Process for manufacturing a fluoropolymer having electrocaloric properties

Abstract

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

Description

Title of the invention: Method for manufacturing a fluorinated polymer having electrocaloric properties Field of invention

[0001] The present invention relates to a method for manufacturing a fluoropolymer obtained by reacting an ethylenic fluoropolymer with a peroxide such as metachloroperbenzoic acid (mCPBA). The fluoropolymer obtainable by this method 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 which manifests itself by a variation in temperature when they are subjected to a variable electric field. The physical origin of this phenomenon is linked to the change in the dipolar order, and therefore to a variation in the dipolar 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 causes a decrease in their dipolar entropy and an increase in their temperature under adiabatic conditions. Conversely, the reduction or removal of the electric field causes an increase in their dipolar entropy and a decrease in their temperature under adiabatic conditions. Thus, an electrocaloric material is characterized, under given experimental conditions, by an adiabatic temperature variation ATEC for an applied electric field Ec under adiabatic conditions.

[0003] The electrocaloric performances 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, more environmentally friendly and more energy efficient than systems operating on the basis of gas compression, the thermoelectric effect or the magnetocaloric effect. Ferroelectric and relaxor-ferroelectric materials, due to a strong coupling between the applied electric fields and their dipolar structure, are the materials that arouse the most interest for these applications because they are likely to have significant electrocaloric performances. In particular, this coupling is maximal near or slightly above the phase transitions: Ferroelectric -> Paraelectric (FE -> PE) or Relaxer-Ferroelectric -> Paraelectric (RFE -> PE), due in particular to a strong reversible variation in 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 variation in the electric field generates significant variations in entropy and temperature. The good flexibility and ease of processing of these materials in the form of large-surface thin films are other parameters that make them particularly suitable for use in solid refrigeration systems.

[0007] Vinylidene fluoride (VDF)-based fluoropolymers represent a class of compounds with remarkable properties for a large number of applications. PVDF and copolymers comprising VDF and trifluoroethylene (TrFE) are particularly interesting due to their piezo- and pyroelectric properties. VDF- and TrFE-based fluoropolymers are also among these materials with "ferroelectric" and "relaxer-ferroelectric" properties, and are among the most studied.

[0008] The electrocaloric properties of P(VDF-TrFE) type ferroelectric copolymers are maximal near the Ferroelectric -> Paraelectric (FE -> PE) transition. The FE -> PE transition of this type of polymer is narrow, i.e. it takes place over a small temperature range, and is located at relatively high temperatures, typically strictly above 60°C. This prevents their use in cooling systems that must operate around room temperature and / or over a wide temperature range.

[0009] The use of ferroelectric relaxor polymers makes it possible to overcome at least some of the drawbacks mentioned above. Indeed, ferroelectric relaxor 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 broadened compared to the FE -> PE phase transition of ferroelectric polymers, i.e. which takes place over a wider temperature range. In addition, the RFE -> PE transition is generally at lower temperatures than those of the FE -> PE transition of ferroelectric polymers. Thus, this makes it possible to envisage the use of ferroelectric relaxor polymers in various cooling systems, in particular in cooling systems that must operate around ambient temperature and / or over a wide range of temperatures.

[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 fluorinated polymers P(VDF-TrFE) or P(VDF-TrFE-CFE) 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 fluorinated polymers (EFPs) by two successive steps: a Williamson etherification reaction then a photo-catalyzed crosslinking reaction. This modification of EFPs allowed an improvement in the electroactive properties, particularly in terms of relative permittivity. Application WO 2019 / 020906 A1 is also an example of this application.

