Process for the production of fluoropolymers with electrocaloric properties

Abstract

The present invention relates to a process for the preparation of a fluoropolymer from an olefinic fluoropolymer by reaction with a peroxide. The process is particularly capable of modifying the electroactive properties of the polymer. The present invention also relates to a fluoropolymer which can be used in a composition, or in the form of a film or a multilayer system for heat transfer and energy storage applications.

Description

Invention Field

[0001] This invention relates to a method for manufacturing a fluoropolymer obtained by reacting an olefinic fluoropolymer with a peroxide (such as m-chloroperoxybenzoic acid (mCPBA)). The fluoropolymer obtained by this method preferably has electrothermal properties and can be molded into a film. Background Technology

[0002] The electrothermal effect is a property of certain dipole dielectric materials, manifesting as a temperature change when subjected to a variable electric field. The physical origin of this phenomenon is related to changes in dipole order, and therefore to changes in dipole entropy induced by the applied electric field. The applied electric field E... c This causes the dipoles in these materials to become ordered and oriented, resulting in a decrease in their dipole entropy and an increase in temperature under adiabatic conditions. Conversely, a reduction or elimination of the electric field will cause an increase in their dipole entropy and a decrease in temperature under adiabatic conditions. Therefore, under given experimental conditions, the characteristic of an electrothermal material is that, under adiabatic conditions, it reacts with respect to an applied electric field E. c With adiabatic temperature change ΔT EC .

[0003] The electrothermal properties of a material can theoretically be evaluated (indirectly) by the change of its dielectric properties with temperature, particularly by the values ​​of relative permittivity, maximum polarization, coercive field, and remanent polarization.

[0004] Alternatively, the electrothermal material can also be heated by the applied electric field E under isothermal conditions. c Isothermal entropy change ΔS EC To characterize.

[0005] Currently, the electrothermal effect is the subject of much research, aiming to develop novel cooling systems that are more environmentally friendly and energy-efficient than those based on gas compression, thermoelectric effects, or magnetocaloric effects. Ferroelectric and relaxor ferroelectric materials are of particular interest in these applications due to the strong coupling between the applied electric field and their dipole structure, as they possess remarkable electrothermal properties. In particular, this coupling is maximized near or slightly above the phase transition temperature (ferroelectric → paraelectric (FE → PE) or relaxor ferroelectric → paraelectric (RFE → PE)), which is specifically attributed to the strong reversible change in polarization of these materials under an electric field and their high dielectric constant.

[0006] In other words, near the FE→PE or RFE→PE phase transition, a relatively small change in the electric field can cause significant changes in entropy and temperature. The good flexibility and ease of implementation of these materials, enabling their application in large-area thin films, are other parameters that make them particularly suitable for solid-state refrigeration systems.

[0007] Fluoropolymers based on vinylidene fluoride (VDF) represent a class of compounds with significant performance in a wide range of applications. PVDF, as well as copolymers containing VDF and trifluoroethylene (TrFE), are particularly advantageous due to their piezoelectric and pyroelectric properties. Fluoropolymers based on VDF and TrFE also belong to the category of materials with "ferroelectric" and "relaxed ferroelectric" properties and are among the most studied materials.

[0008] The electrothermal properties of P(VDF-TrFE) type ferroelectric copolymers are maximized near the ferroelectric to paraelectric (FE→PE) phase transition. The FE→PE transition of these polymers is narrow, meaning it occurs over a small temperature range and at relatively high temperatures, typically strictly above 60°C. This hinders their use in cooling systems required to operate near ambient temperatures and / or over a wide temperature range.

[0009] The use of relaxor ferroelectric polymers can overcome at least some of the aforementioned drawbacks. In fact, irradiated P(VDF-TrFE), P(VDF-TrFE-CFE), or P(VDF-TrFE-CTFE) type relaxor ferroelectric polymers exhibit a broadened (RFE→PE) phase transition relative to the FE→PE phase transition of ferroelectric polymers, meaning it occurs over a wider temperature range. Furthermore, the RFE→PE transition typically occurs at a lower temperature than the FE→PE transition temperature of ferroelectric polymers. Therefore, it is conceivable to use relaxor ferroelectric polymers in a variety of cooling systems, particularly in cooling systems required to operate near ambient temperatures and / or over a wide temperature range.

[0010] The articles “Large electrocaloric effect in ferroelectric polymers near room temperature” (B. Neese et al., Science, 2008, 321, 5890, 921-823) and “Tunable temperature dependence of electrocaloric effect in ferroelectric relaxor poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene terpolymer)” (X. Li et al., Appl. Phys. Lett., 2011, 99, 052907) describe P(VDF-TrFE) or P(VDF-TrFE-CFE) fluoropolymers with electrocaloric properties.

[0011] The article "Introducing Functionality to Fluorinated Electroactive Polymers" (Kallitsis K. et al., Macromolecules, 2019, 52, 21, 8503-8513) describes the functionalization of electroactive fluoropolymers (EFPs) through two consecutive steps: Williamson etherification followed by photocatalytic crosslinking. This modification of EFPs enables improved electroactive properties, particularly in terms of relative permittivity. Application WO 2019 / 020906 A1 is also an example of this application.

[0012] In another type of modification, the article "Ferroelectric Polymer Nanocomposites with Complementary Nanostructured Fillers for Electrocaloric Cooling with High Power Density and Great Efficiency" (G. Zhang et al., 2018, 1, 3, 1344-1354) adds nanoscale fillers, such as barium strontium titanate (BST) nanowires, to P(VDF-TrFE-CFE). However, introducing nanoscale fillers into the polymer matrix has several drawbacks. First, it requires very good dispersion of these fillers, thus complicating the molding of the material. Furthermore, handling nanoparticles in polymer manufacturing processes is complex because free nanoparticles pose potential risks to human health. Finally, the presence of fillers tends to mechanically weaken the material and reduce its dielectric strength.

[0013] Double bonds can also be introduced into polymers through dehydrohalogenation reactions.

[0014] Application WO 2019 / 075061 A1 describes the manufacture of a polymer containing double bonds, obtained by dehydrofluorinating PVDF with a sodium hydroxide-saturated isopropanol solution in dimethylacetamide. The electrothermal properties of the resulting polymer were not measured. The type of double bonds in the resulting polymer was also not characterized. This dehalogenation method is similar to that in application US4904739 A, where a high proportion of conjugated double bonds are present. Furthermore, the fluoropolymer containing conjugated double bonds obtained by dehydrofluorination with a strong base has poor thermal stability, is yellow in color, is easily degraded, and may crosslink during the strong base treatment. In addition, this method has a practical disadvantage: it uses harmful dimethylacetamide as a solvent.

[0015] The article "Enhanced Electrocaloric Response of Vinylidene Fluoride-Based Polymers via One-Step Molecular Engineering" (Le Goupil F. et al., Adv. Funct. Mater., 2021, 31, 1, 2007043) describes the chemical modification of EFP (i.e., P(VDF-TrFE-CTFE)) through a reaction in the presence of a base, which allows for the controlled introduction of double bonds within the polymer. This modification, by increasing the dielectric constant, enables alteration of the polymer's crystal structure and its dielectric properties. Patent FR 3104583 B1 and application WO 2021 / 116618 A1 also disclose this chemical modification involving the introduction of conjugated double bonds.

[0016] These strategies for generating double bond compositions do indeed improve the dielectric properties of polymers; however, double bonds, whether conjugated or not, cause crosslinking of the polymer, which is not always desirable.

[0017] Despite the efforts mentioned above, performance improvements remain limited. Given these limitations, it is therefore necessary to explore other methods to improve the dielectric properties of relaxor ferroelectric polymers.

[0018] In order to develop more efficient cooling equipment, there is indeed a need for a method for manufacturing VDF-based fluoropolymers that have improved electrothermal properties or generally improved dielectric properties compared to existing technologies. Summary of the Invention

[0019] This invention relates to a method for manufacturing fluoropolymers from olefinic fluoropolymers, wherein the olefinic fluoropolymer comprises:

[0020] -The first unit, its formula is -(CF2-CH2)-,

[0021] -Optionally, at least one second unit, which has the formula -(CX1X2-CX3X4)-,

[0022] -Optionally, at least one third unit, which has the formula -(CY1Y2-CY3Z)-,

[0023] - At least one fourth unit, which is of the form -(CY3=CF)-, -(CY3=CX1)-, -(CY3=CX2)-, -(CY1=CY3)- or -(CY2=CY3)-;

[0024] in:

[0025] X1 and X2 independently represent -H, -F, or optionally partially or fully fluorinated alkyl groups containing 1 to 3 carbon atoms.

