Structure and particles

Abstract

The present invention provides a structure capable of yielding particles having a unimodal particle size distribution in a solvent. The structure according to the present invention contains a compound A having three or more polylactic acid chains with terminal carboxyl groups, and a compound B having a plurality of functional groups that interact with the terminal carboxyl groups.

Description

structures, particles

[0001] This invention relates to structures and particles.

[0002] In recent years, environmental pollution (marine pollution) and adverse effects on ecosystems caused by plastics have become a problem, and various efforts to reduce the environmental burden have begun. Among these, attention is being drawn to the development and widespread use of biodegradable resins. For example, Patent Document 1 discloses an ionic supramolecular structure consisting of a telechelic diacid, which is a carboxylic acid having reactive functional groups at both ends, and a telechelic dibase, which is a nitrogen-containing basic compound having reactive functional groups at both ends. In the examples of Patent Document 1, a compound containing a polyester chain formed using a dicarboxylic acid such as succinic acid and a diol such as 1,4-butanediol is used as the telechelic diacid.

[0003] Japanese Patent Publication No. 2024-065788

[0004] On the other hand, in recent years, various applications of polylactic acid with biodegradable properties have been investigated. The present inventors, referring to Patent Document 1, investigated the properties of a structure obtained using a telechelic diacid containing a polylactic acid chain and a telechelic dibase, and found that the particle size distribution of the particles obtained using the above structure in a solvent was broad and needed improvement. More specifically, the particle size distribution of the particles obtained using the above structure was multimodal. Considering the application of the above particles to various uses, a unimodal particle size distribution is desirable from the standpoint of handling and other factors. In view of the above circumstances, the present invention aims to provide a structure that can produce particles with a unimodal particle size distribution in a solvent. The present invention also aims to provide particles containing the structure.

[0005] The inventors have found that the above problems can be solved by the following configuration.

[0006] (1) A structure comprising compound A having three or more polylactic acid chains having terminal carboxyl groups, and compound B having multiple functional groups that interact with terminal carboxyl groups. (2) The structure according to (1), wherein compound A is a compound represented by formula (A1) described later. (3) The structure according to (1) or (2), wherein the functional group that interacts with the terminal carboxyl group is a group selected from the group consisting of primary amino groups, secondary amino groups, and tertiary amino groups. (4) The structure according to any one of (1) to (3), wherein compound B is a compound represented by formula (B) described later. (5) A particle containing the structure according to any one of (1) to (4).

[0007] According to the present invention, a structure can be provided that allows for the production of particles with a unimodal particle size distribution in a solvent. Furthermore, according to the present invention, particles containing this structure can be provided.

[0008] This figure schematically shows the particles of the present invention. This figure shows the particle size distribution of the aqueous solution obtained in Example 1 by dynamic light scattering. This figure shows the particle size distribution of the aqueous solution obtained in Comparative Example 1 by dynamic light scattering.

[0009] The present invention will now be described in detail. The following descriptions of constituent elements may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In this specification, numerical ranges expressed using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits.

[0010] A key feature of the structure of the present invention is the use of compound A, which has three or more polylactic acid chains having terminal carboxyl groups. In other words, the present invention has found that by using compound A, particles with a unimodal particle size distribution in a solvent can be obtained. The details of why the above characteristics are obtained are unknown, but the following is speculated. Compound A has three or more polylactic acid chains having terminal carboxyl groups, so it has a radially spreading structure and is thought to have superior solubility in various solvents compared to telechelic diacitic acid as described in Patent Document 1. Therefore, when using telechelic diacitic acid as described in Patent Document 1, the solubility is poor, so aggregates of telechelic diacitic acid and other substances exist in the solvent system, and these aggregates and compound B form a structure, resulting in a multimodal particle size distribution of the resulting particles. In contrast, as mentioned above, compound A used in the present invention has superior solubility in solvents due to its structural characteristics, so there is almost no presence of such aggregates, and as a result, the particle size distribution of the resulting particles tends to be unimodal.

[0011] The structure of the present invention comprises compound A having three or more polylactic acid chains having terminal carboxyl groups, and compound B having multiple functional groups that interact with terminal carboxyl groups (hereinafter also simply referred to as "specific functional groups"). Within the structure, interactions are formed between the terminal carboxyl groups of compound A and the specific functional groups of compound B. As a result, the structure is formed by the bonding of compound A and compound B through these interactions. For example, taking as one embodiment a compound A represented by formula (A1) described later, where m is 3, and compound B represented by formula (B1) described later, where p is 2, and X is a primary amino group, as shown in Figure 1, in a particle 10 containing a structure obtained using compound A having three carboxyl groups and compound B having two primary amino groups, these compounds function as building blocks. That is, ionic bonds (-COO) are formed between the carboxyl groups and primary amino groups. － NH ３ ＋-) is formed, and a structure is formed within particle 10.

