Process for manufacturing a terpolymer of homogeneous chemical composition and polymers thus obtained.

Abstract

The invention relates to a process for manufacturing a terpolymer essentially consisting of, or consisting of, repeating units resulting from the suspension polymerization in liquid of vinylidene fluoride, a second monomer of formula (I) and a third monomer of formula (II), to obtain a terpolymer having a homogeneous chemical composition. Figure for the abstract: Figure 1

Description

Title of the invention: Process for manufacturing a terpolymer of homogeneous chemical composition and polymers thus obtained. technical field

[0001] The invention relates to the field of manufacturing terpolymers, that is, polymers essentially composed of, or composed of, three different repeating units, by a suspension polymerization process. In particular, the invention relates to terpolymers comprising vinylidene fluoride as a repeating unit. The invention also relates to polymers of homogeneous chemical composition as such, in particular those that can be obtained according to the process of the invention, the homogeneity of whose chemical composition has been evaluated by differential scanning calorimetry. Previous art

[0002] It is known in the prior art to manufacture terpolymers comprising VDF, such as a P(VDF-TrFE-CTFE) or a P(VDF-TrFE-CFE), by a suspension polymerization process.

[0003] For example, it is known from WO2016 / 055712 to initially inject all the monomers and then initiate polymerization while maintaining constant pressure in the reactor during polymerization. A P(VDF-TrFE-CTFE) with a VDF / TrFE / CTFE molar composition of 62.5 / 32.8 / 4.7 has been exemplified.

[0004] It is also known from WO2010 / 116105 to load an initial mixture of VDF and TrFE, devoid of CTFE and CFE, into an autoclave and to inject a secondary mixture of VDF, TrFE, and CTFE or CFE, so as to maintain constant pressure in the reactor during polymerization. The example given relates to a P(VDF-TrFE-CFE) with a molar composition of VDF / TrFE / CFE 61.7 / 29.8 / 8.5. A similar process is described in WO2014 / 091130, which discloses P(VDF-TrFE-CTFE) having a CTFE molar proportion of 1.97% to 8.5% relative to the total number of moles of VDF, TrFE, and CTFE monomers. This process ensures better polymer homogeneity and reproducibility than the aforementioned process where all monomers are added initially. The resulting polymer, although having a more homogeneous chemical composition, still exhibits significant heterogeneity, which the inventors were able to assess using DSC measurements.

[0005] Furthermore, P(VDF-TrFE-CTFE) and / or P(VDF-TrFE-CFE) are known for their ferroelectric-relaxer properties. "Ferroelectric-relaxer" polymers are characterized by a relaxer-ferroelectric crystal transition. (RFE) paraelectric (PE) over a wide temperature range. At this transition, a broad peak in dielectric permittivity is observed, the temperature of this maximum depending on the frequency of the applied electric field: the lower the frequency of the electric field, the more the dielectric permittivity maximum is shifted towards lower temperatures. They are also characterized by a fairly narrow hysteresis loop in the "electric displacement" curve as a function of the "applied electric field".

[0006] There is currently a need to supply such terpolymers with an even thinner hysteresis loop, i.e., with an even lower remanent polarization value. These characteristics can be particularly useful for energy storage applications. There is also a need to supply terpolymers with a higher dielectric constant, which is particularly useful for applications in organic electronics. Objective of the invention

[0007] An objective of the invention is to propose a process for the manufacture of terpolymer having a more homogeneous chemical composition than that of prior art terpolymers.

[0008] Another objective of the invention is to provide such terpolymers having a more homogeneous chemical composition.

[0009] According to at least some embodiments, an objective is to propose terpolymers having a thinner hysteresis ring compared to prior art terpolymers of similar average chemical composition.

[0010] According to at least some embodiments, an objective is to propose terpolymers having a higher dielectric constant than prior art terpolymers of similar average chemical composition. Summary of the invention

[0011] The invention relates to a method for manufacturing a terpolymer P by suspension polymerization in a suspension liquid. The polymer P is essentially composed of, or consists of, repeating units resulting from the polymerization of vinylidene fluoride, a second monomer and a third monomer.

[0012] The second monomer has the chemical formula: CRiR2-CR3R4(I), in which: - C denotes a carbon atom, - each of the Rb R2, R3 and R4 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated.

[0013] The third monomer has the chemical formula: CR5R6-CR7R8 (II), in which: - C denotes carbon atony, - each of R5, R6 and R7 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, - R8 is chosen from -Cl, -Br, and -I.

[0014] The process comprises: - the injection into a reactor of a composition Ci in VDF, second monomer and third monomer, to form a mixture of monomers Mi in the suspension liquid, - the initiation of polymerization of the Mi mixture of monomers, and, - the continuation of polymerization by:

[0015] - injection into the VDF reactor, second monomer and third monomer of composition C2,

[0016] - and optionally, injection into the reactor of a suspension liquid;

[0017] The process is characterized in that the continuation of the polymerization is carried out in the reactor at a substantially constant pressure and at a substantially constant monomer composition.

[0018] According to some embodiments, the second monomer is selected from vinyl fluoride, 1,2-difluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, and mixtures thereof. Preferably, the second monomer is trifluoroethylene.

[0019] According to certain embodiments, each of the R5, R6, and R7 in the compound of formula (II) is independently selected from -H and -F. Preferably, the third monomer is chlorotrifluoroethylene, a chlorofluoroethylene, in particular 1-chloro-1-fluoroethylene, or a mixture thereof. The third monomer may, in particular, be chlorotrifluoroethylene or 1-chloro-1-fluoroethylene.

[0020] The polymer Po obtainable by low-conversion polymerization of said mixture Mi has a composition Cp_>0 |XP>0 ; Yp.>0], where Xp >0 represents the mole proportion, expressed as a percentage, of VDF monomer relative to the total number of moles of VDF and second monomer in polymer Po, where Yp >0 represents the mole proportion, expressed as a percentage, of third monomer relative to the total number of moles of VDF, second monomer, and third monomer in polymer Po, and where low conversion rate means that less than 10% by weight, and preferably less than 5% by weight, of the monomers of mixture Mi have reacted relative to the total weight of monomers injected for the formation of mixture Mb. According to some embodiments, the composition C2 [X2 ;Y2] of VDF, second monomer, and third monomer, injected during the continuation of the polymerization, has a composition substantially identical to the composition Cp >o [Xp>0 ; Yp >o], so as to have a composition in monomers substantially constant in the reactor during the continuation of polymerization. Parameter X2 represents the molar proportion, expressed as a percentage, of VDF monomer relative to the total number of moles of VDF and second monomer in composition C2. Parameter Y2 represents the molar proportion, expressed as a percentage, of third monomer relative to the total number of moles of VDF, second monomer, and third monomer in composition C2.

[0021] According to some embodiments, the parameter Yp > 0 satisfies the inequality:

[0022] 0.1 < Yp.>0 < 15.0 (eq. 1). Preferably, the parameter Yp >0 satisfies the inequality: 1.0 < Yp >0 < 10.0 (eq. la).

