JP3520609B2 - Method for producing 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 producing an aliphatic polyester from which a low molecular weight compound has been substantially removed, and more particularly, it has good thermal stability.
The present invention relates to a method for producing an aliphatic polyester having biodegradability that is easily melt-molded.

[0002]

BACKGROUND ART α-Oxyacid polyesters represented by polylactic acid and polyglycolic acid have good biodegradability and are suitable for biodegradable medical materials such as surgical sutures and microcapsules for injection. It's being used. Further, in recent years, plastic waste has become a problem, and attention has been paid to it as a biodegradable plastic that is expected to be decomposed by enzymes and microorganisms, and research and development has been advanced.

As a method for obtaining a high molecular weight product of the α-oxy acid polyester, there has been known a method in which a cyclic dimer of an α-oxy acid is heated in the presence of a tin catalyst to perform ring-opening polymerization. However, the obtained polylactic acid is relatively easily pyrolyzed at a temperature slightly higher than the melting temperature, which causes a problem during melt molding. One of the causes for this is the residual metal catalyst in the polyester. For example, it is known that the tin-based catalyst causes depolymerization and transesterification of the produced polyester at high temperature.

Therefore, in order to remove the residual metal which acts as a thermal decomposition catalyst, the obtained polyester is dissolved in an organic solvent for reprecipitation, the polyester is extracted with an organic solvent and water, or the polyester is used. There is known from the prior art a method of adding a phosphorus compound as a deactivating agent for metal catalysts. However, in the above method, a complicated removal operation is required, and problems such as recovery of the solvent and residual of the solvent in the polyester occur. Therefore, these polyesters usually produced by the bulk polymerization method are industrially preferable. Not a thing. In addition, the fact is that the method described below has not yet reached a high-viscosity molten state. On the other hand, performing polymerization without using a metal catalyst requires a very long time to obtain a high molecular weight substance, and it is completely impractical to use a catalyst industrially.
Therefore, while containing a catalyst from an industrial point of view,
There is a need for aliphatic polyesters with good thermal stability.

Further, when an α-oxy acid polyester is produced, a low molecular weight compound such as a cyclic dimer of α-oxy acid as an unreacted monomer, an impurity produced by a side reaction, a chain or cyclic oligomer, etc. is contained in the polymer. Remains in. The residual low molecular weight compound in the polymer causes thermal decomposition at the time of melt molding at high temperature, causing a decrease in the molecular weight of the polymer,
It also reduces the water resistance and storage stability of the polymer. Examples of methods for removing these include a method of re-precipitation by dissolving in an organic solvent and a method of extracting a low molecular weight compound, but these methods are not industrially preferable as described above.

A method for removing low molecular weight volatiles is disclosed in Japanese Patent Application Laid-Open No. 3-14829.
In this method, low molecular weight volatiles are treated by reducing the pressure in the reaction system while maintaining the molten state of the polymer at the latter stage of the polymerization or after the completion of the polymerization. Specifically, glycolide, lactide, etc. are treated with octanoic acid primary Polymerization is carried out using tin as a catalyst, followed by treatment to remove low molecular weight volatiles. However, when a tin-based catalyst is used for polymerization,
Since the equilibrium constant of the polymerization is low, the depolymerization reaction proceeds in parallel with the ring-opening polymerization. Therefore, it is practically difficult to remove the low molecular weight compound from the polymer by this method.

[0007]

As mentioned above, although the production of an aliphatic polyester having good thermal stability by a simple method is desired, a method for producing such an aliphatic polyester is still established. The current situation is that it has not been done. For this reason, it is an object of the present invention to propose a simple method for producing an aliphatic polyester having excellent thermal stability.

[0008]

The inventors of the present invention have conducted extensive studies in order to solve the above problems, and as a result, by using an aluminum compound as a ring-opening polymerization catalyst for polymerization, it is possible to easily reduce the temperature. It was found that it is possible to remove a molecular weight compound from the system, and finally the present invention has been completed.

That is, according to the present invention, in the step of producing an aliphatic polyester from a cyclic dimer of α-oxy acid by a ring-opening polymerization reaction using an aluminum compound as a catalyst, the polymer is in a molten state at the latter stage or after the completion of the polymerization. A method for producing an aliphatic polyester, comprising a step of reducing the pressure in the reaction system.

