Asymmetric active chain extender, preparation method and application thereof, and preparation method of waterborne polyurethane

Abstract

The present invention provides an asymmetric active chain extender, a preparation method and application thereof, and a preparation method of waterborne polyurethane, and relates to the technical field of waterborne polyurethane synthesis. The asymmetric active chain extender of the present invention, the molecular chain of the chain extender contains asymmetric active primary amine and secondary amine groups respectively, once the highly active primary amine group in the chain extender reacts with the isocyanate group of the prepolymer, the chain extender is tethered to a particle, and the secondary amino group on the chain extender continues to react with the isocyanate group inside the particle to complete the chain extension of the prepolymer, thereby reducing the probability of the secondary amine group in the chain extender reacting with other prepolymer particles, and forming a waterborne polyurethane with a small particle size. The chain extender makes the prepared waterborne polyurethane have excellent stability, and can be used to prepare waterborne polyurethane with high solid content.

Description

Technical Field

[0001] The invention relates to the technical field of waterborne polyurethane synthesis, and in particular to an asymmetric active chain extender and a preparation method and application thereof, and a preparation method of waterborne polyurethane. Background Art

[0002] Waterborne polyurethane has a wide range of applications in coatings, inks, textiles, leather, adhesives and other industries. At present, a major preparation method for waterborne polyurethane is to introduce hydrophilic groups, such as carboxyl groups, tertiary amine groups, or oligo(poly)ethylene glycol segments into polyurethane prepolymers containing isocyanate end groups, and then quickly disperse the polyurethane prepolymers in water, and then add chain extenders for chain extension reactions to form anionic, cationic and nonionic waterborne polyurethanes. When a polyurethane prepolymer containing isocyanate end groups is placed in water, two competitive reactions can occur. First, the isocyanate end groups react with water to generate carbamic acid, which is unstable and decomposes into carbon dioxide and amines. In the case of an excess of isocyanate end groups, the generated amines will further react with the isocyanate end groups to generate urea. Second, the isocyanate end groups react with chain extenders to form polyurethane or urea. Generally speaking, the order of reaction rates of isocyanates with substances containing active hydrogen is: primary amine> secondary amine> alcohol> water> phenol. Therefore, in the preparation process of waterborne polyurethane, in order to inhibit the reaction of the polyurethane prepolymer containing isocyanate end groups with water, a chain extender containing primary amine or secondary amine is often used to carry out a chain extension reaction.

[0003] Studies have found that the chain extension reaction of polyurethane prepolymers may occur inside a single particle or between two or more particles (Langmuir 2018, 34, 11772-11783). The chain extension reaction occurring inside the particle can keep the particle size basically unchanged while increasing the molecular weight of the polyurethane, and the particle stability remains unchanged. The chain extension reaction occurring between two or more particles will increase the particle size and deteriorate the particle stability. Therefore, reducing the probability of chain extension reaction between particles and increasing the probability of chain extension reaction occurring inside particles are important ways to prepare high-performance waterborne polyurethane.

[0004] Commonly used amine chain extenders include ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, and isophoronediamine. These amine chain extenders contain two primary amine groups with basically the same activity. In the case of high concentration of prepolymer, the two primary amine groups react with the isocyanate groups on the prepolymer almost simultaneously, and the chain extension reaction between particles is difficult to avoid. Sodium ethylenediamine ethanesulfonate contains a primary amine group and a secondary amine group. On the one hand, it can reduce the chain extension reaction between particles. On the other hand, the soluble sodium sulfonate group can also improve the stability of waterborne polyurethane. It is a chain extender with excellent performance. However, sodium ethylenediamine ethanesulfonate is expensive. Summary of the invention

[0005] The purpose of the present invention is to provide an asymmetric active chain extender and a preparation method and application thereof, and a method for preparing waterborne polyurethane. The chain extender provided by the present invention has active asymmetric primary amine and secondary amine groups at both ends of the molecule, and the chain extender enables the prepared waterborne polyurethane to have excellent stability, and can be used to prepare high-concentration waterborne polyurethane with low preparation cost.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides an asymmetric active chain extender having a structure shown in Formula I:

[0008]

[0009] In formula I, R1 is an alkylene group, a cycloalkylene group, an aralkylene group or an alkyleneamino group, and R2 is an alkoxy group, a hydroxyl group or a methoxypolyethoxy group.

