JPH07157553A - Production of biodegradable polyester copolymer - Google Patents

Abstract

PURPOSE:To obtain the subject copolymer which is excellent in biodegradability, strength, heat resistance and useful for disposable vessel or thread for surgery by effecting ester-interchange reactions between specific polyester mixture in the presence of a glycol until a substance melting at a specified temperature is obtained, and then subjecting the ester-interchanged product to the polymerization. CONSTITUTION:A mixture of aliphatic polyester such as polyglycolide or polylactide with an aromatic polyester such as polyethylene terephthalate is subjected to ester-interchange reaction in the presence of a glycol such as ethylene glycol or 1,2-propanediol or water, until a substance having a melting point lower than those of the aliphatic polyester and the aromatic polyester is obtained, then the product is polymerized under a reduced pressure to give the object copolymer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel method for producing a biodegradable polyester copolymer,
More specifically, it relates to a method for producing a polyester having a high degree of polymerization and having a high efficiency of transesterification.

[0002]

2. Description of the Related Art Recently, research and development of synthetic polymers having biodegradability have been actively promoted, and in the fields of medicine, agriculture, forestry and general packaging related to recent environmental conservation and waste plastic treatment problems. It is being applied in a wide range of fields such as. Among them, aliphatic polyesters are generally known to be hydrolyzed by various lipases and pig liver esterases [Nature, Vol.
270, November 3, 76, 1977]. However, such an aliphatic polyester is biodegradable but has a low melting point, and it is generally difficult to obtain a high molecular weight polymer, so that it is not practical in terms of heat resistance and strength, and it is widely used in containers, films, fibers, etc. It could not be used as a general-purpose resin in the field.

In order to solve these problems, a polyester copolymer is formed from an aliphatic polyester having excellent biodegradability and an aromatic polyester having excellent physical properties by a transesterification reaction to obtain physical properties such as heat resistance and strength. Attempts have been made to obtain polymers with excellent biodegradability and biodegradability (Journal of Applied Polymers).
Science (J. of Appl. Polym. Sc
i. 26, 441, (1981)). In these methods, the transesterification reaction is carried out in a temperature range considerably higher than the melting points of the aliphatic polyester and the aromatic polyester (particularly, the melting point of the aliphatic polyester), so that the thermal decomposition is performed by the thermal history until the desired product is obtained. Occurs, the molecular weight of the copolymer is significantly reduced, and there is a problem that it is difficult to obtain a polyester copolymer having sufficient mechanical properties.

[0004]

In view of the above points, the present invention provides a biodegradable polyester copolymer having practically excellent physical properties such as heat resistance and strength and having high biodegradability. The purpose is to provide a method.

[0005]

As a result of intensive studies to solve such problems, the present inventors have found that a mixture of an aliphatic polyester and an aromatic polyester undergoes a predetermined polymerization in the presence of water or glycol. By carrying out the treatment, it was found that a polyester copolymer having a higher molecular weight and a narrower molecular weight distribution than the prior art can be produced, and the present invention has been completed.

That is, according to the present invention, a mixture of an aliphatic polyester and an aromatic polyester is heated and melted in the presence of water or glycol to obtain a substance having a melting point lower than the melting points of the aliphatic polyester and the aromatic polyester. The present invention provides a method for producing a biodegradable polyester copolymer, which comprises performing a transesterification reaction until the reaction is completed and then performing dehydration or deglycol condensation polymerization under reduced pressure.

In the present specification, as the aliphatic polyester (including alicyclic polyester), either a linear aliphatic polyester or a side chain aliphatic polyester can be used, and the structure thereof is not particularly limited. The polyester may be obtained by any known method, and examples thereof include polymerization of a diol and a dicarboxylic acid, polymerization of a carboxylic acid having a hydroxy group, ring-opening polymerization of caprolactone, and those produced by a microorganism.

