JP3135484B2 - Method for producing polyhydroxycarboxylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polyhydroxycarboxylic acid useful as a biodegradable polymer as a substitute for a medical material or a general-purpose resin.

[0002]

2. Description of the Related Art Polyhydroxycarboxylic acids have excellent mechanical, physical and chemical properties, and are decomposed in a natural environment without harm to others. It has a biodegradable function of becoming carbon dioxide gas and has been attracting attention in various fields such as medical materials and alternatives to general-purpose resins from the viewpoint of environmental protection in recent years. Have been.

[0003] In general, a method for producing a polyhydroxycarboxylic acid includes, in the case of a hydroxycarboxylic acid such as lactic acid or glycolic acid, dehydration and dimerization to obtain a cyclic dimer and then ring opening in the presence of various catalysts. It is known that a high molecular weight polymer can be obtained by melt polymerization. This method
The production of lactide or glycolide, which is a cyclic dimer, is uneconomic because it requires a great deal of labor and cost. Some hydroxycarboxylic acids do not form a cyclic dimer, in which case this method cannot be used.

On the other hand, several methods for obtaining polyhydroxycarboxylic acids from hydroxycarboxylic acids and oligomers thereof by direct dehydration have been disclosed (Japanese Patent Application Laid-Open No. 59-1984).
No.-096123, JP-A-61-028521). However, the logarithmic viscosity of the polymer obtained by these methods is limited to about 0.3 dl / g, and the polymer does not have sufficient mechanical properties and cannot be used depending on its use or purpose. The applicant of the present invention heated and refluxed a hydroxycarboxylic acid or an oligomer thereof in an organic solvent in the presence of a catalyst, and in this case, dehydrated the solvent distilled off with a drying agent and then returned it to the system again. Several methods for obtaining about 100,000 polyhydroxycarboxylic acid have been disclosed previously (Japanese Patent Laid-Open Publication No.
-172502, JP-A-06-65360). However, even in this method, to obtain a polyhydroxycarboxylic acid having an average molecular weight of about 200,000, a reaction temperature of 130.degree.
When the obtained polyhydroxycarboxylic acid is formed into a sheet, a film, etc., it takes a long time of about 30 hours under reflux at ℃, and only a low-transparent product is obtained due to coloring of the polymer at the time of polymerization. There was a problem that there was not, and it was not satisfactory.

[0005]

The direct polymerization of hydroxycarboxylic acids such as lactic acid and glycolic acid is a sequential reaction, similar to the esterification reaction between dibasic acids and polyhydric alcohols, and the molecular weight increases with the reaction time. . In addition, since water molecules generated at this time have a function of reducing the molecular weight of the polycondensate by a reverse reaction due to hydrolysis, it is necessary to efficiently remove generated water to the outside of the system to obtain a high molecular weight polymer. It is necessary for

Usually, as a means for removing water, a method of distilling a solvent and entraining or azeotropically entraining water is employed.
By increasing the amount of the solvent distilled off as much as possible, the generated water can be removed more quickly and out of the system.

[0007] In order to increase the amount of the solvent distilled off, supply of heat into the reactor by external heating can be mentioned. However, since the viscosity of the reaction system increases significantly with an increase in the molecular weight,
The thermal conductivity to the inside of the reaction system deteriorates, and the amount of distillate decreases significantly. As a countermeasure, there are a method of increasing the stirring speed and a method of increasing the temperature of external heating. However, the stirring speed is limited, and if the temperature of the external heating is too high, the polymer and the catalyst are thermally degraded, which causes coloring of the polymer and a decrease in the molecular weight.

[0008]

The present inventors have conducted intensive studies on a direct dehydration polymerization method capable of producing polyhydroxycarboxylic acid efficiently, easily and inexpensively on an industrial scale. As a result, the reaction temperature and the polymerization rate were determined. There is a close relationship between the color of the obtained polymer and the color tone of the obtained polymer. By controlling the reaction temperature, it has been found that a polymer with less coloring can be obtained, and the present invention has been achieved.

That is, the present invention provides a method for obtaining a polyhydroxycarboxylic acid by subjecting a hydroxycarboxylic acid or an oligomer thereof to heating and refluxing in an organic solvent in the presence of a catalyst to carry out a dehydration polycondensation reaction.
The reaction temperature until reaching 100,000 is 80 to 200 ° C.
A method for producing a polyhydroxycarboxylic acid, characterized in that the reaction temperature when it exceeds 10,000 is 80 to 125 ° C.

