JP3353853B2 - Polylactic acid having ester-blocked substantially all terminal hydroxyl groups and process for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a polylactic acid having ester-blocked substantially all terminal hydroxyl groups and a method for producing the same, and more particularly to a biodegradable polymer having a molecular weight of at least about 1000 and having terminal hydroxyl groups blocked during polymerization. And a method for producing the same.

[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 biodegradable plastics, which are expected to be decomposed by enzymes and microorganisms, have attracted attention and research and development have been promoted.

As a method for obtaining a high molecular weight polylactic acid,
BACKGROUND ART Heretofore, a method has been known in which lactide, which is a cyclic dimer of lactic acid represented by the following formula (VI), is heated and subjected to ring-opening polymerization in the presence of a catalyst. However, the polylactic acid obtained in this direction thermally decomposes relatively easily at a temperature slightly higher than the melting temperature (180 ° C.), and thus has a problem during melt molding.

[0004]

Embedded image In the case of polyglycolic acid and copolymers of glycolic acid and lactic acid, which are similar α-oxyacid polyesters, in order to improve their thermal stability, the obtained polyester is powdered or granulated, and a suitable acetylating agent is used. And 0-20
Acetylation of terminal hydroxyl groups by reacting at 0 ° C. is disclosed (JP-A-56-157422).

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.

In order to obtain the above-mentioned polylactic acid having good thermal stability when ring-opening polymerization of lactide is carried out, an appropriate amount of an aliphatic carboxylic acid is added at the time of ring-opening polymerization in accordance with the target molecular weight to obtain a terminal hydroxyl group. It is considered that the esterification of poly (lactic acid) has good thermal stability, and further increases the degree of polymerization during polymerization, so that polylactic acid can be easily adjusted to an arbitrary molecular weight.

[0007]

However, as described above, since the thermal stability of polylactic acid is significantly affected by the amount of terminal hydroxyl groups, it is necessary to obtain polylactic acid having good thermal stability during ring-opening polymerization. It is necessary to reduce the number of terminal hydroxyl groups by ester-blocking the terminal hydroxyl groups as much as possible to suppress the thermal decomposition reaction of polylactic acid, and the degree of polymerization of polylactic acid in which terminal hydroxyl groups are almost completely esterified. It is necessary to efficiently esterify the aliphatic carboxylic acid added in advance to the terminal hydroxyl group of polylactic acid in order to control the molecular weight.

[0008]

Means for Solving the Problems Accordingly, the present inventors have conducted further intensive studies to efficiently esterify the terminal hydroxyl group of the polylactic acid with an aliphatic carboxylic acid as much as possible. As a result, the amount of the aliphatic carboxylic acid, It has been found that the terminal hydroxyl groups are almost completely ester-blocked by the relationship of the amount of the catalyst and the polymerization time, and that the molecular weight of the polylactic acid can be easily controlled by the amount of the added aliphatic carboxylic acid and / or aliphatic alcohol. It was completed.

That is, according to the present invention, a polylactic acid having a structure represented by the formula (I) is ester-blocked with an aliphatic carboxylic acid at an end of a hydroxyl group, and is subjected to δ1.1-NMR measurement by ¹ H-NMR measurement.
Wherein substantially all terminal hydroxyl groups are ester-blocked, wherein the signal intensities of protons of 1.3, δ 1.8 to 2.0 and δ 4.9 to 5.3 satisfy the relationship represented by the formula (II). Polylactic acid,

[0010]

Embedded image (In the formula (I), n is an integer of 10 or more, and X is 2 to 5 carbon atoms.
And 0 represents an acyl group. )

[0011]

(Equation 5) (In the formula (II), A is the signal intensity of a proton of δ 4.9 to 5.3, B is the signal intensity of a proton of δ 1.1 to 1.3, and C is the signal intensity of a proton of δ 1.8 to 2.0. And Z represents the number of carbon atoms of the acyl group in formula (I).) When lactide which is a dimer of lactic acid is polymerized, the relationship represented by formula (III) at a temperature equal to or higher than the melting point of lactide. A method for producing polylactic acid, comprising adding an aliphatic carboxylic acid having 2 to 51 carbon atoms and a catalyst that satisfies the formula, and polymerizing for a time obtained according to the formula (IV),

