JP2537945B2 - Method for producing high degree of polymerization polyvinyl ester-based polymer and method for producing high degree of polymerization polyvinyl alcohol-based polymer - Google Patents

Description

The present invention relates to a novel method for producing a high polymerization degree polyvinyl ester-based polymer and a novel method for producing a high polymerization degree polyvinyl alcohol-based polymer.

Specifically, the vinyl ester monomer is emulsion-polymerized under the following conditions a, b, c and d:
The present invention relates to a method for producing a high polymerization degree polyvinyl ester polymer having an intrinsic viscosity of 1.5 dl / g or more, preferably 3.2 dl / g or more.

The medium is water or a mixture of water and the following (A), the emulsifier is at least one of the following (B), (C) and (D), and the initiator is the following (E). And (F) or a combination of (E), (F) and (G) below, wherein the polymerization temperature is -60 ° C or higher and 15 ° C or lower.

[Where (A) is dimethyl sulfoxide alone or a combination of dimethyl sulfoxide and at least one selected from water-soluble alcohols, glycols, glycerin or inorganic salts, (B) is a nonionic emulsifier, and (C) is Nonionic-anionic emulsifier, (D) is an anionic emulsifier, (E) is at least one selected from hydroperoxides, peroxides or peresters, and (F) is subject to one electron transfer. Possible metal ions, (G) represent a reducing substance.

The intrinsic viscosity of the polyvinyl ester-based polymer is defined as the value of polyvinyl acetate resaponified after saponifying the polyvinyl ester-based polymer in acetone at 30 ° C. ] Furthermore, the intrinsic viscosity characterized by saponifying a polyvinyl ester polymer obtained by emulsion polymerization under the above conditions has an intrinsic viscosity of 1.5 dl / g or more, preferably a high polymerization degree polyvinyl alcohol of more than 3.2 dl / g ( (Hereinafter abbreviated as PVA) The present invention relates to a novel method for producing a polymer. (PV here
The intrinsic viscosity of the A-based polymer is defined as the value of polyvinyl acetate obtained by reacetylating the PVA-based polymer in acetone at 30 ° C. ) Polyvinyl ester-based polymers, especially polyvinyl acetate-based polymers, are widely used as adhesive base polymers, and are extremely important as raw materials for PVA-based polymers. In addition, since PVA-based polymers have excellent interface properties and strength properties as a few crystalline water-soluble polymers, they are used as stabilizers for paper processing, fiber processing, emulsion, etc. As is well known, it also occupies an important position as a raw material for vinylon fiber and vinylon fiber.

However, the polymerization degree of the conventional PVA-based polymer is 2,000 as the upper limit, from the viewpoint of processing characteristics and ease of handling, and the fact that it is difficult to obtain a raw material polyvinyl acetate-based polymer having a high degree of polymerization. Only about 3000 special items are found.

On the other hand, rapid advances in processing technology in recent years have made it possible to process polymers having an ultra-high degree of polymerization, thereby succeeding in bringing out previously unknown physical properties. PVA-based polymers are expected to have new possibilities in new fields such as high-strength fibers, as well as improving physical properties in conventional applications by increasing the degree of polymerization.

B. Prior Art In general, polymers having a high degree of polymerization are obtained by polymerizing at a low temperature and at a low speed, and some examples of vinyl acetate have been reported.

[For example, AR Shultz; J. Am. Chem. Soc. 76 3422 (195
4), GMBurnett, MHGeorge, HWMelville; J. Poly
m.Sci. 16 31 (1955), M.Matsumoto, Y.Ohyanagi; J.Poly
m.Sci. 46 148 (1960)] However, these methods are all bulk polymerization methods,
Since the polymerization system has an extremely high viscosity, there are problems that stirring is difficult, a homogeneous polymer cannot be obtained, and heat removal is difficult. It is therefore believed that production on an industrial scale using these bulk polymerization processes would be almost impossible.

