JP2013007012A - Method for producing core-shell type polymer microparticle containing sodium sulfonate group - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polymer microparticle having a sodium sulfonate group, which is a nanometer-level polymer microparticle having a core-shell type structure introduced in the shell part with a large amount of sodium sulfonate groups, which is not soluble in water, and has excellent proton conductivity, and which is preferably used for a membrane-electrode assembly (MEA) or the like in a solid fuel cell.SOLUTION: This method for producing the core-shell type polymer microparticle containing a sodium sulfonate group comprises: a step (a) of preparing a seed latex microparticle to be the core part by dispersing a monomer containing the aromatic vinylic compound in the presence or absence of a surfactant, and emulsion-polymerizing by a polymerization initiator; and a step (b) of forming a polymer having a core-shell structure by performing seeded emulsion polymerization of the seeded latex microparticle to be the core part obtained by the step (a) and a monomer containing an aromatic vinylic compound introduced with a sodium sulfonate group on the aromatic ring containing a water-soluble crosslinking agent by using a polymerization initiator in the presence or absence of a surfactant.

Description

  The present invention relates to a method for producing core / shell type polymer fine particles containing sodium sulfonate groups, and more specifically, nanometer level polymer fine particles having a core / shell type structure in which a large amount of sodium sulfonate groups are introduced into a shell portion. A core-shell type polymer fine particle containing sodium sulfonate group, which is excellent in proton conductivity without being dissolved in water and is suitably used for a membrane-electrode assembly (MEA) in a solid fuel cell It is related with the manufacturing method.

  Polymer particles having sodium sulfonate groups have long been known as cation exchange resins and are widely used in various fields. In the case of this cation exchange resin, the particle diameter of the polymer particles is usually about several hundred μm, and the amount of sodium sulfonate groups introduced is at most about 3 mol%. This cation exchange resin is generally produced by suspension polymerization or emulsion polymerization of divinylbenzene, which is a crosslinkable monomer, and sodium styrenesulfonate in order to improve water resistance.

  On the other hand, in recent years, fuel cells have attracted attention as a clean power generation system that is friendly to the global environment. Fuel cells are classified into phosphoric acid type, molten carbonate type, solid oxide type, solid polymer type, etc., depending on the type of electrolyte. Among these, polymer electrolyte fuel cells are applicable to electric vehicle power supplies, portable equipment power supplies, and household cogeneration systems that use both electricity and heat from the viewpoints of low-temperature operability, small size, and light weight. It is being considered.

  A polymer electrolyte fuel cell is generally configured as follows. First, catalyst layers containing carbon powder carrying a white metal catalyst and a proton conductive binder made of a polymer electrolyte are formed on both sides of an electrolyte membrane having proton conductivity. A gas diffusion layer, which is a porous material through which fuel gas and oxidant gas are passed, is formed outside each catalyst layer. Carbon paper, carbon cloth, or the like is used as the gas diffusion layer. A structure in which the catalyst layer and the gas diffusion layer are integrated is called a gas diffusion electrode, and a structure in which a pair of gas diffusion electrodes is bonded to the electrolyte membrane so that the catalyst layer faces the electrolyte membrane is a membrane-electrode assembly ( MEA (Mebrane Electrode Assembly). On both sides of this membrane-electrode assembly, separators having electrical conductivity and airtightness are disposed. A gas flow path for supplying a fuel gas or an oxidant gas (for example, air) to the electrode surface is formed in a contact portion of the membrane-electrode assembly and the separator or in the separator. Electric power is generated by supplying a fuel gas such as hydrogen or methanol to one electrode (fuel electrode) and an oxidant gas containing oxygen such as air to the other electrode (oxygen electrode).

  That is, at the fuel electrode, the fuel is ionized to produce protons and electrons, the protons pass through the electrolyte membrane, the electrons travel through an external electric circuit formed by connecting both electrodes, and are sent to the oxygen electrode, Water is produced by the reaction. In this way, the chemical energy of the fuel can be directly converted into electric energy and taken out.

In such a membrane-electrode assembly used for a solid fuel cell, polymer fine particles having a sodium sulfonate group excellent in proton conductivity in a catalyst layer containing a carbon powder carrying a white metal catalyst and a proton conductive binder A membrane-electrode assembly having excellent proton conductivity by forming a layer of nano-level polymer fine particles having a sodium sulfonate group and having excellent proton conductivity by spray drying on the catalyst layer by a method such as spraying It can be.
When the polymer sulfonate-containing polymer fine particles are used in the membrane-electrode assembly in the solid fuel cell, the proton conductivity is as high as possible (the amount of sodium sulfonate groups introduced is large), and the carbon-supported platinum catalyst is used. Since the particle diameter of the platinum particles is usually 1 to 30 nm, the sodium sulfonate group-containing polymer fine particles are required to have a particle diameter as close as possible to that of the platinum particles.

However, when the amount of sodium sulfonate group-containing monomer is increased in order to increase the amount of sodium sulfonate groups, the copolymer itself dissolves in water because sodium styrenesulfonate groups are highly soluble in water. Thus, the emulsion copolymerization containing sodium styrenesulfonate groups became extremely unstable, and polymer fine particles containing sodium sulfonate groups at a high concentration could not be obtained.
That is, in the sodium sulfonate group-containing polymer particles, how to increase the amount of sodium styrenesulfonate group is important.

