Method for producing polymer particles

Abstract

To provide a method for producing polymer particles that enables production of a polymer having a narrow molecular weight distribution, even when the polymerization using a RAFT agent is conducted through miniemulsion polymerization without high-shear processing and without addition of an emulsification aid.SOLUTION: The present disclosure provides a method for producing polymer particles, comprising a polymerization step of dispersing a solution containing a radical-polymerizable monomer and an RAFT agent in an aqueous solution containing an emulsifier to prepare a miniemulsion, and subjecting the radical-polymerizable monomer to miniemulsion polymerization, wherein the amount of the RAFT agent is 0.20 mol or more relative to 100 mol of the total amount of the radical-polymerizable monomer, and the amount of the emulsifier is from 2.20 mol to 10.00 mol relative to 100 mol of the total amount of the radical-polymerizable monomer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing polymer particles. [Background technology]

[0002] Living radical polymerization is a well-known precision polymerization method that allows for control of the degree of polymerization of polymers and the arrangement of monomers in the molecular chain. Examples of living radical polymerization include nitroxide polymerization (NMP method), atom transfer radical polymerization (ATRP method), and reversible addition-fragmentation chain transfer (RAFT) polymerization.

[0003] RAFT polymerization is characterized by its high oxygen resistance and the absence of the need for metal catalysts. In RAFT polymerization, a chain transfer agent (also known as a RAFT agent) with a specific functional group, such as a thiocarbonylthio group, is used. Polymerization proceeds through a chain reaction with monomers, with repeated exchange of active radicals between the growing end of the polymerization and the specific functional group, such as a thiocarbonylthio group, of the chain transfer agent. Because of these characteristics, RAFT polymerization has attracted attention as a method for industrially utilizing living radical polymerization.

[0004] In recent years, in consideration of environmental issues, the application of living radical polymerization to emulsion polymerization, mini-emulsion polymerization, and suspension polymerization, which can reduce the use of volatile organic compounds such as organic solvents, has been studied (e.g., Patent Document 1, Patent Document 2, etc.). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 022227 [Patent Document 2] Japanese Patent Publication No. 2022-015395 Summary of the Invention [Problem to be solved by the invention]

[0006] Miniemulsion polymerization typically involves adding a hydrophobic monomer to an aqueous solution, stirring the resulting emulsion, and then applying strong shear forces, such as ultrasonic waves, to break down the monomer oil droplets (dispersed phase) to form a miniemulsion containing a fine dispersed phase (e.g., 500 nm or less). Because the dispersed phase is so fine in miniemulsions, even when the conditions for applying high shear forces are adjusted to achieve uniform dispersed particle size, slight differences in particle size remain between dispersed phase particles. This can lead to Ostwald ripening, in which the fine dispersed phase particles are absorbed by the relatively large dispersed phase and disappear. This can result in a broadening or coarsening of the particle size distribution of the dispersed phase. To mitigate this Ostwald ripening, highly hydrophobic compounds, such as hexadecane, are added as emulsifiers to stabilize the dispersed phase. Since emulsifiers are generally dissolved in the monomer oil droplets, when the dispersed particles begin to coarsen due to Ostwald ripening, the emulsifier concentration in the coarse particles becomes relatively diluted, resulting in an imbalance in the emulsifier concentration between the dispersed phases, and an equilibrium pressure is generated to restore the original equilibrium state. This counters Ostwald ripening and stabilizes the dispersed phase. However, it is not easy to increase the size of the equipment that applies strong shear force, and depending on the application of the polymer particles prepared by miniemulsion polymerization, it may be desirable to avoid the contamination of components such as hexadecane. Therefore, there is room for improvement when considering industrial-scale use.

[0007] Furthermore, it is not easy to convert the dispersed phase into a uniform miniemulsion without applying strong shear, and when polymerization is carried out without adding an emulsifying aid, the molecular weight distribution of the resulting polymer tends to increase, reflecting variations in the particle size of the dispersed phase, and the characteristics of living radical polymerization cannot be utilized.

[0008] An object of the present disclosure is to provide a method for producing polymer particles that can produce a polymer with a narrow molecular weight distribution when polymerization using a RAFT agent is carried out by miniemulsion polymerization, even when high shear treatment and the addition of an emulsifying aid are not performed. [Means for solving the problem]

[0009] The present inventors have conducted research and found that by adjusting the amounts of the RAFT agent and the emulsifier, it is possible to form a miniemulsion of the dispersed phase even under normal stirring conditions, and that a polymer with a narrow molecular weight dispersity can be produced by miniemulsion polymerization. The present disclosure is based on these findings.

[0010] This disclosure provides the following [1].

[0011] a polymerization step of dispersing a solution containing a radical polymerizable monomer and a RAFT agent in an aqueous solution containing an emulsifier to prepare a mini-emulsion, and then mini-emulsion polymerizing the radical polymerizable monomer; the amount of the RAFT agent is 0.20 mol or more relative to 100 mol of the total amount of the radical polymerizable monomers; The method for producing polymer particles, wherein the amount of the emulsifier is 2.20 to 10.00 mol per 100 mol of the total amount of the radical polymerizable monomers.

[0012] In the above-mentioned method for producing polymer particles, the amount of the RAFT agent and the amount of the emulsifier are adjusted to predetermined amounts relative to the radical polymerizable monomer, and therefore, even without high shear treatment or addition of an emulsifying aid, the dispersed phase can be mini-emulsified to obtain polymer particles with a small molecular weight dispersity.

