Polymer, aqueous solution, and dispersant for suspension polymerization

Abstract

Provided is a vinyl alcohol-based polymer which has a relatively low saponification degree and from which an aqueous solution having a sufficiently low viscosity can be prepared even in the case of high concentration. This polymer has a vinyl ester unit, a vinyl alcohol unit, and a structural unit derived from a monomer (M), wherein: the monomer (M) is a monomer represented by formula (1); the content of the structural unit derived from the monomer (M) is 2-70 mol% with respect to all the structural units; and the saponification degree is higher than 0 mol% and lower than 70 mol%. In formula (1), R1 is a hydrogen atom or a methyl group. X is a hydroxy group, an amino group, a morpholino group, a polyethylene glycol group, or a group represented by –ORA. RA is a C1-C12 alkyl group or a C6-C12 aryl group.

Description

Dispersants for polymers, aqueous solutions and suspension polymerization

[0001] The present invention relates to polymers, aqueous solutions and dispersants for suspension polymerization.

[0002] Vinyl alcohol polymers (hereinafter also referred to as "PVA") are used in a variety of applications, such as raw materials for films and fibers, additives for paper processing and fiber processing, adhesives, binders for inorganic substances, dispersants for suspension polymerization (also referred to as dispersion stabilizers, etc.), etc. Patent Document 1 describes a dispersant for suspension polymerization that is a powder containing PVA having a predetermined terminal structure.

[0003] International Publication No. 2021 / 100638

[0004] PVA is sometimes stored, distributed, sold, used, etc., in the form of an aqueous solution. When storing, using, etc., a polymer as an aqueous solution, a high concentration and low viscosity are required, particularly in terms of productivity and handleability. However, depending on the structure of the polymer, it may not even be possible to prepare a high-concentration aqueous solution. In addition, since the viscosity generally increases as the concentration increases, it is difficult to prepare an aqueous solution that is both high-concentration and low-viscosity. Here, if the saponification degree of PVA is increased, it may be possible to prepare an aqueous solution that is high-concentration and relatively low-viscosity. However, since a PVA with a low saponification degree is sometimes required depending on the application, etc., the development of an aqueous solution that contains a high concentration of PVA with a relatively low saponification degree but has a low viscosity is desired.

[0005] An object of the present invention is to provide a vinyl alcohol polymer having a relatively low degree of saponification, which can be used to prepare an aqueous solution having a sufficiently low viscosity even at a high concentration. Another object of the present invention is to provide an aqueous solution containing such a polymer, and a dispersant for suspension polymerization containing such a polymer and having good performance.

[0006] The object of the present invention is to provide a polymer having a vinyl ester unit, a vinyl alcohol unit, and a structural unit derived from a monomer (M), wherein the monomer (M) is a monomer represented by the following formula (1), the content of the structural unit derived from the monomer (M) being 2 mol % or more and 70 mol % or less based on the total structural units, and the degree of saponification being more than 0 mol % and less than 70 mol %; (In formula (1), R １ is a hydrogen atom or a methyl group. X is a hydroxy group, an amino group, a morpholino group, a polyethylene glycol group, or -OR Ａ R is a group represented by the formula: Ａ is an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms.) [2] The polymer of [1], wherein the viscosity-average degree of polymerization of the polymer (A) is 30 to 2000; [3] The polymer of [1] or [2], wherein the total content of the structural units derived from the vinyl ester unit, the vinyl alcohol unit, and the monomer (M) is 90 mol% or more based on the total structural units; [4] The polymer of any of [1] to [3], wherein the viscosity at 20°C when 40 parts by mass of the polymer is dissolved in 60 parts by mass of water is 2000 mPa s; [5] An aqueous solution containing the polymer of any of [1] to [4]; [6] The aqueous solution of [5], wherein the content of the polymer is 10% by mass or more; [7] The aqueous solution of [5] or [6], wherein the viscosity at 20°C is 2000 mPa s or less; [8] The aqueous solution of any of [5] to [7], wherein the content of the polymer is 90% by mass or more based on the total amount of solids; [9] A dispersant for suspension polymerization containing a polymer of any one of [1] to [4] or an aqueous solution of any one of [5] to [8];

[10] A dispersant for suspension polymerization containing a polymer having a vinyl ester unit, a vinyl alcohol unit, and a structural unit derived from a monomer (M), wherein the monomer (M) is at least one selected from the group consisting of a monomer represented by the following formula (1) and a monomer represented by the following formula (2), the content of the structural unit derived from the monomer (M) in the polymer is 2 mol % or more and 70 mol % or less based on all structural units, and the degree of saponification of the polymer is more than 0 mol % and less than 70 mol %; (In formula (1), R １is a hydrogen atom or a methyl group. X is a hydroxy group, an amino group, a morpholino group, a polyethylene glycol group, or -OR Ａ R is a group represented by the formula: Ａ is an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms. (In formula (2), R ２ is a hydrogen atom or a methyl group.

[0007] According to the present invention, it is possible to provide a vinyl alcohol polymer having a relatively low degree of saponification, which can be used to prepare an aqueous solution having a sufficiently low viscosity even at a high concentration. Furthermore, according to the present invention, it is possible to provide an aqueous solution having a sufficiently low viscosity by using such a polymer. Furthermore, according to the present invention, it is possible to provide a dispersant for suspension polymerization having good performance by using such a polymer.

[0008] In this specification, a numerical range described using "to" means that the numerical values ​​described before and after "to" are included as the lower and upper limits. In other words, "α to β" means "not less than α and not more than β." In addition, in this specification, the upper and lower limit values ​​of numerical ranges (content, physical properties, etc.) can be combined as appropriate.

