JP7473068B2 - Crosslinked product of modified polyaspartic acid or its salt, and thickening composition - Google Patents

Description

The present invention relates to a crosslinked product of a modified polyaspartic acid or a salt thereof, and a thickening composition.
This application claims priority based on Japanese Patent Application No. 2022-044604, filed on March 18, 2022, the contents of which are incorporated herein by reference.

Carbomer is the most widely used cosmetic thickener on the market. Carbomer has unique features that other thickeners do not have, including extremely high viscosity and a refreshing feel when applied to the skin. Carbomer is a polyacrylic acid polymer.
Polyaspartic acid has a chemical structure similar to that of polyacrylic acid, and is capable of exerting similar functions and is biodegradable, so it is expected to be an alternative material with low environmental impact. In addition, polyaspartic acid (salt) in which the chains are partially crosslinked by a polyamine compound has been reported (Patent Document 1).

JP 2002-179791 A

However, when cross-linked polyaspartic acid is mixed with water to create a thickening solution, there is a problem that the viscosity decreases over time.

The present invention has been made to solve the above problems, and aims to provide a thickening composition that can maintain a certain level of viscosity for a longer period of time by using a crosslinked product of modified polyaspartic acid or its salt to which a compound having an amino group and a carboxy group, such as an amino acid, has been added. Another aim is to provide a crosslinked product of modified polyaspartic acid or its salt contained in the thickening composition.

（式（１）中、Ｇがカルボン酸基又はその塩を表す。）
［９］ 多官能エポキシ（Ｂ）を架橋剤として用いて、前記ポリアスパラギン酸またはその塩を架橋してなる、［６］～［８］の何れかに記載の、変性ポリアスパラギン酸またはその塩の架橋体。
［１０］ 架橋度が、０．５～１０モル％である、［１］～［９］の何れかに記載の、変性ポリアスパラギン酸またはその塩の架橋体。
［１１］ 前記変性ポリアスパラギン酸の塩が、有機塩基からなる塩又はアルカリ金属塩である、［１］～［１０］の何れかに記載の、変性ポリアスパラギン酸またはその塩の架橋体。
［１２］ ［１］～［１１］の何れかに記載の、変性ポリアスパラギン酸またはその塩の架橋体を含むことを特徴とする増粘組成物。
［１３］ 水をさらに含む［１２］に記載の増粘組成物。
［１４］ 前記増粘組成物の合計１００質量％に対して、前記変性ポリアスパラギン酸またはその塩の架橋体の含有量が０．０５～１０質量％である［１３］に記載の増粘組成物。
［１５］ ［１２］～［１４］の何れかに記載の増粘組成物と、
化粧料有効成分と、
を含む化粧料組成物。 The present disclosure includes the following embodiments [1] to [15].
[1] A crosslinked product of a modified polyaspartic acid or a salt thereof,
A crosslinked product of a modified polyaspartic acid or a salt thereof, characterized in that the modified polyaspartic acid is obtained by adding a compound having an amino group and a carboxy group to a polyaspartic acid.
[2] The crosslinked product of the modified polyaspartic acid or a salt thereof according to [1], wherein the compound having an amino group and a carboxy group is at least one selected from the group consisting of an amino acid, a carboxylate of an amino acid, and an amino acid ester.
[3] The crosslinked product of the modified polyaspartic acid or its salt according to [1] or [2], wherein the modified polyaspartic acid is a reaction product of polysuccinimide (PSI) and the compound having an amino group and a carboxy group.
[4] The crosslinked product of the modified polyaspartic acid or its salt according to [3], which is obtained by crosslinking the modified polyaspartic acid or its salt using a polyfunctional amine as a crosslinking agent.
[5] The crosslinked product of the modified polyaspartic acid or a salt thereof according to [4], wherein the polyfunctional amine is at least one selected from the group consisting of an aliphatic diamine, an alicyclic diamine, and an ether-based diamine.
[6] The modified polyaspartic acid is
Polysuccinimide (PSI);
The compound having an amino group and a carboxy group,
A compound (A: a1-A1-a2) having a first functional group (a1) and a second functional group (a2),
The crosslinked product of the modified polyaspartic acid or its salt according to [1] or [2], which is a reaction product of the following:
[7] The first functional group (a1) is an amino group (NH ₂ —),
the second functional group (a2) is at least one selected from the group consisting of an amino group (NH ₂ —) and a phosphonooxy group ((OH) ₂ P(═O)—O—);
The crosslinked product of the modified polyaspartic acid or its salt according to [6], wherein when the second functional group (a2) is an amino group (NH ₂ -), it has lower reactivity with polysuccinimide (PSI) than the first functional group (a1).
[8] The first functional group (a1) is an amino group (NH ₂ —),
the second functional group (a2) is an amino group (NH ₂ —);
The crosslinked product of the modified polyaspartic acid or its salt according to [6] or [7], wherein in the compound (A), the amino group of the second functional group (a2) is an amino group in a structure represented by the following formula (1):

(In formula (1), G represents a carboxylic acid group or a salt thereof.)
[9] A crosslinked product of the modified polyaspartic acid or its salt according to any one of [6] to [8], which is obtained by crosslinking the polyaspartic acid or its salt using a multifunctional epoxy (B) as a crosslinking agent.
[10] The crosslinked product of the modified polyaspartic acid or a salt thereof according to any one of [1] to [9], having a degree of crosslinking of 0.5 to 10 mol %.
[11] The crosslinked product of the modified polyaspartic acid or its salt according to any one of [1] to [10], wherein the salt of the modified polyaspartic acid is a salt of an organic base or an alkali metal salt.
[12] A thickening composition comprising a crosslinked product of the modified polyaspartic acid or a salt thereof according to any one of [1] to [11].
[13] The thickening composition according to [12], further comprising water.
[14] The thickening composition according to [13], wherein the content of the crosslinked product of the modified polyaspartic acid or a salt thereof is 0.05 to 10% by mass relative to 100% by mass of the total of the thickening composition.
[15] A thickening composition according to any one of [12] to [14],
A cosmetic active ingredient,
A cosmetic composition comprising:

The present invention provides a thickening composition that can maintain a certain level of viscosity for a longer period of time, and a crosslinked product of modified polyaspartic acid or its salt contained in the thickening composition.

The present invention will be described in more detail below. Note that the present invention is not limited to the embodiments shown below.

"~" means greater than or equal to the value before "~" and less than or equal to the value after "~".

(Crosslinked product of modified polyaspartic acid or its salt)
First Embodiment
In the crosslinked product of modified polyaspartic acid or a salt thereof according to the first embodiment of the present invention (sometimes referred to as the "crosslinked product of this embodiment"), the modified polyaspartic acid is obtained by adding a compound having an amino group and a carboxy group to polyaspartic acid. The modified polyaspartic acid according to this embodiment is preferably a reaction product of polysuccinimide (PSI) and the compound having an amino group and a carboxy group. By adding a carboxy group to the compound, the thickening property is improved when the crosslinked product of modified polyaspartic acid or a salt thereof is used as a thickening composition.

<Modified polyaspartic acid or its salt>
The modified polyaspartic acid according to the present embodiment is preferably obtained by ring-opening polysuccinimide (PSI) using a compound having an amino group and a carboxy group.

[Polysuccinimide (PSI)]
The polysuccinimide (PSI) according to this embodiment is a polymer represented by the following formula (2).

（式中、ｎ＝１０～１００００）

(Wherein, n = 10 to 10,000)

There is no particular limitation on the method for producing polysuccinimide (PSI), but for example, aspartic acid is heated in a vacuum at 170 to 190°C in the presence of phosphoric acid and dehydrated and condensed. To obtain a polysuccinimide (PSI) with a higher molecular weight, the polysuccinimide (PSI) obtained as described above may be treated with a condensing agent such as dicyclohexylcarbodiimide. There is no particular limitation on the molecular weight of polysuccinimide (PSI). For example, the weight average molecular weight is preferably 20,000 or more, more preferably 50,000 or more, and even more preferably 70,000 or more. The molecular weight of polysuccinimide (PSI) is preferably 500,000 or less, and more preferably 200,000 or less. The weight average molecular weight in this case is a conversion value using polystyrene as a standard substance by the GPC method.

[Compounds having an amino group and a carboxy group]
The compound having an amino group and a carboxy group according to this embodiment is preferably at least one selected from the group consisting of amino acids, carboxylates of amino acids, and amino acid esters.
Alternatively, a compound having an amino group and a carboxy group or an acid salt thereof may be used as a raw material. Examples of the acid salt of the compound having an amino group and a carboxy group include hydrochlorides such as lysine hydrochloride, ornithine hydrochloride, and arginine hydrochloride, and similar sulfates.

