Polymer, its aqueous solution and its manufacturing method

Abstract

To provide a water-soluble polymer not damaging water solubility even in an acidic region, and having transparency, regardless of a high content of a hydrophobic copolymerization unit.SOLUTION: A polymer comprises 10-50 mol% copolymerization unit (a) derived from a hydrophobic polymerizable monomer (A), and 50-90 mol% copolymerization unit (b) derived from a hydrophilic polymerizable monomer (B). When pH of polymer aqueous solution is 5.5-8.0, which is formed by dissolving the polymer into water, a turbidity of the polymer aqueous solution is 1.5 NTU or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polymer, an aqueous solution of the polymer in water, and a method for producing the same. In particular, the present invention relates to a water-soluble polymer that has an abundance of hydrophobic substituents, does not lose its water solubility even at acidic pH, and can give a transparent aqueous solution. [Background technology]

[0002] Water-soluble polymers are polymers that have hydrophilic groups in their molecules and are used by dissolving them in water. Examples of water-soluble polymers include polyvinyl alcohol-based, polyamine- and polyamide-based, and polyacrylic acid-based polymers. In particular, water-soluble polyacrylic acid-based polymers are used in a wide variety of applications, including aqueous cleaning agents, scale inhibitors, inorganic dispersants, food additives, thickeners, and water absorbents. To be suitable for these applications, it goes without saying that the water-soluble polymer must be able to dissolve in water, and it must be able to completely dissolve in water to form a transparent aqueous solution, unlike cloudy mixed liquids such as so-called dispersions and emulsions.

[0003] Previously, patent documents 1 and 2 have proposed polymers in which a polymer polymerized primarily from acrylic acid is neutralized with an alkaline agent such as an alkali metal or ammonia to render the polymer water-soluble. However, as described in the examples of these patent documents, the polymers contain approximately 90% or more of an acrylic acid component. While this is not particularly problematic for copolymers in which the other polymeric component copolymerized with acrylic acid has water-soluble groups derived from amino groups, amide groups, sulfonic acid groups, or salts thereof, it is difficult to completely dissolve the polymer in water when copolymerized with other hydrophobic polymerizable monomers with low water solubility, especially at a high ratio exceeding 10%. Furthermore, while such poorly water-soluble polymers can be dissolved by adjusting the pH of the aqueous solution containing the polymer to a neutral or alkaline pH of approximately 7-10, as in patent document 2, they are difficult to completely dissolve in an acidic aqueous solution with a pH of 7 or less. Therefore, from the viewpoint of the physical properties required for the intended use, it was necessary to establish a water-soluble polymer that is copolymerized with more than 10% hydrophobic polymerizable monomers and that is completely soluble in an acidic aqueous solution with a pH of 7 or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5221184 [Patent Document 2] Patent No. 6375909 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention relates to a polymer that is copolymerized with a certain amount of hydrophobic polymerizable monomers and yet maintains sufficient water solubility even when dissolved in an aqueous solution at an acidic pH range. Specifically, the present invention aims to provide a water-soluble polymer that overcomes the drawback of conventional polymer products, which are difficult to completely dissolve in water due to the low water solubility of the polymer, an aqueous solution of the polymer, and a method for producing the same. [Means for solving the problem]

[0006] The polymer of the present invention is a polymer comprising 10 to 50 mol % of copolymer units (a) derived from a hydrophobic polymerizable monomer (A) and 50 to 90 mol % of copolymer units (b) derived from a hydrophilic polymerizable monomer (B), and is characterized in that when the polymer is dissolved in water to form an aqueous polymer solution with a pH of 5.5 to 8.0, the turbidity of the aqueous polymer solution is 1.5 NTU or less.

[0007] According to the aqueous polymer solution of the present invention, there is provided an aqueous polymer solution in which the above-mentioned polymer is dissolved in water, and the concentration of the polymer is 10 to 50 mass %.

