Cross-linked polyrotaxanes and elastomers

Abstract

To provide a polyrotaxane having excellent solubility in various solvents while having heat resistance of a certain level or higher.SOLUTION: A polyrotaxane has a straight chain molecule, a circular molecule including the straight chain molecule in a skewered state, and blocking groups placed on both terminals of the straight chain molecule, in which the circular molecule containing an aromatic ring with a phenolic hydroxy group in its side chain, where further at least a portion of the phenolic hydroxy group is substituted with a specific substituent. The specific substituent is a nonionic group such as a hydroxypropyl group. The polyrotaxane can be a cross-linked polyrotaxane in which a plurality of circular molecules of the polyrotaxane are intermolecularly cross-linked.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to polyrotaxane.

Background Art

[0002] Polyrotaxane is a molecular aggregate having a structure composed of a linear molecule, a cyclic molecule that clathrates the linear molecule in a pierced state (incorporated into the pores), and blocking groups arranged at both ends of the linear molecule. Since the cyclic molecule is slidable with respect to the linear molecule, it is called a slide-ring material (SRM). Although various types of cyclic molecules and linear molecules are known, cyclodextrin is often used as the cyclic molecule and polyethylene glycol is often used as the linear molecule (Patent Documents 1 and 2).

[0003] Cyclodextrin has a structure in which D-glucose is linked in a cyclic manner. The structural formula of α-cyclodextrin in which the number of ring members of D-glucose is 6 is shown in FIG. 4. Cyclodextrin has many hydroxyl groups at the ends of the pores, and ether-bonded oxygen atoms and hydrogen atoms in the pores.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, polyrotaxane in which the cyclic molecule is cyclodextrin (hereinafter sometimes referred to as "cyclodextrin-type polyrotaxane") had room for improvement in heat resistance and solubility in various solvents according to the studies by the present inventors (see Comparative Example 3 in Table 1 described later).

[0006] Therefore, the applicant previously developed a polyrotaxane using pillararene as a cyclic molecule (hereinafter sometimes referred to as "pillararene-type polyrotaxane") and found that it had improved heat resistance compared to the conventional cyclodextrin type (Japanese Patent Application No. 2020-036286 (not published at the time of this application)). However, this pillararene-type polyrotaxane has very poor solubility in various solvents (see Comparative Example 2 in Table 1), and although it dissolves in alkaline aqueous solutions, it dissolves only slightly in dimethyl sulfoxide (DMSO) among other solvents. Consequently, there are limitations when, for example, crosslinking the polyrotaxane.

[0007] Therefore, the object of the present invention is to provide a polyrotaxane that has a certain level of heat resistance while also having good solubility in various solvents. [Means for solving the problem]

[0008] The inventors investigated and found that the reason the above-mentioned pillararene-type polyrotaxanes had very poor solubility was that the pillararenes had phenolic hydroxyl groups, causing the rotaxanes to aggregate through hydrogen bonding. This aggregation required high temperatures to untangle, making them difficult to process. Therefore, after further investigation, the inventors discovered that aggregation could be suppressed by substituting at least a portion of the phenolic hydroxyl groups of the cyclic molecule containing the aromatic ring with specific substituents, leading to the present invention.

[0009] [1] Polyrotaxane A polyrotaxane having a linear molecule, a cyclic molecule that encloses the linear molecule in a skewer-like manner, and a chokeholding group positioned at both ends of the linear molecule, The cyclic molecule comprises an aromatic ring having a phenolic hydroxyl group in its side chain, and furthermore, at least a portion of the phenolic hydroxyl group is substituted with a specific substituent. The polyrotaxane is characterized in that the specific substituent has a chemical structure represented by -ORX, where R is a group obtained by removing one hydrogen atom from a linear or branched alkyl group having 1 to 12 carbon atoms, a group obtained by removing one hydrogen atom from a linear or branched alkyl group having 2 to 12 carbon atoms containing at least one ether group, a group obtained by removing one hydrogen atom from a cyclic alkyl group having 3 to 12 carbon atoms, a group obtained by removing one hydrogen atom from a cyclic alkyl ether group having 2 to 12 carbon atoms, or a group obtained by removing one hydrogen atom from a cyclic alkyl thioether group having 2 to 12 carbon atoms, and X is OH, NH2, or SH. All of the aforementioned specific substituents are nonionic groups. Among the specified substituents, a hydroxypropyl group is preferred among the nonionic groups in which R is a branched alkyl group with 3 carbon atoms from which one hydrogen atom has been removed, and X is an OH group. Substituting at least a portion of the phenolic hydroxyl group with a hydroxypropyl group may hereafter be referred to as "hydroxypropyl modification".

