Selectively decomposable polymer fine particle molded body, method for producing same, and method for decomposing same

Abstract

There is provided a selectively decomposable polymer fine particle molded body which comprises a plurality of polymer fine particles and a crosslinked structure connecting the plurality of polymer fine particles to each other. The polymer fine particles have on their surface a first functional group capable of bonding to a crosslinking agent for forming the crosslinked structure. The crosslinking agent has a second functional group capable of chemically bonding to the first functional group, and the crosslinked structure is formed by chemically bonding the first functional groups and the second functional groups. The selective decomposability of the selectively decomposable polymer fine particle molded body is preferably decomposability by the synergistic action of light irradiation and acid.

Description

Selectively degradable polymer microparticle molded article, and method for producing the same and method for degrading the same.

[0001] The present invention relates to selectively degradable polymer microparticle molded articles, as well as methods for producing and degrading the same. This application claims priority based on Japanese Patent Application No. 2025-007886, filed in Japan on January 20, 2025, the contents of which are incorporated herein by reference.

[0002] In recent years, there has been a surge in the development of polymer recycling methods from the perspective of curbing resource depletion and environmental pollution. From this viewpoint, materials formed from molded polymer microparticles have been proposed as polymer molded bodies. Furthermore, while the production volume of polymer materials has increased in recent years, microplastics, which are formed when polymer materials decompose and degrade due to external stimuli such as ultraviolet light, have become a major social problem. As the demand for polymer material recycling increases, it is necessary to impart high selectivity to the decomposition of polymer materials in order to solve this problem.

[0003] Various proposals have been made regarding polymer fine particles as described above. For example, Patent Document 1 discloses particles made of methoxyethyl polyacrylate, characterized in that the diameter is 100 nm or more and 300 nm or less. Patent Document 1 also discloses that when manufacturing the particles, other monomers, particularly oligoethylene glycol methacrylate and a crosslinking agent, are added at the same time and copolymerized to produce composite particles of methoxyethyl polyacrylate particles and a gel-like polymer.

[0004] Patent documents 2 and 3 disclose polymeric fine particles made of crosslinked rotaxane copolymers, which are copolymers of a rotaxane having at least one polymerizable unsaturated group and a polymerizable unsaturated monomer (such as methyl acrylate).

[0005] Patent Document 4 discloses polymeric microparticles comprising a copolymer of a rotaxane having a cyclic molecule and an axial molecule penetrating the cyclic molecule, and a (meth)acrylate, wherein at least one of the cyclic molecule and the axial molecule has a polymerizable unsaturated group-containing group, and the axial molecule has 4 to 12 carbon atoms.

[0006] Patent Document 5 discloses a rotaxane having two or more cyclic molecules and axial molecules penetrating the cyclic molecules, wherein the cyclic molecules have reactive functional group-containing groups and the axial molecules are two or more polymer chains linked via linking groups, and the polymer fine particles are made of a crosslinked polymer using a rotaxane.

[0007] Japanese Patent Publication No. 2018-30917, Japanese Patent Publication No. 2018-030928, Japanese Patent Publication No. 2019-99607, Japanese Patent Publication No. 2022-091113, Japanese Patent Publication No. 2023-124226

[0008] When recycling polymer materials, degradability is required from the standpoint of recyclability and separation when used in composite materials, while physical stability is required from the standpoint of extending the lifespan of polymer materials and expanding the range of usage environments. However, molded articles formed from polymer microparticles using conventional technology become so brittle in the presence of a good solvent for the polymer components that make up the polymer microparticles (hereinafter sometimes referred to as constituent polymer components) that the molded article cannot maintain its shape.

[0009] This invention has been made in view of the above circumstances, and aims to provide a selectively degradable polymer microparticle molded article that exhibits stability even in the presence of a good solvent for the constituent polymer components and decomposes only when an arbitrary external stimulus is applied, as well as a method for producing the same and a method for decomposition.

[0010] To solve the above problems, the present invention has the following embodiments: [1] A selectively degradable polymer microparticle molded article comprising a plurality of polymer microparticles and a crosslinking structure that connects the plurality of polymer microparticles, wherein the polymer microparticles have a first functional group on their surface that can bond with a crosslinking agent for forming the crosslinking structure, the crosslinking agent has a second functional group that can chemically bond with the first functional group, and the crosslinking structure is formed by the chemical bonding of the first functional group and the second functional group. [2] The selectively degradable polymer microparticle molded article according to [1], wherein the selective degradability of the selectively degradable polymer microparticle molded article is degradability due to the cooperative action of light irradiation and acid. [3] The selectively degradable polymer microparticle molded article according to [1] or [2], wherein the crosslinking structure is bonded in a manner that allows for bond cleavage by the cooperative action of light irradiation and acid. [4] A selectively degradable polymer microparticle molded article according to any one of [1] to [3], wherein the crosslinked structure is formed in which a conjugated carbon atom of a condensed polycyclic aromatic ring group and a silicon atom are bonded in a manner that allows for bond cleavage by the cooperative action of light irradiation and acid. [5] A selectively degradable polymer microparticle molded article according to any one of [1] to [4], wherein the chemical bond between a first functional group having on the surface of the polymer microparticle and a second functional group having the crosslinking agent is formed by a condensation reaction between condensation-reactive groups or an addition reaction by a ring-opening group. [6] A selectively degradable polymer microparticle molded article according to [5], wherein the bond formed is a carbon-nitrogen bond. [7] A selectively degradable polymer microparticle molded article according to [5], wherein the bond formed is an amide bond. [8] A selectively degradable polymer microparticle molded article according to [5], wherein the bond formed is a urethane bond. [9] A selectively degradable polymer microparticle molded article according to any one of [1] to [8], wherein the combination of a first functional group having on the surface of the polymer microparticles and a second functional group having on the crosslinking agent is a combination of an amino group and a carboxyl group.

[10] A selectively degradable polymer microparticle molded article according to any one of [1] to [9], wherein the combination of a first functional group having on the surface of the polymer microparticles and a second functional group having the crosslinking agent is a combination of an amino group and a functional group selected from the group consisting of a cyclocarbonate group and an oxocyclopropyl group.

[11] A selectively degradable polymer microparticle molded article according to any one of [1] to

[10] , wherein the crosslinking agent is a reactive compound having a structure in which a conjugated carbon atom of a condensed polycyclic aromatic ring group and a silicon atom are bonded in a manner that can be cleaved by the cooperative action of light irradiation and acid, and has one or more amino groups as the second functional group.

[12] A selectively degradable polymer microparticle molded article according to any one of [1] to

[11] , wherein the polymer component that constitutes the polymer microparticles is a polymer that, in the presence of a poor solvent, can form aggregates in which the plurality of polymer microparticles are bound together by the entanglement of polymer chains present on the surfaces of adjacent polymer microparticles, and in the presence of a good solvent, the good solvent can enter between the entangled polymer chains, causing the polymer chains to unravel and the aggregates to decompose into polymer microparticles.

[13] A selectively degradable polymer microparticle molded article according to any one of [1] to

[12] , wherein the polymer component that constitutes the polymer microparticles is stable even when brought into contact with a good solvent.

[14] A selectively degradable polymer microparticle molded article according to any one of [1] to

[13] , wherein the polymer component that constitutes the polymer microparticles is an acrylic polymer or a styrene polymer.

[15] A selectively degradable polymer microparticle molded article according to

[14] , wherein the acrylic polymer is a (meth)acrylate polymer or a poly(meth)acrylamide polymer.

[16] A selectively degradable polymer microparticle molded article according to any one of [1] to

[15] , wherein 80 mol% or more of the monomer constituting the polymer component that constitutes the polymer microparticles is at least one monomer selected from the group consisting of polyalkylene glycol (meth)acrylate, alkoxy group-containing methacrylate, alkoxy group-containing acrylate having 2 or more carbon atoms, (meth)acrylamide, and derivatives thereof.

[17] The selectively degradable polymer microparticle molded body according to [3], wherein the light irradiation is irradiation light with light including an absorption wavelength region of a structure formed by bonding in the form capable of bond cleavage.

[18] The selectively degradable polymer microparticle molded body according to [3], wherein the structure formed by bonding in the form capable of bond cleavage is represented by the following formula (1). (In formula (1), X １ is a substituted or unsubstituted monovalent or divalent condensed polycyclic aromatic ring group, X ２ is a substituted or unsubstituted divalent condensed polycyclic aromatic ring group or a single bond, Y is a single bond, an oxygen atom or an alkylene group, R １ is an alkyl group or an alkoxy group, R ２ is an alkyl group or an alkoxy group, n is 0 or 1, m is an integer of 0 to 5, and * is a bond. However, when Y is a single bond, n is 0, and when Y is an oxygen atom and n is 0, m is 1.)

[19] The selectively degradable polymer microparticle molded body according to [3], wherein the structure formed by bonding in the form capable of bond cleavage is represented by the following formula (2). (In formula (1), X １ is a substituted or unsubstituted monovalent or divalent condensed polycyclic aromatic ring group, X ２ is a substituted or unsubstituted divalent condensed polycyclic aromatic ring group or a single bond, Y is a single bond, an oxygen atom or an alkylene group, R １ is an alkyl group or an alkoxy group, R ２ is an alkyl group or an alkoxy group, n is 0 or 1, m is an integer of 0 to 5, provided that when Y is a single bond, n is 0, and when Y is an oxygen atom and n is 0, m is 1.)

[20] The selectively degradable polymer microparticle molded body according to [an item selected from 18 or 19], wherein the condensed polycyclic aromatic ring group as the said X １ and the said X ２ is formed by condensing 2 to 6 aromatic rings.

[21] The selectively degradable polymer microparticle molded body according to [an item selected from 18 or 19], wherein m is 0.

[22] The selectively degradable polymer microparticle molded body according to [an item selected from 18 or 19], wherein m is 1.

[23] The said R １ and R ２The selectively degradable polymer microparticle molded article according to

[17] or

[18] , wherein each is independently a methyl group or an ethyl group.

