(METH)acrylic acid nitroxide polymer particle, and method for producing same

Abstract

Provided is a method for producing (meth)acrylic acid nitroxide polymer particles which suppress generation of bulky aggregates and deposits and have excellent productivity. This method for producing (meth)acrylic acid nitroxide polymer particles comprises: step a for dispersing, in an aqueous medium as oil droplets, a solution obtained by dissolving a (meth)acrylic acid nitroxide polymer (A) in a hydrophobic organic solvent; step b for removing the solvent in the oil droplets to obtain a slurry; and step c for dehydrating and drying the slurry. The polymer (A) has a repeating unit represented by formula (1). The aqueous medium contains a polyvinyl alcohol-based polymer (B). The mass ratio (RD) of the PVA-based polymer (B) with respect to the solution, the degree of polymerization (DP) of the PVA-based polymer (B), and the degree of saponification (DS) of the PVA-based polymer (B) satisfy the relationship of RD×DP×(100-DS)2 / 100≥850.

Description

(Meth)acrylic acid nitroxide polymer particles and method for producing the same

[0001] The present disclosure relates to (meth)acrylic acid nitroxide polymer particles and methods for making the same.

[0002] Polymers containing a nitroxide radical structure have attracted attention as electrode active materials because they have high energy density, can carry large currents, and have excellent cycle characteristics. For example, Patent Document 1 proposes radical materials such as poly(2,2,6,6-tetramethylpiperidinoxy methacrylate) as active materials for secondary battery electrodes.

[0003] In addition, Patent Document 2 discloses a method for producing a CO 2 -depleted battery by using an electrolyte layer containing a redox compound made of a polymer containing a nitroxide radical structure. ２ Electrochemically adsorbing and desorbing CO ２ Furthermore, Patent Document 3 proposes a method of isolating a polymer containing a nitroxide radical structure by distillation or decantation, followed by filtration.

[0004] Japanese Patent Publication No. 2002-304996 Japanese Patent No. 6792969 Japanese Patent Publication No. 2012-193273

[0005] Polymers containing a nitroxide radical structure are used in a variety of applications, including as active materials for electrodes, and there is a demand in the market for a technology that is highly productive and can suppress the formation of coarse aggregates and deposits.

[0006] The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to provide (meth)acrylic acid nitroxide polymer particles that suppress the generation of coarse aggregates and deposits and have excellent productivity, and a method for producing the same.

[0007] As a result of extensive research conducted by the present inventors to achieve the above object, the present disclosure has been completed, including the following aspects. [1]: A method for producing (meth)acrylic acid nitroxide polymer particles, comprising: a step a) of dissolving a (meth)acrylic acid nitroxide polymer (A) (hereinafter referred to as polymer (A)) in a hydrophobic organic solvent and dispersing the resulting solution as oil droplets in an aqueous medium; a step b) of removing the hydrophobic organic solvent from the oil droplets dispersed in the aqueous medium after step a to obtain a slurry; and a step c) of dehydrating and drying the slurry after step b to obtain (meth)acrylic acid nitroxide polymer particles, wherein polymer (A) has a repeating unit represented by formula (1), and the aqueous medium contains a polyvinyl alcohol-based polymer (B) (hereinafter referred to as PVA-based polymer (B)), and the mass ratio (RD) of the PVA-based polymer (B) to the solution in step a, the degree of polymerization (DP) of the PVA-based polymer (B), and the degree of saponification (DS) of the PVA-based polymer (B) are expressed as follows: RD×DP×(100−DS) ２ / 100≧850 (In formula (1), R １ , R ２ , R ３ and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that R １ and R ２ At least one of R is an alkyl group having 1 to 6 carbon atoms, and R ３ and R ４ At least one of R is an alkyl group having 1 to 6 carbon atoms, １ and R ２ may be bonded to each other to form a cyclic structure, and R ３ and R ４ may be bonded to each other to form a cyclic structure, and R １１represents a hydrogen atom or a methyl group, X represents a single bond or a divalent linking group, and n is 0 or 1.) [2]: A method for producing (meth)acrylic acid nitroxide polymer particles according to [1], wherein the ratio of particles of the (meth)acrylic acid nitroxide polymer (A) in the slurry obtained in step b having a volume-based particle size of 1,000 μm or more in a particle size distribution measured by a light scattering method is 0 to 5%. [3]: A method for producing (meth)acrylic acid nitroxide polymer particles according to [1] or [2], wherein the PVA-based polymer (B) has a degree of polymerization of 500 to 5,000 and a degree of saponification of 50 to 90 mol %. [4]: ​​A method for producing (meth)acrylic acid nitroxide polymer particles according to any one of [1] to [3], wherein the PVA-based polymer (B) has a total amount of vinyl acetate units and vinyl alcohol units of 95 to 100 mol %. [5]: (Meth)acrylic acid nitroxide polymer particles comprising a (meth)acrylic acid nitroxide polymer (A) (hereinafter referred to as polymer (A)) having a repeating unit represented by formula (1), wherein the volume average particle size of an aqueous dispersion measured by a light scattering method is 10 to 1,000 μm, and the ratio of particles with a volume-based particle size of 1,000 μm or more is 0 to 5%. (However, in formula (1), R １ , R ２ , R ３ and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that R １ and R ２ At least one of R is an alkyl group having 1 to 6 carbon atoms, and R ３ and R ４ At least one of R is an alkyl group having 1 to 6 carbon atoms, １ and R ２ may be bonded to each other to form a cyclic structure, and R ３ and R ４ may be bonded to each other to form a cyclic structure, and R １１represents a hydrogen atom or a methyl group, X represents a single bond or a divalent linking group, and n is 0 or 1.) [6]: The (meth)acrylic acid nitroxide polymer particles according to [5], further containing 0.001 to 5 mass % of a polyvinyl alcohol-based polymer (B) (hereinafter referred to as PVA-based polymer (B)). [7]: The (meth)acrylic acid nitroxide polymer particles according to [6], wherein the total amount of vinyl acetate units and vinyl alcohol units in the PVA-based polymer (B) is 95 to 100 mol %.

