Carboxylic acid polymer

Abstract

To improve the storage stability of a carboxylic acid polymer.SOLUTION: A carboxylic acid polymer has a weight average molecular weight of 27000 or more and 1000000 or less and contains a constitutional unit derived from a chain transfer agent in the polymer. Relative to 100 mol% of total of all the monomer-derived constitutional units, a carboxylic acid monomer-derived constitutional unit is 85 mol% or more. The neutralization rate of carboxyl groups contained in the polymer is 30 mol% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carboxylic acid polymer, and more particularly to a carboxylic acid polymer useful for various industrial applications such as inorganic particle dispersants, water treatment agents, detergent additives, fiber treatment agents, and thickeners. [Background technology]

[0002] Carboxylic acid polymers are polymers having a carboxyl group or a salt thereof, and are widely used in various industrial applications, such as inorganic particle dispersants, water treatment agents, detergent additives, fiber treatment agents, thickeners, etc. From the viewpoint of handling, it is desirable that carboxylic acid copolymers have high storage stability over time. For example, Patent Document 1 discloses a method for producing a (meth)acrylic acid (salt) polymer by adding a polymerization initiator to an aqueous solution containing a (meth)acrylic acid (salt) monomer to polymerize the polymer, the method comprising: step (A) of gradually adding the entire amount of the aqueous solution containing the (meth)acrylic acid (salt) monomer and the polymerization initiator to a reactor to initiate polymerization; step (B) of subsequently continuing the polymerization while further adding the polymerization initiator; and step (C) of maturing the reaction solution after the addition of the polymerization initiator; in step (A), the time for dropping the aqueous solution containing the (meth)acrylic acid (salt) monomer and the polymerization initiator is 40 to 110 minutes, and the total time for steps (B) and (C) is 50 minutes or more, and the reaction mixture is aged. The method for producing a (meth)acrylic acid (salt) polymer having a degree of neutralization of 30 mol % or less and a weight-average molecular weight of 100,000 to 300,000 is disclosed, characterized in that step (C) is 30 minutes or more, and in step (A), the concentration of a (meth)acrylic acid (salt) monomer represented by the following formula in the reaction liquid is controlled to 10 to 60 mass % for polymerization, and the amount of polymerization initiator remaining in the resulting (meth)acrylic acid (salt) polymer is 10 mass ppm or less relative to the aqueous solution immediately after the preparation of the polymer, and it is disclosed that the (meth)acrylic acid (salt) polymer shows a weight-average molecular weight that does not fluctuate by 6% or less even two weeks after production, and that an increase in viscosity is also suppressed. For example, Patent Document 2 discloses a stable acid-form poly(meth)acrylate polymer and a method for producing the same. It discloses that the polymer has a molecular weight of about 1,000 g / mol to about 10,000 g / mol, and that the polymer is obtained by a production method in the presence of a polymerization initiator, a chain transfer agent, and optionally a polymerization stabilizer. It has been shown that the molecular weight of the polymer does not substantially increase after one month. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4067807 [Patent Document 2] Special Publication No. 2014-505753 Summary of the Invention [Problem to be solved by the invention]

[0004] Many (meth)acrylic acid (salt)-based polymers and methods for producing the same have been disclosed. However, when a (meth)acrylic acid (salt)-based polymer is handled as an acidic aqueous solution, there are problems that the molecular weight fluctuates during storage, and even when the molecular weight does not fluctuate, the viscosity fluctuates. The present invention has been made in view of the above-mentioned current situation, and has as its object to improve the storage stability of carboxylic acid polymers. [Means for solving the problem]

[0005] The present inventors have conducted various studies to achieve the above object and have arrived at the present invention. That is, the carboxylic acid polymer of the present disclosure has a weight-average molecular weight of 27,000 or more and 1,000,000 or less, contains structural units derived from a chain transfer agent in the polymer, contains structural units derived from carboxylic acid monomers at 85 mol % or more relative to a total of 100 mol % of structural units derived from all monomers, and has a neutralization rate of 30 mol % or less of carboxyl groups contained in the polymer. [Effects of the Invention]

[0006] The carboxylic acid polymer of the present disclosure can suppress fluctuations in molecular weight and viscosity after long-term storage, and therefore can be suitably used in various industrial applications such as inorganic particle dispersants, water treatment agents, detergent additives, fiber treatment agents, and thickeners. DETAILED DESCRIPTION OF THE INVENTION

[0007] The present invention will be described in detail below. In addition, a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[0008] [Carboxylic Acid Polymer of the Present Disclosure] The carboxylic acid polymer of the present disclosure has a weight-average molecular weight of 27,000 to 1,000,000, contains structural units derived from a chain transfer agent, and the structural units derived from carboxylic acid monomers account for 85 mol % or more relative to 100 mol % in total of structural units derived from all monomers, and has a neutralization rate of 30 mol % or less of carboxyl groups contained in the polymer. The polymer is also referred to as the "polymer of the present disclosure."

[0009] <Carboxylic Acid Polymer> In the present disclosure, a carboxylic acid polymer refers to a polymer containing a carboxyl group. The carboxylic acid polymer is a polymer having structural units derived from an unsaturated carboxylic acid monomer. The unsaturated carboxylic acid monomer is not particularly limited as long as it has an ethylenically unsaturated group and a carboxyl group, and examples thereof include an unsaturated monocarboxylic acid monomer and an unsaturated dicarboxylic acid monomer. The unsaturated monocarboxylic acid monomer may be any monomer having one group capable of forming a carbanion together with an ethylenically unsaturated group in the molecule, and examples thereof include (meth)acrylic acid, crotonic acid, isocrotonic acid, tiglic acid, 3-methylcrotonic acid, 2-methyl-2-pentenoic acid, α-hydroxyacrylic acid, etc.; monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts thereof; half esters of the following unsaturated dicarboxylic acid monomers and alcohols having 1 to 22 carbon atoms or glycols having 2 to 4 carbon atoms; and half amides of unsaturated dicarboxylic acid monomers and amines having 1 to 22 carbon atoms. The unsaturated dicarboxylic acid monomer may be any monomer having an ethylenically unsaturated group and two groups capable of forming a carbanion in the molecule, and examples thereof include maleic acid, itaconic acid, mesaconic acid, citraconic acid, fumaric acid, etc., their monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts, and their anhydrides. The unsaturated carboxylic acid monomer is preferably (meth)acrylic acid (salt), maleic acid (salt), or maleic anhydride. The technical significance of the present invention is more effectively achieved with a carboxylic acid polymer having structural units derived from these monomers. More preferably, it is (meth)acrylic acid (salt), and particularly preferably, it is acrylic acid (salt).