An object of the present invention is to provide a method for obtaining a highly transparent polyhydroxycarboxylic acid with less coloring by a direct dehydration polycondensation reaction of a hydroxycarboxylic acid. It provides a method for efficient manufacturing

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of the hydroxycarboxylic acid used in the present invention include the following.
Glycolic acid, lactic acid, 2-hydroxybutanoic acid, 2-hydroxypentanoic acid, 2-hydroxyhexanoic acid, 2-hydroxyheptanoic acid, 2-hydroxyoctanoic acid, 2-hydroxy-2 -Methylpropanoic acid, 2-hydroxy-2-methylbutanoic acid, 2-hydroxy-2-ethylbutanoic acid, 2-hydroxy-2-methylpentanoic acid, 2-hydroxy-2-ethyl Pentanoic acid, 2-hydroxy-2-propylpentanoic acid, 2-hydroxy-2-butylpentanoic acid, 2-hydroxy-2-methylhexanoic acid, 2-hydroxy-2-ethylhexano Ic acid, 2-hydro Ci-2-propylhexanoic acid, 2-hydroxy-2-butylhexanoic acid, 2-hydroxy-2-pentylhexanoic acid, 2-hydroxy-2-methylheptanoic acid, 2-hydroxy- 2-methylheptanoic acid, 2-hydroxy-2-ethylheptanoic acid, 2-hydroxy-2-propylheptanoic acid, 2-hydroxy-2-butylheptanoic acid, 2-hydroxy-2 -Pentylheptanoic acid, 2-hydroxy-2-hexylheptanoic acid, 2-hydroxy-2-methyloctanoic acid, 2-hydroxy-2-ethyloctanoic acid, 2-hydroxy-2- Propyl octanoic acid, 2-hydroxy 2 × butyl octanoic acid, 2-hydroxy-2-pentyl octanoic acid, 2-hydroxy-2-hexyl octanoic acid, 2-hydroxy-2-heptyl octanoic acid, 3-hydroxypropanoic Acid, 3-hydroxybutanoic acid, 3
-Hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid,
3-hydroxy-3-methylbutanoic acid, 3
-Hydroxy-3-methylpentanoic acid, 3
-Hydroxy-3-ethylpentanoic acid, 3
-Hydroxy-3-methylhexanoic acid, 3
-Hydroxy-3-ethylhexanoic acid, 3
-Hydroxy-3-propylhexanoic acid,
3-hydroxy-3-methylheptanoic acid,
3-hydroxy-3-ethylheptanoic acid,
3-hydroxy-3-propylheptanoic acid, 3-hydroxy-3-butylheptanoic acid, 3-hydroxy-3-methyloctanoic acid, 3-hydroxy-3-ethyloctanoic acid, 3- Hydroxy-3-propyl octanoic acid, 3-hydroxy-3-butyl octanoic acid, 3-hydroxy-3-pentyl octanoic acid, 4-hydroxybutanoic acid, 4-hydroxypentanoic acid, 4-hydroxyhexanoic acid, 4-hydroxyheptanoic acid, 4-hydroxyoctanoic acid, 4-
Hydroxy-4-methylpentanoic acid, 4-
Hydroxy-4-methylhexanoic acid, 4-
Hydroxy-4-ethylhexanoic acid, 4-
Hydroxy-4-methylheptanoic acid, 4-
Hydroxy-4-ethylheptanoic acid, 4-
Hydroxy-4-propylheptanoic acid, 4
-Hydroxy-4-methyloctanoic acid, 4
-Hydroxy-4-ethyloctanoic acid, 4
-Hydroxy-4-propyloctanoic acid,
4-hydroxy-4-butyloctanoic acid,
5-hydroxypentanoic acid, 5-hydroxahexanoic acid, 5-hydroxyheptanoic acid, 5-hydroxyoctanoic acid, 5-hydroxy-5-methylhexanoic acid, 5-hydroxy-5 -Methylheptanoic acid, 5-hydroxy-5-ethylheptanoic acid, 5-hydroxy-5-methyloctanoic acid, 5-hydroxy-5-ethyloctanoic acid, 5-hydroxy-5-propyl Octanoic acid, 6-hydroxyhexanoic acid, 6-hydroxyheptanoic acid, 6-hydroxyoctanoic acid, 6-hydroxy-6-methylheptanoic acid, 6-hydroxy-6-methyloctano Ic Acid 6-hydroxy-6-ethyl-octanoic acid, 7-hydroxy-heptanoate dichroic acid, 7-hydroxy-octanoic acid, 7-
Hydroxy-7-methyloctanoic acid, 8-
And aliphatic hydroxycarboxylic acids such as hydroxyoctanoic acid. These may be used alone or as a mixture of two or more. Particularly preferably used hydroxycarboxylic acids are lactic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, or a mixture thereof.

