Dry powder and method for producing the same

Abstract

To provide a dry powder having a polymer formed with an alkyl methacrylate as one of its monomers, which has a high molecular weight and low dispersion, and in particular a dry powder in which blocking between polymer particles does not occur even when the dry powder is handled in an environment above the glass transition temperature of the polymer. [Solution] The above problem is solved by a dry powder having a copolymer formed by i) methyl methacrylate (MMA) and ii) at least one alkyl methacrylate having 2 or more carbon atoms as monomers, wherein the weight-average molecular weight of the copolymer is 10,000 to 500,000 and the molecular weight distribution is less than 1.5.

Description

Technical Field

[0001] The present invention relates to a dry powder having a polymer derived from an alkyl methacrylate and a method for producing the same.

Background Art

[0002] In recent years, due to considerations for the environment such as reduction of volatile organic compounds (VOCs), polymer production processes under organic solvent-free conditions have attracted attention. Among them, polymer production in an aqueous system such as suspension polymerization, emulsion polymerization, and miniemulsion polymerization uses water as a dispersion medium, so the use of organic solvents is unnecessary or can be minimized, and a process design considering the environment is possible.

[0003] Among the above polymerization methods, suspension polymerization in particular can easily obtain a polymer as particles without performing steps such as salting out, and can be used by adding it to an arbitrary solvent or monomer during blending, so it can be developed for a wide range of applications.

[0004] In addition, since the molecular weight distribution is relatively narrow, end-modified polymers and block polymers can be synthesized, and the scope of polymer design is very wide, living radical polymerizations such as the NMP method (nitroxide-mediated radical polymerization method), ATRP method (atom transfer radical polymerization method), TERP method (radical polymerization method using an organic tellurium compound), and RAFT polymerization method (reversible addition fragmentation chain transfer polymerization method) have been conventionally studied. Among them, the RAFT polymerization method has attracted attention because it can be synthesized under mild conditions without using a metal catalyst.

[0005] Patent Document 1 discloses a method for producing a block polymer by miniemulsion polymerization using a RAFT agent. However, since the final form of the method of Patent Document 1 is an emulsion, its applications are limited. In addition, as a method for recovering as particles, coagulation using a coagulant or spray drying method is described, and risks such as complication of the production process and contamination of the coagulant are considered.

[0006] Patent Document 2 discloses a method for producing functional spherical composite fine particles by dispersion polymerization using a RAFT agent. However, the method described in Patent Document 2 requires the use of a large amount of solvent in the dispersion medium, and the treatment of the waste solvent requires a large amount of energy and cost. Furthermore, depending on the type of solvent used, there is a concern that it may remain in the resin, which could be one of the reasons for limiting its applications.

[0007] Patent Document 3 lists suspension polymerization as one method of producing acrylic resin using a RAFT agent. However, the conditions in Patent Document 3 result in severe blocking when the particles are extracted individually, making it difficult to obtain polymer particles as primary particles. This leads to reduced work efficiency due to poor handling and requires a large amount of energy to dissolve in solvents, etc. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2022-15395. [Patent Document 2] Japanese Patent Publication No. 2004-18557. [Patent Document 3] Japanese Patent Publication No. 2010-53170. [Overview of the project] [Problems that the invention aims to solve]

[0009] Therefore, the object of the present invention is to provide a dry powder having a polymer formed with an alkyl methacrylate as one of the monomers, which has a high molecular weight and low dispersion, and in particular a dry powder in which blocking between polymer particles does not occur even when the dry powder is handled in an environment above the glass transition temperature of the polymer. Furthermore, an object of the present invention is to provide a method for preparing the above-mentioned dried powder, in addition to or in addition to the above-mentioned object.

[0010] To achieve the above objective, the inventors have discovered the following invention. <1> A dry powder having a copolymer formed by i) methyl methacrylate (MMA) and ii) at least one alkyl methacrylate having 2 or more carbon atoms as monomers, wherein the weight-average molecular weight of the copolymer is 10,000 to 500,000, preferably 10,000 to 450,000, more preferably 10,000 to 430,000, most preferably 10,000 to 400,000, and the molecular weight distribution is less than 1.5, preferably less than 1.45, more preferably less than 1.4.

[0011] <2> A dry powder having a homopolymer consisting of an alkyl methacrylate monomer having 1 or more carbon atoms, preferably 1 to 12 carbon atoms, more preferably 2 to 12 carbon atoms, and most preferably 4 to 12 carbon atoms, wherein the weight-average molecular weight of the homopolymer is 10,000 to 500,000, preferably 10,000 to 490,000, more preferably 10,000 to 480,000, most preferably 10,000 to 470,000, and the molecular weight distribution is less than 1.5, preferably less than 1.45, and more preferably less than 1.4.

[0012] <3> the above <1> or <2> In this case, it is preferable that the dried powder has one, two, three, or all of the following characteristics i) to iv). i) The glass transition temperature of the copolymer or homopolymer (if it has multiple glass transition temperatures, the lowest glass transition temperature) is -40°C or higher, preferably -40 to 150°C, more preferably -40 to 120°C, and most preferably -40 to 100°C; ii) The dried powder consists substantially of primary particles, and the volume-average particle diameter of the primary particles is 10 to 300 μm, preferably 20 to 290 μm, more preferably 25 to 275 μm, and most preferably 30 to 250 μm. iii) The amount of non-volatile components in 100% by weight of the dried powder is preferably 98% by weight or more, preferably 98.5% by weight or more, more preferably 99% by weight or more, and most preferably 99.5% by weight or more. iv) The sieve residue of the copolymer or homopolymer after the blocking test is 40% or less, preferably 35% or less, more preferably 33% or less, and most preferably 30% or less.

[0013] <4> the above <1> ~ <3> In any of the above, the dried powder preferably contains a compound represented by the following general formula (I) (wherein R is a group that can react with radicals generated from a radical initiator, and Z is a group that controls the radical addition reaction). RSC(=S)-Z (I).

[0014] <5> (I) A step of dispersing a reaction mixture containing a monomer, an initiator, a dispersant, and a RAFT agent represented by general formula (I) (wherein R is a group that can react with radicals generated from the radical initiator, and Z is a group that controls the radical addition reaction) in an aqueous medium: RSC(=S)-Z (I); (II) A step of heating the reaction mixture to carry out suspension polymerization to form a slurry having polymer particles; (III) A step of washing the slurry with water and separating and recovering polymer particles by solid-liquid separation; and (IV) A step to remove moisture from the polymer particles separated in the above step; A method for preparing a dry powder having polymer particles, wherein the polymer particles have a weight-average molecular weight of 10,000 to 500,000 and a molecular weight distribution of less than 1.5.

[0015] <6> the above <5> In this, the monomer is one or more types, and it is preferable that the monomer has at least one selected from the group consisting of alkyl methacrylates having 1 or more carbon atoms, preferably 1 to 12 carbon atoms, more preferably 2 to 12 carbon atoms, and most preferably 4 to 12 carbon atoms.

[0016] <7> Step of dispersing a reaction mixture containing a first monomer, an initiator, a dispersant, and a RAFT agent represented by the general formula (I) (where R is a group reactive with a radical generated from a radical initiator, and Z is a group controlling radical addition reaction) in an aqueous medium: R-S-C(=S)-Z (I); (IIa) Step of heating the reaction mixture to perform suspension polymerization to form a first slurry having a first polymer; (IIb) Step of adding a second monomer to the first slurry, heating it, and performing suspension polymerization to form a second slurry having a second polymer; (III’) Step of subjecting the second slurry obtained in the above step to a water washing treatment, and separating and recovering particles of the second polymer by solid-liquid separation; and (IV’) Step of removing moisture from the particles of the second polymer separated in the above step; A method for preparing a dry powder having particles of a second polymer, which comprises obtaining a dry powder having particles of a second polymer with a weight average molecular weight of 10,000 to 500,000 and a molecular weight distribution of less than 1.5.

