JP2024075281A - Polyester polymer and method for producing polyester polymer - Google Patents

Abstract

The present invention provides a polyester polymer which has excellent heat resistance and excellent marine biodegradability compared to conventional polyester polymers.
[Solution] A polyester-based polymer containing a structural unit (1) represented by the following general formula (1) and a structural unit (2) represented by the following general formula (2), the molar ratio of structural unit (1)/structural unit (2) being in the range of 4 or more and 2,000 or less.
-[O- ^X1 -C(=O)]- (1)
-[O-X ² -C(=O)]- (2)
(In formula (1), -X ¹ - represents a linear divalent hydrocarbon group having 1 to 50 carbon atoms which may have a substituent. In formula (2), -X ² - represents a branched divalent hydrocarbon group having 2 to 50 carbon atoms which may have a substituent.)
[Selected Figure] Figure 1

Description

The present invention relates to a polyester polymer and a method for producing a polyester polymer.

Because polyester resins have excellent toughness, heat resistance, chemical resistance, and mechanical properties, they are used in a variety of everyday packaging materials, including food packaging, medical packaging, pesticide packaging, packaging materials and containers for reagent bottles, packaging for electronic components, and various molded products and textile products.

On the other hand, in recent years, social demands for protecting the natural environment have been increasing, and resins with excellent marine biodegradability (hereinafter referred to as "marine biodegradability") are required due to environmental pollution caused by the disposal of used plastic products, particularly the impact on marine life of microplastics caused by the disposal of used plastic products in the ocean. There is also a demand for polyester resins with marine biodegradability.

Resin products made from polyester resins, which have excellent marine biodegradability, can not only be disposed of as home compost after use, but also biodegrade in the ocean even if they are discarded in the ocean, eliminating the adverse effects of microplastics on marine life.

As examples of polyester-based polymers, Patent Document 1 discloses polyester-based polymers containing structural units derived from hydroxycarboxylic acids having a branched structure, which are obtained by polycondensation of hydroxycarboxylic acids having a branched structure. Patent Documents 2 and 3 disclose polyester-based polymers having no branched structure, which contain structural units derived from α,ω-hydroxy fatty acids. Patent Document 4 discloses polycarbonate-based polymers and polyester-based polymers made of diols and dicarboxylic acids.

US Patent Application Publication No. 2021/0047580 US Patent Application Publication No. 2014/0051780 Japanese Patent Application Laid-Open No. 8-295726 International Publication No. 2021/224303

However, the polyester polymer described in Patent Document 1 does not have sufficient heat resistance such as heat distortion temperature. Furthermore, the polyester polymer specifically disclosed in Patent Document 1 is only a polyester polymer composed of structural units derived from hydroxycarboxylic acid having a branched structure, and there is no teaching about improving biodegradability or heat resistance in the sea.
In addition, the polyester polymers described in Patent Documents 2 and 3 do not have sufficient biodegradability in the sea. Furthermore, the polyester polymers specifically disclosed in Patent Documents 2 and 3 are only polyester polymers composed of structural units derived from hydroxycarboxylic acid having no branched structure, and there is no teaching about improving biodegradability in the sea.

The present invention was made in consideration of the problems of the conventional technology described above, and aims to provide a polyester-based polymer that has excellent heat resistance and excellent marine biodegradability compared to conventional polyester-based polymers.

As a result of extensive research into solving the above problems, the present inventors have discovered that the above problems can be solved by a polyester polymer that has a branched structure and contains a specific structure derived from hydroxycarboxylic acid at a specific content ratio.

That is, the gist of the present invention is as follows:

[1] A polyester-based polymer comprising a structural unit (1) represented by the following general formula (1) and a structural unit (2) represented by the following general formula (2), in which the molar ratio of the structural unit (1)/structural unit (2) is in the range of 4 or more and 2,000 or less.
-[O- ^X1 -C(=O)]- (1)
-[O-X ² -C(=O)]- (2)
(In formula (1), -X ¹ - represents a linear divalent hydrocarbon group having 1 to 50 carbon atoms which may have a substituent. In formula (2), -X ² - represents a branched divalent hydrocarbon group having 2 to 50 carbon atoms which may have a substituent.)

[2] The polyester polymer according to [1], having a mass average molecular weight (Mw) of 20,000 or more and 300,000 or less.

[3] The polyester-based polymer according to [1] or [2], wherein in the structural unit (2), -X ² - contains 1 to 5 methine groups.

[4] The polyester-based polymer according to any one of [1] to [3], wherein in the structural unit (2), the branched structure contained in -X ² - is an aliphatic hydrocarbon group having 1 to 20 carbon atoms which may have a substituent.

[5] In the structural unit (2), -X ² - includes a structural unit (2-1) represented by the following general formula (2-1) and a structural unit (2-2) represented by the following general formula (2-2), with the molar ratio of the structural unit (2-1)/structural unit (2-2) being in the range of 1 to 49:
The polyester-based polymer according to any one of [1] to [4], wherein the total number of structural units, that is, the structural units (2-1) and the structural units (2-2) in the structural unit (2) is within a range of 2 to 50.
-( _CH2 )-(2-1)
-(CHR)- (2-2)
(In formula (2-2), R represents at least one selected from alkyl groups having 1 to 10 carbon atoms which may contain an oxygen atom.)

[6] The polyester-based polymer according to [5], wherein the structural unit (2) is a structural unit (2-3) derived from a compound represented by the following general formula (2-3):
HO- ^X2'- C(=O)-OH (2-3)
(In formula (2-3),
-X ^2' - includes a structural unit (2-3-1) represented by the following general formula (2-3-1) and a structural unit (2-3-2) represented by the following general formula (2-3-2), with the molar ratio of the structural unit (2-3-1)/structural unit (2-3-2) being in the range of 1 or more and 49 or less:
The total number of structural units (2-3-1) and (2-3-2) in one molecule of the compound is within the range of 2 to 50.
-( _CH2 )- (2-3-1)
-(CHR)- (2-3-2)
(In formula (2-2), R represents at least one selected from alkyl groups having 1 to 10 carbon atoms which may contain an oxygen atom.)

