METHOD FOR PRODUCING POLYASPARTIC ACID BY MEANS OF A PRECONDENSATE

Abstract

Compositions including polyaspartic acid and methods for preparing polyaspartic acid using a precondensate of aspartic acid and polyaspartimide are provided herein. Uses for such compositions are also described.

Claims

1. A method for preparing polyaspartic acid, comprising the following steps: (a) precondensing aspartic acid at a temperature of 100 to 250° C. up to a degree of conversion of at least 2% to obtain a precondensate; (b) adding 1 to 25 mol % of an acidic catalyst to the precondensate to form a reaction mixture; (c) polycondensing the reaction mixture at 170 to 250° C. to obtain polycondensates; and (d) hydrolyzing the polycondensates with addition of a base.

2. A method for preparing polyaspartic acid, comprising the following steps: (i) contacting a mixture of: aspartic acid and 3 to 35 wt % polyaspartimide with 1 to 25 mol % of an acidic catalyst in a reactor; (ii) polycondensing the mixture at a temperature of 170 to 250° C. to obtain polycondensates; and (iii) hydrolyzing the polycondensates according to (ii) with addition of a base to obtain polyaspartic acid.

3. The method according to claim 1, wherein step (b) comprises adding 3 to 15 mol % of the acidic catalyst.

4. The method according to claim 1, wherein the acidic catalyst is methanesulfonic acid.

5. The method according to claim 1, wherein step (c) comprises polycondensing the reaction mixture at 200 to 250° C.

6. The method according to claim 1, wherein the base is selected from a group consisting of aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, calcium hydroxide, barium hydroxide, sodium carbonate, potassium carbonate, ammonia, and ammonium hydroxide.

7. The method according to claim 1, further comprising acidifying salts of the polyaspartic acid.

8. The method according to claim 1, wherein step (a) comprises precondensing the aspartic acid up to a degree of conversion of at least 5%.

9. The method according to claim 1, wherein step (a) comprises precondensing the aspartic acid at the temperature of 220 to 250° C.

10. The method according to claim 2, wherein the mixture after step (i) comprises 5 to 25 wt % polyaspartimide.

11. A composition comprising a polyaspartic acid obtained using a method selected from a group consisting of: (A) precondensing aspartic acid at a temperature of 100 to 250° C. up to a degree of conversion of at least 2% to obtain a precondensate, adding 1 to 25 mol % of an acidic catalyst to the precondensate to form a reaction mixture, polycondensing the reaction mixture at 170 to 250° C. to obtain polycondensates, and hydrolyzing the polycondensates with addition of a base; and (B) contacting a mixture of aspartic acid and 3 to 35 wt % polyaspartimide with 1 to 25 mol % of an acidic catalyst in a reactor, polycondensing the mixture at a temperature of 170 to 250° C. to obtain polycondensates, and hydrolyzing the polycondensates with addition of a base to obtain polyaspartic acid.

12. (canceled)

13. (canceled)

14. (canceled)

15. (canceled)

16. The method according to claim 7, wherein acidifying the salts comprises acidifying the salts with one of a mineral acid and an acidic ion exchanger.

17. The method according to claim 1 further comprising cooling the precondensate prior to step (b).

18. The method according to claim 2, wherein step (i) comprises adding 3 to 15 mol % of the acidic catalyst.

19. The method according to claim 2, wherein the acidic catalyst is methanesulfonic acid.

20. The method according to claim 2, wherein step (ii) comprises polycondensing the mixture at 200 to 250° C.

21. The method according to claim 2, wherein the base is selected from a group consisting of aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, calcium hydroxide, barium hydroxide, sodium carbonate, potassium carbonate, ammonia, and ammonium hydroxide.

22. The method according to claim 2 further comprising acidifying salts of the polyaspartic acid.

23. The method according to claim 22, wherein acidifying the salts comprises acidifying the salts with one of a mineral acid and an acidic ion exchanger.

