Chemical gel convertible to physical gel, physical gel convertible to chemical gel, and network polymer capable of reversibly converting between chemical gel and physical gel

Abstract

Since none of the conventional gels can reversibly change the crosslinking mode of the gel, they are limited to specific applications based on the characteristics of the crosslinking mode of each gel. It is considered that if the crosslinking mode can be converted in one gel, characteristics such as viscoelasticity and glass transition temperature can be controlled in a wide range, and the gel can be a material having a wide range of applications, but a network gel in which the crosslinking mode is reversibly converted has not been known so far.SOLUTION: The network polymer contains a polymer having a crown ether in the main chain and a maleimide unit in the side chain, and a compound having furan at both terminals and two ammonium salt units, wherein the furan and the ammonium salt are separated by one carbon chain, and can reversibly convert a chemical gel and a physical gel.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a chemical gel that can be converted into a physical gel, a physical gel that can be converted into a chemical gel, a network polymer that can be reversibly converted between a chemical gel and a physical gel, and polymers and compounds used in such chemical gels, physical gels, and network polymers. [Background technology]

[0002] Network polymers with three-dimensional network structures gel by absorbing and retaining various solvents. They can be classified as chemical gels or physical gels depending on the method of network structure construction. Chemical gel network polymers are constructed by chemical crosslinking, in which all crosslinking points in the network are formed by chemical bonds. They can be constructed using bifunctional or higher-functional compounds as crosslinkers. For example, a chemical gel can be obtained by polymerizing a vinyl monomer with a small amount of divinyl monomer. On the other hand, physical gel network polymers are constructed by physical crosslinking, in which pseudo-crosslinking points are formed by the entanglement of polymer chains or intermolecular interactions such as electrostatic interactions and hydrogen bonds. The structural images, crosslinking points, mechanical strength, thermal stability, and reversibility (at room temperature) of chemical gels and physical gels are shown in Table 1 below. As can be seen from Table 1, chemical gels generally have excellent mechanical and thermal resistance, while physical gels have stress dispersion and easy processability. [Table 1]

[0003] Rotaxanes are supramolecular compounds in which a linear molecule (axis molecule) penetrates the interior of a ring molecule, with stoppers (compounds) attached to both ends of the axis molecule that are larger than the pore size of the ring molecule. In this state, the ring molecule is confined on the axis by the two stoppers, allowing it to exist in a stable state where it cannot dissociate. Furthermore, when multiple ring molecules are incorporated, they are called polyrotaxanes. By bonding these ring molecules together, they become flexible and tough network polymer materials in which the ring molecules can move on the axis. This network polymer material forms hydrogels (water-based gels) that combine the advantages of both conventional chemical and physical gels. Because they can uniformly distribute external stress throughout the material, they are positioned as the "third gel" in addition to chemical and physical gels.

[0004] The present inventors have developed a network polymer containing an interdigitated rotaxane by reacting an interdigitated rotaxane ([c2]daisy-chain rotaxane) containing a compound in which a ring molecule and an axis molecule are integrated with a crosslinker having a thiol group at the end, and have filed a patent application (Japanese Patent Application No. 2022-188248). Such a network polymer has chemical crosslinks at the crosslinking points, and also has physical crosslinks because it contains a rotaxane structure. This allows the crosslinker to expand and contract over a certain range, and it has compression resistance. However, the composition ratio of chemical crosslinks and physical crosslinks in a network polymer is always constant, and it is not possible to significantly shift this ratio in either direction. Furthermore, Non-Patent Documents 1 and 2 disclose network polymers constituted by chemical crosslinks formed by a Diels-Alder reaction using a resin having a furan skeleton in the side chain and a bismaleimide compound. While these polymers allow for reversible cleavage and reconstruction of the chemical crosslinks, they do not allow for switching of crosslinking points, such as converting the chemical crosslinks into physical crosslinks. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] ACS Appl. Mater. Interfaces, 2017, 9, 20797-20807 [Non-patent document 2] Ind. Eng. Chem. Res. 2014, 53, 16156-16163 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, the crosslinked structures constituting the network polymers known to date cannot be reversibly converted, and therefore their applications have been limited to specific applications based on the properties of the crosslinked structures constituting each network polymer. Therefore, if the crosslinked structure of a single network polymer could be converted, it would be possible to control physical properties such as viscoelasticity and glass transition temperature over a wide range, making it a material with a wide range of applications. However, no network polymer with a reversible crosslinked structure has been known to date. [Means for solving the problem]

[0007] The present inventors discovered that a chemical gel chemically crosslinked by a Diels-Alder reaction undergoes a retro Diels-Alder reaction, and then undergoes an inclusion reaction in a specific solvent to form physical crosslinks, thereby converting it into a physically crosslinked physical gel, and that the physical crosslinks then re-form chemical crosslinks in a specific solvent, thereby re-converting it into a chemically crosslinked chemical gel, thereby completing the present invention.

