Method for producing fluoropolymers containing ion exchange groups

Abstract

The present invention is -SO3X a and -COOX a (In the formula, X a is H, an ammonium group or a monovalent metal). The present invention further relates to a fluoropolymer dispersion comprising a fluorinated polymer having ion exchange groups and a polymer derivative comprising ionic groups.

Description

[Technical field]

[0001] REFERENCE TO RELATED APPLICATIONS This application claims priority from European Patent Application No. 22159375.9, filed March 1, 2022, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to a method for making a fluoropolymer dispersion using certain multifunctional polymer derivatives, and to the fluoropolymers obtained therefrom. [Background technology]

[0003] Fluoropolymers, i.e. polymers with a fluorinated backbone, have been known for a long time and have been used in various applications due to several desirable properties such as heat resistance, chemical resistance, weather resistance, UV stability, etc. Fluorinated polymers containing ion exchange groups have been used for the manufacture of proton exchange membranes, e.g. for use in fuel cell applications.

[0004] A frequently used method for making fluoropolymers involves the aqueous emulsion polymerization of one or more fluorinated monomers, which usually involves the use of fluorinated surfactants, including perfluorooctanoic acid and its salts, particularly ammonium perfluorooctanoate.

[0005] More recently, perfluoroalkanoic acids with 8 or more carbon atoms have raised environmental concerns. For example, they have been found to exhibit bioaccumulation. Thus, efforts are currently being made to phase out such compounds and to develop methods for producing fluoropolymer products that use alternative surfactants with more favorable toxicity profiles.

[0006] EP 0 341 716 A (Asahi Glass Co., Ltd.) Nov. 15, 1989 is directed to a process for the preparation of aqueous dispersions, which comprises subjecting monomers to emulsion polymerization in an aqueous medium in the presence of a fluorine-containing copolymer having units derived from fluoroolefins and hydrophilic side chains having (i) carboxylic or carboxylate groups of formula -COOM, (ii) sulfonic or sulfonate groups of formula -SO3M and (iii) phosphonic or phosphonate groups of formula -PO3M, where M is hydrogen, an alkali metal, a quaternary ammonium group or a quaternary phosphonium group, and (iv) groups which may be amide groups, and having a number average molecular weight at the level of 1000 to 500000, in particular 3000 to 400000. The monomers to be polymerized are fluoroolefins having 2 to 4 carbon atoms, such as hexafluoropropylene, pentafluoropropylene, tetrafluoroethylene, chlorotrifluoroethylene, trifluoroethylene or vinylidene fluoride, with vinyl compounds, allyl compounds, fluorinated vinyl compounds or fluorinated allyl compounds being preferred, since their polymerization results in an aqueous dispersion capable of providing a coating layer with excellent weather resistance.

[0007] WO 2012 / 082707A1 (3M INNOVATIVE PROPERTIES COMPANY) discloses microemulsions obtained by mixing water, at least one ethylenically unsaturated fluoromonomer, at least one oligomeric fluorosulfinic acid compound and / or at least one ethylenically unsaturated, polymerizable monomeric fluorosulfinic acid compound, and their use for the polymerization of at least one ethylenically unsaturated fluoromonomer. The oligomeric and polymerizable monomeric fluorosulfinic acid compound has low molecular weight and is characterized by the presence of sulfinic acid / sulfinate functional group -SO2M, where M is a cation.

[0008] WO 2018 / 167190A1 (SOLVAY SPECIALTY POLYMERS ITALY SpA) September 28, 2018 discloses a process for the preparation of a polymerizable composition comprising the steps of: reacting one or more fluorinated monomers in an aqueous medium with at least one radical initiator; - comprises a backbone chain comprising repeat units derived from one or more ethylenically unsaturated monomers, - the dispersant has a molecular weight and a molecular weight distribution such that it is substantially free of a fraction having a molecular weight below 3000; -SO3X in an amount of at least 1.75 meq / g based on the weight of the dispersant a , -PO3X a and -COOX a (In the formula, X a is H, an ammonium group, or a monovalent metal WO 2018 / 167190A1 discloses a method for preparing a fluoropolymer comprising emulsion polymerization in the presence of at least one polyfunctional dispersant, the dispersant being used in an amount between 0.01% and 5.00% by weight, based on the total weight of the aqueous medium. a The preparation of PTFE in the presence of a dispersing agent (D) containing ionic groups is disclosed.

[0009] It has been found that the use of certain multifunctional dispersing agents disclosed in WO 2018 / 167190 A1 can be advantageously used in aqueous emulsion polymerization processes of monomers that contain hydrolyzable groups to provide surfactant-free dispersions of polymers that contain hydrolyzable groups. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A first object of the present invention is a method for the preparation of a fluoropolymer [polymer (P)] containing a plurality of hydrolyzable groups, said method comprising the steps of: - tetrafluoroethylene, at least one ethylenically unsaturated fluorinated monomer containing at least one hydrolyzable group; of, At least one radical initiator and at least one polyfunctional dispersant [dispersant (D)] [the dispersant (D) is - weight average molecular weight (M) of at least 15,000 and at most 800,000 w ) - comprises a backbone chain comprising repeat units derived from one or more ethylenically unsaturated monomers, -SO3X a and -COOX a (In the formula, X a is H, an ammonium group, or a monovalent metal.

[0011] The Applicant has surprisingly found that the dispersant (D), despite its high molecular weight, has sufficient surface-active effect and dispersing capacity to ensure efficient stabilization of the fluoropolymer in the aqueous polymerization environment, thanks to the presence of ionic groups as pendant groups in the fluorinated chains.

[0012] Advantageously, the dispersant (D) has a molecular weight and molecular weight distribution such that it is substantially free of fractions having a molecular weight below 3000.

[0013] The ionic groups in dispersant (D) are in an amount of at least 1.00 meq / g, based on the weight of dispersant (D).

[0014] The hydrolyzable groups in the polymer (P) are preferably selected from -SO2X and -COOZ, where X is a halogen atom and Z is a C1-C4 alkoxy group.

[0015] The dispersant (D) is used in an amount of 0.01% by weight to 5.00% by weight based on the total weight of the aqueous medium.

[0016] In an advantageous embodiment of the present invention, the ionic groups in the dispersant (D) are obtained from the hydrolyzable groups of the polymer (P), which is the product of the emulsion polymerization process. In this embodiment, at the end of the polymerization process, the polymer (P) does not require any purification step to remove the residues of the dispersant (D). In fact, the presence of the dispersant (D) will not have any detrimental effect on the properties of the polymer (P) due to their similar chemical nature.

[0017] In an even more advantageous embodiment of the invention, the dispersant (D) has the same monomer composition as the polymer (P) obtained at the end of the process, the only difference being the presence of ionic groups -SO3X instead of the hydrolyzable groups -SO2X and -COOZ, as defined above. a and -COOX a The existence of

[0018] definition The expression "fluorinated monomer" is intended herein to mean an ethylenically unsaturated monomer which contains at least one fluorine atom.

[0019] The phrase "consisting essentially of," when used in reference to a polymer composition that includes a dispersant (D), is intended to indicate that the polymer contains no more than 1 mol % of impurities, defects, and other spurious repeat units in addition to the recited repeat units, based on the total moles of end group repeat units.

[0020] Polymer (P) The process of the present invention comprises emulsion polymerizing in an aqueous medium tetrafluoroethylene and at least one ethylenically unsaturated fluorinated monomer containing at least one hydrolyzable group selected from the group consisting of -SO2X and -COOZ, where X is a halogen atom and Z is a C1-C4 alkoxy group.

