Aspartic acid copolymers and their preparation

Abstract

aspartic acid precursors such as mono and diammonium maleate, maleamic acid, ammonium maleamate, ammonium malate and mixtures of these and other precursors are copolycondensed thermally with a variety of mono, di and multifunctional monomers containing amino, hydroxyl and carboxyl functional groups. The resulting condensation copolymers and terpolymers contain succinimide units derived from aspartic acid precursors, condensed with other functional group monomers usually though through amide and ester linkages. Hydrolysis of the polysuccinimide copolymers and terpolymers with alkali, alkaline earth and ammonium hydroxide produces aspartic acid copolymer and terpolymer salts.

Description

FIELD OF THE INVENTION

This invention is in the field of condensation polymer formation. More specifically, this invention is in the field of copolymers of polysuccinimide with other functional group monomers and conversion of these copolymers to salts of the copolymers of aspartic acid.

BACKGROUND OF THE INVENTION AND PRIOR ART

A variety of methods for preparation of polysuccinimide and subsequent hydrolysis to polyaspartic acid (or salts) have been described in the literature and patents. In addition methods of preparation of copolymers of polyaspartic acid have also been reported in the literature.

In a series of patents, Koskan et al. discloses a method for thermal polymerization of aspartic acid in a fluidized bed to form polysuccinimide which is then hydrolyzed to polyaspartic acid (sodium salt) using sodium hydroxide (U.S. Pat No. 5,057,597; U.S. Pat No. 5,116,513; U.S. Pat. No. 5,152,902 and U.S. Pat. No. 5,221,733). Uses of polyaspartic acid as calcium carbonate, calcium and barium sulfate and calcium phosphate scale inhibitors are also described in these patents.

Production of polysuccinimide and polyaspartic acid (and salts) from maleic anhydride, water and aqueous ammonia is taught in patents by Koskan and Meah (U.S. Pat. No. 5,219,952 and U.S. Pat. No. 5,296,578). Polysuccinimide is produced in at least 90% of theoretical yield by heating the maleic anhydride, water, ammonia mixture at 220°-260°C In U.S. Pat. No. 4,839,461, Boemke teaches the production of a polyaspartic acid salt by the reaction of maleic acid and aqueous ammonia at 120°-150°C followed by hydrolysis of the resulting acid with metal hydroxides or ammonium hydroxide. A process is disclosed (in U.S. Pat. No. 5,288,783) for the preparation of a salt of polyaspartic acid by reacting maleic acid and ammonia in a molar ratio of 1:1-

The thin layer polymerization process as utilized in the copolycondensation reactions of this invention involves four steps which are:

1. Synthesis of the aspartic acid precursor such as mono or diammoniummaleate diammonium maleate, maleamic acid, ammonium maleamate, mono or diammonium fumarate or mono and diammoniummalate.

2. Thorough mixing of the aspartic acid precursor with the functional monomer, usually accomplished by grinding the two or more reactants together.

3. Spreading the reactant mixture as a thin layer onto a surface which is heated or is in a heated zone and heating the layer to produce polysuccinimide condensation copolymers, as water of imidization is removed. Water removal can be facilitated using an inert gas sweep or by applying vacuum.

4. Removal of the product from the heated surface or heating zone.

For step 1, the aspartic acid precursor such as monoammonium maleate can be prepared in a conventional stirred reactor which has cooling capability and can be siphoned from the top or has a bottom valve. The precursor material can be isolated from the reaction mixture by filtration, spray drying or centrifuging. The thermal copolycondensation of step 3 can be done on a conveyor belt (stainless steel or temperature resistant composite) that enters an oven which consists of one or several heating zones. Air handling equipment is needed to quickly remove evolved gases and condensation vapors during step 3.

To demonstrate the thin layer polymerization process, copolycondensation reactions are described below in Examples 2, 3, 4, 5 and 10.