[0010] Preferably, the alkylene group in R1 is an alkylene group having 1 to 6 carbon atoms; the cycloalkylene group in R1 is a cycloalkylene group having 5 to 10 carbon atoms; the arylalkylene group in R1 is an arylalkylene group having 6 to 10 carbon atoms; and the alkyleneamino group in R1 is an alkyleneamino group having 2 to 6 carbon atoms.

[0011] Preferably, the alkoxy group in R2 is an alkoxy group having 1 to 10 carbon atoms.

[0012] Preferably, the chain extender comprises:

[0013]

[0014]

[0015] The present invention provides a method for preparing the chain extender described in the above technical solution, comprising the following steps:

[0016] The polyamine is mixed with acrylic acid or / and acrylic acid ester to carry out addition reaction to obtain an asymmetric active chain extender; the structural formula of the polyamine is NH2-R1-NH2; the structural formula of the acrylic acid or / and acrylic acid ester is

[0017] Preferably, the polyamine comprises a diamine and / or a triamine containing 2 primary amine groups;

[0018] The acrylic acid or / and acrylic acid ester includes one or more of acrylic acid, ethyl acrylate, propyl acrylate, butyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate and methoxy polyethylene glycol monoacrylate.

[0019] Preferably, the addition reaction includes a first addition reaction and a second addition reaction performed sequentially; the temperature of the first addition reaction is 5 to 45° C.; the time of the first addition reaction is 1 to 4 hours; the temperature of the second addition reaction is 40 to 60° C.; the time of the second addition reaction is 1 to 5 hours.

[0020] The present invention provides the use of the chain extender described in the above technical solution or the asymmetric active chain extender prepared by the preparation method described in the above technical solution in the preparation of waterborne polyurethane.

[0021] The present invention provides a method for preparing waterborne polyurethane, comprising the following steps:

[0022] A chain extender and an aqueous polyurethane prepolymer containing isocyanate end groups are mixed to carry out a chain extension reaction to obtain an aqueous polyurethane; the chain extender is the chain extender described in the above technical solution or an asymmetric active chain extender prepared by the preparation method described in the above technical solution.

[0023] Preferably, the amount of the primary amine group in the chain extender to the isocyanate terminal group in the waterborne polyurethane prepolymer is 0.3-0.5:1.

[0024] The present invention provides an asymmetric active chain extender, wherein the molecular chain of the chain extender contains asymmetric active primary amine and secondary amine groups respectively, and once the highly active primary amine group in the chain extender reacts with the isocyanate group of the prepolymer, the chain extender is tethered to a particle, and the secondary amine group on the chain extender continues to react with the isocyanate group inside the particle to complete the chain extension of the prepolymer, thereby reducing the probability of the secondary amine group in the chain extender reacting with other prepolymer particles, and forming a waterborne polyurethane with a small particle size. The chain extender of the present invention enables the prepared waterborne polyurethane to have excellent stability, and can be used to prepare waterborne polyurethane with high solid content. DETAILED DESCRIPTION

[0025] The present invention provides an asymmetric active chain extender having a structure shown in Formula I:

[0026]

[0027] In formula I, R1 is an alkylene group, a cycloalkylene group, an aralkylene group or an alkyleneamino group, and R2 is an alkoxy group, a hydroxyl group or a methoxypolyethoxy group.

[0028] In the present invention, the alkylene group in R1 is an alkylene group with 1 to 6 carbon atoms; the cycloalkylene group in R1 is a cycloalkylene group with 5 to 10 carbon atoms; the aralkylene group in R1 is an aralkylene group with 6 to 10 carbon atoms; the alkyleneamino group in R1 is an alkyleneamino group with 2 to 6 carbon atoms. In a specific embodiment of the present invention, R1 is ethylene, butyl or tetramethylcyclohexyl.

[0029] In the present invention, the alkoxy group in R2 is an alkoxy group having 1 to 10 carbon atoms. In the present invention, the structural formula of the methoxypolyethoxy group in R2 is In the methoxypolyethoxy group, n is preferably 10-12.

