JP7266055B2 - (Meth) acrylamide-based water-soluble polymer powder and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a (meth)acrylamide-based water-soluble polymer powder and a method for producing the same. More specifically, the present invention relates to a (meth)acrylamide water-soluble polymer powder redox-polymerized in the presence of thiosulfate, which has a low insoluble content, and its It relates to a manufacturing method.

Powdery acrylamide-based water-soluble polymers composed of homopolymers of acrylamide or copolymers obtained by copolymerizing acrylamide with anionic or cationic monomers are used as coagulants, coagulants, agents for papermaking processes, petroleum Widely used in various industries as a tertiary recovery agent. In these applications, higher molecular weights often provide better performance, and may require polymers with molecular weights in excess of 10 million. Such polymers are generally produced by radical polymerization followed by drying and pulverization.

As an industrial drying method, a method in which a polymer obtained by aqueous solution polymerization is generally dried using a hot air dryer such as a rotary aeration dryer or a fluidized bed dryer is used. However, in the case of a very high molecular weight, if it is dried at a high temperature in an attempt to improve productivity, intramolecular and intermolecular cross-linking will occur and a large amount of water-insoluble components will be generated. Therefore, it ceases to play a role as a flocculant or the like.

Various methods have been proposed as methods for reducing the water-insoluble matter without lowering productivity. In Patent Document 1, an azo compound is allowed to coexist with a monomer mixed solution for polymerization, and the resulting gel-like polymer is heated at a temperature of 80° C. to 150° C. while maintaining the water content, thereby removing the water-insoluble portion. It is disclosed that the amount is significantly reduced.

Further, as a method of adding a compound having an effect of preventing dissolution, Patent Document 2 discloses a method of adding an amine, and Patent Document 3 discloses a method of adding a urea compound and a water-soluble nitrogen compound in combination. 4, a method of adding a sulfur compound such as ethylene trithiocarbonate and thionicotinamide; Patent Document 5, a method of adding pyridine or a pyridine derivative; Patent Document 6, a 1,3-dione residue. Disclosed is a method of adding a cyclic organic compound containing However, these methods are not sufficient as a method for producing a water-soluble acrylamide polymer having a high molecular weight and a very small amount of water-insoluble matter.

There are several ways to add thiosulfate to radical polymerization systems. Patent Document 7 discloses a method of using a thiosulfate as a reducing agent for a redox initiator to adjust the polymerization rate of a water-swellable polymer, and Patent Document 8 discloses a method of using a thiosulfate as a reducing agent for suspension polymerization. Patent Document 9 discloses a method of using a thiosulfate as an oxygen absorbent for improving polymerizability, and Patent Document 10 discloses a method of adding a thiosulfate as an oxygen absorbent in the polymerization system. However, there is no description regarding reduction of insoluble matter.

In Patent Document 11, a (meth)acrylic acid monomer containing aldehyde as an impurity and a monomer copolymerizable therewith are used, and a thiosulfate is added as a reducing agent for a redox initiator at a specific ratio to the oxidizing agent. It is described that the solubility of the dried polymer obtained by the aqueous solution polymerization is improved. However, when producing an acrylamide-based water-soluble polymer with a high degree of polymerization on an industrial scale, it is common to use a monomer that does not substantially contain aldehyde, which is not within the scope of the present invention.

Japanese Examined Patent Publication No. 63-20842 Japanese Patent Publication No. 56-39657 Japanese Examined Patent Publication No. 60-50808 Japanese Patent Laid-Open No. 5-230141 Japanese Patent Laid-Open No. 8-208720 Japanese Patent Laid-Open No. 56-67312 Japanese Patent Laid-Open No. 1-234402 JP 2000-026512 Japanese Patent Laid-Open No. 10-049810 Patent 4287284 Japanese Patent Application Laid-Open No. 61-275308

An object of the present invention is to provide a (meth)acrylamide-based water-soluble polymer powder in which the formation of insoluble matter is suppressed, and a method for producing the same.

As a result of extensive studies on the above problems, the present inventors have found that a monomer mixture containing at least a (meth)acrylamide compound is redox polymerized in the presence of a predetermined amount of thiosulfate and then dried ( The inventors have found that the meth)acrylamide-based water-soluble polymer powder significantly suppresses the formation of insoluble matter during drying, and have completed the present invention.