[0026] X3 and X4 independently represent -F, or an alkyl group optionally partially or fully fluorinated containing 1 to 3 carbon atoms, excluding combinations where X1 and X2 are both -H and X3 and X4 are both -F.

[0027] Y1 and Y2 independently represent -H, -F, -Cl, or optionally partially or fully fluorinated alkyl groups containing 1 to 3 carbon atoms.

[0028] Y3 represents -F, -Cl, or an alkyl group that is optionally partially or fully fluorinated, containing 1 to 3 carbon atoms.

[0029] Z represents a halogen atom that is different from -F.

[0030] The method includes the step of reacting the olefinic fluoropolymer with a peroxide.

[0031] In the implementation scheme, X1 represents -H or -F, and X2, X3 and X4 all represent -F.

[0032] In the implementation scheme, Y3 represents -F, and Y1 and Y2 both represent -H or -F.

[0033] In the embodiments, the olefinic fluoropolymer comprises:

[0034] The first unit is from -30 mol% to less than 100 mol%.

[0035] The second unit, ranging from -0 mol% to 60 mol%,

[0036] The third unit, ranging from -0 mol% to less than 20 mol%,

[0037] - The fourth unit, greater than 0 mol% to 20 mol%.

[0038] In an embodiment, the olefinic fluoropolymer comprises at least one second unit having the formula -(CX1X2-CX3X4)-.

[0039] Therefore, the olefinic fluoropolymer may comprise:

[0040] The first unit is from -30 mol% to less than 100 mol%.

[0041] - The second unit, greater than 0 mol% to 60 mol%,

[0042] The third unit, ranging from -0 mol% to less than 20 mol%,

[0043] - The fourth unit, greater than 0 mol% to 20 mol%.

[0044] In one embodiment, the method includes the step of preparing the olefinic fluoropolymer by dehydrohalogenation of an initial polymer, the initial polymer comprising:

[0045] -The first unit, its formula is -(CF2-CH2)-,

[0046] -Optionally, at least one second unit, which has the formula -(CX1X2-CX3X4)-,

[0047] -At least one third unit, which is of the form -(CY1Y2-CY3Z)-.

[0048] In an embodiment, the step of preparing the olefinic fluoropolymer includes contacting the initial polymer with an alkali, preferably ethylenediamine, and preferably used in an amount of 10 to 30 µL / g of the initial polymer.

[0049] In the embodiment, the relative permittivity of the fluoropolymer is at least 5% higher than that of the initial polymer, preferably at least 10% higher, preferably at least 15% higher, preferably at least 20% higher, preferably at least 25% higher, preferably at least 30% higher, preferably at least 35% higher, and even more preferably at least 40% higher, and the relative permittivity is measured at a frequency of 1,000 Hz and a temperature of 40°C.

[0050] In the implementation scheme, the fluoropolymer is expressed at µC / cm 2The maximum polarization intensity is at least 1%, preferably at least 5%, preferably at least 10%, preferably at least 15%, preferably at least 20%, and even more preferably at least 25% higher than the initial polymer, and the maximum polarization intensity is measured at a frequency of 100 Hz, at 25 °C, and at an electric field of 1,300 kV / cm.

[0051] In the embodiment, the coercive field of the fluoropolymer, measured in kV / cm, is at least 1%, preferably at least 5%, preferably at least 10%, preferably at least 15%, preferably at least 20%, and even more preferably at least 25% lower than that of the initial polymer, and the coercive field is measured at a frequency of 100 Hz and at 25°C.

[0052] In the embodiments, the percentage of crystallinity of the polymer is at least 1% higher than that of the initial polymer, preferably at least 5% higher, preferably at least 10% higher, preferably at least 15% higher, preferably at least 20% higher, preferably at least 25% higher, and even more preferably at least 30% higher.

[0053] In the embodiments, the amount of the peroxide is 0.005 to 50 mmol / g of fluoropolymer, preferably 0.5 to 10 mmol / g of fluoropolymer, and even more preferably 1 to 6 mmol / g of fluoropolymer.

[0054] In the implementation scheme, the peroxide is an inorganic peroxide selected from hydrogen peroxide and peroxyacids (such as peroxymonosulfuric acid), or an organic peroxide selected from peracetic acid, magnesium monoperoxyphthalate, or m-chloroperoxybenzoic acid.

[0055] The present invention also relates to fluoropolymers that can be obtained by the methods defined above.

[0056] In the embodiments, the weight-average molecular weight of the fluoropolymer is less than or equal to 500,000 g / mol, preferably less than or equal to 450,000 g / mol, preferably less than or equal to 400,000 g / mol, preferably less than or equal to 350,000 g / mol, preferably less than or equal to 300,000 g / mol, preferably less than or equal to 250,000 g / mol, preferably less than or equal to 200,000 g / mol, preferably less than or equal to 150,000 g / mol, and most preferably less than or equal to 100,000 g / mol.

[0057] In the embodiment, the remanent polarization of the fluoropolymer is 0.1 to 5 µC / cm. 2 Preferably, the concentration is 0.15 to 2.5 µC / cm. 2 Preferably, the concentration is 0.3 to 0.6 µC / cm.2 The residual polarization intensity was measured at a frequency of 100 Hz, at 25°C, and at a field of 1,300 kV / cm.

[0058] The present invention also relates to compositions comprising at least one fluoropolymer as defined above and at least one liquid carrier of said polymer.

[0059] The present invention also relates to membranes comprising the fluoropolymers defined above.

[0060] In an embodiment, the thickness of the membrane is greater than or equal to 0.1 µm, preferably the thickness of the membrane is 1 to 100 µm, more preferably the thickness of the membrane is 1 to 50 µm, and even more preferably the thickness of the membrane is 1 to 10 µm.

[0061] The present invention also relates to a multilayer system comprising at least one layer formed of the membrane described above, wherein other layers may comprise a fluoropolymer, another polymer, or a non-polymer material having the same or different composition according to the present invention.

[0062] The present invention also relates to the use of the fluoropolymers, membranes, or multilayer systems described above in heat transfer systems, preferably cooling systems.

[0063] The present invention also relates to the use of the fluoropolymers, membranes, or multilayer systems described above in energy storage systems, preferably capacitors, organic transistors, actuators, or electrostatic clutches.

[0064] This invention fulfills the requirements expressed above. More specifically, it provides a manufacturing method capable of producing VDF-based fluoropolymers with improved electrothermal properties compared to existing technologies, i.e., for example, exhibiting a higher adiabatic temperature change ΔT in a given variable electric field. EC Or it usually has improved dielectric properties.

[0065] The present invention relates to improving the dielectric properties of VDF-based fluoropolymers through functionalization via chemical modification. This specifically involves obtaining polymers with more pronounced relaxor ferroelectric properties, exhibiting high dielectric constants and maximum polarization, as well as low remanent polarization and low coercivity. These properties are sought for a variety of applications, particularly for electrothermal applications that allow for use in cooling systems.

[0066] The initial polymer is modified through two consecutive chemical reactions: first, the initial polymer is dehydrohalogenated while introducing double bonds into the chain of the initial polymer to obtain an olefinic fluoropolymer containing double bonds; and second, the olefinic fluoropolymer is reacted with a peroxide, which reacts with the previously formed double bonds.

[0067] These chemical modifications enable the acquisition of fluoropolymers exhibiting superior dielectric properties, particularly electrothermal properties, compared to the initial polymer. The fluoropolymers obtained by this method preferably have increased relative permittivity and maximum polarization, and decreased coercivity and remanent polarization compared to the initial polymer. Attached Figure Description

[0068] Figure 1 The graph represents the maximum relative permittivity measured using an AC voltage signal of 1V and a signal frequency of 1kHz for the samples after dehydrochlorination (square) and reaction with mCPBA (circle), according to Example 4 below. The x-axis represents the ethylenediamine concentration in µL / g polymer; the y-axis represents the actual maximum relative permittivity.

[0069] Figure 2 This represents the maximum polarization intensity measured by a continuous triangular signal at a frequency of 100 Hz under a field of 1,300 kV / cm for the samples after dehydrochlorination (square) and after reaction with mCPBA (circle), according to Example 5 below. Horizontal axis: ethylenediamine concentration, in µL / g polymer; Vertical axis: maximum polarization intensity, in µC / cm². 2 count.

[0070] Figure 3 The values ​​represent the coercivity values ​​of the samples after dehydrochlorination (squares) and after reaction with mCPBA (circles), according to Example 5 below. Horizontal axis: ethylenediamine concentration, in µL / g polymer; Vertical axis: coercivity value, in kV / cm.

