Preparation of Rigid Hydrogels Based on Multi-branched Epoxy Oligopolymer Crosslinked Polyurethane and Their Application in Moisture-locking and Fragrance-preserving Packaging Materials

Abstract

This invention belongs to the field of polymer materials technology and relates to a method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane. The method includes: weighing a polyurethane prepolymer, stirring and heating to 60-90°C, slowly adding a multi-branched epoxy oligomer dispersion, and reacting for 1-5 hours; determining the theoretical content of isocyanate groups using the di-n-butylamine method, and adjusting the system temperature to 35-55°C after reaching the theoretical value, and slowly adding a salting agent; cooling to room temperature, and removing the solvent by vacuum distillation using residual heat during the cooling stage; adding deionized water, and stirring until a white emulsion is obtained. This invention also applies the prepared rigid hydrogel to moisture-locking and fragrance-preserving packaging materials. The rigid hydrogel prepared by this invention exhibits stronger rigidity due to the introduction of a branched framework in its structure. When combined with aluminized paper, it forms a composite paper with moisturizing properties and excellent water absorption, making it widely applicable in the field of moisture-locking and fragrance preservation technology.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and relates to a method for preparing hydrogels, particularly a method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane and its application in moisture-locking and fragrance-preserving packaging materials. Background Technology

[0002] Paper packaging materials have long been a popular choice in pharmaceuticals, tobacco products, and other industries. However, the porous nature of paper, its susceptibility to moisture absorption and mildew, has limited its further development as a packaging material. Therefore, in earlier years, researchers had to turn their attention to plastic products, attempting to develop a range of polymer packaging materials with different functions. This, however, led to problems such as environmental pollution and the depletion of fossil resources. In recent years, researchers have re-examined paper packaging materials and are attempting to mitigate their negative effects through surface modification.

[0003] Patent ZL200610113539.3, Hydrogel Containing Natural Polymers and Radiation Preparation Method Thereof, provides a hydrogel containing natural polymers and its preparation method. The degree of crosslinking of the hydrogel is 70-95%, and the water absorption rate is 500-80000% times. There is also a report on the performance and anti-aging application of nano-TiO2 / polyvinyl alcohol composite hydrogel film material, Chemical New Materials, 2020, 48(6):252-256. In order to explore the protective effect of nano-TiO2 / polyvinyl alcohol (PVA) composite hydrogel film on textile materials, the PVA hydrogel film was modified with nano-TiO2 and the content of nano-TiO2 was changed. The results showed that when the amount of nano-TiO2 added was 5.0%, its comprehensive performance was better. At this time, the tensile strength of the composite hydrogel film was 9.41MPa, the maximum ultraviolet transmittance was only 74.94%, and the transparency reached 69.82%. The composite hydrogel film with a nano-TiO2 content of 5% was selected, and the synthesized composite hydrogel was used to treat textile material samples. It was found that the weight loss rate of the treated samples did not change much after being irradiated with ultraviolet light for a period of time.

[0004] If hydrogels are combined with paper to create a paper with moisture-locking and fragrance-preserving functions, it may solve many of the shortcomings of previous paper-based packaging materials. Summary of the Invention

[0005] In view of the shortcomings of the prior art, one object of the present invention is to disclose a method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane.

[0006] A method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane includes: weighing a polyurethane prepolymer, stirring and heating to 60-90℃ (preferably 85℃), slowly adding a multi-branched epoxy oligomer dispersion, and reacting for 1-5 hours (preferably 4 hours); determining the theoretical content of isocyanate groups using the di-n-butylamine method, and adjusting the system temperature to 35-55℃ (preferably 40℃) after reaching the theoretical value, and slowly adding a salting agent; cooling to room temperature, and removing the solvent by vacuum distillation using residual heat during the cooling stage; adding deionized water, and stirring until a white emulsion is obtained; wherein the mass-volume ratio of the multi-branched epoxy oligomer, polyurethane prepolymer, salting agent, and deionized water is 9-12g:90-240g:0.3-0.6mmol:120-250ml, preferably 10g:200g:0.5mmol:240ml.

[0007] The multi-branched epoxy oligomer is any one or more of the first-generation, second-generation, third-generation, or fourth-generation multi-branched epoxy oligomers.

[0008] The solvent is N,N-dimethylamide, N-methylpyrrolidone, cyclohexanone, 1,4-dioxane, or methyl tert-butyl ether, preferably methyl tert-butyl ether.

[0009] The salt-forming agent is triethylamine, diethylamine, or N,N-dimethylethylamine, preferably triethylamine.

[0010] Another objective of this invention is to apply the obtained rigid hydrogel to moisture-locking and fragrance-preserving packaging materials.

[0011] Specifically, the rigid hydrogel is coated onto the aluminum layer side of the aluminized paper and dried to cure, thus obtaining rigid hydrogel composite aluminized paper, which can be used as a moisture-locking and aroma-preserving packaging material.

[0012] Furthermore, the wet coating amount of the rigid hydrogel is 5.6–31.9 g / m³. 2 Preferred 22.9g / m 2 The drying process, with a drying temperature of 80-105℃ (preferably 98℃), completes the coating and curing of the rigid hydrogel on the aluminum layer surface.

[0013] The metallized paper, wherein the basis weight of ordinary virgin paper is 30-55 g / m². 2 The dry coating amount of the anti-seepage coating is 0.9–2.4 g / m². 2 The thickness of the aluminum coating

[0014] The preparation method of the multi-branched epoxy oligomer of the present invention includes the following steps:

[0015] A. Dissolve the polyhydroxy compound in a solvent and stir. Adjust the temperature to 50-70°C, preferably 55°C, then add the catalyst, followed by the slow addition of the epoxy halide. After 0.5-2 hours, preferably 1 hour, stop the reaction and adjust the temperature to room temperature, then stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the first-generation multi-branched epoxy oligomer. The molar, mass, and volume ratio of the polyhydroxy compound, epoxy halide, catalyst, and solvent is 1.0 mmol: 2.9-3.2 mmol: 0.001-0.01 g: 80-200 ml, preferably 1.0 mmol: 3.1 mmol: 0.002 g: 160 ml.

[0016] B. Dissolve the first-generation multi-branched epoxy oligomer and the multi-hydroxy compound in a solvent and stir thoroughly. Adjust the temperature to 50-80℃, preferably 60℃, and then add the epoxy halide. Stop the reaction after 0.5-3 hours, preferably 1.5 hours, and adjust the temperature to room temperature and stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the second-generation multi-branched epoxy oligomer. The molar, mass, and volume ratio of the multi-hydroxy compound, epoxy halide, solvent, and multi-hydroxy compound used in the preparation of the first-generation multi-branched epoxy oligomer is 2.8-3.0 mmol:2.4-3.0 mmol:20-50 ml:1.0 mmol, preferably 2.9 mmol:2.6 mmol:30 ml:1.0 mmol.

[0017] C. Dissolve the second-generation multi-branched epoxy oligomer and the multi-hydroxy compound in a solvent and stir thoroughly. Adjust the temperature to 60-90℃, preferably 70℃, and then add the epoxy halide. Stop the reaction after 0.5-3 hours, preferably 2 hours, and adjust the temperature to room temperature and stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the third-generation multi-branched epoxy oligomer. The molar, mass, and volume ratio of the multi-hydroxy compound, epoxy halide, solvent, and multi-hydroxy compound used in the preparation of the first-generation multi-branched epoxy oligomer is 2.6-3.0 mmol:2.4-3.0 mmol:20-40 ml:1.0 mmol, preferably 2.8 mmol:2.6 mmol:30 ml:1.0 mmol.

