JP2001181273A - Method for producing glycolides - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and readily produce a high-purity glycolide usable for a polymer raw material, etc. SOLUTION: This method for producing a first process for producing a higher alcohol ester of an α-hydroxy acid oligomer by subjecting an α-hydroxy acid ester and a higher alcohol to dealcoholization condensation and a second process for heating under reduced pressure the higher alcohol ester of an α-hydroxy acid oligomer obtained by the first process to distill off the glycolide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a first step for producing a higher alcohol ester of an oligomer of an .alpha.-oxy acid by subjecting an ester of an .alpha.-oxy acid to a higher alcohol by de-alcohol condensation, and a first step. A method for producing glycolides comprising a second step of heating the obtained higher alcohol ester of the oligomer of α-oxyacid under reduced pressure to distill off the glycolides. Glycolide produced in the present invention has very low content of impurities having active hydrogen such as water and α-oxyacids and α-oxyacid esters, and has a low molecular weight even when polymerized without further purification. 2
It is possible to obtain a polymer of α-oxyacid having a molecular weight of 10,000 or more.

[0002]

2. Description of the Related Art Polymers of α-oxy acids such as polylactic acid and polyglycolic acid have good biodegradability, and thus have been used as biodegradable materials such as surgical sutures. In recent years, while plastic waste has become a problem, such as lack of landfills and incineration of waste, α-oxyacid polymers have been gradually becoming more demanding and available as hydrolyzable and biodegradable plastics. The situation is increasing. The polymer of α-oxyacid can be easily obtained by ring-opening polymerization of glycolides which are cyclic dimers of α-oxyacid. However, glycolides are generally α
Is produced by a method in which an oligomer of α-oxyacid obtained by dehydration-condensation of oxyacid is heated and depolymerized under reduced pressure to distill off glycolides, and the glycolides thus obtained are water-soluble. It contains a large amount of impurities having active hydrogen such as oxyacids and oxyacids, and if it is subjected to polymerization as it is, only a polymer having a low molecular weight of about 10,000 to at most 10,000 can be obtained. For this reason, in order to obtain a high molecular weight α-oxyacid polymer, the glycolides obtained by the above-mentioned production method had to be further purified several times by recrystallization or solvent washing.

However, since recrystallization and solvent washing require complicated steps and a great deal of labor, various production methods and purification methods for glycolides have been proposed.
For example, British Patent No. 1108720 discloses a method for producing lactide having a small acid value by using lactic acid ester as a raw material. However, even if the acid value decreases, contamination with lactic acid ester having active hydrogen like oxyacid is inevitable, and it is clear that further purification is required. In addition, Tokio Table 7
No. 503490 discloses a method for producing polylactide by polymerizing lactide purified by distillation without the step of solvent extraction or recrystallization. However, as described by the applicant in the gazette, this production method requires multiple distillations, which is economically disadvantageous.

On the other hand, Japanese Patent Application Laid-Open No. 63-152375 discloses a method for producing lactide by thermally depolymerizing a copolymer of a thermostable polyether core and an α-hydroxy acid. The thermal decomposition by-product derived from polyether is mixed in, and in the publication, lactide is purified by recrystallization. JP-T-7-504916 discloses a method for producing lactide directly from octadecyl lactoyl lactate corresponding to an average degree of polymerization of 2. However, there is no description about an octadecanol ester of an oligomer having an average degree of polymerization of 4 or more. According to the method disclosed in the publication, a large amount of octadecanol of at least 188 parts by weight is required to theoretically produce 100 parts by weight of lactide. Necessary and not economical. Japanese Patent Application Laid-Open No. 6-65230 discloses a method for producing lactide in which a low molecular weight polylactic acid obtained by dehydrating and condensing lactic acid under reduced pressure in the presence of a high boiling alcohol is heated and depolymerized in the presence of an alkali metal compound. Is disclosed. However, there is no description of a lactic acid ester in the gazette regarding the raw material, and when lactic acid is used as the raw material as in the gazette, it is unavoidable that the acid value of lactide increases (see Comparative Example 2). In addition, Japanese Patent Application Laid-Open No. 6-28727
In Japanese Patent Application Publication No. 8 (1994) -208, the precursor polymer having a carboxyl group concentration of 100 equivalents / 106 g or less obtained by polycondensation of an α-oxyacid in the presence of a polyhydric alcohol containing at least 3 or more hydroxyl groups is heated and depolymerized. A method for producing an aliphatic polyester by ring-opening polymerization of the obtained cyclic dimer is disclosed. However, the acid value of the resulting cyclic dimer is still at a high level because α-oxy acid is used as a raw material, and in the publication, a purification step such as solvent washing is required to obtain a high molecular weight polymer. It is stated.

