Block copolymer

Abstract

To provide a block copolymer excellent in biodegradability, hydrolysis resistance, hot-water degradability, and handleability in active sludge and compost.SOLUTION: A block copolymer includes: a block structural unit (A) including a polylactic acid unit (a) as a main constituent; and a block structural unit (B) including a polyester unit (b) as a main constituent, where the polyester unit (b) includes a unit derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), the aliphatic diol (b1) is a 5-9C aliphatic diol having an alkyl group as a branched-chain, the carbon number of the aliphatic dicarboxylic acid (b2) is 2 or more and 4 or less, and the number average molecular weight is 36,000 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a block copolymer having excellent biodegradability, hydrolysis resistance, hot water decomposition property and handleability. [Background technology]

[0002] From the viewpoint of environmental protection, bioplastics have been actively developed. Polylactic acid, a bioplastic, is made from renewable resources derived from plants such as corn, which are produced by photosynthesis, and is expected to be used in a wide range of fields. However, polylactic acid is known to be brittle, inferior in viscosity, flexibility, impact resistance, heat resistance, etc., and moreover susceptible to hydrolysis, compared to petroleum-based plastics. In an attempt to improve the shortcomings of polylactic acid, for example, a technique utilizing a stereocomplex of polylactic acid has been studied. For example, Patent Document 1 describes a polyester resin that is a block copolymer (I) mainly composed of polylactic acid units (a) and polyester units (b) and that is characterized as being a stereocomplex, with the aim of achieving excellent heat resistance and mechanical properties, and a resin composition that contains two or more types of polyester resins that are the block copolymer (I) and that is characterized as being a stereocomplex. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-153275 A Summary of the Invention [Problem to be solved by the invention]

[0004] It can be assumed that the resin or resin composition containing polylactic acid described in Patent Document 1 has a certain degree of biodegradability. Here, biodegradability refers to the property of being ultimately decomposed into water and carbon dioxide by organisms such as microorganisms, and it is known that resins containing polylactic acid exhibit biodegradability in compost. However, due to increasing environmental awareness, there is a demand for biodegradability to be expressed over a wider range. Furthermore, final products made of resin materials are required to have hydrolysis resistance in order to suppress the progression of deterioration over time. On the other hand, from the viewpoint of environmental protection, it is also useful for resin materials to have recyclability. In order to reuse the raw materials used in the resin materials, it is desired that the resin materials be easily decomposed by hot water, for example. Furthermore, it is known that resin materials are used in inks, paints, and the like, and there is a demand for improving the handleability of resin materials so that they can be easily applied. Therefore, an object of the present invention is to provide a block copolymer which is excellent in biodegradability in activated sludge and compost, hydrolysis resistance, hot water decomposition property, and handleability. [Means for solving the problem]

[0005] As a result of intensive research aimed at solving the above problems, the present inventors have conceived the following invention and found that the problems can be solved. That is, the present invention is as follows.

[0006] [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) is an aliphatic diol having 5 to 9 carbon atoms and having an alkyl group as a branched chain, the aliphatic dicarboxylic acid (b2) has 2 to 4 carbon atoms, and the number average molecular weight is 36,000 or less. [2] The block copolymer according to [1] above, wherein the block structural unit (A) accounts for 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 [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 the above [1] to [3], wherein the aliphatic diol (b1) is 3-methyl-1,5-pentanediol. [5] The block copolymer according to any one of the above [1] to [4], wherein the aliphatic dicarboxylic acid (b2) is succinic acid. [6] The block copolymer according to any one of the above [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 the above [1] to [6], which has a melting point of less than 185°C. Effect of the Invention

[0007] According to the present invention, it is possible to provide a block copolymer which is excellent in biodegradability in activated sludge and compost, hydrolysis resistance, hot water decomposition property, and handleability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the present invention will be described based on an example of an embodiment. However, the embodiment shown below is an example for embodying the technical idea of ​​the present invention, and the present invention is not limited to the following description. In addition, in this specification, preferred embodiments are shown, but a combination of two or more of the individual preferred embodiments is also a preferred embodiment. When there are several numerical ranges for matters shown as numerical ranges, the lower limit and upper limit can be selectively combined to form a preferred embodiment. In this specification, when a numerical range is stated as "XX to YY", it means "not less than XX and not more than YY". In this specification, "unit" (where "" indicates a polymer) means "structural unit derived from". For example, "polylactic acid unit" means "structural unit derived from polylactic acid", and "polyester unit" means "structural unit derived from polyester".

