Polymer, hydrogel, method for producing polymer, method for producing molding and method for producing hydrogel

Abstract

To provide a noble polymer having essentially high biodegradability, capable of fabricating, and capable of controlling biodegradability.SOLUTION: A polymer obtained by condensation polymerization of inositol and dicarboxylic acids, containing structural units represented by the following general formula (1). In the formula, n is an integer from 1 to 6, m is an integer from 0 to 5, and n+m is 2 to 6. R1 is a linear or cyclic alkylene group with 1 to 7 carbon atoms, which may independently have branching, and R2 is a linear or cyclic alkylene group with 8 to 12 carbon atoms, which may independently have branching. [Chem. 1]SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel biodegradable polymer, a hydrogel, a method for producing a polymer, a method for producing a molded article, and a method for producing a hydrogel. [Background technology]

[0002] Biodegradable polymers are ultimately decomposed into water and carbon dioxide by microorganisms in the natural environment, and therefore do not remain in the environment as resin molded products or in microscopic forms such as microplastics or nanoplastics. Biodegradable polymers have attracted attention as polymers that can contribute to solving the problem of plastic residues in the marine environment. Examples of such biodegradable polymers include polyesters such as polyglycolic acid (PGA), polylactic acid (PLA), polybutylene adipate-co-terephthalate (PBAT), polybutylene succinate (PBS), polybutylene succinate-co-adipate (PBSA), poly-3-hydroxybutyrate (PHB), and poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBH), which are used as various general-purpose resins. Patent Document 1 describes a method for improving the molecular weight and physical properties of such biodegradable polymers by adding inositol-containing polyols as crosslinking agents during polymerization. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2008-101031 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a growing demand for polymers that are highly biodegradable, especially in marine environments. Polymer biodegradation is defined as a series of processes in which specific chemical bonds constituting a polymer are cleaved by degradative enzymes secreted by microorganisms, and the cleaved (lower molecular weight) polymer fragments are further incorporated into the microorganism's body, ultimately decomposing them into water and carbon dioxide. Therefore, introducing a chemical structure capable of interacting with the degradative enzymes secreted by microorganisms, such as a hydroxyl group capable of forming hydrogen bonds with the enzyme, into the polymer is considered to be one of the most effective ways to dramatically improve the biodegradability of a polymer. The aforementioned Patent Document 1 describes a polymer containing 0.0001 to 10 mol % of inositol-containing polyols relative to specific constituents, but does not provide any insight into the effect of this on the polymer's biodegradability. Furthermore, the content of the inositol-containing polyols added as crosslinkers in this patent document is limited to 0.0001 to 10 mol %, which makes it easy to infer that no hydroxyl groups capable of interacting with the degradative enzymes secreted by microorganisms remain in the final polymer structure. The reason why the amount added is so small can be easily guessed by those involved in the polymer manufacturing industry, but if the content of polyols such as inositol is increased, multiple hydroxyl groups will polymerize in a disordered manner, causing unintended gelation and making molding processing difficult. In order to solve the above problems, the present invention provides a novel biodegradable polymer, a hydrogel, a method for producing a polymer, a method for producing a molded article, and a method for producing a hydrogel. [Means for solving the problem]

[0005] The present inventors have found that biodegradability is also exhibited in an embodiment in which a polymer obtained by condensation polymerization of inositol and a dicarboxylic acid is used.

[0006] That is, the present invention is as follows. [1] A polymer obtained by condensation polymerization of inositol and dicarboxylic acids, which comprises a constitutional unit represented by the following general formula (1):

[0007] [ka]

[0008] {In the formula, n is an integer of 1 to 6 and m is an integer of 0 to 5, n+m is an integer of 2 to 6, R1's each independently represent an optionally branched linear or cyclic alkylene group having 1 to 7 carbon atoms, and R2's each independently represent an optionally branched linear or cyclic alkylene group having 8 to 12 carbon atoms.} [2] The polymer according to [1], wherein, in the general formula (1), n+m is 2, R1's are each independently a linear or cyclic alkylene group having 4 to 7 carbon atoms which may have a branch, and R2's are each independently a linear or cyclic alkylene group having 8 to 12 carbon atoms which may have a branch. [3] The polymer according to [1] or [2], which exhibits fluidity at temperatures of 190°C or less. [4] A hydrogel obtained by allowing the polymer according to any one of [1] to [3], wherein n+m in the general formula (1) is 2, to absorb water. [5] A method for producing a polymer, comprising a step of condensation polymerizing inositol and dicarboxylic acids to obtain a polymer, wherein the molar ratio of the inositol to the dicarboxylic acids is in the range of 0.3 to 1.0. [6] A step of melting or dissolving the polymer according to any one of [1] to [3] in water to obtain a polymer solution; applying the polymer solution to a substrate and then curing it; A method for producing a molded body, comprising: [7] A method for producing a hydrogel, comprising a step of allowing the polymer according to any one of [1] to [3] to absorb water after polymerization. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide novel polymers, hydrogels, methods for producing polymers, methods for producing molded articles, and methods for producing hydrogels that are highly biodegradable and have an extremely low environmental impact, using inositol, a natural raw material, as a monomer. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (hereinafter also referred to as "the present embodiment") will be described in detail. However, the present invention is not limited to the following embodiments, and can be practiced in various modified forms within the scope of the gist thereof.

[0011] <Polymer> The polymer of this embodiment is a polymer obtained by condensation polymerization of inositol and dicarboxylic acids, and contains a constitutional unit represented by the following general formula (1).

[0012] [ka]

[0013] {In the formula, n is an integer of 1 to 6 and m is an integer of 0 to 5, n+m is an integer of 2 to 6, R1 is an optionally branched linear or cyclic alkylene group having 1 to 7 carbon atoms, which may not all be identical, and R2 is an optionally branched linear or cyclic alkylene group having 8 to 12 carbon atoms, which may not all be identical.} This polymer will be described below.

