US006072O24A United States Patent (19) 11 Patent Number: 6,072,024 Irizato et al. (45) Date of Patent: Jun. 6, 2000

54 PRODUCTION PROCESS OF CROSS Primary Examiner Duc Truong LINKED POLYASPARTIC ACID RESIN Attorney, Agent, or Firm-Burns, Doane, Swecker & 75 Inventors: Yoshihiro Irizatio; Makoto Sukegawa, Mathis, L.L.P. both of Kanagawa; Toshio Katoh, Saitama; Hiroaki Tamatani, Kanagawa; 57 ABSTRACT Akinori Nagatomo; Masaru Wada, both of Fukuoka, all of Japan A process is disclosed for producing with good productivity a croSS-linked polyaspartic acid resin having biodegradabil 73 Assignee: Mitsui Chemicals, Inc., Japan ity and high water absorbency. The process features inclu Sion of one of the following Steps: (a) a poly Succinimide, 21 Appl. No.: 09/042,942 which has been brought into a dispersed State by a 22 Filed: Mar 17, 1998 dispersant, and a cross-linking agent are reacted to produce 30 Foreign Application Priority Data the cross-linked polyaspartic acid resin; (b) imide rings of a croSS-linked poly Succinimide are Subjected to a hydrolysis Mar. 21, 1997 JP Japan ...... 9-068.185 Mar. 21, 1997 JP Japan ... reaction while controlling a Swelling degree of a resulting Apr. 18, 1997 JP Japan ... gel, whereby the cross-linked polyaspartic acid resin is Apr. 18, 1997 JP Japan ... Apr. 18, 1997 JP Japan ... produced; and (c) a gel of a cross-linked poly Succinimide, Apr. 24, 1997 JP Japan . 9-10770 which has been obtained by reacting a croSS-linking agent to (51) Int. Cl...... C08G 69/10 a Solution of a poly Succinimide in an organic Solvent, is 52 U.S. Cl...... 528/328; 528/322; 528/332; disintegrated to Subject imide rings of the croSS-linked 528/335; 528/345; 528/363; 528/488; 528/491; polySuccinimide to a hydrolysis reaction, So that the croSS 528/499; 525/420; 525/421; 525/422; 524/457; linked polyaspartic acid resin is produced. The process may 524/475; 524/514; 524/522; 524/538 58 Field of Search ...... 528/328,332, also include one or both of the following steps as needed: (d) 528/335,345, 363, 488, 491, 499; 525/420, a gel of the cross-linked polyaspartic acid resin is washed 421, 422; 524/457, 475, 514,522,538 with water and/or a water-miscible organic Solvent; and (e) the poly Succinimide is produced using a basic amino acid as 56) References Cited a croSS-linking agent. U.S. PATENT DOCUMENTS 5,461,085 10/1995 Nagamoto et al...... 521/183 15 Claims, No Drawings 6,072,024 1 2 PRODUCTION PROCESS OF CROSS needed. A cautious attitude towards their use is hence LINKED POLYASPARTIC ACID RESIN desirable. Likewise, non-ionic resins have a potential prob lem of accumulating in Soil due to their undegradable nature BACKGROUND OF THE INVENTION although they do not form complexes. It is therefore likely 1. Field of the Invention that they would have adverse effects on the natural world. This invention relates to a process for the production of a Furthermore, these polymerized resins use monomers cross-linked polyaspartic acid resin having (bio) which are highly toxic to human skin and the like. A great degradability and high water absorbency and also to a deal of work has been conducted to eliminate Such mono proceSS for the production of a croSS-linked polySuccinimide mers from polymerized products. Nonetheless, their com plete elimination is difficult. Still higher difficulties are useful as a precursor for the croSS-linked polyaspartic acid expected especially in the production on an industrial Scale. CS. Technical Background of Superabsorbent Polymers Hav 2. Description of the Related Art ing Biodegradability Technical Background of Superabsorbent Polymers On the other hand, biodegradable polymers have been A Superabsorbent polymer is a resin capable of absorbing 15 attracting interest as “globe-compatible materials” in recent water from Several tens of times to Several thousands of years. Their use as Superabsorbent polymerS has also been times its own weight, and is used in Sanitary products, Such proposed. as Sanitary napkins and disposable diapers, and also in a Known examples of biodegradable Superabsorbent poly variety of other fields. merS employed in Such applications include croSS-linked Related Art on Superabsorbent Polymers polyethylene oxide (JP Kokai 6-157795, etc.), cross-linked Known examples of Superabsorbent polymers employed polyvinyl alcohol, croSS-linked carboxymethylcellulose in Such applications include partial neutralization products (U.S. Pat. No. 4,650,716), cross-linked alginic acid, cross of cross-linked polyacrylic acids (JP Kokai No. 55-84304, linked Starches, and cross-linked polyamino acids. Among U.S. Pat. No. 4,625,001), partial hydrolysis products of 25 these, the cross-linked polyethylene oxide and croSS-linked starch-acrylonitrile copolymers (JP Kokai 46-43995), polyvinyl alcohol have Small water absorption and are hence starch-acrylic acid graft copolymers (JP Kokai 51-125468), not particularly Suited for use as materials in products hydrolyzation products of vinyl acetate-acrylate ester requiring high water-absorbency Such as Sanitary products, copolymers (JP Kokai 52-14689), cross-linked copolymers disposable diapers, disposable dustcloths and paper towels. of 2-acrylamido-2-methylpropanesulfonic acid and acrylic Further, these compounds can be biodegraded only by acid (EP0068.189), cross-linked polymers of cationic mono certain particular bacteria, So that under general conditions, mers (U.S. Pat. No. 4,906,717), and hydrolysis products of their biodegradation will be slow or will not take place at all. cross-linked isobutylene-maleic anhydride copolymers Moreover, the biodegradability will be reduced extremely as (U.S. Pat. No. 4,389,513). the molecular weight becomes greater. These Superabsorbent polymers however are accompa 35 In addition, croSS-linked Saccharides Such as cross-linked nied by the problem that they do not degrade following carboxymethylcellulose, cross-linked alginic acid and croSS disposal after use. linked Starches contain many firm hydrogen bonds in their Under the circumstances, these Superabsorbent polymers molecules, thereby exhibiting Strong interaction between are currently disposed of by incineration or reclamation. molecules and/or polymers. Accordingly, molecular chains However, it is indicated that disposal in incinerators is a 40 cannot be opened widely meaning that their water cause of global warming and acid rain in addition to a cause absorbency is not high. of damage to incinerator materials due to heat occurring during incineration. On the other hand, reclamation disposal Technical Background of Polyamino Acid Superabsor is accompanied by problems. Such as poor Stabilization of bent Polymers reclaimed grounds due to the bulky and undegradable nature 45 On the other hand, polymers which are available by of plastics and, moreover, is facing a Serious problem in that croSS-linking polyamino acids do have biodegradability and there are no longer many Sites Suited for reclamation. are thus compatible with the global environment. It has also Described Specifically, these polymers are poor in degrad been found that, even when absorbed in the body, they are ability and remain Semipermanently in water or Soil. Their digested and absorbed by enzymatic action and moreover, disposal presents a very Serious problem from the viewpoint 50 they do not exhibit antigenecity in the body and their of environmental preservation. For example, in the case of metabolites are free of toxicity. These polymers are accord polymers for disposable applications, led by Sanitary prod ingly materials which are also Safe for human beings. ucts Such as disposable diaperS and Sanitary napkins, their As a disclosed example of Such a polymer, a process for recycling, if tried, would require Substantial expenditure the production of a polymer having high water-absorbency, while their incineration, if attempted, would significantly 55 which comprises irradiating Y rays to poly-Y-glutamic acid, affect the global environment due to the enormous quantities was reported by Kunioka et al. in KOBUNSHI RONBUN involved. On the other hand, it has been reported that use of SHU (The Journal of the Society of Polymer Science, a croSS-linked polyacrylic acid resin as an agricultural and Japan), 50(10), 755 (1993). From an industrial viewpoint, horticultural water-holding material leads to the formation however, a 'Co irradiation system for use in this technology of complexes with multivalent ions such as Ca" in soil and 60 requires considerable equipment for Shielding radiation, and hence results in the formation of an insoluble layer Sufficient care is also required for its control. This technol Matsumoto et al., KOBUNSHI (High Polymer, Japan), 42, ogy is therefore not practical. As a further problem, the high August, 1993). Such a layer is considered to have low cost of polyglutamic acid as the Starting Substance can also toxicity by itself but is not found at all in the natural world. be mentioned. Nothing is known about their influence on the ecosystem 65 In addition, processes for obtaining a hydrogel by croSS resulting from an accumulation of Such polymers in Soil over linking an acidic amino acid were reported by Akamatsu et a long period and therefore, a thorough investigation is al. in U.S. Pat. No. 3,948,863 (corres.JP Kokoku 52-41309) 6,072,024 3 4 and Iwatsuki et al. in JP Kokai 5-279416. Further, use of the reaction system is thus solidified. This makes it difficult croSS-linked amino acid polymers as Superabsorbent poly to perform the reaction under Stirring, or post-reaction mers was reported by Sikes et al. in JPPCT Kokai 6-506244 treatments become extremely difficult. This production pro (corres. U.S. Pat. No. 5,247,068 and U.S. Pat. No. 5,284, ceSS is therefore not Suited for industrial production. The 936), Suzuki et al. in JP Kokai 7-309943 and Harada et al. production process of a croSS-linked polySuccinimide as a in JP Kokai 8-59820. precursor of a cross-linked polyaspartic acid resin has room In all the above reports, however, these polymers did not for improvements in connection with Simplification and have Sufficient water or Saline absorbency and were not improvements of process control and process Steps them practically usable. Further, these resins are accompanied by Selves. a problem that their gels have low Strength and become In JP Kokai 7-224163 and JP Kokai 9-169840, it is sticky with time. described that use of a basic amino acid, Such as lysine or Background of Technical Concept of the Present Inven ornithine, as a polyamine for use as a croSS-linking agent is torS preferred from the Standpoint of the Safety of the remaining As is described in JP Kokai 7-224163, the present inven unreacted cross-linking agent and decomposition products. tors disclosed a technique for the production of a croSS 15 However, the basic polyamino acids Specifically disclosed in linked polyaspartic acid resin having high Saline absorbency, these publications involve problems such that they are low which comprises reacting a poly Succinimide with a croSS in reactivity and that, although use of their esters can provide linking agent to hydrolyze remaining imide rings. improvements in reactivity, these esters themselves are costly. Further, as is disclosed in JP Kokai 9-169840, the present inventors also disclosed a technique for the production of a SUMMARY OF THE INVENTION cross-linked polyaspartic acid resin having Saline A general object of the present invention is to make absorbency, which comprises crosslinking a poly Succinim further improvements in the inventions already disclosed by ide and then hydrolyzing remaining imide rings in an the present inventors. intimately mixed Solvent of a water-miscible organic Solvent 25 and water. Specifically, a first object of the present invention is to Cross-linked polyaspartic acid resins available by these provide a process which, through hydrolysis of imide rings techniques are very useful for their globe-compatibility and of a croSS-linked polySuccinimide, can easily produce at high water absorbency. From the industrial viewpoint, high Volumetric efficiency a croSS-linked polyaspartic acid however, there is room for further improvements. Described resin having high water absorbency. Specifically, the concentrations of croSS-linked polyaspartic A Second object of the present invention is to provide a acid resins produced in these production processes are as process for producing a croSS-linked polyaspartic acid resin, low as about 5 wt.%, indicating the existence of room for which is equipped with excellent gel Strength, is improved an improvement in Volumetric efficiency. Further, according in the Stickiness at gel Surfaces and has high water absorbency, by removing water-Soluble by-products in the to the knowledge of the present inventors, hydrolysis of 35 imide rings of a croSS-linked poly Succinimide in water upon purification of the resin. production of a croSS-linked polyaspartic acid resin causes A third object of the present invention is to provide a the resin in the reaction System to absorb water and Swell, process which, through Simple Steps, can produce a croSS resulting in Significant gelation. This makes it difficult to Stir linked poly Succinimide useful as a precursor for a croSS the reaction System. A hydrolyzing reagent can no longer 40 linked polyaspartic acid resin. Spread So that the reaction is not allowed to proceed Suffi A fourth object of the present invention is to provide a ciently. This results in a problem that the thus-produced process for the production of a cross-linked polyaspartic croSS-linked polyaspartic acid resin is not provided with acid resin, which in order to provide the cross-linked pol high water absorbency. On the other hand, hydrolysis in an yaspartic acid resin with excellent Safety, permits an efficient organic Solvent or a mixed Solvent of water and an organic 45 reaction by using a basic amino acid, Such as lysine or Solvent, Said mixed Solvent containing the organic Solvent in ornithine, as a croSS-linking agent excellent in Safety. a high proportion, tends to allow the resin in the reaction The first object can be achieved by a process for produc System to undergo a hydrolysis reaction only at Surfaces of ing a cross-linked polyaspartic acid resin by Subjecting resin particles, So that the reaction Velocity of the hydrolysis imide rings of a croSS-linked poly Succinimide to a hydroly becomes very slow. This also results in the problem that the 50 sis reaction, wherein Said hydrolysis reaction is conducted thus-produced croSS-linked polyaspartic acid resin is not while controlling a Swelling degree of a resin in a reaction provided with high water absorbency. system within a range of from 3 to 100 times. The present inventors found that croSS-linked polyaspartic The degree of gelation of the resin can be optimized acid resins produced as described above contain water provided that reaction conditions for the hydrolysis-Such Soluble impurities Such as water-Soluble polymers and Salts. 55 as the ratio of water to a water-miscible organic Solvent, the Accordingly, they have room for further improvements Such concentration of a Salt and temperature-are Set So that the as an improvement in gel Strength, the elimination of Sticki hydrolysis reaction is conducted while maintaining the neSS on a gel Surface and improvements in absorbency for Swelling degree within the range of from 3 to 100 times. As Salt-containing aqueous Solutions. a result, the hydrolyzing Velocity can be accelerated to allow In the production process of JP Kokai 7-224163, a failure 60 the hydrolysis reaction to proceed Sufficiently. As a result, in the full control of the production Step of a croSS-linked the resulting croSS-linked polyaspartic acid resin is provided poly Succinimide may not allow the croSS-linking to proceed with improved water absorbency. In addition, Stirring can be Sufficiently So that a Superabsorbent resin having high water easily performed. This makes it possible to increase the resin absorbency may not be obtained. According to the produc concentration in the reaction System and hence to achieve a tion process disclosed in JP Kokai 9-169840, the resin 65 higher Volumetric efficiency. absorbs a reaction Solvent during a croSS-linking reaction in The Second object can be attained by a proceSS for the the production Step of a cross-linked polySuccinimide and production of a cross-linked polyaspartic acid resin, which 6,072,024 S 6 comprises washing or reprecipitating a gel of a feed croSS Specific examples of the amino acid other than aspartic linked polyaspartic acid resin with water and/or a water acid can include 19 types of indispensable amino acids with miscible organic Solvent. the exception of aspartic acid, L-ornithine, a Series of The Washing or reprecipitation of the gel with water C.-amino acids, B-alanine, Y-aminobutyric acid, neutral and/or the water-miscible organic Solvent can provide the amino acids, acidic amino acids, co-esters of acidic amino croSS-linked polyaspartic acid resin with improved water acids, basic amino acids, N-Substituted derivatives of basic absorbency and gel strength. This is believed to be attrib amino acids, aspartic acid-L-phenylalanine dimer utable to elimination of water-Soluble components contained (aspartame); and aminosulfonic acids Such as L-cysteic acid. in the gel of the resin and detrimental to properties of the Each C.-amino acid may be in the form of either an optically resin, Such as monomers, oligomers, and an inorganic or active Substance (L-form or D-form) or a racemic modifi organic Salt. cation. The third object can be accomplished by a process for the Further, the polymer may be a copolymer containing production of a croSS-linked poly Succinimide resin, which recurring units other than an amino acid. comprises reacting a feed polySuccinimide, which has been Illustrative of the recurring units of the copolymer can be brought into a dispersed State by a dispersant, with a 15 dehydrating condensation products of aminocarboxylic croSS-linking agent. acids, aminosulfonic acids, aminophosphonic acids, When the croSS-linking reaction of the feed polySuccin hydroxycarboxylic acids, mercaptocarboxylic acids, mer imide is conducted with the feed poly Succinimide main captosulfonic acids, mercaptophosphonic acids, and the like. tained in the dispersed State as described above, it is possible Also included can be hydrating condensation products, to omit a proceSS control which would otherwise be required addition products and Substituted derivatives of polyamines, to avoid over-gelation and, moreover, to allow the croSS polyhydric alcohols, polythiols, polycarboxylic acids, linking reaction to proceed well. The cross-linked poly Sulfonic acids, polyphosphoric acids, polyhydrazine poly Succinimide, which is useful as a precursor for a croSS compounds, polycarbamoyl compounds, polysulfonamide linked polyaspartic acid resin having (bio)degradability and compounds, polyphosphonamide compounds, polyepoxy high water absorbency, can therefore be produced at high 25 compounds, polyisocyanate compounds, polythioisocyanate productivity by the Simple process. compounds, polyaZiridine compounds, polycarbamate The first and third objects can also be achieved by a compounds, polycarbamic acid compounds, polyoxazoline proceSS for the production of a cross-linked polyaspartic compounds, compounds containing multivalent reactive acid resin, which comprises disintegrating a gel of a croSS unsaturated bonds, multivalent metals, and the like. linked polySuccinimide, which has been gelled as a result of In the case of a copolymer, it can be either a block inclusion of an organic Solvent in a croSS-linking reaction, to copolymer or a random copolymer. The copolymer can also Subject remaining imide rings to hydrolysis although be a graft copolymer. hydrolysis treatment of the gel has heretofore been very No particular limitation is imposed on the number of difficult. recurring units composed of polyaspartic acid residual The fourth object can be realized by a process for the 35 groups, but based on the total number of the recurring production of a cross-linked polyaspartic acid resin, which number making up the molecule, 1 to 99.8% is preferred comprises efficiently Subjecting a poly Succinimide to a with 10 to 99.8% being more preferred. croSS-linking reaction by using as a croSS-linking agent a AS the recurring units of the backbone basic skeleton of basic amino acid, Such as lysine or ornithine, in the form of the croSS-linked polyaspartic acid resin, they may preferably 40 be formed of aspartic acid residual groups alone or of a its carboxylate Salt, preferably, its alkali metal or alkaline copolymer with glutamic acid or lysine from the Standpoint earth metal Salt. of providing high water absorbency. From the viewpoint of The croSS-linked polyaspartic acid resin available in industrial production, it is particularly preferred that the accordance with the present invention is compatible with the recurring units are composed of aspartic acid residual groups global environment owing to its biodegradation after its use, 45 alone. and is therefore very useful as a Superabsorbent polymer for Amide bonds in a backbone basic skeleton of polyaspartic disposable diapers, agricultural or horticultural applications acid can be either C-bonds or B-bonds or the like. Namely, in the case of polyaspartic acid or a copolymer DETAILED DESCRIPTION OF THE thereof, an O-bond is formed when an amino group or the INVENTION AND PREFERRED 50 like in aspartic acid or a monomer of the copolymer is EMBODIMENTS bonded with the C-carboxyl group of aspartic acid, whereas 1 Structure of the cross-linked polyaspartic acid resin a B-bond is formed when the amino group or the like is Roughly dividing, the polymer according to the present bonded with the B-carboxyl group of the aspartic acid. invention is structurally composed of a backbone basic Such C-bonds and B-bonds are generally found together in skeleton, Side chain portions and cross-linking portions. 55 polyaspartic acid. No particular limitation is imposed on the These three constituents will hereinafter be described sepa Style of bonding. rately. Side chain groups and cross-linking groups in the present 1-1 Structure of the backbone basic skeleton of the cross invention are basically carboxylic acid derivatives formed as linked polyaspartic acid resin a result of Substitution of carboxyl groups in polyaspartic Recurring units of the backbone basic skeleton of the 60 acid. A description will hereinafter be made about their croSS-linked polyaspartic acid resin produced in the present details. invention may be formed of aspartic acid residual groups 1-2 Structure of the side chains in the cross-linked pol alone or may be a copolymer of aspartic acid and an amino yaspartic acid resin acid other than aspartic acid. Incidentally, the recurring units Each Side chain in the croSS-linked polyaspartic acid resin of aspartic acid in the polymer is called “a polyaspartic acid 65 have a structure formed by Subjecting an imide ring in the residual group' in the present invention irrespective of the croSS-linked poly Succinimide to ring-opening through Style of bonding. hydrolysis, and contains a carboxyl group formed by the 6,072,024 7 8 hydrolysis. The croSS-linked polyaspartic acid resin may No particular limitation is imposed on the linkage por additionally contain Side chains which contain other Sub tions in the croSS-linking portions in the croSS-linked pol Stituent groups. Examples of Such other Substituent groups yaspartic acid resin. The followings are specific examples of can include, but are not limited to, pendant groups which contain one or more of hydroxyl, amino, mercapto, Such linkage portions. carboxyl, Sulfonic, phosphonic, alkyl, aryl, aralkyl and like groups. The pendant groups may be alkyl, aryl or aralkyl -CH-, -CHCH-, -CHCHCH-, groups which have no Substituent group. These pendant groups are connected to the polyaspartic acid residue group -CH2CH2CHCH-, -(CH2)5- -, -(CH2)-, via amide, ester, thioester or like bonds. -(CH)-, -(CH)s-, -(CH2)6-, Each carboxyl group formed by hydrolysis may be in the free form or in the form of a Salt. Specific examples of an ion -(CH2)o-, -(CH2) , -(CH2)2-, which forms the Salt can include alkali metal ions Such as -(CH2)-, -(CH2)4-, -(CH2) is , Sodium, potassium, and lithium ions, ammonium ions Such S ammonium, tetra methylam monium, -(CH2)6-, -(CH2)7-, -(CH2) is , tetraethylam monium, tetra propylam monium, 15 -CHCH-O-CH-CH , tetrabutylam monium, tetrap enty lammonium, tetrahe Xylammonium, ethyltrimethylammonium, -(CH2CH2O)2CH-CH-, trimethylpropylammonium, butyltrimethylammonium, pentyltrimethylammonium, hexyltrimethylammonium, - (CH-CHO)CHCH-, -(CH2CH2O). CHCH-, cyclohexyltrim ethylam monium, - (CH2CH2O)3CHCH-, - (CH2CH2O)-CHCH-, benzyltrimethylammonium, triethylpropylammonium, -CHCHCHOCH2CHCH-, triethylbutylammonium, triethylpenty lammonium, triethylhexylammonium, cyclohexyltriethylammonium, and - (CH2CH2CH2O)2CH2CH2-CH2-, benzyltriethylammonium ions, and amine ions Such as (CH2CH2CH2O)3CH2CH2CH2 , trimethylamine, triethylamine, tripropylamine, 25 tributylamine, trip enty lamine, trihe Xylamine, (CH2CH2CH2O)4CH2CH2CH2 , trie thanolamine, tripropanolamine, tributanolamine, (CH2CH2CH2O)5CH2CH2CH2 , tripentanolamine, trihexanolamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dicyclohexylamine, dibenzylamine, ethylmethylamine, methylpropylamine, butylmethylamine, -circury- -circury metylpenty lamine, methylhexylamine, methylamine, COOCH, COOH ethylamine, propylamine, butylamine, pentylamine, o CHCH2CH2CHCH - o CHCH2CH2CHCH -s hexylamine, octylamine, decylamine, dodecylamine, and COOCH, COOH hexadecylamine ions. 35 Among these ions, those having Smaller atomic or o CH2CH2CH2CH2CH- o CH2CH2CH2CH2CH - molecular weights are preferable because, as the atomic or molecular weight of an ion increases, the molecular weight COOCHs, COOCH4, per monomer unit relatively becomes greater and the water absorption per unit weight relatively becomes Smaller. 40 —culti- -city Where there is possibility of being brought into contact with COOCH, COOH human skin or the like, those having lower toxicity are desirable, meaning that use of Sodium, potassium, lithium, th th ammonium or triethanolamine is preferred and further that -cy- —cy use of Sodium or potassium is particularly preferred from the 45 COOCH, COOH Standpoint of cost. 1-3 Structure of the cross-linking portions in the cross linked polyaspartic acid resin CHCH Concerning the croSS-linking portions in the cross-linked COOCH, polyaspartic acid resin, no particular limitation is imposed 50 on their molecular Structures. The croSS-linking portions in the cross-linked polyaspartic acid resin can be discussed by cut dividing each of them into a “bonded portion” bonded to the COOH basic skeleton of the polymer backbone and a "linkage OH HO portion' croSS-linking the bonded portions. A description 55 will hereinafter be made about these divided portions. 1-3-1 Bonded portions in the cross-linking portions in the / ( O O s croSS-linked polyaspartic acid resin OH HO No particular limitation is imposed on the bonded por tions in the croSS-linking portions in the cross-linked pol 60 yaspartic acid resin. Their specific examples can include / K. d ) \ s 2 Structures formed of an amide bond, an ester bond and a thioester bond, respectively. Structures of only one type may OH HO be contained, or Structures of plural types may be contained together. 65 1-3-2 Linkage portions in the cross-linking portions in the croSS-linked polyaspartic acid resin 6,072,024 9 10 -continued -continued —co-O- (CH)-, o ci-O- (CH2)4, 1O —co-O- (CH2)5- -,