[0012]

(Equation 6)

[0013]

(Equation 7) (In the formulas (III) and (IV), D is the amount of catalyst (mol%), E is the amount of aliphatic carboxylic acid (mol%), and T is the polymerization time (hour).
Is shown. ) Further, when polymerizing lactide which is a dimer of lactic acid, an aliphatic alcohol which satisfies the relational expression represented by the formula (V) in addition to the conditions represented by the above formulas (III) and (IV) is added and polymerized. Polylactic acid which satisfies the relational expression (II) obtained by

[0014]

(Equation 8) (In the formula (V), F represents an amount (mol%) of an aliphatic alcohol having 2 to 51 carbon atoms, and G represents an OH value in one molecule of the alcohol.) Further, polymerization is performed using organotin as a catalyst. The present invention also relates to a method for producing the polylactic acid, which further comprises polymerizing using stannous octylate as a catalyst.

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.

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. Especially stearic acid, palmitic acid, myristic acid, linoleic acid,
Oleic acid is a flavoring agent, emulsifier, vitamin fortifier, fumaric acid, succinic acid, adipic acid is also included in food additives as a seasoning, sour amount or 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 have some differences depending on conditions such as the kind of acid used, but are measured by ¹ H-NMR measurement with δ1.1 to 1.3, δ1.8 to δ1.8.
When the signal intensities of the protons of 2.0 and δ 4.9 to 5.3 are B, C, and A, respectively, [｛(CB) /
(Z-4) × 2｝ / A] × 2 × 100 is 0.001
The carboxylic acid is added in a range such that it becomes に な る 0.525. Above all, a range of 0.005 to 0.50 is preferable,
Further, the range is particularly preferably 0.075 to 0.48, and most preferably the range is 0.09 to 0.45. When this value is less than 0.001, the effect of improving the thermal stability is reduced. On the other hand, when it exceeds 0.525, it becomes difficult to block the terminal hydroxyl groups of polylactic acid due to the effect of water generated when the aliphatic carboxylic acid is esterified, and the hydroxyl group terminal blocking rate is significantly reduced. It is appropriately selected within this predetermined range according to the application.

In the polymerization, the aliphatic alcohol to be added together with the aliphatic carboxylic acid may be a mono-, di- or higher polyhydric alcohol, and may be saturated or unsaturated. Specifically, methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, nonanol, decanol,
Monoalcohols such as lauryl alcohol, myristyl alcohol, cetyl alcohol, and stearyl alcohol;
Examples thereof include dialcohols such as ethylene glycol, butanediol, hexanediol, nonanediol, and tetramethylene glycol; polyhydric alcohols such as glycerol, sorbitol, xylitol, ribitol, and erythritol; and methyl lactate and ethyl lactate. Particularly preferably decanol, lauryl alcohol,
Long-chain aliphatic alcohols such as myristyl alcohol, cetyl alcohol, and stearyl alcohol. 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 slightly different depending on the conditions such as the type of alcohol used, but the mole fraction of the carboxylic acid to be added is E, the mole fraction of the alcohol is F, and the OH group value of the alcohol. Is set to G, and the value of K = F / (E / G) is used in the range of 0 to 1.5. Especially, it is preferable to add in the range of 0.3-1.4. Further, it is preferably in the range of 0.5 to 1.4, and more preferably 0.7 to 1.3. Most preferably, it is used in the range of 0.8 to 1.2. If the amount used exceeds 1.5, the terminal hydroxyl value of the added polylactic acid will increase, and the rate of hydroxyl group terminal blocking by carboxylic acid will decrease significantly. It is appropriately selected within this predetermined range according to the application.

A catalyst is generally used for the polymerization,
For this, known catalysts usually used for lactide polymerization can be used. Among them, organotin compound catalysts such as tin formate, tin acetate, tin propionate, tin n-butyrate, tin n-valerate, n-tin Tin caproate, tin n-caprylate, tin caprate, tin laurate, tin myristate, tin palmitate, tin stearate,
Stannous octylate, tin glycooxide and the like can be suitably used. Of these, stannous octoate is most preferred.
One or more of these catalysts may be used in combination.

