WO2025126940A1 - Polymer, aromatic polyamide, molded object, film, vibration sensor, speaker, and structural-health monitoring system - Google Patents

Abstract

[Problem] To provide a polymer, an aromatic polyamide, a molded object, and a film which have excellent piezoelectric properties and mechanical properties. [Solution] A polymer that has a repeating unit in which hydrogen-bonding groups are bonded to ring-member atoms and the number of atoms present on the shortest of paths which each connect an atom of one hydrogen-bonding group to an atom of another hydrogen-bonding group is an odd number, and that has a residual polarization of 15 mC/m2 to 300 mC/m2.

Description

Polymers, aromatic polyamides, moldings, films, vibration sensors, speakers, structural health monitoring systems

The present invention relates to ferroelectric polymers, aromatic polyamides, molded bodies, and films.

Ferroelectric materials are used in various sensors and image recording applications due to their piezoelectricity and pyroelectricity. Conventionally, inorganic materials such as PbZrTiO ₃ (PZT) and polymeric materials such as vinylidene fluoride polymers such as polyvinylidene fluoride (PVDF), polylactic acid, and odd-numbered nylon are known as ferroelectric materials. Among these, inorganic materials have advantages in terms of characteristics such as excellent pyroelectricity and heat resistance, but are poor in flexibility and difficult to mold, making them unsuitable as materials for large-area, thin-film, and complex-shaped piezoelectric elements.
On the other hand, while polymer-based materials have lower piezoelectric and pyroelectric coefficients than inorganic materials, their specific heat and dielectric constant are small and therefore their performance index is good. They are therefore used as piezoelectric elements in applications that require flexibility, light weight, and large area, such as wearable devices, and their applications as memory materials, etc. are being investigated.
In the case of polymer-based materials, remanent polarization is formed by aligning the dipoles in the polymer in one direction, and ferroelectricity is expressed. In many cases, the orientation of the dipoles is achieved by controlling the higher-order structure of the polymer chains through the molecular orientation and crystal system in the material. For example, the polymer is heated to a temperature above the glass transition temperature and below the melting point so that the polymer chains can move, and then an electric field is applied to the polymer for a certain period of time to fix the structure while maintaining the electric field, which is called poling treatment, or mechanical uniaxial or biaxial stretching. However, the higher-order structure is destroyed by stress or heat generated in the material during use, which deactivates the ferroelectricity, and this limits the durability and usage environment, which is an issue for polymer-based materials.

Aromatic polyamides are polymeric materials that are expected to have high durability in addition to ferroelectricity. In particular, fully aromatic polyamides have excellent heat resistance and chemical resistance, and are therefore used as heat-resistant and highly elastic fibers. On the other hand, because they have amide bonds with large dipole moments, it is expected that they will exhibit ferroelectricity similar to that of odd-numbered nylons by appropriately selecting the aromatic structure. As an example of such a material, for example, Patent Document 1 discloses a polyamide film with residual polarization. Patent Document 2 discloses a polyamide-based liquid crystal alignment agent varnish. Patent Document 3 discloses a mixture of ferroelectric aromatic polyamide and liquid crystal polymer. Patent Document 4 discloses a block copolymer of ferroelectric aromatic polyamide and a polymer having a melting point and glass transition temperature. Patent Document 5 discloses a manufacturing method in which an aliphatic polyamide dissolved in an organic solvent is applied to a substrate, dried, the resulting film is heat-treated and cooled, and then uniaxially stretched to obtain a piezoelectric polyamide film.

Japanese Patent Application Publication No. 8-302036 JP 2002-363280 A JP 2002-37889 A JP 2001-279117 A JP 2020-167203 A

However, the aromatic polyamides disclosed in Patent Documents 1 and 2 are not fully aromatic polyamides, and the inclusion of alkyl moieties in the structure may reduce the dielectric constant and residual polarization. In addition, the aromatic polyamide-based materials disclosed in Patent Documents 3 and 4 introduce a flexible polymer structure to make the glass transition temperature and/or melting point of the polymer industrially easy to handle, but this may reduce the content of aromatic polyamide moieties and reduce ferroelectricity. The manufacturing method for piezoelectric films disclosed in Patent Document 5 is limited to aliphatic polyamides, and due to differences in the solubility and packing properties of the polymers, it is difficult to apply the described manufacturing method to fully aromatic polyamides. In addition, due to the above-mentioned structural differences, all of the materials disclosed in Patent Documents 1 to 5 may have inferior durability to heat and stress compared to fully aromatic polyamides.

The present invention aims to provide a molded article and/or film with excellent piezoelectric properties, mechanical properties, and heat resistance by forming a ferroelectric aromatic polyamide in which each amide group in the repeating unit is connected via an odd number of atoms and the amide group is bonded to an aromatic ring atom.

In order to achieve the above object, the present invention is characterized as follows.
(1) A polymer containing a structure represented by the following chemical formula (I) as a repeating unit, which satisfies the following (i) and (ii):
(i): The hydrogen-bonding group A in the chemical formula (I) is bonded to a ring atom.
(ii): In the chemical formula (I), the number of atoms on the shortest path connecting the two A atoms is odd.
Chemical formula (I):

A is a hydrogen-bonding group, and B ¹ and B ² are n-membered ring groups (n is a natural number of 5 or more and 10 or less).
(2) The polymer according to (1), having a remanent polarization of 15 mC/ ^m2 or more and 300 mC/ ^m2 or less.
(3) The polymer according to (1) or (2), wherein the hydrogen-bonding group A is at least one of an amide group, a urea group, and a urethane group.
(4) An aromatic polyamide, in which the hydrogen-bonding group A is an amide group, and both B ¹ and B ² are aromatic groups.
(5) An aromatic polyamide containing a structure represented by the following chemical formula (II) as a repeating unit, which satisfies the following (iii) and (iv) and has a remanent polarization of 15 mC/m2 or ^more .
(iii): X in the chemical formula (II) is bonded to an aromatic ring atom.
(iv): In the chemical formula (II), the number of atoms on the shortest path connecting the two X atoms is odd.
Chemical formula (II):

X is an amide group, and Ar ¹ and Ar ² are aromatic groups.
(6) The polymer and/or aromatic polyamide according to any one of (1) to (5), wherein the structure in the repeating unit satisfies at least any one of the following (v) to (viii):
(v): An electron-donating group is bonded to an atom on the shortest path along the bonds connecting the N atoms of the two amide groups.
(vi): An electron-withdrawing group is bonded to an atom on the shortest path along the bond connecting the two C atoms of the amide groups.
(vii): An electron-withdrawing group is bonded to an atom that is not on the shortest path along the bond connecting the two N atoms of the amide groups.
(viii): An electron-donating group is bonded to an atom that is not on the shortest path along the bond connecting the two C atoms of the amide groups.
(7) The polymer and/or aromatic polyamide according to any one of (1) to (6) above, which has a molecular skeleton structure represented by the following chemical formula (III):
Chemical formula (III):

