Method for regulating and controlling alcoholysis degree of polyvinyl alcohol

Abstract

The invention provides a method for regulating and controlling the alcoholysis degree of polyvinyl alcohol, which comprises the following steps: carrying out acetylation reaction on a polyvinyl alcohol raw material and an acetylation reagent to obtain a polyvinyl alcohol product with the alcoholysis degree different from that of the polyvinyl alcohol raw material. According to the method for regulating and controlling the alcoholysis degree of polyvinyl alcohol provided by the invention, polyvinyl alcohol is taken as a raw material, acetyl is reversely inoculated through acetylation reaction, polyvinyl alcohol products with different alcoholysis degrees can be obtained, and the method is relatively high in stability, simple and suitable for large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of polymers, and in particular relates to a method for regulating the alcoholysis degree of polyvinyl alcohol. Background Art

[0002] Polyvinyl alcohol (PVA) is an important water-soluble polymer material, widely used in textile, papermaking, adhesives, coatings and packaging materials. The preparation of PVA is usually achieved through the alcoholysis reaction of polyvinyl acetate (PVAc), in which PVAc undergoes an ester exchange reaction with methanol under alkaline conditions, and the acetyl group (-OCOCH3) on the side chain is replaced by a hydroxyl group (-OH). The alcoholysis degree is an important indicator of PVA, which refers to the percentage of hydroxyl groups in the product to the original acetyl groups. It significantly affects the physical and chemical properties of PVA, such as solubility, viscosity and mechanical strength.

[0003] However, the preparation of PVA with different alcoholysis degrees, especially PVA with low alcoholysis degrees, is difficult to achieve large-scale high-quality production, because multiple reaction parameters need to be precisely controlled during the alcoholysis process, and corresponding alcoholysis equipment needs to be matched. Therefore, developing a simple and universal preparation method for PVA with stable control of alcoholysis degree is a technical problem that needs to be solved at this stage. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for regulating the alcoholysis degree of polyvinyl alcohol, which can prepare polyvinyl alcohol with different alcoholysis degrees, has high stability, and the preparation method is simple and controllable.

[0005] The present invention provides a method for regulating the alcoholysis degree of polyvinyl alcohol, comprising the following steps:

[0006] The polyvinyl alcohol raw material is subjected to an acetylation reaction with an acetylation agent to obtain a polyvinyl alcohol product having a different alcoholysis degree from the polyvinyl alcohol raw material.

[0007] In the method for regulating the alcoholysis degree of polyvinyl alcohol as described above, the difference in alcoholysis degree between the polyvinyl alcohol raw material and the polyvinyl alcohol product is 1%-80%.

[0008] According to the method for regulating the alcoholysis degree of polyvinyl alcohol as described above, the alcoholysis degree of the polyvinyl alcohol product is 5%-95%.

[0009] In the method for regulating the alcoholysis degree of polyvinyl alcohol as described above, the polyvinyl alcohol raw material includes at least one of PVA-1799, PVA-2099, PVA-2499, PVA-2699, PVA-0388, PVA-0588, PVA-2088, PVA-1788, and PVA-2488.

[0010] The method for regulating the degree of alcoholysis of polyvinyl alcohol as described above, wherein the temperature of the acetylation reaction is 90°C - 120°C and the time is 8h - 30h.

[0011] The method for regulating the degree of alcoholysis of polyvinyl alcohol as described above, wherein the acetylation reaction is carried out in a solvent.

[0012] The method for regulating the degree of alcoholysis of polyvinyl alcohol as described above, wherein the mass ratio of the acetylation reagent to the polyvinyl alcohol raw material is (0.1 - 2):1;

[0013] Preferably, the acetylation reagent includes acetyl chloride and / or acetic anhydride.

[0014] The method for regulating the degree of alcoholysis of polyvinyl alcohol as described above, wherein the acetylation reaction is carried out in the presence of a catalyst;

[0015] Preferably, the mass ratio of the catalyst to the polyvinyl alcohol raw material is (1 - 5):1;

[0016] Preferably, the catalyst includes at least one of pyridine, dimethylpyridine, 4-dimethylaminopyridine, quinoline, tetrabutylammonium bromide, and tetramethylammonium bromide.