On the other hand, Patent Document 1 discloses an aqueous resin emulsion containing core-shell structured particles, in which the core layer is a polymer (B) obtained by emulsion polymerization of an ethylenically unsaturated monomer, and the shell layer is And a polymer (A) having an acid value of 60 to 500 mgKOH / g, a number average molecular weight of 1000 to 30000, and a weight average molecular weight / number average molecular weight ratio of 1.0 to 1.5. An aqueous resin emulsion characterized by a weight ratio of A) / polymer (B) of 5/95 to 50/50 is disclosed.
The average particle diameter of the core-shell structure particles in this technique is usually 100 nm or less, and the subclaim 4 has a neutralized carboxyl group or sulfonic acid group in the polymer (A). Are listed. The aqueous resin emulsion is considered to be useful for coatings, inks, and various coating agents because it forms a film with excellent gloss when formed into a film.

JP 2003-3037 A

According to the technique described in Patent Document 1, a polymer (A) having a carboxylate or a sulfonate is first formed by living radical polymerization of an ethylenically unsaturated monomer, and this is polymerized with a polymer surfactant. In the presence of the polymer (A) as an agent, an ethylenically unsaturated monomer is emulsion-polymerized to form the polymer (B), thereby obtaining an aqueous resin emulsion containing core / shell structure particles. It is done.
According to this technique, the formed core-shell structure particles are supposed to have a carboxylate or sulfonate in the shell portion, but the sulfonate is not mentioned in the invention. Also, in the examples, a shell portion having a carboxylate is formed, but there is no example of a shell portion having a sulfonate.
The present invention has been made under such circumstances, and is a nanomail level polymer fine particle having a core-shell structure in which a large amount of sodium sulfonate groups are introduced into the shell portion, and is dissolved in water. It is intended to provide a method for efficiently producing polymer fine particles containing sodium sulfonate groups that are excellent in proton conductivity and are suitably used for membrane-electrode assemblies (MEA) in solid fuel cells. is there.

As a result of intensive studies to achieve the above object, the present inventors have obtained the following knowledge.
That is, a step of preparing seed latex fine particles as a core portion by a specific method, a seed latex particle as a core portion obtained in this step, and an aromatic vinyl system in which a sodium sulfonate group is introduced on an aromatic ring It has been found that sodium sulfonate group-containing core-shell type polymer fine particles that can meet the above-mentioned purpose can be efficiently obtained by a production method including a step of subjecting a compound to seed emulsion polymerization by a specific method. The present invention has been completed based on such findings.

That is, the present invention
A method for producing polymer fine particles comprising a core-shell type polymer containing a sodium sulfonate group,
(A) A step of dispersing seeds containing an aromatic vinyl compound in water in the presence or absence of a surfactant and emulsion-polymerizing with a polymerization initiator to prepare seed latex fine particles as a core part And (b) a single particle containing the seed latex fine particles as the core obtained in the step (a) and an aromatic vinyl compound in which a sodium sulfonate group is introduced on an aromatic ring containing a water-soluble crosslinking agent. A step of carrying out seed emulsion polymerization using a polymerization initiator in the presence or absence of a surfactant to form a polymer having a core-shell structure,
A method for producing sodium sulfonate-based oil-impregnated core / shell type polymer fine particles, comprising:

  According to the present invention, a polymer fine particle having a nanometer level particle diameter having a core-shell structure in which a large amount of sodium sulfonate groups are introduced into a shell portion, without dissolving in water and proton conduction It is possible to provide a method for efficiently producing polymer fine particles having a sodium sulfonate group which is excellent in properties and is suitably used for a membrane-electrode assembly (MEA) or the like in a solid fuel cell.

It is explanatory drawing of the method of measuring the swelling degree of a polymer microparticle using a capillary. A seed latex S _SF, is a TEM photograph of a seed latex x-S _SF. And the seed latex S _SF, is a SEM photograph of a seed latex x-S _SF. A seed latex S _SF, is a particle size distribution curve of the seed latex x-S _SF. It is a TEM photograph of polymer fine particles SF2. It is a TEM photograph of polymer fine particles S _OP-S N ₀ , S _OP-S N ₄ , S _OP-S N ₈ and S _OP-S N ₁₂ .

The method for producing core-shell type polymer fine particles containing sodium sulfonate group (hereinafter sometimes referred to as “SO ₃ Na group-containing”) of the present invention comprises a core-shell type structure containing SO ₃ Na groups. A method for producing polymer fine particles comprising a coalesced product, wherein (a) a monomer containing an aromatic vinyl compound is dispersed in water in the presence or absence of a surfactant, and emulsion polymerization is performed by a polymerization initiator. A step of preparing seed latex fine particles as a core portion, and (b) a seed latex fine particle as a core portion obtained in the step (a) and a sodium sulfonate group on an aromatic ring containing a water-soluble crosslinking agent. A monomer containing an aromatic vinyl compound into which is introduced is subjected to seed emulsion polymerization using a polymerization initiator in the presence or absence of a surfactant to form a polymer having a core-shell structure Characterized in that it comprises causing step.