Ar ³ and Ar ⁴ are groups containing the molecular skeleton structures shown in chemical formulas (IV) to (VIII).
Chemical formula (IV):

Chemical formula (V):

Chemical formula (VI):

Chemical formula (VII):

R ¹ is any group satisfying (v) to (viii) in (6).
Chemical formula (VIII):

^R2 is any group satisfying (v) to (viii) in (6).
(8) The polymer and/or aromatic polyamide according to any one of (1) to (7) above, having a structure represented by the following chemical formula (IX):
Chemical formula (IX):

Ar ⁵ is a group including a structure represented by any one of chemical formulas (X) to (XII), and Ar ⁶ is a group including a structure represented by any one of chemical formulas (XIII) to (XV).
Chemical formula (X):

^R3 is --H or an electron donating group, and ^R4 is an electron withdrawing group.
Chemical formula (XI):

^R5 is an electron donating group.
Chemical formula (XII):

^R6 is an electron withdrawing group.
Chemical formula (XIII):

R ⁷ is an electron withdrawing group and R ⁸ is --H or an electron donating group.
Chemical formula (XIV):

^R9 is an electron withdrawing group.
Chemical formula (XV):

^R10 is an electron donating group.
(9) The polymer and/or aromatic polyamide according to any one of (1) to (8), which contains at least one group selected from the group consisting of a perfluoroalkyl group having from 1 to 3 carbon atoms, a nitro group, a cyano group, and a sulfone group.
(10) The polymer and/or aromatic polyamide according to any one of (1) to (9), having a glass transition temperature of 130° C. or higher and 400° C. or lower.
(11) A molded article comprising as a main component the polymer and/or aromatic polyamide according to any one of (1) to (10).
(12) The molded article according to (11), wherein at least one of the piezoelectric constants _d31 and _d33 is greater than 0 pC/N and less than or equal to 50.0 pC/N.
(13) A film comprising as a main component the polymer and/or aromatic polyamide according to (1) to (10).
(14) The film according to (13), characterized in that the elastic modulus measured by AFM is 4.0 GPa or more and 15.0 GPa or less.
(15) The film according to (13), having a normalized molecular orientation MORc of 1.1 or more and 15 or less.
(16) The molded body according to (11), in which, when the electrostatic constant after heat treatment at 150° C. for 10 minutes is d', the larger of the absolute values of changes in the piezoelectric constant due to heat treatment, |(d ₃₁ - d' ₃₁ )/d ₃₁ | and |(d ₃₃ - d' ₃₃ )/ _d 33 |, is 0 or more and 0.5 or less.
(17) A piezoelectric element comprising the molded article according to (11) and/or the film according to (13).
(18) An actuator comprising the molded article according to (11) and/or the film according to (13).
(19) A vibrator comprising the molded article according to (11) and/or the film according to (13).
(20) A vibration sensor comprising the piezoelectric element according to (17).
(21) A speaker having an actuator as described in (18).
(22) A structural health monitoring system comprising at least the vibration sensor according to (20) and a communication device, the vibration sensor detecting the vibration state of a structure and diagnosing the structure.

According to the present invention, the polymer and/or aromatic polyamide of the present invention can provide a molded article and/or film that has excellent piezoelectric properties, mechanical properties, and heat resistance. Therefore, the polymer, aromatic polyamide, molded article, and film of the present invention can be suitably used as components for piezoelectric elements, actuators, vibrators, and the like.

The polymer of the present invention is a polymer containing a structure represented by chemical formula (I) as a repeating unit, and is characterized by satisfying the following (i) and (ii):
(i): The hydrogen-bonding group A in the chemical formula (I) is bonded to a ring atom.
(ii): In the chemical formula (I), the number of atoms on the shortest path connecting the two A atoms is odd.

By satisfying these characteristics, it is possible to simultaneously achieve excellent mechanical properties and thermal stability derived from the hydrogen-bonding groups and ferroelectricity due to the molecular shape and orientation.
From the viewpoint of exhibiting excellent ferroelectricity, the polymer of the present invention preferably has a remanent polarization of 15 mC/m ² or more and 300 mC/m ² or less. In addition, in order to obtain efficient hydrogen bonding, the polymer of the present invention preferably has the hydrogen bonding group A in chemical formula (I) being at least one of an amide group, a urea group, and a urethane group.
The aromatic polyamide of the present invention is characterized in that it contains a structure represented by the following chemical formula (II) as a repeating unit and satisfies the following (iii) and (iv).
(iii): X in the chemical formula (II) is bonded to an aromatic ring atom.
(iv): In the chemical formula (II), the number of atoms on the shortest path connecting the two X atoms is odd.
Chemical formula (II):

X is an amide group, and Ar ¹ and Ar ² are aromatic groups.

By satisfying these characteristics, it is possible to combine the excellent mechanical properties and thermal stability derived from aromatic polyamide with the ferroelectric properties resulting from molecular shape and orientation.

Here, the aromatic ring member atom is a constituent atom forming a ring structure in a cyclic molecular structure having aromaticity. In addition, the path connecting the atoms between two Xs in chemical formula (II) refers to a path connecting the atoms present from the atom to which one X is bonded to the atom to which the other X is bonded in two adjacent Xs along the bond. The shortest path refers to a path in which the number of atoms present on the path connecting the atoms between the two Xs is the smallest. For example, when X is bonded to the 1st and 3rd positions of the benzene ring as Ar ¹ and Ar ² in chemical formula (II) (the number of atoms on the shortest path is 3), or when X is bonded to the 2nd and 7th positions of the naphthalene ring (the number of atoms on the shortest path is 5), both of the above (iii) and (iv) are satisfied, but when X is bonded to the 1st and 4th positions of the benzene ring (the number of atoms on the shortest path is 4), (iv) is not satisfied.

The polymer and/or aromatic polyamide of the present invention preferably has a lower limit of residual polarization of 15 mC/m ² or more. More preferably, the lower limit of residual polarization is 20 mC/m ² or more, and even more preferably, 25 mC/m ^2. If the lower limit of residual polarization is less than 15 mC/m ² , the ferroelectricity is low, so that piezoelectricity may not be obtained when the molded body or film is formed. In addition, the upper limit of residual polarization is preferably 300 mC/m ² or less, and more preferably 50 mC/m ^2. The range of residual polarization is preferably 15 mC/m ² or more and 300 mC/m ² or less, more preferably 20 mC/m ² or more and 300 mC/m ² or less, more preferably 25 mC/m ² or more and 300 mC/m ² or less, and most preferably 25 mC/m ² or more and 50 mC/m ² or less. In order to set the remanent polarization within the above range, it is important that the aromatic polyamide contains the above-mentioned structure and that the aromatic polyamide is subjected to a treatment such as stretching or poling to improve the packing and anisotropy of the aromatic polyamide. It is preferable that the structure in the repeating unit represented by chemical formula (II) of the aromatic polyamide of the present invention satisfies at least any one of the following (v) to (viii):

(v): An electron-donating group is bonded to an atom on the shortest path along the bonds connecting the N atoms of the two amide groups.
(vi): An electron-withdrawing group is bonded to an atom on the shortest path along the bond connecting the two C atoms of the amide groups.
(vii): An electron-withdrawing group is bonded to an atom that is not on the shortest path along the bond connecting the two N atoms of the amide groups.
(viii): An electron-donating group is bonded to an atom that is not on the shortest path along the bond connecting the two C atoms of the amide groups.

