JP2021054977A - Method for producing polyimide succinate, and method for producing polyaspartate - Google Patents

Abstract

To provide a method for producing polyimide succinate that achieves a reduced content of maleic acid while suppressing the hydrolysis of polyimide succinate.SOLUTION: A method for producing polyimide succinate includes a step of heating a dispersion with crude synthetic polyimide succinate dispersed in a solvent at 35°C or higher and 85°C or lower.SELECTED DRAWING: None

Description

The present disclosure relates to a method for producing an imide polysuccinate and a method for producing a polyaspartate.

The polysuccinate imide is a suitable precursor or intermediate in the production of polyamino acid derivatives such as polyaspartic acid.
It is known that polysuccinate imide is treated with an organic acid for the purpose of producing a polyaspartic acid derivative having excellent biodegradability (see, for example, Patent Document 1).
Further, for example, in Patent Document 2, a non-fluid bed type that can be stirred in a method of obtaining succinimide by heating and polycondensing a product obtained from maleic acid and ammonia, maleamic acid and / or aspartic acid under reduced pressure. A method for producing a porris succinimide, which comprises using a reactor, is disclosed.
Further, for example, in Patent Document 3, (1) a step of heating aspartic acid in a water-insoluble solvent to obtain poriscinimide (2) a step of adding an alkaline aqueous solution and hydrolyzing to obtain polyaspartate (3) polyaspartic acid. Disclosure of a method for producing a polyaspartate, which comprises a step of separating the aqueous acid salt solution layer from a water-insoluble solvent layer and (4) a step of treating the polyaspartate aqueous solution with an inorganic or organic powder. Has been done.

Japanese Unexamined Patent Publication No. 8-302009 Japanese Unexamined Patent Publication No. 9-176313 Japanese Unexamined Patent Publication No. 8-059821

The polysuccinate imide can be obtained, for example, by polycondensing aspartic acid. Here, the obtained polysuccinic acid imide contains maleic acid, maleic anhydride, fumaric acid, succinic acid and the like as impurities. However, when the polysuccinate imide was washed with water to remove impurities, the polysuccinate imide was sometimes hydrolyzed more than necessary.

An object of one aspect of the present disclosure is to provide a method for producing an imide polysuccinate in which the content of maleic acid is reduced while suppressing the hydrolysis of the imide polysuccinate.
An object of another aspect of the present disclosure is to provide a method for producing a polyaspartate in which the content of maleic acid is reduced while suppressing the hydrolysis of the polysuccinate imide.

Means for solving the above problems include the following aspects.
<1>
A method for producing an imide polysuccinate, which comprises a step of heat-treating a dispersion liquid in which a crude synthetic polysuccinate imide is dispersed in a solvent at a temperature of 35 ° C. or higher and 85 ° C. or lower.
<2>
The method for producing an imide of polysuccinate according to <1>, wherein the crude synthetic polysuccinate imide is obtained by solid phase polymerization.
<3>
The method for producing an imide polysuccinate according to <1> or <2>, wherein the solvent is water or a mixed solvent of water and a water-soluble organic solvent.
<4>
The polysuccinic acid according to any one of <1> to <3>, further comprising a step of extracting a solid content containing an imide polysuccinate from the dispersion liquid after the heat treatment and a step of washing the solid content. Method for producing imide.
<5>
An alkaline aqueous solution is added to the polysuccinate imide obtained by the method for producing a polysuccinate imide according to any one of <1> to <4> to hydrolyze the polysuccinate imide to obtain a polyaspartate. A method for producing polyaspartate, which comprises a step.

According to one aspect of the present disclosure, there is provided a method for producing an imide polysuccinate in which the content of maleic acid is reduced while suppressing the hydrolysis of the imide polysuccinate.
According to another aspect of the present disclosure, there is provided a method for producing a polyaspartate in which the content of maleic acid is reduced while suppressing the hydrolysis of the polysuccinate imide.

