Polyester composition

Abstract

The purpose of the present invention is to provide a polyester composition which has hydrolysis resistance and retains high restorability as a single polyester. The present invention provides a polyester composition which contains a polyester copolymer and a carbodiimide compound, has a restoration rate of 10-100%, and contains 0.3-20.0 parts by weight of the carbodiimide compound per 100 parts by weight of the polyester copolymer.

Description

Polyester composition

[0001] The present invention relates to a polyester composition.

[0002] Polyesters are used in a variety of fields, including automotive parts, electronic components, fibers, paints, and medical devices. The ester bonds that make up polyesters are susceptible to hydrolysis depending on the usage environment, posing a problem of degradation over long-term use. To address this problem, a method of incorporating a carbodiimide compound into polyester is known as a method of suppressing hydrolysis (Patent Documents 1 to 3). Furthermore, biodegradable polyesters require sterilization when used in medical applications. A method of incorporating a carbodiimide compound into biodegradable polyester is known as a method of preventing a decrease in strength and impact resistance due to ionizing radiation sterilization (Patent Document 4). Carbodiimide compounds apparently suppress hydrolysis by rebonding molecular chains that have been hydrolyzed.

[0003] Japanese Patent Publication No. 2021-143439 Japanese Patent No. 7213218 Japanese Patent No. 6111079 International Publication No. 2009 / 119512

[0004] When biodegradable polyesters are used in medical applications, they are required to have high recovery properties so that they can follow the movements of a living body. Patent Documents 1 to 4 mention the improvement of hydrolysis resistance, i.e., the suppression of molecular weight reduction, by adding a carbodiimide compound, but do not disclose the effect on the recovery properties of polyesters.

[0005] Therefore, an object of the present invention is to provide a polyester composition which has hydrolysis resistance and maintains high recovery properties of the polyester itself.

[0006] The present invention to solve the above problems includes the following [1] to

[13] . [1] A polyester composition containing a polyester copolymer and a carbodiimide compound, having a recovery rate of 10% to 100%, and containing the carbodiimide compound in an amount of 0.3 parts by weight to 20.0 parts by weight per 100 parts by weight of the polyester copolymer. [2] The polyester composition according to [1], wherein the carbodiimide compound has an n-octanol / water partition coefficient of 3.0 to 15.0. [3] The polyester composition according to [1] or [2], wherein the carbodiimide compound is an aliphatic polycarbodiimide, an aromatic polycarbodiimide, or an aromatic monocarbodiimide. [4] The polyester composition according to [1] or [2], wherein the carbodiimide compound is poly(cyclohexylenecarbodiimide), poly(trimethylcyclohexylcarbodiimide), poly(triisopropylphenylenecarbodiimide), dicyclohexylcarbodiimide, bis(2,6-diisopropylphenyl)carbodiimide, or bis(diphenylcyclocarbodiimide). [5] A polyester composition comprising a polyester copolymer and a carbodiimide compound, wherein the composition is molded into a film having a thickness of 0.3 mm, a width of 1.0 cm, and a length of 1.0 cm, and the film satisfies the following formula (1): X / Y>10.0...formula (1) [In formula (1), X represents the mass % of nitrogen atoms when the elemental composition (atomic %) on the surface of the film, as measured by X-ray photoelectron spectroscopy, is converted to mass %, and Y represents the mass % of nitrogen atoms, as measured using an elemental analyzer, when the mass of the film is taken as 100%. [6] A polyester composition containing a polyester copolymer and a carbodiimide compound, wherein the polyester composition has an organic nitrogen peak intensity of more than 18.0 when the intensity of the entire spectrum measured by time-of-flight secondary ion mass spectrometry is set to 100. [7] The polyester composition according to any one of [1] to [6], wherein the polyester copolymer is a copolymer having hydroxycarboxylic acid as a main structural unit. [8] The polyester composition according to any one of [1] to [7], wherein the polyester copolymer has a weight average molecular weight of 120,000 or more.[9] A molded article comprising the polyester composition according to any one of [1] to [8].

[10] A medical device comprising the polyester composition according to any one of [1] to [8].

[11] The medical device according to

[10] , which is an implant medical device.

[12] The medical device according to

[11] , which is a suture, an artificial bone, an artificial skin, a wound dressing, a carrier for a DDS, a microneedle, a stent, or a scaffold material for tissue or organ regeneration.

[13] A method for regenerating biological tissue, which uses the polyester composition according to any one of [1] to [8] as a scaffold material for tissue or organ regeneration.

[0007] The present invention also includes the following items

[14] to

[23] .

[14] A polyester composition containing a polyester copolymer and a carbodiimide compound (excluding diisopropylcarbodiimide and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride), wherein the carbodiimide compound is contained in an amount of 0.3 parts by weight to 20.0 parts by weight per 100 parts by weight of the polyester copolymer.

[15] The polyester composition according to item

[14] , wherein the polyester copolymer is a copolymer having a hydroxycarboxylic acid as a main structural unit.

[16] The polyester composition according to item

[14] or

[15] , wherein the carbodiimide compound is an aliphatic polycarbodiimide, an aromatic polycarbodiimide, or an aromatic monocarbodiimide.

[17] The polyester composition according to any one of

[14] to

[16] , wherein the carbodiimide compound is poly(cyclohexylenecarbodiimide), poly(triisopropylphenylenecarbodiimide), or bis(2,6-diisopropylphenyl)carbodiimide.

[18] The polyester composition according to any one of

[14] to

[17] , wherein the weight-average molecular weight of the polyester copolymer is 120,000 or more.

[19] The polyester composition according to any one of

[14] to

[18] , wherein the composition is molded into a film having a thickness of 0.3 mm, a width of 1.0 cm, and a length of 1.0 cm, and the film satisfies the following formula (A): 0.0≦X / Y≦10.0 ... formula (A) [In formula (A), X represents the mass % of nitrogen atoms when the elemental composition (atomic %) on the surface of the film measured by X-ray photoelectron spectroscopy is converted to mass %, and Y represents the mass % of nitrogen atoms when the mass of the film is taken as 100%, as measured using an elemental analyzer.

[20] The polyester composition according to any one of

[14] to

[18] , wherein the peak intensity of organic nitrogen measured by time-of-flight secondary ion mass spectrometry is more than 0.0 and not more than 18.0, where the intensity of the entire spectrum is taken as 100.

[21] A molded article comprising the polyester composition according to any one of

[14] to

[20] .

[22] A medical device comprising the polyester composition according to any one of

[14] to

[20] .

[23] The medical device according to

[22] , which is an implant medical device.

[0008] The present invention also includes the following items

[24] to

[33] .

[24] A polyester composition containing a polyester copolymer and a carbodiimide compound, wherein a film obtained by molding the composition into a size of 0.3 mm thick x 1.0 cm wide x 1.0 cm long satisfies the following formula (B): X / Y>10.0...formula (B) [In formula (B), X represents the mass % of nitrogen atoms when the elemental composition (atomic %) on the surface of the film is converted to mass % as measured by X-ray photoelectron spectroscopy, and Y represents the mass % of nitrogen atoms when the mass of the film is taken as 100% as measured using an elemental analyzer.]

[25] A polyester composition containing a polyester copolymer and a carbodiimide compound, wherein the peak intensity of organic nitrogen measured by time-of-flight secondary ion mass spectrometry exceeds 18.0 when the intensity of the entire spectrum is taken as 100.

[26] The polyester composition according to

[24] or

[25] , wherein the polyester copolymer is a copolymer having hydroxycarboxylic acid as a main structural unit.

[27] The polyester composition according to any one of

[24] to

[26] , wherein the carbodiimide compound is contained in an amount of 0.3 parts by weight or more and 100.0 parts by weight or less per 100 parts by weight of the polyester copolymer.

[28] The polyester composition according to any one of

[24] to

[27] , wherein the carbodiimide compound is an aromatic polycarbodiimide.

[29] The polyester composition according to any one of

[24] to

[28] , wherein the carbodiimide compound is poly(triisopropylphenylenecarbodiimide).

[30] The polyester composition according to any one of

[24] to

[29] , wherein the polyester copolymer has a weight-average molecular weight of 120,000 or more.

[31] A molded article comprising the polyester composition according to any one of

[24] to

[30] .

[32] A medical device comprising the polyester composition according to any one of

[24] to

[30] .

[33] The medical device according to

[32] , which is an implantable medical device.

[0009] According to the present invention, a polyester composition can be obtained that has hydrolysis resistance and maintains high recovery properties as a polyester alone, and medical devices that have excellent adaptability to the movements of living bodies can be produced.

[0010] The polyester composition of the present invention contains a polyester copolymer and a carbodiimide compound, has a recovery rate of 10% or more and 100% or less, and contains 0.3 parts by weight or more and 20.0 parts by weight or less of the carbodiimide compound per 100 parts by weight of the polyester copolymer.

[0011] <Polyester Copolymer> The polyester copolymer is preferably a copolymer having two types of ester bond-forming monomer residues as main structural units. In this specification, the two types of ester bond-forming monomers may be referred to as “monomer A” and “monomer B,” respectively.

[0012] The term "ester bond-forming monomer" refers to a monomer that, after polymerization, produces a polymer in which the monomer units are linked by ester bonds, i.e., a polyester.

[0013] As the ester bond-forming monomer, a hydroxycarboxylic acid is preferably used. Also preferably used are lactones, which are cyclic compounds formed by intramolecular dehydration condensation of the hydroxy group and the carboxyl group of a hydroxycarboxylic acid, and lactides, which are cyclic compounds formed by dehydration condensation of the hydroxy group and the carboxyl group of two molecules of hydroxycarboxylic acid.