The thermal bulk polymerization method (Method B) for preparing the copolycondensation polymers of this invention involves heating the mixture of aspartic acid precursors and functional monomers together in a reaction vessel that is heated by a heat transfer fluid. Stirring of the reaction vessel is not convenient as the solid polysuccinimide condensation copolymer forms during the reaction from the melt of starting reactants. Heat transfer is less effective than with the thin layer process and as a result longer reaction times are employed. A one stage heating procedure is used i.e. the product is not returned to the reaction vessel (after grinding ) for further heating. Examples 7, 8 and 9 describe thermal bulk polymerization.

The third method (Method C) for preparing the copolycondensation polymers of this invention utilizes the thin layer polymerization technique of Method A but in addition the aspartic acid precursor is produced in situ as for example from maleic anhydride and ammonium carbonate. Polysuccinimide has been prepared by this technique whereby the ammonia necessary for the aspartic acid precursor is provided in situ during the condensation reaction by thermal decomposition of ammonium salts, preferably ammonium carbonate. Ammonia released from ammonium carbonate reacts directly with the maleic anhydride, producing water and carbon dioxide as the by-products of the ammonium salt decomposition. (Patent application in progress.)

In Method C, the functional monomer is mixed thoroughly with maleic acid or anhydride or substituted maleic anhydride and the ammonium salt, (ammonium carbonate) which had previously been thoroughly mixed. The mixture of three reactants then is placed on a heated reaction surface for thin layer polymerization. A convection oven is used to supply the heat for this method. A continuous moving belt in a heat zone or oven could also be used to permit a continuous condensation process. An Example of this method is included in the experimental section as Example 6.

The polysuccinimide condensation copolymers made by any of the three methods are hydrolyzed to polyaspartic acid copolymers using alkali and alkaline earth or ammonium hydroxides. The hydroxides useful in hydrolysis of the copolymers have cations which are Na+, K+, Mg⁺⁺, Li+, Ca⁺⁺, Zn⁺⁺, Ba⁺⁺, Co⁺⁺, Fe⁺⁺+, Fe⁺⁺+ and NH₄+.

The copolycondensation aspartic acid polymers obtained by the present invention are useful as scale inhibitors in water treatment to prevent deposition of calcium carbonate, calcium and barium sulfate and calcium phosphate in cooling water and boiler water. They are also useful in detergent formulations as a builder and anti-redeposition agent. They are useful in oral health care products and cosmetic formulations. Additional uses are for enhancing uptake of fertilizers and micronutrients in agriculture. Certain copolymers also may act as corrosion inhibitors in water systems. The copolymers can disperse solids in cooling water systems and act as dispersants for slurries of solids. These copolymers are useful as dispersants for ceramic slurries and as dispersants for pigments in paints.

Molecular weight The molecular weights of the copolycondensation polymers of this invention are determined by first hydrolyzing the polysuccinimide copolymers to form the salt of an aspartic acid copolymer using aqueous metal or ammonium hydroxides. The aspartate copolymer then is analyzed by GPC to obtain molecular weight and molecular weight distributions.

Molecular weight of the copolycondensation polymers can vary depending upon type and amount of aspartic acid precursor used and type and amount of functional group monomer used. A preferred molecular weight range is from Mw 600 to 100,000. A more preferred range is from Mw 1000 to 60,000. A most preferred range is from Mw 1000 to 30,000.

Some copolycondensation reactions of the aspartic acid precursor and the functional group monomer result in production of lower molecular weight polyaspartic acid polymers than when the aspartic acid precursor is used alone. As an example, polymerization of monoammonium maleate produces a polysuccinimide which when hydrolyzed with hydroxide results in a polymer of molecular weight, Mw 1000-3000, usually Mw is about 2000. Copolymerization of monoammonium maleate with lactic acid, citric acid, alanine, maleic acid and itaconic acid resulted in polyaspartic acid copolymers with Mw of about 1000. This molecular weight lowering effect can be overcome by using a small amount of diamine or polyamine to crosslink the copolymer, resulting in a terpolymer. The crosslinking and copolymerization reactions were done simultaneously by mixing the three reactants together and performing the thermal condensation polymerization.

