JPH1135663A - Production of lactic acid-based polyester and lactic acid-based polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject polymer useful for e. g. coating materials without the need of using expensive DL-lactide or mesolactide, by ring opening polymerization of L-lactide and/or D-lactide in the presence of a polymerization catalyst and a specified amount of an alkali (alkaline earth) metal compound. SOLUTION: Feedstock monomer(s), i. e. L-lactide and/or D-lactide is subjected to ring opening polymerization in a molten state in the presence of a polymerization catalyst such as a tin compound and, as racemizing agent, 0.005-0.2 mol% (based on the monomer(s)) of at least one kind of alkali metal compound and/or 0.02-0.5 mol% of at least one kind of alkaline earth metal compound such as magnesium or calcium compound to obtain the objective lactic acid-based polyester satisfying the relationships I and II [L-D is the absolute value of the difference between the L-lactic acid proportion (L%) and D-lactic acid proportion(D%) in the final polyester; ηsp /c is the reduced viscosity (concentration 0/5g/dL) determined at 25 deg.C in chloroform using an Ubbelohde's viscometer].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a lactic acid-based polyester which is known to have biodegradability. More specifically, the present invention relates to a method for producing a lactic acid-based polyester without using expensive DL-lactide.

[0002]

2. Description of the Related Art In recent years, development of biodegradable aliphatic polyesters has been actively conducted due to increasing awareness of environmental problems. Since these aliphatic polyesters are finally decomposed into water and carbon dioxide by microorganisms and enzymes, the load on the environment of products using the polyesters is greatly reduced. Among various aliphatic polyesters, lactic acid-based polyester synthesized from lactic acid is thermoplastic,
Its excellent physical properties have attracted attention as compared with other polyesters.

A lactic acid-based polyester having a practical molecular weight can be obtained by ring-opening polymerization of a cyclic diester of lactic acid generally called lactide. For example, poly-L-lactic acid can be obtained from optically active L-lactide, which has a melting point of 175 ° C. or higher, is a crystalline polymer, and has a possibility of physically replacing polyethylene terephthalate and polystyrene. Also, it is soluble only in a special solvent such as chloroform, and the solution has optical rotation like L-lactic acid.

[0004] On the other hand, poly-DL-lactic acid can be obtained from optically inactive DL-lactide (racemic lactide, an equal mixture of L-lactide and D-lactide) or meso-lactide (meso-form), but has a melting point. It is an amorphous polymer that does not dissolve in general-purpose solvents such as toluene, methyl ethyl ketone and ethyl acetate. Of course, the solution has no optical rotation.

From a mixture of L-lactide and DL-lactide and / or meso-lactide at various ratios, polylactic acid having an intermediate optical purity between poly-L-lactic acid and poly-DL-lactic acid can be obtained. Hereinafter, in the present invention, a lactic acid-based polyester in which an L-lactic acid unit and a D-lactic acid unit such as polylactic acid and poly-DL-lactic acid are mixed in a main chain is collectively referred to as a lactic acid-based polyester in which a lactic acid unit is racemized. I will do it. For example, it is known that the melting point is lowered when D-lactic acid units are contained in poly-L-lactic acid. It becomes crystalline and becomes considerably soluble in general-purpose solvents.

[0006] A lactic acid-based polyester having a racemic lactic acid unit has a lowered melting point or becomes amorphous and becomes soluble in a general-purpose solvent, so that it can be used in various applications as a functional resin.
Further, since the crystallinity is reduced or becomes amorphous, the hydrolysis is accelerated as compared with poly-L-lactic acid, and therefore, application to a use requiring a high decomposition rate is expected. However, DL-lactide and meso-lactide required for the synthesis have a problem that the yield in the synthesis is low and expensive.

[0007]

An object of the present invention is to provide a method for producing a lactic acid-based polyester in which lactic acid units are racemized without using expensive DL-lactide or meso-lactide. .