[0008] The method for producing a polymer of the present invention is characterized by copolymerizing 10 to 50 mol % of a hydrophobic polymerizable monomer (A) and 50 to 90 mol % of a hydrophilic polymerizable monomer (B) without using a surfactant. [Effects of the Invention]

[0009] The polymer of the present invention is a polymer containing 10 to 50 mol % of copolymerized units (a) derived from a hydrophobic polymerizable monomer (A), yet is completely soluble in water even in an acidic pH range of 5 to 7. By using this polymer, a type of copolymer that is rich in hydrophobic polymerizable monomer units and that was previously only usable in aqueous solutions in the neutral to alkaline range can now be used in weakly acidic aqueous solutions, thereby expanding the range of applicable products and applications. DETAILED DESCRIPTION OF THE INVENTION

[0010] The polymer of the present invention comprises 10 to 50 mol % of copolymer units (a) derived from a hydrophobic polymerizable monomer (A) and 50 to 90 mol % of copolymer units (b) derived from a hydrophilic polymerizable monomer (B).

[0011] In the present invention, the hydrophobic polymerizable monomer (A) is a polymerizable monomer having a solubility in water of 2.0 g / L or less at 25°C. The value and information on this solubility in water can be obtained from the SDS published by each raw material manufacturer. Alternatively, the solubility of various monomers in 1 L of water at 25°C may be measured in accordance with OECD (Organization for Economic Cooperation and Development) Test Guideline No. 105.

[0012] The hydrophobic polymerizable monomer (A) preferably has an aromatic or alicyclic substituent, which allows the monomer to exhibit properties specific to the substituent. Examples of aromatic substituents include phenyl, α-alkylphenyl, and naphthyl groups. Examples of alicyclic substituents include cycloalkyl groups such as cyclopentyl and cyclohexyl groups; and polycyclic alkyl groups such as isobornyl, norbornyl, and dicyclopentanyl groups.

[0013] Examples of the hydrophobic polymerizable monomer (A) include acrylates such as butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and isobornyl acrylate, methacrylates such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, and isobornyl methacrylate, and vinyl group-containing monomers such as styrene and vinyl naphthalene. These monomers may be used alone or in a mixture of two or more, and can be selected appropriately depending on the desired physical properties of the polymer. However, styrene is preferred in terms of versatility, cost, and availability.

[0014] In the polymer of the present invention, copolymerization units (a) derived from hydrophobic polymerizable monomer (A) account for 10 to 50 mol %, preferably 15 to 45 mol %, and more preferably 20 to 40 mol %, of the total 100 mol % of all polymerizable monomers constituting the polymer. If the copolymerization units (a) are less than 10 mol %, the physical properties expected from the hydrophobic polymerizable monomer (A) tend to be impaired, while if they exceed 50 mol %, the solubility of the copolymerized polymer in water tends to decrease.

[0015] In the present invention, the hydrophilic polymerizable monomer (B) is a polymerizable monomer that is soluble in or freely miscible with water at 25°C. It also includes polymerizable monomers containing a substituent (e.g., a carboxyl group, a tertiary amino group, etc.) that becomes water-soluble when neutralized to form a salt. Information about the water-soluble properties and solubility in water can be obtained from the SDS published by each raw material manufacturer. The solubility of various monomers in 1 L of water at 25°C may also be measured in accordance with OECD (Organization for Economic Cooperation and Development) Test Guideline No. 105.

[0016] Preferred examples of the hydrophilic polymerizable monomer (B) include polymerizable monomers having a carboxyl group or a salt thereof, such as acrylic acid, methacrylic acid; tertiary amines such as 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, and N-vinyl-2-pyrrolidone; and hydroxyl group-containing polymerizable monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and (meth)acrylic acid monoesters of ethylene glycol derivatives.

[0017] Here, examples of substituents that become water-soluble by neutralization to form a salt include, for example, in the case of a polymerizable monomer having a carboxyl group such as acrylic acid, those that have been neutralized with an alkaline agent to form ammonium acrylate, sodium acrylate, etc. Similarly, in the case of a polymerizable monomer having a tertiary amino group such as dimethylaminoethyl acrylate, examples include dimethylaminoethyl acrylate chloride salt, dimethylaminoethyl acrylate bromide salt, etc.

[0018] These hydrophilic polymerizable monomers (B) may be used alone or in a mixture of two or more kinds, and acrylic acid is preferred in view of versatility, cost and availability.

