JP3287425B2 - Polylactic acid having hydroxyl-terminated ester ester and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a polymerization reaction product, more particularly a polylactic acid having a molecular weight of at least about 1000 and having a hydroxyl-terminated capped biodegradable during polymerization.
And its manufacturing method.

[0002]

2. Description of the Related Art α-Hydroxy acid polyesters represented by polylactic acid and polyglycolic acid have good biodegradability and are used as biodegradable medical materials such as surgical sutures and microcapsules for injections. It's being used. In recent years, plastic waste has become a problem, and has attracted attention as a biodegradable plastic that is expected to be decomposed by enzymes and microorganisms.
R & D is underway.

As a method for obtaining the high molecular weight polylactic acid, a method has conventionally been known in which lactide which is a cyclic dimer of lactic acid represented by the following formula (II) is heated and ring-opening-polymerized in the presence of a catalyst. ing. However, the obtained polylactic acid is relatively easily thermally decomposed at a temperature slightly higher than the melting temperature (180 ° C.), and thus poses a problem during melt molding.

[0004]

Embedded image Therefore, in the case of polyglycolic acid or a copolymer of glycolic acid and lactic acid, which is a similar α-oxy acid polyester, in order to improve their thermal stability, the obtained polyester is powdered or granulated, and a suitable acetyl is added. Acetylation of terminal hydroxyl groups by reacting with an agent at 0 to 200 ° C. is disclosed (JP-A-56-15742).
2).

[0005]

However, the above-mentioned method is not industrially preferable because a more complicated acetylation step is required after the ordinary ring-opening polymerization. Further, when the polylactic acid is obtained by ring-opening polymerization, the degree of polymerization is sharply increased, so that it is difficult to arbitrarily obtain a polyester having an appropriate molecular weight. For this reason, there is a demand for obtaining a polylactic acid which has good thermal stability and can be easily adjusted to an arbitrary molecular weight in production at the time of ring-opening polymerization.

[0006]

The inventors of the present invention have conducted intensive studies to obtain the above-mentioned polylactic acid having good thermal stability when lactide is subjected to ring-opening polymerization. By adding an acid in an appropriate amount according to the target molecular weight, it is possible to obtain polylactic acid which has good thermal stability, and can be easily adjusted to an arbitrary molecular weight because the degree of polymerization increases slowly during polymerization. Finally, the present invention has been completed.

That is, the present invention provides a polylactic acid represented by the formula (I), wherein the hydroxyl terminal is ester-blocked.

[0008]

Embedded image (In the formula (I), n is an integer of 10 or more, and X is 1 to 5 carbon atoms.
0 represents an alkyl group and / or 1 carboxyalkyl group having 1 to 50 carbon atoms. ).

The aliphatic carboxylic acid having 2 to 51 carbon atoms used in the present invention may be a mono- or 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, undecandioic acid, dodecandioic acid, dimer acid, fumaric acid and the like can be used. Further, it does not matter even if these acid anhydrides are added. One or more of these carboxylic acids may be used in combination. In particular, stearic acid, palmitic acid, myristic acid, linoleic acid, and oleic acid are flavoring agents, emulsifiers, vitamin fortifiers, and fumaric acid, succinic acid, and adipic acid are seasonings, acidulants, and food additives as their raw materials. It is a preferred carboxylic acid because its safety has been confirmed. More preferably, stearic acid, which is a raw material of calcium stearyl lactate used as an auxiliary for baking, is exemplified.

When these are added to lactide, they may be used 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- and dicarboxylic acids are used in a proportion of 0.001 to 5 mol% with respect to the monomer lactide, although there are some differences depending on conditions such as the kind of acid used. Among them, 0.02 mol% or more,
It is preferably at most 1 mol%, more preferably 0.05 to 0.6 mol%. When the amount is less than 0.001 mol%, the effect of improving the thermal stability is reduced, and it is difficult to arbitrarily control the molecular weight. If the amount is more than 5 mol%, the carboxylic acid acts as an excessive terminal terminator, and it is difficult to increase the degree of polymerization to a practically necessary degree for suppressing polymerization. It is appropriately selected within this predetermined range according to the application.