[0021] Polymer (P) preferably comprises repeat units derived from at least one ethylenically unsaturated fluorinated monomer (hereinafter referred to as [monomer (A)]) comprising at least one hydrolyzable group -SO2X, where X is a halogen.

[0022] Non-limiting examples of suitable monomers (A) are: - X is halogen, preferably F or Cl, more preferably F, formula CF2=CF(CF2) p Sulfonyl halide fluoroolefins of the formula SO2X, where p is an integer from 0 to 10, preferably from 1 to 6, and more preferably p is equal to 1, 2 or 3; - X is halogen, preferably F or Cl, more preferably F, in the formula CF2=CF-O-(CF2) m Sulfonyl halide fluorovinyl ethers of the formula SO2X, where m is an integer from 1 to 10, preferably from 1 to 6, more preferably from 2 to 4, and even more preferably m is equal to 2; - X is a halogen, preferably F or Cl, more preferably F, of the formula: CF2=CF-(OCF2CF(R F1 )) w -O-CF2(CF(R F2 )) y SO2X (Wherein, w is an integer of 0 to 2, and R F1 and R F2 are independently F, Cl, or C1-C optionally substituted with one or more ether oxygen atoms; 10 is a fluoroalkyl group, y is an integer of 0 to 6; preferably, w is 1; R F1 is -CF3, y is 1, and R F2 is F); - a compound of the formula CF2=CF-Ar-SO2X, where X is a halogen, preferably F or Cl, more preferably F, where Ar is a C5-C 15 The sulfonyl halide aromatic fluoroolefin, which is an aromatic or heteroaromatic group, is selected from the group consisting of:

[0023] Preferably, the monomer (A) has the formula CF2=CF-O-(CF2) m The sulfonyl fluoride fluorovinyl ether is selected from the group of sulfonyl fluoride fluorovinyl ethers of the formula -SO2F (wherein m is an integer of 1 to 6, preferably 2 to 4).

[0024] More preferably, monomer (A) is CF2=CFOCF2CF2-SO2F (perfluoro-5-sulfonylfluoride-3-oxa-1-pentene).

[0025] Additional fluorinated monomers may be present during the polymerization process and incorporated into the polymer (P).

[0026] Non-limiting examples of suitable ethylenically unsaturated fluorinated monomers include: - C2-C8 perfluoroolefins, such as hexafluoropropylene, perfluoroisobutylene; - C2-C8 hydrogen-containing fluoroolefins, such as trifluoroethylene, vinylidene fluoride, vinyl fluoride, pentafluoropropylene, and hexafluoroisobutylene; - C2 to C8 chloro- and / or bromo- and / or iodo-containing fluoroolefins, such as chlorotrifluoroethylene and bromotrifluoroethylene; - Formula CF2=CFOR f1 (In the formula, R f1 is C1-C6 fluoroalkyl, for example, -CF3, -C2F5, -C3F7) fluoroalkyl vinyl ether; - In particular, the formula CF2=CFOCF2OR f2 (R f2 fluoromethoxyalkyl vinyl ethers of the formula CF2=CFOX0 (wherein X0 is a C1-C3 fluoro(oxy)alkyl group, such as -CF2CF3, -CF2CF2-O-CF3 and -CF3), 12 fluorooxyalkyl vinyl ethers, - Formula: [ka] (Wherein, R f3 , R f4 , R f5 , R f6 each independently represents a C1-C6 fluoro(halo)fluoroalkyl group containing a fluorine atom and optionally one or more oxygen atoms, e.g., -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3) It is.

[0027] In addition to tetrafluoroethylene, preferred fluoromonomers for use in the process of the present invention include chlorotrifluoroethylene, hexafluoropropylene, vinyl fluoride, and vinylidene fluoride.

[0028] The polymer (P) is preferably - from 50 to 99 mol %, preferably from 50 to 98 mol %, even from 5 to 95 mol %, of repeat units deriving from tetrafluoroethylene (TFE), relative to the total moles of the polymer (P); from 1 to 50 mol %, preferably from 2 to 50 mol %, even from 5 to 50 mol %, relative to the total moles of polymer (P), (j) X is a halogen, preferably F or Cl, more preferably F, in the formula CF2=CF-O-(CF2). m Sulfonyl halide fluorovinyl ethers of the formula SO2X, where m is an integer from 1 to 10, preferably from 1 to 6, more preferably from 2 to 4, and even more preferably m is equal to 2; (jj) X is a halogen, preferably F or Cl, more preferably F, of the formula: CF2=CF-(OCF2CF(R F1 )) w -O-CF2(CF(R F2 )) y SO2X (wherein w is an integer of 0 to 2, and may be equal or different from each other); F1 and R F2are independently F, Cl, or C1-C optionally substituted with one or more ether oxygen atoms; 10 is a fluoroalkyl group, y is an integer of 0 to 6; preferably, w is 1; R F1 is -CF3, y is 1, and R F2 is F); and (jjj) A mixture of these and a repeat unit derived from at least one monomer selected from the group consisting of: - from 0 to 45 mol %, preferably from 0 to 40 mol %, even from 0 to 25 mol %, of at least one hydrogen-containing monomer and / or fluorinated monomer different from TFE, preferably hexafluoropropylene, of formula CF2=CFOR', relative to the total moles of polymer (P); f1 (In the formula, R' f1 is C1-C6 perfluoroalkyl, for example -CF3, -C2F5, -C3F7); perfluorinated monomers typically selected from the group consisting of perfluoroalkyl vinyl ethers of the formula CF2=CFOCF2OR' f2 (In the formula, R' f2 is a C1-C6 perfluoroalkyl, for example a C1-C6 perfluorooxyalkyl having one or more ether groups, such as -CF3, -C2F5, -C3F7, or -C2F5-O-CF3, such as perfluoroalkyl-methoxy-vinyl ethers of the formula CF2=CFOR' O1 (In the formula, R' O1 is a C2-C alkyl group having one or more ether groups 12 perfluoro-oxyalkyl vinyl ethers of the formula: [ka] (Wherein, R f3 , R f4 , R f5 , R f6each independently is a C1-C6 fluoro(halo)fluoroalkyl containing a fluorine atom and optionally one or more oxygen atoms, e.g., -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3). and a repeating unit derived from fluorodioxole of The polymer is selected from the group consisting of polymers comprising or consisting essentially of:

[0029] According to a particular embodiment, the polymer (P) is (1) 50 to 95 mol %, preferably 55 to 93 mol %, of repeating units derived from TFE; (2) 5 to 50 mol %, preferably 7 to 45 mol %, of repeat units derived from the -SO2X group-containing monomer (A) as detailed above; (3) 0 to 25 mol %, preferably 0 to 20 mol %, of repeating units derived from a fluorinated monomer other than TFE, as detailed above. Comprises, consists essentially of, consists of.

[0030] The polymer (P) usually has a weight average molecular weight (M), as measured by GPC against polystyrene standards using dimethylacetamide as eluent, of at least 50,000, preferably at least 85,000, more preferably at least 100,000. w ).

[0031] The weight average molecular weight (M) of the polymer (P), as measured by GPC against polystyrene standards using dimethylacetamide as the eluent, w ) is usually at most 700000, preferably at most 600000, more preferably at most 500000. A suitable range for most applications of the polymer (P) is, for example, 150000 to 600000, preferably 180000 to 500000.