Amines which are suitable for the crosslinking and molecular weight building process are any polyamine which has at least two primary or secondary amine groups available for reaction. The preferred polyamines are those that have two primary amine groups present in the molecule. Another preferred polyamine can have at least one primary amine group and the other amine group in the molecule can be a primary or secondary amine. Examples of polyamines include ethylenediamine, diethylenetriamine, triethylenetetramine triethylenetetraamine, tetraethylenepentamine, 1,6-hexanediamine, polyoxyalkyleneamines, polyoxyalkylenediamines, polyoxyalkylenetriamines, alkyldiamines, alkyltriamines, melamine, urea, diaminocyclohexane, carbohydrazide, polyethyleneimine,polyvinylamine, polyethyleneimine, polyvinylamine and lysine.

Of the many diamines and polyamines useful for the crosslinking terpolymerization reaction during copolycondensation, lysine is especially interesting since the resulting aspartic acid-lysine terpolymers can be largely biodegradable. Fully biodegradable combinations can result from use of aspartic acid precursors, lysine and functional group monomers such as lactic acid, glycolic acid, citric acid, sugar acids, carbohydrates and amino sugars. This type of terpolymer is described in Example 9 using monoammonium maleate, lysine and lactic acid as the monomers.

In order to further describe the copolycondensation aspartic acid copolymers and terpolymers of this invention the following examples are given. Methods of preparation of these polymers are demonstrated using monoammonium maleate as the aspartic acid precursor, however other precursors can also be used. A partially wet form of monoammonium maleate was used in all reactions, however a fully dried monoammonium maleate can be used or a concentrated solution of monoammonium maleate can be used.

EXAMPLE 1

PAC Synthesis of Wet Monoammonium Maleate

Deionized water (21.8 Kg) was added to a chilled 20 gallon jacketed reactor. Next, crushed maleic anhydride powder (21.8 Kg, 222.28 mol) was added carefully to the reactor. The resulting suspension was stirred with a mechanical stirrer and was cooled to 15°C Next, aqueous ammonia (30 % w/w, 14.08 Kg, 244.89 mol) was slowly added to the stirred reaction contents by means of a dip tube over a one hour period. The temperature of the reaction contents was maintained below 30°C during this time. After he the ammonia addition was completed, the resulting suspension was filtered. The wet solid was stored in a drum. Three additional experiments were conducted using the above procedure and the solids were combined with the solid obtained from the first experiment. The wet solids from all four experiments were allowed to air dry for two days to give a moist colorless product (56.3 Kg). The product was identified as monoammonium maleate by TLC (1:5 MeOH:EtOAc Me-OH:EtOAc; Polygram SiO₂ ; Rf 0.09) and was found to contain 6% water by weight by Karl Fisher titration. A sodium hydroxide titration indicated that the product contained 93.4% monoammonium maleate and 6.6% diammoniummaleate diammonium maleate.

EXAMPLE 2

PAC General Procedure of Thin Layer Polymerization

Monoammonium maleate or other aspartic acid precursor and a functional group comonomer such as an a hydroxycarboxylic acid, diamine or triamine, polybasic acid etc. or another amino acid were thoroughly mixed by grinding together in a mortar and pestle. The resulting mash or solid mass of crystals was then placed in a glass or aluminum reaction vessel (5 cm diameter×1.5 cm deep) and spread out to form a layer on the bottom of the vessel. Sample sizes of 3 to 4 g were normally used. Composition of the mix of aspartic acid precursor and functional group comonomer varied from 1 to 99.9 mole % of monoammonium maleate or other aspartic acid precursor to 99 to 0.1M % of the functional group comonomer or amino acid. The vessel containing the reaction mixture was then placed in a convection oven that had been preheated to a selected reaction temperature. Reaction temperature was chosen in the range of 100° to 350°C with the most preferred range being 170° to 260°C A reaction time of 2 minutes to 6 hours was used depending on the temperature of the reaction. A more preferred reaction time was 5 minutes to 3 hours. The most preferred reaction time was 5 minutes to 2 hour hours. During the heating time, water of crystallization, if present, and water of condensation rapidly boiled off to leave a brittle, foamed solid polysuccinimide copolymer, usually an orange-red colored product. After the reaction was completed, the sample was quickly removed from the oven and was left to cool to room temperature. The cooled product was weighed to determine weight loss during reaction as a measure of extent of reaction. The sample was crushed and retained for hydrolysis to aspartic acid copolymer.

