JP3319884B2 - Purification method of aliphatic polyester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying an aliphatic polyester useful as a biodegradable polymer as a substitute for a medical material or a general-purpose resin. More specifically, the present invention relates to a method for purifying an aliphatic polyester for obtaining an aliphatic polyester having almost no unreacted monomer or low-molecular-weight volatile component remaining.

[0002]

2. Description of the Related Art Among aliphatic polyesters, polylactic acid can be produced from a cyclic dimer of lactic acid, usually called lactide, and its production method is described in US Pat.
70, USP 2,362,511, USP 2,683,
136. In addition, copolymers of lactic acid and other hydroxycarboxylic acids are usually produced from lactide, which is a cyclic dimer of lactic acid, and a cyclic ester intermediate of hydroxycarboxylic acid (glycolide, which is usually a dimer of glycolic acid). Regarding the manufacturing method, refer to USP
3,636,956 and US Pat. No. 3,797,499.

In the case of direct dehydration polycondensation of lactic acid or lactic acid and other hydroxycarboxylic acids, azeotropic dehydration condensation of raw material lactic acid or lactic acid and other hydroxycarboxylic acids is preferably carried out in an organic solvent in the presence of a catalyst. By removing water from the solvent distilled off by azeotropic distillation and returning the substantially anhydrous solvent to the reaction system, high-molecular-weight polylactic acid having practical strength and lactic acid and other hydroxycarboxylic acids are used. (EP 0 572 675)
Gazette).

[0004] Among the aliphatic polyesters, with respect to a method for producing a polyester comprising an aliphatic polyhydric alcohol and an aliphatic polybasic acid, there is a method for obtaining a high-molecular weight aliphatic polyester having practical strength. And JP-A-4-189822 and JP-A-4-189823.

Japanese Patent Application Laid-Open No. 62-25121 discloses a method for producing polyglycolide or polylactide by directly polycondensing glycolic acid or lactic acid with a tin compound as a catalyst. A method for producing polyglycolide or polylactide having a high molecular weight by reducing the activity of a tin catalyst to suppress the decomposition of a polymer that occurs together with the polycondensation reaction is described, but the molecular weight is expressed by weight average molecular weight. At most tens of thousands (approximately 10,000 in number average molecular weight), and a practically usable polymer cannot be obtained.

In these methods, after the melt polymerization, the obtained polymer is pelletized as it is, so that the used catalyst remains in the polymer, and even if the aliphatic polyester polymer is decomposed, the catalyst remains. There is a problem that depolymerization reaction of the polymer is easily caused by heating at the time of molding, and the molecular weight of the polymer is reduced to deteriorate physical properties. Further, in these methods, it is not possible to avoid that the monomer used as a raw material remains as an unreacted substance in the polymer at several percent. It is also known that impurities having a relatively low boiling point and low molecular weight volatiles such as chain or cyclic oligomers generated by side reactions during the polymerization remain in the polymer. Unreacted monomers and low-molecular-weight volatiles remaining in the polymer cause deterioration of the storage stability and processability of the polymer and a decrease in the strength of the molded product.

Therefore, in order to obtain an aliphatic polyester having a sufficiently high molecular weight and containing no catalyst, it is necessary to remove the catalyst by purification. For example, JP-A-63-1453
No. 27 discloses that after dissolving a polymer containing a catalyst in an organic solvent immiscible with water, the catalyst is brought into contact with an aqueous phase or water containing an inorganic acid, a water-soluble organic acid or a water-soluble complexing agent to form a catalyst. A method of removing is disclosed. However, in this method, when the polymer solution becomes viscous, the contact efficiency with the aqueous phase is reduced, so that the polymer solution must be treated with a dilute solution such as 0.5 to 4.0% by weight. There is a problem that the liquid separation property after mixing with the aqueous phase is poor. Japanese Patent Application Laid-Open No. 63-254128 discloses a method of purifying a polymer solution by adding a precipitant in a turbulent shearing field. There is a problem in industrial removal, such as poor removal efficiency and special equipment. Further, a method for removing a catalyst from a polyester comprising an aliphatic polyhydric alcohol and an aliphatic polybasic acid is not known.

Further, as a method for reducing the content of unreacted monomers and low-molecular-weight volatiles, JP-A-62-648 discloses a method.
No. 24 discloses a method of purifying a polymer by a reprecipitation method after completion of polymerization. In this method, a polymer is dissolved in a good solvent such as chloroform and poured into a poor solvent such as methanol to precipitate only an insoluble polymer and remove a soluble monomer. However, this method is not industrially preferable because the process becomes complicated and the yield of the polymer decreases.

Further, Japanese Patent Application Laid-Open No. Hei 3-14829 discloses that
When producing a bioabsorbable polyester by the reaction of glycolide and / or lactide, unreacted by reducing the pressure in the reaction system while maintaining the polymer in a molten state in the latter half of the polymerization reaction or after the end of the reaction. A method for producing a polyester having a low residual amount of monomers and low molecular weight volatiles is described. However, also in this method, since the unreacted monomer of 0.3 to 0.9% is present in the polymer and the active catalyst remains, the heat resistance and weather resistance are not sufficient, and this polymer is not sufficient. Therefore, a molded article that can withstand long-term use cannot be obtained.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to remove low-molecular compounds such as unreacted monomers and volatiles remaining in an aliphatic polyester obtained by a polycondensation reaction industrially at low cost and easily. An object of the present invention is to provide a purification method for obtaining an aliphatic polyester having a low content of unreacted monomers and low molecular weight volatiles, and having excellent heat resistance and weather resistance.

[0011]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that aliphatic polyesters are kept in a molten or solution state and the catalyst is inactivated, By dissolving the aliphatic polyester in a solvent and contacting it with an acidic substance, the catalyst in the aliphatic polyester is insolubilized and removed, and then distillation or crystallization is performed to remove the low-molecular compound contained in the aliphatic polyester. , Low content of low molecular compounds,
The inventors have found that an aliphatic polyester having excellent heat resistance and weather resistance can be obtained, and have completed the present invention.

That is, according to the present invention, (i)
Aliphatic hydroxycarboxylic acids, (ii) cyclic esters thereof, (iii) aliphatic polyhydric alcohols and aliphatic polybasic acids, or (iv) a mixture of two or more of the above (i)-(iii). When purifying the resulting aliphatic polyesters, removing the low molecular weight compounds after inactivating the catalyst or separating by insolubilizing the catalyst while keeping the aliphatic polyesters in a molten or solution state. A method for purifying aliphatic polyesters characterized by the following.

