Preparation method of light-cured polyurethane-urea acrylate based on unequal-activity polymerization

Abstract

The invention relates to the field of high polymer materials and the field of light-cured resin, in particular to an efficient and controllable preparation method of ureido-containing polyurethane-urea acrylate based on temperature control. According to the invention, carbamido is introduced by using an amino alcohol compound, so that polyurethane-urea acrylate is successfully prepared. The amino group and the hydroxyl group can react with isocyanate step by step through temperature regulation and control, so that a relatively high reaction rate is ensured, and meanwhile, the ureido group can be controllably introduced into the light-cured resin under a mild condition. The method disclosed by the invention has good controllability and reproducibility, and the prepared polyurethane-urea acrylate is relatively low in molecular weight distribution coefficient. And when the modified epoxy resin is applied to a photocureable coating, the hardness of a coating is remarkably improved, the tensile strength can reach 29.4 MPa to the maximum extent, the elongation at break can reach 117.9% to the maximum extent, and the modified epoxy resin has relatively good comprehensive performance. According to the invention, ureido is introduced into the light-cured resin, the original designability of polyurethane is retained, and the light-cured resin has great application potential in the field of light-cured coatings.

Description

Technical Field

[0001] The present invention relates to the fields of polymer materials and photocurable resins, and particularly to a method for efficiently and controllably preparing polyurethane-urea acrylate. Background Art

[0002] Due to the advantages of rapid curing and low VOCs emissions, photocurable materials have been widely used in fields such as coatings, adhesives, food packaging, and 3D printing. Photocurable coatings endow the coating with good mechanical and thermal properties due to the high crosslinking density of the curing system. However, in the actual production and application process, photocurable coatings often lack sufficient toughness due to the high crosslinking density, which limits their application. Polyurethane acrylate is a polyurethane prepolymer capped with acrylate groups. The main synthesis raw materials include diisocyanates, polyols, and photosensitive capping agents, etc. It has extremely strong structural designability and is one of the most commonly used photocurable resins.

[0003] Compared with the urethane group (─NHCOO─) formed by the reaction of isocyanate and hydroxyl group, the urea group (─NHCONH─) formed by the reaction of isocyanate and amino group is easier to form stronger hydrogen bond interactions, which can effectively improve the mechanical strength of the coating. And under the action of external force, more energy can be absorbed by sacrificing hydrogen bonds, and the movement ability of polymer chains can be improved, thereby improving the toughness of the coating.

[0004] Using the reaction of amino group and isocyanate to prepare polyurethane-urea acrylate is an effective means to improve the comprehensive performance of photocurable coatings. However, the reaction of isocyanate and primary amine is violent and accompanied by significant heat release. The generated heat will accelerate the reaction of the two, resulting in difficult process control. And due to the high polarity of the urea group, the product is difficult to dissolve, which also increases the difficulty of preparation and use. Although the viscosity and solubility of polyurea acrylate can be improved by extending the flexible chain, the increase in the molecular weight of polyurea acrylate will cause the system to easily gel and fail. In addition, polyurea acrylate can be prepared by adding solvents and controlling the temperature. However, the conditions of this synthesis method are extremely harsh, and isopropyl alcohol needs to be used as a solvent for construction, losing the advantage of environmental friendliness of photocuring.

[0005] The prior art faces problems such as difficult reaction control, high product viscosity, the need to use solvents to reduce viscosity, and difficult to increase the molecular weight when synthesizing urea group-containing acrylate; therefore, it is necessary to develop a new method to solve this problem. Summary of the Invention

[0006] To solve the problems existing in the prior art, the present invention proposes a method for preparing polyurethane-urea acrylate. An amino alcohol compound is used to introduce a urea group, and polyurethane-urea acrylate is successfully prepared. By controlling the temperature, the amino group and the hydroxyl group can react with isocyanate step by step, ensuring a high reaction rate while being able to introduce the urea group into the photocurable resin controllably under mild conditions.

