Polymer Actuators and Sensors

Abstract

To provide a polymer actuator including a dielectric elastomer layer that improves the dielectric constant while maintaining flexibility (elastic modulus) and suppresses reduction in volume resistivity.SOLUTION: The polymer actuator includes a dielectric elastomer layer and two electrodes arranged on both sides of the dielectric elastomer layer. The dielectric elastomer layer is composed of a cured product of a composition containing a resin component containing polyrotaxane and a (meth)acrylic polymer having a polyalkylene glycol chain and a cyclic carbonate structure in a side chain.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polymer actuators and sensors, and more particularly to polymer actuators and sensors that include a dielectric elastomer layer. [Background technology]

[0002] Polymer actuators having a dielectric elastomer layer containing polyrotaxane have been known as polymer actuators with large displacements (for example, JP 2017-66318 A (Patent Document 1)). However, conventional polymer actuators having a dielectric elastomer layer containing polyrotaxane do not necessarily have sufficiently high output, and there has been a demand for higher output.

[0003] In general, improving the dielectric constant of a polymer actuator having a dielectric elastomer layer is considered effective for increasing the output. Furthermore, incorporating a high-dielectric-constant filler, such as barium titanate or titania, is considered effective for improving the dielectric constant of the dielectric elastomer layer. However, since many high-dielectric-constant fillers are made of ceramics with high elastic moduli, incorporating such high-dielectric-constant fillers into a dielectric elastomer layer improves the dielectric constant of the dielectric elastomer layer. However, incorporating such high-dielectric-constant fillers into a dielectric elastomer layer significantly increases the elastic modulus, resulting in a problem of reduced displacement of the polymer actuator during operation. For this reason, there has been a demand for a technology that improves the dielectric constant of a polymer actuator having a dielectric elastomer layer while maintaining the flexibility of the dielectric elastomer layer.

[0004] Furthermore, Japanese Patent Application Laid-Open Publication No. 2018-59042 (Patent Document 2) discloses a dielectric elastomer material containing a copolymer having polar groups such as carbonate groups introduced into its side chains, and describes that the introduction of the polar groups increases the dielectric constant of the dielectric elastomer material. However, dielectric elastomer materials containing copolymers having only polar groups such as carbonate groups introduced into their side chains have problems such as insufficient improvement in dielectric constant and lower volume resistivity compared to dielectric elastomer materials that do not contain copolymers having polar groups such as carbonate groups introduced into their side chains. Furthermore, actuators and sensors using this dielectric elastomer material have problems such as repeated deformation of the dielectric elastomer material due to their operation, causing the dielectric elastomer material to wear down and impairing the reversibility of operation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-66318 [Patent Document 2] Japanese Patent Application Publication No. 2018-59042 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the problems associated with the above-mentioned conventional technology, and aims to provide a polymer actuator and sensor having a dielectric elastomer layer that improves the dielectric constant and suppresses a decrease in volume resistivity while maintaining flexibility (elastic modulus). [Means for solving the problem]

[0007] As a result of extensive research to achieve the above object, the inventors have discovered that by blending a (meth)acrylic polymer having a polyalkylene glycol chain and a cyclic carbonate structure in its side chain with a dielectric elastomer layer containing polyrotaxane, it is possible to improve the dielectric constant and suppress a decrease in volume resistivity while maintaining the flexibility (elastic modulus) of the dielectric elastomer layer, and have thus completed the present invention.

[0008] That is, the polymer actuator of the present invention comprises a dielectric elastomer layer and two electrodes arranged on both sides of the dielectric elastomer layer, and is characterized in that the dielectric elastomer layer is made of a cured product of a composition containing a resin component including polyrotaxane and a (meth)acrylic polymer having a polyalkylene glycol chain and a cyclic carbonate structure in its side chain.

[0009] In the polymer actuator of the present invention, the (meth)acrylic polymer is represented by the following formula (1):

[0010] [ka]

[0011] (In the above formula, R 1 represents a hydrogen atom or a methyl group, AO represents an alkyleneoxy group, and R 2 represents an alkyl group, and p represents the degree of polymerization of the alkyleneoxy group. and a repeating unit represented by the following formula (2):

[0012] [ka]

[0013] (In the above formula, R 3 represents a hydrogen atom or a methyl group, and R 4 represents an alkylene group, and B represents the cyclic carbonate structure. and a repeating unit represented by the following formula (1):

[0014] In the polymer actuator of the present invention, the cyclic carbonate structure is preferably an ethylene carbonate structure.

[0015] Furthermore, a sensor of the present invention is characterized by comprising the polymer actuator of the present invention.

