Ferroelectric polymer

Abstract

The invention relates to a polymer essentially made up of, or consisting of, repeating motifs from vinylidene fluoride (VDF), trifluoroethylene (TrFE), and at least one third monomer different from vinylidene fluoride and trifluoroethylene, the TrFE:VDF molar ratio between the number of moles of motifs from trifluoroethylene and those of motifs from vinylidene fluoride in the polymer being from 14.0:86.0 to 50.0:50.0, 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 motifs from VDF and TrFE in the polymer.

Description

Title of the invention: Ferroelectric polymer technical field

[0001] The invention relates to the field of ferroelectric polymers.

[0002] The invention relates more particularly to copolymers, in the broad sense, comprising repeating motifs derived from vinylidene fluoride and trifluoroethylene. Previous art

[0003] The copolymer consisting of repeating units from vinylidene fluoride and trifluoroethylene, poly(VDF-co-TrFE), also denoted P(VDF-TrFE), is a polymer known for its ferroelectric properties. It is notably characterized by a broad hysteresis loop in the electric polarization curve as a function of the applied electric field.

[0004] Applying to the P(VDF-TrFE) an electric field with a value greater than a characteristic field called coercive field (Ec), makes it possible to orient dipoles formed by CF bonds in the same direction, in a sufficiently stable manner, so as to obtain a remanent polarization (Pr) with zero electric field.

[0005] There is currently a need to supply ferroelectric polymers having a higher remanent polarization, in order to increase the sensitivity of electronic devices, for example a sensor or a memory, incorporating these materials.

[0006] Furthermore, when a ferroelectric material has a high coercive field, it is then necessary to apply significant voltages to it in order to polarize it, which leads to increased 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.

[0007] 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, into the crystal structure of P(VDF-TrFE), to decrease the size of the polar domains so as to transform the copolymer with ferroelectric properties into a terpolymer with "ferroelectric relaxer" properties. Ferroelectric relaxer polymers are characterized in particular by a much narrower hysteresis loop of the electric polarization curve as a function of the applied electric field than the hysteresis loop of ferroelectric polymers: they therefore have a considerably lower coercive field but also a lower remanent polarization than the ferroelectric polymers. Objectives of the invention

[0008] The objective of the invention is to provide a polymer with advantageous ferroelectric properties, in particular ferroelectric properties comparable to or improved compared with P(VDF-TrFE).

[0009] An objective of the invention is, according to at least some embodiments, to provide a polymer having a high remanent polarization, in particular a remanent polarization comparable to or higher than P(VDF-TrFE).

[0010] An objective of the invention is, according to at least some embodiments, to provide a polymer having a sufficiently low coercive field, in particular a coercive field of the same order, or lower than P(VDF-TrFE).

[0011] An objective of the invention is, according to at least some embodiments,

[0012] to provide a polymer having a lower coercive field and a higher remanent polarization than P(VDF-TrFE).

[0013] Another objective of the invention is, according to at least some embodiments, to provide a manufacturing process less expensive than that of the manufacture of P(VDF-TrFE), to obtain a polymer having at least ferroelectric properties comparable to those of P(VDF-TrFE).

[0014] Another objective of the invention is to be able to provide electronic devices incorporating these materials, in particular in the form of films. Summary of the invention

[0015] The invention relates to a polymer essentially made up 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:

[0016] CX!X2=CX3Z (I)

[0017] wherein each of the Xb X2, X3 is independently selected from H, F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I,

[0018] the TrFE:VDF molar ratio between the number of moles of trifluoroethylene motif and that of vinylidene fluoride motif in the polymer being from 14.0:86.0 to 50.0:50.0,

[0019] said repeating motif from said at least one third monomer having a mole fraction xt greater than or equal to Ippm and less than or equal to 5000 ppm, relative to the total number of moles of motifs from VDF and TrFE in the polymer.

[0020] Given that the addition of a few percent of a third monomer, such as chlorotrifluoroethylene, or chlorofluoroethylene, or even chlorodifluoroethylene, to P(VDF-TrFE) transforms the polymer with ferroelectric properties into a polymer with ferroelectric relaxer properties, having lower crystallinity and lower remanent polarization than P(VDF-TrFE). A person skilled in the art would have expected that the introduction of the third monomer to P(VDF-TrFE), at a mole fraction of 1 ppm to 5000 ppm, would also lead to a decrease in ferroelectric performance, in particular a decrease in the polymer's remanent polarization.

[0021] On the contrary, the inventors surprisingly discovered that the presence of the third monomer at a mole fraction of 1 ppm to 5000 ppm in the polymer at least preserved, and even preferentially improved, the polymer's ferroelectric performance.

[0022] More specifically, the inventors discovered that a content of Ippm to 5000 ppm of third monomer in the polymer made it possible to maintain, and preferably increase, the remanent polarization of the polymer.

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

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

[0025] According to certain embodiments, each of the Xb X2, X3 in the chemical formula (I) is independently chosen 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 l-chloro-2,2-difluoroethylene (CDFE), chlorofluoroethylene, in particular 1,1-chlorofluoroethylene (CFE), and mixtures thereof.