[0008] The present disclosure has the excellent effect of providing (meth)acrylic acid nitroxide polymer particles that suppress the generation of coarse aggregates and deposits and have excellent productivity, and a method for producing the same.

[0009] An example of an embodiment to which the present disclosure is applied will be described below. The present disclosure is not limited to this embodiment, and other embodiments may also fall within the scope of the present disclosure as long as they conform to the spirit of the present disclosure. Furthermore, the numerical values ​​"A to B" specified in this specification include numerical values ​​A and B. The numerical values ​​specified in this specification are values ​​obtained by the methods disclosed in the embodiments or examples. Furthermore, the terms "sheet" and "film" in this specification have the same meaning. Unless otherwise noted, the various components appearing in this specification may each be used independently, either alone or in combination of two or more types. (Meth)acrylic is a general term for acrylic and methacrylic. Unless otherwise specified in this specification, a "unit" contained in a polymer is a repeating unit contained in the polymer, and is a monomer unit derived from a raw material monomer or a derived unit derived from one or more monomer units.

[0010] 1. (Meth)acrylic acid nitroxide polymer particles The (meth)acrylic acid nitroxide polymer particles of the present disclosure (hereinafter also referred to as the present polymer particles) contain one or more (meth)acrylic acid nitroxide polymers (A) (hereinafter also referred to as the polymer (A)). The content of the polymer (A) in the present polymer particles is preferably 95 to 100% by mass. The lower limit of the content is more preferably 96% by mass, even more preferably 97% by mass, and particularly preferably 98% by mass. The upper limit of the content is more preferably 99.9% by mass, even more preferably 99.7% by mass, and particularly preferably 99.5% by mass.

[0011] 1-1. (Meth)acrylic acid nitroxide polymer (A) The polymer (A) is a polymer containing (meth)acrylic acid nitroxide units represented by the following formula (1), and, if necessary, one or more other monomer units.

[0012] In formula (1), R １ , R ２ , R ３ and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that R １ and R ２ At least one of R is an alkyl group having 1 to 6 carbon atoms, and R ３ and R ４ At least one of R represents an alkyl group having 1 to 6 carbon atoms. １ and R ２ may be bonded to each other to form a cyclic structure, and R ３ and R ４ and may be bonded to each other to form a cyclic structure. １１ represents a hydrogen atom or a methyl group; X represents a single bond or a divalent linking group; and n represents 0 or 1.

[0013] The content of (meth)acrylic acid nitroxide units in polymer (A) is not particularly limited, and is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, or may be 100% by mass. The content of other monomer units in polymer (A) (total amount when multiple types are present) is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, based on all structural units.

[0014] The method for introducing the (meth)acrylic acid nitroxide unit into the polymer (A) is not particularly limited, but for example, there is a method in which the secondary amino group of a polymer containing a secondary amino group-containing (meth)acrylate monomer unit represented by formula (2) is oxidized to form a nitroxide.

[0015] In formula (2), R １ , R ２ , R ３ and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that R １ and R ２ At least one of R is an alkyl group having 1 to 6 carbon atoms, and R ３ and R ４ At least one of R represents an alkyl group having 1 to 6 carbon atoms. １ and R ２ may be bonded to each other to form a cyclic structure, and R ３ and R ４ and may be bonded to each other to form a cyclic structure. １１ represents a hydrogen atom or a methyl group; X represents a single bond or a divalent linking group; and n represents 0 or 1.

[0016] The polymer (A) after the nitroxidation reaction may contain unreacted secondary amino group-containing (meth)acrylate monomer units. The content of secondary amino group-containing (meth)acrylate monomer units in the polymer (A) is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0017] In addition to the secondary amino group-containing (meth)acrylate monomer units, other monomer units contained in polymer (A) include alkyl methacrylate units such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate; aryl methacrylate units such as phenyl methacrylate; cycloalkyl methacrylate units such as cyclohexyl methacrylate and norbornenyl methacrylate; alkyl acrylate units such as methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate; aryl acrylate units such as phenyl acrylate; cycloalkyl acrylate units such as cyclohexyl acrylate and norbornenyl acrylate; aromatic vinyl monomer units such as styrene and α-methylstyrene; acrylamide units; methacrylamide units; vinyl cyanide monomer units such as acrylonitrile and methacrylonitrile; etc. The method for introducing the other monomer units is not particularly limited, but examples include a method in which a corresponding monomer is copolymerized during polymerization of the secondary amino group-containing (meth)acrylate monomer. Among these monomer units, from the viewpoint of thermal decomposition resistance of the methacrylic copolymer, preferred are methacrylic acid alkyl ester units, acrylic acid alkyl ester units, aromatic vinyl monomer units, and vinyl cyanide monomer units, and more preferred are methyl methacrylate, methyl acrylate, and styrene. On the other hand, in order to improve the solubility of the polymer (A) in solvents and to achieve excellent film formability, it is preferred that the polymer (A) does not have a crosslinked structure and does not contain a crosslinkable monomer unit.