[0010] In the present disclosure, a structural unit derived from an unsaturated carboxylic acid monomer refers to a structural unit in which a carbon-carbon double bond of an ethylenically unsaturated group of an unsaturated carboxylic acid monomer is replaced with a carbon-carbon single bond. For example, in the case of acrylic acid, CH═CH(COOH), the structural unit derived from acrylic acid can be represented by -CH-CH(COOH)-. A structural unit derived from (meth)acrylic acid (salt) can be formed, for example, by radical polymerization of (meth)acrylic acid (salt). Note that the structural unit derived from an unsaturated carboxylic acid monomer is not limited to a structural unit formed by polymerizing an unsaturated carboxylic acid monomer, as long as it has the same structure as the structure in which a carbon-carbon double bond of an unsaturated carboxylic acid monomer is replaced with a carbon-carbon single bond, and may be a structural unit formed, for example, by a reaction other than polymerization. The content of structural units derived from carboxylic acid monomers in the polymer of the present disclosure is 85 mol% or more, relative to 100 mol% of structural units derived from all monomers (unsaturated carboxylic acid monomers and other monomers) constituting the polymer of the present disclosure. The content of the structural units is preferably 90 mol% or more, more preferably 92 mol% or more, even more preferably 95 mol% or more, and most preferably 100 mol%. One of the causes of viscosity fluctuation without molecular weight fluctuation is thought to be intermolecular interactions derived from carboxyl groups in the polymer, and therefore the technical significance of the present invention is more effectively achieved within the above range.

[0011] <Structural units derived from chain transfer agents> In the present disclosure, the structural unit derived from a chain transfer agent refers to a structural unit derived from a chain transfer agent used in polymerization. The weight-average molecular weight of the carboxylic acid polymer of the present disclosure can be adjusted to 27,000 or more and 1,000,000 or less by increasing or decreasing the amount of polymerization initiator. Furthermore, adjusting the molecular weight using a chain transfer agent can reduce the amount of polymerization initiator used, which can cause side reactions, and therefore the storage stability of the molecular weight of the polymer of the present disclosure tends to be improved. On the other hand, the storage stability of the viscosity of the polymer of the present disclosure tends to be reduced. This is presumably due to the interaction between the structural units derived from the chain transfer agent in the polymer and the carboxyl groups. The chain transfer agent is not particularly limited, but is preferably one having a phosphorus atom or a sulfur atom. When a chain transfer agent having a phosphorus atom or a sulfur atom is used, the interaction between the structural units derived from the chain transfer agent in the polymer and the carboxyl groups is strengthened, and the technical significance of the present invention is more effectively realized. More preferred chain transfer agents having a phosphorus atom or a sulfur atom are those having a phosphorus atom or a sulfur atom and an oxygen atom, such as phosphorous acid, hypophosphorous acid, sulfurous acid, hydrogen sulfite, dithionous acid, metabisulfite, and salts thereof, still more preferred are phosphorous acid, hypophosphorous acid, hydrogen sulfite, and salts thereof, particularly preferred are phosphorous acid, hypophosphorous acid, and salts thereof, and most preferred is hypophosphorous acid (salt).

[0012] The content of the structure derived from the chain transfer agent in the polycarboxylic acid polymer is preferably 0.01 mol% or more and 1.8 mol% or less, based on 100 mol% of structural units derived from all monomers. It is more preferably 0.05 mol% or more, even more preferably 0.1 mol% or more, particularly preferably 0.15 mol% or more, and most preferably 0.2 mol% or more. It is also more preferably 1.6 mol% or less, even more preferably 1.4 mol% or less, particularly preferably 1.2 mol% or less, and most preferably 0.8 mol% or less. When the chain transfer agent is within the above range, it is possible to optimize the amount of polymerization initiator, and by suppressing the interaction between the structure derived from the chain transfer agent and the carboxyl groups in the polymer, the storage stability of the carboxylic acid polymer tends to be improved.

[0013] <base> In the present disclosure, the term "base" refers to a compound that neutralizes the carboxyl groups of the carboxylic acid polymer. Examples include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide, alkali metal carbonates such as sodium bicarbonate and sodium carbonate, alkanolamines such as monoethanolamine and diethanolamine, ammonia, monomethylamine, dimethylamine, trimethylamine, n-butylamine, triethylamine, tributylamine, and cyclohexylamine. Among these, alkali metal hydroxides are preferred due to their ease of availability, with sodium hydroxide being particularly preferred. The neutralization rate achieved by the base can be calculated, for example, by conventional acid-base titration. In the polymer of the present disclosure, the neutralization rate of the carboxyl groups is preferably 30 mol% or less. More preferably, it is 15 mol% or less, even more preferably 10 mol% or less, particularly preferably 5 mol% or less, and most preferably 3 mol% or less. Within the above ranges, the technical significance of the present invention is more effectively realized.

[0014] <Structural units derived from other monomers> The polymer of the present disclosure may, if desired, have structural units derived from monomers other than structural units derived from carboxylic acid monomers (also referred to as structural units derived from other monomers). In the present disclosure, the structural unit derived from another monomer refers to a structural unit in which at least one carbon-carbon double bond of the other monomer is replaced with a carbon-carbon single bond. Note that the structural unit derived from the other monomer may have the same structure as the structure in which at least one carbon-carbon double bond of the other monomer is replaced with a carbon-carbon single bond, and is not limited to a structural unit formed by polymerizing the other monomer, and may be, for example, a structural unit formed by a reaction other than polymerization. The content of structural units derived from other monomers in the polymer of the present disclosure is 0 mol% or more and 15 mol% or less, preferably 0 mol% or more and 10 mol% or less, more preferably 0 mol% or more and 8 mol% or less, even more preferably 0 mol% or more and 5 mol% or less, and most preferably 0 mol%, relative to 100 mol% of structural units derived from all monomers constituting the polymer of the present disclosure. Within the above range, the technical significance of the present invention can be more effectively exhibited.

