JP7782797B2 - Branched biodegradable polyester and its use - Google Patents

Description

The present invention relates to branched biodegradable polyesters and their uses.

Biodegradable resins have long been attracting attention as alternatives to petroleum-derived plastics, with the aim of reducing environmental impact. Polylactic acid is a particularly popular biodegradable resin, and there is a growing demand for its widespread use in a variety of applications.

For example, Patent Document 1 describes a stereocomplex multiblock copolymer comprising a block of polylactic acid and a block of polycaprolactone, in which the block of polylactic acid is stereocomplexed with a chiral polymer composed of a chiral monomer that is enantiomeric with the lactic acid that constitutes the polylactic acid.

For example, Patent Document 2 describes a branched biodegradable polyester having a polyglycerin main chain and polyester chains as side chains connected via the hydroxyl groups of the polyglycerin.

For example, Patent Document 3 describes a branched polymer having at least three arms made of a lactic acid-ε-caprolactone copolymer and having a weight-average molecular weight of 150,000 or more.

JP 2016-210894 A Japanese Patent Application Laid-Open No. 2008-222768 WO2014-061341 publication

For example, Patent Document 1 discloses a stereocomplex multiblock copolymer of polylactic acid and polycaprolactone. However, while the formation of a stereocomplex improves heat resistance, it also suffers from the problem of loss of flexibility.

In addition, Patent Document 2 discloses a branched biodegradable polyester that uses polyglycerin as the main chain, but polyesters with rigid branched chain skeletons, such as polylactic acid, have the problem of insufficient flexibility.

Patent Document 3 discloses a branched polymer having at least three arms made of a lactic acid-ε-caprolactone copolymer, but the branched polymer itself has low breaking strength, and there is a problem in that even when blended with polylactic acid, sufficient breaking strength cannot be imparted.

The objective of the present invention is to provide a novel branched biodegradable polyester and related technologies that exhibit high flexibility and high breaking strength.

As a result of extensive research to solve the above-mentioned problems, the inventors discovered that by using a trivalent or higher polyhydric alcohol as the main chain and extending polyester chains to the multiple hydroxyl groups of this polyhydric alcohol (hereinafter also referred to as "branched polyester"), it is possible to improve the problem of poor flexibility that is inherent in polylactic acid and to impart sufficient flexibility.

In other words, the branched biodegradable polyester according to one embodiment of the present invention has a block structure containing a random copolymer segment of lactide and caprolactone and a homopolymer segment of lactide, with a trivalent or higher polyhydric alcohol bonded to the end of the block structure.

One aspect of the present invention provides a novel branched biodegradable polyester and related technologies that exhibit high flexibility and high breaking strength.

<Branched biodegradable polyester>
The branched biodegradable polyester according to one embodiment of the present invention will be described in detail below.

A branched biodegradable polyester according to one embodiment of the present invention is a branched biodegradable polyester (hereinafter sometimes simply referred to as "branched biodegradable polyester according to one embodiment") that has a block structure containing a random copolymer segment of lactide and caprolactone and a homopolymer segment of lactide, with a trivalent or higher polyhydric alcohol bonded to the end of the block structure. The branched biodegradable polyester according to one embodiment has an ester bond derived from a hydroxyl group of the trivalent or higher polyhydric alcohol and a carboxyl group at the end of the block structure.

High-melting-point biodegradable polyesters, such as polylactic acid, have the disadvantage of being hard and brittle due to the rigidity of their molecular structure. On the other hand, low-melting-point biodegradable polyesters, such as polycaprolactone, are flexible but have a low melting point, which makes them unsuitable for practical use as molded articles, for example. The branched biodegradable polyester of one aspect of the present invention comprises both a random copolymer segment of lactide and caprolactone and a homopolymer segment of lactide, and has a crosslinked structure with a trivalent or higher polyhydric alcohol, meaning that the branched biodegradable polyester itself has physical properties that allow it to be used as a molded article material.

(Trihydric or higher polyhydric alcohols)
The trihydric or higher polyhydric alcohol is not particularly limited, but includes polyhydric alcohols such as polyglycerin, cyclic polyols, and polysaccharides, as well as polyhydric alcohols such as glycerin, sorbitol, and xylitol. An example of a cyclic polyol is quebrachitol, and an example of a polysaccharide is dextran. Among them, the trihydric or higher polyhydric alcohol is most preferably polyglycerin because it is easy to adjust the number of hydroxyl groups. Polyglycerin is represented by the following general formula (A):

In formula (A), n represents an integer of 1 to 30.