Examples of linear aliphatic polyesters include polyglycolide, polycaprolactone and poly-3-.
Hydroxypropionate, poly-4-hydroxybutyrate, poly-5-hydroxyvalerate, poly-7-
Hydroxyheptanoate, poly-8-hydroxyoctanoate, poly-9-hydroxynonanoate, poly-10-hydroxydecanoate, poly-11-hydroxyundecanoate, poly-12-hydroxydodecanoate, polyethylene Succinate, polybutylene succinate, polyethylene oxalate, polybutylene oxalate, polyethylene sebacate, polydiethylene sebacate, polymethylethylene adipate, polymethylethylene sebacate, polytetramethylene succinate, polytetramethylene adipate, polyhexa Examples thereof include methylene adipate and polypropylene oxalate.

As the side chain aliphatic polyester, for example, polylactide, poly-3-hydroxybutyrate,
Poly-3-hydroxyvalerate, poly-3-hydroxycaproate, poly-3-hydroxyheptanoate, poly-3-hydroxyoctanoate, poly-3-
Hydroxynonanoate, poly-3-hydroxydecanoate, poly-3-hydroxydodecanoate, poly-
Examples thereof include, but are not limited to, 3-methyl-5-hydroxyvalerate, polypivalolactone, poly-3,3-dimethylpropylene oxalate, poly-3,3-dimethylpropylene adipate, and the like. However, from the viewpoint of biodegradability, the substituent is preferably an alkyl group having 1 to 9 carbon atoms. These aliphatic polyesters can be used alone or in combination of two or more.

The aromatic polyester used in the present invention may be produced by a known method. For example, a dicarboxylic acid having an aromatic ring and a diol are generally polymerized. Examples of suitable aromatic polyesters include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, polytetramethylene terephthalate, poly-1,4-cyclohexanedimethylene terephthalate, polyethylene-2,6-naphthalate and the like. These may be used alone or in combination of two or more.

The aliphatic polyester and aromatic polyester as the raw materials are not particularly limited in their molecular weights, and commercially available products can be used as they are. The number average molecular weight of the aliphatic polyester is 500 to 50,000.
0, particularly preferably about 4000 to 100,000. The number average molecular weight of the aromatic polyester is 500 to 10
0000, particularly preferably 20,000 to 50,000.

As the content of the aromatic polyester with respect to the aliphatic polyester increases, a copolymer having excellent physical properties can be obtained. However, when the content of the aromatic polyester is too large, the aromatic concentration increases and the rigidity of the molecular chain increases. Its biodegradability deteriorates. Therefore, the aromatic polyester content is 90% based on the total amount of the aliphatic polyester and the aromatic polyester.
It is preferably not more than mol%. To obtain a copolymer having practical properties, the aromatic polyester content is 5
It is preferably at least mol%. More preferably, the content of aromatic polyester is 20 to 70 mol%.

The glycol used in the present invention may be a commonly used one, specifically, having 2 to 1 carbon atoms.
0, preferably 2 to 8 carbon atoms, more preferably 2 carbon atoms
~ 4. Examples of suitable glycols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 3,3-dimethyl-1,3-propanediol, 1,4 -Butanediol,
1,5-pentanediol, 1,6-hexanediol,
1,7-heptanediol, 1,8-octanediol and the like can be mentioned. From the aspect of compatibility with aliphatic polyester and aromatic polyester, ethylene glycol, 1,
2-propanediol, 1,3-propanediol, 1,
3-Butanediol, 3,3-dimethyl-1,3-propanediol and 1,4-butanediol are preferred.

The amount of water or glycol added is important as a factor involved in the reaction rate of the transesterification reaction, and is generally 100 to 1 with respect to the total number of units constituting the copolymer.
It is preferable to add mol%, particularly preferably about 30 to 4 mol%. This is because the added water or glycol is used for the depolymerization reaction of the aliphatic polyester and / or the aromatic polyester. Therefore, if the amount of water or glycol added is too large, the proportion of the depolymerization product having a low boiling point becomes high, and the distillation yield of these depolymerization products in the depressurization step becomes high. It will be effective. On the other hand, when the amount of water or glycol added is too small, the transesterification reaction rate is not improved, and a high molecular weight copolymer cannot be obtained even if the depressurization step is performed.