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

[0028] According to some embodiments, said at least one third monomer is chlorotrifluoroethylene (CTFE).

[0029] According to some embodiments, xt > 5 ppm, preferably xt > 10 ppm, and more preferably xt > 20 ppm.

[0030] According to some embodiments, xt < 4000 ppm, preferably xt < 3000 ppm, and more preferably xt < 2500 ppm.

[0031] According to some embodiments, xt < 1000 ppm.

[0032] According to 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.

[0033] According to certain embodiments, the polymer has a melt flow index at 230°C under a 10 kg load, as measured according to ASTM D1238-10, of 0.1 g / 10 min at 100 g / 10 min, preferably from 0.5 g / 10 min to 50 g / 10 min and even 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

[0035] preferably 10 ppm < xt < 3000 ppm, and even more preferably

[0036] 100 ppm < xt < 2500 ppm.

[0037] According to certain embodiments, the TrFE:VDF molar ratio in the polymer is from 20.1:79.9 to 20.9:79.1, and

[0038] preferably 10 ppm < xt < 3000 ppm, and even more preferably 100 ppm < xt < 2500 ppm.

[0039] According to certain embodiments, the polymer according to any one of the preceding claims is obtained by a suspension polymerization process, preferably in water.

[0040] The invention also relates to a film comprising essentially or made up of the polymer according to the invention.

[0041] Furthermore, the invention relates to the use of a third monomer having the chemical formula:

[0042] CXiX2=CX3Z (I)

[0043] wherein each of the Xb X2, X3 is independently selected from H, F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I,

[0044] as a termonomer in the structure of a polymer essentially consisting of repeating motifs from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) in molar proportions xt from 1 ppm to 5000 ppm relative to the total number of moles of motifs from VDF and TrFE in the polymer,

[0045] the TrFE:VDF molar ratio in the polymer between the TrFE motif and the VDF motif being from 14.0:86.0 to 50.0:50.0,

[0046] to increase its remanent polarization. The remanent polarization can 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 the P(VDF-TrFE) having the same proportion in TrFE:VDF.

[0047] Furthermore, the invention relates to the use of a third monomer having the chemical formula:

[0048] CX^CXsZ (I)

[0049] wherein each of the Xb X2, X3 is independently selected from H, F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I,

[0050] as a termonomer in the structure of a polymer essentially consisting of repeating motifs derived from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) in molar proportions xt from 1 ppm to 5000 ppm relative to the total number of moles of motifs derived from VDF and TrFE in the polymer,

[0051] The TrFE:VDF molar ratio in the polymer between the TrFE motif and the VDF motif is from 14.0:86.0 to 50.0:50.0, in order to reduce its coercive field. The coercive field can 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 the P(VDF-TrFE) having the same TrFE:VDF proportion.

[0052] According to advantageous embodiments, the invention relates to the use of a third monomer having the chemical formula:

[0053] CX!X2=CX3Z (I)

[0054] wherein each of the Xb X2, X3 is independently selected from H, F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I,

[0055] as a termonomer in the structure of a polymer essentially consisting of repeating motifs from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) in molar proportions xt from 1 ppm to 5000 ppm relative to the total number of moles of motifs from VDF and TrFE in the polymer,

[0056] the molar ratio TrFE:VDF in the polymer between the motif from TrFE and that from VDF being from 14.0:86.0 to 50.0:50.0, to increase its remanent polarization and to decrease its coercive field.

[0057] 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).

[0058] 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. Detailed description of the invention List of Figures

[0059] Fig. 1 represents superimposed the curves: polarization (mC / m2) as a function of the applied electric field (V / pm), for comparative example #1 (mark: “■”) and for example 6 (mark: “▲”).

[0060] Fig. 2 represents the remanent polarization Pr (mC / m2) as a function of the proportion xt in CTFE for experimental results #1 to #15. Different marks were used to differentiate samples having a molar proportion of TrFE / (VDF+TrFE) of about 20% (mark “■”), about 25% (mark “▲”) and about 30% (mark “•”). Definitions

[0061] The term "copolymer," in its broad sense, refers to a polymer resulting from the copolymerization of at least two chemically different types of monomers, called co-monomers. A copolymer, in its broad sense, comprises at least two types of repeating units, the (at least two) types being determined by different chemical formulas. It may, for example, be formed of two, three, or four types of repeating units. A copolymer, in its strict sense, is formed of exactly two types of repeating units, such as P(VDF-TrFE).

[0062] The term "terpolymer," in a broad sense, refers to a polymer resulting from the copolymerization of at least three types of chemically different monomers. A ter-polymer, in a strict sense, is formed of exactly three types of repeating units, such as P(VDF-TrFE-CTFE).

[0063] The term "polymer essentially consisting of repeating motifs" means that the polymer comprises at least 99% by moles, or at least 99.5% by moles, or at least 99.9% by moles of these motifs relative to the total number of moles of motifs constituting the polymer.

[0064] The term "polymer consisting of repeating motifs" means that the polymer comprises more than 99.9%, in particular 100%, by moles of these motifs relative to the total number of moles of motifs constituting the polymer.

[0065] In all the ranges stated, the limits are included unless otherwise stated.