[0012] On another register of modifications, 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). The introduction of nanometric fillers into the polymer matrix nevertheless has several drawbacks. First, it requires very good dispersion of these fillers and therefore complicates the shaping of the material. In addition, the manipulation of nanoparticles in the polymer manufacturing process is complex due to the potential risks of nanoparticles in the free state for 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 discloses the manufacture of a polymer comprising double bonds, this polymer being manufactured from the dehydrofluorination of PVDF in dimethylacetamide by a saturated solution of sodium hydroxide in isopropanol. No measurement of the electrocaloric properties of the manufactured polymer was carried out. The type of double bonds in the manufactured polymer was also not characterized. This dehalogenation method is similar to that of application US 4904739 A in which there is a high proportion of conjugated double bonds. Furthermore, fluorinated polymers comprising conjugated double bonds obtained by dehydrofluorination through the action of a strong base are not very thermally stable, turn yellow, degrade easily and are likely to crosslink during the action of a strong base.Furthermore, the method 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 Polymers via One-Step Molecular Engineering » (Le Goupil F. et al., Adv. Funct. Mater., 2021, 31, 1, 2007043), describes the chemical modification of a 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 allows a change in the crystalline structure of the polymer as well as its dielectric properties by increasing the electrical permittivity. Patent FR 3104583 B1 and application WO 2021 / 116618 A1 also disclose this chemical modification with the introduction of conjugated double bonds.

[0016] These strategies consisting of the generation of double bonds in fact make it possible to improve the dielectric properties of polymers; nevertheless, the double bonds, whether conjugated or not, induce a crosslinking of the polymer which is not always desired.

[0017] Despite the efforts described above, however, the improvement in performance remains limited. Faced with these limitations, it therefore becomes essential to explore other methods for improving the dielectric properties of relaxor-ferroelectric polymers.

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

[0019] The invention relates to a method for manufacturing a fluoropolymer from an ethylenic fluoropolymer comprising: • a first unit of formula -(CF2-CH2)-, • optionally, at least one second unit of formula -(CXiX2-CX3X4)-, • optionally, at least one third unit of formula -(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 from 1 to 3 carbon atoms optionally partially or completely fluorinated,

[0022] X3 and X4 independently denote -F, or an alkyl group comprising from 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 from 1 to 3 carbon atoms optionally partially or completely fluorinated,

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

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

[0026] the method 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 embodiments, Y3 denotes -F and Y1 and Y2 both denote -H or -F.

[0029] In embodiments, the ethylenic fluoropolymer 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% mol of the third unit, • from more than 0% to 20% mol of the fourth unit.

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

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

[0032] In embodiments, the method comprises 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 unit of formula -(CXiX2-CX3X4)-, • at least one third unit of formula -(CYiY2-CY3Z)-.

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

[0034] In embodiments, the fluoropolymer 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 still more preferably at least 40% higher, relative 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 fluoropolymer has a polarization maximum 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, and even more preferably at least 25% higher, relative to the initial polymer, said polarization maximum being measured at a frequency of 100 Hz, at 25°C and under an electric field of 1300 kV / cm.

[0036] In embodiments, the fluoropolymer 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, and even more preferably at least 25% lower, relative 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, and still preferably at least 30% higher, relative to the initial polymer.

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

[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 capable of being obtained by the process as defined above.

[0041] In embodiments, the fluoropolymer has a weight average molecular weight of 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 fluoropolymer has a remanent polarization of 0.1 to 5 pC / cm2, preferably of 0.15 to 2.5 pC / cm2 and 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 fluoropolymer as defined above and at least one liquid vehicle of said polymer.

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

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

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

[0047] The invention also relates to the use of a fluoropolymer as described above, of a film as described above or of 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 fluoropolymer as described above, of a film as described above or of 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 method making it possible to produce VDF-based fluorinated polymers having improved electrocaloric properties compared to those of the prior art, i.e. having, for example, a higher adiabatic temperature variation ATEC, in a given variable electric field or, in general, having improved dielectric properties.

[0050] The invention consists in improving the dielectric properties of VDF-based fluorinated polymers by functionalization via a chemical modification. This involves in particular obtaining a polymer having a more marked relaxor-ferroelectric character, resulting in a high dielectric constant and maximum polarization as well as a low remanent polarization and coercive field. These properties are sought for several applications, in particular for the electrocaloric application allowing application 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 on 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 which reacts on the previously formed double bonds.

