Acetoacetamide-modified polyvinyl alcohol and a method for preparing the same

Abstract

The application discloses acetoacetamide modified polyvinyl alcohol and a preparation method thereof, and the preparation method comprises the following steps: reacting p-ester and an acetoacetamide reagent at 20-80 DEG C for 1-3h in a polar solvent to generate N-acetoacetyl p-ester; then, the N-acetoacetyl p-ester is mixed with an alkaline catalyst and polyvinyl alcohol, and is added into a double-screw reaction extruder to generate N-acetoacetyl p-ester modified polyvinyl alcohol crude product; finally, the crude product is powdered, washed with methanol for three times to remove the catalyst and reaction inorganic salt, and is filtered and dried to obtain the N-acetoacetyl p-ester modified polyvinyl alcohol. The AAE-PVA prepared by the application can be used as a protective colloid for polyvinyl acetate emulsion polymerization, has better water resistance than common polyvinyl alcohol, and the water resistance, tensile strength and stability of the prepared emulsion adhesive are obviously improved. The synthesis steps of the application are simple, the safety risk is low, and the reaction yield is high.

Description

Technical Field

[0001] This invention belongs to the field of polymer material modification, specifically relating to an acetylacetamide-modified polyvinyl alcohol and its preparation method. Background Technology

[0002] With socio-economic progress and improved living standards, people's demand for timber is not only continuously increasing in quantity but also in quality. Against this backdrop, engineered wood products, made from timber or other plant fibers bonded together with adhesives, are gradually becoming important materials to meet market demands. As a major category of engineered wood products, the production quality and performance of plywood largely depend on the adhesives used. Therefore, optimizing adhesive performance has become a crucial task in the timber processing industry.

[0003] In my country's wood processing industry, adhesives widely used are primarily phenolic resins, urea-formaldehyde resins, and melamine-formaldehyde resins, often categorized as "three-aldehyde adhesives." Epoxy resin adhesives and polyvinyl acetate emulsions also have some applications. Currently, the adhesives used in the domestic wood-based panel industry still revolve around "three-aldehyde adhesives" and their various modified products. These adhesives possess significant performance advantages, such as excellent water resistance, heat resistance, and chemical stability, resulting in boards with good weather resistance and reliability. Furthermore, their readily available raw materials and low production costs have led to their widespread use in plywood production. However, "three-aldehyde adhesives" gradually release volatile harmful substances such as formaldehyde during manufacturing and subsequent use, polluting the workshop environment and indoor air quality, and posing potential health risks. With increasing public awareness of environmental protection and safety, traditional "three-aldehyde adhesives" are no longer fully adapted to the industry requirements of green manufacturing and sustainable development. Against this backdrop, promoting the environmental transformation of adhesive systems has become a clear direction for industry development. Water-based adhesives such as polyvinyl acetate have attracted attention due to their low formaldehyde emission and environmental friendliness.

[0004] Polyvinyl acetate (PVC) adhesive is a thermoplastic adhesive prepared by polymerization of vinyl acetate monomer as the main raw material. Its development history can be traced back to a related synthesis patent in Germany in 1912. This adhesive is typically produced using emulsion polymerization, where water is used as the dispersion medium, and vinyl acetate polymerizes to form a stable emulsion under the action of an initiator. This adhesive features high molecular weight, good bonding strength, and wide compatibility, making it easy to combine with various additives. Viscosity and performance can be flexibly controlled by adjusting the formulation. Due to these advantages, PVC adhesive has been regarded as a general-purpose environmentally friendly adhesive to replace traditional aldehyde-based adhesives in many fields. However, it still has certain limitations in practical applications, especially its poor water resistance and damp heat resistance, and relatively insufficient stability to acidic and alkaline media. These shortcomings limit its widespread application in certain demanding situations and make it difficult to completely replace aldehyde-based adhesives at the current stage.

[0005] In emulsion polymerization, protective colloids are water-soluble polymers that function similarly to emulsifiers in terms of stability and are important components of the emulsion system. Their mechanism of action primarily relies on steric hindrance: by adsorbing onto the surface of latex particles and forming a protective barrier, they effectively prevent particle aggregation, thereby reducing surface tension and maintaining emulsion stability. In the preparation of polyvinyl acetate emulsions, the addition of protective colloids helps regulate the particle size distribution of latex particles and significantly improves the storage and mechanical stability of the emulsion. Compared with conventional emulsifiers, protective colloids can further improve film-forming properties, enhancing the mechanical strength and crack resistance of the film. Commonly used protective colloids include synthetic polymers such as polyvinyl alcohol (PVA), polyvinylpyrrolidone, and hydroxyethyl cellulose, as well as natural materials such as gelatin and animal glue. Among these, polyvinyl alcohol (PVA) has become the most widely used protective colloid due to its excellent overall performance and wide applicability.

[0006] Polyvinyl alcohol (PVA) is a water-soluble polymer that is non-toxic, odorless, and environmentally friendly, exhibiting excellent eco-compatibility. This material has a dense structure, high crystallinity, and strong adhesive properties. In applications, PVA is commonly used as an emulsifying stabilizer (i.e., a protective colloid) in the synthesis of polyvinyl acetate emulsions (PVAc). It can also be used to prepare water-soluble adhesives, benzene-resistant sealing materials, and thermal coatings in thermal paper, making it a versatile functional polymer material.

[0007]

[0008] To improve the water resistance of PVA and broaden its application areas, people often modify PVA with acetyl groups to prepare acetyl-modified polyvinyl alcohol (AA-PVA), which is then used in emulsion protective colloids. Patents US20030186811A1, US20040209014A1, US4624985A, and US 20030083200A1 describe the formation of AA-PVA by introducing acetylacetyl groups into polyvinyl alcohol, which can improve the water resistance and other properties of PVA to a certain extent. Patents CN200780000122.9, CN201010117420.X, CN201580046964.2, CN202311454792.5, and CN202410260710.1 describe the application of AA-PVA in the adhesives of polarizers, which can improve the performance and lifespan of polarizers. However, the improved water resistance achieved by modifying the acetoacetyl group alone is still insufficient to fully support its application in adhesives and protective colloids. This is because the acetoacetyl group is easily hydrolyzed under acidic or alkaline conditions, which reduces the degree of acetylation in PVA. This directly affects the performance of AA-PVA, thereby reducing its ability to act as a protective colloid in emulsion polymerization. Ultimately, this results in insufficient film strength, water resistance, and crosslinking properties after the emulsion film is formed.

[0009]

[0010] Atsushi Mori et al. (Journal of Applied Polymer Science, 2004, 91(5): 2739-3420) found in their study of wood melamine adhesives that the bonding strength increases with the degree of acetylation of AA-PVA. Patent US20070148483A1 describes how the use of AA-PVA with a crosslinking agent as a polarizer adhesive layer can effectively improve the adhesive durability of polarizers, but the improvement in durability is still affected by the crosslinking agent. Patent US20050197441A1 also describes an aqueous emulsion prepared by combining AA-PVA and acrylic monomers, which can be used as an adhesive for particleboard, thereby effectively improving the stability of the adhesive. Patent CN202311454758.8 describes a vinyl acetate-ethylene copolymer emulsion and its adhesive, which improves the performance of the emulsion by adding different polymer monomers to make it act as a protective colloid.