[0007] The first aspect of the present invention lies in providing a synthesis method of polyurethane-urea acrylate based on non-equivalent reactivity polymerization, including the steps:

[0008] S1. Drop polypropylene glycol into diisocyanate, and stir and react at 35-50 °C for 1.5-3 h. The catalyst is an organotin catalyst;

[0009] S2. Drop the amino alcohol chain extender into the system obtained after the reaction in step S1, stir and react at 20-30 °C for 0.5-1.5 h, and then raise the temperature to 50-65 °C and continue to react for 1-2 h;

[0010] S3. After adding a radical inhibitor, slowly drop hydroxyethyl acrylate and react for 1.5-3 h to obtain polyurethane-urea acrylate.

[0011] Furthermore, the diisocyanate is selected from one or a combination of isophorone diisocyanate, 1,6-hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate, and toluene diisocyanate.

[0012] In some embodiments of the present invention, in step S1, the molar ratio of diisocyanate to polypropylene glycol is 2:1-4:1;

[0013] Furthermore, in step S1, the molecular weight of the polypropylene glycol is 200-1000; including but not limited to one or a combination of polypropylene glycol-200, polypropylene glycol-400, polypropylene glycol-600, polypropylene glycol-800, and polypropylene glycol-1000;

[0014] In some embodiments of the present invention, the organotin catalyst includes one or several of dibutyltin dilaurate, stannous octoate, bis(dodecylthio)dibutyltin, and dibutyltin diacetate.

[0015] In some embodiments of the present invention, in step S1, the molar ratio of the polypropylene glycol to the organotin catalyst is 1:0.0002-1:0.0004.

[0016] Furthermore, in step S2, the molar ratio of the amino alcohol chain extender to the diisocyanate is 1:4-2:5;

[0017] In some embodiments of the present invention, the amino alcohol chain extender is a compound containing hydroxyl and amino groups in its molecular structure, including but not limited to one or more of 2-(2-aminoethoxy)ethanol, ethanolamine, and 4-aminocyclohexanol.

[0018] More preferably, the amino alcohol chain extender is an amino alcohol compound containing a primary amine group, which has a higher hydrogen bond strength and a greater activity difference with a hydroxyl group.

[0019] The invention utilizes the difference in the reactivity of amino groups and hydroxyl groups in amino alcohol compounds with isocyanate and controls the reaction conditions to make isocyanate react with primary amine first to introduce urea groups.

[0020] Furthermore, in step S3, the molar ratio of hydroxyethyl acrylate to diisocyanate is 1:2-1:5.

[0021] Furthermore, the free radical inhibitor includes one or more of p-methoxyphenol, hydroquinone, and p-tert-butylcatechol;

[0022] In some embodiments of the present invention, the molar ratio of the free radical inhibitor to hydroxyethyl acrylate is 1:50.

[0023] The second aspect of the present invention provides polyurethane-urea acrylate prepared by the preparation method. The polyurethane-urea acrylate prepared by the method of the present invention has good controllability.

[0024] Furthermore, the polyurethane-urea acrylate has a molecular weight distribution coefficient of less than 1.8, and a number average molecular weight range of 2000-3000, 3000-4000, 4000-5000, or 5000-6000.

[0025] In some preferred embodiments, the polyurethane-urea acrylate has a molecular weight distribution of no more than 1.7 and a number average molecular weight between 2450 and 2550.

[0026] In some embodiments of the present invention, the structural formula of the polyurethane-urea acrylate is:

[0027]

[0028] The value of n ranges from 2 to 27.

[0029] The third aspect of the present invention is to provide the use of the polyurethane-urea acrylate in photocurable coatings, adhesives, and functional materials.