The products were analyzed for molecular weight by size exclusion chromatography. In this procedure the product (0.5 g) was combined with sodium hydroxide solution (1 N, 5.2 mL) and stirred to give a solution. A portion of this solution (0.5 g) was combined with potassium phosphate dibasic solution(0.1 M, 5.5 g) solution (0.1 M, 5.5 g). The resultant solution was filtered through a 0.45 μm filter (nylon) and subjected to instrumental analysis. The instrumental setup consisted of (1) an HPLC pump (Shimadzu model LC-10AD), (2) a mobile phase (0.05 M KH₂ PO₄ soln.) which carried the analyte (20 uL) (20 μL) at a rate of 0.4 mL/min, (3) two size exclusion chromatography columns (SynChropak GPC 100, GPC 500), and (4) an ultraviolet (220 nm) detector. The instrument was standardized using sodium polyacrylate standards (Polysciences, Inc.) of narrow molecular weight distributions. Weight average (Mw) and number average (Mn) molecular weights were obtained using an algorithm in the data handling system (Hitachi D-2520 GPC integrator).

Examples of functional group monomers and amino acids used in this procedure are:

citric acid, lactic acid, maleic acid, succinic acid, ethylene

glycol, sorbitol, glycerol, glucose, low molecular weight

(Mw 1200) polysuccinimide, maleamic acid, alanine,

lysine, ammonium lactate, diethylenetriamine and Jeffamime JEFFAMINE ED-600 (an oxyalkylated diamine).

EXAMPLE 3

Monoammonium maleate (2,627 2.627 g of 94% concentration wet salt, 0.0186 mole) and citric acid (0,395 #x2205;395 g, 0.0021 mole) were ground together and thoroughly mixed to form a slightly wetted mass. This mixture was placed in the aluminum reaction vessel to form a layer and then was heated at about 240°-260°C for 40 minutes in a convection oven. The resulting product was a red-brown solid foam, weight 1.991 g, representing 92% theoretical yield of polysuccinimidecitric acid poly-succinimide-citric copolymer. Hydrolysis of this product with sodium hydroxide at room temperature produced an aspartic acid-citric acid copolymer having molecular weights by GPC of Mw 1196, Mn 613, Mw/Mn 1.95.

EXAMPLE 4

Monoammonium maleate (3.00 g of 94% wet salt, 0.0212 mole) and succinic acid (0,278 #x2205;278 g, 0.0024 mole) were thoroughly mixed together and then were reacted as in Example 2 and 3 by heating in a convection oven at 230°240° 230°-240° C. for 40 minutes. A brittle, red-brown solid was obtained which weighed 2,204 2.204 g. Hydrolysis of this product with sodium hydroxide produced an aspartic acid copolymer having molecular weights by GPC of Mw 1717, Mn 1016, Mw/Mn 1.69.

EXAMPLE 5

Monoammonium maleate (2.993 g of 94% wet salt, 0.0212 mole) and diethylenetriamine(0,115 #x2205;115 g, 0.0011 mole) were mixed together and reacted according to the procedure of Example 2 and 3 at 230° -255° 230°-255° C. for 40 minutes. The resulting polysuccinimide-diethylenetriamine crosslinked copolymer weighed 1,970 1.970 g. Hydrolysis of this product produced an aspartic acid-diethylenetriamine copolymer having molecular weights by GPC of Mw 5207, Mn 1359, Mw/Mn 3.83.