The amount of the catalyst used in the present invention depends on the amount of the aliphatic carboxylic acid added during the polymerization.
It is determined by using the 0.0244E ^0.454. The range of I is used in the range of more than -0.003 and less than 0.003, but is preferably in the range of -0.0025 to 0.0025. More preferably, -0.002 to 0.002.
And most preferably from -0.0015 to 0.
Used in the range of 0015. I obtained by the relational expression
Is less than -0.003, all of the aliphatic carboxylic acids added do not ester-block the terminal hydroxyl groups and remain in the system unreacted. If the value of I is 0.003 or more, the rate of the ring-opening polymerization reaction is higher than that of ester-blocking with aliphatic carboxylic acid, so that many polymers whose hydroxyl terminal is not blocked are generated, and the polymer is virtually blocked. The rate drops.

In the present invention, the polymerization time of the ring-opening polymerization reaction is calculated from a relational expression obtained by the amount of the aliphatic carboxylic acid to be added. The value J = T-1 obtained by the relational expression
0.34E is in the range of more than -0.2 and less than 0.2,
Preferably it is in the range of -0.18 to 0.18. It is more preferably used in the range of -0.15 to 0.15, and most preferably used in the range of -0.12 to 0.12. When the value of J is smaller than -0.2, the conversion of the polymer is low, and thus the terminal hydroxyl group blocking rate is low. When the polymerization time is long, the transesterification reaction of polylactic acid proceeds to increase the molecular chains which are not ester-blocked, so that the terminal blocking ratio is lowered.

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 have been sufficiently purified by ordinary purification operations, that is, recrystallization, rectification, sublimation and the like. The reaction may be performed in an inert atmosphere such as nitrogen or argon, or under reduced pressure or increased pressure. At that time, a catalyst, a carboxylic acid, or an alcohol may be sequentially added.

The polylactic acid thus obtained after the completion of the ring-opening polymerization has an arbitrary molecular weight and has improved thermal stability, so that melt molding is facilitated, and various biodegradable molded products are obtained. Can be manufactured. Further, by blocking the terminal of the carboxyl group by using an alcohol, it becomes possible to improve the thermal stability, control the mechanical properties, and simultaneously control the decomposition properties. An epoxy compound may be added to block the carboxyl group terminal without any problem. If necessary, additives such as a pigment, an antioxidant, a deterioration inhibitor, a plasticizer, a matting agent, a fluorescent brightener, and an ultraviolet absorber may be added.

The polylactic acid of 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 applications include fishing lines, fishing nets, nonwoven fabrics for agricultural and horticultural use, woven fabrics, etc. for fibers, packaging films, agricultural multi-films, shopping bags, tapes, fertilizer bags, separation membranes, etc. for films, and beverages for molded products. And cosmetic bottles,
Containers such as disposable cups and 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, ε-caprolactone and glycolide are copolymerized with other oxyacid components or other aliphatic compounds such as poly (ε-caprolactone) in order to change mechanical properties and decomposition properties in various ways. It is also possible to mix with polyester.

(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 is determined, and the following known viscosity equation of poly L-lactic acid is obtained.

[0029]

(Equation 9) It was calculated viscosity average molecular weight (M _V) is substituted into.

(2) Acid value 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 a 0.1N-NaOCH3 methanol solution using a phenolphthalein solution as an indicator.

(3) Hydroxyl Terminal Blocking Ratio The ratio of the amount of aliphatic carboxylic acid terminal esterified to the terminal hydroxyl group of polylactic acid as determined by ¹ H-NMR spectrum measurement to the amount of carboxyl group terminal group of polylactic acid by acid value measurement. I asked.