Description

EXAMPLES

Polymer C1 (Comparative Example): Polycondensation of L-Aspartic Acid in the Presence of 5 Mol % Methanesulfonic Acid in a Glass Reactor

[0133] 133.10 g of L-aspartic acid, 30 g of water and 4.81 g of methanesulfonic acid were initially charged in a 2 l capacity glass reactor equipped with stirrer and temperature sensor. The reaction mixture was heated to the condensation temperature of 210° C. to 220° C. with stirring under a gentle stream of nitrogen with simultaneous removal of water by distillation. After 15 minutes, a highly viscous paste formed which could no longer be stirred. Within a further 15 minutes, the reaction product had solidified to a solid mass. The reactor was cooled to room temperature. The caked reaction mixture was removed from the reactor with a spatula and comminuted to a powder using a pestle and mortar. The comminuted reaction mixture was again placed in the reactor, heated to the condensation temperature of 210° C. to 220° C. with stirring under a gentle stream of nitrogen and condensed at this temperature for a further 5.5 hours with simultaneous removal of water by distillation. In order to prepare the aqueous sodium salt solution of the polyaspartic acid, 100 g of the cooled reaction product were dispersed in 100 g of water, the mixture was heated to 70° C. and sufficient 50% aqueous sodium hydroxide solution was added at this temperature that the pH was in the range of 7 to 9. The powder dispersed in water dissolved gradually and a clear aqueous sodium salt solution of polyaspartic acid was obtained. The weight-average molecular weight Mw was 7700 g/mol.

C2: Polycondensation of Precondensed L-Aspartic Acid in the Presence of 5 Mol % Methanesulfonic Acid in a Glass Reactor

[0134] 266.20 g of L-aspartic acid were initially charged in a 2 l capacity glass reactor equipped with stirrer and temperature sensor. The reactor content was heated to a condensation temperature of 210° C. to 220° C. for 15 min with stirring under a gentle stream of nitrogen with simultaneous removal of water by distillation and subsequently cooled again to room temperature. The degree of conversion of L-aspartic acid after this precondensation step was 20% (measured as described below). A solution of 9.61 g of methanesulfonic acid was then added to 60 g of water with stirring. The moist pulverulent reaction mixture was heated to the condensation temperature of 210° C. to 220° C. with stirring under a gentle stream of nitrogen with simultaneous removal of water by distillation for 5.5 h, without a hard reaction mixture being formed which could no longer be stirred. Manual commination with the aid of a spatula or mortar was not required. Hydrolysis of the resulting end product to give the aqueous sodium salt solution of polyaspartic acid was carried out as described in C1. The weight-average molecular weight Mw was 7200 g/mol.

C3 (Comparative Example): Polycondensation of L-Asp in the Presence of 5 Mol % Methanesulfonic Acid in a 0.7 L LIST Discotherm B Reactor

[0135] 266.20 g of L-aspartic acid, 60 g of water and 9.62 g of methanesulfonic acid were initially charged in a 0.7 l LIST Discotherm B reactor. The reactor content was heated to the condensation temperature of 230° C. with stirring at 20 revolutions per minute under a gentle stream of nitrogen with simultaneous removal of water by distillation. After 15 minutes a highly viscous, sticky paste was formed and a high torque increase was observed. After a further 15 minutes, the reaction product solidified to a solid mass and the stirrer shaft finally came to a standstill. After cooling to room temperature, the caked reaction mixture was removed from the reactor with the aid of a spatula and comminuted to a powder using a pestle and mortar. The comminuted reaction mixture was again placed in the reactor, heated to the condensation temperature of 230° C. with stirring under a gentle stream of nitrogen and condensed at this temperature for a further 5.5 hours with simultaneous removal of water by distillation. Hydrolysis of the resulting end product to give the aqueous sodium salt solution of polyaspartic acid was carried out as described in C1. The weight-average molecular weight Mw was 7700 g/mol.