[0032] Preferably the polymer (P) has a number average molecular weight, as measured by GPC against polystyrene standards using dimethylacetamide as eluent, of at least 50000, preferably at least 90000 and / or advantageously at most 500000, preferably at most 450000. The GPC method is detailed in the experimental section.

[0033] Dispersant (D) The polyfunctional dispersant (D) is a polyfunctional dispersant having a repeating unit derived from one or more ethylenically unsaturated monomers and -SO3X a and -COOX a (In the formula, X a is H, an ammonium group, or a monovalent metal. Dispersant (D) does not contain unsaturated carbon-carbon bonds.

[0034] The dispersant (D) is used in an amount of 0.01% to 5.00% by weight, based on the total weight of the aqueous medium.

[0035] The amount of dispersant (D) in the emulsion polymerization process is at least 0.05% by weight, preferably at least 0.10% by weight, advantageously at most 4.00% by weight, preferably at most 3.50% by weight, even more preferably at most 3.00% by weight, based on the total weight of the aqueous medium. A practical range is 0.10% to 2.75% by weight, preferably 0.25% to 2.00% by weight, even 0.50% to 1.75% by weight, based on the total weight of the aqueous medium. In a particular embodiment, the dispersant (D) is present in an amount of 0.25% to 1.50% by weight, based on the total weight of the aqueous medium.

[0036] The polymerization is usually initiated in the presence of dispersing agent (D) and, although it is not excluded to add further dispersing agent (D) during the polymerization, such will not usually be necessary.

[0037] The dispersant (D) typically has a weight average molecular weight (M), as measured by GPC against polystyrene standards using dimethylacetamide as the eluent, of at least 15,000. w The GPC method is detailed in the experimental section.

[0038] The weight average molecular weight (M) of the dispersant (D), as measured by GPC against polystyrene standards using dimethylacetamide as the eluent, is w The upper limit for (D) is not particularly critical, provided that the dispersant has an amount of ionic groups per weight of dispersant that enables the dispersant (D) to have sufficient dispersing properties.

[0039] Nevertheless, it will be appreciated that a practical range for the weight average molecular weight of the dispersant (D) is usually at most 800,000, at most 600,000, preferably at most 500,000, more preferably at most 400,000.

[0040] Preferably the dispersant (D) has a weight average molecular weight of at least 20,000, preferably at least 25,000, advantageously at least 50,000, at least 100,000 or even at least 150,000.

[0041] Particularly good results have been obtained with dispersants having a weight average molecular weight of 50,000 to 400,000, even 150,000 to 400,000.

[0042] The dispersant (D) advantageously has a number average molecular weight (M) of between 7000 and 500000, preferably between 25000 and 400000, even between 50000 and 250000. n ).

[0043] Advantageously, the dispersant (D) is a polymer having a molecular weight and molecular weight distribution such that it is substantially free of fractions with a molecular weight below 3000.

[0044] The determination of the substantial absence of fractions having molecular weights below 3000 can be carried out using GPC techniques against polystyrene standards using dimethylacetamide as the eluent. The GPC method is detailed in the experimental section.

[0045] The expression "substantially free" in relation to the dispersant (D) and the fractions having a molecular weight below 3000 is intended to mean that said fractions are present in an amount of at most 0.03% by weight, preferably at most 0.01% by weight, more preferably that they are not detectable by the GPC technique, as detailed above.

[0046] Dispersant (D) is -SO3X a and -COOX a (In the formula, X a is H, an ammonium group, or a monovalent metal. The monovalent metal is typically selected from the group of alkali metals, preferably it is sodium or potassium.

[0047] Preferably, the dispersant (D) is -SO3X a (In the formula, X a is H, an ammonium group, or a monovalent metal.

[0048] The amount of said ionic groups in dispersant (D) is usually at least 1.00 meq / g, at least 1.10 meq / g, preferably at least 1.20 meq / g, more preferably at least 1.30 meq / g, based on the weight of dispersant (D). Dispersant (D) having an amount of ionic groups less than 1.00 meq / g is considered to lack sufficient polarity to solubilize in the aqueous phase and produce a stabilizing / surfactant-like effect. There is no practical limit on the maximum amount of said ionic groups in dispersant (D). In general, it is understood that said ionic groups are usually present in an amount of at most 2.50 meq / g, preferably at most 2.20 meq / g, more preferably at most 2.00 meq / g.

[0049] Dispersant (D) contains said ionic groups as pendant groups covalently attached to repeat units derived from an ethylenically unsaturated functional monomer [monomer (X)].

[0050] The dispersant (D) may consist essentially of repeat units derived from one or more monomers (X) or it may be a copolymer comprising repeat units derived from one or more monomers (X) and one or more additional monomers different from the monomers (X).

[0051] Typically, monomer (X) is a fluorinated monomer, and one or more additional monomers different from monomer (X) may also be fluorinated monomers.

[0052] According to a particular embodiment of the present invention, the dispersant (D) is a compound having a plurality of -SO3X a The polymer comprises a group.

[0053] Dispersant (D) is -SO3X a Alternatively, the dispersant (D) may consist essentially of repeat units derived from one or more ethylenically unsaturated monomers containing the -SO3X group. a Repeating units derived from one or more monomers containing a -SO3X group a and repeat units derived from one or more monomers that do not contain a group.

[0054] -SO3X a The expression "repeating unit derived from" in relation to a monomer containing a -SOX group refers to i) such a repeating unit derived / obtained directly from polymerizing said monomer, and ii) such a repeating unit derived from -SOX a It is intended to encompass both repeat units derived / obtained from the polymerization of monomers containing functional group precursors to the group, followed by modification and / or post-treatment of the polymer, for example by hydrolysis. In other words, -SO3X aDispersants containing repeat units derived from one or more monomers containing -SO2X groups may be obtained by polymerization of monomers containing -SO3X groups followed by hydrolysis thereof. For the avoidance of doubt, dispersants (D) may be obtained by polymerization of monomers containing ionic -SO3X groups. a Contains a group.

[0055] Multiple -SO3X a Suitable dispersants (D) containing groups are at least one -SO2X group, where X is a halogen (e.g. F) or -OX a (X a is H, an ammonium group, or a monovalent metal); and - repeating units derived from at least one ethylenically unsaturated fluorinated monomer not containing -SO2X groups, hereinafter referred to as [monomer (B)] It is a polymer containing repeating units derived from:

[0056] Ethylenically unsaturated fluorinated monomers containing at least one -SO2X group suitable for the preparation of the dispersant (D) are the monomers (A) detailed above, in which X is a halogen (e.g. F) or -OX a (X a ═H, an ammonium group, or a monovalent metal).

[0057] The phrase "at least one monomer" is used herein with respect to monomers of both types (A) and (B) to indicate that one or more monomers of each type can be present in dispersant (D). Hereinafter, the term monomer will be used to refer to both one and more than one monomer of a given type.

