JPH0337208A - Production of polyvinyl alcohol polymer - Google Patents

Abstract

PURPOSE:To produce a polyvinyl alcohol polymer while preventing a decrease in its degree of polymerization by saponifying a polyvinyl ester polymer in the presence of a specified saponification catalyst. CONSTITUTION:A solution of at least one saponification catalyst selected from among alkali metal (hydrogen) carbonates (e.g. Na2CO3) and LiOH in a solvent (e.g. dimethylformamide) is added to a polyvinyl ester polymer of an intrinsic viscosity -i 1.1dl/g, obtained by copolymerizing a vinyl ester monomer (e.g. vinyl acetate) with optionally a copolymerizable monomer (e.g. acrylic acid) in a molar ratio of the saponification catalyst to the total vinyl ester units of 0.005-10, and, the polymer is saponified ar 10-120 deg.C in the presence of optionally 5-1000ppm of a radical scavenger e.g. hydroquinone) in an atmosphere of an oxigen concentration <=5X10<-4>mol/l.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for producing polyvinyl alcohol polymers. (Hereinafter, polyvinyl alcohol may be abbreviated as PVA.) More specifically, it relates to a method for producing a polyvinyl alcohol polymer obtained by saponifying a polyvinyl ester polymer. The intrinsic viscosity of is preferably 1.1 dl! /g or more, more preferably 1.4dff/g or more, particularly preferably 3
．． It concerns something larger than 2df2/g.

(Here, the intrinsic viscosity of the polyvinyl ester polymer is
It is defined as the value measured in acetone at a temperature of 30° C. for polyvinyl acetate obtained by saponifying the polyvinyl ester polymer to a degree of saponification of 99.0 mol% or more and then reacetylating it. In addition, if the degree of saponification of the PVA-based polymer is less than 99.0 mol%, the intrinsic viscosity of the PVA-based polymer is determined by saponifying the PVA-based polymer to a degree of saponification of 99.0 mol% or more, and then reacetylating it. It is defined as the value measured for the obtained polyvinyl acetate in acetone at a temperature of 30°C. ) B. Conventional technology As one of the few crystalline water-soluble polymers, PVA-based polymers have excellent interfacial properties and strength properties, making them suitable for paper processing.
It is well known that it is used not only as a stabilizer for fiber processing and emulsions, but also as a raw material for vinylon film and fiber.

However, the degree of polymerization of conventional PVA-based polymers has been limited because of its processing characteristics and ease of removal, and because it is difficult to obtain a high degree of polymerization from the raw material polyvinyl acetate-based polymer. The upper limit of the degree of polymerization is 2,000, and only special products with a degree of polymerization of about 3,000 are found.

On the other hand, rapid advances in processing technology in recent years have made it possible to process polymers in the ultra-high degree of polymerization range, and are now succeeding in bringing out previously unknown physical properties. In the case of PVA-based polymers as well, by increasing the degree of polymerization, it is expected that not only physical properties will be improved in conventional applications, but also new possibilities will be found in new fields such as high strength m*.

Generally, PVA-based polymers are obtained in powder form by saponifying polyvinyl ester-based polymers, particularly polyvinyl acetate-based polymers, in a methanol solution. In addition, a method for producing PVA polymer using oxide in dimethyl sulfate, in which the PVA polymer after saponification is obtained as a homogeneous solution, was published in Japanese Patent Publication No. 36
It is publicly known from the publication No.-4539. However, when the present inventors investigated this method, the polyvinyl alcohol polymer obtained was reddish brown and the degree of polymerization decreased due to saponification, making it difficult to obtain the desired product. In particular, as the degree of polymerization of the PVA-based polymer increases, this tendency becomes even more pronounced, causing problems such as coloring and a decrease in the degree of polymerization of the PVA-based polymer.
It was found that a satisfactory highly polymerized 11PVA-based polymer could not be obtained.

Furthermore, it is known that the molecular weight of PVA-based polymers in dimethyl sulfoxide solution, which is said to be a good solvent for PVA-based polymers, decreases significantly when heated (e.g., Kobunshi Kagaku 16.217 (1959)). It is not preferable to saponify it. Furthermore, as the degree of saponification of the high polymerization degree PVA polymer increases, it is necessary to make the saponification conditions more severe, and the resulting PVA polymer becomes more heavily colored and the degree of polymerization decreases significantly. Completely saponified PVA
No polymer was obtained.