[0066] The term "monomer motif" refers to the repeating unit derived directly from that monomer by polymerization. For example, the motif derived from chloro-trifluoroethylene: C(F)(C1)=CF2 is: -C(F)(C1)-CF2-. The motif derived from trifluoroethylene: C(F)(H)=CF2 is: -C(F)(H)-CF2-, etc.

[0067] The term "approximately a numerical value" means that numerical value plus or minus 5%.

[0068] The term "Curie temperature" refers to the temperature at which a ferroelectric to paraelectric crystal structure transition, known as the Curie transition, occurs. The Curie temperature of a ferroelectric polymer therefore defines a maximum operating temperature beyond which the polymer loses its ferroelectric properties, unless further low-temperature polarization is performed. It can be determined, for example, by Differential Calorimetry at Scanning (DSC), such 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, such as the temperature corresponding to the maximum of the dielectric permittivity peak during heating at 10°C / min at a frequency of 1kHz.

[0069] The term "melting temperature" refers to the temperature at which the crystalline structure transitions from a solid to a liquid state. It can be determined, for example, by Differential Scanning Calorimetry (DSC), as the maximum temperature of the endotherm corresponding to this transition, during the first or second heating, preferably during the second heating, at 10°C / min. Terpolymer according to the invention

[0070] The polymer according to the invention is essentially made up of, or made up of, repeating motifs derived from vinylidene fluoride (VDF), trifluoroethylene (TrFE) and at least one third monomer, different from vinylidene fluoride and trifluoroethylene.

[0071] The third monomer has the following chemical formula:

[0072] CX1X2=CX3Z (I)

[0073] wherein each of the Xb X2, X3 is independently selected from H, F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and wherein Z is selected from Cl, Br, and I.

[0074] The polymer may comprise one or more different third monomers. In some embodiments, the polymer comprises several different third monomers. In particular, the polymer may comprise CTFE and at least one other third monomer, with CTFE representing at least 50% by mole relative to the total number of moles of third monomers. 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 monomers.

[0075] According to some embodiments, Z in the chemical formula (I) is Cl.

[0076] According to certain embodiments, each of the Xb X2, X3 in the chemical formula (I) is independently chosen from H and F.

[0077] According to some embodiments, Z in the chemical formula (I) is Cl and each of the Xi, X2, X3 in the chemical formula (I) is independently chosen from H and F. The third monomer, or where applicable one of the third monomers, may be chosen from the group consisting of: chlorotrifluoroethylene (CTFE), 1,1-chlorofluoroethylene (CFE) and 1-chloro-2,2-difluoroethylene (CDFE).

[0078] According to certain embodiments, said at least one third monomer may be: chlorotrifluoroethylene (CTFE), 1,1-chlorofluoroethylene (CFE), l-chloro-2,2-difluoroethylene (CDFE), or a mixture thereof.

[0079] According to some embodiments, the third monomer can be: chlorotrifluoroethylene (CTFE) or 1,1-chlorofluoroethylene (CFE).

[0080] According to particular embodiments, the third monomer may be: 1,1-chlorofluoroethylene (CFE). Thus, the polymer according to the invention may be a tert-polymer, essentially composed of, or composed of, repeating units derived from VDF, TrFE and CFE.

[0081] 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 composed of, or composed 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 later. Thus, even in embodiments where the polymer according to the invention has ferroelectric properties comparable to those of P(VDF-TrFE), particularly for a high xt value, its manufacturing process has a lower cost than that of manufacturing P(VDF-TrFE) using extremely pure and expensive TrFE.

[0082] The polymer according to the invention has a molar proportion of trifluoroethylene motif relative to vinylidene fluoride motif of 14.0:86.0 to 50.0:50.0.

[0083] According to certain embodiments, the TrFE:VDF molar ratio of trifluoroethylene motif to vinylidene fluoride motif in the polymer is 50.0:50.0 to 40.0:60.0, or 40.0:60.0 to 32.5:67.5, or 32.5:67.5 to 27.5:72.5, or 27.5:72.5 to 22.5:77.5, or 22.5:77.5 to 21.5:78.5, or 21.5:78.5 to 21.0:79.0, or 21.0:79.0 to 20.5:79.5, or 20.5:79.5 to 20.0:80.0, or 20.0:80.0 at 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.

[0084] According to advantageous embodiments, the molar proportion of the motif from trifluoroethylene relative to the motif from vinylidene fluoride in the polymer is from 17.5:82.5 to 27.5:72.5.

[0085] According to highly advantageous embodiments, the mole ratio of trifluoroethylene motif to vinylidene fluoride motif in the polymer is 21.5:78.5 to 18.5:81.5. Indeed, it is known for P(VDF-TrFE) that remanent polarization increases as the proportion of TrFE decreases and that the polymer loses its ferroelectric properties at a TrFE:VDF mole ratio of approximately 14.0:86.0. Furthermore, for a TrFE:VDF mole ratio in the polymer of 21.5:78.5 to 18.5:81.5, the Curie temperature is sufficiently far from the polymer's melting temperature and thus allows for easier annealing between these points. two temperatures, as explained later.