[0009] <Polymer> A polymer according to one embodiment of the present invention (hereinafter also referred to as "polymer (A)") has a vinyl ester unit, a vinyl alcohol unit, and a structural unit derived from a monomer (M), wherein the monomer (M) is a monomer represented by formula (1) described below, the content of the structural unit derived from the monomer (M) is 2 mol % or more and 70 mol % or less based on all structural units, and the degree of saponification is more than 0 mol % and less than 70 mol %.

[0010] The polymer (A) is a vinyl alcohol polymer having a relatively low degree of saponification, less than 70 mol%. The polymer (A) has a predetermined content of structural units derived from the monomer (M), which allows the preparation of an aqueous solution with sufficiently low viscosity even at high concentrations. Therefore, an aqueous solution containing the polymer (A) is excellent in productivity, handleability, etc. Furthermore, the polymer (A) also performs well as a dispersant for suspension polymerization, due to the degree of saponification being within a predetermined range. Specifically, by using the polymer (A) or an aqueous solution containing the polymer (A) as a dispersant in suspension polymerization, polymer particles with a small average particle size and good plasticizer absorption can be obtained.

[0011] The water solubility of the polymer (A) and the physical properties of the resulting aqueous solution may also be affected by the degree of polymerization of the polymer (A). However, for example, even when a polymer (A) with a high degree of polymerization is used, the viscosity is reduced compared to a polymer with the same degree of polymerization. Therefore, in this specification, it is considered that the problem has been solved if an aqueous solution with a sufficiently low viscosity is obtained when compared with polymers with the same degree of polymerization.

[0012] The polymer (A) according to one embodiment of the present invention will be described in detail below.

[0013] The polymer (A) has a vinyl ester unit. The vinyl ester unit is a structural unit formed by polymerizing a vinyl ester monomer. Examples of the vinyl ester monomer include vinyl carboxylates such as vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among these, vinyl acetate is preferred.

[0014] The vinyl ester unit is —CH ２It may be a structural unit represented by -CH(OCOR)- (R is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms). R is preferably a hydrocarbon group, more preferably an aliphatic hydrocarbon group, and even more preferably an alkyl group. The number of carbon atoms in R is preferably 1 to 6, more preferably 1 to 3. R is particularly preferably a methyl group.

[0015] The lower limit of the content of vinyl ester units in polymer (A) is preferably 10 mol%, more preferably 20 mol%, even more preferably 30 mol%, and may be 40 mol%, based on all structural units. By setting the content of vinyl ester units at or above this lower limit, performance as a dispersant for suspension polymerization tends to be better. The upper limit of the content of vinyl ester units in polymer (A) is preferably 90 mol%, based on all structural units, and may be 80 mol%, 70 mol%, 60 mol%, or 50 mol%. By setting the content of vinyl ester units at or below this upper limit, water solubility increases, and the viscosity of the resulting aqueous solution tends to be lower.

[0016] The polymer (A) contains a vinyl alcohol unit (—CH ２ The vinyl alcohol unit is usually formed by saponification of the vinyl ester unit. When the polymer (A) has the vinyl alcohol unit, the water solubility tends to be increased and the viscosity of the aqueous solution tends to be reduced.

[0017] The degree of saponification of the polymer (A) is more than 0 mol% and less than 70 mol%. By setting the degree of saponification to more than 0 mol%, the water solubility of the polymer (A) increases, and the viscosity of the aqueous solution decreases. On the other hand, by setting the degree of saponification to less than 70 mol%, the performance as a dispersant for suspension polymerization improves. The degree of saponification is preferably 10 mol% or more, more preferably 30 mol% or more, and even more preferably 43 mol% or more. The degree of saponification may be 65 mol% or less, or may be 60 mol% or less. The degree of saponification refers to the ratio (mol%) of vinyl alcohol units to the total number of moles of vinyl ester units and vinyl alcohol units. The degree of saponification is a value measured by the method described in JIS K6726:1994.

[0018] The content of vinyl alcohol units in the polymer (A) is preferably 10 mol% or more and 80 mol% or less, more preferably 20 mol% or more and 75 mol% or less, even more preferably 30 mol% or more and 70 mol% or less, and even more preferably 40 mol% or more and 65 mol% or less, based on all structural units.

[0019] The polymer (A) has a structural unit derived from a monomer (M). The monomer (M) is a monomer represented by the following formula (1).

[0020]

[0021] In formula (1), R １ is a hydrogen atom or a methyl group. X is a hydroxy group, an amino group, a morpholino group, a polyethylene glycol group, or -OR Ａ R is a group represented by the formula: Ａ is an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms.

[0022] It is believed that the polymer (A) has high water solubility and can reduce the viscosity of the resulting aqueous solution by having, in addition to the vinyl alcohol unit, a structural unit derived from the monomer (M) having such a specific group.

[0023] R １ is preferably a hydrogen atom.

[0024] The polyethylene glycol group represented by X is —O—(CH ２ CH ２ O) ｎ -H (n is a number of 1 or more and 20 or less). n is an average value and does not have to be an integer. The upper limit of n is preferably 10, more preferably 6, and even more preferably 4.

[0025] R Ａ Examples of the alkyl group as R include a methyl group, an ethyl group, a propyl group, a hexyl group, and an octyl group. Ａ Examples of the aryl group as R include a phenyl group, a tolyl group, and a naphthyl group. Ａ As the alkyl group, an alkyl group having 1 to 3 carbon atoms is preferable, and a methyl group is even more preferable.

[0026] X is a morpholino group, a polyethylene glycol group, or -OR Ａ A group represented by the formula (I) is preferred, a morpholino group or a polyethylene glycol group is more preferred, and a morpholino group is even more preferred. When X is a morpholino group, the viscosity of the aqueous solution can be further reduced, and the performance as a dispersant for suspension polymerization is particularly good. The morpholino group refers to a substituent in which a hydrogen atom of the secondary amine of morpholine is removed.

