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

Abstract

Provided are a novel vinyl alcohol-based polymer and a method for producing the same, and a method for producing a vinyl-based polymer, a dispersant for suspension polymerization, a dispersion aid for suspension polymerization, and polymer particles having a small average particle diameter, few coarse particles, and good plasticizer absorption, which can be obtained by the method. The present invention is a vinyl alcohol-based polymer having a carbonyl group, a formyl group, and an alkenyl group in the same or different molecules. In addition, the present invention is a method for producing a vinyl alcohol-based polymer, which includes a step of polymerizing a vinyl ester in the presence of an aliphatic unsaturated aldehyde, and a step of saponifying the obtained vinyl ester-based polymer.

Description

Technical Field

[0001] This invention relates to vinyl alcohol polymers, methods for manufacturing vinyl alcohol polymers, dispersants for suspension polymerization, dispersing aids for suspension polymerization, and methods for manufacturing 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 fiber processing, an adhesive, a dispersant (also known as a dispersion stabilizer, etc.) and dispersing aid for emulsion polymerization and suspension polymerization, and a binder for inorganic materials.

[0003] To improve the performance of PVA, various modified PVAs have been put into practical use or are under development. For example, Patent Document 1 describes a dispersion stabilizer for suspension polymerization, characterized in that it contains a polyvinyl alcohol polymer (B) with double bonds in its side chains, wherein the polyvinyl alcohol polymer (B) is obtained by acetalizing the polyvinyl alcohol polymer (A) with a monoaldehyde having olefinic unsaturated double bonds.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2015 / 182567 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] To further enhance the performance of PVA, new PVA technologies are needed. For example, when PVA is used as a dispersant in suspension polymerization, it is desirable to obtain polymer particles with small and uniform particle size and good plasticizer absorption.

[0009] The purpose of this invention is to provide novel vinyl alcohol-based polymers and their manufacturing methods, as well as dispersants for suspension polymerization, dispersing aids for suspension polymerization, and manufacturing methods for vinyl polymers that can produce polymer particles with small average particle size, few coarse particles, and good plasticizer absorption.

[0010] Methods for solving problems

[0011] The above objective is achieved by providing any of the following options.

[0012] [1] Vinyl alcohol polymers, which have carbonyl, formyl and alkenyl groups in the same or different molecules;

[0013] [2] According to [1], the vinyl alcohol polymer has the structure shown in the following formula (1) containing the carbonyl group described above;

[0014] [Chemistry 1]

[0015]

[0016] In equation (1), m is an integer from 1 to 11.

[0017] [3] A vinyl alcohol polymer having a group at the end of the polymer chain as shown in formula (2);

[0018] [Chemistry 2]

[0019]

[0020] In equation (2), R 1 It is an alkenyl group.

[0021] [4] According to the vinyl alcohol polymer of [3], wherein R in the above formula (2) is 1 The alkenyl group shown has a methylene group at the end on the carbonyl side;

[0022] [5] A vinyl alcohol polymer according to any one of [1] to [4] has tertiary carbon atoms;

[0023] [6] A vinyl alcohol polymer according to any one of [1] to [5], which has a structural unit derived from an aliphatic unsaturated aldehyde;

[0024] [7] According to the vinyl alcohol polymer of [6], wherein the number of carbon atoms of the above aliphatic unsaturated aldehyde is 3 to 14;

[0025] [8] According to [6] or [7], the vinyl alcohol polymers, wherein the above-mentioned aliphatic unsaturated aldehydes have carbon-carbon double bonds at the ends;

[0026] [9] A method for manufacturing vinyl alcohol polymers, comprising: a step of polymerizing vinyl esters in the presence of aliphatic unsaturated aldehydes; and a step of saponifying the resulting vinyl ester polymers.

[0027]

[10] A dispersant for suspension polymerization, comprising any one of the following vinyl alcohol polymers: [1] to [8];

[0028]

[11] A dispersant for suspension polymerization, comprising any one of the following vinyl alcohol polymers: [1] to [8];

[0029]

[12] A method for manufacturing vinyl polymers, comprising: a step of polymerizing a vinyl compound in the presence of any one of the vinyl alcohol polymers in [1] to [8].

[0030] Invention Effects

[0031] According to the present invention, novel vinyl alcohol-based polymers and methods for manufacturing the same are provided, as well as dispersants for suspension polymerization, dispersing aids for suspension polymerization, and methods for manufacturing vinyl polymers that can produce polymer particles with small average particle size, few coarse particles, and good plasticizer absorption. Detailed Implementation

[0032] <Vinyl Alcohol-based Polymers>

[0033] The vinyl alcohol polymer (PVA) of the first aspect of the present invention has carbonyl, formyl, and alkenyl groups in the same or different molecules. In this PVA, not all of the carbonyl, formyl, and alkenyl groups may be included in a single molecule. That is, the PVA may be, for example, a mixture of PVA(a) having two of the carbonyl, formyl, and alkenyl groups and PVA(b) having the remaining group. In this case, both PVA(a) and PVA(b) may have one or more of the carbonyl, formyl, and alkenyl groups. The PVA may be a mixture of three or more types of PVA. It should be noted that the form of PVA having all of the carbonyl, formyl, and alkenyl groups in a single molecule and the form of a mixture containing multiple PVAs having carbonyl, formyl, and alkenyl groups have substantially the same properties. Furthermore, it is generally very difficult to distinguish between these two forms through analysis or the like.