That is, the first aspect of the present invention is
[1] a polymer containing at least a monomer unit derived from a (meth)acrylamide-based compound;
thiosulfate;
A (meth) acrylamide-based water-soluble polymer powder containing
The (meth)acrylamide-based water-soluble polymer powder is characterized in that the content of the thiosulfate is 2×10 ⁻³ mol % or more with respect to the total monomer units constituting the polymer. .

In the first invention,
[2] The thiosulfate is preferably sodium thiosulfate,
[3] the polymer is a (meth)acrylamide compound,
at least one selected from (meth)acrylic acid and its salts, 2-acrylamido-2-methylpropanesulfonic acid and its salts, dimethylaminoethyl (meth)acrylate and its quaternary salts;
is preferably a copolymer of
[4] preferably contains a compound having a 1,3-dione structure in the molecule,
[5] preferably contains thiourea or formate,
[6] The water-insoluble content is preferably 10% by mass or less.

A second aspect of the present invention is
[7] A method for producing a (meth)acrylamide-based water-soluble polymer powder comprising: polymerizing an aqueous solution of a monomer mixture containing at least a (meth)acrylamide-based compound to obtain a polymer gel; and then drying and pulverizing the polymer gel. and
A method for producing a (meth)acrylamide-based water-soluble polymer powder, wherein the aqueous polymerization is carried out in the presence of a thiosulfate using a redox initiator consisting of a combination of an oxidizing agent and a reducing agent. .

In the second invention,
[8] The thiosulfate is preferably sodium thiosulfate,
[9] The amount of thiosulfate added is preferably more than 10 times the molar amount of the oxidizing agent,
[10] a monomer mixture comprising a (meth)acrylamide-based compound;
at least one selected from (meth)acrylic acid and its salts, 2-acrylamido-2-methylpropanesulfonic acid and its salts, dimethylaminoethyl (meth)acrylate and its quaternary salts;
preferably containing
[11] The aqueous solution polymerization is preferably adiabatic aqueous solution polymerization,
[12] the oxidizing agent is at least one selected from organic peroxides and persulfates;
The reducing agent is preferably at least one selected from inorganic salts and amines,
[13] It is preferable to add the azo compound before starting the aqueous solution polymerization,
[14] It is preferable to add a compound having a 1,3-dione structure in the molecule before starting the aqueous solution polymerization,
[15] Preferably, thiourea or formate is added before starting the aqueous solution polymerization,
[16] It is preferable to further include a heat treatment step of heating at 90 to 120° C. while maintaining the water content of the polymer gel.

The (meth)acrylamide-based water-soluble polymer powder of the present invention is easily soluble in water and has a low water-insoluble content. This (meth)acrylamide-based water-soluble polymer powder is used as a coagulant for sludge from domestic and industrial wastewater; papermaking agents such as retention aids, drainage improvers, and formation aids; drilling and muddy water treatment; additives for increasing crude oil production; organic coagulants; thickeners; dispersants; scale inhibitors;
Moreover, according to the production method of the present invention, the above (meth)acrylamide-based water-soluble polymer powder can be produced economically without introducing new equipment.

The present invention will be described in detail below.
In the present specification, acrylate and/or methacrylate are represented as (meth)acrylate; acrylamide and/or methacrylamide are represented as (meth)acrylamide; acrylic acid and/or methacrylic acid are represented as (meth)acrylic acid It is sometimes expressed as

The present invention provides a polymer containing at least a monomer unit derived from a (meth)acrylamide compound,
thiosulfate;
A (meth) acrylamide-based water-soluble polymer powder containing
The (meth)acrylamide-based water-soluble polymer powder is characterized in that the content of the thiosulfate is 2×10 ⁻³ mol % or more with respect to the total monomer units constituting the polymer. .

A (meth)acrylamide compound is represented by the following chemical formula (1).
CH ₂ ═CR ₁ —CO—NR ₂ R ₃ (1)
However, in the above chemical formula (1), R ₁ is a hydrogen atom or a methyl group, and R ₂ and R ₃ are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.