[0017] <8> In the above <7>, the first monomer is one or more kinds, and the first monomer has at least one selected from the group consisting of alkyl methacrylate esters having 1 or more carbon atoms, preferably 1 to 12 carbon atoms, more preferably 2 to 12 carbon atoms, and most preferably 4 to 12 carbon atoms, the second monomer is one or more kinds, and the second monomer is different from the first monomer (however, when the first monomer is two or more kinds, it may be the same as the two kinds), and the second monomer preferably has at least one selected from the group consisting of alkyl methacrylate esters having 1 or more carbon atoms, preferably 1 to 12 carbon atoms, more preferably 2 to 12 carbon atoms, and most preferably 4 to 12 carbon atoms.<e000088>Among two or more kinds of monomers, one kind may be methyl methacrylate (MMA).

[0018] <9> (I’) Dispersing a reaction mixture containing a first monomer, an initiator, a dispersant, and a RAFT agent represented by the general formula (I) (wherein R is a group capable of reacting with a radical generated from a radical initiator, and Z is a group for controlling radical addition reaction) in an aqueous medium: R-S-C(=S)-Z (I); (IIa) Heating the reaction mixture to conduct suspension polymerization to form a first slurry having a first polymer; (IIb) Adding a second monomer to the first slurry, heating it, and conducting suspension polymerization to form a second slurry having a second polymer; (IIc) Adding a (n + 1)-th monomer to the n-th slurry, heating it, and conducting suspension polymerization to form a (n + 1)-th slurry having a (n + 1)-th polymer; (III”) Subjecting the (n + 1)-th slurry obtained in the above step to a water washing treatment, and separating and recovering the particles of the (n + 1)-th polymer by solid-liquid separation (in this claim, n is an integer of 2 or more); and (IV”) Removing moisture from the particles of the (n + 1)-th polymer separated in the above step;​​​​​​​​​​​​​​

[0020] This application provides a dry powder having a polymer, wherein the weight-average molecular weight of the polymer is 10,000 to 500,000 and the molecular weight distribution is less than 1.5. Specifically, the present application provides a dry powder having a copolymer formed with i) methyl methacrylate (MMA) and ii) at least one alkyl methacrylate having 2 or more carbon atoms as monomers, wherein the weight-average molecular weight of the copolymer is 10,000 to 500,000, preferably 10,000 to 450,000, more preferably 10,000 to 430,000, most preferably 10,000 to 400,000, and the molecular weight distribution is less than 1.5, preferably less than 1.45, more preferably less than 1.4.

[0021] Furthermore, the present application provides a dry powder having a homopolymer composed of an alkyl methacrylate having 1 or more carbon atoms, preferably 1 to 12 carbon atoms, more preferably 2 to 12 carbon atoms, and most preferably 4 to 12 carbon atoms, wherein the weight-average molecular weight of the homopolymer is 10,000 to 500,000, preferably 10,000 to 490,000, more preferably 10,000 to 480,000, most preferably 10,000 to 470,000, and the molecular weight distribution is less than 1.5, preferably less than 1.45, and more preferably less than 1.4. Furthermore, this application provides a method for preparing the above-mentioned dried powder. The invention described in this application, namely the dried powder and the method for preparing the dried powder, will be explained in detail below.

[0022] <Dry powder> The dried powder of the present invention is a) Copolymer having a weight-average molecular weight of 10,000 to 500,000, preferably 10,000 to 450,000, more preferably 10,000 to 430,000, most preferably 10,000 to 400,000, and a molecular weight distribution of less than 1.5, preferably less than 1.45, more preferably less than 1.4; or b) Weight-average molecular weight is 10,000 to 500,000, preferably A homopolymer having a molecular weight distribution of 10,000 to 490,000, more preferably 10,000 to 480,000, most preferably 10,000 to 470,000, and less than 1.5, preferably less than 1.45, more preferably less than 1.4; It comprises.

[0023] The dried powder of the present invention preferably consists substantially of the copolymer or homopolymer alone, or consists solely of the copolymer or homopolymer. Here, "substantially consisting solely of" the copolymer or homopolymer means that the copolymer or homopolymer accounts for 90% or more, more preferably 95% by weight, of 100% by weight of the dried powder of the present invention. In the case where the dried powder consists substantially of only the copolymer or homopolymer, other components may be present as long as they do not impair the effects of the present invention. Other components may include, but are not limited to, resins, rubbers, fillers, functionalants, unavoidable impurities, etc.

[0024] The dried powder of the present invention is "dried" and preferably substantially free of solvents, and more preferably substantially free of organic solvents. Specifically, the dried powder of the present invention is iii) The amount of non-volatile components in 100% by weight of the dried powder is preferably 98% by weight or more, preferably 98.5% by weight or more, more preferably 99% by weight or more, and most preferably 99.5% by weight or more. The non-volatile components in the powder can be obtained by accurately weighing the pre-drying weight of the dried powder sample after removing the weight of the cup, drying the sample in the cup in a hot air dryer at 110°C for 2 hours, accurately weighing the post-drying weight after removing the weight of the cup, and calculating the difference in weight before and after drying as the non-volatile components.

[0025] If the dried powder of the present invention comprises a copolymer formed from two or more monomers, substantially consists solely of the copolymer, or consists solely of the copolymer, the copolymer may be a random copolymer or a block copolymer. The copolymer is formed by having i) methyl methacrylate (MMA) and ii) at least one alkyl methacrylate having 2 or more carbon atoms as monomers. ii) Examples of alkyl methacrylates having 2 or more carbon atoms include ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, and lauryl methacrylate. Of these, propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, and n-octyl methacrylate are preferred, more preferably n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, hexyl methacrylate, and 2-ethylhexyl methacrylate, and most preferably n-butyl methacrylate, hexyl methacrylate, and 2-ethylhexyl methacrylate.

[0026] If the dried powder of the present invention comprises a homopolymer formed from one monomer, substantially consists solely of the homopolymer, or consists solely of the homopolymer, the homopolymer is preferably composed of an alkyl methacrylate having 1 or more carbon atoms, preferably 1 to 12 carbon atoms, more preferably 2 to 12 carbon atoms, and most preferably 4 to 12 carbon atoms. The dried powder of the present invention may contain, for example, water in addition to homopolymers or copolymers. However, the amount of water should be 2% by weight or less, preferably 1.5% by weight or less, more preferably 1% by weight or less, and most preferably 0.5% by weight or less, based on 100% by weight of the dried powder.

[0027] The dried powder of the present invention preferably has one, two, three, or all of the following characteristics i) to iv). Note that iii) relates to the "non-volatile components" mentioned above. i) The glass transition temperature of the copolymer or homopolymer (if it has multiple glass transition temperatures, the lowest glass transition temperature) is -40°C or higher, preferably -40 to 150°C, more preferably -40 to 120°C, and most preferably -40 to 100°C.