[0017] The method for regulating the degree of alcoholysis of polyvinyl alcohol as described above further includes: after the acetylation reaction, adding the obtained reaction system to a poor solvent for precipitation treatment to obtain the polyvinyl alcohol product.

[0018] The method for regulating the degree of alcoholysis of polyvinyl alcohol as described above, wherein the mass ratio of the poor solvent to the polyvinyl alcohol raw material is (10 - 30):1.

[0019] The method for regulating the degree of alcoholysis of polyvinyl alcohol provided by the present invention uses polyvinyl alcohol as a raw material and reversely incorporates acetyl groups through an acetylation reaction, and polyvinyl alcohol products with different degrees of alcoholysis can be obtained. This method has high stability, and at the same time, it is simple and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention or related technologies. Obviously, the following drawings are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0021] Figure 1 1H NMR spectrum of the polyvinyl alcohol product in Example 1 of the present invention;

[0022] Figure 21H NMR spectrum of the polyvinyl alcohol product of Example 2 of the present invention;

[0023] Figure 3 1H NMR spectrum of the polyvinyl alcohol product of Example 3 of the present invention;

[0024] Figure 4 1H NMR spectrum of the polyvinyl alcohol product of Example 4 of the present invention;

[0025] Figure 5 1H NMR spectrum of the polyvinyl alcohol product of Example 5 of the present invention. Detailed implementation manners

[0026] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0027] Polyvinyl alcohol (PVA) has become an important water-soluble polymer material due to its excellent physical and chemical properties and wide application fields. Its preparation process is mainly achieved through the alcoholysis reaction of polyvinyl acetate (PVAc). In this process, PVAc undergoes a transesterification reaction with methanol under alkaline conditions, and the acetyl group (-OCOCH3) is replaced by a hydroxyl group (-OH), thereby forming PVA. One of the key parameters in this process is the degree of alcoholysis, which represents the molar percentage of hydroxyl groups in the polyvinyl alcohol product among all substituents in the polyvinyl alcohol product.

[0028] The degree of alcoholysis is the core index determining the properties of PVA, as it directly affects the solubility, viscosity, mechanical strength and other physical and chemical properties of PVA. PVA with a high degree of alcoholysis usually has better water solubility and is suitable for applications such as water-soluble coatings, adhesives and films. While PVA with a low degree of alcoholysis, due to its poor water solubility and high strength, is commonly used in applications requiring water resistance, such as textile coatings and building materials.

[0029] In the traditional PVA preparation process, the control of the degree of alcoholysis depends on factors such as the concentration of PVAc, the amount of alkali used, the alcoholysis reaction temperature and the reaction time. For PVA with a high degree of alcoholysis, the alcoholysis rate is usually slowed down by reducing the reaction temperature and the concentration of the catalytic alkali to achieve a higher degree of alcoholysis. For PVA with a low degree of alcoholysis, it is usually necessary to add a phase change promoter to the reaction system or adjust the solubility parameter of the solvent to achieve the insolubility of the polymer at a low degree of alcoholysis.

[0030] However, there are some deficiencies in the existing preparation methods. First, it is difficult to achieve large-scale high-quality production of low-degree alcoholysis PVA because multiple reaction parameters need to be precisely controlled during the alcoholysis process. In addition, the termination of the alcoholysis site is also an important consideration, and usually specific chemical reagents are required to terminate the alcoholysis reaction during the crushing or drying stage. Therefore, developing a simple and general method to prepare PVA, especially low-degree alcoholysis PVA, has become an important research direction. The inventors of this application found through research that using high-degree alcoholysis PVA to produce low-degree alcoholysis PVA can stably control the degree of alcoholysis and the yield, thereby realizing the stable synthesis of PVA with the target degree of alcoholysis, and this method does not require strict equipment matching and reaction conditions.

[0031] Based on this, the present invention provides a method for regulating the degree of alcoholysis of polyvinyl alcohol (PVA), comprising the following steps:

[0032] Performing an acetylation reaction on a polyvinyl alcohol raw material and an acetylation reagent to obtain a polyvinyl alcohol product with a different degree of alcoholysis from the polyvinyl alcohol raw material.