[0086] The molar proportion of the trifluoroethylene motif relative to the vinylidene fluoride motif 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 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, 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 to 18.7:81.3, or from 18.7:81.3 to 18.6:81.4, or from 18.6:81.4 to 18.5:81.5.

[0087] According to particular embodiments, the molar proportion in pattern resulting from sorting fluoroethylene relative to the pattern from vinylidene fluoride is 20.9:79.1 to 20.8:79.2, or 20.8:79.2 to 20.7:79.3, or 20.7:79.3 to 20.6:79.4, or 20.6:79.4 to 20.5:79.5, or 20.5:79.5 to 20.4:79.6, or 20.4:79.6 to 20.3:79.7, or 20.3:79.7 to 20.2:79.8, or 20.2:79.8 to 20.1:79.9.

[0088] The polymer according to the invention has a mole fraction xt of third monomer(s), expressed in parts per million (ppm), greater than or equal to 1 ppm and less than or equal to 5000 ppm. Indeed, a sharp increase in remanent polarization has been observed from the first ppm, and / or tens of ppm of third monomer(s) in the polymer. Considering increasing quantities of third monomer, on the order of hundreds of ppm or a few thousand ppm, the remanent polarization continues to increase until it reaches a plateau before decreasing again.

[0089] In embodiments where the polymer comprises several third monomers, the fraction xt expresses the sum of the mole fractions of all the third monomers.

[0090] We preferentially have xt> 5 ppm, more preferably xt> 10 ppm, and even more preferably xt> 20 ppm.

[0091] For example, we can have xt> 25ppm, xt> 30ppm, or xt>40 ppm, or xt>50 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>800 ppm.

[0092] We preferentially have xt < 4000 ppm, more preferably xt < 3000 ppm, and even more preferably xt < 2500.

[0093] 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 <l 100 ppm, ou xt<1000 ppm.

[0094] In view of the examples, it has been 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 polymer structure and / or the xt range where the remanent polarization remains at a value significantly higher than the remanent polarization of P(VDF-TrFE) having the same VDF:TrFE ratio is more reduced.

[0095] According to particular embodiments, the polymer according to the invention has a molar proportion of trifluoroethylene motif relative to vinylidene fluoride motif of 14.0:86.0 to 18.5:81.5 and 5 ppm < xt < 5000 ppm.

[0096] 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 < 800 ppm, or 800 ppm < xt < 1500 ppm, or 1500 ppm < xt < 3000 ppm, or 3000 ppm < xt < 4500 ppm. On at least one of these intervals, the remanent polarization of the polymer is either of the same order, or greater 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, than the remanent polarization of P(VDF-TrFE) having the same proportion of TrFE:VDF.

[0097] The third monomer may in particular be chlorotrifluoroethylene.

[0098] According to certain embodiments, in particular when the molar proportion of trifluoroethylene motifs relative to the sum of vinylidene fluoride and trifluoroethylene motifs (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

[0099] greater than 17.5%, or greater than 18.0%, or greater than 18.5%, or greater than 19.0%,

[0100] particularly when the molar ratio (TrFE / (VDF+TrFE)) is approximately 20.0%,

[0101] the remanent polarization, as measured in the examples, may advantageously have a value greater than or equal to 88 mC / m², or greater than or equal to 90 mC / m², or greater than or equal to 92 C / m² or greater than or equal to 94 mC / m² at 25°C in an alternating electric field (sinusoidal signal with a period of 18 s) with a maximum amplitude of 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.

[0102] According to particular embodiments, the polymer according to the invention has a molar proportion of trifluoroethylene motif relative to vinylidene fluoride motif of 17.5:82.5 to 22.5:77.5 and 5 ppm < xt < 5000 ppm. Preferably, 10 ppm < xt < 3000 ppm, and preferably 100 ppm < xt < 2500 ppm. It is also possible to have 100 ppm < xt < 200 ppm, or 200 ppm < xt < 1000 ppm, or 1000 ppm < xt < 2000 ppm, or 2000 ppm < xt < 2500 ppm.

[0103] We can have 25 ppm < xt < 100 ppm, or 100 ppm < xt < 200 ppm, or 200 ppm < xt < 600 ppm, or 600 ppm < xt < 800 ppm, or 800 ppm < xt < 1000 ppm, or 1000 ppm < xt < 2000 ppm, or 2000 ppm < xt < 2500 ppm. On at least one of these intervals, the The remanent polarization of the polymer is either of the same order, or greater 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, 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 less 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 than the coercive field of P(VDF-TrFE) having the same TrFE:VDF ratio.

[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 trifluoroethylene motif relative to the vinylidene fluoride motif 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.

[0106] We can have 25 ppm < xt < 100 ppm, or 100 ppm < xt < 200 ppm, or 200 ppm < xt < 600 ppm, or 600 ppm < 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 greater 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, 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 less 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 than the coercive field of P(VDF-TrFE) having the same TrFE:VDF ratio.

[0107] The third monomer may in particular be chlorotrifluoroethylene.

[0108] According to particular embodiments, the polymer according to the invention has a molar proportion of trifluoroethylene motif relative to vinylidene fluoride motif of 20.1:79.9 to 20.9:79.1 and 5 ppm < xt < 5000 ppm. Preferably, 10 ppm < xt < 3000 ppm, and preferably 100 ppm < xt < 2500 ppm.