[0015] Examples of the other monomers include unsaturated alcohols such as (meth)allyl alcohol and isoprenol, and monomers obtained by adding alkylene oxides to these; polyalkylene glycol chain-containing monomers such as (meth)acrylic acid esters of alkoxyalkylene glycols; vinyl aromatic monomers having heterocyclic aromatic hydrocarbon groups such as vinylpyridine and vinylimidazole; amino group-containing monomers such as dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and dimethylaminopropyl acrylate; dialkylaminoalkyl (meth)acrylamides such as dimethylaminoethyl acrylamide, dimethylaminoethyl methacrylamide, and dimethylaminopropyl acrylamide; and allylamines such as diallyl alkylamines such as diallyl amine and diallyl dimethyl amine; and quaternized products thereof; N-vinyl N-vinyl monomers such as diethylpyrrolidone, N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylformamide, N-vinyl-N-methylacetamide, and N-vinyloxazolidone; amide monomers such as (meth)acrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, and t-butylacrylamide; hydroxyl group-containing monomers such as (meth)allyl alcohol and isoprenol; (meth)acrylic acid alkyl ester monomers such as butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and dodecyl (meth)acrylate; (meth)acrylic acid hydroxyalkyl monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyhexyl (meth)acrylate;Examples of suitable monomers include 3-(meth)allyloxy-2-hydroxypropanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-((meth)acryloyloxy)ethanesulfonic acid, p-styrenesulfonic acid, α-methyl-p-styrenesulfonic acid, vinylsulfonic acid, (meth)allyl sulfonic acid, isoprene sulfonic acid, 1-methyl-2-propene-1-sulfonic acid, 1,1-dimethyl-2-propene-1-sulfonic acid, 3-butene-1-sulfonic acid, and 1-butene-3-sulfonic acid, as well as their salts; vinylphosphonic acid, (meth)allylphosphonic acid, and other monomers containing a phosphonic acid group; vinylaryl monomers such as styrene, indene, and vinylaniline; isobutylene; and vinyl acetate. The polymers of the present disclosure may contain one or more structural units derived from other monomers, if necessary.

[0016] <Physical Properties of the Polymer of the Present Disclosure> The polymer of the present disclosure preferably has a weight average molecular weight (Mw) of 27,000 or more and 1,000,000 or less. It is more preferably 29,000 or more, even more preferably 35,000 or more, particularly preferably 40,000 or more, and most preferably 45,000 or more. It is also more preferably 500,000 or less, even more preferably 300,000 or less, particularly preferably 200,000 or less, and most preferably 150,000 or less. When the Mw is within the above range, the storage stability of the polymer of the present disclosure tends to be improved. For example, when the molecular weight of the polymer is 27,000 or less, the carboxylic acid polymer of the present disclosure having a neutralization rate of 30 mol % or less has a large proportion of the structure derived from the chain transfer agent and the carboxyl group, and the interaction between these is strong, which may cause cloudiness and thickening.

[0017] An embodiment in which the polymer of the present disclosure contains a solvent is one of the preferred embodiments of the present disclosure. The solvent is not particularly limited, but in view of the main uses of the polymer of the present disclosure, the solvent is preferably water-soluble, and various types of water and water-soluble organic solvents can be used. In particular, water, water-soluble alcohols, and mixtures thereof are preferred, and water is more preferred.

[0018] The polymer of the present disclosure may be stored for long periods of time for commercial use. Storage conditions vary, but the material of the storage container is not particularly limited, and commonly used containers can be used. Examples include resin containers such as polyethylene, metal containers such as stainless steel, and glass containers. The storage temperature can be set appropriately. The storage atmosphere may be either an air atmosphere or an inert gas atmosphere. When the polymer of the present disclosure is stored at 2°C for 45 days, the rate of change in molecular weight is preferably 10% or less. When the polymer of the present disclosure is stored at 50°C for 45 days, the rate of change in molecular weight is preferably 10% or less. When the polymer of the present disclosure is stored in the above-mentioned range, the polymer after storage can be used for various applications without any problems. Furthermore, when the polymer of the present disclosure is stored at 2°C for 45 days, the rate of change in viscosity is preferably 25% or less. It is more preferably 20% or less, even more preferably 15% or less, and particularly preferably 10% or less. When the polymer of the present disclosure is stored at 50°C for 45 days, the rate of change in viscosity is preferably 10% or less. When the polymer of the present disclosure is stored in the above-mentioned range, the polymer after storage can be easily removed from the storage container or transferred using a pump. The viscosity change when stored at 50°C is presumed to be mainly caused by an irreversible side reaction derived from the remaining initiator, while the viscosity change when stored at 2°C is presumed to be mainly caused by a reversible interaction between the structure derived from the chain transfer agent and the carboxyl group in the polymer. Because the viscosity change when stored at 2°C is presumed to be reversible, a larger rate of viscosity change compared to when stored at 50°C is acceptable.