[0033] It can be understood that the degree of alcoholysis refers to the molar percentage of hydroxyl groups in the polyvinyl alcohol product among all substituents in the polyvinyl alcohol product. Generally, the substituents include hydroxyl groups and acetyl groups, and the degree of alcoholysis = number of moles of hydroxyl groups / (number of moles of hydroxyl groups + number of moles of acetyl groups).

[0034] The method for regulating the degree of alcoholysis of polyvinyl alcohol provided by the present invention uses polyvinyl alcohol as a raw material and reversely introduces acetyl groups through an acetylation reaction, which can stably control the degree of alcoholysis of polyvinyl alcohol, obtain polyvinyl alcohol with different degrees of alcoholysis, adjust the hydrophilicity and lipophilicity of polyvinyl alcohol, and meet different application requirements.

[0035] Specifically, in the present invention, after mixing the polyvinyl alcohol raw material and the acetylation reagent, an acetylation reaction is carried out to convert some of the hydroxyl groups in the polyvinyl alcohol raw material into acetoxy groups, change the degree of alcoholysis of the polyvinyl alcohol, and obtain a polyvinyl alcohol product. Therefore, the degree of alcoholysis of the polyvinyl alcohol product is different from that of the polyvinyl alcohol raw material.

[0036] The present invention controls the introduction amount of acetyl groups in the polyvinyl alcohol raw material through an acetylation reaction, thereby regulating the degree of alcoholysis of the polyvinyl alcohol product. Since the acetylation reaction can proceed uniformly at the molecular level, the degree of alcoholysis of the obtained polyvinyl alcohol product can be stably controlled, that is, the reproducibility is better, and the occurrence of side reactions can also be reduced to ensure the purity and performance stability of the product.

[0037] In addition, the acetylation reaction is relatively simple and does not require complex equipment and process flows, making this method highly operable in industrial production and suitable for large-scale industrial production.

[0038] Accordingly, the method for regulating the degree of alcoholysis of polyvinyl alcohol provided by the present invention uses polyvinyl alcohol as a raw material and reversely incorporates acetyl groups through an acetylation reaction, and polyvinyl alcohol products with different degrees of alcoholysis can be obtained. This method has high stability, and at the same time, it is simple and suitable for large-scale production.

[0039] In the present invention, the degree of alcoholysis of the polyvinyl alcohol raw material is greater than that of the polyvinyl alcohol product.

[0040] In some embodiments of the present invention, the difference in the degree of alcoholysis between the polyvinyl alcohol raw material and the polyvinyl alcohol product is 1% - 80%. For example, it can be 1%, 8%, 16%, 38%, 48%, 60%, 70%, 80% or any range therebetween.

[0041] In the present invention, when the difference in the degree of alcoholysis between the polyvinyl alcohol raw material and the polyvinyl alcohol product is within the above range, it is beneficial to further stably control the degree of alcoholysis of the polyvinyl alcohol product to meet the requirements of specific applications.

[0042] In some embodiments of the present invention, the degree of alcoholysis of the polyvinyl alcohol product is 5% - 95%. For example, it can be 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, 95% or any range therebetween.

[0043] In the present invention, when the degree of alcoholysis of the polyvinyl alcohol product is within the above range, it is generally referred to as partially alcoholyzed polyvinyl alcohol, which has a moderate dissolution rate and solubility in specific applications, and this partially alcoholyzed polyvinyl alcohol has good mechanical strength and toughness.

[0044] The polyvinyl alcohol with the above degree of alcoholysis is beneficial to be prepared from the polyvinyl alcohol raw material through an acetylation reaction, and the degree of alcoholysis of the prepared polyvinyl alcohol product can be stably controlled.

[0045] In some embodiments of the present invention, the polyvinyl alcohol raw material includes at least one of PVA - 1799, PVA - 2099, PVA - 2499, PVA - 2699, PVA - 0388, PVA - 0588, PVA - 2088, PVA - 1788, PVA - 2488.