[7] The polyester-based polymer according to any one of [1] to [6], wherein the structural unit (1) includes a structural unit (1-1) represented by the following general formula (1-1):
-[O-(CH ₂ ) _a -C(═O)]- (1-1)
(In formula (1-1), a represents an integer of 1 to 50.)

[8] The polyester-based polymer according to [7], wherein the structural unit (1-1) is a structural unit derived from a compound represented by the following general formula (1-2):
HO-(CH ₂ ) _a -C(═O)-OH (1-2)
(In formula (1-2), a represents an integer of 1 to 50.)

[9] A method for producing a polyester polymer according to any one of [1] to [8], comprising subjecting a composition containing a compound represented by the following general formula (1-4) and a compound represented by the following general formula (2-4) to a condensation polymerization reaction in the presence of a catalyst at a temperature within a range of 170 to 250° C.
HO-X ¹ -C(═O)-OH (1-4)
HO-X ² -C(═O)-OH (2-4)
(In formula (1-4), -X ¹ - represents a linear divalent hydrocarbon group having 1 to 50 carbon atoms which may have a substituent. In formula (2-4), -X ² - represents a branched divalent hydrocarbon group having 2 to 50 carbon atoms which may have a substituent. n represents an integer of 1 to 20.)

According to the present invention, a polyester polymer having excellent marine biodegradability and excellent heat resistance can be provided.
Since the polyester-based polymer of the present invention has excellent marine biodegradability, it is expected that plastic products formed from the polymer can reduce environmental pollution caused by the disposal of used plastic products, in particular the impact on marine life of microplastics caused by the disposal of used plastic products in the ocean.

1 is a graph showing the results of a marine biodegradability test of polyester polymers obtained in Examples and Comparative Examples.

The following describes in detail an embodiment of the present invention, but the present invention is not limited to the following description, and can be modified as desired without departing from the gist of the present invention.

In this specification, unless otherwise specified, the term "structural unit" refers to a unit derived from a raw material compound used in the production of the polyester polymer of the present invention, formed by polymerization of the raw material compound, and refers to a partial structure sandwiched between any linking groups in the obtained polymer. It also includes a partial structure at the terminal portion of the polymer, one of which is a linking group and the other of which is a polymerization reactive group. The structural unit may be a unit formed directly by a polymerization reaction, or may be a unit in which a part of the unit is converted into a different structure by treating the obtained polymer.
In this specification, the term "repeating unit" is synonymous with the term "structural unit."

In this specification, unless otherwise specified, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower and upper limits, and "A~B" means greater than or equal to A and less than or equal to B.

In this specification, "mass %" indicates the content ratio of a given component contained in a total amount of 100 mass %.
In addition, in this specification, the number of carbon atoms in a hydrocarbon group means the total number of carbon atoms including the number of carbon atoms in the substituent when the hydrocarbon group has a substituent.

<Polyester Polymer>
The polyester-based polymer of the present invention is a polyester-based polymer containing a structural unit (1) represented by the following general formula (1) and a structural unit (2) represented by the following general formula (2), in which the molar ratio of the structural unit (1)/structural unit (2) is in the range of 4 or more and 2,000 or less.
-[O- ^X1 -C(=O)]- (1)
-[O-X ² -C(=O)]- (2)
(In formula (1), -X ¹ - represents a linear divalent hydrocarbon group having 1 to 50 carbon atoms, preferably 7 to 50 carbon atoms, which may have a substituent. In formula (2), -X ² - represents a branched divalent hydrocarbon group having 2 to 50 carbon atoms, preferably 7 to 50 carbon atoms, which may have a substituent.)

The polyester-based polymer of the present invention may contain a structural unit (3) other than the structural unit (1) and the structural unit (2) for the purpose of imparting mechanical properties, chemical resistance, and the like to the polyester-based polymer, so long as the effects of the present invention are not significantly impaired.
The other structural unit (3) is not particularly limited, and examples thereof include linear or cyclic structural units formed by derivatives such as esters or lactones of aliphatic oxycarboxylic acids such as α,ω-hydroxycarboxylic acids and α-hydroxycarboxylic acids, lactides, or oxycarboxylic acid polymers, and are structural units other than the structural units (1) and (2).

When the polyester polymer of the present invention contains other structural units (3), the content of the other structural units (3) is not particularly limited as long as it does not impair the physical properties of the polyester polymer. However, from the viewpoint of maintaining good heat resistance and marine degradability of the polyester polymer, the content of the other structural units (3) can be usually 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less, based on 100% of the total mass of the polyester polymer. Of course, it is also possible to not contain the other structural units (3).

In the polyester-based polymer of the present invention, the arrangement of the structural unit (1) and the structural unit (2) is not particularly limited, and may be any arrangement that does not reduce the marine biodegradability and heat resistance of the polyester-based polymer.
Specific embodiments of the polyester polymer of the present invention include the following.
A copolymer in which one structural unit (2) is irregularly arranged between chain structures of two or more consecutive structural units (1) (a random copolymer. The structural unit (2) does not form a chain structure but exists as a single unit).
A copolymer in which a chain structure of two or more consecutive structural units (2) is irregularly arranged between chain structures of two or more consecutive structural units (1) (random copolymer, including a chain structure of two or more structural units (2)).
A copolymer (multiblock copolymer) in which chain structures of slightly longer structural units (2) are irregularly arranged between chain structures of relatively long structural units (1).
(Note that, here, the slightly long chain structure of the structural unit (2) refers to a chain structure in which about 2 to 10 structural units (2) are consecutively arranged, and the relatively long chain structure of the structural unit (1) refers to a chain structure in which about 2 to 1,000 structural units (1) are consecutively arranged.)
A copolymer in which one unit of the structural unit (1) and one unit of the structural unit (2) are arranged alternately (alternating copolymer).
The structural unit (1) and the structural unit (2) may each independently be a structural unit derived from one type of compound, or may be a structural unit derived from two or more types of compounds.