Among the (meth)acrylamide-based compounds represented by the above chemical formula (1), (meth)acrylamide is preferred, and acrylamide is particularly preferred, because it is water-soluble and has particularly excellent performance as a polymer flocculant. These (meth)acrylamide compounds may be used alone or in combination of two or more.

Polymers containing monomer units derived from (meth)acrylamide compounds include (meth)acrylamide compounds and anionic monomers or cationic monomers copolymerizable with the (meth)acrylamide compounds. It is preferably a copolymer of

Examples of anionic monomers include (meth)acrylic acid, vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, maleic acid, and salts thereof. Preferred salts are alkali metal salts such as ammonium, sodium and potassium salts. Among these, (meth)acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and salts thereof are preferred. These anionic monomers may be used alone or in combination of two or more.

Examples of cationic monomers include diallyldialkylammonium halides such as diallyldimethylammonium chloride as well as compounds represented by the following chemical formula (2). Among these cationic monomers, it has excellent radical polymerization reactivity, is easy to increase in molecular weight, and the obtained polymer has excellent performance as a polymer flocculant. The compounds represented are preferred.
CH ₂ ═CR ¹ —CO—X—Q—N ⁺ R ² R ³ R ^{4.Z —} (2)
provided that R ¹ is a hydrogen atom or a methyl group, R ² and R ³ are each independently an alkyl group having 1 to 3 carbon atoms or a benzyl group, and R ⁴ is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms or a benzyl group. Yes, it can be of the same or different species. X is an oxygen atom or NH, Q is an alkylene group having 1 to 4 carbon atoms or a hydroxyalkylene group having 2 to 4 carbon atoms, Z ^- represents a counter anion, and Z ^- is a halide ion such as a chloride ion. and sulfate ions are exemplified.

Examples of the cationic monomer represented by the above chemical formula (2) include dialkylaminoalkyl (meth)acrylate such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylamino-2-hydroxypropyl (meth)acrylate and the like. ) acrylates and hydrochlorides and sulfates of dialkylaminoalkyl(meth)acrylamides such as dimethylaminopropyl(meth)acrylamide. In addition, alkyl halide adducts such as methyl chloride of dialkylaminoalkyl (meth)acrylates and dialkylaminoalkyl (meth)acrylamides, benzyl halide adducts such as benzyl chloride, dialkyl sulfate adducts such as dimethyl sulfate, etc. Quaternary salts are exemplified. In particular, the methyl chloride quaternary salt and the benzyl chloride quaternary salt of dimethylaminoethyl (meth)acrylate are preferred because they facilitate the increase in the molecular weight required for the polymer flocculant. These cationic monomers may be used alone or in combination of two or more.

In the present invention, there is no particular limitation on the compounding ratio (molar ratio) of each monomer in the monomer mixture. The compounding ratio (molar ratio) of each monomer in the monomer mixture is cationic monomer:anionic monomer:(meth)acrylamide compound=0 to 99:0 to 99:1 to 100. Yes, preferably 0-90:0-90:10-100.

Thiosulfate salts include ammonium, calcium, potassium, and sodium salts of thiosulfate. A particularly preferred thiosulfate is sodium thiosulfate.

The content of thiosulfate is 2×10 ⁻³ mol % or more, preferably 5×10 ⁻³ mol % or more, and 8×10 ⁻ It is more preferably ³ mol % or more. If it is less than 2×10 ⁻³ mol %, the effect of suppressing insoluble matter may be insufficient. The upper limit of the content of thiosulfate is not particularly limited, but it is preferably 5×10 ⁻¹ mol% or less, and 1×10 ⁻¹ mol% or less based on the total monomer units constituting the polymer. It is more preferable to have If it exceeds 5×10 ⁻¹ mol %, it may not be preferable mainly from the viewpoint of economy.

Although the effect of thiosulfate in the present invention is not clear, it reductively decomposes and inactivates the peroxide generated by the oxidation of the polymer in the high-temperature drying process in the presence of oxygen, thereby suppressing the generation of radicals. The present inventors speculate that intramolecular and intermolecular cross-linking is suppressed by this.

