MXPA97001888A - Superabsorben polymeric nets - Google Patents

Abstract

Method for producing polymeric superabsorbent networks of polyaspartates from cross-linked polysuccinimide is disclosed. In one aspect of the preferred method, the polysuccinimide is first reacted with an organic crosslinking agent, preferably an organic base containing at least two primary amine groups, to form a crosslinked polysuccinimide. Then the crosslinked polysuccinimide is hydrolyzed to obtain a polyaspartate polymer network, which demonstrates a superabsorbent capacity in water and in a saline solution. Alternative aspect of the method is described wherein poly-superabsorbent polymer networks of polyaspartates are produced in a single reaction vessel, by crosslinking in sequence the polysuccinimide with the organic cross-linking agent in an aqueous reaction mixture, and then the reaction product is hydrolysed to produce a poliasparta polymer network

Description

SUPERABSORBENT POLYMERIC NETWORKS Field of the Invention The present invention relates to the field of polymers. More particularly, the invention relates to new polymer networks capable of absorbing large amounts of water, aqueous solutions, or polar organic solvents, and to methods for the preparation of these superabsorbent polymer networks.

Background of the Invention The term "water-swellable polymer networks", as used herein, refers to highly cross-linked polymers that are prone to swell or gel in the presence of water. Water-swellable polymer networks have found wide use in a variety of applications. See, for example, Odian, G., Principies of Polymerization. 3rd edition, published by Wiley-Interscience, New York, 1991, and Glass, JE, Ed. "Polymers in Aqueous Media Performance Through Association," Advances in Chemistry Series 223, published by the American Chemical Society, Washington, DC, 1989) . Water-swellable polymeric networks that are well known in the art of polymers include, but are not limited to. carboxymethylcellulose, crosslinked polyacrylates, hydrolysis products with starch-acrylonitrile graft copolymer, polyvinyl alcohol resins, polyethylene oxide resins, and polyacrylonitrile resins. There are several problems associated with these polymer networks. First, their water absorbency properties are greatly reduced in the presence of salts, such as sodium chloride, which are often present in the environments where these polymeric materials are used. Second, most of these polymeric materials are not readily biodegradable, and therefore contribute to the total chemical load on the environment when released to the effluent streams. Some crosslinked polypeptides containing a high percentage of anionic amino acids, such as aspartic acid or glutamic acid, are useful as superabsorbent materials. Some of these are described in International Patent Publication Number Wo 92/17525 and in United States Patent Number 5,284,936 to Sikes et al. These materials have a better salt absorbency, and are biodegradable. However, they require amino acids as starting materials, and these are relatively expensive. Koskan et al., In the Patents of the United States of North America Nos. 5,057, 597; 5, 116, 513; 5,219,952 and 5,221,733, describe economic methods for the manufacture of polysuccinimide and polyaspartic acid. The chemical modification of the polysuccinimide to produce useful polyaspartates is well known. For example, Neri et al., In the article "Synthesis of alpha, beta-Poly [(2-hydroxyethyl) DL-aspartamide], to New Plasma Expander," Journal of Medicinal Chemistry, volume 16, pages 893-897, (1973 ) describe the modification of polysuccinimide with ethanolamine. Fujimoto et al., In U.S. Patent No. 3,846,380, describe the formation of modified polypeptides having hydrophobic and hydrophilic substituents as side chains, obtained by the polysuccinimide reaction with at least one primary or secondary aliphatic amine, and the hydrolyzing the resulting polyamide derivative with alkali, to produce polypeptides that are useful as surface active agents. There is still a need and a desire, therefore, for biodegradable superabsorbent polymer networks with a better salt tolerance, which can be prepared by an economical method. This invention satisfies that need.