[0030] In some embodiments of the present invention, a photocurable coating composition is prepared, and the photocurable coating composition includes the following components:

[0031]

[0032] Further, the reactive diluent includes one or more of isobornyl acrylate, tetrahydrofurfuryl acrylate, and trimethylolpropane formal acrylate;

[0033] Further, the photoinitiator includes one or more of photoinitiator 1173, photoinitiator 819, photoinitiator 2959, and photoinitiator TPO;

[0034] Further, the adhesion promoter includes one or more of CD-9051, EM-2, and EM-3.

[0035] In some embodiments of the present invention, the photocurable coating composition is a metal-based photocurable coating, and the method for preparing the coating includes the steps:

[0036] (1) Mix the above polyurethane-urea acrylate with a photoinitiator, a reactive diluent, and an adhesion promoter;

[0037] (2) After dispersing the weighed sample evenly using a homogenizer, ultrasonicate for 30 - 60 min to fully eliminate air bubbles;

[0038] (3) Prepare a coating using a 60 μm wet film thickness applicator and then cure it using a UV lamp.

[0039] Beneficial effects:

[0040] (1) The preparation method provided by the present invention uses an amino alcohol compound to introduce a urea group, and successfully prepares polyurethane-urea acrylate; by controlling the temperature, the amino group and the hydroxyl group can react with the isocyanate step by step, ensuring a high reaction rate while being able to controllably introduce the urea group into the photocurable resin under mild conditions.

[0041] (2) The synthesis method based on temperature-controlled activity provided by the present invention has good controllability and reproducibility, and the polyurethane-urea acrylate prepared has a low polydispersity index (not higher than 1.7); the number average molecular weight is between 2450 and 2550.

[0042] (3) The present invention further applies the prepared polyurethane-urea acrylate to the photocurable resin. The urethane group replaces part of the urea group, reducing the resin viscosity and facilitating operation and construction without the need to add additional solvents. The urea hydrogen bond acts as a physical crosslinking point, making the polyurethane-urea acrylate exhibit higher tensile strength and modulus, and significantly improving the hardness of the prepared coating.

[0043] (4) The present invention not only introduces urea groups into the photocurable resin but also retains the original designability of polyurethane; different resin properties can be achieved through different amino alcohol structures (such as structures containing ether bonds, rigid rings, etc.); it has great application potential in the field of photocurable coatings. Description of the Drawings

[0044] The drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation to the present application. In the drawings:

[0045] Figure 1 Synthesis routes of polyurethane-urea acrylate in Examples 1-3 of the present invention;

[0046] Figure 2 Synthesis route of Comparative Example 1;

[0047] Figure 3 Non-equivalent activity polymerization process (isocyanate concentration monitoring) in Example 1;

[0048] Figure 4 NMR & IR spectra of the products prepared in Examples 1-3 and Comparative Example 1;

[0049] Figure 5 Gel permeation chromatography of the products prepared in Examples 1-3 and Comparative Example 1;

[0050] Figure 6 Stress-strain diagrams of the coatings prepared in Examples 4-6 and Comparative Example 2. Detailed Description of the Invention

[0051] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following describes the specific embodiments of the present invention in detail in conjunction with the embodiments of the specification. Many specific details are set forth in the following description to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0052] The experimental methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0053] Test and characterization methods used in the examples:

[0054] Determination of isocyanate content: The concentration of isocyanate in the reaction system was tested using the dibutylamine / toluene titration method. The specific steps are as follows: (1) Weigh approximately 10 mg of the reaction mixture into a conical flask, add 25 ml of 0.1 mol / L dibutylamine / toluene solution, and add 10 ml of isopropanol as a solvent. After thorough homogenization, seal it and let it stand in the dark for 10 min; (2) Add 25 ml of isopropanol and 2 drops of bromocresol green indicator, and shake well; (3) Titrate with a calibrated hydrochloric acid solution until the solution in the conical flask changes from blue to yellow and does not fade within 30 s, which is regarded as the end point of titration. Additionally, a sample without adding the reaction mixture was used as a blank group for titration.

