Dispersion stabilizer and method for producing vinyl polymer

Abstract

The present invention provides a new dispersant or the like for suspension polymerization.　This dispersion stabilizer for suspension polymerization contains a polyvinyl alcohol-based polymer (A) including an acetal skeleton that has an ionic group.

Description

[Technical field]

[0001] The present invention relates to a polyvinyl alcohol-based polymer that can be suitably used as a dispersion stabilizer [for example, a dispersion stabilizer for suspension polymerization of a vinyl-based monomer (particularly a vinyl chloride monomer)], and a method for producing a vinyl-based polymer [particularly a vinyl chloride-based polymer (resin)] by using the polyvinyl alcohol-based polymer (or dispersion stabilizer), and the like. [Background technology]

[0002] The industrial production method of vinyl chloride resin is generally performed by batch suspension polymerization, in which vinyl monomers such as vinyl chloride are dispersed in an aqueous medium in the presence of a dispersion stabilizer, and polymerization is performed using an oil-soluble polymerization initiator. Factors in the polymerization process that govern the quality of vinyl chloride resin include the polymerization rate, the ratio of aqueous medium to monomer, polymerization temperature, the type and amount of polymerization initiator, the type of polymerization tank, the stirring speed, and the type and amount of dispersion stabilizer, among which the influence of the dispersion stabilizer is very large.

[0003] The role of a dispersion stabilizer in suspension polymerization to obtain a vinyl chloride resin is to disperse a monomer in an aqueous medium, form stable droplets, regulate the size of the droplets that repeat dispersion and coalescence, and control the coagulation tendency of the polymerized particles. For this reason, the performance required of such a dispersion stabilizer is as follows: <1> Controlling the particle size of the resulting vinyl chloride resin particles within an appropriate range; <2> To improve moldability by increasing the plasticizer absorption of the obtained vinyl chloride resin particles; <3> The porosity of the resulting vinyl chloride resin particles is set within a certain range, making it easier to remove the residual monomer.

[0004] That is, the above-mentioned dispersion stabilizer is required to exhibit, for example, excellent dispersing power and to control the particle size, particle shape, etc. of the vinyl chloride resin to an appropriate state.

[0005] As the dispersion stabilizer, generally, polyvinyl alcohol resins (hereinafter sometimes abbreviated as PVA, etc.), cellulose derivatives, etc. are used alone or in appropriate combination.

[0006] For example, Non-Patent Document 1 describes a method of using, as a dispersion stabilizer for suspension polymerization of vinyl chloride, PVA having a viscosity average degree of polymerization of 2000 and a degree of saponification of 88 mol % or 80 mol % and considered to have high emulsifying power, or PVA having a viscosity average degree of polymerization of 600 to 700 and a degree of saponification of about 70 mol %. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] "Poval", Polymer Publishing Association, 1981 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, PVA is used as a dispersion stabilizer, but according to the studies by the present inventors, further improvement is required in PVA as well.

[0009] For example, PVA with a relatively low degree of saponification (e.g., around 70 mol%) is less hydrophilic than PVA with a higher degree of saponification, making it difficult to prepare an aqueous solution. In addition, the cloud point of a 4% aqueous solution is low (e.g., around 30°C), and there is a risk of the PVA precipitating (separating) if the aqueous solution is stored in a tank or the like at a temperature above the cloud point.

[0010] Furthermore, since the polymerization temperature of vinyl chloride monomer is generally 40 to 70°C, which is above the cloud point of PVA, it is necessary to prevent the PVA from precipitating in the polymerizer when the aqueous PVA solution is added to the polymerizer (hot water at 40 to 70°C).

[0011] Thus, PVA as a dispersion stabilizer (such as a dispersion stabilizer for suspension polymerization) is required to have ease of preparation of an aqueous solution, stability of the aqueous solution (and further dispersibility in warm water), and the like, in addition to its inherent performance as a dispersion stabilizer. However, these properties become more difficult to maintain as the degree of saponification of PVA decreases and as the degree of polymerization of PVA increases.

[0012] Under these circumstances, the present inventors attempted to introduce units derived from itaconic acid into PVA in the hope of improving hydrophilicity. However, perhaps due to a decrease in interfacial activity, the inherent performance as a dispersion stabilizer was sometimes reduced (for example, polymerization destabilization occurred, the particle size of the resulting polyvinyl chloride resin increased, and the plasticizer absorption was easily reduced), and it was extremely difficult to achieve ease of preparation of an aqueous solution, stability of the aqueous solution, dispersibility in warm water, and the like, while ensuring the performance as a dispersion stabilizer.

[0013] In view of the above-mentioned points, an object of the present invention is to provide a novel dispersion stabilizer and the like. [Means for solving the problem]

[0014] Means for Solving the Problems The present inventors conducted extensive research to solve the above problems and found that a specific PVA polymer is useful as a dispersion stabilizer (e.g., a dispersion stabilizer for suspension polymerization), and further conducted research to complete the present invention.

[0015] That is, the present invention relates to the following inventions, etc. [1] A dispersion stabilizer (or dispersant) containing a polyvinyl alcohol-based polymer (A) having an acetal skeleton (acetal group, acetal unit) having an ionic group. [2] The agent according to [1], wherein the acetal skeleton having an ionic group contains a skeleton (structural unit, constitutional unit) represented by the following formula (1):

[0016] [ka] (In the formula, R represents a group having an ionic group.) [3] The agent according to [2], wherein the acetal skeleton having an ionic group comprises a skeleton represented by formula (1), in which R is a hydrocarbon group having an ionic group. [4] The agent according to any one of [1] to [3], wherein the acetal skeleton having an ionic group includes at least one skeleton selected from the skeleton represented by the formula (1) in which R is an ionic group, and the skeleton represented by the following formula (1-1):

[0017] [ka] (In the formula, R1 to R5 represent a hydrogen atom or a substituent, provided that at least one of R1 to R5 is an ionic group.) [5] The agent according to any one of [1] to [4], wherein the ionic group includes at least one selected from an acid group (for example, a carboxyl group, a sulfonic acid group) and a salt thereof. [6] The agent according to any one of [1] to [5], wherein the acetal skeleton having an ionic group includes a skeleton derived from at least one selected from glyoxylic acid, 4-formylbenzoic acid, 2-formylbenzenesulfonic acid, and salts thereof. [7] The agent according to any one of [1] to [6], wherein the content (proportion, content ratio) of an acetal skeleton having an ionic group (e.g., a skeleton represented by formula (1)) in the polyvinyl alcohol-based polymer (A) is 0.01 to 5 mol % per monomer unit. [8] The agent according to any one of [1] to [7], wherein in the polyvinyl alcohol polymer (A), a ratio of the acetal skeleton having an ionic group is 0.2 to 5 mol per 100 mol of the vinyl ester unit. [9] The agent according to any one of [1] to [8], wherein the polyvinyl alcohol polymer (A) has a degree of saponification of 20 to 90 mol %.

[10] The agent according to any one of [1] to [9], wherein the polyvinyl alcohol polymer (A) has a degree of polymerization of 120 to 3,000.

[11] The agent according to any one of [1] to

[10] , wherein the polyvinyl alcohol polymer (A) has a polymerizable unsaturated bond (for example, an ethylenic double bond).

[12] The agent according to any one of [1] to

[11] , wherein the polyvinyl alcohol polymer (A) has polymerizable unsaturated bonds in a proportion of 0.05 to 5 mol % per monomer unit.

[13] The agent according to any one of [1] to

[12] , wherein a 4% by mass aqueous solution of the polyvinyl alcohol-based polymer (A) has a cloud point of 25° C. or higher.

[14] The agent according to any one of [1] to

[13] , which is a dispersion stabilizer for polymerization.

[15] The agent according to any one of [1] to

[14] , which is a dispersion stabilizer for suspension polymerization.

[16] The agent according to any one of [1] to

[15] , which is a dispersion stabilizer for suspension polymerization of vinyl monomers including vinyl chloride.

[17] The polyvinyl alcohol polymer (A) according to any one of [1] to

[16] .

[18] An aqueous liquid containing the polyvinyl alcohol-based polymer (A) or agent according to any one of [1] to

[16] .

[19] A method for producing a vinyl polymer, comprising polymerizing a vinyl monomer in the presence of the polyvinyl alcohol polymer (A) or agent according to any one of [1] to

[16] .