[0014] The polymer of this embodiment may be a polyester obtained by condensation polymerization of an alcohol containing inositol and a dicarboxylic acid, and having an ester bond as a polymer linking structure. The resulting polymer may be a polymer that can be molded through melting or dissolution, or a xerogel that cannot be melted or dissolved. Obtaining a moldable polymer through melting or dissolution by controlling the polymerization temperature and time is particularly preferable from the viewpoint of processability. It is quite unexpected that a polymer that can be dissolved and melt-molded can be obtained, even though inositol, a hexaol that normally crosslinks rapidly, is used as a monomer. The reason for this is unclear, but it is presumed that the essential difference in reactivity between the multiple hydroxyl groups based on the three-dimensional structure of inositol allows for the extension of the polymer chain while suppressing rapid crosslinking.

[0015] From the viewpoint of enabling molding by melting or dissolving, it is preferable that the polymer has the structural unit of general formula (1) and exhibits fluidity at temperatures of 190°C or less. Such fluidity can be determined, for example, by placing a polymer in a glass container with a diameter of 10 mm, fixing the container so that it faces vertically downward with the mouth open, and heating it to a temperature of 190°C or less, and observing whether 50% or more of the total amount of polymer flows out and falls. The temperature at which the polymer is allowed to flow is preferably 190°C or lower, more preferably 160°C or lower, and even more preferably 130°C or lower, because this is a temperature at which polymerization and curing do not proceed. Furthermore, the temperature is preferably 90°C or higher, more preferably 110°C or higher, because fluidity tends to be observed. The flow temperature can be unexpectedly low compared to the melting points of the monomers, inositol (melting point 224°C) and dicarboxylic acids. While the reason for this is unclear, it is presumed that the essential difference in reactivity between the multiple hydroxyl groups based on the three-dimensional structure of inositol prevents rapid crosslinking, allowing the polymer chain to extend to a molecular weight at which the properties of the monomer are not apparent.

[0016] When polymer molding is performed with a molten polymer, if the polymer has a high viscosity and stringiness or other problems arise, adding water can prepare a substantially uniform aqueous solution or a low-viscosity composition, which can then be used for coating. Here, a substantially uniform aqueous solution refers to a liquid in which no solids are visible to the naked eye and no liquid-liquid phase separation is observed. Because the aqueous solution behaves substantially like a liquid, it is particularly easy to process. Even when a substantially uniform aqueous solution is not obtained, adding water can reduce the viscosity of the melted solution and produce a low-viscosity composition, improving processability. The temperature at which water is added is not particularly limited; however, since this is below the boiling point of water, a temperature of 90°C or less is preferred, and 80°C or less is more preferred. Furthermore, since a heating device is not required, a temperature above room temperature is most preferred, but 40°C or higher is also preferred, as this tends to result in a more uniform solution. The polymer concentration when obtaining a substantially uniform aqueous solution is not particularly limited; a smaller amount of water is advantageous in terms of cost; however, if a viscous liquid results and productivity decreases, a lower concentration can be used. For example, the range is preferably 10% by mass or more and 80% by mass or less, and more preferably 20% by mass or more and 70% by mass or less. As described above, polymers that exhibit fluidity at temperatures of 190°C or less can be molded by melting or dissolving in water and then coating the polymer, and can be processed into practical product forms, making them particularly suitable for use. Polymers that exhibit fluidity at temperatures of 190°C or less can be obtained by controlling the reaction temperature, reaction pressure, reaction time, and other factors in accordance with the method for producing a polymer described below, allowing the polymer to react while visually checking the fluidity, and stopping the reaction when the polymer has the above-mentioned fluidity. The method for coating the polymer is not limited, and a wide range of known methods can be applied, including spray coating, spin coating, dip coating, and bar coating. After molding, it is desirable to increase the strength by carrying out polymerization in accordance with the following polymer production method until the glass transition temperature reaches a desired temperature, preferably 110°C or higher. This can prevent a decrease in strength that can occur in polymers that melt when heated or dissolve in a solvent.

[0017] The polymer in this embodiment is characterized in that in general formula (1), n ​​is 1 to 6, m is 0 to 5, and n+m is 2 to 6. Here, n and m in general formula (1) are average values ​​in the theoretically predicted structural units, as is clear from the fact that general formula (1) represents a structural unit. When n+m is large, for example, when it is 4 to 6, a polymer with a high degree of crosslinking is obtained, and when n+m is small, for example, when it is 2 to 3, a polymer with reduced crosslinking and with residual hydroxyl groups is obtained. The biodegradability of the polymer in this embodiment can be controlled by n+m in general formula (1). When high biodegradability is to be imparted, a polymer with residual hydroxyl groups and n+m of 2 to 3 is suitable. On the other hand, when degradability is to be suppressed, a highly crosslinked polymer with n+m of 4 to 6 is suitable. The fact that biodegradability can be controlled by n+m in general formula (1) even though the polymers are produced from the same raw materials provides new findings, particularly in the field of biodegradable resins. The reason why biodegradability can be controlled by n+m in general formula (1) is not clear, but it can be assumed that the smaller n+m and the more hydroxyl groups remaining, the better the compatibility with degrading enzymes and the higher the biodegradability, while the larger n+m and the higher the crosslinking progress, the more difficult it is for degrading enzymes to penetrate, resulting in lower biodegradability.

[0018] In general formula (1), it is preferred that n+m is 2, R1's are each independently a linear or cyclic alkylene group having 4 to 7 carbon atoms which may be branched, and R2's are each independently a linear or cyclic alkylene group having 8 to 12 carbon atoms which may be branched.