Specific examples of the above amino acids include aliphatic amino acids such as glycine, alanine, valine, leucine, and isoleucine; oxyamino acids such as serine and threonine; sulfur-containing amino acids such as methionine, cysteine, and cystine; acidic amino acids such as aspartic acid and glutamic acid; basic amino acids such as lysine, ornithine, and arginine; aromatic amino acids such as phenylalanine and tyrosine; heterocyclic amino acids such as tryptophan, histidine, proline, and oxyproline; and amino acids having an amide group such as asparagine and glutamine. These can be used regardless of whether they are L-, D-, or DL-form.

The amino acid is preferably a compound represented by the following formula (3):

(In the above formula, R represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms. The alkyl group having 1 to 5 carbon atoms and the alkoxy group having 1 to 5 carbon atoms may be further substituted with another organic group. Examples of such organic groups include an amino group and a carboxy group. It is preferable that n is an integer of 1 to 3. It is preferable that R is a hydrogen atom, a methyl group, or an ethyl group, and it is more preferable that R is a hydrogen atom.)

Examples of the carboxylate salt of the amino acid include alkali metal salts and alkaline earth metal salts. It is preferable that the carboxylate salt of the amino acid is a sodium salt, a potassium salt, a calcium salt, or the like.

The above amino acid esters include alkyl esters, cycloalkyl esters, and benzyl esters of the above amino acids.

The amino acid carboxylate or amino acid ester is preferably a compound represented by the following formula (4):

(In the above formula, X represents an alkyl group, a cycloalkyl group, a benzyl group, an alkali metal, or an alkaline earth metal; R and n are the same as in the general formula (3). X is preferably an alkyl group such as a methyl group or an ethyl group; or an alkali metal. n is preferably an integer of 1 to 3. When X is an alkali metal or an alkaline earth metal, "-CO-O-X" in the above formula (4) means a carboxylate.)

"Method of producing amino acid ester"
The method for producing the amino acid ester according to the present embodiment is not particularly limited. The amino acid ester according to the present embodiment is generally produced by heating an amino acid in an excess of alcohol in the presence of a mineral acid catalyst such as sulfuric acid or hydrochloric acid.

[Method for producing modified polyaspartic acid or its salt]
The method for producing the modified polyaspartic acid or its salt according to the present embodiment includes a ring-opening reaction method of polysuccinimide (PSI) by reacting with a compound having an amino group and a carboxy group. By reacting polysuccinimide (PSI) with the compound having an amino group and a carboxy group, the imide ring of polysuccinimide (PSI) is opened. When the ring-opening reaction is carried out using an amount of the compound having an amino group and a carboxy group less than 1 equivalent to the equivalent of the monomer unit of polysuccinimide (PSI), generally, unreacted imide rings remain.

It is preferable that the compound having an amino group and a carboxy group is an amino acid ester. When an amino acid ester is used as the compound having an amino group and a carboxy group, the modified polyaspartic acid or its salt according to this embodiment is an amino acid ester modified polyaspartic acid or its salt (sometimes referred to as an "amino acid ester modified product"). In the method for producing the amino acid ester modified product according to this embodiment, polysuccinimide (PSI) is reacted with the amino acid ester to open the imide ring of polysuccinimide (PSI).

The unreacted imide ring may remain, or may be further subjected to a ring-opening reaction using another compound having an amino group and a carboxy group. If desired, the unreacted imide ring may be opened with a substituted amine such as ethanolamine, cysteamine, or dibutylamine.

"Organic solvent"
In the method for producing a modified polyaspartic acid or a salt thereof according to the present embodiment, the organic solvent is not particularly limited as long as it substantially dissolves polysuccinimide (PSI) and the compound having an amino group and a carboxy group and/or does not substantially inhibit the progress of the reaction.

Specific examples of the organic solvent include aprotic polar organic solvents such as dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), dimethylimidazolidinone (DMI), dimethylsulfoxide (DMSO), and sulfolane. These can be used alone or in combination.

"Amount of compound having amino and carboxy groups used"
The amount of the compound having an amino group and a carboxy group according to the present embodiment is not particularly limited as long as it is substantially soluble in an organic solvent and/or does not substantially inhibit the progress of the reaction. The amount of the compound is generally 0.1 to 10 times the equivalent of the monomer unit of polysuccinimide (PSI), and preferably 0.1 to 1.0 times the equivalent.

"Basic catalyst"
In the method for producing a modified polyaspartic acid or a salt thereof according to the present embodiment, the basic catalyst optionally used is not particularly limited as long as it substantially accelerates the reaction rate. Specific examples of the basic catalyst include aliphatic tertiary amines such as trimethylamine, triethylamine, tripropylamine, tributylamine, diisopropylethylamine (DIEA), triethanolamine, and triethylenediamine (DABCO); alicyclic tertiary amines such as N-methylmorpholine; aromatic tertiary amines such as dimethylaniline and diethylaniline; and tetramethylguanidine. These may be used alone or in combination.

"Amount of basic catalyst used"
In the method for producing a modified polyaspartic acid or a salt thereof according to the present embodiment, the amount of the basic catalyst used is not particularly limited as long as it substantially accelerates the reaction rate. The amount of the basic catalyst used is generally 0 to 2 equivalents relative to the equivalent of the compound having an amino group and a carboxy group. When the amino acid ester is a mineral acid salt, a neutralization equivalent of a base is further added.

"Reaction temperature"
In the method for producing a modified polyaspartic acid or a salt thereof according to the present embodiment, the reaction temperature is not particularly limited as long as the reaction can be substantially maintained. The reaction temperature is generally selected from a temperature range of 5 to 150° C., and room temperature is usually selected. The reaction temperature can also be selected from a temperature range of 5 to 150° C., so as to be optimal for the compound having an amino group and a carboxy group used.

"Concentration of reaction system"
The concentration of the reaction system employed in the method for producing a modified polyaspartic acid or a salt thereof according to the present embodiment is not particularly limited as long as the progress of the reaction can be substantially maintained. The concentration of the reaction system is selected based on the concentration of polysuccinimide (PSI), and generally, the polysuccinimide (PSI) concentration is selected from a concentration range of 1 to 50% by weight. The concentration of the reaction system can also be selected from a polysuccinimide (PSI) concentration range of 1 to 50% by weight, so that the optimum concentration for the compound having an amino group and a carboxy group to be used is selected.

<Method for isolating modified polyaspartic acid or its salt>
The method for isolating the polymer produced from the reaction solution after the reaction in the method for producing the modified polyaspartic acid or its salt according to the present embodiment is not particularly limited as long as it can isolate the reaction product with a desired purity. The isolation method may be any known or publicly used method. Generally, known or publicly used isolation procedures such as concentration, recrystallization, or reprecipitation are used.

Specific examples of the isolation method include a method including the following steps A1 to A3.
Step A1: After completion of the reaction, an excess of a poor solvent (e.g., methyl alcohol, ethyl alcohol, isopropyl alcohol, etc.) is added to the reaction liquid in which the reaction product is dissolved at an appropriate temperature to precipitate crystals of the reaction product.
Step A2: The crystals of the reaction product precipitated in step A1 are isolated by decantation, filtration, suction filtration, or the like.
Step A3: The crystals isolated in step 2 are thoroughly washed with a poor solvent that does not dissolve the crystals, and then dried.
Other specific examples include a method including the following steps B1 to B3.
Step B1: After the reaction is completed, the reaction liquid in which the reaction product is dissolved is added to an excess of the same poor solvent as above at an appropriate temperature to precipitate crystals of the reaction product.
Step B2: The crystals of the reaction product precipitated in step 1 are isolated in the same manner as in step A2.
Step B3: The crystals isolated in step 2 are washed and dried in the same manner as in step A3.

In the method for producing a modified polyaspartic acid or a salt thereof according to this embodiment, the obtained modified polyaspartic acid or a salt thereof may not be isolated, and the mixed liquid after the reaction may be used as is to participate in the crosslinking reaction described below. Also, if necessary, only a portion of the unreacted raw materials other than the solvent may be removed to participate in the crosslinking reaction described below. Also, the concentration may be adjusted by increasing or decreasing the amount of the solvent in the mixed liquid.

<Structure of Crosslinked Body>
The crosslinked product of the modified polyaspartic acid or its salt according to this embodiment (sometimes referred to as the crosslinked product of this embodiment) is polyaspartic acid or its salt crosslinked using a polyfunctional amine as a crosslinking agent. The crosslinked product according to this embodiment has a polyaspartic acid skeleton and a structure in which polyaspartic acid chains are linked together by polyfunctional groups. The degree of crosslinking of the crosslinked product is preferably 1.0 to 5.0 mol %.