[20] The method according to

[19] , wherein the polymerization is suspension polymerization. [twenty one] The production method according to

[19] or

[20] , comprising suspension polymerization of a vinyl monomer including vinyl chloride. Effect of the Invention

[0018] According to the present invention, a novel dispersion stabilizer and the like can be provided.

[0019] Such a dispersion stabilizer (specific PVA polymer) can realize not only easy preparation of an aqueous solution (particularly an aqueous solution) but also excellent storage stability and hot water dispersibility of the aqueous solution.

[0020] In addition, the dispersion stabilizer (specific PVA polymer) of the present invention also has performance as a dispersion stabilizer. For example, it is possible to efficiently obtain a resin (e.g., a vinyl polymer such as a vinyl chloride resin) that can realize excellent polymerization stability, has an appropriate average particle size, and has sufficient plasticizer absorption.

[0021] In particular, the dispersion stabilizer of the present invention (specific PVA-based polymer) can realize the above-mentioned easy preparation of an aqueous solution, excellent storage stability of the aqueous solution, and dispersibility in hot water, without impairing (while ensuring) the performance as a dispersion stabilizer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the preferred embodiments. However, the present invention is not limited to the preferred embodiments described below.

[0023] The present invention can provide a specific polyvinyl alcohol-based polymer, that is, a polyvinyl alcohol-based polymer (A) (hereinafter, sometimes referred to as PVA-based polymer (A) etc.). Such a PVA polymer (A) is useful as a dispersion stabilizer (dispersant, particularly a dispersion stabilizer for suspension polymerization) and the like. Therefore, the present invention can also provide a dispersion stabilizer containing the PVA polymer (A). Such a dispersion stabilizer may contain a PVA polymer (A) either alone or in combination of two or more kinds. The present invention will be described in detail below.

[0024] [Polyvinyl alcohol polymer (A)] The PVA polymer (A) is characterized by having an acetal skeleton (acetal group, acetal unit) having an ionic group.

[0025] Examples of the ionic group include anionic groups {e.g., acid groups [e.g., carboxyl groups, sulfonic acid groups (-SOH), phosphate groups, etc.]}, cationic groups [e.g., amino groups, ammonium (ammonium cation)], and salts thereof (groups formed by these in the form of salts).

[0026] The salt may be anionic, cationic, or the like, and examples of the salt include metal salts [e.g., alkali or alkaline earth metal salts (e.g., lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts, etc.)] and halides (e.g., chlorides, bromides, iodides, etc.). When the ionic group is a polybasic acid or the like, the salt may be a single salt (of the same kind) or a combination of two or more kinds.

[0027] Among these ionic groups, acid groups (particularly, carboxyl groups and sulfonic acid groups) and salts thereof {salts of acid groups, for example, carboxylates [e.g., -COOM (M is an alkali metal such as sodium (or its cation))], sulfonates [e.g., -SOM (M is an alkali metal such as sodium (or its cation))], etc.} are preferred.

[0028] As described above, the ionic group is contained in the acetal skeleton (acetal group, acetal unit) (is substituted on the acetal skeleton).

[0029] The acetal may be either a cyclic acetal or an acyclic (chain) acetal, and is preferably a cyclic acetal.

[0030] A representative acetal skeleton having an ionic group includes a skeleton (structural unit) represented by the following formula (1). Therefore, the acetal skeleton having an ionic group may include a skeleton represented by the following formula (1).

[0031] [ka] (In the formula, R represents a group having an ionic group.)

[0032] In the above formula (1), R is a group having an ionic group. R may be the ionic group itself, or may be a linking group having an ionic group (a group composed of an ionic group and a linking group substituted with this ionic group).

[0033] Examples of the linking group (base group) include a hydrocarbon group. Examples of the hydrocarbon group include aliphatic hydrocarbon groups [e.g., alkyl groups [e.g., chain alkyl groups (e.g., C groups such as methyl groups, ethyl groups, propyl groups, butyl groups, pentyl groups, hexyl groups, heptyl groups, octyl groups, nonyl groups, decyl groups, and undecyl groups]. 1-30 alkyl group), cycloalkyl group (e.g., cyclopentyl group, cyclohexyl group, etc. 3-10 saturated aliphatic hydrocarbon groups such as cycloalkyl groups, aromatic hydrocarbon groups such as aryl groups (e.g., phenyl, tolyl, xylyl, naphthyl groups, etc.); 6-20 aryl group), aralkyl group (e.g., benzyl group, phenethyl group, etc. 6-20 Aryl-C 1-4 alkyl group, etc.

[0034] The linking group (hydrocarbon group) may have a substituent (a substituent that is not an ionic group) other than the ionic group. The substituent is not particularly limited, and examples thereof include a hydroxyl group, a halogen atom, an acyl group, an ester group, an alkoxy group, a nitro group, and a group different from the base group (for example, an aromatic group such as an aryl group). The substituents may be used alone or in combination of two or more kinds to substitute for the linking group (hydrocarbon group).

[0035] In a linking group having an ionic group (such as a hydrocarbon group), the number of the ionic group may be one or more, and two or more ionic groups may be substituted on the linking group.

[0036] Specific examples of the acetal skeleton having an ionic group (skeleton represented by formula (1)) include a skeleton in which R in the above formula (1) is an ionic group (e.g., a carboxyl group and a salt thereof), and a skeleton represented by the following formula (1-1).

[0037] [ka] (In the formula, R1 to R5 represent a hydrogen atom or a substituent, provided that at least one of R1 to R5 is an ionic group.)

[0038] In the above formula (1-1), the ionic group and the substituent may be those exemplified above. At least one of R1 to R5 is an ionic group, and preferably any one of them may be an ionic group. Typically, one of R1 to R5 may be an ionic group (e.g., a carboxyl group, a sulfonic acid group, or a salt thereof), and four may be hydrogen atoms.

[0039] The acetal skeleton having an ionic group {e.g., a group represented by formula (1) (or R-< in formula (1)}} may be derived from a corresponding carbonyl compound (e.g., an aldehyde, its acetal, a ketone, etc.), in particular, an aldehyde (e.g., RCHO). The carbonyl compound may have a substituent.

[0040] Examples of such carbonyl compounds include aldehydes (particularly monoaldehydes) such as alkanals having an ionic group (e.g., alkanals having an acid group or a salt thereof, such as glyoxylic acid, formylacetic acid, formylpropionic acid, and salts thereof), arenecarbaldehydes having an ionic group [e.g., arenecarbaldehydes having an acid group or a salt thereof, such as formylbenzoic acid (e.g., 4-formylbenzoic acid), formylbenzenesulfonic acid (e.g., 2-formylbenzenesulfonic acid, 4-formylbenzene-1,3-disulfonic acid), and salts thereof], and the like; and the corresponding ketones and acetals. When a carbonyl compound has isomers (for example, cis-trans isomers, etc.), both isomers (for example, both cis and trans isomers, etc.) are included.

[0041] In the PVA polymer (A), the ionic group in the carbonyl compound may be derivatized (esterified, anhydrified, etc.) so long as it is capable of forming an ionic group. For example, esters (e.g., alkyl esters) and acid anhydrides can be used as long as they can form a corresponding acid group (carboxy group, sulfonic acid group) or a salt thereof (e.g., by hydrolysis) in the PVA polymer (A) (the same applies to ionic groups hereinafter).

[0042] These carbonyl compounds can be used alone or in combination of two or more.

[0043] From the viewpoint of water solubility, etc., it is preferable that the carbonyl compound is a monocarbonyl compound (monoaldehyde, etc.), and even when a polyvalent carbonyl compound (for example, a polyvalent aldehyde such as a dialdehyde) is used, the amount is often reduced or otherwise used at a level that ensures water solubility, etc.

[0044] The acetal skeleton having an ionic group (for example, the acetal skeleton represented by the above formula (1)) may be a skeleton that can be introduced via a hydroxy group, and may be, for example, an acetal skeleton derived from (introduced via) two adjacent hydroxy groups (for example, hydroxy groups of a vinyl alcohol unit). For example, when a carbonyl compound having an ionic group (aldehyde, ketone, etc.) is used, for example, two adjacent OH groups in a PVA polymer can be acetalized with the carbonyl compound having an ionic group to obtain a PVA polymer (A) having an acetal skeleton having an ionic group. The acetal skeleton having an ionic group (for example, the acetal skeleton represented by the above formula (1)) may or may not have a polymerizable unsaturated bond.

