Ferroelectric polymer

Abstract

The invention relates to a polymer essentially consisting of, or consisting of, repeating units derived from vinylidene fluoride (VDF), trifluoroethylene (TrFE), and at least one third monomer different from vinylidene fluoride and trifluoroethylene, the molar ratio TrFE:VDF between the number of moles in the unit derived from trifluoroethylene and that in the unit derived from vinylidene fluoride in the polymer being 14.0:86.0 to 50.0:50.0, the at least one third monomer having a mole fraction xt greater than or equal to 1 ppm and less than or equal to 5000 ppm relative to the total number of moles in the units derived from VDF and TrFE in the polymer.

Description

[0001] Description

[0002] Title: Ferroelectric Polymer

[0003] Technical field

[0004] The invention relates to the field of ferroelectric polymers.

[0005] The invention relates more particularly to copolymers, in the broad sense, comprising repeating units derived from vinylidene fluoride and trifluoroethylene.

[0006] Prior art

[0007] The copolymer consisting of repeating units derived from vinylidene fluoride and trifluoroethylene, poly(VDF-co-TrFE) also referred to as P(VDF-TrFE), is a polymer known for its ferroelectric properties. It is notably characterized by a wide hysteresis cycle of the electric polarization curve as a function of the applied electric field.

[0008] The application to the P(VDF-TrFE) of an electric field at a value greater than a characteristic field called coercive field (Ec), makes it possible to orient dipoles formed by the CF bonds in the same direction, in a sufficiently stable manner, so as to obtain a remanent polarization (P r ) at zero electric field.

[0009] There is currently a need to provide ferroelectric polymers with higher remanent polarization, in order to be able to increase the sensitivity of electronic devices, for example a sensor or a memory, incorporating these materials.

[0010] Furthermore, when a ferroelectric material has a high coercive field, it is then necessary to apply high voltages to it in order to polarize it, which leads to excess energy consumption and / or an increased risk of electrical breakdown, and / or requires reducing the thickness of the ferroelectric material layer. It is therefore advantageous to be able to maintain a sufficiently low coercive field.

[0011] Finally, it is also known to introduce a few percent, typically 2% to 20%, for example about 6% to 8%, of repeating units from a third monomer, in particular chlorotrifluoroethylene or a chlorofluoroethylene in the crystalline structure of P(VDF-TrFE), to reduce the size of the polar domains so as to transform the copolymer with ferroelectric properties into a terpolymer with "ferroelectric relaxor" properties. Ferroelectric relaxor polymers are notably characterized by a hysteresis cycle of the electric polarization curve as a function of the applied electric field that is much finer than the hysteresis cycle of ferroelectric polymers: they therefore have a considerably weaker coercive field but also a weaker remanent polarization than ferroelectric polymers.

[0012] Objectives of the invention

[0013] The objective of the invention is to provide a polymer having advantageous ferroelectric properties, in particular ferroelectric properties comparable to or improved compared to P(VDF-TrFE).

[0014] An objective of the invention is, according to at least certain embodiments, to provide a polymer having a high remanent polarization, in particular a remanent polarization comparable to or higher than P(VDF-TrFE).

[0015] An objective of the invention is, according to certain embodiments at least, to provide a polymer having a sufficiently weak coercive field, in particular a coercive field of the same order, or weaker than P(VDF-TrFE).

[0016] An objective of the invention is, according to at least certain embodiments, to provide a polymer having a lower coercive field and a higher remanent polarization than P(VDF-TrFE).

[0017] Another objective of the invention is, according to at least certain embodiments, to provide a manufacturing process that is less expensive than that of manufacturing P(VDF-TrFE), to obtain a polymer having at least ferroelectric properties comparable to those of P(VDF-TrFE). Another objective of the invention is to be able to provide electronic devices incorporating these materials, in particular in the form of films.

[0018] Summary of the invention

[0019] The invention relates to a polymer essentially consisting of, or consisting of, repeating units derived from vinylidene fluoride (VDF), trifluoroethylene (TrFE), and at least one third monomer other than vinylidene fluoride and trifluoroethylene, having the chemical formula:

[0020] CXiX2=CX3Z (I) wherein each of Xi, X2, X3is independently selected from H, F and alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I, the TrFE:VDF molar ratio between the number of moles of unit derived from trifluoroethylene and that of unit derived from vinylidene fluoride in the polymer being from 14.0:86.0 to 50.0:50.0, said repeating unit derived from said at least one third monomer having a mole fraction xt greater than or equal to 1 ppm and less than or equal to 5000 ppm, relative to the total number of moles of units derived from VDF and TrFE in the polymer.

[0021] Knowing that the addition of a few percent of a third party monomer, such as chlorotrifluoroethylene, or a chlorofluoroethylene, or a chlorodifluoroethylene, to P(VDF-TrFE) transforms the polymer with ferroelectric properties into a polymer with ferroelectric relaxor properties, having a lower crystallinity and a lower remanent polarization than P(VDF-TrFE), the person skilled in the art would have expected that the introduction of the third party monomer to P(VDF-TrFE), at a mole fraction of 1 ppm to 5000 ppm, would also result in a decrease in ferroelectric performance, including a decrease in the remanent polarization of the polymer.

[0022] On the contrary, the inventors surprisingly discovered that the presence of the third monomer at a molar fraction of 1 ppm to 5000 ppm in the polymer made it possible at least to preserve, or even preferentially to improve, the ferroelectric performance of the polymer. More specifically, the inventors discovered that a content of 1 ppm to 5000 ppm of third monomer in the polymer made it possible to maintain, and preferably to increase, the remanent polarization of the polymer.

[0023] Furthermore, the inventors discovered that a content of 1 ppm to 5000 ppm of third-party monomer in the polymer made it possible to maintain, and preferably to reduce, the coercive field of the polymer.

[0024] In some embodiments, Z in chemical formula (I) is Cl.

[0025] In some embodiments, each of X1, X2, X3 in chemical formula (I) is independently selected from H and F.

[0026] According to certain embodiments, said at least one third monomer comprises at least one monomer selected from the group consisting of chlorotrifluoroethylene (CTFE), chlorodifluoroethylene, in particular 1-chloro-2,2-difluoroethylene (CDFE), chlorofluoroethylene, in particular 1,1-chlorofluoroethylene (CFE), and a mixture thereof.

[0027] According to certain embodiments, the polymer according to the invention comprises a single third monomer selected from the group consisting of: chlorotrifluoroethylene (CTFE), chlorodifluoroethylene, in particular 1-chloro-2,2-difluoroethylene (CDFE), and chlorofluoroethylene, in particular 1,1-chlorofluoroethylene (CFE). According to certain embodiments, said at least one third monomer is chlorotrifluoroethylene (CTFE).

[0028] According to certain embodiments, xt > 5 ppm, preferably xt > 10 ppm, and more preferably xt > 20 ppm.

[0029] According to some embodiments, xt > 400 ppm.

[0030] According to some embodiments, xt > 600 ppm.

[0031] According to certain embodiments, xt < 4000 ppm, preferably xt < 3000 ppm, and more preferably xt < 2500 ppm.

[0032] According to some embodiments, xt < 1000 ppm.

[0033] In some embodiments, the TrFE:VDF molar ratio in the polymer is from 15.0:85.0 to 40.0:60.0, or from 16.0:84.0 to 35.0:65.0, or from 17.5:82.5 to 27.5:72.5. In some embodiments, the polymer has a melt flow rate at 230°C under a load of 10 kg, as measured according to ASTM D1238-10, of from 0.1 g / 10 min to 100 g / 10 min, preferably from 0.5 g / 10 min to 50 g / 10 min, and more preferably from 1 g / 10 min to 10 g / 10 min.