[0028] ii) The dried powder consists substantially of primary particles, and the volume-average particle diameter of the primary particles is 10 to 300 μm, preferably 20 to 290 μm, more preferably 25 to 275 μm, and most preferably 30 to 250 μm. iii) The amount of non-volatile components in 100% by weight of the dried powder is 98% by weight or more, preferably 98.5% by weight or more, more preferably 99% by weight or more, and most preferably 99.5% by weight or more.

[0029] iv) The sieve residue of the copolymer or homopolymer after the blocking test is 40% or less, preferably 35% or less, more preferably 33% or less, and most preferably 30% or less.

[0030] Regarding item "i)" above, the glass transition temperature of a polymer can be obtained by measuring the polymer using a DSC (differential scanning calorimeter). If there are multiple glass transition temperatures, focus on the lowest glass transition temperature. It is preferable that the glass transition temperature of focus is within the above-mentioned range, i.e., -40°C or higher, preferably -40 to 150°C, more preferably -40 to 120°C, and most preferably -40 to 100°C.

[0031] The matter in item "ii)" above relates to the volume-average particle diameter of primary particles. The polymer contained in the dried powder of the present invention preferably consists substantially of primary particles. In this specification, "the polymer consists substantially of primary particles" means that the number of particles is counted and detected using a scanning electron microscope or an optical microscope, and the proportion of primary particles, i.e., the "proportion of primary particles" expressed by the following formula, is 90% or more, preferably 91% or more, more preferably 92% or more, and most preferably 93% or more. The proportion of primary particles = number of primary particles detected / total number of particles detected * 100.

[0032] Furthermore, the volume-average particle diameter of the primary particles is preferably 10 to 300 μm, more preferably 20 to 290 μm, more preferably 25 to 275 μm, and most preferably 30 to 250 μm. Here, the volume-average particle size can be obtained by measuring it using a laser diffraction particle size distribution analyzer.

[0033] The item in "iv)" above concerns the sieve residue after the blocking test. In this application, the blocking test is performed as follows. The dry polymer particles are sieved through a 1.5 mm sieve, and 10 g of the polymer particles that pass through the sieve are used. 10 g of polymer particles are placed in a constant temperature bath set to a temperature 20°C higher than the glass transition temperature of the polymer particles (the glass transition temperature is defined as above) for 2 hours, and heated or cooled. After that, the polymer particles are removed from the constant temperature bath and allowed to stand at room temperature. The sample is then placed on a 1.5 mm sieve and sieved by vibrating it back and forth in a horizontal plane at an amplitude of 70 mm and a rate of 60 reciprocations per minute for 30 seconds, and the weight x (g) of the sample remaining on the sieve is measured. Using the obtained x(g), the "sieve residue" is calculated as "10x" (%) (=x / 10 × 100).

[0034] By possessing one, two, three, or all of the above characteristics i) to iv), blocking between polymer particles does not occur during handling of the dried powder, even in environments above the glass transition temperature of the polymer contained in the dried powder, thus making it possible to provide the desired dried powder.

[0035] The dried powder of the present invention preferably contains a compound represented by the following general formula (I) (wherein R is a group that can react with radicals generated from a radical initiator, and Z is a group that controls the radical addition reaction). RSC(=S)-Z (I).

[0036] Compounds represented by general formula (I) are so-called RAFT agents (exchange chain transfer radical polymerization initiators). R and Z may be the same or different, and may include, but are not limited to, (i) a hydrogen atom, (ii) an alkyl group, allyl group, substituted alkyl group, oxyalkyl group, amino group or substituted amino group having 1 to 20 carbon atoms, or (iii) an aryl group, alkylaryl group, oxyaryl group, substituted alkylaryl group having 6 to 20 carbon atoms. Furthermore, may include, but are not limited to, alkyl groups, aryl groups, carboxyl groups, carbonyl groups, hydroxyl groups, amino groups, nitro groups, and nitrile groups as substituents.

[0037] Compounds represented by general formula (I), so-called RAFT agents, include benzyl dityl benzoate, 1-phenylethyl dithiobenzoate, 2-phenylpropane-2-yl dithiobenzoate, 1-acetoxyethyl dithiobenzoate, 1,4-bis(thiobenzoylthiomethyl)benzene, 1,2,4,5-tetra-thiobenzoylthiomethylbenzene, 1,4-bis(2-(thiobenzoylthio)propane-2-yl)benzene, 1-(4-methoxyphenyl)ethyl dithiobenzoate, benzyl dithioacetate, ethoxycarbonylmethyl dithioacetate, 2-(ethoxycarbonyl)propane-2-yl dithiobenzoate, 2-cyanopropane-2-yl dithiobenzoate, tert-butyl dithiobenzoate, 2,4,4-trimethylpentane-2-yl dithiobenzoate, and 3 or 4-vinyl Didithiobenzoate, S-benzyldiethoxyphosphenyl dithioformate, tert-butyl trithioperbenzoate, 2-phenylpropane-2-yl dithionaphthalate, 4-cyanopentanoate dithiobenzoate, dibenzyltetrathioterephthalate, dibenzyl trithiocarbonate, carboxymethyl dithiobenzoate, 1-phenylethyl dithioacetate, 2-phenylpropane-2-yl dithioacetate, 2-(ethoxycarbonyl)propane-2-yl dithioacetate, 4-cyanopentanoate dithioacetate, 1-phenylethyl N,N-diethylaminodithioformate, 2-phenylpropane-2-yl N,N-diethylaminodithioformate, 2-(ethoxycarbonyl)propane-2-yl N,N-diethylaminodithioformate, 4-cyanopentanoate N,N-Diethylaminodithioformate, O-phenyl-S-(2-phenylethane)dithiocarbonate, O-phenyl-S-(2-phenylpropane)dithiocarbonate, O-phenyl-S-(2-(ethoxycarbonyl)propane)dithiocarbonate, O-phenyl-S-(4-cyanopentanoic acid)dithiocarbonate, benzylbutyltrithiocarbonate, 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid, 2-cyano-2-propyldodecyltrithiocarbonate, dibenzyltrithiocarbonate, 2-[[(butylthio)thioxomethyl]thio]propionic acid, 2-[[(dodecylthio)thioxomethyl]thio]propionic acid, 2-[[(butylthio)thioxomethyl]thio]succinic acid, 2-[[(dodecylthio)thiox Examples include, but are not limited to, somethyl]thio]succinic acid, 2-[[(dodecylthio)thioxomethyl]thio]-2-methylpropionic acid, 2,2'-[carbonothioylbis(thio)]bis[2-methylpropionic acid], 2-amino-1-methyl-2-oxoethylbutyltrithiocarbonate, benzyl 2-[(2-hydroxyethyl)amino]-1-methyl-2-oxoethyltrithiocarbonate, 3-[[[(tert-butyl)thio]thioxomethyl]thio]propionic acid, cyanomethyldodecyltrithiocarbonate, diethylaminobenzyltrithiocarbonate, and dibutylaminobenzyltrithiocarbonate.

[0038] Of the compounds represented by general formula (I), the trithiocarbonate type is preferred over the dithio type from the viewpoint of being more stable to hydrolysis. The compound represented by general formula (I) is preferably present in an amount of 1.0% by weight or less, preferably 0.8% by weight or less, more preferably 0.5% by weight or less, and most preferably 0.2% by weight or less, per 100% by weight of the dry powder.

[0039] The dried powder of the present invention is suitable for use in sealants, ceramic binders, adhesives, and the like.