[0045] The PVA polymer (A) may have one or more kinds of acetal skeletons having an ionic group, either singly or in combination.

[0046] In the PVA polymer (A), the content (proportion, content ratio) of an acetal skeleton having an ionic group (e.g., a skeleton represented by formula (1) or formula (1-1)) may be selected from a range of about 0.001 mol % or more (e.g., 0.005 mol % or more) per monomer unit, and may be, for example, 0.01 mol % or more, preferably 0.03 mol % or more, more preferably 0.05 mol % or more, or may be 10 mol % or less [for example, 8 mol % or less (e.g., 5 mol % or less, 3 mol % or less), preferably 2 mol % or less, more preferably 1 mol % or less].

[0047] In addition, these ranges (upper limit and lower limit) may be appropriately combined to select a range (for example, 0.01 to 3 mol %, 0.03 to 5 mol %, etc.; the same applies to the following range descriptions).

[0048] Specifically, the content of the acetal skeleton having an ionic group per monomer unit may be about 0.01 to 5 mol %, preferably about 0.03 to 2 mol %, and more preferably about 0.05 to 1 mol %.

[0049] The content of 1 mol % refers to the case where there is one acetal skeleton having an ionic group (for example, a skeleton represented by formula (1) or a skeleton represented by formula (1-1)) per 100 monomer units (for example, a total of monomer units such as vinyl alcohol units and vinyl ester units).

[0050] When the content falls within the above range, the hydrophilicity of the PVA polymer (A) is improved, and the ease of preparation of an aqueous solution, storage stability, and dispersibility in warm water are easily improved.

[0051] In addition, by not setting the upper limit too high, the hydrophilicity of the PVA polymer (A) is not too high, and the performance as a dispersion stabilizer can be efficiently realized (for example, a vinyl chloride resin excellent in plasticizer absorption, etc. can be efficiently obtained).

[0052] The method for measuring the content of an acetal skeleton having an ionic group (e.g., a skeleton represented by formula (1) or formula (1-1)) is not particularly limited, and can be measured, for example, by using NMR, titration, UV absorbance, or the like. As a specific example, the content of the skeleton represented by formula (1-1) can be determined by dissolving the PVA polymer (A) in an appropriate solvent (e.g., d6-DMSO) and measuring the content of the skeleton represented by formula (1-1). 1 It may be measured by H-NMR and analyzing signals derived from substituents (e.g., hydrogen) on the benzene ring. In addition, the PVA polymer (A) is completely saponified, and the sample after Soxhlet extraction (e.g., after removing sodium acetate) is dissolved in water, and a small amount of sodium hydroxide (NaOH) is added, followed by conductometric titration with dilute hydrochloric acid, whereby the amount of carboxyl groups can be determined from the titration amount of hydrochloric acid. In addition, when the acetal skeleton having an ionic group has UV (ultraviolet) absorption, the content of the acetal skeleton having an ionic group can be measured by measuring the UV absorbance of an aqueous solution containing the PVA polymer (A).

[0053] The method for incorporating (introducing) an acetal skeleton having an ionic group (e.g., an acetal skeleton having a carboxyl group, a sulfonic acid group, or a salt thereof) into the PVA polymer (A) is not particularly limited, and any conventional method can be used.

[0054] In a representative method, as described later, the PVA polymer (B) may be acetalized with a carbonyl compound having an ionic group (an aldehyde, its acetal, a ketone, or the like).

[0055] Examples of aldehydes having an ionic group include glyoxylic acid, 2-formylbenzoic acid, 4-formylbenzoic acid, sodium 2-formylbenzenesulfonate, sodium 4-formylbenzenesulfonate, and disodium 4-formylbenzene-1,3-disulfonate. Of these, 4-formylbenzoic acid or sodium 2-formylbenzenesulfonate is preferred.

[0056] As described above, the carbonyl compound may be an acetal, which is a condensation product of an aldehyde and an alcohol. The acetal is not particularly limited, but may be, for example, a condensation product with a primary alcohol (e.g., methanol, etc.).

[0057] The carbonyl compounds can be used alone or in combination of two or more kinds.

[0058] The PVA polymer (A) may or may not have a polymerizable unsaturated bond (radically polymerizable unsaturated bond, radically polymerizable group).

[0059] In such a PVA polymer (A), the form of the polymerizable unsaturated bond is not limited, and for example, the polymerizable unsaturated bond may be contained as an acetal skeleton (acetal group, acetal unit) having a polymerizable unsaturated bond. The PVA polymer (A) may or may not have an acetal skeleton (acetal group, acetal unit) having a polymerizable unsaturated bond (radically polymerizable unsaturated bond, radically polymerizable group).

[0060] In the acetal skeleton, the number of polymerizable unsaturated bonds is not particularly limited as long as it is 1 or more (for example, 1 to 5, etc.).

[0061] In such an acetal skeleton, the acetal may be either a cyclic acetal or an acyclic (chain) acetal, and is preferably a cyclic acetal.

[0062] A representative acetal skeleton having a polymerizable unsaturated bond includes a skeleton (structural unit) represented by the following formula (2). Therefore, the acetal skeleton having a polymerizable unsaturated bond may include a skeleton represented by the following formula (2).

[0063] [ka] (In the formula, R' represents a group having a polymerizable unsaturated bond.)

[0064] In the above formula (2), R' is a group having a polymerizable unsaturated bond. R' may be a polymerizable unsaturated bond group itself, or may be a group containing a polymerizable unsaturated bond (for example, a hydrocarbon group). In addition, the group having a polymerizable unsaturated bond may have a substituent in addition to the polymerizable unsaturated bond. The substituent can be appropriately selected according to the type of the group having a polymerizable unsaturated bond, and is not particularly limited, and examples thereof include a hydroxyl group, a halogen atom, an acyl group, an ester group, an alkoxy group, a nitro group, a substituted amino group, and a group different from the base group (for example, an aromatic group such as an aryl group). The substituents may be used alone or in combination of two or more kinds.

[0065] Examples of the group having a polymerizable unsaturated bond [particularly a double bond (ethylenic double bond)] include a group having one polymerizable unsaturated bond {for example, an alkenyl group [for example, a hydrocarbon group (which may have a substituent) having 2 or more carbon atoms (for example, 2 to 30, preferably 2 to 14, more preferably about 2 to 10 carbon atoms), such as a vinyl group, an allyl group, a propenyl group (1-propenyl group, 2-propenyl group, etc.), a butenyl group, a pentenyl group, a 6-methyl-5-hexenyl group, a decenyl group, a 2-(dimethylamino)vinyl group, a cyclohexenyl group, a 2-phenylethenyl group, etc.], and the like}, a group having two or more polymerizable unsaturated bonds {for example, an alkadienyl group [for example, a 1,3-pentadienyl group, a 2,6-diphenyl Examples of the alkyl group include an alkadienyl group having 4 or more carbon atoms (e.g., about 4 to 30, preferably about 4 to 14, and more preferably about 4 to 10), such as a methyl-1,5-hexadienyl group, a cyclohexadienyl group, or a propenylcyclohexenyl group), an alkatrienyl group [e.g., an alkatrienyl group having 6 or more carbon atoms (e.g., about 6 to 30, and preferably about 6 to 24)], an alkatetraenyl group [e.g., an alkatetraenyl group having 8 or more carbon atoms (e.g., about 8 to 30, and preferably about 8 to 24)], and an alcapentaenyl group [e.g., an alcapentaenyl group having 10 or more carbon atoms (e.g., about 10 to 30, and preferably about 10 to 24)] (hydrocarbon groups which may have a substituent, for example, an alkapolyenyl group).

[0066] The acetal skeleton having a polymerizable unsaturated bond {for example, a group represented by formula (2) (or R'-< in formula (2)}) may be derived from a corresponding carbonyl compound (for example, an aldehyde, its acetal, or a ketone, etc.), in particular, an aldehyde [for example, R'CHO (an aldehyde in which R' is a hydrocarbon group having a polymerizable unsaturated bond), etc.]. The carbonyl compound may have a substituent, as described above.

