A method for preparing high-polymerization degree polyvinyl alcohol by aqueous phase precipitation polymerization

Abstract

The present invention provides a method for preparing polyvinyl alcohol with high polymerization degree by aqueous phase precipitation polymerization, wherein polyvinyl acetate is prepared by aqueous phase precipitation polymerization, and then the prepared polyvinyl acetate is subjected to alcoholysis to obtain polyvinyl alcohol with high polymerization degree; wherein the polyvinyl acetate is prepared by aqueous phase precipitation polymerization, wherein vinyl acetate and azobisisobutyronitrile are mixed as a mixed solution, and then the mixed solution is dripped into deionized water, the reaction temperature is maintained during the dripping process, and the reaction is continued to be stirred after the dripping is completed, and the solid product is collected to obtain polyvinyl acetate with high polymerization degree. The polyvinyl acetate polymerized product of the technical solution of the present invention is directly precipitated in water, and polyvinyl acetate with high polymerization degree can be obtained without post-treatment steps such as precipitating agent or removing organic reagent, and also has a significantly higher monomer conversion rate.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of polyvinyl alcohol with high polymerization degree, and particularly relates to a method for preparing polyvinyl alcohol with high polymerization degree through aqueous phase precipitation polymerization. Technical Background

[0002] Polyvinyl alcohol is a high molecular polymer with good water solubility and degradability. It is widely used in food, chemical industry, pesticide, wood processing, papermaking and other fields. The performance and application range of polyvinyl alcohol are also affected by molecular structure, alcoholysis degree and polymerization degree. Polyvinyl alcohol with high polymerization degree has long molecular chain, large entanglement and strong intermolecular force. It has broad application prospects when used as fiber and film. At present, the polymerization degree of industrially produced polyvinyl alcohol is generally distributed between 300 and 3000. The production of polyvinyl alcohol with a polymerization degree of more than 3000 still has the problems of high cost and complicated process.

[0003] At present, the conventional process for producing polyvinyl alcohol is to polymerize vinyl acetate monomer to generate polyvinyl acetate, and then alcoholyze to obtain polyvinyl alcohol. Therefore, the degree of polymerization of polyvinyl alcohol is mainly determined by polyvinyl acetate. According to the process method, the preparation of polyvinyl acetate can be divided into bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization. Solution polymerization is generally used in industry, and the solvent used is usually methanol. It is prepared by adding an initiator to vinyl acetate monomer and solvent for polymerization reaction.

[0004] For example, the Chinese Public Invention Patent Application "Synthesis Process of Low Molecular Weight Polyvinyl Alcohol" (CN108456271A) of Inner Mongolia University discloses a synthesis process of low molecular weight polyvinyl alcohol, which uses vinyl acetate as raw material and methanol as solvent to prepare low molecular weight polyvinyl alcohol by solution polymerization.

[0005] However, in the above-mentioned documents and prior art, the polyvinyl acetate prepared by the above-mentioned solution polymerization method is a viscous solution, which is essentially a mixture of an organic solvent, vinyl acetate and polyvinyl acetate. However, polyvinyl acetate with a high degree of polymerization will make the viscosity of the product too high, which is very unfavorable for direct alcoholysis in the industrial link. Therefore, the industrial production of polyvinyl alcohol with a degree of polymerization exceeding 3000 must adopt post-treatment or other processes, resulting in increased costs. In the prior art, some researchers also use emulsion polymerization to prepare vinyl acetate, and the dispersant is water. The product prepared is in a viscous emulsion state, so it is necessary to add a precipitant to precipitate polyvinyl acetate, but the addition of this step makes it unfavorable for continuous industrial production, and the use of the precipitant will also incur a certain cost, and the post-treatment is also more troublesome.

[0006] In addition, in the prior art literature, researchers in this field generally believe that the choice of initiator will also greatly affect the degree of polymerization of polyvinyl acetate. Some literature records that when an oil-soluble initiator is used for solution polymerization in their experiments, the relative molecular mass of the polyvinyl acetate obtained by polymerization is difficult to exceed 0.28×10 6 , making the degree of polymerization of the final polyvinyl alcohol product far below 4000. Summary of the invention

[0007] In order to solve the problems in the above-mentioned background technology, the present invention provides a method for preparing polyvinyl alcohol with a high degree of polymerization by aqueous precipitation polymerization. By changing the traditional preparation method of aqueous precipitation polymerization, vinyl acetate and azobisisobutyronitrile are pre-mixed and then dropwise added into water, so that the polymerization product polyvinyl acetate is directly precipitated in water, and polyvinyl acetate with a high degree of polymerization can be obtained without post-treatment steps such as precipitating agent or removing organic reagent; in addition, the method of the present invention also has a significantly higher monomer conversion rate, simplifies the preparation steps, and has the advantages of novel method, unique route, and suitability for industrial production.