[0027] The lower limit of the content of structural units derived from the monomer (M) in the polymer (A) is 2 mol%, preferably 3 mol%, more preferably 5 mol%, and even more preferably 10 mol%, based on the total structural units. The upper limit of the content of structural units derived from the monomer (M) in the polymer (A) is 70 mol%, preferably 60 mol%, more preferably 50 mol%, even more preferably 40 mol%, even more preferably 30 mol%, and particularly preferably 25 mol% based on the total structural units. By setting the content of structural units derived from the monomer (M) to the above lower limit or more, water solubility tends to be increased and the viscosity of the aqueous solution tends to be low. Furthermore, by setting the content of structural units derived from the monomer (M) within the above range, the performance as a dispersant for suspension polymerization is also improved. The content of structural units derived from the monomer (M) based on the total structural units in the polymer (A) is also referred to as the degree of modification (mol%).

[0028] The lower limit of the total content of the vinyl alcohol units and the structural units derived from the monomer (M) in the polymer (A) is preferably 20 mol%, more preferably 30 mol%, even more preferably 40 mol%, and may be 50 mol% based on the total structural units. By setting the total content of these structural units having a specific group to be equal to or greater than the lower limit, the water solubility of the polymer (A) tends to be increased and the viscosity of the aqueous solution tends to be reduced. The upper limit of the total content of the vinyl alcohol units and the structural units derived from the monomer (M) in the polymer (A) is preferably 80 mol%, and may be 75 mol%, 70 mol%, or 65 mol% based on the total structural units.

[0029] The polymer (A) may further have other structural units in addition to the vinyl ester unit, the vinyl alcohol unit, and the structural units derived from the monomer (M). Examples of monomers that provide the other structural units include α-olefins such as ethylene, propylene, 1-butene, isobutene, and 1-hexene; acrylamide derivatives such as N-methylacrylamide and N-ethylacrylamide; methacrylamide derivatives such as N-methylmethacrylamide and N-ethylmethacrylamide; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and n-butyl vinyl ether; hydroxy group-containing vinyl ethers such as ethylene glycol vinyl ether, 1,3-propanediol vinyl ether, and 1,4-butanediol vinyl ether; allyl acetate; and propyl allyl ether. allyl ethers such as butyl allyl ether and hexyl allyl ether; isopropenyl acetate; hydroxy group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 9-decen-1-ol and 3-methyl-3-buten-1-ol; and monomers having a silyl group such as vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3-(meth)acrylamidopropyltrimethoxysilane and 3-(meth)acrylamidopropyltriethoxysilane.

[0030] The lower limit of the total content of vinyl ester units, vinyl alcohol units, and structural units derived from the monomer (M) in the polymer (A) is preferably 90 mol%, more preferably 95 mol%, even more preferably 99 mol%, and may be 99.9 mol%, based on all structural units. Thus, when the content of structural units other than vinyl ester units, vinyl alcohol units, and structural units derived from the monomer (M) is low, the viscosity of the aqueous solution tends to be lower, and the performance as a dispersant for suspension polymerization tends to be improved. The upper limit of the total content of vinyl ester units, vinyl alcohol units, and structural units derived from the monomer (M) in the polymer (A) may be 100 mol%, based on all structural units.

[0031] The lower limit of the viscosity average degree of polymerization of the polymer (A) is preferably 30, more preferably 50, and even more preferably 100. The upper limit of the viscosity average degree of polymerization of the polymer (A) is preferably 2000, more preferably 1200, even more preferably 600, even more preferably 400, and particularly preferably 300. When the viscosity average degree of polymerization of the polymer (A) is within the above range, the viscosity of the aqueous solution tends to be lower, and the performance as a dispersant for suspension polymerization tends to be improved. The viscosity average degree of polymerization of the polymer (A) is a value measured in accordance with JIS K6726:1994.

[0032] The polymer (A) preferably has a viscosity of 2000 mPa·s or less, more preferably 1500 mPa·s or less, at 20°C when 40 parts by mass of the polymer (A) is dissolved in 60 parts by mass of water. That is, the viscosity of an aqueous solution of the polymer (A) at 20°C with a concentration of 40% by mass is preferably 2000 mPa·s or less, more preferably 1500 mPa·s or less. In such a case, the viscosity of the aqueous solution can be particularly sufficiently low. The viscosity at 20°C when 40 parts by mass of the polymer (A) is dissolved in 60 parts by mass of water may be 10 mPa·s or more, 100 mPa·s or more, or 300 mPa·s or more.

[0033] The viscosity is a value measured using a Brookfield viscometer (spindle LV-03 to LV-04) under conditions of a rotor rotation speed of 60 rpm and a temperature of 20°C.

[0034] The polymer (A) is preferably a saponified product of a random copolymer of a vinyl ester monomer and a monomer (M). In other words, the polymer (A) preferably has a structure in which structural units derived from the monomer (M) are randomly present. In such a case, the structural units derived from the monomer (M) particularly effectively improve water solubility and reduce viscosity. The random copolymer may also contain a monomer other than the vinyl ester monomer and the monomer (M) randomly copolymerized. The random copolymer of a vinyl ester monomer and a monomer (M) can be produced by a method of radical copolymerizing each monomer as described below.

[0035] When the polymer (A) is a saponification product of a random copolymer of a vinyl ester monomer and a monomer (M), the saponification product is preferably an alkali saponification product. PVA obtained by alkali saponification usually has low randomness of vinyl alcohol units, low water solubility, and tends to produce an aqueous solution with high viscosity. Therefore, when the present invention is applied to an alkali saponification product, the advantages of increased water solubility and reduced viscosity of the resulting aqueous solution are particularly pronounced.