[0010] (action) By substituting at least a portion of the phenolic hydroxyl groups of a cyclic molecule containing an aromatic ring with specific substituents, molecules that previously only dissolved in highly polar solvents such as alkaline aqueous solutions and DMSO become soluble in less polar solvents such as tetrahydrofuran (THF), chloroform, and toluene (see Examples in Table 1). This is thought to be because the substitution of the phenolic hydroxyl groups of the cyclic molecule with nonionic substituents suppresses aggregation due to hydrogen bonding between rotaxanes.

[0011] Thus, the improved solubility in various solvents not only enhances processability (handling) but also improves compatibility, allowing for better mixing with various compounds and polymers. This increases the range of chemical structural options for the crosslinking agent used when crosslinking the polyrotaxane. For example, based on polarity indicators using SP values, good mixing can be expected with polymers such as polypropylene (SP value: 18.8), which are well compatible with toluene (SP value: 18.2) to THF (SP value: 19.4).

[0012] However, the polyrotaxane obtained by hydroxypropyl-modifying a cyclic molecule containing an aromatic ring has a reduced heat resistance compared to the polyrotaxane without hydroxypropyl-modifying the cyclic molecule containing an aromatic ring (see the examples and Comparative Example 2 in Table 1). Similarly, in an attempt to improve the solubility in various solvents, the polyrotaxane obtained by hydroxypropyl-modifying cyclodextrin has a reduced heat resistance compared to the polyrotaxane without hydroxypropyl-modifying cyclodextrin (see Comparative Example 1 and Comparative Example 3 in Table 1). Comparing these, the polyrotaxane obtained by hydroxypropyl-modifying a cyclic molecule containing an aromatic ring has a higher thermal decomposition temperature compared to the polyrotaxane obtained by hydroxypropyl-modifying cyclodextrin (see the examples and Comparative Example 1 in Table 1), and has a certain level of heat resistance.

[0013] [2] Crosslinked polyrotaxane A crosslinked polyrotaxane in which the cyclic molecules of the plurality of polyrotaxanes in [1] above are crosslinked by a crosslinking agent.

[0014] [4] Elastomer An elastomer containing the crosslinked polyrotaxane in [2] above.

[0015] The use of the elastomer is not particularly limited. For example, an electrode can be attached to the elastomer and used as a polymer actuator or a polymer sensor. [Advantages of the Invention]

[0016] According to the present invention, it is possible to provide a polyrotaxane that has a certain level of heat resistance and good solubility in various solvents. [Brief Description of the Drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram for explaining the first half of the production process of the polyrotaxane of the example. [Figure 2] FIG. 2 is a schematic diagram of the pillararene-type polyrotaxane (before hydroxypropyl modification) obtained in the first half. [Figure 3] Figure 3 is a schematic diagram explaining the latter half of the production process of the polyrotaxane of the embodiment (hydroxypropyl modification) and the crosslinking of the obtained polyrotaxane. [Figure 4] Figure 4 is a schematic diagram of the polyrotaxane of Comparative Example 3.

Embodiments for Carrying out the Invention

[0018] 1. Polyrotaxane (a) Cyclic molecule Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, etc. Examples of the cyclic molecule include pillararenes and calixarenes having a phenolic hydroxyl group in the side chain. As described above, at least a part of the phenolic hydroxyl group in the side chain of the cyclic molecule is substituted with a specific substituent, but another part of the phenolic hydroxyl group may be substituted with another group such as -SH, -NH2, -COOH, -SO3H, -PO4H, etc., or may be substituted with a substituent having a graft chain (for example, a graft chain formed by ring-opening polymerization of a lactone monomer) so as to be soluble in various organic solvents.

[0019] Pillararene is an oligomer having a structure in which arenes (aromatic rings) are connected in a cyclic and prismatic shape, and is generally denoted as pillar[n]arene, where [n] is the number of ring members of the arene. [n] is not particularly limited, but is preferably 5 to 6. Calixarene is an oligomer having a structure in which phenols are connected cyclically via methylene groups, and is generally denoted as calix[n]arene, where [n] is the number of ring members of the phenol. [n] is not particularly limited, but is preferably 3 to 10.

