Improved fluorinated polymer composition and use thereof in an electrochemical device

Abstract

The invention relates to a polymer composition comprising: - from 65.0 wt% to 99.0 wt% of an amorphous polymer (AP) comprising: a. recurring units deriving from tetrafluoroethylene (TFE); b. recurring units deriving from one or more than one monomer (A) of general formula (I) CF2=CF - (CF2)m - (OCF2CF(RF1))n - O - (CF2)p - SO2X (I) c. recurring units deriving from at least one monomer (B) of formula (II) - from 1.0 wt% to 35.0 wt% of a semicrystalline copolymer (SP) comprising: (i) recurring units deriving from tetrafluoroethylene, and (ii) recurring units deriving from one or more than one ethylenically unsaturated fluorinated monomer (C) containing at least one ionic group selected from -SO3X, -PO3X, -COOX and a combination thereof, wherein X is H, NH4 or alkali metal; wherein the above weight percentages (wt.%) refer to the total weight of the amorphous polymer (AP) and the semicrystalline polymer (SP).

Description

DescriptionImproved fluorinated polymer composition and use thereof in an electrochemical deviceTechnical Field

[0001] The present invention relates to an improved fluorinated polymer composition and its use in an electrochemical device.Background Art

[0002] Fluorinated polymers, i.e. fluorocarbon-based polymers having multiple fluorine-carbon bonds, have been long known and used in a variety of applications because of several desirable properties such as heat resistance, chemical resistance, weatherability, UV-stability etc. Particularly, fluorinated polymers containing sulfonic acid ion exchange groups, such as perfluorosulfonic acid ionomers, due to their ion conducting properties, have found widespread use in the manufacture of electrolyte membranes for electrochemical devices such as electrolysis cells and fuel cells. Notable examples are Proton Exchange Membrane (PEM) fuel cells, which employ hydrogen as the fuel and oxygen or air as the oxidant

[0003] Fuel cells are typically formed as stacks of membrane electrode assemblies (MEAs). Each MEA includes a PEM, an anode electrode, a cathode electrode and other optional components. The fuel cells typically also comprise a porous electrically conductive sheet material that is in electrical contact with each of the electrodes and permits diffusion of the reactants to the electrodes, which is known as a gas diffusion layer, gas diffusion substrate or gas diffusion backing. On either side of the PEM there is a catalyst layer containing an electrocatalyst, i.e. a catalyst material suitable for the fuel oxidation or oxygen reduction reaction, depending on whether the layer is to be used at the anode or cathode. The electrocatalyst is typically based on platinum or platinum alloyed with one or more other metals. The catalyst layer also generally comprises a proton conductingmaterial, such as a proton conducting polymer, to aid transfer of protons from the anode catalyst to the membrane and / or from the membrane to the cathode catalyst. The proton conducting material is generally known as “binder” or “binder material”.

[0004] Perfluorinated sulfonic acid polymers are among the most used materials for manufacturing both membranes and electrode binders for electrochemical devices such as fuel cells. These ionomers are generally derived from copolymerization of tetrafluoroethylene (TFE) and a perfluorovinyl ether terminating in a sulfonyl fluoride group. The sulfonyl fluoride group can then be hydrolysed to give sulfonic acid groups (-SO3H) or metal sulfonates (-SOs- Me+).

[0005] When used as binder materials, it is advantageous that the ionomers exhibit relatively high permeability to gaseous molecules, such as oxygen and hydrogen, since this allows to minimize the amount of the highly expensive metal used as catalysts in the catalyst layer, especially at the cathode. In fact, a higher gas permeability of the catalyst layer lowers the mass transfer resistance of the gaseous molecules (e.g. oxygen molecules at the cathode) thus increasing their concentration on the electrode surface.