[0040] <Method for preparing dried powder> The above-mentioned dried powder can be prepared by the following method. (I) A step of dispersing a reaction mixture containing a monomer, an initiator, a dispersant, and a RAFT agent represented by general formula (I) (wherein R is a group that can react with radicals generated from the radical initiator, and Z is a group that controls the radical addition reaction) in an aqueous medium: RSC(=S)-Z (I); (II) A step of heating the reaction mixture to carry out suspension polymerization to form a slurry having polymer particles; (III) A step of washing the slurry with water and separating and recovering polymer particles by solid-liquid separation; and (IV) A step to remove moisture from the polymer particles separated in the above step; By having this, it is possible to obtain the above-mentioned dry powder, specifically a dry powder having polymer particles with a weight-average molecular weight of 10,000 to 500,000 and a molecular weight distribution of less than 1.5.

[0041] Step (I) is a step of dispersing a reaction mixture containing a monomer, an initiator, a dispersant, and a RAFT agent represented by general formula (I) in an aqueous medium. The RAFT agent represented by general formula (I) has the same definition as described above. The aqueous medium depends on the monomer used, the initiator used, the dispersant used, and the dry powder to be obtained, but water is one example, though it is not limited to these.

[0042] The initiator depends on the aqueous medium used, the monomer used, the dispersant used, and the dry powder to be obtained. Examples of organic peroxides include benzoyl peroxide (10-hour half-life temperature: 74°C), dilauroyl peroxide (10-hour half-life temperature: 62°C), t-butyl peroxybenzoate (10-hour half-life temperature: 104°C), m-toluyl peroxide, diisopropyl peroxydicarbonate (10-hour half-life temperature: 41°C), t-butyl peroxypivalate (10-hour half-life temperature: 58°C), and cumyl peroxyneodecanoate (10 Examples of such substances include, but are not limited to, t-butyl peroxy-2-ethyl hexanoate (10-hour half-life temperature: 77°C), octanoyl peroxide (10-hour half-life temperature: 62°C), decanoyl peroxide, t-butyl peroxy-2-ethyl hexanoate (10-hour half-life temperature: 72°C), t-butyl peroxyisopropyl carbonate (10-hour half-life temperature: 99°C), cumyl peroxyoctaate, etc. Examples of azo compounds include, but are not limited to, 2,2-azobisisobutyronitrile (10-hour half-life temperature: 65°C), 2,2-azobis(2,4-dimethylvaleronitrile) (10-hour half-life temperature: 51°C), and 1,1-azobis(cyclohexane-1-carbonitrile) (10-hour half-life temperature: 88°C).

[0043] The dispersant used depends on the aqueous medium, monomer, initiator, and the resulting dry powder. Examples include, but are not limited to, cellulosic water-soluble resins (e.g., methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, etc.), polyvinyl alcohol, polyacrylates, polyethylene glycol, polyvinylpyrrolidone, polyacrylamide, and tertiary phosphates.

[0044] Furthermore, a surfactant may be added to the water to stabilize the suspension. The surfactant used depends on the aqueous medium, monomer, initiator, and the dry powder to be obtained, but may be anionic surfactants, cationic surfactants, nonionic surfactants, or amphoteric surfactants, or two or more may be used.

[0045] When obtaining a homopolymer, it is preferable to use one monomer selected from the group consisting of alkyl methacrylates having 1 or more carbon atoms, preferably 1 to 12 carbon atoms, more preferably 2 to 12 carbon atoms, and most preferably 4 to 12 carbon atoms. Furthermore, when obtaining copolymers, it is preferable to use two or more monomers selected from the group consisting of alkyl methacrylates having 1 or more carbon atoms, preferably 1 to 12 carbon atoms, more preferably 2 to 12 carbon atoms, most preferably 3 to 12 carbon atoms, and even more preferably 4 to 12 carbon atoms. It is preferable that one of the two or more monomers is methyl methacrylate (MMA).

[0046] (I) Process (I) should be carried out at a temperature of 30-100°C and under normal pressure.

[0047] (II) The step involves heating the reaction mixture to carry out suspension polymerization and forming a slurry having polymer particles. The heating is not particularly limited as long as it is at a temperature at which suspension polymerization takes place. The heating depends on the aqueous medium, monomer, initiator, dispersant, etc. used in step (I), but it is preferable to heat at, for example, 30 to 100°C under atmospheric pressure. In addition, polymer particles are obtained in step (II). If one monomer is used in step (I), a homopolymer can be obtained, and if two or more monomers are used, a copolymer, particularly a random copolymer, can be obtained.

[0048] (III) The step involves washing the slurry with water and separating and recovering the polymer particles by solid-liquid separation. The washing process can be carried out by conventionally known methods. For example, it can be done by repeatedly adding water to the slurry after solid-liquid separation such as filtration or sedimentation to re-slurry it, but is not limited to this. Solid-liquid separation can be carried out by conventionally known methods. For example, polymer particles can be recovered by solid-liquid separation such as filtration or precipitation, but the method is not limited to these.

[0049] (IV) Step (IV) is a step to remove moisture from the polymer particles separated in the above step. The removal of moisture can be carried out by conventionally known methods. Examples include, but are not limited to, heat drying, vacuum drying, and airflow drying.

[0050] By going through steps (I) to (IV) above, it is possible to obtain the above-mentioned dried powder, specifically a dried powder having polymer particles with a weight-average molecular weight of 10,000 to 500,000 and a molecular weight distribution of less than 1.5.

[0051] The above-mentioned dried powder can also be prepared by the following method. (I') A step of dispersing a reaction mixture containing a first monomer, an initiator, a dispersant, and a RAFT agent represented by general formula (I) (wherein R is a group that can react with radicals generated from the radical initiator, and Z is a group that controls the radical addition reaction) in an aqueous medium: RSC(=S)-Z (I); (IIa) A step of heating the reaction mixture to carry out suspension polymerization to form a first slurry having the first polymer; (IIb) A step of adding a second monomer to the first slurry and heating it to carry out suspension polymerization to form a second slurry having a second polymer; (III') A step of washing the second slurry obtained in the above step with water and separating and recovering the particles of the second polymer by solid-liquid separation; and (IV') A step to remove moisture from the second polymer particles separated in the above step; By having this, it is possible to obtain the above-mentioned dry powder, specifically a dry powder having polymer particles with a weight-average molecular weight of 10,000 to 500,000 and a molecular weight distribution of less than 1.5. The method comprising steps (I'), (IIa), (IIb), (III'), and (IV') described above can be used in particular to form a block copolymer as a second polymer.

[0052] Step (I') is almost identical to step (I) described above, and the "aqueous medium," "initiator," "dispersant," and "RAFT agent represented by general formula (I)" have the same definitions as described above. One or more monomers can be used as the first monomer, and the monomer used in step (I) can be used as the monomer. For example, if only one monomer is used as the first monomer and only one monomer other than the first monomer is used as the second monomer, a block copolymer of the two monomers can be obtained as the second polymer.

[0053] Step (IIa) is a step in which the reaction mixture is heated to carry out suspension polymerization to form a first slurry having the first polymer. (IIb) Step (IIb) is a step in which the second monomer is added to the first slurry and heated to carry out suspension polymerization, thereby forming a second slurry having the second polymer. Steps (IIa) and (IIb) are substantially the same as step (II) described above, and the definitions of "heating" and "suspension polymerization" are as described above. By having steps (IIa) and (IIb), a block copolymer can be obtained having a block made of a first monomer and a block made of a second monomer.

