JP7704033B2 - Method for producing polymer microparticles and dispersion stabilizer - Google Patents

Description

This specification relates to a method for producing polymer microparticles, etc.

(Cross-reference to related applications) This application is a related application of Japanese patent application No. 2019-207465, filed on November 15, 2019, and claims priority based on this application, incorporating all contents contained in this application by reference.

Polymer microparticles are used in a wide range of fields, including electrical and electronic materials such as conductive microparticles, spacers (for LCD cells, touch panel seals, etc.), resin film modifiers, thickeners (for paints, cosmetics, etc.), etc. Conventional methods for producing polymer microparticles of micron size or less include emulsion polymerization, suspension polymerization, precipitation polymerization, and dispersion polymerization.

The emulsion polymerization method is a method of obtaining nano-order polymer particles by mixing a solvent, a polymerizable monomer that is poorly soluble in the solvent, and an emulsifier (surfactant), and polymerizing the mixture using a polymerization initiator that is soluble in the solvent. However, since a large amount of a low-molecular-weight emulsifier is required, there is concern that the final product may be adversely affected (turbidity, water resistance, etc.). In addition, the suspension polymerization method is a method of obtaining polymer particles by mechanically stirring the polymerizable monomer in water in the presence of a dispersion stabilizer to form droplets, and polymerizing the resulting mixture using an appropriate oil-soluble polymerization initiator. The precipitation polymerization method is a method of obtaining polymer particles in a system in which the polymerizable monomer dissolves in the solvent, but the resulting polymer is insoluble in the solvent and precipitates. Here, the suspension polymerization method generally produces polymer particles with a particle size of several tens of μm or more, and the precipitation polymerization method generally produces polymer particles with a particle size of several μm to several hundreds of μm, but neither of these methods is applicable to applications requiring smaller particle sizes.

In contrast, the dispersion polymerization method is a method in which precipitation polymerization is carried out in the presence of a dispersion stabilizer, and it is possible to control the particle size of the resulting microparticles by adjusting the type and amount of polymerizable monomer, solvent, and dispersion stabilizer, and the microparticles also have the characteristic of having a narrow particle size distribution.

Various methods are known for producing polymer microparticles by dispersion polymerization. Patent Document 1 discloses a method for forming homopolymers or copolymers of monomers, or copolymers with other monomers, such as acrylamide and its derivatives, p-styrenesulfonic acid and its salts, (meth)acrylic acid and their salts, into fine particles, in which a water-miscible organic solvent such as ethanol is used as the polymerization solvent, and a polymer soluble in a water-miscible organic solvent or a water-miscible solvent is made to exist beforehand during polymerization, and the monomers are polymerized to produce hydrophilic polymer microparticles. The average particle size range of the polymer microparticles specifically disclosed in the examples is 0.34 to 2.40 μm.

Patent Document 2 discloses a method for producing polymer microparticles by polymerizing acrylamide or neutralized acrylic acid, either alone or in a mixture, in a mixed solvent of water and a water-miscible organic solvent in the presence of polyvinylpyrrolidone or a polyvinylpyrrolidone copolymer having a weight-average molecular weight of 10,000 or more, and the range of average particle diameter of the polymer microparticles specifically disclosed in the examples is 0.7 to 1.30 μm.

Patent Document 3 discloses a method for producing monodisperse polymer microparticles by polymerizing one or more vinyl monomers in an alcoholic medium in the presence of a polymer (dispersion stabilizer) obtained by polymerizing a specific monomer, which is soluble in the alcoholic medium but the resulting polymer is insoluble or almost insoluble in the alcoholic medium. The average particle size of the polymer microparticles specifically disclosed in the examples is in the range of 0.19 to 9.0 μm. More specifically, it is disclosed that in this dispersion polymerization method, when acrylamide is used as the vinyl monomer, polymer microparticles with average particle sizes of 0.19 μm and 0.20 μm can be obtained, and when ammonium acrylate is used as the vinyl monomer, polymer microparticles with an average particle size of 0.21 μm can be obtained.

Patent Document 4 discloses that by carrying out solution polymerization, preferably dispersion polymerization or a similar precipitation polymerization, of raw material monomers including a monomer having two or more unsaturated double bonds and an unsaturated monomer having a hydrophilic functional group or an active hydrogen group, using a polymerization initiator in a medium in which the raw material monomers dissolve but the resulting polymer does not dissolve, crosslinked polymer microparticles having a narrow particle size distribution and a relatively uniform particle size can be efficiently obtained without using seed particles, and further that by adding an organic compound having 5 or more carbon atoms and a melting point of 80°C or less to the reaction system, the dispersibility of the particles can be improved, the particle size distribution can be more uniformly controlled, and monodisperse polymer microparticles can be efficiently obtained. The average particle size range of the polymer microparticles specifically disclosed in the examples is 2.5 μm to 5.2 μm.

Japanese Patent Application Publication No. 04-132705 Japanese Patent Application Publication No. 04-279604 Japanese Patent Application Publication No. 09-316106 JP 2006-282772 A

However, the dispersion polymerization methods described in Patent Documents 1, 2, and 4 were unable to produce polymer microparticles with a small particle size (e.g., 0.20 μm or less). According to Patent Document 3, when ammonium acrylate was used as a monomer, the particle size was 0.21 μm.

In addition, according to the present inventors, when vinyl monomers other than the vinyl polymers specifically disclosed in Patent Document 3 were used, problems with polymerization stability could arise, such as a decrease in dispersibility of fine particles during the polymerization reaction, leading to aggregation. Also, there was a problem with the degree of freedom in selecting vinyl monomers.

This specification provides a manufacturing method and a dispersion stabilizer therefor that can obtain polymer microparticles having excellent polymerization stability and small particle diameters (e.g., average particle diameter of 0.20 μm or less).

The present inventors have focused on polymers having polymerizable groups, which are used, for example, as dispersion stabilizers. They have discovered that by using a polymer having a specific living radical polymerization active unit as a dispersion stabilizer and carrying out dispersion polymerization using living radical polymerization utilizing the specific living radical polymerization activity, it is possible to stably obtain small-sized polymer microparticles while suppressing secondary aggregation during the polymerization process. According to this specification, the following means are provided based on such findings.

[1] A step of producing polymer microparticles by polymerizing one or more types of second vinyl monomers by dispersion polymerization in the presence of a first polymer having a polymer chain of one or more types of first vinyl monomers and a living radical polymerization activity unit using living radical polymerization based on the living radical polymerization activity;
Equipped with
The method of claim 1, wherein the living radical polymerization active unit is an active unit in living radical polymerization by a chain exchange mechanism or a bond-dissociation mechanism.
[2] The method according to [1], wherein the living radical polymerization active unit is a living radical polymerization by the chain exchange mechanism.
[3] The method according to [1] or [2], wherein the living radical polymerization active unit is an active unit in living radical polymerization by reversible addition-fragmentation chain transfer polymerization or iodine transfer polymerization.
[4] The method according to any one of [1] to [3], wherein the first polymer has a molecular weight distribution of 2.0 or less.
[5] The method according to any one of [1] to [4], wherein the production process of the polymer microparticles uses 0.3 parts by mass or more and 50 parts by mass or less of the first polymer per 100 parts by mass of the one or more second vinyl monomers.
[6] The method according to [5], wherein the production process of the polymer microparticles uses 0.3 parts by mass or more and 20 parts by mass or less of the first polymer per 100 parts by mass of the one or more second vinyl monomers.
[7] The method according to any one of [1] to [6], wherein the one or more second vinyl monomers comprise acrylic acid or a salt thereof, and the polymerization solvent in the production process of the polymer microparticles comprises acetonitrile.
[8] The method according to [7], wherein the one or more first vinyl monomers are two or more selected from the group consisting of styrenes, (meth)acrylonitrile compounds, maleimide compounds, unsaturated acid anhydrides, and unsaturated carboxylic acid compounds.
[9] The method according to any one of [1] to [8], wherein the one or more second vinyl monomers contain acrylic acid in an amount of 50% by mass or more and 100% by mass or less of the total mass of the second vinyl monomers.
[10] The method according to [9], wherein the one or more first vinyl monomers contain 20 mass % or more of styrenes based on the total mass of the first vinyl monomers.
[11] The one or more first vinyl monomers contain styrenes in an amount of 20 mass% or more of a total mass thereof, and the one or more second vinyl monomers contain acrylic acid or a salt thereof in an amount of 50 mass% or more and 100 mass% or less of a total mass thereof,
the first polymer has a living radical polymerization active unit by reversible addition-fragmentation chain transfer polymerization,
The method according to [1], wherein the first polymer is used in an amount of 0.3 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the one or more second vinyl monomers.
[12] A dispersion stabilizer for use in the production of polymer microparticles, comprising a polymer having one or more polymer chains of a first vinyl monomer and living polymerization active units provided in at least a portion of the polymer chains.