[0014] The hydroxycarboxylic acid is preferably an aliphatic hydroxycarboxylic acid, such as lactic acid, glycolic acid, hydroxybutyric acid, hydroxypentanoic acid, hydroxycaproic acid, hydroxyheptanoic acid, hydroxyoctanoic acid, hydroxynonanoic acid, hydroxydecanoic acid, hydroxyundecanoic acid, hydroxydodecanoic acid, and (2-hydroxyethoxy)acetic acid, and among these, lactic acid, glycolic acid, hydroxypentanoic acid, or hydroxycaproic acid is preferred.

[0015] Although L-lactic acid, D-lactic acid, and mixtures thereof can be used as the lactic acid, it is preferable to use L-lactic acid in terms of the physical properties and biocompatibility of the resulting polymer. When a mixture is used as the monomer, the content of the L-isomer is preferably 85% or more, and more preferably 95% or more.

[0016] Examples of lactones that can be used include caprolactone, dioxepanone, ethylene oxalate, dioxanone, 1,4-dioxane-2,3-dione, β-propiolactone, δ-valerolactone, β-propiolactone, β-butyrolactone, γ-butyrolactone, and pivalolactone.

[0017] As the lactide, dilactide obtained by dehydration condensation of two molecules of lactic acid, glycolide obtained by dehydration condensation of two molecules of glycolic acid, or tetramethyl glycolide can be used.

[0018] As the ester bond-forming monomer, derivatives of the above-exemplified monomers can also be used.

[0019] In this specification, the term "monomer residue" generally refers to a repeating unit of a chemical structure derived from a monomer in the chemical structure of a copolymer obtained by polymerizing two or more monomers including the monomer. For example, lactic acid (CH ３ When a copolymer of lactic acid and caprolactone is prepared by polymerizing lactic acid (CH(OH)COOH) and caprolactone (ε-caprolactone: formula (I) below), the unit represented by formula (R1) below is a lactic acid monomer residue, and the unit represented by formula (R2) below is a caprolactone monomer residue.

[0020]

[0021]

[0022]

[0023] As an exception, when a dimer such as lactide is used as a monomer, the term "monomer residue" refers to one of the two repeating structures derived from the dimer. For example, when dilactide (L-(-)-lactide: formula (II) below) is polymerized with caprolactone, the resulting copolymer has a chemical structure in which the structure shown in formula (R1) above is repeated twice as the dilactide residue.

[0024]

[0025] In this case, one of the lactic acid units is considered to be a "monomer residue", and two "monomer residues", i.e., two lactic acid residues, are considered to have been formed from dilactide.

[0026] "Two types of monomer residues are the "main structural units"" means that the sum of the number of the two types of monomer residues is 50 mol% or more of the total number of residues in the entire polymer including other monomer residues, and the number of each of the two types of monomer residues is 20 mol% or more of the total number of residues in the entire polymer. For example, "monomer A residues and monomer B residues are the main structural units" means that the sum of the number of residues of monomer A residues and monomer B residues is 50 mol% or more of the total number of residues in the entire polymer, the number of residues of monomer A residues is 20 mol% or more of the total number of residues in the entire polymer, and the number of residues of monomer B residues is 20 mol% or more of the total number of residues in the entire polymer.

[0027] Here, the molar fractions of the monomer A residue, the monomer B residue, and other monomer residues can be determined by nuclear magnetic resonance (NMR) measurement from the area values ​​of the signals derived from each residue. For example, when the monomer A residue is a lactic acid residue and the monomer B residue is a caprolactone residue, they can be measured by the method described in Measurement Method 2 below. When the monomer is lactide, the area value of the signal derived from the lactic acid residue is regarded as the area value of the signal derived from the lactide residue, and the molar fraction of the lactic acid residue is regarded as the molar fraction of the lactide residue.

[0028] The sum of the monomer A residues and the monomer B residues, based on the above definition, is 50 mol% or more, preferably 75 mol% or more, and more preferably 90 mol% or more, of the entire polymer including other monomer residues. Also, based on the above definition, the monomer A residues and the monomer B residues each account for 20 mol% or more, preferably 30 mol% or more, and more preferably 40 mol% or more. A polymer in which the sum of the monomer A residues and the monomer B residues accounts for 100% of the entire polymer, i.e., a polymer consisting only of monomer A and monomer B, is a particularly preferred embodiment.

[0029] In the polyester copolymer, the molar ratio of monomer A residues to monomer B residues is preferably 7 / 3 to 3 / 7, more preferably 6 / 4 to 4 / 6, since the presence of an excess of one monomer approaches homopolymer-like properties.

[0030] As long as the effects of the present invention are not impaired, other monomers that can be copolymerized with the two ester bond-forming monomers that constitute the main structural units can also be copolymerized. As such a monomer, other than the above-mentioned ester bond-forming monomers can be used.

[0031] Copolymerization of a monomer that functions as a linker is also a preferred embodiment. Examples of the monomer that functions as a linker include hydroxycarboxylic acids, dialcohols, dicarboxylic acids, amino acids, diamines, diisocyanates, and diepoxides other than the two ester bond-forming monomers that constitute the main structural units.

[0032] In this specification, the term "polyester copolymer" also includes copolymers that contain monomers other than ester bond-forming monomers as constituent units, and thereby contain constituent units that are linked in part by bonds other than ester bonds.

[0033] The polyester copolymer is preferably biodegradable or bioabsorbable. Those skilled in the art can synthesize copolymers that exhibit appropriate biodegradability or bioabsorbability depending on the application by appropriately combining the above-exemplified monomers or adjusting the ratio of the monomers within the range specified in the present invention.

[0034] The polyester copolymer is made by copolymerizing the two aforementioned ester bond-forming monomers in equimolar amounts. The monomer with a relatively high initial polymerization rate is designated as "monomer A" and the monomer with a low initial polymerization rate is designated as "monomer B." The initial polymerization rates when these two monomers are copolymerized in equimolar amounts are V Ａ , V Ｂ When V is Ａ / V Ｂ It is preferable that the value satisfies ≦40.

[0035] Here, V Ａ and V Ｂ can be determined by the following method. Monomer A and monomer B are mixed in equimolar amounts, a solvent and / or a catalyst are added as necessary, and the polymerization reaction is initiated by adjusting conditions such as temperature so that the R value, which will be described later, of the polyester copolymer finally synthesized or to be synthesized falls within an error range of the preferred range of R value, which will be described later. Sampling is performed periodically from the sample during polymerization, and the remaining amounts of monomer A and monomer B are measured. The remaining amounts are measured, for example, by chromatography or nuclear magnetic resonance (NMR) measurement. The amount of monomer used in the polymerization reaction can be determined by subtracting the remaining amount from the charged amount. When the amount of monomer used in the polymerization reaction is plotted against the sampling time, if the initial slope of the curve is V Ａ , V Ｂ is.

[0036] When such a monomer A and a monomer B are reacted, there is a high probability that the monomer A will bond to the end of the polymer during polymerization in the early stage of polymerization. On the other hand, in the later stage of polymerization when the monomer A is consumed and its concentration in the reaction solution decreases, there is a high probability that the monomer B will bond to the end of the polymer during polymerization. As a result, a gradient polymer is obtained in which the proportion of the monomer A residue gradually decreases from one end. Such a gradient polymer has low crystallinity and suppresses the increase in Young's modulus. To facilitate the formation of such a gradient structure, V Ａ / V Ｂ On the other hand, if the difference in the polymerization rate between the monomer A and the monomer B is too large, the resulting structure is similar to a block polymer in which only the monomer A is polymerized and then the monomer B is polymerized, which may result in high crystallinity and an increase in the Young's modulus. Ａ / V Ｂ is more preferably 30 or less, even more preferably 20 or less, and most preferably 10 or less.

[0037] Preferred combinations of such monomer A and monomer B include dilactide and ε-caprolactone, glycolide and ε-caprolactone, glycolide and dilactide, dilactide and dioxepanone, ethylene oxalate and dilactide, dilactide and δ-valerolactone, and glycolide and δ-valerolactone.

[0038] In the present invention, particularly preferred embodiments include a lactic acid residue as the monomer A residue and a caprolactone residue as the monomer B residue.

[0039] (1) R Value When the two types of ester bond-forming monomers described above are defined as "monomer A" and "monomer B," respectively, the polyester copolymer preferably has an R value represented by the following formula of 0.45 or more and 0.99 or less: R Value = [AB] / (2 [A] [B]) x 100 [A]: Molar fraction of monomer A residue in the polyester copolymer [B]: Molar fraction of monomer B residue in the polyester copolymer [AB]: Molar fraction of structures (A-B and B-A) in which monomer A residue and monomer B residue are adjacent to each other in the polyester copolymer

[0040] The R value is used as an index showing the randomness of the arrangement of monomer residues in a copolymer whose main structural units are two types of ester bond-forming monomer residues, i.e., monomer A residue and monomer B residue. For example, a random copolymer in which the monomer arrangement is completely random has an R value of 1. In addition, the R value of a block copolymer is 0 to 0.44.

[0041] The R value can be determined by quantifying the ratio of the combinations of two adjacent monomers (A-A, B-B, A-B, B-A) by nuclear magnetic resonance (NMR) measurement, for example, by the method described in Measurement Method 2 below. If the R value is less than 0.45, the crystallinity is high, and the molded product of the copolymer becomes hard and the Young's modulus increases. On the other hand, if the R value exceeds 0.99, the molded product of the copolymer becomes too soft and sticky, resulting in poor handleability. Therefore, it is more preferable that the R value of the polyester copolymer is 0.50 or more and 0.80 or less.