[0016] Although the reason why the present invention enables the dielectric constant to be improved and the volume resistivity to be prevented from decreasing while maintaining the flexibility (elastic modulus) of the dielectric elastomer layer is not entirely clear, the inventors speculate as follows: Cyclic carbonates have a large dielectric polarization and therefore exhibit a high dielectric constant. However, when a (meth)acrylic polymer having only cyclic carbonate structures in its side chains is blended into a dielectric elastomer layer, the large dielectric polarization of the cyclic carbonate structures tends to cause aggregation of the cyclic carbonate structures, and polarization is canceled within the aggregate structure. Therefore, even when an electric field is applied to the dielectric elastomer layer, the (meth)acrylic polymer is unlikely to orient in the direction of the applied electric field, making it difficult to improve the dielectric constant. Furthermore, aggregation of the cyclic carbonate structures tends to decrease the volume resistivity of the dielectric elastomer layer. On the other hand, when a (meth)acrylic polymer having a polyalkylene glycol chain and a cyclic carbonate structure in its side chain is blended, the polyalkylene glycol chain, which has high mobility and is likely to induce large polarization, acts to suppress the aggregation of the cyclic carbonate structures.Therefore, when an electric field is applied to the dielectric elastomer layer, the (meth)acrylic polymer is aligned in the direction of the applied electric field, thereby improving the dielectric constant and suppressing a decrease in volume resistivity. [Effects of the Invention]

[0017] According to the present invention, it is possible to obtain a polymer actuator and a sensor having a dielectric elastomer layer that maintains flexibility (elastic modulus), improves the dielectric constant, and suppresses a decrease in volume resistivity. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below based on preferred embodiments thereof.

[0019] The polymer actuator of the present invention comprises a dielectric elastomer layer and two electrodes arranged on both sides of the dielectric elastomer layer, and the dielectric elastomer layer is made of a cured product of a composition containing a resin component including polyrotaxane and a (meth)acrylic polymer having a polyalkylene glycol chain and a cyclic carbonate structure in its side chain.

[0020] (Polyrotaxane) Polyrotaxane is a molecular assembly having a structure in which a rod-shaped molecule (axial molecule) penetrates a hole in a ring-shaped molecule, with bulky moieties (terminal groups) attached to both ends of the rod-shaped molecule. By incorporating such a polyrotaxane into a dielectric elastomer layer, the dielectric constant of the dielectric elastomer layer can be improved while suppressing a decrease in the breakdown voltage, thereby enabling the output of the actuator to be improved. Furthermore, a dielectric elastomer layer containing the polyrotaxane is less likely to become worn because the polyrotaxane serves as a dynamic crosslinking point, preventing the crosslinking point from being broken by deformation. This results in excellent reversibility (reversible responsiveness) and stability of the operation. In the present invention, there are no particular limitations on the type of polyrotaxane, and conventionally known polyrotaxanes can be used.

[0021] The ring-shaped molecule is not particularly limited, and examples thereof include cyclodextrins (e.g., α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin), crown ethers, cyclophanes, calixarenes, cucurbiturils, and cyclic amides. These ring-shaped molecules may be used alone or in combination of two or more. Such ring-shaped molecules may also have a substituent or a side chain. Among these ring-shaped molecules, cyclodextrins having caprolactone chains as graft chains are preferred from the viewpoint of obtaining appropriate flexibility and dielectric constant.

[0022] The axial molecule is not particularly limited, and examples thereof include polyethylene glycol, polypropylene glycol, polyethylene, polypropylene, polyisoprene, polyisobutylene, polybutadiene, polylactic acid, polytetrahydrofuran, polydimethylsiloxane, polyvinyl alcohol, and polyvinyl methyl ether. These axial molecules may be used alone or in combination of two or more. Among these axial molecules, polyethylene glycol and polypropylene glycol are preferred because they have a low glass transition temperature and allow the ring-shaped molecule to move smoothly.

[0023] Furthermore, the bulky terminal group is not particularly limited, and examples thereof include a dinitrophenyl group, a cyclodextrin group, an adamantane group, a trityl group, a fluorescein group, a pyrene group, a substituted benzene ring, a polycyclic aromatic ring, and a steroid group. These terminal groups may be used alone or in combination of two or more. Among these terminal groups, the dinitrophenyl group, the cyclodextrin group, the adamantane group, the trityl group, the fluorescein group, and the pyrene group are preferred, with the adamantane group being more preferred, from the viewpoints of being easily introduced into the terminal of the axial molecule and having sufficient bulk to prevent the ring-shaped molecule from coming off.

[0024] ((Meth)acrylic polymer) The (meth)acrylic polymer used in the present invention has a polyalkylene glycol chain and a cyclic carbonate structure in the side chain. Such a (meth)acrylic polymer has a low glass transition temperature, and by incorporating it into the dielectric elastomer layer, it is possible to improve the dielectric constant while maintaining the flexibility (elastic modulus) of the dielectric elastomer layer.