[0034] According to certain embodiments, the TrFE:VDF molar ratio in the polymer is from 17.5:82.5 to 22.5:77.5, and preferably 10 ppm < xt < 3000 ppm, even more preferably

[0035] 200 ppm < xt < 2500 ppm, and more preferably 400 ppm < xt < 2000 ppm. According to certain embodiments, the TrFE:VDF molar ratio in the polymer is from 20.1:79.9 to 20.9:79.1, and more preferably 10 ppm < xt < 3000 ppm, more preferably 200 ppm < xt < 2500 ppm, and more preferably 400 ppm < xt < 2000 ppm.

[0036] According to certain embodiments, the polymer according to any one of the preceding claims is obtained by a suspension polymerization process, preferably in water.

[0037] The invention also relates to a film essentially comprising or consisting of the polymer according to the invention.

[0038] Furthermore, the invention relates to the use of a third-party monomer having the chemical formula:

[0039] CXiX2=CX3Z (I) wherein each of Xi, X2, X3 is independently selected from H, F and alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I, as a termonomer in the structure of a polymer essentially consisting of repeating units derived from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) in a molar proportion xt of 1 ppm to 5000 ppm relative to the total number of moles of units derived from VDF and TrFE in the polymer, the molar ratio TrFE:VDF in the polymer between the unit derived from TrFE and that derived from VDF being from 14.0:86.0 to 50.0:50.0, to increase the remanent polarization thereof.The remanent polarization may in particular be increased by 1% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 7.5% or more, or 10.0% or more, or 11.0% or more, or 12.0% or more, compared to the remanent polarization of P(VDF-TrFE) having the same proportion of TrFE:VDF.

[0040] Furthermore, the invention relates to the use of a third-party monomer having the chemical formula:

[0041] CXiX2=CX3Z (I) wherein each of Xi, X2, X3 is independently selected from H, F and alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I, as a termonomer in the structure of a polymer essentially consisting of repeating units derived from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) in a molar proportion xt of 1 ppm to 5000 ppm relative to the total number of moles of units derived from VDF and TrFE in the polymer, the molar ratio TrFE:VDF in the polymer between the unit derived from TrFE and that derived from VDF being from 14.0:86.0 to 50.0:50.0, to reduce the coercive field thereof. The coercive field may in particular be reduced by 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, compared to the coercive field of P(VDF-TrFE) having the same proportion in TrFE:VDF.

[0042] According to advantageous embodiments, the invention relates to the use of a third-party monomer having the chemical formula:

[0043] CXiX2=CX3Z (I) wherein each of Xi, X2, X3 is independently selected from H, F and alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I, as a termonomer in the structure of a polymer essentially consisting of repeating units derived from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) in a molar proportion xt of 1 ppm to 5000 ppm relative to the total number of moles of units derived from VDF and TrFE in the polymer, the molar ratio TrFE:VDF in the polymer between the unit derived from TrFE and that derived from VDF being from 14.0:86.0 to 50.0:50.0, to increase the remanent polarization thereof and to decrease the coercive field thereof.

[0044] In the aforementioned uses, according to certain embodiments it is possible to have xt > 25 ppm.

[0045] In the aforementioned uses, according to certain embodiments it is possible to have xt < 2500 ppm, or even xt < 800 ppm.

[0046] The invention also relates to the use of trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene in a process for manufacturing a polymer according to the invention, said at least one third monomer comprising chlorotrifluoroethylene, and said manufacturing process comprising a polymerization reaction step between vinylidene fluoride (VDF), trifluoroethylene (TrFE) and chlorotrifluoroethylene (CTFE).

[0047] According to advantageous embodiments of this use, the trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene comprises from 2 ppm to 5000 ppm or from 5 ppm to 4000 ppm, or from 20 ppm to 3000 ppm, or from 50 ppm to 2500 ppm, or from 75 ppm to 1500 ppm of chlorotrifluoroethylene per mole of trifluoroethylene.

[0048] In some embodiments, the trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene comprises from 1500 ppm to 4500 ppm of chlorotrifluoroethylene per mole of trifluoroethylene.

[0049] Detailed description of the invention

[0050] List of Figures

[0051] Figure 1 shows the following curves superimposed: polarization (mC / m 2 ) as a function of the applied electric field (V / pm), for comparative example #1 (mark: “■”) and for example 6 (mark: “▲”).

[0052] Figure 2 represents the remanent polarization Pr (mC / m 2) as a function of the CTFE proportion xt for experimental results #1 to #15. Different marks were used to differentiate samples with a TrFE / (VDF+TrFE) molar proportion of approximately 20% (mark “■”), approximately 25% (mark “▲”) and approximately 30% (mark “•”).

[0053] Definitions

[0054] The term "copolymer", in the broad sense, refers to a polymer resulting from the copolymerization of at least two types of chemically different monomers, called comonomers. A copolymer, in the broad sense, has at least two types of repeating units, the (at least two) types being determined by different chemical formulas. It can, for example, be formed from two, three or four types of repeating units. A copolymer, in the strict sense, is formed from exactly two types of repeating units, such as P(VDF-TrFE).

[0055] A terpolymer, in the broad sense, refers to a polymer resulting from the copolymerization of at least three types of chemically different monomers. A terpolymer, in the strict sense, is formed from exactly three types of repeating units, such as P(VDF-TrFE-CTFE).

[0056] The term “polymer consisting essentially of repeating units” means that the polymer comprises at least 99 mol%, or at least 99.5 mol%, or at least 99.9 mol% of such units relative to the total number of moles of units constituting the polymer.

[0057] The term “polymer consisting of repeating units” means that the polymer comprises more than 99.9%, in particular 100%, by mole of these units relative to the total number of moles of units constituting the polymer.

[0058] In all ranges listed, terminals are included unless otherwise stated.

[0059] The term "monomer-derived unit" means the repeating unit derived directly from this monomer by polymerization. For example, the unit derived from chlorotrifluoroethylene: C(F)(CI)=CF2 is: -C(F)(CI)-CF2- The unit derived from trifluoroethylene: C(F)(H)=CF2 is: -C(F)(H)-CF2-, etc. The term "approximately a numerical value" means this numerical value plus or minus 5%.

[0060] The term "Curie Temperature" refers to the temperature at which a ferroelectric -> paraelectric crystal structure transition, called the Curie transition, takes place. The Curie temperature of a ferroelectric polymer therefore defines a maximum operating temperature beyond which the polymer loses its ferroelectric properties, unless a new low-temperature polarization is carried out. It can be determined, for example, by Differential Scanning Calorimetry (DSC), as the temperature of the maximum of the endotherm corresponding to this transition, during the first or second heating, preferably during the second heating, at 10°C / min, or by Dielectric Spectroscopy, as the temperature corresponding to the maximum of the dielectric permittivity peak during heating at 10°C / min at a frequency of 1 kHz.

[0061] "Melting temperature" means the temperature at which the crystalline structure changes from a solid state to a liquid state. It can be determined, for example, by Differential Scanning Calorimetry (DSC), as the temperature of the maximum of the endotherm corresponding to this transition, during the first or second heating, preferably during the second heating, at 10°C / min

[0062] Terpolymer according to the invention

[0063] The polymer according to the invention is essentially composed of, or consisting of, repeating units derived from vinylidene fluoride (VDF), trifluoroethylene (TrFE) and at least one third monomer, different from vinylidene fluoride and trifluoroethylene.

[0064] The third monomer has the chemical formula:

[0065] CXiX2=CX3Z (I) wherein each of Xi, X2, X3is independently selected from H, F and alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I.

[0066] The polymer may comprise one or more different third-party monomers. According to certain embodiments, the polymer comprises several different third-party monomers. The polymer may notably comprise CTFE and at least one other third-party monomer, the CTFE representing at least 50% by mole relative to the total number of moles of third-party monomers. The CTFE may in particular represent at least 60%, or at least 70%, or at least 80%, or at least 90% by mole relative to the total number of moles of third-party monomers.

[0067] In some embodiments, Z in chemical formula (I) is Cl.

[0068] In some embodiments, each of X1, X2, X3 in chemical formula (I) is independently selected from H and F.

