Vinyl alcohol polymer, method for producing vinyl alcohol polymer, dispersant for suspension polymerization, dispersant aid for suspension polymerization, and method for producing vinyl polymer

Abstract

The present invention provides: a novel vinyl alcohol polymer; a method for producing this vinyl alcohol polymer; a dispersant for suspension polymerization, said dispersant enabling the achievement of polymer particles which have a small average particle diameter, while containing fewer coarse particles, and which exhibit good plasticizer absorption; a dispersion assistant for suspension polymerization; and a method for producing a vinyl polymer. The present invention provides a vinyl alcohol polymer which comprises a carbonyl group, a formyl group and an alkenyl group in a same molecule or in different molecules. The present invention also provides a method for producing a vinyl alcohol polymer, said method comprising: a step for polymerizing a vinyl ester in the presence of an aliphatic unsaturated aldehyde; and a step for saponifying the thus-obtained vinyl ester polymer.

Description

[Technical Field]

[0001] The present invention relates to vinyl alcohol polymers, methods for producing vinyl alcohol polymers, dispersants for suspension polymerization, dispersing aids for suspension polymerization, and methods for producing vinyl polymers. [Background technology]

[0002] Vinyl alcohol polymers (hereinafter also referred to as "PVA") are known as water-soluble synthetic polymers. PVA is used in a variety of applications, including as a raw material for films and fibers, an additive for paper and textile processing, an adhesive, a dispersant (also referred to as a dispersion stabilizer, etc.) and dispersion aid for emulsion polymerization and suspension polymerization, and an inorganic binder.

[0003] Various modified forms of PVA have been put into practical use or developed to improve the performance of PVA. For example, Patent Document 1 describes a dispersion stabilizer for suspension polymerization that contains a polyvinyl alcohol polymer (B) having double bonds in its side chains, which is obtained by acetalizing a polyvinyl alcohol polymer (A) with an olefin-based monoaldehyde having unsaturated double bonds. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2015 / 182567 [Overview of the project] [Problems that the invention aims to solve]

[0005] Further improvements in the performance of PVA necessitate the development of new PVA compounds. For example, when PVA is used as a dispersant for suspension polymerization, it is desirable to obtain polymer particles that are small in size, uniform in size, and have good plasticizer absorption properties.

[0006] The present invention aims to provide a novel vinyl alcohol-based polymer and a method for producing the same, as well as a dispersant for suspension polymerization, a dispersant aid for suspension polymerization, and a method for producing a vinyl polymer, which can produce polymer particles with a small average particle size, few coarse particles, and good plasticizer absorption. [Means for solving the problem]

[0007] The above purpose is, [1] Vinyl alcohol polymers having carbonyl groups, formyl groups, and alkenyl groups in the same or different molecules; [2] A vinyl alcohol polymer of [1] having a structure represented by the following formula (1) containing the above carbonyl group; [ka] In equation (1), m is an integer between 1 and 11. [3] A vinyl alcohol polymer having a group represented by the following formula (2) at the end of the polymer chain; [ka] In formula (2), R 1 This is an alkenyl group. [4] R in equation (2) above 1 A vinyl alcohol polymer of [3] in which the alkenyl group represented by has a methylene group at the carbonyl end; [5] A vinyl alcohol polymer having a tertiary carbon atom, one of the [1] to [4]; [6] A vinyl alcohol polymer having a structural unit derived from an aliphatic unsaturated aldehyde, any of [1] to [5]; [7] A vinyl alcohol polymer of the above aliphatic unsaturated aldehyde having 3 to 14 carbon atoms; [8] The vinyl alcohol polymer of [6] or [7] having the above aliphatic unsaturated aldehyde having a carbon-carbon double bond at its terminus; [9] A process for polymerizing a vinyl ester in the presence of an aliphatic unsaturated aldehyde, and a process for saponifying the obtained vinyl ester polymer, a method for producing a vinyl alcohol polymer;

[10] A dispersant for suspension polymerization containing any one of the vinyl alcohol polymers of [1] to [8];

[11] A dispersion aid for suspension polymerization containing any one of the vinyl alcohol polymers of [1] to [8];

[12] A method for producing a vinyl polymer comprising a step of polymerizing a vinyl compound in the presence of any one of the vinyl alcohol polymers of [1] to [8]; is achieved by providing any of the above. [Advantages of the Invention]

[0008] According to the present invention, a novel vinyl alcohol polymer and a method for producing the same, and a dispersant for suspension polymerization, a dispersion aid for suspension polymerization, and a method for producing a vinyl polymer that can obtain polymer particles having a small average particle size, few coarse particles, and good plasticizer absorbability can be provided. [Modes for Carrying Out the Invention]

[0009] [Vinyl Alcohol Polymer] The vinyl alcohol polymer (PVA) according to the first embodiment of the present invention has a carbonyl group, a formyl group, and an alkenyl group in the same or different molecules. In the PVA, all of the carbonyl group, the formyl group, and the alkenyl group may not be included in one molecule. That is, the PVA may be, for example, a mixture of PVA (a) having two of the carbonyl group, the formyl group, and the alkenyl group and PVA (b) having the remaining one group. At this time, one or more of the carbonyl group, the formyl group, and the alkenyl group may be possessed by both PVA (a) and PVA (b). The PVA may be a mixture of three or more types of PVA. Note that the form of PVA having all of the carbonyl group, the formyl group, and the alkenyl group in one molecule and the mixture composed of a plurality of types of PVA, where this mixture has the carbonyl group, the formyl group, and the alkenyl group, have substantially the same properties, and it is generally extremely difficult to distinguish these two forms by analysis or the like.