[0042] (2) Crystallinity It is known that the crystallinity of a polymer has a significant effect on its mechanical strength. Generally, low-crystalline polymers exhibit a low Young's modulus, so low crystallinity is desirable for flexibility. The crystallinity of a polymer can be determined from the heat of fusion by differential scanning calorimetry (DSC) measurement.

[0043] In the polyester copolymer, the crystallinity of at least one of the monomer A residue and the monomer B residue is preferably less than 14%. If the crystallinity is less than 14%, an increase in Young's modulus is suppressed, and the polyester copolymer can be used for medical materials and elastomer applications. The crystallinity of at least one of the monomer A residue and / or the monomer B residue is more preferably 10% or less, and even more preferably 5% or less.

[0044] The crystallization ratio of a monomer residue referred to here is the ratio of the heat of fusion per unit weight of a monomer residue in a polyester copolymer to the product of the heat of fusion per unit weight of a homopolymer consisting of only a certain monomer residue and the weight fraction of that monomer residue in the polyester copolymer. In other words, the crystallization ratio of a monomer A residue is the ratio of the heat of fusion per unit weight of a monomer A residue in a polyester copolymer to the product of the heat of fusion per unit weight of a homopolymer consisting of only monomer A and the weight fraction of the monomer A residue in the polyester copolymer. The crystallization ratios of the monomer A residue and the monomer B residue indicate the proportions of the monomer A residue and the monomer B residue that form a crystalline structure in the polyester copolymer, respectively. When the monomer is lactide, the lactic acid residue is considered to be the lactide residue.

[0045] In particular, when the monomer A residue is a lactic acid residue and the monomer B residue is a caprolactone residue, the crystallinity of the lactic acid residue is preferably less than 14%, more preferably 10% or less. The crystallinity can be determined, for example, by the method described in Measurement Method 3 below.

[0046] The weight-average molecular weight of the polyester copolymer of the present invention is preferably 60,000 or more in order to obtain the effect of improving tensile strength due to entanglement of polymer chains. However, if the weight-average molecular weight of the polyester copolymer is too low, the recovery rate will be low, so the weight-average molecular weight of the polyester copolymer is more preferably 120,000 or more, even more preferably 200,000 or more, and most preferably 250,000 or more. On the other hand, if the weight-average molecular weight is too high, the melt viscosity will be high, making extrusion molding difficult in either case. Therefore, from the viewpoint of handling during extrusion molding, the weight-average molecular weight of the polyester copolymer is preferably 500,000 or less, more preferably 400,000 or less, and even more preferably 300,000 or less.

[0047] The weight average molecular weight can be determined by gel permeation chromatography (GPC), for example, by the method described in Measurement Method 1 below.

[0048] <Method for Producing Polyester Copolymer> As an example, a polyester copolymer can be produced by a production method comprising: a macromer synthesis step of blending and polymerizing two types of ester bond-forming monomers, namely, Monomer A and Monomer B, so that the sum of Monomer A residues and Monomer B residues accounts for 50 mol % or more of all residues and Monomer A residues and Monomer B residues each account for 20 mol % or more of all residues at the completion of polymerization; and a multiplication step of linking the macromers obtained in the macromer synthesis step to each other or by adding Monomer A and Monomer B to the macromer solution obtained in the macromer synthesis step to produce a multimer.

[0049] [Macromer Synthesis Step] In the macromer synthesis step, monomer A and monomer B are blended and polymerized so that, theoretically, at the completion of polymerization, the sum of monomer A residues and monomer B residues will account for 50 mol % or more of all residues, and monomer A residues and monomer B residues will each account for 20 mol % or more of all residues. This produces a polyester copolymer having monomer A residues and monomer B residues as main structural units, but because this production method further includes a multi-component synthesis step, which will be described later, the polyester copolymer produced by this step will be referred to as a "macromer" in this specification.

[0050] As the ester bond-forming monomer, the same ones as those described above can be used, and the preferred combinations etc. are also as described above.

[0051] The randomness of the distribution of monomer residues constituting a polyester copolymer whose main structural units are two types of ester bond-forming monomer residues varies depending on the reactivity of the monomers during polymerization. That is, if one of the two types of monomers is bound to the same monomer and the other monomer with equal probability during polymerization, a random copolymer in which the monomer residues are distributed completely randomly is obtained. However, if there is a tendency for one monomer to be bound to the other monomer, a gradient copolymer in which the distribution of monomer residues is biased is obtained. The resulting gradient copolymer has a continuously changing composition of monomer residues along its molecular chain from the polymerization initiation end to the polymerization termination end.

[0052] If monomer A has a higher initial polymerization rate than monomer B, then when monomer A and monomer B are copolymerized in the macromer synthesis step, monomer A is likely to bond after monomer A. As a result, the synthesized macromer forms a gradient structure in which the proportion of monomer A units gradually decreases from the polymerization initiation end to the polymerization termination end. In other words, the macromer obtained in this step has a gradient structure in which monomer A residues and monomer B residues form a compositional gradient in the skeleton due to the difference in the initial polymerization rates of monomer A and monomer B. Such macromers may be referred to herein as "gradient macromers."

[0053] In order to realize such a gradient structure, it is desirable to synthesize the macromer in the macromer synthesis step by a polymerization reaction that occurs in one direction from the initiation terminal. Preferred examples of such synthesis reactions include ring-opening polymerization and living polymerization. The macromer obtained in the macromer synthesis step preferably satisfies the R value range described in (1) above, in order to facilitate the final production of a polyester copolymer that satisfies the R value range described in (1) above. That is, the macromer preferably has an R value represented by the following formula of 0.45 or more and 0.99 or less, and more preferably 0.50 or more and 0.80 or less. R value = [AB] / (2 [A] [B]) × 100 [A]: mole fraction of monomer A residue in the macromer [B]: mole fraction of monomer B residue in the macromer [AB]: mole fraction of structures in the macromer in which a monomer A residue and a monomer B residue are adjacent (A-B and B-A)

[0054] Similarly, the macromer obtained in the macromer synthesis step preferably satisfies the range of crystallinity of the monomer residues described in (2) above, in order to facilitate the final production of a polyester copolymer in which the range of crystallinity of the monomer A residue or the monomer B residue described in (2) above is satisfied. That is, the macromer preferably has a crystallinity of at least one of the monomer A residue or the monomer B residue of less than 14%, more preferably 10% or less, even more preferably 5% or less, and most preferably 1% or less. The weight-average molecular weight of the macromer synthesized in the macromer synthesis step is preferably 10,000 or more, more preferably 20,000 or more. Furthermore, in order to suppress crystallinity and maintain flexibility, it is preferably 150,000 or less, more preferably 100,000 or less.

[0055] [Multiplication Step] In the multiplication step, the macromers obtained in the macromer synthesis step are linked together, or the macromer solution obtained in the macromer synthesis step is multiplied by additionally adding monomer A and monomer B. In this step, macromers obtained in one macromer synthesis step may be linked together, or multiple macromers obtained in two or more macromer synthesis steps may be linked. Note that "multiplication" means that, by either of these methods, a structure is formed in which multiple repeating molecular chains have a gradient structure in which monomer A residues and monomer B residues have a composition gradient in the skeleton.

[0056] The number of multi-linked macromer units may be 2 or more, but since a larger number of linked units results in improved tensile strength due to entanglement of molecular chains, the number is preferably 3 or more, more preferably 4 or more, and even more preferably 6 or more. On the other hand, if the molecular weight of the polyester copolymer increases excessively as a result, there is a concern that the viscosity will increase and adversely affect moldability, so the number of macromer units is preferably 80 or less, more preferably 40 or less, and even more preferably 20 or less.

[0057] The number of linked macromer units can be adjusted by the catalyst used in the multi-polymerization process and the reaction time. When linking macromers to each other to form multi-polymers, the number of macromer units can be determined by dividing the weight-average molecular weight of the final polyester copolymer by the weight-average molecular weight of the macromer.

[0058] The polyester copolymer of the present invention may be a linear polymer in which macromer units are linearly linked, or a branched polymer in which macromer units are branched and linked.

[0059] A linear polyester copolymer can be synthesized, for example, by bonding one molecule of a gradient macromer to each end of a gradient macromer via the ends.

[0060] When the gradient macromer has a hydroxyl group and a carboxyl group at each end, the ends can be condensed with a condensing agent to obtain a multi-polyester copolymer. Examples of the condensing agent include 4,4-dimethylaminopyridinium p-toluenesulfonate, 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, N,N'-carbonyldiimidazole, 1,1'-carbonyldi(1,2,4-triazole), and 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholino. Trifluoromethanesulfonate (4,6-dimethoxy-1,3,5-triazin-2-yl)-(2-octoxy-2-oxoethyl)dimethylammonium, 1H-benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate, 1H-benzotriazol-1-yloxytripyrrolidinophosphonium hexafluorophosphate, (7-azabenzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate, Lorotripyrrolidinophosphonium hexafluorophosphate, Bromotris(dimethylamino)phosphonium hexafluorophosphate, 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(N-succinimidyl)-N,N, N',N'-tetramethyluronium tetrafluoroborate, O-(N-succinimidyl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(3,4-dihydro-4-oxo-1,2,3-benzotriazin-3-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, S-(1-oxido-2-pyridyl)-N,N,N',N'-tetramethylthiuronium tetrafluoroborate, O-[2-oxo-1(2H)-pyridyl]-N,N,N',Examples of usable hexafluorophosphates include N'-tetramethyluronium tetrafluoroborate, {{[(1-cyano-2-ethoxy-2-oxoethylidene)amino]oxy}-4-morpholinomethylene}dimethylammonium hexafluorophosphate, 2-chloro-1,3-dimethylimidazolinium hexafluorophosphate, 1-(chloro-1-pyrrolidinylmethylene)pyrrolidinium hexafluorophosphate, 2-fluoro-1,3-dimethylimidazolinium hexafluorophosphate, and fluoro-N,N,N',N'-tetramethylformamidinium hexafluorophosphate.