[0036] The polymer (A) can be suitably used as a dispersant for suspension polymerization. The polymer (A) may be used for applications other than as a dispersant for suspension polymerization. The polymer (A) may be used as a dispersant for emulsion polymerization, or for applications other than as a dispersant. Applications other than as a dispersant include applications similar to those of conventional PVA, such as raw materials for films and fibers, additives for paper processing and fiber processing, adhesives, and inorganic binders.

[0037] (Method for Producing Polymer (A)) The polymer (A) can be produced, for example, by copolymerizing a vinyl ester monomer with a monomer (M) and saponifying the resulting copolymer. The copolymerization of the vinyl ester monomer with the monomer (M) is preferably random copolymerization.

[0038] Methods for copolymerizing a vinyl ester monomer and a monomer (M) include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these methods, bulk polymerization carried out without a solvent or solution polymerization carried out using a solvent such as alcohol is preferred, and solution polymerization carried out in the presence of a lower alcohol is more preferred. As the lower alcohol, an alcohol having 3 or less carbon atoms is preferred, methanol, ethanol, n-propanol, or isopropanol is more preferred, and methanol is even more preferred. When carrying out the polymerization reaction by bulk polymerization or solution polymerization, either a batch system or a continuous system can be used as the reaction system.

[0039] Examples of the polymerization initiator used in the polymerization reaction include known polymerization initiators such as azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and organic peroxide initiators such as benzoyl peroxide, n-propyl peroxycarbonate, cumyl peroxyneodecanoate, and t-butyl peroxyneodecanoate. The polymerization temperature when carrying out the polymerization reaction is not particularly limited, but is preferably in the range of 5°C to 200°C.

[0040] When copolymerizing the vinyl ester monomer with the monomer (M), other copolymerizable monomers can be further copolymerized. Examples of the other monomers include those mentioned above as monomers that provide other structural units.

[0041] The copolymerization may be carried out in the presence of a predetermined chain transfer agent, such as aldehydes (e.g., acetaldehyde, propionaldehyde, butylaldehyde, etc.), ketones (e.g., acetone, methyl ethyl ketone, etc.), mercaptans (e.g., 2-hydroxyethanethiol, 3-mercaptopropionic acid, etc.), thiocarboxylic acids (e.g., thioacetic acid, etc.), and halogenated hydrocarbons (e.g., trichloroethylene, perchloroethylene, etc.).

[0042] The resulting copolymer can be saponified, for example, by treating the vinyl ester polymer in an alcohol solution with an alkali or acid catalyst. The saponification reaction of the vinyl ester polymer can be carried out by conventional alcoholysis or hydrolysis using an alkali catalyst such as sodium hydroxide, potassium hydroxide, or sodium methoxide, or an acid catalyst such as p-toluenesulfonic acid. 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 solvents can be used alone or in combination. Among these, it is preferable to use methanol or a mixed solution of methanol and methyl acetate as the solvent and carry out the saponification reaction in the presence of sodium hydroxide as an alkali catalyst, as this is simple and convenient. Saponification can be carried out using a belt reactor, kneader reactor, tower reactor, or the like.

[0043] The polymer obtained through saponification may be subjected to washing treatment and drying treatment.

[0044] <Aqueous Solution> An aqueous solution according to one embodiment of the present invention contains a polymer (A). Because the aqueous solution contains a polymer (A) having a structural unit derived from a monomer (M) represented by formula (1), it has a sufficiently low viscosity. Therefore, the aqueous solution is excellent in productivity, ease of handling, and the like. Furthermore, the aqueous solution also performs well as a dispersant for suspension polymerization. Specifically, by using the aqueous solution as a dispersant in suspension polymerization, polymer particles having a small average particle size and good plasticizer absorption can be obtained. Because the aqueous solution is a liquid, there is no need to dissolve the polymer when used as a dispersant for suspension polymerization, and it is therefore easy to handle.

[0045] An aqueous solution according to one embodiment of the present invention contains a polymer (A) and water (B). The aqueous solution may further contain other components in addition to the polymer (A) and water (B).

[0046] (Polymer (A)) The polymer (A) contained in the aqueous solution according to one embodiment of the present invention is the polymer according to one embodiment of the present invention described above. The aqueous solution may contain one or more types of polymer (A).

[0047] The lower limit of the content of polymer (A) in the aqueous solution according to one embodiment of the present invention is preferably 10% by mass, more preferably 15% by mass, more preferably 20% by mass, and even more preferably 25%, 30%, 35% by mass, or 40% by mass. By setting the content of polymer (A) to the above-mentioned lower limit or more, a highly concentrated aqueous solution is obtained, which allows for efficient distribution, storage, etc. The upper limit of the content of polymer (A) may be 70% by mass, or may be 60%, 50%, 45%, or 40% by mass. By setting the content of polymer (A) to the above-mentioned upper limit or less, it is possible to reduce the viscosity of the aqueous solution, etc.

[0048] (Water (B) and other components, etc.) The aqueous solution according to one embodiment of the present invention contains water (B) as a solvent. In addition, components other than the polymer (A) and water (B) that may be contained in the aqueous solution include solids other than the polymer (A) and solvents other than water (B). Examples of solids other than the polymer (A) include resins other than the polymer (A), surfactants, plasticizers, and various compounds used during production. Examples of solvents other than water (B) include alcohols such as ethanol. The solids refer to components other than water (B) and other solvents. The solids may be components that are solid at 20°C.

[0049] The lower limit of the content of polymer (A) relative to the total amount of solids in the aqueous solution according to one embodiment of the present invention is preferably 90% by mass, more preferably 95% by mass, or even 99% by mass. When the solids in the aqueous solution are mainly polymer (A), the viscosity can be further reduced, and the performance as a dispersant for suspension polymerization tends to be better. The upper limit of the content of polymer (A) relative to the total amount of solids in the aqueous solution may be 100% by mass, 99.9% by mass, or even 99% by mass.