[0030] In a specific embodiment of the present invention, the chain extender comprises

[0031]

[0032]

[0033] The present invention provides a method for preparing the chain extender described in the above technical solution, comprising the following steps:

[0034] The polyamine is mixed with acrylic acid or / and acrylic acid ester to carry out addition reaction to obtain an asymmetric active chain extender; the structural formula of the polyamine is NH2-R1-NH2; the structural formula of the acrylic acid or / and acrylic acid ester is

[0035] In the present invention, the polyamine preferably includes a diamine and / or a triamine containing two primary amine groups. In the present invention, the polyamine preferably includes an amine containing at least two primary amine groups. In the present invention, the diamine preferably includes one or more of ethylenediamine, propylenediamine, butanediamine, 2-methylpentanediamine, hexamethylenediamine and isophoronediamine; the triamine containing two primary amine groups is preferably diethylenetriamine. In a specific embodiment of the present invention, when the polyamine is 1,4-butanediamine, it is preferred to heat the 1,4-butanediamine to melt and then mix it with acrylic acid or / and acrylate.

[0036] In the present invention, the acrylic acid or / and acrylate preferably includes one or more of acrylic acid, ethyl acrylate, propyl acrylate, butyl acrylate, n-hexyl acrylate, n-octyl acrylate, isooctyl acrylate and methoxy polyethylene glycol monoacrylate. In the present invention, the molecular weight of the methoxy polyethylene glycol monoacrylate is preferably 300 to 2000 Da. In a specific embodiment of the present invention, the molecular weight of the methoxy polyethylene glycol monoacrylate is about 550 Da. It should be noted that the molecular weight of the substance is an approximate value, whether it is an industrial product or a chemical reagent, wherein the ethoxy repeating unit number 10 is the main substance.

[0037] In the present invention, the ratio of the amount of the acrylic group in the acrylic acid or / and acrylic ester to the amount of the primary amine group in the polyamine is preferably 1:1.

[0038] In the present invention, the polyamine is preferably mixed with acrylic acid or / and acrylic ester by dropping acrylic acid or / and acrylic ester into the polyamine. In the present invention, the dropping is preferably completed within 2 hours.

[0039] In the present invention, the acrylic acid or / and acrylic acid ester is preferably dissolved in water first and then mixed with the polyamine. In the present invention, the concentration of the aqueous solution of acrylic acid or / and acrylic acid ester is preferably 30-100 wt%.

[0040] In the present invention, the addition reaction preferably includes a first addition reaction and a second addition reaction performed sequentially; the temperature of the first addition reaction is preferably 5 to 45°C, more preferably 25°C; the time of the first addition reaction is preferably 1 to 4 hours, more preferably 2 hours; the temperature of the second addition reaction is preferably 40 to 60°C, more preferably 50°C; the time of the second addition reaction is preferably 1 to 5 hours, more preferably 2 hours. In the present invention, the addition reaction is preferably carried out in a protective atmosphere, more preferably in a nitrogen atmosphere.

[0041] In the present invention, after the addition reaction, the obtained reaction system is preferably cooled to room temperature to obtain an asymmetric active chain extender.

[0042] The present invention provides the use of the chain extender described in the above technical solution or the asymmetric active chain extender prepared by the preparation method described in the above technical solution in the preparation of waterborne polyurethane. In the present invention, the solid content of the waterborne polyurethane is preferably 30-40%, more preferably 35%.

[0043] The present invention provides a method for preparing waterborne polyurethane, comprising the following steps:

[0044] A chain extender and an aqueous polyurethane prepolymer containing isocyanate end groups are mixed to carry out a chain extension reaction to obtain an aqueous polyurethane; the chain extender is the chain extender described in the above technical solution or an asymmetric active chain extender prepared by the preparation method described in the above technical solution.

[0045] In the present invention, the waterborne polyurethane prepolymer containing isocyanate terminal groups preferably includes one or more of waterborne aliphatic polyurethane prepolymers and waterborne aromatic polyurethane prepolymers, and more preferably is a waterborne aliphatic polyurethane prepolymer.

[0046] In the present invention, the amount of the primary amine group in the chain extender to the isocyanate terminal group in the waterborne polyurethane prepolymer is preferably 0.3-0.5:1.