In general formula (A), the degree of polymerization n of polyglycerin is preferably 1 to 30, more preferably 2 to 20, and most preferably 4 to 10. When the degree of polymerization n of polyglycerin is greater than 1, the flexibility of the branched biodegradable polyester itself can be increased. Furthermore, when the degree of polymerization n of polyglycerin is less than 30, the breaking strength of the branched biodegradable polyester itself can be maintained. Furthermore, as described below, flexibility can be imparted to resin compositions containing branched biodegradable polyesters, and high breaking strength can be imparted to resin compositions containing branched biodegradable polyesters.

(Block structure)
The block structure of the branched biodegradable polyester according to one embodiment is a block structure including a random copolymer segment and a homopolymer segment.

The random copolymer segment contains a copolymer of a monomer unit derived from one type of lactide (L-lactide, D-lactide, or DL-lactide) and a monomer unit derived from caprolactone. The random copolymer segment is formed by ring-opening polymerization of lactide and caprolactone, and the monomer unit derived from lactide is sometimes called a "polylactic acid unit," and the monomer unit derived from caprolactone is sometimes called a "caprolactone unit." The random copolymer segment can function as a so-called soft segment in the block structure.

The degree of polymerization (P1) of the polylactic acid units contained in the random copolymer segments is preferably 5 or more and 200 or less, more preferably 10 or more and 150 or less, and even more preferably 15 or more and 100 or less. By increasing the degree of polymerization (P1) of the polylactic acid units contained in the random copolymer segments to 5 or more, the breaking strength of the branched biodegradable polyester itself can be increased. Furthermore, high flexibility can be imparted to resin compositions containing the branched biodegradable polyester. Furthermore, by ensuring that the degree of polymerization (P1) of the polylactic acid units contained in the random copolymer segments is 200 or less, the flexibility of the branched biodegradable polyester itself can be prevented from being impaired.

The degree of polymerization (P2) of the caprolactone units contained in the random copolymer segment is preferably 5 or more and 200 or less, more preferably 10 or more and 150 or less, and even more preferably 15 or more and 100 or less. When the degree of polymerization (P2) of the caprolactone units contained in the random copolymer segment is 5 or more, the flexibility of the branched biodegradable polyester itself can be increased. Furthermore, when the degree of polymerization (P2) of the caprolactone units contained in the random copolymer segment is 200 or less, the breaking strength of the branched biodegradable polyester itself can be prevented from being impaired.

In addition, in the branched biodegradable polyester, the ratio (P2/P1) of the degree of polymerization of caprolactone units (P2) to the degree of polymerization of polylactic acid units (P1) is preferably 0.5 or more and 3 or less. If this ratio (P2/P1) is too small, the flexibility of the branched biodegradable polyester itself may decrease, and if it is too large, the breaking strength of the branched biodegradable polyester itself may decrease.

The homopolymer segment is preferably a lactide homopolymer segment, and although not particularly limited, contains a monomer derived from a homopolymer of any one of L-lactide, D-lactide, and DL-lactide. The homopolymer segment can function as a so-called hard segment in the block structure.

The degree of polymerization (P3) of the lactide homopolymer segment is preferably 5 or more and 200 or less, more preferably 10 or more and 150 or less, and even more preferably 15 or more and 100 or less. When the degree of polymerization (P3) of the lactide homopolymer segment is 5 or more, the breaking strength of the branched biodegradable polyester itself can be increased. Furthermore, when the degree of polymerization (P3) of the lactide homopolymer segment is 200 or less, the flexibility of the branched biodegradable polyester itself can be prevented from decreasing.

The block structure consisting of a random copolymer segment of lactide and caprolactone and a lactide homopolymer segment is represented by the following general formula (B):

(In general formula (B), m, l and k each independently represent an integer of 5 to 200.)

The number average molecular weight (Mn) of the block structure comprising random copolymer segments and homopolymer segments is, for example, 3,000 to 500,000, preferably 10,000 to 300,000, and more preferably 20,000 to 200,000.

The branched biodegradable polyester according to one aspect of the present invention is represented by the following general formula (C):

(In general formula (C), each R is independently a hydrogen atom or the general formula (B) above, and n is an integer of 1 to 30.)

The block structure is not limited to that of general formula (B), and may have at least one block structure exemplified by an X-Y-X block structure and a Y-X-Y block structure, where X represents a random copolymer segment and Y represents a homopolymer segment.

The number-average molecular weight (Mn) of the branched biodegradable polyester of the present invention is, for example, 5,000 to 1,000,000, preferably 10,000 to 500,000, and most preferably 30,000 to 200,000. A number-average molecular weight of 5,000 to 1,000,000 allows for the polyester to have sufficient rigidity for use as a molded article.