The present inventors have already proposed a method by the suspension polymerization method as a method that overcomes the drawbacks of the bulk polymerization method. (JP-A-61-148209) However, in a system having a large chain transfer such as vinyl ester, it is an essential condition to lower the polymerization temperature in order to increase the polymerization degree. The polymerization rate in the polymerization method and the above-mentioned suspension polymerization method proposed by the present inventors must be extremely low.

On the other hand, the emulsion polymerization method has a different polymerization mechanism from the bulk polymerization and suspension polymerization, and may polymerize at a relatively high rate to obtain a high degree of polymerization, and the greatest drawback of the bulk polymerization method. It is considered to be one effective polymerization method as a method for producing a polyvinyl ester-based polymer and a polyvinyl alcohol-based polymer having a high degree of polymerization, with almost no problems relating to stirring and heat removal.

And high polymerization degree polyvinyl acetate by emulsion polymerization method,
And a method for obtaining polyvinyl alcohol saponified from this is proposed as radiation polymerization in CANADIAN PATENT No. 663, 529 (1963).

However, this method is: (1) Polymerization at a temperature of substantially 0 ° C. or higher, (2) It is considered that cleavage of the polymer or gelation is likely to occur due to the use of radiation, (3) Since the emulsifier used needs to be stable against irradiation, it is limited to extremely special ones such as stearylamidopropyldimethyl-θ-hydroxyethylammonium dihydrogen phosphite. It cannot be said that the method for producing a high degree of polymerization is an excellent method. Generally, the lower limit of the polymerization temperature in emulsion polymerization is about 0 ° C. This is because the emulsion particles are destroyed by the freezing of water, which is the medium, and the purpose cannot be achieved. However, as already mentioned, in order to obtain a high degree of polymerization polyvinyl ester-based polymer and a high degree of polymerization PVA-based polymer, at low temperature, especially at 0 ° C.
It is important to carry out emulsion polymerization below, and it is not possible to obtain a polyvinyl ester polymer and a polyvinyl alcohol polymer having a sufficiently high degree of polymerization by the method described in the above Canadian patent.

C. PROBLEMS TO BE SOLVED BY THE INVENTION The present invention provides a polyvinyl ester polymer having a high degree of polymerization and a PVA polymer having a high degree of polymerization obtained by saponifying the polyvinyl ester polymer, on an industrial scale. It is intended to provide a novel manufacturing method that can be easily obtained.

D. Means for Solving the Problems The inventors of the present invention have earnestly studied a production method capable of easily obtaining a polyvinyl ester-based polymer having a high degree of polymerization on an industrial scale. It was found that a high-polymerization degree polyvinyl ester polymer having an intrinsic viscosity of 1.5 dl / g or more, preferably 3.2 dl / g or more, can be obtained by emulsion polymerization under the conditions of B, C, C and D.

The medium is water or a mixture of water and the following (A), the emulsifier is at least one of the following (B), (C) and (D), and the initiator is the following (E). And (F) or a combination of (E), (F) and (G) below, wherein the polymerization temperature is -60 ° C or higher and 15 ° C or lower.

[Where (A) is dimethyl sulfoxide alone or a combination of dimethyl sulfoxide and at least one selected from water-soluble alcohols, glycols, glycerin or inorganic salts, (B) is a nonionic emulsifier, and (C) is Nonionic-anionic emulsifier, (D) is an anionic emulsifier, (E) is at least one selected from hydroperoxides, peroxides or peresters, and (F) is subject to one electron transfer. Possible metal ions, (G) represents a reducing substance, respectively.

The intrinsic viscosity of the polyvinyl ester-based polymer is defined as the value of polyvinyl acetate resaponified after saponifying the polyvinyl ester-based polymer in acetone at 30 ° C. Further, by saponifying a polyvinyl ester-based polymer obtained by emulsion-polymerizing a vinyl ester monomer under the conditions I to D, the intrinsic viscosity is 1.5 dl / g or more, preferably greater than 3.2 dl / g. The inventors have found that a high degree of polymerization PVA-based polymer can be obtained, and have completed the present invention. (Here, the intrinsic viscosity of the PVA-based polymer is 30% in acetone for polyvinyl acetate obtained by re-acetylating the PVA-based polymer.
It is defined as the value measured at ° C. ) The emulsion polymerization of the present invention will be described in detail below.

