JP7256059B2 - Method for producing sulfonic acid group-containing copolymer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a sulfonic acid group-containing copolymer. More particularly, it relates to a method for producing a sulfonic acid group-containing copolymer useful as a raw material for detergent additives and the like.

Conventionally, detergents used for clothes and the like are blended with detergent builders (detergent aids) such as zeolite, carboxymethylcellulose, and polyethylene glycol for the purpose of improving the cleaning effect of the detergent. In addition to the various detergent builders described above, in recent years, polymers have been added to detergent compositions as detergent builders.
Regarding such a polymer, for example, Patent Document 1 discloses a carboxyl group-containing polymer, which is represented by a predetermined structure derived from an ether bond-containing monomer (A). Essentially comprising a structural unit (a), a structural unit (b) derived from a sulfonic acid group-containing monomer (B), and a structural unit (c) derived from an acrylic monomer (C), The carboxyl group-containing polymer contains 0.5% by mass or more and 9% by mass of the structural unit (a) with respect to 100% by mass of the total amount of structural units derived from all the monomers forming the carboxyl group-containing polymer. % or less, the structural unit (b) is 0.5% by mass or more and 25% by mass or less, and the structural unit (c) is 55% by mass or more and 99% by mass or less, and the weight average molecular weight is 30,000 to 60, 000 is disclosed.

Further, Patent Document 2 discloses an ether bond-containing compound represented by a predetermined structure, a predetermined diol compound in an amount of 0 to 20% by mass, and a predetermined compound having two carbon-carbon double bonds in an amount of 1 to 20% by mass. %, 0-1% by weight of a given epoxy compound, and silica scale dispersibility for copolymers prepared using such compositions and acrylic acid.

Japanese Patent No. 6275131 JP 2014-62176 A

As described above, conventionally, sulfonic acid group-containing copolymers for use in detergents have been developed. For example, Patent Document 1 reports anti-soil redeposition ability using carbon black. However, as various detergents are becoming more sophisticated and more compact, there is a demand for polymers used in detergents to have better cleaning performance than conventional polymers. There has been a demand for a technique for improving the dispersibility of complex stains that are combined with hydrophobic substances such as sebum and soot.

The present invention has been made in view of the above-mentioned current situation, and it is an object of the present invention to provide a method for producing a sulfonic acid group-containing copolymer that is superior in dispersibility to complex stains than polymers obtained by conventional production methods. aim.

The present inventors conducted various studies on methods for producing a sulfonic acid group-containing copolymer, and found that the content of hydrogen sulfite in the sulfonic acid group-containing monomer used for polymerization is set to a specific amount or less. The present inventors have found that the dispersibility of the copolymer obtained with the above-mentioned compound is improved, and conceived that the above-mentioned problems can be solved admirably, and arrived at the present invention.

That is, the present invention is a method for producing a sulfonic acid group-containing copolymer, the above production method comprising a sulfonic acid group-containing monomer (A), an ether bond-containing monomer (B), and a carboxyl group A sulfonic acid group-containing copolymer comprising a step of polymerizing a monomer composition containing the sulfonic acid group-containing monomer (C), wherein the content of hydrogen sulfite in the sulfonic acid group-containing monomer (A) is 18000 ppm or less. A method for producing a polymer.

The sulfonic acid group-containing monomer (A) has the following formula (1);

(Wherein, R ¹ represents a hydrogen atom or a methyl group. R ² represents a CH ₂ group, a CH ₂ CH ₂ group, or a direct bond.) It is preferably obtained.

The sulfonic acid group-containing monomer (A) has the following formula (2);

(wherein R ¹ represents a hydrogen atom or a methyl group; R ² represents a CH ₂ group, a CH ₂ CH ₂ group or a direct bond; R ³ and R ⁴ represent a hydroxyl group or -SO ₃ Z; , Z represents a hydrogen atom, a metal atom, an ammonium group or an organic amine group, provided that one of R ³ and R ⁴ represents —SO ₃ Z and the other represents a hydroxyl group. A structure is preferred.

The ether bond-containing monomer (B) has the following formula (3);

(In the formula, R ⁵ represents a hydrogen atom or a methyl group. R ⁶ represents a CH ₂ group, a CH ₂ CH ₂ group, or a direct bond. X represents a hydroxyl group, a group represented by the following formula (4) or a group represented by the following formula (5), Y represents a hydroxyl group, a group represented by the following formula (4), or a group represented by the following formula (5), provided that X , Y represents a hydroxyl group, and the other represents a group represented by the following formula (4) or a group represented by the following formula (5).)

(In the formula, R ⁷ is the same or different and represents an alkylene group having 2 to 4 carbon atoms; n is the average number of added moles of the oxyalkylene group (—OR ⁷ —), R ⁸ , R ⁹ and R ¹⁰ are the same or different and each represents an alkyl group having 1 to 4 carbon atoms.).

The method for producing a sulfonic acid group-containing copolymer of the present invention comprises the above-described structure, and the obtained sulfonic acid group-containing copolymer has better dispersibility for complex stains than polymers obtained by conventional production methods. Since it is excellent, it can be suitably used as a raw material for detergent additives and the like.

Preferred embodiments of the present invention will be specifically described below, but the present invention is not limited to the following description, and can be appropriately modified and applied without changing the gist of the present invention. In addition, the form which combined 2 or 3 or more of each preferable form of this invention described below also corresponds to the preferable form of this invention.

The method for producing a sulfonic acid group-containing copolymer of the present invention comprises a monomer containing a sulfonic acid group-containing monomer (A), an ether bond-containing monomer (B), and a carboxyl group-containing monomer (C). The content of hydrogen sulfite in the sulfonic acid group-containing monomer (A) is 18000 ppm or less. Since the hydrogen sulfite acts as a chain transfer agent in the polymerization process, by setting the content of the hydrogen sulfite in the monomer component to a specific amount or less, an unexpected chain transfer reaction can be sufficiently suppressed, The formation of a copolymer with a small molecular weight and the amount of impurities derived from hydrogen sulfite can be sufficiently suppressed. As a result, the dispersibility of the resulting copolymer against complex stains can be improved.
The content of hydrogen sulfite in the sulfonic acid group-containing monomer (A) is preferably 15,000 ppm or less, more preferably 13,000 ppm or less, and still more preferably 11,000 ppm or less.
The lower limit of the hydrogen sulfite content in the sulfonic acid group-containing monomer (A) is not particularly limited, but is usually 10 ppm or more, and may be 100 ppm or more, or 1000 ppm or more. .
The content of hydrogen sulfite in the sulfonic acid group-containing monomer (A) can be measured by the method described in Examples.

