Thixotropy imparting agent and liquid composition

Abstract

To provide a thixotropy imparting agent in place of fibrous cellulose or the like without requiring a processing step for application in organic solvents and a liquid composition comprising the thixotropy imparting agent.SOLUTION: There is provided a thixotropy imparting agent which contains polymer nanofibers 10 having a core-shell form having a hydrophobic core 20 and a hydrophilic shell 30, in which the hydrophobic core 20 of the polymer nanofibers 10 is crosslinked. There are provided polymer nanofibers 10 which may be formed by self-assembly of amphiphilic block copolymers having a hydrophobic block and a hydrophilic block.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thixotropic agent and a liquid composition. [Background technology]

[0002] Patent Document 1 discloses that thixotropy (thixotropy) is imparted by dispersing fibrous cellulose in an organic solvent. Patent Document 2 discloses that cellulose nanofibers are dispersed in an organic solvent by using additives such as plasticizers and resins such as epoxy resins. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-63104 [Patent Document 2] Japanese Patent Application Publication No. 2018-70851 Summary of the Invention [Problem to be solved by the invention]

[0004] However, although fibrous cellulose and the like are hydrophilic polymers and therefore easily dispersible in aqueous media, they are difficult to disperse in organic solvents due to their nature. Therefore, in order to apply a thixotropy-imparting agent containing fibrous cellulose and the like to an organic solvent, a treatment process such as surface modification of cellulose or the use of additives is required, as disclosed in Patent Documents 1 and 2, respectively.

[0005] The present invention provides a thixotropic agent that can replace fibrous cellulose and the like, which does not require a treatment process for application to an organic solvent, and a liquid composition containing the thixotropic agent. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A polymer nanofiber having a core-shell morphology with a lyophilic core and a lyophilic shell, A thixotropic agent crosslinking the lyophobic core of the polymer nanofiber. [2] The thixotropic agent according to [1], wherein the polymer nanofibers are formed by self-assembly of an amphiphilic block copolymer having a lyophobic block and a lyophilic block. [3] The thixotropic agent according to [2], wherein the solvophobic block has at least one selected from the group consisting of units based on benzyl (meth)acrylate, units based on styrene, and units based on n-butyl (meth)acrylate. [4] The thixotropic agent according to [2] or [3], wherein the philic block has at least one selected from the group consisting of units based on poly(ethylene glycol) methyl ether acrylate, units based on poly(ethylene glycol) methyl ether methacrylate, units based on (meth)acrylic acid, and units based on methyl (meth)acrylate. [5] A liquid composition comprising the thixotropy-imparting agent according to any one of [1] to [4] and an organic solvent. [6] At a temperature of 25°C, a shear rate of 100 s -1 Viscosity η1 at shear rate 10 s -1 The liquid composition according to [5], wherein the thixotropy index (TI), which is the ratio η2 / η1 of the viscosities η2 at 1000 rpm and η1 at 1000 rpm, is greater than 1. [Effects of the Invention]

[0007] According to the present invention, there are provided a thixotropic agent which does not require a treatment process for application to an organic solvent and which can be used as an alternative to fibrous cellulose, and a liquid composition containing the thixotropic agent. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an example of a polymer nanofiber. [Figure 2]FIG. 2 is a schematic diagram showing an example of an amphiphilic block copolymer that forms polymer nanofibers by self-assembly. DETAILED DESCRIPTION OF THE INVENTION

[0009] The meanings of the terms are as follows: "(Meth)acrylic" is a general term for acrylic and methacrylic. "Lyophobic" means that the affinity for a solvent is relatively low and that the molecules tend to aggregate with each other. "Medophilic" means that the affinity for the solvent is relatively high and that the substance is easily compatible with the solvent. The symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. The numerical ranges disclosed in this specification can be combined in any manner to form new numerical ranges.

[0010] Hereinafter, several embodiments of the present invention will be described with reference to the drawings. However, the following description is of typical examples, and the present invention is not limited to the following description. The dimensional ratios of each drawing are for the convenience of explanation and may differ from the actual ones.

[0011] [Thixotropic agent] One aspect of the present invention relates to a thixotropic agent, which contains polymer nanofibers. The polymer nanofibers have a core-shell morphology with a lyophobic core and a lyophilic shell, and the lyophobic core of the polymer nanofibers is crosslinked.