15

25 RSCC 35

s

40 CH

OR H OR H OR OR

RO OR, CH 45 H OR H OR H H HO These linkage portions may be in unsubstituted forms or in forms substituted by Substituted groups. Illustrative examples of the Substituent groups can include linear or 50 branched alkyl groups having 1-18 carbon atoms, cycloalkyl groups having 3-8 carbon atoms, aralkyl groups, Substituted or unsubstituted phenyl groups; Substituted or unsubstituted naphthyl groups, linear or branched alkoxy groups having 1-18 carbon atoms, aralkyloxy groups, phe -O-O-) 55 nylthio groups, linear or branched alkylthio groups having 1-18 carbon atoms, linear or branched alkylamino groups ( ) C ( ) s having 1-18 carbon atoms, dialkylamino groups in which H each alkyl group is either linear or branched and has 1-18 carbon atoms, trialkylammonium groups in which each alkyl 60 group is either linear or branched and has 1-18 carbon atoms, hydroxyl, amino, mercapto, carboxyl, Sulfonic acid --( )—cil and phosphonic acid groupS and Salts thereof; alkoxycarbo nyl groups, and alkylcarbonyloxy groups. More specific examples can include alkyl groupS. Such as 65 methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, o cur-O- (CH) , nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl; 6,072,024 11 12 cycloalkyl groups Such as cyclopropyl, cyclobutyl, hydroxy, amino, mercapto, carboxyl, Sulfonic acid and/or cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl, phosphonic acid groups, and/or salts thereof). aralkyl groupS. Such as benzyl, phenylethyl, phenylpropyl, When the cross-linked polyaspartic acid resin is used as a and phenylbutyl, phenyl groups Such as phenyl, tolyl, Xylyl, water-holding material, inclusion of polar groups in the chlorophenyl, and biphenyl, naphthyl groupS. Such as naph molecule of the resin is preferred. Accordingly, it is particu thyl and methylnaphthyl, alkoxy groupS. Such as methoxy, larly preferred for the croSS-linking portions either to be ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, unsubstituted and to contain polar groups or to be Substituted octyloxy, decyloxy, undecyloxy, dodecyloxy, tridecyloxy, by polar-group-containing Substituent groups (for example, tetrade cyloxy, p enta decyl oxy, he Xade cyloxy, hydroxyl, amino, mercapto, carboxyl, Sulfonic acid and/or heptyldecyloxy, and octyldecyloxy, aralkyloxy groupS Such 1O phosphonic acid groups, and/or salts thereof) as phenoxy, benzyloxy, and tolyloxy; alkylthio groupS Such Although no particular limitation is imposed on the pro as methylthio, ethylthio, propylthio, butylthio, pentylthio, portion of Such cross-linking portions, recurring units with hexylthio, heptylthio, octylthio, nonylthio, decylthio, the cross-linking portions carried thereon may account, in undecylthio, dodecylthio, tridecylthio, tetradecylthio, number, preferably for 0.1 to 20%, more preferably 0.5 to pentadecylthio, hexadecylthio, heptyldecylthio, and octyl 15 10% of entire recurring units of the polymer. decylthio; aralkylthio groupS. Such as phenylthio, benzylthio, 2 Production process of the poly Succinimide and tolylthio; alkylamino groupS. Such as methylamino, Although no particular limitation is imposed on the pro ethylamino, propylamino, butylamino, pentylamino, duction process of the uncroSS-linked poly Succinimide use hexylamino, heptylamino, octylamino, nonylamino, ful in the practice of the present invention, a process decylamino, undecylamino, dodecylamino, tridecylamino, reported in J. Amer. Chem. Soc., 80, 3361 et seq., 1958 or tetradecylamino, pentadecylamino, hexadecylamino, the like can be mentioned as a Specific example. heptyldecylamino, and octyldecylamino; dialkylamino No particular limitation is imposed on the molecular group S Such as dimethylamino, diethylamino, weight of the poly Succinimide to be used, but a higher dipropylamino, dibutylamino, dip enty lamino, molecular weight provides higher ability as a water-holding dihexylamino, diheptylamino, dioctylamino, dinonylamino, 25 material. The molecular weight is generally 30,000 or dide cylamino, diundecylamino, didodecylamino, higher, preferably 60,000 or higher, more preferably 90,000 ditridecylamino, ditetradecylamino, dipentadecylamino, or higher. dihexadecylamino, diheptyldecylamino, dioctyldecylamino, Further, the poly Succinimide can be in either a linear ethylmethylamino, and methylpropylamino; trialkylammo Structure or a branched Structure. nium groupS. Such as trimethylammonio, triethylammonio, 3 Production process of the cross-linked polySuccinimide tripropylammonio, tributylammonio, tripentylammonio, Although no particular limitation is imposed on the pro trihexylammonio, triheptylammonio, trioctylammonio, duction process of the cross-linked poly Succinimide trinonylammonio, tridecylammonio, triundecylammonio, employed in the practice of the present invention, illustrative trido de cylam monio, tride cylam monio, exemplary processes can include a process in which a trite trade cylammonio, trip ent a de cylammonio, 35 croSS-linking agent is reacted to a Solution of poly Succin trihexadecyl ammonio, trihepty lde cylammonio, imide in an organic Solvent and a process in which trioctylde cylammonio, dimethylethylammonio, poly Succinimide, which is in a form dispersed by a dimethylbenzylammonio, and methyldibenzylammonio, dispersant, and a croSS-linking agent are reacted. hydroxyl, amino, mercapto, carboxyl, Sulfonic acid and AS the former process, reference may be had, for example, phosphonic acid groups, and Salts thereof; alkyloxycarbonyl 40 to JP Kokai 7-224163, in which a cross-linking agent is groups Such as methyloxycarbonyl, ethyloxycarbonyl, added to a Solution of poly Succinimide in an organic Solvent propyloxycarbonyl, butyloxycarbonyl, pentyloxycarbonyl, to conduct a cross-linking reaction. When this croSS-linking hexyloxycarbonyl, heptyloxycarbonyl, octyloxycarbonyl, reaction proceeds to a high croSS-linking degree, the thus nonyloxycarbonyl, decyloxycarbonyl, undecyloxycarbonyl, crosslinked polySuccinimide is obtained in the form of a gel. do de cylo Xy carbonyl, tride cylo Xy carbonyl, 45 This gel is then treated in a manner to be described Subse tetradecyloxycarbonyl, pentade cyloxycarbonyl, quently herein. hexadecyloxycarbonyl, heptyldecyloxycarbonyl, and octyl On the other hand, the latter process is one of the decyloxycarbonyl; and alkylcarbonyloxy groups Such as characteristic features of the present invention. Namely, the methylcarbonyloxy, ethylcarbonyloxy, propylcarbonyloxy, reaction between polySuccinimide, which has been brought butylcarbonyloxy, pentylcarbonyloxy, hexylcarbonyloxy, 50 into a dispersed State by a dispersant, and a croSS-linking heptylcarbonyloxy, octylcarbonyloxy, nonylcarbonyloxy, agent in accordance with the present invention makes it de cylcarbonyl oxy, unde cylcarbonyl oxy, possible to produce croSS-linked poly Succinimide at high do de cylcarbonyl oxy, tride cylcarbonyl oxy, productivity by the Simple process. AS the dispersant, a poor tetradecylcarbonyloxy, pentade cylcarbonyloxy, Solvent Selected from the group consisting of organic hexadecylcarbonyloxy, heptyldecylcarbonyloxy, and octyl 55 Solvents, which cannot achieve Substantially complete dis decylcarbonyloxy. Solution of the polySuccinimide, and water is preferred. Selection of one having a Smaller molecular weight from AS examples of the process in which poly Succinimide, these illustrative Substituent groups is preferred, because which has been brought into a dispersed State by a poor Selection of one having a larger molecular weight leads to a Solvent (for example, water and/or another poor Solvent) as croSS-linking portion having a larger molecular weight, a 60 a dispersant, the following processes 3-1 to 3-5 can be relatively larger molecular weight per recurring unit, and mentioned. hence, a Smaller water absorption per unit weight. In 3-1 PolySuccinimide is brought into a dispersed State in general, it is also preferable to Select a Substituent group a poor Solvent as a dispersant and is then reacted with which permits a simpler production process. For example, a croSS-linking agent. unsubstituted linkage portions or linkage portions Substi 65 3-2 Polysuccinimide is dissolved in a good solvent to tuted by Substituent groups (e.g., methyl, ethyl, methoxy, prepare a polySuccinimide Solution. This Solution is methyloxycarbonyl and/or methylcarbonyloxy groups; mixed with a poor Solvent as a dispersant, So that the 6,072,024 13 14 polySuccinimide is brought into a dispersed State and is as permitting Substantial dissolution of a cross-linking agent reacted with a croSS-linking agent. to be used. For example, a mixed Solvent having higher 3-3A mixed Solvent of a good Solvent and a poor Solvent polarity is preferred when a cross-linking agent having as a disperSant is prepared. PolySuccinimide is added to higher hydrophilicity is used, whereas a mixed Solvent this mixed Solvent, and is brought into a dispersed State, having lower polarity is preferred when a croSS-linking followed by a reaction with a cross-linking agent. agent having higher hydrophobicity is employed. 3-4 AS a first step, poly Succinimide is dissolved in a Specific examples of good Solvents can include N,N- good Solvent to prepare a poly Succinimide Solution, to dimethyl formamide, N,N-dimethylace tamide, which a croSS-linking agent is added to allow a croSS N-methylpyrrollidone, N,N'-dimethylimidazolidinone, linking reaction to proceed partially. As a Second step, dimethylsulfoxide, and sulfolane. Of these, N,N- before the polySuccinimide is gelled by the croSS dimethylformamide and N,N-dimethylacetamide are par linking reaction in the first Step, a poor Solvent as a ticularly preferred for their high solubility of polysuccinim dispersant is added to bring the polySuccinimide into a ide. These Solvents may be used either Singly or in dispersed State So that the cross-linking reaction is combination. allowed to proceed further. 15 4-2 Poor Solvent for use in the cross-linking reaction 3-5 Polysuccinimide is dissolved in a good solvent to The term “poor solvent as used herein should be inter prepare a poly Succinimide Solution, to which a poor preted to embrace organic Solvents, which cannot achieve Solvent as a dispersant is slowly added to bring the Substantially complete dissolution of poly Succinimide, and polySuccinimide into a dispersed State, followed by a water. In the present invention, this poor Solvent can be reaction with a croSS-linking agent. Suitably used as a dispersant. According to the process 3-1, the polySuccinimide is No particular limitation is imposed on the poor Solvent for brought into the dispersed State in the poor Solvent as the use in the present invention. Any Solvent can be used insofar dispersant. The poly Succinimide during the progreSS of the as it is employed in general chemical reactions and has low croSS-linking reaction has been neither dissolved in nor solubility for polysuccinimide. When a poor solvent is used Swollen by the solvent. The process 3-2, on the other hand, 25 in combination with a good Solvent, one having miscibility is different in that the poly Succinimide is once dissolved in with the good Solvent is preferred as the poor Solvent. Like the good Solvent and the resultant polySuccinimide Solution the good Solvent described above, it is generally preferred to and the poor Solvent as the dispersant are mixed to disperse use Such a poor Solvent as permitting Substantial dissolution the poly Succinimide. In the process 3-2), the polySuccin of a croSS-linking agent to be used. imide during the progreSS of the croSS-linking reaction is in Specific examples of poor Solvents can include water; the dispersed State and is in a form Somewhat dissolved in alcohols Such as methanol, ethanol, propanol, isopropanol, or Swollen by the good Solvent. Compared with the proceSS butanol, pentanol, he Xanol, heptanol, octanol, 3-1, the process 3-2 therefore allows the cross-linking 2-methoxyethanol, and 2-ethoxyethanol; glycols Such as reaction to proceed evenly with ease. Further, the dispersed ethylene glycol, diethylene glycol, triethylene glycol, pro State of the polySuccinimide is good because the once 35 pylene glycol, and dipropylene glycol, glycoSolves Such as dissolved poly Succinimide is finely dispersed by reprecipi methylglycosolve and ethylglycoSolve, ketones Such as tation. acetone, methyl ethyl ketone, and methyl isobutyl ketone; In the process 3-4), the addition of the poor solvent cyclic etherS Such as tetrahydrofuran and dioxane, petroleum before the gelation is needed, because it becomes difficult to ether; pentane, hexane, heptane; octane, cyclohexane, ben perform the dispersion by the dispersant once the poly Suc 40 Zene, toluene, ethylbenzene, Xylene, decalin; diphenyl ether; cinimide during the progress of the croSS-linking reaction is aniSole; and creSol. Of these, water, methanol, ethanol, gelled. Optionally, either before or after the addition of the propanol and isopropanol are particularly preferred as then croSS-linking agent, a Suitable amount of a poor Solvent, an can dissolve croSS-linking agents or carboxylate Salts of acid or the like may be added with a view to slowing down amino acids. These Solvents can be used either Singly or in the cross-linking reaction for the prevention of gelation. 45 combination. Further, it is possible to conduct a hydrolysis reaction of Incidentally, these poor Solvents can also be used for imide rings in the croSS-linked poly Succinimide in the first purposes other than dispersing poly Succinimide, for Step and the Second Step. example, for slowing down the cross-linking reaction. Specific examples of the poor Solvents employed in the 4-3 Mixing ratio of a good Solvent to a poor Solvent for use processes 3-1 to 3-5 will be described subsequently 50 in the croSS-linking reaction herein. Especially in each of the processes 3-2 to 3-5), the When a good Solvent and a poor Solvent are used in good Solvent and the poor Solvent are used in combination combination, no particular limitation is imposed on their so that these solvents preferably have mutual miscibility. mixing ratio. Use of the poor Solvent in an appropriately 4) Production conditions for the cross-linked polySuccin large proportion results in the development of the effect of imide 55 the poor Solvent, whereby poly Succinimide is brought into a A description will hereinafter be made about production dispersed State and gelation can be avoided. On the other conditions common to the above-described processes 3-1 hand, use of the poor Solvent in an adequately Small pro to 3-5). portion results in the development of the effect of the good 4-1 Good Solvent for use in the cross-linking reaction Solvent, So that poly Succinimide is brought into a uniformly The term “good solvent” as used therein should be 60 dispersed State. Further, use of the poor Solvent in Such an interpreted to embrace therein organic Solvents which can adequately Small proportion generally reduces the cost for achieve Substantially complete dissolution of poly Succinim Solvent recovery and is hence advantageous economically. ide. AS already mentioned above individually with respect to No particular limitation is imposed on the good Solvent the good Solvent and the poor Solvent, it is generally for use in the present invention, but one having miscibility 65 preferred to use Such good Solvent and poor Solvent as with a poor Solvent employed in combination is preferred in permitting Substantial dissolution of a cross-linking agent, general. Generally, it is preferred to use Such a good Solvent which is to be used, when combined into a mixed solvent. 6,072,024 15 16 4-4 Concentration of polySuccinimide for use in the cross as Nö-(2-amino-2-carboxyethyl) ornithine, N6-(2-amino-2- linking reaction carboxyethyl)lysine, O-(2-amino-3-hydroxypropyl) No particular limitation is imposed on the concentration homoserine, kynurenine, C.f3-diaminoSuccinic acid, C.e- of poly Succinimide in the poly Succinimide-containing dis diaminopimelic acid, 2,6-diamino-7-hydroxyaZelaic acid, persion during the progress of the croSS-linking reaction but, isolysine, 3,5-diaminohexanoic acid, C.Y-diaminobutyric in general, a concentration of from 0.1 to 50 wt.% is acid, djenkolic acid, cyStathionine, cystine disulfoxide, C.e- preferred with a range of from 1 to 40 wt. % being dia mino-B-hydrop ime lic acid, hyp usine, particularly preferred. Y-hydroxy ornithine, C.-hydroxyly Sine, lanthionine, 4-5 Particle size of polysuccinimide for use in the cross lysinonorleucine, lySOvitoxine, and loseanine, amino acid linking reaction derivatives Such as lysinetriamine; and polyamines formed Concerning the particle size of polySuccinimide in the by connecting molecules of amino-containing compounds, dispersed State, a Smaller particle size is preferred as the Such as cystine and cyStamine, Via disulfide bonds. reaction is facilitated. Using as a Standard the particle size When these polyamines are in the form of salts such as (average particle diameter) of poly Succinimide in a dry mineral acid Salts Such as hydrochlorides, Sulfates or hydro form, the particle size is preferably 100 um or Smaller, more 15 bromides or organic acid Salts. Such as p-toluenesulfonates or preferably 10 um or smaller. When the particles of polysuc acetates, the mineral acid Salts or organic acid Salts can be cinimide are appropriately Small as mentioned above, the used after neutralizing them in advance. When an amino croSS-linking reaction is allowed to easily proceed to the acid in the form of a polyamine is used as a croSS-linking inside So that, when hydrolysis is conducted Subsequently, agent, it is necessary to dissociate an intramolecular Salt uncroSS-linked, water-Soluble portions are reduced, thereby because, for the Structure of the amino acid, each carboxyl making it possible to prevent reductions in yield and per group and its associated amino group are contained in the formance. form of Salt in the molecule. When the above-described In this regard, it is preferred for the minimization of an amino acid is used as a polyamine, the polyamine should be uneven cross-linking reaction to adopt Such a method as used after converting each amino group into its free form by positively realizing a more uniformly dispersed State of 25 adding a base to the polyamine to neutralize each carboxyl poly Succinimide by wet grinding. This wet grinding is very group into a carboxylate Salt. No particular limitation is useful especially for the process 3-1). Details of this wet imposed on the base to be used for the neutralization, but an grinding will be described in the explanation of disintegra alkali metal hydroxide Such as Sodium hydroxide or potas tion. sium hydroxide, an alkali metal carbonate Such as Sodium 4-6 Cross-linking agent for use in the cross-linking reac carbonate or potassium carbonate, an alkali metal hydro tion gencarbonate Such as Sodium hydrogencarbonate or potas No particular limitation is imposed on the cross-linking sium hydrogencarbonate, or an organic amine Such as agent for use in the present invention, insofar as it is a triethylamine, trimethylamine, triethanolamine, pyridine, polyfunctional compound having reactivity with imide rings N-methylmorpholine or picoline is generally employed. in poly Succinimide. For example, polyfunctional com 35 Among these cross-linking agents, preferred are those pounds Such as polyamines and polythiols can be men having less odor and high reactivity with imide rings in tioned. Their specific examples can include polyamines, for poly Succinimide, that is, ethylene diamine, example, aliphatic polyamines Such as hydrazine, propylene diamine, 1,4-butane diamine, ethylenediamine, propylenediamine, 1,4-butanediamine, heptamethylenediamine, hexamethylenediamine, and cysta pentamethylene diamine, he Xa methylene diamine, 40 mine. In addition, protein-constituting amino acids Such as heptamethylene diamine, octamethylene diamine, lysine, ornithine and cystine, and Salts and ester derivatives no name thylene diamine, decame thylene diamine, thereof, amino acids other than the protein-constituting undecamethylene diamine, dodecamethylene diamine, amino acids, Such as C-hydroxylysine, Y-hydroxyornithine tetradecamethylenediamine, hexadecamethylenediamine, and C.Y-diaminobutyric acid, and Salt and ester derivatives 1-amino-2,2-bis(aminomethyl)butane, tetraaminomethane, 45 thereof, amino acid derivatives Such as lysinetriamine; and diethylenetriamine and triethylenetetramine, alicyclic cyStamine are also preferred, because resulting croSS-linked polyamine S Such as norborne ne diamine, 1,4- polyaspartic acid resins are Safe to living organisms and the diaminocyclohexane, 1,3,5-triaminocyclohexane and environment after their degradation and/or biodegradation. isophorone diamine, aromatic polyamines Such as Among these, lysine, ornithine and cystine and their deriva phenylenediamine, tolylenediamine and Xylylenediamine, 50 tives Such as Salts and esters are particularly preferred as basic amino acids, led by lysine and ornithine, and esters they are inexpensive and are readily available. thereof, compounds formed as a result of bonding of two or They can be used either Singly or in combination. more molecules of monoamino compounds through one or For the croSS-linked polyaspartic acid resin according to more disulfide bonds, Such as cyStamine, and derivatives the present invention, use of a basic amino acid as a thereof, aliphatic polythiols Such as 1,2-ethanedithiol, 1,3- 55 croSS-linking agent is also preferred from the Standpoint of propanedithiol, 1,4-butanedithiol, 1,6-hexanedithiol and Safety. pentaerythritol, alicyclic polythiols Such as cyclohex Although no particular limitation is imposed on the basic anedithiol, aromatic polythiols Such as Xylylenedithiol, ben amino acid, it can be represented generally by the following Zenedithiol and toluenedithiol, and esterS Such as trimethy formula (1): lolpropane tris(thioglycolate), trimethylolpropane tris(3- 60 mercaptopropionate), pentaerythritol tetrakis(thioglycolate) (1) and pentaerythritol tetrakis( 3-mercaptopropionate) HN-R-CH-NH. polythiol. Other examples can include protein-constituting amino COOH acids represented by lysine, cystine and ornithine, and Salts 65 and esters thereof, amino acids other than the protein wherein R represents an alkylene, aralkylene or arylene constituting amino acids, and Salts and esters thereof, Such grOup. 6,072,024 17 18 The alkylene, aralkylene or arylene group as R can be of -continued either a linear or a branched Structure or of a cyclic Structure. Further, some of its carbon atoms may be substituted by substituent groups which contain O, N, S, P, B, Sior the like. Namely, the alkylene, aralkylene or arylene group may be Substituted by one or more Substituent groups containing O, N, S, P, B, Si or the like, Such as ether, ester, carbonyl, urea, thioester, thiocarbonyl, Sulfone, Sulfonyl, Sulfonamido, Sec ondary amino, tertiary amino, amido, phosphonic or phos phonamido groups. Further, no particular limitation is imposed on the Substituting position of the amino group to R. Further, R may contain one or more Substituent groups Such as alkyl, cycloalkyl, aralkyl, aryl, alkoxyalkyl, polyoxyalkylene, aryloxyalkylene, aralkyloxyalkyl, alkylthioalkyl, polythioalkylene, arylthioalkylene, 15 a ralkylthio alkyl, alkylamino, dialkylamino, trialkylammonio, alkyloxycarbonylalkyl, and/or alkylcarbo nyloxyalkyl groups. The followings are specific examples of R.

-CH2-, -CHCH-, -CH2CHCH -CH2CH2CH2CH2-, -(CH2)5- -, -(CH2)4-, -(CH2)4-, -(CH2)s-, -(CH2)6-, 25 - (CH)o-, -(CH) , -(CH2)2-, -(CH2)4-, -(CH2)4-, -(CH2)5- -, -(CH2)6-, -(CH2)7- -, -(CH2) is , -CHCHO-CHCH-, OR H OR H OR OR -(CH2CH2O)2CHCH-, - (CH2CH2O)CHCH-, - (CH2CH2O)4CH2CH2-, RO OR, -(CH2CH2O)3CH2CH2-, -(CH2CH2O)-CH2CH2-, 35 H OR H OR H H HO - CHCHCHOCH2CHCH , - (CH2CH2CH2O)2CHCH-CH2-,

(CH2CH2CH2O)3CH2CH2CH2 , 40 (CH2CH2CH2O)4CH2CH2CH2 , (CH2CH2CH2O)5CH2CH2CH2 , —( )— -Q (CH2CH2CH2O)6CH2CH2CH2 , 45 OH HO

OH HO 50 --K)-cis 2 OH HO —cur-OX- (CH2)2-, / K. ( \, )) \, 55 OH HO —cur-OX- (CH2) , / K. ( \, )) \, 60 -cir-O- (CH2)4-, OH HO / K. ( \, )) \, 65 —cur-OX- (CH2)5-, 6,072,024 19 20 -continued (3) - (CH2) (CH2)4-, HN-R-CH-NH COMR

-HC -HC s wherein R has the same meaning as defined above, R' represents an alkyl, aralkyl or aryl group, and M represents -NH-, -N(R"), R" being an alkyl, aralkyl or aryl CH-, -HC 1O group, -S- or -O-.