In addition, when -X ¹ - in the structural unit (1) and -X ² - in the structural unit (2) have a substituent, the substituent is not particularly limited as long as it can realize a polyester polymer having excellent marine biodegradability and heat resistance, which is the object of the present invention, and examples of the substituent include an ether group and an amino group.

The lower limit of the total content of the structural unit (1) and the structural unit (2) in the polyester polymer of the present invention is not particularly limited as long as it does not impair the physical properties of the polyester polymer, but from the viewpoint of making the heat resistance and marine degradability of the polyester polymer excellent, it is preferably 85% by mass or more, more preferably 87% by mass or more, and even more preferably 90% by mass or more relative to 100% of the total mass of the polyester polymer. On the other hand, the upper limit of the total content of the structural unit (1) and the structural unit (2) is not particularly limited, and may be 100% by mass relative to the total mass of the polyester polymer, or may be preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 96% by mass or less.
The upper and lower limits can be combined in any combination. For example, the total content of the structural unit (1) and the structural unit (2) in the polyester polymer of the present invention is preferably 85% by mass or more and 100% by mass or less, more preferably 87% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less, based on 100% of the total mass of the polyester polymer.

Furthermore, in the polyester polymer of the present invention, the lower limit of the molar ratio of the structural unit (1)/the structural unit (2) is 4 (=80/20) or more from the viewpoint of improving the biodegradability of the polyester polymer and maintaining good heat resistance. The molar ratio of the structural unit (1)/the structural unit (2) is preferably 85/15 or more, more preferably 87/13 or more, and even more preferably 90/10 or more. On the other hand, the upper limit of the molar ratio of the structural unit (1)/the structural unit (2) is 2000 (≒99.95/0.05) or less from the viewpoint of maintaining good marine biodegradability of the polyester polymer. The molar ratio of the structural unit (1)/the structural unit (2) is preferably 99.9/0.1 or less, more preferably 99.5/0.5 or less, and even more preferably 99.2/0.8 or less.
The upper and lower limits can be combined in any combination. For example, in the polyester polymer of the present invention, the molar ratio of the structural unit (1)/the structural unit (2) is 4 or more and 2000 or less, preferably 85/15 or more and 99.9/0.1 or less, more preferably 87/13 or more and 99.5/0.5 or less, and even more preferably 90/10 or more and 99.2/0.8 or less.

The content ratio of each structural unit in the polyester polymer of the present invention can be determined by composition analysis using NMR, as described in the Examples below.

The lower limit of the mass average molecular weight (Mw) of the polyester polymer of the present invention is preferably 20,000 or more, more preferably 22,000 or more, even more preferably 24,000 or more, and particularly preferably 28,000 or more, from the viewpoint of improving the heat resistance of the polyester polymer. On the other hand, the upper limit of the mass average molecular weight (Mw) is preferably 300,000 or less, more preferably 270,000 or less, even more preferably 250,000 or less, and particularly preferably 230,000 or less, from the viewpoint of maintaining good marine biodegradability of the polyester polymer.
The above upper and lower limits can be combined in any combination. For example, the mass average molecular weight (Mw) of the polyester polymer of the present invention is preferably 20,000 to 300,000, more preferably 22,000 to 270,000, even more preferably 24,000 to 250,000, and particularly preferably 28,000 to 230,000.

Furthermore, if the molecular weight distribution (mass average molecular weight/number average molecular weight: Mw/Mn) of the polyester-based polymer of the present invention is too small, the molding processability of the polyester-based polymer may be reduced, whereas if it is too large, the mechanical properties and heat resistance of the polyester-based polymer may be reduced due to the low molecular weight components contained therein. Therefore, Mw/Mn is preferably 1.7 to 20, more preferably 1.8 to 15, and even more preferably 1.9 to 10.
The Mw and Mw/Mn are values measured by gel permeation chromatography (GPC), and the measurement conditions are as described in the Examples below.

The mass average molecular weight (Mw) of the polyester polymer of the present invention can be freely controlled by appropriately optimizing known conditions such as the polymerization method and polymerization conditions for the polyester polymer, the types and blending ratios of the raw materials for the polyester polymer, and the type and amount of the polymerization catalyst.

<Structural unit (1)>
The structural unit (1) is a structural unit constituting the polyester polymer of the present invention and is represented by the following general formula (1).
-[O- ^X1 -C(=O)]- (1)
(In formula (1), -X ¹ - represents a linear divalent hydrocarbon group having 1 to 50 carbon atoms, preferably 7 to 50 carbon atoms, which may have a substituent.)
The polyester polymer of the present invention can have excellent heat resistance by containing the structural unit (1).

The lower limit of the content of the structural unit (1) in the polyester polymer of the present invention is not particularly limited as long as the physical properties of the polyester polymer are not impaired, but from the viewpoint of making the heat resistance and stickiness of the polyester polymer excellent, it is preferably 84% by mass or more, more preferably 86% by mass or more, and even more preferably 89% by mass or more relative to 100% of the total mass of the polyester polymer. On the other hand, the upper limit of the content of the structural unit (1) is not particularly limited, but is preferably 99.9% by mass or less, more preferably 99.4% by mass or less, and even more preferably 99.1% by mass or less relative to 100% of the total mass of the polyester polymer.
The upper and lower limits can be combined in any combination. For example, the content of the structural unit (1) in the polyester polymer of the present invention is preferably 84% by mass or more and 99.9% by mass or less, more preferably 86% by mass or more and 99.4% by mass or less, and even more preferably 89% by mass or more and 99.1% by mass or less, based on 100% of the total mass of the polyester polymer.

<Structural unit (1-1)>
In the polyester-based polymer of the present invention, the structural unit (1) may include a structural unit (1-1) represented by the following general formula (1-1).
-[O-(CH ₂ ) _a -C(═O)]- (1-1)
(In formula (1-1), a represents an integer of 1 to 50, preferably 7 to 50.)

The polyester polymer of the present invention has structural unit (1) containing structural unit (1-1) represented by the above general formula (1-1), which makes it possible to provide the obtained polyester polymer with superior heat resistance.