[0013] The above [1] may be the following [2] to

[10] . [2] The partition coefficient LogP of the RAFT agent ow The manufacturing method according to [1], wherein the value is 3.50 or more. [3] The manufacturing method according to [1] or [2], wherein the polymerization step is carried out under conditions adjusted so that the particle size of the dispersed phase is 500 nm or less when the cumulative value from small particle sizes reaches 50% of the total in the scattering intensity-based cumulative particle size distribution obtained by dynamic light scattering of the mini-emulsion. [4] The manufacturing method according to any one of [1] to [3], wherein the polymerization step is carried out in a state where the distribution of the dispersed phase is adjusted so that the value of (D90-D10) / D50 is 1.00 or less, where D10, D50, and D90 are the particle sizes of the dispersed phase when the integrated values ​​from small particle sizes reach 10%, 50%, and 90% of the total, respectively, in a scattering intensity-based cumulative particle size distribution obtained by a dynamic light scattering method for the mini-emulsion. [5] The production method according to any one of [1] to [4], wherein in the polymerization step, the cumulative particle size distribution based on scattering intensity obtained by dynamic light scattering for the mini-emulsion is unimodal. [6] The manufacturing method according to any one of [1] to [5], wherein the emulsifier comprises at least one selected from the group consisting of anionic surfactants, nonionic surfactants, and amphoteric surfactants. [7] The method according to any one of [1] to [6], wherein the amount of the RAFT agent is 2.00 mol or less per 100 mol of the total amount of the radical polymerizable monomers. [8] The method according to any one of [1] to [7], wherein the RAFT agent is a trithiocarbonate having at least one of an aryl group and an arylene group as a substituent. [9] The method according to any one of [1] to [8], wherein the radical polymerizable monomer contains at least one of an aromatic vinyl compound and a vinyl cyanide compound.

[10] The method according to any one of [1] to [9], further comprising a seed polymerization step of reacting a monomer containing a (meth)acrylic acid ester using the polymer particles obtained in the polymerization step as seed particles. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a method for producing polymer particles that can produce a polymer with a narrow molecular weight dispersity when polymerization using a RAFT agent is carried out by miniemulsion polymerization, even when high shear treatment and addition of an emulsifying aid are not performed. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described, occasionally with reference to the drawings. However, the following embodiments are merely examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following content. In this specification, a numerical range indicated by the symbol "to" includes a lower limit and an upper limit. In other words, a numerical range indicated by "x to y" means greater than or equal to x and less than or equal to y.

[0016] Unless otherwise specified, the materials exemplified in this specification can be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified.

[0017] In this specification, the term "(meth)acrylate" is used to encompass both the acrylate and the corresponding methacrylate. The same applies to similar expressions such as (meth)acrylic acid and (meth)acrylamide.

[0018] One embodiment of the method for producing polymer particles according to the present disclosure includes a polymerization step of dispersing a solution containing a radical polymerizable monomer and a RAFT agent in an aqueous solution containing an emulsifier to prepare a miniemulsion, and then polymerizing the radical polymerizable monomer through miniemulsion polymerization. The miniemulsion is a dispersion in which oil droplets (dispersed phase) containing the radical polymerizable monomer and the RAFT agent are dispersed in water as a dispersion medium, and is a so-called O / W (oil-in-water) emulsion.

[0019] The polymerization step may include dispersing a solution containing a radical polymerizable monomer and a RAFT agent in an aqueous solution containing an emulsifier to prepare a miniemulsion, and adding a polymerization initiator to the miniemulsion to miniemulsion polymerize the radical polymerizable monomer.

[0020] The radical polymerizable monomer used in the above production method is a compound (monomer) having at least one radical polymerizable functional group. Examples of the radical polymerizable functional group include an ethylenically unsaturated bond. The number of radical polymerizable functional groups that the radical polymerizable monomer has is 1 or more, and may be, for example, 1 to 4, 1 to 3, or 1 to 2.

[0021] Examples of the radical polymerizable monomer include an aromatic vinyl compound, a vinyl cyanide compound, an ethylenically unsaturated carboxylic acid ester, an ethylenically unsaturated carboxylic acid, an N-substituted maleimide, and a (meth)acrylamide. The radical polymerizable monomer preferably includes at least one of an aromatic vinyl compound and a vinyl cyanide compound.

[0022] Examples of aromatic vinyl compounds include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, β-methylstyrene, 2,6-dimethylstyrene, 2,4-dimethylstyrene, α-methyl-o-methylstyrene, α-methyl-m-methylstyrene, α-methyl-p-methylstyrene, β-methyl-o-methylstyrene, β-methyl-m-methylstyrene, β-methyl-p-methylstyrene, 2,4,6-trimethylstyrene, α-methyl-2,6-dimethylstyrene, α-methyl-2,4-dimethylstyrene, β-methyl-2,6-dimethylstyrene, β-methyl-2,4-dimethylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,6-dichlorostyrene, 2,4-dichlorostyrene, α-chloro-o-chlorostyrene, α-chlorostyrene, Examples of aromatic vinyl compounds include o-m-chlorostyrene, α-chloro-p-chlorostyrene, β-chloro-o-chlorostyrene, β-chloro-m-chlorostyrene, β-chloro-p-chlorostyrene, 2,4,6-trichlorostyrene, α-chloro-2,6-dichlorostyrene, α-chloro-2,4-dichlorostyrene, β-chloro-2,6-dichlorostyrene, β-chloro-2,4-dichlorostyrene, ot-butylstyrene, mt-butylstyrene, pt-butylstyrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, o-chloromethylstyrene, m-chloromethylstyrene, p-chloromethylstyrene, o-bromomethylstyrene, m-bromomethylstyrene, p-bromomethylstyrene, styrene derivatives substituted with silyl groups, indene, vinylnaphthalene, and vinylanthracene. Among the above, the aromatic vinyl compound preferably contains at least one selected from the group consisting of styrene, α-methylstyrene, and p-methylstyrene, and more preferably contains styrene, from the viewpoint of the balance between production cost and physical properties.