[0069] In some embodiments, Z in chemical formula (I) is Cl and each of X1, X2, X3 in chemical formula (I) is independently selected from H and F. The third monomer, or optionally one of the third monomers, may be selected from the group consisting of: chlorotrifluoroethylene (CTFE), 1,1-chlorofluoroethylene (CFE) and 1-chloro-2,2-difluoroethylene (CDFE).

[0070] According to certain embodiments, said at least one third monomer may be: chlorotrifluoroethylene (CTFE), 1,1-chlorofluoroethylene (CFE), 1-chloro-2,2-difluoroethylene (CDFE), or a mixture thereof.

[0071] According to some embodiments, the third-party monomer may be: chlorotrifluoroethylene (CTFE) or 1,1-chlorofluoroethylene (CFE).

[0072] According to particular embodiments, the third monomer may be: 1,1-chlorofluoroethylene (CFE). Thus, the polymer according to the invention may be a terpolymer, essentially consisting of, or consisting of, repeating units derived from VDF, TrFE and CFE. According to particular embodiments, as illustrated in the examples, the third monomer may be: chlorotrifluoroethylene (CTFE). Thus, the polymer according to the invention may be a terpolymer, essentially consisting of, or consisting of, repeating units derived from VDF, TrFE and CTFE. In these embodiments, the CTFE may be provided at least in part by TrFE obtained by hydrogenolysis of CTFE and purified so as to retain a small amount of CTFE, as detailed below.Thus, even in embodiments where the polymer according to the invention has ferroelectric properties comparable to those of P(VDF-TrFE), in particular for a high xt value, its manufacturing process has a lower cost price than that of manufacturing P(VDF-TrFE) using an extremely pure TrFE which is expensive to produce.

[0073] The polymer according to the invention has a molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride of 14.0:86.0 to 50.0:50.0. This molar proportion can in particular be determined by proton NMR on the polymer.

[0074] In some embodiments, the molar ratio of TrFE:VDF in the trifluoroethylene derived unit relative to the vinylidene fluoride derived unit in the polymer is from 50.0:50.0 to 40.0:60.0, or from 40.0:60.0 to 32.5:67.5, or from 32.5:67.5 to 27.5:72.5, or from 27.5:72.5 to 22.5:77.5, or from 22.5:77.5 to 21.5:78.5, or from 21.5:78.5 to 21.0:79.0, or from 21.0:79.0 to 20.5:79.5, or from 20.5:79.5 to 20.0:80.0, or 20.0:80.0 to 19.5:80.5, or from 19.5:80.5 to 19.0:81.0, or from 19.0:81.0 to 18.5:81.5, or from 18.5:81.5 to 18.0:82.0, or from 18.0:82.0 to 17.5:82.5, or from 17.5:82.5 to 17.0:83.0, or from 17.0:83.0 to 16.0:84.0, or from 16.0:84.0 to 15.0:85.0, or from 15.0:85.0 to 14.0:86.0.

[0075] According to advantageous embodiments, the molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride in the polymer is from 17.5:82.5 to 27.5:72.5.

[0076] According to extremely advantageous embodiments, the molar proportion of the unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride in the polymer is from 21.5:78.5 to 18.5:81.5. Indeed, it is known for P(VDF-TrFE) that the remanent polarization increases when the proportion of TrFE decreases and that the polymer loses its ferroelectric properties at a molar proportion TrFE:VDF of approximately 1.0:86.0. Furthermore, for a molar proportion TrFE:VDF in the polymer of 21.5:78.5 to 18.5:81.5, the Curie temperature is sufficiently far from the melting temperature of the polymer and therefore allows for easy annealing between these two temperatures, as explained below.

[0077] The molar proportion of the unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride may in particular be from 21.5:78.5 to 21.4:78.6, or from 21.4:78.6 to 21.3:78.7, or from 21.3:78.7 to 21.2:78.8, or from 21.2:78.8 to 21.1:78.9, or from 21.1:78.9 to 21.0:79.0, or from 21.0:79.0 to 20.9:79.1, or 20.9:79.1 to 20.8:79.2, or from 20.8:79.2 to 20.7:79.3, or 20.7:79.3 to 20.6:79.4, or from 20.6:79.4 to 20.5:79.5, or from 20.5:79.5 to 20.4:79.6, or from 20.4:79.6 to 20.3:79.7, or from 20.3:79.7 to 20.2:79.8, or from 20.2:79.8 to 20.1:79.9, or from 20.1:79.9 to 20:80, or from 20:80 to 19.9:80.1, or from 19.9:80.1 to 19.8:80.2, or from 19.8:80.2 to 19.7:80.3, or from 19.7:80.3 to 19.6:80.4, or from 19.6:80.4 to 19.5:80.5 or from 19.5:80.5 to 19.4:80.6, or from 19.5:80.5 to 19.4:80.6, or from 19.4:80.6 to 19.3:80.7, or from 19.3:80.7 to 19.2:80.8, or from 19.2:80.8 to 19.1:80.9, or from 19.1:80.9 to 19.0:81.0, or from 19.0:81.0 to 18.9:81.1, or from 18.9:81.1 to 18.8:81.2, or from 18.8:81.2 at 18.7:81,3, or 18,7:81,3 to 18,6:81,4, or from 18,6:81,4 to 18,5:81,5.,

[0078] According to particular embodiments, the molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride is from 20.9:79.1 to 20.8:79.2, or from 20.8:79.2 to 20.7:79.3, or from 20.7:79.3 to 20.6:79.4, or from 20.6:79.4 to 20.5:79.5, or from 20.5:79.5 to 20.4:79.6, or from 20.4:79.6 to 20.3:79.7, or from 20.3:79.7 to 20.2:79.8, or from 20.2:79.8 to 20.1:79.9.

[0079] The polymer according to the invention has a molar fraction xt of third-party monomer(s), expressed in parts per million (ppm), greater than or equal to 1 ppm and less than or equal to 5000 ppm. This molar fraction can in particular be determined by elemental analysis of the element Z on the polymer. It is expressed relative to the total number of moles of units derived from VDF and TrFE in the polymer. A strong increase in the remanent polarization was observed from the first ppm, and / or tens of ppm of third-party monomer(s) in the polymer. Considering increasing quantities of third-party monomer, of the order of a hundred ppm or a few thousand ppm, the remanent polarization continues to increase until reaching a plateau before decreasing again.

[0080] Similarly, a decrease in the coercive field was observed from the first ppm, and / or tens of ppm of third-party monomer(s) in the polymer. Considering increasing quantities of third-party monomer, of the order of hundreds of ppm or a few thousand ppm, the coercive field continues to decrease until reaching a plateau before increasing again.

[0081] The remanent polarization and coercive field can be measured as in the examples.

[0082] In embodiments where the polymer comprises multiple third-party monomers, the fraction xt expresses the sum of the mole fractions of all third-party monomers.

[0083] Preferably xt > 5 ppm, more preferably xt > 10 ppm, and even more preferably xt > 20 ppm.

[0084] For example, we can have xts 25ppm, xts 30ppm, or xt S40 ppm, or xt S50 ppm, or xt >60 ppm, or xt >70 ppm, or xt >80 ppm, or xt >90 ppm, or xt ^100 ppm, or xt ^200 ppm, or xt ^400 ppm, or xt ^600 ppm, or xt ^800 ppm.

[0085] Preferably xt ^ 4000 ppm, more preferably xt < 3000 ppm, and even more preferably xt < 2500.

[0086] For example, we can have xt^2000 ppm, or xt^1750 ppm or xt^1500 ppm, or xt <1400 ppm, or xt^1300 ppm, or xt^1200 ppm, or xt^1100 ppm, or xt^1000 ppm.