((A) Process)
The step (a) in the method for producing SO ₃ Na group-containing polymer fine particles of the present invention (hereinafter sometimes simply referred to as “polymer fine particle production method”) is performed in the presence or absence of a surfactant. In this step, a monomer containing a group vinyl compound is dispersed in water and emulsion polymerized with a polymerization initiator to prepare seed latex fine particles to be a core part.

<Monomers containing aromatic vinyl compounds>
Although there is no restriction | limiting in particular as a monomer containing the aromatic vinyl type compound used at the said (a) process, Styrene and / or alpha-methylstyrene are preferable and styrene is more preferable. The monomer may include (meth) acrylic acid together with the styrenes. Here, (meth) acrylic acid refers to both acrylic acid and methacrylic acid.
Among these, methacrylic acid (MAA) is suitable from the viewpoint of the performance of the polymer fine particles obtained.
The amount of the (meth) acrylic acid used is preferably 10% by mass or less, and 8% by mass or less, from the viewpoint of the performance of the polymer fine particles obtained with respect to the total amount with the aromatic vinyl compound. It is more preferable that

In addition, the monomer containing the aromatic vinyl compound can include a crosslinkable monomer having two or more vinyl groups in the molecule.
The crosslinkable monomer having two or more vinyl groups is not particularly limited, and examples thereof include divinylbenzene, divinylnaphthalene, ethylene glycol di (meth) acrylate, and tetraethylene glycol di (meth) acrylate. Of these, divinylbenzene (DVB) is preferred from the viewpoint of the performance and availability of the polymer fine particles obtained.
When the crosslinkable monomer is divinylbenzene, the amount of the crosslinkable monomer used is preferably 5% by mass or less based on the total amount of monomers other than the crosslinkable monomer.

<Surfactant>
In the emulsion polymerization in the step (a), when a surfactant is used as an emulsifier, an anionic and / or nonionic surfactant is preferably used as the surfactant. Examples of the anionic surfactant include higher alkyl sodium sulfate such as sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium alkyl ether sulfate, sodium alkyl naphthalene sulfonate, and sodium dialkyl sulfosuccinate. Higher sodium alkyl sulfate is preferred.
On the other hand, examples of nonionic surfactants include polyoxyethylene alkyl aryl ethers such as polyoxyethylene octylphenyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkyl ethers, polyoxyethylene sorbitan, and the like. Examples thereof include polyoxyethylene sorbitan esters such as monolaurate and polyoxyethylene sorbitan monostearate, among which polyoxyethylene alkylaryl ethers are preferred. In addition, you may use together the said anionic surfactant and nonionic surfactant as surfactant.

In the emulsion polymerization in the step (a), a water-soluble polymerization initiator is used as a polymerization initiator, and examples of the water-soluble polymerization initiator include persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate. be able to.
The amount of the water-soluble polymerization initiator used is about 1 to 5% by mass relative to the total amount of monomers.

<Preparation of seed latex as core part>
The seed latex used as the core can be prepared, for example, as follows.
Polymerization is performed by a reactor equipped with a reflux condenser, a mechanical stirrer, and a thermometer, and a seed latex is prepared with a predetermined composition. That is, with or without the presence of a surfactant such as sodium dodecyl sulfate (SDS), all the monomers and 100 parts by weight of water are charged into a flask while stirring, and the system is heated to 70 ° C. Next, a persulfate such as ammonium persulfate (APS), which is a water-soluble polymerization initiator dissolved in 25 parts by mass of water, is added to the system in three stages, that is, at the beginning, 2 hours and 4 hours after the polymerization. And added at a mass ratio of 12/8/5 and polymerized for about 7 hours. The seed latex can then be obtained by cooling the system to room temperature.
(1) Soap-free emulsion polymerization In emulsion polymerization without the presence of a surfactant, seed latex introduced with crosslinking using divinylbenzene (DVB) as a crosslinking agent, and seed latex particles without crosslinking without using a crosslinking agent From the transmission electron microscope (TEM) photograph, the scanning electron microscope (SEM) photograph, and the particle size distribution diagram, it can be seen that the surface of the latex latex becomes rougher due to the introduction of DVB, that is, crosslinking. It can be seen that the particles have a narrow particle size distribution. The monomer conversion by soap-free emulsion polymerization is 90% or more.
(2) Ordinary emulsion polymerization Next, in the method of emulsion polymerization of seed latex using an emulsifier (surfactant), emulsion polymerization can be carried out by the same formulation as the soap-free polymerization except that an emulsifier is used. In comparison with the soap-free polymerization, it can be seen that:
In the soap-free emulsion polymerization of the above (1), it is not easy to adjust the size of the seed latex particles. Therefore, by using conventional emulsion polymerization for the preparation of the seed latex particles, a relatively small seed latex is prepared. Can be prepared.
Also, the surface of the seed latex particles is rougher than that obtained by soap-free emulsion polymerization.

((B) Process)
The step (b) in the method for producing the SO ₃ Na group-containing polymer fine particles of the present invention comprises the step of forming SO particles on the seed latex fine particles serving as the core obtained in the step (a) and the aromatic ring containing a water-soluble crosslinking agent. ₃ A monomer containing an aromatic vinyl compound introduced with Na groups is subjected to seed emulsion polymerization using a polymerization initiator in the presence or absence of a surfactant to produce a polymer having a core-shell structure. This is a step of forming a coalescence.