[0012] The type of interaction is not particularly limited, but examples include ionic bonds and hydrogen bonds, with ionic bonds being preferred. In other words, it is preferable that the terminal carboxyl group of compound A and the specific functional group of compound B interact via ionic bonds within the structure. The compounds constituting the structure will be described in detail below.

[0013] <Compound A> Compound A has three or more polylactic acid chains having terminal carboxyl groups. A polylactic acid chain is a polymer chain composed of repeating units derived from lactic acid. In compound A, the polylactic acid chain has a carboxyl group at its end. Compound A only needs to have three or more polylactic acid chains having terminal carboxyl groups, and in terms of having a smaller particle size distribution of the particles obtained using the structure (hereinafter also simply referred to as "the advantage of the present invention"), it is preferable that compound A has 3 to 10 polylactic acid chains having terminal carboxyl groups, more preferably 3 to 6, and even more preferably 4.

[0014] The weight-average molecular weight (Mw) of compound A is not particularly limited, but in terms of superior effects of the present invention, it is preferably 250 to 100,000, more preferably 500 to 80,000, even more preferably 500 to 40,000, particularly preferably 500 to 10,000, and most preferably 500 to 5,000. The number-average molecular weight (Mn) of compound A is not particularly limited, but in terms of superior effects of the present invention, it is preferably 250 to 50,000, more preferably 500 to 40,000, even more preferably 500 to 20,000, particularly preferably 500 to 5,000, and most preferably 500 to 2,500. The Mw / Mn ratio is not particularly limited, but in terms of superior effects of the present invention, it is preferably 1.0 to 10.0, more preferably 1.0 to 8.0, and even more preferably 1.0 to 7.0. The above weight-average molecular weight and number-average molecular weight are measured by gel permission chromatography (GPC). More specifically, the measurements will use Shimadzu SCL-10A VP, Shimadzu LC-20AD, and Shimadzu RID-10A. Two TSK gel-GMH columns will also be used. ＨＲ Using -M, 1,3-dioxolane is flowed at a flow rate of 0.75 mL / min in an oven at 45°C. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) are calibrated using polystyrene as the standard.

[0015] The carboxylic acid value of compound A is not particularly limited, but 5 to 400 KOH mg / g is preferred, 10 to 300 KOH mg / g is more preferred, and 20 to 250 KOH mg / g is even more preferred, in terms of superior effects of the present invention. The above carboxylic acid value is calculated by the titration method of acid value according to JIS K0070-1992 (1). Specifically, 1.0 g of the sample to be measured is dissolved in 100 mL of methylene chloride. A few drops of aqueous phenolphthalein solution are added to the obtained solution. Then, 0.1 N ethanolic potassium hydroxide solution is added dropwise using a burette, and the amount added is taken as the endpoint after it turns reddish-purple and is held for 30 seconds. The above procedure is repeated three times, and the average of the three measured values ​​obtained is taken as the carboxylic acid value of compound A.

[0016] For the effects of the present invention to be more superior, it is preferable that compound A is a compound represented by formula (A1).

[0017]

[0018] R ａ１ represents an n-valent linking group. The n-valent linking group is not particularly limited, but examples include n-valent hydrocarbon groups which may have heteroatoms. The number of carbon atoms in the n-valent linking group is not particularly limited, but is preferably 2 to 40, more preferably 3 to 30, even more preferably 3 to 20, particularly preferably 3 to 10, and most preferably 5 to 10. Examples of n-valent hydrocarbon groups include aliphatic hydrocarbon groups, aromatic hydrocarbon groups, and groups which are combinations thereof. The aliphatic hydrocarbon group may be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be linear, branched, or cyclic. The aromatic hydrocarbon group may be monocyclic or polycyclic. Examples of aromatic hydrocarbon rings which constitute the aromatic hydrocarbon group include benzene rings and naphthalene rings. The n-valent hydrocarbon group may have heteroatoms, and examples of heteroatoms include oxygen atoms, sulfur atoms, nitrogen atoms, and phosphorus atoms.