[0008] That is, the present invention is as specified by the following items. [1] A chemical gel that can be converted into a physical gel, comprising a polymer having a crown ether in its main chain and a maleimide unit in its side chain, and a compound having furan at both ends and two ammonium salt units, where the furan and the ammonium salt are separated by one carbon chain, and in which the furan is chemically crosslinked with the maleimide unit. [2] The chemical gel according to [1], wherein the chemical crosslinking between the furan and the maleimide unit is a chemical crosslinking represented by the following formula 1: [ka] In the formula, X - represents an anion, and R represents an optional linking group. [3] A physical gel that can be converted into a chemical gel, comprising a polymer having a crown ether in its main chain and a maleimide unit in its side chain, and a compound having furan at both ends and two ammonium salt units, where the furan and the ammonium salt are separated by one carbon chain, and wherein the ammonium salt units are physically crosslinked with the crown ether. [4] The physical gel according to [3], wherein the physical crosslinking between the ammonium salt unit and the crown ether is a physical crosslinking represented by the following formula 2: [ka] In the formula, X - and R are the same as in Formula 1. The position of n can be any position within the crown ether. [5] A network polymer that can reversibly convert between the chemical gel described in [1] and the physical gel described in [3], comprising a polymer having a crown ether in its main chain and a maleimide unit in its side chain, and a compound having furan at both ends and two ammonium salt units, where the furan and the ammonium salt are separated by one carbon chain. [6] The polymer according to [1], [3] or [5], wherein the polymer having a crown ether in its main chain and a maleimide unit in its side chain is a polymer having partial structures represented by the following formulas 3 and 4: [ka] In the formula, n is the same as in formula 2. [7] The compound according to [1], [3] or [5], wherein the compound has furan at both ends and two ammonium salt units, and the furan and the ammonium salt are separated by one carbon chain, is a compound represented by the following formula 5: [ka] In the formula, X - and R is the same as in Equation 1. [8] The network polymer according to [5], characterized in that the network polymer, which is a chemical gel, can be converted into a physical gel at room temperature in a solution capable of inclusion by heating. [9] The network polymer according to [5], characterized in that the network polymer, which is a physical gel, can be converted into a chemical gel at room temperature in a solvent incapable of forming an inclusion complex. [Effects of the Invention]

[0009] The chemical gel of the present invention in which furan and maleimide units are chemically crosslinked is a chemical gel that can be converted into a physical gel, and the physical gel of the present invention in which a compound having furans at both ends is physically crosslinked with a crown ether is a physical gel that can be converted into a chemical gel. Furthermore, the network polymer of the present invention can be reversibly converted between a physical crosslink formed by a reversible inclusion structure between a crown ether and a bis-secondary ammonium salt and a chemical crosslink formed by a reversible Diels-Alder reaction between a maleimide and furan, thereby allowing for control of changes in the physical properties of the network polymer. [Brief explanation of the drawings]

[0010] [Figure 1] The chemical structure of a 24-membered crown ether polymer having a maleimide unit in the side chain and its 1H NMR spectrum are shown below. [Figure 2]The chemical structure of the furan-terminated bis(ammonium salt) compound and its 1H NMR spectrum are shown below. [Figure 3] The FT-IR spectra of (A) a furan-terminated bis(ammonium salt) compound (FN-terminated bis(ammonium salt)) and (B) a network polymer (chemical-crosslinked crown ether network) composed of a chemically crosslinked structure are shown. [Figure 4] FT-IR spectra of (A) a network polymer (chemically crosslinked crown ether network) composed of a chemically crosslinked structure and (B) a network polymer (physical-crosslinked inclusion network) composed of a physically crosslinked structure are shown. [Figure 5] The solubility and swelling of chemical and physical gels in three different organic solvents are shown. [Figure 6] 1 shows DSC charts of chemical gel and physical gel. [Figure 7] The storage modulus (E') of the chemical gel (DA Gel) and the physical gel (Inclusion Gel) is shown. [Figure 8] The loss tangent tanδ(E″ / E′) of the chemical gel (DA Gel) and the physical gel (Inclusion Gel) is shown. [Figure 9] The loss tangent tanδ(E'' / E') of the chemical gel (Chemical-crosslinked Crown ether Network), the chemical gel reconverted from the physical gel (Chemical-crosslinked Crown ether Network (2nd)), and the physical gel (Physical-crosslinked Inclusion Network) is shown. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Chemical gel] The chemical gel of the present invention includes a polymer having a crown ether in its main chain and a maleimide unit in its side chain, and a compound having furans at both ends and two ammonium salt units, where the furan and the ammonium salt are separated by one carbon chain. The chemical gel is chemically crosslinked with the maleimide unit and can be converted into a physical gel. The chemical gel of the present invention is synthesized by forming a chemical crosslink between a dienophile (MI-grafted poly(crown ether)) and a diene (FN-terminated bis(ammonium salt)) through a Diels-Alder reaction in DMF (dimethylformamide). The physical gel to which the chemical gel of the present invention can be converted may be a physical gel in which the ammonium salt unit is physically crosslinked with the crown ether. The structure of the chemical crosslink between the furan and the maleimide unit is exemplified by the following formula 1. [ka] In the formula, X - represents an anion, and R represents an optional linking group. An example of the optional linking group is an alkyl chain, which may be saturated or unsaturated, and may contain atoms other than carbon atoms (heteroatoms; for example, oxygen, nitrogen, sulfur, etc.), functional groups (esters, ethers, amides, thioethers, alkenes, alkynes, ureas, urethanes, carbonyls, carbonate esters, imines, amines, disulfides, etc.), or aromatic groups. The chemically crosslinked maleimide unit is located on a side chain of the main chain having the crown ether, and the maleimide unit and the crown ether unit are linked by an arbitrary linking group, and the unit containing the maleimide and the crown ether undergoes a polymerization reaction to form a polymer.

