Modified vinyl alcohol polymer, dispersion stabilizer for suspension polymerization, and method for polymerizing vinyl compounds

Abstract

Provided is a dispersion stabilizer for suspension polymerization, the dispersion stabilizer making it possible to obtain, through suspension polymerization of a vinyl compound such as vinyl chloride, resin particles having uniform particle diameters and few large particles, and also having a high porosity and a large plasticizer absorption. A modified vinyl alcohol polymer has a hydrodynamic radius (Rh) (unit: nm) that satisfies equation (1) where x is the viscosity average polymerization degree. (1): 0.186x0.542 × 1.30 ≥ Rh ≥ 0.186x0.542 × 1.06

Description

Technical Field

[0001] The present invention relates to a modified vinyl alcohol polymer, a dispersion stabilizer for suspension polymerization, and a method for polymerizing a vinyl compound. In particular, the present invention relates to a dispersion stabilizer for suspension polymerization suitable for suspension polymerization of vinyl compounds, especially vinyl chloride.

Background Art

[0002] When suspension-polymerizing a vinyl compound such as vinyl chloride or a mixture of vinyl chloride and a monomer copolymerizable therewith, dispersion stabilizers such as polyvinyl alcohol and methylol cellulose are used. Among these, polyvinyl alcohol (PVA) has excellent properties and is generally used. As a dispersion stabilizer for suspension polymerization of vinyl compounds, for example, a modified PVA in which a carbonyl group derived from an aldehyde is introduced at the terminal of a vinyl alcohol polymer and an unsaturated double bond is introduced by undergoing a dehydration reaction or a deacetylation reaction during saponification (see, for example, Patent Document 1), and a modified PVA having a specific oxyalkylene group in the side chain (see, for example, Patent Documents 2 and 3) have been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] The modified PVA obtained by these methods has not been able to fully meet the suspension polymerization in various types of polymerization tanks such as large polymerization tanks used in recent years. That is, regarding the polymer of the vinyl-based compound obtained, (1) there are few coarse particles in the resin particles, (2) resin particles with as uniform a particle diameter as possible can be obtained, and (3) a resin with high porosity is obtained, resulting in easy removal of the monomer component and a resin with high absorbability of the plasticizer. It is hard to say that the required performance has necessarily been obtained.

[0005] Therefore, an object of the present invention is to provide a dispersion stabilizer for suspension polymerization that can obtain resin particles with a uniform particle diameter, few coarse particles, high porosity, and a large plasticizer absorption amount during the suspension polymerization of vinyl-based compounds such as vinyl chloride.

Means for Solving the Problems

[0006] As a result of intensive research to solve the above problems, the present inventor has found that it is effective to use a modified vinyl alcohol-based polymer whose hydrodynamic radius (Rh) (unit: nm) satisfies the formula (1) with respect to the viscosity average degree of polymerization (x) as a dispersion stabilizer for suspension polymerization of vinyl-based compounds. Therefore, in one aspect, the present invention is a modified vinyl alcohol-based polymer that satisfies the formula (1). 0.186x 0.542 ×1.30 ≥ Rh ≥ 0.186x 0.542 ×1.06 (1)

[0007] In one embodiment, the modified vinyl alcohol-based polymer according to the present invention has a saponification degree of 65 mol% or more and 99.9 mol% or less.

[0008] In another embodiment, the modified vinyl alcohol-based polymer according to the present invention has a hydrophilic unit in the side chain.

[0009] In still another embodiment, the hydrophilic unit of the modified vinyl alcohol-based polymer according to the present invention is a polyethylene oxide group.

[0010] In another aspect, the present invention provides a dispersion stabilizer for suspension polymerization containing the modified vinyl alcohol polymer of the present invention.