[0047] In the present invention, the chain extender and the aqueous polyurethane prepolymer containing isocyanate end groups are preferably mixed in a manner that the chain extender or the aqueous chain extender solution is added to the aqueous polyurethane prepolymer containing isocyanate end groups. In the present invention, the mass concentration of the aqueous chain extender solution is preferably 30 to 100%, more preferably 30 to 50%.

[0048] In the present invention, the temperature of the chain extension reaction is preferably 2 to 30°C; the time of the chain extension reaction is preferably 1 to 5 hours; the atmosphere of the chain extension reaction is preferably air or nitrogen. In the present invention, the chain extension reaction is preferably carried out under stirring conditions.

[0049] In the present invention, preferably, after the chain extension reaction, the solvent is removed to obtain waterborne polyurethane. In the present invention, the method for removing the solvent is preferably reduced pressure distillation.

[0050] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Example 1

[0052] Under nitrogen protection, at 20°C, 601 g of ethylenediamine was added to a reactor equipped with a stirring blade and a cooling jacket. 1843 g of n-octyl acrylate was placed in a constant pressure dropping funnel and the n-octyl acrylate was dripped into the reactor within 2 hours, and the temperature of the reactor was controlled not to exceed 45°C. After the addition was completed, the reaction was continued at 25°C for another 2 hours. The reactor was then heated to 50°C, reacted for 2 hours, and cooled to room temperature to obtain asymmetric active chain extender A1.

[0053] The structural formula of the asymmetric active chain extender prepared in this example is:

[0054]

[0055] The hydrogen spectrum data are: 1 H NMR (400MHz, DMSO-d6) δ4.95(s,2H),3.93(t,J=6.0Hz,2H),2.92(t,J=4.1Hz,2H),2.72(t,J=4 .1Hz,2H),2.51(t,J=4.1Hz,2H),2.36(t,J=6.2Hz,2H),1.38-1.17(m,13H),0.89-0.81(m,3H).

[0056] The carbon spectrum data are: 13 C NMR (100MHz, DMSO-d6) δ171.13,64.82,50.57,44.32,41.09,34.08,31.81,29.32,28.86,28.67,25.88,22.67,14.07.

[0057] Example 2

[0058] Under nitrogen protection, 601 g of ethylenediamine was added to a reactor equipped with a stirring blade and a cooling jacket at 20°C. 1000 g of ethyl acrylate was placed in a constant pressure dropping funnel and dripped into the reactor within 2 hours under stirring, and the temperature of the reactor was controlled not to exceed 45°C. After the dripping was completed, the reaction was carried out at 25°C for 2 hours, and then the reactor was heated to 50°C, reacted for 2 hours, and cooled to room temperature to obtain asymmetric active chain extender A2.

[0059] The structural formula of the asymmetric active chain extender prepared in this example is:

[0060]

[0061] The hydrogen spectrum data are: 1 H NMR (400MHz, DMSO-d6) δ4.98 (s, 2H), 4.03 (q, J = 6.9Hz, 2H), 3.01 (t, J = 4.1Hz, 2H), 2.75 (t, J=5.8Hz,2H),2.62-2.54(m,2H),2.39(t,J=6.2Hz,2H),1.35(s,1H),1.13(t,J=6.9Hz,3H).

[0062] The carbon spectrum data are: 13 C NMR (100MHz, DMSO-d6) δ171.07,60.37,51.79,44.55,41.14,35.29,14.19.

[0063] Example 3

[0064] Under nitrogen protection, at 20°C, 882 g of 1,4-butanediamine was added to a reactor equipped with a stirring blade and a cooling jacket, and the temperature was raised to 30°C until the 1,4-butanediamine was melted. 1000 g of ethyl acrylate was placed in a constant pressure dropping funnel, and the ethyl acrylate was dripped into the reactor within 2 hours under stirring, and the temperature of the reactor was controlled not to exceed 45°C. After the addition was completed, the reaction was carried out at 25°C for 2 hours, and then the reactor was heated to 50°C, reacted for 2 hours, and cooled to room temperature to obtain an asymmetric active chain extender A3.

[0065] The structural formula of the asymmetric active chain extender prepared in this example is:

[0066]

[0067] The hydrogen spectrum data are: 1 H NMR (400MHz, DMSO-d6) δ4.95 (s, 2H), 4.00 (q, J = 6.9Hz, 2H), 3.07-2.92 (m, 4H), 2.7 9(t,J=4.1Hz,2H),2.34(t,J=6.2Hz,2H),1.39-1.21(m,5H),1.13(t,J=6.9Hz,3H).

