Dendritic photocurable waterborne polyurethane and method for preparing the same

Abstract

This invention belongs to the field of polymer materials technology, specifically relating to a dendritic photocurable waterborne polyurethane and its preparation method. The preparation method includes the following steps: Step S1, mixing and reacting a macromolecular polyol, a small molecule monomer containing monohydroxyl and allyl ether groups with a diisocyanate to prepare prepolymer A; Step S2, adding a hydrophilic chain extender to prepolymer A and reacting, then adding a hydroxyl-containing acrylate monomer for end-capping to obtain prepolymer B; Step S3, dispersing prepolymer B in an aqueous solution containing a terminal amino dendritic polymer, performing a post-chain extension reaction and emulsification to obtain a dendritic photocurable waterborne polyurethane. The dendritic photocurable waterborne polyurethane prepared by this invention exhibits excellent performance after curing, meeting the application requirements of high-demand fields such as PET optical films.

Description

Technical Field

[0001] This invention relates to a dendritic photocurable waterborne polyurethane and its preparation method, belonging to the field of polymer materials technology. Background Technology

[0002] UV-curable waterborne polyurethane (UV-WPU) is a new type of environmentally friendly functional material developed in the field of polymer materials to meet the demands of upgraded environmental policies, more efficient industrial production, and higher-end material performance. It integrates waterborne polyurethane systems with UV curing technology. Its technological development stems from breakthroughs in the application bottlenecks of traditional polyurethane materials and the synergistic innovation of UV curing and waterborne technologies. It has now become one of the core technological directions for achieving green upgrades in coatings, adhesives, inks, and other fields.

[0003] UV-curable waterborne polyurethane uses water as the dispersion medium, overcoming the dependence of traditional UV-curable resins on organic solvents. It offers advantages such as environmental friendliness, low viscosity, good leveling properties on various substrates, and short application time. Currently, the most widely used UV-curable waterborne polyurethanes in the industry mostly use carboxylates as hydrophilic monomers, a system with low raw material costs and ease of preparation. However, existing products of this type are predominantly linear in structure, and the crosslinking sites are mostly distributed at the ends of polyurethane chain segments, making it difficult to effectively increase the crosslinking density. To improve the physicochemical properties of UV-curable coatings, the key lies in increasing the number and crosslinking density of photosensitive groups on the polymer molecular chain. Increasing the amount of double bonds introduced provides more UV crosslinking sites, which is beneficial for elongating the resin molecular chain, thereby obtaining UV-curable waterborne polyurethanes with larger molecular weights and stronger cohesive energy.

[0004] Therefore, how to effectively increase the crosslinking density and double bond content while maintaining good processing and film-forming properties of the aqueous system, without introducing excessively high viscosity or complex synthesis processes, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned deficiencies in the prior art, this invention provides a dendritic photocurable waterborne polyurethane and its preparation method.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: One objective of this invention is to provide a method for preparing dendritic photocurable waterborne polyurethane, comprising the following steps: Step S1: Mix macromolecular polyol, small molecule monomers containing monohydroxyl and allyl ether groups with diisocyanate and react them to prepare prepolymer A; Step S2: Add a hydrophilic chain extender to the prepolymer A and react it, then add a hydroxyl-containing acrylate monomer for end capping to obtain prepolymer B; Step S3: Disperse the prepolymer B in an aqueous solution containing a terminal amino dendritic polymer, and carry out a post-chain extension reaction and emulsification to obtain the dendritic photocurable waterborne polyurethane.

[0007] Furthermore, in step S1, the small molecule monomer is trimethylolpropane monoallyl ether.

[0008] Furthermore, in step S1, the macromolecular polyol is at least one of polypentyl adipate, polyethylene glycol, polytetrahydrofuran glycol, polycaprolactone diol, polycarbonate diol, and polypropylene glycol.

[0009] Furthermore, in step S1, the diisocyanate is at least one of isophorone diisocyanate, toluene diisocyanate, and hexamethylene diisocyanate.

[0010] Furthermore, in step S1, the molar ratio of the macromolecular polyol, the small molecule monomer, and the diisocyanate is 1:0.2-0.8:3-5.