[0011] In yet another aspect, the present invention provides a method for polymerizing a vinyl compound, comprising dispersing a vinyl compound or a mixture of a vinyl compound and a monomer copolymerizable therewith in water using the dispersion stabilizer for suspension polymerization according to the present invention, and carrying out suspension polymerization. [Effects of the Invention]

[0012] According to the present invention, there is provided a dispersion stabilizer for suspension polymerization which, when subjected to suspension polymerization of a vinyl compound such as vinyl chloride, gives resin particles having a uniform particle size, few coarse particles, high porosity, and a large plasticizer absorption capacity. Thus, the dispersion stabilizer for suspension polymerization of the present invention can simultaneously satisfy required performances that have been difficult to achieve with conventional techniques. [Brief explanation of the drawings]

[0013]

Figure 1

[0014] The modified vinyl alcohol polymer has a hydrodynamic radius (Rh) (unit: nm) relative to the viscosity-average degree of polymerization (x) that satisfies formula (1). A dispersion stabilizer for suspension polymerization containing such a modified vinyl alcohol polymer suppresses the generation of coarse particles, resulting in particles with a highly uniform particle size. In addition, polymer particles with high porosity can be obtained. 0.186x 0.542 ×1.30≧Rh≧0.186x 0.542 ×1.06 (1)

[0015] Using FIG. 1, the meaning of formula (1) will be described. FIG. 1 is a graph with the viscosity-average degree of polymerization (x) on the horizontal axis and the hydrodynamic radius (Rh) on the vertical axis, plotting commercially available vinyl alcohol-based polymers with different degrees of polymerization (Denka Co., Ltd.'s "K-03", "K-05", "K-17C", "K-24E") and the modified vinyl alcohol-based polymer of the example of the present invention. As shown in FIG. 1, the hydrodynamic radius (Rh) of the commercially available vinyl alcohol-based polymer is represented by an exponential function of the viscosity-average degree of polymerization (x) as shown in formula (2). 0.186x 0.542 =Rh (2)

[0016] When polymerizing using the same addition amount of the suspension polymerization dispersant stabilizer, from the viewpoint that many molecules act, it is preferable that the viscosity-average degree of polymerization (x) of the vinyl alcohol-based polymer is small. On the other hand, from the viewpoint of protective colloid properties, it is preferable that the hydrodynamic radius (Rh) of the vinyl alcohol-based polymer is large in that it can inhibit the coalescence of particles. However, especially in the case of general-purpose vinyl alcohol-based polymers that are not particularly modified, as shown in FIG. 1, since the hydrodynamic radius (Rh) is plotted on the exponential function of the viscosity-average degree of polymerization (x), it is not easy to increase the hydrodynamic radius while lowering the viscosity-average degree of polymerization. As a result of the study by the present inventor, a vinyl alcohol-based polymer having a large hydrodynamic radius while having a low viscosity-average degree of polymerization could be obtained. For example, by adjusting the reaction conditions for copolymerizing a monomer having a hydrophilic unit in the side chain with a vinyl ester-based monomer such as vinyl acetate, the properties of these vinyl alcohol-based polymers can be adjusted.

[0017] Regarding Examples 1 to 7 described later, their viscosity-average degree of polymerization and hydrodynamic radius were also measured and plotted in FIG. 1. As shown in FIG. 1, in the modified vinyl alcohol-based polymer of the present invention, it was plotted outside the curve represented by the above formula (2). Therefore, the ranges of the viscosity-average degree of polymerization (x) and the hydrodynamic radius (Rh) of the modified vinyl alcohol-based polymer of the present invention were defined by formula (1). 0.186x 0.542 ×1.30≧Rh≧0.186x 0.542 ×1.06 (1)

[0018] In the above formula (1), when Rh / 0.186x 0.542 is less than 1.06, it becomes a dispersion stabilizer for suspension polymerization with poor particle size controllability. Therefore, the value of Rh / 0.186x 0.542 is preferably 1.06 or more, and more preferably 1.08 or more. On the other hand, those with Rh / 0.186x 0.542 exceeding 1.30 are difficult to manufacture. In one embodiment, the range of the viscosity average degree of polymerization (x) and the hydrodynamic radius (Rh) of the modified vinyl alcohol-based polymer of the present invention is represented by formula (3). 0.186x 0.542 ×1.20 ≥ Rh ≥ 0.186x 0.542 ×1.06 (3) In another embodiment, the range of the viscosity average degree of polymerization (x) and the hydrodynamic radius (Rh) of the modified vinyl alcohol-based polymer of the present invention is represented by formula (4). 0.186x 0.542 ×1.15 ≥ Rh ≥ 0.186x 0.542 ×1.06 (4)

[0019] In the present invention, the method for satisfying the general formula (1) is not particularly limited, but it is simple and preferable to introduce a hydrophilic unit into the side chain of polyvinyl alcohol. The method is not particularly limited, but examples include a method of reacting and bonding a compound having a hydrophilic unit to polyvinyl alcohol, a method of graft-polymerizing a compound having a hydrophilic unit to polyvinyl alcohol, a method of graft-polymerizing a vinyl ester monomer such as vinyl acetate to polyvinyl alcohol and then saponifying it, and a method of saponifying a polyvinyl ester copolymerized with a macromonomer such as a reactive surfactant having a hydrophilic unit. Among them, from the viewpoints of short process and economy, a method of saponifying polyvinyl acetate copolymerized with a macromonomer such as a reactive surfactant having a hydrophilic unit is simple and preferable.