The (meth)acrylamide-based water-soluble polymer powder of the present invention may contain other compounds having an effect of preventing dissolution in addition to the thiosulfate described above. Compounds having an effect of preventing dissolution include compounds having a 1,3-dione structure in the molecule, thiourea, and formate. Examples of compounds having a 1,3-dione structure in the molecule include 5,5-dimethyl-1,3-cyclohexanedione, 1,3-cyclohexanedione, and barbituric acid, but 5,5-dimethyl -1,3-cyclohexanedione is particularly preferred. Examples of formates include sodium formate. These compounds may be used in combination of two or more.

The content of these compounds is preferably 5×10 ⁻⁴ to 1000×10 ⁻⁴ mol %, more preferably 10×10 ⁻⁴ to 500×10 ⁻⁴ mol %, relative to the total monomer units. is more preferable.

The (meth)acrylamide-based water-soluble polymer powder of the present invention preferably has a water-insoluble content of 10% by mass or less, more preferably 6% by mass or less, as measured by the method described below.

The (meth)acrylamide-based water-soluble polymer powder of the present invention preferably has a standard viscosity of 1 to 15 mPa s, more preferably 2 to 15 mPa s, as measured by the method described below. More preferably, it is 10 mPa·s.

Next, the method for producing the (meth)acrylamide-based water-soluble polymer powder of the present invention will be described. The (meth)acrylamide-based water-soluble polymer powder of the present invention is obtained by aqueous polymerization of a monomer mixture containing at least a (meth)acrylamide-based compound to obtain a polymer gel, and then drying and pulverizing the polymer gel. can be manufactured by Here, said aqueous polymerization is carried out in the presence of thiosulfate using a redox initiator consisting of a combination of an oxidizing agent and a reducing agent.

First, an aqueous solution of a monomer mixture containing at least a (meth)acrylamide compound is prepared, and this monomer mixture is subjected to aqueous polymerization using a redox initiator in the presence of thiosulfate to obtain a polymer gel.

The (meth)acrylamide-based compound, the monomer copolymerizable with the (meth)acrylamide-based compound, and the thiosulfate are as described above.

The amount of the thiosulfate added is more than 10 times the molar amount of the oxidizing agent that constitutes the redox initiator, preferably more than 12 times the molar amount, more preferably more than 20 times the molar amount, and 50 times the molar amount. More than molar is more preferred. If it is less than 10-fold mol, the effect of suppressing insoluble matter may be insufficient. The upper limit of the amount of thiosulfate to be added is not particularly limited, but it is preferably less than 3000-fold mol, more preferably less than 1500-fold mol, as much as the oxidizing agent constituting the redox initiator. If it is 3000 times the molar amount or more, it may not be preferable mainly from the viewpoint of economy.

In the method for producing a (meth)acrylamide-based water-soluble polymer powder according to the present invention, the viscosity of the aqueous solution of the monomer mixture increases after the initiation of polymerization, and a gel-like substance is formed. Therefore, it becomes difficult to uniformly add the thiosulfate after the initiation of polymerization. Therefore, the thiosulfate is preferably mixed in advance with the aqueous solution of the monomer mixture. The thiosulfate is preferably added 24 hours to 1 hour before the initiation of polymerization.

In the production method of the present invention, other compounds having an effect of preventing dissolution may be added together with the above thiosulfate. Other compounds having an anti-dissolution effect are as described above. Moreover, these compounds are preferably mixed in advance with the aqueous solution of the monomer mixture. Addition is preferably from 24 hours to 1 hour before the start of polymerization.

Redox initiators consist of combinations of known oxidizing and reducing agents.

Oxidants include organic peroxides, persulfates and hydrogen peroxide. Organic peroxides include hydroperoxides and dihydroperoxides. Hydroperoxides include t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, and p-menthane hydroperoxide, and dihydroperoxides include 2,5- Dimethylhexane-2,5-dihydroperoxide is exemplified, and persulfates are exemplified by ammonium persulfate, sodium persulfate and potassium persulfate. These may be used in combination of two or more. The amount of the oxidizing agent added is preferably 0.1×10 ⁻⁴ to 50×10 ⁻⁴ mol %, more preferably 0.3 to 25×10 ⁻⁴ mol %, relative to the number of moles of the total monomers. is more preferable.