[0087] In view of the examples, it could be observed that with an increasing proportion of TrFE / (VDF+TrFE) in the polymer, the remanent polarization increases more rapidly from the first ppm of third monomer in the structure of the polymer and / or the xt range where the remanent polarization remains at a significantly higher value than the remanent polarization of P(VDF-TrFE) having the same VDF:TrFE ratio is more reduced.

[0088] According to particular embodiments, the polymer according to the invention has a molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride of 14.0:86.0 to 18.5:81.5 and 5 ppm < xt < 5000 ppm.

[0089] Preferably, we have 10 ppm < xt < 4500 ppm. We can have 10 ppm < xt < 25 ppm, or 25 ppm < xt < 100 ppm, or 100 ppm < xt < 200 ppm, or 200 ppm < xt < 400 ppm, or 400 ppm < xt < 600 ppm, or 600 < xt < 800 ppm, or 800 ppm < xt < 1500 ppm, or 1500 ppm < xt < 3000 ppm, or 3000 ppm < xt < 4500 ppm. Over at least one of these intervals, the remanent polarization of the polymer is either of the same order, or 1% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 7.5% or more, or 10.0% or more, or 11.0% or more, or 12.0% or more, greater than the remanent polarization of P(VDF-TrFE) having the same TrFE:VDF ratio. Over at least one of these intervals, the coercive field is either of the same order, or 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more less than the coercive field of P(VDF-TrFE) having the same TrFE:VDF ratio.

[0090] The third monomer may in particular be chlorotrifluoroethylene.

[0091] According to certain embodiments, in particular when the molar proportion of units derived from trifluoroethylene relative to the sum of the units derived from vinylidene fluoride and trifluoroethylene (TrFE / (VDF+TrFE)) in the polymer is less than 22.5%, or less than 22.0%, or less than 21.5%, or less than 21.0%, and / or greater than 17.5%, or greater than 18.0%, or greater than 18.5%, or greater than 19.0%, in particular when the molar proportion (TrFE / (VDF+TrFE)) is approximately 20.0%, the remanent polarization, as measured in the examples, may advantageously have a value greater than or equal to 88 mC / m 2 , or greater than or equal to 90 mC / m 2 , or greater than or equal to 92 C / m 2 or greater than or equal to 94 mC / m 2at 25°C to an alternating electric field (sinusoidal signal with a period of 18 s) with a maximum amplitude equal to 150 V / pm. The coercive field may advantageously have a value less than or equal to 50 V / pm, or less than or equal to 49 V / pm, or less than or equal to 48 V / pm.

[0092] According to particular embodiments, the polymer according to the invention has a molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride of 17.5:82.5 to 22.5:77.5 and 5 ppm < xt < 5000 ppm. 10 ppm < xt < 3000 ppm is preferentially used, and 100 ppm < xt < 2500 ppm is preferentially used. 100 ppm < xt < 200 ppm can be used, or 200 ppm < xt < 1000 ppm, or 1000 ppm < xt < 2000 ppm, or 2000 ppm < xt < 2500 ppm can be used.

[0093] We can have 25 ppm < xt^ 100 ppm, or 100 ppm < xt < 200 ppm, or 200 ppm < xt < 400 ppm, or 400 ppm< xt < 600 ppm, or 600 < xt< 800 ppm , or 800 ppm < xt< 1000 ppm, or 1000 ppm < xt< 2000 ppm, or 2000 ppm < xt< 2500 ppm. Over at least one of these intervals, the remanent polarization of the polymer is either of the same order, or 1% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 7.5% or more, or 10.0% or more, or 11.0% or more, or 12.0% or more, greater than the remanent polarization of P(VDF-TrFE) having the same TrFE:VDF ratio. Over at least one of these intervals, the coercive field is either of the same order, or 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more less than the coercive field of P(VDF-TrFE) having the same TrFE:VDF ratio.

[0094] The third monomer may in particular be chlorotrifluoroethylene. According to particular embodiments, the polymer according to the invention has a molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride of 19.0:81.0 to 21.0:79.0 and 5 ppm < xt < 5000 ppm. Preferably 10 ppm < xt < 3000 ppm, and preferably 100 ppm < xt < 2500 ppm.

[0095] We can have 25 ppm < xt < 100 ppm, or 100 ppm < xt < 200 ppm, or 200 ppm < xt< 400 ppm, or 400 ppm< xt< 600 ppm, or 600 < xt< 800 ppm, or 800 ppm < xt < 1000 ppm, or 1000 ppm < xt^ 2000 ppm, or 2000 ppm < xt < 2500 ppm. Over at least one of these intervals, the remanent polarization of the polymer is either of the same order, or 1% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 7.5% or more, or 10.0% or more, or 11.0% or more, or 12.0% or more, greater than the remanent polarization of P(VDF-TrFE) having the same TrFE:VDF ratio. Over at least one of these intervals, the coercive field is either of the same order, or 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more less than the coercive field of P(VDF-TrFE) having the same TrFE:VDF ratio.

[0096] The third monomer may in particular be chlorotrifluoroethylene.

[0097] According to particular embodiments, the polymer according to the invention has a molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride of 20.1:79.9 to 20.9:79.1 and 5 ppm < xt < 5000 ppm. 10 ppm < xt < 3000 ppm is preferentially used, and 100 ppm < xt < 2500 ppm is preferentially used.

[0098] We can have 25 ppm < xt< 100 ppm, or 100 ppm < xt< 200 ppm, or 200 ppm < xt< 400 ppm, or 400 ppm < xt s 600 ppm, or 600 < xt^ 800 ppm, or 800 ppm < xt

[0099] < 1000 ppm, or 1000 ppm < xt^ 2000 ppm, or 2000 ppm < xt< 2500 ppm. Over at least one of these ranges, the remanent polarization of the polymer is either of the same order, or 1% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 7.5% or more, or 10.0% or more, or 11.0% or more, or 12.0% or more, greater than the remanent polarization of P(VDF-TrFE) having the same TrFE:VDF ratio. Over at least one of these intervals, the coercive field is either of the same order, or 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more lower than the coercive field of P(VDF-TrFE) having the same proportion of TrFE:VDF.

[0100] The third monomer may in particular be chlorotrifluoroethylene.

[0101] According to particular embodiments, the polymer according to the invention has a molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride of 22.5:77.5 to 27.5:72.5 and 5 ppm < xt < 5000 ppm. 10 ppm < xt < 2000 ppm is preferentially used, and even more preferentially 50 ppm < xt < 1500 ppm.

[0102] We can have 25 ppm < xt^ 50 ppm, or 50 ppm < xt < 100 ppm, or 200 ppm < xt

[0103] < 400 ppm, or 400 ppm< xt< 600 ppm, or 600 < xt< 800 ppm, or 800 ppm < xt< 1200 ppm, or 1200 ppm < xt < 1500 ppm. Over at least one of these ranges, the remanent polarization of the polymer is either of the same order, or 1% or more, or 2.5% or more, or 5.0% or more, or 7.5% or more, or 10.0% or more, or 11.0% or more, or 12.0% or more, greater than the remanent polarization of P(VDF-TrFE) having the same TrFE:VDF ratio. Over at least one of these intervals, the coercive field is either of the same order, or 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more lower than the coercive field of P(VDF-TrFE) having the same proportion of TrFE:VDF.

[0104] The third monomer may in particular be chlorotrifluoroethylene.

[0105] According to particular embodiments, the polymer according to the invention has a molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride of 23.5:76.5 to 26.5:73.5 and 5 ppm < xt < 5000 ppm. 10 ppm < xt < 2000 ppm is preferentially used, and even more preferentially 50 ppm < xt < 1500 ppm.

