Block copolymer

Abstract

A block copolymer that contains a block structural unit (A) having a polylactic acid unit (a) as a main component, and a block structural unit (B) having a polyester unit (b) as a main component, the polyester unit (b) containing a unit derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), the aliphatic diol (b1) being a C5-9 aliphatic diol that has an alkyl group as a side chain, the carbon number of the aliphatic dicarboxylic acid (b2) being 5-12, and the number-average molecular weight being greater than 10,000.

Description

block copolymer

[0001] The present invention relates to a block copolymer that is excellent in biodegradability, hydrolysis resistance, and handleability.

[0002] From the perspective of environmental protection, bioplastics have been actively developed. Polylactic acid, a bioplastic, is made from renewable plant-derived resources such as corn, which are produced by photosynthesis, and is expected to be used in a wide range of fields. However, compared to petroleum-based plastics, polylactic acid is known to be brittle, inferior in viscosity, flexibility, impact resistance, and heat resistance, and is also prone to hydrolysis. This sometimes limits its use as a resin material. Attempts to overcome the drawbacks of polylactic acid have included, for example, copolymerization of polylactic acid with polyesters having various characteristics, compositions prepared by adding additives such as chain extenders and fillers (see, for example, Patent Documents 1 to 4), and the use of stereocomplexes of polylactic acid (see, for example, Patent Document 5). Furthermore, applications of compositions containing polylactic acid are also being investigated. For example, a pressure-sensitive adhesive composition using biodegradable raw materials that satisfies adhesive properties has been disclosed (see, for example, Patent Document 6).

[0003] Japanese Patent Laid-Open No. 9-100344 Japanese Patent Laid-Open No. 2004-231772 Japanese Patent Laid-Open No. 2005-330318 Japanese Patent Laid-Open No. 2007-269842 Japanese Patent Laid-Open No. 2011-153275 Japanese Patent Laid-Open No. 2021-169586

[0004] It can be assumed that the resins or resin compositions containing polylactic acid described in Patent Documents 1 to 6 have a certain degree of biodegradability. Here, biodegradability refers to the property of ultimately being decomposed into water and carbon dioxide by organisms such as microorganisms, and resins containing polylactic acid are known to exhibit biodegradability in compost. However, growing environmental awareness has led to a demand for broader biodegradability. Furthermore, final products made from resin materials are required to be hydrolytically resistant to prevent deterioration over time. Therefore, bioplastics must possess both biodegradability and hydrolytic resistance depending on the application. Furthermore, bioplastics are desired to be easy to handle as resin materials.

[0005] Therefore, an object of the present invention is to provide a block copolymer that is excellent in biodegradability, hydrolysis resistance, and handleability in activated sludge and compost.

[0006] As a result of intensive research to solve the above problems, the present inventors have conceived the following invention and found that the above problems can be solved.

[0007] [1] A block copolymer comprising block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b), wherein the polyester units (b) contain units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), the aliphatic diol (b1) being an aliphatic diol having from 5 to 9 carbon atoms and having an alkyl group as a branched chain, the aliphatic dicarboxylic acid (b2) having from 5 to 12 carbon atoms, and having a number average molecular weight of more than 10,000. [2] The block copolymer according to [1] above, wherein the content of the block structural units (A) is from 5 to 95 mass% relative to 100 mass% of the total of the block structural units (A) and the block structural units (B). [3] The block copolymer according to [1] or [2] above, wherein the aliphatic diol (b1) has hydroxyl groups at both ends of the main chain. [4] The block copolymer according to any one of [1] to [3], wherein the aliphatic diol (b1) is 3-methyl-1,5-pentanediol. [5] The block copolymer according to any one of [1] to [4], wherein the aliphatic dicarboxylic acid (b2) is adipic acid. [6] The block copolymer according to any one of [1] to [5], wherein the block structural unit (A) comprises a structural unit derived from poly-L-lactic acid or a structural unit derived from poly-D-lactic acid. [7] The block copolymer according to any one of [1] to [6], wherein the melting point is 125°C or higher and lower than 185°C.

[0008] According to the present invention, it is possible to provide a block copolymer that is excellent in biodegradability, hydrolysis resistance, and handleability in activated sludge and compost.

[0009] The following describes an embodiment of the present invention. However, the embodiment described below is merely an example for embodying the technical concept of the present invention, and the present invention is not limited to the following description. In this specification, preferred embodiments are shown, but a combination of two or more of the individual preferred embodiments is also a preferred embodiment. For matters indicated as numerical ranges, when there are several numerical ranges, the lower and upper limits can be selectively combined to create a preferred embodiment. Furthermore, when a numerical range is described as "XX to YY," it means "XX or more and YY or less." In this specification, "~ unit" (where "~" indicates a polymer) means "a structural unit derived from ~." For example, "polylactic acid unit" means "a structural unit derived from polylactic acid," and "polyester unit" means "a structural unit derived from polyester." In this specification, the "main chain" of a polymer refers to the longest molecular chain in the polymer molecule, unless otherwise specified. Furthermore, "branched chain" refers to a molecular chain other than the main chain in the molecule. In this specification, "solid" means a non-fluid state at room temperature (23°C) and under no pressure.