[0012] For example, the polymer nanofiber 10 shown schematically in Figure 1 has a core-shell morphology with a lyophobic core 20 and a lyophilic shell 30. Figure 1 shows a core-shell morphology in which multiple lyophilic shells 30 are attached to the surface of the fibrous lyophobic core 20 in a corona-like configuration.

[0013] The polymer nanofiber 10 shown in Fig. 1 may be formed, for example, by the self-assembly of multiple amphiphilic block copolymers 1 having a lyophobic block 2 and a lyophilic block 3 as shown in Fig. 2. This self-assembly is sometimes called PISA (Polymerization-induced self-assembly).

[0014] The solubility-containing block 2 may have units based on only one type of monomer, or may have units based on multiple types of monomers. The solubility-containing block 3 may also have units based on only one type of monomer, or may have units based on multiple types of monomers. That is, the solubility-containing block 2 and the solubility-containing block 3 may each be a homopolymer or a copolymer. Typically, the polymer compositions of the solubility-containing block 2 and the solubility-containing block 3 are different from each other, but this is not particularly limited.

[0015] The constituent monomers of the lyophobic block 2 and the lyophilic block 3 can be appropriately selected from various monomers by those skilled in the art so as to exhibit the desired lyophobicity and lyophilicity, respectively. Suitable monomers for forming the polymer nanofiber 10 include, for example, monomers represented by the following formula (1).

[0016] [ka]

[0017] In formula (1), H is a hydrogen atom. In formula (1), U and W each independently represent -COOH, -COOR 1 , -COR 1 , -CSR 1 , -CSOR 1 , -COSR 1 , -CONH2, -CONHR 1 , -CONR 12. At least one selected from the group consisting of a hydrogen atom, a halogen atom, and an alkyl group having 1 to 4 carbon atoms which may have a substituent, or U and W bond to each other to form a cyclic ester which may have a substituent, an acid anhydride group which may have a substituent, or an imide ring which may have a substituent.

[0018] The substituents referred to here are hydrogen atoms, -COOH, -COOR 1 , -COR 1 , -CSR 1 , -CSOR 1 , -COSR 1 , -CN, -CONH2, -CONHR 1 , -CONR 1 2, -OR 1 , -SR 1 , -OOCR 1 , -SCOR 1 , and OCSR 1 At least one selected from the group consisting of:

[0019] In formula (1), V is a hydrogen atom, R 1 , -COOH, -COOR 1 , -COR 1 , -CSR 1 , -CSOR 1 , COSR 1 , -CONH2, -CONHR 1 , -CONR 1 2, -OR 1 , -SR 1 , -OOCR 1 , -SCOR 1 , and -OCSR 1 At least one selected from the group consisting of:

[0020] R 1are each independently at least one selected from the group consisting of an optionally substituted alkyl group, an optionally substituted alkenyl group, an optionally substituted alkynyl group, an optionally substituted aryl group, an optionally substituted heteroaryl group, an optionally substituted carbocyclyl group, an optionally substituted heterocyclyl group, an optionally substituted arylalkyl group, an optionally substituted heteroarylalkyl group, an optionally substituted alkylaryl group, an optionally substituted alkylheteroaryl group, and an optionally substituted polymer chain.

[0021] R 1 Examples of the optional substituent include, but are not limited to, an epoxy group, a hydroxy group, an alkoxy group, an acyl group, an alkylcarbonyl group, a carboxy group, a sulfonic acid group, an isocyanate group, a cyano group, a silyl group, an amino group, salts thereof, and derivatives thereof.

[0022] R 1 Examples of the polymer chain include, but are not limited to, polyalkylene oxide, polyarylene ether, and polyalkylene ether.

