Process for preparing polysuccinimides from aspartic acid

Abstract: A process is provided for preparing polysuccinimides by forming a polymerization mixture comprising poly(alkylene glycol), aspartic acid and, optionally, one or more other amino acid; heating the mixture to an elevated temperature; and maintaining the mixture at the elevated temperature to form polysuccinimides. Poly(amino acids) can be produced by hydrolyzing the polysuccinimides.

Description: The present invention relates to a process for preparing polysuccinimides by the polycondensation of aspartic acid, optionally in the presence of one or more other amino acids. Several methods are known for obtaining polysuccinimides which, when hydrolyzed to form the corresponding poly(amino acid), are useful as absorbents, hard-surface cleaners, water-treatment additives for boiler waters and cooling towers and as a detergent additives acting therein as a builder, anti-filming agent, dispersant, sequestering agent and encrustation inhibitor. However, all of the previously known methods for preparing polysuccinimides suffer from the drawbacks of excessively long process times, expensive starting materials, or require the handling of solid materials which poses many difficulties in a manufacturing environment. United States Patent 5,057,597 to Koskan discloses a solid-phase process for preparing polysuccinimide by fluidizing an amino acid with agitation in a nitrogen atmosphere at a temperature of at least 180°C for three to six hours. The resultant polysuccinimide is then hydrolyzed to form a poly(amino acid). United States Patent 4,839,461 to Boehmke, et al. discloses a process for preparing poly(aspartic acid) by combining maleic acid or maleic anhydride and an ammonia solution in a molar ratio of 1:1-1.5. The mixture is then heated to 120°-150°C. and the resulting solution of ammonium salt and maleic acid is evaporated, leaving a crystal mash. The crystal mash is then melted, during which time the waters of condensation and crystallization distill off. A porous mass of poly(aspartic acid) results. The entire process requires six to eight hours to complete. Japanese Patent 52-008873 B assigned to Ajinomoto, discloses a solvent-based process for preparing poly(aspartic acid). The process described therein utilizes a hydrohalic acid salt of aspartic acid anhydride in one or more organic solvents. The solvents disclosed are organic acids such as propionic acid, butyric acid, and valeric acid; alcohols such as tert-butyl alcohol and tert-amyl alcohol, esters such as ethyl acetate and butyl acetate; ketones such as methyl isobutyl ketone and cyclohexanol; ethers such as tetrahydrofuran and dioxane; halogenated hydrocarbons such as ethylene dichloride and dichlorobenzene; hydrocarbons such as toluene, xylene and decalin; and amides such as dimethylformamide. These solvents may impart additional hazards, expense, odor, toxicity and removal steps to obtain the final product. These prior art methods for the synthesis of polysuccinimides and poly(amino acids) are time consuming, complex and/or use large volumes of volatile organic solvents or inert gases which have to be removed. In accordance with the present invention we have developed a process for producing polysuccinimides avoids a final product separation step. This process comprises forming a reaction mixture containing aspartic acid and, optionally, one or more other amino acids, in admixture with a poly(alkylene glycol), optionally terminated at one or both ends by carboxylic acid groups, alkyl groups of from 1 to 30 carbon atoms, or amino or alkylamino groups in which the alkyl group contains from 1 to 10 carbon atoms, or any combination thereof, and having a molecular weight in the range 300 to 30,000, and heating the reaction mixture to an elevated temperature to effect the polycondensation of the aspartic acid, and other amino acids, if present, and thereby to form a solution of the product polysuccinimide in the poly(alkylene glycol). The poly(alkylene glycols) useful in the present invention are those which are fluid at the reaction temperature and include poly(tetramethylene glycol), poly(ethylene glycol), and poly(propylene glycol). Preferably the poly(alkylene glycol) is selected from poly(ethylene glycol), methyl-terminated poly(ethylene glycol), and poly(propylene glycol). More preferably the poly(alkylene glycol) is poly(ethylene glycol). The molecular weight of the poly(alkylene glycol) is preferably from about 300 to about 20,000, and most preferably from about 1,000 to about 15,000. The poly(alkylene glycol) is preferably added to the polymerization mixture at a level of from 2 to about 90 percent by weight relative to the aspartic acid, more preferably from about 20 to about 90, and most preferably from about 30 to about 85 percent by weight relative to the aspartic acid. When used, the one or more other amino acid may, for example, be present in an amount of up to 80 percent by weight (based on the weight of aspartic acid). Preferably, when used, the one or more other amino acid is present at a level of from 5 to about 70 percent by weight based on the weight of aspartic acid. Most preferably, when used the one or more other amino acid is present at a level of from about 10 to about 60 percent by weight based on the weight of aspartic acid. Preferred other amino acids are alanine, glycine, lysine, asparagine, and glutamic acid. More preferably the one or more other amino acid is alanine. The atmosphere of the polymerization is preferably substantially free of oxygen, including the oxygen present in air. An atmosphere substantially free of oxygen is preferred since, at the temperatures needed for the polycondensation reaction to occur, the poly(alkylene glycols) will oxidize, discolor or degrade. Suitable means for achieving an atmosphere substantially free of oxygen includes blanketing, sweeping or bubbling the reactor with an inert gas, preferably nitrogen, or conducting the polymerization at reduced pressure. The elevated temperature for the process of the present invention must be high enough to provide polycondensation. The preferred temperature will vary with the operating conditions. For example, the preferred temperature may increase as the ratio of aspartic acid to poly(alkylene glycol) increases, or as the pressure at which the polycondensation is conducted increases. However, the preferred temperature may decrease, for example, in the presence of azeotropic solvents. In general, the preferred elevated temperature is from about 120 to about 300°C. The polysuccinimides are formed by a condensation reaction. It is therefore desirable to remove the by-products, such as water or alcohol, which are liberated in order to drive the reaction toward completion. Suitable means of removing water include addition of one or more azeotropic solvents to the polymerization mixture such as toluene, xylene, or tetralin, and removing the azeotropic distillate from the polymerization mixture. Another means of removing the water is by adding to the polymerization mixture one or more drying agents such as aluminosilicates. Another means of removing the water is by bubbling an inert gas through the polymerization mixture, or sweeping an inert gas over the surface of the polymerization mixture. Another means of removing the water is by conducting the polymerization under reduced pressure. The polymerization can be conducted as a batch or continuous process. Suitable reactors include batch tank reactors, continuous stirred tank reactors, plug-flow reactors, pipe reactors and scraped-wall reactors. The temperature of the reaction must be sufficient to effect the condensation reaction. This temperature will vary according to whether an azeotropic solvent is employed and the pressure at which the polymerization is conducted which can be subatmospheric, atmospheric or supraatmospheric. The products which result from the process of the present invention are solutions, suspensions or dispersions of polysuccinimides in poly(alkylene glycol). Poly(alkylene glycols) are useful in many of the applications for the poly(succinimides) such as, for example, in detergent formulations. Thus, there is no need for a separation step to isolate the poly(succinimides) from the poly(alkylene glycol) when the product is used in a detergent application. If desired, the poly(succinimides) can be hydrolyzed, for example by any conventional means, to form the corresponding poly(amino acids), such as poly(aspartic acid). A preferred means of hydrolysis is by contacting the product with an aqueous alkaline solution such as sodium hydroxide or sodium carbonate. The polysuccinimides and poly(amino acids) prepared according to the process of the present invention may, for example, be used as absorbents, hard-surface cleaners, water-treatment additives for boiler waters and cooling towers, and as detergent additives. The following Examples are presented to illustrate certain embodiments of the present invention. EXAMPLE 1 Preparation of Poly(succinimide) To a 100 milliliter three-neck round bottom flask equipped with a magnetic stirring bar, Dewar condenser, and an inlet and outlet for nitrogen was added 5.0 grams of L-aspartic acid and 5.0 grams of poly(ethylene glycol), methyl ether having a molecular weight of 350. The flask was continuously swept with nitrogen and immersed in an oil bath maintained at 200°C for 15 hours then cooled to room temperature. Analysis by 1 H NMR spectroscopy indicated that no aspartic acid remained. The polysuccinimide was hydrolzed with dilute aqueous sodium carbonate to form poly(aspartic acid). Analysis by 1 H NMR spectroscopy confirmed that poly(aspartic acid) was formed.