[0034] This PVA is a polymer having vinyl alcohol units as structural units. Typically, as detailed later, this PVA is obtained by polymerizing vinyl esters in the presence of aliphatic unsaturated aldehydes and then saponifying the resulting vinyl ester polymer. The lower limit of the degree of saponification of this PVA can be, for example, 20 mol%, 30 mol%, or 40 mol%, preferably 50 mol%, more preferably 60 mol%, and even more preferably 70 mol%. On the other hand, the upper limit of the above-mentioned degree of saponification can be 100 mol%, preferably 95 mol%, more preferably 90 mol%, even more preferably 85 mol%, and even more preferably 80 mol%. By setting the degree of saponification of this PVA within the above range, surface activity properties are optimized, thereby improving various properties when used, for example, as a dispersant for suspension polymerization (e.g., obtaining polymer particles with small average particle size and few coarse particles, and good plasticizer absorption). On the other hand, when this PVA is used as a dispersant for suspension polymerization, the lower limit of the degree of saponification of this PVA is, for example, preferably 20 mol%, and more preferably 30 mol%. As an upper limit for the degree of saponification of the PVA in this case, it is sometimes preferred, for example, to be 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.

[0035] The carbonyl group (-C(=O)-) in this PVA is a divalent group formed by two connecting bonds bonded together with a carbon atom. That is, the -C(=O)- in the formyl group (-C(=O)H) is not included in the carbonyl group of this PVA. The PVA preferably has a structure containing the carbonyl group as shown in the following formula (1).

[0036] [Chemistry 3]

[0037]

[0038] In equation (1), m is an integer from 1 to 11. m is sometimes preferably an integer from 2 to 9, and more preferably an integer from 3 to 7.

[0039] It should be noted that, in this specification, the numerical range recorded using "~" includes the values ​​recorded before and after "~" as the lower and upper limits.

[0040] The carbonyl content in the PVA, relative to the total content of vinyl alcohol units and vinyl ester units, is preferably 0.001 mol% or more and 5 mol% or less, more preferably 0.005 mol% or more and 1 mol% or less, further preferably 0.008 mol% or more and 0.1 mol% or less, and even more preferably 0.01 mol% or more and 0.05 mol% or less. When the carbonyl content in the PVA is within the above range, its various properties are improved when used as a dispersant for, for example, suspension polymerization. The carbonyl content is set as a value obtained by the method described in the examples below.

[0041] The formyl group in this PVA is a monovalent group represented by -C(=O)H.

[0042] 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% or more and 5 mol% or less, more preferably 0.03 mol% or more and 3 mol% or less, even more preferably 0.05 mol% or more and 2 mol% or less, and even more preferably 0.07 mol% or more and 1 mol% or less. When the formyl group content in the PVA is within the above range, various properties are improved when used as a dispersant for, for example, suspension polymerization. The above-mentioned formyl group content is set as a value obtained by the method described in the examples below.

[0043] The alkenyl group in this PVA is a monovalent group formed by removing any one hydrogen atom from an olefin. The number of carbon atoms in the alkenyl group is sometimes preferably 2 to 13, more preferably 3 to 12, even more preferably 4 to 11, and still more preferably 5 to 9. The alkenyl group can be linear or branched, but is preferably linear. The alkenyl group is preferably located at the end of the polymer chain.

[0044] The alkenyl group of the PVA preferably has a carbon-carbon double bond at the end (front). That is, the PVA preferably has a vinyl group at the end (front). The alkenyl group of the PVA is more preferably a group represented by the following formula (5).

[0045] [Chemistry 4]

[0046]

[0047] In equation (5), n is an integer from 1 to 11. n is sometimes preferably an integer from 2 to 9, and more preferably an integer from 3 to 7.

[0048] The content of alkenyl groups in the PVA, relative to the total content of vinyl alcohol units and vinyl ester units, is sometimes preferably 0.005 mol% or more and 5 mol% or less, more preferably 0.01 mol% or more and 3 mol% or less, further preferably 0.02 mol% or more and 1 mol% or less, and even more preferably 0.03 mol% or more and 0.5 mol% or less. When the alkenyl group content in the PVA is within the above range, various properties are improved when used as a dispersant for, for example, suspension polymerization. The alkenyl group content is set as a value obtained by the method described in the examples below. The suitable range of vinyl group content in the PVA, relative to the total content of vinyl alcohol units and vinyl ester units, is the same as the suitable range of alkenyl group content described above.

[0049] The PVA preferably has a terminal group derived from an aliphatic unsaturated aldehyde or a structural unit derived from an aliphatic unsaturated aldehyde. The number of carbon atoms in the aforementioned aliphatic unsaturated aldehyde is sometimes preferred to be 3 to 14, more preferably 4 to 12, and even more preferably 6 to 10.

[0050] The aforementioned aliphatic unsaturated aldehydes preferably have carbon-carbon double bonds, more preferably carbon-carbon double bonds at the terminal (front end). That is, the aforementioned aliphatic unsaturated aldehydes preferably contain vinyl groups. As the aforementioned aliphatic unsaturated aldehydes having carbon-carbon double bonds, aliphatic unsaturated aldehydes containing an alkenyl group with a methylene group at the end on the carbonyl side, i.e., an R-CH2- (R is an alkenyl) group. In other words, the aforementioned aliphatic unsaturated aldehydes are preferably aliphatic unsaturated aldehydes other than α,β-unsaturated aldehydes. By using aliphatic unsaturated aldehydes having the structure described above, the reactivity during polymerization is improved, and PVA with a sufficient amount of functional groups (carbonyl groups, etc.) is effectively obtained.

[0051] The aforementioned aliphatic unsaturated aldehydes are particularly preferred to be compounds represented by the following formula (6).

[0052] [Chemistry 5]

[0053]

[0054] In equation (6), p is an integer from 1 to 11. p is sometimes preferably an integer from 2 to 9, and more preferably an integer from 3 to 7.

[0055] Examples of 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.

[0056] As a preferred terminal group derived from aliphatic unsaturated aldehydes, the group shown in formula (2) below can be listed.

[0057] [Chemistry 6]

[0058]

[0059] In equation (2), R 1 It is an alkenyl group.