Examples of reducing agents include inorganic salts and amine compounds, and examples of inorganic salts include ferrous sulfate, ferrous sulfate, and sulfites. Examples of ferrous sulfates include ferrous ammonium sulfate, and examples of sulfites include sodium sulfite, sodium hydrogensulfite, and sodium disulfite. The amine compound includes tertiary amines, exemplified by trimethylamine. These may be used in combination of two or more. The amount of the reducing agent added is preferably 0.1×10 ⁻⁴ to 50×10 ⁻⁴ mol %, more preferably 0.3 to 25×10 ⁻⁴ mol %, relative to the number of moles of all monomers. is more preferable.

Polymerization may be performed by adding an azo initiator in addition to the redox initiator. If the azo initiator is added to the monomer mixture before polymerization, it will decompose due to the heat generated during polymerization, promote the polymerization of the water-soluble polymer, and have the effect of reducing residual monomers. Although the azo initiator is not particularly limited, it preferably has a 10-hour half-life temperature in the range of 30 to 100°C. Azo compounds within this range include water-soluble 2,2′-azobis(2-methylpropionamidine) dihydrochloride, 4,4′-azobiscyanovaleric acid, 2,2′-azobis[2-methyl-N- (2-hydroxyethyl)propionamide], 2,2′-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, oil-soluble 2,2′-azobis(2-methylbutyronitrile) ), dimethyl 2,2′-azobis(2-methylpropionate), and the like. The amount of addition of at least one of these azo compounds is preferably 0.02 to 0.2 mol % based on the number of moles of all monomers. Also, the azo initiator is preferably added to the monomer mixture in advance.

A redox initiator initiates the polymerization reaction. Although the effects of the present invention can be sufficiently obtained by heating during the polymerization reaction or removing the reaction heat generated during the polymerization reaction, the adiabatic aqueous solution is aqueous solution polymerization without intentional heating or heat removal. It is preferred to employ polymerization. In adiabatic aqueous solution polymerization, the reaction temperature rises as the polymerization starts, and when the polymerization is almost completed, the temperature rise stops and reaches the maximum temperature. In the present invention, it is preferable to set the maximum temperature to 50 to 100°C. Since this maximum temperature varies depending on the monomer concentration in the aqueous solution and the polymerization initiation temperature, the maximum temperature can be controlled by appropriately adjusting these.

The concentration of the monomer mixture in the aqueous solution is preferably 15-50 mass %, particularly preferably 20-35 mass %. The pH of the aqueous solution of the monomer mixture is preferably adjusted to 3-10. The polymerization initiation temperature is preferably -15 to 30°C, more preferably -10 to 15°C.

The aqueous solution containing the polymer thus obtained is a gel-like substance. Polymerization can be carried out batchwise in a suitable reaction vessel, or can be carried out continuously by continuously pouring onto a belt conveyor or the like.

A chain transfer agent may be used for the purpose of controlling the molecular weight. Its type is not particularly limited. Chain transfer agents that can be used in the present invention include alcohols such as methanol, ethanol, isopropyl alcohol, ethylene glycol and propylene glycol; amines such as methylamine and dimethylamine; thiols such as methanethiol and ethanethiol; Thiol compounds such as mercaptoethanol and mercaptopropionic acid lylsulfonate; reducing inorganic salts such as sodium sulfite, sodium hydrogensulfite and sodium hypophosphite; organic sulfonic acid compounds such as sodium methallylsulfonate. Among these, methanol, ethanol, isopropyl alcohol, sodium hypophosphite, methallyl, and the like are highly soluble in aqueous solutions of monomer mixtures, are highly effective even when added in small amounts, and can easily adjust the molecular weight. Sodium sulfonate is preferred.
These chain transfer agents may be used alone or in combination of two or more. Moreover, it is preferable to add these chain transfer agents to the monomer mixture in advance.

The amount of chain transfer agent added is not particularly limited. In the case of alcohols, the total mass of each monomer in the monomer mixture is preferably 0.01 to 10% by mass, and in the case of sodium hypophosphite and sodium methallylsulfonate, 5 × 10 ^{- 4} to 0.1% by mass is preferred.