The method for producing the sulfonic acid group-containing copolymer is not particularly limited as long as it includes a step of polymerizing the monomer composition, but the polymerization step has a hydrogen sulfite content of 18000 ppm or less. It preferably includes a step of mixing the sulfonic acid group-containing monomer (A), the ether bond-containing monomer (B), and the carboxyl group-containing monomer (C).

The above-mentioned hydrogen sulfite is not particularly limited, but examples thereof include alkali metal salts of hydrogen sulfite such as sodium hydrogen sulfite and potassium hydrogen sulfite; and salts of hydrogen sulfite with ammonium or organic amines. Examples of organic amines include alkanolamines such as monoethanolamine, diethanolamine and triethanolamine; triethylamine and the like.
As the hydrogen sulfite, sodium hydrogen sulfite and potassium hydrogen sulfite are preferable.

The content of the sulfonic acid group-containing monomer (A) in the monomer composition in the polymerization step is preferably 1 to 30 mol % with respect to 100 mol % of the total monomers. When the copolymer obtained by this is used as a detergent builder or the like, the interaction between the copolymer and the soil component is good, so the particles of the soil component interacting with the polymer should be dispersed. It is possible to exhibit the ability to prevent redeposition. The content of the sulfonic acid group-containing monomer (A) is more preferably 2 to 25 mol%, still more preferably 3 to 20 mol%, even more preferably 4 to 15 mol%, particularly preferably It is 5 to 10 mol %.

The content ratio of the ether bond-containing monomer (B) in the monomer composition in the polymerization step is preferably 0.1 to 10 mol % with respect to 100 mol % of all monomers. When the copolymer obtained by this is used as a detergent builder or the like, the interaction between the copolymer and the soil component is good, so the particles of the soil component interacting with the polymer should be dispersed. It is possible to exhibit the ability to prevent redeposition. In addition, a remarkable effect of improving compatibility with surfactants can be obtained. The content of the ether bond-containing monomer (B) is more preferably 0.5 to 8 mol%, still more preferably 1 to 6 mol%, still more preferably 1.5 to 5 mol%, Particularly preferably, it is 2 to 4 mol %.

The content ratio of the carboxyl group-containing monomer (C) in the monomer composition in the polymerization step is preferably 60 to 99 mol % with respect to 100 mol % of the total monomers. When the copolymer obtained by this is used as a detergent builder or the like, the interaction between the copolymer and the soil component is good, so the particles of the soil component interacting with the polymer should be dispersed. It is possible to exhibit the ability to prevent redeposition. The content of the carboxyl group-containing monomer (C) is more preferably 70 to 98 mol%, still more preferably 75 to 97 mol%, still more preferably 80 to 96 mol%, particularly preferably 85 ~95 mol%.

The monomer composition in the polymerization step includes the sulfonic acid group-containing monomer (A), the ether bond-containing monomer (B), and other monomers other than the carboxyl group-containing monomer (C). (E) may be included. The content of the other monomer (E) in the monomer composition is preferably 0 to 10 mol % with respect to 100 mol % of all monomers. It is more preferably 0 to 5 mol %, still more preferably 0 to 3 mol %, and most preferably 0 mol %.

<Sulfonic Acid Group-Containing Monomer (A)>
The sulfonic acid group-containing monomer (A) is not particularly limited as long as it has a sulfonic acid (salt) group and an ethylenically unsaturated hydrocarbon group. For example, 3-(meth)allyloxy-2-hydroxy propanesulfonic acid, 2-(meth)allyloxyethylenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, p-styrenesulfonic acid, α-methyl-p-styrenesulfonic acid, vinylsulfonic acid, vinylsulfamic acid, (Meth)allylsulfonic acid, isoprenesulfonic acid, 4-(allyloxy)benzenesulfonic acid, 1-methyl-2-propene-1-sulfonic acid, 1,1-dimethyl-2-propene-1-sulfonic acid, 3- butene-1-sulfonic acid, 1-butene-3-sulfonic acid, 2-acrylamido-1-methylpropanesulfonic acid, 2-acrylamidopropanesulfonic acid, 2-acrylamido-n-butanesulfonic acid, 2-acrylamide-2- Unsaturated sulfonic acids such as phenylpropanesulfonic acid, 2-((meth)acryloyloxy)ethanesulfonic acid, salts thereof, and the like.

As the sulfonic acid group-containing monomer (A), the following formula (2);

(wherein R ¹ represents a hydrogen atom or a methyl group; R ² represents a CH ₂ group, a CH ₂ CH ₂ group or a direct bond; R ³ and R ⁴ represent a hydroxyl group or -SO ₃ Z; , Z represents a hydrogen atom, a metal atom, an ammonium group or an organic amine group, provided that one of R ³ and R ⁴ represents —SO ₃ Z and the other represents a hydroxyl group. A structure is preferred.
In the above formula (2), when R ² is a direct bond, H ₂ C=C(R ¹ )-R ² -O- in formula (2) is H ₂ C=C(R ¹ )- It means to be represented by O-.
In formula (2) above, R ¹ is preferably a hydrogen atom. ^R2 is preferably a _CH2 group.

The above Z represents a hydrogen atom, a metal atom, an ammonium group, or an organic amine group, and when Z is a metal atom, an ammonium group, or an organic amine group, —SO ₃ Z is a metal salt of sulfonic acid, an ammonium salt, or an organic amine. represents salt.
Examples of the metal atom for Z include alkali metal atoms such as lithium, sodium and potassium; alkaline earth metal atoms such as magnesium and calcium; and aluminum and iron.
Examples of the organic amine group include alkanolamines such as monoethanolamine, diethanolamine and triethanolamine; alkylamines such as monoethylamine, diethylamine and triethylamine; polyamines such as ethylenediamine and triethylenediamine.
Z is preferably a hydrogen atom, an alkali metal atom or an ammonium group, more preferably a hydrogen atom, sodium or potassium, still more preferably a hydrogen atom or sodium.