[0067] Examples of such carbonyl compounds include alkenals [e.g., acrolein, crotonaldehyde, methacrolein, 3-butenal, 3-methyl-2-butenal, 2-methyl-2-butenal, 2-pentenal, 3-pentenal, 4-pentenal, 2-hexenal, 3-hexenal, 4-hexenal, 5-hexenal, 2-ethylcrotonaldehyde, 2-methyl-2-pentenal, 3-( dimethylamino)acrolein, 10-undecenal, myristolein aldehyde, palmitolein aldehyde, olein aldehyde, elaidin aldehyde, vaccenaldehyde, gadolein aldehyde, erucaldehyde, nervonaldehyde, linoleic aldehyde, citronellal, cinnamaldehyde, and other alkenals having 3 to 15 carbon atoms, preferably alkenals having 3 to 10 carbon atoms], alkadienals [e.g., Alkadienals having 5 to 15 carbon atoms, such as 2,4-pentadienal, 2,4-hexadienal, 2,6-nonadienal, citral, and perilla aldehyde, preferably alkadienals having 5 to 10 carbon atoms], alkatrienals [for example, alkatrienals having 7 to 30 carbon atoms, such as linolenic aldehyde and eleostearic aldehyde, preferably alkatrienals having 7 to 25 carbon atoms], and alkatetraenals [for example, sucrose aldehyde and sucrose aldehyde]. Examples of the aldehyde include unsaturated aldehydes (particularly monoaldehydes) such as alkatetraenals having 9 to 30 carbon atoms, such as thearidone aldehyde and arachidone aldehyde, preferably alkatetraenals having 9 to 25 carbon atoms, and alkpentaenals (for example, alkapentaenals having 11 to 30 carbon atoms, such as eicosapentaenaldehyde, preferably alkapentaenals having 11 to 25 carbon atoms), and ketones and acetals corresponding thereto. When a carbonyl compound has isomers (for example, cis-trans isomers, etc.), both isomers (for example, both cis and trans isomers, etc.) are included.

[0068] These carbonyl compounds can be used alone or in combination of two or more.

[0069] From the viewpoint of water solubility, etc., it is preferable that the carbonyl compound is a monocarbonyl compound (monoaldehyde, etc.), and even when a polyvalent carbonyl compound (for example, a polyvalent aldehyde such as a dialdehyde) is used, the amount is often reduced or otherwise used at a level that ensures water solubility, etc.

[0070] The acetal skeleton having a polymerizable unsaturated bond (for example, the acetal skeleton represented by the above formula (2)) may be a skeleton that can be introduced via a hydroxy group, and may be, for example, an acetal skeleton derived from (introduced via) two adjacent hydroxy groups (for example, hydroxy groups of a vinyl alcohol unit). For example, when a carbonyl compound (aldehyde, ketone, etc.) having a polymerizable unsaturated bond is used, for example, two adjacent OH groups in a PVA polymer can be acetalized with the carbonyl compound having a polymerizable unsaturated bond to obtain a PVA polymer (A) having an acetal skeleton having a polymerizable unsaturated bond. The acetal skeleton having a polymerizable unsaturated bond (for example, the acetal skeleton represented by the above formula (2)) may or may not have an ionic group (ionic skeleton).

[0071] The PVA polymer (A) may have one or more polymerizable unsaturated bonds, and may have one or more types of acetal skeletons having polymerizable unsaturated bonds.

[0072] When the PVA-based polymer (A) has a polymerizable unsaturated bond (such as an ethylenic double bond), the content of the polymerizable unsaturated bond [for example, an acetal skeleton having a polymerizable unsaturated bond (such as a skeleton represented by formula (2))] may be selected from a range of about 0.001 mol % or more (for example, 0.005 mol % or more) per monomer unit in the PVA-based polymer (A), and may be, for example, 0.01 mol % or more, preferably 0.05 mol % or more, more preferably 0.1 mol % or more, particularly 0.2 mol % or more, or may be 10 mol % or less [for example, 8 mol % or less (for example, 5 mol % or less, 3 mol % or less), preferably 2 mol % or less, more preferably 1 mol % or less].

[0073] Specifically, the content of the polymerizable unsaturated bond in the PVA polymer (A) may be about 0.05 to 5 mol %, preferably about 0.1 to 3 mol %, and more preferably about 0.2 to 2 mol %, per monomer unit.

[0074] The above content makes it easy to obtain high polymerization stability. In addition, by making the content not too high, the hydrophobicity of the PVA polymer (A) is not too high, and the aqueous solution preparation property, storage stability, and dispersibility in warm water are excellent.

[0075] When the PVA polymer (A) has a polymerizable unsaturated bond (such as an ethylenic double bond), the content of the polymerizable unsaturated bond (content per monomer unit) in the PVA polymer (A) may be 50 mol or less (e.g., 30 mol or less, 20 mol or less), preferably 15 mol or less, more preferably 10 mol or less, or may be 0.05 mol or more (e.g., 0.1 mol or more, 0.5 mol or more), preferably 1 mol or more, more preferably 2 mol or more, particularly preferably 3 mol or more, per mol of the acetal skeleton having an ionic group (e.g., the skeleton represented by formula (1) or formula (1-1)).

[0076] At such a ratio, it is easy to achieve both excellent aqueous solution preparation properties, storage stability, and the like, as well as excellent performance as a dispersion stabilizer.

[0077] The method for obtaining the PVA polymer (A) having a polymerizable unsaturated bond is not particularly limited and a conventional method can be used. For example, as described later, it is preferable to obtain the PVA polymer (B) by acetalization with an aldehyde having a polymerizable unsaturated bond or an acetal thereof.

[0078] The aldehyde having a polymerizable unsaturated bond is not particularly limited, and examples thereof include the aldehydes exemplified above (e.g., acrolein, methacrolein, crotonaldehyde, cinnamaldehyde, 2,4-hexadienal, citral, citronellal, perillaldehyde, 10-undecenal, etc.).

[0079] The PVA polymer (A) may have another acetal skeleton (acetal group, acetal unit) that does not belong to the category of an acetal skeleton having an ionic group or an acetal skeleton having a polymerizable unsaturated bond. Examples of such other acetal skeletons include a skeleton in which R in the above formula (1) is a group not having an ionic group or a polymerizable unsaturated bond (e.g., an aliphatic group, an aromatic group, etc.). Examples of such groups include aliphatic groups [e.g., alkyl groups (e.g., C groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, and undecyl groups], 1-30 alkyl group), cycloalkyl group (e.g., cyclopentyl group, cyclohexyl group, etc. 3-20 cycloalkyl groups, etc.)], aromatic groups [e.g., aryl groups (e.g., C groups such as phenyl groups, naphthyl groups, etc. 6-20 Aryl groups, etc.

[0080] The method for introducing such another acetal skeleton is not particularly limited and may be a conventional method, for example, a method of acetalizing a PVA polymer (B) described below with an aldehyde corresponding to the other acetal skeleton. In such a method, the other acetal skeleton is usually formed from two adjacent vinyl alcohol units.

[0081] Examples of such aldehydes include aliphatic aldehydes such as alkanals (e.g., acetaldehyde, propionaldehyde, butanal, pentanal, hexanal, heptanal, octanal, nonanal, decanal, undecanal, dodecanal, 2-methylbutanal, 2-ethylbutanal, 2-methylpentanal, and 2-ethylhexanal) and cycloalkanecarbaldehydes (e.g., cyclopentanecarboxaldehyde, cyclohexanecarbaldehyde, and the like), and aromatic aldehydes such as arenecarbaldehydes (e.g., benzaldehyde, naphthaldehyde, and the like).

[0082] The PVA polymer (A) has at least a vinyl alcohol unit, but may also have a vinyl alcohol unit and a unit that has not been hydrolyzed (saponified) [for example, a vinyl ester unit (or a unit derived from a vinyl ester monomer, for example, a vinyl acetate unit)].

[0083] In addition, the PVA polymer (A) may contain other units (units other than the above-mentioned units such as vinyl alcohol units, non-hydrolyzed units, and acetal skeletons having ionic groups) as necessary. Examples of such units include units derived from other monomers exemplified in the section on the PVA polymer (B) described later.

[0084] The saponification degree of the PVA polymer (A) may be, for example, 20 mol% or more (e.g., 25 mol% or more), preferably 30 mol% or more (e.g., 35 mol% or more), and more preferably 40 mol% or more (e.g., 45 mol% or more).

[0085] The upper limit of the saponification degree of the PVA polymer (A) may be, for example, 95 mol% or less (e.g., 93 mol% or less), preferably 90 mol% or less (e.g., 85 mol% or less), and more preferably 80 mol% or less (e.g., 75 mol% or less).