In the present invention, in order to further reduce the insoluble matter, the heat treatment is preferably carried out without substantially changing the water content of the gel-like polymer obtained by aqueous polymerization. The heat treatment temperature is preferably 90 to 120°C, more preferably 91 to 100°C for economic reasons. Also, the heat treatment time is preferably 50 to 200 minutes. In the present invention, as a method of heat-treating without substantially changing the water content, a method of heating the gel-like polymer in a saturated steam atmosphere, or a method of sealing it in a water-impermeable resin material and placing it in a hot bath. and other methods are exemplified. The fact that the water content is not substantially varied means that the water content after the heat treatment is in the range of 90 to 120% by mass of the water content before the heat treatment. If it is less than 90% by mass, the water-insoluble content may increase, and if it is more than 120% by mass, handling of the gel polymer may be hindered.

The gel-like polymer that has undergone aqueous polymerization or the gel-like polymer that has undergone heat treatment is cut into small pieces by an appropriate method and then dried. The method of cutting may be a known method, such as cutting with a meat chopper. The drying method may be a known method, and hot air drying is preferable from the viewpoint of efficiency, and examples thereof include hot air drying using a ventilation dryer, a rotary dryer, a fluidized bed dryer, or the like. After drying, it may be pulverized by a known method.

The (meth)acrylamide-based water-soluble polymer powder obtained by the production method of the present invention is mainly used as a polymer flocculant. Specifically, in addition to sludge generated from sewage treatment, night soil treatment, domestic wastewater treatment, etc., sludge generated from various industrial wastewater treatment such as food factories, meat processing and chemical factories, and sludge generated from livestock such as pig farms It is added to various kinds of sludge such as night soil and sludge generated in wastewater treatment thereof, pulp or sludge generated in the paper industry to form flocs, and then dewatered. Examples of the dehydrator include, but are not limited to, a screw press dehydrator, a belt press dehydrator, a filter press dehydrator, a screw decanter, and a multi-disc dehydrator.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples. Methods for measuring various physical properties are as follows. The temperature condition in the measurement of various physical properties is 25° C. unless otherwise specified.

[Solid content]
The samples were dried at 105°C for 90 minutes. The solid content was calculated from the mass before and after drying.

[Standard viscosity]
A sample was dissolved in distilled water to prepare a 0.1% by mass solution in terms of solid content. This aqueous solution was thoroughly filtered using a 150-mesh stainless wire mesh, and sodium chloride was added to the filtrate to make it 1 mol % and dissolved to obtain a salt solution. The viscosity of this solution was measured with a TVB10M viscometer manufactured by Toki Sangyo Co., Ltd. using a TML adapter at a rotation speed of 60 rpm while being immersed in a constant temperature water bath at 25°C. A viscosity value that was stable for 1 minute or longer after 3 minutes from the start of measurement was taken as the standard viscosity. When the standard viscosity exceeded 10, the rotation speed was changed to 30 rpm and measured. It should be noted that the higher the standard viscosity, the larger the molecular weight.

[Water-insoluble content]
A sample was weighed and dissolved in distilled water to prepare 400 ml of a 0.1% by mass solution in terms of solid content. After the residue was washed with 200 ml of distilled water and dried together with the wire mesh at 105° C. for about 16 hours, the mass of the residue remaining on the wire mesh was measured. The insoluble content was defined as the ratio of the residue to the solid content of the sample. Samples that could not be dead end filtered are indicated as such.

