Process for manufacturing a fluorinated polymer having electrocalorific properties

Abstract

The invention relates to a process for preparing a fluorinated polymer from an ethylenic fluorinated polymer by reaction with a peroxide. The process notably allows for a modification of the polymer's electroactive properties. The invention also relates to a fluorinated polymer that can be used in compositions, in the form of films, or in multilayer systems for heat transfer and energy storage applications. Figure for the abstract: no figure.

Description

Title of the invention: Process for manufacturing a fluorinated polymer having electrocalorific properties Scope of the invention

[0001] The present invention relates to a process for manufacturing a fluorinated polymer obtained by reacting an ethylenic fluorinated polymer with a peroxide such as metachloroperbenzoic acid (mCPBA). The fluorinated polymer obtainable by this process preferably has electrocaloric properties and can be formed into a film. Technical background

[0002] The electrocaloric effect is a property of certain dipolar dielectric materials that manifests as a temperature change when they are subjected to a changing electric field. The physical origin of this phenomenon is linked to a change in the dipole order, and therefore to a change in dipole entropy induced by the application of an electric field. The application of an electric field Ec orders and orients the dipoles of these materials, which leads to a decrease in their dipole entropy and an increase in their temperature under adiabatic conditions. Conversely, decreasing or removing the electric field leads to an increase in their dipole entropy and a decrease in their temperature under adiabatic conditions. Thus, an electrocaloric material is characterized, under given experimental conditions, by an adiabatic temperature change ATEC for an applied electric field Ec under adiabatic conditions.

[0003] The electrocaloric performance of a material can be estimated theoretically (indirect method) from the evolution as a function of temperature of its dielectric properties in particular with the values ​​of relative permittivity, maximum polarization, coercive field and remanent polarization.

[0004] Alternatively, an electrocaloric material can also be characterized by an isothermal entropy change ASEC for an applied electric field Ec under isothermal conditions.

[0005] The electrocaloric effect is currently the subject of numerous studies for the development of new cooling systems that are more environmentally friendly and more energy-efficient than systems based on gas compression, the thermoelectric effect, or the magnetocaloric effect. Ferroelectric and ferroelectric relaxor materials, due to the strong coupling between applied electric fields and their dipolar structure, are the materials that are attracting the most interest for these applications because they are susceptible to possess significant electrocaloric performance. In particular, this coupling is maximal near or slightly above the phase transitions: Ferroelectric -> Paraelectric (FE -> PE) or Relaxor-Ferroelectric -> Paraelectric (RFE -> PE), due in particular to a strong reversible variation of the polarization of these materials under an electric field, as well as a high dielectric permittivity.

[0006] In other words, near the FE -> PE or RFE -> PE phase transitions, a relatively small change in the electric field generates significant changes in entropy and temperature. The good flexibility and ease of processing of these materials in the form of large-area thin films are other parameters that make them particularly suitable for use in solid-state refrigeration systems.

[0007] Fluorinated polymers based on vinylidene fluoride (VDF) represent a class of compounds with remarkable properties for a wide range of applications. PVDF and copolymers comprising VDF and trifluoroethylene (TrFE) are particularly interesting because of their piezoelectric and pyroelectric properties. Fluorinated polymers based on VDF and TrFE also belong to this class of materials possessing ferroelectric and ferroelectric-relaxing properties and are among the most studied.

[0008] The electrocalorific properties of P(VDF-TrFE) type ferroelectric copolymers are maximal near the ferroelectric to paraelectric (FE -> PE) transition. The FE -> PE transition of this type of polymer is narrow, meaning it occurs over a small temperature range and is located at relatively high temperatures, typically strictly above 60°C. This precludes their use in cooling systems intended to operate around ambient temperature and / or over a wide temperature range.

[0009] The use of ferroelectric relaxer polymers makes it possible to overcome at least some of the drawbacks mentioned above. Indeed, ferroelectric relaxer polymers of the type: irradiated P(VDF-TrFE), P(VDF-TrFE-CFE), or P(VDF-TrFE-CTFE, have a phase transition (RFE -> PE) that is broader than the FE -> PE phase transition of ferroelectric polymers, i.e., it occurs over a wider temperature range. Furthermore, the RFE -> PE transition generally occurs at lower temperatures than the FE -> PE transition of ferroelectric polymers. Thus, this makes it possible to consider using ferroelectric relaxer polymers in various cooling systems, particularly in cooling systems that must operate around ambient temperature and / or over a wide temperature range.

[0010] The article “Large electrocaloric effect in ferroelectric polymers near room temperature” (B. Neese et al., Science, 2008, 321, 5890, 921-823) and the article “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) fluorinated polymers having 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 fluorinated polymers (EFPs) by two successive steps: a Williamson etherification reaction followed by a photocatalyzed crosslinking reaction. This modification of the EFPs led to an improvement in electroactive properties, particularly in terms of relative permittivity. Application WO 2019 / 020906 Al is also an example of this application.

[0012] In another area of ​​modification, in 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), nanometric fillers, such as barium strontium titanate (BST) nanowires, were added to a P(VDF-TrFE-CFE). However, the introduction of nanometric fillers into the polymer matrix presents several drawbacks. First, it requires very good dispersion of these fillers, thus complicating the shaping of the material. Furthermore, the handling of nanoparticles in the polymer manufacturing process is complex due to the potential risks of free nanoparticles to human health. Finally, the presence of fillers tends to mechanically weaken the material and reduce its dielectric strength.

[0013] It is also possible to introduce double bonds within the polymer by dehydrohalogenation reaction.

[0014] Application WO 2019 / 075061 A1 describes the manufacture of a polymer comprising double bonds, this polymer being produced by the dehydrofluoration of PVDF in dimethylacetamide with a saturated solution of sodium hydroxide in isopropanol. No measurements of the electrocaloric properties of the manufactured polymer were carried out. The type of double bonds in the manufactured polymer was also not characterized. This dehalogenation method is similar to that of US application 4904739 A, in which there is a high proportion of conjugated double bonds. Furthermore, fluorinated polymers with conjugated double bonds obtained by dehydrofluoration with a strong base are thermally unstable, yellow, degrade easily, and are susceptible to crosslinking upon the action of a strong base.Furthermore, the process has an implementation disadvantage in that it uses dimethylacetamide as a solvent, which is harmful.

[0015] The article “Enhanced Electrocaloric Response of Vinylidene Fluoride-Based The article "Polymers via One-Step Molecular Engineering" (Le Goupil F. et al., Adv. Funct. Mater., 2021, 31, 1, 2007043) describes the chemical modification of a polymeric polymer (PFE), P(VDF-TrFE-CTFE), by reaction in the presence of a base, which allows the controlled introduction of double bonds within the polymer. This modification alters the polymer's crystalline structure and its dielectric properties by increasing the electrical permittivity. French patent FR 3104583 B1 and German patent application WO 2021 / 116618 Al also disclose this chemical modification with the introduction of conjugated double bonds.

[0016] These strategies consisting of the generation of double bonds do indeed improve the dielectric properties of polymers; however, double bonds, whether conjugated or not, induce cross-linking of the polymer which is not always desired.

[0017] Despite the efforts described above, performance improvement remains limited. Given these limitations, it is therefore essential to explore other methods for improving the dielectric properties of ferroelectric relaxor polymers.