[0109] We can have 25 ppm < xt < 100 ppm, or 100 ppm < xt < 200 ppm, or 200 ppm < xt < 600 ppm, or 600 ppm < 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 greater 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, 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 less 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 than the coercive field of P(VDF-TrFE) having the same TrFE:VDF ratio.

[0110] The third monomer may in particular be chlorotrifluoroethylene.

[0111] According to particular embodiments, the polymer according to the invention has a molar proportion of trifluoroethylene motif relative to vinylidene fluoride motif of 22.5:77.5 to 27.5:72.5 and 5 ppm < xt < 5000 ppm. Preferably, 10 ppm < xt < 2000 ppm, and even more preferably 50 ppm < xt < 1500 ppm.

[0112] We can have 25 ppm < xt < 50 ppm, or 50 ppm < xt < 100 ppm, or 200 ppm < xt < 400 ppm, or 400 ppm < xt < 800 ppm, or 800 ppm < xt < 1200 ppm, or 1200 ppm < xt < 1500 ppm. Over at least one of these intervals, the remanent polarization of the polymer is either of the same order, or greater by 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, than the remanent polarization of the P(VDF-TrFE) having the same TrFE:VDF ratio. On at least one of these intervals, the coercive field is either of the same order, or less than 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more than the coercive field of the P(VDF-TrFE) having the same proportion in TrFE:VDF.

[0113] The third monomer may in particular be chlorotrifluoroethylene.

[0114] According to particular embodiments, the polymer according to the invention has a molar proportion of trifluoroethylene motif relative to vinylidene fluoride motif of 23.5:76.5 to 26.5:73.5 and 5 ppm < xt < 5000 ppm. Preferably, 10 ppm < xt < 2000 ppm, and even more preferably 50 ppm < xt < 1500 ppm.

[0115] We can have 25 ppm < xt < 50 ppm, or 50 ppm < xt < 100 ppm, or 200 ppm < xt < 400 ppm, or 400 ppm < xt < 800 ppm, or 800 ppm < xt < 1200 ppm, or 1200 ppm < xt < 1500 ppm. Over at least one of these intervals, the remanent polarization of the polymer is either of the same order, or greater 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, than the remanent polarization of the P(VDF-TrFE) having the same TrFE:VDF ratio. On at least one of these intervals, the coercive field is either of the same order, or less than 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more than the coercive field of the P(VDF-TrFE) having the same proportion in TrFE:VDF.

[0116] The third monomer may in particular be chlorotrifluoroethylene.

[0117] According to particular embodiments, the polymer according to the invention has a molar proportion of trifluoroethylene motif relative to vinylidene fluoride motif of 27.5:72.5 to 32.5:67.5 and 5 ppm < xt < 5000 ppm. Preferably, 10 ppm < xt < 1200 ppm, and even more preferably 25 ppm < xt < 1000 ppm.

[0118] 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 greater 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, than the remanent polarization of P(VDF-TrFE) having the same TrFE:VDF proportion. On at least one of these intervals, the coercive field is either of the same order, or less than 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more than the coercive field of the P(VDF-TrFE) having the same proportion in TrFE:VDF.

[0119] The third monomer may in particular be chlorotrifluoroethylene.

[0120] According to particular embodiments, the polymer according to the invention has a molar proportion of trifluoroethylene motif relative to vinylidene fluoride motif of 28.5:71.5 to 31.5:68.5 and 5 ppm < xt < 5000 ppm. Preferably, 10 ppm < xt < 1200 ppm, and even more preferably 25 ppm < xt < 1000 ppm.

[0121] 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 greater 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, 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 less 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 than the coercive field of P(VDF-TrFE) having the same TrFE:VDF ratio.

[0122] The third monomer may in particular be chlorotrifluoroethylene.

[0123] According to particular embodiments, the polymer according to the invention has a molar proportion of trifluoroethylene motif relative to vinylidene fluoride motif of 32.5:67.5 to 50.0:50.0 and 5 ppm < xt < 5000 ppm. Preferably, 10 ppm < xt < 1000 ppm, and preferably 15 ppm < xt < 500 ppm.

[0124] 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 greater 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, than the remanent polarization of the 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 less than 1.0% or more, or 2.0% or more, or 3.0% or more, or 4.0% or more, or 5.0% or more than the coercive field of P(VDF-TrFE) having the same proportion in TrFE:VDF.

[0125] The third monomer may in particular be chlorotrifluoroethylene. Manufacturing process

[0126] The polymer can be obtained according to processes known from prior art.

[0127] 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 monomers.

[0128] 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 vinylidene fluoride and trifluoroethylene motifs, the suspension polymerization process is generally capable of providing the polymer with the highest remanent polarization.

[0129] Advantageously, the polymer is prepared by a suspension polymerization process carried out in water.

[0130] The polymer can in particular be processed according to the method described in WO2016 / 055712 by adapting the monomer proportions according to the present invention. This method comprises successively: • the injection into a reactor of all the monomers to be reacted; • the initiation of monomer polymerization; • a step (a) of continuing the polymerization of the monomers, during which a drop in pressure in the reactor is compensated, in other words the pressure in the reactor is maintained at a substantially constant value; and, • an optional step (b) during which a temperature increase is carried out (without necessarily controlling the pressure).