More preferred as the sulfonic acid group-containing monomer (A) are 3-(meth)allyloxy-2-hydroxypropanesulfonic acid and salts thereof, and particularly preferred are 3-allyloxy-2-hydroxypropanesulfonic acid and its salts. Sodium salt.

The method for preparing the above sulfonic acid group-containing monomer (A) is not particularly limited, and it can be prepared by any appropriate method. In addition, a commercially available product may be used, but the following formula (1);

(Wherein, R ¹ represents a hydrogen atom or a methyl group. R ² represents a CH ₂ group, a CH ₂ CH ₂ group, or a direct bond.) It is preferably obtained.
Preferred forms of R ¹ and R ² in formula (1) above are the same as those of R ¹ and R ² in formula (2) above.

Specific examples of the epoxy compound represented by formula (1) include (meth)allyl glycidyl ether, glycidyl vinyl ether, glycidyl isopropenyl ether, and the like. (Meth)allyl glycidyl ether and glycidyl vinyl ether are preferred, (meth)allyl glycidyl ether is more preferred, and allyl glycidyl ether is most preferred.

The amount of hydrogen sulfite used in the reaction between the epoxy compound represented by formula (1) and hydrogen sulfite is 0.8 to 1.5 mol per 1 mol of the epoxy compound represented by formula (1). is preferably This allows the sulfonation reaction to proceed sufficiently. It is more preferably 0.85 to 1.3 mol, still more preferably 0.9 to 1.1 mol.
When the sulfonic acid group-containing monomer (A) is produced by the above method, it is preferable to use a predetermined amount of hydrogen sulfite from the viewpoint of sufficiently advancing the sulfonation. Hydrogen sulfite tends to remain in the group-containing monomer (A). The sulfonation rate in the group-containing monomer (A) is sufficiently high, and is obtained when the sulfonic acid group-containing monomer (A) is used in the production of the sulfonic acid group-containing copolymer The copolymer is excellent in dispersibility for complex stains.

The method for obtaining the sulfonic acid group-containing monomer (A) having a hydrogen sulfite content of 18000 ppm or less is not particularly limited, and a sulfonic acid group-containing monomer (A) having a low hydrogen sulfite content is commercially available. selection of products, adjustment of the amount of hydrogen sulfite used in the reaction between the epoxy compound represented by the above formula (1) and hydrogen sulfite, purification of the sulfonic acid group-containing monomer (A), etc. and reducing the content of hydrogen sulfite.
A method for purifying the sulfonic acid group-containing monomer (A) is not particularly limited, and examples thereof include a method of crystallization.

<Ether bond-containing monomer (B)>
The ether bond-containing monomer (B) is not particularly limited as long as it has an ether bond and an ethylenically unsaturated hydrocarbon group and does not have a sulfonic acid (salt) group. ;

(In the formula, R ⁵ represents a hydrogen atom or a methyl group. R ⁶ represents a CH ₂ group, a CH ₂ CH ₂ group, or a direct bond. X represents a hydroxyl group, a group represented by the following formula (4) or a group represented by the following formula (5), Y represents a hydroxyl group, a group represented by the following formula (4), or a group represented by the following formula (5), provided that X , Y represents a hydroxyl group, and the other represents a group represented by the following formula (4) or a group represented by the following formula (5).)

(In the formula, R ⁷ is the same or different and represents an alkylene group having 2 to 4 carbon atoms; n is the average number of added moles of the oxyalkylene group (—OR ⁷ —), R ⁸ , R ⁹ and R ¹⁰ are the same or different and each represents an alkyl group having 1 to 4 carbon atoms.).
In the above formula (3), H ₂ C=C(R ⁵ )-R ⁶ - is a methallyl group when R ⁵ is a methyl group and R ⁶ is a CH ₂ group; R ⁵ is a methyl group and R ⁶ is a CH ₂ isoprenyl group if it is a _CH2 group; isopropenyl group if ^R5 is a methyl group and ^R6 is a direct bond; allyl group if ^R5 is a hydrogen atom and ^R6 is a _CH2 group; ^R5 is hydrogen Atom, butenyl group when ^R6 is a _CH2CH2 group; vinyl group when ^R5 is _a hydrogen atom and ^R6 is a direct bond.
H ₂ C=C(R ⁵ )-R ⁶ - is preferably an isoprenyl group, a methallyl group, an allyl group, or a vinyl group. From the viewpoint of enhancing polymerizability, an isoprenyl group, a methallyl group, and an allyl group are more preferred, and an isoprenyl group and a methallyl group are even more preferred.

X and Y in the above formula (3) represent a hydroxyl group, a group represented by the above formula (4), or a group represented by the above formula (5), and one of X and Y represents a hydroxyl group. and the other represents a group represented by formula (4) or a group represented by formula (5).

R ⁷ in the above formulas (4) and (5) is the same or different and represents an alkylene group having 2 to 4 carbon atoms. Examples of the alkylene group having 2 to 4 carbon atoms include ethylene group, propylene group and butylene group. Also, from the viewpoint of improving the polymerizability of the ether bond-containing monomer (A), an alkylene group having 2 to 3 carbon atoms such as an ethylene group and a propylene group is preferred. As the alkylene group, one type or two or more types can be used.
n in the above formulas (4) and (5) is the average number of added moles of the oxyalkylene group (—OR ⁷ —) and represents a number from 0 to 5. From the standpoint of detergency against mud stains, n is preferably 0 to 4, more preferably 0 to 3, even more preferably 0 to 2, particularly preferably 0 to 1, and most preferably 0.

R ⁸ , R ⁹ and R ¹⁰ in the above formulas (4) and (5) are the same or different and represent an alkyl group having 1 to 4 carbon atoms. Examples of alkyl groups having 1 to 4 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group and t-butyl group. A hydrogen atom of the alkyl group having 1 to 4 carbon atoms may be substituted by a substituent. Substituents include amino groups, hydroxyl groups, and the like. Among the alkyl groups having 1 to 4 carbon atoms, a methyl group, an ethyl group, and a butyl group are preferred, and a butyl group is more preferred, from the viewpoint of improving the anti-soil redeposition ability of the resulting polymer.