C4: Polycondensation of L-Asp in the Presence of 5 Mol % Methanesulfonic Acid and 10 wt % Polyaspartimide in a Discotherm B Reactor

[0136] 239.4 g of L-aspartic acid, 23.9 g of polyaspartimide T (prepared as in C5), 54 g of water and 8.7 g of methanesulfonic acid were initially charged in a 0.7 l LIST Discotherm B reactor. The reactor content was heated to the condensation temperature of 230° C. with stirring at 20 revolutions per minute under a gentle stream of nitrogen with simultaneous removal of water by distillation for 6 h. Caking of the reaction mixture and thus standstill of the apparatus did not occur. Manual commination with the aid of a spatula or mortar was not required. Hydrolysis of the resulting end product to give the aqueous sodium salt solution of polyaspartic acid was carried out as described in C1. The weight-average molecular weight Mw was 7200 g/mol.

C5 (Comparative Example): Preparation of Polyaspartimide-T

[0137] 133.10 g of L-aspartic acid were polycondensed to a constant weight at a temperature of 220-240° C. in a rotary evaporator. The weight-average molecular weight Mw was 5400 g/mol.

C6: Polycondensation of Precondensed L-Aspartic Acid in the Presence of 5 Mol % Methanesulfonic Acid in a Glass Reactor

[0138] 266.20 g of L-aspartic acid were initially charged in a 2 l capacity glass reactor equipped with stirrer and temperature sensor. The reactor content was heated to a condensation temperature of 210° C. to 220° C. for 30 min with stirring under a gentle stream of nitrogen with simultaneous removal of water by distillation and subsequently cooled again to room temperature. The degree of conversion of L-aspartic acid after this precondensation step was 36% (measured as described below). A solution of 9.61 g of methanesulfonic acid was then added to 60 g of water with stirring. The moist pulverulent reaction mixture was heated to the condensation temperature of 210° C. to 220° C. with stirring under a gentle stream of nitrogen and polycondensed at this temperature for 5.5 h with simultaneous removal of water by distillation, without a hard reaction mixture being formed which could no longer be stirred. Manual comminution with the aid of a spatula or mortar was not required. Hydrolysis of the resulting end product to give the aqueous sodium salt solution of polyaspartic acid was carried out as described in C1. The weight-average molecular weight Mw was 7100 g/mol.

C7: Polycondensation of Precondensed L-Aspartic Acid in the Presence of 5 Mol % Methanesulfonic Acid in a Glass Reactor

[0139] 266.20 g of L-aspartic acid were initially charged in a 2 l capacity glass reactor equipped with stirrer and temperature sensor. The reactor content was heated to a condensation temperature of 210° C. to 220° C. for 5 min with stirring under a gentle stream of nitrogen with simultaneous removal of water by distillation and subsequently cooled again to room temperature. The degree of conversion of L-aspartic acid after this precondensation step was 12% (measured as described below). A solution of 9.61 g of methanesulfonic acid was then added to 60 g of water with stirring. The moist pulverulent reaction mixture was heated to the condensation temperature of 210° C. to 220° C. with stirring under a gentle stream of nitrogen and polycondensed at this temperature for 5.5 h with simultaneous removal of water by distillation, without a hard reaction mixture being formed which could no longer be stirred. Manual comminution with the aid of a spatula or mortar was not required. Hydrolysis of the resulting end product to give the aqueous sodium salt solution of polyaspartic acid was carried out as described in C1. The weight-average molecular weight Mw was 7600 g/mol.