[0052] These chemical modifications make it possible to obtain a fluorinated polymer demonstrating dielectric and in particular electrocaloric properties superior to those of the initial polymer. Compared to the initial polymer, the fluorinated polymer obtained by this process preferably has relative permittivity and maximum polarization values ​​which are increased, and coercive field and remanent polarization values ​​which are reduced. Brief description of the figures

[0053] [Fig.l] [Fig.l] represents the relative permittivity maximum measured with an alternating voltage signal of 1 V with 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 relative permittivity maximum values.

[0054] [Fig.2] [Fig.2] represents the maximum polarization measured under a tri signal continuous angular frequency with a frequency of 100 Hz under a field of 1300 kV / cm 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: polarization maximum 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 crystallinity percentage values ​​%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: %X crystallinity percentage values.

[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 unit of formula: -(CXiX2-CX3X4)-optionally a third unit of formula: -(CYiY2-CY3Z)-,

[0060] in which: Xi and X2 independently denote -H, -F, or an alkyl group comprising from 1 to 3 carbon atoms optionally partially or completely fluorinated, X3 and X4 independently denote -F, or an alkyl group comprising from 1 to 3 carbon atoms optionally partially or completely fluorinated, except the combination where X1 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 from 1 to 3 carbon atoms optionally partially or completely fluorinated, Y3 denotes -F, -Cl or an alkyl group comprising from 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 of, or even consist of, the first unit described above. Alternatively, the initial polymer may consist essentially of, or even consist of, the first and second units described above. Alternatively, the initial polymer may consist essentially of, or even consist of, the first and third units described above. Alternatively, the initial polymer may consist essentially of, 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 comes from the VDF.

[0063] The initial polymer may comprise a single second unit or, on the contrary, several different second units. According to certain embodiments, the second unit(s) may be derived from monomers chosen from the list consisting of: 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. In some variations, second units from several different fluorinated monomers may be present in the initial polymer.

[0064] According to certain embodiments, X1 may denote -H or -F; and X2, X3 and X4 all denote -F. In other words, the second unit may be derived from trifluoroethylene (TrFE) and / or tetrafluoroethylene (TFE).

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

[0066] The initial polymer may comprise a single third unit or, on the contrary, several different third units. According to certain embodiments, the third unit(s) may be derived from monomer(s) chosen 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), 1-chloro-3,3,3-trifluoropropene (1233zd), 1,2-dichloro-1,2-difluoroethylene, 1,1-dichloro-1,1-difluoroethylene and 1,1,2-trichloro-2-fluoroethylene.

[0067] Advantageously, Y3 may denote -F and Yi and Y2 may both denote -H or -F. In other words, according to these embodiments, the third unit may 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 and CTFE.

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

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

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

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

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

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

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

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

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

[0078] Preferred contents for the initial polymer are as follows: • from 40% to 80% mol of first unit, from 15% to 50% mol of second unit and from 1% to 20% mol of third unit; • from 50% to 70% mol of first unit, from 20% to 40% mol of second unit and from 3% to 15% mol of third unit; • from 55% to 65% mol of first unit, from 27% to 37% mol of second unit and from 5% to 12% mol 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 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 or bromine or iodine elements, such as X-ray fluorescence spectroscopy, make it possible to calculate unambiguously the mass composition of the polymers, from which the molar composition is deduced. Multi-nucleus NMR techniques can also be used, notably proton (*H) and fluorine (19F), by analysis of a solution of the polymer in an appropriate deuterated solvent. The NMR spectrum is recorded on an NMR-FT spectrometer equipped with a multi-nuclear probe. The specific signals given by the different monomers are then identified in the spectra produced according to one or the other nucleus.

[0081] Thus, for example, the unit resulting from the polymerization of VDF gives in proton NMR a specific signal for the -CH2- groups (mass centered at 3 ppm). Similarly, the unit resulting from TrFE gives in proton NMR a specific signal characteristic of the -CHF- group (at approximately 5 ppm). In fluorine NMR, the signals resulting from the -CF2- and -CFCI- units, from CFE and CTFE, are confused with 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 makes it possible to deduce the molar composition of the polymers unambiguously.