[0023] Examples of the vinyl cyanide compound include acrylonitrile, methacrylonitrile, and ethacrylonitrile. Among the above-mentioned vinyl cyanide compounds, it is preferable to include acrylonitrile from the viewpoint of the balance between production cost and physical properties.

[0024] Examples of the ethylenically unsaturated carboxylic acid ester include (meth)acrylic acid alkyl ester, (meth)acrylic acid ester, fumaric acid alkyl ester, maleic acid alkyl ester, and itaconic acid alkyl ester.

[0025] The number of carbon atoms in the alkyl group constituting the (meth)acrylic acid alkyl ester may be, for example, 1 to 20, 1 to 18, 1 to 10, 1 to 8, 1 to 6, or 1 to 4. Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, and cyclohexyl (meth)acrylate. Among the above, from the viewpoint of balancing production costs and physical properties, the (meth)acrylic acid alkyl ester preferably includes a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 4 carbon atoms, and more preferably includes n-butyl acrylate.

[0026] The (meth)acrylic acid ester is an ester other than the above-mentioned (meth)acrylic acid alkyl esters. Examples of the (meth)acrylic acid ester include benzyl (meth)acrylate and phenyl (meth)acrylate.

[0027] Examples of alkyl (meth)acrylates include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, dodecyl acrylate, stearyl acrylate, and behenyl acrylate.

[0028] Examples of alkyl fumarate esters include monomethyl fumarate, monoethyl fumarate, mono-n-butyl fumarate, monomethyl maleate, monoethyl maleate, mono-n-butyl maleate, monocyclopentyl fumarate, monocyclohexyl fumarate, and monocyclohexeny fumarate.

[0029] Examples of alkyl maleates include monocyclopentyl maleate and monocyclohexyl maleate, etc. Examples of alkyl itaconates include monomethyl itaconate, monoethyl itaconate, mono-n-butyl itaconate, and monocyclohexyl itaconate, etc.

[0030] Examples of the ethylenically unsaturated carboxylic acid include α-ethylacrylic acid, crotonic acid, and cinnamic acid.

[0031] Examples of N-substituted maleimides include N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, Ni-propylmaleimide, Nn-butylmaleimide, Ni-butylmaleimide, N-tert-butylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-(2-methylphenyl)maleimide, N-(4-hydroxyphenyl)maleimide, and N-chlorophenylmaleimide.

[0032] Examples of (meth)acrylamides include (meth)acrylamide, N-methylol(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-dibutylacrylamide, N,N-dibutylmethacrylamide, N,N-dioctylacrylamide, N,N-dioctylmethacrylamide, N-monobutylacrylamide, N-monobutylmethacrylamide, N-monooctylacrylamide, and N-monooctylmethacrylamide.

[0033] The upper limit of the amount of radical polymerizable monomer to be blended may be, for example, 40% by mass or less, 35% by mass or less, or 30% by mass or less, relative to the total amount of the miniemulsion. When the upper limit of the amount of radical polymerizable monomer to be blended is within the above range, the occurrence of Ostwald ripening in the miniemulsion can be further suppressed, and the molecular weight dispersion of the resulting polymer can be further reduced. The lower limit of the amount of radical polymerizable monomer to be blended may be, for example, 20% by mass or more, or 25% by mass or more, relative to the total amount of the miniemulsion. When the lower limit of the amount of radical polymerizable monomer to be blended is within the above range, the repulsive force between oil droplets coated with the emulsifier is strengthened, and the dispersed phase in the miniemulsion can be further stabilized.

[0034] In the above production method, a RAFT agent is blended in a predetermined amount or more. RAFT agents are generally compounds with low hydrophilicity and exist dissolved in the monomer oil droplets during miniemulsion polymerization. By adjusting the amount of RAFT agent blended, when dispersed particles attempt to coarsen due to Ostwald ripening, the RAFT agent concentration in the coarse particles is relatively diluted, resulting in a RAFT agent concentration imbalance between the dispersed phases. By generating an equilibrium pressure that restores this imbalance to the original equilibrium state, the dispersed phase can be stabilized.

[0035] The RAFT agent used in the above production method is a chain transfer agent that enables reversible addition-fragmentation chain transfer (RAFT) polymerization. The RAFT agent may be a compound having a structure represented by the following general formula (1), such as a thiocarbonylthio compound such as dithiobenzoate, trithiocarbamate, dithiocarbamate, or xanthate.

[0036] [ka]

[0037] In the above general formula (1), Z represents a functional group that controls the reactivity of the C=S bond and affects the rate of addition and cleavage of radicals, and R represents a homolytic leaving group that restarts the polymerization reaction and is favorable for the propagating radical.

[0038] Z and R in general formula (1) must be appropriately selected depending on the type of radical polymerizable monomer used. Guidelines for selecting Z and R are described in many documents. Examples of such documents include Keddie, DJ, Moad, G., Rizzardo, E., Thang, SH: Macromolecules, 45, 5321 (2012).