[0018] The weight average molecular weight (Mw) of the polymer (A) is not particularly limited, but is preferably 1,000 to 200,000 g / mol. The lower limit of the Mw is more preferably 2,000 g / mol, even more preferably 3,000 g / mol, particularly preferably 4,000 g / mol, and most preferably 5,000 g / mol. The upper limit of the Mw is more preferably 180,000 g / mol, even more preferably 150,000 g / mol, particularly preferably 130,000 g / mol, and most preferably 100,000 g / mol. When the Mw is 1,000 g / mol or more, the electrochemical stability of the polymer (A) is improved. When the Mw is 200,000 g / mol or less, the film-forming properties of the polymer particles are improved. Mw is a value calculated by converting a chromatogram measured by gel permeation chromatography (GPC) into the molecular weight of standard polystyrene.

[0019] 1-2. Volume average particle diameter of the present polymer particles The volume average particle diameter (hereinafter also referred to as particle diameter) of the present polymer particles is 10 to 1,000 μm. The lower limit of the particle diameter is preferably 20 μm, more preferably 50 μm. The upper limit of the particle diameter is preferably 800 μm, more preferably 700 μm. By setting the particle diameter of the present polymer particles within the above range, dissolution in a solvent is facilitated, resulting in good coatability and film-forming properties of the solution. The volume average particle diameter can be determined by measuring an aqueous dispersion of (meth)acrylic acid nitroxide polymer particles or a dispersion obtained by redispersing the present polymer particles in an aqueous medium using a light scattering method.

[0020] In the present polymer particles, the proportion of particles having a volume-based particle size of 1000 μm or more is 0 to 5%. The upper limit of this proportion is preferably 4%, more preferably 3%. By setting the proportion of particles having a volume-based particle size of 1000 μm or more in the present polymer particles to fall within the above range, dissolution in a solvent becomes easier, improving the coatability and film-forming properties of the solution. This proportion can be determined by measuring an aqueous dispersion of (meth)acrylic acid nitroxide polymer particles using a light scattering method.

[0021] 1-3. Polyvinyl Alcohol-Based Polymer (B) The present polymer particles may further contain a polyvinyl alcohol-based polymer (B) (hereinafter also referred to as a PVA-based polymer (B)). The content of the PVA-based polymer (B) in the present polymer particles is preferably 0.001 to 5% by mass. The lower limit is more preferably 0.002% by mass, even more preferably 0.003% by mass, and particularly preferably 0.005% by mass. The upper limit is more preferably 4% by mass, even more preferably 3% by mass, and particularly preferably 2% by mass. When the present polymer particles contain a PVA-based polymer (B), the (meth)acrylic acid nitroxide polymer particles are easily dissolved in a solvent, improving film-forming properties. When the content is 5% by mass or less, the electrochemical properties of a member using the (meth)acrylic acid nitroxide polymer particles are improved.

[0022] The PVA polymer (B) is a polymer having vinyl alcohol units, and in some cases, a polymer having vinyl alcohol units and vinyl alcohol derivative units. The vinyl alcohol units are structural units linked at vinyl group sites and having hydroxyl groups as side chains. The derivative units are not particularly limited, but examples include (1) structural units in which the hydroxyl groups of the vinyl alcohol units are converted to acetoxy groups, and (2) structural units in which two vinyl alcohol units are acetalized. Note that the vinyl alcohol derivative units do not necessarily have to be derived from vinyl alcohol as long as the structural units can be derived from vinyl alcohol units or the derivative units can be converted to vinyl alcohol.

[0023] The PVA-based polymer (B) may be an unmodified PVA and / or a modified PVA. Here, "unmodified PVA" refers to a polymer obtained by saponifying a vinyl ester homopolymer or a polymer obtained by saponifying a copolymer of two or more vinyl esters. Furthermore, "modified PVA" refers to a PVA in which at least a portion of the molecular terminals, main chain, and side chains of the unmodified PVA are substituted (including crosslinked) with reactive groups, or a PVA obtained by saponifying a copolymer of a vinyl ester and another ethylenically unsaturated monomer, or both. Among these, unmodified PVA is preferred as the PVA-based polymer (B).