[0019] [Carboxylic Acid Polymer Composition of the Present Disclosure] The carboxylic acid polymer composition of the present disclosure contains the polymer of the present disclosure. The carboxylic acid polymer composition of the present disclosure contains the polymer of the present disclosure in an amount of, for example, 0.01% by mass or more and 100% by mass or less. The carboxylic acid polymer composition of the present disclosure may contain optional components such as a solvent such as water, unreacted residual monomers, a polymerization initiator, a chain transfer agent, a preservative, and an antifoaming agent. When the carboxylic acid polymer composition of the present disclosure contains water, the water content is preferably, for example, 40% by mass or more and 99% by mass or less. More preferably, it is 45% by mass or more, even more preferably 50% by mass or more, particularly preferably 53% by mass or more, and most preferably 55% by mass or more. Furthermore, it is more preferably 90% by mass or less, even more preferably 85% by mass or less, particularly preferably 80% by mass or less, and most preferably 75% by mass or less. When the carboxylic acid polymer composition of the present disclosure contains water, it may be referred to as the aqueous solution of the present disclosure. When the carboxylic acid polymer composition of the present disclosure contains water, the pH is preferably, for example, 1.0 or more and 4.5 or less. The polymer of the present disclosure contains, for example, 100 ppm or more and 2000 ppm or less of free acrylic acid. The polymer of the present disclosure has excellent storage stability regardless of the amount of free acrylic acid contained.

[0020] [Method for producing polymer of the present disclosure] The method for producing the polymer of the present disclosure is not particularly limited, but it is usually preferable to produce it by polymerizing a carboxylic acid monomer and, if necessary, other monomers. For example, there is a polymerization method including: step (A) of charging a reactor with a solvent and part of the raw materials and raising the temperature to 60°C or higher; step (B) of gradually and separately adding the carboxylic acid monomer, a polymerization initiator, a chain transfer agent, and a solvent while maintaining the temperature of (A) to initiate and advance the polymerization; and step (C) of maintaining a high temperature after the addition of the carboxylic acid monomer to reduce unreacted raw materials.

[0021] For example, in step (A), the reaction vessel may be any vessel equipped with a reflux condenser and a stirrer, and the solvent to be used can be charged therein. The solvent can be used without particular limitations, but it is best to select it according to the intended use of the polymer to be produced. For example, carboxylic acid polymers are water-soluble, and in view of the main intended use, the solvent is preferably water-soluble, and various water-soluble organic solvents can be used. In particular, water, water-soluble alcohols, and mixtures thereof are preferred, with water being even more preferred. Step (A) is preferably carried out at 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher.

[0022] For example, in step (B), the carboxylic acid monomer and / or a solution of the carboxylic acid monomer (hereinafter also referred to as the carboxylic acid monomer), a solution containing a polymerization initiator (hereinafter also referred to as the polymerization initiator), a solution containing a chain transfer agent (hereinafter also referred to as the chain transfer agent), and a solvent can be added all at once, or a portion or all of the amounts used can be added dropwise. It is preferable to include a step of adding dropwise each of the polymerization initiator, the chain transfer agent, and the carboxylic acid monomer. When polymerizing by dropping, the dropping rates of the carboxylic acid monomer, the polymerization initiator, the chain transfer agent, and the solvent can be set appropriately and may be changed or constant over the dropping time. When the dropping rate is changed, multi-stage dropping in which the rate is changed stepwise may be used. The dropping may be performed using separate pumps or by mixing them as appropriate. However, it is preferable to add the droppings using separate pumps because this facilitates molecular weight control and reduction of residual monomers.

[0023] The amount of the total chain transfer agent used in the polymerization process is preferably 50 mol% or more relative to 100 mol% of the total amount of polymerization initiators used in the polymerization process. It is more preferably 60 mol% or more, even more preferably 70 mol% or more, particularly preferably 85 mol% or more, and most preferably 100 mol% or more. It is also preferably 750 mol% or less, more preferably 600 mol% or less, even more preferably 500 mol% or less, particularly preferably 450 mol% or less, and most preferably 400 mol% or less. By keeping it within the above range, the storage stability of the polymer of the present disclosure tends to be improved. The amount of the total chain transfer agent used in the polymerization process is preferably 0.01 mol% or more and 1.8 mol% or less relative to 100 mol% of the structural units derived from all monomers. It is more preferably 0.05 mol% or more, even more preferably 0.1 mol% or more, particularly preferably 0.15 mol% or more, and most preferably 0.2 mol% or more. Furthermore, it is more preferably 1.6 mol% or less, even more preferably 1.4 mol% or less, particularly preferably 1.2 mol% or less, and most preferably 0.8 mol% or less. By being in the above range, the storage stability of the polymer of the present disclosure tends to be improved. The total dropwise addition time of the solution containing the chain transfer agent is preferably 75% or more, more preferably 80% or more, and even more preferably 90% or more of the total dropwise addition time of the carboxylic acid monomer. This tends to improve the storage stability of the polymer of the present disclosure.

[0024] It is preferable to add the chain transfer agent dropwise in multiple stages. Adding the agent dropwise in multiple stages makes it easier to control the molecular weight. It is preferable to adjust the dropping rate so that the dropping rate in the second stage and thereafter is slower than the dropping rate in the first stage. When adding the chain transfer agent dropwise in multiple stages, it is preferable that the dropping time of the chain transfer agent in the first stage be 0.10 to 0.50 times the total dropping time of the chain transfer agent. The dropwise addition of the polymerization initiator is preferably started simultaneously with the dropwise addition of the carboxylic acid monomer and / or carboxylic acid monomer solution and the chain transfer agent, and is continued for a certain period of time after the dropwise addition of the carboxylic acid monomer and / or carboxylic acid monomer solution and the chain transfer agent has been completed. This allows the amount of remaining monomer to be reduced. The polymerization initiator is preferably added dropwise at a constant rate. By adding dropwise at a constant rate, the amount of remaining monomer can be reduced. The total dropwise addition time of the chain transfer agent is preferably 60% or more of the total dropwise addition time of the polymerization initiator, more preferably 70% or more, even more preferably 80% or more, and most preferably 90% or more. This tends to improve the storage stability of the polymer of the present disclosure.