[0060] As R in equation (2) 1 The number of carbon atoms in the alkenyl group shown is sometimes preferably 2 to 13, more preferably 3 to 12, even more preferably 4 to 11, and even more preferably 5 to 9. R 1 The alkenyl group shown can be linear or branched, preferably linear. As R... 1 The alkenyl group shown is preferably a group with a methylene group at the end on the carbonyl side (a group shown as R-CH2- (R is an alkenyl group)), more preferably a group with a carbon-carbon double bond at the end (front end), and even more preferably a group shown in formula (5) above. The terminal group shown in formula (2) is usually formed when an aliphatic unsaturated aldehyde is used as a chain transfer agent.

[0061] As a preferred structural unit derived from aliphatic unsaturated aldehydes in this PVA, the structural units shown in formula (3) or (4) below can be listed.

[0062] [Chemistry 7]

[0063]

[0064] In equations (3) and (4), R 2 ~R 7 Each is independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. q is an integer from 1 to 11. r is an integer from 1 to 11.

[0065] R in equation (3) 2 ~R 4The preferred atom is hydrogen. q is sometimes also preferred to be an integer from 2 to 9, and more preferably an integer from 3 to 7. The structural unit shown in formula (3) is usually formed when an aliphatic unsaturated aldehyde is used as a monomer and is introduced into the polymer chain.

[0066] R in equation (4) 5 ~R 7 The preferred atom is hydrogen. r is sometimes also preferred to be an integer from 2 to 9, and more preferably an integer from 3 to 7. The structural unit shown in formula (4) is usually formed when the formyl group in the structural unit shown in formula (3) above is further used as a chain transfer agent.

[0067] 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 this case, i.e., when the PVA has a branched structure, its various properties are improved when used as a dispersant for suspension polymerization, for example. The PVA has, for example, the structural units shown in formula (3) or (4) above, and R... 2 ~R 7 When the atom is hydrogen, the PVA has tertiary carbon atoms.

[0068] The PVA can have structural units other than those derived from vinyl esters (vinyl alcohol units and vinyl ester units) and structural units derived from aliphatic unsaturated aldehydes. Examples of monomers providing these other structural units include α-olefins such as ethylene, propylene, 1-butene, isobutene, and 1-hexene; acrylic acid and methacrylic acid; acrylates such as methyl acrylate and ethyl acrylate; methacrylates such as methyl methacrylate and ethyl methacrylate; acrylamide derivatives such as N-methacrylamide, N-ethylacrylamide, and 2-acrylamide-2-methylpropanesulfonic acid; methacrylamide derivatives such as N-methylmethacrylamide and N-ethylmethacrylamide; maleic acid; maleic acid monomethyl ester and dimethyl maleate; fumaric acid; fumaric acid monomethyl ester 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. Ethylene glycol vinyl ether, 1,3-propanediol vinyl ether, 1,4-butanediol vinyl ether and other hydroxyl-containing vinyl ethers; allyl acetate; propyl allyl ether, butyl allyl ether, hexyl allyl ether and other allyl ethers; monomers with oxyalkylene groups; isopropyl acetate; α-olefins containing hydroxyl groups such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 9-decen-1-ol, 3-methyl-3-buten-1-ol; monomers with silyl groups such as vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3-(meth)acrylamidopropyltrimethoxysilane, 3-(meth)acrylamidopropyltriethoxysilane, etc.

[0069] The proportion of the aforementioned other structural units in all structural units of the PVA is sometimes preferably 20 mol% or less, sometimes more preferably 10 mol% or less, and sometimes even more preferably 5 mol% or 1 mol%. On the other hand, the proportion of the aforementioned other structural units may, for example, be 0.1 mol% or more, or 1 mol% or more.

[0070] The lower limit of the viscosity-uniform polymerization degree of the PVA is, for example, 50 or 100, sometimes preferably 200, more preferably 300, further preferably 400, and even more preferably 500. By setting the viscosity-uniform polymerization degree to the above-mentioned lower limit or above, the protective colloidal property is improved, and various properties are improved when used as a dispersant for suspension polymerization, for example. On the other hand, the upper limit of the viscosity-uniform polymerization degree is preferably 2,000, more preferably 1,500, further preferably 1,000, and even more preferably 800. By setting the viscosity-uniform polymerization degree to the above-mentioned upper limit or below, the surface activity property is improved, and various properties are improved when used as a dispersant for suspension polymerization, for example. On the other hand, when the PVA is used as a dispersant for suspension polymerization, the lower limit of the viscosity-uniform polymerization degree of the PVA is, for example, sometimes preferably 50, more preferably 70, further preferably 100, even more preferably 120, particularly preferably 160, and extremely preferably 200. The upper limit of the viscosity-uniform degree of polymerization of the PVA under this condition is preferably 800, more preferably 700, and even more preferably 600. The viscosity-uniform degree of polymerization is a value measured according to JIS K6726:1994. That is, it can be calculated from the intrinsic viscosity [η] (unit: L / g) using the following formula, which is measured in water at 30°C after the PVA has been resaponified to a degree of saponification of 99.5 mol% or more and purified.

[0071] Viscosity-uniform degree of polymerization = ([η] × 10 4 / 8.29) (1 / 0.62)

[0072] The PVA of the second aspect of the present invention has a group shown in the following formula (2) at the end of the polymer chain.

[0073] [Chemistry 8]

[0074]

[0075] In equation (2), R 1 The group is an alkenyl group. The specific and suitable forms of the group (terminal group) shown in formula (2) above are as described above. As described above, when vinyl esters are polymerized in the presence of aliphatic unsaturated aldehydes, the group shown in formula (2) above is introduced to the end of the polymer chain when the aliphatic unsaturated aldehyde is used as a chain transfer agent. The PVA may consist of only one type of PVA or a mixture of two or more types of PVA. The specific and suitable forms of the PVA described in the second aspect of the present invention are the same as those described in the first aspect of the present invention, except that it does not require "having carbonyl, formyl and alkenyl groups in the same or different molecules".