[0011] Furthermore, in step S2, the hydrophilic chain extender is dimethylolpropionic acid or dimethylolbutyric acid.

[0012] Furthermore, in step S2, the hydroxyl-containing acrylate monomer is hydroxyethyl methacrylate.

[0013] Furthermore, in step S3, the terminal amino dendritic polymer is a polyamide-amine dendritic polymer, and its generation is selected from G1, G2, G3 or G4.

[0014] Further, in step S3, a post-chain extension reaction and emulsification are carried out at 15℃~40℃ for 10~40 minutes to obtain the dendritic photocurable waterborne polyurethane; wherein, the molar ratio of amino groups (-NH2) in the terminal amino dendritic polymer to isocyanate groups (-NCO) in the prepolymer B is 0.8:1~1.5:1.

[0015] Furthermore, the solid content of the dendritic photocurable waterborne polyurethane obtained in step S3 is 20% to 40%.

[0016] The second objective of this invention is to provide a dendritic photocurable waterborne polyurethane, which is prepared using the above-described method for preparing dendritic photocurable waterborne polyurethane.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves the effect of simultaneously introducing double bond structures into both the side chains and end groups of the polyurethane molecular chain by using a small monomer containing monohydroxyl and allyl ether groups (such as trimethylolpropane monoallyl ether) in step S1 to pre-introduce allyl ether double bonds on the side chains of the polyurethane backbone, and then introducing double bonds at the ends through acrylate end-capping in step S2. During photocuring, these double bonds participate in the crosslinking reaction, forming a denser three-dimensional network structure than traditional systems that only contain double bonds at the ends.

[0018] In step S3 of this invention, terminal amino dendritic polymers are used for post-chain extension. Their highly branched structure and multiple terminal amino groups react with the isocyanate groups in prepolymer B to form a core-shell structure with the dendritic polymer as the core, which further increases the crosslinking density and the regularity of the molecular chain.

[0019] This invention utilizes the synergistic effect of two strategies: "side chain / terminal double bond photocrosslinking" and "dendritic polymer chemical crosslinking center" to produce a dendritic photocurable waterborne polyurethane that exhibits excellent ethanol wiping resistance, high hardness, good water resistance, and high tensile strength after curing, thus meeting the application requirements of high-demand fields such as PET optical films. Detailed Implementation

[0020] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0021] Example 1 I. Preparation of Dendritic Photocurable Waterborne Polyurethane Emulsion Step S1, Preparation of prepolymer A: 80.00 g (0.04 mol) of poly(neopentyl adipate) with a molecular weight of 2000, 3.48 g (0.02 mol) of trimethylolpropane monoallyl ether (TMPME), and 33.30 g (0.15 mol) of isophorone diisocyanate (IPDI) were added to a dry reaction vessel. The reaction was carried out at 70 °C for 1.5 h. During the reaction, the free NCO in the system was determined by the di-n-butylamine method, and prepolymer A was obtained with NCO content of 3.24%.

[0022] Step S2, Preparation of prepolymer B: 5.36 g (0.04 mol) of dimethylolpropionic acid (DMPA) and 0.10 g of catalyst MB20 (organic bismuth catalyst, Xindian Chemical) were added to prepolymer A above, and the reaction was continued for 2.5 h. During this period, the free NCO content in the system was measured. When the NCO content in the system reached 1.73%, 3.25 g (0.025 mol) of hydroxyethyl methacrylate (HEMA) was added for end-capping, and the reaction continued until the isocyanate group (-NCO) content dropped to below 0.1% (measured by di-n-butylamine method). The temperature was lowered to 60 °C, and 4.25 g (0.042 mol) of triethylamine was added to neutralize the carboxyl groups in the hydrophilic chain extender, to obtain aqueous polyurethane prepolymer B with single-end and double-bonded side chains.