[0055] The NCO% is calculated by the following formula:

[0056]

[0057] where V0 (ml) is the volume of hydrochloric acid consumed in the titration of the blank group, V x (ml) is the volume of hydrochloric acid consumed in the titration of the experimental group, c (mol / L) is the concentration of the hydrochloric acid solution, and m (g) is the mass of the reaction mixture.

[0058] Infrared spectroscopy: The Fourier transform infrared spectrometer was used to detect the characteristic absorption peaks of the oligomer structure.

[0059] 1H nuclear magnetic resonance spectroscopy: The 1H nuclear magnetic resonance spectrum of the oligomer was tested using a nuclear magnetic resonance spectrometer. The internal standard used during the test was TMS (tetramethylsilane), the solvent was deuterated dimethyl sulfoxide (DMSO), and the frequency was 400 MHz.

[0060] Gel permeation chromatography: Gel permeation chromatography (GPC) was used to test the relative molecular mass and relative molecular mass distribution (PDI). Among them, tetrahydrofuran (1.0 mL / min) was used as the mobile phase, polystyrene standards were used to determine the relative molecular mass, and the mass concentration of the sample to be detected was 5 - 10 mg / mL.

[0061] Tensile test: A universal testing machine was used to test the tensile behavior of the specimen. The test temperature was 25 °C, and the tensile rate was 5 mm / min. The specimen was a dumbbell-shaped specimen with dimensions of 16 mm × 4 mm × 2 mm. Each material was tested at least three times, and the average value of the test results was taken.

[0062] Basic performance tests of the coating: The gloss (60°) of the coating was tested according to GB / T 9754—2007; the thickness of the coating was tested according to GB / T 13452.2—2008; the pencil hardness of the coating was tested according to GB / T 6739—2006; the impact resistance of the coating was tested using an impact tester according to GB / T 1732—2020; the pendulum hardness of the coating was tested according to ASTM D 4366-2016; the pull-off adhesion of the coating was tested according to ASTM D 4541—2009.

[0063] The synthetic routes of polyurethane-urea acrylate in Examples 1-3 of the present invention are as Figure 1 shown; the synthetic route of Comparative Example 1 is as Figure 2 shown.

[0064] Example 1:

[0065] The amounts of chemical reagents used for synthesizing polyurethane-urea acrylate in this example are as follows: isophorone diisocyanate 22.2 g, polypropylene glycol-400, 20 g, aminoethanol 1.53 g, 2-hydroxyethyl acrylate 5.8 g, dibutyltin dilaurate 0.011 g, p-methoxyphenol 0.02 g;

[0066] The synthesis steps are as follows:

[0067] 1. Place isophorone diisocyanate and dibutyltin dilaurate in a 100 ml three-necked flask and stir mechanically. Slowly add polypropylene glycol 400 at 40 °C. After the addition is complete, react for 2 h;

[0068] 2. Control the temperature at 30 °C, slowly add aminoethanol. After the addition is complete, stir and react for 1 h, then raise the temperature to 60 °C and continue to react for 1 h;

[0069] 3. After adding p-methoxyphenol, slowly add 2-hydroxyethyl acrylate and react for 2 h to obtain polyurethane-urea acrylate.

[0070] Example 2:

[0071] The amounts of chemical reagents used for synthesizing polyurethane-urea acrylate in this example are as follows:

[0072] isophorone diisocyanate 22.2 g, polypropylene glycol 400 20 g, 2-(2-aminoethoxy)ethanol 2.63 g, 2-hydroxyethyl acrylate 5.8 g, dibutyltin dilaurate 0.011 g, p-methoxyphenol 0.02 g;

[0073] The synthesis steps are as follows:

[0074] 1. Place isophorone diisocyanate and dibutyltin dilaurate in a 100 ml three-necked flask and stir mechanically. Slowly add polypropylene glycol 400 dropwise at 35 °C. After the addition is complete, react for 2.5 h;

[0075] 2. Control the temperature at 30 °C and slowly add 2-(2-aminoethoxy)ethanol dropwise. After the addition is complete, stir and react for 0.5 h, then raise the temperature to 60 °C and continue to react for 1.5 h;

[0076] 3. After adding p-methoxyphenol, slowly add hydroxyethyl acrylate and react for 2.5 h to obtain polyurethane-urea acrylate.