[0058] Non-limiting examples of suitable ethylenically unsaturated fluorinated monomers of type (B) are: - C2-C8 perfluoroolefins, such as tetrafluoroethylene, hexafluoropropylene, and perfluoroisobutylene; - C2-C8 hydrogen-containing fluoroolefins, such as trifluoroethylene, vinylidene fluoride, vinyl fluoride, pentafluoropropylene, and hexafluoroisobutylene; - C2 to C8 chloro- and / or bromo- and / or iodo-fluoroolefins, such as chlorotrifluoroethylene and bromotrifluoroethylene; - Formula CF2=CFOR f1 (In the formula, R f1 is C1-C6 fluoroalkyl, for example, -CF3, -C2F5, -C3F7) fluoroalkyl vinyl ether; - In particular, the formula CF2=CFOCF2OR f2 (R f2 fluoromethoxyalkyl vinyl ethers of the formula CF2=CFOX0 (wherein X0 is a C1-C3 fluoro(oxy)alkyl group such as CF2CF3, -CF2CF2-O-CF3 and -CF3), 12 fluorooxyalkyl vinyl ethers, - Formula: [ka] (Wherein, R f3 , R f4 , R f5 , R f6 each independently is a C1-C6 fluoro(halo)fluoroalkyl containing a fluorine atom and optionally one or more oxygen atoms, e.g., -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3). Fluorodioxole It is.

[0059] Preferably, the monomer (B) is - C2 to C8 perfluoroolefins selected from tetrafluoroethylene and / or hexafluoropropylene; - a C2 to C8 hydrogen-containing fluoroolefin selected from trifluoroethylene, vinylidene fluoride, and vinyl fluoride; and - A mixture of them is selected among.

[0060] More preferably, monomer (B) is tetrafluoroethylene.

[0061] In a preferred embodiment, the dispersant (D) is a mixture of a plurality of -SO3X a Contains at least one -SO3X functional group a The fluorinated polymer is essentially composed of repeat units derived from at least one ethylenically unsaturated fluorinated monomer (B) containing a group.

[0062] According to a particular embodiment, at least one monomer (B) of the dispersant (D) is TFE.

[0063] Preferred dispersants (D) are - 50 to 99 mol %, preferably 50 to 98 mol %, even 50 to 95 mol %, of repeat units derived from tetrafluoroethylene (TFE), relative to the total moles of dispersant (D); from 1 to 50 mol %, preferably from 2 to 50 mol %, even from 5 to 50 mol %, relative to the total moles of dispersant (D), (j) X is OXa, and Xa or X as detailed above is halogen, preferably F or Cl, more preferably F, of the formula CF2=CF-O-(CF2). m Sulfonyl halide fluorovinyl ethers of the formula SO2X, where m is an integer from 1 to 10, preferably from 1 to 6, more preferably from 2 to 4, and even more preferably m is equal to 2; (jj) X is OXa, and Xa or X as detailed above is halogen, preferably F or Cl, more preferably F, of the formula: CF2=CF-(OCF2CF(R F1 )) w -O-CF2(CF(RF2 )) y SO2X (Wherein, w is an integer of 0 to 2, and may be equal to or different from each other. R F1 and R F2 are independently F, Cl, or C1-C optionally substituted with one or more ether oxygen atoms; 10 is a fluoroalkyl group, y is an integer from 0 to 6; preferably, w is 1; R F1 is -CF3, y is 1, and R F2 is F); and (jjj) A mixture of these and a repeat unit derived from at least one monomer selected from the group consisting of: - from 0 to 45 mol %, preferably from 0 to 40 mol %, even from 0 to 25 mol %, of at least one hydrogen-containing monomer and / or fluorinated monomer different from TFE, preferably hexafluoropropylene, of formula CF2=CFOR', relative to the total moles of dispersant (D); f1 (In the formula, R' f1 is C1-C6 perfluoroalkyl, for example, -CF3, -C2F5, -C3F7), for example, a perfluoroalkyl vinyl ether of the formula CF2=CFOCF2OR' f2 (In the formula, R' f2 is a C1-C6 perfluoroalkyl, for example a C1-C6 perfluorooxyalkyl having one or more ether groups, such as -CF3, -C2F5, -C3F7, or -C2F5-O-CF3, such as perfluoroalkyl-methoxy-vinyl ethers of the formula CF2=CFOR' O1 (In the formula, R' O1 is a C2-C alkyl group having one or more ether groups 12 and repeat units derived from perfluorinated monomers, typically selected from the group consisting of perfluoro-oxyalkyl vinyl ethers, The polymer is selected from the group consisting of polymers consisting essentially of:

[0064] According to a particular embodiment, preferred dispersants (D) are - 50 to 95 mol %, preferably 55 to 93 mol %, of repeat units derived from TFE; - 5 to 50 mol %, preferably 7 to 45 mol %, of repeat units derived from the -SO2X group-containing monomer, monomer (A); - 0 to 25 mol %, preferably 0 to 20 mol %, of repeating units derived from a fluorinated monomer other than TFE, monomer (B). The term "constitutes" refers to a set of components that are essentially the same as those described above.

[0065] In an advantageous embodiment of the invention, both the polymer (P) and the dispersant (D) are - 50 to 95 mol %, preferably 55 to 93 mol %, of repeat units derived from TFE; - 5 to 50 mol %, preferably 7 to 45 mol %, of repeat units derived from the -SO2X group-containing monomer, monomer (A); - 0 to 25 mol %, preferably 0 to 20 mol %, of repeating units derived from a fluorinated monomer other than TFE, monomer (B). Includes.

[0066] In a particular embodiment of the invention, the dispersant (D) has the same molar composition as the polymer (P).

[0067] In a highly advantageous embodiment of the present invention, the polymer (P), after hydrolysis of the hydrolyzable groups, is used as a dispersing agent in a further polymerization process.

[0068] Therefore, the process of the present invention comprises the steps of recovering the polymer (P) and hydrolyzing the hydrolyzable -SO2X groups to -SO3X to obtain the dispersant (D). a and obtaining a group.

[0069] The process of the invention therefore comprises the steps of: - tetrafluoroethylene, at least one ethylenically unsaturated fluorinated monomer containing at least one hydrolyzable group selected from -SO2X and -COOZ, where X is a halogen atom and Z is a C1-C4 alkoxy group; in the presence of at least one radical initiator and a dispersant [dispersant (Dx)] to obtain a polymer containing a plurality of hydrolyzable groups; a and -COOX a (In the formula, X a is H, an ammonium group or a monovalent metal) to prepare a dispersant (D).

[0070] The dispersant (Dx) is present in an amount of 0.01% to 5.00% by weight, based on the total weight of the aqueous medium.

[0071] The dispersant (D) may be any dispersant known in the art for preparing fluoropolymers. Advantageously, the dispersant (Dx) is a dispersant (D).

[0072] Therefore, in an advantageous embodiment, the process of the invention comprises the steps of: - tetrafluoroethylene, at least one ethylenically unsaturated fluorinated monomer containing at least one hydrolyzable group selected from -SO2X and -COOZ, where X is a halogen atom and Z is a C1-C4 alkoxy group; of, At least one radical initiator, and a skeletal chain having a weight average molecular weight of 15,000 to 800,000 and including a repeating unit derived from one or more ethylenically unsaturated monomers, and -SO3X a and -COOX a (In the formula, X a is H, an ammonium group, or a monovalent metal), To obtain a polymer containing multiple hydrolyzable groups; hydrolyzing the hydrolyzable groups to the corresponding ionic groups -SO3Xa and -COOX a (In the formula, X a is H, an ammonium group or a monovalent metal) to prepare a dispersant (D).

[0073] The dispersant (Dx) has a molecular weight and molecular weight distribution such that it is substantially free of fractions having a molecular weight less than 3000 as measured by GPC against polystyrene standards using dimethylacetamide as the eluent. The GPC method is detailed in the experimental section.

[0074] The ionic groups in the dispersant (Dx) are in an amount of at least 1.00 meq / g, relative to the total weight of the dispersant (Dx).