The aliphatic polyester used in the present invention may be a homopolymer or a copolymer thereof obtained from a hydroxycarboxylic acid or a cyclic ester thereof, or a polyester obtained from an aliphatic polyhydric alcohol and an aliphatic polybasic acid. It is a polyester obtained from those mixed raw materials.

As a method for synthesizing these polymers, a method of directly dehydrating polycondensation from raw materials of hydroxycarboxylic acids, aliphatic polyhydric alcohols, and aliphatic polybasic acids, and an intermediate of a cyclic ester of hydroxycarboxylic acid such as lactic acid Ring opening in the presence of a catalyst using a copolymerizable monomer such as lactide, which is a cyclic dimer, glycolide, which is a dimer of glycolic acid, and ε-caprolactone, which is a cyclic ester of 6-hydroxycaproic acid, as appropriate. A method of polymerizing is used.

In the case of direct dehydration polycondensation, the starting hydroxycarboxylic acids, aliphatic polyhydric alcohols, and aliphatic polybasic acids are azeotropically dehydrated and condensed, preferably in an organic solvent and in the presence of a catalyst. A high-molecular-weight aliphatic polyester can be obtained by a method in which water is removed from the solvent that has flowed off by azeotropic distillation, and the substantially anhydrous solvent is returned to the reaction system.

The aliphatic polyester obtained by these methods has a weight-average molecular weight of 5 to have practical strength.
It is preferably at least 000. Such an aliphatic polyester has sufficient strength and toughness when processed into a film, a molded product or the like, and can be used as it is for a container or the like.

The starting hydroxycarboxylic acids or cyclic esters include lactic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxyvaleric acid. Examples include hydroxycaproic acid, lactide which is a cyclic dimer of lactic acid, glycolide which is a dimer of glycolic acid, and ε-caprolactone which is a cyclic ester of 6-hydroxycaproic acid. When the compound has an asymmetric carbon in the molecule, it may be a D-form or an L-form alone, or a mixture of the D-form and the L-form, that is, a racemic form.

The polyhydric alcohols have an aliphatic hydroxyl group and include, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4 -Butanediol, 3-methyl-1,5-pentanediol,
1,6-hexanediol, 1,9-nonanediol,
Neopentyl glycol, polytetramethylene glycol, 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol and the like can be mentioned.

Polybasic acids having an aliphatic carboxyl group include succinic acid, oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and undecane diacid. Acids, dodecanedioic acid, 1,4-phenylenediacetic acid, phenylsuccinic acid and the like.

Preferred combinations of polyhydric alcohols and polybasic acids include polymers having a melting point of 100, such as ethylene glycol and succinic acid, 1,4-butanediol and succinic acid, and 1,4-cyclohexanedimethanol and succinic acid.
It is above ℃. The polymer obtained from such a combination can be used for applications requiring heat resistance, such as for a microwave oven.

In the synthesis of the polymer of the present invention, a catalyst is usually used in both the method of direct condensation and the method of ring-opening polymerization of a hydroxycarboxylic acid cyclic ester intermediate. Commonly used catalysts include II, III, and I in the periodic table.
Group V and V metals, oxides and salts thereof, and the like. Specifically, metals such as zinc dust, tin dust, aluminum and magnesium, metal oxides such as antimony oxide, zinc oxide, tin oxide, aluminum oxide, magnesium oxide and titanium oxide, stannous chloride, stannic chloride Metal halides, such as stannous bromide, stannic bromide, antimony fluoride, zinc chloride, magnesium chloride, aluminum chloride,
Magnesium carbonate, carbonates such as zinc carbonate, tin acetate, tin octoate, tin lactate, zinc acetate, organic carboxylate such as aluminum acetate, tin trifluoromethanesulfonate, zinc trifluoromethanesulfonate, magnesium trifluoromethanesulfonate, Organic sulfonates such as tin methanesulfonate, tin p-toluenesulfonate, and the like. In addition, organic metal oxides of the above metals such as dibutyltin oxide, or metal alkoxides of the above metals such as titanium isopropoxide, or alkyl metals of the above metals such as diethylzinc, ion exchange such as Dowex and Amberlite Examples thereof include resins and the like, and protic acids such as sulfuric acid, methanesulfonic acid, and p-toluenesulfonic acid. In order to obtain a polymer having a high molecular weight, a metal or a metal compound is generally used as a catalyst. Preferably, a tin or zinc metal or metal compound, more preferably a metal tin or tin compound, is used, which has a high polymerization rate and gives a high molecular weight polymer.

The amount used is 0.0001 to
It is used in an amount of about 10% by weight, preferably 0.001 to 5% by weight.

The state of the reaction after the ring-opening polymerization of the hydroxycarboxylic acid cyclic ester usually does not use a solvent in the polymerization, so that the polymer exists in a molten state. Further, in the state after the reaction in the case of direct dehydration polycondensation, since a solvent is used, the polymer exists in a state of being dissolved in the solvent.

In the aliphatic polyester polymerized mass thus polymerized by a known method, several percent of unreacted substances and chains,
It contains a low molecular compound such as a cyclic oligomer, an active catalyst used for polymerization, and a solvent depending on the polymerization method.

In the method of the present invention, after the aliphatic polyesters thus obtained are kept in a molten or solution state, the catalyst is inactivated, or after the catalyst is insolubilized and separated, low molecular weight Remove the compound. For purification of an aliphatic polyester by ring-opening polymerization in which a polymer after a polymerization reaction is present in a molten state, a method of inactivating a catalyst and then removing a low molecular compound is easy in terms of operation. The purification of the aliphatic polyester by direct dehydration polycondensation using a solvent for the polymerization reaction preferably removes the low molecular weight compound after insolubilizing and separating the catalyst.

The low molecular compounds include oligomers having a molecular weight of 500 or less, unreacted raw materials, and the like. Above all, it is preferable to remove hydroxycarboxylic acid cyclic esters such as lactide, glycolide, and ε-caprolactone.

Examples of the method for inactivating the catalyst of the present invention include a method in which a protonic acid is used as a catalyst, a basic compound is added to the obtained aliphatic polyester, and a method in which a metal compound is used as a catalyst to obtain a polymerized polymer. There is a method of adding acids to the aliphatic polyester after completion. In order to obtain a high molecular weight polymer, a metal compound is generally used as a catalyst, and thus a method of adding an acid is preferably used.
Examples of the types of acids used include, for example, sulfuric acid, phosphoric acid,
Phosphorous acid, pyrophosphoric acid and the like can be mentioned, but phosphoric acid and pyrophosphoric acid are preferable from the viewpoint of the effect, and these can be added directly or dissolved in an appropriate organic solvent.

