JP3417671B2 - Improved novel degradable polyesters, their production method and products - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a novel degradable polyester which can be used for fibers, films, containers, etc. and has versatility and improved toughness, decomposability, gas barrier property, heat resistance and dyeability. The manufacturing method is related.

[0002]

2. Description of the Related Art In recent years, biodegradable polymers that are decomposed by microorganisms and / or hydrolyzable polymers that are hydrolyzed in a neutral environment have received great attention from the viewpoint of environmental protection. For example,
Polyhydroxybutyrate (hereinafter referred to as PHB) and polycaprolactone (hereinafter referred to as PCL) are known as melt-moldable biodegradable polymers. Not only is the manufacturing cost of PHB too high, but also the moldability and the transparency of the molded product are poor, and the melting point of PCL is too low at 60 ° C., which is a serious problem and obstacle in practical use.

Polylactic acid is relatively inexpensive and has a melting point of 1
It is a thermoplastic resin having a sufficient heat resistance of 78 ° C., and is expected to be a biodegradable polymer that is melt-moldable and is excellent in practical use. However, polylactic acid still has some drawbacks to be improved, and the improvement is desired. The first point to be improved is that the homopolymer of polylactic acid is too high in crystallinity, the molded product is not sufficient, and it is brittle and has low impact strength.
The second point to be improved is that the decomposition rate is considerably low, and it may be unsuitable for applications requiring a high decomposition rate. The third point is that the gas barrier property is low, and the fourth point is poor dyeability. It is a point.

[0004]

The present inventors have arrived at the present invention as a result of intensive studies. That is, the first object of the present invention is to provide a novel degradable polyester having improved decomposition rate, impact strength, gas barrier property and / or dyeability, and a second object is the effect of the novel polyester. To provide a general manufacturing method.

[0005]

The present invention provides L and / or D
A degradable polyester containing lactic acid as a main component, which is obtained by copolymerizing 0.5 to 20% by weight of a sulfonic acid group-containing ester-forming compound represented by the following formula (I) or (II) with respect to the entire polymer, and having a molecular weight: Is a novel decomposable copolyester having a melting point of 200 ° C. comprising a sulfonic acid group-containing ester-forming compound represented by the following formula (I) or (II): The following polyesters or oligomers thereof and L and / or D lactic acid,
Alternatively, it is characterized by reacting with L and / or D lactide.

[0006]

[Chemical 3]

[0007]

[Chemical 4]

Specific examples of the compound represented by the above general formula (I) include 5-sodium sulfoisophthalic acid, 5-sodium sulfoisophthalic acid dimethyl ester, 5-potassium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid dimethyl ester, 5-Potassium sulfoisophthalic acid diethyl ester, 5-lithium sulfoisophthalic acid, 5-lithium sulfoisophthalic acid dimethyl ester, 2-sodium sulfoterephthalic acid or other metal sulfonated benzenedicarboxylic acid or its lower alkyl ester; 4-sodium Sulfo-2,6-naphthalenedicarboxylic acid, 4-sodium sulfo-2,6-naphthalenedicarboxylic acid dimethyl ester, 4-sodium sulfo-1,4-naphthalenedicarboxylic acid, 5-sodium sulfo-1,4 And metal sulfonated naphthalene dicarboxylic acid or a lower alcohol kills esters such as naphthalene dicarboxylate acid.

Specific examples of the compound represented by the general formula (II) include 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt, 3,5-dicarboxybenzenesulfonic acid ethyltributylphosphonium salt and 3,5-
Benzyltributylphosphonium dicarboxybenzenesulfonate, 3,5-dicarboxybenzenesulfonic acid phenyltributylphosphonium salt, 3,5-dicarboxybenzenesulfonic acid tetraphenylphosphonium salt, 3,5-dicarboxybenzenesulfonic acid butyltriphenyl Phosphonium salt, 3,5-dicarboxybenzenesulfonic acid benzyltriphenylphosphonium salt,
3,5-Dicarbomethoxybenzenesulfonic acid tetrabutylphosphonium salt, 3,5-dicarbomethoxyoxybenzenesulfonic acid ethyltributylphosphonium salt, 3
-Carboxybenzene sulfonic acid tetraphenylphosphonium salt and the like.