[0010] The block copolymer of this embodiment contains a block structural unit (A) mainly composed of a polylactic acid unit (a) and a block structural unit (B) mainly composed of a polyester unit (b), and has a number-average molecular weight of more than 10,000. The inventors have conducted extensive research into formulations for imparting a wide range of biodegradability, excellent hydrolysis resistance, and ease of handling to the block copolymer. As a result, the inventors have found that containing the block structural unit (A) and the block structural unit (B) is an effective formulation for achieving biodegradability not only in compost but also in activated sludge and excellent hydrolysis resistance. In addition, they have found that if the number-average molecular weight of the block copolymer is within a specific range, it becomes solid, has excellent handleability, and also has excellent hydrolysis resistance.

[0011] The polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), characterized in that the aliphatic diol (b1) is an aliphatic diol having 5 to 9 carbon atoms and a branched alkyl group, and the aliphatic dicarboxylic acid (b2) has 5 to 12 carbon atoms. These characteristics facilitate the formation of an amorphous polymer in the block structural unit (B), which is believed to facilitate the incorporation of microorganisms into the polymer structure during biodegradation, resulting in excellent broad-spectrum biodegradability. Furthermore, the presence of an alkyl group in the branched alkyl group in the aliphatic diol (b1) is believed to improve hydrolysis resistance. On the other hand, if the block structural unit (B) is not an amorphous polymer, it is believed that microorganisms will have difficulty incorporation into the polymer structure, resulting in poor biodegradation, and the effects of the present invention will not be achieved. However, being an amorphous polymer is only one factor affecting biodegradability and hydrolysis. This is because biodegradation and hydrolysis are thought to be caused by a combination of various factors, such as whether microorganisms recognize the amorphous structure as food, whether enzymes and microorganisms can easily access it, steric hindrance of the main chain, melting point, and crystallinity. Therefore, it is not the case that the effects of the present invention can be achieved simply by using an amorphous polymer. In addition, it is unclear why the inclusion of the polyester unit (b) allows the realization of both a wide range of biodegradability and excellent hydrolysis resistance, which are mutually exclusive properties.

[0012] [Block structural unit (A)] <Polylactic acid unit (a)> The block structural unit (A) is mainly composed of polylactic acid unit (a). The "main component" refers to the unit that is contained in the block structural unit (A) at the highest content ratio. Preferably, the "main component" is the unit that is contained in the block structural unit (A) at the highest content ratio by mass percentage. The content of polylactic acid unit (a) in the block structural unit (A) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 85% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass. There is no upper limit to the amount of polylactic acid unit (a) contained in the block structural unit (A), and it may be, for example, 100% by mass or less.

[0013] The polylactic acid constituting the polylactic acid unit (a) may be prepared by direct condensation of lactic acid or by ring-opening polymerization of lactide. The lactic acid may be, for example, at least one selected from the group consisting of L-lactic acid, D-lactic acid, and DL-lactic acid. The lactide may be, for example, at least one selected from the group consisting of L-lactide, D-lactide, DL-lactide, and meso-lactide. Furthermore, the polylactic acid may be poly-L-lactic acid, poly-D-lactic acid, poly-DL-lactic acid, or a stereocomplex polylactic acid obtained by mixing poly-L-lactic acid and poly-D-lactic acid. From the viewpoints of cost, availability of raw materials, and handleability of the block copolymer, poly-L-lactic acid, poly-D-lactic acid, and poly-DL-lactic acid are preferred, with poly-L-lactic acid and poly-D-lactic acid being more preferred. On the other hand, from the viewpoints of synthesis cost, complexity, and processability of the block copolymer, it is preferable that the polylactic acid is not a stereocomplex polylactic acid. From the viewpoint of even better biodegradability and hydrolysis resistance, the block structural units (A) contain structural units derived from poly-L-lactic acid or structural units derived from poly-D-lactic acid in an amount of preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. For example, in one preferred embodiment, the block structural units (A) are composed of structural units derived from poly-L-lactic acid or structural units derived from poly-D-lactic acid, i.e., the structural units derived from poly-L-lactic acid or structural units derived from poly-D-lactic acid account for 100% by mass.

[0014] <Units (a') Other Than Polylactic Acid Units (a)> The block structural units (A) may or may not contain units (a') other than the polylactic acid units (a). The monomer constituting the units (a') is not particularly limited as long as the effects of the present invention are not impaired. The content of units (a') in the block structural units (A) is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0015] <Number-Average Molecular Weight of Block Structural Unit (A)> The number-average molecular weight of the block structural unit (A) is preferably 1,000 to 100,000, more preferably 5,000 to 25,000, and even more preferably 8,200 to 15,000. Within the above numerical range, even better hydrolysis resistance can be exhibited. When a block copolymer has multiple block structural units (A), the number-average molecular weight of the block structural unit (A) refers to the total of all blocks. The number-average molecular weight of the block structural unit (A) can be determined from the number-average molecular weight of the block copolymer described below and the mass content of the block structural unit (A). The number-average molecular weight of the block structural unit (A) can be changed, for example, by adjusting the polymerization conditions of polylactic acid.