[0071] Figure 4 The x-axis represents the percentage of crystallinity (X%) for the samples after dehydrochlorination (square) and after reaction with mCPBA (circle) according to Example 6 below. x-axis: ethylenediamine concentration, in µL / g polymer; y-axis: percentage of crystallinity (X%).

[0072] Figure 5 The values ​​represent the molar mass, in g / mol, for the samples after dehydrochlorination (squares) and after reaction with mCPBA (circles), according to Example 7 below. Horizontal axis: ethylenediamine concentration, in µL / g polymer; Vertical axis: molar mass, in g / mol. Detailed Implementation

[0073] The present invention will now be described in more detail and in a non-limiting manner in the following description.

[0074] Initial polymer

[0075] The initial polymer contains:

[0076] - The first unit, its formula is: -(CF2-CH2)-,

[0077] -Optionally, the second unit has the formula -(CX1X2-CX3X4)-.

[0078] -Optionally, the third unit has the formula: -(CY1Y2-CY3Z)-,

[0079] -in:

[0080] -X1 and X2 independently represent -H, -F, or optionally partially or fully fluorinated alkyl groups containing 1 to 3 carbon atoms.

[0081] -X3 and X4 independently represent -F, or an alkyl group optionally partially or fully fluorinated containing 1 to 3 carbon atoms, excluding combinations where X1 and X2 are both -H and X3 and X4 are both -F.

[0082] -Y1 and Y2 independently represent -H, -F, -Cl, or optionally partially or fully fluorinated alkyl groups containing 1 to 3 carbon atoms.

[0083] -Y3 represents -F, -Cl, or an alkyl group that is optionally partially or fully fluorinated, containing 1 to 3 carbon atoms.

[0084] -Z indicates a halogen atom that is different from -F.

[0085] The initial polymer may consist substantially of or even entirely of the first unit described above. Alternatively, the initial polymer may consist substantially of or even entirely of the first and second units described above. Alternatively, the initial polymer may consist substantially of or even entirely of the first and third units described above. Alternatively, the initial polymer may consist substantially of or even entirely of the first, second, and third units described above. Alternatively, the initial polymer may include one or more additional units besides the first, second, and third units.

[0086] The first unit is derived from VDF.

[0087] The initial polymer may contain a single second unit, or conversely, several different second units. According to some embodiments, the second unit may be derived from monomers selected from the list of the following compositions: trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), trifluoropropylene (especially 3,3,3-trifluoropropylene), tetrafluoropropylene (especially 2,3,3,3-tetrafluoropropylene or 1,3,3,3-tetrafluoropropylene), hexafluoroisobutylene, perfluorobutylethylene, and pentafluoropropylene (especially 1,1,3,3,3-pentafluoropropylene or 1,2,3,3,3-pentafluoropropylene). According to some variations, second units derived from several different fluorinated monomers may be present in the initial polymer.

[0088] According to certain implementations, X1 may represent -H or -F; and X2, X3, and X4 may all represent -F. In other words, the second unit may be derived from trifluoroethylene (TrFE) and / or tetrafluoroethylene (TFE).

[0089] According to certain implementations, Z can represent -Cl, -Br, or -I. Advantageously, Z can represent -Cl.

[0090] The initial polymer may contain a single third unit, or conversely, several different third units. According to some embodiments, the third unit may be derived from monomers selected from the following list: 1,1-chlorofluoroethylene (1,1-CFE), 1,2-chlorofluoroethylene (1,2-CFE), trifluorochloroethylene (CTFE), 2-chloro-3,3,3-trifluoropropylene (1233xf), 1-chloro-3,3,3-trifluoropropylene (12332d), 1,2-dichloro-1,2-difluoroethylene, 1,1-dichloro-1,1-difluoroethylene, and 1,1,2-trichloro-2-fluoroethylene.

[0091] Advantageously, Y3 can represent -F and both Y1 and Y2 can represent -H or -F. In other words, according to these embodiments, the third unit can be derived from vinyl chlorofluoroethylene (CFE) and / or trifluorochloroethylene (CTFE).

[0092] In particular, according to certain embodiments, the polymer may comprise units derived from vinylidene fluoride (VDF), TrFE, and CFE, or units derived from VDF, TrFE, and CTFE, or units derived from VDF, TrFE, CFE, and CTFE, or units derived from VDF, TFE, and CFE, or units derived from VDF, TFE, and CTFE, or units derived from VDF, TFE, CFE, and CTFE.

[0093] The polymers in the list above may also contain units derived from one or more additional monomers, such as units derived from hexafluoropropylene (HFP).

[0094] The second unit is preferably derived from a single monomer (preferably TrFE or TFE) or from only two monomers (preferably TrFE and TFE, and even more preferably TrFE). The third unit is preferably derived from a single monomer (preferably CFE or CTFE, and even more preferably CTFE) or from only two monomers (preferably CFE and CTFE). As the initial polymer, polymer P(VDF-TrFE-CTFE) is particularly preferred.

[0095] The initial polymer may contain:

[0096] Unit 1, ranging from -30 mol% to 100 mol%.

[0097] Unit 2, ranging from -0 mol% to 60 mol%,

[0098] Unit 3, ranging from -0 mol% to 20 mol%.

[0099] Preferably, the initial polymer comprises:

[0100] Unit 1, ranging from -30 mol% to less than 100 mol%,

[0101] Unit 2, ranging from -0 mol% to 60 mol%,

[0102] - The third unit, greater than 0 mol% to 20 mol%.

[0103] More preferably, the initial polymer comprises:

[0104] Unit 1, ranging from -30 mol% to 90 mol%.

[0105] Unit 2, ranging from -0 mol% to 60 mol%,

[0106] - The third unit, greater than 0 mol% to 20 mol%.

[0107] It should be understood that when there are multiple second units or multiple third units, the stated content corresponds to the sum of all second units and the sum of all third units, respectively.

[0108] The initial polymer may specifically comprise 30 mol% to 35 mol%, 35 mol% to 40 mol%, 40 mol% to 45 mol%, 45 mol% to 50 mol%, 50 mol% to 60 mol%, 60 mol% to 70 mol%, 70 mol% to 80 mol%, 80 mol% to 85 mol%, 85 mol% to 90 mol%, 90 mol% to 95 mol%, or 95 mol% to less than 100 mol%, or alternatively 100% of the first unit.

[0109] The initial polymer may specifically contain 0 mol% to 5 mol%, 5 mol% to 10 mol%, 10 mol% to 15 mol%, 15 mol% to 20 mol%, 20 mol% to 30 mol%, 40 mol% to 50 mol%, 50 mol% to 55 mol%, or 55 mol% to 60 mol% of a second unit.

[0110] The initial polymer may specifically contain 0%, or greater than 0 mol% to 1 mol%, 1 mol% to 5 mol%, 5 mol% to 10 mol%, 10 mol% to 15 mol%, or 15 mol% to 20 mol% of a third unit.

[0111] The preferred content of the initial polymer is as follows:

[0112] Unit 1: -40 mol% to 80 mol%; Unit 2: 15 mol% to 50 mol%; and Unit 3: 1 mol% to 20 mol%.

[0113] Unit 1: 50 mol% to 70 mol%; Unit 2: 20 mol% to 40 mol%; and Unit 3: 3 mol% to 15 mol%.

[0114] Unit 1: -55 mol% to 65 mol%; Unit 2: 27 mol% to 37 mol%; and Unit 3: 5 mol% to 12 mol%.

[0115] These contents are particularly suitable for initial polymers of the P(VDF-TrFE-CTFE), P(VDF-TrFE-CFE), P(VDF-TFE-CTFE), and P(VDF-TFE-CFE) types.

[0116] The molar composition of units in fluoropolymers can be determined in various ways, such as infrared spectroscopy or Raman spectroscopy. Conventional elemental analysis methods for carbon, fluorine, and chlorine, bromine, or iodine, such as X-ray fluorescence spectroscopy, allow for the precise calculation of the polymer's mass composition, from which the molar composition can be derived. Multinuclear NMR techniques, particularly proton NMR, can also be performed. 1 H) and fluorine ( 19 F) NMR is performed by analyzing a solution of the polymer in a suitable deuterated solvent. NMR spectra are recorded on an FT-NMR spectrometer equipped with multinuclear probes. Specific signals from different monomers in the spectra produced by one or more nuclei are then identified.