[0106] We can have 25 ppm < xt < 50 ppm, or 50 ppm < xt < 100 ppm, or 200 ppm < xt

[0107] < 400 ppm, or 400 ppm< xt< 600 ppm, or 600 < xt< 800 ppm, or 800 ppm < xt< 1200 ppm, or 1200 ppm < xt < 1500 ppm. Over at least one of these ranges, the remanent polarization of the polymer is either of the same order, or 1% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 7.5% or more, or 10.0% or more, or 11.0% or more, or 12.0% or more, greater than the remanent polarization of P(VDF-TrFE) having the same proportion of T rFE:VDF. Over at least one of these intervals, the coercive field is either of the same order, or 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more lower than the coercive field of P(VDF-TrFE) having the same proportion of TrFE:VDF.

[0108] The third monomer may in particular be chlorotrifluoroethylene.

[0109] According to particular embodiments, the polymer according to the invention has a molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride of 27.5:72.5 to 32.5:67.5 and 5 ppm < xt < 5000 ppm. 10 ppm < xt < 1200 ppm is preferentially used, and even more preferentially 25 ppm.

[0110] < xt< 1000 ppm. We can have 25 ppm < xt < 50 ppm, 50 ppm < xt < 100 ppm, or 100 ppm < xt < 200 ppm, or 200 ppm < xt < 400 ppm, or 400 ppm < xt < 600, or 600 ppm < xt < 800 ppm, or 800 ppm < xt < 1000 ppm. Over at least one of these intervals, the remanent polarization of the polymer is either of the same order, or 1% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 7.5% or more, or 10.0% or more, or 11.0% or more, or 12.0% or more, greater than the remanent polarization of P(VDF-TrFE) having the same ratio of TrFE:VDF. Over at least one of these intervals, the coercive field is either of the same order, or 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more less than the coercive field of P(VDF-TrFE) having the same ratio of TrFE:VDF.

[0111] The third monomer may in particular be chlorotrifluoroethylene.

[0112] According to particular embodiments, the polymer according to the invention has a molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride of 28.5:71.5 to 31.5:68.5 and 5 ppm < xt < 5000 ppm. 10 ppm < xt < 1200 ppm is preferentially used, and even more preferentially 25 ppm < xt < 1000 ppm.

[0113] We can have 25 ppm < xt ^ 50 ppm, 50 ppm < xt < 100 ppm, or 100 ppm < xt < 200 ppm, or 200 ppm < xt < 400 ppm, or 400 ppm < xt < 600, or 600 ppm < xt < 800 ppm, or 800 ppm < Xi < 1000 ppm. Over at least one of these intervals, the remanent polarization of the polymer is either of the same order, or 1% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 7.5% or more, or 10.0% or more, or 11.0% or more, or 12.0% or more, greater than the remanent polarization of P(VDF-TrFE) having the same TrFE:VDF ratio. Over at least one of these intervals, the coercive field is either of the same order, or 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more less than the coercive field of P(VDF-TrFE) having the same TrFE:VDF ratio.

[0114] The third monomer may in particular be chlorotrifluoroethylene.

[0115] According to particular embodiments, the polymer according to the invention has a molar proportion of unit derived from trifluoroethylene relative to the unit derived from vinylidene fluoride of 32.5:67.5 to 50.0:50.0 and 5 ppm < xt < 5000 ppm. 10 ppm < xt < 1000 ppm is preferentially used, and 15 ppm < xt < 500 ppm is preferentially used.

[0116] We can have 15 ppm < xt < 25 ppm, 25 ppm < xt < 50 ppm, or 50 ppm < xt < 100 ppm, or 100 ppm < xt < 200 ppm, or 200 ppm < xt < 300, or 300 ppm < xt < 400 ppm, or 400 ppm < xt< 500 ppm, or 500 ppm < xt < 600 ppm. Over at least one of these intervals, the remanent polarization of the polymer is either of the same order, or 1% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more, or 7.5% or more, or 10.0% or more, or 11.0% or more, or 12.0% or more, greater than the remanent polarization of P(VDF-TrFE) having the same TrFE:VDF ratio. Over at least one of these intervals, the coercive field is either of the same order, or 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more less than the coercive field of P(VDF-TrFE) having the same TrFE:VDF ratio.

[0117] The third monomer may in particular be chlorotrifluoroethylene.

[0118] Manufacturing process

[0119] The polymer can be obtained according to methods known from the prior art.

[0120] It can in particular be prepared by radical polymerization according to a solution, suspension, emulsion or microemulsion polymerization process of vinylidene fluoride monomers, trifluoroethylene and one or more third-party monomers.

[0121] Preferably, the polymer is prepared by a suspension polymerization process. Indeed, it is known to those skilled in the art that for a given proportion of units derived from vinylidene fluoride and trifluoroethylene, it is the suspension polymerization process which is generally capable of providing the polymer with the highest remanent polarization.

[0122] Advantageously, the polymer is prepared by a suspension polymerization process carried out in water.

[0123] The polymer can in particular be implemented according to the method described in WO2016 / 055712 by adapting the proportions of monomers according to the present invention. This method successively comprises: - injecting into a reactor all of the monomers to be reacted;

[0124] - the initiation of polymerization of the monomers;

[0125] - a step (a) of continuing the polymerization of the monomers, during which a pressure drop in the reactor is compensated, in other words the pressure in the reactor is maintained at a substantially constant value; and,

[0126] - an optional step (b) during which the temperature is increased (without necessarily controlling the pressure).

[0127] Compensation for the pressure drop during step (a) makes it possible to avoid the significant slowdown in reaction kinetics which is observed in the absence of such compensation, and which leads to a significant limitation of the conversion rate, or to polymerization times incompatible with industrial productivity and capacity requirements.

[0128] To compensate for the pressure drop, one may consider using a variable volume reactor, the volume of which is reduced (preferably continuously) during step (a).

[0129] Alternatively, and more simply, a stream is injected into the reactor during step (a), preferably continuously, so as to compensate for the elimination of the polymerizing monomers. The composition of the stream is chosen so as not to interfere with the polymerization reaction. It is thus possible to inject a stream of water into the reactor, or a stream of any other liquid that is immiscible with the monomers and inert with respect to the polymerization.

[0130] The pressure drop in the reactor is preferably fully compensated. Alternatively, it is partially compensated, in which case some reduction in pressure in the reactor is still observed during step (a).

[0131] According to certain embodiments, the pressure during step (a) can be maintained substantially equal to a reference value of between 50 and 130 bars absolute, and preferably between 70 and 110 bars absolute.

[0132] According to certain embodiments, the temperature inside the reactor during step (a) is less than or equal to 55°C, and preferably less than or equal to 52°C. The increase in temperature during step (b) is advantageous in order to maximize the conversion rate and the consumption of the monomers and also in order to reduce the residual quantity of undecomposed initiator at the end of the reaction (the residual presence of the initiator not being favorable from the point of view of the purity and thermal stability characteristics of the product).

[0133] During step (b), pressure control can either continue or be stopped. In this case, during step (b), the pressure in the reactor generally decreases, while polymerization continues.

[0134] Initiation of the reaction can be achieved by adding a radical polymerization initiator, which may in particular be an organic peroxide such as a peroxydicarbonate. It is generally used in an amount of 0.1 to 10 g per kilogram of the total monomer loading. Preferably, the amount used may be 0.5 to 5 g / kg.

[0135] Generally, the initiation of the reaction as such is carried out by the combined action of an addition of the polymerization initiator and a rise in temperature, which is accompanied by a rise in pressure (the initiator can be added to the reactor after the monomers or before the monomers and before or after the rise in temperature).

[0136] Furthermore, it may be advantageous to add a suspending agent to the reaction medium. In particular, a cellulose derivative may be used, in particular a cellulose ether such as methylcellulose, ethylhydroxyethylcellulose, or hydroxypropylmethylcellulose, in an amount of 0.1 to 5 g per kilogram of the total monomer loading. Preferably, the amount used may be 0.3 to 1.5 g / kg.

[0137] Finally, according to certain embodiments, a chain length regulating agent may be added to the reaction medium. In particular, ethyl acetate, or diethyl carbonate, or an alcohol such as isopropanol, for example, may be used in an amount of 5 to 100 g per kilogram of the total monomer loading. Preferably, the amount used may be 10 to 40 g / kg.