The disclosure of this specification relates to a method for producing polymer microparticles and a dispersion stabilizer. According to the method for producing polymer microparticles disclosed in this specification, a second vinyl monomer is polymerized in the presence of a first polymer having a polymer chain (hereinafter also referred to as a first polymer chain) containing a unit derived from a first vinyl monomer and a living polymerization active unit, whereby the second vinyl monomer is polymerized with the first polymer chain as a base point, and the polymer chain (hereinafter also referred to as a second polymer chain) is extended from the living polymerization active unit. The extension of the second polymer chain forms a nucleus of the polymer microparticle, and then the extension of the second polymer chain and the interaction between the second polymer chains form particles, and the particle diameter of the particles increases.

The first polymer or the second polymer chain is polymerized by living radical polymerization based on active units in living radical polymerization by a chain exchange mechanism or a bond-dissociation mechanism, and therefore generally has a narrow molecular weight distribution and acts to stabilize the dispersion of the polymer microparticles as they grow. In addition, the living polymerization activity derived from the first polymer allows for the production of polymer microparticles that have a first polymer chain and a second polymer chain and have excellent uniformity in the molecular weight of these polymer chains and the entire polymer chain.

By selecting the types of the first polymer chain and the second polymer chain, it is possible to produce polymer microparticles having the first polymer chain of the first polymer on the surface layer of the polymer microparticle and the second polymer chain as the core.

The above method can be applied to a dispersion polymerization method in which, at the start of polymerization, the monomer, initiator, etc. are all dissolved in the medium to form a homogeneous solution, and the polymer generated by the start of polymerization precipitates and aggregates to form particles, resulting in a heterogeneous solution. At this time, the first polymer chain is arranged on the surface side of the polymer microparticle, and the second polymer chain is arranged inside the polymer microparticle, and these polymer chains are organized to generate and grow the polymer microparticle. The first polymer or the first polymer chain functions as an excellent dispersion stabilizer, ensuring the dispersion stability of the polymer microparticles in the polymer microparticle manufacturing process, so that even polymer microparticles with an average particle size of 0.2 μm or less can be easily obtained.

Representative and non-limiting specific examples of the present disclosure are described in detail below. This detailed description is intended simply to provide those skilled in the art with details for implementing preferred examples of the present disclosure, and is not intended to limit the scope of the present disclosure. In addition, the additional features and inventions disclosed below can be used separately or together with other features and inventions to provide a further improved "method for producing polymer microparticles and dispersion stabilizer".

In addition, the combinations of features and steps disclosed in the following detailed description are not essential to implementing the present disclosure in the broadest sense, but are described only to specifically illustrate representative examples of the present disclosure. Furthermore, the various features of the representative examples described above and below, as well as the various features of those described in the independent and dependent claims, do not have to be combined in the specific examples described herein or in the order listed to provide additional and useful embodiments of the present disclosure.

All features described in the specification and/or claims are intended to be disclosed individually and independently of one another as limitations to the original disclosure and claimed particulars, apart from the configuration of features described in the examples and/or claims. Furthermore, all numerical ranges and group or aggregate descriptions are intended to disclose intermediate configurations thereof as limitations to the original disclosure and claimed particulars.

Various embodiments disclosed in this specification are described in detail below. In this specification, "(meth)acrylic" means acrylic and/or methacrylic, and "(meth)acrylate" means acrylate and/or methacrylate. Furthermore, "(meth)acryloyl group" means acryloyl group and/or methacryloyl group.

(Method for producing polymer microparticles)
The method for producing polymer microparticles disclosed in the present specification (hereinafter also simply referred to as the present production method) can include a step of producing polymer microparticles by polymerizing one or more types of second vinyl monomers (hereinafter also simply referred to as second monomers) in the presence of a first polymer chain containing a monomer unit derived from one or more types of first vinyl monomers (hereinafter also simply referred to as first monomers) and a first polymer having a living polymerization active unit.

(First polymer) In this method, a first polymer can be used. The first polymer can have a first polymer chain containing units derived from one or more first monomers and a living polymerization active unit. The first monomer varies depending on the function and application of the polymer microparticles to be obtained, and various vinyl monomers can be used without any particular limitation.

(First polymer chain) The first polymer chain is obtained by polymerizing a monomer composition containing a first monomer. Examples of the first monomer include styrenes, (meth)acrylonitrile compounds, maleimide compounds, unsaturated acid anhydrides, and unsaturated carboxylic acid compounds. One or more of these can be used in combination.

Styrenes include styrene and its derivatives. Specific examples of compounds include styrene, α-methylstyrene, β-methylstyrene, vinylxylene, vinylnaphthalene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene, p-n-butylstyrene, p-isobutylstyrene, p-t-butylstyrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, o-chloromethylstyrene, p-chloromethylstyrene, o-chlorostyrene, p-chlorostyrene, o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, divinylbenzene, and the like. One or more of these can be used. Among these, from the viewpoint of polymerizability, styrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, o-hydroxystyrene, m-hydroxystyrene, and p-hydroxystyrene are preferred.

(Meth)acrylonitrile compounds include (meth)acrylonitrile, α-methylacrylonitrile, etc. For example, acrylonitrile is used.

Maleimide compounds include maleimide and N-substituted maleimide compounds. Specific examples of N-substituted maleimide compounds include N-alkyl-substituted maleimide compounds such as N-methylmaleimide, N-ethylmaleimide, N-n-propylmaleimide, N-isopropylmaleimide, N-n-butylmaleimide, N-isobutylmaleimide, N-tert-butylmaleimide, N-pentylmaleimide, N-hexylmaleimide, N-heptylmaleimide, N-octylmaleimide, N-laurylmaleimide, and N-stearylmaleimide; N-cyclopentylmaleimide, and N-cyclohexylmaleimide. N-cycloalkyl-substituted maleimide compounds such as N-phenylmaleimide, N-(4-hydroxyphenyl)maleimide, N-(4-acetylphenyl)maleimide, N-(4-methoxyphenyl)maleimide, N-(4-ethoxyphenyl)maleimide, N-(4-chlorophenyl)maleimide, N-(4-bromophenyl)maleimide, and N-aryl-substituted maleimide compounds such as N-benzylmaleimide, and one or more of these may be used. For example, N-phenylmaleimide is used.

In addition, examples of unsaturated acid anhydrides include maleic anhydride, itaconic anhydride, citraconic anhydride, etc., and one or more of these can be used.

Examples of unsaturated carboxylic acid compounds include (meth)acrylic acid, cinnamic acid, crotonic acid, and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, crotonic acid, and citraconic acid, as well as monoalkyl esters of unsaturated dicarboxylic acids, of which one or more can be used.

Among these, it is preferable that the first monomer contains at least a styrene. This is because styrenes are easy to undergo living polymerization and can impart moderate hydrophobicity and affinity to organic solvents. It is possible to impart hydrophobicity or affinity to organic solvents to the first polymer chain. In this way, for example, when polymer microparticles are produced by dispersion polymerization in a polar organic solvent, the first polymer tends to be present on the surface layer of the polymer microparticles, improving the dispersion stability of the polymer microparticles.

The styrenes are, for example, 20% by mass or more of the total mass of the first monomer (first monomer unit of the first polymer chain) for polymerizing the first polymer chain. This is because 20% by mass or more facilitates living polymerization and can appropriately impart moderate hydrophobicity and affinity to organic solvents. Also, for example, 30% by mass or more, for example, 35% by mass or more, for example, 40% by mass or more, for example, 50% by mass or more, for example, 60% by mass or more, for example, 65% by mass or more, for example, 70% by mass or more, or for example, 75% by mass or more. Also, the styrenes are, for example, 100% by mass or less of the total mass, for example, 95% by mass or less, for example, 90% by mass or less, for example, 85% by mass or less, for example, 80% by mass or less, or for example, 75% by mass or less. The range of the styrenes relative to the total mass can be set by appropriately combining the above-mentioned lower and upper limits, and is, for example, 20 mass% or more and 95 mass% or less, for example, 30 mass% or more and 75 mass% or less, and for example, 35 mass% or more and 85 mass% or less.