[0117] Therefore, for example, units derived from VDF polymerization give a specific signal (multiplexed peaks centered at 3 ppm) for the -CH2- group in proton NMR. Similarly, units derived from TrFE show a specific signal (approximately 5 ppm) characterizing the -CHF- group in proton NMR. In fluorine NMR, the signals of the -CF2- and -CFCl- units derived from CFE and CTFE merge with the signals of the -CF2- units derived from VDF and TrFE between -90 and -132 ppm. The -CHF unit of TrFE exhibits a characteristic signal between -194 and -220 ppm. The combination of proton NMR and fluorine NMR spectra allows for the definitive derivation of the molar composition of the polymer.

[0118] The initial polymer can be obtained according to methods known in the prior art. Specifically, the initial polymer can be prepared by free radical polymerization according to solution, suspension, emulsion, or microemulsion polymerization methods.

[0119] Copolymerization reactions are typically carried out in the presence of a free radical initiator. Free radical initiators can be, for example, tertiary alkyl peroxide esters, such as tert-butyl peroxypentanoate (or TPPPI), tert-amyl peroxypentanoate; peroxydicarbonates, such as bis(4-tert-butylcyclohexyl) peroxydicarbonate; sodium persulfate, ammonium persulfate, or potassium persulfate; benzoyl peroxide and its derivatives; tertiary alkyl hydroperoxides, such as tert-butyl hydroperoxide; tertiary alkyl peroxides, such as tert-butyl peroxide; or tertiary alkyl peroxides, such as 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane. Alternatively or additionally, azo initiators or redox systems can be used as free radical initiators. The polymer can also be obtained by reducing the P(VDF-CTFE) type copolymer to obtain the P(VDF-TrFE-CTFE) type copolymer (see: Z. Wang et al., "High dielectric VDF / TrFE / CTFE terpolymers prepared by hydrogenation of VDF / CTFE copolymers: synthesis and characterization", Macromolecules, 2006, 39, 13, 4268-4271).

[0120] The initial polymer can be selected based on its known electrothermal properties. It is advantageous to select an initial polymer that has good electrothermal properties at operating temperatures close to those of the polymer according to the invention.

[0121] Alternatively or additionally, the initial polymer can be selected based on the temperature at which its dielectric constant is maximized. It is advantageous to select an initial polymer that has the maximum dielectric constant at a temperature close to the operating temperature of the polymer according to the invention.

[0122] The initial polymer is preferably random. The initial polymer is preferably linear.

[0123] Dehydrohalogenation reaction

[0124] Dehydrohalogenation of the initial polymer enables the formation of carbon-carbon double bonds, thereby forming the olefinic fluoropolymer described above. When a third unit is present, dehydrohalogenation may primarily involve the removal of a -Z atom and a hydrogen atom on the carbon adjacent to the removed -Z atom.

[0125] Dehydrohalogenation, in the preferred case where -Cl is the leaving halogen atom, is called dehydrochlorination. It is carried out by mixing with a specific base at a specific concentration, under specific temperature conditions, and for a specific duration to promote the elimination of halogen -Z (or fluorine atom).

[0126] The base must preferably be a sufficiently strong base to eliminate fluorine atoms or -Z. Specifically, the base may have a pKa of 8 to 12, preferably 9 to 11. The base may advantageously be a non-aromatic and non-nucleophilic amine, such as triethylamine or ethylenediamine. The amount of base per gram of initial polymer can be adjusted according to the strength of the base and the number of basic functional groups on it. For example, the base (particularly in the case of ethylenediamine) may be 0.1 to 100 µL per 1 g of initial polymer. According to some embodiments, the proportion of base (e.g., ethylenediamine) is preferably adjusted so that the third unit of the formula -(CY1Y2-CY3Z)- is partially retained within the polymer at the end of the dehydrohalogenation step. Specifically, the base may be 5 to 50 µL per 1 g of initial polymer, or alternatively 10 to 30 µL per 1 g of initial polymer.

[0127] The base may be 0.01 to 2 molar equivalents relative to the number of moles of the third unit. In particular, the base may be 0.1 to 1 molar equivalent relative to the number of moles of the third unit, or alternatively 0.15 to 0.5 molar equivalents.

[0128] According to certain embodiments, the dehydrohalogenation step may be carried out, particularly at a temperature of 10 to 100°C, preferably 20 to 60°C, for a duration of 0.1 to 10 hours, preferably 1 to 8 hours, and even more preferably 2 to 4 hours.

[0129] Furthermore, those skilled in the art can adjust the amount of alkali used, the temperature conditions for dehydrohalogenation, and the duration of dehydrohalogenation to regulate the reaction progress. According to some embodiments, dehydrohalogenation is carried out with a reaction progress of at least 0.25, preferably at least 0.5. According to some embodiments, dehydrohalogenation is carried out in a quasi-complete or complete manner (the introduced alkali reacts substantially all or all of its components).

[0130] According to some embodiments, the step of reacting the initial polymer with the alkali can be followed by a step of removing excess alkali. According to some embodiments, the removal of alkali is carried out by a washing solution containing water and / or alcohol.

[0131] Alkene fluoropolymers

[0132] The fluoroolefinic polymer obtained at the end of the dehydrohalogenation reaction comprises:

[0133] - The first unit, its formula is: -(CF2-CH2)-,

[0134] -Optionally, the second unit has the formula -(CX1X2-CX3X4)-.

[0135] -Optionally, the third unit has the formula: -(CY1Y2-CY3Z)-,

[0136] - Unit 4, whose formula is -(CY3=CF)-, -(CY3=CX1)-, -(CY3=CX2)-, -(CY1=CY3)- or -(CY2=CY3)-;

[0137] The meanings of X1, X2, X3, X4, Y1, Y2, Y3, and Z are as described above.

[0138] The fourth unit may contain a mixture of units corresponding to one of the above formulas.

[0139] All the information above regarding the first and second units in the initial polymer also applies to olefinic fluoropolymers, especially regarding the properties and molar ratio of the first and second units.

[0140] All the information above regarding the properties of the third unit in the initial polymer also applies to fluoroolefins.

[0141] Preferably, the olefinic fluoropolymer comprises:

[0142] Unit 1, ranging from -30 mol% to less than 100 mol%,

[0143] Unit 2, ranging from -0 mol% to 60 mol%,

[0144] Unit 3, ranging from -0 mol% to less than 20 mol%.

[0145] - Unit 4, greater than 0 mol% to 20 mol%.

[0146] It should be understood that when there are multiple second units, multiple third units, or multiple fourth units, the stated content corresponds to the sum of all second units, the sum of all third units, and the sum of all fourth units, respectively.

[0147] Alkene fluoropolymers may particularly contain 0 mol% to 5 mol%, 5 mol% to 10 mol%, 10 mol% to 15 mol%, or 15 mol% to 19.9 mol% of a third unit.

[0148] According to certain embodiments, the olefinic fluoropolymer may contain at least 1 mol%, preferably at least 2 mol%, more preferably at least 3 mol%, and most preferably at least 4 mol% of a third unit. The presence of the third unit generally enables the production of relaxor ferroelectric olefinic fluoropolymers, the advantages of which are detailed below. In particular, the polymer may contain 4 mol% to 15 mol% of the third unit.

[0149] The olefinic fluoropolymer may contain 0.1 mol% to 20 mol% of a fourth unit. The molar percentage of the fourth unit relative to the total moles of units in the olefinic fluoropolymer composition may be 0.1 mol% to 0.2 mol%, or 0.2 mol% to 0.3 mol%, or 0.3 mol% to 0.5 mol%, or 0.5 mol% to 1 mol%, or 1 mol% to 2 mol%, or 2 mol% to 3 mol%, or 3 mol% to 4 mol%, or 4 mol% to 5 mol%, or 5 mol% to 6 mol%, or 6 mol% to 7 mol%, or 7 mol% to 8 mol%, or 8 mol% to 9 mol%, or 9 mol% to 10 mol%, or 10 mol% to 12 mol%, or 12 mol% to 14 mol%, or 14 mol% to 16 mol%, or 16 mol% to 18 mol%, or 18 mol% to 20 mol%. The molar percentage of the fourth unit may be selected such that the dielectric constant is maximized at the intended operating temperature of the polymer.

[0150] The preferred contents of olefinic fluoropolymers are as follows:

[0151] The sum of Unit 1 (-40 mol% to 80 mol%), Unit 2 (15 mol% to 50 mol%), and Units 3 and 4 (1 mol% to 20 mol%).

[0152] The sum of Unit 1 (-50 mol% to 70 mol%), Unit 2 (20 mol% to 40 mol%), and Units 3 mol% to 15 mol%;

[0153] The sum of Unit 1 (-55 mol% to 65 mol%), Unit 2 (27 mol% to 37 mol%), and Units 3 and 4 (5 mol% to 12 mol%).

