JP7031900B2 - Method for manufacturing layered particles and layered particles - Google Patents

Description

The present invention relates to polymer particles, and more particularly to particles having a hierarchical structure in which components having different physical properties are laminated in layers, and a method for producing the same.

Hollow fine particles have characteristics such as low density, high specific surface area, low thermal expansion coefficient, and low refractive index, so that they are catalytic materials, antireflection coating agents, solar cells, rechargeable batteries, gas sensors, and DNA. / It is expected to be applied to various fields such as drug-supporting carriers. So far, research on the synthesis of hollow particles has been actively carried out, and many methods such as the Layer-by-Layer method, the chemical precipitation method, and the chemisorption method have been proposed. Most of the hollow-structured particles produced by these methods have a single-layer structure, and although many attempts have been made to make them functional, there are still many problems. Under such circumstances, in recent years, attention has been focused on the synthesis of hierarchically structured particles from the viewpoint of improving the function of materials.

By constructing a hierarchical structure, the non-surface area is dramatically increased, and it is expected that molecular adsorption, reactivity, and thermal stability will be improved. Furthermore, in some reports, the synthesis of multi-layered composite metal fine particles having a shell has also been achieved, and more remarkable functional improvement is expected (Non-Patent Documents 1-4).

Xu, H. Wang, W. et al. Template Synthesis of Multisheled Cu2O Hollw Surfaces with a Single-Crystalline Shell Wall. Angew. Chem. Int. Ed. 2007,46,1489-1492. Gao, S.A. Chang, J. et al. Fang, L. et al. Wu, L. Metal Nanoparticles Confined in the Nanospace of Double-Sheled Hollow Silka Phases for Highly Efficient and Selective Catalysis. Chem. Mater. 2016, 28, 5596-5600. Li, J. Wang, J. et al. Liang, X. Zhang, Z. Liu, H. et al. Quant, Y. Xiong, S.M. Hollow MnCo2O4 Submicrospheres with Multilevel Inters.: FromMotherous Phases to Yolk-in-Double-Thell Structures. ACS Apple. Mater. Interfaces. 2014, 6, 24-30. Yabu, H. et al. Jinno, T. et al. Koike, K.K. Higuchi, T.I. Shimamura, M. et al. Nanoparticle Arrangements in Block Copolymer Particles With Microphase-Specified Structures. J. Polym. Sci. BPolym. Phys. 2011, 49, 1717-1722.

However, the conventional method for synthesizing hierarchical fine particles has problems that a complicated procedure in multiple steps is required and the structure becomes multi-dispersed. In addition, there are very few reports of hierarchical structure fine particles composed of polymers (also called polymers), and only those that utilize the self-accumulation of block copolymers. It can only be manufactured with a polymer that cannot be introduced, that the particle structure and its characteristics depend on the one-dimensional polymer composition and is not applicable, and that it has poor compatibility with the solvent (a poorly water-soluble polymer if used in water). Many issues remained when advancing application development, such as the lack of points. Therefore, it has been desired to develop hierarchical fine particles having a crosslinked structure and having high industrial applicability, and a synthetic method capable of synthesizing them easily and in large quantities and applying them to various components.

The inventors have been diligently researching to solve the above problems. As a result, it is possible to create solid composite gel fine particles by seed emulsification polymerization using temperature-sensitive hydrogel fine particles as a template, and this method provides stimulus responsiveness and excellent dispersion of the hydrogel fine particles as a template. It has been found that it is a method that can easily, in large quantities, and produce high-yield deformed composite gel fine particles having a uniform particle size while inheriting stability, and is applicable to various components.

At the same time, from the viewpoint of the reactivity ratio, the present inventors use gel fine particles composed of a desired polymer whose charge is localized in the center of the gel fine particles as seeds, and perform seed emulsification polymerization under basic conditions. As a result, it was found that the solid component in the composite particle was localized on the surface of the gel fine particles, and the present invention was completed. That is, it is an object of the present invention to provide hierarchical structure particles which are composed of a polymer and have a hierarchical structure as the structure thereof.