The present invention provides a method for producing superabsorbent polymer networks that are biodegradable, by chemical modification of polysuccinimide. The term "polymer networks" as used hereinrefers to random copolymers of cross-linked polyaspartate that can swell or gel in water or in salt solutions. The term "superabsorbent polymer networks", and the grammatical variations thereof, as used herein, refer to polymeric polyaspartate networks that can absorb from at least three times up to more than 90 times their weight in water, and from when less twice to more than 20 times its weight in 1 percent aqueous sodium chloride (saline). The term "polyaspartate" and the grammatical variations thereof as used herein, include polyaspartic acid, as well as salts of polyaspartic acid. The polyaspartates suitable for the preparation of superabsorbent polymer networks of the present invention can be synthesized by various methods, all of which initially involve the polysuccinimide reaction with an organic crosslinking agent. More particularly, a preferred method comprises reacting polysuccinimide with an organic crosslinking agent which is an organic base comprising at least two primary amine groups in an amount sufficient to form cross-linked polysuccinimide. Subsequently, the cross-linked polysuccinimide is hydrolyzed with a base to form a cross-linked polyaspartate polymer network. In one aspect of the preferred method, the polysuccinimide is first reacted with an organic crosslinking agent in a polar aprotic solvent, to obtain cross-linked polysuccinimide. The crosslinked polysuccinimide is then harvested for subsequent hydrolysis, in order to produce a polyaspartate superabsorbent polymer network. Conveniently, the superabsorbent polymer networks of this invention can be prepared in a single reaction vessel in the alternative preferred method aspects, using aqueous media. In one aspect of the method, the polysuccinimide crosslink in an aqueous reaction mixture containing an effective crosslinking amount of organic crosslinking agent or a salt thereof, from which the free organic crosslinking agent can be released by hydrolysis with base, to produce cross-linked polysuccinimide. Then, the crosslinked polysuccinimide product can be further hydrolyzed with base to produce a polyaspartate polymer network. The polymer networks of the present invention are useful in a wide variety of applications, where liquid absorption, viscosity modification, chemical sequestration, or dehydration are required or desired. For example, applications include the use of polymeric networks such as superabsorbents in diapers, incontinence products, and sanitary napkins; as humectants in agricultural products; as mud coagulants in water treatment; as viscosity modifiers in the petroleum industry; as dehydrating agents, - as chemical absorbers (for example, for cleaning chemical spills), - for controlled release of chemicals; for microencapsulation; as thickening agents; as a means for electrophoresis and chromatography, (for example, for gel permeation chromatography, capillary electrophoresis, etc.); in the manufacture of soft contact lenses, - and as wetting components in consumer products, such as personal care products or the like.

BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a graphic illustration of a superabsorbent polymer network incorporating the principles of this invention, comprised of linker monomer units, crosslinked polysuccinimide, and crosslinked polyaspartate chains.

Detailed Description of the Invention The term "polysuccinimide" as used herein, defines a homopolymer having the structural formula (I), wherein n is greater than about 5.

(I) The polymer networks of this invention are structurally comprised random copolymers of monomeric units of succinimide (structural formula S), alpha-aspartate (structural formula A), beta-aspartate (structural formula B), and crosslinking dimeric aspartamides (structural formula having any of the following three structural formulas, L1, L2, and L3 For convenience, these will generally be referred to as the structural formula (L)).