[0068] The carbon spectrum data are: 13 C NMR (100MHz, DMSO-d6) δ172.65,60.17,48.34,39.81,39.41,33.64,28.71,26.85,15.12.

[0069] Example 4

[0070] Under nitrogen protection, at 20°C, 601 g of ethylenediamine was added to a reactor equipped with a stirring blade and a cooling jacket, 5500 g of methoxy polyethylene glycol monoacrylate (molecular weight 550 Da) and 2034 g of water were charged into a constant pressure dropping funnel, and the methoxy polyethylene glycol monoacrylate aqueous solution was dripped into the reactor under stirring within 2 hours, and the temperature of the reactor was controlled not to exceed 45°C. After the dropwise addition, the reaction was carried out at 25°C for 2 hours, and then the reactor was heated to 50°C, reacted for 2 hours, and cooled to room temperature to obtain asymmetric active chain extender A4.

[0071] The structural formula of the asymmetric active chain extender prepared in this example is:

[0072]

[0073] The hydrogen spectrum data are:1 H NMR (400MHz, DMSO-d6) δ4.98 (s, 2H), 4.15 (t, J=6.2Hz, 2H), 3.57-3.49 (m, 18H), 3.50-3.40 (m, 5H), 3.32 (t, J= 6.2Hz,18H),2.90(t,J=6.2,2H),2.74(t,J=5.9Hz,2H),2.57-2.48(m,2H),2.36(t,J=6.2Hz,2H),1.33(s,1H).

[0074] The carbon spectrum data are: 13 C NMR (100MHz, DMSO-d6) δ170.67,71.71,70.56,68.34,62.91,59.01,50.63,44.31,41.09,34.25.

[0075] Example 5

[0076] Under nitrogen protection, at 20°C, 882 g of 1,4-butanediamine was added to a reactor equipped with a stirring blade and a cooling jacket, and the temperature was raised to 30°C until the 1,4-butanediamine was melted. 5500 g of methoxy polyethylene glycol monoacrylate (molecular weight 550 Da) and 2127 g of water were placed in a constant pressure dropping funnel, and the methoxy polyethylene glycol monoacrylate aqueous solution was dripped into the reactor within 2 hours under stirring, and the temperature of the reactor was controlled not to exceed 45°C. After the addition was completed, the reaction was carried out at 25°C for 2 hours, and then the reactor was heated to 50°C, reacted for 2 hours, and cooled to room temperature to obtain asymmetric active chain extender A5.

[0077] The structural formula of the asymmetric active chain extender prepared in this example is:

[0078]

[0079] The hydrogen spectrum data are: 1 H NMR (400MHz, DMSO-d6) δ4.93 (s, 2H), 4.08 (t, J = 6.2Hz, 2H), 3.57-3.39 (m, 23H), 3.30 (t, J = 6. 2Hz,18H),3.06-2.92(m,4H),2.79(t,J=4.1Hz,2H),2.33(t,J=6.2Hz,2H),1.40-1.21(m,5H).

[0080] The carbon spectrum data are: 13C NMR (100MHz, DMSO-d6) δ170.95,71.72,70.55,68.34,62.92,59.01,48.59,42.42,40.63,34.09,27.78,25.54.

[0081] Example 6

[0082] Under nitrogen protection, at 20°C, 1703 g of isophorone diamine was added to a reactor equipped with a stirring blade and a cooling jacket, 5500 g of methoxy polyethylene glycol monoacrylate (molecular weight 550 Da) and 2401 g of water were charged into a constant pressure dropping funnel, and the methoxy polyethylene glycol monoacrylate aqueous solution was dripped into the reactor under stirring within 2 hours, and the temperature of the reactor was controlled not to exceed 45°C. After the dropwise addition, the reaction was carried out at 25°C for 2 hours, and then the reactor was heated to 50°C, reacted for 2 hours, and cooled to room temperature to obtain asymmetric active chain extender A6.