[0061] Furthermore, when the polymerization reaction has a living property, i.e., when the polymerization reaction can be initiated continuously from the end of the polymer, multimerization can be achieved by repeatedly adding additional monomers A and B to the gradient macromer solution after the polymerization reaction has been completed.

[0062] Alternatively, gradient macromers may be multi-linked via a linker, provided that the mechanical properties of the polymer are not affected. In particular, by using a linker having multiple carboxyl groups and / or multiple hydroxyl groups, such as 2,2-bis(hydroxymethyl)propionic acid, it is possible to synthesize a branched polyester copolymer in which the linker serves as a branch point.

[0063] The polyester copolymer obtained by the above-described production method is a copolymer having a structure in which two or more macromer units, in which monomer A residues and monomer B residues have a composition gradient in the skeleton, are linked together, and this is a preferred embodiment of the polyester copolymer. In this specification, for convenience, such a structure may be referred to as a "multi-gradient" and a copolymer having a multi-gradient structure may be referred to as a "multi-gradient copolymer." A multi-gradient copolymer preferably has a structure in which two or more macromer units, in which monomer A residues and the above-described monomer B residues have a gradient structure in which a composition gradient is formed in the skeleton, are linked together, and more preferably has a structure in which three or more macromer units are linked together.

[0064] As described above, a particularly preferred embodiment is a polyester copolymer in which the residue of monomer A is a lactic acid residue and the residue of monomer B is a caprolactone residue. Such a polyester copolymer is preferably produced by the following production method.

[0065] First, in the macromer synthesis step, dilactide and ε-caprolactone are polymerized in the presence of a catalyst. The dilactide and ε-caprolactone are preferably purified to remove impurities before use. For example, dilactide can be purified by recrystallization from toluene dried with sodium hydroxide. ε-caprolactone can be purified by, for example, recrystallization from toluene dried with CaH ２ From N ２ It can be purified by vacuum distillation under atmospheric pressure.

[0066] The reactivity of dilactide and ε-caprolactone is significantly different, as described in the literature (D. W. Grijpma and A. J. Pennings, Polymer Bulletin, Vol. 25, 335-341), and the initial polymerization rate of dilactide monomer is higher than that of ε-caprolactone. Ａ The reaction rate (%) was 3.6% / h, and the V Ｂ is 0.88% / h, and V Ａ / V Ｂ is 4.1. Therefore, the macromer obtained by copolymerizing dilactide and ε-caprolactone is a gradient macromer.

[0067] As a catalyst for the synthesis of a macromer having lactic acid residues and caprolactone residues, conventional polyester polymerization catalysts such as germanium-, titanium-, antimony-, or tin-based catalysts can be used. Specific examples of such polyester polymerization catalysts include tin octoate, antimony trifluoride, zinc powder, dibutyltin oxide, and tin oxalate. The method for adding the catalyst to the reaction system is not particularly limited, but it is preferably added in a state dispersed in the raw materials when they are charged, or in a state dispersed at the start of depressurization. The amount of catalyst used is preferably 0.01 to 3 wt %, more preferably 0.05 to 1.5 wt %, calculated as metal atoms, based on the total amount of monomers used.

[0068] A macromer having lactic acid residues and caprolactone residues can be obtained by placing dilactide, caprolactone, and a catalyst in a reaction vessel equipped with a stirrer and reacting them at 120 to 250°C under a nitrogen stream. When water is used as a co-initiator, it is preferable to carry out a co-catalyst reaction at around 90°C prior to the polymerization reaction. The reaction time for the co-catalyst reaction is 2 hours or more, preferably 4 hours or more, and in order to further increase the degree of polymerization, a longer reaction time, for example, 8 hours or more, is more preferable. However, since carrying out the reaction for a long period of time can cause problems with coloration of the polymer, the reaction time for the co-catalyst reaction is preferably 12 hours or less.

[0069] Next, in the multi-polymerization step, the terminals of the gradient macromers having lactic acid residues and caprolactone residues are linked to each other by a condensation reaction to form multi-polymers. The reaction temperature for the condensation reaction is preferably 10 to 100°C, more preferably 20 to 50°C. The reaction time for the condensation reaction is preferably one day or more, and more preferably two days or more. However, since carrying out the reaction for a long period of time can cause problems with coloration of the polymer, the reaction time for the condensation reaction is preferably four days or less.

[0070] <Carbodiimide Compound> Examples of the carbodiimide compound include aliphatic polycarbodiimides, aromatic polycarbodiimides, aliphatic monocarbodiimides, and aromatic monocarbodiimides.

[0071] From the viewpoint of exhibiting a high recovery retention rate of the polyester composition, the carbodiimide compound is preferably an aliphatic polycarbodiimide, an aromatic polycarbodiimide, or an aromatic monocarbodiimide. By selecting the above carbodiimide compound as the carbodiimide compound, the carbodiimide compound is not incorporated into the hard segments during the process of repairing the hard segments in the polyester copolymer that have once been degraded by hydrolysis, and as a result, a high recovery retention rate can be exhibited.

[0072] From the viewpoint of transparency, the carbodiimide compound is preferably an aliphatic polycarbodiimide, an aromatic monocarbodiimide, or an aliphatic monocarbodiimide.

[0073] Examples of aliphatic polycarbodiimides include poly(cyclohexylenecarbodiimide), poly(hexamethylenecarbodiimide), poly(methylenebiscyclohexylcarbodiimide), and poly(trimethylcyclohexylcarbodiimide). Among these, poly(cyclohexylenecarbodiimide) or poly(trimethylcyclohexylcarbodiimide) is preferred.

[0074] Examples of aromatic polycarbodiimides include poly(methylenebiscyclohexylcarbodiimide), poly(diphenylmethanecarbodiimide), poly(dimethyl-diphenylmethanecarbodiimide), poly(naphthylenecarbodiimide), poly(p-phenylenecarbodiimide), poly(m-phenylenecarbodiimide), poly(tolylcarbodiimide), poly(diisopropylphenylenecarbodiimide), poly(methyl-diisopropylphenylenecarbodiimide), poly(triethylphenylenecarbodiimide), and poly(triisopropylphenylenecarbodiimide). Among these, poly(diisopropylphenylenecarbodiimide), poly(methyl-diisopropylphenylenecarbodiimide), poly(triethylphenylenecarbodiimide), or poly(triisopropylphenylenecarbodiimide) is preferred, and poly(triisopropylphenylenecarbodiimide) is more preferred.

[0075] Examples of aliphatic monocarbodiimides include N,N'-dioctyldecylcarbodiimide, hexamethylene-bis-dicyclohexylcarbodiimide, dicyclohexylcarbodiimide, diisopropylcarbodiimide, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and among these, dicyclohexylcarbodiimide is preferred.

[0076] Examples of aromatic monocarbodiimides include p-phenylene-bis-p-chlorophenylcarbodiimide, bis(o-tolylcarbodiimide), bis(diphenylcarbodiimide), bis(2,6-dimethylphenylcarbodiimide), N-tolyl-N'-cyclohexylcarbodiimide, bis(2,6-diisopropylphenylcarbodiimide), bis(2,6-di-tert.-butylphenylcarbodiimide), N-tolyl-N'-phenylcarbodiimide, bis(p-nitrophenylcarbodiimide), bis(p-aminophenylcarbodiimide), bis(p-hydroxyphenylcarbodiimide), bis(p-tolylcarbodiimide), Examples of suitable carbodiimides include bis(2,6-dimethylphenylcarbodiimide), p-phenylene-bis-di-o-tolylcarbodiimide, p-phenylene-bis-di-o-dicyclohexylcarbodiimide, ethylene-bis-diphenylcarbodiimide, and bis(diphenylcyclocarbodiimide). Among these, bis(2,6-dimethylphenylcarbodiimide), bis(2,6-diisopropylphenylcarbodiimide), bis(2,6-di-tert.-butylphenylcarbodiimide), or bis(diphenylcyclocarbodiimide) are preferred, and bis(2,6-diisopropylphenyl)carbodiimide or bis(diphenylcyclocarbodiimide) are more preferred. Bis(diphenylcyclocarbodiimide) has a chemical structure represented by formula (III).

[0077] Furthermore, from the viewpoint of exhibiting a high recovery retention rate of the polyester composition, the n-octanol / water partition coefficient of the carbodiimide compound is preferably 3.0 or more and 15.0 or less, more preferably 4.0 or more and 13.0 or less, and even more preferably 4.7 or more and 12.1 or less.

[0078] The partition coefficient is an index that represents the hydrophobicity of a substance, and the n-octanol / water partition coefficient is the ratio of the concentration of the substance in n-octanol to the concentration in water when the substance is dissolved in a mixture of n-octanol and water.

[0079] The n-octanol / water partition coefficient of a carbodiimide compound can be determined experimentally or by a computational chemistry method. The n-octanol / water partition coefficient determined by a computational chemistry method is referred to as the n-octanol / water partition coefficient determined by a computational chemistry method. The n-octanol / water partition coefficient determined by a computational chemistry method is, for example, the n-octanol / water partition coefficient (Log P) calculated by the method described in Measurement Method 10 below. In Measurement Method 10, a molecular model of the carbodiimide compound is optimized using density functional theory, and the free energy in n-octanol, water, or the gas phase is calculated for the optimized molecular model (a continuum dielectric model using the SMD method is used to calculate the free energy in n-octanol or water), and the n-octanol / water partition coefficient is determined from these values.