Generally, in the production of aliphatic polyester by ring-opening polymerization of a cyclic dimer of α-oxy acid, the ring-opening polymerization reaction and the depolymerization reaction are in equilibrium, so that the monomer remains in the polymer and The amount depends on the type of polymerization catalyst used. Also, if the catalyst remains in the polymer, new monomers may form during melt molding at high temperatures. Monomers present in the polymer cause frequent yarn breakage and variations in yarn strength during molding, for example, when melt spinning is performed. Further, these monomers are decomposed by a small amount of water at a high temperature when the polymer melts, and also increase the acid value of the polymer, and the oligomers in the system also increase the acid value. The presence of molecular weight compounds causes thermal decomposition. Therefore, in order to obtain a resin having good thermal stability, it is necessary to remove the low molecular weight compound in the polymer and at the same time suppress the regeneration of the monomer to reduce the amount of the low molecular weight compound.

In the present invention, the cyclic dimer of α-oxy acid is used.
During the production of aliphatic polyester by ring-opening polymerization of the body,
An aluminum compound catalyst is used as a catalyst for ring polymerization.
Specific aluminum compound catalysts include, for example:
Formula (I) (wherein R_A , R_CEach independently
R group, cycloalkyl group or aryl group, R _B 
Is a hydrogen atom or an alkyl group, a cycloalkyl group or
An aryl group (which may contain a substituted halogen)
Luminium β-diketone uncharged complex, and / or satiety
Aluminium with 2 or more and 20 or less saturated or unsaturated carbon atoms
Mucarboxylic acid salts are mentioned.

[0012]

[Chemical 1]

Here, β-coordinated to aluminum
More specifically, the diketones are acetylacetone (2,
4-pentanedione), propionylacetone (2,4
-Hexanedione), 2,4-heptanedione, 2,4
-Octanedione, 2,4-decanedione, 3,5-heptanedione, 2-methyl-3,5-heptanedione,
2,2-dimethyl-3,5-heptanedione, 2,6-
Dimethyl-3,5-heptanedione, pivaloylmethane (2,2,6,6-tetramethyl-3,5-heptanedione), benzoylacetone (1-phenyl-1,3-)
Butanedione), 1,3-diphenyl-1,3-propanedione, trifluoroacetylacetone (1,1,
1,5,5,5-hexafluoro-2,4-pentanedione) and the like, but are not limited thereto.

These complexes are usually easily synthesized by reacting an aluminum alcoholate with a corresponding β-diketone in an organic solvent such as toluene or by reacting aluminum sulfate with a corresponding β-diketone in water. Furthermore, most of these complexes are easily soluble in general-purpose organic solvents and have sublimability, so that purification is easy. The acetylacetone complex is preferable because of its good catalytic activity, easy availability, and easy production of a pure substance.

The carboxylic acid used as the carboxylic acid salt is specifically acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, Examples thereof include, but are not limited to, linoleic acid, linolenic acid, and oleic acid.

The aluminum compound catalyst has a high equilibrium constant for polymerization, and depolymerization reaction or transesterification reaction hardly occurs apparently during ring-opening polymerization, so that the monomer is regenerated even if the molten state at high temperature continues for a relatively long time. Almost never.
Therefore, the obtained polymer has excellent thermal stability as compared with the conventional one.

In the present invention, low molecular weight compounds such as monomers and oligomers remaining in the polymer during the ring-opening polymerization are subjected to removal treatment by depressurizing the system in the molten state of the polymer at the latter stage of the polymerization or after the completion of the polymerization. Specifically, the depressurization treatment is carried out at a temperature above the melting state of the polymer, that is, above the temperature at which the polymer exhibits fluidity. If the temperature is lower than that, the low molecular weight compound is not smoothly removed because the reaction system solidifies, and if the temperature in the system is too high, the polymer is easily decomposed, which is not preferable. In order to efficiently remove the low molecular weight compound, it is preferable to carry out a reduced pressure treatment within the range of the melting point of the polymer to the melting point + 50 ° C. or the glass transition point to the glass transition point + 200 ° C. Further, the pressure reduction operation can obtain the expected effect at 500 mmHg or less, but at 200 mmHg or less, preferably 20 in order to perform the treatment efficiently in a short time.
It is carried out in mmHg or less under. Further, it is more preferable to carry out the pressure reduction treatment under an inert gas stream.