The present invention according to claim 1 has a core made of a gel containing a polymer having no charged group , which is formed by free radical polymerization into which a cross-linked structure by a cross-linking agent is introduced, and is charged on the outside thereof. A polymer obtained by copolymerizing a monomer having no group and a comonomer having a charged group of a carboxyl group or a sulfonic acid group having a different reactivity ratio from the monomer by precipitation polymerization, and introducing a cross-linking structure by a cross-linking agent. A core shell gel particle composed of one shell layer in which a charged group is unevenly distributed inside or a plurality of shell layers formed by laminating the shell layer is used as a seed particle and has a component different from that of the seed particle. The polymer obtained by emulsifying and cross-linking the hydrophobic monomer of the above is a layered structure particle formed in the core and further formed in a layer in the one or a plurality of shell layers .

The hierarchy according to claim 1, wherein at least one of the uncharged monomer and the charged comonomer has an external stimulus response. It is a structural particle.

According to the third aspect of the present invention, the polymer having no charged group is a polyalkylene oxide derivative, a polyethylene glycol (PEG) derivative, a polyethylene oxide (PEO) derivative, or a polypropylene oxide prepared by free radical polymerization. The layer according to claim 1 or 2, wherein the LCST polymer is at least one selected from the group consisting of PPO) derivatives, polymethyl vinyl ethers, poly-N-vinyl caprolactams and polyacrylamide derivatives. It is a structural particle.

In the present invention according to claim 4, the comonomer having a charged group comprises methacrylic acid, acrylic acid, fumaric acid, vinylacetic acid, maleic acid, 2-acrylamide-methylpropanesulfonic acid, and styrenesulfonic acid . The layered structure particle according to any one of claims 1 to 3, characterized in that it is at least one vinyl monomer selected from the group.

The fifth aspect of the present invention is the hierarchical structure particle according to any one of claims 1 to 4, wherein the hydrophobic monomer is styrene.

According to the sixth aspect of the present invention, a gel layer in which a charged group is localized is further provided on the surface of the core-shell gel particles, and the gel layer is emulsified and polymerized as seed particles on the surface of the outermost polymer. Is the hierarchical structure particle according to any one of claims 1 to 5, characterized in that an electrolyte gel layer is present.

The sixth aspect of the present invention according to claim 6, wherein the gel layer in which the charged group is localized is a copolymer of a monomer having no charged group and fumaric acid. It is a hierarchical structure particle of.

The present invention according to claim 8 is the method for producing hierarchical structural particles according to any one of claims 1 to 7.
The first step of adding a cross-linking agent to a monomer having no charged group in ion-exchanged water and preparing core gel particles by free radical polymerization, and
The core-shell gel particles are prepared by adding a monomer having no charged group, a cross-linking agent, and a comonomer having a charged group of a carboxyl group or a sulfonic acid group to ion-exchanged water containing the core gel particles and performing seed precipitation polymerization. Step 2 and
A method for producing hierarchical structure particles, which comprises a third step of adding a hydrophobic monomer to ion-exchanged water containing the core-shell gel particles and performing seed emulsion polymerization after performing the second step one or more times. be.

The hierarchical structure particles according to the present invention can provide industrially useful hierarchical structure particles composed of a polymer. Further, the hierarchical structure particles according to the present invention are expected to exhibit excellent functions such as stimulus responsiveness derived from the core-shell gel particles used as seeds.

In the method for producing hierarchical structure particles according to the present invention, hydrogel particles can be used as seeds. Hydrogel particles are substances whose size, rigidity, charge density, and other physical properties can be easily changed, and the obtained hierarchical structure particles change their size and interdomain distance in response to stimuli. Can be done.

Further, the hierarchical structure particles according to the present invention can be given new uses and functionality by compounding known substances. Examples of the compounding substance include an elastomer, a hydrophobic (water-repellent) material, and a biocompatible material.