In the method of the present invention, an oligomer derived from the above-mentioned hydroxycarboxylic acid can be used as a raw material. And they may be used as one kind or a mixture of two or more kinds.

These hydroxycarboxylic acids and their oligomers have an optically active carbon and have D-form and L-form, respectively.
Although it may take the form of a body or a D / L body, the form is not limited in the present invention.

Examples of the catalyst used in the present invention include metals belonging to Groups I, II, III, IV and V of the periodic table of the elements, or salts, hydroxides and oxides thereof.

Metals such as zinc, tin, aluminum, magnesium, antimony, titanium, zirconium and the like;
Metal oxides such as tin oxide, antimony oxide, lead oxide, aluminum oxide, magnesium oxide, and titanium oxide; zinc chloride, stannous chloride, stannous bromide, antimony fluoride, zinc chloride, magnesium chloride, and aluminum chloride Metal halides such as tin hydroxide, sodium hydroxide,
Potassium hydroxide, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, zinc hydroxide, iron hydroxide, cobalt hydroxide, nickel hydroxide, copper hydroxide, cesium hydroxide, strontium hydroxide, barium hydroxide, hydroxide Metal hydroxides such as lithium and zirconium hydroxide; sulfates such as tin sulfate, zinc sulfate, and aluminum sulfate; carbonates such as magnesium carbonate, zinc carbonate, and calcium carbonate; tin acetate, tin octoate, tin lactate, and zinc acetate And organic carboxylate salts such as aluminum acetate and iron lactate; and organic sulfonic acid salts such as tin trifluoromethanesulfonate and tin p-toluenesulfonate.

In addition, an organic metal oxide of the above metal such as dibutyltin oxide or a metal alkoxide of the above metal such as titanium isopropoxide or an alkyl metal of the above metal such as diethyl zinc, and ion exchange such as Dowex or Amberlite Resins. In particular, in order to obtain a polymer having little coloring and a high molecular weight, it is preferable to use tin and / or a divalent tin compound. The amount used is 0.0001 to 10 of the above hydroxycarboxylic acid or an oligomer thereof.
It is preferred to use% by weight.

The organic solvent used in the present invention is not particularly limited, but is preferably an aromatic hydrocarbon, an ether-based aromatic hydrocarbon, or the like. Examples of the aromatic hydrocarbons include toluene, xylene, biphenyl, naphthalene, chlorobenzene, o-dichlorobenzene, m-dichlorobenzene, and p.
-Dichlorobenzene, 1-chloronaphthalene and the like. Examples of the ether-based aromatic hydrocarbons include alkoxybenzenes and diphenyl ethers. Examples of the alkoxybenzenes include anisole, ethoxybenzene, propoxybenzene, butoxybenzene, pentoxybenzene, 2,4-dimethoxybenzene, 2-chloromethoxybenzene, 2-bromomethoxybenzene,
-Chloromethoxybenzene, 4-bromomethoxybenzene, 2,4-dichloromethoxybenzene and the like. As diphenyl ethers, diphenyl ether, 4,4'-dimethyldiphenyl ether, 3,3 '
Alkyl-substituted diphenyl ethers such as dimethyl diphenyl ether and 3-methyl diphenyl ether;
'-Dibromodiphenyl ether, 4-methyl-4'-
Halogen-substituted diphenyl ethers such as bromodiphenyl ether; 4-methoxydiphenyl ether, 4,4 '
Alkoxy-substituted diphenyl ethers such as -dimethoxydiphenylether, 3,3'-dimethoxydiphenylether and 4-methyl-4'-methoxydiphenylether; and cyclic diphenylethers such as dibenzofuran and xanthene. Preferably, anisole, diphenyl ether, naphthalene, o-dichlorobenzene and the like are preferred. These may be one kind or a mixture of two or more kinds, and there is no limitation.