The sulfonic acid-containing compound contained in the polyester may be only one kind or two or more kinds. Preferably, the sulfonic acid-containing compound is 5-sulfoisophthalic acid, 5-sulfoterephthalic acid and alkali metal (for example, potassium, sodium, lithium or ammonium or alkylphosphonium) salts thereof, and more preferably both of them. It is a product obtained by esterifying a terminal carboxyl group with a lower diol such as ethylene glycol or polypropylene glycol.

In the present invention, the weight ratio of the sulfoisophthalic acid component in the copolymer is calculated by formulating the sulfoisophthalic acid component as the formula C ₈ H ₃ O ₆ S ₁ (molecular weight 237). For example, if there are two sulfoisophthalic acid components in one molecule of a polymer having a molecular weight of 90,000, the ratio of the sulfoisophthalic acid component in the polymer is 0.5%.

The polylactic acid copolymer of the present invention contains L and / or D lactic acid as a main component. That is, usually 50% by weight or more, preferably 60 to 97% by weight, and most preferably 70 to 95% by weight of the copolymer of the present invention is composed of L and / or D lactic acid components. The lactic acid component includes those derived from L lactic acid, D lactic acid and a mixture of L / D lactic acid. However, L / D copolymers generally have low crystallinity and heat resistance, and therefore, polymers of any optically active monomer. Is preferred. When the L-form is predominant, the L-form is usually 80% or more (D-form 20% or less), preferably 90% or more, and more preferably 95% or more. Similarly, when the D-form is mainly contained, the D-form is usually 80% or more, preferably 90% or more, and more preferably 9% or more.
It is desirable to be 5% or more.

The polylactic acid copolymer of the present invention contains lactic acid as a main component and a sulfoisophthalic acid component as another copolymerization component, and further contains other polyethylene glycol, propylene glycol, butanediol as a third component, etc. A diol compound such as known diols such as hexanediol, octanediol, decanediol, cyclohexanedimethanol, diethylene glycol, and triethylene glycol may be used.

In particular, a straight-chain diol having a carbon number of 6 or more may contain a branched chain, but if the crystal structure of the fiber is disturbed too much, the strength and heat resistance of the obtained fiber will be deteriorated. The size of the branched chain is preferably 3 or less, and preferably 2 or less.

Further, since the strength and heat resistance of the obtained fiber are deteriorated when the carbon number of the linear diol is too large, the linear carbon number is preferably at most 15, and more preferably at most 12. Further, the carbon chain may contain an unsaturated bond.

Examples of the dicarboxylic acid which can be used in the present invention include succinic acid, adipic acid, sebacic acid, decanedicarboxylic acid, terephthalic acid and isophthalic acid.

In particular, the bifunctional carboxylic acid component having 6 or more carbon atoms may contain a branched chain as long as the linear carbon number is 6 or more, but if the crystal structure of the fiber is disturbed too much. Since the strength and heat resistance of the obtained fiber are deteriorated, the size of the branched chain is preferably 3 or less, and the number of carbon atoms is preferably 2 or less.

Further, since the strength and heat resistance of the obtained fiber are lowered even if the number of linear carbon atoms is too large, the number of linear carbon atoms is preferably at most 15, and more preferably at most 12.

Examples of such a bifunctional carboxylic acid component include
There are saturated aliphatic dicarboxylic acids such as adipic acid, azelaic acid and sebacic acid, and unsaturated aliphatic dicarboxylic acids such as fumaric acid and citraconic acid.

Further, cyclic carboxylic acids such as caprolactone, hyvalolactone and octanolactone can be used.

Copolymerization of sulfoisophthalic acid with polylactic acid in an amount of 0.5% by weight or more is rather difficult.
That is, the sulfonic acid group (particularly metal salt) is hygroscopic and has a high water content, and when water is mixed into the polylactic acid polymerization system, the resulting polymer is hydrolyzed and a high degree of polymerization cannot be obtained. However, the prepolymer (containing a small amount of water) having a sulfonic acid group obtained by previously reacting another aliphatic polyester-forming component having relatively high stability with sulfoisophthalic acid in a sufficiently dehydrated (vacuum) state ( When the oligomer or polymer) is reacted with the polylactic acid polymerization raw material, the copolymerization is relatively easy. In the case of this method, it is preferred that both ends or one of the ends of the prepolymer molecule having a sulfonic acid group is a hydroxyl group. Therefore, when synthesizing a prepolymer having a sulfonic acid group by an esterification reaction, it is desirable that the molar ratio of the carboxyl group and the hydroxyl group is equimolar or the hydroxyl group is excessive by about 0.1 to 30%.