Further, in the method for producing hierarchically structured particles according to the present invention, if the core-shell gel fine particles used as templates are monodisperse, it is possible to obtain hierarchically structured particles having a uniform particle size and composite morphology. In addition, there is no strict limit on the number of layers, and it is possible to create particles having various hierarchical structures such as two layers, three layers, and four layers.

It is an image diagram about the manufacturing procedure of a hierarchical structure particle. FE-SEM images of core gel particles (N particles) and core shell gel particles (N-NM particles). It is an image of a core-shell gel particle having a charge distribution having a three-layer structure. FE-SEM images of hierarchical structure particles (N-NM (40 mM) -S300 particles) and TEM images of ultrathin sections. FE-SEM images of hierarchical structure particles (N-NM (150 mM) -S300 particles) and TEM images of ultrathin sections. FE-SEM images of hierarchical structure particles (N-NM-NM-S100 particles) and TEM images of ultrathin sections. FE-SEM images of hierarchical structure particles (N-NM-NM-NF-S200 particles) and TEM images of ultrathin sections.

Hereinafter, embodiments of the particles according to the present invention and the method for producing the same will be described.

The present invention provides novel composite gel fine particles having a hierarchical structure by performing seed emulsion polymerization of hydrophobic monomers using core-shell gel particles whose charge distribution is clearly distinguished in layers. be.

In the present invention, the hierarchical structure particle means that a solid layer composed of a solid component and a gel layer composed of a gel component are periodically present at least one or two, respectively, from the center of the particle toward the surface of the particle. It may be called a structure that presents a hierarchical structure as a whole. The term "solid" as used herein is an expression that distinguishes a gel layer from a gel layer by comparing the relative viscosity and fluidity of the other layer with respect to one of the laminated layers. Both are in a low state. For example, polystyrene particles introduced into core-shell gel particles by seed emulsion polymerization may be referred to as a solid or a solid layer.

The core-shell gel particles are formed by laminating a charged gel portion and an uncharged gel portion from the center of the particles toward the surface. In the core-shell gel particles according to the present invention, the distribution of charge group monomers in the particles can be controlled . In order to prepare core-shell gel particles, different types of monomers are compounded and prepared. In the presence of the appropriate polymer, it is necessary to select the monomer and the appropriate comonomer with a different reactivity ratio. Examples include a composite of an LCST polymer having no charged group, a monomer having no charged group, and a comonomer having a charged group.

The LCST polymer is a polymer that is soluble in a solvent at a low temperature, and is a polymer that deposits as another phase from a solution when the temperature is raised and the so-called LCST (lower limit critical dissolution temperature) is reached. Examples of non-charged LCST polymers include polyalkylene oxide derivatives, preferably polyethylene glycol (PEG) derivatives, polyethylene oxide (PEO) derivatives, polypropylene oxide (PPO) derivatives, prepared by free radical polymerization . Examples thereof include polyethers such as polymethyl vinyl ether, poly-N-vinylcaprolactum, polyacrylamide derivatives, and polysiloxane.

The comonomer having a charged group is not particularly limited as long as it is a vinyl monomer, and examples thereof include a methacrylic acid monomer such as methacrylic acid, an acrylic acid monomer such as acrylic acid, fumaric acid, vinyl acetic acid, and maleic acid. -Acrylic-methylpropanesulfonic acid (AMPS) , sulfonic acid-based vinyl monomers such as styrenesulfonic acid, and the like. There is no particular limitation, but it can be arbitrarily selected from substances having a known reactivity ratio with the monomer.

The seed emulsion polymerization method used in the present invention is a polymerization method capable of compounding polymers having different components with seed particles by performing emulsion polymerization in the presence of polymer particles. These methods have been widely studied so far, but most of them have been studied using solid-like fine particles (water-insoluble, high-density, hard particles) as seed particles. That is, solid-solid composite fine particles have been produced by a polymerization method using a water-insoluble oil for a hydrophobic substance that dislikes water.

