Polyvinyl alcohol as well as preparation method and application thereof

Abstract

The invention relates to the technical field of high-molecular polymers, in particular to polyvinyl alcohol as well as a preparation method and application thereof. The block degree of the polyvinyl alcohol provided by the invention is 0.38 to 0.45, the average polymerization degree is 300 to 2400, and the alcoholysis degree is 78 mol% to 80 mol%. The preparation method of the polyvinyl alcohol comprises the following steps: in an environment in which a mixed solution of alcohol and trichloromethane is used as a solvent, taking alkali as a catalyst, and carrying out transesterification on polyvinyl acetate and the alcohol to prepare the polyvinyl alcohol. The polyvinyl alcohol has a specific block degree, has a stable dispersion effect as a dispersing agent, and can control particle size distribution in a narrow range in various polymer particle systems.

Description

Technical Field

[0001] This application relates to the field of polymer technology, and in particular to polyvinyl alcohol, its preparation methods and applications. Background Technology

[0002] Polymer microspheres are micron-sized particles made from natural or synthetic polymers through chemical or physical methods, such as polystyrene, polymethyl methacrylate, and polylactic acid. They are typically spherical or near-spherical in shape. During the synthesis of polymer microspheres, the newly formed tiny latex particles have a strong tendency to collide, merge, and aggregate, ultimately forming aggregates with uneven particle size and irregular shapes. Dispersants help control the size and particle size distribution of the microspheres, thus affecting their properties.

[0003] Polyvinyl alcohol (PVA) is a water-soluble polymer with a long carbon-carbon backbone and hydrophilic hydroxyl groups on the side chains. It is produced by the alcoholysis of polyvinyl acetate. Industrially, polyvinyl acetate is first polymerized from vinyl acetate, and then it undergoes alcoholysis with methanol under alkaline or acidic catalysts, causing the acetate groups on the side chains to be replaced by hydroxyl groups, ultimately producing PVA.

[0004] Polyvinyl alcohol (PVA) is an indispensable key dispersant in the suspension polymerization of polymer microspheres, exhibiting better stability and biocompatibility compared to smaller molecule dispersants. The performance of PVA directly affects core indicators such as the morphology, particle size distribution, and pore structure of polymer microspheres. For a long time, those skilled in the art have generally believed that the dispersing performance of PVA is mainly determined by its average degree of polymerization (DP) and degree of hydrolysis (DH), two macroscopic structural parameters. However, in actual industrial production and applications, it has been found that controlling only DP and DH is insufficient to stabilize the performance of PVA as a dispersant. First, even with strict control of DP and DH, the application effect of PVA from different batches or processes can still exhibit unpredictable fluctuations, leading to poor quality stability of the final polymerized resin. Second, while adjusting DP and DH can improve dispersion uniformity within a limited range, it is difficult to prepare a dispersant that simultaneously possesses extremely low interfacial tension, high dispersion efficiency, and strong adhesive retention. Some literature mentions that the sequence distribution of acetyl and hydroxyl groups in the PVA molecular chain may affect the particle size distribution of PVA itself, but it has not revealed its impact on its performance as a dispersant. For the reasons mentioned above, the application of polyvinyl alcohol as a dispersant is limited, typically achieving only a specific dispersing effect in specific formulations. Therefore, it is necessary to develop a polyvinyl alcohol with a wider range of applications and more controllable performance when used as a dispersant.

[0005] Polystyrene microspheres are polymer microspheres with important applications, such as in flow cytometry where they can be used as calibration microspheres to calibrate the optical path, flow rate, and sensitivity of the flow cytometer, ensuring the accuracy of the detection results. The narrow particle size distribution of polystyrene microspheres, with a high center and low ends (monodisperse), is beneficial to improving their detection accuracy. Summary of the Invention

[0006] Based on this, one or more embodiments of this application provide polyvinyl alcohol, its preparation method, and its applications. This polyvinyl alcohol has a specific block size, exhibits stable dispersion as a dispersant, and can control the particle size distribution within a narrow range in polymer microparticle systems to prepare monodisperse polymer microspheres.