[0075] The dispersant (Dx) is present in the emulsion polymerization medium in an amount of 0.01% to 5.00% by weight, based on the total weight of the aqueous medium.

[0076] The dispersant (Dx) has the same monomer composition, average molecular weight and molecular weight distribution as the dispersant (D) obtained at the end of the process.

[0077] Dispersant (D) as well as polymer (P) can be prepared by any polymerization process known in the art.Suitable methods for preparing such polymers are, for example, those described in U.S. Pat. No. 4,940,525 (THE DOW CHEMICAL COMPANY) of July 10, 1990, EP-A-1323751A (SOLVAY SOLEXIS SPA) of July 2, 2003, and EP-A-1172382A (SOLVAY SOLEXIS SPA) of November 16, 2002.

[0078] The aqueous emulsion polymerization may be carried out at a temperature of from 10° C. to 150° C., preferably from 20° C. to 130° C., and the pressure is typically from 2 to 60 bar, in particular from 5 to 45 bar.

[0079] The reaction temperature may be varied during the polymerization, for example to influence the molecular weight distribution, i.e. to obtain a broad molecular weight distribution or to obtain a bimodal or multimodal molecular weight distribution.

[0080] The pH of the polymerization medium may range from pH 1 to 10, preferably from 2 to 10.

[0081] As mentioned above, the process of the present invention is carried out in an aqueous medium in the presence of at least one radical initiator, i.e. any of the initiators known for initiating the free radical polymerization of ethylenically unsaturated monomers. Suitable radical initiators include, inter alia, peroxides and azo compounds as well as redox initiators. Specific examples of peroxide initiators include hydrogen peroxide, sodium or barium peroxide, diacyl peroxides such as diacetyl peroxide, disuccinyl peroxide, dipropionyl peroxide, dibutyryl peroxide, dibenzoyl peroxide, di-tert-butyl-peroxide, benzoylacetyl peroxide, diglutaric acid peroxide and dilauryl peroxide, and also peracids and their salts, for example ammonium, sodium or potassium salts. Examples of peracids include peracetic acid. Esters of peracids can be used as well, examples of which include tert.-butyl peroxyacetate and tert.-butyl peroxypivalate. Examples of inorganic initiators include, for example, ammonium, alkali or alkaline earth salts of persulfate, permanganate or manganate. Persulfate initiators, such as ammonium persulfate (APS), can be used alone or in combination with a reducing agent. Suitable reducing agents include bisulfites, such as ammonium bisulfite or sodium metabisulfite, thiosulfates, such as ammonium, potassium or sodium thiosulfate, hydrazine, azodicarboxylate and azodicarboxyldiamide (ADA). Additional reducing agents that can be used include sodium hydroxymethanesulfinate (Rongalite) or fluoroalkylsulfinates, such as those disclosed in U.S. Pat. No. 5,285,002. Reducing agents typically shorten the half-life of persulfate initiators. In addition, metal salt catalysts, such as copper, iron or silver salts, can be added.

[0082] The amount of initiator may be from 0.01% by weight (based on the fluoropolymer produced) to 1.00% by weight, and more preferably from 0.05 to 0.50% by weight, more preferably from 0.05 to 0.30% by weight, based on the fluoropolymer produced.

[0083] The aqueous emulsion polymerization can be carried out in the presence of other materials such as paraffin wax, buffers and, if necessary, complex-forming or chain transfer agents.

[0084] Examples of chain transfer agents that can be used include alkanes having 1 to 5 carbon atoms, such as dimethyl ether, methyl t-butyl ether, ethane, propane and n-pentane, halogenated hydrocarbons, such as CCl4, CHCl3 and CH2Cl2, and hydrofluorocarbon compounds, such as CH2F-CF3 (R134a). Additionally, esters, such as ethyl acetate and malonic acid esters, can be effective as chain transfer agents in the process of the present invention.

[0085] Furthermore, the aqueous emulsion polymerization of the process of the present invention can be carried out in the presence of certain fluorinated fluids that are devoid of ionic groups, typically allowing the formation of nano-sized droplets (average size less than 50 nm, preferably less than 30 nm), advantageously stabilized in the aqueous dispersion by the presence of a dispersing agent (D).

[0086] When the process of the invention is carried out in the presence of a fluorinated fluid, as detailed above, it may be preferred to first mix the dispersant (D) and said fluid homogeneously in an aqueous medium and then feed the aqueous mixture of dispersant (D) and said fluid thus obtained to the polymerization medium. This technique is particularly advantageous since this premix can advantageously allow the preparation of an emulsion of said fluid in an aqueous phase containing dispersant (D), said emulsion comprising dispersed droplets of said fluid having an average size preferably less than 50 nm, more preferably less than 40 nm, even more preferably less than 30 nm.

[0087] The fluids that can be used according to this embodiment are preferably (per)fluoropolyethers comprising a repeating unit (R1), said repeating unit comprising at least one ether bond in the main chain and at least one fluorine atom (fluoropolyoxyalkene chain). Preferably, the repeating unit R1 of the (per)fluoropolyether is (I) -CF-O- (wherein X is -F or -CF); and (II) -CF2-CFX-O- (wherein X is -F or -CF3); and (III)-CF2-CF 2- CF2-O-; and (IV) -CF2-CF2-CF2-CF2-O-; and (V)-(CF2) j -CFZ-O-, where j is an integer selected from 0 and 1, and Z is a fluoropolyoxyalkene chain containing 1 to 10 repeat units selected within classes (I) to (IV) herein above. is selected from the group consisting of:

[0088] When the (per)fluoropolyether comprises different types of repeating units R1, advantageously said repeating units are randomly distributed along the fluoropolyoxyalkene chain.

[0089] Preferably, the (per)fluoropolyether has the following formula (Ip) herein: T1-(CFX) p -OR f -(CFX) p’ -T2(Ip) [In formula: - each X is independently F or CF3; - p and p', which are equal to or different from each other, are integers from 0 to 3; - R f is a fluoropolyoxyalkene chain comprising a repeat unit R°, said repeat unit being (i) -CFXO- (wherein X is F or CF3), (ii) -CF2CFXO- (wherein X is F or CF3), (iii) -CF2CF2CF2O-, (iv) -CF2CF2CF2CF2O-, (v)-(CF2) j -CFZ-O-, where j is an integer selected from 0 and 1, and Z is a group of the general formula -OR f 'T3(wherein, R f X' is a fluoropolyoxyalkene chain containing 0 to 10 repeat units, said repeat units being selected from among -CFXO-, -CF2CFXO-, -CF2CF2CF2O-, -CF2CF2CF2CF2O-, where each X is independently F or CF3; T3 is a C1 to C3 perfluoroalkyl group; and A mixture of them Selected from the group consisting of: - T1 and T2, which are the same as or different from each other, are H, a halogen atom, or a C1-C3 fluoroalkyl group, optionally containing one or more H or halogen atoms different from fluorine. It is a compound according to the following:

[0090] Generally speaking, the process of the present invention is carried out in the substantial absence of fluorinated emulsifiers having a molecular weight of less than 1000.

[0091] The term "substantially absent" when used in relation to fluorinated emulsifiers means that no surfactants are intentionally added to the polymerization. Impurities that may be considered fluorinated surfactants having molecular weights less than 1000 may be tolerated, but their amounts are usually below the detection limits of standard analytical techniques (less than 1 ppm for aqueous media).

[0092] More typically, the process of the present invention is carried out in the substantial absence of fluorinated emulsifiers having a molecular weight of less than 3000.