Each of the (meth)acrylonitrile compound, maleimide compound, acid anhydride and unsaturated carboxylic acid compound can be used alone, and it is preferable to use one or more of these four types in combination with styrenes. This is because all of these four types can maintain, adjust or impart hydrophobicity or organic solvent affinity to the first polymer chain. Among them, one or more of (meth)acrylonitrile compounds such as acrylonitrile, maleimide compounds such as N-phenylmaleimide and acid anhydrides are preferred, and combinations such as styrene and acrylonitrile, styrene and N-phenylmaleimide are suitable. In addition, unsaturated carboxylic acid compounds are preferred in that they can easily change the polarity of the first polymer.

When used in combination with styrenes, the total amount of these one or more first monomers other than styrenes is, for example, 20% by mass or more of the total mass of the first monomer (first monomer unit of the first polymer chain) for polymerizing the first polymer chain. Also, for example, 25% by mass or more, for example, 30% by mass or more, for example, 35% by mass or more, for example, 40% by mass or more, for example, 50% by mass or more, for example, 60% by mass or more. Also, the (meth)acrylonitrile compound is 80% by mass or less, for example, 75% by mass or less, for example, 70% by mass or less, for example, 65% by mass or less, for example, 60% by mass or less, for example, 55% by mass or less, for example, 50% by mass or less of the total mass. The total amount of these one or more first monomers other than styrenes can be set by appropriately combining the above-mentioned lower and upper limits, and is, for example, 20 mass% or more and 65 mass% or less, and also, for example, 25 mass% or more and 50 mass% or less.

The first polymer chain may be a polymer chain of only the first monomer described above, but if necessary, other vinyl monomers other than the above can be used as the first monomer. For example, known vinyl monomers such as (meth)acrylic acid esters such as alkyl (meth)acrylate can be used. The amount of such other monomers is, for example, 10% by mass or less, or, for example, 5% by mass or less, or, for example, 3% by mass or less, or, for example, 1% by mass or less, or, for example, 0.5% by mass or less of the total mass of the monomers constituting the first polymer chain.

In addition, the first polymer may have a polymer chain as another block in addition to the first polymer chain. Examples of vinyl monomers constituting such polymer chains include (meth)acrylic acid, known (meth)acrylic acid alkyl esters, and known (meth)acrylic acid hydroxyalkyl esters. Such vinyl monomers may be the second monomer described later. Such other polymer chains may be added in a separate synthesis step after the formation of the first polymer chain. By being provided so as to be directly linked to the living radical active unit described later and linked to the first polymer chain, a portion of the monomer common to the second monomer used in the polymer microparticles can be provided in advance in the first polymer.

(Living radical polymerization active unit)
The first polymer may have a living radical polymerization active unit. Living radical polymerization is generally considered to be a polymerization reaction that consists of only an initiation reaction and a propagation reaction in a polymerization process, does not involve side reactions such as chain transfer reactions or termination reactions that deactivate the propagation end, and the propagation end always maintains propagation activity (living radical polymerization activity) based on radical species during polymerization. The living radical polymerization active unit is a propagation active unit in living radical polymerization. The living radical polymerization active unit is also a unit derived from a control agent for living radical polymerization.

Various living radical polymerizations are known based on their reaction mechanisms, but the living radical polymerization active units can be active units in living radical polymerization by chain exchange mechanism or bond-dissociation mechanism. These living radical polymerizations make it easy to obtain a first polymer with a narrow molecular weight distribution, and in dispersion polymerization of polymer microparticles, various monomers can be selected for the solubility of the first polymer in the polymerization solvent and for its function as a dispersion stabilizer.

Examples of living radical polymerization by the exchange chain mechanism include reversible addition-fragmentation chain transfer polymerization (RAFT), iodine transfer polymerization, polymerization using an organotellurium compound (TERP), polymerization using an organoantimony compound (SBRP), and polymerization using an organobismuth compound (BIRP). Living radical polymerization by the exchange chain mechanism is preferred in that it can reduce the average particle size of the polymer particles. Among these, the RAFT and iodine transfer polymerization are preferred in that they can narrow the molecular weight distribution of the first polymer. Furthermore, the RAFT method is preferably used.

An example of living radical polymerization by a bond-dissociation mechanism is the nitroxy radical method (NMP method). Living radical polymerization by a bond-dissociation mechanism is preferable because it can reduce the average particle size of the polymer microparticles. Among these, the NMP method is preferable because it can narrow the molecular weight distribution of the first polymer.

The polymerization conditions for these various living radical polymerizations are well known to those skilled in the art, and as necessary, the synthesis of the first polymer by the RAFT method, the iodine transfer polymerization method, and the NMP method will be exemplified. Note that there are various living radical polymerization processes such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization, but considering that it is a polymerization base point in the production of polymer microparticles and functions as a dispersion stabilizer, for example, solution polymerization can be used in the production of the first polymer.

The first polymer can be synthesized by the RAFT method, for example, using a control agent for the RAFT method. The RAFT method is a living radical polymerization method suitable for obtaining a first polymer having a molecular weight distribution of 2.0 or less. The control agent for living radical polymerization in the RAFT method (RAFT agent) is not particularly limited, and a known RAFT agent can be used. For example, dithioester compounds, xanthate compounds, trithiocarbonate compounds, and dithiocarbamate compounds can be mentioned. The RAFT agent may be a monofunctional agent having one active site, or a bifunctional or higher agent having two or more active sites. A bifunctional or higher functional RAFT agent is one in which the polymer chain extends in two or more directions. From the viewpoint of producing polymer microparticles, it may be preferable to use a bifunctional or trifunctional or higher functional RAFT agent.

The substituents in the RAFT agent can be appropriately determined in consideration of the first monomer and the second monomer. The amount of the RAFT agent used is appropriately adjusted according to the target Mn, and can be, for example, 0.1 parts by mass or more and 10 parts by mass or less, or, for example, 0.5 parts by mass or more and 5 parts by mass or less, or, for example, 1 part by mass or more and 4 parts by mass or less, or, for example, 1 part by mass or more and 3 parts by mass or less, relative to 100 parts by mass of the first monomer.

As the RAFT agent, various known RAFT agents can be used, such as dithioester compounds, xanthate compounds, trithiocarbonate compounds, and dithiocarbamate compounds. More specifically, for example, dibenzyl trithiocarbonate, dithiobenzoate, 2-cyano-2-propyl benzodithioate, 2-phenyl-2-propyl benzodithioate, trithiocarbonate, 2-cyano-2-propyl dodecyl trithiocarbonate, 2-(dodecylthiocarbonothioylthio)-2-methyl methyl propanoate, distyryl trithiocarbonate, dicumyl trithiocarbonate, dithiocarbamate, cyanomethyl N-methyl-N-phenyl dithiocarbamate, etc.

As the radical polymerization initiator (radical generator) used in polymerization by the RAFT method, known radical polymerization initiators such as azo compounds, organic peroxides, and persulfates can be used, but azo compounds are preferred because they are safe and easy to handle and are less likely to cause side reactions during radical polymerization. Specific examples of the azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl-2,2'-azobis(2-methylpropionate), and 2,2'-azobis(2-methylbutyronitrile). One or more of the above radical polymerization initiators can be used.

The proportion of such radical polymerization initiator used is not particularly limited, but from the viewpoint of obtaining a polymer with a narrower molecular weight distribution, the proportion of such radical polymerization initiator used is not particularly limited, but from the viewpoint of obtaining a polymer with a narrower molecular weight distribution, it can be used in an amount of, for example, 0.005% by mass or more and 2% by mass or less, or, for example, 0.005% by mass or more and 1% by mass or less, or, for example, 0.005% by mass or more and 0.5% by mass or less, relative to 100 parts by mass of the total mass of the first monomer.

The RAFT method may be carried out in the presence of a chain transfer agent, if necessary. One or more known chain transfer agents may be used.