[0025] Examples of the polyalkylene glycol chain include a polyethylene glycol chain and a polypropylene glycol chain, and among them, a polyethylene glycol chain is preferred from the viewpoint of high chain mobility and not interfering with the movement of the cyclic carbonate structure. Furthermore, since the polyethylene glycol chain has affinity with polypropylene glycol, when polypropylene glycol is used as a matrix in the composition for forming the dielectric elastomer layer, the (meth)acrylic polymer is well dispersed in the matrix, making it possible to suppress breakage due to aggregation.

[0026] The degree of polymerization of the alkylene glycol in the polyalkylene glycol chain is preferably 4 to 100, more preferably 4 to 80, even more preferably 4 to 50, still more preferably 4 to 20, and particularly preferably 4 to 10. If the degree of polymerization of the alkylene glycol is below the lower limit, aggregation of cyclic carbonate structures cannot be sufficiently suppressed, and therefore the dielectric constant does not improve sufficiently and a decrease in volume resistivity tends to be unable to be sufficiently suppressed. On the other hand, if the degree of polymerization exceeds the upper limit, the mobility of the polyalkylene glycol chain decreases, and the movement of the cyclic carbonate structures tends to be hindered.

[0027] The (meth)acrylic polymer used in the present invention has a repeating unit containing such a polyalkylene glycol chain, for example, a repeating unit represented by the following formula (1):

[0028] [ka]

[0029] The repeating unit has the following structure:

[0030] In the formula (1), R 1represents a hydrogen atom or a methyl group. AO represents an alkyleneoxy group, such as an ethyleneoxy group or a propyleneoxy group. Among these, an ethyleneoxy group is preferred from the viewpoint of increasing the dielectric constant relative to the amount added because it has a large polarization despite its small molecular weight. 2 represents an alkyl group, examples of which include a methyl group and an ethyl group. p represents the degree of polymerization of the alkyleneoxy group and is preferably 4 to 100, more preferably 4 to 80, even more preferably 4 to 50, even more preferably 4 to 20, and particularly preferably 4 to 10. If p is below the lower limit, aggregation of cyclic carbonate structures cannot be sufficiently suppressed, so the dielectric constant does not improve sufficiently and a decrease in volume resistivity tends to be unable to be sufficiently suppressed. On the other hand, if p exceeds the upper limit, the mobility of the polyalkylene glycol chain decreases, hindering polarization of the cyclic carbonate structure, so the dielectric constant tends to be difficult to improve.

[0031] Examples of the cyclic carbonate structure include alkylene carbonate structures such as an ethylene carbonate structure.

[0032] The (meth)acrylic polymer used in the present invention contains a repeating unit containing such a cyclic carbonate structure, for example, a repeating unit represented by the following formula (2):

[0033] [ka]

[0034] The repeating unit has the following structure:

[0035] In the formula (2), R 3 represents a hydrogen atom or a methyl group. 4 represents an alkylene group, for example, a methylene group, an ethylene group, a propylene group, etc. B represents the cyclic carbonate structure, for example, an alkylene carbonate structure such as an ethylene carbonate structure.

[0036] Furthermore, the (meth)acrylic polymer used in the present invention may contain other (meth)acrylic monomer units in addition to the repeating units containing the polyalkylene glycol chain and the repeating units containing the cyclic carbonate structure, provided that the effects of the present invention are not impaired. Examples of such other (meth)acrylic monomer units include (meth)acrylic monomer units having a hydroxyl group in the side chain, such as hydroxyalkyl (meth)acrylate units such as hydroxymethyl (meth)acrylate units and hydroxyethyl (meth)acrylate units.

[0037] The degree of polymerization of the (meth)acrylic monomer in the (meth)acrylic polymer used in the present invention (i.e., the total number of repeating units containing the polyalkylene glycol chain, repeating units containing the cyclic carbonate structure, and other (meth)acrylic monomer units) is preferably from 30,000 to 10,000, more preferably from 5 to 1,000, and particularly preferably from 5 to 100. If the degree of polymerization of the (meth)acrylic monomer is below the lower limit, the (meth)acrylic polymer tends to easily bleed out from the dielectric elastomer layer. On the other hand, if it exceeds the upper limit, the (meth)acrylic polymer does not disperse uniformly within the dielectric elastomer layer, and therefore the dielectric constant does not improve sufficiently and the decrease in volume resistivity tends not to be sufficiently suppressed.