[0131] Compensating for the pressure drop during step (a) avoids the strong slowing of the 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.

[0132] To compensate for the pressure drop, consideration may be given to using a variable volume reactor, the volume of which is reduced (preferably continuously) during step (a).

[0133] Alternatively, and more simply, a flux is injected into the reactor during step (a), preferably continuously, so as to compensate for the removal of the polymerizing monomers. The composition of the flux is chosen so as not to interfere with the polymerization reaction. Thus, inject a stream of water into the reactor, or a stream of any other liquid that is immiscible with monomers and inert with respect to polymerization.

[0134] The pressure drop in the reactor is preferably fully compensated. Alternatively, it is partially compensated, in which case a certain decrease in pressure in the reactor is still observed during step (a).

[0135] According to some embodiments, the pressure during step (a) can be maintained substantially equal to a reference value between 50 and 130 absolute bars, and preferably between 70 and 110 absolute bars.

[0136] According to some 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.

[0137] The temperature increase during step (b) is advantageous in order to maximize the conversion rate and consumption of monomers and also in order to reduce the residual amount of undecomposed initiator at the end of the reaction (the residual presence of the initiator is not favorable from the point of view of the purity characteristics and thermal stability of the product).

[0138] During step (b), pressure control can either continue or cease. In the latter case, during step (b), the pressure in the reactor generally decreases, and polymerization continues.

[0139] The reaction can be initiated by adding a radical polymerization initiator, which may, in particular, be an organic peroxide such as a peroxy-dicarbonate. 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.

[0140] Generally, the initiation of the reaction as such is carried out by the combined action of an addition of the polymerization initiator and a temperature increase, which is accompanied by a pressure increase (the initiator can be added to the reactor after the monomers or before the monomers and before or after the temperature increase).

[0141] Furthermore, it may be advantageous to add a suspending agent to the reaction medium. In particular, a cellulose derivative, especially a cellulose ether such as methylcellulose, ethylhydroxyethylcellulose, or hydroxypropylmethylcellulose, may be used 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.

[0142] Finally, according to certain embodiments, a chain length regulating agent may be added to the reaction medium. Ethyl acetate, 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 load. Preferably, the amount used can be from 10 to 40 g / kg.

[0143] Various manufacturing processes for trifluoroethylene are known.

[0144] The production of trifluoroethylene by hydrogenolysis of chlorotrifluoroethylene is known. Such a process is described, for example, in applications EP 2 819 979 and EP 2 993 213. At the end of the process, a distillation step allows the recovery of pure trifluoroethylene, or conversely, trifluoroethylene containing a small amount of chlorotrifluoroethylene, depending on the distillation conditions.

[0145] The production of trifluoroethylene by thermal decomposition of chlorodifluoromethane and chlorofluoromethane is also known. Such a process is described, for example, in EP 2 993 213.

[0146] In embodiments where the third monomer is chlorotrifluoroethylene, the trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene, and used in the polymer preparation reaction according to the invention, can advantageously be purified so as to contribute to the supply of chlorotrifluoroethylene in the polymerization reaction.

[0147] The trifluoroethylene obtained by hydrogenolysis of chlorotrifluoroethylene can 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 required to carry out the polymerization reaction according to the invention.

[0148] 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.

[0149] 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 most preferably greater than or equal to 99.0%. According to preferred embodiments, trifluoroethylene may have a purity greater than or equal to 99.5%. For example, trifluoroethylene may 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%.

[0150] Films can be prepared using the polymer according to the invention, for example by solvent casting or extrusion or hot melt compression.

[0151] For example, a polymer powder can be dissolved in methyl ethyl ketone. The solution can be poured onto a plate and then dried. The dried film can be annealed at a temperature below the melting point and above the Curie temperature of the polymer to optimize its crystallinity.

[0152] These films can have a thickness of 1 pm to 50 pm, preferably from 2 pm to 25 pm, and extremely preferably from 5 pm to 15 pm.

[0153] According to some embodiments, films having an intermediate thickness of 15 to 25 pm can be prepared, then can be stretched by a factor of 2 to 10, preferably 5 to 7 to obtain a thickness of 1 pm to 5 pm.

[0154] 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, thinner films can be manufactured 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.

[0155] Due to the weaker 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 at a weaker electric field.

[0156] 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.

[0157] 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 ratio. Examples

[0158] In the experiments carried out 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.

[0159] A trifluoroethylene, obtained by a hydrogenolysis process 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 type “B” trifluoroethylene.

[0160] A trifluoroethylene, obtained by a hydrogenolysis process 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 type “C” trifluoroethylene.

[0161] The chlorofluoroethylene already present in the trifluoroethylene was taken into consideration for the calculation of the total chlorotrifluoroethylene introduced into the medium action. The total chlorofluoroethylene therefore corresponds to the sum of the masses of the chlorofluoroethylene present in small quantities in the trifluoroethylene and the additionally introduced chlorofluoroethylene.

