JP7073663B2 - How to get polymer components for soil spraying - Google Patents

Description

The present invention relates to a method for obtaining a polymer component for soil spraying by reducing the molecular weight of the polymer component made of an aliphatic polyester.

Contaminated soil generated in factories has been detoxified by transporting it to treatment facilities and incinerating it for many years. This method is excellent in that it can be treated in a short time and that it can be treated regardless of the type of pollutant, but it has a drawback that it requires a cost such as transportation cost.

Therefore, recently, a soil purification method using microorganisms called bioremediation has been actively studied. Bioremediation involves the presence of specific microorganisms in contaminated soil and feeding them to detoxify the pollutants and purify the soil.

In bioremediation, it is widely practiced to spray nutrients such as organic acids on contaminated soil to make the growth and activity of microorganisms more active. However, since organic acids are generally liquid at room temperature, it is difficult to determine the timing and amount of nutrient addition, and there is a problem that workability is poor. In addition, there is also a problem that the effect of spraying the nutritional supplement disappears in a short time because it is not sustained release.

In order to solve such a problem, Patent Document 1 proposes to use a polylactic acid-based resin in a solid state and having a weight average molecular weight of 12,000 or less as a nutritional supplement. If it is polylactic acid or the like in a solid state, workability is greatly improved, and the timing and amount of nutritional supplement addition can be accurately determined. In addition, it gradually decomposes with time to release acids such as lactic acid, which functions as a nutritional supplement, and is therefore excellent in terms of sustained release.

Japanese Unexamined Patent Publication No. 2011-104551

However, the polylactic acid-based resin of Patent Document 1 must be manufactured by using polylactic acid or the like having a large molecular weight as a raw material and reducing the molecular weight under pressure by using an autoclave or the like, which costs a lot for manufacturing equipment and the like. rice field. Furthermore, if it is desired to recover a polylactic acid-based resin having a specific average molecular weight, it is necessary to appropriately sample the solid components in the reaction solution and measure the average molecular weight to confirm the progress of the reduction in molecular weight. The method of reducing the molecular weight under pressure is inconvenient because sampling is troublesome. The present inventors have studied the production under normal pressure, but the general method has a problem that it takes time.

Therefore, an object of the present invention is to provide a method for obtaining a polymer component for soil spraying by reducing the molecular weight of a polymer component composed of polylactic acid with high efficiency and low molecular weight while suppressing the cost.

According to the present invention
Prepare a solution containing 31 to 60% by mass of carboxylic acid .
Under normal pressure, a polymer component composed of polylactic acid having a weight average molecular weight Mw in the range of 100,000 to 300,000 is put into the solution and heated to have a weight average molecular weight Mw of 10,000 to 20. Provided is a method comprising obtaining a polymer component having a low molecular weight in the range of 000 as an insoluble matter in the solution and recovering the insoluble matter as polylactic acid for soil spraying .

In the method of the present invention, the following aspects are suitable.
(1) A low molecular weight reduction-promoting resin that releases acid by hydrolysis is added to the solution together with polylactic acid.
(2) The low molecular weight reduction promoting resin is polyoxalate.
(3) The carboxylic acid is at least one organic acid selected from the group consisting of lactic acid, acetic acid and citric acid.
(4) The carboxylic acid is lactic acid.
(5) The solution selectively contains the carboxylic acid as a solute.
(6) The heating temperature is 90 ° C. or higher.
(7) The yield X calculated from the following equation (1) is 90% or more.
X = 100 × (Wf / Wi) ・ ・ ・ (1)
In the formula, Wf represents the mass (g) of the low molecular weight polymer component.
Wi represents the mass (g) of the polymer component before hydrolysis.

In the present invention, the polymer component mainly composed of an aliphatic polyester is hydrolyzed in an organic acid solution under normal pressure to reduce the molecular weight. Surprisingly, the organic acid concentration of the solution used is within a specific range (polymer component). By a simple means of adjusting the polymer component to 31 to 60% by mass at the time before charging, the polymer component can be reduced in molecular weight to a desired degree with high efficiency while suppressing the cost. In particular, we have succeeded in obtaining a low molecular weight polymer component having a weight average molecular weight (hereinafter, abbreviated as average molecular weight) of 10,000 to 20,000 in a solid state with high efficiency.