I heard P Monomer of Monomer of Succinimide Monomer (S) Alpha-aspartate (A) Beta-aspartate (B) Monomer Monomer Crosslinker (L1) Crosslinker (L2) In the structural units A and B, M can be hydrogen, an alkali metal cation, such as Na +, K +, or Li +, ammonium, or quaternary ammonium. In the structural units L, L1, L2, and preferably L3, R is a bivalent organic linking group derived from the organic crosslinking agent. The organic crosslinking agent is preferably an organic base containing at least two primary amine groups capable of reacting with a monomeric succinimide unit to form a crosslinking thereof. For convenience, the reference to "L units" includes any of the above monomeric crosslinking structural units L without limitation. The term "cross-linked polyaspartate" or "cross-linked polyaspartic acid" as used herein, refers to polymer networks that are water-swellable, swellable, and water-swellable random copolymers, structurally comprised primarily of units A, B, and L. preferably, the crosslinked polyaspartates do not contain S units, or have a relatively small amount thereof, for example, less than about 20 percent S units. The term "crosslinked polysuccinimide", as used herein, refers to to random copolymers comprised primarily of units S and L. The crosslinked polysuccinimides preferably do not contain units A and B, or have relatively small proportions of units A and B, such that the combined amount of units A + B is less than about 20 percent. For convenience, the methods of this invention will be illustrated and described using diamine crosslinking agents. A "diamine crosslinking agent" refers herein to organic bases having two primary amine groups available to react with the monomeric succinimide units of the polysuccinimide, to form a crosslink. The polysuccinimide useful for the methods of this invention can be synthesized by any method, for example, by thermal polymerization of aspartic acid, by thermal polymerization of aspartic acid in the presence of phosphoric acid or polyphosphoric acid, by thermal polymerization of maleic acid and ammonia. , or any other method. Preferably, the weight average molecular weight (Mw) of the polysuccinimide is from about 500 to more than about 100,000, more preferably from about 1,500 to about 50,000, and most preferably from about 5,000 to about 30,000. The amount of diamine crosslinking agent is preferably from about 0.001 moles to about 5 moles per kilogram of succinimide. Using a weight of the formula (PF) of 97 for the polysuccinimide (the weight of the formula of a monomeric unit of succinimide), the amount of organic diamine components can also be expressed as moles of diamine per mole of monomeric units of succinimide per 100 percent, hereinafter referred to as "molar%". On this basis, the amount of diamine crosslinking agent can be from a molar percentage of about 0.1 to about 50. The preferred molar percentage of diamine depends on the weight average molecular weight. { 1) of the polysuccinimide starting material. For the polysuccinimides of an Mw between about 500 and about 4,000, the preferred molar percentage amount of diamine crosslinking agent is from about 10 to about 30. For the polysuccinimides of an Mw between about 4,000 and about 10,000, the percentage amount preferred molar of diamine crosslinking agent is from about 1 to about 20 mole percent. For polysuccinimides of an Mw greater than about 10,000, the preferred molar percentage amount of diamine crosslinking agent is from about 0.5 to about 15. The crosslinking may occur between adjacent polymer chains, or within the same polymer chain, or both . Multiple cross-links can also be incorporated into the polymer chains. Compounds useful as diamine crosslinking agents in the practice of the methods of the present invention include, but are not limited to, aliphatic diamines, such as ethylenediamine (EDA), 1,3-bis (aminoethyl) cyclohexane (1,3 -BAC), and hexamethylenediamine (HMDA); arylaliphatic diamines, such as meta-xylylenediamine (MXDA), - and polyetherdiamines, such as polyoxyalkylene diamines, polyoxyalkylene / polyalkylene glycol amine-terminated block copolymers, sold in different approximate molecular weights from about 280 to 2,000 under the registered trademark JEFFAMINAMR by Texaco Chemical Company. According to the supplier, the products of the JEFFAMINAM® D series are amine terminated polypropylene glycols having an average of about 2 to about 68 propylene oxide units; The JEFFAMINEMR ED series of products, are polyethylene glycols / polypropylene glycols, terminated in amine having a predominantly polyethylene oxide base structure, and the following general structural formula (II) wherein the average approximate value of the a + c structural units is of about 2.5, and that of the structural unit b is from about 8 to about 40. 5 . (II) H2] C-NH2 Other useful polyetheramines are diamine triethylene glycol (JEFFAMINEMR EDR-148), and tetraethylene glycol diamine (JEFFAMINEMR EDR-192). Also useful are amine-terminated polyalkyleneimines, such as the amine-terminated polyethyleneimines, including, for example, triamines and pentamines, such as diethylenetriamine (DETA), and tetraethylenepentamine (TEPA). Additionally, organic triamine, tetraamino, and polyamino compounds can also be used as organic crosslinking agents to form new polymer networks of the present invention. The use of these amino compounds can additionally lead to the incorporation of monomeric linking units, such as the following structural formulas L4 and L5, wherein R2 is a linking group of a trivalent or tetravalent organic radical derived from the organic crosslinking Monomer Crosslinker Trivalent Monomer (Tetravalent L4) Trivalent (L5) Examples of the triamine, tetraamino, and polyamino compounds useful as organic crosslinking agents in the present invention include, but are not limited to, tris (2-aminoethyl) amine ( TAEA), polyamine compounds sold under the registered trademark of STARBURSTMR Dendrimers by Dendritech, Inc .; the triamine series based on propylene oxide sold in different approximate molecular weights from about 440 to about 5,000, under the registered trademark JEFFAMINEMR T by Texaco Chemical Company, and polyvinylamine polymers. It was found that aromatic diamines, such as meta-phenylenediamine, hydrazine, carbohydrazine, and other bis-hydrazides, are less effective as organic crosslinking agents in the present invention. Preferably, the superabsorbent polymer networks of the present invention swell or gel in the presence of water up to at least 3 times to more than 90 times their dry weight, and in the presence of serum, such as aqueous sodium chloride at 1 percent (NaCl), up from at least twice to more than 20 times its dry weight. Briefly described, in one aspect of the preferred method, crosslinked polyaspartate polymer networks were produced, first crosslinking polysuccinimide with an organic crosslinking agent in the presence of a polar aprotic solvent. The crosslinked polysuccinimide product was then isolated from the reaction mixture, collected, and hydrolysed to a polymeric network gel comprising polyaspartate. The gel can then be dried to be used as a superabsorbent polymer network. Useful polar aprotic solvents include dimethyl sulfoxide, dimethylformamide, and dimethylacetamide, but are not limited thereto. Preferably, the aprotic solvent is at least miscible in water. The crosslinked polysuccinimide product is preferably isolated by mixing the reaction mixture with a polar solvent, preferably water or an alcohol, wherein the polar aprotic solvent is soluble, but where the crosslinked polysuccinimide product is not soluble, to precipitate the polymers. Then the precipitated crosslinked polysuccinimide polymer can be harvested for hydrolysis, to obtain a polyaspartate superabsorbent polymer network. In the alternative aspect of the method, a polyaspartate superabsorbent polymer network can be produced in an aqueous reaction mixture, using a single reaction vessel. For example, first an aqueous solution of organic crosslinking agent is neutralized with a sufficient amount of a relatively strong mineral acid, preferably hydrochloric acid, to form a water soluble acid salt thereof. Next, polysuccinimide is mixed therein to form an aqueous paste with the salt solution. Subsequently, the polysuccinimide is crosslinked by the addition of sufficient aqueous sodium hydroxide to release a crosslinking amount of free organic crosslinking agent in the reaction mixture., to produce the cross-linked polysuccinimide. Then the crosslinked polysuccinimide product is additionally hydrolysed, to obtain a polyaspartate superabsorbent polymer network. In another aspect of the method, the polysuccinimide can be formed into a paste with water, and the paste is mixed with an effective crosslinking amount of organic crosslinking agent, to produce cross-linked polysuccinimide, which is then further hydrolyzed with base to obtain a network polymeric polyaspartate superabsorbent. The following examples illustrate the preparation of polyaspartate superabsorbent polymer network embodiments from crosslinked polysuccinimide, by the methods described. The examples and methods presented are illustrations of the preferred embodiments, and do not pretend to be limitations.