First, the polymerization temperature is preferably as low as possible in order to suppress chain transfer as described above. However, since the growth rate constant also decreases as the temperature decreases, if the temperature is excessively lowered, problems such as a decrease in the polymerization rate and susceptibility to oxygen are caused. Therefore, the polymerization temperature is -60 ℃ or higher, 15 ℃
It is necessary to be in the range of preferably -60 ° C or higher and 10 ° C or lower, more preferably -50 ° C or higher and 0 ° C or lower, particularly preferably -50 ° C or higher and lower than -15 ° C.

When the temperature is 0 ° C. or lower, it is necessary to prevent the aqueous phase from condensing, and dimethyl sulfoxide alone or a combination of dimethyl sulfoxide and water-soluble alcohols, glycols, glycerins, inorganic salts [these ((A It is essential to add)) to the aqueous phase.

Specific examples of substances that can be used in combination with dimethyl sulfoxide include methanol, ethanol, propanol, t-butanol, ethylene glycol, glycerin, LiCl, NaC.
l, KCl, etc. And it is necessary to prevent condensation (A)
The addition amount of water varies depending on the polymerization temperature, but the weight ratio of water / water
(A) = 100/0 to 45/55 is preferable, and water / (A) = 90/10 to 50/50 is more preferable.

Next is an emulsifier, but temperature -60 ℃ or more, 15 ℃ or less,
And water / (A) = 100/0 to 50/50 are required to be dissolved and capable of stabilizing the produced polymer particles and maintaining the emulsion state. Nonionic emulsifiers (B), nonionic-anionic emulsifiers (C), and anionic emulsifiers (D) can be used as emulsifiers satisfying these requirements. Cationic emulsifiers are not preferred. Specifically, as (B), polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether,
Polyoxyethylene alkyl ester, polyoxyethylene sorbitan alkyl ester, (C) polyoxyethylene alkylphenyl ether sulfate ester,
Polyoxyethylene alkyl ether phosphate,
Examples of (D) include sulfates of higher alcohols, alkylallyl sulfonates, phosphates of aliphatic alcohols, and the like. Although (B), (C) and (D) are used alone or in combination, the amount added to the vinyl ester monomer is 0.5 to 50% by weight, preferably 1 to 30% by weight. Among (B), (C) and (D), (B) is particularly preferable.

Finally, the initiator will be described. In the polymerization at low temperature as in the present invention, the thermal decomposition type initiator used in ordinary emulsion polymerization cannot be used because the decomposition rate is too small. Although a redox reaction system is known as a system that effectively generates radicals at low temperatures, the redox initiator is most effective even under the emulsion polymerization conditions of the present invention.

The redox-based initiator that can be used in the present invention is (E) at least one selected from hydroperoxides, peroxides or peroxyesters, (F) metal ions capable of undergoing one electron transfer, (G) ) A reducing substance, (E) / (F) or (E) / (F) /
Used in combination with (G). Specifically, (E) is hydrogen peroxide, cumene hydroperoxide, t-butyl hydroperoxide, persulfate (K, Na, ammonium salt), t-butyl peracetate, t-butyl perbenzoate. ,
^{Examples of} (F) include Fe ²⁺ , Cr ²⁺ , V ²⁺ , Ti ³⁺ , Co ²⁺ , Cu ⁺ ,
Examples of (G) include rongalite, 1-ascorbic acid, and the like. Among them, (E) is hydrogen peroxide, persulfate (K, Na, ammonium salt) cumene hydroperoxide, and (F) is Fe. ^{As 2+} and (G), Rongalit is most preferably used.

