JPH06322091A - Production of high-molecular aliphatic polyester - Google Patents

Abstract

PURPOSE:To provide a method for producing a high-mol. aliphatic polyester which retains intact biodegradability, has a melting point of 80 deg.C or higher, and is hence usable as a molding. CONSTITUTION:A tetracarboxylic dianhydride is reacted with an aliphatic polyester comprising poly(ethylene succinate), as the main structural unit, which has a hydroxyl group at each end and has a number-average mol.wt. as determined by the end-group titration method of 10,000 or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention decomposes an aliphatic polyester containing a specific polyethylene succinate as a main constituent unit with tetracarboxylic dianhydride and decomposes it with microorganisms in soil, and The present invention relates to a method for producing a high molecular weight aliphatic polyester that can be used as a molded product.

[0002]

2. Description of the Related Art Plastics, which are used as synthetic fibers, films, and other molded products, have the advantages of being light and durable, and of being inexpensive and capable of being stably supplied in large quantities. It has brought convenience and built a modern society that can be called a plastic civilization. However, in recent years, in response to environmental problems on a global scale, there has been a demand for the development of polymer materials that decompose in the natural environment. Among them, plastics that are decomposed by microorganisms are especially environmentally friendly. There are great expectations in the industry as materials and new types of functional materials.

It is well known that aliphatic polyesters are biodegradable, and among them, poly-3-hydroxybutyric acid ester (PHB) produced by microorganisms and poly-ε which is a synthetic polymer are known. Caprolactone (PCL) and polyglycolic acid (PGA) are the typical ones.

[0004] PHB-based biopolyesters are industrially produced because they have excellent environmental compatibility and physical properties, but they are poor in productivity and are generally used from the viewpoint of cost as represented by polyethylene. There are limits to what can be substituted as plastics (Fiber and Industry, 47, 532)
Page (1991)). In addition, although PCL has a high degree of polymerization that can be formed into fibers and films, it has a melting point of 65 ° C or less and poor heat resistance, making it unsuitable for a wide range of applications [Polymer Science Technology (Polym. Sci. Technol., Volume 3, p. 61 (197)
3)]. Furthermore, PGA and glycolide-lactide (9: which are practically used as bioabsorbable sutures:
1) Copolymers are metabolized and absorbed in vivo after being subjected to abiotic hydrolysis, but are expensive and have poor water resistance, so they are suitable for use as general-purpose plastics. Absent.

On the other hand, α, ω-aliphatic diols and α, ω-
Aliphatic polyesters produced by melt polycondensation with aliphatic dicarboxylic acids, such as polyethylene succinate (PES), polyethylene adipate (PEA) and polybutylene succinate (PBS), are long-known polymers and are inexpensive. It has been confirmed that it can be produced and that it is biodegraded by microorganisms even when it is buried in the soil [Int. Biodetetn. Bull., Vol. 11, p. 127 (1975) and Polymer Science Technology. (See Polym. Sci. Technol.), Vol. 3, p. 61 (1973)], these polymers have poor thermal stability.
Decomposition reaction occurs at the time of polycondensation, so it is usually 2,000-
Molecular weight of about 6,000 (concentration of 0.5 using chloroform)
g / deciliter, reduced specific viscosity ηsp measured at 30 ° C.
/ C was less than 0.3), which was not sufficient for processing into fiber or film. Among them, polyethylene succinate, in particular, has been reported to have excellent biodegradability, but its thermal stability is remarkably poor. I can't get one.

Therefore, it has been reported to treat these aliphatic polyesters with diisocyanates such as hexamethylene diisocyanate and toluene diisocyanate in order to increase the molecular weight [Polymer J., 2 pp. 387 (1971) and JP-A-4-189822].

[0007]

However, although the above-mentioned method has the effect of increasing the molecular weight, it usually involves two reaction steps, which complicates the process. However, in addition to a slight decrease in its crystallinity and melting point, there was the problem that the biodegradability was somewhat inferior because the urethane bond was included in the molecule. The present invention has a melting point of 80 ° C. that can be used as a molded body without impairing the original property of biodegradability.
It is an object of the present invention to provide a method for producing an aliphatic polyester capable of maintaining the above and increasing the molecular weight.

[0008]

Means for Solving the Problems As a result of various investigations for solving the above problems, the inventors of the present invention mainly use polyethylene succinate having a specific molecular weight, which is produced from succinic acid and ethylene glycol as a main constituent unit. The present inventors have obtained the finding that the above problems can be solved by reacting an aliphatic polyester with tetracarboxylic acid dianhydride, and arrived at the present invention based on this finding.