[0010] The PVA in question is a polymer having vinyl alcohol units as structural units. Typically, as will be detailed later, the PVA is obtained by polymerizing a vinyl ester in the presence of an aliphatic unsaturated aldehyde and then saponifying the resulting vinyl ester polymer. The lower limit of the degree of saponification of the PVA may be, for example, 20 mol%, 30 mol%, or 40 mol%, but 50 mol% is preferred, 60 mol% is more preferred, and 70 mol% is even more preferred. On the other hand, the upper limit of the degree of saponification may be 100 mol%, but 95 mol% is preferred, 90 mol% is more preferred, 85 mol% is even more preferred, and 80 mol% is even more preferred. When the degree of saponification of the PVA is within the above range, the surfactant performance is optimized, and various properties are improved, for example, when used as a dispersant for suspension polymerization (such as obtaining polymer particles with a small average particle size, few coarse particles, and good plasticizer absorption). On the other hand, when the PVA is used as a dispersion aid for suspension polymerization, the lower limit of the degree of saponification of the PVA is preferably 20 mol%, and more preferably 30 mol%. In such cases, the upper limit of the degree of saponification of the PVA is preferably 80 mol%, more preferably 70 mol%, and even more preferably 60 mol%. The degree of saponification is a value measured by the method described in JIS K6726:1994.

[0011] The carbonyl group (-C(=O)-) in the PVA is a divalent group in which both bonds are connected to a carbon atom. That is, the -C(=O)- in the formyl group (-C(=O)H) is not included in the carboxyl group of the PVA. The PVA preferably has a structure represented by the following formula (1) which includes a carbonyl group.

[0012] [ka]

[0013] In equation (1), m is an integer between 1 and 11. Preferably, m is an integer between 2 and 9, and sometimes it is an integer between 3 and 7.

[0014] In this specification, numerical ranges indicated using "~" include the numbers before and after the "~" as the lower and upper limits, respectively.

[0015] The carbonyl group content in the PVA relative to the total content of vinyl alcohol units and vinyl ester units is preferably 0.001 mol% to 5 mol%, more preferably 0.005 mol% to 1 mol%, even more preferably 0.008 mol% to 0.1 mol%, and even more preferably 0.01 mol% to 0.05 mol%. When the carbonyl group content in the PVA is within the above range, various performances are improved, for example, when used as a dispersant for suspension polymerization. The carbonyl group content is determined by the method described in the examples below.

[0016] The formyl group in the PVA is a monovalent group represented by -C(=O)H.

[0017] The formyl group content in the PVA relative to the total content of vinyl alcohol units and vinyl ester units is preferably 0.01 mol% to 5 mol%, more preferably 0.03 mol% to 3 mol%, even more preferably 0.05 mol% to 2 mol%, and still more preferably 0.07 mol% to 1 mol%. When the formyl group content in the PVA is within the above range, various performances are improved, for example, when used as a dispersant for suspension polymerization. The formyl group content is determined by the method described in the examples below.

[0018] The alkenyl group in the PVA is a monovalent group obtained by removing any one hydrogen atom from an alkene. The number of carbon atoms in the alkenyl group is preferably 2 to 13, more preferably 3 to 12, even more preferably 4 to 11, and in some cases 5 to 9. The alkenyl group may be linear or have a branched structure, but it is preferably linear. The alkenyl group is preferably located at the end of the polymer chain.

[0019] The alkenyl group in the PVA preferably has a carbon-carbon double bond at its terminal (tip). That is, the PVA preferably has a vinyl group at its terminal (tip). More preferably, the alkenyl group in the PVA is a group represented by the following formula (5).

[0020] [ka]

[0021] In equation (5), n is an integer between 1 and 11. It is preferable that n is an integer between 2 and 9, and more preferably an integer between 3 and 7.

[0022] The content of alkenyl groups relative to the total content of vinyl alcohol units and vinyl ester units in the PVA is preferably 0.005 mol% to 5 mol%, more preferably 0.01 mol% to 3 mol%, even more preferably 0.02 mol% to 1 mol%, and in some cases even more preferably 0.03 mol% to 0.5 mol%. When the content of alkenyl groups in the PVA is within the above range, various performances are improved, for example, when used as a dispersant for suspension polymerization. The above content of alkenyl groups is determined by the method described in the examples below. The range of suitable content of vinyl groups relative to the total content of vinyl alcohol units and vinyl ester units in the PVA is the same as the range of suitable content of alkenyl groups.

[0023] The PVA preferably has terminal groups derived from an aliphatic unsaturated aldehyde, or structural units derived from an aliphatic unsaturated aldehyde. The aliphatic unsaturated aldehyde has 3 to 14 carbon atoms, more preferably 4 to 12, and in some cases 6 to 10.

[0024] The above aliphatic unsaturated aldehyde preferably has a carbon-carbon double bond, and more preferably has a carbon-carbon double bond at the terminal (tip). That is, the above aliphatic unsaturated aldehyde preferably contains a vinyl group. As the above aliphatic unsaturated aldehyde having a carbon-carbon double bond, it is preferable to have an alkenyl group having a methylene group at the carbonyl group end, i.e., an aliphatic unsaturated aldehyde having a group represented as R-CH2- (where R is an alkenyl group). In other words, it is preferable that the above aliphatic unsaturated aldehyde is an aliphatic unsaturated aldehyde other than an α,β-unsaturated aldehyde. By using an aliphatic unsaturated aldehyde having the above structure, the reactivity during polymerization is improved, and PVA with a sufficient amount of functional groups (carbonyl groups, etc.) can be effectively obtained.

[0025] The above aliphatic unsaturated aldehyde is particularly preferably a compound represented by the following formula (6).

[0026] [ka]

[0027] In equation (6), p is an integer between 1 and 11. It is preferable that p is an integer between 2 and 9, and more preferably an integer between 3 and 7.

[0028] Examples of the above-mentioned aliphatic unsaturated aldehydes include 2-propenal, 3-butenal, 4-pentenal, 5-hexenal, 3-methyl-5-hexanal, 6-heptenal, 6-octenal, 7-octenal, 7-methyl-7-octenal, 3,7-dimethyl-7-octenal, 8-nonenal, 9-decenal, 10-undecenal, and 11-dodecenal.

[0029] Examples of terminal groups derived from aliphatic unsaturated aldehydes that the PVA preferably possesses include the group represented by the following formula (2).

[0030] [ka]

[0031] In formula (2), R 1 is an alkenyl group.