[0050] The aqueous solution according to one embodiment of the present invention may contain an insoluble component. The upper limit of the content of the insoluble component in the aqueous solution is preferably 0.1% by mass, more preferably 0.01% by mass. The insoluble component may be a part of the polymer (A), or may be another component that is not inherently water-soluble.

[0051] The upper limit of the viscosity at 20°C of the aqueous solution according to one embodiment of the present invention may be, for example, 10,000 mPa·s, 4,000 mPa·s, or 2,500 mPa·s, with 2,000 mPa·s being preferred and 1,500 mPa·s being more preferred. Having a viscosity of the aqueous solution equal to or less than the upper limit can improve ease of handling. The lower limit of the viscosity may be 10 mPa·s, 100 mPa·s, or 300 mPa·s.

[0052] The aqueous solution according to one embodiment of the present invention can be suitably used as a dispersant for suspension polymerization. The aqueous solution may be used for applications other than as a dispersant for suspension polymerization. The aqueous solution may be used as a dispersant for emulsion polymerization, or for applications other than as a dispersant. Applications other than as a dispersant include applications similar to those of conventional PVA, such as raw materials for films and fibers, additives for paper processing and fiber processing, adhesives, and inorganic binders.

[0053] (Preparation of Aqueous Solution) The method for preparing the aqueous solution according to one embodiment of the present invention is not particularly limited. For example, the aqueous solution can be obtained by adding the polymer (A) to water (B) and dissolving the polymer (A). The polymer (A) may be added in multiple portions. Furthermore, other components may be further added, and heating may be performed during dissolution.

[0054] <Dispersant for suspension polymerization> The dispersant for suspension polymerization (X) according to one embodiment of the present invention contains the polymer according to one embodiment of the present invention or the aqueous solution according to one embodiment of the present invention. The dispersant for suspension polymerization (X) may further contain other components in addition to the polymer according to one embodiment of the present invention or the aqueous solution according to one embodiment of the present invention. The dispersant for suspension polymerization (X) may be the polymer according to one embodiment of the present invention or the aqueous solution according to one embodiment of the present invention.

[0055] A dispersant for suspension polymerization (Y) according to another embodiment of the present invention comprises a polymer (A) having a vinyl ester unit, a vinyl alcohol unit, and a structural unit derived from a monomer (M), wherein the monomer (M) is at least one selected from the group consisting of a monomer represented by the following formula (1) and a monomer represented by the following formula (2), wherein the content of the structural unit derived from the monomer (M) in the polymer (A) is 2 mol % or more and 70 mol % or less based on all structural units, and the degree of saponification of the polymer (A) is more than 0 mol % and less than 70 mol %:

[0056] In formula (1), R １ is a hydrogen atom or a methyl group, and X is a hydroxy group, an amino group, a morpholino group, or a polyethylene glycol group.

[0057] In formula (2), R ２ is a hydrogen atom or a methyl group.

[0058] The specific and preferred forms of the polymer (A) contained in the dispersant for suspension polymerization (Y) are the same as the specific and preferred forms of the polymer according to one embodiment of the present invention described above, except that the monomer (M) may be a monomer represented by formula (2). The dispersant for suspension polymerization (Y) may contain an aqueous solution containing the polymer (A), or may be an aqueous solution containing the polymer (A). When the dispersant for suspension polymerization (Y) contains an aqueous solution or is an aqueous solution, the specific and preferred forms of this aqueous solution are the same as the specific and preferred forms of the aqueous solution according to one embodiment of the present invention described above, except that the monomer (M) may be a monomer represented by formula (2).

[0059] R ２ is preferably a hydrogen atom.

[0060] In the dispersant for suspension polymerization (Y), the monomer (M) is a monomer in which X is a morpholino group, a polyethylene glycol group, or -OR Ａ A monomer represented by formula (1) or a monomer represented by formula (2) in which X is a group represented by the formula (1) or (2) is preferred, and a monomer represented by formula (1) or (2) in which X is a morpholino group is more preferred.

[0061] The dispersant for suspension polymerization (Y) may further contain other components other than the polymer (A). Examples of other components other than the polymer (A) include water and the other components exemplified as those that may be contained in the aqueous solution according to one embodiment of the present invention. Even when the dispersant for suspension polymerization (Y) contains the aqueous solution described above, it may further contain other components (e.g., other polymers) other than the aqueous solution. The dispersant for suspension polymerization (Y) may be in a solid form (e.g., powder form) or a liquid form.

[0062] The dispersant (X) for suspension polymerization and the dispersant (Y) for suspension polymerization according to one embodiment of the present invention (hereinafter, the dispersant (X) and the dispersant (Y) for suspension polymerization may be abbreviated as "dispersant") have excellent performance as a dispersant for suspension polymerization. These dispersants are suitable as dispersants for suspension polymerization of vinyl compounds, and can efficiently produce polymer particles with a small average particle size. Furthermore, the polymer particles obtained by suspension polymerization using these dispersants also have good plasticizer absorption.

[0063] The lower limit of the content of polymer (A) in the dispersant in the liquid form is preferably 10% by mass, more preferably 15% by mass, even more preferably 20% by mass, and even more preferably 25% by mass, 30% by mass, 35% by mass, or 40% by mass. By setting the content of polymer (A) to the above lower limit or more, a high-concentration dispersant is obtained, allowing for efficient distribution, storage, etc. The upper limit of the content of polymer (A) in the dispersant in the liquid form may be 70% by mass, or may be 60% by mass, 50% by mass, 45% by mass, or 40% by mass. By setting the content of polymer (A) to the above upper limit or less, it is possible to reduce the viscosity of the dispersant, etc. The dispersant can also be used in a diluted form.