[0020] As the polymerization method employed for these polymerizations, any of batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization may be used. As the polymerization method, any known method such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. can be adopted. Among them, since the modifying species to be used often has water solubility or surface activity that affects the polymer particle size, solution polymerization or bulk polymerization in which polymerization is carried out in the presence of an alcohol-based solvent or without using a solvent, rather than suspension polymerization and emulsion polymerization that require control of the polymer particle size, is preferably adopted. As the alcohol-based solvent used in solution polymerization, methanol, ethanol, isopropanol, etc. can be used, but it is not limited thereto. These solvents may be used alone or in combination of two or more kinds.

[0021] The polymerization initiator for radical polymerization of vinyl ester monomers is not particularly limited, but azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobis(4-methoxy-2,4-dimethylvaleronitrile), azobisdimethylvaleronitrile, azobismethoxyvaleronitrile, peroxides such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxy phenoxyacetate, percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate, perester compounds such as t-butyl peroxyneodecanoate, α-cumyl peroxyneodecanoate, etc. can be used alone or in combination of two or more kinds.

[0022] Also, when copolymerization is carried out at a high temperature, coloring of PVA etc. may be observed due to decomposition of vinyl ester monomers. In that case, for the purpose of preventing coloring, it is perfectly acceptable to add an antioxidant such as citric acid in an amount of about 1 ppm or more and 100 ppm or less (based on the mass of the vinyl ester monomer).

[0023] The saponification method used to produce the modified vinyl alcohol polymer of the present invention is not particularly limited. It is preferable to use an alcohol as a solvent for the polymer obtained by the above-described method, as in the conventional method. Examples of alcohols include methanol, ethanol, and butanol. The polymer concentration in the alcohol can be selected from a range of 20 to 50% by mass. Examples of alkali catalysts that can be used include alkali metal hydroxides and alcoholates such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, and potassium methylate. Examples of acid catalysts that can be used include aqueous solutions of inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as p-toluenesulfonic acid. The amount of these catalysts used should be 1 to 100 millimolar equivalents relative to the vinyl ester monomer. In this case, the saponification temperature is not particularly limited, but is typically in the range of 10 to 70°C, preferably 30 to 50°C. The reaction is typically carried out for 0.5 to 3 hours.

[0024] Examples of vinyl ester monomers include vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate.

[0025] The saponification degree of the modified vinyl alcohol polymer is preferably 65 mol% or more, more preferably 68 mol% or more, and even more preferably 70 mol% or more in order to increase water solubility and ease of handling. Furthermore, the saponification degree of the modified vinyl alcohol polymer is preferably 99.9 mol% or less, more preferably 99 mol% or less, even more preferably 90 mol% or less, and even more preferably 80 mol% or less in order to increase the porosity of particles obtained by suspension polymerization of a vinyl compound and thereby enhance plasticizer absorption.

[0026] The saponification degree of the modified vinyl alcohol-based polymer is measured in accordance with JIS K6726:1994. That is, the residual acetic acid groups (mol%) in the sample are quantified with sodium hydroxide, and it can be obtained by subtracting the result from 100.

