Method for producing a fluorinated polymer

Abstract

The present invention relates to the use of an additive A2 as an anti-fouling agent in a method for producing a fluorinated polymer P1. The present invention also relates to the implementation of a method for producing a fluorinated polymer P1 in the presence of said additive A2.

Description

[0001]DescriptionTitle: Process for producing a fluoropolymerTechnical field The present invention relates to a process for producing a fluoropolymer. In particular, the present invention relates to a process for producing a fluoropolymer in the presence of an antifouling agent. Technological background of the inventionFluoropolymers have excellent mechanical and thermal properties, in addition to their exceptional chemical inertness. They are used in high-performance applications such as lithium-ion batteries, coatings or water treatment. Fluoropolymers are in particular prepared by aqueous emulsion of free radicals or suspension polymerization. Among the fluoropolymers, vinylidene fluoride is of particular importance in applications related to new energies.Since vinylidene fluoride is a gas or supercritical fluid depending on the polymerization process, the polymerization mechanism can be more complex than most emulsion polymerization processes. However, the overall polymerization mechanism follows the standard emulsion polymerization process and the recipe includes water, vinylidene fluoride, a surfactant, a water-soluble initiator, and some additives (chain transfer agent, buffer, antifouling agent). The polymerization takes place in a high-pressure reactor, where vinylidene fluoride is initially present in both the gas and aqueous phases, and in the PVDF particles during polymerization. Polyvinylidene fluoride (PVDF) is used as a binder in lithium-ion batteries due to its excellent electrochemical stability, good bonding ability, and strong adhesion to electrode materials and current collectors.In wet slurry processes for electrode preparation, active ingredients and binders are dispersed in a liquid solution. The liquid solution is usually based on organic solvents or water. The dispersion is cast onto a current collector and then dried in a high-temperature oven to produce an electrode. Unfortunately, the excellent properties provided by fluoropolymers such as PVDF can also limit the applications in which they can be used. For example, fluoropolymers are difficult to adhere to other materials. Therefore, organic solvents and other organic additives are typically used in a coating formulation to provide good adhesion (non-reversible adhesion) between PVDF-based polymers, a porous separator or electrode, and possibly added powder particles.Alternatively, fluoropolymer binders can carry functional groups to promote the adhesive behavior of the polymer. The functional groups are usually introduced by a functionalized vinyl compound used as a comonomer during fluoropolymer production. However, the use of these functionalized vinyl compounds leads to significant reactor fouling during the polymerization step. Therefore, it is necessary to find new solutions for the production of fluoropolymers by limiting reactor fouling during polymerization.Summary of the inventionAccording to a first aspect, the present invention relates to a process for producing a fluorinated polymer P1 comprising a step of polymerizing, in a reactor, a fluorinated monomer M1a and a monomer M1b in the presence of an initiator and from 0.05% to 50% by weight of an additive A2 based on the total weight of fluorinated monomer M1a; said additive A2 comprising repeating units derived from a monomer M2; said monomer M1b and said monomer M2 are independently of each other of formula (I), (II), (III), (IV), (V) or a mixture thereofR. 1 R 2 C=C(R 3 )((X 2 )p'-C(O)R 4 ) (I) R 5 R 6 C=C(R 7 )(OC(O)R 8 ) (II) R 30 R 31 C=CR 32 (CN) (VI) R 33 R 34 C=CR 35 (C(O)NR 36 R 37 ) (VII) in which R 1 , R 2 and R 3are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3 and –OR 25 with R 25 selected from the group consisting of H and C1-C18 alkyl optionally substituted with one or more group(s) selected from the group consisting of –OH, -CO2H, -SO3H, - PO3H2, -C(O)OR 25’ , -OC(O)R 25’, and a five- or six-membered heterocycle comprising at least one nitrogen atom in its ring chain;R25' is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl;p' is 0 or 1;R 5 , R 6 and R 7are independently of each other selected from the group consisting ofH and C1-C5 alkyl;R8 is C1-C5 alkyl;R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19, R20, R21, R22, R23, R24, R30, R31, R32, R33, R34, R35are independently of each other selected from the group consisting of H and C1-C5 alkyl, preferably selected from the group consisting of H and CH3; R 36 and R 37 are, independently of each other, selected from the group consisting of H and C1-C10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 38 , -OC(O)R 38 ; R 38is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted with one or more CO2H functional groups.According to a preferred embodiment, said monomer M1b is of formula R1R2C=C(R3)((X2)p'C(O)R4) in which the substituents R1, R2 and R3 are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; R4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3 or –OR 25 with R 25 selected from the group consisting of H and C1-C18 alkyl optionally substituted with one or more –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R group(s) 25’ , -C(O)OR 25’ or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its ring chain; R25' being selected from the group consisting of C1-C6alkyl or C6-C 12aryl optionally substituted by one or more –OH, -CO2H, -SO3H, -PO3H2 groups; p' is 0 or 1; X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester groups; with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5alkyl.According to a preferred embodiment, said monomer M1b is added, in said reactor, in the form of an aqueous solution and continuously.According to a preferred embodiment, said additive A2 is added before the initiation of the reaction when the pressure in said reactor is lower than the critical pressure of said fluorinated monomer M1a, preferably vinylidene fluoride, or said additive A2 is added continuously in said reactor. According to a preferred embodiment, said additive A2 is water-soluble.According to a preferred embodiment, said fluorinated monomer M1a selected from the group consisting of vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R. 