[0006] In the state of the art, it is known that the gas permeability of perfluorinated polymers can be tuned by copolymerizing tetrafluoroethylene (TFE) and perfluorodioxole compounds (e.g. commercial polymers Teflon© AF and Hyflon© AD). As disclosed in Y. Okamoto et al., Journal of Membrane Science 471 (2014) 412-419, the presence of dioxole rings in the polymer structure in appropriate amounts increases the gas permeability. The dioxole rings hinder the polymer chain packing leading to the formation of amorphous polymers.

[0007] Perfluorinated sulfonic acid polymers having increased gas permeability are disclosed in A. Rolfi et al., Journal of Power Sources 396 (2018) 95-101. The polymers disclosed in the paper are amorphous terpolymers comprising recurring units deriving from TFE, a sulfonyl fluoride vinyl ether of formula CF2=CF-O-CF2CF2-SO2F (perfluoro-5-sulfonylfluoride-3-oxa-1 -pentene) and 2,2,4-trifluoro-5-trifluoromethoxy-1 ,3-dioxole (MDO).

[0008] The use of perfluoro dioxoles and perfluoro dioxolanes to prepare ionomers having improved gas permeability is also disclosed in US 2013 / 0252134.

[0009] However, increasing the gas permeability through the incorporation of perfluorodioxole monomers as disclosed in the state of the art inevitably leads to a decrease in the crystallinity of the ionomer. Lower crystallinity may weaken the polymer mechanical properties, such as the mechanical stability and integrity (e.g. resistance to swelling in water) of articles made from these polymers, which are particularly important requirements of ionomeric membranes or binder materials.

[0010] It is therefore desirable to improve the crystallinity of an ionomer containing perfluorodioxole monomers, without however impairing other useful properties, especially gas permeability and ion conductivity.Disclosure of the invention

[0011] It has now been found that if amorphous fluorinated ionomers, which are based on terpolymers of TFE with a perfluorinated vinyl ether sulfonyl fluoride and a perfluorodioxole compound, are combined with appropriate amounts of certain semicrystalline fluorinated copolymers comprising a plurality of ionic groups but free of recurring units deriving from perfluorodioxole monomers, the resulting polymer composition exhibits enhanced crystallinity compared to the amorphous ionomer alone, while the other properties of the ionomer, especially the ionic conductivity and gas permeability, remain substantially unchanged.

[0012] Moreover, the semicrystalline polymers described herein are known in the art as effective dispersing agents that can be used in the preparation of perfluorosulfonic acid polymers via aqueous emulsion polymerization in replacement of less environmental-friendly non-polymeric (low molecular weight) fluorinated surfactants. Therefore, very advantageously, the polymer composition of the present invention comprising the amorphous polymer and the semicrystalline polymer can be directly obtained as the product of an aqueous emulsion polymerization process to prepare the amorphous polymer starting from its building monomers and in the presence of the semicrystalline polymer as dispersing agent. The polymercomposition of the invention can therefore be prepared in an easy way and with a low environmental impact.

[0013] According to a first aspect, the present invention relates to a polymer composition comprising:- from 65.0 wt.% to 99.0 wt.% of an amorphous polymer (AP) comprising: a. recurring units deriving from tetrafluoroethylene (TFE); b. recurring units deriving from one or more than one monomer (A) of general formula (I)CF2=CF - (CF2)m - (OCF2CF(RFI ))n - 0 - (CF2)P- SO2X (I) wherein:- m and n are integers each equal to 0 or 1 , p is an integer within the range from 1 to 10, with the proviso that when m is 1 then n is 0;- RFI is F or a C1-C3 perfluoroalkyl group;- X is a halogen atom or a -OZ group, Z being H, NF or alkali metal; c. recurring units deriving from at least one monomer (B) of formula (II) cz1cz20 0wherein: Z1and Z2, equal or different from each other, are F, Cl, H or OR1T where R1is a perfluoroalkylene radical having from 1 to 5 carbon atoms, and T is F or Cl, with the proviso that Z1and Z2cannot be both Cl or OR1T; Y1and Y2, equal or different from each other, are F or CF3;- from 1.0 wt.% to 35.0 wt.% of a semicrystalline copolymer (SP) comprising:(i) recurring units deriving from tetrafluoroethylene, and(ii) recurring units deriving from one or more than one ethylenically unsaturated fluorinated monomer (C) containing at least one ionic group selected from -SO3X, -PO3X, -COOX and a combination thereof, wherein X is H, NH4 or alkali metal; wherein the above weight percentages (wt.%) refer to the total weight of the amorphous polymer (AP) and the semicrystalline polymer (SP).