Further, in using these initiators, it is important to use them so that (F) or the sum of (F) and (G) is always present in a sufficient excess relative to (E) during the polymerization. If not, (E) remains in the polymerization system after the polymerization, and an undesired post-polymerization reaction occurs when the temperature of the system is raised in a step such as post-treatment, resulting in the purpose of the present invention. Therefore, a high degree of polymerization cannot be obtained.

In this sense, (E), (F) and (G) are added to the polymerization system by adding (F) or (F) + (G) from the beginning and adding (E) to the delay It is preferable to add. The concentration ratio of (E), (F), and (G) to each other and the method of addition are important factors that greatly affect the degree of polymerization of the polyvinyl ester-based polymer or the PVA-based polymer as described above, and are important. is there.

In carrying out the emulsion polymerization at low temperature of the present invention described above, it is necessary to pay sufficient attention to the following points as compared with the usual emulsion polymerization at high temperature. That is, since the radical concentration of the polymerization system is low, it is easily affected by oxygen and impurities in the polymerization system. In particular, oxygen acts as a strong inhibitor, so special care must be taken regarding its removal from the polymerization system before polymerization and its entry into the polymerization system during polymerization.

Therefore, it is necessary to sufficiently deoxidize both the water and the monomer used in the present invention before use. The vinyl ester monomers are preferably purified by a conventional method before use.

Examples of the vinyl ester monomer used in the present invention include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, and the like. Is preferred.

It is also possible to copolymerize monomers copolymerizable with the above-mentioned vinyl ester monomers. Examples of these monomers include (meth) acrylic acid and (meth) acrylic acid.
Acrylic acid ester, itaconic acid or its ester,
Examples thereof include maleic acid ester or maleic anhydride, (meth) acrylamide or derivatives thereof, vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride, acrylonitrile, vinylalkoxysilane and the like.

The present invention provides a method for obtaining a high degree of polymerization polyvinyl ester polymer and PVA polymer, the polymerization rate in the emulsion polymerization of the present invention is important for affecting the polymerization degree, usually 10 % To 90%, preferably 20% to 80
%, More preferably 30% to 70%.

The polyvinyl ester polymer emulsion obtained by the emulsion polymerization of the present invention is usually coagulated, and the polymer can be deposited and recovered by stripping, of course, but when a PVA polymer is obtained, it is produced. It is preferable that the emulsion is charged and dissolved in a large amount of methanol containing an inhibitor, and unreacted vinyl ester (most preferably vinyl acetate) is removed by distillation to obtain a methanol solution of a polyvinyl ester polymer. Although this methanol solution contains water, it can undergo alcoholysis using NaOH, NaOCH ₃ , NaOC ₂ H ₅ or the like as a catalyst, and a PVA polymer can be obtained. The completely saponified PVA polymer obtained in the present invention can be washed with cold water, and impurities such as sodium acetate, an emulsifier and an initiator can be removed. Furthermore, washing with an acid aqueous solution is effective for removing metal ions.

E. Action and Effect of the Invention The present invention has a high polymerization degree polyvinyl ester polymer having an intrinsic viscosity of 1.5 dl / g or more, preferably greater than 3.2 dl / g, as defined above, and saponifying the polyvinyl ester polymer. The intrinsic viscosity obtained by the above definition is 1.5 dl / g
As described above, it is an object of the present invention to provide a novel production method capable of easily obtaining a PVA polymer having a high degree of polymerization of more than 3.2 dl / g on an industrial scale. Was carried out by emulsion polymerization under the following conditions (1) to (4) to saponify the obtained polyvinyl ester polymer.

The medium is water or a mixture of water and the following (A), the emulsifier is at least one of the following (B), (C) and (D), and the initiator is the following (E) And (F), or the following combinations (E), (F) and (G), wherein the polymerization temperature is -60 ° C or higher and 15 ° C or lower.