[0018] D. Dissolve the third-generation multi-branched epoxy oligomer and the multi-hydroxy compound in a solvent and stir thoroughly. Adjust the temperature to 60-100℃, preferably 75℃, and then add the epoxy halide. Stop the reaction after 1-3 hours, preferably 2 hours, and adjust the temperature to room temperature and stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the fourth-generation multi-branched epoxy oligomer. The molar, mass, and volume ratio of the multi-hydroxy compound, epoxy halide, solvent, and multi-hydroxy compound used in the preparation of the first-generation multi-branched epoxy oligomer is 2.5-3.0 mmol:2.4-3.0 mmol:20-40 ml:1.0 mmol, preferably 2.7 mmol:2.6 mmol:30 ml:1.0 mmol.

[0019] The polyhydroxy compound is 3,4',5-trihydroxystilbene, phloroglucinol, 1,2,6-hexanetriol, 1,2,4-butanetriol or 1,3,5-cyclohexanetriol, preferably 1,2,6-hexanetriol;

[0020] The solvent is toluene, xylene, butanone, cyclohexanone, or 1,4-dioxane, preferably toluene;

[0021] The catalyst is an inorganic base or an organic base; further, the inorganic base is KOH or NaOH; the organic base is sodium methoxide, sodium ethoxide, n-butyllithium, lithium aminoide, triethylamine, or N,N-dimethylamine.

[0022] The epoxy halide is epichlorohydrin, methyl epichlorohydrin, epifluorohydrin, epibromopropane, 4-bromo-1,2-epoxybutane, or 6-bromo-1,2-epoxyhexane, preferably epichlorohydrin.

[0023] The polyurethane prepolymer of this invention is prepared by means of: dispersing polyisocyanate in a solvent, heating, maintaining a N2 atmosphere, adjusting the temperature to 40-60°C, preferably 55°C, adding a chain extender and a few drops of catalyst, maintaining for 30-120 min, preferably 70 min; adjusting the temperature to 50-75°C, preferably 60°C, adding a polymeric polyol and a polyamino alkane, maintaining for 1-4 h, preferably 2 h, stopping the reaction, cooling to room temperature, removing most of the solvent by vacuum distillation until the mass of the system does not change significantly, the main component of the viscous liquid is the polyurethane prepolymer, wherein the ratio of polyisocyanate, polymeric polyol, chain extender, polyamino alkane, catalyst, and solvent is 0.9-1.2 mmol:0.6-0.9 mmol:0.3-0.6 mmol:0.2-0.4 mmol:1-5 drops:120 ml; preferably 1.1 mmol:0.7 mmol:0.4 mmol:0.3 mmol:4 drops:120 ml.

[0024] The polyisocyanate is 3,3'-dimethyl-4,4'-biphenyl diisocyanate, toluene-2,4-diisocyanate, isophorone diisocyanate or diphenylmethane-4,4'-diisocyanate, preferably isophorone diisocyanate.

[0025] The solvent is acetone, butanone, N,N-dimethylamide or N-methylpyrrolidone, preferably N-methylpyrrolidone.

[0026] The chain extender is 2,2-dihydroxymethylpropionic acid, 2,4-dihydroxy-3,3-dimethylbutyric acid, 2,4,6-trihydroxybenzoic acid, or 2,4-dihydroxybenzoic acid, preferably 2,4,6-trihydroxybenzoic acid.

[0027] The catalyst is diisobutyltin dilaurate, stannous octoate, di(dodecyl sulfide)dibutyltin, or dibutyltin diacetate, preferably di(dodecyl sulfide)dibutyltin.

[0028] The polymeric polyol is polypropylene glycol, polytetrahydrofuran ether glycol, polyethylene glycol, copolyether glycol, polyethylene adipate, or polyhexanediol adipate, preferably polyethylene glycol.

[0029] The polyaminoalkane is ethylenediamine, 1,4-butanediamine, 1,5-diaminopentane, 1,3-diaminopentane or 1,2-diaminocyclohexane, preferably 1,5-diaminopentane.

[0030] The purity and manufacturers of some of the reagents involved in the reaction are as follows.

[0031] 3,4',5-Trihydroxystilbene (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); Phloroglucinol (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); 1,2,6-Hexanetriol (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); 1,2,4-Butanetriol (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); 1,3,5-Cyclohexanetriol (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); Toluene (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); Xylene (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); Butanone (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); Acetone (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); Cyclohexanone (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); 1,4-Dioxane (analytical grade, Sinopharm Chemical Reagent Co., Ltd.) N,N-Dimethylamide (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); N-Methylpyrrolidone (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); Methyl tert-butyl ether (analytical grade, Sinopharm Chemical Reagent Co., Ltd.); KOH (analytical grade, Tianjin Chemical Reagent Research Institute); NaOH (analytical grade, Tianjin Chemical Reagent Research Institute); Sodium methoxide (analytical grade, Tianjin Chemical Reagent Research Institute); Sodium ethoxide (analytical grade, Tianjin Chemical Reagent Research Institute); n-Butyllithium (analytical grade, Tianjin Chemical Reagent Research Institute); Lithium aminoide (analytical grade, Tianjin Chemical Reagent Research Institute); Triethylamine (analytical grade, Changsha Fenlukou Plastic Chemical Plant); N,N-Dimethylamine (analytical grade, Changsha Fenlukou Plastic Chemical Plant); Epichlorohydrin (chemical... Chemically pure (Tianjin Damao Chemical Reagent Co., Ltd.); Methyl epichlorohydrin (chemically pure, Tianjin Damao Chemical Reagent Co., Ltd.); Epifluoropropane (analytical grade, Tianjin Kemeio Chemical Reagent Co., Ltd.); Epibromopropane (chemically pure, Tianjin Damao Chemical Reagent Co., Ltd.); 4-Bromo-1,2-epoxybutane (chemically pure, Tianjin Damao Chemical Reagent Co., Ltd.); 6-Bromo-1,2-epoxyhexane (chemically pure, Tianjin Damao Chemical Reagent Co., Ltd.); 3,3'-Dimethyl-4,4'-biphenyl diisocyanate (chemically pure, Tianjin Damao Chemical Reagent Co., Ltd.); Toluene-2,4-diisocyanate (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); Isophorone diisocyanate (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); Phenylmethane-4,4'-diisocyanate (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); 2,2-dihydroxymethylpropionic acid (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); 2,4-dihydroxy-3,3-dimethylbutyric acid (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); 2,4,6-trihydroxybenzoic acid (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); 2,4-dihydroxybenzoic acid (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); diisobutyltin dilaurate (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); stannous octoate (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); di(dodecyl sulfide)dibutyltin (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); dibutyltin diacetate (chemically pure, Sinopharm Chemical Reagent Co., Ltd.);Polypropylene glycol (industrial grade, Macklin Biotechnology Co., Ltd.); Polytetrahydrofuran ether glycol (industrial grade, Macklin Biotechnology Co., Ltd.); Polyethylene glycol (industrial grade, Macklin Biotechnology Co., Ltd.); Copolyether glycol (industrial grade, Macklin Biotechnology Co., Ltd.); Polyethylene adipate (industrial grade, Macklin Biotechnology Co., Ltd.); Polyhexanediol adipate (analytical grade, Aladdin Biotechnology Co., Ltd.); Ethylenediamine (analytical grade, Aladdin Biotechnology Co., Ltd.); 1,4-Butanediamine (analytical grade, Aladdin Biotechnology Co., Ltd.); 1,5-Diaminopentane (analytical grade, Aladdin Biotechnology Co., Ltd.); 1,3-Diaminopentane (analytical grade, Aladdin Biotechnology Co., Ltd.); 1,2-Diaminocyclohexane (analytical grade, Aladdin Biotechnology Co., Ltd.); Diethylamine (analytical grade, Aladdin Biotechnology Co., Ltd.); N,N-Dimethylethylamine (chemically pure, Sinopharm Chemical Reagent Co., Ltd.); Metallized paper (Jiangsu Jiayi Packaging Materials Co., Ltd.); Deionized water (self-made).