[0023] Examples of constituent monomers of the solubility block 2 and the solubility block 3 include maleic anhydride, N-alkylmaleimide, N-allylmaleimide, dialkyl fumarate, (meth)acrylic acid ester, (meth)acrylic styrene, (meth)acrylamide, (meth)acrylonitrile, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, (meth)acrylic acid, (meth)acrylic acid, ) Benzyl acrylate, (meth) phenyl acrylate, α-methylstyrene, glycidyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, N,N-dimethylaminoethyl (meth) acrylate, N,N-diethylaminoethyl (meth) acrylate, triethylene glycol (meth) acrylate, itaconic anhydride, itaconic acid, glycidyl (meth) acrylate, N-methyl (meth) acrylamide, N,N-dimethyl(meth)acrylamide, N-tert-butyl(meth)acrylamide, N-methylol(meth)acrylamide, N-ethylol(meth)acrylamide, vinylbenzoic acid, diethylaminostyrene, α-methylvinylbenzoic acid, diethylamino α-methylstyrene, p-vinylbenzenesulfonic acid, p-vinylbenzenesulfonic acid sodium salt, trimethoxysilylpropyl(meth)acrylate, triethoxysilylpropyl(meth)acrylate, tributoxysilylpropyl(meth)acrylate, dimethoxymethylsilylpropyl(meth)acrylate, dibutoxymethylsilylpropyl(meth)acrylate ) acrylate, dibutoxymethylsilylpropyl (meth)acrylate, dimethoxysilylpropyl (meth)acrylate, diethoxysilylpropyl (meth)acrylate, dibutoxysilylpropyl (meth)acrylate, diisopropoxysilylpropyl (meth)acrylate, diisopropoxymethylsilylpropyl (meth)acrylate, vinyl acetate, vinyl butyrate, vinyl benzoate, vinyl chloride, vinyl fluoride, vinyl bromide, maleic anhydride, N-phenylmaleimide, N-butylmaleimide, N-vinylpyrrolidone, N-vinylcarbazole, butadiene, ethylene, chloroprene, and styrene are examples. However, the monomers are not limited to these examples.

[0024] In one example, the constituent monomers of the solvophobic block are selected so that the solvophobic core has at least one selected from the group consisting of units based on styrene, units based on n-butyl (meth)acrylate, units based on methyl (meth)acrylate, and units based on benzyl (meth)acrylate.

[0025] In a preferred example, the amphiphilic block of the amphiphilic block copolymer can be prepared from at least one monomer selected from the group consisting of poly(ethylene glycol) methyl ether acrylate (PEGA), poly(ethylene glycol) methyl ether methacrylate (PEGMA), (meth)acrylic acid, and methyl (meth)acrylate. In this case, the amphiphilic block has at least one monomer selected from the group consisting of PEGA-based units, PEGMA-based units, (meth)acrylic acid-based units, and methyl (meth)acrylate-based units.

[0026] In a preferred example, the lyophobic block of the amphiphilic block copolymer can be prepared from at least one monomer selected from the group consisting of benzyl (meth)acrylate, styrene, and n-butyl (meth)acrylate. In this case, the lyophobic block has at least one monomer selected from the group consisting of units based on benzyl (meth)acrylate, units based on styrene, and units based on n-butyl (meth)acrylate.

[0027] The lyophobic core of the polymer nanofiber is crosslinked. By crosslinking the lyophobic core of two or more amphiphilic block copolymers with a crosslinking agent, the polymer nanofiber can be prevented from dissolving in various solvents and can be made thixotropic.

[0028] The lyophobic core may be crosslinked using a crosslinking agent after the synthesis of the polymer nanofiber, but depending on the composition, it is also possible to use a crosslinking agent as a constituent monomer during polymerization of the lyophobic block to form the lyophobic core.

[0029] The crosslinking agent is not particularly limited, and various crosslinking agents can be used. The crosslinking agent can be selected depending on the constituent monomer of the lyophobic core. For example, when the constituent monomer contains (meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol dimethacrylate, etc. can be used as the crosslinking agent.

[0030] Other examples of crosslinking agents include diethylene glycol diacrylate, dipropylene glycol diacrylate, 1,4-butanediol diacrylate, tetraethylene glycol diacrylate, 3-methyl-1,5-pentanediol diacrylate, tripropylene glycol diacrylate, tricyclodecane dimethanol diacrylate, tricyclodecane dimethanol diacrylate, trimethylolpropane triacrylate, and pentaerythritol (tri / tetra)acrylate. Details of the crosslinking agent are described in paragraphs

[0105] to

[0111] of WO 2023 / 102600, the contents of which are incorporated herein by reference.

[0031] The conditions for RAFT polymerization of amphiphilic block copolymers to form polymer nanofibers can be appropriately selected by those skilled in the art depending on the polymerization initiator, the type and amount of monomer used, and the polymerization medium. Details of the RAFT polymerization conditions are described in paragraphs

[0080] to

[0091] of WO 2023 / 102600, the contents of which are incorporated herein by reference.