[0007] In one aspect, this application provides polyvinyl alcohol, wherein the polyvinyl alcohol has a block size of 0.38-0.45, an average degree of polymerization of 300-2400, and a degree of alcoholysis of 78mol%-80mol%.

[0008] In some embodiments, the block size of the polyvinyl alcohol is 0.41-0.43.

[0009] In some embodiments, the viscosity of the 4 wt% polyvinyl alcohol aqueous solution measured at 25°C is 1 mPa·s to 40 mPa·s.

[0010] Secondly, this application provides a method for preparing polyvinyl alcohol, comprising the following steps:

[0011] Polyvinyl acetate, alkali, primary alcohol and haloalkane are mixed and subjected to transesterification reaction to prepare the polyvinyl alcohol;

[0012] The polyvinyl alcohol has a block size of 0.38-0.45, an average degree of polymerization of 300-2400, and a degree of alcoholysis of 78 mol%-80 mol%.

[0013] Optionally, the first alcohol includes at least one of methanol, ethanol, and isopropanol;

[0014] Optionally, the haloalkane includes at least one selected from chloromethane, dichloromethane, trichloromethane, chloroethane, dichloroethane, and trichloroethane.

[0015] In some embodiments, the step of preparing the polyvinyl alcohol by mixing polyvinyl acetate, a base, a primary alcohol, and a haloalkane and carrying out a transesterification reaction includes:

[0016] The polyvinyl acetate, the first alcohol, and the haloalkane are mixed and stirred at a first temperature for a first time to obtain a first solution; the first temperature is 40℃-50℃, and the first time is 20min-40min; the mass ratio of the polyvinyl acetate, the first alcohol, and the trichloromethane is 1:(5-10):(0.4-0.7).

[0017] The base is added to the first solution and mixed. After stirring at a second temperature for a second time, the reaction is terminated by adding acid to obtain a second solution. The second temperature is 40℃-50℃ and the second time is 20min-60min. Optionally, the molar ratio of the acid to the base is (1-1.1):1.

[0018] The second solution is post-treated to obtain the polyvinyl alcohol.

[0019] In some embodiments, the step of adding the alkali to the first solution includes: dissolving the alkali in a second alcohol to obtain an alkali solution;

[0020] Add the alkaline solution to the first solution and mix.

[0021] Optionally, the second alcohol includes at least one of methanol, ethanol, and isopropanol;

[0022] Optionally, the mass concentration of alkali in the alkaline solution is 4.5%-5%; and / or,

[0023] The step of post-processing the second solution to obtain the polyvinyl alcohol includes: precipitation in petroleum ether, filtration, collection of solids, and drying.

[0024] In some embodiments, the alkali includes at least one of sodium hydroxide and potassium hydroxide; and / or,

[0025] The mass ratio of the polyvinyl acetate to the alkali is 1:(0.004-0.005); and / or,

[0026] The acid includes at least one of glacial acetic acid, hydrochloric acid, and sulfonic acid.

[0027] Thirdly, this application provides the use of the polyvinyl alcohol described above or the polyvinyl alcohol prepared by the method described above as a dispersant in the preparation of polymer microspheres.

[0028] Fourthly, a method for preparing polystyrene microspheres is provided, including the following steps:

[0029] Styrene monomer, initiator, dispersant and water are mixed and stirred at a third temperature for a third time to obtain the polystyrene microspheres; the dispersant is polyvinyl alcohol as described above or polyvinyl alcohol prepared by the preparation method described above;

[0030] Optionally, the third temperature is 80℃-90℃, and the third time is 3h-5h.

[0031] Fifthly, polystyrene microspheres are provided, prepared using the method described above.

