JPH0543665A - Production of aliphatic polyester - Google Patents

Abstract

PURPOSE:To obtain efficiently a high-molecular aliphatic polyester by polycondensing a hydroxy acid represented by lactic or glycolic acid. CONSTITUTION:A process for producing an aliphatic polyester by polycondensing a hydroxy acid, wherein dehydration is performed by heating in the presence of a germanium compound in an inert gas stream or in a vacuum. Side reaction can be suppressed and a noncolored high-molecular aliphatic polyester can be obtained in high yields.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aliphatic polyester starting from oxy acid,
More specifically, it relates to a method for obtaining the above aliphatic polyester in a high molecular weight.

[0002]

2. Description of the Related Art Conventionally, aliphatic polyesters represented by polylactic acid and polyglycolic acid have been used as sustained-release polymers as biodegradable medical materials such as surgical sutures and microcapsules for injections, and herbicides. It is used as a pesticide composition. In recent years, plastic pollution has become a problem, and it has been attracting attention as a biodegradable plastic that is expected to be decomposed by enzymes and microorganisms, and research and development has been advanced.

By the way, as a method for increasing the molecular weight of the above-mentioned aliphatic polyester, conventionally, for example, a method in which a lactone or a lactide which is a cyclic dimer is heated in the presence of a catalyst and subjected to ring-opening polymerization is known. Are known.
However, in the above method, first, an oligomer is produced from glycolic acid by a dehydration reaction, a cyclic dimer is obtained by depolymerizing the oligomer, and the product purified by recrystallization must be used as a starting material. The production and purification of the cyclic dimers required a lot of labor and cost. In recent years, a method for obtaining a high molecular weight aliphatic polyester by direct dehydration polycondensation using an oxy acid as a starting material has been known, but a polymer having a satisfactory molecular weight has not yet been obtained.

[0004]

Therefore, the present inventors have found that
When a study was conducted to obtain a high molecular weight aliphatic polyester by direct dehydration polycondensation from oxyacid, direct dehydration polycondensation of oxyacid is a sequential reaction, and the molecular weight increases with the reaction time. Since it is an equilibrium reaction and its equilibrium constant is small, it was found that a catalyst is required to obtain a high molecular weight substance. Further, metal oxides, metal salts, etc., especially tin compounds are usually used as catalysts. In order to obtain a molecular weight product, when the reaction temperature and the degree of reduced pressure are increased and the reaction conditions are stricter, depolymerization is accompanied, and by-products of the cyclic dimer, deterioration of the polymer and coloring occur, and the high molecular weight product is obtained. It turned out to be difficult to obtain.

[0005]

In view of the above circumstances, the inventors of the present invention have made earnest studies to obtain a high molecular weight aliphatic polyester by direct dehydration polycondensation using an oxy acid as a starting material, and as a result, a germanium compound has been obtained. By using as a catalyst, it was found that a side reaction is suppressed, and a high molecular weight aliphatic polyester without deterioration and coloration is obtained,
Finally, the present invention has been completed. That is, the present invention is characterized in that, when an aliphatic polyester is produced by dehydration polycondensation of an oxyacid, in the presence of a germanium compound, the aliphatic polyester is heated and dehydrated under an inert gas stream or under reduced pressure. Is a manufacturing method.

The oxyacid used as a starting material in the present invention has one hydroxy group and one carboxylic acid group in one molecule, for example, glycolic acid,
Examples thereof include lactic acid, 3-hydroxybutyric acid, and 4-hydroxybutyric acid, but are not limited thereto. They can be used alone or in a mixture. Further, the compound having asymmetric carbon may be any of D-form, L-form and racemic form, and there is no problem even if the form is solid, liquid or aqueous solution. When an aqueous solution is used, it is desirable to appropriately perform concentration before starting the reaction.

The germanium compound used as the catalyst includes metal germanium, germanium tetrachloride, germanium oxide, etc., but is not limited to these and may be used in combination with other catalysts in some cases. .. The amount of catalyst used is 0.005-0.50mo
1% is preferable, and 0.03 to 0.10 mol% is particularly preferable. If it is 0.005 mol% or less, almost no catalytic effect is observed, and if it is 0.5 mol% or more, side reactions and coloration are accompanied during polymerization, which is not preferable. The catalyst may be added at the same time as the starting materials, or when the initial polymerization is completed and the system is in a reduced pressure state. When the starting material is an aqueous solution, it is desirable to add it after the concentration is completed. The catalyst may be added as a solid or liquid as it is, or may be added as a solution in a suitable solvent.

The polycondensation reaction in the present invention can be carried out, for example, as follows. First, after replacing the starting material and the catalyst charged in the reaction vessel with an inert gas, the temperature is gradually raised under an inert gas stream, and initial polymerization is carried out at a predetermined temperature for a predetermined time. Then, the pressure reduction is started, and the reaction is stopped when a predetermined time or a predetermined torque is reached. The polymerization temperature is determined by the target polymer, but the degree of vacuum is finally 10 mmHg or less, especially 1 m.
It is desirable to set it to mHg or less. Although it is possible to obtain a sufficiently high molecular weight aliphatic polyester by using a germanium catalyst by such an operation, it is possible to further increase the molecular weight by solid phase polymerization or the like.