[0038] In the (meth)acrylic polymer used in the present invention, the molar ratio (polyalkylene glycol chain unit:cyclic carbonate structural unit) of the repeating unit containing the polyalkylene glycol chain (hereinafter also referred to as "polyalkylene glycol chain unit") to the repeating unit containing the cyclic carbonate structure (hereinafter also referred to as "cyclic carbonate structural unit") is preferably 90:10 to 30:70, more preferably 80:20 to 40:60, and particularly preferably 80:20 to 50:50. If the ratio of polyalkylene glycol chain unit:cyclic carbonate structural unit is less than the lower limit, the amount of cyclic carbonate structure introduced tends to be small, making it difficult to improve the dielectric constant. On the other hand, if the ratio exceeds the upper limit, aggregation of the cyclic carbonate structures cannot be sufficiently suppressed, so the dielectric constant does not sufficiently improve and the decrease in volume resistivity tends to be insufficient.

[0039] In the composition for forming the dielectric elastomer layer, the content of the (meth)acrylic polymer is preferably 5 to 60 parts by mass, and more preferably 10 to 40 parts by mass, per 100 parts by mass of the resin component for forming the dielectric elastomer layer. If the content of the (meth)acrylic polymer is less than the lower limit, the effects of the polyalkylene glycol chain and the cyclic carbonate structure cannot be fully obtained, and for example, the dielectric constant does not improve sufficiently and a decrease in volume resistivity tends to be unable to be sufficiently suppressed. On the other hand, if the content exceeds the upper limit, the (meth)acrylic polymer tends to undergo phase separation.

[0040] Furthermore, in the composition for forming the dielectric elastomer layer, the content of the (meth)acrylic polymer is preferably 5 to 5,000 parts by mass, more preferably 100 to 3,000 parts by mass, relative to 100 parts by mass of the polyrotaxane. If the content of the (meth)acrylic polymer is less than the lower limit, the effects of the polyalkylene glycol chain and the cyclic carbonate structure cannot be fully obtained, and for example, the dielectric constant does not improve sufficiently and a decrease in volume resistivity tends to be unable to be sufficiently suppressed. On the other hand, if the content exceeds the upper limit, the (meth)acrylic polymer tends to undergo phase separation.

[0041] The synthesis method of such a (meth)acrylic polymer is not particularly limited, and for example, a method can be mentioned in which the (meth)acrylic monomer containing the polyalkylene glycol chain, a heterocyclic (meth)acrylate containing one oxygen atom in the cyclic structure (e.g., glycidyl (meth)acrylate), and another (meth)acrylic monomer are heated in the presence of lithium bromide in a carbon dioxide atmosphere to copolymerize the (meth)acrylate while converting the cyclic structure containing one oxygen atom into a cyclic carbonate structure. The (meth)acrylic polymer can also be synthesized by copolymerizing the (meth)acrylic monomer containing the polyalkylene glycol chain, the (meth)acrylic monomer containing the cyclic carbonate structure, and the other (meth)acrylic monomer using a conventionally known method.

[0042] The reaction conditions for these synthesis methods are not particularly limited, and conventionally known reaction conditions can be appropriately adopted, and it is preferable to adopt optimized reaction conditions.

[0043] (Other resin components) The composition for forming the dielectric elastomer layer may optionally contain a polysiloxane-containing block copolymer or a polysiloxane-free polymer. The polysiloxane is not particularly limited, but examples thereof include polydimethylsiloxane, polymethylphenylsiloxane, and modified polydimethylsiloxane. The polysiloxane-containing block copolymer is not particularly limited, but examples thereof include polycaprolactone-polysiloxane block copolymer, polyadipate-polysiloxane block copolymer, and polyethylene glycol-polysiloxane block copolymer. The polysiloxane-free polymer is not particularly limited, but examples thereof include polypropylene glycol, polytetramethylene glycol, polycarbonate, polycaprolactone, polyethylene adipate, polybutylene adipate, and polypropylene glycol monobutyl ether.

[0044] The dielectric elastomer layer of the present invention can be formed by curing a composition containing at least the resin component containing the polyrotaxane and the (meth)acrylic polymer, and optionally containing a block copolymer containing polysiloxane or a polymer not containing polysiloxane. Therefore, the composition preferably contains a crosslinking agent as needed.

[0045] The crosslinking agent can be appropriately selected depending on the resin components contained in the composition, such as the polyrotaxane, the block copolymer containing the polysiloxane, or the polymer not containing the polysiloxane, and is not particularly limited, and examples thereof include aliphatic polyols, aliphatic polyethers, aliphatic polycarbonates, and block copolymers thereof, each having a functional group. Examples of the functional group include an isocyanate group, a blocked isocyanate group, and an epoxy group.

[0046] The method for forming the dielectric elastomer layer is not particularly limited, and examples thereof include a method in which the composition is coated by a known film-forming method such as spin coating, slit die coating, screen printing, or inkjet printing, and then cured.