The molecular weight distribution of the branched biodegradable polyester, i.e., the ratio of the weight average molecular weight to the number average molecular weight (Mw/Mn), is preferably 1.00 to 3.00, more preferably 1.00 to 2.50, and most preferably 1.00 to 2.00. Having an Mw/Mn ratio of 1.00 to 3.00 can improve mechanical properties such as tensile strength and impact resistance. Here, the number average molecular weight and weight average molecular weight can be measured using known methods, such as GPC (eluent: chloroform, standard: polystyrene).

The branched biodegradable polyester according to one embodiment has high flexibility. This flexibility can be confirmed by the breaking stress and breaking strain of a molded article of the branched biodegradable polyester. The branched biodegradable polyester preferably has a breaking stress of 5 to 100 MPa, and more preferably 10 to 50 MPa. Furthermore, the branched biodegradable polyester preferably has a breaking strain of 50 to 1000%, and more preferably 100 to 1000%.

As described above, the branched biodegradable polyester according to one embodiment has high flexibility and high breaking strength. In other words, the branched biodegradable polyester according to one embodiment is a novel branched biodegradable polyester that has improved brittleness characteristic of biodegradable polyesters and has high breaking strength. For this reason, the branched biodegradable polyester according to one embodiment is expected to be used as a biodegradable polyester material for molding molded articles. Therefore, molded articles obtained by molding the branched biodegradable polyester according to one embodiment also fall within the scope of the present invention.

The molded article obtained by molding the branched biodegradable polyester according to one embodiment can be blended with known additives, as in the case of the molded article of the resin composition according to one embodiment, for example, as described below.

<Resin composition>
The branched biodegradable polyester according to one embodiment comprises both a random copolymer segment and a lactide homopolymer segment, and has a crosslinked structure with a trivalent or higher polyhydric alcohol, thereby improving compatibility with polyester resins such as biodegradable polyesters. Therefore, the branched biodegradable polyester according to one embodiment can be suitably used as a modifier for biodegradable polyester resins. Therefore, a modifier containing the branched biodegradable polyester according to one embodiment and a resin composition containing the branched biodegradable polyester according to one embodiment also fall within the scope of the present invention.

A resin composition containing a branched biodegradable polyester according to one embodiment can typically be blended with polylactic acid, a biodegradable resin. Here, the resin composition preferably contains 1 to 50% by weight of the branched biodegradable polyester and polylactic acid, with the total content of the branched biodegradable polyester and polylactic acid being 100% by weight, and more preferably 5 to 40% by weight. A branched biodegradable polyester content of 1 to 50% by weight can impart high flexibility and high breaking strength to a molded article of the resin composition.

In the branched biodegradable polyester contained in the resin composition, the degree of polymerization (n) of the polyglycerin is preferably 1 to 30, more preferably 2 to 20, and most preferably 4 to 10. When the degree of polymerization (n) of the polyglycerin is greater than 1, the flexibility of the resin composition can be increased. Furthermore, when the degree of polymerization (n) of the polyglycerin is less than 30, the resin composition can be given high flexibility while also being given high breaking strength.

Furthermore, in the branched biodegradable polyester contained in the resin composition, the degree of polymerization (P1) of the polylactic acid units contained in the random copolymer segment is greater than or equal to 5 and less than or equal to 200, thereby imparting high breaking strength to the resin composition containing the branched biodegradable polyester.

Furthermore, in the branched biodegradable polyester contained in the resin composition, the degree of polymerization (P2) of the caprolactone units contained in the random copolymer segments is greater than or equal to 5 and less than or equal to 200, thereby imparting high flexibility to the resin composition containing the branched biodegradable polyester. Furthermore, the degree of polymerization (P2) of the caprolactone units contained in the random copolymer segments is smaller than or equal to 200, thereby preventing the breaking strength of the resin composition from decreasing.

Furthermore, in the branched biodegradable polyester contained in the resin composition, the ratio (P2/P1) of the degree of polymerization of caprolactone units (P2) to the degree of polymerization of polylactic acid units (P1) is preferably 0.5 or greater and 3 or less. If this ratio (P2/P1) is too small, the flexibility of the resin composition may decrease, and if it is too large, the breaking strength of the resin composition may decrease.

Furthermore, in the branched biodegradable polyester contained in the resin composition, the degree of polymerization (P3) of the lactide homopolymer segment is greater than or equal to 5 and less than or equal to 200, thereby increasing compatibility with polylactic acid and increasing the breaking strength of the resin composition.