The modified polyaspartic acid according to this embodiment is a polymer formed by peptide bonds of aspartic acid. The amide bonds in the main chain of polyaspartic acid may be α bonds or β bonds. These bond modes may be the same or different for each structural unit. The α bond is when the amino group of the modified aspartic acid is bonded to the carboxy group at the α position of the modified aspartic acid, and the β bond is when the amino group is bonded to the carboxy group at the β position of the aspartic acid. The side chain of the modified polyaspartic acid is represented by -CH ₂ -COOH (in the case of α bonds) or -COOH (in the case of β bonds). In the crosslinked body of this embodiment, for example, when the polyfunctional amine is a diamine, a carboxy group present in a side chain on a certain modified polyaspartic acid chain and a carboxy group present in a side chain on another polyaspartic acid chain form amide bonds with the amino group of the diamine, thereby crosslinking the polyaspartic acid chains.

When the polyfunctional amine is a diamine, in the modified polyaspartic acid of this embodiment obtained by the reaction of the amino group with a compound having a carboxy group, the carboxy group (referred to as an "addition-derived carboxy group") derived from the compound having an amino group and a carboxy group is also present in a side chain on the chain. In the crosslinked product of this embodiment, the addition-derived carboxy group and a carboxy group present in a side chain on another polyaspartic acid chain may form an amide bond with the amino group of the diamine, thereby crosslinking the polyaspartic acid chains. In addition, the addition-derived carboxy group and an addition-derived carboxy group present in a side chain on another polyaspartic acid chain may form an amide bond with the amino group of the diamine, thereby crosslinking the polyaspartic acid chains.

In the crosslinked product of this embodiment, some of the carboxy groups on the side chains of the modified polyaspartic acid form such crosslinks. Another part (which may be the entire remainder) of the carboxy groups on the side chains of the polyaspartic acid may be a free carboxylic acid or may form a salt. The salt is not particularly limited, and examples thereof include alkali metal salts such as sodium salts and potassium salts, and salts of organic bases such as triethylamine, N-methylmorpholine, triethanolamine, and diisopropylethylamine. A specific example of a salt of polyaspartic acid is, for example, the sodium salt of polyaspartic acid.

The carboxyl group of the unmodified polyaspartic acid side chain can bond with -NH- in the amide bond of the main chain to form an imide ring. Therefore, an imide ring may be present in part of the main chain. In other words, the main chain portion in some of the structural units in the crosslinked body of this embodiment may form part of the imide ring formed as described above. In this embodiment, "partially crosslinked" refers to a part of the carboxyl group on the side chain of the polyaspartic acid forming a crosslink.

In addition, the weight average molecular weight of each modified polyaspartic acid chain linked to each other by crosslinking in the crosslinked product of this embodiment is preferably 40,000 or more, more preferably 80,000 or more, and even more preferably 100,000 or more. The higher the weight average molecular weight of the modified polyaspartic acid chain, the greater the thickening effect. For example, when polysuccinimide (PSI) is used as a raw material for producing modified polyaspartic acid as described below, these weight average molecular weights can be determined as values converted into pullulan, a standard substance, by measuring the salt of polyaspartic acid obtained by hydrolyzing the polysuccinimide (PSI) used as the raw material by GPC.

<Method of producing crosslinked body>
The method for producing the crosslinked product of the modified polyaspartic acid or its salt according to this embodiment (sometimes referred to as the method for producing the crosslinked product of this embodiment) is not particularly limited, but for example, the crosslinked product can be obtained by reacting the modified polyaspartic acid or its salt with a polyfunctional amine compound, and then hydrolyzing the reaction product while adjusting the pH in an aqueous solution. Alternatively, the crosslinked product can be obtained by reacting the modified polyaspartic acid or its salt with a polyfunctional amine in an aqueous solution while hydrolyzing the reaction product. In this case, imide rings may remain in some of the constituent units.

[Polyfunctional amine]
The polyfunctional amine according to this embodiment is preferably an amine having at least two primary and/or secondary amino groups.
Examples of diamine compounds include aliphatic diamines such as ethylenediamine and hexamethylenediamine; aliphatic diamines containing an aromatic ring such as xylylenediamine; alicyclic diamines such as norbornenediamine; ether-based diamines such as 1,2-bis(2-aminoethoxy)ethane, diethylene glycol bis(3-aminopropyl)ether, polyoxyethylenediamine, and polyoxypropylenediamine; amino acids and derivatives thereof having an amino group in the side chain such as lysine and ornithine; monoamino compounds linked by disulfide bonds such as cystine and cystamine; and derivatives thereof. Among these, preferred are lysine, ornithine, cystine, cystamine, and derivatives thereof, which are polymer decomposition products with high safety. Derivatives include diketopiperazines, which are cyclic dimers of lysine and ornithine, and esters of lysine, ornithine, and cystine.

Examples of polyfunctional amine compounds other than diamines include tris(2-aminoethyl)amine, tris(3-aminopropyl)amine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, etc.

The method of reacting the modified polyaspartic acid or its salt with the polyfunctional amine of the present embodiment may be, for example, a method of reacting in an organic solvent. The following will explain the reaction using an example in which the polyfunctional amine according to the present embodiment is a diamine.
In the method of reacting the modified polyaspartic acid or its salt with the diamine in an organic solvent, the modified polyaspartic acid or its salt is dissolved in an aprotic polar organic solvent, and then the diamine or a solution of the diamine in the organic solvent is dropped. Examples of the aprotic polar organic solvent include dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), dimethylimidazolidinone (DMI), dimethylsulfoxide (DMSO), and sulfolane. The amount of the organic solvent used to dissolve the modified polyaspartic acid or its salt is not particularly limited, but the organic solvent is usually used so that the polymer concentration is 1 to 50 mass%.

The temperature at which the modified polyaspartic acid or its salt in this embodiment is reacted with the diamine is not particularly limited, but is, for example, room temperature to 80°C.

The reaction conditions (reaction temperature, reaction time, reaction concentration, amount of diamine used, etc.) are not particularly limited, but it is better to maintain the reaction temperature in order to allow the reaction of the modified polyaspartic acid or its salt of this embodiment with the diamine to proceed even after the reaction has gelled to the point where stirring becomes difficult.

To isolate the precursor of the crosslinked body of this embodiment produced by the reaction, known isolation procedures such as recrystallization, reprecipitation, filtration, and concentration can be used.

After isolating the generated precursor of the crosslinked body of this embodiment, the imide ring of the isolated precursor of the crosslinked body is subjected to hydrolysis reaction. In addition, in the method for producing modified polyaspartic acid or a salt thereof, the compound having an amino group and a carboxy group used is preferably an amino acid ester. In this case, the obtained modified polyaspartic acid or a salt thereof has an ester portion derived from the amino acid ester. After isolating the generated precursor of the crosslinked body of this embodiment, the ester portion derived from the amino acid ester is also subjected to hydrolysis reaction in the hydrolysis reaction.
The hydrolysis reaction conditions (reaction system, pH, temperature, polymer concentration, type of alkali, alkali concentration, etc.) are not particularly limited as long as the following can be achieved.

The reaction system for hydrolysis of the precursor of the crosslinked body of this embodiment is usually carried out by suspending the precursor of the crosslinked body of this embodiment in an aqueous solution, but various organic solvents miscible with water may be contained. Specific examples of various organic solvents miscible with water include alcohols such as methyl alcohol and ethyl alcohol, acetone, and tetrahydrofuran. The pH during hydrolysis of the crosslinked polysuccinimide (PSI) is usually preferably 8.0 to 11.5, more preferably 9.0 to 11.0. The higher this value, the greater the efficiency of hydrolysis of the imide ring, and the lower this value, the smaller the degree of undesirable hydrolysis of the amide bond in the main chain. In general, the more water there is in the polymer concentration during hydrolysis of the crosslinked polysuccinimide (PSI), the faster the reaction will be, but when considering productivity, it is preferable to carry out the hydrolysis at a polymer concentration of 0.5 to 10% by mass.

Specific examples of alkalis that can be used for hydrolysis of the crosslinked precursor of this embodiment include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; and organic bases such as triethylamine, N-methylmorpholine, triethanolamine, and diisopropylethylamine.

The alkali used for hydrolysis of the crosslinked precursor of the present embodiment is usually used in the form of an aqueous solution. The concentration of the alkali is not particularly limited as long as it is within the following range, but is preferably 5 to 48%, and more preferably 10 to 30%.
A concentration at which the efficiency of hydrolysis of imide rings is substantially sufficient, the degree of hydrolysis of amide bonds in the main chain is small, and the pH can be controlled.
The higher this value, the greater the efficiency of hydrolysis of the imide ring, and the lower this value, the smaller the degree of undesirable hydrolysis of the amide bond in the main chain.