[24] The X ２A selectively degradable polymer microparticle molded article according to

[18] or

[19] , wherein the condensed polycyclic aromatic ring group is a substituted or unsubstituted pyrenylene group.

[25] A method for producing a selectively degradable polymer microparticle molded article according to any one of [1] to

[24] , comprising: a first step of forming a polymer microparticle molded article by removing a dispersion medium from a dispersion containing a plurality of polymer microparticles; and a second step of contacting the obtained polymer microparticle molded article with a reaction solution containing the crosslinking agent to chemically bond the first functional group present on the surface of the polymer microparticles with the second functional group of the crosslinking agent, thereby bonding the polymer microparticles together via a crosslinked structure derived from the crosslinking agent.

[26] The method for producing a selectively degradable polymer microparticle molded article according to

[25] , wherein in the second step, the solvent used in the reaction solution containing the crosslinking agent is a good solvent for the polymer components that constitute the polymer microparticles.

[27] The manufacturing method according to

[24] , wherein the first step is to form a polymer microparticle molded body by applying a dispersion containing the plurality of polymer microparticles onto a substrate to form a coating film, and the second step is to immerse the obtained polymer microparticle molded body in a reaction solution containing the crosslinking agent, and then remove the polymer microparticle molded body from the reaction solution, thereby chemically bonding the first functional group present on the surface of the polymer microparticles with the second functional group of the crosslinking agent, and bonding the polymer microparticles to each other via the crosslinking agent.

[28] A method for decomposing a selectively degradable polymer microparticle molded body according to any one of [1] to

[24] , comprising the step of decomposing the crosslinking structure of the polymer microparticle molded body by simultaneously applying external stimuli to the polymer microparticle molded body by light irradiation and acid.

[29] A method for obtaining polymer microparticles constituting a selectively degradable polymer microparticle molded body according to any one of [1] to

[24] , comprising: (1) a first A step of decomposing the crosslink structure having a polymer microparticle molded body by simultaneously applying external stimuli by both light irradiation and acid in the presence of a good solvent for the polymer components that constitute the polymer microparticles; or (2) a first B step of contacting the obtained polymer microparticle molded body with a good solvent for the polymer components that constitute the polymer microparticles after decomposing the crosslink structure having a polymer microparticle molded body by simultaneously applying external stimuli by both light irradiation and acid; and a second step of recovering the polymer microparticles generated in the first A step or the B step.

[0011] According to the present invention, it is possible to provide a selectively degradable polymer microparticle molded article that exhibits stability even in the presence of a good solvent for the constituent polymer components and decomposes only when a specific external stimulus is applied, as well as a method for producing the same and a method for decomposition.

[0012] The following are SEM images of the polymer microparticles obtained in Production Example 1. The results of the swelling characteristic evaluation of the polymer microparticles obtained in Production Example 1 are shown. The results of the glass transition temperature measurement of the polymer microparticles obtained in Production Example 1 are shown. The results of the crosslinked polymer chain amount evaluation of the selectively degradable polymer microparticle molded body obtained in Example 1 are shown. The results of the mechanical evaluation in the uniaxial elongation test of the selectively degradable polymer microparticle molded body obtained in Example 1 are shown. The results of the interparticle crosslinking evaluation by stress relaxation test of the selectively degradable polymer microparticle molded body obtained in Example 1 are shown. The results of the multi-stimulus degradability evaluation of the selectively degradable polymer microparticle molded body obtained in Example 1 are shown. The results of the multi-stimulus degradability evaluation of the selectively degradable polymer microparticle molded body obtained in Example 1 are shown. The SEM images of the polymer microparticles before film formation and the SEM images of the polymer microparticles obtained by degrading the selectively degradable polymer microparticle molded body obtained in Example 1 by applying light irradiation and acid stimulation are shown.

[0013] <Selectively Degradable Polymer Fine Particle Molded Body>The selectively degradable polymer fine particle molded body of this embodiment is composed of a plurality of polymer fine particles and a crosslinked structure that connects the plurality of polymer fine particles to each other. The polymer fine particles have, on their surfaces, a first functional group that can bind to a crosslinking agent for forming the crosslinked structure, and the crosslinked structure is formed by a chemical bond between the first functional group and a second functional group that can chemically bond to the first functional group of the crosslinking agent. The polymer fine particles are a molded body that is an aggregate formed by the entanglement of polymer chains between the polymer fine particles. The molded body formed by such characteristics has the characteristics of the polymer itself such as toughness, but can be decomposed, recovered, and reused. The selectively degradable polymer fine particle molded body is not particularly limited, but may be a coating film formed on a substrate, or may be a self-supporting molded body such as a self-supporting film.

[0014] 《Polymer Fine Particles》 The polymer component that is a constituent of the polymer fine particles may be a homopolymer (homopolymer) composed of a single type of monomer, or may be a copolymer (copolymer) composed of a plurality of types of monomers. In the case of a copolymer, it may be a block copolymer or a random copolymer. The polymer component that is a constituent of the polymer fine particles is preferably an acrylic polymer or a styrene polymer. Examples of the acrylic polymer include (meth)acrylate polymers and poly(meth)acrylamide polymers. <Elementary substance

[0015] The (meth)acrylates used in the manufacture of (meth)acrylic polymers are not particularly limited, and specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isononyl (meth)acrylate. Linear or branched alkyl (meth)acrylates such as isodecyl (meth)acrylate, dodecyl (meth)acrylate, and stearyl (meth)acrylate; cyclic alkyl (meth)acrylates such as cyclohexyl (meth)acrylate, dicyclohexyl (meth)acrylate, and isobornyl (meth)acrylate; hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate. Polyalkylene glycol (meth)acrylates such as hydroxyl group-containing (meth)acrylate, 2-(2-methoxyethoxy)ethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, butoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxytripropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, polyalkylene glycol (meth)acrylate such as poly(ethylene glycol-tetramethylene glycol) (meth)acrylate, poly(propylene glycol-tetramethylene glycol) (meth)acrylate, polyethylene glycol-polypropylene glycol (meth)acrylate, aromatic group-containing (meth)acrylates such as benzyl (meth)acrylate, 9-anthryl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and N,Examples include amino group-containing (meth)acrylates such as N-diethylaminoethyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, and alkoxyethyl (meth)acrylates such as 2-cyclohexyloxyethyl (meth)acrylate, aryloxyethyl (meth)acrylates such as phenoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and 2-morpholinoethyl (meth)acrylate. Among these, linear or branched alkyl (meth)acrylates, polyalkylene glycol (meth)acrylates, and alkoxyethyl (meth)acrylates are preferred due to their ease of decomposition. More preferably, linear or branched alkyl (meth)acrylates with 1 to 4 carbon atoms in the alkyl group, polyalkylene glycol (meth)acrylates containing diethylene glycol units, and alkoxyethyl (meth)acrylates with 1 to 3 carbon atoms in the alkoxy group are preferred. Even more preferably, methyl (meth)acrylate, 2-(2-methoxyethoxy)ethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, 2-methoxyethyl (meth)acrylate, and 2-ethoxyethyl (meth)acrylate are preferred. (Meth)acrylates may be used alone, or two or more may be used in any ratio and combination.

[0016] In one embodiment, the (meth)acrylic polymer is a homopolymer or copolymer of (meth)acrylate. The (meth)acrylic polymer may also be a copolymer of (meth)acrylate and other monomers. The other monomers are not particularly limited, and specific examples include (meth)acrylamide, (meth)acrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, acrylonitrile, styrene, p-methylstyrene, α-methylstyrene, vinyl acetate, vinyl chloride, and rotaxane having one polymerizable unsaturated group. The other monomers may be used alone or two or more may be used in any ratio and combination.

[0017] The (meth)acrylamide used in the production of the poly(meth)acrylamide-based polymer is not particularly limited, and specific examples thereof include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-tert-butyl(meth)acrylamide, and N-benzyl acrylamide (meth)acrylamide and the like. The (meth)acrylamide may be used alone, or two or more thereof may be used in combination at an arbitrary ratio and combination.

[0018] The styrene-based monomer used in the production of the styrene-based polymer is not particularly limited, and specific examples thereof include styrene, vinyltoluene, 4-tert-butylstyrene, α-methylstyrene, 4-chlorostyrene, 4-methylstyrene, 4-chloromethylstyrene, divinylbenzene and the like. The styrene-based monomer may be used alone, or two or more thereof may be used in combination at an arbitrary ratio and combination.

[0019] Further, it is preferable that 80 mol% or more of the monomer constituting the polymer component that is a component of the polymer is at least one monomer selected from the group consisting of polyalkylene glycol (meth)acrylate, methacrylate containing an alkoxy group, acrylate containing an alkoxy group having 2 or more carbon atoms, (meth)acrylamide, and derivatives thereof.

[0020] The weight average molecular weight of the polymer component that is a component of the polymer particles is not limited, but the lower limit can usually be 10,000 or more, or 50,000 or more, or 80,000 or more, and the upper limit can usually be 5,000,000 or less, or 4,000,000 or less, or 3,000,000 or less. In this specification, the weight average molecular weight means the standard polystyrene conversion value measured by gel permeation chromatography (GPC).

[0021] The average particle size of the polymer particles used in this embodiment is not particularly limited, but is preferably 50 nm to 5 μm, more preferably 60 nm to 1500 nm, and still more preferably 70 nm to 1200 nm.

[0022] In this embodiment, the average particle size of polymer microparticles is the average value obtained by analyzing the particle width at which the particle height (maximum value - minimum value) of the polymer microparticles is halved using image analysis software, selecting 100 arbitrary polymer microparticles, and analyzing the particle width at which the particle height (maximum value - minimum value) of the polymer microparticles is halved from images obtained using a scanning electron microscope (SEM) or atomic force microscope (AFM).

[0023] The polymer microparticles used in this embodiment do not necessarily have a hierarchical structure, but may have a hierarchical structure such as a core-shell structure.