[0025] The polymerization initiator used is not particularly limited, but examples include hydrogen peroxide; persulfates such as sodium persulfate, ammonium persulfate, and potassium persulfate; organic peroxides such as benzoyl peroxide, lauroyl peroxide, peracetic acid, persuccinic acid, di-t-butyl peroxide, t-butyl hydroperoxide, and cumene hydroperoxide; and azo compounds such as 2,2'-azobis(2-aminodipropane) dihydrochloride, 4,4'-azobis(4-cyanovaleric acid), and azobisisobutylnitrile 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Among these polymerization initiators, hydrogen peroxide, persulfates, and organic peroxides are preferred. In this case, the technical significance of the present invention is more effectively realized. Hydrogen peroxide and persulfates are more preferred as polymerization initiators, and persulfates are even more preferred. These polymerization initiators may be used alone or in combination. Alternatively, a redox initiator, such as a persulfate and a metal salt, which generates radicals by combining an oxidizing agent and a reducing agent, may be used as the polymerization initiator. The metal of the metal salt is not particularly limited, but examples include iron. The concentration of the polymerization initiator during dropwise addition is not particularly limited. However, when a persulfate is used as the initiator, it is preferably a 3 to 50% by mass solution, more preferably a 5 to 40% by mass solution, and even more preferably a 10 to 30% by mass solution. While the solvent can be used without particular limitations, it is best to select it depending on the intended use of the resulting polymer. Carboxylic acid polymers are water-soluble, and considering the main intended use, a water-soluble solvent is preferred. Various water-soluble organic solvents can be used. Water, water-soluble alcohols, and mixtures thereof are particularly preferred, with water being even more preferred.

[0026] The total amount of the polymerization initiator used is preferably 0.05 mol% or more and 2 mol% or less, based on 100 mol% of the structural units derived from all monomers. If the total amount of the polymerization initiator used is less than 0.05 mol% based on 100 mol% of the structural units derived from all monomers, the amount of residual monomers may increase. Furthermore, if the total amount of the polymerization initiator used is 2 mol% or more based on 100 mol% of the structural units derived from all monomers, the storage stability of the polymer of the present disclosure tends to decrease. Such an amount is more preferably 0.1 mol% or more, even more preferably 0.12 mol% or more, and most preferably 0.15 mol% or more. Furthermore, it is more preferably 1 mol% or less, even more preferably 0.6 mol% or less, and most preferably 0.4 mol% or less. The polymerization temperature is preferably equal to or higher than the half-life temperature of the polymerization initiator used, and is usually preferably 60° C. or higher and 105° C. or lower. Within this temperature range, polymerization proceeds efficiently.

[0027] For example, step (C) is an aging step, which is preferably carried out at the polymerization temperature or a temperature higher than the polymerization temperature for a certain period of time or more. The aging step is usually preferably carried out at a temperature of 60°C or higher and 105°C or lower.

[0028] One embodiment of the presently disclosed invention is a method for producing a carboxylic acid polymer, the method comprising: adding dropwise a polymerization initiator, a chain transfer agent, and at least a portion of a carboxylic acid monomer; the dropwise addition time of the chain transfer agent is 60% or more of the dropwise addition time of the polymerization initiator; and the total amount of chain transfer agent used is 50 mol% to 750 mol% relative to 100 mol% of the total amount of polymerization initiator used; the method for producing a carboxylic acid polymer obtained has a weight-average molecular weight of 27,000 to 1,000,000; the polymer contains structural units derived from the chain transfer agent; the structural units derived from the carboxylic acid monomer account for 85 mol% or more relative to 100 mol% of the total structural units derived from all monomers; and the neutralization rate of the carboxyl groups contained in the polymer is 30 mol% or less.

[0029] The method for producing a carboxylic acid polymer according to claim 5, in which the total amount of the chain transfer agent used is 0.01 mol % or more and 1.8 mol % or less, relative to 100 mol % of structural units derived from all monomers, is also one embodiment of the presently disclosed invention.

[0030] [Uses of the polymer of the present disclosure] The polymers of the present disclosure can be used as coagulants, flocculants, printing inks, adhesives, soil conditioners (modifiers), flame retardants, skin care agents, hair care agents, additives for shampoos, hair sprays, soaps, and cosmetics, anion exchange resins, dye mordants and auxiliaries for fibers and photographic films, pigment spreaders in papermaking, paper strength agents, emulsifiers, preservatives, softeners for textiles and paper, additives for lubricating oils, water treatment agents, fiber treatment agents, dispersants, detergent additives, scale inhibitors (scale inhibitors), metal ion sequestering agents, thickeners, various binders, emulsifiers, hydrophilizing agents, and the like. [Example]

[0031] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

[0032] <Measurement conditions for weight average molecular weight (10,000 or less) (GPC)> Equipment: Tosoh Corporation HLC-8320GPC Detector: RI Column: Tosoh TSK-GEL G3000PWXL (two connected in series) Column temperature: 40℃ Flow rate: 0.5mL / min. Sample solution injection volume: 10 μL (sample concentration: 0.5% by mass) Calibration curve: Created using a cubic equation based on Mp and elution time using polyacrylic acid standards (Mp = 900, 1250, 1770, 2925, 4100, 7500, 16000, 28000, 47500) manufactured by American Polymer Standards Corporation and sodium acetate (Mp = 94). Eluent: A mixture of sodium dihydrogen phosphate dodecahydrate / disodium hydrogen phosphate dihydrate (34.5 g / 46.2 g) diluted to 5000 g with purified water.

[0033] <Measurement conditions for weight average molecular weight (10,000 or more) (GPC)> Equipment: Tosoh Corporation HLC-8320GPC Detector: RI Column: Tosoh TSKgel GMPWXL (two columns connected in series) Column temperature: 40℃ Flow rate: 1mL / min Sample solution injection volume: 20 μL (sample concentration: 0.5% by mass) Calibration curve: Created using polyacrylic acid standards (Mp = 1250, 28000, 47500, 193800, 392600, 589700, 1102000) manufactured by American Polymer Standards Corporation, using a cubic equation based on Mp and elution time. Eluent: (60.84 mM sodium carbonate aqueous solution + 60.84 mM sodium bicarbonate aqueous solution) / acetonitrile = 83.74 / 16.26 (weight ratio)

[0034] <Method for measuring the solid content of polymer aqueous solution> 1 g of the polymer aqueous solution was weighed into an aluminum dish, diluted with approximately 1 g of deionized water, and spread evenly. This was dried in an oven at 150°C for 60 minutes, allowed to cool in a desiccator, and then weighed after drying. The solid content (non-volatile content) concentration was calculated from the difference in mass before and after drying using the following formula. Unless otherwise specified, the solid content measured using the above procedure was used as the concentration of the polymer aqueous solution. Solid content (%) = [evaporation residue after drying (g) / mass of polymer aqueous solution before drying (g)] × 100

[0035] <Conditions for measuring viscosity of polymer aqueous solution> Measuring device: B type viscometer Temperature of the aqueous solution during viscosity measurement: 25°C

[0036] <Analysis of phosphorus-containing groups> 31 The phosphorus atoms introduced into the polymer and the phosphorus atoms present in the form of inorganic phosphorus salts without being introduced into the polymer were analyzed by P-NMR analysis.