To isolate the crosslinked body of this embodiment produced by the hydrolysis reaction of the precursor of the crosslinked body of this embodiment, a known normal isolation procedure such as recrystallization, reprecipitation, filtration, concentration, etc. can be used.

In the method for producing a crosslinked body of this embodiment, the modified polyaspartic acid or its salt may be produced first, and then the modified polyaspartic acid or its salt may be reacted with a polyfunctional amine to produce a crosslinked body. In addition, the reaction for producing the modified polyaspartic acid or its salt and the crosslinking reaction may be carried out simultaneously, for example, as follows.

In the case where the reaction for producing modified polyaspartic acid or its salt and the crosslinking reaction are carried out simultaneously, the order of reaction (order of addition) of polysuccinimide (PSI), the compound having an amino group and a carboxy group, and the polyfunctional amine is not particularly limited, and for example, the following three production methods can be mentioned.
(I) A production method comprising the steps of: reacting polysuccinimide (PSI) with a compound having an amino group and a carboxy group to obtain the polyaspartic acid or a salt thereof (P1); and reacting the reaction product (P1) obtained in the above step with a polyfunctional amine (hereinafter, referred to as method (I)).
(II) A production method in which polysuccinimide (PSI) and the compound having an amino group and a carboxy group are first mixed and reacted with each other, and then a polyfunctional amine is added at a constant rate (hereinafter, referred to as method (II)).
(III) A production method in which polysuccinimide (PSI), the compound having an amino group and a carboxy group, and a polyfunctional amine are mixed and then reacted (hereinafter, referred to as method (III)).
Method (I) or method (II) is preferred, and method (I) is more preferred.

The size (average particle size) of the crosslinked body in this embodiment is not particularly limited, but is preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less. By making the average particle size 150 μm or less, advantages such as excellent transparency of the thickened solution and smooth texture can be obtained.

[Degree of cross-linking]
The amount of the polyfunctional amine used according to this embodiment may be appropriately selected according to the desired degree of crosslinking. For example, in the case of the above-mentioned example of the manufacturing method using diamine and polysuccinimide (PSI), from the viewpoint of imparting high water absorption to the generated crosslinked body, the amount of diamine used is 0.5 to 25 moles, preferably 1.0 to 20 moles, more preferably 1.5 to 15 moles, and even more preferably 2.0 to 10 moles, relative to 100 moles of polysuccinimide (PSI). When the amount of diamine used is 3 moles relative to 100 moles of polysuccinimide (PSI), it is simply referred to as "the amount of diamine used is 3 mole%". When the amount of diamine used is within the above range, the thickening composition of this embodiment can maintain a certain level of viscosity for a longer period of time. Here, the equivalent moles of polysuccinimide (PSI) means the moles of aspartic acid, which is the raw material used, in the case of the above-mentioned synthesis method of polysuccinimide (PSI).
The amount (mol %) of the polyfunctional amine used relative to the polysuccinimide (PSI) refers to the "degree of crosslinking" in the present invention. The unit of the degree of crosslinking is "mol %."
When the crosslinked body according to this embodiment is produced by a production method using a diamine and polysuccinimide (PSI), the degree of crosslinking of the crosslinked body according to this embodiment is obtained from the degree of crosslinking of the crosslinked polysuccinimide (PSI) before hydrolysis. The degree of crosslinking of the crosslinked body according to this embodiment is 0.5 to 25 mol%, preferably 1.0 to 20 mol%, more preferably 1.5 to 15 mol%, and even more preferably 2.0 to 10 mol%.

Second Embodiment
In the crosslinked product of modified polyaspartic acid or a salt thereof according to a second embodiment of the present invention (hereinafter referred to as "the crosslinked product of modified polyaspartic acid or a salt thereof according to this embodiment" or "the crosslinked product according to this embodiment"), the modified polyaspartic acid is a reaction product of polysuccinimide (PSI), the compound having an amino group and a carboxy group, and a compound having a first functional group (a1) and a second functional group (a2) (A: a1-A1-a2).

<Modified polyaspartic acid or its salt>
The modified polyaspartic acid or a salt thereof according to this embodiment is preferably obtained by ring-opening polysuccinimide (PSI) using a compound having an amino group and a carboxy group and a compound (A: a1-A1-a2), which has a first functional group (a1) and a second functional group (a2).

[Polysuccinimide (PSI)]
The polysuccinimide (PSI) according to this embodiment may be the same as the "polysuccinimide (PSI)" described in the first embodiment.

[Compounds having an amino group and a carboxy group]
The compound having an amino group and a carboxy group according to this embodiment may be a compound having an amino group and a carboxy group similar to the "compound having an amino group and a carboxy group" described in the first embodiment. By having this compound have a carboxy group, the thickening property is improved when the crosslinked material of the modified polyaspartic acid or its salt is used as a thickening composition.

[Compound (A)]
The first functional group (a1) of the compound (A) according to this embodiment is preferably an amino group (NH ₂ —), and more preferably an NH ₂ —CH ₂ — amino group.

The second functional group (a2) of the compound (A) according to this embodiment is preferably an amino group (NH ₂ —) or a phosphonooxy group ((OH) ₂ P(═O)—O—) group, and the second functional group (a2) is more preferably an amino group (NH ₂ —).

When the first functional group (a1) of the compound (A) according to this embodiment is an amino group (NH ₂ -) and the second functional group (a2) is also an amino group (NH ₂ -), the compound (A) according to this embodiment may be the multifunctional amine according to the first embodiment described above. Similarly to the multifunctional amine described above, when the compound (A) according to this embodiment is a multifunctional amine, it is preferably a diamine compound. Specific examples of the diamine compound according to this embodiment may also be the same as the specific examples described in the first embodiment.

When the first functional group (a1) of the compound (A) according to this embodiment is an amino group (NH ₂ -) and the second functional group (a2) is also an amino group (NH2-), it is more preferable that the amino group of the second functional group (a2) is an amino group in the structure represented by the following formula (1).

（式（１）中、Ｇがカルボン酸基又はその塩を表す。）
Ｇがカルボン酸基の塩の場合、当該塩としては、ナトリウム塩、カリウム塩等のアルカリ金属塩；カルシウム塩、マグネシウム塩等のアルカリ土類金属塩；アミン塩等の有機塩基塩、リシン塩、アルギニン塩等の塩基性アミノ酸塩等が挙げられる。中でも好ましい塩はアルカリ金属塩であり、より好ましい塩としてはナトリウム塩、カリウム塩が挙げられる。

(In formula (1), G represents a carboxylic acid group or a salt thereof.)
When G is a salt of a carboxylic acid group, examples of the salt include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as calcium salts and magnesium salts, organic base salts such as amine salts, basic amino acid salts such as lysine salts and arginine salts, etc. Among these, preferred salts are alkali metal salts, and more preferred salts include sodium salts and potassium salts.

When the first functional group (a1) of the compound (A) according to this embodiment is an amino group (NH ₂ -), and the second functional group (a2) of the compound (A) according to this embodiment is also an amino group (NH ₂ -), it is preferable that the amino group of the second functional group of the compound (A) has a lower reactivity with polysuccinimide (PSI) than the amino group of the first functional group. That is, examples of such a compound (A) include diamines having different terminal structures containing the respective amino groups. For example, asymmetric diamines can be mentioned.

An example of the compound (A) according to this embodiment in which the first functional group (a1) is an amino group of NH ₂ —CH ₂ — and the second functional group (a2) is an amino group in the structure represented by the above formula (1) is the compound represented by the following formula (5).

(where n = 1 to 10, preferably 2 to 8, more preferably 3 to 5)

Compound (A) according to this embodiment may be a salt of the carboxylic acid group of the compound represented by formula (5) above. In this case, examples of the salt include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; organic base salts such as amine salts; and basic amino acid salts such as lysine salts and arginine salts. Among these, alkali metal salts are preferred, and sodium salts and potassium salts are more preferred.

When the first functional group (a1) of the compound (A) according to this embodiment is an amino group and the second functional group (a2) is also an amino group, an example of the compound (A) in which the first functional group (a1) is an amino group of NH ₂ —CH ₂ — and the amino group of the second functional group (a2) is an amino group in the structure represented by the above formula (1) is the compound represented by the following formula (6).

(In the formula, L represents a divalent linking group, preferably one or more divalent linking groups such as -CH ₂ - and C=O, and more preferably -CH ₂ -. n represents an integer of 1 to 10, preferably 2 to 8, and more preferably 3 to 5.)