[0020] (b) Linear molecule The linear molecules are not particularly limited, but examples include polyethylene glycol, polylactic acid, polyisoprene, polyisobutylene, polybutadiene, polypropylene glycol, polytetrahydrofuran, polydimethylsiloxane, polyethylene, polypropylene, polyvinyl alcohol, and polyvinyl methyl ether. Polyethylene glycol is preferred as the linear molecule, and other linear molecules may be included together with polyethylene glycol.

[0021] (c) Blocking group The chelating group is not particularly limited, but examples include dinitrophenyl groups, cyclodextrins, adamantane groups, trityl groups, fluoresceins, pyrenes, substituted benzenes (examples of substituents include alkyl, alkyloxy, hydroxy, halogen, cyano, sulfonyl, carboxyl, amino, and phenyl; one or more substituents may be present), substituted polynuclear aromatics (examples of substituents include the same as above; one or more substituents may be present), and steroids. Preferably, it is selected from the group consisting of dinitrophenyl groups, cyclodextrins, adamantane groups, trityl groups, fluoresceins, and pyrenes, and more preferably, it is an adamantane group or a trityl group.

[0022] 2. Crosslinking agent The crosslinking agent for polyrotaxanes is not particularly limited, but examples include isocyanates, polyethers, polyesters, polysiloxanes, polycarbonates, poly(meth)acrylates, or polyenes, or copolymers thereof, or mixtures thereof. The functional groups located at each end of the crosslinking agent are not particularly limited, but isocyanate groups that can react with the phenolic hydroxyl groups of the cyclic molecule are preferred, and blocked isocyanates are more preferred.

[0023] 3. Elastomer The elastomer may consist solely of cross-linked polyrotaxane, or it may be a mixture of cross-linked polyrotaxane and other elastomers. Other elastomers, though not particularly limited, include silicone elastomers, styrene-based thermoplastic elastomers, natural rubber, nitrile rubber, acrylic rubber, urethane rubber, urea rubber, and fluororubber. [Examples]

[0024] The polyrotaxanes of the examples were prepared by following the steps (1) to (5) below.

[0025] (1) Activation of both ends of polyethylene glycol (abbreviated as PEG) As shown in Figure 1(1), an aqueous solution of polyethylene glycol (PEG20000) was reacted with 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), NaBr, and NaClO according to the method described in the literature (Macromolecules, 2005, 38, 7524-7527) and the mixture was reacted at pH 10-11 for 15 minutes. The reaction solution was treated with dilute hydrochloric acid, and the resulting mixture was extracted twice with dichloromethane. The resulting dichloromethane solution was recovered, concentrated under reduced pressure, and recrystallized with ethanol to obtain polyethylene glycol (abbreviated as PEG-COOH) with carboxyl groups at both ends of the molecule in a weight yield of 91%.

[0026] (2) Pillar[5] Synthesis of allenes As shown in Figure 1(2), dimethoxypillar[5]arene (2.00 g, 2.67 mmol) was dissolved in anhydrous chloroform (150 mL) according to the method described in the literature (J. Org. Chem. 2011, 76, 328-331.), and boron tribromide (13.6 g, 54.3 mmol) was added to the solution and stirred at 25°C for 72 hours. Water was added to the reaction solution, and the resulting precipitate was collected and washed with 0.5 M aqueous HCl and chloroform to quantitatively obtain pillar[5]arene (abbreviated as P5AOH) (1.61 g, 2.64 mmol) containing an aromatic ring with a phenolic hydroxyl group in the side chain.

[0027] (3) Synthesis of pseudopolyrotaxanes As shown in Figure 1(3), 10 mL (0.0121 mol / L) of P5AOH solution prepared using 10 mL of methanol aqueous solution (methanol:water = 1:1 by weight) as the solvent was mixed with 0.6 mL (1.894 mol / L) of PEG-COOH solution and left to stand at room temperature for 1 day. The resulting precipitate was washed with 10 mL of water, and the resulting residue was dried under vacuum at 50°C for 1 day to obtain a pseudo-polyrotaxane (abbreviated as PseudoP5AOH-PEG) in which P5AOH encapsulates PEG-COOH.