[0023] The parameter AY2 is defined as follows:

[0024] [Math.l]

[0025] According to some embodiments, the parameter AY2 satisfies the inequality:

[0026] -0.40 < AY2 < 0.65 (eq. 3). Preferably, the parameter AY2 satisfies The inequality: -0.25 < AY2 < 0.50 (eq. 3a). More preferably, the parameter AY2 satisfies the inequality: -0.12 < AY2 < 0.36 (eq. 3b).

[0027] According to some embodiments, the parameter Xp > 0 satisfies the inequality:

[0028] 30,0 < Xp.>0 < 100 (eq. 4). Preferably, the parameter Xp.>0 satisfies The inequality: 45.0 < Xp > 0 < 90.0 (eq. 4a). More preferably, the parameter Xp_> 0 satisfies the inequality: 50.0 < Xp > 0 < 80.0 (eq. 4b).

[0029] The parameter AX2 is defined as follows:

[0030] [Math.2] P 2 ^°) x 100 X Xp >;> /

[0031] According to some embodiments, the parameter AX2 satisfies the inequality:

[0032] -8.0 < AX2 < 8.0 (eq. 6). Preferably, the parameter AX2 satisfies the inequality: -4.0 < AX2 < 4.0 (eq. 6a). Preferably, the parameter AX2 satisfies the inequality: -2.0 < AX2 < 2.0 (eq. 6b).

[0033] According to some embodiments, the suspension liquid is water or an aqueous solution.

[0034] According to some embodiments, polymerization is essentially carried out under temperature and pressure conditions for which the monomers in the reactor are in a supercritical state.

[0035] According to some embodiments, the polymerization is essentially carried out at a pressure of 50 to 130 bars, and preferably ranging from 70 to 110 bars.

[0036] According to some embodiments, the continuation of the polymerization is carried out without injection of suspension liquid, in order to maintain a substantially constant pressure in the reactor.

[0037] According to some embodiments, the parameters X2 and Y2 remain constant during the continuation of the polymerization, where X2 represents the molar proportion, expressed as a percentage, of VDF monomer relative to the total number of moles of VDF and second monomer in composition C2, and where Y2 represents the molar proportion, expressed as a percentage, of third monomer relative to the total number of moles of VDF, second monomer and third monomer in composition C2.

[0038] The invention also relates to a terpolymer P, of homogeneous chemical composition, essentially consisting of, or consisting of, repeating units resulting from the polymerization of vinylidene fluoride, a second monomer and a third monomer.

[0039] The second monomer has the chemical formula: CRiR2-CR3R4 (I), in which: - C denotes a carbon atom, - each of the RB R2, R3 and R4 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated.

[0040] The third monomer has the chemical formula: CR5R6-CR7R8 (II), in which: - C designates a carbon atom, - each of R5, R6 and R7 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, - R8 is chosen from -Cl, -Br, and -I.

[0041] The terpolymer P according to the invention has the composition C [X;Y], where X represents the molar proportion, expressed as a percentage, in units resulting from the polymerization of VDF relative to the total number of moles in units resulting from the polymerization of VDF and the second monomer in the terpolymer, and where Y represents the molar proportion, expressed as a percentage, in units resulting from the polymerization of the third monomer relative to the total number of moles in units resulting from the polymerization of VDF, the second monomer and the third monomer in the terpolymer,

[0042] The parameter X satisfies the inequality: 30 < X ​​< 100 (eq. 7), and the parameter Y satisfies the inequality 0.1 < Y ​​< 15.0 (eq. 8).

[0043] The AT parameter is defined as follows:

[0044] [Math.3] _ Tfm a~Tim a •>

[0045] where Tfm and Timare respectively represent the final temperature of the melting peak, and the initial temperature of the melting peak on a DSCa differential scanning calorimetry thermogram of said terpolymer P,

[0046] where Tfm_bet Timbre respectively represent the final temperature of the melting peak and the initial temperature of the melting peak on a DSCb differential scanning calorimetry thermogram of a comparative terpolymer P', the comparative terpolymer P' having an average chemical composition similar to that of terpolymer P, and being obtained by a suspension polymerization process in which the entire VDF, the second monomer, and the third monomer used for polymerization are initially injected before the initiation of polymerization. The DSCa and DSCb differential scanning calorimetries are carried out with heating and cooling ramps of 10°C / min.

[0047] The homogeneity of chemical composition of the terpolymer P according to the invention is characterized by the parameter AT, satisfying the following inequality: AT < 0.70 (eq. 9), preferably satisfying the following inequality: AT < 0.60 (eq. 9a), and more preferably satisfying the following inequality: AT < 0.50 (eq. 9b). Detailed description of the invention Figures

[0048] [Fig-1] illustrates the shape of a DSC thermogram during the second heating cycle, with heating and cooling ramps at 10°C / min, of a P(VDF-TrFE-CTFE) according to the invention (thermogram A) and of a P(VDF-TrFE-CTFE) according to the prior art (thermogram B). The x-axis represents the temperature reached during the second heating cycle and the y-axis the measured heat flux.

[0049] [Fig.2] illustrates the shape of the "first quadrant", i.e. the The upper right quadrant shows the hysteresis loop obtained during the polarization of a P(VDF-TrFE-CTFE) polymer according to the invention (loop A) and a P(VDF-TrFE-CTFE) polymer according to the prior art (loop B). The x-axis represents the applied electric field. The y-axis represents the polymer polarization. Process

[0050] The present invention relates to a method for manufacturing a terpolymer P.

[0051] The terpolymer P is essentially made up of, or made up of, repeating units resulting from the polymerization of vinylidene fluoride, a second monomer and a third monomer, by polymerization in suspension in a suspension liquid.

[0052] The second monomer has the chemical formula: CRiR2-CR3R4(I), in which: - C designates a carbon atom, - each of the Rb R2, R3 and R4 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated.

[0053] The second monomer is a different monomer from VDF.

[0054] The third monomer has the chemical formula: CR5R6-CR7R8 (II), in which: - C designates a carbon atom, - each of R5, R6 and R7 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, - R8 is chosen from -Cl, -Br, and -I.

[0055] According to preferred embodiments, the second monomer is selected from vinyl fluoride, 1,2-difluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, and mixtures thereof. The second monomer may, in particular, be selected from vinyl fluoride, 1,2-difluoroethylene, trifluoroethylene, tetrafluoroethylene, and hexafluoropropylene.

[0056] In a particularly preferred embodiment, the second monomer is trifluoroethylene.

[0057] According to preferred embodiments, each of the R5, R6 and R7 in the compound of formula (II) is independently chosen from -H and -F.

[0058] According to equally preferred embodiments, R8 is: -CL

[0059] Thus, in particularly preferred embodiments, the third monomer is selected from chlorotrifluoroethylene (CTFE), a chlorofluoroethylene, in particular 1-chloro-1-fluoroethylene (CFE), or a mixture thereof. The third monomer may in particular be chlorotrifluoroethylene or 1-chloro-1-fluoroethylene.

[0060] According to one particular embodiment, the terpolymer is P(VDF-TrFE-CTFE).

[0061] According to another particular embodiment, the terpolymer is P(VDF-TrFE-CFE).