In carrying out the present invention, a mixture of one or more kinds of aliphatic polyester and one or more kinds of aromatic polyester is melted by heating in an inert gas in the presence of water or glycol. After stirring, the reaction is carried out until a product polymer having a melting point lower than that of the raw material polymers (aliphatic polyester and aromatic polyester) is obtained, and then polymerization is carried out under reduced pressure. In the present invention, to measure the melting point, Perkin Elmer (PERK)
(IN ELMER) differential scanning calorimeter DSC7. At this time, the “low melting point” means a melting point at which the product polymer is at least 5 ° C. lower than the starting polymer (a mixture of an aliphatic polyester and an aliphatic polyamide),
More preferably it means having a melting point at least 10 ° C lower. The heating temperature may be equal to or higher than the temperature at which the raw material polymer is uniformly dissolved, and if it is too high, the raw material polymer may be thermally decomposed, which is not preferable.

In this case, a conventional transesterification catalyst such as anhydrous zinc acetate, zinc stearate, zinc benzoate or tetra-n-butyl titanate may be used as the catalyst,
The transesterification rate can be increased by stirring the reaction system.

In the reaction in the presence of water or glycol,
First, the depolymerization reaction of a mixture of an aliphatic polyester and an aromatic polyester causes a reduction in molecular weight, and the transesterification reaction proceeds continuously or in competition with this,
The transesterification rate increases with the elapse of the reaction time, and the co-polymer is composed of many low-molecular weight aliphatic polyester blocks and low-molecular weight aromatic polyester blocks, which have a significantly lower molecular weight than the raw material aliphatic polyester and aromatic polyester. A coalescence is obtained.

The present invention is characterized by a depolymerization reaction with coexisting water or glycol, whereby the melt viscosity of a melt mixture of an aliphatic polyester and an aromatic polyester is rapidly lowered in the initial stage of the reaction, Conventional method without water or glycol (Journal
Of Applied Polymer Science, 26, 4
41, (1981)), the transesterification reaction efficiency is greatly improved. Further, when a copolymer having a melting point distinctly lower than that of the raw material polymer is obtained, a dehydration reaction or a deglycolization reaction occurs by reducing the pressure in the reaction system. At the same time, condensation polymerization takes place, resulting in a polyester copolymer having a very large molecular weight as compared with the conventional method and a narrow molecular weight distribution. When the copolymer is synthesized only by the transesterification reaction without preliminarily coexisting water or glycol, in the temperature range having a sufficient transesterification rate, the molecular weight of the copolymer tends to remarkably decrease with the passage of reaction time. Therefore, coloring of the copolymer due to thermal decomposition becomes remarkable. Further, even when the pressure of the reaction system is reduced, the decomposition and coloration of the copolymer are significantly accelerated, and the rapid increase in the molecular weight of the copolymer as seen in the present invention does not occur.

The polyester copolymer obtained in the present invention has a structure in which a large number of low molecular weight aliphatic polyester blocks and low molecular weight aromatic polyester blocks are alternately bonded, and has a melting point higher than that of the raw material aromatic polyester. Lower values include lower molecular weight blocks. The aliphatic polyester copolymer exhibits biodegradability due to the above structure, and the shorter the average aromatic polyester block length (the lower the molecular weight), the more the average degree of polymerization of the aromatic polyester block in the copolymer is 25. In the case of the following integers, it has been reported that the biodegradability is excellent (Journal of Applied Polymer Science,
26, 441 (1981)). Therefore, the polyester copolymer having the desired biodegradability can be obtained by changing the raw material type and composition, reaction temperature, reaction time, catalyst type and amount, water or glycol amount, etc. to control the melting point of the product. Can be obtained.