[0028] (4) Synthesis of pillararene-type polyrotaxanes As shown in Figure 1(4), a solution of adamantaneamine (0.016 g, 0.11 mmol), BOP reagent (0.048 g, 0.11 mmol), and diisopropylethylamine (0.019 mL, 0.12 mmol) dissolved in dimethylformamide (dryDMF) (10 mL) was thoroughly cooled on ice, and PseudoP5AOH-PEG (150 mg) was added and stirred at 4°C overnight. The resulting solution was concentrated under reduced pressure using a rotary evaporator, and excess water was added and stirred. The precipitate was filtered, and the resulting residue was ultrasonically washed with acetone, the supernatant was removed, and it was vacuum dried to obtain a pillararene-type polyrotaxane (abbreviated as P5AOH-PEG) (104 mg) in which adamantane groups were arranged at both ends of PEG. A schematic diagram of this P5AOH-PEG (and the structural formula for P5AOH) is shown in Figure 2.

[0029] (5) Synthesis of hydroxypropyl-modified pillararene-type polyrotaxanes As shown in Figure 3(5), 804 mg of P5AOH-PEG (804 mg initial charge, of which 459 mg is pillararene) was dissolved in 30.1 mL (10 equivalents) of 0.01 M NaOH aqueous solution. 131.4 g (3000 eq.) of propylene oxide was added to this solution, and the mixture was stirred at room temperature for 24 hours. The reaction mixture was concentrated under reduced pressure to remove residual propylene oxide. The residue was acid-treated with 3 M HCl aqueous solution to pH=3-4, and the acid-treated solution was concentrated under reduced pressure to remove water. THF was added to the residue, filtered, and the soluble portion was concentrated under reduced pressure. 1.5 g of the obtained liquid compound was added to ethanol, filtered, and the insoluble portion was vacuum-dried at 40°C for 1 day to obtain 154 mg of a pillararene-type polyrotaxane (abbreviated as P5AOHP-PEG) in which at least some of the phenolic hydroxyl groups of pillararene were replaced with hydroxypropyl groups (hydroxypropyl modified).

[0030] [Comparative Example 2] The P5AOH-PEG (before hydroxypropyl modification) obtained in (4) above (Figure 2) was designated as Comparative Example 2.

[0031] [Comparative Example 3] (1) above A similar method obtained Molecular weight 35,000 Using PEG-COOH and commercially available α-cyclodextrin (abbreviated as CD), the polyrotaxane of Comparative Example 3 was prepared by the following method. Following the method described in the literature (Macromolecules, 2005, 38, 7524-7527), PEG-COOH 3.0g (8.6 × 10) -5 (mol) and α-cyclodextrin (12g, 1.2×10) -2 The adamantanamine (0.16 g, 1.1 × 10⁻⁶ mol) was dissolved in water (100 mL) and left to stand in the refrigerator overnight. The resulting paste-like mixture was freeze-dried, and the dried solid was extracted. -3 (mol), BOP reagent (0.48g, 1.1×10) -3 (mol), ethyldiisopropylamine (0.19 mL, 1.2 × 10) -3The mixture was dissolved in 100 mL of DMF along with (mol) and reacted at 4°C overnight. The resulting mixture was centrifuged twice each in a DMF / MeOH (1:1) mixed solvent and MeOH. The recovered precipitate was washed with 80 mL of DMSO, and the precipitate was centrifuged with 800 mL of H2O. The resulting solid was freeze-dried to obtain 9.55 g to 10.3 g of the cyclodextrin-type polyrotaxane (abbreviated as CD-PEG) of Comparative Example 3. A schematic diagram of this CD-PEG (and the structural formula for CD) is shown in Figure 4.

[0032] [Comparative Example 1] The CD of the CD-PEG in Comparative Example 3 was modified with hydroxypropyl by the method described in paragraph 0092 of International Publication No. 2005 / 080469 to obtain the hydroxypropyl-modified cyclodextrin-type polyrotaxane (abbreviated as CDP-PEG) of Comparative Example 1.

[0033] [measurement] The following measurements were performed for the examples and comparative examples 1-3.