[Where (A) is dimethyl sulfoxide alone or a combination of dimethyl sulfoxide and at least one selected from water-soluble alcohols, glycols, glycerin or inorganic salts, (B) is a nonionic emulsifier, and (C) is Nonionic-anionic emulsifier, (D) is an anionic emulsifier, (E) is at least one selected from hydroperoxides, peroxides or peresters, and (F) is subject to one electron transfer. Possible metal ions, (G) represents a reducing substance, respectively. ] The greatest feature of the present invention is -60 ° C or higher and 15 ° C or lower, preferably -60 ° C or higher and 10 ° C or lower, more preferably -50 ° C or lower, 0 ° C or higher, and particularly preferably -50 ° C or lower,- 15 ° C
Emulsion polymerization is performed at a low temperature of less than, which results in a high degree of polymerization of a polyvinyl ester polymer and a higher degree of polymerization.
The PVA polymer was obtained without causing engineering problems such as stirring and heat removal during the polymerization, and at a speed that was incomparable to that of the bulk polymerization or the suspension polymerization. Further, the conversion of the polyvinyl ester polymer into the PVA polymer can be performed extremely easily as described above.

The high degree of polymerization polyvinyl ester polymer thus obtained has a high strength and can be used as a sheet or a film. Furthermore, by saponifying the above-mentioned high degree of polymerization polyvinyl ester polymer, a high degree of polymerization PVA type polymer can be easily obtained, which is a PVA type high strength sheet or PVA type high strength fiber. Is preferably used as.

Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to these.
In addition, "%" and "part" in Examples mean "% by weight" and "part by weight", respectively.

Example 1 700 parts of ion-exchanged water, 700 parts of vinyl acetate, 590 parts of dimethyl sulfoxide, polyoxyethylene [POE (50)] in a reactor equipped with a stirrer, a thermometer, a nitrogen introducing tube and a cooling tube.
Weigh 28 parts of nonylphenyl ether (Nonipol 500, Sanyo Kasei Co., Ltd.), 0.02 parts of FeSO ₄ .7H ₂ O and 0.47 parts of Rongalit and boil for 30 minutes, then while introducing nitrogen, to -20 ° C. Polymerization was started while continuously cooling and adding 0.01% hydrogen peroxide solution adjusted with separately degassed ion-exchanged water uniformly at 20 parts / hr. During the polymerization, the system was sealed with nitrogen gas to prevent oxygen from entering. After 2.5 hours, when the polymerization rate reached 50% (maximum polymerization rate of 25% hr), the addition of hydrogen peroxide solution was stopped, and then the stirring was continued for 0.5 hour to stop the polymerization.

The emulsion obtained here was added to methanol 8000 at room temperature.
1 part of hydroquinone monomethyl ether was dissolved in 1 part and the solution was dissolved with stirring. After dissolution, unreacted vinyl acetate monomer was removed while adding methanol under reduced pressure to obtain a methanol solution of polyvinyl acetate. A portion of this solution was taken and saponified at a concentration of 5%, [NaOH] / [VAc] (molar ratio) = 0.1 at a temperature of 40 ° C., and 0.1 part of the obtained polyvinyl alcohol (PVA) was mixed with 8 parts of acetic anhydride and pyridine. Polyvinyl acetate was reacetated in a mixed solution of 2 parts at 105 ° C. for 20 hours with occasional stirring, and repeated reprecipitation purification with an acetone-ether or acetone-water system.
Intrinsic viscosity measured at ℃, [η] = 4.10 (dl / g)
It was. (Measurement by a dilution method using an Ubbelohde type viscosity tube) Next, a methanol solution of polyvinyl acetate was added at a concentration of 5%,
[NaOH] / [VAc] (molar ratio) = 0.15, saponified at a temperature of 40 ° C., the PVA obtained was deliquored, and then the same amount of NaOH as that used for saponification was added and immersed in methanol. 24 at 40 ° C
Time re-ken. After that, neutralize with 1N sulfuric acid, wash with 0.0001N sulfuric acid, wash with ion-exchanged water repeatedly, and finally wash with methanol, remove the liquid, and dry at 40 ° C.
I got This PVA has a saponification degree of 99.8 mol%,
Re-acetate VA under the same conditions as above, for polyvinyl acetate repeated reprecipitation purification in the same manner as above, in acetone,
When the intrinsic viscosity was measured at 30 ° C, [η] = 4.10 (dl /
g)