The contents of the present disclosure will be described in detail below. The description of the constituent elements described below may be based on the representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments.
In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in another stepwise description. .. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

In addition, the term "process" in the present specification is not limited to an independent process, and even if it cannot be clearly distinguished from other processes, the term "process" will be used as long as the intended purpose of the process is achieved. included.
Further, in the present disclosure, "% by mass" and "% by weight" are synonymous, and "parts by mass" and "parts by weight" are synonymous.
Further, in the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

Hereinafter, the method for producing polyaspartate according to the present disclosure and the method for producing polyaspartate according to the present disclosure will be described in detail together with the method for producing polysuccinate imide according to the present disclosure.

[Method for producing imide polysuccinate]
The method for producing an imide polysuccinate of the present disclosure includes a step of heat-treating a dispersion liquid in which a crude synthetic polysuccinimide is dispersed in a solvent at a temperature of 35 ° C. or higher and 85 ° C. or lower (hereinafter, also referred to as “first step”). Including. The "crude synthetic polysuccinate imide" refers to the polysuccinate imide prepared before the first step.
According to the method for producing an imide polysuccinate of the present disclosure, the content of maleic acid is reduced while suppressing the hydrolysis of the imide polysuccinate.
The reason for this effect is not clear, but it is presumed as follows.

It is considered that the hydrolysis of the polysuccinate imide can be suppressed by setting the temperature of the solvent for treating the crude synthetic polysuccinate imide in the first step to 35 ° C. or higher and 85 ° C. or lower. Further, by performing this treatment, the maleic acid contained in the polysuccinate imide becomes easily eluted in the solvent, and the maleic anhydride contained in the polysuccinate imide is changed to maleic acid, which is also the maleic acid. Is also considered to be in a state where it easily elutes in the solvent. Therefore, the content of maleic acid in the polysuccinate imide after the above treatment is reduced.
Further, by the same action, the polysuccinic acid imide after the first step can also reduce the content of impurities other than maleic acid, that is, the content of maleic anhydride, fumaric acid, succinic acid and the like.

The polysuccinic acid imide used in the first step (that is, “crude synthetic polysuccinate imide”) is not particularly limited, and may be prepared by any conventionally known method.
For example, by solid phase polymerization, solubilized solvent polymerization, insolubilizing solvent polymerization, or a method of thermally polymerizing an ammonium salt and / or amide of at least one acid selected from the group consisting of maleic acid, fumaric acid, and malic acid. It can be mentioned that it is obtained, but among these, it is preferable that it is obtained by solid phase polymerization.
Examples of the solid phase polymerization include direct thermal polycondensation reaction of aspartic acid in a solid phase state, and preparing a polysuccinate imide obtained by solid phase polymerization of aspartic acid is advantageous in terms of cost.

The weight average molecular weight (Mw) of the crude polysuccinate imide is not particularly limited, but is preferably 5,000 or more and 100,000 or less, and 10,000 or more and 30,000 or less. More preferred.
The number average molecular weight (Mn) of the crude polysuccinate imide is not particularly limited, but is preferably 10,000 or more and 70,000 or less, and 12,000 or more and 15,000 or less. Is more preferable.