In the reaction of the present invention, the viscosity of the solution extremely increases with the increase in the degree of polymerization. Therefore, the polymerization can be carried out while diluting with a solvent to lower the viscosity. The amount of the solvent can be used within a range where the polymer concentration becomes 3 to 80% by weight, preferably 3 to 70% by weight, more preferably 3 to 60% by weight, and still more preferably 3 to 50% by weight. % Is preferable.

If the content is more than 80% by weight, the viscosity when the polymer is heated and melted becomes extremely high, and the polymer is thermally deteriorated by local heating, which causes coloring. 3% by weight
If it is lower, there is no problem in the reaction, but the volumetric efficiency is poor and productivity is disadvantageous.

The reaction conditions for the dehydration polycondensation reaction in the method of the present invention may be either normal pressure or reduced pressure, and the reaction temperature may be up to the reflux temperature of the solvent used (usually within the range of 80 to 200 ° C.). ) In order to obtain a high-molecular-weight polyhydroxycarboxylic acid with less coloring, which is the object of the present invention, the reaction temperature when the molecular weight of the polymer exceeds 100,000 must be within the range of 80 to 125 ° C. Is preferred.

The reason is that there is a close relationship between the reaction temperature and the polymerization rate and the color tone of the obtained polymer,
For example, when the reaction temperature is high, the reaction rate is high, but thermal degradation, alteration and depolymerization due to overheating in the reaction system are likely to occur, so that the reaction solution is colored and a relatively low molecular weight polymer is obtained. When the reaction temperature is low, it is considered that a relatively high molecular weight polymer having a low reaction rate but a low coloration with little heat deterioration, deterioration and depolymerization hardly occurs. In particular, when the molecular weight of the polymer exceeds 100,000, the reaction temperature is 13
At 0 ° C or higher, coloring is remarkable.

Therefore, when it is desired to obtain a polymer having relatively little coloring industrially in a short time, the initial reaction temperature is increased (1.
30-200 ° C.), then the reaction temperature is intermittent,
Alternatively, the reaction can be achieved by continuously lowering the reaction, and by setting the reaction temperature from the time when the molecular weight of the polymer exceeds 100,000 to a range of 80 to 125 ° C., using a reaction apparatus and reaction conditions (reflux amount, reaction concentration) , Stirring speed, etc.), and appropriate temperature conditions can be appropriately set depending on the molecular weight and coloring degree of the target polymer.

There are many possible methods for setting the temperature conditions (the molecular weight of the polymer and the reaction temperature at that time). For example, when the molecular weight of the polymer is up to 100,000, the reaction is carried out at 150 ° C., and the molecular weight exceeds 100,000. The reaction may be switched to 120 ° C. at the time, and the reaction temperature when the molecular weight at which thermal degradation of the polymer becomes remarkable exceeds 100,000 is 80 to 125 ° C.
Any temperature condition may be used as long as it is within the range, and there is no limitation on the method of setting the temperature condition. When the reaction temperature is higher than 125 ° C. and the molecular weight of the polymer is higher than 100,000, coloring of the polymer during the reaction becomes remarkable, and furthermore, the reached molecular weight of the polymer tends to be relatively low, which is not preferable. If the reaction temperature is lower than 80 ° C., the solubility of the polymer in an organic solvent becomes worse with an increase in the molecular weight of the polymer, and the polymer may precipitate, which is not preferable.

When it is desired to obtain a polymer having a better color tone, it is preferable to lower the reaction temperature as early as possible, preferably at the time of exceeding 750,000, more preferably 50,000, and further preferably at the point of exceeding 20,000. The reaction temperature is preferably set to 80 to 125 ° C.

When the dehydration polycondensation reaction is carried out intermittently or continuously by lowering the reaction temperature, for example, the initial reaction temperature may be reduced by 5%.
The temperature was continuously lowered to 110 ° C in 1 hour at
The reaction may be carried out at 0 ° C. or the temperature may be intermittently lowered to 110 ° C. by 10 ° C. every 5 hours.
There is no limitation as long as the reaction temperature when the temperature exceeds 10,000 is in the range of 80 to 125 ° C.