[0019] The copolymerization unit (b) derived from the hydrophilic polymerizable monomer (B) accounts for 50 to 90 mol %, preferably 55 to 85 mol %, and more preferably 60 to 80 mol % of the total polymerizable monomers constituting the polymer (100 mol %). If the copolymerization unit (b) is less than 50 mol %, the solubility of the water-soluble polymer in water tends to decrease, while if it exceeds 90 mol %, the physical properties expected from the hydrophobic polymerizable monomer (A) tend to be impaired.

[0020] The polymer of the present invention is characterized in that when the pH of the polymer aqueous solution obtained by dissolving the polymer in water is adjusted to 5.5 to 8.0, the turbidity of the polymer aqueous solution is 1.5 NTU or less. Here, the turbidity of the polymer aqueous solution is an index of the cloudiness of the aqueous solution, and NTU is a unit of turbidity, and can be measured using a turbidimeter. The turbidity of the polymer aqueous solution represents the state of dissolution of the polymer in water. Generally, a turbidity of 1.5 NTU or less is a level that can be judged to be almost transparent even when visually observed by a human, and the state of dissolution of the polymer can be judged to be good. The turbidity of the polymer aqueous solution is preferably 1.0 NTU or less, more preferably 0.5 NTU or less. In this specification, the turbidity of the polymer aqueous solution can be measured by nephelometry, for example, using a turbidimeter such as a LaMotte 2020we, using ion-exchanged water as a blank.

[0021] The pH of the aqueous polymer solution can be adjusted by the amount of acid or alkali added. For example, it can be adjusted by adding an alkali such as aqueous ammonia or a tertiary amine to a polymer copolymerized with acrylic acid until the desired pH is reached. If the pH is adjusted to less than 5.5, the water solubility of the polymer tends to decrease significantly. Although solubility is not impaired even if the pH exceeds 8.0, the polymer will no longer be suitable for applications in acidic to neutral pH ranges. Therefore, the pH is preferably adjusted to 5.5 to 8.0, preferably 5.5 to 7.5, and more preferably 5.5 to 7.0.

[0022] The polymer of the present invention preferably has a weight-average molecular weight of 3,000 to 20,000, more preferably 5,000 to 20,000, and even more preferably 5,000 to 10,000. If the weight-average molecular weight is less than 3,000, large amounts of molecular weight modifiers and polymerization initiators are required, and high-pressure equipment is required, making production using typical equipment and conditions difficult. If the weight-average molecular weight exceeds 20,000, water solubility tends to be impaired. In this specification, the weight-average molecular weight of the polymer can be determined by the method described in the Examples.

[0023] In the present invention, the arrangement of copolymer units (a) and (b) in the polymer is 13 When determined by C NMR, the ratio (mol %) of the triads having the sequence (a)-(b)-(a) to the total triads to the content (mol %) of copolymerization unit (a) in the polymer is preferably 0.8 or more. 13 When measured by C NMR, the following triads are theoretically determined: (a)-(a)-(a) (a)-(b)-(a) (a)-(a)-(b), or (b)-(a)-(a) (b)-(a)-(b) (a)-(b)-(b), or (b)-(b)-(a) (b)-(b)-(b) The percentage (mol %) of triads with the sequence (a)-(b)-(a) among all triads is the mole % of triads with the sequence (a)-(b)-(a) when the total of the measured triads is taken as 100 mole %.

[0024] The content (mol %) of the copolymerization unit (a) in the polymer is determined by the copolymerization ratio of the polymer, i.e., 13 Each of the 13 Based on the area ratio of the C NMR spectrum, it is the ratio (mol %) of the content of copolymerization unit (a) to the total content of copolymerization units (a) and (b) in the polymer, 100 mol %.

[0025] When the ratio of the proportion (mol%) of triads having the (a)-(b)-(a) sequence to the content (mol%) of copolymerization unit (a) in the polymer is 0.8 or more, it means that the copolymerization unit (a) is well distributed in the polymer, and the solubility in water can be increased. The ratio of the proportion (mol%) of triads having the (a)-(b)-(a) sequence to the content (mol%) of copolymerization unit (a) is preferably 0.7 or more, more preferably 0.85 or more, and particularly preferably 0.9 or more.