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2 in which R 2is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.According to a preferred embodiment, said monomer M1a is vinylidene fluoride.According to a preferred embodiment, said monomer M1b is of formulaR1R2C=C(R3)((X2)p'C(O)R4) wherein the substituents R1, R2 and R3 are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl; R4 is –OR25with R 25 selected from the group consisting of H and C1-C 10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 25’ , -C(O)OR 25’ ; R 25’being selected from the group consisting of C1-C5 alkyl or C6 aryl optionally substituted by one or more –OH, -CO2H, -SO3H, -PO3H2 groups; p' is 0 or 1; X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C5alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester groups; with w1 being an integer from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C3 alkyl.According to a preferred embodiment, said additive A2 comprises repeating units derived from a monomer M2 of formula (I), (II), (VI), (VII) or a mixture thereofR 1 R 2 C=C(R 3 )((X 2 ) p’ -HORN 4 ) (I) R 5 R 6 C=C(R 7 )(OC(O)R 8 ) (II) R 30 R 31 C=CR 32 (CN) (VI) R 33 R 34C=CR 35 (C(O)NR 36 R 37 ) (VII) in which R 1 , R 2 and R 3 are independently of each other selected from the group consisting ofH, CO2H and C1-C5 alkyl;R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3and –OR 25 with R 25 selected from the group consisting of H and C1-C 18 alkyl optionally substituted by one or more group(s) selected from the group consisting of -OH, -CO2H, -SO3H, - PO3H2, -C(O)OR 25’ , -OC(O)R 25’ , and a five- or six-membered heterocycle comprising at least one nitrogen atom in its ring chain;R25' is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C hydrocarbon group 10alkyl optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl;p' is 0 or 1;R 5 , R 6 and R 7 are independently of each other selected from the group consisting ofH and C1-C5 alkyl;R8 is C1-C5 alkyl; R 30 , R 31 , R 32 , R 33 , R 34 , R 35 are independently of each other selected from the group consisting of H and C1-C5 alkyl, preferably selected from the group consisting of H and CH3; R 36 and R 37 are, independently of each other, selected from the group consisting of H and C1-C 10alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 38 , -OC(O)R 38 ; R 38 is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted by one or more CO2H functional groups.According to a preferred embodiment, said additive A2 comprises repeating units derived from a monomer M2 of formula R1R2C=C(R3)(C(O)R4) (I) in whichR 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl;R4 is -OR25 with R25 selected from the group consisting of H and C1-C5 alkyl optionally substituted with one or more group(s) selected from the group consisting of -OH, - CO2H, -SO3H, -PO3H2, -C(O)OR 25’ , -OC(O)R 25’;R25' is selected from the group consisting of C1-C5 alkyl and C6 aryl substituted by one or more CO2H functional groups.According to another aspect, the present invention relates to the use of an additive A2 as defined in the present application as an anti-fouling agent in a process for producing a fluoropolymer P1.According to a preferred embodiment, said fluoropolymer P1 comprises repeating units derived from a fluorinated monomer M1a selected from the group consisting of vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R. 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2 in which R 2is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.According to a preferred embodiment, said fluoropolymer P1 comprises repeating units derived from a fluoromonomer M1a being vinylidene fluoride.According to a preferred embodiment, said fluoropolymer P1 also comprises repeating units derived from a monomer M1b as defined in the present application.According to a preferred embodiment, said fluoropolymer P1 also comprises repeating units derived from a monomer M1b of formula R1R2C=C(R3)(C(O)R4) in which the substituents R 1 , R 2 and R 3are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl; R4 is –OR25 with R25 selected from the group consisting of H and C1-C10 alkyl optionally substituted by one or more group(s) – OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 25’ , -C(O)O-; R d'' being selected from the group consisting of C1-C5alkyl or C6aryl optionally substituted by one or more –OH, -CO2H, -SO3H, -PO3H2 group(s). Detailed description of the inventionThe present invention makes it possible to prepare a functionalized fluoropolymer while avoiding the problems of reactor fouling which may occur during polymerization reactions. According to a first aspect of the present invention, a method for producing a fluoropolymer P1 is provided. Said method comprises a step of polymerizing, in a reactor, a fluoromonomer M1a and a monomer M1b.Fluorinated monomer M1aSaid fluorinated monomer M1a used in the present method is selected from the group consisting of vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R. 1 CH2OCF=CF2in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R 2is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof. Among the trifluoropropenes, mention may be made of 3,3,3-trifluoropropene. Among the tetrafluoropropenes, mention may be made of 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene. Among the pentafluoropropenes, mention may be made of 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene. Chlorofluoroethylene can refer to either 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. The 1-chloro-1-fluoroethylene isomer is preferred. Chlorotrifluoropropene is preferably 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene.Preferably, said monomer M1a is selected from the group consisting of vinyl fluoride, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene and hexafluoropropylene. In particular, said monomer M1a is vinylidene fluoride. Monomer M1b According to a preferred embodiment, said process is carried out in the presence of a monomer M1b. Said monomer M1b may be of formula (I), (II), (III), (IV), (V), (VI) or (VII) or a mixture thereof R. 1 R 2 C=C(R 3 )((X 2 ) p’ -HORN 4 ) (I) R 5 R 6 C=C(R 7 )(OC(O)R 8 ) (II) R 30 R 31 C=CR 32 (CN) (VI) R 33 R 34 C=CR 35 (C(O)NR 36 R 37 ) (VII) in which R 1 , R 2 and R 3are independently of each other selected from the group consisting ofH, CO2H and C1-C5 alkyl;R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3 and –OR 25 with R 25 selected from the group consisting of H and C1-C18 alkyl optionally substituted with one or more group(s) selected from the group consisting of –OH, -CO2H, -SO3H, - PO3H2, -C(O)OR 25’ , -OC(O)R 25’, and a five- or six-membered heterocycle comprising at least one nitrogen atom in its ring chain;R25' is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5alkyl;p' is 0 or 1;R 5 , R 6 and R 7are independently of each other selected from the group consisting ofH and C1-C5 alkyl;R8 is C1-C5 alkyl;R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19, R20, R21, R22, R23, R24, R30, R31, R32, R33, R34, R35are independently of each other selected from the group consisting of H and C1-C5 alkyl, preferably selected from the group consisting of H and CH3; R 36 and R 37 are, independently of each other, selected from the group consisting of H and C1-C10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 38 , -OC(O)R 38 ; R 38 is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted with one or more CO2H functional groups.Preferably, said monomer M1b may be of formula (I), (II), (III), (IV), (V), (VI) or (VII) or a mixture thereof R 1 R 2 C=C(R 3 )((X 2 )p’ -HORN 4 ) (I) R 5 R 6 C=C(R 7 )(OC(O)R 8 ) (II) R 9 R 10 C=CR 11 C(O)OC(O)CR 12 =CR 13 R 14 (III) R 30 R 31 C=CR 32 (CN) (VI) R 33 R 34 C=CR 35 (C(O)NR 36 R 37 ) (VII) in which R 1 , R 2 and R 3 are independently of each other selected from the group consisting ofH, CO2H and C1-C5 alkyl;R 4 is –OR 25 with R 25 selected from the group consisting of H and C1-C 10 alkyl optionally substituted by one or more group(s) selected from the group consisting of –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 25’ , -OC(O)R 25’;R25' is selected from the group consisting of C1-C5 alkyl and C6-C10 