[0039] The RAFT agent may be a highly hydrophobic compound. When a highly hydrophobic compound is used as the RAFT agent, the equilibrium pressure due to the concentration imbalance of the RAFT agent between the dispersed phases when the dispersed particles become coarse can be increased. This can further improve the stability of the miniemulsion, reduce the occurrence of Ostwald ripening, and obtain a polymer with a smaller molecular weight dispersity. The partition coefficient LogP of the RAFT agent ow The partition coefficient LogP may be, for example, 3.50 or more, or 4.00 or more. ow The higher the value of LogP, the lower the water solubility of the RAFT agent. ow The upper limit of is not particularly limited, but may be 10.00 or less, 8.00 or less, or 7.00 or less.

[0040] The partition coefficient in this specification is a value defined as the ratio of the concentrations of a target substance in each phase when the target substance is dissolved in two phases including a 1-octanol phase and an aqueous phase, and means a value measured in accordance with the description in JIS Z 7260-107:2000 "Measurement of partition coefficient (1-octanol / water) - Shake flask method."

[0041] Examples of the RAFT agent include trithiocarbamates, dithiocarbamates, dithioesters, etc. From the viewpoint of improving hydrophobicity, the RAFT agent preferably contains a trithiocarbonate having at least one of an aryl group and an arylene group as a substituent.

[0042] Examples of trithiocarbamates include benzyl butyl trithiocarbonate, 2-cyano-2-propyl dodecyl trithiocarbonate, dibenzyl trithiocarbonate, 2-[[(butylthio)thioxomethyl]thio]propionic acid, 2-[[(dodecylthio)thioxomethyl]thio]propionic acid, 2-[[(butylthio)thioxomethyl]thio]succinic acid, 2-[[(dodecylthio)thioxomethyl]thio]succinic acid, 2-[[(dodecylthio)thioxomethyl]thio]-2-methylpropionic acid, 2,2'-[ Examples of suitable trithiocarbonates include trithiocarbonates such as [thiocarbonothioylbis(thio)]bis[2-methylpropionic acid], 2-amino-1-methyl-2-oxoethylbutyl trithiocarbonate, benzyl 2-[(2-hydroxyethyl)amino]-1-methyl-2-oxoethyltrithiocarbonate, 3-[[[(tert-butyl)thio]thioxomethyl]thio]propionic acid, cyanomethyldodecyltrithiocarbonate, diethylaminobenzyltrithiocarbonate, and dibutylaminobenzyltrithiocarbonate. Among the trithiocarbamates, the RAFT agent preferably contains benzyl butyl trithiocarbonate, or preferably consists solely of benzyl butyl trithiocarbonate, in order to facilitate control of the molecular weight of the polymer.

[0043] Examples of dithiocarbamates include benzyl 1-pyrrolecarbodithioate (common name: benzyl 1-pyrroledithiocarbamate), benzyl phenylcarbodithioate, 1-benzyl-N,N-dimethyl-4-aminodithiobenzoate, 1-benzyl-4-methoxydithiobenzoate, 1-phenylethylimidazolecarbodithioate (common name: 1-phenylethylimidazoledithiocarbamate), benzyl-1-(2-pyrrolidinone)carbodithioate (common name: benzyl-1-(2-pyrrolidinone)dithiocarbamate), benzyl phthalimidylcarbodithioate (common name: benzyl phthalimidyldithiocarbamate), 2-cyanoprop-2-yl-1-pyrrolecarbo dithioate (trivial name: 2-cyanoprop-2-yl-1-pyrrole dithiocarbamate), 2-cyanoprop-2-yl-1-pyrrole carbodithioate (trivial name: 2-cyanobut-2-yl-1-pyrrole dithiocarbamate), benzyl-1-imidazole carbodithioate (trivial name: benzyl-1-imidazole dithiocarbamate), 2-cyanoprop-2-yl-N,N-dimethyldithiocarbamate, benzyl-N,N-diethyldithiocarbamate, cyanomethyl-1-(2-pyrrolidone)dithiocarbamate, 2-(ethoxycarbonylbenzyl)prop-2-yl-N,N-diethyldithiocarbamate, cyanomethyl-N-methyl-N-phenyldithiocarbamate, and the like.

[0044] Examples of dithioesters include 1-phenylethyl dithiobenzoate, 2-phenylprop-2-yldithiobenzoate, 1-acetic acid-1-yl-ethyl dithiobenzoate, 1-(4-methoxyphenyl)ethyl dithiobenzoate, benzyl dithioacetate, ethoxycarbonylmethyl dithioacetate, 2-(ethoxycarbonyl)prop-2-yldithiobenzoate, 2-cyanoprop-2-yldithiobenzoate, tert-butyl dithiobenzoate, 2,4,4-trimethylpent-2-yldithiobenzoate, 2-(4-chlorophenyl)-prop-2-yldithiobenzoate, 3-vinylbenzyl dithiobenzoate, 4-vinylbenzyl dithiobenzoate, benzyl diethoxyphosphinyldithioformate, tert-butyl trithioperbenzoate, 2-phenylprop-2-yl-4-chlorodithiobenzoate, dibenzyl tetrathioterephthalate, carboxymethyl dithiobenzoate, 3,5-dimethyl-1H-pyrazole-1-carbodithioate potassium, cyanomethyl-3,5-dimethyl-1H-pyrazole-1-carbodithioate, benzyl-4-chlorodithiobenzoate, phenylmethyl-4-chlorodithiobenzoate, 4-nitrobenzyl-4-chlorodithiobenzoate, phenylprop-2-yl-4-chlorodithiobenzoate, 1-cyano-1-methylethyl-4-chlorodithiobenzoate, 3-chloro-2-butenyl-4-chlorodithiobenzoate, 2-chloro-2-butenyl dithiobenzoate, and benzyl dithioacetate.