[0005]

As described above, water and α-
As a matter of fact, no method has been developed for inexpensively and easily producing glycolides having an extremely low content of impurities having active hydrogen such as oxyacids and esters of α-oxyacids. An object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a method for inexpensively and easily producing glycolide which can be used as a polymer raw material without further purification with high purity.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that higher alcohol esters of oligomers of α-oxy acids obtained by subjecting the esters of α-oxy acids to higher alcohols by de-alcohol condensation. The inventors have found that the above problem can be solved by heating under reduced pressure and distilling off glycolides, and have reached the present invention. That is,
The present invention relates to a first step of producing an alcoholic higher ester of an α-oxy acid oligomer by subjecting an ester of an α-oxy acid and a higher alcohol to de-alcohol condensation, and a method of producing the higher alcohol ester of the α-oxy acid obtained in the first step. This is a method for producing glycolides comprising a second step of heating the oligomeric higher alcohol ester under reduced pressure to distill off the glycolides. The glycolide produced in the present invention is water or oxyacid,
The content of impurities having active hydrogen such as oxyacid esters is extremely low, and even when polymerized without further purification, a polymer of high molecular weight α-oxyacid having a molecular weight of 20,000 or more can be obtained.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described below in detail. The present invention relates to a first step of producing an alcoholic higher ester of an α-oxy acid oligomer by subjecting an ester of an α-oxy acid and a higher alcohol to de-alcohol condensation, and a method of producing the higher alcohol ester of the α-oxy acid obtained in the first step. It comprises a second step of heating the higher alcohol ester of the oligomer under reduced pressure to distill off glycolides. The ester of the α-hydroxy acid used in the present invention is not particularly limited, but for example, glycolic acid, lactic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid, α-hydroxy
Esters such as valeric acid, α-hydroxyisovaleric acid, α-hydroxycaproic acid, and α-hydroxyisocaproic acid. Any optical isomer may be used, and a mixture thereof may be used. Lactic acid esters are preferred, and methyl lactate is particularly preferred, in view of the availability of raw materials and the production cost.

The higher alcohol referred to in the present invention is an alcohol having a boiling point higher than that of glycolides.
-Tetradecanol, 1-pentadecanol, 1-hexadecanol, 1-heptadecanol, 1-octadecanol, 1-nonadecanol, 1-eicosanol, 1
Monoalcohols such as hentriacontanol, 9-hexadecene-1-ol, 9-octadecene-1-ol, 10-eicosen-1-ol, 1,7-heptanediol, 1,8-octanediol, 1,9 Glycols such as nonanediol, 1,10-decanediol,
Polyhydric alcohols such as pentaerythritol, dipentaerythritol, tripentaerythritol, trimethylolethane, trimethylolpropane, 2-phenylphenol, 2,4-di-t-butylphenol, 4-octylphenol, 4,4'-isopropyl Dendiphenol, 2,4-dimethyl-6- (1-methylcyclohexyl) -phenol, nonylphenol, 4-methyl-
Examples thereof include phenols such as 2,6-di-t-butylphenol, but are not limited thereto. These may be used alone or in combination of two or more.