In fact, referring to the examples described later, when polylactic acid or a kneaded product of polylactic acid and polyoxalate is prepared as a polymer component and hydrolyzed in an organic acid aqueous solution having a concentration of 50% by mass, 10 hours from the start. Less than, low molecular weight polylactic acid with an average molecular weight of 10,000 to 20,000 can be recovered. Moreover, when the insoluble matter in the reaction solution was sampled at an appropriate time interval, the average molecular weight was measured, and the change over time of hydrolysis was observed, the average molecular weight reached 10,000 to 20,000. Since the hydrolysis rate is slowed down, it takes a long time to recover the target low molecular weight polymer component. If the recoverable time is long, there is no concern that the recovery timing will be missed even if sampling or measurement takes time at the site such as a factory, which is extremely advantageous in industry.

On the other hand, when pure water is prepared as in Comparative Example 1 and polylactic acid is hydrolyzed in the pure water, low molecular weight polylactic acid having an average molecular weight of 10,000 to 20,000 can be recovered even after 10 hours of heat treatment. It cannot be done and the manufacturing time is long.

Further, when a high-concentration (90% by mass) organic acid aqueous solution is used as in Comparative Example 2 and Comparative Example 3, hydrolysis proceeds rapidly, which is preferable. However, since the acids in these aqueous solutions have a high affinity with polylactic acid, polylactic acid having an average molecular weight of 20,000 or less is dissolved in a high-concentration organic acid aqueous solution immediately after production. Therefore, it is difficult to recover the target low molecular weight polymer component in a solid state.

Therefore, it is possible to efficiently recover the polymer component having a desired degree of low molecular weight in a solid state only by using an organic acid solution having a specific concentration as in the present invention.

Moreover, since the method of the present invention does not use a low boiling point acid such as an inorganic acid, it is safe because there is no need to worry about the volatilization of the acid during the reaction, and no equipment for the volatilized acid is provided. May be good. Further, since the molecular weight can be reduced at a sufficient speed even under normal pressure, a large-scale device such as an autoclave is not required. Therefore, it is possible to reduce the molecular weight at low cost.

It is a graph which shows the relationship between the heat treatment time and the weight average molecular weight of a solid component in Example 4 and Comparative Example 6.

In the present invention, a solution in which an organic acid is dissolved is prepared, a polymer component made of an aliphatic polyester is added to the solution, and the polymer component is hydrolyzed while heating to reduce the molecular weight of the polymer component.

As the aliphatic polyester contained in the polymer component, known ones can be used without any limitation. For example, poly (α-hydroxy acid), poly (β-hydroxy alkanoate), poly (ω-hydroxy alkanoate), polyalkylene dicarboxylate and the like can be mentioned.

These may be used alone or in combination of two or more. Further, although it may be a homopolymer, it may be in the state of a copolymer together with the copolymerization component under the condition that the effect of the present invention is not impaired.

Examples of the components forming the copolymer include polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, dodecanediol, neopentylglycol, glycerin, pentaerythritol, sorbitan, bisphenol A, and polyethylene glycol; Dicarboxylic acids such as acids, adipic acids, sebacic acids, glutaric acids, decandicarboxylic acids, cyclohexhexanedicarboxylic acids, terephthalic acids, isophthalic acids, anthracendicarboxylic acids and their diesters; glycolic acid, L-lactic acid, D-lactic acid, hydroxypropion. Hydroxycarboxylic acids such as acids, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, mandelic acid, hydroxybenzoic acid; lactones such as glycolide, caprolactone, butyrolactone, valerolactone, propiolactone, undecalactone; etc. ..

As the aliphatic polyester, poly (α-hydroxy acid) is preferable, and polylactic acid is particularly preferable, because it is easily available. The polylactic acid may be either 100% poly-L-lactic acid or 100% poly-D-lactic acid, may be a molten blend of poly-L-lactic acid and poly-D-lactic acid, and may be L-. It may be a random copolymer of lactic acid and D-lactic acid or a block copolymer.

The weight average molecular weight of polylactic acid used for low molecular weight reduction is in the range of 100,000 to 300,000. According to the studies by the present inventors, it has been confirmed that the various reaction conditions and the behavior (rate, etc.) of reducing the molecular weight are substantially the same in the case of polylactic acid having such a molecular weight.

From the viewpoint of the balance between the reaction rate and the cost, the aliphatic polyester is preferably used in an amount of 100 g to 2 kg per liter of the organic acid aqueous solution.