[0062] The process according to the invention comprises: - the injection into a reactor of a composition Ci [Xi ;YJ in VDF, second monomer and third monomer, to form a mixture of monomers Mi in the suspension liquid, - the initiation of the polymerization of the Mb monomer mixture and - the continuation of the polymerization at a substantially constant pressure in the reactor and at a substantially constant monomer composition in the reactor, by injection into the reactor of VDF, TrFE and CTFE monomers of composition C2 [X2 ;Y2].

[0063] The parameter Xi represents the molar proportion, expressed as a percentage, of VDF monomer relative to the total number of moles of VDF and second monomer in the composition Ci,

[0064] The parameter Yi represents the mole proportion, expressed as a percentage, of the third monomer relative to the total number of moles of VDF, second monomer and third monomer in the composition Cp

[0065] The parameter X2 represents the molar proportion, expressed as a percentage, of VDF monomer relative to the total number of moles of VDF and the second monomer in composition C2,

[0066] The parameter Y2 represents the molar proportion, expressed as a percentage, of third monomer relative to the total number of moles of VDF, second monomer and third monomer in composition C2.

[0067] The inventors have focused on maintaining a substantially constant monomer composition in the reactor, thereby obtaining a terpolymer P with a more homogeneous chemical composition. For the purposes of this invention, "homogeneity" means that the different polymer chains have essentially the same composition in terms of units resulting from the polymerization of the VDF, the second monomer, and the third monomer. The homogeneity of chemical composition is easily assessed in this invention by examining the differential scanning calorimetry (DSC) thermogram of the terpolymer P during the second heating.

[0068] The mixture Mi of monomers of composition Ci [Xi; YJ] allows for the immediate obtaining, after the initiation of polymerization, i.e., at a low conversion rate of the monomers in the mixture Mb, of a terpolymer Po having a composition Cp > 0 | XP > 0 | Yp > 0]. The injection of VDF, a second monomer, and a third monomer of composition C2 [X2; Y2] compensates for the consumption of monomers in the reactor, and thus maintains the composition of VDF, the second monomer, and the third monomer substantially constant in the reactor, so that the polymer chains formed at any time during polymerization all have a molar composition equal to or close to Cp > 0 [Xp > 0; Yp > 0].

[0069] The parameter Xp >0 represents the molar proportion, expressed as a percentage, of VDF monomer relative to the total number of moles of VDF and second monomer in the polymer Po.

[0070] The parameter Yp_>0 represents the molar proportion, expressed as a percentage, of third monomer relative to the total number of moles of VDF, second monomer and third monomer in the polymer Po.

[0071] The parameter AY2 is defined as follows:

[0072] [Math.4]

[0073] The parameter AX2 is also defined as follows:

[0074] [Math.5]

[0075] The parameter Yp >o generally satisfies the inequality:

[0076] 0.1 < Yp.>0 < 15.0 (eq. 1), and preferentially satisfies the inequality:

[0077] 1.0 <Yp_>0 <10.0 (eq. la).

[0078] According to particular embodiments, Yp > 0 satisfies one of the following inequalities: 1.0 < Yp > 0 < 3.0, or 3.0 < Yp > 0 < 5.0, or 5.0 < Yp > 0 < 7.0,

[0079] or 7.0 <Yp>0 <9.0, or 9.0 <Yp_>0 <10.0.

[0080] The evaluation of Cp > 0 [Xp > 0; Yp > 0] is advantageously implemented by: an injection into a reactor of a composition Ci [Xi ;YJ in VDF, second monomer and third monomer, to form a mixture of monomers Mi in the suspension liquid, then an initiation of the polymerization of the mixture of monomers Mi under the same temperature and pressure conditions as those used to implement the initiation of polymerization in the process according to the invention, and finally, contrary to the invention, an abrupt stopping of the polymerization reaction by the addition of a termination agent and / or by rapid cooling of the reaction medium in order to obtain a low conversion rate polymer Po.

[0081] The value of the parameters Xp >0 and Yp >0 can be evaluated by one or more chemical composition analysis techniques, and in particular by NMR and / or by elemental analysis.

[0082] The evaluation of Cp > 0 [Xp > 0; Yp > 0] can be carried out in a reactor other than the one used to implement the process according to the invention. For example, the evaluation of Cp > 0 [Xp > 0; Yp > 0] can be carried out in a small laboratory reactor, while the process according to the invention can be carried out in a reactor of any size, including an industrial reactor for the production of terpolymer P.

[0083] The term "low conversion rate" means that less than 10% by weight, and preferably less than 5% by weight, of the monomers in mixture Mi have reacted relative to the total weight of monomers injected to form mixture Mp

[0084] Ideally we should have: AY2 = 0. In practice, the parameter AY2 generally satisfies the inequality: -0.40 < AY2 < 0.65 (eq. 3).

[0085] Preferably the parameter AY2 satisfies the inequality: -0.25 < AY2 < 0.50 (eq. 3a), and more preferably satisfies the inequality: -0.12 < AY2 < 0.36 (eq. 3b).

[0086] According to particular embodiments, AY2 satisfies one of the following inequalities: -0.12 < AY2 < -0.09, or -0.09 < AY2 < 0, or 0 < AY2 < 0.09, or 0.09 < AY2 < 0.18, or 0.18 < AY2 < 0.36.

[0087] The parameter Xp >0 generally satisfies the inequality: 30.0 < Xp >0 < 100 (eq. 4), preferentially satisfies the inequality: 45.0 < Xp >0 < 90.0 (eq. 4a), and more preferably satisfies the inequality: 50.0 < Xp >0 < 80.0 (eq. 4b).

[0088] According to particular embodiments, Xp >0 satisfies one of the following inequalities: 50.0 < Xp >0 < 60.0, or 60.0 < Xp >0 < 70.0, or 70.0 < Xp >0 < 80.0.

[0089] Ideally we should have: AX2 = 0. In practice, the parameter AX2 generally satisfies the inequality: -8.0 < AX2 < 8.0 (eq. 6).

[0090] Preferably the parameter AX2 satisfies the inequality:

[0091] -4.0 < AX2 < 4.0 (eq. 6a), and

[0092] preferably still satisfies the inequality: -2.0 < AX2 < 2.0 (eq. 6b).

[0093] The polymerization involved is a suspension polymerization in a liquid, referred to in the present invention as the suspension liquid. It is carried out by suspending VDF, the second monomer, and the third monomer in the suspension liquid. The suspension liquid is advantageously water or an aqueous solution.

[0094] The reaction can be initiated 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 charge. Preferably, the amount used is 0.5 to 5 g / kg. The amount used may be 0.5 to 1.5 g / kg, or 1.5 to 3 g / kg, or 3.0 to 5 g / kg. Generally, the initiation of the reaction itself is carried out by the combined action of adding the polymerization initiator and a temperature increase, which is accompanied by a pressure increase. The initiator may be added to the reactor after or before the monomer composition Ci has been injected. in the reactor. In some embodiments, the initiator is added to the reactor after the monomer composition Ci has been injected into the reactor. In some embodiments, the initiator is added to the reactor after heating the reactor to a predetermined temperature, in particular to a predetermined temperature close to the temperature at which polymerization is initiated.

