JP2024080378A - Polymers and their uses - Google Patents

Abstract

[Problem] The present invention provides a polymer that has excellent heat resistance, biodegradability and mechanical properties, and uses thereof. [Solution] The polymer of the present invention has multiple triblock structures. In the triblock structure, polylactic acid units are bonded to both ends of a polycaprolactone unit via ester bonds. Multiple triblock structures are bonded together via units containing urethane bonds. [Selected Figures] None

Description

The present invention relates to a polymer and its uses.

As biodegradable polymers, polylactic acid, polycaprolactone, and copolymers thereof have been proposed (for example, Patent Documents 1 to 6). However, while polylactic acid generally has excellent heat resistance, its biodegradability is insufficient due to its high glass transition temperature. Therefore, there is a problem that it is difficult to decompose in natural environments such as seawater and soil.
Moreover, polycaprolactone generally has insufficient heat resistance, which may limit the uses and versatility of polycaprolactone.

Japanese Patent Application Laid-Open No. 8-3262 JP 2006-183042 A JP 2019-505624 A Japanese Patent Application Laid-Open No. 8-27256 JP 2022-77948 A JP 2016-210894 A

According to the present inventors' investigations, the polymers proposed in Patent Documents 1 to 6 have the following problems: The polymers proposed in Patent Documents 1 to 3 have insufficient biodegradability. The polymer proposed in Patent Document 3 has low elongation at break and insufficient mechanical properties.
The polymer of Patent Document 4 has a low breaking elongation and insufficient mechanical properties. The polymers of Patent Documents 5 and 6 have a low elastic modulus and insufficient mechanical properties.

The present invention provides a polymer that has excellent heat resistance, biodegradability and mechanical properties, and uses thereof.

The present invention has the following aspects.
[1] A polymer having a plurality of triblock structures in which polylactic acid units are bonded to both ends of a polycaprolactone unit via ester bonds, and the plurality of triblock structures are bonded to each other via units containing urethane bonds.
[2] The polymer according to [1], having a glass transition temperature of 30° C. or lower.
[3] The polymer according to [1] or [2], wherein when the polymer is molded into a film under the following conditions, the film has a breaking elongation of 200% or more.
Film molding conditions: hot press molding was performed using a mold having a thickness of 0.1 mm under conditions of 20 MPa, 10 minutes, and 180°C.
[4] The polymer according to any one of [1] to [3], wherein when the polymer is molded into a film under the following conditions, the total light transmittance of the film is 85% or more and the haze of the film is 50% or less.
Film molding conditions: hot press molding was performed using a mold having a thickness of 0.1 mm under conditions of 20 MPa, 10 minutes, and 180°C.
[5] A molded article comprising the polymer according to any one of [1] to [4].

The present invention provides a polymer that has excellent heat resistance, biodegradability, and mechanical properties, and uses thereof.

FIG. 1 shows a schematic diagram of an example of the chemical structure of the polymer of the present invention. FIG. 2 shows a schematic diagram of an example of the chemical structure of a conventional polymer.

In this specification, the use of "to" indicating a range of values means that the values before and after it are included as the lower and upper limits.
The lower and upper limits of the numerical ranges disclosed in this specification can be combined in any manner to create new numerical ranges.

<Polymer>
The polymer of the present invention has a plurality of triblock structures in which polylactic acid units are bonded to both ends of a polycaprolactone unit via ester bonds, and the plurality of triblock structures are bonded to each other via units containing urethane bonds.

Fig. 1 is a schematic diagram showing an example of the chemical structure of the polymer of the present invention. As shown in Fig. 1, a plurality of triblock structures 4 are formed in the polymer 1, in which a polylactic acid unit 3 is bonded to both ends of a polycaprolactone unit 2. These plurality of triblock structures 4 are repeatedly bonded to each other by a unit 5 containing a urethane bond.
2, the polycaprolactone units 2 and the polylactic acid units 3 are bonded to each other via units 5 containing urethane bonds. In addition, the polycaprolactone units 2 and the polylactic acid units 3 are bonded to each other via units 5 containing urethane bonds.

As shown in the example of polymer 1, the polymer of the present invention has triblock structures bonded together by units containing urethane bonds. The polymer of the present invention having such a chemical structure exhibits properties that cannot be exhibited by conventional polymers. Specifically, it is possible to simultaneously achieve excellent heat resistance, biodegradability, and mechanical properties. An example of the polymer of the present invention is described in detail below. However, the following description discloses a representative example, and the present invention is not limited to such disclosure.

(Triblock structure)
In the triblock structure, polylactide units are bonded to both ends of the polycaprolactone unit via ester bonds.

The polycaprolactone unit is typically a polymer unit obtained by ring-opening polymerization of ε-caprolactone. In a typical example, the polycaprolactone unit has units based on ε-caprolactone. However, in one example, the polycaprolactone unit may have units based on a monomer in which an optional side chain, such as an alkyl chain, is bonded to any carbon atom of ε-caprolactone instead of or in addition to the units based on ε-caprolactone.