[0082] The initial polymer can be obtained according to methods known from the prior art. It can in particular be prepared by radical polymerization according to a solution, suspension, emulsion or microemulsion polymerization method.

[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 peroxydicarbonate such as bis(4-tert-butylcyclohexyl) peroxydicarbonate, sodium, ammonium or potassium persulfate, benzoyl peroxide and its derivatives, a tert-alkyl hydroperoxide such as tert-butyl 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 the 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 initial polymer can be selected according to its known electrocaloric properties. An initial polymer having good electrocaloric properties at temperatures close to the usage temperatures of the polymer according to the invention can be advantageously chosen.

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

[0086] The initial polymer is preferably statistical. The initial polymer is preferably linear. Dehydrohalogenation reaction

[0087] Dehydrohalogenation of the initial polymer allows carbon-carbon double bonds to be obtained and thus the ethylenic fluorinated polymer mentioned above to be formed. When the third unit is present, the dehydrohalogenation may consist of an elimination mainly of a -Z atom and a hydrogen on a carbon adjacent to that of the leaving -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 a fluorine atom).

[0089] The base must preferably be a base strong enough to be able to eliminate a fluorine atom, or -Z. The base may in particular have a pKa ranging from 8 to 12, preferably ranging from 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 g of initial polymer, may be adapted according to the strength of the base and the number of basic functions on it. For example, the base, in particular in the case of ethylenediamine, may represent from 0.1 to 100 μL per 1 g of initial polymer. According to certain embodiments, the proportion of base, for example ethylenediamine, is preferably adjusted so as to partially retain the third unit of formula -(CYiY2CY3Z)- within the polymer at the end of the dehydrohalogenation step.The base can notably represent from 5 to 50 pL for 1 g of initial polymer, or from 10 to 30 pL for 1 g of initial polymer.

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

[0091] According to certain 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 more preferably from 2 to 4 hours.

[0092] In addition, the volume of the base, the temperature conditions of the dehydrohalogenation and the duration of the dehydrohalogenation can be adapted by a person skilled in the art to adjust the progress of the dehydrohalogenation reaction. According to certain embodiments, the dehydrohalogenation is carried out with a reaction progress of at least 0.25, preferably with a reaction progress of at least 0.5. According to certain embodiments, the dehydrohalogenation is carried out so as to be almost total, or total (reaction of essentially any, or all, of the base introduced).

[0093] According to certain embodiments, the step of reacting the initial polymer with the base can be followed by a step of removing the base which is in excess. According to certain embodiments, the removal of the base is carried out with a wash comprising 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 unit of formula -(CXiX2-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 corresponding 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 the molar proportions of the first unit and the second unit.

[0098] All of what has been mentioned above about 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 first unit, • from 0% to 60% mol of second unit, • from 0% to less than 20% mol of third unit, • from more than 0% to 20% mol of fourth unit.

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

[0101] The ethylenic fluorinated polymer may in particular comprise from 0% to 5 mol%, from 5% to 10 mol%, from 10% to 15 mol% or from 15% to 19.9 mol% of third unit.

[0102] According to certain embodiments, the ethylenic fluoropolymer may comprise at least 1 mol%, preferably at least 2 mol%, more preferably at least 3 mol% and extremely preferably at least 4% molar of third unit. The presence of the third unit generally makes it possible to obtain an ethylenic fluorinated polymer of the relaxor-ferroelectric type, the advantages of which are detailed below. In particular, the polymer may comprise from 4% to 15% molar of third unit.

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

[0104] Preferred contents for the ethylenic fluorinated polymer are as follows: • from 40% to 80% mol of first unit, from 15% to 50% mol of second unit and from 1% to 20% mol of the total of third unit and fourth unit; • from 50% to 70% mol of first unit, from 20% to 40% mol of second unit and from 3% to 15% mol of the total of third unit and fourth unit; • from 55% to 65% mol of first unit, from 27% to 37% mol of second unit and from 5% to 12% mol of the total of third unit 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 evaluated by different spectroscopy methods and in particular RAMAN spectroscopy. The valence vibration band at 1720 cm1 corresponds to the presence of a single type of C=C double bonds, attributable to the -CF=CH- bonds. The presence of double bonds can be quantified by proton NMR thanks to the appearance of signals between 6.0 and 6.7 ppm and / or by fluorine NMR thanks to the appearance of signals between -87.0 and -90.0 ppm.