[0024] The morphology of the polymer microparticles used in this embodiment is not particularly limited, but they may be spherical, ellipsoidal, or rod-shaped. The polymer microparticles may also be hollow.

[0025] The glass transition temperature (Tg) of the polymer fine particles used in this embodiment is not particularly limited, but is preferably -50 to 150°C, and more preferably -50 to 25°C. When Tg is within this range, film formation is easier.

[0026] (Method for producing polymer microparticles from monomers) The method for producing polymer components from monomers that constitute the polymer microparticles is not particularly limited, and polymer microparticles capable of producing the polymer microparticle molded articles used in this embodiment can be produced as appropriate. In one embodiment, polymer microparticles can be produced by polymerizing the monomers constituting the polymer components that constitute the polymer microparticles into fine particles by a standard method and purifying them as necessary. In one specific embodiment, polymer microparticles can be produced as a polymer microparticle dispersion. Polymer microparticle dispersions will be described below.

[0027] The polymer microparticle dispersion comprises polymer microparticles and a dispersion medium. The polymer microparticles used here are the same as those described above.

[0028] Examples of dispersion media include solvents and air. When the dispersion media is a solvent, the polymer particulate dispersion is provided as a liquid dispersion. When the dispersion media is air, the polymer particulate dispersion is provided as a powder.

[0029] In one embodiment, the dispersion medium is an aqueous solvent. In this specification, an aqueous solvent means a solvent with a water content of more than 50% by volume. The water content in the dispersion medium may be 80% or more by volume, 90% or more by volume, 95% or more by volume, 99% or more by volume, or 100% by volume. The aqueous solvent may contain water and a water-miscible organic solvent. Examples of water-miscible organic solvents include methanol, ethanol, propanol, N,N-dimethylformamide (DMF), and acetone. The aqueous solvent is preferably water. As water, distilled water, deionized water, and pure water can be used.

[0030] In this embodiment, the polymer microparticle dispersion is provided as an aqueous solvent dispersion of polymer microparticles. The content of polymer microparticles in the aqueous solvent dispersion is preferably 1% to 50% by mass, and more preferably 3% to 40% by mass. Within this range, the dispersion stability of the polymer microparticles in the aqueous solvent dispersion is good.

[0031] A dispersion of polymer fine particles in an aqueous solvent may contain a functionalizing agent. The functionalizing agent is not particularly limited as long as it imparts a specific function to the molded article and is soluble or dispersible in an aqueous solvent. Specific examples include pigments, dyes, organic fillers, and inorganic fillers. The size of the dispersible functionalizing agent is usually between 1 nm and 1 mm. The functionalizing agent may be used alone or in combination of two or more types in any ratio and combination.

[0032] Examples of pigments include inorganic pigments and organic pigments.

[0033] Examples of inorganic fillers include silica filler and carbon black.

[0034] The content of the functionalizing agent in the aqueous solvent dispersion of polymer fine particles is preferably 0.01% to 20% by mass, and more preferably 0.01% to 5% by mass. Within this range, the dispersion stability of the functionalizing agent in the aqueous solvent is good.

[0035] The amount of functionalizing agent used is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of polymer fine particles. If the amount is 50 parts by mass or less, the moldability of the polymer fine particles is good.

[0036] The aqueous solvent dispersion of polymer microparticles may optionally contain additives such as fuses, softeners, and spacers. By using at least one selected from the group consisting of fuses, softeners, and spacers, the moldability of the polymer microparticles can be improved.

[0037] The aqueous solvent dispersion of polymer microparticles may contain unreacted monomers, polymers not incorporated into the polymer microparticles, and surfactants and polymerization initiators that are optionally used in the method for producing the polymer microparticle dispersion described later.

[0038] In one embodiment, the dispersion medium is air. In this embodiment, the polymer microparticle dispersion is provided as a powder of polymer microparticles.

[0039] (Method for producing polymer microparticle dispersions from monomers) The method for producing polymer microparticle dispersions is not particularly limited. For example, one method is to polymerize monomers in an aqueous solvent to obtain an aqueous solvent dispersion of polymer microparticles, and then perform a purification operation as necessary to obtain a polymer microparticle dispersion.

[0040] Polymerization methods include emulsion polymerization, soap-free emulsion polymerization, suspension polymerization, dispersion polymerization, microemulsion polymerization, miniemulsion polymerization, and microsuspension polymerization. From the viewpoint of easy size control of polymer fine particles, emulsion polymerization and soap-free emulsion polymerization are preferred. Here, soap-free emulsion polymerization is a method of emulsion polymerization carried out in a reaction solution that substantially does not contain emulsifiers such as surfactants, high molecular weight emulsifiers (nonionic, anionic, cationic), and reactive surfactants. In the present invention, substantially free of emulsifiers means that the emulsifier content in the polymerization reaction system is 0.1% by mass or less, preferably 0.01% by mass or less, more preferably 0.001% by mass or less, and may even be 0% by mass, and even more preferably 0% by mass.

[0041] When polymerizing monomers, at least one selected from the group consisting of surfactants, polymerization initiators, spacers, and inorganic salts may be used as needed.

[0042] The surfactant is not particularly limited, but examples include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants.

[0043] Examples of anionic surfactants include sodium oleate, sodium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium alkylsulfonate, sodium polyoxyethylene alkyl ether sulfate, and their equivalent potassium salts, calcium salts, alkylnaphthalene sulfonates, and alkyl phosphate esters.

[0044] Examples of cationic surfactants include alkylamine salts such as laurylamine acetate and stearylamine acetate, as well as quaternary ammonium salts such as lauryltrimethylammonium chloride.

[0045] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkylamines, and glycerin fatty acid esters.

[0046] Examples of amphoteric surfactants include lauryldimethylamine oxide.

[0047] The surfactant can be appropriately selected depending on the type of monomer used and the polymerization method. When producing (meth)acrylic polymers or poly(meth)acrylamide by emulsion polymerization, the surfactant is preferably an anionic surfactant, and more preferably sodium dodecylbenzenesulfonate.

[0048] Surfactants may be used alone, or two or more may be used in any ratio and combination.

[0049] The amount of surfactant used is preferably 0.0001 to 10 parts by mass, more preferably 0.001 to 8 parts by mass, and even more preferably 0.01 to 5 parts by mass, per 100 parts by mass of monomer. Within this range, the size of the resulting polymer fine particles is appropriate.

[0050] When using radical polymerizable monomers, it is preferable to use a polymerization initiator. While not particularly limited, examples of polymerization initiators include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; benzoyl peroxide; lauroyl peroxide; o-chlorobenzoyl peroxide; o-methoxybenzoyl peroxide; 3,5,5-trimethylhexanoyl peroxide; tert-butylperoxy-2-ethylhexanoate; di-tert-butyl peroxide; cumenehydroperoxide; and t-butyl peroxide. Examples include organic peroxides such as droperoxides, and azo compounds such as 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis(2-methylpropionamidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine], 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], and 4,4'-azobis(4-cyanovaleric acid). Among these, persulfates are preferred, and potassium persulfate is more preferred. Polymerization initiators may be used alone, or two or more may be used in any ratio and combination.

[0051] The amount of polymerization initiator used is preferably 0.05 to 15 parts by mass, and more preferably 0.5 to 12 parts by mass or more, per 100 parts by mass of monomer.

[0052] The spacer can be any compound having two or more functional groups that are reactive with monomers, and is different from the crosslinking agent used in the present invention described later (i.e., a crosslinking agent for forming a crosslinked structure on the surface of polymer microparticles). When using radical polymerizable monomers, examples of spacers include ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, nonanediol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,4-cyclohexanediol di(meth)acrylate, and dicyclopentenyloxyethyl(meth)acrylate. Among these, ethylene glycol di(meth)acrylate and 1,6-hexanediol di(meth)acrylate are preferred. Of these, 1,6-hexanediol di(meth)acrylate is preferred from the viewpoint of the physical and mechanical properties of the resulting crosslinked polymer structure. Rotaxanes having two or more polymerizable unsaturated groups can also be used as spacers. A rotaxane consists of a cyclic molecule, a linear molecule encapsulated in a skewer-like manner within the cyclic molecule, and bulky end groups to prevent the cyclic molecule from detaching from the linear molecule. At least one of the cyclic molecule and the linear molecule may have two or more polymerizable unsaturated groups, and preferably both the cyclic molecule and the linear molecule have polymerizable unsaturated groups. A rotaxane having two or more polymerizable unsaturated groups can be obtained, for example, by reacting a rotaxane with a compound having a functional group that is reactive to the functional group of the rotaxane and a polymerizable unsaturated group. For example, if the functional group of the rotaxane is a hydroxyl group, a compound having an isocyanato group and a polymerizable unsaturated group, such as 2-isocyanatoethyl(meth)acrylate, can be used. Examples of polymerizable unsaturated groups include vinyl groups and (meth)acrylic groups. As rotaxanes having hydroxyl groups, SH2400P and SH1300P (both from ASM Co., Ltd.) can be used.

[0053] Spacers may be used individually, or two or more types may be used in any ratio and combination.

[0054] The amount of spacer used is preferably 0.001 to 50 parts by mass, more preferably 0.001 to 25 parts by mass, per 100 parts by mass of monomer. Particularly preferably, it is 2 to 20 parts by mass. Alternatively, the amount of spacer used may be 0.001 to 50 moles, more preferably 0.001 to 25 moles, per 100 moles of monomer. Particularly preferably, it may be 2 to 20 moles. Spacers such as 1,6-hexanediol dimethacrylate (HDD) are useful for providing crosslinking or branching to the polymer structure. Spacer portions between acrylic end groups are often effective in determining the physical and mechanical properties of the resulting polymer structure.