[0032] R in formula (2) 1 The number of carbon atoms of the alkenyl group represented by is preferably 2 to 13, more preferably 3 to 12, still more preferably 4 to 11, and even more preferably 5 to 9 in some cases. R 1 The alkenyl group represented by may be linear or may have a branched structure, but is preferably linear. R 1 As the alkenyl group represented by, a group having a methylene group at the terminal on the carbonyl group side (a group represented by R-CH2- (R is an alkenyl group)) is preferable, a group having a carbon-carbon double bond at the terminal (tip) is more preferable, and a group represented by the above formula (5) is even more preferable. The terminal group represented by formula (2) is usually formed when an aliphatic unsaturated aldehyde acts as a chain transfer agent.

[0033] Examples of the structural unit derived from the aliphatic unsaturated aldehyde that the PVA preferably has include structural units represented by the following formula (3) or (4).

[0034]

Chemical formula

[0035] In formulas (3) and (4), R 2 ~R 7 are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. q is an integer of 1 to 11. r is an integer of 1 to 11.

[0036] R in formula (3) 2 ~R 4is preferably a hydrogen atom. q is preferably an integer between 2 and 9, and more preferably an integer between 3 and 7. The structural unit represented by formula (3) is usually formed when an aliphatic unsaturated aldehyde acts as a monomer and is introduced into the polymer chain.

[0037] R in equation (4) 5 ~R 7 is preferably a hydrogen atom. r is preferably an integer between 2 and 9, and more preferably an integer between 3 and 7. The structural unit represented by formula (4) is usually formed when the formyl group in the structural unit represented by formula (3) acts as a chain transfer agent.

[0038] The PVA preferably has tertiary carbon atoms (carbon atoms directly bonded to three carbon atoms). Furthermore, the PVA preferably has structural units containing tertiary carbon atoms. In such cases, i.e., when the PVA has a branched structure, various performance characteristics are improved when used, for example, as a dispersant for suspension polymerization. For example, if the PVA has structural units represented by formula (3) or (4) above, R 2 ~R 7 If the atom is a hydrogen atom, the PVA has a tertiary carbon atom.

[0039] The PVA may have structural units other than those derived from vinyl esters (vinyl alcohol units and vinyl ester units) and aliphatic unsaturated aldehydes. Monomers that give the above-mentioned other structural units include α-olefins such as ethylene, propylene, 1-butene, isobutene, and 1-hexene; acrylic acid and methacrylic acid; acrylic acid esters such as methyl acrylate and ethyl acrylate; methacrylic acid esters such as methyl methacrylate and ethyl methacrylate; acrylamide derivatives such as N-methylacrylamide, N-ethylacrylamide, and 2-acrylamide-2-methylpropanesulfonic acid; methacrylamide derivatives such as N-methylmethacrylamide and N-ethylmethacrylamide; maleic acid; maleic acid esters such as monomethyl maleate and dimethyl maleate; fumaric acid; fumaric acid esters such as monomethyl fumarate and dimethyl fumarate; itaconic acid; 3,4-diacetoxy-1-butene; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and n-butyl vinyl ether; ethyl Examples include hydroxyl group-containing vinyl ethers such as glycol vinyl ether, 1,3-propanediol vinyl ether, and 1,4-butanediol vinyl ether; allyl acetate; allyl ethers such as propyl allyl ether, butyl allyl ether, and hexyl allyl ether; monomers having an oxyalkylene group; isopropenyl acetate; hydroxyl group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 9-decen-1-ol, and 3-methyl-3-buten-1-ol; and monomers having a silyl group such as vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3-(meth)acrylamidopropyltrimethoxysilane, and 3-(meth)acrylamidopropyltriethoxysilane.

[0040] The proportion of the above-mentioned other structural units in the total structural units of the PVA is preferably 20 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or 1 mol%. On the other hand, the proportion of the above-mentioned other structural units may be, for example, 0.1 mol% or more, or 1 mol% or more.

[0041] The lower limit of the viscosity-average degree of polymerization of the PVA may be, for example, 50 or 100, but 200 is preferred, 300 is more preferred, 400 is even more preferred, and 500 is even more preferred. When the viscosity-average degree of polymerization is above the above lower limit, the protective colloidal properties are enhanced, and various properties are improved, for example, when used as a dispersant for suspension polymerization. On the other hand, the upper limit of this viscosity-average degree of polymerization is preferably 2,000, more preferably 1,500, even more preferably 1,000, and even more preferably 800. When the viscosity-average degree of polymerization is below the above upper limit, the surfactant properties are enhanced, and various properties are improved, for example, when used as a dispersant for suspension polymerization. On the other hand, when the PVA is used as a dispersion aid for suspension polymerization, the lower limit of the viscosity-average degree of polymerization of the PVA may be, for example, 50, more preferably 70, even more preferably 100, even more preferably 120, particularly preferably 160, and even more preferably 200. In such cases, the upper limit of the viscosity-average degree of polymerization of the PVA is preferably 800, more preferably 700, and even more preferably 600. The viscosity-average degree of polymerization is a value measured in accordance with JIS K6726:1994. That is, after resaponifying the PVA to a degree of saponification of 99.5 mol% or more and purifying it, the intrinsic viscosity [η] (unit: liters / g) measured in water at 30°C can be calculated using the following formula. Viscosity average degree of polymerization=([η]×10 4 (8.29) (1 / 0.62)

[0042] The PVA according to the second embodiment of the present invention has a group represented by the following formula (2) at the end of the polymer chain.

[0043] [ka]

[0044] In formula (2), R 1 This is an alkenyl group. The specific form and preferred form of the group (terminal group) represented by formula (2) above is as described above. As described above, the group represented by formula (2) above is introduced to the end of the polymer chain when a vinyl ester is polymerized in the presence of an aliphatic unsaturated aldehyde, and the aliphatic unsaturated aldehyde acts as a chain transfer agent. The PVA may consist of only one type of PVA, or it may be a mixture of two or more types of PVA. The specific form and preferred form of the PVA according to the second embodiment of the present invention is the same as the specific form and preferred form of the PVA according to the first embodiment of the present invention described above, except that it is not essential that "the same or different molecules have a carbonyl group, a formyl group, and an alkenyl group."

