JPH0912688A - Polylactic acid resin composition - Google Patents

Abstract

PURPOSE: To obtain a polylactic acid resin composition excellent in hydrolysis resistance and stability under natural environment. CONSTITUTION: This polylactic acid resin composition has characters such that, when it is immersed in a phosphoric acid buffer with a pH of 7.0 in a temperature range from Tg or over to 90 deg.C or below, the following expressions (I) and (II) are satisfied: (3.28-lnk)×(3Tg+168)>=4,500... (I) and kt = log [A/(A-b)]... (II), wherein A: the number of moles of the ester bond in 1mol of the initial polymer; (b): the number of moles of water reacted with 1mol of the polymer; (t): the immersed time (hr); Tg: the glass transition time of the polymer ( deg.C); and (k): the hydrolysis reaction rate constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to polylactic acid and / or its copolymer having excellent hydrolysis resistance and stability in natural environment.

[0002]

2. Description of the Related Art α-Oxyacid polyesters represented by polylactic acid and polyglycolic acid have good biodegradability and biocompatibility and are used as bioabsorbable medical materials. 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. Polylactic acid-based resin has thermal and mechanical properties,
It has outstanding properties such as biodegradability, and it has remarkable properties such as complete degradability with almost no residue after decomposition, and the safety of degradable products. Is very much expected.

Due to the above properties, polylactic acid resins have been researched and developed in the field of biodegradable medical materials such as surgical sutures, microcapsules for injections, etc. It is desired to be decomposed and absorbed in the living body as quickly as possible. Therefore, various studies have been conducted so far to improve the decomposition rate of polylactic acid resins. However, such polymers are not sufficiently stable in water or humidity,
It is extremely disadvantageous to use a polylactic acid-based resin as a biodegradable plastic, and the current situation is that the development of the resin for general purpose is hindered.

An attempt to improve the storage stability and processability deterioration of a polymer by paying attention to a low molecular weight compound is disclosed in, for example, JP-A-3-14829. However, this method aims to remove volatile low molecular weight compounds from the polymer, and does not mention low molecular weight compounds such as non-volatile oligomers. Further, there is a correlation between the hydrolyzability of the polylactic acid-based resin and the number of terminal carboxyl groups of the polymer, and since the polylactic acid-based resin generally has many terminal carboxyl groups, it is easily hydrolyzed. On the other hand, a method of polymerizing a polymer using a hydroxyl compound as a polymerization initiator and blocking the carboxyl group at the terminal of the molecular chain is known, but this is intended to control the molecular weight of the polymer, and thus the above-mentioned problems are solved. It does not solve.

[0005]

Despite the desire for improved hydrolysis resistance as described above, a polylactic acid resin having good hydrolysis resistance has not yet been obtained.
For this reason, it is an object of the present invention to provide a polylactic acid resin having good hydrolysis resistance, which can exist stably in water or in a humidity atmosphere.

[0006]

The inventors of the present invention have conducted extensive studies to obtain a polylactic acid-based resin having good hydrolysis resistance. As a result, the hydrolysis reaction rate constant of the polymer and the glass transition temperature have been improved. It was found that hydrolysis resistance was improved only when a certain relational expression shown was satisfied, and finally the present invention was completed. That is, the present invention
PH of 7.
A polylactic acid-based resin composition characterized by satisfying both of the following formulas (I) and (II) when immersed in a phosphate buffer solution of No. 0.

(3.28-lnk) × (3Tg + 168) ≧ 4500 (I) kt = log [A / (Ab)] (II) A: mol number of ester bond in 1 mol of initial polymer b: polymer Number of mol of water reacted with 1 mol t: Immersion time [hr] T _g : Glass transition temperature of polymer [° C] k: Hydrolysis reaction rate constant [hr ^-1 ]

One of the methods for improving the hydrolysis resistance of polylactic acid-based resin is to reduce the amount of low molecular weight compounds such as unreacted monomers in polymers, impurities produced by side reactions, chain-like and cyclic oligomers. Can be mentioned. Usually, polylactic acid-based resin is produced by ring-opening polymerization of lactide which is a cyclic diester and corresponding lactone, so-called lactide method. In this case, the ring-opening polymerization reaction and the thermal ring-closing (depolymerization) reaction are in an equilibrium relationship, and a low molecular weight compound such as lactide, lactones, lactic acid or oligomer remains in the polymer. These low molecular weight compounds have very strong hydrophilicity, and as such or their hydrolyzates show strong acidity, they significantly accelerate the hydrolysis of the polymer.