[0019] <Inositol> Inositol refers to 1,2,3,4,5,6-hexahydroxycyclohexane. Examples of inositol include allo-inositol, chiro-inositol, cis-inositol, epi-inositol, muco-inositol, neo-inositol, scyllo-inositol, and myo-inositol. Of these, myo-inositol, which is the most abundant in nature, is the most preferred because of its low environmental impact and low cost. Inositol may be extracted from natural products, chemically treated phytin or phytic acid, or produced from natural raw materials by fermentation.

[0020] Although it is not preferable from the viewpoint of productivity, modified inositol can also be used in which one or more hydroxyl groups of inositol are chemically modified for the purpose of imparting a specific function. The functional group to be modified can be any of the widely known hydroxyl group modifications, including ether groups, ester groups, urethane groups, carbonate groups, silyl groups, sulfonic acid groups, sulfonate groups, phosphate groups, and phosphonate groups. These modifying groups may also have a cyclic structure in which multiple hydroxyl groups of inositol, adjacent to each other or at positions suitable for modification, have reacted.

[0021] <Other alcoholic beverages> Alcohols other than inositol can also be copolymerized within the scope that does not limit the effects of the present invention. Examples of diols include α,ω-alkylene glycols (such as 1,2-ethanediol and 1,4-butanediol), 1,2-propanediol, neopentyl glycol, isosorbide, isomannide, terminal-unmodified polyethylene glycol, terminal-unmodified polytetramethylene glycol, catechol, resorcinol, hydroquinone, and bisphenol A.

[0022] Examples of triols include glycerol, trimethylolpropane, 1,2,3-butanetriol, 1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,3-cyclohexanetriol, 1,3,5-cyclohexanetriol, 1,2,4-cyclohexanetriol, and pyrogallol.

[0023] Two or more of the above-mentioned alcohols may be used in combination, and it goes without saying that these alcohols may further have a substituent.

[0024] In the polymer of this embodiment, the inositol content relative to the total amount of inositol and other alcohols is preferably 20 mol % because it provides excellent biodegradability. The inositol content in the alcohols is more preferably 50 mol % or more, and most preferably 100 mol %.

[0025] <Dicarboxylic acids> Dicarboxylic acids can be used as the component having R1 and R2 in general formula (1). Dicarboxylic acids include dicarboxylic acids having two carboxy groups, as well as esters in which one or two carboxy groups are esterified, acid anhydrides in which one or two carboxy groups are esterified, and acid halides in which one or two carboxy groups are halogenated. Among these, dicarboxylic acids or acid anhydrides are particularly preferred because the product of condensation polymerization is water, which is non-flammable, non-toxic, and has a low environmental impact. Dicarboxylic acids are most preferred because the production of the raw materials has a low environmental impact.

[0026] Examples of dicarboxylic acids include straight-chain aliphatic dicarboxylic acids including α,ω-aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid; alicyclic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and 1,5-furandicarboxylic acid; and other dicarboxylic acids such as aconitic acid, citraconic acid, mesaconic acid, maleic acid, fumaric acid, phenylmalonic acid, and phenylsuccinic acid. However, straight-chain aliphatic dicarboxylic acids are more preferred because they result in superior biodegradability of the polymer.

[0027] Although it is not preferable from the viewpoint of inhibiting the crosslinking reaction, polycarboxylic acids having three or more carboxy groups can also be used, and examples thereof include aconitic acid, trimellitic acid, pyromellitic acid, and 1,2,4,5-cyclohexanetetracarboxylic acid.

[0028] Two or more of the above dicarboxylic acids may be used in combination, and it goes without saying that these dicarboxylic acids may further have a substituent.

[0029] <Other copolymerizable components> The polymer of this embodiment can be copolymerized with any component that does not inhibit the condensation polymerization of alcohols and dicarboxylic acids, and copolymerization may be carried out within a range that does not limit the effects of the present invention. Examples of such components include ε-caprolactone, lactic acid, lactide, glycolic acid, glycolide, β-butyrolactone, 3-hydroxybutanoic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, tartaric acid, ricinoleic acid, saccharinic acid, mucic acid, quinic acid, shikimic acid, and gallic acid. Two or more of these components may be used in combination.

[0030] According to the inventors' investigations, polymers in which n+m in general formula (1) is 2, R1 is an optionally branched linear or cyclic alkylene group having 4 to 7 carbon atoms, and R2 is an optionally branched linear or cyclic alkylene group having 8 to 12 carbon atoms, tend to have excellent strength. While dicarboxylic acids having R1 are not particularly limited, adipic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid are preferred from the viewpoint of availability, and adipic acid and 1,4-cyclohexanedicarboxylic acid are more preferred due to their low cost. Furthermore, dicarboxylic acids having R2 are not particularly limited, and sebacic acid and dodecanedioic acid are preferred due to their low cost and availability. It is clear that a combination of these components may also be used. Furthermore, the ratio of dicarboxylic acids having R1 to dicarboxylic acids having R2 is not limited as long as n+m in general formula (1) is in the range of 2, but in order to achieve excellent miscibility, it is preferable that the ratio be 1:1, i.e., the dicarboxylic acids having R1 and the dicarboxylic acids having R2 are in equimolar amounts and n and m are 1. From the viewpoint of miscibility, it is not preferable to react only dicarboxylic acids in which n in general formula (1) is 0, i.e., dicarboxylic acids having R2 that are linear or cyclic alkylene groups having 8 to 12 carbon atoms, which may be branched and may not all be identical, but not including dicarboxylic acids having R1 that are linear or cyclic alkylene groups having 1 to 7 carbon atoms, which may be branched and may not all be identical, with inositol.