In the present disclosure, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the crude polysuccinate imide are the values measured by the following GPC measurement methods using gel permeation chromatography (GPC), respectively. Point to.
Analytical sample preparation: 20 mg of imide polysuccinate is weighed, 1.5 ml of 1% by mass sodium hydroxide aqueous solution is added and dissolved, and then diluted to 10 ml with 0.1 mol / l NaCl aqueous solution.
Analyzer: LC-Solution (manufactured by Shimadzu Corporation),
Detector: RID-10A (manufactured by Shimadzu Corporation),
Degasser: DGU-20A (manufactured by Shimadzu Corporation),
Pump: LC-20AD (manufactured by Shimadzu Corporation),
Autosampler: SIL-20A (manufactured by Shimadzu Corporation),
Liquid transfer unit: CTO-20A (manufactured by Shimadzu Corporation),
Column: Shodex Asahipak GF-7M HQ x 1 (manufactured by Showa Denko KK),
Guard column: Shodex Asahipak GF-1G7B (manufactured by Showa Denko KK)
Oven temperature: 45 ° C
Mobile phase: 0.1 mol / l NaCl aqueous solution Sample injection amount: 50 μl
Standard: Pullulan (Shodex STANDARD P-82 (Showa Denko Co., Ltd. standard kit)), of which P-5, P-10, P-20, P-50, P-100 and P-200. Was used to create a cubic calibration curve.
Among the obtained elution curves, Mw and Mn and the degree of polydispersity (Mw / Mn) were calculated from the main peak of the polymer.

The temperature at which solid-phase polymerization is carried out is not particularly limited, and examples thereof include 180 ° C. to 250 ° C. The time for solid-phase polymerization is preferably 200 ° C. or higher, and more preferably 220 ° C. or higher, from the viewpoint of stably producing the crude synthetic polysuccinate imide. From the same viewpoint, the temperature is preferably 240 ° C. or lower, more preferably 230 ° C. or lower.

The time for performing solid phase polymerization is not particularly limited, and examples thereof include 1 to 40 hours. The time for solid-phase polymerization is preferably 4 hours or more from the viewpoint of stably producing the crude polysuccinate imide. Further, from the same viewpoint, it is preferably 20 hours or less.

The pressure at which solid-phase polymerization is carried out is not particularly limited and may be either under negative pressure or under normal pressure. The pressure may be, for example, 0.001 MPa to 0.10 MPa. The time for solid-phase polymerization is preferably 0.01 MPa or more from the viewpoint of stably producing the crude polysuccinate imide. Further, from the same viewpoint, it is preferably 0.04 MPa or less.

For example, a crude synthetic polysuccinate imide is prepared by solid-phase polymerization of aspartic acid as shown in the reaction formula below.

Aspartic acid may be any of L-form, D-form, and DL-form. The aspartic acid is preferably L-aspartic acid, which is an L form. Aspartic acid may be a commercially available product or may be produced. When aspartic acid is produced, it may be produced by a known method. In the present disclosure, when simply describing "aspartic acid", aspartic acid may be any of L-form, D-form, and DL-form.

The inert gas for solid-phase polymerization is not particularly limited, and examples thereof include nitrogen gas, argon gas, helium gas, and carbon dioxide gas. As the inert gas, one type of gas may be used alone, or two or more types of gases may be mixed and used. Among these, from the viewpoint of stably producing the imide polysuccinate, the inert gas is preferably at least one of nitrogen gas and argon gas.

The apparatus for performing solid-phase polymerization may be provided with an apparatus for solid-phase polymerization of aspartic acid in the presence of an inert gas.

The apparatus for performing solid phase polymerization is not particularly limited, and examples thereof include a batch type or a continuous type apparatus. The batch type device and the continuous type device may be a vertical device or a horizontal device, respectively. Examples of the apparatus for performing solid-phase polymerization include an apparatus for performing a continuous operation or a batch operation. Solid phase polymerization includes, for example, hot air transfer dryers, material stirring dryers (fluidized bed dryers, etc.), material transport and static dryers, cylindrical dryers, infrared dryers, microwave dryers, and superheated steam. It may be carried out using at least one device selected from the group consisting of dryers. Further, the solid phase polymerization may be carried out using at least one device selected from the group consisting of, for example, a fluidized bed reactor, a mobile layer reactor, a fixed layer reactor, and a stir-dryer type reactor. ..

Water is also produced during solid phase polymerization. Therefore, it is preferable that the device for performing solid-phase polymerization is provided with a device for distilling off the generated water.

The method for producing an imide of polysuccinate of the present disclosure may include a step of synthesizing a crude synthetic polysuccinate imide by solid phase polymerization of aspartic acid before the first step.