[0032] Experimental methods

[0033] (1) Infrared spectroscopy (FTIR) characterization of multi-branched epoxy oligomers

[0034] The infrared spectrometer was a Nicoiet 8700 from THERMOVG, USA. Using KBr as a control, an appropriate amount of KBr was first ground into an extremely fine powder in an agate mortar. This powder was then pressed into a transparent sheet using a mold, and an infrared scan was performed to generate a background image. Next, a small amount of the fourth-generation multi-branched epoxy oligomer prepared according to Example 1 was mixed evenly with the aforementioned extremely fine KBr powder, and an infrared scan was performed to generate a test image. Finally, the KBr background value was subtracted to obtain the infrared spectrum curve of the fourth-generation multi-branched epoxy oligomer.

[0035] (2) Determination of hydrogel formation

[0036] The test tube inversion method can be used to simply and easily determine gel formation. Approximately 20g of the multi-branched epoxy oligomer crosslinked polyurethane emulsion prepared in Example 1 was weighed and placed in an ampoule of appropriate size immediately. The changes in the properties and flow dynamics of the emulsion inside the ampoule were observed.

[0037] (3) Hydrogel swelling performance test

[0038] The swelling rate of the hydrogel dry gel after immersion at room temperature for different times was determined by gravimetric method, and the swelling rate was expressed as the water absorption rate of the sample. The hydrogel composite aluminized paper from Example 1 was cut into 10cm × 10cm pieces, weighed, and recorded as W0; it was then completely immersed in deionized water. The sample was removed at regular intervals, the surface moisture of the sample paper was wiped dry with filter paper, and the weight was recorded as W. t Weigh the sample until its mass no longer increases, and record the weight as W. e The water absorption swelling rate (SR) of the sample at different times and the equilibrium swelling rate (ESR) of the sample at swelling equilibrium were calculated by analyzing the following formulas (1) and (2). All tests were repeated three times in parallel and the average value was taken.

[0039] SR = (W t -W0) / W0×100% (1)

[0040] ESR=(W e -W0) / W0×100% (2)

[0041] (4) Hydrogel moisturizing performance test

[0042] The hydrogel composite aluminized paper that has reached swelling equilibrium is drained and weighed, and its mass is recorded as E0. It is then placed at room temperature, and every 24 hours, the surface moisture is wiped dry with filter paper and the mass is recorded as E0. t The water retention rate (WR) of the hydrogel composite aluminized paper at time T is the ratio of the mass of the paper sample at time T to the mass at which swelling equilibrium is reached, and the calculation formula is shown in equation (3).

[0043] WR=(E t -E0) / E0×100% (3)

[0044] Beneficial effects

[0045] This invention prepares a series of multi-component branched epoxy polymers through a multi-layer iterative process. Each generation of these multi-component branched epoxy polymers can be used individually for crosslinking polyurethane prepolymers, or multiple generations can be mixed in any ratio for crosslinking polyurethane prepolymers to form a hydrogel with a rigid structure. When laminated with aluminized paper, this forms a composite paper with excellent water absorption properties, achieving an ESR of up to approximately 1600%. It also exhibits excellent water retention properties within one week, with its WR value remaining at 75% after one week. Due to the introduction of a branched backbone in its structure, this hydrogel exhibits stronger rigidity. The prepared hydrogel composite paper can be cut and processed according to actual needs, and can be widely applied in the fields of moisture-locking and aroma-preserving technology in food, pharmaceuticals, and tobacco products. Attached Figure Description

[0046] Figure 1Infrared spectrum of the IV-generation multi-branched epoxy oligomer obtained in Example 1;

[0047] Figure 2 . Schematic diagram of the transformation process of multi-branched epoxy oligomer crosslinked polyurethane emulsion into hydrogel;

[0048] Figure 3 Data on swelling and moisturizing properties of hydrogel dry gel, where (1) represents the water absorption property of the hydrogel dry gel and (2) represents the water retention property of the hydrogel after it is saturated with water. Detailed Implementation

[0049] The present invention will be described in detail below with reference to embodiments, so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0050] Example 1

[0051] Weigh 1.0 mmol of 1,2,6-hexanetriol and 160 ml of toluene into a 500 ml three-necked flask. The flask is equipped with a condenser, thermometer, constant pressure dropping funnel, and magnetic stirrer and placed in an oil bath. Maintain a stirring rate of 500 r / min. After adjusting the temperature to 55 °C, add 0.002 g of n-butyllithium in one go. Then, slowly add 3.1 mmol of epichlorohydrin through the constant pressure dropping funnel over 15 min. Rinse the tube wall with 5 ml of toluene. After maintaining the reaction for 1 h, stop the reaction and adjust the temperature to room temperature. Stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the first-generation multi-branched epoxy oligomer.

[0052] The aforementioned first-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.9 mmol of 1,2,6-hexanetriol and 30 ml of toluene were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 60 °C, 2.6 mmol of epichlorohydrin was slowly added over 25 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of toluene, and the reaction was stopped after 1.5 h. The temperature was then adjusted to room temperature, and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the second-generation multi-branched epoxy oligomer.

[0053] The aforementioned second-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.8 mmol of 1,2,6-hexanetriol and 30 ml of toluene were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 70 °C, 2.6 mmol of epichlorohydrin was slowly added over 40 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of toluene, and the reaction was stopped after 2 h. The temperature was then adjusted to room temperature and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the third-generation multi-branched epoxy oligomer.

[0054] The aforementioned third-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.7 mmol of 1,2,6-hexanetriol and 30 ml of toluene were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 75 °C, 2.6 mmol of epichlorohydrin was slowly added over 50 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of toluene, and the reaction was stopped after 2 h. The temperature was then adjusted to room temperature and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the fourth-generation multi-branched epoxy oligomer.

[0055] Weigh 1.1 mmol of isophorone diisocyanate and 120 ml of N-methylpyrrolidone into a 500 ml four-necked flask. The four-necked flask is equipped with a condenser, thermometer, constant pressure dropping funnel, magnetic stirrer, and three-way check valve and is placed in an oil bath. The three-way check valve is connected to N2 to replace the gas atmosphere of the reaction system and ensure that the internal pressure is positive. Maintain the stirring speed at 300 r / min. After adjusting the temperature to 55 °C, add 0.4 mmol of 2,4,6-trihydroxybenzoic acid and 4 drops of di(dodecyl sulfide)dibutyltin in one go through the constant pressure dropping funnel. Rinse the tube wall with 5 ml of toluene and maintain for 70 min. After adjusting the temperature to 60 °C, add 0.7 mmol of polyethylene glycol and 0.3 mmol of 1,5-diaminopentane. Rinse the tube wall with 5 ml of toluene and maintain for 2 h. Stop the reaction and adjust the temperature to room temperature. Stop stirring and remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the viscous liquid is polyurethane prepolymer, which is used for later use.

[0056] Weigh 10g of the prepared generation IV multi-branched epoxy oligomer and dilute to 100ml with methyl tert-butyl ether to obtain a multi-branched epoxy oligomer dispersion for later use.