Also, R ⁹ and R ¹⁰ in the above formula (5) may be combined to form a cyclic structure. In this case, in order to stabilize the cyclic structure, the cyclic structure formed by the nitrogen atom, R ⁹ and R ¹⁰ should be a 3- to 7-membered ring, that is, the total number of carbon atoms of R ⁹ and R ¹⁰ should be 2-6. Preferably.

As the combination of X and Y, X is a hydroxyl group and Y is a group represented by the above formula (4); X is a hydroxyl group and Y is a group represented by the above formula (5); X is the above formula (4). Y is a hydroxyl group; X is a group represented by the above formula (5); and Y is a hydroxyl group. From the viewpoint of improving anti-soil redeposition ability, preferably X is a hydroxyl group and Y is a group represented by the above formula (4); X is a hydroxyl group and Y is a group represented by the above formula (5), more preferably X is a hydroxyl group, and Y is a group represented by the above formula (4).

The method for preparing the ether bond-containing monomer (B) is not particularly limited, and it can be prepared by any appropriate method. Examples of such a preparation method include, for example, the hydroxyl group and/or amino group of a compound having an alkyl group having 1 to 4 carbon atoms and a hydroxyl group and/or an amino group in the epoxy ring of a compound having a carbon-carbon double bond and an epoxy ring. Alternatively, a simple method such as a method of producing by reacting an amino group can be mentioned. Examples of the compound having a carbon-carbon double bond and an epoxy ring include (meth)allyl glycidyl ether, glycidyl vinyl ether, and the like. Examples of compounds having an alkyl group having 1 to 4 carbon atoms and a hydroxyl group and/or an amino group include methanol, ethanol, isopropanol, n-butanol, di-n-isopropylamine and di-n-butylamine. The above reaction may be carried out without a catalyst, but may be carried out in the presence of an acidic catalyst such as boron trifluoride or a basic catalyst such as sodium hydroxide or potassium hydroxide.

<Carboxyl Group-Containing Monomer (C)>
The carboxyl group-containing monomer (C) is not particularly limited as long as it has a carboxyl group or a salt group thereof and an ethylenically unsaturated hydrocarbon group. Saturated dicarboxylic acid-based monomers are suitable, and unsaturated monocarboxylic acid-based monomers include, for example, (meth)acrylic acid, crotonic acid, tiglic acid, 3-methylcrotonic acid, 2-methyl-2 - pentenoic acid, itaconic acid, etc.; their monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts are preferred.

Examples of the unsaturated dicarboxylic acid monomers include maleic acid, itaconic acid, mesaconic acid, citraconic acid, fumaric acid, monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts thereof. , anhydrides or half esters thereof are preferred.
The carboxyl group-containing monomer (C) is preferably (meth)acrylic acid (salt) or maleic acid (salt), more preferably (meth)acrylic acid (salt), and particularly preferably acrylic acid ( salt).
The salt of the carboxyl group-containing monomer (C) is not particularly limited, but includes the metal salts, ammonium salts and organic amine salts described for Z in formula (2) above. Alkali metal salts such as sodium and potassium are preferred.

As described above, the monomer composition in the polymerization step includes the sulfonic acid group-containing monomer (A), the ether bond-containing monomer (B), and other monomers other than the carboxyl group-containing monomer (C). It may contain a monomer (E), and as the other monomer (E), specifically, a monomer obtained by adding an alkylene oxide to an unsaturated alcohol such as (meth)allyl alcohol or isoprenol , polyalkylene glycol chain-containing monomers such as (meth)acrylic acid esters of alkoxyalkylene glycol; vinyl aromatic monomers having heterocyclic aromatic hydrocarbon groups such as vinylpyridine and vinylimidazole; dimethylaminoethyl acrylates, dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl methacrylate and dimethylaminopropyl acrylate; dialkylaminoalkyl (meth)acrylamides such as dimethylaminoethylacrylamide, dimethylaminoethyl methacrylamide and dimethylaminopropylacrylamide; diallylamine; diallyldimethyl Amino group-containing monomers such as allylamine such as diallylalkylamine such as amine, and quaternized products thereof; N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylformamide, N- N-vinyl monomers such as vinyl-N-methylacetamide and N-vinyloxazolidone; amide monomers such as (meth)acrylamide, N,N-dimethylacrylamide and N-isopropylacrylamide; (meth)allyl alcohol, Hydroxyl group-containing monomers such as isoprenol; (meth)acrylic acid alkyl ester monomers such as butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate and dodecyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate , 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxyhexyl (meth) acrylate and other hydroxyalkyl (meth) acrylate monomers; Vinylaryl monomers such as styrene, indene and vinylaniline; isobutylene, vinyl acetate and the like.
The quaternized product is obtained by reacting the amino group-containing monomer with a quaternizing agent that is commonly used. Examples of the quaternizing agent include alkyl halides and dialkyl sulfates.

The polymerization method in the polymerization step is not particularly limited, and a commonly used polymerization method or a modified method thereof can be employed. Examples of the polymerization method include radical polymerization methods, and specific examples include oil-in-water emulsion polymerization method, water-in-oil emulsion polymerization method, suspension polymerization method, dispersion polymerization method, precipitation polymerization method, and solution polymerization method. , an aqueous solution polymerization method, a bulk polymerization method, and the like can be employed. Among the polymerization methods exemplified above, it is preferable to employ the solution polymerization method in terms of high safety and reduction in production cost (polymerization cost).

In the solution polymerization method, the monomer components are polymerized in a solvent.
As the solvent, it is possible to use only an organic solvent, but it is preferable that water is included. It is more preferable to use 50% by mass or more of water, more preferably 80% by mass or more of water, and particularly preferably 100% by mass of water based on 100% by mass of the total solvent used. Examples of the organic solvent that can be used alone or together with water include lower alcohols such as ethanol and isopropanol; amides such as N,N-dimethylformamide; ethers such as diethyl ether and dioxane; glycol, glycerin, and polyethylene glycol. Aqueous organic solvents such as the following are suitable.
Only one kind of the solvent may be used, or two or more kinds thereof may be used in combination.