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C hydrocarbon group 10 alkyl optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl;p' is 0 or 1;R 5 , R 6 and R 7are independently of each other selected from the group consisting ofH and C1-C3 alkyl;R8 is C1-C3 alkyl;R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19, R20, R21, R22, R23, R24, R30, R31, R32, R33, R34, R35are independently of each other selected from the group consisting of H and C1-C3 alkyl, preferably selected from the group consisting of H and CH3; R 36 and R 37 are, independently of each other, selected from the group consisting of H and C1-C5 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 38 , -OC(O)R 38 ; R 38is selected from the group consisting of C1-C3alkyl and C6-C10 aryl substituted with one or more CO2H functional groups. According to a particular embodiment, said monomer M1b is of formula R1R2C=C(R3)((X2)p'C(O)R4) in which the substituents R1 and R3 are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; R4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3 or –OR 25 with R 25 selected from the group consisting of H and C1-C18 alkyl optionally substituted with one or more –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R group(s) 25’ , -C(O)OR 25’ or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its ring chain; R25' being selected from the group consisting of C1-C6alkyl or C6-C 12aryl optionally substituted by one or more groups –OH, -CO2H, -SO3H, -PO3H2; p' is 0 or 1; X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C hydrocarbon group 10alkyl optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w2, selected from the group consisting of H and C1-C5alkyl. Said heterocycle may be saturated or unsaturated or aromatic. Said heterocycle may be monocyclic or bicyclic. Said heterocycle may be a pyrrole, pyrrolidine, pyridine, piperidine, pyrimidine, pyrazine, 1,4-dihydropyridine, indole, oxindole, isatin, quinoline, isoquinoline, quinazoline, imidazoline, pyrazolidine, 2-pyrrolidone, deltalactam, succinimide, 2-imidazolidinone, 4-imidazolidinone ring. Said heterocycle may be substituted by one or more C1-C5 alkyl groups. As mentioned above, C1-C18 alkyl is optionally substituted by said heterocycle.The latter may be linked to the alkyl chain by the nitrogen atom or any other atom forming the heterocycle. Preferably the heterocycle is 2-pyrrolidone, delta-lactam, succinimide, 2-imidazolidinone, 4-imidazolidinone. Advantageously, said monomer M1b may be of formula R1R2C=C(R3)((X2)p'C(O)R4) in which the substituents R. 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; R4 is –OR25 with R25 selected from the group consisting of H and C1-C 18 alkyl optionally substituted by one or more group(s) – OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 25’ , -C(O)OR 25’or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its ring chain; R25' being selected from the group consisting of C1-C6 alkyl or C6-C12 aryl optionally substituted by one or more –OH, -CO2H, -SO3H, -PO3H2 groups; p' is 0 or 1; X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester groups; with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl.Preferably, said monomer M1b may be of formula R1R2C=C(R3)((X2)p'C(O)R4) in which the substituents R 1 , R 2 and R 3are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; R4 is –OR25 with R25 selected from the group consisting of H and C1-C 15 alkyl optionally substituted by one or more group(s) – OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 25’ , -C(O)OR 25’ ; R 25’being selected from the group consisting of C1-C5 alkyl or C6-C10 aryl optionally substituted by one or more –OH, -CO2H, -SO3H, -PO3H2 groups; p' is 0 or 1; X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester groups; with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl.More preferably, said monomer M1b may be of formula R1R2C=C(R3)((X2)p'C(O)R4)in which the substituents R 1 , R 2 and R 3are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl; R4 is –OR25 with R25 selected from the group consisting of H and C1-C 10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 25’ , -C(O)OR 25’ ; R 25’being selected from the group consisting of C1-C5 alkyl or C6 aryl optionally substituted by one or more –OH, -CO2H, -SO3H, -PO3H2 groups; p' is 0 or 1; X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C5 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester groups; with w1 being an integer from 1 to 5; R26, R27, R28, R29 are independently of each other,independently for each unit w1, selected from the group consisting of H and C1-C3alkyl.In particular, said monomer M1b may be of formula R1R2C=C(R3)((X2)p'C(O)R4) in which the substituents R 1 , R 2 and R 3are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl; R4 is –OR25 with R25 selected from the group consisting of H and C1-C10 alkyl optionally substituted with one or more groups – OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 25’ , -C(O)OR 25’ ; R 25’being selected from the group consisting of C1-C5alkyl or C6aryl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2.More particularly, said monomer M1b may be acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-dodecyl acrylate, amyl acrylate, isoamyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, diacetone acrylamide, lauryl acrylate, n-octyl acrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate, acrylate hydroxypropyl, hydroxybutyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-dodecyl methacrylate, amyl methacrylate,isoamyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, n-octyl methacrylate, ureido methacrylate, monomers of formula CH2=CH(CO2CH2CH2CO2H), CH2=CH(CO2CH2CH2-OC(O)-CH2CH2CO2H), CH2=CH(CO2CH2CH2CH2-OC(O)-CH2CH2CO2H), CH2=CH(CO2CH(CH3)CH2-OC(O)- CH2CH2CO2H),CH2=CH(CO2CH2CH2-OC(O)-C6H4CO2H),CH2=CH(CO2CH2CH2CH2CH(CO2H)CH2CH2CO2H); and mixtures thereof.Monomer M1cSaid process may also be carried out in the presence of a monomer M1c, different from the monomer M1a. Preferably, said monomer M1c is selected from the group consisting of vinyl fluoride, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene, hexafluoropropylene, perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R, 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2 in which R 2is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof. More preferably, when said monomer M1a is vinylidene fluoride, said fluorinated monomer M1c is selected from the group consisting of vinyl fluoride; trifluoroethylene; chlorotrifluoroethylene; 1,2-difluoroethylene, tetrafluoroethylene; hexafluoropropylene; perfluoro(alkyl vinyl)ethers such as perfluoro(methyl vinyl)ether, perfluoro(ethyl vinyl)ether or perfluoro(propyl vinyl)ether; perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F;the product of formula F(CF2)nCH2OCF=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R'CH2OCF=CF2in which R' is hydrogen or F(CF2)z and z is 1, 2, 3 or 4; the product of formula R''OCF=CH2 in which R'' is F(CF2)z and z is 1, 2, 3 or 4;trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene or 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof. In particular, when said monomer M1a is vinylidene fluoride, said fluorinated monomer M1c is selected from the group consisting of trifluoroethylene, chlorotrifluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene and hexafluoropropylene or a mixture thereof. Additive A2As mentioned above, in the present process, an additive A2 is added. This acts as an anti-fouling agent for the reactor. According to a preferred embodiment, said additive A2 comprises repeating units derived from a monomer M2 of formula (I), (II), (III), (IV), (V), (VI), (VII) or a mixture thereofR; 1 R 2 C=C(R 3 )((X 2 )p'-C(O)R 4 ) (I) R 5 R 6 C=C(R 7)(OC(O)R 8 ) (II) R 30 R 31 C=CR 32 (CN) (VI) R 33 R 34 C=CR 35 (C(O)NR 36 R 37 ) (VII) in which R 1 , R 2 and R 3 are independently of each other selected from the group consisting ofH, CO2H and C1-C5 alkyl;R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3and –OR 25 with R 25 selected from the group consisting of H and C1-C 18 alkyl optionally substituted by one or more group(s) selected from the group consisting of –OH, -CO2H, -SO3H, - PO3H2, -C(O)OR 25’ , -OC(O)R 25’, and a five- or six-membered heterocycle comprising at least one nitrogen atom in its ring chain;R25' is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl;p' is 0 or 1;R 5 , R 6 and R 7are independently of each other selected from the group consisting ofH and C1-C5 alkyl;R8 is C1-C5 alkyl;R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19, R20, R21, R22, R23, R24, R30, R31, R32, R33, R34, R35are independently of each other selected from the group consisting of H and C1-C5 alkyl, preferably selected from the group consisting of H and CH3; R 36 and R 37 are, independently of each other, selected from the group consisting of H and C1-C10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 38 , -OC(O)R 38 ; R 38 is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted by one or more CO2H functional groups. Advantageously, the additive A2 comprises repeating units derived from a monomer M2 of formula (I), (II), (III), (IV), (V), (VI), (VII) or a mixture thereofR 1 R 2 C=C(R3 )((X 2 )p'-C(O)R 4 ) (I) R 5 R 6 C=C(R 7 )(OC(O)R 8 ) (II) R 9 R 10 C=CR 11 C(O)OC(O)CR 12 =CR 13 R 14 (III) R 30 R 31 C=CR 32 (CN) (VI) R 33 R 34 C=CR 35 (C(O)NR 36 R 37 ) (VII) in which R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3 and –OR 25 with R 25 selected from the group consisting of H and C1-C15 alkyl optionally substituted with one or more group(s) selected from the group consisting of –OH, -CO2H, -SO3H, - PO3H2, -C(O)OR 25’ , -OC(O)R 25’, and a five- or six-membered heterocycle comprising at least one nitrogen atom in its ring chain;R25' is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl;p' is 0 or 1;R 5 , R 6 and R 7are independently of each other selected from the group consisting ofH and C1-C3 alkyl;R8 is C1-C3 alkyl;R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19, R20, R21, R22, R23, R24, R30, R31, R32, R33, R34, R35 areindependently of each other selected from the group consisting of H and C1-C3 alkyl, preferably selected from the group consisting of H and CH3; R 36 and R 37 are, independently of each other, selected from the group consisting of H and C1-C5 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 38 , -OC(O)R 38 ; R 38 is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted by one or more CO2H functional groups.Preferably, said additive A2 comprises repeating units derived from a monomer M2 of formula (I), (II), (VI), (VII) or a mixture thereof R 1 R 2 C=C(R 3)((X 2 )p'-C(O)R 4 ) (I) R 5 R 6 C=C(R 7 )(OC(O)R 8 ) (II) R 30 R 31 C=CR 32 (CN) (VI) R 33 R 34 C=CR 35 (C(O)NR 36 R 37 ) (VII) in which R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl; R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3 and –OR 25 with R 25 selected from the group consisting of H and C1-C18 alkyl optionally substituted with one or more group(s) selected from the group consisting of -OH, -CO2H, -SO3H, - PO3H2, -C(O)OR 25’ , -OC(O)R 25’, and a five- or six-membered heterocycle comprising at least one nitrogen atom in its ring chain;R25' is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl;p' is 0 or 1;R 5 , R 6 and R 7 are independently of each other selected from the group consisting ofH and C1-C5 alkyl;R8 is C1-C5 alkyl;R 30 , R 31 , R 32 , R 33 , R 34 , R 35are independently of each other selected from the group consisting of H and C1-C5alkyl, preferably selected from the group consisting of H and CH3; R 36 and R 37 are, independently of each other, selected from the group consisting of H and C1-C10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 38 , -OC(O)R 38 ; R 38 is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted by one or more CO2H functional groups. More preferably, said additive A2 is of formula R1R2C=C(R3)((X2)p'-C(O)R4) (I) in which R 1 , R 2 and R 3are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl;R4 is –OR25 with R25 selected from the group consisting of H and C1-C15 alkyloptionally substituted with one or more group(s) selected from the group consisting of –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 25’ , -OC(O)R 25’, and a five- or six-membered heterocycle comprising at least one nitrogen atom in its ring chain;R25' is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl; p' is 0 or 1.In particular, said additive A2 is of formula R1R2C=C(R3)((X2)p'-C(O)R4) (I) in which R1, R2 andR 3 are independently selected from the group consisting of H, CO2H et C1-C3 alkyle ;R4 is –OR25 with R25 selected from the group consisting of H and C1-C10 alkyl optionally substituted with one or more group(s) selected from the group consisting of –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 25’ , -OC(O)R 25’, and a five- or six-membered heterocycle comprising at least one nitrogen atom in its ring chain;R25' is selected from the group consisting of C1-C5 alkyl and C6 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C5alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl; p' is 0 or 1.More particularly, additive A2 comprises repeating units derived from a monomer M2 of formula (I) R1R2C=C(R3)((X2)p'-C(O)R4) (I) in whichR 1 , R 2 and R 3are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl;R4 is -OR25 with R25 selected from the group consisting of H and C1-C10 alkyl optionally substituted with one or more group(s) selected from the group consisting of –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 25’ , -OC(O)R 25’;R25' is selected from the group consisting of C1-C5 alkyl and C6 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C5alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5alkyl; p' is 0 or 1. Preferably, the additive A2 comprises repeating units derived from a monomer M2 of formula (I) R1R2C=C(R3)(C(O)R4) (I) in whichR 1 , R 2 and R 3are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl;R4 is -OR25 with R25 selected from the group consisting of H and C1-C10 alkyl optionally substituted with one or more group(s) selected from the group consisting of –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 25’ , -OC(O)R 25’;R25' is selected from the group consisting of C1-C3 alkyl and C6 aryl substituted by one or more CO2H functional groups.According to one embodiment, said additive A2 is a homopolymer of said monomer M2 according to any one of formulas (I) to (VII) above. According to another embodiment, said additive A2 is a copolymer of several monomers M2 according to any one of formulas (I) to (VII) above. By copolymer is meant repeating units derived from at least two monomers