[0055] Inorganic salts are used to adjust the separation (dispersion) stability of emulsions and polymer microparticles. Specific examples of inorganic salts include sodium chloride, sodium bromide, sodium iodide, sodium carbonate, sodium sulfate, sodium thiosulfate, sodium dihydrogen phosphate, sodium nitrate, sodium perchlorate, sodium thiocyanate, potassium chloride, potassium bromide, potassium iodide, potassium carbonate, potassium sulfate, potassium thiosulfate, potassium dihydrogen phosphate, potassium nitrate, potassium perchlorate, potassium thiocyanate, and magnesium sulfate. Inorganic salts may be used alone or in combination of two or more types in any ratio and combination.

[0056] The amount of inorganic salt used is preferably 0.0001 to 10 parts by mass, and more preferably 0.01 to 5 parts by mass, per 100 parts by mass of monomer. If the amount of inorganic salt used is 0.0001 parts by mass or more, the separation (dispersion) stability derived from the inorganic salt can be easily adjusted. If the amount of inorganic salt used is 10 parts by mass or less, the polymer fine particles do not aggregate, and the resulting polymer fine particles have an appropriate size.

[0057] The temperature and time of the polymerization reaction can be appropriately selected depending on the monomer used, the polymerization method, and the polymerization initiator. For example, when using at least one monomer selected from the group consisting of (meth)acrylate, (meth)acrylamide, and (meth)acrylamide derivatives, and performing emulsion polymerization or soap-free emulsion polymerization, the preferred range for the reaction temperature and time is 25 to 90°C and 5 to 36 hours, and a more preferred range is 60 to 80°C and 10 to 24 hours.

[0058] In embodiments where the dispersion medium is an aqueous solvent, a molded article may be produced by directly molding the aqueous solvent dispersion of polymer fine particles obtained by the polymerization reaction. However, from the viewpoint of improving the quality of the molded article, it is preferable to perform purification operations such as centrifugation, filtration, and dialysis, and, if necessary, redisperse the polymer fine particles in the aqueous solvent to obtain a polymer fine particle dispersion (aqueous solvent dispersion of polymer fine particles).

[0059] In embodiments where the dispersion medium is an aqueous solvent, optional components such as functionalizing agents and additives can be added to the aqueous solvent dispersion of polymer fine particles as needed.

[0060] In embodiments where the dispersion medium is air, the polymer microparticle dispersion obtained by the polymerization reaction can be purified by centrifugation and dialysis, etc., as needed, and then the solvent can be removed to obtain a polymer microparticle dispersion (polymer microparticle powder). The method for removing the solvent is not particularly limited, but freeze-drying is one example.

[0061] There are no particular limitations on the method for modifying the surface of the polymer fine particles with a molecule having a carboxyl group, a cyclocarbonate group, or an oxocyclopropyl group at its terminus, and it can be carried out by known methods. For example, one method is to copolymerize acrylic acid with an acrylic acid derivative containing a carboxyl group, a cyclocarbonate group, or an oxocyclopropyl group. Specific examples of acrylic acid derivatives containing a cyclocarbonate group include (2-oxo-1,3-dioxolan-4-yl)methyl methacrylic acid (DOMA). When producing copolymer polymer fine particles by soap-free emulsion polymerization, for example, the charging ratio (molar ratio) of the acrylic acid to the acrylic acid derivative is preferably 100:0.1 to 100:20, more preferably 100:1 to 100:10, and particularly preferably 100:2 to 100:10. Furthermore, the surface of copolymer polymer fine particles using an acrylic acid derivative containing a cyclocarbonate group is preferably cross-linked in the presence of a non-ketone solvent using a cross-linking agent that is a primary amine compound.

[0062] 《Crosslinking Agent》 Next, the crosslinking agent used in the present invention will be described. The crosslinking agent is capable of forming a crosslinked structure on the surface of the polymer fine particles and has a second functional group that can chemically bond with a first functional group present on the surface of the polymer fine particles. Preferably, the crosslinking agent is a reactive compound having a structure in which a conjugated system of carbon atoms of a condensed polycyclic aromatic ring group and a silicon atom are bonded in a manner that can be cleaved by the cooperative action of light irradiation and acid, and has one or more amino groups as functional groups that can bond with other compounds. Here, the amino group is a monovalent functional group (-NH) obtained by removing a hydrogen atom from ammonia, a primary amine, or a secondary amine. ２ The functional group is (-NHR, -NRR'), preferably containing one nitrogen atom and one or two hydrogen atoms. ２ A functional group (-NH) containing one nitrogen atom and two hydrogen atoms is preferable. ２) is preferable. Here, "irradiating with light" means, for example, irradiating with light that includes the absorption wavelength range of the structure in which the above-mentioned "bond cleavage" is possible. Furthermore, "cooperative action of light irradiation and acid" means, for example, that light irradiation and acid, each having different effects, work together, sharing roles and effects within the mechanism necessary to cleave the bond between the conjugated carbon atom and the silicon atom, thereby enabling the cleavage of the bond. "Cooperative action of light irradiation and acid" may be the cooperative action of light irradiation and an acid that is directly applied, or the cooperative action of light irradiation and an acid that is indirectly applied. In the case of "cooperative action of light irradiation and an acid that is indirectly applied," in order to indirectly apply the acid, it is possible to replace it with the superficial cooperative action of light irradiation and water that is directly applied by adding a method of pre-containing the acid in the polymer matrix. In the selectively biodegradable polymer microparticle molded article of this embodiment, for example, a first functional group on the surface of the polymer microparticles and a second functional group on the crosslinking agent form a chemical bond, and the polymer particles are crosslinked by the crosslinking agent via the chemical bond on the surface of the polymer microparticles. The portion derived from the crosslinking agent in the selectively biodegradable polymer microparticle molded article of this embodiment may also be referred to as the "crosslinked structure" or "crosslinked portion." Preferably, the chemical bond between the first functional group and the second functional group is a bond formed by a condensation reaction between condensation-reactive groups or an addition reaction by a ring-opening group. Examples of such chemical bonds include carbon-nitrogen bonds (where carbon may be carbon contained in a carbonyl group or carbon contained in a hydrocarbon group). Preferably, amide bonds (-NHC(=O)-) and urethane bonds (-NHC(=O)-O-) are used. More specifically, the combination of the first functional group and the second functional group is preferably a combination of an amino group and a functional group selected from the group consisting of a carboxyl group, a cyclocarbonate group, and an oxocyclopropyl group.When the chemical bond is formed by a dehydration condensation reaction between the first functional group, a carboxyl group, and the second functional group, an amino group, forming an amide bond (-CONH-), it is preferable that the dehydration condensation reaction be carried out in the presence of a condensing agent soluble in a solvent (i.e., a good solvent) capable of decomposing the polymer microparticle molded body into the polymer microparticles. As the condensing agent, for example, at least one compound selected from the group consisting of O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HATU), (N,N'-dicyclohexylcarbodiimide) (DCC), and 4-(4,6-dimethoxy-1,3,5-triazine-2-yl)-4-methylmorpholinium chloride (DMT-MM) can be used. The amount of condensing agent is preferably 1 to 10 equivalents, and more preferably 3 to 6 equivalents, relative to the functional group.

[0063] A structure in which a conjugated carbon atom and a silicon atom are bonded in a manner that allows for bond cleavage by the cooperative action of light irradiation and acid imparts selective degradability to the selectively degradable polymer microparticle molded article, such as degradability by the cooperative action of light irradiation and acid. The structure is, for example, a structure in which a conjugated carbon atom of a condensed polycyclic aromatic ring group and a silicon atom are bonded in a manner that allows for bond cleavage by the cooperative action of light irradiation and acid. Preferably, the structure is one in which a conjugated carbon atom of a condensed polycyclic aromatic ring group and a silicon atom directly form a covalent bond, and an electron-donating group such as an alkyl group or alkoxy group is bonded to the silicon atom.

[0064] The aforementioned crosslinked structure includes a structure (hereinafter sometimes referred to as a cleavable structure) in which the conjugated carbon atoms of a condensed polycyclic aromatic ring group and silicon atoms are bonded in a manner that allows for bond cleavage through the cooperative action of light irradiation and acid. In the selectively degradable polymer microparticle molded article, polymer microparticles are crosslinked with each other via the cleavable structure. By irradiating the cleavable structure with light in the presence of acid, the bond between the conjugated carbon atoms and silicon atoms is cleaved, enabling photoprocessing. That is, the bond between the conjugated carbon atoms and silicon atoms is cleaved through the cooperative action of light irradiation and acid, enabling photoprocessing. In the absence of acid, the bond between the conjugated carbon atoms and silicon atoms in the selectively degradable polymer microparticle molded article does not cleave even when irradiated with light, so it is stable under ambient light. One possible mechanism by which bond cleavage occurs is, for example, a reaction process in which a cleavable structure is irradiated with light in the presence of an acid, leading to the formation of a protonated aromatic ring, such as a Whileand intermediate, or a structure having the same function as such an intermediate.

[0065] A structure in which conjugated carbon atoms and silicon atoms are bonded in a manner that allows for bond cleavage through the cooperative action of light irradiation and acid is preferably represented by the following formula (1). In the following formula (1), X １ X is a substituted or unsubstituted divalent condensed polycyclic aromatic ring group, ２ R is a substituted or unsubstituted divalent condensed polycyclic aromatic ring group or single bond, Y is a single bond, an oxygen atom or an alkylene group, and R １ R is an alkyl group or alkoxy group, ２ is an alkyl group or alkoxy group, n is 0 or 1, m is an integer from 0 to 5, and * is a bond. However, if Y is a single bond, n is 0, and if Y is an oxygen atom and n is 0, m is 1. m may be 0 or 1.

[0066]

[0067] X １ X is a substituted or unsubstituted divalent condensed polycyclic aromatic ring group, ２This is a substituted or unsubstituted divalent fused polycyclic aromatic ring group or a single bond. １ and X ２ These may be the same or different. Here, a divalent fused polycyclic aromatic ring group is a group obtained by removing two hydrogen atoms from a fused polycyclic aromatic ring. A fused polycyclic aromatic ring is an aromatic ring formed when two or more monorings share (condense) one edge of each ring with each other. The rings constituting the fused polycyclic aromatic ring group may be only aromatic rings, or they may be heteroaromatic rings, or they may contain both aromatic rings and heteroaromatic rings. Preferably, they should be only aromatic rings.