[0016] [Block structural unit (B)] The block structural unit (B) is mainly composed of polyester units (b). The term "main component" refers to the unit that is most abundant among the units constituting the block structural unit (B). Preferably, the "main component" is the unit that is most abundant, in terms of mass percentage, among the units constituting the block structural unit (B). The content of polyester units (b) in the block structural unit (B) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, and particularly preferably 90% by mass or more, and may even be 100% by mass. There is no upper limit to the content of polyester units (b) in the block structural unit (B), and it may be, for example, 100% by mass or less. The polyester units (b) contain units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2). Specifically, the polyester unit (b) contains units derived from a polyester obtained by reacting an aliphatic diol (b1) with an aliphatic dicarboxylic acid (b2). The polyester unit (b) may or may not contain units derived from a monomer other than the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2). The monomer other than the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) is not particularly limited as long as it does not impair the effects of the present invention. The total amount of the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) in the polyester unit (b) is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 99 mol% or more, and may be 100 mol%.

[0017] <Aliphatic Diol (b1)> The aliphatic diol (b1) is an aliphatic diol having 5 to 9 carbon atoms and an alkyl group as a branched chain. The aliphatic diol has two hydroxyl groups. Geminal diols are generally excluded from the aliphatic diol (b1). Preferably, the two hydroxyl groups in the aliphatic diol (b1) are primary hydroxyl groups. The "primary hydroxyl group" refers to a hydroxyl group bonded to a primary atom, preferably a primary carbon atom. The "number of carbon atoms" refers to the total number of carbon atoms in the aliphatic diol (b1), including the number of carbon atoms constituting the alkyl group. The "branched chain" in the aliphatic diol (b1) refers to a partial structure branching from the "main chain" in the aliphatic diol (b1), and preferably does not have a hydroxyl group bonded to its terminal. The "main chain" of the aliphatic diol (b1) preferably refers to a partial structure that is a molecular chain composed of two primary hydroxyl groups in the molecule at both ends and a plurality of carbon atoms connecting the two primary hydroxyl groups. Therefore, the two primary hydroxyl groups in the aliphatic diol (b1) are preferably located at both ends of the "main chain" of the aliphatic diol (b1). In other words, the aliphatic diol (b1) preferably has hydroxyl groups at both ends of the main chain. This facilitates reaction with dicarboxylic acids, facilitates production of triblock copolymers, and allows for the production of block copolymers with even better biodegradability and hydrolysis resistance. If the aliphatic diol (b1) has 4 or fewer carbon atoms, hydrolysis resistance may be poor. Furthermore, if the aliphatic diol (b1) has 10 or more carbon atoms, biodegradability may be poor. The carbon number of the aliphatic diol (b1) is preferably 6 to 9. The number of carbon atoms in the main chain of the aliphatic diol (b1) depends on the number of carbon atoms in the branched chains, but is preferably 2 or more and 8 or less, more preferably 3 or more, even more preferably 4 or more, and still more preferably 5 or more.

[0018] If the aliphatic diol (b1) does not have a branched chain that is an alkyl group, the block structural unit (B) is likely to crystallize, and the hydrolysis resistance of the block structural unit (B) tends to deteriorate, so the block copolymer cannot exhibit a wide range of biodegradability and excellent hydrolysis resistance. Furthermore, the number of branched chains in the aliphatic diol (b1) is preferably one or two, more preferably one. Furthermore, the branched chain is preferably at least one of a methyl group, an ethyl group, and a propyl group, more preferably at least one of a methyl group and an ethyl group, and even more preferably a methyl group. Furthermore, when the aliphatic diol (b1) has multiple branched chains, the respective branched chains may be the same or different.

[0019] Examples of the aliphatic diol (b1) include 2,2-dimethyl-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, 2-methyl-1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 2-methyl-2,4-pentanediol, 1,4-pentanediol, and 2-methyl-1,5-pentanediol. Examples of the aliphatic diol (b1) include 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2-ethyl-1,5-pentanediol, 2,4-dimethyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 2-ethyl-1,6-hexanediol, and 2-methyl-1,8-octanediol. The aliphatic diol (b1) is preferably at least one of 3-methyl-1,5-pentanediol and 2,4-diethyl-1,5-pentanediol, and more preferably 3-methyl-1,5-pentanediol. One type of aliphatic diol (b1) may be used alone, or two or more types may be used in combination.