[0138] Various processes for manufacturing trifluoroethylene are known. In particular, trifluoroethylene is obtained by hydrogenolysis of chlorotrifluoroethylene. Such a process is described, for example, in applications EP 2 819979 and EP 2 993213. At the end of the process, a distillation step makes it possible to recover pure trifluoroethylene, or, conversely, trifluoroethylene containing a small quantity of chlorotrifluoroethylene, depending on the distillation conditions.

[0139] It is also known to obtain trifluoroethylene by thermal decomposition of chlorodifluoromethane and chlorofluoromethane. Such a process is for example described in application EP 2 993 213.

[0140] In embodiments where the third monomer is chlorotrifluoroethylene, the trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene, and used in the reaction for preparing the polymer according to the invention, can advantageously be purified so as to contribute to the supply of chlorotrifluoroethylene in the polymerization reaction.

[0141] The trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene may in particular contribute to providing at least 25%, or at least 50%, or at least 60%, or at least 70%, or at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 95%, or 100% in moles of chlorotrifluoroethylene relative to the total number of moles of chlorotrifluoroethylene necessary to carry out the polymerization reaction according to the invention.

[0142] Trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene may in particular contain from 2 ppm to 5000 ppm, or from 5 ppm to 4000 ppm, or from 20 ppm to 3000 ppm, or from 50 ppm to 2500 ppm, or from 75 ppm to 1500 ppm of chlorotrifluoroethylene per mole of trifluoroethylene.

[0143] In some embodiments, the trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene may contain from 2 ppm to 75 ppm, or from 75 ppm to 150 ppm, or from 150 ppm to 250 ppm, or from 250 ppm to 500 ppm, or from 500 ppm to 1000 ppm, or from 1000 ppm to 1500 ppm, or from 1500 ppm to 2000 ppm, or from 2000 ppm to 2500 ppm, or from 2500 ppm to 3000 ppm, or from 3000 ppm to 3500 ppm, or from 3500 ppm to 4000 ppm, or from 4000 ppm to 4500 ppm, or from 4500 ppm to 5000 ppm of chlorotrifluoroethylene per mole of trifluoroethylene. According to certain embodiments, trifluoroethylene, in particular trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene, may have a purity greater than or equal to 95.0%, preferably greater than or equal to 98.0%, and extremely preferably greater than or equal to 99.0%. According to preferred embodiments, trifluoroethylene may have a purity greater than or equal to 99.5%.Trifluoroethylene may, for example, have a purity greater than or equal to 99.6%, or greater than or equal to 99.7%, or greater than or equal to 99.8%, or greater than 99.9%.

[0144] Films may be prepared using the polymer of the invention, for example, by solvent casting or extrusion or hot melt pressing. For example, a polymer powder may be dissolved in methyl ethyl ketone. The solution may be poured onto a plate and then dried. The dried film may be annealed at a temperature below the melting temperature and above the Curie temperature of the polymer to optimize its crystallinity.

[0145] These films may have a thickness of 1 pm to 50 pm, preferably of 2 pm to 25 pm, and extremely preferably of 5 pm to 15 pm.

[0146] In some embodiments, films having an intermediate thickness of 15 to 25 μm may be prepared and then may be stretched by a factor of 2 to 10, preferably 5 to 7 to obtain a thickness of 1 μm to 5 μm.

[0147] Due to the higher remanent polarization of at least some of the polymers according to the invention compared to P(VDF-TrFE) of the same VDF:TrFE composition, films of lower thickness can be produced with equal performance. Conversely, at equal film thickness, the polymer films according to the invention have better performance than P(VDF-TrFE) films of the same VDF:TrFE composition.

[0148] Due to the lower coercive field of at least some of the polymers according to the invention compared to P(VDF-TrFE) of the same VDF:TrFE composition, films of a given thickness can be polarized to a lower electric field.

[0149] The polymers according to the invention can be used in the manufacture of electronic objects, in particular sensors, actuators, memories, electrocaloric devices or any other application exploiting the ferroelectric properties of the material and in particular a high value of remanent polarization.

[0150] The following examples disclose polymers according to the invention which have a higher remanent polarization and a lower coercive field compared to P(VDF-TrFE) having the same VDF:TrFE proportion.

[0151] Examples

[0152] In the experiments performed below, a high purity trifluoroethylene not containing CTFE was used to implement comparative examples #1, #8 and #12. It is denoted below as type “A” trifluoroethylene.

[0153] A trifluoroethylene, obtained by a process of hydrogenolysis of chlorotrifluoroethylene, containing 98 ppm of chlorotrifluoroethylene relative to the number of moles of trifluoroethylene, was used to implement examples #2, #3, #9 and #15. It is denoted below as trifluoroethylene of type “B”.

[0154] A trifluoroethylene, obtained by a process of hydrogenolysis of chlorotrifluoroethylene, containing 2010 ppm of chlorotrifluoroethylene relative to the number of moles of trifluoroethylene, was used to implement the other examples. It is denoted below as trifluoroethylene of type "C".

[0155] The chlorofluoroethylene already present in the trifluoroethylene was taken into account for the calculation of the total chlorotrifluoroethylene introduced into the reaction medium. The total chlorofluoroethylene therefore corresponds to the sum of the masses of the chlorofluoroethylene present in small quantities in the trifluoroethylene and the chlorofluoroethylene introduced additionally.

[0156] The vinylidene fluoride and trifluoroethylene weights correspond to the actual weights introduced of each species. Example #1

[0157] Vinylidene fluoride (767 g) was reacted with type A trifluoroethylene (253 g) in a 3.0 L reactor containing deionized water (1670 g), methylhydroxypropyl cellulose (0.60 g), and propyl peroxydicarbonate (1.53 g).

[0158] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction resulted in a drop in reactor pressure, which was compensated by continuous injection of water (980 g). When all the water to compensate for the pressure drop had been injected, the pressure dropped to 65 bars. The reactor was then heated to 65°C, with the pressure continuing to drop. When the pressure reached 38 bars, the reactor was allowed to cool and then drained. The collected reaction mixture was filtered and the resulting cake was washed with water 5 times before being dried in an oven at 70°C to constant weight.

[0159] Vinylidene fluoride (716 g) was reacted with type A trifluoroethylene (305 g) in a 3.4 L reactor containing deionized water (1730 g), methylhydroxypropyl cellulose (0.60 g), and propyl peroxydicarbonate (1.6 g).

[0160] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure which was compensated by continuous injection of water (930 g). When all the water to compensate for the pressure drop was injected, the pressure dropped to 65 bars. The final steps are the same as for example #1.

[0161] Vinylidene fluoride (700 g) was reacted with trifluoroethylene type A (386 g) in a 3.4 L reactor containing deionized water (1680 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.7 g). The reactor was then heated to a temperature of 50°C and a pressure of 75 bar as quickly as possible to initiate the reaction. The start of the reaction resulted in a drop in reactor pressure which was compensated by continuous injection of water (870 g). When all the water to compensate for the pressure drop had been injected, the pressure had dropped to 65 bar. The final steps were the same as for Example #1.

[0162] Example #2

[0163] Vinylidene fluoride (767 g) was reacted with trifluoroethylene (253 g; type B) in a 3.4 L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g), and propyl peroxydicarbonate (1.53 g). The reaction medium also contained 0.035 g of CTFE supplied by the type B trifluoroethylene.

[0164] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure which was compensated by continuous injection of water (980 g). When all the water to compensate for the pressure drop was injected, the pressure dropped to 65 bars. The reactor was then heated to 65°C, with the pressure continuing to drop. The final steps are the same as for example #1.

[0165] Vinylidene fluoride (767 g) was reacted with trifluoroethylene (253 g, type B) and chlorotrifluoroethylene (total amount of chlorotrifluoroethylene: 0.29 g, of which 0.035 g was contributed by type B trifluoroethylene) in a 3.4 L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.53 g).