[0057] Weigh 200g of the obtained viscous liquid polyurethane prepolymer into a 1000ml three-necked flask. The flask is equipped with a thermometer, a constant-pressure dropping funnel, and a magnetic stirrer, and is placed in an oil-water bath. Adjust the temperature to 85℃ and the stirring speed to 300r / min. Slowly add 100ml of the above-mentioned multi-branched epoxy oligomer dispersion through the constant-pressure dropping funnel over 60min. Rinse the tube wall with 5ml of methyl tert-butyl ether. After the addition is complete, maintain the reaction for 4h. Determine the theoretical content of isocyanate groups using the di-n-butylamine method. When the theoretical value is reached... The system temperature was then adjusted to 40°C. 0.5 mmol of triethylamine and 5 ml of methyl tert-butyl ether were slowly added dropwise over 30 min using a constant-pressure dropping funnel to rinse the tube wall, and this process was maintained for 80 min. Heating was then stopped, and the temperature was adjusted to room temperature. During the cooling phase, residual heat was used for vacuum distillation to remove as much solvent as possible. The stirring speed was adjusted to 2000 r / min, and 240 ml of deionized water was added to the system at once. Stirring was maintained for 20 min, and a white emulsion was obtained, which is the multi-branched epoxy oligomer crosslinked polyurethane emulsion.

[0058] The coating machine was set to a speed of 40 m / min, a drying temperature of 98℃, and a wet coating weight of 22.9 g / m³. 2 After the cross-linked emulsion is coated and cured on the surface of the aluminized paper, a rigid hydrogel composite paper is obtained, which can be used as a moisture-locking and aroma-preserving packaging material after reabsorbing water; the basis weight of ordinary virgin paper in the aluminized paper structure is 48 g / m². 2 The dry coating amount of the anti-seepage coating is 1.7 g / m². 2 Thickness of aluminum coating

[0059] Example 2

[0060] Weigh 1.0 mmol of 1,2,6-hexanetriol and 80 ml of toluene into a 500 ml three-necked flask. The flask is equipped with a condenser, thermometer, constant pressure dropping funnel, and magnetic stirrer and placed in an oil bath. Maintain a stirring rate of 500 r / min. After adjusting the temperature to 50 °C, add 0.001 g of n-butyllithium in one go. Then, slowly add 2.9 mmol of epichlorohydrin through the constant pressure dropping funnel over 10 min. Rinse the tube wall with 5 ml of solvent. After maintaining the reaction for 0.5 h, stop the reaction and adjust the temperature to room temperature. Stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the first-generation multi-branched epoxy oligomer.

[0061] The aforementioned first-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.8 mmol of 1,2,6-hexanetriol and 20 ml of toluene were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 50 °C, 2.4 mmol of epichlorohydrin was slowly added over 20 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of toluene, and the reaction was stopped after maintaining this temperature for 0.5 h. The temperature was then adjusted to room temperature, and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the second-generation multi-branched epoxy oligomer.

[0062] The aforementioned second-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.6 mmol of 1,2,6-hexanetriol and 20 ml of toluene were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 60 °C, 2.4 mmol of epichlorohydrin was slowly added over 10 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of toluene, and the reaction was stopped after 0.5 h. The temperature was then adjusted to room temperature, and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the third-generation multi-branched epoxy oligomer.

[0063] The aforementioned third-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.5 mmol of 1,2,6-hexanetriol and 20 ml of toluene were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 60 °C, 2.4 mmol of epichlorohydrin was slowly added over 20 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of solvent, and the reaction was stopped after 1 h. The temperature was then adjusted to room temperature and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the fourth-generation multi-branched epoxy oligomer.

[0064] Weigh 0.9 mmol of isophorone diisocyanate and 120 ml of N-methylpyrrolidone into a 500 ml four-necked flask. The flask is equipped with a condenser, thermometer, constant pressure dropping funnel, magnetic stirrer, and three-way check valve, and is placed in an oil bath. The three-way check valve is connected to N2 to displace the gaseous atmosphere of the reaction system and ensure that the internal pressure is positive. Maintain the stirring speed at 300 r / min. After adjusting the temperature to 40 °C, add 0.3 mmol of 2,4,6-trihydroxybenzoic acid and 1 drop of di(dodecyl sulfide)dibutyltin in one go through the constant pressure dropping funnel. Rinse the tube wall with 5 ml of N-methylpyrrolidone and maintain for 30 min. After adjusting the temperature to 50 °C, add 0.6 mmol of polyethylene glycol and 0.2 mmol of 1,5-diaminopentane, and 5 ml of N-methylpyrrolidone. The tube wall was rinsed with N-methylpyrrolidone and the reaction was stopped after 1 hour. The temperature was adjusted to room temperature and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system did not change significantly. The viscous liquid was mainly composed of polyurethane prepolymer, which was then set aside.

[0065] Weigh 9g of the obtained generation IV multi-branched epoxy oligomer and dilute to 100ml with methyl tert-butyl ether to obtain a multi-branched epoxy oligomer dispersion for later use.

[0066] Weigh 90g of the obtained viscous liquid polyurethane prepolymer into a 1000ml three-necked flask. The flask is equipped with a thermometer, a constant-pressure dropping funnel, and a magnetic stirrer, and is placed in an oil-water bath. Adjust the temperature to 60℃ and the stirring speed to 300r / min. Slowly add 100ml of the above-mentioned multi-branched epoxy oligomer dispersion through the constant-pressure dropping funnel over 15min. Rinse the tube wall with 5ml of methyl tert-butyl ether. After the addition is complete, maintain the reaction for 1h. Determine the theoretical content of isocyanate groups using the di-n-butylamine method. When the theoretical value is reached... The system temperature was then adjusted to 35°C. 0.3 mmol of triethylamine and 5 ml of methyl tert-butyl ether were slowly added dropwise over 10 min using a constant-pressure dropping funnel to rinse the tube wall, and this process was maintained for 40 min. Heating was then stopped, and the temperature was adjusted to room temperature. During the cooling phase, residual heat was used for vacuum distillation to remove as much solvent as possible. The stirring speed was adjusted to 2000 r / min, and 120 ml of deionized water was added to the system at once. Stirring was maintained for 20 min, and a white emulsion was obtained, which is the multi-branched epoxy oligomer crosslinked polyurethane emulsion.

[0067] The coating machine operating speed was set at 30 m / min, the drying temperature at 80℃, and the wet coating amount at 5.6 g / m. 2 After the cross-linked emulsion is coated and cured on the surface of the aluminized paper, a rigid hydrogel composite paper is obtained, which can be used as a moisture-locking and aroma-preserving packaging material after reabsorbing water; the basis weight of ordinary virgin paper in the aluminized paper structure is 30 g / m². 2 The dry coating amount of the anti-seepage coating is 0.9 g / m². 2 Thickness of aluminum coating

[0068] Example 3

[0069] Weigh 1.0 mmol of 1,2,6-hexanetriol and 200 ml of toluene into a 500 ml three-necked flask. The flask is equipped with a condenser, thermometer, constant pressure dropping funnel, and magnetic stirrer and placed in an oil bath. Maintain a stirring rate of 500 r / min. After adjusting the temperature to 70 °C, add 0.01 g of n-butyllithium in one go. Then, slowly add 3.2 mmol of epichlorohydrin through the constant pressure dropping funnel over 50 min. Rinse the tube wall with 5 ml of solvent. After maintaining the reaction for 2 h, stop the reaction and adjust the temperature to room temperature. Stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the first-generation multi-branched epoxy oligomer.