Preparation of Cross-linked Polysuccinimide (Method A) To illustrate the methods of this invention, the cross-linked polysuccinimide described in Examples 1 to 17 was synthesized by the following general method referred to as Method A. Polysuccinimide is dissolved from a given Mw in an aprotic solvent polar, in about 10 milliliters of solvent / gram, for example, dimethyl sulfoxide (DMSO) or dimethylformamide (DMF), as indicated below. Then a selected molar percentage of diamine crosslinking agent is added. The reaction mixture can be heated to accelerate the crosslinking reaction. Preferably, the temperature of the reaction mixture is in the range of about 25 ° C to about 60 ° C, and more preferably in the range of about 45 ° C to about 50 ° C. The resulting cross-linked polysuccinimide product is generally in the form of a gel or a solid precipitate. This product is then isolated by pouring the reaction mixture into a solvent, such as water or an alcohol, where the aprotic solar solvent is soluble, but where the polymer is not soluble. This produces a solid or precipitate, which can be isolated by filtration, and dried.

Example 1: Synthesis of Crosslinked Polysuccinimide By Method A. As shown in Table 1, polysuccinimide was dissolved with an Mw of about 5,100 grams (about 9.78 grams, 100 millimoles of succinimide units), in dimethyl sulfoxide solvent (approximately 100 milliliters) at a temperature of approximately 40 ° C. Then ethylenediamine (EDA) about 1 gram, 10 millimole) was added with stirring, for a period of about 5 minutes at a temperature of about 45 ° C to about 50 ° C. After a few minutes, a crosslinked polysuccinimide gelatinous reaction mixture was formed. Next, the gelatinous reaction mixture was heated to a temperature of about 50 ° C, for about an additional 2 hours, to ensure a complete reaction. The gelatinous reaction mixture was then cooled to about room temperature. The cooled reaction mixture was poured into about 600 milliliters of methanol, with stirring. A pinkish-tan precipitate was produced. The product was collected by filtration, and dried substantially at about 70 ° C. The yield was approximately 10.2 grams.

Examples 2-17: Synthesis of Reticulated Polysuccinimides Other examples of crosslinked polysuccinimides made successfully following the method of Example 1, with the exception that the diamine crosslinking agent, its molar percentage amount, the polysuccinimide of a given Mw, and the solvent employed, were as mentioned in Table 1.