[0154] These contents are particularly suitable for fluoroolefins obtained by dehydrohalogenation of P(VDF-TrFE-CTFE), P(VDF-TrFE-CFE), P(VDF-TFE-CTFE), and P(VDF-TFE-CFE).

[0155] The presence of carbon-carbon double bonds in fluoropolymers can be assessed using various spectroscopic methods, particularly Raman spectroscopy. (1720cm) -1 The valence vibration band at that point corresponds to the presence of a single type of C=C double bond, which can be attributed to the -CF=CH- bond. The presence of the double bond can be quantified by the presence of a signal between 6.0 and 6.7 ppm on proton NMR and / or by the presence of a signal between -87.0 and -90.0 ppm on fluorine NMR.

[0156] Alkene fluoropolymers are preferably atactic. Alkene fluoropolymers are preferably linear.

[0157] Reaction with peroxides

[0158] Chemical modification of olefinic fluoropolymers is carried out through a reaction between peroxides and double bonds present in the olefinic fluoropolymers (on the fourth unit).

[0159] The peroxide is selected from organic and inorganic peroxides. Inorganic peroxides may be hydrogen peroxide (H₂O₂) or peroxyacids, such as peroxymonosulfuric acid. Organic peroxides may be peracetic acid, magnesium monoperoxyphthalate, or m-chloroperoxybenzoic acid (mCPBA). The peroxide (e.g., mCPBA) may be 0.005 to 50 mmol / g of the fluoropolymer. According to certain embodiments, the proportion of the peroxide (e.g., mCPBA) is preferably adjusted so that a portion of the fourth unit is retained in the fluoropolymer at the end of the reaction step with the peroxide. In particular, the proportion of the peroxide may be 1 to 15 mmol / g of the fluoropolymer, or alternatively 1 to 6 mmol / g of the fluoropolymer, or alternatively 1 to 3 mmol / g.

[0160] According to certain embodiments, the reaction step with the peroxide can be carried out, particularly at a temperature of 0 to 60°C, preferably 5 to 40°C, for a duration of 0.1 to 20 hours, preferably 1 to 12 hours, and even more preferably 2 to 6 hours.

[0161] The reaction with the peroxide can be carried out in a solvent. The solvent can be chosen to be non-interfering with the reaction and capable of dissolving the fluoropolymer and the peroxide. The solvent can be a polar aprotic solvent, particularly selected from: lactones, especially γ-butyrolactone; furans, especially tetrahydrofuran; esters, especially methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and propylene glycol methyl ether acetate, glyceryl triacetate, diethylene glycol monobutyl ether acetate, and ethyl acetoacetate; carbonates, especially dimethyl carbonate and propylene carbonate; and phosphate esters, especially trimethyl phosphate and triethyl phosphate; or mixtures thereof. Esters, especially ethyl acetate, are preferred.

[0162] The mass concentration of the fluoropolymer in the solvent can be, for example, 2.5 to 250 g / L, preferably 5 to 125 g / L, even more preferably 10 to 75 g / L, and even more preferably 15 to 50 g / L.

[0163] Furthermore, the proportion of peroxide, the temperature conditions for the reaction with the peroxide, and the duration of the reaction can be adjusted by those skilled in the art to regulate the reaction process.

[0164] According to some embodiments, the step of reacting the fluoropolymer with the peroxide can be followed by a step of removing excess peroxide and reaction byproducts. According to some embodiments, after evaporating the reaction solvent, alkali removal is performed using a washing solution containing an alcohol.

[0165] The obtained fluoropolymer

[0166] Compared to olefinic fluoropolymers, the fluoropolymers obtained by reacting with peroxides may contain epoxy, alcohol, ketone, and / or aldehyde functional groups. Unbound by theory, the inventors believe these functional groups are formed by double bonds in the fourth unit of the olefinic fluoropolymer. This polymer is also prone to chain scission, which may lead to a decrease in its average molar mass.

[0167] The fluoropolymer is preferably random.

[0168] The fluoropolymer preferably exhibits an electrothermal effect under the action of a variable electric field.

[0169] Advantageously, the fluoropolymer has an adiabatic temperature change ΔT of at least 1 °C at at least one measurement temperature. EC The measurement of the adiabatic temperature change is performed under a given electric field amplitude ΔE. The measured temperature corresponds to the temperature reached by the sample before it undergoes the electric field change ΔE that causes the electrothermal effect.

[0170] Preferably, the fluoropolymer has an adiabatic temperature variation ΔT of at least 1.5°C, or at least 2°C, or at least 2.5°C, or at least 3°C, or at least 3.5°C, or at least 4.0°C, or at least 4.5°C, or at least 5°C, or at least 6°C, or at least 7°C, or at least 8°C, or at least 9°C, or at least 10°C under a given variable electric field and a given measurement temperature. EC .

[0171] The electric field used to verify the electrothermal effect must be variable. In fact, it is the change in the electric field that causes the electrothermal effect.

[0172] Generally, the higher the amplitude of the electric field, the greater the electrothermal effect. However, the maximum amplitude of the electric field must be adjusted so that it does not reach the breakdown voltage of the polymer. Furthermore, generating high voltage requires energy-intensive specialized equipment, which is not necessarily desirable. According to some embodiments, the electric field used to verify a significant electrothermal effect for the applications described below may have a maximum amplitude of less than or equal to 500 V / µm, or less than or equal to 400 V / µm, or less than or equal to 300 V / µm, or less than or equal to 200 V / µm, or less than or equal to 150 V / µm, or less than or equal to 140 V / µm, or less than or equal to 130 V / µm, or less than or equal to 120 V / µm, or less than or equal to 110 V / µm, or less than or equal to 100 V / µm, or less than or equal to 90 V / µm.

[0173] According to certain implementation schemes, the electric field may have an amplitude greater than or equal to 30 V / µm, or greater than or equal to 40 V / µm, or greater than or equal to 50 V / µm.

[0174] According to certain embodiments, the dielectric strength of the fluoropolymer is greater than or equal to 200 V / µm, preferably greater than or equal to 300 V / µm, even more preferably greater than or equal to 400 V / µm, and most preferably greater than or equal to 500 V / µm. The dielectric strength can be measured according to the standard ASTM D3755-97.

[0175] A square wave electric field with a maximum value equal to ΔE and a minimum value equal to 0 can usually be used.

[0176] In order to accurately measure ΔT EC The frequency of the electric field must be low enough to allow heat to diffuse within the polymer. Frequencies in the range of 1 mHz to 100 Hz can be used, preferably in the range of 0.1 Hz to 10 Hz.

[0177] The temperature can be measured between the glass transition temperature and the melting temperature of the polymer. The term "glass transition temperature" refers to the temperature at which an amorphous polymer at least partially transitions from a rubbery state to a glassy state or vice versa, measured by differential scanning calorimetry (DSC) during a second heating at a heating rate of 10 °C / min, according to standard ISO 11357-2:2013. The term "melting temperature" refers to the temperature at which a crystalline polymer at least partially transitions to a viscous liquid state, measured by differential scanning calorimetry (DSC) during a second heating at a heating rate of 10 °C / min, according to standard ISO 11357-3:2018. Therefore, the measurement temperature can particularly be from -20 °C to 150 °C, preferably from 0 °C to 100 °C, even more preferably from 15 °C to 60 °C, and most preferably from 20 °C to 40 °C.

[0178] The fluoropolymers according to the present invention can be ferroelectric polymers. "Classical ferroelectric" polymers, commonly referred to simply as "ferroelectric," are characterized by a broad hysteresis loop in the electric displacement-applied electric field curve. For these materials, this loop is characterized by a high coercive field (typically greater than 45 V / µm in absolute value) and a high remanent polarization intensity (typically greater than 50 mC / m) at 25 °C. 2 These materials exhibit maximum electrothermal properties at temperatures close to their Curie temperature. At this temperature, a ferroelectric to paraelectric (FE → PE) crystal structure transition occurs, known as the Curie transition, corresponding to the abrupt depolarization of macroscopic ferroelectric domains. This transition is narrow, first-order, and characterized by a narrow maxima of the dielectric constant, the location of which is independent of the frequency of the applied electric field. The Curie temperature can be adjusted according to the polymer composition: the higher the proportion of the first unit cell (VDF), the higher the Curie temperature. This temperature typically varies between 60°C and 150°C.