(stereo complex)
In the resin composition, the branched biodegradable polyester and the base polylactic acid preferably form a stereocomplex. This can enhance the modifying effect on the resin composition. The stereocomplex refers to an interaction between the D-lactide homopolymer portion of the branched biodegradable polyester of the present invention when the base polylactic acid is poly-L-lactic acid, and an interaction between the L-lactide homopolymer portion of the branched biodegradable polyester of the present invention when the base polylactic acid is poly-D-lactic acid.

Whether a resin composition forms a stereocomplex can be confirmed by the presence or absence of peaks at specific diffraction angles using X-ray diffraction.

A resin composition containing a branched biodegradable polyester according to one embodiment combines high breaking strain (resulting in high flexibility) with high breaking strength. For example, when the amount of branched biodegradable polyester added relative to linear PLA is 5 to 15%, the breaking strain of the branched biodegradable polyester is preferably 4% or more, and more preferably 10% or more. Furthermore, when the amount of branched biodegradable polyester added relative to linear PLA is 5 to 15%, the breaking stress of the resin composition is preferably 30 MPa or more, and more preferably 40 MPa or more. Furthermore, when the amount of branched biodegradable polyester added relative to linear PLA is 25 to 35%, the elastic modulus of the resin composition is preferably 1000 to 2200 MPa, and more preferably 1000 to 2000 MPa. The flexibility, breaking stress, and elastic modulus of the resin composition can be adjusted by the blending ratio of the branched biodegradable polyester and polylactic acid depending on the physical properties required of the molded article formed from the resin composition.

The resin composition may contain additives such as antistatic agents, light stabilizers, UV absorbers, nucleating agents, lubricants, antioxidants, antiblocking agents, flow improvers, mold release agents, flame retardants, colorants, inorganic neutralizing agents, hydrochloric acid absorbers, filler conductive agents, chain extenders, and hydrolysis inhibitors, as long as they do not impair the effects of the present invention.

[Method for producing branched biodegradable polyester]
A method for producing a branched biodegradable polyester according to one embodiment will be described in detail below.
The branched biodegradable polyester of the present invention can be produced by using a trivalent or higher polyhydric alcohol as an initiator and reacting a monomer that constitutes a polyester chain with all or part of the hydroxyl groups of the trivalent or higher polyhydric alcohol to extend the polyester chain.

An example of a synthesis method when the trihydric or higher polyhydric alcohol is a polyglycerol represented by general formula (A) is as follows:
General formula (A):

(In general formula (A), n is an integer of 1 to 30.)
The polyglycerol represented by the following general formula (D):

and a compound represented by the following general formula (E):

After polymerizing a compound represented by the general formula (B), a compound represented by the general formula (C) may be polymerized. This allows the production of branched biodegradable polyesters represented by the following general formulas (B) and (C).

General formula (B) represents a polyester chain having a block structure formed from the compounds of general formulas (E) and (D) described above, and in general formula (B), m, l, and k each independently represent an integer of 5 to 200.

In general formula (C), R each independently represents a hydrogen atom or the following general formula (B), and n represents an integer of 1 to 30.

More specifically, in one embodiment, the branched biodegradable polyester can be produced by polymerizing a polyglycerol represented by general formula (A) with a compound represented by formula (D) and a compound represented by formula (E) in the presence of a catalyst, and then further polymerizing the compound represented by formula (D), thereby producing the compounds represented by general formulas (B) and (C).

Examples of compounds represented by general formula (D) include cyclic dimers of lactic acid (e.g., D-lactide, L-lactide, DL-lactide). The amount of compound represented by general formula (D) used is preferably 5 to 200 moles, and more preferably 15 to 100 moles, per mole of hydroxyl groups in polyglycerol represented by general formula (C).

The amount of the compound represented by general formula (E) used is preferably 5 to 200 moles, and more preferably 15 to 100 moles, per mole of hydroxyl groups in the polyglycerol represented by general formula (A).

The catalyst may be a known transesterification catalyst, such as an organotin catalyst such as tin(II) 2-ethylhexanoate, or potassium/naphthalene. The amount of catalyst used is 0.005 to 0.5 mol, preferably 0.01 to 0.1 mol, per 1 mol of hydroxyl groups in the polyglycerol represented by general formula (A).

The reaction is not particularly limited, but may be carried out by first polymerizing (bulk polymerization, etc.) a polyglycerol represented by general formula (A), a compound represented by general formula (D), a compound represented by general formula (E), and a catalyst under an inert gas atmosphere (e.g., argon, etc.) to polymerize the compounds represented by general formulas (G) and (H). More preferably, the polyglycerol represented by general formula (A), a compound represented by general formula (D), a compound represented by general formula (E), and a catalyst under an inert gas atmosphere (e.g., argon, etc.) to produce branched polyesters represented by the following general formulas (G) and (H).