[0032] The polyvinyl alcohol of this application has good water solubility and exhibits better dispersion effect. When used as a dispersant for preparing polymer microspheres, it can achieve better dispersion effect, thereby making the polymer microsphere system more stable and uniform, and controlling the PDI value (polydispersity index) of the polymer microspheres to ≤0.4 and the D50 particle size to be 260nm-270nm.

[0033] The preparation method of this application can obtain polyvinyl alcohol with a target block size and stable yield through simple operation, simple equipment and reaction conditions. The block size of the polyvinyl alcohol is 0.38-0.45, the average degree of polymerization is 300-2400, and the degree of alcoholysis is 78mol%-80mol%. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 The 1H NMR spectrum of polyvinyl alcohol from Example 1 of this application;

[0036] Figure 2 The 1H NMR spectrum of polyvinyl alcohol in Comparative Example 1 of this application;

[0037] Figure 3 The 1H NMR spectrum of polyvinyl alcohol in Comparative Example 2 of this application;

[0038] Figure 4 The 1H NMR spectrum of polyvinyl alcohol in Comparative Example 3 of this application;

[0039] Figure 5 The particle size distribution of polystyrene microspheres obtained by using polyvinyl alcohol as a dispersant in Examples 1, 1, 2, and 3 of this application.

[0040] Figure 6 The images show ultra-depth-of-field microscopic images of polystyrene microspheres prepared using polyvinyl alcohol as a dispersant in Examples 1, 1, 2, and 3 of this application, with a scale bar of 500 μm. Detailed Implementation

[0041] The present application is further described below with reference to embodiments and examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Furthermore, it should be understood that after reading the teachings of this application, those skilled in the art can make various alterations or modifications to this application, and these equivalent forms also fall within the protection scope of the appended claims.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0043] The main structural parameters of polyvinyl alcohol include average degree of polymerization, degree of alcoholysis, and hydroxyl distribution.

[0044] The average degree of polymerization refers to the average number of ethylene alcohol units contained in the polyvinyl alcohol molecular chain. It can be tested according to the "GB / T12010.9-1989 Determination of Average Degree of Polymerization of Polyvinyl Alcohol Resins".

[0045] The degree of hydrolysis refers to the percentage of hydroxyl groups in polyvinyl alcohol obtained after the hydrolysis of polyvinyl acetate relative to the original acetate group. It can be detected by the "GB 12010.5-89 Determination of Residual Acetate (or Degree of Hydrolysis) in Polyvinyl Alcohol Resin".

[0046] The distribution of hydroxyl groups refers to the distribution of hydroxyl and acetyl groups on the main chain of polyvinyl alcohol. In this application, it is represented by the block characteristic coefficient (η), which is the block degree of polyvinyl alcohol. η can be determined by proton or carbon spectroscopy and then calculated by equation (1).

[0047] η=p(OH,OAc) / 2·p(OH)·p(OAc) (1);

[0048] P(OH)=(p(OH,OH)+1 / 2p(OH,OAc)) / ((p(OH,OH)+p(OH,OAc)+p(OAc,OAc));

[0049] P(OAc)=(p(OAc,OAc)+1 / 2p(OH,OAc)) / ((p(OH,OH)+p(OH,OAc)+p(OAc,OAc));

[0050] In the formula, p(OH,OAc) is the molar fraction of the -CH(OH)CH2CH(OAc)- segment; p(OH,OH) is the molar fraction of the -CH(OH)CH2CH(OH)- segment; and p(OAc,OAc) is the molar fraction of the -CH(OAc)CH2CH(OAc)- segment. η=1 indicates that the copolymer exhibits a random statistical distribution; η<1 indicates that the copolymer exhibits a block distribution, with a smaller η value indicating a stronger block characteristic; and η>1 indicates that the copolymer exhibits an alternating distribution.

[0051] The solubility parameter is a physical constant that measures the compatibility of liquid materials. Its physical meaning is the square root of the material's cohesive energy density, expressed by the formula: SP=(E / V). 1 / 2 SP is the solubility parameter, E is the cohesive energy, V is the volume, and E / V is the cohesive energy density. The closer the solubility parameters of the two polymer materials are, the better the blending effect.