[0019] As the n-valent linking group, a residue obtained by removing the OH group from a carboxyl group in a compound having n carboxyl groups is preferred. Examples of compounds having n carboxyl groups include butanetetracarboxylic acid, pyromellitic acid, tetrahydrofuran-2,3,4,5-tetracarboxylic acid, 1,2,3-propanetricarboxylic acid, 1,3,5-pentanetricarboxylic acid, (1α,2α,4α)-1,2,4-cyclohexanetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, trimesic acid, trans-aconitic acid, 1,4,5,8-naphthalenetetracarboxylic acid, 1,2,3,4-cyclobutanetetracarboxylic acid, and 1,2,3,4-cyclopentanetetracarboxylic acid.

[0020] m represents 2 or more. From the viewpoint of further improving the effects of the present invention, m is preferably 3 to 300, more preferably 3 to 200, still more preferably 3 to 100, particularly preferably 3 to 20, and particularly preferably 3 to 10. m represents the average number of repeating units. That is, the compound represented by formula (A1) has n [(O-CHCH ３ -CO) ｍ -OH] groups, and m is the average of the number of lactic acid-derived repeating units in each of these n groups. The average number of repeating units represented by m can be １ calculated by 1H-NMR (proton nuclear magnetic resonance). n represents 3 or more. From the viewpoint of further improving the effects of the present invention, n is preferably 3 to 20, more preferably 3 to 12, still more preferably 3 to 6, and even more preferably 4.

[0021] From the viewpoint of further improving the effects of the present invention, compound A is preferably a compound represented by formula (A2).

[0022]

[0023] R ａ２ represents an n-valent hydrocarbon group that may optionally contain an oxygen atom. The number of carbon atoms contained in the n-valent hydrocarbon group is not particularly limited, but is preferably 2 to 40, more preferably 3 to 30, still more preferably 3 to 20, particularly preferably 3 to 10, and most preferably 5 to 10. Examples of the n-valent hydrocarbon group include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, and a group combining these. The aliphatic hydrocarbon group may be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be linear, branched, or cyclic. Examples of the aromatic hydrocarbon ring constituting the aromatic hydrocarbon group include a benzene ring and a naphthalene ring. The aromatic hydrocarbon group may be monocyclic or polycyclic. The n-valent hydrocarbon group may optionally contain an oxygen atom. For example, the n-valent hydrocarbon group may be cyclic, and the oxygen atom may be contained as a ring member atom.

[0024] The definitions and preferred ranges of m and n in formula (A2) are the same as those of m and n in formula (A1).

[0025] The method for producing compound A is not particularly limited, and known methods can be employed. For example, a method of polymerizing lactic acid in the presence of an acid catalyst and a compound having n carboxyl groups can be used. Known acid catalysts can be used as the acid catalyst. A volatile acid catalyst is preferred as the acid catalyst. By using a volatile acid catalyst, the acid catalyst can be removed from the product obtained by heat treatment. A pKa of -2.0 to -1.7 is preferred as the acid catalyst. Examples of acid catalysts include sulfonic acid compounds, carboxylic acid compounds, and phosphoric acid compounds, with sulfonic acid compounds being preferred. Examples of sulfonic acid compounds include monoalkylbenzenesulfonic acid, dialkylbenzenesulfonic acid, and trialkylbenzenesulfonic acid.

[0026] When polymerizing lactic acid, it is preferable to perform a heat treatment. The heating temperature is not particularly limited, but 100 to 200°C is preferred, and 120 to 180°C is more preferred. When polymerizing lactic acid, a treatment to remove water generated in the reaction system may be performed. An example of a treatment to remove water is a treatment to reduce the pressure.

[0027] Compounds having n carboxyl groups are as described above. Polymerization of lactic acid proceeds from the carboxyl groups of compounds having n carboxyl groups. Either D-lactic acid or L-lactic acid can be used as the lactic acid.