[0054] Step (III') involves washing the obtained second slurry with water and separating and recovering the particles of the second polymer by solid-liquid separation. Furthermore, step (IV') is a step in which moisture is removed from the separated second polymer particles. The operations performed in steps (III') and (IV') are the same as those in steps (III) and (IV), and "washing," "solid-liquid separation," and "moisture removal" have the same definitions as those described in steps (III) and (IV).

[0055] As described above, the method comprising steps (I'), (IIa), (IIb), (III'), and (IV') can be used in particular to form a block copolymer as the second polymer.

[0056] The above-mentioned dried powder can also be prepared by the following method. The following method can be used to obtain a dry powder having a copolymer with further block portions. Specifically, in the method comprising steps (I'), (IIa), (IIb), (III'), and (IV') described above, by performing step (IIc) once or more times, a dried powder having a copolymer with further block portions can be obtained. That is, the method is (I') A step of dispersing a reaction mixture containing a first monomer, an initiator, a dispersant, and a RAFT agent represented by general formula (I) (wherein R is a group that can react with radicals generated from the radical initiator, and Z is a group that controls the radical addition reaction) in an aqueous medium: RSC(=S)-Z (I); (IIa) A step of heating the reaction mixture to carry out suspension polymerization to form a first slurry having the first polymer; (IIb) A step of adding a second monomer to the first slurry and heating it to carry out suspension polymerization to form a second slurry having a second polymer; (IIc) A step of adding the (n+1) monomer to the n slurry and heating it to carry out suspension polymerization to form a (n+1) slurry having the (n+1) polymer; (III) A step of washing the (n+1) slurry obtained in the above step with water and separating and recovering the (n+1) polymer particles by solid-liquid separation (in this claim, n is an integer of 2 or more); and (IV) A step to remove water from the (n+1)th polymer particles separated in the above step; It has.

[0057] Steps (I'), (IIa), and (IIb) are as described above. The operations performed in steps (III) and (IV) are the same as those in steps (III) and (IV), and "washing," "solid-liquid separation," and "moisture removal" have the same definitions as those described in steps (III) and (IV).

[0058] The method described above may include steps other than steps (I) to (IV), steps other than steps (I') to (IV'), and steps other than steps (I') to (IV)). Examples of such steps include, but are not limited to, treatment with acids or bases in the washing step. [Examples]

[0059] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. (Example 1) Dispersion medium D1 was prepared by dissolving 2.0 g of sodium polyacrylate and 0.2 g of polyethylene oxide in a 1 L separable flask equipped with a stirrer. Separately from the dispersion medium D1, 180.0 g of n-butyl methacrylate, 0.050 g of benzoyl peroxide (10-hour half-life temperature: 74°C), which is a radical polymerization initiator, and 0.20 g of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid as a RAFT agent were mixed to prepare the first-step monomer mixture M1-1. In addition, 20.0 g of methyl methacrylate (MMA) was used as the second monomer solution M1-2.

[0060] While stirring the dispersion medium D1 at a stirrer speed of 300 rpm, the above-mentioned first-stage monomer preparation solution M1-1 was added under a nitrogen gas stream to prepare the polymerization suspension S1. While continuing to stir, the polymerization suspension S1 was heated to 74.5°C and reacted for 16 hours to obtain slurry SL1-1 (first polymerization step). Next, the second-stage monomer solution M1-2 was added to the slurry SL1-1 obtained in the polymerization step, and the mixture was reacted at 74.5°C for 16 hours (second polymerization step) to obtain slurry SL1-2 in which particles were dispersed. After the slurry SL1-2 was cooled to room temperature, the solid-liquid separation was performed by filtration. The recovered solid was thoroughly washed with water and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles P1.

[0061] <Measurement of number-average molecular weight Mn and weight-average molecular weight Mw, and determination of dispersion ratio Mw / Mn> The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the obtained spherical resin particles P1 were measured using GPC (gel permeation chromatography). Furthermore, the dispersion ratio (Mw / Mn) was determined from the measured number-average molecular weight (Mn) and weight-average molecular weight (Mw). These values ​​are shown in Table 1.

[0062] <Measurement of volume-average particle diameter> The volume-average particle size of the obtained spherical resin particles P1 was measured using a laser diffraction particle size distribution analyzer. The result showed that the volume-average particle size of the spherical resin particles P1 was 161 μm. This value is also shown in Table 1.

[0063] <Measurement of glass transition temperature> The glass transition temperature of the obtained spherical resin particles P1 was measured using a differential scanning calorimeter (DSC). The result showed that the glass transition temperature (Tg) of the spherical resin particles P1 was 35°C. This value is also shown in Table 1.

[0064] <Measurement of sieve residue> The sieve residue of the obtained spherical resin particles P1 was measured. The "sieve residue" was obtained by heating 10g of spherical resin particles P1 that had passed through a 1.5mm sieve in a hot air dryer set to a temperature 20°C higher than the glass transition temperature of P1, specifically 55°C (=35°C (Tg of P1) + 20°C) for 2 hours, then removing it from the dryer, cooling it to room temperature, placing the sample on a 1.5mm sieve, and sieving it by vibrating it back and forth in a horizontal plane for 30 seconds at a rate of 60 reciprocations per minute with an amplitude of 70mm, measuring the weight x (g) of the sample remaining on the sieve, and calculating "x / 10 × 100 = 10x" (%). The sieve residue of spherical resin particles P1 was "0"%. This value is also shown in Table 1.

[0065] <Measurement of solvent content in powder consisting of spherical resin particles> The amount of solvent contained in the powder consisting of the obtained spherical resin particles P1 was measured. The measurement was performed by gas chromatography (GC). As a result, no solvent was detected in the spherical resin particles P1, indicating that almost no solvent remained.

[0066] <Properties of spherical resin particles in powder> When the properties of spherical resin particles P1 in the powder were observed using a scanning electron microscope, it was found that the proportion of primary particles was 99%. This result is recorded as "Primary Particles" in the "Powder Properties" column of Table 1.

[0067] (Example 2) Dispersion medium D2 was prepared by dissolving 550g of water in a 1L separable flask equipped with a stirrer, and 5.5g of hydroxypropyl cellulose and 0.3g of sodium di-2-ethylhexyl sulfosuccinate in it. Separately from the dispersion medium D2, 100.0 g of n-butyl methacrylate (n-BMA), 0.050 g of benzoyl peroxide (10-hour half-life temperature: 74°C), which is a radical polymerization initiator, and 0.20 g of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid as a RAFT agent were mixed to prepare the first-step monomer preparation solution M2-1. Additionally, 100.0g of MMA was used as the second stage monomer solution M2-2.

[0068] While stirring the dispersion medium D2 at a stirrer speed of 350 rpm, the above-mentioned first-stage monomer preparation solution M2-1 was added under a nitrogen gas stream to prepare the polymerization suspension S2. While continuing to stir, the polymerization suspension S2 was heated to 74.5°C and reacted for 16 hours to obtain slurry SL2-1 (first polymerization step). Next, the second-stage monomer solution M2-2 was added to the slurry SL2-1 obtained in the polymerization step, and the mixture was reacted at 74.5°C for 16 hours (second polymerization step) to obtain slurry SL2-2 in which particles were dispersed. After the slurry SL2-2 was cooled to room temperature, the solid-liquid was separated by filtration, the recovered solid was thoroughly washed with water, and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles P2.

[0069] For the spherical resin particles P2, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle diameter, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of spherical resin particles P2, and powder properties were measured in the same manner as in Example 1. The results are shown in Table 1. The measurement of powder properties revealed that the proportion of primary particles was 99%, and this is indicated as "Primary particles" in the "Powder Properties" column of Table 1.

