional solvent-based polyurethane. This molecular weight indicates that the polymer molecular chain contains only two or three polyether segments as soft segments.

[0087] Although the molecular weight of the prepolymer in Example 1 is still at a low level after curing, it can be seen from the mechanical test results that the mechanical properties of the one-component moisture-curing polyurethane prepared using an amide bond-containing chain extender are far superior to those of the one-component moisture-curing polyurethane prepared using traditional 1,4-butanediol as a chain extender. Since the amount of chain extender used in the formula accounts for a small proportion, this solution can obtain extremely significant mechanical performance improvements at a small cost increase, close to the mechanical strength (30MPa) of conventional solution-type polyurethane. In addition, since the chain extender used in the preparation process has very excellent solvent solubility, the transmittance of the cured one-component moisture-curing polyurethane coating can reach 91.5%, which is even slightly better than the one-component moisture-curing polyurethane prepared with 1,4-butanediol as a chain extender. Excellent mechanical properties and light transmittance can expand the application range of this high-solid content, low-viscosity moisture-curing polyurethane to the application field of conventional solution-type polyurethane, and have obvious advantages in VOCs emissions. There is great potential in structural adhesives in the construction field (wood structure bonding) and even in other fields (battery pack bonding, automotive interior lamination, etc.).

[0088] The degree of curing of the single-component moisture-cured polyurethane prepolymer increases, the viscosity of the system increases, the difficulty of the polymer molecular chain movement increases, and the chain end groups are difficult to contact and react with each other, resulting in poor microphase separation structure of the cured single-component moisture-cured polyurethane, low polymer molecular weight, poor mechanical properties and other problems. In the comparative example, the chain extender is 1,4-butanediol, and the hydroxyl groups at both ends react with -NCO to produce a carbamate group that can only form a single hydrogen bond. In contrast, the chain extender used in Example 1 has a hydrazide including an amide bond in its structure, and the group can react with -NCO to generate an acylaminourea group that can produce multiple hydrogen bonds. The groups can increase the interaction force between the hard segments through multiple hydrogen bonds, improve the microphase separation structure, and help improve the mechanical strength of the material. When subjected to external stress, the material can dissipate a large amount of energy by breaking and reorganizing the hydrogen bonds between the hard segments. In Example 1, there are multiple hydrogen bonds between the hard segments of the polyurethane, so that it exhibits excellent mechanical properties. In the comparative example, the material hard segments are only single hydrogen bonds between carbamates, and the interaction force is poor, resulting in poor mechanical properties.

[0089] In summary, by using an amide bond-containing chain extender, one-component moisture-curing polyurethane can significantly improve the mechanical properties of the material while ensuring excellent transmittance performance, thereby helping to broaden its application areas.

Claims

1. A high-strength one-component moisture-curing polyurethane containing amide bonds, characterized in that It has the following structural formula: Wherein m = 33-38, n = 25-30; R1 is one of the following groups: R2 is one of the following groups:

2. The method for preparing a high-strength one-component moisture-curing polyurethane containing an amide bond according to claim 1, characterized in that The following steps are involved: (1) dissolving a lactone bond-containing monomer in an organic solvent, adding a monomer containing a primary amine or containing both a hydroxyl group and a primary amine in the molecular structure, 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 an amide bond-containing chain extender; (2) washing the amide bond-containing chain extender with a low boiling point solvent, removing the low boiling point solvent, and obtaining the amide bond-containing chain extender; (3) reacting the chain extender containing an amide bond with a polyether polyol, a catalyst and a diisocyanate to obtain a one-component moisture-curable polyurethane prepolymer having an -NCO content of 2-6 wt.%, and curing the one-component moisture-curable polyurethane prepolymer to obtain a high-strength one-component moisture-curable polyurethane containing an amide bond; the catalyst is one or more of dibutyltin dilaurate, triethylenediamine, stannous octoate, zinc isooctanoate and bismuth cyclohexanecarboxylate.

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

4. The method for preparing a high-strength one-component moisture-curing polyurethane containing an amide bond according to claim 2, characterized in that: The monomer containing primary amine or hydroxyl group and primary amine in the molecular structure is one or more of hydrazine, ethylenediamine, 1,4-diaminobutane, ethanolamine and 4-amino-1-butanol.

5. The method for preparing a high-strength one-component moisture-curing polyurethane containing an amide bond according to claim 2 or 4, characterized in that: The molar ratio of the lactone monomer to the monomer containing primary amine or hydroxyl group and primary amine in the molecular structure in the mixed solution is 1:1-1:

10.

6. The method for preparing a high-strength one-component moisture-curing polyurethane containing an amide bond according to claim 2, characterized in that: The organic solvent is one or more of ethanol, isopropanol, tetrahydrofuran, ethyl acetate and N,N-dimethylformamide; the mass ratio of the lactone-containing monomer to the organic solvent is 1:9-5:

5.

7. The method for preparing a high-strength one-component moisture-curing polyurethane containing amide bonds according to claim 2, characterized in that: The low boiling point solvent is one or more of ether, petroleum ether, n-pentane and isopentane.

8. The method for preparing a high-strength one-component moisture-curing polyurethane containing amide bonds according to claim 2 or 7, characterized in that: The mass ratio of the amide bond-containing chain extender to the low boiling point solvent is 1:9-3:7; the removal of the low boiling point solvent is to control the temperature of the product obtained by washing the amide bond-containing chain extender with the low boiling point solvent at 60-80°C and let it stand for 8-24 hours under negative pressure.

9. The method for preparing a high-strength one-component moisture-curing polyurethane containing amide bonds according to claim 2, characterized in that: In step (3), the molar ratio of polyether polyol, diisocyanate and catalyst in the prepolymer preparation process is 1:3.0:0.0001-1:4.5:0.0001.

10. The method for preparing a high-strength one-component moisture-curing polyurethane containing amide bonds according to claim 2, characterized in that: The curing temperature is 10-40°C, the relative humidity is 40-80%, and the curing time is 48-72 hours.

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