JP7640987B2 - Method for releasing chemical species included in metal-organic framework, polymer gel and method for producing same - Google Patents

Description

The present invention relates to a method for releasing a chemical species encapsulated in a metal-organic framework. The present invention also relates to a polymer gel in which a metal-organic framework is covalently bonded as a cross-linking point, in particular, a polymer gel in which a metal-organic framework encapsulating a chemical species is covalently bonded as a cross-linking point. Furthermore, the present invention relates to a method for producing such a polymer gel.

In recent years, metal-organic frameworks (also called porous coordination polymers) have been attracting attention as adsorbents for gases, ions, etc. Composites that can be molded while maintaining the performance of such metal-organic frameworks have been proposed in the past (see, for example, Patent Document 1 below).

Incidentally, as a method for desorbing a gas from a metal-organic framework that adsorbs the gas, there is usually a method in which the atmospheric pressure of the metal-organic framework is reduced below the pressure at the time of adsorption (hereinafter, sometimes referred to as the "reduced pressure desorption method"). However, there are very few application fields of metal-organic frameworks to which such reduced pressure desorption method can be applied.

In light of this situation, attempts have been made to expand the field of application of metal-organic frameworks by designing them so that gases, ions, etc. are released from the metal-organic framework when light is irradiated or heat is applied to the framework (see, for example, Non-Patent Documents 1 and 2 below).

International Publication No. 2015/012373

Matthew.R.H. et al., “Dynamic photo-switching in metal-organic frameworks as a route to low-energy carbon dioxide capture and release”, Angew. Chem. Int. Ed., 2013 Mar. 25, 52(13), 3695-3698 Sada, K. et al., “Metal-organic framework tethering PNIPAM for ON-OFF controlled release in solution”, Chem. Commun., 2015, 51, 8614-8617

The objective of the present invention is to further expand the fields of application of the technology for adsorption and desorption of gases, etc. using metal-organic frameworks.

In the method according to the first aspect of the present invention, a mechanical external force is applied to a polymer gel having a crosslinking point of a metal-organic framework that encapsulates the chemical species, thereby releasing the chemical species to the outside of the metal-organic framework. The metal-organic framework is also called a porous coordination polymer. Note that the term "encapsulation" is synonymous with terms such as "containment," "adsorption," and "storage." The mechanical external force may be any force that can distort the metal structure, such as a compressive force, a tensile force, or a shear force. The chemical species may be, for example, an ion, an atom, an atomic group, a molecule, or a compound. The ion may include not only an atomic ion but also a molecular ion.

As far as the inventors know, the method of releasing chemical species to the outside of a metal-organic framework located at the crosslinking points of a polymer gel by applying a mechanical external force to the polymer gel as described above has not been proposed until now. Therefore, this method can further expand the application field of the technology of adsorption and desorption of chemical species by metal-organic frameworks.

The polymer gel according to the second aspect of the present invention has a metal-organic framework covalently bonded as a crosslinking point.

The inventors of the present application have discovered that applying a mechanical external force to such a polymer gel can release chemical species to the outside of the metal-organic framework. As far as the inventors of the present application know, such a discovery has never been made. Therefore, such a polymer gel can further expand the field of application of the technology of adsorption and desorption of chemical species by metal-organic frameworks.

The polymer gel according to the third aspect of the present invention is the polymer gel according to the second aspect, in which the metal-organic framework encapsulates a chemical species.

Therefore, chemical species can be released by applying an external mechanical force to the polymer gel.

The method for producing a polymer gel according to a fourth aspect of the present invention includes a functional group introduction step and a gelation step. In the functional group introduction step, a plurality of first functional groups are introduced into the metal organic framework to prepare a first functional group-containing metal organic framework. The introduction of the first functional group is preferably performed using a first functional group-containing compound having a functional group capable of covalently bonding to an organic ligand in the metal organic framework. In the gelation step, a second functional group of a polymer having a plurality of second functional groups capable of reacting with the first functional group is reacted with the first functional group to form a covalent bond, thereby obtaining a polymer gel.