[0032] The number-average molecular weight of the amphiphilic block copolymer is not particularly limited, but may be, for example, within the range of 5,000 to 100,000. The number-average molecular weight of the amphiphilic block copolymer is a value calculated by converting the value measured by gel permeation chromatography (GPC) into that of standard polystyrene.

[0033] The glass transition temperature of the lyophobic core can be adjusted by the monomer composition of the lyophobic block. The glass transition temperature of the lyophobic core is appropriately selected depending on the application of the thixotropy-imparting agent and is not particularly limited, but can be, for example, within the range of -70°C to 110°C. The glass transition temperature of the lyophobic core of a polymer nanofiber is measured as the glass transition temperature of the lyophobic block of the amphiphilic block copolymer that forms the polymer nanofiber. The glass transition temperature is a value calculated using the relational expression for the glass transition temperature Tg (°C) of the copolymer according to the Fox equation below.

[0034] 1 / (273+Tg)=Σ{W i / (273+Tg i )} W i : mass fraction of monomer i Tg i : Tg (℃) of the homopolymer of monomer i Here, the glass transition temperature of the homopolymer is a value using the numerical values ​​described in "Polymer Handbook, 4th Edition, John Wiley & Sons."

[0035] The fiber length of the polymer nanofiber is not particularly limited, but can be, for example, within the range of 5 nm to 2 mm. The fiber width of the polymer nanofiber is not particularly limited, but can be, for example, within the range of 1 nm to 250 nm. The ratio of fiber length to fiber width of the polymer nanofiber is not particularly limited, but can be, for example, within the range of 5 / 1 to 200,000 / 1. The fiber length and fiber width of the polymer nanofibers are values ​​determined by images observed with a transmission electron microscope (TEM).

[0036] The amphiphilic block copolymers that form polymer nanofibers via PISA can be synthesized by RAFT polymerization. RAFT stands for Reversible Addition-Fragmentation Chain Transfer, a type of living radical polymerization. RAFT-mediated PISA facilitates the formation of polymer nanofibers from amphiphilic block copolymers.

[0037] RAFT polymerization can be applied to most monomers that undergo radical polymerization by appropriately selecting a chain transfer agent (RAFT agent) depending on the monomer and reaction conditions. For example, when preparing amphiphilic block copolymers in the presence of a chain transfer agent, the terminals of the growing blocks are endowed with specific functionality that controls the block growth through reversible deactivation radical polymerization (RDRP). The functionalities of the block terminals here refer to the property that allows the formation of covalent bonds between ethylenically unsaturated monomers by reactivating the growing block in the second or third stage of the polymerization process.

[0038] The amphiphilic block copolymer forming the polymer nanofiber is preferably a polymer synthesized by RAFT polymerization. Details of RAFT polymerization are described in, for example, Polymer, 2008, volume 49, 1079-1131; Chemical Society Reviews, 2014, volume 43, 496-505; Macromolecules, 1998, volume 31, 5559-5562; and Polymer, 2013, volume 54, 2011-2019, the contents of which are incorporated herein by reference.

[0039] In the RAFT polymerization of the amphiphilic block copolymer, a radical initiator may be used, selected to ensure an adequate half-life at the polymerization temperature sufficient to initiate the polymerization reaction.

[0040] Examples of the radical initiator include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-cyanobutane), 2,2'-azobis(isobutyric acid) dimethyl, 4,4'-azobis(4-cyanovaleric acid), 4,4'-azobis-(4-cyanopentanoic acid), 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 1,1'-azobis(cyclohexanecarbonitrile), 2-(t-butylazo)-2-cyanopropane, 2,2'- Azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl))propionamide], 2,2'-azobis(N,N'-dimethyleneisobutylamidine) dihydrochloride, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis{2-methyl-N-[1,1-bis (hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-ethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2'-azobis(isobutylamide) dihydrate, 2,2'-azobis(2,2,4-trimethylpentane), 2,2'-azobis(2-methylpropane), t-butylperoxyacetic acid, t- Examples of the radical initiator include butylperoxybenzoic acid, t-butylperoxyneodecanoic acid, t-butylperoxyisobutyric acid, t-amylperoxypivalic acid, t-butylperoxypivalate, diisopropylperoxydicarbonate, dicyclohexylperoxydicarbonate, dicumyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, potassium peroxydisulfate, ammonium peroxydisulfate, di-t-butyl hyponitrite, and dicumyl hyponitrite. However, the radical initiator is not limited to these examples.