[0046] It can be understood that in the product grades of the polyvinyl alcohol raw material, generally, the thousands and hundreds digits of the degree of polymerization are placed in front, and the percentage of the degree of alcoholysis is placed behind. For example, PVA - 1799 refers to polyvinyl alcohol with a degree of polymerization of 1700 and a degree of alcoholysis of 99%; PVA - 0388 refers to polyvinyl alcohol with a degree of polymerization of 300 and a degree of alcoholysis of 88%.

[0047] In the present invention, the types of polyvinyl alcohol raw materials include the above range, providing diverse choices, and the appropriate polyvinyl alcohol raw material can be selected according to the performance requirements of the target product. Moreover, the selection of multiple raw materials makes the process development of the acetylation reaction more flexible, and the production process can be quickly adjusted according to the target product to develop polyvinyl alcohol products with different degrees of alcoholysis. By using these different polyvinyl alcohol raw materials, higher flexibility can be achieved in the acetylation reaction to meet the requirements of specific applications.

[0048] In some embodiments of the present invention, the temperature of the acetylation reaction is 90°C - 120°C. For example, it can be 90°C, 95°C, 100°C, 105°C, 110°C, 120°C or any range therein; the time is 8h - 30h. For example, it can be 8h, 10h, 12h, 14h, 16h, 20h, 25h, 30h or any range therein.

[0049] In the present invention, when the temperature and time of the acetylation reaction are within the above ranges, it is beneficial to accelerate the acetylation reaction, improve production efficiency, and the moderate temperature is also conducive to further reducing the occurrence of side reactions and can further precisely control the degree of alcoholysis of the polyvinyl alcohol product.

[0050] In the present invention, the stirring method of the acetylation reaction can be magnetic stirring or mechanical stirring.

[0051] In some embodiments of the present invention, the acetylation reaction is carried out in a solvent.

[0052] In the present invention, when the acetylation reaction is carried out in a solvent, the solvent can increase the solubility of the reactants, thereby increasing the contact opportunities between the reactants, that is, it is beneficial to the full reaction of the polyvinyl alcohol raw material and the acetylation reagent, improving the reaction rate, and can also improve the uniformity and controllability of the reaction.

[0053] The solvent for carrying out the acetylation reaction in the present invention can be, for example, dimethyl sulfoxide, and the mass ratio of dimethyl sulfoxide to the polyvinyl alcohol raw material can be (5 - 20):1. For example, it can be 5:1, 10:1, 13:1, 15:1, 18:1, 20:1 or any range therein.

[0054] In some embodiments of the present invention, the mass ratio of the acetylation reagent to the polyvinyl alcohol raw material is (0.1 - 2):1. For example, it can be 0.1:1, 0.5:1, 1:1, 1.3:1, 1.5:1, 1.8:1, 2:1 or any range therein.

[0055] In the present invention, when the mass ratio of the acetylation reagent to the polyvinyl alcohol raw material is within the above range, the degree of the acetylation reaction can be further precisely controlled, which is beneficial to further stably controlling the degree of alcoholysis of the polyvinyl alcohol product and meeting the requirements of different applications.

[0056] In some embodiments, the acetylation reagent includes acetyl chloride and / or acetic anhydride. Acetyl chloride and acetic anhydride can sufficiently provide acetyl groups, improve the efficiency of the acetylation reaction, and usually the acetylation reaction can be carried out under relatively mild conditions, reducing the requirements for equipment and energy consumption.

[0057] In some embodiments of the present invention, the acetylation reaction is carried out in the presence of a catalyst. The catalyst can lower the activation energy of the reaction, increase the reaction rate, enable the acetylation reaction to be completed in a shorter time, improve production efficiency, and can also improve the selectivity of the acetylation reaction, reduce the occurrence of side reactions, and improve the purity and yield of the target product, namely the polyvinyl alcohol product. Moreover, the use of the catalyst enables the acetylation reaction to be carried out under relatively mild conditions, reducing the requirements for temperature and pressure, and reducing energy consumption and equipment costs.