[0020]

EXAMPLES Next, the present invention will be specifically described with reference to examples. Example 1 Polycaprolactone (number average molecular weight 80,000, manufactured by Nippon Unicar Co., Ltd., Tone (trademark) P-787) 2.2k
g, polyethylene terephthalate (number average molecular weight 250
00, Unitika Ltd., NES-2040) 2.8k
g, anhydrous zinc acetate 25 g (0.5% by weight) and water 200 g
(4% by weight) and put in a reactor capable of pressurizing and depressurizing,
The temperature was raised to 270 ° C. under a nitrogen atmosphere, and the reaction was carried out for 4 hours while stirring. After that, decompress the atmosphere in the device,
Water was distilled off, and when the torque was sufficiently increased, the pressure was returned to normal pressure, and after discharging, the molten reaction product was allowed to cool to obtain a copolymer.

The melting point of the obtained sample was measured using a differential scanning calorimeter DSC7 manufactured by Perkin Elmer. The melting point of the sample was 154 ° C, which was about 110 ° C lower than that of the raw material polyethylene terephthalate. Next, Soxhlet extraction was performed using chloroform, which is a good solvent for the aliphatic polyester and a poor solvent for the aromatic polyester, to separate the soluble and insoluble components. Infrared absorption spectrum analysis was performed on the soluble content (recovery rate 9.7% by weight) and the insoluble content (85.4% by weight). As a result, both the soluble content and the insoluble content showed an infrared absorption spectrum specific to polycaprolactone (around 2950 cm ^-1 ) and an absorption spectrum specific to polyethylene terephthalate (around 730 cm ^-1 ), and the obtained sample was a fat sample. It was confirmed to be a polyester copolymer of group and aromatic.

Next, the solution viscosity of this sample (phenol +
1,1,2,2-tetrachloroethane (1: 1) solvent,
As a result of measuring the measurement temperature: 20 ° C., the intrinsic viscosity is 0.9.
It was 6. Further, gel permeation chromatography using ALC / GPC manufactured by Waters (column: Waters ultrasty).
label linear (7.8mmφ × 30cm)
Two, m-cresol solvent, detector: differential refractometer, standard substance: monodisperse polystyrene) results of molecular weight measurement,
Number average molecular weight 32,000, weight average molecular weight 5800
The dispersity was 0 and the dispersity was 1.8. The color tone of the obtained copolymer was good, and almost no coloring was observed.

Example 2 Polycaprolactone (number average molecular weight 80,000, manufactured by Nippon Unicar Co., Ltd., Tone (trademark) P-787) 1.3k
g, polyethylene terephthalate (number average molecular weight 250
00, Unitika Ltd., NES-2040) 3.7k
g, anhydrous zinc acetate 25 g (0.5% by weight) and water 200 g
A copolymer was obtained in the same manner as in Example 1 except that (4% by weight) was used.

The melting point of the obtained sample was measured by using a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer. The melting point of the sample was 196 ° C. Next, Soxhlet extraction was performed in the same manner as in Example 1, and an infrared absorption spectrum analysis was performed on the soluble content (recovery rate: 5.7% by weight) and the insoluble content (91.3% by weight). As a result, it was confirmed that the obtained sample was an aliphatic and aromatic polyester copolymer. The intrinsic viscosity of this sample is 1.0
3, number average molecular weight 37,000, weight average molecular weight 68
000, and the dispersity was 1.7. The color tone of the obtained copolymer was good, and no coloring was observed at all.

Example 3 Polycaprolactone (number average molecular weight 80,000, manufactured by Nippon Unicar Co., Ltd., Tone (trademark) P-787) 3.2k
g, polyethylene terephthalate (number average molecular weight 250
00, Unitika Ltd., NES-2040) 1.8k
g, anhydrous zinc acetate 25 g (0.5% by weight) and water 200 g
A copolymer was obtained in the same manner as in Example 1 except that (4% by weight) was used.

The melting point of the obtained sample was measured using a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer. The melting point of the sample was 132 ° C. Next, Soxhlet extraction was performed in the same manner as in Example 1, and the infrared absorption spectrum analysis was performed on the soluble content and the insoluble content. As a result, it was confirmed that the obtained sample was an aliphatic and aromatic polyester copolymer. The intrinsic viscosity of this sample was 0.89, the number average molecular weight was 26000, the weight average molecular weight was 45,000, and the dispersity was 1.7. The color tone of the obtained copolymer was good, and no coloring was observed at all.