In general formula (G), R is independently selected from a hydrogen atom or a polyester chain represented by the following general formula (H), 50% or more of R are polyester chains of general formula (H), and n is an integer of 1 to 30.

In formula (H), m and l each independently represent an integer of 5 to 200.
Thereafter, it is preferable to isolate and purify the compounds represented by general formulas (G) and (H). Next, the compound represented by general formulas (G) and (H), the compound represented by general formula (D), and the catalyst are polymerized (bulk polymerization, etc.) in an inert gas atmosphere (e.g., argon, etc.). This preferably produces the branched biodegradable polyester represented by the above general formula (B).

The reaction temperature and reaction time can be, for example, 80 to 180°C (preferably 100 to 160°C) for approximately 2 minutes to 24 hours. After the reaction, the target product can be obtained by dissolving the reactant in a soluble solvent and then adding a poor solvent to precipitate the target product.

[Method for producing resin composition]
The resin composition of the present invention can be mixed by pre-blending the polylactic acid and the branched biodegradable polyester of the present invention in a mixer such as a Henschel mixer or a tumbler, and then kneading them together in a kneading device.

There are no particular limitations on the kneading equipment, as long as it can uniformly disperse each component, and production can be carried out using any commonly used resin kneading equipment. Examples include single-screw extruders, multi-screw extruders, Banbury mixers, pressure kneaders, rotating rolls, and internal mixers. The kneading temperature is not limited, but is preferably between the melting point of polylactic acid and approximately 300°C.

[Method for producing molded body]
The branched biodegradable polyester according to one embodiment and its resin composition can be suitably molded by various molding methods such as film molding, blow molding, foam molding, and extrusion molding.

The present invention will be explained below using examples and comparative examples, but the present invention is not limited to these.

The branched PCLA-b-PLA of Examples 1 to 6 was synthesized, and molded bodies thereof, as well as molded bodies of resin compositions containing these branched PCLA-b-PLA, were fabricated. Additionally, the linear PCLA-b-PLA of Comparative Examples 1 and 2 and the branched PCLA of Comparative Example 3 were synthesized, and molded bodies thereof, as well as molded bodies of resin compositions containing these, were fabricated. The physical properties of the molded bodies obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were evaluated.

Example 1
(1) Synthesis of branched PCLA (polycaprolactone lactide) Oligoglycerin (0.564 g, 1.23 × 10 ^-3 mol, 8-branch, manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.) was weighed into a 200 mL recovery flask. Then, an oil bath was heated to 120°C, and the oligoglycerin was dehydrated by drying under reduced pressure for 6 hours. Next, the weight of the dehydrated oligoglycerin (0.500 g, 1.07 × 10 ^-3 mol) was measured, and L-lactide (12.7 g, 8.79 × 10 ^-2 mol, manufactured by Musashino Chemical Laboratory Co., Ltd.), ε-caprolactone (10.0 g, 8.79 × 10 ^-2 mol, manufactured by Tokyo Chemical Industry Co., Ltd.), and tin(II) 2-ethylhexanoate (0.0682 g, 1.68 × 10 ^-4 mol, manufactured by Tokyo Chemical Industry Co., Ltd.) were added to an eggplant flask to prepare a reaction solution. A polymerization tube was then attached to the eggplant flask, and the reaction solution was frozen with liquid nitrogen and then dried under reduced pressure overnight. The oil bath was then heated to 120°C, and the polymerization reaction was carried out for 12 hours. This yielded a crude product of branched PCLA. Subsequently, the crude branched PCLA product was purified by reprecipitation. In the reprecipitation, chloroform (134 mL, manufactured by Wako Pure Chemical Industries, Ltd.) was used as a good solvent, and methanol (2000 mL, manufactured by Wako Pure Chemical Industries, Ltd.) was used as a poor solvent. The precipitate was collected and then dried under reduced pressure to obtain branched PCLA (yield: 86%) in the form of a colorless, transparent, viscous liquid.

The branched PCLA obtained as the product was identified by ¹ H-NMR and GPC.
^1H -NMR measurement:
Deuterated solvent: deuterated chloroform Measuring device: JNM-ECS400 or JNM-AL400 (both manufactured by JEOL)
In the identification by ¹ H-NMR, the number average molecular weight (Mn) was also measured.
GPC Measurement:
Eluent: chloroform Standard substance: polystyrene Flow rate: 1.0 mL/min
Measuring device: GPC-8020 series (manufactured by Tosoh Corporation)
Column: TSKgel G4000HHR, 7.8 mm x 300 mm, 1 column (manufactured by Tosoh Corporation)
In the GPC measurement, the number average molecular weight (Mn) and the weight average molecular weight (Mw) were measured, and the weight average molecular weight (Mw)/number average molecular weight (Mn) was calculated.