[0041] In the RAFT polymerization of the amphiphilic block copolymer, a chain transfer agent may be used. Details of the chain transfer agent are described in paragraphs

[0046] to

[0057] of WO 2023 / 102600, the contents of which are incorporated herein by reference.

[0042] (Action and effect) The thixotropy-imparting agent described above contains polymer nanofibers having a core-shell structure with a lyophobic core and a lyophilic shell, and the lyophobic core of the polymer nanofiber is crosslinked. Polymer nanofibers with such characteristics can be easily dispersed in organic solvents. In addition, they can impart thixotropy to organic solvents, as shown in the examples described below.

[0043] [Application example] (Liquid composition) The liquid composition contains the above-mentioned thixotropy-imparting agent and an organic solvent. The liquid composition may further contain other components in addition to the thixotropy-imparting agent and the organic solvent.

[0044] The organic solvent is not particularly limited, but examples thereof include γ-butyrolactone, acetone, methyl ethyl ketone, hexane, heptane, octane, 2-heptanone, cycloheptanone, cyclohexanone, cyclohexane, methylcyclohexane, ethylcyclohexane, methyl-n-pentyl ketone, methyl isobutyl ketone, methyl isopentyl ketone, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, ethylene glycol monoacetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoacetate, diethylene glycol diethyl ether, propylene glycol monoacetate, dipropylene glycol monoacetate, propylene glycol diacetate, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate. , propylene glycol monoethyl ether acetate, cyclohexyl acetate, ethyl 3-ethoxypropionate, dioxane, methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethyl ethoxypropionate, anisole, ethyl benzyl ether, cresyl methyl ether, diphenyl ether, dibenzyl ether, phenetole, butyl phenyl ether, benzene, ethylbenzene, diethylbenzene, pentylbenzene, isopropylbenzene, toluene, xylene, cymene, mesitylene, methanol, ethanol, isopropanol, butanol, methyl monoglycidyl ether, ethyl monoglycidyl ether, dimethylformamide, mineral spirits, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and various silicone oils. However, the organic solvent is not limited to these examples. The organic solvent may be used alone or in combination of two or more kinds.

[0045] The content of the thixotropy-imparting agent (polymer nanofibers with crosslinked lyophobic cores) is preferably 0.1 to 20 mass %, more preferably 0.1 to 10 mass %, of the total amount of the liquid composition.

[0046] The thixotropy index (TI) of a liquid composition is measured at a temperature of 25°C and a shear rate of 100 s -1 Viscosity η1 at shear rate 10 s -1 The thixotropy index (TI) of the liquid composition is preferably greater than 1, more preferably 2 or more, and even more preferably 2.5 or more. The higher the thixotropy index (TI), the greater the effect of the thixotropy-imparting agent in providing thixotropy. The upper limit of the thixotropy index (TI) is not particularly limited, but may be, for example, 100 or less, 20 or less, or 10 or less.

[0047] Examples of other components of the liquid composition include resins (excluding polymer nanofibers with crosslinked lyophobic cores), surfactants, organic ions, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, antifoaming agents, organic particles, lubricants, antistatic agents, UV protection agents, dyes, pigments, stabilizers, magnetic powders, alignment promoters, plasticizers, dispersants, crosslinking agents, colorants, penetrating agents, anti-drying agents, pH adjusters, preservatives, and anti-fungal agents. However, the other components are not limited to these examples. The other components may be used alone or in combination of two or more.

[0048] Examples of resins (excluding polymer nanofibers with crosslinked lyophobic cores) include acrylic resins, polycarbonate resins, polyester resins, polyamide resins, silicone resins, fluorine-based resins, chlorine-based resins, epoxy resins, melamine resins, phenolic resins, polyurethane resins, diallyl phthalate resins, alcohol-based resins, cellulose derivatives, and precursors of these resins. However, the resins are not limited to these examples. The resins may be used alone or in combination of two or more. [Example]

[0049] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following description.

