JPH0368604A - New polyvinyl alcohol polymer and preparation thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of Application The present invention relates to a novel polyvinyl alcohol polymer having a large amount of bonding. Compared to ordinary polyvinyl alcohol, it has superior heat resistance, water resistance, and strength, and also has good solubility and processability, so it can be used in a wide variety of fields.

B. Conventional technology As one of the few crystalline water-soluble polymers, polyvinyl alcohol-based polymers have excellent interfacial and strength properties, and are therefore used in paper processing, fiber processing, emulsion stabilizers, etc. It is well known that it plays an important role as a raw material for vinylon film and vinylon fibers, but it is also actively expanding into new fields, such as recently attracting attention as a material for gels. It is planned.

By the way, the steric intercalation properties of conventional commercially available polyvinyl alcohol polymers are actuistic (syndiotacticity content of about 53 mol % in diad representation).

Polyvinyl alcohol polymers with excellent stereoregularity are
It is known that due to the influence of hydrogen bonds, it exhibits physical properties that are significantly different from active polyvinyl alcohol polymers, and in particular, polyvinyl alcohol polymers with syndiotacticity of 55 mol% or more tend to crystallize. , can be expected to expand the possibilities of conventional polyvinyl alcohol polymers.

Several methods have been proposed for obtaining polyvinyl alcohol polymers with high syndiotacticity. One of them is a method of saponifying a polymer of vinyl trichloroacetate or vinyl trifluoroacetate (S, N
ozakura et, at, J.

Polymer Sci,, Po1ya+, Che
M, Ed, voi, 11, 279 (1973)
reference).

C1 Problems to be Solved by the Invention Although polyvinyl alcohol-based polymers with high syndiotacticity are superior in various physical properties such as water resistance, heat resistance, and strength compared to ordinary polyvinyl alcohol, they are not very strong. Due to the strong intermolecular hydrogen bonds, it has poor solubility and processability, so its application has only been developed in very limited fields.

Under such circumstances, the present invention aims to provide a novel polyvinyl alcohol-based polymer with improved solubility and processability and rich in syndiotacticity, as well as a method for producing the same.

09 Means for Solving the Problems The present inventors have discovered a method of saponifying a vinyl pivalate polymer as a method for obtaining a highly syndiotactic polyvinyl alcohol polymer (Patent Application No. 1999). −
No. 55799), the solubility and processability of the polymer are insufficient depending on the application, and as a result of intensive studies aimed at solving the above problems, we found that in the main chain of the highly syndiotactic polyvinyl alcohol polymer, By having 1,2-glycol bonds present in a certain amount or more, it has physical properties such as water resistance, heat resistance, and high strength, which are characteristics of highly syndiotactic polyvinyl vinyl alcohol polymers, while improving solubility and The present invention was completed by discovering a new polyvinyl alcohol polymer with excellent processability and a method for producing the same.

The present invention will be explained in detail below.

First, a new polyvinyl alcohol polymer will be described. According to the present invention, a polyvinyl alcohol-based polymer having a syndiotacticity of 55 mol% or more in diad representation and a 1.2-glycol bond amount of 1.8 mol% or more is a highly syndiotactic polyvinyl alcohol-based polymer. A new polyvinyl alcohol-based polymer that is completely different from conventional polyvinyl alcohols, having physical properties such as water resistance, heat resistance, and high strength that are characteristic of vinyl alcohol-based polymers, as well as excellent solubility and processability. It is a polymer.

Here, the toughness and the amount of 1,2-glycol bond are determined by the d6-DMSO of the polyvinyl alcohol polymer.
This is a value determined by NMR measurement of a solution.

The effects of the present invention were first brought about when both the syndiotacticity and the amount of 1,2-glycol bond had high values at the same time, and the syndiotacticity was 5.
5 mol% or more, preferably 58 mol% or more, and 1.
The amount of 2-glycol bond is 1.8 mol% or more, preferably 1.9 mol% or more.

There is no particular restriction on the degree of polymerization of the polymer of the present invention, but in order to take advantage of the characteristics of the highly syndiotactic polyvinyl alcohol polymer, polyvinyl acetate-based polymers obtained by acetylating the vinyl alcohol moiety of the polymer The intrinsic viscosity (hereinafter abbreviated as [η]) of the polymer measured in benzene at 30°C is 0.05 to 10 dl! /H polymers are preferred. Furthermore, according to the manufacturing method of the present invention, [η
It is also possible to manufacture products with a weight of about 0d12/g.