[0031] <Hydrogel> The hydrogel of this embodiment is obtained by allowing the polymer of this embodiment, in which n+m in the above general formula (1) is 2, to absorb water. According to the inventors' investigations, polymers in which n+m is 2 in general formula (1), i.e., polymers having four hydroxyl groups in the polymer's structural units, are characterized by their water-absorbing properties. A polymer cured by a method similar to the following polymer production method is a xerogel obtained through polycondensation, and since a polymer in which n+m is 2 is characterized by having hydroxyl groups, it is presumed that it can incorporate water molecules into the xerogel structure through hydrogen bonds via the hydroxyl groups, resulting in a water-absorbed hydrogel.

[0032] <Polymer manufacturing method> The method for producing the polymer of this embodiment is not particularly limited, and the polymer can be produced using a known apparatus capable of heating and mixing a mixture of monomer components. The reaction temperature is preferably 160°C or higher, more preferably 180°C or higher, as this is necessary for the esterification reaction to proceed. The reaction temperature is preferably 300°C or lower, more preferably 280°C or lower, and even more preferably 260°C or lower, from the viewpoint of suppressing decomposition of the polymer and monomer.

[0033] The method for producing a polymer of this embodiment includes a step of obtaining a polymer by condensation polymerization of inositol and dicarboxylic acids, and the molar ratio of the inositol to the dicarboxylic acids is preferably in the range of 0.3 to 1.0.

[0034] In the method for producing a polymer according to the present embodiment, condensation polymerization is preferably performed at a molar ratio of inositol to dicarboxylic acids in the range of 0.3 to 1.0. Here, the "molar ratio of inositol to dicarboxylic acids" refers to the molar ratio of inositol to the total molar amount of dicarboxylic acids having R1 and dicarboxylic acids having R2. Increasing the amount of inositol within this ratio range decreases n+m in general formula (1), and when the molar ratio of inositol to dicarboxylic acids is 1, n+m becomes 2. The molar ratio of inositol to dicarboxylic acids in the method for producing a polymer according to the present embodiment and n+m in general formula (1) can be determined, for example, by completely hydrolyzing the polymer by refluxing it in a high-concentration aqueous sodium hydroxide solution, and quantifying the concentration ratio of inositol to dicarboxylic acid sodium salt in the resulting aqueous solution using a commonly used analytical method such as high-performance liquid chromatography.

[0035] From the viewpoint of obtaining a polymer, the polymerization reaction is preferably carried out without a solvent, but a solvent can be added as appropriate to uniformly mix the monomers. As the solvent, a highly polar solvent is preferred from the viewpoint of being able to dissolve inositol, and examples thereof include water, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and N,N-dimethylethyleneurea. To obtain a polymer, it is preferable that the solvent be volatilized during the reaction and removed from the reaction mixture, and water is the most preferred.

[0036] The polymerization reaction proceeds without the addition of a catalyst, making it possible to obtain polymers with high glass transition temperatures without the use of a catalyst. The advantage of not using a catalyst is that no catalyst remains even when the polymer biodegrades in the environment. Known catalysts can also be added to accelerate the reaction, such as tin bis(2-ethylhexanoate), germanium oxide, antimony oxide, titanium tetraisopropoxide, and titanium tetrabutoxide.

[0037] The reaction can be carried out under reduced pressure in order to remove by-products such as water produced during the condensation polymerization from the mixture. When precise reaction control is required to obtain a moldable polymer by melting or dissolving in water, it is preferable to control the reaction temperature and pressure in stages.

[0038] From the viewpoint of suppressing decomposition of the monomer or polymer, it is preferable to carry out the reaction in an inert gas atmosphere such as nitrogen or argon.

[0039] The method for producing a molded article of this embodiment includes the steps of melting or dissolving the polymer of this embodiment in water to obtain a polymer solution, and applying the polymer solution to a substrate and then curing the substrate. The substrate may be any suitable substrate. For example, a glass plate or the like may be used as the substrate.

[0040] The method for producing a hydrogel of this embodiment includes a step of allowing the polymer according to claim 1 to absorb water after polymerization.

[0041] <Polymer applications> The applications of the polymer of this embodiment are not particularly limited, and it can be used in a wide range of applications due to its high biodegradability. In particular, it can be suitably used in applications where leakage into the environment is unavoidable, such as fibers, abrasives, blasting agents, and lost circulation prevention agents. In addition, since it can be melted or dissolved in water, molded, and then cured, it can also be suitably used for coating the surface of a substrate. [Example]

[0042] Examples that specifically explain this embodiment are given below, but the present invention is not limited to the following examples as long as they do not depart from the gist of the present invention.

[0043] <Analysis method> The analytical methods used in the examples and comparative examples are as follows.

[0044] (glass transition temperature) The glass transition temperatures of the products obtained in the examples were measured under the following measurement conditions. A sample weighing 2–10 mg was weighed into an aluminum pan (product number GAA-0065, Hitachi High-Tech Corporation), and an aluminum cover (product number GAA-0064, Hitachi High-Tech Corporation) was attached using a hand press. Using the sample enclosed in the aluminum pan, a differential scanning calorimeter (DSC-7000X, Hitachi High-Tech Corporation) was used. Under a nitrogen flow (pressure 0.1 MPa), the sample was heated from 30 °C to 130 °C (maximum 220 °C) at a heating rate of 50 °C / min, held for 10 min, then cooled to 70 °C at 30 °C at 20 °C / min, and heated from 30 °C to 150 °C (maximum 250 °C) at a heating rate of 10 °C / min. A DSC curve was obtained. The maximum value of the differential curve (DDSC) in the DSC curve during the second heating run was determined as the glass transition temperature.

[0045] (polymerization equipment) Glass tube oven: GTO-3000 rotating heating type (Shibata Scientific Co., Ltd.) Vacuum oven: ETTAS Vacuum Dryer AVO-250V (manufactured by AS ONE Corporation)

[0046] <Raw materials used> The raw materials used in the examples and comparative examples are shown below. Myo-inositol (Fujifilm Wako Pure Chemical Industries, Ltd.) Succinic acid (Fujifilm Wako Pure Chemical Industries, Ltd.) Glutaric acid (Tokyo Chemical Industry Co., Ltd.) Adipic acid (Fujifilm Wako Pure Chemical Industries, Ltd.)