The number average molecular weight of the polycaprolactone unit is preferably 300 to 2,000, more preferably 400 to 10,000, and even more preferably 500 to 5,000.
When the number average molecular weight of the polycaprolactone unit is equal to or greater than the lower limit of the above-mentioned range, biodegradability is likely to be improved. When the number average molecular weight of the polycaprolactone unit is equal to or less than the upper limit of the above-mentioned range, heat resistance and mechanical properties are likely to be improved. In addition, the polymer is easily synthesized.
The number average molecular weight of the polycaprolactone units can be adjusted during the synthesis of the triblock structure.

A polylactic acid unit is typically a polymer unit obtained by polymerizing lactide. In a typical example, the polylactic acid unit has a unit based on lactide. However, the polylactic acid unit may have a unit based on a monomer having an arbitrary side chain, such as an alkyl chain, bonded to any carbon atom of lactide instead of or in addition to the unit based on lactide.
In one example, units based on each monomer are bonded to each other via ester bonds to form a polylactic acid unit.

The polylactic acid unit is bonded to both ends of the polycaprolactone unit. The polylactic acid unit is bonded to both ends of the polycaprolactone unit by ester bonds containing oxygen atoms at both ends of the polycaprolactone unit. The repeating number and monomer unit composition of the two polylactic acid units bonded to both ends of the polycaprolactone unit may be different from each other or may be the same.

The number average molecular weight of the polylactic acid unit is preferably 300 to 30,000, more preferably 400 to 15,000, and even more preferably 500 to 10,000.
When the number average molecular weight of the polylactic acid unit is equal to or greater than the lower limit of the above-mentioned range, the heat resistance is easily improved, and the polymer is easily synthesized. When the number average molecular weight of the polylactic acid unit is equal to or less than the upper limit of the above-mentioned range, the biodegradability is easily improved.
The number average molecular weight of the polylactic acid unit can be adjusted during the synthesis of the triblock structure.

(unit containing urethane bond)
In the polymer of the present invention, a plurality of triblock structures are bonded to each other through a unit containing a urethane bond (-NH-CO-). When the polymer of the present invention is subjected to ¹ H NMR measurement, a peak due to the "-NH-" of the urethane bond can be detected at about 3.1 ppm.
The polymer of the present invention can also be said to be a thermoplastic polyurethane polymer. Also, the polymer of the present invention can also be said to be a copolymer in which a polyol having a triblock structure is one constituent unit and a plurality of such constituent units are bonded to each other via a unit containing a urethane bond.

The unit containing a urethane bond is typically a unit based on an aliphatic diisocyanate, such as tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, or 3-methylpentane-1,5-diisocyanate.
However, the compounds capable of imparting units containing urethane bonds are not limited to these examples of aliphatic diisocyanates.

(Chemical Structure)
An example of the chemical structure of the polymer of the present invention is shown below.

In the above chemical structural formula, R ₁ is not particularly limited, but is preferably an aliphatic ether having 2 to 12 carbon atoms derived from an aliphatic diol, or an aliphatic hydrocarbon having 1 to 12 carbon atoms.
Examples of aliphatic diols include ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,3-butanediol, 2-methyl-propanediol, 1,4-butanediol, neopentyl glycol, pentamethylene glycol, hexamethylene glycol, octamethylene glycol, decamethylene glycol, dodecamethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, dipropylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and polyethylene glycol having a molecular weight of 1000 or less.
The aliphatic diols may be used alone or in combination of two or more kinds.

In the above chemical structural formula, _R2 is not particularly limited as long as it is a structure derived from an aliphatic diisocyanate, but is preferably an aliphatic hydrocarbon.

In the above chemical structural formula, m is 1 or more. m is preferably 1 to 150, more preferably 1 to 70, and even more preferably 1 to 35. When m is equal to or greater than the lower limit of the above numerical range, biodegradability is likely to be improved. When m is equal to or less than the upper limit of the above numerical range, heat resistance and mechanical properties are likely to be improved.

In the above chemical structural formula, n is 1 or more. n is preferably 4 to 500, more preferably 5 to 300, and even more preferably 6 to 150. When n is equal to or greater than the lower limit of the above numerical range, heat resistance is likely to be improved. When n is equal to or less than the upper limit of the above numerical range, biodegradability is likely to be improved.

In the above chemical structural formula, l is the number of repetitions of the triblock structure and the associated isocyanate structure. l is preferably 1 to 300, and more preferably 2 to 100. When l is equal to or greater than the lower limit of the above numerical range, the mechanical properties tend to improve.

(Characteristics)
The number average molecular weight (Mn) of the polymer is preferably from 10,000 to 300,000, more preferably from 20,000 to 200,000, and even more preferably from 30,000 to 100,000.
When the Mn of the polymer is equal to or greater than the lower limit of the aforementioned numerical range, mechanical properties such as toughness tend to be improved.