[0012] [Physical gel] The physical gel of the present invention includes a polymer having a crown ether in its main chain and a maleimide unit in its side chain, and a compound having furans at both ends and two ammonium salt units, where the furan and the ammonium salt are separated by one carbon chain. The ammonium salt units are physically crosslinked with the crown ether, and the physical gel can be converted into a chemical gel. The physical gel of the present invention is synthesized in sulfolane by the inclusion of a secondary ammonium salt contained in a diene with a crown ether contained in a dienophile (polymer) to form a physical crosslink. The chemical gel to which the physical gel of the present invention can be converted may be a chemical gel in which a furan and a maleimide unit are chemically crosslinked. The structure of the physical crosslink between the ammonium salt unit and the crown ether is shown in Formula 2 below. [ka] In the formula, X - and R are the same as in Formula 1. The position of n can be any position within the crown ether. The physically crosslinked crown ether is contained in the main chain of a polymer having a maleimide unit in its side chain. As in Formula 1, the maleimide unit and the crown ether unit are linked by an arbitrary linking group, and the unit containing the maleimide and the crown ether undergoes a polymerization reaction to form a polymer.

[0013] [Network polymer] The network polymer of the present invention comprises a polymer having a crown ether in its main chain and a maleimide unit in its side chain, and a compound having furan at both ends and two ammonium salt units, where the furan and the ammonium salt are separated by one carbon chain, and allows the crosslinked structure to be reversibly converted.

[0014] The construction of a chemically crosslinked network polymer as a chemical gel and its conversion to a physically crosslinked network polymer as a physical gel in the network polymer of the present invention are shown in [Chemical Formula 7]. In DMF (dimethylformamide), chemical crosslinks are formed by the Diels-Alder reaction between a dienophile (MI-grafted poly(crown ether)) and a diene (FN-terminated bis(ammonium salt)), resulting in the construction of a chemically crosslinked network polymer as a chemical gel (referred to as a "Chemical-Crosslinked Crown Ether Network" in [Chemical Formula 7]). Furthermore, a retro Diels-Alder reaction occurs upon heating, causing the chemical crosslinks to collapse. In sulfolane, physical crosslinks are formed by the inclusion of a secondary ammonium salt contained in the diene with a crown ether contained in the dienophile (polymer), resulting in the construction of a physically crosslinked network polymer as a physical gel (referred to as a "Physical-Crosslinked Inclusion Network" in [Chemical Formula 7]). The structure of the network polymer as a physical gel is specifically described as follows: + It is thought that the inclusion structure (non-covalent bond) is formed by electrostatic interactions and hydrogen bonds in the electron-rich vacancy provided by the oxygen of the crown ether. [ka]

[0015] Similarly, in the network polymer of the present invention, the inclusion structure of the network polymer as a physically crosslinked physical gel (referred to as Physical-crosslinked Inclusion Network in [Chemical Formula 8]) is broken in DMF (dimethylformamide), and the inclusion structure is again broken by the Diels-Alder reaction to form a chemically crosslinked chemical gel network polymer (referred to as Chemical-crosslinked Crown ether Network (2 in [Chemical Formula 8]). nd The manner in which the compound is reconverted to the compound (denoted as ) is shown in [Chemical Formula 8]. [ka]