(2) Synthesis of Branched PCLA-b-PLA The branched PCLA (2.00 g, 6.05 × ¹⁰ mol) obtained in (1) above and D-lactide (1.39 g, 9.62 × ¹⁰ mol, manufactured by Musashino Chemical Laboratory Co., Ltd.) were weighed into a 100 mL three-necked recovery flask. A reflux condenser was then attached to the recovery flask, and the mixture was dried under reduced pressure overnight. The atmosphere inside the flask was then replaced with a nitrogen atmosphere, and toluene (3 mL, manufactured by Wako Pure Chemical Industries, Ltd.) was added. The flask with the nitrogen atmosphere replaced was then heated in an oil bath at 130°C to uniformly dissolve the branched PCLA and D-lactide in toluene. A solution of tin(II) 2-ethylhexanoate (0.0043 g, 1.06 × ¹⁰ mol) and toluene (0.5 mL) was then added using a syringe to obtain a reaction solution. Thereafter, a polymerization reaction was carried out at a temperature of 130° C. for 8 hours, thereby obtaining a crude product of branched PCLA-b-PLA.

The crude branched PCLA-b-PLA product obtained by polymerization was purified by reprecipitation. Chloroform (27 mL) was used as the good solvent, and diethyl ether (300 mL, Wako Pure Chemical Industries, Ltd.) was used as the poor solvent. The reprecipitated precipitate was collected and dried under reduced pressure to obtain the branched PCLA-b-PLA of Example 1 (yield: 84%) as a white solid.

The branched PCLA-b-PLA was identified using ¹ H-NMR and GPC.
^1H -NMR measurement:
Deuterated solvent: deuterated chloroform Measuring device: JNM-ECS400 or JNM-AL400 (both manufactured by JEOL)
GPC Measurement:
Eluent: chloroform Standard: polystyrene Flow rate: 1.0 mL/min
Measuring device: GPC-8020 series (manufactured by Tosoh Corporation)
Column: TSKgel G4000HHR, 7.8 mm x 300 mm, 1 column (manufactured by Tosoh Corporation)
Table 1 below shows the composition of the branched PCLA-b-PLA of Example 1, as well as the number average molecular weight (Mn) and weight average molecular weight (Mw) determined by ¹ H-NMR and GPC. The weight average molecular weight (Mw)/number average molecular weight (Mn) is shown.

Examples 2 to 6
As shown in Table 1, the branched PCLA-b-PLA of Examples 2 to 4 was synthesized under the same conditions as in Example 1, except that in the synthesis of branched PCLA-b-PLA, D-lactide was replaced with L-lactide or the amount of these lactides was changed.

As shown in Table 1, the branched PCLA-b-PLA of Examples 5 and 6 was synthesized under conditions similar to those of Example 1, except that the amounts of oligoglycerin, L-lactide, and ε-caprolactone used in the synthesis of branched PCLA were changed, and the amount of D-lactide or L-lactide used in the synthesis of branched PCLA-b-PLA was changed.

Table 1 below shows the weight average molecular weight (Mw)/number average molecular weight (Mn) ratio of the branched PCLA-b-PLA of Examples 2 to 6, which were determined by ¹ H-NMR and GPC.

Comparative Example 1
(1) Synthesis of linear PCLA A reaction solution was prepared by weighing 1,12-dodecanediol (0.0647 g, 3.20 × ¹⁰ mol, manufactured by Tokyo Chemical Industry Co., Ltd.), L-lactide (5.52 g, 3.83 × ¹⁰ mol, manufactured by Musashino Chemical Laboratory Co., Ltd.), ε-caprolactone (4.38 g, 3.83 × ¹⁰ mol, manufactured by Tokyo Chemical Industry Co., Ltd.), and tin(II) 2-ethylhexanoate (0.0315 g, 7.78 × ¹⁰ mol, manufactured by Tokyo Chemical Industry Co., Ltd.) into a 200 ml recovery flask. A polymerization tube was then attached to the recovery flask, and the reaction solution was frozen with liquid nitrogen and then dried under reduced pressure overnight.