[0070] The aforementioned first-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 3.0 mmol of 1,2,6-hexanetriol and 50 ml of toluene were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 80 °C, 3.0 mmol of epichlorohydrin was slowly added over 60 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of toluene, and the reaction was stopped after 3 h. The temperature was then adjusted to room temperature, and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the second-generation multi-branched epoxy oligomer.

[0071] The aforementioned second-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 3.0 mmol of 1,2,6-hexanetriol and 40 ml of toluene were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 90 °C, 3.0 mmol of epichlorohydrin was slowly added over 70 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of toluene, and the reaction was stopped after 3 h. The temperature was then adjusted to room temperature and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the third-generation multi-branched epoxy oligomer.

[0072] The aforementioned third-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 3.0 mmol of 1,2,6-hexanetriol and 40 ml of toluene were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 100 °C, 3.0 mmol of epichlorohydrin was slowly added over 70 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of toluene, and the reaction was stopped after 3 h. The temperature was then adjusted to room temperature, and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the fourth-generation multi-branched epoxy oligomer.

[0073] Weigh 1.2 mmol of isophorone diisocyanate and 120 ml of N-methylpyrrolidone into a 500 ml four-necked flask. The flask is equipped with a condenser, thermometer, constant-pressure dropping funnel, magnetic stirrer, and three-way check valve, and is placed in an oil bath. The three-way check valve is connected to N2 to displace the gaseous atmosphere of the reaction system and ensure that the internal pressure is positive. Maintain a stirring speed of 300 r / min. After adjusting the temperature to 60 °C, add 0.6 mmol of 2,4,6-trihydroxybenzoic acid and 5 drops of di(dodecyl sulfide)dibutyltin in one go through the constant-pressure dropping funnel. Rinse the tube wall with 5 ml of N-methylpyrrolidone and maintain for 120 min. After adjusting the temperature to 70 °C, add 0.9 mmol of polyethylene glycol and 0.4 mmol of N-methylpyrrolidone. Rinse the tube wall with 1,5-diaminopentane and 5 ml of N-methylpyrrolidone. After maintaining the reaction for 4 hours, stop the reaction and adjust the temperature to room temperature. Stop stirring and remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The viscous liquid is mainly composed of polyurethane prepolymer, which is ready for use.

[0074] Weigh 12g of the obtained generation IV multi-branched epoxy oligomer and dilute to 100ml with methyl tert-butyl ether to obtain a multi-branched epoxy oligomer dispersion for later use.

[0075] Weigh 240g of the obtained viscous liquid polyurethane prepolymer into a 1000ml three-necked flask. The flask is equipped with a thermometer, a constant-pressure dropping funnel, and a magnetic stirrer, and is placed in an oil-water bath. Adjust the temperature to 90℃ and the stirring speed to 300r / min. Slowly add 100ml of the above-mentioned multi-branched epoxy oligomer dispersion through the constant-pressure dropping funnel over 90min. Rinse the tube wall with 5ml of methyl tert-butyl ether. After the addition is complete, maintain the reaction for 5h. Determine the theoretical content of isocyanate groups using the di-n-butylamine method. When the theoretical value is reached... The system temperature was then adjusted to 55°C. 0.6 mmol of triethylamine and 5 ml of methyl tert-butyl ether were slowly added dropwise over 40 min using a constant-pressure dropping funnel to rinse the tube wall, and this process was maintained for 120 min. Heating was then stopped, and the temperature was adjusted to room temperature. During the cooling phase, residual heat was used for vacuum distillation to remove as much solvent as possible. The stirring speed was adjusted to 2000 r / min, and 250 ml of deionized water was added to the system at once. Stirring was maintained for 20 min, and a white emulsion was obtained, which is the multi-branched epoxy oligomer crosslinked polyurethane emulsion.

[0076] The coating machine operating speed was set at 55 m / min, the drying temperature at 105℃, and the wet coating amount at 31.9 g / m³. 2 After the cross-linked emulsion is coated and cured on the surface of the aluminized paper, a rigid hydrogel composite paper is obtained, which can be used as a moisture-locking and aroma-preserving packaging material after reabsorbing water; the basis weight of ordinary virgin paper in the aluminized paper structure is 55 g / m². 2 The dry coating amount of the anti-seepage coating is 2.4 g / m². 2Thickness of aluminum coating

[0077] Example 4

[0078] Weigh 1.0 mmol of 3,4',5-trihydroxystilbene and 180 ml of cyclohexanone into a 500 ml three-necked flask. The three-necked flask is equipped with a condenser, thermometer, constant pressure dropping funnel, and magnetic stirrer and is placed in an oil bath. Maintain the stirring rate at 500 r / min. After adjusting the temperature to 60 °C, add 0.008 g of NaOH at once. Then, slowly add 3.0 mmol of methyl epichlorohydrin through the constant pressure dropping funnel over 20 min. Rinse the tube wall with 5 ml of solvent. After maintaining the reaction for 0.521 h, stop the reaction and adjust the temperature to room temperature. Stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the first-generation multi-branched epoxy oligomer.

[0079] The aforementioned first-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.8 mmol of 3,4',5-trihydroxystilbene and 35 ml of cyclohexanone were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 70 °C, 2.7 mmol of methyl epichlorohydrin was slowly added over 30 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of cyclohexanone, and the reaction was stopped after 2 h. The temperature was then adjusted to room temperature and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the second-generation multi-branched epoxy oligomer.

[0080] The aforementioned second-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.7 mmol of 3,4',5-trihydroxystilbene and 25 ml of cyclohexanone were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 65 °C, 2.7 mmol of methyl epichlorohydrin was slowly added over 25 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of cyclohexanone, and the reaction was stopped after maintaining this temperature for 0.532 h. The temperature was then adjusted to room temperature, and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the third-generation multi-branched epoxy oligomer.

[0081] The aforementioned third-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.8 mmol of 3,4',5-trihydroxystilbene and 35 ml of cyclohexanone were weighed, and the stirring speed was adjusted to 500 r / min to ensure thorough mixing. After adjusting the temperature to 90 °C, 2.9 mmol of methyl epichlorohydrin was slowly added over 65 min through a constant-pressure dropping funnel. The tube wall was rinsed with 5 ml of cyclohexanone, and the reaction was stopped after 1 h. The temperature was then adjusted to room temperature, and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the fourth-generation multi-branched epoxy oligomer.

[0082] Weigh 1.0 mmol of 3,3'-dimethyl-4,4'-biphenyl diisocyanate and 120 ml of N,N-dimethylamide into a 500 ml four-necked flask. The flask is equipped with a condenser, thermometer, constant pressure dropping funnel, magnetic stirrer, and three-way check valve, and is placed in an oil bath. The three-way check valve is connected to N2 to displace the gaseous atmosphere of the reaction system and ensure that the internal pressure is positive. Maintain the stirring speed at 300 r / min. After adjusting the temperature to 42°C, add 0.5 mmol of 2,2-dihydroxymethylpropionic acid and 2 drops of diisobutyltin dilaurate in one go through the constant pressure dropping funnel. Rinse the tube wall with 5 ml of N,N-dimethylamide and maintain for 35 min. After adjusting the temperature to 55°C, add 0.8 mmol of polypropylene glycol and 0.2 mmol of ethylenediamine, and 5 ml of N,N-dimethylamide. The tube wall was rinsed with N,N-dimethylamide and the reaction was stopped after 3 hours. The temperature was adjusted to room temperature and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system did not change significantly. The viscous liquid was mainly composed of polyurethane prepolymer, which was then set aside.

[0083] Weigh 11g of the obtained third-generation multi-branched epoxy oligomer and dilute to 100ml with cyclohexanone to obtain a multi-branched epoxy oligomer dispersion for later use.