[0047] <Reaction temperature> When an external heating / cooling device such as a glass tube oven or a vacuum oven was used, the temperature indicated on the device was used as the reaction temperature.

[0048] <Reaction pressure> The reaction pressure was controlled using a vacuum controller (Tokyo Rikakiki Co., Ltd., model number: NVC-2300A), and the displayed pressure was taken as the reaction pressure.

[0049] [Example 1-1] A 100 mL glass sample bulb was filled with 2.20 g of succinic acid, 3.39 g of myo-inositol (corresponding to n = 2, m = 0 in general formula (1)), and 10 mL of water. Three glass cooling bulbs were attached to the center joint of a glass tube oven. After replacing the atmosphere inside the sample bulb with nitrogen, the sample bulb and two cooling bulbs were positioned inside the oven and secured in place. Rotation was started at 60 rpm, and the temperature was set to 180 °C to begin heating. After 30 minutes, the temperature was set to 220 °C and heating was initiated. The water inside the sample bulb was distilled off by continuously cooling the cooling bulb. After the contents had dried, the mixture inside the sample bulb began to melt immediately. After confirming that the contents had completely melted, the reaction was continued at 220 °C for 30 minutes. After 30 minutes, the glass tube oven was stopped, and the sample bulb was immediately air-cooled. From the change in weight before and after the reaction, it was confirmed that 0.26 g of condensed water was distilled off, confirming the progress of the polymerization reaction. The sample ball was removed and heated in a vacuum oven at 130°C for 1 hour to melt the polymer, and then removed onto a polytetrafluoroethylene sheet. For the curing process, the vacuum oven was heated to 220°C, the pressure was reduced to 860 hPa, and the polymer on the sheet was polymerized for another 3 hours. The temperature was then increased to 220°C and full vacuum, and the polymer was polymerized for another 7 hours. A highly transparent, candy-like xerogel was obtained, and the glass transition temperature was 172.9°C.

[0050] [Example 1-2] The same procedure as in Example 1-1 was carried out except that 2.70 g of succinic acid and 2.75 g of myo-inositol (corresponding to n = 3, m = 0 in general formula (1)) were used, and a highly transparent, candy-like xerogel was obtained. No glass transition temperature was detected.

[0051] [Example 2-1] A highly transparent, candy-like xerogel was obtained in the same manner as in Example 1-1, except that 2.20 g of glutaric acid and 3.00 g of myo-inositol (corresponding to n = 2, m = 0 in general formula (1)) were used. The glass transition temperature was 146.7°C.

[0052] [Example 2-2] A highly transparent, candy-like xerogel was obtained in the same manner as in Example 1-1, except that 2.90 g of glutaric acid and 2.64 g of myo-inositol (corresponding to n = 3, m = 0 in general formula (1)) were used. The glass transition temperature was 205.6°C.

[0053] [Example 2-3] The same procedure as in Example 1-1 was carried out except that 3.80 g of glutaric acid and 1.73 g of myo-inositol (corresponding to n = 6, m = 0 in general formula (1)) were used, and a highly transparent, candy-like xerogel was obtained. No glass transition temperature was detected.

[0054] [Example 3-1] A highly transparent, candy-like xerogel was obtained in the same manner as in Example 1-1, except that 2.50 g of adipic acid and 3.08 g of myo-inositol (corresponding to n = 2, m = 0 in general formula (1)) were used. The glass transition temperature was 133.1°C.

[0055] [Example 3-2] A highly transparent, candy-like xerogel was obtained in the same manner as in Example 1-1, except that 3.00 g of adipic acid and 2.47 g of myo-inositol (corresponding to n = 3, m = 0 in general formula (1)) were used. The glass transition temperature was 190.3°C.

[0056] [Example 4-1] 2.58 g of 1,4-cyclohexanedicarboxylic acid (corresponding to the dicarboxylic acid with R1 in general formula (1)), 3.03 g of sebacic acid (corresponding to the dicarboxylic acid with R2 in general formula (1)), and 5.40 g of myo-inositol (corresponding to n = m = 1 in general formula (1)) were weighed into a 100 mL glass sample bulb, and three glass cooling bulbs were attached to the center joint of a glass tube oven. After replacing the atmosphere inside the sample bulb with nitrogen, the sample bulb and two cooling bulbs were positioned inside the heating oven and fixed in place. Rotation was started at 2 rpm, and the temperature was set to 240 °C to begin heating. After 30 minutes, rotation was changed to 60 rpm and continued for an additional 15 minutes. 45 minutes after the start of heating, the contents became a homogeneous molten liquid. The reaction continued for another 30 minutes at 240 °C. After 30 minutes (75 minutes after the start of the temperature increase), the glass tube oven was stopped and the sample was immediately cooled in air. From the weight change before and after the reaction, it was confirmed that 0.64 g of condensed water had distilled off, confirming the progress of the polymerization reaction. The polymer was confirmed to have fluidity at 130°C, but because it was a viscous liquid, 5 g of water was added to the removed sample ball and heated in a vacuum oven heated to 80°C for 1 hour. A low-viscosity composition was obtained by scraping the polymer surface with a spatula while immersed in 80°C water. The polymer was then removed onto a polytetrafluoroethylene sheet by heating in a vacuum oven heated to 130°C for 1 hour. The removed polymer was further dried in a vacuum oven at 80°C for 3 hours in full vacuum to obtain a coatable polymer. For the curing process, the vacuum oven was heated to 220°C, the pressure was reduced to 860 hPa, and the polymer was polymerized for another 3 hours. The temperature was then returned to 220°C and full vacuum, and the polymer was polymerized for another 7 hours. The polymer was obtained as a highly transparent, candy-like xerogel, and the glass transition temperature was 137.4°C.