That is, according to the present invention, an aliphatic polyester having polyethylene succinate as a main constituent unit having hydroxyl groups at both ends and having a number average molecular weight of 10,000 or more as determined by an end group titration method, and tetra The gist is a method for producing a high molecular weight aliphatic polyester, which comprises reacting with a carboxylic acid dianhydride.

The present invention will be described in detail below. In the present invention, examples of the aliphatic polyester mainly containing polyethylene succinate having hydroxyl groups at both ends and having a number average molecular weight of 10,000 or more as determined by an end group titration method include succinic acid and / Or α, ω-aliphatic dicarboxylic acid represented by the general formula (1) and ethylene glycol and / or glycol represented by the general formula (2) are transesterified in the presence of an ester conversion catalyst in the presence of an excess of glycol. To obtain the oligomer,
It can be obtained by adding a polymerization catalyst and polymerizing by deglycolization.

HOOC- (CH ₂ ) _k -COOH (1) [In the formula, k represents an integer of 0 to 32 other than 2. ] HO-A-OH (2) wherein, A is _{- (CH 2) n -,} - (CH 2 CH 2 O) m -C
H ₂ CH ₂ -,

[0012]

[Chemical 1]

## EQU3 ## where n is an integer of 2 to 20 excluding 2, m is an integer of 1 to 20, and l is an integer of 0 to 20. R ₁ and R ₂ represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R ₁ and R ₂ are not hydrogen atoms at the same time. ]

In the present invention, as the α, ω-aliphatic dicarboxylic acid represented by the general formula (1), for example, oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid,
Suberic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, tridecanedicarboxylic acid,
Tetradecanedicarboxylic acid, pentadecanedicarboxylic acid, hexadecanedicarboxylic acid, heptadecanedicarboxylic acid, octadecanedicarboxylic acid, nonadecanedicarboxylic acid, aicosanedicarboxylic acid, heneicosanedicarboxylic acid, docosanedicarboxylic acid, tricosanedicarboxylic acid, tetracosanedicarboxylic acid, Hexacosane dicarboxylic acid, triacontane dicarboxylic acid, tetratriacontane dicarboxylic acid and the like can be mentioned, of which adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid are preferred.

Specific examples of the glycol represented by the general formula (2) used in the present invention include trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, heptamethylene glycol, octamethylene glycol, nonamethylene glycol. , Decamethylene glycol, undecamethylene glycol, dodecamethylene glycol, tridecamethylene glycol, eicosane methylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 2,2-dimethylpropane-1,3-diol, etc. Among them, tetramethylene glycol, diethylene glycol and propylene glycol are preferable.

In the present invention, succinic acid and / or α, ω-represented by the general formula (1) when synthesizing an oligomer is used.
The charge ratio of the aliphatic dicarboxylic acid and ethylene glycol and / or the glycol represented by the general formula (2) is usually preferably 1: 1 to 1: 2.2 in terms of molar ratio, and 1: 1. It is more preferable that the ratio is 05 to 1: 1.6,
Optimally, 1: 1 to 1: 1.5. The charge ratio of succinic acid to the α, ω-aliphatic dicarboxylic acid represented by the general formula (1) is preferably 1: 0 to 1: 0.3, and ethylene glycol and the general formula (2 ), As the charging ratio with glycol, is 1: 0 to 1: 0.
3 is preferable.

Regarding the reaction conditions, when an ester is transesterified to form an oligomer, the temperature is preferably 120 to 250 ° C. for 1 to 10 hours, and 150 to 220 ° C. for 2 hours.
More preferably, it is carried out under atmospheric pressure and nitrogen stream for a period of up to 5 hours. In addition, the polymerization reaction by deglycolization is
1-1 at 150-250 ℃ under reduced pressure of 0.01-10mmHg
It is preferably carried out for 0 hour, more preferably at 190 to 240 ° C. for 2 to 5 hours under a reduced pressure of 0.1 to 1 mmHg.