In addition, in the RAFT method, known polymerization solvents can be used, such as nitrile solvents, aromatic solvents, ketone solvents, ester solvents, orthoester solvents, dimethylformamide, dimethyl sulfoxide, alcohol, and water. Specific examples of nitrile solvents include acetonitrile, isobutyronitrile, and benzonitrile. Specific examples of aromatic solvents include benzene, toluene, xylene, and anisole. Specific examples of ketone solvents include acetone, methyl ethyl ketone, and methyl isobutyl ketone. Specific examples of ester solvents include methyl acetate, ethyl acetate, propyl acetate, and butyl acetate. Specific examples of orthoester solvents include trimethyl orthoformate, triethyl orthoformate, tri(n-propyl) orthoformate, tri(isopropyl) orthoformate, trimethyl orthoacetate, triethyl orthoacetate, triethyl orthopropionate, trimethyl ortho-n-butyrate, and trimethyl orthoisobutyrate. Preferably, a nitrile solvent such as acetonitrile and/or an aromatic solvent such as anisole can be used.

The concentration of the first monomer when polymerizing the first polymer by living radical polymerization is not particularly limited relative to the total mass of the polymerization solvent and the first monomer, but can be, for example, 10% by mass or more and 80% by mass or less, or, for example, 15% by mass or more and 70% by mass or less, or 20% by mass or more and 70% by mass or less, etc.

The reaction temperature during the polymerization reaction by the RAFT method is preferably 40°C or higher and 100°C or lower, more preferably 45°C or higher and 90°C or lower, and even more preferably 50°C or higher and 80°C or lower. If the reaction temperature is 40°C or higher, the polymerization reaction can proceed smoothly. On the other hand, if the reaction temperature is 100°C or lower, side reactions can be suppressed and restrictions on the initiators and solvents that can be used are relaxed.

The first polymer can also be synthesized by iodine transfer polymerization using, for example, a control agent for iodine transfer polymerization. The control agent in iodine transfer polymerization is not particularly limited, and known control agents can be used, such as methyl iodide, methylene iodide, iodoform, carbon tetraiodide, 1-phenylethyl iodide, benzyl iodide, methyl 2-iodoisobutyrate, ethyl 2-iodoisobutyrate, ethyl 2-iodo-2-phenylacetate, ethylene glycol bis(2-iodo-2-phenylacetic acid), and ethylene glycol bis(2-iodoisobutyrate).

The amount of the iodine transfer reaction control agent used is adjusted appropriately depending on the target Mn, but for example, 0.1 parts by mass to 10 parts by mass, or for example, 0.5 parts by mass to 5 parts by mass, or for example, 1 part by mass to 4 parts by mass, can be used relative to 100 parts by mass of the first monomer. For example, 0.1 parts by mass to 10 parts by mass, or for example, 0.5 parts by mass to 5 parts by mass, or for example, 1 part by mass to 4 parts by mass, can be used relative to 100 parts by mass of the first monomer.

As the radical polymerization initiator (radical generator) used in polymerization by the iodine transfer polymerization method, known radical polymerization initiators such as azo compounds, organic peroxides, and persulfates can be used in the same manner and amount as in the RAFT method. The reaction temperature, polymerization solvent, and first monomer concentration in the iodine transfer polymerization method can be appropriately selected from the same manner as in the RAFT method.

The first polymer can also be synthesized by the NMP method using a control agent for the NMP method. The control agent in the NMP method is not particularly limited, and any known control agent can be used, such as 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO), N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)]nitroxide (DEPN), 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO), N-tert-butyl-N-(1-tert-butyl-2-ethylsulfinyl)propyl-N-oxyl (BESN), etc.

The amount of the control agent used in the NMP method is appropriately adjusted depending on the target Mn, but for example, 0.1 parts by mass to 10 parts by mass, or for example, 0.5 parts by mass to 5 parts by mass, or for example, 1 part by mass to 4 parts by mass, can be used relative to 100 parts by mass of the first monomer. For example, 0.1 parts by mass to 10 parts by mass, or for example, 0.5 parts by mass to 5 parts by mass, or for example, 1 part by mass to 4 parts by mass, can be used relative to 100 parts by mass of the first monomer.

As the radical polymerization initiator (radical generator) used in polymerization by the NMP method, known radical polymerization initiators such as azo compounds, organic peroxides, and persulfates can be used in the same manner and amount as in the RAFT method. The reaction temperature, polymerization solvent, and first monomer concentration in the NMP method can be appropriately selected from the same manner as in the RAFT method.

By synthesizing a first polymer by a predetermined living radical polymerization, a first polymer having a first polymer chain containing a first monomer and a living polymerization active unit can be obtained. The first polymer can also have two or more types of first polymer chains. For example, by performing living radical polymerization or the like using one or more types of first monomers of a certain composition, and then performing living radical polymerization or the like using one or more types of first monomers of another composition, a first polymer having a first polymer chain (block) having a unit derived from a first monomer of a different composition can be obtained.

According to a specific living radical polymerization, a first polymer having a controlled number average molecular weight (Mn) and weight average molecular weight (Mw) can be obtained. The Mn of the first polymer is not particularly limited, but is, for example, 3,000 or more, for example, 5,000 or more, for example, 7,000 or more, for example, 8,000 or more, or for example, 10,000 or more. The Mn is 50,000 or less, for example, 30,000 or less, for example, 25,000 or less, for example, 20,000 or less, for example, 15,000 or less, for example, 14,000 or less, or for example, 12,000 or less. The range of Mn can be set by appropriately combining the above-mentioned lower and upper limits, and is, for example, 5,000 or more and 25,000 or less, for example, 10,000 or more and 25,000 or less, for example, 10,000 or more and 15,000 or less, and for example, 10,000 or more and 14,000 or less.

The Mw of the first polymer is not particularly limited, but is, for example, 5,000 or more, for example, 7,000 or more, for example, 9,000 or more, for example, 10,000 or more, for example, 13,000 or more, or for example, 15,000 or more. The Mw is 60,000 or less, for example, 55,000 or less, for example, 50,000 or less, for example, 45,000 or less, for example, 40,000 or less, for example, 36,000 or less, for example, 35,000 or less, for example, 30,000 or less, or for example, 25,000 or less. The range of Mw can be set by appropriately combining the above-mentioned lower and upper limits, and is, for example, 1,000 or more and 40,000 or less, for example, 10,000 or more and 35,000 or less, for example, 10,000 or more and 30,000 or less, and for example, 15,000 or more and 25,000 or less.

The Mw and Mn of the first polymer can be measured by gel permeation chromatography using polystyrene as a standard substance. Details of the chromatography conditions can be those disclosed in the examples below.

The molecular weight distribution (Mw/Mn) of the first polymer is not particularly limited, but may be, for example, 2.5 or less, for example, 2.4 or less, for example, 2.3 or less, for example, 2.0 or less, for example, 1.6 or less, for example, 1.5 or less, for example, 1.4 or less, or for example, 1.3 or less. The molecular weight distribution may be, for example, 1.1 or more, for example, 1.2 or more, for example, 1.3 or more, for example, 1.4 or more, or for example, 1.5 or more. The range of the molecular weight distribution may be set by appropriately combining the above-mentioned lower and upper limits, and may be, for example, 1.1 or more and 2.5 or less, for example, 1.1 or more and 2.4 or less, for example, 1.1 or more and 2.3 or less, or for example, 1.1 or more and 2.0 or less.

The narrower the molecular weight distribution, the smaller the average particle size of the resulting polymer microparticles tends to be. To obtain polymer microparticles with an average particle size of 0.2 μm or less, it is preferable that the molecular weight distribution is 2.4 or less, and to obtain polymer microparticles with an even smaller average particle size, it is preferable that the molecular weight distribution is 1.7 or less, more preferably 1.6 or less, and even more preferably 1.4 or less.

The first polymer can have a first polymer chain and a living polymerization active unit, but typically, when a monofunctional control agent is used, the living polymerization active unit is provided at the end of the first polymer chain, and when a bifunctional or higher control agent is used, the polymer branches in two or more directions from the living polymerization active unit as a base point, and each of the first polymer chains is provided. In either case, when another polymer chain is provided, the other polymer chain is directly bonded to the living polymerization active unit, and the first polymer chain is bonded to the distal end of the other polymer chain so that the first polymer chain is provided on the more distal side of the living polymerization active unit.

