JP2002145988A - Cross-linked polymer and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a biodegradable water-absorbing resin an excellent water- absorbing performance in high productivity at a low cost. SOLUTION: This cross-linked polymer obtained by cross-linking repeating units is represented by formula (1a) and/or formula (1b) [R is a pendant group having a carboxyl group; X is NH, N(R') (R' is an alkyl, an aryl or an aralkyl), O or S; (n) is 1 or 2] with a polyvalent epoxy compound; and the method for producing the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a crosslinked polymer obtained by reacting a repeating unit having a specific structure in a polymer with a crosslinking agent, and a method for producing the same.

[0002]

2. Description of the Related Art [Technical background of water-absorbent resin] A water-absorbent resin is a resin that can absorb water of several tens to several thousand times its own weight, such as sanitary products such as sanitary products, disposable diapers, and various other fields. Used in

[Prior art relating to water-absorbing resin] Examples of the water-absorbing resin used in such applications include:
Crosslinked polyacrylic acid partially neutralized product (JP-A-55-8430)
No. 4, U.S. Pat. No. 4,625,001), a partially hydrolyzed starch-acrylonitrile copolymer (JP-A-46-43).
No. 995), a starch-acrylic acid graft copolymer (JP-A-51-125468), and a hydrolyzate of a vinyl acetate-acrylic ester copolymer (JP-A-52-14689).
No.), copolymerized crosslinked product of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid (European patent 00681)
No. 89), a crosslinked polymer of a cationic monomer (US Pat. No. 4,906,717), and a hydrolyzate of a crosslinked isobutylene-maleic anhydride copolymer (US Pat. No. 4,389,513)
No.) etc. are known.

[0004] However, since these water-absorbent resins have substantially no decomposability, disposal after use is a problem. At present, at the time of disposal, these water-absorbent resins are incinerated and landfilled.
It has been pointed out that the method of treating incinerators causes damage to furnace materials due to heat generated during incineration, as well as global warming and acid rain. In addition, in the landfill method, plastics do not have bulky bulk and do not rot, so there is a problem that the ground after the landfill is not stable, etc. In addition, it is difficult to secure land suitable for landfill. It has become. That is, these resins are poorly decomposable and exist substantially semipermanently in water and soil, which is a very troublesome and serious problem in view of environmental conservation in waste treatment.

For example, in the case of a resin used in disposable applications represented by sanitary materials such as disposable diapers and sanitary products, it is costly to recycle the resin, and the resin is incinerated in large quantities. Heavy load. It has also been reported that when a crosslinked polyacrylic acid resin is used as a water retention material for agriculture and horticulture, it forms a complex with polyvalent ions such as Ca ²⁺ in soil and forms an insoluble layer (Matsumoto). Et al., Polymer, Vol. 42, August, 1993
Year).

[0006] Such a layer is said to have low toxicity per se, but has not originally existed in nature at all. The long-term effects of are unknown,
It is desired to use after careful and sufficient confirmation of safety.

[0007] In the case of a nonionic resin, a complex is not formed, but since it is nondegradable, it may accumulate in the soil. Similarly, the accumulation of the resin in the soil may impair the ecosystem. The effects over a long period of time are unknown, and it is desired to use them after careful and sufficient confirmation of safety.

[0008] Further, as these polymer resins, those having high toxicity to the skin and mucous membranes of mammals are used as monomer raw materials. In order to remove these from the product after polymerization, Many considerations have been made. Usually, it is difficult to remove unreacted polymer from the product after polymerization,
In particular, it is expected to be more difficult in industrial-scale production.

[Technical background of water-absorbing resin having biodegradability] In recent years, biodegradable polymers have attracted attention as "earth-friendly materials", and it has been proposed to use this as a water-absorbing resin. .

[0010] Examples of the biodegradable water-absorbing resin used for such applications include cross-linked polyethylene oxide (Japanese Patent Laid-Open No. 6-157795), cross-linked polyvinyl alcohol, cross-linked carboxymethyl cellulose (US (Patent No. 4,650,716), cross-linked alginic acid, cross-linked starch, cross-linked polyamino acid and the like are known. Among these, crosslinked polyethylene oxide and crosslinked polyvinyl alcohol have low water absorption, and are usually used as materials for products requiring high water absorption such as sanitary products, disposable diapers, disposable rags, and paper towels. not appropriate. In addition, since these compounds cannot be biodegraded without special bacteria, biodegradation is extremely slow or not decomposed under general conditions. When these compounds have a large molecular weight, their degradability is further extremely reduced.

Crosslinked saccharides such as crosslinked carboxymethylcellulose, crosslinked alginic acid, and crosslinked starch have many strong hydrogen bonds in their molecules, and therefore have a strong interaction between molecules and between polymers. The molecular chains cannot open widely, and as a result, the water absorption capacity is not high.

[Technical Background of Polyamino Acid-Based Water-Absorbent Resin] The resin obtained by crosslinking a polyamino acid is biodegradable and thus is friendly to the global environment. Since it has been shown that it does not show antigenicity and that degradation products have no toxicity, it is a material that is easy on mammals.

As a specific example of such a method for producing a resin, for example, a method for producing a resin having high water absorbing ability by irradiating poly-γ-glutamic acid with γ rays (Kunioka et al. Vol. 50, No. 10, p. 755 (199
3 years)).

[0014] However, from the industrial point of view, ⁶⁰ Co irradiation equipment used in this technique, in order to shut off radioactivity requires large-scale equipment is required sufficient consideration to the management It is not realistic. Another problem is that polyglutamic acid as a starting material is expensive.

Another specific example of a method for producing such a resin is a method of obtaining a hydrogel by cross-linking an acidic amino acid [Akamatsu et al., US Pat. No. 3,948,863 (Japanese Patent Publication No. 52-41309), Iwazuki et al., JP-A-5-279416].

Still another specific example of the method for producing such a resin is, for example, a method using a crosslinked amino acid resin as a water-absorbing polymer (Sikes et al., Japanese Patent Application Laid-Open Publication No. Hei.
U.S. Pat. Nos. 5,247,068 and 5,284,936, Suzuki et al., JP-A-7-309943.
No. Harada et al., JP-A-8-59820). However, these polymers did not have sufficient performance as a water-absorbing polymer.

On the other hand, methods for producing these crosslinked polyamino acids by reacting polyaspartic acid or aspartic acid with a crosslinking agent by heat are disclosed in JP-A-6-506244 and JP-A-8-504219. ing.

Japanese Patent Application Laid-Open No. 8-59820 discloses a method of obtaining a water-absorbing polymer by mixing an acidic polyamino acid and a basic polyamino acid, and heating and crosslinking the mixture.

However, these methods are characterized in that the cross-linking reaction is carried out in a solid state, so that the cross-linking reaction is difficult to be uniform, so that the physical properties such as water absorption capacity are not sufficient, and the reaction temperature of the cross-linking reaction is low. Since a high temperature is required, there is a problem that decomposition is remarkable and the hue is yellowed or browned.

On the other hand, JP-A-7-224163 discloses a method in which a polysuccinimide is cross-linked with a diamine, and the remaining imide ring is hydrolyzed with an alkali to obtain a water-absorbing resin having a high salt-water-absorbing ability. Similarly, a method of hydrolyzing a partially crosslinked product of an anhydrous polyacidic amino acid with a polyamine with an alkali metal compound is disclosed in JP-A-7-30.
No. 9943.

In these methods, polysuccinimide is uniformly and efficiently cross-linked, and the degree of cross-linking is easily controlled, so that a water-absorbing polymer having high water-absorbing ability can be obtained in a high yield. This is extremely significant in that it is a production method that is optimally used.

However, in order to crosslink polysuccinimide with diamine, since polysuccinimide is dissolved in an aprotic polar solvent, equipment for handling the organic solvent and recovery of the organic solvent are required, and further improvement is desired. Was rare.

The present inventors have disclosed in Japanese Patent Application Laid-Open No. 11-060.
No. 729 and Japanese Patent Application No. 11-24201 disclose a method for producing a crosslinked polyamino acid by reacting a polyamino acid with a crosslinking agent such as a polyepoxy compound, a polyol, a polythiol, a polyisocyanate, a polyaziridine, or a polyvalent metal.

These methods are characterized in that an aprotic polar solvent for dissolving polysuccinimide is not required, and uniform crosslinking can be performed.

Japanese Patent Application Laid-Open No. 10-298282 discloses that
A method for producing a polyamino acid-based water-absorbent resin which is crosslinked with a polyglycidyl compound or an epihalohydrin-modified amino compound in an aqueous solution of a water-soluble polyamino acid having a concentration of 2 to 40% by mass is disclosed.

However, in the production method described in this publication, the number of reaction sites is small, and a high-concentration reaction cannot be performed, so that the crosslinking reaction speed is slow, and the reaction requires a long time, so that the side chain of the polymer main chain , And the epoxy group of the cross-linking agent was cleaved, so that the yield was low, and the performance (water absorption capacity) of the obtained polymer was very low. In addition to the side reactions, as described in this publication, since the polarity of the polymer is high, when the polymer concentration is high, many entanglements between the polymers are present or the polymer chain shrinks. Does not progress well.