[0076] In the PVA of the present invention, in addition to the alkenyl group described above, carbon-carbon double bonds may also be present, and -CO-(CH=CH) is particularly preferred. p The structure shown is represented by -(p is an integer from 1 to 5). This structure is introduced, for example, by heat-treating the PVA of the present invention.

[0077] The PVA of the present invention can be used for a variety of purposes similar to those of conventionally known PVA, such as a raw material for films and fibers, an additive for paper and fiber processing, an adhesive, a dispersant and dispersing aid for emulsion polymerization and suspension polymerization, and a binder for inorganic materials. Among these, as will be detailed later, it is particularly suitable as a dispersant and dispersing aid for suspension polymerization of vinyl compounds and the like.

[0078] <Manufacturing Methods of Vinyl Alcohol-Based Polymers>

[0079] The method for manufacturing the vinyl alcohol-based polymer of the present invention comprises:

[0080] The process of polymerizing vinyl esters in the presence of aliphatic unsaturated aldehydes (Process A); and

[0081] The process of saponifying the obtained vinyl ester polymer (process B).

[0082] (Process A)

[0083] In step A, vinyl esters are polymerized in the presence of aliphatic unsaturated aldehydes to obtain vinyl ester-based polymers. Methods for polymerizing vinyl esters include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these methods, bulk polymerization carried out under solvent-free conditions and solution polymerization using solvents such as alcohols are preferred. The alcohols mentioned above are preferably alcohols 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, the reaction can be carried out in either a batch or continuous manner. There are no particular limitations on the polymerization temperature during the polymerization reaction; a range of 5°C to 200°C is suitable.

[0084] Examples of vinyl esters include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl decanoate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl tert-carbonate. Vinyl acetate is preferred.

[0085] Examples of polymerization initiators used in polymerization reactions include azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylpentanonitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylpentanonitrile); and known polymerization initiators such as benzoyl peroxide, n-propyl peroxide carbonate, and diisopropyl peroxide carbonate. The amount of polymerization initiator used is preferably, for example, 0.01 to 5% by mass relative to the vinyl ester used.

[0086] Specific examples and suitable examples of aliphatic unsaturated aldehydes present during the polymerization of vinyl esters are described above. One or more aliphatic unsaturated aldehydes may be used. The amount of aliphatic unsaturated aldehyde used is preferably 0.1 to 10% by mass relative to the vinyl ester, for example. During the polymerization of vinyl esters, other chain transfer agents, etc., may coexist. 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; thiols such as 2-hydroxyethanethiol and 3-mercaptopropionic acid; thiocarboxylic acids such as thioacetic acid; and halogenated hydrocarbons such as trichloroethylene and perchloroethylene.

[0087] When polymerizing vinyl esters, copolymerizable monomers may be further copolymerized without prejudice to the spirit of the invention. Examples of such copolymerizable monomers include those described above that provide other structural units.

[0088] (Process B)

[0089] 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. The saponification reaction of the vinyl ester polymer can be carried out using existing known alkaline catalysts such as sodium hydroxide, potassium hydroxide, and sodium methoxide, or acidic catalysts such as p-toluenesulfonic acid, through alcohol decomposition or hydrolysis. Examples of 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 alone or in combination of two or more. Among these, using methanol or a mixture of methanol and methyl acetate as the solvent and carrying out the saponification reaction in the presence of sodium hydroxide as an alkaline catalyst is simple and therefore preferred. Saponification can be carried out using a belt reactor, a kneader reactor, a tower reactor, etc.

[0090] A resin solid containing PVA is obtained through step B. In this manufacturing method, the steps following step B may further include: a step of cleaning 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.

[0091] <Dispersants for suspension polymerization>

[0092] The dispersant for suspension polymerization of the present invention (hereinafter also referred to as "dispersant") comprises the PVA of the present invention described above. A dispersant refers to an additive used during suspension polymerization to improve the dispersibility of monomers and control the particle size of the resulting polymer particles. The lower limit of the content of PVA in the non-volatile component of the dispersant of the present invention is sometimes preferably 30% by mass, more preferably 50% by mass, and even more preferably 70% by mass, 90% by mass, or 99% by mass. The upper limit of the content of PVA in the non-volatile component of the dispersant of the present invention can be 100% by mass. Examples of non-volatile components that may be included in the dispersant of the present invention, besides PVA, include PVA other than the PVA of the present invention, resins other than PVA, surfactants, plasticizers, and other additives, as well as various compounds used in the manufacturing process. The lower limit of the content of all PVA in the non-volatile component of the dispersant of the present invention is sometimes preferably 50% by mass, more preferably 70% by mass, and even more preferably 80% by mass, 90% by mass, or 99% by mass. The upper limit of the content of all PVA in the non-volatile component of the dispersant of the present invention can be 100% by mass. Furthermore, the content of volatile components in the dispersant of the present invention is generally 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 dispersant of the present invention include alcohols and water. That is, the dispersant of the present invention can be substantially formed from the PVA of the present invention. The shape of the dispersant of the present invention is not particularly limited, and it is generally a powder.

[0093] 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, polymer particles with improved polymerization stability, small average particle size, and few coarse particles can be effectively obtained. In addition, the polymer particles obtained by suspension polymerization using the dispersant of the present invention also have good plasticizer absorption.