<Aromatic vinyl compound having SO ₃ Na group introduced on aromatic ring>
As the (b) aromatic vinyl compound SO ₃ Na group was introduced on the aromatic ring to be used in the step is not particularly limited, for example, sodium styrene sulfonate, sodium alkyl styrene sulfonate, alpha-alkyl styrene sulfonic acid Examples thereof include sodium, sodium vinyl naphthalene sulfonate, and sodium α-alkyl vinyl naphthalene sulfonate. In addition, there is no restriction | limiting in particular about the coupling | bonding position with respect to the vinyl group of the sodium sulfonate group introduce | transduced on an aromatic ring. Of these, sodium styrenesulfonate and / or sodium α-methylstyrenesulfonate are preferable, and sodium styrenesulfonate is particularly preferable from the viewpoint of the performance and availability of the polymer fine particles obtained.

In the present invention, the monomer containing an aromatic vinyl compound in which a sodium sulfonate group is introduced on an aromatic ring can further contain an aromatic vinyl compound as a copolymerization monomer. As this aromatic vinyl compound, styrene and / or α-methylstyrene are preferable, and styrene is particularly preferable from the viewpoint of the performance and availability of the obtained polymer particles.
The amount of the aromatic vinyl compound used is about 10 to 70% by mass with respect to the total amount of the aromatic vinyl compound into which the SO ₃ Na group has been introduced, from the viewpoint of the performance of the resulting polymer fine particles. Is preferable, and 15-55 mass% is more preferable.

In the step (b), a water-soluble crosslinking agent is used as an essential component. As the water-soluble crosslinking agent, N, N′-methylenebisacrylamide (BAA) is suitable. By copolymerizing this BAA with an aromatic vinyl compound into which a sodium sulfonate group has been introduced or a mixture of this compound and an aromatic vinyl compound, a crosslinked structure can be formed in the shell portion. Thus, by introducing a cross-linked structure into the shell portion, the obtained polymer fine particles are prevented from being dissolved in water, and the yield of the polymer fine particles obtained by emulsion polymerization with the seed particles that will be described later is the core. The effect which can improve is produced.
If the amount of the water-soluble crosslinking agent used is too large, the emulsion polymerization process becomes unstable, gelation occurs and aggregates are formed. On the other hand, if the amount is too small, the above-described effects cannot be sufficiently exhibited. The amount of the crosslinking agent used is in the range of 1 to 5 mol%, preferably 1.5 to 3.5 mol%, based on 50 mol% of the monomer excluding the crosslinking agent.

<Surfactant>
In the step (b), when a surfactant is used as an emulsifier during emulsion polymerization, an anionic and / or nonionic surfactant is preferably used as the surfactant. About the kind of anionic surfactant and nonionic surfactant, it is as having shown by description of the above-mentioned (a) process.

<Polymerization initiator>
In the step (b), an oil-soluble polymerization initiator is used as the polymerization initiator. The oil-soluble polymerization initiator is not particularly limited. For example, 2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis-2-methylbutyronitrile, 2,2′-azobis Examples include azo compounds such as dimethylvaleronitrile, and organic peroxides such as diacyl peroxides, peroxydicarbonates, and peroxyesters. Among these, azo compounds, particularly 2,2′-azobis. Isobutyronitrile is preferred. These polymerization initiators are about 0.5-3.0 mass% with respect to the monomer whole quantity.

<Manufacture of core / shell type polymer by seed emulsion polymerization to seed latex>
Next, for example, 20 parts by mass of the seed latex obtained in the step (a) is used to prepare a core / shell type latex by a predetermined blending.
Polymerization was carried out using a reactor equipped with a reflux condenser, a mechanical stirrer and a thermometer. The seed latex, AIBN, water and St obtained in the step (a) were charged into a reactor, and the seed particles were swollen by gently stirring at room temperature for 3 hours. Next, an aqueous solution of NaSS, BAA and SDS is charged and heated to about 70 ° C. Polymerization is performed for a total of 10 hours, and the resulting dispersion containing fine polymer particles is cooled to room temperature.
Subsequently, the obtained polymer fine particles are dried at about 80 ° C. for 5 hours, then dried at about 120 ° C. for 2 hours, and the obtained solid is extracted with water by a Soxhlet extractor for 48 hours. By removing the polymer, purification is performed to obtain polymer fine particles of a core-shell type polymer.
AIBN represents azobisisobutyronitrile, St represents styrene, and BAA represents N, N′-methylenebisacrylamide.
In this manner, SO ₃ Na group-containing polymer fine particles comprising the polymer having the core / shell structure of the present invention can be produced.

Next, the properties of the SO ₃ Na group-containing core / shell polymer fine particles obtained by the above-described method for producing polymer fine particles of the present invention will be described.
[Properties of SO ₃ Na group-containing core / shell type polymer fine particles]
<Content of SO ₃ Na group-containing aromatic vinyl compound unit>
The content of the compound unit is much higher than that of a conventional cation exchange resin or the like, and can be 10% by mass or more with respect to the total amount of the polymer fine particles and 35% by mass or more with respect to the shell part. .
The content of the compound unit is determined by performing elemental analysis of the polymer fine particles with an ICP emission spectroscopic analyzer and measuring the amount of sulfur in the polymer fine particles. Based on the amount of sulfur, the sodium sulfonate group in the polymer fine particles is measured. It is obtained by calculating the content of.