[0050] [Abbreviation] AA: Acrylic acid MMA: Methyl methacrylate St: Styrene BA: Butyl acrylate BzMA: Benzyl methacrylate PEGA: Poly(ethylene glycol) methyl ether acrylate BTPA: 2-(butylthiocarbonothioylthio)propanoic acid (Boron Molecular Corporation) CPADB: 4-cyano-4-(phenylcarbonothionylthio)pentanoic acid (Sigma-Aldrich product) EGDA: Ethylene glycol diacrylate EGDMA: Ethylene glycol dimethacrylate AIBN: 2,2'-azobis(isobutyronitrile) ACPA: 4,4'-azobis(4-cyanopentanoic acid) THF: Tetrahydrofuran M1: Phillips block 1 (homopolymer of MMA) that forms the phillips shell M2: Philophilic block 2 that forms the philic shell (copolymer composition: PEGA / AA = 50 / 50 (molar ratio) copolymer)

[0051] [Preparation of M1] M1 used in each example was synthesized as follows. MMA was charged into a reactor, and water was added to adjust the solids content to 50% by mass. Subsequently, CPADB and AIBN were added to achieve a molar ratio of monomer / CPADB / AIBN = 300 / 1 / 0.1, followed by 15 minutes of nitrogen bubbling. The reactor was then immersed in an 80°C oil bath and polymerized for 6 hours with stirring. The polymerization solution was diluted 2-fold with THF and reprecipitated in hexane, yielding polymer M1 as a powder. The number-average molecular weight of M1 was 11,700.

[0052] [Preparation of M2] M2 used in each example was synthesized as follows. PEGA and AA were charged into a reaction vessel at a molar ratio of 50 / 50, and water was added to adjust the solids content to 20% by mass. Next, BTPA and ACPA were added to adjust the molar ratio of monomer / BTPA / ACPA to 44 / 1 / 0.1, and nitrogen bubbling was performed in an ice bath for 30 minutes. The reaction vessel was then immersed in an 80°C oil bath, and polymerization was carried out for 3 hours with stirring, yielding an aqueous solution of M2. The number-average molecular weight of M2 was 12,400.

[0053] [Production Example 1: Synthesis of Polymer Nanofiber 1] The amphiphilic block copolymer forming the polymer nanofibers of Example 1 was synthesized as follows. M1, BzMA, and AIBN were charged into a reaction vessel in the molar ratios shown in Table 1, and a water / ethanol mixed solvent (water / ethanol = 20:80 (weight ratio)) was added to achieve a solids content of 10% by mass. After 15 minutes of nitrogen bubbling, the reaction vessel was immersed in an 80°C oil bath and polymerized for 40 minutes with stirring. EGDMA was then added to achieve the molar ratio shown in Table 1, and polymerized for 25 minutes. The polymerization solution was diluted 2-fold with THF and reprecipitated in hexane to obtain a powder of polymer nanofiber 1, in which the amphiphilic block copolymer was self-assembled. In polymer nanofiber 1, the lyophobic core formed from the lyophobic block is crosslinked with EGDMA.

[0054] [Production Example 2: Synthesis of Polymer Nanofiber 2] M2, St, BA, ACPA, and NaHCO3 were charged into a reaction vessel in the molar ratios shown in Table 1, and water was added to adjust the solids content to 20% by mass. Next, 1M aqueous sodium hydroxide was added to adjust the pH of the solution to the value shown in Table 1, and nitrogen bubbling was performed in an ice bath for 30 minutes. The reaction vessel was then immersed in an 80°C oil bath and polymerization was carried out for 6 hours with stirring. The polymerization solution was diluted 5-fold with ethanol and reprecipitated in diisopropyl ether to obtain a powder of polymer nanofiber 2, in which the amphiphilic block copolymer was self-assembled. In polymer nanofiber 2, the lyophobic core formed from the lyophobic block is crosslinked with EGDA.

[0055] [Production Example 3: Synthesis of Polymer Nanofiber 3] Polymer nanofibers 3 of each example were obtained in the same manner as in Example 1, except that the copolymerization compositions of the lyophilic block and lyophobic block and the polymerization time were changed as shown in Table 1 and no crosslinking agent was used. Regarding the synthesis of polymer nanofibers 3, the copolymerization compositions (unit: eq) shown in Table 1 are also values ​​converted into molar ratios. In polymer nanofibers 3, the lyophobic core is not crosslinked.

[0056] [Table 1]

[0057] [Example 1] Toluene was added to polymer nanofiber 1 so that the solid content was 10% by mass (4 g in total), and the mixture was stirred at 40°C and 80 rpm for 6 hours using a mix rotor (AS ONE Corporation, MRC-5, VMRC-5) to prepare a liquid composition. The TI of the liquid composition was determined. The results are shown in Table 2.