A catalyst is generally used for the polymerization.
This includes known catalysts commonly used for lactide polymerization,
For example, tin, antimony, zinc, lead, titanium, iron, aluminum compounds and the like can be suitably used. One or more of these catalysts may be used in combination. Of these, stannous octylate, which is approved by the FDA (American Food and Drug Administration), is particularly preferred. Zinc octylate is also a preferred catalyst with low toxicity.

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 in an inert atmosphere such as nitrogen or argon, or under reduced pressure or increased pressure. At that time, a catalyst and a carboxylic acid may be added sequentially.

The polylactic acid thus obtained after the completion of the ring-opening polymerization has an arbitrary molecular weight, and has improved thermal stability to facilitate melt molding. It is possible to manufacture things. Further, in order to improve the thermal stability and control the mechanical properties and the decomposition properties, the terminal of the carboxyl group may be blocked with an epoxy compound, alcohol, or the like. If necessary, additives such as pigments, antioxidants, anti-deterioration agents, plasticizers, matting agents, antistatic agents, fluorescent brighteners, and ultraviolet absorbers may be added.

The polylactic acid in the present invention can be formed into a fiber, a film, or various molded products from a molten or solution state, and is useful as a biodegradable material. Specific uses include fishing line, fish net, non-woven fabric, etc. for fibers, films for packaging, multi-film for agriculture, shopping bags, tapes, fertilizer bags, separation membranes, etc. for films, bottles for beverages and cosmetics for molded products, 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 are conceivable. Further, as medical applications, applications to the DDS field such as sutures, artificial bones, artificial skins, microcapsules, and the like can be considered, but the present invention is not limited thereto.

In the present invention, in order to change various mechanical properties and decomposition properties, other aliphatic polyester-forming products, that is, succinic acid, adipic acid, sebacic acid and the like as an acid component, ethylene glycol and a glycol component as a glycol component, etc. , 4-butanediol or the like, or ε-caprolactone, or the like, can be mixed and copolymerized.

[0017]

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) Viscosity average molecular weight 0.125 g of polymer was dissolved in chloroform,
Measured at 0.1 ° C. to calculate the reduced viscosity. From this, the intrinsic viscosity was determined, and the viscosity average molecular weight (Mv) was calculated by substituting into the known viscosity formula of poly L-lactic acid [η] = 5.45 × 10 ⁻⁴ · Mv ^0.73 .

(2) 10% Weight Loss Temperature The thermal stability was evaluated using a TGA-50 manufactured by Shimadzu Corporation in an argon atmosphere at a heating rate of 10 ° C./min.

(3) Melting point The melting point was measured at a temperature rising / falling rate of 10 ° C./min in an argon atmosphere using a DSC-50 manufactured by Shimadzu Corporation.

[0021] Example 1 L-lactide 10.0g (6.94 × 10 ^-2 mol), 57 mg of stearic acid (2.00 × 10 ^-4 mol), octyl stannous 3mg (7.4 × 10 ^{- 6} mol) of a toluene solution was charged into a polymerization tube equipped with a stirrer and a nitrogen inlet tube,
After vacuum drying for 2 hours and purging with nitrogen, the mixture was heated to 200 ° C. in a nitrogen atmosphere to effect ring-opening polymerization. The degree of polymerization increased slowly. The polymer obtained by terminating the reaction for 1 hour was dissolved in 60 ml of chloroform, and 400 ml of methanol was dissolved.
And reprecipitated. The obtained white powder was sequentially washed with methanol and ether, and then dried at 60 ° C. in vacuo. The polymer had a Mv = 3.24 × 10 ⁴ , a TGA 10% weight loss temperature of 321 ° C. and a melting point of 177 ° C. This was dissolved in deuterated chloroform and the ¹ H-NMR spectrum was measured. The peak (1.23 pp) attributed to the terminal stearyl group was obtained.
m) was confirmed.