Under such circumstances, the present inventors have created gel-solid composite gel fine particles by seed emulsion polymerization using hydrogel fine particles as seeds. Such composite gel fine particles inherit the external stimulus responsiveness (temperature / pH, etc.) derived from the gel fine particles and have a modified structure, so that light scattering cannot be achieved by the gel fine particles alone. It is a novel composite material that is superior in terms of properties and wettability. External stimulus responsiveness refers to the property of reversibly or irreversibly changing the physicochemical properties in response to various stimuli from the external environment. For example, when NIPAm is used as a monomer, the produced particles Will have temperature responsiveness, and when acrylic acid or methacrylic acid is used as the comonomer, it will have pH responsiveness. In addition, it is possible to inherit the external stimulus responsiveness of the material, such as the photoresponsiveness of the azobenzene monomer.

Hereinafter, as an example of the hierarchical structure particles according to the present invention, an example in which composite gel fine particles with polystyrene are prepared by using N-isopropylacrylamide (NIPAm) and methacrylic acid (MAc) copolymer gel particles as seeds will be described. do.

pNIPAm is a temperature sensitive polymer having a lower string critical symbiotic temperature (LCST) near 33 degrees Celsius. The particles produced in this example are hydrogel fine particles having pNIPAm as a main skeleton, and inherit the temperature responsiveness. Shrink. Furthermore, when a comonomer having a charged group such as MAc is copolymerized with pNIPAm, the LCST shifts to a high temperature under the condition that the charged group is dissociated, so that the gel fine particles are in a swollen state even in a high temperature state (about 70 degrees Celsius or higher). It is known to keep. Similarly, the particles produced in this example can inherit the pH responsiveness of pNIPAm.

In the production method according to the present invention, water-based polymerization can be suitably applied to the production of particles. In the aqueous precipitation polymerization method, the globule chains of pNIPAm precipitated in water aggregate with each other due to hydrophobic attraction to form nuclei. Then, gel fine particles are formed by depositing newly formed globule chains on the nucleus. That is, the polymer chain formed in the early stage of polymerization is present in the center of the obtained gel fine particles, and the polymer chain formed in the late stage of polymerization is present in the vicinity of the surface layer of the obtained gel fine particles. According to this mechanism, the center of the particles is obtained by (1) selecting an appropriate comonomer having a different reaction ratio with NIPAm, (2) performing precipitation polymerization in the presence of seed particles, and performing seed precipitation polymerization. It becomes possible to unevenly distribute the portion and the surface portion, respectively. In this example, core-shell gel particles having a shell layer of pNIPAm-co-MAc copolymer gel fine particles were prepared by a seed precipitation polymerization method using pNIPAm gel fine particles as seeds. An image diagram of the manufacturing procedure is shown in FIG.

(Preparation of core gel particles)
First, core gel particles of pNIPAm were prepared. N-isopropylacrylamide (N-Isotropylacrylamide (NIPAm, purity 98%, manufactured by Wako Pure Chemical Industries, Ltd.)) and N, N'-methylenebis (acrylamide) (N, N'-methylenebis (acrylamide) (BIS, purity 97%, sum) (Made by Kojunyaku), ion-exchanged water was placed in a three-necked round-bottom flask and mixed using a stirrer. By adding BIS as a cross-linking agent, it became possible to introduce a cross-linking structure into the prepared particles. It is suitable for improving the physical properties of the obtained particles. The mixed solution was heated to 70 ° C. under stirring (250 rpm) and nitrogen bubbling (30 minutes). Then, potassium peroxodisulfate (KPS,). (Purity 95%, manufactured by Wako Pure Chemical Industries, Ltd.)) Aqueous solution (5 mL) was added and free radical polymerization was carried out. The reaction was carried out for 4 hours and then naturally cooled to room temperature. The reaction time, reaction temperature, stirring speed and others were selected. Appropriate experimental conditions can be arbitrarily set depending on the type of monomer to be used and the type of initiator.