[0018] In order to develop more efficient cooling devices, there is currently a real need to provide a process for manufacturing VDF-based fluoropolymers with improved electrocalorific properties compared to those of the prior art, or more generally, with improved dielectric properties. Summary of the invention

[0019] The invention relates to a process for manufacturing a fluorinated polymer from an ethylenic fluorinated polymer comprising: • a first unit of formula -(CF2-CH2)-, • optionally, at least one second formula unit -(CX1X2-CX3X4)-, • optionally, at least one third formula unit -(CYiY2-CY3Z)-, • at least one fourth unit of formula -(CY3=CF)-, -(CY3=CXi)-, -(CY3 =CX2)-, -(CY1=CY3)- or -(CY2=CY3)-;

[0020] in which:

[0021] Xi and X2 independently denote -H, -F, or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated,

[0022] X3 and X4 independently denote -F, or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated, except for the combination where Xi and X2 are both -H and X3 and X4 are both -F,

[0023] Yi and Y2 independently denote -H, -F, -Cl or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated,

[0024] Y3 denotes -F, -Cl or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluoridated,

[0025] Z denotes a halogen atom other than -F,

[0026] the process comprising a step of reacting the ethylenic fluorinated polymer with a peroxide.

[0027] In embodiments, Xi denotes -H or -F and X2, X3 and X4 all denote -F.

[0028] In some embodiments, Y3 denotes -F and Y1 and Y2 both denote -H or -F.

[0029] In embodiments, the ethylenic fluorinated polymer comprises: • from 30% to less than 100% mol of the first unit, • from 0% to 60% mol of the second unit, • from 0% to less than 20% molar of the third unit, • from more than 0% to 20% molar of the fourth unit.

[0030] In embodiments, the ethylenic fluorinated polymer comprises at least one second unit of formula -(CXiX2-CX3X4)-.

[0031] Thus, the ethylenic fluorinated polymer may comprise: • from 30% to less than 100% molar of the first unit, • from more than 0% to 60% molar of the second unit, • from 0% to less than 20% molar of the third unit, • from more than 0% to 20% molar of the fourth unit.

[0032] In some embodiments, the process includes a step of preparing the ethylenic fluorinated polymer by dehydrohalogenation of an initial polymer, said initial polymer comprising: • a first unit of formula -(CF2-CH2)-, • optionally, at least one second formula unit -(CX1X2-CX3X4)-, • at least one third unit of formula -(CYiY2-CY3Z)-.

[0033] In embodiments, the step of preparing the ethylenic fluorinated polymer includes contacting the initial polymer with a base, said base preferably being ethylene diamine and preferably being used in an amount of 10 to 30 pL / g of initial polymer.

[0034] In embodiments, the fluorinated polymer has a relative dielectric permittivity that is at least 5% higher, 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 preferably still at least 40% higher, compared to the initial polymer, said relative dielectric permittivity being measured at a frequency of 1000 Hz and at a temperature of 40 °C.

[0035] In embodiments, the fluorinated polymer has a maximum polarization in pC / cm2 which is at least 1% higher, preferably at least 5% higher, preferably at least 10% higher, preferably at least 15% higher, preferably at least 20% higher, preferably still at least 25% higher, compared to the initial polymer, said maximum polarization being measured at a frequency of 100 Hz, at 25 °C and under an electric field of 1300 kV / cm.

[0036] In embodiments, the fluorinated polymer has a coercive field in kV / cm which is at least 1% lower, preferably at least 5% lower, preferably at least 10% lower, preferably at least 15% lower, preferably at least 20% lower, preferably still at least 25% lower, compared to the initial polymer, said coercive field being measured at a frequency of 100 Hz, at 25 °C.

[0037] In embodiments, the polymer has a percentage of crystallinity which is at least 1% higher, 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, preferably still at least 30% higher, compared to the initial polymer.

[0038] In embodiments, the peroxide is used in an amount of 0.005 to 50 mmol / g of ethylenic fluorinated polymer, preferably 0.5 to 10 mmol / g of ethylenic fluorinated polymer, even more preferably 1 to 6 mmol / g of ethylenic fluorinated polymer.

[0039] In embodiments, the peroxide is an inorganic peroxide selected from hydrogen peroxide and peracids such as peroxy monosulfuric acid, or an organic peroxide selected from peracetic acid, magnesium monoperoxyphthalate or metachloroperbenzoic acid.

[0040] The invention also relates to a fluorinated polymer that can be obtained by the process as defined above.

[0041] In embodiments, the fluorinated polymer has a weight average molecular mass 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.

[0042] In embodiments, the fluorinated polymer has a remanent polarization of 0.1 to 5 pC / cm2, preferably of 0.15 to 2.5 pC / cm2 and even more preferably of 0.3 to 0.6 pC / cm2, said remanent polarization being measured at a frequency of 100 Hz, at 25 °C and under a field of 1300 kV / cm.

[0043] The invention also relates to a composition comprising at least one fluorinated polymer as defined above and at least one liquid vehicle of said polymer.

[0044] The invention also relates to a film comprising the fluorinated polymer as defined above.

[0045] In embodiments, the film has a thickness greater than or equal to 0.1 pm, preferably a thickness of 1 to 100 pm, more preferably a thickness of 1 to 50 pm, and even more preferably a thickness of 1 to 10 pm.

[0046] The invention also relates to a multilayer system, comprising at least one layer formed by a film as described above, the other layers being able to comprise a fluorinated polymer according to the invention, of the same or different composition, another polymer or a non-polymer material.

[0047] The invention also relates to the use of a fluorinated polymer as described above, a film as described above or a multilayer system as described above, in a heat transfer system, preferably a cooling system.

[0048] The invention also relates to the use of a fluorinated polymer as described above, a film as described above or a multilayer system as described above in an energy storage system, preferably a capacitor, an organic transistor, an actuator, an electrostatic clutch.

[0049] The present invention makes it possible to meet the need expressed above. More particularly, it provides a manufacturing process for producing VDF-based fluorinated polymers having improved electrocalorific properties compared to those of the prior art, i.e., exhibiting, for example, a higher adiabatic temperature change (ATEC) in a given variable electric field or, in general, exhibiting improved dielectric properties.

[0050] The invention consists of improving the dielectric properties of VDF-based fluorinated polymers by functionalization through chemical modification. Specifically, it involves obtaining a polymer with a more pronounced ferroelectric-relaxant character, resulting in a high dielectric constant and maximum polarization, as well as low remanent polarization and coercive fields. These properties are desirable for several applications, particularly for electrocaloric applications in cooling systems.

[0051] The initial polymer is modified by two successive chemical reactions: a first step of dehydrohalogenation of the initial polymer with the introduction of double bonds onto the chain of said initial polymer, so as to obtain an ethylenic fluorinated polymer, containing double bonds; and a second step of reaction of the ethylene fluorinated polymer with a peroxide that reacts on previously formed double bonds.

[0052] These chemical modifications result in a fluorinated polymer exhibiting superior dielectric and, in particular, electrocaloric properties compared to the initial polymer. Compared to the initial polymer, the fluorinated polymer obtained by this process preferably exhibits increased relative permittivity and maximum polarization values, and decreased coercive field and remanent polarization values. Brief description of the figures

[0053] [Fig. 1] Fig. 1 represents the maximum relative permittivity measured with a 1 V alternating voltage signal at a signal frequency of 1 kHz for samples after dehydrochlorination (squares) and after reaction with mCPBA (circles), according to Example 4 below. Abscissa: ethylenediamine concentration values ​​in pL / g of polymer; ordinate: actual maximum relative permittivity values.

[0054] [Fig.2] Fig.2 represents the maximum polarization measured under a three-phase signal Continuous angular polarization with a frequency of 100 Hz under a 1300 kV / cm field for samples after dehydrochlorination (squares) and after reaction with mCPBA (circles), according to Example 5 below. Abscissa: ethylenediamine concentration values ​​in pL / g of polymer; ordinate: maximum polarization in pC / cm².

[0055] [Fig. 3] Fig. 3 represents the coercive field values ​​for the samples after dehydrochlorination (squares) and after reaction with mCPBA (circles), according to Example 5 below. Abscissa: ethylenediamine concentration values ​​in pL / g of polymer; ordinate: coercive field values ​​in kV / cm.