That is, in this production method, since the crosslinking reaction does not proceed efficiently, the time required for the reaction is long, polyaspartic acid is hydrolyzed, the main chain is cut, and the resulting water-absorbent resin is obtained. However, there were many problems such as insufficient physical properties, generation of a large amount of water-soluble components, and low yield. In particular, it has been difficult to use it for sanitary articles such as disposable diapers because of its low water absorbing ability.

In this production method, high-molecular-weight polyaspartic acid is required in order for the crosslinking reaction to proceed successfully. For this reason, the number of steps was increased, for example, it was necessary to treat the precursor, polysuccinimide, with dicyclohexylcarbodiimide or the like, and the handling operation was complicated.

Also, in Japanese Patent Application Laid-Open No. Hei 10-330478,
A method for producing a crosslinked polyamino acid is disclosed in which an aqueous solution of a polyamino acid is brought into contact with a diglycidyl compound or a diaziridine compound, water is removed by freeze-drying or the like, and heat treatment is performed. However, freeze-drying has the problems of requiring enormous energy, requiring special equipment, and being uneconomical in terms of equipment.

[0030]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior arts.

That is, one of the problems to be solved by the present invention is to provide a crosslinked polymer having high productivity and biodegradability, and to provide a method by which it can be produced at low cost. It is in.

One of the problems to be solved by the present invention is to further improve the performance of the crosslinked polymer, particularly the performance as a water-absorbing resin such as water retention and water absorption.

[0033]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, have found that a polymer having a specific structure such as a polyaspartic acid derivative having a pendant group containing a carboxyl group in a repeating unit is obtained. The present inventors have found that a crosslinked polymer exhibiting high performance as a water-absorbing resin can be efficiently obtained by crosslinking with a polyvalent epoxy compound, thereby completing the present invention.

That is, in the present invention, a repeating unit represented by the following general formula (1a) and / or a repeating unit represented by the following general formula (1b) in a polymer is crosslinked with a polyvalent epoxy compound. It is a crosslinked polymer reacted.

[0035]

Embedded image

[In the formulas (1a) and (1b), R is a pendant group having a carboxyl group, and X is NH, N
(R ′) (R ′ is an alkyl group, an aryl group or an aralkyl group), O or S, and n is 1 or 2. ].

Further, the present invention provides a method for crosslinking a repeating unit represented by the general formula (1a) and / or a repeating unit represented by the general formula (1b) in a polymer with a polyepoxy compound. A method for producing a crosslinked polymer characterized by reacting.

In the present invention, "carboxyl group"
Means that a salt is formed.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION (1) Structure of crosslinked polymer The crosslinked polymer of the present invention is, for example, a compound represented by the above general formula (1a)
It is obtained by a method of cross-linking between molecules of an acidic polyamino acid derivative having a repeating unit represented by (1b) with a polyvalent epoxy compound as a crosslinking agent.

That is, the molecular structure of the crosslinked polymer of the present invention comprises a polymer basic skeleton composed of a specific acidic polyamino acid derivative and the like, and a crosslinked portion composed of a polyvalent epoxy compound. Hereinafter, these will be described in two parts.

(1-1) Basic polymer skeleton of crosslinked polymer The basic polymer skeleton of the crosslinked polymer of the present invention is represented by the general formula (1)
a) As shown in (1b), it consists of polyaspartic acid and polyglutamic acid among acidic polyamino acids.
In the present invention, irrespective of the mode of bonding, the monomer portion composed of aspartic acid in the polymer is a `` polyaspartic acid residue '', and the monomer portion composed of glutamic acid in the polymer is a `` polyglutamic acid residue ''. Are collectively referred to as “acidic polyamino acid residues”.

These may contain another amino acid as a repeating unit. Specific examples of other amino acid components include, for example, 20 kinds of protein constituent amino acids, L-ornithine, a series of α-amino acids, β-alanine, γ-aminobutyric acid, neutral amino acids, acidic amino acids, and ω- of acidic amino acids. Examples include esters, basic amino acids, N-substituted basic amino acids, amino acids and amino acid derivatives such as aspartic acid-L-phenylalanine dimer (aspartame), and aminosulfonic acids such as L-cysteic acid. The α-amino acid is an optically active form (L
, D-form) or a racemic form. Further, the polymer may be a copolymer containing a repeating unit other than an amino acid.

Examples of the repeating unit of the copolymer include dehydration condensates such as aminocarboxylic acid, aminosulfonic acid, aminophosphonic acid, hydroxycarboxylic acid, mercaptocarboxylic acid, mercaptosulfonic acid, and mercaptophosphonic acid.

Further, polyamines, polyhydric alcohols, polythiols, polycarboxylic acids, polysulfonic acids, polyphosphonic acids, polyhydrazine compounds, polycarbamoyl compounds, polysulfonamide compounds, polyvalent sulfonamide compounds, Phosphonamide compounds, polyepoxy compounds, polyvalent isocyanate compounds, polyvalent isothiocyanate compounds, polyvalent aziridine compounds, polyvalent carbamate compounds, polyvalent carbamic acid compounds, polyvalent oxazoline compounds, polyvalent unsaturated bonds Examples include compounds, dehydration condensates of polyvalent metals, adducts, and substituted products.

When it is a copolymer, it may be a block copolymer or a random copolymer. Further, it may be a graft copolymer. Among them, the degree of polymerization is high, and from the viewpoint of excellent biodegradability, it is preferable to use polyaspartic acid and polyglutamic acid as the basic skeleton, and a homopolymer of polyaspartic acid suitable for industrial production is particularly preferable. preferable.

When the polymer basic skeleton is polyaspartic acid, the amide bond in the main chain is an α bond,
It may be a β bond. For polyglutamic acid,
The amide bond in the main chain may be an α bond or a γ bond.

That is, in the case of polyaspartic acid and a copolymer thereof, an α bond is formed when the amino group of aspartic acid or a copolymer monomer is bonded to a carboxyl group at the α-position of aspartic acid. The case where the amino acid is bonded to the β-carboxyl group of aspartic acid is a β bond.
In the case of polyglutamic acid and its copolymer, an amino group of glutamic acid or a copolymer monomer and an α-carboxyl group bonded to the α-position carboxyl group of glutamic acid are α-bonds, and a γ-position carboxyl group of glutamic acid. Bonding is γ-bonding. Α-bond and β-bond in the case of polyaspartic acid, α-bond and γ in the case of polyglutamic acid
The bonding mode of the bonding is not particularly limited.

(1-2) Side Chain Structure of the Polymer The polymer used in the present invention is a compound represented by the above general formula (1) in which at least a carboxyl group of a polyamino acid residue is further derived.
It has a repeating unit represented by a) and / or a repeating unit represented by the general formula (1b). That is, the side chain of this polymer has a structure having a specific pendant group (R) from the carboxy group of the acidic polyamino acid which is the polymer main chain.

The number of repeating units of the general formulas (1a) and (1b) is generally 40 to the total number of all repeating units constituting the polymer molecule in the polymer basic skeleton.
-100% is preferable, 60-100% is more preferable, and 80-100% is particularly preferable.

In the general formulas (1a) and (1b), the side chain structure is composed of X bonded to the polymer main chain and a pendant group (R) having a specific functional group. The pendant group (R) is a group having a carboxyl group. X is-
It is a bond selected from NH-, -N (R ')-, -O-, and -S-. Here, R ′ is, for example, 1 to 16 carbon atoms.
And an optionally branched alkyl group, aralkyl group and aryl group.

In the case of an aspartic acid residue, the side chain group may be substituted at the α-position or β-position with respect to the amide bond of the polymer main chain, and may be substituted at the β-position. In such a case, it may be substituted at the α-position or at the γ-position.

In the general formulas (1a) and (1b), the pendant group (R) has a carboxyl group as described above, but the other parts mainly consist of carbon and hydrogen. In the present invention, the other portions are conveniently referred to as hydrocarbon groups.
Examples of the hydrocarbon group include, but are not particularly limited to, alkylene, aralkylene, phenylene, and naphthylene groups. These may be linear, branched, or cyclic.

In the hydrocarbon group, a part of the carbon atoms may be substituted by a substituent containing O, N, S, P, B, Si or the like. That is, in the case of a ring structure, a part of carbon atoms may be substituted with O, N, S, P, B, Si, or the like, and O, N, S, P, B, Si, or the like may be introduced. Ether group, ester group, carbonyl group, urea group, thioester group, thiocarbonyl group, sulfone group,
It may be substituted with a substituent such as a sulfonyl group, a sulfonamide group, a secondary amino group, a tertiary amino group, an amide group, a phosphon group, and a phosphonamide group.

The substitution position of the carboxyl group with respect to the hydrocarbon group is not particularly limited. Specific examples of the hydrocarbon group are shown below. In addition, the following example illustrates the part of the hydrocarbon group of a pendant group for convenience. An actual pendant group has a structure in which hydrogen of these hydrocarbon groups is substituted with a specific functional group (carboxyl group).