[0047] The polymer actuator of the present invention comprises a dielectric with an electrode layer, which consists of such a dielectric elastomer layer and two electrodes arranged on both sides of the dielectric elastomer layer. There are no particular restrictions on the shape of the dielectric with an electrode layer, and examples include a cylindrical shape formed by multiple spiral wounds, or a curtain-like shape formed by bending and folding the dielectric in a wavy pattern.

[0048] The electrodes are not particularly limited, and known electrodes used in conventional actuators can be used. Examples include conductive polymer films made of silicone, natural rubber, resin, etc., in which conductive particles such as noble metals (e.g., silver nanowires, etc.) and carbon (e.g., carbon black, carbon nanotubes, graphene, etc.) are dispersed.

[0049] The sensor of the present invention is equipped with the polymer actuator of the present invention. [Example]

[0050] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0051] (Synthesis Example 1) <Synthesis of (meth)acrylic polymer> 0.4 g of glycidyl acrylate, 0.6 g of methoxytriethylene glycol acrylate, 0.155 g of S,S-dibenzyltrithiocarbonate, 9 mg of azobisisobutyronitrile (AIBN), 15 mg of lithium bromide monohydrate (LiBr·HO), and 1.4 g of N-methyl-2-pyrrolidone (NMP) were mixed and polymerized under a carbon dioxide atmosphere at 1 atmosphere pressure for 20 hours with stirring at 70°C. The resulting solution was poured into 20 ml of diethyl ether and cooled to -70°C, resulting in the precipitation of a solid component. This precipitate was recovered by centrifugation (5000 rpm), dissolved in 0.5 ml of tetrahydrofuran (THF), and then reprecipitated in diethyl ether at -70°C. The resulting precipitate was dried in vacuo to obtain the compound of the following formula:

[0052] [ka]

[0053] The designed molecular weight of this acrylic polymer was approximately 2,200.

[0054] (Comparative Synthesis Example 1) <Synthesis of (meth)acrylic polymer> A mixture of 4 g of glycidyl acrylate, 6 g of 2-ethylhexyl acrylate, 1.67 g of S,S-dibenzyltrithiocarbonate, 90 mg of azobisisobutyronitrile (AIBN), 150 mg of lithium bromide monohydrate (LiBr·HO), and 14 g of N-methyl-2-pyrrolidone (NMP) was polymerized under a carbon dioxide atmosphere at 1 atmosphere pressure and stirred at 70°C for 20 hours. The resulting solution was poured into 150 ml of methanol and cooled to -70°C, resulting in the precipitation of a solid component. This precipitate was recovered by centrifugation (4800 rpm), dissolved in 5 ml of tetrahydrofuran (THF), and then reprecipitated in 125 ml of methanol at -70°C. The resulting precipitate was dried in vacuo to obtain the compound of the following formula:

[0055] [ka]

[0056] The resulting polymer had a designed molecular weight of about 2030 and was 7.46 g of an acrylic polymer having a 2-ethylhexyl group and an ethylene carbonate structure in the side chain, as shown in the following formula:

[0057] (Comparative Synthesis Example 2) <Synthesis of (meth)acrylic polymer> 1 g of methoxytriethylene glycol acrylate, 0.242 g of S,S-dibenzyltrithiocarbonate, 9 mg of azobisisobutyronitrile (AIBN), and 1.4 g of N-methyl-2-pyrrolidone (NMP) were mixed and stirred under a nitrogen atmosphere at 70°C for 20 hours to carry out a polymerization reaction. The solution after the reaction was poured into 15 ml of diethyl ether and cooled to -70°C, whereupon a solid component precipitated. This precipitate was recovered by centrifugation (5000 rpm), dissolved in 0.5 ml of tetrahydrofuran (THF), and then reprecipitated in diethyl ether at -70°C. The resulting precipitate was dried in vacuum to obtain the compound of the following formula:

[0058] [ka]

[0059] The designed molecular weight of this acrylic polymer was approximately 2,000.

[0060] (Comparative Synthesis Example 3) <Synthesis of (meth)acrylic polymer> 1 g of 2-ethylhexyl acrylate, 0.24 g of S,S-dibenzyltrithiocarbonate, 9 mg of azobisisobutyronitrile (AIBN), and 1.4 g of N-methyl-2-pyrrolidone (NMP) were mixed and stirred at 70°C for 20 hours under a nitrogen atmosphere to carry out a polymerization reaction. The reaction solution was poured into 15 ml of methanol and cooled to -70°C, resulting in the precipitation of a solid component. This precipitate was recovered by centrifugation (5000 rpm), dissolved in 0.5 ml of tetrahydrofuran (THF), and then reprecipitated in diethyl ether at -70°C. The resulting precipitate was dried in a vacuum to obtain the compound of the following formula:

[0061] [ka]

[0062] The designed molecular weight of this acrylic polymer was approximately 2,000.