[Example 1]
744.0 g of 50% by weight acrylamide aqueous solution, 300.0 g of 31% by weight sodium acrylate aqueous solution, and 376.0 g of deionized water were mixed. To this, a solution of 0.6581 g of 2,2'-azobis(2-methylbutyronitrile) (0.055 mol% relative to the total number of moles of monomers) dissolved in 12.75 g of methanol was added, 0.2418 g of sodium thiosulfate pentahydrate (157×10 ⁻⁴ mol % relative to the total number of moles of monomers) was added and dissolved. The solution pH was brought to 7.5 using sodium hydroxide solution. This monomer mixture was allowed to stand for 1 hour.
After cooling this monomer mixed solution, it was placed in a Dewar bottle, covered, and nitrogen was introduced at a rate of 2 L/min for sufficient deoxidation. When the temperature reached 2°C, 40 ml of an aqueous solution containing 2.343 mg of nitrogen-deoxygenated ammonium persulfate (1.65 × 10 ^-4 mol% relative to the total number of moles of monomers) and ferrous ammonium sulfate were added. 40 ml of an aqueous solution containing 3.66 mg (1.5×10 ⁻⁴ mol % with respect to the total number of moles of monomers) was taken into a syringe and simultaneously put into a Dewar bottle and stirred quickly to initiate the reaction. The monomer concentration at this stage was 31% by mass. A maximum temperature of 95° C. was reached in 60 minutes after the start of the reaction. After holding for an additional 180 minutes, the gel polymer was removed from the Dewar vessel. This was cut into granules of 2 to 3 mm by a meat chopper and dried for 90 minutes in a ventilation dryer at 95°C. This dried product was pulverized and used as a sample. The solids content of the sample was 93% by weight. The standard viscosity was 5.9 mPa·s, and the water-insoluble content was 3.01% by mass.

[Examples 2 to 5, 7 to 11, 13 to 17, Comparative Examples 1 to 4, 6]
A sample was prepared in the same manner as in Example 1, except that the composition and conditions were changed as shown in Table 1.
The results are shown in Table 1.

[Example 6]
594.0 g of a 50 mass % acrylamide aqueous solution, 493.6 g of a 31 mass % sodium acrylate aqueous solution, and 332.4 g of distilled water were mixed. To this, a solution of 0.6698 g of 2,2'-azobis(2-methylbutyronitrile) dissolved in 11.25 g of methanol was added, and 0.1931 g of sodium thiosulfate pentahydrate (total number of monomer moles 134×10 ⁻⁴ mol %) was added and dissolved. The pH was brought to 8.0 using sodium hydroxide solution. This monomer mixture was allowed to stand for 3 hours.
After cooling this monomer mixed solution, it was placed in a Dewar bottle, covered, and nitrogen was introduced at a rate of 2 L/min for sufficient deoxidation. When the temperature reached −1° C., 40 ml of an aqueous solution containing 1.192 mg of nitrogen-deoxygenated ammonium persulfate (0.9×10 ⁻⁴ mol % relative to the total number of moles of monomers) and ferrous sulfate 40 ml of an aqueous solution containing 2.049 mg of ammonium (0.9×10 ⁻⁴ mol % with respect to the total number of moles of the monomers) was put into a syringe and simultaneously put into a Dewar bottle and stirred quickly to initiate the reaction. The monomer concentration at this stage was 30% by mass. A maximum temperature of 84° C. was reached in 120 minutes after the start of the reaction. Furthermore, after continuing holding for 120 minutes, the gel polymer was taken out from the Dewar bottle. This was cut into pieces of about 10 cm diameter x 7 to 10 cm and closely packed in a polyethylene bag. After being put into a hot water bath at 95°C and heat-treated for 100 minutes, the meat was cut into granules of 2 to 3 mm with a meat chopper and dried for 90 minutes in a ventilation dryer with an internal temperature of 95°C. This dried product was pulverized and used as a sample. The solids content of the sample was 93% by weight. The standard viscosity was 7.2 mPa·s, and the water-insoluble content was 0.65% by mass.

[Example 12, Comparative Examples 5 and 7]
A sample was prepared in the same manner as in Example 6, except that the composition and conditions were changed as shown in Table 1.
The results are shown in Table 1.