There is no particular restriction on the degree of saponification of the polymer of the present invention, but it is preferably in the range of 55 to 99.99 mol%.

In addition, when the polyvinyl alcohol-based polymer contains 0.01 to 45 mol% of vinyl pivalate units, especially 1 to 45 mol% of vinyl pivalate units,
When the content is 45 mol%, the alkali resistance of the polymer is improved. The polymerization degree and saponification degree of the polymer are appropriately selected depending on the use of the polymer.

The polyvinyl alcohol polymer of the present invention is based on a vinyl ester having a homopolymer syndiotacticity of 55 mol% or more, and has a 1.2-glycol bond content of 1.8 mol% or more. It can be obtained by saponifying a homopolymer or copolymer of the vinyl ester obtained by polymerization under the following conditions.

Vinyl esters that satisfy such conditions include vinyl pivalate, vinyl trifluoroacetate, vinyl trichloroacetate, vinyl formate, and the like.

Among these vinyl esters, when considering the influence of polymerization temperature on the syndiotacticity and the amount of 1,2-glycol bonds, it is found that the syndiotacticity is high and the amount of 1,2-glycol bonds is high when compared at the same temperature. Vinyl pivalate from which a large amount of polyvinyl alcohol polymer can be obtained is most preferred because it has a high boiling point and can easily yield a polyvinyl alcohol polymer with a high degree of polymerization.

The polymerization temperature of vinyl ester is not particularly limited, but is appropriately selected from the range of -80 to 300°C. In the case of vinyl pivalate, when the polymerization temperature is 70 to 200°C, the obtained polyvinyl alcohol-based polymer has a 1.2-
The amount of glycol binding is 1.8 mol% or more, and the syndiotacticity is 55 mol% or more. Polymerization temperature is 7
When the temperature is less than 0°C, the amount of 1.2-glycol bond is 1.
When the polymerization temperature exceeds 300°C, the syndiotacticity becomes less than 55 mol%.

In the polymerization of these vinyl esters, the selection of polymerization temperature is important because the sonodiotacticity and 1.2=glycol bond content of the resulting polymer show opposite temperature dependence. , syndiotactic city is 55
Polymerization is carried out in a temperature range where the mol% or higher. If the amount of 1.2-glycol bond is less than 1.8 mol%, by copolymerizing vinylene carbonate,
The desired polymer can be obtained.

The comonomer in the case of a copolymer is a monomer that can be copolymerized with the above vinyl ester, and is not particularly limited as long as the copolymerization does not impair the spirit of the present invention. Copolymerization with vinyl ester and vinylene carbonate is carried out. Specific examples of comonomers include vinyl esters such as vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, and vinyl laurate, as well as ethylene, propylene, isobutylene, l-octene, 1-dodecene, l- -Olefins such as octadecene, acrylics, methacryls, crotons, unsaturated acids such as maleic anhydride and itaconic acid, or salts thereof, noalkyl esters, nitrites such as acrylonitrile and methacrylonitrile, acrylamide, Amides such as methacrylamide, olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, 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,
Unsaturated monomers containing oxyalkylene groups Examples include unsaturated vinyl monomers containing amines or quaternary ammonium salts.

Saponification as used in the present invention refers to transesterification reactions using basic catalysts and direct saponification reactions using basic substances. As a basic substance, for example, KO
H, NaOH, CH3ONa, cu3o1[.

C, HsO! la, Cat(sOK, t-CaFI
sO)I etc. are used. Using these basic substances,
The saponification reaction is carried out as follows. That is, a solvent that can dissolve or sufficiently swell the above-mentioned vinyl ester homopolymer or copolymer is selected, and the above-mentioned basic substance is used in a substantially oxygen-free state or in a state in which an antioxidant is added. To make a difference.