[0026] In this specification, the sequence of copolymerized units (a) and (b) in a polymer can be measured using the following apparatus and conditions. Equipment: ECA-400 (JEOL RESONANCE) Measurement method: single 13 C pulse with inverse gated 1 H decoupling can be measured under the conditions described in the examples. The resulting copolymer units (a) and (b) 13 Assign the peaks in the C NMR spectrum and 13 The copolymerization ratio of polymerizable monomers (A) and (B) can be calculated from the area ratio of the C NMR spectrum. 13 C NMR spectrum triplet peak assignments and their respective 13 The triad ratio can be calculated from the C NMR spectral area ratio.

[0027] The polymer of the present invention is a water-soluble polymer that dissolves in water. Here, "a polymer dissolves in water" can be defined as "the aqueous solution in which the polymer is dissolved is colorless and transparent." Turbidity (unit: NTU) can be used as an indicator of whether an aqueous solution is colorless and transparent. Generally, if the turbidity is 5 NTU or higher, the turbidity is noticeable to the naked eye, and if the turbidity is 1.5 NTU or lower, the solution is judged to be almost transparent to the naked eye, and can be judged to be dissolved in water.

[0028] An aqueous polymer solution can be obtained by dissolving the polymer of the present invention in water. This aqueous polymer solution has a turbidity of 1.5 NTU or less when its pH is 5.5 to 8.0. By keeping the turbidity at 1.5 NTU or less, it can be visually evaluated as being almost transparent, making it applicable to a wider range of uses. The turbidity of the aqueous polymer solution is preferably 1.0 NTU or less, and more preferably 0.5 NTU or less.

[0029] The pH of the aqueous polymer solution can be adjusted by the amount of acid or alkali added. For example, an alkali such as aqueous ammonia or a tertiary amine can be added to a polymer copolymerized with acrylic acid until the desired pH is reached. If the pH is adjusted to less than 5.5, the water solubility of the polymer tends to decrease significantly. Although solubility is not impaired even if the pH exceeds 8.0, the polymer will no longer be suitable for applications in the acidic to neutral range. Therefore, the pH is preferably adjusted to 5.5 to 8.0, preferably 5.5 to 7.5, and more preferably 5.5 to 7.0.

[0030] The polymer aqueous solution preferably has a polymer concentration of 10 to 50% by mass, more preferably 10 to 30% by mass, even more preferably 10 to 20% by mass, and particularly preferably 14 to 16% by mass. By keeping the polymer concentration within this range, the polymer aqueous solution becomes a low-viscosity solution that is easy to handle for various applications, which is preferable.

[0031] It is more preferable that the aqueous polymer solution contains 14 to 16% by mass of polymer and 86 to 84% by mass of water. The amount of water added can be adjusted according to the concentration of the polymer contained, thereby producing an aqueous polymer solution with a polymer concentration of 14 to 16%.

[0032] The method for producing the polymer of the present invention is not particularly limited as long as it is a production method that can produce a polymer having the above-mentioned properties, but it is preferable to produce it by a method of copolymerizing polymerizable monomers (A) and (B) by radical polymerization.

[0033] In radical polymerization, general azo-based and peroxide-based polymerization initiators can be used as polymerization initiators. Furthermore, thiol compounds, α-methylstyrene dimer, etc. can also be used as molecular weight regulators, if necessary.

[0034] The method for producing the polymer of the present invention is preferably to copolymerize 10 to 50 mol % of a hydrophobic polymerizable monomer (A) and 50 to 90 mol % of a hydrophilic polymerizable monomer (B) without using a surfactant. That is, it is desirable to produce the polymer by a polymerization method that does not use a surfactant, which prevents uniform dissolution when forming an aqueous solution. When water is used as the polymerization solvent, emulsion polymerization or suspension polymerization using a surfactant is commonly used. However, the water-soluble polymer of the present invention is preferably produced by homogeneous polymerization, in which the polymerization reaction is carried out without using a surfactant and all raw materials are dissolved in a solvent, and particularly preferably by solution polymerization using a solvent as the polymerization solvent.