In terms of the ratio of use, it depends on the type of acid used, the type of raw material to be polymerized, the type and concentration of the catalyst, and the like. More than 1.00 equivalent,
Preferably it is 1.05 to 4.5 equivalent. If the amount is less than the above range, the contained catalyst cannot be completely inactivated, which adversely affects the heat resistance and weather resistance of the finally obtained aliphatic polyester. Further, even if it is added in an amount exceeding 4.5 equivalents, the effect of the addition no longer changes, which is uneconomical.

As a condition for inactivating the catalyst by contacting with an acid, stirring is continued at a usual polymerization temperature for 0.5 to 20 hours, preferably 1 to 10 hours, more preferably 1 to 5 hours.

In the method for insolubilizing and separating the catalyst of the present invention, when a solvent is used in treating the aliphatic polyester, the solvent may be any solvent which dissolves the aliphatic polyester, such as benzene, toluene, and the like. Hydrocarbon solvents such as xylene, ketone solvents such as acetone, methyl ethyl ketone and acetophenone, methylene chloride,
Halogenated hydrocarbon solvents such as chloroform and 1,2-dichloroethane, aprotic polar solvents such as N, N-dimethylformamide, dimethylacetamide and dimethylsulfoxide; ether solvents such as diphenyl ether and anisole; or various organic solvents May be used as a mixture. The concentration of the soluble aliphatic polyester is usually 3 to
The concentration is 50% by weight, but the concentration is not particularly limited as long as the aliphatic polyester solution can be stirred. When an organic solvent is used during the polymerization, the polymerization liquid can be used as it is after the polymerization reaction.

The acidic substance used in the method for insolubilizing and separating the catalyst includes hydrogen chloride, sulfuric acid, nitric acid, phosphoric acid, and the like.
Inorganic acids such as pyrophosphoric acid, or methanesulfonic acid, p-
Examples thereof include organic sulfonic acids such as toluenesulfonic acid, and among inorganic acids, sulfuric acid, phosphoric acid, and pyrophosphoric acid are preferable.

The amount of the acidic substance used is 1.00 to 10.0 equivalents, preferably 1.05 to 8.0 equivalents, based on the contained catalyst.
It is 0 equivalent. If the amount is less than the above range, the effect of removing the catalyst tends to decrease. If the amount is more than 10.0 equivalents, problems such as deterioration of the polymer may occur. Further, the use of an excessive amount of the acidic substance does not have any effect on the removal of the catalyst, and further requires excessive purification for removing the acidic substance. The temperature when treating with an acidic substance is usually 0 to
It is carried out in the range of 150 ° C., but it depends on the type of acidic substance used. For example, when using an organic sulfonic acid such as sulfuric acid, methanesulfonic acid, or p-toluenesulfonic acid, 0 to 60 ° C, preferably 10 to 50 ° C, a phosphoric acid compound such as phosphoric acid or pyrophosphoric acid is used. In that case, 20
The temperature is 150 ° C, preferably 50 to 130 ° C. If the temperature is lower than the above temperature range, the rate of conversion of the catalyst into a precipitate will be low, and if it is too high, the polymer will deteriorate. The contact time of the acidic substance may be 0.1 to 24 hours, preferably 0.5 to 24 hours.
~ 12 hours. If the time is less than 0.1 hour, the removal of the catalyst may be insufficient, and if the time exceeds 24 hours, some compounds may deteriorate.

The contact method of the acidic substance may be any of a batch system, a semi-batch system and a continuous system.

The aliphatic polyester solution in which the catalyst has been insolubilized in this manner contains an excessive amount of acidic substances. In some cases, such as in the course of operations such as concentration for isolating the aliphatic polyester, the aliphatic polyester is In order to decompose, it is necessary to neutralize excess acidic substances depending on the subsequent operation. As a neutralizing agent for acidic substances, use carbonates of alkali metals and alkaline earth metals such as sodium carbonate, potassium carbonate, calcium carbonate, and magnesium carbonate. After neutralization, insolubles are removed by filtration together with catalyst insolubilized substances. As a result, an aliphatic polyester solution containing no insoluble matter is obtained. The amount of the neutralizing agent used for the neutralization may be an amount sufficient to neutralize the acidic substance remaining in the aliphatic polyester solution, and the neutralization time is such that the acidic substance reacts with the neutralizing agent. It is sufficient that the neutralizing agent is added to the aliphatic polyester solution and stirred for 10 minutes or more, preferably 30 minutes or more. The neutralization temperature is not particularly limited, and is usually at the same temperature as the treatment temperature with an acidic substance.

As described above, the low molecular weight compound is removed from the aliphatic polyester removed by inactivating the catalyst or by insolubilizing the catalyst to isolate the aliphatic polyester. After cooling to crystallize and isolate the aliphatic polyester,
A method in which a poor solvent is added to an aliphatic polyester in a solution state to isolate the aliphatic polyester by precipitation and crystallization, and a method in which the aliphatic polyester is isolated by removing the solvent and low-molecular compounds by distillation, and preferably by distillation To remove.

In the present invention, the distillation of the low molecular weight compound includes the evaporation of the low molecular weight compound contained in the polymer in addition to the distillation of the low molecular weight compound dissolved in the solvent. The conditions for isolating the aliphatic polyester by distillation depend on the distillation apparatus, but are usually performed at 300 ° C. or lower. If kept at a very high temperature for a long time, decomposition of the aliphatic polyester is likely to occur.
50 ° C. or lower is preferred. If the temperature is too low, the removal of the low-molecular compound by distillation takes a long time, so that the temperature is preferably 120 ° C. or higher. The pressure in the system depends on the operating temperature, but is usually 50
mmHg or less, preferably 10 mmHg or less, more preferably 5 mmHg or less.

It is also possible to enhance the effect of removing low molecular compounds contained in the aliphatic polyester by passing an inert gas into the system during vacuum distillation. Examples of the inert gas include nitrogen, helium, neon, and argon. Preferably, nitrogen is used.