[0014] According to a second aspect, the present invention relates to a method of preparation of a polymer composition according to the first aspect, which comprises polymerizing a reaction mixture (RM) comprising: a. tetrafluoroethylene (TFE); b. at least one monomer (A) of general formula (I)CF2=CF - (CF2)m - (OCF2CF(RFI ))n - 0 - (CF2)P- SO2X (I) wherein:- m and n are integers each equal to 0 or 1 , p is an integer within the range from 1 to 10, with the proviso that when m is 1 then n is 0;- RFI is F or a C1-C3 perfluoroalkyl group;- X is a halogen atom or an -OZ group, Z being H, NF or alkali metal; c. at least one monomer (B) of formula (II) cz1cz20 0wherein: Z1and Z2, equal or different from each other, are F, Cl, H or OR1T where R1is a perfluoroalkylene radical having from 1 to 5 carbon atoms, and T is F or Cl, with the proviso that Z1and Z2cannot be both Cl or OR1T; Y1and Y2, equal or different from each other, are F or CF3; in the presence of a semicrystalline polymer (SP) comprising:(i) recurring units deriving from tetrafluoroethylene, and(ii) recurring units deriving from one or more than one ethylenically unsaturated fluorinated monomer (C) containing at least one ionic group selected from -SO3X, -PO3X, -COOX and a combination thereof, wherein X is H, NH4 or alkali metal; wherein the polymer composition comprises from 65.0 wt.% to 99.0 wt.% of the amorphous polymer (AP) and from 1.0 wt.% to 35.0 wt.% of the semicrystalline polymer (SP), the weight percentages (wt.%) being referred to the total weight of the amorphous polymer (AP) and the semicrystalline polymer (SP).

[0015] Preferably, the polymerization is an aqueous emulsion polymerization, more preferably an aqueous emulsion polymerization carried out in the absence of a non-polymeric surfactant.

[0016] According to a third aspect, the present invention relates to a catalyst ink comprising: (i) catalyst particles, (ii) polymer particles of the polymer composition according to the first aspect, and (iii) an aqueous medium.

[0017] According to a fourth aspect, the present invention relates to a catalyst coated membrane comprising a proton exchange membrane and a catalyst layer in contact with the membrane, wherein the catalyst layer comprises catalyst particles and the polymer composition according to the first aspect.

[0018] Definitions

[0019] Herein, the term "polymer" embraces the terms "homopolymer", "copolymer", “terpolymer” as well as polymeric compounds prepared by copolymerization of four or more types of monomers.

[0020] Herein, the term “semicrystalline polymer” is intended to denote a polymer which exhibits a detectable melting point. Preferably, the semicrystalline polymer of the invention is characterized by a heat of fusion of at least 0.1 J / g, preferably within the range 0.1 - 1 J / g, as determined according to ASTM D 3418.

[0021] Herein, the term “amorphous polymer” is intended to indicate a polymer that exhibits a glass transition temperature Tg and no detectable melting point as measured according to ASTM D 3418.

[0022] Herein, the expression “recurring units deriving from” in connection with a monomer (A) comprising a -SO2X group, where X is a halogen atom or a - OZ group, Z being H, NH4 or alkali metal, is intended to encompass both: i) recurring units as directly obtained from polymerizing said monomer comprising a -SO2X group, and ii) recurring units obtained from polymerizing a monomer comprising a functional group precursor to a -SO2X group, followed by modification and / or post-treatment of the polymer, e.g. by hydrolysis.For example, an amorphous polymer (AP) comprising recurring units deriving from a monomer (A) comprising a -SO2X group, X being ONa, may be obtained by polymerizing monomers comprising -SO2X groups (e.g. -SO2F), followed by hydrolysis of the same, for example by means of a NaOH aqueous solution.