[0035] The solvent used in the solution polymerization to produce the polymer is preferably an organic solvent having an alcoholic hydroxyl group and a solubility in water of 5.0 to 50.0 g / L at 25°C. This solubility in water can be obtained from the SDS or solvent handbook published by each raw material manufacturer. Alternatively, the solubility of various solvents in 1 L of water at 25°C may be measured in accordance with OECD (Organization for Economic Cooperation and Development) Test Guideline No. 105.

[0036] Examples of organic solvents having an alcoholic hydroxyl group and a solubility in water of 5.0 to 50.0 g / L at 25°C include straight-chain or branched alcohols having 5 to 6 carbon atoms, such as amyl alcohol, isopentyl alcohol, n-hexanol, and 2-methyl-4-pentanol. These solvents may be used alone or in a mixture of two or more, and can be appropriately selected depending on the desired polymerization temperature and other factors.

[0037] The amount of solvent used when polymerizing the polymer is preferably 100 to 900 parts by mass, more preferably 150 to 600 parts by mass, and even more preferably 200 to 600 parts by mass, assuming the total amount of polymerizable monomers to be 100 parts by mass. If this ratio is less than 100 parts by mass, the viscosity tends to increase and handling properties tend to be impaired, while if it exceeds 900 parts by mass, the polymerizable monomers tend to be diluted and the polymerization rate tends to be insufficient.

[0038] When solution polymerization is carried out using an organic solvent, if the hydrophilic polymerizable monomer (B) is neutralized in advance, the polymer produced by polymerization tends to have poor solubility in the solvent and to hinder uniform polymerization. For this reason, it is preferable to carry out solution polymerization without neutralizing the hydrophilic polymerizable monomer (B).

[0039] The aqueous polymer solution can be obtained by dissolving the polymer obtained by the above-mentioned production method in water, for example by neutralizing it in water as needed. That is, it is preferable to neutralize the copolymerized polymer. For example, in the case of a polymer obtained by selecting a carboxyl group-containing monomer as the hydrophilic polymerizable monomer (B), water solubility can be imparted to the polymer by neutralizing the copolymerized units derived from the hydrophilic polymerizable monomer (B) with an alkaline agent. In this case, preferred examples of the alkaline agent include ammonia or aqueous ammonia. The polymer content of the aqueous polymer solution can be adjusted by adjusting the amount of water added depending on the concentration of the polymer contained.

[0040] The method for producing the aqueous polymer solution is not particularly limited as long as it is a method capable of adjusting the polymer content and pH, but a method in which a polymer polymerized in a solvent is diluted with water to neutralize it, and then the solvent is removed by liquid-liquid separation is preferred. A method in which a polymer polymerized in a solvent is isolated from the solvent by reprecipitation or the like, and then neutralized and dissolved in water to produce the aqueous polymer solution, or a method in which a polymer polymerized in a solvent is diluted with water to neutralize it, and then the solvent is removed by distillation or the like can also be applied, but these methods are not preferred because they can become complicated depending on the type of solvent used in polymer polymerization. [Example]

[0041] The present invention will be described in detail below with reference to the following examples. Unless otherwise specified, reagents were used as raw materials. In the following examples, the measurement methods, evaluation methods, etc. were as follows.

[0042] 1) Polymer concentration (unit: mass%) The heating residue (mass %) of the sample was measured and used as the polymer content (mass %). The heating conditions were a temperature of 170°C and a time of 60 minutes.

[0043] 2) Weight average molecular weight (Mw) of the polymer Measurements were performed using a gel permeation chromatography (GPC) "HLC-8220GPC" (Tosoh Corporation test equipment) with a multipore column using tetrahydrofuran as the carrier. The weight average molecular weight (Mw) was calculated in terms of standard polystyrene.

[0044] 3) pH of the aqueous solution The sample at 25°C was measured using a pH meter (HORIBA LAQUAact D-71).

[0045] 4) Turbidity of aqueous solution (unit: NTU) The sample at 25°C was measured using a turbidity meter (2020we: manufactured by LaMotte) with ion-exchanged water as a blank.