[0020] <Aliphatic dicarboxylic acid (b2)> The carbon number of the aliphatic dicarboxylic acid (b2) is 5 or more and 12 or less. If the carbon number of the aliphatic dicarboxylic acid (b2) is 4 or less, the hydrolysis resistance may be poor. Furthermore, if the carbon number of the aliphatic dicarboxylic acid (b2) is 13 or more, the biodegradability may be poor. From the viewpoint of hydrolysis resistance, the carbon number of the aliphatic dicarboxylic acid (b2) is preferably 5 or more, more preferably 6 or more. Furthermore, from the viewpoint of biodegradability, the carbon number of the aliphatic dicarboxylic acid (b2) is preferably 10 or less, more preferably 8 or less.

[0021] Examples of the aliphatic dicarboxylic acid (b2) include glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and decanedicarboxylic acid. The aliphatic dicarboxylic acid (b2) is preferably adipic acid or sebacic acid, and more preferably adipic acid. The aliphatic dicarboxylic acid (b2) may be used alone or in combination of two or more.

[0022] <Preferred Combinations of Aliphatic Diol (b1) and Aliphatic Dicarboxylic Acid (b2)> From the viewpoint of exhibiting even better biodegradability and hydrolysis resistance, a combination of 3-methyl-1,5-pentanediol and adipic acid and a combination of 2,4-diethyl-1,5-pentanediol and adipic acid are preferred examples of an embodiment, and a combination of 3-methyl-1,5-pentanediol and adipic acid is a more preferred example of an embodiment.

[0023] <Ratio of Aliphatic Diol (b1) and Aliphatic Dicarboxylic Acid (b2)> The molar ratio of the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) charged when reacting them [aliphatic diol (b1) / aliphatic dicarboxylic acid (b2)] is preferably 1.4 / 1 to 1 / 1.4, more preferably 1.2 / 1 to 1 / 1.2.

[0024] <Units (b') Other Than Polyester Units (b)> The block structural unit (B) may or may not contain units (b') other than the polyester units (b). The monomer constituting the units (b') is not particularly limited as long as the effects of the present invention are not impaired. The content of units (b') in the block structural unit (B) is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, still more preferably 15% by mass or less, and particularly preferably 10% by mass or less.

[0025] <Number Average Molecular Weight of Block Structural Unit (B)> The number average molecular weight of the block structural unit (B) is preferably 2,500 or more, more preferably 4,000 or more, and even more preferably 5,000 or more. The number average molecular weight of the block structural unit (B) is preferably less than 100,000, more preferably less than 50,000, even more preferably less than 40,000, even more preferably less than 36,000, and even more preferably less than 25,000. It may be less than 20,000 or even less than 15,000. Within the above numerical range, the block copolymer tends to have excellent flexibility and impact resistance. The number average molecular weight of the block structural unit (B) can be determined by gel permeation chromatography (GPC), specifically, by the method described in the Examples. The number average molecular weight of the block structural unit (B) can also be determined from the number average molecular weight of the block copolymer described below and the mass content of the block structural unit (B). The number average molecular weight of the block structural unit (B) can be changed by adjusting, for example, the polymerization conditions for the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2).

[0026] [Structural Unit Proportion] The content of the block structural unit (A) is preferably 5% by mass or more and 95% by mass or less, relative to 100% by mass of the total of the block structural unit (A) and the block structural unit (B). When the proportion of the block structural unit (A) is 5% by mass or more, the handleability of the block copolymer tends to be even better. Furthermore, when the proportion of the block structural unit (A) is 95% by mass or less, the flexibility and impact resistance of the block copolymer tends to be excellent. From the viewpoint of handleability, the proportion of the block structural unit (A) is more preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, from the viewpoint of flexibility and impact resistance, the proportion of the block structural unit (A) is more preferably 80% by mass or less, even more preferably 75% by mass or less, even more preferably 70% by mass or less, and even more preferably 60% by mass or less. The proportion of the block structural unit (A) is １ It can be determined by H-NMR, specifically by the method described in the Examples.

[0027] The total content of the block structural unit (A) and the block structural unit (B) in the block copolymer is preferably 90% by mass or more, more preferably 95% by mass or more, and may be 100% by mass. There is no upper limit to the total content of the block structural unit (A) and the block structural unit (B) in the block copolymer, and it may be, for example, 100% by mass or less.

[0028] The block copolymer may or may not contain units other than the block structural unit (A) and the block structural unit (B). The units other than the block structural unit (A) and the block structural unit (B) are not particularly limited as long as the effects of the present invention are not impaired. The content of units other than the block structural unit (A) and the block structural unit (B) in the block copolymer is preferably 10% by mass or less, more preferably 5% by mass or less.

[0029] [Number-Average Molecular Weight of Block Copolymer] The number-average molecular weight of the block copolymer is greater than 10,000. If the number-average molecular weight of the block copolymer is less than 10,000, the block copolymer may become liquid and have poor handleability. Furthermore, hydrolysis resistance tends to deteriorate. From the viewpoint of handleability and hydrolysis resistance, the number-average molecular weight of the block copolymer is preferably 12,000 or more, more preferably 15,000 or more, and even more preferably 18,000 or more. From the viewpoint of processability, the number-average molecular weight of the block copolymer is preferably less than 100,000, more preferably less than 82,000, even more preferably less than 60,000, still more preferably 58,000 or less, even more preferably 44,000 or less, and even more preferably 35,000 or less, and may even be 30,000 or less. The number-average molecular weight of the block copolymer can be determined by gel permeation chromatography (GPC), specifically, by the method described in the Examples. The number average molecular weight of the block copolymer can be adjusted, for example, by adjusting the number average molecular weight of the block structural unit (B), the number average molecular weight of the block structural unit (A), or the number of each block structural unit. The number average molecular weight of the block structural unit (B) can be changed, for example, by adjusting the polymerization conditions for the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2). The number average molecular weight of the block structural unit (A) can be changed, for example, by adjusting the polymerization conditions for polylactic acid.