[0068] More preferably, the structure is a structure represented by the following formula (2). In the following formula (2), X １ X is a substituted or unsubstituted divalent condensed polycyclic aromatic ring group, ２ R is a substituted or unsubstituted divalent condensed polycyclic aromatic ring group or single bond, Y is a single bond, an oxygen atom or an alkylene group, and R １ R is an alkyl group or alkoxy group, ２ m is an alkyl group or alkoxy group, n is 0 or 1, and m is an integer from 0 to 5. However, if Y is a single bond, n is 0, and if Y is an oxygen atom and n is 0, m is 1. m may be 0 or 1.

[0069]

[0070] Furthermore, in the structures represented by the above formulas (1) and (2), R １ and R ２ It is even more preferable that each of these groups is independently a methyl group or an ethyl group.

[0071] The number of rings in the fused polycyclic aromatic ring is two or more. More preferably, the number of rings is four or more. Preferably, the number of rings in the fused polycyclic aromatic ring is nine or less. More preferably, the number of rings in the fused polycyclic aromatic ring is six or less. The fused polycyclic aromatic ring group is preferably formed by the condensation of two to six aromatic rings, and particularly preferably by the condensation of four aromatic rings.

[0072] When the condensed polycyclic aromatic ring constituting the divalent condensed polycyclic aromatic ring group is a condensed polycyclic hydrocarbon, examples of condensed polycyclic hydrocarbons include pentalene, indene, naphthalene, azulene, heptalene, biphenylene, as-indacene, s-indacene, acenaphthylene, fluorene, phenalene, phenanthrene, anthracene, fluoranthen, acephenanthrene, aceanthrene, triphenylene, pyrene, chrysene, tetracene, pleiadene, picene, perylene, pentaphene, pentacene, tetraphenylene, and hexaphene. Pyrene is preferred as the condensed polycyclic hydrocarbon. In this case, the divalent condensed polycyclic aromatic ring group is a pyrenylene group. Specific examples of reactive compounds (crosslinking agents) when the divalent condensed polycyclic aromatic ring group is a pyrenylene group include the compound represented by the following formula (2).

[0073]

[0074] When the condensed polycyclic aromatic ring constituting the divalent condensed polycyclic aromatic ring group is a condensed heterocycle, examples of condensed heterocycles include indole, indoline, indazole, chromene, quinoline, isoquinoline, phthalazine, quinazoline, quinoxaline, carbazole, phenazine, phenanthidine, and phenoxazine.

[0075] The hydrogen atoms in the ring structure of a divalent condensed polycyclic aromatic ring group may be substituted. The substituents used to substitute the hydrogen atoms in the ring structure are not particularly limited, as long as they do not suppress photoreactions. Examples of substituents include alkyl groups, alkoxy groups, carboxyl groups, hydroxyl groups, cyano groups, and nitro groups. The number of substituents is not particularly limited, as long as they do not suppress photoreactions. For example, the number of substituents in a divalent condensed polycyclic aromatic ring group is 1 to 4.

[0076] R １ and R ２ R is an alkyl group or an alkoxy group. １ and R ２These may be the same or different. Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups, but linear lower alkyl groups are preferred. １ and R ２ If it is an alkyl group, it is preferably a methyl group or an ethyl group. Examples of alkoxy groups include methoxy group, ethoxy group, propoxy group, isopropoxy group, butoxy group, isobutoxy group, s-butoxy group, t-butoxy group, pentyloxy group, hexyloxy group, heptyloxy group, octyloxy group, nonyloxy group, decyloxy group, etc., but linear lower alkoxy groups are preferred. １ and R ２ If it is an alkoxy group, it is preferably a methoxy group or an ethoxy group. １ and R ２ By using a linear lower alkyl group such as a methyl group or an ethyl group, or a linear lower alkoxy group such as a methoxy group or an ethoxy group, the effects of steric hindrance can be reduced.

[0077] The ratio of the crosslinking agent to the polymer fine particles is determined by the first functional group that the polymer fine particles have on their surface (specifically, for example, a carboxyl group (-COOH), a cyclocarbonate group (-CH(*): *-O-C(=O)-O-CH) ２ -* (* indicates the binding site), oxocyclopropyl group (-CH(*): *-O-CH ２ - * (where * indicates the bonding site.))) The second functional group of the crosslinking agent (specifically, for example, an amino group (-NH ２ The numerical ratio of -NHR, -NRR') (i.e., the equivalent ratio of the second functional group to the first functional group) (specifically, for example, -NH ２ , -NHR or -NRR' / -COOH, -CH(*):*-OC(=O)-O-CH ２ -* (* indicates the bonding site) or -CH(*):*-O-CH ２-* (where * indicates a bonding site)) is preferably 0.01 to 10, and more preferably 0.1 to 1. When this equivalent ratio is within the above range, the selectively degradable polymer microparticle molded article not only exhibits excellent selective degradability, but also improves the strength of the molded article. The selectively degradable polymer microparticle molded article with improved strength thus is endowed with mechanical properties such as a larger Young's modulus (MPa), a smaller fracture strain (%), a larger fracture stress (MPa), and a longer relaxation time τ(s) compared to the case without the crosslinking structure. More specifically, for example, when the Young's modulus (MPa) is 10 MJm －３ In summary, the mechanical properties include a fracture strain (%) of 1400% or less, a fracture stress (MPa) of 1 or more, and a relaxation time τ(s) of 1500 or more.

[0078] The reactive compound used as a crosslinking agent can have its bonds cleaved by irradiation with light in the presence of an acid, making it possible to divide the selectively degradable polymer microparticle molded body by light irradiation. Furthermore, if there is no acid, no bond cleavage occurs even when irradiated with light, so the selectively degradable polymer microparticle molded body is stable under ambient light. In addition, since silicon is used in the cleavable structure of the reactive compound, it is inexpensive.

[0079] <Method for producing selectively degradable polymer microparticle molded articles> The method for producing selectively degradable polymer microparticle molded articles of this embodiment includes: a first step of forming a polymer microparticle molded article by removing a dispersion medium from a dispersion containing a plurality of polymer microparticles; and a second step of contacting the obtained polymer microparticle molded article with a reaction solution containing a crosslinking agent to chemically bond the first functional group present on the surface of the polymer microparticles with the second functional group of the crosslinking agent, thereby bonding the polymer microparticles to each other via a crosslinked structure derived from the crosslinking agent. The selectively degradable polymer microparticle molded article produced in this manner is stable even when in contact with a good solvent for the polymer components that constitute the polymer microparticles. Here, "stable" means that it does not decompose into the polymer microparticles.

[0080] In the first step described above, the dispersion medium can be removed from the dispersion by, for example, volatilizing the solvent used as the dispersion medium. The solvent can be volatilized by, for example, volatilizing it under atmospheric pressure or reduced pressure while heating as necessary.

[0081] For the dispersion containing the plurality of polymer microparticles, the polymer microparticle dispersion (aqueous solvent dispersion of polymer microparticles) described above can be used. The amount of crosslinking agent contained in the reaction solution is preferably selected so that the ratio of polymer microparticles to the crosslinking agent falls within the range described above. The aqueous solvent can be used as the solvent for the reaction solution.

[0082] If the polymer microparticle molded body is a thin film, it may be manufactured by the above manufacturing method which includes the following steps: The first step is to form a polymer microparticle molded body by applying or spraying a dispersion containing the plurality of polymer microparticles onto a substrate to form a coating film, and the second step is to immerse the obtained polymer microparticle molded body in a reaction solution containing the crosslinking agent, and then remove the polymer microparticle molded body from the reaction solution, thereby chemically bonding the first functional group present on the surface of the polymer microparticles with the second functional group of the crosslinking agent, and bonding the polymer microparticles to each other via the crosslinking agent.

[0083] In the second step, the solvent used in the reaction solution containing the crosslinking agent is preferably a good solvent for the polymer components that make up the polymer microparticles. More specifically, for example, when the chemical bond between the first functional group and the second functional group is formed by a condensation reaction between condensation-reactive groups or an addition reaction by a ring-opening group, it is preferable that the condensation reaction or addition reaction be carried out in the presence of a condensing agent (in the case of a condensation reaction) or a nucleophile (in the case of an addition reaction) that is soluble in a solvent (i.e., a good solvent) capable of decomposing the film into polymer microparticles. That is, it is preferable that the reaction solution further contains a condensing agent (in the case of a condensation reaction) or a nucleophile (in the case of an addition reaction). If the condensation reaction is a dehydration condensation reaction, at least one compound selected from the group consisting of O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HATU), (N,N'-dicyclohexylcarbodiimide) (DCC), and 4-(4,6-dimethoxy-1,3,5-triazine-2-yl)-4-methylmorpholinium chloride (DMT-MM) can be used as the condensing agent. The amount of the condensing agent is preferably 1 to 10 equivalents, and more preferably 3 to 6 equivalents, relative to the functional group. The amount of base in the reaction system is preferably 1 to 20 equivalents relative to the functional group. By increasing the amounts of the condensing agent and the base, the moldability of the resulting polymer fine particle molded article can be improved. In the first step described above, the amount of dispersion liquid applied or sprayed onto the substrate is preferably adjusted so that the final film thickness of the polymer microparticle molded body is, for example, 1 to 5 mm, more preferably 0.1 to 0.5 mm. The coating film is preferably dried at 4 to 70°C for about 12 to 48 hours.