[0046] 5) 13 C NMR Equipment used: ECA-400 (manufactured by JEOL RESONANCE) Measurement method: single 13 C pulse with inverse gated 1 H decoupling Measurement frequency: 100.53 MHz Pulse width: 5.78 μs Lock solvent: Dimetylsulfoxide (DMSO)-d6 Chemical shift reference: DMSO (39.50 ppm) Accumulation count: 10,000 times Measurement temperature: 90℃ Sample rotation speed: 15 Hz The resulting copolymer units (a) and (b) 13 Assign the peaks in the C NMR spectrum and 13 The copolymerization ratio of polymerizable monomers (A) and (B) was calculated from the area ratio of the C spectrum. 13 C NMR spectrum triplet peak assignments and their respective 13 The triad ratio was calculated from the C NMR spectral area ratio.

[0047] [Synthesis Example A1] A 0.5 L four-neck flask equipped with a nitrogen gas inlet, reflux condenser, stirrer, and inlet was charged with 234 g of methyl isobutyl carbinol. The mixture was stirred while nitrogen gas was sealed in and the temperature was adjusted to 95°C. Next, 73 g of acrylic acid, 27 g of styrene, 2 g of mercaptopropionic acid, 2 g of mercaptoacetic acid, and 2 g of 2,2'-azobis(isobutyronitrile) were charged to an Erlenmeyer flask and dissolved and mixed until homogeneous. This mixture was added dropwise to the four-neck flask at 95°C over 3 hours. The mixture was then aged and polymerized at 95°C for 3 hours to obtain Polymer Solution A1. Polymer Solution A1 had an acrylic acid / styrene ratio of 80 / 20 (molar ratio), a polymer concentration of 30.9% by mass, and a weight-average molecular weight (Mw) of 4,400.

[0048] [Synthesis example B1 ] Polymer solution B1 was obtained in the same manner as in Synthesis Example A1, except that the amount of acrylic acid charged was 62 g and the amount of styrene charged was 38 g. Polymer solution B1 had an acrylic acid / styrene ratio of 70 / 30 (molar ratio), a polymer concentration of 30.8% by mass, and a weight-average molecular weight (Mw) of 5,400.

[0049] [Synthesis example C1 ] Polymer solution C1 was obtained in the same manner as in Synthesis Example A1, except that the amounts of acrylic acid and styrene were changed to 51 g and 49 g, respectively. Polymer solution C1 had an acrylic acid / styrene ratio of 60 / 40 (molar ratio), a polymer concentration of 30.4% by mass, and a weight-average molecular weight (Mw) of 6,200.

[0050] [Synthesis example B2] Polymer solution B2 was obtained in the same manner as in Synthesis Example A2, except that the solvent used was changed from methyl isobutyl carbinol to isopropyl alcohol. Next, 900 g of ion-exchanged water and 50 g of polymer solution B2 were charged into a 1 L mixer and mixed for 10 seconds. The precipitated polymer was collected by filtration using a 200-mesh filter cloth and washed with stirring in approximately 3 L of ion-exchanged water. This process was repeated three times, and then dried in a vacuum dryer at 50°C for 72 hours to obtain polymer powder B2. Polymer powder B2 had an acrylic acid / styrene ratio of 70 / 30 (molar ratio), a polymer concentration of 99.6 mass%, and a weight-average molecular weight (Mw) of 4,800.

[0051] [Synthesis Example B3] Polymer Slurry B3 was obtained in the same manner as in Synthesis Example A2, except that the solvent used was changed from methyl isobutyl carbinol to ion-exchanged water and Rheodol TW-O120V (POE sorbitan monooleate: manufactured by Kao Corporation). Polymer Slurry B3 had an acrylic acid / styrene ratio of 70 / 30 (molar ratio), a polymer concentration of 33.1% by mass, and a weight-average molecular weight (Mw) of 4,600.

[0052] Example 1 A 2-L beaker was charged with 340 g of polymer solution A1 and 539 g of ion-exchanged water and stirred. The liquid temperature was maintained at 20-30°C, and 58 g of 28% aqueous ammonia was added dropwise over 2 hours. Stirring was continued for another hour, and the mixture was then transferred to a separatory funnel and allowed to stand at room temperature. After visually confirming that the solution had completely separated into two phases, the water bath (heavy phase side) in which the polymer had dissolved was removed, yielding an aqueous solution of Example 1. The aqueous solution of Example 1 had a polymer concentration of 14.5% by mass and a pH of 6.9.