[0084] Weigh 120g of the obtained viscous liquid polyurethane prepolymer into a 1000ml three-necked flask. The flask is equipped with a thermometer, a constant-pressure dropping funnel, and a magnetic stirrer, and is placed in an oil-water bath. Adjust the temperature to 70℃ and the stirring speed to 300r / min. Slowly add 100ml of the above-mentioned multi-branched epoxy oligomer dispersion through the constant-pressure dropping funnel over 20min. Rinse the tube wall with 5ml of cyclohexanone. After the addition is complete, maintain the reaction for 2h. Determine the theoretical content of isocyanate groups using the di-n-butylamine method. When the theoretical value is reached... The system temperature was then adjusted to 45°C. 0.4 mmol of diethylamine was slowly added dropwise over 20 min through a constant-pressure dropping funnel, and 5 ml of cyclohexanone was used to rinse the tube wall. This process was maintained for 50 min. Heating was then stopped, and the temperature was adjusted to room temperature. During the cooling phase, residual heat was used for vacuum distillation to remove as much solvent as possible. The stirring speed was adjusted to 2000 r / min, and 140 ml of deionized water was added to the system at once. Stirring was maintained for 20 min, and a white emulsion was obtained, which is the multi-branched epoxy oligomer crosslinked polyurethane emulsion.

[0085] The coating machine was set to a speed of 50 m / min, a drying temperature of 88℃, and a wet coating weight of 13.8 g / m² to complete the coating and curing of the crosslinked emulsion on the surface of the aluminized paper, resulting in a rigid hydrogel composite paper. After reabsorbing water, it can be used as a moisture-locking and aroma-preserving packaging material. The aluminized paper structure contains a basis weight of 38 g / m² for ordinary virgin paper and a dry coating weight of 2.1 g / m² for the anti-seepage coating. 2 Thickness of aluminum coating

[0086] Example 5

[0087] Weigh 1.0 mmol of 1,3,5-cyclohexanetriol and 120 ml of 1,4-dioxane into a 500 ml three-necked flask. The flask is equipped with a condenser, thermometer, constant pressure dropping funnel, and magnetic stirrer and placed in an oil bath. Maintain a stirring rate of 500 rpm. After adjusting the temperature to 62 °C, add 0.009 g of triethylamine in one go. Then, slowly add 2.9 mmol of 6-bromo-1,2-epoxyhexane through the constant pressure dropping funnel over 42 min. Rinse the tube wall with 5 ml of 1,4-dioxane. After maintaining this for 1.5 h, stop the reaction, adjust the temperature to room temperature, and stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the first-generation multi-branched epoxy oligomer.

[0088] The aforementioned first-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 3.0 mmol of 1,3,5-cyclohexanetriol and 26 ml of 1,4-dioxane were weighed, and the stirring speed was adjusted to 500 rpm to ensure thorough mixing. After adjusting the temperature to 74 °C, 2.5 mmol of 6-bromo-1,2-epoxyhexane was slowly added over 48 min via a constant-pressure dropping funnel. The tube walls were rinsed with 5 ml of 1,4-dioxane, and the reaction was maintained for 2.5 h. The reaction was then stopped, and the temperature was adjusted to room temperature, and stirring was stopped. Most of the solvent was removed by vacuum distillation until the system mass showed no significant change. The main component of the residue was the second-generation multi-branched epoxy oligomer.

[0089] The aforementioned second-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.9 mmol of 1,3,5-cyclohexanetriol and 33 ml of 1,4-dioxane were weighed, and the stirring speed was adjusted to 500 rpm to ensure thorough mixing. After adjusting the temperature to 81 °C, 2.7 mmol of 6-bromo-1,2-epoxyhexane was slowly added over 33 min via a constant-pressure dropping funnel. The tube walls were rinsed with 5 ml of 1,4-dioxane, and the reaction was maintained for 1.5 h. The reaction was then stopped, and the temperature was adjusted to room temperature, and stirring was stopped. Most of the solvent was removed by vacuum distillation until the mass of the system showed no significant change. The main component of the residue was the third-generation multi-branched epoxy oligomer.

[0090] The aforementioned third-generation multi-branched epoxy oligomers were transferred to a new 500 ml three-necked flask, with the reaction apparatus as described above. 2.6 mmol of 1,3,5-cyclohexanetriol and 29 ml of 1,4-dioxane were weighed, and the stirring speed was adjusted to 500 rpm to ensure thorough mixing. After adjusting the temperature to 68 °C, 2.5 mmol of 6-bromo-1,2-epoxyhexane was slowly added over 30 min via a constant-pressure dropping funnel. The tube walls were rinsed with 5 ml of solvent, and the reaction was stopped after 1.5 h. The temperature was then adjusted to room temperature, and stirring was stopped. Most of the solvent was removed by vacuum distillation until the system mass showed no significant change. The main component of the residue was the fourth-generation multi-branched epoxy oligomer.

[0091] Weigh 1.2 mmol of diphenylmethane-4,4'-diisocyanate and 120 ml of butanone into a 500 ml four-necked flask. The flask is equipped with a condenser, thermometer, constant-pressure dropping funnel, magnetic stirrer, and three-way check valve, and is placed in an oil bath. The three-way check valve is connected to N2 to displace the gaseous atmosphere of the reaction system and ensure that the internal pressure is positive. Maintain a stirring rate of 300 r / min. After adjusting the temperature to 48 °C, add 0.5 mmol of diphenylmethane-4,4'-diisocyanate in one go through the constant-pressure dropping funnel. Add 2,4-dihydroxy-3,3-dimethylbutyric acid, 2 drops of stannous octoate, and 5 ml of butanone to rinse the tube wall. Maintain the reaction for 80 min. Adjust the temperature to 72 °C, then add 0.8 mmol of polyethylene adipate and 0.3 mmol of 1,2-diaminocyclohexane. Rinse the tube wall with 5 ml of butanone and maintain the reaction for 2.5 h. Stop the reaction, adjust the temperature to room temperature, stop stirring, and remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the viscous liquid is the polyurethane prepolymer, which is ready for use.

[0092] Weigh 11g of the obtained third-generation multi-branched epoxy oligomer and dilute to 100ml with N-methylpyrrolidone to obtain a multi-branched epoxy oligomer dispersion for later use.

[0093] 160g of the obtained viscous liquid polyurethane prepolymer was weighed and placed in a 1000ml three-necked flask equipped with a thermometer, a constant-pressure dropping funnel, a magnetic stirrer, and placed in an oil-water bath. The temperature was adjusted to 75℃ and the stirring speed to 300r / min. 100ml of the above-mentioned multi-branched epoxy oligomer dispersion was slowly added dropwise through the constant-pressure dropping funnel over 33min. 5ml of N-methylpyrrolidone was used to rinse the tube wall, and the reaction was maintained for 2.5h after the addition was complete. The theoretical content of isocyanate groups was determined using the di-n-butylamine method. Once the theoretical value was reached, the system temperature was adjusted to 42℃, and 0.4mmol was slowly added dropwise through the constant-pressure dropping funnel over 18min. Rinse the tube wall with 5 ml of N,N-dimethylethylamine and 5 ml of N-methylpyrrolidone for 65 min; stop heating and adjust the temperature to room temperature. During the cooling phase, use the residual heat to distill under reduced pressure and remove as much solvent as possible; adjust the stirring speed to 2000 r / min and add 190 ml of deionized water to the system at once, and maintain stirring for 20 min to obtain a white emulsion, which is the multi-branched epoxy oligomer crosslinked polyurethane emulsion.