(Production of polymer microparticles) This method can produce polymer microparticles by dispersion polymerizing one or more types of second monomers in the presence of a first polymer. In this method, the first polymer is used as a starting point for polymerization of the second monomer during the production of polymer microparticles, and can also be used as a dispersion stabilizer for the polymer microparticles in the polymerization solvent. In this way, polymerization stability, i.e., aggregation of polymer microparticles during the polymerization process, can be suppressed to suppress the generation of coarse aggregated particles, and polymer microparticles with a small average particle size and a narrow particle size distribution can be obtained.

(Second vinyl monomer) The second vinyl monomer is not particularly limited, and can be appropriately selected from known vinyl monomers depending on the application of the polymer microparticles. For example, in order to allow the first polymer to effectively exert its function as a dispersion stabilizer and to be present on the surface side of the polymer microparticles, and to allow the second polymer chain to be present on the core side as the main component of the polymer microparticles, the second monomer can be a vinyl monomer having a hydrophilic group. Considering this viewpoint, examples of the second monomer include a carboxyl group-containing vinyl monomer and a hydroxyl group-containing vinyl monomer.

Examples of carboxyl group-containing vinyl monomers include unsaturated carboxylic acids such as (meth)acrylic acid and crotonic acid, as well as unsaturated dicarboxylic acids such as itaconic acid, maleic acid and fumaric acid, and monoalkyl esters of unsaturated dicarboxylic acids. Of these, (meth)acrylic acid is preferred.

(Meth)acrylic acid may be in the form of a salt. Here, (meth)acrylic acid (salt) includes (meth)acrylic acid and (meth)acrylic acid salts. The salt of the (meth)acrylic acid salt is an alkali metal salt, an alkaline earth metal salt, an ammonium salt, or an organic amine salt. Specifically, alkali metal salts such as sodium salt, lithium salt, potassium salt, rubidium salt, and cesium salt; alkaline earth metal salts such as magnesium salt, calcium salt, strontium salt, and barium salt; organic amine salts include alkanolamine salts such as monoethanolamine salt, diethanolamine salt, and triethanolamine salt, alkylamine salts such as monoethylamine salt, diethylamine salt, and triethylamine salt, and salts of organic amines such as polyamines such as ethylenediamine salt and triethylenediamine salt.

Examples of hydroxy group-containing vinyl monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and mono(meth)acrylic acid esters of polyalkylene glycols such as polyethylene glycol and polypropylene glycol. These compounds may be used alone or in combination of two or more.

Such second monomers can be used alone or in combination of two or more. The amount of the carboxyl group-containing vinyl monomer relative to the total mass of the second monomer can be, for example, 40% by mass or more, or, for example, 50% by mass or more, or, for example, 60% by mass or more, or, for example, 70% by mass or more, or, for example, 80% by mass or more, or, for example, 90% by mass or more, or, for example, 95% by mass or more, or, for example, 100% by mass. The range of the carboxyl group-containing vinyl monomer relative to the total mass of the second monomer can be set by appropriately combining the above-mentioned lower and upper limits, and is, for example, 60% by mass or more and 100% by mass or less, or, for example, 80% by mass or more and 100% by mass or less, or, for example, 90% by mass or more and 100% by mass or less.

The hydroxyl group-containing vinyl monomer is, for example, 5% by mass or more, for example, 10% by mass or more, for example, 20% by mass or more, for example, 30% by mass or more, or for example, 40% by mass or more, relative to the total mass of the second monomer. It is also 50% by mass or less, for example, 40% by mass or less, for example, 30% by mass or less, for example, 20% by mass or less, for example, 10% by mass or less, or for example, 5% by mass or less. The range of use of the hydroxyl group-containing vinyl monomer relative to the total mass of the second monomer can be set by appropriately combining the above-mentioned lower and upper limits, for example, 0% by mass or more and 40% by mass or less, for example, 0% by mass or more and 20% by mass or less, or for example, 0% by mass or more and 10% by mass or less.

The second monomer may contain other vinyl monomers as long as they do not impair the intended function of the second polymer chain in the polymer microparticles. Such vinyl monomers are not particularly limited, but include, for example, (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters. Such second monomers may be contained, for example, in an amount of 20% by mass or less, or, for example, 10% by mass or less, or, for example, 5% by mass or less, or, for example, 3% by mass or less, or, for example, 1% by mass or less, based on the total mass of the second monomer.

Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, and (meth)acrylic acid. linear or branched alkyl ester compounds of (meth)acrylic acid, such as decyl (meth)acrylate and dodecyl (meth)acrylate; and aliphatic cyclic ester compounds of (meth)acrylic acid, such as cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

Examples of (meth)acrylic acid alkoxyalkyl esters include methoxymethyl (meth)acrylate, ethoxymethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 3-propoxypropyl (meth)acrylate, 3-butoxypropyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 3-ethoxybutyl (meth)acrylate, 3-propoxybutyl (meth)acrylate, and 3-butoxybutyl (meth)acrylate.

In the manufacturing process of polymer microparticles, a crosslinked structure can be introduced into the second polymer chain.

The method for introducing the crosslinked structure is not particularly limited, and examples thereof include the following methods.
1) Copolymerization of a crosslinkable monomer; 2) Utilizing chain transfer to a polymer chain during radical polymerization; 3) After synthesizing a polymer having a reactive functional group, a crosslinking agent is added as necessary to post-crosslink. Among these, the method using copolymerization of a crosslinkable monomer is preferred because it is simple to operate and the degree of crosslinking can be easily controlled.

Examples of crosslinkable monomers include polyfunctional polymerizable monomers having two or more polymerizable unsaturated groups, and monomers having self-crosslinkable crosslinkable functional groups such as hydrolyzable silyl groups. The polyfunctional polymerizable monomers are compounds having two or more polymerizable functional groups such as (meth)acryloyl groups and alkenyl groups in the molecule, and examples of such compounds include polyfunctional (meth)acrylate compounds, polyfunctional alkenyl compounds, and compounds having both (meth)acryloyl groups and alkenyl groups. These compounds may be used alone or in combination of two or more. Among these, polyfunctional alkenyl compounds are preferred in that they are easy to obtain a uniform crosslinked structure, and polyfunctional allyl ether compounds having multiple allyl ether groups in the molecule are particularly preferred.

Examples of polyfunctional (meth)acrylate compounds include di(meth)acrylates of dihydric alcohols such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate; tri(meth)acrylates of trihydric or higher polyhydric alcohols such as trimethylolpropane tri(meth)acrylate, tri(meth)acrylate of trimethylolpropane ethylene oxide modified product, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and poly(meth)acrylates such as tetra(meth)acrylate; and bisamides such as methylene bisacrylamide and hydroxyethylene bisacrylamide.

Examples of polyfunctional alkenyl compounds include polyfunctional allyl ether compounds such as trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, tetraallyloxyethane, and polyallyl sucrose; polyfunctional allyl compounds such as diallyl phthalate; and polyfunctional vinyl compounds such as divinylbenzene.

Examples of compounds having both a (meth)acryloyl group and an alkenyl group include allyl (meth)acrylate, isopropenyl (meth)acrylate, butenyl (meth)acrylate, pentenyl (meth)acrylate, and 2-(2-vinyloxyethoxy)ethyl (meth)acrylate.

Specific examples of the monomer having a self-crosslinkable crosslinking functional group include hydrolyzable silyl group-containing vinyl monomer, N-methylol (meth)acrylamide, N-methoxyalkyl (meth)acrylamide, etc. These compounds can be used alone or in combination of two or more.

The hydrolyzable silyl group-containing vinyl monomer is not particularly limited as long as it is a vinyl monomer having at least one hydrolyzable silyl group. For example, vinyl silanes such as vinyl trimethoxysilane, vinyl triethoxysilane, vinyl methyl dimethoxysilane, vinyl dimethyl methoxysilane, etc.; silyl group-containing acrylic acid esters such as trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, methyl dimethoxysilylpropyl acrylate, etc.; silyl group-containing methacrylic acid esters such as trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, methyl dimethoxysilylpropyl methacrylate, dimethyl methoxysilylpropyl methacrylate, etc.; silyl group-containing vinyl ethers such as trimethoxysilylpropyl vinyl ether; silyl group-containing vinyl esters such as vinyl trimethoxysilyl undecanoate, etc. can be mentioned.

The amount of the crosslinkable monomer used is, for example, 0.1% by mass or more and 5% by mass or less, for example, 0.5% by mass or more and 3% by mass or less, based on the total mass of monomers other than the crosslinkable monomer (non-crosslinkable monomers). The amount of the crosslinkable monomer used is, for example, 0.01 mol% or more and 2 mol% or less, for example, 0.03 mol% or more and 2 mol% or less, for example, 0.5 mol% or more and 1 mol% or less, based on the total molar amount of the non-crosslinkable monomers.