Here, the electron-withdrawing group and the electron-donating group are determined by the Hammett substituent constant (Chem. Rev. 1991, 91, 99-257, etc.), and a functional group with a positive σ _p value is an electron-withdrawing group, and a functional group with a negative σ _p value is an electron-donating group. In the present invention, the electron-withdrawing group is a group containing at least one of a perfluoroalkyl group, a sulfone group, a nitro group, and a cyano group having 1 to 3 carbon atoms, and the electron-donating group is preferably a group containing at least one of an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a hydroxyl group, but is not limited to these structures. By satisfying at least one of the above (v) to (viii), a dipole moment is induced to increase the remanent polarization, and the piezoelectric properties can be improved.

An example of an aromatic polyamide that satisfies these characteristics is a meta-junction type wholly aromatic polyamide. From the viewpoint of polymerizability and availability of raw materials, it is particularly preferable that the polyamide has a structure represented by the following chemical formula (III).
Chemical formula (III):

Ar ³ and Ar ⁴ are groups containing the molecular skeleton structures shown in chemical formulas (IV) to (VIII), and any group satisfying any of the above (v) to (viii) may be bonded to each of the molecular skeleton structures.
Chemical formula (IV):

Chemical formula (V):

Chemical formula (VI):

Chemical formula (VII):

R ¹ is any group satisfying the above (v) to (viii).
Chemical formula (VIII):

^R2 is any group satisfying the above (v) to (viii).

Among the above, it is particularly preferable that the structural unit represented by the following chemical formula (IX) is contained in order to realize high rigidity.
Chemical formula (IX):

Ar ⁵ is a group including a structure represented by any one of chemical formulas (X) to (XII), and Ar ⁶ is a group including a structure represented by any one of chemical formulas (XIII) to (XV).
Chemical formula (X):

^R3 is --H or an electron donating group, and ^R4 is an electron withdrawing group.
Chemical formula (XI):

^R5 is an electron donating group.
Chemical formula (XII):

^R6 is an electron withdrawing group.
Chemical formula (XIII):

R ⁷ is an electron withdrawing group and R ⁸ is --H or an electron withdrawing group.
Chemical formula (XIV):

^R9 is an electron withdrawing group.
Chemical formula (XV):

^R10 is an electron donating group.

In the aromatic polyamide of the present invention, the number of repeating units containing the above-mentioned structure is preferably 80% or more and 100% or less of the total number of repeating units in the polymer. If the ratio of repeating units containing the above-mentioned structure is less than 80%, the orientation of the polymer chain and dipole moment may deteriorate, resulting in reduced ferroelectricity.

The polymer and/or aromatic polyamide of the present invention preferably has a glass transition temperature of 130°C or higher, more preferably 200°C or higher. The range is preferably 130°C or higher and 400°C or lower, more preferably 200°C or higher and 400°C or lower. By having a glass transition temperature of 130°C or higher and 400°C or lower, it is possible to prevent the ferroelectricity from decreasing due to heat or over time. In order to achieve a glass transition temperature of 130°C or higher and 400°C or lower, the aromatic polyamide may include the above-mentioned structure or the content of components with low glass transition temperatures may be reduced.

An embodiment of the present invention is a molded article and/or film that contains as a main component the polymer and/or aromatic polyamide of the present invention. Here, "containing as a main component the polymer and/or aromatic polyamide" means that the component contained in the largest amount in the molded article and/or film is the polymer and/or aromatic polyamide described in the present invention. The amount of the component is not particularly limited, but the lower limit is preferably 70% by weight or more, and more preferably 80% by weight or more, based on the entire film. The amount of the component is preferably in the range of 70% by weight to 100% by weight, and more preferably 80% by weight to 100% by weight, based on the entire film, so that the mechanical properties derived from the aromatic polyamide can be more effectively exhibited.

The molded article and/or film of the present invention may contain a ferroelectric material. When the molded article and/or film of the present invention contains a ferroelectric material, the ferroelectricity may be improved and excellent piezoelectric performance may be obtained. Here, the ferroelectric material may be either an organic material or an inorganic material. For example, organic ferroelectric materials include polyvinylidene fluoride (PVDF), copolymers of vinylidene fluoride and trifluoroethylene, nylon, etc., and inorganic ferroelectric materials include lead zirconate titanate (PZT), barium titanate (BTO), lead titanate (PTO), bismuth sodium titanate-barium titanate (BNT-BT), etc. It is preferable that the ferroelectric material contained is a material that has a larger remanent polarization than the polymer and/or aromatic polyamide of the present invention when poling treatment is performed under the same conditions.

Furthermore, it is preferable that the film of the present invention has a thickness of 1 μm or more and 200 μm or less. If the thickness is less than 1 μm, handling properties may deteriorate. If the thickness is more than 200 μm, flexibility may decrease, and workability as a film may decrease.

In the molded body of the present invention, at least one of the piezoelectric constants d ₃₁ and d ₃₃ is preferably greater than 0 pC/N as a lower limit, and more preferably 5 pC/N or more. Moreover, as an upper limit, it is preferably 50 pC/N or less, and more preferably 40 pC/N. As a range, it is preferable that it is greater than 0 pC/N and 50.0 pC/N or less, and more preferably greater than 0 pC/N and 40.0 pC/N or less. In the present invention, the measurement method of the piezoelectric constants d ₃₁ and d ₃₃ is not particularly limited as long as it is a method that can obtain sufficiently accurate values, and can be measured and determined by any method. For example, aluminum electrodes are vapor-deposited on the upper and lower surfaces of the measurement sample so that an overlapping area of 6 × 10 ^-5 m ² appears in a planar view. Two leads made of aluminum foil reinforced with insulating adhesive tape are bonded to each of the upper and lower planar electrodes using a conductive epoxy resin. Using a dynamic viscoelasticity measuring device, a piezoelectric signal that appears when a displacement is applied to both ends of the sample at a constant frequency and amplitude can be measured with a logger via a charge amplifier, and the amount of generated charge per unit area can be calculated. In order to set the piezoelectric constant of the molded article of the present invention within the above range, it is preferable to increase the residual polarization of the molded article by performing a poling treatment or an orientation treatment by stretching.