Then, a polymerization reaction was carried out in an oil bath at 120°C for 12 hours, yielding a crude linear PCLA product. The crude product was then purified by reprecipitation. Chloroform (60 mL, manufactured by Wako Pure Chemical Industries, Ltd.) was used as the good solvent, and methanol (700 mL, manufactured by Wako Pure Chemical Industries, Ltd.) was used as the poor solvent. After collecting the precipitate, it was dried under reduced pressure to yield linear dodecanediol-PCLA (yield: 85%) in the form of a colorless, transparent, viscous liquid.

Dodecanediol-PCLA was identified by ¹ H-NMR and GPC under the same conditions as in Examples 1 to 6.

(2) Synthesis of linear PCLA-b-PLA The synthesized dodecanediol-PCLA (2.51 g, 7.75 × 10 ^-5 mol) and D-lactide (0.45 g, 3.10 × 10 ^-3 mol, manufactured by Musashino Chemical Laboratory Co., Ltd.) were weighed into a 100 mL three-necked recovery flask. A reflux condenser was then attached to the recovery flask, and the mixture was dried under reduced pressure overnight. After drying, the atmosphere inside the flask was replaced with nitrogen, and toluene (5 mL, manufactured by Wako Pure Chemical Industries, Ltd.) was added. Next, the recovery flask, purged with nitrogen, was heated to 130°C in an oil bath, and dodecanediol-PCLA (2.51 g, 7.75 × ¹⁰ mol) and D-lactide were uniformly dissolved in toluene. Then, a solution of tin(II) 2-ethylhexanoate (0.0104 g, 2.57 × ¹⁰ mol) and toluene (0.5 mL) was added using a syringe. The polymerization reaction was then carried out at a temperature of 130°C for 8 hours, thereby obtaining a crude linear PCLA-b-PLA product of Comparative Example 1.

The crude linear PCLA-b-PLA product obtained by polymerization was purified by reprecipitation. Chloroform (18 mL) was used as the good solvent, and diethyl ether (200 mL, Wako Pure Chemical Industries, Ltd.) was used as the poor solvent. The reprecipitated precipitate was collected and dried under reduced pressure to obtain linear PCLA-b-PLA of Comparative Example 1 in the form of a white solid (yield: 91%).

The linear PCLA-b-PLA was identified using ¹ H-NMR and GPC under the same conditions as in Examples 1 to 6.

Comparative Example 2
As shown in Table 1, linear PCLA-b-PLA of Comparative Example 2 was synthesized under the same conditions as those of Comparative Example 1, except that D-lactide was changed to L-lactide when synthesizing linear PCLA-b-PLA.

Comparative Example 3
As shown in Table 1, branched PCLA of Comparative Example 3 was synthesized under the same conditions as in Examples 5 and 6, except that branched PCLA-b-PLA was not synthesized.

Table 1 shows the compositions of the branched biodegradable polyesters of Examples 1 to 5 and the biodegradable polyesters of Comparative Examples 1 to 3.

[Evaluation of physical properties]
(1) Preparation of Test Pieces Linear PLA (Ingeo® Biopolymer 4032D, L-form, manufactured by NatureWorks) (hereinafter referred to as "linear PLLA") and the branched PCLA-b-PLA of Example 1 were weighed into a sample tube so that the weight ratio was 9:1. Dichloromethane (15 mL) was then added and stirred for 2 hours to prepare a 2 wt % solution. The solution was cast into a Teflon® Petri dish (diameter 6 cm) and allowed to stand in a desiccator to dry overnight. After drying, the specimen was dried at 60°C for 4 hours using a vacuum oven (Vacuum Oven ADP200, manufactured by Yamato Scientific Co., Ltd.), followed by drying at 80°C for 4 hours. This resulted in a film of the resin composition containing the branched PCLA-b-PLA of Example 1. The obtained film was punched into a dumbbell shape using a test piece punching blade (No. 7 dumbbell type) to be used as a test piece for a tensile test.

The film other than the punched portion was cut with a razor into pieces approximately 2 cm square and used for X-ray diffraction measurements.

Following the same procedure as when the weight ratio of linear PLLA to branched PCLA-b-PLA of Example 1 was 9:1, linear PLLA and molded articles of Example 1 were obtained in the following weight ratios.
Linear PLLA only Linear PLLA: branched PCLA-b-PLA = 8:2
Linear PLLA: branched PCLA-b-PLA = 7:3
Branched PCLA-b-PLA only (single unit)

Following the same procedure as in Example 1, films were produced from the resin compositions of Examples 2 to 6 and Comparative Examples 1 to 3.