[0070] (Example 3) Dispersion medium D3 was prepared by dissolving 3.0 g of sodium polyacrylate, 0.2 g of polyethylene oxide, and 0.1 g of polyoxyethylene lauryl ether in a 1 L separable flask equipped with a stirrer. Separately from the dispersion medium D3, monomer mixture M3 was prepared by mixing 20.0 g of MMA, 180.0 g of n-BMA, 0.050 g of benzoyl peroxide (10-hour half-life temperature: 74°C), which is a radical polymerization initiator, and 0.20 g of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid as a RAFT agent.

[0071] The above-mentioned monomer preparation solution M3 was added to the dispersion medium D3 while stirring with a stirrer at a rotation speed of 300 rpm under a nitrogen gas stream to prepare the polymerization suspension S3. While continuing to stir, the polymerization suspension S3 was heated to 74.5°C and reacted for 16 hours to obtain slurry SL3. After the slurry SL3 was cooled to room temperature, the solid-liquid separation was performed by filtration. The recovered solid was thoroughly washed with water, and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles P3.

[0072] For the spherical resin particles P3, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle size, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of spherical resin particles P3, and powder properties were measured in the same manner as in Examples 1 and 2. The results are shown in Table 1. The measurement of powder properties revealed that the proportion of primary particles was 98%, and this is indicated as "Primary particles" in the "Powder Properties" column of Table 1.

[0073] (Example 4) Dispersion medium D4 was prepared by dissolving 2.0 g of sodium polyacrylate and 0.2 g of polyethylene oxide in a 1 L separable flask equipped with a stirrer, which contained 550 g of water. Separately from the dispersion medium D4, monomer preparation solution M4 was prepared by mixing 180.0 g of MMA, 20.0 g of lauryl methacrylate (LMA), 0.20 g of benzoyl peroxide (10-hour half-life temperature: 74°C), which is a radical polymerization initiator, and 0.60 g of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid as a RAFT agent.

[0074] While stirring the above dispersion medium D4 at a stirrer speed of 300 rpm, the above monomer preparation solution M4 was added under a nitrogen gas stream to prepare the polymerization suspension S4. While continuing to stir, the polymerization suspension S4 was heated to 74.5°C and reacted for 16 hours to obtain slurry SL4. After the slurry SL4 was cooled to room temperature, the solid-liquid was separated by filtration, the recovered solid was thoroughly washed with water, and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles P4.

[0075] For the spherical resin particles P4, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle diameter, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of spherical resin particles P4, and powder properties were measured in the same manner as in Examples 1 to 3. The results are shown in Table 1. The measurement of powder properties revealed that the proportion of primary particles was 98%, and this is indicated as "Primary particles" in the "Powder Properties" column of Table 1.

[0076] (Example 5) Dispersion medium D5 was prepared by dissolving 2.5 g of sodium polyacrylate, 0.2 g of polyethylene oxide, and 0.1 g of lauryl betaine in a 1 L separable flask equipped with a stirrer. Separately from the dispersion medium D5, monomer preparation solution M5 was prepared by mixing 230.0 g of n-BMA, 0.6 g of benzoyl peroxide (10-hour half-life temperature: 74°C), which is a radical polymerization initiator, and 0.20 g of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid as a RAFT agent.

[0077] The above-mentioned dispersion medium D5 was stirred at a stirrer speed of 300 rpm, and the above-mentioned monomer preparation solution M5 was added under a nitrogen gas stream to prepare the polymerization suspension S5. While continuing to stir, the polymerization suspension S5 was heated to 74.5°C and reacted for 16 hours to obtain slurry SL5. After the slurry SL5 was cooled to room temperature, the solid-liquid separation was performed by filtration. The recovered solid was thoroughly washed with water and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles P5.

[0078] For the spherical resin particles P5, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle diameter, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of spherical resin particles P5, and powder properties were measured in the same manner as in Examples 1 to 4. The results are shown in Table 1. The measurement of powder properties revealed that the proportion of primary particles was 94%, and this is indicated as "Primary particles" in the "Powder Properties" column of Table 1.

[0079] (Example 6) Dispersion medium D6 was prepared by dissolving 1.5 g of sodium polyacrylate, 0.2 g of polyethylene oxide, and 0.1 g of lauryltrimethylammonium chloride in a 1 L separable flask equipped with a stirrer. Separately from the dispersion medium D6, monomer preparation solution M6 was prepared by mixing 200.0 g of n-BMA, 0.05 g of benzoyl peroxide (10-hour half-life temperature: 74°C), which is a radical polymerization initiator, and 0.1 g of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid as a RAFT agent.

[0080] The above-mentioned monomer preparation solution M6 was added to the dispersion medium D6 while stirring with a stirrer at a rotation speed of 300 rpm under a nitrogen gas stream to prepare the polymerization suspension S6. While continuing to stir, the polymerization suspension S6 was heated to 74.5°C and reacted for 16 hours to obtain slurry SL6. After the slurry SL6 was cooled to room temperature, the solid-liquid separation was performed by filtration, the recovered solid was thoroughly washed with water, and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles P6.

[0081] For the spherical resin particles P6, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle diameter, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of spherical resin particles P6, and powder properties were measured in the same manner as in Examples 1 to 5. The results are shown in Table 1. The measurement of powder properties revealed that the proportion of primary particles was 93%, and this is indicated as "Primary particles" in the "Powder Properties" column of Table 1.

[0082] (Example 7) Dispersion medium D7 was prepared by dissolving 2.0 g of sodium polyacrylate (Alonbis MX, manufactured by Toagosei Co., Ltd.) and 0.2 g of polyethylene oxide (Alcox E-75, manufactured by Meisei Chemical Industry Co., Ltd.) in a 1 L separable flask equipped with a stirrer. Separately from the dispersion medium D7, monomer preparation solution M7 was prepared by mixing 100 g of MMA, 1.0 g of benzoyl peroxide (half-life temperature: 74°C), which is a radical polymerization initiator, and 3.0 g of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid as a RAFT agent.

[0083] The above-mentioned monomer preparation solution M7 was added to the dispersion medium D7 while stirring with a stirrer at a rotation speed of 300 rpm under a nitrogen gas stream to prepare the polymerization suspension S7. While continuing to stir, the polymerization suspension S7 was heated to 74.5°C and reacted for 16 hours to obtain slurry SL7. After the slurry SL7 was cooled to room temperature, the solid-liquid separation was performed by filtration. The recovered solid was thoroughly washed with water and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles P7.

[0084] For the spherical resin particles P7, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle diameter, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of spherical resin particles P7, and powder properties were measured in the same manner as in Examples 1 to 6. The results are shown in Table 1. The measurement of powder properties revealed that the proportion of primary particles was 98%, and this is indicated as "Primary particles" in the "Powder Properties" column of Table 1.

[0085] (Example 8) Dispersion medium D8 was prepared by dissolving 2.0 g of sodium polyacrylate and 0.2 g of polyethylene oxide (Alcox E-75, manufactured by Meisei Chemical Industry Co., Ltd.) in a 1 L separable flask equipped with a stirrer. Separately from the dispersion medium D8, monomer preparation solution M8 was prepared by mixing 200.0 g of n-BMA, 0.20 g of benzoyl peroxide (10-hour half-life temperature: 74°C), which is a radical polymerization initiator, and 0.60 g of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid as a RAFT agent.