The prepolymer having a sulfonic acid group and the polylactic acid raw material can be polymerized even in a solvent, but melt polymerization is most efficient. In the case of melt polymerization, polylactic acid is 22
Polymerization occurs at a temperature of about 0 ° C or lower (decomposition reaction is promoted at too high a temperature). Therefore, the melting point of the prepolymer is 220 ° C.
The following is preferable, and 200 ° C. or less is more preferable.

The prepolymer having a sulfonic acid group is obtained by esterifying a sulfonic acid group-containing ester-forming compound represented by the above formula (I) or (II) with a lower diol such as ethylene glycol, propylene glycol or diethylene glycol. Alternatively, it can be obtained by condensing the esterified product. For example, one having the smallest molecular weight is one obtained by reacting two molecules of a diol with one molecule of a sulfonic acid-containing compound, and examples thereof include bishydroxyethylsulfoisophthalate, bishydroxybutylsulfoisophthalate, and bishydroxyhexylsulfoisophthalate. If sufficiently dehydrated, it can be reacted with lactic acid or lactide.

The reaction of 2 molecules of the sulfonic acid group-containing compound with 3 molecules of the diol is an oligomer, which is an example of the above prepolymer. The number average molecular weight of the prepolymer is 700 to 30,000, especially 1,000 to 20,000.
Is preferred. The weight ratio of the sulfonic acid group-containing compound in the prepolymer is usually 10 to 80%, particularly preferably 30 to 60%.

For example, when lactide is polymerized by the hydroxyl groups at both ends of a prepolymer having a molecular weight of 10,000 and a sulfonic acid group-containing compound of 40% as polymerization initiation points, the molecular weight of the polylactide (polylactic acid) portion is 80,000 each. Then, the total molecular weight is 170,000, and the content of the sulfonic acid group-containing compound is 2.4% by weight. Similarly, when the molecular weight of the polylactide portion is 40,000, the total molecular weight is 90,000 and the content of the sulfonic acid group-containing compound is 4.4% by weight.

The copolymer of the present invention is obtained by reacting lactic acid and / or lactide with a compound having a sulfonic acid group-containing compound and having two ester bond-forming functional groups (hydroxyl group and carboxyl group) per molecule. It can be manufactured.
As described above, a prepolymer obtained by reacting sulfoisophthalic acid with another polyester-forming raw material is particularly preferable as the compound having a sulfonic acid group-containing compound and a functional group capable of forming an ester bond. In order to obtain a polymer having a larger molecular weight, a small amount (1% or less) of trifunctional components (glycerin, hydroxyglycylic acid, benzenetriol, etc.) and tricarboxylic acid trimeric acid, etc. Compound) can also be added.

The polymerization reaction may be either a melting method or a solvent method using a solvent, but the melting polymerization method is often excellent in terms of safety and efficiency.

As the polymerization apparatus, a batch-type or continuous-type reaction vessel capable of heating, stirring, vacuum, etc. can be used. As a method for polymerizing polylactic acid, in the case of heating polymerization of lactide, a twin-screw kneading extruder with a vent capable of effectively heating, stirring, and feeding the reactants and reducing the pressure is excellent. It can also be connected in series.

As the catalyst used for the polymerization reaction, those used for the polymerization of lactic acid and lactide and the polymerization of polyester can be used. For example, as the transesterification catalyst, alcoholates of Na and Mg with various alcohols, fatty acid salts and carbon salts such as Zn, Cd, Mn, Co, Ca and Ba, sulfates, phosphates Mg, Pb and Zu, S
There are oxides, hydroxides, halides, etc. of b, Ge, etc., but they are selected taking into consideration not only the catalytic function but also coloring, side reaction, or formation of aggregated foreign matter in the product. The amount of the catalyst is usually 10 ⁻³ to 10 ⁻⁶ mol / mol with respect to the amount of the ester, but is appropriately selected depending on the temperature and the reaction system. As the polyester polymerization catalyst, usual catalysts such as antimony trioxide and germanium oxide can be used. It is well known that zinc oxide or the like is used in the reaction to obtain lactide from lactic acid, and tetraphenyl tin, stannous chloride, diethyl zinc, tin octylate or the like is used in the polymerization reaction of lactide. As a matter of course, those other than the above can be used as long as they are excellent ones having a high reaction rate and little coloring or side reaction.