[0179] Advantageously, the fluoropolymers according to the invention can be relaxor ferroelectrics. Relaxor ferroelectric polymers are characterized by a relaxor ferroelectric (RFE) → paraelectric (PE) crystal transition over a wide temperature range. At this transition, a broad peak in the dielectric constant is observed, the temperature of which the maximum value depends on the frequency of the applied electric field: the lower the frequency of the electric field, the lower the temperature at which the maximum dielectric constant shifts. At or slightly above the (RFE) → (PE) transition temperature, the applied electric field can generate and align nano-polar regions, causing entropy changes and thus producing significant electrothermal effects over a wide temperature range. Relaxor ferroelectric polymers are characterized by having a much narrower hysteresis loop in their "electric displacement" versus "applied electric field" curve at 25°C and a frequency of about 1 Hz compared to ferroelectric polymers. They typically have a coercive field of less than or equal to 45 V / µm and less than or equal to 40 mC / m². 2 The remanent polarization intensity. Compared with classical ferroelectric polymers, this corresponds to the maximum dielectric constant and / or maximum ΔT.EC The phase transition can be achieved at lower temperatures, particularly between 0°C and 100°C, and in some cases between 20°C and 60°C. Therefore, relaxor ferroelectric polymers exhibit favorable electrothermal properties over a wide temperature range, especially close to ambient temperature. Consequently, they are particularly advantageous for the production of electrothermal devices.

[0180] According to certain embodiments, the relative permittivity of the fluoropolymer is at least 5%, preferably at least 10%, preferably at least 15%, preferably at least 20%, preferably at least 25%, preferably at least 30%, preferably at least 35%, and even more preferably at least 40% higher than that of the initial polymer, said relative permittivity being measured at a frequency of 1,000 Hz and a temperature of 40°C.

[0181] According to certain embodiments, particularly when the initial fluoropolymer is P(VDF-TrFE-CTFE) as exemplified below, the obtained fluoropolymer has a relative permittivity greater than or equal to 40, preferably greater than or equal to 50, even more preferably greater than or equal to 60, and most preferably greater than or equal to 70 at a temperature of 40°C, said relative permittivity being measured at 1 kHz.

[0182] According to certain embodiments, the fluoropolymer has a maximum dielectric constant at a temperature less than or equal to 60°C, preferably less than or equal to 50°C, and even more preferably less than or equal to 40°C, wherein the relative dielectric constant is measured at 1 kHz.

[0183] According to certain embodiments, the fluoropolymer has an increased dielectric constant relative to the initial polymer and relative to the olefinic fluoropolymer.

[0184] According to certain embodiments, the fluoropolymer has a value of µC / cm 2 The maximum polarization intensity is at least 1%, preferably at least 5%, preferably at least 10%, preferably at least 15%, preferably at least 20%, and even more preferably at least 25% higher than the initial polymer, and the maximum polarization intensity is measured at a frequency of 100 Hz, at 25 °C, and at an electric field of 1,300 kV / cm.

[0185] According to certain embodiments, for example when the initial fluoropolymer is P (VDF-TrFE-CTFE) as exemplified below, the maximum polarization intensity of the obtained fluoropolymer is greater than or equal to 0.5 µC / cm. 2 Preferably, it is greater than or equal to 1µC / cm 2 Preferably, it is greater than or equal to 1.5 µC / cm 2 Preferably, it is greater than or equal to 2µC / cm 2Preferably, it is greater than or equal to 2.5 µC / cm 2 Preferably, it is greater than or equal to 3µC / cm 2 Preferably, it is greater than or equal to 3.5µC / cm 2 Preferably, it is greater than or equal to 4µC / cm 2 Preferably, it is greater than or equal to 4.5 µC / cm 2 The maximum polarization intensity was measured at a frequency of 100 Hz, at 25 °C, and at an electric field of 1,300 kV / cm.

[0186] According to certain implementations, the fluoropolymer has an increased maximum polarization intensity relative to the initial polymer and relative to the olefinic fluoropolymer.

[0187] According to certain embodiments, the coercive field of the fluoropolymer, measured in kV / cm, is at least 1%, preferably at least 5%, preferably at least 10%, preferably at least 15%, preferably at least 20%, and even more preferably at least 25% lower than that of the initial polymer, said coercive field being measured at a frequency of 100 Hz and at 25°C.

[0188] According to certain embodiments, the coercive field of the fluoropolymer is preferably less than or equal to 2,000 kV / cm, preferably less than or equal to 1,500 kV / cm, preferably less than or equal to 1,000 kV / cm, and preferably less than or equal to 500 kV / cm, and the coercive field is measured at a frequency of 100 Hz and at 25°C.

[0189] According to certain implementations, the fluoropolymer has a reduced coercive field relative to the initial polymer and relative to the olefinic fluoropolymer.

[0190] According to certain embodiments, the crystallinity percentage of the fluoropolymer is at least 1%, preferably at least 5%, preferably at least 10%, preferably at least 15%, preferably at least 20%, preferably at least 25%, and even more preferably at least 30% higher than the initial polymer, said crystallinity percentage being measured at 25°C according to Example 6.

[0191] According to certain embodiments, particularly when the initial fluoropolymer is P(VDF-TrFE-CTFE) as exemplified below, the obtained fluoropolymer has a crystallinity percentage greater than or equal to 19%, preferably greater than or equal to 21%, preferably greater than or equal to 23%, preferably greater than or equal to 25%, and even more preferably greater than or equal to 27%, the crystallinity percentage being measured at 25°C.

[0192] According to certain embodiments, the remanent polarization of the fluoropolymer is preferably between 0.1 and 5 µC / cm. 2Between, preferably, 0.15 and 2.5 µC / cm 2 Between, preferably, 0.3 to 0.6 µC / cm 2 The residual polarization intensity was measured at a frequency of 100 Hz, at 25 °C, and at a field of 1,300 kV / cm.

[0193] All electroactive properties of fluoropolymers can be determined as shown in the examples below.

[0194] According to certain embodiments, the weight-average molecular weight of the fluoropolymer may be less than or equal to 500,000 g / mol, preferably less than or equal to 450,000 g / mol, preferably less than or equal to 400,000 g / mol, preferably less than or equal to 350,000 g / mol, preferably less than or equal to 300,000 g / mol, preferably less than or equal to 250,000 g / mol, preferably less than or equal to 200,000 g / mol, preferably less than or equal to 150,000 g / mol, and preferably less than or equal to 100,000 g / mol. This enables the membranes prepared from the polymer according to the invention to possess the desired mechanical properties. The mass distribution of the polymer can be determined by size exclusion chromatography (SEC) using, for example, dimethyl sulfoxide (DMSO + lithium bromide LiBr 1 g / L) as the eluent.

[0195] Composition

[0196] The fluoropolymers according to the invention can be formulated into compositions. These compositions comprise a single fluoropolymer according to the invention or, alternatively, a mixture of fluoropolymers.

[0197] According to certain embodiments, the composition may comprise at least one fluoropolymer according to the invention and at least one liquid carrier of said at least one polymer. This composition, commonly referred to as "ink," can be prepared by dissolving or suspending the polymer according to the invention in a liquid carrier. Preferably, the liquid carrier is a solvent. Advantageously, the solvent is a polar aprotic solvent, particularly selected from: amides, especially dimethylformamide, N-methyl-2-pyrrolidone, dimethylacetamide; sulfoxides, especially dimethyl sulfoxide; lactones, especially γ-butyrolactone; ketones, especially acetone, methyl ethyl ketone (or but-2-one), methyl isobutyl ketone, cyclopentanone, cyclohexanone, diisobutyl ketone; furans, especially tetrahydrofuran; esters, especially methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propylene glycol methyl ether acetate, glyceryl triacetate, diethylene glycol monobutyl ether acetate, and ethyl acetoacetate; carbonates, especially dimethyl carbonate and propylene carbonate; phosphates, especially trimethyl phosphate and triethyl phosphate; or mixtures thereof.

[0198] The total mass concentration of the polymer in the liquid carrier may particularly be from 0.1% to 30%, preferably from 0.5% to 20%.

[0199] According to certain embodiments, the composition may comprise one or more polymers that are different from the polymers of the present invention but also have the target electrothermal effect. For example, the composition may comprise one or more ferroelectric polymers or relaxor ferroelectric polymers that do not have carbon-carbon double bonds. The composition may particularly comprise the initial polymer as described above.

[0200] According to certain embodiments, the composition may comprise one or more polymers different from the polymers of the present invention, particularly those having polar or reactive functional groups, thereby improving the adhesion of the composition to a given substrate. The composition may optionally comprise one or more additives, particularly selected from surface tension modifiers, rheology modifiers, heat capacity modifiers, anti-aging modifiers, adhesion modifiers, pigments or dyes, flame retardants, or crosslinking aids.