Example 6

Maleic anhydride (1,924 1.924 g, 0.0196 mole) was ground together with ammonium carbonate (31.3% as ammonia) (1.117 g, 0.0206 equiv. of ammonia) to form a premix. To the premix was added diethylenetriamine (0.183 g, 0.0018 mole) and the mixture was ground together to thoroughly mix the components. This mixture was then placed as a layer in an aluminum reaction vessel as described in Example 2. The mixture was heated in a convection oven at 230°-255°C for 40 minutes to produce a brittle, red-brown crosslinked polysuccinimide copolymer. Weight of product from this reaction was 2,101 2.101 g. The polysuccinimide was hydrolyzed with sodium hydroxide to produce polyaspartic acid-diethylenetriamine crosslinked copolymer having molecular weight by GPC of Mw 3030, Mn 364.

EXAMPLE 7

Monoammonium maleate (2.859 g of 94% wet salt, 0.0202 mole) and lysine (0.165 g, 0.0011 mole) were ground together for thorough mixing. This mixture was transferred into an open reaction vessel and the vessel was placed in an oil bath which was preheated to 245°-250°C Heating of the reaction mixture was continued for one hour at 245°-250°C The reaction product was then cooled and weighed 2.161 g., about 100% yield of polysuccinimide-lysine crosslinked copolymer. Hydrolysis of this copolymer using sodium hydroxide at room temperature produced aspartic acid-lysine copolymer having a molecular weight by GPC of Mw 10,989, Mn 1928, Mw/Mn 5.70.

EXAMPLE 8

Using the same procedure as described in Example 7, monoammonium maleate (2.824 g of 94% wet salt, 0.0200 mole) was mixed thoroughly with lactic acid (0.200 g., 0.0022 mole) and reacted together for an hour at 245°-250°C A Yield yield of 2,134 2.134 g of polysuccinimide-lactic acid copolymer was obtained. Hydrolysis of this copolymer at room temperature produced aspartic acid-lactic and copolymer having GPC molecular weights of Mw 1025, Mn 521, Mw/Mn 1.96).

EXAMPLE 9

Using the same procedure as employed in Examples 7 and 8, monoammonium maleate (2,738 2.738 g of 94% wet salt, 0.0194 mole), lactic acid (0,215 #x2205;215 g, 0.0024 mole) and diethylenetriamine (0,116 #x2205;116 g, 0.0011 mole) were mixed thoroughly and then were reacted together at 245°-250° C. for one hour. A yield of 2.1 01 2.101 g of polysuccinimide-lactic acid-diethylenetriamine diethylene-triamine terpolymer was obtained. Upon hydrolysis with sodium hydroxide, polyaspartic acid-lactic acid-diethylenetriamine diethylene-triamine crosslinked terpolymer was produced. Molecular weights were determined by GPC to be Mw 3925, Mn 1063, Mw/Mn 3.69.

Using the same procedure and reaction conditions as for Examples 8 and 9, monoammonium maleate was thermally polymerized to produce polysuccinimide. Upon hydrolysis of this polysuccinimide, a polyaspartic acid was produced having GPC molecular weights of Mw 1975, Mn 958, Mw/Mn 2.06.

Comparing the molecular weight of polyaspartic acid made by the above procedure (Mw 1975) to the molecular weight of the aspartic acid-lactic acid copolymer of Example 8 (Mw 1025) it can be seen that molecular weight was reduced in the copolymer. This reduction of molecular weight effect was overcome by using a small amount (4.8M%) of diethylenetriamine in Example 9 (Mw 3925). Similarly other diamines and polyamines can be used to make crosslinked polyaspartic acid terpolymers. The utilization of lysine as the crosslinking diamine is of special interest since its use, as for example, in .an an aspartic acid, lactic acid, lysine terpolymer, permits formation of a fully biodegradable polymer. Other terpolymer combinations which would be nearly fully biodegradable are:

a) aspartic acid (made by using aspartic acid precursors) plus lysine, terpolymerized with

b) citric acid, malic acid, glycolic acid, tartaric acid, gluconic acid, glucaric acid, glucuronic acid, carbohydrates, glycerol, sorbitol, sugar carboxylic acids, amino-sugars, diols, triols, triols or polyols.