[0057] [Example 5-1] A highly transparent, candy-like xerogel was obtained in the same manner as in Example 4-1, except that 2.27 g of adipic acid, 3.14 g of sebacic acid, and 5.60 g of myo-inositol (corresponding to n=m=1 in general formula (1)) were used. The glass transition temperature was 114.3°C.

[0058] [Example 6-1] A highly transparent, candy-like xerogel was obtained in the same manner as in Example 4-1, except that 3.52 g of adipic acid, 5.56 g of dodecanedioic acid, and 8.68 g of myo-inositol (corresponding to n=m=1 in general formula (1)) were used, and the amount of water added before dissolving at 80°C was 7.5 g. The glass transition temperature was 113.5°C.

[0059] [Comparative Example 7-1] One gram of polylactic acid (PLA, manufactured by Nature Works, model number 3001D) was dissolved in 9 grams of chloroform. The resulting solution was air-dried on an aluminum dish at room temperature, and then thoroughly dried in a vacuum dryer until no chloroform remained. This produced a cast film of polylactic acid, yielding a polylactic acid film (polymer).

[0060] [Comparative Example 7-2] As the polymer of Comparative Example 7-2, polybutylene adipate-co-terephthalate (PBAT, manufactured by BASF, model number ECOFLEX F Blend C1200) was used.

[0061] [Comparative Example 7-3] As the polymer of Comparative Example 7-3, polybutylene succinate (PBS, manufactured by Mitsubishi Chemical Corporation, model number BioPBS FZ71PM) was used.

[0062] (biodegradable) The polymers obtained in the examples and comparative examples were evaluated for biodegradability under the following conditions. <Inoculum source preparation> 250 mL of distilled water was placed in a 500 mL polycarbonate bottle and sterilized by autoclaving. 0.4 mL of 1 M MgSO4 aqueous solution, 1 mL of 20 mM CaCl2 aqueous solution, 1 mL of 10 mM FeCl3 aqueous solution, and 1 mL of 10 mM MnCl2 aqueous solution, each of which had been filter-sterilized, were added to the autoclaved water in a sterile environment to prepare a liquid medium. The entire contents of one BOD Seed (BI-CHEM, Novozymes Biotechnology) capsule was added to this liquid medium and cultured overnight with shaking at 30°C under aerobic conditions. 1 mL of the resulting culture was dropped onto LB agar medium (Unitech Co., Ltd., product code LBA-ABF) in a sterile environment, spread evenly, then covered and left to stand overnight in an incubator at 37°C to allow colony formation, thereby preparing a BOD Seed agar medium. The prepared BOD Seed agar medium was wrapped in plastic wrap to prevent drying and stored in a cold room maintained at 5°C. LB medium was prepared by measuring out 10 g of tryptone (Sigma-Aldrich, product code T7293), 5 g of yeast extract (Solavia Biocar Diagnostics, product code A1202HA), 10 g of NaCl (Fujifilm Wako Pure Chemical Industries, Ltd., product code 191-01665), and 1 L of distilled water into a 1 L polycarbonate bottle and sterilizing it in an autoclave. A 20 mL polycarbonate container was charged with 75 mg of glucose (Fujifilm Wako Pure Chemical Industries, Ltd., product code 049-31165), 75 mg of sodium hydrogen glutamate monohydrate (Fujifilm Wako Pure Chemical Industries, Ltd., product code 198-02035), and 10 mL of distilled water. The solution was dissolved and then sterilized by filtration to prepare a glucose-glutamate standard solution. Two mL of the above LB medium was placed in a 14 mL polystyrene culture tube (Corning, model number 352057), and 100 μL of the above glucose-glutamic acid standard solution was added to prepare the medium. A colony from the above BOD seed agar medium was picked with the tip of a toothpick and immersed in the medium. The tube was then capped and incubated with shaking at 37°C in an aerobic environment for one day to prepare the inoculum.

[0063] <Preparation of polymer-containing medium> M9 liquid medium was prepared by weighing out 5.64 g of M9 minimal medium (MP Biomedicals, product code 3037-012) into a 1 L polycarbonate container, adding 1 L of distilled water, and sterilizing by autoclaving. 2 mL of this M9 liquid medium was placed in a polystyrene culture tube (Corning, model number 352057), and 20 mg of the polymer obtained in each example or comparative example was weighed into this tube to prepare a medium for biodegradability evaluation.

[0064] <Biodegradability evaluation value> 100 μL of the inoculum solution prepared above was added dropwise to the medium for biodegradability evaluation prepared above, and the medium was covered and cultured with shaking at 37° C. under aerobic conditions for 7 days. Similarly, 100 μL of the inoculum was added dropwise to M9 liquid medium without polymer, and the resulting solution was incubated at 37°C under aerobic conditions with shaking for 7 days to prepare a background test. Triplicate incubations were performed for each polymer. After incubation, the solution was thoroughly shaken by hand to ensure uniform dispersion. 100 μL or 200 μL was transferred to a quartz cuvette with a 1 cm path length and diluted 10-fold or 5-fold with distilled water. The transmittance of this solution at 660 nm was measured using a spectrophotometer (Thermo Scientific, Multiskan 60). The 660 nm transmittance of the stock culture solution was calculated by multiplying the value by the dilution factor. For each polymer or background test, the 660 nm transmittance of the stock culture solution was measured for three tested tubes, and the average of the three was calculated. The biodegradability evaluation value was calculated by dividing the average of the three 660 nm light transmittances of the polymer biodegradation evaluation culture solution by the average of the three 660 nm light transmittances of the background test solution containing no polymer, and this was used as an index for biodegradability evaluation. The results are shown in Table 1. The greater this biodegradability evaluation index is in excess of 1, the more the microorganisms derived from the inoculum grow as the added polymer biodegrades, i.e., the higher the biodegradability of the polymer.