For example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl,
Octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, alkyl groups such as octadecyl, cyclopropyl, cyclobutyl,
Cycloalkyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, tujanyl, calanyl, bornanyl, norbornanyl, pinanyl, decalinyl, etc. , Cyclohexadienyl group, cycloheptenyl group, cyclooctatetraenyl group, cyclopolyenyl group such as fulbenyl group, benzyl group, phenylethyl group, phenylpropyl group, aralkyl group such as phenylbutyl group, ethoxyethyl group,
Propoxyethyl group, butoxyethyl group, pentyloxyethyl group, hexyloxyethyl group, heptyloxyethyl group, octyloxyethyl group, decyloxyethyl group, undecyloxyethyl group, dodecyloxyethyl group, tridecyloxyethyl group, An alkoxyalkyl group such as a tetradecyloxyethyl group, a pentadecyloxyethyl group, a hexadecyloxyethyl group, a heptyldecyloxyethyl group, an octyldecyloxyethyl group,
Aryloxyalkyl group such as phenoxyethyl group, benzyloxyethyl group, aralkyloxyalkyl group such as tolyloxyethyl group, methylthioethyl group, ethylthioethyl group, propylthioethyl group, butylthioethyl group, pentylthioethyl group, Hexylthioethyl group,
Heptylthioethyl, octylthioethyl, nonylthioethyl, decylthioethyl, undecylthioethyl, dodecylthioethyl, tridecylthioethyl, tetradecylthioethyl, pentadecylthioethyl, hexa Alkylthioalkyl groups such as decylthioethyl group, heptyldecylthioethyl group and octyldecylthioethyl group; arylthioalkyl groups such as phenylthioethyl group and tolylthioethyl group; aralkylthioalkyl groups such as benzylthioethyl group; methyl Oxycarbonylethyl group, ethyloxycarbonylethyl group, propyloxycarbonylethyl group, butyloxycarbonylethyl group, pentyloxycarbonylethyl group, hexyloxycarbonylethyl group, heptyloxycarbonylethyl group, Tyloxycarbonylethyl group, nonyloxycarbonylethyl group, decyloxycarbonylethyl group, undecyloxycarbonylethyl group, dodecyloxycarbonylethyl group, tridecyloxycarbonylethyl group, tetradecyloxycarbonylethyl group, pentadecyloxycarbonylethyl Group, hexadecyloxycarbonylethyl group, heptyldecyloxycarbonylethyl group, alkyloxycarbonylalkyl group such as octyldecyloxycarbonylethyl group,
Methylcarbonyloxyethyl group, ethylcarbonyloxyethyl group, propylcarbonyloxyethyl group, butylcarbonyloxyethyl group, pentylcarbonyloxyethyl group, hexylcarbonyloxyethyl group, heptylcarbonyloxyethyl group, octylcarbonyloxyethyl group, nonylcarbonyl Oxyethyl group, decylcarbonyloxyethyl group, undecylcarbonyloxyethyl group, dodecylcarbonyloxyethyl group,
Tridecylcarbonyloxyethyl group, tetradecylcarbonyloxyethyl group, pentadecylcarbonyloxyethyl group, hexadecylcarbonyloxyethyl group,
Heptyldecylcarbonyloxyethyl group, alkylcarbonyloxyalkyloxy group such as octyldecylcarbonyloxyethyl group, phenyl group, biphenyl group,
Indenyl group, indanyl group, naphthyl group, 1,4-dihydronaphthyl group, tetralinyl group, binaphthyl group, azulenyl group, biphenylenyl group, acenaphthyl group, acenaphthenyl group, fluorenyl group, phenanthrenyl group,
Arthyl groups such as anthracenyl group, fluoranthenyl group, aceanthrenyl group, triphenyl group, pyrenyl group, chrysenyl group, naphthacenyl group, picenyl group, perylenyl group, rubicenyl, coronel group, opalenyl group, oxetanyl group, and thietanyl group , Azetidine group, furanyl group, tetrahydrofuranyl group, dioxolanyl group, thiophenyl group, thiolanyl group, pyrrole group, pyrroline group,
Pyrrolidine group, pyrazole group, pyrazoline group, pyrazolidine group, imidazole group, imidazoline group, imidazolidine group, triazole group, tetrazole group, isoxazole group, oxazole group, furazane group, isothiazole group, thiazole group, pyranyl group, oxanyl group , Dioxanyl group, thianyl group, dithianyl group, pyridinyl group, piperidinyl group, pyridazinyl group, pyrimidinyl group, pyrazinyl group, piperazinyl group, triazinyl group,
Tetrazinyl group, oxazinyl group, morpholinyl group, thiazinyl group, thienothiophenyl group, benzofuranyl group, dihydrobenzofuranyl group, benzothiophenyl group, indole group, indoline group, isoindole group,
Isoindoline group, indolizine group, indazole group,
Benzimidazole group, benzotriazole group, benzoxazole group, benzothiazole group, benzothiazoline group, purine group, chromene group, chroman group, isochromene group, icycloman group, quinoline group, isoquinoline group,
Quinolidine group, cinnoline group, quinazoline group, quinoxaline group, phthalazine group, naphthyridine group, pteridine group, dibenzofuran group, carbazole group, xanthene group, dibenzothiopyran group, acridine group, thianthrene group, phenazine, phenoxazine group, phenoxazine group , Phenothiazine group, phenanthridine group, phenanthroline, benzocinnoline group, heterocycle such as quinuclidine group, benzoquinone group, tropolone group, benzophenone group, benzidine group, naphthoquinone, phenanthrenequinone group, anthrone group, anthraquinone group, benzoanthrone group , Pyrone group, pyrazolone group, hydantoin group, barbituric acid group, phthalide group, coumarin group, isocoumarin group, chromone group, flavone group, xanthine group, uric acid group,
And a cyclic group such as a tropone group.

The counter ion of the carboxyl group of the pendant group (R) is not particularly limited, but may be an alkali metal salt such as sodium, potassium and lithium, ammonium, tetramethylammonium, tetraethylammonium, tetrapropylammonium and tetrabutylammonium. , Tetrapentylammonium, tetrahexylammonium, ethyltrimethylammonium, trimethylpropylammonium, butyltrimethylammonium, pentyltrimethylammonium, hexyltrimethylammonium, cyclohexyltrimethylammonium, benzyltrimethylammonium, triethylpropylammonium, triethylbutylammonium, triethylpentylammonium, triethylammonium Ethylhexyl ammonium , Ammonium salts such as cyclohexyltriethylammonium and benzyltriethylammonium, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triethanolamine, tripropanolamine, tributanolamine, tripentanolamine, tripentanolamine Hexanolamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dicyclohexylamine, dibenzylamine, ethylmethylamine, methylpropylamine, butylmethylamine, methylpentylamine, methylhexylamine, methylamine , Ethylamine, propylamine, butylamine, pentylamine, hexylamine, octane Triethanolamine, decylamine, dodecylamine, amine salt of hexadecyl amine, and the like.

Among these, in order to exhibit high hydrophilicity, it is preferable that the molecular weight of the counter ion is small. Also,
When there is a possibility of touching human skin or the like, it is better that the irritation is low, and alkali metal salts such as sodium, potassium and lithium, and ammonium are preferable.

The repeating unit of the polymer is represented by the general formula (1)
a) A repeating unit of a simple acidic polyaspartic acid or a simple acidic polyglutamic acid containing a pendant group (R) having a carboxyl group but not containing a pendant group (R) as represented by (1b) May be contained in the molecule. Further, a repeating unit containing a pendant group having another hydrophilic substituent may be contained in the molecule instead of the carboxyl group. Examples of other hydrophilic substituents include an acidic group such as a sulfonic acid group, a phosphonic acid group, and a sulfate group, a quaternary ammonium group, an amino group, and a hydroxyl group. In addition, examples of the acidic amino acid residue include a formyl group, a carboxylic acid alkylamide group, a carboxylic acid dialkylamide group, and a thiocarboxylic acid group.

(1-3) Cross-Linked Structure of Cross-Linked Polymer The cross-linked structure of the cross-linked polymer of the present invention comprises a carboxyl group of R in the general formulas (1a) and (1b) of the polymer and a polyvalent epoxy compound. Are formed by a cross-linking reaction with two or more epoxy groups possessed by

When the carboxyl group and the epoxy group react, a structure covalently linked by an ester group is obtained.
That is, the epoxy group becomes an ester on the side attacked by the carboxyl group, and the other carbon has a hydroxyl group. It is not specified on which side of the epoxy group the ester group is formed, and usually both are mixed. That is, the portion other than the carboxy group of the polymer is R,
When a portion other than the epoxy group of the polyvalent epoxy compound is represented by R ′, it is represented as follows.

[0061]

Embedded image Here, by reacting two or more epoxy groups of the polyvalent epoxy compound (crosslinking agent) to bond with the polymer,
A crosslinked structure is formed. However, the crosslinked polymer of the present invention,
Only one epoxy group of the polyepoxy compound may have a portion that has reacted to form a pendant structure.
In addition, the polyvalent epoxy compound may be trifunctional or more and include an unreacted portion. In the structure of the crosslinked portion and the pendant portion in the crosslinked polymer of the present invention, the portion where the epoxy group has reacted or the structure other than the epoxy group will be described in "(2) Method for producing crosslinked polymer" described below.
In the section of the cross-linking agent.

(2) Method for Producing Cross-Linked Polymer The method for producing a cross-linked polymer of the present invention is a method for producing a cross-linked polymer according to the present invention, wherein the repeating unit represented by the general formula (1a) and / or the general formula (1b) A cross-linking reaction of the repeating unit represented by the formula (1) with a polyvalent epoxy compound. Particularly, the crosslinking reaction is preferably performed in water.