Claims: A process for the preparation of a polysuccinimide, which comprises forming a reaction mixture containing aspartic acid, an organic solvent and, optionally, one or more other other amino acids; heating the reaction mixture to an elevated temperature; and maintaining the mixture at the elevated temperature, thereby to produce a solution, suspension or dispersion of the product polysuccinimide in said solvent, characterised in that the solvent used is a poly(alkyene glycol), optionally terminated at one or both ends by a terminal group selected from carboxylic acid, alkyl of from 1 to 30 carbon atoms, amino or alkylamino in which the alkyl group contains from 1 to 10 carbon atoms, said poly(alkylene glycol) having a molecular weight in the range 300 to 30,000. A process as claimed in claim 1, wherein the poly(alkylene glycol) solvent has a molecular weight in the range 300 to 20,000, preferably in the range 1000 to 15,000. A process as claimed in claim 1 for 2, wherein the solvent is selected from: poly(tetramethylene glycol), poly(ethylene glycol), poly(propylene glycol) and methyl-terminated poly(ethylene glycol). A process as claimed in claim 1, 2 or 3, wherein the poly(alkylene glycol) solvent is present in the reaction mixture in an amount of from 2 to 90% by weight relative to the weight of aspartic acid, preferably 20 to 90%. A process as claimed in any one of the preceding claims, wherein the reaction mixture contains up to 80% by weight of one or more other amino acids, based on the weight of aspartic acid, preferably from 5 to 70%. A process as claimed in claim 5, wherein the reaction mixture contains one or more other amino acids selected from alanine, glycine, lysine, asparagine, and glutamic acid. A process as claimed in any one of the preceding claims, wherein the reaction mixture is maintained at said elevated temperature in an atmosphere substantially free of oxygen. A process according to any one of the preceding claims, wherein the reaction mixture is heated to and maintained at a temperature in the range 120 to 300°C A process as claimed in any one of the preceding claims, which further comprises the step of hydrolyzing the product polysuccinimide to form the corresponding poly(amino acid).

Inventors: PAIK YI HYON, SIMON ETHAN SCOTT, SWIFT GRAHAM, PAIK, YI HYON, SIMON, ETHAN SCOTT, SWIFT, GRAHAM
Applicants: ROHM & HAAS, ROHM AND HAAS COMPANY
Application year: 1993
Main classification: C08G69
IPC codes: C08G63, C08G69, C08G65, C08G73