[0095] Furthermore, it may be advantageous to add a suspending agent to the reaction medium to facilitate the suspension of the monomers in the suspension liquid. 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 weight of the monomers in the mixture Mb. Preferably, the amount used is 0.25 to 3.5 g / kg. The amount used may be 0.25 to 1.0 g / kg, or 1.0 to 3.0 g / kg, or 3.0 to 3.5 g / kg. The suspending agent may be added to the reactor after or before the monomer composition Ci has been injected into the reactor. According to advantageous embodiments, the suspending agent is added to the reactor after the composition Ci of VDF, TrFE and CTFE monomers has been injected into the reactor.

[0096] Finally, a chain length regulating agent can, according to certain embodiments, be added to the reaction medium. Ethyl acetate, diethyl carbonate, or an alcohol such as isopropanol, for example, can be used in an amount of 1 to 100 g per kilogram of the total monomer loading. Preferably, the amount used is 2 to 40 g / kg. The chain length regulating agent can be added to the reactor after or before the monomer composition Ci has been injected into the reactor. It can be added all at once or in fractions over several injections.

[0097] The reaction medium is preferably stirred to suspend the monomers in the suspension liquid and / or during the polymerization reaction.

[0098] Preferably, the polymerization is essentially carried out under temperature and pressure conditions for which the monomers in the reactor are in a supercritical state.

[0099] Polymerization can be carried out at a target polymerization pressure, in particular a target polymerization continuation pressure, of 50 to 130 bar, and preferably at a pressure of 60 to 110 bar. The initiation of polymerization and then the continuation of polymerization cause a decrease in pressure in the reactor due to the consumption of some of the monomers. This The pressure decrease is compensated by the injection into the reactor of VDF, second monomer and third monomer, of composition C2, and optionally by the injection into the reactor of a suspension liquid, in order to maintain a substantially constant pressure in the reactor.

[0100] By substantially constant, we mean a pressure that can vary by plus or minus 30%, preferably by plus or minus 20%, preferably still by plus or minus 15%. According to certain embodiments, the pressure can vary by plus or minus 10% or by plus or minus 5%.

[0101] According to some advantageous embodiments, the pressure in the reactor increases slightly as the polymerization reaction progresses in order to take into account the decrease in the volume available for the monomers due to the space occupied by the polymer obtained. For example, the pressure may increase by 1% or less, or 2% or less, or 4% or less, or 8% or less, or 10% or less, or 12% or less, or even 15% or less, between the beginning and the end of the polymerization continuation step at substantially constant pressure.

[0102] According to some non-preferred embodiments, the pressure decrease during polymerization is partially compensated by the injection of a suspension liquid, of the same or different nature, as the suspension liquid used to suspend the VDF, second monomer, and third monomer of mixture Mi in the reactor. According to some embodiments, the suspension liquid injected to maintain a substantially constant pressure during polymerization is of the same nature as the suspension liquid used to suspend the VDF, second monomer, and third monomer of mixture Mi in the reactor.

[0103] According to preferred embodiments, the pressure decrease during polymerization is compensated by injecting into the reactor only the VDF, the second monomer, and the third monomer, of composition C2. In other words, preferably, the pressure is maintained substantially constant during polymerization without additional injection of suspension liquid.

[0104] Polymerization can, in particular, be carried out essentially at a reaction medium temperature higher than the critical temperature of the monomer mixture in the reactor. This temperature is generally less than or equal to 80°C. This temperature is generally greater than or equal to 35°C. In order to control the temperature of the reaction medium, the reactor is equipped with temperature control means (for example, with a double jacket through which a heat transfer fluid circulates).

[0105] According to certain preferred embodiments, the temperature is maintained substantially constant during the continuation of polymerization at substantially constant pressure. By substantially constant, a temperature that can vary by plus or minus 30%, preferably by plus or minus 20%, preferably still by plus or minus 15%, and more preferably by plus or minus 10%, around a target polymerization temperature, in particular around a target polymerization continuation temperature.

[0106] The initiation of polymerization and subsequent continuation of polymerization lead to a decrease in the quantity of monomers as well as a variation in the monomer composition in the reactor. Continuing polymerization with a substantially constant monomer composition in the reactor is made possible by injecting VDF, the second monomer, and the third monomer, of composition C2 [X2;Y2], into the reactor.

[0107] According to certain embodiments, the continuation of polymerization at substantially constant pressure and monomer composition in the reactor is implemented using VDF, the second monomer, and the third monomer, of composition C2, where the values ​​of the parameters X2 and Y2 remain constant during polymerization. This is particularly the case when composition C2 is injected as a pre-prepared gas mixture.

[0108] According to certain embodiments, the continuation of polymerization at substantially constant pressure is implemented using a composition C2 with a variable chemical composition [X2; Y2]. This is particularly the case when the composition C2 is injected as a stream of independent monomers. These embodiments make it possible to take into account the reduction in the volume available for the monomers due to the space occupied by the resulting polymer.

[0109] The decrease in the volume available for monomers in the reactor during polymerization is generally neglected, so that in practice polymerization can be carried out at constant pressure and constant injected C2 composition, resulting in a more homogeneous terpolymer than those of the prior art. According to some embodiments, a variable-volume reactor can be used, so that the volume available for monomers remains constant throughout polymerization.

[0110] The polymerization continuation step at substantially constant pressure ends when the injection of monomers of composition C2 is stopped. In one scenario, this stoppage can occur either when the reactor has reached its full capacity, with the polymer and water occupying the entire volume of the reactor. In a second scenario, this stoppage can be implemented because a quantity A predetermined amount of monomers with C2 composition was added during the polymerization continuation step at substantially constant pressure. In this case, it is advantageous to abruptly stop the polymerization reaction by adding a terminating agent and / or by rapidly cooling the reaction medium to avoid chemical inhomogeneity in the terpolymer P. The reactor can then be drained. The collected product can be filtered, washed, and dried using methods known per se.

[0111] An advantage of the process according to the invention is that it can be implemented at any mass ratio between the total mass quantity Q2 of VDF, second monomer and third monomer, of composition C2, injected during the continuation of the polymerization, and the total mass quantity Qien of VDF, second monomer and third monomer, injected initially to form the mixture Mb. This is made possible by the fact that at any point during the polymerization the terpolymer has a chemical composition equal to or close to the target composition Cp → 0 [Xp > 0; Yp → 0]. Advantageously, the ratio Q2 / Qi is generally greater than or equal to 0.5. Preferably, the ratio Q2 / Qi is greater than or equal to 0.75. Even more preferably, the ratio Q2 / Qi is greater than or equal to 0.90. Most preferably, the ratio Q2 / Qi is greater than or equal to 1.0.