[0009] In this specification, the "main chain" of a polymer means the longest molecular chain in the polymer molecule, unless otherwise specified. In the present invention, the term "hydrolysis resistance" means resistance to hydrolysis in water at 60° C. or less, preferably 50° C. or less. Specifically, the hydrolysis resistance can be evaluated by the method described in the examples. In the present invention, the term "hot water decomposability" means decomposability in hot water of more than 60° C., preferably 70° C. or higher. Specifically, the hot water decomposability can be evaluated by the method described in the Examples. In the present invention, the term "handleability" refers to the viscosity of the block copolymer that is suitable for facilitating application when the block copolymer is used as a resin material in, for example, ink, paint, etc. Specifically, the handleability can be evaluated by the method described in the examples.

[0010] The block copolymer of this embodiment contains block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b), and has a number average molecular weight of 36,000 or less. The present inventors have conducted various studies on formulations for imparting a wide range of biodegradability, excellent hydrolysis resistance, hot water decomposability, and handleability to a block copolymer. As a result, the present inventors have found that a block copolymer containing a block structural unit (A) and a block structural unit (B) is one of the effective formulations for realizing biodegradability not only in compost but also in activated sludge, and excellent hydrolysis resistance and hot water decomposability. In addition, the present inventors have found that one of the effective formulations for realizing excellent handleability is that the number average molecular weight of the block copolymer is within a specific numerical range. Based on the above results, the present inventors have conducted extensive studies and arrived at the present invention.

[0011] The polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), and is characterized in that the aliphatic diol (b1) is an aliphatic diol having 5 to 9 carbon atoms and an alkyl group as a branched chain, and the aliphatic dicarboxylic acid (b2) has 2 to 4 carbon atoms. The above characteristics make the block structural unit (B) more likely to become an amorphous polymer, so that when the block copolymer is biodegraded, microorganisms can easily enter the polymer structure, and it is presumed that the block copolymer has excellent wide-range biodegradability. In addition, it is believed that the aliphatic diol (b1) is composed of a specific number of carbon atoms and has an alkyl group as a branched chain, which contributes to improving biodegradability and hydrolysis resistance. On the other hand, if the block structural unit (B) is not an amorphous polymer, it is believed that microorganisms cannot easily enter the polymer structure when the block copolymer is biodegraded, and the effects of the present invention cannot be obtained. However, being an amorphous polymer is only one factor that affects biodegradability. This is because it is believed that various factors such as whether microorganisms recognize the amorphous structure as food, whether enzymes and microorganisms are easy to approach, steric hindrance of the main chain, melting point, and crystallinity affect biodegradability in combination. Therefore, it is not true that the effects of the present invention can be obtained if the block copolymer is an amorphous polymer. However, it is not clear why the block copolymer has the polyester unit (b) and can achieve both wide-range biodegradability and excellent hydrolysis resistance, which are in a contradictory relationship. In addition, it is believed that the fact that the aliphatic diol (b1) is composed of a specific number of carbon atoms, has an alkyl group as a branched chain, and that the aliphatic dicarboxylic acid (b2) is composed of a specific number of carbon atoms contributes to the expression of decomposability of the block copolymer in hot water of a certain temperature or higher (preferably 70° C. or higher). However, the reason why the block copolymer can achieve hot water decomposability that makes it easily decomposed in hot water of a certain temperature or higher (preferably 70° C. or higher) while having hydrolysis resistance that can withstand water of a certain temperature or lower (preferably 50° C. or lower) is not clear.