C0 Problems to be Solved by the Invention The purpose of the present invention is to overcome the above-mentioned problems in producing PVA-based polymers obtained by saponifying polyvinyl ester-based polymers, and to easily produce them on an industrial scale. The present invention provides a novel manufacturing method that can be implemented.

01 Means for Solving the Problems The present inventors have developed a polyvinyl ester system having an intrinsic viscosity of preferably 1.1 di'g or more, more preferably 1.4 d12/g or more, particularly preferably 3.2 dQ/g or more. From the polymer, the intrinsic viscosity is preferably 1.1 dQ/g or more,
More preferably, x, ad (1/g or more, particularly preferably 3,26Q/g or more. A manufacturing method in which a polyvinyl ester polymer is saponified mainly using at least one selected from salts, alkali metal hydrogen carbonate salts, and lithium hydroxide (hereinafter sometimes abbreviated as manufacturing method (A)). , a manufacturing method in which a polyvinyl ester polymer is saponified while substantially removing oxygen from the reaction system (hereinafter referred to as
It may be abbreviated as manufacturing method (B). ) or a production method in which a radical scavenger is added to saponify the polyvinyl ester polymer (hereinafter sometimes abbreviated as production method (C)), surprisingly the obtained PV
It was discovered that the A-based polymer exhibits less decrease in the degree of polymerization and less coloring, and the present invention was completed.

Hereinafter, the manufacturing method of the present invention will be explained in detail.

First, regarding the method for producing a polyvinyl ester polymer, the polyvinyl ester polymer of the present invention can be produced by a bulk polymerization method,
Although it is produced by a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method, there are no particular restrictions on the polymerization method, and any method can be used. In particular, when producing a highly polymerized polyvinyl ester polymer with an intrinsic viscosity of 1.4 d12/g or more, it is necessary to polymerize at a low temperature, and low-temperature emulsion polymerization is particularly preferred when producing on an industrial scale. .

Examples of such polyvinyl ester polymers include polymers such as vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, and vinyl stearate, and vinyl acetate polymers are particularly preferred.

It may also be a copolymer obtained by copolymerizing monomers that can be copolymerized with the above vinyl ester monomers, and these monomers include, for example, acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, itaconic acid, etc. unsaturated acids, salts thereof, mono- or dialkyl esters, nitriles such as acrylonitrile and methacrylonitrile, amides such as acrylamide and methacrylamide, olefins such as ethylene sulfonic acid, allylsulfonic acid, and methallylsulfonic acid. Sulfonic acids, or their salts, alkyl vinyl ethers, polyoxyalkyl allyl ethers, alkyl allyl ethers, saturated carboxylic acid allyl esters, vinyl ketones, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, vinyl fluoride, fluoride Vinylidene, oxyalkylene group-containing unsaturated monomers, amine- or quaternary ammonium salt-containing unsaturated vinyl monomers, vinylalkoxysilanes, and the like.

Regarding the intrinsic viscosity of the polyvinyl ester polymer,
Although there is no particular restriction, the intrinsic viscosity is preferably 1. ld&/
It is particularly effective in the case of a polyvinyl ester polymer with a high polymerization degree of 1.4 d12/g or more, particularly preferably 3.2 d&/g or more.

Next, regarding the saponification method, the saponification solvent used in the present invention is required to be one that substantially dissolves the polyvinyl ester polymer. As saponification solvents that meet this requirement, aprotic polar solvents, aprotic nonpolar solvents, and lower di- or triamine compounds can be used. Lower alcohols conventionally used as saponification solvents for polyvinyl ester polymers are not preferred as saponification solvents in the present invention because they are protic solvents. The aprotic polar solvent used in the present invention is a polar solvent that does not have protic hydrogen, and specifically, dimethyl sulfoxide,
Dimethylformamide, dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, dimethyltetrahydrofuran, dioxane, acetone, methyl ethyl ketone, a nonpolar solvent containing hydrogen, and specific examples include benzene. Examples of lower di- or triamine compounds include ethylenediamine and diethylenetriamine. The above solvents may be used alone or in combination, including methanol, ethanol, propanol,
Alcohols and glycols such as ethylene glycol, propylene glycol, glycerin, and diethylene glycol, and in some cases, water, acetic acid, methyl acetate, etc., may be used as a solvent as long as they dissolve the polyvinyl ester polymer. .