[0093] More specifically, the method of the present invention comprises reacting a compound of formula: R f§ (X- ) j (M + ) j [In the formula, R f§ is C3~C 30 (per)fluoroalkyl chain, (per)fluoro(poly)oxyalkylene chain, X - -COO - , -PO3 - or -SO3 - And M + is H + , NH4 + , an alkali metal ion, j can be 1, or 2 can be used. in an aqueous medium substantially free of fluorinated emulsifiers [surfactants (FS)].

[0094] Non-limiting examples of surfactants (FS) may include ammonium and / or sodium (per)fluoro(oxy)carboxylates and / or (per)fluoropolyoxyalkylenes having one or more carboxylic acid end groups.

[0095] Examples of fluorinated surfactants, in particular (per)fluorooxyalkylene surfactants, are described, inter alia, in US Patent Application Publication No. 2007015864 (3M INNOVATIVE PROPERTIES) January 8, 2007, US Patent Application Publication No. 2007015865 (3M INNOVATIVE PROPERTIES CO) January 18, 2007, US Patent Application Publication No. 2007015866 (3M INNOVATIVE PROPERTIES CO) January 18, 2007, US Patent Application Publication No. 2007025902 (3M INNOVATIVE PROPERTIES CO) February 1, 2007.

[0096] For example, fluorinated emulsifiers [surfactants (FS)] that are substantially excluded from the process of the present invention are, inter alia: - CF3 (CF2) n1COOM', where n1 is an integer ranging from 4 to 10, preferably from 5 to 7, more preferably equal to 6; M' represents H, NH4, Na, Li or K, preferably NH4; - T(C3F6O) n0 (CFXO) m0 CF2COOM″ (wherein T is Cl or k F 2k+1 O perfluoroalkoxide group (k is an integer of 1 to 3, and one F atom is optionally replaced with a Cl atom; n0 is an integer ranging from 1 to 6; m0 is an integer ranging from 0 to 6; M″ represents H, NH4, Na, Li, or K; X represents F or CF3); - F-(CF2CF2) n2 -CH2-CH2-RO3M''', where R is P or S, preferably S, M''', represents H, NH4, Na, Li or K, preferably H; n2 is an integer ranging from 2 to 5, preferably n2=3; - AR f -B bifunctional fluorinated surfactant (wherein A and B are equal or different from each other and are -(O) p CFX-COOM*; M* represents H, NH4, Na, Li or K, preferably M* represents NH4; X=F or CF3; p is an integer equal to 0 or 1; R f AR f - B is a linear or branched perfluoroalkyl chain or a (per)fluoropolyether chain such that the number average molecular weight of B is in the range of 300 to 1,000; - R' f -O-(CF2) r -OL-COOM' (where R' f is a linear or branched perfluoroalkyl chain, optionally containing a catenary oxygen atom; M' is H, NH4, Na, Li or K, preferably M' represents NH4; r is 1 to 3; L is a divalent fluorinated bridging group, preferably -CF2CF2- or -CFX-, with X=F or CF3); - R'' f -(OCF2) u -O-(CF2)v -COOM''(in the formula, R'' f is a linear or branched perfluoroalkyl chain, optionally containing a catenary oxygen atom, M″ is H, NH4, Na, Li or K, preferably M″ represents NH4; u and v are integers from 1 to 3; - R''' f -(O) t -CHQ-L-COOM''' (in the formula, R''' f is a linear or branched perfluoroalkyl chain, optionally containing a catenary oxygen atom, Q=F or CF3, t is 0 or 1, M''' is H, NH4, Na, Li or K, preferably M''' is NH4; L is a divalent fluorinated bridging group, preferably -CF2CF2- or -CFX-, and X=F or CF3); - of the following formula (I): [ka] [wherein X1, X2, and X3, which are equal to or different from each other, independently contain H, F, and optionally one or more catenary or non-catenary oxygen atoms; 1~6 (per)fluoroalkyl groups; L represents a bond or a divalent group; R F is a divalent fluorinated C 1~3 is a bridging group; Y is a group of the formula: [ka] (In the formula, X a is H, a monovalent metal (preferably an alkali metal) or a group of the formula -N(R' n ) 4 (wherein, for each occurrence, R' n is a hydrogen atom or C 1~6 represents a hydrocarbon group) is a hydrophilic functional group selected from the group Cyclic fluoro compounds It is.

[0097] The process of the present invention typically results in an aqueous dispersion of fluoropolymer further comprising a dispersing agent (D), as detailed above.

[0098] The particle size (volume average diameter) of the fluoropolymer is typically from 40 nm to 400 nm, with typical particle sizes of 60 nm to about 350 nm being preferred.

[0099] The fluoropolymer may be isolated from the dispersion by coagulation or any other suitable technique if a solid form of the polymer is desired.

[0100] Advantageously, the present invention further comprises -SO3X a and -COOX a (In the formula, X a is H, an ammonium group or a metal, preferably a monovalent metal), said process comprising the steps of: obtaining a polymer (P) in its ionic form as a powdery material [material (PP)] consisting of a plurality of particles of at least one polymer comprising a plurality of ionic groups selected from the group consisting of: (1)-SO2X x and -COOX y (In the formula, X x is halogen, in particular F or Cl, X y providing an aqueous dispersion comprising particles of a polymer (P) comprising a plurality of hydrolyzable groups selected from the group consisting of: (2) To obtain an aqueous dispersion of particles of the polymer (P) in ionic form, said aqueous dispersion is contacted with a basic hydrolyzing agent to remove the groups -SO2X without causing any significant coagulation. x and -COOX y to the corresponding group -SO3X b and -COOX b (In the formula, X b is an ammonium group or a monovalent metal; and optionally (3) contacting the dispersion obtained at the end of step (2) with at least one ion exchange resin in order to at least partially remove any residues of the basic hydrolysis agent and / or other contaminants; (4) spray drying the dispersion obtained at the end of step (2) and, optionally, step (3) to obtain a material (PP); The method includes the steps of:

[0101] The at least one ion exchange resin in step (3) may be an anion exchange resin, a cation exchange resin, or both.

[0102] X a is H, the process proceeds with the cation X b is the cation H + The ion exchange can be carried out using a cation exchange resin in step (3) or by any other known means, such as electrodialysis on a bipolar membrane.

[0103] A process for recovering the polymer (P) as a powder from an emulsion polymerization latex is described in WO 2020 / 094563 A1, the contents of which are incorporated herein by reference.

[0104] The process for obtaining the material (PP) may include further steps for purification of the dispersion. Examples of suitable techniques include dialysis, electrodialysis and ultrafiltration. Said further purification step may be carried out at any stage, typically between steps (2) and (4). If the optional step (3) is present, the further purification step is carried out between steps (2) and (3) or preferably between steps (3) and (4).

[0105] Additional processes for recovering the polymer (P) as a powder from an emulsion polymerization latex are disclosed, for example, in WO 22224105 A1, the contents of which are incorporated herein by reference.

[0106] Depending on the requirements of the application in which the fluoropolymer is to be used, the fluoropolymer in powder form may be post-fluorinated to convert any chemically unstable end groups to stable -CF3 end groups.

[0107] For coating applications, an aqueous dispersion of fluoropolymer is desired, and therefore the fluoropolymer will not need to be separated or coagulated from the dispersion. To obtain a fluoropolymer dispersion suitable for use in coating applications, such as in the impregnation of fabrics or other porous supports, it will usually be desirable to add additional stabilizing surfactants and / or further increase the fluoropolymer solids content. For example, non-ionic stabilizing surfactants may be added to the fluoropolymer dispersion.