TABLE 1 RETICULATED POLYESCYCINIMIDES Polysuccinimide% Molar Example Diamine1 Molar Weight (Mw) d.Diamine Solvent " 1 EDA 5100 10 DMSO 2 EDA 5100 5 DMSO 3 EDA 5100 15 DMSO 4 MXDA 5100 7 DMSO 5 EDA 5100 10 DMF 6 MXDA 5100 11 DMSO 7 1,3-BAC 5100 7 DMF 8 1,3-BAC 5100 11 DMF 9 EDR -148 5100 10 DMF 10 EDR-148 5100 • 15 DMF 11 EDR-48 5100 20 DMF 12 MXDA 5100 15 DMF 13 DETA 5100 '10 DMF 14 TAEA 5100 10 DMF 15 EDA 1500 20 DMF 16 EDR-148 30,000 13 DMSO 17 EDA 30,000 4. • DMF Notes for Table 1 1) Diamine = diamine crosslinking agent MXDA = metaxylylenediamine EDA = ethylenediamine 1,3-BAC = 1,3-bis (aminomethyl) cyclohexane EDR-148 = triethylene glycol diamine, approximate molecular weight 148 (JEFFAMINEMR EDR-148, Texaco Chemical Company) DETA = diethylenetriamine TAEA = tris (2-aminoethyl) amine 2) DMSO = dimethyl sulfoxide DMF = dimethylformamide Preparation of Crosslinked Polyaspartate Polymer Networks (Method B) In Examples 18-23 and 25-29, examples of crosslinked polyaspartate polymer networks were synthesized by Method B, generally described as follows. First a cross-linked polysuccinimide was prepared by the general Method A described above. Then the crosslinked polysuccinimide was suspended in a sufficient amount of aqueous sodium hydroxide solution to theoretically hydrolyse the polysuccinimide and any remaining succinimide units in the polymer in a complete manner., to produce a cross-linked polyaspartate aqueous gel. The pH of the resultant polymer network aqueous gel was then adjusted to any desired value. The gel may be dried substantially to a solid at this point, or alternatively, it may be diluted with an excess of water, and may be washed or dialyzed before the drying step.

Example 18: Synthesis of a Crosslinked Polyaspartate Polymer Net Using Method B A polyaspartate polymer network, as shown in Table 2, was prepared from polysuccinimide with an N ^ of about 5,100 (30 millimoles of succinimide units) , crosslinked by the method of Method A, with 15 molar percent of MXDA. The cross-linked polysuccinimide (approximately 6 grams) was mixed with about 30 milliliters of IN aqueous sodium hydroxide (30 mmol) to obtain a cross-linked polysuccinimide paste. A gel reaction mixture was formed in about 1 minute. Next, water (approximately 50 milliliters) was added to make the gel reaction mixture agitated. The gel reaction mixture was heated with stirring at about 50 ° C for about 4 hours. The initial pH was 12.6. After about 4 hours, the pH was about 10.8. Next, the gel reaction mixture was allowed to stand at room temperature for about 20 hours. The pH was then adjusted to about 9.5 with about 4 milliliters of IN HCl. A gel was produced in a polymeric network, which was allowed to settle. The supernatant liquid was decanted, and then the gel was dried substantially at about 50 ° C for about 24 hours. A solid tan was produced. The yield was approximately 5.9 grams.

Examples 19-23 v 25-29; Additional Syntheses Other polyaspartate polymer networks were successfully synthesized by Method B, following the procedure of Example 18, with the exception that the polysuccinimide, the diamine crosslinking agent, the molar percentage amounts, and the pH values used , were as mentioned in Table 2. TABLE 2 RETICULATED POLYGYARDATES > olisuccinimidia% Molar of Example Diamine molar weight (Mu,) Diamine pH Method 18 MXDA 5100 15 9.5 B 13 EDA 5100 10 4.0 B EDA 5100 10 3.8 B 21 EDA 5100 15 4.0 B 22 EDA 5100 10 9.5 B 23 EDA 5100 15 9.3 B 24 HMDA 5000 15 10 D 1.3-BAC 5100 11 9.5 B 26 EDR-148 5100 15 9.7 B 27 EDR-148 5100 20 9.5 B 28 DETA 5100 10 9.5 B 29 TAEA 5100 10 9.5 B EDA 30000 5 8.5 C 31 EDA 1500 20 9.5 C 32 EDA 30000 4 9.5 C 33 EDR-148 30000 13 9.5 C 34 EDR-148 5000 30 10 D HMDA 5000 7 10 D Notes for Table 2 1) Diamine = diamine crosslinking agent (see identification note 1 for Table 1). HMDA = hexamethylenediamine Preparation of Polyaspartate Polymer Networks (Method Cl Examples 30-33 illustrate the preparation of polyaspartate polymer networks by a modality of the alternative method referred to as Method C. First, polysuccinimide was dissolved from a given Mw in a polar aprotic solvent, and added a diamine crosslinking agent to form crosslinked polysuccinimide generally as described in Method A. The mixture can be heated to ensure a complete reaction.When a gel or solid suspension was produced, it was then diluted with a sufficient amount of solution Sodium hydroxide aqueous, to completely hydrolyze the crosslinked polysuccinimide and any remaining succinimide monomer units of the polymer After finishing the hydrolysis to a polyaspartate polymer network, the pH can be adjusted to any desired value.