In the structural unit (1-1), if the value of a, which indicates the number of repeating methylene groups in the general formula (1-1), is too small, the heat resistance of the obtained polyester polymer tends to decrease, whereas if the value of a is too large, the reactivity during polymerization of the polyester polymer tends to decrease.
Therefore, the value of a is an integer of 1 to 50, preferably 5 to 50, more preferably 7 to 50, further preferably 9 to 39, and particularly preferably 11 to 33.

<Compound represented by general formula (1-2)>
By using a structural unit derived from a compound represented by the following general formula (1-2) (hereinafter referred to as “compound (1-2)”) as the structural unit (1-1), the heat resistance of the obtained polyester polymer can be made more excellent.
Compound (1-2) represented by the following general formula (1-2) is an α,ω-hydroxycarboxylic acid in which the value of “a” in general formula (1-2) (hereinafter referred to as “main chain methylene number”) is within the range of 1 to 50.
That is, the structural unit (1-1) in the polyester polymer of the present invention can be formed from a structural unit derived from the compound (1-2).
HO-(CH ₂ ) _a -C(═O)-OH (1-2)
(In formula (1-2), a represents an integer of 1 to 50, preferably 7 to 50.)

In the compound (1-2), if the number of main chain methylenes is too small, the melting point of the resulting polyester polymer tends to decrease and the heat resistance tends to decrease. On the other hand, if the number of main chain methylenes is too large, the polycondensation reaction does not proceed easily when polymerizing the polyester polymer, and the molecular weight of the resulting polyester polymer tends to decrease and the mechanical strength tends to decrease. For this reason, the number of main chain methylenes is an integer of 1 to 50, preferably 5 to 50, more preferably 7 to 50, even more preferably 9 to 39, and particularly preferably 11 to 33.

In the polyester polymer of the present invention, the compound (1-2) is not particularly limited, and examples thereof include 6-hydroxyhexanoic acid, 7-hydroxyheptanoic acid, 8-hydroxyoctanoic acid, 9-hydroxynonanoic acid, 10-hydroxydecanoic acid, 11-hydroxyundecanoic acid, 12-hydroxydodecanoic acid, 13-hydroxytridecanoic acid, 14-hydroxytetradecanoic acid, 15-hydroxypentadecanoic acid, 16-hydroxyhexadecanoic acid, 17-hydroxyheptadecanoic acid, 18-hydroxyoctadecanoic acid, 19-hydroxynonadecanoic acid, 20-hydroxyeicosanoic acid, 21-hydroxyheneicosanoic acid, 22-hydroxydocosanoic acid, 23-hydroxytricosanoic acid, 24-hydroxytetracosanoic acid, 25-hydroxypentacosanoic acid, 26-hydroxyhexacosanoic acid, 27-hydroxyheptacosanoic acid, 28-hydroxyoctacosanoic acid, 29-hydroxynonacosanoic acid, 30-hydroxy Examples of the compounds include triacontanoic acid, 31-hydroxyuntriacontanoic acid, 32-hydroxydotriacontanoic acid, 33-hydroxytritriacontanoic acid, 34-hydroxytetratriacontanoic acid, 35-hydroxypentatriacontanoic acid, 36-hydroxyhexatriacontanoic acid, 37-hydroxyheptatriacontanoic acid, 38-hydroxyoctatriacontanoic acid, 39-hydroxynonatriacontanoic acid, 40-hydroxytetracontanoic acid, 41-hydroxyuntetracontanoic acid, 42-hydroxydotetracontanoic acid, 43-hydroxytritetracontanoic acid, 44-hydroxytetratetracontanoic acid, 45-hydroxypentatetracontanoic acid, 46-hydroxyhexatetracontanoic acid, 47-hydroxyheptatetracontanoic acid, 48-hydroxyoctatetracontanoic acid, 49-hydroxynonatetracontanoic acid, 50-hydroxypentacontanoic acid, and 51-hydroxyhenpentacontanoic acid. These compounds may be used alone or in combination of two or more.

<Structural unit (2)>
The structural unit (2) is a structural unit constituting the polyester polymer of the present invention, and is represented by the following general formula (2).
-[O-X ² -C(=O)]- (2)
(In formula (2), -X ² - represents a divalent hydrocarbon group having a branched structure, which may have a substituent, and which has 2 to 50 carbon atoms, preferably 7 to 50 carbon atoms.)

The polyester polymer of the present invention can have excellent marine biodegradability by containing the structural unit (2).

Furthermore, in the structural unit (2), -X ² - contains 1 to 5 methine groups, which improves the marine biodegradability of the resulting polyester polymer. From the viewpoint of heat resistance, the number of methine groups in -X ² - is preferably 1 to 3.

Furthermore, in the structural unit (2), the branched structure contained in -X ² - can be an aliphatic hydrocarbon group having 1 to 20 carbon atoms which may have a substituent.
When the branched structure is an aliphatic hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, the resulting polyester polymer has better marine biodegradability and heat resistance.

The lower limit of the content of the structural unit (2) in the polyester polymer of the present invention is not particularly limited as long as the physical properties of the polyester polymer are not impaired, but from the viewpoint of making the polyester polymer excellent in marine degradability, it is preferably 0.1 mass% or more, more preferably 0.6 mass% or more, and even more preferably 0.9 mass% or more relative to 100% of the total mass of the polyester polymer. On the other hand, the upper limit of the content of the structural unit (2) is not particularly limited, but is preferably 16 mass% or less, more preferably 14 mass% or less, and even more preferably 11 mass% or less relative to 100% of the total mass of the polyester polymer.
The upper and lower limits can be combined in any combination. For example, the content of the structural unit (2) in the polyester polymer of the present invention is preferably 0.1% by mass or more and 16% by mass or less, more preferably 0.6% by mass or more and 14% by mass or less, and even more preferably 0.9% by mass or more and 11% by mass or less, based on 100% of the total mass of the polyester polymer.

<Structural unit (2-1) and structural unit (2-2)>
Furthermore, in the structural unit (2), it is preferable that -X ² - contains a structural unit (2-1) represented by the following general formula (2-1) and a structural unit (2-2) represented by the following general formula (2-2) in a molar ratio of structural unit (2-1)/structural unit (2-2) in the range of 1 to 49, from the viewpoint of improving the marine biodegradability and heat resistance of the obtained polyester polymer.
-( _CH2 )-(2-1)
-(CHR)- (2-2)
(In formula (2-2), R represents at least one selected from alkyl groups having 1 to 10 carbon atoms which may contain an oxygen atom.)