[0016] [Polymer with crown ether in the main chain and maleimide in the side chain] The polymer having a crown ether in the main chain and a maleimide unit in the side chain, which is used in the chemical gel, physical gel, or network polymer of the present invention, is a polymer having partial structures represented by the following formulas 3 and 4. [ka] In the formula, the position of n can be any position within the crown ether. In the formula, the maleimide unit and the main chain having the crown ether are linked by an optional linking group, which may be a heteroatom, a functional group, an aromatic group, or a saturated or unsaturated alkyl chain. In the case of an alkyl chain, the alkyl chain may contain an atom other than a carbon atom (heteroatom; for example, oxygen, nitrogen, sulfur, etc.), a functional group (ester, ether, amide, thioether, alkene, alkyne, urea, urethane, carbonyl, carbonate ester, imine, amine, disulfide, etc.), or an aromatic group. The linking group is not particularly limited as long as it is a functional group that can randomly link the maleimide unit and the crown ether unit, and examples thereof include a hydroxyl group, a carboxyl group, an amino group, an alkene, an alkyne, an azide group, a vinyl group, a thiol group, an aldehyde group, a halogen atom, and an isocyanate group. The maleimide and crown ether unit polymerize via a polymerization reaction (radical reaction, condensation reaction, polyaddition reaction, cyclization reaction, coupling reaction, etc.). The crown ether is not particularly limited as long as it has a 21- to 30-membered ring (n=0 to 3), and a 24-membered ring is preferred from the viewpoint of synthesis.

[0017] [Compounds with furans at both ends and two ammonium salt units] The compound used in the chemical gel, physical gel, or network polymer of the present invention, which has a furan at its terminal and two ammonium salt units, and in which the furan and the ammonium salt are separated by one carbon chain, is represented by the following formula 5. [ka] In the formula, R represents an alkyl chain, and X - represents an anion. There are no particular restrictions on the length of the alkyl chains of the two ammonium salts, as long as the chain is 6 or more carbon atoms. The alkyl chains may be saturated or unsaturated, and the alkyl chains may contain atoms other than carbon atoms (heteroatoms; for example, oxygen, nitrogen, sulfur, etc.), functional groups (esters, ethers, amides, thioethers, alkenes, alkynes, ureas, urethanes, carbonyls, carbonate esters, imines, amines, disulfides, etc.), or aromatic groups. The anion that serves as the counterion to the bis(secondary ammonium salt) is preferably an anion with high ionic dissociation, and PF6 - ,CF3COO - , CF3SO3 - ,TFSI - (Bis(trifluoromethanesulfonyl)imide anion),BH4 - Examples include:

[0018] [Synthesis of network polymers as chemical gels] A network polymer as a chemically crosslinked chemical gel can be synthesized as follows. First, a polymer having maleimide (MI) units in the side chains of a main chain composed of many linked crown ethers is synthesized, which serves as the dienophile. A bis-secondary ammonium salt having furan (FN) units at both ends is synthesized as the diene. The Diels-Alder reaction proceeds quantitatively by dissolving this dienophile and diene in the aprotic polar solvent DMF (dimethylformamide). Under typical synthesis conditions, crown ethers and bis-secondary ammonium salts may form inclusion compounds (rotaxanes) in organic solvents. However, in the present invention, the formation of clathrate compounds is suppressed by using a solvent such as DMF, which inhibits the formation of clathrate compounds, resulting in a network polymer as a chemically crosslinked chemical gel. In the above synthesis reaction, solvents that inhibit the formation of clathrate compounds generally include solvents with high polarity or dielectric constants. Examples of the single solvent include DMF, DMSO (dimethyl sulfoxide), dimethylacetamide, and the like, and examples of the mixed solvent include a 3:1 or 1:1 solvent of chloroform and DMSO.

[0019] [Conversion to physical gel] The synthesized chemical gel network is converted into a physically crosslinked physical gel network polymer as follows. The organic solvent used in the synthesis of the chemical gel network is replaced with a specific solvent, and the mixture is heated to 130°C to allow a retro Diels-Alder reaction to proceed, temporarily forming a homogeneous solution. Subsequently, during the process of cooling to room temperature (25°C), the crosslinked structure is converted from a chemically crosslinked structure to a physically crosslinked structure. During the reconstruction of the crosslinked structure, two gelation processes are expected to occur. Specifically, a Diels-Alder reaction occurs again to return to the original chemically crosslinked structure, and an inclusion reaction proceeds to convert the chemically crosslinked structure to a physically crosslinked structure. In the present invention, the conversion process from a chemically crosslinked structure to a physically crosslinked structure must be the process that proceeds preferentially. Therefore, the distance between the furan and the bis-secondary ammonium salt in the furan (FN) unit is adjusted to one carbon chain, thereby suppressing the Diels-Alder reaction due to steric hindrance and allowing the inclusion reaction to proceed preferentially. The specific solvent used in the conversion to a network polymer as a physical gel is not particularly limited as long as it does not inhibit the formation of an inclusion compound. However, since heating to 100°C or higher is preferred for the conversion to a physical gel, solvents with a boiling point of 100°C or higher are preferred, such as sulfolane, dioxane, toluene, chlorobenzene, 1,2-dichloroethane, and nitromethane.