[0056] [Fig.4] Fig.4 represents the percentage values ​​of crystallinity %X for the Samples after dehydrochlorination (squares) and after reaction with mCPBA (circles), according to Example 6 below. Abscissa: ethylenediamine concentration values ​​in pL / g of polymer; ordinate: percentage crystallinity values ​​%X.

[0057] [Fig. 5] Fig. 5 represents the molar mass values ​​in g / mol for the samples after dehydrochlorination (squares) and after reaction with mCPBA (circles), according to Example 7 below. Abscissa: ethylenediamine concentration values ​​in pL / g of polymer; ordinate: molar mass values ​​in g / mol. Detailed description

[0058] The invention is now described in more detail and in a non-limiting manner in the following description. Initial polymer

[0059] The initial polymer comprises: a first unit of formula: -(CF2-CH2)- Optionally, a second formula unit: -(CXiX2-CX3X4)-optionally a third formula unit: -(CYiY2-CY3Z)-,

[0060] in which: Xi and X2 independently denote -H, -F, or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated, X3 and X4 independently denote -F, or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated, except for the combination where Xi and X2 are both -H and X3 and X4 are both -F, Yi and Y2 independently denote -H, -F, -Cl or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated, Y3 denotes -F, -Cl or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated, Z denotes a halogen atom other than -F.

[0061] The initial polymer may consist essentially, or even consist, of the first unit described above. Alternatively, the initial polymer may consist essentially, or even consist, of the first and second units described above. Alternatively, the initial polymer may consist essentially, or even consist, of the first and third units described above. Alternatively, the initial polymer may consist essentially, or even consist, of the first, second, and third units described above. Alternatively, the initial polymer may comprise one or more additional units other than the first, second, and third units.

[0062] The first unit is derived from the VDF.

[0063] The initial polymer may comprise a single second unit or, conversely, several different second units. According to certain embodiments, the second unit(s) may be derived from monomers selected from the following list: trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), trifluoropropenes, and in particular 3,3,3-trifluoropropene, tetrafluoropropenes, and in particular 2,3,3,3-tetrafluoropropene or 1,3,3,3-tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropenes, and in particular 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene. Depending on certain variations, second units derived from several different fluorinated monomers may be present in the initial polymer.

[0064] According to some embodiments, Xi can designate -H or -F; and X2, X3 and X4 all three designate -F. In other words, the second unit can be derived from trifluoroethylene (TrFE) and / or tetrafluoroethylene (TFE).

[0065] According to some embodiments, Z can denote -Cl, -Br or -I. Advantageously, Z can denote -Cl.

[0066] The initial polymer may comprise a single third unit or, conversely, several different third units. According to certain embodiments, the third unit(s) may be derived from monomer(s) selected from the list consisting of: 1,1-chlorofluoroethylene (1,1-CFE), 1,2-chlorofluoroethylene (1,2-CFE), chlorotrifluoroethylene (CTFE), 2-chloro-3,3,3-trifluoropropene (1233xf), l-chloro-3,3,3-trifluoropropene (1233zd), l,2-dichloro-l,2-difluoroethylene, l,l-dichloro-l,l-difluoroethylene and 1,1,2-trichloro-2-fluoroethylene.

[0067] Advantageously, Y3 can designate -F and Yi and Y2 can both designate -H or -F. In other words, according to these embodiments, the third unit can be derived from chlorofluoroethylene (CFE) and / or chlorotrifluoroethylene (CTFE).

[0068] In particular, according to certain embodiments, the polymer may comprise units derived from vinylidene fluoride (VDF), TrFE and CFE, or comprise units derived from VDF, TrFE and CTFE, or comprise units derived from VDF, TrFE, CFE and CTFE, or comprise units derived from VDF, TFE and CFE, or comprise units derived from VDF, TFE and CTFE, or comprise units derived from VDF, TFE, CFE and CTFE.

[0069] The polymers in the above list may further comprise units derived from one or more additional monomers, such as units derived from hexafluoropropylene HFP.

[0070] The second unit is preferably derived from a single monomer (preferably TrFE or TFE) or from only two monomers (preferably TrFE and TFE, preferably TrFE again). The third unit is preferably derived from a single monomer (preferably CFE or CTFE, preferably CTFE again) or from only two monomers (preferably CFE and CTFE). The P(VDF-TrFE-CTFE) polymer is particularly preferred as the starting polymer.

[0071] The initial polymer may comprise: • from 30% to 100% molar of the first unit, • from 0% to 60% molar of the second unit, • from 0% to 20% molar of third unit.

[0072] Preferably, the initial polymer comprises: • from 30% to less than 100% molar of the first unit, • from 0% to 60% molar of the second unit, • from more than 0% to 20% molar of third unit.

[0073] Preferably, the initial polymer comprises: • from 30% to 90% molar of the first unit, • from 0% to 60% molar of the second unit, • from more than 0% to 20% molar of third unit.

[0074] It is understood that when several second units or several third units are present, the contents announced correspond to the total of all the second units, respectively of all the third units.

[0075] The initial polymer may include, in particular, 30% to 35% mol, 35% to 40% mol, 40% to 45% mol, 45% to 50% mol, 50% to 60% mol, 60% to 70% mol, 70% to 80% mol, 80% to 85% mol, 85% to 90% mol, 90% to 95% or 95% to less than 100%, or 100% of the first unit.

[0076] The initial polymer may in particular comprise 0% to 5% molar, 5% to 10% molar, 10% to 15% molar, 15% to 20% molar, 20% to 30% molar, 40% to 50% molar, 50% to 55% molar, or 55% to 60% molar of a second unit.

[0077] The initial polymer may in particular comprise 0%, or more than 0% to 1% molar, 1% to 5% molar, 5% to 10% molar, 10% to 15% molar or 15% to 20% molar of third unit.

[0078] Preferred contents for the initial polymer are as follows: • 40% to 80% molar of first unit, 15% to 50% molar of second unit and 1% to 20% molar of third unit; • 50% to 70% molar of the first unit, 20% to 40% molar of the second unit and 3% to 15% molar of the third unit; • 55% to 65% molar of first unit, 27% to 37% molar of second unit and 5% to 12% molar of third unit.

[0079] These contents apply in particular to initial polymers of type P(VDF-TrFE-CTFE), P(VDF-TrFE-CFE), P(VDF-TFE-CTFE), P(VDF-TFE-CFE).

[0080] The molar composition of the repeating units in fluorinated polymers can be determined by various means such as infrared spectroscopy or Raman spectroscopy. Conventional methods of elemental analysis in carbon, fluorine, and chlorine, bromine, or iodine, such as X-ray fluorescence spectroscopy, allow for the unambiguous calculation of the mass composition of the polymers, from which the molar composition can be deduced. Multinuclear NMR techniques can also be used. Specifically, proton (*H) and fluorine (19F) are detected by analyzing a solution of the polymer in a suitable deuterated solvent. The NMR spectrum is recorded on an FT-NMR spectrometer equipped with a multinuclear probe. The specific signals given by the different monomers are then identified in the spectra acquired for each nucleus.

[0081] Thus, for example, the unit resulting from the polymerization of VDF gives a specific signal for the -CH2- groups in proton NMR (bulk centered at 3 ppm). Similarly, the unit resulting from TrFE gives a specific signal characteristic of the -CHF- group in proton NMR (at approximately 5 ppm). In fluorine NMR, the signals from the -CF2- and -CFCI- units of CFE and CTFE are indistinguishable from those of the -CF2- units of VDF and TrFE between -90 and -132 ppm. The -CHF unit of TrFE gives characteristic signals between -194 and -220 ppm. The combination of the proton and fluorine NMR spectra allows the molar composition of the polymers to be deduced unambiguously.