[0112] The process allows for the production of terpolymers of any molar mass. The terpolymers according to the invention, which can be obtained by a process of the invention, generally have a weight-average molar mass Mw greater than or equal to 50,000 g / mol and less than or equal to 5,000,000 g / mol. The weight-average molar mass can be adjusted by modifying certain process parameters, such as the temperature in the reactor, or by adding a chain-regulating agent. The molecular weight distribution can be estimated by SEC (size-exclusion chromatography) with dimethylformamide (DMF) as the eluent, using a set of three columns of increasing porosity. The stationary phase is a styrene-DVB gel. The detection method is based on a measurement of the refractive index, and calibration is performed with polystyrene standards.The sample is dissolved at 0.5 g / L in DMF and filtered through a 0.45 µm nylon filter. According to some embodiments, the weight average molar mass Mw of the polymer is at least 550,000 g / mol, or at least 600,000 g / mol, or at least 700,000 g / mol, or at least 750,000 g / mol, or at least 800,000 g / mol, or at least 850,000 g / mol. In some embodiments, the weight-average molar mass Mw of the polymer is at most 4,000,000 g / mol, or at most 3,000,000 g / mol, or at most 2,000,000 g / mol, or at most 1,500,000 g / mol. In some embodiments, the weight-average molar mass Mw of the polymer is from 550,000 g / mol to 1,500,000 g / mol. Polymer

[0113] The invention also relates to a terpolymer P, of homogeneous chemical composition, essentially consisting of, or consisting of, repeating units resulting from the polymerization of vinylidene fluoride, a second monomer and a third monomer,

[0114] said second monomer having the chemical formula: CR1R2-CR3R4 (I), wherein: - C denotes a carbon atom, - each of the RB R2, R3 and R4 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, and

[0115] said third monomer having the chemical formula: CR5R6-CR7R8 (II), wherein: - C denotes a carbon atom, - each of R5, R6 and R7 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, - R8 is chosen from -Cl, -Br, and -I.

[0116] The preferred monomers of formula (II) and formula (III) are those stated in the part concerning the process according to the invention.

[0117] In particular, the terpolymer according to the invention can be a P(VDF-TrFE-CTFE) or a P(VDF-TrFE-CFE).

[0118] The terpolymer P has the composition C [X ;Y]. The parameter X represents the molar proportion, expressed as a percentage, in units resulting from the polymerization of VDF relative to the total number of moles in units resulting from the polymerization of VDF and the second monomer in the terpolymer.

[0119] The parameter Y represents the mole proportion, expressed as a percentage, in units resulting from the polymerization of the third monomer relative to the total number of moles in units resulting from the polymerization of VDF, the second monomer, and the third monomer in the terpolymer. The parameter X satisfies the inequality: 30 < X ​​< 100 (eq. 7). The parameter Y satisfies the inequality: 0.1 < Y ​​< 15.0 (eq. 8).

[0120] Preferably, the parameter X satisfies the inequality: 45.0 < X ​​< 90.0 (eq. 7a).

[0121] Preferably still, the parameter X satisfies the inequality: 50.0 < X ​​< 80.0 (eq. 7b). According to some embodiments, X satisfies one of the following inequalities: 50.0 < X ​​< 60.0, or 60.0 < X ​​< 70.0, or 70.0 < X ​​< 80.0.

[0122] Preferably, the parameter Y satisfies the inequality 1.0 < Y < 10.0 (eq. 8a). In particular, the parameter Y may satisfy one of the following inequalities:

[0123] 1.0 < Y < 3.0, or 3.0 < Y < 5.0, or 5.0 < Y < 7.0, or 7.0 < Y < 9.0,

[0124] or 9.0 < Y < 10.0.

[0125] According to other embodiments, Y < 1.0, or Y > 10.0 may also be.

[0126] The homogeneity of chemical composition of the terpolymer P is characterized by

[0127] the parameter AT, satisfying the following inequality: AT < 0.70 (eq. 9).

[0128] Preferably, the parameter AT satisfies the following inequality: AT < 0.60 (eq. 9a).

[0129] More preferably, AT satisfies the following inequality: AT < 0.50. (eq. 9b). According to some embodiments, AT satisfies one of the following inequalities: AT < 0.45, or AT < 0.40, or AT < 0.35, or AT < 0.30.

[0130] The AT parameter is defined as follows:

[0131] [Math.6] _ Tfma Tj.in a Tfm_b — Tim_b

[0132] The parameters Tfm and Timare respectively represent the final temperature of the melting peak, and the initial temperature of the melting peak, on a DSCa differential scanning calorimetry thermogram of said terpolymer P according to the invention,

[0133] The parameters Tfm bet Tim bre represent respectively the final temperature of the melting peak, and the initial temperature of the melting peak, on a DSCb thermogram of differential scanning calorimetry of a comparative terpolymer P'.

[0134] The comparative terpolymer P' has an average chemical composition similar to that of the terpolymer P, and can be obtained by a suspension polymerization process in which all of the VDF, the second monomer, and the third monomer used for polymerization are initially injected before the initiation of polymerization. Preferably, the polymerization of the comparative terpolymer P' is carried out under pressure and temperature conditions similar to those used to produce the terpolymer P according to the invention.

[0135] Differential scanning calorimetry (DSCa and DSCb) is carried out with heating and cooling ramps of 10°C / min, according to standard 11357-3:2018. The following temperatures can be identified on each differential scanning calorimetry thermogram:

[0136] Tfm, the final temperature of the melting peak. If there are several melting peaks, it corresponds to the highest final temperature;

[0137] Tim, the initial temperature of the melting peak. If there are several melting peaks, it corresponds to the lowest initial temperature.

[0138] The temperatures Tfm and Tim correspond to temperatures at which the melting endotherm detaches from the baseline.

[0139] The terpolymer P according to the invention is advantageously obtained by a suspension polymerization process, in particular by a process according to the invention. Composition

[0140] The polymer according to the invention can be formulated within a composition. The composition comprises a single or alternatively a mixture of polymers according to the invention.

[0141] According to certain embodiments, the composition may comprise at least one polymer according to the invention and at least one liquid vehicle of said at least one polymer. This composition, commonly referred to as "ink," may be prepared by dissolving or suspending the polymer(s) according to the invention in the liquid vehicle. Preferably, the liquid vehicle is a solvent. Advantageously, this solvent is a polar aprotic solvent, in particular one that may be selected from: dimethylformamide; dimethylacetamide; dimethyl sulfoxide; ketones, in particular acetone, methylethyl ketone, methylisobutyl ketone, and cyclopentanone; furans, in particular tetrahydrofuran; esters, in particular methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and propylene glycol methyl ether; carbonates, in particular dimethyl carbonate; phosphates, in particular triethyl phosphate, or mixtures thereof.The total mass concentration of polymers in the liquid vehicle can be from 0.1 to 30%, preferably from 0.5 to 20%.

[0142] According to certain embodiments, the composition may comprise one or more other polymers than those of the invention, having in particular polar or reactive functions enabling improvement of the adhesion of the composition to a given substrate.

[0143] The composition may optionally include one or more additives, in particular selected from surface tension modifying agents, rheology modifying agents, heat capacity modifying agents, resistance to aging modifying agents, adhesion modifying agents, pigments or dyes, flame retardants or crosslinking aid additives.

[0144] The composition may optionally include fillers, including nanofillers, such as barium strontium titanate (BST) nanowires. Film

[0145] The polymer according to the invention has, according to certain embodiments at least, sufficient mechanical properties to allow it to be shaped into a film.

[0146] The film can be prepared using the polymer according to the invention or a composition comprising it, for example by applying an ink to a substrate or by hot melt extrusion or compression.

[0147] The substrate may be of any nature and in particular consist of one or more layers of glass or metal(s) or organic (in particular polymeric).