(4) HN-R-CH-NH

15 COOX wherein R has the same meaning as defined above, and X represents an alkali metalion, an alkaline earth metal ion or an ammonium ion. No particular limitation is imposed on the alcohol, thiol or amine component of the basic amino acid ester, thioester or amide for use in the present invention, but one having a Smaller molecular weight is preferred. On the other hand, no RO C OR HO particular limitation is imposed on the ion which forms the 25 Salt with the carboxylic acid of the basic amino acid for use H ) \ in the practice of the present invention. R= s Specific examples of the ion which forms the carboxylate and Salt can include alkali metal ions Such as Sodium, potassium, and lithium ions, ammonium ions Such as ammonium, tetra methylammonium, tetraethylammonium, th tetrap ropylammonium, tetrabutylam monium, RO C OR HO tetrap enty lammonium, tetrahe Xylammonium, hi, ) \ ethyltrimethylammonium, trimethylpropylammonium, R butyltrimethylammonium, pentyltrimethylammonium, 35 hexyltrimethylammonium, cyclohexyltrimethylammonium, benzyltrimethylammonium, triethylpropylammonium, triethylbutylammonium, triethylpenty lammonium, Further, amino acid dimers and basic polyamino acids triethylhexylammonium, cyclohexyltriethylammonium, and Such as polylysine can also be used. Among these, lysine and benzyltriethylammonium ions, and amine ions Such as ornithine are preferred. 40 trimethylamine, triethylamine, tripropylamine, tributylamine, trip enty lamine, trihe Xylamine, Although no particular limitation is imposed on the man triethanolamine, tripropanolamine, tributanolamine, ner of use of Such a basic amino acid as a cross-linking agent tripentanolamine, trihexanolamine, dimethylamine, in the present invention, the C-amino group and the carboxyl diethylamine, dipropylamine, dibutylamine, dipentylamine, group take an amphoteric ion Structure as shown in Formula 45 dihexylamine, dicyclohexylamine, dibenzylamine, (2) if the basic amino acid is used as is. In this case, the ethylmethylamine, methylpropylamine, butylmethylamine, reactivity of the O.-amino group is lowered So that the methylpentylamine, methylhexylamine, methylamine, reaction Velocity of the basic amino acid as a croSS-linking ethylamine, propylamine, butylamine, pentylamine, agent becomes very low. hexylamine, octylamine, decylamine, dodecylamine, and 50 hexadecylamine ions. (2) Among these ions, those having Smaller atomic or -- molecular weights are preferred because a greater atomic or HN-R-CHH-NH HN-R-CH-NH res molecular weight leads to a relatively greater molecular COOH COO weight per monomer unit and hence to a Smaller water 55 absorption per unit weight. Further, those having lower toxicity are preferred when the resulting croSS-linked pol yaspartic acid resin has possibility of being brought into wherein R has the same meaning as defined above. contact with human skin or the like. For these reasons, it is preferred to use Sodium, potassium, lithium, ammonium or In the reaction, the basic amino acid is therefore used in 60 triethanolamine. Use of Sodium or potassium is particularly the form of a derivative Such as an ester, thioester or amide preferred from the Standpoint of cost. or as one of the characteristic features of the present 4-7. Amount of the cross-linking agent to be employed in invention, in the form of its carboxylate Salt as represented the cross-linking agent by the below-described formula (3) or (4). By using its The amount of the croSS-linking agent is not particularly derivative or its carboxylate salt, the reactivity of the 65 limited, and can be determined as needed depending on the C.-amino group is increased So that it acts effectively as a croSS-linking degree of the resulting croSS-linked resin, Said croSS-linking agent. croSS-linking degree being governed by the number of 6,072,024 21 22 functional groups in the croSS-linking agent and the molecu which has been brought into a dispersed State by a lar weight of the croSS-linking agent, and also on the dispersant, with a croSS-linking agent, Sufficient control of application purpose of the resulting croSS-linked resin. Here, the reaction Step makes it possible to obtain a croSS-linked the term “croSS-linking degree” as used herein is defined to polyaspartic acid resin having a high water absorption Speed indicate the distance or the number of constituent monomer 5 when the imide rings of the cross-linked polySuccinimide units between adjacent croSS-links or the proportion of are hydrolyzed. croSS-linking portions relative to the polymer backbone. In general, an unduly large amount of a cross-linking Examples of this method can include, but not particularly agent leads to an excessively high cross-linking degree, limited to, the following three methods: resulting in reduced water absorbency when formed into a 5-1 To control the manner of charging of a cross-linking croSS-linked polyaspartic acid resin. An unduly Small agent and a dispersant. amount of a cross-linking agent, on the other hand, leads to 5-2To introduce a cross-linking agent as pendant groups an excessively low croSS-linking degree, resulting in a into the polymer backbone, followed by cross-linking polyaspartic acid resin which has been croSS-linked only of the pendant groups. partially, is water-Soluble and does not exhibit water absor 5-3. To react an internal cross-linking agent to poly Suc bency. The amount of the croSS-linking agent can therefore 15 cinimide and then to have a Surface croSS-linking agent be determined Such a way as needed to achieve an appro priate croSS-linking degree. In general, the amount of the reacted for achieving croSS-linking. cross-linking agent may preferably be from 0.1 to 30%, Although no particular limitation is imposed on how to notably from 1-20% based on the total of monomer units in actually conduct these methods, Specific examples of the the poly Succinimide. individual methods will hereinafter be described. 4-8 Catalyst for use in the cross-linking agent 5-1' To a Solution of poly Succinimide in a good Solvent, In the cross-linking reaction, a catalyst may be used as a dispersant and a croSS-linking agent are added at the needed. AS the catalyst, a basic catalyst is generally used. Same time, and cross-linking is then conducted while Illustrative of the basic catalyst are inorganic basic creating a dispersed State. reagents, for example, alkali metal hydroxides Such as 25 5-2. To a Solution of poly Succinimide in a good Solvent, Sodium hydroxide, potassium hydroxide and lithium a cross-linking agent is added for its introduction as hydroxide, alkali metal carbonates Such as Sodium pendant groups. A dispersant is then charged to bring carbonate, potassium carbonate and lithium carbonate, alkali the reaction System into a dispersed State, followed by metal hydrogencarbonates Such as Sodium hydrogencarbon the addition of a base to conduct a cross-linking reac ate and potassium hydrogencarbonate, alkali metal acetates tion. Such as Sodium acetate and potassium acetate, alkali metal 5-3. To a Solution of poly Succinimide in a good Solvent, Salts. Such as Sodium oxalate, and ammonia; and organic an internal croSS-linking agent is added to conduct basic reagents, for example, amines Such as trimethylamine, cross-linking. Either after bring the reaction system trie thylamine, trip ropylamine, tributylamine, into a dispersed State by adding a dispersant or con tripenty lamine, trihe Xylamine, trie thanolamine, 35 currently with the addition of the dispersant, a Surface tripropanolamine, tributanolamine, tripentanolamine, croSS-linking agent is added further to conduct a croSS trihexanolamine, dimethylamine, diethylamine, linking reaction. dipropylamine, dibutylamine, dipentylamine, dihexylamine, These methods 5-1 to 5-3 are all intended to provide dicyclohexylamine, dibenzylamine, ethylmethylamine, the resulting resin with a gradient or a difference in croSS methylpropylamine, butylmethylamine, methylpentylamine, 40 link density between its inner part and its outer part. In methylhexylamine, methylamine, ethylamine, propylamine, particular, provision of an increased croSS-linking degree to butylamine, pentylamine, he Xylamine, octylamine, a resin Surface makes it possible to achieve an excellent decylamine, dodecylamine, hexadecylamine, pyridine, water absorption speed when the resin is used as a Super picoline, and quinoline. absorbent polymer. This is one of the characteristic features 4-9 Reaction temperature of the cross-linking reaction 45 of the present invention. The reaction temperature of the croSS-linking reaction is The conditions described above under 3 and 4 apply not particularly limited, and can be determined as needed in likewise to these methods. A description will hereinafter be View of the reactivity of the croSS-linking agent and the State made about conditions different from the above-mentioned of dispersion of the polySuccinimide. In generally, it may OCS. preferably be from 0 to 200° C., with 10–80° C. being more 50 5-1 How to control the manner of charging of a cross preferred. linking agent and a dispersant 4-10 Procedures after the cross-linking reaction This method is to produce an excellent resin by control After the completion of the cross-linking reaction, the ling the manner of charging (including the timing of proceSS may proceed to the next hydrolysis Step as is without charging) of the cross-linking agent and the dispersant. Separation of the organic Solvent employed in the croSS 55 In this method, the croSS-linking agent and the dispersant linking reaction, or alternatively, may proceed to the next are added at the same time to a Solution of polySuccinimide hydrolysis Step after the croSS-linked poly Succinimide is in a good Solvent, and a croSS-linking reaction is initiated isolated by Separating the organic Solvent. while bringing the reaction System into a dispersed State. The Separation between the croSS-linked polySuccinimide The croSS-linking agent and the dispersant may be added at and the organic Solvent can be conducted by a method 60 the same time through different inlets, respectively, or may known per Se in the art. For example, filtration, decantation, be added through a Single inlet after either mixing or centrifugal Separation or the like can be adopted. dissolving them in advance. As a still further alternative, the 5 Cross-linking method of poly Succinimide in a dispersed croSS-linking agent may be dissolved in a Suitable organic State for the production of a croSS-linked polyaspartic acid Solvent or water and may then be added in a similar manner resin with an increased water absorption Speed 65 as the above-described manner. No particular limitation is In the process of the present invention for obtaining a imposed on the Suitable organic Solvent insofar as it can croSS-linked poly Succinimide by reacting poly Succinimide, achieve Substantially complete dissolution of the croSS 6,072,024 23 24 linking agent. No particular limitation is imposed either on No particular limitation is imposed on the base which is the amount of the organic Solvent to be used. employed to activate the croSS-linking agent introduced as Upon concurrent addition of the cross-linking agent and pendant groups, insofar as it can dissociate hydrogen bonds the dispersant, the rate of their addition is not particularly between amino groups and carboxyl groups. Illustrative are limited, but in general, they are charged dropwise over 10 alkali metal hydroxides Such as Sodium hydroxide, potas minutes to 3 hours. A considerably fast addition rate Such as sium hydroxide and lithium hydroxide, alkali metal acetates that observed, for example, upon adding them at once leads Such as Sodium acetate and potassium acetate; and tertiary not only to the development of Substantial heat in the amine S Such as trimethylamine, triethylamine, reaction System but also to a failure in obtaining a good trip ropylamine, tributylamine, trip enty lamine, dispersed State. If it takes more than 3 hours for charging them, the productivity is lowered. trihexylamine, trie thanolamine, tripropanolamine, In this method, a catalyst may also be used, as needed, tributanolamine, tripentanolamine, trihexanolamine, upon conducting the croSS-linking reaction. In this case, no N-methylmorpholine, pyridine, quinoline, and picoline. particular limitation is imposed on the timing of its addition. To have the croSS-linking agent, which have been intro 5-2) How to introduce a cross-linking agent as pendant duced as pendant groups, reacted Substantially in its entirety, groups into a polymer backbone and then to have the 15 it is necessary to use the base in a molar amount equivalent pendant groups cross-linked to carboxyl groups contained in the pendant groups. It is This method is to achieve cross-linking of poly Succinim however possible to control the croSS-linking degree by ide by first reacting the poly Succinimide with only one of adjusting the amount of the base to be used. Namely, when reactive groups of a croSS-linking agent to introduce it as a base is caused to act in an amount Smaller than the pendant groupS and then activating the other reactive group carboxyl groups in the croSS-linking agent introduced as to react and cross-link the pendant groups together. The pendant groups, the resulting croSS-linking degree is lower croSS-linking agent employed in this method may be one than that calculated from the amount of the croSS-linking having reactive groups of equivalent reactivity, but one agent So that a portion of the croSS-linking agent Still remains having two or more reactive groups of different reactivities as pendant groups. Accordingly, the above-mentioned pre is particularly preferred. 25 ferred amount of the cross-linking agent means, in a narrow AS examples of the croSS-linking agent, the basic amino Sense, an amount of the base required to activate the acids exemplified above under 4 can be mentioned. croSS-linking agent. In each of the amino acids, Such as lysine or ornithine, out 5-3. How to react an internal cross-linking agent with of the cross-linking agents uSable in the present invention, polySuccinimide and then to react a croSS-linking agent for one of the two amino groups is in a form associated with the conducting croSS-linking carboxyl group through a hydrogen bond. Structurally, it is According to this method, poly Succinimide is first reacted hence a monofunctional amine. In this form, it does not with an internal cross-linking agent, and a Surface function as a cross-linking agent. Through a reaction with croSSlinking agent is then reacted for conducting croSS poly Succinimide, it can be introduced as pendant groups into linking. Compared with the methods 5-1 and 5-2), this the polymer. Addition of a base to the polySuccinimide with 35 method 5-3 can more easily develop a difference or gra Such pendant groups introduced therein results in neutral dient in croSS-link density between an inner part and an outer ization of each carboxylic acid which has formed a hydrogen part of each resin particle. bond with the other amino group, whereby the amino group This method can also make use of the principles of the becomes free and reacts with an imide ring. In this manner, method 5-1 and 5-2). the croSS-linking reaction proceeds. In the present invention, 40 The term “internal cross-linking agent” as used herein the above-mentioned amino acid is therefore added to a means a croSS-linking agent which is reacted to poly Succin Solution of polySuccinimide in Such a form that only one imide in a homogeneous System before the addition of a amino group in its molecule becomes free. For example, a dispersant. On the other hand, the term "Surface croSS diaminomonocarboxylic acid Such as lysine is added as is linking agent’ means a croSS-linking agent which is reacted but, when a mineral acid Salt of a diaminomonocarboxylic 45 with polySuccinimide in a dispersed State after the addition acid, Such as lysine monochloride, is used, only the mineral of a dispersant. acid is neutralized. In this manner, one of the amino groups AS has already been explained in connection with the is rendered free and is introduced as a pendant group into the process 5-2), when a (polyamino)polycarboxylic acid, polysuccinimide. When ornithine methyl or the like is used, which has been neutralized beforehand with a base and for example, a cross-linking reaction would undesirably take 50 contains at least two amino groups (i.e., a polyamine con place if it were used as is. It is therefore used in the form of taining at least one carboxyl group in a molecule), and/or a the monochloride, that is, with one amino group blocked in conventional polyamine or polythiol is used as a croSS an inactive form, for the reaction. linking agent, it induces a cross-linking reaction as an The term “pendant groups' as used herein means that a ordinary cross-linking agent, and, when a (polyamino) compound having a functional group, which has reactivity 55 polycarboxylic acid in which one amino group is free is with an imide rings in polySuccinimide, has opened the used, it is first introduced as pendant groups. Therefore, this imide ring and is in a form “pendant' relative to the process 5-3 will hereinafter be described by dividing it into backbone of the polySuccinimide. two Sections depending upon which one of these two types In this method, the cross-linking reaction may be of cross-lining agents is used as an internal croSS-linking conducted, for example, through the following three Stages. 60 agent. (1) A cross-linking agent is introduced as pendant groups. 5-3-1 Use of a (polyamino)polycarboxylic acid, which has (2) The reaction System is brought into a dispersed State been neutralized beforehand with a base and contains at least to keep it free from a potential problem of gelation even two amino groups (i.e., a polyamine containing at least one when the croSS-linking reaction proceeds. carboxyl group in a molecule), and/or a conventional (3) A base is added to activate the cross-linking agent 65 polyamine or polythiol an internal cross-linking agent introduced as pendant groups, whereby the croSS In this method, the cross-linking reaction may be linking reaction is initiated. conducted, for example, through the following three Stages. 6,072,024 25 26 (1) An internal cross-linking agent in Such an amount as AS the Surface cross-linking agent, the above-mentioned not causing gelation of the reaction System is reacted polyfunctional compound having reactivity with imide with polySuccinimide. rings, Such as a polyamine or a polythiol, can be used. (2) A dispersant is charged to bring the reaction System In this case too, no particular limitation is imposed on the into a dispersed State. amount of the cross-linking agent to be used. However, the (3) A Surface cross-linking agent is added further to amount of the croSS-linking agent is generally adjusted So conduct the croSS-linking reaction. that the Sum of the internal croSS-linking agent introduced as The stages (2) and (3) may be effected at the same time. pendant groups and the Surface croSS-linking agent added Namely, the Surface croSS-linking agent may be charged after dispersion accounts for 0.1 to 30 mole % of the total together with the dispersant into the reaction System or the number of monomer units in the backbone of the poly Suc Surface cross-linking agent may be charged in a form cinimide. dissolved in the dispersant. AS the Surface croSS-linking Although no particular limitation is imposed on the molar agent in this method, one of the above-mentioned polyfunc ratio of a Surface croSS-linking agent, which is to be added tional compounds having reactivity with imide rings, Such as after dispersion, to an internal croSS-linking agent to be polyamines and polythiols, can be used. 15 introduced as pendant groups, a greater proportion of the In this case, no particular limitation is imposed on the Surface croSS-linking agent to be added after dispersion, in amount of the cross-linking agent to be used (the total other words, a higher percentage of Surface croSS-linking amount of the internal croSS-linking agent and/or the Surface tends to eventually result in a Superabsorbent polymer which cross-linking agent to be used), and a Suitable amount can be has a higher water absorption Speed and conversely pos chosen in accordance with a target croSS-linking degree. The SeSSes a lower water absorption. A Suitable molar ratio can term “croSS-linking degree' as used herein means a propor therefore be chosen depending on the application purpose. tion of croSS-linking portions relative to the polymer back Concerning the kind and amount of the base to be used bone. In general, an unduly large amount of a croSS-linking and the controllability of the croSS-linking degree by the agent leads to an excessively high cross-linking degree, amount of the base to be used, the corresponding descrip resulting in reduced water absorbency when formed into a 25 tions made above under 5-3-1 apply likewise. Superabsorbent polymer. An unduly Small amount of a In the case mentioned above under 5-3-2, no particular croSS-linking agent, on the other hand, leads to an exces limitations are imposed on the reaction temperatures upon Sively low croSS-linking degree, resulting in a polyaspartic introducing the internal croSS-linking agent as pendant acid which has been cross-linked only partially, is water groups, upon conducting croSS-linking by the addition of the soluble and does not exhibit water absorbency. The amount base, and upon performing Surface croSS-linking by the of the cross-linking agent (the total amount of the internal addition of the Surface croSS-linking agent. In general, cross-linking agent and/or the Surface cross-linking agent) is however, these reactions are conducted at -10° C. to 200 therefore adjusted to generally account for 0.1 to 30 mole % C., preferably at 10° C. to 80° C. although they may vary of the total number of monomer units in the backbone of the depending on the reactivities of the cross-linking agents, the poly Succinimide. The amount of the internal croSS-linking 35 presence or absence of a catalyst, the molecular weight of agent referred to in the above description of step (1) as not polySuccinimide, and the like. causing the gelation of the reaction System is generally from 6) Cross-linking method of poly Succinimide in a non 0.01 to 3 mole % based on the total number of monomer dispersed State units in the backbone of the poly Succinimide, although it In the above description, the description was made about varies depending on the kind of the croSS-linking agent, the 40 the process for producing a cross-linked polySuccinimide by reaction temperature and the molecular weight of the reacting poly Succinimide, which has been brought into a poly Succinimide. Namely, the croSS-linking reaction is con dispersed State by a dispersant, with a cross-linking agent. ducted to a cross-linking degree of from about 0.01 to 3% in According to the above process, a croSS-linked poly Succin a homogeneous System and, after the reaction is brought into imide can be obtained at high productivity by the Simple a dispersed State by a dispersant or concurrently with 45 proceSS. dispersion of the reaction System, the Surface croSS-linking It is however to be noted that the present invention agent is added in an amount Sufficient to give a croSS-linking includes not only the process featuring croSS-linking of degree of from 0.1 to 30% in terms of an overall cross polySuccinimide in a dispersed State but also a process in linking degree including the croSS-linking degree achieved which polySuccinimide in the form of a Solution is croSS by the internal cross-linking agent, and the croSS-linking 50 linked into a gel and the thus-obtained gel of the croSS-linked reaction is then continued further. polySuccinimide is then Subjected to disintegration. AS will 5-3-2. Use of a (polyamino)polycarboxylic acid, in which be described Subsequently herein, the present invention also only one amino group is free, as an internal croSS-linking encompasses a hydrolysis proceSS featuring an adjustment of agent a Swelling degree of a resin and, further, a proceSS featuring In this method, croSS-linking may be conducted, for 55 Washing and reprecipitation of a gel of a croSS-linked example, through the following four stages. polyaspartic acid resin with water and/or a water-miscible organic Solvent. (1) An internal cross-linking agent is introduced as pen These processes become more useful from the practical dant groups. Standpoint when they are carried out in combination with the (2) The reaction System is brought into a dispersed State 60 process featuring cross-linking of poly Succinimide in a to avoid a potential problem of gelation of the reaction dispersed State or the process in which polySuccinimide in System even when the cross-linking reaction proceeds. the form of a Solution is croSS-linked into a gel and the (3) A base is added to activate the internal cross-linking thus-obtained gel of the croSS-linked poly Succinimide is agent introduced as the pendant groups, whereby the Subjected to disintegration. A description will hereinafter be croSS-linking reaction is conducted. 65 made about a proceSS for cross-linking polySuccinimide in a (4) A Surface cross-linking agent is then added to perform non-dispersed State. By the way, the term “non-dispersed Surface croSS-linking. State' as used herein means a uniform Solution of poly Suc 6,072,024 27 28 cinimide or a State not exactly the same as the Solution but The term “disintegration” as used herein should be inter close to the Solution So that a State, in which a croSS-linking preted to embrace an embodiment in which a material (a gel agent is not in a dissolved State but also in a dispersed State or the like) to be processed is disintegrated as is and an is embraced. Also included is a State in which a portion of embodiment in which a material to be processed is ground poly Succinimide has not been dissolved and is precipitated. in water and/or an organic Solvent. Further, this term should In this case, poly Succinimide and a cross-linking agent are also be interpreted to include “wet-grinding” as meant in an reacted in a good Solvent, that is, an organic Solvent having ordinary Sense. solubility for polysuccinimide. Illustrative are N,N- As a disintegrating operation, it is preferred to conducting dimethylform amide, N,N-dimethylace tamide, disintegration in water and/or an organic Solvent or to N-methylpyrrollidone, N,N'-dimethylimidazolidinone, disintegrate the material, which is to be processed, as is and dimethylsulfoxide, and sulfolane. Among these, N,N- then to add a transport Solvent (water and/or an organic dimethylformamide and N,N-dimethylacetamide are par solvent) to impart fluidity thereto in view of transportation ticularly preferred for their high solubility of polysuccinim and the like. ide. These Solvents may be used either Singly or in 7-1 Solvent for use in disintegration combination. 