The mass average molecular weight (Mw) of the polymer is preferably from 10,000 to 300,000, more preferably from 20,000 to 200,000, and even more preferably from 30,000 to 150,000.
When the Mw of the polymer is equal to or greater than the lower limit of the aforementioned numerical range, mechanical properties such as toughness tend to be improved.

The glass transition temperature (Tg) of the polymer is preferably 30° C. or lower, more preferably 5 to 25° C., and even more preferably 5 to 20° C. The lower limit of the Tg of the polymer is not particularly limited, and there is no problem even if it is 0° C. or lower. When the Tg of the polymer is within the above numerical range, it is preferable in terms of preventing adhesion during storage of the film and formability. When the Tg of the polymer is equal to or lower than the above upper limit, the biodegradability of the polymer is further excellent.
The Tg of the polymer is a value determined by the method described in the Examples below.

The melting point (Tm) of the polymer is preferably 130° C. or higher, more preferably 140° C. or higher, and even more preferably 145° C. or higher. When the Tm of the polymer is equal to or higher than the lower limit of the above-mentioned numerical range, the heat resistance of the polymer is further improved. The upper limit of the Tm of the polymer is not particularly limited.
The Tm of a polymer is a value determined by the method described in the Examples below.

The crystallization temperature (Tc) of the polymer is not particularly limited. Tc can be set appropriately taking into consideration the moldability of the polymer. The Tc of the polymer is a value determined by the method described in the examples below.

The heat resistance of the polymer can be easily maintained by reducing the amount of polycaprolactone units used. For example, the desired heat resistance can be achieved by adjusting the ratio of the amounts or molecular weights of the polylactic acid units and the polycaprolactone units used in the triblock synthesis stage.
The PLA ratio (%) is preferably 30-100, more preferably 40-95, and even more preferably 50-90.
When the PLA ratio is equal to or greater than the lower limit of the above-mentioned range, the melting point is easily improved, and heat resistance is easily maintained. When the PLA ratio is equal to or less than the upper limit of the above-mentioned range, Tg is easily decreased. Therefore, it is preferable in terms of the biodegradability of the polymer. However, the upper limit of the PLA ratio is not limited in any way in terms of heat resistance.
The PLA ratio (%) can be adjusted by the amount of the oligomer fed in the synthesis step, and can also be calculated by analyzing the oligomer described in the examples below by NMR or GPC.
PLA ratio (%) = (mass of lactide charged (charged value)) / (total charged mass) x 100
= (Molecular weight of PLA in oligomer (NMR analysis value)) / (Total molecular weight of oligomer (GPC analysis value)) × 100

When the polymer is hot-press molded using a 0.1 mm thick mold at 20 MPa, 10 minutes, and 180° C. to form a film, the film preferably has a breaking elongation of 200% or more, more preferably 300% or more, and even more preferably 320% or more. When the breaking elongation of the film is equal to or more than the lower limit, the mechanical properties such as toughness are further improved. The upper limit of the breaking elongation of the film is not particularly limited.
The breaking elongation is a value determined by the method described in the Examples section below.

When the polymer is hot-press molded into a film using a 0.1 mm thick mold at 20 MPa, 10 minutes, and 180° C., the tensile modulus of the film is preferably 200 MPa or more, more preferably 500 MPa or more, and even more preferably 800 MPa or more. When the tensile modulus of the film is equal to or more than the lower limit, the mechanical properties are further improved. The upper limit of the tensile modulus of the film is not particularly limited.
The tensile modulus is a value determined by the method described in the Examples section below.

When the polymer is hot-press molded using a 0.1 mm thick mold at 20 MPa, 10 minutes, and 180° C. to form a film, the maximum stress of the film is preferably 10 MPa or more, more preferably 20 MPa or more, and even more preferably 28 MPa or more. When the maximum stress of the film is equal to or more than the lower limit, the mechanical properties are further improved. The upper limit of the maximum stress of the film is not particularly limited.
The maximum stress is a value determined by the method described in the Examples section below.

When the polymer is hot-press molded into a film using a 0.1 mm thick mold under conditions of 20 MPa, 10 minutes, and 180° C., the toughness of the film is preferably 20 MJ/m ³ or more, more preferably 40 MJ/m ³ or more, and even more preferably 60 MJ/m ³ or more. When the toughness of the film is equal to or more than the lower limit, the mechanical properties are further improved. The upper limit of the toughness of the film is not particularly limited.
The toughness is a value determined by the method described in the Examples section below.

When the polymer is hot-press molded using a 0.1 mm thick mold at 20 MPa, 10 minutes, and 180° C. to form a film, it is preferred that the total light transmittance of the film is 85% or more and the haze is 50% or less.
The total light transmittance of the film is more preferably 88% or more, and even more preferably 90% or more. When the total light transmittance of the film is equal to or more than the lower limit, the polymer has excellent transparency and visibility. The upper limit of the total light transmittance of the film is not particularly limited.
The haze of the film is more preferably 45% or less, and even more preferably 40% or less. When the haze of the film is equal to or less than the upper limit, the polymer has excellent transparency and visibility. The lower limit of the haze of the film is not particularly limited.
The total light transmittance and haze are values that are determined by the methods described in the Examples section below.