In the first step, the crude polysuccinate imide is treated in a solvent. The above treatment can be performed under normal pressure, reduced pressure, or pressurized pressure.

The temperature of the solvent in the first step is preferably 35 ° C. or higher and 85 ° C. or lower, preferably 45 ° C. or higher and 75 ° C. or lower, from the viewpoint of reducing the content of maleic acid while suppressing the hydrolysis of the polysuccinate imide. It is more preferable that the temperature is 45 ° C. or higher and 65 ° C. or lower.
It is preferable to set the temperature of the solvent in the first step within the above range from the viewpoint of reducing the contents of maleic anhydride, fumaric acid, succinic acid and the like.

The treatment time for the treatment in the solvent in the first step may be 0.1 hours or more from the viewpoint of reducing the content of maleic acid while suppressing the hydrolysis of the polysuccinate imide, which is 0.5. The time is more preferably 10 hours or less, further preferably 1 hour or more and 5 hours or less, and particularly preferably 2 hours or more and 4 hours or less.
It is preferable that the treatment time for performing the treatment in the solvent in the first step is within the above range from the viewpoint of reducing the contents of maleic anhydride, fumaric acid, succinic acid and the like.

The solvent in the first step is not particularly limited as long as it is an inert compound in the above treatment, and examples thereof include water and a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, a known water-soluble organic solvent can be used, and examples thereof include a water-soluble ether solvent, a water-soluble ketone solvent, and a water-soluble alcohol solvent. In addition, water-soluble means that the target substance dissolves in water in an amount of 1% by mass or more at 25 ° C. Of these, the solvent used in the first step is preferably water.

The method for producing an imide polysuccinate of the present disclosure may further include the following steps.
The method for producing an imide polysuccinate of the present disclosure includes a step of extracting a solid content containing the imide polysuccinate from the dispersion liquid after heat treatment in the first step (hereinafter, also referred to as a “second step”) and the solid content. It is preferable to include a step of cleaning (hereinafter, also referred to as “third step”).

In the second step, the solid content containing the imide polysuccinate is taken out from the dispersion obtained in the first step by, for example, removing the solvent contained in the dispersion. Since it is considered that maleic acid separated from the polysuccinate imide is eluted in the solvent of the dispersion obtained in the first step, the solvent is considered from the viewpoint of reducing the content of maleic acid in the polysuccinate imide. It is preferable to remove.
Removing the solvent is preferable from the viewpoint of reducing the contents of maleic anhydride, fumaric acid, succinic acid and the like.

The specific method for removing the solvent is not particularly limited, and any filter material such as filter paper, filter cloth, metal mesh, membrane filter, etc., which is generally performed by natural filtration, pressure filtration, vacuum filtration, centrifugal filtration, etc. You may do it by the method.

The temperature at the time of solvent removal in the second step can be 35 ° C. or higher and 85 ° C. or lower because the dispersion liquid obtained in the first step can be directly transferred to the removal operation, but it is particularly heated and kept warm. When removing by filtration, it may be performed at any temperature of 85 ° C. or lower, which is settled in the filter during the filtration operation.

The third step is a step of cleaning the solid content containing the imide polysuccinate extracted in the second step with, for example, water. In the method for producing an imide polysuccinate of the present disclosure, it is preferable to carry out the cleaning treatment from the viewpoint of reducing the content of maleic acid in the imide polysuccinate.
The cleaning treatment is preferable from the viewpoint of reducing the content of maleic anhydride, fumaric acid, succinic acid and the like.

The specific cleaning method for the solid content is not particularly limited, and it is sufficient that maleic acid adhering to the solid content can be removed by using water, a mixed solvent of water and a water-soluble organic solvent, or the like. It is even better if maleic anhydride, fumaric acid, succinic acid and the like can be removed. The water-soluble organic solvent has the same meaning as the water-soluble organic solvent described in the first step, and the same applies to the examples.