15 No particular limitation is imposed on the Solvent for use Further, with a view to Slowing down the cross-linking in disintegration. Solvents, which are commonly used for reaction, it is also possible to add a poor Solvent, which does this purpose, are all usable. Specific examples can include not dissolve or can only sparingly dissolve poly Succinimide. water, N,N-dimethylformamide, N,N-dimethylacetamide, AS this poor Solvent, those Similar to the poor Solvents N-methylpyrrollidone, N,N'-dimethylimidazolidinone, exemplified above can be used. dimethylsulfoxide, and Sulfolane, alcohols Such as The croSS-linking reaction System is progressively gelled methanol, ethanol, propanol, isopropanol, butanol, pentanol, as the croSS-linking reaction proceeds. The hydrolysis can be hexanol, heptanol, octanol, 2-methoxyethanol and conducted either before the reaction System is entirely gelled 2-ethoxyethanol, glycols Such as ethylene glycol, diethylene or after the reaction System is completely gelled. The degree glycol, triethylene glycol, propylene glycol and dipropylene of gelation differS depending on reaction conditions Such as 25 glycol, glycosolves Such as methylglycosolve and the concentration of the polymer, the amount of the croSS ethylglycosolve, ketones Such as acetone, methyl ethyl linking agent, the croSS-linking degree, and the proportion of ketone and methyl isobutyl ketone, cyclic etherS Such as a poor Solvent if any. The resulting gel is hard under tetrahydrofuran and dioxane, petroleum ether, pentane, conditions Such as a high polymer concentration, a large hexane, heptane, octane, cyclohexane, benzene, toluene, amount of the cross-linking agent, a high croSS-linking ethylbenzene, Xylene, decalin, diphenyl ether, anioSole, and degree or a low proportion of the poor Solvent. The gel creSol. These Solvent can be used either Singly or in com becomes Soft in an opposite case. In this case, the gel to be bination. formed is chosen in accordance With the application purpose 7-2 Grinding mill for use in disintegration of a cross-linked polyaspartic acid resin to be obtained No particular limitation is imposed on the grinding mill through hydrolysis. To obtain a resin having high gel 35 (machine for disintegration) to be used, insofar as it can Strength, for example, it is only necessary to increase the Substantially disintegrate a Solid, a gel-like material, a Solid croSS-linking degree. In the case of a Soft gel, the gel can be in a liquid, or a gel-like material in a liquid. AS Specific disintegrated by dispersing it in a poor Solvent or water as examples, those of the type that a Stirring blade having disclosed in JP Kokai 7-224163. In the case of a hard gel, cutting edges or an ordinary Stirring blade is rotated at a high however, this method cannot Sufficiently disintegrate the gel 40 Speed are preferred. To increase the efficiency of in a short time, thereby making it difficult to conduct the disintegration, a grinding mill equipped with baffles is also hydrolysis. Very effective in this case is the process in which preferred. Further, a grinding mill having both disintegrating a gel of cross-linked poly Succinimide is Subjected to disin and transporting functions is preferred. No particular limi tegration as one of the characteristic features of the present tation is imposed on the shape of the Stirring blade, and the invention. Namely, the cross-linked poly Succinimide as a 45 stirring blade may be in the form of a screw blade or in the reaction product after the croSS-linking reaction turns to a form of a ribbon-shaped or wire-shaped blade which gel Swollen as a result of absorption of the organic Solvent. remains rather free from large load. It is preferable to use this gel after Subjecting it to disinte Illustrative can be a pipeline homomixer, a homomix line gration. In this case, the gel may be taken out Subsequent to mill, a goratol pump, a disintegrator, a mixer, a Spike mill, the cross-linking reaction and may then be charged into a 50 a homogenizer, a meat chopper, a noodle-making machine, wet-grinding mill, or the cross-linking reaction itself may be a coffee mill, a juicer mixer, a Vortex mixer, a tumbler mixer conducted in a wet-grinding mill and gelation may be and the like. conducted in the mill. No particular limitation is imposed on the Speed of The wet-grinding of the cross-linked polySuccinimide, rotation (rpm, revolutions per minute) of the stirring blade which pertains to the present invention, is effective even 55 having cutting edges or the conventional Stirring blade, when the gel is Soft, to Say nothing of a Soft gel, So that insofar as disintegration is achieved practically. In general, hydrolysis can be conducted in a short time. a higher Speed is preferred within a range in which the 7 Disintegration temperature of the grinding System does not rise by fric It is preferred to apply disintegration especially to a tional heat. When the resin is employed in disposable croSS-linked polySuccinimide which has been obtained by 60 diaperS or for agricultural or horticultural purposes in the croSS-linking poly Succinimide in a non-dispersed State. In form of large particles, 10 to 10,000 rpm is preferred, with addition, it is also preferred to develop a more uniformly 100 to 5,000 rpm being more preferred. When the resin is dispersed State by conducting a cross-linking reaction under employed as a thickener or an additive for polymers, 100 to disintegration, that is, wet grinding when croSS-linking is 100,000 rpm is preferred, with 1,000 to 50,000 rpm being conducted using poly Succinimide in a State dispersed by a 65 more preferred. dispersant as described above. Both the cases will herein Disintegration can be performed in a single Step or after be described together. Stepwise in Several Steps. No particular limitation is imposed 6,072,024 29 30 on the particle size (average particle diameter) of the a dispersed State by a dispersant, is reacted with a croSS poly Succinimide gel, Said particle size being achieved by the linking agent. AS an alternative, it is also possible to produce disintegration, or the particle size (average particle a croSS-linked poly Succinimide by the simple process that a diameter) of the poly Succinimide in the dispersed State upon gel of a croSS-linked poly Succinimide is Subjected to disin conducting the croSS-linking reaction. It is preferable for the tegration. In the croSS-linking reaction of the former process, croSS-linked poly Succinimide to have a Smaller particle size Some imide rings of the poly Succinimide react with the because the reaction can be performed in a more uniformly croSS-linking agent and are opened. Alkaline hydrolysis of dispersed State. The particle size may generally range from imide rings remaining in the resulting croSS-linked poly Suc 0.00001 to 1 mm, with 0.0001 to 0.1 mm being more cinimide makes it possible to obtain a good croSS-linked preferred. In general, the reaction Velocity is reduced when polyaspartic acid resin. Namely, this cross-linked poly Suc the particle size of the dispersed product is too large. On the cinimide is very useful as an intermediate for the production other hand, the particle size of the cross-linked polySuccin of a croSS-linked polyaspartic acid resin. imide varies depending on the application purpose of the It is however to be noted that the application purpose of resulting croSS-linked polyaspartic acid resin or the like. the croSS-linked poly Succinimide is not limited to this use as When the cross-linked polySuccinimide is used by adding it 15 an intermediate. As a resin material, this croSS-linked to another resin or the like, it is preferable to make the polySuccinimide itself is uSable for various application pur particle size of the cross-linked poly Succinimide resin poses. It can also take use modes Similar to those to be Smaller because the particle size of primary particles of the mentioned Subsequently herein under "Use modes of croSS resulting croSS-linked polyaspartic acid resin becomes linked polyaspartic acid resin'. Concerning its shape in use, smaller. The particle size may generally range from 0.00001 it can also be formed into shapes similar to those to be to 1 mm, with 0.0001 to 0.1 mm being more preferred. In mentioned Subsequently herein under "Shape of croSS general, the reaction Velocity is reduced when the particle linked polyaspartic acid resin'. Size of the dispersed product is too large. When the croSS 9 Hydrolysis of imide rings of cross-linked poly Succinim linked polyaspartic acid resin is employed in disposable ide with an advance adjustment in Swelling degree diaperS or for agricultural or horticultural purposes, it is 25 In the process of the present invention for the production preferable for the croSS-linked polyaspartic acid resin to of a cross-linked polyaspartic acid resin, the Swelling degree have a relatively large particle size So that the croSS-linked of the resin in the reaction system is controlled within the poly Succinimide during the disintegration may preferably range of from 3 to 100 times upon Subjecting imide rings of have a greater particle size. Its particle size varies depending the cross-linked polySuccinimide to a hydrolysis reaction. on the reaction conditions in the cross-linking reaction and By this control, the hydrolysis is allowed to promptly cannot be specified in a wholesale manner. Nonetheless, a proceed, thereby making it possible to provide the resultant range of from 0.01 to 20 mm is preferred, with 0.1 to 2 mm croSS-linked polyaspartic acid resin with improved water being more preferred. absorbency. The term “Swelling degree” as used herein When Such disintegration is applied to a cross-linked means the absorption level (amount) of water, organic poly Succinimide gel obtained by croSS-linking polySuccin 35 Solvents, Salts, oligomers and the like in the resin from the imide in a non-dispersed State, a disintegrated gel is next reaction System when the resin is Subjected to a hydrolysis Subjected to a hydrolysis reaction of imide rings. This reaction. At this moment, the resin is in the State of Swelling hydrolysis reaction Step generally uses water as an essential by absorbing them. It is difficult to stir the resin in the state component. When disintegration is conducted in water and/ of Swelling, but it is possible if an exceSS liquid is present. or a water-miscible organic Solvent, the next hydrolysis Step 40 Such hydrolysis reaction is allowed to proceed in the pres may be conducted as is without Separating the disintegrated ence of excess water. Therefore, the Stirring can be Smoothly gel. conducted while maintaining the Swelling degree of the resin Further, it is also possible to have a salt for the hydrolysis within the Specific range of the present invention. The reaction (an organic Salt and/or inorganic salt) included amount of the exceSS liquid depends on the efficiency of a beforehand in a material to be disintegrated and, Subsequent 45 Stirring machine. When the Stirring machine can be driven at to disintegration, to Subject the resultant disintegrated mix a high rotation Speed with a high torque, the exceSS liquid ture directly to the next hydrolysis Step. Moreover, an may be in a Small amount but, when it cannot be driven So, aqueous alkaline Solution for the hydrolysis reaction may be the exceSS liquid must be in a large amount. added at the same time as disintegration So that the disin In addition, it is also possible to prevent the gel-like resin tegration and the hydrolysis reaction can be conducted 50 from absorbing more water into a Solid form as a result of concurrently. a further progreSS of the hydrolysis. Further, it is also When a slurry of a solid in an organic solvent is obtained possible to avoid Such a potential problem that Stirring by the disintegration and the Solid is then Separated from the becomes difficult due to solidification of the gel-like resin organic Solvent, the Solid may be separated with a view to and coagulation of a precipitate. This makes it possible to achieving recovery or the like of the organic Solvent. AS a 55 increase the concentration of the resin in the reaction mix preferred Separation method, a general chemical Separation ture and, hence, to increase the Volumetric efficiency. method Such as decantation or centrifugal Separation can be It is preferred to control the Swelling degree within a mentioned. The thus-obtained solid may be subjected to the range of from 3 to 100 times, with a range of from 5 to 20 next hydrolysis Step either after being dried or directly in the times being more preferred. form of a wet cake. In other words, the organic Solvent may 60 In the present invention, it is not necessary to conduct the be removed before the hydrolysis step or the hydrolysis step hydrolysis reaction of imide rings within this range through may be conducted directly without removing the organic out the reaction. At certain Stages, the Swelling degree may Solvent. temporarily fall outside this range. Such temporary depar 8 Application purposes of cross-linked poly Succinimide tures are acceptable. For example, the Swelling degree of the AS has been described above, a cross-linked polySuccin 65 resin at an initial Stage of the reaction, where the hydrolysis imide can be produced at high productivity by the Simple has not proceeded Sufficiently, may Substantially be Zero (0) process that poly Succinimide, which has been brought into and, therefore, may departs from the above range. When a 6,072,024 31 32 resin is produced without any particular advance indication is therefore not allowed to spread So that the reaction does of a particular target SWelling degree, its Swelling degree not proceed sufficiently. This results in a problem that the may significantly depart from the above range. The produc resulting croSS-linked polyaspartic acid resin is not provided tion process of the present invention can easily correct the with high water absorbency. Further, a hydrolysis reaction in Swelling degree of a resin even when it departs significantly an organic Solvent or a mixed Solvent of water and an from the above range. The present invention can promptly organic Solvent, Said mixed Solvent containing the organic perform the hydrolysis reaction of the imide rings of the Solvent in a large proportion, tends to allow the resin in the croSS-linked polySuccinimide and is also excellent in work reaction System to undergo the hydrolysis reaction only at ability. In View of these, this process is also embraced in the particle Surfaces, leading to a Substantial reduction in the present invention even when it is employed as a general reaction velocity of the hydrolysis. This also results in the proceSS in Steps other than Such a hydrolysis reaction. problem that the resulting croSS-linked polyaspartic acid Specific examples of a method for controlling the Swell resin is not provided with high water absorbency. ing degree within the range of from 3 to 100 times can When a mixed solvent of water and a water-miscible include the following four methods. organic Solvent is used, the Swelling degree of the resulting croSS-linked polyaspartic acid resin is determined by their 9-1 To conduct the hydrolysis reaction in a solution 15 ratio as described above. In the process of the present which contains a water-miscible organic Solvent. invention, the Swelling degree of a resin in a reaction System 9-2 To conduct the hydrolysis reaction in an aqueous during the hydrolysis reaction is therefore controlled within Solution which contains an inorganic Salt and/or an the range of from 3 to 100 times by adjusting their ratio as organic Salt. needed. Transference of a liquid Such as water or an organic 9-3 To conduct the hydrolysis reaction in a solvent of Solvent takes a longer time in a resin under Swelling than in from 40° C. to 100° C. Solution. A relaxation time is necessary for the equilibrium 9-4) To conduct the hydrolysis reaction by combining at of the resin through absorption or release of the liquid. After least two of these methods 9-1 to 9-3 as needed. controlling the ratio of water to an organic Solvent to provide A description will hereinafter be made about the methods the resin with a desired Swelling degree, it therefore takes 9-1 to 9-4). 25 Some time until the desired Swelling degree is achieved. 9-1 Method for conducting the hydrolysis reaction in an Further, the ratio of water to a water-miscible organic aqueous Solution which contains a water-miscible organic Solvent in a reaction System can be changed as needed by Solvent adding a fresh Supply of water or the water-miscible organic In this method, the Swelling of a gel-like resin in a Solvent to a reaction mixture as needed in the course of a reaction System is controlled by Suitably determining the progreSS of a hydrolysis reaction of imide rings of a croSS ratio of the water to the water-miscible organic Solvent in the linked poly Succinimide in the mixed Solvent of the water aqueous Solution and other conditions (the kind of the and the water-miscible organic Solvent after the initiation of organic Solvent, etc.). the reaction. No particular limitation is imposed on the water-miscible For example, when the water absorption of a cross-linked organic Solvent insofar as it is an organic Solvent miscible 35 polyaspartic acid resin to be produced is not limited to a with water. Specific examples can include alcohols Such as particular value, a hydrolysis reaction of imide rings may be methanol, ethanol, propanol, isopropanol, butanol, initiated in water or a mixed Solvent of water and a water 2-methoxyethanol and 2-ethoxyethanol, glycols Such as miscible organic Solvent, Said mixed Solvent containing the ethylene glycol, diethylene glycol, triethylene glycol, pro water-miscible organic Solvent at a high ratio relative to the pylene glycol and dipropylene glycol, ketones Such as 40 water. When thickening of the resin has proceeded as a result acetone, methyl ethyl ketone and methyl isobutyl ketone, of gelation, the water-miscible organic Solvent may be added cyclic etherS Such as tetrahydrofuran and dioxane, N,N- to the reaction mixture as much as needed, thereby making dimethylform amide, N,N-dimethylace tamide, it possible to prevent the thickening. N-methylpyrrollidone, N,N'-dimethylimidazolidinone, It is also possible, for example, to initiate a hydrolysis dimethylsulfoxide, and Sulfolane. Among these, methanol, 45 reaction of imide rings in a water-miscible organic Solvent ethanol, propanol, isopropanol and butanol are preferred or in a mixed Solvent of water and a water-miscible organic especially in that the resulting resin can be easily dried and Solvent, Said mixed Solvent containing the water-miscible the Solvent Scarcely remains in the resin after the drying. organic Solvent at a high ratio relative to the water and then Amounts of the water-miscible organic Solvent and water to add water to the reaction mixture as much as needed to and their ratio are particularly important in the hydrolysis. 50 prevent coagulation of a precipitate. Namely, the process of Their Suitable values vary depending on the polarity of the the present invention is very effective not only where the water-miscible organic Solvent and are thus determined by water absorption of a resin to be produced is Specified in the polarity of the mixed solvent of the water and the advance but also where the water absorption of a resin to be water-miscible organic solvent. When their ratio is set at produced is not Specified beforehand. 100% water, for example, the croSS-linked polyaspartic acid 55 In a mixed Solvent of water and a water-miscible organic resin is provided with a maximum water absorption. The solvent, the proportion of the water may preferably 5 wt.% water absorption becomes Smaller as the proportion of the or higher, with a range of from 20 to 80 wt. % being organic Solvent becomes higher. When the proportion of the especially preferred. organic Solvent is increased beyond a level, the resulting Further, the Separated cross-linked poly Succinimide may resin ShowS Substantially no water absorbency. 60 be subjected to the next hydrolysis step either in the form of According to a finding of the present inventors, a hydroly wet cake with the solvent still contained therein or in a form sis reaction in water upon production of a croSS-linked rendered free of the solvent by drying. polyaspartic acid resin by the hydrolysis of imide rings of a 9-2 Method for conducting the hydrolysis reaction in an croSS-linked polySuccinimide results in Swelling and Sub aqueous Solution which contains an inorganic Salt and/or an Stantial gelation of the resin in the reaction System as a result 65 organic Salt of absorption of water, whereby it becomes difficult to In this method, a hydrolysis reaction is conducted in the conduct Stirring of the reaction System. A hydrolyzing agent presence of an inorganic Salt and/or an organic Salt. The 6,072,024 33 34 concentration and kind of the inorganic Salt and/or the tetrahe Xylammonium, ethyltrimethylammonium, organic Salt are Suitably determined to adjust the Osmosis trimethylproylammonium, butyltrimethylammonium, preSSure in a reaction System, whereby the Swelling degree pentyltrimethylammonium, hexyltrimethylammonium, of a gel-like resin is controlled. cyclohexyltrim ethylam monium, No particular limitation is imposed on the inorganic Salt benzyltrimethylammonium, triethylpropylammonium, and the organic Salt, and a wide variety of ordinary Salts. Such triethylbutylammonium, triethylpenty lammonium, as neutral Salts, basic Salts and acidic Salts can be used. triethylhexylammonium, cyclohexyltriethylammonium, and When a multivalent metal salt is used, it is preferable to use benzyltriethylammonium; and amine Salts. Such as the Salt at an appropriately reduced concentration, because trimethylamine, triethylamine, tripropylamine, the multivalent metal Salt induces ionic cross-linking of tributylamine, trip enty lamine, trihe Xylamine, carboxyl groups formed by hydrolysis of imide rings and the triethanolamine, tripropanolamine, tributanolamine, resulting croSS-linked polyaspartic acid resin is thus pro tripentanolamine, trihexanolamine, dimethylamine, Vided with a higher cross-linking degree. diethylamine, dipropylamine, dibutylamine, dipentylamine, A Solution which was prepared by adding the inorganic dihexylamine, dicyclohexylamine, dibenzylamine, Salt or the organic Salt may be used, or alternatively a Salt 15 ethylmethylamine, methylpropylamine, butylmethylamine, which was produced by neutralization in water may be used. metylpenty lamine, methylhexylamine, methylamine, Further, if a Salt was produced in the previous croSS-linking ethylamine, propylamine, butylamine, pentylamine, reaction, the Salt may be used as is. hexylamine, octylamine, decylamine, dodecylamine, and Illustrative usable Salts can include metal Salts, organic hexadecylamine. base Salts, oxides and the like of inorganic mineral acids Among these, particularly preferred in View of Solubility Such as hydrochloric acid, hydrobromic acid, hydroiodic in water, odor, Safety and cost are ammonium Salts Such as acid, hydrofluoric acid, Sulfuric acid, Sulfurous acid, disul tetra methylammonium, tetraethylammonium, furous acid, amidoSulfuric acid, thiosulfuric acid, nitric acid, tetrap ropylammonium, tetrabutylam monium, nitrous acid, phosphoric acid, phosphorous acid, orthophoS ethyltrimethylammonium, benzyltrimethylammonium and phoric acid, metaphosphoric acid, hypophosphoric acid, 25 benzyltriethylammonium; and amine Salts. Such as pyrophosphoric acid, phosphinic acid, phosphonic acid, trimethylamine, triethylamine, tripropylamine, carbonic acid, percarbonic acid, boric acid, orthoboric acid, tributylamine, and triethanolamine. metaboric acid, chloric acid, perchloric acid, hypochlorous Other Specific examples can include chlorides Such as acid, bromic acid, perbromic acid, hypobromous acid, iodic Sodium chloride, potassium chloride, lithium chloride, acid, periodic acid, hypoiodous acid, Silicic acid, orthosilicic ammonium chloride, calcium chloride, magnesium chloride, acid, metasilicic acid, aluminic acid, telluric acid, isocyanic beryllium chloride, aluminum chloride, titanium acid, thiocyanic acid, manganic acid, permanganic acid, tetrachloride, Vanadium chloride, chromium chloride, man periodic acid, chromic acid, dichromic acid, metaanti ganese chloride, iron chloride, cobalt chloride, nickel monous acid, metavanadic acid, and molybdic acid; and of chloride, copper chloride, Zinc chloride, Strontium chloride, organic acids Such as organic phosphonic acids, organic 35 yttrium chloride, Zirconium chloride, molybdenum chloride, Sulfonic acids, organic carboxylic acid, oxalic acid, and ruthenium chloride, rhodium chloride, palladium chloride, organic phenols. Silver chloride, cadmium chloride, tin chloride, tellurium Among these, metal Salts and organic base Salts of hydro chloride, cesium chloride, barium chloride, Serium chloride, chloric acid, hydrobromic acid, hydroiodic acid, hydrofluo lead chloride, tetramethylammonium chloride, tetraethylam ric acid, Sulfuric acid, Sulfurous acid, nitric acid, nitrous 40 monium chloride, tetrabutylammonium chloride and trietha acid, phosphoric acid, Orthophosphoric acid, metaphospho nolamine hydrochloride, Sodium bromide, potassium ric acid, pyrophosphoric acid, phosphinic acid, phosphonic bromide, lithium bromide, ammonium bromide, tetramethy acid, carbonic acid, boric acid, orthoboric acid, metaboric lammonium bromide, tetraethylammonium bromide, tet acid Silicic acid, orthosilicic acid, metasilicic acid, oxalic rabutylammonium bromide, triethanolamine hydrobromide, acid, organic phosphoric acids, organic Sulfonic acids and 45 Sodium iodide, potassium iodide, lithium iodide, ammonium organic carboxylic acids are preferred, as they have low iodide, tetramethylammonium iodide, tetraethylammonium toxicity, have no oxidative or reductive property and are of iodide, tetrabutylammonium iodide, trie thanolamine low cost. Particularly preferred are metal Salts and organic hydroiodide, Sodium Sulfate, potassium Sulfate, lithium base Salts of various acids Such as hydrochloric acid, Sulfuric Sulfate, ammonium Sulfate, tetramethylammonium Sulfate, acid, nitric acid, phosphoric acid, carbonic acid, boric acid, 50 tetraethylammonium Sulfate, tetrabutylammonium Sulfate, organic phosphonic acid, organic Sulfonic acid and organic triethanolamine Sulfate, Sodium nitrate, potassium nitrate, carboxylic acids. lithium nitrate, ammonium nitrate, tetramethylammonium Examples of the metals making up the metal Salts can nitrate, tetraethylammonium nitrate, tetrabutylammonium include lithium, Sodium, potassium, beryllium, magnesium, nitrate, triethanolamine nitrate, Sodium phosphate, potas aluminum, calcium, Scandium, titanium, Vanadium, 55 sium phosphate, lithium phosphate, ammonium phosphate, chromium, manganese, iron, cobalt, nickel, copper, Zinc, Sodium carbonate, potassium carbonate, lithium carbonate, gallium, germanium, rubidium, Strontium, yttrium, ammonium carbonate, tetramethylammonium carbonate, Zirconium, niobium, molybdenum, ruthenium, rhodium, tetraethylammonium carbonate, tetrabutylammonium palladium, Silver, cadmium, indium, tin, tellurium, cesium, carbonate, triethanolamine carbonate, Sodium borate, potas barium, Serium, gold, mercury, thallium, and lead. Among 60 sium borate, lithium borate, ammonium borate, Sodium these, lithium, Sodium and potassium are preferred because benzeneSulfonate, potassium benzeneSulfonate, lithium they have low toxicity, are of low cost and have high benzensulfonate, ammonium benzeneSulfonate, tetramethy solubility in water. lammonium benzenesulfonate, tetraethylammonium Further, illustrative organic Salts can include ammonium benzeneSulfonate, tetrabutylammonium benzeneSulfonate, SaltS Such as ammonium, tetramethylammonium, 65 trie than olamine ben Zene Sulfonate, Sodium tetraethylam monium, tetra propylam monium, p-tolueneSulfonate, potassium p-toluenesulfonate, lithium tetrabutylam monium, tetrap enty lammonium, p-tolueneSulfonate, ammonium p-toluenesulfonate, tetram 6,072,024 35 36 ethylammonium p-toluenesulfonate, tetraethylammonium benzeneSulfonate, tetramethylammonium benzeneSulfonate, p-tolue n e Sulfonate, tetrabutylam monium tetraethylammonium benzeneSulfonate, tetrabutylammo p-toluenesulfonate, triethanolamine p-toluenesulfonate, nium benzeneSulfonate, triethanolamine benzeneSulfonate, Sodium benzoate, potassium benzoate, lithium benzoate, Sodium p-toluenesulfonate, potassium p-toluenesulfonate, ammonium benzoate, tetramethylammonium benzoate, tet ammonium p-toluenesulfonate, tetramethylammonium raethylammonium benzoate, tetrabutylammonium benzoate, p-tolu e ne Sulfonate, tetra ethylam monium triethanolamine benzoate, Sodium oxalate, potassium p-tolu e ne Sulfonate, tetrabutyl ammonium oxalate, lithium oxalate, ammonium oxalate, tetramethylam p-toluenesulfonate, triethanolamine p-toluenesulfonate, monium oxalate, tetraethylammonium oxalate, tetrabuty Sodium benzoate, potassium benzoate, ammonium benzoate, lammonium oxalate, triethanolamine oxalate, Sodium Sodium oxalate, potassium oxalate, ammonium oxalate, acetate, potassium acetate, lithium acetate, ammonium Sodium acetate, potassium acetate, ammonium acetate, acetate, tetramethylammonium acetate, tetraethylammo Sodium propionate, and potassium propionate. nium acetate, tetrabutylammonium acetate, triethanolamine The above-exemplified individual salts may be used either acetate, Sodium propionate, potassium propionate, lithium Singly or in combination. In Some instances, they can also be propionate, ammonium propionate, tetramethylammonium 15 used in combination with inorganic Salts and organic Salts. propionate, tetraethylammonium propionate, tetrabutylam In this process, the Salt may be added in an initial Stage of monium propionate, and triethanolamine propionate. the reaction or may be added as needed during the reaction. Among these, preferred are Sodium chloride, potassium The addition of the salt makes it possible to control the chloride, lithium chloride, ammonium chloride, tetramethy Swelling degree of the resulting gel. lammonium chloride, tetraethylammonium chloride, tet The concentration of the Salt in the reaction mixture may rabutylammonium chloride, triethanolamine hydrochloride, preferably be from 0.01 to 20 wt.