Polymer components include known plasticizers, heat stabilizers, light stabilizers, antioxidants, UV absorbers, flame retardants, colorants, pigments, fillers, fillers, mold release agents, and antistatic agents, as required. Additives such as agents, fragrances, lubricants, foaming agents, antibacterial / antifungal agents, nucleating agents, and carboxyl group-binding compounds may be further contained. The blending amount of the additive is appropriately determined under the condition that the effect of the present invention is not impaired, but is usually 5 parts by mass or less per 100 parts by mass of the aliphatic polyester.

Further, as the polymer component, a resin that is more easily hydrolyzed and releases an acid by hydrolysis than the above-mentioned aliphatic polyester, that is, a resin that easily hydrolyzes and releases an acid when mixed with water is low. It may be contained as a molecular weight hydrolysis promoting resin. In particular, when a poorly hydrolyzable aliphatic polyester such as polylactic acid is used as a raw material, a resin for promoting low molecular weight is preferable because it promotes hydrolysis of the aliphatic polyester to promote low molecular weight. used. As the acid released from the low molecular weight reduction promoting resin, an acid having a pH (25 ° C.) of 4 or less, particularly 3 or less, in an aqueous solution or an aqueous dispersion having a concentration of 0.005 g / ml is particularly preferable. Examples of the released acid include oxalic acid and glycolic acid.

Examples of the resin for promoting low molecular weight include polyoxalate and polyglycolic acid, but polyoxalate is preferable. These may be used in the form of a copolymer. Further, one type may be used alone, or two or more types may be used in combination. As the component forming the copolymer, the component forming the copolymer mentioned in the description of the raw material aliphatic polyester can be adopted.

The weight average molecular weight of the low molecular weight reduction promoting resin is generally 1,000 to 200,000.

The blending amount of the low molecular weight promoting resin is not particularly limited, but is preferably 1 part by mass or more and less than 100 parts by mass with respect to 100 parts by mass of the aliphatic polyester. It is more preferably 1 part by mass or more and less than 50 parts by mass, and particularly preferably 1 part by mass or more and less than 30 parts by mass.

If necessary, the low molecular weight reduction-promoting resin may be used by itself in an organic acid solution instead of being blended with a polymer component.

Examples of the form of the polymer component include a film to a sheet, a cut form of the film to a sheet, pellets, and particles, and the particles are preferable. This is because when the particulate polymer component is used, the finally obtained solid content (polymer component after reducing the molecular weight) is also in the form of particles, and there is an advantage that it can be directly used as a nutritional supplement for microorganisms.

In the present invention, it is important to use organic acids. If a solute other than an acid (for example, a basic substance) is used, the yield will be low. Low boiling point acids such as inorganic acids volatilize by heating, which increases equipment costs. In addition, since the hydrolysis is excessively fast, it is difficult to complete the reduction in molecular weight to a desired degree, and the yield is lower than that of the organic acid.

As the organic acid, a carboxylic acid is preferable, at least one selected from the group consisting of lactic acid, acetic acid and citric acid is more preferable, and lactic acid is particularly preferable.

As the solvent, water is preferable from the viewpoint of handleability. Alcohol may be used in combination if necessary. Alcohol may be appropriately selected from known alcohols in consideration of the type of solute and the like.

Other solutes such as inorganic acids, alkali metals, and basic substances may be dissolved in the organic acid solution as long as the effects of the present invention are not impaired, but as solutes from the viewpoint of environmental consideration and cost. It is preferable that the organic acid is selectively contained, in other words, other solutes are not contained.

In the present invention, it is also important that the concentration of the organic acid in the organic acid solution is 31 to 60% by mass before the polymer component is added. If the concentration of organic acid is too low, the rate of hydrolysis will be slow. If the concentration of the organic acid is too high, the affinity between the organic acid in the solution and the aliphatic polyester is high, so that the polymer component having a low molecular weight dissolves and is difficult to recover in a solid state. With respect to the 20,000 low molecular weight polymer components, it is virtually unrecoverable.

In the present invention, a reaction device equipped with a reaction vessel, a heating device and a stirring device is usually used, and a polymer component is added to an organic acid solution under normal pressure (approximately 1 atm) for stirring and heating. The heating temperature is determined by the composition of the solution, the type of aliphatic polyester used, and the like, but is usually 90 ° C. or higher. If the heating temperature is too low, the hydrolysis rate will be slow.

