Electrocaloric polymer, ink and film comprising same, and uses thereof

Abstract

A polymer including VDF-based units having an electrocaloric effect under the effect of a variable electric field. The polymer includes 0.1 to 10.0 mol % double bonds, which are substantially non-conjugated. Also, a corresponding composition including the polymer, a corresponding film including the polymer, and to various uses of the polymer.

Claims

1. A polymer exhibiting an electrocaloric effect under the effect of a variable electric field, said polymer comprising: from 30 mol % to 90 mol % of unit of formula: -(CF2-CH2)-(III), from 1 mol % to 59.9 mol % of at least one unit of formula: -(CX1X2-CX3X4)-(IV), from 0 mol % to (20-N) mol % of at least one unit of formula: -(CY1Y2-CY3Z)—(V), N mol % of ethylenic unit(s) chosen from the list consisting of: —(CY3═CF)—, —(CY3═CX1)-, -(CY3═CX2)-, -(CY1═CY3)-, -(CY2═CY3)- and their mixture; in which: X1 and X2 independently denote: —H, —F or alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, X3 and X4 independently denote: —F or alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, except for the combination where: X1 and X2 are both: —H and X3 and X4 are both: —F, Y1 and Y2 independently denote: —H, —F, —CI or alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, Y3 denotes: —F, —Cl or alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, Z denotes a halogen atom other than: —F, N is a number ranging from 0.1 to 10.0; said polymer essentially not exhibiting a conjugated carbon-carbon double bond.

2. The polymer as claimed in claim 1, in which X1 denotes: —H or —F; and X2, X3 and X4 denote, all three: —F.

3. The polymer as claimed in claim 1, in which Z denotes: —Cl.

4. The polymer as claimed in claim 1, in which Y3 denotes: —F, and Y1 and Y2 both denote: —H or —F.

5. The polymer as claimed in claim 1, said polymer comprising at least 1 mol % of unit of formula (V).

6. The polymer as claimed in claim 1, said polymer being relaxor ferroelectric.

7. The polymer as claimed in claim 1, said polymer having a remanent polarization of less than or equal to 20 mC/m2 and/or a coercive field of less than or equal to 25 V.Math.μm−1, the remanent polarization and coercive field measurements both being carried out at 25° C., at a frequency of 1 Hz and at a field of 150 V/μm.

8. The polymer as claimed in claim 1, having a weight-average molecular weight of greater than or equal to 200 000 g/mol.

9. The polymer as claimed in claim 1, having an enthalpy of fusion of greater than or equal to 10 J/g, the enthalpy of fusion being measured according to the standard ISO 11357-2: 2013, in second heating with temperature gradients of 10° C./min.

10. The polymer as claimed in claim 1, having a relative dielectric permittivity of greater than or equal to 15, over a range of temperatures of at least 5° C. said relative dielectric permittivity being measured at 1 kHz.

11. The polymer as claimed in claim 1, having a permittivity maximum at a temperature of less than or equal to 60° C.; said relative dielectric permittivity being measured at 1 kHz.

12. The polymer as claimed in claim 1, said polymer being capable of being obtained by a process comprising: a) the provision of an initial polymer comprising, in total moles of polymer: from 40 mol % to 90 mol % of unit of formula: —(CF2-CH2)-(III), from 9.9 mol % to 59.9 mol % of at least one unit of formula: —(CX1X2-CX3X4)-(IV), from 0.1 mol % to 20 mol % of at least one unit of formula: —(CY1Y2-CY.sub.3Z)— (V); b) the dehydrohalogenation of said initial polymer, said dehydrohalogenation consisting essentially of the elimination, at least partially, of: —Z and of an adjacent hydrogen.

13. The polymer as claimed in claim 10, having a variation in adiabatic temperature which is at least greater by 0.5° C., with respect to the variation in adiabatic temperature of said initial polymer, at at least one measurement temperature, the measurements of variations in adiabatic temperatures being carried out at a variable electric field having a maximum amplitude equal to 86 V/μm.