[0063] (Comparative Synthesis Example 4) <Synthesis of (meth)acrylic polymer> 1 g of glycidyl acrylate, 0.243 g of S,S-dibenzyltrithiocarbonate, 9 mg of azobisisobutyronitrile (AIBN), 15 mg of lithium bromide monohydrate (LiBr·HO), and 1.4 g of N-methyl-2-pyrrolidone (NMP) were mixed and polymerized under a carbon dioxide atmosphere at 1 atmosphere pressure for 20 hours with stirring at 70°C. The resulting solution was poured into 20 ml of diethyl ether and cooled to -70°C, resulting in the precipitation of a solid component. This precipitate was recovered by centrifugation (5000 rpm), dissolved in 0.5 ml of tetrahydrofuran (THF), and then reprecipitated in diethyl ether at -70°C. The resulting precipitate was dried in vacuo to obtain the compound of the following formula:

[0064] [ka]

[0065] The designed molecular weight of this acrylic polymer was approximately 2,000.

[0066] [Glass transition temperature] The glass transition temperatures (Tg [°C]) of the acrylic polymers obtained in Synthesis Example 1 and Comparative Synthesis Examples 1 to 4 were measured using a thermogravimetric differential thermal analyzer (TA5000, manufactured by TA Instruments Inc.). The results are shown in Table 1.

[0067] [Relative permittivity and dielectric loss tangent] The acrylic polymers obtained in Synthesis Example 1 and Comparative Synthesis Examples 1 to 4 were sandwiched and fixed between 5 cm diameter stainless steel plates with a gap of 100 to 1000 μm to prepare measurement samples. These measurement samples were connected to an LCR meter ("IM3523" manufactured by Hioki E.E. Corporation), and the relative permittivity and dielectric loss tangent were measured at room temperature and a frequency of 1 kHz. The results are shown in Table 1.

[0068] [Table 1]

[0069] As shown in Table 1, when a polyalkylene glycol chain and a cyclic carbonate structure were introduced as side chains into a (meth)acrylic polymer (Synthesis Example 1), a (meth)acrylic polymer with a large relative dielectric constant and a small dielectric dissipation factor was obtained.

[0070] On the other hand, when an alkyl chain was introduced instead of a polyalkylene glycol chain (Comparative Synthesis Examples 1 and 3), the dielectric constant did not increase sufficiently. Furthermore, when only a polyalkylene glycol chain was introduced as a side chain (Comparative Synthesis Example 2) and when only a cyclic carbonate structure was introduced (Comparative Synthesis Example 4), the dielectric loss tangent increased. In particular, when only a polyalkylene glycol chain was introduced as a side chain (Comparative Synthesis Example 2), the dielectric constant did not increase sufficiently.

[0071] (Synthesis Example 2) <Synthesis of (meth)acrylic polymer> A 200 mL flask was charged with 8 g (62.4 mmol) of glycidyl acrylate, 16 g (33.2 mmol) of polyethylene glycol methoxyacrylate (degree of polymerization 9), 1.22 g (10.5 mmol) of hydroxyethyl acrylate, 0.94 g of azobisisobutyronitrile (AIBN), 0.47 g of lithium bromide monohydrate (LiBr·HO), and 93 mL of N-methyl-2-pyrrolidone (NMP). Degassing and carbon dioxide introduction were repeated three times. After adjusting the atmosphere in the flask to 1 atm of carbon dioxide, the polymerization reaction was carried out with stirring at 80°C for 10 hours. The reaction solution was poured into 800 mL of diethyl ether to precipitate a solid component. This precipitate was collected, dried under vacuum, and then dissolved in acetonitrile. The resulting solution was filtered through a 0.2 μm filter. The filtrate was poured into diethyl ether to reprecipitate the solid component. The resulting precipitate was dried under vacuum to obtain the compound of the following formula:

[0072] [ka]

[0073] The weight average molecular weight of this acrylic polymer was measured by gel permeation chromatography (GPC) and found to be 3600 in terms of standard polystyrene.

[0074] (Synthesis Example 3) <Synthesis of crosslinking agent> 100 g of polycaprolactone-grafted polypropylene glycol was placed in a three-necked recovery flask and stirred in a nitrogen stream in an oil bath at 90°C. 7.45 g of 1,3-bis(isocyanatomethyl)cyclohexane (Takenate 600, manufactured by Mitsui Chemicals, Inc.) was slowly added dropwise to the resulting solution over 1 hour, and the mixture was stirred for an additional 2 hours to obtain an oligomer.