[0094] <Dispersing aids for suspension polymerization>

[0095] The dispersion aid for suspension polymerization of the present invention (hereinafter also referred to as "dispersion aid") comprises the PVA of the present invention as described above. Dispersion aids generally refer to additives used together with dispersants, especially to improve the porosity of the resulting polymer particles. Furthermore, by using a dispersion aid together with a dispersant, dispersibility can be further improved. The lower limit of the content of PVA in the non-volatile component of the dispersion aid of the present invention is sometimes preferably 30% by mass, more preferably 50% by mass, and even more preferably 70% by mass, 90% by mass, or 99% by mass. The upper limit of the content of PVA in the non-volatile component of the dispersion aid of the present invention can be 100% by mass. Examples of non-volatile components that may be included in the dispersion aid of the present invention, besides PVA, include PVA other than the PVA of the present invention, resins other than PVA, surfactants, plasticizers, and other additives, as well as various compounds used in the manufacturing process. The lower limit of the content of all PVA in the non-volatile component of the dispersion aid of the present invention is sometimes preferably 50% by mass, more preferably 70% by mass, and even more preferably 80% by mass, 90% by mass, or 99% by mass. The maximum content of all PVA in the non-volatile components of the dispersing agent of the present invention can be 100% by mass. Furthermore, the content of volatile components in the dispersing agent of the present invention is typically 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 dispersing agent of the present invention include alcohols and water. That is, the dispersing agent of the present invention can be substantially formed from the PVA of the present invention. The shape of the dispersing agent of the present invention is not particularly limited, and it is typically a powder.

[0096] 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, polymer particles with improved polymerization stability, small average particle size, and few coarse particles can be effectively obtained. In addition, the polymer particles obtained by suspension polymerization using the dispersant of the present invention also have good plasticizer absorption.

[0097] <Manufacturing Methods of Vinyl Polymers>

[0098] The method for manufacturing the vinyl polymer of the present invention includes a step of suspension polymerization of a vinyl compound using the PVA (dispersant or dispersing aid of the present invention). This manufacturing method is identical to known methods for manufacturing vinyl polymers, except that it uses the PVA of the present invention as a dispersant or dispersing aid.

[0099] In the method for manufacturing the vinyl polymer of the present invention, the vinyl compound is typically subjected to suspension polymerization in an aqueous medium using the PVA of the present invention. As the aqueous medium, in addition to pure water, aqueous solutions containing various additives or aqueous media containing other organic solvents may also be used.

[0100] When performing suspension polymerization of vinyl compounds, the amount of PVA added according to the present invention is not particularly limited. Relative to vinyl compounds, it is sometimes preferred to be 100 ppm or more and 50,000 ppm or less by mass, more preferably 200 ppm or more and 20,000 ppm or less, and even more preferably 10,000 ppm or less, 5,000 ppm or less or 2,000 ppm or less.

[0101] The PVA of this invention can be used alone or 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 in suspension polymerization of vinyl compounds in an aqueous medium; water-soluble polymers such as PVA and gelatin, other than the PVA of this invention; oil-soluble emulsifiers such as sorbitol monolaurate, sorbitol trioleate, glyceryl tristearate, and ethylene oxide-propylene oxide block copolymers; and water-soluble emulsifiers such as polyoxyethylene sorbitol monolaurate, polyoxyethylene glyceryl oleate, and sodium laurate.

[0102] As the polymerization initiator used in the method for manufacturing vinyl polymers of the present invention, a polymerization initiator conventionally used in the polymerization of vinyl compounds can be used. Specifically, the same polymerization initiator as the substance exemplified in the polymerization of the vinyl ester monomers described above can be used.

[0103] In the method for manufacturing the vinyl polymer of the present invention, various other additives can be added to the polymerization system as needed. Examples of additives include polymerization regulators such as aldehydes, halogenated hydrocarbons, and thiols, and polymerization inhibitors such as phenolic compounds, sulfur compounds, and N-oxide compounds. Additionally, pH adjusters, antioxidants, and crosslinking agents can also be added. Multiple additives can also be used in combination.

[0104] Examples of vinyl compounds that can be suspension polymerized in the method for manufacturing vinyl polymers of the present invention include halogenated vinyl groups 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 ethers, etc. Among these vinyl compounds, vinyl chloride is preferred. The method for manufacturing vinyl polymers of the present invention is particularly suitable for use when vinyl chloride is suspension polymerized alone or when vinyl chloride is suspension polymerized together with monomers capable of copolymerizing with vinyl chloride. Examples of monomers capable of copolymerizing with vinyl chloride include vinyl esters such as vinyl acetate and vinyl propionate; (meth)acrylates 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 ethers, etc.

[0105] In the method for manufacturing vinyl polymers of the present invention, when the vinyl compound is subjected to suspension polymerization, the feeding ratio of each component, polymerization temperature, polymerization time, etc., can be set to the same conditions as those used in the conventional suspension polymerization of vinyl compounds such as vinyl chloride. Furthermore, there are no limitations on the feeding order or ratio of the vinyl compound, polymerization initiator, dispersant, aqueous medium, and other additives.

[0106] According to the method for manufacturing vinyl polymers of the present invention, vinyl polymer particles with high stability during polymerization, small average particle size, and few coarse particles can be effectively obtained. Furthermore, the vinyl polymer particles obtained by the manufacturing method of the present invention also exhibit excellent plasticizer absorption.

[0107] Example

[0108] The present invention is illustrated by the following embodiments, but the present invention is not limited to these embodiments at all. It should be noted that the following shows the various measurement methods used in the following embodiments and comparative examples.

[0109] [Viscosity-uniform degree of polymerization of PVA]

[0110] The viscosity-uniform polymerization degree of PVA was determined according to JIS K6726:1994. Specifically, for PVA with a saponification degree of less than 99.5 mol%, the degree of polymerization was determined in water at 30°C for PVA obtained by saponification to a saponification degree of 99.5 mol% or more. The intrinsic viscosity [η] (L / g) obtained therefrom was used, and the viscosity-uniform polymerization degree was calculated using the following formula.

[0111] Viscosity-uniform degree of polymerization = ([η] × 10 4 / 8.29) (1 / 0.62)

[0112] [Degree of saponification of PVA]

[0113] The degree of saponification of PVA was determined using the method described in JIS K6726:1994.