[0082] The initial polymer can be obtained by processes known in the prior art. In particular, it can be prepared by radical polymerization according to a solution, suspension, emulsion, or microemulsion polymerization process.

[0083] The copolymerization reaction is generally carried out in the presence of a radical initiator. This may be, for example, a t-alkyl peroxyester such as tert-butyl peroxypivalate (or TBPPI), tert-amyl peroxypivalate, a peroxy dicarbonate such as bis(4-tert-butyl cyclohexyl) peroxydicarbonate, sodium, ammonium, or potassium persulfate, benzoyl peroxide and its derivatives, a tert-alkyl hydroperoxide such as tert-butyl p-hydroxyperoxide, a t-alkyl peroxide such as tert-butyl peroxide, or a t-alkyl peroxyalkane such as 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane. Alternatively, or in addition, an azo initiator or a redox system may be used as a radical initiator. The polymer can also be obtained by reduction of a P(VDF-CTFE) type copolymer to give a 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). .

[0084] The starting polymer can be selected based on its known electrocalorific properties. An starting polymer having good electrocalorific properties at temperatures close to the service temperatures of the polymer according to the invention can advantageously be chosen.

[0085] Alternatively or in addition, the starting polymer can be selected based on the temperature at which its dielectric constant is maximum. An starting polymer having a maximum dielectric constant at a temperature close to the operating temperatures of the polymer according to the invention will advantageously be chosen.

[0086] The initial polymer is preferably statistically determined. The initial polymer is preferably linearly determined. Dehydrohalogenation reaction

[0087] Dehydrohalogenation of the initial polymer allows for the formation of carbon-carbon double bonds and thus the ethylenic fluorinated polymer mentioned above. When the third unit is present, the dehydrohalogenation can consist primarily of the removal of a -Z atom and a hydrogen atom from a carbon atom adjacent to that of the departing -Z atom.

[0088] Dehydrohalogenation, called dehydrochlorination in the preferred case where -Cl is the leaving halogen atom, is carried out by mixing with a certain base, at a certain concentration, under certain temperature conditions and for a certain duration so as to promote the elimination of the halogen -Z (or of a fluorine atom).

[0089] The base should preferably be sufficiently strong to eliminate a fluorine atom, or -Z. The base may, in particular, have a pKa ranging from 8 to 12, preferably from 9 to 11. The base may advantageously be a non-aromatic, non-nucleophilic amine such as triethylamine or ethylenediamine. The amount of base, per gram of starting 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 represent from 0.1 to 100 pL per gram of starting polymer. In some embodiments, the proportion of base, for example ethylenediamine, is preferably adjusted so as to partially retain the third unit of the formula -(CY1Y2CY3Z)- within the polymer after the dehydrohalogenation step.The base can represent, in particular, from 5 to 50 pL per 1 g of initial polymer, or from 10 to 30 pL per 1 g of initial polymer.

[0090] The base can represent from 0.01 to 2 molar equivalents relative to the number of moles of the third unit. In particular, the base can represent from 0.1 to 1 molar equivalent, or even from 0.15 to 0.5 molar equivalents relative to the number of moles of the third unit.

[0091] According to some embodiments, the dehydrohalogenation step can in particular be carried out at a temperature ranging from 10 to 100°C, preferably from 20 to 60°C, for a duration ranging from 0.1 to 10 hours, preferably from 1 to 8 hours, and preferably still from 2 to 4 hours.

[0092] Furthermore, the volume of the base, the temperature conditions of the dehydrohalogenation, and the duration of the dehydrohalogenation can be adjusted by those skilled in the art to regulate the extent of the dehydrohalogenation reaction. According to some embodiments, the dehydrohalogenation is carried out with a reaction extent of at least 0.25, preferably with a reaction extent of at least 0.5. According to some embodiments, the dehydrohalogenation is carried out in such a way as to be almost complete, or complete (reaction of essentially all (or all, the base introduced).

[0093] According to some embodiments, the step of reacting the initial polymer with the base can be followed by a step of removing the excess base. In some embodiments, the base is removed by washing with water and / or an alcohol. Ethylene fluorinated polymer

[0094] The ethylenic fluorinated polymer obtained at the end of the dehydrohalogenation reaction comprises: • a first unit of formula -(CF2-CH2)-, • optionally, a second formula unit -(CX1X2-CX3X4)-, • optionally, a third unit of formula -(CYiY2-CY3Z)-, • a fourth unit of formula -(CY3=CF)-, -(CY3=CXi)-, -(CY3=CX2)-, -(CY1=CY3)- or -(CY2=CY3)-.

[0095] The meanings of Xb X2, X3, X4, Yb Y2, Y3 and Z are as described above.

[0096] The fourth unit may comprise a mixture of units conforming to one of the above formulas.

[0097] All of what has been mentioned above concerning the first unit and the second unit in the initial polymer applies in the same way to the ethylenic fluorinated polymer, in particular with regard to the nature and molar proportions of the first unit and the second unit.

[0098] All of what has been mentioned above concerning the nature of the third unit in the initial polymer applies in the same way to the ethylenic fluorinated polymer.

[0099] Preferably, the ethylenic fluorinated polymer comprises: • from 30% to less than 100% molar of the first unit, • from 0% to 60% molar of the second unit, • from 0% to less than 20% molar of the third unit, • from more than 0% to 20% molar of fourth unit.

[0100] It is understood that when several second units or several third units or several fourth units are present, the contents announced correspond to the total of all the second units, respectively of all the third units, respectively of all the fourth units.

[0101] The ethylene fluorinated polymer may include, in particular, 0% to 5% mol, 5% to 10% mol, 10% to 15% mol or 15% to 19.9% ​​mol of third unit.

[0102] According to certain embodiments, the ethylenic fluorinated polymer may comprise at least 1 mol%, preferably at least 2 mol%, more preferably at least 3 mol%, and most preferably at least 4% molar third unit. The presence of the third unit generally allows for the production of a fluoroethylene polymer of the relaxer-ferroelectric type, the advantages of which are detailed below. In particular, the polymer may comprise from 4% to 15% molar third unit.

[0103] The ethylene fluorinated polymer may comprise 0.1 to 20 mol% of the fourth unit. The mole percentage of the fourth unit relative to the total number of moles of units in the composition of the ethylenic fluorinated polymer may be 0.1 to 0.2 mol% or 0.2 to 0.3 mol% or 0.3 to 0.5 mol% or 0.5 to 1 mol% or 1 to 2 mol% or 2 to 3 mol% or 3 to 4 mol% or 4 to 5 mol% or 5 to 6 mol% or 6 to 7 mol% or 7 to 8 mol% or 8 to 9 mol% or 9 to 10 mol% or 10 to 12 mol% or 12 to 14 mol% or 14 to 16 mol%, or 16 to 18 mol%, or 18 % to 20% molar. The molar percentage of the fourth unit may be chosen so that at a envisaged operating temperature of the polymer, the dielectric permittivity is at its maximum.

[0104] Preferred contents for the ethylenic fluorinated polymer are as follows: • 40% to 80% mol of first unit, 15% to 50% mol of second unit and 1% to 20% mol of total third and fourth unit; • 50% to 70% molar of first unit, 20% to 40% molar of second unit and 3% to 15% molar of total third and fourth unit; • 55% to 65% molar of first unit, 27% to 37% molar of second unit and 5% to 12% molar of total third and fourth unit.

[0105] These contents apply in particular to ethylenic fluorinated polymers obtained by dehydrohalogenation of P(VDF-TrFE-CTFE), P(VDF-TrFE-CFE), P(VDF-TFE-CTFE) and P(VDF-TFE-CFE).