[0045] The PVA of the present invention may have carbon-carbon double bonds in addition to the above-mentioned alkenyl group, particularly -CO-(CH=CH) p It is preferable to have a structure represented by -(p is an integer from 1 to 5). Such a structure is introduced, for example, by heat-treating the PVA of the present invention.

[0046] The PVA of the present invention can be used in a variety of applications similar to conventionally known PVAs, such as raw materials for films and fibers, additives for paper and fiber processing, adhesives, dispersants and dispersing aids for emulsion polymerization and suspension polymerization, and inorganic binders. Among these, as will be described in detail later, it can be used particularly suitably as a dispersant and dispersing aid for suspension polymerization of vinyl compounds and the like.

[0047] <Method for producing vinyl alcohol-based polymers> The method for producing vinyl alcohol-based polymers of the present invention is as follows: A step of polymerizing vinyl esters in the presence of aliphatic unsaturated aldehydes (Step A), and Step B: Saponification of the obtained vinyl ester polymer. It is equipped with.

[0048] (Process A) In step A, a vinyl ester polymer is obtained by polymerizing a vinyl ester in the presence of an aliphatic unsaturated aldehyde. Examples of known methods for polymerizing vinyl esters include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Of these methods, bulk polymerization, which is carried out without a solvent, and solution polymerization, which uses a solvent such as an alcohol, are preferred. The alcohol is preferably one with 3 or fewer carbon atoms, more preferably methanol, ethanol, n-propanol, and isopropanol, and even more preferably methanol. When carrying out the polymerization reaction using these methods, either a batch or continuous reaction method can be employed. There are no particular restrictions on the polymerization temperature during the polymerization reaction, but a range of 5°C to 200°C is appropriate.

[0049] Examples of the vinyl esters mentioned above include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among these, vinyl acetate is preferred.

[0050] Examples of polymerization initiators used in polymerization reactions include azo-based initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile); and known polymerization initiators such as organic peroxide-based initiators such as benzoyl peroxide, n-propyl peroxycarbonate, and diisopropyl peroxydicarbonate. The amount of polymerization initiator used is preferably 0.01 to 5% by mass relative to the vinyl ester used.

[0051] Specific examples and preferred examples of aliphatic unsaturated aldehydes to be present during the polymerization of vinyl esters are as described above. One or more types of aliphatic unsaturated aldehydes can be used. The amount of aliphatic unsaturated aldehyde used is preferably, for example, 0.1 to 10% by mass relative to the vinyl ester. Other chain transfer agents other than aliphatic unsaturated aldehydes may be present during the polymerization of vinyl esters. Examples of other chain transfer agents include aliphatic saturated aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde, 1-pentanal, 1-hexanal, 1-octanal, 1-nonanal, and 1-decanal; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol and 3-mercaptopropionic acid; thiocarboxylic acids such as thioacetic acid; and halogenated hydrocarbons such as trichloroethylene and perchloroethylene.

[0052] When polymerizing vinyl esters, copolymerizable monomers can be further copolymerized without impairing the spirit of the present invention. Examples of such copolymerizable monomers include those described above, which provide other structural units.

[0053] (Process B) In step B, the vinyl ester polymer obtained in step A is saponified, for example, in an alcohol solution using an alkaline or acidic catalyst to obtain PVA. For the saponification reaction of vinyl ester polymers, conventionally known basic catalysts such as sodium hydroxide, potassium hydroxide, or sodium methoxide, or acidic catalysts such as p-toluenesulfonic acid, can be used for alcohol decomposition or hydrolysis reactions. Solvents used in the saponification reaction include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; and aromatic hydrocarbons such as benzene and toluene. These can be used individually or in combination of two or more. Among these, it is convenient and preferable to use methanol or a mixed solution of methanol and methyl acetate as the solvent and carry out the saponification reaction in the presence of sodium hydroxide, which is a basic catalyst. Saponification can be carried out using a belt reactor, a kneader reactor, a tower reactor, etc.

[0054] A resin solid containing PVA is obtained by going through step B. The manufacturing method may further include steps after step B such as a step of washing the resin solid containing PVA, a step of drying the resin solid containing PVA, and a step of heat treating the resin solid containing PVA.

[0055] <Dispersant for suspension polymerization> The dispersant for suspension polymerization of the present invention (hereinafter also referred to as "dispersant") contains the PVA of the present invention as described above. A dispersant is an additive used to improve the dispersibility of monomers during suspension polymerization and to control the particle size of the resulting polymer particles. The lower limit of the PVA content in the nonvolatile content of the dispersant of the present invention is preferably 30% by mass, more preferably 50% by mass, and may be even more preferably 70% by mass, 90% by mass, or 99% by mass. The upper limit of the PVA content in the nonvolatile content of the dispersant of the present invention may be 100% by mass. Nonvolatile components other than the PVA that may be included in the dispersant of the present invention include PVA other than the PVA of the present invention, resins other than PVA, additives such as surfactants and plasticizers, and various compounds used during production. The lower limit of the total PVA content in the nonvolatile content of the dispersant of the present invention is preferably 50% by mass, more preferably 70% by mass, and may be even more preferably 80% by mass, 90% by mass, or 99% by mass. The upper limit of the total PVA content in the nonvolatile content of the dispersant of the present invention may be 100% by mass. Furthermore, the volatile content in the dispersant of the present invention is usually 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less. Examples of volatile components that may be contained in the dispersant of the present invention include alcohol and water. In other words, the dispersant of the present invention may be substantially composed of the PVA of the present invention. The shape of the dispersant of the present invention is not particularly limited, but is usually in powder form.

[0056] The dispersant of the present invention is suitable as a dispersant for suspension polymerization of vinyl compounds. By using the dispersant of the present invention, polymerization stability is enhanced, and polymer particles with a small average particle size and few coarse particles can be efficiently obtained. Furthermore, polymer particles obtained by suspension polymerization using the dispersant of the present invention also have good plasticizer absorption properties.