[0065] <Remaining polymer after culture> The state of polymer remaining after cultivation is shown in Table 1.

[0066] <Biodegradability evaluation> The biodegradability was evaluated according to the following evaluation criteria. ~Evaluation Criteria~ A: Extremely well biodegraded. B: Well biodegraded. C: Biodegraded. D: Not biodegradable.

[0067] [Table 1]

[0068] As is clear from the results in Table 1, each of the polymers of Examples 1-1, 2-1, 3-1, 4-1, 5-1, and 6-1 (where n or n+m in general formula (1) corresponds to 2) prepared from inositol and dicarboxylic acid was biodegraded even under conditions where even the general biodegradable resin of Comparative Example 7 was not biodegradable, demonstrating that they are inherently highly biodegradable. On the other hand, Examples 1-2 and 3-2 (where n corresponds to 3 in general formula (1)), in which the ratio of inositol to dicarboxylic acid during polymerization was changed, were biodegradable, but the degree of biodegradation was significantly smaller than in Examples 1-1 and 3-1, in which the same dicarboxylic acid was used. This clearly demonstrates that biodegradability can be controlled by changing the feed ratio.

[0069] [Example 8] (Saturated sodium bicarbonate water decomposition test) [Example 8-1] 0.5 g of each of the polymers obtained in Example 2-1 was placed in a 20 mL glass vial, and 20 g of saturated sodium bicarbonate water that had been passed through a syringe filter with a pore size of 10 μm was added to each vial. The glass vials were then capped and allowed to stand in an incubator at 37° C. for 2 weeks. The degree of polymer solubility was evaluated visually according to the following criteria, and the results are shown in Table 2. ~Evaluation Criteria~ A: Completely dissolved. B: Almost completely dissolved. C: A small amount of solid remained, but dissolution was observed. D: Did not dissolve.

[0070] [Example 8-2] The saturated sodium bicarbonate water decomposition test was carried out in the same manner as in Example 8-1, except that the polymer used was the polymer obtained in Example 2-2. The results are shown in Table 2.

[0071] [Example 8-3] The saturated sodium bicarbonate water decomposition test was carried out in the same manner as in Example 8-1, except that the polymer used was the polymer obtained in Example 2-3. The results are shown in Table 2. After the saturated sodium bicarbonate water decomposition test, the solid was removed and washed five times with an excess amount of water. The solid was then dried at 70°C in a full vacuum for three hours. The biodegradability of the solid was evaluated for two weeks as described in the "Biodegradability Evaluation" section of the "Biodegradability" section. The results are shown in Table 2.

[0072] [Comparative Example 8-1] The saturated sodium bicarbonate water decomposition test and biodegradability evaluation were carried out in the same manner as in Example 8-3, except that the polymer was the same PLA film as in Comparative Example 7-1. The results are shown in Table 2.

[0073] [Comparative Example 8-2] The saturated sodium bicarbonate water decomposition test and biodegradability evaluation were carried out in the same manner as in Example 8-3, except that the polymer was the same PBS film as in Comparative Example 7-2. The results are shown in Table 2.

[0074] [Comparative Example 8-3] The saturated sodium bicarbonate water decomposition test and biodegradability evaluation were carried out in the same manner as in Example 8-3, except that the polymer was a PBSA film similar to that used in Comparative Example 7-3. The results are shown in Table 2.

[0075] [Table 2]

[0076] As is clear from the results in Table 2, in saturated sodium bicarbonate water, which is weakly basic, the polymer of Example 2-1 (where n in general formula (1) corresponds to 2) is almost completely decomposed in just one day. On the other hand, the polymer of Example 2-2 (where n in general formula (1) corresponds to 3) is hardly decomposed after one day, but is completely decomposed after one week. Furthermore, the polymer of Example 2-3 (where n in general formula (1) corresponds to 6) begins to decompose after two weeks and is completely decomposed after four weeks. Thus, the decomposition rate of the polymer of this example can be widely controlled under weakly basic conditions. Since the decomposition rate under basic conditions is correlated with the biodegradation rate, this example, together with Example 7, illustrates that biodegradability can also be controlled. In addition, the biodegradability evaluation of the polymer of Example 2-3, which was decomposed in saturated sodium bicarbonate water for two weeks, clearly shows that the polymer, which was not biodegradable before treatment with sodium bicarbonate water, was biodegraded after treatment with sodium bicarbonate water. Although the reason for this is unclear, it is thought that biodegradability was achieved by partially hydrolyzing the crosslinking points of the highly crosslinked polymer of Example 2-3 under weakly basic conditions. The above properties indicate that it is possible to provide a polymer that can be particularly suitably used in the weakly basic marine environment, and that has controllable degradability and is ultimately decomposed.

[0077] [Example 9-1] A polymer was obtained in the same manner as in Example 1-1, except that 2.20 g of glutaric acid and 3.00 g of myo-inositol were used and no curing treatment was performed. The polymer was liquid at 110°C. Water was added to this polymer to a concentration of 50% by mass, resulting in a homogeneous aqueous solution with no visible solids. A drop of this solution was placed on a glass plate and coated with a bar coater. The curing process involved heating the vacuum oven to 220°C, reducing the pressure to 860 hPa, and polymerizing for 3 hours. The temperature was then further increased to 220°C and full vacuum, and polymerization continued for another 7 hours. The static water contact angle of the resulting cured film was 62.8°.