14. The polymer as claimed in claim 12, having a relative dielectric permittivity maximum which is at least greater by 5%, with respect to the dielectric permittivity maximum of said initial polymer; said relative dielectric permittivity being measured at 1 kHz.

15. The polymer as claimed in claim 12, in which the dehydrohalogenation is carried out with a reaction progress of at least 0.1.

16. A composition comprising: at least one polymer as claimed in claim 1, and at least one liquid vehicle for said polymer.

17. A film comprising the polymer as claimed in claim 1.

18. The film as claimed in claim 17, having a thickness of greater than or equal to 0.1 micrometer.

19. A heat transfer system comprising a polymer as claimed in claim 1.

20. An energy storage system comprising a polymer as claimed in claim 21.

21. The polymer as claimed in claim 1, in which X1 denotes: —H; X2, X3 and X4 denote, all three: —F; Y3 denotes: —F; Y1 and Y2 both denote: —H; and Z denotes —Cl; in which N is chosen between 0.1 and 2.

22. The polymer as claimed in claim 1, in which X1 denotes: —H; X2, X3 and X4 denote, all three: —F; Y1, Y2 and Y3 denote, all three: —F; and Z denotes: —Cl; in which N is chosen between 0.1 and 10.0.

Description

FIGURES

[0175] FIG. 1 represents a test bench 1 used to measure the electrocaloric performance qualities of polymers as a function of the temperature.

[0176] FIG. 2 represents a typical variation in temperature of a plate 2 in a test bench 1 during the application of a square-wave electric field with a height ΔE. ΔE corresponds to the maximum amplitude of the applied electric field and is expressed in volt/meter (V/m). The temperature variation peak, ΔT, comparable to an adiabatic temperature variation, is expressed in Kelvin (K). The x axis represented corresponds to the time in seconds (s).

[0177] FIG. 3 represents the liquid .sup.1H NMR spectrograms, measured using a Bruker Advance DPX 400 MHz appliance, of comparative example 1 and examples 1 to 5. The x axis represented corresponds to the chemical shift .sup.6H in ppm.

[0178] FIG. 4 represents the Raman spectrograms, standardized with respect to the vibration band corresponding to —CF.sub.2— between 775 and 950 cm.sup.−1, of the P(VDF-TrFE-CTFE) terpolymers unmodified (Comp. Ex. 1) and modified (Ex. 1 to Ex. 5). The x axis corresponds to the wavenumber in cm.sup.−1 and the y axis to the relative intensity.

[0179] FIG. 5 represents the Raman spectrograms, standardized with respect to the vibration band corresponding to —CF.sub.2— between 775 and 950 cm.sup.−1, of the P(VDF-TrFE-CFE) terpolymers unmodified (Comp. Ex. 2) and modified (Comp. Ex. 3 and Ex. 6-7). The x axis corresponds to the wavenumber in cm.sup.−1 and the y axis to the relative intensity.

[0180] FIG. 6A represents the variation in adiabatic temperature ΔT.sub.EC measured on a test bench, such as that of FIG. 1, at a measurement temperature of 25° C. as a function of the maximum amplitude of the applied electric field (expressed in MV/m), for the unmodified P(VDF-TrFE-CTFE) according to comparative example 1 (bottom curve) and for a modified P(VDF-TrFE-CTFE) according to example 4 (top curve).

[0181] FIG. 6B represents the variation in adiabatic temperature ΔT.sub.EC (expressed in K) measured on a test bench, such as that of FIG. 1, at a measurement temperature gradient of 10° C./min (expressed in ° C.) and under an electric field with a maximum amplitude ΔE=86 MV.Math.m.sup.−1, for the unmodified P(VDF-TrFE-CTFE) according to comparative example 1 (bottom curve) and for a modified P(VDF-TrFE-CTFE) according to example 4 (top curve).