The time required to remove the low molecular weight compound by distillation varies depending on the type of aliphatic polyester, the distillation temperature, the degree of reduced pressure, the apparatus for performing the distillation, and the like. Removal of low molecular weight compounds
In the case of performing at 180 to 200 ° C. and a degree of reduced pressure of 5 mmHg or less, about 5 to 6 hours is sufficient. Distillation temperature 250
If carried out at a temperature of not less than ° C., the effect of removing low molecular compounds is further improved, and the distillation time can be shortened. However, if the temperature is kept too high, decomposition of the polymer tends to occur, which is not preferable.
At a temperature of 120 ° C. or lower, it takes a long time to remove the low-molecular compound. By increasing the degree of vacuum and keeping the degree of vacuum high, the distillation time can be further reduced.

The catalyst contains a catalyst deactivated by these methods, preferably has an amount of 100 ppm or less, more preferably 50 ppm or less, and has a residual amount of low molecular weight compound of 1% or less. An aliphatic polyester having excellent weather resistance can be obtained.

[0040]

Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, the physical property value in an Example, etc. were measured by the following methods.

Average molecular weight of polymer The average molecular weight (weight average molecular weight) of the polymer was measured by gel permeation chromatography using polystyrene as a standard under the following conditions. Apparatus: Shimadzu LC-10AD Detector: Shimadzu RID-6A Column: Hitachi Chemical GL-S350DT-5 + GL-S3
70DT-5 Solvent: chloroform Concentration: 1% Injection volume: 20 μl Flow rate: 1.0 ml / min

Content of Low Molecular Weight Compound The aliphatic polyester was dissolved in chloroform and measured by flame ionization detector (FID) gas chromatography (column: silicon OV-210: 2 m × 3 mmφ, column temperature: 140 ° C.). . Hereinafter, the amount of the low-molecular compound is represented by weight%.

The content of the catalyst was measured by X-ray fluorescence analysis.

Heat resistance test Using TG / DTA220 manufactured by Seiko Denshi Kogyo Co., Ltd., in dry Air at a temperature rising rate of 10 ° C./min.
The temperature at the time of weight loss was measured.

A weather resistance test A pressed film (thickness: 100 μm) was prepared under the conditions of 180 ° C./100 kg / cm ² . The resulting film was converted to a Suga Standard Sunshine Weather Meter (W
E-SUN) using a carbon arc light source at 120
It was held for 400 hours under the condition of minutes (18 minutes shower). A tensile strength test was performed on the film before and after the test, and the strength retention was calculated.

Production Example 1 10 kg of L-lactide and 0.2% by weight of tin octoate
(20 g) and 2% by weight of lauryl alcohol (200
g) was sealed in a thick cylindrical stainless steel polymerization vessel equipped with a stirrer, degassed under vacuum for 2 hours, and then replaced with nitrogen gas. The mixture was stirred at 180 ° C. under a nitrogen atmosphere.
For 3 hours. While maintaining the temperature as it was, it was gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver, and the pressure inside the reaction vessel was reduced to 3 mmHg. One hour after the start of degassing, the inside of the vessel was replaced with nitrogen, and the polymer was drawn out from the lower part of the vessel in a string form and pelletized to obtain poly L-lactic acid. The average molecular weight of this polymer is 90,000 and the Sn content is 5
The content of lactide was 50 ppm and 2.8%.

Production Example 2 10 kg of L-lactide, 8 kg of L-lactide and D
Pelletization was performed in the same manner as in Production Example 1 except that L-lactide was changed to 2 kg to obtain poly-DL-lactic acid. The average molecular weight of this polymer was 70,000, the Sn content was 600 ppm, and the lactide content was 3.1%.

Production Example 3 Pelletization was carried out in the same manner as in Production Example 1 except that 10 kg of L-lactide was changed to 8 kg of L-lactide and 2 kg of glycolide to obtain a copolymer of L-lactide and glycolide. The average molecular weight of this polymer was 80,000, the Sn content was 600 ppm, the content of lactide was 2.5%, and the content of glycolide was 0.5%.

Production Example 4 10 kg of 90% by weight L-lactic acid was added at 150 ° C./50 mmHg.
After distilling water while stirring for 3 hours, 57.0 g of stannous chloride (dihydrate) was added, and 150 ° C./30 mmH
g was further stirred for 2 hours to oligomerize. To this oligomer, 21.1 kg of diphenyl ether was added and 150
An azeotropic dehydration reaction was performed at a temperature of 35 ° C./35 mmHg, and the distilled water and the solvent were separated by a water separator, and only the solvent was returned to the reactor.
Four hours later, the organic solvent to be returned to the reactor was passed through a column packed with 4.6 kg of molecular sieve 3A, and then returned to the reactor. A polylactic acid solution having a molecular weight of 120,000 was obtained. The Sn content in this polymer solution is 800 pp
m (about 3200 ppm based on the polymer) and the amount of lactide in the solution was 1.2% (about 4.8% based on the polymer).

Production Example 5 5 kg of 90 wt% L-lactic acid and 0.6 kg of 70 wt% glycolic acid were distilled at a temperature of 140 ° C./50 mmHg for 3 hours to distill water, and then stannous chloride (dihydrate) was added. ) 22.
4 g was added, and the mixture was further stirred at 150 ° C./50 mmHg for 3 hours to be oligomerized. 6 kg of diphenyl ether was added to this oligomer, and the solvent was returned to the reactor through a column filled with molecular sieve 3A.
Reflux at 50 ° C./25 mmHg for 50 hours to give an average molecular weight of 1
0,000 copolymer solutions were obtained. S in this polymer solution
n content is 1200 ppm (about 304
0 ppm), 1.3% of lactide in solution (about 3.3% based on copolymer), 0.2 of glycolide in solution
% (About 0.5% based on the copolymer).

Production Example 6 12.0 kg of diphenyl ether and 29.0 g of tin metal powder were added to 2.0 kg of ethylene glycol and 3.8 kg of succinic acid.
And heated and stirred at 130 ° C./140 mmHg for 7 hours while distilling water out of the system to oligomerize.
The azeotropic dehydration was performed at 0 ° C./30 mmHg for 8 hours. Further, a column packed with molecular sieve 3A was attached, and the distilled solvent was returned to the reactor via the column packed with molecular sieve 5A, and the temperature was changed to 130 ° C./17 mmHg.
For 50 hours to obtain a copolymer solution having an average molecular weight of about 120,000. This solution was filtered to remove insoluble metallic tin powder. The Sn content in this copolymer solution is 900 ppm
Met.