The general formula (1) used in the production method of the present invention
a) The polymer having the repeating unit (1b) is typically an acidic polyaspartic acid derivative. The method for producing this polyaspartic acid derivative is not particularly limited,
It is preferable to use a derivative of polysuccinimide suitable for industrial production. Therefore, in the following description, a method for producing polysuccinimide, a method for producing an acidic polyamino acid derivative, and a method for cross-linking a polymer are described in the order of steps.

(2-1) Method for Producing Polysuccinimide A known method can be used for producing polysuccinimide. For example, J. Amer. Chem. Soc,
80, 3361 (1958) discloses a method of heating and condensing aspartic acid as a raw material at 200 ° C. for several hours. In addition, Japanese Patent Publication No.
A method is disclosed in which a high-molecular-weight polysuccinimide is obtained by performing a reaction in the form of a thin film using a rotary evaporator with the use of% phosphoric acid as a catalyst. U.S. Pat. No. 5,057,597 discloses a method of industrially obtaining polysuccinimide by heating and condensing polyaspartic acid with a fluidized bed.

In addition, the method of P. Neri et al. (Jour
nal of Medicinal Chemistr
y, 1973, Vol. 16, No. 8), US Pat. No. 5,142,06.
No. 2, JP-A-7-216084, JP-A-8-2317
No. 10, U.S. Pat. No. 4,363,797, JP-B-52-8
873, JP-A-7-196796, JP-A-8-1
76297, JP-A-9-143265 and the like can be employed.

When a higher molecular weight polysuccinimide is required, the polysuccinimide obtained by each of the above methods and the like can be treated with a condensing agent such as dicyclohexylcarbodiimide.

The raw materials for producing polysuccinimide include:
In addition to aspartic acid, asparagine, aspartic acid ester, aspartic acid diester, maleamide, maleimide, maleic acid and ammonia, ammonium maleate, fumaric acid amide, fumaric acid and ammonia, ammonium fumarate and the like can be used. . These raw materials can be used alone or as a mixture of two or more.

The polysuccinimide may be a polymer containing, in its main chain, a repeating unit derived from a copolymerizable bifunctional or higher-functional monomer such as an amino acid.

Specific examples of amino acids include, for example, the following 20 types of amino acids. Amino acids with non-polar or hydrophobic R groups: alanine, valine, leucine, isoleucine, methionine,
Tryptophan, phenylalanine, proline Polar but uncharged amino acids: glycine, serine,
Threonine, cysteine, tyrosine, asparagine, glutamine Positively charged amino acid having an R group: lysine, histidine, arginine Negatively charged amino acid having an R group: aspartic acid, glutamic acid.

Other specific examples of amino acids include, for example,
L-ornithine, a series of α-amino acids, β-alanine,
Amino acids and amino acid derivatives such as γ-aminobutyric acid, ω-esters of acidic amino acids, N-substituted basic amino acids, aspartic acid-L-phenylalanine dimer (aspartame), aminosulfonic acids such as L-cysteic acid, etc. No. α-amino acids are optically active forms (L-form, D-form)
Body) or a racemic body.

Examples of other copolymerizable difunctional or higher-functional monomers include aminocarboxylic acids, aminosulfonic acids, aminophosphonic acids, hydroxycarboxylic acids, mercaptocarboxylic acids, mercaptosulfonic acids, and mercaptophosphonic acids. And the like. In addition, polyamines, polyhydric alcohols, polythiols, polycarboxylic acids, polysulfonic acids, polyphosphonic acids, polyhydrazine compounds, polycarbamoyl compounds, polysulfonamide compounds, polyphosphonamide compounds , Polyvalent epoxy compounds, polyvalent isocyanate compounds, polyvalent isothiocyanate compounds, polyvalent aziridine compounds, polyvalent carbamate compounds, polyvalent carbamic acid compounds, polyvalent oxazoline compounds, polyvalent reactive unsaturated bond compounds, Valent metals and the like.

When the polysuccinimide is a copolymer, it may be a block copolymer or a random copolymer. Further, it may be a graft copolymer.

(2-2) Method for Producing Acidic Polyamino Acid Derivative In the present invention, the acidic polyamino acid derivative used for the crosslinking reaction is a polymer having a repeating unit represented by the above general formulas (1a) and (1b), that is, an acidic polyamino acid. It is a polymer having a structure into which a pendant group is introduced. Therefore, in a method for producing an acidic polyamino acid derivative, introduction of a pendant group into a polymer is one of the main steps.

However, the method for producing the acidic polyamino acid derivative is not particularly limited. For example, a method of ring-opening a polysuccinimide with an aminocarboxylic acid or the like described in the section of “(2-1) Method for producing polysuccinimide”, or a method of introducing an aminocarboxylic acid or the like into a previously produced acidic polyamino acid And the like.

Among them, the method of ring opening polysuccinimide with aminocarboxylic acid or the like is industrially preferable. In the other methods, the reaction is inhibited unless the carboxyl group contained in the pendant group is protected, so that a step of protecting and deprotecting the carboxyl group is required, and the number of steps increases, which is not preferable.

(2-2-1) Pendant Group Introduction Reaction A method for introducing a pendant group into a polymer is not particularly limited. For example, an amine or alcohol having at least one carboxyl group in polysuccinimide may be used. A method of reacting at least one compound selected from the group consisting of thiol and thiol, a method of subjecting the above compound to a dehydration condensation reaction with an acidic polyamino acid, a method of subjecting the above compound to an ester / amide exchange reaction with an acidic polyamino acid ester, and the like. No. The molecular weight of the polysuccinimide used is not particularly limited, but is preferably higher, from 10,000 to
1,000,000 is preferred, 30,000 to 200,000 is more preferred, and
Particularly preferred is 10,000 to 100,000.

The reaction reagent used for the pendant group introduction reaction may contain a carboxyl group or may contain a substituent (precursor) that can be a carboxyl group. In the present invention, for convenience, a substituent that can be a carboxyl group is referred to as a precursor.

As representative examples of the reaction reagent, at least one
Examples include amines, thiols, and alcohols having one carboxyl group or a precursor thereof. The basic skeleton corresponds to R in the general formulas (1a) and (1b). In the pendant group introduction reaction, a pendant group (R) may be introduced in one step, or a pendant group (R) may be introduced once by introducing a substituent and then reacting the substituent with another substituent. May be used.

Hereinafter, specific examples of the method for introducing a pendant group will be described.

(2-2-2) Method of reacting polysuccinimide with an amine having a carboxyl group When polysuccinimide is reacted with an amine having a carboxyl group, the solvent used is not particularly limited, and the polysuccinic acid is not limited. Any solvent capable of dissolving an imide or polysuccinimide derivative or a reagent capable of forming a pendant group may be used, and any common solvent used in chemical reactions can be used.

In particular, since a reaction reagent containing an acidic group has a high polarity, it is preferable to use a polar solvent. As the polar solvent, water, methanol, ethanol, propanol, isopropanol, acetone and the like are preferable, and water is particularly preferable. These solvents may be used alone or in combination of two or more.

The concentration of the polysuccinimide at the time of the reaction of introducing a pendant group into the polysuccinimide is not particularly limited, but is preferably 0.1 to 50% by mass, particularly preferably 1 to 40% by mass. In the pendant group introduction reaction, a catalyst may be used if necessary. Generally, a base catalyst is used as the catalyst.

Examples of the basic catalyst include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, alkali metal carbonates such as sodium carbonate, potassium carbonate and lithium carbonate, sodium hydrogen carbonate and hydrogen carbonate. Inorganic base reagents such as alkali metal bicarbonates such as potassium, alkali metal acetates such as sodium acetate and potassium acetate, alkali metal salts such as sodium oxalate, and ammonia; trimethylamine, triethylamine, tripropylamine, tributylamine, tributylamine Pentylamine, trihexylamine, triethanolamine, tripropanolamine, tributanolamine, tripentanolamine, trihexanolamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentyne Organic base reagents such as amines, amines such as amine, dihexylamine, dicyclohexylamine, dibenzylamine, ethylmethylamine, methylpropylamine, butylmethylamine, methylpentylamine, methylhexylamine, pyridine, picoline, and quinoline. .

The reaction temperature in the pendant group introduction reaction is not particularly limited, but is preferably from 0 to 120 ° C., particularly preferably from 10 to 60 ° C.

(2-2-3) Method of Dehydrating and Condensing Acidic Polyamino Acid or Its Derivative with Amines Having Carboxyl Group As a method for introducing a pendant group into an acidic polyamino acid, a reaction reagent and an acidic polyamino acid are dehydrated. The method of condensation is common.

However, when a pendant group having an acidic group is introduced, the acidic group itself may react with an amine or the like depending on the reaction conditions for dehydration condensation. In this case, elongation of the side chain occurs, but as a result, the ratio of the hydrophilic group decreases. Therefore, in some cases, it is necessary to take a method of protecting acidic groups.

When performing dehydration condensation, any of a method of removing generated water by azeotropic distillation with a solvent, a method of adding molecular sieve as a dehydrating agent, a method of reacting with a dehydrating condensing agent, and a method of using an enzyme are used. You can take a method.