Example 4 Polycaprolactone (number average molecular weight 80,000, manufactured by Nippon Unicar Co., Ltd., Tone (trademark) P-787) 2.2k
g, polyethylene terephthalate (number average molecular weight 250
00, Unitika Ltd., NES-2040) 2.8k
A copolymer was obtained in the same manner as in Example 1, except that 25 g (0.5% by weight) of anhydrous zinc acetate and 500 g (10% by weight) of ethylene glycol were used.

The melting point of the obtained sample was measured by using a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer. The melting point of the sample was 168 ° C. Next, Soxhlet extraction was performed in the same manner as in Example 1, and the infrared absorption spectrum analysis was performed on the soluble content and the insoluble content. As a result, it was confirmed that the obtained sample was an aliphatic and aromatic polyester copolymer. The intrinsic viscosity of this sample was 0.92, the number average molecular weight was 30,000, the weight average molecular weight was 85,000, and the dispersity was 2.8. The color tone of the obtained copolymer was good, and no coloring was observed at all.

Example 5 Instead of 200 g of water, 500 g of ethylene glycol (1
A copolymer was obtained in the same manner as in Example 2 except that 0% by weight) was used. The melting point of the obtained sample was measured using a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer. The melting point of the sample was 209 ° C. Next, Soxhlet extraction was performed in the same manner as in Example 1, and the infrared absorption spectrum analysis was performed on the soluble content and the insoluble content. As a result, it was confirmed that the obtained sample was an aliphatic and aromatic polyester copolymer. The intrinsic viscosity of this sample was 1.06, the number average molecular weight was 38,000, the weight average molecular weight was 90,000, and the dispersity was 2.4. The color tone of the obtained copolymer was good, and no coloring was observed at all.

Example 6 Instead of 200 g of water, 500 g of ethylene glycol (1
A copolymer was obtained in the same manner as in Example 3 except that 0% by weight) was used. The melting point of the obtained sample was measured using a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer. The melting point of the sample was 148 ° C. Next, Soxhlet extraction was performed in the same manner as in Example 1, and the infrared absorption spectrum analysis was performed on the soluble content and the insoluble content. As a result, it was confirmed that the obtained sample was an aliphatic and aromatic polyester copolymer. The intrinsic viscosity of this sample was 0.92, the number average molecular weight was 27,000, the weight average molecular weight was 105,000, and the dispersity was 3.8. The color tone of the obtained copolymer was good, and no coloring was observed at all.

Example 7 Polycaprolactone (number average molecular weight 80,000, manufactured by Nippon Unicar Co., Ltd., Tone (trademark) P-787) 2.0 k
g, polybutylene terephthalate (number average molecular weight 300
00) 3.0 kg, anhydrous zinc acetate 25 g (0.5% by weight) and water 200 g (4% by weight) were used to obtain a copolymer in the same manner as in Example 1.

The melting point of the obtained sample was measured using a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer. The melting point of the sample was 133 ° C. Next, Soxhlet extraction was performed in the same manner as in Example 1, and the infrared absorption spectrum analysis was performed on the soluble content and the insoluble content. As a result, it was confirmed that the obtained sample was an aliphatic and aromatic polyester copolymer. The intrinsic viscosity of this sample was 0.92, the number average molecular weight was 28,000, the weight average molecular weight was 49,000, and the dispersity was 1.7. The color tone of the obtained copolymer was good, and no coloring was observed at all.

Example 8 Polycaprolactone (number average molecular weight 80,000, manufactured by Nippon Unicar Co., Ltd., Tone (trademark) P-787) 2.0 k
g, polybutylene terephthalate (number average molecular weight 300
00) 3.0 kg, anhydrous zinc acetate 25 g (0.5% by weight) and butanediol 500 g (10% by weight) were used to obtain a copolymer in the same manner as in Example 1.