[0052] In this application, the solubility parameter was determined by turbidity titration.

[0053] In one aspect, this application provides polyvinyl alcohol, wherein the polyvinyl alcohol has a block size of 0.38-0.45, an average degree of polymerization of 300-2400, and a degree of alcoholysis of 78mol%-80mol%.

[0054] This application, through extensive experiments, discovered a correlation between the block size of polyvinyl alcohol (PVA) and its dispersing performance as a dispersant. When the block size of PVA is controlled at 0.38-0.45, the average degree of polymerization is 300-2400, and the degree of alcoholysis is 78mol%-80mol%, PVA exhibits good water solubility, resulting in better dispersion when used as a dispersant for preparing polymer microspheres. This leads to a more stable and uniform polymer microsphere system, and the PDI (polydispersity index) of the polymer microspheres is controlled to ≤0.4, with a D50 particle size of 260nm-270nm. The PDI value was determined using a PL-GPC220 gel permeation chromatography system with tetrahydrofuran as the mobile phase. The D50 particle size was measured using a Bettersize 2600 laser particle size analyzer from Dandong Bettersize.

[0055] In some embodiments, the block size of polyvinyl alcohol is 0.41-0.43.

[0056] In some embodiments, the viscosity of a 4 wt% polyvinyl alcohol aqueous solution measured at 25°C is 1 mPa·s to 40 mPa·s.

[0057] In some embodiments, the average degree of polymerization of polyvinyl alcohol is 300-800, and more particularly, it is 300-600.

[0058] Secondly, this application provides a method for preparing polyvinyl alcohol, comprising the following steps:

[0059] Polyvinyl alcohol is prepared by mixing polyvinyl acetate, alkali, primary alcohol and haloalkanes and carrying out transesterification reaction.

[0060] The block size of polyvinyl alcohol is 0.38-0.45, the average degree of polymerization is 300-2400, and the degree of alcoholysis is 78mol%-80mol%.

[0061] The preparation method of this application can obtain polyvinyl alcohol with a target block size and stable yield through simple operation, simple equipment and reaction conditions. The block size of the polyvinyl alcohol is 0.38-0.45, the average degree of polymerization is 300-2400, and the degree of alcoholysis is 78mol%-80mol%. The polyvinyl alcohol has good water solubility and exhibits better dispersion effect. When used as a dispersant for preparing polymer microspheres, it can achieve better dispersion effect, thereby making the polymer microsphere system more stable and uniform. The PDI value (polydispersity index) of the polymer microspheres is controlled at ≤0.4, and the D50 particle size is 260nm-270nm.

[0062] In some embodiments, the step of preparing the polyvinyl alcohol by mixing polyvinyl acetate, a base, a primary alcohol, and a haloalkane and carrying out a transesterification reaction includes:

[0063] The polyvinyl acetate, the first alcohol, and the haloalkane are mixed and stirred at a first temperature for a first time to obtain a first solution; the first temperature is 40℃-50℃, and the first time is 20min-40min; the mass ratio of polyvinyl acetate, the first alcohol, and the haloalkane is 1:(5-10):(0.4-0.7), for example 1:5:0.4, 1:6:0.45, 1:7:0.5, 1:8:0.6, 1:8:0.7, 1:10:0.7, etc.

[0064] Add alkali to the first solution and mix. Stir at a second temperature for a second time, then add acid to terminate the reaction to obtain the second solution. The second temperature is 40℃-50℃, and the second time is 0.5h-1h. Optionally, the molar ratio of acid to alkali is (1-1.1):1.

[0065] The second solution is post-treated to obtain the polyvinyl alcohol.

[0066] The average degree of polymerization of polyvinyl acetate is 300-2400, which is the same as that of polyvinyl alcohol.