[0108] The amount of fluoropolymer solids in the dispersion may be increased as necessary or desired up to an amount of 30-70% by weight. Any known concentration technique may be used, such as ultrafiltration and thermal concentration.

[0109] In a preferred embodiment of the invention, the polymer (P) is used in the preparation of a membrane for use in a polymer electrolyte membrane fuel cell.

[0110] To the extent that the disclosures of any patents, patent applications, and publications incorporated herein by reference conflict with the statements of this application to the extent that any term may be unclear, this statement shall control.

[0111] The present invention will now be described in more detail with reference to the following examples, the purpose of which is merely illustrative and is not intended to limit the scope of the invention.

[0112] Preparation Example 1 - Preparation of Dispersant (D-1) by Polymerization of Tetrafluoroethylene (TFE) and Perfluoro-5-Sulfonyl Fluoride-3-Oxa-1-Pentene (SFVE) and Subsequent Hydrolysis Step 1 - Polymerization In a 5 L autoclave, add the following reagents: - 1.8L demineralized water; - 533g of monomer (SFVE) with the formula: CF2=CF-O-CF2CF2-SO2F - 89g, formula: [ka] (Xa is NH4) A 46% by weight aqueous solution of the ammonium salt of the fluoro compound was loaded.

[0113] The autoclave, stirred at 650 rpm, was heated at 58° C. An aqueous solution of 16 g / L ammonium persulfate was added in a volume of 90 mL. The pressure was maintained at a value of 8.5 bar (absolute) by feeding 8.2 bar tetrafluoroethylene (TFE). After an initial addition of 83 g, SFVE was added in portions (23 g) for each 5% of TFE to be converted. The reaction was stopped after 200 min by stopping the stirring, cooling the autoclave and reducing the pressure by venting the TFE; a total of 340 g of TFE was fed to the autoclave. In total, 0.12 grams of surfactant were used for each gram of TFE converted.

[0114] The latex thus obtained was degassed for 48 h in a stream of air to remove the remaining monomers and then coagulated by freeze-thawing. The powder was washed with deionized water (4 x 1 L) for 30 min and dried in an oven at 120 °C overnight.

[0115] A copolymer was obtained, said copolymer having an equivalent weight (EW) of 720 g / mol and the following composition as determined by FT-IR measurements: TFE: 81.5 mol %; SFVE: 18.5 mol %.

[0116] The polymer has a number average molecular weight (M n ) and a weight average molecular weight (M w). Fractions with molecular weights below 3000 were virtually not detected by GPC.

[0117] GPC measurements were performed against polystyrene standards in dimethylacetamide as eluent using an RI detector. The concentration of the copolymer in the test solution was 0.5% by volume.

[0118] Step 2 - Stabilization, hydrolysis and dissolution in water 250 g of the powder obtained in step 1 was treated with a mixture of 10 L / h fluorine and 4 L / h nitrogen for 3 h at 70 °C to end-cap the backbone with -CF3 functional groups and remove undesired carboxylic acid groups. The powder was treated with 1.5 L of a solution of NaOH / H2O (20 wt%) under stirring and heated at 80 °C. The ionic -SO3 - The complete conversion of the originally contained -SO2F to ionic groups was confirmed by solid-state NMR. The amount of ionic groups in the polymer was 1.39 meq / g. After 10 h, the powder was washed with deionized water (4 x 1 L) under stirring for 30 min and dissolved in deionized water in a pressure vessel heated at 250 °C.

[0119] Polymerization Example 2: Polymerization of tetrafluoroethylene (TFE) and perfluoro-5-sulfonylfluoride-3-oxa-1-pentene (SFVE) in the presence of a dispersant (D-1) In a 5 L autoclave, add the following reagents: - 1.8L demineralized water; 20 g of a 25% by weight aqueous dispersion of dispersant (D-1) obtained from Preparation Example 1, thus corresponding to a concentration of about 1.05% by weight based on the initial aqueous phase (i.e. corresponding to 5 g of dispersant (D-1)). was loaded.

[0120] The autoclave, stirred at 650 rpm, was heated at 50° C. An aqueous solution of 16 g / L sodium persulfate was added in an amount of 90 mL. The pressure was maintained at a value of 7.6 bar (absolute) by feeding tetrafluoroethylene (TFE).

[0121] 82 g of SFVE was fed into the reactor and the pressure of the autoclave was maintained at a constant value of 7.8 bar by feeding TFE and SFVE (23 g) each for 5% TFE conversion. After 230 minutes, when an amount of 340 grams of TFE and 443 g of SFVE had been fed, the TFE feed was stopped. The autoclave was cooled to ambient temperature by keeping a constant stirring of 650 rpm and the latex was removed after keeping it under air bubbling for 48 h to remove residual monomers from the polymerization and then stored in a plastic tank. No signs of coagulation / precipitation of the latex were observed.

[0122] The latex so produced was characterized by laser light scattering to measure the average particle size, which was found to be 107 nm. The polymer thus obtained had an equivalent weight (EW) of 758 g / mol and a composition, as measured by FT-IR, of TFE: 82.7 mol% and SFVE: 17.3 mol%.

Claims

1. A method for producing a fluoropolymer [polymer (P)] containing a plurality of hydrolyzable groups, said method comprising the steps of: - tetrafluoroethylene, at least one ethylenically unsaturated fluorinated monomer containing at least one hydrolyzable group, of, At least one radical initiator and at least one polyfunctional dispersant [dispersant (D)] [the dispersant (D) is a weight average molecular weight (M), as measured by GPC, of ​​at least 15,000 and at most 800,000; ｗ ) having - comprises a backbone chain comprising repeat units derived from one or more ethylenically unsaturated monomers; - -SO ３ X ａ and -COOX ａ (In the formula, X ａ wherein R is H, an ammonium group, or a monovalent metal.

2. 10. The method of claim 1, wherein the dispersant (D) has a molecular weight and molecular weight distribution such that it is substantially free of fractions having a molecular weight of less than 3000 as determined by GPC.

3. The dispersant (D) has a weight average molecular weight (M) of 150,000 to 600,000, preferably 180,000 to 500,000, as measured by GPC. ｗ 10. The method of claim 1, wherein

4. 2. The method of claim 1, wherein the amount of ionic groups in the dispersant (D) is at least 1.00 meq / g and / or at most 2.50 meq / g, based on the weight of the dispersant (D).

5. 10. The method of claim 1, wherein the amount of dispersant (D) is from 0.01% to 5.00% by weight, based on the total weight of the aqueous medium.

6. The dispersant (D) contains at least one group -SO ２ X (X is -OX ａ where X ａ The method of claim 1, wherein the polymer comprises repeat units derived from at least one ethylenically unsaturated fluorinated monomer containing an —SO 2 X group; and repeat units derived from at least one ethylenically unsaturated fluorinated monomer that does not contain an —SO 2 X group.

7. -SO ２ 7. The method of claim 6, wherein the at least one ethylenically unsaturated fluorinated monomer that does not contain an X group is tetrafluoroethylene.

8. The polymer (P) is —SO ２ 2. The method of claim 1, comprising repeat units derived from at least one ethylenically unsaturated fluorinated monomer containing at least one hydrolyzable group selected from the group consisting of X and -COOZ, where X is a halogen atom and Z is a C1-C4 alkoxy group.