Examples of the dehydrating condensing agent include carbodiimides such as dicyclohexylcarbodiimide and N-ethyl-N '-(3-dimethylaminopropyl) carbodiimide;
1-acylimidazolide, 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline, triphenylphosphine / carbon tetrachloride, triphenylphosphine / bromotrichloromethane, bis (2-phenylphenylphosphonate)
Phosphorus-containing compounds such as nitrophenyl ester), diethyl cyanophosphonate, and diphenylphosphoroazide;
Oxidation-reduction condensing agents such as fluoro-1-ethylpyridium tetrafluoroborate, triphenylphosphine / bis (benzothiazole) disulfide, and tributylphosphine / bis (benzothiazole) disulfide.

The reaction temperature during the dehydration condensation is from 20 to 250 ° C.
Is preferable, and 100 to 180 ° C. is more preferable.

Further, a method of subjecting the acidic polyamino acid derivative to esterification, amidation, or thioesterification to a derivative of the acidic polyamino acid by a dehydration condensation reaction may be used. For the esterification and the like, conventionally known ordinary reaction conditions in organic chemistry can be used. For example, a carboxyl group of an acidic amino acid residue may be reacted with a reagent for forming an ester, an amide or a thioester, or an ester, an amide or a thioester may be prepared by increasing the reactivity of an acidic polyamino acid as a derivative in advance. It may be reacted with a reagent for forming.

More specifically, for example, a method in which a carboxyl group of an acidic amino acid residue is subjected to a dehydration condensation reaction with an alcohol, an amine, a thiol or the like, a method in which the carboxyl group of an acidic amino acid residue is converted to an acid anhydride, an acid halide, Activating with an acid azide or the like and reacting with an alcohol, amine, thiol, or the like, or activating the carboxyl group of an acidic amino acid residue with an activated alcohol (eg, a halide, an ester, a sulfonic ester or a sulfate of an alcohol) A method of reacting a carboxyl group of an acidic amino acid residue with an epoxy compound, an isocyanate compound, an aziridine compound, an alkyl metal, etc. For reacting carboxyl groups as halides with halides The carboxyl group of an acidic amino acid residue as an active ester group, and a method of reacting an ester interchange, by transamidation.

(2-2-4) A method of subjecting an acidic polyamino acid ester to an amine having a carboxyl group or the like by ester / amide exchange reaction.
Although not particularly limited, a method of reacting an acidic polyamino acid ester with a reaction reagent in an organic solvent is generally used. Examples of the ester to be used include an alcohol component having a small molecule such as methyl and ethyl, an alcohol component having an electron withdrawing group such as chloromethyl and dichloromethyl, and an esterified ester with an alcohol such as N-hydroxysuccinimide.

In some cases, a catalyst such as an acid catalyst or a base catalyst may be used. When the reaction system becomes heterogeneous or when the raw materials used are insoluble, a phase transfer catalyst may be used. Also, in this method, depending on the reaction conditions of the ester / amide exchange reaction, the acidic group itself reacts with the amine or the like, and the elongation of the side chain group increases as in the case of the method (2-2-3). As a result, the ratio of the hydrophilic group may decrease.

(2-2-5) Method Using Precursor In the pendant group introduction reaction, a pendant group having a carboxyl group precursor is introduced according to each of the above methods, and then the precursor is converted to a carboxyl group. be able to. The reaction product after the introduction of the pendant group containing the precursor may be taken out of the system or, if necessary, may be continuously subjected to a substitution reaction with a carboxyl group or a cationization reaction as it is. Here, when the reaction product is taken out of the system, the reaction product may be dried before use.

Of the above-described methods (2-2-2) to (2-2-5), a method capable of efficiently reacting under mild conditions is preferable. Particularly, polysuccinimide and amine having a carboxyl group are preferred. And the like, and a method of introducing a pendant group containing a precursor and further derivatizing the precursor to a carboxyl group.

(2-2-6) Treatment after Introducing Pendant Group The treatment after the pendant group introduction reaction and the conversion reaction of the precursor into a specific functional group is not particularly limited, and is generally used in the production of compounds. Conventional techniques can be used. For example, the method for isolating the produced polymer from the reaction solution after the completion of the reaction may be any method capable of substantially isolating the reaction product with a desired purity, and may be any conventionally known method. . Generally, isolation operations such as concentration, recrystallization, and reprecipitation can be employed.

For example, after completion of the reaction, an excess poor solvent (eg, methyl alcohol, ethyl alcohol, isopropyl alcohol) is added to the reaction solution in which the reaction product is dissolved at an appropriate temperature, and To
Decantation, isolation by filtration or suction filtration,
A method of sufficiently washing with a poor solvent that does not dissolve the precipitate and drying the precipitate is exemplified. Further, as another example, after the reaction is completed, at an appropriate temperature, the reaction solution in which the reaction product is dissolved is added to the same excess of the poor solvent as described above, and the precipitate of the deposited reaction product is treated as the above. In the same way, isolate, wash,
Drying method is mentioned.

The drying temperature of the resin is not particularly limited.
Generally, 20 to 150 ° C. is preferable, and particularly 40 to 1 ° C.
00 ° C is preferred. The method for drying the resin is not particularly limited, either.
Drying can be performed by various methods such as hot air drying, drying with specific steam, microwave drying, drying under reduced pressure, drum drying, and drying by azeotropic dehydration in a hydrophobic organic solvent.

The carboxyl group of the acidic polyamino acid derivative forms an alkali metal salt or ammonium salt, and the reaction solution is alkaline. However, if necessary, a mineral acid such as hydrochloric acid or sulfuric acid, or a acetic acid or the like may be used. The pH can be adjusted by adding a sulfonic acid such as carboxylic acid or methanesulfonic acid.

Further, it can be isolated as a salt of an acidic polyamino acid derivative using an ion exchange resin. However,
Since the acidic polyamino acid derivative is easily hydrolyzed on the acidic side, it is preferable to perform isolation on the alkaline side when isolating it.

(2-3) Crosslinking Method of Acidic Polyamino Acid Derivative The polymer concentration in the crosslinking reaction for obtaining a crosslinked polymer is not particularly limited. However, in order to carry out the crosslinking reaction efficiently, it is preferable to carry out the reaction at a high concentration. here,
The polymer concentration refers to the mass of the acidic polyamino acid derivative with respect to the total mass (including water and solvent) of all the reagents used in the crosslinking reaction.

The suitable polymer concentration varies depending on the type of the acidic polyamino acid derivative, but is generally 20 to 7%.
0 mass% is preferable, 30 to 60 mass% is more preferable, and 40 to 60 mass% is particularly preferable. The upper limit of these ranges is that the polymer does not dissolve and is not only difficult to stir,
It is significant in preventing problems such as the inability to perform a uniform cross-linking reaction and, as a result, an increase in water-soluble components and a decrease in both yield and water absorption capacity. On the other hand, the lower limit is significant in preventing problems such as side reactions such as cleavage of the polymer main chain due to a slow reaction rate, resulting in an increase in water-soluble components and a decrease in both yield and water absorption capacity. There is.

The solubility of a polymer is related to its molecular weight, counter ion and degree of neutralization. In general, high molecular weight polymers have low solubility and low molecular weight polymers have high solubility. The counter ion is a monovalent ion, and relatively small ions such as sodium, potassium, and ammonium have high solubility. As for the degree of neutralization, the solubility is higher when a salt is formed than when a free carboxylic acid is formed. In the present invention, the crosslinking reaction is preferably performed at a concentration lower than the solubility. For example, in the case of an acidic polyamino acid derivative having a weight average molecular weight of 60,000, the concentration of the polymer is preferably 40 to 60% by mass.

In the crosslinking reaction, the reaction temperature, pH, the amount of the crosslinking agent (the polyvalent epoxy compound in the present invention) and the like are important. Preferred reaction conditions vary depending on these combinations.

For example, in the present invention, the cross-linking reaction is carried out on the acidic side, but the cross-linking reaction between the polymer and the epoxy group of the cross-linking agent is accelerated under conditions of high temperature and low pH. But,
Under conditions of high temperature and low pH, the hydrolysis reaction of the main chain of the acidic polyamino acid and the hydrolysis reaction of the epoxy group of the crosslinking agent also become faster. That is, under conditions of high temperature and low pH, the crosslinking reaction and side reactions (hydrolysis reaction of the acidic polyamino acid main chain, cleavage reaction of the epoxy group of the crosslinking agent) are similarly promoted.

Therefore, in the present invention, the crosslinking reaction is
It is preferable to take any of the following methods: performing the reaction under mild conditions in which a side reaction is unlikely to occur, or adopting a condition in which a crosslinking reaction can proceed in a short time and suppressing the side reaction. In the latter case, generally, the use of a large amount of a crosslinking agent is effective for the crosslinking reaction.

As described above, the crosslinking reaction is preferably performed in water. In this case, the amount of the carboxyl group involved in the crosslinking reaction is determined by the pH of the aqueous solution.
The pH of the aqueous solution is preferably 3 to 7, more preferably 4 to 6, and particularly preferably 4.5 to 5.5.