In the present invention, the transesterification catalyst used for synthesizing an oligomer by transesterification includes 2A group elements, 4A group elements, 5A group elements, 7A group elements, 8 group elements, 2B group elements and 3B group elements. , 4B group element and 5B group element type catalysts are used. Specific examples thereof include magnesium, calcium, strontium, barium, titanium, zirconium, barium, manganese, iron, cobalt, nickel, palladium, zinc, gallium, It is indium, germanium, tin, antimony, bismuth, etc. Among them, magnesium, calcium, titanium, tin, cobalt, nickel and germanium are preferable. These metals are used as organic metal compounds, organic acid salts, metal complexes, metal alkoxides, metal oxides, metal hydroxides, carbonates, phosphates, sulfates, nitrates, chlorides, etc. Above all, it is preferable to use in the form of acetate, acetylacetone metal complex and metal oxide. A specific example of a particularly preferable catalyst is magnesium acetate-4
Hydrate, calcium acetate monohydrate, stannous acetate, nickel acetate tetrahydrate, cobalt acetate tetrahydrate, calcium acetylacetonate dihydrate, magnesium acetylacetonate dihydrate A solvate, titanium (IV) oxyacetylacetonate, tetra-n-butyl titanate, tetraisopropyl titanate, di-n-butyltin oxide, tetra-n-butoxy germanium, tetraethoxy germanium, germanium acetate (IV), etc., You may use 2 or more types of these catalysts. Also,
At that time, the amount of the catalyst used is preferably 1 × 10 ^{−4 to} 5 × 10 ⁻³ mol per 1 mol of succinic acid, and 2 × 10 4
^It is more preferably used in the range of ^-4 to 1 x 10 ^-3 mol.

As the polymerization catalyst for deglycolization and polymerization, 4A group element, 5A group element and 4B group element based catalysts are used. Specific examples thereof include titanium, zirconium, vanadium and germanium. , Metals such as tin, organic acid salts thereof, metal alkoxides, metal oxides, metal hydroxides, carbonates, phosphates, sulfates, nitrates, chlorides, etc. , Tetra-n-butyl titanate, tetraisopropyl titanate, penta-n-butyl vananate, tetra-n-butoxy germanium, germanium oxide (I
V), di-n-butyltin oxide, titanium (IV) oxyacetylacetonate and the like, and two or more kinds of these catalysts may be used. The amount of the catalyst used in that case is preferably 1 × 10 ^{−4 to} 5 × 10 ⁻³ mol, and 2 × 10 ⁻⁴ to 2 × 10 ⁻³ mol per 1 mol of succinic acid. More preferable.

The thus obtained aliphatic polyester containing polyethylene succinate as a main constituent unit has hydroxyl groups at both ends, and has a number average molecular weight of 10,000 or more as determined by the end group titration method. (Reduced specific viscosity ηsp / c is 0.4 or more measured at 30 ° C. at a concentration of 0.5 g / deciliter using chloroform), and if the number average molecular weight is less than 10,000, the tetracarboxylic dianhydride As the amount used increases, gelation tends to occur, and it is difficult to obtain the desired high molecular weight aliphatic polyester, and the unit of acid anhydride increases in the polymer, resulting in low biodegradability. The aliphatic polyester mainly composed of polyethylene succinate thus obtained may have a part as a copolymer, and the content of the ethylene succinate is 70 mol%.
The above is preferable.

When the aliphatic polyester containing polyethylene succinate as the main constituent unit is reacted with the tetracarboxylic dianhydride described below, the aliphatic polyester containing the polyethylene succinate as the main constituent unit and the tetracarboxylic dianhydride are reacted. The product is linked by an ester bond, and a high-molecular-weight aliphatic polyester having a reduced specific viscosity of 0.7 or more can be obtained without impairing the original property of biodegradability.

Examples of the tetracarboxylic acid dianhydride used in the present invention include 1,2-, 3,4-butanetetracarboxylic acid dianhydride and 1,3-, 2,4-butanetetracarboxylic acid dianhydride. Anhydride, 1,4-, 2,3-tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3 ', 4,4'-
Biphenyltetracarboxylic dianhydride, 3,3 ', 4,4'
-Benzophenone tetracarboxylic dianhydride, 3,3 ',
4,4'-diphenylsulfone tetracarboxylic acid dianhydride, 3,3 ', 4,4'-diphenyl ether tetracarboxylic acid dianhydride, ethylene glycol bis (anhydrotrimellitate), and by heating Some of them include those which become tetracarboxylic dianhydrides, and specific examples thereof include 1,2,3,4-butanetetracarboxylic acid. Among them, 1,2-, 3,4-butanetetracarboxylic dianhydride, 1,3-, 2,4-butanetetracarboxylic dianhydride, ethylene glycol bis (anhydrotrimellitate), 1, 2 , 3,4-Butanetetracarboxylic acid is preferable, and these can be used as a mixture.