1 is a graph showing the pressure dependence of carbon dioxide adsorption/desorption of Zn(AzDC)(BPE) _0.5 . 1 is a graph showing the viscoelastic behavior of a polymer gel according to Example 1. FIG. 2 is a schematic diagram showing the content of a carbon dioxide release experiment from a polymer gel carried out in Example 1. 1 is a graph showing the amount of carbon dioxide released from Zn(AzDC)(BPE) _0.5 derived units when a weight is placed on the polymer gel of Example 1. FIG. 2 is a schematic diagram showing the content of another carbon dioxide release experiment of a polymer gel carried out in Example 1. 1 is a graph showing the amount of change in absorbance of an aqueous solution of Basic Red versus the number of compressions when the polymer gel according to Example 1 and the polymer gel according to Comparative Example 1 are compressed. 1 is a graph showing the amount of change in pH of an aqueous solution of Basic Red 5 with respect to compressive stress when the polymer gel of Example 1 and the polymer gel of Comparative Example 1 are compressed in the aqueous solution of Basic Red 5.

<Method for releasing chemical species encapsulated in metal-organic frameworks>
The method according to the embodiment of the present invention is a method for releasing chemical species to the outside of the metal-organic framework by applying a mechanical external force to a polymer gel having a metal-organic framework that encapsulates chemical species as a crosslinking point.

Please note that the term "encapsulation" is synonymous with terms such as containment, adsorption, and storage.

The "external mechanical force" referred to here may be any force that can distort the metal structure through the polymer chain, such as a compressive force, a tensile force, or a shear force.

The "chemical species" referred to here may be, for example, an ion, an atom, an atomic group, a molecule, or a compound. The ion may include not only an atomic ion but also a molecular ion. The "chemical species" referred to here may be in a gaseous state, a liquid state, or a solid state at normal pressure. However, when the chemical species is in a liquid state or a solid state, it is preferable that the chemical species dissolve in the liquid that constitutes the polymer gel. When the chemical species is a gas, the chemical species is not particularly limited, but may be, for example, inorganic gases such as carbon monoxide, carbon dioxide, oxygen, nitrogen, nitrous oxide, ammonia, hydrogen, arsine, nitric oxide, hydrogen chloride, chlorine, germane, phosphorus pentafluoride, boron trichloride, nitrogen trifluoride, boron trifluoride, phosphorus trifluoride, dichlorosilane, diborane, silane, stibine, hydrogen selenide, hydrogen telluride, nitrogen dioxide, phosphine, silicon tetrafluoride, hydrogen sulfide, and sulfur hexafluoride, fluorocarbons, and the like. These include rare gases such as carbons, helium, neon, argon, krypton, and xenon; alkanes such as methane, ethane, propane, butane, pentane, hexane, heptane, and octane; alkenes such as ethylene, propylene, butenes, pentenes, and hexenes; alkynes such as acetylene; aromatic compounds such as benzene, toluene, and xylenes; cycloalkanes, alkyl halides, ethers, alcohols, amines, epoxy compounds, and carbonyl compounds.

<Polymer gel structure>
The metal organic framework is also called a porous coordination polymer. The metal organic framework that can be used in the embodiment of the present invention is not particularly limited as long as it has a function of encapsulating chemical species and a function of releasing the chemical species by deformation (through the polymer chain in the polymer gel). Meanwhile, the metal organic framework is formed from metal ions and organic ligands. In the embodiment of the present invention, the organic ligand has a functional group for introducing a functional group into the metal organic framework.

Examples of the metal ions include Mg2 ⁺ , Ca2 ⁺ , Sr2 ⁺ , Ba2 ⁺ , Sc3 ⁺ , Y3 ⁺ , Ti4 ⁺ , Zr4 ⁺ , Hf4 ⁺ , V4 ^{+, V3+} , V2 ⁺ , Nb3 ⁺ , Ta3 ⁺ , Cr3 ⁺ , Mo3 ⁺ , W3 ⁺ , Mn3 ⁺ , Mn2 ⁺ , Re3 ⁺ , Re2 ⁺ , Fe3 ⁺ , Fe2 ⁺ , Ru3 ⁺ , Ru2 ⁺ , Os3 ⁺ , Os2 ⁺ , Co3 ⁺ , Co2 ⁺ , Rh2 ⁺ , Rh ⁺ , ^{Ir2+ ,} Ir ⁺ , Ni2 ⁺ , Ni ^+. , Pd ²⁺ , Pd ⁺ , Pt ²⁺ , Pt ⁺ , Cu ²⁺ , Cu ⁺ , Ag ⁺ , Au ⁺ , Zn ²⁺ , Cd ²⁺ , Hg ²⁺ , Al ³⁺ , Ga ³⁺ , In ³⁺ , Tl ³⁺ , Si ⁴⁺ , Si ²⁺ , Ge ⁴⁺ , Ge ²⁺ , Sn ⁴⁺ , Sn ²⁺ , Pb ⁴⁺ , Pb ²⁺ , As ⁵⁺ , As ³⁺ , As ⁺ , Sb ⁵⁺ , Sb ³⁺ , Sb ⁺ , Bi ⁵⁺ , Bi ³⁺ , Bi ⁺ and the like.