9. The polymer (P) contains at least one —SO ２ 10. The method of claim 1, comprising repeat units derived from at least one ethylenically unsaturated fluorinated monomer containing an X group, where X is a halogen.

10. The polymer (P) and the dispersant (D) are - Formula: CF ２ =CF(CF ２ ) ｐ SO ２ X [wherein, in the dispersant (D), X is OX ａ (X ａ is H, an ammonium group or a monovalent metal, and in the polymer (P), X is a halogen, preferably F or Cl, more preferably F, and p is an integer from 0 to 10, preferably from 1 to 6, more preferably p is 1, 2 or 3; - Formula: CF ２ =CF-O-(CF ２ ) ｍ SO ２ X [wherein, in the dispersant (D), X is OX ａ (X ａ is H, an ammonium group or a monovalent metal, and in the polymer (P) X is a halogen, preferably F or Cl, more preferably F, and m is an integer from 1 to 10, preferably from 1 to 6, more preferably from 2 to 4, and even more preferably m is equal to 2; - Formula: CF ２ = CF-(OCF ２ CF(R Ｆ１ )) ｗ -O-CF ２ (CF(R Ｆ２ )) ｙ SO ２ X [wherein, in the dispersant (D), X is OX ａ (X ａ is H, an ammonium group or a monovalent metal, and in the polymer (P), X is a halogen, preferably F or Cl, more preferably F, and w is an integer of 0 to 2, and may be equal to or different from each other; R Ｆ１ and R Ｆ２ is independently F, Cl, or C optionally substituted with one or more ether oxygens; １ ~C １０ is a fluoroalkyl group, y is an integer from 0 to 6; preferably, w is 1, and R Ｆ１ Ha-CF ３ y is 1, and R Ｆ２ is F; - Formula CF ２ =CF-Ar-SO ２ X [wherein, in the dispersant (D), X is OX ａ (X ａ is H, an ammonium group or a monovalent metal, and in the polymer (P), X is a halogen, preferably F or Cl, more preferably F, and Ar is C ５ ~C １５ a sulfonyl halide aromatic fluoroolefin, wherein the aromatic or heteroaromatic group At least one —SO selected from the group consisting of ２ 10. The method of claim 1, comprising repeat units derived from at least one ethylenically unsaturated fluorinated monomer containing an X group.

11. The polymer (P) and the dispersant (D) are - 50 to 99 mol % of repeating units derived from tetrafluoroethylene, based on the total moles of polymer (P) or dispersant (D); 1 to 50 mol %, relative to the total moles of polymer (P) or dispersant (D), (j) Formula: CF ２ =CF-O-(CF ２ ) ｍ SO ２ X [wherein, in the dispersant (D), X is OX ａ (X ａ is H, an ammonium group or a monovalent metal, and in the polymer (P) X is a halogen, preferably F or Cl, more preferably F, and m is an integer from 1 to 10, preferably from 1 to 6, more preferably from 2 to 4, and even more preferably m is equal to 2; (jj) X is OX ａ is of the formula: CF ２ =CF-(OCF ２ CF (R Ｆ１ )) ｗ -O-CF ２ (CF(R Ｆ２ )) ｙ SO ２ X [Wherein, in the dispersant (D), X is OX ａ (X ａ is H, an ammonium group or a monovalent metal, and in the polymer (P), X is a halogen, preferably F or Cl, more preferably F, and w is an integer of 0 to 2, and may be equal to or different from each other; R Ｆ１ and R Ｆ２ are independently F, Cl, or C optionally substituted with one or more ether oxygen atoms. １ ~C １０ is a fluoroalkyl group, y is an integer from 0 to 6; preferably, w is 1, and R Ｆ１ Ha-CF ３ y is 1, and R Ｆ２ is F; and (jjj) A mixture of these a repeat unit derived from at least one monomer selected from the group consisting of: - 0 to 40 mol %, relative to the total moles of polymer (P) or dispersant (D), of at least one hydrogen-containing monomer and / or fluorinated monomer different from tetrafluoroethylene, preferably hexafluoropropylene, of formula CF ２ =CFOR' ｆ１ (In the formula, R' ｆ１ is C １ ~C ６ perfluorinated monomers selected from the group consisting of perfluoroalkyl vinyl ethers of the formula CF ２ = CFOCF ２ OR' ｆ２ (In the formula, R' ｆ２ is C １ ~C ６ perfluoroalkyl or C having one or more ether groups １ ~C ６ perfluoroalkyl-methoxy-vinyl ethers of formula CF ２ =CFOR' Ｏ１ (In the formula, R' Ｏ１ is a C having one or more ether groups ２ ~C １２ perfluoro-oxyalkyl vinyl ethers of the formula: 【Chemistry 1】 (wherein R ｆ３ , R ｆ４ , R ｆ５ , R ｆ６ each independently containing a fluorine atom, one or more oxygen atoms, １ ~C ６ fluoro(halo)fluoroalkyl) and a repeating unit derived from fluorodioxole of The method of claim 1 , comprising:

12. In an aqueous medium: tetrafluoroethylene and —SO ２ and at least one ethylenically unsaturated fluorinated monomer containing at least one hydrolyzable group selected from X and -COOZ (wherein X is a halogen atom and Z is a C1-C4 alkoxy group) in the presence of at least one radical initiator and a dispersant (Dx) to obtain a polymer containing a plurality of hydrolyzable groups; and hydrolyzing the hydrolyzable groups to obtain corresponding ionic groups -SO ３ X ａ and -COOX ａ (In the formula, X ａ is H, an ammonium group, or a monovalent metal.

13. 13. The method of claim 12, wherein the dispersant (Dx) is present in an amount of 0.01% to 5.00% by weight, based on the total weight of the aqueous medium.

14. 12. The method of claim 11, wherein the dispersant (Dx) is dispersant (D).

15. An aqueous dispersion of particles of a fluoropolymer [polymer (P)] containing a plurality of hydrolyzable groups, said dispersion comprising at least one dispersant (D), said dispersant comprising: - comprises a backbone chain comprising repeat units derived from one or more ethylenically unsaturated monomers, a weight average molecular weight (M) of at least 15,000 and at most 800,000; ｗ ) - -SO ３ X ａ and -COOX ａ (In the formula, X ａ is H, an ammonium group, or a monovalent metal; Aqueous dispersion.

16. A method for obtaining a polymer (P) in its ionic form as a powder material [material (PP)], said method comprising the steps of: (1): Providing the aqueous dispersion of claim 15; (2): contacting said aqueous dispersion with a basic hydrolyzing agent to at least partially convert the hydrolyzable groups of the polymer (P) into the corresponding ionic groups, without causing any significant coagulation, in order to obtain an aqueous dispersion of particles of the polymer (P) in ionic form; Optionally (3): contacting the dispersion obtained at the end of step (2) with at least one ion exchange resin to at least partially remove residues of the basic hydrolysis agent and / or other contaminants; (4): spray drying the dispersion obtained at the end of step (2) and optional step (3) to obtain the material (PP); A method comprising:

17. The hydrolyzable group is a group —SO ２ 17. The method of claim 16, wherein X and -COOZ, where X is a halogen atom and Z is a C1-C4 alkoxy group.

18. 17. The method of claim 16, comprising a further purification step carried out between steps (2) and (4), in particular between steps (3) and (4) if optional step (3) is present.

19. 20. The method of claim 18, wherein the purification step is carried out using a method selected from dialysis, electrodialysis, and ultrafiltration.

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