[0086] Specifically, the saponification degree of the PVA polymer (A) may be, for example, about 20 to 90 mol %, preferably about 30 to 80 mol %, and more preferably about 40 to 75 mol %.

[0087] If the saponification degree is not too low (e.g., about 20 mol % or more), it is preferable because the aqueous solution can be easily prepared, the storage stability can be excellent, and the hot water dispersibility can be excellent. If the saponification degree is not too high (e.g., about 90 mol % or less), it is preferable because it is easy to exhibit excellent performance as a dispersant (e.g., it is easy to efficiently obtain a vinyl chloride resin with excellent plasticizer absorption, etc.).

[0088] The saponification degree can be determined, for example, by the method for measuring the saponification degree of PVA specified in JIS K 6726.

[0089] The saponification degree of the PVA polymer (A) can be adjusted, for example, by the saponification degree of the raw material PVA polymer (B). When the PVA polymer (B) is converted into the PVA polymer (A), the saponification degree may increase. In such a case, the saponification degree of the PVA polymer (B) may be adjusted to be lower in anticipation of the increase (according to the change), or the saponification degree may be substantially increased (for example, the saponification degree is not increased or is increased by about 2 mol % or less) by controlling the reaction conditions when the PVA polymer (A) is converted (for example, acetalization with an aldehyde having an ionic group is performed).

[0090] When the PVA polymer (A) has vinyl ester units, the ratio (ratio in monomer units) of the acetal skeleton having an ionic group (e.g., the skeleton represented by formula (1) or formula (1-1)) may be 10 mol or less, preferably 5 mol or less, more preferably 3 mol or less, or may be 0.01 mol or more (e.g., 0.05 mol or more, 0.1 mol or more), preferably 0.2 mol or more, more preferably 0.3 mol or more, relative to 100 mol of the vinyl ester units.

[0091] At such a ratio, it is easy to achieve both excellent aqueous solution preparation properties, storage stability, and the like, as well as excellent performance as a dispersion stabilizer.

[0092] The (average) degree of polymerization of the PVA-based polymer (A) is not particularly limited, and may be, for example, 100 or more (e.g., 120 or more), preferably 150 or more (e.g., 160 or more), and more preferably 180 or more (e.g., 200 or more, 220 or more, 250 or more, 280 or more).

[0093] The upper limit of the (average) polymerization degree of the PVA polymer (A) is not particularly limited, and may be selected from the range of about 10,000 or less (e.g., 8,000 or less, 5,000 or less), and may be 3,000 or less (e.g., 2,500 or less), preferably 2,000 or less (e.g., 1,500 or less), and more preferably 1,000 or less (e.g., 800 or less).

[0094] Specifically, the (average) degree of polymerization of the PVA polymer (A) may be, for example, about 120 to 3,000, preferably about 150 to 2,000, and more preferably about 180 to 1,000.

[0095] If the degree of polymerization of the PVA polymer (A) is not too small (for example, about 120 or more), it is advantageous in terms of polymerization stability, inhibition of scale adhesion, inhibition of coarsening of the obtained vinyl resin, etc. Also, if the degree of polymerization is not too large (for example, about 3000 or less), it is advantageous in terms of excellent preparation properties of an aqueous solution, storage stability, hot water dispersibility, etc.

[0096] The (average) degree of polymerization of PVA can be determined, for example, by the measurement method specified in JIS K 6726.

[0097] The (average) degree of polymerization of the PVA polymer (A) can be adjusted, for example, by the degree of polymerization of the raw material PVA polymer (B), and can usually reflect the degree of polymerization of the PVA polymer (B).

[0098] The cloud point of a 4% by mass aqueous solution of the PVA-based polymer (A) is, for example, preferably 20°C or higher (e.g., more than 20°C, 22°C or higher, 23°C or higher, 24°C or higher, or 25°C or higher), more preferably 27°C or higher (e.g., 28°C or higher), and may be 30°C or higher, etc.

[0099] The upper limit of the cloud point of a 4% by mass aqueous solution of the PVA polymer (A) is not particularly limited, and may be, for example, 75°C, 70°C, 65°C, 60°C, 55°C, 50°C, or the like. Typically, the cloud point of a 4% by mass aqueous solution of the PVA polymer (A) may be, for example, 30 to 50°C.

[0100] Such a cloud point provides excellent preparation properties and storage stability of the aqueous solution.

[0101] The cloud point of a 4% by mass aqueous solution can be adjusted by the degree of saponification, degree of polymerization, and content of acetal skeleton having an ionic group of the PVA polymer (A).

[0102] [Aqueous liquid] The PVA polymer (A) may be used as it is as a dispersion stabilizer (dispersant) or the like, or may be used as an aqueous liquid by dissolving it in water. The aqueous liquid of the present invention may contain the PVA polymer (A) and water. The aqueous liquid is, for example, a liquid in which the PVA polymer (A) is dispersed or dissolved in water as a dispersoid.

[0103] In the aqueous liquid, the content of the PVA polymer (A) is not particularly limited, and may be, for example, about 1 mass% or more (e.g., 2 mass% or more, 3 mass% or more) or about 80 mass% or less (e.g., 70 mass% or less, 60 mass% or less, 50 mass% or less, 40 mass% or less, 30 mass% or less).

[0104] The aqueous liquid of the present invention has good stability.

[0105] The aqueous liquid may contain a water-soluble organic solvent from the viewpoint of improving storage stability. Examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; esters such as methyl acetate and ethyl acetate; glycol derivatives such as ethylene glycol, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether; and the like. Two or more of these organic solvents may be mixed and used.

[0106] When a water-soluble organic solvent is contained, the ratio of the water-soluble organic solvent to the entire solvent may be, for example, 70 mass % or less (e.g., 60 mass % or less), preferably 50 mass % or less, and more preferably 30 mass % or less. In particular, from the viewpoint of environmental considerations and improving workability, the content of the organic solvent is preferably 5 mass % or less with respect to the entire solvent or aqueous liquid.

[0107] [Manufacturing method] In the present invention, the method for producing the PVA polymer (A) is not particularly limited, but for example, the PVA polymer (A) can be obtained by acetalizing the PVA polymer (B) with an aldehyde having an ionic group or the like. The PVA polymer (B) and the acetalization will be described in detail below.

[0108] [PVA polymer (B)] The PVA polymer (B) is not particularly limited, but for example, a PVA polymer [a saponified product of a vinyl ester polymer (a polymer having a vinyl ester monomer as a polymerization component)] obtained by saponifying (reacting) a vinyl ester polymer can be used.

[0109] The vinyl ester polymer can be obtained by polymerizing at least a vinyl ester monomer (polymerizing it as a polymerization component). The polymerization method is not particularly limited, and may be according to a conventionally known method, for example, bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. Considering the control of the polymerization degree and the saponification reaction performed after polymerization, solution polymerization using methanol as a solvent or suspension polymerization using water or water / methanol as a dispersion medium is preferable, but is not limited thereto.

[0110] The vinyl ester monomer usable in the polymerization is not particularly limited, but examples thereof include fatty acid vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl caprylate, and vinyl versatate, and these vinyl ester monomers can be used alone or in combination. Among these, vinyl acetate is preferred from an industrial viewpoint.

[0111] In the polymerization of the vinyl ester monomer, the vinyl ester monomer may be copolymerized with other monomers as long as the effects of the present invention are achieved. In other words, the polymerization components of the vinyl ester polymer may contain the vinyl ester monomer and other monomers. Examples of other monomers that can be used include, but are not limited to, α-olefins (e.g., ethylene, propylene, n-butene, isobutylene, etc.), (meth)acrylic acid and its salts, (meth)acrylic acid esters [e.g., (meth)acrylic acid alkyl esters (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, etc. (meth)acrylic acid C] 1-20alkyl, etc.)], (meth)acrylamide, (meth)acrylamide derivatives (e.g., N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone(meth)acrylamide, (meth)acrylamidopropanesulfonic acid and its salts, (meth)acrylamidopropyldimethylamine and its salts or its quaternary salts, N-methylol(meth)acrylamide, etc.), vinyl ethers (e.g., methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. 1-20 Examples of the monomer include alkyl vinyl ethers, nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl halides (e.g., vinyl chloride, vinyl fluoride, etc.), vinylidene halides (e.g., vinylidene chloride, vinylidene fluoride, etc.), allyl compounds (e.g., allyl acetate, allyl chloride, sodium allylsulfonate, etc.), unsaturated dicarboxylic acids (e.g., maleic acid, itaconic acid, fumaric acid, etc.) and their salts or esters, vinylsilyl compounds (e.g., vinyltrimethoxysilane, etc.), fatty acid alkenyl esters (e.g., isopropenyl acetate, etc.), etc. These other monomers can be used alone or in combination.