[0114] [Carbonyl group content of PVA]

[0115] conduct 1 The carbonyl content of PVA was calculated by ¹H-NMR determination. Samples were cleaned with methyl acetate for 10 hours using a sogralitt method and then vacuum dried at 40°C for 16 hours to remove impurities before analysis. Samples prepared with 1% DMSO-d6 solution (with 0.03% tetramethylsilane as an internal standard) were analyzed at 400 MHz (80°C, 256 times cumulatively). In the methine groups of the PVA backbone, the CH peak associated with the OH group appeared at 3.8–4.0 ppm (integrated value [M]), and the CH peak associated with the OAc group appeared at 4.2–4.6 ppm (integrated value [N]). Additionally, the peak of the methylene group adjacent to the formyl and carbonyl groups appeared at 2.3–2.5 ppm (integrated value [O]). Furthermore, the peak of the proton constituting the formyl group appeared at 9.5–10.0 ppm (integrated value [P]). The carbonyl content of PVA is determined by the following formula, in terms of its value relative to the structural units (vinyl alcohol units and vinyl ester units) derived from vinyl alcohol monomers.

[0116] Carbonyl group content (mol%) = [{([O] / 2)-[P]} / ([M]+[N])]×100

[0117] [Alkene content of PVA]

[0118] conduct 1The alkenyl (vinyl) content of PVA was calculated by ¹H-NMR determination. Samples were purified by Sogret washing with methyl acetate for 10 hours and vacuum drying at 40 °C for 16 hours to remove impurities before analysis. Samples prepared in 1% DMSO-d6 solution (with 0.03% tetramethylsilane as an internal standard) were analyzed at 400 MHz (80 °C, 256 times cumulatively). In the methine groups of the PVA backbone, the CH peak associated with the OH group appeared at 3.8–4.0 ppm (integrated value [M]), and the CH peak associated with the OAc group appeared at 4.2–4.6 ppm (integrated value [N]). Additionally, the peak of a proton constituting the vinyl group (H at position 1 of the vinyl group; CH₂=C“H”-) appeared at 5.7–6.0 ppm (integrated value [Q]). The alkenyl content of PVA is determined by the following formula, in terms of its value relative to the structural units (vinyl alcohol units and vinyl ester units) derived from vinyl alcohol monomers.

[0119] Alkenyl group content (mol%) = {[Q] / ([M]+[N])}×100

[0120] [Formyl group content of PVA]

[0121] conduct 1 The formyl group content of PVA was calculated by ¹H-NMR determination. Samples were washed with methyl acetate for 10 hours using a sogralitt method and then vacuum dried at 40°C for 16 hours to remove impurities before analysis. Samples prepared with 1% DMSO-d6 solution (with 0.03% tetramethylsilane as an internal standard) were analyzed at 400 MHz (80°C, 256 times cumulatively). In the methine groups of the PVA backbone, the CH peak associated with the OH group appeared at 3.8–4.0 ppm (integrated value [M]), and the CH peak associated with the OAc group appeared at 4.2–4.6 ppm (integrated value [N]). The proton peak constituting the formyl group appeared at 9.5–10.0 ppm (integrated value [P]). The formyl group content of PVA was determined relative to the structural units (vinyl alcohol units and vinyl ester units) derived from vinyl alcohol monomers using the following formula.

[0122] The content of formyl groups (mol%) = {[P] / ([M]+[N])}×100

[0123] [Example 1] (Manufacturing of PVA-1)

[0124] 1600 parts by mass of vinyl acetate and 35.0 parts by mass of 7-octenal were added to a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, and polymerization initiator inlet. Nitrogen purging was performed on the system for 30 minutes while simultaneously bubbling nitrogen. The reactor temperature was then increased, and 2.4 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) were added when the internal temperature reached 60°C to initiate polymerization. Polymerization was stopped after 3 hours at 60°C by cooling. The solids concentration at polymerization stop was 44.3% by mass, and the polymerization rate was 45%. Subsequently, unreacted monomers were removed by intermittently adding methanol at 30°C under reduced pressure, yielding a methanol solution of the vinyl ester polymer (concentration 38.2% by mass). Next, in a methanol solution of a vinyl ester polymer prepared by further adding methanol to the methanol solution (containing 34 parts by mass of the polymer), 1.0 part by mass of a 10% by mass 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 (the concentration of the polymer in the saponification solution was 30% by mass, the water content of the saponification solution was 1% by mass, and the molar ratio of sodium hydroxide to vinyl acetate units in the polymer was 0.0072). A gel-like substance was formed approximately 15 minutes after the addition of the sodium hydroxide methanol solution; therefore, it was pulverized and further saponified at 40°C for 1 hour. Subsequently, 160 parts by mass of methyl acetate and 40 parts by mass of methanol were added, and the mixture was washed at 40°C for 30 minutes. This washing operation was repeated twice, followed by dehydration. The resulting white solid 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.

[0125] [Examples 2, 3, 6-8, 10, 11, 14, Comparative Example 1] (Manufacturing of PVA-2, 3, 6-8, 10, 11, 14, 15)

[0126] As shown in Table 1, the polymerization conditions, such as the amount of vinyl acetate added, the type and amount of aldehyde (a) used in polymerization, the concentration of the vinyl ester polymer during saponification, and the molar ratio of sodium hydroxide to vinyl acetate units, were varied. Otherwise, the PVAs (PVA-2, 3, 6-8, 10, 11, 14, and Comparative Example 1) of Examples 2, 3, 6-8, 10, 11, 14, and 15 were manufactured using the same method as in Example 1. In Examples 6-8 and 14, as described in Table 1, a chain transfer agent (b) was also used along with the aldehyde (a). The physical properties of PVA-2, 3, 6-8, 10, 11, 14, and 15 are shown in Table 2.