The elastic modulus of the film of the present invention, as measured by an atomic force microscope (AFM), is preferably 4.0 GPa or more as a lower limit, and more preferably 5.0 GPa or more. The upper limit is preferably 15.0 GPa or less, and more preferably 7.0 GPa or less. The elastic modulus is preferably in the range of 4.0 GPa to 15.0 GPa. More preferably, it is 5.0 GPa to 15.0 GPa, and even more preferably, it is 5.0 GPa to 15.0 GPa. If the elastic modulus is less than 4.0 GPa, it is likely to break or be damaged when used as a molded body or film. If the elastic modulus is greater than 15.0 GPa, it may become difficult to deform and piezoelectric properties may not be obtained. By setting the elastic modulus of the film within the above range, piezoelectricity with excellent response to strain and/or electric field changes can be obtained, the responsiveness of the sensor can be improved, and the vibration frequency of the vibrator can be made wider.

Here, the elastic modulus obtained by AFM is measured by performing force curve mapping measurement of AFM. AFM is a scanning probe microscope that obtains information about the surface of a sample by utilizing the atomic force between the sample and the probe (tip). While changing the distance between the sample and the probe attached to the cantilever, the force acting on the probe (the amount of deflection of the cantilever) is measured to obtain a force curve. This force curve contains various information about the sample surface, and various physicochemical properties of the sample surface can be evaluated by analyzing the force curve. Force curve mapping measurement obtains this force curve at multiple points on the sample surface by scanning parallel to the sample surface. The sample is fixed to the sample fixing stage of the AFM, and the shape image of the sample is measured in PeakForceQNM mode (a mode that automatically measures force curves at multiple points continuously). The elastic modulus of the sample can be evaluated by analyzing the elastic modulus using existing software based on the results of the force curve mapping measurement.

The normalized molecular orientation MORc of the film of the present invention is preferably 1.1 or more as a lower limit, more preferably 1.2 or more, and even more preferably 1.3 or more. The upper limit is preferably 15 or less, and even more preferably 2 or less. It is preferable that MORc is in the range of 1.1 to 15. More preferably, MORc is 1.2 to 15, and even more preferably, MORc is 1.3 to 15. Here, the normalized molecular orientation MORc is a value determined based on the molecular orientation degree MOR, which is an index showing the degree of orientation of polymer chains in the film. The molecular orientation degree MOR is measured by the following microwave measurement method.

That is, the polymer piezoelectric film is placed in a microwave resonant waveguide of a well-known microwave transmission type molecular orientation system, rotated 0 to 360° in a plane perpendicular to the direction of microwave propagation, and the microwave intensity transmitted through the sample is measured, thereby determining the molecular orientation ratio MOR.
The normalized molecular orientation MORc is the degree of molecular orientation MOR when the reference thickness tc is set to 50 μm, and can be calculated by the following formula.
MORc=(tc/t)×(MOR-1)+1
where tc is the reference thickness and t is the film thickness.
The normalized molecular orientation MORc can be measured by a known molecular orientation meter, for example, MOR-7015 manufactured by Oji Scientific Instruments Co., Ltd. When the film is a stretched film, the normalized molecular orientation MORc can be controlled by the stretching conditions such as the stretch ratio and stretching temperature of the film, and the film-forming conditions such as the temperature and speed. By setting the normalized molecular orientation MORc within the above range, the orientation and/or packing of the molecular chains in the film is improved, and excellent piezoelectricity can be obtained. In order to set the MORc within the above range, it is preferable that the main component of the molded body and/or film is the polymer and/or aromatic polyamide described in the present invention, or that the film is uniaxially stretched.
In the molded article and/or film of the present invention, when the piezoelectric constant after heat treatment at 150° C. for 10 minutes is d', the larger of the absolute values of the rate of change in the piezoelectric constant due to heat treatment |(d ₃₁ -d' ₃₁ )/d ₃₁ | and |(d ₃₃ -d' ₃₃ )/d ₃₃ | is preferably 0 to 0.5, more preferably 0 to 0.3, and even more preferably 0 to 0.2. By setting the rate of change in the piezoelectric constant due to heat treatment within the above range, the piezoelectric characteristics become less dependent on temperature conditions, and the performance of sensors and actuators can be stabilized under high temperature conditions or when used for a long time. In order to set the rate of change in the piezoelectric constant due to heat treatment within the above range, it is preferable that the molded article and/or film is mainly composed of the polymer and/or aromatic polyamide described in the present invention.
Here, the piezoelectric constants d' ₃₁ and d' ₃₃ after 10 minutes of heat treatment at 150°C can be measured in the same manner as _d31 and _d33 described above, except that the heat-treated molded body and/or film is used as the sample. The heat treatment of the molded body and/or film is preferably performed by leaving the molded body and/or film in a hot air oven set at 150°C for 10 minutes. The molded body and/or film of the present invention may contain organic-inorganic hybrid resins such as thermosetting resins, ultraviolet-curing resins, hydrolysis/condensation resins, and alkoxysilane compounds for the purpose of adjusting mechanical properties and density. Particles may also be included. Here, the particles may be either inorganic particles or organic particles. The inorganic particles are not particularly limited, but include oxides, silicides, nitrides, borides, chlorides, carbonates, etc. of metals or semimetals, and specific examples thereof include silica (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), zinc oxide (ZnO), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), antimony oxide (Sb ₂ O ₃ ), indium tin oxide (ITO), etc. In addition, for the purpose of increasing ferroelectric properties, lead zirconate titanate (PZT), barium titanate (BTO), lead titanate (PTO), bismuth sodium titanate-barium titanate (BNT-BT), etc. may be contained.

If it is necessary to identify the chemical structure, functional groups, or composition ratio of the polymers, aromatic polyamides, molded articles, films, and other contents of the present invention, each component separated using a combination of techniques such as chromatography, distillation, separation, and reprecipitation can be analyzed using a combination of nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), mass spectrometry (MS), elemental analysis, and single crystal structure analysis.

　The methods for producing the polymer, aromatic polyamide, molded body, and solution of the present invention are described below, but the present invention is not limited thereto.

Polymers and/or aromatic polyamides can be obtained by various known methods such as solution polymerization and precipitation polymerization. For example, when polymerizing aromatic polyamides by solution polymerization, the raw materials, acid dichloride and diamine, can be reacted in an aprotic solvent at low temperature to polymerize. Here, an aprotic solvent is a polar solvent that does not have proton (hydrogen ion) donating properties, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylisobutyramide, 3-methoxy-N,N-dimethylpropanamide, tetrahydrofuran, γ-butyrolactone, ethyl acetate, acetonitrile, dimethylformamide, and dimethylsulfoxide. In order to suppress the deactivation of the acid dichloride, it is preferable that the water content of the solvent used in polymerization is more than 0 ppm and less than 500 ppm (by mass, the same applies below), and more preferably more than 0 ppm and less than 200 ppm. Here, if the molar ratio of the acid dichloride and the diamine is equal, a polymer with an ultra-high molecular weight tends to be produced, so it is preferable to adjust the molar ratio so that one is 96.0 to 99.8% of the other, more preferably 96.0 to 99.0%. If polymerization is carried out at this molar ratio, the diamine will be in excess relative to the acid dichloride, and the terminal functional group will be an amino group. In addition, the polymerization reaction of aromatic polyamide is accompanied by heat generation, so it is preferable to keep the temperature of the solution during polymerization at 40°C or less. If it exceeds 40°C, side reactions may occur and the degree of polymerization may not increase sufficiently. It is more preferable to keep the temperature of the solution during polymerization at 30°C or less.