[0037] <Quantitative conditions for monomers contained in polymer aqueous solution (liquid chromatography)> Equipment: Waters Alliance (2695) Detector: UV (wavelength: 200 nm) (Waters 2489) Column: Shodex RSpak DE-413L Column temperature: 40℃ Flow rate: 1mL / min Eluent: 0.1% by weight phosphoric acid aqueous solution

[0038] <Conditions for determining the amount of sodium bisulfite in an aqueous solution (ion chromatography)> Equipment: Tosoh Corporation IC-2010 Detector: Conductivity detector Column: Shodex IC SI-90 4E, Shodex IC SI-90G Column temperature: 25℃ Preparation: Sodium sulfite Eluent: 1 mM sodium carbonate + 4 mM sodium bicarbonate + 5% acetone solution

[0039] <Production Example 1> A 2.5 L stainless steel reaction vessel equipped with a reflux condenser and a stirrer was charged with 422.5 g of deionized water, and the temperature was raised to the boiling point while stirring. Next, 632.8 g (i.e., 7.03 mol) of 80 wt% aqueous acrylic acid (hereafter referred to as "80% AA") was added dropwise to the boiling polymerization system under stirring over 120 min. 31.3 g (i.e., 0.0197 mol) of 15 wt% aqueous sodium persulfate (hereafter referred to as "15% NaPS") was added over 130 min. 2.5 g (i.e., 0.0106 mol) of 45 wt% aqueous sodium hypophosphite monohydrate (hereafter referred to as "45% SHP") was added over 15 min, followed by 8.7 g (i.e., 0.0369 mol) of 45 wt% aqueous sodium hypophosphite monohydrate (hereafter referred to as "45% SHP") over 105 min. 10.8 g of deionized water was added over 15 min, followed by 37.9 g of deionized water over 105 min. The addition of 80% AA and 15% NaPS was carried out continuously at a constant rate. After the dropwise addition of AA was completed, the reaction solution was maintained at the boiling point (aged) for an additional 90 minutes to complete the polymerization. After the polymerization was completed, 53.3 g of deionized water was added dropwise to the reaction solution with stirring to obtain an aqueous polymer solution (1) of the present disclosure. The weight-average molecular weight (Mw) of the aqueous solution was 47,000, the solids content was 43.6%, the viscosity was 1250 mPa·s, and the acrylic acid concentration in the aqueous solution was 400 ppm. Phosphorus atom analysis revealed that the ratio of phosphorus atoms introduced into the polymer chain, phosphorus atoms introduced at the polymer terminal, and phosphorus atoms not introduced into the polymer but present in the form of inorganic phosphorus salt was 61:16:23. Therefore, the content of structures derived from the chain transfer agent relative to 100 mol % of structural units derived from all monomers in the polymer was 0.52 mol %.

[0040] <Production Example 2> A 10 L stainless steel reactor equipped with a reflux condenser and agitator was charged with 3353.3 g of deionized water and heated to the boiling point with stirring. Next, with stirring, 5019.4 g (i.e., 55.8 mol) of 80% AA was added dropwise from the nozzle tip through separate feed paths to the polymerization system at the boiling point. The mixture was then added dropwise in two stages: 120 min, 248.5 g (i.e., 0.157 mol) of 15% NaPS, 130 min, and 9.8 g (i.e., 0.0416 mol) of 45% SHP over 15 min, followed by 34.4 g (i.e., 0.146 mol) over 105 min. The mixture was then added dropwise through separate feed paths. The 80% AA and 15% NaPS were added continuously at a constant rate. After the dropwise addition of AA was completed, the reaction solution was maintained at the boiling point (aged) for an additional 105 minutes to complete the polymerization. After the polymerization was completed, 1667.2 g of deionized water was added dropwise to the reaction solution with stirring to obtain an aqueous polymer solution (2) of the present disclosure. The weight-average molecular weight (Mw) of the aqueous solution was 90,000, the solids content was 38.5%, the viscosity was 1250 mPa·s, and the acrylic acid concentration in the aqueous solution was 630 ppm. Analysis of phosphorus atoms revealed that the ratio of phosphorus atoms introduced into the polymer chain, phosphorus atoms introduced at the polymer terminal, and phosphorus atoms not introduced into the polymer but present in the form of inorganic phosphorus salt was 49:16:35. Therefore, the content of structures derived from the chain transfer agent relative to 100 mol % of structural units derived from all monomers in the polymer was 0.22 mol %.

[0041] <Production Example 3> A 5 L stainless steel reactor equipped with a reflux condenser and agitator was charged with 833.9 g of deionized water and heated to the boiling point with stirring. Next, with stirring, 1233.0 g (i.e., 13.7 mol) of 80% AA was added dropwise from the nozzle tip through separate feed paths to the polymerization system at the boiling point. The following two feed rates were added: 1233.0 g (i.e., 13.7 mol) of 80% AA over 120 min, 46.3 g (i.e., 0.0292 mol) of 15% NaPS over 130 min, and 1.7 g (i.e., 0.00722 mol) of 45% SHP over 15 min, followed by 5.5 g (i.e., 0.0234 mol) over 105 min. The following two feed rates were added: 52.8 g of deionized water over 15 min, followed by 171.7 g over 105 min. The 80% AA and 15% NaPS were added continuously at a constant rate. After the dropwise addition of AA was completed, the reaction solution was maintained at the boiling point (aged) for an additional 105 minutes to complete the polymerization. After the polymerization was completed, 675.1 g of deionized water was added dropwise to the reaction solution with stirring to obtain an aqueous polymer solution (3) of the present disclosure. The weight-average molecular weight (Mw) of the aqueous solution was 140,000, the solids content was 33.4%, the viscosity was 1100 mPa·s, and the acrylic acid concentration in the aqueous solution was 900 ppm. Phosphorus atom analysis revealed that the ratio of phosphorus atoms introduced into the polymer chain, phosphorus atoms introduced at the polymer terminal, and phosphorus atoms not introduced into the polymer but present in the form of inorganic phosphorus salt was 42:17:41. Therefore, the content of structures derived from the chain transfer agent relative to 100 mol % of structural units derived from all monomers in the polymer was 0.13 mol %.