[0064] The upper limit of the viscosity of the dispersant at 20°C in the liquid form may be, for example, 10,000 mPa·s, 4,000 mPa·s, or 2,500 mPa·s, with 2,000 mPa·s being preferred and 1,500 mPa·s being more preferred. Having a viscosity of the dispersant below the upper limit can improve ease of handling, etc. The lower limit of the viscosity may be 10 mPa·s, 100 mPa·s, or 300 mPa·s.

[0065] The lower limit of the content of polymer (A) relative to the total amount of solids in the dispersant according to one embodiment of the present invention is preferably 90% by mass, more preferably 95% by mass, or even 99% by mass. When the solids in the dispersant are mainly polymer (A), the performance as a dispersant for suspension polymerization tends to be better. The upper limit of the content of polymer (A) relative to the total amount of solids in the dispersant may be 100% by mass, 99.9% by mass, or even 99% by mass.

[0066] The dispersant according to one embodiment of the present invention may contain an insoluble component. The upper limit of the content of the insoluble component in the dispersant is preferably 0.1% by mass, more preferably 0.01% by mass. The insoluble component may be a part of the polymer (A), or may be another component that is not inherently water-soluble.

[0067] (Method for polymerizing vinyl compounds) Hereinafter, as a method using a dispersant according to one embodiment of the present invention, a method for polymerizing vinyl compounds using the dispersant will be described. The method for polymerizing vinyl compounds comprises a step of polymerizing a vinyl compound in the presence of a dispersant according to one embodiment of the present invention. This polymerization method is similar to the conventionally known methods for polymerizing vinyl compounds, except that a dispersant according to one embodiment of the present invention is used as the dispersant.

[0068] In this polymerization method, a vinyl compound is usually suspension polymerized in an aqueous medium. As the aqueous medium, pure water, an aqueous solution containing various additives, or an aqueous medium containing other organic solvents can be used. A dispersant is added to this aqueous medium. A polymerization initiator and a vinyl compound are further added to the aqueous medium, and suspension polymerization is carried out under stirring.

[0069] The amount of the dispersant according to one embodiment of the present invention to be added when carrying out suspension polymerization of a vinyl compound is not particularly limited, but is preferably 1 ppm or more and 50,000 ppm or less, more preferably 10 ppm or more and 10,000 ppm or less, even more preferably 30 ppm or more and 5,000 ppm or less, and even more preferably 50 ppm or more and 1,000 ppm or less, based on the mass of the solid content, relative to the vinyl compound.

[0070] The dispersant according to one embodiment of the present invention may be used alone or in combination with other dispersants. Examples of other dispersants include various dispersants that are commonly used when a vinyl compound is suspension polymerized in an aqueous medium. Specific examples include water-soluble cellulose ethers such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropylmethyl cellulose; water-soluble polymers other than the polymer (A), such as PVA and gelatin; oil-soluble emulsifiers such as sorbitan monolaurate, sorbitan trioleate, glycerin tristearate, and ethylene oxide-propylene oxide block copolymers; and water-soluble emulsifiers such as polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerin oleate, and sodium laurate.

[0071] As the polymerization initiator used in the polymerization method, any of those conventionally used for the polymerization of vinyl compounds can be used. Specifically, the same polymerization initiators as those exemplified in the polymerization of the vinyl ester monomers described above can be used.

[0072] In this polymerization method, various other additives can be added to the polymerization system as needed. Examples of additives include polymerization regulators such as aldehydes, halogenated hydrocarbons, and mercaptans; and polymerization inhibitors such as phenol compounds, sulfur compounds, and N-oxide compounds. In addition, pH adjusters, scale inhibitors, crosslinking agents, and the like can also be added. Multiple additives can be used in combination.

[0073] Examples of vinyl compounds that can be suspension polymerized in this polymerization method include vinyl halides such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; acrylic acid, methacrylic acid, esters and salts thereof; maleic acid, fumaric acid, esters and anhydrides thereof; styrene; acrylonitrile; vinylidene chloride; and vinyl ethers. Among these vinyl compounds, vinyl halides are preferred, and vinyl chloride is more preferred. This polymerization method is particularly suitable as a method for suspension polymerizing vinyl chloride alone or as a method for suspension polymerizing vinyl chloride and a monomer copolymerizable with vinyl chloride together. Examples of monomers that can be copolymerized with vinyl chloride include vinyl esters such as vinyl acetate and vinyl propionate; (meth)acrylic acid esters such as methyl (meth)acrylate and ethyl (meth)acrylate; α-olefins such as ethylene and propylene; unsaturated dicarboxylic acids such as maleic anhydride and itaconic acid; acrylonitrile; styrene; vinylidene chloride; and vinyl ethers.

[0074] When a vinyl compound is suspension polymerized in this polymerization method, the charging ratio of each component, polymerization temperature, polymerization time, etc. can be the same as those used in conventional suspension polymerization of vinyl compounds. There are also no limitations on the charging order or ratio of the vinyl compound, polymerization initiator, dispersant, aqueous medium, and other additives.

[0075] According to the polymerization method using the dispersant according to one embodiment of the present invention, vinyl polymer particles having a small average particle size can be efficiently obtained. Furthermore, the vinyl polymer particles obtained by this polymerization method also have good plasticizer absorption.

[0076] 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. The physical properties of the polymer (A) were measured according to the following methods.

[0077] [Viscosity-Average Degree of Polymerization] When the polymer (A) was PVA, a methanol solution of polyvinyl acetate (PVAc) obtained previously, from which unreacted vinyl acetate had been removed and prior to the saponification reaction, was poured into n-hexane to precipitate PVAc. When the polymer (A) was PVAc, the resulting PVAc was used. The PVAc was dissolved in acetone and purified three times by reprecipitation, followed by drying under reduced pressure at 60°C to obtain a purified PVAc product. The methanol solution of this purified PVAc product was saponified at an alkali molar ratio of 0.2, followed by Soxhlet extraction with methanol for three days and subsequent drying to obtain a purified PVA product. The viscosity-average degree of polymerization of the resulting PVA was measured in accordance with JIS K6726:1994.