[0057] <Dispersing aid for suspension polymerization> The dispersion aid for suspension polymerization of the present invention (hereinafter also referred to as "dispersion aid") contains the PVA of the present invention as described above. A dispersion aid is an additive that is usually used together with a dispersant, particularly to increase the porosity of the resulting polymer particles. Furthermore, dispersibility can be further improved by using a dispersion aid together with a dispersant. The lower limit of the content of the PVA in the nonvolatile content of the dispersion aid of the present invention is preferably 30% by mass, more preferably 50% by mass, and may be even more preferably 70% by mass, 90% by mass, or 99% by mass. The upper limit of the content of the PVA in the nonvolatile content of the dispersion aid of the present invention may be 100% by mass. Nonvolatile components other than the PVA that may be included in the dispersion aid of the present invention include PVA other than the PVA of the present invention, resins other than PVA, additives such as surfactants and plasticizers, and various compounds used during production. The lower limit of the total PVA content in the nonvolatile content of the dispersion aid of the present invention is preferably 50% by mass, more preferably 70% by mass, and may be even more preferably 80% by mass, 90% by mass, or 99% by mass. The upper limit of the total PVA content in the non-volatile components of the dispersion aid of the present invention may be 100% by mass. Furthermore, the volatile component content in the dispersion aid of the present invention is usually 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less. Examples of volatile components that may be included in the dispersion aid of the present invention include alcohol and water. In other words, the dispersion aid of the present invention may consist substantially of the PVA of the present invention. The form of the dispersion aid of the present invention is not particularly limited, but is usually in powder form.

[0058] The dispersion agent of the present invention is suitable as a dispersion agent for suspension polymerization of vinyl compounds. By using the dispersion agent of the present invention, polymerization stability is enhanced, and polymer particles with a small average particle size and few coarse particles can be efficiently obtained. Furthermore, polymer particles obtained by suspension polymerization using the dispersion agent of the present invention also have good plasticizer absorption properties.

[0059] <Method for producing vinyl polymers> The present invention provides a method for producing vinyl polymers, comprising the step of suspension polymerization of a vinyl compound using PVA (the dispersant or dispersing aid of the present invention). This method is the same as known methods for producing vinyl polymers, except that PVA of the present invention is used as the dispersant or dispersing aid.

[0060] The method for producing vinyl polymers of the present invention typically involves suspension polymerization of a vinyl compound in an aqueous medium using the PVA of the present invention. As the aqueous medium, in addition to pure water, an aqueous solution containing various additive components or an aqueous medium containing other organic solvents can be used.

[0061] When performing suspension polymerization of vinyl compounds, there are no particular restrictions on the amount of PVA added according to the present invention, but it is preferably 100 ppm to 50,000 ppm by mass relative to the vinyl compound, more preferably 200 ppm to 20,000 ppm, and even more preferably 10,000 ppm or less, 5,000 ppm or less, or 2,000 ppm or less.

[0062] The PVA of the present invention may be used alone, or it may be used in combination with other dispersants. Examples of other dispersants include water-soluble cellulose ethers such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose, which are commonly used when suspend polymerization of vinyl compounds in an aqueous medium; water-soluble polymers such as PVA other than the PVA of the present invention and gelatin; oil-soluble emulsifiers such as sorbitan monolaurate, sorbitan triolate, glycerin tristearate, and ethylene oxide-propylene oxide block copolymer; and water-soluble emulsifiers such as polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerin oleate, and sodium laurate.

[0063] In the method for producing vinyl polymers of the present invention, polymerization initiators conventionally used in the polymerization of vinyl compounds can be used, and specifically, polymerization initiators similar to those exemplified in the polymerization of vinyl ester monomers can be used.

[0064] In the method for producing vinyl polymers of the present invention, various other additives may be added to the polymerization system as needed. Examples of additives include polymerization regulators such as aldehydes, halogenated hydrocarbons, and mercaptans, and polymerization inhibitors such as phenol compounds, sulfur compounds, and N-oxide compounds. pH adjusters, scale inhibitors, and crosslinking agents may also be added. Multiple of the above additives may be used in combination.

[0065] Examples of vinyl compounds that can be subjected to suspension polymerization in the method for producing vinyl polymers of the present invention include vinyl halides such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid, methacrylic acid, their esters and salts; maleic acid, fumaric acid, their esters and anhydrides; styrene; acrylonitrile; vinylidene chloride; vinyl ether, etc. Among these vinyl compounds, vinyl chloride is preferred. The method for producing vinyl polymers of the present invention is particularly suitable for suspension polymerization of vinyl chloride alone or together with monomers capable of copolymerizing vinyl chloride. Examples of monomers capable of copolymerizing with 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.

[0066] In the method for producing vinyl polymers of the present invention, when a vinyl compound is subjected to suspension polymerization, the charging ratio of each component, polymerization temperature, polymerization time, etc., can be the same as the conditions used in the conventional suspension polymerization of vinyl compounds such as vinyl chloride. Furthermore, there are no restrictions on the charging order or ratio of the vinyl compound, polymerization initiator, dispersant, aqueous medium, and other additives.

[0067] The method for producing vinyl polymers according to the present invention makes it possible to efficiently obtain vinyl polymer particles that have high stability during polymerization, a small average particle size, and few coarse particles. Furthermore, the vinyl polymer particles obtained by the production method of the present invention also have good plasticizer absorption properties. [Examples]

[0068] The present invention will be specifically described by the following examples, but the present invention is not limited in any way by these examples. The measurement methods used in the following examples and comparative examples are shown below.

[0069] [Viscosity-average degree of polymerization of PVA] The viscosity-average degree of polymerization of PVA was measured in accordance with JIS K6726:1994. Specifically, if the degree of saponification of PVA was less than 99.5 mol%, it was saponified until the degree of saponification was 99.5 mol% or higher. The viscosity-average degree of polymerization of the obtained PVA was then calculated using the following formula with the intrinsic viscosity [η] (liters / g) measured in water at 30°C. Viscosity average degree of polymerization=([η]×10 4 (8.29) (1 / 0.62)

[0070] [Degree of saponification of PVA] The degree of saponification of PVA was determined by the method described in JIS K6726:1994.