[0008] To achieve the above objectives, the present invention is implemented by adopting a technical solution consisting of the following technical measures.

[0009] A method for preparing polyvinyl alcohol with a high degree of polymerization by aqueous phase precipitation polymerization, wherein polyvinyl acetate is prepared by aqueous phase precipitation polymerization, and then the prepared polyvinyl acetate is subjected to alcoholysis to obtain the polyvinyl alcohol with a high degree of polymerization;

[0010] The method of preparing polyvinyl acetate by aqueous precipitation polymerization mainly comprises the following steps by weight:

[0011] (1) mixing 24 to 36 parts of vinyl acetate and azobisisobutyronitrile to prepare a mixed solution, wherein the amount of azobisisobutyronitrile added is 0.16 to 2.00 wt % of the vinyl acetate;

[0012] (2) preheating 44 to 56 parts of deionized water to 60 to 70° C., then dropping the mixed solution obtained in step (1) into the deionized water, maintaining the reaction temperature at 60 to 70° C. and stirring during the dropping process, and continuing to stir the reaction for at least 2.5 hours after the dropping is completed; after the time is up, collecting the solid product to obtain polyvinyl acetate with a high degree of polymerization;

[0013] The total amount of vinyl acetate and deionized water is 80 parts.

[0014] In this article, the mixed liquid in step (1) contains vinyl acetate and azobisisobutyronitrile, which are polymerization monomers and initiators respectively, and is therefore not suitable for standby storage. It is preferably prepared on-site before performing step (2). In actual industrial production, a continuous process is preferably used.

[0015] In this article, in step (2), the mixed solution obtained in step (1) is added dropwise into deionized water, and the dropping rate is preferably controlled within 2 to 3 hours under laboratory conditions; in actual industrial production, it can be appropriately enlarged according to actual process conditions to ensure industrial efficiency.

[0016] In one of the technical solutions, in order to ensure a high monomer conversion rate and a high degree of polymerization of the prepared polyvinyl alcohol, the amount of azobisisobutyronitrile added in step (1) is 0.16-0.75 wt % of vinyl acetate.

[0017] In this article, the prepared polyvinyl acetate is subjected to alcoholysis to obtain polyvinyl alcohol with a high degree of polymerization. It should be noted that those skilled in the art can refer to the existing technology of polyvinyl acetate alcoholysis to obtain specific alcoholysis steps; therefore, the technical scheme provided below in the present invention does not mean the sole designation or limitation of the preparation method of the present invention.

[0018] In order to better illustrate the present invention and provide a technical solution for reference, the polyvinyl acetate prepared is subjected to alcoholysis to obtain polyvinyl alcohol with a high degree of polymerization, which comprises the following steps by weight:

[0019] 30 parts of the prepared polyvinyl acetate are added to 500-800 parts of methanol, and heated to 40-50°C to completely dissolve the polyvinyl acetate; then 3-10 parts of sodium hydroxide methanol solution are added, and the mixture is stirred for reaction for 0.5-2 hours. After the reaction time is reached, the obtained reactant is washed and dried to obtain polyvinyl alcohol with a high degree of polymerization.

[0020] Herein, the concentration of the sodium hydroxide methanol solution is the concentration of the sodium hydroxide methanol solution used in conventional alcoholysis in the prior art; in order to better illustrate the present invention and provide a technical solution for reference: the concentration of the sodium hydroxide methanol solution is 3-5wt%.

[0021] It should be noted that the solid product collected in step (2) can be directly used as the raw material for the next step of alcoholysis in actual industrial production. The collection method includes conventional filtration or other conventional methods capable of separating water, such as centrifugal filtration, vacuum filtration, pressure filtration, etc.