[0083] The structural formula of the asymmetric active chain extender prepared in this example is:

[0084]

[0085] The hydrogen spectrum data are: 1 H NMR (400MHz, DMSO-d6) δ4.37(t,J=6.1Hz,2H),3.86(s,2H),3.65(t,J=6.2Hz,18 H),3.48(s,3H),3.45-3.14(m,23H),2.67(dt,J=12.8,5.7Hz,1H),2.48(dt,J=12 .8,5.7Hz,1H),2.36(dt,J=15.9,6.2Hz,2H),1.86(s,1H),1.34(dd,J=13.4,6.7H z,1H),1.25(dd,J=13.3,6.7Hz,1H),1.16(d,J=12.9Hz,1H),0.99-0.86(m,12H).

[0086] The carbon spectrum data are: 13 C NMR (100MHz, DMSO-d6) δ172.05,71.72,70.55,68.35,62.96,59.01,54.33,50.96,48.86,47.04,44.71,42.93,35.22,34.02,32.29,30.35,24.68.

[0087] Example 7

[0088] 5000 g of dried polyether diol (DL2000, molecular weight 2000Da, Bluestar Dongda), 1112 g of isophorone diisocyanate, 201 g of dimethylol propionic acid and 2.0 g of bismuth catalyst (MC-710, Beijing Baiyuan Chemical) were added to the reactor, stirred evenly, heated to 75°C for reaction for 1.5 hours, 2154 g of acetone was added, the reaction was continued for 2 hours, the temperature was cooled to room temperature, 150 g of triethylamine was added, and the mixture was stirred for 5 minutes until uniform to obtain a polyurethane prepolymer solution B1 with a solid content of 75%, which was set aside.

[0089] Example 8

[0090] 5000 g of dried polyether diol (DL2000, molecular weight 2000Da, Bluestar Dongda), 871 g of toluene diisocyanate, 201 g of dimethylol propionic acid and 1.0 g of bismuth catalyst (MC-710, Beijing Baiyuan Chemical) were added to the reactor, stirred evenly, heated to 75°C and reacted for 1.5 hours, 2074 g of acetone was added, the reaction was continued for 2 hours, the temperature was cooled to room temperature, 150 g of triethylamine was added, and stirred for 5 minutes until uniform, to obtain a polyurethane prepolymer solution B2 with a solid content of 75%, which was set aside.

[0091] Application Examples

[0092] A certain amount of 5°C water was added to a certain amount of the polyurethane prepolymer solution of Examples 7-8, and the mixture was rapidly stirred for 4 minutes. A certain amount of asymmetric reactive chain extenders A1-A6 prepared in Examples 1-6 was then added within 2 minutes, and the mixture was stirred for 60 minutes. Acetone was removed by distillation under reduced pressure to obtain an aqueous polyurethane having a solid content of 35%. The details are shown in Tables 1 and 2.

[0093] Comparison samples 1-2

[0094] Comparative samples 1 and 2 use 50% ethylenediamine aqueous solution as a chain extender to prepare waterborne polyurethane. The implementation steps are the same as those of the application example except that 50% ethylenediamine aqueous solution is used as the chain extender. The details are shown in Table 1 and Table 2.

[0095] Table 1: Formula of water-based fatty polyurethane formed by chain extension of polyurethane prepolymer solution B1

[0096]

[0097] Table 2 Formulation of waterborne aromatic polyurethane formed by chain extension of polyurethane prepolymer solution B2

[0098]

[0099] Parameters and results analysis of waterborne polyurethane dispersion

[0100] The basic parameters of waterborne polyurethanes 1 to 12 and comparative samples 1 to 2 are shown in Table 3, wherein waterborne polyurethanes 1 to 6 and comparative sample 1 are waterborne fatty polyurethanes, and waterborne polyurethanes 7 to 12 and comparative sample 2 are waterborne aromatic polyurethanes. The appearance, solid content, viscosity, freeze-thaw stability and centrifugal stability of waterborne polyurethanes were tested with reference to GB / T 11175-2002; viscosity testing instrument: Brookfield viscometer DV1, determination method: direct test at 25°C. Volatile organic matter: tested with reference to GB / T 23986-2009. Freeze-thaw stability: 50 mL of waterborne polyurethane was placed in a -5±2°C low temperature box, taken out after 18 hours, and placed at 23±2°C for 6 hours, and the operation was repeated to observe whether there was precipitation. Centrifugal stability: 30 mL of water-based polyurethane was placed in a centrifuge and the centrifugal stability of the water-based polyurethane was tested at 3000 r / min for 30 min. The water-based polyurethane particle size testing instrument was ZetasizerNano ZS. The water-based polyurethane was diluted with water to a mass concentration of 1% for testing.