Compound (A) according to this embodiment may be a salt of the carboxylic acid group of the compound represented by formula (6) above. In this case, examples of the salt include alkali metal salts such as sodium salt and potassium salt; alkaline earth metal salts such as calcium salt and magnesium salt; organic base salts such as amine salt; basic amino acid salts such as lysine salt and arginine salt; etc. Among these, alkali metal salts are preferred, and sodium salt and potassium salt are more preferred.

In the compound (A) according to this embodiment, when the first functional group (a1) is an amino group and the second functional group (a2) is a phosphonooxy group ((OH) ₂ P(═O)—O—) group, examples of the compound include the compound represented by the following formula (7).

(In the formula, L represents a divalent linking group, preferably one or more divalent linking groups such as -CH ₂ - and -(C=O)-, and more preferably -CH ₂ -. n represents an integer of 1 to 10, preferably 2 to 8, and more preferably 3 to 5.)

Compound (A) according to this embodiment may be a salt of the phosphonooxy group of the compound represented by formula (7) above. In this case, examples of the salt include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; organic base salts such as amine salts; and basic amino acid salts such as lysine salts and arginine salts. Among these, alkali metal salts are preferred, and sodium salts and potassium salts are more preferred.

Examples of the compound (A) according to this embodiment include lysine, ornithine, and arginine.
In addition, when the compound (A) according to the present embodiment contains an amino group, an acid salt of the compound (A) may be used as a raw material. Examples of the acid salt of the compound (A) include hydrochlorides such as lysine hydrochloride, ornithine hydrochloride, and arginine hydrochloride, and similar sulfates.

Furthermore, a dipeptide can be used as the compound (A) according to this embodiment. Examples of the dipeptide include dipeptides having a basic amino acid residue at the C-terminus, such as glycine-lysine (isopeptide bond), alanine-lysine (isopeptide bond), glycine-ornithine (isopeptide bond), and alanine-ornithine (isopeptide bond); dipeptides having a basic amino acid residue at the N-terminus, such as lysine-glycine, lysine-alanine, ornithine-glycine, and ornithine-alanine.
Among them, for example, glycine-lysine is a dipeptide represented by the following formula (8), and lysine-glycine is a dipeptide represented by the following formula (9).

[Method for producing modified polyaspartic acid or its salt]
The method for producing the modified polyaspartic acid or a salt thereof according to the present embodiment includes a ring-opening reaction method of polysuccinimide (PSI) by reacting the compound having an amino group and a carboxy group with the compound (A: a1-A1-a2). By reacting polysuccinimide (PSI) with the compound having an amino group and a carboxy group and the compound (A) (a1-A1-a2), the imide ring of polysuccinimide (PSI) is opened.

The compound having an amino group and a carboxy group is preferably an amino acid ester. When an amino acid ester is used as the compound having an amino group and a carboxy group, the modified polyaspartic acid or its salt according to this embodiment is an amino acid ester modified polyaspartic acid or its salt (sometimes referred to as an "amino acid ester modified product"). A method for producing the amino acid ester modified product according to this embodiment includes a ring-opening reaction method of polysuccinimide (PSI) by reacting the amino acid ester with the compound (A) (a1-A1-a2). By reacting polysuccinimide (PSI) with the amino acid ester and the compound (A) (a1-A1-a2), the imide ring of polysuccinimide (PSI) is opened.

"Organic solvent"
In the method for producing a modified polyaspartic acid or a salt thereof according to the present embodiment, the organic solvent is not particularly limited as long as it substantially dissolves the following compounds and does not substantially inhibit the progress of the reaction. The above compounds include polysuccinimide (PSI), a compound having an amino group and a carboxy group, and the above-mentioned compound (A).

Specific examples of the organic solvent include aprotic polar organic solvents such as dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), dimethylimidazolidinone (DMI), dimethylsulfoxide (DMSO), and sulfolane, which can be used alone or in combination.

"Amount of compound having amino and carboxy groups used"
The amount of the compound having an amino group and a carboxy group according to the present embodiment is not particularly limited as long as it is substantially soluble in an organic solvent and/or does not substantially inhibit the progress of the reaction. The amount of the compound is generally 0.1 to 10 times the equivalent of the monomer unit of polysuccinimide (PSI), and preferably 0.1 to 1.0 times the equivalent.

"Basic catalyst"
In the method for producing a modified polyaspartic acid or a salt thereof according to this embodiment, the basic catalyst optionally used may be the same as that described in the method for producing a modified polyaspartic acid or a salt thereof according to the first embodiment.

"Amount of basic catalyst used"
In the method for producing a modified polyaspartic acid or a salt thereof according to this embodiment, the amount of the basic catalyst used is the same as that described in the method for producing a modified polyaspartic acid or a salt thereof according to the first embodiment.

"Reaction temperature"
In the method for producing a modified polyaspartic acid or a salt thereof according to this embodiment, the reaction temperature may be the same as that described in the method for producing a modified polyaspartic acid or a salt thereof according to the first embodiment.

"Concentration of reaction system"
The concentration of the reaction system employed in the method for producing a modified polyaspartic acid or a salt thereof according to the present embodiment is not particularly limited as long as the progress of the reaction can be substantially maintained. The concentration of the reaction system is selected based on the concentration of polysuccinimide (PSI), and generally, the polysuccinimide (PSI) concentration is selected from a concentration range of 1 to 50% by weight. The concentration of the reaction system may be selected from a polysuccinimide (PSI) concentration range of 1 to 50% by weight, and an optimum concentration for the compound having an amino group and a carboxy group to be used. The concentration of the compound (A) to be used may be appropriately selected depending on the degree of crosslinking to be described later.

<Method for isolating modified polyaspartic acid or its salt>
The method for isolating the produced polymer from the reaction solution after completion of the reaction, which is employed in the method for producing a modified polyaspartic acid or a salt thereof according to this embodiment, may be the same as that described in the method for producing a modified polyaspartic acid or a salt thereof according to the first embodiment.

In the method for producing a modified polyaspartic acid or a salt thereof according to this embodiment, the obtained modified polyaspartic acid or a salt thereof may not be isolated, and the mixed liquid after the reaction may be used as is to participate in the crosslinking reaction described below. Also, if necessary, only a portion of the unreacted raw materials other than the solvent may be removed to participate in the crosslinking reaction described below. Also, the concentration may be adjusted by increasing or decreasing the amount of the solvent in the mixed liquid.

<Structure of Crosslinked Body>
The crosslinked product of the modified polyaspartic acid or its salt according to the present embodiment (sometimes referred to as the crosslinked product of the present embodiment) is a reaction product of the modified polyaspartic acid or its salt according to the present embodiment and a multifunctional epoxy (B). The modified polyaspartic acid or its salt contains a PSI-a1(A) bond formed by an addition reaction between the first functional group (a1) and polysuccinimide (PSI). The crosslinked product according to the present embodiment contains a B-a2(A) bond formed by a reaction between the second functional group (a2) and a multifunctional epoxy (B). The crosslinked product contains a crosslinked structure (PABAP) represented by PSI-a1-A1-a2-B-a2-A1-a1-PSI.

[Multifunctional Epoxy (B)]
Examples of the polyfunctional epoxy compound according to the present embodiment include polyglycidyl ethers of (C2-C6) alkane polyols and poly(alkylene glycols), such as ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, and butanediol diglycidyl ether; sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, erythritol polyglycidyl ether, and the like. Examples of such polyglycidyl ethers include (C4-C8) diepoxyalkanes and diepoxyalalkanes such as tall polyglycidyl ether, trimethylolethane polyglycidyl ether, trimethylolpropane polyglycidyl ether, 1,2,3,4-diepoxybutane, 1,2,4,5-diepoxypentane, 1,2,5,6-diepoxyhexane, 1,2,7,8-diepoxyoctane, 1,4- and 1,3-divinylbenzene epoxide; and (C6-C15) polyphenol polyglycidyl ethers such as 4,4'-isopropylidenediphenol diglycidyl ether (bisphenol A diglycidyl ether) and hydroquinone diglycidyl ether.
Further examples include polyfunctional epoxy compounds EX-810, EX-861, EX-313, EX-614B, and EX-512 manufactured by Nagase ChemteX.

(Method for producing crosslinked body)
The method for producing a crosslinked product of a modified polyaspartic acid or its salt according to the present embodiment (hereinafter sometimes referred to as the "method for producing a crosslinked product according to the present embodiment") includes the steps of first hydrolyzing the modified polyaspartic acid or its salt according to the present embodiment to obtain the modified polyaspartic acid or its salt after hydrolysis (sometimes referred to as the "hydrolyzed modified product"), and then reacting the hydrolyzed modified product with a multifunctional epoxy (B) in water or a water-containing solvent to produce a crosslinked product. The modified polyaspartic acid or its salt and the multifunctional epoxy (B) are the same as those described for the crosslinked product according to the present embodiment, and preferred examples thereof are also the same.