[0058] In some embodiments, the mass ratio of the catalyst to the polyvinyl alcohol raw material is (1 - 5):1. For example, it can be 1:1, 2:1, 3:1, 4:1, 5:1 or any range therebetween, which can further improve the efficiency of the acetylation reaction, the selectivity of the acetylation reaction, and the purity and yield of the polyvinyl alcohol product.

[0059] Specifically, the catalyst includes at least one of pyridine, dimethylpyridine, 4-dimethylaminopyridine, benzo[b]pyridine, tetrabutylammonium bromide, and tetramethylammonium bromide, which can effectively play a catalytic role, better control the degree of the acetylation reaction, and reduce the dosage of the acetylation reagent and the generation of by-products.

[0060] In the present invention, when the catalyst is selected as pyridine (Py) and the acetylation reagent is selected as acetic anhydride, the acetylation reaction that occurs can be:

[0061] 。

[0062] In some embodiments of the present invention, it further includes: after the acetylation reaction, adding the obtained reaction system to a poor solvent for precipitation treatment to obtain a polyvinyl alcohol product.

[0063] Since the acetylation reaction is carried out in a solvent, a polyvinyl alcohol solution is obtained after the acetylation reaction. Adding the obtained reaction system to a poor solvent can effectively precipitate the target product, while dissolving impurities and by-products, thereby improving the purity of the final product, namely the polyvinyl alcohol product. And the precipitation method is a simple and effective separation technique, which does not require complex equipment and operations, can quickly separate the polyvinyl alcohol product from the reaction mixture, and can reduce production costs.

[0064] In some embodiments of the present invention, the mass ratio of the poor solvent to the polyvinyl alcohol raw material is (10 - 30):1. For example, it can be 10:1, 15:1, 20:1, 25:1, 30:1, or any range therebetween.

[0065] In the present invention, when the mass ratio of the poor solvent to the polyvinyl alcohol raw material is within the above range, the polyvinyl alcohol product can be fully precipitated from the solution, which is beneficial to the complete separation of the target product, improves the precipitation efficiency, and can also more effectively dissolve impurities and by-products, so that the precipitated polyvinyl alcohol product has a higher purity.

[0066] Hereinafter, the technical solutions of the present invention will be further described in conjunction with specific embodiments.

[0067] All chemicals involved in the following examples and comparative examples were purchased from Aladdin Reagent Co., Ltd.

[0068] Example 1

[0069] The method for regulating the degree of alcoholysis of polyvinyl alcohol in this example includes the following steps:

[0070] Quickly weigh 2 g of pre-dried PVA-0388 (polyvinyl alcohol raw material), 0.34 g of acetic anhydride ((CH3CO)2O) (acetylation reagent), 20 g of anhydrous dimethyl sulfoxide (DMSO) (solvent), and 6 g of anhydrous pyridine (catalyst), and add them to a 100 mL three-necked flask equipped with a magnetic stirrer. Among them, the mass ratio of the acetylation reagent to the polyvinyl alcohol raw material is 0.17:1; the mass ratio of the catalyst to the polyvinyl alcohol raw material is 3:1. Under the protection of N2 atmosphere, stir well for 18 h to swell PVA-0388, raise the temperature to 110 °C and carry out the acetylation reaction for 24 h to obtain a mixed solution. Drop the mixed solution into 50 g of ethanol (poor solvent) to precipitate a solid, and filter and separate to obtain the polyvinyl alcohol product, where the mass ratio of the poor solvent to the polyvinyl alcohol raw material is 25:1.

[0071] Figure 1 This is the 1H NMR spectrum of the polyvinyl alcohol product. From the analysis of this spectrum, it can be obtained that the degree of alcoholysis of the polyvinyl alcohol product is 84.3%.