[0084] In the second step described above, instead of the manufacturing method in which the coating film is immersed in the reaction solution (hereinafter sometimes referred to as the "immersion method"), a manufacturing method in which film formation (casting) and crosslinking between polymer microparticles proceed simultaneously (hereinafter sometimes referred to as the "simultaneous method") may also be adopted. In the simultaneous method, an aqueous solvent dispersion of polymer microparticles is converted into an organic solvent dispersion by solvent substitution, a crosslinking agent and a condensing agent are added to this, and a film is formed and dried to produce a selectively degradable polymer microparticle molded article. Incidentally, the immersion method is preferred in view of the fact that existing polymer microparticle molded articles can be used as is and by-products can be easily removed. The polymer microparticle molded article (e.g., coating film, film formation) obtained using such an immersion method or simultaneous method has a content of, for example, 1 to 1000 mg (solids: polymer microparticles) / cm ２ This is often the case, with a concentration of 10-600 mg / cm². ２ Preferably, 20 to 400 mg / cm³ ２ This is preferable.

[0085] <Method for Decomposing Selectively Degradable Polymer Microparticle Molded Article> The method for decomposing a selectively degradable polymer microparticle molded article according to this embodiment includes the step of decomposing the crosslinked structure of the polymer microparticle molded article by simultaneously applying external stimuli to the polymer microparticle molded article by light irradiation and acid.

[0086] "Acid Conditions" The type of acid is not particularly limited as long as the cleavable structure can be decomposed by irradiating it with light in the presence of an acid. Brønsted acids can be used as the acid. Specifically, examples of acids include hydrogen halides such as hydrogen chloride and hydrogen bromide, oxo acids such as sulfuric acid and nitric acid, and organic acids such as acetic acid and sulfonic acid.

[0087] The concentration of the acid is not particularly limited. The higher the acid concentration, the faster the decomposition reaction proceeds.

[0088] The method of introducing the acid is not particularly limited. The acid may be directly applied to the selectively degradable polymer microparticle molded body with light irradiation, or it may be applied indirectly to the selectively degradable polymer microparticle molded body with light irradiation. When applying the acid indirectly, it is preferable to apply the acid in an inert state beforehand. Here, an inert state means a state in which no synergistic effect occurs between the light irradiation and the acid even when light is irradiated. Methods of directly applying the acid include immersing the selectively degradable polymer microparticle molded body in an acid solution, or introducing gaseous acid into a container containing the selectively degradable polymer microparticle molded body. Methods of indirectly applying an inert acid include, for example, introducing the acid while the selectively degradable polymer microparticle molded body (gel) is swollen, and then drying the swollen selectively degradable polymer microparticle molded body after the acid has been incorporated into the selectively degradable polymer microparticle molded body. By drying the selectively degradable polymer microparticle molded body, the action of the acid within the selectively degradable polymer microparticle molded body is suppressed. This suppresses the synergistic effect between light irradiation and the acid.

[0089] "Light Irradiation Conditions" It is preferable that the wavelength of the irradiation light be within the absorption wavelength range of the cleavable structure. By irradiating with light in the absorption wavelength range, the bonds in the cleavable structure can be cleaved through the cooperative action of the light irradiation and the acid. The intensity of the light is not particularly limited. Note that the higher the light intensity, the faster the decomposition reaction will proceed.

[0090] "Reaction Time" The longer the reaction time, the more the decomposition reaction proceeds. The reaction time can be set appropriately according to the strength of the acid, the concentration of the acid, and the intensity of the light. The stronger the acid, the higher the acid concentration, and the higher the intensity of the irradiated light, the shorter the reaction time can be.

[0091] "Post-reaction treatment" The method for removing the acid after the decomposition reaction is not particularly limited. For example, the acid after the decomposition reaction may be removed by immersing the selectively decomposable polymer microparticle molded body in an acid-free solution, or by placing the selectively decomposable polymer microparticle molded body after the decomposition reaction under a reduced pressure environment.

[0092] In the decomposition method according to this embodiment, the selectively degradable polymer microparticle molded article can be photoprocessed because its bonds can be cleaved by irradiation with light in the presence of acid. Furthermore, if acid is absent, bond cleavage does not occur even when irradiated with light, so the selectively degradable polymer microparticle molded article is stable under ambient light. In addition, since silicon is used in the cleavable structure of the selectively degradable polymer microparticle molded article, it is inexpensive.

[0093] <Method for obtaining polymer microparticles constituting a selectively degradable polymer microparticle molded body> The method for obtaining polymer microparticles constituting a selectively degradable polymer microparticle molded body according to this embodiment includes: (1) a first A step in which the crosslinking structure of the polymer microparticle molded body is degraded by simultaneously applying external stimuli, namely light irradiation and acid, in the presence of a good solvent for the polymer components that constitute the polymer microparticles; or (2) a first B step in which, after degrading the crosslinking structure of the polymer microparticle molded body by simultaneously applying external stimuli, namely light irradiation and acid, the obtained polymer microparticle molded body is brought into contact with a good solvent for the polymer components that constitute the polymer microparticles; and a second step in which the polymer microparticles generated in the first A step or B step are recovered. The polymer microparticles recovered by the above acquisition method can be recycled and reused as raw materials for manufacturing a selectively degradable polymer microparticle molded body.

[0094] The selectively degradable polymer microparticle molded articles, their manufacturing methods, and decomposition methods according to the present invention have been described above. It should be noted that the technical scope of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. Furthermore, it is possible to replace the components in the embodiments with well-known components as appropriate, without departing from the spirit of the invention.

[0095] The effects of the present invention will be made clearer by the following examples. However, the present invention is not limited to the following examples and can be modified as appropriate without altering its essence.

[0096] First, let me explain the analysis and measurement methods. The various analyses and measurements were performed as follows.

[0097] <Size evaluation by SEM> The average particle size of polymer microparticles was determined by analyzing the particle width at which the particle height (maximum value - minimum value) of the polymer microparticles was halved using image analysis software, selecting 100 arbitrary polymer microparticles, and taking the average value of the results.

[0098] <Evaluation of Swelling Characteristics by DLS Measurement> The polymer microparticles obtained in the examples were immersed in water and ethyl acetate (EtOAc) at 25°C for 10 minutes, and then the mean hydrodynamic diameter (Dh) (nm) was evaluated by DLS measurement using a Zetasizer Nano S (Malvern Instruments). Sample preparation method: A 0.01 mass% aqueous dispersion of polymer microparticles was used. The data were averaged over 30 measurements with an acquisition time of 30 seconds using intensity autocorrelation. Scattering intensity was detected at a total scattering angle of 173°. The hydrodynamic diameter of the polymer microparticles in water was calculated using the Stokes-Einstein equation. Each sample was evaluated three times using the above procedure, and the average value of the obtained hydrodynamic diameters was determined as the mean hydrodynamic diameter.

[0099] <Measurement of Glass Transition Temperature by DSC> The glass transition temperature Tg was measured by the method described in JIS K7121:1987 and JIS K7121:2012. However, the sampling method and temperature conditions were as follows. Polymer fine particles obtained in the example were packed into the bottom of an aluminum measuring container at a density of 5.5 ± 0.5 mg, ensuring no gaps, and then an aluminum lid was placed over them. Differential scanning calorimetry was then performed using a Hitachi High-Tech Science Corporation "DSC7000X, AS-3" differential scanning calorimetry meter. Under a nitrogen gas flow rate of 20 mL / min, the sample was heated and cooled in the following steps 1 to 4 to obtain a DSC curve. (Step 1) Hold at 30°C for 2 minutes. (Step 2) Increase the temperature from 30°C to 300°C at a rate of 10°C / min (first heating process), and hold for 10 minutes. (Step 3) Quickly remove the sample and allow it to cool in an environment of 25 ± 10°C. (Step 4) The temperature was increased from 30°C to 300°C at a rate of 10°C / min (second heating process). Alumina was used as the reference material. Using the analysis software attached to the instrument, the temperatures at the top of the melting peak and crystallization peak observed during the second heating process were read and used as the melting point and crystallization temperature. The glass transition temperature Tg was calculated from the DSC curve observed during the second heating process using the analysis software attached to the instrument to determine the midpoint glass transition temperature. This midpoint glass transition temperature was determined from the standard (9.3). The glass transition temperature Tg used was the glass transition temperature Tg at a temperature lower than the crystallization peak observed during the second heating process in the heat flux differential scanning calorimetry chart (DSC curve) at a heating rate of 10°C / min. However, if no crystallization peak was observed during the second heating process, the glass transition temperature Tg within the temperature range of the second heating process (30 to 300°C) was used.

[0100] <Evaluation of Crosslinked Polymer Chain Amount> The gel content of the polymer microparticles obtained in the examples was determined using the following formula: Gel content (mass%) = Mass of gel component / Total mass of molded body × 100

[0101] <Mechanical evaluation in uniaxial elongation test> Test specimens were cut into dumbbell shapes from the selectively degradable polymer microparticle molded articles obtained in the examples, according to JIS: K6251-7 or ISO: 37-4. The dimensions of the dumbbell test specimens were a thickness of 0.1 to 0.3 mm, a total length of 35 mm, and an initial length of 12 mm and a width of 2 mm for the intermediate shaft portion. At a temperature of 25°C ± 0.5°C and a humidity of 50% Rh ± 0.5% Rh, the test specimens were pulled along their longitudinal direction on both sides at a tensile speed of 10 mm / min, and the strain (%) relative to the tensile stress was measured.

[0102] <Evaluation of interparticle crosslinking by stress relaxation test> Test specimens of selectively degradable polymer microparticle molded bodies cut under the above conditions were pulled along the longitudinal direction at a tensile speed of 100 mm / min on both sides until the strain reached 800%, and then the change in stress was measured while the strain remained constant.

[0103] <Evaluation of Multi-Stimulus Degradation of Selectively Degradable Polymer Microparticle Molded Products> A 20 mg fragment of the selectively degradable polymer microparticle molded product obtained in the example was immersed in a 1 M hydrogen chloride / ethyl acetate solution. While maintaining this state, the fragment was irradiated with ultraviolet light using a UV lamp at 25°C (365 nm, 1010 mW / cm²). ２ ).