Comparative Example 1 A reactor equipped with a stirrer, a thermometer, a nitrogen inlet tube and a cooling tube was charged with PVA-217 (polymerization degree 1700, saponification degree 88 mol%,
(Kuraray Co., Ltd.) 0.3 parts and distilled water 3000 parts were charged at 90 ° C.
After PVA-217 was dissolved in, the mixture was cooled to a temperature of 5 ° C. in a thermostat while introducing nitrogen. After replacing 1,500 parts of a vinyl acetate monomer purified by a conventional method with nitrogen at 60 ° C, the product was cooled to 5 ° C while introducing nitrogen.
-Azobis (4-methoxy-2,4-dimethylvaleronitrile) (0.125 parts) was quickly dissolved, and polymerization was started by adding the solution to an aqueous PVA-217 solution with stirring. During the polymerization, the polymerization system was sealed with nitrogen gas to suppress the invasion of oxygen. Polymerization is 5
It proceeded at an initial rate of 1.0% / hour at 0 ° C. 95 hours later, 5
After removing unreacted monomer for 48 hours under reduced pressure at ℃, separate the pearl-like polymer produced, and repeat washing with water,
It was dried under reduced pressure at 30 ° C. The weight of the polymer obtained after drying is
It was 1226 copies.

A part of the obtained polyvinyl acetate was dissolved in methanol and the concentration was 6%, [NaON] / [VAc] (molar ratio) = 0.05,
Saponified at a temperature of 40 ° C., and 0.1 part of the obtained PVA is
Parts and pyridine in a mixed solution of 2 parts and 105 ° C for 20 hours with re-acetic acid with stirring, and acetone-ether, acetone-
About polyvinyl acetate which repeated reprecipitation purification in aqueous system,
When the intrinsic viscosity was measured at 30 ° C. in acetone, [η] = 3.
It was 15 (dl / g). (Measurement by a dilution method using an Ubbelohde type viscosity tube) Further, the polyvinyl acetate was dissolved in methanol and saponified under the same conditions as described above, and the saponification degree was 98.9 mol%.
Got the PVA of. This PVA is re-acetylated under the same conditions as above,
When the intrinsic viscosity was measured at 30 ° C. in acetone for the polyvinyl acetate that was subjected to reprecipitation purification in the same manner as above,
[Η] = 3.15 (dl / g).

In order to obtain a polymer having almost the same degree of polymerization as described above, the suspension polymerization method (although engineering problems such as stirring and heat removal during the polymerization have been solved as compared with the bulk polymerization method) requires an initial polymerization rate. In contrast to 1.0% / hr, in the emulsion polymerization method of the present invention shown in Example 1, the maximum polymerization rate is 25% / hr, which is a very high polymerization rate.

Comparative Example 2 In a reactor equipped with a thermometer, a nitrogen introducing tube and a cooling tube, 2,
Weigh 1.08 parts of 2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), replace with nitrogen, and then at 15 ° C.
And cooled in a constant temperature bath. Subsequently, 300 parts of a vinyl acetate monomer purified by a conventional method was replaced with nitrogen at 60 ° C, then cooled to 15 ° C while introducing nitrogen, and charged with stirring to start polymerization. During the polymerization, the polymerization system was sealed with nitrogen gas to suppress the invasion of oxygen. Polymerization proceeded at 15 ° C. at an initial rate of 7.5% time, but after about 2 hours, the viscosity became considerably high, and stirring gradually became difficult. After 4 hours, almost no stirring was possible and the internal temperature could not be kept at 15 ° C.