[0045] The lower limit of the amount of the RAFT agent is 0.20 mol or more relative to 100 mol of the total amount of the radical polymerizable monomers. The lower limit of the amount of the RAFT agent may be 0.25 mol or more, 0.30 mol or more, 0.40 mol or more, or 0.50 mol or more relative to 100 mol of the total amount of the radical polymerizable monomers. By using a RAFT agent with a lower limit within the above range, the stability of the dispersed phase in the miniemulsion can be further improved. The upper limit of the amount of the RAFT agent may be, for example, 2.00 mol or less, 1.50 mol or less, 1.20 mol or less, 1.00 mol or less, 0.80 mol or less, or 0.60 mol or less relative to 100 mol of the total amount of the radical polymerizable monomers. By using a RAFT agent with a lower limit within the above range, the RAFT polymerization reaction can be more sufficiently promoted while maintaining the stability of the dispersed phase in the miniemulsion.

[0046] The emulsifier may contain at least one selected from the group consisting of anionic surfactants, nonionic surfactants, and amphoteric surfactants, and preferably contains an anionic surfactant, and more preferably contains only an anionic surfactant.

[0047] Examples of anionic surfactants include sulfate esters of higher alcohols (e.g., alcohols having 6 to 30 carbon atoms), alkylbenzenesulfonates, fatty acid sulfonates, phosphates (e.g., ammonium monoglyceride phosphate), fatty acid salts (e.g., dipotassium alkenyl succinate), and amino acid derivative salts.

[0048] Examples of nonionic surfactants include sugar ester surfactants, fatty acid ester surfactants, and ether surfactants. Examples of sugar ester surfactants include sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters. Examples of fatty acid ester surfactants include polyoxyethylene resin acid esters and polyoxyethylene fatty acid diethyl esters. Examples of ether surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyethylene polypropylene glycols.

[0049] Examples of amphoteric surfactants include compounds having, for example, a carboxylate, a sulfate, a sulfonate, or a phosphate in the anion moiety, and an amine salt or a quaternary ammonium salt in the cation moiety. Examples of amphoteric surfactants include alkyl betaine surfactants and amine oxide surfactants. Examples of alkyl betaine surfactants include lauryl dimethyl amino acetic acid betaine. Examples of amine oxide surfactants include lauryl dimethyl amine N-oxide.

[0050] The amount of the emulsifier is 2.20 to 10.00 mol, relative to 100 mol of the total amount of the radical polymerizable monomers. The upper limit of the amount of the emulsifier may be, for example, 9.00 mol or less, 8.00 mol or less, 7.00 mol or less, 6.00 mol or less, 5.00 mol or less, or 4.00 mol or less, relative to 100 mol of the total amount of the radical polymerizable monomers. When the upper limit of the amount of the emulsifier is within the above range, micelle formation due to excess emulsifier can be suppressed. The lower limit of the amount of the emulsifier may be, for example, 2.40 mol or more, 2.50 mol or more, or 2.60 mol or more, relative to 100 mol of the total amount of the radical polymerizable monomers. When the lower limit of the amount of the emulsifier is within the above range, the stability of the dispersed phase in the miniemulsion can be maintained, and the RAFT polymerization reaction can be more easily controlled.

[0051] The water used to prepare the aqueous solution containing an emulsifier may be, for example, deionized water, pure water, ultrapure water, or ion-exchanged water.

[0052] In the above production method, mini-emulsification is possible without applying high shear or the like by adjusting the blending amounts of the RAFT agent and the emulsifier. It is not essential to blend an emulsifier into the mixed solution, and from the viewpoint of avoiding the inclusion of unnecessary components, it is preferable not to use an emulsifier.

[0053] The emulsifier is a hydrophobic compound. Since the emulsifier generally dissolves in the monomer oil droplets, when the dispersed particles begin to coarsen due to Ostwald ripening, an imbalance in the concentration of the emulsifier occurs between the dispersed phases, generating an equilibrium pressure that restores the original equilibrium state. Taking advantage of this, an emulsifier is used to stabilize the dispersion. On the other hand, the method according to the present disclosure aims to stabilize the dispersion in the miniemulsion by adjusting the blending amounts of the RAFT agent and the emulsifier, and therefore the use of an emulsifier is not essential. Examples of the emulsifier include long-chain hydrocarbons such as tetradecane, pentadecane, hexadecane, heptadecane, and octadecane, and higher alcohols such as 1-hexadecanol, 1-heptadecanol, and 1-octadecanol.

[0054] In the above production method, a mixed solution containing water, an emulsifier, a radical polymerizable monomer, and a RAFT agent is prepared by stirring. During this process, a mini-emulsion is obtained in which oil droplets (dispersed phase) containing the radical polymerizable monomer and the RAFT agent are dispersed in an aqueous medium. In the production method according to the present disclosure, high shear (for example, a shear rate of 70 s -1 It is not essential to apply a shear force (such as a shear force or more) to the specimen.

[0055] The stirring in the preparation of the mixed solution can be carried out using, for example, a general stirring device equipped with a paddle blade, a propeller blade, a turbine blade, or the like, or a magnetic stirrer. The upper limit of the shear rate during stirring is, for example, 20 s -1 Below, 18 seconds -1 or less, or 16 seconds -1 The lower limit of the shear rate during stirring may be, for example, 2.0 s -1 or more, or 2.5 seconds -1 It may be more than that.

[0056] In the polymerization step, miniemulsion polymerization may be carried out in a state in which the particle size distribution of the dispersed phase in the miniemulsion is adjusted.