[0028] <Compound B> Compound B has multiple functional groups (specific functional groups) that interact with terminal carboxyl groups. Compound B may have multiple (two or more) specific functional groups, but 2 to 20 is preferred, 2 to 10 is more preferred, and 2 to 6 is even more preferred in terms of superior effects of the present invention. The type of specific functional group is not particularly limited as long as it interacts with terminal carboxyl groups, but examples include nitrogen-containing basic groups. Examples of nitrogen-containing basic groups include primary amino groups (-NH ２), secondary amino groups (e.g., -NHR, where R represents an alkyl group), tertiary amino groups (e.g., -NR ２ R independently represents an alkyl group), a guanidino group, an amidino group, and a nitrogen-containing aromatic group. Examples of nitrogen-containing aromatic groups include a five-membered ring nitrogen-containing aromatic group (e.g., an imidazole group) and a six-membered ring nitrogen-containing aromatic group (e.g., a pyridine group). The number of carbon atoms in the alkyl group represented by R is not particularly limited, but 1 to 6 is preferred. As for the specific functional group, a primary amino group, a secondary amino group, or a tertiary amino group is preferred in terms of superior effects of the present invention, and a primary amino group is more preferred. Compound B may be a polymer having repeating units having the specific functional group. Examples of polymers include chitosan and polyethyleneimine.

[0029] For superior effects of the present invention, compound B is preferably a compound represented by formula (B).

[0030]

[0031] R ｂ１ represents a p-valent hydrocarbon group, which may have substituents. The number of carbon atoms in the p-valent hydrocarbon group is not particularly limited, but is preferably 2 to 20, more preferably 2 to 10, and even more preferably 3 to 6. Examples of p-valent hydrocarbon groups include aliphatic hydrocarbon groups, aromatic hydrocarbon groups, and groups combining these. The aliphatic hydrocarbon group may be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be linear, branched, or cyclic. The aromatic hydrocarbon group may be monocyclic or polycyclic.

[0032] Examples of substituents that a p-valent hydrocarbon group may have include carboxyl groups, alkyloxycarbonyl groups, cyano groups, nitro groups, and alkoxy groups. The p-valent hydrocarbon group may contain -NH-, -C(=NH)-, or -N<.

[0033] X represents a primary amino group, a secondary amino group, a tertiary amino group, or a nitrogen-containing aromatic group. A primary amino group is preferred for X in terms of superior effects of the present invention. p represents 2 or more. A value of p is preferably 2 to 10, more preferably 2 to 5, and even more preferably 2 to 3, in terms of superior effects of the present invention.

[0034] Examples of compound B include ethylenediamine, trimethylenediamine, tetramethylenediamine, 1,5-pentadiamine, 1,7-heptanediamine, 1,6-hexamethylenediamine, 1,7-heptenediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine, 2-methyl-1,5-pentanediamine, 1,3-pentanediamine, 1,2-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, lysine, lysine esters, spermidine, spermine, arginine, histidine, creatinine, triethylenetetramine, tris(2-aminoethyl)amine, chitosan, and polyethyleneimine.

[0035] <Structure> The structure comprises compound A and compound B as described above. As described above, in the structure, the terminal carboxyl group of compound A and a specific functional group of compound B interact, preferably forming an ionic bond. The method for producing the structure is not particularly limited, and one method is to mix compound A and compound B. Among these, a method of mixing compound A and compound B in a solvent is preferred in that the effects of the present invention are superior, and a method of mixing solution A obtained by dissolving compound A in a solvent with solution B obtained by dissolving compound B in a solvent is more preferred. The solvent used to dissolve compound A or compound B is not particularly limited, but examples include water, ketone solvents (e.g., acetone, 2-butanone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and cyclopentanone), ether solvents (e.g., dioxane and tetrahydrofuran), aliphatic hydrocarbon solvents (e.g., hexane), alicyclic hydrocarbon solvents (e.g., cyclohexane), aromatic hydrocarbon solvents (e.g., toluene, xylene, and trimethylbenzene), halogenated solvents (e.g., chloroform, dichloro Examples of suitable solvents include methane, dichloroethane, dichlorobenzene, and chlorotoluene, ester solvents (e.g., methyl acetate, ethyl acetate, and butyl acetate), alcohol solvents (e.g., ethanol, isopropanol, butanol, and cyclohexanol), cellosolve solvents (e.g., methyl cellosolve and ethyl cellosolve), cellosolve acetate solvents, sulfoxide solvents (e.g., dimethyl sulfoxide), and amide solvents (e.g., dimethylformamide and dimethylacetamide). Preferred solvents for solution A are ketone solvents, ether solvents, alcohol solvents, amide solvents, sulfoxide solvents, or halogen solvents. Preferred solvents for solution B are water, ether solvents, alcohol solvents, halogen solvents, amide solvents, and sulfoxide solvents.