The average degree of polymerization of the higher alcohol ester of the oligomer of α-oxy acid used in the present invention is preferably 4 or more and 50 or less, particularly preferably 4 or more and 30 or less. When the average degree of polymerization is less than 4, it is economically disadvantageous to use a large amount of higher alcohol, which is not preferable. When the average degree of polymerization is 50 or more, it takes a long time to produce lactide, which is not preferable. The average degree of polymerization referred to in the present invention means an oligomer unit of an α-oxy acid which is continuously condensed, and when a higher alcohol having two or more hydroxyl groups is used, an α-oxy acid which is condensed with each hydroxyl group is used. The oligomer units are considered separately. The average degree of polymerization of the higher alcohol ester of the oligomer of the α-oxy acid is determined by the ratio of the ester of the α-oxy acid to the hydroxyl group of the higher alcohol. When 0.02 equivalents are used, the average degree of polymerization of the higher alcohol ester of the oligomer of α-oxy acid is 4 to 50.

The first step uses a reaction apparatus equipped with a general distillation apparatus, and has a temperature of 100 to 250 ° C., preferably 150 ° C.
Perform at ~ 220 ° C. If the temperature is lower than 100 ° C., the reaction rate is decreased, which is not preferable. If the temperature is higher than 250 ° C., side reactions tend to occur, which is not preferable. The reaction can be carried out at a pressure higher than the atmospheric pressure or lower than the atmospheric pressure. Preferably, the reaction is started at a pressure higher than the atmospheric pressure, and the pressure is gradually lowered to 300 mmHg or lower as the distillation of alcohol decreases. Is preferred. The first step is carried out in the presence of 0.0001 to 20 parts by weight, preferably 0.001 to 1 part by weight of an esterification reaction catalyst based on 100 parts by weight of the ester of α-oxy acid. The esterification reaction catalyst is not particularly limited, but lithium, sodium, potassium, magnesium, zinc, aluminum,
Metals such as tin, zinc, lead, titanium, bismuth, zirconium, germanium, cobalt and organic metal compounds, organic acid salts, inorganic acid salts, halides, metal compounds such as hydroxides, alkoxides, sulfuric acid, hydrochloric acid, phosphoric acid, Inorganic acids such as polyphosphoric acid, organic sulfonic acids such as benzenesulfonic acid, paratoluenesulfonic acid, methanesulfonic acid and trifluoromethanesulfonic acid, ion exchange resins, zeolites, silica-alumina, silica-titania, bentonite, montmorillonite, activity And solid acids such as clay. These catalysts may be used alone, or two or more kinds may be mixed or used stepwise.

In general, esters of α-oxy acids and chain dimers thereof have lower boiling points than glycolides, and therefore, in the present invention, esters of α-oxy acids and chain dimers thereof remaining before the second step are used. Can be previously removed by distillation to prevent contamination with glycolides. On the other hand, when α-oxyacid is used as a raw material, α-oxyacid and its chain dimer have a boiling point close to glycolides, so that the remaining α-oxyacid and its chain dimer Is difficult to distill in advance, and even when the higher alcohol referred to in the present invention is used, a large amount of α-oxyacid and its linear dimer are mixed into glycolides in the second step. The second step of producing glycolides by heating and depolymerizing a higher alcohol ester of an oligomer of an α-oxy acid is performed at 120 to 250 ° C., preferably 150 to 22 ° C. using a reaction apparatus equipped with a general distillation apparatus.
The reaction is carried out at a temperature of 0 ° C. while distilling the glycolides. 120
If the temperature is lower than 0 ° C, the rate of formation of glycolides is decreased, which is not preferable. The pressure is preferably a pressure at which glycolides are efficiently distilled out in the above-mentioned reaction temperature range, that is, 100 mmHg or less.
-30 mmHg is preferred. In the second step, the above catalyst can be used, and the catalyst used in the first step may be used as it is, or may be newly added.