[0067] In the preparation method of this application, during the transesterification reaction of polyvinyl acetate, alkali, primary alcohol, and haloalkane, by using a suitable compound solvent (a compound of primary alcohol and haloalkane), a whitish change in the solution can be clearly observed after a certain reaction time (approximately 25-35 minutes). Continuing to stir for a period of time (approximately 200-300 seconds) yields a suitable degree of alcoholysis. Therefore, the preparation method of this application allows for more convenient and accurate determination of the reaction endpoint (degree of alcoholysis at 78 mol%-80 mol%). If only a single alcohol is used as the solvent, the resulting polyvinyl alcohol has a block size of 0.37. Furthermore, it is not conducive to determining the reaction endpoint, and the degree of alcoholysis is difficult to control.

[0068] In some embodiments, the step of adding alkali to the first solution includes: dissolving the alkali in methanol to obtain an alkali solution;

[0069] Add an alkaline solution to the first solution and mix.

[0070] Optionally, the mass concentration of alkali in the alkaline solution is 4.5%-5%.

[0071] In some embodiments, the step of post-processing the second solution to obtain polyvinyl alcohol includes: precipitation in petroleum ether, filtration, collection of solids, and drying.

[0072] In this embodiment, the precipitation step in petroleum ether includes pouring the second solution into petroleum ether at room temperature (about 20°C-40°C), letting it stand for about 5-10 seconds, and precipitating out the precipitate.

[0073] In some embodiments, the alkali includes at least one of sodium hydroxide and potassium hydroxide; and / or,

[0074] The mass ratio of polyvinyl acetate to the alkali is 1:(0.004-0.005); and / or,

[0075] The acid includes at least one of glacial acetic acid, hydrochloric acid, and sulfonic acid.

[0076] Thirdly, this application provides the use of the polyvinyl alcohol described above or the polyvinyl alcohol prepared by the method described above as a dispersant in the preparation of polymer microspheres.

[0077] For example, polymer microspheres can be polystyrene microspheres, vinyl chloride microspheres, polymethyl methacrylate microspheres, urea-formaldehyde polymer microspheres, etc.

[0078] Polystyrene microspheres are preferred, as they allow for a narrower size distribution.

[0079] Fourthly, this application provides a method for preparing polystyrene microspheres, comprising the following steps:

[0080] Styrene monomer, initiator, dispersant and water are mixed and stirred at a third temperature for a third time to obtain the polystyrene microspheres; the dispersant is polyvinyl alcohol as described above or polyvinyl alcohol prepared by the preparation method described above.

[0081] In the preparation method of polystyrene microspheres of this application, the initiator can be selected from peroxides such as benzoyl peroxide and dicumyl peroxide, or from azo compounds such as azobisisobutyronitrile. The amount of initiator added can be 0.5%-5% of the mass of styrene monomer, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.; water is used as a medium to ensure uniform dispersion of the material. In some embodiments, the mass ratio of water to styrene monomer is 100:(9-11). The amount of initiator added can be 0.5%-2% of the mass of styrene monomer, for example, 0.5%, 1%, 1.5%, 2%, etc.

[0082] Optionally, the third temperature is 80℃-90℃, the third time is 3h-5h, and the stirring speed is 200rpm-300rpm.

[0083] In some embodiments, the step of mixing styrene monomer, initiator, dispersant and water includes:

[0084] The dispersant and water are mixed, and the resulting mixture is stirred at 80℃-90℃ for 1-3 hours. Then, styrene and the initiator are added and mixed.

[0085] Optionally, the stirring speed is 200 rpm to 300 rpm.

[0086] Fifthly, polystyrene microspheres are provided, prepared using the method described above.

[0087] In some embodiments, the PDI (polydispersity index) of the polymer microspheres is controlled to be ≤0.4, and the D50 particle size is 260nm-270nm.

[0088] The following are some specific examples.