[0101] Table 3 Waterborne polyurethane parameters

[0102]

[0103] The results in Table 3 show that there are significant differences in particle size and stability between waterborne polyurethanes 1 to 12 and comparative samples 1 to 2. This indicates that the waterborne polyurethane dispersions obtained by using the chain extenders prepared in Examples 1 to 6 have small particle sizes and improved stability. The waterborne polyurethane dispersions obtained by using conventional ethylenediamine chain extenders have relatively large particle sizes, especially the waterborne aromatic polyurethane dispersions have relatively large particle sizes and slightly poor stability.

[0104] Analysis of parameters and results of dry film of waterborne polyurethane dispersion

[0105] The basic parameters of the waterborne polyurethane dry films of waterborne polyurethanes 1 to 12 and comparative samples 1 to 2 are shown in Table 4. Among them, the test method of the modulus of 100% tensile elongation (referred to as 100% modulus) and elongation at break is as follows: 3 grams of waterborne polyurethane is placed in a polytetrafluoroethylene mold, left for 2 days, dried naturally, and the 100% modulus and elongation at break are measured using a Shanghai Sonton WDW-5 universal material testing machine; gloss measurement: 60° gloss is measured using a microscopic three-dimensional light gloss meter (CS-380).

[0106] Table 4 Dry film performance parameters of waterborne polyurethane

[0107]

[0108] The results in Table 4 show that the dry films of waterborne polyurethanes prepared from waterborne polyurethanes 1 to 12 and comparative samples 1 to 2 are all transparent, and the glossiness is similar or the same. In Examples 1 to 6, the 100% modulus of the dry films of waterborne polyurethanes prepared from chain extenders containing low molecular weight polyethylene glycol segments is significantly lower than that of conventional ethylenediamine chain extension, and the elongation at break is improved (compared with waterborne polyurethanes 3, 4, 5, 6 and comparative sample 1, and waterborne polyurethanes 9, 10, 11, 12 and comparative sample 2); In Examples 1 to 6, the 100% modulus, elongation at break and glossiness of the dry films of waterborne polyurethanes prepared from chain extenders not containing low molecular weight polyethylene glycol segments are similar to that of conventional ethylenediamine chain extension (waterborne polyurethanes 1, 2 and comparative sample 1, and waterborne polyurethanes 7, 8 and comparative sample 2).

[0109] The above results show that the asymmetric active chain extender of the present invention can be used for the synthesis of highly stable waterborne polyurethane, and the physical properties of the waterborne polyurethane dry film can be adjusted by adjusting the structure of the chain extender to meet different requirements.

[0110] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. Application of an asymmetric active chain extender in the preparation of waterborne polyurethane, the preparation method of the asymmetric active chain extender is as follows: Under nitrogen protection, at 20°C, 1703 g of isophorone diamine was added to a reaction kettle equipped with a stirring paddle and a cooling jacket, 5500 g of methoxy polyethylene glycol monoacrylate and 2401 g of water were charged into a constant pressure dropping funnel, and under stirring, the methoxy polyethylene glycol monoacrylate aqueous solution was dripped into the reaction kettle within 2 hours, and the temperature of the reaction kettle was controlled not to exceed 45°C; after the dripping was completed, the reaction was carried out at 25°C for 2 hours, and then the reaction kettle was heated to 50°C, reacted for 2 hours, and cooled to room temperature to obtain an asymmetric active chain extender; the molecular weight of the methoxy polyethylene glycol monoacrylate was 550Da; The structural formula of the asymmetrically active chain extender is:

2. A method for preparing waterborne polyurethane, characterized in that: The following steps are involved: A chain extender is mixed with a waterborne polyurethane prepolymer containing isocyanate terminal groups to carry out a chain extension reaction to obtain a waterborne polyurethane; the chain extender is the asymmetric active chain extender as claimed in claim 1.

3. The preparation method according to claim 2, characterized in that: The amount of the primary amine group in the chain extender and the isocyanate terminal group in the waterborne polyurethane prepolymer is 0.3-0.5:1.

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