It is difficult to obtain a sufficiently high molecular weight compound by a method other than the lactide method, for example, a direct dehydration condensation method of lactic acid or a polycondensation method of formalin and carbon dioxide, but the polymers obtained by these methods are exactly the same. In addition, low molecular weight compounds are one of the main causes of hydrolysis. Therefore, it is necessary to reduce low molecular weight compounds in the polymer.

As a method for reducing the low molecular weight compound in the polymer, the following methods generally used can be used. For example, a re-precipitation method in which a polymer is dissolved in a solvent and poured into a poor solvent for the polymer to precipitate the polymer, a method of extracting with a solvent in which only a low molecular weight compound or a residual monomer is dissolved, and the like are used. In addition, a low molecular weight compound can be efficiently removed by a method of reducing the pressure in the molten state of the polymer at the latter stage of polymerization of the polymer or after completion of the polymerization.
For example, in the case of polylactic acid, from the melting point of the polymer to the melting point +
50 ℃ or glass transition point to glass transition point +200
The pressure reduction treatment may be performed within the range of ° C. Furthermore, low molecular weight compounds can be reduced by solid phase heat treatment of the polymer. For example, in the case of polylactic acid, 120 ° C or higher and 150
The heat treatment may be performed at a temperature of ℃ or less in an absolutely dry state. In this case, there is no problem under any flow of an inert gas or the like, under reduced pressure, or under increased pressure. When both the melt depressurization treatment and the solid phase heat treatment of the polymer are used, the low molecular weight compound can be removed more effectively. Examples of the method for reducing the low molecular weight compound include, but are not limited to, those described above.

The hydrolysis resistance of a polyester of an α-oxy acid ester such as polylactic acid is correlated with the number of terminal carboxyl groups in its molecular chain, and the hydrolysis resistance decreases as the number of carboxyl groups in the polymer increases. Tend to do. Therefore, as a method of improving the hydrolysis resistance of the polylactic acid-based resin, a method of blocking the carboxyl group at the terminal of the polymer molecular chain can be mentioned.

As a method for blocking the terminal carboxyl group of the polymer molecular chain, when a polylactic acid resin is produced by the lactide method, the ring-opening polymerization reaction may be carried out in the presence of lactide and other lactones and an aliphatic alcohol. .

The aliphatic alcohol used may be a mono-, di-, or polyhydric alcohol, and may be saturated or unsaturated. Specifically, methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, nonanol, decanol, lauryl alcohol, myristyl alcohol,
Cetyl alcohol, monoalcohols such as stearyl alcohol, ethylene glycol, butanediol, hexanediol, nonanediol, dialcohols such as tetramethylene glycol, dialcohols, glycerol, sorbitol,
Polyhydric alcohols such as xylitol, ribitol, and erythritol, and methyl lactate and ethyl lactate can be used, but are not limited thereto. Particularly preferably, long-chain aliphatic alcohols such as decanol, lauryl alcohol, myristyl alcohol, cetyl alcohol and stearyl alcohol are used. One or more of these alcohols can be used in combination. When the boiling point of the alcohol used is lower than the polymerization temperature, it is necessary to carry out the reaction under pressure.

The amount of alcohol varies depending on the purpose,
If the amount is too large, the molecular weight hardly increases, and the amount of the low molecular weight compound increases, which is not preferable. 0.01 to the total amount of monomer
It is used in a proportion of 1 mol%.

Further, instead of the aliphatic alcohol, an aliphatic polyester having a hydroxyl group at the terminal of the molecular chain can be used. The term "aliphatic polyester" as used herein means, for example, poly- (β-butyrolactone), poly-
(Γ-butyrolactone), poly- (ε-caprolactone), polypropiolactone, poly- (δ-valerolactone), poly- (4-valerolactone), poly- (β-
Examples thereof include methyl-δ-valerolactone), polyglycolic acid, and polyesters of the type obtained by polycondensing an aliphatic carboxylic acid and an aliphatic alcohol.

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.