[0057] In the polymerization step, the particle size (D50) of the dispersed phase when the integrated value from the small particle size reaches 50% of the total in the scattering intensity-based cumulative particle size distribution obtained by dynamic light scattering for the miniemulsion may be, for example, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, or 200 nm or less. When the upper limit of D50 of the dispersed phase is within the above range, the particle size of the dispersed phase in the miniemulsion can be made more uniform. The lower limit of D50 of the dispersed phase may be, for example, 10 nm or more, 30 nm or more, 50 nm or more, 80 nm or more, or 90 nm or more. When the lower limit of D50 of the dispersed phase is within the above range, the dispersed phase in the miniemulsion can be more stabilized.

[0058] In the polymerization process, the dispersion phase distribution may be adjusted so that the value (D90-D10) / D50 (span value) is, for example, 1.00 or less, where D10, D50, and D90 are the particle diameters of the dispersed phase at which the integrated values ​​from the smallest particle size reach 10%, 50%, and 90% of the total, respectively, in the scattering intensity-based cumulative particle size distribution obtained by dynamic light scattering of the miniemulsion. By adjusting the dispersion state so that the span value falls within the above range, the uniformity within the miniemulsion can be further improved, and the molecular weight distribution of the resulting polymer can be made smaller. The upper limit of the span value may be, for example, 0.90 or less, 0.80 or less, 0.75 or less, or 0.70 or less. The lower limit of the span value is not particularly limited, but may be, for example, 0.20 or more or 0.30 or more.

[0059] In this specification, the D10, D50 (average particle size), and D90 of the dispersed phase refer to values ​​measured by dynamic light scattering. Specifically, a miniemulsion was measured using dynamic light scattering, and the results were analyzed using the cumulant method to create a cumulative distribution based on scattering intensity. The particle sizes of the dispersed phase at which the integrated values ​​from the smallest particle size reached 10%, 50%, and 90% of the total were defined as D10, D50, and D90, respectively. Measurements can be performed using, for example, a zeta potential, particle size, and molecular weight measurement system (manufactured by Otsuka Electronics Co., Ltd., product name: ELSZ-2000ZS). The measurement conditions were a temperature of 25°C, 25 integration times, and the refractive index of the dispersion medium was the same as that of water (1.333). Measurements were performed immediately after preparation of the mixed solution.

[0060] The cumulative particle size distribution based on scattering intensity obtained by dynamic light scattering for a miniemulsion may be unimodal. In this specification, the term "unimodal" means that there is one peak on the distribution curve where the scattering intensity is 1% or more, and the span value of that peak is 1.0 or less. Here, the peak portion where the scattering intensity is less than 1% is excluded in order to eliminate the influence of noise, etc.

[0061] In the above production method, after the miniemulsion is obtained as described above, a polymerization initiator may be added to proceed with miniemulsion polymerization.

[0062] Examples of the polymerization initiator include an azo compound, a persulfate, sodium persulfate, hydrogen peroxide, and tert-butyl hydroperoxide. From the viewpoint of suppressing side reactions caused by the initiator, the polymerization initiator preferably contains an azo compound, and more preferably consists of only an azo compound.

[0063] Examples of azo compounds include 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 1-[(1-cyano-1-methylethyl)azo]formamide, 4,4'-azobis(4-cyanovaleric acid), dimethyl 2,2'-azobis(2- methylpropionate), dimethyl 1,1'-azobis(1-cyclohexanecarboxylate), 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-azobis[2-(2-imidazolin-2-yl)propane], and 2,2'-azobis(2,4,4-trimethylpentane).

[0064] The amount of the polymerization initiator may be, for example, 10 to 50 mol relative to 100 mol of the total amount of the RAFT agent.

[0065] The temperature during miniemulsion polymerization in the polymerization step can be adjusted depending on the initiator, and may be, for example, 10 to 100° C., 25 to 100° C., 25 to 80° C., 50 to 80° C., or 60 to 80° C. The timing of temperature adjustment of the miniemulsion in the polymerization step may be, for example, by adding the polymerization initiator to the miniemulsion that has been adjusted to the desired temperature in advance, or by adding the polymerization initiator to the miniemulsion and then starting heating to adjust to the desired temperature.

[0066] The polymerization time of the mini-emulsion polymerization in the polymerization step may be, for example, 1 to 30 hours, or 2 to 15 hours. The polymerization time in the polymerization step may be adjusted based on the monomer conversion rate. The polymerization step may be a step in which mini-emulsion polymerization is carried out until the monomer conversion rate reaches, for example, 70 to 100%, or 80 to 100%.

[0067] The method for producing polymer particles according to the present disclosure may be carried out by using the polymer particles obtained by the above-described mini-emulsion polymerization as seed particles to carry out additional polymerization to produce polymer particles having a multilayer structure. For example, the production method may further include a seed polymerization step in which a monomer containing a (meth)acrylic acid ester is reacted with the polymer particles obtained in the polymerization step as seed particles. The (meth)acrylic acid ester in this step may be any of the compounds exemplified as radical polymerizable monomers.

[0068] Although several embodiments have been described above, the present disclosure is not limited to the above embodiments. Furthermore, the descriptions of the above embodiments can be applied to each other. [Example]

[0069] The present disclosure will be described in more detail below using examples and comparative examples, but the present disclosure is not limited to the following examples.