[0086] The above-mentioned monomer preparation solution M8 was added to the dispersion medium D8 while stirring with a stirrer at a rotation speed of 300 rpm under a nitrogen gas stream to prepare the polymerization suspension S8. While continuing to stir, the polymerization suspension S8 was heated to 74.5°C and reacted for 16 hours to obtain slurry SL8. After the slurry SL8 was cooled to room temperature, the solid-liquid was separated by filtration, the recovered solid was thoroughly washed with water, and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles P8.

[0087] For the spherical resin particles P8, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle diameter, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of spherical resin particles P8, and powder properties were measured in the same manner as in Examples 1 to 7. The results are shown in Table 1. The measurement of powder properties revealed that the proportion of primary particles was 93%, and this is indicated as "Primary particles" in the "Powder Properties" column of Table 1.

[0088] (Example 9) Dispersion medium D9 was prepared by dissolving 2.0 g of sodium polyacrylate and 0.2 g of polyethylene oxide in a 1 L separable flask equipped with a stirrer, which contained 550 g of water. Separately from the dispersion medium D9, 20.0 g of 2-ethylhexyl methacrylate (2-EHMA), 0.050 g of benzoyl peroxide (10-hour half-life temperature: 74°C), a radical polymerization initiator, and 0.20 g of 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid as a RAFT agent were mixed to prepare the first-step monomer mixture M9-1. Furthermore, 180.0g of MMA was used as the second stage monomer solution M9-2.

[0089] While stirring the dispersion medium D9 at a stirrer speed of 300 rpm, the above-mentioned first-stage monomer preparation solution M9-1 was added under a nitrogen gas stream to prepare the polymerization suspension S9. While continuing to stir, the polymerization suspension S9 was heated to 74.5°C and reacted for 16 hours to obtain slurry SL9-1 (first polymerization step). Next, the second-stage monomer solution M9-2 was added to the slurry SL9-1 obtained in the polymerization step, and the mixture was reacted at 74.5°C for 16 hours (second polymerization step) to obtain slurry SL9-2 in which particles were dispersed. After cooling the slurry SL9-2 to room temperature, the solid-liquid separation was performed by filtration. The recovered solid was thoroughly washed with water and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles P9.

[0090] For the spherical resin particles CP9, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle diameter, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of resin particles P9, and powder properties were measured in the same manner as in Examples 1 to 8. The results are shown in Table 1. The measurement of powder properties revealed that the proportion of primary particles was 97%, and this is indicated as "Primary particles" in the "Powder Properties" column of Table 1.

[0091] (Comparative Example 1) 550 g of water was placed in a 1 L separable flask equipped with a stirrer, and 2.0 g of sodium polyacrylate and 0.2 g of polyethylene oxide were dissolved in it to prepare dispersion medium CD1. Separately from the dispersion medium CD1, monomer preparation solution CM1 was prepared by mixing 20.0 g of MMA, 180.0 g of n-BMA, 2.0 g of benzoyl peroxide (10-hour half-life temperature: 74°C), a radical polymerization initiator, and 0.1 g of n-dodecyl mercaptan as a chain transfer agent.

[0092] The above dispersion medium CD1 was stirred at a stirrer speed of 300 rpm, and the monomer preparation liquid CM1 was added under a nitrogen gas stream to prepare the polymerization suspension CS1. While continuing to stir, the polymerization suspension CS1 was heated to 74.5°C and reacted for 4 hours to obtain slurry CSL1. After the slurry CSL1 was cooled to room temperature, the solid-liquid was separated by filtration, the recovered solid was thoroughly washed with water, and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles CP1.

[0093] For the spherical resin particles CP1, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle size, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of resin particles CP1, and powder properties were measured in the same manner as in Examples 1 to 9 and Comparative Example 1. The results are shown in Table 1.

[0094] (Comparative Example 2) Dispersion medium CD1 was prepared in the same manner as in Comparative Example 1. Separately from the dispersion medium CD1, monomer preparation solution CM2 was prepared by mixing 200 g of n-BMA, 2.0 g of benzoyl peroxide (10-hour half-life temperature: 74°C), a radical polymerization initiator, and 0.1 g of n-dodecyl mercaptan as a chain transfer agent.

[0095] The above-mentioned monomer preparation solution CM2 was added to the dispersion medium CD1 while stirring with a stirrer at a rotation speed of 300 rpm under a nitrogen gas stream to prepare the polymerization suspension CS2. While continuing to stir, the polymerization suspension CS2 was heated to 74.5°C and reacted for 4 hours to obtain slurry CSL2. After the slurry CSL2 was cooled to room temperature, the solid-liquid was separated by filtration, the recovered solid was thoroughly washed with water, and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles CP2.

[0096] For the spherical resin particles CP2, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle size, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of resin particles CP2, and powder properties were measured in the same manner as in Examples 1 to 9 and Comparative Example 1. The results are shown in Table 1.

[0097] (Comparative Example 3) Dispersion medium CD1 was prepared in the same manner as in Comparative Example 1 and Comparative Example 2. Separately from the dispersion medium CD1, monomer mixture CM3 was prepared by mixing 180 g of MMA, 2.0 g of benzoyl peroxide (half-life temperature: 74°C), a radical polymerization initiator, and 0.2 g of n-dodecyl mercaptan, a chain transfer agent.

[0098] The above-mentioned monomer preparation solution CM3 was added to the dispersion medium CD1 while stirring with a stirrer at a rotation speed of 300 rpm under a nitrogen gas stream to prepare the polymerization suspension CS3. While continuing to stir, the polymerization suspension CS3 was heated to 74.5°C and reacted for 4 hours to obtain slurry CSL3. After the slurry CSL3 was cooled to room temperature, the solid-liquid separation was performed by filtration. The recovered solid was thoroughly washed with water and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles CP3.

[0099] For the spherical resin particles CP3, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle size, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of resin particles CP3, and powder properties were measured in the same manner as in Examples 1-9, Comparative Examples 1 and 2. The results are shown in Table 1.

[0100] (Comparative Example 4) 550 g of water was placed in a 1 L separable flask equipped with a stirrer, and 1.0 g of sodium polyacrylate and 0.1 g of polyethylene oxide were dissolved in it to prepare the dispersion medium CD4. Separately from the dispersion medium CD4, monomer preparation solution CM4 was prepared by mixing 180.0 g of n-BMA, 1.5 g of benzoyl peroxide (half-life temperature: 74°C), a radical polymerization initiator, and 0.2 g of n-dodecyl mercaptan, a chain transfer agent.

[0101] The above-mentioned monomer preparation solution CM4 was added to the dispersion medium CD4 while stirring with a stirrer at a rotation speed of 200 rpm under a nitrogen gas stream to prepare the polymerization suspension CS4. While continuing to stir, the polymerization suspension CS4 was heated to 74.5°C and reacted for 4 hours to obtain slurry CSL4. After the slurry CSL4 was cooled to room temperature, the solid-liquid was separated by filtration, the recovered solid was thoroughly washed with water, and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles CP4.

[0102] For the spherical resin particles CP4, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle diameter, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of resin particles CP4, and powder properties were measured in the same manner as in Examples 1-9 and Comparative Examples 1-3. The results are shown in Table 1.

[0103] (Comparative Example 5) 550 g of water was placed in a 1 L separable flask equipped with a stirrer, and 5.5 g of hydroxypropyl cellulose and 1.0 g of sodium di-2-ethylhexyl sulfosuccinate were dissolved in it to prepare the dispersion medium CD5. Separately from the dispersion medium CD5, 200.0 g of MMA, 0.050 g of benzoyl peroxide (10-hour half-life temperature: 74°C), a radical polymerization initiator, and 0.20 g of Rtt-050 as a RAFT agent were mixed to prepare the first-step monomer preparation solution CM5.