The upper limit of the heating temperature is usually below the boiling point of the solution. The boiling point of the solution means the boiling point of the solution before the polymer component is added. Depending on the composition of the solution, the boiling point may not be clearly specified. In that case, the upper limit may be set to 140 ° C. In any case, if the heating temperature is too high, organic acids and solvents may volatilize.

Since the time of the low molecular weight reduction treatment varies depending on the degree of low molecular weight reduction, the composition of the solution, the scale of the apparatus, the heating temperature, etc., the solid components in the reaction solution are sampled at appropriate time intervals and the weight average molecular weight is measured. Then, the reaction should be terminated when the average molecular weight reaches the desired value. The shorter the molecular weight reduction treatment time is, the better. For example, when obtaining a low molecular weight polymer component having an average molecular weight of 10,000 to 20,000, it is preferably within 10 hours, more preferably within 8 hours, and even more preferably. Within 6 hours.

After completion of the reaction, the insoluble matter in the reaction solution is collected by filtration or the like, and washed and dried as appropriate.

According to the method of the present invention, a low molecular weight polymer component having a weight average molecular weight of 10,000 to 20,000 is produced in high yield. For example, in the examples described below, the yield has been shown to exceed 90%. The yield is calculated by the following formula.
Yield (%) = {W _f / _Wi} x 100
In the formula, W _f represents the mass (g) of the low molecular weight polymer component.
Wi represents the mass ( _g ) of the polymer component before hydrolysis.

The use of the produced low molecular weight polymer component is not particularly limited, that is, it may be applied to a desired use.

For example, a low molecular weight polymer component having an average molecular weight of 10,000 to 20,000 obtained by hydrolyzing a polymer component mainly containing polylactic acid is pulverized into a powder, and is used in the field of bioremediation. It is useful as a nutritional supplement. This is because such a nutritional supplement has good workability because it is in a solid state, and it is easy to accurately determine the timing and amount of the nutritional supplement dripping. Further, it is easy to crush and has excellent sustained release property.

Alternatively, the low molecular weight polymer component can be applied to additives for fishing nets and paints for ship bottoms. This makes it difficult for aquatic pests such as barnacles to adhere to fishing nets and the bottom of ships. Alternatively, in the field of resource mining such as shale gas, addition to a fracturing fluid, a finishing fluid, an excavation fluid or the like can be applied. Especially in the field of resource mining, crushability and hydrolyzability are required. With such a low molecular weight polymer component, crushing to a desired particle size is good, and even in an underground environment, if there is water, it will be natural. Can be hydrolyzed.

The present invention will be described with reference to the following examples.

<Material used>
As PLA (polylactic acid resin), REVODE 101 (d-lactic acid 4.62%) manufactured by Kaisei Biomaterial was used. When the molecular weight of this PLA was measured by the method described later, it was in the range of 120,000 <Mw <170,000.
As 50% lactic acid and 90% lactic acid, Musashino lactic acid 50F (50% by mass) and Musashino lactic acid 90F (90% by mass) manufactured by Musashino Chemical Research Institute were used.
50% acetic acid and 90% acetic acid were prepared by treating reagent special grade acetic acid (purity 99.7 +%) manufactured by Wako Pure Chemical Industries, Ltd. as 100% acetic acid and diluting each with arbitrary pure water.
50% citric acid was prepared by dissolving special grade citric acid (purity 98.0% or more) manufactured by Wako Pure Chemical Industries, Ltd. in heated pure water.
As 35% hydrochloric acid, Wako Pure Chemical Industries, Ltd. reagent special grade hydrochloric acid (35.0% to 37.0%) was used.

As the polyethylene oxalate (PEOx), which is a resin for promoting low molecular weight, one polymerized by the following method was used.
In a 1 L separable flask equipped with a mantle heater, a liquid temperature thermometer, a stirrer, a nitrogen introduction tube and a distillate column, 354 g (3 mol) of dimethyl oxalate, 201 g (3.24 mol) of ethylene glycol and dibutyltin oxide 0. 15 g was added, and the liquid temperature in the flask was heated to 110 ° C. under a nitrogen stream to perform atmospheric pressure polymerization. After the start of distillation of methanol, the mixture was kept warm for 1 hour for reaction. After 1 hour, the temperature was raised to 150 ° C. at a heating rate of 10 ° C./30 minutes, and normal pressure polymerization was carried out. 32.4 g (0.36 mol) of 1,4-butanediol was added at 150 ° C., and the mixture was reacted for 1 hour. Then, the temperature was raised to 180 ° C. at 10 ° C./30 minutes. The amount of liquid recovered was 192 g.
Then, the liquid temperature in the flask was polymerized under reduced pressure at 190 ° C. and a reduced pressure of 0.1 kPa to 0.8 kPa, and the obtained polymer was taken out. It was crystallized by vacuum heat treatment at 90 ° C. for 2 hours and 120 ° C. for 2 hours. The weight average molecular weight of PEOx thus obtained was measured by the method described below and found to be 100,000.