[0027] The modified vinyl alcohol-based polymer preferably has a hydrophilic unit in the side chain. When having a hydrophilic unit in the side chain, the effect of increasing the hydrodynamic radius can be obtained, and the particle size controllability is improved. The weight average molecular weight of the hydrophilic unit is preferably from 400 to 4000. When the weight average molecular weight of the hydrophilic unit in the side chain is less than 400, the effect of increasing the hydrodynamic radius is insufficient, and the particle size controllability may be inferior. The weight average molecular weight of the hydrophilic unit in the side chain is preferably 500 or more, more preferably 600 or more. On the other hand, when the weight average molecular weight exceeds 4000, the ratio of the polyvinyl alcohol moiety becomes relatively small, and the particle size controllability may be inferior. Therefore, the weight average molecular weight of the hydrophilic unit in the side chain is preferably 3500 or less, more preferably 3000 or less. The molecular weight of the hydrophilic unit can be determined by gel permeation chromatography. The measurement conditions in the examples are as follows. Apparatus: GPC-101 manufactured by Showa Denko Column: OHpack SB-806M HQ × 2 manufactured by Shodex Guard column: OHpack SB-G × 1 manufactured by Shodex Measurement temperature: 40 °C Injection volume: 200 μL Injection concentration: 0.25% Mobile phase: 0.1 M - NaNO3 solution (water / methanol = 70 / 30 vol%) Mobile phase flow rate: 1 ml / min

[0028] Examples of the hydrophilic unit include a polyethylene oxide group, an ethenol group, saccharides such as cellulose, an acrylic acid group, a carboxyl group, a pyrrolidone group, an acrylate group, an acrylamide group, and the like.

[0029] The hydrophilic unit of the modified vinyl alcohol polymer is preferably a polyethylene oxide group. Examples of the unsaturated monomer that induces the polyethylene oxide group include polyoxyalkylene alkenyl ether, polyoxyalkylene mono(meth)allyl ether, polyoxyalkylene monovinyl ether, etc. Specifically, polyoxybutylene polyoxyethylene alkenyl ether, polyoxypropylene polyoxyethylene alkenyl ether, polyoxybutylene alkenyl ether, polyoxybutylene polyoxypropylene alkenyl ether, polyoxypropylene alkenyl ether, polyoxypropylene oxyethylene alkenyl ether, polyoxybutylene polyoxyethylene monoallyl ether, polyoxypropylene polyoxyethylene monoallyl ether, polyoxybutylene monoallyl ether, polyoxybutylene polyoxypropylene monoallyl ether, polyoxypropylene monoallyl ether, polyoxypropylene oxyethylene monoallyl ether, polyoxybutylene polyoxyethylene monovinyl ether, polyoxypropylene polyoxyethylene monovinyl ether, polyoxybutylene monovinyl ether, polyoxybutylene polyoxypropylene monovinyl ether, polyoxypropylene monovinyl ether, polyoxypropylene oxyethylene monovinyl ether, polyethylene glycol - polypropylene glycol - allyl ether, polyoxyethylene - alkyl allyl ether, polyethylene glycol - allyl ether, etc. can be mentioned.

[0030] Although the modified vinyl alcohol polymer depends on the type of the modifying group, the modification rate is preferably 0.01 mol% or more and 1 mol% or less. If the modification rate is 1 mol% or less, while the dispersing power is strong, the protective colloid property is also exhibited, and it can be suitably used as a dispersion stabilizer for suspension polymerization. The modification rate is more preferably 0.2 mol% or less, and even more preferably 0.15 mol% or less. On the other hand, by setting the modification rate to 0.01 mol% or more, the required characteristics as a dispersion stabilizer for suspension polymerization are sufficiently expressed. The modification rate is more preferably 0.05 mol% or more, and even more preferably 0.1 mol% or more.

[0031] The modification rate of the modified vinyl alcohol polymer is the molar fraction of the hydrophilic group having the above hydrophilic unit with respect to all monomer units constituting the molecular chain of the modified vinyl alcohol polymer. The modification rate can be determined by proton NMR. Specifically, after saponifying the modified vinyl alcohol polymer to a saponification degree of 99.95 mol% or more, it is thoroughly washed with methanol to prepare a sample for analysis. The prepared sample is dissolved in heavy water, and after adding several drops of an aqueous NaOH solution to adjust the pH to 14, it is measured at 80 °C using proton NMR. When calculating from the oxyethylene moiety, the content is calculated by a conventional method from the integral value of the peak at 1.2 to 1.8 ppm attributed to the methylene group of the polyvinyl alcohol chain and the integral value of the peak at 3.6 to 3.7 ppm attributed to the oxyethylene moiety. Specifically, assuming that the integral value of the methylene group of the polyvinyl alcohol chain is b, the integral value of the oxyethylene moiety is a, and the number of repeating units of the oxyethylene moiety is x, in view of the number of protons (2H for the methylene group and 4H for the ethylene group), the modification rate is calculated as {a / (4×x)} / (b / 2)×100 (mol%). For example, when a = 1, x = 1, and b = 100, it is calculated as 0.5 mol%.