[0078] [Example 9-2] A polymer was obtained in the same manner as in Example 1-1, except that 2.90 g of glutaric acid and 2.64 g of myo-inositol were used and no curing treatment was performed. The polymer was liquid at 110°C. Water was added to this polymer to a concentration of 50% by mass, resulting in a homogeneous aqueous solution with no visible solids. A drop of this solution was placed on a glass plate and coated with a bar coater. The curing process involved heating the vacuum oven to 220°C, reducing the pressure to 860 hPa, and polymerizing for 3 hours. The temperature was then further increased to 220°C and full vacuum, and polymerization continued for another 7 hours. The static water contact angle of the resulting cured film was 69.1°.

[0079] [Example 9-3] A polymer was obtained in the same manner as in Example 1-1, except that 2.20 g of glutaric acid and 3.00 g of myo-inositol were used and no curing treatment was performed. This polymer was further polymerized at 190°C and 300 hPa for 3 hours and at 190°C and 50 hPa for 1 hour. The glass transition temperature was 108.9°C. The obtained polymer was liquid at 160°C.

[0080] [Example 9-4] A polymer was obtained in the same manner as in Example 1-1, except that 2.90 g of glutaric acid and 2.64 g of myo-inositol were used and no curing treatment was performed. This polymer was further polymerized at 190°C and 300 hPa for 30 minutes. The glass transition temperature was 87.9°C. The obtained polymer was liquid at 160°C.

[0081] [Comparative Example 9-5] The polymer obtained in Example 9-3 was further polymerized at 190°C and 50 hPa for 2 hours. The glass transition temperature was 119.7°C. The obtained polymer was solid at 160°C and insoluble in water, and could not be used for coating.

[0082] [Examples 10-1 to 10-6] Pieces of the polymers obtained in Examples 1-1, 2-1, 3-1, 4-1, 5-1, and 6-1 (where n+m in general formula (1) corresponds to 2) were immersed in ion-exchanged water so that the entire polymer pieces were completely immersed, and then allowed to stand overnight at room temperature. All of the polymer pieces hydrogelled and softened.

[0083] <Hydrogel strength> The hydrogels obtained in Examples 10-1 to 10-6 were pressed vertically with a finger, and the strength was evaluated according to the following evaluation criteria. The results are shown in Table 3. ~Evaluation Criteria~ A: The shape was maintained. B: It collapsed and could not maintain its shape.

[0084] [Table 3]

[0085] [Example 11-1] A polymer was obtained in the same manner as in Example 3-1, except that no curing treatment was performed. The obtained polymer was sandwiched between 8 mm parallel plates made of Al in a rheometer ARES-G2 (manufactured by TA Instruments) and cured at 240°C under a nitrogen atmosphere while applying a shear stress at a frequency of 1 Hz. The complex modulus was measured 100 minutes after the start of curing and used as an index of the toughness of the xerogel. The results are shown in Table 4.

[0086] [Example 11-2] A polymer was obtained in the same manner as in Example 4-1, except that no curing treatment was performed. The complex modulus of elasticity of the obtained polymer was measured in the same manner as in Example 11-1. The results are shown in Table 4.

[0087] [Example 11-3] A polymer was obtained in the same manner as in Example 5-1, except that no curing treatment was performed. The complex modulus of elasticity of the obtained polymer was measured in the same manner as in Example 11-1. The results are shown in Table 4.

[0088] [Example 11-4] A polymer was obtained in the same manner as in Example 6-1, except that no curing treatment was performed. The complex modulus of elasticity of the obtained polymer was measured in the same manner as in Example 11-1. The results are shown in Table 4.

[0089] [Table 4]

[0090] The results in Table 3 clearly demonstrate that hydrogels made from polymers incorporating sebacic acid or dodecanedioic acid as the dicarboxylic acid having R2 have excellent strength. Furthermore, the results in Table 4 also show that the complex modulus of the xerogels as viscoelastic bodies is high for polymers incorporating sebacic acid or dodecanedioic acid as the dicarboxylic acid having R2, suggesting high toughness. These results suggest that polymers incorporating sebacic acid or dodecanedioic acid as the dicarboxylic acid having R2 can be particularly suitable for applications requiring durability. [Industrial Applicability]

[0091] According to the present invention, a novel polymer with extremely high biodegradability can be provided. This allows it to be used in a wide range of applications as a material with low environmental impact. Furthermore, since the biodegradability can be controlled from the same raw material, it is particularly suitable for use as a material that biodegrades only after use.

Claims

1. A polymer obtained by condensation polymerization of inositol and dicarboxylic acids, which contains a constituent unit represented by the following general formula (1): 【Chemistry 1】 {In the formula, n is an integer of 1 to 6, m is an integer of 0 to 5, n+m is an integer of 2 to 6, R1's each independently represent an optionally branched linear or cyclic alkylene group having 1 to 7 carbon atoms, and R2's each independently represent an optionally branched linear or cyclic alkylene group having 8 to 12 carbon atoms.}

2. In the general formula (1), n+m is 2, R1 each independently represents an optionally branched linear or cyclic alkylene group having 4 to 7 carbon atoms, 2. The polymer according to claim 1, wherein each R2 is independently an optionally branched linear or cyclic alkylene group having 8 to 12 carbon atoms.

3. 10. The polymer of claim 1, which exhibits flowability at temperatures of 190°C or less.

4. A hydrogel obtained by absorbing water into the polymer according to claim 1, wherein n+m in the general formula (1) is 2.

5. a step of condensation polymerizing inositol and dicarboxylic acids to obtain a polymer, A method for producing a polymer, wherein the molar ratio of the inositol to the dicarboxylic acid is in the range of 0.3 to 1.

0.

6. a step of melting or dissolving the polymer of claim 1 in water to obtain a polymer solution; applying the polymer solution to a substrate and then curing it; A method for producing a molded body, comprising:

7. A method for producing a hydrogel, comprising a step of allowing the polymer of claim 1 to absorb water after polymerization.

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