When an amino acid ester is used as the compound having an amino group and a carboxy group in producing the modified polyaspartic acid or its salt according to this embodiment, the modified polyaspartic acid or its salt according to this embodiment is an amino acid ester modified polyaspartic acid or its salt (sometimes referred to as an "amino acid ester modified product"). In the method for producing a crosslinked product of the modified polyaspartic acid or its salt according to this embodiment, it is preferable to use the amino acid ester modified product. In the method for producing a crosslinked product of the modified polyaspartic acid or its salt according to this embodiment, when the amino acid ester modified product is used, the method for producing the crosslinked product according to this embodiment includes a step of first hydrolyzing the amino acid ester modified product to obtain an amino acid modified product, and a step of reacting the amino acid modified product with a multifunctional epoxy (B) in water or a water-containing solvent to produce a crosslinked product.

The method for producing a crosslinked product of the modified polyaspartic acid or its salt according to the present embodiment (hereinafter sometimes referred to as the method for producing the crosslinked product according to the present embodiment) may include a step of reacting the modified polyaspartic acid or its salt according to the present embodiment with a multifunctional epoxy (B) in water or a water-containing solvent to produce a crosslinked product.

In the method for producing the crosslinked body of this embodiment, the modified polyaspartic acid or its salt may be produced first, and then the modified polyaspartic acid or its salt may be reacted with the multifunctional epoxy (B) to produce the crosslinked body. The reaction for producing the modified polyaspartic acid or its salt and the crosslinking reaction may be carried out simultaneously. For example, the following methods (i) to (iii) may be mentioned.

(i) A production method comprising the steps of reacting polysuccinimide (PSI), the compound having an amino group and a carboxy group, and a compound (A) to obtain the modified polyaspartic acid or a salt thereof (P1), and reacting the reaction product (P1) obtained in the above step with a polyfunctional epoxy compound (hereinafter, referred to as method (i)).
(ii) A production method in which polysuccinimide (PSI), the compound having an amino group and a carboxy group, and compound (A) are first mixed and reacted with each other, and then a polyfunctional epoxy compound is added at a constant rate (hereinafter, method (ii)).
(iii) A production method in which polysuccinimide (PSI), the compound having an amino group and a carboxy group, compound (A), and a polyfunctional epoxy compound are mixed and then reacted (hereinafter, referred to as method (iii)).
From the viewpoint of ease of controlling the structure of the resulting modified crosslinked polyaspartic acid, method (i) or method (ii) is preferred, and method (i) is more preferred.

The manufacturing method of this embodiment will be described in detail below by taking the above method (i) as an example.
In the method (i), the step of obtaining the reactant (P1) preferably includes a step of hydrolyzing the modified polyaspartic acid or its salt obtained by the above-mentioned method for producing a modified polyaspartic acid or its salt of the present embodiment to obtain a modified polyaspartic acid or its salt after hydrolysis. The modified polyaspartic acid or its salt after hydrolysis can be converted into a polyfunctional epoxy compound as the reactant (P1) in a subsequent step.
In addition, when the modified polyaspartic acid or its salt obtained by the above-mentioned method for producing a modified polyaspartic acid or its salt of the present embodiment is the amino acid ester modified product, the step of obtaining the reactant (P1) preferably includes a step of hydrolyzing the amino acid ester modified product to obtain the amino acid modified product. The amino acid modified product is preferably converted into a polyfunctional epoxy compound as the reactant (P1) in a subsequent step.

In the method (i), the step of obtaining the reactant (P1) may be the following method. It is preferable to dissolve the compound having an amino group and a carboxy group and the compound (A) in water first. For example, 0.2 to 2.0 parts by mass of the compound having an amino group and a carboxy group are preferable for 1 part by mass of the compound (A), and 0.5 to 1.5 parts by mass of the compound having an amino group and a carboxy group are more preferable. For 1 part by mass of the compound (A), 5 to 50 parts by mass of water are preferable, and 7 to 15 parts by mass of water are more preferable. Polysuccinimide (PSI) is mixed into the aqueous solution. The compounding ratio is preferably 0.5 to 20 parts by mass of the compound (A) for 10 parts by mass of polysuccinimide (PSI), more preferably 1 to 15 parts by mass, and even more preferably 1.5 to 10 parts by mass. For 10 parts by mass of polysuccinimide (PSI), the mass parts of the compound having an amino group and a carboxy group are preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 1.5 to 10 parts by mass.

In the mixture after blending, an organic or inorganic base compound such as NaOH or an amine is added to adjust the pH of the aqueous solution to preferably 8 to 13, more preferably 9 to 12.
In the obtained product, the ratio of units to which compound (A) is added is preferably 2 to 50%, more preferably 5 to 35%, and even more preferably 8 to 25% of all units. The ratio of units to which compound (A) is added is determined from the ratio (Ib/(Ia+Ib+Ic)) of the integral value Ia of the peak derived from the protons of -CH ₂ - in the polyaspartic acid main chain skeleton, the integral value Ib of the peak derived from the protons of -CH ₂ - in compound (A), and the integral value Ic of the peak derived from the protons of -CH ₂ - in the compound having an amino group and a carboxy group, in proton NMR.
In the obtained product, the ratio of the units to which the compound having an amino group and a carboxy group is added to the total units is preferably 50 to 99, more preferably 60 to 95, and even more preferably 70 to 90. The ratio of the units to which the compound having an amino group and a carboxy group is added is determined from the ratio Ic/(Ia+Ib+Ic) of the integral value Ia of the peak derived from the protons of -CH ₂ - in the polyaspartic acid main chain skeleton, the integral value Ib of the peak derived from the protons of -CH ₂ - in compound (A), and the integral value Ic of the peak derived from the protons of -CH ₂ - in the compound having an amino group and a carboxy group, in proton NMR.

In the method (i), in the step of reacting the reactant (P1) with a polyfunctional epoxy compound, the amount of the polyfunctional epoxy compound is preferably 0.5 to 10 parts by mass, and more preferably 1.0 to 5.0 parts by mass, per 100 parts by mass of the reactant (P1).
As the reactant (P1), a solid reactant (P1) obtained by isolating the reactant (P1) from the reaction liquid obtained in the step of producing the reactant (P1) can be used. In this case, it is preferable to prepare an aqueous solution of the reactant (P1) before mixing with the polyfunctional epoxy compound.
As the reactant (P1), a polyfunctional epoxy compound can be blended as it is in a solution state from the reaction liquid obtained in the reactant (P1) production step without isolating the reactant (P1).

The reaction temperature between the reactant (P1) and the polyfunctional epoxy compound can be 30°C to 100°C. It is preferably 40°C to 80°C, and more preferably 50°C to 70°C. The reaction time, for example, when it is 60°C, can be 10 minutes to 600 minutes. It is more preferably 20 minutes to 300 minutes.

To isolate the crosslinked product of the modified polyaspartic acid or its salt of this embodiment produced by the reaction, known isolation procedures such as recrystallization, reprecipitation, filtration, and concentration can be used.

The size (average particle size) of the crosslinked body in this embodiment is not particularly limited, but for example, in applications as thickening compositions, it is preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less. By setting the average particle size to 150 μm or less, advantages such as excellent transparency of the thickening solution and smooth feel can be obtained.

[Degree of cross-linking]
The amount of the compound having an amino group and a carboxy group, the compound (A), and the polyfunctional epoxy (B) used with respect to the polysuccinimide (PSI) according to this embodiment may be appropriately selected according to the desired degree of crosslinking. For example, in the case of an example of the manufacturing method using the above-mentioned method (i), the compounding ratio of the polysuccinimide (PSI), the compound having an amino group and a carboxy group, and the compound (A) is adjusted within the above-mentioned range, and further, the polyfunctional epoxy (B) is adjusted to control the degree of crosslinking. Depending on the application of the polyaspartic acid crosslinked body produced in the end, for example, in applications requiring high water absorption and water retention, the ratio of the unit to which the compound (A) is added in the polysuccinimide (PSI) (addition rate) is preferably 1 to 30% relative to the total units, more preferably 2 to 25%, and even more preferably 3 to 20%. The addition rate can be measured by NMR.

(Thickening composition)
The thickening composition of one embodiment of the present invention (hereinafter, this embodiment) preferably contains one or more types selected from the group consisting of the crosslinked body of the first embodiment and the crosslinked body of the second embodiment (sometimes referred to as the crosslinked body of this embodiment).