[0078] [Content of Structural Unit Derived from Monomer (M) (Degree of Modification)] The content of structural units derived from the monomer (M) in the polymer (A) (degree of modification (mol %)) is １ The values ​​were calculated from the spectrum of the modified species by H-NMR spectral analysis.

[0079] [Saponification Degree] The saponification degree of the polymer (A) was measured in accordance with JIS K6726:1994.

[0080] [Production Example 1] (Production of PVA-1) A 3-L reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet, additive inlet, and initiator inlet was charged with 330.0 parts by mass of vinyl acetate, 100.0 parts by mass of acryloylmorpholine (the monomer (M)), and 1,170.0 parts by mass of methanol. The temperature was raised to 60°C, and the system was then purged with nitrogen by nitrogen bubbling for 30 minutes. 2.0 parts by mass of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (AIBN) was added to initiate polymerization. The polymerization temperature was maintained at 60°C during the polymerization, and after 4 hours, the polymerization was terminated by cooling when the conversion reached 50%. Next, unreacted vinyl acetate was removed under reduced pressure to obtain a methanol solution of polyvinyl acetate. A 30% by mass PVAc solution was saponified by adding a 10% by mass NaOH methanol solution to the PVAc solution so that the NaOH molar ratio (moles of NaOH / moles of vinyl ester units in PVAc) was 0.0005. The water content of the saponification solution was adjusted to 1% by mass. After saponification, the solution was washed and dried to obtain a powder of vinyl alcohol polymer (PVA-1). The physical properties of PVA-1 are shown in Table 2.

[0081] [Production Examples 2 to 7, Comparative Production Examples 1 and 2] (Production of PVA-2 to 9) PVA-2 to 9 were produced in the same manner as in Production Example 1, except that the type of monomer (M) used in polymerization, the amounts of each monomer, methanol, and AIBN used, and the molar ratio of NaOH in saponification were as shown in Table 1. The physical properties of PVA-2 to 9 are shown in Table 2.

[0082] Comparative Production Example 3 (Production of PVAc-1) 270.0 parts by mass of vinyl acetate, 34.8 parts by mass of methyl acrylate (the monomer (M)), and 1,230.0 parts by mass of methanol were charged into a 3-L reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen inlet, an additive inlet, and an initiator inlet. The temperature was raised to 60°C, and the system was then purged with nitrogen by nitrogen bubbling for 30 minutes. Polymerization was initiated by adding 1.0 part by mass of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (AIBN). The polymerization temperature was maintained at 60°C during the polymerization, and after 4 hours, the polymerization was terminated by cooling when the conversion reached 50%. Next, unreacted vinyl acetate was removed under reduced pressure to obtain a methanol solution of polyvinyl acetate. The methanol solution of polyvinyl acetate was poured into n-hexane to precipitate polyvinyl acetate. The precipitate was washed and dried to obtain a powder of polyvinyl acetate (PVAc-1). The physical properties of PVAc-1 are shown in Table 2.

[0083] Example 1 PVA-1 was dissolved in water as the polymer (A) to obtain an aqueous solution of Example 1 containing 39.2% by mass of the polymer (A).

[0084] [Examples 2 to 7, Comparative Example 1] Aqueous solutions of Examples 2 to 7 and Comparative Example 1 were obtained in the same manner as in Example 1, except that the type and content of polymer (A) were changed as shown in Table 2.

[0085] Comparative Examples 2 and 3 An attempt was made to prepare an aqueous solution containing 40% by mass of polymer (A) by changing the type of polymer (A) as shown in Table 2. However, a large amount of polymer (A) remained undissolved, and an aqueous solution containing at least 35% by mass of dissolved polymer (A) could not be obtained.

[0086] [Evaluation] (Viscosity of aqueous solution) Viscosity measurements were carried out for each of the aqueous solutions obtained in Examples 1 to 7 and Comparative Example 1. The viscosity measurements of the aqueous solutions were carried out using a Brookfield viscometer BLII (spindle LV-04) manufactured by Toki Sangyo Co., Ltd. under conditions of a rotor rotation speed of 60 rpm and a temperature of 20°C. In this evaluation, a viscosity of 2500 mPa s or less was determined to be sufficiently low. The results are shown in Table 2.

[0087] (Suspension Polymerization of Vinyl Chloride) Using each of the aqueous solutions of Examples 1 to 7 and Comparative Example 1 as a dispersant, suspension polymerization of vinyl chloride was carried out by the following method. Note that for Comparative Examples 2 and 3, it was not possible to prepare an aqueous solution with a content of at least 35% by mass, so suspension polymerization was not carried out. The resulting vinyl chloride polymer particles were then evaluated for average particle size and plasticizer absorption as described below. The evaluation results are shown in Table 2.