<SO ₃ Na group density on the surface of polymer fine particles>
The density of SO ₃ Na groups on the particle surface was determined by electric conductivity titration using an electric conductivity meter (Shanghai Precision & Scientific Instrument CO. LTD model DDS-307, CN) as follows.
First, the polymer fine particles obtained by seed emulsion polymerization were redispersed several times in water using centrifugal separation and gentle ultrasonic waves until the electrical conductivity of the supernatant reached 10 μS / cm or less. Next, 10 g of ion exchange resin (H type) was added to 40 ml of the purified polymer fine particle dispersion (latex solid content was about 0.5% by mass) and stirred at room temperature. After 24 hours, the mixture of latex and ion exchange resin was filtered to obtain a treated polymer fine particle dispersion. Finally, electrical conductivity titration of the treated polymer fine particle dispersion was performed at room temperature. Titration was performed in a forward and reverse directions using a 9.4 mmol / L NaOH solution and a 7.2 mmol / L HCl solution, respectively, under a nitrogen atmosphere. The surface density of the SO ₃ Na group of the polymer fine particles obtained by seed emulsion polymerization was calculated from the following formula.

σ: surface density of SO ₃ Na group (mol / cm ² )
N: Amount of NaOH used for titration (mol)
s: Solid content (%) of purified fine polymer particle dispersion obtained by seed emulsion polymerization
M: total mass (g) of purified fine polymer particle dispersion obtained by seed emulsion polymerization
S: Average surface area (nm ² ) of polymer fine particles obtained by seed emulsion polymerization
ρ: Average density (g / cm ³ ) of polymer fine particles obtained by seed emulsion polymerization
V: Average volume (nm ³ ) of polymer fine particles obtained by seed emulsion polymerization per piece
r: Average radius (nm) of polymer fine particles obtained by seed emulsion polymerization
The surface density σ (mol / cm ² ) of the SO ₃ Na group was 5.90 × 10 ⁻¹¹ mol / cm ^{2 in} Example 4 to be described later, and 6.88 × 10 ⁻¹¹ mol / cm ² in Example 10. is there.

<Particle size and particle size distribution PI of polymer fine particles>
The average particle diameter of the polymer fine particles measured with a transmission electron microscope (TEM) is usually about 50 to 1000 nm. When the average particle diameter is less than 50 nm, it is difficult to maintain a spherical particle shape, and it tends to be indefinite. On the other hand, if it exceeds 1000 nm, sufficient proton conductivity may not be exhibited. From the above viewpoint, the average particle size of the polymer fine particles is preferably 70 to 500 nm, and particularly preferably 100 to 300 nm.
The particle diameter of the polymer fine particles measured by the dynamic light scattering method is about 100 to 1000 nm. Furthermore, the particle size distribution PI (poly index) measured by the dynamic light scattering method is usually in the range of 0.002 to 1.0 and shows a value close to monodispersion.

<Swelling degree>
FIG. 1 is an explanatory diagram of a method for measuring the degree of swelling of polymer fine particles using a capillary.
As shown in FIG. 1, the degree of swelling of the polymer sample was measured using a capillary 1 having a scale. The purified powder is packed in a capillary (2 in FIG. 1), and the scale value (L ₁ ) is read. Then an appropriate amount of solvent (deionized water, methanol, butanone, toluene) with different polarity is added to the capillary to swell the polymer sample (3 in FIG. 1). After 24 hours, the scale value (L ₂ ) of the swollen sample was read (4 in FIG. 1), and the degree of swelling (ε) was calculated using the following equation.
ε (%) = [(L ₂ −L ₁ ) / L ₁ ] × 100

<Mass ratio of core part to shell part>
The mass ratio of the core portion to the shell portion of the SO ₃ Na group-containing polymer fine particles is usually 9: 1 to 5: 5.
The mass ratio of the core part to the shell part should be calculated by calculation from the amount of charged core latex and the amount of monomer and the amount of water-insoluble part obtained by water extraction of the produced polymer during seed emulsion polymerization. Can do.

  The polymer fine particles having a sodium sulfonate group obtained by the production method of the present invention can be easily changed to a sulfonic acid group by being immersed in an aqueous acid solution such as hydrochloric acid or sulfuric acid, and have a sulfonic acid group. The polymer fine particles can be used for applications. Further, the polymer fine particles having a sulfonic acid group can be easily changed to a sodium sulfonate group by immersing in an aqueous alkali solution such as sodium hydroxide.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these Examples.
The properties of the seed particles and the SO ₃ Na group-containing polymer fine particles that are the core portions obtained in each example were determined according to the following method.

(1) Hydrodynamic particle size and particle size distribution of each particle Using a dynamic light scattering (DLS) photometer [Malvern (UK) “Zetasizer 3000HS”], the particle size by dynamic light scattering at 25 ° C. ( D _P ^DLS ) and its particle size distribution (Poly Index, PI) were determined.