Here, when acid dichloride and diamine are used as raw materials, hydrogen chloride is produced as a by-product as the reaction proceeds, and the resulting aromatic polyamide solution is a highly acidic solution. This solution is highly corrosive, and if used as is, it may corrode components such as metal substrates used in the manufacturing process of molded bodies and films, making them unusable. Methods for removing the by-product hydrogen chloride include a method of neutralizing and removing hydrogen chloride by adding a neutralizing agent during polymerization, and a method of precipitating and isolating the polymer. When neutralizing and removing hydrogen chloride during polymerization, for example, a method of neutralizing with an inorganic neutralizing agent such as lithium carbonate, calcium carbonate, or calcium hydroxide can be used. When neutralizing with an inorganic neutralizing agent, the solution contains inorganic salts (e.g., lithium chloride) produced by the neutralization reaction. These inorganic salts ionize in the solvent and coordinate with the amide groups of the aromatic polyamide, acting as a dissolving aid in the solvent, and are therefore effective in improving the pot life of the solution and suppressing the aggregation of the polymer during molding. However, since a washing process for removing the inorganic salts is required during the molding process, it may not be usable depending on the dimensions of the molded body and/or film and the manufacturing process.

In addition, when isolating the polymer by precipitating it, the polymer solution obtained by solution polymerization is mixed with a large amount of a poor solvent such as water to precipitate the polymer as a solid, and the polymer can be separated from the solution by filtration or other methods to separate the polymer and hydrogen chloride. The isolated polymer can be redissolved in the aprotic solvent mentioned above to make it into a solution. By precipitating the polymer and separating it from the hydrogen chloride, it does not contain neutralization products generated by the reaction of the neutralizing agent with hydrogen chloride, and the amount of impurities remaining in the molded product or film can be reduced.

The method of introducing electron-withdrawing groups and/or electron-donating groups into the aromatic polyamide of the present invention so as to satisfy at least one of the above (v) to (viii) includes a method of polymerizing an aromatic polyamide using a monomer in which an electron-withdrawing group and/or an electron-donating group has been substituted at the desired position as a raw material, and a method of introducing the groups by polymerizing the aromatic polyamide as a raw material and then functionalizing it. When introducing the groups by functionalizing an aromatic polyamide, a method of derivatizing the desired functional group from a leaving group such as -H or a halogen group introduced on the aromatic group as a starting point is included. However, depending on the functional group conversion reaction used, the position selectivity may be poor, resulting in an unintended structure, or the reactivity may be insufficient, resulting in a low introduction rate of the functional group. For this reason, a method of using a monomer in which an electron-withdrawing group and/or an electron-donating group has been substituted at the desired position as a raw material is preferable.

The molded article and/or film of the present invention is preferably obtained by filling a solution containing the polymer and/or aromatic polyamide of the present invention into a mold or casting it onto a substrate, followed by curing. There are no limitations on the material or shape of the mold or substrate, or the filling and/or casting method, and any method can be used depending on the purpose and use of the molded article and/or film.

The film of the present invention can be obtained by dissolving the polymer obtained as described above in a solvent and applying the solution to a substrate to form a film. There are no limitations on the solvent as long as it dissolves the polymer, but it is preferable that the solvent is an aprotic solvent. The solution may also contain the above-mentioned resin, electrolyte, particles, etc., in order to improve the properties of the film. Examples of film formation methods include a dry-wet method in which a preliminary drying step and a washing step in a wet bath are followed by a heat treatment, a dry method in which a solvent is dried without a washing step, or a wet method in which a heat treatment is performed after introduction into a wet bath without a solvent drying step. Any of these methods may be used to form a film, but it is preferable to form a film by a dry method from the viewpoints of process simplicity and processability that allows a film to be formed on an object in the device manufacturing process.

The method of coating the substrate can be selected from known methods such as die coating, roller coating, wire bar coating, gravure coating, etc. The substrate may be any material that is not corroded by the raw material solution and does not deform or denature when heated for drying the solvent, and examples of the substrate include glass plates, thin glass films, resin films, metal plates, quartz plates, silicon wafers, etc. The surface structure of the substrate may be smooth or may have a fine structure.
Methods for drying the solvent include, but are not limited to, hot air, infrared irradiation, microwave irradiation, etc. The drying temperature is preferably 50 to 400°C. From the viewpoint of improving thermal dimensional stability, it is more preferable that the drying step includes a step in the temperature range of 150 to 400°C. For the purpose of preventing surface roughening due to rapid solvent evaporation, it is even more preferable to perform preliminary drying at 50 to 200°C and then stepwise solvent drying at 200 to 400°C.

As a method of imparting residual polarization to the polymer, aromatic polyamide, molded article, and film of the present invention, stretching or poling treatment may be performed during molding. When stretching is performed, it is preferable to stretch the film after the drying process described above using a stretching machine. Furthermore, when poling treatment is performed, it can be performed by applying a voltage to the obtained film and/or molded article. Methods for applying voltage include known methods such as DC voltage application treatment, AC voltage application treatment, and corona discharge treatment, and an appropriate method can be selected depending on the shape of the film or molded article. The applied electric field is preferably in the range of 10 kV/mm to 150 kV/mm. As electrodes, needle electrodes, wire electrodes, mesh electrodes, and flat electrodes have been conventionally used, but the present invention is not limited to these. Furthermore, a magnetic field may be used for poling treatment.

The polymer, aromatic polyamide, molded article and film of the present invention can be suitably used as a piezoelectric element, a sensor, an actuator, a diaphragm, a vibrator, and a raw material thereof.
The piezoelectric element, actuator, and vibrator comprising the molded article and/or film of the present invention are characterized by having a conductive thin film on at least one surface of the molded article and/or film of the present invention. This allows the piezoelectric element, actuator, and vibrator to exhibit excellent response and heat resistance while maintaining the same ease of use as conventional piezoelectric elements, actuators, and vibrators containing polymer-based piezoelectric materials. The piezoelectric element, actuator, and vibrator of the present invention can be suitably used as a member to be mounted on a vibration sensor, a speaker, etc.
The structural monitoring system of the present invention is characterized by comprising at least the vibration sensor and communication device described in the present invention, and diagnosing the vibration state of a structure using the vibration sensor. The structural monitoring system of the present invention is characterized by comprising the vibration sensor of the present invention, thereby improving durability and reducing the frequency of maintenance. Here, the structural health monitoring system is a system that measures the vibration state of a target structure in response to external factors such as earthquakes and vibrations generated by driving parts such as motors, thereby diagnosing the durability of the structure, detecting deterioration over time, and calculating the timing of repairs to the structure, etc.