By introducing a sulfonic acid group-containing ester-forming compound into polylactic acid by incorporating a sulfoisophthalic acid component (and other polyester-forming components associated therewith) by a copolymerization method, the crystallinity is lowered and fragility is caused. Is reduced,
Impact strength increases. The sulfoisophthalic acid component has a large strain in the molecular chain, so that a relatively small amount of copolymerization, for example, 2 to
A sufficient effect can be obtained at 20% by weight.

Further, an important change in physical properties due to the introduction of a sulfonic acid group-containing ester-forming compound is an increase in decomposition rate. The decomposition rate also occurs when the crystallinity decreases due to the copolymerization, but it is presumed that the effect of the hydrophilicity of the sulfonic acid group is particularly large. In all cases, the alkali metal salt (sodium salt, potassium salt, etc.) is more effective than the sulfonic acid group alone. The third effect of introducing the ester-forming compound containing a sulfonic acid group is to increase the gas barrier property of the polymer. The gas barrier property is the ability to prevent passage of oxygen, water vapor, carbon dioxide gas, etc. when formed into a film or a container (bottle etc.), and is particularly important for applications such as food packaging and containers. Polylactic acid is superior to polyolefins in gas barrier properties, but inferior to polyamides and the like, and its improvement has been desired. However, introduction of a sulfonic acid group provides a considerable improvement effect.

The fourth effect of introducing a sulfonic acid group-containing ester-forming compound is improvement in dyeability. Although polylactic acid can be dyed with a disperse dye, it is inferior in dyeing fastness (dye friction and migration phenomenon of dye by heating), and improvement has been desired for clothing and non-clothing fibers. By introducing a sulfonic acid group, clear dyeing with a basic dye is possible and dyeing fastness is improved.

In order to obtain the above effects, it is more effective that the sulfonic acid group-containing ester-forming compound of the polymer has a larger sulfonic acid group content. On the other hand, however, the introduction of a sulfonic acid group causes a decrease in crystallinity and a decrease in heat resistance, so it is desirable to select a balanced sulfonic acid group content according to the purpose and application. Generally, the weight fraction of the sulfonic acid group-containing ester-forming compound with respect to the entire polymer is preferably 1 to 20%, particularly preferably 2 to 15%.
In most cases, 3 to 10% is most preferable.

The molecular weight of the copolymer of the present invention must be 50,000 or more. When the molecular weight is 50,000 or less, the strength of the fiber, film or molded product is insufficient. The molecular weight is preferably 60,000 to 300,000, more preferably 80,000 to 200,000. Since the melt viscosity is increased by introducing a sulfonic acid group, a polylactic acid having a relatively low molecular weight (50,000 to 80,000) can also be used.

The copolymerized polyester of the present invention contains, if necessary, antioxidants, ultraviolet absorbers, lubricants, pigments, colorants, inorganic particles, antistatic agents, release agents, and other well-known organic and inorganic substances. Additives and fillers can be mixed and mixed.

As examples of antioxidants added during or after polymerization, Ciba-Gaiki's "Irganox" series for hindered phenols, "Tinuvin" series for hindered amines, and Benzotriazole-based UV absorbers There are "Tinuvin" series and "Irgafos" series which is a mixture of them and phosphite stabilizer. Similarly, Sumitomo Chemical Co., Ltd.'s phenolic antioxidants include "Sumilyzer" series, and light stabilizers include "Sumisorb". Antioxidants other than those mentioned above include thioether-based ones, and it is often preferable to use two or more of the above stabilizers in combination. Further, from the viewpoint of heat resistance, those having a large molecular weight and a high boiling point or sublimation temperature are preferable. For example, the molecular weight is 50
0 or more is preferable and 700 or more is the most preferable. The aforementioned Irganox 1010 (molecular weight 1178) is the most preferred example. Further, as the antioxidant and the ultraviolet absorber, safe ones which are not toxic or skin irritation are preferable.

In the present invention, the average molecular weight of the polymer is the polymer (molecular weight 100) obtained by GPC analysis of a 0.1% solution of chloroform in the sample (calibrated by polystyrene standard sample).
(Excluding those of 0 or less). The molecular weight of the prepolymer is the number average value excluding the monomers.

In the present invention, the melting points of the polymers and prepolymers are the melting points of the main crystals when measured by the differential calorimetry (DSC) method of a sample which has been sufficiently heat-treated and crystallized (heating rate 10 ° C./min). The endothermic peak value is used.