Examples of the organic ligand include aromatic compounds, aliphatic compounds, alicyclic compounds, heteroaromatic compounds, and heterocyclic compounds having multiple functional groups capable of coordinating with metal ions. As the organic ligand, aromatic compounds, aliphatic compounds, alicyclic compounds, heteroaromatic compounds, and heterocyclic compounds having one functional group capable of coordinating with metal ions may be used in combination with aromatic compounds, aliphatic compounds, alicyclic compounds, heteroaromatic compounds, and heterocyclic compounds having multiple functional groups capable of coordinating with metal ions. In the organic ligand, it is preferable that one to five functional groups capable of coordinating with metal ions are present, more preferably two to four functional groups are present, and even more preferably two to three functional groups are present per aromatic compound, aliphatic compound, alicyclic compound, heteroaromatic compound, and heterocyclic compound. Such functional groups include a glycidyl group, a carboxyl group, a carboxylic anhydride group, a hydroxyl group, a thiol group, a dithiocarboxyl group, a sulfinyl group, a sulfonyl group, a sulfo group, a nitro group, a sulfide group, a disulfide group, an amino group, a primary amino group, a secondary amino group, Si(OH) ₃ , Ge _{(OH)3 ,} Sn(OH) ₃ , Si(SH) ₄ , Ge(SH) ₄ , Sn(SH) ₄ , a phosphate group, AsO3H, _AsO4H , P(SH) ₃ , As(SH) ₃ , CH(SH) ₂ , C(SH) ₃ , CH( _NH2 ) ₂ , C( _NH2 ) ₃ , CH(OH) ₂ , C(OH) ₃ , CH(CN) ₂ , C(CN) ₃ , CH(RSH) ₂ , C(RSH) ₃ , CH(RNH ₂ ) ₂ , C(RNH ₂ ) ₃ , CH(ROH) ₂ , C(ROH) ₃ , CH(RCN) ₂ , C(RCN) ₃ , nitrogen atoms constituting aromatic rings, etc. In the above chemical formula, R represents an alkyl group or an aryl group having ₁ to ₅ carbon atoms. The nitrogen atoms constituting aromatic rings refer to nitrogen atoms in rings such as pyridine, pyrimidine, pyridazine, pyrazine, triazine, imidazole, thiazole, oxazole, phenanthroline, quinoline, isoquinoline, naphthyridine, purine, bipyridine, and terpyridine. The functional groups contained in the organic ligands are not particularly limited, and examples thereof include alkenyl groups, alkynyl groups, amino groups, carboxyl groups, glycidyl groups, isocyanate groups, hydroxyl groups, and thiol groups.

The monomers constituting the polymer chains in the polymer gel are not particularly limited as long as they are capable of synthesizing a gel such as a hydrogel and reacting with the functional groups introduced into the metal-organic framework. Examples of such monomers include (meth)acrylic acid, sodium (meth)acrylate, potassium (meth)acrylate, lithium (meth)acrylate, vinyl benzoic acid, sodium vinyl benzoate, potassium vinyl benzoate, lithium vinyl benzoate, vinyl acetic acid, sodium vinyl acetate, potassium vinyl acetate, lithium vinyl acetate, vinyl sulfonic acid, sodium vinyl sulfonate, and potassium vinyl sulfonate. Examples of the monomers include lithium vinyl sulfonate, p-styrene sulfonic acid, sodium p-styrene sulfonate, potassium p-styrene sulfonate, lithium p-styrene sulfonate, allyl sulfonic acid, sodium allyl sulfonate, potassium allyl sulfonate, lithium allyl sulfonate, 2-acrylamido-2-methylpropane sulfonic acid, sodium 2-acrylamido-2-methylpropane sulfonate, potassium 2-acrylamido-2-methylpropane sulfonate, lithium 2-acrylamido-2-methylpropane sulfonate, (meth)acrylic acid esters, etc. In addition, when a vinyl acetate-based monomer is used, saponification may be performed after the polymerization reaction. In addition, the above-mentioned monomers may be used alone or in combination. In addition, other monomers may be copolymerized within a range that does not impair the gist of the present invention.

