Copolymer, piezoelectric material, piezoelectric film and piezoelectric element

Abstract

This copolymer has a structural unit represented by formula (1) (where R1 and R2 are each any one selected from the group consisting of a hydrogen atom, a methyl group, a dimethyl group, an ethyl group, an isopropyl group, an isobutyl group, a phenyl group, and a benzyl group, or R1 and R2 form a benzooxazolidinone skeleton together with an oxazolidinone ring), and a structural unit represented by formula (2).

Description

[Technical Field]

[0001] The present invention relates to a copolymer, a piezoelectric material, a piezoelectric film, and a piezoelectric element. This application claims priority based on Japanese Patent Application No. 2021-054912, filed on March 29, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Traditionally, the ceramic material PZT (PbZrO3-PbTiO3 solid solution) has been widely used as the piezoelectric material that forms the piezoelectric body of piezoelectric elements. However, PZT has the disadvantage of being brittle because it contains lead and is a ceramic. For this reason, there is a demand for piezoelectric materials that are environmentally friendly and highly flexible.

[0003] One piezoelectric material that can meet these requirements is polymer piezoelectric materials. Polymer piezoelectric materials include ferroelectric polymers such as polyvinylidene fluoride (PVDF) and vinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)). However, these ferroelectric polymers have insufficient heat resistance. As a result, piezoelectric elements made from conventional ferroelectric polymers lose their piezoelectric properties at high temperatures, and their physical properties, such as elastic modulus, also deteriorate. Therefore, piezoelectric elements made from conventional ferroelectric polymers have a narrow usable temperature range.

[0004] Another piezoelectric material is amorphous polymer piezoelectric material, which acquires piezoelectricity by cooling while polarizing it at a temperature near its glass transition temperature. Amorphous polymers lose their piezoelectric properties when heated to temperatures near their glass transition temperature. Therefore, amorphous polymer piezoelectric materials with high glass transition temperatures and good heat resistance are in demand.

[0005] An example of an amorphous polymer piezoelectric material with a high glass transition temperature is vinylidene cyanide-vinyl acetate copolymer (see, for example, Patent Document 1). However, vinylidene cyanide-vinyl acetate copolymer requires the use of vinylidene cyanide, which is difficult to handle, as a raw material monomer.

[0006] It is also possible to use acrylonitrile, which is easy to handle, as the raw material monomer for polymeric piezoelectric materials instead of vinylidene cyanide. However, polymers using acrylonitrile as the raw material monomer have a low glass transition temperature. Furthermore, polymers using acrylonitrile as the raw material monomer also have poor piezoelectric properties (see, for example, Non-Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 1991 / 013922 [Non-patent literature]

[0008] [Non-Patent Document 1] H. Ueda, S. Carr, Piezoelectricity in Polyacrylonitrile. Polym J 16, 661-667 (1984). [Non-patent document 2] H. von Berlepsch, W. Kunstler, Piezoelectricity in acrylonitrile / methylacrylate copolymer. Polymer Bulletin 19, 305-309 (1988). Summary of the Invention [Problem to be solved by the invention]

[0009] There has been a demand for polymeric piezoelectric materials that can be used to form piezoelectric films with high heat resistance and piezoelectric properties. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a copolymer that can be used as a piezoelectric material from which a piezoelectric film having high heat resistance and piezoelectric properties can be obtained.

[0010] Another object of the present invention is to provide a piezoelectric material that contains the copolymer of the present invention and that can give a piezoelectric film having high heat resistance and piezoelectric properties. Another object of the present invention is to provide a piezoelectric film containing the piezoelectric material of the present invention and having high heat resistance and piezoelectric properties, and a piezoelectric element having the piezoelectric film of the present invention and having high heat resistance and piezoelectric properties. [Means for solving the problem]

[0011] [1] A copolymer having a structural unit represented by the following general formula (1) and a structural unit represented by the following formula (2):

[0012] [ka] (In general formula (1), R 1 and R 2 is any one selected from the group consisting of a hydrogen atom, a methyl group, a dimethyl group, an ethyl group, an isopropyl group, an isobutyl group, a phenyl group, and a benzyl group, or R 1 and R 2 forms a benzoxazolidinone skeleton together with the oxazolidinone ring.

[0013] [2] In the general formula (1), R 1 is a hydrogen atom, and R 2 is one selected from the group consisting of a hydrogen atom, a methyl group, and a dimethyl group, or R 1 is one selected from the group consisting of a methyl group, a dimethyl group, an ethyl group, and an isopropyl group, and R 2 is a hydrogen atom. [3] In the general formula (1), R 1 is a hydrogen atom, and R 2is one selected from the group consisting of a hydrogen atom, a methyl group, and a dimethyl group. [4] In the general formula (1), R 1 is one selected from the group consisting of a methyl group, a dimethyl group, an ethyl group, and an isopropyl group, and R 2 is a hydrogen atom. [5] The copolymer according to any one of [1] to [4], wherein the content of the structural unit represented by the formula (2) is 10 to 80 mol %.

[0014] [6] A piezoelectric material comprising the copolymer according to any one of [1] to [5]. [7] A piezoelectric film comprising the copolymer according to any one of [1] to [5]. [8] [7] and an electrode disposed on a surface of the piezoelectric film. [Effects of the Invention]

[0015] The copolymer of the present invention has a structural unit represented by general formula (1) and a structural unit represented by formula (2). Therefore, the copolymer of the present invention can be used as a piezoelectric material from which a piezoelectric film having high heat resistance and piezoelectric properties can be obtained. Furthermore, since the piezoelectric material of the present invention contains the copolymer of the present invention, a piezoelectric film having high heat resistance and piezoelectric properties can be obtained. Furthermore, the piezoelectric film of the present invention contains the copolymer of the present invention, and therefore the piezoelectric film of the present invention and the piezoelectric element of the present invention having the piezoelectric film of the present invention have excellent heat resistance and piezoelectric properties. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a 1H-NMR measurement chart of the polymer of Example 1. [Figure 2] FIG. 2 is a 1H-NMR measurement chart of the polymer of Example 6. [Figure 3] FIG. 3 is a 1H-NMR measurement chart of the polymer of Example 10. [Figure 4]FIG. 4 is a 1H-NMR measurement chart of the polymer of Example 14. [Figure 5] FIG. 5 is a 1H-NMR measurement chart of the polymer of Example 18. [Figure 6] FIG. 6 is a 1H-NMR measurement chart of the polymer of Example 22. [Figure 7] FIG. 7 is a 1H-NMR measurement chart of the polymer of Example 27. DETAILED DESCRIPTION OF THE INVENTION

[0017] In order to solve the above problems, the present inventors have focused on the heat resistance of polymers using acrylonitrile as a raw material monomer and have conducted extensive research. As a result, they found that a copolymer having a specific structural unit containing an oxazolidinone skeleton and a structural unit derived from acrylonitrile would be sufficient.

[0018] A compound in which a vinyl group is bonded to a nitrogen atom of an oxazolidinone skeleton has a high affinity with acrylonitrile. Therefore, a compound in which a vinyl group is bonded to a nitrogen atom of an oxazolidinone skeleton can form a copolymer with acrylonitrile. Furthermore, a compound in which a vinyl group is bonded to a nitrogen atom of an oxazolidinone skeleton has high polarity, so when copolymerized with acrylonitrile, it forms a copolymer with better heat resistance than polyacrylonitrile.

[0019] Specifically, the dipole moment of a compound containing an oxazolidinone skeleton is about 6.0 Debye, while the dipole moment of acrylonitrile is about 3.8 Debye. In other words, structural units containing an oxazolidinone skeleton are more polar than structural units derived from acrylonitrile. As a result, in copolymers having structural units containing an oxazolidinone skeleton and structural units derived from acrylonitrile, the highly polar structural units containing the oxazolidinone skeleton disrupt the ordered structure that can be formed by the nitrile groups, which are polar groups derived from acrylonitrile, making it difficult for them to orient so that their polarities cancel each other out. For this reason, it is estimated that copolymers having structural units containing an oxazolidinone skeleton and structural units derived from acrylonitrile can be used as piezoelectric materials that can produce piezoelectric films with excellent heat resistance and piezoelectric properties.

[0020] Furthermore, the present inventors produced a copolymer having a specific structural unit containing an oxazolidinone skeleton and a structural unit derived from acrylonitrile, and confirmed that the copolymer had good heat resistance and that a piezoelectric film using the copolymer as a piezoelectric material had good piezoelectric properties, thereby conceiving the present invention.

[0021] The copolymer, piezoelectric material, piezoelectric film, and piezoelectric element of the present invention will be described in detail below. [Copolymer] The copolymer of this embodiment has a structural unit represented by the following general formula (1) and a structural unit represented by the following formula (2).

[0022] [ka] (In general formula (1), R 1 and R 2 is any one selected from the group consisting of a hydrogen atom, a methyl group, a dimethyl group, an ethyl group, an isopropyl group, an isobutyl group, a phenyl group, and a benzyl group, or R 1 and R 2 forms a benzoxazolidinone skeleton together with the oxazolidinone ring.

[0023] In the structural unit represented by formula (1) of the copolymer of this embodiment, R 1 and R 2 is any one selected from the group consisting of a hydrogen atom, a methyl group, a dimethyl group, an ethyl group, an isopropyl group, an isobutyl group, a phenyl group, and a benzyl group. 1 and R 2 Since the structural unit R of the copolymer of the present embodiment is as described above, it can be easily produced. 1 and R 2 Since the above formula is satisfied, it can be used as a material for a piezoelectric film having good heat resistance and piezoelectric properties. 1 and R 2 Since the copolymer does not have polarity, it is preferable that the volume is small, because the volume ratio of the polar portion to the entire copolymer increases relatively, which contributes to improving the piezoelectric properties of the piezoelectric film using the copolymer. Specifically, R 1 is a hydrogen atom, and R 2 is preferably one selected from the group consisting of a hydrogen atom, a methyl group, and a dimethyl group. 1 is one selected from the group consisting of a methyl group, a dimethyl group, an ethyl group, and an isopropyl group, and R 2 is preferably a hydrogen atom. In addition, R 1 is any one selected from the group consisting of a hydrogen atom, a methyl group, a dimethyl group, an ethyl group, an isopropyl group, an isobutyl group, a phenyl group, and a benzyl group, and R 2 may be a hydrogen atom or a methyl group. 1 is a hydrogen atom, and R 2 may be a hydrogen atom or a methyl group. In particular, it can be used as a material for piezoelectric films with good heat resistance and piezoelectric properties, so it is particularly suitable for R 1 is a hydrogen atom, and R 2 is preferably a methyl group.

[0024] The structural unit represented by formula (1) is R1 and R 2 In the copolymer of the present embodiment, R of the structural unit represented by formula (1) may form a benzoxazolidinone skeleton together with the oxazolidinone ring. 1 and R 2 However, even when the benzoxazolidinone skeleton is formed together with the oxazolidinone ring, it can be easily produced and can be used as a material for a piezoelectric film having good heat resistance and piezoelectric properties.

[0025] In the copolymer of this embodiment, the arrangement order of the repeating units, the structural units represented by formula (1) and the structural units represented by formula (2), is not particularly limited. Furthermore, in the copolymer of this embodiment, the number of structural units represented by formula (1) and the number of structural units represented by formula (2) may be the same or different. Therefore, the copolymer of this embodiment may have an alternating arrangement portion in which the structural units represented by formula (1) and the structural units represented by formula (2) are alternately arranged, a random arrangement portion in which the structural units represented by formula (1) and the structural units represented by formula (2) are arranged in an unordered manner, and a block arrangement portion having a portion in which the structural units represented by formula (1) are arranged consecutively and a portion in which the structural units represented by formula (2) are arranged consecutively, distributed in any proportion. The copolymer of this embodiment preferably contains an alternating arrangement portion because the nitrile groups contained in the structural units represented by formula (2) are less likely to be oriented so as to cancel out each other's polarity, making it usable as a piezoelectric material with excellent heat resistance and piezoelectric properties.

[0026] The copolymer of this embodiment preferably has a content of the structural unit represented by formula (1) of 10 to 80 mol %, more preferably 20 to 70 mol %, and even more preferably 30 to 60 mol %. When the content of the structural unit represented by formula (1) is 10 mol % or more, the copolymer has even better heat resistance. Furthermore, when the content of the structural unit represented by formula (1) is 80 mol % or less, it is possible to prevent a piezoelectric film containing the copolymer from becoming hard and brittle due to an excessive content of the structural unit represented by formula (1). Furthermore, when the content of the structural unit represented by formula (1) is 80 mol % or less, it is possible to prevent a decrease in the insulation resistance of the copolymer due to moisture absorption by the structural unit represented by formula (1).

[0027] The copolymer of this embodiment preferably has a content of the structural unit represented by formula (2) of 10 to 80 mol %, more preferably 20 to 70 mol %, and even more preferably 30 to 60 mol %. When the content of the structural unit represented by formula (2) is 10 mol % or more, the copolymer can form a flexible piezoelectric film with high insulation resistance. Furthermore, when the content of the structural unit represented by formula (2) is 80 mol % or less, the content of the structural unit represented by formula (1) can be easily ensured. As a result, the nitrile groups contained in the structural unit represented by formula (2) are less likely to be oriented so as to cancel out their polarities, resulting in a copolymer that can form a piezoelectric film with better heat resistance and piezoelectric properties.

[0028] The copolymer of the present embodiment may, if necessary, contain one or more structural units other than the structural unit represented by formula (1) and the structural unit represented by formula (2). Examples of the other structural units include structural units derived from known monomers or oligomers having a polymerizable unsaturated bond. Of the structural units contained in the copolymer of the present embodiment, the total content of the structural units represented by formula (1) and the structural units represented by formula (2) is preferably 50% by mass or more, more preferably 80% by mass or more, and may be 90% by mass or more, and may consist of only the structural units represented by formula (1) and the structural units represented by formula (2).

[0029] The weight-average molecular weight (Mw) of the copolymer of this embodiment is preferably 10,000 to 1,000,000. When the weight-average molecular weight (Mw) of the copolymer is 10,000 or more, the film-forming properties are good, and a piezoelectric film containing the copolymer of this embodiment can be easily produced. When the weight-average molecular weight (Mw) of the copolymer is 1,000,000 or less, the copolymer can be easily dissolved in a solvent, and a piezoelectric film can be easily produced using a coating liquid dissolved in a solvent.

[0030] "Method for producing copolymers" The copolymer of the present embodiment can be produced, for example, by a known radical copolymerization method using a compound from which the structural unit represented by formula (1) is derived, raw material monomers including acrylonitrile, and a polymerization initiator such as azobisbutyronitrile. The polymerization conditions, such as the reaction temperature and reaction time, used in producing the copolymer of this embodiment can be appropriately determined depending on the composition of the raw material monomers.

[0031] The compound from which the structural unit represented by formula (1) is derived is a compound in which the oxazolidinone skeleton and the atoms bonded to the carbon atoms of the oxazolidinone skeleton are the same as those of the structural unit represented by formula (1), and a vinyl group is bonded to the nitrogen atom of the oxazolidinone skeleton. Specific examples of the compound from which the structural unit represented by formula (1) is derived include N-vinyl-oxazolidinone, N-vinyl-5-methyloxazolidinone, N-vinyl-4-methyloxazolidinone, N-vinyl-4,4-dimethyloxazolidinone, N-vinyl-4-ethyloxazolidinone, N-vinyl-4-propyloxazolidinone, N-vinyl-4-isopropyloxazolidinone, N-vinyl-4-isobutyloxazolidinone, N-vinyl-4-phenyloxazolidinone, N-vinyl-4-benzyloxazolidinone, and N-vinyl-2-benzoxazolinone, and the like, and is appropriately determined depending on the structure of the copolymer of the present embodiment, which is the target product.

[0032] "Piezoelectric materials" The piezoelectric material of this embodiment contains the copolymer of this embodiment. The copolymer of this embodiment contained in the piezoelectric material of this embodiment may be only one type, or two or more types. Furthermore, the piezoelectric material of this embodiment may contain, as necessary, one or more types of known polymers other than the copolymer of this embodiment, together with the copolymer of this embodiment.

[0033] "Piezoelectric film" The piezoelectric film of this embodiment includes the copolymer of this embodiment. The piezoelectric film of this embodiment can be manufactured, for example, by the method described below. The piezoelectric material of this embodiment, including the copolymer of this embodiment, is dissolved in a solvent to form a coating liquid. Next, the coating liquid is applied to a peelable substrate to a predetermined thickness to form a coating film. Known substrates, such as resin films, can be used. Known methods can be used to apply the coating liquid depending on the coating thickness, viscosity of the coating liquid, and the like. The coating film is then dried to remove the solvent in the coating film, resulting in a piezoelectric material sheet.

[0034] The piezoelectric material sheet is then peeled off from the substrate, and electrodes made of a known conductive material such as aluminum are placed on one side of the piezoelectric material sheet and the other side. A voltage is applied at a temperature near the glass transition temperature of the piezoelectric material forming the piezoelectric material sheet, and the sheet is then cooled with the voltage still applied. This gives the sheet piezoelectricity. Through these steps, a sheet-like piezoelectric film is obtained. The electrodes used to obtain piezoelectricity may be used as they are to form the piezoelectric element, or may be removed.

[0035] "Piezoelectric element" The piezoelectric element of this embodiment includes the piezoelectric film of this embodiment and electrodes disposed on the surface of the piezoelectric film. Specifically, the piezoelectric element may include a sheet-like piezoelectric film and electrodes disposed on one side and the other side of the piezoelectric film. The electrodes may be made of a known conductive material such as aluminum. The piezoelectric element of this embodiment can be manufactured by providing electrodes on one surface and the other surface of the piezoelectric film by a known method such as vapor deposition.

[0036] The copolymer of this embodiment has a structural unit represented by general formula (1) and a structural unit represented by formula (2). Therefore, the copolymer of this embodiment can be used as a piezoelectric material from which a piezoelectric film having high heat resistance and piezoelectric properties can be obtained. Furthermore, since the piezoelectric material of this embodiment contains the copolymer of this embodiment, a piezoelectric film having high heat resistance and piezoelectric properties can be obtained. Furthermore, the piezoelectric film of this embodiment contains the copolymer of this embodiment, and therefore the piezoelectric film of this embodiment and the piezoelectric element of this embodiment having the piezoelectric film of this embodiment have excellent heat resistance and piezoelectric properties.

[0037] The above describes the embodiments of the present invention in detail, but each configuration and combination thereof in each embodiment is an example, and additions, omissions, substitutions, and other modifications of the configurations are possible within the scope that does not deviate from the spirit of the present invention. [Example]

[0038] "Example 1" In a 100 ml Schlenk tube, 0.4 ml (4 mmol) of N-vinyl-oxazolidinone represented by the following general formula (11) was mixed with 1.2 ml (16 mmol) of acrylonitrile, and 11.5 mg (0.07 mmol) of azobisisobutyronitrile was added, followed by a reaction at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 1.1 g of the polymer of Example 1. The yield was 78%.

[0039] [ka] (In general formula (11), R 2 is a hydrogen atom.)

[0040] The polymer of Example 1 was analyzed using an NMR (nuclear magnetic resonance) apparatus (trade name JNM-ECA500, manufactured by JEOL Ltd.) and dimethyl sulfoxide d6 (DMSO-d6) as a solvent. 1 The molecular structure was identified by H-NMR measurement. 1 1 is a H-NMR measurement chart. As a result, the polymer of Example 1 contained the structural unit A represented by general formula (1) (R 1 and R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, in Example 1 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) contained in the polymer of Example 1 was 70%.

[0041] "Example 2" In a 100 ml Schlenk tube, 0.4 ml (4 mmol) of N-vinyl oxazolidinone and 0.4 ml (7 mmol) of acrylonitrile were mixed, and 6.8 mg (0.04 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.5 g of the polymer of Example 3. The yield was 68%.

[0042] The polymer of Example 2 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 3, like the polymer of Example 1, had a structural unit A represented by general formula (1) (R 1 and R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, in Example 2 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum. 2The content of the structural unit represented by formula (2) in the polymer was 49%.

[0043] "Example 3" In a 100 ml Schlenk tube, 0.4 ml (4 mmol) of N-vinyl-oxazolidinone and 0.3 ml (4 mmol) of acrylonitrile were mixed, and 5.9 mg (0.04 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.6 g of the polymer of Example 3. The yield was 87%.

[0044] The polymer of Example 3 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 3, like the polymer of Example 1, had a structural unit A represented by general formula (1) (R 1 and R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, in Example 3 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum. 3 The content of the structural unit represented by formula (2) in the polymer was 24%.

[0045] Example 4 In a 100 ml Schlenk tube, 1.2 ml (12 mmol) of N-vinyl-oxazolidinone and 0.1 ml (2 mmol) of acrylonitrile were mixed, and 7.9 mg (0.05 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 1.1 g of the polymer of Example 4. The yield was 73%.

[0046] The polymer of Example 4 was prepared in the same manner as the polymer of Example 1. 1H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 4, like the polymer of Example 1, had a structural unit A represented by general formula (1) (R 1 and R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, in Example 4 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 4 was 14%.

[0047] "Example 5" In a 100 ml Schlenk tube, 0.6 ml (5 mmol) of N-vinyl-4-methyl-oxazolidinone and 0.7 ml (10 mmol) of acrylonitrile were mixed, and 9.4 mg (0.06 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.5 g of the polymer of Example 5. The yield was 44%.

[0048] The polymer of Example 5 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 5 had a structural unit B represented by general formula (1) (R 1 is a methyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, in Example 5 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 5 was 75%.

[0049] "Example 6" In a 100 ml Schlenk tube, 0.6 ml (5 mmol) of N-vinyl-4-methyl-oxazolidinone and 0.3 ml (5 mmol) of acrylonitrile were mixed, and 7.4 mg (0.04 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.7 g of the polymer of Example 6. The yield was 68%.

[0050] The polymer of Example 6 was prepared in the same manner as the polymer of Example 1. 1 The molecular structure was identified by H-NMR measurement. 1 1 is a H-NMR measurement chart. As a result, the polymer of Example 6, like Example 5, contained the structural unit B represented by general formula (1) (R 1 is a methyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, in Example 6 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 6 was 55%.

[0051] "Example 7" In a 100 ml Schlenk tube, 0.6 ml (5 mmol) of N-vinyl-4-methyl-oxazolidinone and 0.7 ml (10 mmol) of acrylonitrile were mixed, and 9.4 mg (0.06 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.7 g of the polymer of Example 7. The yield was 59%.

[0052] The polymer of Example 7 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 7, like Example 5, had a structural unit B represented by general formula (1) (R 1is a methyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 7 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 7 was 33%.

[0053] "Example 8" In a 100 ml Schlenk tube, 1.2 ml (10 mmol) of N-vinyl-4-methyl-oxazolidinone and 0.1 ml (2 mmol) of acrylonitrile were mixed, and 11.2 mg (0.07 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.9 g of the polymer of Example 8. The yield was 62%.

[0054] The polymer of Example 8 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 8, like Example 5, had a structural unit B represented by general formula (1) (R 1 is a methyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 8 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 8 was 14%.

[0055] "Example 9" In a 100 ml Schlenk tube, 0.6 ml (5 mmol) of N-vinyl-4-ethyl-oxazolidinone and 0.6 ml (10 mmol) of acrylonitrile were mixed, and 9.8 mg (0.06 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.7 g of the polymer of Example 9. The yield was 55%.

[0056] The polymer of Example 9 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 9 contained a structural unit C represented by general formula (1) (R 1 is an ethyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 9 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 9 was 73%.

[0057] "Example 10" In a 100 ml Schlenk tube, 0.6 ml (5 mmol) of N-vinyl-4-ethyl-oxazolidinone and 0.3 ml (5 mmol) of acrylonitrile were mixed, and 7.7 mg (0.05 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.4 g of the polymer of Example 10. The yield was 44%.

[0058] The polymer of Example 10 was prepared in the same manner as the polymer of Example 1. 1 The molecular structure was identified by H-NMR measurement. 1 1 is a H-NMR measurement chart. As a result, the polymer of Example 10, like Example 9, contained the structural unit C represented by general formula (1) (R 1 is an ethyl group, R2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 10 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 10 was 60%.

[0059] "Example 11" In a 100 ml Schlenk tube, 0.6 ml (5 mmol) of N-vinyl-4-ethyl-oxazolidinone and 0.1 ml (2 mmol) of acrylonitrile were mixed, and 6.4 mg (0.06 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.5 g of the polymer of Example 11. The yield was 62%.

[0060] The polymer of Example 11 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 11, like Example 9, had a structural unit C represented by general formula (1) (R 1 is an ethyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 11 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 11 was 39%.

[0061] "Example 12" In a 100 ml Schlenk tube, 1.2 ml (10 mmol) of N-vinyl-4-ethyl-oxazolidinone and 0.1 ml (2 mmol) of acrylonitrile were mixed, and 12.0 mg (0.07 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.7 g of the polymer of Example 12. The yield was 45%.

[0062] The polymer of Example 12 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 12, like Example 9, has a structural unit C represented by general formula (1) (R 1 is an ethyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 12 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 12 was 21%.

[0063] "Example 13" In a 100 ml Schlenk tube, 0.7 ml (5 mmol) of N-vinyl-4-isopropyl-oxazolidinone and 0.7 ml (10 mmol) of acrylonitrile were mixed, and 10.2 mg (0.06 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.7 g of the polymer of Example 13. The yield was 55%.

[0064] The polymer of Example 13 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, the polymer of Example 13 contained the structural unit D represented by the general formula (1) (R 1 is an isopropyl group (iPr), R 2is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 13 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 13 was 67%.

[0065] "Example 14" In a 100 ml Schlenk tube, 0.6 ml (5 mmol) of N-vinyl-4-isopropyl-oxazolidinone and 0.3 ml (5 mmol) of acrylonitrile were mixed, and 7.5 mg (0.05 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.6 g of the polymer of Example 14. The yield was 66%.

[0066] The polymer of Example 14 was prepared in the same manner as the polymer of Example 1. 1 The molecular structure was identified by H-NMR measurement. 1 1 is a H-NMR measurement chart. As a result, the polymer of Example 14, like Example 13, contained the structural unit D represented by general formula (1) (R 1 is an isopropyl group (iPr), R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 14 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 14 was 44%.

[0067] "Example 15" In a 100 ml Schlenk tube, 0.7 ml (5 mmol) of N-vinyl-4-isopropyl-oxazolidinone and 0.1 ml (2 mmol) of acrylonitrile were mixed, and 6.8 mg (0.04 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.6 g of the polymer of Example 15. The yield was 72%.

[0068] The polymer of Example 15 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 15, like Example 13, has a structural unit D represented by general formula (1) (R 1 is an isopropyl group (iPr), R 2 is a hydrogen atom.) and a structural unit represented by formula (2). Also, in Example 15 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 15 was 32%.

[0069] "Example 16" In a 100 ml Schlenk tube, 1.4 ml (10 mmol) of N-vinyl-4-isopropyl-oxazolidinone and 0.1 ml (2 mmol) of acrylonitrile were mixed, and 13.2 mg (0.08 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.9 g of the polymer of Example 16. The yield was 57%.

[0070] The polymer of Example 16 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 16, like Example 13, contained the structural unit D represented by the general formula (1) (R 1 is an isopropyl group (iPr), R 2is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 16 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 16 was 18%.

[0071] "Example 17" In a 100 ml Schlenk tube, 0.8 ml (6 mmol) of N-vinyl-4,4-dimethyl-oxazolidinone and 0.8 ml (12 mmol) of acrylonitrile were mixed, and 12.6 mg (0.08 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.8 g of the polymer of Example 17. The yield was 50%.

[0072] The polymer of Example 17 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, the polymer of Example 17 contained the structural unit E represented by general formula (1) (R 1 is a dimethyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 17 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 17 was 73%.

[0073] "Example 18" In a 100 ml Schlenk tube, 0.8 ml (6 mmol) of N-vinyl-4,4-dimethyl-oxazolidinone and 0.4 ml (6 mmol) of acrylonitrile were mixed, and 9.9 mg (0.06 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.7 g of the polymer of Example 18. The yield was 53%.

[0074] The polymer of Example 18 was prepared in the same manner as the polymer of Example 1. 1 The molecular structure was identified by H-NMR measurement. 1 1 is a H-NMR measurement chart. As a result, the polymer of Example 18 contained the structural unit E represented by general formula (1) (R 1 is a dimethyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 18 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 18 was 50%.

[0075] "Example 19" In a 100 ml Schlenk tube, 0.8 ml (6 mmol) of N-vinyl-4,4-dimethyl-oxazolidinone and 0.2 ml (3 mmol) of acrylonitrile were mixed, and 8.6 mg (0.05 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.4 g of the polymer of Example 19. The yield was 41%.

[0076] The polymer of Example 19 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 19 contained the structural unit E (R in general formula (1)) represented by the general formula (1) in the same manner as in Example 17.1 is a dimethyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 19 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 19 was 33%.

[0077] "Example 20" In a 100 ml Schlenk tube, 1 ml (8 mmol) of N-vinyl-4,4-dimethyl-oxazolidinone and 0.1 ml (2 mmol) of acrylonitrile were mixed, and 10.0 mg (0.06 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.8 g of the polymer of Example 20. The yield was 61%.

[0078] The polymer of Example 20 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 20 contained the structural unit E represented by general formula (1) (R in general formula (1)) in the same manner as in Example 17. 1 is a dimethyl group, R 2 is a hydrogen atom.) and a structural unit represented by formula (2). In addition, Example 20 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 20 was 17%.

[0079] "Example 21" In a 100 ml Schlenk tube, 0.5 ml (4 mmol) of N-vinyl-5-methyloxazolidinone (R in general formula (11)) was added. 2A compound in which the methyl group is present) was mixed with 1.0 ml (16 mmol) of acrylonitrile, and 10.7 mg (0.07 mmol) of azobisisobutyronitrile was added, followed by a reaction at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.9 g of the polymer of Example 21. The yield was 68%.

[0080] The polymer of Example 21 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, the polymer of Example 21 contained the structural unit F represented by the general formula (1) (R 1 is a hydrogen atom, and R 2 is a methyl group.) and a structural unit represented by formula (2). In addition, Example 21 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum. 21 The content of the structural unit represented by formula (2) in the polymer was 76%.

[0081] "Example 22" In a 100 ml Schlenk tube, 1.4 ml (12 mmol) of N-vinyl-5-methyloxazolidinone and 1.0 ml (16 mmol) of acrylonitrile were mixed, and 10.8 mg (0.07 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 1.5 g of the polymer of Example 22. The yield was 67%.

[0082] The polymer of Example 22 was prepared in the same manner as the polymer of Example 1. 1 The molecular structure was identified by H-NMR measurement. 1 1 is a H-NMR measurement chart. As a result, the polymer of Example 22, like the polymer of Example 21, contained the structural unit F represented by general formula (1) (R 1is a hydrogen atom, and R 2 is a methyl group.) and a structural unit represented by formula (2). In addition, Example 22 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 22 was 44%.

[0083] "Example 23" In a 100 ml Schlenk tube, 1.4 ml (12 mmol) of N-vinyl-5-methyloxazolidinone and 0.8 ml (12 mmol) of acrylonitrile were mixed, and 9.1 mg (0.06 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 1.3 g of the polymer of Example 23. The yield was 60%.

[0084] The polymer of Example 23 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 23, like the polymer of Example 21, contained the structural unit F represented by general formula (1) (R 1 is a hydrogen atom, and R 2 is a methyl group.) and a structural unit represented by formula (2). In addition, Example 23 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 23 was 28%.

[0085] "Example 24" In a 100 ml Schlenk tube, 1.4 ml (12 mmol) of N-vinyl-5-methyloxazolidinone and 0.4 ml (6 mmol) of acrylonitrile were mixed, and 14.8 mg (0.09 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 1.1 g of the polymer of Example 24. The yield was 60%.

[0086] The polymer of Example 24 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 24, like the polymer of Example 21, has a structural unit F represented by general formula (1) (R 1 is a hydrogen atom, and R 2 is a methyl group.) and a structural unit represented by formula (2). In addition, Example 24 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 24 was 13%.

[0087] "Example 25" In a 100 ml Schlenk tube, 0.5 ml (4 mmol) of N-vinyl-5,5-dimethyl-oxazolidinone and 1 ml (16 mmol) of acrylonitrile were mixed, and 11.2 mg (0.07 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.8 g of the polymer of Example 25. The yield was 54%.

[0088] The polymer of Example 25 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, the polymer of Example 25 contained the structural unit G represented by the general formula (1) (R 1 is a hydrogen atom, R 2is a dimethyl group.) and a structural unit represented by formula (2). In addition, Example 25 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 25 was 74%.

[0089] "Example 26" In a 100 ml Schlenk tube, 1.5 ml (12 mmol) of N-vinyl-5,5-dimethyl-oxazolidinone and 1 ml (16 mmol) of acrylonitrile were mixed, and 20.4 mg (0.12 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 1.1 g of the polymer of Example 26. The yield was 45%.

[0090] The polymer of Example 26 was prepared in the same manner as the polymer of Example 1. 1 H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 26, like Example 25, has a structural unit G represented by general formula (1) (R in general formula (1)). 1 is a hydrogen atom, R 2 is a dimethyl group.) and a structural unit represented by formula (2). In addition, Example 26 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 26 was 58%.

[0091] "Example 27" In a 100 ml Schlenk tube, 1.5 ml (12 mmol) of N-vinyl-5,5-dimethyl-oxazolidinone and 0.8 ml (12 mmol) of acrylonitrile were mixed, and 18.7 mg (0.11 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 0.9 g of the polymer of Example 27. The yield was 38%.

[0092] The polymer of Example 27 was prepared in the same manner as the polymer of Example 1. 1 The molecular structure was identified by H-NMR measurement. 1 1 is a H-NMR measurement chart. As a result, the polymer of Example 27, like Example 25, contained the structural unit G represented by general formula (1) (R 1 is a hydrogen atom, R 2 is a dimethyl group.) and a structural unit represented by formula (2). In addition, Example 27 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 27 was 41%.

[0093] "Example 28" In a 100 ml Schlenk tube, 1.5 ml (12 mmol) of N-vinyl-5,5-dimethyl-oxazolidinone and 0.4 ml (6 mmol) of acrylonitrile were mixed, and 16.1 mg (0.10 mmol) of azobisisobutyronitrile was added and reacted at 60°C for 2 hours. The reaction product was poured into 200 ml of methanol for reprecipitation, and then filtered and dried to obtain 1.0 g of the polymer of Example 28. The yield was 49%.

[0094] The polymer of Example 28 was prepared in the same manner as the polymer of Example 1. 1H-NMR measurement was carried out to identify the molecular structure. As a result, it was found that the polymer of Example 28, like Example 25, had a structural unit G represented by general formula (1) (R in general formula (1)). 1 is a hydrogen atom, R 2 is a dimethyl group.) and a structural unit represented by formula (2). In addition, Example 28 1 The composition ratio was calculated from the integral value of each signal in the H-NMR spectrum, and the result was that the content of the structural unit represented by formula (2) in the polymer of Example 28 was 19%.

[0095] "Comparative Example 1" Polyacrylonitrile (product name 181315, manufactured by Sigma-Aldrich) was used as the polymer in Comparative Example 1. "Comparative Example 2" Poly(acrylonitrile-co-methyl acrylate) (product name 517941, manufactured by Sigma-Aldrich) was used as the polymer in Comparative Example 2.

[0096] For each of the polymers of Examples 1 to 28 obtained in this manner, the R 2 Table 1 shows the amount of the structural unit represented by formula (2) and the content of the structural unit represented by formula (2). The names of the polymer compounds in Comparative Examples 1 and 2 are shown in Table 1.

[0097] [Table 1]

[0098] The glass transition temperature (Tg) of each of the polymers of Examples 1 to 28, Comparative Examples 1 and 2 was measured by the method described below. The results are shown in Table 1. (Method for measuring glass transition temperature (Tg)) Using a high-sensitivity differential scanning calorimeter (trade name: DSC6200, manufactured by Seiko Instruments Inc.), the temperature was raised and lowered in a nitrogen atmosphere from 30°C to 200°C at a heating rate of 20°C per minute, from 200°C to 30°C at a heating rate of 40°C per minute, and then from 30°C to 200°C at a heating rate of 20°C per minute.The inflection point at the second heating was determined and taken as the glass transition temperature (Tg).

[0099] Furthermore, the polymers of Examples 1 to 28, Comparative Example 1, and Comparative Example 2 were used as piezoelectric materials to manufacture piezoelectric films by the following method, and the piezoelectric constant d 33 The results are shown in Table 1.

[0100] (Piezoelectric film manufacturing) The piezoelectric material was dissolved in N,N-dimethylformamide as a solvent to prepare a 20% by mass polymer solution (coating solution). The obtained polymer solution was applied to a PET film (trade name: Lumirror (registered trademark), manufactured by Toray Industries, Inc.) as a substrate so that the thickness after drying would be 50 μm to form a coating film. The coating film formed on the PET film was then dried on a hot plate at 120°C for 6 hours to remove the solvent in the coating film, and a piezoelectric material sheet was obtained.

[0101] The resulting piezoelectric sheet was peeled off from the PET film, and aluminum electrodes were formed on one side and the other side of the piezoelectric sheet by vapor deposition. The electrodes of the piezoelectric sheet were then electrically connected to a high-voltage power supply HARB-20R60 (manufactured by Matsusada Precision Co., Ltd.), and the sheet was held at 140°C for 15 minutes with an electric field of 100 MV / m applied. The sheet was then gradually cooled to room temperature with the voltage still applied, and subjected to a poling treatment to obtain a sheet-like piezoelectric film.

[0102] (piezoelectric constant d 33 (Method of measurement) The piezoelectric film was attached to the measurement device using a pin with a tip diameter of 1.5 mm as a sample fixing jig. 33 The measuring device used was a piezometer system PM200 manufactured by PIEZOTEST. Piezoelectric constant d33 The measured value of d is either a positive or negative value depending on the front and back of the piezoelectric film being measured. 33 The absolute value of the actual measurement is recorded as the value.

[0103] As shown in Table 1, it was confirmed that the polymers of Examples 1 to 28 had higher glass transition temperatures (Tg) and better heat resistance than the polymers of Comparative Examples 1 and 2. Furthermore, the piezoelectric films formed using the polymers of Examples 1 to 28 as the piezoelectric material have a piezoelectric constant d 33 The piezoelectric properties were good. In particular, the piezoelectric films formed using the polymers of Example 2, Example 6, Example 7, Example 10, Example 11, Example 14, Example 15, Example 18, Example 19, Example 22, Example 26, and Example 27, in which the content of the structural units represented by formula (2) is 30 to 60 mol %, as piezoelectric materials, have a piezoelectric constant d 33 The piezoelectric properties were good.

Claims

1. A copolymer having a structural unit represented by the following general formula (1) and a structural unit represented by the following formula (2): 【Chemistry 1】 (In general formula (1), R 1 and R 2 are hydrogen atoms, one of R 3 and R 4 is a hydrogen atom, and one of them is a methyl group, or R 1 and R 2 are hydrogen atoms, and R 3 and R 4 are methyl groups, or one of R 1 and R 2 is a hydrogen atom, and one of them is one selected from the group consisting of a methyl group, an ethyl group, and an isopropyl group, and R 3 and R 4 are hydrogen atoms, or R 1 and R 2 are methyl groups, and R 3 and R 4 are hydrogen atoms.)

2. 2. The copolymer according to claim 1, wherein the content of the structural unit represented by the formula (2) is 10 to 80 mol %.

3. A piezoelectric material comprising the copolymer according to claim 1 or 2.

4. A piezoelectric film comprising the copolymer according to claim 1 or 2.

5. A piezoelectric element comprising the piezoelectric film according to claim 4 and an electrode disposed on the surface of the piezoelectric film.

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