[0030] [Bonding Form of Block Copolymer] The bonding form of the block copolymer is preferably a triblock type or a diblock type, and more preferably a triblock type. The block copolymer may be a mixture of a triblock type and a diblock type. Specifically, the bonding form is preferably [block structural unit (A)]-[block structural unit (B)]-[block structural unit (A)].

[0031] [Melting Point of Block Copolymer] The melting point of the block copolymer is preferably 125°C or higher but lower than 185°C, more preferably 130°C or higher but lower than 180°C, and even more preferably 140°C or higher but lower than 170°C. When the melting point of the block copolymer is within the above range, the handleability, hydrolysis resistance, and biodegradability are more likely to be excellent. The melting point of the block copolymer can be determined using a differential scanning calorimeter, and specifically, can be measured by the method described in the examples.

[0032] <Glass Transition Temperature of Block Copolymer> The glass transition temperature of the block copolymer is preferably −80° C. or higher and −15° C. or lower. Within the above range, the block copolymer tends to have excellent flexibility and impact resistance. From the viewpoint of low-temperature properties such as low-temperature impact resistance, the glass transition temperature of the block copolymer is more preferably −20° C. or lower, even more preferably −25° C. or lower, and may be −30° C. or lower, −40° C. or lower, or −50° C. or lower. The lower limit of the glass transition temperature of the block copolymer is preferably low, but may be, for example, −75° C. or higher, −70° C. or higher, −65° C. or higher, or −60° C. or higher. The glass transition temperature of the block copolymer can be determined by differential scanning calorimetry, specifically, by the method described in the examples.

[0033] (Hydrolysis Resistance of Block Copolymer) The hydrolysis resistance of a block copolymer can be evaluated by the method described in the Examples, for example, by dissolving the block copolymer in chloroform at a concentration of 10% by mass, pouring the solution onto a glass plate to form a 200 μm-thick film, and then cutting out a test sample weighing 0.15 g. The resulting sample is immersed in 50 mL of ion-exchanged water at pH 7 and left at 50°C. The number average molecular weight is measured at predetermined intervals to determine the time until the number average molecular weight becomes less than 90% of the initial number average molecular weight. The hydrolysis resistance of the block copolymer is not particularly limited, but the time until the number average molecular weight becomes less than 90% of the initial number average molecular weight is preferably 50 hours or more, more preferably 100 hours or more, even more preferably 150 hours or more, even more preferably 200 hours or more, particularly preferably 250 hours or more, and most preferably more than 400 hours. When the hydrolysis resistance of the block copolymer is within the above range, for example, the block copolymer can be used to produce products with excellent long-term reliability in mechanical properties.

[0034] (Biodegradability of Block Copolymer in Compost) The biodegradability of a block copolymer in compost can be measured, for example, by the method described in the Examples in accordance with ISO 14855-2:2018. There are no particular limitations on the biodegradability of the block copolymer in compost, but the decomposition rate after 15 days is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more. When the biodegradability of the block copolymer in compost is within the above range, for example, the block copolymer can be used to produce products that have excellent compost biodegradability and a low environmental impact.

[0035] (Biodegradability of Block Copolymer in Activated Sludge) The biodegradability of the block copolymer in activated sludge can be measured, for example, by the method described in the Examples in accordance with the method in accordance with ISO 14851:2019. There are no particular limitations on the biodegradability of the block copolymer in activated sludge, but the decomposition rate after 90 days is preferably 5% by mass or more. When the biodegradability of the block copolymer in activated sludge is within the above range, it is possible to produce, for example, products that are highly biodegradable and have a low environmental impact in wastewater treatment facilities using the block copolymer.

[0036] [Method for Producing Block Copolymer] A known production method can be used to produce a block copolymer. (1) A known method for producing a block copolymer may be, for example, a method of synthesizing a polyester constituting the polyester unit (b) and polymerizing the polyester with lactide. The polyester can be synthesized by a known method. For example, an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2) can be reacted using an esterification catalyst (e.g., tin octoate, tin chloride, tin oxide) to synthesize a polyester. When polymerizing a polyester and lactide, it is preferable to use a ring-opening polymerization catalyst (e.g., tin octoate, tin chloride, tin oxide). The polymerization reaction can be performed using solution polymerization, melt polymerization, interfacial polycondensation, etc., and known polymerization reaction conditions can be set for each.