[0089] For experimental parameters not specified in the following specific embodiments, please refer to the guidelines given in this application document first, or refer to experimental manuals or other experimental methods known in the art, or refer to the experimental conditions recommended by the manufacturer.

[0090] The raw materials and reagents involved in the following specific embodiments can be obtained commercially or prepared by those skilled in the art using known methods.

[0091] Preparation method of sodium hydroxide methanol solution: Mix 1g of sodium hydroxide solid and 20g of methanol, and stir at room temperature until the solid is completely dissolved.

[0092] Preparation method of acetic acid methanol solution: Mix 3g glacial acetic acid and 40g methanol, and stir evenly at room temperature.

[0093] Vinyl acetate polymerization solution: a methanol solution of PVAc, wherein the solid content of PVAc is 23.2% and the average degree of polymerization is 565.

[0094] I. Preparation of Polyvinyl Alcohol

[0095] Example 1

[0096] This embodiment provides a polyvinyl alcohol according to this application, and the preparation steps of the polyvinyl alcohol are as follows:

[0097] (1) Add 28.62g vinyl acetate polymerization solution, 31.38g methanol and 4g chloroform to a 100mL three-necked flask equipped with a mechanical stirrer, and stir at 45℃ for 0.5h to obtain the first mixture.

[0098] (2) Add 0.6972 mL of sodium hydroxide methanol solution to the first mixture. After stirring for about 35 min, it was observed that the liquid in the three-necked bottle turned from colorless and transparent to white. Continue stirring for 240 s to obtain the second mixture.

[0099] (3) Add 1 mL of acetic acid methanol solution to the second mixture and turn off the heating. After cooling to room temperature, pour the liquid in the three-necked flask into petroleum ether for precipitation, filter to collect the solid, dry it, and obtain polyvinyl alcohol. See the 1H NMR spectrum. Figure 1 .

[0100] Example 2

[0101] This embodiment provides a polyvinyl alcohol according to this application, and the preparation steps of the polyvinyl alcohol are as follows:

[0102] (1) Add 28.62g vinyl acetate polymerization solution, 17.5g methanol and 3g chloroform to a 100mL three-necked flask equipped with a mechanical stirrer, and stir at 40℃ for 40min to obtain the first mixture.

[0103] (2) Add 0.6972 mL of sodium hydroxide methanol solution to the first mixture. After stirring for about 25 min, the liquid in the three-necked bottle was observed to turn from colorless and transparent to white. Continue stirring for 240 s to obtain the second mixture.

[0104] (3) Add 1 mL of acetic acid methanol solution to the second mixture and turn off the heating. After cooling to room temperature, pour the liquid in the three-necked flask into petroleum ether for precipitation, filter to collect the solid, dry it, and obtain polyvinyl alcohol.

[0105] Example 3

[0106] This embodiment provides a polyvinyl alcohol according to this application, and the preparation steps of the polyvinyl alcohol are as follows:

[0107] (1) Add 28.62g vinyl acetate polymerization solution, 30.62g methanol and 4.6g chloroform to a 100mL three-necked flask equipped with a mechanical stirrer, and stir at 50℃ for 20min to obtain the first mixture.

[0108] (2) Add 0.6972 mL of sodium hydroxide methanol solution to the first mixture. After stirring for about 30 min, it was observed that the liquid in the three-necked bottle turned from colorless and transparent to white. Continue stirring for 240 s to obtain the second mixture.

[0109] (3) Add 1 mL of acetic acid methanol solution to the second mixture and turn off the heating. After cooling to room temperature, pour the liquid in the three-necked flask into petroleum ether for precipitation, filter to collect the solid, dry it, and obtain polyvinyl alcohol.

[0110] Comparative Example 1

[0111] This comparative example provides another polyvinyl alcohol, the preparation steps of which are basically the same as those in Example 1, except that benzene is used instead of chloroform in step (1). The 1H NMR spectrum of this polyvinyl alcohol is shown in [reference needed]. Figure 2 .