M2 according to any one of formulae (I) to (VII) above. Said additive A2 may have a molar mass by weight of between 500 g / mol and 10000000 g / mol, advantageously between 600 g / mol and 9000000 g / mol, preferably between 700 g / mol and 8000000 g / mol, more preferably between 700 g / mol and 7000000 g / mol, in particular between 800 g / mol and 6000000 g / mol, more particularly between 900 g / mol and 5000000 g / mol, preferably between 1000 g / mol and 4000000 g / mol.The molecular or molar mass is determined by Size Exclusion Chromatography (SEC). A sample of the polymer solution corresponding to 90 mg of dry matter is introduced into a 10 mL flask. Mobile phase, containing 0.04% dimethylformamide (DMF), is added to a total mass of 10 g. The composition of this mobile phase is as follows: NaHCO3: 0.05 mol / L, NaNO3: 0.1 mol / L, triethanolamine: 0.02 mol / L, NaN30.03% by mass. The CES system consists of a Waters 510 isocratic pump with a flow rate set at 0.8 mL / min, a Waters 717+ autosampler, an oven containing a 6 cm long, 40 mm inner diameter Waters GuardColumn Ultrahydrogel precolumn, followed by a 30 cm long, 7.8 mm inner diameter Waters Ultrahydrogel linear column. Detection is performed using a Waters RI 410 differential refractometer.The oven is heated to 60°C and the refractometer is heated to 45°C. The CES device is calibrated with a series of sodium polyacrylate standards supplied by Polymer Standards Service with a peak molecular weight between 1000g / mol and 1.10. 6g / mol and a polydispersity index of between 1.4 and 1.7. The calibration curve is linear and takes into account the correction obtained using the flow marker: dimethylformamide (DMF). Process The polymerization step can be carried out at a temperature above the critical temperature of the monomers used therein. The polymerization step can be carried out at a temperature above 20°C, advantageously above 30°C, preferably above 40°C. The polymerization step can be carried out at a temperature of 20°C to 120°C, preferably from 30°C to 110°C, in particular from 40°C to 90°C. The polymerization step can be carried out over a wide pressure range. Generally, the polymerization step can be carried out at a pressure of 10 to 150 bara, advantageously at a pressure of 15 bara to 130 bara, preferably at a pressure of 20 bara to 120 bara, in particular 40 to 110 bara.Preferably, said monomer M1b is added, in said reactor, in the form of an aqueous solution. According to a preferred embodiment, said monomer M1b is added, in said reactor, continuously. Said additive A2 is added before the initiation of the reaction when the pressure in said reactor is lower than the critical pressure of vinylidene fluoride. Alternatively, said additive A2 is added continuously in said reactor. Said additive A2 is added in a mass content of 0.05% to 50% based on the total weight of fluorinated monomer M1a. The total weight of monomer M1a is that added over the entire polymerization step.Said additive A2 may be added in a mass content of 0.05 to 48% or 0.05 to 46% or 0.05 to 44% or 0.05 to 42% or 0.05 to 40% or 0.05 to 38% or 0.05 to 36% or 0.05 to 34% or 0.05 to 32% or 0.05 to 30% or 0.05 to 28% or 0.05 to 26% or 0.05 to 24% or 0.05 to 22% or 0.05 to 20% or 0.05 to 18% or 0.05 to 16% or 0.05 to 14% or 0.05 to 12% or 0.05 to 10% or 0.05 to 8% or 0.05 to 6% or 0.05 to 5%. Said additive A2 may be added in a mass content of 0.1 to 48% or 0.1 to 46% or 0.1 to 44% or 0.1 to 42% or 0.1 to 40% or 0.1 to 38% or 0.1 to 36% or 0.1 to 34% or 0.1 to 32% or 0.1 to 30% or 0.1 to 28% or 0.1 to 26% or 0.1 to 24% or 0.1 to 22% or 0.1 to 20% or 0.1 to 18% or 0.1 to 16% or 0.1 to 14% or 0.1 to 12% or 0.1 to 10% or 0.1 to 8% or 0.1 to 6% or 0.1 to 5%.Said additive A2 may be added in a mass content of 0.25 to 48% or 0.25 to 46% or 0.25 to 44% or 0.25 to 42% or 0.25 to 40% or 0.25 to 38% or 0.25 to 36% or 0.25 to 34% or 0.25 to 32% or 0.25 to 30% or 0.25 to 28% or 0.25 to 26% or 0.25 to 24% or 0.25 to 22% or 0.25 to 20% or 0.25 to 18% or 0.25 to 16% or 0.25 to 14% or 0.25 to 12% or 0.25 to 10% or 0.25 to 8% or 0.25 to 6% or 0.25 to 5%. Said additive A2 may be added in a mass content of 0.5 to 48% or 0.5 to 46% or 0.5 to 44% or 0.5 to 42% or 0.5 to 40% or 0.5 to 38% or 0.5 to 36% or 0.5 to 34% or 0.5 to 32% or 0.5 to 30% or 0.5 to 28% or 0.5 to 26% or 0.5 to 24% or 0.5 to 22% or 0.5 to 20% or 0.5 to 18% or 0.5 to 16% or 0.5 to 14% or 0.5 to 12% or 0.5 to 10% or 0.5 to 8% or from 0.5 to 6% or from 0.5 to 5%. Said method is preferably carried out in the presence of an initiator.The initiator may be one or a combination of several of the initiators known in the art to be useful in the dispersion polymerization of halogenated monomers. Suitable non-limiting classes of initiators include persulfate salts, peroxides, and redox systems. Examples of persulfate salts are sodium persulfate, potassium persulfate, or ammonium persulfate. The amount of persulfate salt added to the reaction mixture based on the total weight of monomer added to the reaction mixture is typically from about 0.005 to about 1.0 wt. %. The initiator may comprise a redox system. By "redox system" is meant a system comprising an oxidizing agent, a reducing agent, and optionally a promoter acting as an electron transfer medium.The promoter is a component that, in different oxidation states, is capable of reacting with both the oxidant and the reducing agent, thereby accelerating the overall reaction. Oxidizing agents include, for example, persulfate salts; peroxides, such as hydrogen peroxide; hydroperoxides, such as tert-butyl hydroperoxide and cumene hydroperoxide; and oxidizing metal salts such as, for example, ferric sulfate and potassium permanganate. Examples of reducing agents include sodium formaldehyde sulfoxylate; sodium or potassium sulfite, bisulfite, or metabisulfite; ascorbic acid; oxalic acid; and reduced metal salts. Typical promoters include transition metal salts such as ferrous sulfate.In redox systems, the oxidizing agent and reducing agent are typically used in an amount of about 0.01 to about 0.5 wt.% based on the total weight of monomer added to the reaction mixture. The promoter, if used, is typically employed in an amount of about 0.005 to about 0.025 wt.% based on the total weight of monomer added to the reaction mixture. Preferably, the initiator is selected from organic peroxides which are useful include dialkyl peroxides, alkyl hydroperoxides, peroxyesters and peroxydicarbonates. A suitable example of a dialkyl peroxide is di-tert-butyl peroxide. Examples of suitable peroxy esters include tert-amyl peroxypivalate, tert-butyl peroxypivalate and succinic acid peroxide.Examples of suitable peroxydicarbonate initiators include di-n-propyl peroxydicarbonate (NPP) and diisopropyl peroxydicarbonate, which are typically added to the reaction mixture in an amount based on the total weight of monomer added to the reaction mixture of about 0.05 to about 2.5 wt.