Example 1 2 kg of the poly L-lactic acid obtained in Production Example 1 was heated and melted at 180 ° C. under a nitrogen atmosphere, and 1.65 g of pyrophosphoric acid (Sn
Was calculated in terms of divalent and 2.0 equivalents), and heated and stirred at 180 ° C. for 1 hour to inactivate the catalyst. Thereafter, while maintaining the temperature as it was, the air was gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver, and the pressure in the system was finally reduced to 3 mmHg, and the contained low molecular compounds were distilled off. After 5 hours with the system at 3 mmHg, the inside of the vessel was replaced with nitrogen,
The poly-L-lactic acid was extracted into a string and pelletized. The average molecular weight of the poly-L-lactic acid thus obtained was 90,000 and did not change. The amount of residual lactide in the poly-L-lactic acid was 0.1.
2%. A heat resistance test of the resulting polymer showed that the 5% weight loss temperature was 320 ° C. Also,
The tensile strength of the obtained press film before the weathering test is 60.
It was 0 kg / cm ² , and the strength retention after 400 hours of the weathering test was 90%.

Example 2 A treatment was performed in the same manner as in Example 1 except that nitrogen gas was coupled from the lower part of the vessel through a capillary tube when removing low-molecular compounds by distillation. The average molecular weight of the poly-L-lactic acid thus obtained was 90,000 and did not change. Further, the amount of residual lactide in poly L-lactic acid was 0.1%. When a heat resistance test was performed on the obtained polymer, the 5% weight loss temperature was 320 ° C. The tensile strength of the obtained press film before the weather resistance test was 600 kg / cm ² ,
The strength retention after 400 hours of the weather resistance test was 95%.

Example 3 Example 1 was repeated except that 1.4 g of 98% phosphoric acid (2.0 equivalents calculated based on Sn as divalent) was added instead of pyrophosphoric acid.
The same processing was performed. The average molecular weight of the obtained poly L-lactic acid was 90,000, which was not changed. The amount of residual lactide in poly L-lactic acid was 0.2%. A heat resistance test was performed on the obtained polymer.
° C. The tensile strength of the obtained press film before the weather resistance test was 550 kg / cm ² , and the strength retention after 400 hours of the weather resistance test was 90%.

Example 4 2 kg of the poly DL-lactic acid obtained in Production Example 2 was heated and melted at 180 ° C. in a nitrogen atmosphere, and 1.65 g of pyrophosphoric acid (S
n is calculated as divalent and 2.0 equivalents) are added at 180 ° C.
The mixture was heated and stirred for an hour to inactivate the catalyst. Thereafter, while maintaining the temperature, the air was gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver, and finally the inside of the system was 3 mmH
g, and the contained low molecular weight compound was distilled off. After 5 hours with the inside of the system being 3 mmHg, the inside of the system was replaced with nitrogen, and the polymer was extracted in a string form and pelletized. The average molecular weight of the copolymer thus obtained was unchanged at 70,000. The amount of residual lactide in the copolymer was 0.2%. When a heat resistance test was performed on the obtained copolymer, the 5% weight loss temperature was 310 ° C. The tensile strength of the obtained press film before the weather resistance test was 530.
kg / cm ² , and the strength retention after 400 hours of the weather resistance test was 90%.

Example 5 2 kg of the copolymer of L-lactide and glycolide obtained in Production Example 3 was heated and melted at 180 ° C. under a nitrogen atmosphere, and 1.8 g of pyrophosphoric acid (Sn was calculated as divalent to 2 .0
The catalyst was heated and stirred at 180 ° C. for 1 hour to inactivate the catalyst. Thereafter, while keeping the temperature as it was, the system was gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver, and the pressure in the system was finally reduced to 3 mmHg, and the contained low-molecular compounds were distilled off. After 5 hours at 3 mmHg in the system, the inside of the system was replaced with nitrogen and the copolymer was extracted in a string form and pelletized. The average molecular weight of the copolymer thus obtained was unchanged at 80,000. The amount of residual lactide and the amount of glycolide in the copolymer were each 0.1%.
% And 0.1%. When a heat resistance test was performed on the obtained copolymer, the 5% weight loss temperature was 320 ° C. The tensile strength of the obtained press film before the weather resistance test was 590 kg / cm ² , and the weather resistance test 4
The strength retention after 00 hours was 90%.

Example 6 4 kg of the poly-L-lactic acid solution obtained in Production Example 4 was kept at 150 ° C. under a nitrogen atmosphere, and 2.4 g of pyrophosphoric acid (Sn was 2
(2.0 equivalents calculated based on the value), and the mixture was heated with stirring for 1 hour to inactivate the catalyst. Thereafter, the temperature was increased to 180 ° C., and the system was gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver. The pressure in the system was finally reduced to 3 mmHg, and diphenyl ether and low-molecular compounds of the solvent were distilled off. After 5 hours with the inside of the system being 3 mmHg, the inside of the system was replaced with nitrogen, and the polymer was extracted in a string form and pelletized. The average molecular weight of the poly L-lactic acid thus obtained was 120,000, which was unchanged. The residual lactide content in the polymer was 0.2%. When a heat resistance test was performed on the obtained polymer, the 5% weight loss temperature was 315 ° C. The tensile strength of the obtained press film before the weather resistance test was 620.
kg / cm ² , and the strength retention after 400 hours of the weather resistance test was 90%.

Example 7 4 kg of the poly-L-lactic acid solution obtained in Production Example 4 was heated to 150 ° C. under a nitrogen atmosphere, and 2.4 g of pyrophosphoric acid (2.0 equivalents, calculated based on divalent Sn) was added. Then, the mixture was heated and stirred at 150 ° C. for 1 hour to inactivate the catalyst. Thereafter, 4 kg of diphenyl ether was added to the solution, and the solution was cooled to 40 ° C., and the polymer was cooled and crystallized. The polymer was filtered and separated from the solvent, and the polymer was washed with isopropyl alcohol to remove low molecular weight compounds. The poly L-lactic acid thus obtained was dried under reduced pressure to remove the solvent, thereby obtaining a powdery poly L-lactic acid.
The average molecular weight of the resulting polymer was unchanged at 120,000. The amount of lactide remaining in the polymer was 0.1%. When a heat resistance test of the obtained polymer was performed,
The 5% weight loss temperature was 320 ° C. The tensile strength of the obtained press film before the weather resistance test was 600 kg.
/ Cm ² , and the strength retention after 400 hours of the weather resistance test was 95%.