[0112] When the other monomer is used, the content of the other monomer is, for example, 0.1 to 20 mass % based on the total amount of the monomers.

[0113] In the polymerization of the vinyl ester monomer, a chain transfer agent may be used in the presence of the vinyl ester monomer in order to adjust the degree of polymerization of the resulting vinyl ester polymer. The chain transfer agent is not particularly limited, but examples thereof include aldehydes such as acetaldehyde, propionaldehyde, butylaldehyde, and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone, and cyclohexanone; mercaptans such as 2-hydroxyethanethiol, dodecyl mercaptan, 3-mercaptopropionic acid, mercaptosuccinic acid, and sodium 3-mercapto-1-propanesulfonate; and organic halogens such as carbon tetrachloride, trichloroethylene, and perchloroethylene. Among these, aldehydes and ketones are preferably used. The amount of the chain transfer agent to be added is determined according to the chain transfer constant of the chain transfer agent to be added and the polymerization degree of the desired vinyl ester polymer, but is generally preferably 0.1 to 10% by mass based on the total amount of monomers.

[0114] The vinyl ester polymer obtained as described above is subjected to a saponification reaction to produce the PVA polymer (B). The method of saponification of the vinyl ester polymer is not particularly limited, and may be a conventionally known method. For example, alcoholysis or hydrolysis using an acid catalyst such as an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid, or an organic acid such as formic acid, acetic acid, oxalic acid or p-toluenesulfonic acid can be used. Examples of the solvent 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 kinds.

[0115] The saponification degree of the PVA polymer (B) is not particularly limited. However, the saponification degree of the PVA polymer (A) may become higher than that of the raw material PVA polymer (B) during the subsequent acetalization reaction or the like. In such a case, it is preferable to adjust the saponification degree to a lower value (e.g., a saponification degree lower by 0 to 5 mol%) than the target saponification degree of the PVA polymer (A).

[0116] The degree of polymerization of the PVA polymer (B) is not particularly limited. However, since the degree of polymerization of the PVA polymer (A) can usually reflect the PVA polymer (B) as a raw material during the subsequent acetalization reaction or the like, it is preferable to adjust the degree of polymerization of the PVA polymer (A) to a target degree.

[0117] [Acetalization] In the present invention, the method of introducing an acetal skeleton having an ionic group (such as a carboxyl group, a sulfonic acid group, or a salt thereof) into the PVA polymer (A) is not particularly limited. For example, the PVA polymer (A) can be obtained by acetalizing the PVA polymer (B) with a carbonyl compound having an ionic group (such as an aldehyde, its acetal, or a ketone). The acetalization method is not particularly limited, and any known acetalization method can be used.

[0118] In the acetalization, the amount of the carbonyl compound having an ionic group used is not particularly limited and can be selected depending on the content of the acetal skeleton having a desired ionic group in the PVA polymer (A), and may be, for example, about 0.05 to 50 parts by mass, preferably 0.1 to 20 parts by mass, and more preferably 0.2 to 10 parts by mass relative to 100 parts by mass of the PVA polymer (B).

[0119] The acetalization reaction is preferably carried out in the presence of an acid catalyst, which is not particularly limited, but includes, for example, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and organic acids such as formic acid, acetic acid, oxalic acid, and p-toluenesulfonic acid.

[0120] The amount of the acid catalyst used is not particularly limited, but may be, for example, about 0.1 to 10 parts by mass relative to 100 parts by mass of the PVA polymer (B).

[0121] Specific examples of the acetalization method include: (i) a method in which a vinyl ester polymer is saponified in a solvent such as methanol with a basic catalyst such as sodium hydroxide to obtain a solution of a PVA polymer (B), and then an aldehyde or the like having an ionic group and an acid catalyst are added to the solution to acetalize the polymer, followed by neutralization with a basic substance to obtain a solution of a PVA polymer (A); (ii) a vinyl ester polymer is saponified in a solvent such as methanol in the presence of an acid catalyst as a saponification catalyst to obtain a PVA polymer (B), and then an aldehyde or the like having an ionic group is added to the solution to acetalize the polymer using the acid catalyst used in the saponification reaction as it is, followed by neutralization with a basic substance to obtain a solution of a PVA polymer (A); (iv) a method in which an aldehyde or the like having an ionic group is added to an aqueous solution of a PVA polymer (B) and reacted in the presence of an acid catalyst, followed by neutralization with a basic substance to obtain an aqueous solution of the PVA polymer (A); (v) a method in which an aldehyde or the like having an ionic group is directly added to a slurry or powdered PVA polymer (B) or a liquid in which it is dissolved or dispersed in an organic solvent or water is added, followed by reaction in the presence of an acid catalyst, followed by neutralization with a basic substance, and then excess solvent is removed to obtain the PVA polymer (A). In the methods (i) to (iii), the solvent can then be dried to obtain a solid, or the solvent can be replaced with water to obtain an aqueous liquid. In the method (iv), since an aqueous liquid can be obtained, it can be used as it is in the suspension polymerization of a vinyl monomer (for example, vinyl chloride). The method (v) of reacting in a slurry state allows the PVA polymer to be obtained as a solid, which is easy to handle. In the methods (i) to (v), the method for preparing the PVA polymer (A) and the PVA polymer (B) into an aqueous liquid, and the methods for saponification, neutralization, dissolution, dispersion and drying are not particularly limited, and conventional methods can be used.

[0122] The basic substance used for neutralization is not particularly limited, but examples thereof include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide.

[0123] The pH of the reaction solution during the acetalization reaction is preferably 3.0 or less from the viewpoint of reaction rate, more preferably 1.0 or less, and the pH of the reaction solution after neutralization is preferably 4.7 to 9.0, more preferably 7.0 to 8.5.

[0124] [Uses, manufacturing method of vinyl polymers, etc.] The PVA polymer (A) can be used for various applications (e.g., dispersant, film application, etc.), but as described above, it can be suitably used particularly as a dispersion stabilizer [or dispersant, for example, a dispersion stabilizer (dispersant) for polymerization (e.g., suspension polymerization)]. Therefore, the following describes the use of the dispersion stabilizer of the present invention (or PVA polymer (A), hereinafter the same) or a method for producing a vinyl polymer by polymerization (particularly suspension polymerization) of a vinyl monomer using the dispersion stabilizer.

[0125] The suspension polymerization in the present invention is a polymerization mode in which an insoluble vinyl monomer and an oil-soluble polymerization initiator are added to an aqueous medium, and the mixture is stirred to form minute droplets containing the vinyl monomer, and polymerization is carried out in the droplets. The aqueous medium that can be used here is not particularly limited, and examples thereof include water, an aqueous solution containing various additives, and a mixed solvent of water and an organic solvent compatible with water.

[0126] The PVA polymer (A) of the present invention can be used as a dispersion stabilizer when carrying out suspension polymerization of a vinyl monomer. The vinyl monomer is not particularly limited, but for example, vinyl chloride, vinylidene chloride, styrene, acrylic acid ester, methacrylic acid ester, vinyl acetate, acrylonitrile, and other vinyl monomers that are generally used in suspension polymerization are preferred, and among them, vinyl chloride monomers are particularly preferred. Examples of vinyl chloride monomers include vinyl chloride monomers (vinyl chloride), and mixtures of vinyl chloride monomers with other monomers that can be copolymerized with vinyl chloride monomers. Examples of other monomers that can be copolymerized with vinyl chloride monomers include monomers such as vinylidene chloride, vinyl acetate, ethylene, propylene, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, styrene, vinylalkoxysilane, maleic acid, hydroxyalkyl acrylates, allylsulfonic acid, and vinylsulfonic acid.

[0127] Therefore, the dispersion stabilizer of the present invention is suitable for suspension polymerization of vinyl monomers including vinyl chloride monomers (particularly vinyl chloride), and can be particularly suitably used for homopolymerization of vinyl chloride by suspension polymerization. It can also be used for binary or multi-component copolymerization of vinyl chloride and one or more known monomers copolymerizable with vinyl chloride by suspension polymerization, and can be particularly suitably used as a dispersion stabilizer in copolymerization of vinyl chloride and vinyl acetate by suspension polymerization.