[0012] Block structure unit <Polylactic acid unit (a)> The block structural unit (A) is mainly composed of a polylactic acid unit (a). The above-mentioned "main component" refers to the unit that is contained at the highest content ratio among the units that constitute the block structural unit (A). The content of polylactic acid units (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 content of polylactic acid units (a) in the block structural unit (A), and it is, 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. As the lactic acid, for example, at least one selected from the group consisting of L-lactic acid, D-lactic acid, and DL-lactic acid can be used. As the lactide, for example, at least one selected from the group consisting of L-lactide, D-lactide, DL-lactide, and meso-lactide can be used. 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 viewpoint of cost and availability of raw materials, the polylactic acid is preferably at least one selected from the group consisting of poly-L-lactic acid, poly-D-lactic acid, and poly-DL-lactic acid, and more preferably at least one selected from the group consisting of poly-L-lactic acid and poly-D-lactic acid. 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 unit (A) contains preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more of structural units derived from poly-L-lactic acid or poly-D-lactic acid. For example, in one preferred embodiment, the block structural unit (A) is composed of structural units derived from poly-L-lactic acid or structural units derived from poly-D-lactic acid, that is, the structural units derived from poly-L-lactic acid or structural units derived from poly-D-lactic acid constitute 100% by mass.

[0014] <Units (a') other than polylactic acid units (a)> The block structural unit (A) may or may not contain a unit (a') other than the polylactic acid unit (a). The monomer constituting the unit (a') is not particularly limited as long as it does not impair the effects of the present invention. The content of units (a') in the block structural unit (A) is preferably 30 mass % or less, more preferably 20 mass % or less, even more preferably 15 mass % or less, and even more preferably 10 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 2,000 to 50,000, and further preferably 3,000 to 25,000, and may be 3,000 to 15,000. Within the above numerical range, even better hydrolysis resistance and handleability can be exhibited. When the block copolymer has a plurality of block structural units (A), the number average molecular weight of the block structural unit (A) means the total number average molecular weight of all the block structural units. 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).

[0016] Block structure unit The block structural unit (B) is composed mainly of a polyester unit (b). The above-mentioned "main component" refers to the unit that is contained at the highest content ratio among the units that constitute the block structural unit (B). The content of the polyester unit (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, still more preferably 85% by mass or more, particularly preferably 90% by mass or more, and may be 100% by mass. There is no upper limit to the content of the polyester unit (b) in the block structural unit (B), and it is, for example, 100% by mass or less. The polyester unit (b) contains 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 monomers 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 the effects of the present invention are not impaired. The total amount of the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) in the polyester unit (b) is preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 99% by mass or more, and may be 100% by mass. There is no upper limit to the total amount of the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) in the polyester unit (b), and it is, for example, 100% by mass or less.

[0017] Aliphatic diol (b1) The aliphatic diol (b1) is an aliphatic diol having 5 to 9 carbon atoms and having an alkyl group as a branched chain. Here, the "branched chain" in the aliphatic diol (b1) refers to a partial structure branching off from the "main chain" in the aliphatic diol (b1), and no hydroxyl group is bonded to the end thereof. The "main chain" in the aliphatic diol (b1) refers to a molecular chain consisting of a plurality of atoms, preferably carbon atoms, connecting two hydroxyl groups in the molecule at both ends. Therefore, the two hydroxyl groups in the aliphatic diol (b1) are located at both ends of the "main chain" in the aliphatic diol (b1).

[0018] 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. If the carbon number of the aliphatic diol (b1) is 4 or less, the hydrolysis resistance may be poor. If the carbon number of the aliphatic diol (b1) is 10 or more, the biodegradability may be poor. From the viewpoint of achieving even better hydrolysis resistance, the aliphatic diol (b1) preferably has 6 or more and 9 or less carbon atoms.

[0019] When 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 tends to deteriorate, so that the block copolymer cannot exhibit a wide range of biodegradability and excellent hydrolysis resistance. In the aliphatic diol (b1), the number of branched chains is preferably 1 or 2, more preferably 1. In addition, the branched chains are preferably methyl groups, ethyl groups, and propyl groups, more preferably methyl groups and ethyl groups, and even more preferably methyl groups. In addition, when the aliphatic diol (b1) has a plurality of branched chains, each branched chain may be the same or different.

[0020] 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. Aliphatic diol (b1) is preferably 3-methyl-1,5-pentanediol and 2,4-diethyl-1,5-pentanediol, more preferably 3-methyl-1,5-pentanediol. The aliphatic diol (b1) may be used alone or in combination of two or more kinds.