Example 8 2 kg of the poly-L-lactic acid obtained in Production Example 1 was charged into a table-type kneader, heated and melted at 180 ° C. under a nitrogen atmosphere, and 1.65 g of pyrophosphoric acid (Sn divalent) was added. Calculate 2.0
The catalyst was heated and stirred at 180 ° C. for 1 hour to inactivate the catalyst. Thereafter, the temperature was lowered to 120 ° C., and the system was gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver. The pressure in the system was finally reduced to 3 mmHg, and the contained low molecular weight compounds were distilled off. System temperature is 120 ℃
Since the poly-L-lactic acid was solidified, the removal of the low molecular weight compound by distillation was carried out while forcibly pulverizing the poly-L-lactic acid with a tabletop kneader. After 8 hours with the inside of the system being 3 mmHg, the inside of the system was replaced with nitrogen to take out the ground poly-L-lactic acid. The average molecular weight of the obtained poly L-lactic acid was 90,000, which was not changed. The residual amount of lactide was 0.2%.
When a heat resistance test was performed on the obtained polymer, the 5% weight loss temperature was 320 ° C. The tensile strength of the obtained press film before the weather resistance test was 600 kg / cm.
² , and the strength retention after 400 hours of the weathering test was 90%.
%Met.

Example 9 0.5 kg of poly L-lactic acid obtained in Production Example 1 was dissolved in 4.5 kg of chloroform, and 0.5 g of 98% sulfuric acid was added thereto.
(2.2 equivalents of Sn calculated as divalent) and added at 25 ° C.
After stirring for 1 hour, 15.0 g of calcium carbonate was added, and the mixture was further stirred at 25 ° C for 30 minutes. Next, this solution was filtered to remove precipitated insoluble matter such as a catalyst. After chloroform as a solvent was distilled off from the polymer solution under reduced pressure, the pressure inside the system was finally reduced to 180 ° C. and 3 mmHg to remove low molecular compounds. After keeping the inside of the system at 180 ° C./3 mmHg for 5 hours, the inside of the system was replaced with nitrogen, and the polymer was extracted in a string form and pelletized. The molecular weight of the resulting polymer was unchanged at 90,000. The remaining lactide amount is 0.2%, S
The n content was 10 ppm. A heat resistance test was performed on the obtained polymer, and the 5% weight loss temperature was 320 ° C.
Met. Further, the tensile strength of the obtained press film before the weather resistance test was 610 kg / cm ² , the strength retention after 400 hours of the weather resistance test was 100%, and both heat resistance and weather resistance were good.

Example 10 0.5 kg of the poly DL-lactic acid obtained in Production Example 2 was added to 1,2
Dissolved in 4.5 kg of dichloroethane, to which 98%
0.5 g of sulfuric acid (2.2 equivalents of Sn calculated as divalent) was added, and the mixture was stirred at 25 ° C. for 4 hours.
0 g was added and the mixture was further stirred at 25 ° C. for 30 minutes. Next, this solution was filtered to remove precipitated insoluble matter such as a catalyst. After distilling off 1,2-dichloroethane as a solvent from the polymer solution under reduced pressure, the pressure in the system was finally reduced to 180 ° C. and 3 mmHg to remove low molecular compounds. 180 ° C /
After 5 hours while maintaining the pressure at 3 mmHg, the inside of the system was replaced with nitrogen, and the copolymer was extracted in a string form and pelletized. The average molecular weight of the obtained polymer was unchanged at 70,000. The residual lactide amount was 0.2%, and the Sn content was 7 ppm. When a heat resistance test was performed on the obtained copolymer, the 5% weight loss temperature was 310 ° C. The tensile strength of the obtained press film before the weather resistance test was 540.
kg / cm ² , the strength retention after 400 hours of weathering test was 100%, and both heat resistance and weather resistance were good.

Example 11 0.5 kg of the copolymer of L-lactide and glycolide obtained in Production Example 3 was dissolved in 4.5 kg of chloroform, and 0.6 g of 98% sulfuric acid was added thereto. (2.4 equivalents) and stirred at 25 ° C. for 4 hours. Then, 20.0 g of calcium carbonate was added and the mixture was further stirred at 25 ° C. for 30 minutes. Next, this solution was filtered to remove precipitated insoluble matter such as a catalyst. After the solvent chloroform was distilled off under reduced pressure from the polymer solution, the inside of the system was finally heated to 180 ° C., 3 mm
The pressure was reduced to Hg to remove low molecular compounds. 1 in the system
After 5 hours while maintaining the temperature at 80 ° C./3 mmHg, the inside of the system was replaced with nitrogen, and the polymer was extracted in a string form and pelletized. The average molecular weight of the obtained polymer was 80,000 and did not change. The amounts of residual lactide and glycolide were 0.1% and 0.1%, respectively, and the Sn content was 10 ppm. When a heat resistance test was performed on the obtained copolymer, the 5% weight loss temperature was 315 ° C. The tensile strength of the obtained press film before the weather resistance test was 580.
kg / cm ² , the strength retention after 400 hours of weathering test was 95%, and both heat resistance and weather resistance were good.

Example 12 To 2.0 kg of the poly L-lactic acid solution obtained in Production Example 4, 3.0 kg of chloroform was added, and 2.7 g of 98% sulfuric acid was added thereto.
(2.0 equivalents of Sn calculated as divalent) was added, and the mixture was stirred at 25 ° C. for 5 hours. Then, 15.0 g of calcium carbonate was added, and the mixture was further stirred for 30 minutes. Next, this solution was filtered to remove insoluble matters such as a catalyst. From this polymer solution, chloroform and diphenyl ether as solvents were distilled off under reduced pressure, and the pressure in the system was finally reduced to 180 ° C. and 3 mmHg to remove low molecular compounds. After keeping the inside of the system at 180 ° C./3 mmHg for 5 hours, the inside of the system was replaced with nitrogen, and the polymer was extracted in a string form and pelletized. The average molecular weight of the resulting polymer was unchanged at 120,000. Further, the residual lactide amount was 0.2% and the Sn content was 7 ppm. When a heat resistance test was performed on the obtained polymer, the 5% weight loss temperature was 320 ° C. The tensile strength of the obtained press film before the weather resistance test was 600 kg / cm ² ,
The strength retention after 400 hours of the weather resistance test was 100%, and both heat resistance and weather resistance were good.