[0023] Step S3, Post-chain extension and emulsification: 5.40 g of PAMAM G3-NH2 (molar mass approximately 6908 g / mol, terminally containing 32 -NH2 groups) was dissolved in 167 g of deionized water. Under stirring conditions, prepolymer B obtained in step S2 was slowly added to the above PAMAM G3-NH2 aqueous solution, with the temperature controlled at 40 °C. The mixture was dispersed and stirred for 20 min to obtain a dendritic photocurable waterborne polyurethane emulsion with a solid content of approximately 30.1%. The emulsion particle size was measured to be 246 nm using a Malvern particle size analyzer.

[0024] II. Preparation of Photocurable Coatings Weigh 5g of the above emulsion, add 0.3% of the emulsion solids content of wetting agent RT-111 (Shanghai Zhixia Technology Co., Ltd.), 0.4% of the thickener Vesmody U605 (Wanhua Chemical), and 3% of the photoinitiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, stir and mix evenly to obtain a photocurable composition.

[0025] The above composition was uniformly coated onto a clean galvanized iron sheet (25 mm × 120 mm × 0.2 mm) using a 100 μm wire bar coater. The sheet was dried in a 60 °C oven for 10 min and then cured in a 4 kW UV curing machine for 30 s to obtain a cured coating.

[0026] Example 2 Step S1, Preparation of prepolymer A: 80.00 g (0.04 mol) of poly(neopentyl adipate) with a molecular weight of 2000, 3.48 g (0.02 mol) of trimethylolpropane monoallyl ether (TMPME), and 33.30 g (0.15 mol) of isophorone diisocyanate (IPDI) were added to a dry reaction vessel. The reaction was carried out at 70 °C for 1.5 h. During the reaction, the free NCO in the system was determined by the di-n-butylamine method, and prepolymer A was obtained with NCO content of 3.24%.

[0027] Step S2, Preparation of prepolymer B: 5.92 g (0.04 mol) of dimethylolbutyric acid (DMBA) and 0.10 g of catalyst MB20 were added to prepolymer A, and the reaction was continued for 2.5 h. During this period, the free NCO content in the system was measured. When the NCO content in the system reached 1.71%, 3.25 g (0.025 mol) of hydroxyethyl methacrylate (HEMA) was added for end-capping, and the reaction continued until the isocyanate group content decreased to below 0.1% (measured using the di-n-butylamine method). The temperature was lowered to 60 °C, and 4.25 g (0.042 mol) of triethylamine was added to neutralize the carboxyl groups in the hydrophilic chain extender, yielding aqueous polyurethane prepolymer B with single-end and double-bonded side chains.

[0028] Step S3, Post-chain extension and emulsification: 10.18 g of PAMAM G2-NH2 (molar mass approximately 3256 g / mol, terminally containing 8 -NH2 groups) was dissolved in 278 g of deionized water. Under stirring conditions, prepolymer B obtained in step S2 was slowly added to the above PAMAM G2-NH2 aqueous solution, with the temperature controlled at 40°C. The mixture was dispersed and stirred for 20 min to obtain a dendritic photocurable waterborne polyurethane emulsion with a solid content of approximately 30.2%. The emulsion particle size was measured to be 195 nm using a Malvern particle size analyzer.

[0029] II. Preparation of Photocurable Coatings The preparation method is the same as in Example 1.

[0030] Example 3 I. Preparation of Dendritic Photocurable Waterborne Polyurethane Emulsion Step S1, Preparation of prepolymer A: 80.00 g (0.04 mol) of poly(neopentyl adipate) with a molecular weight of 2000, 3.48 g (0.02 mol) of trimethylolpropane monoallyl ether (TMPME), and 33.30 g (0.15 mol) of isophorone diisocyanate (IPDI) were added to a dry reaction vessel. The reaction was carried out at 70 °C for 1.5 h. During the reaction, the free NCO in the system was determined by the di-n-butylamine method, and prepolymer A was obtained with NCO content of 3.24%.