[0162] The weights of vinylidene fluoride and trifluoroethylene correspond to the actual weights introduced of each species. Example #1

[0163] Vinylidene fluoride (767 g) was reacted with type A trifluoroethylene (253 g) in a 3.4L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.53 g).

[0164] The reactor was then heated to 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 the continuous injection of water (980 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The reactor was then heated to 65°C, with the pressure continuing to fall. When the pressure reached 38 bar, the reactor was cooled and then drained. The collected reaction mixture was filtered, and the resulting cake was washed with water five times before being dried in an oven at 70°C until it reached a constant weight. Example #8

[0165] Vinylidene fluoride (716 g) was reacted with type A trifluoroethylene (305 g) in a 3.4L reactor containing demineralized water (1730 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.6 g).

[0166] The reactor was then brought 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 the continuous injection of water (930 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The final steps are the same as in Example #1. Example #12

[0167] Vinylidene fluoride (700 g) was reacted with type A trifluoroethylene (386 g) in a 3.4L reactor containing demineralized water (1680 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.7 g).

[0168] The reactor was then brought 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 needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The final steps are the same as for example #1 Example #2

[0169] 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.

[0170] The reactor was then heated to 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 the continuous injection of water (980 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The reactor was then heated to 65°C, with the pressure continuing to fall. The final steps are the same as in Example #1. Example #3

[0171] 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 brought by type B trifluoroethylene) in a 3.4L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.53 g).

[0172] The reactor was then brought 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 the continuous injection of water (980 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The final steps are the same as in Example #1. Example #9

[0173] Vinylidene fluoride (712 g) was reacted with trifluoroethylene (310 g; type B) in a 3.4 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.

[0174] The reactor was then brought 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 (930 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The final steps are the same as for example #1. Example #15

[0175] 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 g was provided 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).

[0176] The reactor was then brought 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 the continuous injection of water (870 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The final steps are the same as in Example #1. Example #5

[0177] 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.

[0178] The reactor was then heated to 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 the continuous injection of water (980 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The reactor was then heated to 65°C, with the pressure continuing to fall. The final steps are the same as in Example #1. Example #4

[0179] Vinylidene fluoride (767 g) was reacted with trifluoroethylene (253 g; type C) and chlorotrifluoroethylene (total amount of chlorotrifluoroethylene: 0.86 g, of which 0.72 g of CTFE was provided by type C trifluoroethylene) in a 3.4L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.53 g).

[0180] 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 (980 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The reactor was then heated to 65°C, the pressure continues to fall. The final steps are the same as for example #1. Example #6

[0181] Vinylidene fluoride (767 g) was reacted with trifluoroethylene (253 g; type C) and chlorotrifluoroethylene (total amount of chlorotrifluoroethylene: 1.61 g, of which 0.72 g of CTFE was provided by type C trifluoroethylene) in a 3.4L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.53 g).

[0182] The reactor was then heated to 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 the continuous injection of water (980 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The reactor was then heated to 65°C, with the pressure continuing to fall. The final steps are the same as in Example #1. Example #7

[0183] 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 provided by type C trifluoroethylene) in a 3.4L reactor containing demineralized water (1670 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.53 g).

[0184] The reactor was then heated to 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 the continuous injection of water (980 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The reactor was then heated to 65°C, with the pressure continuing to fall. The final steps are the same as in Example #1. Example #10

[0185] 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.

[0186] The reactor was then brought 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 (930 g). When all the water needed to compensate for the pressure drop had been injected, the pressure dropped to 65 bar. The reactor was then heated to 65°C, with the pressure continuing to fall. The final steps are the same as in example #1. Example #11

[0187] 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 provided by type C trifluoroethylene) in a 3.4L reactor containing demineralized water (1730 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.6 g).

[0188] The reactor was then heated to 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 the continuous injection of water (930 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The reactor was then heated to 65°C, with the pressure continuing to fall. The final steps are the same as in Example #1. 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 provided by type C trifluoroethylene) in a 3.4L reactor containing demineralized water (1680 g), methylhydroxypropyl cellulose (0.60 g) and propyl peroxydicarbonate (1.7 g).

[0190] The reactor was then heated to 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 the continuous injection of water (870 g). When all the water needed to compensate for the pressure drop had been injected, the pressure fell to 65 bar. The reactor was then heated to 65°C, with the pressure continuing to fall. The final steps are the same as in 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 provided by type C trifluoroethylene) in a 3.4L 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 on as quickly as possible to initiate the reaction. The start of the reaction is marked by a drop in reactor pressure, which was compensated by the continuous injection of water (870 g). When all the water needed to compensate for the pressure drop had been injected, the pressure dropped to 65 bar. The reactor was then heated to 65°C, with the pressure continuing to fall. The final steps are the same as in example #1. Polymer characterization

[0193] Determination of the TrFE / (VDF+TrFE) molar ratio in the polymer

[0194] The TrFE / (VDF+TrFE) molar ratio in the polymer, denoted xTrFE, was determined by proton NMR. The polymer was dissolved in a suitable deuterated solvent, and the NMR spectrum was recorded on an FT-NMR spectrometer equipped with a multinuclear probe. The hydrogen nucleus of the TrFE unit (CHF-CF2) gives a distinctive signal at approximately 5 ppm, while the two hydrogen atoms of the CH2 group of the VDF units give a centered bulk at 3 ppm.