Example 13 To 2.0 kg of the poly-L-lactic acid solution obtained in Production Example 4, 3.0 kg of diphenyl ether was added, and 3.6 g of pyrophosphoric acid (3.0 equivalents of Sn calculated as divalent) was added thereto. Plus 11
After stirring at 0 ° C. for 5 hours, the solution was filtered to remove the insolubilized catalyst. Next, the solution was cooled to 40 ° C., and the polymer was crystallized. After the crystallized polymer was separated from the catalyst by filtration, the low molecular weight compound adhering to the polymer was further removed by washing with isopropyl alcohol, and dried under reduced pressure to obtain powdery poly-L-lactic acid. The average molecular weight of the resulting polymer was unchanged at 120,000. Further, the residual lactide amount was 0.1% and the Sn content was 8 ppm.
When a heat resistance test was performed on the obtained polymer, the 5% weight loss temperature was 320 ° C. The tensile strength of the obtained press film before the weather resistance test was 600 kg / cm.
² , and the strength retention after 400 hours of the weather resistance test was 10
At 0%, both heat resistance and weather resistance were good.

Example 14 3.75 kg of chloroform was added to 1.25 kg of the copolymer solution obtained in Production Example 5, and 2.5% of 98% sulfuric acid was added thereto.
g (2.0 equivalents of Sn calculated as divalent) and added at 25 ° C.
After stirring for 1 hour, 15.0 g of calcium carbonate was added, and the mixture was further stirred for 30 minutes. Next, this solution was filtered to remove precipitated insoluble matters such as a catalyst. From this copolymer solution, the solvent chloroform and diphenyl ether were distilled off under reduced pressure, and the pressure in the system was finally reduced to 180 ° C. and 3 mmHg to remove low molecular compounds. 220 ° C / 3 in the system
After 5 hours while maintaining the mmHg, the inside of the system was replaced with nitrogen, and the polymer was extracted in a string form and pelletized. The average molecular weight of the copolymer obtained was unchanged at 100,000. The amount of residual lactide and the amount of glycolide were each 0.1%.
And 0.1%, and the Sn content was 10 ppm. When a heat resistance test of the obtained polymer was performed,
The 5% weight loss temperature was 310 ° C. The tensile strength of the obtained press film before the weather resistance test was 570 kg.
/ Cm ² , the strength retention after 400 hours of weathering test was 95%, and both heat resistance and weather resistance were good.

Example 15 3.0 kg of chloroform was added to 2.0 kg of the copolymer solution obtained in Production Example 6, and 2.7 g of pyrophosphoric acid was added thereto.
(2.0 equivalents of Sn calculated as divalent) and added at 60 ° C.
After stirring for 1 hour, 15.0 g of calcium carbonate was added, and the mixture was further stirred at 60 ° C. for 1 hour. Next, this solution was filtered to remove precipitated insoluble matter such as a catalyst. From the polymer solution, chloroform and diphenyl ether as solvents were distilled off under reduced pressure, and the pressure in the system was finally reduced to 180 ° C. and 3 mmHg, and the low molecular weight compound was distilled off under reduced pressure. Five hours after finally maintaining the inside of the system at 180 ° C. and 3 mmHg, after the distillation of the low molecular weight compound was stopped, the inside of the system was replaced with nitrogen, and the polymer was extracted in a string form and pelletized. The average molecular weight of the copolymer obtained was unchanged at 120,000. The Sn content was 7 ppm. When a heat resistance test was performed on the obtained polymer, the 5% weight loss temperature was 300 ° C.
The tensile strength of the obtained press film before the weather resistance test was 350 kg / cm ² , the strength retention after 400 hours of the weather resistance test was 100%, and both the heat resistance and the weather resistance were good.

Comparative Example 1 The same treatment as in Example 1 was carried out except that 0.4 g of pyrophosphoric acid (0.5 equivalent calculated as Sn divalent) was added. The average molecular weight of the obtained poly L-lactic acid was 90,000, which was not changed.
The amount of residual lactide in poly L-lactic acid was 0.3%. A heat resistance test of the obtained polymer showed that the 5% weight loss temperature was 280 ° C. The tensile strength of the obtained press film before the weather resistance test was 600.
kg / cm ² , the strength retention after 400 hours of the weather resistance test was reduced to 60%, and both the heat resistance and the weather resistance were inferior to those of Example 1.

Comparative Example 2 The same treatment as in Example 1 was performed except that the distillation temperature of the low-molecular compound by distillation was kept at 260 ° C. Poly L obtained
-Lactic acid was colored deep brown, and the average molecular weight of poly L-lactic acid was reduced to 40,000.

Comparative Example 3 Removal of low molecular weight compounds by distillation was performed at 180 ° C. and a reduced pressure of 20 m.
The processing was performed in the same manner as in Example 1 except that the processing was performed at mHg. The average molecular weight of the obtained poly L-lactic acid was 90,000, which was not changed, but the residual lactide amount was 1.5%. A heat resistance test of the obtained polymer showed that the 5% weight loss temperature was 280 ° C. The tensile strength of the obtained press film before the weather resistance test was 590 kg / cm ² ,
The strength retention after 400 hours of the weather resistance test was reduced to 70%, and both the heat resistance and the weather resistance were inferior to those of Example 1.

Comparative Example 4 2 kg of the poly L-lactic acid obtained in Production Example 1 was heated and melted at 180 ° C. under a nitrogen atmosphere, and gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver. Finally 3
The pressure was reduced to mmHg, and the low-molecular compounds contained therein were distilled off. After 5 hours with the inside of the system at 3 mmHg, the inside of the container was replaced with nitrogen, and the poly-L-lactic acid was extracted in a string form and pelletized. The average molecular weight of the obtained poly L-lactic acid was 90,000, which was not changed. Further, the residual lactide amount in the poly-L-lactic acid was 0.7%, and the Sn content was 560 ppm. When a heat resistance test of the obtained polymer was performed, the 5% weight loss temperature was 270 ° C. The tensile strength of the obtained press film before the weather resistance test was 600 kg / cm ² , the strength retention after 400 hours of the weather resistance test was reduced to 50%, and both the heat resistance and the weather resistance were the same as those of Example 1. Inferior compared.

Comparative Example 5 2 kg of the copolymer obtained in Production Example 2 was heated and melted at 180 ° C. in a nitrogen atmosphere, and gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver, and the system was finally heated. 3m
The pressure was reduced to mHg, and the low-molecular compounds contained therein were distilled off. After 5 hours with the inside of the system at 3 mmHg, the inside of the vessel was replaced with nitrogen, and the copolymer was extracted in a string form and pelletized.
The average molecular weight of the obtained copolymer was unchanged at 70,000. The amount of residual lactide in the copolymer was 0.6
%, Sn content was 560 ppm. When a heat resistance test was performed on the obtained copolymer, the 5% weight loss temperature was 270 ° C. Further, the tensile strength of the obtained press film before the weather resistance test was 540 kg / cm ² ,
The strength retention after 400 hours of the weather resistance test was reduced to 40%, and both heat resistance and weather resistance were inferior.