The melting point of the obtained sample was measured using a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer. The melting point of the sample was 139 ° C. Next, Soxhlet extraction was performed in the same manner as in Example 1, and the infrared absorption spectrum analysis was performed on the soluble content and the insoluble content. As a result, it was confirmed that the obtained sample was an aliphatic and aromatic polyester copolymer. The intrinsic viscosity of this sample was 0.86, the number average molecular weight was 29000, the weight average molecular weight was 55,000, and the dispersity was 1.9. The color tone of the obtained copolymer was good, and no coloring was observed at all.

Example 9 A copolymer was obtained in the same manner as in Example 1 except that the heating temperature in a nitrogen atmosphere was 280 ° C. About the obtained sample, a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer
Was used to measure the melting point. The melting point of the sample was 122 ° C. Next, Soxhlet extraction was performed in the same manner as in Example 1, and the infrared absorption spectrum analysis was performed on the soluble content and the insoluble content. As a result, it was confirmed that the obtained sample was an aliphatic and aromatic polyester copolymer. Also,
This sample has an intrinsic viscosity of 1.02 and a number average molecular weight of 320.
00, the weight average molecular weight was 73,000, and the dispersity was 1.6. The color tone of the obtained copolymer was good, and no coloring was observed at all.

Example 10 A copolymer was obtained in the same manner as in Example 1 except that the heating temperature under a nitrogen atmosphere was 280 ° C. About the obtained sample, a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer
Was used to measure the melting point. The melting point of the sample was 143 ° C. Next, Soxhlet extraction was performed in the same manner as in Example 1, and the infrared absorption spectrum analysis was performed on the soluble content and the insoluble content. As a result, it was confirmed that the obtained sample was an aliphatic and aromatic polyester copolymer. Also,
This sample has an intrinsic viscosity of 0.88 and a number average molecular weight of 250.
00, the weight average molecular weight was 46,000, and the dispersity was 1.8. The color tone of the obtained copolymer was good, and no coloring was observed at all.

Comparative Example 1 Polycaprolactone (number average molecular weight 80,000, manufactured by Nippon Unicar Co., Ltd., Tone (trademark) P-787) 2.2k
g, polyethylene terephthalate (number average molecular weight 250
00, Unitika Ltd., NES-2040) 2.8k
g, and 25 g (0.5% by weight) of anhydrous zinc acetate were placed in a reactor capable of pressurizing and depressurizing, and under a nitrogen atmosphere at 280 ° C.
The temperature was raised to 4, and the reaction was carried out for 4 hours with stirring. After paying out, the molten reaction product was allowed to cool to obtain a copolymer.

The melting point of the obtained sample was measured using a differential scanning calorimeter DSC7 manufactured by PERKIN ELMER. The melting point of the sample is 208
It was ℃. Next, Soxhlet extraction was performed using chloroform, which is a good solvent for the aliphatic polyester and a poor solvent for the aromatic polyester, to separate the soluble and insoluble components. The soluble content (recovery rate 29.7% by weight) and the insoluble content (55.4% by weight) were subjected to infrared absorption spectrum analysis. As a result, both the soluble content and the insoluble content showed an infrared absorption spectrum peculiar to polycaprolactone (around 2950 cm ^-1 ) and an infrared absorption spectrum peculiar to polyethylene terephthalate (around 730 cm ^-1 ), and the obtained sample was It was confirmed to be an aliphatic and aromatic polyester copolymer.

Next, the solution viscosity of this sample (phenol +
1,1,2,2-tetrachloroethane (1: 1) solvent,
As a result of measuring the measuring temperature: 20 ° C., the intrinsic viscosity is 0.3.
It was 2. The obtained copolymer was extremely brittle.

Comparative Example 2 A copolymer was obtained in the same manner as in Comparative Example 1 except that the reaction time was 6 hours. The melting point of the obtained sample was measured using a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer. The melting point of the sample was 177 ° C. The intrinsic viscosity of this sample was 0.28.