[0053] <Example 2> Except for changing the polymer solution to B1, changing the amount of ion-exchanged water to 485 g, and changing the amount of 28% ammonia water to 27 g, an aqueous polymer solution of Example 2 was obtained in the same manner as in Example 1. The aqueous solution of Example 2 had a polymer concentration of 14.8 mass % and a pH of 5.6.

[0054] Example 3 An aqueous polymer solution of Example 3 was obtained in the same manner as in Example 2, except that the amount of ion-exchanged water charged was 530 g and the amount of 28% ammonia water charged was 38 g. The aqueous solution of Example 3 had a polymer concentration of 14.6 mass % and a pH of 6.1.

[0055] Example 4 An aqueous polymer solution of Example 4 was obtained in the same manner as in Example 2, except that the amount of ion-exchanged water charged was 548 g and the amount of 28% ammonia water charged was 49 g. The aqueous solution of Example 4 had a polymer concentration of 14.6 mass % and a pH of 6.8.

[0056] <Example 5> An aqueous polymer solution of Example 5 was obtained in the same manner as in Example 2, except that the amount of ion-exchanged water charged was 546 g and the amount of 28% ammonia water charged was 55 g. The aqueous solution of Example 5 had a polymer concentration of 14.6 mass % and a pH of 7.9.

[0057] Example 6 Except for changing the polymer solution to C1, changing the amount of ion-exchanged water to 556 g, and changing the amount of 28% ammonia water to 41 g, an aqueous polymer solution of Example 6 was obtained in the same manner as in Example 1. The aqueous solution of Example 6 had a polymer concentration of 14.4 mass% and a pH of 7.3.

[0058] <Comparative Example 1> Except for changing the amount of ion-exchanged water charged to 452 g and the amount of 28% ammonia water charged to 22 g, an aqueous polymer solution of Comparative Example 1 was obtained in the same manner as in Example 2. The aqueous solution of Comparative Example 1 had a polymer concentration of 14.7 mass % and a pH of 5.4.

[0059] <Comparative Example 2> A 2 L beaker was charged with 100 g of polymer powder B2 and 515 g of ion-exchanged water and stirred. While maintaining the liquid temperature at 20-30°C, 50 g of 28% aqueous ammonia was added dropwise over 2 hours, and stirring was continued for 3 hours to obtain an aqueous solution of Comparative Example 2. The aqueous solution of Comparative Example 2 had a polymer concentration of 15.1 mass % and a pH of 7.3.

[0060] <Comparative Example 3> A 2-L beaker was charged with 340 g of polymer slurry B3 and 300 g of ion-exchanged water and stirred. While maintaining the liquid temperature at 20 to 30°C, 60 g of 28% aqueous ammonia was added dropwise over two hours, and stirring was continued for three hours to obtain an aqueous solution of Comparative Example 3. The aqueous solution of Comparative Example 3 had a polymer concentration of 15.1% by mass and a pH of 8.5.

[0061] The synthesis examples above are shown in Table 1, and the synthesis results and turbidity evaluation results of the examples and comparative examples are shown in Tables 2 and 3.

[0062] [Table 1]

[0063] [Table 2]

[0064] [Table 3]

[0065] Although the polymers of Examples 1 to 6 contain 20 to 40 mol % of hydrophobic polymerizable monomers, their aqueous solutions have extremely low turbidity and are highly soluble in water. Furthermore, Examples 2, 3, and 4 show that the water-soluble polymers of the present invention exhibit high solubility in water even at acidic pH.

[0066] On the other hand, it is clear that when neutralization is insufficient and the pH is too low, as in Comparative Example 1, the turbidity increases and the solubility decreases. This shows that there is an appropriate range for the pH.

[0067] Furthermore, it was found that the turbidity increased when a water-soluble alcohol was used as a solvent during polymerization as in Comparative Example 2, or when a surfactant was used in the polymerization as in Comparative Example 3. This shows that there are polymers with similar copolymer compositions that differ in water solubility, and that the polymers of the present invention are polymers that particularly exhibit water solubility. This is considered as follows.