In the present invention, the amount of the tetracarboxylic dianhydride to be reacted with the aliphatic polyester having polyethylene succinate as a main constituent unit is 1 equivalent of hydroxyl group of the aliphatic polyester having polyethylene succinate as a main constituent unit. To 0.3 to 2 equivalents of carboxylic anhydride (tetracarboxylic dianhydride 0.15 to
1 mol), preferably 0.5 to 1.1 equivalents. The equivalent of carboxylic anhydride of tetracarboxylic dianhydride is 0.
If it is smaller than 3 or larger than 2, it is difficult to obtain the desired high molecular weight aliphatic polyester.

The reaction conditions for the aliphatic polyester containing polyethylene succinate as the main constituent unit and the tetracarboxylic dianhydride are as follows: The aliphatic polyester containing the polyethylene succinate as the main constituent unit and the tetracarboxylic dianhydride are used. It depends on the product,
Usually, it is preferably carried out at 100 to 200 ° C. under normal pressure nitrogen for 0.5 to 5 hours or under reduced pressure of 0.1 to 10 mmHg.

Since the high molecular weight aliphatic polyester obtained by the present invention is thermoplastic and has moldability, it can be applied to various uses. For example, it can be processed into a film, fiber, sheet or the like as a biodegradable polymer and used as various bottles, shopping bags, packaging materials, synthetic threads, fishing lines, fishing nets, non-woven fabrics, agricultural mulch films, and the like. In addition, the high molecular weight aliphatic polyester obtained by the present invention can be used as a base resin for hot melt adhesives, paints, and urethane elastomers.

When the high-molecular-weight aliphatic polyester obtained by the present invention is used as a biodegradable polymer, its microbial selectivity is not particularly clear, but it is adopted in ordinary soil burial tests and sewage treatment plants. The biodegradability can be easily confirmed by immersing it in an activated sludge aeration tank. That is, it can be confirmed by immersing the molded product in soil for a predetermined period of time and then measuring the molecular weight of this molded product or by comparing its surface morphology with that before burial.

[0027]

EXAMPLES The present invention will be specifically described below with reference to examples. Each value was obtained as follows. (1) OH value (milliequivalent / g) A polymer (aliphatic polyester having polyethylene succinate as a main constituent unit) is allowed to react with excess succinic anhydride in a molten state to convert a terminal into a COOH group,
The polymer was dissolved in chloroform and then purified by repeated reprecipitation with acetone, and determined by non-aqueous titration with N / 50 sodium hydroxide ethanol solution using phenolphthalein as an indicator. (2) COOH value (milliequivalent / g) The above polymer was dissolved in chloroform, and non-aqueous titration was performed with N / 50 sodium hydroxide ethanol solution using phenolphthalein as an indicator. (3) Number average molecular weight (Mn) determined by end group titration method. Mn = [1,000 / (OH value + COOH value)] × 2 (4) Reduced specific viscosity (ηsp / c) By measuring the polymer solution viscosity at a concentration of 0.5 g / deciliter using an Ubbelohde viscometer. It was determined and used as a guide for the molecular weight. Measurement conditions: Chloroform was used as a solvent, and measurement was performed at 30 ° C. (5) Melting point Using a minute melting point measuring device MP-S3 manufactured by Yanaco Co., Ltd., the melting point was measured at a temperature rising rate of 1 to 2 ° C./min. (6) Appearance It was judged visually or by optical microscope observation. A: Severe damage B: Significant damage C: Some damage
D: Invariant (7) Film strength A sample having a predetermined size was prepared in accordance with JIS K-7327, and measured using a precision universal testing machine 2020 manufactured by Intesco.

Example 1 First, 47.2 g (0.400 mol) of succinic acid and 32.3 g (0.520 mol) of ethylene glycol were placed in a three-necked flask equipped with a stirrer, a Wigley fractionation pipe and a gas introduction pipe. And magnesium acetate tetrahydrate 0.026 g (1.2 x 10
^-4 mol) and soaked in an oil bath. This oil bath at 200 ℃
The temperature was raised to 0, nitrogen was slowly flown into the melt, and the esterification reaction was carried out at a temperature of 200 ° C. for 3 hours to distill off the produced water and excess ethylene glycol. Then, 0.14 g (4.0 × 10 ^-4 mol) of tetra-n-butyl titanate was added, and the temperature was kept at 200 ° C. under nitrogen at 2 mmHg.
By heating under reduced pressure for 2 hours and further under reduced pressure of 1 mmHg or less for 2 hours, 57.6 g of a viscous polymer liquid was obtained.