[0104] [Production Example 1] Production of Polymer Microparticle Aqueous Dispersion Polymer microparticles were produced by soap-free emulsion polymerization such that the weight-average molecular weight of the polymer components was in the range of 10,000 to 5,000,000. The specific procedure is as follows: 98 mol% methyl acrylate, 1 mol% (2-oxo-1,3-dioxolan-4-yl)methyl methacrylic acid (DOMA), and 1 mol% 1,6-hexanediol dimethacrylate (HDD) were added to 600 mL of water. The total monomer concentration in the resulting mixture was 1000 mM. The resulting mixture was stirred at 70°C and 300 rpm for 30 minutes while bubbling nitrogen gas. After stirring, potassium persulfate (KPS) (2 mM) was added to the resulting mixture as a polymerization initiator, and the mixture was reacted under reflux of nitrogen gas for 1 hour. Subsequently, the supply of nitrogen gas was stopped, and the reaction was carried out for another 11 hours to obtain polymer fine particles in which the weight-average molecular weight of the polymer component was in the range of 10,000 to 5,000,000. The average particle size of the obtained polymer fine particles was evaluated using the method described above. SEM images are shown in Figure 1. As can be seen from Figure 1, the average primary particle size (D ＳＥＭ The particle size was 489 nm, and the coefficient of variation (CV), which indicates the monodispersity of the particles, was 6.7% (n=100). Furthermore, the swelling properties and glass transition temperature of the obtained polymer fine particles were evaluated using the method described above. The results are shown in Figures 2 and 3.

[0105] [Production Example 2] Production of the crosslinking agent The compound represented by the following formula (3) was synthesized based on the synthesis scheme shown in the following formula (4).

[0106]

[0107] Specifically, under a nitrogen atmosphere, 4,4'-((dimethylsilanediyl)bis(pyrene-6,1-diyl))diphenol (1.00 g, 1.55 mmol) and dried potassium carbonate (1.19 g, 7.75 mmol) were mixed with N,N-dimethylformamide (60 mL). To the resulting mixture, 2-(1,3-dioxoisoindolin-2-yl)ethyl 4-methylbenzenesulfonate (2.09 g, 6.20 mmol), which had been previously synthesized according to conventional methods in the art, was added at 70°C (incidentally, commercially available compounds may also be used). The resulting mixture was stirred in the dark at 75°C for 15 hours, and then the reaction solution was quenched by adding saturated brine at room temperature. (2,2'-(((((dimethylsilanediyl)bis(pyrene-6,1-diyl))bis(4,1-phenylene))bis(oxy))bis(ethane-2,1-diyl))bis(isoindoline-1,3-dione)) was extracted from the reaction solution with dichloromethane, and the dichloromethane solution of the extracted target product was washed with water. The resulting solution was dehydrated with magnesium sulfate, filtered, and the solvent was removed by distillation. Then, (2,2'-(((((dimethylsilanediyl)bis(pyrene-6,1-diyl))bis(4,1-phenylene))bis(oxy))bis(ethane-2,1-diyl))bis(isoindoline-1,3-dione)) was isolated from the obtained solid by preparative size exclusion chromatography to obtain a yellow solid (700 mg, yield 46%). Next, tetrahydrofuran (90 mL) and ethanol (60 mL) were added to 2,2'-(((((dimethylsilanediyl)bis(pyrene-6,1-diyl))bis(4,1-phenylene))bis(oxy))bis(ethane-2,1-diyl))bis(isoindoline-1,3-dione) (700 mg, 0.706 mmol), and then hydrazine monohydrate (14 mL) was added to the resulting solution.The obtained solution was stirred at 60°C for 6 hours under light shielding, and then the reaction solution was quenched by adding saturated brine at room temperature. The target product (2,2'-((((dimethylsilanediyl)bis(pyrene-6,1-diyl))bis(4,1-phenylene))bis(oxy))bis(ethan-1-amine)) was extracted from the reaction solution with dichloromethane, and the dichloromethane solution of the extracted target product was washed with saturated brine. The resulting solution was dehydrated with magnesium sulfate, filtered, and the solvent was removed by distillation. The target product was then washed with methanol (10 mL) from the obtained solid and filtered to obtain a pale yellow solid (460 mg, yield 89%). 　1 H NMR (500 MHz; DMSO-d6): δ 8.51 (d, J = 7.7 Hz, 2H), 8.37 (d, J = 7.8 Hz, 2H), 8.20-8.12 (m, 8H), 7.93 (m, 4H), 7.51 (d, J = 8.7 Hz, 4H), 7.16 (d, J = 8.7 Hz, 4H), 4.06 (s, 4H), 2.98 (s, 4H), 1.09 (s, 6H).

[0108] [Example 1] Production of selectively degradable polymer microparticle molded articles (Part 1) Selectively degradable polymer microparticle molded articles were produced using the polymer microparticles obtained in Production Example 1 and the crosslinking agent obtained in Production Example 2. The specific procedure is as follows: The aqueous dispersion of polymer microparticles obtained in Production Example 1 was placed in a silicone rubber mold (3.5 cm long, 3.5 cm wide, 1 mm deep) at a rate of 48 mg (solids: polymer microparticles) / cm². ２ After adding the polymer microparticle aqueous dispersion in this manner, the polymer microparticle film was obtained by drying the dispersion at 25°C for 24 hours in a low-temperature constant-temperature oven (LTI-2100, Tokyo Rikakikai Co., Ltd.).

[0109] The obtained polymer microparticle film was immersed in a solvent capable of dissolving the crosslinking agent (e.g., chloroform; chloroform is a good solvent for the polymer components that make up the polymer microparticle film). Then, the amount of crosslinking agent shown in Table 1 (when chloroform is used as the solvent) was added, and the mixture was left to stand at room temperature for 24 hours to allow the solvent to evaporate, thereby obtaining a molded article. The obtained selectively degradable polymer microparticle molded article was subjected to evaluation of the amount of polymer chains crosslinked by the above method, mechanical evaluation in a uniaxial elongation test, evaluation of interparticle crosslinking by a stress relaxation test, and evaluation of the multi-stimulus degradability of the microparticle molded article. The results are shown in Table 1 and Figures 4 to 6.

[0110]

[0111] [Example 2] Production of selectively degradable polymer microparticle molded articles (Part 2) Instead of the polymer microparticles obtained in Production Example 1 (where the chemical bond between the first and second functional groups is a urethane bond), polymer microparticles obtained by the following procedure (where the chemical bond between the first and second functional groups is an amide bond) were used, and a selectively degradable polymer microparticle molded article was produced using these and the crosslinking agent obtained in Production Example 2. The specific procedure is as follows. First, polymer microparticles were produced by soap-free emulsion polymerization so that the weight-average molecular weight of the polymer components was in the range of 10,000 to 5,000,000. The specific procedure is as follows. 98 mol% methyl acrylate, 0.1, 1 or 10 mol% acrylic acid (AAc), and 0 or 1 mol% 1,6-hexanediol dimethacrylate (HDD) were added to 600 mL of water. The total monomer concentration in the resulting mixture was 1000 mM. The obtained mixture was stirred at 70°C and 300 rpm for 30 minutes while bubbling nitrogen gas. After stirring, potassium persulfate (KPS) (2 mM) was added to the mixture as a polymerization initiator, and the mixture was reacted under reflux of nitrogen gas for 1 hour. After that, the supply of nitrogen gas was stopped, and the reaction was carried out for a further 11 hours to obtain polymer fine particles in which the weight-average molecular weight of the polymer components was in the range of 10,000 to 5,000,000. The average particle size of the obtained polymer fine particles was evaluated using the method described above. The average primary particle size and monodispersity of the particles were measured in addition to confirming the SEM image. When the charge ratio (mol%) relative to the total monomer of 100 mol%) was 98 mol% methyl acrylate, 1 mol% acrylic acid (AAc), and 1 mol% 1,6-hexanediol dimethacrylate (HDD), the average primary particle size (D ＳＥＭ The particle size was 578 nm, and the coefficient of variation (CV) indicating the monodispersity of the particles was 11% (n=100). The polymer microparticle aqueous dispersion obtained above was placed in a silicone rubber mold (3.5 cm long, 3.5 cm wide, 1 mm deep) at a rate of 294 mg (solids: polymer microparticles) / cm². ２After adding the polymer microparticle aqueous dispersion in such a manner, the polymer microparticle film was obtained by drying the dispersion at 25°C for 24 hours in a low-temperature constant-temperature oven (LTI-2100, Tokyo Rikakikai Co., Ltd.). The obtained polymer microparticle film was immersed in a solvent capable of dissolving the crosslinking agent, and then a predetermined amount of crosslinking agent (specifically, when DCC was used as the condensing agent: 0.0425 mol of -COOH contained in 24 mg of polymer microparticle film / 0.8 mg (0.001 mol) of crosslinking agent (1 / 20 of -NH relative to the amount of -COOH) was added. ２ (equivalent to the amount of) / Addition amount 0.9 mg (0.425 mol) of binder (-NH ２ (Equivalent to 2 equivalents for the amount); When HATU is used as a condensing agent: The ratio of the molar amounts of each component contained in a 294 mg polymer microparticle film is 100 mol of -COOH / 1 mol of crosslinking agent (1 / 100 of -NH relative to the amount of -COOH) ２ (equivalent to the amount of) / Molar amount of binder 1, 1.5 or 4.5 mol (-NH ２ A molded article was obtained by adding 1, 1.5, or 4.5 equivalents of (to the amount of ), allowing the solvent to evaporate while standing at room temperature. As a result, it was confirmed that inter-microparticle crosslinking was formed in the obtained selectively degradable polymer microparticle molded article. Furthermore, when the selectively degradable polymer microparticle molded article was evaluated for multi-stimulus degradation (25°C, 365 nm LED lamp, 4h irradiation, 0.5 M HCl-containing EtOAc), it was confirmed that degradation proceeded to the polymer microparticle unit level.