EXAMPLE 10

Using the procedure of Example 2 monoammonium maleate (3.068g of 95% wet salt, 0.0217 mole) and glycerol (0.264g., 0.0029 mole) were reacted together as a thin layer at 230°-240°C for 40 minutes to produce polysuccinimide-glycerol copolymer. A brittle, red-brown foamed solid product was obtained, 2,344g 2.344 g. Hydrolysis of this product with sodium hydroxide produced polyaspartic acid-glycerol copolymer having a GPC molecular weight of Mw 2217, Mn 1265, Mw/Mn 1.75.

Claims

1. A method for producing aspartic acid copolymers and salts which comprises heating mixtures of a mixture comprising (a) an aspartic acid precursors and precursor, a substituted aspartic acid precursors with amino, hydroxyl, and substituted aspartic acid precursors with precursor or combination thereof and (b) an amino, hydroxyl, and or carboxyl functional group-containing monomers monomer at a temperature of at least 120°C for a sufficient length of time for thermal polymerization to a polysuccinimide copolymer to occur and subsequently hydrolyzing the polysuccinimide copolymer with alkali, metal hydroxide, alkaline earth, metal hydroxide or ammonium hydroxides, to form the aspartic acid copolymer and salts thereof, wherein the component (a) of said mixture of comprises as said aspartic acid precursors and precursor or substituted aspartic acid precursors comprise precursor at least one of the following combinations of compounds: maleic anhydride and ammonium carbonate, citraconic anhydride and ammonium carbonate, itaconic anhydride and ammonium carbonate, maleic anhydride and asparagine, citraconic anhydride and asparagine, iraconic itaconic anhydride and asparagine, maleic anhydride and ammonium maleamate, citraconic anhydride and ammonium maleamate, itaconic anhydride and ammonium maleamate, maleic anhydride and monoammonium aspartate, itaconic anhydride and monoammonium aspartate, maleic acid and ammonium carbonate, citraconic acid and ammonium carbonate, itaconic acid and ammonium carbonate, maleic acid and asparagine, citraconic acid and asparagine, itaconic acid and asparagine, maleic acid and ammonium maleamate, citraconic acid and ammonium maleamate, iraconic itaconic acid and ammonium maleamate, maleic acid and monoammonium aspartate, citraconic acid and monoamonium monoammonium aspartate, itaconic acid and monoammonium aspartate, malic acid and ammonium carbonate, malic acid and asparagine, malic acid and ammonium maleamate, malic acid and monoammonium aspartate, fumaric acid and ammonium carbonate, fumaric acid and asparagine, fumaric acid and ammonium maleamate, fumaric acid and monoammonium aspartate, maleic anhydride and mono and or diammonium maleate, citraconic anhydride and mono and or diammonium maleate, iraconic itaconic anhydride and mono and or diammonium maleamate, maleic acid and mono and or diammonium maleamate maleate, fumaric acid and mono or diammonium maleate, malic acid and mono and or diammonium maleamate, iraconic maleate, itaconic acid and mono and or diammonium maleate, citraconic acid and mono and or diammonium maleate.