After the completion of the second step, higher alcohol, a small amount of higher alcohol ester of α-oxyacid oligomer and catalyst remain in the reactor, and these can be recycled for the next production. By circulating, the production cost can be significantly reduced. In the conventional production method, impurities having a boiling point lower than that of glycolides, such as water, alcohol, oxyacid, and oxyacid ester, are generated from the oligomer terminals due to the thermal depolymerization of oligomers of α-oxy acids or esters of α-oxy acids. However, since it is mixed in a large amount with glycolides, it is necessary to further purify the distilled glycolides by a method such as recrystallization, solvent washing, and redistillation.
On the other hand, in the present invention, glycolide is used for heat depolymerization of the higher alcohol ester of the oligomer of the α-oxy acid obtained by dealcoholizing and condensing the ester of the α-oxy acid with the higher alcohol having a higher boiling point than the glycolide. Water and oxyacid are hardly mixed in the class, the water content is 300 ppm or less, and the acid value is 100 meq / kg or less. Furthermore, since the oligomer terminal is an ester of a higher alcohol, a higher alcohol or a higher alcohol ester of an α-oxy acid generated from the oligomer terminal due to heat depolymerization has a higher boiling point than glycolides and is not mixed into glycolide. Α-Hydroxy acid ester derived from an oligomer that does not have a higher alcohol terminal and its chain dimer are mixed in a small amount in glycolide, but the total concentration is 1% or less.

As described above, the glycolide produced in the present invention has a very low content of impurities having active hydrogen such as water, oxyacids and oxyesters, and is thus obtained when polymerized without further purification. In addition, a high molecular weight α-oxyacid polymer having a molecular weight of 20,000 or more can be obtained.
The α-oxyacid polymer obtained by polymerizing the glycolide of the present invention can be used for various uses. For example, packaging materials, agricultural multi-films, films such as afforestation cups, fishing lines and fishing nets, fibers such as non-woven fabrics, bottles,
Examples thereof include, but are not limited to, molded products such as pipes and temporary fixing materials, foams such as cushioning materials and food trays, resins for adhesives, and resins for paints. Further, at the time of molding, various molding auxiliaries, for example, fillers, coloring agents, reinforcing agents, waxes, thermoplastic polymers, oligomers, and the like can be used in combination depending on the application.

[0014]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited by these examples. The characteristic values in the examples were measured by the methods described below. Acid value measuring method: Approximately 5 g of glycolides are precisely weighed, and molecular sieves 3A (1/16 inch, manufactured by Wako Pure Chemical Industries)
To dissolve in methylene chloride previously dried. Using phenol red (0.05% by weight / volume in dry methanol) as an indicator for endpoint determination, add 10 drops to the sample solution. The solution is titrated with 0.025 N-potassium methoxide (benzene / methanol solution) (prepared by diluting 0.1 mol / potassium methoxide for non-aqueous titration / potassium methoxide with dry methanol, manufactured by Wako Pure Chemical Industries, Ltd.). . Gas chromatography analysis conditions: The composition of glycolides is analyzed. Glycolides are precisely weighed and dissolved in tetrahydrofuran for analysis. The column uses TC-17 (GL Science). The measurement is performed by setting the inlet temperature and the FID detector temperature both to 250 ° C. and raising the column temperature from 60 ° C. to 240 ° C. Moisture measurement method: 1 g of glycolides are dissolved in 5 g of methylene chloride, and a water measuring device (formerly a trace moisture measuring device C manufactured by Mitsubishi Kasei)
A-5). High-performance liquid chromatography analysis conditions: The molecular weights of the oligomer of α-oxy acid and the polymer of α-oxy acid are measured. An oligomer of α-oxy acid, a polymer of α-oxy acid 0.023 g is dissolved in 15 g of tetrahydrofuran,
The measurement was performed using a Shodex GPC SYSTEM-11 (eluate tetrahydrofuran, 40 ° C.) equipped with four columns of Shodex GPC KF804L.