When the polymer is hot-press molded into a film using a 0.1 mm thick mold at 20 MPa, 10 minutes, and 180° C., the crystallinity of the film when treated at 0.1 MPa, 70° C., and 12 hours is preferably 50% or less, more preferably 48% or less, and even more preferably 46% or less. The lower limit of the crystallinity is not particularly limited, but is thought to be, for example, about 1%.
The crystallinity is a value determined by X-ray analysis as described in the Examples below.

(Method of Producing Polymer)
The method for producing the polymer of the present invention is not particularly limited as long as a predetermined chemical structure can be obtained. For example, the polymer of the present invention can be synthesized by adding polylactic acid units to both ends of a polycaprolactone unit to synthesize a triblock structure, and then carrying out a urethane reaction to bond the triblock structures together using a unit containing a urethane bond. In this case, after synthesizing the triblock structure, the triblock structure may be purified and recovered before carrying out the urethane reaction.

The polycaprolactone unit can be synthesized, for example, by polymerizing a monomer component (1) containing ε-caprolactone. The monomer component (1) typically contains ε-caprolactone. However, in one example, the monomer component (1) can contain, instead of or in addition to ε-caprolactone, a monomer in which an arbitrary side chain, such as an alkyl chain, is bonded to any carbon atom of ε-caprolactone. In addition, commercially available polycaprolactone or commercially available polycaprolactone diol may be used as the polycaprolactone unit.
The molecular weight of the polycaprolactone unit may be controlled by the composition of the monomer component (1), the polymerization reaction, and the polymerization conditions. A commercially available product having a molecular weight within the desired range may also be purchased.

In synthesizing a triblock structure, for example, a monomer component (2) containing lactide can be addition polymerized to both ends of a polycaprolactone unit. In one example, a monomer undergoes an addition reaction with the hydroxyl groups (-OH) at both ends of a polycaprolactone unit, resulting in the elongation of each of the polylactic acid units, resulting in the synthesis of a triblock structure.

Monomer component (2) typically includes lactide. However, in one example, monomer component (2) may include, instead of or in addition to lactide, a monomer having an optional side chain, such as an alkyl chain, bonded to any carbon atom of lactide. The molecular weight of the polylactic acid unit can be controlled by the composition of monomer component (2), the polymerization reaction, and the polymerization conditions.

In a typical example of a urethanization reaction, a triblock structure is reacted with an aliphatic diisocyanate, and the triblock structures are bonded together by units containing urethane bonds. The urethanization reaction produces a polymer having the chemical structure of the present invention.

(Mechanism of action)
The polymer of the present invention has excellent heat resistance because each of the multiple triblock structures has a polylactic acid unit. In addition, in each triblock structure, the polylactic acid unit is bonded to both ends of the polycaprolactone unit by an ester bond. Therefore, the glass transition temperature of the polymer can be lowered while maintaining excellent heat resistance.
When the glass transition temperature is lowered, the mobility of the polymer in the natural environment becomes sufficiently high. In addition, in the triblock structure, the polycaprolactone unit and the polylactic acid unit are bonded by ester bonds, so that the polymer has good biodegradability. As a result, the polymer is easily hydrolyzed and the polymer chain is easily cut, so that a polymer with excellent biodegradability is obtained.
In the polymer of the present invention, the triblock structures are bonded together by units containing urethane bonds. This gives the polymer tenacity, i.e., toughness. As a result, the elongation at break and modulus of elasticity are increased, and mechanical properties are improved. Therefore, the polymer of the present invention is highly versatile and can be used in a variety of applications.

<Applications>
The application of the polymer of the present invention is not particularly limited. For example, it can be used as a material for various articles such as films, sheets, injection molded products, fibers, containers, medical products, and toys. The fibers can be applied to textile products such as nonwoven fabrics and woven fabrics. The films and containers can be used in various fields such as the food field, the clothing field, the medical product field, and the pharmaceutical field.
Possible applications in the medical and pharmaceutical fields include sutures, artificial bones, artificial skin, wound dressings, microcapsules and other DDS applications, and scaffolding materials for tissue and organ regeneration, etc. In addition, the polymer of the present invention may be used as a binder in toners and thermal transfer inks, but the applications of the polymer of the present invention are not limited to these.

The polymer of the present invention may be used alone or in the form of a composition in combination with additives, etc. The additives are not particularly limited and can be appropriately selected depending on the application and molding method.
The polymer of the present invention can be applied to various molding methods. The molding method is not particularly limited. For example, various molding methods such as heat press molding, injection molding, solvent casting, and extrusion molding can be applied. Specific forms of the molded product include, but are not limited to, sheets, films, containers, petri dishes, plates, housings, fibers, and nonwoven fabrics.