[0080] When the carbodiimide compound is a low molecular weight compound, the molecular model, i.e., the calculation target, used for computationally determining the n-octanol / water partition coefficient of the carbodiimide compound is the chemical structure of the carbodiimide compound itself. When the carbodiimide compound is a polymer compound, the molecular model is a chemical structure in which repeating units are arranged at both ends of a certain carbodiimide group, and in which a carbon atom bonded to another carbodiimide group in the repeating unit is replaced with a methyl group. For example, when the carbodiimide compound is a poly(cyclohexylenecarbodiimide) represented by formula (IV), the molecular model is a chemical structure represented by formula (V). Note that when the carbodiimide compound is a copolymer composed of multiple types of repeating units, the partition coefficients for each repeating unit are calculated, and the sum of the values ​​multiplied by the copolymerization ratio of each repeating unit is used as the partition coefficient of the carbodiimide compound.

[0081] <Polyester Composition> The polyester composition is a composition containing a polyester copolymer and a carbodiimide compound.

[0082] If the content of the carbodiimide compound in the polyester composition is too low, the effect of maintaining the weight-average molecular weight cannot be obtained, and if it is too high, the recovery property of the polyester copolymer itself is impaired. Therefore, the polyester composition contains 0.3 parts by weight or more and 20.0 parts by weight or less of the carbodiimide compound per 100 parts by weight of the polyester copolymer. The content of the carbodiimide compound is preferably 0.5 parts by weight or more and 15.0 parts by weight or less, more preferably 1.0 parts by weight or more and 12.0 parts by weight or less.

[0083] The polyester composition satisfies the following formula (1) when a film obtained by molding the polyester composition into a thickness of 0.3 mm, a width of 1.0 cm, and a length of 1.0 cm is formed from the polyester composition: X / Y>10.0 (1) (In formula (1), X represents the mass % of nitrogen atoms when the elemental composition (atomic %) on the surface of the film is converted to mass %, as measured by X-ray photoelectron spectroscopy, and Y represents the mass % of nitrogen atoms, as measured using an elemental analyzer, when the mass of the film is taken as 100%).)

[0084] Since the measurement depth of X-ray photoelectron spectroscopy is on the order of a few nm, nitrogen atoms on the outermost surface of a film are observed, whereas measurements using an elemental analyzer observe nitrogen atoms throughout the entire film. In other words, X / Y in formula (1) represents the uniformity of nitrogen atom distribution in the thickness direction of the film. That is, when the value of X / Y is less than 1, nitrogen atoms are localized within the film; when the value of X / Y is 1, nitrogen atoms are uniformly distributed in the thickness direction; and when the value of X / Y is greater than 1, nitrogen atoms are localized on the film surface. By setting the value of X / Y within the above range, the polyester composition can exhibit hydrolysis resistance over a long period of time.

[0085] From the viewpoint of transparency, the value of X / Y in the above formula (1) of the polyester composition is preferably 0.0 or more and 10.0 or less, more preferably 0.1 or more and 5.0 or less, and even more preferably 0.2 or more and 1.0 or less.

[0086] The thickness of the film can be measured at any three points within the film, and the average value can be regarded as the thickness of the film.

[0087] Methods for measuring X and Y include the methods described in Measurement Methods 4 and 5 in the Examples below.

[0088] An example of a method for determining the value of X / Y of the polyester composition of the present invention contained in a molded article or medical device is as follows.

[0089] The polyester composition contained in the molded article or medical device is dissolved in chloroform to a concentration of 60 g / L to prepare a polyester composition solution. Next, the solution is poured into a polytetrafluoroethylene (PTFE) container so that the liquid height is 7±1 mm, and the solution is air-dried at room temperature for 48 hours, followed by vacuum drying at 50°C for 12 hours to prepare a 0.3 mm thick film. The film is cut into a 1.0 cm wide x 1.0 cm long piece, and the X / Y value is determined by the above-mentioned measurement.

[0090] When the amount of the polyester composition of the present invention contained in the molded article or medical device is 1.2 g or more, it is preferable to prepare a film by the following method.

[0091] 1.2 g of the polyester composition of the present invention contained in the molded article or medical device was collected in a 30 mL glass vial, 20 mL of chloroform was added, and the mixture was stirred for 7.5 hours to confirm that the polyester composition was dissolved. Next, the solution was poured into a 6 cm diameter PTFE dish so that the liquid height was 7 ± 1 mm, and the dish was covered with aluminum foil and air-dried at room temperature for 48 hours. After that, the aluminum foil was removed and the dish was vacuum-dried at 50 ° C for 12 hours to produce a 0.3 mm thick film.

[0092] The transparency of the polyester composition can be evaluated by measuring the transmittance using, for example, a haze meter or a color computer. In order for the polyester composition to have high transparency, the transmittance of a film obtained by molding the polyester composition into a thickness of 0.3 mm, a width of 1.0 cm, and a length of 1.0 cm is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more.

[0093] The permeability of the polyester composition of the present invention contained in a molded article or medical device can be measured by preparing a film in the same manner as in the method for determining the value of X / Y described above, and measuring the permeability of the film.

[0094] The polyester composition of the present invention has an organic nitrogen peak intensity of more than 18.0 when the intensity of the entire spectrum is taken as 100, as measured by time-of-flight secondary ion mass spectrometry. The intensity of the entire spectrum refers to the integral value of the peak intensities detected within the mass number (m / z) range of 0 to 1500, and organic nitrogen refers to CN. － The organic nitrogen ion is an ion. When the intensity of the entire spectrum is taken as 100, the polyester composition exhibits hydrolysis resistance over a long period of time by setting the peak intensity of the organic nitrogen within the above range. From the viewpoint of the long-term hydrolysis resistance of the polyester composition, when the intensity of the entire spectrum is taken as 100, the peak intensity of the organic nitrogen is preferably 20.0 or more, more preferably 30.0 or more, and even more preferably 40.0 or more.

[0095] From the viewpoint of transparency, the polyester composition of the present invention preferably has an organic nitrogen peak intensity of 0.0 or more and 18.0 or less, more preferably 0.0 or more and 10.0 or less, even more preferably 0.0 or more and 5.0 or less, and most preferably 0.0 or more and 1.0 or less, when the intensity of the entire spectrum is taken as 100, as measured by time-of-flight secondary ion mass spectrometry.

[0096] The polyester composition of the present invention has high resilience. The resilience index can be exemplified by the resilience rate. In the present invention, the resilience rate is an index that indicates the extent to which the composition returns to its original shape relative to the length at which it was stretched when the load is removed after stretching the composition. From the viewpoint of the ability to follow the movements of a living body, the resilience rate of the polyester composition is 10% or more and 100% or less, preferably 70% or more and 100% or less, more preferably 80% or more and 100% or less, even more preferably 90% or more and 100% or less, and most preferably 100%.

[0097] The recovery retention rate in the polyester composition of the present invention is an index showing the degree to which the recovery rate of the polyester copolymer alone is maintained in a polyester composition obtained by adding a carbodiimide compound to the polyester copolymer. In other words, it is an index showing the degree to which the recovery rate of the polyester copolymer alone changes due to the addition of a carbodiimide compound. The recovery retention rate of the polyester composition can be determined by dividing the recovery rate of the polyester composition by the recovery rate of the polyester copolymer contained therein.

[0098] The recovery retention rate of the polyester copolymer is preferably 85% or more, more preferably 90% or more, and even more preferably 92% or more. The upper limit of the recovery retention rate is not particularly limited, but is preferably 110% from the viewpoint of minimizing the change from the recovery rate of the polyester copolymer.

[0099] The recovery rate in the present invention is an index showing the extent to which the recovery rate of a composition is maintained under humid conditions such as those in vivo. For example, it can be determined by placing a polyester composition in vivo for a certain period of time and comparing the recovery rates before and after placement. Specifically, the recovery rate can be determined by dividing the recovery rate after placement by the recovery rate before placement. Alternatively, it can be determined by immersing the polyester composition in a solution simulating an in vivo environment (e.g., blood, serum, phosphate-buffered saline, saline, distilled water, ion-exchanged water, etc.) for a certain period of time and comparing the recovery rates before and after immersion. Specifically, the recovery rate can be determined by dividing the recovery rate after immersion by the recovery rate before immersion.

[0100] The period of placement or immersion is not particularly limited, but it is preferable to evaluate it according to the intended use. For example, when used as an implant medical device, it is generally placed for three months or more, so it is preferable that the device exhibits a high retention rate of recovery even after placement or immersion for three months. When immersing in the above solution, any temperature can be selected, but 37°C is selected to reproduce the in vivo environment. On the other hand, accelerated testing can also be performed by immersing at a temperature higher than 37°C; for example, immersion at 50°C can be treated as an accelerated test approximately three times faster than immersion at 37°C. However, if the temperature of the immersion solution is extremely low or high, it will deviate from the in vivo environment, so the temperature of the immersion solution is preferably 15°C to 60°C.

[0101] In order to suitably use the polyester composition of the present invention as an implantable medical device, the recovery rate is preferably 75% or more, more preferably 80% or more, even more preferably 85% or more, and most preferably 90% or more. There is no particular upper limit, but from the viewpoint of minimizing change from before immersion, it is preferably 110% or less.