[0042] <Production Example 4> A 5 L stainless steel reactor equipped with a reflux condenser and agitator was charged with 1439.6 g of deionized water and heated to the boiling point with stirring. Next, with stirring, 2128.5 g (i.e., 23.7 mol) of 80% AA was added dropwise from the nozzle tip to the polymerization system at the boiling point. The polymerization system was then added dropwise through separate feed paths in two stages: 2128.5 g (i.e., 23.7 mol) of 80% AA over 120 min, 79.9 g (i.e., 0.0503 mol) of 15% NaPS over 130 min, and 2.9 g (i.e., 0.0123 mol) of 45% SHP over 15 min, followed by 9.5 g (i.e., 0.0403 mol) over 105 min. The two stages were 69.3 g of deionized water over 15 min, followed by 225.2 g over 105 min. The 80% AA and 15% NaPS were added continuously at a constant rate. After the dropwise addition of AA was completed, the reaction solution was maintained at the boiling point (aged) for an additional 30 minutes to complete the polymerization. After the polymerization was completed, 1258.3 g of deionized water was added dropwise to the reaction solution with stirring to obtain an aqueous polymer solution (4) of the present disclosure. The weight-average molecular weight (Mw) of the aqueous solution was 140,000, the solids content was 33.4%, the viscosity was 1100 mPa·s, and the acrylic acid concentration in the aqueous solution was 1300 ppm. Phosphorus atom analysis revealed that the ratio of phosphorus atoms introduced into the polymer chain, phosphorus atoms introduced at the polymer terminal, and phosphorus atoms not introduced into the polymer but present in the form of inorganic phosphorus salt was 42:17:41. Therefore, the content of structures derived from the chain transfer agent relative to 100 mol % of structural units derived from all monomers in the polymer was 0.13 mol %.

[0043] <Production Example 5> Aqueous polymer solution (2) of the present disclosure obtained in Production Example 2 was mixed with 489.4 g of 48 wt % aqueous sodium hydroxide solution (hereinafter referred to as "48% NaOH") and 10.6 g (i.e., 0.127 mol, 5 mol % relative to the carboxyl groups in aqueous solution (B)) to obtain aqueous polymer solution (5) of the present disclosure. The aqueous solution had a weight-average molecular weight (Mw) of 90,000, a solids content of 38.4%, a viscosity of 1650 mPa s, and an acrylic acid concentration of 620 ppm.

[0044] <Production Example 6> 751.1 g of the aqueous polymer solution (2) of the present disclosure obtained in Production Example 2 and 48.9 g of 48% NaOH (i.e., 0.587 mol, 15 mol% relative to the carboxyl groups in aqueous solution (B)) were thoroughly stirred to obtain an aqueous polymer solution (6) of the present disclosure. The aqueous solution had a weight-average molecular weight (Mw) of 90,000, a solids content of 38.8%, a viscosity of 4000 mPa s, and an acrylic acid concentration of 590 ppm.

[0045] <Production Example 7> A 2.5 L stainless steel reactor equipped with a reflux condenser and a stirrer was charged with 508.0 g of deionized water and 0.010 g of Mohr's salt and heated to 85 °C under stirring. Next, with stirring, 438.0 g (i.e., 4.87 mol) of 80% AA, 20.0 g (i.e., 0.013 mol) of 15% NaPS, and 27.8 g (i.e., 0.0936 mol) of 35 wt% aqueous sodium bisulfite solution (hereinafter referred to as "35% SBS") were added dropwise from the nozzle tip through separate supply paths into the polymerization reaction system at 85 °C over 120 minutes, 160 minutes, and 115 minutes, respectively. Each component was added dropwise at a constant rate. After the addition of AA was completed, the reaction solution was maintained at 85 °C (aged) for an additional 90 minutes to complete the polymerization, yielding the aqueous polymer solution (7) of the present disclosure. The aqueous solution had a weight-average molecular weight (Mw) of 35,000, a solids content of 37.2%, a viscosity of 330 mPa·s, and an acrylic acid concentration of 8 ppm. The resulting aqueous polymer solution was dried under reduced pressure at room temperature to remove water, and then subjected to 1H NMR analysis using heavy water as a solvent. A peak at 2.7 ppm was observed, indicating the introduction of sulfonic acid groups to the polymer main chain terminals. Since the amount of unreacted sodium bisulfite in the aqueous solution was 2375 ppm (i.e., 24.2% of the added sodium bisulfite), 75.8 mol % of the added sodium bisulfite was introduced to the polymer terminals. The proportion of chain transfer agent-derived structures relative to 100 mol % of all monomer-derived structural units in the polymer was 0.47 mol %.