The cross-linking reaction largely depends on the carboxyl groups in the polymer and the concentration of the cross-linking agent. If the concentration of the polymer is too low, the number of carboxyl groups involved in the reaction is small even in the preferred pH range described above (pH 3 to 7),
The crosslinking reaction time is prolonged, and the hydrolysis reaction proceeds, which is disadvantageous for the crosslinking reaction. If the polymer concentration is high,
In the preferred pH range described above (pH 3 to 7), even if the number of carboxyl groups involved in the reaction is small, the concentration is high, so that the crosslinking reaction time is short, and the hydrolysis reaction does not proceed, which is advantageous for the crosslinking reaction.

The pH of the aqueous solution at the time of performing the crosslinking reaction
Is too low, the main chain such as polyaspartic acid is broken,
It is uneconomical because a large amount of the crosslinking agent is required, and the water absorption of the resulting water-absorbing resin tends to be low. Conversely, if the pH is too high, the reactivity between the carboxyl group of the polymer and the epoxy group of the crosslinking agent decreases, and the crosslinking reaction tends to substantially not proceed.

It is preferable that the carboxyl group of the polymer is usually neutralized as a salt such as an alkali metal salt or an ammonium salt. For example, the pH of the reaction solution can be changed by changing the degree of neutralization of a carboxyl group such as polyaspartic acid. After the crosslinking reaction, an acid or an alkali can be added to adjust the pH to a value suitable for the intended use of the crosslinked polymer. For example, in a sanitary article such as a disposable diaper, the pH is preferably 6 to 8.

The temperature for carrying out the crosslinking reaction is 10 to 10
0 ° C. is preferred, 30 to 80 ° C. is more preferred, and 40 to 80 ° C.
60 ° C. is particularly preferred. The upper limit of the range of these reaction temperatures, the main chain is cut, a large amount of a crosslinking agent is required,
This is significant in preventing the problem that the performance of the obtained water-absorbent resin is low. Further, the lower limit is significant in preventing the problem that the reaction between the polymer and the cross-linking agent is slowed down, which is uneconomical in industry. And, within the above preferred range, at a relatively high reaction temperature, when the amount of the crosslinking agent is large,
It is preferable because the crosslinking reaction time is shortened and side reactions such as polymer chain cleavage can be suppressed. On the other hand, within the above preferred range, at a relatively low temperature, the progress of the side reaction is slow, so the crosslinking reaction proceeds even with a small amount of the crosslinking agent, and the crosslinking reaction time can be shortened by increasing the amount of the crosslinking agent. it can. Which one to select may be appropriately selected depending on the setting of the crosslinking reaction time in consideration of the reaction apparatus and the like.

The polyepoxy compound used in the present invention acts as a crosslinking agent. Specific examples thereof include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and propylene glycol diglycidyl ether. , Butanediol diglycidyl ether and the like (C2-
C6) polyglycidyl ethers of alkane polyols and poly (alkylene glycols); sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, erythritol 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
(C4-C8) diepoxyalkanes and diepoxyalkanes such as diepoxyoctane, 1,4- and 1,3-divinylbenzene epoxide; 4,4'-isopropylidene diphenol diglycidyl ether (bisphenol A diglycidyl) (C6-C15) polyphenol polyglycidyl ethers such as ether) and hydroquinone diglycidyl ether.

The amount of the crosslinking agent used is such that the number of functional groups of the polymer is 1
When it is 00 mol, it is preferably 0.1 to 30 mol, more preferably 1 to 15 mol, particularly preferably 3 to 8 mol. The upper limit of each of the above ranges is significant in terms of economic efficiency and preventing the degree of cross-linking from becoming too high, thereby reducing the amount of water absorption, and preventing the unreacted cross-linking agent from remaining. On the other hand, the lower limit is such that cross-linking cannot be sufficiently performed, and that the cross-linking reaction time is long, the amount of water absorption is low, the amount of water-soluble components is large, and the yield is reduced. It is significant in that

The crosslinking reaction time varies depending on the reaction temperature, the reaction concentration, and the amount of the crosslinking agent used. Although it can be adjusted by these reaction conditions, it is usually 1 minute to 20 hours. Further, although it depends on the reactor, 5 minutes to 10 hours are preferable, and
Minutes to 5 hours are more preferable, and 5 minutes to 1 hour are particularly preferable.

(2-4) Post-Treatment of Crosslinked Polymer Regarding the post-treatment of the crosslinked polymer of the present invention after the crosslinking reaction,
There is no particular limitation. For example, treatments such as neutralization, salt exchange, drying, purification, granulation, and surface cross-linking treatment may be performed as necessary. Hereinafter, the processes of neutralization, salt exchange, and drying will be particularly described.

The neutralization treatment of the crosslinked polymer may be performed as needed. By this neutralization treatment, the carboxyl group present in the molecule of the crosslinked polymer can be converted into a salt or a free carboxylic acid. That is, the carboxylic acid salt in the polymer can be changed to a free carboxylic acid by using an acid, and the free carboxylic acid in the polymer can be changed to a carboxylic acid salt by using an alkali.

Although the degree of neutralization is not particularly limited, the ratio of carboxyl groups forming a salt is generally 0 to 0 based on the total number of all carboxyl groups in the molecule of the crosslinked polymer.
50% is preferable, and 0 to 30% is more preferable.

Specific examples of the acid include hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, sulfurous acid, nitric acid, nitrous acid, and the like.
Carbonic acid, phosphoric acid, formic acid, acetic acid, propionic acid, oxalic acid,
Examples thereof include carboxylic acids such as benzoic acid, sulfonic acids such as methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, and toluenesulfonic acid, and phosphonic acids such as benzenephosphonic acid.

Specific examples of the alkali include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, alkali metal carbonates such as sodium carbonate, potassium carbonate and lithium carbonate, sodium hydrogen carbonate and hydrogen carbonate. Examples include alkali metal bicarbonates such as potassium, alkali metal acetates such as sodium acetate and potassium acetate, alkali metal salts of organic carboxylic acids such as sodium oxalate, and tertiary amines such as triethylamine and triethanolamine.

When the carboxyl group present in the molecule of the crosslinked polymer is converted into a salt by the neutralization treatment, if necessary,
The salt can be exchanged for another type of salt.

Specific examples of the reagent used for this salt exchange include, for example, alkali metal salts, ammonium salts, amine salts and the like. More specifically, sodium, potassium, alkali metal salts such as lithium, tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium,
Tetrapentylammonium, tetrahexylammonium, ethyltrimethylammonium, trimethylpropylammonium, butyltrimethylammonium, pentyltrimethylammonium, hexyltrimethylammonium, cyclohexyltrimethylammonium,
Ammonium salts such as benzyltrimethylammonium, triethylpropylammonium, triethylbutylammonium, triethylpentylammonium, triethylhexylammonium, cyclohexyltriethylammonium, benzyltriethylammonium, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine , Triethanolamine, tripropanolamine, tributanolamine, tripentanolamine, trihexanolamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dicyclohexylamine, dibenzylamine, ethylmethylamine , Methylpropylamine, spot Methylamine, methyl pentyl amine, methyl hexyl amine, methyl amine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, octylamine, decylamine,
Examples thereof include amine salts such as dodecylamine and hexadecylamine.

Of these, the higher the molecular weight, the higher the molecular weight per monomer unit and the smaller the water absorption per unit mass. Therefore, the smaller the molecular weight, the better. When there is a possibility of touching human skin or the like, it is preferable that skin irritation and the like be low.
From these points, it is preferable to use sodium, potassium, lithium, ammonium, and triethanolamine, and further, it is preferable to use sodium and potassium.
Particularly preferred in terms of cost.

The method for drying the crosslinked polymer is not particularly limited. For example, known methods such as hot air drying, drying with specific steam, microwave drying, reduced pressure drying, drum dryer drying, and drying by azeotropic dehydration in a hydrophobic organic solvent can be used. The drying temperature is generally between 20 and 200
C. is preferable, and 50 to 120 C. is more preferable.

The dried cross-linked polymer may be further subjected to purification treatment, granulation treatment, surface cross-linking treatment and the like.

(3) Water Absorbing Ability of Crosslinked Polymer The water absorbing ability of the crosslinked polymer of the present invention is not particularly limited. However, when used for sanitary articles such as disposable diapers, high performance is required. You.

For example, 1 measured by the tea bag method
It is preferable that the amount of water absorbed in physiological saline over time is 28 to 200 times the mass of the polymer,
More preferably, it is 50 times, and practically 40 to 1 times.
It is particularly preferable that the ratio is 00 times. In addition, the amount of water absorbed by distilled water in one hour measured by the tea bag method is as follows:
It is preferably from 200 to 1500 times, more preferably from 300 to 1000 times, particularly preferably from 400 to 1000 times, the mass of the polymer. The tea bag method for evaluating the amount of water absorption will be described in Examples described later.

Further, if a water-soluble component is contained in the crosslinked polymer, a decrease in water absorption or stickiness occurs, so that it is preferable that no water-soluble component is contained. That is, the water-soluble content is preferably from 0 to 18% by mass, more preferably from 0 to 5% by mass, particularly preferably from 0 to 1% by mass based on the mass of the polymer.