The core gel particles produced were centrifuged (70,000 xg) twice for purification. FIG. 2A shows an FE-SEM image of the core gel particles (N particles) obtained. Further, considering the mechanism of the polymerization reaction, a negative charge derived from the terminal group of KPS, which is an initiator, exists inside the N particles. However, since this charge is very small, it does not affect the solubilization of the oil-soluble polymer. In the present invention, when the amount of electric charge is less than or equal to the extent that does not affect the solubilization of the oil-soluble polymer, this is regarded as neutral, and the layer made of neutral gel is regarded as a neutral gel layer.

(Preparation of core shell gel particles)
It is known that methacrylic acid used as a comonomer in producing core-shell gel particles is displaced toward the center of the gel particles and the charge is localized from the viewpoint of the reactivity ratio . Therefore , the core-shell gel particles obtained in this example have a charge distribution having a three-layer structure of a neutral gel layer-charged gel layer-neutral gel layer from the center. FIG. 3 shows an image of core-shell gel particles having a three-layered charge distribution.

The dispersion liquid (core gel solid component concentration: 0.4 wt%) in which the core gel particles prepared in the above experiment were dispersed in ion-exchanged water was heated to 70 degrees Celsius under stirring (250 rpm) and nitrogen bubbling (30 minutes). .. Then, NIPAm (45 mol.%), BIS (5 mol.%), MAc (50 mol.%), And KPS aqueous solution (5 mL) were added, and seed precipitation polymerization was carried out. The reaction was carried out for 4 hours and then naturally cooled to room temperature.

The core-shell gel particles produced were centrifuged (70,000 xg) twice for purification. The FE-SEM images of the core-shell gel particles (N-NM particles) obtained in FIGS. 2 (b) and 2 (c) are shown. By using N-NM particles as seeds and performing the same polymerization as described above, the number of layers of the core-shell particles produced is increased, for example, N-NM-NM and N-NM-NM-NM. At the same time, it was confirmed that it was possible.

(Control of shell thickness)
An attempt was made to control the shell thickness of the obtained core-shell gel particles by changing the monomer concentration during seed precipitation polymerization. The polymerization conditions are shown in Table 1.

From the FE-SEM observation results, no secondary particles composed of shell monomer components were observed in any of the gel fine particles. The particle diameters of the N gel fine particles, N-NM (40 mM) gel particles, and N-NM (150 mM) gel particles at the time of drying are D = 325 ± 13 nm (CV = 4%) and D = 351 ± 16 nm (CV). = 4%), D = 423 ± 21 nm (CV = 5%).

The particle size at the time of drying is larger in the core-shell gel particles than in the core particles, and the case where the monomer concentration at the time of polymerization is high (N-NM (150 mM) gel particles) is compared with the case where the monomer concentration is low. (N-NM (40 mM) gel particles), the particle size increased.

In addition, when the hydrodynamic diameter of the gel particles in water was measured, Dh = 320 ± 13 nm (N gel particles, pH 3,70 °) and Dh = 352 ± 14 nm (N-NM (40 mM) gel, respectively). Particles, pH 3,70 ° C), Dh = 519 ± 5 nm (N-NM (150 mM) gel particles, pH 3,70 ° C). The shell thickness of the core-shell gel particles is calculated by the following formula:

shell thickness = α
= (D _h (core-shell microgel)) (pH 3,70 ° C) --D _h (core microgel)) (pH 3,70 ° C)) / 2

The shell thickness is α = 21 nm (N-NM (40 mM) gel particles) and α = 100 nm (N-NM (150 mM) gel particles), respectively. From this, it was confirmed that the shell thickness can be controlled by changing the concentration of the monomer.

(Creation of hierarchical particles)
Subsequently, the hierarchical structure particles were prepared by seed emulsion polymerization of styrene using the core-shell gel particles prepared above as seeds. In order to dissociate the carboxy group inside the gel particles, the pH in the polymerization system was adjusted to about 10 with a 1 M NaOH solution during the seed emulsion polymerization in all the polymerizations.