[0031] Step S2, Preparation of prepolymer B: 5.92 g (0.04 mol) of dimethylolbutyric acid (DMBA) and 0.10 g of catalyst MB20 were added to prepolymer A, and the reaction was continued for 2.5 h. During this period, the free NCO content in the system was measured. When the NCO content in the system reached 1.71%, 3.25 g (0.025 mol) of hydroxyethyl methacrylate (HEMA) was added for end-capping, and the reaction continued until the isocyanate group content decreased to below 0.1% (measured using the di-n-butylamine method). The temperature was lowered to 60 °C, and 4.25 g (0.042 mol) of triethylamine was added to neutralize the carboxyl groups in the hydrophilic chain extender, yielding aqueous polyurethane prepolymer B with single-end and double-bonded side chains.

[0032] Step S3, Post-chain extension and emulsification: 8.94 g of PAMAM G1-NH2 (molar mass approximately 1430 g / mol, containing 4 -NH2 groups at the end) was dissolved in 246 g of deionized water. Under stirring conditions, prepolymer B obtained in step S2 was slowly added to the above PAMAM G1-NH2 aqueous solution, with the temperature controlled at 40 °C. The mixture was dispersed and stirred for 20 min to obtain a dendritic photocurable waterborne polyurethane emulsion with a solid content of approximately 30.6%. The emulsion particle size was measured to be 170 nm using a Malvern particle size analyzer.

[0033] II. Preparation of Photocurable Coatings The preparation method is the same as in Example 1.

[0034] In the preparation method of the above embodiments, the reaction temperature of step S1 can be 60-85℃, and the reaction time can be 1-3h; the reaction temperature of step S2 can be 60℃-80℃, and the reaction time can be 1h-4h; the emulsification and dispersion of step S3 can be carried out at room temperature, the stirring speed can be 200rpm-1500rpm, and the dispersion time can be 10min-40min. Those skilled in the art can determine the reaction endpoint by monitoring the content of isocyanate groups (-NCO) in the system according to the type and ratio of raw materials.

[0035] Comparative Example 1 The raw materials and preparation process of this comparative example are basically the same as those in Example 3, except that in step S1, TMPME is replaced with 1,4-butanediol (BDO) in equal molar amounts, thus avoiding the introduction of side-chain double bonds and obtaining a dendritic photocurable waterborne polyurethane emulsion. The particle size of the emulsion was measured to be 172 nm using a Malvern particle size analyzer, and the solid content was approximately 30.2%.

[0036] Comparative Example 2 The raw materials and preparation process of this comparative example are basically the same as those of Example 3, except that in step S3, PAMAM is not used. Instead, prepolymer B is directly dispersed in deionized water for emulsification. The specific operation is as follows: 239g of deionized water was weighed and added to prepolymer B obtained in step S2 under stirring. Simultaneously, 3.5g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester and 2.98g (0.0125mol) of 3,3'-dimethyl-4,4-diaminodicyclohexylmethane were added dropwise. The temperature was controlled at 40℃, and the mixture was dispersed and stirred for 20 min to obtain a UV-curable waterborne polyurethane resin. The particle size of the emulsion was measured to be 160nm using a Malvern particle size analyzer, and the solid content was approximately 29.8%.

[0037] Performance testing The performance of the photocurable coatings prepared in each embodiment and comparative example was tested using the following methods: Pencil hardness: Select pencils with hardness grades of 9B-9H in sequence, place them in the pencil hardness tester at a 45° angle to the paint film, and slowly move the instrument on the sample. The pencil hardness value when the coating film is scratched is recorded as the hardness of the sample film.

[0038] Water resistance: After curing the coated sample at room temperature for 7 days, immerse it in deionized water and observe the surface condition of the paint film after 7 days.

[0039] Ethanol wiping resistance: After curing the coated sample in a well-ventilated indoor area for 7 days without light, use a cotton ball soaked in anhydrous ethanol to wipe the paint film repeatedly with a force of about 10N, and record the number of times the paint film is damaged.

[0040] Tensile strength and elongation at break: The cured independent film was tested in accordance with GB / T 1040.3-2023 standard.

[0041] The test results are shown in Table 1.