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, using either L-lactide or D-lactide as one of the starting monomers, a polymerization catalyst was prepared. When ring-opening polymerization is carried out in the presence of at least one of an alkali metal compound and an alkaline earth metal compound as a racemizing agent in the presence of a specific range of concentration, a lactic acid-based polyester in which lactic acid units are racemized Was obtained, and the present invention was completed. That is, the present invention relates to L-lactide or D-lactide.
When performing ring-opening polymerization in the presence of a polymerization catalyst using at least one of lactide as one of the raw material monomers, at least one alkali metal compound is used as a racemizing agent in an amount of 0.005 to 0.2 mol% and / or Alternatively, there is provided a method for producing a lactic acid-based polyester, wherein 0.02 to 0.5 mol% of at least one alkaline earth metal compound is present in the monomer.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The composition of the lactic acid-based polyester obtained in the present invention is a polylactic acid homopolymer or a copolymer thereof. In the case of a polylactic acid homopolymer, one containing L-lactic acid and D-lactic acid in various ratios is obtained.

When at least one of L-lactide and D-lactide is used as a raw material, the following formula (1) is used depending on the polymerization time, temperature, type and amount of polymerization catalyst, and type and amount of racemizing agent. The absolute value of (L-lactic acid ratio)-(D-lactic acid ratio) is 0% or more and 98% in all lactic acid units
The following are obtained and are preferred. More preferably, it is 0 to 90%, and still more preferably 0 to 80%.

[0011]

(Equation 2)

The monomer components copolymerized in the case of the copolymer include, for example, lactones such as glycolide, butyrolactone, valerolactone, and caprolactone; cyclic carbonates such as trimethylene carbonate and neopentylene carbonate; polyethylene glycol, polypropylene glycol; Polyalkylene glycols such as polyethylene / propylene glycol, aliphatic dibasic acids such as succinic acid, adipic acid, sebacic acid, azelaic acid and dimer acid, and ethylene glycol, propylene glycol, butanediol, hexanediol, polyalkylene glycol, glycerin, etc. And aliphatic polyesters obtained by polycondensation of aliphatic glycols.

The above compounds can be used alone or in combination of two or more. In general, it is known that when two or more kinds are used in combination, they become amorphous depending on the ratio of both. The amount to be copolymerized is not particularly limited, but is usually within 50 mol% of the whole. By copolymerization, the physical properties can be complemented even when the lactic acid unit cannot be sufficiently racemized under the polymerization conditions used, that is, when the melting point does not sufficiently decrease or the solubility does not improve in the case of a homopolymer.

The lactic acid-based polyester obtained in the present invention has a reduced viscosity (concentration: 0.5 g / dl) measured at 25 ° C. in chloroform using an Ubbelohde viscosity tube.
Is 0.1 dl / g or more and 1.2 d as shown in the equation (2).
It is preferably a relatively high molecular weight of 1 / g or less. If the reduced viscosity is less than 0.1 dl / g, the lactic acid-based polyester does not exhibit practically sufficient physical properties,
If it is larger than g, it becomes difficult to handle, for example, it is not possible to prepare a varnish with a high concentration when dissolved and used.

The present invention can be used for both solution polymerization and melt polymerization. Solution polymerization is carried out by heating in a solvent having a relatively high boiling point that does not react with monomers such as toluene and xylene. In the present invention, from the viewpoints of polymerization rate, polymerization cost, and the like, it is preferable to carry out melt polymerization, and the temperature is usually in the range of 100 to 220 ° C., which is a temperature higher than the melting point of lactide. More preferably, it is carried out at 150 to 200 ° C., which is near the melting point of poly L-lactic acid. When the temperature is lower than 100 ° C., a large amount of time is required for the progress of polymerization and racemization, and when the temperature is higher than 220 ° C., the formed polyester is decomposed. The above reaction can be performed under any of normal pressure, reduced pressure, and increased pressure, but it is necessary to maintain a gas atmosphere inert to polymerization, for example, a nitrogen gas atmosphere.

The racemizing agent used in the present invention is at least one alkali metal compound and / or alkaline earth metal compound. As the alkali metal compound,
For example, lithium compounds, sodium compounds, potassium compounds, examples of alkaline earth metal compounds include magnesium compounds and calcium compounds, and acetates thereof.
Propionate, octylate, laurate, myristate, palmitate, stearate, benzoate, salicylate, oxalate, lactate, tartrate, citrate, borate, phosphorus Acid salts, carbonates, acetylacetone complex salts, chlorides, oxides, hydrides, hydroxides and the like are used.