[0077] Example 3:

[0078] The amounts of chemical reagents for synthesizing polyurethane-urea acrylate in this example are as follows:

[0079] Isophorone diisocyanate 22.2 g, polypropylene glycol 400 20 g, 4-aminocyclohexanol 2.88 g, 2-hydroxyethyl acrylate 5.8 g, dibutyltin dilaurate 0.011 g, p-methoxyphenol 0.02 g;

[0080] The synthesis steps are as follows:

[0081] 1. Place isophorone diisocyanate and dibutyltin dilaurate in a 100 ml three-necked flask and stir mechanically. Slowly add polypropylene glycol 400 dropwise at 45 °C. After the addition is complete, react for 2 h;

[0082] 2. Control the temperature at 25 °C and slowly add 4-aminocyclohexanol dropwise. After the addition is complete, stir and react for 2 h, then raise the temperature to 65 °C and continue to react for 2 h;

[0083] 3. After adding p-methoxyphenol, slowly add hydroxyethyl acrylate and react for 3 h to obtain polyurethane-urea acrylate.

[0084] Comparative Example 1:

[0085] The amounts of chemical reagents for synthesizing polyurethane acrylate are as follows:

[0086] Isophorone diisocyanate 22.2 g, polypropylene glycol 400 30 g, 2-hydroxyethyl acrylate 5.8 g, dibutyltin dilaurate 0.011 g, p-methoxyphenol 0.02 g.

[0087] The steps are as follows:

[0088] 1. Place isophorone diisocyanate and dibutyltin dilaurate in a 100 ml three-necked flask and stir mechanically. Slowly add polypropylene glycol 400 dropwise at 45 °C. After the addition is complete, react for 4 h;

[0089] 2. After adding p-methoxyphenol, the temperature was raised to 65 °C, and hydroxyethyl acrylate was slowly added dropwise and reacted for 3 h to obtain polyurethane acrylate.

[0090] Monitoring of non-equivalent reactivity polymerization process: The change in isocyanate concentration during step 2 in Example 1 was monitored using titration method. As Figure 3 shown, at 30 °C, NCO reacted rapidly and approached the reaction midpoint within 5 min. Continuing the reaction to 60 min, the isocyanate concentration hardly changed. After raising the temperature to 60 °C, the isocyanate concentration decreased again, proving that the reaction activity can be controlled by temperature to achieve the controllable preparation of polyurethane-urea acrylate.

[0091] As Figure 4 shown by the NMR test results: The characteristic absorption peaks at δ = 6.7 - 7.2 belong to the hydrogen protons on the carbamate or urea group, the signal peaks at δ = 5.9 - 6.4 correspond to the hydrogen protons on the acrylate double bond, the absorption peaks at δ = 4.1 - 4.7 are generated by the hydrogen protons of the methylene or methine group connected to the oxygen atom of the carbamate structure, δ = 2.7 - 3.7 corresponds to the absorption peaks generated by the hydrogen protons of the methylene or methine group connected to the secondary amino group of the carbamate or urea group in the resin structure, δ = 2.5 is the hydrogen proton peak of deuterated DMSO, and δ = 0.6 - 1.6 is the characteristic absorption peaks of the hydrogen protons on the methyl group and the methyl or methylene group on the six-membered ring in the PPG400 chain segment of the resin structure. This series of results further indicates the successful preparation of polyurethane-urea acrylate and polyurethane acrylate.