In addition, P generated after saponification in the above solvents
It is possible to completely dissolve VA-based polymers; dimethyl sulfoxide, dimethylformamide, dimethylacetamide, ethylenediamine, diethylenetriamine, and N-methylpyrrolidone. It is a particularly preferred saponification solvent in the present invention because it has great effects such as being able to use it as it is depending on the purpose without dissolving the P V and A-based polymers. In addition, other solvents can be used in place of the above-mentioned solvents as long as they do not reduce the effects of the present invention.
The type and mixing ratio of the solvent are not particularly limited.

As the saponification catalyst used in the production method (A) of the present invention, one containing at least IN selected from alkali metal carbonate, alkali metal hydrogen carbonate, and lithium hydroxide is suitably used; in this case, The obtained PV
The decrease in the degree of polymerization of the A-based polymer is also small, and no coloration occurs. Examples of alkali metal carbonate salts include sodium carbonate and potassium carbonate, and examples of alkali metal hydrogen carbonate salts include sodium hydrogen carbonate and potassium hydrogen carbonate, but it is better to use a red saponification catalyst that can be dissolved in a saponification solvent. preferable. For example, when dimethyl sulfoxide is used as the saponification solvent, the saponification catalyst is preferably potassium carbonate that dissolves in dimethyl sulfoxide. The amount of saponification catalyst added is expressed as the molar ratio of saponification catalyst to all the vinyl esters contained in the polyvinyl ester polymer, and usually saponification catalyst/total vinyl ester units (molar ratio) = 0.
．． It is set to 005 to lO. This value varies depending on the target degree of saponification, the solvent used, and the type of saponification catalyst, but if it is less than 0.005, the degree of saponification will not increase sufficiently, and if it is greater than 1O, the saponification reaction will proceed without problems. is likely to cause a decrease in the degree of polymerization due to oxidation. Since the oxygen in the reaction system is mainly at least 1N selected from alkali metal carbonate, alkali metal hydrogen carbonate, and lithium hydroxide as a saponification catalyst, an operation to remove oxygen from the reaction system must be performed in particular. The purpose of the present invention can be achieved without any problem.

Next, the removal of oxygen from the reaction system used in the production method (B) of the present invention will be explained. A PVA-based polymer obtained by saponifying the saponified system in a state in which oxygen is substantially removed has a small decrease in polymerization-1 and does not cause coloration. Oxygen concentration in the reaction system: A lower one is preferable, but preferably the oxygen concentration in the reaction system is 5x 10-'a+off/1
2 or less is better, more preferably 2X 10-'moQ
/ Q or lower is better. In order to reduce the oxygen concentration in the reaction system to below this level, replace it with nitrogen gas with a vrA degree of 99.9% or higher, or deoxygenate it by heating preferably at 60°C or higher, and then remove the oxygen with a purity of 99.99% or higher. After purging with high-purity nitrogen or argon gas, or more preferably adding a small amount of a low boiling point solvent such as methanol that dissolves the polyvinyl ester polymer, heating to remove the added low boiling point solvent. Although it is necessary to substitute nitrogen or argon gas with a purity of 99.99% or higher, there are no particular limitations on the means or method in the present invention. Manufacturing method of the present invention (B)
When using the method of removing oxygen from the reaction system, saponification catalysts can also be obtained using conventionally known sodium hydroxide, potassium hydroxide, alkali metal alcoholades, amines, or mineral acids. The decrease in the degree of polymerization of PVA was small and no coloring occurred.

Finally, the radical scavenger added to the reaction system used in the production method (C) of the present invention will be explained.

As the radical scavenger, phenolic antioxidants, hindered phenolic antioxidants, hindered amine antioxidants, or urea can be used. Phenolic antioxidants include hydroquinone, hydroquinone monomethyl ether and nuclear alkyl substituted catechols.

As a hindered phenolic antioxidant, IRG AN OX 1010 manufactured by Nippon Ciba Geigy Co., Ltd.
Examples of hindered amine antioxidants include SAN OL L S-77Q manufactured by Nippon Ciba Geigy Co., Ltd.
etc.