Regarding the water retention capacity of the crosslinked polymer, it is preferable that the water retention capacity with respect to physiological saline measured by the centrifugal dehydration method is 10 to 50 times the mass of the polymer.
More preferably, it is 5 to 50 times. In addition, the water retention rate for physiological saline measured by the centrifugal dehydration method is 50 to
It is preferably 100%, more preferably 60 to 100%, particularly preferably 70 to 100%. The method for measuring the water retention amount and the water retention ratio by the centrifugal dehydration method will be described in Examples described later.

(4) Shape of crosslinked polymer Specific examples of the shape of the crosslinked polymer include irregularly crushed, spherical, granular, granular, granulated, scaly, massive, pearl, and fine powder. , Fibrous, rod-like, film-like, sheet-like, etc., and a preferable shape can be selected according to the use. Also, fibrous base material, porous body,
It may be a foam, a granulated product, or the like.

(5) Particle Size of Crosslinked Polymer The particle size (average particle diameter) of the crosslinked polymer is not particularly limited, and a preferable particle size can be selected according to the application. For example,
When used in a disposable diaper, it is desirable that a high absorption rate and no gel blocking occur, so that the average particle size is preferably 100 to 1000 μm, and 150 to 600 μm.
μm is more preferred. Further, for example, when used for kneading into a resin such as a water-stopping material, the average particle size is 1 to 10 μm
m is preferable, and when it is used for a water retention material for agriculture and horticulture, it is preferably 100 μm to 5 mm in consideration of dispersibility with soil.

(6) Form of Use of Crosslinked Polymer The form of use of the crosslinked polymer is not particularly limited, and it may be used alone or in combination with other materials.

For example, when used in combination with another resin,
A method of kneading a thermoplastic resin and molding by injection molding or the like, a method of mixing a monomer of a constituent resin and a crosslinked polymer and an initiator as necessary, and then polymerizing with light or heat, etc., and using a resin and a crosslinked polymer as a solvent. There are a method of dispersing, casting and removing the solvent, a method of mixing the prepolymer and the crosslinked polymer and then crosslinking, a method of mixing the resin and the crosslinked polymer and then crosslinking.

The molded article of the crosslinked polymer is not particularly limited, and may be a solid, a sheet, a film, a fiber,
It can be used as non-woven fabric, foam, rubber and the like. Also, the molding method is not particularly limited.

When the crosslinked polymer is used as a composite in combination with another material, the structure of the composite is not particularly limited. For example, a method of sandwiching a pulp layer, a nonwoven fabric, or the like, forming a sandwich structure, a resin sheet, The composite can be obtained by a method of forming a multilayer structure using the film as a support, or a method of casting a resin sheet to form a two-layer structure. For example, if the crosslinked polymer is formed into a sheet, a water-absorbing sheet (including a water-absorbing film) can be obtained.

The crosslinked polymer may be used by mixing with one or more other water-absorbing resins, if necessary. If necessary, an inorganic compound such as salt, colloidal silica, white carbon, ultrafine silica, titanium oxide powder, or an organic compound such as a chelating agent may be added. Further, an oxidizing agent, an antioxidant, a reducing agent, an ultraviolet absorber, an antibacterial agent, a bactericide, a fungicide, a fertilizer, a fragrance, a deodorant, a pigment and the like may be mixed.

The crosslinked polymer can be used as a gel or as a solid. For example, when used as a water retention material for agricultural and horticultural use, a cut flower life-promoting agent, a gel fragrance, a gel deodorant, etc., it is used as a gel, and an absorbent for disposable diapers is used as a solid.

(7) Use of Crosslinked Polymer The use of the crosslinked polymer is not particularly limited, and it can be used in any of the applications in which conventional water-absorbing resins can be used.

For example, sanitary articles such as sanitary articles, disposable diapers, breast milk pads, disposable rags, dressings for protecting wounds, medical articles such as medical underpads, cataplasms,
Pet seats, portable toilets, gel air fresheners, gel deodorants, sweat-absorbing fibers, household items such as disposable warmers, toiletries such as shampoos, set gels, moisturizers, and water retention materials for agriculture and horticulture. Agricultural and horticultural supplies, food trays such as cut flower prolonging agents, floral foam (cutting flower fixing material), nursery beds, hydroponic vegetation sheets, seed tapes, fluid seeding media, dew condensation prevention agricultural sheets, etc. Food packaging materials such as freshness preservation materials, drip absorbent sheets, cold insulation materials,
Transportation materials such as water-absorbent sheets for transporting fresh vegetables, building materials for preventing dew condensation, sealing materials for civil engineering and construction, anti-sedimentation agents for shielding methods, concrete admixtures, civil engineering construction materials such as gaskets and packing, and electronic equipment , Sealing materials such as optical fibers, waterproof materials for communication cables, electrical equipment related materials such as inkjet recording paper, sludge coagulants, gasoline, dehydration of oils, water treatment agents such as water removing agents, printing pastes, Water-swellable toys, artificial snow, sustained-release fertilizers, sustained-release pesticides,
Sustained-release drugs, humidity control materials, antistatic agents, and the like.

[0139]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples. Hereinafter, “parts” means “parts by mass”.

Measurement of Weight Average Molecular Weight Weight average molecular weight (Mw) of polyaspartic acid (salt) and the like
Was measured by GPC (gel permeation chromatography) using polyethylene oxide as a standard. Apparatus: Shodex GPC SYSTEM-11 Detector: Shodex RI SE-61 Column: Shodex OHpak SB-804 Solvent: 0.1M-KCl aqueous solution Concentration: 0.1% Injection amount: 100 μl Flow rate: 1.0 ml / min.

Measurement of water absorption The water absorption was measured using distilled water and physiological saline using the tea bag method. That is, in the case of distilled water, about 0.05 part of the dry water-absorbent resin, and in the case of physiological saline, about 0.1 part of the dry water-absorbent resin, are put in a nonwoven tea bag (80 mm × 50 mm). Immersed in excess distilled water or saline at 20 ° C.
After swelling for a time, the tea bag was pulled up and drained for 1 minute, and the mass of the tea bag containing the swollen resin was measured. Assuming that the same operation was performed only with the tea bag as a blank, the value obtained by subtracting the mass of the blank and the mass of the water-absorbent resin from the mass of the tea bag containing the swollen resin was divided by the mass of the water-absorbent resin. This value is taken as the water absorption (g /
1 g of resin). The physiological saline is 0.9% by mass.
It is an aqueous solution of sodium chloride.

Measurement of Water Retention and Water Retention Rate The water retention was measured using a centrifuge for physiological saline. That is, about 0.1 part of the dry water-absorbent resin is put into a nonwoven fabric tea bag (80 mm × 50 mm), and immersed in a centrifuge tube for centrifugal dehydrator containing an excess amount of physiological saline at 20 ° C. After the resin was allowed to swell for 1 hour, the tea bag was pulled up and drained for 1 minute, and the liquid adhering to the surface was sucked into a sufficient amount of tissue paper to measure the mass of the tea bag containing the swollen resin. Assuming that the same operation was performed only with the tea bag as a blank, the value obtained by subtracting the mass of the blank and the mass of the water-absorbent resin from the mass of the tea bag containing the swollen resin was divided by the mass of the water-absorbent resin. This value is determined by the amount of water absorption (g
/ Resin 1 g). Further, the resin containing this solution was put into a centrifugal dehydration tube containing glass beads at the bottom together with the tea bag, and centrifuged at 4000 rpm for 10 minutes using a centrifugal dehydrator. After centrifugation, pull up the tea bag and let the liquid adhering to the surface be sucked into a sufficient amount of tissue paper,
The mass of the tea bag containing the swollen resin was measured. Similarly, measurement is performed on the blank, and the value obtained by subtracting the mass of the blank and the mass of the water-absorbent resin from the mass of the tea bag containing the swollen resin is divided by the mass of the water-absorbent resin. g / g of resin).

The retention was calculated from the measurement result by the following equation: retention (%) = (water retention / water absorption) × 100.

Measurement of Biodegradability Biodegradability was measured by a compost method. The composting method is an application of ASTM D-5338.92, IS
Performed according to O CD 14855. That is, first, the amount of carbon contained in the test sample was measured by elemental analysis, and then 15 parts of the test sample was added to 800 parts of the inoculum, and biodegraded at 58 ° C. for 40 days. The amount of carbon dioxide generated was measured and the amount of carbon dioxide generated relative to the amount of carbon contained in the test sample converted to carbon dioxide was expressed as a biodegradation rate (%). Here, some of the samples that are easily biodegradable promote the decomposition of even the carbon content in the inocula, and in this case, some of the samples have a value exceeding 100%.

[Production Example 1] 150 parts of L-aspartic acid and 75 parts of 85% phosphoric acid were mixed and reacted at 200 mmHg and 200 ° C for 4 hours using a rotary evaporator. The reaction mixture was diluted with dimethylformamide (DMF) 10
Dissolved in 00 parts and discharged into 5000 parts of water. The obtained precipitate was separated by filtration, washed with water until the washing liquid became neutral, and dried at 60 ° C. to obtain a polysuccinimide 1 having a Mw of 96,000.
08 parts were obtained.

[Production Example 2] 108 parts of polysuccinimide having Mw of 146,000 was obtained in the same manner as in Production Example 1, except that the reaction temperature and time of L-aspartic acid were changed to 220 ° C for 10 hours. Was.