[0072] Example 2

[0073] The method for regulating the degree of alcoholysis of polyvinyl alcohol in this example includes the following steps:

[0074] Quickly weigh 2 g of pre-dried polyvinyl alcohol (PVA-0388) (polyvinyl alcohol raw material), 0.67 g of acetic anhydride ((CH3CO)2O) (acetylation reagent), 20 g of anhydrous dimethyl sulfoxide (DMSO) (solvent), and 5 g of anhydrous pyridine (catalyst), and add them to a 100 mL three-necked flask equipped with a magnetic stirrer. Among them, the mass ratio of the acetylation reagent to the polyvinyl alcohol raw material is 0.335:1; the mass ratio of the catalyst to the polyvinyl alcohol raw material is 2.5:1. Stir well for 17 h under a N2 protection atmosphere to swell PVA-0388, and raise the temperature to 110 °C for acetylation reaction for 24 h to obtain a mixed solution. Drop the mixed solution into 50 g of ethanol (poor solvent) to precipitate a solid, and filter and separate to obtain the polyvinyl alcohol product. Among them, the mass ratio of the poor solvent to the polyvinyl alcohol raw material is 25:1.

[0075] Figure 2 Figure 4 is the 1H NMR spectrum of the polyvinyl alcohol product. It can be concluded from the analysis of this figure that the degree of alcoholysis of the polyvinyl alcohol product is 81.72%.

[0076] Example 3

[0077] The method for regulating the degree of alcoholysis of polyvinyl alcohol in this example includes the following steps:

[0078] Quickly weigh 2 g of pre-dried polyvinyl alcohol (PVA-0388) (polyvinyl alcohol raw material), 1.17 g of acetic anhydride ((CH3CO)2O) (acetylation reagent), 20 g of anhydrous dimethyl sulfoxide (DMSO) (solvent), and 5 g of anhydrous pyridine (catalyst), and add them to a 100 mL three-necked flask equipped with a magnetic stirrer. Among them, the mass ratio of the acetylation reagent to the polyvinyl alcohol raw material is 0.585:1; the mass ratio of the catalyst to the polyvinyl alcohol raw material is 2.5:1. Stir well for 15 h under a N2 protection atmosphere to swell PVA-0388, and raise the temperature to 110 °C for acetylation reaction for 24 h to obtain a mixed solution. Drop the mixed solution into 50 g of ethanol (poor solvent) to precipitate a solid, and filter and separate to obtain the polyvinyl alcohol product. Among them, the mass ratio of the poor solvent to the polyvinyl alcohol raw material is 25:1.

[0079] Figure 3 Figure 5 is the 1H NMR spectrum of the polyvinyl alcohol product. It can be concluded from the analysis of this figure that the degree of alcoholysis of the polyvinyl alcohol product is 57.98%.

[0080] Example 4

[0081] The method for regulating the degree of alcoholysis of polyvinyl alcohol in this example includes the following steps:

[0082] Quickly weigh 2 g of pre-dried polyvinyl alcohol (PVA-0388) (polyvinyl alcohol raw material), 1.58 g of acetic anhydride ((CH3CO)2O) (acetylation reagent), 20 g of anhydrous dimethyl sulfoxide (DMSO) (solvent), and 6 g of anhydrous pyridine (catalyst), and add them to a 100 mL three-necked flask equipped with a magnetic stirrer. Among them, the mass ratio of the acetylation reagent to the polyvinyl alcohol raw material is 0.79:1; the mass ratio of the catalyst to the polyvinyl alcohol raw material is 3:1. Stir well for 13 h under a N2 protection atmosphere to swell PVA-0388, raise the temperature to 110 °C and carry out the acetylation reaction for 24 h to obtain a mixed solution. Drop the mixed solution into 50 g of ethanol (poor solvent), precipitate out the solid, and filter and separate to obtain the polyvinyl alcohol product. Among them, the mass ratio of the poor solvent to the polyvinyl alcohol raw material is 25:1.

[0083] Figure 4 It is the 1H NMR spectrum of the polyvinyl alcohol product. From the analysis of this spectrum, it can be obtained that the degree of alcoholysis of the polyvinyl alcohol product is 50.50%.