[0024] As described above, the modified PVA includes a PVA obtained by saponifying a copolymer of a vinyl ester and another ethylenically unsaturated monomer. In this case, the PVA contains at least one other ethylenically unsaturated monomer unit in addition to vinyl alcohol units. The other ethylenically unsaturated monomer is not particularly limited as long as it is copolymerizable with the vinyl ester. Examples of the other ethylenically unsaturated monomer include ethylene, α-olefins, halogen-containing monomers, carboxylic acid-containing monomers and their anhydrides or esters, (meth)acrylic acid esters, vinyl ethers, sulfonic acid group-containing monomers, amide group-containing monomers, amino group-containing monomers, quaternary ammonium base-containing monomers, silyl group-containing monomers, hydroxyl group-containing monomers, and acetyl group-containing monomers. The PVA-based polymer (B) may be used alone or in combination of two or more.

[0025] The total amount of vinyl acetate units and vinyl alcohol units in the PVA polymer (B) is preferably 95 to 100 mol %, more preferably 96 to 100 mol %, particularly preferably 97 to 100 mol %, and most preferably 98 to 100 mol %.

[0026] Use of the PVA-based polymer (B) as an additive to the aqueous medium can improve the dispersion stability of droplets containing the polymer (A) in the step a described below. Similarly, use of the PVA-based polymer (B) as an additive to the aqueous medium can improve the dispersion stability of particles of the polymer (A) in the slurry in the step b. As a result, the generation of coarse particles can be significantly reduced. Furthermore, adhesion to equipment such as a stirring tank can be relatively reduced. As a result, the productivity of the present polymer particles can be significantly improved, and high-quality polymer particles can be produced.

[0027] (Viscosity Average Degree of Polymerization) The viscosity average degree of polymerization (hereinafter also referred to as degree of polymerization) of the PVA-based polymer (B) is preferably 500 to 5,000. The lower limit of the degree of polymerization is more preferably 600, even more preferably 700, particularly preferably 1,000, and most preferably 1,500. The upper limit of the degree of polymerization is more preferably 4,000, even more preferably 3,000. By setting the degree of polymerization to 500 or more, a decrease in yield in the slurrying step described below can be suppressed. Furthermore, by setting the degree of polymerization to 5,000 or less, a decrease in the solubility of the PVA-based polymer (B) can be suppressed, resulting in excellent productivity in the slurrying step. The degree of polymerization of the PVA-based polymer (B) is a value measured by the method described in "3.7 Average Degree of Polymerization" of JIS K6726 (1994).

[0028] (Saponification degree) The saponification degree of the PVA polymer (B) is preferably 50 to 90 mol%. The lower limit of the saponification degree is more preferably 60 mol%, and even more preferably 70 mol%. The upper limit of the saponification degree is more preferably 88 mol%, and even more preferably 85 mol%. By setting the saponification degree to 50 mol% or more, the solubility in water tends to be improved, and an aqueous solution of the PVA polymer (B) tends to be easily prepared. Furthermore, by setting the saponification degree to 90 mol% or less, the yield in the slurrying step described below tends to be improved. The saponification degree of the PVA polymer (B) is a value measured by the method described in "3.5 Saponification degree" of JIS K6726 (1994).

[0029] The content of the PVA polymer (B) in the (meth)acrylic acid nitroxide polymer particles can be determined, for example, by Soxhlet extraction. Specifically, (meth)acrylic acid nitroxide polymer particles are used as a sample and extracted in a Soxhlet extractor using a solvent (e.g., water) that dissolves the PVA polymer (B) contained in the (meth)acrylic acid nitroxide polymer particles but does not substantially dissolve components other than the PVA polymer (B). The extracted solution (e.g., an aqueous solution) is then concentrated and vacuum-dried to obtain a solid mass, which is then precisely weighed. The content of the PVA polymer (B) can be determined by calculating the mass of the extracted solid mass relative to the mass of the (meth)acrylic acid nitroxide polymer particles before extraction. Note that if the (meth)acrylic acid nitroxide polymer particles contain components other than the PVA polymer (B) that are soluble in the extraction solvent (e.g., hot water), these components may be extracted in the Soxhlet extraction. In this case, the extract obtained by the Soxhlet extraction operation may be analyzed by infrared spectroscopy (IR) or the like, and the content of the PVA polymer (B) in the extract may be separately determined by taking the difference between the spectrum of the PVA polymer (B) and that of the PVA polymer (B), and the content of the PVA polymer (B) in the (meth)acrylic acid nitroxide polymer particles may then be corrected.

[0030] 2. Method for Producing (Meth)acrylic Acid Nitroxide Polymer Particles The method for producing polymer particles comprises: (1) step a) of dispersing a solution of polymer (A) dissolved in a hydrophobic organic solvent as oil droplets in an aqueous medium containing a PVA-based polymer (B); (2) after step a) step b) of removing the hydrophobic organic solvent from the oil droplets dispersed in the aqueous medium to obtain a slurry; and (3) after step b) step c) of dehydrating and drying the slurry to obtain (meth)acrylic acid nitroxide polymer particles.

[0031] The production method of the present disclosure, in which a solution of polymer (A) dissolved in a hydrophobic organic solvent is dispersed as oil droplets in an aqueous medium containing a PVA-based polymer (B) and then the hydrophobic organic solvent is removed from the oil droplets, significantly improves the dispersion stability of the droplets in the aqueous medium, thereby significantly suppressing the generation of coarse particles in the droplet formation step (b). Furthermore, the deposition of material on equipment such as a stirring tank and stirring blades in the step (b) can be significantly reduced compared to the case of an aqueous medium containing a PVA-based polymer (B). As a result, the polymer particles obtained through steps (a) to (c) are less likely to produce coarse aggregates and deposits, and are therefore highly productive.