[0148] The film may optionally be stretched if necessary. Stretching (when performed) is preferably carried out with a stretch ratio of at least 10% to 700%. In particular, the film may have a stretch ratio of at least 150%, or at least 200%, or at least 250%, or at least 300%, or at least 350%, or at least 400%. The stretch ratio corresponds to the ratio of the surface area of ​​the film after stretching to the surface area of ​​the film before stretching.

[0149] The films can also, after optionally being stretched, be annealed, that is to say, heated to a temperature below Tfm, preferably below Tim, for several hours, and then cooled. The annealing temperature is generally from 70°C to 140°C, and can, according to certain embodiments, be from 100°C to 120°C.

[0150] Stretching and annealing most often allow the crystallinity and dielectric strength to be increased.

[0151] The invention makes it possible to obtain films of desired thickness. In particular, the film can have a thickness from 1 micrometer to 100 micrometers. Among these thicknesses, the thinnest may be preferred to avoid generating excessively high voltages. Thus, films with a thickness of 1 to 50 micrometers and even 1 to 10 micrometers are particularly preferred.

[0152] Electrodes can be deposited on the film, in particular by metallization or by deposition of conductive material (silver, copper, conductive polymer, silver nanowires, carbon black, NTC, etc...).

[0153] According to some embodiments, the film prepared from the polymer according to the invention can be a layer of a multilayer device. Applications

[0154] According to at least some embodiments, the polymer according to the invention has electroactive properties, in particular ferroelectric or ferroelectric relaxor properties. It can then be used in actuators, and in particular for haptics, microfluidics, or in loudspeakers.

[0155] According to at least some embodiments, the polymer according to the invention has a high dielectric constant and / or high efficiency as defined in the examples, the polymer according to the invention can also be used in an energy storage system, in particular a capacitor, an organic transistor, or an electrostatic clutch. Examples

[0156] Comparative example 1: Synthesis of a P(VDF-TrFE-CTFE) according to the prior art, with an initial mixture devoid of CTFE.

[0157] A first mixture Mi of monomers consisting of 130 g of TrFE and 210 g of VDF, i.e., of composition [Xi;Yi] = [67.5% mol; 0% mol], was injected at room temperature into a stirred reactor containing 2.69 kg of demineralized water. Methylhydroxypropyl cellulose was then used to facilitate the suspension of the monomer mixture Mi in the water.

[0158] The monomer suspension was then heated to a temperature of 46°C. Once this temperature was reached, 1 g of polymerization initiator (dipropyl peroxydicarbonate) was introduced into the reactor. The pressure in the reactor reached 90 bar before polymerization began. Polymerization initiation was detected by a decrease in reactor pressure caused by monomer consumption. From the moment polymerization began, a C2 composition of VDF, TrFE, CTFE with [X2; Y2] = [67.5 mol%; 14.5 mol%] was continuously injected to maintain a pressure of approximately 90 bar in the reactor.

[0159] The reaction was stopped after the introduction of 408 g of the secondary mixture by cooling the reactor. The polymer produced was washed with demineralized water.

[0160] The polymer obtained is a P(VDF-TrFE-CTFE) had a molar composition [X;Y] of [67.4%mol ;8.2%mol] the unit contents resulting from the polymerization of VDF, TrFE and CTFE being determined by NMR, and an average molar mass by weight of 776,000 g / mol determined by SEC with polystyrene standards.

[0161] Example 1 (invention): Synthesis of a P(VDF-TrFE-CTFE) according to the invention with an average composition similar to that of comparative example 1

[0162] A first monomer mixture Mi consisting of 359 g of VDF, 208 g of TrFE and 45 g of CTFE, i.e., of composition [Xi;Yi] = [68.0 mol%; 5.5 mol%], was introduced at room temperature into a stirred reactor containing 2.22 kg of demineralized water. Methylhydroxypropyl cellulose was then used to facilitate the suspension of the monomer mixture Mi in the water.

[0163] The monomer suspension was then heated to a temperature of 46°C. Once this temperature was reached, 3.7 g of polymerization initiator (dipropyl peroxydicarbonate) was introduced into the reactor. The pressure in the reactor reached 90 bar before polymerization began. Polymerization initiation can be detected by a decrease in reactor pressure due to monomer consumption. Upon polymerization initiation, a C2 composition of VDF, TrFE, CTFE with [X2; Y2] = [67.5 mol%; 9.6 mol%] was injected into continuous so as to maintain in the reactor a pressure essentially equal to 90 bars.

[0164] The reaction was stopped after the introduction of 523 g of the secondary mixture by cooling the reactor. The polymer produced was washed with demineralized water.

[0165] The polymer obtained is a P(VDF-TrFE-CTFE) had a molar composition [X;Y] of [69.9%mol;8.1%mol] the contents in units resulting from the polymerization of VDF, TrFE and CTFE being determined by NMR and an average molar mass by weight of 866,000 g / mol determined by SEC with polystyrene standards.

[0166] Examples 2-3 and comparative examples 2-3: Synthesis of other P(VDF-TrFE-CTFE) according to the invention and according to the prior art

[0167] Other syntheses were carried out under operating conditions similar to those of Example 1, modifying the compositions [X1; YJ and [X2; Y2] in order to obtain for Examples 2 and 3 P(VDF-TrFE-CTFE) of composition [X;Y] different from the polymer according to Example 1.

[0168] Other syntheses were carried out under operating conditions similar to those of comparative example 1, modifying the compositions [X1; YJ and [X2; Y2] in order to obtain for comparative examples 2 and 3 P(VDF-TrFE-CTFE) of composition [X;Y] different from the polymer according to example 1.

[0169] Comparative example 4: Synthesis of a P(VDF-TrFE-CTFE) according to the prior art, all the monomers being added initially

[0170] A monomer mixture consisting of 316 g of TrFE, 478 g of VDF, and 90 g of CTFE, i.e., of composition [Xi;Yi] = [66.0 mol%; 6.4 mol%], was injected at room temperature into a stirred reactor containing 2.37 kg of demineralized water. Methylhydroxypropyl cellulose was then used to facilitate the suspension of the monomer mixture Mi in the water.

[0171] The monomer suspension was then heated to a temperature of 46°C. Once this temperature was reached, 1.7 g of polymerization initiator (dipropyl peroxydicarbonate) was introduced into the reactor. The pressure in the reactor reached 90 bar before polymerization began. Polymerization initiation can be detected by a decrease in reactor pressure due to monomer consumption. From the moment polymerization began, only water was added to the reactor throughout the polymerization process to maintain a pressure of approximately 90 bar. The reaction was stopped after the introduction of 510 g of water by cooling the reactor. The resulting polymer was washed with demineralized water.

[0172] The polymer obtained is a P(VDF-TrFE-CTFE) having a molar composition [X;Y] of [67.3%mol; 7.1%mol] the unit contents resulting from the polymerization of VDF, TrFE and CTFE being determined by NMR, and a weight average molar mass of 802,000 g / mol determined by SEC with polystyrene standards.

[0173] The set of values ​​[Xi; YJ, [X2; Y2] and [X; Y] for all examples and comparative examples has been compiled in Table 1 below. The parameters AX2 -, AY2 • have also been calculated.