[0084] Example 5

[0085] The method for regulating the degree of alcoholysis of polyvinyl alcohol in this example includes the following steps:

[0086] Quickly weigh 2 g of pre-dried polyvinyl alcohol (PVA-0388) (polyvinyl alcohol raw material), 2 g of acetic anhydride ((CH3CO)2O) (acetylation reagent), 20 g of anhydrous dimethyl sulfoxide (DMSO) (solvent), and 5 g of anhydrous pyridine (catalyst), and add them to a 100 mL three-necked flask equipped with a magnetic stirrer. Among them, the mass ratio of the acetylation reagent to the polyvinyl alcohol raw material is 1:1; the mass ratio of the catalyst to the polyvinyl alcohol raw material is 2.5:1. Stir well for 11 h under a N2 protection atmosphere to swell PVA-0388, raise the temperature to 110 °C and carry out the acetylation reaction for 24 h to obtain a mixed solution. Drop the mixed solution into 50 g of ethanol (poor solvent), precipitate out the solid, and filter and separate to obtain the polyvinyl alcohol product. Among them, the mass ratio of the poor solvent to the polyvinyl alcohol raw material is 25:1.

[0087] Figure 5 It is the 1H NMR spectrum of the polyvinyl alcohol product. From the analysis of this spectrum, it can be obtained that the degree of alcoholysis of the polyvinyl alcohol product is 35.07%.

[0088] Example 6

[0089] The method for regulating the degree of alcoholysis of polyvinyl alcohol in Example 6 is basically the same as that in Example 1, except that the temperature of the acetylation reaction is changed to 90 °C and the time is 30 h. The degree of alcoholysis of the obtained polyvinyl alcohol product is 85.5%.

[0090] Example 7

[0091] Example 7 is basically the same as Example 1 in the method for regulating the degree of alcoholysis of polyvinyl alcohol. The difference is that the temperature of the acetylation reaction is changed to 120 °C and the time is 8 h. The degree of alcoholysis of the obtained polyvinyl alcohol product is 86.2%.

[0092] Example 8

[0093] Example 8 is basically the same as Example 1 in the method for regulating the degree of alcoholysis of polyvinyl alcohol. The difference is that the addition amount of acetic anhydride ((CH3CO)2O) (acetylation reagent) is changed to 4 g, and the mass ratio of the acetylation reagent to the polyvinyl alcohol raw material is 2:1. The degree of alcoholysis of the obtained polyvinyl alcohol product is 8.7%.

[0094] Example 9

[0095] Example 9 is basically the same as Example 1 in the method for regulating the degree of alcoholysis of polyvinyl alcohol. The difference is that the addition amount of anhydrous pyridine (catalyst) is changed to 2 g, and the mass ratio of the catalyst to the polyvinyl alcohol raw material is 1:1. The degree of alcoholysis of the obtained polyvinyl alcohol product is 85.3%.

[0096] Example 10

[0097] Example 10 is basically the same as Example 1 in the method for regulating the degree of alcoholysis of polyvinyl alcohol. The difference is that the addition amount of anhydrous pyridine (catalyst) is changed to 10 g, and the mass ratio of the catalyst to the polyvinyl alcohol raw material is 5:1. The degree of alcoholysis of the obtained polyvinyl alcohol product is 84.3%.

[0098] Example 11

[0099] Example 11 is basically the same as Example 1 in the method for regulating the degree of alcoholysis of polyvinyl alcohol. The difference is that the polyvinyl alcohol raw material is changed to polyvinyl alcohol of type 1799 (PVA-1799), and the degree of alcoholysis of the obtained polyvinyl alcohol product is 92.2%.

[0100] Comparative Example 1

[0101] Referring to Example 1 in CN117467062A, the method for regulating the degree of alcoholysis of polyvinyl alcohol includes the following steps:

[0102] First, nitrogen is introduced into the reactor to displace air. Then, 100 parts of vinyl acetate and 0.05 part of sodium methallyl sulfonate are subjected to solution polymerization in 20 parts of benzene solvent in the presence of 0.08 part of azobisisobutyronitrile. The polymerization temperature is 65 °C, and the reaction lasts for 3 h. When the polymerization reaction ends, 80 parts of benzene are added, and then the temperature is controlled at 60 °C for vacuum distillation to remove the unreacted comonomers, obtaining a polyvinyl acetate copolymer solution. A part of the polyvinyl acetate copolymer solution is prepared into 100 parts of a benzene solution with a concentration of 10.0 wt%, and then alcoholysis is carried out with 1.9 parts of a methanol solution containing 0.003 wt% sodium hydroxide at 35 °C. After 12 min of alcoholysis, the organic solvent is removed by vacuum distillation, and the degree of alcoholysis of the obtained polyvinyl alcohol is 36.82%.