[0166] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure which was compensated by continuous injection of water (980 g). When all the water to compensate for the pressure drop was injected, the pressure dropped to 65 bars. The final steps are the same as for example #1.

[0167] Example #9

[0168] Vinylidene fluoride (712 g) was reacted with trifluoroethylene (310 g; type B) in a 3.0 L reactor containing demineralized water (1730 g), methylhydroxypropyl cellulose (0.60 g), and propyl peroxydicarbonate (1.6 g). The reaction medium also contained 0.043 g of CTFE supplied by the type B trifluoroethylene.

[0169] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure which was compensated by continuous injection of water (930 g). When all the water to compensate for the pressure drop was injected, the pressure dropped to 65 bars. The final steps are the same as for example #1.

[0170] Example #15

[0171] Vinylidene fluoride (700 g) was reacted with trifluoroethylene (385 g; type B) and chlorotrifluoroethylene (total amount of chlorotrifluoroethylene: 0.47 g, of which 0.054 was contributed by type B trifluoroethylene) in a 3.4 L reactor containing demineralized water (1680 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.7 g).

[0172] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure which was compensated by continuous injection of water (870 g). When all the water to compensate for the pressure drop was injected, the pressure dropped to 65 bars. The final steps are the same as for example #1.

[0173] Example #5

[0174] Vinylidene fluoride (767 g) was reacted with trifluoroethylene (253 g; type C) in a 3.4 L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g), and propyl peroxydicarbonate (1.53 g). The reaction medium also contained 0.72 g of CTFE supplied by the type C trifluoroethylene.

[0175] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure which was compensated by continuous injection of water (980 g). When all the water to compensate for the pressure drop was injected, the pressure dropped to 65 bars. The reactor was then heated to 65°C, with the pressure continuing to drop. The final steps are the same as for example #1.

[0176] Example #4

[0177] Vinylidene fluoride (767 g) was reacted with trifluoroethylene (253 g; type C) and chlorotrifluoroethylene (total amount of chlorotrifluoroethylene: 0.86 g, including 0.72 g of CTFE contributed by type C trifluoroethylene) in a 3.4 L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.53 g).

[0178] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure which was compensated by continuous injection of water (980 g). When all the water to compensate for the pressure drop was injected, the pressure dropped to 65 bars. The reactor was then heated to 65°C, with the pressure continuing to drop. The final steps are the same as for example #1.

[0179] Vinylidene fluoride (767 g) was reacted with trifluoroethylene (253 g; type C) and chlorotrifluoroethylene (total amount of chlorotrifluoroethylene: 1.61 g, including 0.72 g of CTFE contributed by type C trifluoroethylene) in a 3. L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.53 g)-

[0180] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure which was compensated by continuous injection of water (980 g). When all the water to compensate for the pressure drop was injected, the pressure dropped to 65 bars. The reactor was then heated to 65°C, with the pressure continuing to drop. The final steps are the same as for example #1.

[0181] Vinylidene fluoride (765 g) was reacted with trifluoroethylene (256 g; type C) and chlorotrifluoroethylene (total amount of chlorotrifluoroethylene: 0.80 g, of which 0.73 g was contributed by type C trifluoroethylene) in a 3.4 L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.53 g).

[0182] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure which was compensated by continuous injection of water (980 g). When all the water to compensate for the pressure drop was injected, the pressure dropped to 65 bars. The reactor was then heated to 65°C, with the pressure continuing to drop. The final steps are the same as for example #1.

[0183] Vinylidene fluoride (714 g) was reacted with trifluoroethylene (306 g; type C) in a 3.4 L reactor containing demineralized water (1730 g), methylhydroxypropyl cellulose (0.60 g), and propyl peroxydicarbonate (1.60 g). The reaction medium also contained 0.87 g of CTFE supplied by the type C trifluoroethylene.

[0184] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure, which was compensated by continuous injection of water (930 g). When all the water to compensate for the pressure drop had been injected, the pressure had dropped to 65 bars. The reactor was then heated to 65°C, with the pressure continuing to drop. The final steps are the same as for example #1.

[0185] Example #11

[0186] Vinylidene fluoride (714 g) was reacted with trifluoroethylene (306 g; type C) and chlorotrifluoroethylene (total amount of chlorotrifluoroethylene: 0.92 g, of which 0.87 g was contributed by type C trifluoroethylene) in a 3.0 L reactor containing demineralized water (1730 g), methylhydroxypropyl cellulose (0.60 g), and propyl peroxydicarbonate (1.6 g).

[0187] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure, which was compensated by continuous injection of water (930 g). When all the water to compensate for the pressure drop had been injected, the pressure had dropped to 65 bars. The reactor was then heated to 65°C, with the pressure continuing to drop. The final steps are the same as for example #1.

[0188] Example #13

[0189] Vinylidene fluoride (703 g) was reacted with trifluoroethylene (385 g; type C) and chlorotrifluoroethylene (total amount of chlorotrifluoroethylene: 1.49 g, of which 1.10 g was contributed by type C trifluoroethylene) in a 3.4 L reactor containing demineralized water (1680 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.7 g).

[0190] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction resulted in a drop in reactor pressure, which was compensated by continuous injection of water (870 g). When all the water to compensate for the pressure drop had been injected, the pressure had dropped to 65 bars. The reactor was then heated to 65°C, with the pressure continuing to drop. The final steps are the same as for example #1. Example #14

[0191] Vinylidene fluoride (703 g) was reacted with trifluoroethylene (385 g; type C) and chlorotrifluoroethylene (total amount of chlorotrifluoroethylene: 40.15 g, of which 1.10 g was contributed by type C trifluoroethylene) in a 3.4 L reactor containing demineralized water (1680 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.7 g).

[0192] The reactor was then brought to a temperature of 50°C and a pressure of 75 bars as quickly as possible to initiate the reaction. The start of the reaction results in a drop in reactor pressure which was compensated by continuous injection of water (870 g). When all the water to compensate for the pressure drop was injected, the pressure dropped to 65 bars. The reactor was then heated to 65°C, with the pressure continuing to drop. The final steps are the same as for example #1.

[0193] Characterization of

[0194] Determination of the molar proportion TrFE / (VDF+TrFE) in the polymer

[0195] The molar ratio TrFE / (VDF+TrFE) in the polymer, denoted XTPFE, was determined by proton NMR. The polymer was dissolved in an appropriate deuterated solvent and the NMR spectrum was recorded on a FT-NMR spectrometer equipped with a multi-nuclear probe. The hydrogen nucleus of the TrFE unit (CHF-CF2) gives a distinctive signal at about 5 ppm, while the 2 hydrogen atoms of the CH2 group of the VDF units give a centered cluster at 3 ppm. The relative integration of the two signals gives the relative abundance of the two monomers, i.e., their molar ratio.

[0196] Determination of the molar proportion CTFE / (VDF+TrFE) in the polymer

[0197] The molar proportion CTFE / (VDF+TrFE) in the polymer, denoted xt, can be determined by measuring the chlorine content by elemental analysis.

[0198] Due to the reactivity of CTFE compared to VDF and TrFE, and the quantities introduced into the reaction medium, it can also be considered that all of the CTFE introduced into the reaction medium is also introduced into the structure of the polymer.

[0199] Determination of remanent polarization and coercive field

[0200] Polymer films were prepared from a 14 wt% solution in 0.2 μm filtered methyl ethyl ketone. The solution was coated onto a glass plate and allowed to dry for 12 hours. The films were peeled off the surface and placed in a vacuum oven at 80°C for 4 hours for solvent evaporation. The films were then placed in an oven for 1 hour at 15°C below the polymer melting temperature as measured by differential scanning calorimetry.

[0201] The ferroelectric characteristics of the material, in particular its remanent polarization and its coercive field were measured at 25°C at an alternating electric field (sinusoidal signal with a period of 18 s) with a maximum amplitude equal to 150 V / pm.