[0112] Comparative Example 2

[0113] This comparative example provides another polyvinyl alcohol, the preparation steps of which are basically the same as those in Example 1, except that acetone is used instead of chloroform in step (1). The 1H NMR spectrum of this polyvinyl alcohol is shown in [reference needed]. Figure 3 .

[0114] Comparative Example 3

[0115] This comparative example provides another polyvinyl alcohol, the preparation steps of which are basically the same as those in Example 1, except that pyridine is used instead of chloroform in step (1). The 1H NMR spectrum of this polyvinyl alcohol is shown in [reference needed]. Figure 4 .

[0116] II. Performance Testing of Polyvinyl Alcohol

[0117] The block size, degree of hydrolysis, average degree of polymerization, viscosity, and surface tension of polyvinyl alcohol (PVA) were determined. The definitions of block size, degree of hydrolysis, and average degree of polymerization are provided above. Viscosity was measured using a 4 wt% aqueous solution at room temperature. Surface tension was measured as follows: 0.2 g of PVA and 200 g of deionized water were accurately weighed and stirred thoroughly at 90°C for 2 hours to ensure complete dissolution of the PVA in the deionized water. After cooling to room temperature, the surface tension of the PVA aqueous solution was measured using a fully automated surface tension meter. The results are shown in Table 1.

[0118] Table 1. Determination results of polyvinyl alcohol in each example and comparative example.

[0119]

[0120] III. Application of Polyvinyl Alcohol as a Dispersant in the Preparation of Polymer Microspheres

[0121] (1) Wash the styrene monomer twice with sodium hydroxide solution to remove the polymerization inhibitor. Accurately weigh 20g of styrene with the polymerization inhibitor removed and 0.8g of benzoyl peroxide (initiator) to obtain a mixed solution.

[0122] (2) Quickly weigh 0.2g of polyvinyl alcohol (dispersant) and 200g of deionized water, add them to a 500mL three-necked flask equipped with a mechanical stirrer, stir at 90℃ for 2h, cool down to 85℃, add the mixed solution obtained in step (1) to the three-necked flask, stir at 220rpm at 85℃ for 4h to end the reaction, cool to room temperature, filter, and obtain filter residue.

[0123] (4) The filter residue was rinsed with deionized water and dried at 60°C to obtain polystyrene microspheres.

[0124] IV. Performance Determination of Polystyrene Microspheres

[0125] The particle size, particle size distribution, and dispersibility of the polystyrene microspheres were tested. The results are shown in Table 2.

[0126] Table 2. Particle size distribution and properties of polymer particles

[0127]

[0128] As shown in Table 2, the polyvinyl alcohol of Example 1 controlled the PDI (polydispersity index) of the polymer microspheres to ≤0.4, with a D50 particle size of 260nm-270nm, exhibiting suitable particle size distribution and size. This indicates that the polyvinyl alcohol of Example 1 has better dispersibility. Among the polyvinyl alcohols of Comparative Examples 1-3, the average degree of polymerization and degree of alcoholysis are basically the same, and the viscosity and surface tension measurements are also basically the same, differing only in the block size. However, comparison revealed that the polymer microspheres prepared from the polyvinyl alcohol of Comparative Examples 1-3 have a larger PDI value and a wider particle size distribution. Furthermore, the dispersion uniformity of the polymer is not as good as that of Example 1 (see Table 2). Figure 5 Particle size distribution statistics and Figure 6 (Ultra-depth-of-field microscope image) The dispersion effect is significantly worse than that of Example 1. This indicates that the polyvinyl alcohol of this application, when the block size is controlled within a suitable range, significantly improves the dispersion performance of the dispersant, enabling the polymer particles to exhibit a narrow distribution with a high center and low ends.