[0102] The polyester composition of the present invention has high hydrolysis resistance. An example of an indicator of hydrolysis resistance is the weight-average molecular weight retention rate. In the present invention, the weight-average molecular weight retention rate is an indicator of the extent to which the weight-average molecular weight of a composition is maintained under humid conditions such as those found in vivo. The weight-average molecular weight retention rate can be determined, for example, by indwelling the polyester composition in vivo for a certain period of time and dividing the weight-average molecular weight after indwelling by the weight-average molecular weight before indwelling. Alternatively, the polyester composition can be immersed in a solution simulating an in vivo environment (e.g., blood, serum, phosphate-buffered saline, saline, distilled water, ion-exchanged water, etc.) for a certain period of time and comparing the weight-average molecular weight values ​​before and after immersion. Specifically, the weight-average molecular weight retention rate can be determined by dividing the weight-average molecular weight after immersion by the weight-average molecular weight before immersion.

[0103] The polyester composition of the present invention can be suitably used as a molded article. The molded article of the present invention will be described below.

[0104] The molded article of the present invention is made from the polyester composition of the present invention. In the present invention, the molded article refers to an object obtained by molding the polyester composition of the present invention into various shapes by a known method depending on the purpose. Examples of the molded article include membranes (membranes, films, and sheets), boards, rods, cylinders (pipes and tubes), filaments, meshes, bags, woven fabrics, and nonwoven fabrics.

[0105] The molded article of the present invention may be produced by molding a polyester composition obtained by previously blending a polyester copolymer with a carbodiimide compound, or by coating a molded article obtained by molding a polyester copolymer with a carbodiimide compound. However, it is more preferable to produce the molded article by molding a polyester composition obtained by previously blending a polyester copolymer with a carbodiimide compound.

[0106] Furthermore, the polyester composition of the present invention can be suitably used in medical applications, and can be suitably used in medical devices. It can be more suitably used in implant medical devices. An implant medical device refers to a medical device that is used by being implanted in the body. Preferred examples of implant medical devices include sutures, artificial bones, artificial skin, wound dressings, carriers for DDS, microneedles, stents, and scaffolding materials for tissue or organ regeneration.

[0107] In order to suitably use the polyester composition of the present invention as an implantable medical device, the contact angle of the polyester composition with water is preferably 90 degrees or more, more preferably 100 degrees or more.

[0108] EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these.

[0109] (Measurement Method 1: Weight-Average Molecular Weight of Polyester Copolymer) The polyester copolymer was dissolved in chloroform to a concentration of 1 mg / mL, and the solution was passed through a 0.45 μm syringe filter (DISMIC-13HP; manufactured by ADVANTEC) to remove impurities, etc., and then gel permeation chromatography was performed under the following measurement conditions to measure the weight-average molecular weight of the polyester copolymer. [Measurement Conditions] Instrument name: Prominence (registered trademark; manufactured by Shimadzu Corporation) Mobile phase: Chloroform (for HPLC) (manufactured by Wako Pure Chemical Industries, Ltd.) Flow rate: 1 mL / min Column: TSKgel GMHHR-M (φ7.8 mm×300 mm; manufactured by Tosoh Corporation) Detector: UV (254 nm), RI Column and detector temperatures: 35° C. Standard material: polystyrene

[0110] (Measurement Method 2: Molar Fraction and R Value of Each Residue of Polyester Copolymer) The purified polyester copolymer was dissolved in deuterated chloroform. １ H-NMR spectrum was measured to calculate the mole fraction (%) of the monomer residue in the polyester copolymer.

[0111] As will be described later, the polyester copolymer in this example has two types of hydroxycarboxylic acid monomers (L,L-dilactide and ε-caprolactone) as main structural units, and these two types of hydroxycarboxylic acid monomers are referred to as "monomer A" and "monomer B," respectively, and the molar fractions (%) of the monomer A residues and the monomer B residues were calculated. １ By H homospin decoupling, the peaks of monomer A and monomer B were separated by signals derived from adjacent monomer residues of monomer A or monomer B, and the respective peak areas were quantified. Specifically, under the following measurement conditions, the methine group of L,L-dilactide (near 5.10 ppm) and the α-methylene group of ε-caprolactone (near 2.35 ppm) and ε-methylene group (near 4.10 ppm) were separated by signals derived from adjacent monomer residues of L,L-dilactide or ε-caprolactone, and the respective peak areas were quantified. [Measurement conditions] Instrument name: JNM-ECZ400R (manufactured by JEOL Ltd.) １ H homospin decoupling Irradiation position: 1.66 ppm Solvent: deuterated chloroform Measurement temperature: room temperature

[0112] [AB] was calculated from the respective peak area ratios, and the R value was calculated from the following formula (2): R value = [AB] / (2 [A] [B]) × 100 Formula (2) [A]: Molar fraction (%) of monomer A residue in the polyester copolymer [B]: Molar fraction (%) of monomer B residue in the polyester copolymer [AB]: Molar fraction (%) of structures in which monomer A residue and monomer B residue are adjacent to each other (A-B and B-A) in the polyester copolymer

[0113] Here, [AB] is the molar fraction (%) of structures in which a monomer A residue and a monomer B residue are adjacent to each other (A-B and B-A) in the polyester copolymer, and specifically, is the ratio of the number of A-B and B-A to the total number of A-A, A-B, B-A, and B-B.

[0114] (Measurement Method 3: Crystallization Ratio of Polyester Copolymer) A polyester copolymer (approximately 5 mg) and a homopolymer (approximately 5 mg) consisting only of the monomers constituting the polyester copolymer were collected in an aluminum pan and subjected to differential scanning calorimetry (DSC) under the measurement conditions below. The heat of fusion was calculated from the measurement results under temperature conditions (D) to (E), and the crystallization ratio of the monomer residues in the polyester copolymer was calculated from the following formula (3). Crystallinity ratio of monomer residue in polyester copolymer=(heat of fusion per unit weight of monomer residue in polyester copolymer) / {(heat of fusion per unit weight of homopolymer consisting only of monomer residues)×(weight fraction of monomer residue in polyester copolymer)}×100 (Equation (3)) [Measurement conditions] Instrument name: EXSTAR 6000 (manufactured by Seiko Instruments Inc.) Temperature conditions: (A) 25°C → (B) 250°C (10°C / min) → (C) 250°C (5 min) → (D) −70°C (10°C / min) → (E) 250°C (10°C / min) → (F) 250°C (5 min) → (G) 25°C (100°C / min) Standard material: alumina

[0115] (Measurement Method 4: Nitrogen Content Measurement Using X-ray Photoelectron Spectroscopy) The films produced in Examples 1 to 14 or Comparative Examples 1 to 3 described below were cut into 1.0 cm x 1.0 cm pieces and measured using X-ray photoelectron spectroscopy under the measurement conditions described below. The obtained data was analyzed using the data processing method described below to determine the elemental composition (atomic %) of the film surface. Furthermore, the mass % (X) of nitrogen atoms was determined when the obtained elemental composition (atomic %) was converted to mass %. [Measurement Conditions] Instrument name: Quantera SXM (Ulvac-PHI) Excitation X-ray: monochromatic Al K α１，２ ray (1486.6 eV) X-ray diameter: 200 μm Photoelectron escape angle (inclination of detector with respect to sample surface): 45° [Data processing method] Smoothing: 9-point smoothing Horizontal axis correction: C1s The main peak was set to 284.6 eV.

[0116] (Measurement method 5: Measurement of nitrogen content using an elemental analyzer) Films produced in Examples 1 to 14 or Comparative Examples 1 to 3 described below were cut into 1.0 cm x 1.0 cm pieces, weighed on a quartz board, and then the mass % (Y) of nitrogen atoms was measured using an elemental analyzer under the following measurement conditions. The measurement was performed twice, and the arithmetic mean value was used as the measured value. [Measurement conditions] Apparatus: NC-22F (manufactured by Sumika Chemical Analysis Service Co., Ltd.) Combustion furnace: 900°C Reduction furnace: 600°C Supply gas: oxygen Detector: TCD (thermal conductivity detector)

[0117] (Measurement Method 6: Surface Analysis Using Time-of-Flight Secondary Ion Mass Spectrometry) The films prepared in Examples 1 to 14 or Comparative Examples 1 to 3 described below were cut into 1.0 cm x 1.0 cm pieces, and surface analysis was performed using time-of-flight secondary ion mass spectrometry under the following measurement conditions. In this measurement, the peak intensity of the entire spectrum, that is, the integral value of the peak intensity detected within the mass number (m / z) range of 0 to 1500, was set to 100, and the organic nitrogen (CN) － The peak intensity of the observed negative secondary ions and their mass numbers is shown in Table 1. [Measurement conditions] Instrument name: TOF SIMS 5 (manufactured by ION-TOF) Primary ions: Bi ３ ＋＋ Secondary ion polarity: negative only Mass range (m / z): 0 to 1500 Raster size: 50 μm x 50 μm Number of scans: 48 Number of pixels (per side): 256 x 256 Measurement vacuum level (before sample introduction): 4 x 10 －７ Pa (4 x 10 －９ mbar) or less Primary ion acceleration voltage: 30 kV Pulse width: 127.3 ns Bunching: None (high mass resolution measurement) Charge neutralization: Yes Post-acceleration: 9.5 kV

[0118]

[0119] (Measurement Method 7: Weight-Average Molecular Weight Retention Rate) The films produced in Examples 1 to 14 or Comparative Examples 1 to 3 described below were cut into dumbbell shapes (dumbbell No. 7 as defined in JIS K6251 (2017)) and used as test pieces before degradation treatment. These were subjected to degradation treatment by the following method and used as test pieces after degradation treatment.

[0120] Dumbbell-shaped films were immersed in a solution simulating the in vivo environment and subjected to degradation treatment. Specifically, the test specimens were placed in 15 mL plastic centrifuge tubes, and 11.5 mL of D-PBS(-) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added. The tubes were then left to stand at 50°C for 2, 4, or 16 weeks. The test specimens were then washed with ion-exchanged water and dried under reduced pressure at 50°C for 24 hours.