[0032] 2-1. Step a In step a, a solution of polymer (A) dissolved in a hydrophobic organic solvent is dispersed as oil droplets in an aqueous medium containing a PVA-based polymer (B). In step a, the method for dispersing the solution as oil droplets in an aqueous medium containing a PVA-based polymer (B) is not particularly limited. However, a preferred example is a method in which a solution of polymer (A) dissolved in a hydrophobic organic solvent is prepared, an aqueous medium containing a PVA-based polymer (B) is separately prepared, and then the two solutions are mixed.

[0033] The method for preparing a solution in which the polymer (A) is dissolved in a hydrophobic organic solvent is not particularly limited, and examples thereof include a method in which a solid polymer (A) is mixed with a hydrophobic organic solvent to dissolve it, and a method in which the polymer (A) is synthesized in the presence of a hydrophobic organic solvent to obtain a solution in which the polymer (A) is dissolved in a hydrophobic organic solvent.

[0034] The hydrophobic organic solvent used in step a is not particularly limited as long as it is a solvent that is immiscible with water, and examples thereof include toluene, xylene, chloroform, methylene chloride, etc. In addition to the polymer (A), this solution may contain an additive that is soluble in the hydrophobic organic solvent used, within the scope of the present disclosure.

[0035] In preparing the aqueous medium containing the PVA-based polymer (B), the mixing temperature of the PVA-based polymer (B) and water is not particularly limited, but is preferably 40 to 120°C from the viewpoint of sufficiently dissolving the PVA-based polymer (B). The lower limit of the temperature is more preferably 45°C, and even more preferably 50°C. The upper limit of the temperature is more preferably 110°C, and even more preferably 100°C. It is preferable to thoroughly stir the PVA-based polymer (B) and water to sufficiently dissolve the PVA-based polymer (B). From this viewpoint, the stirring time is preferably 0.5 to 5 hours, more preferably 1 to 4 hours, and even more preferably 1 to 3 hours. The aqueous medium may contain additives soluble in the aqueous medium in addition to the PVA-based polymer (B), within the scope of the present disclosure.

[0036] The mass ratio (RD) of the PVA-based polymer (B) to the solution obtained by dissolving the polymer (A) in a hydrophobic organic solvent is preferably 0.01 to 5 mass%. The lower limit of the RD is more preferably 0.02 mass%, and even more preferably 0.03%. The upper limit of the RD is more preferably 4 mass%, and even more preferably 3 mass%. By setting the RD to 0.01 to 5 mass%, the suspension state becomes stable, and the generation of aggregates and deposits can be suppressed.

[0037] In the production method of the present disclosure, the ratio (RD) of the PVA-based polymer (B) to 100% by mass of a solution obtained by dissolving the polymer (A) in a hydrophobic organic solvent, the degree of polymerization (DP) of the PVA-based polymer (B), and the degree of saponification (DS) of the PVA-based polymer (B) are expressed by the following formula: RD × DP × (100 − DS). ２ The relationship RD × DP × (100 - DS) must be satisfied. ２ The ratio RD×DP×(100−DS) / 100 is 850 or more, preferably 900 or more, more preferably 950 or more, and particularly preferably 1000 or more. ２ By making the molecular weight ratio / 100 equal to or greater than 850, the suspension state can be stabilized and the occurrence of aggregates and deposits can be suppressed. There is no particular upper limit, but it is usually 600,000 or less.

[0038] The solution of the polymer (A) dissolved in the hydrophobic organic solvent can be dispersed in the aqueous medium containing the PVA polymer (B) by a common method, such as stirring using a reaction vessel equipped with a stirring blade, using an emulsifying device such as a high-pressure homogenizer, a colloid mill, an ultrasonic emulsifier, a homomixer, or a homodisper, a membrane emulsification method using a porous material such as an SPG (Shirasu Porous Glass) membrane, or an emulsification method utilizing a phase transition phenomenon such as a phase inversion emulsification method or a phase inversion temperature emulsification method.

[0039] 2-2. Step b Step b is a step of forming an aqueous slurry of particles containing polymer (A) by removing the hydrophobic organic solvent from the aqueous medium in which the oil phase (oil droplets) prepared in step a has been dispersed. In this specification, the particles obtained in step b are referred to as "particles of (meth)acrylic acid nitroxide polymer (A)" to distinguish them from (meth)acrylic acid nitroxide polymer particles containing a specific amount of PVA-based polymer obtained in step c.

[0040] The method for removing the hydrophobic organic solvent in step b is not particularly limited. For example, the suspension of step a may be heated and / or decompressed under stirring to vaporize and remove the hydrophobic organic solvent. The conditions for heating, decompression, etc. may be determined based on general knowledge, taking into account the boiling point, vapor pressure, azeotropic conditions, etc. of the hydrophobic organic solvent used.