Further, low molecular weight compounds can be reduced by performing solid phase heat treatment. For example, in the case of polylactic acid, the heat treatment may be performed at a temperature of 120 ° C. or higher and 150 ° C. or lower in an absolutely dry state. In this case, there is no problem under a flow of an inert gas or the like, under reduced pressure or under pressure.

In the present invention, since a catalyst is used as the ring-opening polymerization catalyst using an aluminum compound, when the pressure reduction treatment is carried out in the molten state of the polymer, the monomer is not regenerated or transesterification reaction occurs during the treatment. It is possible to remove low molecular weight compounds almost completely and efficiently with substantially no substance.

As the cyclic dimer of α-oxy acid used in the present invention, specifically, glycolide, lactide,
Furthermore, α-hydroxybutyric acid, α-hydroxyvaleric acid, α
-Hydroxyisovaleric acid, α-hydroxycaproic acid,
α-hydroxyisocaproic acid, α-hydroxy-β-
Examples include cyclic dimers such as methylvaleric acid and α-hydroxyheptanoic acid. Among these, glycolide and lactide are easily available, and the physical properties of the polymer are practical and preferable. The compound having an asymmetric carbon may be any of L-form, D-form, racemic form and meso-form. Moreover, the cyclic dimer may be formed by different α-oxy acid molecules. Specific examples thereof include 3-methyl-2,5-dione-1,4-dioxane, which is a cyclic dimer of glycolic acid and lactic acid, and which is known by a common name of monomethyl glycolide.

In the present invention, the hydroxyl group terminal of the aliphatic polyester may be blocked with an aliphatic carboxylic acid having 2 to 51 carbon atoms. The C2-C51 aliphatic carboxylic acid used may be either a monocarboxylic acid or a dicarboxylic acid, and may be saturated or unsaturated. Specifically, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid,
Caprylic acid, pelargonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, linoleic acid, oleic acid, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecane Diacid, dimer acid, fumaric acid and the like can be used. Moreover, it does not matter even if these acid anhydrides are added. These carboxylic acids may be used alone or in combination of two or more. However, when an acid having a boiling point lower than the polymerization temperature is used, it is necessary to carry out the reaction under pressure. In particular, stearic acid, palmitic acid, myristic acid, linoleic acid, oleic acid are flavoring agents, emulsifiers, vitamin fortifiers, and fumaric acid, succinic acid, adipic acid are also seasonings, sourness or food additives as their raw materials. It is mentioned and is a preferable carboxylic acid since its safety is confirmed.
More preferably, stearic acid, which is a raw material of calcium stearyl lactate used as an auxiliary agent for bread making, can be mentioned.

When these are added to lactide, they may be added as they are (liquid or solid) or may be dissolved in an appropriate solvent. However, when a solvent is used, it is desirable that the solvent can be easily distilled off before or during the reaction.

These aliphatic mono- or dicarboxylic acids may vary from 0.001 to 1 with respect to the monomeric cyclic dimer, although there are some differences depending on the conditions such as the type of acid used.
It is used in the proportion of mol%. By blocking the hydroxyl end in this way, the thermal stability of the aliphatic polyester is further improved.

In the present invention, as the molecular weight regulator,
In addition, an aliphatic alcohol having 1 to 50 carbon atoms may be used in order to increase the apparent polymerization rate and to block the carboxyl group end of the polyester formed of an alkyl group or an alkenyl group. Specifically, the aliphatic alcohol may be mono, di, or a polyhydric alcohol,
Further, it may be saturated or unsaturated. Specifically, methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, nonanol, decanol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol and other monoalcohols, ethylene glycol, butanediol, hexanediol, nonanediol. , Tetramethylene glycol, etc., dialcohol, glycerol,
Polyhydric alcohols such as sorbitol, xylitol, ribitol, erythritol and methyl lactate, ethyl lactate and the like can be used. Particularly preferably decanol,
A long-chain aliphatic alcohol such as lauryl alcohol, myristyl alcohol, cetyl alcohol, or stearyl alcohol is used. When the boiling point of the alcohol used is lower than the polymerization temperature, it is necessary to carry out the reaction under pressure.

These aliphatic alcohols are usually 0.01% relative to the cyclic dimer which is a monomer, although there are some differences depending on the conditions such as the type of alcohol used.
Used at a rate of ˜1 mol%.

In the present invention, the ring-opening polymerization reaction of the cyclic dimer of α-oxy acid is carried out in an inert atmosphere such as nitrogen or argon,
Alternatively, the reaction may be carried out under reduced pressure or increased pressure, in which case the catalyst, carboxylic acid, and alcohol may be added successively.