[0070] Example 1 A solution of 9.75 parts by mass of sodium dodecylbenzenesulfonate and 2 parts by mass of sodium bicarbonate as emulsifiers in 220 parts by mass of nitrogen-substituted deionized water was charged into a polymerization vessel equipped with a stirrer. Next, while stirring the aqueous solution in the polymerization vessel, styrene (distribution coefficient LogP ow 100 parts by mass of benzyl butyl trithiocarbonate (distribution coefficient LogP 2.95) as a RAFT agent ow 1.39 parts by mass of 5.80 was dissolved in the solution and added to a 1000 mL scale reactor. The solution was stirred at 23°C at a speed of 3.33 s using a two-stage stirring blade consisting of a disk turbine blade with a blade diameter of 4 cm and a paddle blade with a blade diameter of 4 cm. -1 A mini-emulsified mixed solution was prepared while stirring under the conditions. The mixed solution was heated and the internal temperature was adjusted to 80°C. In the mixed solution, the amount of RAFT agent blended per 100 moles of radical polymerizable monomer was 0.54 moles, and the amount of emulsifier blended was 2.80 moles.

[0071] To the above mixed solvent, whose temperature was adjusted to 80°C, 2.5 parts by mass of an aqueous solution of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (concentration: 20% by mass) was added as a polymerization initiator to prepare a polymerization solution. Miniemulsion polymerization was performed to obtain polymer particles composed of styrene units. The monomer conversion rate was 90%. The polymerization initiator was blended in an amount of 50 moles per 100 moles of the total amount of RAFT agent.

[0072] [Evaluation of dispersibility in mixed solutions] The cumulative particle size distribution of the mixed solution prepared as described above was measured using dynamic light scattering based on the scattering intensity of the dispersed phase, and D10, D50 (average particle size), and D90 were determined. A zeta potential, particle size, and molecular weight measurement system (Otsuka Electronics Co., Ltd., product name: ELSZ-2000ZS) was used for the measurements, and D10, D50, and D90 were determined using cumulant analysis. The measurement conditions were a temperature of 25°C, 25 accumulations, and the refractive index of the dispersion medium was that of water (1.333). The measurements were performed immediately after the preparation of the mixed solution.

[0073] The span value ((D90 - D10) / D50) was calculated from the obtained D10, D50, and D90 values. The dispersibility was evaluated based on the following criteria from the obtained span value. A: The span value is 0.20 or less. B: The span value is more than 0.20 and 0.50 or less. C: The span value is more than 0.50 and 0.80 or less. D: The span value is more than 0.80 and 1.50 or less. E: The span value is more than 1.50 and 10.00 or less. F: The span value is more than 10.00.

[0074] [Evaluation of Polymer Particle Properties Measurement and Polymerization System Control] For the polymer particles obtained as described above, measurements of the average particle diameter, weight-average molecular weight Mw, number-average molecular weight Mn, and molecular weight distribution were carried out under the following conditions.

[0075] [Measurement of Average Particle Diameter] For the solution after polymerization, the average particle diameter of the polymer particles was measured based on the dynamic light scattering method. For the measurement, a zeta potential / particle size / molecular weight measurement system (manufactured by Otsuka Electronics Co., Ltd., product name: ELSZ-2000ZS) was used. The average particle diameter was calculated by cumulant method analysis. The measurement conditions were a temperature of 25°C and an integration number of 25 times, and the refractive index of water (1.333) was adopted as the refractive index of the dispersion medium.

[0076] [Measurement of Mw and Mn] The Mw and Mn of the polymer were measured by gel permeation chromatography (GPC) under the following conditions. Note that standard polystyrene (PS) was used for the preparation of the calibration curve. Apparatus: High-speed GPC apparatus (manufactured by Tosoh Corporation, product name: HLC-8320GPC) Column: Three TSKgel GMHHR-H columns in series Temperature: 40°C Detection: Differential refractive index Solvent: Tetrahydrofuran (THF) Sample concentration: 0.9% by mass Injection volume: 10μL

[0077] The controllability of the polymerization system was evaluated based on the obtained molecular weight dispersion value and the following criteria. The results are shown in Table 1. The closer the molecular weight dispersion (Mw / Mn) is to 1, the higher the controllability of the polymerization system. A: The molecular weight distribution (Mw / Mn) is 1.20 or less. B: The molecular weight distribution (Mw / Mn) is more than 1.20 and not more than 1.30. C: The molecular weight distribution (Mw / Mn) is more than 1.30 and 1.50 or less. D: The molecular weight distribution (Mw / Mn) is more than 1.50 and 1.80 or less. E: The molecular weight distribution (Mw / Mn) is more than 1.80 and not more than 2.50. F: The molecular weight distribution (Mw / Mn) is greater than 2.50.