The liquid constituting the polymer gel is not particularly limited, but examples thereof include water and organic solvents. The liquid may also contain dissolved solutes such as salts, as long as the purpose of the present invention is not impaired.

The amount of metal-organic framework relative to the polymer in the polymer gel may be any amount necessary for the polymer to gel and release the desired amount of chemical species, but is preferably 5% by weight or more, more preferably 10% by weight or more, even more preferably 20% by weight or more, and particularly preferably 30% by weight or more.

<Method of Producing Polymer Gel>
The polymer gel according to the embodiment of the present invention can be manufactured, for example, through a functional group introduction step and a gelation step. In the functional group introduction step, a first functional group-containing metal organic framework is prepared by introducing a plurality of first functional groups into the metal organic framework. In the gelation step, a second functional group of a polymer having a plurality of second functional groups capable of reacting with the first functional group is reacted with the first functional group to form a covalent bond, thereby obtaining a polymer gel. The polymer having a plurality of second functional groups may be a homopolymer or a copolymer.

When the first functional group is an amino group or a hydroxyl group, the second functional group is, for example, a carboxyl group, and when the first functional group is a carboxyl group, the second functional group is, for example, an amino group or a hydroxyl group.

In another method for producing a polymer gel, the polymer gel may be obtained by polymerizing a monomer having a second functional group capable of undergoing a polymerization reaction with the first functional group and a metal organic framework having the first functional group in the gelation step.

The present invention will be described in more detail below with reference to examples and comparative examples. Note that the present invention is not limited to the following examples.

1. Synthesis of MOF cross-linked polymer gel (1) Synthesis of metal-organic framework 0.279 g (0.936 mmol) of zinc nitrate hexahydrate (Zn(NO ₃ ) _{2.6H 2} O), 0.253 g (0.936 mmol) of azobenzene-4,4'-dicarboxylic acid (hereinafter sometimes referred to as "AzDC"), and 0.085 g (0.466 mmol) of 1,2-bis(4-pyridyl)ethylene (hereinafter sometimes referred to as "BPE") were dissolved in 100 mL of dimethylformamide (hereinafter sometimes referred to as "DMF"), and the solution was heated to 100°C and stirred for 11 hours to obtain block-shaped red crystals. The obtained red crystals were washed with 100 mL of DMF and 100 mL of hexane, and the washed red crystals were then distilled off under reduced pressure to obtain the target metal-organic framework Zn(AzDC)(BPE) _0.5 . The synthesis scheme is shown in the following chemical reaction formula (A).

(2) Introduction of amino groups into metal-organic framework 5.8 mg (0.075 mmol) of aminoethanethiol was dissolved in 20 mL of ultrapure water. Then, 100 mg of Zn(AzDC)(BPE) _0.5 was added to the aminoethanethiol aqueous solution, and the solution was stirred for 1 hour. Then, the solution was dialyzed with ultrapure water for 3 days using a cellulose dialysis membrane (molecular weight cutoff: 1000). At this time, the dialysis external solution was exchanged nine times. After the dialysis was completed, the solvent was removed from the solution under reduced pressure and freeze-dried to synthesize the target Zn(AzDC)(BPE) _0.5 - _NH2 . The synthesis scheme is as shown in the following chemical reaction formula (B).

(3) Synthesis of polymethacrylic acid 5 g (58.1 mmol) of methacrylic acid from which the polymerization inhibitor had been removed using an alumina column and 94 mg (0.29 mmol) of 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (water-soluble azo polymerization initiator VA-044 manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were dissolved in 5 mL of degassed ultrapure water. Then, the aqueous solution was shaken at 60°C for 1 hour under a nitrogen atmosphere to obtain a white solid. The obtained white solid was dissolved in 40 mL of ultrapure water. Then, the aqueous solution was dialyzed with ultrapure water for 1 day using a cellulose dialysis membrane (molecular weight cutoff 3500 Da). At this time, the external solution for dialysis was exchanged three times. After the dialysis was completed, the aqueous solution was freeze-dried to obtain the target polymethacrylic acid. The synthesis scheme is as shown in the following chemical reaction formula (C).