In the structural unit (2), if the structural unit (2-1) is too small, the heat resistance tends to decrease, and if it is too large, the reactivity tends to be poor. Also, if the structural unit (2-2) is too large, the heat resistance tends to decrease. For this reason, it is preferable that the structural unit (2) contains the structural unit (2-1) and the structural unit (2-2) in a molar ratio of the structural unit (2-1)/structural unit (2-2) in the range of 1 to 49. The molar ratio is preferably 4/1 to 40/1, more preferably 5/1 to 30/1, and even more preferably 6/1 to 20/1.

Furthermore, in the structural unit (2), if the carbonyl group and the alkoxy group are too close to each other, the reactivity decreases, and the molecular weight of the resulting polyester polymer tends to be low. Therefore, the lower limit of the total number of the structural formula (2-1) and the structural formula (2-2) between the carbonyl group and the alkoxy group is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more.

R in the structural unit (2-2) is an alkyl group having 1 to 10 carbon atoms which may contain an oxygen atom. If the alkyl chain length of R is too short, the impact resistance of the resulting polyester polymer tends to decrease, and if it is too long, polymerization of the polyester polymer tends to become difficult. R is preferably an alkyl group having 2 to 8 carbon atoms, more preferably an alkyl group having 2 to 7 carbon atoms, and even more preferably an alkyl group having 3 to 7 carbon atoms.

Specific examples of the alkyl group of R include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups. Examples of the alkyl group containing an oxygen atom include ether-based oxygen-containing aliphatic hydrocarbon groups such as methoxyethyl, methoxyethoxyethyl, methoxybutyl, methoxypentyl, methoxyhexyl, methoxyheptyl, methoxyoctyl, and methoxynonyl groups, and ester-based oxygen-containing aliphatic hydrocarbon groups such as acetoxyethyl, acetoxypropyl, acetoxybutyl, acetoxyhexyl, acetoxyheptyl, and acetoxyoctyl groups. These alkyl groups may be used alone or in combination of two or more.

<Structural unit (2-3)>
Furthermore, it is preferable that the structural unit (2) is a structural unit (2-3) derived from a compound represented by the following general formula (2-3) (hereinafter referred to as “compound (2-3)”), from the viewpoint of improving the marine biodegradability and heat resistance of the obtained polyester polymer.
HO- ^X2'- C(=O)-OH (2-3)
(In formula (2-3),
-X ^2' - includes a structural unit (2-3-1) represented by the following general formula (2-3-1) and a structural unit (2-3-2) represented by the following general formula (2-3-2), with the molar ratio of the structural unit (2-3-1)/structural unit (2-3-2) being in the range of 1 or more and 49 or less:
The total number of structural units (2-3-1) and (2-3-2) in one molecule of the compound (2-3) is within the range of 2 to 50, preferably 3 to 50.
-( _CH2 )- (2-3-1)
-(CHR)- (2-3-2)
(In formula (2-3-2), R represents at least one selected from alkyl groups having 1 to 10 carbon atoms which may contain an oxygen atom.)

In the structural unit (2), if the structural unit (2-3-1) is too small, the heat resistance of the resulting polyester polymer tends to decrease, whereas if it is too large, the reactivity tends to be poor. Also, if the structural unit (2-3-2) is too large in the structural unit (2), the heat resistance of the resulting polyester polymer tends to decrease.
For this reason, the structural unit (2) preferably contains the structural unit (2-3-1) and the structural unit (2-3-2) in a molar ratio of the structural unit (2-3-1)/structural unit (2-3-2) in the range of 1 to 49. The molar ratio is preferably 4/1 to 40/1, more preferably 5/1 to 30/1, and even more preferably 6/1 to 20/1.

Furthermore, in the structural unit (2), if the carbonyl group and the alkoxy group are too close to each other, the reactivity decreases, and the molecular weight of the resulting polyester polymer may become low. For this reason, the total number of structural units (2-3-1) and structural units (2-3-2) present between the carbonyl group and the alkoxy group is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more.