The present invention will be explained in more detail below with reference to the following examples.

The physical properties of the present invention were evaluated in the form of a film, for example. The sample films used for evaluating the physical properties were prepared according to the following method using the aromatic polyamide of the present invention.

First, the sample solution was cast into a film shape using an applicator onto a glass plate with an Al electrode attached. At this time, the temperatures of the sample solution, glass plate, and casting atmosphere were room temperature. The cast thickness was adjusted so that the film thickness after the solvent dried would be 10 μm. Next, the glass plate was placed in a hot air oven and dried for 10 minutes at Tb-50°C, where Tb is the boiling point of the aprotic solvent that makes up the solution (in the case of a mixed solvent, the boiling point of the solvent with the highest boiling point among those that are contained in 30 mass% or more of the total solvent amount).

Next, an aluminum electrode layer (100 nm) was attached to the surface of the resulting dried film by vapor deposition, and the temperature was raised to Tb+40°C at a rate of 5°C/min while an electric field of 100 kV/mm was applied using a DC high-voltage stabilized power supply EV10-1AVR+ (Kasuga Electric Co., Ltd.) connected to a wire electrode. After maintaining the film at this temperature for 15 minutes, the film was slowly cooled to room temperature with the voltage still applied, thereby carrying out a poling treatment.

The methods for measuring physical properties and evaluating the effects of the present invention were as follows:

(1) Residual polarization An aluminum electrode (flat electrode) was vacuum-deposited on the central 5 mm x 5 mm area of a sample film cut to 20 mm x 20 mm. Two aluminum foil lead electrodes (3 mm x 80 mm) reinforced with insulating tape were attached to the flat electrode with conductive double-sided tape. The sample film, a function generator, a high-voltage amplifier, and an oscilloscope were assembled into a Sawyer Tower circuit, and a triangular wave was applied to the sample film (maximum ±10 kV). The response of the sample film was measured using an oscilloscope to determine the residual polarization at an applied electric field of 100 kV/mm.

(2) Glass transition temperature: The glass transition temperature of the sample film was determined from the inflection point of the storage modulus (E') by dynamic mechanical analysis (DMA) in accordance with ASTM E1640-13. DMA was performed using the following apparatus and conditions.

Apparatus: Viscoelasticity measuring device DMS6100 (Seiko Instruments Inc.)
Measurement mode: Tensile mode Measurement frequency: 1 Hz
Heating rate: 5°C/min Temperature range: 25°C to 400°C
Holding time: 2 minutes.

(3) Piezoelectric constant Using a piezometer YE2730 manufactured by SINOCERA PIEZOTRONICS or an equivalent product, _d31 and _d33 were measured at 10 selected points on the sample by applying a force of 0.25 N and 110 Hz. The arithmetic average values of the measured _d31 and _d33 were compared, and the larger average value was taken as the value of the piezoelectric constant of the sample. Note that the measured values of _d31 and _d33 are positive or negative depending on the front, back, and orientation of the sample being measured, but in this specification, the absolute values are treated as the measured values.

(4) Rate of change in piezoelectric constant due to heat treatment The sample was left to stand for 10 minutes. After being removed from the hot air oven and air-cooled to room temperature, d' ₃₁ and d' ₃₃ were measured in the same manner as in the method described in (3) Piezoelectric constant above. Using the obtained _d31 , _d33 , d' ₃₁ , and d' ₃₃ , |( _d31 - _d'31 )/ _d31 | and |( _d33 - _d'33 )/ _d33 | were calculated, and the larger of these values was taken as the rate of change in piezoelectric constant due to heat treatment of the sample.

(5) Elastic modulus Measurement was performed using an AFM (Dimension Icon manufactured by Burker Corporation) in PeakForceQNM mode, and the elastic modulus distribution was determined from the obtained force curve using the attached analysis software NanoScopeAnalysis V1.40 based on the JKR contact theory.

Specifically, the cantilever's warpage sensitivity, spring constant, and tip curvature were calibrated according to the PeakForceQNM mode manual, and then measurements were performed under the following conditions, and the data obtained from the DMT Modulus channel was adopted as one piece of data for the elastic modulus. Note that although the spring constant and tip curvature vary depending on the individual cantilever, a cantilever that satisfies the conditions of a spring constant of 0.3 N/m to 0.5 N/m and a tip curvature radius of 15 nm or less was adopted and used for the measurement, as a range that does not affect the measurement.
The above measurements were carried out on five randomly selected samples, and the numerical average of the obtained data was regarded as the elastic modulus of the sample film.

The measurement conditions are shown below.
Measurement equipment: Atomic force microscope (AFM) manufactured by Burker Corporation
Measurement mode: PeakForceQNM (force curve method)
Cantilever: Bruker AXS SCANASYST-AIR
(Material: Si, spring constant K: 0.4 N/m, tip curvature radius R: 2 nm)
Measurement atmosphere: 23°C, in air Measurement range: 3 μm Square resolution: 512 x 512
Cantilever movement speed: 10 μm/s
Maximum pressing load: 10 nN.

(6) Normalized Molecular Orientation A sample piece measuring 10 cm x 10 cm was cut out from the sample film, and the normalized molecular orientation MORc was measured under the following measurement conditions.
Measuring device: Oji Measurement Instruments MOR-7015
Frequency: 15 GHz
Reference thickness tc: 50 mm.

Example 1
In dehydrated DMAc (boiling point 165°C), 5-nitro-m-phenylenediamine, which corresponds to 100 mol% of the total amount of diamine as a diamine, was dissolved under nitrogen flow, and the liquid temperature was cooled to 5°C in an ice water bath. 2-nitroisophthalic acid dichloride, which corresponds to 99 mol% of the total amount of diamine, was added thereto over 30 minutes while keeping the inside of the system in an ice water bath under nitrogen flow, and after the entire amount was added, the mixture was stirred for about 1 hour to polymerize aromatic polyamide (polymer A). The obtained polymerization solution was added to a large amount of pure water while stirring, so that polymer A was solidified into a fibrous form, which was then crushed in a mixer for 5 minutes, and dried in a hot air oven at 80°C for 1 hour and in a vacuum oven at 120°C for 12 hours to obtain a powder of polymer A.
A solution was obtained by dissolving polymer A in DMAc so that the polymer concentration was 10% by mass. A film of the polymer A solution was applied to a glass plate with an Al electrode, and the plate was dried in a hot air oven at 130°C for 10 minutes, and then subjected to a poling treatment under the above-mentioned conditions to obtain a film of polymer A having a thickness of 10 μm. Here, a safety oven SPH100 (manufactured by Espec Corporation) was used as the hot air oven, and the oven was used 1 hour after the temperature display reached the set temperature with the opening and closing damper at 50%. The evaluation results of the obtained sample are shown in Table 1. The polymer A has a structure described in chemical formula (VIV) in which Ar ⁵ is chemical formula (X) and Ar ⁶ is chemical formula (XIII).