[0182] FIG. 7A represents the variation in adiabatic temperature ΔT.sub.EC measured on a test bench, such as that of FIG. 1, at a measurement temperature of 25° C. as a function of the maximum amplitude of the applied electric field (expressed in MV/m), for the unmodified P(VDF-TrFE-CFE) according to comparative example 3 (bottom curve) and for a modified P(VDF-TrFE-CFE) according to example 8 (top curve).

[0183] FIG. 7B and

[0184] FIG. 7C represent the variation in adiabatic temperature ΔT.sub.EC (expressed in K) measured on a test bench, such as that of FIG. 1, at a measurement temperature gradient of 10° C./min (expressed in ° C.) and under an electric field with a maximum amplitude of: ΔE=60 MV.Math.m.sup.−1 (7B) and, respectively: ΔE=75 MV.Math.m.sup.−1 (7C) for the unmodified P(VDF-TrFE-CFE) according to comparative example 2 (bottom curve) and for a modified P(VDF-TrFE-CFE) according to example 8 (top curve).

[0185] FIG. 8 represents the relative dielectric permittivity as a function of the measurement temperature of films annealed at 110° C. for 1 hour of the polymers according to examples 1 to 5 and of comparative example 1. The x axis corresponds to the temperature in ° C. and the y axis to the relative dielectric permittivity.

[0186] FIG. 9 represents the polarization as a function of the electric field at 25° C. of films annealed at 110° C. for 1 h of the polymers according to examples 1-5 and according to comparative example 1. The x axis corresponds to the electric field in MV/m and the y axis to the polarization in μC/cm.sup.2.

[0187] FIG. 10 represents the relative dielectric permittivity as a function of the temperature of films annealed at 110° C. for 1 h of the polymers according to example 7 and comparative examples 2 and 3. The x axis corresponds to the temperature in ° C. and the y axis to the relative dielectric permittivity.

[0188] FIG. 11 represents the polarization as a function of the electric field at 25° C. of films annealed at 110° C. for 1 h of the polymers according to example 8 and according to comparative example 2. The x axis corresponds to the electric field in MV/m and the y axis to the polarization in μC/cm.sup.2.

[0189] FIG. 12 represents superimposed infrared spectrograms of the polymer according to example 3 after storage at 110° C. for 1 h, 5 h and 3 d. The x axis corresponds to the wavenumber in cm.sup.−1 and the y axis to the standardized absorbance.

CHARACTERIZATION OF THE POLYMERS

Measurements of the Electroactive and Electrocaloric Performance Qualities of a Polymer Film

[0190] With reference to FIG. 1, a polymer film 21 is prepared by blade coating starting from a 100 mg/ml solution in a solvent in which it is soluble. For the polymers tested in the examples below, the solvent used was cyclopentanone.

[0191] The solution is prepared at ambient temperature (25° C.) under magnetic stirring for 24 h. Films 21 of 14 μm are deposited on a substrate 22. The substrate 22 is made of PET, has a thickness of 50 μm and was metallized beforehand (10 nm of Cr and 100 nm of Ag). After drying at 90° C. for 2 h, the upper electrodes 23 are evaporated. An annealing is subsequently carried out at 105° C. for 12 h under vacuum. A plate 2 comprising a film of the polymer to be characterized is obtained.

[0192] The low-field dielectric data are obtained with a “Solartron SI 1260” device, sold by Solartron Analytical, equipped with the “Solartron 1296 dielectric interface” interface and with a “TP94 Linkam” chamber, sold by Linkam Scientific, for the control of the temperature. The measurements are carried out at 1 kHz at different temperatures.

[0193] The polarization curves (electric displacement (D) as a function of the electric field (E)) are produced with an “aixACCT TF Analyzer 2000” device, sold by aixACCT Systems, equipped with a “Treck 20/20C-HS” high-voltage amplifier, sold by Treck.