[0075] A three-necked recovery flask was charged with 16.66 g of 1,3-bis(isocyanatomethyl)cyclohexane (Mitsui Chemicals, Inc., "Takenate 600") and stirred in a 90°C oil bath under a nitrogen stream. A solution of 80 g of the oligomer in 80 g of toluene was slowly added dropwise to the resulting solution over 2 hours, followed by stirring for an additional 2 hours. The liquid temperature was then lowered to 40°C, and 10.95 g of 2-butanone oxime (Tokyo Chemical Industry Co., Ltd.) was slowly added dropwise, ensuring that the liquid temperature did not exceed 60°C. After the addition was complete, the mixture was stirred at 40°C for 5 hours to obtain a crosslinking agent consisting of polypropylene glycol (Mn: 5422) with end-blocked isocyanate groups. This crosslinking agent was added to butyl acetate to prepare a 50% by mass crosslinking agent solution.

[0076] Example 1 <Preparation of (meth)acrylic polymer-containing polyethylene glycol film> 27.29 g of the crosslinker solution obtained in Synthesis Example 3 (crosslinker concentration: 50% by mass), 5.43 g of polyrotaxane having caprolactone side chains ("SH3400P" manufactured by ASM Corporation, ring-shaped molecule: cyclodextrin having caprolactone side chains, axial molecule: polyethylene glycol (molecular weight: 35,000), terminal group: adamantane group), 1.27 g of polyoxypropylene diol (manufactured by Wako Pure Chemical Industries, Ltd., polypropylene glycol 700, diol type, average molecular weight: approximately 700), 3.62 g of polyoxypropylene monobutyl ether (manufactured by Sigma-Aldrich Corporation, polypropylene glycol monobutyl ether 1K, monool, average molecular weight: approximately 1,000), 0.40 g of a silicone additive (Gelest "DBL-C31," a silicone modified at both ends with alcohol: caprolactone-dimethylsiloxane-caprolactone block copolymer, a toluene solution with a solids concentration of 30% by weight), 0.80 g of a hydrolysis inhibitor (Nisshinbo Chemical Inc. "Carbodilite V-09GB," a toluene solution with a concentration of 30% by weight), 0.48 g of an antioxidant (BASF "Irganox 1726," 2,4-bis(dodecylthiomethyl)-6-methylphenol), and 0.40 g of a catalyst solution containing 3% by weight of dibutyltin dilaurate in toluene were dissolved in 9.60 g of methyl cellosolve and stirred to obtain a homogeneous solution. To this solution, the acrylic polymer having polyethylene glycol chains, ethylene carbonate structures, and hydroxyethyl groups in its side chains obtained in Synthesis Example 2 was added to obtain a resin solution with a concentration of 20% by weight. After degassing the resin solution, it was coated onto a substrate film using a slit die coater, and the resulting coating was cured by standing in an oven at 130°C under reduced pressure for 5 hours. The resulting cured film was then peeled off from the substrate film. The thickness of the cured film was 0.05 mm.

[0077] (Comparative Example 1) <Preparation of polyethylene glycol film> A cured film was obtained in the same manner as in Example 1, except that the acrylic polymer having a polyethylene glycol chain, an ethylene carbonate structure, and a hydroxyethyl group in the side chain obtained in Synthesis Example 2 was not used and the amount of methyl cellosolve was changed to 10.80 g. The thickness of this cured film was 0.05 mm.

[0078] (Comparative Example 2) A cured film was obtained in the same manner as in Example 1, except that the acrylic polymer having only methoxytriethylene glycol chains in the side chains obtained in Comparative Synthesis Example 2 was used instead of the acrylic polymer having polyethylene glycol chains, ethylene carbonate structures, and hydroxyethyl groups in the side chains obtained in Synthesis Example 2. The thickness of this cured film was 0.05 mm.

[0079] (Comparative Example 3) A cured film was obtained in the same manner as in Example 1, except that the acrylic polymer having only 2-ethylhexyl groups in the side chains obtained in Comparative Synthesis Example 3 was used instead of the acrylic polymer having polyethylene glycol chains, ethylene carbonate structures, and hydroxyethyl groups in the side chains obtained in Synthesis Example 2. The thickness of this cured film was 0.05 mm.

[0080] Comparative Example 4 A cured film was obtained in the same manner as in Example 1, except that the acrylic polymer having only an ethylene carbonate structure in the side chain obtained in Comparative Synthesis Example 4 was used instead of the acrylic polymer having a polyethylene glycol chain, an ethylene carbonate structure, and a hydroxyethyl group in the side chain obtained in Synthesis Example 2. The thickness of this cured film was 0.05 mm.

[0081] [Dielectric constant] Gold was evaporated onto both sides of the resulting cured film using an auto-fine coater (JEOL Ltd., "JEC-3000FC") to form electrode films (15 mm diameter). The capacitance was measured using a precision impedance analyzer (Agilent Corp., "4294A") with a dielectric constant measurement probe, and the relative dielectric constant was calculated. The results are shown in Table 2.