The solvent used for saponification can be used as long as it can dissolve or swell the vinyl ester homopolymer or copolymer, but it is also possible to use a solvent that has a high solubility for basic substances or that can be formed. It is desirable that the material swells or dissolves the polyvinyl alcohol polymer.
Solvents with these properties include, for example, cyclic ethers such as tetrahydrofuran and dioxane; acetone;
Ketones such as methyl ethyl ketone; sulfoxides such as dimethyl sulfoxide; amides such as dimethylformamide and dimethylacetamide; aromatic hydrocarbons such as toluene and benzene; methanol, ethanol, isopropyl alcohol, n-propyl alcohol, n-butanol, isobutanol, 5elC -butanol, t-
Alcohols such as butanol, amyl alcohol, and soclohexanol are used alone or in combination.

In particular, tetrahydrofuran, dioxane, dimethyl sulfoxide, alcohol, and the like are preferably used.

Note that there is no particular problem even if these solvents contain a small amount of water.

As a method to make the filament substantially oxygen-free,
Usually, a method is adopted in which an inert gas such as nitrogen gas or argon gas from which oxygen has been removed is introduced into the system and bubbled. It is also possible to make the system substantially free of oxygen by adding an oxygen adsorbent that does not affect the reaction to the filament. The dissolved oxygen concentration in the polymer-containing reaction mixture in the filament under conditions such as polymer solution, polymer swelling with a solvent, and polymer dispersion is 5X 10-' mol/Q or less as determined by Winkler's dissolved oxygen quantitative method. It is desirable that When a saponification reaction is carried out in the substantial presence of oxygen, unless an antioxidant is added to the reaction system, a high degree of saponification is not required because the degree of polymerization of the vinyl ester homopolymer or copolymer is significantly reduced. It is difficult to obtain a polyvinyl alcohol polymer with a high degree of polymerization.

The antioxidant that can be used in the method of the present invention is an antioxidant that does not adversely affect the saponification reaction and does not lose its anti-thinning activity in the filament (manufactured by Ciba Geigy).
) etc.; Phenolic antioxidants such as hydroquinone: 5ANOL LS-
Examples include hindered amine antioxidants such as 770 (manufactured by Nippon Ciba Geigy). These antioxidants may be used alone or in combination of two or more.

By adding an antioxidant, it is possible to suppress the decrease in the degree of polymerization of vinyl ester homopolymerization or copolymerization in the saponification process without performing a special operation to remove oxygen from the filaments. . Furthermore, when using an antioxidant, even if the amount of antioxidant used is reduced by removing part of the oxygen present in the saponification system, the above-mentioned effect of suppressing the decrease in the degree of polymerization can be sufficiently achieved. becomes possible.

The concentration of the vinyl ester homopolymer or copolymer and the polyvinyl alcohol-based polymer formed therefrom in the polymer-containing reaction mixture in the filament depends on the degree of polymerization of the vinyl ester homopolymer or copolymer. The amount of the basic substance added is determined as appropriate, but is usually set between 2 and 70%.The amount of the basic substance added is determined by the molar ratio of the basic substance to all vinyl ester units contained in the vinyl ester homopolymer or copolymer. It is usually expressed as a basic substance /
Total vinyl ester units (molar ratio) are 0.005 to 1O
set between These upper and lower limits are based on the target degree of saponification, the solvent used, and the basic substance! ! Although it varies depending on the species, in general, if it is less than 0.005, the degree of saponification will not increase sufficiently, and if it is more than 1O, the saponification reaction will proceed without any problem, but the molecular weight will tend to decrease due to oxidation.

The amount of this basic substance to be used is limited when the vinyl ester copolymer contains a group (for example, a carboxyl group) that clearly reacts with a basic substance in monomer units other than all vinyl ester units, and when the antioxidant is basic. When reacting with substances, the amount is set to compensate for the amount consumed by these substances. The saponification temperature is usually set between 20°C and 120°C, but high temperatures tend to cause a decrease in molecular weight. The time required for saponification varies depending on the desired degree of saponification, the solvent used in saponification, the basic substance, the molar ratio, the temperature, etc., but unnecessary heating in the presence of a basic substance after saponification is It should be avoided as it causes coloration and molecular weight reduction.

After the saponification reaction is completed, it is preferable to immediately neutralize the basic substance remaining in the saponification reaction system using an acid. Examples of acids include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and carbonic acid, and organic acids such as formic acid, acetic acid, and benzoic acid.
Among these, organic acids are preferred, and among the organic acids, acetic acid is most preferred.