[0032] The viscosity average degree of polymerization of the modified vinyl alcohol polymer is preferably 300 or more, more preferably 400 or more, and even more preferably 500 or more in order to enhance the dispersion stability during suspension polymerization of vinyl-based compounds. Also, from the viewpoint that many molecules act when the same amount of the suspension polymerization dispersant is used, the viscosity average degree of polymerization of the modified vinyl alcohol polymer is preferably 5000 or less, more preferably 4000 or less, even more preferably 3000 or less, even more preferably 2000 or less, and even more preferably 1500 or less.

[0033] The viscosity average degree of polymerization is measured in accordance with JIS K6726:1994. That is, it is determined from the limiting viscosity [η] measured in water at 30 °C after completely saponifying and purifying the modified PVA.

[0034] The dispersant stabilizer for suspension polymerization may be the above-mentioned modified vinyl alcohol polymer alone, and may contain PVA other than the above-mentioned modified vinyl alcohol polymer and various other additives as long as the gist of the present invention is not impaired. Examples of the additives include polymerization regulators such as aldehydes, halogenated hydrocarbons, and mercaptans; polymerization inhibitors such as phenolic compounds, sulfur compounds, and N-oxide compounds; pH adjusters; crosslinking agents; preservatives; antifungal agents, antiblocking agents; defoaming agents, etc. From the viewpoint of significantly exerting the effects of the present invention, the dispersant stabilizer for suspension polymerization preferably contains 10% by mass or more of the modified PVA according to the embodiment of the present invention, more preferably 30% by mass or more, and even more preferably 70% by mass or more.

[0035] The dispersant stabilizer for suspension polymerization can be particularly preferably used for the suspension polymerization of vinyl-based compounds. Therefore, according to one embodiment of the present invention, there is provided a method for polymerizing a vinyl-based compound including dispersing a vinyl-based compound or a mixture of a vinyl-based compound and a monomer copolymerizable therewith in water and performing suspension polymerization. Examples of the vinyl-based compound include vinyl halides such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid, methacrylic acid, esters and salts thereof; maleic acid, fumaric acid, esters and anhydrides thereof; styrene, acrylonitrile, vinylidene chloride, vinyl ether, etc. Among these, the dispersant stabilizer for suspension polymerization is particularly preferably used when vinyl chloride is suspended and polymerized alone or together with a monomer copolymerizable with vinyl chloride. Examples of the monomer copolymerizable with a vinyl-based compound such as vinyl chloride include vinyl esters such as vinyl acetate and vinyl propionate; (meth)acrylic acid esters such as methyl (meth)acrylate and ethyl (meth)acrylate; α-olefins such as ethylene and propylene; unsaturated dicarboxylic acids such as maleic anhydride and itaconic acid; acrylonitrile, styrene, vinylidene chloride, vinyl ether, etc.

[0036] The dispersant stabilizer for suspension polymerization is suitable for the production of vinyl chloride resins for soft applications in terms of producing vinyl chloride resin particles with excellent plasticizer absorbency, and can also be applied to the production of vinyl chloride resins for rigid applications because of its excellent monomer removal property, particle size distribution, etc. The dispersant stabilizer for suspension polymerization can be used alone or in combination with other stabilizers such as cellulose derivatives and surfactants.

[0037] By using the dispersant stabilizer for suspension polymerization, resins of vinyl-based compounds such as vinyl chloride resins with excellent physical properties can be obtained, including uniform particle size, few coarse particles, high porosity, and high plasticizer absorption. Hereinafter, examples of the polymerization method of vinyl-based compounds will be given and specifically described, but it is not limited thereto.

[0038] When producing resin particles of vinyl-based compounds such as vinyl chloride resin particles, 0.01% by mass to 0.3% by mass, preferably 0.04% by mass to 0.15% by mass of the above-mentioned dispersant stabilizer for suspension polymerization is added to the vinyl-based compound. Also, the ratio of the vinyl-based compound to water can be vinyl-based compound: water = 1:0.9 to 1:3 by mass ratio, preferably vinyl-based compound: water = 1:1 to 1:1.5.