In producing polymer microparticles, since the first polymer has a living polymerization active unit, the second monomer is polymerized to the living polymerization active unit by adding an appropriate radical polymerization initiator (radical generator). The radical polymerization initiator can be appropriately selected from the various aspects described for the RAFT agent. The proportion of the radical polymerization initiator used is not particularly limited, but from the viewpoint of obtaining a polymer with a narrower molecular weight distribution, for example, 0.01% by mass or more and 5% by mass or less, or, for example, 0.02% by mass or more and 3% by mass or less, or, for example, 0.03% by mass or more and 3% by mass or less can be used relative to 100 parts by mass of the total mass of the second monomer.

By employing a dispersion polymerization method for the production of polymer microparticles, polymer microparticles with a small average particle size can be easily obtained. The polymerization solvent used in the production of polymer microparticles can be appropriately selected depending on the polymerization method employed and the types of the first monomer, second monomer, etc. When employing a dispersion polymerization method, for example, various solvents used in the synthesis of the first polymer can be appropriately used. For example, a nitrile-based solvent such as acetonitrile can be used.

By using the polymerization solvent used in the synthesis of the first polymer, the first polymer can be dissolved and the solvent is a good solvent that easily dissolves the first polymer chain and the control agent for living radical polymerization, so that the first polymer chain is present on the surface side of the polymer microparticles, and the second polymer chain side consisting of acrylic acid or the like that becomes the extension end can be organized and polymerized so as to be present inside the polymer microparticles. This makes it easier to form a microparticle structure with excellent dispersion stability.

The polymerization solvent used in the production of polymer microparticles can further be determined taking into account dispersion polymerization, and must be a poor solvent in which the second monomer, etc. dissolves but the polymer microparticles containing the polymer chains do not dissolve.

For example, examples of polymerization solvents used in the production of polymer microparticles include nitrile-based solvents such as acetonitrile, alcohol-based solvents such as methanol and t-butyl alcohol, ketone-based solvents such as acetone, furan-based solvents such as tetrahydrofuran, ether-based solvents such as tetrahydrofuran, as well as benzene, ethyl acetate, dichloroethane, n-hexane, cyclohexane, and n-heptane. These solvents can be used alone or in combination of two or more. Furthermore, these solvents can also be used as mixed solvents with highly polar solvents such as water. When the polymerization solvent for the polymer microparticles contains a highly polar solvent such as water, (meth)acrylic acid can be quickly neutralized in the polymerization process. The amount of the highly polar solvent used is preferably 0.05 to 10.0% by mass, more preferably 0.1 to 5.0% by mass, and even more preferably 0.1 to 1.0% by mass, based on the total mass of the medium. If the proportion of the highly polar solvent is 0.05% by mass or more, an effect on the neutralization reaction is observed, and if it is 10.0% by mass or less, no adverse effect on the polymerization reaction is observed.

The concentration of the second monomer in the polymerization solvent is not particularly limited and can be set appropriately, for example, to 5% by mass or more and 30% by mass or less, and can also be, for example, to 10% by mass or more and 20% by mass or less.

The reaction temperature during the polymerization reaction in the production of polymer microparticles is not particularly limited, but is, for example, 40°C or higher and 100°C or lower. Also, for example, it is 45°C or higher and 90°C or lower, and also, for example, it is 50°C or higher and 80°C or lower. If the reaction temperature is 40°C or higher, the polymerization reaction can proceed smoothly. On the other hand, if the reaction temperature is 100°C or lower, side reactions can be suppressed and restrictions on the initiators and solvents that can be used are relaxed.

The second monomer will be described in detail later, but in order to make the first polymer function as a dispersion stabilizer when polymerizing the second monomer in the presence of the first polymer to produce polymer microparticles, for example, 0.3 parts by mass or more and 50 parts by mass or less of the first polymer can be used with respect to 100 parts by mass of the total mass of the second monomer. By using in such a range, it is possible to produce polymer microparticles mainly containing the second monomer while making the first polymer function as a dispersion stabilizer. In addition, if the first polymer is less than 0.3 parts by mass, it is difficult to obtain a sufficient dispersion stabilizing effect, and the average particle diameter of the polymer microparticles is likely to exceed 0.2 μm, and even if it exceeds 50 parts by mass, the functionality as a dispersion stabilizer is difficult to improve, and the effect of decreasing the average particle diameter of the polymer microparticles is also small.

The first polymer can be used in an amount of, for example, 0.5 parts by mass or more, or, for example, 1 part by mass or more, relative to 100 parts by mass of the total mass of the second monomer. The first polymer can be used in an amount of, for example, 50 parts by mass or less, or, for example, 40 parts by mass or less, or, for example, 30 parts by mass or less, or, for example, 20 parts by mass or less. The range of the amount of the first polymer used relative to 100 parts by mass of the total mass of the second monomer can be set by appropriately combining the above upper and lower limits, and is, for example, 0.3 parts by mass or more and 30 parts by mass or less, or, for example, 0.3 parts by mass or more and 20 parts by mass or less, or, for example, 0.5 parts by mass or more and 20 parts by mass or less, or, for example, 1 part by mass or more and 20 parts by mass or less.

Polymer microparticles can be produced by the above method. According to this method, polymer microparticles having an average particle size of 0.2 μm or less can be easily obtained. In addition, since the polymerization stability is excellent, the generation of aggregates during the polymerization process can be suppressed, and the generation of coarse particles can be suppressed. In this specification, the average particle size of the polymer microparticles can be obtained by measuring the particle size of the polymer microparticles observed under a microscope using image analysis software or the like and calculating the average value of these. The average value of the particle sizes of 400 particles in an image observed with a field emission scanning electron microscope can be used as the average particle size of the microparticles. More specifically, the following method can be adopted. Using a field emission scanning electron microscope (FE-SEM, JSM-6330F manufactured by JEOL Ltd.) or a microscope with a resolution equivalent to that of the electron microscope, multiple images in which 50 to 100 particles can be observed per image are obtained, and the obtained images are counted using image analysis software "WinROOF" manufactured by Mitani Shoji Co., Ltd. or software capable of counting the number of particles and particle diameter with the same accuracy and precision as that software, until the number of particles reaches 200 in total, and the particle diameter (circle equivalent diameter) of the 200 particles is measured. Furthermore, this operation is repeated for another captured image, and the particle diameter of 200 particles is measured in the same manner. The average value of the particle diameters of these 400 particles in total can be regarded as the average particle diameter. Furthermore, particles that are twice or more the average particle diameter thus obtained are regarded as coarse particles, and the number of coarse particles among 100 particles can be counted to obtain the number of coarse particles.

In particular, polymer microparticles can be obtained in which the residual aggregates in the polymerization stability test disclosed in the examples are, for example, 200 ppm or less, or, for example, 150 ppm or less, or, for example, 100 ppm or less, or, for example, 60 ppm or less, or, for example, 40 ppm or less, or, for example, 20 ppm or less, or, for example, 10 ppm or less.

In addition, polymer microparticles can be obtained in which the number of coarse particles per 100 particles disclosed in the examples is 2 or less, for example 1 or less.

As described above, the first polymer disclosed in this specification is useful as a dispersion stabilizer for producing polymer microparticles. By producing polymer microparticles using the first polymer as a dispersion stabilizer, a base point for polymerization of polymer microparticles that can be dissolved in a polymerization solvent with a uniform number average molecular weight is provided, and self-organization of the first polymer chains and the second polymer chains that are suitable for particle nucleation and particle growth by the second monomer in the polymerization solvent is promoted, making it possible to easily produce polymer microparticles with a small average particle size while maintaining good polymerization stability.

Below, specific examples are described to more specifically explain the disclosure of this specification. The following examples are intended to explain the disclosure of this specification and are not intended to limit its scope. In the following examples, % represents % by mass and parts represents parts by mass, unless otherwise specified.

(Method of measuring molecular weight of polymer)
In the following examples, the molecular weight of the polymer was measured by gel permeation chromatography (GPC). That is, the number average molecular weight (Mn) and weight average molecular weight (Mw) were obtained in terms of polystyrene by THF-based GPC. The molecular weight distribution (Mw/Mn) was calculated from the obtained values. GPC was performed under the following conditions.