[0078] Example 2 Polymer particles composed of styrene units were obtained in the same manner as in Example 1, except that the temperature during preparation of the mini-emulsified mixed solution was changed to 80°C. The monomer conversion rate was 95.7%, and the molecular weight distribution (Mw / Mn) was 1.25. The obtained mixed solution and polymer particles were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0079] Example 3 Polymer particles composed of styrene units were obtained in the same manner as in Example 1, except that the amount of emulsifier was changed as shown in Table 1 and the temperature during preparation of the mini-emulsified mixed solution was changed to 80°C. The monomer conversion was 97.9%, and the molecular weight distribution (Mw / Mn) was 1.15. The obtained mixed solution and polymer particles were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0080] Example 4 Polymer particles composed of styrene units were obtained in the same manner as in Example 1, except that the amount of emulsifier was changed as shown in Table 1 and the temperature during preparation of the mini-emulsified mixed solution was changed to 80°C. The monomer conversion was 98.4%, and the molecular weight distribution (Mw / Mn) was 1.15. The obtained mixed solution and polymer particles were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0081] Example 5 As monomers, 85 parts by mass of styrene and acrylonitrile (manufactured by Junsei Chemical Co., Ltd., distribution coefficient LogP ow Particles of a random copolymer (polymer) composed of styrene units and acrylonitrile units were obtained in the same manner as in Example 1, except that 15 parts by mass of styrene (0.25) (total 100 parts by mass) was used, the amount of RAFT agent and the amount of emulsifier were changed as shown in Table 1, and the temperature during preparation of the mini-emulsified mixed solution was changed to 70°C. The monomer conversion was 98.3%, and the molecular weight distribution (Mw / Mn) was 1.28. The obtained mixed solution and polymer particles were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0082] Example 6 Particles of a random copolymer (polymer) composed of styrene units and acrylonitrile units were obtained in the same manner as in Example 1, except that 85 parts by mass of styrene and 15 parts by mass of acrylonitrile (total 100 parts by mass) were used as monomers, the amount of RAFT agent and the amount of emulsifier were changed as shown in Table 1, and the temperature during preparation of the mini-emulsified mixed solution was changed to 70°C. The monomer conversion was 97.6%, and the molecular weight distribution (Mw / Mn) was 1.27. The obtained mixed solution and polymer particles were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0083] [Table 1]

[0084] (Comparative Example 1) Polymer particles composed of styrene units were obtained in the same manner as in Example 1, except that a RAFT agent was not added. The resulting mixed solution and polymer particles were evaluated in the same manner as in Example 1. The results are shown in Table 2. Because a normal radical polymerization system was used without using a RAFT agent, the monomer conversion rate was high, but the molecular weight distribution (Mw / Mn) was broad.

[0085] (Comparative Example 2) Polymer particles composed of styrene units were obtained in the same manner as in Example 1, except that a RAFT agent was not added and the temperature during preparation of the mini-emulsified mixed solution was changed to 80°C. The obtained mixed solution and polymer particles were evaluated in the same manner as in Example 1. The results are shown in Table 2. Because a normal radical polymerization system was used without using a RAFT agent, the monomer conversion rate was high, but the molecular weight distribution (Mw / Mn) was broad.

[0086] (Comparative Example 3) Polymer particles composed of styrene units were obtained in the same manner as in Example 1, except that the amount of emulsifier was changed as shown in Table 2 and the temperature during preparation of the mini-emulsified mixed solution was changed to 80°C. The monomer conversion rate was 98.7%, and the molecular weight distribution (Mw / Mn) was 2.78. The obtained mixed solution and polymer particles were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0087] Comparative Example 4 Polymer particles composed of styrene units were obtained in the same manner as in Example 1, except that the amount of emulsifier was changed as shown in Table 2 and the temperature during preparation of the mini-emulsified mixed solution was changed to 80°C. The monomer conversion rate was 99.2%, and the molecular weight distribution (Mw / Mn) was 2.31. The obtained mixed solution and polymer particles were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0088] [Table 2] [Industrial Applicability]

[0089] According to the present disclosure, it is possible to provide a method for producing polymer particles that can produce a polymer with a narrow molecular weight dispersity when polymerization using a RAFT agent is carried out by miniemulsion polymerization, even when high shear treatment and addition of an emulsifying aid are not performed.

Claims

1. a polymerization step of dispersing a solution containing a radical polymerizable monomer and a RAFT agent in an aqueous solution containing an emulsifier to prepare a mini-emulsion, and then mini-emulsion polymerizing the radical polymerizable monomer; the amount of the RAFT agent is 0.20 mol or more relative to 100 mol of the total amount of the radical polymerizable monomers, The method for producing polymer particles, wherein the amount of the emulsifier is 2.20 to 10.00 mol per 100 mol of the total amount of the radical polymerizable monomers.

2. The partition coefficient LogP of the RAFT agent ｏｗ The method according to claim 1, wherein the σ is 3.50 or more.

3. 3. The production method according to claim 1 or 2, wherein the polymerization step is carried out under conditions adjusted such that the particle size of the dispersed phase is 500 nm or less when the integrated value from small particle sizes reaches 50% of the total in a scattering intensity-based cumulative particle size distribution obtained by a dynamic light scattering method for the mini-emulsion.

4. 3. The production method according to claim 1 or 2, wherein the polymerization step is carried out in a state in which the distribution of the dispersed phase is adjusted so that the value of (D90-D10) / D50 is 1.00 or less, where D10, D50, and D90 are particle diameters of the dispersed phase when integrated values ​​from small particle diameters reach 10%, 50%, and 90%, respectively, in a scattering intensity-based cumulative particle size distribution obtained by a dynamic light scattering method for the miniemulsion.

5. 3. The method according to claim 1, wherein in the polymerization step, the mini-emulsion has a unimodal cumulative particle size distribution based on scattering intensity obtained by dynamic light scattering.

6. The method according to claim 1 or 2, wherein the emulsifier comprises at least one selected from the group consisting of anionic surfactants, nonionic surfactants, and amphoteric surfactants.

7. The method according to claim 1 or 2, wherein the amount of the RAFT agent is 2.00 mol or less relative to 100 mol of the total amount of the radical polymerizable monomers.

8. The method according to claim 1 or 2, wherein the RAFT agent is a trithiocarbonate having at least one substituent selected from the group consisting of an aryl group and an arylene group.

9. The method according to claim 1 or 2, wherein the radical polymerizable monomer comprises at least one of an aromatic vinyl compound and a vinyl cyanide compound.

10. The method according to claim 1 or 2, further comprising a seed polymerization step of reacting a monomer containing a (meth)acrylic acid ester using the polymer particles obtained in the polymerization step as seed particles.

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