If the remaining basic substance is not neutralized immediately after the saponification reaction is completed, the degree of polymerization of the obtained polyvinyl alcohol polymer will decrease, which is not preferable. Further, unnecessary heating after the completion of the saponification reaction should be avoided since it causes coloration and a decrease in molecular weight.

The polyvinyl alcohol polymer produced as described above is purified by a commonly employed method (for example, neutralization with a basic substance and subsequent washing operation).

E. Examples Hereinafter, the present invention will be further explained with reference to Examples, but the present invention is not limited to the Examples in any way. In addition, "part" in the examples means "1 part by weight" unless otherwise specified.
represents.

Example! In a pressure-resistant container equipped with a stirrer, add vinyl pivalate monomer.
Part 9Q was charged, and the system was purged with nitrogen by repeating pressurization and release with nitrogen gas. Separately 10 vinyl pivalate monomers
2,2-azobis(2,2,4-trimethylpentane) (VR-0; manufactured by Wako Pure Chemical Industries, Ltd.) as an initiator.
A solution containing 0.000277 parts was prepared and replaced with nitrogen by bubbling with nitrogen gas.

The temperature of the pressure-resistant container was raised, and when the internal temperature reached 120° C., a pivalic acid monomer solution in which an initiator was dissolved was injected to start polymerization. After 2 hours, the polymerization was stopped by cooling, and the contents were poured into a large amount of methanol to recover the produced polymer. The polymer was reprecipitated twice in an acetone-methanol system and dried at 60°C under reduced pressure. The amount of polymer obtained was 9.5 parts.

Next, 1 part of this polymer was dissolved in 49 ml of nitrogen-substituted tetrahydroquinfuran and kept at 60°C, and then 95 parts of a separately prepared 25% methanol solution of potassium hydroxide, which had been purged with nitrogen, was added and thoroughly stirred. did. At this time, the dissolved oxygen concentration in the polymer solution and potassium hydroxide solution was determined by Winkler's method, and both were found to be 3X
It was 10-5 mol/Q or less. The filament gelled in about 5 minutes, but after being kept at 60°C for an additional 25 minutes, 34 parts of acetic acid was added along with 1.1 part of methanol to neutralize the potassium hydroxide. After pulverizing the gel, Soxhlet washing with methanol was performed to obtain polyvinyl alcohol.

10 parts of acetic anhydride to 0.1 part of the obtained polyvinyl alcohol
After adding 2 parts of pyridine and sealing the tube, it was heated at 120°C for 3 hours to acetylate. Polyvinyl acetate was purified by precipitating it in n-hexane and repeating reprecipitation twice in an acetone-n-hexane system.

The obtained polyvinyl alcohol was d6DMs.

As a result of NMR measurement, the degree of saponification was 99.6 mol%, the syndiotacticity was 60.2 mol%, and 1.
The 2-glycol bond was 12.29 mol%. Furthermore, for polyvinyl acetate obtained by acetylating the polyvinyl alcohol, [η] measured at 30°C in benzene was 3.65.
dll/g.

Example 2 In a pressure-resistant container equipped with a stirrer, 90 parts of vinyl pivalate monomer and 0.86 IK of vinylene carbonate were charged,
The system was purged with nitrogen by repeating pressurization and release with nitrogen gas. Separately, a solution was prepared by dissolving 0.00827 parts of 2.2'-azobis-4-methoxy-2,4-dimethylvaleronitrile as an initiator in 10 parts of vinyl pivalate monomer, and the solution was purged with nitrogen by bubbling with nitrogen gas.

The temperature of the pressure-resistant container was raised, and when the internal temperature reached 30° C., a pivalic acid monomer solution in which an initiator was dissolved was injected to start polymerization. After 3 hours, the polymerization was stopped by cooling, and the contents were poured into a large amount of methanol to recover the produced polymer.

The polymer was reprecipitated twice in an acetone-methanol system and dried at 60°C under reduced pressure. The amount of polymer obtained was 9.5 parts.