[0023] Herein, the expression “recurring units deriving from” in connection with a monomer (C) containing at least one ionic group selected from -SO3X, - PO3X, -COOX and a combination thereof, wherein X is H, NH4 or alkali metal, is intended to encompass both: i) recurring units as directly obtained from polymerizing said monomer comprising an ionic group selected from -SO3X, -PO3X, -COOX and a combination thereof, and ii) recurring units obtained from polymerizing a monomer comprising a functional group precursor to said ionic groups -SO3X, -PO3X, -COOX, followed by modification and / or post-treatment of the polymer, e.g. by hydrolysis.For example, a semicrystalline polymer (SP) comprising recurring units deriving from a monomer (C) comprising a -SO3X group, X being ONa, may be obtained by polymerizing monomers comprising -SO2X groups (e.g. - SO2F), followed by hydrolysis of the same. Similarly, a semicrystalline polymer (SP) comprising recurring units deriving from a monomer (C) comprising a -COOH group, may be obtained by polymerizing monomers comprising -COO-(Ci-C4 alkoxy) groups (e.g. -OCH3), followed by hydrolysis of the same.

[0024] Herein, the molecular weight of a polymer is expressed as weight average molecular weight (Mw) or number average molecular weight (Mn). Mw and Mn are determined by Gel Permeation Chromatography analysis with respect to polystyrene standards, using dimethylacetamide as the eluent and a refractive index detector (concentration of the polymer in the testing solution equal to 0.5% wt / vol).

[0025] Herein, the particle size of a polymer in a polymer latex is expressed as volume average diameter and is intended to be determined by Dynamic Light Scattering Analysis according to the method ISO 22412:2017.

[0026] As used herein, the compositions of the present invention may “comprise”, “consists of” or “consists essentially of” the essential and optional components disclosed in the description and annexed claims. Theexpression “consists essentially of” means that the composition or the component may include additional ingredients insofar they do not materially affect the essential characteristics of the composition or component.

[0027] As used herein, the terms “fluorinated” or ’’fluoro-” refer to compounds, polymers, monomers, etc. that are either fully or partially fluorinated, i.e. wherein all or only a part of the hydrogen atoms have been replaced by fluorine atoms. Analogously, the terms ’’perfluorinated” or ’’perfluoro-” refer to compounds that are fully fluorinated. In the present invention, the terms ’’(per)fluorinated” or ’’(per)fluoro-” refer to both partially fluorinated and perfluorinated compounds.

[0028] As used herein, the term “sulfonate group” refers to either a sulfonic acid group or a salt of a sulfonic acid group, preferably alkali metal or ammonium salt.

[0029] Amorphous polymer (AP)

[0030] The amorphous polymer (AP) is a fluorinated polymer comprising a plurality of sulfonyl halide or sulfonate groups.

[0031] The amorphous polymer (AP) derives from the polymerization of at least the following monomers: tetrafluoroethylene (TFE), an ethylenically unsaturated monomer (A) of formula (I) and a perfluorodioxole of formula (II).

[0032] The ethylenically unsaturated monomer (A) has the following general formula (I)CF2=CF - (CF2)m - (OCF2CF(RFI ))n - O - (CF2)P- SO2X (I) wherein:- m and n are integers each equal to 0 or 1 , p is an integer within the range from 1 to 10, with the proviso that when m is 1 then n is 0;- RFI is F or a C1-C3 perfluoroalkyl group;- X is a halogen atom or a -OZ group, Z being H, NF or alkali metal.

[0033] The alkali metal is preferably selected from lithium, sodium and potassium.