[0020] [Reconversion to chemical gel] By heating a network polymer as a physical gel in DMF, the inclusion structure that constitutes the network polymer as a physical gel is disrupted, and the Diels-Alder reaction is preferentially promoted, thereby enabling the network polymer as a physical gel to be reconverted into a network polymer as a chemical gel. The solvent used in this process can be any solvent that can be used to synthesize a network polymer as a chemical gel and that inhibits the formation of inclusion compounds. The reaction temperature in DMF is not particularly limited, as long as it is a temperature at which the crosslinked structures that constitute the network polymer as a physical gel are disrupted, the components dissolve, and the Diels-Alder reaction proceeds. [Example]

[0021] EXAMPLES Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

[0022] [Synthesis of maleimide compounds] A maleimide compound (referred to as Maleimide 3 in the following reaction steps) was synthesized by the following method. The reaction steps will be explained in order below. [ka]

[0023] A methanol solution of exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride (3.01 g, 18.1 mmol) and 2-amino-1,3-propanediol (1.67 g, 18.3 mmol) was refluxed at 60 °C for 20 h. The reaction mixture was concentrated and purified by reprecipitation with diethyl ether and methanol. The residue was concentrated. After concentration, maleimide 1 was obtained as a colorless viscous liquid (4.37 g, 94.5% yield).

[0024] A solution of maleimide 1 (3.07 g, 18.0 mmol), triethylamine (5.5 mL, 39.6 mmol), and 10-undesenoyl chloride (9.11 g, 44.9 mmol) in dichloromethane (150 mL) was stirred at room temperature. Water (30 mL) was added to the reaction mixture, which was then extracted with dichloromethane. The organic layer was washed with water. The organic layer was dried over anhydrous magnesium sulfate and concentrated. The residue was purified by column chromatography (silica gel, dichloromethane) to give maleinide 2 as a colorless liquid (3.45 g, 44.6%).

[0025] Maleimide 2 (3.07 g, 18.0 mmol) was added to toluene (100 mL) and refluxed at 120 °C for 24 hours. After refluxing, the mixture was stirred at 100 °C for 1 hour and then concentrated. After concentration, colorless solid maleimide 3 was obtained (yield 2.60 g, 98.9%).

[0026] [Synthesis of 24-membered crown ether compounds] A 24-membered ring crown ether compound (referred to as BUMB24C8 in the following reaction steps) was synthesized by the following method. The reaction steps will be explained below in order. [ka]

[0027] A mixed solution of crown ether / Dibenzo-24-crown-8 (DB24C8: 5.00 g, 11.1 mmol), hexamethylene tetramine (12.5 g, 89.2 mmol), and trifluoroacetic acid (60 mL, 0.78 mol) was refluxed at 60 °C for 10 hours. Water (50 mL) was added to the reaction mixture, which was then extracted with dichloromethane. The organic layer was washed with water. The organic layer was dried over anhydrous magnesium sulfate and concentrated. After concentration, a brown solid, DFB24C8, was obtained (yield 4.60 g, 82.0%). The compound DFB24C8 was synthesized. 1 The H-NMR spectrum confirmed the following: 1 H-NMR (CDCl3) δ (ppm from TMS): 9.83-9.78 (s, 2H), 7.43-6.85 (d, 6H), 4.31-3.54 (t, 24H).

[0028] Sodium tetrahydroborate (13.8 g, 36.5 mmol) was slowly added to a solution of DFB24C8 (4.60 g, 9.12 mmol) in a mixture of tetrahydrofuran (THF) and methanol, and the mixture was refluxed for 12 hours. Water (50 mL) was then added, and the mixture was extracted with dichloromethane. The organic layer was washed with water. The organic layer was dried over anhydrous magnesium sulfate and concentrated. After concentration, a brown solid, DHMB24C8, was obtained (yield 4.88 g, 100%). The compound DHMB24C8 was synthesized. 1 The H-NMR spectrum confirmed the following: 1 H-NMR (CDCl3) δ (ppm from TMS): 6.92-6.79 (d, 6H),4.62-4.58 (s, 4H), 4.31-3.77 (t, 24H).