[0036] The mixing ratio of Compound A and Compound B is not particularly limited, but from the viewpoint of further improving the effect of the present invention, the molar ratio of the molar amount of the specific functional group contained in Compound B to the molar amount of the terminal carboxy group contained in Compound A (molar amount of the specific functional group contained in Compound B / molar amount of the terminal carboxy group contained in Compound A) is preferably 0.1 to 10, more preferably 0.3 to 3.0, still more preferably 0.5 to 2.0, and even more preferably 0.75 to 1.25.

[0037] A structure is obtained by mixing the above-described solution A and solution B. After mixing solution A and solution B, part of the solvent may be removed as necessary. For example, after mixing solution A containing an organic solvent and solution B containing water, the organic solvent may be removed to obtain solution C containing water and the structure.

[0038] The structure obtained by the above-described procedure may exist in the form of particles. That is, for example, particles containing the structure can be obtained in a solution obtained by the method of mixing Compound A and Compound B in a solvent. As described above, in the present invention, particles having a unimodal particle size distribution can be obtained.

[0039] The particle size of the particles containing the structure is not particularly limited, but is preferably 0.08 to 500 µm, and more preferably 0.1 to 100 µm.

[0040] <Uses and Characteristics> The structure of the present invention can be applied to various uses. Examples of uses to which the structure of the present invention is applied include cosmetics, absorbents, adsorbents, inks, adhesives, lubricants, molding materials, abrasives, medical carriers, soil conditioners, and fertilizer coating materials.

[0041] By reacting various compounds with the structure of the present invention, compound A and compound B can be cleaved. For example, if the terminal carboxyl group of compound A and a specific functional group of compound B form an ionic bond, reacting the structure with an ionic compound (e.g., a salt) can cause cleavage between compound A and compound B. Therefore, for example, by adding the structure (or particles) of the present invention to seawater, the interaction (especially the ionic bond) between the terminal carboxyl group of compound A and the specific functional group of compound B is weakened by salt exchange, allowing for cleavage between compound A and compound B. Compounds A and B (especially compound A) resulting from the cleavage are easily decomposed by microorganisms, and as a result, marine pollution can be suppressed.

[0042] Examples of the ionic compounds mentioned above include ionic salts comprising a pair of at least one cation selected from alkali metal ions, alkaline earth metal ions, metal ions, and ammonium ions, and at least one anion selected from halide ions (e.g., chloride ions, bromide ions, and iodide ions), hydroxide ions, acetate ions, carbonate ions, sulfate ions, nitrate ions, nitrite ions, and phosphate ions.

[0043] As described above, the structure may be obtained as particles or molded into other shapes. The structure of the present invention can be molded into shapes such as films, fibers, plates, foamed molded bodies, and other shapes depending on the application. The molding method is not particularly limited, and various conventionally known molding methods can be used. Specific examples include blow molding, injection molding, extrusion molding, compression molding, melt extrusion molding, solution casting molding, and calendering.

[0044] The structure of the present invention may be mixed with various additives depending on the purpose. Examples of additives include plasticizers, fillers, antioxidants, ultraviolet absorbers, heat stabilizers, flame retardants, mold release agents, inorganic additives, crystal nucleating agents, antistatic agents, pigments, and antiblocking agents. Therefore, particles containing the structure of the present invention may contain the above-mentioned various additives.

[0045] The features of the present invention will be described in more detail below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0046] <Preparation Example 1> L-lactic acid (9.06 g, 100.0 mmol), succinic acid (935 mg, 7.92 mmol), and ethylbenzenesulfonic acid (0.1 wt%) were added to a test tube and heated to 150°C. The mixture was stirred for 20 hours while removing water at 30 Torr. The 0.1 wt% amount of ethylbenzenesulfonic acid used corresponds to the amount of ethylbenzenesulfonic acid used relative to the total mass of the reaction system. The resulting polymer was cooled to room temperature to obtain compound C, which has two polylactic acid chains with carboxyl groups at the ends (yield: 80.7%). The number-average molecular weight of compound C was 1000, the weight-average molecular weight was 1720, the Mw / Mn was 1.7, and the carboxylic acid value was 151.5 KOH mg / g.