Further, a plasticizer may be added in order to improve the hydrolysis resistance of the polylactic acid resin. Examples of the plasticizer to be used include phthalic acid derivatives such as di-n-octyl phthalate, di-2-ethylhexyl phthalate and dibenzyl phthalate, isophthalic acid derivatives such as diisooctyl phthalate, di-n-butyl adipate and dioctyl adipate. Adipic acid derivatives such as dioctyl sebacate, sebacic acid derivatives such as di-n-butyl maleate, maleic acid derivatives such as di-n-butyl maleate, citric acid derivatives such as tri-n-butyl citrate, oleic acid derivatives such as butyl oleate, Examples thereof include itaconic acid derivatives such as monobutyl itaconate, ricinoleic acid derivatives such as glycerin monolysylate, and phosphate ester plasticizers such as tricresyl phosphate and trixylenyl phosphate. These plasticizers may be used alone or in combination of two or more. By adding the plasticizer to the lactic acid-based resin, the hydrophobicity of the polymer is increased and the hydrolysis resistance is improved, and at the same time, the lactic acid-based resin is effectively plasticized, and the resulting resin composition is flexible and melts. Moldability such as extrusion and stretching is improved.

The polylactic acid-based resin having excellent hydrolysis resistance in the present invention is realized by using a plurality of the methods for reducing the amount of the low molecular weight compound described above and other methods. When each of these methods is used alone, a great effect cannot be obtained.

A catalyst is generally used for polymerizing the polylactic acid resin, and a known catalyst is used for these.
In the case of producing by the lactide method, specifically, tin, antimony, zinc, titanium, iron and aluminum compounds can be exemplified, but the invention is not limited thereto. Of these, tin catalysts and aluminum catalysts are particularly preferred, and tin octylate and aluminum acetylacetonate are particularly preferred.

In the present invention, the hydroxyl group at the terminal of the molecular chain may be blocked with an aliphatic carboxylic acid. The C2-C51 aliphatic carboxylic acid used may be any of mono-, di-, and polyvalent carboxylic acids, 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, dodecanedioic acid, dimer acid, fumaric acid and the like can be used. Further, 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, and oleic acid are flavoring agents, emulsifiers, vitamin enhancers, and fumaric acid, succinic acid, and adipic acid are seasonings, sour amounts, or food additives as their raw materials. It is a preferred carboxylic acid because its safety has been confirmed. Still more preferably, stearic acid, which is a raw material of calcium stearyl lactate used as an auxiliary for baking, is exemplified. By blocking the hydroxyl group terminal in this manner, the hydrophilicity of the polymer is reduced, and the hydrolysis resistance is improved, and at the same time, the melt stability of the polymer is improved.

The lactide used in the present invention is L
-Lactide, D-lactide, DL-lactide, meso-lactide may be used. It is desirable to use those which are sufficiently purified by ordinary purification operations, that is, recrystallization, rectification, sublimation and the like. The reaction may be carried out under an inert atmosphere such as nitrogen, argon or the like, or under reduced pressure or increased pressure, in which case the catalyst, carboxylic acid and alcohol may be added successively.

In the present invention, the second component may be mixed with the polylactic acid resin in order to change various mechanical properties, degradability and the like, and among them, a component having biodegradability is preferable. Examples of the mixed component include an aliphatic polyester such as an oxyacid ester polymer comprising an alkylene group having 1 to 20 carbon atoms. Specifically, poly-
(Β-butyrolactone), poly- (γ-butyrolactone), poly- (ε-caprolactone), poly- (propiolactone), poly- (δ-valerolactone), poly-
(4-valerolactone), poly- (β-methyl-δ-valerolactone), and other polylactones, polyglycolic acid, and polyesters of the type obtained by polycondensing an aliphatic carboxylic acid and an aliphatic alcohol However, the present invention is not limited to these.

The polylactic acid-based resin thus obtained has an arbitrary molecular weight depending on the application, but in the application where hydrolysis resistance is particularly required, the number average molecular weight is 1
It is preferably 0000 or more, more preferably 20,000 or more, and most preferably 50,000 or more. If necessary, additives such as pigments, antioxidants, deterioration inhibitors, plasticizers, matting agents, optical brighteners, and ultraviolet absorbers may be added.

The polylactic acid of the present invention can be molded into fibers, films and various molded products from a molten or solution state and has better hydrolysis resistance than conventional products. Available over a wide range. 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 bottles of cosmetics,
Disposable cups, trays, knives, forks,
Tableware such as spoons, agricultural flowerpots, nursery beds, pipes that do not need to be dug up, and building materials such as temporary fixing materials are considered. Further, as medical applications, application to the field of DDS such as sutures, artificial bones, artificial skin, and microcapsules is conceivable, but not limited to these.