[Manufacturing method of polyaspartate]
The method for producing polyaspartate of the present disclosure includes a step of adding an alkaline aqueous solution to hydrolyzed polyaspartate imide to obtain polyaspartate imide obtained by the method for producing polyaspartate imide.

The alkaline aqueous solution preferably has a pH of 10 to 14 at 25 ° C., and more preferably 12 to 14.
Specific examples of the alkaline aqueous solution include an aqueous solution of an alkali metal or alkaline earth metal hydroxide or carbonate, ammonia water, and the like. In particular, an aqueous solution of NaOH, KOH or LiOH is preferable, and an aqueous solution of NaOH is more preferable. The concentration of the base in the alkaline aqueous solution is not particularly limited, but usually a 0.5 to 50% by mass solution is preferable.

The amount of the alkaline aqueous solution used may be an amount sufficient to convert the polysuccinate imide obtained by the method for producing the polysuccinate imide of the present disclosure into polyaspartate. Usually, there is no particular problem as long as the number of moles of the base used is within the range of 90 to 120% of the total number of moles of the carboxyl group and the imide group in the imide polysuccinate.
The temperature at the time of treatment with an alkaline aqueous solution may be a temperature at which hydrolysis of the polymer main chain does not occur, and is usually preferably 10 ° C to 70 ° C, more preferably 40 to 60 ° C. The time for treatment with an alkaline aqueous solution is preferably 1 hour to 6 hours.

The polyaspartate aqueous solution obtained as described above can be used as it is, or can be taken out as a powder (that is, polyaspartate powder) by means such as freeze-drying. It can also be appropriately neutralized with an acid and taken out as polyaspartic acid.

Next, taking sodium polyaspartate, which is one of the polyaspartates of the present disclosure, as an example, an example of the method for producing the polyaspartate of the present disclosure will be shown.

In an example of the method for producing sodium polyaspartate, distilled water is added to the polysuccinate imide obtained by the method for producing polysuccinate imide of the present disclosure to adjust the concentration of the solution. Then, the sodium hydroxide aqueous solution was added dropwise little by little while controlling the temperature of the solution to be 45 ° C. to 55 ° C., and when the reaction mass acquired fluidity, pH measurement was started, and water was measured while measuring pH. The aqueous sodium oxide solution is further added dropwise, and when the pH does not fluctuate in the range of pH 10 to pH 10.5, the addition is terminated to obtain sodium polyaspartate. Then, water is added to obtain a sodium polyaspartate aqueous solution having a desired concentration.

When sodium polyaspartate is obtained by hydrolysis of imide polysuccinimide, some unhydrolyzed imide succinimide structural units may remain in the polymer. In other words, the polyaspartate of the present disclosure contains a part of the succinimide structural unit (for example, 3% or less or 1% or less of the total number of structural units), but completely contains the succinimide structural unit. It does not have to be.

The imide polysuccinate according to the present disclosure may be used as it is as the imide polysuccinate. Further, the polysuccinate imide according to the present disclosure may be derivatized and used as a polyaspartic acid derivative. Examples of the polyaspartic acid derivative include polyaspartate hydrolyzed with an alkali, amine, etc., crosslinked polyaspartic acid which is a water-absorbing polymer having a partially crosslinked structure, and surface active ability having a hydrophobic group and a hydrophilic group introduced therein. Examples thereof include polyaspartic acid derivatives. Among these, polyaspartate can be used as a raw material for cosmetics. Examples of cosmetics include skin care cosmetics, makeup cosmetics, hair care cosmetics, body care cosmetics, and the like, for example, facial cleansers, beauty liquids, milky lotions, creams, packs, eyeliners, eye shadows, mascara, and eyebrow. , Foundation, Face Powder, Makeup Base, Teak, Washing Pigment, Hair Styling Agent, Hair Dyeing Agent, Hair Dyeing Agent, Decolorizing Agent, Hair Growth Agent, Shampoo, Treatment, Conditioner, Cleansing, Lipstick, Gloss, Toothpaste, Tooth Whitening, Examples include sunscreens, body powders, body soaps, hand soaps, deodorants, and bathing agents.