[0128] A vinyl chloride resin can be obtained by suspension polymerization of vinyl monomers including vinyl chloride. In the production of the vinyl chloride resin, it is preferable that vinyl chloride accounts for 50 to 100 mol % (or 50 to 100 mass %) of the total amount of vinyl monomers used.

[0129] The polymerization initiator in the suspension polymerization of vinyl monomers may be a known one, and examples thereof include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as benzoyl peroxide, t-butyl peroxyneodecanoate, α-cumyl peroxyneodecanoate, and t-butyl peroxydecanoate; peroxides such as acetylcyclohexylsulfonyl peroxide and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; azo compounds such as 2,2'-azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, and azobis(4-methoxy-2,4-dimethylvaleronitrile); benzoyl peroxide; and lauroyl peroxide. These may also be used in combination with potassium persulfate, ammonium persulfate, hydrogen peroxide, and the like.

[0130] The main role of a dispersion stabilizer in suspension polymerization of a vinyl monomer is to stabilize droplets consisting of the vinyl monomer and its polymer and to prevent polymer particles produced from the droplets from fusing together to form large agglomerates. The dispersion stabilizer of the present invention has excellent dispersion performance and can form stable droplets with a small amount used, thereby preventing the formation of agglomerates due to the above-mentioned fusing. The term "the droplets are stable" means that fine droplets of a substantially uniform size are stably dispersed in the dispersion medium of the suspension polymerization.

[0131] In the suspension polymerization of a vinyl monomer, the amount of the dispersion stabilizer of the present invention (or the PVA polymer (A)) used is not particularly limited, but is usually 5 parts by mass or less, preferably 0.005 to 1 part by mass, and more preferably 0.01 to 0.2 parts by mass, based on 100 parts by mass of the vinyl monomer. Like ordinary dispersion stabilizers, the dispersion stabilizer of the present invention is generally used by dissolving it in a dispersion medium for suspension polymerization in advance using a conventional method before charging the vinyl monomer.

[0132] As a dispersion stabilizer in suspension polymerization of vinyl monomers, the dispersion stabilizer of the present invention may be used alone, but other dispersion stabilizers may be used in combination. Examples of such other dispersion stabilizers include known dispersion stabilizers used when suspension polymerizing vinyl monomers such as vinyl chloride in an aqueous medium, such as PVA with an average polymerization degree of 100 to 4500 and a saponification degree of 30 to 100 mol% and modified PVA polymers other than those of the present invention, water-soluble cellulose ethers such as methylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose, water-soluble polymers such as gelatin, oil-soluble emulsions such as sorbitan monolaurate, sorbitan trioleate, glycerin tristearate, and ethylene oxide propylene oxide block polymers, water-soluble emulsifiers such as polyoxyethylene glycerin oleate and sodium laurate, etc. These other dispersants may be used alone or in combination of two or more.

[0133] In the present invention, it is preferable to use two or more PVA-based polymers having different degrees of polymerization and saponification as a dispersion stabilizer in combination, and it is preferable that one or more of them is the PVA-based polymer (A) which is the dispersion stabilizer of the present invention. More preferably, a PVA-based polymer having a degree of polymerization of 1700 or more and high dispersion stability is used in combination with a PVA-based polymer having a degree of polymerization of 1000 or less, and one or more of them is the PVA-based polymer (A) of the present invention.

[0134] In the suspension polymerization using the dispersion stabilizer of the present invention, it is possible to use various known dispersion assistants in combination. As such a dispersion assistant, a low saponification degree PVA or the like, preferably having a saponification degree of 30 to 60 mol%, more preferably 35 to 55 mol%, is used. In addition, as the dispersion assistant, a PVA or the like, preferably having an average polymerization degree of 160 to 900, more preferably 200 to 500, is used.

[0135] In addition to the dispersion aid, various additives known in the suspension polymerization of vinyl compounds, such as chain transfer agents, polymerization inhibitors, pH adjusters, scale inhibitors, and crosslinking agents, may be used in combination.

[0136] The polymerization temperature in the suspension polymerization is not limited and can be arbitrarily selected depending on the type of vinyl monomer used, the polymerization degree of the target polymer, the polymerization yield, etc., but is usually preferably 40 to 70° C. The polymerization time is also not particularly limited and may be appropriately set depending on the target polymerization yield, etc.

[0137] The vinyl polymer obtained by the above-mentioned production method of the present invention can be processed into various molded articles, etc. In particular, vinyl chloride resins, for example, have an average particle size in an appropriate range and can be efficiently obtained as those with excellent plasticizer absorption properties, and often have good processability into various molded articles. EXAMPLES

[0138] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples in any way. In the following examples and comparative examples, "%" and "parts" mean "% by mass" and "parts by mass" unless otherwise specified.

[0139] First, the methods for measuring the cloud point of the aqueous PVA solution and evaluating the storage stability, as well as the methods for evaluating the vinyl chloride polymer (vinyl chloride resin) in the present examples, are described below. (Method for measuring the cloud point of a PVA aqueous solution) A 4% PVA aqueous solution at 20°C was placed in a quartz cell with an optical path length of 1 mm, and the transmittance at 430 mm was continuously measured at a heating rate of 2°C / min from 20°C. The temperature at which the transmittance was 50% of that of the blank (pure water) was defined as the cloud point.

[0140] (Method for evaluating storage stability of PVA aqueous solution) A beaker containing a 4% PVA aqueous solution was placed in a thermostatic water bath at 30°C, and the state of the aqueous solution after 24 hours was visually inspected and evaluated according to the following criteria. ◯: The aqueous solution remained homogeneous. ×: The aqueous solution separated into two layers.

[0141] (Evaluation of vinyl chloride polymers) The vinyl chloride polymer was evaluated for average particle size, plasticizer absorption, and amount of scale adhesion as follows.

[0142] <Average particle size> The particle size distribution was measured using a low tap vibrating sieve (JIS sieve was used) to determine the average particle size.

[0143] <Plasticizer absorption> The resin obtained was placed in a cylindrical container with glass fiber packed at the bottom, and excess dioctyl phthalate (hereinafter abbreviated as DOP) was added and allowed to stand for 30 minutes to allow the DOP to penetrate the resin. The resin was then centrifuged at 3000 rpm to remove excess DOP, after which the mass of the resin was measured and the DOP absorption per 100 parts of polymer was calculated. A larger DOP absorption indicates better plasticizer absorption and superior molding processability.

[0144] <Amount of scale buildup> After the polymer slurry was taken out of the polymerizer, the state of adhesion of scale to the inner wall of the polymerizer was visually observed and evaluated according to the following criteria. ◎: No or almost no scale adhesion 〇: Little scale buildup ×: Significant white scale adhesion

[0145] [Example 1] (Synthesis of PVA-based polymer (B)) A reactor equipped with a stirrer, a condenser, a nitrogen gas inlet, and an initiator inlet was charged with 55 parts of methanol and 45 parts of vinyl acetate monomer, and the temperature was raised to 60°C while circulating nitrogen gas through the system. 5 parts of a 1% methanol solution of 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) was added as an initiator to start polymerization. The system was kept at 60°C during the polymerization, and while nitrogen gas was flowing through the system, 90 parts of vinyl acetate monomer was added continuously over a period of 4 hours starting immediately after the start of polymerization. One part of a 1% methanol solution of ADVN was added at one hour and two hours after the start of polymerization. When the reaction yield of vinyl acetate reached 85%, the system was cooled and the polymerization was terminated. Methanol vapor was added to the resulting polymer to distill off the remaining vinyl acetate monomer, yielding a 50% methanol solution of polyvinyl acetate. Next, 15 parts of methyl acetate and 5 parts of a 3% methanol solution of sodium hydroxide were added to 100 parts of the 50% methanol solution of polyvinyl acetate obtained above, and mixed thoroughly to carry out a saponification reaction at 40°C. The resulting gel-like material was pulverized, neutralized with acetic acid, and then dried. Analysis revealed that a powder of PVA-based polymer (B) with a saponification degree of 69 mol% and an average polymerization degree of 600 was obtained.