[0107] The ethylenic fluoropolymer is preferably random. The ethylenic fluoropolymer is preferably linear. Reaction with peroxide

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

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

[0110] According to certain 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 more preferably from 2 to 6 hours.

[0111] The reaction step with the peroxide may be carried out in a solvent. The solvent may be chosen so as not to interfere with the reaction and so as to dissolve the ethylenic fluoropolymer and the peroxide. It may be an aprotic polar solvent, in particular being able to 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 dimethylcarbonate, and propylene carbonate; and phosphates, in particular trimethylphosphate and triethylphosphate; or mixtures thereof. Esters, and particularly ethyl acetate, are preferred.

[0112] The mass concentration of ethylenic fluorinated polymer in the solvent may be, for example, from 2.5 to 250 g / L, preferably from 5 to 125 g / L, more preferably from 10 to 75 g / L, and more preferably 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 certain embodiments, the step of reacting the ethylenic fluoropolymer with the peroxide can be followed by a step of removing the excess peroxide as well as the side products of the reaction. According to certain embodiments, after evaporation of the reaction solvent, the base is removed with a wash comprising an alcohol. Fluorinated polymer obtained

[0115] Compared to the ethylenic fluorinated polymer, the fluorinated polymer obtained after reaction with the peroxide may comprise epoxide, alcohol, ketone and / or aldehyde functions. Without wishing to be bound by a theory, the inventors believe that these functions are formed from the double bonds of the fourth unit of the ethylenic fluorinated polymer. The polymer is also likely to be cleaved, which may lead to a reduction in its average molar mass.

[0116] The fluoropolymer is preferably random.

[0117] The fluoropolymer preferably exhibits an electrocaloric effect under the effect of a variable electric field.

[0118] Advantageously, the fluoropolymer has an adiabatic temperature variation ATEC of at least 1°C at at least one measurement temperature, the adiabatic temperature variation measurements being carried out at an electric field of given amplitude AE. The measurement temperature corresponds to the temperature to which the sample is brought before it is subjected to the electric field variation AE causing the electrocaloric effect.

[0119] Preferably, the fluoropolymer has an adiabatic temperature variation ATEC 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 in the electric field that causes the electrocaloric effect.

[0121] Generally, the higher the amplitude of the electric field, the greater the electrocaloric effect. However, the maximum amplitude of the electric field must be adapted so as not to reach the breakdown voltage of the polymer. In addition, the production of high voltages requires specific equipment that is highly energy-intensive, which is not necessarily desirable. According to certain embodiments, the electric field used to demonstrate a significant electrocaloric effect for use 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 certain 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 fluoropolymer has a dielectric strength greater than or equal to 200 V / qm, preferably greater than or equal to 300 V / qm, more preferably greater than or equal to 400 V / qm and extremely preferably greater than or equal to 500 V / qm. The dielectric strength can be measured according to the ASTM D3755-97 standard.

[0124] A square wave 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 low enough 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, changes from a rubbery state to a glassy state, or vice versa, as measured by differential scanning calorimetry (DSC) according to ISO 11357-2:2013, in second heating, using a heating rate of 10°C / min. The term "melting temperature" means the temperature at which a crystalline polymer, at least partially, changes to the viscous liquid state, as measured by differential scanning calorimetry (DSC) according to ISO 11357-3:2018, in second heating, using a heating rate of 10°C / min.Thus, the measurement temperature may in particular be from -20°C to 150°C, preferably from 0°C to 100°C, more preferably from 15°C to 60°C and extremely preferably from 20°C to 40°C.