(4) Inclusion of Carbon Dioxide in the Metal-Organic Framework Zn(AzDC)(BPE) _0.5 - _NH2 was vacuum dried to remove the gas and solution inside Zn(AzDC)(BPE) _0.5 , and then carbon dioxide was supplied to Zn(AzDC)(BPE) _0.5 - _NH2 to include the carbon dioxide in Zn(AzDC)(BPE) _0.5 .

(5) Synthesis of MOF crosslinked polymer gel 50 mg (0.581 mmol) of polymethacrylic acid (hereinafter sometimes referred to as "PMAc") was dissolved in 400 μL of ultrapure water, and the pH of the PMAc aqueous solution was adjusted to pH 7 to 8 with solid sodium hydroxide. Next, to the pH-adjusted PMAc aqueous solution, an EDC aqueous solution in which 22.27 mg (0.1162 mmol) of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (hereinafter sometimes referred to as "EDC") was dissolved in 50 μL of ultrapure water, and an NHS aqueous solution in which 13.37 mg (0.1162 mmol) of N-hydroxysuccinimide (hereinafter sometimes referred to as "NHS") was dissolved in 50 μL of ultrapure water were added. Next, 20 mg of Zn(AzDC)(BPE) _0.5 -NH ₂ (already encapsulated with carbon dioxide) was added to the PMAc aqueous solution to which the EDC aqueous solution and the NHS aqueous solution had been added, and the mixture was stirred until it was sufficiently dispersed in the aqueous solution. The dispersion was then allowed to stand to obtain the desired MOF crosslinked polymer gel. The synthesis scheme is shown in the following chemical reaction formula (D).

2. Evaluation of physical properties of Zn(AzDC)(BPE) _0.5 and MOF crosslinked polymer gel (1) Confirmation of carbon dioxide adsorption and desorption behavior of Zn(AzDC)(BPE) _0.5 The carbon dioxide adsorption and desorption behavior of Zn(AzDC)(BPE) _0.5 was confirmed using a high-pressure gas adsorption amount measuring device (BELSORP HP manufactured by Microtrack Bell Co., Ltd.). Specifically, after 250 mg of Zn(AzDC)(BPE) _0.5 was vacuum-dried, the adsorption temperature was set to 298 K, the saturated vapor pressure was set to 6444.8 kPa, and the carbon dioxide adsorption amount (mg/g) of Zn(AzDC)(BPE) _0.5 was measured while changing the pressure from 0 kPa to 220 kPa with carbon dioxide.

As shown in Fig. 1, it was revealed that Zn(AzDC)(BPE) _0.5 increases the amount of carbon dioxide (CO ₂ ) adsorbed as the pressure increases, and decreases the amount of carbon dioxide adsorbed as the pressure decreases. In other words, Zn(AzDC)(BPE) _0.5 adsorbs more carbon dioxide (CO ₂ ) as the pressure increases, and releases more carbon dioxide as the pressure decreases. As is clear from Fig. 1, the amount of carbon dioxide adsorbed when the pressure is decreased is slightly higher than the amount of carbon dioxide adsorbed when the pressure is increased, but it can be said that the adsorption and desorption of carbon dioxide is almost reversible.

(2) Viscoelasticity evaluation of polymer gel The viscoelastic properties of the MOF crosslinked polymer gel were measured using a Modular Compact Rheometer manufactured by Anton Paar. Specifically, after synthesizing the MOF crosslinked polymer gel on the bottom side of the sample tube using the above-mentioned MOF crosslinked polymer gel synthesis method, the MOF crosslinked polymer gel was removed from the sample tube and cut out to fit the size of an 8 mm parallel plate to prepare a sample piece. The sample piece was then set together with the parallel plate in the Modular Compact Rheometer, and its viscoelastic properties were measured at a measurement temperature of 25°C.