Example 2
An aromatic polyamide (polymer B) and a film thereof were obtained in the same manner as in Example 1, except that 5-trifluoro-m-phenylenediamine was used instead of 5-nitro-m-phenylenediamine. The evaluation results of the obtained sample are shown in Table 1. Polymer B has a structure represented by chemical formula (IX), in which Ar ⁵ is represented by chemical formula (X) and Ar ⁶ is represented by chemical formula (XIII).

Example 3
An aromatic polyamide (polymer C) and a film thereof were obtained in the same manner as in Example 1, except that 3,3'-sulfonylbisbenzoic acid dichloride was used instead of 2-nitroisophthalic acid dichloride. The evaluation results of the obtained sample are shown in Table 1. Polymer C has a structure represented by chemical formula (IX), in which Ar ⁵ is represented by chemical formula (X) and Ar ⁶ is represented by chemical formula (XIV).

Example 4
An aromatic polyamide (polymer D) and a film thereof were obtained in the same manner as in Example 1, except that 4,4'-diaminodiphenylsulfone was used instead of 5-nitro-m-phenylenediamine. The evaluation results of the obtained sample are shown in Table 1. Polymer D has a structure represented by chemical formula (IX) in which Ar ⁵ is represented by chemical formula (X) and Ar ⁶ is represented by chemical formula (XI).

(Example 5)
An aromatic polyamide (polymer E) and a film thereof were obtained in the same manner as in Example 1, except that 2,7-naphthalenedicarbonyl dichloride was used instead of 2-nitroisophthalic acid dichloride. The evaluation results of the obtained sample are shown in Table 1. Polymer E has a structure represented by chemical formula (III), in which Ar ³ is represented by chemical formula (IV) and Ar ⁴ is represented by chemical formula (V).

Example 6
An aromatic polyamide (polymer F) and a film thereof were obtained in the same manner as in Example 1, except that 1,6-naphthalenedicarbonyl dichloride was used instead of 2-nitroisophthalic acid dichloride. The evaluation results of the obtained sample are shown in Table 1. Polymer F has a structure represented by chemical formula (III) in which Ar ³ is represented by chemical formula (IV) and Ar ⁴ is represented by chemical formula (VI).

(Example 7)
After dissolving 2,5-thiophenedicarboxylic acid-1,1-dioxide in dehydrated chlorobenzene, oxalyl chloride equivalent to 2.2 molar equivalents relative to the dicarboxylic acid was added dropwise at room temperature. The solution was heated to 60°C and stirred for 2 hours, then returned to room temperature and distilled under reduced pressure to remove excess oxalyl chloride. Heptane was added to the reaction solution to precipitate 2,5-thiophenedicarboxylic acid dichloride-1,1-dioxide. The powder was filtered and then dried under reduced pressure to isolate it.
An aromatic polyamide (Polymer G) and a film thereof were obtained in the same manner as in Example 1, except that the 2,5-thiophenedicarboxylic acid dichloride-1,1-dioxide obtained by the above method was used instead of 2-nitroisophthalic acid dichloride. The evaluation results of the obtained sample are shown in Table 1. Note that Polymer G does not have any of the structures shown in chemical formulas (III) and (IX).

(Example 8)
An aromatic polyamide (polymer H) and a film thereof were obtained in the same manner as in Example 1, except that 5-nitro-m-phenylenediamine equivalent to 80 mol % and 2-chloro-p-phenylenediamine equivalent to 20 mol % were added instead of 5-nitro-m-phenylenediamine equivalent to 100 mol % based on the total amount of diamines. The evaluation results of the obtained sample are shown in Table 1. Polymer H contains a structure represented by chemical formula (IX), in which Ar ⁵ is chemical formula (IX) and Ar ⁶ is chemical formula (XIII).

(Example 9)
An aromatic polyamide (polymer I) and a film thereof were obtained in the same manner as in Example 1, except that 2-nitroisophthalic acid dichloride corresponding to 80 mol % and 2-chloroterephthalic acid dichloride corresponding to 19 mol % were added instead of 2-nitroisophthalic acid dichloride corresponding to 99 mol % based on the total amount of diamine. The evaluation results of the obtained sample are shown in Table 1. Polymer I contains a structure represented by chemical formula (IX) in which Ar ⁵ is chemical formula (X) and Ar ⁶ is chemical formula (XIII).
(Example 10)
An aromatic polyamide (polymer A) and a film thereof were obtained in the same manner as in Example 1, except that instead of carrying out the poling treatment, both ends of the dried film were supported and the film was uniaxially stretched to 1.1 times at 130° C. using a stretching machine. The evaluation results of the obtained sample are shown in Table 1.
(Comparative Example 1)
In the dehydrated DMAc, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB) was dissolved in an amount equivalent to 100 mol% of the total amount of diamines under a nitrogen stream, and the liquid temperature was cooled to 5°C in an ice water bath. 2-chloroterephthaloyl chloride (CTPC) equivalent to 99 mol% of the total amount of diamines was added thereto over 30 minutes while keeping the inside of the system in an ice water bath under a nitrogen stream, and after the entire amount was added, the mixture was stirred for about 1 hour to polymerize aromatic polyamide (polymer J). The obtained polymerization solution was added to a large amount of pure water while stirring to solidify polymer J into a fibrous form, which was then crushed in a mixer for 5 minutes and dried in a hot air oven at 80°C for 1 hour and in a vacuum oven at 120°C for 12 hours to obtain a powder of polymer J. Thereafter, a film made of polymer J was obtained in the same manner as in Example 1. The evaluation results of the obtained sample are shown in Table 1. Polymer J does not have any of the structures shown in chemical formulas (III) and (IX).

(Comparative Example 2)
In the dehydrated DMAc, 5-nitro-m-phenylenediamine, which corresponds to 100 mol % of the total amount of diamine as a diamine, was dissolved under a nitrogen stream, and the liquid temperature was cooled to 5° C. in an ice water bath. CTPC, which corresponds to 99 mol % of the total amount of diamine, was added thereto over 30 minutes while keeping the inside of the system in an ice water bath under a nitrogen stream, and after the entire amount was added, the mixture was stirred for about 1 hour to polymerize aromatic polyamide (polymer K). The obtained polymerization solution was added to a large amount of pure water while stirring to solidify polymer K into a fibrous form, which was then crushed in a mixer for 5 minutes, and dried in a hot air oven at 80° C. for 1 hour and in a vacuum oven at 120° C. for 12 hours to obtain a powder of polymer K.
A solution was obtained by dissolving polymer K in DMAc so that the polymer concentration was 10% by mass. A film of the solution of polymer K was applied onto a glass plate with an Al electrode, and the film was dried in a hot air oven at 130° C. for 10 minutes, and then subjected to a poling treatment under the above-mentioned conditions to obtain a film of polymer K having a thickness of 10 μm. The evaluation results of the obtained sample are shown in Table 1. Note that polymer K does not have any of the structures described in chemical formulas (III) and (IX).