A dispersion (100 mL, core-shell gel solid component concentration: 0.17 wt%) in which the core-shell gel particles prepared in the above experiment were dispersed in ion-exchanged water was stirred (250 rpm) and nitrogen bubbling (30 minutes) at 70 degrees Celsius. Heated to a degree. Then, KPS (0.0271 g, 1 mM) and styrene monomer were added, and seed emulsion polymerization was carried out. The reaction was carried out for 24 hours and then naturally cooled to room temperature.

The core-shell gel particles produced were centrifuged (20,000 xg) twice for purification. FIG. 4 shows an FE-SEM image of the obtained hierarchical structure particles (N-NM (40 mM) -S300 particles) using core shell gel particles (N-NM (40 mM) particles) having a relatively thin shell thickness as seeds. Is shown. In the figure, FIG. 4B is an observation result of an ultrathin section of the produced hierarchical structure particles. From the figure, many polystyrene particles are formed inside the particles, and the particles are composed of two layers of different sizes of polystyrene particles. It can be confirmed that the hierarchical structure of is formed. When the diameter of the hierarchical structure particles and the protrusion diameter of polystyrene are measured, the composite particle diameter D = 867 ± 51 nm (CV = 6%), the large protrusion diameter D ₁ = 213 ± 31 nm (CV = 15 nm), and the small protrusion diameter D. ₂ = 64 ± 8.3 nm (CV = 13%).

(Preparation of hierarchical structure particles with different concentrations)
Hierarchical particles were prepared using N-NM50 (150 mM) gel particles having a thicker shell than N-NM50 (40 mM) gel fine particles as seeds. The sample and method used are the same as in Example 1 except for the core-shell gel particles of the seed. The FE-SEM image and the TEM image of the obtained hierarchical structure particles (N-NM (150 mM) -S300 particles) are shown in FIG. In FIG. 5, (a) and (b) are FE-SEM images, and (c) and (d) are TEM images.

From FIG. 5, it was confirmed that when the styrene concentration at the time of polymerization was 100 mM (FIG. 5 (a)), the hierarchical structure particles had a crushed shape under vacuum conditions. At this time, the hierarchical structure particle diameter D = 666 ± 50 nm (CV = 8%) and the small protrusion diameter D = 57 ± 9 nm (CV = 15%). When the styrene concentration at the time of polymerization is increased to 300 mM, the hierarchical structure particle diameter D = 969 ± 31 nm (CV = 4%) and the small protrusion diameter D = 166 ± 38 nm (CV = 23%). Both protrusion diameters increased (FIG. 5 (b)).

In the N-NM (150 mM) -S300 particles, the variation in the surface structure as seen in the N-NM (40 mM) -S300 particles is not confirmed. When the internal structure of the hierarchical structure particles is evaluated by the observation of the ultrathin section shown in FIG. 5 (c), the N-NM (150 mM) -S300 particles have a three-layer structure of polystyrene-intermediate layer-polystyrene from the center. It can be confirmed that there is. The thickness of the gel in the center was measured and found to be about 75 nm. Although the density of gel particles is low and its network structure cannot be confirmed with an electron microscope, it is considered that a hydrogel layer is present in the intermediate layer. It is not possible to clearly confirm such an intermediate layer from the observation results of ultrathin sections of N-NM (150 mM) -S100 gel particles, but this is because the composite amount of polystyrene is low and the particles are embedded in the resin. Is thought to be due to the deformation. Probably, the N-NM (40 mM) -S300 gel fine particles also have a solid-gel-solid three-layer structure, but since the shell gel layer is thin, the solid-solid is evaluated by an electron microscope. It is considered that it was observed like the two-layer particles of. From this, it was shown that the spacing between the solid (polystyrene) layers can be adjusted by changing the thickness of the shell gel layer.