%, with 0.1 to 5 wt.% Sodium bromide, potassium bromide, lithium bromide, being more preferred. Setting of the concentration of the Salt ammonium bromide, tetramethylammonium bromide, tetra at an appropriately high level makes it possible to exhibit the ethylammonium bromide, tetrabutylammonium bromide, effect of the Salt, whereas Setting of its concentration at an triethanolamine hydrobromide, Sodium iodide, potassium 25 adequately low level makes it possible to prevent mixing of iodide, ammonium iodide, tetramethylammonium iodide, the Salt into the resin. tetraethylammonium iodide, tetrabutylammonium iodide, In this process, an organic Solvent may be mixed with an triethanolamine hydroiodide, Sodium Sulfate, potassium aqueous Solution of an inorganic Salt and/or an organic Salt. Sulfate, ammonium Sulfate, tetramethylammonium Sulfate, Organic Solvents include both water-miscible organic Sol tetraethylammonium Sulfate, tetrabutylammonium Sulfate, vents and water-immiscible organic Solvents, and they are triethanolamine Sulfate, Sodium nitrate, potassium nitrate, both usable. ammonium nitrate, tetramethylammonium nitrate, tetraethy Specific examples of the water-miscible organic Solvents lammonium nitrate, tetrabutylammonium nitrate, triethano can be those similar to the water-miscible organic Solvents lamine nitrate, Sodium phosphate, potassium phosphate, exemplified above in the description of the method 9-1. On ammonium phosphate, Sodium carbonate, potassium 35 the other hand, Specific examples of the water-immiscible carbonate, lithium carbonate, ammonium carbonate, tetram organic Solvents can include petroleum ether, pentane, ethylammonium carbonate, tetraethylammonium carbonate, hexane, heptane, octane, cyclohexane, benzene, toluene, tetrabutylammonium carbonate, triethanolamine carbonate, ethylbenzene, Xylene, decalin, and diphenyl ether. Sodium borate, potassium borate, ammonium borate, Sodium Especially, methanol, ethanol, propanol, isopropanol and benzeneSulfonate, potassium benzensulfonate, ammonium 40 butanol, which are water-miscible organic Solvents, are benzeneSulfonate, tetramethylammonium benzeneSulfonate, preferred in that the cross-linked polyaspartic acid resin tetraethylammonium benzenesulfonate, tetrabutylammo available by the hydrolysis reaction can be easily dried and nium benzeneSulfonate, triethanolamine benzeneSulfonate, the Solvents Scarcely remain in the resin after the drying. Sodium p-toluenesulfonate, potassium p-toluenesulfonate, When a mixed Solvent of water and an organic Solvent is ammonium p-toluenesulfonate, tetramethylammonium 45 used, the proportion of the water in the mixed Solvent may p-tolue n e Sulfonate, tetra ethylam monium preferably be 5 wt.% or higher, with a range of from 20 to p-tolue n e Sulfonate, tetrabutylam monium 80 wt.% being particularly preferred. p-toluenesulfonate, triethanolamine p-toluenesulfonate, 9-3 Method for conducting the hydrolysis reaction in a Sodium benzoate, potassium benzoate, ammonium benzoate, Solvent of from 40° C. to 100° C. tetramethylammonium benzoate, tetraethylammonium 50 In this method, the temperature of the reaction mixture is benzoate, tetrabutylammonium benzoate, triethanolamine Suitably adjusted by making use of the characteristic that the benzoate, Sodium oxalate, potassium oxalate, ammonium water absorbency of a croSS-linked polyaspartic acid resin is oxalate, Sodium acetate, potassium acetate, ammonium reduced at high temperatures, whereby the Swelling degree acetate, tetramethylammonium acetate, tetraethylammo of the gel-like resin in the reaction System is controlled. nium acetate, tetrabutylammonium acetate, triethanolamine 55 The solvent employed in this method may be water or an acetate, Sodium propionate, and potassium propionate. Espe aqueous Solution containing an organic Solvent mixed cially preferred are Sodium chloride, potassium chloride, therein. Organic solvents include both water-miscible ammonium chloride, tetramethylammonium chloride, tetra organic Solvents and water-immiscible organic Solvents, and ethylammonium chloride, tetrabutylammonium chloride, they are both usable. AS Specific examples of the water triethanolamine hydrochloride, Sodium Sulfate, potassium 60 miscible organic Solvents and water-immiscible organic Sulfate, ammonium Sulfate, tetramethylammonium Sulfate, Solvents, those similar to the organic Solvents mentioned tetraethylammonium Sulfate, tetrabutylammonium Sulfate, above in the descriptions of the methods 9-1 and 9-2 can triethanolamine Sulfate, Sodium phosphate, potassium be mentioned. phosphate, ammonium phosphate, Sodium carbonate, potas When a mixed Solvent of water and an organic Solvent is sium carbonate, ammonium carbonate, Sodium borate, 65 used, the proportion of the water in the mixed Solvent may potassium borate, ammonium borate, Sodium also preferably be 5 wt.% or higher, with a range of from benzeneSulfonate, potassium benzensulfonate, ammonium 20 to 80 wt.% being particularly preferred. 6,072,024 37 38 9-4 Method for conducting the hydrolysis reaction by cinimide in a dispersed State and the below-described pro combining at least two of these methods 9-1 to 9-3 as ceSS featuring Washing of a gel of a croSS-linked polyaspartic needed acid resin, Said gel having been obtained by hydrolysis, as is No particular limitation is imposed on the manner of the with water and/or a water-miscible organic Solvent. combination. A Suitable combination may be chosen in View These processes become more useful from the practical of the kind of the desired resin, the production apparatus, the Viewpoint when they are conducted in combination with the reaction conditions and the like. In general, the temperature process featuring the adjustment of the Swelling degree of a of the reaction system may preferably be from 5 C. to 100 resin in the hydrolysis reaction. It is however to be noted C., more preferably from 10° C. to 60°C. when the Swelling that, even if the hydrolysis reaction is conducted without any degree is not controlled, namely, when the method 9-3 is control of the Swelling degree, these processes can bring not adopted. By combining these methods, the Swelling about their own effects. degree of the resin an be easily controlled So that the When the hydrolysis reaction of imide rings of a cross hydrolysis reaction is effectively conducted to obtain an linked poly Succinimide is conducted without controlling the excellent resin. Swelling degree, no particular limitation is imposed on each 9-5 Amount of water for use in the hydrolysis reaction 15 Specific condition insofar as the process can Substantially It is necessary to conduct the croSS-linking reaction of open the imide rings by alkaline hydrolysis and can form imide rings of a cross-linked polySuccinimide in the pres carboxyl groups (or salts thereof) by the ring opening. It is ence of water. The amount of this water can be determined however preferred to adopt conditions Similar to the above as desired. In each of the above-described methods 9-1 to described preferable conditions for conducting a hydrolysis 9-4), the preferred amount of water may generally be 1 to reaction while controlling the Swelling degree. When the 50 times by weight as much as the resulting croSS-linked Swelling degree is not controlled, the preferred temperature polyaspartic acid resin, with 1 to 20 times by weight being of the reaction system may generally be from 5 C. to 100 particularly preferred. In the method 9-1), the amount of C., with 10° C. to 60° C. being more preferred. water should be determined by also taking into consideration 11 Post-treatment of a cross-linked polyaspartic acid resin the ratio of water to a water-miscible organic Solvent. 25 No particular limitation is imposed on post-treatment of a 9-6 Alkaline reagent for use in the hydrolysis reaction croSS-linked polyaspartic acid resin available as a result of No particular limitation is imposed on an alkaline reagent an alkaline hydrolysis reaction of imide rings of a croSS which is employed to Subject imide rings of a croSS-linked linked poly Succinimide. For example, treatments or proceSS poly Succinimide to a hydrolysis reaction, but an aqueous ings Such as neutralization, Salt interchange, drying, alkaline Solution is generally used. purification, granulation and Surface cross-linking can be Examples of the aqueous alkaline Solution can include conducted as needed. A description will hereinafter be made various aqueous Solutions making use of alkali metal Salts, especially about neutralization, Salt interchange and drying. for example, alkali metal hydroxides Such as Sodium 11-1 Neutralization treatment of a cross-linked polyaspar hydroxide, potassium hydroxide and lithium hydroxide, tic acid resin alkali metal carbonates Such as Sodium carbonate, potassium 35 Neutralization treatment of a cross-linked polyaspartic carbonate and lithium carbonate, alkali metal hydrogencar acid resin can be conducted as needed. It is however to be bonates Such as Sodium hydrogencarbonate and potassium noted that the reaction mixture after the hydrolysis reaction, hydrogencarbonate, alkali metal acetates Such as Sodium which contains the croSS-linked polyaspartic acid resin, is acetate and potassium acetate, and Sodium oxalate; and usually alkaline. It is therefore preferred to neutralize it by aqueous ammonia. Among these, aqueous Solutions of 40 adding an acid or the like. By this neutralization treatment, Sodium hydroxide and potassium hydroxide are preferred for carboxyl groups contained in the molecules of the croSS their economical costs. They can be used either Singly or in linked polyaspartic acid resin can be converted into Salts. combination. Although no particular limitation is imposed on this neu 9-7 pH of the hydrolysis reaction system tralization degree, the proportion of carboxyl groups in the The pH of a reaction mixture upon conducting a hydroly 45 form of the salts may preferably account for 0 to 50%, with sis reaction varies depending on the concentration of a 0 to 30% being more preferred, both based on the total reagent Such as an aqueous alkaline Solution. When this pH number of aspartic acid residual groups in the molecules of is adequately lowered, it is possible to prevent cutting of the cross-linked polyaspartic acid resin. molecules of the resin and, as a result, to avoid a reduction No particular limitation is imposed in the method of the in water absorbency. If the pH is appropriately raised, the 50 neutralization treatment, but it is commonly practiced to reaction Velocity can be accelerated So that a practical Step adjust the pH by adding an acid after the hydrolysis reaction. can be established. In general, this pH may preferably from Specific examples of the acid can include mineral acids Such 7.5 to 13, more preferably from 9 to 12. as hydrochloric acid, hydrobromic acid, hydroiodic acid, 10 Hydrolysis of imide rings of a cross-linked polysuc Sulfuric acid, Sulfurous acid, nitric acid, nitrous acid, car cinimide without any adjustment of Swelling degree. 55 bonic acid and phosphoric acid; carboxylic acids Such as In the foregoing, the description was made about the formic acid, acetic acid, propionic acid, oxalic acid and methods in each of which the Swelling degree of a resin in benzoic acid, Sulfonic acids Such as methaneSulfonic acid, a reaction System was controlled within the range of from 3 trifluoromethaneSulfonic acid, benzeneSulfonic acid and to 100 times upon Subjecting imide rings of a croSS-linked toluenesulfonic acid; and phosphonic acid Such as benzene poly Succinimide to a hydrolysis reaction. These methods 60 phosphonic acid. can bring about excellent effects in connection with the Among these, hydrochloric acid and Sulfuric acid are water absorbency of the resulting croSS-linked polyaspartic preferred, with hydrochloric acid being particularly acid resin and the Volumetric efficiency. preferred, in View of the cost and the readineSS in removal. It is however to be noted that the present invention is not 11-2 Salt-interchange treatment of a cross-linked polyas limited only to the proceSS featuring control of the Swelling 65 partic acid resin. degree of a resin in a hydrolysis reaction but also include the When carboxyl groups contained in molecules of a croSS above-described proceSS featuring croSS-linking of poly Suc linked polyaspartic acid resin are converted into Salts by 6,072,024 39 40 neutralization treatment, the Salts may be converted into Solvent, as is by using water and/or a water-miscible Salts of a different kind as needed. organic Solvent AS examples of a reagent usable in this Salt interchange, 12-2) To wash a cross-linked polyaspartic acid resin by alkali metal Salts, ammonium Salts, amine Salts and the like repricipitating its gel, which has been caused to Swell by can be mentioned. Specific examples can include alkali water or a mixed Solvent of water and a water-miscible metal Salts. Such as Sodium, potassium, and lithium Salts; organic Solvent, by using a water-miscible organic Sol ammonium Salts Such S ammonium, Vent. tetra methylammonium, tetraethylammonium, These methods 12-1 and 12-2 can be applied to a tetrap ropylammonium, tetrabutylam monium, croSS-linked polyaspartic acid resin in an isolated form and tetrap enty lam monium, tetrahe Xylammonium, also to a cross-linked polyaspartic acid resin in an unisolated ethyltrimethylammonium, trimethylpropylammonium, State, namely, in the form of a wet cake, a pressed cake, a butyltrimethylammonium, pentyltrimethylammonium, slurry or the like. hexyltrimethylammonium, cyclohexyltrimethylammonium, A description will hereinafter be made about these meth benzyltrimethylammonium, triethylpropylammonium, ods 12-1 and 12-2). triethylbutylammonium, triethylpenty lammonium, 15 12-1) Method for filtering and washing a gel by using water triethylhexylammonium, cyclohexyltriethylammonium, and and/or a water-miscible organic Solvent benzyltriethylammonium Salts, and amine Salts. Such as According to this method, a gel of a croSS-linked polyas trimethylamine, triethylamine, tripropylamine, partic acid resin-which has been caused to Swell, for tributylamine, trip enty lamine, trihe Xylamine, example, by water or a mixed Solvent of water and a trie thanolamine, tripropanolamine, tributanolamine, water-miscible organic Solvent-is filtered as is by using tripentanolamine, trihexanolamine, dimethylamine, water and/or the water-miscible organic Solvent, and a diethylamine, dipropylamine, dibutylamine, dipentylamine, hydrogel obtained by the filtration is then washed with water dihexylamine, dicyclohexylamine, dibenzylamine, and/or the water-miscible organic Solvent. By the filtration, ethylmethylamine, methylpropylamine, butylmethylamine, impurities Smaller than the openings of a filter medium can metylpenty lamine, methylhexylamine, methylamine, 25 be filtered off and, if desired, the remaining impurities can ethylamine, propylamine, butylamine, pentylamine, be removed by additional washing. hexylamine, octylamine, decylamine, dodecylamine, and No particular limitation is imposed on the water-miscible hexadecylamine Salts. organic Solvent to be used, insofar as it is an organic Solvent Among these Salts, those having Smaller molecular having miscibility with water. Specific examples can include weights are preferred because a greater molecular weight alcohols Such as methanol, ethanol, propanol, isopropanol, leads to a relatively greater molecular weight per monomer butanol, 2-methoxyethanol and 2-ethoxyethanol, glycols unit and hence to a Smaller water absorption per unit weight. Such as ethylene glycol, diethylene glycol, triethylene Further, those having lower toxicity are preferred when the glycol, propylene glycol and dipropylene glycol, ketones resulting cross-linked polyaspartic acid resin has possibility Such as acetone, methyl ethyl ketone and methyl isobutyl of being brought into contact with human Skin or the like. 35 ketone, cyclic etherS Such as tetrahydrofuran and dioxane, For these reasons, it is preferred to use a Sodium, potassium, N,N-dimethylformamide, N,N-dimethylacetamide, lithium, ammonium or triethanolamine Salt. Use of Sodium N-methylpyrrollidone, N,N'-dimethylimidazolidinone, or potassium Salt is particularly preferred from the Stand dimethylsulfoxide, and Sulfolane. Among these, methanol, point of cost. ethanol, propanol, isopropanol and butanol are preferred 11-3 Drying of a cross-linked polyaspartic acid resin 40 especially in that the resulting cross-linked polyaspartic acid No particular limitation is imposed on a drying method resin can be easily dried and the Solvent Scarcely remains in for a cross-linked polyaspartic acid resin. For example, a the resin after the drying. conventional method can be mentioned, Such as drying in The amounts of the water and the water-miscible organic hot air, drying with Specific vapor, microwave drying, Solvent, which are used for causing the Swelling of the resin, Vacuum drying, drying in a drum drier, or drying by azeo 45 are not limited Specifically, insofar as they can achieve tropic dehydration in a hydrophobic organic Solvent. In Sufficient Swelling of the resin. The Swelling degree of the general, the drying temperature may preferably from 20 to resin varies depending on the water absorbency of the resin. 200° C., with 50 to 120° C. being more preferred. In this method, it is particularly preferred to achieve the To the cross-linked polyaspartic acid resin already Sub Swelling by using distilled water or deionized water in an jected to Such drying, purification, granulation, Surface 50 exceSS amount. However, it is not economical to use water croSS-linking and the like can be applied further. in an unduly large amount. In View of these, the preferred 12 Washing of a cross-linked polyaspartic acid resin amount of distilled water or deionized water to be used may In the process of this invention for the production of a be from 0.001 to 10 times by weight as much the amount of croSS-linked polyaspartic acid resin, a gel of the croSS-linked distilled water or deionized water absorbable in the resin, polyaspartic acid resin is washed or reprecipitated with 55 with 0.02 to 5 times by weight being more preferred. water and/or a water-miscible organic Solvent. No particular limitation is imposed on the amount of the By this purification method, the croSS-linked polyaspartic water and/or the water-miscible organic Solvent employed acid resin is improved in water absorbency and gel Strength. for washing the gel of the Swollen resin. Nonetheless, from This is believed to be attributable to the elimination of the Standpoint of Washing effects and economy, the preferred water-Soluble components-Such as monomers, oligomers, 60 amount may be from 1 to 50 times by weight as much the and an inorganic or organic Salt-which are contained in the weight of the resin, with 3 to 20 times by weight being gel of the resin and reduce properties of the resin. particularly preferred. When a mixed solvent of water and a AS Specific examples of the Washing, the following two water-miscible organic Solvent is used for Washing the gel of methods can be mentioned. the Swollen resin, on the other hand, no particular limitation 12-1) To wash a cross-linked polyaspartic acid resin by 65 is imposed on their ratio but, from the Standpoint of Washing filtering its gel, which has been caused to Swell by water effects, the proportion of the water may preferably be 20 wt. or a mixed Solvent of water and a water-miscible organic % or higher. Here, a higher proportion of the organic Solvent 6,072,024 41 42 results in Shrinkage of the gel So that, as in the method 12-2), gel or a slurry of the gel is Soaked in a water-miscible the resin is brought into a reprecipitated State. organic Solvent, the resin may aggregate into a rigid mass in Although no particular limitation is imposed on the the course of the Soaking. In Such a case, it is preferred to stir medium to be used for the filtration, a Steel Sieve, a non it at a high Speed during the Soaking or to grind the mass in woven nylon fabric, a glass filter or the like can be men a grinding mill having Stirring blades with cutting edges. tioned by way of example. The mesh size of the filter may Illustrative of the water-miscible organic solvent preferably be from 50 um to 2 mm in terms of openings, with employed for the reprecipitation can be acetone, methyl 100 um to 1 mm being more preferred. The speed of ethyl ketone, methanol, ethanol, propanol, butanol, filtration becomes faster when the mesh Size is adequately heptanol, ethylene glycol, propylene glycol, 1,2- increased, whereas the recovery rate of gel becomes higher dimethoxyethane, methoxymethanol, 2-methoxyethanol, when the mesh size is appropriately decreased. tetrahydrofuran, dioxane, N,N-dimethylaminoformamide, The filtration may be conducted while maintaining the N,N-dimethylaminoacetamide, dimethylsulfoxide, N,N- filtered mixture Standstill or under Stirring. As a further dime thy limidazolid in one, Sulfo lane, and alternative, the filtration may be conducted while vibrating N-methylpyrrollidone. From the industrial viewpoint, or rotating the filtered mixture together with the filter. 15 acetone, methanol and ethanol are preferred for their high Further, the filtration may be conducted under atmospheric Safety and easy recovery. They can be used either Singly or preSSure or elevated pressure or may be performed as in combination. The water-miscible organic Solvent Suction filtration under reduced pressure. employed for the precipitation may be the same as the AS the Washing method of the gel, the gel may be washed water-miscible organic Solvent used for the Swelling of the in a usual manner, or the gel may be filtered and washed by resin. It may contain water if necessary. filtering the gel to obtain a hydrogel, dispersing the hydrogel No particular limitation is imposed on the amount of the in distilled water or deionized water and then allowing the water-miscible organic Solvent used for the reprecipitation, hydrogel to precipitate there. Although the method involving insofar as the gel can be reprecipitated (full reprecipitation the dispersion and the Subsequent precipitation requires a or gel-reprecipitation). In general, its amount may be pref greater number of procedures, it can achieve higher washing 25 erably from 0.5 to 10 times by weight, more preferably from efficiency. 1 to 5 times by weight as much as the weight of the resin Further, the gel which fell through the openings upon although it varies depending on the kind of the Solvent. filtration precipitated on the bottom, So that the gel So 13 Production of a cross-linked polyaspartic acid resin precipitated can be recovered and used. without washing The filtered and washed gel may be dried as is, or may be The foregoing description was about the method in which precipitated in a water-miscible organic Solvent, followed by a gel of a croSS-linked polyaspartic acid resin, Said gel the collection and drying of the precipitate. having been obtained by hydrolysis, is washed as is with Although no particular limitation is imposed on the water water and/or a water-miscible organic Solvent. This method miscible organic Solvent for use in the reprecipitation, can bring about excellent effects for the water absorbency general examples can include alcohols Such as methanol, 35 and gel Strength of the croSS-linked polyaspartic acid resin. ethanol, propanol, isopropanol, butanol, 2-methoxyethanol However, this invention becomes more useful from the and 2-ethoxyethanol, glycols Such as ethylene glycol, dieth practical viewpoint if it is not performed only as the proceSS ylene glycol, triethylene glycol, propylene glycol and dipro featuring the Washing or reprecipitation of a gel of a croSS pylene glycol, ketones Such as acetone, methyl ethyl ketone linked polyaspartic acid resin with water and/or a water and methyl isobutyl ketone, cyclic etherS Such as tetrahy 40 miscible organic Solvent but is conducted as a combination drofuran and dioxane, N,N-dimethylformamide, N,N- of the above process and the process featuring the above dimethylacetamide, N-methylpyrrollidone, N,N'- described crosslinking of poly Succinimide in a dispersed dimethylimidazolidinone, dimethylsulfoxide, and Sulfolane. State. It is however to be noted that the latter proceSS can Among these, methanol, ethanol, propanol, isopropanol and bring about its own effects even when the gel of the acetone are preferred for their availability at economical 45 croSS-linked polyaspartic acid resin is not Subjected to prices. Washing or reprecipitation. Namely, the above washing or 12-2 Method for washing a gel by reprecipitation which reprecipitation can be conducted as needed depending on the makes use of a water-miscible organic Solvent application purpose of the resin or properties required there According to this method, a gel of a cross-linked polyas for. partic acid resin, which has been caused to Swell, for 50 14 Shape of a cross-linked polyaspartic acid resin example, by water or a mixed Solvent of water and a Specific examples of the shape of a cross-linked polyas water-miscible organic Solvent-is poured as is into a water partic acid resin can include various shapes Such as crushed miscible organic Solvent to reprecipitate the resin, or a pieces of irregular shapes, Spheres, grains, granules, granu water-miscible organic Solvent is charged into the gel to lated particles, flakes, lumps, pearls, fine powder, fibers, reprecipitate the resin. 