[0127] [Example 4] (Manufacturing of PVA-4)

[0128] 960 parts by mass of vinyl acetate, 640 parts by mass of methanol, and 17.5 parts by mass of 7-octenal were added to a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, chain transfer agent dropper, and polymerization initiator inlet. Nitrogen purging was performed on the system for 30 minutes while simultaneously bubbling nitrogen. The reactor temperature was then increased, and 1.5 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added when the internal temperature reached 60°C to initiate polymerization. Polymerization was stopped after 3 hours at 60°C by cooling. The solids concentration at polymerization stop was 39.4% by mass, and the polymerization rate was 65%. Subsequently, unreacted monomers were removed by intermittently adding methanol at 30°C under reduced pressure, yielding a methanol solution of the vinyl ester polymer (concentration 40.5% by mass). Next, in a methanol solution of a vinyl ester polymer prepared by further adding methanol to the methanol solution (containing 30 parts by mass of the polymer), 1.0 part by mass of a 10% by mass 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 (the concentration of the polymer in the saponification solution was 30% by mass, the water content of the saponification solution was 1% by mass, and the molar ratio of sodium hydroxide to vinyl acetate units in the polymer was 0.0075). Approximately 10 minutes after the addition of the sodium hydroxide methanol solution, a gel-like substance was formed. Therefore, it was pulverized and further saponified at 40°C for 1 hour. Subsequently, 160 parts by mass of methyl acetate and 40 parts by mass of methanol were added, and the mixture was washed at 40°C for 30 minutes. This washing operation was repeated twice, followed by dehydration. The resulting white solid 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.

[0129] [Examples 5, 9, and Comparative Example 3] (Manufacturing of PVA-5, 9, and 17)

[0130] As shown in Table 1, the polymerization conditions, including the amounts of vinyl acetate and methanol, the type and amount of aldehyde (a) used in polymerization, the concentration of the vinyl ester polymer during saponification, and the molar ratio of sodium hydroxide to vinyl acetate units, were varied. Otherwise, the PVAs (PVA-5, 9, 17) of Examples 5, 9, and Comparative Example 3 were manufactured using the same method as in Example 4. In Comparative Example 3, aldehyde (a) was not used. The properties of PVA-5, 9, and 17 are shown in Table 2.

[0131] [Example 12] (PVA-12)

[0132] 1050 parts by mass of vinyl acetate, 450 parts by mass of methanol, and 9.0 parts by mass of 7-octenal were added to a reactor equipped with a stirrer, reflux condenser, nitrogen inlet, chain transfer agent dropper, and polymerization initiator inlet. Nitrogen purging was performed on the system for 30 minutes while simultaneously bubbling nitrogen. The reactor temperature was then increased, and 1.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added when the internal temperature reached 60°C to initiate polymerization. A methanol solution (6% by mass) of 3-mercaptopropionic acid, used as chain transfer agent (b), was added dropwise to the reactor. The addition was carried out while maintaining a constant ratio of AIBN to vinyl acetate in the polymerization solution (total addition was 43.3 parts by mass). Polymerization was carried out at 60°C for 4 hours, followed by cooling to stop the polymerization. The solids concentration at the point of polymerization cessation was 27.6% by mass, and the polymerization rate was 40%. Next, unreacted monomers were removed by adding methanol intermittently under reduced pressure at 30°C, yielding a methanol solution of vinyl ester polymer (concentration 54.0% by mass). Then, 93.7 parts by mass of the methanol solution of vinyl ester polymer prepared by further adding methanol to this methanol solution (42.6 parts by mass of the polymer in the solution) were 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 saponification solution was 40% by mass, water content in the saponification solution was 1% by mass, and the molar ratio of sodium hydroxide to vinyl acetate units in the polymer was 0.0298). Saponification was carried out by standing at 40°C for 1 hour. Afterwards, 160 parts by mass of methyl acetate and 40 parts by mass of methanol were added, and the mixture was washed at 40°C for 30 minutes. After repeating the washing operation twice, the liquid was removed, and the resulting white solid 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.

[0133] [Example 13] (Manufacturing of PVA-13)

[0134] As shown in Table 1, the polymerization conditions, such as the amount of vinyl acetate and methanol, the amount of aldehyde (a) used in polymerization and 3-mercaptopropionic acid as a chain transfer agent (b), the concentration of the vinyl ester polymer during saponification, and the molar ratio of sodium hydroxide to vinyl acetate units, were changed. Otherwise, PVA-13 of Example 13 was manufactured using the same method as in Example 12.

[0135] [Comparative Example 2] (Manufacturing of PVA-16)

[0136] 100 parts by weight of the PVA-16 powder obtained above were impregnated in 500 parts by weight of a methanol solution (0.5% by weight) of 7-octenal for 3 hours. Then, 30 parts by weight of a 1N hydrochloric acid aqueous solution were added, and the reaction was carried out at 40°C for 2 hours. Subsequently, the mixture was neutralized with 30 parts by weight of a 1N sodium hydroxide aqueous solution, and the reaction solution was removed by filtration. Then, 160 parts by weight of methyl acetate and 40 parts by weight of methanol were added, and the mixture was washed at 40°C for 30 minutes. This washing operation was repeated twice, followed by dehydration. The resulting white solid was dried at 70°C for 16 hours to produce the acetalized PVA (PVA-16) of Comparative Example 2. The physical properties of PVA-16 are shown in Table 2.

[0137] [evaluate]

[0138] The PVAs obtained in Examples 1-11 and Comparative Examples 1-3 were used as dispersants for suspension polymerization, and the suspension polymerization of vinyl chloride was carried out using the method described below. Next, the average particle size, amount of coarse particles, and plasticizer absorption of the resulting vinyl chloride polymers were evaluated. The evaluation results are shown in Table 2.