[0037] (2) Furthermore, a known method for producing a block copolymer may be, for example, a method in which polylactic acid constituting the polylactic acid unit (a) and a polyester constituting the polyester unit (b) are separately synthesized and then the polylactic acid and the polyester are reacted. Polylactic acid can be synthesized by a known method. For example, polylactic acid may be synthesized by reacting lactic acid by a direct condensation method, or polylactic acid may be synthesized by reacting lactide by a ring-opening polymerization method. When polymerizing polylactic acid and polyester, it is preferable to use an esterification catalyst (e.g., tin octoate, tin chloride, tin oxide). Examples of the polymerization reaction include solution polymerization, melt polymerization, and interfacial polycondensation, and known polymerization reaction conditions can be set for each.

[0038] The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these.

[0039] The compounds used in the examples and comparative examples are as follows: 3-methyl-1,5-pentanediol (manufactured by Kuraray Co., Ltd.) Adipic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) Stannous octoate (manufactured by Tokyo Chemical Industry Co., Ltd.) Toluene (manufactured by Kishida Chemical Co., Ltd.) L-lactide (manufactured by Tokyo Chemical Industry Co., Ltd.) Methanol (manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.) 2,4-diethyl-1,5-pentanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 2-methyl-1,3-propanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) Succinic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) 1,4-butanediol (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0040] The physical properties of the block copolymers in the examples and comparative examples were measured or evaluated by the following methods. (1) Number-average molecular weight (Mn) The number-average molecular weight (Mn) of the block copolymer was determined in terms of standard polystyrene by gel permeation chromatography (GPC). The Mn of the block structural unit (B) was determined from the Mn of the block copolymer and the mass content of the block structural unit (B). <GPC measurement conditions> Apparatus: GPC apparatus "HLC-8220" manufactured by Tosoh Corporation Separation column: "TSKgel SuperMultiporeHZ-M (column diameter = 4.6 mm, column length = 15 cm)" manufactured by Tosoh Corporation (two columns connected in series) Eluent: tetrahydrofuran (THF) Eluent flow rate: 0.35 mL / min Column temperature: 40°C Detection method: refractive index (RI) Injection volume: 10 μL Concentration: 1 mg / 1 mL (block copolymer / THF)

[0041] (2) Hard Ratio (% by Mass) (% by Mass of Block Structure Unit (A) Mainly Containing Polylactic Acid Unit (a)) １The hard ratio of the block copolymer was calculated by H-NMR. The molar ratio of the block structural unit (A) to the block structural unit (B) was calculated from the area ratio of the signal at around 5.2 ppm derived from the polylactic acid unit in the obtained spectrum to the signal at around 0.9 ppm derived from the structural unit (B) mainly composed of polyester unit (b). The molar ratio was multiplied by the molecular weight of each monomer structural unit to obtain a mass ratio, and the mass ratio of the block structural unit (A) when adjusted so that the sum of the mass ratios became 100 was taken as the hard ratio. １ H-NMR measurement conditions> Apparatus: Nuclear magnetic resonance apparatus "JNM-ECX400" manufactured by JEOL Ltd. Solvent: deuterated chloroform Measurement temperature: 50°C Number of accumulations: 1024 Measurement conditions: Temperature rise rate 10°C / min

[0042] (3) Biodegradability (Compost) Biodegradability in compost was measured according to the method of ISO 14855-2: 2018. If the decomposition rate after 15 days was 20% by mass or more, it was rated as A; if it was 10% by mass or more but less than 20% by mass, it was rated as B; if it was 5% by mass or more but less than 10% by mass, it was rated as C; and if it was less than 5% by mass, it was rated as D.

[0043] (4) Biodegradability (activated sludge) Biodegradability in activated sludge was measured according to the method of ISO 14851: 2019. If the decomposition rate after 90 days was 5% by mass or more, it was evaluated as A, and if it was less than 5% by mass, it was evaluated as B.

[0044] (5) Handling Efficiency The block copolymer was evaluated as A when it was solid at room temperature (23° C.), and as B when it was liquid.

[0045] (6) Hydrolysis Resistance (h) The block copolymer was dissolved in chloroform at a concentration of 10% by mass, poured onto a glass plate to produce a film 200 μm thick, and then cut into a test sample weighing 0.15 g. The obtained test sample was immersed in 50 mL of ion-exchanged water at pH 7 and left at 50 ° C. The number average molecular weight was measured every predetermined time (specifically, every 50 hours), and evaluated based on the elapsed time until the number average molecular weight became less than 90% of the initial number average molecular weight from the plotted approximation curve. Note that if the elapsed time exceeds 400 hours, it is indicated as ">400 h" in Tables 1-1 and 1-2.