Example 1 10.0 g (6.94 × 10 ⁻² mol) of L-lactide and 57 mg (2.00 × 10 ⁻⁴ ) of stearic acid according to the formula (II)
Mol), 4.2 mg stannous octoate (9.72 × 1
0 stirrer a toluene solution of ^-6 moles) were charged in a polymerization tube equipped with a nitrogen inlet tube, 2 hr. After vacuum drying and purging with nitrogen, the mixture was heated to 190 ° C. in a nitrogen atmosphere to effect ring-opening polymerization. The degree of polymerization increased slowly. The polymer obtained by terminating the reaction at 3 hours was dissolved in 60 ml of chloroform and poured into 400 ml of methanol to cause reprecipitation. The obtained white powder was sequentially washed with methanol and ether, and then dried at 60 ° C. in vacuo. H, I in this polymerization,
The values of J were 0.289, 0.001, and 0.001, respectively. This polymer had M _V = 6.49 × 10 ⁴ , the hydroxyl group terminal blocking ratio obtained from the acid value measurement and the ¹ H-NMR spectrum measurement was 99.2%, and the terminal hydroxyl group was almost completely stearic acid. Blocked by.

Examples 2 and 6 Polymerization was carried out in the same manner as in Example 1 except that an aliphatic alcohol was added simultaneously with stearic acid. In Examples 2 and 6, the value of K was 1.01 and 0.98, respectively. Tables 1 and 2 show the types, amounts, catalyst amounts, polymerization times, H, I, and J values of the added aliphatic carboxylic acids and aliphatic alcohols, Mv of the obtained polymer, and the hydroxyl group terminal blocking ratio.

Examples 3 and 7 Polymerization was carried out in the same manner as in Example 1. Type, amount, catalyst amount, polymerization time, H, I, J of the added aliphatic carboxylic acid
And the Mv of the obtained polymer and the hydroxyl group terminal blocking ratio are shown in Tables 1 and 2.

Examples 4, 8 Polymerization was carried out in the same manner as in Example 1 except that 9.5 g of L-lactide and 0.5 g of DL-lactide were used, and an aliphatic alcohol was added simultaneously with stearic acid. Example 4,
At 8, the values of K were 1.10 and 1.03, respectively. The type of aliphatic carboxylic acid and aliphatic alcohol added,
The amounts of the catalyst, the amount of the catalyst, the polymerization time, the values of H, I, and J, the M _{V of} the obtained polymer, and the hydroxyl group terminal blocking ratio are shown in Tables 1 and 2.

Examples 4, 8 Polymerization was carried out in the same manner as in Example 1 except that 9.5 g of L-lactide and 0.5 g of DL-lactide were used. Type, amount, amount of catalyst, polymerization time, H,
I, M _V values and the resulting polymer J, hydroxyl endblocking rate shown in Table 1 and Table 2.

Examples 5, 9 Polymerization was carried out in the same manner as in Example 1 except that 5 g of L-lactide and 5 g of DL-lactide were used. Tables 1 and 2 show the type, amount, catalyst amount, polymerization time H, I, and J of the added aliphatic carboxylic acid, M _{V of} the obtained polymer, and hydroxyl terminal blocking ratio.

COMPARATIVE EXAMPLE 1 10.0 g (6.94 × 10 ⁻² mol) of L-lactide were dissolved in a toluene solution of stearic acid and tin octylate in the amounts shown in Table 2 in the same manner as in Example 1 below. The polymerization was carried out for the polymerization time shown in. Table 2 shows the values of H, I, and J.
3.5 hr. The M _V and hydroxyl endblocking rate of the polymer obtained by the reaction was completed in the same manner as in Example 1 aftertreated resulting polymer are shown in Table 2. The hydroxyl group terminal blocking rate was as extremely low as 63.0%.

Comparative Example 2 9.5 g of L-lactide and 0.5 g of DL-lactide (6.
94 × 10 ⁻² mol) of a toluene solution of stearic acid and tin octylate in the amounts shown in Table 2 were polymerized for the polymerization times shown in Table 2 in the same manner as in Example 1 below. Table 2 shows the values of H, I, and J. The degree of polymerization increased sharply, and it was difficult to obtain those having an arbitrary molecular weight. 1hr. The M _V and the hydroxyl group terminal blocking ratio of the polymer obtained to complete the reaction obtained sintered and worked up as in Example 1 polymer are shown in Table 2. The hydroxyl group terminal blocking rate was only 25.5%.