[0021] <Aliphatic dicarboxylic acid (b2)> The aliphatic dicarboxylic acid (b2) has 2 or more and 4 or less carbon atoms. If the carbon number of the aliphatic dicarboxylic acid (b2) is 5 or more, the hydrothermal decomposition property may be poor. If the carbon number of the aliphatic dicarboxylic acid (b2) is 4 or less, it is effective in achieving both hydrolysis resistance and hydrothermal decomposition property. From the viewpoint of ease of production of the block copolymer due to the thermal stability of the monomer, the aliphatic dicarboxylic acid (b2) preferably has 3 or 4 carbon atoms, and more preferably has 4 carbon atoms.

[0022] Examples of the aliphatic dicarboxylic acid (b2) include oxalic acid, malonic acid, and succinic acid. From the viewpoint of easily achieving both excellent hydrolysis resistance and hot water decomposition property and ease of production of the block copolymer, the aliphatic dicarboxylic acid (b2) is preferably succinic acid. The aliphatic dicarboxylic acid (b2) may be used alone or in combination of two or more kinds.

[0023] <Preferable combination of aliphatic diol (b1) and aliphatic dicarboxylic acid (b2)> From the viewpoint of exhibiting even better biodegradability, hydrolysis resistance, and hydrothermal decomposition property, a combination of 3-methyl-1,5-pentanediol and succinic acid, and a combination of 2,4-diethyl-1,5-pentanediol and succinic acid are examples of preferred embodiments, and a combination of 3-methyl-1,5-pentanediol and succinic acid is an example of a more preferred embodiment.

[0024] <Ratio of aliphatic diol (b1) and aliphatic dicarboxylic acid (b2)> The molar ratio of the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) fed in the reaction is preferably 1.4 / 1 to 1 / 1.4, more preferably 1.2 / 1 to 1 / 1.2.

[0025] <Units (b') other than polyester units (b)> The block structural unit (B) may or may not contain a unit (b') other than the polyester unit (b). The monomer constituting the unit (b') is not particularly limited as long as it does not impair the effects of the present invention. The content of units (b') in the block structural unit (B) is preferably 50 mass % or less, more preferably 30 mass % or less, even more preferably 20 mass % or less, still more preferably 15 mass % or less, and particularly preferably 10 mass % or less.

[0026] <Number average molecular weight of block structural unit (B)> The number average molecular weight of the block structural unit (B) is preferably from 1,000 to 100,000, more preferably from 2,000 to 50,000, further preferably from 3,000 to 30,000, and may be from 4,000 to 25,000. Within the above numerical range, the block copolymer tends to be easily produced. The number average molecular weight of the block structural unit (B) can be determined from the number average molecular weight of the block copolymer described below and the mass content of the block structural unit (B), and specifically, it can be measured by the method described in the Examples.

[0027] [Structural unit ratio] The block structural unit (A) preferably accounts for 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 block copolymer tends to have excellent strength and heat resistance, and when the proportion of the block structural unit (A) is 95% by mass or less, the block copolymer tends to have excellent flexibility, impact resistance, and biodegradability. From the viewpoints of strength and heat resistance, 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. Also, from the viewpoints of flexibility, impact resistance, and biodegradability, the proportion of the block structural unit (A) is more preferably 80% by mass or less, and even more preferably 75% by mass or less. The proportion of block structural units (A) is: 1 It can be determined by H-NMR, specifically, by the method described in the Examples.

[0028] 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 is, for example, 100% by mass or less.

[0029] 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 they do not impair the effects of the present invention. In the block copolymer, the content of units other than the block structural unit (A) and the block structural unit (B) is preferably 10 mass % or less, more preferably 5 mass % or less.

[0030] [Block copolymer bond type] 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] [Number average molecular weight of block copolymer] The block copolymer has a number average molecular weight of 36,000 or less. If the number average molecular weight of the block copolymer exceeds 36,000, the viscosity of the block copolymer may become high, resulting in poor handleability. From the viewpoint of ease of production and processability of the block copolymer, the number average molecular weight of the block copolymer is preferably 35,000 or less, and more preferably 25,000 or less. From the viewpoint of strength and heat resistance of the block copolymer, the number average molecular weight of the block copolymer is preferably 5,000 or more, more preferably 8,000 or more, and even more preferably 10,000 or more. That is, the number average molecular weight of the block copolymer is preferably 5,000 or more and 35,000 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.