Next, 0 parts of this polymer was dissolved in 49 parts of nitrogen-substituted tetrahydroxyfuran and kept at 60°C, and then a separately prepared and nitrogen-substituted 25% potassium hydroxide solution in methanol was prepared. 10.5 parts of fL was added and thoroughly stirred. At this time, the dissolved oxygen concentration in the polymer solution and the potassium hydroxide solution was determined by Winkler's method, and both were found to be less than 3X to'' mole/Q.The filament gelled in about 5 minutes. However, after holding at 60°C for an additional 25 minutes, 3.4 parts of acetic acid was added along with 10.1 parts of methanol to neutralize the potassium hydroxide.The gel was then crushed and a Soxhlet wash with methanol was performed. Polyvinyl alcohol was obtained.

10 parts of acetic anhydride to 0.1 part of the obtained polyvinyl alcohol
After adding 2 parts of pyridine and sealing the tube, it was heated at 120℃ for 10 minutes.
Heat for an hour to acetylate. Polyvinyl acetate was purified by precipitating it in n-hexane and repeating reprecipitation twice in an acetone-n-hexane system.

The obtained polyvinyl alcohol was dissolved in da-DMSO and NMR measurement revealed that the degree of saponification was 99.6 mol%.
Syndiotacticity - 602 mol%, 1.2-glycol bond! It was 2.5 mol%. In addition, polyvinyl acetate obtained by acetylating the polyvinyl alcohol was measured in benzene at 30°C [η is 4.15 df2/g
Met.

Example 3 99 parts of vinyl trifluoroacetate monomer, 1 part of vinylene carbonate and 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile) as an initiator were placed in a reaction tube.
006 parts were charged, and the system was degassed by repeating freezing and thawing. The reaction tube was heated to 30°C to start polymerization. After 2 hours, the polymerization was stopped by cooling, and the contents were poured into a large amount of petroleum ether to recover the produced polymer. The polymer was re-precipitated twice in an acetone-petroleum ether system and then heated under reduced pressure for 6 hrs.
It was dried at 0°C. The amount of polymer obtained was 9.5 parts.

Next, 1 part of this polymer was dissolved in 49 parts of nitrogen-substituted tetrahydroxyfuran and kept at 60°C, and then 10.5 parts of a separately prepared and nitrogen-substituted 25% methanol solution of potassium hydroxide was added to give a sufficient amount. The mixture was stirred. At this time, the dissolved oxygen concentration in the polymer solution and potassium hydroxide solution was determined by Winkler's method.
It was less than 10-'mol/L2. The number of threads is approximately 5
After a further 25 minutes of holding at 60° C., 3.4 parts of acetic acid was added together with 101 parts of methanol to neutralize the potassium hydroxide. Subsequently, after pulverizing the gel, Soxhlet washing with methanol was performed to obtain polyvinyl alcohol.

10 parts of acetic anhydride to 0.1 part of the obtained polyvinyl alcohol
After adding 2 parts of pyridine and sealing the tube, 1 part was added at 120"c.
It was heated for 0 hours and acetylated. Polyvinyl acetate was purified by precipitating it in n-hexane and repeating reprecipitation twice in an acetone-n-hexane system.

The obtained polyvinyl alcohol was dissolved in d6-DMSO, and NMR measurement revealed that the degree of saponification was 996 mol%, the syndiotacticity was 58.2 mol%, and the 1.2-glycol bond i! It was 1.95 mol%. Furthermore, for polyvinyl acetate obtained by acetylating the polyvinyl alcohol, [η] measured at 30°C in benzene was 1.80 di2
/g.

Comparative Example 1 4 mQ vinyl pivalate, 1 m12 vinyl acetate, 1
01aQ distilled water, 0.5m12 emulsifier (Levenol WZ, Kao Corporation) and a Teflon rotor in a Pyrex
The mixture was placed in a Kjeldahl flask made by Kjeldahl, and the tube was degassed by repeated freezing and thawing, and the tube was sealed under reduced pressure. This was kept in a constant temperature bath at 0°C, and while stirring and irradiating with a 150W high pressure mercury lamp,
Polymerization was carried out for 10 hours. After the polymerization was completed, the polymer was collected by pouring it into a large amount of methanol, purified by reprecipitation using a methyl ethyl ketone-water system, and dried under reduced pressure at 60°C. The polymerization rate was 55.5%.