Example 1 D, L-methyl lactate 640 was placed in a 1,000 ml reactor equipped with a stirrer, a fractionating condenser, a thermometer and a gas inlet tube.
g, 1-octadecanol (166 g) was added, monobutyltin oxide (3.2 g) was added, and the mixture was reacted at 140 to 200 ° C. for 3 hours under a nitrogen atmosphere under atmospheric pressure to distill methanol. Then, gradually increase the pressure to 100 over 2 hours.
mmHg, and methanol was distilled off to proceed the condensation reaction. 190 g of methanol corresponding to 96% of the theoretical amount was distilled off, and the average polymerization degree of 1-octadecanol ester of lactic acid oligomer was 9.3 by GPC analysis. When the pressure was further reduced, a small amount of methyl lactate and methyl lactoyl lactate were distilled out. The pressure was reduced to 5 mmHg to distill lactide, and 403 g of lactide was obtained in 4 hours. Yield 91%. Gas chromatography analysis showed that this lactide had a purity of 99.8% (D, L-lactide 59.9%, mesolactide 39.9).
%, Methyl lactate 0.07%, methyl lactoyl lactate 0.
12%). Acid value 8.8 meq / kg. 55 ppm water.
0.04 g of tin octylate was added to 20 g of the lactide, and lactide was polymerized at 160 ° C. for 2 hours to obtain a polylactide having a weight average molecular weight of 124,000.

Example 2 Pentaerythritol 2 in place of 1-octadecanol
A pentaerythritol ester of lactic acid oligomer was produced in the same manner as in Example 1 except that 1 g was charged. 185 g of methanol corresponding to 94% of the theoretical amount was distilled off, and the average degree of polymerization of pentaerythritol ester of lactic acid oligomer was 9.1 by GPC analysis. When the pressure was further reduced, a small amount of methyl lactate and methyl lactoyl lactate were distilled out. The pressure was reduced to 5 mmHg to distill lactide, and 365 g of lactide was obtained in 4 hours. Yield 82
%. Gas chromatography analysis showed that the lactide had a purity of 99.7% (D, L-lactide 62.2%, mesolactide 37.5%, methyl lactate 0.09%, methyl lactoyl lactate 0.1%). 17%). Acid value 11.2 meq / kg. 50 ppm water. 0.04 g of tin octylate was added to 20 g of the lactide, and lactide was polymerized at 160 ° C. for 2 hours to obtain a weight average molecular weight of 82,000.
A polylactide of 0 was obtained.

Example 3 A 1-octadecanol ester of a lactic acid oligomer was produced in the same manner as in Example 1 except that the amount of 1-octadecanol charged was changed to 55 g. After a reaction time of 7 hours, 177 g of methanol, corresponding to 90% of the theoretical amount, were distilled off.
According to the PC analysis, the average degree of polymerization of the 1-octadecanol ester of the lactic acid oligomer was 24.5. When the pressure was further reduced, a small amount of methyl lactate and methyl lactoyl lactate were distilled out. The pressure was reduced to 5 mmHg to distill lactide, and 337 g of lactide was obtained in 6 hours. Yield 76%.
Gas chromatography analysis showed that this lactide had a purity of 99.5% (D, L-lactide 55.9%, mesolactide 43.6%, methyl lactate 0.5%).
16%, methyl lactoyl lactate 0.26%). Acid value7.
9 meq / kg. 88 ppm water. 20 g of this lactide
Then, 0.04 g of tin octylate was added thereto, and lactide was polymerized at 160 ° C. for 2 hours to obtain a polylactide having a weight average molecular weight of 57,000.

Example 4 640 g of methyl D, L-lactate was newly charged into the reactor of Example 1 where the residue remained, and 1-octadecanol ester of lactic acid oligomer was produced in the same manner as in Example 1. . 187 g of methanol corresponding to 95% of the theoretical amount was distilled off, and the average degree of polymerization of 1-octadecanol ester of lactic acid oligomer was 9.9 by GPC analysis. When the pressure was further reduced, a small amount of methyl lactate and methyl lactoyl lactate were distilled out. The pressure was reduced to 5 mmHg to distill lactide, and 381 g of lactide was obtained in 4 hours. Yield 8
6%. Gas chromatography analysis showed that the lactide had a purity of 99.6% (D, L-lactide 57.9%, mesolactide 42.7%, methyl lactate 0.14%, methyl lactoyl lactate 0.1%). 11%).
Acid value 7.5 meq / kg. 63 ppm water. 20 g of this lactide is added to tin octylate 0.1 g. 04 g, 160
Polymerization of lactide at 2 ° C. for 2 hours gives a weight average molecular weight of 95,
000 polylactides were obtained.