[0042] Table 1 Performance test results of each embodiment and comparative example

[0043] As shown in Table 1, the dendritic photocurable waterborne polyurethanes (Examples 1-3) prepared using the method of this invention exhibit significantly better hardness, water resistance, ethanol wiping resistance, and tensile strength than the comparative examples. Comparative Example 1, lacking double bonds, has a low crosslinking density and poor performance; Comparative Example 2, although incorporating side-chain double bonds, lacks post-chain extension by the dendritic polymer, resulting in significantly lower crosslinking density and performance compared to Examples 1-3. This indicates that the present invention successfully constructs a highly dense and orderly crosslinked network through the synergistic effect of introducing double bonds via side chains and post-chain extension by the dendritic polymer, achieving a significant improvement in coating performance.

[0044] Example 3 used PAMAM G1-NH2 for crosslinking. The reactant contained fewer crosslinking groups (-NH2) than in Examples 1 and 2, therefore, the tensile strength of Example 3 was lower than that of Examples 1 and 2, while the elongation at break was higher. Even so, compared to Example 3, Comparative Example 1 used BDO instead of TMPME, and BDO does not contain carbon-carbon double bonds that can participate in the photocrosslinking reaction; Comparative Example 2 did not introduce PAMAM and lacked crosslinking groups (-NH2). Therefore, the water resistance and ethanol wiping resistance of the coating in Example 3 were still superior to the two comparative examples.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing dendritic photocurable waterborne polyurethane, characterized in that, Includes the following steps: Step S1: Mix macromolecular polyol, small molecule monomers containing monohydroxyl and allyl ether groups with diisocyanate and react them to prepare prepolymer A; Step S2: Add a hydrophilic chain extender to the prepolymer A and react it, then add a hydroxyl-containing acrylate monomer for end capping to obtain prepolymer B; Step S3: Disperse the prepolymer B in an aqueous solution containing a terminal amino dendritic polymer, and carry out a post-chain extension reaction and emulsification to obtain the dendritic photocurable waterborne polyurethane.

2. The method for preparing dendritic photocurable waterborne polyurethane according to claim 1, characterized in that, In step S1, the small molecule monomer is trimethylolpropane monoallyl ether; the macromolecular polyol is at least one of polypentyl adipate, polyethylene glycol, polytetrahydrofuran glycol, polycaprolactone diol, polycarbonate diol, and polypropylene glycol.

3. The method for preparing dendritic photocurable waterborne polyurethane according to claim 1, characterized in that, In step S1, the diisocyanate is at least one of isophorone diisocyanate, toluene diisocyanate, and hexamethylene diisocyanate.

4. The method for preparing dendritic photocurable waterborne polyurethane according to claim 1, characterized in that, In step S1, the molar ratio of the macromolecular polyol, the small molecule monomer, and the diisocyanate is 1:0.2-0.8:3-5.

5. The method for preparing dendritic photocurable waterborne polyurethane according to claim 1, characterized in that, In step S2, the hydrophilic chain extender is dimethylolpropionic acid or dimethylolbutyric acid.

6. The method for preparing dendritic photocurable waterborne polyurethane according to claim 1, characterized in that, In step S2, the hydroxyl-containing acrylate monomer is hydroxyethyl methacrylate.

7. The method for preparing dendritic photocurable waterborne polyurethane according to claim 1, characterized in that, In step S3, the terminal amino dendritic polymer is a polyamide-amine dendritic polymer, and its generation is selected from G1, G2, G3 or G4.

8. The method for preparing dendritic photocurable waterborne polyurethane according to claim 1, characterized in that, In step S3, a post-chain extension reaction and emulsification are carried out at 15℃~40℃ for 10~40 minutes to obtain the dendritic photocurable waterborne polyurethane; wherein, the molar ratio of amino groups in the terminal amino dendritic polymer to isocyanate groups in the prepolymer B is 0.8:1~1.5:

1.

9. The method for preparing dendritic photocurable waterborne polyurethane according to claim 1, characterized in that, The solid content of the dendritic photocurable waterborne polyurethane obtained in step S3 is 20% to 40%.

10. A dendritic light-curing waterborne polyurethane, characterized in that, It is prepared by the method of any one of claims 1 to 9 for the preparation of dendritic photocurable waterborne polyurethane.

Images