[0112] Table 1 shows the results of the evaluation of the amount of crosslinked polymer chains, indicating that the amount of crosslinked polymer chains increases as the amount of crosslinking agent increases. Table 1 and Figure 4 show the results of the mechanical evaluation in the uniaxial elongation test, indicating that the selectively degradable polymer microparticle molded body becomes stronger as the amount of crosslinking agent increases. Table 1 and Figures 5-6 show the evaluation results of interparticle crosslinking by stress relaxation tests, suggesting that the polymer chains are fixed by crosslinking and stress dissipation from the particle interface is suppressed. Figures 7-9 show the results of the multi-stimulus degradability evaluation of the selectively degradable polymer microparticle molded body. Figure 7 shows the change over time when both light irradiation and acid external stimuli are applied to the molded body of sample No. 3 (1.0 equivalent of crosslinking agent). It can be seen that only the parts of this molded body that came into contact with acid and were irradiated with light are selectively degraded. Figure 8 shows the results when a small piece of the molded body of sample No. 3 (1.0 equivalent of crosslinking agent) is subjected to external stimuli of acid only, external stimuli of light only, and external stimuli of both acid and light. It can be seen that the molded body decomposes only when both external stimuli, acid and light irradiation, are applied. Figure 9 shows the changes over time when both external stimuli, light irradiation and acid, are applied to molded bodies of Sample No. 2 (0.1 equivalent of crosslinking agent) and Sample No. 3 (1.0 equivalent of crosslinking agent). It can be seen that the decomposition rate changes depending on the amount of crosslinking agent used. It can be seen that increasing the amount of crosslinking agent gives resistance to the selective decomposition of selectively degradable polymer microparticle molded bodies. Figure 10 shows an SEM image of polymer microparticles before film formation and an SEM image of polymer microparticles obtained by decomposing the molded body of Sample No. 3 (1.0 equivalent of crosslinking agent) by applying both external stimuli, light irradiation and acid. It can be seen that the decomposition has progressed to the polymer microparticle level.

Claims

1. A selectively degradable polymer microparticle molded article comprising a plurality of polymer microparticles and a crosslinking structure that connects the plurality of polymer microparticles, wherein the polymer microparticles have a first functional group on their surface that can bond with a crosslinking agent for forming the crosslinking structure, the crosslinking agent has a second functional group that can chemically bond with the first functional group, and the crosslinking structure is formed by the chemical bonding of the first functional group and the second functional group.

2. The selectively degradable polymer microparticle molded article according to claim 1, wherein the selective degradability of the selectively degradable polymer microparticle molded article is degradability due to the cooperative action of light irradiation and acid.

3. The selectively degradable polymer microparticle molded article according to claim 1, wherein the crosslinked structure is bonded in a manner that allows for bond cleavage by the cooperative action of light irradiation and acid.

4. The selectively degradable polymer microparticle molded article according to claim 1, wherein the crosslinked structure has a structure in which conjugated carbon atoms of a condensed polycyclic aromatic ring group and silicon atoms are bonded in a manner that allows for bond cleavage by the cooperative action of light irradiation and acid.

5. The selectively degradable polymer microparticle molded article according to claim 1, wherein the chemical bond between the first functional group having on the surface of the polymer microparticles and the second functional group having on the crosslinking agent is a bond formed by a condensation reaction between condensation-reactive groups or an addition reaction by a ring-opening group.

6. The selectively degradable polymer microparticle molded article according to claim 5, wherein the bond formed is a carbon-nitrogen bond.

7. The selectively degradable polymer microparticle molded article according to claim 5, wherein the bond formed is an amide bond.

8. The selectively degradable polymer microparticle molded article according to claim 5, wherein the bond formed is a urethane bond.

9. The selectively degradable polymer microparticle molded article according to claim 1, wherein the combination of the first functional group having on the surface of the polymer microparticles and the second functional group having in the crosslinking agent is a combination of an amino group and a carboxyl group.

10. The selectively degradable polymer microparticle molded article according to claim 1, wherein the combination of a first functional group having on the surface of the polymer microparticles and a second functional group having on the crosslinking agent is a combination of an amino group and a functional group selected from the group consisting of a cyclocarbonate group and an oxocyclopropyl group.

11. The selectively degradable polymer microparticle molded article according to claim 1, wherein the crosslinking agent is a reactive compound having a structure in which a conjugated system of carbon atoms of a condensed polycyclic aromatic ring group and a silicon atom are bonded in a manner that allows for bond cleavage by the cooperative action of light irradiation and acid, and having one or more amino groups as a second functional group.

12. The selectively degradable polymer microparticle molded article according to claim 1, wherein the polymer component that constitutes the polymer microparticles is a polymer that, in the presence of a poor solvent, can form aggregates in which the plurality of polymer microparticles are bound together by the entanglement of polymer chains present on the surfaces of adjacent polymer microparticles, and in the presence of a good solvent, the good solvent can enter between the entangled polymer chains, causing the polymer chains to unravel and the aggregates to decompose into polymer microparticles.

13. The selectively degradable polymer microparticle molded article according to claim 1, wherein the polymer component that constitutes the polymer microparticle is stable even when in contact with a good solvent.

14. The selectively degradable polymer microparticle molded article according to claim 1, wherein the polymer component that constitutes the polymer microparticles is an acrylic polymer or a styrene polymer.

15. The selectively degradable polymer fine particle molded article according to claim 14, wherein the acrylic polymer is a (meth)acrylate polymer or a poly(meth)acrylamide polymer.

16. The selectively degradable polymer microparticle molded article according to claim 1, wherein 80 mol% or more of the monomers constituting the polymer components that make up the polymer microparticles are at least one monomer selected from the group consisting of polyalkylene glycol (meth)acrylate, alkoxy group-containing methacrylate, alkoxy group-containing acrylate having 2 or more carbon atoms, (meth)acrylamide, and derivatives thereof.

17. The selectively degradable polymer microparticle molded article according to claim 3, wherein the light irradiation is light that includes the absorption wavelength region of the structure formed by bonding in a bond-cleavable manner.

18. The selectively degradable polymer microparticle molded article according to claim 3, wherein the structure formed by bonding in a bond-cleavable manner is represented by the following formula (1). (In formula (1), X １ X is a substituted or unsubstituted monovalent or divalent condensed polycyclic aromatic ring group, ２ R is a substituted or unsubstituted divalent condensed polycyclic aromatic ring group or single bond, Y is a single bond, an oxygen atom or an alkylene group, and R １ R is an alkyl group or alkoxy group, ２ (where n is an alkyl or alkoxy group, n is 0 or 1, m is an integer from 0 to 5, and * is a bond. However, if Y is a single bond, n is 0, and if Y is an oxygen atom and n is 0, m is 1.) 19. The selectively degradable polymer microparticle molded article according to claim 3, wherein the structure formed by bonding in a bond-cleavable manner is represented by the following formula (2). (In formula (1), X １ X is a substituted or unsubstituted monovalent or divalent condensed polycyclic aromatic ring group, ２ R is a substituted or unsubstituted divalent condensed polycyclic aromatic ring group or single bond, Y is a single bond, an oxygen atom or an alkylene group, and R １ R is an alkyl group or alkoxy group, ２ (where n is an alkyl group or alkoxy group, n is 0 or 1, and m is an integer from 0 to 5, except that n is 0 when Y is a single bond, and m is 1 when Y is an oxygen atom and n is 0.) 20. Said X １ and said X ２ The selectively degradable polymer microparticle molded body according to claim 18 or 19, wherein the condensed polycyclic aromatic ring group as is formed by condensation of 2 to 6 aromatic rings.

21. The selectively degradable polymer microparticle molded article according to claim 18 or 19, wherein m is 0.

22. The selectively degradable polymer microparticle molded article according to claim 18 or 19, wherein m is 1.

23. The aforementioned R １ and R ２ The selectively degradable polymer microparticle molded article according to claim 18 or 19, wherein each is independently a methyl group or an ethyl group.

24. The aforementioned X ２ The selectively degradable polymer microparticle molded article according to claim 18 or 19, wherein the condensed polycyclic aromatic ring group is a substituted or unsubstituted pyrenylene group.

25. A method for producing a selectively degradable polymer microparticle molded article according to claim 1, comprising: a first step of forming a polymer microparticle molded article by removing a dispersion medium from a dispersion containing a plurality of polymer microparticles; and a second step of contacting the obtained polymer microparticle molded article with a reaction solution containing the crosslinking agent to chemically bond the first functional group present on the surface of the polymer microparticles with the second functional group of the crosslinking agent, thereby bonding the polymer microparticles together via a crosslinked structure derived from the crosslinking agent.

26. The manufacturing method according to claim 25, wherein in the second step, the solvent used in the reaction solution containing the crosslinking agent is a good solvent for the polymer components that constitute the polymer fine particles.

27. The manufacturing method according to claim 25, wherein the first step is to form a polymer microparticle molded body by applying a dispersion containing the plurality of polymer microparticles onto a substrate to form a coating film, and the second step is to immerse the obtained polymer microparticle molded body in a reaction solution containing the crosslinking agent, and then remove the polymer microparticle molded body from the reaction solution, thereby chemically bonding the first functional group present on the surface of the polymer microparticles with the second functional group of the crosslinking agent, and bonding the polymer microparticles to each other via the crosslinking agent.

28. A method for decomposing a selectively degradable polymer microparticle molded article according to claim 1, comprising the step of decomposing the crosslinking structure of the polymer microparticle molded article by simultaneously applying external stimuli to the polymer microparticle molded article by light irradiation and an acid.

29. A method for obtaining polymer microparticles constituting a selectively degradable polymer microparticle molded body according to claim 1, comprising: (1) a first A step of decomposing the crosslinking structure of the polymer microparticle molded body by simultaneously applying external stimuli of both light irradiation and acid in the presence of a good solvent for the polymer components that constitute the polymer microparticles; or (2) a first B step of contacting the obtained polymer microparticle molded body with a good solvent for the polymer components that constitute the polymer microparticles after decomposing the crosslinking structure of the polymer microparticle molded body by simultaneously applying external stimuli of both light irradiation and acid; and a second step of recovering the polymer microparticles generated in the first A step or the B step.

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