[0121] The test pieces before and after the degradation treatment were dissolved in chloroform to a concentration of 1 mg / mL, and the solution was passed through a 0.45 μm syringe filter (DISMIC-13HP; manufactured by ADVANTEC) to remove impurities, and then gel permeation chromatography was performed under the same measurement conditions as in Measurement Method 1 to measure the weight-average molecular weights of the test pieces before and after the degradation treatment.

[0122] Based on the measured weight-average molecular weight, the weight-average molecular weight retention rate was calculated from the following formula (4). The weight-average molecular weight retention rate was calculated by rounding off the first decimal place. Weight-average molecular weight retention rate (%) = weight-average molecular weight of film after decomposition treatment / weight-average molecular weight of film before decomposition treatment Formula (4)

[0123] (Measurement Method 8: Recovery Rate and Recovery Maintenance Rate) The films produced in Examples 1 to 14 or Comparative Examples 1 to 3 described below were cut into dumbbell shapes (dumbbell No. 7 as defined in JIS K6251 (2017)) and used as test pieces before degradation treatment. The test pieces were subjected to degradation treatment by the following method and used as test pieces after degradation treatment.

[0124] The dumbbell-shaped specimens were immersed in a solution simulating the in vivo environment and decomposed. Specifically, the specimens were placed in a 15 mL plastic centrifuge tube, and 11.5 mL of D-PBS(-) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added. The tube was then left to stand at 50°C for 4 weeks. The specimens were then washed with ion-exchanged water and dried under reduced pressure at 50°C for 24 hours.

[0125] Using the test pieces before and after the decomposition treatment, a tensile test was performed under the following measurement conditions in accordance with the method specified in JIS K7161 (2014), and the recovery rate was measured. [Measurement conditions] Device name: EZ-LX (manufactured by Shimadzu Corporation) Gauge distance before test: 10 mm Grip distance: 10 mm (the position of the gauge was gripped) Tensile speed: 500 mm / min Load cell: 1 kN

[0126] Specifically, in the tensile test, two benchmark lines were drawn on the test specimen using an appropriate marker. The test specimen was in a relaxed state, and the benchmark lines were drawn accurately and clearly, perpendicular to the parallel portion of the test specimen and equidistant from the center of the test specimen. The test specimen was then stretched 90 mm at a tensile speed of 500 mm / min to generate tensile strain (Operation 1).

[0127] Immediately after operation 1 (i.e., the shape retention time was set to 0 seconds), the tensile strain was relaxed at a rate of 500 mm / min to return the distance between the grippers to 10 mm (operation 2).

[0128] Immediately after Operation 2 (i.e., the shape retention time was set to 0 seconds), the above-described Operations 1 and 2 were carried out again.

[0129] This was repeated, and after performing operations 1 and 2 a total of 30 times, the obtained values ​​of L1 and L2 were used to calculate the restoration rate according to the following formula (5). The restoration rate was calculated by rounding off the first decimal place. The measurement was performed three times, and the number average value was taken as the restoration rate of the polyester composition. Restoration rate (%) = (L1 - L2) / (L1 - L0) x 100 Formula (5) L0: initial length (gauge line distance before test) L1: film length when stretched to 90 mm (gauge line distance when stretched to 90 mm) (meaning the value obtained by adding 90 mm to the initial length L0) L2: film length after 30 repeated stretching (gauge line distance after test)

[0130] The restoration retention rate was calculated from the following formula (6). The value of the restoration retention rate was rounded to the nearest whole number. Restoration retention rate (%) = restoration rate of film after decomposition treatment / restoration rate of film before decomposition treatment Formula (6)

[0131] (Measurement Method 9: Retention of Restoration Property) For the films produced in Examples 1 to 14 or Comparative Examples 1 to 3 described below, the retention of restoration property was calculated from the restoration property before the decomposition treatment measured by Measurement Method 8 and the following formula (7). Retention of restoration property (%) = restoration property of polyester copolymer film / restoration property of polyester composition film ... formula (7)

[0132] Here, the polyester copolymer film refers to a film of the polyester copolymer alone contained in the polyester composition. That is, the polyester copolymer film corresponding to the polyester composition films produced in Examples 1 to 6 or 8 to 14 or Comparative Examples 1 to 3 is the film produced in Comparative Example 1, and the polyester copolymer film corresponding to the polyester composition film produced in Example 7 is the film produced in Reference Example 1. Note that the film produced in Comparative Example 1 did not contain any carbodiimide compound, so its recovery retention rate was set to 100%.

[0133] (Measurement Method 10: n-Octanol / Water Partition Coefficient of Carbodiimide Compound) The n-octanol / water partition coefficient Log P of the carbodiimide compound was calculated from the following formula (8): Log P = {ΔG(oct) - ΔG(watt)} / 2.30RT (8)

[0134] In formula (8), ΔG(wat) is the solvation free energy for water, ΔG(oct) is the solvation free energy for n-octanol, R is the gas constant 1.987 cal / mol·K, and T is the absolute temperature 298.15. Here, the solvation free energy ΔG is the difference between the free energy in the solution and the free energy in the gas phase, and ΔG(wat) and ΔG(oct) are calculated by formulas (9) and (10), respectively. ΔG(wat)=G(wat)-G(gas) ...formula (9) ΔG(oct)=G(oct)-G(gas) ...formula (10)

[0135] G(gas), G(wat), and G(oct) were calculated by computational chemistry using the following method: Quantum chemistry calculation software Gaussian (registered trademark) 16 (manufactured by Gaussian Corporation) was used for the calculation.

[0136] First, the molecular model of the carbodiimide compound shown in Table 2 was optimized using density functional theory. In the optimization using density functional theory, the functional used was B3LYP, the basis set was 6-311++g(d,p), and the keyword written in the input file was set to "opt," which means optimization.

[0137]

[0138] Next, in the optimized molecular model, G(gas), G(wat), and G(oct) were calculated using density functional theory under the conditions shown in Table 3. In calculating G(wat) and G(oct), a continuous dielectric model using the SMD method was used. In Table 3, "freq" means calculation of free energy, and "opt freq" means calculation of free energy in the optimized structure after optimization. In the analysis using Gaussian 16, the value in the row marked "Sum of electronic and thermal Free Energies=" is the value of free energy.

[0139]

[0140] ΔG(wat) and ΔG(oct) were calculated from the calculated G(gas), G(wat), and G(oct), and the n-octanol / water partition coefficient LogP of the carbodiimide compound was calculated from ΔG(wat) and ΔG(oct).

[0141] Synthesis Example 1 50.0 g of L,L-dilactide (PURASORB® L; manufactured by PURAC Corporation), 39.6 g of ε-caprolactone (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 0.45 g of hydroxypivalic acid, which serve as monomers for a polyester copolymer, were placed in a separable flask. Under an argon atmosphere, 0.27 g of tin(II) octoate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a catalyst dissolved in 3.0 mL of toluene (ultra-dehydrated) (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added, and the mixture was allowed to react at 130°C for 9.5 hours to obtain a crude macromer. The obtained crude macromer was dissolved in 200 mL of chloroform and added dropwise to 3,000 mL of hexane with stirring to obtain a precipitate. The precipitate was dried under reduced pressure at 50°C to obtain a macromer.

[0142] 50 g of the macromer, 2.1 g of the catalyst 4,4-dimethylaminopyridinium p-toluenesulfonate (synthetic product), and 0.80 g of 4,4-dimethylaminopyridine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were collected and dissolved in 200 mL of dichloromethane (dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) under an argon atmosphere, and 1.7 mL of the condensation agent diisopropylcarbodiimide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added, followed by condensation polymerization at room temperature overnight.

[0143] The mixture after condensation polymerization was diluted with 220 mL of chloroform, and 470 mL of 0.5 M hydrochloric acid was added. The mixture was stirred for 30 minutes, and the aqueous layer was removed by decantation. Then, 470 mL of ion-exchanged water was added, and the mixture was stirred for 10 minutes. The aqueous layer was removed by decantation. This procedure was repeated until the pH of the aqueous layer removed by decantation reached 7. The remaining organic layer was added dropwise to 3,000 mL of stirred methanol to obtain a precipitate. The precipitate was dried under reduced pressure at 50°C to obtain polyester copolymer 1.

[0144] Measurements of polyester copolymer 1 were carried out according to the methods described in Measurement methods 1 to 3, and the results were as follows: weight average molecular weight 260,000, when the sum of the numbers of all monomer residues contained in the entire polymer was 100 mol %, the molar fraction of dilactide residues was 50 mol %, the molar fraction of caprolactone residues was 50 mol %, the R value was 0.53, and the crystallinity of the dilactide residues was 0%.

[0145] Synthesis Example 2 Polyester copolymer 2 was obtained by the same procedure as in Synthesis Example 1, except that the amount of 4,4-dimethylaminopyridinium p-toluenesulfonate was changed to 1.5 g, the amount of 4,4-dimethylaminopyridine to 0.56 g, and the amount of diisopropylcarbodiimide to 1.2 mL.

[0146] Measurements of polyester copolymer 2 were carried out according to the methods described in Measurement methods 1 to 3, and the results were as follows: weight average molecular weight was 110,000, the molar fraction of dilactide residues was 50 mol % and the molar fraction of caprolactone residues was 50 mol % when the sum of the numbers of all monomer residues contained in the entire polymer was 100 mol %, the R value was 0.69, and the crystallinity of the dilactide residues was 0%.