The amount of these antioxidants to be used is 5 to 1GOOppw+, more preferably 10 to 500% of the total reaction wave.
Used in ppm terms. If the amount of the antioxidant used is less than this, the effect of the addition will be small, and if the amount used is more than this, there is no particular problem, but it is unnecessary to add more than the necessary amount. These antioxidants can be used alone or in combination. When the radical scavenger used in the production method (C) of the present invention is used, the saponification catalyst is a conventionally known sodium hydroxide, potassium hydroxide, alkali metal alcoholade, amines, or mineral acids. Even if saponification is performed without removing oxygen from the system, PVA
The decrease in the degree of polymerization of the system polymer is small and no coloration occurs.

In addition, when saponification is performed, the manufacturing method of the present invention (^)
, 2 selected from manufacturing method (B) and manufacturing method (C)
If more than one method is used at the same time, the effects of the present invention will be doubled, and the degree of polymerization of the resulting PVA polymer will hardly decrease and no coloration will occur.

The polymer concentration during saponification is determined by the degree of polymerization of the polyvinyl ester polymer, and is usually set between 2 and 70%. The saponification temperature is usually set between lO<0>C and 120<0>C, and this value varies depending on the type of saponification solvent and saponification catalyst used.

Note that high temperatures tend to cause discoloration and a decrease in the degree of polymerization, so care must be taken. The time required for saponification depends on the desired degree of saponification,
It varies depending on the saponification solvent, saponification catalyst, molar ratio of the saponification catalyst, temperature, etc.

There are no particular restrictions on the degree of saponification of the PVA polymer thus obtained, and partial saponification can be achieved by changing the saponification solvent, saponification catalyst, molar ratio of the saponification catalyst, saponification temperature, saponification time, etc. Both PVA and fully saponified PVA can be obtained.

E. Examples Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to these in any way.

In addition, "%" and "parts" in the examples refer to "% by weight" and "parts by weight", respectively, unless otherwise specified.

Example 1 300@i! equipped with a stirrer and cooling pipe! In a glass reaction vessel, 20 parts of polyvinyl acetate with an intrinsic viscosity of 0.92 (d(1/g) obtained by methanol solution polymerization at a normal temperature of 60 °C, 180 g of dimethyl sulfoxide!5, and 37 parts of methanol were added. After partially charging and dissolving polyvinyl acetate with stirring, the dimethyl sulfoxide solution of polyvinyl acetate was set at 60° C., which is the saponification temperature.

Next, 9.8 parts of a slurry of dimethyl sulfoxide having a concentration of potassium carbonate of 1% (1%), which had been separately adjusted, was added to a reaction vessel at a temperature of 60°C, and a saponification reaction was carried out at a temperature of 60°C for 30 minutes. Potassium carbonate After 30 minutes of adding dimethyl sulfoxide slurry with a concentration of 10%, 20% of IN-acetic acid was added.
part was added to stop the reaction. Take some of this solution and
After repeated reprecipitation purification in a water-acetone system, and further purification by acetone Soxhlet, the temperature was 60°C.
The powder was dried to obtain white powder PVA. Obtained PVA
When the degree of saponification was measured, it was 99.8 mol%. 0.1 part of the PVA was reacetylated in a mixed solution of 8 parts of acetic anhydride and 2 parts of pyridine at a temperature of 105°C for 20 hours with occasional stirring, and reprecipitation purification was repeated in an acetone-ether and acetone-water system. When the intrinsic viscosity of polyvinyl acetate was measured in acetone at a temperature of 30°C, [η] =
It was 0.92 (dQ/g). The saponification conditions and results are summarized in Table 1.

Examples 2 to 9 and Comparative Examples 1 to 3 Polyvinyl acetate with an intrinsic viscosity of 0.92 (dQ/g) obtained by combining a methanol solution at a temperature of 60°C, a temperature of 4
The intrinsic viscosity obtained by methanol solution polymerization at 0°C is 1.
68 (d(/g) of polyvinyl acetate and temperature -20°C
The intrinsic viscosity obtained by emulsion polymerization was 4.85.
(dQ/g) of polyvinyl acetate was saponified in the same manner as in Example 1 to obtain PVA. The saponification conditions and results are shown in Table 1 together with those in Example 1.