The effect as a racemizing agent is generally higher when an alkali metal compound is used than when an alkaline earth metal compound is used. However, magnesium compounds and calcium compounds are preferred because alkali metal compounds also have a considerably high thermal decomposition activity and often reduce the molecular weight of the resulting polyester. Among them, magnesium acetate, magnesium octylate, magnesium stearate, magnesium acetylacetonate,
Calcium acetate, calcium stearate, calcium lactate, calcium acetylacetonate, calcium hydride and the like are particularly preferably used. These compounds can be used alone or in combination of two or more.

When the alkali metal compound is used, the amount of the racemizing agent used is 0.005 to 0.2 m
ol%. Preferably 0.01 to 0.
15 mol%, more preferably 0.01 to 0.10 m
ol%. If the amount is less than 0.005 mol%, the effect as a racemizing agent is not observed, and if it is more than 0.2 mol%, the molecular weight of the produced polyester is remarkably reduced and the polyester is undesirably colored.

On the other hand, when an alkaline earth metal is used, it is used in the range of 0.02 to 0.5 mol% based on the monomer. Preferably it is 0.05 to 0.3 mol%, more preferably 0.05 to 0.25 mol%. 0.0
If it is less than 2 mol%, no effect as a racemizing agent is obtained, and if it is more than 0.5 mol%, the molecular weight of the produced polyester decreases.

The racemizing agent is added when the raw materials are charged, or when the polymerization has progressed to some extent.
In order to maximize the effect of the racemizing agent, it is preferable to add it at the time of charging the raw materials. These can be added as powders or dispersed in a solvent inert to polymerization.

The polymerization catalyst used in the present invention may be any of those used for ring-opening polymerization of lactones. Examples of the tin compound include tin powder, tin oxide, tin chloride, tin octylate, dibutyltin laurate. , Dibutyltin oxide, tetraphenyltin, aluminum compounds as aluminum isopropoxide, aluminum acetylacetonate, titanium compounds as titanium tetrabutoxide, titanium tetraisopropoxide, titanium oxyacetylacetonate, zirconium compounds as zirconium oxyacetylacetonate, zinc As compounds, zinc powder, zinc oxide, zinc acetate, zinc octylate, zinc stearate, zinc acetylacetonate,
Antimony compounds, antimony oxide, tetrabutoxyantimony, rare earth compounds, lanthanum acetate,
Lanthanum trisacetylacetonate, lanthanum trisdipivaloyl methanate, yttrium trisacetylacetonate, yttrium isopropoxide and the like can be mentioned. Preferred are tin compounds and aluminum compounds, and more preferred are tin compounds in terms of polymerization rate and physical properties of the resulting lactic acid-based polyester. Specifically, tin octylate, tin chloride, dibutyltin laurate and the like are particularly preferable. Even if these compounds are used alone,
Alternatively, two or more kinds may be used in combination.

The amount of the polymerization catalyst used is preferably in the range of 0.001 to 0.4 mol% based on the monomer. More preferably, it is 0.005 to 0.2 mol%. 0.0
If the amount is less than 01 mol%, a large amount of time is required for the polymerization. If the amount is more than 0.4 mol%, the polymerization speed is high, but the resulting polymer is intensely colored and has poor physical properties such as low thermal stability. The polymerization catalyst is added at the time of charging the raw materials, or at a point when a certain period of time has passed after the monomer was melted. It is also possible to add it as a powder or liquid, or after dissolving it in a solvent inert to polymerization.

In order to control the molecular weight of the polyester produced in the present invention, an active hydrogen compound can be added. Examples of the active hydrogen compound include alcohols and carboxylic acids. Specifically, examples of alcohols include aliphatic long-chain monoalcohols such as lauryl alcohol, myristyl alcohol, palmityl alcohol, and stearyl alcohol, and aliphatic glycols such as ethylene glycol, propylene glycol, butanediol, hexamethylene glycol, and glycerin. Is mentioned. Examples of the carboxylic acid include lactic acid, acetic acid, propionic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oxalic acid, succinic acid, and adipic acid. Considering the effect on the polymerization rate,
Alcohols are particularly preferred.

In the present invention, the stability of the lactic acid-based polyester can be increased by removing the monomers such as lactide and the catalyst remaining after the polymerization is completed. As a removal method, after dissolving in a solvent, a method of reprecipitating using a solvent in which the polyester is insoluble, a method of separating after dissolving in the solvent or directly contacting with acidic water, or a quenching agent Any known method can be used, such as a method in which a low molecular weight substance is volatilized by holding it under a reduced pressure in a molten state after or without the addition.