[0009]

EXAMPLES In order to describe the present invention more specifically, examples will be described below, but the present invention is not limited thereto. The characteristic values in the examples were measured by the following methods. Reduced viscosity (ηsp / c): 0.125 g of the polymer was dissolved in a mixed solvent of trichlorophenol / phenol (7/10 wt%) and measured at 30 ° C. Melting point, glass transition temperature: Perkin Elmer DSC7
Was measured at a temperature rising / falling rate of 10 ° C./min under a nitrogen stream.

Example 1 50 g of glycolic acid and 0.034 g of germanium oxide
(0.05 mol%) was charged into a reaction vessel equipped with a stirrer and a nitrogen introducing tube, and after performing nitrogen replacement three times, the temperature was raised to 200 ° C. at 10 ° C./min under a nitrogen stream for 1 hour. It was stirred. Then, the temperature was raised to 240 ° C and gradually increased to 1 over 30 minutes.
Reduce the pressure to 0 mmHg, stir and react for 1 hour, and further 1 m
After continuing the stirring reaction at mHg for 2 hours, the molten polyglycolic acid was taken out. Almost no distillate other than water was observed during the polymerization. The obtained polymer was white and had a reduced viscosity of 0.69 and a melting point of 232 ° C.

Example 2 In a reaction vessel similar to that of Example 1, 50 g of glycolic acid, L-
Lactic acid (90% aqueous solution) 5g, germanium oxide 0.03
6 g was added and the same operation as in Example 1 was performed except that the final reaction temperature was set to 218 ° C. to obtain a white copolymer. This polymer had a reduced viscosity of 0.67 and a melting point of 201 ° C. The obtained polymer was spun at 220 ° C. using a plunger type spinning machine, and the monofilament stretched 4 times at 100 ° C. had a strength of 7.2 g / d and an elongation of 25%.
Met.

Example 3 The copolymer obtained in Example 2 was treated at 180 ° C.
When solid phase polymerization was carried out at 5 mmHg for 20 hours, a polymer having a reduced viscosity of 0.89 was obtained.

Comparative Example 1 In Example 1, 0.05 m of tin octylate was used as a catalyst.
When polyglycolic acid was synthesized in exactly the same manner as in Example 1 except that ol% was used, coloring was observed during the reaction and the obtained polymer was brown. The reduced viscosity was 0.32 and the melting point was 227 ° C.

Comparative Example 2 Polyglycolic acid was synthesized in the same manner as in Example 1 except that the catalyst was not used. The obtained polymer was white, but the reduced viscosity was 0.28.

Example 4 50 g of DL-lactic acid (90% aqueous solution) was placed in the same reaction vessel as in Example 1, and stirred at 180 ° C. under a nitrogen stream.
The temperature was raised to ℃ and concentrated. At this point, germanium oxide 0.
After adding 026 g and continuing the reaction at 200 ° C. for 2 hours,
Reduce pressure to 20 mmHg in 30 minutes for 1 hour, then 5 m
The reaction was performed at mHg and 1 mmHg for 2 hours each. By taking out the molten polymer, colorless and transparent polylactic acid was obtained. This polymer had no melting point, was amorphous, had a glass transition temperature of 54 ° C., and had a reduced viscosity of 0.74. During the reaction, a small amount of a side reaction product was observed along with water, and this substance was lactide, which is a cyclic dimer of lactic acid.

Comparative Examples 3 to 9 Polylactic acid was synthesized in the same manner as in Example 4 except that the catalyst was changed. The results are shown in Table 1.

[Table 1] As shown in Table 1, it can be seen that by using germanium as a catalyst, the distillation of lactide, which is a by-product, is suppressed, and high molecular weight polylactic acid is obtained.

Example 5 In a reaction vessel similar to Example 1, 50 g of glycolic acid,
(L-) 3-Hydroxybutyric acid (10 g) and germanium oxide (0.034 g) were added and reacted at 180 ° C. for 2 hours.
The degree of reduced pressure was increased, and finally the reaction was performed at 1 mmHg and 200 ° C. for 4 hours. The polymer taken out was pale yellow and had a reduced viscosity of 0.68.

[0018]

By adopting the method of the present invention having the above constitution, it is possible to dehydrate polycondensate an oxyacid and obtain a high molecular weight aliphatic polyester without side reactions. These aliphatic polyesters have a sufficiently high molecular weight so that they can be molded into films, fibers and the like, and can be expected to have a wide range of applications, and therefore they greatly contribute to industry and environmental protection.

Claims (1)

[Claims] 1. By dehydration polycondensation of an oxy acid,
A method for producing an aliphatic polyester, which comprises heating and dehydrating an aliphatic polyester in the presence of a germanium compound under an inert gas stream or under reduced pressure.