[0029] To a solution of bis(hydroxy methyl benzo) 24-crown-8 ether (DHMB24C8: 4.88 g, 9.59 mmol) in tetrahydrofuran (THF (50 mL)) was added triethylamine (4.00 mL, 28.8 mmol). 10-Undecenoyl chloride (4.86 g, 24.0 mmol) in tetrahydrofuran (THF (100 mL)) was slowly added with stirring. After 10 minutes, the mixture was returned to room temperature and stirred for 12 hours. The reaction was quenched with saturated aqueous sodium bicarbonate and extracted with ethyl acetate. The organic layer was dried over anhydrous magnesium sulfate and concentrated. The residue was purified by column chromatography (silica gel, CHCl / EtOAc = 1 / 1; v / v) to give DHMB24C8 as a white solid (yield 6.80 g, 84.3%). The synthesis of compound BUMB24C8 was confirmed as follows. 1 H-NMR (CDCl3) δ (ppm from TMS): 6.90-6.75 (d, 6H), 5.85-5.72 (q, 2H), 5.03-4.98 (s, 4H), 4.98-4.87 (d, 4H), 4.31-3.64 (t, 24H), 1.40-1.20 (q, 20H), 2.38-2.25 (t, 4H), 2.09-1.98 (d, 4H), 1.70-1.57 (t, 4H).

[0030] [Synthesis of 24-membered crown ether polymers with maleimide units in the side chains] A 24-membered ring crown ether polymer having a maleimide unit in the side chain (referred to as MI-grafted poly(crown ether) in the following reaction steps) was synthesized by the following method. [ka]

[0031] BUMB24C8 (0.337 g, 0.400 mmol), Maleimide3 (0.151 g, 0.350 mmol), Grubbs 1 st (72.9 mg, 88.6 A solution of 100 mol of chloroform (CHCl3 (5 mL)) was stirred at 60 °C under reduced pressure. The resulting product was dissolved in chloroform (CHCl 3) The mixture was homogeneously dissolved in hexane and purified by reprecipitation with methanol to obtain a brown solid MI-grafted poly(crown ether) (yield: 0.542 g, 80.4%). The MI-grafted poly(crown ether) was synthesized. 1 The chemical structure of the 24-membered crown ether polymer with maleimide units in the side chain was confirmed by H NMR spectroscopy. 1 The H NMR spectrum is shown in Figure 1.

[0032] [Synthesis of Furan-Terminated Bis-Secondary Ammonium Salt Compounds] A furan-terminated bis(ammonium salt) compound (hereinafter referred to as FN-terminated bis(ammonium salt)) was synthesized by the following method. The reaction steps are explained below in order. [ka]

[0033] 10-Undecenal (1.90 g, 11.3 mmol), 3,6-Dioxa-1,8-octanedithiol (DODT) (1.02 g, 5.60 mmol), and a small amount of benzophenone were added, and the mixture was irradiated twice with UV light for 5 minutes. After UV irradiation, a small amount of chloroform and a large amount of n-hexane were added, and the product was purified by recrystallization to obtain the bisaldehyde as a white solid (yield 2.31 g, 79.7%).

[0034] A chloroform solution of bisaldehyde (1.03 g, 1.99 mmol) and furfurylamine (0.413 g, 4.25 mmol) was stirred, and the reaction mixture was concentrated. After concentration, a colorless liquid, bisfuran 1, was obtained. (Yield 1.33 g, 98.7%)

[0035] Bisfuran 1 (1.33 g, 1.95 mmol), dichloromethane (CHCl), and methanol were added to an ice bath, and sodium tetrahydroborate (NaBH) (0.411 g, 11.7 mmol) was slowly added and stirred until dissolved. The mixture was then stirred at room temperature, and water (20 mL) was added to quench the reaction. The reaction mixture was extracted with dichloromethane (CHCl) and washed three times with water. The organic layer was dried over anhydrous magnesium sulfate (MgSO), and the filtrate was concentrated. After concentration, a colorless liquid, bisfuran 2, was obtained (yield 1.15 g, 86.1%).

[0036] A solution of bisfuran 2 (0.913 g, 1.34 mmol) and trifluoroacetic acid (CF3COOH (1 mL, 13.1 mmol)) in chloroform (CHCl3 (5 mL)) was stirred at room temperature for 4 hours, and the reaction mixture was concentrated. After concentration, it was extracted with dichloromethane (CHCl2) and washed with saturated aqueous potassium tetrafluorophosphate (Sat.KPF6 aq.). The organic layer was dehydrated over anhydrous magnesium sulfate (MgSO4), and the filtrate was concentrated. After concentration, a colorless viscous liquid, FN-terminated bis(ammonium salt), was obtained (yield 0.902 g, 81.4%). The synthesis of a furan-terminated bis(ammonium salt) compound was confirmed by the following: 1 The chemical structure of the furan-terminated bis-secondary ammonium salt compound was confirmed by H NMR spectroscopy. 1 The 1 H NMR spectrum is shown in Figure 2.