[0127] The fluorinated polymer according to the invention may be a ferroelectric polymer. “Conventional ferroelectric” polymers, often simply referred to as “ferroelectrics”, are characterized by a wide hysteresis cycle of the electric displacement-applied electric field curve. For these materials, this cycle is characterized by a high coercive field at 25°C, typically greater in absolute value than 45 V / qm and a high remanent polarization at 25°C, typically greater than 50 mC / m2. These materials have a maximum of their electrocaloric properties at temperatures close to their Curie temperature. At this temperature, a ferroelectric -> paraelectric (FE -> PE) crystal structure transition, called the Curie transition, takes place, corresponding to a sudden depolarization of the ferroelectric domains. macroscopic. This transition is narrow, of the first order, and is 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 composition of the polymer: 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 relaxor-ferroelectric. “Relaxer ferroelectric” polymers are characterized by a relaxor-ferroelectric (RFE) -> 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 maximum of dielectric permittivity is shifted towards low temperatures. At the temperatures of the transition (RFE) -> (PE) or slightly higher, the application of an electric field makes it possible to generate and align the nanopolar regions, inducing a variation in entropy, and thus a significant electrocaloric effect over a wide temperature range.Relaxant-ferroelectric polymers are characterized at 25°C, and at a frequency of about 1 Hz by a hysteresis cycle of the "electric displacement" curve as a function of the "applied electric field" much finer than the hysteresis cycle of a ferroelectric polymer. They typically have a coercive field less than or equal in absolute value to 45 V / qm 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, in particular between 0°C and 100°C, and in certain cases between 20°C and 60°C. Thus, relaxant-ferroelectric polymers have interesting electrocaloric properties over a wide temperature range, and in particular at temperatures close to room temperature.They are therefore particularly interesting for the production of electrocaloric devices.

[0129] According to certain embodiments, the fluoropolymer 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 still preferably at least 40% higher, relative 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) as exemplified below, the fluoropolymer obtained has a relative dielectric permittivity greater than or equal to 40, preferably greater than or equal to 50, still 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 certain embodiments, the fluoropolymer 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 more preferably at a temperature less than or equal to 40°C, said relative dielectric permittivity being measured at 1 kHz.

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

[0133] According to certain embodiments, the fluoropolymer has a polarization maximum 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, and even more preferably at least 25% higher, relative to the initial polymer, said polarization maximum 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 fluoropolymer is a P(VDF-TrFE-CTFE) as exemplified below, the fluoropolymer obtained has a polarization maximum 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 polarization maximum being measured at a frequency of 1000 Hz, at 25°C and under an electric field of 1300 kV / cm.

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

[0136] According to certain embodiments, the fluoropolymer 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, and even more preferably 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 some embodiments, the fluoropolymer has a preferred coercive field potentially 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 certain embodiments, the fluoropolymer has a reduced coercive field compared to the initial polymer and compared to the ethylenic fluoropolymer.

[0139] According to certain embodiments, the fluoropolymer 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, and even more preferably at least 30% higher, relative 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 fluorinated polymer obtained 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%, and even more preferably greater than or equal to 27%, said percentage of crystallinity being measured at 25°C.

[0141] According to certain embodiments, the fluoropolymer has a remanent polarization preferably between 0.1 to 5 pC / cm2, preferably between 0.15 to 2.5 pC / cm2, preferably between 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.

[0142] All of the electroactive properties of the fluoropolymer can be determined as indicated in the examples below.

[0143] According to certain embodiments, the fluoropolymer may have a weight-average molecular weight 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 give films derived from the polymer according to the invention desirable mechanical properties. The mass distribution of polymers can be determined by size exclusion chromatography (SEC) using, for example, dimethyl sulfoxide (DMSO + lithium bromide LiBr 1g / L) as eluent. Composition

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

[0145] According to certain embodiments, the composition may comprise at least one fluoropolymer according to the invention and at least one liquid vehicle of said at least one polymer. This composition, commonly called "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 an aprotic polar solvent, which may in particular be chosen from: amides, in particular dimethylformamide, N-methyl-2-pyrrolidone, dimethylacetamide; sulfoxides, in particular dimethyl sulfoxide; lactones, in particular γ-butyrolactone; ketones, in particular acetone, methyl ethyl ketone (or butan-2-one), methyl isobutyl ketone, cyclopentanone, cyclohexanone, diisobutyl ketone; furans, in particular tetrahydrofuran; esters, in particular methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propylene glycol methyl ether acetate, glyceryl triacetate, diethylene glycol monobutyl ether acetate, and ethyl acetoacetate; carbonates, including dimethylcarbonate and propylene carbonate; phosphates, including trimethylphosphate and triethylphosphate; .