In the present invention, parts and% are parts by weight and% by weight, unless otherwise specified.

The copolymer of the present invention can be melted, dry, wet,
Fibers can be formed by a well-known spinning method such as dry and wet, and if necessary, stretching, heat treatment, crimping, etc. are performed. In particular, melt spinning is preferable because it can be performed at high speed and high efficiency. Furthermore, a partially oriented yarn (POY) can be obtained by increasing the spinning speed to 3,000 m / min or more.
A highly oriented yarn (HOY) can also be obtained by setting m / min or more.

Similarly, the copolymer of the present invention can be formed into a film by a melt extrusion method or the like, and if necessary, stretched and heat-treated to produce a sheet or a film. Similarly, the copolyester of the present invention can be manufactured into various molded products by a melt extrusion method or an injection molding method.

[0042]

EXAMPLES In the following examples, the strength deterioration test of fibers was conducted as follows. Sample fiber is 150 denier / 4
A continuous filament of 8 filaments (single yarn 3.1 denier), a rectangular frame made by bending a stainless steel rod with a diameter of 6 mm, and wound at a distance of 10 cm in a tension state (tension 20 mg / d). Attach and fix. Samples to be compared and contrasted are similarly wound next to each other with a distance of 1 cm. Attach the stainless steel frame with the sample (thread) to the fertile field soil under neutral (PH 6.5-7.0) under agricultural gauze,
It is buried horizontally at a depth of 10 cm. Care should be taken that the soil does not become excessively dry or moist, and the temperature is kept within the range of 25 ° C ± 5 ° C.

A sample is taken out at a predetermined time, for example, every one week or every one month, washed with water and naturally dried, and then three single fibers are taken out from each sample, and a tensile test is performed with a single yarn. The length of the sample is 5 cm, the pulling speed is 5 cm / min, the cutting strength is determined, and the average value of 10 measurements is used as a representative value.
The temperature of the tensile test room is 20 ° C. and the humidity is 65% RH. From the relationship curve between the burial time and the cutting strength of the sample, the time at which the strength becomes 1/2 of the initial (non-deteriorated) value is obtained, and is defined as the half-life. The smaller the half-life, the faster the rate of deterioration (decomposition).

Example 1 Bishydroxyethyl sulfoisophthalic acid sodium salt, bishydroxyethyl isophthalic acid and bishydroxyethyl adipic acid were added in a molar ratio of 2.10 / 1.00 /.
The mixture was mixed at 1.00 and reacted at 260 ° C. for 1 hour under normal pressure, and further gradually reduced in pressure for 15 minutes to reach a vacuum degree of 0.1 Torr and maintained for 17 minutes to obtain a prepolymer PP1. P
The average molecular weight of P1 is about 9000, and the melting point cannot be confirmed because of low crystallinity, and the content of the sulfoisophthalic acid component is about 51%. 18 parts of L-lactide was melt-mixed with 1,1 parts of PP, and 0.3% of dioctyltin was added as a polymerization catalyst, and the mixture was stirred with a biaxial kneader to 190
After polymerizing at 35 ° C. for 35 minutes, it was extruded through a nozzle having a diameter of 2 mm, cooled with water, and then cut to obtain a chip C1. C
1 was centrifugally dehydrated and then vacuum dried at 80 ° C. for 48 hours at 0.1 Torr or less to remove water and residual monomer (lactide) to obtain a copolymer P1. P1 has a molecular weight of 155,0
00, melting point 173 ° C., content rate (copolymerization rate) of sulfoisophthalic acid component is 3%. For comparison, polylactic acid (homopolymer) P2 was obtained by polymerizing only L-lactide with 0.3% of the dissolvable dioctyltin and polymerizing into chips in the same manner as P1. P2 has a molecular weight of 162,000 and a melting point of 175 ° C.

The copolymer P1 was melted by a screw extruder at 200 ° C., spun out from an orifice having a pore size of 0.2 mm and a temperature of 190 ° C., cooled in air and oiled to 800 m.
The undrawn yarn UDY1 was obtained by winding at a speed of m / min.
UDY1 was drawn at a temperature of 70 ° C. and a draw ratio of 4.2 times, and heat-treated under tension at 120 ° C. to obtain a drawn yarn DY1 having 150 denier / 48 filaments. The strength of DY1 is 4.4 g /
d and the elongation was 29.3%. Also, the polymer P2 is 19
Spun at 5 ° C, stretched and heat treated in the same manner as P1, stretched yarn D
Y2 was obtained. DY2 has a strength of 3.2 d / d and an elongation of 25.
It was 6%.