(2) Average Particle Diameter The average particle diameter (D _P ^TEM ) was determined by image processing of a transmission electron microscope (TEM) “Hitach 800 manufactured by Hitachi, Ltd.” photograph.

(3) Content of SO ₃ Na group-containing aromatic vinyl compound unit in SO ₃ Na group-containing polymer fine particles Soxhlet extraction using an ICP emission spectroscopic analyzer [“VISTA-MPX ACPOES” manufactured by Seiko Instruments Inc.] Elemental analysis of the polymer fine particles excluding the water-soluble part in a vessel was performed, and the amount of sulfur in the polymer fine particles was measured. Based on this amount of sulfur, the SO ₃ Na group-containing aromatic in the whole polymer fine particles and in the shell polymer The content of vinyl compound units was determined.

(4) SO ₃ Na group density on the surface of the polymer fine particles The density was measured according to the method described in the specification.
(5) Swelling degree of polymer fine particles Measured according to the method described in the specification.

A reflux condenser in Production Example 1 seed latex S _SF, four-necked flask equipped with a mechanical stirrer and a thermometer, and water 100 mL, styrene (St) 18.66 g and methacrylic acid (MAA) 1.34 g A monomer mixture (St / MAA molar ratio: 92/8) was charged with stirring, and the system was heated to 70 ° C.
Next, an aqueous solution in which 0.336 g of ammonium persulfate (APS) was dissolved in 25 mL of water was added to the system in three stages, that is, a mass ratio of 12/8/5 at the beginning, 2 hours and 4 hours after the polymerization. And polymerized for 7 hours. Thereafter, the system was cooled to room temperature, to obtain a seed latex S _SF.
St and MAA were distilled under reduced pressure, and APS was recrystallized with water before use. The same applies hereinafter.
Table 1 shows the charged amount of the material, the monomer conversion rate, the particle size D _P ^{DLS of} the seed latex by the dynamic light scattering method, its particle size distribution PI, and the average particle size D _P ^TEM .

Production Example 2 Production of Seed Latex x-S _{SF In} Production Example 1, a monomer mixture containing 0.72 g of divinylbenzene (DVB), which is a crosslinkable monomer, as the monomer mixture (St / MAA / DVB molar ratio: 89.46) /7.77/2.77) except for using, make the same manner as in production example 1 operation, to obtain crosslinked seed latex x-S _SF.
As DVB, a commercially available DVB was used as it was. The same applies hereinafter.
Table 1 shows the amount of materials charged, the monomer conversion rate, the particle size D _P ^{DLS of} the seed latex by the dynamic light scattering method, its particle size distribution PI, and the average particle size D _P ^TEM .
Further, in FIG. 2, with shows a TEM photograph of a seed latex S _SF (a) and TEM photograph of a seed latex x-S _SF (b), Figure 3, SEM photographs of the seed latex S _SF (a) and seed latex The SEM photograph (b) of x-S _SF is shown.
Further Figure 4 shows the particle size distribution curve (a) and the particle size distribution curve of the seed latex x-S _SF of the seed latex S _SF and (b).
The seed latex S _SF and x-S _SF are both monodisperse particles with a small particle size.
The transmission electron microscope (TEM) used was Hitachi 800 manufactured by Hitachi, Ltd., and the scanning electron microscope (SEM) used was JSM-7401 manufactured by JEOL.

Production Example 3 Production of Seed Latex x-S _{OP-S As} monomer mixture, one containing 18.660 g of styrene, 1.340 g of methacrylic acid and 0.723 g of divinylbenzene (St / MAA / DVB mass ratio: 89.46 /7.77/2.77) and 0.1-1 g of sodium dodecyl sulfate (SDS) as a surfactant and OP-1 [trade name] manufactured by Nikko Chemicals Co., Ltd., which is polyoxyethylene octylphenyl ether Except for using 0.088 g, the same operation as in Production Example 1 was performed to obtain a seed latex x-S _OP-S .
Table 2 shows the charged amount of the material, the monomer conversion rate, the particle size D _P ^{DLS of} the seed latex by the dynamic light scattering method, its particle size distribution PI, and the average particle size D _P ^TEM .

Production Example 4 seed latex _{x-S OP-S *} in Production Example 3, without using the methacrylic acid, and except that the styrene was used 20g, make the same manner as in Production Example 3 operation, seed latex x-S _{OP -Obtained S *} .
Table 2 shows the charged amount of the material, the monomer conversion rate, the particle size D _P ^{DLS of} the seed latex by the dynamic light scattering method, its particle size distribution PI, and the average particle size D _P ^TEM .

Production Example 5 Production of Seed Latex x-S _S 1 The same procedure as in Production Example 3 was carried out except that 0.572 g of SDS was used and OP-10 was not used in Production Example 3, and seed latex x-S was produced. _S 1 was obtained.
Table 2 shows the charged amount of the material, the monomer conversion rate, the particle size D _P ^{DLS of} the seed latex by the dynamic light scattering method, its particle size distribution PI, and the average particle size D _P ^TEM .

  When a mixture of SDS and OP-10 is used as an emulsifier, the monomer conversion is reduced and the particle size is increased as compared with the case of SDS alone.