The present invention will be specifically described below using examples, but the present invention is not limited to the following description.

Example 1
20 g of lactide (molar number: 0.139 mol, Mn: 144.13 g/mol) and 5 g of polycaprolactone diol (molar number: 0.0025 mol, Mn: 2000 g/mol, Sigma-Aldrich product) were placed in a 200 mL three-neck flask, dried under reduced pressure, and dehydrated. 20 mg of tin(II) 2-ethylhexanoate (molar number: 0.00005 mol, Mn: 405.12 g/mol) was added dropwise, and nitrogen replacement was repeated to place the flask in a nitrogen atmosphere. Then, the mixture was stirred at 180° C. for 3 hours under a nitrogen atmosphere to synthesize an oligomer having a triblock structure.
After taking a part of the sample for analysis, 412 mg of hexamethylene diisocyanate (molar number: 2.45 mmol, Mn: 168.2 g/mol) was dropped to the molten oligomer so that NCO/OH=1/1 (mmol), and the mixture was reacted at 180° C. for 30 minutes under a nitrogen atmosphere. The reactant was then dissolved in chloroform and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180° C. and pressed at 20 MPa for 10 minutes to obtain a 0.1 mm thick film.

Example 2
A polymer was synthesized in the same manner as in Example 1, except that the amount of hexamethylene diisocyanate used was changed so that NCO/OH=2/1 (mmol) when hexamethylene diisocyanate was dropped, and a film having a thickness of 0.1 mm was obtained.

Example 3
A polymer was synthesized in the same manner as in Example 2. The recovered polymer was dissolved in chloroform and a film having a thickness of 0.1 mm was obtained by a solvent casting method.

Example 4
After synthesizing an oligomer having a triblock structure in Example 1, a step of reprecipitating the reaction product and removing impurities was added before forming urethane bonds between the triblock structures. Specifically, the following operations were performed.
20g of lactide (molar number: 0.139 mol, Mn: 144.13 g/mol) and 5g of polycaprolactone diol (molar number: 0.0025 mol, Mn: 2000 g/mol, Sigma-Aldrich product) were placed in a 200mL three-neck flask, dried under reduced pressure, and dehydrated. 20mg of tin(II) 2-ethylhexanoate (molar number: 0.00005 mol, Mn: 405.12 g/mol) was added dropwise, and nitrogen replacement was repeated to create a nitrogen atmosphere in the flask. The mixture was stirred at 180°C for 3 hours under a nitrogen atmosphere to synthesize a triblock structure. The reactant was then dissolved in chloroform and reprecipitated with methanol to recover an oligomer having a triblock structure.
6 g of the recovered oligomer was placed in another flask and melted at 180° C. 68 mg of hexamethylene diisocyanate (molar number: 0.40 mmol, Mn: 168.2 g/mol) was dropped to the molten triblock structure so that NCO/OH=1/1 (mmol), and the mixture was reacted at 180° C. for 30 minutes under a nitrogen atmosphere. The reactant was then dissolved in chloroform and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180° C. and pressed at 20 MPa for 10 minutes to obtain a 0.1 mm thick film.

<Comparative Example 1>
In a 200 mL three-neck flask, 20 g of lactide (molar number: 0.139 mol, Mn: 144.13 g/mol) and 0.106 g of polycaprolactone diol (molar number: 0.002 mol, Mn: 530 g/mol, Sigma-Aldrich product) were placed, dried under reduced pressure, and dehydrated. After dropping 1.62 mg of tin (II) 2-ethylhexanoate (molar number: 0.00004 mol, Mn: 405.12 g/mol), nitrogen replacement was repeated to place the flask under a nitrogen atmosphere. Then, the mixture was stirred at 180° C. for 3 hours under a nitrogen atmosphere to synthesize a polymer having a triblock structure. Then, the reactant was dissolved in chloroform, and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180° C. and pressed at 20 MPa for 10 minutes to obtain a 0.1 mm thick film. In this manner, in Comparative Example 1, a urethane-forming reaction was not carried out, and a polymer having a high molecular weight was synthesized by the ester bond in the triblock structure.

<Comparative Example 2>
In a 200 mL three-neck flask, 40 g of lactide (molar number: 0.278 mol, Mn: 144.13 g/mol) and 0.8 g of polycaprolactone diol (molar number: 0.004 mol, Mn: 2000 g/mol, Sigma-Aldrich product) were placed, dried under reduced pressure, and dehydrated. After dropping 3.24 mg of tin (II) 2-ethylhexanoate (molar number: 0.00008 mol, Mn: 405.12 g/mol), nitrogen replacement was repeated to place the flask under a nitrogen atmosphere. Then, the mixture was stirred at 180° C. for 3 hours under a nitrogen atmosphere to synthesize a polymer having a triblock structure. Then, the reactant was dissolved in chloroform, and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180° C. and pressed at 20 MPa for 10 minutes to obtain a 0.1 mm thick film. In this manner, also in Comparative Example 2, a polymer having a high molecular weight was synthesized by the ester bond in the triblock structure without carrying out a urethane-forming reaction.