<Measurement of molecular weight of PLA and PEOx10% PLA>
Using GPC, the molecular weight of PLA was measured under the conditions shown below.
Equipment: Gel Permeation Chromatograph GPC
Detector: Differential refractometer detector RI
Column: SuperMultipore HZ-M (2)
Solvent: Chloroform Flow rate: 0.5 mL / min
Column temperature: 40 ° C
Sample preparation: 3 mL of solvent was added to about 10 mg of sample, and the sample was left at room temperature.
After visually confirming the dissolution, the mixture was filtered through a 0.45 μm filter.
Polystyrene was used as the standard.

<Measurement of molecular weight of PEOx>
Equipment: Gel Permeation Chromatograph GPC
Detector: Differential refractometer detector RI
Columns: Shodex HFIP-LG (1), HFIP-806M (2)
(Showa Denko)
Solvent: Hexafluoroisopropanol (added 5 mM sodium trifluoroacetate)
Flow velocity: 0.5 mL / min
Column temperature: 40 ° C
Sample preparation: 5 mL of solvent was added to about 1.5 mg of sample, and the mixture was gently stirred at room temperature (sample concentration).
About 0.03%).
After visually confirming the dissolution, the mixture was filtered through a 0.45 μm filter.
Polymethylmethacrylate was used as the standard.

(Example 1)
1.0 g of PLA was immersed in 10 mL of 50% lactic acid in a 20 mL vial and allowed to stand for 10 hours while being heated to 95 ° C.

(Example 2)
1.0 g of PLA was immersed in 10 mL of 50% acetic acid in a 20 mL vial and allowed to stand for 6 hours while being heated to 95 ° C.

(Example 3)
1.0 g of PLA was immersed in 10 mL of 50% citric acid in a 20 mL vial and allowed to stand for 10 hours while being heated to 95 ° C.

(Comparative Example 1)
1.0 g of PLA was immersed in 10 mL of pure water in a 20 mL vial and allowed to stand for 10 hours while being heated to 95 ° C.

(Comparative Example 2)
50 g of PLA was immersed in 300 mL of 90% lactic acid in a 500 mL separable flask and heated to 120 ° C. with stirring for 5 hours with a mechanical stirrer at 130 rpm.

(Comparative Example 3)
1.0 g of PLA was immersed in 10 mL of 90% acetic acid in a 20 mL vial and allowed to stand for 2 hours while being heated to 95 ° C.

(Comparative Example 4)
1.0 g of PLA was immersed in 10 mL of 35% hydrochloric acid in a 20 mL vial and allowed to stand for 2 hours while being heated to 95 ° C.

After heat treatment for each sample, the solution was removed with a Pasteur pipette, and the samples were washed twice or more with 20 mL of pure water. The mixture was heated and dried at 95 ° C. for 1 hour, and then the mass (W _f ) was measured. The yield (%) was calculated by the percentage [100 × ( _{W f} / _Wi )] with the mass (Wi) of the raw material PLA. In addition, the weight average molecular weight (Mw) was measured from the sample pieces after drying and mass (W _f ) measurement. The molecular weight and yield are shown in Table 1.

As can be seen from Table 1, the treatment with 50% lactic acid, 50% acetic acid and 50% citric acid reached a molecular weight of 10,000 to 20,000 after 6 to 10 hours of heat treatment.
In the same treatment with pure water, the molecular weight did not reach 20,000 even after 10 hours.
Treatment with 90% lactic acid and 90% acetic acid proceeded at high speed, but with 90% lactic acid the molecular weight decreased to 20,000 after 4 hours of treatment and the solid dissolved after 5 hours of treatment. Even with 90% acetic acid, the molecular weight decreased to 30,000 after 2 hours of treatment, and after 3 hours of treatment, the solid shape was lost and dissolved. If the solid dissolves after only one hour, it is difficult to recover the low molecular weight aliphatic polyester as a solid in an actual manufacturing site.
Even with 35% hydrochloric acid, the molecular weight decreased to 8,800 after 2 hours of treatment and lost its solid shape after 4 hours of treatment. When the molecular weight is less than 10,000 after only 2 hours of treatment, it is difficult to recover the solid in the molecular weight range of 10,000 to 20,000.