[0046] (7) Melting Point (°C) The melting point of the block copolymer was measured by a differential scanning calorimeter according to the method described in JIS K7121:2012. When multiple peaks were observed, the melting point corresponding to the highest peak was determined as the melting point of the block copolymer. Apparatus: Mettler-Toledo Differential Scanning Calorimeter "DSC822" Measurement conditions: Heating rate 10°C / min

[0047] (8) Glass Transition Temperature (°C) The glass transition temperature of the block copolymer was measured by a differential scanning calorimeter according to the method described in JIS K7121:2012. Apparatus: Mettler Toledo K.K. Differential Scanning Calorimeter "DSC822" Measurement conditions: Heating rate 10°C / min

[0048] [Example 1] A flask equipped with an apparatus capable of distilling off the generated liquid and a vacuum pump was charged with 3-methyl-1,5-pentanediol and adipic acid in a molar ratio of 3-methyl-1,5-pentanediol / adipic acid = 1.1 / 1, and tin octoate was added so that the amount was 0.1% by mass relative to the total weight of 3-methyl-1,5-pentanediol and adipic acid. The mixture was then heated under a nitrogen atmosphere at normal pressure, 160 ° C. for 3 hours, and then at 220 ° C. for 3 hours, and the reaction was carried out while distilling off water. Next, the pressure was reduced to 2,000 Pa and the reaction was carried out for 3 hours. After that, the pressure was reduced to 80 Pa and the reaction was continued while appropriately checking until the number average molecular weight reached 9,500, thereby synthesizing a polymer composed of structural units (B') mainly composed of polyester units. After the reaction was completed, the pressure was returned to normal pressure and the temperature was cooled to 80 ° C., and toluene was added to dilute the solids concentration to 40% by mass. The above toluene solution was then poured into methanol in an amount twice the total volume of the solution. The supernatant was discarded, and the same amount of methanol as the amount of the toluene solution added was added again for washing. The supernatant was discarded, and the recovered insoluble matter was dried in a vacuum dryer at 40°C to remove organic volatiles, thereby obtaining a polymer consisting of structural units (B') mainly composed of polyester units. １H-NMR measurement confirmed that the structure at both ends was primarily hydroxyl groups derived from 3-methyl-1,5-pentanediol. Toluene was added again to the purified polymer consisting of structural unit (B') to dilute it to a solids concentration of 33% by mass, and the temperature was then raised to 140°C to distill off 10% by mass of the added toluene, thereby dehydrating the system. The mixture was then cooled to 80°C, and a polymer consisting of structural unit (B') and L-lactide were added in a mass ratio of polymer consisting of structural unit (B') / L-lactide = 50 / 50. The amount of toluene removed was further added to adjust the solids concentration to 50% by mass. The mixture was then heated to 100°C, and 0.1% by mass of tin octoate was added to the polymer consisting of structural unit (B'). The mixture was then allowed to react for 4 hours, yielding a toluene solution of a block copolymer consisting of block structural units (A) primarily composed of polylactic acid units (a) and block structural units (B) primarily composed of polyester units (b). Toluene was added to this solution to dilute the solid content to 40% by mass, and the toluene solution was then poured into methanol in an amount twice the total volume of the solution to precipitate a solid. The supernatant methanol was discarded, and the same amount of methanol as the amount of the toluene solution added was added again for washing. After discarding the methanol, the recovered solid was dried in a vacuum dryer at 40°C to remove organic volatiles, yielding a block copolymer consisting of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b). １ H-NMR measurement confirmed that the peaks derived from the methylene groups adjacent to both hydroxyl terminals of the polymer consisting of structural unit (B') disappeared, and that a triblock copolymer consisting of the structure [block structural unit (A)]-[block structural unit (B)]-[block structural unit (A)] was mainly produced. The obtained block copolymer was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1-1. The obtained block copolymer had good handleability, biodegradability, and hydrolysis resistance.

[0049] Examples 2 to 5 Block copolymers composed of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b) were synthesized in the same manner as in Example 1, except that the number average molecular weight was adjusted by adjusting the reaction time during synthesis of the polymer composed of structural units (B') mainly composed of polyester units, the mass ratio of L-lactide used was changed, and the dilution concentration during synthesis was appropriately changed to a concentration that was easy to handle. The obtained block copolymers were subjected to the above-mentioned measurements and evaluations. The results are shown in Table 1-1. The obtained block copolymers had good handleability, biodegradability, and hydrolysis resistance.

[0050] Example 6 A block copolymer composed of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b) was synthesized in the same manner as in Example 1, except that 2,4-diethyl-1,5-pentanediol was used instead of 3-methyl-1,5-pentanediol and the number average molecular weight was adjusted by adjusting the reaction time during synthesis of the polymer composed of structural units (B') mainly composed of polyester units. The obtained block copolymer was subjected to the above-described measurements and evaluations. The results are shown in Table 1-1. The obtained block copolymer had good handleability, biodegradability, and hydrolysis resistance.