Example 1
Reflux condenser, a four-neck flask equipped with a mechanical stirrer and a thermometer, seed latex obtained in Preparation Example 1 S _SF 20 g, as a polymerization initiator azobisisobutyronitrile (AIBN) 0.034 g Then, 10 g of water and 0.923 g of styrene were charged, and the seed particles were swollen by gently stirring at room temperature for 3 hours. Next, an aqueous solution containing 1.829 g of sodium styrenesulfonate (NaSS), 0.109 g of N, N′-methylenebisacrylamide (BAA) as a crosslinking agent, 0.068 g of sodium dodecyl sulfate (SDS), and 25 g of water was charged at 70 ° C. Heated. Polymerization was performed for a total of 10 hours, and the resulting dispersion containing the polymer fine particles was cooled to room temperature.
Next, the obtained polymer fine particles were dried at 80 ° C. for 5 hours, then dried at 120 ° C. for 2 hours, and then extracted with water by a Soxhlet extractor for 48 hours to remove the water-soluble polymer and purified. A core-shell polymer fine polymer particle SF2 was obtained.
Table 3 shows the types and amounts of each component used in the reaction, Table 5 shows the molar ratio of each component constituting the obtained polymer fine particle SF2, and the mass loss in the water extraction operation. The characteristic value of the obtained polymer fine particle SF2 is shown. FIG. 5 shows a TEM photograph of the polymer fine particle SF2.

Example 2
In Example 1, except that NaSS 1.829g and BAA 0.164g were used, the same operation as in Example 1 was performed to obtain polymer fine particles SF3 of a core-shell type polymer. Table 3 shows the types of each component used in the reaction, Table 5 shows the molar ratio and mass loss of each component constituting the obtained polymer fine particle SF3, and Table 6 shows the characteristics of the polymer fine particle SF3 obtained. Indicates the value.

Example 3
In Example 1, the same procedure as in Example 1 was carried out except that 20 g of the seed latex x-S _SF obtained in Production Example 2 was used instead of the seed latex S _SF. Polymer fine particle XSF6 was obtained.
Table 4 shows the type and amount of each component used in the reaction, Table 5 shows the molar ratio and mass loss of each component constituting the polymer fine particle XSF6 obtained, and Table 6 shows the polymer fine particle XSF6 obtained. Indicates the characteristic value.

Example 4
In Example 1, instead of the seed latex S _SF, using the seed latex x-S _OP-S 20g obtained in Production Example 3, 0.164 g of BAA, 0.034 g of SDS, the OP-10 0. Except for using 034 g, the same operation as in Example 1 was performed to obtain polymer fine particles S _{OP-S *} N ₁₂ of a core / shell type polymer.
Table 4 shows the type and amount of each component used in the reaction.
Table 5 shows the molar ratio of each component constituting the polymer fine particle S _{OP-S *} N ₁₂ and the mass loss due to Soxhlet extraction. Table 6 shows the polymer fine particle S _{OP-S *} N obtained. ₁₂ characteristic values are shown.
Moreover, as a result of examining the surface density of the sodium sulfonate group in the polymer fine particles S _{OP-S *} N ₁₂ , the surface density σ was 5.90 × 10 ⁻¹¹ mol / cm ² .

Examples 5-7 and Comparative Example 1
Using the seed latex x-S _S 1 obtained in Production Example 5, the BAA / NaSS / (St + MAA + DVB) molar ratio was 1/25/75 (Example 5) and 2/25 / as shown in Table 7. 75 (Example 6), 3/25/75 (Example 7) and 0/25/75 (Comparative Example 1), and a solid content of 10.5% by mass, the same operation as in Example 1 was performed. As a result, core-shell type polymer fine particles S1N4C, S1N8C, S1N12C and S1N0C were obtained.
Table 7 shows the characteristic values of each polymer fine particle together with the molar ratio and solid content of each component constituting each polymer fine particle obtained.

As can be seen from Table 7, the mass loss of S1N0C of Comparative Example 1 where the molar ratio of the crosslinking agent BAA is 0 is the largest at 42.51% by mass, and the mass loss decreases as the molar ratio of BAA increases. The mass loss of S1N12C of Example 7 in which the molar ratio of BAA is 3 is the smallest at 26.93% by mass.
In addition, D _P ^DLS is in the range of 240 to 260 nm, PI is in the range of 0.14 to 0.20, and is a monodisperse particle having a small particle size.

Examples 8 to 10 and Comparative Example 2
Using the seed latex obtained in Production Example 3, the BAA / NaSS / (St + MAA + DVB) molar ratio was 1/25/75 (Example 8) and 2/25/75 (Example 9) as shown in Table 8. ) 3/25/75 (Example 10) and 0/25/75 (Comparative Example 2), SDS was set to 0.034 g, OP-10 was set to 0.034 g, and the same operation as in Example 1 was performed. Core-shell polymer fine particles S _OP-S N ₄ , S _OP-S N ₈ , S _OP-S N ₁₂ and S _OP-S N ₀ were obtained, respectively.
Table 8 shows the mass loss and D _P ^DLS and PI during the water extraction operation together with the molar ratio of each component constituting each polymer fine particle obtained.