[0071] [Carbonyl group content of PVA] 1The carbonyl group content of PVA was calculated by 1H-NMR measurement. Samples were subjected to Soxhlet washing with methyl acetate for 10 hours and vacuum drying at 40°C for 16 hours to remove impurities before measurement. Samples prepared as 1 mass% DMSO-d6 solution (with 0.03 mass% tetramethylsilane added as an internal standard) were measured at 400 MHz (80°C, 256 cumulative measurements). Among the methine groups in the PVA main chain, the CH peak linked to the OH group appeared at 3.8–4.0 ppm (integral value [M]), and the CH peak linked to the OAc group appeared at 4.2–4.6 ppm (integral value [N]). In addition, the peaks of the formyl group and the methylene group adjacent to the carbonyl group appeared at 2.3–2.5 ppm (integral value [O]). Furthermore, the peak of the proton constituting the formyl group appeared at 9.5–10.0 ppm (integral value [P]). The carbonyl group content of PVA was determined as a value relative to structural units (vinyl alcohol units and vinyl ester units) derived from vinyl alcohol monomers, using the following formula. Carbonyl group content (mol %) = [{([O] / 2)-[P]} / ([M]+[N])] × 100

[0072] [Alkenyl group content of PVA] 1¹H-NMR measurements were performed to calculate the alkenyl group (vinyl group) content of PVA. Samples were subjected to Soxhlet washing with methyl acetate for 10 hours and vacuum drying at 40°C for 16 hours to remove impurities before measurement. Samples prepared as 1 mass% DMSO-d6 solution (with 0.03 mass% tetramethylsilane added as an internal standard) were measured at 400 MHz (80°C, 256 cumulative measurements). Among the methine groups in the PVA main chain, the CH peak linked to the OH group appeared at 3.8–4.0 ppm (integral value [M]), and the CH peak linked to the OAc group appeared at 4.2–4.6 ppm (integral value [N]). In addition, the peak for one proton constituting the vinyl group in the alkenyl group (H at position 1 in the ethenyl group; CH2=C"H"-) appeared at 5.7–6.0 ppm (integral value [Q]). The alkenyl group content of PVA was determined as a value relative to structural units (vinyl alcohol units and vinyl ester units) derived from vinyl alcohol monomers, using the following formula. Alkenyl group content (mol%) = {[Q] / ([M]+[N])} × 100

[0073] [Formyl group content of PVA] 1 The formyl group content of PVA was calculated by 1H-NMR measurement. Samples were subjected to Soxhlet washing with methyl acetate for 10 hours and vacuum drying at 40°C for 16 hours to remove impurities before measurement. Samples prepared as 1 mass% DMSO-d6 solution (with 0.03 mass% tetramethylsilane added as an internal standard) were measured at 400 MHz (80°C, 256 cumulative measurements). Among the methine groups in the PVA main chain, the CH peak with an OH group attached appeared at 3.8-4.0 ppm (integral value [M]), and the CH peak with an OAc group attached appeared at 4.2-4.6 ppm (integral value [N]). The proton peak constituting the formyl group appeared at 9.5-10.0 ppm (integral value [P]). The formyl group content of PVA was determined as a value relative to structural units (vinyl alcohol units and vinyl ester units) derived from vinyl alcohol monomers using the following formula. Formyl group content (mol %) = {[P] / ([M]+[N])} × 100

[0074] [Example 1] (Production of PVA-1) In a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, and polymerization initiator inlet, 1600 parts by mass of vinyl acetate and 35.0 parts by mass of 7-octenal were charged, and the system was purged with nitrogen for 30 minutes while bubbling with nitrogen. The reactor was heated, and when the internal temperature reached 60°C, 2.4 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added to start polymerization. Polymerization was carried out at 60°C for 3 hours, and then cooled to stop the polymerization. At the time of polymerization cessation, the solid content concentration was 44.3% by mass, and the polymerization rate was 45%. Subsequently, unreacted monomers were removed by occasionally adding methanol at 30°C under reduced pressure to obtain a methanol solution of the vinyl ester polymer (concentration 38.2% by mass). Next, 58.0 parts by mass of a methanol solution of a vinyl ester polymer (34 parts by mass of the polymer in the solution) was prepared by adding more methanol to the methanol solution. To this, 1.0 part by mass of a 10% methanol solution of sodium hydroxide, 0.88 parts by mass of deionized water, and 10 parts by mass of methyl acetate were added, and saponification was carried out at 40°C (polymer concentration in the saponification solution: 30% by mass, water content of the saponification solution: 1% by mass, molar ratio of sodium hydroxide to vinyl acetate units in the polymer: 0.0072). A gel-like substance was formed about 15 minutes after the addition of the methanol solution of sodium hydroxide, so this was pulverized in a pulverizer and left to stand at 40°C for 1 hour to allow saponification to proceed. After that, 160 parts by mass of methyl acetate and 40 parts by mass of methanol were added, and the mixture was washed by standing at 40°C for 30 minutes. After repeating this washing operation twice, the white solid obtained by deliquing was vacuum dried at 40°C for 16 hours to obtain PVA (PVA-1). The physical properties of PVA-1 are shown in Table 2.

[0075] [Examples 2, 3, 6-8, 10, 11, 14, Comparative Example 1] (Manufacturing of PVA-2, 3, 6-8, 10, 11, 14, 15) Examples 2, 3, 6-8, 10, 11, 14, and Comparative Example 1 (PVA-2, 3, 6-8, 10, 11, 14, 15) were produced in the same manner as in Example 1, except that the polymerization conditions, such as the amount of vinyl acetate charged, the type and amount of aldehyde (a) used during polymerization, the concentration of the vinyl ester polymer during saponification, and the saponification conditions, such as the molar ratio of sodium hydroxide to vinyl acetate units, were changed as shown in Table 1. In Examples 6-8 and 14, a chain transfer agent (b) was also used along with aldehyde (a) as shown in Table 1. The physical properties of PVA-2, 3, 6-8, 10, 11, 14, and 15 are shown in Table 2.