[0174]

[0175] The AX2- parameter is defined as follows: [Math.7] / ¾ - ÀX ax2, = — X 100 \ X /

[0176] The AY2- parameter is defined as follows:

[0177] [Math.8]

[0178] [Tables] Ex. 0.16 -1.34 Comp.2 70.6 2.2 72.0 0.0 72.0 7.9 2.61 2.05 Ex.2 69.0 2.0 69.8 0.9 67.5 1.9 -0.05 -2.16 Comp.3 66.6 5.2 65.5 0.0 65.5 9.3 0.80 -1.65 Ex.3 68.1 5.1 69.0 3.2 67.5 5.8 0.13 -0.88 Comp.4 67.3 7.1 66.0 6.4 - - - - Characterizations

[0179] Differential scanning calorimetry (DSC) analyses were performed on a Mettler Toledo apparatus equipped with an internal cooler and operating under a nitrogen (N2) flow on the polymers of the examples and comparative examples.

[0180] The thermal measurement procedure consists of two successive thermal cycles, each cycle consisting of: an isothermal period of 5 min at -50°C; a temperature increase at 10°C / min up to 250°C; an isothermal period of 5 minutes at 250°C; - a temperature cooling at 10°C / min down to -50°C, marking the end of a cycle.

[0181] The temperatures Tim and Tfm were identified on the second heating thermograms. Table 2 summarizes the measurements taken as well as the differences Tfm-Tim, representative of the spreading of the phase transition during melting.

[0182] [Tables2] Ex. Tim (°C) Tfm (°C) Tfm- Tim (°C) Comp.l 85.0 150.0 65.0 Ex.l 102.0 131.0 29.0 Comp.2 110.0 164.0 54.0 Ex.2 128.0 150.0 22.0 Comp. 3 100.0 154.0 54.0 Ex. 3 116.0 143.0 27.0 Comp.4 77.4 158.7 81.3

[0183] The polymers according to the invention have a phase transition in melting that is narrow over a narrow temperature range, which is indicative of better homogeneity of the chemical composition of the terpolymer, compared to polymers according to the prior art which have a phase transition in melting spread over a wide temperature range, which is indicative of significant heterogeneity of the chemical composition of the terpolymer.

[0184] By way of illustration, [Fig.1] represents the second heating thermograms of a polymer according to the invention (thermogram A) and of a polymer according to the prior art (thermogram B).

[0185] It is verified here that a prior art polymerization comprising the injection of an initial mixture free of CTFE and then the injection of a secondary mixture of monomers improves the homogeneity of the terpolymer obtained compared to an injection of all the monomers initially (see sample Comp. 1 having a Tfm-Tim value of 65°C and sample Comp. 4 having a Tfm-Tim value of 81.3 °C, i.e. a ratio of 65 / 81.3 equal to about 0.80). The polymerization process according to the invention makes it possible to further improve the homogeneity of the terpolymer compared to an injection of all the monomers initially (see sample Ex. 1 having a Tfm-Tim value of 29.0°C and sample Comp. 4 having a Tfm-Tim value of 81.3 °C, i.e. a ratio of 29.0 / 81.3 equal to about 0.36).

[0186] To evaluate the electroactive properties of polymers, devices were fabricated as follows. A 10 nm thick chromium electrode followed by a 100 nm thick silver electrode was deposited onto a 15 x 15 mm glass substrate by chemical vapor deposition (CVD). A polymer film was deposited on the substrate using a Dr. Blade from a 7 wt% polymer solution in ethyl acetate. The film thickness after solvent evaporation was measured at 3 µm. Annealing was performed at 105 °C on a hot plate for 2 hours. A 100 nm thick silver electrode was then evaporated over the film by CVD.

[0187] Permittivity measurements were performed using a broadband dielectric spectroscopy system and a Solartron 1260 A impedance analyzer, at various temperatures between -30°C and 70°C. Sample temperature control was performed using a Linkam LTS 350 temperature control system. Measurements were carried out with a 1 V AC voltage signal, with a signal frequency of 1 kHz.

[0188] Table 3 sets together the maximum relative permittivity measurements (emax, unitless), and the temperature at which these permittivities were measured (T, °C).

[0189] [Tables3] Ref. P ^max T (°C) Comp.l 48.7 40.0 Ex.l 56.3 40.0 Ex. 3 72.5 50.0

[0190] Comparison of the dielectric measurements carried out on the polymer according to example 1 with the measurements carried out on the polymer according to comparative example 1 shows that the polymer of homogeneous chemical composition according to the invention has a maximum permittivity higher than that of the comparative polymer of the same chemical composition but heterogeneous (increase of the order of 15%), and that this permittivity is maximum for the same temperature.

[0191] Polarization hysteresis was also measured by recording several polarization hysteresis cycles with an aixACCT Systems TF Analyzer 2000E. The measurements were performed by applying a continuous triangular signal with a frequency of 10 Hz, at room temperature (25 °C), and with an applied electric field of 1700 kV / cm.

[0192] The maximum polarization (Pmax, pC.cm2) and remanent polarization (Pr, pC.cm2) measurements of the polarization hysteresis have been compiled in Table 4.

[0193] Table 4 also contains recoverable energy density values ​​(WreCuP, KJ / m3) and efficiency 0 / ,%) calculated as follows.

[0194] The recoverable energy density (WrecUp) is interpreted visually as the area above the hysteresis loop of the first quadrant, while the lost energy density (Wioss) is represented by the area inside the loop of the first quadrant.

[0195] The efficiency (z?) is calculated according to the equation:

[0196] [Math.9] Wrecup 4"

[0197] A graphic illustration of the regions corresponding to the recoverable and lost energy density is provided in [Fig.2] for a polymer according to the invention (hysteresis curve (A)) and for a prior art polymer of the same average chemical composition (hysteresis curve (B)).

[0198] [Tables3] Ex. Pmax (ddC.cm'2) Pr (ddC.cm'2) Wrecup. (kJ / m3) Efficiency (%) Comp.1 4.7 0.8 2200.0 63.0 Ex.1 5.0 0.7 2307.0 66.0 Ex.2 7.6 4.9 1728.0 30.0 Ex.3 6.2 1.8 2284.0 54.0

[0199] By comparing the results for the polymer according to Example 1 with the results for the polymer according to Comparative Example 1, it can be seen that better homogeneity of the chemical composition of the polymer, such as that obtained according to the invention, makes it possible to achieve a higher maximum polarization (+6%) and to form a thinned hysteresis characterized by a decrease in the remanent polarization of (-12.5%). The recoverable energy density is increased (+5%) as well as the efficiency (+5%).