Column: Tosoh TSKgel SuperMultiporeHZ-M x 4 Solvent: Tetrahydrofuran Temperature: 40°C Detector: RI Flow rate: 600 μL/min

(Synthesis of polymers having living polymerization activity)
(Polymer 1:P(St/PhMI))
A 1L flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 2.0 parts of RAFT agent (dibenzyl trithiocarbonate: hereinafter also referred to as "DBTTC"). 0.014 parts of 2,2'-azobis(2-methylbutyronitrile) (manufactured by Japan Finechem Co., Ltd., trade name "ABN-E": hereinafter also referred to as "ABN-E"). 38 parts of styrene (hereinafter also referred to as "St"), 62 parts of N-phenylmaleimide (hereinafter also referred to as "PhMI"), and 222 parts of acetonitrile. The mixture was thoroughly degassed by nitrogen bubbling, and polymerization was initiated in a thermostatic bath at 70 ° C. After 4 hours, the mixture was cooled to room temperature to stop the reaction. The above polymerization solution was purified by reprecipitation from methanol/water = 90/10 (vol%) and vacuum dried to obtain polymer 1. As a result of analysis by gas chromatography, the reaction rate of the obtained polymer 1 was St 75% and PhMI 75%. The molecular weight of the polymer 1 was Mn 10,200, Mw 15,300, and Mw/Mn was 1.51. St and PhMI correspond to the first monomer. The composition and molecular weight distribution of the polymer are shown in Table 1 (hereinafter the same).

(Polymer 2: P(St/AN))
A 1L flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 2.0 parts of RAFT agent (DBTTC), 0.41 parts of ABN-E, 75 parts of St, 25 parts of acrylonitrile (hereinafter also referred to as "AN") and 67 parts of anisole, which were thoroughly degassed by nitrogen bubbling, and polymerization was started in a thermostatic bath at 80 ° C. After 4 hours, the reaction was stopped by cooling to room temperature. The above polymerization solution was purified by reprecipitation from methanol / water = 90 / 10 (vol%) and vacuum dried to obtain polymer 2. As a result of analysis by gas chromatography, the reaction rate of polymer 2 was St 73% and AN 72%. The molecular weight of polymer 2 was Mn 11,900, Mw 15,500, and Mw / Mn was 1.30. St and AN correspond to the first monomer.

(Polymer 3: P(St/maleic anhydride))
In a 1 L flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, 2.0 parts of a RAFT agent (DBTTC), 0.070 parts of ABN-E, 52 parts of St, 48 parts of maleic anhydride, and 207 parts of acetonitrile were charged, thoroughly degassed by nitrogen bubbling, and polymerization was initiated in a thermostatic bath at 70° C. After 4 hours,
The reaction was stopped by cooling to room temperature. The polymerization solution was purified by reprecipitation from toluene and dried in vacuum to obtain polymer 3. As a result of analysis by gas chromatography, the reaction rate of the obtained polymer 3 was St 71% and maleic anhydride 71%. The molecular weight of polymer 3 was Mn 13,800, Mw 22,200, and Mw/Mn 1.61. St and maleic anhydride correspond to the first monomer.

(Polymer 4:P(St/PhMI))
In a 1L flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube, 3.24 parts of 1-phenylethyl iodide (1-PEI), 0.019 parts of ABN-E, 38 parts of St, 62 parts of PhMI and 221 parts of acetonitrile were charged, and the mixture was thoroughly degassed by nitrogen bubbling, and polymerization was started in a thermostatic bath at 70 ° C. After 4 hours, the mixture was cooled to room temperature to stop the reaction. The above polymerization solution was purified by reprecipitation from methanol / water = 90 / 10 (vol%) and vacuum dried to obtain polymer 4. As a result of analysis by gas chromatography, the reaction rate of polymer 4 was St 74% and PhMI 74%. The molecular weight of polymer 4 was Mn 13,100, Mw 31,100, and Mw / Mn was 2.37. St and PhMI correspond to the first monomer.

(Polymer 5: P(St/AN)-b-PAA)
In a 1L flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube, 70 parts of polymer 2, 0.019 parts of ABN-E, 100 parts of acrylic acid (hereinafter also referred to as "AA") and 255 parts of acetonitrile were charged, thoroughly degassed by nitrogen bubbling, and polymerization was started in a thermostatic bath at 70 ° C. After 4 hours, the reaction was stopped by cooling to room temperature. The above polymerization solution was purified by reprecipitation from hexane and vacuum dried to obtain polymer 5. As a result of analysis by gas chromatography, the reaction rate of AA was 74%. The molecular weight of polymer 5 after methyl esterification was Mn 24,800, Mw 35,500, and Mw / Mn 1.43. St and AN correspond to the first monomer.

(Synthesis of polymers not having living polymerization activity)
(Polymer 1':P(St/AN))
A 1L flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube was charged with 1.0 parts of RAFT agent (DBTTC), 0.38 parts of ABN-E, 75 parts of St, 25 parts of AN and 66 parts of anisole, and the mixture was thoroughly degassed by nitrogen bubbling, and polymerization was initiated in a thermostatic bath at 80 ° C. After 4 hours, a part of the polymerization solution was collected, and the resulting monomer reaction rate measured by gas chromatography was St 73% and AN 72%. Next, the reaction solution was cooled to 40 ° C., and then 4.14 parts of n-propylamine that had been thoroughly degassed by nitrogen bubbling was charged, and the decomposition reaction of the RAFT group was carried out. After another 4 hours, 9.04 parts of methyl acrylate (MA) that had been thoroughly degassed by nitrogen bubbling was charged, and the terminal inactivation reaction was carried out at 40 ° C. for 4 hours. The above polymerization solution was purified by reprecipitation from methanol / water = 90 / 10 (vol%) and vacuum dried to obtain polymer 1'. The molecular weight of polymer 1' was Mn 11,200, Mw 15,100, and Mw/Mn was 1.35.

Here, the decomposition rate of the RAFT group (thiocarbonylthio group) for polymer 1' was calculated according to the following measurement method, and was found to be 100%, confirming that polymer 1' does not have living polymerization activity.

<Method for measuring the decomposition rate of thiocarbonylthio groups>
After dissolving 5 g of the polymer 1' in 15 g of acetone, the solution was cast onto a polypropylene disposable tray (100 mm x 70 mm x 13 mm, manufactured by AS ONE), and then naturally dried at room temperature for 16 hours, followed by drying at 70°C and 4.5 Torr for 16 hours to prepare a sheet-like sample. Next, using the obtained sheet-like sample, fluorescent X-ray analysis was performed under the following measurement conditions to quantify the sulfur content (%) in the sample. Using the obtained sulfur content, the decomposition rate (%) of the thiocarbonylthio group by n-propylamine was calculated according to the following formula. The results are shown in Table 1.
Decomposition rate of thiocarbonylthio group = {(B-A)/B} x {N/(N-1)} x 100
B: Sulfur content (%) in the sample before reaction with n-propylamine
A: Sulfur content (%) in the sample after reaction with n-propylamine
N: Number of sulfur atoms in one thiocarbonylthio group molecule Measurement conditions Measurement equipment: ZSX Primus II manufactured by Rigaku Corporation X-ray: Rh (50 kV, 50 mA)
Measurement elements: C to U (C, N, O, S measured at fixed angles)
Analysis diameter: 20mm
Analysis: Semi-quantitative analysis of detected elements using the fundamental parameter method (FP method)

Ｓｔ：スチレン
ＰｈＭＩ：N－フェニルマレイミド
ＡＮ：アクリロニトリル
ＡＡ：アクリル酸
ＤＢＴＴＣ：ジベンジルトリチオカーボネート
１－ＰＥＩ:１－フェニルエチルヨージド
ＡＢＮ－Ｅ：２，２－アゾビス（２－メチルブチロニトリル）、日本ファインケム製、商品名「ＡＢＮ－Ｅ」
ＭＡ：アクリル酸メチル

St: styrene PhMI: N-phenylmaleimide AN: acrylonitrile AA: acrylic acid DBTTC: dibenzyl trithiocarbonate 1-PEI: 1-phenylethyl iodide ABN-E: 2,2-azobis(2-methylbutyronitrile), manufactured by Nippon Finechem Co., Ltd., product name "ABN-E"
MA: methyl acrylate