[0106] The presence of carbon-carbon double bonds in fluorinated polymers can be assessed by various spectroscopic methods, including Raman spectroscopy. The valence vibration band at 1720 cm⁻¹ corresponds to the presence of only one type of C=C double bond, attributable to -CF=CH- bonds. The presence of double bonds can be quantified by proton NMR through the appearance of signals between 6.0 and 6.7 ppm and / or by fluorine NMR through the appearance of signals between -87.0 and -90.0 ppm.

[0107] The ethylene fluorinated polymer is preferably statistically oriented. The ethylene fluorinated polymer is preferably linearly oriented. Reaction with peroxide

[0108] The chemical modification of the ethylenic fluorinated polymer is done by reaction between a peroxide and the double bonds present in the ethylenic fluorinated polymer (on the fourth unit).

[0109] The peroxide is selected from organic and inorganic peroxides. The inorganic peroxide may be hydrogen peroxide (H₂O₂) or selected from peracids such as peroxymonosulfuric acid. The organic peroxide may be selected from peracetic acid, magnesium monoperoxyphthalate, or metachloroperbenzoic acid (mCPBA). The peroxide, for example mCPBA, may represent from 0.005 to 50 mmol / g of ethylenic fluorinated polymer. According to some embodiments, the proportion of peroxide, for example mCPBA, is preferably adjusted so as to retain a portion of the fourth unit(s) within the fluorinated polymer after the reaction step with the peroxide. The proportion of peroxide can represent, in particular, 1 to 15 mmol / g of ethylenic fluorinated polymer or 1 to 6 mmol / g of ethylenic fluorinated polymer, or 1 to 3 mmol / g.

[0110] According to some embodiments, the reaction step with the peroxide can in particular be carried out at a temperature ranging from 0 to 60°C, preferably from 5 to 40°C, for a duration ranging from 0.1 to 20 hours, preferably from 1 to 12 hours, and preferably still from 2 to 6 hours.

[0111] The reaction step with the peroxide can be carried out in a solvent. The solvent can be chosen so as not to interfere with the reaction and so as to dissolve the ethylenic fluorinated polymer and the peroxide. It can be a polar aprotic solvent, in particular one that can be chosen from: lactones, in particular γ-butyrolactone; furans, in particular tetrahydrofuran; esters, in particular 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, in particular dimethyl carbonate, and propylene carbonate; and phosphates, in particular trimethyl phosphate and triethyl phosphate; or mixtures thereof. Esters, and in particular ethyl acetate, are preferred.

[0112] The mass concentration of ethylenic fluorinated polymer in the solvent can be, for example, from 2.5 to 250 g / L, preferably from 5 to 125 g / L, preferably still from 10 to 75 g / L, and preferably still from 15 to 50 g / L.

[0113] In addition, the proportions of peroxide, the temperature conditions of the reaction with the peroxide as well as the duration of the reaction can be adapted by a person skilled in the art to adjust the progress of the reaction.

[0114] According to some embodiments, the step of reacting the ethylenic fluorinated polymer with the peroxide can be followed by a step of removing the excess peroxide and the reaction by-products. According to some In the embodiments, after evaporation of the reaction solvent, the base is removed with a wash including an alcohol. Fluorinated polymer obtained

[0115] Compared to the ethylenic fluorinated polymer, the fluorinated polymer obtained after reaction with peroxide may include epoxide, alcohol, ketone, and / or aldehyde functional groups. Without being bound by any particular theory, the inventors believe that these functional groups are formed from the double bonds of the fourth unit of the ethylenic fluorinated polymer. The polymer is also susceptible to cleavage, which may lead to a reduction in its average molar mass.

[0116] The fluorinated polymer is statistically preferred.

[0117] The fluorinated polymer preferably exhibits an electrocaloric effect under the effect of a varying electric field.

[0118] Advantageously, the fluorinated polymer exhibits an adiabatic temperature change (ATEC) of at least 1°C at at least one measurement temperature, the adiabatic temperature change measurements being carried out at an electric field of a given amplitude (AE). The measurement temperature corresponds to the temperature to which the sample is brought before it is subjected to the electric field change (AE) that induces the electrocaloric effect.

[0119] Preferably, the fluorinated polymer exhibits an ATEC adiabatic temperature variation 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, in a given variable field, at a given measurement temperature.

[0120] The electric field used to demonstrate an electrocaloric effect must be variable. Indeed, it is the variation of the electric field that causes the electrocaloric effect.

[0121] Generally, the higher the amplitude of the electric field, the greater the electrocalorific effect. However, the maximum amplitude of the electric field must be adjusted so as not to reach the breakdown voltage of the polymer. Furthermore, generating high voltages requires specific equipment that is energy-intensive, which is not necessarily desirable. According to some embodiments, the electric field used to demonstrate a significant electrocalorific effect for an application as described below may have a maximum amplitude less than or equal to 500 V / pm, or less than or equal to 400 V / pm, or less than or equal to 300 V / pm, or less than or equal to 200 V / pm, or less than or equal to 150 V / pm, or less than or equal to 140 V / pm, or less than or equal to 130 V / pm, or less than or equal to 120 V / pm, or less than or equal to 110 V / pm, or less than or equal to 100 V / qm, or less than or equal to 90 V / qm.

[0122] According to some embodiments, the electric field may have an amplitude greater than or equal to 30 V / qm, or greater than or equal to 40 V / qm, or greater than or equal to 50 V / qm.

[0123] According to certain embodiments, the fluorinated polymer has a dielectric strength greater than or equal to 200 V / m, preferably greater than or equal to 300 V / m, more preferably greater than or equal to 400 V / m, and most preferably greater than or equal to 500 V / m. The dielectric strength can be measured according to ASTM D3755-97.

[0124] A square-type electric field, with a maximum value equal to AE and a minimum value equal to 0, can typically be used.

[0125] To properly measure ATEC, the frequency of the electric field must be sufficiently low to allow heat to diffuse through the polymer. Frequencies ranging from 1 mHz to 100 Hz, preferably frequencies ranging from 0.1 Hz to 10 Hz, can be used.

[0126] The measurement temperature may be between the glass transition temperature and the melting temperature of the polymer. The term "glass transition temperature" means the temperature at which an amorphous polymer, at least partially, transitions from a rubbery to a glassy state, or vice versa, as measured by differential scanning calorimetry (DSC) according to ISO 11357-2:2013, in a second heating cycle, using a heating rate of 10°C / min. The term "melting temperature" means the temperature at which a crystalline polymer, at least partially, transitions to a viscous liquid state, as measured by differential scanning calorimetry (DSC) according to ISO 11357-3:2018, in a second heating cycle, using a heating rate of 10°C / min.Thus, the measurement temperature can be from -20°C to 150°C, preferably from 0°C to 100°C, preferably from 15°C to 60°C and extremely preferably from 20°C to 40°C.

[0127] The fluorinated polymer according to the invention can be a ferroelectric polymer. "Conventional ferroelectric" polymers, often simply referred to as "ferroelectric," are characterized by a wide hysteresis loop in the electric displacement-applied electric field curve. For these materials, this loop is characterized by a high coercive field at 25°C, typically exceeding 45 V / qm in absolute value, and a high remanent polarization at 25°C, typically exceeding 50 mC / m². These materials exhibit a maximum of their electrocaloric properties at temperatures close to their Curie temperature. At this temperature, a ferroelectric to paraelectric (FE to PE) crystal structure transition, called the Curie transition, occurs, corresponding to an abrupt depolarization of the ferroelectric domains. macroscopic. This transition is narrow, first-order, and characterized by a narrow maximum in dielectric permittivity whose position does not depend on the frequency of application of the electric field. The Curie temperature can be adjusted according to the polymer composition: the higher the proportion of first unit (VDF), the higher the Curie temperature. This temperature typically varies between 60°C and 150°C.