[0034] The amorphous polymer (AP) may include recurring units deriving from one monomer (A) or a combination of different monomers (A), preferably from one monomer (A).

[0035] The monomer (A) may be a monomer of formula (III)CF2=CF-O-(CF2)qSO2X (III) wherein:- X is a halogen atom or an -OZ group, Z being H, NH4 or alkali metal;- q is an integer within the range from 1 to 10, preferably from 1 to 6, more preferably from 2 to 4.

[0036] In the formula (III), X is preferably halogen, more preferably F or Cl, even more preferably F.

[0037] Preferably, the monomer (A) is the compound CF2=CF-O-CF2CF2-SO2X, where X is a halogen atom or an -OZ group, Z being H, NH4 or alkali metal. Preferably, the monomer (A) is the compound CF2=CF-O-CF2CF2-SO2F (perfluoro-5-sulfonylfluoride-3-oxa-1 -pentene).

[0038] The monomer (A) may also be a monomer of formula (IV)CF2=CF- OCF2CF(RFi)-O-(CF2)rSO2X (IV) wherein:- X is a halogen atom or a -OZ group, Z being H, NH4 or alkali metal;- RFI is F or a C1-C10 fluoroalkyl group, optionally substituted with one or more ether oxygen atoms;- r is an integer within the range from 1 to 10.

[0039] In the formula (IV), X is preferably halogen, more preferably F or Cl, even more preferably F.

[0040] The monomer (B) is a perfluorodioxole compound of formula (II) cz1cz20 0

[0041] wherein: Z1and Z2, equal or different from each other, are F, Cl, H or OR1T where R1is a perfluoroalkylene radical having from 1 to 5 carbon atoms, and T is F or Cl, with the proviso that Z1and Z2cannot be both Cl or OR1T; Y1and Y2, equal or different from each other, are F or CF3.

[0042] The amorphous polymer (AP) may include one monomer (B) or a combination of different monomers (B); preferably it includes one monomer (B).

[0043] The monomer (B) may be a monomer of formula (II) in which: Z1is F; Z2is F or OR1F where R1is a perfluoroalkylene radical having from 1 to 5 carbon atoms; Y1and Y2, equal or different from each other, are F or CF3.

[0044] The monomer (B) may be a monomer of formula (II) in which: Z1is F; Z2is OR1F where R1is a perfluoroalkylene radical having from 1 to 3 carbon atoms, preferably 1 carbon atom; Y1and Y2are F.

[0045] Preferably, the monomer (B) is selected from the compound 2,2,4-trifluoro- 5-trifluoromethoxy-1 ,3-dioxole (hereinafter referred to also as MDO) or the compound 4,5-difluoro-bis-2,2 (trifluoromethyl)-l ,3-dioxole (hereinafter referred to also as PDD)

[0046] More preferably the monomer (B) is MDO.

[0047] The amorphous polymer (AP) is preferably selected from those having the following composition: a. from 0.5 mol% to 40.0 mol%, preferably from 3.0 mol% to 20.0 mol%, of recurring units deriving from one or more than one monomer (A) of any of the formulae (I), (III) and (IV) as described above; b. from 0.5 mol% to 40.0 mol%, preferably from 1 .0 mol% to 15.0 mol% of recurring units deriving from one or more than one monomer (B) of formula (II) as described above; c. recurring units deriving from tetrafluoroethylene (TFE) in an amount up to 100 mol%; wherein the above molar percentages (mol%) are based on the total number of moles of units constituting the amorphous polymer (AP).

[0048] The amorphous polymer (AP), in addition to monomers (A), (B) and TFE, may also comprise recurring units deriving from ethylenically unsaturated fluorinated monomers (hereinafter monomer (D)) different from monomers (A), (B) and TFE, preferably not containing ionic or ionizable groups.