Examples in the margin below Polyvinyl acetate with an intrinsic viscosity of 0.92 (df2/g) obtained by methanol solution polymerization at a normal temperature of 60°C was placed in a 300 m12 glass reaction vessel equipped with a stirrer and a cooling tube. 20 parts of dimethyl sulfoxide, 180 parts of dimethyl sulfoxide, and 37 parts of methanol were added, and after dissolving polyvinyl acetate with stirring, the purity was reduced to 99.9% at a temperature of 80°C for 30 minutes.
After bubbling 99% nitrogen gas into the reaction system to remove oxygen, the reaction system was cooled to a saponification temperature of 60° C. under a nitrogen flow. The Winkler method was used to measure the oxygen concentration in the reaction solution. In other words, when manganese hydroxide is oxidized to manganese dioxide with dissolved oxygen, and potassium iodide is added to acidify it with hydrochloric acid, iodine is liberated.
．． Determined by titration with 0IN sodium thiosulfate standard solution.

When sampling and analyzing the reaction solution, utmost care was taken to avoid contamination with external oxygen. The oxygen concentration in the reaction solution determined in this way is 3. lX 10
-'soQ/12.

Next, Na was added by bubbling with nitrogen to remove oxygen.
0) 3 parts of 10% a degree methanol solution of 1 was added to the reaction solution at 60°C, and a saponification reaction was carried out at a temperature of 60°C for 30 minutes. Thirty minutes after addition of the alkali catalyst, 20 parts of IN-acetic acid was added to stop the reaction. A portion of this solution was taken out, and after repeating reprecipitation purification with a water-acetone system, it was further purified sufficiently with an acetone Soxhlet, and then dried at a temperature of 60° C. to obtain PVA as a white powder. When the degree of saponification was measured, it was 99.8 mol%. The PVA
1 part of the above was re-acetylated in a mixture of 8 parts of acetic anhydride and 2 parts of pyridine at a temperature of 105°C for 20 hours with occasional stirring, and repeated reprecipitation purification in an acetone-ether and acetone-water system. When the intrinsic viscosity of vinyl acetate was measured in acetone at a temperature of 30°C, it was found that [η] = 0.92
(dc/g). All saponification conditions and results are shown in Table 2.

Comparative Example 4 Example 1O except that saponification was performed without nitrogen substitution
Saponification was carried out under exactly the same conditions as PVA.
was purified to obtain brown PVA. The degree of saponification was measured and found to be 99.8 mol%. In addition, the intrinsic viscosity of polyvinyl acetate obtained by reacetylating and purifying the PVA in the same manner was measured and found to be 0.78 (d12/g).

The oxygen a degree in the saponification reaction solution was measured by the Winkler method in the same manner as in Example 1O, and was found to be 1.6X 10-
It was 3mo12/Q. The saponification conditions and results are summarized in Table 2.

Examples 11 and 12 The intrinsic viscosity obtained by methanol solution polymerization at a temperature of 40°C is 1
．． 611 (dQl g) of polyvinyl acetate and the intrinsic viscosity obtained by emulsion polymerization at a temperature of -20°C is 4.8.
Polyvinyl acetate 5 (dQl g) was saponified by bubbling nitrogen into the reaction system under heating in the same manner as in Example 10 to remove oxygen. The saponification conditions and results are shown in Table 2.

Comparative Example 5.6 The intrinsic viscosity used in Example it and Example 12 was 1.6.
8 (dQl g) and 4.85 (d12/g) <
7) Polyvinyl acetate was saponified in the same manner as in Comparative Example 4 without nitrogen substitution. The saponification conditions and results are shown in Table 2.

Example +3.14 The intrinsic viscosity used in Example 11 and Example 12 was 1.6
8 (dQ/g) and 4.85 (d12/g')
After dissolving polyvinyl acetate under the saponification conditions (methanol excess system) shown in Table 2, the purity was 99.99.
% of nitrogen gas was bubbled into the reaction system to drive out 37 parts of excess methanol, and then cooled to the saponification temperature under a nitrogen flow. Saponification was carried out in the same manner as in Example 11 except for this. Saponification conditions a′jl″7″ Result 2 Second drawing 1・88 Bottom margin Example 15 Methanol at a normal temperature of 60°C was placed in a 300ra (l) glass reaction vessel equipped with a stirrer and a cooling tube. Weighed out 20 parts of polyvinyl acetate with an intrinsic viscosity of 0.92 (dff/g) obtained by solution polymerization, 181 parts of nomethyl sulfoxide, 37 parts of methanol, and 0.02 parts of hydroquinone, and while stirring the polyvinyl acetate. After dissolving, the dimethyl sulfoxide solution of polyvinyl acetate was set at 60°C, which is the saponification temperature.