[0032] [Melting point of block copolymer] From the viewpoint of processability, such as ease of melt processing, the melting point of the block copolymer is preferably less than 185°C, more preferably 180°C or lower, further preferably 160°C or lower, and may be 150°C or lower. From the viewpoint of practical heat resistance as a resin material, the melting point of the block copolymer is preferably 110° C. or higher, more preferably 120° C. or higher, and even more preferably 125° C. or higher. From the above, in terms of good processability and heat resistance, the melting point of the block copolymer is preferably 110°C or higher and lower than 185°C. The melting point of the block copolymer can be determined by a differential scanning calorimeter, specifically, by the method described in the examples.

[0033] <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 impact resistance at low temperatures, the glass transition temperature of the block copolymer is more preferably -20°C or lower, further preferably -25°C or lower, and may be -30°C or lower. The lower limit of the glass transition temperature of the block copolymer is preferably low, and may be, for example, -70°C or higher, -60°C or higher, -50°C or higher, or -40°C or higher. The glass transition temperature of the block copolymer can be determined by differential scanning calorimetry.

[0034] [Method of manufacturing block copolymer] The block copolymer can be produced by a known production method. A known method for producing a block copolymer may be, for example, a method in which a polyester constituting the polyester unit (b) is synthesized and the polyester is polymerized with lactide. The polyester can be synthesized by a known method. For example, the polyester can be synthesized by reacting an aliphatic diol (b1) with an aliphatic dicarboxylic acid (b2) using an esterification catalyst (e.g., tin octylate, tin chloride, tin oxide). When the polyester and the lactide are polymerized, it is preferable to use a ring-opening polymerization catalyst (e.g., tin octoate, tin chloride, tin oxide). The polymerization reaction may be performed by solution polymerization, melt polymerization, interfacial polycondensation, or the like, and any of the polymerization reaction conditions may be set as known in the art.

[0035] Another known method for producing a block copolymer may be, for example, a method in which a 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 with each other. 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 polylactic acid and polyester are polymerized, it is preferable to use an esterification catalyst (e.g., tin octoate, tin chloride, tin oxide). The polymerization reaction may be solution polymerization, melt polymerization, interfacial polycondensation, or the like, and any of these may be carried out under known polymerization reaction conditions. EXAMPLES

[0036] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0037] The compounds used in the examples and comparative examples are as follows. 3-Methyl-1,5-pentanediol (Kuraray Co., Ltd.) Adipic acid (Tokyo Chemical Industry Co., Ltd.) Stannous octoate (Tokyo Chemical Industry Co., Ltd.) Toluene (Kishida Chemical Co., Ltd.) L-lactide (Tokyo Chemical Industry Co., Ltd.) Methanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) 2,4-Diethyl-1,5-pentanediol (Tokyo Chemical Industry Co., Ltd.) 2-Methyl-1,3-propanediol (Tokyo Chemical Industry Co., Ltd.) Succinic acid (Tokyo Chemical Industry Co., Ltd.) 1,4-Butanediol (Tokyo Chemical Industry Co., Ltd.)

[0038] 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> Equipment: Tosoh Corporation GPC equipment "HLC-8220" Separation column: Tosoh Corporation's "TSKgel SuperMultiporeHZ-M (column diameter = 4.6 mm, column length = 15 cm)" (two columns connected in series) Eluent: tetrahydrofuran (THF) Eluent flow rate: 0.35mL / min Column temperature: 40℃ Detection method: Refractive index (RI) Injection volume: 10μL Concentration: 1mg / 1mL (block copolymer / THF)

[0039] (2) Hard ratio (mass%) (mass content of block structural unit (A) mainly composed of polylactic acid unit (a)) 1 The 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 about 5.2 ppm originating from the polylactic acid unit in the obtained spectrum to the signal at about 0.9 ppm originating from the structural unit (B) mainly composed of the polyester unit (b). The molar ratio was multiplied by the molecular weight of the block structural unit to obtain a mass ratio, and the mass ratio of the block structural unit (A) when the total of the mass ratios was adjusted to 100 was determined as the hard ratio. < 1 H-NMR measurement conditions Equipment: Nuclear magnetic resonance apparatus “JNM-ECX400” manufactured by JEOL Ltd. Solvent: deuterated chloroform Measurement temperature: 50℃ Number of times accumulated: 1024

[0040] (3) Biodegradable (compostable) The biodegradability of the above block copolymers in compost was measured according to the method in accordance with 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, and if it was 5% by mass or more but less than 10% by mass, it was rated as C.