[0049] Non limiting examples of suitable ethylenically unsaturated fluorinated monomers (D) are:- C2-C8 perfluoroolefins, such as hexafluoropropylene, perfluoroisobutylene;- C2-C8 hydrogen-containing fluoroolefins, such as trifluoroethylene, vinylidene fluoride, vinyl fluoride, pentafluoropropylene, and hexafluoroisobutylene;- C2-C8 chloro- and / or bromo- and / or iodo-containing fluoroolefins, such as chlorotrifluoroethylene and bromotrifluoroethylene;- fluoroalkylvinyl ethers of formula CF2=CFORfi, wherein Rn is a C1- Ce fluoroalkyl, e.g. -CF3, -C2F5, -C3F7;- fluorooxyalkyl vinyl ethers of formula CF2=CFOXo, wherein Xo is a C1-C12 fluorooxyalkyl group comprising one or more than one ethereal oxygen atom, including notably fluoromethoxyalkyl vinyl ethers of formula CF2=CFOCF2ORf2, with Rf2 being a C1-C3 fluoro(oxy)alkyl group, such as - CF2CF3, -CF2CF2-O-CF3 and -CF3.

[0050] The amorphous polymer (AP) may comprise recurring units deriving from one or more than one monomer (D) in an amount from 0 to 45 mol%, preferably 0 to 40 mol%, even 0 to 25 mol%, with respect to total number of moles of units constituting the amorphous polymer (AP).

[0051] Preferably, the amount of sulfonyl halide or sulfonate groups in the amorphous polymer (AP) is at least 0.80 meq / g, preferably at least 0.90 meq / g, more preferably at least 1.00 meq / g, even more preferably at least 1.10 meq / g, with respect to the weight of the amorphous polymer (AP). The amount of sulfonyl halide or sulfonate groups in the amorphous polymer (AP) is generally at most 2.20 meq / g, preferably at most 2.00 meq / g, more preferably at most 1 .80 meq / g, with respect to the weight of the amorphous polymer (AP).

[0052] The amorphous polymer (AP) generally has a weight average molecular weight (Mw) of at least 50000, preferably of at least 85000 more preferably of at least 100000.

[0053] The weight average molecular weight (Mw) of the amorphous polymer (AP) is generally of at most 700000, preferably at most 600000, more preferablyat most 500000. Suitable ranges for most applications of the polymer (P) are for instance from 150000 to 600000, preferably from 180000 to 500000.

[0054] Preferably, the amorphous polymer (AP) has a number average molecular weight of at least 50000, preferably of at least 90000 and / or advantageously of at most 500000, preferably of at most 450000.

[0055] The aforementioned monomers (A) are known in the art and can be prepared according to methods well-known to the skilled person.

[0056] Methods of preparation of the monomers (B) are also known in the art, for example, from EP 0633257 A1 and US 2013 / 0252134.

[0057] The amorphous polymer (AP) may be obtained in its neutral form or ionic (acid or salified) form. The expression "neutral form" indicates that the polymer comprises -SO2X functional groups in which X is F, Cl, Br or I. The expression "ionic form" indicates that the polymer comprises -SO2X functional groups in which X is OZ, Z being H, NH4 or alkali metal.

[0058] The amorphous polymer (AP) comprising -SO2OZ functional groups are typically prepared from fluorinated polymers comprising -SO2X functional groups, preferably -SO2F functional groups, by methods known in the art.

[0059] The amorphous polymer (AP) comprising -SO2OZ can be obtained in its salified form, i.e. wherein Z is a cation selected from NH4+and alkali metal ion, by treating the corresponding polymer comprising -SO2X functional groups, typically -SO2F functional groups, with a strong base (e.g. NaOH, KOH).

[0060] The amorphous polymer (P) comprising -SO2OZ functional groups can be obtained in its acid form, i.e. wherein Z is H, by treatment of the corresponding salified form of the polymer with a concentrated acid solution (e.g. HNO3).