[0094] The coating machine was set to a speed of 42 m / min, a drying temperature of 87℃, and a wet coating weight of 25.4 g / m³. 2 After the cross-linked emulsion is coated and cured on the surface of the aluminized paper, a rigid hydrogel composite paper is obtained, which can be used as a moisture-locking and aroma-preserving packaging material after reabsorbing water; the basis weight of ordinary virgin paper in the aluminized paper structure is 46 g / m². 2 The dry coating amount of the anti-seepage coating is 1.5 g / m². 2 Thickness of aluminum coating

[0095] The infrared spectrum of the generation IV multi-branched epoxy oligomer obtained in Example 1 is shown below. Figure 1 As shown, at 3490cm -1 A broad absorption peak is observed at 1695 cm⁻¹, mainly due to the stretching vibration of excess -OH groups generated during the reaction of 1,2,6-hexanetriol with epichlorohydrin to form a branched structure; -1 The obvious absorption peak at 1510 cm⁻¹ is mainly due to the C-O stretching vibration formed by the condensation of -OH and Cl-R; -1 The obvious absorption peak at 1325 cm⁻¹ mainly originates from the C-H stretching vibration in the epoxide group; -1 The obvious absorption peak at 1250 cm⁻¹ mainly originates from the stretching vibration of the C-H structure of the 1,2,6-hexanetriol aliphatic structure; -1 940cm -1 750cm -1 The presence of a distinct absorption band at each of the three locations indicates the presence of significant epoxy C-O stretching vibrations in the system.

[0096] The inverted test tube method allows for direct observation of gel formation. The newly prepared multi-branched epoxy oligomer crosslinked polyurethane emulsion from Example 1 was immediately placed in an ampoule, such as... Figure 2 As shown. The flowability of the mixture was observed by tilting the ampoule at regular intervals. As the reaction proceeded, the crosslinking density gradually increased and the viscosity of the system gradually increased. The flowability gradually decreased when tilted, and disappeared when the highly crosslinked gel point was reached. It could be determined that the multi-branched epoxy oligomer crosslinked polyurethane emulsion had completed the gelation transformation.

[0097] The swelling rate of the hydrogel composite aluminized paper from Example 1 was determined by gravimetric method after immersion at room temperature for different times. The curves showing the change in swelling rate with swelling time are shown below. Figure 3 As shown in Figure (1), it can be seen that the swelling rate of the hydrogel gradually increases with the extension of swelling time. In the first 60 minutes, the swelling rate of the hydrogel increases rapidly, and it can absorb water quickly. After 80 minutes, the rate of increase in swelling rate slows down, and the swelling rate remains basically unchanged at 120 minutes. In addition, the water retention performance of the hydrogel composite aluminized paper in Example 1 after being saturated with water was tested. The curve of water retention rate changing with time is shown in Figure (1). Figure 3 As shown in (2), it can be seen that the water retention rate of the hydrogel decreased significantly in the first 3 days, and then decreased slowly in the 3 to 7 days and finally remained at 70%, which shows good water retention performance.

[0098] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a rigid hydrogel based on a multi-branched epoxy oligomer crosslinked polyurethane, wherein the multi-branched epoxy oligomer is any one or more of generation I, II, III, or IV multi-branched epoxy oligomers, characterized in that, include: Weigh out the polyurethane prepolymer, stir and heat to 60-90°C, slowly add the multi-branched epoxy oligomer dispersion, and react for 1-5 hours. The theoretical content of isocyanate groups was determined using the di-n-butylamine method. Once the theoretical value was reached, the system temperature was adjusted to 35–55°C, and the salt-forming agent was slowly added dropwise. The mixture was then cooled to room temperature, and the solvent was removed by vacuum distillation using residual heat during the cooling phase. Deionized water was added, and the mixture was stirred until a white emulsion was obtained. The mass-to-volume ratio of the multi-branched epoxy oligomer, polyurethane prepolymer, salt-forming agent, and deionized water was 9–12 g: 90–240 g: 0.3–0.6 mmol: 120–250 ml. The preparation method of the multi-branched epoxy oligomer includes the following steps: A. Dissolve the polyhydroxy compound in a solvent and stir. Adjust the temperature to 50–70°C, then add the catalyst, followed by the slow addition of the epoxy halide. After 0.5–2 hours, stop the reaction, adjust the temperature to room temperature, and stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system shows no significant change. The main component of the residue is the first-generation multi-branched epoxy oligomer. The molar, mass, and volume ratio of the polyhydroxy compound, epoxy halide, catalyst, and solvent is 1.0 mmol: 2.9–3.2 mmol: 0.001–0.01 g: 80–200 ml. The catalyst is an inorganic or organic base. B. Dissolve the first-generation multi-branched epoxy oligomer and the multi-hydroxy compound in a solvent and stir thoroughly. After adjusting the temperature to 50-80℃, add the epoxy halide. After 0.5-3 hours, stop the reaction and adjust the temperature to room temperature and stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the second-generation multi-branched epoxy oligomer. The molar, mass, and volume ratio of the multi-hydroxy compound, epoxy halide, solvent, and multi-hydroxy compound used in the preparation of the first-generation multi-branched epoxy oligomer is 2.8-3.0 mmol: 2.4-3.0 mmol: 20-50 ml: 1.0 mmol. C. Dissolve the second-generation multi-branched epoxy oligomer and the multi-hydroxy compound in a solvent and stir thoroughly. Adjust the temperature to 60-90℃ and add the epoxy halide. Stop the reaction after 0.5-3 hours and adjust the temperature to room temperature and stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the third-generation multi-branched epoxy oligomer. The molar, mass, and volume ratio of the multi-hydroxy compound, epoxy halide, solvent, and multi-hydroxy compound used in the preparation of the first-generation multi-branched epoxy oligomer is 2.6-3.0 mmol: 2.4-3.0 mmol: 20-40 ml: 1.0 mmol. D. Dissolve the third-generation multi-branched epoxy oligomer and the multi-hydroxy compound in a solvent and stir thoroughly. Adjust the temperature to 60-100℃ and add the epoxy halide. Stop the reaction after 1-3 hours and adjust the temperature to room temperature and stop stirring. Remove most of the solvent by vacuum distillation until the mass of the system does not change significantly. The main component of the residue is the fourth-generation multi-branched epoxy oligomer. The molar, mass, and volume ratio of the multi-hydroxy compound, epoxy halide, solvent, and multi-hydroxy compound used in the preparation of the first-generation multi-branched epoxy oligomer is 2.5-3.0 mmol: 2.4-3.0 mmol: 20-40 ml: 1.0 mmol. The polyhydroxy compound is 3,4',5-trihydroxystilbene, phloroglucinol, 1,2,6-hexanetriol, 1,2,4-butanetriol or 1,3,5-cyclohexanetriol; The solvent is toluene, xylene, butanone, cyclohexanone, or 1,4-dioxane; The epoxy halide is epichlorohydrin, methyl epichlorohydrin, epifluorohydrin, epibromopropane, 4-bromo-1,2-epoxybutane, or 6-bromo-1,2-epoxyhexane. The polyurethane prepolymer is prepared by dispersing polyisocyanate in a solvent, heating, maintaining a N2 atmosphere, adjusting the temperature to 40-60°C, adding a chain extender and a few drops of catalyst, and maintaining the temperature for 30-120 min; adjusting the temperature to 50-75°C, adding a polymeric polyol and a polyamino alkane, maintaining the temperature for 1-4 h, stopping the reaction, cooling to room temperature, and removing most of the solvent by vacuum distillation until the mass of the system does not change significantly. The viscous liquid is mainly composed of the polyurethane prepolymer, wherein the ratio of polyisocyanate, polymeric polyol, chain extender, polyamino alkane, catalyst, and solvent is 0.9-1.2 mmol: 0.6-0.9 mmol: 0.3-0.6 mmol: 0.2-0.4 mmol: 1-5 drops: 120 ml; The polyisocyanate is 3,3'-dimethyl-4,4'-biphenyl diisocyanate, toluene-2,4-diisocyanate, isophorone diisocyanate or diphenylmethane-4,4'-diisocyanate; The solvent is acetone, butanone, N,N-dimethylamide or N-methylpyrrolidone; The chain extender is 2,2-dihydroxymethylpropionic acid, 2,4-dihydroxy-3,3-dimethylbutyric acid, 2,4,6-trihydroxybenzoic acid, or 2,4-dihydroxybenzoic acid; The catalyst is diisobutyltin dilaurate, stannous octanoate, di(dodecyl sulfide)dibutyltin, or dibutyltin diacetate; The polymeric polyol is polypropylene glycol, polytetrahydrofuran ether glycol, polyethylene glycol, copolyether glycol, polyethylene adipate, or polyhexanediol adipate. The polyaminoalkane is ethylenediamine, 1,4-butanediamine, 1,5-diaminopentane, 1,3-diaminopentane, or 1,2-diaminocyclohexane.

2. The method for preparing rigid hydrogels based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: Weigh out the polyurethane prepolymer, stir and heat to 85°C, slowly add the multi-branched epoxy oligomer dispersion, and react for 4 hours.

3. The method for preparing rigid hydrogels based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: Once the theoretical value is reached, adjust the system temperature to 40°C and slowly add the salt-forming agent.

4. The method for preparing rigid hydrogels based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: The mass-to-volume ratio of the multi-branched epoxy oligomer, polyurethane prepolymer, salting agent, and deionized water is 10g:200g:0.5mmol:240ml.

5. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In step A, the polyhydroxy compound is dissolved in a solvent and stirred. After adjusting the temperature to 55°C, the catalyst is added, followed by the slow addition of the epoxy halide. After 1 hour, the reaction is stopped, the temperature is adjusted to room temperature, and stirring is stopped.

6. The method for preparing rigid hydrogels based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In step A, the molar, mass, and volume ratio of the polyhydroxy compound, epoxy halide, catalyst, and solvent is 1.0 mmol:3.1 mmol:0.002 g:160 ml.

7. The method for preparing rigid hydrogels based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In step A, the inorganic base is KOH or NaOH.

8. The method for preparing rigid hydrogels based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In step A, the organic base is sodium methoxide, sodium ethoxide, n-butyllithium, lithium aminoide, triethylamine, or N,N-dimethylamine.

9. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In step B, the first-generation multi-branched epoxy oligomer and the multi-hydroxy compound are dissolved in a solvent and stirred thoroughly. After adjusting the temperature to 60°C, the epoxy halide is added. After 1.5 hours, the reaction is stopped, the temperature is adjusted to room temperature, and stirring is stopped.

10. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In step B, the molar, mass, and volume ratio of the polyhydroxy compound, epoxy halide, solvent, and polyhydroxy compound used in the preparation of the first-generation multi-branched epoxy oligomer is 2.9 mmol:2.6 mmol:30 ml:1.0 mmol.

11. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In step C, the second-generation multi-branched epoxy oligomer and the multi-hydroxy compound are dissolved in a solvent and stirred thoroughly. After adjusting the temperature to 70°C, the epoxy halide is added. After 2 hours, the reaction is stopped, the temperature is adjusted to room temperature, and stirring is stopped.

12. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In step C, the molar, mass, and volume ratio of the polyhydroxy compound, epoxy halide, solvent, and polyhydroxy compound used in the preparation of the first-generation multi-branched epoxy oligomer is 2.8 mmol: 2.6 mmol: 30 ml: 1.0 mmol.

13. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In step D, the third-generation multi-branched epoxy oligomer and the multi-hydroxy compound are dissolved in a solvent and stirred thoroughly. After adjusting the temperature to 75°C, the epoxy halide is added. After 2 hours, the reaction is stopped, the temperature is adjusted to room temperature, and stirring is stopped.

14. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In step D, the molar, mass, and volume ratio of the polyhydroxy compound, epoxy halide, solvent, and polyhydroxy compound used in the preparation of the first-generation multi-branched epoxy oligomer is 2.7 mmol:2.6 mmol:30 ml:1.0 mmol.

15. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In the preparation of multi-branched epoxy oligomers, the multi-hydroxy compound is 1,2,6-hexanetriol.

16. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In the preparation of multi-branched epoxy oligomers, the solvent is toluene.

17. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In the preparation of multi-branched epoxy oligomers, the epoxy halide is epichlorohydrin.

18. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: The polyisocyanate was dispersed in a solvent, heated, and kept under a nitrogen atmosphere. After adjusting the temperature to 55°C, a chain extender and a few drops of catalyst were added, and the mixture was maintained for 70 min. After adjusting the temperature to 60°C, a polymerized polyol and a polyamino alkane were added, and the reaction was stopped after maintaining the temperature for 2 h.

19. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: The ratio of the polyisocyanate, polymeric polyol, chain extender, polyaminoalkane, catalyst, and solvent is 1.1 mmol: 0.7 mmol: 0.4 mmol: 0.3 mmol: 4 drops: 120 ml.

20. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: The polyisocyanate is isophorone diisocyanate.

21. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In the preparation of the polyurethane prepolymer, the solvent is N-methylpyrrolidone.

22. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In the preparation of polyurethane prepolymer, the chain extender is 2,4,6-trihydroxybenzoic acid.

23. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In the preparation of the polyurethane prepolymer, the catalyst is di(dodecylsulfide)dibutyltin.

24. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In the preparation of polyurethane prepolymer, the polymeric polyol is polyethylene glycol.

25. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: In the preparation of the polyurethane prepolymer, the polyaminoalkane is 1,5-diaminopentane.

26. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: The solvent removed by vacuum distillation using residual heat during the cooling stage is N,N-dimethylamide, N-methylpyrrolidone, cyclohexanone, 1,4-dioxane, or methyl tert-butyl ether.

27. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 26, characterized in that: The solvent is methyl tert-butyl ether.

28. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 1, characterized in that: The salt-forming agent is triethylamine, diethylamine, or N,N-dimethylethylamine.

29. The method for preparing a rigid hydrogel based on multi-branched epoxy oligomer crosslinked polyurethane according to claim 28, characterized in that: The salt-forming agent is triethylamine.

30. An application of a rigid hydrogel prepared by the method according to any one of claims 1-29, characterized in that: It is used in moisture-locking and fragrance-preserving packaging materials.

31. The application of the rigid hydrogel according to claim 30, characterized in that: The rigid hydrogel is coated onto the aluminum layer side of the aluminized paper and then dried and cured to obtain the rigid hydrogel composite aluminized paper.

32. The application of the rigid hydrogel according to claim 31, characterized in that: The coating process involves a wet coating amount of 5.6–31.9 g / m² for the rigid hydrogel. 2 .

33. The application of the rigid hydrogel according to claim 32, characterized in that: The wet coating amount of the rigid hydrogel is 22.9 g / m³. 2 .

34. The application of the rigid hydrogel according to claim 31, characterized in that: The drying process is carried out at a temperature of 80–105°C.

35. The application of the rigid hydrogel according to claim 34, characterized in that: The drying temperature is 98°C.

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