Comparative Example 3 5.0 g of L-lactide and 5.0 g of DL-lactide (6.
94 × 10 ⁻² mol) of a toluene solution of stearic acid and tin octylate in the amounts shown in Table 2 were polymerized in the same manner as in Example 1 for the polymerization times shown in Table 2. H, I, J
Are shown in Table 2. 1hr. The M _V and the hydroxyl group terminal blocking ratio of the polymer obtained to complete the reaction obtained sintered and worked up as in Example 1 polymer are shown in Table 2.
The hydroxyl group terminal blocking rate was extremely low at 60.0%.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

As is apparent from the above examples, the method shown in the present invention makes it possible to produce polylactic acid in which terminal hydroxyl groups are almost completely ester-blocked and carboxyl group terminals are also blocked. . Such a polylactic acid can be adjusted to an arbitrary molecular weight by the amount of the aliphatic carboxylic acid and the aliphatic alcohol to be added, and has good thermal stability, so that melt molding is easy and relatively simple. It can be produced by a simple method, and the degradability of the polymer can be controlled. From the obtained polylactic acid, it is possible to produce a variety of backgrounds with revised components, and since it can be expected to be used in a wide range of applications, it greatly contributes to solving the industry or environmental problems.

[Brief description of the drawings]

FIG. 1 is an example of a schematic diagram of ¹ H-NMR spectrum measurement of general polylactic acid. A is δ4.9 to 5.
3, B is δ 1.1 to 1.3 and C is δ 1.8 to 2.0
2 shows the signal intensity of the proton of FIG.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Tomohiro Aoyama 2-1-1 Katata, Otsu-shi, Shiga Prefecture Inside Toyo Spinning Co., Ltd. (72) Keiichi Uno 2-1-1 Katata, Otsu-shi, Shiga Prefecture (56) References JP-A-4-218528 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08G 63/00-63/91 WPI / L (QUESTEL)

Claims (5)

(57) [Claims] 1. A polylactic acid having a structure represented by the formula (I) is ester-blocked with an aliphatic carboxylic acid at an end of a hydroxyl group, and δ1.1 to 1.3, δ1.8 to δ1.8 in ¹ H-NMR measurement.
A polylactic acid having substantially all terminal hydroxyl groups ester-blocked, wherein the signal intensities of protons having 2.0 and δ 4.9 to 5.3 satisfy the relationship represented by the formula (II). Embedded image (In the formula (I), n is an integer of 10 or more, and X is 2 to 5 carbon atoms.
And 0 represents an acyl group. ) (Equation 1) (In the formula (II), A is the signal intensity of a proton of δ 4.9 to 5.3, B is the signal intensity of a proton of δ 1.1 to 1.3, and C is the signal intensity of a proton of δ 1.8 to 2.0. And Z represents the number of carbon atoms of the acyl group in formula (I).) 2. A method for polymerizing lactide, which is a dimer of lactic acid, comprising: an aliphatic carboxylic acid having 2 to 51 carbon atoms which satisfies the relational expression represented by the formula (III) at a temperature not lower than the melting point of lactide and 2. The process for producing polylactic acid according to claim 1, wherein a catalyst is added and polymerization is carried out for a time obtained according to the formula (IV). (Equation 2) (Equation 3) (In the formulas (III) and (IV), D is the amount of catalyst (mol%), E is the amount of aliphatic carboxylic acid (mol%), and T is the polymerization time (hour).
Is shown. ) 3. The polymerization of lactide, which is a dimer of lactic acid, by adding an aliphatic alcohol that satisfies the relational expression represented by the formula (V) in addition to the conditions described in the above item 2. The polylactic acid according to claim 1, which is obtained by carrying out the method. (Equation 4) (In the formula (V), F is an amount of an aliphatic alcohol (mol%),
G represents the OH group value in one molecule of alcohol. ) 4. The method for producing polylactic acid according to claim 2, wherein an organotin is used as a catalyst. 5. The method for producing polylactic acid according to claim 4, wherein stannous octylate is used as a catalyst.