%. Said method may be carried out in the presence of a phase transfer agent. This may be a dispersant. The dispersant may be polyvinyl alcohol (PVA) or a compound comprising a cellulose unit such as cellulose ethers, for example methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose carboxymethyl cellulose, ethylhydroxy ethyl cellulose. Said phase transfer agent may be a surfactant. For example, said surfactant comprises a polyethylene glycol segment and a polypropylene glycol segment. Preferably, said surfactant has an HLB value of 1 to 20, in particular an HLB value of 1 to 5 or 10 to 15.In particular, said surfactant comprising a polyethylene glycol segment and a polypropylene glycol segment, has an HLB value of 1 to 5 and a weight average molecular weight of 2500 to 10000 g.mol-1. Alternatively, said surfactant comprising a polyethylene glycol segment and a polypropylene glycol segment, has an HLB value of 10 to 15 and a weight average molecular weight of 500 to 2500 g.mol- 1. A paraffin antifoulant is optionally used in the polymerization. Any long chain saturated hydrocarbon wax or oil may be used. The oil or wax is added to the reactor prior to fluoropolymer formation, in an amount sufficient to minimize polymer adhesion to the reactor components. This amount is generally proportional to the interior surface area of ​​the reactor and may vary from about 1 to about 40 mg / cm2 of interior surface area of ​​the reactor.If paraffin wax or hydrocarbon oil is used as an antifoulant, the amount used is typically about 5 mg / cm2 of the inner surface of the reactor. The polymerization reaction mixture may optionally contain a buffering agent to maintain a controlled pH during the polymerization reaction. The pH is typically controlled in the range of 3 to 8. The buffering agent may be added at the beginning, at various points, or throughout the polymerization. Suitable exemplary buffering agents are phosphate buffers and acetate buffers, which are well known to those skilled in the art. Molecular weight regulators, also known as chain transfer agents, may optionally be used to adjust the molecular weight profile of the product. They may be added in a single portion at the beginning of the reaction, gradually, or continuously throughout the reaction.The amount of molecular weight regulator added to the polymerization reaction is generally from about 0.05 to about 5 wt. %, more generally from about 0.1 to about 2 wt. % based on the total weight of monomer added to the reaction mixture. Oxygenated compounds such as alcohols, carbonates, ketones, esters and ethers can serve as molecular weight regulators. Examples of suitable oxygenated compounds include isopropyl alcohol, acetone, ethyl acetate and diethyl carbonate. Other classes of molecular weight regulators include halogenated compounds such as chlorocarbons, hydrochlorocarbons, hydrofluorocarbons, chlorofluorocarbons and hydrochlorofluorocarbons. Particular examples of halogenated molecular weight regulators include 1-fluoroethane, trichlorofluoromethane and 1,1-dichloro-2,2,2-trifluoroethane.Certain hydrocarbons can be used as molecular weight regulators, such as hydrocarbons that contain from two to five carbon atoms, with ethane and propane as particular examples.The fluoropolymer P1 obtained at the end of the reaction can be washed and dried to form a powder.Alternatively, the fluoropolymer P1 obtained at the end of the reaction can be washed and used in the form of a latex.Fluoropolymer P1The present invention allows the production of a fluoropolymer P1. In this, the mass content of repeating units derived from the monomer M1a is at least 50%, preferably at least 60%, more preferably at least 70%, in particular at least 80%, more particularly at least 90%, preferably at least 95%.Preferably, when it contains it, said fluoropolymer P1 comprises from 0.01% to 10%, preferably from 0.05% to 5%, in particular from 0.1% to 5% by weight of repeating units derived from said monomer M1b as defined in the present application based on the total weight of said fluoropolymer P1. Preferably, when it contains it, said fluoropolymer P1 comprises from 1% to 40%, preferably from 1% to 30%, in particular from 2% to 20% by weight of repeating units derived from said monomer M1c as defined in the present application based on the total weight of said polymer. Said fluoropolymer P1 may comprise repeating units derived from a monomer M1a being vinylidene fluoride, repeating units derived from a monomer M1b, repeating units derived from a monomer M1c; said monomers M1b and M1c being as defined above in the proportions as defined above.According to one embodiment, the average particle size of said fluoropolymer P1 is between 10 and 1000 nm. According to another embodiment, the average particle size is between 1 µm and 500 µm, preferably between 10 µm and 500 µm. The average particle size is determined by laser granulometry. A particle size analyzer of the Malvern INSITEC System type is used for the measurement. This is carried out dry by laser diffraction on a powder with a focal length of 100 mm. The method can be implemented in a vertical reactor. Use Said additive A2 as described in the present application is used as an anti-fouling agent in a process for producing a fluoropolymer P1. Said fluoropolymer P1 is as defined in the present application according to any one of the embodiments.It may therefore comprise repeating units derived from a monomer M1a and a monomer M1b and optionally from a monomer M1c; said monomers M1a, M1b or M1c are as defined above. Said additive A2 may be used according to any of the embodiments described in the present application. Example 1 The reaction was carried out in a 3L high-pressure reactor. 1373 g of demineralized water and 30 g of a phase transfer agent (dispersant or surfactant) were introduced into the reactor followed by 1224 g of vinylidene fluoride. The pressure increased. 1.84 g of di-n-propyl peroxydicarbonate (NPP) were introduced into the reactor. The reactor was then heated to 50°C. Demineralized water was introduced to increase the pressure. The reactor was stirred at 750 rpm and the pressure was kept constant by the continuous injection of an aqueous solution containing 12 g / L of acrylic acid and 4 g / L of polyacrylic acid.The reaction was stopped after 325 minutes by degassing the reactor to atmospheric pressure. A total of 784 g of solution was injected during the polymerization. The product was finally washed and dried. 945 g of dry powder were recovered, representing a conversion rate of around 77%. The incorporation of acrylic acid was measured at 0.77 mol% relative to the VF2 unit by NMR. No reactor fouling was observed. Example 2Example 1 was reproduced with a 12 g / L solution of acrylic acid and 32 g / L of polyacrylic acid. 886 g of solution were injected over 395 minutes before degassing the reactor to atmospheric pressure. 900 g of dry product were recovered, representing a conversion rate of approximately 73%. No reactor fouling was observed.Example 3 Example 2 was reproduced by introducing a 32 g / L solution of polyacrylic acid before the initiation of the reaction, i.e. when the pressure in the reactor was lower than the critical pressure of vinylidene fluoride. The injection of a 12 g / L solution of acrylic acid was carried out continuously as in Example 2. No fouling was observed. Comparative Example 1 Example 1 was reproduced with a 20 g / L solution of acrylic acid and without polyacrylic acid. 790 g of solution were injected in 280 minutes before degassing the reactor to atmospheric pressure. 1050 g of dry product were recovered, i.e. a conversion rate of approximately 86%. Block formation was observed and the reactor was heavily fouled.