[0061] Semicrystalline polymer (SP)

[0062] The semicrystalline polymer (SP) of the invention is a fluorinated polymer having a backbone chain deriving from tetrafluoroethylene and comprising a plurality of ionic groups as pendant groups covalently bound to the tetrafluoroethylene recurring units. The semicrystalline polymer (SP) does not comprise recurring units deriving from perfluorodioxole monomers (B)and, preferably, from any perfluorodioxole monomer, i.e. also perfluorodioxole monomers different from those of formula (II).

[0063] The semicrystalline polymer (SP) of the invention comprises:(i) recurring units deriving from tetrafluoroethylene, and(ii) recurring units deriving from at least one ethylenically unsaturated fluorinated monomer (C) containing at least one group selected from -SO3X, -PO3X, -COOX and a combination thereof, wherein X is H, NH4 or alkali metal.

[0064] The alkali metal is preferably selected from lithium, sodium and potassium.

[0065] Advantageously, the semicrystalline polymer (SP) comprises recurring units deriving from at least one monomer (C) containing a plurality of -SO3X groups, wherein X is H, NH4 or alkali metal, for example Na or K.

[0066] Ethylenically unsaturated fluorinated monomers (C) containing at least one -SO3X group, where X is H, NH4 or alkali metal, suitable for the preparation of the semicrystalline polymer (SP) may be selected from the list of monomers suitable as monomers (A) of formula (I) as detailed above for the amorphous polymer (AP). Preferably, the ethylenically unsaturated monomer (C) is selected from the monomers (A) of any of the general formulae (I), (III) and (IV) detailed above for the amorphous polymer (AP).

[0067] In an embodiment, the monomer (C) is the compound CF2=CF-O-CF2CF2- SO2F (perfluoro-5-sulfonylfluoride-3-oxa-1 -pentene).

[0068] The semicrystalline polymer (SP), in addition to TFE and monomer (C), may also comprise recurring units deriving from ethylenically unsaturated fluorinated monomers different from TFE and monomer (C), which preferably do not contain ionic or ionizable groups (hereinafter referred to as “monomer (E)”).

[0069] Non-limiting examples of suitable ethylenically unsaturated fluorinated monomers (E) different from TFE and monomer (C) may be selected from the list of monomers suitable as monomers (D) as detailed above for the amorphous polymer (AP).

[0070] Preferred semicrystalline polymers (SP) are selected from the polymers comprising, or essentially consisting of:- 50 to 99 mol%, preferably 50 to 98 mol%, even 50 to 95 mol%, withrespect to the total number of moles of units constituting the semicrystalline polymers (SP), of recurring units deriving from tetrafluoroethylene;- 1 to 50 mol%, preferably 2 to 50 mol%, even 5 to 50 mol%, with respect to the total number of moles of units constituting the semicrystalline polymers (SP), of recurring units deriving from at least one monomer (C) as described above, preferably CF2=CF-O-CF2CF2-SO2F; and- 0 to 45 mol%, preferably 0 to 40 mol%, even 0 to 25 mol%, with respect to total number of moles of units constituting the semicrystalline polymers (SP), of recurring units deriving from at least one monomer (E) different from TFE and monomer (C).

[0071] Preferably, the at least one monomer (E) is selected from hydrogenated and / or fluorinated monomer, more preferably a perfluorinated monomer.

[0072] Preferably, the monomer (E) is selected from: hexafluoropropylene, perfluoroalkylvinylethers of formula CF2=CFOR’fi, wherein R’n is a Ci-Ce perfluoroalkyl, e.g. -CF3, -C2F5, -C3F7; perfluoro-oxyalkylvinylethers of formula CF2=CFOR’OI , wherein R’01 is a C2-C12 perfluoro-oxyalkyl having one or more ether groups, including e.g. perfluoroalkyl-methoxy-vinylethers of formula CF2=CFOCF2OR’f2 in which R’f2 is a Ci-Ce perfluoroalkyl, e.g. - CF3, -C2F5, -C3F7 or a Ci-Ce perfluorooxyalkyl having one or more ether groups, like -C2F5-O-CF3.