The amount of the solvent used is preferably 40 to 300 parts by mass, more preferably 100 parts by mass, based on the total amount of all monomers (monomers (A), (B), (C), (E)). is 45 to 200 parts by mass, more preferably 50 to 150 parts by mass. When the amount of the solvent used is 40 parts by mass or more per 100 parts by mass of the total amount of all monomers, it is possible to sufficiently prevent the molecular weight of the resulting polymer from becoming too high. On the other hand, when the amount of solvent used is 300 parts by mass or less with respect to the total amount of all monomers of 100 parts by mass, it is possible to sufficiently suppress the concentration of the resulting polymer from becoming low, and the solvent removal step is omitted. You can also
A part or the whole of the solvent may be charged into the reaction vessel at the beginning of the polymerization, but part of the solvent may be added (dripped) into the reaction system during the polymerization reaction. The components, the polymerization initiator, etc. may be dissolved in advance in a solvent and added (dropped) into the reaction system during the polymerization reaction together with these components.

The reaction form of the solution polymerization method is not particularly limited, and the reaction can be carried out in a form commonly used. and a polymerization initiator (hereinafter also referred to as "initiator") are added dropwise to carry out the reaction. In such a reaction mode, the concentration of each solution to be added dropwise is not particularly limited, and any appropriate concentration can be adopted.
Examples of the form in which the monomer and the initiator are added dropwise to the solvent previously charged in the reaction system to carry out the reaction include the monomer (A), the monomer (B), the monomer Body (C), optionally monomer (E), initiator components, and optionally other additives are each dissolved in a solvent, or as they are without being dissolved in a solvent, during polymerization 2) is appropriately added (dropped) into the reaction system to carry out polymerization. Moreover, in this reaction mode, part or all of the total amount of the monomer (A) used can be previously added (initial charging) to the reaction system before the initiation of polymerization.

<Polymerization initiator>
As the polymerization initiator used in the above production method, a commonly used one can be used. Specifically, hydrogen peroxide; persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate; 2,2′-azobis(2-amidinopropane) hydrochloride, 4,4′-azobis-4-cyanovalerin Azo compounds such as acids, azobisisobutyronitrile, 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile); benzoyl peroxide, lauroyl peroxide, peracetic acid, di-t-butyl Preferred examples include organic peroxides such as peroxides and cumene hydroperoxides. Among these polymerization initiators, hydrogen peroxide, persulfate and 2,2'-azobis(2-amidinopropane) hydrochloride are preferred, and persulfate and 2,2'-azobis(2-amidinopropane) hydrochloride are preferred. Salt is more preferred. These polymerization initiators may be used alone or in combination of two or more.

<Chain transfer agent>
In the above production method, it is preferable to use a chain transfer agent as a molecular weight modifier for the polymer. When a chain transfer agent is used, it is possible to prevent the polymer to be produced from having a higher molecular weight than necessary, and to efficiently produce a low-molecular-weight copolymer.
In the above production method, it is preferable to use a hydrogen sulfite and/or a compound capable of generating a hydrogen sulfite as the chain transfer agent. In that case, it is more preferable to use a polymerization initiator in addition to the hydrogen sulfite and the compound capable of generating the hydrogen sulfite. Furthermore, heavy metal ions may be used in combination as a reaction accelerator.
Further, when a hydrogen sulfite and/or a compound capable of generating a hydrogen sulfite is used as a chain transfer agent, a polymer having a sulfonic acid (salt) group at least one of the main chain ends can be obtained.

Examples of the compound capable of generating the hydrogen sulfite include pyrosulfite (salt), dithionous acid (salt), sulfurous acid (salt) and the like, with pyrosulfite (salt) being preferred.
As the above salt, salts with metal atoms, ammonium or organic amines are suitable. Specific examples of the metal atom and the organic amine are as described above.
Of the hydrogen sulfites and compounds capable of generating hydrogen sulfites, hydrogen sulfites are preferred.
Examples of the hydrogen sulfite include sodium hydrogen sulfite, potassium hydrogen sulfite, ammonium hydrogen sulfite and the like, and sodium hydrogen sulfite is more preferable.
Examples of compounds capable of generating hydrogen sulfite include sodium pyrosulfite, potassium pyrosulfite; sodium dithionite, potassium dithionite; sodium sulfite, potassium sulfite, ammonium sulfite; is more preferred.
Each of the hydrogen sulfites and compounds capable of generating hydrogen sulfites may be used alone, or two or more of them may be used in combination.

In addition to the above hydrogen sulfites and compounds capable of generating hydrogen sulfites, the following may also be used as the chain transfer agent. Examples of the chain transfer agent include mercaptoethanol, thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, octyl 3-mercaptopropionate, 2-mercaptoethanesulfonic acid, n-dodecylmercaptan, and other thiol chain transfer agents. Agent; Halides such as carbon tetrachloride, methylene chloride, bromoform, bromotrichloroethane; Secondary alcohols such as isopropanol and glycerin; Phosphorous acid, hypophosphorous acid and its salts (sodium hypophosphite, hypophosphite potassium, etc.) and salts thereof; One or two or more of the chain transfer agents may be used.

The combination of the chain transfer agent, the polymerization initiator and the reaction accelerator is not particularly limited and can be appropriately selected from the above examples. Either one of the polymerization initiator and the reaction accelerator may be used. Combinations of the chain transfer agent/polymerization initiator/reaction accelerator are listed in this order, for example, sodium bisulfite/hydrogen peroxide/none, sodium bisulfite/sodium persulfate/none, sodium bisulfite/none /Fe (ion), sodium bisulfite/hydrogen peroxide/Fe (ion), sodium bisulfite/sodium persulfate/Fe (ion), sodium bisulfite/sodium persulfate, hydrogen peroxide/none, etc. are preferred. More preferred are sodium bisulfite/sodium persulfate/none and sodium bisulfite/sodium persulfate/Fe (ion), and still more preferred is sodium bisulfite/sodium persulfate/Fe (ion). In the above, "none" means that the component is not used.

<Use amount of polymerization initiator etc.>
The total amount of the polymerization initiator used is not particularly limited as long as it is an amount capable of initiating copolymerization of the monomers, but all monomer components (monomers (A), (B), (C) and ( It is preferably 15 g or less with respect to 1 mol of the total amount of E)). More preferably 1 to 12 g.
When hydrogen peroxide is used as the polymerization initiator, the amount of hydrogen peroxide added is preferably 1.0 to 10.0 g per 1 mol of the total amount of all monomer components, and 2.0 g. More preferably ~8.0 g. If the amount of hydrogen peroxide added is less than 1.0 g, the resulting polymer tends to have a high weight average molecular weight. On the other hand, if the added amount exceeds 10.0 g, the effect corresponding to the increase in the added amount cannot be obtained, and furthermore, there is a risk of adverse effects such as an increase in the amount of remaining hydrogen peroxide.