[0034] (a) TG-DTA measurement (confirmation of heat resistance) TG-DTA measurements were performed on each of the polyrotaxanes in the Examples and Comparative Examples 1-3. For details, differential thermal and thermogravimetric (TG-DTA) simultaneous measurement device (STA7200, Hitachi High-Technologies Corporation) was used, and platinum was used as the sample pan. Measurements were taken in an N2 gas stream (10 mL / min) under the conditions of thermal decomposition heating rate: 1°C / min for 100-300°C and 10°C / min for 300-900°C. The thermal decomposition temperature (50% weight loss) is shown in Table 1, with the weight before heating as the reference (100%), and the temperature at which the weight decreased by 50% relative to the weight before heating is used.

[0035] (i) Solubility test To each of the polyrotaxane samples from Examples and Comparative Examples 1-3, 1 mL of solvent was added and allowed to stand at room temperature for 24 hours. Solubility was then determined by visual inspection to check for any remaining solids or gels. Five types of solvents were used: aqueous NaOH solution, DMSO, THF, chloroform, and toluene. The results are shown in Table 1.

[0036] [Table 1]

[0037] As shown in Figure 3(6), the P5AOHP-PEG of the example can be a crosslinked polyrotaxane in which the cyclic molecules of multiple adjacent P5AOHP-PEGs are crosslinked by a crosslinking agent. This cross-linked polyrotaxane can be used alone or in mixture with other elastomers to produce a highly heat-resistant elastomer. Furthermore, the P5AOHP-PEG of the example can be mixed with other elastomers and used as a highly heat-resistant elastomer by directly crosslinking the cyclic molecules of P5AOHP-PEG with the functional groups of the other elastomer, or by using a crosslinking agent. These highly heat-resistant elastomers can be used as highly heat-resistant polymer actuators or polymer sensors by attaching electrodes (for example, by attaching stretchable electrode layers to both sides of a film-like elastomer).

[0038] Specifically, the cross-linked polyrotaxane was prepared using the following method. 22 mg of P5AOHP-PEG from the example was mixed with 20 mL of THF, then 4 mL of a crosslinking agent (hexamethylene diisocyanate) and 2 mL of dibutyltin dilaurate, and the mixture was stirred at room temperature for about 1 day. When THF was evaporated from the above liquid (at room temperature for about half a day), a gel-like substance was obtained. This gel-like substance was applied to a glass substrate and then left to stand and dry overnight at room temperature in a fume hood to obtain a cross-linked polyrotaxane film.

[0039] It should be noted that the present invention is not limited to the embodiments described above, and can be appropriately modified and implemented without departing from the spirit of the invention.

Claims

1. A polyrotaxane having a linear molecule, a cyclic molecule that encloses the linear molecule in a skewer-like manner, and a chokeholding group positioned at both ends of the linear molecule, The aforementioned cyclic molecule has a structure in which multiple aromatic rings are linked in a ring, The aforementioned aromatic ring comprises multiple aromatic rings having phenolic hydroxyl groups in their side chains, and furthermore, at least a portion of the phenolic hydroxyl groups are substituted with specific substituents. The aforementioned specific substituent has a chemical structure represented by -O-R-X, where R is a group obtained by removing one hydrogen atom from a linear or branched alkyl group having 1 to 12 carbon atoms, a group obtained by removing one hydrogen atom from a linear or branched alkyl group having 2 to 12 carbon atoms containing at least one ether group, a group obtained by removing one hydrogen atom from a cyclic alkyl group having 3 to 12 carbon atoms, a group obtained by removing one hydrogen atom from a cyclic alkyl ether group having 2 to 12 carbon atoms, or a group obtained by removing one hydrogen atom from a cyclic alkyl thioether group having 2 to 12 carbon atoms, and X is OH, NH 2 , or SH, A crosslinked polyrotaxane characterized in that the cyclic molecules of a plurality of the aforementioned polyrotaxanes are crosslinked with an isocyanate, polyether, polyester, polysiloxane, polycarbonate, poly(meth)acrylate or polyene, or copolymers thereof, or mixtures thereof, as a crosslinking agent.

2. The crosslinked polyrotaxane according to claim 1, wherein the specified substituent is a hydroxypropyloxy group.

3. An elastomer comprising only the crosslinked polyrotaxane described in claim 1 or 2, or a mixture of the crosslinked polyrotaxane described in claim 1 or 2 and another elastomer.

4. A polymer actuator or polymer sensor comprising an electrode attached to the elastomer according to claim 3.

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