[0128] Advantageously, the fluorinated polymer according to the invention can be a relaxer-ferroelectric. "Relaxing ferroelectric" polymers are characterized by a relaxer-ferroelectric (RFE) to paraelectric (PE) crystalline transition over a wide temperature range. At this transition, a broad peak of dielectric permittivity is observed, the temperature of this maximum depending on the frequency of the applied electric field: the lower the frequency of the electric field, the more the dielectric permittivity maximum is shifted towards lower temperatures. At the (RFE) to (PE) transition temperatures or slightly above, the application of an electric field generates and aligns the nanopolar regions, inducing a change in entropy, and thus a significant electrocaloric effect over a wide temperature range.Relaxant-ferroelectric polymers are characterized at 25°C and a frequency of approximately 1 Hz by a hysteresis loop of the "electric displacement" curve versus the "applied electric field" that is much finer than the hysteresis loop of a ferroelectric polymer. They typically have a coercive field less than or equal to 45 V / m² and a remanent polarization less than or equal to 40 mC / m². Compared to conventional ferroelectric polymers, the phase transition corresponding to the maximum dielectric permittivity and / or the maximum ATEC can be obtained at lower temperatures, particularly between 0°C and 100°C, and in some cases between 20°C and 60°C. Thus, relaxant-ferroelectric polymers possess interesting electrocalorific properties over a wide temperature range, especially at temperatures close to room temperature.They are therefore particularly interesting for the construction of electrocalorific devices.

[0129] According to certain embodiments, the fluorinated polymer has a relative dielectric permittivity which is at least 5% higher, 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 preferably at least 40% higher, compared to the initial polymer, said relative dielectric permittivity being measured at a frequency of 1000 Hz and at a temperature of 40°C.

[0130] According to certain embodiments, in particular when the initial fluorinated polymer is a P(VDF-TrFE-CTFE) such as exemplified below, the resulting fluorinated polymer has a relative dielectric permittivity greater than or equal to 40, preferably greater than or equal to 50, even more preferably greater than or equal to 60, and extremely preferably greater than or equal to 70, at a temperature of 40°C, said relative dielectric permittivity being measured at 1 kHz.

[0131] According to some embodiments, the fluorinated polymer has a maximum permittivity at a temperature less than or equal to 60°C, preferably at a temperature less than or equal to 50°C and even more preferably at a temperature less than or equal to 40°C, said relative dielectric permittivity being measured at 1 kHz.

[0132] According to some embodiments, the fluorinated polymer has an increased dielectric permittivity compared to the initial polymer and compared to the ethylenic fluorinated polymer.

[0133] According to certain embodiments, the fluorinated polymer has a maximum polarization in pC / cm2 which is at least 1% higher, preferably at least 5% higher, preferably at least 10% higher, preferably at least 15% higher, preferably at least 20% higher, preferably still at least 25% higher, compared to the initial polymer, said maximum polarization being measured at a frequency of 100 Hz, at 25 °C and under an electric field of 1300 kV / cm.

[0134] According to certain embodiments, for example when the initial fluorinated polymer is a P(VDF-TrFE-CTFE) as exemplified below, the resulting fluorinated polymer has a maximum polarization greater than or equal to 0.5 pC / cm2, preferably greater than or equal to 1 pC / cm2, preferably greater than or equal to 1.5 pC / cm2, preferably greater than or equal to 2 pC / cm2, preferably greater than or equal to 2.5 pC / cm2, preferably greater than or equal to 3 pC / cm2, preferably greater than or equal to 3.5 pC / cm2, preferably greater than or equal to 4 pC / cm2, preferably greater than or equal to 4.5 pC / cm2, said maximum polarization being measured at a frequency of 1000 Hz, at 25°C and under an electric field of 1300 kV / cm.

[0135] According to some embodiments, the fluorinated polymer has an increased maximum polarization compared to the initial polymer and compared to the ethylenic fluorinated polymer.

[0136] According to certain embodiments, the fluorinated polymer has a coercive field in kV / cm which is at least 1% lower, preferably at least 5% lower, preferably at least 10% lower, preferably at least 15% lower, preferably at least 20% lower, preferably still at least 25% lower, compared to the initial polymer, said coercive field being measured at a frequency of 100 Hz, at 25°C.

[0137] According to certain embodiments, the fluorinated polymer has a preferred coercive field preferably less than or equal to 2000 kV / cm, preferably less than or equal to 1500 kV / cm, preferably less than or equal to 1000 kV / cm, preferably less than or equal to 500 kV / cm, said coercive field being measured at a frequency of 100 Hz, at 25°C.

[0138] According to some embodiments, the fluorinated polymer has a reduced coercive field compared to the initial polymer and compared to the ethylenic fluorinated polymer.

[0139] According to certain embodiments, the fluorinated polymer has a percentage of crystallinity which is at least 1% higher, 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, preferably still at least 30% higher, compared to the initial polymer, said percentage of crystallinity being measured at 25°C according to Example 6.

[0140] According to certain embodiments, in particular when the initial fluorinated polymer is a P(VDF-TrFE-CTFE) as exemplified below, the resulting fluorinated polymer has a percentage of crystallinity which is 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%, preferably even greater than or equal to 27%, said percentage of crystallinity being measured at 25°C.

[0141] According to certain embodiments, the fluorinated polymer has a remanent polarization preferably between 0.1 and 5 pC / cm2, preferably between 0.15 and 2.5 pC / cm2, preferably between 0.3 and 0.6 pC / cm2, said remanent polarization being measured at a frequency of 100 Hz, at 25°C and under a field of 1300 kV / cm.

[0142] The set of electroactive properties of the fluorinated polymer can be determined as shown in the examples below.

[0143] According to certain embodiments, the fluorinated polymer may have a weight-average molecular mass 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, preferably less than or equal to 100,000 g / mol. This makes it possible to impart desirable mechanical properties to films made from the polymer according to the invention. The mass distribution of polymers can be determined by size exclusion chromatography (SEC) using, for example, dimethyl sulfoxide (DMSO + lithium bromide LiBr Ig / L) as the eluent. Composition

[0144] The fluorinated polymer according to the invention can be formulated within a composition. The composition comprises a single or alternatively a mixture of fluorinated polymers according to the invention.

[0145] According to certain embodiments, the composition may comprise at least one fluorinated polymer according to the invention and at least one liquid vehicle for said at least one polymer. This composition, commonly referred to as "ink," may be prepared by dissolving or suspending the polymer(s) according to the invention in the liquid vehicle. Preferably, the liquid vehicle is a solvent.Advantageously, this solvent is a polar aprotic solvent, notably being selectable from: amides, notably dimethylformamide, N-methyl-2-pyrrolidone, dimethylacetamide; sulfoxides, notably dimethyl sulfoxide; lactones, notably γ-butyrolactone; ketones, notably acetone, methylethyl ketone (or butan-2-one), methylisobutyl ketone, cyclopentanone, cyclohexanone, diisobutyl ketone; furans, notably tetrahydrofuran; esters, notably methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propylene glycol methyl ether acetate, glyceryl triacetate, diethylene glycol monobutyl ether acetate, and ethyl acetoacetate; carbonates, in particular dimethyl carbonate and propylene carbonate; phosphates, in particular trimethyl phosphate and triethyl phosphate; .

[0146] or mixtures thereof. The total mass concentration of polymers in the liquid vehicle may be in particular from 0.1 to 30%, preferably from 0.5 to 20%.