After 24 hours, the polymer was taken out and the polymerization rate was measured to be 79%. The vinyl acetate monomer was removed in the presence of thiourea to obtain polyvinyl acetate. Further, a part thereof was saponified in the same manner as in Comparative Example 1 to obtain PVA. The reacylated polyvinyl acetate [η] was 1.42 dl / g.

In this way, the vinyl acetate monomer was 1/5 compared to Comparative Example 1.
However, in the bulk polymerization method, it was difficult to stir from the middle because of the high viscosity in the bulk polymerization method.
I couldn't keep it. As a result, the polymerization rate was almost the same as that of Comparative Example 1, but the re-acetylated product [η] was considerably smaller than that of the suspension polymerization method of Comparative Example 1, and that of the present invention described in Example 1 [Η] was extremely small compared to

Example 2 The polymerization method, saponification method, purification method and the like were the same as those described in Example 1, except that only the polymerization temperature in the polymerization conditions was-
The test was carried out in the same manner as in Example 1 except that the temperature was changed to 25 ° C. As a result, the polymerization proceeded at an average polymerization rate of 22% / hr, and the polymerization rate was 55% at 2.5 hours after the addition of hydrogen peroxide solution. Reached

When the intrinsic viscosity of the reacylated polyvinyl acetate obtained in the same manner as in Example 1 was measured, [η] = 4.
It was 15 (dl / g).

Next, the obtained PVA was re-acetylated in the same manner as in Example 1 and the intrinsic viscosity of the obtained re-acetylated polyvinyl acetate was measured. As a result, it was [η] = 4.15 dl / g. .

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Claims (2)

(57) [Claims] 1. A method for producing a high-polymerization degree polyvinyl ester polymer having an intrinsic viscosity of 1.5 dl / g or more, which comprises emulsion-polymerizing a vinyl ester monomer under the following conditions (a), (b), (c) and (d): . The medium is water or a mixture of water and the following (A), the emulsifier is at least one of the following (B), (C) and (D), and the initiator is the following (E) And (F), or the following combinations (E), (F) and (G), wherein the polymerization temperature is -60 ° C or higher and 15 ° C or lower. [Where (A) is dimethyl sulfoxide alone or a combination of dimethyl sulfoxide and at least one selected from water-soluble alcohols, glycols, glycerin or inorganic salts, (B) is a nonionic emulsifier, and (C) is Nonionic-anionic emulsifier, (D) is an anionic emulsifier, (E) is at least one selected from hydroperoxides, peroxides or peresters, and (F) is subject to one electron transfer. Possible metal ions, (G) represents a reducing substance, respectively. Further, here, the intrinsic viscosity of the polyvinyl ester polymer is
The polyvinyl acetate polymer saponified and then reaceticated is defined as the value measured in acetone at 30 ° C. ] 2. A polyvinyl ester-based polymer obtained by emulsion-polymerizing a vinyl ester monomer under the following conditions (i), (ii), (iii), and (ii) to saponify, and having an intrinsic viscosity of 1.5 dl / g or more. A method for producing a polyvinyl alcohol polymer having a high degree of polymerization. The medium is water or a mixture of water and the following (A), the emulsifier is at least one of the following (B), (C) and (D), and the initiator is the following (E). And (F), or the following combinations (E), (F) and (G), wherein the polymerization temperature is -60 ° C or higher and 15 ° C or lower. [Where (A) is dimethyl sulfoxide alone or a combination of dimethyl sulfoxide and at least one selected from water-soluble alcohols, glycols, glycerin or inorganic salts, (B) is a nonionic emulsifier, and (C) is Nonionic-anionic emulsifier, (D) is an anionic emulsifier, (E) is at least one selected from hydroperoxides, peroxides or peresters, and (F) is subject to one electron transfer. Possible metal ions. (G) represents a reducing substance, respectively. The intrinsic viscosity of the polyvinyl alcohol-based polymer is defined as a value of polyvinyl acetate obtained by reacetylating the polyvinyl alcohol-based polymer in acetone at 30 ° C. ]