[0129] The technical features of the above-described embodiments and examples can be combined in any suitable manner. For the sake of brevity, not all possible combinations of the technical features in the above-described embodiments and examples are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0130] The embodiments described above merely illustrate several implementation methods of this application and should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Furthermore, it should be understood that after reading the above teachings, those skilled in the art can make various alterations or modifications to this application, and the equivalent forms obtained also fall within the protection scope of this application. It should also be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the protection scope of the appended claims. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. Polyvinyl alcohol, characterized in that, The polyvinyl alcohol has a block size of 0.38-0.45, an average degree of polymerization of 300-2400, and a degree of alcoholysis of 78mol%-80mol%.

2. The polyvinyl alcohol according to claim 1, characterized in that, The block size of the polyvinyl alcohol is 0.41-0.

43.

3. The polyvinyl alcohol according to claim 1 or 2, characterized in that, The viscosity of the 4 wt% polyvinyl alcohol aqueous solution measured at 25°C was 1 mPa·s to 40 mPa·s.

4. A method for preparing polyvinyl alcohol, characterized in that, Includes the following steps: Polyvinyl acetate, alkali, primary alcohol and haloalkane are mixed and subjected to transesterification reaction to prepare the polyvinyl alcohol; The polyvinyl alcohol has a block size of 0.38-0.45, an average degree of polymerization of 300-2400, and a degree of alcoholysis of 78 mol%-80 mol%. Optionally, the first alcohol includes at least one of methanol, ethanol, and isopropanol; Optionally, the haloalkane includes at least one selected from chloromethane, dichloromethane, trichloromethane, chloroethane, dichloroethane, and trichloroethane.

5. The preparation method according to claim 4, characterized in that, The steps for preparing the polyvinyl alcohol by mixing polyvinyl acetate, alkali, a primary alcohol, and a haloalkane and carrying out a transesterification reaction include: The polyvinyl acetate, the first alcohol, and the haloalkane are mixed and stirred at a first temperature for a first time to obtain a first solution; optionally, the first temperature is 40℃-50℃, and the first time is 20min-40min; the mass ratio of the polyvinyl acetate, the first alcohol, and the haloalkane is 1:(5-10):(0.4-0.7). The alkali is added to the first solution and mixed. After stirring at a second temperature for a second time, acid is added to terminate the reaction, thus obtaining a second solution. Optionally, the second temperature is 40℃-50℃ and the second time is 20min-60min. Optionally, the molar ratio of the acid to the alkali is (1-1.1):

1. The second solution is post-treated to obtain the polyvinyl alcohol.

6. The preparation method according to claim 5, characterized in that, The step of adding the alkali to the first solution includes: dissolving the alkali in a second alcohol to obtain an alkali solution; Add the alkaline solution to the first solution and mix. Optionally, the second alcohol includes at least one of methanol, ethanol, and isopropanol; Optionally, the mass concentration of alkali in the alkaline solution is 4.5%-5%; and / or, The step of post-processing the second solution to obtain the polyvinyl alcohol includes: precipitation in petroleum ether, filtration, collection of solids, and drying.

7. The preparation method according to claim 5 or 6, characterized in that, The alkali includes at least one of sodium hydroxide and potassium hydroxide; and / or, The mass ratio of the polyvinyl acetate to the alkali is 1:(0.004-0.005); and / or, The acid includes at least one of glacial acetic acid, hydrochloric acid, and sulfonic acid.

8. The use of polyvinyl alcohol according to any one of claims 1-3 or polyvinyl alcohol prepared by any one of claims 4-7 as a dispersant for preparing polymer microspheres.

9. A method for preparing polystyrene microspheres, characterized in that, Includes the following steps: Styrene monomer, initiator, dispersant and water are mixed and stirred at a third temperature for a third time to obtain the polystyrene microspheres; the dispersant is polyvinyl alcohol according to any one of claims 1-3 or polyvinyl alcohol prepared by the preparation method according to any one of claims 4-7; Optionally, the third temperature is 80℃-90℃, and the third time is 3h-5h.

10. Polystyrene microspheres, characterized in that, It was prepared by the method described in claim 9.

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