[0051] Comparative Example 1 A block copolymer consisting of block structural units (A) primarily composed of polylactic acid units (a) and block structural units (B) primarily composed of polyester units (b) was synthesized in the same manner as in Example 1, except that the number-average molecular weight was adjusted by adjusting the reaction time during synthesis of the polymer consisting of structural units (B') primarily composed of polyester units, the mass ratio of L-lactide used was changed, and the dilution concentration during synthesis was appropriately adjusted to a concentration that was easy to handle. The obtained block copolymer was subjected to the above-mentioned measurements and evaluations. The results are shown in Table 1-2. The melting point of the obtained block copolymer was not observed, possibly because the number-average molecular weight was too low. The block copolymer obtained in Comparative Example 1 did not exhibit good handleability and had lower hydrolysis resistance than the Examples. This result is thought to be due to the block copolymer's number-average molecular weight being too low.

[0052] Comparative Example 2 A block copolymer composed of block structural units (A) mainly composed of polylactic acid units (a) and block structural units mainly composed of polyester units was synthesized in the same manner as in Example 1, except that 2-methyl-1,3-propanediol was used instead of 3-methyl-1,5-pentanediol, the number average molecular weight was adjusted by adjusting the reaction time during synthesis of the polymer composed of structural units (B') mainly composed of polyester units, and the dilution concentration during synthesis was appropriately changed to a concentration that was easy to handle. The obtained block copolymer was subjected to the measurements and evaluations described above. The evaluation results are shown in Table 1-2. The block copolymer obtained in Comparative Example 2 had lower hydrolysis resistance than the examples. This result is thought to be due to the diol used as a raw material having less than 5 carbon atoms.

[0053] Comparative Example 3 A block copolymer composed of block structural units (A) mainly composed of polylactic acid units (a) and block structural units mainly composed of polyester units was synthesized in the same manner as in Example 1, except that succinic acid was used instead of adipic acid, the number average molecular weight was adjusted by adjusting the reaction time during synthesis of the polymer composed of structural units (B') mainly composed of polyester units, and the dilution concentration during synthesis was appropriately changed to a concentration that was easy to handle. The obtained block copolymer was subjected to the above-mentioned measurements and evaluations. The evaluation results are shown in Table 1-2. The block copolymer obtained in Comparative Example 3 had lower hydrolysis resistance than the examples. The reason for this result is thought to be that the dicarboxylic acid used as the raw material had fewer than 5 carbon atoms.

[0054] Comparative Example 4 A block copolymer composed of block structural units (A) primarily composed of polylactic acid units (a) and block structural units primarily composed of polyester units was synthesized in the same manner as in Example 1, except that 1,4-butanediol was used instead of 3-methyl-1,5-pentanediol, succinic acid was used instead of adipic acid, the number average molecular weight was adjusted by adjusting the reaction time during synthesis of the polymer composed of structural units (B') primarily composed of polyester units, and the dilution concentration during synthesis was appropriately changed to a concentration that was easy to handle. The resulting block copolymer was subjected to the measurements and evaluations described above. The evaluation results are shown in Table 1-2. The block copolymer obtained in Comparative Example 4 did not exhibit good biodegradability and had lower hydrolysis resistance than the examples. This result is thought to be due to the dicarboxylic acid used as the raw material having less than 5 carbon atoms, the diol having less than 5 carbon atoms, and the lack of an alkyl branched chain.

[0055]

[0056] The compounds represented by the abbreviations in Tables 1-1 and 1-2 are as follows: PLLA: poly-L-lactic acid MPD: 3-methyl-1,5-pentanediol DEPD: 2,4-diethyl-1,5-pentanediol MPDiol: 2-methyl-1,3-propanediol BD: 1,4-butanediol AA: adipic acid SA: succinic acid

[0057] As shown in the examples, the block copolymer of this embodiment, which contains block structural units (A) mainly composed of specific polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b), has good biodegradability and hydrolysis resistance, and is solid, which makes it easy to handle. Therefore, the industrial usefulness of the block copolymer of this embodiment is extremely high.

Claims

1. A block copolymer comprising a block structural unit (A) mainly composed of a polylactic acid unit (a) and a block structural unit (B) mainly composed of a polyester unit (b), the polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), the aliphatic diol (b1) is an aliphatic diol having 5 to 9 carbon atoms and an alkyl group as a branched chain, the aliphatic dicarboxylic acid (b2) has 5 to 12 carbon atoms, A block copolymer having a number average molecular weight of greater than 10,000.

2. 2. The block copolymer according to claim 1, wherein the content of the block structural unit (A) is 5% by mass or more and 95% by mass or less relative to 100% by mass of the total of the block structural unit (A) and the block structural unit (B).

3. The block copolymer according to claim 1 or 2, wherein the aliphatic diol (b1) has hydroxyl groups at both ends of the main chain.

4. The block copolymer according to claim 1 or 2, wherein the aliphatic diol (b1) is 3-methyl-1,5-pentanediol.

5. The block copolymer according to claim 1 or 2, wherein the aliphatic dicarboxylic acid (b2) is adipic acid.

6. 3. The block copolymer according to claim 1, wherein the block structural unit (A) comprises a structural unit derived from poly-L-lactic acid or a structural unit derived from poly-D-lactic acid.

7. The block copolymer according to claim 1 or 2, which has a melting point of 125°C or higher and lower than 185°C.