[0092] As Figure 4 shown by the IR test results: The characteristic peak attributed to the isocyanate group at 2250 cm -1 in the IR spectrum of the resin product disappeared, indicating that there was no free isocyanate group in the raw materials, indicating that the IPDI reaction was complete. The appearance of characteristic peaks attributed to the amino group (─NH─) in the carbamate (─NHCOO─) and urea group (─NHCONH─) was observed at 3330 cm -1 . The successful synthesis of polyurethane and polyurethane-urea structures was indicated. The appearance of characteristic peaks attributed to the carbon-carbon double bond (─C=C─) of the acrylate group was observed at 1650 cm -1 , 1410 cm -1 , and 810 cm -1 . The acrylate group with photocuring activity was successfully introduced into the resin structure. It was proved that the target polyurethane and polyurethane-urea acrylate were successfully synthesized.

[0093] From Figure 5It can be seen that the number-average molecular weights of the three polyurethane-urea acrylates PUUA-AE, PUUA-DEG, and PUUA-ACH prepared in Examples 1-3 are 2447, 2536, and 2504 respectively, and the molecular weight distributions are 1.6, 1.7, and 1.6 respectively; the number-average molecular weight of the polyurethane acrylate PUA-PPG400 prepared in Comparative Example 1 is 2967, and the molecular weight distribution is 1.8. The number-average molecular weights of the four resins are very close to the designed theoretical molecular weights, and the molecular weight distribution coefficients are relatively low, indicating that the target polyurethane-urea acrylate can be successfully synthesized using this synthesis method and has good controllability.

[0094] Example 4:

[0095] The preparation method of the metal-based photocurable coating is as follows:

[0096] 1. Mix the polyurethane-urea acrylate in Example 1 with photoinitiator 1173, reactive diluent isobornyl acrylate, and adhesion promoter CD-9051.

[0097] 2. After dispersing the weighed sample evenly using a homogenizer, ultrasonicate for 30 min to fully eliminate air bubbles.

[0098] 3. Prepare a coating using a 60-μm wet film thickness doctor blade and then cure it using a UV lamp.

[0099] In the preparation method, the dosages of the components of the photocurable coating are as follows: polyurethane-urea acrylate 68%, isobornyl acrylate 30%, photoinitiator 1173 (1%), and adhesion promoter CD-9051 (1%).

[0100] Example 5:

[0101] The preparation method of the metal-based photocurable coating is as follows:

[0102] 1. Mix the polyurethane-urea acrylate in Example 2 with photoinitiator 1173, reactive diluent isobornyl acrylate, and adhesion promoter CD-9051.

[0103] 2. After dispersing the weighed sample evenly using a homogenizer, ultrasonicate for 30 min to fully eliminate air bubbles.

[0104] 3. Prepare a coating using a 60-μm wet film thickness doctor blade and then cure it using a UV lamp.

[0105] In the preparation method, the dosages of the components of the photocurable coating are as follows: polyurethane-urea acrylate 68%, isobornyl acrylate 30%, photoinitiator 1173 (1%), and adhesion promoter CD-9051 (1%).

[0106] Example 6:

[0107] The preparation method of the metal-based photocurable coating is as follows:

[0108] 1. Mix the polyurethane-urea acrylate, photoinitiator 1173, reactive diluent isobornyl acrylate, and adhesion promoter CD-9051 in Example 3.

[0109] 2. After dispersing the weighed sample evenly with a homogenizer, ultrasonicate it for 30 min to fully eliminate air bubbles.

[0110] 3. Prepare a coating using a 60-μm wet film thickness doctor blade and then cure it with a UV lamp.

[0111] In the preparation method, the dosages of the components of the photocurable coating are as follows: polyurethane-urea acrylate 68%, isobornyl acrylate 30%, photoinitiator 1173 (1%), adhesion promoter CD-9051 (1%).

[0112] Comparative Example 2:

[0113] The preparation method of the metal-based photocurable coating is as follows:

[0114] 1. Mix the polyurethane acrylate, photoinitiator 1173, reactive diluent isobornyl acrylate, and adhesion promoter CD-9051 in Comparative Example 1.