Next, 3 parts of a separately prepared 10% methanol solution of sodium hydroxide was added to the reaction vessel at 60°C.
Below, a saponification reaction was carried out for 30 minutes. 30 minutes after addition of a tO% methanol solution of sodium hydroxide, 1N-
The reaction was stopped by adding 20 parts of acetic acid. .

A portion of this solution was taken out, and after repeating reprecipitation purification in a water-acetone system, it was further purified thoroughly by acetone Soxhlet, and then dried at a temperature of 60°C to form a white powder of P.
Got a VA. The degree of saponification was measured and found to be 99.5 mol%. 0.1 part of the PVA was re-acetylated in a mixture of 8 parts of acetic anhydride and 2 parts of pyridine at 105°C for 20 hours with occasional stirring, and repeated reprecipitation purification in an acetone-ether and acetate-water system. When the intrinsic viscosity of vinyl acetate was measured in acetone at 30°C, [η]=
It was 0.92 (+H!/g). The saponification conditions and results are summarized in Table 3.

Examples 16 to 20 and Comparative Examples 7 to 9 Polyvinyl acetate with an intrinsic viscosity of 0.92 (dQ/g) obtained by methanol solution polymerization at a temperature of 60°C, a temperature of 4
The intrinsic viscosity obtained by methanol solution polymerization at 0'C is 1
．． The intrinsic viscosity obtained by polymerizing polyvinyl acetate of 68 (dQ/g) and emulsion at -20°C is 4.85 (d1
2/g) of polyvinyl acetate was saponified in the same manner as in Example 15 to obtain PVA. Obtained PVA
The saponification conditions and saponification results are shown in Table 3.
The following margin is Example 2I The intrinsic viscosity used in Example 19 is 4.85 (d(2/
Regarding polyvinyl acetate in g), NaO is added to the alkali catalyst.
The saponification reaction was carried out in exactly the same manner as in Example i5, except that CO3 was used in the same molar ratio instead of H.

Table 4 shows the saponification conditions and results.

Example 22 The intrinsic viscosity used in Example 21 was 4.85 (d12/
Regarding polyvinyl acetate g), a saponification reaction was carried out in exactly the same manner as in Example 21, except that oxygen in the reaction system was removed by the method used in Example IO. ke'4'' condition m
ff +, "1" 211° 11・ Below margin F1 Effect of the invention As is clear from the above examples, the PVA-based polymer obtained by the saponification method of the present invention has an intrinsic viscosity of 1.
PVA-based polymers with a polymer content of 1di2/g or more have very high industrial value because they have little decrease in the degree of polymerization due to saponification, are free from coloration, and are easy to produce on an industrial scale.

Claims (10)

[Claims] (1) A polyvinyl alcohol polymer characterized in that the polyvinyl ester polymer is saponified mainly using at least one selected from alkali metal carbonate, alkali metal hydrogen carbonate and lithium hydroxide as a saponification catalyst. Method of manufacturing coalescence. (2) A method for producing a polyvinyl alcohol polymer, which comprises saponifying the polyvinyl ester polymer while substantially removing oxygen from the reaction system. (3) A method for producing a polyvinyl alcohol polymer, which comprises saponifying the polyvinyl ester polymer by adding a radical scavenger. (4) The method according to claim 1, wherein the alkali metal carbonate is potassium carbonate. (5) Oxygen concentration in the reaction system is 5 x 10^-^4 mol/l
The manufacturing method according to claim 2, which is as follows. (6) The production method according to claim 3, wherein the radical scavenger is at least one selected from hindered phenolic antioxidants, phenolic antioxidants, hindered amine antioxidants, and urea. (7) The manufacturing method according to any one of claims 1 to 3, wherein the polyvinyl ester polymer is polyvinyl acetate. (8) The intrinsic viscosity of the polyvinyl ester polymer is 1.1
The manufacturing method according to any one of claims 1 to 3, which is dl/g or more. (9) The intrinsic viscosity of the polyvinyl alcohol polymer is 1.
The manufacturing method according to any one of claims 1 to 3, wherein the amount is 1 dl/g or more. (10) A method for producing a polyvinyl alcohol polymer, comprising saponifying a polyvinyl ester polymer by simultaneously using two or more production methods selected from the production methods according to claims 1, 2, and 3. .