[0103] Table 1

[0104]

[0105] As can be seen from Table 1, compared with the comparative example, the method for regulating the degree of alcoholysis of polyvinyl alcohol provided by the present invention uses polyvinyl alcohol as the raw material and reversely introduces acetyl groups through acetylation reaction, which can accurately control the degree of alcoholysis of the polyvinyl alcohol product, obtaining polyvinyl alcohol products with different degrees of alcoholysis. Moreover, this method has high stability. At the same time, this method is simple and suitable for large-scale production.

[0106] Compared with Comparative Example 1, in Examples 1 - 11, the experiments were repeated three times, and the error range of the degree of alcoholysis of the obtained polyvinyl alcohol products was relatively small, within the range of ±1%; while the error range of the polyvinyl alcohol products obtained by repeating the experiment three times in Comparative Example 1 was relatively large, exceeding 5%. Therefore, the method for regulating the degree of alcoholysis of polyvinyl alcohol provided by the present invention has high stability.

[0107] Finally, it should be noted that those skilled in the art will easily think of other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention aims to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include the common general knowledge or conventional technical means in the technical field not disclosed in the present invention. It is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A method for regulating the degree of alcoholysis of polyvinyl alcohol, characterized in that, It includes the following steps: Perform an acetylation reaction on a polyvinyl alcohol raw material and an acetylation reagent to obtain a polyvinyl alcohol product with a degree of alcoholysis different from that of the polyvinyl alcohol raw material.

2. The method for regulating the degree of alcoholysis of polyvinyl alcohol according to claim 1, characterized in that, The difference in the degree of alcoholysis between the polyvinyl alcohol raw material and the polyvinyl alcohol product is 1% - 80%.

3. The method for regulating the degree of alcoholysis of polyvinyl alcohol according to claim 1 or 2, characterized in that, The degree of alcoholysis of the polyvinyl alcohol product is 5% - 95%.

4. The method for regulating the degree of alcoholysis of polyvinyl alcohol according to any one of claims 1-3, characterized in that, The polyvinyl alcohol raw material includes at least one of PVA-1799, PVA-2099, PVA-2499, PVA-2699, PVA-0388, PVA-0588, PVA-2088, PVA-1788, PVA-2488.

5. The method for regulating the degree of alcoholysis of polyvinyl alcohol according to any one of claims 1-4, characterized in that The temperature of the acetylation reaction is 90°C - 120°C, and the time is 8h - 30h.

6. The method for regulating the degree of alcoholysis of polyvinyl alcohol according to any one of claims 1-5, characterized in that, The acetylation reaction is carried out in a solvent.

7. The method for regulating the degree of alcoholysis of polyvinyl alcohol according to any one of claims 1-6, characterized in that, The mass ratio of the acetylation reagent to the polyvinyl alcohol raw material is (0.1 - 2):1; Preferably, the acetylation reagent includes acetyl chloride and / or acetic anhydride.

8. The method for regulating the degree of alcoholysis of polyvinyl alcohol according to any one of claims 1-7, characterized in that, The acetylation reaction is carried out in the presence of a catalyst; Preferably, the mass ratio of the catalyst to the polyvinyl alcohol raw material is (1 - 5):1; Preferably, the catalyst includes at least one of pyridine, dimethylpyridine, 4-dimethylaminopyridine, benzopyridine, tetrabutylammonium bromide, and tetramethylammonium bromide.

9. The method for regulating the degree of alcoholysis of polyvinyl alcohol according to any one of claims 1-8, characterized in that, It also includes: After the acetylation reaction, add the obtained reaction system to a poor solvent for precipitation treatment to obtain the polyvinyl alcohol product.

10. The method for regulating the degree of alcoholysis of polyvinyl alcohol according to claim 9, characterized in that, The mass ratio of the poor solvent to the polyvinyl alcohol raw material is (10 - 30):1.

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