As shown in Figure 2, when the viscoelastic properties of the MOF cross-linked polymer gel according to this embodiment were measured, the storage modulus was found to be greater than the loss modulus. This indicates that the MOF cross-linked polymer gel is sufficiently gelled.

(3) Effect of compressive load on MOF cross-linked polymer gel on the amount of carbon dioxide released from Zn(AzDC)(BPE) _0.5 After synthesizing MOF cross-linked polymer gel on the bottom side of each of the three sample tubes using the above-mentioned MOF cross-linked polymer gel synthesis method, barium hydroxide aqueous solution of the same concentration was added to each of the sample tubes. Next, a 100g weight was placed in one sample tube, a 200g weight was placed in the other sample tube (see FIG. 3), and no weight was placed in the remaining sample tubes. Thirty seconds after the weight was placed, pH titration was performed with hydrochloric acid on the barium hydroxide aqueous solution in all three sample tubes to determine the amount of carbon dioxide released (when carbon dioxide is dissolved in the barium hydroxide aqueous solution, a neutralization reaction shown by Ba(OH) ₂ + _CO2 →BaCO3 _↓ + _H2O occurs, and two hydroxy ions ( ^OH- ) in the aqueous solution are consumed. Here, the amount of carbon dioxide released is determined by determining the amount of hydroxy ions consumed.). The results were graphed, and the graph shown in FIG. 4 was obtained. As is clear from the graph in Figure 4, it was found that the more compressive load is applied to the MOF cross-linked polymer gel of this example, the more carbon dioxide is released from the Zn(AzDC)(BPE) _0.5 -derived units in the MOF cross-linked polymer gel. Note that the presence of carbon dioxide was observed even in the system in which no weight was added, but this is thought to be due to carbon dioxide in the air dissolving in the barium hydroxide aqueous solution.

(Comparative Example 1)
1. Synthesis of polymer gel (1) Synthesis of polymethacrylic acid Polymethacrylic acid was obtained by the same method as that described in the section "(3) Synthesis of polymethacrylic acid" of "1. Synthesis of polymer gel" in Example 1.

(2) Synthesis of polymer gel 75 mg (0.872 mmol) of PMAc was dissolved in 400 μL of ultrapure water, and then 16 μL (0.261 mmol) of ethylenediamine and an EDC aqueous solution prepared by dissolving 50.15 mg (0.2615 mmol) of EDC in 50 μL of ultrapure water were added to the PMAc aqueous solution. The PMAc aqueous solution was stirred and then allowed to stand to obtain the target polymer gel.

(Comparison of physical properties between MOF crosslinked polymer gel according to Example 1 and polymer gel according to Comparative Example 1)
1. Carbon dioxide release behavior when compressive load is applied An aqueous solution (45.4 μM, 3 mL) of Basic Red 5 [absorbance: 0.500 or more (10 mg/L, pH 6.4, 523.0-527.0 nm) (dry matter equivalent)] was poured into a prismatic cell for measurement, and the prismatic cell was set in a spectrophotometer (UV-1800 manufactured by Shimadzu Corporation) to measure the absorbance of the Basic Red 5 aqueous solution at 527 nm. Next, using the synthesis method of the polymer gel shown in each of Example 1 and Comparative Example 1, a polymer gel was formed on the bottom side of each of the two prismatic cells for the compression deformation test, and then the aqueous solution of Basic Red 5 whose absorbance had been measured earlier was poured from above each prismatic cell. Then, as shown in FIG. 5, a glass rod was inserted from above the prismatic cell and the polymer gel was compressed and deformed with the glass rod (first compression deformation). Thereafter, the glass rod was removed from the prismatic cell, and the Basic Red 5 aqueous solution was poured into the measurement prismatic cell. The cell was then set in the above-mentioned spectrophotometer to measure the absorbance of the Basic Red 5 aqueous solution at 527 nm, and the difference from the initially measured absorbance was calculated to obtain the amount of absorbance change.

Next, after carrying out the same procedure as above for each polymer gel (second compressive deformation), the prismatic cell was set in the spectrophotometer as above to measure the absorbance of the Basic Red 5 aqueous solution at 527 nm, and the difference from the absorbance measured during the first compressive deformation was calculated to obtain the amount of absorbance change.