The gel from the resulting polyaspartate polymer network was then separated from the supernatant fluid by decanting or centrifugation, to remove substantially the majority of the polar aprotic solvent. The gel was then washed or dialyzed with water to remove any remaining solvent. This produced a gel in polymer network swollen by water. The water-swollen polymeric gel gel was then dried substantially to a solid.

Example 30: Synthesis of Polyaspartate Polymer Networks Using Method C As shown in Table 2, a polyaspartate polymer network was prepared from a crosslinked polysuccinimide prepared in general by Method A as follows. The polysuccinimide was cross-linked by the addition of ethylenediamine (EDA) (0.25 grams, 2.5 millimoles) over a period of about 3 minutes, to a polysuccinimide solution of one Mw of about 30,000 (5.0 grams, approximately 50 millimoles of succinimide units) in about 50 milliliters of dimethylformamide solvent, at a temperature of about 45 ° C to about 50 ° C. Within minutes, a firm, substantially clear gel was produced. This gel product was allowed to stand at about 50 ° C for about 1 hour, and then cooled to about room temperature. The cooled gel product was allowed to stand at room temperature for approximately 2 additional hours. Next, a polyaspartate polymer network was prepared as follows. The gel product was cut into fine fragments and suspended, with stirring, in a solution of IN NaOH (42 milliliters, 42 millimoles) from about 45 ° C to about 50 ° C. Initially the pH was about 12.9. After about 3 hours, the pH had dropped to about 8.5. A gelatinous solid was produced. Then the supernatant liquid was poured, and the gelatinous solid was diluted with approximately 180 milliliters of water. A gel was formed in a polymeric network, and considerable swelling of the gel was observed. The excess water was then removed from the swollen gel by water by filtration through a 200 mesh wire screen. Then the swollen gel by water was diluted with about 100 milliliters of water, and again filtered, and the gel was collected of polymer network swollen by resulting water. The weight of the polymer network gel swollen by water was determined at about 156 grams. Then the water swollen polymeric gel gel was dried at about 70 ° C for about 20 hours, to provide about 6.85 grams of a white solid. Based on this performance, the water content of the polymer network gel swollen by water represented approximately 23 times the weight of the dry polymer network.

Examples 31-33: Preparation of Polyaspartate Polymer Networks by Method C Other polyaspartate polymer networks were successfully synthesized by Method C, following the procedure of Example 30, with the exception that polysuccinimide, the diamine crosslinking agent. , the amounts in molar percentage, and the pH values used, were as mentioned in Table 2.

Preparation of Poliaspartate Polymer Networks (Method DI Examples 24 and 34-36 illustrate the preparation of polyaspartate polymer networks by another alternative embodiment of the method, referred to as Method D. First, an aqueous salt solution of organic diamine crosslinking agent was prepared by adding the organic crosslinking agent of diamine to water, and neutralization with hydrochloric acid to form the hydrochloride salt thereof. Then polysuccinimide from a selected Mw was added to form a paste. Aqueous sodium hydroxide was then added in an amount calculated to neutralize the diamine hydrochloride, and generate a cross-linking amount of the free diamine crosslinking agent to react with the polysuccinimide and form the cross-linked polysuccinimide. Next, additional aqueous sodium hydroxide was added in an amount sufficient to hydrolyze the crosslinked polysuccinimide and any remaining monomeric succinimide units in the polymer. A gel was produced in a polymer network. The gel can then be collected and dried substantially in a polymeric network. A variation of this method can be practiced by adding the free diamine crosslinking agent to an aqueous polysuccinimide paste, followed by addition of the aqueous sodium hydroxide solution as described above.

Example 34: Synthesis of Polyaspartate Polymer Networks by Method D Triethylene glycol diamine (EDR-148) was acidified (approximately 100 grams, 0.67 moles) with a 6N HCl solution, to a final pH of about 1.7. The final total weight of the solution was approximately 305. 53 grams. Polysuccinimide (approximately 20 grams, 200 millimoles of succinimide units, Mw of approximately 5,000) and water were combined (approximately 10 milliliters) with approximately 28.84 grams (60 millimoles) of the neutralized diamine, and the mixture was stirred vigorously to form a paste. An aqueous solution of sodium hydroxide was added dropwise (at about 50 percent), at a rate of approximately 1 milliliter per minute, until gel formation occurred (approximately 15 minutes).

The gel was dried at about 70 ° C for about 48 hours and then ground to a powder. The yield was approximately 26 grams.