C8: Polycondensation of L-Aspartic Acid in the Presence of 5 Mol % Methanesulfonic Acid and 20 wt % Polyaspartimide in a Glass Reactor

[0140] 266.2 g of L-aspartic acid, 53.2 g of polyaspartimide T (prepared as in C5), 60 g of water and 9.6 g of methanesulfonic acid were initially charged in a 2 l capacity glass reactor equipped with stirrer and temperature sensor. The reactor content was heated to the condensation temperature of 210° C. to 220° C. with stirring under a gentle stream of nitrogen and polycondensed at this temperature for 6 h with simultaneous removal of water by distillation, without a hard reaction mixture being formed which could no longer be stirred. Manual comminution with the aid of a spatula or mortar was not required. Hydrolysis of the resulting end product to give the aqueous sodium salt solution of polyaspartic acid was carried out as described in C1. The weight-average molecular weight Mw was 7000 g/mol.

C9: Polycondensation of L-Aspartic Acid in the Presence of 5 Mol % Methanesulfonic Acid and 5 wt % Polyaspartimide in a Glass Reactor

[0141] 266.2 g of L-aspartic acid, 13.3 g of polyaspartimide T (prepared as in C5), 60 g of water and 9.6 g of methanesulfonic acid were initially charged in a 2 l capacity glass reactor equipped with stirrer and temperature sensor. The reactor content was heated to the condensation temperature of 210° C. to 220° C. with stirring under a gentle stream of nitrogen and polycondensed at this temperature for 6 h with simultaneous removal of water by distillation, without a hard reaction mixture being formed which could no longer be stirred. Manual comminution with the aid of a spatula or mortar was not required. Hydrolysis of the resulting end product to give the aqueous sodium salt solution of polyaspartic acid was carried out as described in C1. The weight-average molecular weight Mw was 7500 g/mol.

C10: Polycondensation of L-Aspartic Acid in the Presence of 7.5 Mol % Methanesulfonic Acid and 30 wt % Polyaspartimide in a Glass Reactor

[0142] 199.7 g of L-aspartic acid, 59.9 g of polyaspartimide T (prepared as in C5), 60 g of water and 10.8 g of methanesulfonic acid were initially charged in a 2 l capacity glass reactor equipped with stirrer and temperature sensor. The reactor content was heated to the condensation temperature of 210° C. to 220° C. with stirring under a gentle stream of nitrogen and polycondensed at this temperature for 6 h with simultaneous removal of water by distillation, without a hard reaction mixture being formed which could no longer be stirred. Manual comminution with the aid of a spatula or mortar was not required. Hydrolysis of the resulting end product to give the aqueous sodium salt solution of polyaspartic acid was carried out as described in C1. The weight-average molecular weight Mw was 8000 g/mol.

C11: Polycondensation of Precondensed L-Aspartic Acid in the Presence of 5 Mol % Phosphoric Acid in a Glass Reactor

[0143] 266.20 g of L-aspartic acid were initially charged in a 2 l capacity glass reactor equipped with stirrer and temperature sensor. The reactor content was heated to a condensation temperature of 210° C. to 220° C. for 15 min with stirring under a gentle stream of nitrogen with simultaneous removal of water by distillation and subsequently cooled again to room temperature. The degree of conversion of L-aspartic acid after this precondensation step was 20% (measured as described below). A solution of 11.53 g of phosphoric acid (85%) was then added to 60 g of water with stirring. The moist pulverulent reaction mixture was heated to the condensation temperature of 210° C. to 220° C. with stirring under a gentle stream of nitrogen and polycondensed at this temperature for 5.5 h with simultaneous removal of water by distillation, without a hard reaction mixture being formed which could no longer be stirred. Manual comminution with the aid of a spatula or mortar was not required. Hydrolysis of the resulting end product to give the aqueous sodium salt solution of polyaspartic acid was carried out as described in C1. The weight-average molecular weight Mw was 7800 g/mol.