Claims

Claims 1. A process for producing a fluoropolymer P1 comprising a step of polymerizing, in a reactor, a fluoromonomer M1a and a monomer M1b in the presence of an initiator and from 0.05% to 50% by weight of an additive A2 based on the total weight of fluoromonomer M1a; said additive A2 comprising repeating units derived from a monomer M2; said monomer M1b and said monomer M2 are independently of each other of formula (I), (II), (III), (IV), (V), (VI) or (VII) or a mixture thereof R 1 R 2 C=C(R 3 )((X 2 ) p’ -HORN 4 ) (I) R 5 R 6 C=C(R 7 )(OC(O)R 8 ) (II) R 9 R 10 C=CR 11 C(O)OC(O)CR 12 =CR 13 R 14 (III) R 30 R 31 C=CR 32 (CN) (VI) R 33 R 34 C=CR 35 (C(O)NR 36 R 37 ) (VII) in which R 1 , R2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl;R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3 and –OR 25 with R 25 selected from the group consisting of H and C1-C18 alkyl optionally substituted with one or more group(s) selected from the group consisting of –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 25’ , -OC(O)R 25’, and a five- or six-membered heterocycle comprising at least one nitrogen atom in its ring chain;R25' is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted by one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R 28 , R 29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5 alkyl; p' is 0 or 1;R 5 , R 6 and R 7are independently of each other selected from the group consisting of H and C1-C5 alkyl;R8 is C1-C5 alkyl;R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19, R20, R21, R22, R23, R24, R30, R31, R32, R33, R34,R 35 are independently of each other selected from the group consisting of H and C1-C5 alkyl, preferably selected from the group consisting of H and CH3; R 36 and R 37 are, independently of each other, selected from the group consisting of H and C1-C 10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 38 , -OC(O)R 38 ; R 38is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted by one or more functional groups CO2H.

2. Process according to the preceding claim characterized in that said monomer M1b is of formula R1R2C=C(R3)((X2)p'C(O)R4) in which the substituents R1, R2 and R3 are independently of each other selected from the group consisting of H, CO2H and C1-C5alkyl; R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3or –OR 25 with R 25 selected from the group consisting of H and C1-C18 alkyl optionally substituted with one or more group(s) –OH, -CO2H, -SO3H, - PO3H2, -OC(O)R 25’ , -C(O)OR 25’ or a five- or ten-membered heterocycle comprising at least one nitrogen atom in its ring chain; R25' being selected from the group consisting of C1-C6alkyl or C6-C 12aryl optionally substituted by one or more –OH, -CO2H, -SO3H, -PO3H2 groups; p' is 0 or 1; X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C10 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester groups; with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5alkyl.