[0194] The electrocaloric performance qualities are measured as a function of the temperature and of the applied electric field from a test bench 1 as represented in FIG. 1. The test bench comprises the plate 2, placed on a thermocouple 3, itself placed on a heat sink 4, itself placed on a heating means 5. The thermocouple 3 measures the temperature of the surface of the plate 2 and the variations in temperature of the plate 2. The heat sink 4 under the thermocouple 3 ensures the best possible thermal contact between the heating means 5, the thermocouple 3 and the film 21. The heating means 5 makes it possible to thermostatically control the system at a measurement temperature. A temperature gradient of 10° C./min can be applied.

[0195] A square-wave electric field, with a minimum value equal to 0 and a maximum value+ΔE, with a period equal to approximately 90 s, is applied, causing an extremely rapid variation in temperature, the peak of this variation, ΔT, being able to be measured and corresponding to what is denoted by variation in adiabatic temperature in the invention.

Chemical Modification of P(VDF-TrFE-CTFE) Polymers to Create Essentially Nonconjugated C—C Double Bonds

[0196] 5 g of a P(VDF-TrFE-CTFE) terpolymer having an estimated weight-average molar mass of between 400 000 and 600 000 g/mol, of molar composition 62/30/8, were dissolved in 100 ml of dimethyl sulfoxide (DMSO) in a 250 ml round-bottomed flask. After dissolution, triethylamine (TEA) is added with magnetic stirring. After the reaction, the polymer is purified by precipitation from water, dried under vacuum, dissolved in acetone and precipitated from a 60/40 ethanol/water mixture by weight. The product is dried under vacuum at 40° C. for 12 h.

[0197] For the various examples, the reaction parameters (amount of TEA, duration and temperature) are shown in table 1. The number of equivalents of TEA is calculated with respect to the number of —Cl atoms in the terpolymer. The content of double bond DB, expressed in molar percentage, was evaluated from the liquid .sup.1H NMR spectra (see FIG. 3) by integrating the signal according to the following relationship:

[00002]$\left[\mathrm{Math}1\right]$$\begin{array}{cc}\mathrm{DB}=\frac{{\int }_{6\mathrm{ppm}}^{6.7\mathrm{ppm}}\left(\mathrm{double}\mathrm{bond}-\mathrm{CH}\right)}{\begin{array}{c}\int \text{?}\left(-\mathrm{CHF}\mathrm{of}\mathrm{TrFE}\right)+0.5.Math.\left[\int \text{?}\left(-{\mathrm{CH}}_3\mathrm{of}\mathrm{VDF}\right)\right]+\\ 2.Math.\left[{\int }_{6\mathrm{ppm}}^{6.7\mathrm{ppm}}\left(\mathrm{double}\mathrm{bond}-\mathrm{CH}\right)\right]\end{array}}& \left(\mathrm{Formula}9\right)\end{array}$$\text{?}\text{indicates text missing or illegible when filed}$

TABLE-US-00001 TABLE 1 Equivalents of Duration Temperature DB content Example TEA (h) (° C.) (mol %) Comp. Ex. 1 0 Ex. 1 0.3 2 20 0.6 Ex. 2 0.3 4 40 1.9 Ex. 3 0.3 4 50 2.2 Ex. 4 0.6 4 40 5 Ex. 5 0.9 4 40 5.8

[0198] There is observed, on the Raman spectrum of the samples (see FIG. 4), the appearance of a single signal at 1720 cm.sup.−1 corresponding to the appearance of a single type of C═C double bond, attributed to the bonds: —CF═CH—, nonconjugated.

Chemical Modification of P(VDF-TrFE-CFE) Polymers to Create C—C Double Bonds

[0199] 5 g of a P(VDF-TrFE-CFE) terpolymer having an estimated weight-average molar mass of between 400 000 and 600 000 g/mol, of molar composition 66/27/7, are dissolved in 100 ml of DMSO in a 250 ml round-bottomed flask. After dissolution, triethylamine (TEA) is added with magnetic stirring. After the reaction, the polymer is purified by precipitation in water, dried under vacuum, dissolved in acetone and precipitated in a 60/40 ethanol/water mass mixture. The product is dried under vacuum at 40° C. for 12 h.