Claims

1. Demands A process for manufacturing a terpolymer P, essentially consisting of, or consisting of, repeating units resulting from the polymerization of vinylidene fluoride, a second monomer and a third monomer, by polymerization in suspension in a suspension liquid, said second monomer having the chemical formula: CRiR2-CR3 R4(I), wherein: - C denotes a carbon atom, - each of the Rh R2, R3 and R4 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, said third monomer having the chemical formula: CR5R6-CR7 R8 (II), wherein: - C denotes a carbon atom, - each of R5, R6 and R7 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, - R8 is chosen from -Cl, -Br, and -I said process comprising: - the injection into a reactor of a composition Ci in VDF, second monomer and third monomer, to form a mixture of monomers Mi in the suspension liquid, - the initiation of polymerization of the Mi mixture of monomers, and, - the continuation of polymerization by: - injection into the VDF reactor, second monomer and third monomer of composition C2, - and optionally, injection of a suspension liquid into the reactor; said process being characterized in that the continuation of the polymerization is carried out in the reactor at a pressure substantially constant and with a substantially constant monomer composition.

2. A method according to claim 1, wherein said second monomer is selected from vinyl fluoride, 1,2-difluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, and mixtures thereof; and preferably said second monomer is trifluoroethylene.

3. A method according to any one of the preceding claims, wherein each of the R5, R6 and R7 in the compound of formula (II) is independently chosen from -H and -F.

4. A process according to any one of the preceding claims, wherein said third monomer is chlorotrifluoroethylene, a chlorofluoroethylene, in particular 1-chloro-l-fluoroethylene, or a mixture thereof.

5. A process according to any one of the preceding claims, wherein the polymer Po represents the polymer capable of being obtained by low-conversion polymerization of said mixture Mi has a composition Cp >o [Xp>0; Yp >0], where Xp >o represents the mole proportion, expressed as a percentage, of VDF monomer relative to the total number of moles of VDF and second monomer in the polymer Po, where Yp >o represents the mole proportion, expressed as a percentage, of third monomer relative to the total number of moles of VDF, second monomer and third monomer in the polymer Po, and where low conversion means that less than 10% by weight, and preferably less than 5% by weight, of the monomers of the mixture Mi have reacted relative to the total weight of monomers injected for the formation of the mixture Mi, said process being characterized in that the composition C2 [X2;Y2 ] in VDF, second monomer and third monomer, injected during the continuation of the polymerization, having a composition substantially identical to the composition Cp >0 [Xp>0 ; Yp >0], so as to have a composition in monomers substantially constant in the reactor during the continuation of the polymerization.; where X2 represents the molar proportion, expressed as a percentage, of VDF monomer relative to the total number of moles of VDF and second monomer in composition C2, and where Y2 represents the molar proportion, expressed as a percentage, of third monomer relative to the total number of moles of VDF, second monomer and third monomer in composition C2.

6. Method according to claim 5, wherein the parameter Yp_>0 satisfies the inequality: 0.1 < Yp >0 < 15.0 (eq. 1), and preferably satisfies the inequality: 1.0 < Yp >0 < 10.0 (eq. 1a).

7. A method according to claim 6, wherein the parameter AY2 satisfies the inequality: -0.40 < AY2 < 0.65 (eq. 3), preferably satisfies the inequality: -0.25 < AY2 < 0.50 (eq. 3a), and more preferably satisfies the inequality: -0.12 < AY2 < 0.36 (eq. 3b), the parameter AY2 being defined as follows: [Math. 10] • 2 i >t! = y

8. A method according to any one of claims 5 to 7, wherein the parameter Xp >0 satisfies the inequality: 30.0 < Xp.>0 < 100 (eq. 4), preferably satisfies the inequality: 45.0 < Xp >0 < 90.0 (eq. 4a), and more preferably satisfies the inequality: 50.0 < Xp_>0 < 80.0 (eq. 4b).

9. A method according to claim 8, wherein the parameter AX2 satisfies the inequality: -8.0 < AX2 < 8.0 (eq. 6), preferably satisfies the inequality: -4.0 < AX2 < 4.0 (eq. 6a), and preferably further satisfies the inequality: -2.0 < AX2 < 2.0 (eq. 6b), the parameter AX2 being defined as follows: [Math. 11] AX2 = x 100

10. A method according to any one of claims 1 to 9, wherein the suspension liquid is water or an aqueous solution.

11. A process according to any one of claims 1 to 10, wherein the polymerization is essentially carried out under temperature and pressure conditions for which the monomers in the reactor are in the supercritical state.

12. A method according to any one of claims 1 to 11, wherein the polymerization is essentially carried out at a pressure of 50 to 130 bars, and preferably from 70 to 110 bars.

13. A process according to any one of claims 1 to 12, wherein the continuation of polymerization is carried out without injection of suspension liquid, in order to maintain a substantially constant pressure in the reactor.

14. A process according to any one of claims 5 to 13, wherein X2 and Y2 remain constant during the continuation of polymerization, where X2 represents the molar proportion, expressed as a percentage, of VDF monomer relative to the total number of moles of VDF and second monomer in composition C2, and where Y2 represents the molar proportion, expressed as a percentage, of third monomer relative to the total number of moles of VDF, second monomer and third monomer in composition C2.

15. Terpolymer P, obtained according to any one of claims 1 to 14, of homogeneous chemical composition, essentially consisting of, or consisting of, repeating units resulting from the polymerization of vinylidene fluoride, a second monomer and a third monomer, said second monomer having the chemical formula: CRiR2-CR3 R4 (I), in which: - C denotes a carbon atom, - each of the Rh R2, R3 and R4 is independently selected from -H, -F and alkyl groups comprising from 1 to 3 carbon atoms which are optionally partially or completely fluorinated, said third monomer having the chemical formula: CR5R6-CR7 R8 (II), in which: - C denotes a carbon atom, Each of R5, R6 and R7 is independently chosen from -H, -F and alkyl groups comprising 1 to 3 carbon atoms which are optionally partially or completely fluorinated, R8 is chosen from -Cl, -Br, and -I, said terpolymer P having the composition [X;Y], where X represents the molar proportion, expressed as a percentage, in units resulting from the polymerization of VDF relative to the total number of moles in units resulting from the polymerization of VDF and the second monomer in the terpolymer, and where Y represents the molar proportion, expressed as a percentage, in units resulting from the polymerization of the third monomer relative to the total number of moles in units resulting from the polymerization of VDF, the second monomer and the third monomer in the terpolymer, parameter X satisfying the inequality: 30 < X ​​< 100 (eq. 7), and parameter Y satisfying the inequality 0.1 < Y ​​< 15.0 (eq. 8), the homogeneity of chemical composition of terpolymer P being characterized by the parameter AT, satisfying the following inequality: AT < 0.70 (eq. 9), preferably satisfying the following inequality: AT < 0.60 (eq. 9a), and even more preferably satisfying the following inequality: AT < 0.50 (eq. 9b), where the parameter AT is defined as follows: [Math. 12] y _y tfmjt timji = —----—-- *fm_b ' iiii. b where Tfm and Timare respectively represent the final temperature of the melting peak, and the initial temperature of the melting peak on a DSCa differential scanning calorimetry thermogram of said terpolymer P, where Tfm_bet Timbre respectively represent the final temperature of the melting peak, and the initial temperature of the melting peak on a DSCb differential scanning calorimetry thermogram of a comparative terpolymer P' having an average chemical composition analogous to that of terpolymer P, and obtained by a suspension polymerization process where the entire VDF, second monomer and third monomer used for polymerization is initially injected before the initiation of polymerization, said differential scanning calorimetries DSCa and DSCb being implemented with heating and cooling ramps at 10°C / min.

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