When most of the lactic acid units in the lactic acid-based polyester obtained in the present invention are racemized, they can be used in various industrial solvents such as toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, tetrahydrofuran and ethyl acetate. Dissolve. Therefore, it is useful as a biodegradable binder resin for various inks, various paints, and coating agents. When the melting point is lowered, it is useful as a hot melt adhesive or a hot melt coating agent. Racemic lactic acid-based polyesters also hydrolyze faster than poly-L-lactic acid, and are therefore useful for molded articles that require a high decomposition rate. In this case, it is natural that inorganic and organic fillers, various stabilizers, coloring agents, waxes and the like can be used in combination as needed. It is also possible to blend the resin itself with various molded articles as a hydrolysis accelerator.

[0026]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, each measurement item in an Example is measured according to the following method.

The reduced viscosity was measured at 25 ° C. in chloroform using an Ubbelohde viscosity tube (solution concentration: 0.5 g / d).
l). The molecular weight is determined by gel filtration permeation chromatography using chloroform as eluent (GPC system manufactured by Hitachi, Ltd .;
RI detector, column: Shodex K-804 + 80
25, a column temperature of 35 ° C.) and a comparison with a polystyrene standard marker. The specific rotation was measured at 20 ° C. in chloroform using a polarimeter (SEPA-200 manufactured by Horiba, Ltd.) (solution concentration: 10 mg / ml). Melting point is D
Using an SC (DSC-50 manufactured by Shimadzu Corporation), measurement was performed by raising the temperature of a 5 mg sample at 10 ° C./min in an argon atmosphere.

Example 1 10.0 g of L-lactide (6
9.4 mmol) and 3 mg (7 μmol, manufactured by Aldrich) of tin octylate (tin 2-ethylhexanoate) in toluene were charged into a polymerization tube having a stirrer and a nitrogen inlet tube, and dried under reduced pressure at room temperature for 1 hour. Subsequently, the atmosphere was sufficiently replaced with nitrogen.

Further, 24 mg (0.14 mol) of calcium acetylacetonate dried under reduced pressure at 50 ° C. for 48 hours.
1%, manufactured by Tokyo Chemical Industry Co., Ltd.) was charged into the polymerization tube in a glove box under a nitrogen atmosphere. The polymerization tube was immersed in an oil bath at 190 ° C. and polymerized under a nitrogen atmosphere for 2 hours. The obtained polylactic acid was dissolved in a minimum amount of chloroform and dropped into 10-fold amount of methanol to reprecipitate. Ηsp / C of the obtained slightly tan polylactic acid is 0.446 dl / g,
The average molecular weight by GPC was 42,000. No melting point was observed, and the mixture was dissolved in a mixed solvent of MEK / toluene (50/50) at a nonvolatile concentration (hereinafter referred to as NV) of 30%.

The specific rotation was measured to be -122.4 °.
It was confirmed that racemization had progressed compared to pure poly L-lactic acid (157.5 °). This polylactic acid determined from the specific rotation measured using a calibration curve obtained by measuring the specific rotation of the racemized polylactic acid previously synthesized from L-lactide and DL-lactide in known ratios The absolute value of (L-lactic acid ratio) − (D-lactic acid ratio) is 78
%.

(Examples 2 to 6) In place of calcium acetylacetonate as a racemizing agent, calcium oxide (manufactured by Wako Pure Chemical; 99.9) was used as shown in Table 1.
%), Calcium lactate (Nacalai Tesque), calcium hydride (Nacalai Tesque), calcium acetate (Nacalai Tesque), and magnesium acetylacetonate (Nacalai Tesque) at 0.14 mol%. Polymerization was carried out in the same manner as in Example 1. The polymerization times are also different. Table 1 shows the results.

Example 7 10.0 g of L-lactide (6
9.4 mmol) and 9 mg of aluminum acetylacetonate (28 μmol, 99.99% manufactured by Kanto Chemical)
Was placed in a polymerization tube having a stirrer and a nitrogen inlet tube, dried under reduced pressure at room temperature for 1 hour, and then sufficiently purged with nitrogen.