In the method of the present invention, a polyhydroxycarboxylic acid having a good color tone is obtained by controlling the reaction temperature while controlling the molecular weight. As a method for controlling the molecular weight, the size exclusion chromatography of a wrap sample is used. Chromatography, light scattering, membrane osmometry, vapor pressure osmometry,
Examples of the method include measuring the weight average molecular weight by a boiling point increasing method or the like, and measuring the logarithmic viscosity or solution viscosity to recognize the process of increasing the molecular weight of the polymer. Generally, industrially, the relationship between the solution viscosity of the reaction solution and the molecular weight is grasped in advance, and the solution viscosity of the reaction solution is measured, for example, by using a falling ball viscometer, a falling ball viscometer, a bubble viscometer, a float viscometer, a vibration A method of sequentially measuring with a viscometer or the like and converting to a weight average molecular weight can be adopted, but any measuring device or measuring method may be used as long as the weight average molecular weight of the polymer under reaction can be recognized substantially. No restrictions.

With respect to the apparatus used in the method of the present invention, the reaction is a dehydration polycondensation reaction, and in order to obtain a high molecular weight polymer, an apparatus capable of removing water generated as the reaction proceeds as it goes out of the reaction system. Need to be As a method for removing generated water, a water-containing solvent distilled under reflux of the solvent is treated with a desiccant and then returned to the system, or the reaction is performed in a reactor equipped with an apparatus having distillation separation ability. A reflux system that removes water by directly distilling the mixture of the refluxing solvent and water to remove water and return only the dehydrated solvent to the system, and further withdrawing the distilling water-containing solvent out of the reaction system and dehydrating in advance. Any method of the system for returning the solvent to the system can be used. That is, as long as the solvent to be returned into the reaction system contains substantially no water, there are no restrictions on the apparatus and dehydration method.

When a drying agent is used, for example, molecular sieves (3A, 4A, 5A, etc.), diphosphorus pentoxide,
Metal hydrides such as calcium hydride, sodium hydride, and lithium aluminum hydride; and alkali metals such as sodium and lithium.

In the method of the present invention, a dehydration polycondensation reaction may be carried out by adding a coloring inhibitor to further suppress coloration due to thermal deterioration during the dehydration polycondensation reaction. Phosphoric acid, triphenyl phosphate, pyrophosphoric acid,
Phosphorus compounds such as phosphorous acid and triphenyl phosphite are preferred. The addition amount is 0.01 to 5% by weight, more preferably 0.5 to 2% by weight based on the polymer. 0.0
If the amount is less than 1% by weight, the effect of preventing coloring becomes small, and 5% by weight
Above, the effect of preventing further coloring is weak, and the degree of polymerization may not be increased.

[0030]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to the methods and apparatuses described below. The weight average molecular weight and YI value of the polymer described in this specification were measured according to the following methods. -Weight average molecular weight (Mw) It was compared with a polystyrene standard sample by gel permeation chromatography (column temperature: 40 ° C). ○ YI value Molding condition 1 using a mini test press made by Toyo Seiki Co., Ltd.
A sheet having a thickness of 1 mm was prepared at 80 ° C., and the yellowness (transmission type Y) was measured using an SM color computer (manufactured by Suga Test Instruments Co., Ltd.)
I value) was measured.

Example 1 83 g of 90% L-lactic acid was charged into a 500 ml four-necked flask equipped with a thermometer, a stirring blade, and a distilling tube, and heated and stirred at 140 ° C. for 3 hours in a nitrogen atmosphere. While distilling water out of the system. Next, the distilling tube was removed, a Dean stack was attached instead, 0.4 g of tin powder and 325 g of o-dichlorobenzene were added, and the mixture was heated and refluxed at 140 ° C./250 mmHg for 8 hours. At this time, the refluxing o-dichlorobenzene and generated water were separated in a Dean-Stack, and an aqueous layer was sequentially extracted. The Dean stack was removed, and a tube filled with 50 g of molecular sieve 3A was attached instead, so that the solvent distilled by reflux returned to the system through the molecular sieve 3A. The dehydration polycondensation reaction conditions were set at 140 ° C./250 mmHg,
Allowed to react for hours. Next, the dehydration polycondensation reaction condition was set at 110 ° C.
/ 100 mmHg, and a dehydration polycondensation reaction was continuously performed for 25 hours while collecting lap samples every 5 hours. After completion of the reaction, 400 ml of chloroform was added to the reaction mass, and after dissolving, the mixture was suction-filtered to remove tin powder. 1400 ml of methanol was added to the obtained chloroform solution, and the precipitated solid was separated by filtration and dried to obtain 56.9 g of polylactic acid as a white solid. The yield was 95.2%, the weight average molecular weight Mw was 300,000 (in terms of polystyrene; the same applies hereinafter),
The YI value of the press sheet was 1.1. Similarly, the weight average molecular weight M of the polylactic acid obtained by treating the lamp sample
The w and YI values were measured. Table 1 shows the results.