Comparative Example 3 After the reaction was carried out for 6 hours in the same manner as in Comparative Example 2, the apparatus atmosphere was depressurized, the mixture was stirred for 2 hours, the pressure was returned to normal pressure, the molten reaction product was discharged, and the mixture was allowed to cool. A polymer was obtained. The obtained product was markedly colored and had a brown color. It is considered that this is because the decompression operation simply promoted the decomposition.

Comparative Example 4 A copolymer was obtained in the same manner as in Comparative Example 1 except that the reaction time was 8 hours and the heating temperature in a nitrogen atmosphere was 270 ° C. The melting point of the obtained sample was measured using a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer. The melting point of the sample was 247 ° C. The intrinsic viscosity of this sample was 0.63. Although this sample has improved brittleness as compared with Comparative Example 1, it is considered that the transesterification reaction has hardly progressed.

Comparative Example 5 Polycaprolactone (number average molecular weight 80,000, manufactured by Nippon Unicar Co., Ltd., Tone (trademark) P-787) 2.0 k
g, polybutylene terephthalate (number average molecular weight 300
00) 3.0 g and anhydrous zinc acetate 25 g (0.5% by weight) were used to obtain a copolymer in the same manner as in Comparative Example 1. The melting point of the obtained sample was measured using a differential scanning calorimeter DSC7 manufactured by Perkin-Elmer. The melting point of the sample was 197 ° C. The intrinsic viscosity of this sample was 0.36.

Next, the results of biodegradability evaluation and physical property evaluation of the copolymers obtained in Examples and Comparative Examples will be described. Test Example 1 As described above, the aliphatic polyester amide copolymer exhibits biodegradability by alternately copolymerizing the low molecular weight aliphatic polyester block and the low molecular weight aromatic polyester block, and also exhibits the average aromaticity. It has been reported that the shorter the polyester block length is, the lower the melting point of the copolymer is, and the better the biodegradability is when the average degree of polymerization of the aromatic polyester block in the copolymer is an integer of 25 or less. (Journal of Applied Polymer Science, 26, 441, (19
81)).

The melting points of the copolymers of the examples were all significantly lower than those of the starting aromatic polyester, and the measurement results confirmed that the average degree of polymerization of the aromatic polyester block was 20 or less. ing. Therefore, it can be said that the copolymers of Examples all have excellent biodegradability.

Further, in order to evaluate the biodegradability of the copolymers shown in the examples, the film of each copolymer was buried in soil for 3 months and the shape was observed. As a result, each of the copolymers of Examples had mold (filamentous fungi) on the film.
It was observed that the film shape was apparent, and that there were innumerable minute holes and the film shape was clearly broken. Therefore,
It can be seen that the copolymer obtained in the present invention has excellent biodegradability.

Test Example 2 The tensile strength of the copolymer films obtained from the examples and comparative examples was measured. The results are shown in Table 1. As is clear from Table 1, the copolymer obtained in the present invention has excellent tensile strength.

[0048]

[Table 1]

[0049]

According to the present invention, a biodegradable polyester copolymer having excellent physical properties can be obtained. The copolymer obtained in the present invention is completely decomposed in a natural environment such as soil, and has good physical properties such as tensile strength and heat resistance (melting point), disposable containers, cups, sheets, bags,
It can be used for strings, films, fibers, coating agents, binders, molded products and the like. Furthermore, in the pharmaceutical field,
By utilizing its biodegradability, it can be used as a thread for surgery or a sustained-release drug carrier in the body, but it is not limited to this and can be expected to be applied in a wide range of fields.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masatoshi Kasai, 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Central Research Institute (72) Inventor, Katsuyuki Mukai 23, Uji Kozakura, Uji City, Kyoto Unitika Stock Company Central Inside the Institute (72) Inventor Yoshiaki Iwaya 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Ltd. Central Research Institute

Claims (1)

[Claims] 1. Transesterification is performed by heating and melting a mixture of an aliphatic polyester and an aromatic polyester in the presence of water or glycol until a substance having a melting point lower than that of the aliphatic polyester and the aromatic polyester is obtained. A method for producing a biodegradable polyester copolymer, which comprises polymerizing under a reduced pressure after the reaction.