The yarns DY1 and DY2 were buried in soil and a deterioration test was conducted. As a result, the half-life of strength deterioration of DY1 according to the present invention was 2.1 months. On the other hand, the yarn DY2 (comparative example) made of unmodified polylactic acid has a half-life of 7.6 months, and a yarn DY obtained by copolymerizing 3% of a sulfoisophthalic acid component.
The degradation rate of 1 is about 3.6 times that of native yarn DY2.

A circular knitted material knitted with the yarn DY1 is mixed with a basic dye.
A dyeing solution was prepared by a conventional method using Kayacrl Blue 2RL-ED 5.0% owf, the temperature was raised from 25 ° C to 95 ° C in 30 minutes at a bath ratio of 50, and further dyeing was performed at 95 ° C for 30 minutes. . The dye exhaustion rate is 94.7% and the dyeing is clear. After washing with water and drying, the dyeing fastness is measured. As a result, discoloration and liquid contamination are 4 to 5 grade and sufficient fastness is found. Was. For comparison, yarn DY2 was similarly used for basic dyeing, but the dye exhaustion rate was only 10.5%, which was merely contaminated. Next is the disperse dye Miketon Polyes
A dyeing solution was prepared by a conventional method using ter Blue 2.5% owf, and the temperature was raised from 25 ° C. to 95 ° C. in 30 minutes at a bath ratio of 50 times, and dyeing was performed at 95 ° C. for 30 minutes. Dyeing rate is 25.0
%, The color is light, and the dyeing fastness is 1 to 2 which is a fading color when washed.
It was inferior in class.

[0048]

The copolymer of the present invention has a high decomposition rate and excellent gas barrier properties as compared with unmodified polylactic acid. Excellent impact strength. It has various features such as excellent dyeability and can be widely applied to fibers, films , and molded products. A high decomposition rate means that decomposition is required at an early stage.For example, packaging films and other single-use applications, excellent gas barrier properties are excellent for food packaging films and food containers, and excellent impact strength is excellent for various molded product applications. The dyeability is suitable for textile applications for clothing and non-clothing. The method for producing a copolyester according to the present invention makes it possible to produce a copolymer having the above-mentioned various features relatively easily and at low cost.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Fujii, No. 1 Kuwabara-cho, Nishinokyo, Nakagyo-ku, Kyoto, Shimadzu Corporation Sanjo Factory (56) Reference JP-A-1-225622 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C08G 63/00-63/91 D01F 6/62-6/92 D01F 8/14 WPI / L (QUESTEL)

Claims (9)

(57) [Claims] 1. A degradable polyester containing L and / or D lactic acid as a main component, wherein 0.5 parts by weight of a sulfonic acid group-containing ester forming compound represented by the following formula (I) or (II) is added to the whole polymer. A novel degradable copolyester characterized by being copolymerized in an amount of up to 20% by weight and having a molecular weight of 50,000 or more. [Chemical 1] [Chemical 2] 2. The copolymerized polyester according to claim 1, wherein the ester-forming compound containing a sulfonic acid group is copolymerized in an amount of 1 to 15% by weight with respect to the entire polymer, and the molecular weight is 60,000 to 300,000. 3. The copolyester according to claim 1, wherein the sulfonic acid group of the ester-forming compound is an alkali metal salt. 4. A block-based copolymerization of a segment containing L and / or D lactic acid as a main component and a segment having a sulfonic acid group-containing ester-forming compound. The copolyester according to any one of 1. 5. A melting point of 2 consisting of a sulfonic acid group-containing ester-forming compound represented by the above formula (I) and / or (II).
A process for producing a novel degradable copolyester, which comprises reacting a polyester or an oligomer thereof at 00 ° C. or lower with L and / or D lactic acid or L and / or D lactide. 6. The method for producing a copolymerized polyester according to claim 5, wherein the polyester or oligomer is polyacylenesulfoisophthalate, a copolymer thereof, or an oligomer thereof. 7. Fibers part or entirely composed of copolymerized polyester according to any one of claims 1 to 4. 8. A part or all of any one of claims 1 to 4.
A film comprising the copolymerized polyester according to 1. 9. A part or all of any one of claims 1 to 4.
A molded article comprising the copolyester according to 1.