[0041] In step b, additives other than the polymer (A) or the PVA-based polymer (B) may be added to the hydrophobic organic solvent phase or the aqueous medium phase as needed, as long as they do not deviate from the spirit of the present disclosure. Examples of such additives include antifoaming agents, thickeners, and surfactants. Examples of such antifoaming agents include mineral oil-based, oil-based, fatty acid-based, fatty acid ester-based, alcohol-based, amide-based, phosphate ester-based, metal soap-based, silicone-based, and oxyalkylene-based antifoaming agents.

[0042] The volume average particle diameter (hereinafter also referred to as particle diameter) of the polymer (A) particles in the slurry obtained in step b is not particularly limited, but is preferably 10 to 1,000 μm. The lower limit of the particle diameter is more preferably 20 μm, and even more preferably 50 μm. The upper limit of the particle diameter is more preferably 800 μm, and even more preferably 700 μm. By setting the particle diameter of the present polymer particles within the above range, the coatability of the solution is improved. The volume average particle diameter is determined by measuring the particles of polymer (A) in the slurry obtained in step b by a light scattering method. Note that the volume average particle diameter of the present polymer particles obtained in step c will be smaller than the volume average particle diameter of the polymer (A) particles in the slurry obtained in step b if the volume average particle diameter is not adjusted by filtration through a mesh or the like, but will be substantially the same if such adjustment is not performed.

[0043] The proportion of particles of polymer (A) in the slurry obtained in step b having a volume-based particle size of 1000 μm or more is preferably 0 to 5%. The upper limit of this proportion is more preferably 4%, and even more preferably 3%. By setting the proportion of particles of polymer (A) in the slurry obtained in step b having a volume-based particle size of 1000 μm or more in the above range, the coatability of the solution is improved.

[0044] 2-3. Step c Step c is a step of removing the aqueous medium from the aqueous slurry of particles containing polymer (A) prepared in step b by dehydration and drying to obtain particles containing polymer (A). The dehydration operation can be performed by a general method for solid-liquid separation. For example, solid-liquid separation can be performed by centrifugal filtration or pressure filtration. The drying operation is performed to remove water contained in the particles containing polymer (A) after the dehydration operation. The drying method is not particularly limited, and for example, water can be removed by vaporizing it by heating, reducing pressure, or both.

[0045] The present disclosure will now be described in more detail with reference to examples, but the present disclosure is not limited to these examples.

[0046] <Methods for measuring physical properties, etc.> (i) Weight-average molecular weight (Mw) A sample solution was prepared by dissolving 12 mg of a 30% by mass toluene solution of polymer (A) in 5 mL of tetrahydrofuran. The column oven temperature was set to 40°C, and 20 μL of the sample solution was injected into the apparatus at an eluent flow rate of 0.35 mL / min, and a chromatogram was measured. Ten standard polystyrenes with molecular weights in the range of 400 to 5,000,000 g / mol were subjected to GPC measurement, and a calibration curve showing the relationship between retention time and molecular weight was created. The Mw of the resin to be measured was determined based on this calibration curve. Apparatus: GPC apparatus HLC-8320 manufactured by Tosoh Corporation Separation column: TSKguard column Super HZ-H, TSKgeI HZM-M, and TSKgeI Super HZ4000 manufactured by Tosoh Corporation connected in series Eluent: tetrahydrofuran Eluent flow rate: 0.35 mL / min Column temperature: 40°C Detection method: differential refractive index (RI)

[0047] (ii) Volume-average particle size: Using the slurry obtained in step b, the volume-average particle size (median size) of the (meth)acrylic acid nitroxide polymer particles in the slurry obtained in step b was determined by a light scattering method with a laser diffraction / scattering particle size distribution analyzer LA-950V2 manufactured by Horiba, Ltd. From the obtained particle size distribution, the cumulative frequency of the (meth)acrylic acid nitroxide polymer particles in the slurry obtained in step b having a volume-based particle size of 1000 μm or more was determined.

[0048] (iii) Slurry Yield In the process of obtaining a slurry containing (meth)acrylic acid nitroxide polymer particles, deposits adhering to the stirring vessel and stirring blades were collected. The obtained slurry was filtered through a 20-mesh (0.98 mm mesh) wire netting, and the residue on the mesh was collected as coarse agglomerates. The liquid that passed through the mesh was filtered using qualitative filter paper (Advantec, No. 131), and the residue on the filter paper was collected as (meth)acrylic acid nitroxide polymer particles. The (meth)acrylic acid nitroxide polymer particles, deposits, and coarse agglomerates were each dried in a vacuum dryer at 80°C for 24 hours, and then their masses were measured to determine the yield, amount of deposits, and amount of coarse agglomerates, respectively. The slurry yield was calculated using the following formula: Slurry Yield (%) = Yield / (Yield + Amount of Deposits + Amount of Coarse Agglomerates)

[0049] (iv) Content of PVA-based polymer (B) 4.5 g of (meth)acrylic acid nitroxide polymer particles were precisely weighed and subjected to Soxhlet extraction with water (refluxing cycle: 100 times). The aqueous solution after extraction was concentrated and vacuum dried, and the resulting solid content was precisely weighed. The ratio of the mass of the extracted solid content to the mass of the (meth)acrylic acid nitroxide polymer particles was calculated and used as the content of PVA-based polymer (B).