[0115] 2. After dispersing the weighed sample evenly with a homogenizer, ultrasonicate it for 30 min to fully eliminate air bubbles.

[0116] 3. Prepare a coating using a 60-μm wet film thickness doctor blade and then cure it with a UV lamp.

[0117] In the said preparation method, the dosages of the components of the photocurable coating are as follows: polyurethane acrylate 68%, isobornyl acrylate 30%, photoinitiator 1173 (1%), adhesion promoter CD-9051 (1%).

[0118] As Figure 6 shown in Table 1, the polyurethane-urea acrylate films prepared in Examples 4 - 6 showed obvious yield behavior during the tensile process. The yield behavior originated from the dissociation of hydrogen bonds under stress and the release of additional tensile length. Examples 4 and 6 had higher tensile strength and elastic modulus, and both yielded at lower tensile strains, with a fracture strain less than 50% and a fracture energy less than 10 MJ / m 3This is because Examples 4 and 6 lack flexible chain segments, resulting in difficult movement of molecular chains during film stretching. Intermolecular hydrogen bonds cannot dissociate to absorb energy, causing the hydrogen bonds in these two samples to be unable to provide additional toughness and brittle fracture to occur prematurely under tensile stress. In contrast, Example 5 not only has a relatively high mechanical strength (22.1 MPa), but also has an elongation at break of 117.9%. This is because it has more ether bond segments compared to the other two polyurethane-urea acrylates, making it easier for hydrogen bonds to dissociate and absorb energy during stretching, thereby playing the role of hydrogen bond strengthening and toughening. In Comparative Example 2, due to the lack of ureido hydrogen bonds, it exhibits the lowest tensile strength.

[0119] Table 1 Mechanical properties of cured films

[0120]

[0121] As can be seen from Table 2, the pencil hardness and pendulum hardness of the coatings prepared in Examples 4 - 6 are relatively high. This is because strong hydrogen bonds in polyurethane-urea acrylate act as physical crosslinking points in the system, increasing the coating hardness. Among them, Example 6 has the highest hardness because its molecular structure contains more rigid rings. In addition, the relatively high bond energy of ureido hydrogen bonds results in inefficient dissociation and absorption of energy under instantaneous impact stress, leading to the destruction of the molecular chain structure. It is worth noting that Example 5 has a relatively high hardness, and its impact strength also reaches 6 J, showing better comprehensive performance. Due to the lack of ureido hydrogen bonds as physical crosslinking points, Comparative Example 2 exhibits the lowest hardness, but has the best impact toughness due to the strongest molecular chain movement ability.

[0122] Table 2 Basic properties of four UV-cured coatings

[0123]

[0124]

[0125] In summary, the present invention successfully prepared polyurethane-urea acrylate using amino alcohols with different structures. The method of the present invention can regulate the reaction sequence of amino / hydroxy groups with isocyanate through temperature, enabling amino and hydroxy groups to react with isocyanate step by step. While ensuring a relatively high reaction rate, it can controllably introduce ureido groups into the photocurable resin under mild conditions. By controlling the reaction conditions, the present invention enables isocyanate to react with primary amine preferentially to introduce ureido groups, and under these reaction conditions, isocyanate does not react with hydroxy groups, restricting the further polycondensation of the resin and avoiding gelation. Then, by changing the reaction conditions, hydroxy groups react with isocyanate, and finally, a photosensitive capping agent is used for capping to prepare the photocurable polyurethane-urea acrylate.

[0126] The polyurethane-urea acrylate synthesized in the present invention has higher mechanical strength and glass transition temperature. The ureido hydrogen bond acts as a physical crosslinking point, enabling the polyurethane-urea acrylate to exhibit higher tensile strength and modulus. When applied to photocurable coatings, the hardness of the coating is significantly improved, the maximum tensile strength can reach 29.4 MPa, and the maximum elongation at break can reach 117.9%, showing good comprehensive performance.