The α-oxy acid polyester thus obtained after completion of the ring-opening polymerization has an arbitrary molecular weight and has improved thermal stability, which facilitates melt molding and results in various biodegradation. It is possible to produce a molded product. Further, by blocking the carboxyl group terminal with alcohol, it becomes possible to improve the thermal stability and control the mechanical properties, and at the same time, control the decomposition properties. There is no problem even if an epoxy compound is added to block the end of the carboxyl group. If necessary, pigments, antioxidants, deterioration inhibitors, plasticizers, matting agents, optical brighteners,
There is no problem even if an additive such as an ultraviolet absorber is added.

In the present invention, the second component and the like may be copolymerized in order to variously change the mechanical properties and the decomposition properties, and among them, a component having biodegradability is preferable.
Specifically, it is an oxyacid component composed of an alkylene group having 1 to 20 carbon atoms or a polymer thereof, and the corresponding lactone or a polymer thereof may be allowed to coexist for polymerization. Specifically, β-propiolactone, β-butyrolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, β-methyl-δ-valerolactone, δ-caprolactone, ε-caprolactone, pivalolactone, enanthlactone, Examples include, but are not limited to, dodecanolactone and the like and polymers thereof. It is also possible to mix with the above aliphatic polyester.

The aliphatic polyester of the present invention can be molded into fibers, films and various molded products from a molten or solution state and is useful as a biodegradable material. Specific applications include fishing lines, fishing nets, non-woven fabrics for agriculture and horticulture, and woven fabrics for fibers, packaging films for films, agricultural mulch films, shopping bags, tapes, fertilizer bags, separation membranes, and beverages for molded products. And cosmetics bottles, disposable cups, containers such as trays, agricultural flower pots, nursery beds, pipes that do not need to be dug out, and building materials such as temporary fixing materials. Furthermore, for medical use,
D for sutures, artificial bones, artificial skin, microcapsules, etc.
Applications to the field of DS, etc. are conceivable, but not limited to these.

[0030]

EXAMPLES Examples will be described below to more specifically describe the present invention, but the present invention is not limited thereto. The characteristic values in the examples were measured by the following methods.

(1) Reduced viscosity (η _sp / C) 0.125 g of a polymer was dissolved in chloroform to obtain 25 ±
The reduced viscosity was calculated by measuring at 0.1 ° C.

(2) Low molecular weight compound amount (Wlow) 2.0 g of polymer sample (W ₁ ) was added to 10 ml of chloroform.
After being dissolved in 100 ml of methanol, the mixture was added to 100 ml of methanol. The deposited polymer precipitate was separated by filtration, dried under reduced pressure at 50 ° C. for 24 hours, and calculated from the obtained polymer amount (W ₂ ) by the following formula. The low molecular weight compound excluded by this method was confirmed by GPC method to have a number average molecular weight of 1,000.
It was: _{Wlow (%) = (W 1} - W 2) / W 1

Example 1 L-lactide 10.0 g (6.94 × 10 ^-2 mol), aluminum acetylacetonate 9 mg (28 × 10 ^-6)
(Mol) toluene solution was charged into a polymerization tube equipped with a stirrer and a nitrogen introduction tube, vacuum dried for 2 hours, and after nitrogen substitution, heated to 190 ° C. in a nitrogen atmosphere to conduct a ring-opening polymerization reaction. I went on time. With the temperature inside the reaction system being maintained, degassing was performed with a vacuum pump, the pressure was reduced to 5 mmHg, and after continuing for 1 hour, the inside of the reactor was replaced with nitrogen and the polymer was taken out.
The obtained polymer showed η _sp /C=2.03. Moreover, Wlow was 0.2%.

Comparative Example 1 A toluene solution of 10.0 g (6.94 × 10 ^-2 mol) of L-lactide and 3 mg (7 × 10 ^-6 mol) of stannous octoate was provided with a stirrer and a nitrogen inlet tube. Charge the polymerization tube,
After vacuum drying and nitrogen substitution for 2 hours, the mixture was heated to 190 ° C. in a nitrogen atmosphere and the ring-opening polymerization reaction was conducted for 2 hours. While maintaining the temperature in the reaction system, degassing was performed with a vacuum pump, the pressure was reduced to 5 mmHg, and the reaction was terminated after continuing for 1 hour. The obtained polymer showed η _sp /C=1.82. Moreover, Wlow was 5.5%.