55 rods, films and Sheets. Depending on the application Swelling of the cross-linked polyaspartic acid resin may purpose, a preferred shape can be chosen. It can also be in be conducted in a similar manner as in the above-described the form of a fibrous base material, a porous body, an method 12-1). expanded body, a granulated material or the like. When the precipitation is effected by pouring the gel into 15 Particle size of a cross-linked polyaspartic acid resin the water-miscible organic Solvent, the Viscosity of the gel 60 No particular limitation is imposed on the particle Size may be adjusted before the pouring as needed. For example, (average particle diameter) of a cross-linked polyaspartic the Viscosity of the gel becomes higher when the proportion acid resin, and a preferred particle Size can be chosen of water contained in the gel is increased, while the gel depending on the application purpose. In the case of dis becomes lower in Viscosity and is turned into a slurry when posable diapers, for example, an average Size of from 100 to the proportion of the water-miscible organic Solvent is 65 1,000 um is preferred, with a range of from 150 to 600 um increased conversely. However, no particular limitation is being more preferred, because a fast absorption Speed and imposed on the manner or timing of the pouring. When the avoidance of gel blocking are desired. When employed in a 6,072,024 43 44 form kneaded in a resin Such as a waterStopping material or table toilets, gel-type aromatics, gel-type deodorants, Sweat for like purposes, its average particle Size may preferably be absorbing fibers, and disposable pocket heaters, toiletry from 1 to 10 um. When used as a water-holding material for products Such as Shampoos, hair-setting gels, and moistur agricultural and horticultural applications, a range of from izers, agricultural and horticultural products Such as agri 100 um to 5 mm is preferred in view of its dispersibility in cultural and horticultural water-holding materials, life Soil. prolonging agents for cut flowers, floral forms (fixing bases 16 Mode of use of a cross-linked polyaspartic acid resin for cut flowers), Seedling nursery beds, Solution culture No particular limitation is imposed on the mode of use of vegetation sheets, Seed tapes, fluidized Seedling media, and a croSS-linked polyaspartic acid resin. It can be used either dew-preventing agricultural sheets, food packaging materi Singly or in combination with another material. als Such as freshness-retaining materials for food trays, and When using the croSS-linked polyaspartic acid resin in drip absorbent sheets, materials for use during combination with another resin, it can be kneaded in a transportation, Such as cold insulators, and water absorbent thermoplastic resin, followed by molding by injection mold sheets for use during the transportation of fresh vegetables, ing or the like; it can be mixed with constituent monomer(s) construction and civil engineering materials. Such as dew of the another resin and, if necessary, an initiator, followed 15 preventing construction materials, Sealing materials for civil by polymerization by light, heat or the like; it can be engineering and construction, lost circulation preventives dispersed along with the another resin in a Solvent, followed for the Shield tunneling method, concrete admixtures, gas by casting and Solvent removal; it can be mixed with a kets and packings, materials relating to electric and elec prepolymer of the another resin, followed by croSS-linking, tronic equipments, Such as Sealing materials for electronic and it can be mixed with the another resin, followed by equipments and optical fibers, waterStopping materials for croSS-linking. communication cables, and inkjet recording papers, water No particular limitation is imposed on the molded or treatment materials, Such as Sludge Solidifiers, and dehydrat otherwise formed product of the cross-linked polyaspartic ing agents for gasoline and oils, textile-printing Sizing acid resin. It can be used in the form of Solid matters, sheets, materials, water-Swelling toys, artificial Snow, Sustained films, fibers, nonwoven fabrics, expanded bodies, rubber and 25 release fertilizers; Sustained-release agrichemicals; the like. Further, no particular limitation is imposed on their Sustained-release drugs, humidity regulating materials, and molding or forming methods. antistatic agents. The croSS-linked polyaspartic acid resin can be used by The present invention will hereinafter be described more itself or in the form of a composite material combined with specifically by Examples. It should however be borne in another material. Although no particular limitation is mind that the present invention is not limited only to the imposed on the Structure of the composite material, it can be Examples. In the following Examples and Comparative formed into a Sandwich Structure by holding it between pulp Examples, all designations of "part or “parts' mean "part layers, nonwoven fabrics or the like; it can be formed into by weight” or “parts by weight”. a multilayer Structure by using a resin sheet or film as a base The water absorption in each Example was measured by material; or it can be formed into a double-layer Structure by 35 the below-described tea bag method, whereas the gel casting it on a resin sheet. For example, formation of the Strength in each Example was measured by the below croSS-linked polyaspartic acid resin into the shape of a sheet described steel-ball placing method. Further, the volumetric provides a Superabsorbent sheet (including a Superabsorbent efficiency of a reaction in the hydrolysis of imide rings of film). each croSS-linked poly Succinimide was expressed in terms Further, the croSS-linked polyaspartic acid resin can also 40 of percentage by weight (wt.%) of the resulting resin based be blended with one or more other superabsorbent resins as on the total weight of the employed Solvent and the croSS needed. It is also possible to add, as needed, inorganic linked polySuccinimide. compounds Such as Salt, colloidal Silica, white carbon, (1) Tea bag method ultrafine Silica and titanium oxide powder; and organic The measurement of water absorption was conducted compounds Such as chelating compounds. Moreover, it is 45 using distilled water and physiological Saline as liquids to be also possible to mix oxidizing agents, antioxidants, reducing absorbed. Specifically, about 0.05 part of a Superabsorbent agents, ultraViolet absorbers, antibacterial agents, resin was placed in a tea bag made of nonwoven fabric (80 fungicides, mildew proofing agents, fertilizers, perfumes, mmx50mm) in the case of distilled water, whereas about 0.1 deodorants, pigments and the like. part of the Superabsorbent resin was filled in a similar tea The croSS-linked polyaspartic acid resin can also be used 50 bag. Each tea bag was immersed in an exceSS amount of the in the form of a gel or Solid matter. It is used in a gel form, corresponding liquid, in which the resin was allowed to for example, when employed in water-holding materials for Swell for 1 hour. The tea bag was then pulled out. After the agricultural and horticultural applications, life prolonging liquid was allowed to drip away for 1 minute, the weight of agents for cut flowers, gel-type aromatics, gel-type deodor the tea bag with the Swollen resin contained therein was ants and the like; and it is used in a Solid form when 55 measured. The above procedures were likewise repeated employed as an absorbent for disposable diapers. using, as a blank, a similar tea bag only. The weight of the 17 Application purposes of a cross-linked polyaspartic acid blank and the weight of the Superabsorbent resin were resin subtracted from the weight of the tea bag with the Swollen No particular limitation is imposed on the application resin contained therein. A value obtained by dividing the purposes of a croSS-linked polyaspartic acid resin. It can be 60 difference with the weight of the Superabsorbent resin was used in any application fields where conventional Superab recorded as a water absorption (g/one-gram resin). Sorbent resins are usable. Incidentally, the physiological saline was a 0.9 wt. % Illustrative applications can include Sanitary products aqueous Solution of Sodium chloride. Such as Sanitary napkins, disposable diapers, breast milk (2) Steel-ball placing method pads, and disposable dustcloths, medical products Such as 65 Physiological saline (250 parts) was added to 5 parts of a wound-protecting dressing materials, medical underpads, Superabsorbent resin, followed by gelation for 1 hour. On the and cataplasms; daily necessaries Such as pet sheets, por gel, Steel balls were placed one after one, one Steel ball on 6,072,024 45 46 the gel each time, Starting from the Steel ball having a dried at 60° C., whereby 140 parts of a cross-linked pol Smallest diameter. The greatest one of the diameters of balls yaspartic acid resin as a Superabsorbent polymer were which were allowed to remain for 30 seconds or longer on obtained. the gel without Sinking was recorded as the gel Strength of The water absorption of the croSS-linked polyaspartic acid the gel. resin was 860 times in the case of distilled water and 70 (A) Examples directed to the use of a dispersant in a times in the case of physiological Saline. croSS-linking reaction: Example A3 Example A1 In 40 parts of distilled water, 7.2 parts of lysine methyl A wet cake of a cross-linked poly Succinimide was ester dihydrochloride and 22.6 parts of lysine monohydro obtained in a Similar manner as in Example A2 except that chloride were dispersed. To the resultant dispersion, 7.8 a Solution of 3.0 parts of hexamethylenediamine as a croSS parts of caustic soda were added little by little for linking agent in 10 parts of distilled water was used instead neutralization, whereby an aqueous Solution of lysine was of the aqueous Solution of lysine. prepared. On the other hand, 100 parts of polySuccinimide The wet cake of the cross-linked poly Succinimide was having a weight average molecular weight of 96,000 were 15 Subjected to hydrolysis, neutralization, collection and drying dissolved in 400 parts of N,N-dimethylformamide in a similar manner as in Example A2 except for the use of (hereinafter abbreviated as “DMF) under a nitrogen gas 148.8 pats of a 27 wt.% aqueous Solution of caustic Soda, Stream, followed by the addition of the aqueous Solution of whereby 108 parts of a croSS-linked polyaspartic acid resin lysine. After the thus-prepared mixture was stirred at room as a Superabsorbent polymer were obtained. temperature for 30 minutes, 400 parts of toluene as a The water absorption of the croSS-linked polyaspartic acid dispersant (poor Solvent) were charged to disperse the resin was 880 times in the case of distilled water and 70 poly Succinimide, followed by a reaction for 2 hours. After times in the case of physiological Saline. the reaction, the reaction mixture was Subjected to Suction Example A4 filtration to collect a precipitate. The precipitate was washed In a similar manner as in Example A1 except that a with toluene and then dried at 60° C. for 2 hours, whereby 25 dispersion of 3.5 parts of m-xylylenediamine as a croSS a croSS-linked poly Succinimide was obtained. linking agent in 20 parts of toluene was used instead of the The cross-linked poly Succinimide (120 parts) was dis aqueous Solution of lysine, a wet cake of a croSS-linked persed in a mixture of 400 parts of distilled water and 400 poly Succinimide was obtained by conducting the Steps parts of methanol, followed by the dropwise addition of 130 before the drying. parts of a 27 wt.% aqueous Solution of caustic Soda over 2 The wet cake of the cross-linked poly Succinimide was hours. After the dropwise addition, the resultant mixture was Subjected to hydrolysis, neutralization, collection and drying stirred for 2 hours. Using a 7 wt.% aqueous solution of in a similar manner as in Example A2 except for the use of hydrochloric acid, the mixture was neutralized to pH 7. After 148.8 pats of a 27 wt.% aqueous Solution of caustic Soda, the neutralization, the mixture was poured into 300 parts of whereby 110 parts of a croSS-linked polyaspartic acid resin methanol, followed by Stirring for 1 hour. A resultant pre 35 as a Superabsorbent polymer were obtained. cipitate was collected by filtration and then dried at 60° C., The water absorption of the croSS-linked polyaspartic acid whereby 125 parts of a croSS-linked polyaspartic acid resin resin was 760 times in the case of distilled water and 65 as a Superabsorbent polymer were obtained. times in the case of physiological Saline. The water absorption of the cross-linked polyaspartic acid Example A5 resin was 890 times in the case of distilled water and 71 40 In 150 parts of distilled water, 75.3 parts of lysine times in the case of physiological Saline. monohydrochloride were Suspended. To the resultant Example A2 Suspension, 40.6 parts of caustic Soda were added for In 80 parts of distilled water, 37.6 parts of lysine mono neutralization, whereby a Suspension of lysine was prepared. hydrochloride were dispersed. To the resultant dispersion, On the other hand, 100 parts of polysuccinimide having a 10.3 parts of caustic Soda were added for neutralization, 45 weight average molecular weight of 96,000 and 500 parts of whereby an aqueous Solution of lysine was prepared. On the distilled water as a dispersant (poor Solvent) were charged in other hand, 100 parts of polySuccinimide having a weight a high-speed mixer equipped with Stirring blades having average molecular weight of 96,000 were dissolved in 400 cutting edges. The poly Succinimide was disintegrated at parts of DMF under a nitrogen gas stream, followed by the 15,000 rpm for 1 hour, followed by the addition of the addition of the aqueous Solution of lysine. After the thus 50 Suspension of lysine. After the thus-prepared mixture was prepared mixture was stirred at room temperature for 10 stirred and reacted for 20 hours, 500 parts of methanol were minutes, 400 parts of methanol as a dispersant (poor Solvent) charged, whereby a dispersion of a cross-linked poly Succin were charged for dispersion, followed by a reaction for 20 imide was obtained. hours. After the reaction, the reaction mixture was Subjected To the dispersion of the croSS-linked poly Succinimide, to Suction filtration to collect a precipitate. The precipitate 55 13.7 parts of a 27 wt.% aqueous solution of caustic soda was washed with methanol, whereby a wet cake of a were added dropwise over 2 hours. After the dropwise croSS-linked poly Succinimide was obtained. addition, the resultant mixture was stirred for 2 hours. Using The wet cake of the croSS-linked poly Succinimide was a 7 wt.% aqueous Solution of hydrochloric acid, the mixture dispersed in a mixture of 400 parts of distilled water and 400 was neutralized to pH 7. After the neutralization, the mixture parts of methanol, followed by the dropwise addition of 60 was poured into 300 parts of methanol, followed by stirring 122.1 parts of a 27 wt.% aqueous Solution of caustic Soda for 1 hour. A resultant precipitate was collected by filtration over 2 hours. After the dropwise addition, the resultant and then dried at 60° C., whereby 95 parts of a cross-linked mixture was stirred for 2 hours. Using a 7 wt.% aqueous polyaspartic acid resin as a Superabsorbent polymer were Solution of hydrochloric acid, the mixture was neutralized to obtained. pH 7. After the neutralization, the mixture was poured into 65 The water absorption of the croSS-linked polyaspartic acid 300 parts of methanol, followed by stirring for 1 hour. A resin was 460 times in the case of distilled water and 63 resultant precipitate was collected by filtration and then times in the case of physiological Saline. 6,072,024 47 48 Example A6) other hand, 100 parts of poly Succinimide having a weight In 100 parts of distilled water, 56.4 parts of lysine average molecular weight of 96,000 were dissolved in a monohydrochloride were Suspended. To the resultant mixed solvent of 400 parts of DMF and 400 parts of Suspension, 25.5 parts of caustic Soda were added little by methanol as a dispersant (poor Solvent), So that the polySuc little for neutralization, whereby an aqueous Solution of cinimide was brought into a dispersed State. The aqueous lysine was prepared. On the other hand, 100 parts of solution of lysine was added to the dispersion, followed by poly Succinimide having a weight average molecular weight Stirring at room temperature for 40 hours. The resultant of 96,000 and 500 parts of methanol as a dispersant (poor mixture was Subjected to Suction filtration to collect a Solvent) were charged in a high-speed mixer equipped with precipitate. The precipitate was washed with methanol, Stirring blades having cutting edges. The polySuccinimide whereby a wet cake of a croSS-linked polySuccinimide was was disintegrated at 15,000 rpm for 1 hour, followed by the obtained. addition of the Suspension of lysine. The thus-prepared The wet cake of the cross-linked poly Succinimide was mixture was stirred for 20 hours, whereby a dispersion of a dispersed in a mixture of 400 parts of distilled water and 400 croSS-linked poly Succinimide was obtained. parts of methanol, followed by the dropwise addition of 130 To the dispersion of the croSS-linked polySuccinimide, 15 parts of a 27 wt.% aqueous Solution of caustic Soda over 2 500 parts of distilled water were added, followed by the hours. After the dropwise addition, the resultant mixture was dropwise addition of 106.8 parts of a 27 wt.% aqueous stirred for 2 hours. Using a 7 wt.% aqueous solution of Solution of caustic Soda over 2 hours. After the dropwise hydrochloric acid, the mixture was neutralized to pH 7. After addition, the resultant mixture was stirred for 2 hours. Using the neutralization, the mixture was poured into 300 parts of a 7 wt.% aqueous Solution of hydrochloric acid, the mixture methanol, followed by Stirring for 1 hour. A resultant pre was neutralized to pH 7. After the neutralization, the mixture cipitate was collected by filtration and then dried at 60° C., was poured into 300 parts of methanol, followed by stirring whereby 94 parts of a cross-linked polyaspartic acid resin as for 1 hour. A resultant precipitate was collected by filtration a Superabsorbent polymer were obtained. and then dried at 60° C., whereby 90 parts of a cross-linked The water absorption of the croSS-linked polyaspartic acid polyaspartic acid resin as a Superabsorbent polymer were 25 resin was 660 times in the case of distilled water and 67 obtained. times in the case of physiological Saline. The water absorption of the cross-linked polyaspartic acid Example A9 resin was 520 times in the case of distilled water and 65 In 40 parts of distilled water, 24.0 parts of lysine methyl times in the case of physiological Saline. ester dihydrochloride and 18.8 parts of lysine monohydro Example A7 chloride were dispersed. To the resultant dispersion, 12.4 In 80 parts of distilled water, 48.0 parts of lysine methyl parts of caustic soda were added little by little for ester dihydrochloride were suspended. To the resultant neutralization, whereby an aqueous Solution of lysine was Suspension, 16.5 parts of caustic Soda were added little by prepared. On the other hand, 100 parts of polySuccinimide little for neutralization, whereby a Suspension of lysine having a weight average molecular weight of 96,000 were methyl ester was prepared, on the other hand, 100 parts of 35 dissolved in 400 parts of DMF under a nitrogen gas stream, poly Succinimide having a weight average molecular weight followed by the addition of the aqueous solution of lysine. of 96,000 were dissolved in 400 parts of DMF under a After the thus-prepared mixture was stirred at room tem nitrogen gas stream, followed by the addition of 400 parts of perature for 10 minutes, the resulting reaction mixture was methanol as a dispersant (poor Solvent) So that the polysuc charged over 30 minutes into 400 parts of toluene as a cinimide was brought into a dispersed State. The Suspension 40 dispersant (poor Solvent) which were placed in a mixer of lysine methyl ester was added to the dispersion, followed equipped with high-speed stirring blades driven at 8,000 by stirring at room temperature for 20 hours. The resultant rpm. Subsequent to a further reaction for 10 hours, the mixture was Subjected to Suction filtration to collect a reaction mixture was Subjected to Suction filtration to collect precipitate. The precipitate was washed with methanol, a precipitate. The precipitate was washed with toluene and whereby a wet cake of a croSS-linked poly Succinimide was 45 then dried at 60° C. for 2 hours, whereby a cross-linked obtained. polySuccinimide was obtained. The wet cake of the croSS-linked poly Succinimide was The cross-linked polysuccinimide (130 parts) was dis dispersed in a mixture of 400 parts of distilled water and 400 persed in a mixture of 400 parts of distilled water and 400 parts of methanol, followed by the dropwise addition of parts of methanol, followed by the dropwise addition of 122.1 parts of a 27 wt.% aqueous Solution of caustic Soda 50 122.1 parts of a 27 wt.% aqueous Solution of caustic Soda over 2 hours. After the dropwise addition, the resultant over 2 hours. After the dropwise addition, the resultant mixture was stirred for 2 hours. Using a 7 wt.% aqueous mixture was stirred for 2 hours. Using a 7 wt.% aqueous Solution of hydrochloric acid, the mixture was neutralized to Solution of hydrochloric acid, the mixture was neutralized to pH 7. After the neutralization, the mixture was poured into pH 7. After the neutralization, the mixture was poured into 300 parts of methanol, followed by stirring for 1 hour. A 55 300 parts of methanol, followed by stirring for 1 hour. A resultant precipitate was collected by filtration and then resultant precipitate was collected by filtration and then dried at 60° C., whereby 98 parts of a cross-linked polyas dried at 60° C., whereby 125 parts of a cross-linked pol partic acid resin as a Superabsorbent polymer were obtained. yaspartic acid resin as a Superabsorbent polymer were The water absorption of the cross-linked polyaspartic acid obtained. resin was 450 times in the case of distilled water and 64 60 The water absorption of the croSS-linked polyaspartic acid times in the case of physiological Saline. resin was 620 times in the case of distilled water and 65 Example A8 times in the case of physiological Saline. In 40 parts of distilled water, 7.2 parts of lysine methyl Comparative Example A1 ester dihydrochloride and 22.6 parts of lysine monohydro In 40 parts of distilled water, 7.2 parts of lysine methyl chloride were dissolved. To the resultant solution, 7.8 parts 65 ester dihydrochloride and 22.6 parts of lysine monohydro of caustic soda were added little by little for neutralization, chloride were dissolved. To the resultant solution, 7.8 parts whereby an aqueous Solution of lysine was prepared. On the of caustic soda were added little by little for neutralization, 6,072,024 49 SO whereby an aqueous Solution of lysine was prepared. On the however not fully good in all aspects, because they did not other hand, 100 parts of polySuccinimide having a weight use any dispersant. Described Specifically, the productivity average molecular weight of 96,000 were dissolved in 400 was considerably low in Comparative Example A1, and the parts of DMF under a nitrogen gas stream, followed by the water absorption of the resin was significantly low in addition of the aqueous Solution of lysine. The thus-prepared Comparative Example A2. mixture was then Stirred at room temperature. In the course In contrast, each of Examples A1-A9 used the dispersant of the Stirring, thickening of the reaction mixture proceeded and conducted the cross-linking reaction in the dispersed So much that the Stirring became no longer feasible. The State. They were hence able to produce at high productivity reaction was therefore conducted for 30 hours without the cross-linked polyaspartic acid resins which showed the Stirring, whereby a reaction product was obtained in the high water absorptions, respectively. form of a gel. AS is evident from the foregoing, advantageous effects This gel of the reaction product was added to 1,000 parts can be brought about with respect to water absorption and of methanol, and the resultant mixture was stirred at room productivity by using a dispersant in a cross-linking reaction temperature. Because precipitated particles were large, it and reacting polySuccinimide in a dispersed State. was impossible to increase the Stirring Speed. It took more 15 (B) Examples directed to a cross-linking reaction within a than one day for the disintegration of the entire croSS-linked range of from 3 to 100 times in water Swelling degree: product, namely, this operation was difficult. A precipitate So Example B1 obtained was collected by Suction filtration and washed first Under a nitrogen gas Stream, 5 parts of polySuccinimide with methanol and then with water, whereby a wet cake of having a weight average molecular weight of 96,000 were a croSS-linked poly Succinimide was obtained. dissolved in 20 parts of DMF, followed by the addition of 1.8 This wet cake of the croSS-linked poly Succinimide was parts of lysine methyl ester dihydrochloride and 3.1 parts of suspended in a mixture of 15 parts of distilled water and 15 triethylamine. After the resultant mixture was Stirred at room parts of methanol, followed by the dropwise addition of 7.3 temperature for 5 hours, the Stirring was stopped and the parts of a 24 wt.% aqueous Solution of Sodium hydroxide So reaction was allowed to proceed for 50 hours. Methanol (100 that the pH of the suspension fell within a range of from 11 25 parts) was added to the reaction mixture, and the resultant to 12. After the pH was not found to drop further, dilute mixture was stirred at room temperature for 2 hours to effect hydrochloric acid was added until the pH of the reaction reprecipitation. The resulting precipitate was collected by mixture dropped to 7. The thus-obtained mixture was poured Suction filtration, and was then washed with methanol and into 100 parts of methanol and the resulting precipitate was further with water, whereby a wet cake of a cross-linked dried and disintegrated, whereby 7.6 parts of a croSS-linked polySuccinimide was obtained. polyaspartic acid resin as a Superabsorbent polymer were This wet cake of the cross-linked poly Succinimide was obtained. suspended in a mixture of 15 parts of distilled water and 15 The water absorption of the cross-linked polyaspartic acid parts of methanol. While maintaining the Swelling degree of resin was 380 times in the case of distilled water and 59 the resin within the range of from 3 to 100 times, 7.3 parts times in the case of physiological Saline. 35 of a 24 wt.% aqueous solution of sodium hydroxide were Comparative Example A2 added so that the pH of the suspension fell within a range of Lysine methyl ester dihydrochloride (6 parts) was Sus from 11 to 12. After the pH was not found to drop further, pended in 200 parts of DMF, followed by the neutralization dilute hydrochloric acid was added until the pH of the with 6 parts of triethylamine. Into the Suspension, a Solution reaction mixture dropped to 7. The thus-obtained mixture of 50 parts of polySuccinimide, which had a weight average 40 was poured into 100 parts of methanol and the resulting molecular weight of 130,000, in 250 parts of DMF was precipitate was dried and disintegrated, whereby 7.6 parts of charged. After the resultant mixture was stirred for 1 hour at a cross-linked polyaspartic acid resin as a Superabsorbent room temperature, 12 parts of triethylamine were added polymer were obtained. dropwise, followed by a reaction at room temperature for 40 The water absorption of the croSS-linked polyaspartic acid hours. The reaction mixture was poured into ethanol and the 45 resin was 480 times in the case of distilled water and 61 resulting precipitate was collected by filtration and then times in the case of physiological Saline. Further, the Volu dried, whereby 50 parts of croSS-linked poly Succinimide was metric efficiency of the reaction in the hydrolysis was obtained. 20.2%. The cross-linked poly Succinimide (26 parts) was Sus Example B2) pended in 5,000 parts of distilled water, followed by the 50 In a similar manner as in Example B1 except for the use dropwise addition of 2N Sodium hydroxide so that the pH of of poly Succinimide having a weight average molecular the suspension fell within 9 to 11 to conduct a hydrolysis weight of 155,000, 146 parts of a cross-linked polyaspartic reaction of the remaining imide rings. The reaction mixture acid resin were obtained. The water absorption of the was collected by filtration and then dried, whereby 86 parts croSS-linked polyaspartic acid resin was 550 times in the of a croSS-linked polyaspartic acid resin as a Superabsorbent 55 case of distilled water and 63 times in the case of physi polymer were obtained. ological Saline. The water absorption of the cross-linked polyaspartic acid Example B3 resin was 110 times in the case of distilled water and 30 A wet cake of a croSS-linked poly Succinimide, Said wet times in the case of physiological Saline. cake having been obtained as in Example B1, was Suspended Comparison and Discussion on Examples A1-A9 and 60 in 30 parts of a 2 wt.% aqueous solution of sodium chloride. Comparative Examples A1-A2) While maintaining the Swelling degree of the resin within Comparative Example A1 is directed to a conventional the range of from 3 to 100 times, 8.6 parts of a 24 wt.% proceSS intended to produce a cross-linked polyaspartic acid aqueous Solution of Sodium hydroxide were added So that capable of achieving a high water absorption, and Compara the pH of the suspension fell within a range of from 11 to 12. tive Example A2 is directed to another conventional proceSS 65 After the pH was not found to drop further, dilute hydro intended to produce a croSS-linking polyaspartic acid at high chloric acid was added until the pH of the reaction mixture productivity. Results of Comparative Examples A1-A2 were dropped to 7. The thus-obtained mixture was poured into 6,072,024 S1 52 100 parts of methanol and the resulting precipitate was dried Comparative Example B1 and disintegrated, whereby 7.7 parts of a cross-linked pol A wet cake of a croSS-linked poly Succinimide, Said wet yaspartic acid resin as a Superabsorbent polymer were cake having been obtained as in Example B1, was Suspended obtained. The water absorption of the croSS-linked polyas in 1,000 parts of distilled water. To the thus-obtained partic acid resin was 460 times in the case of distilled water Suspension, an 8 wt.