In the polyester polymer of the present invention, the compound (2-3) is not particularly limited, but examples thereof include 2-hydroxy-2-methylpentanoic acid, 3-hydroxy-2-methylpentanoic acid, 4-hydroxy-2-methylpentanoic acid, 5-hydroxy-2-methylpentanoic acid, 2-hydroxy-3-methylpentanoic acid, 3-hydroxy-3-methylpentanoic acid, 5-hydroxy-3-methylpentanoic acid, 2-hydroxy-4-methylpentanoic acid, 3-hydroxy-4-methylpentanoic acid, 2-(hydroxymethyl)pentanoic acid, 4-hydroxyhexanoic acid, 5-hydroxyhexanoic acid, 2-ethyl-2-hydroxymethylhexanoic acid, 7-hydroxy-2-methylheptanoic acid, 2-hydroxyoctanoic acid, 3-hydroxyoctanoic acid, 7-hydroxyoctanoic acid, 8-hydroxy-2-propyloctanoic acid, 2-hydroxynonanoic acid, 3-hydroxy Nonanoic acid, 8-hydroxynonanoic acid, 9-hydroxy-3-methylnonanoic acid, 2-hydroxydecanoic acid, 3-hydroxydecanoic acid, 4-hydroxydecanoic acid, 5-hydroxydecanoic acid, 6-hydroxydecanoic acid, 8-hydroxydecanoic acid, 9-hydroxydecanoic acid, 10-hydroxy-2-propyldecanoic acid, 11-hydroxy-4-methylundecanoic acid, 3-hydroxy-2-methyldodecanoic acid, 12-hydroxy-3-methyldodecanoic acid, 3-hydroxy-10-methyldodecanoic acid, 3-hydroxy-11-methyldodecanoic acid, 12-hydroxy-4-butyldodecanoic acid, 2-hydroxytridecanoic acid, 3-hydroxytridecanoic acid, 13-hydroxy-2-methyltridecanoic acid, 2-hydroxytetradecanoic acid, 3-hydroxytetradecanoic acid, 6-hydroxytetradecanoic acid, 10-hydroxytetradecanoic acid, 11-hydroxytetradecanoic acid, 12-hydroxytetradecanoic acid, 13-hydroxytetradecanoic acid, 14-hydroxy-4-methyltetradecanoic acid, 3-hydroxypentadecanoic acid, 15-hydroxy-5-methylpentadecanoic acid, 16-hydroxy-2-methylhexadecanoic acid, 2-hydroxyheptadecanoic acid, 3-hydroxyheptadecanoic acid, 5-hydroxyheptadecanoic acid, 6-hydroxyheptadecanoic acid, 8-hydroxyheptadecanoic acid, 10-hydroxyheptadecanoic acid, 12-hydroxyheptadecanoic acid, 13-hydroxyheptadecanoic acid, 2-hydroxyoctadecanoic acid, 3-hydroxyoctadecanoic acid, 9-hydroxyoctadecanoic acid, 10-hydroxyoctadecanoic acid, 12-hydroxystearic acid, 18-hydroxy-2-methyloctadecanoic acid, 18-hydroxy-5-methyloctadecanoic acid, 19-hydroxy-3-methylnonadecanoic acid, 20-hydroxy Examples of the hydroxy-2-methyleicosanoic acid include 2-hydroxyhenicosanoic acid, 3-hydroxyhenicosanoic acid, 21-hydroxy-6-methylhenicosanoic acid, 3-hydroxy-20-methylhenicosanoic acid, 2-hydroxydocosanoic acid, 3-hydroxydocosanoic acid, 13-hydroxydocosanoic acid, 14-hydroxydocosanoic acid, 22-hydroxy-3-methyldocosanoic acid, 3-hydroxy-20-methyldocosanoic acid, 2-hydroxytricosanoic acid, 3-hydroxytricosanoic acid, 23-hydroxy-6-propyltricosanoic acid, 2-hydroxytetracosanoic acid, 24-hydroxy-2-methyltetracosanoic acid, 25-hydroxy-3-methylpentacosanoic acid, 25-hydroxy-2-propylpentacosanoic acid, 26-hydroxy-6-methylhexacosanoic acid, 27-hydroxy-3-methylheptacosanoic acid, and 29-hydroxy-9-methylnonacosanoic acid. These compounds may be used alone or in combination of two or more.

<Method of producing polyester polymer>
The method for producing the polyester polymer of the present invention is not particularly limited, and examples thereof include known polycondensation methods, ring-opening polymerization methods, etc. Either batch polymerization or continuous polymerization may be used, and either a transesterification reaction or a direct polymerization reaction may be used.

Examples of the transesterification catalyst used in the transesterification reaction include oxides and acetates of Mg, Mn, Zn, Ca, Li, and Ti. Examples of the polycondensation catalyst include compounds such as oxides and acetates of Sb, Ti, Ge, and Al, and organic sulfonic acid compounds. If the film formed using the polyester polymer of the present invention may come into direct contact with food, it is preferable that the film does not contain Sb compounds or organic sulfonic acid compounds, and it is preferable to polymerize the polyester using Ti or Ge compounds as a polycondensation catalyst. Since the polyester after polymerization contains monomers, oligomers, and by-products such as acetaldehyde and tetrahydrofuran, it is preferable to perform solid-phase polymerization at a temperature of 200°C or higher under reduced pressure or in an inert gas flow.

In the polymerization of the polyester polymer of the present invention, known additives such as antioxidants, heat stabilizers, ultraviolet absorbers, and antistatic agents can be added as necessary. Examples of antioxidants include hindered phenol compounds and hindered amine compounds. Examples of heat stabilizers include phosphorus compounds. Examples of ultraviolet absorbers include benzophenone compounds and benzotriazole compounds.

One embodiment of the method for producing a polyester-based polymer of the present invention includes a method in which a compound represented by the following general formula (1-4) (hereinafter referred to as "compound (1-4)") and a compound represented by the following general formula (2-4) (hereinafter referred to as "compound (2-4)") are subjected to a polycondensation reaction in the presence of a catalyst at a temperature within a range of 170 to 250°C to obtain a polyester-based polymer containing a structural unit derived from the compound (1-4), i.e., the structural unit (1) described above, and a structural unit derived from the compound (2-4), i.e., the structural unit (2) described above.
HO-X ¹ -C(═O)-OH (1-4)
HO-X ² -C(═O)-OH (2-4)
(In formula (1-4), -X ¹ - represents a linear divalent hydrocarbon group having 1 to 50 carbon atoms, preferably 7 to 50 carbon atoms, which may have a substituent. In formula (2-4), -X ² - represents a branched divalent hydrocarbon group having 2 to 50 carbon atoms, preferably 7 to 50 carbon atoms, which may have a substituent.)

As the compound (1-4), the aforementioned compounds exemplified as compound (1-2) (e.g., 16-hydroxyhexadecanoic acid) can be used.

As the compound (2-4), the aforementioned compounds exemplified as compound (2-3) (such as 12-hydroxystearic acid) can be used.

In the method for producing a polyester polymer of the present invention, the method of polycondensation reaction is not particularly limited, but a method can be used in which a first-stage initial polymerization is carried out by raising the temperature under an inert gas at normal pressure, and then a second-stage polymerization is carried out under reduced pressure.
Furthermore, by carrying out solid-phase polymerization or the like after carrying out the first and second polymerization reactions, a polyester polymer having a higher molecular weight can be obtained.

The conditions for the first stage initial polymerization are not particularly limited, but it is desirable to raise the temperature from room temperature at a rate of 0.5 to 10°C/min, and when it reaches 170 to 250°C, keep the temperature constant and continue the reaction for another 30 minutes to 24 hours. The conditions for the second stage polymerization, which is carried out after reducing the pressure, are not particularly limited, but it is desirable to maintain the temperature raised in the initial polymerization and polymerize under pressure conditions of 10 mmHg or less, preferably 3 mmHg or less.