[0147] Example 1 1.188 g of polyester copolymer 1 and 0.012 g of poly(cyclohexylenecarbodiimide) [Carbodilite (registered trademark) HMV-15CA (manufactured by Nisshinbo Chemical Inc.)] were placed in a 30 mL glass vial, 20 mL of chloroform (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added, and the mixture was stirred for 7.5 hours to confirm dissolution. Next, the solution was poured into a 6 cm diameter PTFE Petri dish to a liquid height of 7±1 mm, covered with aluminum foil, and air-dried at room temperature for 48 hours. After that, the aluminum foil was removed, and the mixture was vacuum-dried at 50°C for 12 hours to obtain a 0.3 mm thick film of the polyester composition.

[0148] Example 2 The same procedure as in Example 1 was carried out, except that the amount of polyester copolymer 1 was changed to 1.140 g and the amount of poly(cyclohexylenecarbodiimide) was changed to 0.060 g, to obtain a polyester composition film having a thickness of 0.3 mm.

[0149] Example 3 The same procedure as in Example 1 was carried out, except that the amount of polyester copolymer 1 was changed to 1.080 g and the amount of poly(cyclohexylenecarbodiimide) was changed to 0.120 g, to obtain a polyester composition film having a thickness of 0.3 mm.

[0150] Example 4 The same procedure as in Example 2 was carried out, except that poly(triisopropylphenylenecarbodiimide) [Stabaxol (registered trademark) P100 (manufactured by Rhein Chemie)] was used instead of poly(cyclohexylenecarbodiimide), to obtain a polyester composition film having a thickness of 0.3 mm.

[0151] Example 5 The same procedure as in Example 2 was carried out, except that poly(triisopropylphenylenecarbodiimide) [Stabaxol (registered trademark) P (manufactured by Rhein Chemie)] was used instead of poly(cyclohexylenecarbodiimide), to obtain a polyester composition film having a thickness of 0.3 mm.

[0152] Example 6 The same procedure as in Example 2 was carried out, except that bis(2,6-diisopropylphenyl)carbodiimide (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of poly(cyclohexylenecarbodiimide), to obtain a polyester composition film having a thickness of 0.3 mm.

[0153] Example 7 The same procedure as in Example 2 was carried out except that Polyester Copolymer 2 was used instead of Polyester Copolymer 1, to obtain a polyester composition film having a thickness of 0.3 mm.

[0154] Comparative Example 1 The same procedure as in Example 1 was carried out except that the amount of Polyester Copolymer 1 was changed to 1.200 g and poly(cyclohexylenecarbodiimide) was not added, to obtain a polyester composition film having a thickness of 0.3 mm.

[0155] Comparative Example 2 The same procedure as in Example 1 was carried out, except that the amount of Polyester Copolymer 1 was changed to 1.199 g and the amount of poly(cyclohexylenecarbodiimide) was changed to 0.001 g, to obtain a polyester composition film having a thickness of 0.3 mm.

[0156] Comparative Example 3 The same procedure as in Example 1 was carried out, except that the amount of polyester copolymer 1 was changed to 0.960 g and the amount of poly(cyclohexylenecarbodiimide) was changed to 0.240 g, to obtain a polyester composition film having a thickness of 0.3 mm.

[0157] Example 8 The same procedure as in Example 2 was carried out, except that diisopropylcarbodiimide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of poly(cyclohexylenecarbodiimide), to obtain a polyester composition film having a thickness of 0.3 mm.

[0158] Example 9 The same procedure as in Example 2 was carried out, except that 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of poly(cyclohexylenecarbodiimide), to obtain a polyester composition film having a thickness of 0.3 mm.

[0159] Example 10 The same procedure as in Example 5 was carried out, except that the amount of polyester copolymer 1 was changed to 1.176 g and the amount of poly(triisopropylphenylenecarbodiimide) [Stabaxol (registered trademark) P (manufactured by Rhein Chemie)] was changed to 0.024 g, to obtain a polyester composition film having a thickness of 0.3 mm.

[0160] Example 11 The same procedure as in Example 5 was carried out, except that the amount of polyester copolymer 1 was changed to 1.020 g and the amount of poly(triisopropylphenylenecarbodiimide) [Stabaxol (registered trademark) P (manufactured by Rhein Chemie)] was changed to 0.180 g, to obtain a polyester composition film having a thickness of 0.3 mm.

[0161] Example 12 A polyester composition film having a thickness of 0.3 mm was obtained in the same manner as in Example 2, except that dicyclohexylcarbodiimide was used instead of poly(cyclohexylenecarbodiimide).

[0162] Example 13 The same procedure as in Example 2 was carried out, except that poly(trimethylcyclohexylcarbodiimide) [RelcaLink (registered trademark) 72 (manufactured by Stahl)] was used instead of poly(cyclohexylenecarbodiimide), to obtain a polyester composition film having a thickness of 0.3 mm.

[0163] Example 14 The same procedure as in Example 2 was carried out, except that bis(diphenylcyclocarbodiimide) [Carbodista (registered trademark) TCC-FP10M (manufactured by Teijin Limited)] was used instead of poly(cyclohexylenecarbodiimide), to obtain a polyester composition film having a thickness of 0.3 mm.

[0164] Reference Example 1 The same procedure as in Comparative Example 1 was carried out except that Polyester Copolymer 2 was used instead of Polyester Copolymer 1, to obtain a polyester composition film having a thickness of 0.3 mm.

[0165] For the films of the polyester compositions obtained in Examples 1 to 14 or Comparative Examples 1 to 3, the compositions and the measurement results obtained by the method described in Measurement Method 10 are shown in Table 4, and the measurement results obtained by the methods described in Measurement Methods 4 to 9 are shown in Table 5.

[0166]

[0167]

[0168] In Table 4, "-" for the restoration rate indicates that the film was broken during measurement and could not be measured, and "-" for the restoration retention rate indicates that the restoration rate after the decomposition treatment could not be measured and therefore could not be calculated.

[0169] As shown in Table 5, the polyester compositions obtained in Examples 1 to 14 maintained their weight-average molecular weights even after two weeks of degradation treatment, i.e., hydrolysis was suppressed, and the polyester copolymer itself maintained its recovery. On the other hand, the polyester compositions obtained in Comparative Examples 1 to 3 exhibited a decrease in weight-average molecular weight and / or a loss of recovery of the polyester copolymer itself. This demonstrates that the polyester compositions of the present invention are hydrolysis-resistant and maintain high recovery of the polyester copolymer itself. Furthermore, the polyester compositions obtained in Examples 1 to 7 and 10 to 14 maintained their recovery. This demonstrates that adding a carbodiimide compound having a partition coefficient of 3.0 or more and 15.0 or less to a polyester copolymer maintains recovery for a long period of time. Furthermore, it was revealed that the polyester compositions obtained in Examples 5, 10, and 11, i.e., polyester compositions in which X / Y is greater than 10.0 as measured by X-ray photoelectron spectroscopy or the peak intensity of organic nitrogen is greater than 18.0 as measured by time-of-flight secondary ion mass spectrometry, maintain their weight-average molecular weights even after being subjected to a decomposition treatment for an extremely long period of time, such as 16 weeks, unlike the polyester compositions obtained in Examples 2 and 6.

Claims

1. A polyester composition comprising a polyester copolymer and a carbodiimide compound, having a recovery rate of 10% or more and 100% or less, and containing 0.3 parts by weight or more and 20.0 parts by weight or less of the carbodiimide compound per 100 parts by weight of the polyester copolymer.

2. The polyester composition according to claim 1, wherein the n-octanol / water partition coefficient of said carbodiimide compound is 3.0 or more and 15.0 or less.

3. The polyester composition according to claim 1 or 2, wherein the carbodiimide compound is an aliphatic polycarbodiimide, an aromatic polycarbodiimide, or an aromatic monocarbodiimide.

4. The polyester composition according to claim 1 or 2, wherein the carbodiimide compound is poly(cyclohexylenecarbodiimide), poly(trimethylcyclohexylcarbodiimide), poly(triisopropylphenylenecarbodiimide), dicyclohexylcarbodiimide, bis(2,6-diisopropylphenyl)carbodiimide, or bis(diphenylcyclocarbodiimide).

5. A polyester composition containing a polyester copolymer and a carbodiimide compound, wherein a film formed from the composition to a thickness of 0.3 mm, width of 1.0 cm, and length of 1.0 cm satisfies the following formula (1): X / Y>10.0 (1) (In formula (1), X represents the mass % of nitrogen atoms when the elemental composition (atomic %) on the surface of the film is converted to mass %, as measured by X-ray photoelectron spectroscopy, and Y represents the mass % of nitrogen atoms, as measured using an elemental analyzer, when the mass of the film is taken as 100%).) 6. A polyester composition containing a polyester copolymer and a carbodiimide compound, wherein the peak intensity of organic nitrogen measured by time-of-flight secondary ion mass spectrometry exceeds 18.0 when the intensity of the entire spectrum is taken as 100.

7. The polyester composition according to any one of claims 1 to 6, wherein the polyester copolymer is a copolymer having a hydroxycarboxylic acid as a main structural unit.

8. The polyester composition according to any one of claims 1 to 7, wherein the weight average molecular weight of the polyester copolymer is 120,000 or more.

9. A molded article comprising the polyester composition according to any one of claims 1 to 8.

10. A medical device comprising the polyester composition of any one of claims 1 to 8.

11. The medical device according to claim 10, which is an implantable medical device.

12. The medical device according to claim 11, which is a suture, an artificial bone, an artificial skin, a wound dressing, a carrier for a DDS, a microneedle, a stent, or a scaffolding material for tissue or organ regeneration.

13. A method for regenerating biological tissue, which comprises using the polyester composition according to any one of claims 1 to 8 as a scaffold material for regenerating tissue or organs.

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