[0068] Table 4 shows the polymer B1 of Synthesis Example B1 polymerized in a hydrophobic alcohol and the polymer B2 of Synthesis Example B2 polymerized in a hydrophilic alcohol. 13 The copolymerization ratio (%) and copolymerization sequence ratio (triad ratio (%)) calculated from the results of C NMR measurement are shown. In the table, "S" represents a styrene unit, i.e., a copolymerization unit (a) derived from a hydrophobic polymerizable monomer (A), and "A" represents an acrylic acid unit, i.e., a copolymerization unit (b) derived from a hydrophilic polymerizable monomer (B).

[0069] [Table 4]

[0070] Polymer B1 of Synthesis Example B1, which was polymerized in a hydrophobic alcohol, had a ratio (mol %) of triads with the sequence (a)-(b)-(a) [SAS in the table] of 27 mol % of all triads, a content (mol %) of copolymerized unit (a) in polymer B1 [copolymerization ratio of S in the table] of 30 mol %, and a ratio of the triad ratio of SAS sequences to the copolymerization ratio of S [SAS / S] of 0.90.

[0071] On the other hand, polymer B2 of Synthesis Example B2, which was polymerized in a hydrophilic alcohol, had a ratio (mol %) of triplets with the sequence (a)-(b)-(a) [SAS in the table] of 21 mol % of all triplets, a content (mol %) of copolymerized unit (a) in polymer B2 [copolymerization ratio of S in the table] of 31 mol %, and a ratio of the triad ratio of SAS sequences to the copolymerization ratio of S [SAS / S] of 0.68.

[0072] Polymer B1 and polymer B2 were polymerized with acrylic acid / styrene = 70 / 30, 13 The C NMR results indicate that both polymers are similar, polymerized at a copolymerization ratio of approximately 70 / 30. However, the triad ratio reveals that polymer B1 has more SAS chains than polymer B2. The closer these SAS chains are to the 30 mol% copolymerized styrene ratio, i.e., the more likely the polymer structure is to have a high degree of alternation between acrylic acid and styrene, as long as the [SAS / S] ratio is preferably 0.8 or greater. Therefore, polymer B1, whose SAS chain ratio is closer to the copolymerization ratio of styrene and whose [SAS / S] ratio is 0.8 or greater, has less styrene bias than polymer B2, whose [SAS / S] ratio is less than 0.8. This result is believed to be one of the reasons why polymer B1 exhibits high water solubility.

Claims

1. A polymer aqueous solution is prepared by dissolving in water a polymer comprising 20 to 40 mol % of copolymer units (a) derived from styrene and 60 to 80 mol % of copolymer units (b) derived from acrylic acid, wherein the copolymer units derived from acrylic acid are neutralized with aqueous ammonia, the polymer having a polymer concentration of 14 to 16 mass % and a pH of 5.5 to 8.0, the turbidity of the aqueous polymer solution being 1.5 NTU or less, and when the sequence of copolymer units (a) and (b) in the polymer is determined by 13C NMR, the ratio (mol %) of triads having the sequence (a)-(b)-(a) to the content (mol %) of copolymer units (a) in the polymer is 0.8 or more.

2. 2. The aqueous polymer solution according to claim 1, wherein the weight average molecular weight of the polymer is 3,000 to 20,000.

3. A method for producing an aqueous polymer solution comprising copolymerizing 20 to 40 mol % of styrene and 60 to 80 mol % of acrylic acid using a solvent having an alcoholic hydroxyl group and a solubility in water of 5.0 to 50.0 g / L at 25°C as the sole solvent without using a surfactant, neutralizing the resulting polymer with an alkaline agent to a pH of 5.5 to 8.0, and dissolving the polymer in water.

4. 4. The method for producing an aqueous polymer solution according to claim 3, wherein the solvent having an alcoholic hydroxyl group is a linear or branched alcohol having 5 to 6 carbon atoms.

5. 5. The method for producing an aqueous polymer solution according to claim 3, wherein the alkaline agent is ammonia or aqueous ammonia.

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