(Preparation of 5-layer composite gel particles)
In order to create a hierarchical composite gel particle with a controlled structure, an attempt was made to add a poly (NIPAm-co-MAc) copolymer gel shell layer to N-NM (150 mM) gel particles by a seed precipitation polymerization method. (N-NM-NM gel particles). The sample and method used are the same as in Example 1 except for the core-shell gel particles of the seed. When the above N-NM-NM gel particles were used as seeds and soap-free seed emulsion polymerization of styrene was performed, when the styrene concentration at the time of polymerization was 200 mM, coarse aggregates were formed during the polymerization, but the styrene concentration was 100 mM. At the time of, dispersion-stable composite gel particles were obtained (N-NM-NM-S100 particles).

6 (a) and 6 (c) show an FE-SEM image of N-NM-NM-S100 particles and an image diagram of the obtained hierarchical structure particles. From the FE-SEM observation results, it is confirmed that composite gel particles having a particle diameter D = 1017 ± 52 nm (CV = 5%) and a small particle diameter D = 68 ± 5 nm (CV = 7%) were obtained. The composite gel particle size D is increased by about 200 nm as compared with the case where the N-NM50 (40 mM) gel particles are used as seeds, which is considered to be due to the increase in the gel particle size as the seed.

FIG. 6B is the result of observing the internal structure of the hierarchical structure particles in ultrathin sections. Evaluating from the figure, a five-layer structure of solid (1st layer) -gel (2nd layer) -solid (3rd layer) -gel (4th layer) -solid (5th layer) is formed from the center. It can be confirmed that it is done. The thickness of the gel in the second layer was 34 ± 5 nm, and the thickness of the gel in the fourth layer was 45 ± 17 nm. It is considered that the thickness of the second layer became thinner than that of the -NM-S300 gel fine particles (FIG. 5) due to the deformation of the gel due to drying and the compression effect of the 35th layer. However, the N-NM-NM-S100 particles, like the N-MM-S100 gel particles, are greatly deformed when the ultrathin section is observed.

(Change of charge distribution of gel particles)
In order to composite more polystyrene with the core-shell gel particles that serve as seeds, the charged groups are localized on the surface of the gel fine particles and the electrostatic repulsive force between the particles is increased to make the composite gel fine particles. It is effective to improve the dispersion stability.

In order to composite more polystyrene with the seed core-shell gel particles and clarify the hierarchical structure, an attempt was made to add a poly (NIPAm-co-FAc) gel-shell layer to the N-NM-NM particles. The sample and method used are the same as in Example 1 except for the core-shell gel particles of the seed and the monomer (FAc) to be copolymerized. It is known that when NIPAm and FAc are copolymerized, the reactivity of FAc is very low, and FAc is localized on the surface of gel particles. Therefore, a charged group derived from fumaric acid is localized on the surface of the obtained core-shell gel particles (N-NM-NM-NF particles). Further, the size of the produced particles can be arbitrarily set by increasing or decreasing the amount of FAc used.

FIG. 7A shows an FE-SEM image of hierarchical structure particles obtained by performing soap-free emulsion polymerization of styrene using N-NM-NM-NF gel particles as seeds. In this experiment, hierarchically structured particles with high dispersion stability were obtained even under polymerization conditions with a styrene concentration of 200 mM (N-NM-NM-NF-S200 particles). The obtained particles have protrusions of different sizes on the surface, and have a hierarchical structure particle diameter D = 1586 ± 47 nm (CV = 3%) and a large protrusion diameter D ₁ = 217 ± 41 nm (CV = 19%). , Small protrusion diameter D ₂ = 86 ± 8 nm (CV = 9%).

FIG. 7B shows the results of ultrathin section observation of N-NM-NM-NF-S200 particles. From the figure, it can be confirmed that the N-NM-NM-NF-S200 particles are layered particles having a five-layer structure. However, in reality, it is considered that there is an electrolyte gel layer on the surface of the hierarchically structured particles, which contributes to the dispersion stability of the particles and cannot be observed with an electron microscope. Considering this point, the N-NM-NM-NF-S200 particles are actually solid (first layer) -gel (second layer) -solid (third layer) -gel (from the center of the particles. 4th layer) -Solid (5th layer) -Gel (6th layer), 6-layer hierarchical structure particles.