Comparative Example 1 The procedure of Example 1 was repeated except that the dehydration polycondensation reaction temperature was kept constant at 140 ° C. As a result, polylactic acid 55.
6 g were obtained. The yield was 93.0%, the weight average molecular weight Mw was 200,000, and the YI of the pressed sheet was 11.3.
Similarly, the weight average molecular weight Mw and YI value of the wrap sample were measured. Table 1 shows the results.

Example 2 A white solid polylactic acid was obtained in the same manner as in Example 1 except that the dehydration polycondensation reaction temperature was kept constant at 110 ° C.
2 g were obtained. The yield was 95.7%, the weight average molecular weight Mw was 300,000, and the YI of the pressed sheet was 1.1. Similarly, the weight average molecular weight Mw and YI value of the wrap sample were measured. Table 1 shows the results.

[0034]

[Table 1]

Example 3 After heating and refluxing at 140 ° C./23 mmHg for 8 hours using diphenyl ether instead of o-dichlorobenzene as a solvent, a tube filled with molecular sieves 3A was attached, and the tube was filled at 140 ° C./23 mmHg for 5 hours. 110 ° C
The reaction was carried out in the same manner as in Example 1, except that a dehydration polycondensation reaction was carried out at / 15 mmHg for 15 hours. As a result, 56.2 g of a white solid polylactic acid was obtained. The yield was 94.0%, the weight average molecular weight Mw was 245,000, and the YI value of the press sheet was 1.1.

Example 4 Using the reactor described in Example 1, 90% L-lactic acid 83
g, and water was distilled out of the system while heating and stirring at 140 ° C. for 3 hours under a nitrogen atmosphere. Next, remove the distilling pipe,
Instead, a Dean stack was attached, and 0.4 g of tin powder and 150 g of o-dichlorobenzene were added.
The mixture was heated to reflux at 0 ° C./250 mmHg for 8 hours. At this time, the refluxing o-dichlorobenzene and generated water were separated in a Dean-Stack, and an aqueous layer was sequentially extracted. The Dean stack was removed, and a tube filled with 50 g of molecular sieve 3A was attached instead, so that the solvent distilled by reflux returned to the system through the molecular sieve 3A. Dehydration polycondensation reaction conditions are 140 ° C / 25
After setting the pressure at 0 mmHg and heating and refluxing for 5 hours, the sample was subjected to molecular weight analysis to obtain a polymer having a weight average molecular weight Mw of 80,000. 175 g of o-dichlorobenzene was added and diluted, and the dehydration / polycondensation reaction condition was set to 110 ° C. /
The pressure was set to 90 mmHg, and the dehydration polycondensation reaction was continued for 10 minutes.
Time went. After completion of the reaction, chloroform 40 was added to the reaction mass.
After adding 0 ml and dissolving, suction filtration was performed to remove tin powder. 1400 m of methanol was added to the obtained chloroform solution.
was added, and the precipitated solid was separated by filtration and dried to obtain 57.0 g of polylactic acid as a white solid. The yield was 95.4%, the weight average molecular weight Mw was 200,000, and the YI value of the pressed sheet was 1.0.
It was one.

Example-5 Using the reactor described in Example-1, 90% L-lactic acid 83
g, and heated and stirred under a nitrogen atmosphere at 140 ° C. for 3 hours while removing water from the system. Next, remove the distilling pipe,
Instead, a Dean stack was attached, 0.2 g of tin powder, 0.2 g of stannous oxide, and 325 g of o-dichlorobenzene were further added, and the mixture was heated and refluxed at 140 ° C./250 mmHg for 8 hours. At this time, the refluxing o-dichlorobenzene and generated water were separated in a Dean-Stack, and an aqueous layer was sequentially extracted. The Dean stack was removed, and a tube filled with 50 g of molecular sieve 3A was attached instead, so that the solvent distilled by reflux returned to the system through the molecular sieve 3A. The dehydration polycondensation reaction temperature is reduced from 140 ° C. to 110 ° C. under reduced pressure, 3 ° C.
/ 1 hour for 10 hours continuously, then 110
The dehydration polycondensation reaction was performed at 10 ° C. for 10 hours. After the reaction,
400 ml of chloroform was added to the reaction mass, which was dissolved and suction-filtered to remove tin-tin powder. 1400 ml of methanol was added to the obtained chloroform solution, and the precipitated solid was separated by filtration and dried to obtain 57.2 g of white solid polylactic acid. The yield is 95.7% and the weight average molecular weight Mw is 25.0.
The YI value of the press sheet was 1.3.