[0025]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. The characteristic values in the examples were measured by the following methods.

(1) Reduced viscosity (IV) 0.125 g of a polymer or sheet test piece was dissolved in chloroform and measured at 25 ± 0.1 ° C. to calculate the reduced viscosity.

(2) Acid value (eq / ton) 0.8 g of the polymer was dissolved in a mixed solution of 10 ml of chloroform and 10 ml of methanol, and titrated with 0.1N-NaOCH3 methanol solution using a phenolphthalein solution as an indicator.

(3) Low molecular weight compound amount (Wlow) 2.0 g (W ₁ ) of polymer sample 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 precipitated polymer precipitate was separated by filtration, dried under reduced pressure at 50 ° C. for 24 hours, and calculated from the amount (W ₂ ) of the polymer obtained by the following formula (III). Wlow = [(W ₁ −W ₂ ) / w ₁ ] × 100 (III) The low molecular weight compound excluded by this method is GPC.
When confirmed by a method, the number average molecular weight was 1,000 or less.

(4) Evaluation of Hydrolyzability A sheet of 35 mm × 17.5 mm and a thickness of 0.5 mm is p
It was immersed in a H7.0 phosphate buffer for 24 hours, and X in the following formula (IV) was determined. In addition, the weight and reduced viscosity before immersion and after 12 hours were measured. From the obtained results, the weight retention rate (WR) and the viscosity retention rate (BR) were calculated by the following formulas (V) and (VI).

X = (3.28-lnk) × (3Tg + 168) (IV) kt = log [A / (Ab)] A: mol number of ester bond in 1 mol of initial polymer b: reaction with 1 mol of polymer Number of mols of water taken: t: Immersion time [hr] T _g : Glass transition temperature of polymer [° C] k: Hydrolysis reaction rate constant [hr ^-1 ]

WR (%) = (weight of test piece after immersion / weight of test piece before immersion) × 100 (V) BR (%) = (viscosity of test piece after immersion / viscosity of test piece before immersion) × 100 (VI)

Example 1 L-lactide 10.0 g (6.94 × 10 ⁻² mol), stearyl alcohol 27.1 mg (1.00 × 10 ⁻⁴ mol), aluminum acetylacetonate 9 mg (28)
Toluene solution (× 10 ⁻⁶ mol) and dioctyl sebacate (300 mg) were charged into a polymerization tube equipped with a stirrer and a nitrogen introducing tube, vacuum dried for 2 hours, and after nitrogen substitution, the temperature was adjusted to 190 ° C. under a nitrogen atmosphere. The mixture was heated and the ring-opening polymerization reaction was carried out for 2 hours. While maintaining the temperature in the reaction system, degassing was performed with a vacuum pump to reduce the pressure to 5 mmHg. After continuing for 1 hour, the inside of the reactor was replaced with nitrogen and a polymer was taken out. The Wlow of the obtained polymer was zero. When hydrolyzability was evaluated at 90 ° C., A = 730, b = 0.61, Tg = 65.
℃, k = 1.06 × 10 ^-5 , X = 5350, WR
= 100%, BR = 62%, showing good hydrolysis resistance.

Example 2 L-lactide 10.0 g (6.94 × 10 ^-2 mol), stearyl alcohol 54.2 mg (2.00 × 10 ^-4 mol), aluminum acetylacetonate 9 mg (28)
(× 10 ⁻⁶ mol) of toluene solution was charged into a polymerization tube equipped with a stirrer and a nitrogen introducing tube, vacuum dried for 2 hours, and after nitrogen substitution, heated to 190 ° C. in a nitrogen atmosphere to open the ring. The polymerization reaction was carried out for 2 hours. While maintaining the temperature in the reaction system, degassing was performed with a vacuum pump to reduce the pressure to 5 mmHg. After continuing for 1 hour, the inside of the reactor was replaced with nitrogen and a polymer was taken out. The polymer obtained had a Wlow of 0.2. Hereinafter, values of A, b, Tg, k, and X when the hydrolyzability was evaluated at 90 ° C. in the same manner as in Example 1 are shown in Table 1. As a result of the hydrolysis test, X = 5370, WR = 100,
BR = 80, indicating good hydrolysis resistance.