Example 2 Polymerization and reduced pressure treatment were carried out in the same manner as in Example 1 except that 27.1 mg (100 × 10 ⁻⁶ mol) of stearyl alcohol was added to terminate the reaction. The polymer was further treated at 100 ° C. for 12 hours under a reduced pressure of 0.1 mmHg, and then solid-phase treated at 120 ° C. for 24 hours under a nitrogen stream. The η _sp / C and Wlow of the obtained polymer are shown in Table 1.

Comparative Example 2 Polymerization and reduced pressure treatment were carried out in the same manner as in Comparative Example 1 except that 27.1 mg of stearyl alcohol was added to complete the reaction. The η _sp / C and Wlow of the obtained polymer are shown in Table 1.
It was shown to.

Example 3 10 g of DL-lactide instead of L-lactide and 8 mg of aluminum dipivaloyl methanate (14 × 10 ^-6 instead of aluminum acetylacetonate) were used.
Mol) was used, and polymerization and reduced pressure treatment were carried out in the same manner as in Example 2 to terminate the reaction. Η _sp / C of the obtained polymer
And Wlow are shown in Table 1.

Comparative Example 3 Polymerization and reduced pressure treatment were carried out in the same manner as in Comparative Example 2 except that 10 g of DL-lactide was used instead of L-lactide.
The η _sp / C and Wlow of the obtained polymer are shown in Table 1.

Example 4 0.5 g of ε-caprolactone (4.38 × 10 ^-3 mol)
Polymer was polymerized in the same manner as in Example 2 except that was added, and a pressure reduction treatment was performed. Η _sp / C of the obtained polymer
And Wlow are shown in Table 1.

Comparative Example 4 0.5 g of ε-caprolactone (4.38 × 10 4^-3Mol)
The polymer was polymerized in the same manner as in Comparative Example 2 except that it was added.
Then, reduced pressure treatment was performed. Η of the obtained polymer _sp/ C
And Wlow are shown in Table 1.

Example 5 Poly- (ε-caprolactone) (PLACCEL22
Polymerization and reduced pressure treatment were carried out in the same manner as in Example 1 except that 0.3 g was added. The η _sp / C and Wlow of the obtained polymer are shown in Table 1.

Comparative Example 5 Poly- (ε-caprolactone) (PLACCEL22
Polymerization and reduced pressure treatment were carried out in the same manner as in Example 1 except that 0.3 g was added. The η _sp / C and Wlow of the obtained polymer are shown in Table 1.

Example 6 Polymerization and reduced pressure treatment were carried out in the same manner as in Example 1 except that 10 g of glycolide was used instead of L-lactide. The η _sp / C and Wlow of the obtained polymer are shown in Table 1.

Comparative Example 6 Polymerization and reduced pressure treatment were carried out in the same manner as in Example 1 except that 10 g of glycolide was used instead of L-lactide. The η _sp / C and Wlow of the obtained polymer are shown in Table 1.

[0045]

[Table 1]

[0046]

As is clear from the above examples, by using the production method of the present invention, the amount of low molecular weight compound in the polymer can be easily reduced, so that a polymer having good thermal stability can be obtained. It becomes possible to manufacture easily. Since various background materials with modified components can be produced from the obtained aliphatic polyester and a wide range of applications can be expected, it greatly contributes to solving industrial problems or environmental problems.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiichi Uno 2-1-1 Katata, Otsu City, Shiga Toyo Spinning Co., Ltd. Research Institute (56) Reference European Patent Application Publication 58481 (EP, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (5)

(57) [Claims] 1. An aluminum compound is used as a catalyst,
In the step of producing an aliphatic polyester from a cyclic dimer of an α-oxy acid by a ring-opening polymerization reaction, the method comprises a step of reducing the pressure in the reaction system in the molten state of the polymer after the polymerization or after the polymerization. Method for producing aliphatic polyester. 2. The method for producing an aliphatic polyester according to claim 1, further comprising allowing lactones to coexist. 3. The method for producing an aliphatic polyester according to claim 1 or 2, further comprising allowing an aliphatic alcohol to coexist. 4. The method for producing an aliphatic polyester according to claim 1, further comprising coexisting with another biodegradable polymer. 5. The method for producing an aliphatic polyester according to claim 1, wherein the cyclic dimer of α-oxy acid is lactide and / or glycolide.