[0047] <Preparation Example 2> L-lactic acid (8.17 g, 90.8 mmol), 1,2,3,4-tetrabutanecarboxylic acid (1.83 g, 7.82 mmol), and ethylbenzenesulfonic acid (0.1 wt%) were added to a test tube and heated to 150°C, and stirred for 20 hours while distilling off water at 30 Torr. The amount of ethylbenzenesulfonic acid used, 0.1 wt%, corresponds to the amount of ethylbenzenesulfonic acid used relative to the total mass of the reaction system. The obtained polymer was cooled to room temperature to obtain compound A1 having four polylactic acid chains with carboxyl groups at the ends (yield: 80.5%). The number-average molecular weight of compound A1 was 990, the weight-average molecular weight was 1,450, the Mw / Mn was 1.5, and the carboxylic acid value was 222.0 KOH mg / g. Furthermore, compound A1 corresponds to both the compound represented by formula (A1) and the compound represented by formula (A2) described above. Compound A1 is such that n is 4 and m is 4 in formula (A1), and R １ This corresponds to a compound in which the OH group has been removed from the carboxyl group of 1,2,3,4-tetrabutanecarboxylic acid.

[0048] In production examples 1 and 2 above, the number-average molecular weight (Mn) and weight-average molecular weight (Mw) were measured by gel permission chromatography (GPC). Shimadzu SCL-10A VP, Shimadzu LC-20AD, and Shimadzu RID-10A were used for the measurements. Two TSK gel-GMH columns were used. ＨＲ Using -M, 1,3-dioxolane was flowed at a flow rate of 0.75 mL / min in an oven at 45°C. A sample was prepared with 0.4 mL of 1,3-dioxolane per 2.0 mg of polymer, and 10 μL was injected for measurement. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) were calibrated using polystyrene as the standard.

[0049] Furthermore, the carboxylic acid value was calculated according to JIS K0070-1992 (1) Titration method for acid value. Specifically, 1.0 g of the sample was dissolved in 100 mL of methylene chloride. A few drops of phenolphthalein aqueous solution were added to this solution. A 0.1 N ethanolic potassium hydroxide solution was added dropwise using a burette, and the endpoint was defined as the amount added after it turned reddish-purple and was held for 30 seconds. This procedure was repeated three times, and the average of the three measured values ​​obtained was calculated as the carboxylic acid value.

[0050] <Example 1> Compound A1 (0.2 g) obtained above was added to acetone (2 mL), and the resulting solution was heated to 55°C to obtain solution A. Next, hexanemethylenediamine (0.05 g) was added to water (2 mL) to obtain solution B. Next, solution A and solution B were mixed, and the resulting solution was stirred at 55°C for 1 hour. After that, the acetone was evaporated from the obtained solution to obtain an aqueous solution. In the aqueous solution, the presence of structural particles was confirmed by the dynamic light scattering method described later.

[0051] <Comparative Example 1> An aqueous solution was obtained by following the same procedure as in Example 1, except that compound C was used instead of compound A1. The presence of structural particles in the aqueous solution was confirmed by dynamic light scattering, as described later.

[0052] <Particle Size Measurement> The particle size of the structure particles (particulate structures) dispersed in the aqueous solutions obtained in Example 1 and Comparative Example 1 was measured using Dynamic Light Scattering (DLS) (Otsuka Electronics Co., Ltd.: NanoSAQLA multi-sample nanoparticle measurement system). Specifically, the aqueous solutions obtained in Examples 1 and 2 were placed in a glass cell, and measurements were performed at a temperature of 25°C, with a measurement wavelength of 660 nm, a light output of 70 mW, and 25 integration cycles.

[0053] In the obtained DLS measurement results, if there is only one peak in the range of 10 to 2000 nm and the distribution is unimodal, it is evaluated as "A", and if multiple peaks are observed in the range of 10 to 2000 nm and the distribution is multimodal, it is evaluated as "B". In Example 1, as shown in Figure 2, it was confirmed that particles showing a unimodal particle size distribution were obtained, and the evaluation was A. In contrast, in Comparative Example 1, as shown in Figure 3, it was confirmed that particles showing a multimodal particle size distribution were obtained, and the evaluation was B.

Claims

1. A structure comprising compound A having three or more polylactic acid chains having terminal carboxyl groups, and compound B having multiple functional groups that interact with the terminal carboxyl groups.

2. The structure according to claim 1, wherein compound A is a compound represented by formula (A1). R ａ１ represents an n-valent linking group. m represents 2 or more. n represents 3 or more.

3. The structure according to claim 1, wherein the functional group that interacts with the terminal carboxyl group is a group selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group.

4. The structure according to claim 1, wherein the compound B is a compound represented by formula (B). R ｂ１ represents a p-valent hydrocarbon group which may have a substituent. X represents a primary amino group, a secondary amino group, or a tertiary amino group. p represents 2 or greater.

5. A particle comprising the structure described in any one of claims 1 to 4.

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