(2) Tensile Test Using a tensile tester (AGS-J manufactured by Shimadzu Corporation), the mechanical properties of each film of Examples 1 to 6 and Comparative Examples 1 to 3 were determined.
Measurement conditions:
Sample shape: dumbbell type (No. 7), test piece width: 2 mm, film thickness: 80 μm
Jig distance: 15 mm, tensile speed: 30 mm/min
The test was carried out at room temperature, with n = 3, 4 or 5. The average values of the modulus of elasticity, breaking stress and breaking strain of each film of Examples 1 to 6 and Comparative Examples 1 to 3 obtained by the tensile test are shown in Table 2.

(3) X-ray Diffraction Measurement Using an X-ray diffractometer (R-AXIS RAPID GN2 manufactured by Rigaku), it was confirmed whether each film of Examples 1 to 6 and Comparative Examples 1 to 3 exhibited diffraction peaks (12°, 21°, 24°) specific to stereocomplex crystals. The measurement was performed under the conditions of a Cu radiation source, 40 kV, 130 mA, and room temperature.

The evaluation results are shown in Table 2.

The following was confirmed from the evaluation results of films molded from the branched PCLA-b-PLA monomers of Examples 1 to 6, the linear PCLA-b-PLA monomers of Comparative Examples 1 and 2, and the branched PCLA monomer of Comparative Example 3.

The films molded from the branched PCLA-b-PLA monolayers of Examples 1 to 6 exhibited both a high breaking stress and a high breaking strain compared to films molded from linear PCLA-b-PLA monolayers and films molded from branched PCLA. In particular, the films molded from the branched PCLA-b-PLA monolayers of Examples 5 and 6 exhibited a high breaking strain of 385% or more compared to the films molded from the linear PCLA-b-PLA monolayers of Comparative Examples 1 and 2, in which the M/OH (degree of polymerization of caprolactone units and polylactic acid units per hydroxyl group) during PCLA synthesis was similar to the M/OH (degree of polymerization of lactide per hydroxyl group) during PCLA synthesis. These results confirm that the films molded from the branched PCLA-b-PLA monolayers of Examples 1 to 6 possess high breaking strength and flexibility.

Furthermore, evaluation of films molded from linear PLLA containing branched PCLA-b-PLA in Examples 5 and 6, linear PLLA containing linear PCLA-b-PLA in Comparative Examples 1 and 2, and linear PLLA containing branched PCLA in Comparative Example 3 also showed that the films molded from linear PLLA containing branched PCLA-b-PLA in Examples 5 and 6 exhibited higher breaking strains than those in Comparative Examples 1 to 3. Furthermore, it was confirmed that the linear PLLA films containing branched PCLA-b-PLA in Examples 1 to 4, particularly at a linear PLLA:branched PCLA-b-PLA ratio of 9:1, exhibited higher breaking stress and breaking strain values compared to films made only of linear PLLA.

The branched biodegradable polyester of the present invention and a molded article made from the resin composition of the present invention are suitable for use as general packaging materials, food packaging, containers, industrial materials, etc. in the fields of daily necessities, civil engineering and construction, electronics and electrical equipment, automotive vehicle parts, packaging, etc.

Claims (9)

A branched biodegradable polyester having a block structure including a random copolymer segment of lactide and caprolactone and a homopolymer segment of lactide, wherein a trihydric or higher polyhydric alcohol is bonded to an end of the block structure,
The branched biodegradable polyester, wherein the trihydric or higher polyhydric alcohol is polyglycerin having a degree of polymerization of 2 to 30 . The branched biodegradable polyester according to claim 1, wherein a trivalent or higher polyhydric alcohol is bonded to the end of the random copolymer segment of the block structure. 3. The branched biodegradable polyester according to claim 1 , wherein the random copolymer segment is a random copolymer segment of any one of L-lactide, D-lactide, and DL-lactide with ε-caprolactone. 4. The branched biodegradable polyester according to claim 1 , wherein the lactide homopolymer segment is an L-lactide homopolymer segment or a D-lactide homopolymer segment. A molded article obtained by molding the branched biodegradable polyester according to any one of claims 1 to 4 . A modifier comprising the branched biodegradable polyester according to any one of claims 1 to 4 . The total content of the branched biodegradable polyester according to any one of claims 1 to 4 and polylactic acid is taken as 100% by weight,
A resin composition comprising the branched biodegradable polyester in an amount of 1% by weight or more and 50% by weight or less, and the polylactic acid in an amount of 50% by weight or more and 99% by weight or less. The resin composition according to claim 7 , wherein a lactide homopolymer segment contained in the branched biodegradable polyester and the polylactic acid form a stereocomplex. A molded article obtained by molding the resin composition according to claim 7 or 8 .