Example 3 Polymerization and melt decompression treatment were carried out in the same manner as in Example 2 except that 10 g of DL-lactide was used instead of L-lactide. The polymer obtained had a Wlow of 0.3. Hereinafter, values of A, x, Tg, k, and X when the hydrolyzability was evaluated at 60 ° C. in the same manner as in Example 1 are shown in Table 1. As a result of the hydrolysis test, X = 5190, WR = 100,
BR = 85, indicating good hydrolysis resistance.

Example 4 1.0 g of polycaprolactone (PLACCEL 220, manufactured by Daicel Chemical Industries) instead of stearyl alcohol
Polymerization and melt decompression treatment were carried out in the same manner as in Example 2 except that was used. The polymer was further treated at 100 ° C. for 12 hours under a reduced pressure of 0.1 mmHg, and then treated under a nitrogen stream at 120 ° C.
It was subjected to solid phase treatment at 24 ° C. for 24 hours. Wlo of the obtained polymer
w was 0.1. Hereinafter, values of A, b, Tg, k, and X when the hydrolyzability was evaluated at 90 ° C. in the same manner as in Example 1 are shown in Table 1. As a result of the hydrolysis test, X = 532
0, and WR = 100 and BR = 65, indicating good hydrolysis resistance.

Example 5 1.0 g of polycaprolactone (PLACCEL240, manufactured by Daicel Chemical Industries) instead of stearyl alcohol
Polymerization and melt decompression treatment were carried out in the same manner as in Example 2 except that was used. The polymer was further treated at 100 ° C. for 12 hours under a reduced pressure of 0.1 mmHg, and then treated under a nitrogen stream at 120 ° C.
It was subjected to solid phase treatment at 24 ° C. for 24 hours. Wlo of the obtained polymer
w was 0.1. Hereinafter, values of A, b, Tg, k, and X when the hydrolyzability was evaluated at 90 ° C. in the same manner as in Example 1 are shown in Table 1. As a result of the hydrolysis test, X = 530
0, and WR = 100 and BR = 82, indicating good hydrolysis resistance.

Example 6 Instead of stearyl alcohol, poly- (βmethyl-δ
-Valerolactone) (Clapol L2010, manufactured by Kuraray Co., Ltd.) was used, and polymerization and reduced pressure treatment were carried out in the same manner as in Example 2. The polymer obtained had a Wlow of 0.2. Hereinafter, values of A, b, Tg, k, and X when the hydrolyzability was evaluated at 90 ° C. in the same manner as in Example 1 are shown in Table 1. As a result of the hydrolysis test, X = 5310, WR = 100, and BR = 66, indicating good hydrolysis resistance.

Example 7 10.0 g (6.94 × 10 ^-2 mol) of L-lactide and 18.7 mg (1.00 × 10 ^-4 ) of lauryl lauryl alcohol.
Mol), stearic acid 28.4 mg (1.00 × 10 ^-4
Mol), stannous octylate 3 mg (7 × 10 ⁻⁶ mol)
The toluene solution of was charged into a polymerization tube equipped with a stirrer and a nitrogen introduction tube, vacuum-dried for 2 hours, nitrogen-substituted, and then heated to 190 ° C. in a nitrogen atmosphere to carry out a ring-opening polymerization reaction for 2 hours. It was After the reaction was completed, the resulting polymer was dissolved in chloroform (60 ml), poured into methanol (400 ml) and reprecipitated. The obtained white powder was sequentially washed with methanol and ether, and then dried at 60 ° C. in vacuo. The Wlow of the obtained polymer was zero. Thereafter, as in Example 1, 9
A, b, Tg, k when hydrolyzability was evaluated at 0 ° C,
Each X value is shown in Table 1. As a result of the hydrolysis test, X = 5
340, and WR = 100 and BR = 68, showing good hydrolysis resistance.

Comparative Example 1 L-lactide 10.0 g (6.94 × 10 ^-2 mol), stearyl alcohol 27.1 mg (1.00 × 10 ^-4 mol), aluminum acetylacetonate 9 mg (28)
Toluene solution (× 10 ⁻⁶ mol) and dioctyl sebacate (300 mg) were charged into a polymerization tube equipped with a stirrer and a nitrogen introducing tube, vacuum dried for 2 hours, and after nitrogen substitution, the temperature was adjusted to 190 ° C. under a nitrogen atmosphere. The mixture was heated and the ring-opening polymerization reaction was carried out for 2 hours. The obtained polymer 2 had a Wlow of 5.5. Hereinafter, values of A, b, Tg, k, and X when the hydrolyzability was evaluated at 90 ° C. in the same manner as in Example 1 are shown in Table 1. As a result of the hydrolysis test, X = 4460, WR = 94%,
BR was very bad at 30%.