[0037] [Synthesis of network polymers composed of chemically crosslinked structures] A chemically crosslinked network polymer (referred to as "Chemical-crosslinked Crown ether Network" in the following reaction steps) was synthesized from a 24-membered crown ether polymer bearing maleimide units in the side chains and a furan-terminated bis(secondary ammonium salt) compound by the following method. [ka] A 24-membered ring crown ether polymer bearing maleimide units in its side chains (MI-grafted poly(crown ether) (0.101 g)) and a furan-terminated bis(ammonium salt) (39.0 mg, 47.0 mmol) solution in DMF (1 mL) were thoroughly mixed and the solvent was evaporated. After drying, a brown solid, chemically crosslinked network polymer (Chemical-Crosslinked Crown Ether Network: Yield: 0.124 g, 88.4%) was obtained. The synthesis of the chemically crosslinked network polymer (Chemical-Crosslinked Crown Ether Network) was confirmed by FT-IR spectra of (A) the furan-terminated bis(ammonium salt) and (B) the chemically crosslinked network polymer (Chemical-Crosslinked Crown Ether Network). FT-IR spectra are shown in Figure 3. The FT-IR spectrum of Figure 3 shows that the furan-terminated bis(ammonium salt) compound (FN-terminated bis(ammonium salt)) exhibits a peak at 740 cm -1 The peak of the C=C bond originating from the furan unit in the vicinity is relatively decreased in the spectrum of the reaction product, and the peak at 1750 cm -1The appearance of a double bond derived from the oxanorbornene skeleton formed by the Diels-Alder reaction was observed nearby.

[0038] [Conversion to network polymers composed of physically cross-linked structures] The network polymer having a chemically crosslinked structure was converted into a network polymer having a physically crosslinked structure (referred to as a Physical-Crosslinked Inclusion Network in the following reaction steps) by the following method. [ka] Sulfolane (0.2 mL) was added to a chemically crosslinked network polymer (Chemical-Crosslinked Crown Ether Network (0.168 g)) and heated on a hot plate at 130 °C for 1.5 hours. After heating, the product was cooled to room temperature, and the sulfolane was removed by washing with a small amount of water. The mixture was then dried. After drying, a brown solid, physically crosslinked network polymer (Physical-Crosslinked Inclusion Network) was obtained (yield: 0.134 g, 80.0%). The synthesis of a physically crosslinked network polymer was confirmed by the FT-IR spectra of (A) the chemically crosslinked network polymer (Chemical-Crosslinked Crown Ether Network) and (B) the physically crosslinked network polymer (Physical-Crosslinked Inclusion Network). FT-IR spectra are shown in Figure 4. Figure 4 shows the FT-IR spectra of (A) a network polymer (chemical-crosslinked crown ether network) composed of a chemically crosslinked structure and (B) a network polymer (physical gel: physical-crosslinked inclusion network) composed of a physically crosslinked structure. After heating, a peak (740 cm) attributed to the furan double bond appeared. -1), and the peak of the double bond derived from the oxanorbornene skeleton (1750 cm -1 ) was observed, confirming the conversion from a chemically crosslinked structure to a physically crosslinked structure.

[0039] [Reconversion of a network polymer composed of a physically cross-linked structure to a network polymer composed of a chemically cross-linked structure] Approximately 0.1 g of the network polymer (Physical-Crosslinked Inclusion Network) composed of the physically crosslinked structure converted as described above was dissolved in DMF (3 ml) and heated at 60°C for 5 hours. After that, the DMF was removed by vacuum drying, and the polymer was again converted into a network polymer composed of a chemically crosslinked structure.

[0040] [Solubility and swelling of chemical gels and physical gels in organic solvents] The chemically crosslinked network polymer (Chemical-Crosslinked Crown Ether Network, hereafter referred to as "chemical gel") and the physical-crosslinked network polymer (Physical-Crosslinked Inclusion Network, hereafter referred to as "physical gel") synthesized as described above were dissolved in three different organic solvents to examine the differences in solubility and swelling of each gel. The results are shown in Figure 5. Figure 5 shows that the swelling of the physical gel tended to be greater than that of the chemical gel in chloroform (CHCl3) and sulfolane. This suggests that the network (mesh) formed in the physical gel is expanded compared to the chemical gel due to the lower crosslink density caused by inclusion. Furthermore, while the chemical gel swelled in DMF, the majority of the physical gel (73 wt%) was dissolved. This suggests that the network (mesh) structure of the physical gel collapsed in DMF because the crown ether and secondary ammonium salt do not form an inclusion complex.

[0041] [Glass transition temperature between chemical gel and physical gel] Similarly, the glass transition temperatures of the chemical gel and physical gel were determined using DSC charts. Figure 6 shows the DSC charts. For the chemical gel, the DMF was removed by vacuum drying to obtain a dry sample. For the physical gel, sulfolane, which has a high boiling point, was removed by washing, taking advantage of its water solubility, and then the gel was dried to obtain a sample. Figure 6 shows that the glass transition temperature (Tg) of the chemical gel was -2.5°C, while that of the physical gel was significantly lowered to -19.8°C. This suggests that the crosslinking density of the network polymer changed (decreased) as the crosslinking structure changed from a chemically crosslinked structure to a physically crosslinked structure (conversion from a chemical gel to a physical gel).