Comparative Example 1 A methyl ester of a lactic acid oligomer was produced in the same manner as in Example 1 except that 1-octadecanol was not charged. 160 g of methanol corresponding to 81% of the theoretical amount was distilled off, and the average degree of polymerization of the methyl ester of the lactic acid oligomer was 21.0 according to GPC analysis. When the pressure was further reduced, a small amount of methyl lactate and 80 g of methyl lactoyl lactate were distilled off. The pressure was reduced to 5 mmHg to distill lactide, and 314 g of lactide was obtained in 4 hours. Yield 7
1%. Gas chromatography analysis showed that the lactide had a purity of 95.1% (D, L-lactide 53.6%, mesolactide 41.5%, methyl lactate 2.05%, methyl lactoyl lactate 1.0%). 97%). Acid value 8.4 meq / kg. 96 ppm water. 0.04 g of tin octylate was added to 20 g of this lactide, and lactide was polymerized at 160 ° C. for 2 hours to obtain a weight average molecular weight of 9,000.
Of polylactide was obtained.

Comparative Example 2 615 g of 90% lactic acid aqueous solution instead of D, L-methyl lactate
Was prepared in the same manner as in Example 1 except that octadecanol ester of a lactic acid oligomer was prepared. Theoretical 9
161 g of water corresponding to 1% was distilled off, and the average degree of polymerization of octadecanol ester of lactic acid oligomer was 9.2 by GPC analysis. When the pressure was further reduced, a small amount of lactic acid was distilled off. The pressure was reduced to 5 mmHg to distill lactide, and 390 g of lactide was obtained in 4 hours. Yield 88%.
Gas chromatography analysis revealed that this lactide had a purity of 98.2% (D, L-lactide 57.0%, mesolactide 41.2%, lactic acid 0.32%).
%, Lactoyl lactic acid 1.03%). Acid value 101.4m
eq / kg. 510 ppm of moisture. 0.04 g of tin octylate was added to 20 g of this lactide, and lactide was polymerized at 160 ° C. for 2 hours to obtain a polylactide having a weight average molecular weight of 10,000.

[0021]

The higher alcohol ester of the oligomer of the α-oxy acid obtained by subjecting the ester of the α-oxy acid and the higher alcohol to de-alcohol condensation is heated under reduced pressure to distill off the glycolides. Glycolides which can be used as polymer raw materials and the like with high purity can be produced at low cost and easily.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masahiro Kurokawa 5-6-1 Higashi-Hachiman, Hiratsuka-shi, Kanagawa F-term in Hiratsuka Research Laboratory, Sanritsu Gas Chemical Co., Ltd. 4C022 JA04 4J029 AA02 AB07 EH02 EH03

Claims (6)

[Claims] 1. A first step for producing a higher alcohol ester of an oligomer of an α-oxy acid by de-alcohol condensation of an ester of an α-oxy acid and a higher alcohol, and the α-oxy obtained in the first step. A method for producing glycolides, comprising a second step of heating a higher alcohol ester of an acid oligomer under reduced pressure to distill off glycolides. 2. The process for producing glycolides according to claim 1, wherein the ester of α-oxy acid and its chain dimer remaining before the second step are distilled off in advance. 3. The process for producing glycolides according to claim 1, wherein the higher alcohol ester of the α-oxy acid oligomer has an average degree of polymerization of 4 to 50. 4. The method for producing glycolides according to claim 1, wherein the higher alcohol has a boiling point higher than that of glycolides. 5. The glycolide has an impurity concentration of not more than 1% of an α-oxyacid ester and its chain dimer concentration, an acid value of not more than 100 meq / kg, and a water content of 300 ppm.
The following, α- obtained by polymerization of the glycolides
The polymer of oxyacid has a molecular weight of 20,000 or more.
The method for producing glycolides according to the above. 6. The ester of an α-oxy acid is methyl lactate,
The method for producing lactide according to any one of claims 1 to 5, wherein the glycolide is lactide.