[0050] (v) Film Formability 20 g of toluene was added to 5 g of (meth)acrylic acid nitroxide polymer particles and stirred for 30 minutes with a magnetic stirrer. The resulting solution was applied to a PET film using a stainless steel applicator with a clearance of 200 μm, and then heated and dried for 1 hour in a box dryer set at 100°C. The resulting film was peeled from the PET film and observed with an optical microscope to determine the number of defects in an area of ​​100 mm x 100 mm. The film formability was evaluated according to the following criteria: ◯: The number of defects was less than 10; ×: The number of defects was 10 or more.

[0051] <Raw Materials> The following raw materials were used in the following Examples and Comparative Examples. LA-87: "ADEKA STAB LA-87" manufactured by ADEKA CORPORATION (compound name: 2,2,6,6-tetramethyl-4-piperidyl methacrylate) Polyvinyl alcohol (B-1): polyvinyl alcohol having an average degree of polymerization of 2,600 and a degree of saponification of 80 mol% Polyvinyl alcohol (B-2): polyvinyl alcohol having an average degree of polymerization of 1,700 and a degree of saponification of 88 mol% Polyvinyl alcohol (B-3): polyvinyl alcohol having an average degree of polymerization of 500 and a degree of saponification of 98 mol% Nonionic dispersant: "EMULGEN 150" manufactured by Kao Corporation

[0052] (Production Example 1: (Meth)acrylic Acid Nitroxide Polymer (A-1)) Under a nitrogen atmosphere, 98 parts by mass of toluene, 100 parts by mass of LA-87, and 0.62 parts by mass of n-octyl mercaptan (nOM) were placed in an autoclave equipped with a stirrer and heated to 100°C to uniformly dissolve. Next, at the same temperature, a solution prepared by dissolving 0.02 parts by mass of azobisisobutyronitrile (AIBN) in 0.4 parts by mass of toluene was injected and the reaction was continued for 1 hour. Further, a solution prepared by dissolving 0.02 parts by mass of AIBN in 0.4 parts by mass of toluene was injected and the reaction was continued for 1 hour. This operation was repeated four times, and then the autoclave was cooled to room temperature to obtain a precursor polymer (AA-1) solution. The polymerization conversion rate was 93%.

[0053] Under a nitrogen atmosphere, an aqueous solution of 100 parts by mass of the precursor polymer (AA-1) solution, 57.2 parts by mass of toluene, 2.0 parts by mass of methyltri-n-octylammonium chloride, and 2.1 parts by mass of sodium tungstate dihydrate dissolved in 14.8 parts by mass of ion-exchanged water was added to a reactor equipped with a stirring blade, a cooling tube, and a dropping funnel, and the mixture was heated to 40°C with stirring. 94 parts by mass of 30% hydrogen peroxide solution was added dropwise over 3 hours, and the reaction was continued for 8 hours. The reactor was cooled to room temperature, stirring was stopped, the mixture was allowed to stand, and the lower layer of the reaction solution, which had separated into two layers, was extracted. 63 parts by mass of ion-exchanged water was added to the reactor, and after 15 minutes of stirring, stirring was stopped, the mixture was allowed to stand, and the lower layer was extracted. This water washing procedure was repeated three times or more, and after confirming with a test paper that the hydrogen peroxide concentration in the extracted lower layer (aqueous layer) was 0.2 mg / L or less, the upper layer solution was removed to obtain a 30% by mass toluene solution of (meth)acrylic acid nitroxide polymer (A-1). Mw was 22,000 g / mol.

[0054] A 30% by mass toluene solution of (meth)acrylic acid nitroxide polymer (A-2) was obtained in the same manner as in Production Example 1, except that the amount of n-octyl mercaptan used among the polymerization raw materials was 0.2 parts by mass. The Mw was 61,000 g / mol.

[0055] A 30% by mass toluene solution of (meth)acrylic acid nitroxide polymer (A-3) was obtained in the same manner as in Production Example 1, except that the amount of n-octyl mercaptan used among the polymerization raw materials was 1.8 parts by mass. The Mw was 11,000 g / mol.

[0056] Example 1 Under a nitrogen atmosphere, 200 parts by mass of ion-exchanged water and 0.3 parts by mass of polyvinyl alcohol (B-1) were added to a reactor equipped with a distillation apparatus consisting of a stirring blade, a Claisen head, and a Liebig condenser, and the mixture was heated to 60°C to achieve a uniform solution. After cooling the reactor to 30°C or below, 100 parts by mass of a 30% by mass toluene solution of (meth)acrylic acid nitroxide polymer (A-1) was added, and the mixture was stirred at 300 rpm and heated to 110°C. After confirming that toluene had ceased to be distilled from the distillation vessel, the reactor was cooled to obtain a slurry of (meth)acrylic acid nitroxide polymer (A-1) particles. The slurry was filtered using qualitative filter paper (Advantec No. 131), and the filtered powder was dried for 24 hours in a vacuum dryer set at 80°C to obtain (meth)acrylic acid nitroxide polymer (A-1) particles. The evaluation results are shown in Table 1.