<Comparative Example 3>
In a 200 mL three-neck flask, 20 g of lactide (molar number: 0.139 mol, Mn: 144.13 g/mol) and 5 g of polycaprolactone diol (molar number: 0.025 mol, Mn: 2000 g/mol, Sigma-Aldrich product) were placed, dried under reduced pressure, and dehydrated. After dropping 20 mg of tin (II) 2-ethylhexanoate (molar number: 0.00005 mol, Mn: 405.12 g/mol), nitrogen replacement was repeated to place the flask under a nitrogen atmosphere. Then, the mixture was stirred at 180° C. for 3 hours under a nitrogen atmosphere to synthesize a polymer having a triblock structure. Then, the reactant was dissolved in chloroform, and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180° C. and pressed at 20 MPa for 10 minutes to obtain a 0.1 mm thick film. In this way, a polymer having a high molecular weight was synthesized by the ester bond in the triblock structure without carrying out a urethane reaction in Comparative Example 3. In addition, the polymer was synthesized so that the molecular weight was smaller than those of Comparative Examples 1 and 2.

<Comparative Example 4>
20g of lactide (molar number: 0.139 mol, Mn: 144.13 g/mol) and 0.225g of 1,4-butanediol (molar number: 0.0025 mol, Mn: 90.121 g/mol) were placed in a 200mL three-neck flask, dried under reduced pressure, and dehydrated. 20mg of tin(II) 2-ethylhexanoate (molar number: 0.00005 mol, Mn: 405.12 g/mol) was added dropwise, and nitrogen replacement was repeated to make the flask under a nitrogen atmosphere. Then, the mixture was stirred at 180°C for 3 hours under a nitrogen atmosphere to synthesize polylactic acid diol. The reactant was then dissolved in chloroform, reprecipitated with methanol, and polylactic acid diol was collected.
5 g of the recovered polylactic acid diol (molar number 0.41 mmol) and 0.82 g of polycaprolactone diol (molar number: 0.41 mmol, Mn: 2000 g/mol, Sigma-Aldrich product) were placed in another flask and melted at 180°C. 137.2 mg of hexamethylene diisocyanate (molar number: 0.82 mmol, Mn: 168.2 g/mol) was dropped into the molten oligomer so that NCO/OH = 1/1 (mmol), and reacted at 180°C for 30 minutes under a nitrogen atmosphere. Thereafter, the reactant was dissolved in chloroform and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180°C and pressed at 20 MPa for 10 minutes to obtain a 0.1 mm thick film. In this way, in Comparative Example 4, an oligomer having a triblock structure was not synthesized, but a polylactic acid diol was synthesized first, and then the polylactic acid diol and the polycaprolactone diol were subjected to a urethane reaction. The polymer obtained in Comparative Example 4 is a copolymer of the polylactic acid diol and the polycaprolactone diol by urethane bonding. Comparative Example 4 relates to a method of copolymerization without the intervention of a triblock structure. Comparative Example 4 was carried out with reference to JP-A-2006-183042.

<Comparative Example 5>
In a 200 mL three-neck flask, 5 g of commercially available polylactic acid (molar number: 1 mmol, Mn: 5000 g/mol, Sigma-Aldrich product) and 1 g of polycaprolactone diol (molar number: 0.5 mmol, Mn: 2000 g/mol, Sigma-Aldrich product) were melted at 180 ° C. To the molten oligomer, 168.2 mg of hexamethylene diisocyanate (molar number: 1 mmol, Mn: 168.2 g/mol) was dropped so that NCO/OH = 1/1 (mmol), and reacted at 180 ° C. for 30 minutes under a nitrogen atmosphere. Thereafter, the reactant was dissolved in chloroform and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180 ° C. and pressed at 20 MPa for 10 minutes to obtain a film with a thickness of 0.1 mm. In this way, in Comparative Example 5, commercially available polylactic acid and polycaprolactone diol were subjected to a urethane reaction. The polymer obtained in Comparative Example 5 was a copolymer of commercially available polylactic acid and polycaprolactone diol with a urethane bond.

<Comparative Example 6>
In a 200 mL three-neck flask, 4.9 g of commercially available polylactic acid (molar number: 0.49 mmol, Mn: 10000 g/mol, Sigma-Aldrich product) and 0.49 g of polycaprolactone diol (molar number: 0.245 mmol, Mn: 2000 g/mol, Sigma-Aldrich product) were melted at 180 ° C. To the molten oligomer, 82.42 mg of hexamethylene diisocyanate (molar number: 0.49 mmol, Mn: 168.2 g/mol) was dropped so that NCO/OH = 1/1 (mmol), and reacted at 180 ° C. for 30 minutes under a nitrogen atmosphere. Thereafter, the reactant was dissolved in chloroform and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180 ° C. and pressed at 20 MPa for 10 minutes to obtain a 0.1 mm thick film. Thus, commercially available polylactic acid and polycaprolactone diol were subjected to a urethane reaction in Comparative Example 6. The polymer obtained in Comparative Example 6 was a copolymer of commercially available polylactic acid and polycaprolactone diol with a urethane bond.