[0046] <Comparative Manufacturing Example 1> A 2.5 L stainless steel reactor equipped with a reflux condenser and agitator was charged with 283.0 g of deionized water and heated to the boiling point with stirring. Next, with stirring, 702.1 g (i.e., 7.80 mol) of 80% AA was added dropwise to the polymerization system at the boiling point. Subsequently, 702.1 g (i.e., 7.80 mol) of 80% AA was added dropwise over 180 minutes, followed by 39.1 g (i.e., 0.0254 mol) of 15% NaPS over 195 minutes, and 8.7 g (i.e., 0.0369 mol) of 45% SHP over 18 minutes, followed by 8.7 g (i.e., 0.149 mol) over 162 minutes. 132.1 g of deionized water was added dropwise from the nozzle tip through separate feed paths over 53 minutes, starting 92 minutes after the start of the 80% AA addition. The addition of each component, except for the 45% SHP, was carried out continuously at a constant rate. After the dropwise addition of AA was completed, the reaction solution was maintained at the boiling point (aging) for an additional 30 minutes to complete the polymerization, yielding a comparative aqueous polymer solution (1). The aqueous solution had a weight-average molecular weight (Mw) of 10,000, a solids content of 49.8%, a viscosity of 550 mPa·s, and an acrylic acid concentration of 19 ppm. Analysis of phosphorus atoms revealed that the ratio of phosphorus atoms introduced into the polymer chain, phosphorus atoms introduced at the polymer terminals, and phosphorus atoms not introduced into the polymer but present in the form of inorganic phosphorus salts was 75:12:13. Therefore, the content of structures derived from the chain transfer agent relative to 100 mol % of structural units derived from all monomers in the polymer was 2.07 mol %.

[0047] <Comparative Manufacturing Example 2> A 5 L stainless steel reactor equipped with a reflux condenser and agitator was charged with 1467.5 g of deionized water and heated to the boiling point while stirring. Next, 1249.2 g (i.e., 13.9 mol) of 80% AA was added dropwise to the polymerization system at the boiling point over 75 minutes, followed by 63.6 g (i.e., 0.040 mol) of 15% NaPS over 95 minutes, and 380.2 g of deionized water over 75 minutes. Each component was added continuously at a constant rate. After the AA addition was completed, the reaction solution was maintained at the boiling point (aged) for an additional 50 minutes to complete the polymerization, yielding a comparative aqueous polymer solution (2). The weight-average molecular weight (Mw) of the aqueous solution was 220,000, the solids content was 32.6%, the viscosity was 2150 mPa·s, and the acrylic acid concentration in the aqueous solution was 1350 ppm.

[0048] <Comparative Manufacturing Example 3> A carboxylic acid polymer aqueous solution (G) was obtained by thoroughly stirring 900.8 g of the comparative polymer aqueous solution (2) obtained in Comparative Production Example 2, 49.6 g of 48% NaOH (i.e., 0.595 mol, 15 mol % relative to the carboxyl groups in aqueous solution (F)), and 49.6 g of deionized water. The weight-average molecular weight (Mw) of the aqueous solution was 220,000, the solids content was 30.7%, the viscosity was 2300 mPa s, and the acrylic acid concentration in the aqueous solution was 1200 ppm.

[0049] Example 1 The aqueous polymer solution (1) of the present disclosure obtained in Production Example 1 was sealed in a high-density polyethylene container under an air atmosphere and stored in a thermostatic chamber at 2° C. After 45 days of storage, the aqueous solution had a weight-average molecular weight (Mw) of 47,000 and a viscosity of 1250 mPa s.

[0050] <Examples 2 to 5, Comparative Example 1> The weight average molecular weight (Mw) and viscosity after storage in a thermostatic chamber at 2° C. for 45 days were measured in the same manner as in Example 1, except that the aqueous polymer solutions shown in Table 1 were used. The results are shown in Table 1.

[0051] [Table 1] The results in Table 1 demonstrate that the carboxylic acid polymer of the present disclosure has excellent storage stability over time.

[0052] Example 6 The aqueous polymer solution (1) of the present disclosure obtained in Production Example 1 was sealed in a high-density polyethylene container under an air atmosphere and stored in a thermostatic chamber at 50° C. After 45 days of storage, the aqueous solution had a weight-average molecular weight (Mw) of 47,000 and a viscosity of 1250 mPa s.

[0053] <Examples 7 to 12, Comparative Examples 2 and 3> The weight average molecular weight (Mw) and viscosity after storage in a thermostatic bath at 50°C for 45 days were measured in the same manner as in Example 6, except that the aqueous polymer solutions shown in Table 2 were used. The results are shown in Table 2.

[0054] [Table 2] The results in Table 2 reveal that the carboxylic acid polymer of the present disclosure has excellent storage stability over time.

Claims

1. A carboxylic acid polymer having a weight average molecular weight of 27,000 or more and 1,000,000 or less, containing structural units derived from a chain transfer agent in the polymer, in which structural units derived from unsaturated carboxylic acid monomers account for 85 mol % or more relative to 100 mol % in total of structural units derived from all monomers, a neutralization rate of carboxyl groups contained in the polymer is 30 mol % or less, and the content of structures derived from the chain transfer agent is 0.01 mol % or more and 0.8 mol % or less relative to 100 mol % of structural units derived from all monomers (excluding the case where the chain transfer agent includes 2-mercaptoethanol).

2. 2. The carboxylic acid polymer according to claim 1, wherein the chain transfer agent has a phosphorus atom or a sulfur atom.

3. The carboxylic acid polymer according to claim 1 or 2, wherein the unsaturated carboxylic acid monomer is (meth)acrylic acid (salt).

4. 4. The carboxylic acid polymer according to claim 1, wherein the structural units derived from the unsaturated carboxylic acid monomer account for 100 mol % relative to the total of 100 mol % of the structural units derived from all monomers.

5. A method for producing a carboxylic acid polymer, comprising the steps of: the weight-average molecular weight of the resulting carboxylic acid polymer is 27,000 or more and 1,000,000 or less; the polymer contains structural units derived from the chain transfer agent, and the structural units derived from the unsaturated carboxylic acid monomer account for 85 mol % or more, based on 100 mol % of the total structural units derived from all monomers; the neutralization rate of carboxyl groups in the polymer is 30 mol % or less; and the content of the structures derived from the chain transfer agent is 0.01 mol % or more and 0.8 mol % or less, based on 100 mol % of the total structural units derived from all monomers.

6. 6. The method for producing a carboxylic acid polymer according to claim 5, wherein the structural units derived from the unsaturated carboxylic acid monomer account for 100 mol % relative to 100 mol % in total of the structural units derived from all monomers.

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