2. The method in accordance with claim 1 wherein the said amino, hydroxyl and, or carboxyl functional group-containing monomers comprise monomer comprises at least one of the following compounds: lactic acid, citric acid, glycolic acid, malic acid, tartaric acid, succinic acid, adipic acid, butanetetracarboxylic acid, gluconic acid, glucluronic glucuronic acid, glucaric acid, aconitic acid, sulfosuccinic acid, phosphinicosuccinic acid, phosphonosuccinic acid, iminodiacetic acid, nitrilotriacetic acid, stearic acid, palmitic acid, cyclohexanedicarboxylic acid, cyclohexanedicarboxylic acid anhydride, terephthalic acid, phthalic acid, phthalic acid and anhydride, crotonic acid, sorbitol, glycerol, glucose, fructose, sucrose, maltose, glycine, alanine, aspartic acid, glutamic acid, lysine, serine, threonine, cystine, cysteine, ethylenediamine, diethylenetriamine, triethylenetetramine triethylenetetraamine, polyamines, 1,6-diaminohexane, octadecylamine, glucosamine, alkoxylated amines, alkoxylated diamines, alkoxylated triamines, 6-aminocaproic acid, 4-aminobutyric acid, diaminocyclohexane, urea, melamine, carbohydrazide, hydrazine, ascorbic acid, isoascorbic acid, sorbic acid, maleuric acid, cyanuric acid, alkyldiamines, alkyltriamines, acrylic acid, methacrylic acid, alkyltriamines, acrylic acid, methacrylic acid, maleic acid and, maleic anhydride, alkylmaleic acids, alkenylsuccinic acids and anhydrides, methlenemalonic, alkenylsuccinic anhydrides and methylenemalonic acid. 3. The method in accordance with claim 1 wherein the said amino, hydroxyl, and carboxyl functional group-containing monomers comprise at least one of the following compounds: lactic acid, citric acid, glycolic acid, malic acid, tartaric acid, succinic acid adipic acid, butanetetracarboxylic acid, gluconic acid, glucuronic acid, glucaric acid, aconitic acid, sulfosuccinic acid, phosphoinicosuccinic acid, phosphonosuccinic acid, iminodiacetic acid, nitrilotriacetic acid, stearic acid, palmitic acid, cyclohexanedicarboxylic acid, cyclohexanedicarboxylic acid anhydride, terephthalic acid, phthalic acid, phthalic acid anhydride, crotonic acid, sorbitol, glycerol, glucose, fructose, sucrose, maltose, glycine, alanine, glutamic acid, lysine, serine, threonine, cystine, cysteine, ethylenediamine, diethylenetriamine, triethylenetetramine, polyamines, 1,6-diaminohexane, octadecylamine, glucosamine, alkoxylated amines, alkoxylated diamines, alkoxylated triamines, 6-aminocaproic acid, 4-aminobutyric acid, diaminocyclohexane, urea, melamine, carbohydrates, hydrazine, ascorbic acid, isoascorbic acid, sorbic acid, maleuric acid, cyanuric acid, alkyldiamines, alkyltriamines, acrylic acid, methacrylic acid, maleic acid and anhydride, alkylmaleic acids, alkenylsuccinic acids

and anhydrides, methylenemalonic acid.4. The method in accordance with claim 1 wherein the said hydroxides include hydroxide includes at least one of the following compounds: sodium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide, calcium hydroxide, zinc hydroxide, barium hydroxide, cobalt hydroxide, ferric hydroxide, ferrous hydroxide, and ammonium