COMPARATIVE EXAMPLE 1 10.0 g (6.94 × 10 ⁻² mol) of L-lactide was polymerized in the same manner as in Example 1 except that stearic acid was not added. It was difficult to obtain those having a molecular weight of The polymer obtained after the reaction was completed for 1 hour was subjected to post-treatment in the same manner as in Example 1 to obtain a polymer having Mv = 6.71 × 10 ⁴ .
The melting point was 181 ° C and the 10% weight loss temperature by TGA was 283 ° C.

Example 2 Polymerization was carried out in the same manner as in Example 1 except that 10.0 g (6.94 × 10 ⁻² mol) of L-lactide and 114 mg (4.00 × 10 ⁻⁴ mol) of stearic acid were used. The degree of polymerization increased slowly. Similarly, the polymer obtained by post-treatment has Mv =
It had 1.96 × 10 ⁴ , the 10% weight loss temperature by TGA was 310 ° C., and the melting point was 176 ° C.

Example 3 Polymerization and post-treatment in the same manner as in Example 1 except that 10.0 g (6.94 × 10 ⁻² mol) of L-lactide and 14 mg (5.0 × 10 ⁻⁵ mol) of stearic acid were used. did. The resulting polymer has Mv = 4.78 × 10 ⁴ , a 10% weight loss temperature by TGA of 315 ° C. and a melting point of 180
° C.

Example 4 Polymerization and post-treatment were conducted in the same manner as in Example 1 except that 10.0 g (6.94 × 10 ⁻² mol) of L-lactide and 52 mg (2.00 × 10 ⁻⁴ mol) of palmitic acid were used. did. The resulting polymer has a Mv = 3.66 × 10 ⁴ , a 10% weight loss temperature by TGA of 319 ° C. and a melting point of 1
78 ° C.

Example 5 Polymerization and post-treatment were performed in the same manner as in Example 1 except that 10.0 g (6.94 × 10 ⁻² mol) of L-lactide and 46 mg (2.00 × 10 ⁻⁴ mol) of myristic acid were used. did. The resulting polymer has Mv = 3.70 × 10 ⁴ , a 10% weight loss temperature by TGA of 317 ° C. and a melting point of 17
8 ° C.

Example 6 Polymerization and post-treatment were carried out in the same manner as in Example 1 except that 10.0 g (6.94 × 10 ⁻² mol) of L-lactide and 15 mg (1.00 × 10 ⁻⁴ mol) of adipic acid were used. did. The resulting polymer has Mv = 3.02 × 10 ⁴ , has a 10% weight loss temperature by TGA of 310 ° C. and a melting point of 177.
° C.

Example 7 A polymer (Mv = 3.31 × 10 ⁴ ) in which the hydroxyl terminal was ester-blocked with stearic acid and a polymer (Mv = 3.37 × 10 ⁴ ) which had not been blocked were mixed under nitrogen atmosphere for 200 minutes.
When the Mv retention was compared by heating each at 1 ° C. for 1 hour, the Mv retention of the ester-sealed polymer was 94%.
But the unblocked polymer had an Mv retention of 65
It was only%.

[0029]

As is clear from the above examples, the polylactic acid in the present invention can be adjusted to an arbitrary molecular weight and has good thermal stability, so that melt molding is easy and a relatively simple method. Can be manufactured. From the obtained polylactic acid, various biodegradable molded products can be produced, and a wide range of applications can be expected. Therefore, they greatly contribute to solving the industry or environmental problems.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-16792 (JP, A) JP-A-6-228289 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08G 63/00-63/91

Claims (1)

(57) [Claims] 1. A polylactic acid represented by the formula (I), wherein the hydroxyl terminal is ester-blocked. Embedded image (In the formula (I), n is an integer of 10 or more, and X is 1 to 5 carbon atoms.
0 represents an alkyl group and / or a 1-carboxyalkyl group having 1 to 50 carbon atoms. )