[0057] Examples 2 to 9 (Meth)acrylic acid nitroxide polymer particles were obtained in the same manner as in Example 1 except for the formulation shown in Table 1. The evaluation results are shown in Table 1.

[0058] Comparative Examples 1 to 5 (Meth)acrylic acid nitroxide polymer particles were produced in the same manner as in Example 1 except for the formulations shown in Table 1. However, since a large amount of deposits and coarse aggregates were generated in the slurrying step, it was impossible to measure the volume average particle size and particle size distribution of the polymer particles. The evaluation results are shown in Table 1.

[0059] In the table, "-" means that it is not measurable, not subject to measurement, or has no unit.

[0060] As shown in Table 1, the production methods shown in Examples 1 to 9 produced small amounts of deposits and coarse aggregates in the slurrying step, had good slurry yields, and were excellent in productivity. Furthermore, the resulting (meth)acrylic acid nitroxide polymer particles contained few coarse particles, making them easy to handle. On the other hand, the production methods shown in Comparative Examples 1 to 5 produced a large amount of deposits and / or coarse aggregates in the slurrying step, reducing yields and resulting in poor productivity.

[0061] This application claims priority based on Japanese Patent Application No. 2023-136705, filed on August 25, 2023, the disclosure of which is incorporated herein in its entirety.

[0062] The (meth)acrylic acid nitroxide polymer particles of the present disclosure have a high energy density, are capable of carrying a large current, and have excellent cycle characteristics, and therefore can be used in a variety of fields, including as an active material for electrodes.

Claims

1. A method for producing (meth)acrylic acid nitroxide polymer particles, comprising: a step a) of dissolving a (meth)acrylic acid nitroxide polymer (A) (hereinafter referred to as polymer (A)) in a hydrophobic organic solvent and dispersing the resulting solution in an aqueous medium as oil droplets; a step b) of removing the hydrophobic organic solvent from the oil droplets dispersed in the aqueous medium after step a to obtain a slurry; and a step c of dehydrating and drying the slurry after step b to obtain (meth)acrylic acid nitroxide polymer particles, wherein polymer (A) has a repeating unit represented by formula (1), the aqueous medium contains a polyvinyl alcohol-based polymer (B) (hereinafter referred to as PVA-based polymer (B)), and the mass ratio (RD) of the PVA-based polymer (B) to the solution in step a, the degree of polymerization (DP) of the PVA-based polymer (B), and the degree of saponification (DS) of the PVA-based polymer (B) are expressed by the following formula: RD×DP×(100-DS) ２ / 100≧850。 / 100 ≧ 850. (In formula (1), R １ , R ２ , R ３ and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that R １ and R ２ At least one of R is an alkyl group having 1 to 6 carbon atoms, and R ３ and R ４ At least one of R is an alkyl group having 1 to 6 carbon atoms; １ and R ２ may be bonded to each other to form a cyclic structure, R ３ and R ４ may be bonded to each other to form a cyclic structure, R １１ represents a hydrogen atom or a methyl group, X represents a single bond or a divalent linking group, and n is 0 or 1.

2. A method for producing (meth)acrylic acid nitroxide polymer particles according to claim 1, wherein the ratio of particles having a volume-based particle size of 1,000 μm or more in the particle size distribution of the (meth)acrylic acid nitroxide polymer (A) particles in the slurry obtained in step b, as measured by a light scattering method, is 0 to 5%.

3. The method for producing (meth)acrylic acid nitroxide polymer particles according to claim 1, wherein the PVA-based polymer (B) has a degree of polymerization of 500 to 5,000 and a degree of saponification of 50 to 90 mol %.

4. The method for producing (meth)acrylic acid nitroxide polymer particles according to claim 1, wherein the total amount of vinyl acetate units and vinyl alcohol units in the PVA-based polymer (B) is 95 to 100 mol %.

5. (Meth)acrylic acid nitroxide polymer particles comprising a (meth)acrylic acid nitroxide polymer (A) (hereinafter referred to as polymer (A)) having a repeating unit represented by formula (1), the volume average particle diameter of the aqueous dispersion being 10 to 1,000 μm as measured by a light scattering method, and the ratio of particles having a volume-based particle diameter of 1,000 μm or more being 0 to 5%. (In the formula (1), R １ , R ２ , R ３ and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, provided that R １ and R ２ At least one of R is an alkyl group having 1 to 6 carbon atoms, and R ３ and R ４ At least one of R is an alkyl group having 1 to 6 carbon atoms; １ and R ２ may be bonded to each other to form a cyclic structure, R ３ and R ４ may be bonded to each other to form a cyclic structure, R １１ represents a hydrogen atom or a methyl group, X represents a single bond or a divalent linking group, and n is 0 or 1.

6. The (meth)acrylic acid nitroxide polymer particles according to claim 5, further comprising 0.001 to 5% by mass of a polyvinyl alcohol polymer (B) (hereinafter referred to as PVA polymer (B)).

7. The (meth)acrylic acid nitroxide polymer particles according to claim 6, wherein the total amount of vinyl acetate units and vinyl alcohol units in the PVA-based polymer (B) is 95 to 100 mol %.

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