[0202] The remanent polarization, Pr, is defined as the value of the polarization measured at zero field. The coercive field (Ec) is defined as the value of the applied field for which the measured polarization is zero.

[0203] Table 1 lists all the characterization measures for films of composition #1-#15:

[0204] Table 1

[0205] Figure 1 corresponds to the polarization curves as a function of the electric field for a film prepared with the polymer according to comparative example #1 (“■”) and according to example #6 (“▲”). It is visible that the hysteresis curve for the polymer according to the invention is narrower (E clower) and higher (P r higher) than for the comparative polymer.

[0206] Figure 2 represents the remanent polarization of films of composition #1-#13 and #15 as a function of the proportion of CTFE in the polymer.

[0207] From Table 1 and Figure 2, at least the following points can be observed:

[0208] ■ The remanent polarization increases in the polymer for increasing XTPFE, which was known to those skilled in the art (compare for example Pr of comparative examples #1, #8, #12).

[0209] ■ An excessive addition of CTFE in the structure of a P(VDF-T rFE) transforms the polymer with ferroelectric properties into a ferroelectric relaxor, which was known to those skilled in the art (see the very low Pr of comparative example #14 compared to that of comparative example #12)

[0210] ■ The remanent polarization of the polymer having a given TrFE:VDF proportion increases rapidly from the first ppm or tens of ppm in CTFE in the polymer (see for example Pr of example #2 to compare to Pr of comparative example #1, or Pr of example #9 to compare to Pr of comparative example #8). ■ The remanent polarization of the polymer having a given TrFE DF proportion remains high, notably above the remanent polarization of the corresponding P(VDF-TrFE) for xt of the order of 1000 ppm and more.

[0211] ■ Examples #2-#7, #9-#11 and #13-#15 have higher remanent polarization and lower coercive field than the remanent polarization and coercive field values ​​of the corresponding P(VDF-TrFE) (comparative examples #1, #8 and #12 respectively).

Claims

Claims 1. A polymer consisting essentially of, or consisting of, repeating units derived from vinylidene fluoride (VDF), trifluoroethylene (TrFE), and at least one third monomer other than vinylidene fluoride and trifluoroethylene, having the chemical formula: CXiX2=CX3Z (I) wherein each of Xi, X2, X3is independently selected from H, F and alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I, the TrFE:VDF molar ratio between the number of moles of unit derived from trifluoroethylene and that of unit derived from vinylidene fluoride in the polymer being from 14.0:86.0 to 50.0:50.0, said repeating unit derived from said at least one third monomer having a mole fraction xt greater than or equal to 1 ppm and less than or equal to 5000 ppm, relative to the total number of moles of units derived from VDF and TrFE in the polymer.

2. Polymer according to claim 1, wherein said at least one third monomer comprises at least one monomer chosen from the group consisting of chlorotrifluoroethylene (CTFE), chlorodifluoroethylene, in particular 1-chloro-2,2-difluoroethylene (CDFE), chlorofluoroethylene, in particular 1,1-chlorofluoroethylene (CFE), and their mixture.

3. Polymer according to claim 2, comprising a single third monomer chosen from the group consisting of: chlorotrifluoroethylene (CTFE), chlorodifluoroethylene (CDFE), in particular 1-chloro-2,2-difluoroethylene (CDFE), and chlorofluoroethylene, in particular 1,1-chlorofluoroethylene (CFE).

4. A polymer according to any one of claims 1 to 3, wherein said at least one third monomer is chlorotrifluoroethylene (CTFE).

5. Polymer according to any one of the preceding claims, in which xt> 5 ppm, preferably xt^ 10 ppm, and more preferably xt> 20 ppm.

6. Polymer according to any one of the preceding claims, wherein xt > 400 ppm.

7. Polymer according to any one of the preceding claims, wherein xt> 600 ppm.

8. Polymer according to any one of the preceding claims, in which xt < 4000 ppm, preferably xt < 3000 ppm, and more preferably xt s 2500 ppm.

9. Polymer according to any one of the preceding claims, in which xt s 1000 ppm.

10. A polymer according to any preceding claim, wherein the TrFE:VDF molar ratio in the polymer is from 15.0:85.0 to 40.0:60.0, or from 16.0:84.0 to 35.0:65.0, or from 17.5:82.5 to 27.5:72.

5.

11. Polymer according to any one of the preceding claims, having a melt index at 230°C under a load of 10 kg, as measured according to ASTM D1238-10, of 0.1 g / 10 min to 100 g / 10 min, preferably of 0.5 g / 10 min to 50 g / 10 min and more preferably of 1 g / 10 min to 10 g / 10 min.

12. Polymer according to any one of the preceding claims, in which the TrFE:VDF molar ratio in the polymer is from 17.5:82.5 to 22.5:77.5, and preferably 10 ppm < xt < 3000 ppm, more preferably 200 ppm < xt < 2500 ppm, and more preferably 400 ppm < xt < 2000 ppm 13. Polymer according to any one of the preceding claims, in which the TrFE:VDF molar ratio in the polymer is from 20.1:79.9 to 20.9:79.1, and preferably 10 ppm < xt < 3000 ppm, more preferably 200 ppm < xt < 2500 ppm, and more preferably 400 ppm < xt < 2000 ppm.

14. Polymer according to any one of the preceding claims obtained by a suspension polymerization process, preferably in water.

15. Film essentially comprising or consisting of the polymer according to any one of claims 1 to 14.

16. Use of a third-party monomer having the chemical formula: CXiX2=CX3Z (I) wherein each of Xi, X2, X3is independently selected from H, F and alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I, as a termonomer in the structure of a polymer essentially consisting of repeating units derived from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) in a molar proportion xt of 1 ppm to 5000 ppm relative to the total number of moles of units derived from VDF and TrFE in the polymer, the TrFE:VDF molar ratio in the polymer between the TrFE-derived unit and that of the VDF being from 14.0:86.0 to 50.0:50.0, to increase the remanent polarization.

17. Use of a third-party monomer having the chemical formula: CXiX2=CX3Z (I) wherein each of Xi, X2, X3is independently selected from H, F and alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I, as a termonomer in the structure of a polymer essentially consisting of repeating units derived from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) in a molar proportion xt of 1 ppm to 5000 ppm relative to the total number of moles of units derived from VDF and TrFE in the polymer, the molar ratio TrFE:VDF in the polymer between the unit derived from TrFE and that derived from VDF being from 14.0:86.0 to 50.0:50.0, to reduce the coercive field thereof.

18. Use according to claim 16 or according to claim 17, in which the third monomer is chosen from the group consisting of: chlorotrifluoroethylene (CTFE), chlorodifluoroethylene (CDFE), in particular 1-chloro-2,2-difluoroethylene (CDFE), and chlorofluoroethylene, in particular 1,1-chlorofluoroethylene (CFE).

19. Use according to any one of claims 16 to 17, in which the third monomer is chlorotrifluoroethylene.

20. Use according to any one of claims 16 to 19, wherein xt > 25 ppm.

21. Use according to any one of claims 16 to 20, wherein xt < 2500 ppm.

22. Use according to any one of claims 16 to 21, wherein xt 2,800 ppm.

23. Use of trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene in a process for manufacturing a polymer according to any one of claims 1 to 14, wherein said at least one third monomer comprises chlorotrifluoroethylene, said manufacturing process comprising a polymerization reaction step between vinylidene fluoride (VDF), trifluoroethylene (TrFE) and chlorotrifluoroethylene (CTFE).

24. Use according to claim 23, wherein the trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene comprises from 2 ppm to 5000 ppm of chlorotrifluoroethylene per mole of trifluoroethylene.

25. Use according to claim 24, wherein the trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene comprises from 1500 ppm to 4500 ppm of chlorotrifluoroethylene per mole of trifluoroethylene.

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