Examples 35-36: Synthesis of Polyamide Polyamide Networks by Method D Other polymer polyaspartate networks were successfully synthesized following the method of Example 34, with the exception that the polysuccinimide, the amine crosslinking agent, and the molar percentage of amine crosslinking agent employed, were as mentioned in Table 2.

Example 37: Super Absorbable Polyamide Polymer Networks. The superabsorbent characteristics of each of the cross-linked polyaspartate polymer networks of Examples 18-36 were demonstrated by the values obtained in the following protocol, using either deionized water or 1 percent aqueous sodium chloride (saline). they added approximately 100 milligrams (mg) of polyaspartate polymer network to a previously weighed test tube. An amount of deionized water or saline was added in an excess sufficient for the contents of the tube to swell the polymer network and provide a supernatant liquid. Then the tube was left undisturbed for approximately 25 minutes, at the end of which time, the tube was centrifuged at approximately 1 minute., 500 rpm for approximately 5 minutes. The supernatant fluid was then pipetted. The tube with its contents was then weighed, and the amount of liquid that had been absorbed by the polymer network was determined. Water absorbency or serum absorbency was expressed as the ratio of the weight of the gel in polymeric network swollen by water or swollen by serum, divided by its weight when it is dry. Each evaluation was done in triplicate, and an average value was calculated. The average values for the data obtained for water absorbency and for serum absorbency are compared in Table 3 for the crosslinked polyaspartate polymer networks of Examples 18-36. The approximate ratio of the value for serum absorbency to water absorbency is also shown. TABLE 3 ABSORBANCE OF WATER AND SERUM FOR POLYESPARTATES RETICXJLADOS B Proportion Polypropylene Absorbency Absorbency Absorbency of serum water B: A Ex. 18 10.5 7.4 0 Ex. 19 5.6 4.6 0 Ex. 20 8.9 5 8 o Ex. 21 '5.5 4 0 or Ex. 22 '16.9 9 3 or Ex. 23 8 5 3 o Ex. 24 3.7 3 7 1 ' Ex. 25 13.1 7 9 0.6 Ex. 26 14.6 6 2 0.4 Ex. 27 8.3 5, 8 0.7 Ex. 28 8.6 8.3 1 Ex. 29 6.9 5, 6 0.8 Ex. 30 28.3 13, 5 0.5 Ex. 31 5.7 4.4 0.8 Ex. 32 71.3 21.4 0.3 Ex. 33 93 23.4 0.3 Ex. 34 4.2 4 1 Ex. 35 3.1 2.9 1 Ex. 36 5.2 5.3 1 As shown by the water absorbency data in Table 3, all polymeric networks absorbed from about 3 times their weight to more than 90 times their weight. Weight in water. As is generally observed with all known water-swellable polymers, the water absorbency decreased by increasing the ionic concentration of the solution. Accordingly, the overall absorbency is generally reduced in a saline solution, compared to that in water. However, surprisingly, the water and serum absorbency of the polymer networks of Examples 24, 28, 34, 35, and 36, was substantially similar to that shown by the data of the absorbance ratio of serum to absorbency of water. In contrast, it was noted that, while practicing Method A, the crosslinked polysuccinimides of Examples 1-17 did not swell in aqueous solutions, but did swell in the presence of polar organic solvents. It is known from the art, that for most of the polyacrylate-based absorbers, the degree to which the absorbency of water decreases due to the presence of salt is very great. In general, the absorbency of a 1 percent sodium chloride solution is less than about 20 percent of the absorbency of pure water. Accordingly, the water-absorbing properties of the polymer networks of the present invention are less sensitive to the presence of salts, as evidenced by the ratio of the absorbency of serum to the water absorbency in Table 3.

Claims (22)

NOVELTY OF THE INVENTION Having described the above invention, it is considered as a novelty, and therefore, the content of the following is claimed as property: CLAIMS

1. A method for producing polymer networks consisting of cross-linked polyaspartate, which includes the steps of: a) dissolving a polysuccinimide in a polar aprotic organic solvent, b) reacting the dissolved polysuccinimide with an effective cross-linking amount of an organic cross-linking agent. which is an organic base containing at least two primary amine groups, to form a cross-linked polysuccinimide product in the resulting reaction mixture, - c) isolating the obtained cross-linked polysuccinimide product, by mixing the reaction mixture with a solvent wherein the polar aprotic organic solvent is soluble, and the cross-linked polysuccinimide product is not soluble; d) recovering the cross-linked polysuccinimide product; and e) hydrolyzing the reticulated polysuccinimide product recovered to produce a polyaspartate polymer network.