Comparative Example 2 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. While maintaining the temperature in the reaction system, degassing was performed with a vacuum pump to reduce the pressure to 5 mmHg. After continuing for 1 hour, the inside of the reactor was replaced with nitrogen and a polymer was taken out.
The polymer obtained had a Wlow of 0.2. Hereinafter, values of A, b, Tg, k, and X when the hydrolyzability was evaluated at 90 ° C. in the same manner as in Example 1 are shown in Table 1. As a result of the hydrolysis test, X = 4380, WR = 97%, BR
= 21, the hydrolysis resistance was very poor.

[0041] Comparative Example 3 L-lactide 10.0g (6.94 × 10 ^-2 mol), 28.4 mg of stearic acid (1.00 × 10 ^-4 mol), octyl stannous 3mg (7 × 10 ^{- (6} mol) toluene solution was charged into a polymerization tube equipped with a stirrer and a nitrogen introducing 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. After the reaction was completed, the resulting polymer was dissolved in chloroform (60 ml), poured into methanol (400 ml) and reprecipitated.
The obtained white powder was sequentially washed with methanol and ether, and then dried at 60 ° C. in vacuo. Wlo of the obtained polymer
w was 0. Hereinafter, values of A, b, Tg, k, and X when the hydrolyzability was evaluated at 90 ° C. in the same manner as in Example 1 are shown in Table 1. As a result of the hydrolysis test, X = 4420, WR = 98, BR = 25, and the hydrolysis resistance was very poor.

[0042] Comparative Example 4 L-lactide 10.0g (6.94 × 10 ^-2 mol), 28.4 mg of stearic acid (1.00 × 10 ^-4 mol), octyl stannous 3mg (7 × 10 ^{- (6} mol) toluene solution was charged into a polymerization tube equipped with a stirrer and a nitrogen introducing 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. The polymer obtained had a Wlow of 7. Hereinafter, A, b, and T when hydrolyzability was evaluated at 90 ° C. in the same manner as in Example 1.
The values of g, k and X are shown in Table 1. As a result of the hydrolysis test, X = 4280, WR = 90, BR = 22, and the hydrolysis resistance was very poor.

Comparative Example 5 A ring-opening polymerization reaction was carried out in the same manner as in Comparative Example 1 except that 10 g of DL-lactide was used instead of L-lactide. The polymer obtained had a Wlow of 0.3. Hereinafter, A when the hydrolyzability was evaluated at 60 ° C. in the same manner as in Example 1,
The values of b, Tg, k and X are shown in Table 1. As a result of the hydrolysis test, X = 4250, WR = 100, BR = 2
0 and the hydrolysis resistance was very poor.

[0044]

[Table 1]

[0045]

As is apparent from the above examples, the polylactic acid-based resin of the present invention has good hydrolysis resistance and is stable in water or humidity, which has been a problem in the past. The sex is significantly improved. Therefore, from the obtained polylactic acid-based resin, various modified component background materials can be produced, and a wide range of applications can be expected. Therefore, it greatly contributes to solving industrial problems or environmental problems.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Keiichi Uno 2-1-1 Katata, Otsu City, Shiga Prefecture Toyobo Co., Ltd. Research Laboratory

Claims (2)

[Claims] 1. A polymer which satisfies the following formulas (I) and (II) when immersed in a phosphate buffer having a pH of 7.0 at a temperature range not lower than Tg and not higher than 90 ° C. Lactic acid-based resin composition. (3.28-lnk) × (3Tg + 168) ≧ 4500 (I) kt = log [A / (Ab)] (II) A: mol number of ester bond in 1 mol of initial polymer b: reaction with 1 mol of polymer Number of mols of water taken: t: Immersion time [hr] T _g : Glass transition temperature of polymer [° C] k: Hydrolysis reaction rate constant [hr ^-1 ] 2. The polylactic acid-based resin composition according to claim 1, wherein the number average molecular weight of the polymer is 10,000 or more.