Further, from FIG. 7B, the thickness of the second layer was 39 ± 11 nm, and the thickness of the fourth layer was 152 ± 19 nm. It can be confirmed that the thickness of the fourth gel layer is clearly increased in the N-NM-NM-NF-S200 particles as compared with the above-mentioned N-NM-NM-S100 particles. It is thought that this is because the strength of the hierarchical structure particles is improved by the presence of charged groups on the particle surface and the composite of more polystyrene, which makes it difficult to deform during the drying process and resin embedding. Be done. In other words, it is presumed that the gel fine particles serving as seeds are highly swelled in water and show a swelling structure as shown in FIG. 7 (b). This indicates that the method according to the present invention can be utilized not only for the synthesis of hierarchical structure particles but also for the structural evaluation of gel fine particle nanostructures at the time of swelling and the hierarchical structure.

Claims (8)

A core consisting of a gel containing a polymer having no charged group , which is formed by free radical polymerization and has a cross-linked structure introduced by a cross-linking agent .
On the outside thereof , using the core as a seed, a monomer having no charged group and a comonomer having a charged group of a carboxyl group or a sulfonic acid group having a different reactivity ratio from the monomer are copolymerized by precipitation polymerization. , A core-shell gel particle composed of a gel containing a polymer into which a cross-linking structure with a cross-linking agent has been introduced, and one shell layer in which charged groups are unevenly distributed or a plurality of shell layers formed by laminating the shell layer . As a seed particle
Hierarchical particles in which a polymer obtained by emulsion polymerization of hydrophobic monomers having different components with respect to the seed particles is formed in the core and further formed in layers in the one or a plurality of shell layers . The hierarchical structure particle according to claim 1, wherein at least one of the uncharged monomer and the charged comonomer has an external stimulus response. The polymer having no charged group is a polyalkylene oxide derivative, a polyethylene glycol (PEG) derivative, a polyethylene oxide (PEO) derivative, a polypropylene oxide (PPO) derivative, a polymethylvinyl ether, or a poly-, which is prepared by free radical polymerization. The layered structure particle according to claim 1 or 2, wherein the LCST polymer is at least one selected from the group consisting of N-vinylcaprolactum and a polyacrylamide derivative. The comonomer having a charged group is at least one vinyl selected from the group consisting of methacrylic acid, acrylic acid, fumaric acid, vinyl acetic acid, maleic acid, 2-acrylamide-methylpropanesulfonic acid, and styrenesulfonic acid . The hierarchical structure particle according to any one of claims 1 to 3, which is a monomer. The hierarchical structure particle according to any one of claims 1 to 4, wherein the hydrophobic monomer is styrene. A gel layer in which charged groups are localized is further provided on the surface of the core-shell gel particles, and an electrolyte gel layer is present on the surface of the outermost polymer emulsified and polymerized using this as seed particles. The hierarchical structure particle according to any one of claims 1 to 5, which is characterized. The hierarchical structure particle according to claim 6, wherein the gel layer in which the charged group is localized is a copolymer of a monomer having no charged group and fumaric acid. The method for producing hierarchically structured particles according to any one of claims 1 to 7.
The first step of adding a cross-linking agent to a monomer having no charged group in ion-exchanged water and preparing core gel particles by free radical polymerization, and
The core-shell gel particles are prepared by adding a monomer having no charged group, a cross-linking agent, and a comonomer having a charged group of a carboxyl group or a sulfonic acid group to ion-exchanged water containing the core gel particles and performing seed precipitation polymerization. Step 2 and
A method for producing hierarchical structure particles, which comprises a third step of adding a hydrophobic monomer to ion-exchanged water containing the core-shell gel particles and performing seed emulsion polymerization after performing the second step one or more times.

Images