<Production Example of Polymer Microparticles>
Example 1
In Example 1, polymer 1 was used to produce polymer microparticles. A reactor equipped with an agitator, a thermometer, a reflux condenser, and a nitrogen inlet tube was used for polymerization. 567 parts of acetonitrile, 2.20 parts of ion-exchanged water, 100.0 parts of AA, 0.90 parts of trimethylolpropane diallyl ether (manufactured by Daiso Co., Ltd., trade name "Neoallyl T-20"), 1.0 part of polymer 1, and triethylamine equivalent to 1.0 mol% relative to the AA were charged into the reactor. After sufficient nitrogen replacement inside the reactor, the inside temperature was raised to 55°C by heating. After confirming that the inside temperature was stable at 55°C, 0.040 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd., trade name "V-65") was added as a polymerization initiator, and the reaction solution became cloudy, so this point was determined as the polymerization initiation point. The polymerization reaction was continued while maintaining the internal temperature at 55 ° C. by adjusting the external temperature (water bath temperature), and the internal temperature was raised to 65 ° C. when 6 hours had passed from the polymerization start point. The internal temperature was maintained at 65 ° C., and the reaction rate of AA was 97% when 12 hours had passed from the reaction start point, and a reaction solution of a polymer in a slurry state in which particles were dispersed in a medium was obtained. The obtained reaction solution was centrifuged to precipitate the polymer fine particles, and the supernatant was removed. Thereafter, the precipitate was redispersed in the same mass of acetonitrile as the polymerization reaction solution, and then the washing operation of precipitating the polymer fine particles by centrifugation and removing the supernatant was repeated twice. The precipitate was collected and dried at 80 ° C. for 3 hours under reduced pressure conditions to remove the volatiles, thereby obtaining the polymer fine particles described in Example 1.

(Examples 2 to 12, Comparative Examples 1 and 2)
The same operation as in Example 1 was carried out except that the charges were changed as shown in Table 2, to obtain polymer microparticles.

<Evaluation of Polymerization Stability>
The reaction solution of the polymer slurry obtained in each Example and Comparative Example was filtered through a 200-mesh polynet (mesh size: 114 μm), and the mass of the aggregates remaining on the polynet after drying was measured to determine the amount of the aggregates relative to the total amount charged. The results are shown in Table 2.

<Measurement of average particle size and number of coarse particles>
For the polymer microparticles obtained in each Example and Comparative Example, a field emission scanning electron microscope (FE-SEM, JSM-6330F manufactured by JEOL Ltd.) was used to obtain multiple images in which 50 to 100 particles could be observed per image. The images obtained were counted using image analysis software "WinROOF" manufactured by Mitani Shoji Co., Ltd. until the total number of particles reached 200, and the particle diameter (circle equivalent diameter) of the 200 particles was measured. This operation was also performed on another image, and the particle diameter of 200 particles was measured in the same manner. The average value of the particle diameters of these 400 particles in total was taken as the average particle diameter. In addition, particles having a diameter twice or more than the average particle diameter thus obtained were taken as coarse particles, and the number of coarse particles per 100 particles was counted. The results are shown in Table 2.

ＡＡ：アクリル酸
ＨＥＡ：アクリル酸２－ヒドロキシエチル
Ｔ－２０：トリメチロールプロパンジアリルエーテル、ダイソー株式会社製、商品名「ネオアリルＴ－２０」
ＴＥＡ：トリエチルアミン
ＡｃＮ：アセトニトリル
Ｖ－６５：２，２’－アゾビス（２，４－ジメチルバレロニトリル）、和光純薬工業社製、商品名「Ｖ－６５」

AA: acrylic acid HEA: 2-hydroxyethyl acrylate T-20: trimethylolpropane diallyl ether, manufactured by Daiso Co., Ltd., product name "Neoallyl T-20"
TEA: triethylamine AcN: acetonitrile V-65: 2,2'-azobis(2,4-dimethylvaleronitrile), manufactured by Wako Pure Chemical Industries, Ltd., trade name "V-65"

As shown in Table 2, in Examples 1 to 12, polymers 1 to 3 and 5 obtained using RAFT polymerization and having active units in living radical polymerization by an exchange chain mechanism, and polymer 4 obtained using iodine transfer polymerization and having active units in living radical polymerization by a bond-dissociation mechanism were used, and as a result, the polymerization stability during polymerization of the polymer microparticles was excellent, the number of coarse particles was small, and the average particle diameter of the obtained polymer microparticles was 0.20 μm or less. In contrast, Comparative Example 1, in which no such dispersion stabilizer was used, and Comparative Example 2, in which a polymer without living polymerization activity was used as a dispersion stabilizer, had poor polymerization stability, so the number of coarse particles was large, and the average particle diameter of the obtained polymer microparticles was more than 0.50 μm.

Furthermore, Table 2 shows that the narrower the molecular weight distribution of polymers 1 to 5 (dispersion stabilizer) having a specified living radical polymerization active unit, the smaller the average particle diameter of the polymer microparticles. Furthermore, the results of Examples 2 to 6 show that the greater the amount of polymer (dispersion stabilizer) having living polymerization active units used, the smaller the average particle diameter of the polymer microparticles.

Claims (12)

The method comprises a step of producing polymer fine particles by polymerizing one or more second vinyl monomers in the presence of a first polymer having a polymer chain of one or more first vinyl monomers and a living radical polymerization active unit, based on the living radical polymerization activity of the first polymer and using the first polymer as a dispersion stabilizer;
The method, wherein the living radical polymerization active unit is an active unit in living radical polymerization by a chain exchange mechanism or a bond-dissociation mechanism (excluding a polymerization method using an organotellurium compound (TERP method)) . The method according to claim 1, wherein the living radical polymerization active unit is a living radical polymerization by the exchange chain mechanism. The method according to claim 1 or 2, wherein the living radical polymerization active unit is an active unit in living radical polymerization by reversible addition-fragmentation chain transfer polymerization or iodine transfer polymerization. The method according to any one of claims 1 to 3, characterized in that the molecular weight distribution of the first polymer is 2.0 or less. The method according to any one of claims 1 to 4, wherein the process for producing the polymer microparticles uses 0.3 parts by mass or more and 50 parts by mass or less of the first polymer per 100 parts by mass of the one or more second vinyl monomers. The method according to claim 5, wherein the process for producing the polymer microparticles uses 0.3 parts by mass or more and 20 parts by mass or less of the first polymer per 100 parts by mass of the one or more second vinyl monomers. The method according to any one of claims 1 to 6, wherein the one or more second vinyl monomers include acrylic acid or a salt thereof, and the polymerization solvent in the process for producing the polymer microparticles includes acetonitrile. The method according to claim 7, wherein the one or more first vinyl monomers are two or more types including styrenes selected from the group consisting of styrenes, (meth)acrylonitrile compounds, maleimide compounds, unsaturated acid anhydrides, and unsaturated carboxylic acid compounds. The method according to any one of claims 1 to 8, wherein the one or more second vinyl monomers contain acrylic acid in an amount of 50% by mass or more and 100% by mass or less of the total mass of the second vinyl monomers. The method according to claim 9, wherein the one or more first vinyl monomers contain styrenes in an amount of 20% by mass or more of the total mass of the first vinyl monomers. the one or more first vinyl monomers contain styrenes in an amount of 20 mass% or more of a total mass of the one or more second vinyl monomers, and the one or more second vinyl monomers contain acrylic acid or a salt thereof in an amount of 50 mass% or more and 100 mass% or less of a total mass of the one or more second vinyl monomers,
the first polymer has a living radical polymerization active unit by reversible addition-fragmentation chain transfer polymerization,
The method according to claim 1 , wherein the first polymer is used in an amount of 0.3 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the one or more second vinyl monomers. A dispersion stabilizer for use in producing polymer microparticles by polymerizing one or more second vinyl monomers by dispersion polymerization based on the living radical polymerization activity of the polymer and using the polymer as a dispersion stabilizer, the dispersion stabilizer comprising a polymer having a polymer chain of one or more first vinyl monomers and a living polymerization active unit (excluding a polymerization active unit of a polymerization method using an organotellurium compound (TERP method)) provided in at least a part of the polymer chain, the living radical polymerization activity of the polymer being the basis for the production of polymer microparticles by dispersion polymerization using the polymer as a dispersion stabilizer .