[0146] or their mixtures. 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 having an electrocaloric effect of interest. For example, the composition may comprise one or more ferroelectric polymers or relaxor ferroelectric polymers not having a carbon-carbon double bond. The composition may in particular 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 making it possible to improve the adhesion of the composition to a given substrate. The composition may optionally comprise one or more additives, in particular chosen 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 comprise fillers, in particular nanofillers, such as barium strontium titanate (BST) nanowires. Movie

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

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

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

[0153] The film may optionally be stretched if necessary. The stretching (when carried out) is preferably carried out with a rate of at least 10% to 700%. The film may in particular have a stretching rate 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 stretching rate corresponds to the ratio between the surface area of ​​the film after stretching and the surface area of ​​the film before stretching. The stretching (when carried out) may in particular be carried out at a temperature of 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 10°C to 200°C, preferably 15°C to 150°C, preferably 20°C to 140°C and even more preferably 25°C to 100°C.

[0154] The films can also, after having optionally been 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 duration of several seconds to several hours, then cooled.

[0155] Stretching and annealing most often make it possible to increase crystallinity and dielectric strength.

[0156] The invention makes it possible to obtain films with a thickness greater than or equal to 0.1 μm. For optimal exploitation of the electrocaloric effect, their thickness is advantageously from 1 μm to 100 μm. Among these thicknesses, the smallest thicknesses may be preferred so as not to have to generate excessively high voltages. Thus, films with a thickness of 1 to 50 μm and even 1 to 10 μm 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, CNTs, etc.).

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

[0159] The multilayer system may comprise alternating 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 films covered with electrodes. Adhesives can be used to bond layers together.

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

[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 electrocaloric 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, in particular in the form of a film, and in particular in the form of a layer in a multilayer system as described above. The film is capable of being in thermal contact with a load to be cooled and / or a load to be heated and / or a heat transfer fluid. The system also comprises a voltage source intended to be applied to the plate. The heat transfer system can eliminate 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 its 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, etc.). Examples

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

[0167] Example 1: Preparation of 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 solubilized in 20 mL of DMSO. Volumes of 10, 15, 20, 25, 30 μl of ethylenediamine are respectively added to these solutions. The reaction mixture is heated to 30°C and left to react for 4 hours. After reaction, each of the The polymers obtained are precipitated in water and purified by washing with a H2 0 / ethanol solution (60 / 40). An average yield of 95% is obtained. The ethylenic fluorinated polymer obtained is denoted P(VDF-TrFE-CTFE-DB), the DB notation designating 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 lubilized in 20 mL of ethyl acetate. 0.3 g of mCPBA is added to each of the solutions. The reaction mixture is left to react for 6 hours at 15°C. The solvent is then evaporated and the product washed with ethanol to remove excess mCPBA. The fluoropolymer is 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 silver electrode is deposited on a glass substrate (15x15 mm) by chemical vapor deposition (CVD). On the device, a film is deposited using a Dr. Blade blade from a 7% mass polymer solution in ethyl acetate. A film about 3 μm thick is obtained after evaporation of the solvent. Annealing is carried out at 100°C on a hot plate for 2 hours. A 100 nm thick silver electrode is then evaporated over the film by CVD. In order to access the bottom electrode, the polymer film is removed from the bottom part of the device.