[0088] An amount of the first dispersant aqueous solution was sampled from the aqueous solution such that the solid content of the aqueous solution would be 400 ppm relative to the vinyl chloride content described below. The sampled aqueous solution was diluted with deionized water to obtain a first dispersant aqueous solution. 100 parts by mass of the first dispersant aqueous solution was charged into a 5 L autoclave. Similarly, an amount of the first dispersant aqueous solution was sampled from a PVA aqueous solution in which commercially available PVA ("Kuraray Poval 48-80" manufactured by Kuraray) had been dissolved, such that the solid content of the PVA aqueous solution would be 800 ppm relative to the vinyl chloride content. The sampled PVA aqueous solution was diluted with deionized water to obtain a second dispersant aqueous solution. 100 parts by mass of the second dispersant aqueous solution was charged into the autoclave. Next, deionized water was added to the autoclave so that the total amount of deionized water was 1,300 parts by mass. Next, 0.65 parts by mass of a 70% by mass toluene solution of cumyl peroxyneodecanoate and 1.05 parts by mass of a 70% by mass toluene solution of t-butyl peroxyneodecanoate were charged into the autoclave. The autoclave was degassed to remove oxygen until the pressure inside the autoclave reached 0.0067 MPa. Thereafter, 800 parts by mass of vinyl chloride was charged into the autoclave, and the contents inside the autoclave were heated to 57°C to initiate polymerization with stirring. The pressure inside the autoclave at the start of polymerization was 0.83 MPa. 3.5 hours after the start of polymerization, the polymerization was terminated when the pressure inside the autoclave reached 0.70 MPa, and unreacted vinyl chloride was removed. The polymerized slurry was then removed and dried at 65°C for 17 hours to obtain vinyl chloride polymer particles.

[0089] (1) Average particle size of vinyl chloride polymer particles The particle size distribution of the obtained vinyl chloride polymer particles was measured by dry sieve analysis using a wire mesh with a Tyler mesh standard. The results were plotted on the Rosin-Rammler distribution equation to determine the average particle size (d ｐ５０ In this evaluation, when the average particle size was 220 μm or less, the average particle size was determined to be small.

[0090] (2) Plasticizer Absorption of Vinyl Chloride Polymer Particles The mass of a 5 mL syringe filled with 0.02 g of absorbent cotton (referred to as X (g)) was measured, and 0.5 g of vinyl chloride polymer particles was added to the syringe and the mass was measured (referred to as Y (g)). 1 g of dioctyl phthalate (DOP) was added and allowed to stand for 15 minutes. The syringe was then centrifuged at 3,000 rpm for 40 minutes to remove any unabsorbed DOP, and the mass after removal was measured (referred to as Z (g)). The plasticizer absorption (%) of the vinyl chloride polymer particles was then calculated using the following formula. Higher plasticizer absorption indicates easier processing and less likelihood of appearance defects, such as bumps, occurring during processing into a sheet. In this evaluation, a plasticizer absorption of 20% or more was considered to be good. Plasticizer absorption (%) = 100 × [{(Z - X) / (Y - X)} - 1]

[0091]

[0092] In Table 1, n indicates that X in formula (1) is a polyethylene glycol group (—O—(CH ２ CH ２ O) ｎ represents the value of n when

[0093]

[0094] As shown in Table 2, each of the aqueous solutions of Examples 1 to 7 was a high-concentration aqueous solution of a vinyl alcohol-based polymer with a relatively low degree of saponification, yet had a sufficiently low viscosity of 2500 mPa·s or less. Furthermore, when suspension polymerization was carried out using each of the aqueous solutions of Examples 1 to 7 as a dispersant, vinyl chloride polymer particles with a small average particle size and good plasticizer absorption were obtained. It was confirmed that each of the aqueous solutions of Examples 1 to 7 was useful as a dispersant for suspension polymerization. On the other hand, the aqueous solution of Comparative Example 1 used a vinyl alcohol-based polymer with a high degree of saponification, and its performance as a dispersant for suspension polymerization was poor. Furthermore, Comparative Examples 2 and 3 did not produce a high-concentration aqueous solution.

[0095] The polymer and aqueous solution of the present invention can be suitably used as a dispersant for suspension polymerization.

Claims

1. A polymer having a vinyl ester unit, a vinyl alcohol unit, and a structural unit derived from a monomer (M), said monomer (M) being a monomer represented by the following formula (1), the content of the structural units derived from said monomer (M) being 2 mol% or more and 70 mol% or less of the total structural units, and having a degree of saponification of more than 0 mol% and less than 70 mol%. (In formula (1), R １ is a hydrogen atom or a methyl group; X is a hydroxy group, an amino group, a morpholino group, a polyethylene glycol group, or -OR Ａ R is a group represented by the formula: Ａ is an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms.

2. The polymer according to claim 1, wherein the viscosity average degree of polymerization of the polymer (A) is 30 to 2,000.

3. The polymer according to claim 1 or 2, wherein the total content of the vinyl ester units, the vinyl alcohol units and the structural units derived from the monomer (M) is 90 mol % or more based on the total structural units.

4. The polymer according to claim 1 or 2, which has a viscosity of 2000 mPa·s at 20° C. when 40 parts by mass of the polymer is dissolved in 60 parts by mass of water.

5. An aqueous solution containing the polymer according to claim 1 or 2.

6. The aqueous solution according to claim 5, wherein the polymer content is 10% by mass or more.

7. The aqueous solution according to claim 5, having a viscosity at 20°C of 2000 mPa·s or less.

8. The aqueous solution according to claim 5, wherein the content of said polymer relative to the total amount of solids is 90 mass % or more.

9. A dispersant for suspension polymerization, comprising the polymer according to claim 1 or 2.

10. A dispersant for suspension polymerization comprising a polymer having a vinyl ester unit, a vinyl alcohol unit, and a structural unit derived from a monomer (M), wherein the monomer (M) is at least one selected from the group consisting of a monomer represented by the following formula (1) and a monomer represented by the following formula (2), the content of the structural unit derived from the monomer (M) in the polymer is 2 mol % or more and 70 mol % or less based on all structural units, and the degree of saponification of the polymer is more than 0 mol % and less than 70 mol %. (In formula (1), R １ is a hydrogen atom or a methyl group; X is a hydroxy group, an amino group, a morpholino group, a polyethylene glycol group, or -OR Ａ R is a group represented by the formula: Ａ is an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms. (In formula (2), R ２ is a hydrogen atom or a methyl group.

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