The time for adding the transesterification catalyst and polycondensation catalyst is not particularly limited, and they may be added together with the compounds (1-4) and (2-4), or may be added during reduced pressure after the completion of the initial polymerization. However, if the compounds (1-4) and (2-4) are in the form of aqueous solutions, it is preferable to add them after the concentration under reduced pressure is completed.

The polyester polymer of the present invention may contain known additives such as antioxidants, light stabilizers, ultraviolet absorbers, metal soaps, hydrochloric acid absorbers, and other stabilizers, nucleating agents, lubricants, antistatic agents, and antiblocking agents, depending on the intended use, to the extent that the desired performance of the polymer is not impaired.

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[raw materials]
The abbreviations for the compounds used in the following Examples and Comparative Examples are as follows.
16HD: 16-hydroxyhexadecanoic acid (Tokyo Chemical Industry Co., Ltd.)
12HS: 12-hydroxystearic acid (Tokyo Chemical Industry Co., Ltd.)
Ti(OiPr) ₄ : tetraisopropyl titanate (manufactured by Tokyo Chemical Industry Co., Ltd.)
BHT: Dibutylhydroxytoluene (Tokyo Chemical Industry Co., Ltd.)

[Evaluation method]
<Marine biodegradability test of polyester polymer>
The polyester polymers obtained in the examples and comparative examples were pulverized to a particle size (sieving method) of 250 μm or less to obtain pulverized resins. The biodegradability of the pulverized resins was measured according to the following procedure in accordance with ISO 14851.
30 mg of a polyester polymer sample was placed in a 510 mL brown bottle, and 100 mL of a mixture of standard test culture medium and seawater prepared according to a method in accordance with ISO 14851 was added. A pressure sensor (manufactured by WTW, model name: OxiTop (registered trademark)-C type) was attached to the brown bottle, and the test solution was stirred with a stirrer in a high-temperature environment of 25°C. The biodegradability (%) was calculated based on the BOD measurement, and its change over time was examined.

<Mass average molecular weight (Mw) and number average molecular weight (Mn) of polyester polymer>
For the polyester polymers obtained in the examples and comparative examples, the weight average molecular weight (Mw) and number average molecular weight (Mn) were determined by gel permeation chromatography (GPC measurement) according to the following procedure.
A sample of a polyester-based polymer (about 20 mg) was collected in a vial for a high-temperature GPC sample pretreatment device (manufactured by Polymer Laboratory, model name: PL-SP 260VS), and an o-dichlorobenzene solution containing BHT as a stabilizer (BHT concentration: 0.5 g/L) was added so that the concentration of the polyester-based polymer became 0.1% by mass.
Next, the vial containing the sample was placed in the high-temperature GPC sample pretreatment device and heated to 135° C. to dissolve the polyester polymer, and then filtered using a glass filter to obtain a sample for GPC measurement. In any case, no polyester polymer was observed trapped in the glass filter.
Next, using a high-temperature GPC apparatus equipped with an RI detector (manufactured by Tosoh Corporation, model name: HLC-8321GPC/HT, column: Tosoh Corporation TSKgel GMH-HT (30 cm × 4 columns)), GPC measurement was performed under the measurement conditions of a sample injection amount of about 300 μL, a column temperature of 135° C., o-dichlorobenzene as a measurement solvent (mobile phase), and a flow rate of 1.0 mL/min.
The molecular weight of the polyester polymer was calculated based on a calibration curve relating to retention time and molecular weight, which was created from the viscosity equation for the ethylene polymer using a commercially available monodisperse polystyrene as a standard sample, using [η]=K× ^Mα , where K=1.38E ⁻⁴ and α=0.70 for polystyrene and K=4.77E ⁻⁴ and α=0.70 for the ethylene polymer.

<Melting point (Tm) and crystallization temperature (Tc) of polyester polymer>
The melting point (Tm) and crystallization temperature (Tc) of the polyester polymers obtained in the examples and comparative examples were measured using a differential scanning calorimeter (DSC) (manufactured by Hitachi High-Tech Science Corporation, model name: TA7000 DSC7020 AS-3D) according to the following procedure.
Approximately 1 mg of the polyester polymer was placed in a sample container and held at 30°C for 3 minutes under a nitrogen gas atmosphere. Then, the sample was heated from 30°C to 210°C at a heating rate of 10°C/min, and held at 210°C for 5 minutes. Then, the sample was cooled from 210°C to -10°C at a cooling rate of 10°C/min, and held at -10°C for 5 minutes. Then, the sample was heated from -10°C to 210°C at a heating rate of 10°C/min, and the melting point (Tm) and crystallization temperature (Tc) (unit: °C) at this time were determined.

<Composition analysis of polyester polymer>
The composition of the polyester polymers obtained in the examples and comparative examples was analyzed using a ¹³ C-NMR analyzer (manufactured by Bruker, model name: AVANCE 500 MHz) in the following manner.
30 mg of the polyester polymer was dissolved in ODCB (orthodichlorobenzene) _-d (0.6 mL) to prepare an NMR measurement sample. The obtained NMR measurement sample was subjected to ¹³ C-NMR measurement using a 13 C-NMR measurement device under the following conditions: measurement temperature 130° C., pp: zgig (inverse gate decoupling 13 C), number of accumulations ns: ³⁰⁰⁰ times, and D1: 14.8 seconds.