The abbreviations in Table 1 represent the following.
Acrylamide: AMD
Sodium acrylate: SAA
Sodium 2-acrylamido-2-methylpropanesulfonate: AMPS-Na
Dimethylaminoethyl acrylate methyl chloride quaternary salt: DAC
Methyl chloride quaternary salt of dimethylaminoethyl methacrylate: DMC
Ammonium persulfate: APS
Ferrous ammonium sulfate: FAS
Peroxide A: 2,5-dimethylhexane-2,5-dihydroperoxide Peroxide B: 1,1,3,3-tetramethylbutyl hydroperoxide Peroxide C: t-butyl hydroperoxide azo A: 2,2'-azobis(2-methylbutyronitrile)
Azo B: 4,4′-azobiscyanovaleric acid 1,3-dione compound: 5,5-dimethyl-1,3-cyclohexanedione

Claims (15)

A polymer obtained by aqueous polymerization of a monomer mixture containing at least a (meth)acrylamide compound in the presence of a thiosulfate,
a polymer containing at least a monomer unit derived from a (meth)acrylamide-based compound;
the thiosulfate; and
A (meth) acrylamide-based water-soluble polymer powder containing
The content of the thiosulfate is 2 × 10 ^-3 mol% or more and 1 × 10 ^-1 mol% or less with respect to the total monomer units constituting the polymer (meth) Acrylamide water-soluble polymer powder. 2. The (meth)acrylamide water-soluble polymer powder according to claim 1, wherein said thiosulfate is sodium thiosulfate. The polymer is the (meth)acrylamide compound,
at least one selected from (meth)acrylic acid and its salts, 2-acrylamido-2-methylpropanesulfonic acid and its salts, dimethylaminoethyl (meth)acrylate and its quaternary salts;
The (meth)acrylamide water-soluble polymer powder according to claim 1 or 2, which is a copolymer of The (meth)acrylamide-based water-soluble polymer powder according to any one of claims 1 to 3, which contains a compound having a 1,3-dione structure in its molecule. The (meth)acrylamide-based water-soluble polymer powder according to any one of claims 1 to 4, comprising thiourea or formate. The (meth)acrylamide-based water-soluble polymer powder according to any one of claims 1 to 5, having a water-insoluble content of 10% by mass or less. A method for producing a (meth)acrylamide water-soluble polymer powder comprising: polymerizing an aqueous solution of a monomer mixture containing at least a (meth)acrylamide compound to obtain a polymer gel; and then drying and pulverizing the polymer gel. ,
the aqueous polymerization is carried out in the presence of thiosulfate using a redox initiator consisting of a combination of an oxidizing agent and a reducing agent;
The amount of the thiosulfate used is 2×10 ^-3 mol% or more and 5×10 ^-1 mol% or less with respect to the total monomer units constituting the (meth)acrylamide water-soluble polymer ,
The oxidizing agent is at least one selected from organic peroxides, persulfates and hydrogen peroxide,
The reducing agent is at least one selected from inorganic salts selected from ferrous sulfate, ferrous sulfate, and sulfites, and amine compounds. A method for producing coalesced powder. 8. The method for producing a (meth)acrylamide-based water-soluble polymer powder according to claim 7, wherein the thiosulfate is sodium thiosulfate. 9. The method for producing a (meth)acrylamide-based water-soluble polymer powder according to claim 7 or 8, wherein the amount of the thiosulfate added is more than 10 times the amount of the oxidizing agent added. The monomer mixture is the (meth)acrylamide compound,
at least one selected from (meth)acrylic acid and its salts, 2-acrylamido-2-methylpropanesulfonic acid and its salts, dimethylaminoethyl (meth)acrylate and its quaternary salts;
The method for producing a (meth)acrylamide-based water-soluble polymer powder according to any one of claims 7 to 9, comprising: The method for producing a (meth)acrylamide-based water-soluble polymer powder according to any one of claims 7 to 10, wherein the aqueous solution polymerization is adiabatic aqueous solution polymerization. 12. The method for producing a (meth)acrylamide-based water-soluble polymer powder according to any one of claims 7 to 11 , wherein the azo compound is added before starting the aqueous solution polymerization. 13. The method for producing a (meth)acrylamide water-soluble polymer powder according to any one of claims 7 to 12 , wherein a compound having a 1,3-dione structure in the molecule is added before starting the aqueous solution polymerization. 14. The method for producing a (meth)acrylamide-based water-soluble polymer powder according to any one of claims 7 to 13 , wherein thiourea or formate is added before starting the aqueous solution polymerization. The method for producing a (meth)acrylamide-based water-soluble polymer powder according to any one of claims 7 to 14 , further comprising a heat treatment step of heating at 90 to 120°C while maintaining the water content of the polymer gel. .