The method according to claim 1, characterized in that the reaction mixture in step (b) is heated to a temperature range from about 25 ° C to about 60 ° C, and is maintained on this scale of temperature until the cross-linked polysuccinimide product is formed.

3. The method according to claim 2, characterized in that it also includes the step of cooling the reaction mixture to room temperature between step (b) and step (c).

4. The method according to claim 1, characterized in that the crosslinked polysuccinimide is collected in step (d) by filtration and drying of the crosslinked polysuccinimide.

5. The method according to claim 1, characterized in that it also includes the step of collecting the polyaspartate polymer network.

6. The method according to claim 5, characterized in that it also includes the step of substantially drying the polymer network.

7. The method according to claim 1, characterized in that the polyaspartate polymer network is in the form of a gel or a solid.

The method according to claim 1, characterized in that the polysuccinimide of step (a) has a weight average molecular weight in the range from about 500 to more than about 100,000.

9. The method according to claim 1, characterized in that the amount of organic crosslinking agent, based on moles of diamine per mole of succinimide monomer units in the polysuccinimide, is present in a molar percentage amount of about 0.1 to about 50.

The method according to claim 1, characterized in that the polysuccinimide of step (a) has a weight average molecular weight in the range from about 500 to more than about 100,000, and the of organic crosslinking, based on moles of diamine per mole of monomeric units of succinimide in the polysuccinimide, is present in a molar percentage amount of from about 0.1 to about 50.

11. A polyaspartate superabsorbent polymer network obtained by the method in accordance with claimed in claim 1, characterized as a copolymer at eatorio primarily comprised of succinimide units and dimeric aspartamide units, with less than about 20 percent aspartate units in the alpha form, in the beta form, or both.

12. A composition of matter consisting of a polymer network, which includes a random copolymer of cross-linked polyaspartate capable of absorbing water in an amount on the scale of at least 3 times to more than 90 times its dry weight.

13. A composition of matter that 'consists of a polymeric network, which includes a random copolymer of cross-linked polyaspartate capable of absorbing a saline solution in an amount on the scale from at least 2 times to more than 20 times its dry weight.

A method for producing polymer networks including cross-linked polyaspartate, which includes the steps of: a) dissolving a polysuccinimide in a polar aprotic organic solvent, - b) reacting the dissolved polysuccinimide with an effective crosslinking amount of a crosslinking agent organic that is an organic base containing at least two primary amine groups, to form a cross-linked polysuccinimide product, to produce a reaction mixture, -c) form a paste of the reaction mixture with a sufficient aqueous base to form a mixture reaction gel; c) diluting the reaction mixture in gel with sufficient water to allow agitation of this reaction mixture in gel; d) heating and stirring the reaction mixture in gel at a selected temperature, and maintaining this temperature for a selected period, - e) cooling the reaction mixture in gel at about room temperature, and maintaining this temperature for a selected period, to produce a product comprising a polyaspartate polymer network gel, and a supernatant liquid including aprotic solvent.

15. The method according to claim 14, characterized in that it also includes the step of adjusting the pH of the product to a desired pH.

16. The method according to claim 15, characterized in that it also includes the step of collecting the gel in polymer network by decanting the supernatant liquid, to remove substantially all the aprotic solvent.

17. The method according to claim 16, characterized in that it further includes the step of further removing any remaining aprotic solvent by washing or dialyzing the collected polymeric network gel.

18. The method according to claim 16, characterized in that it also includes the step of substantially drying the collected polymer network.

19. A method for producing a polyaspartate polymer network, which includes the steps of: a) preparing an aqueous solution containing a salt of an organic cross-linking agent that is an organic base containing at least two primary amine groups. b) mixing the resulting salt solution with a polysuccinimide to form a reaction mixture; c) adding sufficient aqueous base to the reaction mixture to release an effective cross-linking amount of free organic cross-linking agent, to cross-link the succinimide and form a crosslinked polysuccinimide product; and d) further hydrolyze the crosslinked polysuccinimide product to obtain a polyaspartate polymer network.

20. The method according to claim 19, characterized in that it also includes the step of cooling the salt solution to room temperature between step (a) and step (b).

21. The method according to claim 19, characterized in that it also includes the step of substantially drying the polyaspartate polymer network.

22. A method for producing a polyaspartate polymer network, which includes the steps of: a) preparing an aqueous polysuccinimide paste; b) mixing an organic cross-linking agent including an organic base containing at least two primary amine groups with the pulp, the organic cross-linking agent being present in an active cross-linking amount to form a cross-linked polysuccinimide product; and c) hydrolyzing the crosslinked polysuccinimide product to obtain a cross-linked polyaspartate polymer network.