C12: Polycondensation of L-Aspartic Acid in the Presence of 5 Mol % Phosphoric Acid and 10 wt % Polyaspartimide in a Glass Reactor

[0144] 266.2 g of L-aspartic acid, 26.6 g of polyaspartimide T (prepared as in C5), 60 g of water and 11.53 g of phosphoric acid (85%) were initially charged in a 2 l capacity glass reactor equipped with stirrer and temperature sensor. The reactor content was heated to the condensation temperature of 210° C. to 220° C. with stirring under a gentle stream of nitrogen and polycondensed at this temperature for 6 h with simultaneous removal of water by distillation, without a hard reaction mixture being formed which could no longer be stirred. Manual comminution with the aid of a spatula or mortar was not required. Hydrolysis of the resulting end product to give the aqueous sodium salt solution of polyaspartic acid was carried out as described in C1. The weight-average molecular weight Mw was 8200 g/mol.

Determination of the Molecular Weight (Mw and Mn)

[0145] The weight-average or number-average molecular weight (Mw and Mn) of the examples was determined by GPC (gel permeation chromatography) under the following conditions:

TABLE-US-00001 Column PSS SUPREMA analytical linear M (Material: polyhydroxymethacrylate copolymer network Length: 300 mm, diameter 8 mm, particle size 10μ) Eluent 0.08 mol/L TRIS buffer pH 7.0 in dist. water + 0.15 mol/L NaCl + 0.01 mol/L NaN.sub.3. Column 35° C. temperature Flow rate 0.8 mL/min Injection 100 μL Concentration 1.5 mg/mL Detector DRI Agilent 1100UV GAT-LCD 503 (260 nm)

[0146] To determine the molecular weight, a small amount of the polyaspartimide formed after the polycondensation step was taken and washed repeatedly with water in order to remove the methanesulfonic acid used. The washed powder was then hydrolyzed as described with aqueous sodium hydroxide solution (i.e. the washed powder was dispersed in water, the mixture was heated to 70° C. and sufficient 50% aqueous sodium hydroxide solution was added at this temperature so that the pH was in the range of 7-9. The powder dispersed in water dissolved gradually and a clear aqueous sodium salt solution of polyaspartic acid was obtained. Sample solutions were filtered through Sartorius Minisart RC 25 (0.2 μm). Calibration was performed using narrowly distributed Na-PAA standards from Polymer Standard Service with molecular weights of M=1250 g/mol to M=130 500 g/mol. In addition, Na-acrylate having a molecular weight of M=96 and a PEG standard with M=620, which is synonymous with Na-PAA M=150, was used. The values outside of this elution range were extrapolated. The evaluation limit was 122 g/mol.

Determination of the Degree of Conversion:

[0147] To determine the degree of conversion, the proportion of unreacted monomeric aspartic acid in the precondensate was determined. For this purpose, 100 mg of the precondensate were weighed into a 50 ml glass ampoule, 9.9 mL of 1N HCl were added and the mixture was stirred at 350 rpm for 3 hours. The sample was then filtered through a Spartan 30 mm/0.45 μm RC syringe filter (GE Healthcare) and diluted 1:10 (v/v) with water. The aspartic acid content of this diluted solution was determined by high-performance liquid chromatography (HPLC).

[0148] Example of C2: An aspartic acid content of 80 mg was found in 100 mg of precondensate. The degree of conversion C was then calculated as follows:

C=(100 mg−80 mg)/100 mg=20%.

TABLE-US-00002 Apparatus Agilent 1290 Infinity Series with diode array detector Separating SIELC Primesep 100, 5 μm 100 A (3.2 × 100 mm) column: Temperature 25° C. Injection 5 μL volume: Flow rate 1.0 mL/min Detection 205 nm Eluent Eluent A: water/acetonitrile 7/3 v/v Eluent B: water/acetonitrile/phosphoric acid 700/300/5 v/v/v Gradient: Run time (min) 0 5 6 15 Eluent A (vol %) 95 87.5 100 100 Eluent B (vol %) 5 12.5 0 0 Calibration Two weighings of the L-aspartic acid reference substance (Merck Millipore) were dissolved in 2 mL of 1M HCl and made up with water. The two stock solutions were further diluted to form 4 further calibration solutions. The concentrations of the 6 calibration solutions prepared were selected so that the content of the sample is within the range of the calibration solutions.