When a persulfate is used as the polymerization initiator, the amount of the persulfate added is preferably 1.0 to 5.0 g, preferably 2.0 g, per 1 mol of the total amount of all monomer components. More preferably ~4.0 g. If the amount of persulfate added is less than 1.0 g, the resulting polymer tends to have a high molecular weight. On the other hand, if the added amount exceeds 5.0 g, it becomes difficult to obtain the effect corresponding to the increase in the added amount, and furthermore, there is a possibility that the purity of the obtained polymer is lowered and other adverse effects are caused.
When hydrogen peroxide and persulfate are used together as a polymerization initiator, the mass ratio of persulfate to hydrogen peroxide is preferably 0.1 to 5.0, and preferably 0.2 to 2.0. is more preferable. If the mass ratio of the persulfate is less than 0.1, the resulting copolymer tends to have a high weight average molecular weight. On the other hand, when the mass ratio of the persulfate exceeds 5.0, the effect of lowering the molecular weight due to the addition of the persulfate cannot be obtained to a degree commensurate with the increase in the amount added, and the persulfate is wasted in the polymerization reaction system. may be consumed by

The amount of the chain transfer agent to be added is not limited as long as the monomers (A), (B), (C) and (E) are polymerized well, but the monomers (A), (B), It is preferably 0.5 to 20 g, more preferably 1 to 15 g, per 1 mol of the total amount of all monomer components consisting of (C) and (E). If it is less than 0.5 g, it may be impossible to control the molecular weight. On the other hand, if it exceeds 20 g, a large amount of impurities may be produced, and the polymer purity may decrease. In particular, when a hydrogen sulfite is used, if the amount added exceeds 20 g, the excess hydrogen sulfite may be decomposed in the reaction system to generate sulfurous acid gas, which is also economically disadvantageous. There is a risk.
The amount of the chain transfer agent added does not include the hydrogen sulfite contained in the monomer (A).

As a combination of the initiator and the chain transfer agent, it is preferable to use at least one persulfate and one or more hydrogen sulfites.
In this case, the mixing ratio of the persulfate and the hydrogensulfite is not particularly limited, but it is preferable to use 0.5 to 5 parts by mass of the hydrogensulfite per 1 part by mass of the persulfate. The lower limit of the amount of hydrogen sulfite is more preferably 1 part by mass, still more preferably 2 parts by mass, per 1 part by mass of persulfate. Moreover, the upper limit of the amount of hydrogen sulfite is more preferably 4 parts by mass, still more preferably 3 parts by mass with respect to 1 part by mass of persulfate. If the hydrogen sulfite is less than 0.5 parts by mass with respect to 1 part by mass of the persulfate, the total amount of the initiator required for lowering the molecular weight may increase. Side reactions may increase, resulting in an increase in impurities.

The total amount of the chain transfer agent, initiator and reaction accelerator used is 2 to 20 g is preferred. By setting it as such a range, the sulfonic-acid-group-containing copolymer of this invention can be produced efficiently, and the molecular weight distribution of the said polymer can be made into a desired thing. More preferably 3 to 18 g, still more preferably 4 to 15 g.

<Polymerization conditions>
In the above production method, the polymerization temperature is appropriately determined depending on the polymerization method, solvent, polymerization initiator, etc. used, but is preferably 25 to 200°C. It is more preferably 50 to 150°C, still more preferably 60 to 120°C, and particularly preferably 80 to 110°C. If the polymerization temperature is lower than 25°C, the weight average molecular weight of the resulting polymer may become too high, and the amount of impurities produced may increase.
The polymerization temperature does not need to be kept almost constant in the polymerization reaction. For example, the polymerization is started at room temperature, heated to a set temperature with an appropriate heating time or rate, and then set temperature is increased. The temperature may be maintained, or the temperature may be varied (increased or decreased) over time during the polymerization reaction depending on the dropping method of the monomer component, initiator, and the like. In addition, the polymerization temperature means the temperature of the reaction solution in the polymerization reaction. Moreover, any suitable method and means can be employed as the polymerization temperature measuring method and control means. For example, it may be measured using a commonly used device.

The pressure during polymerization in the production method is not particularly limited, and any appropriate pressure can be adopted. For example, under normal pressure (atmospheric pressure), under reduced pressure, or under increased pressure. Moreover, the atmosphere in the reaction system may be an air atmosphere or an inert gas atmosphere. When the atmosphere in the reaction system is made into an inert gas atmosphere, it can be carried out, for example, by replacing the inside of the reaction system with an inert gas such as nitrogen before starting the polymerization. As a result, the atmosphere gas (for example, oxygen gas) in the reaction system dissolves in the liquid phase and acts as a polymerization inhibitor.

In the production method described above, the solid content concentration in the reaction solution (polymer solution) at the time when the dropping of the total amount of the monomer, the polymerization initiator and the chain transfer agent is completed is preferably 35% by mass or more. . If it is less than 35% by mass, it may not be possible to significantly improve the productivity of the resulting polymer. More preferably 40 to 70% by mass, still more preferably 45 to 65% by mass. As described above, when the solid content concentration at the end of dropping is 35% by mass or more, polymerization can be carried out in a single step in a high-concentration reaction solution. Therefore, a polymer can be obtained efficiently. For example, the concentration step can be omitted, the productivity of the polymer can be greatly improved, and the increase in production cost can be suppressed.
The solid content concentration can be calculated by taking out a part of the reaction solution at the end of the dropwise addition, treating it with a hot air dryer at 130° C. for 1 hour, and determining the non-volatile content.

In the above production method, an aging step may be provided for the purpose of increasing the polymerization rate of the monomers after the addition of all the raw materials used. The aging time is preferably 1 to 120 minutes, more preferably 5 to 60 minutes, still more preferably 10 to 30 minutes. If the aging time is less than 1 minute, the monomer component may remain due to insufficient aging, and impurities resulting from the residual monomer may lead to deterioration in performance. If the aging time exceeds 120 minutes, the polymer solution may be colored.