<Comparative Example 7>
In a 200 mL three-neck flask, 8 g of polycaprolactone diol (molar number: 4 mmol, Mn: 2000 g/mol, Sigma-Aldrich product) was melted at 180° C. To the molten polycaprolactone diol, 672.8 mg of hexamethylene diisocyanate (molar number: 4 mmol, Mn: 168.2 g/mol) was dropped so that NCO/OH=1/1 (mmol), and the mixture was reacted at 180° C. for 30 minutes under a nitrogen atmosphere. Thereafter, the reactant was dissolved in chloroform and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180° C. and pressed at 20 MPa for 10 minutes to obtain a film having a thickness of 0.1 mm. In this way, in Comparative Example 7, a urethane reaction was carried out using only polycaprolactone diol.

<Comparative Example 8>
20g of lactide (molar number: 0.139mol, Mn: 144.13g/mol) and 0.225g of 1,4-butanediol (molar number: 0.0025mol, Mn: 90.121g/mol) were placed in a 200mL three-neck flask, dried under reduced pressure, and dehydrated. 20mg of tin(II) 2-ethylhexanoate (molar number: 0.00005mol, Mn: 405.12g/mol) was added dropwise, and nitrogen replacement was repeated to place the flask under a nitrogen atmosphere. Then, the mixture was stirred at 180°C for 3 hours under a nitrogen atmosphere to synthesize polylactic acid diol. The reactant was then dissolved in chloroform, reprecipitated with methanol, and polylactic acid diol was collected.
7.5 g (molar number 0.64 mmol) of the recovered polylactic acid diol was placed in another flask and melted at 180°C. 107 mg of hexamethylene diisocyanate (molar number: 0.64 mmol, Mn: 168.2 g/mol) was dropped into the molten polylactic acid diol so that NCO/OH=1/1 (mmol), and reacted at 180°C for 30 minutes under a nitrogen atmosphere. Thereafter, the reactant was dissolved in chloroform and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180°C and pressed at 20 MPa for 10 minutes to obtain a film with a thickness of 0.1 mm. In this way, in Comparative Example 8, a urethane reaction was carried out using only polylactic acid diol.

<Comparative Example 9>
20g of lactide (molar number: 0.139 mol, Mn: 144.13 g/mol) and 0.225g of 1,4-butanediol (molar number: 0.0025 mol, Mn: 90.121 g/mol) were placed in a 200mL three-neck flask, dried under reduced pressure, and dehydrated. 20mg of tin(II) 2-ethylhexanoate (molar number: 0.00005 mol, Mn: 405.12 g/mol) was added dropwise, and nitrogen replacement was repeated to make the flask under a nitrogen atmosphere. Then, the mixture was stirred at 180°C for 3 hours under a nitrogen atmosphere to synthesize polylactic acid diol. The reactant was then dissolved in chloroform, reprecipitated with methanol, and polylactic acid diol was collected.
3 g of the recovered polylactic acid diol (molar number 0.26 mmol) and 2 g of polycaprolactone diol (molar number: 1 mmol, Mn: 2000 g/mol, Sigma-Aldrich product) were placed in another flask and melted at 180°C. 211.3 mg of hexamethylene diisocyanate (molar number: 1.26 mmol, Mn: 168.2 g/mol) was dropped into the molten oligomer so that NCO/OH=1/1 (mmol), and reacted at 180°C for 30 minutes under a nitrogen atmosphere. Thereafter, the reactant was dissolved in chloroform and reprecipitated with methanol to recover the polymer. The recovered polymer was melted at 180°C and pressed at 20 MPa for 10 minutes to obtain a film with a thickness of 0.1 mm. In this way, in Comparative Example 9, after the synthesis of polylactic acid diol, it was reacted with polycaprolactone diol for urethane formation. Comparative Example 9 relates to a method of copolymerization without using a triblock structure, similar to Comparative Example 4. Comparative Example 9, similar to Comparative Example 4, was carried out with reference to JP-A-2006-183042.

<Comparative Example 10>
For comparison, commercially available polycaprolactone (Mn 8,0000) (Sigma-Aldrich product) was melted at 180° C. and pressed at 20 MPa for 10 minutes to obtain a film having a thickness of 0.1 mm.

<Comparative Example 11>
For comparison, commercially available polylactic acid (Nature Works product "Ingeo Biopolymer 2003D") was melted at 180°C and pressed at 20 MPa for 10 minutes to obtain a film having a thickness of 0.1 mm.

<Measurement and Evaluation>
The films of the respective examples were measured and evaluated as follows.