The polymer thus obtained (aliphatic polyester having polyethylene succinate as a main constituent unit) had an OH value of 0.144 meq / g and a COOH value of 0.010 meq / g. ， This polymer has hydroxyl group at both ends, Mn is 1.3 × 10 ⁴
Met. Further, ηsp / c was 0.53 (concentration: 0.5 g / deciliter, 30 ° C, in chloroform), and the melting point was 107 ° C.

Next, 0.82 g of 1,2-, 3,4-butanetetracarboxylic dianhydride (4.15 × 10 ^-3 mol, carboxylic anhydride) was added to the above polymer at a temperature of 200 ° C. Substance / OH = 1.0 (equivalent ratio)], and heated at 200 ° C. under reduced pressure of 1 mmHg or less for 1 hour to obtain the target polymer (high molecular weight aliphatic polyester). The ηsp / c of this polymer is 0.85 (concentration: 0.5 g / deciliter, 30 ° C, in chloroform), and the melting point is 105.
It was ℃.

Example 2 1,2-, 3,4-butanetetracarboxylic dianhydride 0.82
Instead of 1 g, ethylene glycol bis (anhydrotrimeritate) (manufactured by Shin Nippon Rika Co., Ltd., RIKACID TMEG)
-200) The target polymer (high molecular weight aliphatic polyester) was obtained in exactly the same manner as in Example 1 except that 1.69 g (4.15 × 10 ^-3 mol) was used. The ηsp / c of this polymer is 0.75 (concentration: 0.5 g / deciliter, 30 ° C, in chloroform), and the melting point is 105.
It was ℃.

Example 3 118 g (1.00 mol) of succinic acid, 80.7 g (1.30 mol) of ethylene glycol and di-n were placed in a three-necked flask equipped with a stirrer, a Wigley fractionation pipe and a gas introduction pipe. −
Butyltin oxide (0.075 g, 3.0 × 10 ^-4 mol) was added and the mixture was immersed in an oil bath. Raise this oil bath to 200 ° C,
Nitrogen was slowly flowed into the melt, the esterification reaction was carried out at a temperature of 200 ° C. for 2 hours, and the produced water and excess ethylene glycol were distilled off. Then, germanium oxide (0.105 g, 1.0 × 10 ⁻³ mol) was added, and the mixture was heated at 200 ° C. under nitrogen under a reduced pressure of 1 mmHg or less for 4 hours to obtain 144 g of a viscous polymer liquid.

The polymer thus obtained (aliphatic polyester having polyethylene succinate as a main constituent unit) had an OH value of 0.112 meq / g and a COOH value of 0.006 meq / g. ， This polymer has hydroxyl groups at both ends, Mn is 1.7 × 10 ⁴
Met. Further, ηsp / c was 0.75 (concentration: 0.5 g / deciliter, 30 ° C, in chloroform), and the melting point was 108 ° C.

Next, 1.10 g (5.56 × 10 ^-3 mol) of 1,2-, 3,4-butanetetracarboxylic dianhydride and 1,1 were added to the above polymer at a temperature of 200 ° C. 3-, 2,4-butanetetracarboxylic dianhydride 0.50 g (2.5 × 10 ^-3
Mol, carboxylic acid anhydride / OH = 1.0 (equivalent ratio)] and heated at 200 ° C. under reduced pressure of 1 mmHg or less for 1 hour to obtain the target polymer (high molecular weight aliphatic polyester). It was Ηsp / c of this polymer is 1.02
(Concentration: 0.5 g / deciliter, 30 ° C., in chloroform), and melting point: 106 ° C.

Example 4 First, 47.2 g (0.400 mol) of succinic acid and 29.1 g (0.468 mol) of ethylene glycol were placed in a three-necked flask equipped with a stirrer, a Wigley fractionating tube and a gas introducing tube. ，
Tetramethylene glycol 4.7 g (0.052 mol) and titanium (IV) oxyacetylacetonate 0.032 g
(1.2 × 10 ⁻⁴ mol) was added and immersed in an oil bath. The temperature of this oil bath was raised to 200 ° C., nitrogen was slowly flowed into the melt, and the esterification reaction was carried out at a temperature of 200 ° C. for 2 hours to distill the produced water and excess ethylene glycol and tetramethylene glycol. I left. Next, 0.11 g (4.0 × 10 ^-4 mol) of tetraisopropyl titanate was added, and the mixture was heated at 200 ° C. under nitrogen at a reduced pressure of 2 mmHg for 2 hours and further at 220 ° C. under a reduced pressure of 1 mmHg or less for 2.5 hours. By heating, 58.7 g of a viscous polymer liquid was obtained.