(Comparative Example 3)
In dehydrated DMAc (boiling point 165°C), m-phenylenediamine equivalent to 100 mol% of the total amount of diamine was dissolved under nitrogen flow, and the liquid temperature was cooled to 5°C in an ice water bath. While the system was kept in an ice water bath under nitrogen flow, isophthalic acid dichloride equivalent to 99 mol% of the total amount of diamine was added over 30 minutes, and after the entire amount was added, the mixture was stirred for about 1 hour to polymerize aromatic polyamide (polymer L). The obtained polymerization solution was added to a large amount of pure water while stirring to solidify polymer L into a fibrous form, which was then crushed in a mixer for 5 minutes and dried in a hot air oven at 80°C for 1 hour and in a vacuum oven at 120°C for 12 hours to obtain a powder of polymer L.
A solution was obtained by dissolving polymer L in DMAc so that the polymer concentration was 10% by mass. A film of the polymer L solution was applied to a glass plate with an Al electrode, and the plate was dried in a hot air oven at 130°C for 10 minutes, and then subjected to a poling treatment under the above-mentioned conditions to obtain a film of polymer L having a thickness of 10 μm. Here, a safety oven SPH100 (manufactured by Espec Corporation) was used as the hot air oven, and the oven was used 1 hour after the temperature display reached the set temperature with the opening and closing damper at 50%. The evaluation results of the obtained sample are shown in Table 1. The polymer L has a structure described in chemical formula (III) in which both Ar ³ and Ar ⁴ are chemical formula (IV).

(Comparative Example 4)
A film made of polymer M was obtained in the same manner as in Example 1, except that nylon 11 (Rilsan(R) PA11, polymer M) was used instead of aromatic polyamide. The evaluation results of the obtained sample are shown in Table 1. Note that polymer M does not have any of the structures shown in chemical formulas (III) and (IX).

(Comparative Example 5)
Each evaluation was performed using a commercially available piezoelectric PVDF film (KF Piezofilm, manufactured by Kureha Corporation) as a sample. The evaluation results are shown in Table 1. Note that PVDF does not have any of the structures shown in chemical formulas (III) and (IX). No normalized molecular orientation measurement was performed.

Claims (21)

A polymer comprising a structure represented by the following chemical formula (I) as a repeating unit, which satisfies the following (i) and (ii):
(i): The hydrogen-bonding group A in the chemical formula (I) is bonded to a ring atom.
(ii): In the chemical formula (I), the number of atoms on the shortest path connecting the two A atoms is odd.
Chemical formula (I):

A is a hydrogen-bonding group, and B ¹ and B ² are n-membered ring groups (n is a natural number of 5 or more and 10 or less). 2. The polymer of claim 1, having a remanent polarization of 15 mC/ ^m2 or more and 300 mC/ ^m2 or less. The polymer according to claim 1, wherein the hydrogen-bonding group A is at least one of an amide group, a urea group, and a urethane group. 2. The polymer according to claim 1, wherein the hydrogen-bonding group A is an amide group, and B ¹ and B ² are both aromatic groups. The aromatic polyamide according to claim 4, wherein the repeating unit has a structure that satisfies at least any one of the following (v) to (viii):
(v): An electron-donating group is bonded to an atom on the shortest path along the bonds connecting the N atoms of the two amide groups.
(vi): An electron-withdrawing group is bonded to an atom on the shortest path along the bond connecting the two C atoms of the amide groups.
(vii): An electron-withdrawing group is bonded to an atom that is not on the shortest path along the bond connecting the two N atoms of the amide groups.
(viii): An electron-donating group is bonded to an atom that is not on the shortest path along the bond connecting the two C atoms of the amide groups. 6. The aromatic polyamide according to claim 5, having a molecular skeleton structure represented by the following chemical formula (III):
Chemical formula (III):

Ar ³ and Ar ⁴ are groups containing the molecular skeleton structures shown in chemical formulas (IV) to (VIII).
Chemical formula (IV):

Chemical formula (V):

Chemical formula (VI):

Chemical formula (VII):

R ¹ is any group satisfying (v) to (viii) in claim 5.
Chemical formula (VIII):

^R2 is any group satisfying (v) to (viii) in claim 5. 6. The aromatic polyamide of claim 5, having a structure represented by the following chemical formula (IX):
Chemical formula (IX):

Ar ⁵ is a group including a structure represented by any one of chemical formulas (X) to (XII), and Ar ⁶ is a group including a structure represented by any one of chemical formulas (XIII) to (XV).
Chemical formula (X):

^R3 is --H or an electron donating group, and ^R4 is an electron withdrawing group.
Chemical formula (XI):

^R5 is an electron donating group.
Chemical formula (XII):

^R6 is an electron withdrawing group.
Chemical formula (XIII):

R ⁷ is an electron withdrawing group and R ⁸ is --H or an electron donating group.
Chemical formula (XIV):

^R9 is an electron withdrawing group.
Chemical formula (XV):

^R10 is an electron donating group. The aromatic polyamide according to claim 7, which contains at least one of a perfluoroalkyl group having 1 to 3 carbon atoms, a nitro group, a cyano group, and a sulfone group. The aromatic polyamide according to claim 4, having a glass transition temperature of 130°C or higher and 400°C or lower. A molded body mainly composed of the aromatic polyamide according to claim 4. The molded article according to claim 10, wherein at least one of the piezoelectric constants _d31 and _d33 is greater than 0 pC/N and less than or equal to 50.0 pC/N. A film mainly composed of the aromatic polyamide described in claim 4. The film described in claim 12, characterized in that the elastic modulus obtained by AFM is 4.0 GPa or more and 15.0 GPa or less. The film according to claim 12, having a normalized molecular orientation MORc of 1.1 or more and 15 or less. The molded body according to claim 10, wherein, when the electrostatic constant after heat treatment at 150° C. for 10 minutes is d', the larger of the absolute values of changes in the piezoelectric constant due to heat treatment, |(d ₃₁ - d' ₃₁ )/d ₃₁ | and |(d ₃₃ - d' ₃₃ )/d ₃₃ |, is 0 or more and 0.5 or less. A piezoelectric element comprising the molded body according to claim 10 and/or the film according to claim 12. An actuator comprising the molded body described in claim 10 and/or the film described in claim 12. A vibrator comprising the molded body according to claim 10 and/or the film according to claim 12. A vibration sensor comprising the piezoelectric element according to claim 16. A speaker having an actuator as described in claim 17. A structural health monitoring system comprising at least the vibration sensor according to claim 19 and a communication device, the structural health monitoring system detecting a vibration state of a structure by the vibration sensor and diagnosing the structure.