[0022] The high-polymerization degree polyvinyl alcohol prepared by the technical scheme of the present invention has a polymerization degree distributed in the range of 4000 to 6200 according to the specific reaction conditions, and a monomer conversion rate of vinyl acetate is not less than 86%.

[0023] One of the inventive points of the present invention is that it is found that in the process of preparing polyvinyl acetate, a process method of premixing vinyl acetate and azobisisobutyronitrile and then dropping them into water is selected. After the polymerization reaction is completed, the polyvinyl acetate obtained by polymerization is directly and completely separated from the water phase, and polyvinyl acetate with a high degree of polymerization can be obtained without the need for post-treatment steps such as precipitating agents or removing organic reagents. The above process method is significantly different from the prior art in which an initiator is dropped into a mixed solution of methanol and vinyl acetate in solution polymerization, or an initiator is dropped into a mixed solution of water and vinyl acetate in emulsion polymerization, thereby requiring a precipitating agent or other post-treatment steps to further alcoholyze and prepare polyvinyl alcohol with a high degree of polymerization.

[0024] Secondly, the azobisisobutyronitrile used in the present invention is an oil-soluble initiator, which is often used in the prior art to prepare low-polymerization degree polyvinyl acetate. Some literatures record that when azobisisobutyronitrile or similar oil-soluble initiators are used for solution polymerization, the relative molecular mass of the polyvinyl acetate obtained by polymerization is difficult to exceed 0.28×10 6 , which makes the degree of polymerization of the final polyvinyl alcohol product far lower than 4000, which has formed a technical prejudice. However, the present invention finds that when using this traditional and low-cost oil-soluble initiator, through the innovation of the above process, vinyl acetate can be used to prepare polyvinyl alcohol with a high degree of polymerization while having a high monomer conversion rate, thus breaking the above technical prejudice.

[0025] The present invention has the following beneficial effects:

[0026] 1. The present invention provides a method for preparing polyvinyl alcohol with a high degree of polymerization by aqueous precipitation polymerization. The method changes the traditional preparation method of aqueous precipitation polymerization, wherein vinyl acetate and azobisisobutyronitrile are premixed and then added dropwise to water, so that the polymerization product polyvinyl acetate is directly precipitated in water, and polyvinyl acetate with a high degree of polymerization can be obtained without post-treatment steps such as a precipitant or removal of an organic reagent.

[0027] 2. The present invention provides a method for preparing polyvinyl alcohol with a high degree of polymerization by aqueous precipitation polymerization, which uses low-cost and universal azobisisobutyronitrile as an initiator, so that polyvinyl alcohol with a high degree of polymerization can be prepared while vinyl acetate has a high monomer conversion rate.

[0028] 3. The present invention provides a method for preparing polyvinyl alcohol with high polymerization degree by aqueous precipitation polymerization, which further improves the preparation process and is more suitable for continuous process. The intermediate product polyvinyl acetate can be directly used as the next raw material of the continuous process after filtration or separation from water.

[0029] 4. The present invention provides a method for preparing high-polymerization degree polyvinyl alcohol by aqueous precipitation polymerization, which has the advantages of novel method, unique route and suitability for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a photograph of the polyvinyl acetate obtained after filtration in Example 1 of the present invention.

[0031] Figure 2 This is a photograph of the polyvinyl acetate obtained before filtration in Example 1 of the present invention. It can be clearly seen from the figure that the polyvinyl acetate precipitated in deionized water is crystalline, rather than the viscous emulsion state of polyvinyl acetate prepared by the traditional process.

[0032] Figure 3 These are photos of the experimental process of preparing polyvinyl acetate in Example 1 of the present invention.

[0033] Figure 4 The experimental process comparison photos of Example 1 of the present invention when the mixed solution was added dropwise and after the stirring reaction time was reached in the process of preparing polyvinyl acetate. The left picture is a picture when the mixed solution was added dropwise in the process of preparing polyvinyl acetate, and the right picture is a picture after the stirring reaction time was reached in the process of preparing polyvinyl acetate. It can be clearly seen that the polyvinyl acetate product has been precipitated in the right picture.

[0034] Figure 5 This is a table showing the calculation results of the gel permeation chromatography molecular weight of the polyvinyl acetate prepared in Example 1.

[0035] Figure 6 This is the NMR spectrum of the polyvinyl acetate prepared in Example 1.