Comparative Example 6 2 kg of the copolymer obtained in Production Example 3 was heated and melted at 180 ° C. in a nitrogen atmosphere, gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver, and finally the system was finally degassed. 3m
The pressure was reduced to mHg, and the low-molecular compounds contained therein were distilled off. After 5 hours with the inside of the system at 3 mmHg, the inside of the vessel was replaced with nitrogen, and the copolymer was extracted in a string form and pelletized.
The average molecular weight of the obtained copolymer was unchanged at 80,000. The amount of residual lactide and the amount of residual glycolide in the copolymer were 0.6% and 0.3%, respectively.
The content was 615 ppm. A heat resistance test of the resulting copolymer showed that the 5% weight loss temperature was 265.
° C. The tensile strength of the obtained press film before the weather resistance test was 570 kg / cm ² , the strength retention after 400 hours of the weather resistance test was reduced to 50%, and both the heat resistance and the weather resistance were inferior.

Comparative Example 7 4 kg of the poly-L-lactic acid solution obtained in Production Example 4 was heated to 180 ° C. under a nitrogen atmosphere, and gradually degassed by a vacuum pump through an exhaust pipe and a glass receiver. Finally 3m
The pressure was reduced to mHg, and the solvent diphenyl ether and low molecular weight compounds were distilled off. After 5 hours at 3 mmHg, the inside of the system was replaced with nitrogen, and the polymer was extracted in a string form and pelletized. The average molecular weight of the obtained poly L-lactic acid was 120,000, which was not changed, but the residual lactide amount was 4.0.
% And Sn content were 3300 ppm. When a heat resistance test was performed on the obtained polymer, the 5% weight loss temperature was 265 ° C. The tensile strength of the obtained press film before the weather resistance test was 600 kg / cm ² ,
Cracks occurred in the film after 400 hours of the weather resistance test, making the test impossible, and the heat resistance and weather resistance were poor.

Comparative Example 8 The same treatment as in Example 1 was carried out except that the distillation temperature of the low molecular weight compound by distillation was kept at 100 ° C. At 100 ° C., the poly-L-lactic acid was solidified. Therefore, the stirring was stopped, and the subsequent processing operation was carried out. The average molecular weight of the obtained poly-L-lactic acid was 90,000, but the residual amount of lactide varied from 2.1 to 5.9% depending on the sample location.

[0075]

Industrial Applicability According to the present invention, it is possible to obtain an aliphatic polyester excellent in heat resistance and weather resistance in which the catalyst contained is inactivated or the content of the catalyst is small and the content of the low molecular weight compound is small. .

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Akihiro Yamaguchi 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Inside Mitsui Toatsu Chemicals Co., Ltd. (56) References JP-A-60-248727 (JP, A) (58) Investigated Field (Int. Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (21)

(57) [Claims] (1) In the presence of a catalyst, (i) an aliphatic hydroxycarboxylic acid, (ii) a cyclic ester thereof, (iii) an aliphatic polyhydric alcohol and an aliphatic polybasic acid, or (iv)
When purifying an aliphatic polyester obtained by polymerizing a mixture of two or more of the above (i) to (iii), after inactivating the catalyst while keeping the aliphatic polyester in a molten or solution state, Or a method for purifying aliphatic polyesters, comprising removing a low molecular weight compound after insolubilizing and separating a catalyst. 2. The method according to claim 1, wherein the catalyst is deactivated by bringing phosphoric acid or phosphorous acid into contact with the aliphatic polyester, and then the low molecular compound is removed.
The described method. 3. The method according to claim 2, wherein the phosphoric acid is phosphoric acid or pyrophosphoric acid. 4. The method according to claim 2, wherein the low molecular weight compound is removed by distillation under reduced pressure. 5. The method according to claim 4, wherein the distillation under reduced pressure is performed at 5 mmHg or less. 6. The method according to claim 5, wherein the distillation is carried out at a temperature in the range of 120 ° C. to 250 ° C. 7. The method according to claim 2, wherein the low molecular weight compound is removed by crystallization. 8. The method according to claim 1, wherein the low molecular weight compound is removed after the aliphatic polyesters are contacted with an acidic substance to insolubilize and separate and remove the catalyst. 9. The method according to claim 8, wherein the acidic substance is an inorganic acid or an organic sulfonic acid. 10. The method according to claim 8, wherein the catalyst is insolubilized and removed after neutralizing excess acidic substances. 11. The method according to claim 8, wherein the low molecular weight compound is removed by distillation under reduced pressure. 12. The method according to claim 11, wherein the distillation under reduced pressure is performed under reduced pressure of 5 mmHg or less. 13. The method according to claim 12, wherein the distillation is performed at a temperature in the range of 120 ° C. to 250 ° C. 14. The method according to claim 8, wherein the low molecular weight compound is removed by crystallization. 15. The method of claim 1, wherein the aliphatic polyester is a homopolymer of an aliphatic hydroxycarboxylic acid or a cyclic ester of an aliphatic hydroxycarboxylic acid. 16. The method of claim 1, wherein the aliphatic polyester is a copolymer of an aliphatic hydroxycarboxylic acid or a cyclic ester of an aliphatic hydroxycarboxylic acid. 17. The method according to claim 15, wherein the aliphatic hydroxycarboxylic acid is lactic acid, glycolic acid, or 6-hydroxycaproic acid. 18. The method according to claim 16, wherein the aliphatic hydroxycarboxylic acid is lactic acid, glycolic acid, or 6-hydroxycaproic acid. 19. The aliphatic polybasic acid is succinic acid, and the aliphatic polyhydric alcohol is ethylene glycol and 1,4.
The method according to claim 1, wherein the at least one diol is selected from -butanediol. 20. In the production of polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid in the presence of a catalyst, it is necessary to deactivate the catalyst after the completion of the polymerization reaction and then remove the low-molecular compound under reduced pressure. A process for producing a characteristic polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid. 21. In the presence of a catalyst, (i) an aliphatic hydroxycarboxylic acid, (ii) a cyclic ester thereof, (iii) an aliphatic polyhydric alcohol and an aliphatic polybasic acid, or (i)
v) When purifying an aliphatic polyester obtained by polymerizing a mixture of two or more of the above (i) to (iii), an acidic substance is brought into contact with the aliphatic polyester dissolved in an organic solvent to form a catalyst. A method for purifying aliphatic polyesters, comprising, after insolubilizing and separating, removing a solvent and a low-molecular compound by distillation.