[0201] The composition may optionally contain fillers, particularly nanofillers, such as barium strontium titanate (BST) nanowires.

[0202] membrane

[0203] According to at least some embodiments, the fluoropolymer according to the invention has sufficient mechanical properties to enable it to be molded into a film.

[0204] The film can be prepared using the fluoropolymer or composition containing the present invention, for example by coating an ink onto a substrate, or by extrusion or hot melt compression molding.

[0205] The substrate can be of any nature and is particularly formed of one or more layers of glass, metal or organic (especially polymer) material.

[0206] The membrane may optionally be stretched if necessary. Stretching (when performed) is preferably carried out at a stretch rate of at least 10% to 700%. The stretch rate of the membrane may particularly be at least 150%, or at least 200%, or at least 250%, or at least 300%, or at least 350%, or at least 400%. The stretch rate corresponds to the ratio of the membrane surface area after stretching to the membrane surface area before stretching. Stretching (when performed) may particularly be carried out at a temperature from 0°C to the melting temperature of the fluoropolymer; stretching is preferably carried out at a temperature from 5°C to 250°C, preferably from 10°C to 200°C, preferably from 15°C to 150°C, preferably from 20°C to 140°C, and even more preferably from 25°C to 100°C.

[0207] The membrane may optionally be stretched and then annealed, i.e. heated at a temperature of 70°C to 140°C, preferably 100°C to 120°C, for several seconds to several hours, and then cooled.

[0208] Stretching and annealing can typically improve crystallinity and dielectric strength.

[0209] This invention enables the production of films with a thickness greater than or equal to 0.1 µm. For optimal utilization of the electrothermal effect, the film thickness is advantageously between 1 µm and 100 µm. Among these thicknesses, the smallest possible thickness is preferred to avoid generating excessively high voltages. Therefore, films with thicknesses of 1 to 50 µm, or even 1 to 10 µm, are particularly preferred.

[0210] Electrodes can be deposited on the film, especially by metallization or by depositing conductive materials (silver, copper, conductive polymers, silver nanowires, carbon black, CNTs, etc.).

[0211] According to certain embodiments, the membrane prepared from the polymer according to the invention can be a layer of a multilayer system, and other layers may contain polymers with the same or different compositions according to the invention, another polymer, or a non-polymer material.

[0212] Multilayer systems can contain alternating electroactive materials and electrodes.

[0213] Multilayer systems can be obtained through continuous printing of electroactive and conductive materials, through a metallization step, or through a layering technique using films covered with electrodes. Adhesives can be used to bond the layers together.

[0214] The thickness of the electroactive polymer layer of the multilayer film can be from 0.1 to 100 µm, preferably from 1 to 50 µm, and even more preferably from 1 to 10 µm.

[0215] The multilayer system may comprise 1 to 1,000 layers of electroactive polymer, preferably 2 to 500 layers, preferably 3 to 250 layers, preferably 4 to 200 layers, preferably 5 to 150 layers, preferably 5 to 125 layers, preferably 6 to 100 layers, preferably 7 to 90 layers, preferably 8 to 80 layers, preferably 9 to 70 layers, preferably 6 to 70 layers.

[0216] application

[0217] Due to their electrothermal properties, the polymers according to the invention can be used in heat transfer systems. The heat transfer system comprises the polymer according to the invention, particularly in the form of a film, and especially as a layer in the multilayer system described above. The film is adapted for thermal contact with the load to be cooled and / or the load to be heated and / or the heat transfer fluid. The system also includes a voltage source intended to be applied to the plate. The heat transfer system can remove heat from or supply heat to another device (e.g., electrical or electronic components). Due to their pyroelectric properties, the polymers according to the invention can be used in heat recovery systems.

[0218] Due to their high dielectric constant, the polymers according to the present invention can also be used in energy storage systems, particularly capacitors, organic transistors, or electrostatic clutches.

[0219] Due to their electroactive properties, particularly ferroelectric or relaxor ferroelectric properties, the polymers according to the present invention can also be used in actuators (for tactile, microfluidic, loudspeaker, etc.).

[0220] Example

[0221] The following examples illustrate the present invention but do not limit it.

[0222] Example 1: Preparation of P(VDF-TrFE-CTFE-DB)

[0223] In five flasks, 1 g of a 62 / 30 / 8 molar composition P(VDF-TrFE-CTFE) polymer was dissolved in 20 mL of DMSO. 10, 15, 20, 25, and 30 µL of ethylenediamine were added to each solution, respectively. The reaction mixture was heated to 30 °C and reacted for 4 hours. After the reaction, the obtained polymers were precipitated in water and purified by washing with a 60 / 40 H₂O / ethanol solution. An average yield of 95% was obtained. The obtained olefinic fluoropolymer is designated P(VDF-TrFE-CTFE-DB), with DB indicating the presence of a double bond.

[0224] Example 2: The reaction of P(VDF-TrFE-CTFE-DB) with mCPBA

[0225] 0.5 g of each dehydrochlorinated polymer P (VDF-TrFE-CTFE-DB) was dissolved in 20 mL of ethyl acetate. 0.3 g of mCPBA was added to each solution. The reaction mixture was reacted at 15 °C for 6 hours. The solvent was then evaporated, and the product was washed with ethanol to remove excess mCPBA. Fluoropolymers were obtained in an average yield of 90%.

[0226] Example 3: Preparation of devices for dielectric characterization

[0227] An electrode consisting of a 10 nm thick chromium layer and a 100 nm thick silver layer was deposited on a glass substrate (15 × 15 mm) by chemical vapor deposition (CVD). On this apparatus, the film was deposited from a 7% by mass polymer solution in ethyl acetate using a Dr. Blade blade. After solvent evaporation, a film with a thickness of approximately 3 µm was obtained. The film was annealed on a hot plate at 100 °C for 2 hours. A 100 nm thick silver electrode was then deposited on top of the film by CVD. To allow contact with the bottom electrode, the polymer film was removed from the bottom of the apparatus.

[0228] Example 4: Measurement of relative permittivity

[0229] Dielectric constants were measured using a broadband dielectric spectroscopy system and a Solartron 1260A impedance analyzer. Sample temperature was controlled using a Linkam LTS 350 temperature control system. Measurements were performed at 40°C using a 1V AC voltage signal with a frequency of 10 Hz. -2 Up to 10 3 kHz. This technique enables the determination of the relative permittivity and loss factor based on the measured capacitance and the sample's geometry. Key results for different samples are as follows: Figure 1 As shown. The point at position 0 along the horizontal axis corresponds to the initial P(VDF-TrFE-CTFE) polymer.

[0230] An increase in relative permittivity was observed after dehydrochlorination of P(VDF-TrFE-CTFE). This increase was even more pronounced after the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA. In fact, the polymer obtained after the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA had a relative permittivity of approximately 67, while the initial polymer P(VDF-TrFE-CTFE) had a relative permittivity of approximately 47.5 (i.e., an increase of 41%).

[0231] Example 5: Polymer polarization

[0232] The polarization hysteresis of the sample was measured by recording multiple polarization hysteresis cycles using a TF Analyzer 2000E analyzer from AixACCT Systems. Measurements were performed by applying a continuous triangular signal at a frequency of 100 Hz at ambient temperature. Figure 2 The maximum polarization intensity value under a field of 1,300 kV / cm is given.

[0233] The increase in maximum polarization intensity relative to the initial polymer after the dehydrochlorinated polymer reacted with mCPBA was more significant. In fact, the polymer obtained after the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA exhibited approximately 4.8 µC / cm². 2 The maximum polarization intensity is [value missing], while the maximum polarization intensity of the initial polymer P(VDF-TrFE-CTFE) is approximately 3.75 µC / cm. 2 (That is, it increased by 28%).

[0234] The coercive field of different samples was also measured. Figure 3A decrease in coercivity was observed after dehydrochlorination. This decrease was more pronounced after reaction with mCPBA. In fact, the polymer obtained after reacting P(VDF-TrFE-CTFE-DB) with mCPBA had a coercivity of approximately 387 kV / cm, while the coercivity of the initial polymer P(VDF-TrFE-CTFE) was approximately 525 kV / cm (i.e., a decrease of 26%).

[0235] Example 6: Sample analysis using WAXS

[0236] The crystal structure of the sample was analyzed in vacuum and at 25 °C using a XENOCS Xeuss 2.0 wide-angle X-ray scattering (WAXS) system at a sample-detector distance of 151 mm and λ = 1.54189 Å (Cu Kα). Diffraction patterns were collected using a DECTRIS PILATUS-300k detector with a wave vector range of q from 0.1 to 3.1 Å. -1 (1.4° to 46°), then azimuth integration was performed for different crystalline phases (ferroelectric and / or relaxor ferroelectric) and amorphous phases. Data analysis was performed using Voigt profiles with Fityk software. The crystallinity percentage corresponds to the quotient of the total area of ​​the peaks of different crystalline phases relative to the total area of ​​the peaks of the crystalline phases and the peaks of the amorphous phases.