Next, the same procedure as above was carried out for each polymer gel (third compression deformation), and then the prismatic cell was set in the spectrophotometer as above to measure the absorbance of the Basic Red 5 aqueous solution at 527 nm. The difference from the absorbance measured during the second compression deformation was calculated to obtain the amount of absorbance change.

Figure 6 shows a histogram of the change in absorbance of the Basic Red 5 aqueous solution versus the number of compressions for the MOF cross-linked polymer gel of Example 1 and the polymer gel of Comparative Example 1. As is clear from Figure 6, the change in absorbance of the Basic Red 5 aqueous solution was almost constant for the polymer gel of Comparative Example 1 regardless of the number of compressions, but the change in absorbance of the Basic Red 5 aqueous solution increased with an increase in the number of compressions for the MOF cross-linked polymer gel of Example 1. This indicates that nothing is released from the inside of the polymer gel of Comparative Example 1 when it is compressed, but carbon dioxide is released from the inside of the MOF cross-linked polymer gel of Example 1 when it is compressed (it is presumed that the pH is lowered by dissolving carbon dioxide in the Basic Red 5 aqueous solution, the redness of the Basic Red 5 aqueous solution increases, and the absorbance of the Basic Red 5 aqueous solution increases).

2. Effect of compressive stress on carbon dioxide release amount A petri dish was set in a compression tester equipped with a load cell, and the MOF crosslinked polymer gel prepared in Example 1 was placed on it. Then, a Basic Red 5 aqueous solution (45.4 μM, 500 μL) was added to the petri dish so that the MOF crosslinked polymer gel was immersed, and the electrodes of the pH meter were brought into contact with the Basic Red 5 aqueous solution. After the pH value indicated by the pH meter stabilized to a certain extent, the pH value was measured while gradually applying a compressive stress to the MOF crosslinked polymer gel. The same measurement was also performed on the polymer gel prepared in Comparative Example 1. The results are shown in FIG. 7. As is clear from FIG. 7, for the polymer gel according to Comparative Example 1, the amount of pH change rapidly increased until the compressive stress reached 10 Pa, but once the compressive stress exceeded 10 Pa, the amount of pH change rapidly decreased and increased slightly, and once the compressive stress exceeded 50 Pa, the amount of pH change increased very slightly or became almost constant. On the other hand, for the MOF cross-linked polymer gel according to Example 1, the pH change increased rapidly until the compressive stress reached 10 Pa, and thereafter, the pH continued to increase steadily, although the increase in pH became smaller as the compressive stress increased. As is clear from FIG. 7, the pH change in each polymer gel did not change until the compressive stress reached 10 Pa, but once the compressive stress exceeded 10 Pa, the difference in pH change between the two gels increased as the compressive stress increased. This indicates that nothing was released from the inside of the polymer gel according to Comparative Example 1 when it was compressed, but carbon dioxide was released from the inside of the MOF cross-linked polymer gel according to Example 1 when it was compressed (pH change was observed in the polymer gel according to Comparative Example 1 until the compressive stress exceeded 10 Pa, which is presumably due to proton release from the carboxylic acid in the polymer gel).

The method for releasing chemical species encapsulated in the metal-organic framework according to the present invention is a novel method that has never been proposed before, and can be applied to, for example, the release of drugs for treating moving parts such as joints, molecular actuators that operate due to the release of chemical species, separation materials for two or more chemical species, and control of cell behavior.

Claims (3)

A method for releasing a chemical species to the outside of a metal-organic framework by applying a mechanical external force (excluding external force load due to reduced pressure) to a polymer gel having a metal-organic framework that encapsulates the chemical species as a crosslinking point. The metal-organic framework is covalently bonded as a crosslinking point.
The metal organic framework encapsulates a chemical species,
A polymer gel that releases the chemical species to the outside of the metal-organic framework by application of an external mechanical force (excluding an external force load due to reduced pressure). a functional group introduction step of introducing a plurality of first functional groups into the metal organic framework to prepare a first functional group-containing metal organic framework;
a chemical species-containing step of preparing a chemical species-containing first functional group-containing metal-organic framework by including a chemical species in the first functional group-containing metal-organic framework;
a gelation step of reacting a second functional group of a polymer having a plurality of second functional groups capable of reacting with the first functional group of the chemical species-encapsulating first functional group-containing metal-organic framework with the first functional group to form a covalent bond, thereby obtaining a polymer gel.