[0076] [Example 4] (Production of PVA-4) In a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, chain transfer agent dropper port, and polymerization initiator port, 960 parts by mass of vinyl acetate, 640 parts by mass of methanol, and 17.5 parts by mass of 7-octenal were charged, and the system was purged with nitrogen for 30 minutes while bubbling with nitrogen. The reactor was heated, and when the internal temperature reached 60°C, 1.5 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added to start polymerization. Polymerization was carried out at 60°C for 3 hours, and then cooled to stop the polymerization. At the time of polymerization cessation, the solid content concentration was 39.4% by mass, and the polymerization rate was 65%. Subsequently, unreacted monomers were removed by occasionally adding methanol at 30°C under reduced pressure to obtain a methanol solution of the vinyl ester polymer (concentration 40.5% by mass). Next, 58.1 parts by mass of a methanol solution of a vinyl ester polymer (30 parts by mass of the polymer in the solution) was prepared by adding more methanol to the methanol solution. To this, 1.0 part by mass of a 10% methanol solution of sodium hydroxide, 0.88 parts by mass of deionized water, and 10 parts by mass of methyl acetate were added, and saponification was carried out at 40°C (polymer concentration in the saponification solution: 30% by mass, water content of the saponification solution: 1% by mass, molar ratio of sodium hydroxide to vinyl acetate units in the polymer: 0.0075). A gel-like substance was formed about 10 minutes after the addition of the methanol solution of sodium hydroxide, so this was pulverized in a pulverizer and left at 40°C for 1 hour to allow saponification to proceed. After that, 160 parts by mass of methyl acetate and 40 parts by mass of methanol were added, and the mixture was washed by leaving it at 40°C for 30 minutes. After repeating this washing operation twice, the white solid obtained by deliquing was vacuum dried at 40°C for 16 hours to obtain PVA (PVA-4). The physical properties of PVA-4 are shown in Table 2.

[0077] [Examples 5, 9, Comparative Example 3] (Manufacturing of PVA-5, 9, 17) PVAs (PVA-5, 9, and 17) for Examples 5, 9, and Comparative Example 3 were produced in the same manner as in Example 4, except that the polymerization conditions, such as the amounts of vinyl acetate and methanol used, the type and amount of aldehyde (a) used during polymerization, the concentration of the vinyl ester polymer during saponification, and the saponification conditions, such as the molar ratio of sodium hydroxide to vinyl acetate units, were changed as shown in Table 1. In Comparative Example 3, aldehyde (a) was not used during production. The physical properties of PVAs 5, 9, and 17 are shown in Table 2.

[0078] [Example 12] (PVA-12) In a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, chain transfer agent dropper port, and polymerization initiator port, 1050 parts by mass of vinyl acetate, 450 parts by mass of methanol, and 9.0 parts by mass of 7-octenal were charged, and the system was purged with nitrogen for 30 minutes while bubbling with nitrogen. The reactor was heated, and when the internal temperature reached 60°C, 1.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added to start polymerization. A methanol solution of 3-mercaptopropionic acid (concentration 6% by mass) was added dropwise as the chain transfer agent (b) to the reactor. The mixture was added dropwise while maintaining a constant composition ratio with vinyl acetate in the polymerization solution (total amount added: 43.3 parts by mass), and polymerization was carried out at 60°C for 4 hours, after which it was cooled to stop polymerization. At the time of polymerization cessation, the solid content concentration was 27.6% by mass, and the polymerization rate was 40%. Next, unreacted monomers were removed by adding methanol occasionally under reduced pressure at 30°C to obtain a methanol solution of the vinyl ester polymer (concentration 54.0% by mass). Then, 93.7 parts by mass of the methanol solution of the vinyl ester polymer (42.6 parts by mass of the polymer in the solution), prepared by adding more methanol to this methanol solution, were to be mixed with 6.3 parts by mass of a 10% by mass methanol solution of sodium hydroxide and 0.88 parts by mass of deionized water, and saponification was carried out at 40°C (polymer concentration in the saponified solution 40% by mass, water content of the saponified solution 1% by mass, molar ratio of sodium hydroxide to vinyl acetate units in the polymer 0.0298). The mixture was left at 40°C for 1 hour to allow saponification to proceed. After that, 160 parts by mass of methyl acetate and 40 parts by mass of methanol were added, and the mixture was left to stand and washed at 40°C for 30 minutes. After repeating this washing operation twice, the white solid obtained by deliquing was vacuum dried at 40°C for 16 hours to obtain PVA (PVA-12). The physical properties of PVA-12 are shown in Table 2.

[0079] [Example 13] (Manufacturing of PVA-13) PVA-13 of Example 13 was produced in the same manner as in Example 12, except that the polymerization conditions, such as the amounts of vinyl acetate and methanol used, the amount of aldehyde (a) and chain transfer agent (b) 3-mercaptopropionic acid used during polymerization, the concentration of the vinyl ester polymer during saponification, and the saponification conditions, such as the molar ratio of sodium hydroxide to vinyl acetate units, were changed as shown in Table 1.

[0080] [Comparative Example 2] (Manufacturing of PVA-16) 100 parts by mass of the PVA-16 powder obtained above was immersed in 500 parts by mass of a methanol solution (0.5% by mass) of 7-octenal for 3 hours. Then, 30 parts by mass of a 1N hydrochloric acid aqueous solution was added and the reaction was carried out at 40°C for 2 hours. After that, the mixture was neutralized with 30 parts by mass of a 1N sodium hydroxide aqueous solution and the reaction solution was removed by filtration. Then, 160 parts by mass of methyl acetate and 40 parts by mass of methanol were added and the mixture was washed by standing at 40°C for 30 minutes. After repeating this washing operation twice, the white solid obtained by deliquing was dried at 70°C for 16 hours to produce acetalized PVA (PVA-16) of Comparative Example 2. The physical properties of PVA-16 are shown in Table 2.

[0081] [evaluation] The PVA obtained in Examples 1-11 and Comparative Examples 1-3 were used as dispersants for suspension polymerization, and vinyl chloride was subjected to suspension polymerization using the method described below. Subsequently, the average particle size, amount of coarse particles, and plasticizer absorption capacity of the resulting vinyl chloride polymer particles were evaluated. The evaluation results are shown in Table 2.