[0237] The calculated percentage of crystallinity is as follows: Figure 4 As shown.

[0238] It was observed that the crystallinity of P(VDF-TrFE-CTFE-DB) increased significantly after reacting with mCPBA. In fact, the crystallinity of the polymer obtained after reacting P(VDF-TrFE-CTFE-DB) with mCPBA was 28%, while the crystallinity of the initial polymer P(VDF-TrFE-CTFE) was 21% (i.e., an increase of 33%).

[0239] Example 7: Molar mass determined by SEC

[0240] The molar mass of the polymer was determined by size exclusion chromatography (SEC) using dimethyl sulfoxide (DMSO + lithium bromide LiBr 1 g / L) as the eluent. Measurements in DMSO were performed on a Thermoscientific Ultimate 3000 system equipped with a diode array detector (DAD). The system also included a multi-angle light scattering detector (MALS) and a differential refractive index detector (dRI) from Wyatt Technology. Measurements were performed on Tosoh TSK G3000HHR and G2000HHR columns (7.8 μm). The polymer was separated at a flow rate of 0.5 ml / min on a column with exclusion limits of 200 Da to 60,000 Da. The column temperature was maintained at 80 °C.

[0241] The absolute molar mass was determined using the refractive index increment (dn / dc). dn / dc was evaluated by measuring the refractive index signal through injection of different polymer solutions with concentrations ranging from 1 to 10 mg / mL. The absolute molar mass was then extracted from the ZIMM equation using ASTRA software. The latter can be found in... Figure 5 .

[0242] A slight increase in molar mass was observed after dehydrochlorination (possibly due to partial cross-linking). This trend was reversed after the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA.

Claims

1. A method for manufacturing a fluoropolymer from an olefinic fluoropolymer, wherein the olefinic fluoropolymer comprises: -The first unit, its formula is -(CF2-CH2)-, -Optionally, at least one second unit, which has the formula -(CX1X2-CX3X4)-, -Optionally, at least one third unit, which has the formula -(CY1Y2-CY3Z)-, - At least one fourth unit, which is of the form -(CY3=CF)-, -(CY3=CX1)-, -(CY3=CX2)-, -(CY1=CY3)- or -(CY2=CY3)-; in: X1 and X2 independently represent -H, -F, or optionally partially or fully fluorinated alkyl groups containing 1 to 3 carbon atoms. X3 and X4 independently represent -F, or an alkyl group optionally partially or fully fluorinated containing 1 to 3 carbon atoms, excluding combinations where X1 and X2 are both -H and X3 and X4 are both -F. Y1 and Y2 independently represent -H, -F, -Cl, or optionally partially or fully fluorinated alkyl groups containing 1 to 3 carbon atoms. Y3 represents -F, -Cl, or an alkyl group that is optionally partially or fully fluorinated, containing 1 to 3 carbon atoms. Z represents a halogen atom that is different from -F. The method includes the step of reacting the olefinic fluoropolymer with a peroxide.

2. The method according to claim 1, wherein X1 represents -H or -F, and X2, X3 and X4 all represent -F.

3. The method according to claim 1 or 2, wherein Y3 represents -F, and Y1 and Y2 both represent -H or -F.

4. The method according to any one of claims 1 to 3, wherein the olefinic fluoropolymer comprises: The first unit is from -30 mol% to less than 100 mol%. The second unit, ranging from -0 mol% to 60 mol%, The third unit, ranging from -0 mol% to less than 20 mol%, - The fourth unit, greater than 0 mol% to 20 mol%.

5. The method according to any one of claims 1 to 4, wherein the olefinic fluoropolymer comprises at least one second unit having the formula -(CX1X2-CX3X4)-.

6. The method according to any one of claims 1 to 5, comprising the step of preparing the olefinic fluoropolymer by dehydrohalogenation of an initial polymer, the initial polymer comprising: -The first unit, its formula is -(CF2-CH2)-, -Optionally, at least one second unit, which has the formula -(CX1X2-CX3X4)-, -At least one third unit, which is of the form -(CY1Y2-CY3Z)-.

7. The method according to claim 6, wherein the step of preparing the olefinic fluoropolymer comprises contacting the initial polymer with a base, preferably ethylenediamine, and preferably used in an amount of 10 to 30 µL / g of the initial polymer.

8. The method according to claim 6 or 7, wherein the relative permittivity of the fluoropolymer is at least 5% higher than that of the initial polymer, preferably at least 10% higher, preferably at least 15% higher, preferably at least 20% higher, preferably at least 25% higher, preferably at least 30% higher, preferably at least 35% higher, and even more preferably at least 40% higher, and the relative permittivity is measured at a frequency of 1,000 Hz and a temperature of 40°C.

9. The method according to any one of claims 6 to 8, wherein the fluoropolymer is at µC / cm 2 The maximum polarization intensity is at least 1%, preferably at least 5%, preferably at least 10%, preferably at least 15%, preferably at least 20%, and even more preferably at least 25% higher than the initial polymer, and the maximum polarization intensity is measured at a frequency of 100 Hz, at 25 °C, and at an electric field of 1,300 kV / cm.

10. The method according to any one of claims 6 to 9, wherein the coercive field of the fluoropolymer, in kV / cm, is at least 1%, preferably at least 5%, preferably at least 10%, preferably at least 15%, preferably at least 20%, and even more preferably at least 25% lower than that of the initial polymer, and the coercive field is measured at a frequency of 100 Hz and at 25°C.

11. The method according to any one of claims 6 to 10, wherein the percentage of crystallinity of the polymer is at least 1% higher than that of the initial polymer, preferably at least 5% higher, preferably at least 10% higher, preferably at least 15% higher, preferably at least 20% higher, preferably at least 25% higher, and even more preferably at least 30% higher.

12. The method according to any one of claims 1 to 11, wherein the amount of said peroxide is 0.005 to 50 mmol / g fluoropolymer, preferably 0.5 to 10 mmol / g fluoropolymer, and even more preferably 1 to 6 mmol / g fluoropolymer.

13. The method according to any one of claims 1 to 12, wherein the peroxide is an inorganic peroxide selected from hydrogen peroxide and peroxyacids such as peroxymonosulfuric acid, or an organic peroxide selected from peracetic acid, magnesium monoperoxyphthalate, or m-chloroperoxybenzoic acid.

14. A fluoropolymer that can be obtained by the method according to any one of claims 1 to 13.

15. The fluoropolymer according to claim 14, wherein the weight-average molecular weight of the fluoropolymer is less than or equal to 500,000 g / mol, preferably less than or equal to 450,000 g / mol, preferably less than or equal to 400,000 g / mol, preferably less than or equal to 350,000 g / mol, preferably less than or equal to 300,000 g / mol, preferably less than or equal to 250,000 g / mol, preferably less than or equal to 200,000 g / mol, preferably less than or equal to 150,000 g / mol, and most preferably less than or equal to 100,000 g / mol.

16. The fluoropolymer according to claim 14 or 15, wherein the remanent polarization of the polymer is 0.1 to 5 µC / cm. 2 Preferably, the concentration is 0.15 to 2.5 µC / cm. 2 Preferably, the concentration is 0.3 to 0.6 µC / cm. 2 The residual polarization intensity was measured at a frequency of 100 Hz, at 25 °C, and at a field of 1300 kV / cm.

17. A composition comprising at least one fluoropolymer according to any one of claims 14 to 16 and at least one liquid carrier of said polymer.

18. A membrane comprising a fluoropolymer according to any one of claims 14 to 16.

19. The membrane according to claim 18, wherein the thickness of the membrane is greater than or equal to 0.1 µm, preferably the thickness of the membrane is 1 to 100 µm, more preferably the thickness of the membrane is 1 to 50 µm, and even more preferably the thickness of the membrane is 1 to 10 µm.

20. A multilayer system comprising at least one layer formed from a membrane according to claim 18 or 19, wherein other layers may comprise a fluoropolymer, another polymer, or a non-polymer material having the same or different composition according to the invention.

21. Use of the fluoropolymer according to any one of claims 14 to 16, or the membrane according to claim 18 or 19, or the multilayer system according to claim 20 in a heat transfer system, preferably a cooling system, or in an energy storage system, preferably a capacitor, an organic transistor, an actuator, or an electrostatic clutch.

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