(Mw, Mn)
The molecular weight (Mw, Mn) of the polymer was measured by gel permeation chromatography (GPC) molecular weight analysis. Specifically, GPC (HLC-8420, product of Tosoh Corporation) was used and the measurement was performed with an RI detector. The column used was TSKgel GMHHR-M (product of Tosoh Corporation). The eluent for GPC was chloroform (CHCl ₃ ). The column temperature was 40° C. and the flow rate was 1.0 ml/min. The standard sample used for the measurement was polystyrene (standard polystyrene kit PStQuick, Tosoh Corporation). A calibration curve was created in terms of polystyrene, and the molecular weight (Mw, Mn) was calculated.

( ^1H NMR Analysis)
¹ H NMR was analyzed using a nuclear magnetic resonance apparatus (JNM-EC400, JEOL Ltd.). The number of accumulations was 32, and chloroform-d (CDCl ₃ ) was used as the deuterated solvent. In the NMR spectrum, the presence or absence of a peak (around 3.1 ppm) due to the "-NH-" of the urethane bond was observed.

(Film Forming)
The feasibility of forming the film was evaluated according to the following criteria.
A: Film formation was possible, and physical properties could be measured.
B: The film crumbled during molding, making it impossible to measure the physical properties.

(Tg, Tm, Tc)
The Tg (°C), Tm (°C), and Tc (°C) of the polymer were measured using a DSC (high sensitivity differential scanning calorimeter DMS-6220, Hitachi High-Tech Science Corporation). The measurement temperature range was −80°C to 200°C, and the heating rate was 10°C/min.

(Tensile test)
A dumbbell-shaped tensile test piece with a balance part of 20 mm in length and 4 mm in width was prepared and measured using a tensile tester (tabletop precision universal testing machine AGS-X, Shimadzu Corporation).
The test conditions were in accordance with JIS K7127. The crosshead speed was 10 mm/min, and the gripper distance was 20 mm. The tensile modulus (MPa), maximum stress (MPa), breaking elongation (%), and toughness (MJ/m ³ ) of the tensile test specimen were measured.

(Total light transmittance, haze)
A haze meter (NDH-4000, Nippon Denshoku Industries Co., Ltd.) was used. The total light transmittance was measured in accordance with JIS K7361-1:1997. The haze was measured in accordance with JIS K7136:2000.

(Crystallization degree)
An X-ray diffraction apparatus (RINT-Ultimate III, Rigaku Corporation) was used. Measurements were performed at a tube voltage of 40 kW, a tube current of 40 mA, a measurement range of a diffraction angle 2θ = 5 to 30°, and a scan speed of 1.0°/min, and the crystallinity (%) was calculated by the following formula.
Crystallinity (%)=(crystalline peak area/(crystalline peak area+amorphous peak area))×100

<Results>
The measurement results and evaluation results of each example are shown in Tables 1 and 2.

As shown in Tables 1 and 2, in Examples 1 to 4, polymers were obtained that had sufficiently high Tm, excellent heat resistance, and low Tg. These polymers with low Tg are considered to have excellent biodegradability. Furthermore, in Examples 1 to 4, the breaking elongation was high when molded into a film. This indicates excellent mechanical properties. In contrast, in Comparative Examples 1 to 11, it was not possible to achieve both a low Tg and good mechanical properties. In Comparative Examples 5 and 7, no Tg was detected.

The films of Comparative Examples 3, 5, 6 and 9 were too hard and brittle, and therefore broke during molding, making it impossible to measure the tensile modulus (MPa), maximum stress (MPa), elongation at break (%) and toughness (MJ/m ³ ).
In Comparative Example 7, the film was too soft and brittle, and therefore the film broke during molding, making it impossible to measure the tensile modulus (MPa), maximum stress (MPa), elongation at break (%), and toughness (MJ/m ³ ).

As shown in Table 3, the polymers of the examples exhibited good appearance, transparency, and visibility when made into films.

The present invention provides a polymer that has excellent heat resistance, biodegradability, and mechanical properties, and uses thereof.

1 Polymer 2 Polycaprolactone unit 3 Polylactic acid unit 4 Triblock structure 5 Unit containing urethane bond

Claims (5)

A polymer comprising:
The polymer has a plurality of triblock structures in which polylactic acid units are bonded to both ends of a polycaprolactone unit via ester bonds,
A polymer in which multiple triblock structures are bonded together through units containing urethane bonds. The polymer according to claim 1, having a glass transition temperature of 30°C or less. 2. The polymer of claim 1, wherein when the polymer is formed into a film under the following conditions, the film has an elongation at break of 200% or more.
Film molding conditions: hot press molding was performed using a mold having a thickness of 0.1 mm under conditions of 20 MPa, 10 minutes, and 180°C. 2. The polymer according to claim 1, wherein when the polymer is molded into a film under the following conditions, the total light transmittance of the film is 85% or more and the haze of the film is 50% or less.
Film molding conditions: hot press molding was performed using a mold having a thickness of 0.1 mm under conditions of 20 MPa, 10 minutes, and 180°C. A molded body comprising the polymer according to any one of claims 1 to 4.

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