Next, the obtained polysuccinimide 100
Is dispersed in 230 parts of water, and 206 parts of a 20% by mass aqueous sodium hydroxide solution is added dropwise while maintaining the pH to 12 or less, and the imide ring is hydrolyzed to open.
An aqueous solution of polyaspartic acid was obtained. This polyaspartic acid aqueous solution was adjusted to pH 8.7 with 2N hydrochloric acid,
The mixture was discharged into 4000 parts of methanol, and the precipitate was filtered.
By drying at ℃, 154 parts of sodium polyaspartate having an Mw of 150,000 was obtained.

[Example 1] 10 parts of the polysuccinimide obtained in Production Example 1 was dispersed in 23 parts of water. A solution obtained by dissolving 9.18 parts of β-alanine in 16.48 parts of a 25% by mass aqueous sodium hydroxide solution was added dropwise to this dispersion,
The reaction was performed at 6 ° C. for 6 hours. After the reaction, the mixture was cooled to room temperature, discharged into 400 parts of acetone, and the supernatant was removed by decantation. The reaction product was solidified by adding 200 parts of methanol, collected by suction filtration, washed with 100 parts of methanol, and dried at 60 ° C. to obtain 17.53 parts of a polymer.

10 parts of this polymer was dissolved in 10 parts of distilled water, and the pH was adjusted to 5.0 using 2N hydrochloric acid. further,
2.62 parts of ethylene glycol diglycidyl ether was added and mixed well. When the reaction was performed at 40 ° C. for 9 hours, the reaction solution gelled. The gel was chopped with a mixer, discharged into 400 parts of methanol, and the precipitate was washed with 50 parts of methanol and dried at 60 ° C. to obtain 19.98 parts of a crosslinked polymer.

The water absorption of the crosslinked polymer was 401 times higher than that of distilled water and 50 times higher than that of physiological saline, and the water retention was 17.7 times and the water retention was as high as 74%. The biodegradability was 109%.

Example 2 A 25% by mass aqueous solution of potassium hydroxide was used instead of a 25% by mass aqueous solution of sodium hydroxide.
18.89 parts of a crosslinked polymer were obtained in the same manner as in Example 1 except that 3.08 parts were used. The water absorption of this crosslinked polymer was 389 times that of distilled water and 4 times that of physiological saline.
6 times higher, water retention is 17.5 times, water retention is 73
% Was high. The biodegradability was 105%.

Example 3 A crosslinked polymer (18.89 parts) was obtained in the same manner as in Example 1 except that 7.73 parts of glycine was used instead of β-alanine. The water absorption of this crosslinked polymer was 415 times higher than that of distilled water and 50 times higher than that of physiological saline, and the water retention was 17.9 times and the water retention was as high as 78%. The biodegradability was 106%.

Example 4 Instead of β-alanine, 4
21.70 parts of a crosslinked polymer were obtained in the same manner as in Example 1 except that 10.63 parts of -aminobutanoic acid was used. The water absorption of this crosslinked polymer is 390 times higher than that of distilled water and 57 times higher than that of physiological saline, and the water retention is 17.
The water retention was twice as high as 75%. The biodegradability is 1
08%.

Example 5 Instead of β-alanine, 6
-Except that 13.51 parts of aminocaproic acid were used
In the same manner as in Example 1, 24.58 parts of a crosslinked polymer was obtained.
The water absorption of this crosslinked polymer is 390 times that of distilled water,
57 times higher than physiological saline, and the water retention is 1
The water retention was 7.2%, which was as high as 75%. The biodegradability was 108%.

Example 6 Instead of β-alanine, 6
Using 8.11 parts of aminocaproic acid, a solution of this dissolved in 9.89 parts of a 25% by weight aqueous sodium hydroxide solution was added dropwise, allowed to stand at 50 ° C for 6 hours, cooled to 30 ° C after the reaction, and further cooled to 25 ° C. 6.59 mass% aqueous sodium hydroxide solution
19.31 parts of a crosslinked polymer was obtained in the same manner as in Example 1 except that the reaction was carried out by dropping parts at pH 11 or lower. The water absorption of this crosslinked polymer is 450 times higher than that of distilled water and 54 times higher than that of physiological saline, and the water retention is 17.
Eight times, the water retention rate was as high as 78%. The biodegradability is 1
06%.

Example 7 Using 13.00 parts of a reaction product of polysuccinimide and β-alanine obtained in Example 1, 6.00 parts of sodium polyaspartate obtained in Production Example 2, and using ethylene glycol 19.93 parts of a crosslinked polymer was obtained in the same manner as in Example 1 except that the amount of diglycidyl ether was changed to 2.50 parts. The water absorption of this crosslinked polymer is 548 times higher than that of distilled water and 55 times higher than that of physiological saline, and the water retention is 20.5 times and the water retention is 7 times.
It was as high as 6%. The biodegradability was 100%.

[Comparative Example 1] 30 parts of the polysuccinimide obtained in Production Example 1 was dissolved in 120 parts of DMF, 1.5 parts of dicyclohexylcarbodiimide was added, and the mixture was allowed to react at 0 to 5 ° C for 1 hour. (25 ° C.) for 24 hours. After the reaction, the reaction solution was discharged into 500 parts of water, washed three times with 200 parts of water, and dried at 60 ° C. to obtain a polysuccinimide having an Mw of 204,000. This polysuccinimide was hydrolyzed in the same manner as in Production Example 1 to obtain 40 parts of sodium polyaspartate having a Mw of 18,000. Next, 30 parts of this sodium polyaspartate was dissolved in 150 parts of distilled water, and converted into an acid form by passing through an ion exchange resin.

30 parts of this polyaspartic acid was mixed with 8 parts of distilled water.
0 parts and neutralized with 10.4 parts of sodium carbonate. 1.72 parts of ethylene glycol diglycidyl ether was added to this aqueous solution and reacted at 40 ° C. for 8 hours. As a result, the reaction solution gelled. At this time, the polymer concentration was 29.5% by mass. When the obtained gel was treated in the same manner as in Example 1, 32 parts of a crosslinked polymer was obtained.

The biodegradability of this crosslinked polymer was as high as 105%. However, its water absorption is 125 to distilled water.
And 27 times that of physiological saline. The water holding capacity was 8.2 times, and the water holding rate was as low as 28%.

[0160]

As described above, according to the present invention, a crosslinked polymer having high productivity and biodegradability can be provided.
In addition, it is possible to provide a method that can be manufactured at low cost. Further, the performance of the crosslinked polymer, particularly the performance as a water-absorbing resin such as water retention capacity and water absorption can be further improved.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) A61L 15/60 (72) Inventor Hiroyuki Yamashita 580-32 Nagaura, Sodegaura-shi, Chiba Mitsui Chemicals F-term (Reference) 2B022 BA22 BA23 BB01 BB03 4C003 AA23 4J001 DA01 DB01 DB04 DB05 DB07 DB09 DC12 DD07 DD14 EA13 EA14 EA33 EE26B EE42A EE46C EE47C EE74D FA03 FA06 FB01 FC01 GE11 JA12 JA20 JB17 JC0 AB01 DC13 AB01

Claims (10)

[Claims] 1. A cross-linking reaction of a repeating unit represented by the following general formula (1a) and / or a repeating unit represented by the following general formula (1b) in a polymer with a polyvalent epoxy compound. Crosslinked polymer. Embedded image [In the formulas (1a) and (1b), R is a pendant group having a carboxyl group, X is NH, N (R ′) (R ′ is an alkyl group, an aryl group or an aralkyl group), O or S
And n is 1 or 2. ] 2. In the general formulas (1a) and (1b), n is
The polymer according to claim 1, which is 1. 3. X in the general formulas (1a) and (1b) is
3. The polymer according to claim 1, which is NH. 4. The number of repeating units represented by the general formulas (1a) and (1b) is 40 with respect to the total number of all repeating units constituting the polymer molecule in the basic polymer skeleton.
The polymer according to any one of claims 1 to 3, wherein the content is from 100% to 100%. 5. The crosslinked polymer according to any one of claims 1 to 4, wherein the water absorption of the physiological saline solution after one hour measured by the tea bag method is 30 to 150 times the mass of the dry crosslinked polymer. Coalescing. 6. The amount of water absorption after 1 hour with respect to distilled water measured by the tea bag method is 2% of the mass of the dry crosslinked polymer.
The crosslinked polymer according to any one of claims 1 to 5, wherein the ratio is from 00 to 1500 times. 7. A crosslinking reaction of a repeating unit represented by the following general formula (1a) and / or a repeating unit represented by the following general formula (1b) in a polymer with a polyvalent epoxy compound. A method for producing a crosslinked polymer, characterized in that: Embedded image [In the formulas (1a) and (1b), R is a pendant group having a carboxyl group, X is NH, N (R ′) (R ′ is an alkyl group, an aryl group or an aralkyl group), O or S
And n is 1 or 2. ] 8. The cross-linking reaction is performed in water.
A method for producing the crosslinked polymer according to the above. 9. The pH of an aqueous solution in which a crosslinking reaction is performed is 3
The method for producing a crosslinked polymer according to claim 7 or 8, wherein 10. The temperature of an aqueous solution in which a crosslinking reaction is performed,
The method for producing a crosslinked polymer according to any one of claims 7 to 9, wherein the temperature is 10 to 100 ° C.