Hereinafter, examples of the present disclosure will be shown, but the present disclosure is not limited to the following examples.

<Preparation of imide polysuccinate (1)>
A 1000 ml separable flask and a glass three-blade swept blade were used as the reactor. Moreover, nitrogen gas was used as the inert gas. A nitrogen introduction line and a thermometer were provided in the flask. The flask was charged with 160.0 g (1.22 mol) of L-aspartic acid as a reaction raw material. Next, the inside of the flask was stirred with a three-blade swept blade stirring blade at a rotation speed of 100 rpm. Nitrogen gas was charged and immersed in an oil bath heated to 250 ° C. under a nitrogen gas stream to heat L-aspartic acid in the flask under atmospheric pressure (0.1 MPa). The water produced by the polycondensation of L-aspartic acid was distilled off from the flask and collected in a cooled trap. After heating for 6 hours, the inside of the flask was cooled to obtain 116.1 g (1.196 mol) of crude polysuccinate imide (also referred to as “pre-treatment PSI”).

[Example 1]
<First process>
In a 300 mL flask equipped with a stirrer, a thermometer, a gas introduction line and an exhaust line, 50.0 g of the crude polysuccinate imide obtained in the preparation of the polysuccinate imide (1) and 150.0 g of distilled water were placed. , Stirring and mixing to disperse the imide polysuccinate in water. Stirring was continued and heat treatment was carried out at a treatment temperature of 50 ° C. for 3 hours to obtain a homogeneous dispersion (slurry) containing polysuccinate imide.

<Second process>
The slurry obtained in the first step is suction-filtered to take out a wet cake containing a solid content containing imide polysuccinate, and then 50.0 g of distilled water is poured into the wet cake in the filter to perform a rinse cleaning treatment. It was. The wet cake was removed after the rinse cleaning solution had finished draining from the filter.
Here, the content of L-aspartic acid (hereinafter, also referred to as "L-Asp") contained in the obtained filtrate in this step (second step) is measured by the method shown below, and the first step is taken. The ratio (mol%) of the content of L-Assp to the polysuccinic acid imide (hereinafter, also referred to as "PSI") charged in one step was calculated. Further, in this step, the content of maleic acid contained in the wet cake taken out was measured by the method shown below. The results are shown in Table 1. The PSI contained in the wet cake taken out in this step is also referred to as "wet PSI".

-L-Method for measuring the content of aspartic acid-
The L-Asp content was measured by the method shown below.
L-Asp was derivatized by a post-column derivatization method using OPA (orthophthalaldehyde) as a reaction reagent after separation on an HPLC column. The derivatized substance was detected by fluorescence detection (Ex [excitation wavelength]: 340 to 350 nm, Em [fluorescence wavelength]: 450 to 460 nm). Moreover, the internal standard method was used as the quantitative method, and L-Val was used as the internal standard substance. Specifically, L-Val was detected after separation by L-Asp and HPLC and then derivatized by the post-column method. RSpack NN-814 (φ8.0 mmX250 mm) Shodex was used as the column, and 10 mM-Na ₂ HPO ₄ (pH = 3.0, pH adjusted by _{H 3} PO _{4) was used as the eluent.} From the obtained measured values, the ratio (mol%) of the L-Asp content to the charged PSI content was calculated as the L-Asp residual ratio, and evaluated according to the following evaluation criteria.
If the residual rate of L-Asp is less than 1 mol%, it can be said that the by-product of L-Asp is within the permissible range and the hydrolysis of PSI is sufficiently suppressed.