[0039] The polymerization initiator may be one conventionally used for the polymerization of vinyl-based compounds, including percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate, perester compounds such as t-butyl peroxyneodecanoate, α-cumyl peroxyneodecanoate, and t-butyl peroxyneodecanoate, peroxides such as acetylcyclohexylsulfonyl peroxide and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, azo compounds such as azobis-2,4-dimethylvaleronitrile and azobis(4-methoxy-2,4-dimethylvaleronitrile), and further potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. can be used alone or in combination.

[0040] Furthermore, it is optional to add a polymerization regulator, a chain transfer agent, a gelation improver, an antistatic agent, a pH adjuster, etc. that are appropriately used in the polymerization of vinyl compounds.

[0041] When carrying out the polymerization of vinyl compounds, the charging ratio of each component, the polymerization temperature, etc. may be determined according to the conditions conventionally adopted in the suspension polymerization of vinyl compounds, and there is no particular reason for limitation.

Examples

[0042] Hereinafter, the present invention will be described in more detail with reference to examples. (Example 1) 1070 g of vinyl acetate, 1130 g of methanol, 120 g of Unilube PKA-5013 (polyethylene glycol - polypropylene glycol - allyl ether) (modified type) manufactured by NOF Corporation, and 0.25 g of azobisisobutyronitrile were charged into a polymerization kettle, and the system was purged with nitrogen for 30 minutes. While dropping vinyl acetate at 83 g / hr, polymerization was carried out at 60°C for 9 hours, then the dropping was stopped and cooling was carried out to stop the polymerization. Next, unreacted monomers were removed by a conventional method, and the obtained modified vinyl acetate polymer was saponified with sodium hydroxide by a conventional method to prepare a modified vinyl alcohol-based polymer. When the viscosity average degree of polymerization, the saponification degree, and the modification rate of the obtained modified vinyl alcohol-based polymer were measured by the above-described analysis method, the viscosity average degree of polymerization was 730, the saponification degree was 73 mol%, and the modification rate was 0.18 mol%. The results of measuring the weight average molecular weight of the modified species (hydrophilic unit) according to the above-described method are shown in Table 1.

[0043] <Evaluation of hydrodynamic radius> The modified vinyl alcohol-based polymer obtained above was dissolved in a water:methanol = 7:3 (vol) solution to a concentration of 0.25 mass%, and its hydrodynamic radius was measured using a gel permeation chromatography apparatus (Malvern Viscotek TDA305 system) connected to a multi-angle light scattering detector (Multi-Angle Light Scattering, MALS) and a viscosity detector (VIS). The measurement conditions are as follows. Column: Shodex OHpack SB-806M × 2 Mobile phase: 0.1 M - NaNO3 solution (water / methanol = 70 / 30 vol%) Measurement temperature: 40 °C Injection volume: 200 μL

[0044] 〈Suspension polymerization of vinyl chloride〉 In a 30 L stainless steel autoclave equipped with a stirrer, 8.5 kg of water at 30 °C under stirring, 11.0 g of the modified vinyl alcohol-based polymer obtained above as a dispersion stabilizer for suspension polymerization, 3.9 g of t-butyl peroxyneodecanoate as a polymerization initiator, and 0.9 g of α-cumyl peroxyneodecanoate were charged. After degassing the autoclave under vacuum, 8.5 kg of vinyl chloride was added and polymerized at 57 °C for 4 hours.

[0045] 〈Evaluation of vinyl chloride resin〉 The average particle diameter, particle size distribution, bulk density, and plasticizer absorption of the obtained vinyl chloride resin were evaluated by the following methods.

[0046] For the measurement of the average particle diameter and particle size distribution, in accordance with JIS Z8815:1994, the vinyl chloride resin obtained was sieved using sieves of 60 mesh (aperture 250 μm), 80 mesh (aperture 180 μm), 100 mesh (aperture 150 μm), 150 mesh (aperture 106 μm), and 200 mesh (aperture 75 μm). The particle diameter (D50) at a cumulative frequency of 50% (by mass) was taken as the average particle diameter, and the difference between the particle diameter (D80) at a cumulative frequency of 80% (by mass) and the particle diameter (D20) at a cumulative frequency of 20% (by mass) was taken as the particle size distribution.

[0047] The bulk density was measured in accordance with JIS K6720-2:1999.

[0048] The plasticizer absorption was measured in accordance with JIS K7386:2002.