<Water>
The thickening composition of the present embodiment may not contain water. For example, the thickening composition of the present embodiment obtained by the method described below may be further subjected to a drying treatment or the like to obtain a powdery thickening composition. The thickening composition of the present embodiment may consist only of the crosslinked body according to the present embodiment. That is, it may not substantially contain other components other than the crosslinked body according to the present embodiment. The meaning of "substantially not containing other components" is, for example, that the content of the crosslinked body in the thickening composition is 95.0 to 100% by mass, preferably 98.0 to 100% by mass, more preferably 99.0 to 100% by mass, and even more preferably 100%.

The thickening composition of the present embodiment may contain water. For example, the thickening composition of the present embodiment obtained by the above-mentioned method may be used as it is without dehydration treatment. Examples of the water of the present embodiment include ion-exchanged water.
Furthermore, when the thickening composition contains water, the "thickening composition containing water" is sometimes referred to as a "thickening solution."
The content of the crosslinked body is preferably 0.05 to 10 mass%, more preferably 0.1 to 7.0 mass%, further preferably 0.3 to 5.0 mass%, and particularly preferably 0.5 to 3.0 mass%, relative to 100 mass% of the total thickening composition (thickening solution) containing water.

When the thickening composition contains water, the pH value is preferably in the range of 4.5 to 10.0, and more preferably in the range of 5.0 to 9.0.
The method for adjusting the pH value is not particularly limited, and may be a method using an acidic or basic substance. Specific examples of acids include organic acids such as citric acid. Specific examples of bases include organic basic compounds such as ammonia and inorganic basic compounds such as sodium hydroxide.

<Other ingredients>
The thickening composition of the present embodiment may further contain other ingredients, such as cosmetic active ingredients, and additives commonly used in cosmetics, such as surfactants, stabilizers, and moisturizers.

<Method of preparing thickening composition>
An example of a method for preparing the thickening composition of the present embodiment is to weigh out a predetermined amount of the crosslinked body according to the present embodiment described above, and, if necessary, add a predetermined amount of water or other components, and stir to prepare the thickening composition.
When the thickening composition of the present embodiment contains water, an aqueous dispersion of the crosslinked body of the present embodiment may be prepared first, and then mixed with other components, if necessary.
When the thickening composition of the present embodiment does not contain water, a predetermined amount of the solid crosslinked body may be weighed out and mixed with other solid components if necessary. Alternatively, a dispersion containing the crosslinked body and water may be prepared first, and if necessary, the mixture may be mixed with other components to prepare a mixed liquid, which may then be dried before preparation.

(Cosmetic composition)
The cosmetic composition according to this embodiment contains the thickening composition and a cosmetic active ingredient. Examples of the cosmetic active ingredient include higher alcohols, lower alcohols, polyhydric alcohols, pH adjusters, surfactants, sequestering agents, antioxidants, physical and chemical sunscreens, vitamins, skin protectants, oils and fats, hydrocarbon oils, moisturizers, antiperspirants, detergents, fragrances, cosmetic colorants, antibacterial agents, germicides, texture improvers and foam stabilizers, other thickeners, etc. The cosmetic composition according to this embodiment may further contain water.
When the cosmetic composition according to this embodiment contains water, the content of the crosslinked material according to this embodiment is preferably 0.05 to 10 mass%, more preferably 0.1 to 7.0 mass%, even more preferably 0.3 to 5.0 mass%, and particularly preferably 0.5 to 3.0 mass%, relative to 100 mass% of the total cosmetic composition.

(Other uses of crosslinked bodies of modified polyaspartic acid or its salts)
One or more types selected from the group consisting of the crosslinked body of the first embodiment and the crosslinked body of the second embodiment (sometimes referred to as the crosslinked body of this embodiment) can be used as a water-absorbent composition constituting an absorbent body of an absorbent article such as a diaper, sanitary goods, etc. When used as the water-absorbent composition, the crosslinked body of this embodiment has a size (average particle size) of preferably 1 to 5000 μm, more preferably 10 to 1000 μm, and even more preferably 100 to 800 μm.
The crosslinked material according to the present embodiment can be used as a thickening composition. When used as the water-absorbing composition, the crosslinked material according to the present embodiment has a size (average particle size) of preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less.

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.
(material)
Aspartic acid: YIXING QIANCHENG BIO-ENGINEERING, purity 99.97% Phosphoric acid: Kanto Chemical, purity 85% Dimethylformamide: Kanto Chemical, purity 99.5% Hexamethylenediamine (HDA): Kanto Chemical, purity 98% Ethanol: Kanto Chemical, purity 99.5% Isopropanol: Kanto Chemical, purity 99.7% Methanol: Kanto Chemical, purity 99.8% Sodium hydroxide: Kanto Chemical, purity 48% β-Alanine ethyl hydrochloride: Tokyo Chemical Industry, purity 98% L-Lysine methyl ester dihydrochloride: Tokyo Chemical Industry, purity 98% Triethylamine: Kanto Chemical, purity 99% Multifunctional epoxy compound: Nagase ChemteX, EX-810

(Synthesis Example 1)
<Synthesis of polysuccinimide (PSI)>
160 parts of aspartic acid and 83 parts of 85% phosphoric acid were mixed in a mortar, transferred to a tray, and reacted for 6 hours at 190° C. and 1.3 kPa. The reaction mixture was pulverized, washed with distilled water until the filtrate became neutral, and vacuum dried at 80° C. to obtain 115 parts of polysuccinimide (PSI) having a weight average molecular weight of 70,000.

<Measurement of weight average molecular weight of polysuccinimide (PSI)>
The weight average molecular weight of polysuccinimide (PSI) was determined as a polystyrene equivalent value by the GPC method (differential refractometer). For the measurement, a G1000HHR column, a G4000HHR column, and a GMHHR-H column (TSKgel (registered trademark), Tosoh Corporation) were used. Dimethylformamide containing 10 mM lithium bromide was used as the eluent.

(Synthesis Example 2)
<Synthesis of β-alanine ethyl ester/L-lysine methyl ester modified compound>
10 parts of polysuccinimide (PSI) obtained in Synthesis Example 1 was mixed with 40 parts of dimethylformamide and dissolved by stirring at 60 ° C. for 5 hours. While heating the solution to 40 ° C., 12.7 parts of β-alanine ethyl ester hydrochloride and 10 parts of triethylamine were added, and the mixture was reacted for 8 hours while maintaining the temperature at 40 ° C. 14.4 parts of L-lysine methyl ester dihydrochloride and 13.1 parts of triethylamine were added, and the mixture was reacted for 8 hours while maintaining the temperature at 40 ° C. After filtering out the triethylamine hydrochloride in the reaction solution, the mixture was poured into 1300 parts of isopropanol, and the precipitate was collected. The precipitate was washed with 600 parts of isopropanol for 1 hour, and the precipitate collected by filtering was vacuum dried at 60 ° C. to obtain 14.1 parts of β-alanine ethyl ester/L-lysine methyl ester modified product.

(Synthesis Example 3)
(Synthesis of β-alanine sodium/L-lysine sodium modified product)
10 parts of the β-alanine ethyl ester/L-lysine methyl ester modified product were dispersed in 15 parts of ion-exchanged water. 9.3 parts of 20% sodium hydroxide were added dropwise over 2 hours, and the mixture was allowed to react for 15 hours. The mixture was then poured into 600 parts of isopropanol, and the precipitate was collected by filtration, and then washed with 350 parts of isopropanol. The precipitate collected by filtration was vacuum-dried at 60° C. to obtain 10.8 parts of the β-alanine sodium/lysine sodium modified product.

Example 1
<Synthesis of β-alanine ethyl ester modified diamine crosslinked product>
5.0 parts of polysuccinimide (PSI) obtained in Synthesis Example 1 was mixed with 20 parts of dimethylformamide and dissolved by stirring at 60 ° C for 5 hours. While heating the solution to 40 ° C, 7.1 parts of β-alanine ethyl ester hydrochloride and 5.6 parts of triethylamine were added, and the mixture was reacted for 8 hours while maintaining the temperature at 40 ° C. After filtering out the triethylamine hydrochloride in the reaction solution, the mixture was heated to 40 ° C again. A solution of 0.78 parts of hexamethylenediamine and 0.78 parts of dimethylformamide was dropped, and the mixture was reacted for 6 hours while maintaining the temperature at 40 ° C. The obtained gel was finely crushed, added to 350 parts of ethyl acetate, and washed for 1 hour. After filtering, the mixture was further washed with 350 parts of ethyl acetate for 1 hour, and vacuum dried at 60 ° C. to obtain 8.6 parts of β-alanine ethyl ester modified diamine crosslinked body.