[0036] Figure 7 This is the infrared spectrum of the polyvinyl acetate prepared in Example 1. DETAILED DESCRIPTION

[0037] In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously change or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention. Although it is believed that those of ordinary skill in the art fully understand the following terms, the following definitions are still stated to help illustrate the subject matter disclosed by the present invention.

[0038] A method for preparing polyvinyl alcohol with a high degree of polymerization by aqueous phase precipitation polymerization, wherein polyvinyl acetate is prepared by aqueous phase precipitation polymerization, and then the prepared polyvinyl acetate is subjected to alcoholysis to obtain the polyvinyl alcohol with a high degree of polymerization;

[0039] The method of preparing polyvinyl acetate by aqueous precipitation polymerization mainly comprises the following steps by weight:

[0040] (1) mixing 24 to 36 parts of vinyl acetate and azobisisobutyronitrile to prepare a mixed solution, wherein the amount of azobisisobutyronitrile added is 0.16 to 2.00 wt % of the vinyl acetate;

[0041] (2) preheating 44 to 56 parts of deionized water to 60 to 70° C., then dropping the mixed solution obtained in step (1) into the deionized water, maintaining the reaction temperature at 60 to 70° C. and stirring during the dropping process, and continuing to stir the reaction for at least 2.5 hours after the dropping is completed; after the time is up, collecting the solid product to obtain polyvinyl acetate with a high degree of polymerization;

[0042] The total amount of vinyl acetate and deionized water is 80 parts.

[0043] In this article, the mixed liquid in step (1) contains vinyl acetate and azobisisobutyronitrile, which are polymerization monomers and initiators respectively, and is therefore not suitable for standby storage. In one embodiment, it is preferably configured on-site before performing step (2). In actual industrial production, a continuous process is preferably used.

[0044] In one embodiment, in step (2), the mixed solution obtained in step (1) is added dropwise into deionized water, and the dropping rate is preferably controlled within 2 to 3 hours under laboratory conditions. In actual industrial production, it can be appropriately enlarged according to actual process conditions to ensure industrial efficiency.

[0045] In one embodiment, the amount of vinyl acetate is 24 to 36 parts, for example, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36 or any range or point value therebetween, and the amount of deionized water is 44 to 56 parts, for example, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56 or any range or point value therebetween, in parts by mass.

[0046] In one embodiment, the amount of azobisisobutyronitrile added in step (1) is 0.16-2.00wt% of vinyl acetate, for example 0.16wt%, 0.18wt%, 0.20wt%, 0.24wt%, 0.28wt%, 0.32wt%, 0.36wt%, 0.40wt%, 0.50wt%, 0.60wt%, 0.70wt%, 0.80wt%, 0.90wt%, 1.00wt%, 1.10wt%, 1.20wt%, 1.30wt%, 1.40wt%, 1.50wt%, 1.60wt%, 1.70wt%, 1.80wt%, 1.90wt%, 2.00wt% or any range or point value therebetween.

[0047] In this article, the prepared polyvinyl acetate is subjected to alcoholysis to obtain polyvinyl alcohol with a high degree of polymerization. It should be noted that those skilled in the art can refer to the existing technology of polyvinyl acetate alcoholysis to obtain specific alcoholysis steps; therefore, the technical scheme provided below in the present invention does not mean the sole designation or limitation of the preparation method of the present invention.

[0048] In order to better illustrate the present invention and provide an implementation method for reference, the process of subjecting the prepared polyvinyl acetate to alcoholysis to obtain polyvinyl alcohol with a high degree of polymerization comprises the following steps by weight:

[0049] 30 parts of the prepared polyvinyl acetate are added to 500-800 parts of methanol, and heated to 40-50°C to completely dissolve the polyvinyl acetate; then 3-10 parts of sodium hydroxide methanol solution are added, and the mixture is stirred for reaction for 0.5-2 hours. After the reaction time is reached, the obtained reactant is washed and dried to obtain polyvinyl alcohol with a high degree of polymerization.

[0050] Herein, the concentration of the sodium hydroxide methanol solution is the concentration of the sodium hydroxide methanol solution used in conventional alcoholysis in the prior art; in order to better illustrate the present invention and provide a technical solution for reference: the concentration of the sodium hydroxide methanol solution is 3-5wt%.

[0051] It should be noted that the solid product collected in step (2) can be directly used as the raw material for the next step of alcoholysis in actual industrial production. The collection method includes conventional filtration or other conventional methods capable of separating water, such as centrifugal filtration, vacuum filtration, pressure filtration, etc.

[0052] The high-polymerization degree polyvinyl alcohol prepared by the technical scheme of the present invention has a polymerization degree distributed in the range of 4000 to 6200 according to the specific reaction conditions, and a monomer conversion rate of vinyl acetate is not less than 86%.

[0053] One of the inventive points of the present invention is that it is found that in the process of preparing polyvinyl acetate, a process method of premixing vinyl acetate and azobisisobutyronitrile and then dropping them into water is selected. After the polymerization reaction is completed, the polyvinyl acetate obtained by polymerization is directly and completely separated from the water phase, and polyvinyl acetate with a high degree of polymerization can be obtained without the need for post-treatment steps such as precipitating agents or removing organic reagents. The above process method is significantly different from the prior art in which an initiator is dropped into a mixed solution of methanol and vinyl acetate in solution polymerization, or an initiator is dropped into a mixed solution of water and vinyl acetate in emulsion polymerization, thereby requiring a precipitating agent or other post-treatment steps to further alcoholyze and prepare polyvinyl alcohol with a high degree of polymerization.

[0054] Secondly, the azobisisobutyronitrile used in the present invention is an oil-soluble initiator, which is often used in the prior art to prepare low-polymerization degree polyvinyl acetate. Some literatures record that when azobisisobutyronitrile or similar oil-soluble initiators are used for solution polymerization, the relative molecular mass of the polyvinyl acetate obtained by polymerization is difficult to exceed 0.28×10 6 , which makes the degree of polymerization of the final polyvinyl alcohol product far lower than 4000, which has formed a technical prejudice. However, the present invention finds that when using this traditional and low-cost oil-soluble initiator, through the innovation of the above process, vinyl acetate can be used to prepare polyvinyl alcohol with a high degree of polymerization while having a high monomer conversion rate, thus breaking the above technical prejudice.

[0055] The present invention will be further explained in detail with reference to the following examples. However, it should be understood by those skilled in the art that these examples are provided for illustrative purposes only and are not intended to limit the present invention.

[0056] Example

[0057] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. The specific conditions not specified in the examples are carried out according to the conditions recommended by normal conditions or manufacturers. The reagents used or the instruments not specified by the manufacturer are all conventional products that can be obtained commercially. The application should not be construed as being limited to the specific examples described.

[0058] 1. Raw materials

[0059] Vinyl acetate: industrial grade, Sichuan Vinylon Factory;

[0060] Azobisisobutyronitrile: analytical grade, Chengdu Best Reagent Co., Ltd.;

[0061] Methanol: analytical grade, from Chengdu Kelong Chemical Reagent Factory;

[0062] Sodium hydroxide: analytical grade, Tianjin Ruijinte Chemical Co., Ltd.;

[0063] Deionized water: homemade in the laboratory.

[0064] 2. Preparation method

[0065] (I) Mixing 240 to 360 parts by mass of vinyl acetate and 0.6 to 1.8 parts by mass of azobisisobutyronitrile to prepare a mixed solution;

[0066] (II) preheating 440-560 parts of deionized water to 60-70° C., then dropping the mixed solution obtained in step (I) into the deionized water, maintaining the reaction temperature at 60-70° C. and stirring during the dropping process, the dropping time is 2.5 hours, and stirring and reacting for 2.5 hours after the dropping is completed; after the time is up, filtering and collecting the solid product to obtain polyvinyl acetate with a high degree of polymerization;

[0067] (III) Add 30 parts of the polyvinyl acetate prepared in step (II) into 600 parts of methanol, heat to 45°C to completely dissolve the polyvinyl acetate; then add 7 parts of 5 wt% sodium hydroxide methanol solution, stir and react for 2 hours. After the reaction time is reached, filter, wash and dry the reactant to obtain polyvinyl alcohol with a high polymerization degree.

[0068] 3. Test Methods

[0069] Infrared spectroscopy (FTIR)

[0070] Fourier transform infrared (FTIR) testing was performed using a Nicolet 6700 Fourier transform infrared tester (ThernoElectron, USA). A trace amount of polyvinyl alcohol sample was fully ground in an agate mortar, then an appropriate amount of KBr was added to grind it evenly, pressed into a sheet, and then tested. The infrared test range was 4000-600cm -1 , resolution 4cm -1 , the number of scans is 24.

[0071] H NMR ( 1 H-NMR)

[0072] About 8 mg of polyvinyl alcohol was dissolved in 0.6 ml of deuterated dimethyl sulfoxide to prepare a uniform solution, and then a Bruker ARX 400 spectrometer was used to perform 400 MHz nuclear magnetic resonance spectrum detection. From the nuclear magnetic resonance spectrum, the alcoholysis degree of polyvinyl alcohol can be calculated.

[0073] Polyvinyl acetate degree of polymerization

[0074] HLC-8320GPC gel permeation chromatograph produced by Tosoh Corporation of Japan, tetrahydrofuran as mobile phase, flow rate 0.6 ml / min, temperature 40°C, polystyrene standard. The molecular weight of polyvinyl acetate was tested by GPC and then converted into degree of polymerization.

[0075] Examples 1 to 9

[0076] Examples 1 to 9 are prepared with reference to the above 2. Preparation method, and the reaction is carried out according to the raw material ratio and reaction temperature conditions in Table 1 below, and the polymerization degree and monomer conversion rate of the polyvinyl alcohol prepared in step (III) are given after testing:

[0077] Table 1 Example data

[0078]

[0079] It is obvious that the orthogonal experiment above proves that the degree of polymerization of the final product polyvinyl alcohol is affected by multiple reaction conditions, and the concentration of the initiator azobisisobutyronitrile is one of the important factors affecting the degree of polymerization. If the concentration of azobisisobutyronitrile is too high, the degree of polymerization will be significantly reduced. Therefore, if vinyl acetate monomer is added dropwise to a mixture of deionized water and azobisisobutyronitrile, polyvinyl alcohol with a high degree of polymerization will inevitably not be prepared.

[0080] In addition, Figures 1 to 4 The experimental process photos of Example 1 in the table are shown respectively. It can be clearly seen that the prepared product is crystalline when precipitated in deionized water, rather than the viscous emulsion of polyvinyl acetate prepared by the traditional process. Figures 5 to 7 The test results of the intermediate product polyvinyl acetate and the final product polyvinyl alcohol prepared in Example 1 are shown in the table. Figure 5 This is a table showing the calculation results of the gel permeation chromatography molecular weight of the polyvinyl acetate prepared in Example 1.

Claims

1. A method for preparing high-polymerization degree polyvinyl alcohol by aqueous phase precipitation polymerization, characterized in that The method is to prepare polyvinyl acetate by aqueous phase precipitation polymerization, and then alcoholyze the prepared polyvinyl acetate to obtain polyvinyl alcohol with high polymerization degree; The method of preparing polyvinyl acetate by aqueous precipitation polymerization mainly comprises the following steps by weight: (1) mixing 24 to 36 parts of vinyl acetate and azobisisobutyronitrile to prepare a mixed solution, wherein the amount of azobisisobutyronitrile added is 0.16 to 0.75 wt % of the vinyl acetate; (2) preheating 44 to 56 parts of deionized water to 60 to 70° C., then dropping the mixed solution obtained in step (1) into the deionized water, maintaining the reaction temperature at 60 to 70° C. and stirring during the dropping process, and controlling the dropping time within 2 to 3 hours. After the dropping is completed, continue stirring the reaction for at least 2.5 hours; after the time is up, collect the solid product to obtain polyvinyl acetate with a high degree of polymerization; The total amount of vinyl acetate and deionized water is 80 parts.

2. The method according to claim 1, characterized in that: The method of subjecting the prepared polyvinyl acetate to alcoholysis to obtain polyvinyl alcohol with a high degree of polymerization comprises the following steps by weight: 30 parts of the prepared polyvinyl acetate are added to 500-800 parts of methanol, and heated to 40-50°C to completely dissolve the polyvinyl acetate; then 3-10 parts of sodium hydroxide methanol solution are added, and the mixture is stirred for reaction for 0.5-2 hours. After the reaction time is reached, the obtained reactant is washed and dried to obtain polyvinyl alcohol with a high degree of polymerization.

3. The method according to claim 2, characterized in that: The concentration of the sodium hydroxide methanol solution is 3-5 wt %.

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