3. Process according to any one of the preceding claims, characterized in that said monomer M1b is added, in said reactor, in the form of an aqueous solution and continuously.

4. Process according to any one of the preceding claims, characterized in that said additive A2 is added before the initiation of the reaction when the pressure in said reactor is lower than the critical pressure of said fluorinated monomer M1a, preferably vinylidene fluoride, or said additive A2 is added continuously in said reactor.

5. Process according to any one of the preceding claims, characterized in that said additive A2 is water-soluble.6.A method according to any one of the preceding claims characterized in thatsaid fluorinated monomer M1a selected from the group consisting of vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R. 1 CH2OCF=CF2 in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2 OCF=CH2in which R 2is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

7. A process according to any one of the preceding claims characterized in thatsaid monomer M1a is vinylidene fluoride.

8. Process according to any one of the preceding claims, characterized in that said monomer M1b is of formula R1R2C=C(R3)((X2)p'C(O)R4) in which the substituents R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl; R4 is –OR25 with R25 selected from the group consisting of H and C1-C 10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -OC(O)R 25’, -C(O)OR 25’ ; R 25’ being selected from the group consisting of C1-C5 alkyl or C6 aryl optionally substituted by one or more –OH, -CO2H, -SO3H, -PO3H2 groups; p' is 0 or 1; X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C5 alkyl hydrocarbon group optionally carrying one or more -OH, -CO2H or ester groups; with w1 being an integer from 1 to 5; R26, R27, R28, R29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C3 alkyl.

9. Process according to any one of the preceding claims, characterized in that said additive A2 comprises repeating units derived from a monomer M2 of formula (I), (II), (VI), (VII) or a mixture thereof. 1 R 2 C=C(R 3 )((X 2 ) p’ -HORN 4 ) (I) R 5 R 6 C=C(R 7 )(OC(O)R 8) (II) R 30 R 31 C=CR 32 (CN) (VI) R 33 R 34 C=CR 35 (C(O)NR 36 R 37 ) (VII) in which R 1 , R 2 and R 3 are independently of each other selected from the group consisting of H, CO2H and C1-C5 alkyl;R 4 is selected from the group consisting of –NHC(CH3)2CH2C(O)CH3and –OR 25 with R 25 selected from the group consisting of H and C1-C18 alkyl optionally substituted with one or more group(s) selected from the group consisting of -OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 25’ , -OC(O)R 25’, and a five- or six-membered heterocycle comprising at least one nitrogen atom in its ring chain;R25' is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted with one or more CO2H functional groups;X2 is selected from the group consisting of –[-C(O)OC(R26)(R27)C(R28)(R29)-]w1- and a C1-C hydrocarbon group 10 alkyl optionally carrying one or more -OH, -CO2H or ester group(s); with w1 being an integer from 1 to 50, advantageously from 1 to 25, preferably from 1 to 10, in particular from 1 to 5; R26, R27,R 28 , R 29 are independently of each other, independently for each unit w1, selected from the group consisting of H and C1-C5alkyl; p' is 0 or 1;R 5 , R 6 and R 7 are independently of each other selected from the group consisting of H and C1-C5 alkyl;R8 is C1-C5 alkyl;R 30 , R 31 , R 32 , R 33, R 34 , R 35 are independently of each other selected from the group consisting of H and C1-C5alkyl, preferably selected from the group consisting of H and CH3; R 36 and R 37 are, independently of each other, selected from the group consisting of H and C1-C10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 38 , -OC(O)R 38 ; R 38 is selected from the group consisting of C1-C5 alkyl and C6-C12 aryl substituted by one or more functional groups CO2H.

10. Process according to any one of the preceding claims characterized in that said additive A2 comprises repeating units derived from a monomer M2 of formula R 1 R 2 C=C(R 3 )(HORN 4 ) (I) in which R 1 , R 2 and R 3are independently of each other selected from the group consisting of H, CO2H and C1-C3 alkyl;R4 is -OR25 with R25 selected from the group consisting of H and C1-C5 alkyloptionally substituted with one or more group(s) selected from the group consisting of -OH, -CO2H, -SO3H, -PO3H2, -C(O)OR 25’ , -OC(O)R 25’ ; R25' is selected from the group consisting of C1-C5 alkyl and C6 aryl substituted by one or more CO2H functional groups.

11. Use of an additive A2 as defined in any one of claims 1, 5, 10 or 11 as an antifouling agent in a process for producing a fluoropolymer P1.

12. Use according to the preceding claim, characterized in that said fluoropolymer P1 comprises repeating units derived from a fluoro monomer M1a selected from the group consisting of vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE) and perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF2=CFOCF2CF(CF3)OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH2OPO3H; the product of formula CF2=CFOCF2CF2SO2F; the product of formula F(CF2)nCH2OCF=CF2in which n is 1, 2, 3, 4 or 5; the product of formula R 1 CH2OCF=CF2in which R 1 is hydrogen or F(CF2)m and m is 1, 2, 3 or 4; the product of formula R 2OCF=CH2 in which R 2is F(CF2)p and p is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); trifluoropropene, tetrafluoropropene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropene, bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene or a mixture thereof.

13. Use according to any one of the preceding claims 12 or 13 characterized in that said fluoropolymer P1 comprises repeating units derived from a fluoromonomer M1a being vinylidene fluoride.

14. Use according to the preceding claim characterized in that said fluoropolymer P1 also comprises repeating units derived from a monomer M1b as defined in claim 1, 2 or 8.15.Use according to the preceding claim, characterized in that said fluoropolymer P1 also comprises repeating units derived from a monomer M1b of formula R1R2C=C(R3)(C(O)R4) in which the substituents R1, R2 and R3 are independently of one another selected from the group consisting of H, CO2H and C1-C3 alkyl; R4 is –OR. 25 with R 25 selected from the group consisting of H and C1-C10 alkyl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, - PO3H2, -OC(O)R 25’ , -C(O)O-; R d '' being selected from the group consisting of C1-C5 alkyl or C6 aryl optionally substituted by one or more group(s) –OH, -CO2H, -SO3H, -PO3H2.

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