As described above, it has been shown that the solid and low molecular weight aliphatic polyester can be obtained in a short time by the method of the present invention while preventing mass loss due to dissolution.

Next, an example of a particulate kneaded product (PEOx 10% PLA) in which polyethylene oxalate (PEOx), which is a resin for promoting low molecular weight, is kneaded with polylactic acid in an amount of 10% by mass will be shown.

(Example 4)
1500 g of PEOx 10% PLA was immersed in 1800 g of 50% lactic acid in a 3 L volume separable flask and heated to 98 ° C. with stirring with a mechanical stirrer at 200 rpm.

(Comparative Example 5)
28 g of PEOx10% PLA was immersed in 200 g of 30% lactic acid in a 500 mL separable flask and heated to 98 ° C. with stirring with a mechanical stirrer at 200 rpm.

(Comparative Example 6)
200 g of PEOx10% PLA was immersed in 300 g of pure water in a 500 mL separable flask and heated to 98 ° C. while stirring with a mechanical stirrer at 170 rpm.

In each Example / Comparative Example, the solid content was collected once every few hours and Mw was measured. The heat treatment was completed when Mw reached 10,000 to 20,000. After that, the solution was filtered off and washed with the same amount of pure water as the solution three times or more. The samples obtained in Example 4 and Comparative Example 5 were dried by heating at 80 ° C. for 3 hours, and the samples obtained in Comparative Example 6 were dried at 50 ° C. for 3 hours. Subsequent mass (W _f ) was measured. The yield (%) was calculated by the percentage [100 × ( _WF / Wi) _] with the mass (Wi) of _PEOx10 % PLA before hydrolysis. The results are shown in Table 2 below.

From Table 2, when heat treatment was performed with 50% lactic acid, the molecular weight of Mw could be reduced to 13,300 in just 5 hours. This time is about half that of the case of treating with pure water to the same molecular weight. The yield at this time was 93%, which was equal to or higher than 91% of the pure water treatment. Further, when treated with 30% lactic acid, the molecular weight was reduced at a slightly faster rate than that of pure water, but the yield was low.

Further, the change in molecular weight during the heat treatment with 50% lactic acid and pure water is shown in FIG. As can be seen from FIG. 1, in the heat treatment with 50% lactic acid, the Mw reaches 20,000 or less in less than 4 hours, whereas in the treatment with water, the Mw reaches 20,000 or less. Was as late as 7.5 hours.

As described above, according to the method of the present invention, it has been shown that even when PEOx is kneaded with polylactic acid, a solid and low molecular weight aliphatic polyester can be obtained quickly while preventing mass loss due to dissolution. rice field.

Claims (8)

Prepare a solution containing 31 to 60% by mass of carboxylic acid .
Under normal pressure, a polymer component composed of polylactic acid having a weight average molecular weight Mw in the range of 100,000 to 300,000 is put into the solution and heated to have a weight average molecular weight Mw of 10,000 to 20. A method characterized in that a polymer component having a low molecular weight in the range of 000 is obtained as an insoluble matter in the solution, and the insoluble matter is recovered as polylactic acid for soil spraying . The method according to claim 1 , wherein a low molecular weight reduction-promoting resin that releases an acid by hydrolysis is added to the solution together with polylactic acid. The method according to claim 2 , wherein the resin for promoting low molecular weight is polyoxalate. The method according to any one of claims 1 to 3, wherein the carboxylic acid is at least one organic acid selected from the group consisting of lactic acid, acetic acid and citric acid. The method according to any one of claims 1 to 4 , wherein the carboxylic acid is lactic acid. The method according to any one of claims 1 to 5 , wherein the solution selectively contains the carboxylic acid as a solute. The method according to any one of claims 1 to 6 , wherein the heating temperature is 90 ° C. or higher.
The method described in. The method according to any one of claims 1 to 7, wherein the yield X calculated from the following formula (1) is 90% or more.
X = 100 × (Wf / Wi) ・ ・ ・ (1)
In the formula, Wf represents the mass (g) of the low molecular weight polymer component.
Wi represents the mass (g) of the polymer component before hydrolysis.

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