[0041] (4) Biodegradability (activated sludge) The biodegradability of the above block copolymer in activated sludge was measured according to the method in accordance with ISO 14851: 2019. If the decomposition rate after 90 days was 5% by mass or more, it was rated as A, and if it was less than 5% by mass, it was rated as B.

[0042] (5) Ease of use The complex viscosity was measured under the following conditions using a rotational viscoelasticity measuring device. For handleability, if the complex viscosity at 160°C was less than 10,000 Pa·s, it was rated as A, and if it was 10,000 Pa·s or more, it was rated as B. <Conditions for measuring complex viscosity> Equipment: TA Instruments Rotational Viscoelasticity Measuring Device "ARES-G2" Angular frequency: 1Hz Heating rate: 2℃ / min If the complex viscosity value is less than 10,000 Pa s, for example, when the block copolymer is used to prepare a paint, the paint tends to have an appropriate viscosity that is easy to apply and has excellent handleability, whereas if the complex viscosity value is 10,000 Pa s or more, for example, when the block copolymer is used to prepare a paint, the paint tends to have a viscosity that is difficult to apply and has poor handleability.

[0043] (6) Hydrolysis resistance (h) The block copolymer was dissolved in chloroform at a concentration of 10% by mass, and then cast onto a glass plate to produce a film with a thickness of 200 μm, which was then cut into a test sample with a mass of 0.15 g. The test sample thus obtained was immersed in 50 mL of ion-exchanged water at pH 7 and allowed to stand at 50° C. The number average molecular weight was measured at predetermined intervals, and the number average molecular weight was evaluated based on the time elapsed until the number average molecular weight became less than 90% of the initial number average molecular weight. The longer the elapsed time, the better the hydrolysis resistance. If the above elapsed time exceeds 400 hours, it will be indicated in the table as ">400h."

[0044] (7) Hydrothermal decomposition (h) The block copolymer was dissolved in chloroform at a concentration of 10% by mass, and then poured onto a glass plate to prepare a film with a thickness of 200 μm, and then cut into a test sample with a mass of 0.15 g. The test sample thus obtained was immersed in 50 mL of ion-exchanged water at pH 7 and allowed to stand at 70° C. The number average molecular weight was measured at predetermined intervals, and the number average molecular weight was evaluated based on the time elapsed until the number average molecular weight became less than 90% of the initial number average molecular weight. The shorter the elapsed time, the more excellent the hydrolytic property. If the above elapsed time exceeds 200 hours, it will be indicated in the table as ">200h."

[0045] (8) Melting point (℃) 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. Equipment: Mettler Toledo DSC822 differential scanning calorimeter Measurement conditions: Heating rate 10℃ / min

[0046] [Example 1] In a flask equipped with a vacuum pump and an apparatus capable of distilling off the generated liquid, 3-methyl-1,5-pentanediol and succinic acid were charged in a molar ratio of 3-methyl-1,5-pentanediol / succinic acid = 1.1 / 1, and tin octylate was added so that it was 0.1% by mass relative to the total mass of 3-methyl-1,5-pentanediol and succinic acid. The mixture was heated under a nitrogen atmosphere at normal pressure at 160 ° C for 3 hours and 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, and then the pressure was reduced to 80 Pa and the reaction was carried out while checking appropriately until the number average molecular weight reached 10,000, 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 then toluene was added to dilute the solid concentration to 40% by mass, and the above-mentioned toluene solution was added to methanol in an amount twice the total amount of the solution. The supernatant was discarded, and the same amount of methanol as the toluene solution added was added again for washing. The supernatant was discarded, and the recovered insoluble matter was dried at 40°C in a vacuum dryer to remove the organic volatile matter, yielding a polymer composed of structural units (B') whose main component is polyester units. Toluene was added again to the polymer consisting of the purified structural unit (B') to dilute it so that the solid concentration became 33% by mass, and then the temperature was raised to 140°C to distill off 10% by mass of the toluene that had been added, thereby dehydrating the system. After that, it was cooled to 80°C, and a polymer consisting of structural unit (B') and L-lactide were added so that the mass ratio of polymer consisting of structural unit (B') / L-lactide was 50 / 50, and toluene was added in the amount of the weight of the distilled off solution described above to adjust the solid concentration to 50 mass%. After that, it was heated to 100°C, and tin octylate was added in an amount of 0.1 mass% relative to the polymer consisting of structural unit (B'), and the reaction was carried out for 4 hours to obtain a toluene solution of a block copolymer consisting of block structural unit (A) mainly composed of polylactic acid unit (a) and block structural unit (B) mainly composed of polyester unit (b). Toluene was added to this solution to dilute the solid concentration to 40% by mass, and the above 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 poured in 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). The block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1.