hydroxide. 5. The method in accordance with claim 3 wherein the said hydroxides include hydroxide includes at least one of the following compounds: sodium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide, calcium hydroxide, zinc hydroxide, barium hydroxide, cobalt hydroxide, ferric hydroxide, ferrous hydroxide, and ammonium hydroxide. 6. A method for producing aspartic acid copolymers and salts thereof which comprises heating (a) an aspartic acid precursor, a substituted aspartic acid precursor or mixture thereof with (b) at least one amino, hydroxyl or carboxyl functional group-containing monomer at a sufficient temperature and for a sufficient length of time for thermal polymerization to a polysuccinimide copolymer to occur and subsequently hydrolyzing the polysuccinimide copolymer to form the aspartic acid copolymer and salts thereof.7. The method in accordance with claim 6 wherein said component (a) comprises at least one compound selected from the group consisting of monoammonium maleate, diammonium maleate, maleamic acid, ammonium maleamate, monoammonium malate, diammonium malate, monoammonium fumarate, diammonium fumarate, asparagine, monammonium aspartate, monoammonium itaconate, diammonium itaconate, monoammonium citraconate, diammonium citraconate, monoammonium mesaconate, diammonium mesaconate, monoammonium chlorosuccinate, diammonium chlorosuccinate, monoammonium bromosuccinate, diammonium bromosuccinate, monoammonium mercaptosuccinate and diammonium mercaptosuccinate.8. The method in accordance with claim 6 wherein said component (a) comprises at least one of the following combinations of compounds: maleic anhydride and ammonium carbonate, citraconic anhydride and ammonium carbonate, itaconic anhydride and ammonium carbonate, maleic anhydride and asparagine, citraconic anhydride and asparagine, itaconic anhydride and asparagine, maleic anhydride and ammonium maleamate, citraconic anhydride and ammonium maleamate, itaconic anhydride and ammonium maleamate, maleic anhydride and monoammonium aspartate, itaconic anhydride and monoammonium aspartate, maleic acid and ammonium carbonate, citraconic acid and ammonium carbonate, itaconic acid and ammonium carbonate, maleic acid and asparagine, citraconic acid and asparagine, itaconic acid and asparagine, maleic acid and ammonium maleamate, citraconic acid and ammonium maleamate, itaconic acid and ammonium maleamate, maleic acid and monoammonium aspartate, citraconic acid and monoammonium aspartate, itaconic acid and monoammonium aspartate, malic acid and ammonium carbonate, malic acid and asparagine, malic acid and ammonium maleamate, malic acid and monoammonium aspartate, fumaric acid and ammonium carbonate, fumaric acid and asparagine, fumaric acid and ammonium maleamate, fumaric acid and monoammonium aspartate, maleic anhydride and monoammonium maleate, maleic anhydride and diammonium maleate, citraconic anhydride and monoammonium maleate, citraconic acid and diammonium maleate, itaconic anhydride and monoammonium maleate, itaconic anhydride and diammonium maleamate, maleic acid and monoammonium maleate, maleic acid and diammonium maleate, fumaric acid and monoammonium maleate, fumaric acid and diammonium maleate, malic acid and monoammonium maleate, malic acid and diammonium maleate, itaconic acid and monoammonium maleate, itaconic acid and diammonium maleate, citraconic acid and monoammonium maleate or citraconic acid and diammonium maleate.9. The method in accordance with claim 6 wherein said functional group-containing monomer is selected from the group consisting of polybasic carboxylic acids and anhydrides thereof, fatty acids, monobasic polyhydroxycarboxylic acids, alcohols, amines, diamines, triamines, polyamines, alkoxylated alcohols, alkoxylated amines, alkoxylated diamines, alkoxylated triamines, amino sugars, carbohydrates, sugar carboxylic acids, amino acids, non-protein forming aminocarboxylic acids, lactams, lactones, diols, triols, polyols, unsaturated dicarboxylic acids, tricarboxylic acids and unsaturated monocarboxylic acids.10. The method in accordance with claim 6 wherein said functional group-containing monomer comprises at least one of the following compounds: lactic acid, citric acid, glycolic acid, malic acid, tartaric acid, succinic acid, adipic acid, butanetetracarboxylic acid, gluconic acid, glucuronic acid, glucaric acid, aconitic acid, sulfosuccinic acid, phosphinicosuccinic acid, phosphonosuccinic acid, iminodiacetic acid, nitrilotriacetic acid, stearic acid, palmitic acid, cyclohexanedicarboxylic acid, cyclohexanedicarboxylic anhydride, terephthalic acid, phthalic acid, phthalic anhydride, crotonic acid, sorbitol, glycerol, glucose, fructose, sucrose, maltose, glycine, alanine, glutamic acid, lysine, serine, threonine, cystine, cysteine, ethylenediamine, diethylenetriamine, triethylenetetraamine, polyamines, 1,6-diaminohexane, octadecylamine, glucosamine, alkoxylated amines, alkoxylated diamines, alkoxylated triamines, 6-aminocaproic acid, 4-aminobutyric acid, diaminocyclohexane, urea, melamine, carbohydrazide, hydrazine, ascorbic acid, isoascorbic acid, sorbic acid, maleuric acid, cyanuric acid, alkyldiamines, alkyltriamines, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, alkylmaleic acids, alkenylsuccinic acids, alkenylsuccinic anhydrides and methylenemalonic

acid.1. The method in accordance with claim 6 wherein said hydrolysis is carried out with a base selected from the group consisting of alkali metal hydroxide, alkaline earth metal hydroxide and ammonium hydroxide.12. The method in accordance with claim 6 wherein said temperature is in the range of from about 100°C to about 350°C13. The method in accordance with claim 6 wherein said temperature is at least 120°C