In the above production method, the polymerization time is not particularly limited, but is preferably 30 to 420 minutes, more preferably 45 to 390 minutes, still more preferably 60 to 360 minutes, and particularly preferably 90 to 300 minutes. minutes. In the present invention, the term "polymerization time" refers to the time during which the monomers are added, that is, the time from the start to the end of the addition of the monomers, unless otherwise specified.

<Sulfonic Acid Group-Containing Copolymer-Containing Composition>
As described above, the production method of the present invention can reduce the amount of impurities derived from hydrogen sulfite in the resulting copolymer. Impurities derived from hydrogen sulfites include, for example, sulfites and sulfates. The salts in the above sulfites and sulfates are not particularly limited, but include the same salts as in the hydrogensulfites.
The present invention includes a sulfonic acid group-containing copolymer obtained by the production method of the present invention, wherein the total content of sulfite and/or sulfate is 1000 to 30000 ppm. It is also a composition. Such a sulfonic acid group-containing copolymer-containing composition has excellent dispersibility for complex stains.
The total content of sulfites and/or sulfates is preferably 3,000 to 20,000 ppm, more preferably 5,000 to 16,000 ppm.
The contents of sulfite and sulfate in the sulfonic acid group-containing copolymer-containing composition can be measured by the method described in Examples.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited only to these examples. Unless otherwise specified, "part" means "mass part" and "%" means "mass %".

<Conditions for measuring weight average molecular weight and number average molecular weight (GPC)>
Apparatus: HLC-8320GPC manufactured by Tosoh Corporation
Column: Two TSKgek PW _XL and TSKgel GMPW _XL manufactured by Tosoh Corporation Column temperature: 40°C
Flow rate: 1ml/min
Calibration curve: Polyacrylic acid standard manufactured by Sowa Chemical Co., Ltd.
Eluent: (60.84 mM sodium carbonate aqueous solution + 60.84 mM sodium bicarbonate aqueous solution)/acetonitrile = 83.74/16.26 (mass ratio).

<Measurement of content of hydrogen sulfite in sulfonic acid group-containing monomer (A)>
The following operations (1) to (8) were performed, and the hydrogen sulfite concentration in the sulfonic acid group-containing monomer (A) was measured based on the following formulas (I) to (III).
(1) 3 g of the sulfonic acid group-containing monomer (A) and 15 g of 0.1% hydrogen peroxide solution are weighed into a 50 ml screw tube and stirred with a magnetic stirrer.
(2) 1 g of potassium iodide is weighed into a 100 ml beaker, 70 g of pure water is added, and the mixture is stirred with a magnetic stirrer.
(3) Add 15 ml of 18N sulfuric acid to the beaker of (2) with a whole pipette while stirring.
(4) Add the solution of (1) to the beaker of (3) with stirring until it turns brown, and stir for 2 minutes.
(5) To the beaker of (4), add 1 ml of 1% starch aqueous solution with a whole pipette while stirring, and confirm that the solution turns dark brown.
(6) After confirming the discoloration in (5), immediately titrate with a 0.1 M sodium thiosulfate aqueous solution while stirring, and the end point is when the color disappears.
(7) Separately, measure a sample in steps (1) to (6) above, excluding step (4).
(8) In steps (1) to (6) above, measure a sample in which 2.5 g of 0.1% hydrogen peroxide solution was added instead of the solution of (1) in step (4). .
- Sulfonic acid group-containing monomer (A) weighing value: A (g)
・ 0.1% hydrogen peroxide water weighing value: B (g)
Amount of solution (1) dropped in step (4): C (g)
・ Sodium thiosulfate titration amount: D (ml)
- 0.1 M sodium thiosulfate aqueous solution introduced in step (7): D ₀ (g)
・Weighing value of 0.1% hydrogen peroxide water dropped in step (8): B ₁ (g)
- 0.1 M sodium thiosulfate aqueous solution dropped in step (8): D ₁ (g)
Hydrogen peroxide concentration E (%) put into the measurement solution = (B × ((D ₁ - D ₀ ) × 0.17/B ₁ ) / 100) / (A + B) × 100 (I)
Actual hydrogen peroxide concentration in the measured solution F (%) = (D-D ₀ ) x 0.17/C (II)
Hydrogen sulfite concentration (ppm) in sulfonic acid group-containing monomer (A) = ((C x (EF) / 100/34 x 104) x A / (C x A / (A + B))) / A x 1000000 (III)

<Measurement of content of sulfite and sulfate in polymer>
Device: IC-2010 manufactured by Tosoh Corporation
Column: Showa Denko Shodex IC SI-90 4E (4.0 mm × 250 mm), Shodex IC SI-90G
Column temperature: 25°C
Flow rate: 1.2ml/min
Eluent: (1.05 mM sodium carbonate aqueous solution + 4.21 mM sodium hydrogen carbonate aqueous solution/acetone = 95/5 (mass ratio)

<Evaluation of dispersibility of composite dirt (carbon black-clay)>
(1) 2.94 g of calcium chloride dihydrate was placed in a 500 mL beaker, and pure water was added to make 500 g to prepare hard water.
(2) 10 g of 0.1% solids aqueous solution of each evaluation sample was prepared in a 20 mL screw tube.
(3) 7.51 g of glycine, 1.18 g of ethanol, and 7.00 g of 48% NaOH were placed in a 1 L beaker, and pure water was added to make 1000 g to prepare a glycine buffer of pH 10.5.
(4) Next, 30 mL test tubes with an inner diameter of 16 mm were prepared for evaluation samples, each containing 0.03 g of carbon black, 0.30 g of JIS class 11 clay, 1.50 g of hard water (1), and 1.50 g of hard water (2). 50 g and 27.0 g of the glycine buffer of (3) were added and capped with a septum. Thus, an aqueous suspension containing 1,000 ppm of carbon black, 10,000 ppm of clay, and 50 ppm of sample solid content was prepared in each test tube.
(5) After slowly inverting each test tube 60 reciprocations, the cap was removed and allowed to stand in a horizontal and stable place for 1 hour. After 1 hour, 5 mL of the supernatant was collected using a whole pipette.
(6) The absorbance of this supernatant at 380 nm was measured using a UV-visible spectrophotometer UV-1800 manufactured by Shimadzu Corporation. This absorbance was defined as dispersibility. A higher absorbance value means a higher dispersibility.