[0104] While stirring the above dispersion medium CD5 at a stirrer speed of 500 rpm, the above first-stage monomer preparation solution CM5 was added under a nitrogen gas stream to prepare the polymerization suspension CS5. While continuing to stir, the polymerization suspension CS5 was heated to 74.5°C and reacted for 16 hours to obtain a slurry CSL5 in which particles were dispersed. After the slurry CSL5 was cooled to room temperature, the solid-liquid separation was performed by filtration. The recovered solid was thoroughly washed with water and then dried at 35°C for 20 hours to obtain a powder consisting of spherical resin particles CP5.

[0105] For the spherical resin particles CP5, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle size, glass transition temperature, sieve residue, amount of solvent contained in the powder consisting of resin particles CP5, and powder properties were measured in the same manner as in Examples 1-9 and Comparative Examples 1-4. The results are shown in Table 1.

[0106] (Comparative Example 6) Dispersion medium CD1 was prepared by dissolving 3.4 g of sodium di-2-ethylhexyl sulfosuccinate in a 1 L separable flask equipped with a stirrer, which contained 600 g of water. Separately from the dispersion medium CD6, monomer mixture CM6 was prepared by mixing 205 g of MMA methyl methacrylate and 0.20 g of n-dodecyl mercaptan as a chain transfer agent.

[0107] The above-mentioned dispersion medium CD1 was stirred at a stirrer speed of 300 rpm, and the monomer preparation liquid CM6 was added under a nitrogen gas stream to prepare crude emulsion CE6-1. While continuing to stir, the crude emulsion CE6-1 was heated to 70°C, and after 1 hour, 0.05 g of ammonium sulfate was added as a polymerization initiator. The mixture was then reacted for 4 hours to obtain emulsion CE6-2, in which particles composed of the above monomers were dispersed. 500 g of the emulsion CE6-2, cooled to room temperature, was added dropwise to an aqueous solution prepared by dissolving 10 g of calcium chloride in 990 g of water. The polymer was recovered as a salting-out precipitate and dried at 35°C for 20 hours to obtain resin particles CP6 as aggregates.

[0108] For resin particles CP6, the number-average molecular weight Mn, weight-average molecular weight Mw, dispersion degree Mw / Mn, volume-average particle size, glass transition temperature, sieve residue, amount of solvent contained in aggregates of resin particles CP1, and powder properties were measured in the same manner as in Examples 1-9 and Comparative Examples 1-5. The results are shown in Table 1. The measurement of powder properties showed that the proportion of primary particles was 1%, and this was indicated as "secondary particles" in the "Powder Properties" column of Table 1.

[0109] [Table 1]

[0110] From the above description and Table 1, it was found that each of the spherical resin particles P1 to P9 obtained in Examples 1 to 9 is a dry powder of a polymer derived from alkyl methacrylate, and that the polymer has a high molecular weight and low dispersion, and is a dry powder that does not cause blocking between particles. On the other hand, the powders consisting of spherical resin particles CP1 to CP6 obtained in Comparative Examples 1 to 6 were polydispersible and were not the desired powders. Furthermore, each of the powders consisting of CP1 to CP6 obtained in Comparative Examples 1 to 6 had a large "sieve residue" and were not the desired dry powders that did not exhibit interparticle blocking.

Claims

1. A dry powder having a copolymer formed by i) methyl methacrylate (MMA) as a monomer; and ii) an alkyl methacrylate, wherein at least one alkyl methacrylate has two or more carbon atoms in the alkyl group of the alkyl methacrylate; wherein the weight-average molecular weight of the copolymer is 10,000 to 500,000 and the molecular weight distribution is less than 1.5, and the sieve residue of the copolymer after a blocking test is 40% or less.

2. A dry powder having a homopolymer composed of an alkyl methacrylate monomer, wherein the alkyl group of the alkyl methacrylate has one or more carbon atoms, the weight-average molecular weight of the homopolymer is 10,000 to 500,000 and the molecular weight distribution is less than 1.5, and the sieve residue of the homopolymer after a blocking test is 40% or less.

3. The dried powder according to claim 1 or 2, having one, two, or all of the following characteristics i) to iii): i) The glass transition temperature of the copolymer or homopolymer (or the lowest glass transition temperature if it has multiple glass transition temperatures) is -40°C or higher; ii) The dried powder consists substantially only of primary particles, and the volume-average particle diameter of the primary particles is 10 to 300 μm. iii) The amount of non-volatile components is 98% by weight or more of 100% by weight of the dried powder.

4. A dry powder according to claim 1 or 2, having a compound represented by the following general formula (I) (wherein R is a group that can react with radicals generated from a radical initiator, and Z is a group that controls the radical addition reaction): R-S-C(=S)-Z (I).

5. (I) A step of dispersing a reaction mixture containing a monomer, an initiator, a dispersant, and a RAFT agent represented by general formula (I) (wherein R is a group that can react with radicals generated from the radical initiator, and Z is a group that controls the radical addition reaction) in an aqueous medium: R-S-C(=S)-Z (I); (II) A step of heating the reaction mixture to carry out suspension polymerization and forming a slurry having polymer particles; (III) A step of washing the slurry obtained in the above step with water and separating and recovering polymer particles by solid-liquid separation; and (IV) A step to remove moisture from the polymer particles separated in the above step; A method for preparing a dry powder containing polymer particles, wherein the polymer particles have a weight-average molecular weight of 10,000 to 500,000 and a molecular weight distribution of less than 1.5, and the sieve residue after a blocking test of the polymer particles is 40% or less.

6. The method according to claim 5, wherein the monomer is one or more types, and the monomer is an alkyl methacrylate, and at least one selected from the group consisting of alkyl methacrylates with one or more carbon atoms in the alkyl group of the alkyl methacrylate.

7. (I') A step of dispersing a reaction mixture containing a first monomer, an initiator, a dispersant, and a RAFT agent represented by general formula (I) (wherein R is a group that can react with radicals generated from the radical initiator, and Z is a group that controls the radical addition reaction) in an aqueous medium: R-S-C(=S)-Z (I); (IIa) A step of heating the reaction mixture to carry out suspension polymerization to form a first slurry having the first polymer; (IIb) A step of adding a second monomer to the first slurry and heating it to carry out suspension polymerization to form a second slurry having a second polymer; (III') A step of washing the second slurry obtained in the above step with water and separating and recovering the particles of the second polymer by solid-liquid separation; and (IV') A step of removing water from the second polymer particles separated in the above step; A method for preparing a dry powder having a second polymer particle, wherein the second polymer particle has a weight-average molecular weight of 10,000 to 500,000 and a molecular weight distribution of less than 1.5, and the sieve residue after a blocking test of the second polymer particle is 40% or less.

8. The first monomer is one or more types, and the first monomer is an alkyl methacrylate, and at least one is selected from the group consisting of alkyl methacrylates with one or more carbon atoms in the alkyl group of the alkyl methacrylate. The method according to claim 7, wherein the second monomer is one or more types, and the second monomer is different from the first monomer (however, if there are two or more first monomers, the second monomer may be the same as the two first monomers), and the second monomer has at least one selected from the group consisting of alkyl methacrylate esters, wherein the alkyl group of the alkyl methacrylate ester has 1 or more carbon atoms.

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