-Measuring method of maleic acid content-
The content of maleic acid in the imide polysuccinate was measured by the method shown below.
A calibration curve was prepared from the area value of the obtained liquid chromatograph using maleic acid having a purity of 99.0% by mass under the analysis conditions by the liquid chromatograph method. For the calibration curve, a calibration curve was prepared between the concentration of maleic acid and the peak area value from the liquid chromatograph of a standard sample having a known maleic acid concentration. With reference to this calibration curve, the concentration (ppm) of maleic acid in the imide polysuccinate in the wet cake was determined.

Analytical sample preparation: Weigh 500 mg of imide polysuccinate, and add 20 mg of sodium p-toluenesulfonate and 5 ml of water as internal standard substances. Then, a 32 mass% sodium hydroxide aqueous solution is added until the pH reaches 12. At this time, the imide polysuccinate becomes sodium polyaspartate and becomes an aqueous solution. Then, a 10 mass% phosphoric acid aqueous solution is added until the pH reaches 7, and the mixture is neutralized. Next, 35 ml of methanol is added to precipitate sodium polyaspartate, and the mixture is filtered through a 0.45 μm syringe filter to obtain a filtrate as an analysis sample.
Column: Hydrosphere C18; L250 mm × φ4.6 mm Particle size 5 μm Pore diameter 12 nm (manufactured by YMC)
Oven temperature: 40 ° C
Mobile phase: acetonitrile / water / 85% phosphoric acid = 800 ml / 1200 ml / 1.41 g
Detection method: UV 230 nm
Sample injection volume: 5 μl

<Third process>
A 500 mL flask equipped with a stirrer, a thermometer, a gas inlet line, and an exhaust line was prepared. The wet cake obtained in the second step and distilled water were added thereto, and an aqueous sodium hydroxide solution was added dropwise little by little while controlling the temperature of the solution to be 25 ° C. to 52 ° C. When the wet cake has acquired fluidity, pH measurement is started, the aqueous sodium hydroxide solution is further added dropwise while measuring the pH, and the addition is terminated when the pH does not fluctuate in the range of pH 10 to pH 10.5. , A sodium polyaspartate aqueous solution (hereinafter, also referred to as “PA-Na aqueous solution”) having a sodium polyaspartate concentration of 40% by mass was obtained.
The content of maleic acid and the content of L-Asp contained in the obtained PA-Na aqueous solution were measured by the above method. The results are shown in Table 1.

[Examples 2 and 3, Comparative Examples 1 and 2]
An aqueous solution of imide polysuccinate and sodium polyaspartate was prepared in the same manner as in Example 1 except that the treatment temperature in the first step was changed so as to have the values shown in Table 1, and the same evaluation as in Example 1 was performed. .. The results are shown in Table 1. In addition, "-" in Table 1 indicates that it has not been measured.

From the results shown in Table 1, it can be seen that the polysuccinate imide and the sodium polyaspartate aqueous solution obtained in the examples have a reduced maleic acid content while suppressing the hydrolysis of the polysuccinate imide. ..

Claims (5)

A method for producing an imide of polysuccinate, which comprises a step of heat-treating a dispersion liquid in which a crude synthetic polysuccinate imide is dispersed in a solvent at a temperature of 35 ° C. or higher and 85 ° C. or lower. The method for producing an imide of polysuccinate according to claim 1, wherein the crude synthetic polysuccinate imide is obtained by solid-phase polymerization. The method for producing an imide polysuccinate according to claim 1 or 2, wherein the solvent is water or a mixed solvent of water and a water-soluble organic solvent. In addition
A step of extracting a solid content containing an imide polysuccinate from the dispersion liquid after the heat treatment, and
The step of cleaning the solid content and
The method for producing an imide polysuccinate according to any one of claims 1 to 3. An alkaline aqueous solution is added to the polysuccinate imide obtained by the method for producing a polysuccinate imide according to any one of claims 1 to 4 to hydrolyze the polysuccinate imide to obtain a polyaspartate. A method for producing polyaspartate, which comprises a step.