Next, 1 part of this polymer was dissolved in 49 parts of nitrogen-substituted tetrahydroquinofuran and kept at 60°C, and then 95 parts of a 25% methanol solution of potassium hydroxide 1O prepared separately and nitrogen-substituted was added and thoroughly stirred. did. At this time, the dissolved oxygen concentration in the polymer solution and potassium hydroxide solution was determined by Winkler's method, and both were found to be 3X
It was 10-' mol/Q or less. The filament gelled in about 5 minutes, but after being kept at 60°C for an additional 25 minutes,
Potassium hydroxide was neutralized by adding 3.4 parts of acetic acid along with 10.1 parts of methanol. After subsequently crushing the gel,
Soxhlet cleaning with methanol was performed to obtain polyvinyl alcohol.

10 parts of acetic anhydride to 0.1 part of the obtained polyvinyl alcohol
After adding 1 part and 2 parts of pyridine and sealing the tube, 1 part at 120°C.
It was heated for 0 hours and acetylated. Polyvinyl acetate was purified by precipitating it in n-hexane and repeating the reprecipitation twice in an acetone-n-hexane system.

The obtained polyvinyl alcohol was dissolved in d6-DMSO and NMR measurement showed that the degree of saponification was 998 mol%, the syndiotacticity was 593 mol%, and the amount of 1.2-glycol bond was 0.95 mol%. Furthermore, regarding polyvinyl acetate obtained by acetylating the polyvinyl alcohol, [η] measured at 30°C in benzene was 3.1 odc/g.
Met.

The solubility of the polyvinyl alcohols obtained in the Examples and Comparative Examples in water and DMSO was examined.

The results are summarized in Table 1.

Table 1 (Symbols) ○: Soluble △ Partially soluble ×: Insoluble F1 Effects of the invention According to the present invention, water resistance, heat resistance, which are characteristics of highly syndiotactic polyvinyl alcohol polymers, A novel polyvinyl alcohol-based polymer is provided, which is different from conventional polyvinyl alcohols in that it has physical properties such as high strength and is also excellent in solubility and processability.

ψ This has been achieved by introducing a 1,2-glycol bond into the highly diotactic polyvinyl alcohol polymer of the present invention. The 1.2-glycol bond exists as a heterobond in conventional polyvinyl alcohol polymers, and has been avoided as a factor that inhibits crystallization. 1.2 to highly non-toxic polyvinyl vinyl alcohol polymers
- Active introduction of glycol bonds has a negative effect on crystallization, but unlike methods using copolymerization or partial saponification, the present invention has been achieved because it positively affects intermolecular hydrogen bonds in the amorphous region. I think it was done.

The novel polyvinyl alcohol polymer of the present invention is characterized by high syndiotacticity and good processability as described above, and can be used not only for the use of known polyvinyl alcohol polymers but also for various purposes. It is suitable for applications that take advantage of the characteristics of polymers, and applications that would like to utilize high syndiotactic polyvinyl alcohol polymers but could not be used due to poor processability.

Examples of these uses include high-strength fibers, high-modulus fibers, water-resistant fibers, heat-resistant fibers, water-resistant films, heat-resistant films, high-strength gel materials, fiber processing agents, and paper processing agents. It is extremely valuable.

Claims (5)

[Claims] (1) Syndiotactic city is 55 in diagonal display
mol% or more, and the amount of 1,2-glycol bond is 1.8
mol% or more, and the intrinsic viscosity at 30°C of the polyvinyl acetate polymer obtained by reacetylation in benzene is 0.05 to 10 dl.
/g of polyvinyl alcohol polymer. (2) The polyvinyl alcohol polymer according to claim 1, wherein the polyvinyl alcohol polymer contains 0.01 to 45 mol% of vinyl pivalate units. (3) The polyvinyl alcohol-based polymer according to claim 1 or 2, wherein the homopolymer or copolymer of vinyl pivalate is saponified in a state in which oxygen is substantially removed or in the presence of an antioxidant. manufacturing method. (4) The method for producing a polyvinyl alcohol polymer according to claim 3, wherein the homopolymer or copolymer of vinyl pivalate is obtained by polymerizing at 70° C. or higher. (5) The method for producing a polyvinyl alcohol polymer according to claim 3 or 4, wherein the copolymer of vinyl pivalate contains vinylene carbonate units.