[0195] The relative integration of the two signals gives the relative abundance of the two monomers, that is to say their molar ratio.

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

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

[0198] Because of the reactivity of CTFE with respect 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 polymer structure.

[0199] Determination of remanent polarization and coercive field

[0200] Polymer films were prepared from a 14 wt% solution in methyl ethyl ketone filtered to 0.2 µm. 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 to evaporate the solvent. The films were then placed in an oven for 1 hour at 15°C below the polymer's melting temperature as measured by differential scanning calorimetry.

[0201] The ferroelectric characteristics of the material, in particular its remanent polarization

[0202] and its coercive field, were measured at 25 °C in an alternating electric field

[0203] (sinusoidal signal with a period of 18 s) with a maximum amplitude of 150 V / pm.

[0204] The remanent polarization, Pr, is defined as the value of the polarization

[0205] measured at zero field. The coercive field (Ec) is defined as the value of the applied field for which the measured polarization is zero.

[0206] Table 1 groups together all the characterization measures for the films of

[0207]

[0208]

[0209]

[0210] composition #1-#15: [Tables 1] Examples XlrFE (mole %) 20.5 920 45 95 #7 20.7 490 48 93 #8 25.1 0 50 69 #9 25.3 25 46 73 # 10 25.2 507 48 75 # 11 25.1 530 48 75 # 12 29.7 0 50 64 #13 30.0 816 49 67 # 14 28.8 22000 51.96 56.3 #15 30.0 276 41.25 70.9 Figure 1 shows 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 can be seen that the hysteresis curve for the polymer according to the invention is narrower (lower Ec) and higher (higher Pr) than for the comparative polymer. Figure [Fig.2] represents the remanent polarization of films of composition #1-#13 and #15 as a function of the proportion of CTFE in the polymer. Based on Table 1 and [Fig.2], at least the following points can be observed: • Remanent polarization increases in the polymer for increasing xTrFE, which was known to the man of the art (compare for example Pr in comparative examples #1, #8, #12). • Excessive addition of CTFE to the structure of a P(VDF-TrFE) transforms the ferroelectric polymer into a ferroelectric relaxer, which was known to the expert (see the very low Pr of comparative example #14 compared to that of comparative example #12) The remanent polarization of the polymer having a given TrFE:VDF ratio increases rapidly from the first ppm or tens of ppm in CTFE in the polymer (see for example Pr of example #2 to compare with Pr of comparative example #1, or Pr of example #9 to compare with Pr of comparative example #8). The remanent polarization of the polymer having a given TrFE:VDF ratio remains high, especially above the remanent polarization of the corresponding P(VDF-TrFE) for xt of the order of 1000 ppm and more. 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) (respectively comparative examples #1, #8 and #12).< / l>

Claims

Demands

1. Use of a third monomer having chemical formula: CX!X2=CX3Z (I) in which each of the Xb X2, X3 is independently selected from H, F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and in which Z is selected from Cl, Br, and I, as a termonomer in the structure of a polymer essentially consisting of repeating motifs from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) in molar proportions xt from 25 ppm to 800 ppm relative to the total number of moles of motifs from VDF and TrFE in the polymer, the TrFE:VDF molar ratio in the polymer between the TrFE motif and the VDF motif being from 14.0:86.0 to 50.0:50.0, to increase the remanent polarization.

2. Use of a third monomer having chemical formula: CX1X2=CX3Z (I) in which each of the Xb X2, X3 is independently selected from H, F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and in which Z is selected from Cl, Br, and I, as a termonomer in the structure of a polymer essentially consisting of repeating motifs from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) in molar proportions xt from 25 ppm to 800 ppm relative to the total number of moles of motifs from VDF and TrFE in the polymer, the TrFE:VDF molar ratio in the polymer between the TrFE motif and the VDF motif being from 14.0:86.0 to 50.0:50.0, to decrease its coercive field.

3. Use according to any one of claims 1 and 2, wherein the third monomer is selected from: chlorotrifluoroethylene (CTFE), chlorodifluoroethylene, in particular 1-chloro-2,2-difluoroethylene (CDFE), and chlorofluoroethylene, in particular 1,1-chlorofluoroethylene (CFE).

4. Use according to any one of claims 1 and 2, wherein the third monomer is chlorotrifluoroethylene.

5. Use according to any one of claims 1 to 4, in said polymer essentially consisting of repeating motifs from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) has a TrFE:VDF molar ratio of 15.0:85.0 to 40.0:60.0, or of 16.0:84.0 to 35.0:65.0, or of 17.5:82.5 to 27.5:72.

5.

6. Use according to any one of claims 1 to 5, wherein said polymer essentially consisting of repeating motifs from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) has a melt flow index at 230°C under a 10kg load, 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.

7. Use according to any one of claims 1 to 6, wherein said polymer essentially consisting of repeating motifs from vinylidene fluoride (VDF) and trifluoroethylene (TrFE) is obtained by a suspension polymerization process, preferably in water.

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