[0173] Example 4: Measurements of relative permittivity

[0174] The permittivity measurements were carried out using a broadband dielectric spectroscopy system and a Solartron 1260 A impedance analyzer. The temperature control of the samples was carried out using a Linkam LTS 350 temperature control system. The measurements were carried out with an alternating voltage signal of 1 V, with a signal frequency of 102 to 103 kHz at a temperature of 40°C. This technique allows the relative dielectric constant and the loss factor to be determined from the measured capacitance and the geometric factors of the sample. The main results of the different samples can be seen in [Fig.l]. The point at position 0 along the x-axis corresponds to the initial P(VDF-TrFE-CTFE) polymer.

[0175] Following the dehydrochlorination of P(VDF-TrFE-CTFE), an increase in the 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) (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 with a TF Analyzer 2000E analyzer from aixACCT Systems. The measurements were carried out by applying a continuous triangular signal with a frequency of 100 Hz, at room temperature. The values ​​of the polarization maxima under a field of 1300 kV / cm are given in [Fig.2].

[0178] The increase in the polarization maximum compared to the initial polymer is more marked after reaction of the dehydrochlorinated polymer with mCPBA. Indeed, the polymer obtained following the reaction of P(VDF-TrFE-CTFE-DB) with mCPBA has a polarization maximum of ~4.8 pC / cm2 compared to a polarization maximum 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]). observed a decrease in the coercive field after dehydrochlorination. This decrease is even more marked 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) (a decrease of 26%).

[0180] Example 6: Analysis of samples by WAXS

[0181] The crystal 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 q range of 0.1 to 3.1 Å-l (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 in relation to 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 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 1g / L) as eluent. The DMSO measurements were carried out on a Thermoscientific Ultimate 3000 system equipped with a diode array detector. (DAD). The system also includes a multi-angle light scattering (MALS) detector and a differential refractive index (dRI) detector from Wyatt Technology. Polymers were separated on Tosoh TSK G3000HHR and G2000HHR (7.8 * 300) columns (exclusion limits from 200 Da to 60,000 Da) at a flow rate of 0.5 mL / min. Column temperature was maintained at 80°C.

[0186] 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

Claims

1. A method of manufacturing a fluoropolymer from an ethylenic fluoropolymer comprising: • a first unit of formula -(CF2-CH2)-, • optionally, at least one second unit of formula -(CXiXz-CX^)-, • optionally, at least one third unit of formula -(CYiYz-CYjZ)-, • at least one 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 from 1 to 3 carbon atoms optionally partially or completely fluorinated, X3 and X4 independently denote -F, or an alkyl group comprising from 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 from 1 to 3 carbon atoms optionally partially or completely fluorinated, Y3 denotes -F, -Cl or an alkyl group comprising from 1 to 3 carbon atoms optionally partially or completely fluorinated, Z denotes a halogen atom other than -F, the method comprising a step of reacting the ethylenic fluoropolymer with a peroxide.;

2. The method of claim 1, wherein X1 is -H or -F and X2, X3 and X4 are all -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 method according to any one of claims 1 to 3, wherein the ethylenic fluoropolymer 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% mol of the third unit, • from more than 0% to 20% mol of the fourth unit.

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

6. 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 one second unit of formula -(CX^-CXsXJ-, • at least one third unit of formula -(CYiY2-CY3Z)-.

7. The method of claim 6, wherein the step of preparing the ethylenic fluoropolymer comprises contacting the initial polymer with a base.

8. A method according to any one of claims 6 to 7, wherein the fluoropolymer has a relative dielectric permittivity which is at least 5% higher than 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 fluoropolymer has a polarization maximum in pC / cm2 which is at least 1% higher than the initial polymer, said polarization maximum 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 fluoropolymer has a coercive field in kV / cm which is at least 1% lower than the initial polymer, said coercive field being measured at a frequency of 100 Hz, at 25°C.

11. A method 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 obtainable by the process according to one of claims 1 to 13.

15. A fluoropolymer according to claim 14, having a weight average molecular weight of less than or equal to 500,000 g / mol.

16. A 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 fluoropolymer according to any one of claims 14 to 16, and at least one liquid vehicle of said polymer.

18. A film comprising the fluoropolymer 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 possibly comprising a fluoropolymer according to the invention, of the same composition or of a different composition, another polymer or a non-polymeric material.

21. Use of a fluoropolymer 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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