As can be seen from Table 8, the mass loss of S _OP-S N ₀ of Comparative Example 2 in which the molar ratio of the crosslinking agent BAA is 0 is the largest at 57.65% by mass, and as the molar ratio of BAA increases, The mass loss of the S _OP-S N ₁₂ of Example 10 in which the mass loss is reduced and the BAA molar ratio is 3 is the smallest at 35.51% by mass.
As a result of examining the content of NaSS units in the whole fine particles and the content of NaSS units in the shell part of S _OP-S N ₁₂ of Example 10, they were 27.29% by mass and 62.45% by mass, respectively.
Moreover, the result of having investigated the swelling degree (epsilon) with respect to a different solvent about S _OP-S N ₁₂ is shown below.
Solvent degree of swelling ε (%)
Water 10
Methanol 15
Butanone 13.3
Toluene 17.6
Furthermore, the surface density σ of the SO ₃ Na group of S _OP-S N ₁₂ was 6.88 × 10 ⁻¹¹ mol / cm ² .
FIG. 6 shows TEM photographs of S _OP-S N ₀ , S _OP-S N ₄ , S _OP-S N ₈ and S _OP-S N ₁₂ , respectively (a), (b), (c) and ( d).
From Table 8, each polymer fine particle is a monodisperse particle having a small particle size, with D _P ^DLS in the range of 280 to 340 nm and PI in the range of 0.2 to 0.3.

  The polymer fine particles containing sodium sulfonate groups obtained by the method of the present invention are polymer fine particles having a nanometer level particle diameter having a core-shell structure in which a large amount of sodium sulfonate groups are introduced into the shell portion. It is excellent in proton conductivity without being dissolved in water, and can be suitably used for a membrane-electrode assembly (MEA) in a solid fuel cell.

1: Capillary having a scale 2: State where purified powder is packed in capillary 3: State where solvent is added to capillary and polymer sample is swollen 4: State 24 hours after swelling PO: Polymer fine particle SO: Solvent ST: plug

Claims (13)

A method for producing polymer fine particles comprising a core-shell type polymer containing a sodium sulfonate group,
(A) A step of dispersing seeds containing an aromatic vinyl compound in water in the presence or absence of a surfactant and emulsion-polymerizing with a polymerization initiator to prepare seed latex fine particles as a core part And (b) a single particle containing the seed latex fine particles as the core obtained in the step (a) and an aromatic vinyl compound in which a sodium sulfonate group is introduced on an aromatic ring containing a water-soluble crosslinking agent. A step of carrying out seed emulsion polymerization using a polymerization initiator in the presence or absence of a surfactant to form a polymer having a core-shell structure,
A process for producing sodium sulfonate-based oil-impregnated core / shell polymer fine particles, comprising:   The core-shell type polymer fine particle containing sodium sulfonate group according to claim 1, wherein the monomer containing an aromatic vinyl compound in step (a) is a monomer containing styrene and / or α-methylstyrene. Manufacturing method.   The manufacturing method of the sodium sulfonate group containing core-shell type polymer microparticles | fine-particles of Claim 1 or 2 in which the monomer containing the aromatic vinyl type compound in (a) process contains (meth) acrylic acid.   The sodium sulfonate group according to any one of claims 1 to 3, wherein the monomer containing the aromatic vinyl compound in step (a) includes a crosslinkable monomer having two or more vinyl groups in the molecule. A method for producing core-shell type polymer fine particles.   The method for producing core-shell type polymer fine particles containing sodium sulfonate groups according to claim 4, wherein the crosslinkable monomer is divinylbenzene.   The method for producing core-shell type polymer fine particles containing sodium sulfonate groups according to any one of claims 1 to 5, wherein the polymerization initiator used in step (a) is a water-soluble persulfate.   In the step (b), the monomer containing an aromatic vinyl compound having a sodium sulfonate group introduced on the aromatic ring is a monomer containing sodium styrene sulfonate and / or α-methyl styrene sulfonate sodium. A method for producing core-shell type polymer fine particles containing sodium sulfonate groups according to any one of claims 1 to 6.   The method for producing core-shell type polymer fine particles containing sodium sulfonate groups according to any one of claims 1 to 7, wherein the water-soluble crosslinking agent in step (b) is N, N'-methylenebisacrylamide.   In the step (b), the monomer containing an aromatic vinyl compound having a sodium sulfonate group introduced on the aromatic ring contains styrene and / or α-methylstyrene as a copolymerization monomer. A method for producing core-shell type polymer fine particles containing a sodium sulfonate group according to any one of the above.   The method for producing sodium sulfonate group-containing core-shell type polymer particles according to any one of claims 1 to 9, wherein the polymerization initiator used in the step (b) is an oil-soluble polymerization initiator.   The method for producing core-shell type polymer fine particles containing sodium sulfonate groups according to claim 10, wherein the oil-soluble polymerization initiator is 2,2'-azobisisobutyronitrile.   In the case of using a surfactant as an emulsifier in the emulsion polymerization in the steps (a) and (b), the surfactant is an anionic and / or nonionic surfactant. The manufacturing method of the sodium sulfonate group containing core-shell type polymer fine particle of description.   13. The method for producing core-shell type polymer fine particles containing sodium sulfonate group according to claim 12, wherein the anionic surfactant is higher alkyl sodium sulfate and the nonionic surfactant is polyoxyethylene alkylaryl ethers. .