[0082] [Volume resistivity] Gold was vapor-deposited on both sides of the obtained cured film using an autofine coater (JEC-3000FC manufactured by JEOL Ltd.) to prepare electrode films (8 mm diameter), and the volume resistivity was measured using a microcurrent meter (Super Insulation Meter SM7120 manufactured by Hioki E.E. Corporation. The results are shown in Table 1.

[0083] [Breaking strength] From the obtained cured film, dumbbell-shaped No. 7 test pieces were prepared in accordance with JIS K6251. These test pieces were subjected to a tensile test using a tensile testing machine (Shimadzu Corporation, Autograph AGS-X 10N) under conditions of a grip distance of 20 mm and a tensile speed of 100 mm / min until fracture, and the fracture strength was calculated from the stress value at the time of fracture. The results are shown in Table 2.

[0084] [Initial modulus of elasticity] Dumbbell-shaped No. 7 test specimens were prepared from the resulting cured films in accordance with JIS K6251. Tensile tests were performed on these specimens using a tensile testing machine (Shimadzu Corporation, Autograph AGS-X 10N) under conditions of a grip distance of 20 mm and a tensile speed of 100 mm / min until the specimens reached 100% of their effective length. They were then retracted at the same speed as the elongation until they reached 0%, and a stress-strain curve was obtained. The stress-strain curve was linearly approximated over the range of 1% to 5% elongation, and the slope was taken as the initial modulus of elasticity. The results are shown in Table 2.

[0085] [Table 2]

[0086] As shown in Table 2, when an acrylic polymer having a polyethylene glycol chain and an ethylene carbonate structure in the side chain was added to a dielectric elastomer layer made of a cured product of a resin component containing polyrotaxane (Example 1), it was confirmed that the relative dielectric constant was improved compared to when no acrylic polymer was added (Comparative Example 1). It was also confirmed that the volume resistivity and breaking strength were maintained, and that the mechanical properties suitable for a polymer actuator were exhibited. Furthermore, it was confirmed that the initial elastic modulus was reduced, and that the properties as an elastomer (particularly flexibility) were not impaired.

[0087] On the other hand, when an acrylic polymer having only methoxytriethylene glycol chains in the side chains was added to the dielectric elastomer layer (Comparative Example 2), dielectric breakdown occurred during measurement of the dielectric constant and volume resistivity, and the breaking strength was also found to be lower than when no acrylic polymer was added (Comparative Example 1). Furthermore, when an acrylic polymer having only 2-ethylhexyl groups in the side chains was added (Comparative Example 3), the dielectric constant was found to be lower and the volume resistivity was found to be higher than when no acrylic polymer was added (Comparative Example 1). Furthermore, when an acrylic polymer having only ethylene carbonate structures in the side chains was added (Comparative Example 4), the volume resistivity and breaking strength were found to be lower than when no acrylic polymer was added (Comparative Example 1).

[0088] From the above results, it was found that by adding a (meth)acrylic polymer having a polyalkylene glycol chain and a cyclic carbonate structure in its side chain to a dielectric elastomer layer consisting of a cured resin component containing polyrotaxane, it is possible to increase the dielectric constant and suppress a decrease in volume resistivity while maintaining the properties of the elastomer (especially flexibility). [Industrial Applicability]

[0089] As described above, according to the present invention, it is possible to form a dielectric elastomer layer that improves the dielectric constant and suppresses a decrease in volume resistivity while maintaining flexibility (elastic modulus). Therefore, since the polymer actuator of the present invention includes such a dielectric elastomer layer, it can be used in a variety of fields, such as industrial and nursing robots, artificial muscles, sensors, and haptics.

Claims

1. a dielectric elastomer layer and two electrodes disposed on opposite sides of the dielectric elastomer layer; A polymer actuator characterized in that the dielectric elastomer layer is made of a cured product of a composition containing a resin component including polyrotaxane and a (meth)acrylic polymer having a polyalkylene glycol chain and a cyclic carbonate structure in its side chain.

2. The (meth)acrylic polymer is represented by the following formula (1): 【Chemical 1】 (In the above formula, R １ represents a hydrogen atom or a methyl group, AO represents an alkyleneoxy group, R ２ represents an alkyl group, and p represents the degree of polymerization of the alkyleneoxy group. and a repeating unit represented by the following formula (2): 【Chemistry 2】 (In the above formula, R ３ represents a hydrogen atom or a methyl group, R ４ represents an alkylene group, and B represents the cyclic carbonate structure.

2. The polymer actuator according to claim 1, wherein the polymer actuator comprises a repeating unit represented by the formula:

3. 3. The polymer actuator according to claim 1, wherein the cyclic carbonate structure is an ethylene carbonate structure.

4. A sensor comprising the polymer actuator according to any one of claims 1 to 3.

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