[0082] (Suspension polymerization of vinyl chloride) Each PVA listed in Table 2 was dissolved in deionized water to an amount equivalent to 1000 ppm relative to vinyl chloride to prepare dispersant aqueous solution (A), and 100 parts by mass of this solution were charged into a 5 L autoclave. Furthermore, as PVA (B), a vinyl alcohol polymer with a viscosity-average degree of polymerization of 450 and a degree of saponification of 40 mol% was dissolved in deionized water to an amount equivalent to 300 ppm relative to vinyl chloride to prepare dispersant aqueous solution (B), and 100 parts by mass were charged into the autoclave. Next, deionized water was added to bring the total amount of deionized water to 1200 parts by mass. Then, 0.65 parts by mass of a 70% by mass toluene solution of cumyl peroxyneodecanoate and 1.05 parts by mass of a 70% by mass toluene solution of t-butyl peroxyneodecanoate were charged into the autoclave. The autoclave was degassed to remove oxygen until the pressure inside the autoclave reached 0.0067 MPa. Subsequently, 800 parts by mass of vinyl chloride were added, and the contents of the autoclave were heated to 57°C. Polymerization was started under stirring. The pressure inside the autoclave at the start of polymerization was 0.83 MPa. After 3.5 hours from the start of polymerization, when the pressure inside the autoclave reached 0.70 MPa, polymerization was stopped and unreacted vinyl chloride was removed. The polymerization slurry was then removed and dried at 65°C for 17 hours to obtain vinyl chloride polymer particles.

[0083] (1) Average particle size of vinyl chloride polymer particles The obtained vinyl chloride polymer particles were analyzed for particle size distribution by dry sieving using a wire mesh based on Tyler mesh standards. The results were plotted on the Rosin-Rammler distribution formula to determine the average particle size (d p50 The median diameter was calculated.

[0084] (2) Amount of coarse vinyl chloride polymer particles The amount of polyvinyl chloride polymer particles that did not pass through a sieve with a mesh size of 250 μm (equivalent to 60 mesh in JIS standard sieve standards) was determined by mass percentage. A smaller value indicates fewer coarse particles and suggests that the dispersant used (PVA) has excellent polymerization stability.

[0085] (3) Plasticizer absorption (CPA) of vinyl chloride polymer particles The mass of a 5 mL syringe filled with 0.02 g of absorbent cotton was weighed (denoted as A(g)), and 0.5 g of polyvinyl chloride polymer particles was added to it and weighed (denoted as B(g)). 1 g of dioctyl phthalate (DOP) was added and allowed to stand for 15 minutes. Then, the unabsorbed DOP was removed by centrifugation at 3000 rpm for 40 minutes, and the mass after removal was weighed (denoted as C(g)). The plasticizer absorbency (%) of the polyvinyl chloride polymer particles was then calculated using the following formula. Higher plasticizer absorbency indicates easier processing and less likelihood of defects such as bumps that occur in appearance, mainly during sheet processing. In this evaluation, a plasticizer absorbency of 28.0% or higher was considered to indicate good plasticizer absorbency. Plasticizer absorption (%) = 100 × [{(CA) / (BA)} - 1]

[0086] [Table 1]

[0087] [Table 2]

[0088] As shown in Table 2, each PVA in Examples 1 to 11 has a carbonyl group, a formyl group, and an alkenyl group. When these were used as dispersants for suspension polymerization, vinyl chloride polymer particles with a small average particle size, few coarse particles, and good plasticizer absorption were obtained. It was confirmed that each PVA in Examples 1 to 11 is useful as a dispersant for suspension polymerization. Furthermore, given that aliphatic unsaturated aldehydes were present during synthesis, and that alkenyl and carbonyl groups were confirmed to be present in the PVA, it can be inferred that the group represented by formula (2) above was formed at the end of the polymer chain in each of the PVAs in each example.

[0089] On the other hand, PVA-15 in Comparative Example 1 lacked alkenyl and formyl groups, resulting in a large average particle size and a high proportion of coarse particles in the resulting vinyl chloride polymer particles. PVA-16 in Comparative Example 2 also lacked carbonyl and formyl groups, resulting in a large average particle size and a high proportion of coarse particles in the resulting vinyl chloride polymer particles. Furthermore, the plasticizer absorption capacity of the resulting vinyl chloride polymer particles was low. In PVA-17 in Comparative Example 3, the vinyl chloride polymer became blocky, making evaluation impossible. [Industrial applicability]

[0090] The PVA of the present invention can be used as a dispersant in the suspension polymerization of vinyl compounds, etc.

Claims

1. Having a carbonyl group, a formyl group and an alkenyl group in the same or different molecules, The above carbonyl group is a divalent group in which both bonds are bonded to a carbon atom. A vinyl alcohol-based polymer having a group represented by the following formula (5) containing the above-mentioned alkenyl group at the end of the polymer chain. 【Chemistry 1】 In equation (5), n is an integer between 1 and 11.

2. The vinyl alcohol-based polymer according to claim 1, having a structure represented by the following formula (1) containing the above carbonyl group. 【Chemistry 2】 In equation (1), m is an integer between 1 and 11.

3. A vinyl alcohol-based polymer according to claim 1 or 2, having a tertiary carbon atom.

4. A vinyl alcohol-based polymer according to any one of claims 1 to 3, having a structural unit derived from an aliphatic unsaturated aldehyde.

5. The vinyl alcohol-based polymer according to claim 4, wherein the aliphatic unsaturated aldehyde has 3 to 14 carbon atoms.

6. The vinyl alcohol-based polymer according to claim 4 or 5, wherein the aliphatic unsaturated aldehyde has a carbon-carbon double bond at its terminus.

7. A step of polymerizing vinyl esters in the presence of aliphatic unsaturated aldehydes, and Steps to saponify the obtained vinyl ester polymer. A method for producing a vinyl alcohol-based polymer according to any one of claims 1 to 6, comprising:

8. A dispersant for suspension polymerization comprising a vinyl alcohol-based polymer according to any one of claims 1 to 6.

9. A dispersion aid for suspension polymerization comprising a vinyl alcohol-based polymer according to any one of claims 1 to 6.

10. A method for producing a vinyl polymer, comprising the step of polymerizing a vinyl compound in the presence of a vinyl alcohol polymer according to any one of claims 1 to 6.

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