[0049] (Example 2) A modified vinyl alcohol-based polymer was prepared in the same manner as in Example 1 except that the amount of methanol was changed to 1510 g. When the viscosity average degree of polymerization, saponification degree, and modification rate of the obtained modified vinyl alcohol-based polymer were measured by the above-described analysis method, the viscosity average degree of polymerization was 550, the saponification degree was 73 mol%, and the modification rate was 0.18 mol%. Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that the obtained modified vinyl alcohol-based polymer was used as a dispersion stabilizer for suspension polymerization, and evaluation was performed.

[0050] (Example 3) A modified vinyl alcohol-based polymer was prepared in the same manner as in Example 1 except that the amount of methanol was changed to 1000 g. When the viscosity average degree of polymerization, saponification degree, and modification rate of the obtained modified vinyl alcohol-based polymer were measured by the above-described analysis method, the viscosity average degree of polymerization was 890, the saponification degree was 71 mol%, and the modification rate was 0.18 mol%. Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that the obtained modified vinyl alcohol-based polymer was used as a dispersion stabilizer for suspension polymerization, and evaluation was performed.

[0051] (Example 4) For the modified vinyl acetate polymer obtained in the intermediate step of Example 1, saponification was carried out by adjusting the amount of sodium hydroxide to prepare a modified vinyl alcohol-based polymer. When the viscosity average degree of polymerization, saponification degree, and modification rate of the obtained modified vinyl alcohol-based polymer were measured by the above-described analysis method, the viscosity average degree of polymerization was 730, the saponification degree was 79 mol%, and the modification rate was 0.18 mol%. Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that the obtained modified vinyl alcohol-based polymer was used as a dispersion stabilizer for suspension polymerization, and evaluation was performed.

[0052] (Example 5) A modified vinyl alcohol-based polymer was prepared in the same manner as in Example 1, except that the modified species (hydrophilic unit) was Adeka Resor ER-40 (polyoxyethylene-alkyl allyl ether) manufactured by Adeka Corporation and the addition amount was 122 g. When the viscosity average degree of polymerization, saponification degree, and modification rate of the obtained modified vinyl alcohol-based polymer were measured by the above-described analysis methods, the viscosity average degree of polymerization was 700, the saponification degree was 73 mol%, and the modification rate was 0.17 mol%. Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that the obtained modified vinyl alcohol-based polymer was used as a dispersion stabilizer for suspension polymerization, and evaluation was performed.

[0053] (Example 6) 2200 g of vinyl acetate, 790 g of methanol, and 77 g of Unionox PKA-5005 (polyethylene glycol-allyl ether) (modified species) manufactured by NOF Corporation were charged into a polymerization kettle, and the system was purged with nitrogen for 30 minutes. After polymerization at 60 °C for 9 hours, it was cooled to stop the polymerization. Next, unreacted monomers were removed by a conventional method, and the obtained modified vinyl acetate polymer was saponified with sodium hydroxide by a conventional method to prepare a modified vinyl alcohol-based polymer. When the viscosity average degree of polymerization, saponification degree, and modification rate of the obtained modified vinyl alcohol-based polymer were measured by the above-described analysis methods, the viscosity average degree of polymerization was 1350, the saponification degree was 73 mol%, and the modification rate was 0.12 mol%. Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that the obtained modified vinyl alcohol-based polymer was used as a dispersion stabilizer for suspension polymerization, and evaluation was performed.

[0054] (Example 7) 1850 g of vinyl acetate, 750 g of methanol, and 6.4 g of a 50% methanol solution of Aqualon RN-50 (polyoxyethylene nonyl propenyl phenyl ether) (modified type) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. were charged into a polymerization kettle, and the system was purged with nitrogen for 30 minutes. While dropping 29 g of a 50% methanol solution of Aqualon RN-50, polymerization was carried out at 60°C for 9 hours. Then, the dropping was stopped and the polymerization was terminated by cooling. Next, unreacted monomers were removed by a conventional method, and the obtained modified vinyl acetate polymer was saponified with sodium hydroxide by a conventional method to prepare a modified vinyl alcohol-based polymer. When the viscosity-average degree of polymerization, saponification degree, and modification rate of the obtained modified vinyl alcohol-based polymer were measured by the analytical methods described above, the viscosity-average degree of polymerization was 780, the saponification degree was 72 mol%, and the modification rate was 0.25 mol%. Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that the obtained modified vinyl alcohol-based polymer was used as a dispersion stabilizer for suspension polymerization, and evaluation was performed.