<Synthesis Example 1>
244.0 parts of deionized water and 114.9 parts of a 48% sodium hydroxide aqueous solution were introduced into a SUS reaction vessel equipped with a thermometer, a stirrer, a cooling trap at the nitrogen inlet pipe and the nitrogen outlet while introducing nitrogen. , and 820.5 parts of a 35% sodium hydrogen sulfite aqueous solution (hereinafter also referred to as "35% SBS") was added. The liquid temperature was raised to 63° C., and 320.6 parts of allyl glycidyl ether was added dropwise over 225 minutes. After the dropwise addition of allyl glycidyl ether was completed, the temperature of the reaction solution was maintained at 63° C. for 30 minutes to complete the reaction and obtain a sulfonic acid group-containing monomer (1).

<Synthesis Example 2>
A sulfonic acid group-containing monomer (2) was obtained in the same manner as in Synthesis Example 1, except that the amount of the 35% sodium hydrogen sulfite aqueous solution was changed to 850.0 parts.

<Synthesis Example 3>
A sulfonic acid group-containing monomer (3) was obtained in the same manner as in Synthesis Example 1, except that the amount of the 35% sodium hydrogen sulfite aqueous solution was changed to 875.0 parts.

<Synthesis Example 4>
370.0 g of n-butyl alcohol and 4.27 g of sodium hydroxide pellets were charged in a 500 mL four-necked glass flask equipped with a reflux condenser and a stirrer (paddle blades), and heated to 60° C. while stirring. heated up. Next, 57.0 g of allyl glycidyl ether was added over 30 minutes and then reacted for 5 hours. This solution was transferred to a 1000 ml eggplant flask and desolvated with a rotary evaporator. 200.0 g of a 20% by mass sodium chloride aqueous solution was added thereto, and the aqueous solution was transferred to a 500 ml separating funnel, shaken well, allowed to stand until the layers were separated, and the lower layer was removed. The remaining upper layer was transferred to a 300 ml eggplant flask, and the solvent was removed by a rotary evaporator. The precipitated salt was removed by filtration to obtain an ether bond-containing monomer (1).

<Example 1>
181.27 g of pure water and 0.0593 g of Mohr's salt were charged into a 2000 mL separable glass flask equipped with a reflux condenser and a stirrer (paddle blade), and the temperature was raised to 85° C. while stirring to initiate a polymerization reaction. system. Next, 327.6 g of an 80% acrylic acid aqueous solution (hereinafter also referred to as "80% AA") and the sulfonic acid group-containing solution obtained in Synthesis Example 1 were added to a polymerization reaction system maintained at 85°C with stirring. 136.7 g of a 40% aqueous solution of monomer (1) (hereinafter also referred to as "40% sulfonic acid group-containing monomer (1)"), the ether bond-containing monomer obtained in Synthesis Example 4 (1 ), 88.0 g of a 15% sodium persulfate aqueous solution (hereinafter also referred to as "15% NaPS"), and 14.1 g of 35% SBS were dropped from separate nozzles. The dropping time of each solution was 180 minutes for 80% AA, 120 minutes for 40% sulfonic acid group-containing monomer (1), 150 minutes for ether bond-containing monomer (1), and 15% NaPS. was 210 minutes and 175 minutes for 35% SBS. Further, the dropping rate of each solution was constant, and the dropping of each solution was performed continuously.
After the dropwise addition of 80% AA was completed, the reaction solution was kept at 85° C. for an additional 30 minutes (aging) to complete the polymerization. After completion of the polymerization, while the polymerization reaction liquid was stirred and allowed to cool, 163.09 g of a 48% sodium hydroxide aqueous solution was gradually added dropwise to neutralize the polymerization reaction liquid.

<Example 2 and Comparative Example 1>
A sulfonic acid group-containing copolymer was synthesized in the same manner as in Example 1, except that the sulfonic acid group-containing monomer having the SBS content shown in Table 1 was used.

The sulfonic acid group-containing copolymers obtained in Examples 1 and 2 and Comparative Example 1 were measured for weight-average molecular weight, number-average molecular weight, sodium sulfite and sodium sulfate contents, and composite soil dispersion performance. is shown in Table 1.

Claims (3)

A method for producing a sulfonic acid group-containing copolymer, comprising:
The production method includes a step of polymerizing a monomer composition containing a sulfonic acid group-containing monomer (A), an ether bond-containing monomer (B), and a carboxyl group-containing monomer (C). ,
The content of hydrogen sulfite in the sulfonic acid group-containing monomer (A) is 18000 ppm or less,
The ether bond-containing monomer (B) has the following formula (3);

(In the formula, R ⁵ represents a hydrogen atom or a methyl group. R ⁶ represents a CH ₂ group, a CH ₂ CH ₂ group, or a direct bond. X represents a hydroxyl group, a group represented by the following formula (4) or a group represented by the following formula (5), Y represents a hydroxyl group, a group represented by the following formula (4), or a group represented by the following formula (5), provided that X , Y represents a hydroxyl group, and the other represents a group represented by the following formula (4) or a group represented by the following formula (5).)

(In the formula, R ⁷ is the same or different and represents an alkylene group having 2 to 4 carbon atoms; n is the average number of added moles of the oxyalkylene group (—OR ⁷ —), R ⁸ , R ⁹ and R ¹⁰ are the same or different and represent an alkyl group having 1 to 4 carbon atoms. A method for producing a polymer. The sulfonic acid group-containing monomer (A) has the following formula (1);

(Wherein, R ¹ represents a hydrogen atom or a methyl group. R ² represents a CH ₂ group, a CH ₂ CH ₂ group, or a direct bond.) 2. The method for producing a sulfonic acid group-containing copolymer according to claim 1, wherein the sulfonic acid group-containing copolymer is obtained. The sulfonic acid group-containing monomer (A) has the following formula (2);

(wherein R ¹ represents a hydrogen atom or a methyl group; R ² represents a CH ₂ group, a CH ₂ CH ₂ group or a direct bond; R ³ and R ⁴ represent a hydroxyl group or -SO ₃ Z; , Z represents a hydrogen atom, a metal atom, an ammonium group or an organic amine group, provided that one of R ³ and R ⁴ represents —SO ₃ Z and the other represents a hydroxyl group. 3. The method for producing a sulfonic acid group-containing copolymer according to claim 1 or 2, wherein the copolymer is a structure.