[0047] [Examples 2 to 5] 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 the number average molecular weight was adjusted by adjusting the reaction time during the synthesis of a 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 block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1.

[0048] [Example 6] 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) 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 consisting of structural units (B') mainly composed of polyester units. The block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1.

[0049] [Comparative Example 1] A block copolymer composed of 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) 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 the synthesis of a polymer composed of structural unit (B') mainly composed of polyester units, and the dilution concentration during the synthesis was appropriately changed to a concentration that was easy to handle. The block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1.

[0050] [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 and the number average molecular weight was adjusted by adjusting the reaction time during the synthesis of the polymer composed of structural units (B') mainly composed of polyester units. The block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1.

[0051] [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 adipic acid was used instead of succinic acid and the number average molecular weight was adjusted by adjusting the reaction time during the synthesis of the polymer composed of structural units (B') mainly composed of polyester units. The block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1.

[0052] [Comparative Example 4] 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 1,4-butanediol 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 block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1.

[0053] [Table 1]

[0054] The compounds represented by the abbreviations in Table 1 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

[0055] As shown in the examples of Table 1, the block copolymer of this embodiment, which includes a block structural unit (A) mainly composed of a specific polylactic acid unit (a) and a block structural unit (B) mainly composed of a polyester unit (b), was confirmed to have excellent biodegradability in both compost and activated sludge. In addition, it was confirmed that the block copolymer of this embodiment shown in the examples of Table 1 has a moderate melting point and is also excellent in handleability. In addition, it was confirmed that the block copolymer of this embodiment shown in the examples of Table 1 has hydrolysis resistance in water at 50°C and hydrolysis resistance in hot water at 70°C, and thus achieves both hydrolysis resistance and hydrolysis resistance. In this way, since the block copolymer of this embodiment has hydrolysis resistance, it is expected that the block copolymer used as a resin material can be reused as a raw material for a resin material by subjecting it to hydrolysis. On the other hand, the block copolymer obtained in Comparative Example 1 had a high complex viscosity and was poor in handleability, which was believed to be due to the block copolymer having a too high number average molecular weight. Moreover, the block copolymer obtained in Comparative Example 2 had lower hydrolysis resistance than those in Examples. The reason for this result is believed to be that the aliphatic diol used as the raw material had less than 5 carbon atoms. Moreover, the block copolymer obtained in Comparative Example 3 was inferior in hot water decomposition property to those in the Examples. The reason for this result is considered to be that the number of carbon atoms of the dicarboxylic acid used as the raw material is greater than 4. Moreover, the block copolymer obtained in Comparative Example 4 did not exhibit good biodegradability and was inferior in hydrolysis resistance to those of the Examples. The reason for this result is believed to be that the aliphatic diol used as the raw material had a carbon number of less than 5, and furthermore, the aliphatic diol did not have an alkyl group as a branched chain.

[0056] As shown in the results of the above examples, the block copolymer of the present embodiment has a wide range of biodegradability, and is excellent in hydrolysis resistance, hot water decomposition property, and handleability. Therefore, the industrial usefulness of the block copolymer of the present embodiment is extremely high.

Claims

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), 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, and the aliphatic dicarboxylic acid (b2) has 2 to 4 carbon atoms, A block copolymer having a number average molecular weight of 36,000 or less.

2. 2. The block copolymer according to claim 1, wherein the block structural unit (A) accounts for 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 succinic 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. 3. The block copolymer according to claim 1, having a melting point of less than 185°C.