[0200] The different reaction parameters (amount of TEA, duration and temperature) are shown in table 2. The number of equivalents of TEA is calculated with respect to the number of —Cl atoms in the terpolymer. The double bond number is calculated as already explained from the liquid .sup.1H NMR spectra.

TABLE-US-00002 TABLE 2 Equivalents of TEA Duration Temperature DB content Comp. Ex. 2 0 Example 6 0.1  4 h 40° C. 0.1 mol % Example 7 0.2  4 h 40° C. 0.1 mol % Example 8 0.35  8 h 40° C. 0.2 mol % Comp. Ex. 3 0.65 24 h 40° C. 2.5 mol %

[0201] There is observed, on the Raman spectrum of the samples (see FIG. 5), the appearance of multiple signals between 1750 and 1500 cm.sup.−1. The vibration band at 1552 cm.sup.−1 increases very intensely for the polymer with the highest degree of modification (Comp. Ex. 3), indicating the presence of conjugated double bonds. The presence of conjugated double bonds is confirmed by the brown coloration of the most modified product (initially white or slightly yellowed).

Electrocaloric Properties of the Samples

[0202] With reference to FIG. 6, a marked improvement in the electrocaloric properties, in particular in the value of variation in adiabatic temperature at a given measurement temperature and under an electric field of given maximum amplitude, of the polymers comprising nonconjugated double bonds according to the invention (Ex. 4) is noticed, in comparison with the polymer of similar structure but not comprising a double bond (Comp. Ex. 1). A maximum of ΔT.sub.EC(MAX) of approximately 2.6 K was determined at a temperature of approximately 35° C. ΔT.sub.EC is equal to at least 0.85*ΔT.sub.EC(MAX) over an interval of several tens of degrees Celsius, between approximately 28° C. and 50° C.

[0203] With reference to FIGS. 7A, 7B and 7C, it is noticed that the electrocaloric properties, in particular the value of variation in adiabatic temperature at a given measurement temperature and under an electric field of given maximum amplitude, of the polymers comprising nonconjugated double bonds according to the invention (Ex. 7) are better than those of a polymer of similar structure but comprising conjugated double bonds (Comp. Ex. 1). In particular, with reference to FIGS. 7B and 7C, the ΔT.sub.EC values vary little over the interval of measurement temperatures: a variation of less than 20% is observed for measurement temperatures ranging from 25° C. to 50° C.

Dielectric Properties

[0204] With reference to FIGS. 8 and 10, it is noticed that the polymers having nonconjugated double bonds according to the invention have a higher dielectric constant (examples 1-5; 6-7) than those of a polymer of similar structure but not comprising a double bond (Comp. Ex. 1; Comp. Ex. 2) or comprising conjugated double bonds (Comp. Ex. 3).

[0205] In addition, a relative permittivity maximum is observed for the polymer according to example 4, in comparison with the polymers according to examples 1-3 and 5.

Polarization

[0206] With reference to FIGS. 9 and 11, the polymers having nonconjugated double bonds according to the invention (examples 1-4; 6-7) are relaxor ferroelectric polymers.

[0207] It is additionally noticed that the increase in the proportion of double bonds leads to an increase in the remanent polarization and in the coercive field.

Melting

[0208] The melting point and the enthalpy of fusion were measured according to the standard ISO 11357-3:2018, in second heating, with a heating gradient of 10° C./min.

TABLE-US-00003 TABLE 3 Melting Temperature Enthalpy (° C.) (J/g) Comp. Ex. 1 123 17 Ex. 1 125 19 Ex. 2 126 17 Ex. 3 126 20 Ex. 4 121 17 Ex. 5 121 17 Comp. Ex. 2 129 22 Ex. 6 132 24 Ex. 7 131 21 Ex. 8 131 21 Comp. Ex. 3 130 17

Thermal Stability

[0209] With reference to FIG. 12, the valence vibration band at 1700 cm.sup.−1 for the polymer according to example 3, corresponding to the carbon-carbon double bonds, is still present after 3 days of storage at 110° C., indicating good thermal stability of the polymer.