[0127] The method for preparing polyurethane-urea acrylate based on amino alcohol in the present invention not only introduces ureido groups into the photocurable resin but also retains the original designability of polyurethane, providing new ideas for the development of novel photocurable resins and having great application potential in the field of photocurable coatings.

[0128] Compared with traditional polyurea acrylate, in the polyurethane-urea acrylate prepared in the present invention, the urethane structure of polyurethane replaces part of the ureido groups, which can reduce the hydrogen bond density and strength (reduce the resin viscosity), so that the coating can be synthesized and fabricated without using organic solvents to reduce the viscosity, facilitating the operation and construction of metal-based photocurable coatings. The synthesized photocurable resin has excellent performance and does not require the use of organic solvents to reduce the viscosity during application, maintaining the green and environmental-friendly characteristics of the photocuring technology.

[0129] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the present invention.

Claims

1. A synthesis method of polyurethane-urea acrylate based on non-equivalent reactivity polymerization, characterized in that, Including the steps: S1. Drop polypropylene glycol into diisocyanate, and stir and react at 35 - 50 °C for 1.5 - 3 h. The catalyst is an organotin catalyst; S2. Drop the amino alcohol chain extender into the system after the reaction in step S1, stir and react at 20 - 30 °C for 0.5 - 1.5 h, and then raise the temperature to 50 - 65 °C and continue to react for 1 - 2 h; S3. After adding a radical inhibitor, slowly dropwise add hydroxyethyl acrylate and react for 1.5 - 3 h to obtain polyurethane-urea acrylate.

2. The synthesis method of polyurethane-urea acrylate according to claim 1, wherein, In step S1, the molar ratio of diisocyanate to polypropylene glycol is 2∶1 - 4∶1; and / or, the diisocyanate is selected from one or a combination of isophorone diisocyanate, 1,6-hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate.

3. The synthesis method of polyurethane-urea acrylate according to claim 1, wherein, In step S1, the molecular weight of the polypropylene glycol is 200 - 1000; including but not limited to one or a combination of polypropylene glycol-200, polypropylene glycol-200, polypropylene glycol-400, polypropylene glycol-600, polypropylene glycol-800, polypropylene glycol-1000; and / or, the organotin catalyst includes one or several of dibutyltin dilaurate, stannous octoate, di(dodecylthio)dibutyltin, dibutyltin diacetate.

4. The synthesis method of polyurethane-urea acrylate according to claim 1, wherein, In step S1, the molar ratio of the polypropylene glycol to the organotin catalyst is 1∶0.0002 - 1∶0.0004.

5. The synthesis method of polyurethane-urea acrylate according to claim 1, wherein, In step S2, the molar ratio of the amino alcohol chain extender to the diisocyanate is 1∶4 - 2∶5; and / or, the amino alcohol chain extender is a compound containing hydroxyl and amino in its molecular structure, including but not limited to one or several of 2-(2-aminoethoxy)ethanol, ethanolamine, 4-aminocyclohexanol.

6. The synthesis method of the polyurethane-urea acrylate according to claim 1, characterized in that, In step S3, the molar ratio of hydroxyethyl acrylate to diisocyanate is 1∶2 - 1∶5.

7. The synthesis method of polyurethane-urea acrylate according to claim 1, characterized in that, In step S3, the radical inhibitor includes one or several of p-methoxyphenol, hydroquinone, p-tert-butylcatechol.

8. A polyurethane-urea acrylate, characterized in that, The structural formula is: wherein, the value range of n is 2 to 27.

9. The application of the polyurethane-urea acrylate according to claim 8 in photocurable coatings, adhesives, and functional materials.

10. The application according to claim 9, characterized in that, For preparing a photocurable coating composition, the photocurable coating composition comprises the following components:

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