<Synthesis of β-alanine-modified diamine crosslinked product>
4.5 parts of the β-alanine ethyl ester modified crosslinked product obtained above were dispersed in 21 parts of ethanol and 10 parts of ion-exchanged water. After adding 1.2 parts of 48% sodium hydroxide, the mixture was allowed to react for 15 hours. While measuring the pH, 10% methanesulfonic acid aqueous solution was added dropwise until the pH reached 5.0. The mixture was poured into 650 parts of ethanol, and the precipitate was collected by filtration, and then washed with 350 parts of ethanol. The precipitate collected by filtration was vacuum-dried at 60°C to obtain 3.7 parts of β-alanine sodium modified crosslinked product. The dried product was pulverized in a mortar and passed through a stainless steel sieve (JIS Z-8801) to a mesh size of 20 to 40 μm to obtain the β-alanine modified diamine crosslinked product of the present invention.

<Preparation of thickening solution and viscosity evaluation>
1.5 parts of the obtained crosslinked product and 98.5 parts of ion-exchanged water were mixed, and then sodium hydroxide was added to adjust the pH to 5.0, thereby obtaining a thickening composition containing water (thickening solution L1) of this example.
After measuring the shear viscosity with a rotational rheometer MCR102, the thickened solution L1 was stored in a thermostatic chamber at 40° C. If the viscosity measured after storage for 7 days retained 60% or more of the initial viscosity, it was evaluated as ◯, and if it was less than 60%, it was evaluated as ×.

Example 2
<Synthesis of β-alanine/L-lysine modified epoxy crosslinked material>
2.0 parts of the β-alanine sodium/L-lysine sodium modified product obtained in Synthesis Example 3 was dissolved in 3.0 parts of ion-exchanged water. 0.16 parts of a 20% aqueous solution of a multifunctional epoxy compound EX-810 (manufactured by Nagase Chemtex) was mixed and reacted at 60°C for 2 hours. The obtained gel composition was vacuum-dried at 60°C. It was then poured into a mixture of 50 parts of ethanol and 20 parts of ion-exchanged water, and a 20% aqueous solution of methanesulfonic acid was added dropwise until the pH reached 5.0. It was poured into 350 parts of ethanol, and the precipitate was collected by filtration, and then washed with 200 parts of ethanol. 2.0 parts of the β-alanine/L-lysine modified epoxy crosslinked product was obtained by vacuum drying at 60°C. The dried product was pulverized in a mortar and passed through a stainless steel sieve (JIS Z-8801) to a mesh size of 20 to 40 μm to obtain a polymer of the present invention.

<Preparation of thickening solution and viscosity evaluation>
1.5 parts of the obtained crosslinked product and 98.5 parts of ion-exchanged water were mixed, and then sodium hydroxide was added to adjust the pH to 5.0, thereby obtaining a thickening composition containing water (thickening solution L2) of this example.
After measuring the shear viscosity with a rotational rheometer MCR102, the thickened solution L2 was stored in a thermostatic chamber at 40° C. If the viscosity measured after storage for 7 days retained 60% or more of the initial viscosity, it was evaluated as ◯, and if it was less than 60%, it was evaluated as ×.

(Comparative Example 1)
<Synthesis of crosslinked polyaspartic acid diamine>
10 parts of polysuccinimide (PSI) was mixed with 40 parts of dimethylformamide and stirred at 60°C for 5 hours to dissolve. While heating the solution to 40°C, a solution of 0.36 parts of hexamethylenediamine and 3.23 parts of dimethylformamide was dropped, and the mixture was reacted for 8 hours while maintaining the temperature at 40°C. The obtained gel was added to 500 parts of ion-exchanged water and crushed with a mixer. After filtering, the mixture was washed with 150 parts of methanol for 1 hour and vacuum dried at 60°C to obtain 10.1 parts of crosslinked polysuccinimide (PSI). 3.0 parts of the obtained crosslinked polysuccinimide (PSI) was dispersed in 67 parts of methanol and 33 parts of ion-exchanged water. A solution of 8.0 parts of 48% sodium hydroxide and 8.0 parts of methanol was divided into 10 portions and added every 30 minutes, and then reacted for 15 hours. The reaction solution was added to 1300 parts of methanol, and the precipitate was collected by filtering and washed with 350 parts of methanol. The mixture was dried in a vacuum at 60° C. The dried product was pulverized in a mortar and passed through a stainless steel sieve (JIS Z-8801) to a mesh size of 20 to 40 μm, to obtain 12 parts of a crosslinked polyaspartic acid diamine product.

<Preparation of thickening solution and viscosity evaluation>
1.5 parts of the obtained crosslinked product and 98.5 parts of ion-exchanged water were mixed, and then sodium hydroxide was added to adjust the pH to 5.0, to obtain a thickening composition containing water (thickening solution cL1) of this comparative example.
After measuring the shear viscosity with a rotational rheometer MCR102, the thickened solution cL1 was stored in a thermostatic chamber at 40° C. If the viscosity measured after storage for 7 days was 60% or more of the initial viscosity, it was evaluated as ◯, and if it was less than 60%, it was evaluated as ×.

(Discussion)
As shown in Table 1, crosslinked polyaspartic acid modified with a compound having an amino group and a carboxy group was observed to have superior viscosity stability compared to crosslinked polyaspartic acid that was not modified. It is said that the main chain of polyaspartic acid is cleaved when the carboxy group in the side chain undergoes a nucleophilic reaction with the amide bond in the main chain. As a result, the viscosity decreases over time. It is presumed that the crosslinked polyaspartic acid modified with a compound having an amino group and a carboxy group has improved viscosity stability by preventing the cleavage of the main chain by moving the carboxy group in the side chain away from the amide bond in the main chain.

Claims (14)

A crosslinked product of a modified polyaspartic acid or a salt thereof,
the modified polyaspartic acid is obtained by adding a compound having an amino group and a carboxy group to a carboxy group of a polyaspartic acid;
the modified polyaspartic acid has a carboxy group derived from the compound having an amino group and a carboxy group in a side chain thereof,
The compound having an amino group and a carboxy group is a compound having only one amino group in the molecule,
A crosslinked product of the modified polyaspartic acid or its salt obtained by crosslinking the modified polyaspartic acid or its salt with a polyfunctional amine as a crosslinking agent. The crosslinked product of modified polyaspartic acid or its salt according to claim 1, wherein the compound having an amino group and a carboxy group is at least one selected from the group consisting of amino acids, carboxylates of amino acids, and amino acid esters. The crosslinked product of the modified polyaspartic acid or its salt according to claim 1, wherein the modified polyaspartic acid is a reaction product of polysuccinimide (PSI) and the compound having an amino group and a carboxy group. The crosslinked product of modified polyaspartic acid or its salt according to claim 1, wherein the polyfunctional amine is at least one selected from the group consisting of aliphatic diamines, alicyclic diamines, and ether-based diamines. The modified polyaspartic acid is
Polysuccinimide (PSI);
The compound having an amino group and a carboxy group,
A compound (A: a1-A1-a2) having a first functional group (a1) and a second functional group (a2),
2. The crosslinked product of the modified polyaspartic acid or its salt according to claim 1, which is a reaction product of: the first functional group (a1) is an amino group (NH ₂ —);
the second functional group (a2) is at least one selected from the group consisting of an amino group (NH ₂ —) and a phosphonooxy group ((OH) ₂ P(═O)—O—);
6. The crosslinked product of a modified polyaspartic acid or a salt thereof according to claim 5, wherein when the second functional group (a2) is an amino group (NH ₂ --), it has lower reactivity with polysuccinimide (PSI) than the first functional group (a1). the first functional group (a1) is an amino group (NH ₂ —);
the second functional group (a2) is an amino group (NH ₂ —);
6. The crosslinked product of a modified polyaspartic acid or a salt thereof according to claim 5, wherein in the compound (A), the amino group of the second functional group (a2) is an amino group in a structure represented by the following formula (1):

(In formula (1), G represents a carboxylic acid group or a salt thereof.) The crosslinked product of modified polyaspartic acid or its salt according to claim 5, which is obtained by crosslinking the modified polyaspartic acid or its salt using a multifunctional epoxy (B) as a crosslinking agent. The crosslinked product of modified polyaspartic acid or its salt according to claim 1, having a degree of crosslinking of 0.5 to 10 mol %. The crosslinked product of modified polyaspartic acid or its salt according to claim 1, wherein the salt of the modified polyaspartic acid is a salt of an organic base or an alkali metal salt. A thickening composition comprising a crosslinked product of the modified polyaspartic acid or its salt according to any one of claims 1, 2, and 4 to 10 . The thickening composition according to claim 11, further comprising water. The thickening composition according to claim 11, wherein the content of the crosslinked body of the modified polyaspartic acid or its salt is 0.05 to 10% by mass relative to 100% by mass of the total of the thickening composition. A thickening composition according to claim 11;
A cosmetic active ingredient,
A cosmetic composition comprising: