Ferroelectric polymer and method for preparing ferroelectric polymer by crosslinking modification

Abstract

This invention belongs to the field of flexible piezoelectric polymer materials and discloses a ferroelectric polymer and a method for preparing a ferroelectric polymer by crosslinking modification. The preparation method includes: (1) dissolving polyvinylidene fluoride ferroelectric polymer in an organic solvent, adding a crosslinking agent with at least two NH2 groups, dispersing evenly, then placing the solution in a mold, drying the solvent, and obtaining a polymer film; (2) heating the polymer film to initiate a nucleophilic addition reaction-elimination of defluorination hydrogen reaction for chemical crosslinking, thereby obtaining a polyvinylidene fluoride ferroelectric polymer film crosslinked by C=N covalent bonds. This invention introduces a disordered structure of local molecular conformation by chemically crosslinking polyvinylidene fluoride ferroelectric polymer with a diamine crosslinking agent, thereby inducing a piezoelectric coefficient. d 33 Significant improvement.

Description

Technical Field

[0001] This invention belongs to the technical field of flexible piezoelectric polymer materials, and more specifically, relates to a ferroelectric polymer and a method for preparing a ferroelectric polymer by crosslinking modification. Background Technology

[0002] The piezoelectric coefficient is a core technical indicator for measuring the piezoelectric properties of materials and an important basis for evaluating the quality of piezoelectric materials. Currently, commercially available piezoelectric materials are mainly inorganic piezoelectric ceramics (or single crystals) and organic ferroelectric polymers. Among them, flexible polyvinylidene fluoride (PVDF) ferroelectric polymers have advantages such as light weight, biocompatibility, acoustic impedance matching with water, and significant application prospects in flexible wearable electronic devices, ultrasonic microscopes, underwater communication sensors, and energy harvesters. However, the piezoelectric coefficients of existing PVDF ferroelectric polymers are generally lower than those of piezoelectric ceramics; for example, the piezoelectric coefficient of ferroelectric polymers... d 33 The size is typically only 20.0-40.0 pC N. -1 Far lower than lead-free piezoelectric ceramics ( d 33 >100 pC N -1 The main bottleneck restricting the widespread application of ferroelectric polymers is the lack of ferroelectric polymers.

[0003] Currently, polyvinylidene fluoride d 33 Approximately -30 pC N -1 Furthermore, its preparation process has undergone over 50 years of optimization, and its piezoelectric coefficient has reached its limit. Polyvinylidene fluoride-trifluoroethylene copolymer P(VDF-TrFE) possesses quasi-isomorphic phase boundaries (MPB), and its optimal composition... d 33 Up to -63.5 pC N -1 Although MPB can significantly improve d 33 However, the synthesis of P(VDF-TrFE) carries certain safety risks, and the reactivity is difficult to control, causing the optimal composition to easily deviate from the feed ratio. Therefore, this MPB technology has not been widely applied. Recent research progress utilizes a combination of biaxial stretching and a highly polarized field, along with electrostriction, to enhance the reactivity of PVDF and P(VDF-TrFE. d 33 However, strong electric fields and complex synthesis processes cannot meet the application requirements for large-scale processing. d 33 The results are not based on the standard. d 33 The tester performs standard tests, but the results are specific under significantly increased dynamic forces. Furthermore, by introducing high... d 33Nanofillers improve the piezoelectric coefficient. Although the doping method for composite materials is relatively simple, the uneven dispersion of fillers and interfacial defects lead to uneven properties and poor processability of the composite materials.

[0004] Therefore, developing a new generation of piezoelectric polymers with high voltage coefficients and their large-scale preparation methods is of great significance for their wide application in fields such as piezoelectric sensors, acoustic devices, mobile communication devices, and underwater communication devices. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a ferroelectric polymer and a method for preparing the ferroelectric polymer through crosslinking modification. The aim is to induce a piezoelectric coefficient by chemically crosslinking a polyvinylidene fluoride ferroelectric polymer with a crosslinking agent containing at least two NH2 groups, thereby introducing a locally disordered molecular conformation. d 33 This significantly improves upon existing technologies, thereby solving technical problems such as the difficulty in improving the piezoelectric properties of polyvinylidene fluoride ferroelectric polymers and the difficulty in scaling up their preparation.

[0006] To achieve the above objectives, in one aspect of the present invention, a method for preparing polyvinylidene fluoride ferroelectric polymers by crosslinking modification is provided, comprising the following steps:

[0007] (1) Dissolve polyvinylidene fluoride ferroelectric polymer in an organic solvent, add a crosslinking agent with at least two NH2 groups, disperse evenly, then place the solution in a mold, dry the solvent, and obtain a polymer film material;

[0008] (2) The polymer membrane is heated to initiate a nucleophilic addition reaction and eliminate the defluorination reaction to carry out chemical crosslinking, thereby obtaining a polyvinylidene fluoride ferroelectric polymer membrane crosslinked by C=N covalent bonds.

[0009] Preferably, in step (1), the crosslinking agent with at least two NH2 groups is an aliphatic diamine crosslinking agent, an alicyclic diamine crosslinking agent, or an aromatic diamine crosslinking agent.

[0010] Preferably, the aliphatic diamine crosslinking agent comprises one of the following: methyldiamine, 1,2-ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, 1,4-butyldiamine, 1,5-pentanediamine, 1,3-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,14-diaminotetradecane, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine, and methyldiamine dihydrochloride.

[0011] The aromatic diamine crosslinking agent includes one of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 1,2-naphthylenediamine, 1,4-naphthylenediamine, 1,5-naphthylenediamine, 1,7-naphthylenediamine, 1,8-naphthylenediamine, 2,6-naphthylenediamine, and 2,7-naphthylenediamine;

[0012] The alicyclic diamine crosslinking agent includes one of cis-cyclopropanediamine hydrochloride, piperazine, 1,2-cyclopropanediamine dihydrochloride, 1,4-cyclohexanediamine, 1,3-cyclohexanediamine, and 1,2-cyclohexanediamine.

[0013] Preferably, in step (1), the polyvinylidene fluoride ferroelectric polymer is polyvinylidene fluoride trifluoroethylene or polyvinylidene fluoride tetrafluoroethylene.

[0014] Preferably, in step (1), the polyvinylidene fluoride ferroelectric polymer and the crosslinking agent are in a molar ratio of 100:(0.01-10); more preferably, it is 100:(0.15-3.5).

[0015] Preferably, in step (1), the temperature of the drying solvent is 40-100℃ and the time is 8-48 h.

[0016] Preferably, in step (2), the polymer is heated, specifically including: under air or inert gas, the heating temperature is 140°C to 300°C, and the heating reaction time is 0.1-24 h.

[0017] Preferably, in step (2), the polymer is dried and heated in a nitrogen atmosphere at a temperature of 170°C to 240°C for a reaction time of 0.5-4 h.

[0018] Preferably, in step (1), the organic solvent is one of cyclohexanone, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0019] In another aspect of the present invention, a polyvinylidene fluoride ferroelectric polymer membrane material prepared according to the method described above is provided.

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0021] 1. This invention provides a ferroelectric polymer and a method for preparing a ferroelectric polymer through crosslinking modification. The method involves chemically crosslinking a polyvinylidene fluoride (PVDF) ferroelectric polymer with a crosslinking agent containing at least two NH₂ groups. The crosslinking structure locally enhances the disordered molecular structure, thereby improving the stability of the 3 / 1 helical conformation relative to the all-trans conformation in the ferroelectric polymer. This allows the material to maintain intense phase competition even under electric field polarization, leading to a "critical" state where the phase transition energy barrier is significantly reduced, making it easier to switch between the two phases. Ultimately, this mechanism enables the material to respond significantly to small external perturbations, achieving a piezoelectric coefficient... d 33 Significant improvement.

[0022] 2. This invention is applicable to a variety of crosslinking agents and polyvinylidene fluoride ferroelectric copolymers. It can be adjusted based on different polymers and crosslinking agents to meet different application scenarios, thus having universality.

[0023] 3. This invention significantly improves the piezoelectric properties of polyvinylidene fluoride ferroelectric polymers. After crosslinking treatment, the piezoelectric coefficient of polyvinylidene fluoride trifluoroethylene is significantly improved. d 33 Improved by 220% (-40.0 pC N) -1 Upgraded to -88.0 pC N -1 Furthermore, the cross-linked polyvinylidene fluoride ferroelectric polymer piezoelectric material obtained by this invention has a simple, convenient, and easy-to-operate preparation process, good thermoplasticity, and can be secondary molded by melt extrusion, hot pressing, hot rolling, etc., and has great potential for large-scale production. Attached Figure Description

[0024] Figure 1 This is a flowchart of the method for preparing polyvinylidene fluoride ferroelectric polymer by crosslinking modification in this invention.

[0025] Figure 2 This is the X-ray photoelectron spectroscopy (XPS) spectrum of the crosslinking agent and the crosslinked P(VDF-TrFE) material in Example 1 of the present invention.

[0026] Figure 3 The P(VDF-TrFE) material before and after crosslinking in Examples 1-5 of this invention is composed of... d 33 Tester measured d 33 contrast.

[0027] Figure 4 This is the strain curve of the sample before and after crosslinking under a 1Hz electric field induction in Example 1 of the present invention.

[0028] Figure 5It refers to the crystallinity of the materials obtained in Examples 1-5 of this invention.

[0029] Figure 6 The crystal structure changes of the sample before and after crosslinking under different polarization electric fields were determined by XRD in Example 1 of this invention.

[0030] Figure 7 The sample obtained in Example 1 of this invention is from d 33 The tester measured the results under different pressure cycles. d 33 data.

[0031] Figure 8 The sample in Embodiment 1 of this invention is made from d 33 The tester measured at different temperatures d 33 data.

[0032] Figure 9 This is an actual sample (a) obtained in Example 1 of the present invention and a schematic diagram of the crosslinking mechanism (b). Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0034] In the following embodiments, all instruments and other equipment used, unless otherwise specified, are conventional products that can be purchased through legitimate channels. Unless otherwise specified, all methods described are conventional methods, and all raw materials are available from publicly available commercial sources.

[0035] This invention provides a polyvinylidene fluoride ferroelectric polymer and a method for preparing the polyvinylidene fluoride ferroelectric polymer through crosslinking modification, such as... Figure 1 As shown, it includes the following steps:

[0036] (1) Dissolve polyvinylidene fluoride ferroelectric polymer in an organic solvent to obtain a polymer solution; add a crosslinking agent with at least two NH2 groups to the polymer solution and stir until it is evenly dispersed; then place the solution in a mold, dry the solvent, and obtain a polymer film.

[0037] (2) The polymer membrane obtained in the above steps is heated to initiate a nucleophilic addition reaction and eliminate the defluorination reaction to carry out chemical crosslinking, so as to obtain a polyvinylidene fluoride ferroelectric polymer membrane crosslinked by C=N covalent bonds.

[0038] Furthermore, the polyvinylidene fluoride ferroelectric polymer is polyvinylidene fluoride trifluoroethylene (P(VDF-TrFE)) or polyvinylidene fluoride tetrafluoroethylene (P(VDF-TFE)); preferably polyvinylidene fluoride-trifluoroethylene.

[0039] Furthermore, the organic solvent is any one of cyclohexanone, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone; preferably cyclohexanone.

[0040] Furthermore, the concentration of the polymer solution is 0.1 mol / mL-4 mol / mL, the stirring time is 6-24 h, and the temperature is 25-45℃; preferably 1 mol / mL, stirred at 40℃ for 12 h.

[0041] Further, a crosslinking agent with at least two NH2 groups is dispersed in the polymer solution by stirring for 1-8 h at a temperature of 25-45°C; preferably, it is stirred at 40°C for 1-4 h.

[0042] Furthermore, the crosslinking agent having at least two NH2 groups includes any one of aliphatic diamines, alicyclic diamines, and aromatic diamines. This crosslinking agent with at least two NH2 groups can act as a nucleophile, undergoing nucleophilic substitution or nucleophilic addition reactions with the vinylidene fluoride (VDF) units on the polyvinylidene fluoride ferroelectric polymer chain, accompanied by defluorination, thereby forming a carbon-nitrogen double bond (C=N) covalent bond.

[0043] Among them, the aliphatic diamine crosslinking agent is characterized by the variable carbon chain length and symmetry in its molecular structure, which consists of 2 to 14 carbon atoms and contains two or more amino groups. It can undergo nucleophilic reactions with polyvinylidene fluoride ferroelectric polymers and form a crosslinked network structure linked by carbon-nitrogen double bonds through two defluorination hydrogen reactions. The aliphatic diamine crosslinking agent is any one of methyldiamine, 1,2-ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, 1,4-butyldiamine, 1,5-pentanediamine, 1,3-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,14-diaminotetradecane, diethylenetriamine, triethylenetetraamine, tetraethylenepentamine, pentaethylenehexamine, and methyldiamine dihydrochloride; preferably 1,2-ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, 1,4-butyldiamine, 1,5-pentanediamine, and 1,3-pentanediamine.

[0044] The aromatic diamine crosslinking agent is characterized by having an aromatic ring in its molecular structure. The aromatic ring can be a monocyclic or polycyclic structure, such as a benzene ring or a naphthalene ring. Its molecular structure contains two or more amino groups, enabling it to undergo a nucleophilic reaction with the vinylidene fluoride (VDF) units on the polyvinylidene fluoride ferroelectric polymer, forming a crosslinked network structure linked by carbon-nitrogen double bonds through two defluorination reactions. The aromatic diamine is any one of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 1,2-naphthylenediamine, 1,4-naphthylenediamine, 1,5-naphthylenediamine, 1,7-naphthylenediamine, 1,8-naphthylenediamine, 2,6-naphthylenediamine, and 2,7-naphthylenediamine; preferably p-phenylenediamine.

[0045] The alicyclic diamine crosslinking agent is characterized by having two or more amino groups in its molecular structure, which react with vinylidene fluoride (VDF) units in the polymer chain to form a crosslinked structure. Its alicyclic structure can be monocyclic or polycyclic. The alicyclic diamine is any one of cis-cyclopropanediamine hydrochloride, piperazine, 1,2-cyclopropanediamine dihydrochloride, 1,4-cyclohexanediamine, 1,3-cyclohexanediamine, and 1,2-cyclohexanediamine; preferably 1,4-cyclohexanediamine.

[0046] Further, the polyvinylidene fluoride ferroelectric polymer and the crosslinking agent are in a molar ratio of 100:(0.01-10); preferably 100:(0.15-3.5).

[0047] Furthermore, the mold is a rectangular flat plate with a smooth surface made of glass or polytetrafluoroethylene.

[0048] Furthermore, in step (1), the drying solvent is carried out in a forced-air drying oven at a temperature range of 40-100°C for 8-48 hours, preferably at 70°C for 12 hours.

[0049] Further, in step (2), the polymer with a fixed shape is heated, specifically including: the thermal crosslinking reaction atmosphere is nitrogen or air, preferably in a nitrogen atmosphere; the thermal crosslinking reaction temperature range is between 140-300℃, and the crosslinking reaction time is between 0.1-24 h; preferably the thermal crosslinking reaction temperature range is 170-240℃, and the crosslinking reaction time is 0.5-4 h.

[0050] A polyvinylidene fluoride (PVDF) ferroelectric polymer membrane was prepared by any of the above-mentioned methods for crosslinking modification. In this PVDF ferroelectric polymer, the monomers are crosslinked via C=N covalent bonds, and the structural formula is as follows:

[0051] ;

[0052] Wherein, R1 is the organic skeleton of the crosslinking agent linking the amino group in the at least two NH2 groups, R2 is H or F element; m represents the number of repeating units of vinylidene fluoride, n represents the number of repeating units of tetrafluoroethylene or trifluoroethylene, and the values ​​of m and n are any integers from 100 to 100000; x is the number of crosslinking reaction units, which is related to the degree of crosslinking.

[0053] The resulting cross-linked polyvinylidene fluoride ferroelectric polymer piezoelectric material not only possesses excellent piezoelectric properties but also thermoplasticity, making it suitable for various molding and processing technologies such as hot pressing, extrusion, hot rolling, injection molding, blow molding, and 3D printing. This material plays a significant role in promoting the widespread application of flexible piezoelectric sensors, acoustic devices, mobile communication devices, and underwater communication devices, providing efficient and practical solutions for the development of related technologies.

[0054] The present invention will now be described in further detail with reference to the accompanying drawings.

[0055] Example 1: Figure 9 This is an actual sample (a) and a schematic diagram (b) of the crosslinking mechanism obtained in Example 1 of this invention. 10 mol of P(VDF-TrFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min for 12 hours at 40°C. Then, 0.009 mol of 1,2-propylenediamine was added to the P(VDF-TrFE) solution, and the mixture was stirred at 300 rpm / min for 1 hour at 40°C. The solution was then poured directly into a quartz glass mold and dried at 80°C for 8 hours to form a film. Subsequently, the temperature was increased to 200°C and reacted for 2 hours to carry out a thermal crosslinking reaction, obtaining a crosslinked P(VDF-TrFE) piezoelectric film material with a piezoelectric coefficient. d 33 The pC / N ratio is 88.0 ± 3.0. The cross-linked P(VDF-TrFE) piezoelectric material prepared in Example 1 is compared with typical polymer piezoelectric materials. d 33 The comparison results are detailed in Table 1.

[0056] Table 1: Examples of typical polymer piezoelectric materials and their composition d 33 Tester measured d 33 contrast

[0057]

[0058] Example 2: 10 mol of P(VDF-TrFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min for 12 hours at 40°C. Then, 0.009 mol of 1,3-propylenediamine was added to the P(VDF-TrFE) solution, and the mixture was stirred at 300 rpm / min for 1 hour at 40°C. The solution was then poured directly into a quartz glass mold and dried at 80°C for 8 hours to form a film. Subsequently, the temperature was increased to 210°C and reacted for 2 hours to carry out a thermal crosslinking reaction, obtaining a crosslinked P(VDF-TrFE) piezoelectric film with a piezoelectric coefficient of... d 33 It is 76.0 ± 2.1 pC N. -1 .

[0059] Example 3: 10 mol of P(VDF-TrFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min for 12 hours at 40°C. Then, 0.009 mol of 1,5-pentanediamine was added to the P(VDF-TrFE) solution, and the mixture was stirred at 300 rpm / min for 1 hour at 40°C. The solution was then poured directly into a polytetrafluoroethylene mold and dried at 80°C for 8 hours to form a film. Subsequently, the temperature was increased to 220°C and reacted for 1.5 hours to carry out a thermal crosslinking reaction, obtaining a crosslinked P(VDF-TrFE) piezoelectric film with a piezoelectric coefficient of... d 33 The value was 71.2 ± 2.2 pC N. -1 .

[0060] Example 4: 10 mol of P(VDF-TrFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min for 12 hours at 40 °C. 0.009 mol of 1,10-diaminodecane was added to the P(VDF-TrFE) solution, and the mixture was stirred at 300 rpm / min for 1 hour at 40 °C. The solution was then poured directly into a quartz glass mold and dried at 80 °C for 8 hours to form a film. Subsequently, the temperature was increased to 190 °C and reacted for 2.5 hours to carry out a thermal crosslinking reaction, obtaining a crosslinked P(VDF-TrFE) piezoelectric film with a piezoelectric coefficient of... d 33 The value was 68.8 ± 3.1 pC N. -1 .

[0061] Example 5: 10 mol of P(VDF-TrFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min for 12 hours at 40°C. Then, 0.009 mol of p-phenylenediamine was added to the P(VDF-TrFE) solution, and the mixture was stirred at 300 rpm / min for 1 hour at 40°C. The solution was then poured directly into a quartz glass mold and dried at 80°C for 8 hours to form a film. Subsequently, the temperature was increased to 200°C and reacted for 2 hours to carry out a thermal crosslinking reaction, obtaining a crosslinked P(VDF-TrFE) piezoelectric film with a piezoelectric coefficient of... d 33 The value was 67.3 ± 2.0 pC N. -1 .

[0062] Example 6: 10 mol of P(VDF-TrFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min for 12 hours at 40°C. Then, 0.009 mol of 1,4-cyclohexanediamine was added to the P(VDF-TrFE) solution, and the mixture was stirred at 300 rpm / min for 1 hour at 40°C. The solution was then poured directly into a quartz glass mold and dried at 80°C for 8 hours to form a film. Subsequently, the temperature was increased to 190°C for 1 hour to carry out a thermal crosslinking reaction, obtaining a crosslinked P(VDF-TrFE) piezoelectric film with a piezoelectric coefficient of... d 33 The value was 67.9 ± 1.9 pC N. -1 .

[0063] Example 7: 10 mol of P(VDF-TFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min for 12 hours at 40°C. 0.012 mol of 1,3-propylenediamine was added to the P(VDF-TFE) solution, and the mixture was stirred at 300 rpm / min for 1 hour at 40°C. The solution was then poured directly into a quartz glass mold and dried at 80°C for 8 hours to form a film. Subsequently, the temperature was increased to 190°C and reacted for 1 hour to carry out a thermal crosslinking reaction, obtaining a crosslinked P(VDF-TFE) piezoelectric film with a piezoelectric coefficient of... d 33 It is 74.3 ± 2.3 pC N. -1 .

[0064] Comparative Example 1: 10 mol of P(VDF-TrFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min for 12 hours at 40 °C. Then, 0.009 mol of 1,12-diaminododecane was added to the P(VDF-TrFE) solution, and the mixture was stirred at 300 rpm / min at 40 °C. -1 The mixture was stirred at a certain rate for 1 hour, and then the solution was poured directly into a quartz glass mold and dried at 60°C for 8 hours to form a film. Subsequently, the temperature was raised to 80°C and reacted for 5 hours to carry out a thermal crosslinking reaction, thereby obtaining a crosslinked P(VDF-TrFE) piezoelectric film.

[0065] Comparative Example 2: 10 mol of P(VDF-TrFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min at 40 °C for 12 hours. 0.009 mol of 1,12-diaminododecane was added to the P(VDF-TrFE) solution, and the solution was stirred at 300 rpm / min at 40 °C for 1 hour. The solution was then poured directly into a quartz glass mold and dried at 60 °C for 8 hours to form a film. Subsequently, the temperature was raised to 180 °C and reacted for 0.05 hours to carry out a thermal crosslinking reaction, thereby obtaining a crosslinked P(VDF-TrFE) piezoelectric film.

[0066] Comparative Example 3: 10 mol of P(VDF-TrFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min for 12 hours at 40 °C. 0.1 mol of pentaethylenehexamine was added to the P(VDF-TrFE) solution, and the solution was stirred at 300 rpm / min for 1 hour at 40 °C. The solution was then poured directly into a quartz glass mold and dried at 60 °C for 8 hours to form a film. The temperature was then raised to 100 °C and reacted for 5 hours to carry out a thermal crosslinking reaction, thereby obtaining a crosslinked P(VDF-TrFE) piezoelectric film.

[0067] Comparative Example 4: 10 mol of P(VDF-TrFE) was added to 10 mL of cyclohexanone solution to prepare a polymer solution with a concentration of 1 mol / mL. The solution was stirred at 300 rpm / min for 12 hours at 40 °C. 0.1 mol of m-phenylenediamine was added to the P(VDF-TrFE) solution, and the solution was stirred at 300 rpm / min for 1 hour at 40 °C. The solution was then poured directly into a quartz glass mold and dried at 60 °C for 8 hours to form a film. The temperature was then increased to 120 °C and reacted for 12 hours to carry out a thermal crosslinking reaction, thereby obtaining a crosslinked P(VDF-TrFE) piezoelectric film.

[0068] Table 2: Examples 1 and Comparative Examples 1-4d 33 Tester measured d 33 contrast

[0069]

[0070] Figure 2 The X-ray photoelectron spectroscopy (XPS) spectra of the crosslinking agent and the crosslinked P(VDF-TrFE) material in Example 1 show that the CN single bond is completely converted into the C=N double bond, verifying the chemical mechanism and integrity of the crosslinking reaction.

[0071] Figure 3 The P(VDF-TrFE) material before and after crosslinking in Examples 1-5 of this invention is composed of... d 33 Tester measured d 33 The comparison showed that its d 33 The piezoelectricity of the materials increases with decreasing C atoms in the crosslinking agent. The materials prepared in the embodiments and comparative examples of this invention were tested using a PolyK Technologies PKD3-2000 piezoelectric coefficient tester, employing the quasi-static Berlincourt method (static force approximately 0.5 N, dynamic force approximately 0.25 N, measurement frequency 110 Hz) to measure the piezoelectric coefficient. d 33 Conduct the test.

[0072] Figure 4 This is the strain curve of the sample before and after crosslinking under a 1Hz electric field induction in Example 1 of the present invention. The slope reflects the strain of the sample. d 33 Size, confirming cross-linking d 33 Enhance.

[0073] Figure 5 The crystallinity of the materials obtained in Examples 1-5 of this invention shows that the materials in these examples still maintain a high degree of crystallinity after cross-linking, ensuring the structural integrity and long-term reliability of the cross-linked materials.

[0074] Figure 6 In Example 1 of this invention, the crystal structure changes of the sample before and after crosslinking were determined by XRD. The results showed that the crosslinking structure locally enhanced the disordered molecular structure, thereby improving the stability of the 3 / 1 helical conformation relative to the all-trans conformation in the ferroelectric polymer. This allows the material to maintain intense phase competition under electric field polarization, leading to a "critical" state where the phase transition energy barrier is significantly reduced, making it easier to switch between the two phases. Ultimately, this mechanism enables the material to respond significantly to small external perturbations, achieving a piezoelectric coefficient.d 33 Significant improvement.

[0075] Figure 7 The measurements were taken from the sample obtained in Example 1 of this invention under different pressure cycles. d 33 Data, and Figure 8 The results of the test sample in Example 1 were measured at different temperatures. d 33 Data and results show that under different pressure cycles and different temperatures... d 33 It still maintains good stability and consistency.

[0076] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of protection of this invention and its equivalents, this invention also intends to include these modifications and variations. The above-described embodiments are merely preferred embodiments given to fully illustrate this invention, and their scope of protection is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on this invention are all within the scope of protection of this invention.

Claims

1. A method for preparing polyvinylidene fluoride ferroelectric polymers through crosslinking modification, characterized in that, Includes the following steps: (1) Dissolve polyvinylidene fluoride ferroelectric polymer in an organic solvent, add a crosslinking agent with at least two NH2 groups, disperse evenly, then place the solution in a mold, dry the solvent, and obtain a polymer film material; the polyvinylidene fluoride ferroelectric polymer is polyvinylidene fluoride trifluoroethylene or polyvinylidene fluoride tetrafluoroethylene; the crosslinking agent with at least two NH2 groups is an aliphatic diamine crosslinking agent, an alicyclic diamine crosslinking agent, or an aromatic diamine crosslinking agent; the aliphatic diamine crosslinking agent includes methyldiamine, 1,2-ethylenediamine, 1,2-propanediamine, 1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,3-pentanediamine; the molar ratio of polyvinylidene fluoride ferroelectric polymer to the crosslinking agent is 100: (0.01-10); (2) The polymer membrane is heated to initiate a nucleophilic addition reaction and eliminate the defluorination reaction to carry out chemical cross-linking, introducing a disordered structure of local molecular conformation, and obtaining a polyvinylidene fluoride ferroelectric polymer membrane cross-linked by C=N covalent bonds.

2. The method for preparing polyvinylidene fluoride ferroelectric polymer by crosslinking modification according to claim 1, characterized in that, The aromatic diamine crosslinking agent includes one of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 1,2-naphthylenediamine, 1,4-naphthylenediamine, 1,5-naphthylenediamine, 1,7-naphthylenediamine, 1,8-naphthylenediamine, 2,6-naphthylenediamine, and 2,7-naphthylenediamine; The alicyclic diamine crosslinking agent includes one of cis-cyclopropanediamine hydrochloride, piperazine, 1,2-cyclopropanediamine dihydrochloride, 1,4-cyclohexanediamine, 1,3-cyclohexanediamine, and 1,2-cyclohexanediamine.

3. The method for preparing polyvinylidene fluoride ferroelectric polymer by crosslinking modification according to claim 1, characterized in that, In step (1), the molar ratio of the polyvinylidene fluoride ferroelectric polymer to the crosslinking agent is 100: (0.15-3.5).

4. The method for preparing polyvinylidene fluoride ferroelectric polymer by crosslinking modification according to claim 1, characterized in that, In step (1), the temperature of the drying solvent is 40-100℃ and the time is 8-48 h.

5. The method for preparing polyvinylidene fluoride ferroelectric polymer by crosslinking modification according to claim 1, characterized in that, In step (2), the polymer film is heated, specifically including: under air or inert gas, the heating temperature is 140°C to 300°C, and the heating reaction time is 0.1-24 h.

6. The method for preparing polyvinylidene fluoride ferroelectric polymer by crosslinking modification according to claim 1, characterized in that, In step (2), the polymer film is heated, including: under a nitrogen atmosphere, the heating temperature is between 170°C and 240°C, and the heating reaction time is 0.5-4 h.

7. The method for preparing polyvinylidene fluoride ferroelectric polymer by crosslinking modification according to claim 1, characterized in that, In step (1), the organic solvent is one of cyclohexanone, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

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