[0011] Therefore, acetylation modification of PVA to enhance the crosslinking of its active sites with the adhesive substrate can improve the performance of the adhesive, including bond strength, solvent resistance and water resistance.

[0012] The acetylacetamide group possesses both the β-dicarbonyl active structure of the acetoacetyl group (i.e., a highly reactive ketone carbonyl group and a methylene group) and better hydrolysis resistance compared to the acetoacetyl ester group. However, the amide group is not easily directly reacted and linked to the hydroxyl groups on PVA. To address this issue, patent CN202411813386.8 describes a method for preparing acetylacetamide-modified polyvinyl alcohol: using triazine as a bridging group, the acetylacetamide group is introduced into PVA through chemical bonds.

[0013]

[0014] Although this method successfully introduced the acetylacetamide group, it also has some problems: the raw material cyanuric chloride used to prepare the structure is highly toxic and can easily cause toxic residues, posing a high safety risk; and the steps for introducing the acetylacetamide group are complicated, requiring a reaction with amine compounds first, followed by a reaction with the remaining chlorine atoms on the triazine ring.

[0015] Para-ester (p-β-hydroxyethyl sulfone sulfate aniline) is an important intermediate for reactive dyes. Under alkaline conditions, it loses the sulfate group and rapidly transforms into a reactive vinyl sulfone structure. This vinyl sulfone group can undergo a nucleophilic addition reaction with the hydroxyl groups on cellulose fibers, and firmly fixes the dye to the fiber by forming covalent bonds (as shown in Figures 1 and 2), thereby giving the dyed fabric excellent wash fastness.

[0016]

[0017] Figure 1. Formation of vinyl sulfone functional groups in β-hydroxyethyl sulfate under alkaline conditions.

[0018]

[0019] Figure 2. Addition reaction between the vinyl sulfone functional group of dye and the hydroxyl group of cellulose.

[0020] Inspired by the reaction between vinyl sulfone-based reactive dyes and cellulose hydroxyl groups, this invention provides a novel approach: reacting a para-ester with an acetylation reagent to directly introduce an acetylacetyl group into the para-ester structure, thereby preparing an N-acetylacetyl para-ester modified PVA (AAE-PVA). The preparation process and mechanism are as follows:

[0021]

[0022] Summary of the Invention

[0023] The technical problem to be solved by this invention is to provide an N-acetylacetyl para-ester modified polyvinyl alcohol and its preparation method. The preparation method has the advantages of being simple, efficient, safe, having good hydrolysis resistance, and being able to quickly introduce acetylacetamide groups. When the N-acetylacetyl para-ester modified polyvinyl alcohol prepared by this invention is applied to the emulsion polymerization of PVAc as a protective colloid for PVAc emulsions, it can significantly improve the strength and hydrolysis resistance of the film after emulsion film formation, as well as the adhesive properties of the downstream product PVAc emulsion adhesive.

[0024] To solve the above-mentioned technical problems, the present invention provides an N-acetyl-acetyl para-ester modified polyvinyl alcohol having a structure as shown in Formula I:

[0025] Formula I;

[0026] Where x and y are both integers, x is 200-2500 and y is 20-400; the value of z is related to the grafting rate.

[0027] This invention also provides a method for preparing N-acetylacetyl para-ester modified polyvinyl alcohol, comprising the following three steps:

[0028] S1. In a polar solvent, the para-ester and the acetylation reagent react at 20-80℃ for 1-3 hours to generate N-acetylacetyl para-ester;

[0029] S2. The N-acetyl-acetyl para-ester prepared in step S1 is mixed with an alkaline catalyst and polyvinyl alcohol, and then added to a twin-screw reactive extruder to react and generate crude N-acetyl-acetyl para-ester modified polyvinyl alcohol.

[0030] S3. The product obtained in S2 is pulverized, washed three times with methanol to remove the catalyst and inorganic salts of the reaction, filtered and dried to obtain N-acetylacetyl para-ester modified polyvinyl alcohol.

[0031] In the preparation process of acetoacetyl-modified PVA of the present invention, the para-ester described in step S1 has the following structure:

[0032] Formula II;

[0033] The polar solvent mentioned in step S1 is one of acetone, methanol, ethanol, 1,4-dioxane, and acetonitrile.

[0034] The acetylation reagent mentioned in step S1 is one of diketene, acetoacetyl methyl ester, acetoacetyl ethyl ester, acetoacetylpropyl ester, and acetoacetyl tert-butyl ester.

[0035] The molar ratio of the acetylation reagent and the para-ester in step S1 is 1:1 to 1.5:1.

[0036] The alkaline catalyst mentioned in step S2 is one of sodium hydroxide, potassium hydroxide, potassium carbonate, or sodium carbonate.

[0037] The degree of polymerization of the polyvinyl alcohol mentioned in step S2 is 300-2400, the degree of alcoholysis is 85-99.9 mol%, and the particle size is 120-300 mesh.

[0038] In step S2, the temperature of each temperature zone of the twin-screw reactive extruder is 20-80℃, and the residence time of the material in the reactive extruder is 5-30 minutes.

[0039] The beneficial effects of the above technical solution of the present invention are as follows:

[0040] 1. This invention provides an N-acetylacetyl para-ester modified polyvinyl alcohol (AAE-PVA), in which acetylacetyl groups are introduced into the para-ester to form acetylacetamide groups, which retains the active groups of acetylacetyl groups while improving hydrolysis resistance compared to acetylacetyl groups.

[0041] 2. The N-acetyl-acetyl para-ester modified polyvinyl alcohol (AAE-PVA) with the structure of Formula I provided by the present invention has better water resistance than ordinary polyvinyl alcohol. When the AAE-PVA of the present invention is used as a protective colloid for polyvinyl acetate (PVAc) emulsion polymerization, it is easier to undergo a grafting reaction with the crosslinking agent, thereby increasing the grafting rate of AA-PVA. This improves the water resistance of PVAc emulsion adhesives while enhancing the tensile strength and stability of the adhesives.

[0042] 3. The AAE-PVA with Formula I structure provided by this invention has a simple synthesis procedure, low safety risk, and high reaction yield; moreover, its structure is novel and has not been reported before. This is of great significance for broadening the types of protective colloids for PVAc emulsion polymerization and their subsequent industrial applications in adhesives. Detailed Implementation

[0043] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0044] Example 1

[0045] (1-a) Preparation of N-acetylacetyl para-ester

[0046] In a 200L stainless steel reactor, add 50L of acetonitrile and start stirring (80 rpm). Add 11.8kg of para-ester in batches, maintaining the reactor temperature at 20±2℃ during the addition process. After the addition is complete, continue stirring for 15 minutes. Slowly add 4.0kg of diketene through a constant-pressure dropping funnel, turning on the jacket cooling water during the addition process and controlling the dropping rate to allow the reaction solution temperature to rise naturally but not exceed 35℃. The total dropping time is 2.5 hours. After the dropping is complete, turn off the cooling water, heat to 80℃, and continue stirring for 3 hours. After the reaction is complete, cool to below 40℃, and recover most of the acetonitrile (approximately 40L) by vacuum distillation. Transfer the concentrate to a cryogenic crystallizer and cool to -5~0℃, allowing it to stand overnight. Centrifuge to separate the acetonitrile, and wash the filter cake twice with 10L of acetonitrile pre-cooled to 0~5℃. The obtained wet product was vacuum dried at 40°C for 4 hours to obtain N-acetylacetyl para-ester (12.7 kg), numbered 1-1a, with a yield of 85%.

[0047] (1-b) Preparation of crude AAE-PVA

[0048] The N-acetylacetyl para-ester (12.0 kg) obtained in step (1-a) was premixed with polyvinyl alcohol (PVA, degree of polymerization 1700, degree of hydrolysis 99%, particle size 200 mesh, 60.0 kg) and anhydrous sodium carbonate (1.8 kg) as an alkaline catalyst in a high-speed mixer for 15 minutes to ensure thorough mixing. The mixture was then fed into a twin-screw compounding extruder (screw diameter 62.4 mm, length-to-diameter ratio L / D = 44:1, Nanjing Nuoda TDS-65B) via a loss-in-weight feeder. The temperatures of each zone of the twin-screw extruder were set as follows: feeding zone 25℃, reaction zone 60℃, 70℃, 80℃, and discharge zone 50℃. The screw speed was adjusted to 180 rpm, and the feeding rate was controlled to ensure an average residence time of 10 minutes for the material in the extruder. The material undergoes acetylation grafting reaction at temperatures below 80°C. After the extruded strip product is cooled by an air-cooled conveyor belt, crude N-acetylacetyl para-ester modified polyvinyl alcohol (71.5 kg) is obtained, numbered 1-2b, with a yield of 96.9%.

[0049] (1-c) Purification and drying

[0050] The crude product obtained in step (1-b) was pulverized (passed through a 60-mesh sieve) using a pulverizer. The powder was added in batches to methanol (180L), and the mixture was stirred and washed at room temperature for 30 minutes. After standing, it was filtered. The methanol washing operation was repeated three times. The filtered solid was dried in a vacuum drying oven at 60℃ (vacuum degree ≤ -0.09MPa) to constant weight, yielding a white to pale yellow powder product, which is N-acetylacetyl para-ester modified polyvinyl alcohol (64.0kg), numbered 1-3c, with a yield of 89.3% and an acetylacetyl grafting rate of 12.3%.

[0051] Example 2

[0052] (2-a) Preparation of N-acetylacetyl para-ester

[0053] In a 200L stainless steel reactor, acetone (50L) was added, and stirring was started (80rpm). Para-ester (11.8kg) was added in batches, maintaining the reactor temperature at 20±2℃ during the addition process. After the addition was complete, stirring continued for 15 minutes. Acetylacetate (5.4kg) was slowly added dropwise through a constant-pressure dropping funnel, with the jacket cooling water turned on during the addition process. The dropping rate was controlled so that the reaction solution temperature naturally rose but did not exceed 35℃. The total dropping time was 2.5 hours. After the addition was complete, the cooling water was turned off, the temperature was raised to 60℃, and the reaction was stirred for another 2 hours. After the reaction was complete, the temperature was lowered to below 40℃, and most of the acetonitrile (approximately 40L) was recovered by vacuum distillation. The concentrate was transferred to a cryogenic crystallization reactor and cooled to -5~0℃, then allowed to stand overnight. The mixture was centrifuged, and the filter cake was washed twice with acetonitrile (10L) pre-cooled to 0~5℃. The obtained wet product was vacuum dried at 40°C for 4 hours to obtain N-acetylacetyl para-ester (12.2 kg), numbered 2-1a, with a yield of 80%.

[0054] (2-b) Preparation of crude AAE-PVA

[0055] The N-acetylacetyl para-ester (12.0 kg) obtained in step (2-a) was premixed with polyvinyl alcohol (PVA, degree of polymerization 500, degree of hydrolysis 88%, particle size 120 mesh, 60.0 kg) and anhydrous potassium carbonate (2.0 kg) as an alkaline catalyst in a high-speed mixer for 15 minutes to ensure thorough mixing. The mixture was then fed into a twin-screw compounding extruder (screw diameter 62.4 mm, length-to-diameter ratio L / D = 44:1, Nanjing Nuoda TDS-65B) via a loss-in-weight feeder. The temperatures of each zone of the twin-screw extruder were set as follows: feeding zone 30℃, reaction zone 65℃, 75℃, 85℃, and discharge zone 55℃. The screw speed was adjusted to 180 rpm, and the feeding rate was controlled to ensure an average residence time of 15 minutes for the material in the extruder. The material undergoes acetylation grafting reaction at temperatures below 80°C. After the extruded strip product is cooled by an air-cooled conveyor belt, crude N-acetylacetyl para-ester modified polyvinyl alcohol (70.9 kg) is obtained, designated as 2-2b, with a yield of 95.5%.

[0056] (2-c) Purification and drying

[0057] The crude product obtained in step (2-b) was pulverized (passed through a 60-mesh sieve) using a pulverizer. The powder was added in batches to methanol (180L), stirred and washed at room temperature for 30 minutes, and then filtered after standing. The methanol washing operation was repeated three times. The filtered solid was dried in a vacuum drying oven at 60℃ (vacuum degree ≤ -0.09MPa) to constant weight, yielding a white to pale yellow powder product, which is N-acetylacetyl para-ester modified polyvinyl alcohol (62.4kg), numbered 2-3c, with a yield of 88% and an acetylacetyl grafting rate of 9.8%.

[0058] Example 3

[0059] (3-a) Preparation of N-acetylacetyl para-ester

[0060] In a 200L stainless steel reactor, methanol (50L) was added, and stirring was started (80rpm). Para-ester (11.8kg) was added in batches, maintaining the reactor temperature at 20±2℃ during the addition process. After the addition was complete, stirring continued for 15 minutes. Ethyl acetoacetate (6.6kg) was slowly added dropwise through a constant-pressure dropping funnel, with the jacket cooling water turned on during the addition to control the dropping rate so that the reaction solution temperature naturally rises but does not exceed 35℃. The total dropping time was 2.5 hours. After the dropping was completed, the cooling water was turned off, the temperature was raised to 50℃, and the reaction was continued with stirring for another 2.5 hours. After the reaction was completed, the temperature was lowered to below 40℃, and most of the acetonitrile (approximately 40L) was recovered by vacuum distillation. The concentrated solution was transferred to a cryogenic crystallization reactor and cooled to -5~0℃, then allowed to stand overnight. The solution was centrifuged, and the filter cake was washed twice with acetonitrile (10L) pre-cooled to 0~5℃. The obtained wet product was vacuum dried at 40°C for 4 hours to obtain N-acetylacetyl para-ester (11.9 kg), numbered 3-1a, with a yield of 78%.

[0061] (3-b) Preparation of crude AAE-PVA

[0062] The N-acetylacetyl para-ester (12.0 kg) obtained in step (3-a) was premixed with polyvinyl alcohol (PVA, degree of polymerization 2400, degree of hydrolysis 95%, particle size 300 mesh, 60.0 kg) and alkaline catalyst sodium hydroxide (1.2 kg) in a high-speed mixer for 15 minutes to ensure thorough mixing. The mixture was then fed into a twin-screw compounding extruder (screw diameter 62.4 mm, length-to-diameter ratio L / D = 44:1, Nanjing Nuoda TDS-65B) via a loss-in-weight feeder. The temperatures of each zone of the twin-screw extruder were set as follows: feeding zone 25℃, reaction zone 70℃, 80℃, 90℃, and discharge zone 50℃. The screw speed was adjusted to 180 rpm, and the feeding rate was controlled to ensure an average residence time of 20 minutes for the material in the extruder. The material undergoes acetylation grafting reaction at temperatures below 80°C. After the extruded strip product is cooled by an air-cooled conveyor belt, crude N-acetylacetyl para-ester modified polyvinyl alcohol (71.3 kg) is obtained, designated as 3-2b, with a yield of 97.2%.

[0063] (3-c) Purification and drying

[0064] The crude product obtained in step (3-b) was pulverized (passed through a 60-mesh sieve) using a pulverizer. The powder was added in batches to methanol (180L), stirred and washed at room temperature for 30 minutes, and then filtered after standing. The methanol washing operation was repeated three times. The filtered solid was dried in a vacuum drying oven at 60℃ (vacuum degree ≤ -0.09MPa) to constant weight, yielding a white to pale yellow powder product, which is N-acetylacetyl para-ester modified polyvinyl alcohol (64.9kg), numbered 3-3c, with a yield of 91% and an acetylacetyl grafting rate of 14.2%.

[0065] Example 4

[0066] (4-a) Preparation of N-acetylacetyl para-ester

[0067] In a 200L stainless steel reactor, add 50L of ethanol and start stirring (80 rpm). Add 11.8kg of para-ester in batches, maintaining the reactor temperature at 20±2℃ during the addition process. After the addition is complete, continue stirring for 15 minutes. Slowly add 7.9kg of acetoacetylpropyl ester through a constant-pressure dropping funnel, turning on the jacket cooling water during the addition process and controlling the dropping rate to allow the reaction solution temperature to rise naturally but not exceed 35℃. The total dropping time is 2.5 hours. After the dropping is complete, turn off the cooling water, heat to 70℃, and continue stirring for 1.5 hours. After the reaction is complete, cool to below 40℃, and recover most of the acetonitrile (approximately 40L) by vacuum distillation. Transfer the concentrate to a cryogenic crystallizer and cool to -5~0℃ overnight. Centrifuge to separate the acetonitrile, and wash the filter cake twice with 10L of acetonitrile pre-cooled to 0~5℃. The obtained wet product was vacuum dried at 40°C for 4 hours to obtain N-acetylacetyl para-ester (12.5 kg), numbered 4-1a, with a yield of 82%.

[0068] (4-b) Preparation of crude AAE-PVA

[0069] The N-acetylacetyl para-ester (12.0 kg) obtained in step (4-a) was premixed with polyvinyl alcohol (PVA, degree of polymerization 1700, degree of hydrolysis 92%, particle size 200 mesh, 60.0 kg) and potassium hydroxide (1.5 kg) as an alkaline catalyst in a high-speed mixer for 15 minutes to ensure thorough mixing. The mixture was then fed into a twin-screw compounding extruder (screw diameter 62.4 mm, length-to-diameter ratio L / D = 44:1, Nanjing Nuoda TDS-65B) via a loss-in-weight feeder. The temperatures of each zone of the twin-screw extruder were set as follows: feeding zone 20℃, reaction zone 60℃, 70℃, 80℃, and discharge zone 45℃. The screw speed was adjusted to 180 rpm, and the feeding rate was controlled to ensure an average residence time of 5 minutes for the material in the extruder. The material undergoes acetylation grafting reaction at temperatures below 80°C. After the extruded strip product is cooled by an air-cooled conveyor belt, crude N-acetylacetyl para-ester modified polyvinyl alcohol (69.1 kg) is obtained, designated as 4-2b, with a yield of 94%.

[0070] (4-c) Purification and drying

[0071] The crude product obtained in step (4-b) was pulverized (passed through a 60-mesh sieve) using a pulverizer. The powder was added in batches to methanol (180L), stirred and washed at room temperature for 30 minutes, and then filtered after standing. The methanol washing operation was repeated three times. The filtered solid was dried in a vacuum drying oven at 60℃ (vacuum degree ≤ -0.09MPa) to constant weight, yielding a white to pale yellow powder product, which is N-acetylacetyl para-ester modified polyvinyl alcohol (59.8kg), numbered 4-3c, with a yield of 86.5% and an acetylacetyl grafting rate of 10.5%.

[0072] Example 5

[0073] (5-a) Preparation of N-acetylacetyl para-ester

[0074] In a 200L stainless steel reactor, add 50L of 1,4-dioxane and start stirring (80 rpm). Add the para-ester (11.8 kg) in batches, maintaining the reactor temperature at 20±2℃ during the addition process. After the addition is complete, continue stirring for 15 minutes. Slowly add 10.0 kg of acetoacetyl tert-butyl ester through a constant-pressure dropping funnel, turning on the jacket cooling water during the addition process and controlling the dropping rate to allow the reaction solution temperature to rise naturally but not exceed 35℃. The total dropping time is 2.5 hours. After the dropping is complete, turn off the cooling water, heat to 40℃, and continue stirring for 3 hours. After the reaction is complete, cool down to below 40℃, and recover most of the acetonitrile (about 40L) by vacuum distillation. Transfer the concentrate to a cryogenic crystallizer and cool to -5~0℃ overnight. Centrifuge to separate the acetonitrile cake, and wash it twice with 10L of acetonitrile pre-cooled to 0~5℃. The obtained wet product was vacuum dried at 40°C for 4 hours to obtain N-acetylacetyl para ester (11.5 kg), numbered 5-1a, with a yield of 75%.

[0075] (5-b) Preparation of crude AAE-PVA

[0076] The N-acetylacetyl para-ester (12.0 kg) obtained in step (5-a) was premixed with polyvinyl alcohol (PVA, degree of polymerization 300, degree of hydrolysis 85%, particle size 250 mesh, 60.0 kg) and anhydrous sodium carbonate (1.9 kg) as an alkaline catalyst in a high-speed mixer for 15 minutes to ensure thorough mixing. The mixture was then fed into a twin-screw compounding extruder (screw diameter 62.4 mm, length-to-diameter ratio L / D = 44:1, Nanjing Nuoda TDS-65B) via a loss-in-weight feeder. The temperatures of each zone of the twin-screw extruder were set as follows: feeding zone 28℃, reaction zones 68℃, 78℃, 88℃, and discharge zone 52℃. The screw speed was adjusted to 180 rpm, and the feeding rate was controlled to ensure an average residence time of 30 minutes for the material in the extruder. The material undergoes acetylation grafting reaction at temperatures below 80°C. After the extruded strip product is cooled by an air-cooled conveyor belt, crude N-acetylacetyl para-ester modified polyvinyl alcohol (69.3 kg) is obtained, designated as 5-2b, with a yield of 93.5%.

[0077] (5-c) Purification and drying

[0078] The crude product obtained in step (5-b) was pulverized (passed through a 60-mesh sieve) using a pulverizer. The powder was added in batches to methanol (180L), stirred and washed at room temperature for 30 minutes, and then filtered after standing. The methanol washing operation was repeated three times. The filtered solid was dried in a vacuum drying oven at 60℃ (vacuum degree ≤ -0.09MPa) to constant weight, yielding a white to pale yellow powder product, which is N-acetylacetyl para-ester modified polyvinyl alcohol (58.9kg), numbered 5-3c, with a yield of 85% and an acetylacetyl grafting rate of 7.6%.

[0079] Example 6

[0080] (6-a) Preparation of N-acetylacetyl para-ester

[0081] In a 200L stainless steel reactor, add acetonitrile (50L) and start stirring (80rpm). Add para-ester (11.8kg) in batches, maintaining the reactor temperature at 20±2℃ during the addition process. After the addition is complete, continue stirring for 15 minutes. Slowly add diketene (3.5kg) dropwise through a constant-pressure dropping funnel, turning on the jacket cooling water during the dropwise addition to control the dropping rate so that the reaction solution temperature rises naturally but does not exceed 35℃. The total dropping time is 2.5 hours. After the dropwise addition is complete, turn off the cooling water, heat to 80℃, and continue stirring for 3 hours. After the reaction is complete, cool to below 40℃, and recover most of the acetonitrile (approximately 40L) by vacuum distillation. Transfer the concentrate to a cryogenic crystallizer and cool to -5~0℃, allowing it to stand overnight. Centrifuge to separate the acetonitrile, and wash the filter cake twice with acetonitrile (10L) pre-cooled to 0~5℃. The obtained wet product was vacuum dried at 40°C for 4 hours to obtain N-acetylacetyl para ester (12.7 kg), numbered 2-1a, with a yield of 85%.

[0082] (6-b) Preparation of crude AAE-PVA

[0083] The N-acetylacetyl para-ester (12.0 kg) obtained in step (6-a) was premixed with polyvinyl alcohol (PVA, degree of polymerization 1700, degree of hydrolysis 99%, particle size 200 mesh, 60.0 kg) and anhydrous sodium carbonate (1.6 kg) as an alkaline catalyst in a high-speed mixer for 15 minutes to ensure thorough mixing. The mixture was then fed into a twin-screw compounding extruder (screw diameter 62.4 mm, length-to-diameter ratio L / D = 44:1, Nanjing Nuoda TDS-65B) via a loss-in-weight feeder. The temperatures of each zone of the twin-screw extruder were set as follows: feeding zone 25℃, reaction zone 60℃, 70℃, 80℃, and discharge zone 50℃. The screw speed was adjusted to 180 rpm, and the feeding rate was controlled to ensure an average residence time of 10 minutes for the material within the extruder. The material undergoes acetylation grafting reaction at temperatures below 80°C. After the extruded strip product is cooled by an air-cooled conveyor belt, crude N-acetylacetyl para-ester modified polyvinyl alcohol (71.2 kg) is obtained, designated as 6-2b, with a yield of 96.5%.

[0084] (6-c) Purification and drying

[0085] The crude product obtained in step (6-b) was pulverized (passed through a 60-mesh sieve) using a pulverizer. The powder was added in batches to methanol (180L), stirred and washed at room temperature for 30 minutes, and then filtered after standing. The methanol washing operation was repeated three times. The filtered solid was dried in a vacuum drying oven at 60℃ (vacuum degree ≤ -0.09MPa) to constant weight, yielding a white to pale yellow powder product, which is N-acetylacetyl para-ester modified polyvinyl alcohol (63.4kg), numbered 6-3c, with a yield of 89% and an acetylacetyl grafting rate of 12.0%.

[0086] Example 7

[0087] (7-a) Preparation of N-acetylacetyl para-ester

[0088] In a 200L stainless steel reactor, acetone (50L) was added, and stirring was started (80rpm). Para-ester (11.8kg) was added in batches, maintaining the reactor temperature at 20±2℃ during the addition process. After the addition was complete, stirring continued for 15 minutes. Diketene (3.7kg) was slowly added dropwise through a constant-pressure dropping funnel, with the jacket cooling water turned on during the addition process. The dropping rate was controlled so that the reaction solution temperature naturally rose but did not exceed 35℃. The total dropping time was 2.5 hours. After the dropping was completed, the cooling water was turned off, and the mixture was heated to 75℃ and stirred for another 2 hours. After the reaction was complete, the temperature was lowered to below 40℃, and most of the acetonitrile (approximately 40L) was recovered by vacuum distillation. The concentrated solution was transferred to a cryogenic crystallization reactor and cooled to -5~0℃, then allowed to stand overnight. The mixture was centrifuged, and the filter cake was washed twice with acetonitrile (10L) pre-cooled to 0~5℃. The obtained wet product was vacuum dried at 40°C for 4 hours to obtain N-acetylacetyl para-ester (13.1 kg), numbered 7-1a, with a yield of 86%.

[0089] (7-b) Preparation of crude AAE-PVA

[0090] The N-acetylacetyl para-ester (12.0 kg) obtained in step (7-a) was premixed with polyvinyl alcohol (PVA, degree of polymerization 2000, degree of hydrolysis 98%, particle size 150 mesh, 60.0 kg) and anhydrous potassium carbonate (2.2 kg) as an alkaline catalyst in a high-speed mixer for 15 minutes to ensure thorough mixing. The mixture was then fed into a twin-screw compounding extruder (screw diameter 62.4 mm, length-to-diameter ratio L / D = 44:1, Nanjing Nuoda TDS-65B) via a loss-in-weight feeder. The temperatures of each zone of the twin-screw extruder were set as follows: feeding zone 22℃, reaction zones 62℃, 72℃, 82℃, and discharge zone 48℃. The screw speed was adjusted to 180 rpm, and the feeding rate was controlled to ensure an average residence time of 23 minutes for the material in the extruder. The material undergoes acetylation grafting reaction at temperatures below 80°C. After the extruded strip product is cooled by an air-cooled conveyor belt, crude N-acetylacetyl para-ester modified polyvinyl alcohol (72.3 kg) is obtained, designated as 7-2b, with a yield of 97.5%.

[0091] (7-c) Purification and drying

[0092] The crude product obtained in step (7-b) was pulverized (passed through a 60-mesh sieve) using a pulverizer. The powder was added in batches to methanol (180L), stirred and washed at room temperature for 30 minutes, and then filtered after standing. The methanol washing operation was repeated three times. The filtered solid was dried in a vacuum drying oven at 60℃ (vacuum degree ≤ -0.09MPa) to constant weight, yielding a white to pale yellow powder product, which is N-acetylacetyl para-ester modified polyvinyl alcohol (66.5kg), numbered 7-3c, with a yield of 92% and an acetylacetyl grafting rate of 13.5%.

[0093] Example 8

[0094] (8-a) Preparation of N-acetylacetyl para-ester

[0095] In a 200L stainless steel reactor, methanol (50L) was added, and stirring was started (80rpm). Para-ester (11.8kg) was added in batches, maintaining the reactor temperature at 20±2℃ during the addition process. After the addition was complete, stirring continued for 15 minutes. Ethyl acetoacetate (6.3kg) was slowly added dropwise through a constant-pressure dropping funnel, with the jacket cooling water turned on during the addition to control the dropping rate so that the reaction solution temperature naturally rises but does not exceed 35℃. The total dropping time was 2.5 hours. After the dropping was completed, the cooling water was turned off, the temperature was raised to 55℃, and the reaction was continued with stirring for 2.8 hours. After the reaction was completed, the temperature was lowered to below 40℃, and most of the acetonitrile (approximately 40L) was recovered by vacuum distillation. The concentrated solution was transferred to a cryogenic crystallization reactor and cooled to -5~0℃, then allowed to stand overnight. The solution was centrifuged, and the filter cake was washed twice with acetonitrile (10L) pre-cooled to 0~5℃. The obtained wet product was vacuum dried at 40°C for 4 hours to obtain N-acetylacetyl para ester (12.1 kg), numbered 8-1a, with a yield of 79%.

[0096] (8-b) Preparation of crude AAE-PVA

[0097] The N-acetylacetyl para-ester (12.0 kg) obtained in step (8-a) was premixed with polyvinyl alcohol (PVA, degree of polymerization 1000, degree of hydrolysis 90%, particle size 180 mesh, 60.0 kg) and anhydrous sodium carbonate (1.8 kg) as an alkaline catalyst in a high-speed mixer for 15 minutes to ensure thorough mixing. The mixture was then fed into a twin-screw compounding extruder (screw diameter 62.4 mm, length-to-diameter ratio L / D = 44:1, Nanjing Nuoda TDS-65B) via a loss-in-weight feeder. The temperatures of each zone of the twin-screw extruder were set as follows: feeding zone 26℃, reaction zones 66℃, 76℃, 86℃, and discharge zone 50℃. The screw speed was adjusted to 180 rpm, and the feeding rate was controlled to ensure an average residence time of 8 minutes for the material within the extruder. The material undergoes acetylation grafting reaction at temperatures below 80°C. After the extruded strip product is cooled by an air-cooled conveyor belt, crude N-acetylacetyl para-ester modified polyvinyl alcohol (69.4 kg) is obtained, designated as 8-2b, with a yield of 95%.

[0098] (8-c) Purification and drying

[0099] The crude product obtained in step (8-b) was pulverized (passed through a 60-mesh sieve) using a pulverizer. The powder was added in batches to methanol (180L), stirred and washed at room temperature for 30 minutes, and then filtered after standing. The methanol washing operation was repeated three times. The filtered solid was dried in a vacuum drying oven at 60℃ (vacuum degree ≤ -0.09MPa) to constant weight, yielding a white to pale yellow powder product, which is N-acetylacetyl para-ester modified polyvinyl alcohol (60.7kg), numbered 8-3c, with a yield of 87.5% and an acetylacetyl grafting rate of 11.0%.

[0100] Example 9

[0101] (9-a) Preparation of N-acetylacetyl para-ester

[0102] In a 200L stainless steel reactor, add 50L of ethanol and start stirring (80 rpm). Add 11.8kg of para-ester in batches, maintaining the reactor temperature at 20±2℃ during the addition process. After the addition is complete, continue stirring for 15 minutes. Slowly add 3.5kg of diketene through a constant-pressure dropping funnel, turning on the jacket cooling water during the addition process and controlling the dropping rate to allow the reaction solution temperature to rise naturally but not exceed 35℃. The total dropping time is 2.5 hours. After the dropping is complete, turn off the cooling water, heat to 65℃, and continue stirring for 2 hours. After the reaction is complete, cool to below 40℃, and recover most of the acetonitrile (approximately 40L) by vacuum distillation. Transfer the concentrate to a cryogenic crystallizer and cool to -5~0℃ overnight. Centrifuge to separate the acetonitrile cake, and wash it twice with 10L of acetonitrile pre-cooled to 0~5℃. The obtained wet product was vacuum dried at 40°C for 4 hours to obtain N-acetylacetyl para ester (12.8 kg), numbered 9-1a, with a yield of 84%.

[0103] (9-b) Preparation of crude AAE-PVA

[0104] The N-acetylacetyl para-ester (12.0 kg) obtained in step (9-a) was premixed with polyvinyl alcohol (PVA, degree of polymerization 1700, degree of hydrolysis 99%, particle size 200 mesh, 60.0 kg) and potassium hydroxide (1.7 kg) as an alkaline catalyst in a high-speed mixer for 15 minutes to ensure thorough mixing. The mixture was then fed into a twin-screw compounding extruder (screw diameter 62.4 mm, length-to-diameter ratio L / D = 44:1, Nanjing Nuoda TDS-65B) via a loss-in-weight feeder. The temperatures of each zone of the twin-screw extruder were set as follows: feeding zone 24℃, reaction zones 64℃, 74℃, 84℃, and discharge zone 46℃. The screw speed was adjusted to 180 rpm, and the feeding rate was controlled to ensure an average residence time of 25 minutes for the material in the extruder. The material undergoes acetylation grafting reaction at temperatures below 80°C. After the extruded strip product is cooled by an air-cooled conveyor belt, crude N-acetylacetyl para-ester modified polyvinyl alcohol (70.9 kg) is obtained, designated as 9-2b, with a yield of 96%.

[0105] (9-c) Purification and drying

[0106] The crude product obtained in step (9-b) was pulverized (passed through a 60-mesh sieve) using a pulverizer. The powder was added in batches to methanol (180L), stirred and washed at room temperature for 30 minutes, and then filtered after standing. The methanol washing operation was repeated three times. The filtered solid was dried in a vacuum drying oven at 60℃ (vacuum degree ≤ -0.09MPa) to constant weight, yielding a white to pale yellow powder product, which is N-acetylacetyl para-ester modified polyvinyl alcohol (63.8kg), numbered 9-3c, with a yield of 90% and an acetylacetyl grafting rate of 12.8%.

[0107] Example 10

[0108] (10-a) Preparation of N-acetylacetyl para-ester

[0109] In a 200L stainless steel reactor, add 50L of 1,4-dioxane and start stirring (80 rpm). Add the para-ester (11.8 kg) in batches, maintaining the reactor temperature at 20±2℃ during the addition process. After the addition is complete, continue stirring for 15 minutes. Slowly add 6.8 kg of acetoacetyl methyl ester through a constant-pressure dropping funnel, turning on the jacket cooling water during the addition process and controlling the dropping rate to allow the reaction solution temperature to rise naturally but not exceed 35℃. The total dropping time is 2.5 hours. After the dropping is complete, turn off the cooling water, heat to 45℃, and continue stirring for 3 hours. After the reaction is complete, cool to below 40℃, and recover most of the acetonitrile (approximately 40L) by vacuum distillation. Transfer the concentrate to a cryogenic crystallizer and cool to -5~0℃ overnight. Centrifuge to separate the acetonitrile cake, and wash it twice with 10L of acetonitrile pre-cooled to 0~5℃. The obtained wet product was vacuum dried at 40°C for 4 hours to obtain N-acetylacetyl para ester (11.6 kg), numbered 10-1a, with a yield of 76%.

[0110] (10-b) Preparation of crude AAE-PVA

[0111] The N-acetylacetyl para-ester (12.0 kg) obtained in step (10-a) was premixed with polyvinyl alcohol (PVA, degree of polymerization 2400, degree of hydrolysis 96%, particle size 300 mesh, 60.0 kg) and anhydrous sodium carbonate (1.8 kg) as an alkaline catalyst in a high-speed mixer for 15 minutes to ensure thorough mixing. The mixture was then fed into a twin-screw compounding extruder (screw diameter 62.4 mm, length-to-diameter ratio L / D = 44:1, Nanjing Nuoda TDS-65B) via a loss-in-weight feeder. The temperatures of each zone of the twin-screw extruder were set as follows: feeding zone 30℃, reaction zone 70℃, 80℃, 90℃, and discharge zone 55℃. The screw speed was adjusted to 180 rpm, and the feeding rate was controlled to ensure an average residence time of 18 minutes for the material within the extruder. The material undergoes acetylation grafting reaction at temperatures below 80°C. After the extruded strip product is cooled by an air-cooled conveyor belt, crude N-acetylacetyl para-ester modified polyvinyl alcohol (70.3 kg) is obtained, designated as 10-2b, with a yield of 94.8%.

[0112] (10-c) Purification and drying

[0113] The crude product obtained in step (10-b) was pulverized (passed through a 60-mesh sieve) using a pulverizer. The powder was added in batches to methanol (180L), stirred and washed at room temperature for 30 minutes, and then filtered after standing. The methanol washing operation was repeated three times. The filtered solid was dried in a vacuum drying oven at 60℃ (vacuum degree ≤ -0.09MPa) to constant weight, yielding a white to pale yellow powder product, which is N-acetylacetyl para-ester modified polyvinyl alcohol (60.5kg), numbered 10-3c, with a yield of 86% and an acetylacetyl grafting rate of 9.2%.

[0114] Comparative Example 1

[0115] Choose PVA series products from China Chuanwei Chemical Co., Ltd., model 9905 (degree of alcoholysis 99%, degree of polymerization 500, viscosity 5-6.5 mPa.s, volatile content max 5%, pH=5-7).

[0116] Comparative Example 2

[0117] Choose GOHSENX™ Z Series product from Mitsubishi Chemical Corporation of Japan, model Z-200 (degree of alcoholysis 99%, degree of polymerization 500, viscosity 11.5-14 mPa.s, volatile content max 5%, pH=3.5-5).

[0118] Comparative Example 3

[0119] Choose GOHSENX™ Z Series product from Mitsubishi Chemical Corporation of Japan, model Z-210 (degree of alcoholysis 95-97%, degree of polymerization 500, viscosity 11.5-15 mPa.s, volatile content max 5%, pH=4-5.3).

[0120] Performance testing

[0121] Test 1: Performance testing as a protective colloid in PVAc emulsion polymerization

[0122] The main relevant indicators of the PVAc emulsions prepared using products 3-3c, 7-3c, and the commercial products in Comparative Examples 1-3 are shown in Table 1. (There are no special requirements for the preparation of PVAc emulsions. You only need to choose one commercially available product and replace the protective colloidal PVA or AA-PVA with the commercial products in products 3-3c, 7-3c, and Comparative Examples 1-3, while keeping other conditions unchanged. Here is a commonly used laboratory preparation method as shown in Example 1.)

[0123] Example 1

[0124] 1. Dissolve polyvinyl alcohol

[0125] In a 250 mL four-necked reaction flask equipped with an electric stirrer, a spherical condenser, a dropping funnel, a thermometer, and a nitrogen delivery tube, add 3 g of 9905PVA (degree of alcoholysis 99%, degree of polymerization 500) from Comparative Example 1 and 50 mL of deionized water, and start stirring; gradually raise the water bath temperature to 80 °C and keep it constant until all polyvinyl alcohol is dissolved.

[0126] 2. Preparation of solution

[0127] Weigh 0.3g of ammonium persulfate, dissolve it in 3mL of water to prepare a 10% solution.

[0128] 3. Aggregation

[0129] (1) Add 1g of emulsifier OP-10 to the dissolved polyvinyl alcohol solution, stir and heat to 60℃.

[0130] (2) Add 11 mL of vinyl acetate and 1 / 4 (about 1.2 mL) of the prepared ammonium persulfate solution to the above emulsion; purge the air with nitrogen and keep the temperature at 60-65℃ (reflux) for reaction.

[0131] (3) When the temperature rises to 80~83℃, the reflux gradually decreases. Start by slowly adding 43mL of vinyl acetate with a dropping funnel to control the dropping rate so that the reaction temperature is kept between 80±2℃ and there is moderate reflux. The addition is completed in about 2 hours. During the addition of vinyl acetate, add 1.2mL of initiator solution in 3-4 portions.

[0132] (4) After the monomer is added, add the remaining initiator solution at once. When the reaction temperature rises to 90-95℃, maintain it for 0.5h and then stop the reaction.

[0133] (5) When the emulsion is cooled to 50°C, adjust the pH to 5-6 with 10% sodium bicarbonate solution; add 5g of dibutyl phthalate, stir evenly, and cool to room temperature to obtain the product.

[0134] Table 1 shows the water resistance of the emulsion, which was tested according to GB / T 23445-2009. The tensile strength and elongation at break of the emulsion were tested, and the results are as follows:

[0135] Tensile strength test: After the emulsion is made into a film, it is tested using a universal testing machine.

[0136] The film-forming method is as follows: Weigh 5g of raw PVA (products 3-3c, 7-3c, and the products in comparative examples 1-3), add 100mL of pure water, heat to above 90℃ until completely dissolved, and prepare a 5% PVA aqueous solution. Then, in a film with dimensions of 23×17cm... 2 A PVA aqueous solution was poured onto a framed glass plate, and a film was formed using the casting method and dried at room temperature. Finally, the film was cut into strips 50 mm long and 20 mm wide and stored in a desiccator. (Tests were conducted using films with a uniform thickness of 0.05 mm.)

[0137] Tensile strength reduction rate = (untreated tensile strength - water-treated tensile strength) * 100% / untreated tensile strength.

[0138] The rate of decrease in elongation at break = (Elongation at break without treatment - Elongation at break with water treatment) * 100% / Elongation at break without treatment.

[0139] Table 1. Water resistance test of emulsions

[0140]

[0141] Table 1 shows that the tensile strength and elongation at break of samples prepared using products 3-3c, 7-3c, and comparative examples 1-3 as protective colloids all decreased to varying degrees after water treatment. Specifically, the emulsion using 3-3c as the protective colloid showed a 7% decrease in tensile strength and a 6% decrease in elongation at break; the emulsion using 7-3c showed a 7% decrease in tensile strength and an 8% decrease in elongation at break; while the emulsions prepared using PVA from Sichuan Weihua or AA-PVA from Mitsubishi Chemical Corporation of Japan showed a 9%-13% decrease in tensile strength and an 11%-22% decrease in elongation at break. This indicates that using AAM-PVA as a protective colloid can significantly improve the water resistance of the emulsion.

[0142] Test 2: Water resistance test after membrane fabrication

[0143] Film Formation: Weigh 5g of raw PVA (products 3-3c, 7-3c, and the products in Comparative Examples 1-3) and add 100mL of pure water. Heat to above 90℃ until completely dissolved to prepare a 5% PVA aqueous solution. Then, film with dimensions of 23×17cm... 2 PVA aqueous solution was poured onto a framed glass plate, and a film was formed using the casting method and dried at room temperature. Finally, it was cut into 50mm diameter discs and stored in a desiccator. (Tests were conducted using films with a uniform thickness of 0.05mm).

[0144] Three circular membranes of 50 mm diameter each (with a uniform thickness of 0.05 mm) were selected from products 3-3c, 7-3c, and Comparative Examples 1-3. The membranes were then immersed in pure water, a 0.1 mol / L NaOH solution, and a 2% (volume fraction) acetic acid solution, respectively, and allowed to stand at room temperature for 24 hours. Their water resistance properties are shown in Table 2 (√ for good performance, × for poor performance, and — for average performance).

[0145] Table 2. Water resistance properties of AAE-PVA membrane

[0146]

[0147] As shown in Table 2, when the products 3-3c, 7-3c and the commercial products of Comparative Examples 1-3 were made into films and tested in neutral, alkaline and acidic solutions, products 3-3c and 7-3c showed the best water resistance and also significantly improved acid resistance.

[0148] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0149] 1. This invention provides an N-acetylacetyl para-ester modified polyvinyl alcohol (AAE-PVA), in which acetylacetyl groups are introduced into the para-ester to form acetylacetamide groups, which retains the active groups of acetylacetyl groups while improving hydrolysis resistance compared to acetylacetyl groups.

[0150] 2. The N-acetyl-acetyl para-ester modified polyvinyl alcohol (AAE-PVA) with the structure of Formula I provided by the present invention has better water resistance than ordinary polyvinyl alcohol. When the AAE-PVA of the present invention is used as a protective colloid for polyvinyl acetate (PVAc) emulsion polymerization, it is easier to undergo a grafting reaction with the crosslinking agent, thereby increasing the grafting rate of AA-PVA. This improves the water resistance of PVAc emulsion adhesives while enhancing the tensile strength and stability of the adhesives.

[0151] 3. The AAE-PVA with Formula I structure provided by this invention has a simple synthesis procedure, low safety risk, and high reaction yield; moreover, its structure is novel and has not been reported before. This is of great significance for broadening the types of protective colloids for PVAc emulsion polymerization and their subsequent industrial applications in adhesives.

[0152] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An acetylacetam-modified polyvinyl alcohol, characterized in that, It has the structure shown in Equation I: Formula I; Where x and y are both integers, x is 200-2500 and y is 20-400; the value of z is related to the grafting rate.

2. A method for preparing acetylacetam-modified polyvinyl alcohol as described in claim 1, characterized in that, It includes the following three steps: S1. In a polar solvent, the para-ester and the acetylation reagent react at 20-80℃ for 1-3 hours to generate N-acetylacetyl para-ester; S2. The N-acetyl-acetyl para-ester prepared in step S1 is mixed with an alkaline catalyst and polyvinyl alcohol, and then added to a twin-screw reactive extruder to react and generate crude N-acetyl-acetyl para-ester modified polyvinyl alcohol. S3. The product obtained in S2 is pulverized, washed three times with methanol to remove the catalyst and inorganic salts of the reaction, filtered and dried to obtain N-acetylacetyl para-ester modified polyvinyl alcohol.

3. The method for preparing acetylacetamide-modified polyvinyl alcohol according to claim 2, characterized in that, The para-ester described in step S1 has the following structure: Formula II.

4. The method for preparing acetylacetamide-modified polyvinyl alcohol according to claim 2, characterized in that, The polar solvent mentioned in step S1 is one of acetone, methanol, ethanol, 1,4-dioxane, and acetonitrile.

5. The method for preparing acetylacetamide-modified polyvinyl alcohol according to claim 2, characterized in that, The acetylation reagent mentioned in step S1 is one of diketene, acetoacetyl methyl ester, acetoacetyl ethyl ester, acetoacetylpropyl ester, and acetoacetyl tert-butyl ester.

6. The method for preparing acetylacetam-modified polyvinyl alcohol according to claim 2, characterized in that, The molar ratio of the acetylation reagent and the para-ester in step S1 is 1:1 to 1.5:

1.

7. The method for preparing acetylacetam-modified polyvinyl alcohol according to claim 2, characterized in that, The alkaline catalyst mentioned in step S2 is one of sodium hydroxide, potassium hydroxide, potassium carbonate, or sodium carbonate.

8. The method for preparing acetylacetam-modified polyvinyl alcohol according to claim 2, characterized in that, The degree of polymerization of the polyvinyl alcohol mentioned in step S2 is 300-2400, the degree of alcoholysis is 85-99.9 mol%, and the particle size is 120-300 mesh.

9. The method for preparing acetylacetamide-modified polyvinyl alcohol according to claim 2, characterized in that, In step S2, the temperature of each temperature zone of the twin-screw reactive extruder is 20-80℃, and the residence time of the material in the reactive extruder is 5-30 minutes.

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