[0139] (Suspension polymerization of vinyl chloride)

[0140] Dispersant aqueous solution (A) was prepared by dissolving each PVA listed in Table 2 in deionized water at an amount equivalent to 1000 ppm relative to vinyl chloride, and 100 parts by mass were added to a 5 L autoclave. Next, a vinyl alcohol polymer (PVA B) with a viscosity-uniform polymerization degree of 450 and a saponification degree of 40 mol% was dissolved in deionized water at an amount equivalent to 300 ppm relative to vinyl chloride, and 100 parts by mass were added to this dispersant aqueous solution (B). Then, deionized water was added to a total of 1200 parts by mass. Next, 0.65 parts by mass of a 70% by mass toluene solution of neodecanoate and 1.05 parts by mass of a 70% by mass toluene solution of neodecanoate were added to the autoclave. Oxygen was removed by degassing 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, and polymerization began with stirring. The initial pressure inside the autoclave was 0.83 MPa. After 3.5 hours, polymerization was stopped when the pressure inside the autoclave reached 0.70 MPa, and unreacted vinyl chloride was removed. The polymer slurry was then removed and dried at 65°C for 17 hours to obtain vinyl chloride polymer particles.

[0141] (1) Average particle size of vinyl chloride polymer particles

[0142] The particle size distribution of the obtained vinyl chloride polymer particles was determined by dry sieving analysis using a Taylor sieve-based metal mesh. The results were plotted in a Rosin-Rammler distribution, and the average particle size (d) was calculated. p50 (Median particle size).

[0143] (2) The amount of coarse particles in vinyl chloride polymer particles

[0144] For the obtained vinyl chloride polymer particles, the content of particles that did not pass through a 250 μm mesh sieve (calculated according to the JIS standard sieve conversion, which is 60 mesh) was determined by mass%. The smaller the value, the fewer coarse particles there are, and the better the polymerization stability of the dispersant (PVA) used.

[0145] (3) Plasticizer absorption (CPA) of vinyl chloride polymer particles

[0146] The mass of a 5mL syringe containing 0.02g of absorbent cotton was measured (denoted as A(g)). 0.5g of vinyl chloride polymer granules were added to the syringe, and their mass was measured (denoted as B(g)). 1g of dioctyl phthalate (DOP) was added, and the mixture was allowed to stand for 15 minutes. Subsequently, the mixture was centrifuged at 3000 rpm for 40 minutes to remove unabsorbed DOP, and the mass of the residue after removal was measured (denoted as C(g)). The plasticizer absorption rate (%) of the vinyl chloride polymer granules was then calculated using the following formula. Higher plasticizer absorption rate indicates easier processing, primarily reducing the likelihood of defects such as particulate matter during sheet formation. In this evaluation, a plasticizer absorption rate of 28.0% or higher was considered good.

[0147] Plasticizer absorption (%) = 100 × [{(CA) / (BA)} - 1]

[0148]

[0149] [Table 2]

[0150]

[0151] As shown in Table 2, when the PVAs of Examples 1 to 11 contain carbonyl, formyl, and alkenyl groups, and are used as dispersants for suspension polymerization, vinyl chloride polymer particles with small average particle size, few coarse particles, and good plasticizer absorption can be obtained. It can be confirmed that the PVAs of Examples 1 to 11 are useful as dispersants for suspension polymerization. It should be noted that since aliphatic unsaturated aldehydes coexist during synthesis, and alkenyl and carbonyl groups can be identified in the PVAs, it can be inferred that the groups shown in formula (2) above are formed at the ends of the polymer chains in the PVAs of each example.

[0152] On the other hand, in Comparative Example 1, PVA-15, which lacks alkenyl and formyl groups, the resulting vinyl chloride polymer particles have a large average particle size and a high proportion of coarse particles. In Comparative Example 2, PVA-16, which also lacks carbonyl and formyl groups, the resulting vinyl chloride polymer particles have a large average particle size and a high proportion of coarse particles. Furthermore, the plasticizer absorption of the resulting vinyl chloride polymer particles is also low. In Comparative Example 3, PVA-17, the vinyl chloride polymer agglomerated, making evaluation impossible.

[0153] Industrial utilization

[0154] The PVA of this invention can be used as a dispersant in the suspension polymerization of vinyl compounds, etc.

Claims

1. Vinyl alcohol polymers, which may contain carbonyl, formyl, and alkenyl groups in the same or different molecules. The -C (=O)- in the formyl group is not included in the carbonyl group. The proportion of structural units other than those derived from vinyl esters and aliphatic unsaturated aldehydes in all structural units is less than 10 mol%. The polymer chain ends with a group represented by the following formula (5) containing the alkenyl group. In equation (5), n is an integer from 1 to 11.

2. The vinyl alcohol polymer according to claim 1, having a structure comprising the carbonyl group shown in formula (1) below, [Chemistry 1] In equation (1), m is an integer from 1 to 11.

3. Vinyl alcohol polymers, which may contain carbonyl, formyl, and alkenyl groups in the same or different molecules. The -C (=O)- in the formyl group is not included in the carbonyl group. The polymer chain ends with a group as shown in formula (2). [Chemistry 2] In equation (2), R 1 An alkenyl group having a methylene group at the end on the carbonyl side.

4. The vinyl alcohol polymer according to any one of claims 1 to 3, wherein it has tertiary carbon atoms.

5. The vinyl alcohol polymer according to any one of claims 1 to 3, wherein it has structural units derived from aliphatic unsaturated aldehydes.

6. The vinyl alcohol-based polymer according to claim 5, wherein, The aforementioned aliphatic unsaturated aldehydes have 3 to 14 carbon atoms.

7. The vinyl alcohol-based polymer according to claim 5, wherein, The aforementioned aliphatic unsaturated aldehydes have carbon-carbon double bonds at their ends.

8. A method for manufacturing the vinyl alcohol-based polymer according to any one of claims 1 to 7, comprising: The process of polymerizing vinyl esters in the presence of aliphatic unsaturated aldehydes; and The process of saponifying the obtained vinyl ester polymer.

9. A dispersant for suspension polymerization, comprising any one of the vinyl alcohol polymers according to claims 1 to 7.

10. A dispersant for suspension polymerization, comprising any one of the vinyl alcohol polymers according to claims 1 to 7.

11. A method for manufacturing a vinyl-based polymer, comprising: a step of polymerizing a vinyl compound in the presence of the vinyl alcohol-based polymer as described in any one of claims 1 to 7.

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