[Example 1]
To a mixture of 16HD (13.77 g, 50.55 mmol) and 12HS (0.40 g, 1.33 mmol), 0.63 mL of a butanol solution of Ti(O-iPr) ₄ (10 mg/mL) (6.3 mg (0.022 mmol) in terms of Ti(O-iPr) ₄ ) was added under a nitrogen atmosphere, and the temperature of the mixture was raised to 200° C. with stirring.
The mixture was stirred for 2 hours while maintaining the temperature at 200° C., and then heated and stirred at 220° C. under reduced pressure (0.39 Torr) for 4 hours.
The mixture was then cooled to room temperature, and toluene (100 mL) was added to the cooled mixture while stirring, and the resulting solution was poured into acetone (500 mL) to obtain a suspension.
The resulting suspension was filtered, and the resulting filtrate was dried at 25° C. for 12 hours to obtain a white powdery polyester polymer (12.75 g).
The polyester polymer thus obtained was evaluated to have Mw of 51,000, Mn of 18,000, Tm of 91°C and Tc of 77°C.
The content of structural units derived from 12-hydroxystearic acid in the polyester polymer calculated by ^13C -NMR measurement was 2.2 mol% (2.5 mass% relative to 100% polyester polymer) when the total number of moles of structural units constituting the polyester polymer was taken as 100 mol%. Therefore, the content of structural units derived from 16HD was calculated to be 97.8 mol% (97.5 mass% relative to 100% polyester polymer).
The results of the marine biodegradability test of this polyester polymer are shown in FIG.

[Comparative Example 1]
The same operation as in Example 1 was carried out, except that only 16HD (15.88 g, 58.29 mmol) was used instead of 16HD and 12HS in Example 1, to obtain a white powdery polyester polymer (15.33 g).
The polyester polymer thus obtained was evaluated to have Mw of 68,000, Mn of 36,000, Tm of 94°C and Tc of 79°C.
The results of the marine biodegradability test of this polyester polymer are shown in FIG.

As is clear from Fig. 1, the polyester polymer of Example 1 was excellent in marine biodegradability. Furthermore, the polyester polymer had sufficient molecular weights (Mw, Mn) and also had high melting points and crystallization temperatures, and therefore it was found to have thermal properties and mechanical properties at levels sufficient for practical use.
On the other hand, the polyester polymer of Comparative Example 1 did not have a branched structure and was therefore inferior in marine biodegradability to the polyester polymer obtained in Example 1 produced under approximately the same conditions.

The polyester-based polymer of the present invention contains a linear structure and a branched structure in a moderate molar ratio in the repeating structural unit, and therefore has excellent marine biodegradability and heat resistance. In addition, in combination with the good toughness, chemical resistance, and mechanical properties that are inherent characteristics of polyester-based polymers, it is expected that the polyester-based polymer can be used for applications such as packaging materials for various everyday items, such as packaging materials and containers for food packaging, medical packaging, pesticides, and reagent bottles, packaging materials for electronic components, as well as various molded products and textile products, to reduce environmental pollution caused by the disposal of used plastic products, in particular the impact on marine life of microplastics caused by the disposal of used plastic products in the ocean.

Claims (9)

A polyester-based polymer comprising a structural unit (1) represented by the following general formula (1) and a structural unit (2) represented by the following general formula (2), the molar ratio of the structural unit (1)/the structural unit (2) being in the range of 4 or more and 2,000 or less.
-[O- ^X1 -C(=O)]- (1)
-[O-X ² -C(=O)]- (2)
(In formula (1), -X ¹ - represents a linear divalent hydrocarbon group having 1 to 50 carbon atoms which may have a substituent. In formula (2), -X ² - represents a branched divalent hydrocarbon group having 2 to 50 carbon atoms which may have a substituent.) The polyester polymer according to claim 1, having a mass average molecular weight (Mw) of 20,000 or more and 300,000 or less. 2. The polyester polymer according to claim 1, wherein in the structural unit (2), --X ² -- contains 1 to 5 methine groups. 2. The polyester-based polymer according to claim 1, wherein in the structural unit (2), the branched structure contained in -X ² - is an aliphatic hydrocarbon group having 1 to 20 carbon atoms which may have a substituent. In the structural unit (2), -X ² - includes a structural unit (2-1) represented by the following general formula (2-1) and a structural unit (2-2) represented by the following general formula (2-2), with the molar ratio of the structural unit (2-1)/structural unit (2-2) being within the range of 1 or more and 49 or less:
2. The polyester-based polymer according to claim 1, wherein the total number of structural units, the structural units (2-1) and the structural units (2-2), in the structural unit (2) is within the range of 2 to 50.
-( _CH2 )-(2-1)
-(CHR)- (2-2)
(In formula (2-2), R represents at least one selected from alkyl groups having 1 to 10 carbon atoms which may contain an oxygen atom.) The polyester-based polymer according to claim 5, wherein the structural unit (2) is a structural unit (2-3) derived from a compound represented by the following general formula (2-3):
HO- ^X2'- C(=O)-OH (2-3)
(In formula (2-3),
-X ^2' - includes a structural unit (2-3-1) represented by the following general formula (2-3-1) and a structural unit (2-3-2) represented by the following general formula (2-3-2), with the molar ratio of the structural unit (2-3-1)/structural unit (2-3-2) being in the range of 1 or more and 49 or less:
The total number of structural units (2-3-1) and (2-3-2) in one molecule of the compound is within the range of 2 to 50.
-( _CH2 )- (2-3-1)
-(CHR)- (2-3-2)
(In formula (2-2), R represents at least one selected from alkyl groups having 1 to 10 carbon atoms which may contain an oxygen atom.) The polyester-based polymer according to claim 1, wherein the structural unit (1) includes a structural unit (1-1) represented by the following general formula (1-1):
-[O-(CH ₂ ) _a -C(═O)]- (1-1)
(In formula (1-1), a represents an integer of 1 to 50.) The polyester-based polymer according to [7], wherein the structural unit (1-1) is a structural unit derived from a compound represented by the following general formula (1-2):
HO-(CH ₂ ) _a -C(═O)-OH (1-2)
(In formula (1-2), a represents an integer of 1 to 50.) A method for producing a polyester polymer according to any one of claims 1 to 8, comprising subjecting a composition containing a compound represented by the following general formula (1-4) and a compound represented by the following general formula (2-4) to a condensation polymerization reaction in the presence of a catalyst at a temperature within a range of 170 to 250°C.
HO-X ¹ -C(═O)-OH (1-4)
HO-X ² -C(═O)-OH (2-4)
(In formula (1-4), -X ¹ - represents a linear divalent hydrocarbon group having 1 to 50 carbon atoms which may have a substituent. In formula (2-4), -X ² - represents a branched divalent hydrocarbon group having 2 to 50 carbon atoms which may have a substituent.)

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