[0058] [Examples 2 to 4, Comparative Examples 1 and 2] Liquid compositions of each example were prepared in the same manner as in Example 1, except that polymer nanofibers and organic solvents were used as shown in Table 2. The TI of each liquid composition was also determined. The results are shown in Table 2.

[0059] [Measurement method] (number average molecular weight) The number average molecular weight (Mn) was calculated from a calibration curve of methyl methacrylate using gel permeation chromatography (GPC). More specifically, 5 mg of the polymer to be measured was dissolved in 5 ml of THF, and the solution was filtered through a 0.45 μm filter to prepare a sample for GPC measurement. A polymer measurement guard column (manufactured by Tosoh Corporation, product name "TSK-guardcolumn SUPER HH 4.6mmφ×35mm") and two polymer measurement columns (manufactured by Tosoh Corporation, product name "TSK-GEL SUPER HM-H 6.0mmφ×150mm") were connected in series to a gel permeation chromatography measurement device (manufactured by Tosoh Corporation, product name "HLC-8420GPC") and used. A differential refractometer (RI) was used as the detector. Measurements were performed under the following conditions: separation column temperature: 40°C, mobile phase: THF, mobile phase flow rate: 0.6 mL / min, sample injection volume: 10 μL. A calibration curve was created using several types of polymethyl methacrylate (Mitsubishi Chemical Corporation products) with known molecular weights as standard polymers, and Mn was determined.

[0060] (TI) TI is the shear rate 100 s -1 Viscosity η1 at shear rate 10 s -1 The viscosity η1 and viscosity η2 were measured at 25°C under each shear condition using a rheometer (HAAKE product "MARS60").

[0061] (Tg of lyophobic core) Based on the copolymer composition of the solubility block shown in Table 1, the glass transition temperature Tg (°C) of the copolymer was calculated using the following Fox equation. 1 / (273+Tg)=Σ{W i / (273+Tg i )} W i : mass fraction of monomer i Tg i : Tg (℃) of the homopolymer of monomer i Here, the glass transition temperature of the homopolymer is a value using the numerical values ​​described in "Polymer Handbook, 4th Edition, John Wiley & Sons."

[0062] [Table 2]

[0063] The liquid compositions of Examples 1 to 4, which contained polymer nanofiber 1 or polymer nanofiber 2 with a crosslinked lyophobic core, exhibited thixotropy, as indicated by a TI of more than 1.00. In contrast, the liquid compositions of Comparative Examples 1 and 2, which contained polymer nanofiber 3 with a non-crosslinked lyophobic core, did not exhibit thixotropy, as indicated by a TI of 1.00. [Industrial Applicability]

[0064] According to the present invention, there are provided a thixotropic agent which does not require a treatment process for application to an organic solvent and which can be used as an alternative to fibrous cellulose, and a liquid composition containing the thixotropic agent. [Explanation of symbols]

[0065] 1. Amphiphilic block copolymer 2. Hydrophobic Block 3. Hydrophilic block 10 Polymer nanofibers 20 Hydrophobic Core 30 Hydrophilic Shell

Claims

1. Contains polymer nanofibers having a core-shell morphology with a lyophobic core and a lyophilic shell, A thixotropic agent crosslinking the lyophobic core of the polymer nanofiber.

2. The thixotropic agent according to claim 1 , wherein the polymer nanofibers are formed by self-assembly of an amphiphilic block copolymer having a lyophobic block and a lyophilic block.

3. 3. The thixotropic agent according to claim 2, wherein the lyophobic block has at least one selected from the group consisting of a unit based on benzyl (meth)acrylate, a unit based on styrene, and a unit based on n-butyl (meth)acrylate.

4. 3. The thixotropic agent according to claim 2, wherein the philic block has at least one selected from the group consisting of units based on poly(ethylene glycol) methyl ether acrylate, units based on poly(ethylene glycol) methyl ether methacrylate, units based on (meth)acrylic acid, and units based on methyl (meth)acrylate.

5. A liquid composition comprising the thixotropy-imparting agent according to any one of claims 1 to 4 and an organic solvent.

6. Shear rate 100 s at 25 ° C －１ Viscosity η at １ Shear rate 10 s －１ Viscosity η at ２ The ratio of η ２ / η １ The liquid composition according to claim 5, wherein the thixotropy index (TI) is greater than 1.

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