[0147] According to certain embodiments, the composition may comprise one or more polymers other than those of the invention and also exhibiting an electrocalorific effect of interest. For example, the composition may comprise one or more ferroelectric polymers or relaxing ferroelectric polymers not possessing a carbon-carbon double bond. In particular, the composition may comprise the initial polymer as described above.

[0148] According to certain embodiments, the composition may comprise one or more polymers other than those of the invention, having in particular polar or reactive functions enabling the adhesion of the composition to a given substrate to be improved. The composition may optionally comprise one or more additives, in particular selected from surface tension modifying agents, rheology modifying agents, heat capacity modifying agents, aging resistance modifying agents, adhesion modifying agents, pigments or dyes, flame retardants or crosslinking aid additives.

[0149] The composition may optionally include fillers, including nanofillers, such as barium strontium titanate (BST) nanowires. Movie

[0150] The fluorinated polymer according to the invention has, according to certain embodiments at least, sufficient mechanical properties to allow it to be shaped into a film.

[0151] The film can be prepared using the fluorinated polymer according to the invention or a composition comprising it, for example by applying an ink to a substrate or by hot melt extrusion or compression.

[0152] The substrate may be of any nature and in particular consist of one or more layers of glass or metal(s) or organic (in particular polymeric).

[0153] The film may optionally be stretched if necessary. Stretching (when performed) is preferably carried out with a stretch ratio of at least 10% to 700%. In particular, the film may have a stretch ratio of 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 ratio corresponds to the ratio of the surface area of ​​the film after stretching to the surface area of ​​the film before stretching. Stretching (when performed) may, in particular, be carried out at a temperature from 0°C up to the melting temperature of the fluoropolymer; It is preferably carried out at a temperature of 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.

[0154] The films can also, after optionally being stretched, be annealed, that is to say be heated to a temperature ranging from 70°C to 140°C, preferably ranging from 100°C to 120°C, for a period of several seconds to several hours, and then cooled.

[0155] Stretching and annealing most often increase the crystallinity and dielectric strength.

[0156] The invention makes it possible to obtain films with a thickness greater than or equal to 0.1 pm. For optimal exploitation of the electrocaloric effect, their thickness is advantageously from 1 pm to 100 pm. Among these thicknesses, the thinnest may be preferred to avoid generating excessively high voltages. Thus, films with a thickness of 1 to 50 pm and even 1 to 10 pm are particularly preferred.

[0157] Electrodes can be deposited on the film, in particular by metallization or by deposition of conductive material (silver, copper, conductive polymer, silver nanowires, carbon black, NTC, etc.).

[0158] According to certain embodiments, the film prepared from the polymer according to the invention can be a layer of a multilayer system, the other layers being able to comprise a polymer according to the invention, of the same or different composition, another polymer or a non-polymer material.

[0159] The multilayer system may comprise an alternation of electroactive materials and electrodes.

[0160] Multilayer systems can be obtained by successive printing of electroactive and conductive materials, by metallization steps, or by delamination technologies of electrode-coated films. Adhesives can be used to bond the layers together.

[0161] The electroactive polymer layers of the multilayer film can have a thickness of 0.1 to 100 pm, preferably from 1 to 50 pm and even more preferably from 1 to 10 pm.

[0162] The multilayer system may comprise from 1 to 1000 layers of electroactive polymers, preferably from 2 to 500, preferably from 3 to 250, preferably from 4 to 200, preferably from 5 to 150, preferably from 5 to 125, preferably from 6 to 100, preferably from 7 to 90, preferably from 8 to 80, preferably from 9 to 70, preferably from 6 to 70. Applications

[0163] Due to its electrocalorific properties, the polymer according to the invention can be used in a heat transfer system. The heat transfer system comprises the polymer according to the invention, particularly in the form of a film, and particularly as a layer in a multilayer system as described above. The film is suitable for thermal contact with a load to be cooled and / or a load to be heated and / or a heat transfer fluid. The system also includes a voltage source for application to the plate. The heat transfer system can remove heat or supply heat to another device, such as an electrical or electronic component. Due to its pyroelectric properties, the polymer according to the invention can be used in a thermal energy recovery system.

[0164] Due to the high dielectric constant, the polymer according to the invention can also be used in an energy storage system, in particular a capacitor, an organic transistor, or an electrostatic clutch.

[0165] Due to its electroactive properties, in particular ferroelectric or ferroelectric relaxors, the polymer according to the invention can also be used in actuators (for haptics, microfluidics, loudspeakers...). Examples

[0166] The following examples illustrate the invention without limiting it.

[0167] Example 1: Preparation of the P(VDF-TrFE-CTFE-DB)

[0168] In 5 flasks, 1 g of P(VDF-TrFE-CTFE) polymer with a molar composition of 62 / 30 / 8 is dissolved in 20 mL of DMSO. Volumes of 10, 15, 20, 25, and 30 µl of ethylenediamine are added to these solutions, respectively. The reaction mixture is heated to 30°C and allowed to react for 4 hours. After reaction, each of the The polymers obtained are precipitated in water and purified by washing with a 60 / 40 H₂O / ethanol solution. An average yield of 95% is obtained. The resulting ethylenic fluorinated polymer is denoted P(VDF-TrFE-CTFE-DB), with DB indicating the presence of double bonds.

[0169] Example 2: Reaction of P(VDF-TrFE-CTFE-DB) with mCPBA

[0170] 0.5 g of each of the dehydrochlorinated polymers P(VDF-TrFE-CTFE-DB) is so The solution was lubricated in 20 mL of ethyl acetate. 0.3 g of mCPBA was added to each solution. The reaction mixture was allowed to react for 6 hours at 15°C. The solvent was then evaporated, and the product was washed with ethanol to remove excess mCPBA. The fluorinated polymer was obtained with an average yield of 90%.

[0171] Example 3: Preparation of devices for dielectric characterization

[0172] A 10 nm thick chromium and 100 nm thick silver electrode is deposited onto a 15x15 mm glass substrate by chemical vapor deposition (CVD). A film is deposited onto the device using a Dr. Blade from a 7 wt% polymer solution in ethyl acetate. A film approximately 3 µm thick is obtained after evaporation of the solvent. The film is annealed at 100°C on a hot plate for 2 hours. A 100 nm thick silver electrode is then evaporated over the film by CVD. To access the lower electrode, the polymer film is removed from the lower part of the device.

[0173] Example 4: Measures of relative permittivity

[0174] Permittivity measurements were performed using a broadband dielectric spectroscopy system and a Solartron 1260 A impedance analyzer. Sample temperature control was achieved using a Linkam LTS 350 temperature control system. Measurements were performed with a 1 V AC voltage signal, with a signal frequency of 102 to 103 kHz at a temperature of 40°C. This technique allows the determination of the relative dielectric constant and the loss factor from the measured capacitance and the geometric factors of the sample. The main results for the different samples are shown in [Fig. 1]. The point at position 0 on the x-axis corresponds to the initial P(VDF-TrFE-CTFE) polymer.

[0175] Following the dehydrochlorination of P(VDF-TrFE-CTFE), an increase in relative permittivity is observed. This increase is even more pronounced after the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA. Indeed, the polymer obtained following the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA has a relative permittivity of -67 compared to a relative permittivity of -47.5 for the initial polymer P(VDF-TrFE-CTFE) (i.e., an increase of 41%).

[0176] Example 5: Polarization of polymers

[0177] The polarization hysteresis of the samples was also measured by recording Several polarization hysteresis cycles were measured using an aixACCT Systems TF Analyzer 2000E. Measurements were performed by applying a continuous triangular signal with a frequency of 100 Hz at room temperature. The polarization maximum values ​​under a 1300 kV / cm field are shown in [Fig. 2].