[0042] [Dynamic viscoelasticity of chemical gels and physical gels] The dynamic viscoelasticity of chemical gels and physical gels was investigated by measuring the storage modulus and loss tangent of the chemical gels and physical gels. The chemical gel and physical gel samples were prepared in the same manner as the samples used to measure the glass transition temperature. The measurement conditions were as follows: frequency: 1 Hz, measurement temperature: -40 to 60°C, strain amplitude: 10 μm, minimum pressure / compression force: 100 (mN), tension / compression force gain: 1.5, initial force amplitude: 100 (mN). The storage modulus (E') of the chemical gel (referred to as DA Gel in the figure) and the physical gel (referred to as Inclusion Gel in the figure) is shown in Figure 7. Figure 7 shows that the chemical gel (DA Gel) has a higher elastic modulus and is a harder material than the physical gel (Inclusion Gel). The loss tangent: tanδ(E'' / E') of the chemical gel (DA Gel) and the physical gel (Inclusion Gel) is shown in Figure 8. Figure 8 shows that the loss tangent of the physical gel (Inclusion Gel) is larger than that of the chemical gel (DA Gel), indicating that the viscosity of the physical gel (Inclusion Gel) is improved near the glass transition temperature. Chemical gel (Chemical-crosslinked Crown ether Network), chemical gel reconverted from physical gel (Chemical-crosslinked Crown ether Network (2 nd The loss tangent, tanδ (E'' / E'), of the chemical gel reconverted from the physical gel and the physical-crosslinked inclusion network is shown in Figure 9. Figure 9 shows that the tanδ of the chemical gel reconverted from the physical gel showed a similar trend to the tanδ of the initial chemical gel, suggesting that the chemical gel reconverted from the physical gel has a similar structure to the chemical gel before conversion. This confirms that the physical gel converted from the chemical gel can be further converted back to the original chemical gel. [Industrial Applicability]

[0043] The network polymer of the present invention can be converted into a chemical gel or a physical gel by changing the crosslinking method, even if it is the same material, and it may be used as a material for a wide range of applications. Furthermore, in this invention, the network collapses and completely dissolves in an environment above a certain temperature in the case of chemical crosslinking, and in an environment in a specific solvent in the case of physical crosslinking, which is also beneficial from the perspective of 100% recycling of materials, and is expected to be a zero-waste crosslinking structure conversion system that does not produce by-products.

Claims

1. A chemical gel comprising a polymer having a crown ether in its main chain and a maleimide unit in its side chain, and a compound having furan at both ends and two ammonium salt units, wherein the furan and the ammonium salt are separated by one carbon chain, the chemical gel being chemically crosslinked with the maleimide unit, and capable of being converted into a physical gel.

2. The chemical gel according to claim 1, wherein the chemical crosslinking between the furan and the maleimide unit is a chemical crosslinking represented by the following formula 1: 【Chemistry 1】 In the formula, X － represents an anion, and R represents an optional linking group.

3. A physical gel comprising a polymer having a crown ether in its main chain and a maleimide unit in its side chain, and a compound having furan at both ends and two ammonium salt units, wherein the furan and the ammonium salt are separated by one carbon chain, the ammonium salt units being physically crosslinked with the crown ether, and which can be converted into a chemical gel.

4. 4. The physical gel according to claim 3, wherein the physical crosslinking between the ammonium salt unit and the crown ether is represented by the following formula 2: 【Chemistry 2】 In the formula, X － and R is the same as in Formula 1. Note that the position of n can be any position within the crown ether.

5. A network polymer that can reversibly convert between the chemical gel described in claim 1 and the physical gel described in claim 3, comprising a polymer having a crown ether in its main chain and a maleimide unit in its side chain, and a compound having furan at both ends and two ammonium salt units, wherein the furan and the ammonium salt are separated by one carbon chain.

6. 6. The polymer according to claim 1, 3 or 5, wherein the polymer having a crown ether in its main chain and a maleimide unit in its side chain is a polymer having partial structures represented by the following formulas (3) and (4): 【Transformation 3】 In the formula, n is the same as in formula (2).

7. The compound according to claim 1, 3 or 5, which has furan at both ends and further has two ammonium salt units, wherein the furan and the ammonium salt are separated by one carbon chain, is a compound represented by the following formula (5): 【Chemistry 4】 In the formula, R and X － is the same as equation (1).

8. 6. The network polymer according to claim 5, wherein the network polymer is a chemical gel and can be converted into a physical gel at room temperature in a solution capable of forming inclusions by heating.

9. 6. The network polymer according to claim 5, wherein the network polymer is a physical gel and can be converted into a chemical gel at room temperature in a solvent that does not allow clathration.

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