Example-6 Instead of 83 g of 90% L-lactic acid, 90% L-lactic acid 75 was used.
g and 15 g of D / L lactic acid, except that a dehydration polycondensation reaction time of 15 hours was performed in the same manner as in Example 1 to obtain 61.6 g of a copolymer of L-lactic acid and D / L lactic acid as a white solid.
I got The yield is 93.3% and the weight average molecular weight Mw is 2
55,000, and the YI value of the press sheet was 1.8.

Example 7 Instead of 83 g of 90% L-lactic acid, 90% L-lactic acid 75 was used.
g and glycolic acid 9.6 g, except that the dehydration polycondensation reaction time was 15 hours in the same manner as in Example 1;
White solid copolymer of L-lactic acid and glycolic acid 5
5.5 g were obtained. Yield 90.4%, weight average molecular weight M
w was 18,000 and the YI value of the press sheet was 1.6.

Example 8 Instead of 83 g of 90% L-lactic acid, 90% L-lactic acid 75 was used.
g and DL-4-hydroxybutanoic acid 6.8
Except for using g, a dehydration polycondensation reaction time of 17 hours was carried out in the same manner as in Example 1, and as a result, a copolymer of L-lactic acid and DL-4-hydroxybutanoic acid was 56.3.
g was obtained. The yield is 94.4% and the weight average molecular weight Mw is 1
77,000, and the YI value of the press sheet was 1.4.

Example 9 Instead of 83 g of 90% L-lactic acid, 90% L-lactic acid 75 was used.
g and DL-3-hydroxybutanoic acid 6.8
Except for using g, the reaction was carried out in the same manner as in Example 1 for 20 hours of dehydration polycondensation reaction. As a result, a copolymer of L-lactic acid and DL-3-hydroxybutanoic acid was 54.7.
g was obtained. The yield is 91.7% and the weight average molecular weight Mw is 1
91,000, and the YI value of the press sheet was 1.7.

[0042]

The method of the present invention makes it possible to obtain a high-molecular weight polymer with little coloration and high transparency from a hydroxycarboxylic acid or its oligomer by dehydration polycondensation directly, industrially, in a short time and at low cost. It is a method.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuharu Watanabe, Inventor Katsuharu Watanabe, 30 Asamuta-cho, Omuta-shi, Fukuoka Prefecture Inside of Mitsui Toatsu Chemicals Co., Ltd. Within Chemical Co., Ltd. (72) Inventor Mitsuhiko Miyamoto 30 Asamuta-cho, Omuta-shi, Fukuoka Prefecture Inside Mitsui-Higashi-Pressure Chemical Co., Ltd. Examiner Satoshi Morikawa (56) References JP-A-7-173264 (JP, A) JP-A-4-168124 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08G 63 / 00-63/91

Claims (4)

(57) [Claims] 1. A method for obtaining a high molecular weight polyhydroxycarboxylic acid having a molecular weight exceeding 100,000 by heating and refluxing a hydroxycarboxylic acid or an oligomer thereof in an organic solvent in the presence of a catalyst to carry out a dehydration polycondensation reaction. The reaction temperature until the molecular weight of the polymer reaches 100,000 is 80 to 20
0 ° C. and the reaction temperature when it exceeds 100,000
A method for producing a polyhydroxycarboxylic acid having an improved color tone, wherein the temperature is 5 ° C. 2. The method according to claim 1, wherein the dehydration polycondensation reaction is carried out while the reaction temperature is lowered intermittently or continuously. 3. The method according to claim 1, wherein the hydroxycarboxylic acid is one or more selected from lactic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, and 3-hydroxyvaleric acid. The production method according to claim 1, wherein 4. The production method according to claim 1, wherein the catalyst used for the dehydration polycondensation is a divalent tin compound and / or tin.