Further, 24 mg (0.14 mol) of calcium acetylacetonate dried under reduced pressure at 50 ° C. for 48 hours.
1%, manufactured by Tokyo Chemical Industry Co., Ltd.) was charged into the polymerization tube in a glove box under a nitrogen atmosphere. The polymerization tube was immersed in a 190 ° C. oil bath to perform polymerization for 5 hours. The obtained polylactic acid was dissolved in a minimum amount of chloroform and dropped into 10 times the amount of methanol to cause reprecipitation. Ηsp / C of the obtained brown polylactic acid was 0.246 dl / g. No melting point was observed, and the mixed solvent of MEK / toluene (50/50)
Dissolved at a rate of V = 30%.

The specific rotation was measured to be -97.9 °, confirming that the racemization had progressed compared to pure poly-L-lactic acid (-157.5 °). The absolute value of (L-lactic acid ratio)-(D-lactic acid ratio) of this polylactic acid determined from the measured specific rotation is 62%.

Examples 8 and 9 0.288 mol% of calcium hydride and 0.036 mol of calcium hydride as racemizing agents
Polymerization was carried out in the same manner as in Example 7 except that% was added. Table 1 shows the results.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1, except that a racemizing agent was not added, and an acid terminal blocking agent and lauryl alcohol as a molecular weight regulator were added. The ηsp / C of the yellow polylactic acid is 1.
It was 455 dl / g. In DSC, a sharp crystal melting peak was observed at 178 ° C. Specific rotation is -15
6.9 ° and racemization did not progress at all.
The obtained polylactic acid only slightly swelled in the mixed solvent of MEK / toluene (50/50) and did not dissolve.

(Comparative Example 2) Polymerization was carried out for 2 hours in the same manner as in Example 1 except that 0.01 mol of calcium acetylacetonate was added. As a result, the obtained polylactic acid was hardly racemized. No effect of adding the racemizing agent was observed.

Comparative Example 3 Polymerization was carried out for 2 hours in the same manner as in Example 1 except that 1.0 mol% of calcium acetylacetonate was added, and the ηsp / C of the obtained polylactic acid was 0.1%. 070 dl / g, which was a very low molecular weight. When the polymerization was further continued for 4 hours, it turned into a black tar, which was not practical.

Comparative Example 4 Polymerization was carried out in the same manner as in Example 1 except that tin octylate as a polymerization catalyst was not added. In 24 hours, the conversion was 35%, and the polymerization almost proceeded. Did not.

[0040]

[Table 1]

In Table 1, Ca (acac) ₂ is calcium acetylacetonate, Ca (lact) ₂ is calcium lactate, Ca (OAc) ₂ is calcium acetate, M
g (acac) ₂ represents magnesium acetylacetonate.

[0042]

As described above, according to the present invention, poly-L
-A lactic acid-based polyester in which a lactic acid unit is racemized, which is more soluble in a general-purpose solvent than lactic acid and has a high decomposition rate, can be produced without using expensive DL-lactide or meso-lactide. Therefore, it greatly contributes to applying lactic acid-based polyester as various functional resins such as paint binders, adhesives, and coating agents.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaya Tokai 2-1-1 Katata, Otsu-shi, Shiga Prefecture Inside Toyobo Co., Ltd. Research Institute (72) Keiichi Uno 2-1-1 Katata, Otsu-shi, Shiga Prefecture No. Toyobo Co., Ltd.

Claims (4)

[Claims] When at least one of L-lactide and D-lactide is used as one of the starting monomers for ring-opening polymerization in the presence of a polymerization catalyst, at least one of the racemizing agents is used.
0.005 alkali metal compounds per monomer
To 0.2 mol% and / or at least one alkaline earth metal compound in an amount of 0.02 to 0.
A method for producing a lactic acid-based polyester, wherein 5 mol% is coexisted. 2. The method for producing a lactic acid-based polyester according to claim 1, wherein the ring-opening polymerization is performed in a molten state. 3. The method for producing a lactic acid-based polyester according to claim 1, wherein the polymerization catalyst is a tin compound, and the racemizing agent is a magnesium compound and / or a calcium compound. 4. A lactic acid-based polyester obtained by the method according to claim 1, which satisfies the following formulas (1) and (2). (Equation 1)