[0055] (Comparative Example 1) 1700 g of vinyl acetate, 1133 g of methanol, and 26.7 g of Latemul PD-450 (polyoxyalkylene alkenyl ether) (modified type) provided by Kao Corporation as a modified species were charged into a polymerization kettle, and the system was purged with nitrogen for 30 minutes. 0.25 g of azobisisobutyronitrile was charged into the polymerization kettle, and polymerization was carried out at 60°C for 9 hours. Then, the polymerization was terminated by cooling. Thereafter, a modified vinyl alcohol-based polymer was prepared in the same manner as in Example 1. Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that the obtained modified vinyl alcohol-based polymer was used as a dispersion stabilizer for suspension polymerization, and evaluation was performed.

[0056] (Comparative Example 2) 2400 g of vinyl acetate and 340 g of methanol were charged into a polymerization kettle, and the system was purged with nitrogen for 30 minutes. 0.77 g of azobisisobutyronitrile was charged into the polymerization kettle, and polymerization was carried out at 60°C for 4 hours. Then, the polymerization was terminated by cooling. Thereafter, an unmodified polyvinyl alcohol-based polymer was prepared in the same manner as in Example 1. Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that the obtained polyvinyl alcohol-based polymer was used as a dispersion stabilizer for suspension polymerization, and evaluation was performed.

[0057] (Comparative Example 3) 1650 g of vinyl acetate, 1980 g of water, 1.4 g of polyvinyl alcohol as a dispersant, 21.5 g of normal butyraldehyde (modified type) as a modifying species, and 0.4 g of azobisisobutyronitrile were charged into a polymerization kettle, heated, and polymerized at 60°C for 6 hours. Subsequently, unreacted monomers were removed by a conventional method, the obtained polymer was dissolved in methanol, and saponified with sodium hydroxide by a conventional method to prepare a modified vinyl alcohol-based polymer. Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that the obtained modified vinyl alcohol-based polymer was used as a dispersion stabilizer for suspension polymerization, and evaluation was performed.

[0058] (Comparative Example 4) 2200 g of vinyl acetate, 790 g of methanol, and 77 g of Unionox PKA-5005 (polyethylene glycol-allyl ether) (modified type) manufactured by NOF Corporation were charged into a polymerization kettle, and the system was purged with nitrogen for 30 minutes. Subsequently, unreacted monomers were removed by a conventional method, the obtained polymer was saponified with sodium hydroxide by a conventional method to prepare a modified vinyl alcohol-based polymer. Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 except that the obtained modified vinyl alcohol-based polymer was used as a dispersion stabilizer for suspension polymerization, and evaluation was performed.

[0059] The results are shown in Tables 1 to 3. It can be seen that when the modified vinyl alcohol-based polymers according to Examples 1 to 7, which exhibit a hydrodynamic radius (Rh) satisfying formula (1), were used, the formation of coarse particles in the vinyl chloride resin was less, and particles with high particle size uniformity were obtained. In addition, polymer particles having a large bulk specific gravity (porosity) and excellent plasticizer absorbability were obtained.

[0060] [Table 1]

[0061] [Table 2]

[0062]

Table 3

Claims

1. A dispersion stabilizer for suspension polymerization containing a modified vinyl alcohol polymer, wherein the modified vinyl alcohol polymer does not have a carbonyl group at the terminal, has a polyethylene oxide group in the side chain, and the hydrodynamic radius (Rh) (unit: nm) satisfies the following formula (1) when the viscosity average degree of polymerization is x, and the viscosity average degree of polymerization is 550 or more, a dispersion stabilizer for suspension polymerization. 0.186x 0.542 ×1.30 ≥ Rh ≥ 0.186x 0.542 ×1.06 (1)

2. The dispersion stabilizer for suspension polymerization according to claim 1, wherein the saponification degree of the modified vinyl alcohol polymer is 65 mol% or more and 99.9 mol% or less.

3. The dispersion stabilizer for suspension polymerization according to claim 1 or claim 2, wherein the viscosity average degree of polymerization of the modified vinyl alcohol polymer is 550 or more and 5000 or less.

4. A method for polymerizing a vinyl-based compound, comprising dispersing a vinyl-based compound or a mixture of a vinyl-based compound and a monomer copolymerizable therewith in water using the dispersion stabilizer for suspension polymerization according to any one of claims 1 to 3 and performing suspension polymerization.

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