[0178] The increase in maximum polarization compared to the initial polymer is more pronounced after the reaction of the dehydrochlorinated polymer with mCPBA. Indeed, the polymer obtained following the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA has a maximum polarization of ~4.8 pC / cm2 compared to a maximum polarization of -3.75 pC / cm2 for the initial polymer P(VDF-TrFE-CTFE) (i.e., an increase of 28%).

[0179] The coercive field was also determined for the different samples ([Fig.3]). On A decrease in the coercive field is observed after dehydrochlorination. This decrease is even more pronounced after reaction with mCPBA. Indeed, the polymer obtained following the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA has a coercive field of -387 kV / cm compared to a coercive field of -525 kV / cm for the initial polymer P(VDF-TrFE-CTFE) (i.e., a decrease of 26%).

[0180] Example 6: Analysis of samples by WAXS

[0181] The crystalline structure of the samples was analyzed using a wide-angle X-ray scattering (WAXS) system, Xeuss 2.0 from XENOCS, under vacuum and at 25°C, with a sample-to-detector distance of 151 mm and X = 1.54189 Å (Cu Ka). The diffraction pattern was collected using a DECTRIS PILATUS-300k detector, for a wave vector range q of 0.1 to 3.1 Å⁻¹ (1.4° to 46°), followed by azimuthal integration of the different crystalline (ferroelectric and / or relaxor-ferroelectric) and non-crystalline phases. Data analysis was performed with Fityk software, using Voigt profiles. The percentage of crystallinity corresponds to the quotient between the total area of ​​the peaks of the different crystalline phases and the total area of ​​the peaks of the crystalline phases and the peaks of the non-crystalline phases.

[0182] The calculated percentage of crystallinity is shown in [Fig.4].

[0183] A considerable increase in crystallinity is observed after the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA. Indeed, the polymer obtained following the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA has a crystallinity of 28% compared to a crystallinity of 21% for the initial polymer P(VDF-TrFE-CTFE) (i.e., an increase of 33%).

[0184] Example 7: Determination of molar mass by SEC

[0185] The molar masses of the polymers were determined by size-exclusion chromatography (SEC) using dimethyl sulfoxide (DMSO + lithium bromide LiBr Ig / L) as the eluent. The DMSO measurements were performed on a Thermoscientific Ultimate 3000 system equipped with a diode array detector (DAD). The system also includes a multi-angle light scattering detector (MALS) and a differential refractive index (dRI) detector from Wyatt Technology. Polymers were separated on Tosoh TSK G3000HHR and G2000HHR (7.8 x 300) columns (exclusion limits from 200 Da to 60,000 Da) at a flow rate of 0.5 mL / min. The column temperature was maintained at 80°C.

[0186] The absolute molar masses were determined using the refractive index increment (dn / dc). The dn / dc was evaluated by measuring the refractive index signal by injecting polymer solutions of different concentrations ranging from 1 to 10 mg / mL. The absolute molar masses were then extracted from the ZIMM equation using ASTRA software. These can be found in [Fig. 5].

[0187] A slight increase in molar mass is observed after dehydrochlorination (probably due to partial crosslinking). This trend is reversed following the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA.

Claims

Demands

1. A process for manufacturing a fluorinated polymer from an ethylenic fluorinated polymer comprising: • a first unit of formula -(CF2-CH2)-, • optionally, at least a second unit of formula -(CXiXz-CX^)-, • optionally, at least a third unit of formula -(CYiYz-CYjZ)-, • at least a fourth unit of formula -(CY3=CF)-, -(CY3=CXÛ-, -(CY3=CX2)-, -(CY1=CY3)- or -(CY2=CY3)-;in which: Xi and X2 independently denote -H, -F, or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated, X3 and X4 independently denote -F, or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated, except the combination where Xi and X2 are both -H and X3 and X4 are both -F, Yi and Y2 independently denote -H, -F, -Cl or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated, Y3 denotes -F, -Cl or an alkyl group comprising 1 to 3 carbon atoms optionally partially or completely fluorinated, Z denotes a halogen atom other than -F, the process comprising a step of reacting the ethylenic fluorinated polymer with a peroxide.;

2. A method according to claim 1, wherein Xi denotes -H or -F and X2, X3 and X4 all denote -F.

3. A method according to any one of claims 1 to 2, wherein Y3 denotes -F and Y1 and Y2 both denote -H or -F.

4. A process according to any one of claims 1 to 3, wherein the ethylenic fluorinated polymer comprises: • from 30% to less than 100% mol of the first unit, • from 0% to 60% mol of the second unit, • from 0% to less than 20% molar of the third unit, • from more than 0% to 20% molar of the fourth unit.

5. A method according to any one of claims 1 to 4, wherein the ethylenic fluorinated polymer comprises at least one second unit of formula -(CX1X2-CX3X4)-.

6. A process according to any one of claims 1 to 5, comprising a step of preparing the ethylenic fluorinated polymer by dehydrohalogenation of an initial polymer, said initial polymer comprising: • a first unit of formula -(CF2-CH2)-, • optionally, at least a second unit of formula -(CX^-CXsXJ-, • at least a third unit of formula -(CYiY2-CY3Z)-.

7. A method according to claim 6, wherein the step of preparing the ethylenic fluorinated polymer includes contacting the initial polymer with a base.

8. A method according to any one of claims 6 to 7, wherein the fluorinated polymer has a relative dielectric permittivity that is at least 5% higher than that of the initial polymer, said relative dielectric permittivity being measured at a frequency of 1000 Hz and at a temperature of 40°C.

9. A method according to any one of claims 6 to 8, wherein the fluorinated polymer has a maximum polarization in pC / cm2 which is at least 1% higher than that of the initial polymer, said maximum polarization being measured at a frequency of 100 Hz, at 25°C and under an electric field of 1300 kV / cm.

10. A method according to any one of claims 6 to 9, wherein the fluorinated polymer has a coercive field in kV / cm which is at least 1% lower than that of the initial polymer, said coercive field being measured at a frequency of 100 Hz, at 25 °C.

11. A process according to any one of claims 6 to 10, said polymer having a percentage of crystallinity which is at least 1% higher than the initial polymer.

12. A method according to any one of claims 1 to 11, wherein the peroxide is used in an amount of 0.005 to 50 mmol / g of ethylene fluorinated polymer.

13. A method according to any one of claims 1 to 12, wherein the peroxide is an inorganic peroxide selected from hydrogen peroxide and peracids such as peroxymonosulfuric acid, or an organic peroxide selected from peracetic acid, magnesium monoperoxyphthalate or metachloroperbenzoic acid.

14. Fluorinated polymer capable of being obtained by the process according to any one of claims 1 to 13.

15. Fluorinated polymer according to claim 14, having a weight average molecular mass less than or equal to 500,000 g / mol.

16. Fluorinated polymer according to any one of claims 14 and 15, said polymer having a remanent polarization of 0.1 to 5 pC / cm2, said remanent polarization being measured at a frequency of 100 Hz, at 25°C and under a field of 1300 kV / cm.

17. Composition comprising at least one fluorinated polymer according to any one of claims 14 to 16, and at least one liquid vehicle of said polymer.

18. Film comprising the fluorinated polymer according to any one of claims 14 to 16.

19. Film according to claim 18, having a thickness greater than or equal to 0.1 pm preferably having a thickness of 1 to 100 pm, more preferably having a thickness of 1 to 50 pm, and even more preferably having a thickness of 1 to 10 pm.

20. Multilayer system, comprising at least one layer formed by a film according to one of claims 18 or 19, the other layers being able to comprise a fluorinated polymer according to the invention, of the same or different composition, another polymer or a non-polymer material.

21. Use of a fluorinated polymer according to any one of claims 14 to 16, or of a film according to any one of claims 18 and 19, or of a multilayer system according to claim 20, in a heat transfer system or in an energy storage system.

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