The polymer thus obtained (aliphatic polyester having polyethylene succinate as a main constituent unit) had an OH value of 0.160 meq / g and a COOH value of 0.007 meq / g. ， This polymer has hydroxyl group at both ends, Mn is 1.2 × 10 ⁴
Met. Further, ηsp / c was 0.50 (concentration: 0.5 g / deciliter, 30 ° C, in chloroform), and the melting point was 90 ° C.

Next, 0.930 g of 1,2-, 3,4-butanetetracarboxylic dianhydride [4.70 × 10 ^-3 mol, carboxylic anhydride was added to the above polymer at a temperature of 200 ° C. Substance / OH = 1.0 (equivalent ratio)], and heated at 200 ° C. under reduced pressure of 1 mmHg or less for 1 hour to obtain the target polymer (high molecular weight aliphatic polyester). Ηsp / c of this polymer is 0.80 (concentration 0.5g / deciliter, 30 ℃, in chloroform), melting point is 88 ℃
Met.

Example 5 First, in a three-necked flask equipped with a stirrer, a Wiggle fractionating tube and a gas introducing tube, 42.5 g (0.360 mol) of succinic acid and 8.1 g (0.040 mol) of sebacic acid were prepared. And acetic acid first
0.028 g (4.0 × 10 ⁻⁴ mol) of tin was added and immersed in an oil bath. The temperature of this oil bath was raised to 200 ° C., nitrogen was slowly poured into the melt, the esterification reaction was carried out at a temperature of 200 ° C. for 3 hours, and the produced water and excess ethylene glycol were distilled off. Then, tetra-n-butyl titanate
By adding 0.14 g (4.0 × 10 ⁻⁴ mol) and heating at 200 ° C. under nitrogen under reduced pressure of 1 mmHg or less for 4 hours,
60.9 g of a viscous polymer liquid was obtained.

The polymer thus obtained (aliphatic polyester having polyethylene succinate as a main constituent unit) had an OH value of 0.135 meq / g and a COOH value of 0.008 meq / g. ， This polymer has hydroxyl groups at both ends, Mn is 1.4 × 10 ⁴
Met. Further, ηsp / c was 0.60 (concentration: 0.5 g / deciliter, 30 ° C, in chloroform), and the melting point was 92 ° C.

Then, 0.84 g of 1,2-, 3,4-butanetetracarboxylic dianhydride was added to the above polymer at a temperature of 200 ° C. [4.11 × 10 ^-3 mol, carboxylic anhydride Substance / OH = 1.0 (equivalent ratio)], and heated at 210 ° C. under reduced pressure of 1 mmHg or less for 1 hour to obtain a target polymer (high molecular weight aliphatic polyester). Ηsp / c of this polymer is 0.91 (concentration 0.5 g / deciliter, 30 ° C, in chloroform), melting point is 91 ° C.
Met.

Reference Examples 1 to 5 The polymers obtained in Examples 1 to 5 were melt-pressed using a hot press machine at a temperature 20 to 30 ° C. higher than their melting points to easily produce a film having a thickness of 50 μm. I was able to. Cut this film into 5 cm x 5 cm and embed it in the soil (5 to 10 cm in the garden of the private house, surface layer).
The state of the film after 3 months and 6 months was examined and biodegradability was evaluated. The results are shown in Table 1.

As a comparative example, commercially available polyethylene film and polyester film (both having a thickness of 50 μm) are used.
Thickness), but no change in appearance or film strength was observed.

[0043]

[Table 1]

From Table 1, it is clear that the high molecular weight aliphatic polyester produced by the method of the present invention has excellent biodegradability.

[0045]

EFFECT OF THE INVENTION According to the present invention, a high molecular weight aliphatic polyester having an increased molecular weight while maintaining a melting point of 80 ° C. or higher which can be used as a molded article without degrading the original property of biodegradability is provided. Can be easily obtained. The high molecular weight aliphatic polyester thus obtained is
Since it has sufficient biodegradability and excellent moldability, it can be used as a biodegradable film, fiber, sheet or processed into various shapes for use.

Claims (1)

[Claims] 1. An aliphatic polyester mainly having polyethylene succinate as a main constituent unit having hydroxyl groups at both ends and having a number average molecular weight of 10,000 or more as determined by an end group titration method, and tetracarboxylic dianhydride. A process for producing a high molecular weight aliphatic polyester, which comprises reacting a product with a product.