% aqueous Solution of Sodium hydrox and 60 times in the case of physiological Saline. Further, the ide was added dropwise so that the pH of the suspension fell volumetric efficiency of the reaction in the hydrolysis was within a range of from 10 to 11. The addition of the 8% 20.4%. aqueous Solution of caustic Soda was continued until the pH Example B4 was not found to drop further. After no further drop was observed in the pH, dilute hydrochloric acid was added until A wet cake of a croSS-linked poly Succinimide, Said wet the pH of the reaction mixture dropped to 7. The thus cake having been obtained as in Example B1, was Suspended obtained mixture was poured into 3,000 parts of acetone and in a mixed solvent of 25 parts of distilled water and 50 parts the resulting precipitate was dried and disintegrated, of isopropyl alcohol, the temperature of which was 70° C. whereby 7.7 parts of a croSS-linked polyaspartic acid resin as While maintaining the Swelling degree of the resin within a Superabsorbent polymer were obtained. The water absorp the range of from 3 to 100 times, 7.6 parts of a 24 wt.% 15 tion of the croSS-linked polyaspartic acid resin was 180 aqueous Solution of Sodium hydroxide were added So that times in the case of distilled water and 38 times in the case the pH of the suspension fell within a range of from 9 to 10. of physiological Saline. Further, the Volumetric efficiency of After the pH was not found to drop further, dilute hydro the reaction in the hydrolysis was 0.8%. chloric acid was added until the pH of the reaction mixture Comparative Example B2) dropped to 7. The thus-obtained mixture was poured into A wet cake of a croSS-linked poly Succinimide, Said wet 100 parts of methanol and the resulting precipitate was dried cake having been obtained as in Example B1, was Suspended and disintegrated, whereby 7.2 parts of a cross-linked pol in a mixed solvent of 30 parts of distilled water and 90 parts yaspartic acid resin as a Superabsorbent polymer were of acetone. To the thus-obtained Suspension, an 8 wt.% obtained. The water absorption of the croSS-linked polyas aqueous Solution of Sodium hydroxide was added dropwise partic acid resin was 460 times in the case of distilled water 25 so that the pH of the suspension fell within a range of from and 60 times in the case of physiological Saline. Further, the 10 to 11. The addition of the 8% aqueous solution of caustic volumetric efficiency of the reaction in the hydrolysis was Soda was continued until the pH was not found to drop 12.6%. further. After no further drop was observed in the pH, dilute Example B5 hydrochloric acid was added until the pH of the reaction A wet cake of a croSS-linked poly Succinimide, Said wet mixture dropped to 7. The thus-obtained mixture was poured cake having been obtained as in Example B1, was Suspended into 3,000 parts of acetone and the resulting precipitate was in a mixed Solvent of 15 parts of a 2 wt.% aqueous Solution dried and disintegrated, whereby 7.1 parts of a croSS-linked of Sodium chloride and 8 parts of methanol. While main polyaspartic acid resin as a Superabsorbent polymer Were taining the Swelling degree of the resin within the range of obtained. The water absorption of the croSS-linked polyas from 3 to 100 times, 8.6 parts of a 24 wt.% aqueous solution 35 partic acid resin was 150 times in the case of distilled water of sodium hydroxide were added so that the pH of the and 36 times in the case of physiological Saline. Further, the suspension fell within a range of from 11 to 12. After the pH volumetric efficiency of the reaction in the hydrolysis was was not found to drop further, dilute hydrochloric acid was 5.6%. added until the pH of the reaction mixture dropped to 7. The Comparison and Discussion on Examples B1-B7 and Com thus-obtained mixture was poured into 100 parts of metha 40 parative Examples B1-B2) nol and the resulting precipitate was dried and disintegrated, In each of Comparative Examples B1-B2, the hydrolysis whereby 7.6 parts of a croSS-linked polyaspartic acid resin as reaction was conducted without controlling the Swelling a Superabsorbent polymer were obtained. The water absorp degree of the resin within the range of from 3 to 100 times, tion of the croSS-linked polyaspartic acid resin was 480 So that the water absorption of the resultant croSS-linked times in the case of distilled water and 61 times in the case 45 polyaspartic acid resin was low and the Volumetric effi of physiological Saline. Further, the Volumetric efficiency of ciency of the reaction in the hydrolysis was very low. the reaction in the hydrolysis was 24.8%. In contrast, in each of Examples B1-B7, the resin was Example B6) Subjected to the hydrolysis reaction while controlling the In a similar manner as in Example B1 except for the use Swelling degree of the resin within the range of from 3 to 100 of 0.15 part of hexamethylenediamine as a croSS-linking 50 times, So that the croSS-linked polyaspartic acid resin agent in lieu of lysine methyl ester dihydrochloride, 7.0 parts capable of showing the large water absorption was obtained of a croSS-linked polyaspartic acid resin were obtained. The and the volumetric efficiency of the reaction in the hydroly water absorption of the croSS-linked polyaspartic acid resin sis was high. was 380 times in the case of distilled water and 59 times in AS is evident from the foregoing, advantageous effects the case of physiological Saline. Further, the Volumetric 55 can be brought about with respect to water absorption and efficiency of the reaction in the hydrolysis was 18.9%. Volumetric efficiency by conducting a hydrolysis reaction of Example B7 imide rings of a cross-linked polySuccinimide while main In a similar manner as in Example B1 except that, as the taining the Swelling degree of the resin within the range of alkaline water employed in the hydrolysis reaction, 8.2 parts from 3 to 100 times inside the reaction system. of a 30 wt.% aqueous Solution of caustic Soda were used in 60 (C) Examples directed to the use of a cross-linked place of the 24 wt.% aqueous Solution of Sodium hydroxide, poly Succinimide, which has been obtained by Subjecting 7.9 parts of a cross-linked polyaspartic acid resin were a gel to wet disintegration, and a hydrolysis reaction obtained. The water absorption of the croSS-linked polyas within the range of from 3 to 100 times in Swelling partic acid resin was 450 times in the case of distilled water degree: and 58 times in the case of physiological Saline. Further, the 65 Example C1 volumetric efficiency of the reaction in the hydrolysis was In 40 parts of distilled water, 7.2 parts of lysine methyl 18.9%. ester dihydrochloride and 22.6 parts of lysine monohydro 6,072,024 S3 S4 chloride were dissolved. To the resultant solution, 7.8 parts Example C4 of caustic soda were added little by little for neutralization, In a similar manner as in Example C1 except that, instead whereby an aqueous Solution of lysine was prepared. On the of lysine methyl ester dihydrochloride, an aqueous Solution other hand, 100 parts of polySuccinimide having a weight of a croSS-linking agent was prepared using 3.0 parts of hexamethylenediamine and was employed, 136 parts of a average molecular weight of 96,000 were dissolved in 400 croSS-linked polyaspartic acid resin were obtained. The parts of DMF under a nitrogen gas stream, followed by the water absorption of the croSS-linked polyaspartic acid resin addition of the aqueous Solution of lysine. After the thus was 780 times in the case of distilled water and 68 times in prepared mixture was Stirred at room temperature for 1 hour, the case of physiological Saline. the Stirring was stopped and the reaction was continued for Example C5 20 hours, whereby a gel of a croSS-linked polySuccinimide In a similar manner as in Example C1 except that, instead was obtained. This gel of the croSS-linked polySuccinimide of lysine methyl ester dihydrochloride, an aqueous Solution was transferred into a mixer equipped with Stirring blades of a croSS-linking agent was prepared using 3.5 parts of having cutting edges, and 400 parts of distilled water and m-xylylenediamine and was employed, 132 parts of a croSS linked polyaspartic acid resin were obtained. The water 400 parts of methanol were added. The gel was then 15 absorption of the croSS-linked polyaspartic acid resin was disintegrated at 8,000 rpm for 5 minutes. 740 times in the case of distilled water and 66 times in the While maintaining the Swelling degree of the resin within case of physiological Saline. the range of from 3 to 100 times, 129.7 parts of a 27 wt.% Comparison and Discussion on Examples C1-C5 aqueous Solution of caustic Soda were added dropwise into In Examples C1-C5 the cross-linked polyaspartic acid the mixer over 2 hours. Subsequent to completion of the resins which showed the high water absorptions were dropwise addition, the contents were stirred further for 2 obtained because, as in Examples B1-B7, the resins were hours. A 7 wt.% aqueous solution of hydrochloric acid was Subjected to hydrolysis while maintaining their Swelling then added So that the resulting mixture was neutralized to degrees within the range of from 3 to 100 times. It was also pH 7. After completion of the neutralization, 300 parts of possible to produce the croSS-linked polyaspartic acid resins, methanol were added further and the resulting precipitate 25 which can achieve high water absorptions, at high produc was collected and dried at 60° C., whereby 145 parts of a tivity since the gels of the cross-linked poly Succinimides croSS-linked polyaspartic acid resin as a Superabsorbent were used by Subjecting them to wet disintegration. In polymer were obtained. contrast, the productivity was considerably low in compara The water absorption of the cross-linked polyaspartic acid tive Example A1, and the water absorption of the resin was resin was 860 times in the case of distilled water and 70 Significantly low in Comparative Example A2. times in the case of physiological Saline. (D) Examples directed to the use of a lysine Salt and/or an Example C2 ornithine Salt as a croSS-linking agent: In a similar manner as in Example C1 except for the use Example D2 of poly Succinimide having a weight average molecular In 80 parts of distilled water, 37.6 parts of lysine mono weight of 155,000, 146 parts of a cross-linked polyaspartic 35 hydrochloride were dispersed. To the resultant dispersion, acid resin were obtained. The water absorption of the 9.5 parts of caustic Soda were added for neutralization, croSS-linked polyaspartic acid resin was 1,050 times in the whereby an aqueous Solution of lysine/lysine Sodium Salt case of distilled water and 72 times in the case of physi was prepared, on the other hand, 100 parts of poly Succin ological Saline. imide having a weight average molecular weight of 96,000 Example C3 40 were dissolved in 400 parts of DMF under a nitrogen gas An aqueous Solution of lysine was prepared in a similar Stream, followed by the addition of the aqueous Solution of manner as in Example C1. On the other hand, 100 parts of lysine. After the thus-prepared mixture was stirred at room poly Succinimide having a weight average molecular weight temperature for 10 minutes, 400 parts of methanol as a of 96,000 were dissolved in 400 parts of DMF under a dispersant (poor Solvent) were charged for dispersion, fol nitrogen gas Stream, followed by the addition of the aqueous 45 lowed by a reaction for 20 hours. After the reaction, the Solution of lysine. In a reactor equipped with a high-speed reaction mixture was Subjected to Suction filtration to collect ribbon stirrer, they were reacted at room temperature for 20 a precipitate. The precipitate was washed with methanol, hours without Stirring, whereby a gel of a croSS-linked whereby a wet cake of a croSS-linked polySuccinimide was poly Succinimide was obtained. This gel of the croSS-linked obtained. poly Succinimide was disintegrated as was in the reactor 50 The wet cake of the cross-linked poly Succinimide was equipped with the high-speed ribbon Stirrer. dispersed in a mixture of 400 parts of distilled water and 400 Distilled water (400 parts) and methanol (400 parts) were parts of methanol, followed by the dropwise addition of 122 charged into the mixer. While maintaining the Swelling parts of a 27 wt.% aqueous Solution of caustic Soda over 2 degree of the resin within the range of from 3 to 100 times, hours. After the dropwise addition, the resultant mixture was 129.7 parts of a 27 wt.% aqueous solution of caustic soda 55 stirred for 2 hours. Using a 7 wt.% aqueous solution of were added dropwise over 2 hours. Subsequent to comple hydrochloric acid, the mixture was neutralized to pH 7. After tion of the dropwise addition, the contents were Stirred the neutralization, the mixture was poured into 300 parts of further for 2 hours. A 7 wt.% aqueous solution of hydro methanol, followed by Stirring for 1 hour. A resultant pre chloric acid was added So that the resulting mixture was cipitate was collected by filtration and then dried at 60° C., neutralized to pH 7. After completion of the neutralization, 60 whereby 140 parts of a croSS-linked polyaspartic acid resin 300 parts of methanol were added further and the resulting as a Superabsorbent polymer were obtained. precipitate was collected and dried at 60° C., whereby 145 The water absorption of the croSS-linked polyaspartic acid parts of a cross-linked polyaspartic acid resin as a Superab resin was 920 times in the case of distilled water and 74 Sorbent polymer were obtained. times in the case of physiological Saline. The water absorption of the cross-linked polyaspartic acid 65 Example D2 resin was 850 times in the case of distilled water and 69 In 20 parts of distilled water, 9.4 parts of lysine mono times in the case of physiological Saline. hydrochloride were dispersed. To the resultant dispersion, 6,072,024 SS S6 2.1 parts of caustic Soda were added for neutralization, were added to the resulting precipitate to induce gelation. whereby an aqueous Solution of lysine Sodium was prepared. The thus-formed gel was collected by filtration through a On the other hand, 100 parts of polysuccinimide having a Sieve having 425 um openings, washed thoroughly with weight average molecular weight of 96,000 were dissolved distilled water, and then dried, whereby 6.9 parts of a in 400 parts of DMF under a nitrogen gas stream, followed croSS-linked polyaspartic acid resin as a Superabsorbent by the addition of the aqueous Solution of lysine Sodium. polymer were obtained. After the thus-prepared mixture was stirred at room tem The water absorption of the croSS-linked polyaspartic acid perature for 1 hour, the Stirring was Stopped and the reaction resin was 490 times in the case of distilled water and 62 was continued for 20 hours, whereby a gel of a croSS-linked times in the case of physiological Saline. Further, the poly Succinimide was obtained. This gel of the croSS-linked Strength of the gel was 2%6 inch. poly Succinimide was transferred into a mixer equipped with Example E2 Stirring blades having cutting edges, and 400 parts of dis In a similar manner as in Example E1, a cross-linked tilled water and 400 parts of methanol were added. The gel polySuccinimide was hydrolyzed and then neutralized. After was then disintegrated at 8,000 rpm for 5 minutes. that, 15 parts of distilled water and 15 parts of methanol While maintaining the Swelling degree of the resin within 15 were added to the resulting precipitate to induce gelation. the range of from 3 to 100 times, 145.0 parts of a 27 wt.% The resulting gel was collected by filtration through a Sieve aqueous Solution of caustic Soda were added dropwise into having 200 um openings, washed twice with 15 parts of a 50 the mixer over 2 hours. Subsequent to completion of the wt. 76 aqueous Solution of methanol, and then dried, dropwise addition, the contents were stirred further for 2 whereby 7.2 parts of a croSS-linked polyaspartic acid resin as hours. A 7 wt.% aqueous solution of hydrochloric acid was a Superabsorbent polymer were obtained. The water absorp then added So that the resulting mixture was neutralized to tion of the croSS-linked polyaspartic acid resin was 550 pH 7. After completion of the neutralization, 300 parts of times in the case of distilled water and 64 times in the case methanol were added further and the resulting precipitate of physiological Saline. Further, the Strength of the gel was was collected and dried at 60° C., whereby 131 parts of a 20/16 inch. croSS-linked polyaspartic acid resin as a Superabsorbent 25 Example E3 polymer were obtained. In a similar manner as in Example E1, a cross-linked The water absorption of the cross-linked polyaspartic acid polySuccinimide was hydrolyzed and then neutralized. After resin was 860 times in the case of distilled water and 70 that, 15 parts of distilled water and 18 parts of methanol times in the case of physiological Saline. were added to the resulting precipitate to induce gelation in Discussion on Examples D1–D2 the form of a slurry. The resulting gel was poured little by In Example D1, the cross-linked polyaspartic acid resin little into 50 parts of methanol over 30 minutes so that the which showed the high water absorption was Successfully gel was caused to reprecipitate. The thus-obtained precipi obtained because, as in Examples A1-A9, the dispersant was tate was collected and then dried, whereby 7.7 parts of a used and the croSS-linking reaction was conducted in a croSS-linked polyaspartic acid resin as a Superabsorbent dispersed State. In Example D2, the croSS-linked polyaspar 35 polymer were obtained. The water absorption of the cross tic acid resin which also exhibited the high water absorption linked polyaspartic acid resin was 450 times in the case of was obtained because, as in Examples B1-B7, the resin was distilled water and 61 times in the case of physiological Subjected to hydrolysis while maintaining its SWelling saline. Further, the strength of the gel was 2%6 inch. degree within the range of from 3 to 100 times. Comparative Example E1 Moreover, owing to the use of the lysine Salt as a 40 In a similar manner as in Example E1, a cross-linked croSS-linking agent, Examples D1-D2 were able to provide polySuccinimide was hydrolyzed and then neutralized. After the croSS-linked polyaspartic acid resins with Still higher that, the resulting precipitate was dried as was at 60° C. and Safety. was then ground, whereby 7.6 parts of a croSS-linked pol (E) Examples directed to the washing of a gel of a cross yaspartic acid resin as a Superabsorbent polymer were linked polyaspartic acid resin: 45 obtained. The water absorption of the croSS-linked polyas Example E1 partic acid resin was 160 times in the case of distilled water Under a nitrogen gas Stream, 5 parts of polySuccinimide and 37 times in the case of physiological Saline. Further, the having a weight average molecular weight of 96,000 were Strength of the gel was $16 inch. dissolved in 20 parts of DMF, followed by the addition of 1.8 Comparison and Discussion on Examples E1-E3 and Com parts of lysine methyl ester dihydrochloride and 3.1 parts of 50 parative Example E1 triethylamine. The resultant mixture was stirred at room Comparative Example E1 resulted in the small water temperature for 20 hours. Methanol (100 parts) was added to absorption and the inferior gel Strength because the gel of the the reaction mixture, and the resultant mixture was stirred at croSS-linked polyaspartic acid resin was used as was without room temperature for 2 hours to disintegrate the resulting conducting its Washing. gel. The resulting precipitate was collected by Suction 55 In contrast, each of Examples E1-E3 produced the croSS filtration, and was then washed with methanol and further linked polyaspartic acid resin which showed the large water with water, whereby a wet cake of a cross-linked poly Suc absorption and had the excellent gel Strength, because the cinimide was obtained. gel of the croSS-linked polyaspartic acid resin was washed. This wet cake of the croSS-linked poly Succinimide was AS is evident from the foregoing, advantageous effects suspended in a mixture of 30 parts of distilled water and 90 60 can be brought about with respect to water absorption and parts of methanol. An 8 wt.% aqueous Solution of Sodium gel Strength when a gel of a croSS-linked polyaspartic acid hydroxide was added so that the pH of the suspension fell resin, which has been obtained by hydrolysis, is washed as within a range of from 11 to 12. The addition of the aqueous is with water and/or a water-miscible organic Solvent. alkaline Solution was continued until no further drop was (F) Examples directed to the provision of a resin of a high observed in the pH. After the pH was not found to drop 65 water absorption Speed: further, dilute hydrochloric acid was added until the pH of In each of the Subsequent Examples, a water absorption the reaction mixture dropped to 7. Distilled water (50 parts) (W10) for distilled water was measured 10 minutes later by 6,072,024 57 58 Similar procedures, and its percentage relative to an absorp chloric acid was added to the thus-hydrolyzed mixture to tion (W60) one hour later was calculated as an index for adjust its pH to 7 to 7.5, and the resulting precipitate was making a comparison in water absorption Speed. collected by decantation. Water (20 g) was added to the Incidentally, in View of variations in water absorption Speed thus-obtained precipitate So that the precipitate was con by resin particle sizes, resins Sifted to have particle sizes verted into a slurry. The slurry was poured into 200 g of only in a range of from 100 to 500 um were used for the methanol to conduct reprecipitation. The resulting precipi measurement. tate was collected by filtration, washed and then dried, Example F1 whereby 12.3 g of a croSS-linked polyaspartic acid resin as a Superabsorbent polymer were obtained. In 1.5 g of distilled water, 2.78 g (0.015 mol) of lysine The water absorption of the croSS-linked polyaspartic acid monohydrochloride were dissolved, followed by the addi resin was 690 times in the case of distilled water and 75 tion of 2.44 g (0.015 mol) of a 24.5 wt.% aqueous solution times in the case of physiological Saline. of sodium hydroxide for neutralization. The resultant solu Further, W10/W60x100 was 75.9%. tion was added dropwise over 0.5 hour into a solution of Example F3 9.71 g (0.10 mol) of poly Succinimide, the weight average In 1.5 g of distilled water, 3.70 g (0.020 mol) of lysine molecular weight of which was 96,000, in 38.8 g of DMF, 15 monohydrochloride were dissolved, followed by the addi and the resultant mixture was reacted for 1 hour. After that, tion of 3.27 g (0.020 mol) of a 24.5 wt.% aqueous solution 38.8g of methanol were added to bring the reaction System of sodium hydroxide for neutralization. The resultant solu into a dispersed state, followed by aging at 25 C. for 3 tion was added dropwise over 0.5 hour into a solution of hours. A 24.5 wt.% aqueous solution of sodium hydroxide 9.71 g (0.10 mol) of polySuccinimide, the weight average (1.63 g, 0.01 mol) was then added dropwise and a cross molecular weight of which was 96,000, in 38.8 g of DMF, linking reaction was conducted at 25 C. for 20 hours. The and the resultant mixture was reacted for 1 hour. After that, resulting precipitate was collected by filtration and then 38.8g of methanol were added to bring the reaction System washed, whereby a wet cake of a cross-linked polySuccin into a dispersed state, followed by aging at 25 C. for 3 imide was obtained. hours. A 24.5 wt.% aqueous solution of sodium hydroxide The wet cake was Suspended in a mixture of 83.1 g of 25 (1.63 g, 0.010 mol) was then added dropwise and a cross water and 116.5 g of methanol. Into the Suspension, a 24.5 linking reaction was conducted at 25 C. for 20 hours. The wt.% aqueous Solution of Sodium hydroxide was added resulting precipitate was collected by filtration and then dropwise to conduct hydrolysis at 25 to 35° C. and pH 9 to washed, whereby a wet cake of a cross-linked poly Succin 11.5. The consumption of the 24.5 wt.% aqueous solution imide was obtained. of sodium hydroxide was 13.8 g (0.085 mol), and 3 hours The wet cake was Suspended in a mixture of 83.1 g of were required until the reaction was brought to completion. water and 116.5 g of methanol. Into the Suspension, 13.5g Hydrochloric acid was added to the thus-hydrolyzed mixture (0.083 mol) of a 24.5 wt.% aqueous solution of sodium to adjust its pH to 7 to 7.5, and the resulting precipitate was hydroxide was added dropwise over 3 hours to conduct collected by decantation. Water (20 g) was added to the hydrolysis at 25 to 35° C. and pH 9 to 11.5. The resulting thus-obtained precipitate So that the precipitate was con 35 reaction mixture was Subjected to aging for 1 hour. Hydro verted into a slurry. The slurry was poured into 200 g of chloric acid was added to the thus-hydrolyzed mixture to methanol to conduct reprecipitation. The resulting precipi adjust its pH to 7 to 7.5, and the resulting precipitate was tate was collected by filtration, washed and then dried, collected by decantation. Water (20 g) was added to the whereby 10.5 g of a croSS-linked polyaspartic acid resin as thus-obtained precipitate So that the precipitate was con a Superabsorbent polymer were obtained. 40 verted into a slurry. The slurry was poured into 200 g of The water absorption of the cross-linked polyaspartic acid methanol to conduct reprecipitation. The resulting precipi resin was 1,090 times in the case of distilled water and 96 tate was collected by filtration, washed and then dried, times in the case of physiological Saline. whereby 12.3 g of a croSS-linked polyaspartic acid resin as Further, W10/W60x100 was 60.2%. a Superabsorbent polymer were obtained. Example F2 45 The water absorption of the croSS-linked polyaspartic acid In 1.5 g of distilled water, 2.78 g (0.015 mol) of lysine resin was 600 times in the case of distilled water and 83 monohydrochloride were dissolved, followed by the addi times in the case of physiological Saline. tion of 2.44 g (0.015 mol) of a 24.5 wt.% aqueous solution Further, W10/W60x100 was 61.9%. of sodium hydroxide for neutralization. The resultant solu Example F4 tion was added dropwise over 0.5 hour into a solution of 50 In 1.5 g of distilled water, 4.63 g (0.025 mol) of lysine 9.71 g (0.10 mol) of poly Succinimide, the weight average monohydrochloride were dissolved, followed by the addi molecular weight of which was 96,000, in 38.8 g of DMF, tion of 4.08 g (0.025 mol) of a 24.5 wt.% aqueous solution and the resultant mixture was reacted for 1 hour. After that, of sodium hydroxide for neutralization. The resultant solu 38.8g of methanol were added to bring the reaction System tion was added dropwise over 0.5 hour into a solution of into a dispersed state, followed by aging at 25 C. for 3 55 9.71 g (0.10 mol) of polySuccinimide, the weight average hours. A 24.5 wt.% aqueous solution of sodium hydroxide molecular weight of which was 96,000, in 38.8 g of DMF, (2.44 g, 0.015 mol) was then added dropwise and a cross and the resultant mixture was reacted for 1 hour. After that, linking reaction was conducted at 25 C. for 20 hours. The 38.8g of methanol were added to bring the reaction System resulting precipitate was collected by filtration and then into a dispersed state, followed by aging at 25 C. for 3 washed, whereby a wet cake of a cross-linked polySuccin 60 hours. A 24.5 wt.% aqueous solution of sodium hydroxide imide was obtained. (1.63 g, 0.010 mol) was then added dropwise and a cross The wet cake was Suspended in a mixture of 83.1 g of linking reaction was conducted at 25 C. for 20 hours. The water and 116.5 g of methanol. Into the Suspension, 13.5g resulting precipitate was collected by filtration and then (0.083 mol) of a 24.5 wt.% aqueous solution of sodium washed, whereby a wet cake of a cross-linked poly Succin hydroxide were added dropwise over 3 hours to conduct 65 imide was obtained. hydrolysis at 25 to 35° C. and pH 9 to 11.5. The resulting The wet cake was Suspended in a mixture of 83.1 g of reaction mixture was Subjected to aging for 1 hour. Hydro water and 116.5 g of methanol. Into the Suspension, 13.5g 6,072,024 59 60 (0.083 mol) of a 24.5 wt.