[0146] (Synthesis of PVA-based polymer (A)) 100 parts of the powder of the PVA polymer (B) obtained above was immersed in a mixed solvent of 150 parts of methanol and 300 parts of methyl acetate, 10 parts of a 10% methanol solution of 4-formylbenzoic acid was added, and the mixture was kept at 50°C for 1 hour. After that, 5 parts of a 50% methanol solution of p-toluenesulfonic acid was added, and the reaction was carried out at 50°C for 1 hour. The mixture was then neutralized with 10 parts of a 5% methanol solution of sodium hydroxide, the pH of which was 7.5 after neutralization. Subsequently, the solvent was removed by centrifugation, and the mixture was dried at 80° C. for 5 hours under a nitrogen atmosphere to obtain a PVA polymer (A). The analytical values ​​of this PVA polymer (A) were a saponification degree of 70 mol%, a polymerization degree of 600, and a cloud point of a 4% aqueous solution of 40° C. The saponification degree and polymerization degree were measured according to the method specified in JIS K 6726. Also, dissolve in d6-DMSO solvent 1 H-NMR measurements showed signals at 7.8 and 7.5 ppm derived from aromatic protons. The content of acetal groups calculated from the signal intensity was 0.1 mol% per monomer unit. Even when a 4% PVA aqueous solution was kept at 30°C for 24 hours, the aqueous solution remained homogeneous.

[0147] (Suspension Polymerization of Vinyl Chloride) Using the PVA polymer (A) obtained above as a dispersion stabilizer, suspension polymerization of vinyl chloride was carried out under the following conditions. In a pressure-resistant stainless steel polymerization reactor, 120 parts of deionized water and 2 parts of the 4% aqueous solution of the PVA polymer (A) obtained above (0.08 parts of the PVA polymer (A) per 100 parts of the vinyl chloride monomer) were charged. Next, the pressure inside the polymerization reactor was reduced to 50 mmHg using a vacuum pump, and after degassing, 100 parts of vinyl chloride monomer were charged, and 0.06 parts of t-butyl peroxy neodecanoate were further charged as a polymerization initiator, followed by stirring and starting to raise the temperature. Suspension polymerization was carried out while maintaining the internal temperature of the polymerization reactor at 57°C, and the polymerization reaction was stopped when the conversion rate of vinyl chloride reached 88%. Then, after recovering the unreacted monomers using a vacuum trap, the polymer slurry was taken out of the polymerization reactor, dehydrated, and dried to obtain a vinyl chloride polymer (vinyl chloride resin).

[0148] [Examples 2 to 14, Reference Examples 1 to 5] The PVA polymer (A) (and PVA polymer (B)) shown in Table 1 was synthesized in the same manner as in Example 1, except that the polymerization conditions, saponification conditions, type and amount of aldehyde used in the acetalization reaction, etc. were appropriately changed. In the synthesis of the PVA polymer (B), in Reference Example 4, itaconic acid (0.2 mol % of the total monomers) was copolymerized with vinyl acetate, and in Comparative Example 5, sodium 2-acrylamido-2-methylpropanesulfonate (0.2 mol % of the total monomers) was copolymerized with vinyl acetate. Using the obtained PVA polymer (A), suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 to obtain a vinyl chloride polymer. In Reference Examples 1, 4 and 5, since the acetalization reaction was not carried out, the PVA polymer (B) was used as the PVA polymer (A) (that is, the PVA polymer (B) and the PVA polymer (A) are the same). The evaluation results of the PVA polymers (B) and (A) and the obtained vinyl chloride polymer are shown in Table 1. In the table, "AMPS" stands for sodium 2-acrylamido-2-methylpropanesulfonate.

[0149] [Table 1]

[0150] As shown in the above table, the PVA polymers (A) obtained in Examples 1 to 14 had good aqueous solution preparation properties, storage stability, and dispersibility in warm water. In addition, when used in suspension polymerization of vinyl chloride, vinyl chloride resins with excellent polymerization stability, an appropriate average particle size, and large plasticizer absorption could be obtained. In particular, the PVA polymers (A) obtained in Examples 11 to 14 allowed more stable suspension polymerization, suppressed aggregation of the vinyl chloride resin, and produced vinyl chloride resins with smaller average particle sizes. [Industrial Applicability]

[0151] The present invention can provide a specific polyvinyl alcohol-based polymer. Such a polymer can be suitably used as a dispersion stabilizer (dispersant) or the like.

Claims

1. A dispersion stabilizer comprising a polyvinyl alcohol-based polymer (A) having an acetal skeleton having an ionic group (excluding a skeleton derived from glyoxylic acid), The agent, wherein the ionic group comprises at least one selected from an anionic group and a salt thereof.

2. A dispersion stabilizer comprising a polyvinyl alcohol-based polymer (A) having an acetal skeleton having an ionic group, The agent, wherein the polyvinyl alcohol-based polymer (A) has a polymerizable unsaturated bond.

3. A dispersion stabilizer comprising a polyvinyl alcohol-based polymer (A) having an acetal skeleton (excluding a skeleton derived from glyoxylic acid) having an ionic group, A dispersion stabilizer for suspension polymerization of vinyl monomers, including vinyl chloride.

4. The agent according to any one of claims 1 to 3, wherein the acetal skeleton having an ionic group contains a skeleton represented by the following formula (1): 【Chemistry 1】 (In the formula, R represents a group having an ionic group.)

5. The agent according to claim 4, wherein the acetal skeleton having an ionic group comprises a skeleton represented by formula (1) in which R is a hydrocarbon group having an ionic group.

6. The agent according to any one of claims 1 to 5, wherein the acetal skeleton having an ionic group includes at least one skeleton selected from the skeleton represented by the formula (1) in which R is an ionic group, and the skeleton represented by the following formula (1-1): 【Chemistry 2】 (In the formula, R １ ~R ５ represents a hydrogen atom or a substituent. １ ~R ５ At least one of the groups is an ionic group.

7. The agent according to any one of claims 1 to 6, wherein the ionic group comprises at least one selected from an acid group and a salt thereof.

8. The agent according to any one of claims 1 to 7, wherein the acetal skeleton having an ionic group comprises a skeleton derived from at least one selected from 4-formylbenzoic acid, 2-formylbenzenesulfonic acid, and salts thereof.

9. The agent according to any one of claims 1 to 8, wherein the content of the acetal skeleton having an ionic group in the polyvinyl alcohol polymer (A) is 0.01 to 5 mol% per monomer unit.

10. The agent according to any one of claims 1 to 9, wherein in the polyvinyl alcohol polymer (A), the ratio of the acetal skeleton having an ionic group is 0.2 to 5 mol per 100 mol of the vinyl ester unit.

11. The agent according to any one of claims 1 to 10, wherein the polyvinyl alcohol polymer (A) has a degree of saponification of 20 to 90 mol %.

12. The agent according to any one of claims 1 to 11, wherein the degree of polymerization of the polyvinyl alcohol-based polymer (A) is 120 to 3,000.

13. The agent according to any one of claims 1 and 3 to 12, wherein the polyvinyl alcohol-based polymer (A) has a polymerizable unsaturated bond.

14. The agent according to any one of claims 1 to 13, wherein the polyvinyl alcohol polymer (A) has polymerizable unsaturated bonds in a ratio of 0.05 to 5 mol % per monomer unit.

15. The agent according to any one of claims 1 to 14, wherein the cloud point of a 4% by mass aqueous solution of the polyvinyl alcohol-based polymer (A) is 25°C or higher.

16. The agent according to any one of claims 1, 2, and 4 to 15, which is a dispersion stabilizer for polymerization.

17. The agent according to any one of claims 1, 2, and 4 to 16, which is a dispersion stabilizer for suspension polymerization.

18. The agent according to any one of claims 1, 2, and 4 to 17, which is a dispersion stabilizer for suspension polymerization of vinyl monomers including vinyl chloride.

19. The polyvinyl alcohol polymer (A) according to any one of claims 1, 2, and 4 to 18.

20. An aqueous liquid containing the polyvinyl alcohol-based polymer (A) or agent according to any one of claims 1, 2, and 4 to 18.

21. A method for producing a vinyl polymer, comprising polymerizing a vinyl monomer in the presence of the polyvinyl alcohol polymer (A) or agent according to any one of claims 1, 2, and 4 to 18.

22. The process according to claim 21, wherein the polymerization is a suspension polymerization.

23. The method according to claim 21 or 22, wherein a vinyl monomer including vinyl chloride is subjected to suspension polymerization.

24. A method for producing a vinyl polymer, comprising suspension polymerizing a vinyl monomer including vinyl chloride in the presence of the polyvinyl alcohol polymer (A) or agent according to any one of claims 3 to 15.

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