% aqueous solution of sodium Further, W10/W60x100 was 92.7%. hydroxide was added dropwise over 3 hours to conduct Example F7 hydrolysis at 25 to 35° C. and pH 9 to 11.5. The resulting A wet cake of a cross-linked poly Succinimide was reaction mixture was Subjected to aging for 1 hour. Hydro obtained following the procedures of Example F6 except chloric acid was added to the thus-hydrolyzed mixture to that the croSS-linking reaction time was changed to 5 hours. adjust its pH to 7 to 7.5, and the resulting precipitate was The wet cake was Subjected to hydrolysis in a similar collected by decantation. Water (20 g) was added to the manner as in Example F6, whereby 11.1 g of a croSS-linked thus-obtained precipitate So that the precipitate was con polyaspartic acid resin as a Superabsorbent polymer were verted into a slurry. The slurry was poured into 200 g of obtained. methanol to conduct reprecipitation. The resulting precipi The water absorption of the croSS-linked polyaspartic acid tate was collected by filtration, washed and then dried, resin was 600 times in the case of distilled water and 60 whereby 14.8 g of a croSS-linked polyaspartic acid resin as times in the case of physiological Saline. a Superabsorbent polymer were obtained. Further, W10/W60x100 was 91.1%. The water absorption of the cross-linked polyaspartic acid Example F8 resin was 450 times in the case of distilled water and 48 15 In 2.0 g of distilled water, 3.70 g (0.020 mol) of lysine times in the case of physiological Saline. monohydrochloride were dissolved, followed by the addi Further, W10/W60x100 was 62.7%. tion of 4.90 g (0.030 mol) of a 24.5 wt.% aqueous solution Example F5 of sodium hydroxide for neutralization. The solution was A wet cake of a cross-linked poly Succinimide was dissolved in 38.8 g of methanol. The resultant solution was obtained following the procedures of Example F1. added dropwise over 1 hour into a solution of 9.71 g (0.10 The thus-obtained wet cake was suspended in 120 g of mol) of polySuccinimide, the weight average molecular methanol. To the Suspension, an aqueous glycine Solution weight of which was 96,000, in 38.8g of DMF. The resultant which had been prepared by dissolving 7.73 g (0.1 mol) of mixture was reacted at 25 C. for 10 hours. The resulting glycine and 4.2 g of NaOH in 30 g of distilled water was precipitate was collected by filtration and then washed, added dropwise, followed by a reaction at 25 C. for 24 25 whereby a wet cake of a croSS-linked polySuccinimide was hours. The reaction mixture was then neutralized to pH 7.5 obtained. with a 9 wt.% aqueous solution of hydrochloric acid. The The wet cake was Suspended in a mixture of 83.1 g of resulting precipitate was collected by filtration, washed and water and 116.5 g of methanol. Hydrolysis was conducted then dried, whereby 18.1 g of a cross-linked polySuccinim while adding 13.1 g of a 24.5 wt.% aqueous solution of ide derivative with glycine introduced as pendant groups Sodium hydroxide dropwise to the Suspension over 3 hours were obtained as a Superabsorbent polymer. at 25 to 35 C. and pH 9 to 11. The resulting reaction mixture The water absorption of the cross-linked poly Succinimide was then Subjected to aging for 1 hour. Hydrochloric acid derivative was 720 times in the case of distilled water and 79 was added to the thus-hydrolyzed mixture to adjust its pH to times in the case of physiological Saline. 7 to 7.5, and the resulting precipitate was collected by Further, W10/W60x100 was 75.5%. 35 decantation. Water (20 g) was added to the thus-obtained Example F6 precipitate So that the precipitate was converted into a Slurry. In 1.5 g of distilled water, 2.78 g (0.015 mol) of lysine The slurry was poured into 200 g of methanol to conduct monohydrochloride were dissolved, followed by the addi reprecipitation. The resulting precipitate was collected by tion of 4.08 g (0.025 mol) of a 24.5 wt.% aqueous solution filtration, washed and then dried, whereby 14.0 g of a of sodium hydroxide for neutralization. The solution was 40 croSS-linked polyaspartic acid resin as a Superabsorbent dissolved in 38.8 g of methanol. The resultant solution was polymer were obtained. added dropwise over 1 hour into a solution of 9.71 g (0.10 The water absorption of the croSS-linked polyaspartic acid mol) of polySuccinimide, the weight average molecular resin was 310 times in the case of distilled water and 43 weight of which was 96,000, in 38.8g of DMF. The resultant times in the case of physiological Saline. mixture was reacted at 25 C. for 10 hours. The resulting 45 Further, W10/W60x100 was 93.5%. precipitate was collected by filtration and then washed, Example F9 whereby a wet cake of a croSS-linked poly Succinimide was In 1.5 g of distilled water, 2.78 g (0.015 mol) of lysine obtained. monohydrochloride were dissolved, followed by the addi The wet cake was Suspended in a mixture of 83.1 g of tion of 4.08 g (0.025 mol) of a 24.5 wt.% aqueous solution water and 116.5 g of methanol. Into the Suspension, a 24.5 50 of sodium hydroxide for neutralization. The resultant solu wt.% aqueous Solution of Sodium hydroxide was added tion and 12.9 g of methanol were added dropwise over 0.5 dropwise to conduct hydrolysis at 25 to 35° C. and pH 9 to hour through different inlets to a solution of 9.71 g (0.10 11.5. The consumption of the 24.5 wt.% aqueous solution mol) of polySuccinimide, the weight average molecular of sodium hydroxide was 13.1 g (0.08 mol), and 4 hours weight of which was 96,000, in 38.8g of DMF. After that, were required until the reaction was brought to completion. 55 25.9 g of methanol were added, and a croSS-linking reaction Hydrochloric acid was added to the thus-hydrolyzed mixture was conducted at 25 C. for 20 hours. The resulting pre to adjust its pH to 7 to 7.5, and the resulting precipitate was cipitate was collected by filtration and then washed, collected by decantation. Water (20 g) was added to the whereby a wet cake of a croSS-linked polySuccinimide was thus-obtained precipitate So that the precipitate was con obtained. verted into a slurry. The slurry was poured into 200 g of 60 The wet cake was Suspended in a mixture of 83.1 g of methanol to conduct reprecipitation. The resulting precipi water and 116.5 g of methanol. Into the Suspension, a 24.5 tate was collected by filtration, washed and then dried, wt.% aqueous Solution of Sodium hydroxide was added whereby 13.3 g of a croSS-linked polyaspartic acid resin as dropwise to conduct hydrolysis at 25 to 35° C. and pH 9 to a Superabsorbent polymer were obtained. 11.5. The resulting reaction mixture was Subjected to aging The water absorption of the cross-linked polyaspartic acid 65 for 1 hour. Three hours were required until the pH became resin was 480 times in the case of distilled water and 51 constant. The mixture was then Subjected to aging for 1 hour. times in the case of physiological Saline. Hydrochloric acid was added to the thus-hydrolyzed mixture 6,072,024 61 62 to adjust its pH to 7 to 7.5, and the resulting precipitate was was added dropwise to the croSS-linked reaction mixture collected by decantation. Water (20 g) was added to the over 0.5 hour, followed by aging at 25 C. for 20 hours. The thus-obtained precipitate So that the precipitate was con resulting precipitate was collected by filtration and then verted into a slurry. The slurry was poured into 200 g of washed, whereby a wet cake of a cross-linked poly Succin methanol to conduct reprecipitation. The resulting precipi imide was obtained. tate was collected by filtration, washed and then dried, The wet cake was Suspended in a mixture of 83.1 g of whereby 12.7 g of a croSS-linked polyaspartic acid resin as water and 116.5 g of methanol. Into the Suspension, a 24.5 a Superabsorbent polymer were obtained. wt.% aqueous Solution of Sodium hydroxide was added The water absorption of the cross-linked polyaspartic acid resin was 580 times in the case of distilled water and 60 dropwise to conduct hydrolysis at 25 to 35° C. and pH 9 to times in the case of physiological Saline. 11.5. The consumption of the 24.5 wt.% aqueous solution Further, W10/W60x100 was 93.5%. of sodium hydroxide was 13.8 g (0.085 mol), and 3 hours Example F10 were required until the reaction was brought to completion. In 1.5 g of distilled water, 2.78 g (0.015 mol) of lysine Hydrochloric acid was added to the thus-hydrolyzed mixture monohydrochloride were dissolved, followed by the addi 15 to adjust its pH to 7 to 7.5, and the resulting precipitate was tion of 4.08 g (0.025 mol) of a 24.5 wt.% aqueous solution collected by decantation. Water (20 g) was added to the of sodium hydroxide for neutralization. The solution was thus-obtained precipitate So that the precipitate was con dissolved in 38.8 g of methanol. The resultant solution was verted into a slurry. The slurry was poured into 200 g of added dropwise over 1 hour into a solution of 9.71 g (0.10 methanol to conduct reprecipitation. The resulting precipi mol) of polySuccinimide, the weight average molecular tate was collected by filtration, washed and then dried, weight of which was 96,000, in 38.8g of DMF. The resultant whereby 12.5g of a croSS-linked polyaspartic acid resin as mixture was reacted at 25 C. for 10 hours. The resulting a Superabsorbent polymer were obtained. precipitate was collected by filtration and then washed, The water absorption of the croSS-linked polyaspartic acid whereby a wet cake of a croSS-linked poly Succinimide was resin was 520 times in the case of distilled water and 65 obtained. 25 times in the case of physiological Saline. The wet cake was suspended in 116.5 g of methanol. To Further, W10/W60x100 was 70.1%. the Suspension, an aqueous glycine Solution which had been Example F13 prepared by dissolving 7.73 g (0.1 mol) of glycine and 4.2 In 1.0 g of distilled water, 1.85 g (0.01 mol) of lysine g of sodium hydroxide in 30 g of distilled water was added monohydrochloride were dissolved, followed by the addi dropwise, followed by a reaction at 25 C. for 24 hours. The reaction mixture was then neutralized to pH 7.5 with a 9 wt. tion of 1.64 g (0.01 mol) of a 24.5 wt.% aqueous solution % aqueous Solution of hydrochloric acid. The resulting of sodium hydroxide to neutralize hydrochloric acid. The precipitate was collected by filtration, washed and then resultant solution was added dropwise over 0.5 hour into a dried, whereby 18.8 g of a cross-linked polySuccinimide solution of 9.71 g (0.10 mol) of polysuccinimide, the weight derivative with glycine introduced as pendant groups were 35 average molecular weight of which was 96,000, in 38.8g of obtained as a Superabsorbent polymer. DMF, and the resultant mixture was reacted for 1 hour. After The water absorption of the cross-linked poly Succinimide that, 38.8 g of methanol were added to bring the reaction derivative was 490 times in the case of distilled water and 53 system into a dispersed state, and 0.82 g (0.005 mol) of a times in the case of physiological Saline. 24.5 wt.% aqueous solution of sodium hydroxide were then Further, W10/W60x100 was 92.1%. 40 added and a cross-linking reaction was conducted at 25 C. Example F11 for 3 hours. On the other hand, 0.93 g (0.005 mol) of lysine The procedures of Example F6 were repeated except for monohydrochloride was dissolved in 1.0 g of distilled water, the use of 1.74 g (0.02 mol) of hexamethylenediamine in followed by the neutralization with 1.64 g (0.01 mol) of a place of lysine monohydrochloride, whereby 10.5 g of a 24.5 wt.% aqueous solution of sodium hydroxide. The croSS-linked polyaspartic acid resin as a Superabsorbent 45 Solution was added dropwise to the croSS-linked reaction polymer were obtained. mixture over 0.5 hour, followed by aging at 25 C. for 20 The water absorption of the cross-linked poly Succinimide hours. The resulting precipitate was collected by filtration derivative was 61 times in the case of distilled water and 25 and then washed, whereby a wet cake of a croSS-linked times in the case of physiological Saline. polySuccinimide was obtained. Further, W10/W60x100 was 95.2%. 50 The wet cake was Suspended in a mixture of 83.1 g of Example F12) water and 116.5 g of methanol. Into the Suspension, 13.5g In 1.0 g of distilled water, 1.85 g (0.01 mol) of lysine (0.083 mol) of a 24.5 wt.% aqueous solution of sodium monohydrochloride were dissolved, followed by the addi hydroxide was added dropwise over 3 hours to conduct tion of 1.64 g (0.01 mol) of a 24.5 wt.% aqueous solution hydrolysis at 25 to 35° C. and pH 9 to 11.5. The resulting of sodium hydroxide to neutralize hydrochloric acid. The 55 reaction mixture was Subjected to aging for 1 hour. Hydro resultant solution was added dropwise over 0.5 hour into a chloric acid was added to the thus-hydrolyzed mixture to solution of 9.71 g (0.10 mol) of polysuccinimide, the weight adjust its pH to 7 to 7.5, and the resulting precipitate was average molecular weight of which was 96,000, in 38.8g of collected by decantation. Water (20 g) was added to the DMF, and the resultant mixture was reacted for 1 hour. After thus-obtained precipitate So that the precipitate was con that, 38.8 g of methanol were added to bring the reaction 60 verted into a slurry. The slurry was poured into 200 g of System into a dispersed State, and 1.64 g (0.01 mol) of a 24.5 methanol to conduct reprecipitation. The resulting precipi wt.% aqueous Solution of Sodium hydroxide were then tate was collected by filtration, washed and then dried, added and a cross-linking reaction was conducted at 25 C. whereby 11.3 g of a croSS-linked polyaspartic acid resin as for 3 hours. On the other hand, 0.93 g of lysine monohy a Superabsorbent polymer were obtained. drochloride was dissolved in 1.0 g of distilled water, fol 65 The water absorption of the croSS-linked polyaspartic acid lowed by the neutralization with 1.64 g (0.01 mol) of a 24.5 resin was 537 times in the case of distilled water and 69 wt.% aqueous solution of sodium hydroxide. The solution times in the case of physiological Saline. 6,072,024 63 64 Further, W10/W60x100 was 71.7%. collected by decantation. Water (20 g) was added to the Example F14 thus-obtained precipitate So that the precipitate was con In 1.0 g of distilled water, 0.56 g (0.003 mol) of lysine verted into a slurry. The slurry was poured into 200 g of monohydrochloride was dissolved, followed by the addition methanol to conduct reprecipitation. The resulting precipi of 0.98 g (0.006 mol) of a 24.5 wt.% aqueous solution of tate was collected by filtration, washed and then dried, Sodium hydroxide to neutralize hydrochloric acid. The whereby 14.8 g of a croSS-linked polyaspartic acid resin as a Superabsorbent polymer were obtained. resultant solution was added dropwise over 0.5 hour into a The water absorption of the croSS-linked polyaspartic acid solution of 9.71 g (0.10 mol) of polysuccinimide, the weight resin was 600 times in the case of distilled water and 71 average molecular weight of which was 96,000, in 38.8g of times in the case of physiological Saline. DMF, and the resultant mixture was reacted for 30 minutes. Further, W10/W60x100 was 91.3%. After that, 38.8 g of methanol were added to bring the Example F16 reaction System into a dispersed State. On the other hand, In 1.0 g of distilled water, 1.85 g (0.01 mol) of lysine 2.24 g (0.012 mol) of lysine monohydrochloride was dis monohydrochloride were dissolved, followed by the addi solved in 1.0 g of distilled water, followed by the neutral tion of 1.64 g (0.01 mol) of a 24.5 wt.% aqueous solution ization with 3.92 g (0.024 mol) of a 24.5 wt.% aqueous 15 of sodium hydroxide to neutralize hydrochloric acid. The solution of sodium hydroxide. The solution was added resultant solution was added dropwise over 0.5 hour into a dropwise to the croSS-linked reaction mixture over 0.5 hour, solution of 9.71 g (0.10 mol) of polysuccinimide, the weight followed by aging at 25 C. for 20 hours. The resulting average molecular weight of which was 96,000, in 38.8g of precipitate was collected by filtration and then washed, DMF, and the resultant mixture was reacted for 1 hour. After whereby a wet cake of a croSS-linked poly Succinimide was that, 38.8 g of methanol were added to bring the reaction obtained. System into a dispersed State, and 1.64 g (0.01 mol) of a 24.5 The wet cake was Suspended in a mixture of 83.1 g of wt. 76 aqueous Solution of Sodium hydroxide were then water and 116.5 g of methanol. Into the Suspension, 13.5g added and a cross-linking reaction was conducted at 25 C. (0.083 mol) of a 24.5 wt.% aqueous solution of sodium for 3 hours. On the other hand, 0.93 g (0.005 mol) of lysine hydroxide was added dropwise over 3 hours to conduct 25 monohydrochloride was dissolved in 1.0 g of distilled water, hydrolysis at 25 to 35° C. and pH 9 to 11.5. The resulting followed by the neutralization with 1.64 g (0.01 mol) of a reaction mixture was Subjected to aging for 1 hour. Hydro 24.5 wt.% aqueous solution of sodium hydroxide. The chloric acid was added to the thus-hydrolyzed mixture to Solution was added dropwise to the croSS-linked reaction adjust its pH to 7 to 7.5, and the resulting precipitate was mixture over 0.5 hour, followed by aging at 25 C. for 20 collected by decantation. Water (20 g) was added to the hours. The resulting precipitate was collected by filtration thus-obtained precipitate So that the precipitate was con and then washed, whereby a wet cake of a croSS-linked verted into a slurry. The slurry was poured into 200 g of polySuccinimide was obtained. methanol to conduct reprecipitation. The resulting precipi The wet cake was Suspended in 116.5 g of methanol. To tate was collected by filtration, washed and then dried, the Suspension, an aqueous glycine Solution which had been whereby 12.8 g of a croSS-linked polyaspartic acid resin as 35 prepared by dissolving 7.73 g (0.1 mol) of glycine and 4.2 a Superabsorbent polymer were obtained. g of sodium hydroxide in 30 g of distilled water was added The water absorption of the cross-linked polyaspartic acid dropwise, followed by a reaction at 25 C. for 24 hours. The resin was 452 times in the case of distilled water and 57 reaction mixture was then neutralized to pH 7.5 with a 9 wt. times in the case of physiological Saline. % aqueous Solution of hydrochloric acid. The resulting Further, W10/W60x100 was 83.3%. 40 precipitate was collected by filtration, washed and then Example F15 dried, whereby 18.8 g of a croSS-linked polySuccinimide In 1.0 g of distilled water, 0.56 g (0.003 mol) of lysine derivative with glycine introduced as pendant groups were monohydrochloride was dissolved, followed by the addition obtained as a Superabsorbent polymer. of 0.98 g (0.006 mol) of a 24.5 wt.% aqueous solution of The water absorption of the cross-linked polySuccinimide Sodium hydroxide to neutralize hydrochloric acid. The 45 derivative was 492 times in the case of distilled water and 51 resultant solution was added dropwise over 0.5 hour into a times in the case of physiological Saline. solution of 9.71 g (0.10 mol) of polysuccinimide, the weight Further, W10/W60x100 was 86.3%. average molecular weight of which was 96,000, in 38.8g of Comparative Example F1 DMF, and the resultant mixture was reacted for 30 minutes. In 1.5 g of distilled water, 2.78 g (0.015 mol) of lysine On the other hand, 2.24 g (0.012 mol) of lysine monohy 50 monohydrochloride were dissolved, followed by the addi drochloride was dissolved in 1.0 g of distilled water, fol tion of 4.08 g (0.025 mol) of a 24.5 wt.% aqueous solution lowed by the neutralization with 3.92 g (0.024 mol) of a 24.5 of sodium hydroxide for neutralization. The resultant solu wt.% aqueous solution of sodium hydroxide. The solution tion was added dropwise over 0.5 hour into a solution of was mixed with 38.8 g of methanol, and the resultant 9.71 g (0.10 mol) of polySuccinimide, the weight average mixture was added dropwise to the cross-linked reaction 55 molecular weight of which was 96,000, in 38.8 g of DMF. mixture over 0.5 hour, followed by aging at 25 C. for 20 In the course of the addition, the Viscosity increased Sub hours. The resulting precipitate was collected by filtration Stantially and the reaction mixture was gelled in its entirety, and then washed, whereby a wet cake of a croSS-linked So that Stirring became no longer feasible. After that, the poly Succinimide was obtained. reaction mixture was therefore Subjected to aging at 25 C. The wet cake was Suspended in a mixture of 83.1 g of 60 for 30 hours without stirring. Methanol (100 g) was added water and 116.5 g of methanol. Into the Suspension, 13.5g to the resultant gel in an attempt to disintegrate it. It however (0.083 mol) of a 24.5 wt.% aqueous solution of sodium took approximately 20 hours to disintegrate the gel in its hydroxide was added dropwise over 3 hours to conduct entirety because stirring was difficult. The thus-obtained hydrolysis at 25 to 35° C. and pH 9 to 11.5. The resulting precipitate was collected by filtration and washed, whereby reaction mixture was Subjected to aging for 1 hour. Hydro 65 a wet cake of a croSS-linked poly Succinimide was obtained. chloric acid was added to the thus-hydrolyzed mixture to The wet cake was suspended in a mixture of 90 g of water adjust its pH to 7 to 7.5, and the resulting precipitate was and 120 g of methanol. Into the Suspension, 13.1 g of a 24.5 6,072,024 65 66 wt.% aqueous Solution of Sodium hydroxide was added Further, W10/W60x100 was 61.2%. dropwise at 25 to 35° C. and pH 9 to 11, whereby hydrolysis Comparison and Discussion on Examples F1-F16 and was conducted. AS the precipitate had a large particle size, Comparative Examples F1-F3 the reaction was slow and about 6 hours were required for In Comparative Example F1, the croSS-linked polyaspar the hydrolysis. A9 wt.% aqueous solution of hydrochloric tic acid resin derived by the hydrolysis had the sufficiently acid was then added to adjust the pH to 7.5, and the resulting high water absorption but the workability was poor to result precipitate was collected by decantation. Water (20g) was in lowered productivity. added to the thus-obtained precipitate So that the precipitate In Comparative Example F2, the workability was very was converted into a slurry. The slurry So obtained was poor. Moreover, the croSS-linked polyaspartic acid resin poured into 200 g of methanol to conduct reprecipitation. derived by the hydrolysis was able to show only the small The resulting precipitate was collected by filtration, washed water absorption of no practical utility. and then dried, whereby 8.8g of a croSS-linked polyaspartic In Comparative Example F3, it was attempted to produce acid resin as a Superabsorbent polymer were obtained. a croSS-linked poly Succinimide at high productivity. AS a The water absorption of the cross-linked polyaspartic acid result, the cross-linked polyaspartic acid resin derived by the resin was 400 times in the case of distilled water and 53 15 hydrolysis was able to achieve only the reduced water times in the case of physiological Saline. absorption. Further, W10/W60x100 was 60.7%. In contrast, each of Examples F1-F16 was able to produce Comparative Example F2 at high productivity the croSS-linked polyaspartic acid resin To a solution of 9.71 of polysuccinimide, the weight which achieved the large water absorption and indicated the average molecular weight of which was 96,000, in 38.8g of excellent water absorption Speed. DMF, 1.74 g (0.015 mol) of hexamethylenediamine were What is claimed is: added. Five minutes later, the reaction mixture was gelled in 1. A proceSS for producing a cross-linked polyaspartic its entirety. The thus-obtained gel was allowed to Stand acid resin by Subjecting imide rings of a croSS-linked overnight. As a result, DMF oozed out of the gel. The gel poly Succinimide to a hydrolysis reaction, wherein Said was separated, washed with methanol and then dried, 25 hydrolysis reaction is conducted while controlling a Swelling whereby a croSS-linked polySuccinimide was obtained. degree of a resin in a reaction System within a range of from The thus-obtained polymer was powdered in a grinder and 3 to 100 times. then suspended in a mixture of 90 g of water and 120 g of 2. The process of claim 1, wherein Said hydrolysis reac methanol. Hydrolysis was conducted while controlling the tion is conducted in an aqueous Solution in which a water pH at 9 to 11 by adding a 24.5 wt.% aqueous solution of miscible organic Solvent is contained. Sodium hydroxide dropwise. It took 50 hours until the 3. The process of claim 2, wherein Said Swelling degree of reaction was brought to completion. The thus-obtained Said resin in Said reaction System is controlled by a polarity hydrolyzed mixture was poured into 500 g of methanol to of Said aqueous Solution in which said water-miscible conduct reprecipitation. The resulting precipitate was col organic Solvent is contained. lected by filtration, washed and then dried, whereby 3.5g of 35 4. The process of claim 1, wherein Said hydrolysis reac a cross-linked polyaspartic acid resin as a Superabsorbent tion is conducted in an aqueous Solution in which an polymer were obtained. inorganic Salt and/or an organic Salt is contained. The water absorption of the cross-linked polyaspartic acid 5. The process of claim 4, wherein Said Swelling degree of resin was 22 times in the case of distilled water and 10 times Said resin in Said reaction System is controlled by changing in the case of physiological Saline. 40 an OSmotic preSSure in Said reaction System with Said Further, W10/W60x100 was 78.6%. inorganic Salt and/or Said organic Salt. Comparative Example F3 6. The process of claim 1, wherein Said hydrolysis reac In 100 g of DMF, 3.50 g (0.015 mol) of lysine methyl tion is conducted in a solvent of from 40° C. to 100° C. ester dihydrochloride were suspended, followed by neutral 7. The process of claim 6, wherein a temperature of said ization with an equimolar amount of triethylamine. The 45 Solvent is varied to change water absorbency of Said resin in resulting solution was added dropwise into a solution of 9.71 Said reaction System, whereby said Swelling degree of Said g (0.10 mol) of poly Succinimide, the weight average resin in Said reaction System is controlled. molecular weight of which was 96,000, in 38.8 g of DMF, 8. The process of claim 1, wherein said cross-linked followed by stirring for 1 hour. Triethylamine (3.03 g, 0.030 polySuccinimide has been obtained by wet-grinding a gel mol) was then added, and a cross-linking reaction was 50 produced by reacting a poly Succinimide and a croSS-linking conducted at 25 C. for 40 hours. The reaction mixture was agent in a Solvent. poured into 300 g of ethanol to conduct reprecipitation. The 9. The process of claim 1, wherein said cross-linked resulting precipitate was collected by filtration and washed, polySuccinimide has been obtained by reacting a poly Suc whereby a wet cake of a croSS-linked poly Succinimide was cinimide with a basic amino acid carboxylate Salt as a obtained. 55 croSS-linking agent. The thus-obtained wet cake was suspended in 2,000 g of 10. The process of claim 1, wherein said cross-linked water. Hydrolysis was conducted while adding a 24.5 wt.% poly Succinimide has been obtained by reacting a aqueous Solution of Sodium hydroxide dropwise to control polySuccinimide, which were brought into a dispersed State the pH within a range of from 9 to 11. The thus-obtained by a dispersant, with a croSS-linking agent. reaction mixture (flowable gel) was poured into 5,000 ml of 60 11. The process of claim 1, which comprises washing or ethanol to conduct reprecipitation. The resulting precipitate reprecipitating a gel of a feed croSS-linked polyaspartic acid was collected by filtration, washed and then dried, whereby resin with water and/or a water-miscible organic Solvent. 12.8 g of a cross-linked polyaspartic acid resin as a Super 12. The process of claim 1, wherein Said cross-linked absorbent polymer were obtained. polySuccinimide is in a form of particles Surfaces of which The water absorption of the cross-linked polyaspartic acid 65 are highly cross-linked. resin was 110 times in the case of distilled water and 30 13. A proceSS for the production of a cross-linked pol times in the case of physiological Saline. yaspartic acid resin by Subjecting imide rings of a croSS 6,072,024 67 68 linked poly Succinimide produced according to a proceSS as 15. The process of claim 1, wherein the Swelling degree defined in claim 17, which has been disintegrated. is controlled during Substantially the whole hydrolysis reac 14. A cross-linked polyaspartic acid resin produced tion. according to a process as defined in claim 1. k . . . .