[0073] More preferably, the semicrystalline polymers (SP) are selected from the polymers comprising, or essentially consisting of:- 50 to 99 mol%, preferably 50 to 98 mol%, even 50 to 95 mol%, with respect to the total number of moles of units constituting the semicrystalline polymers (SP), of recurring units deriving from tetrafluoroethylene;- 1 to 50 mol%, preferably 2 to 50 mol%, even 5 to 50 mol%, with respect to the total number of moles of units constituting the semicrystalline polymers (SP), of recurring units deriving from at least one monomer (C) as described above, preferably CF2=CF-O-CF2CF2-SO2F.

[0074] Preferably, the amount of ionic groups in the semicrystalline polymer (SP) is at least 1.00 meq / g, preferably at least 1.20 meq / g, more preferably at least 1 .30 meq / g, even more preferably at least 1 .40 meq / g, with respect to the weight of the semicrystalline polymer (SP). The amount of ionic groupsin the semicrystalline polymer (SP) is generally at most 2.50 meq / g, preferably at most 2.20 meq / g, more preferably at most 2.00 meq / g, with respect to the weight of the semicrystalline polymer (SP).

[0075] Preferably, the semicrystalline polymer (SP) has a weight-average molecular weight (Mw) of at least 15000.

[0076] The weight-average molecular weight of the semicrystalline polymer (SP) is generally at most 800000, at most 600000, preferably at most 500000, more preferably at most 400000.

[0077] Preferably, the semicrystalline polymer (SP) has a weight-average molecular weight of at least 20000, preferably of at least 25000, advantageously of at least 50000, at least 100000 or even at least 150000.

[0078] Particularly good results are obtainable with semicrystalline polymer (SP) having a weight-average molecular weight of from 50000 to 400000, even 150000 to 400000.

[0079] The semicrystalline polymer (SP) may advantageously have a numberaverage molecular weight (Mn) of 7000 to 500000, preferably from 25000 to 400000, even from 50000 to 250000.

[0080] Advantageously, the semicrystalline polymer (SP) is a polymer having a molecular weight and a molecular weight distribution such that it is substantially free from fractions having average molecular weight Mw of less than 3000.

[0081] The expression “substantially free” in connection with fractions having average molecular weight Mw of less than 3000 is intended to mean that said fractions are present in the semicrystalline polymer (SP) in an amount of at most 0.03 wt%, preferably at most 0.01 wt%.Like the amorphous polymer (AP), also the semicrystalline polymer (SP) may be obtained in its neutral form (X is F, Cl, Br or I) or ionic form (X is OZ, Z being H, NH4 or alkali metal). Typically, the semicrystalline polymer (SP) comprising ionic groups selected from -SO3X, and -PO3X wherein X is H, NH4 or alkali metal is prepared from fluorinated polymers comprising -SO2X and -PO2X functional groups in which X is F, Cl, Br or I, preferably F. The semicrystalline polymer (SP) comprising -COOX group wherein X is H, NH4 or alkali metal is typically prepared from fluorinated polymers comprising -COOZ functional groups, where Z is a C1-C4 alkoxy group (e.g. -OCH3, - OC2H5, etc.).

[0082] The semicrystalline polymer (SP) comprising -SO3X, -PO3X and -COOX functional groups can be obtained in its salified form, i.e. wherein X is a cation selected from NH4+and alkali metal ion, by treating the corresponding polymer comprising -SO3Z, -PO3Z and -COOZ functional groups with a strong base (e.g. NaOH, KOH).

[0083] The semicrystalline polymer (SP) comprising -SO3X, -PO3X and -COOX functional groups can be obtained in its acid form, i.e. wherein X is H, by treatment of the corresponding salified form of the polymer with a concentrated acid solution (e.g. HNO3) or by contacting it with an acid ion exchange resin.

[0084] Both the amorphous polymer (AP) and the semicrystalline polymer (SP) may be prepared by polymerization process known in the art without particular limitations. Suitable processes for the preparation of both types of polymers are for instance described in US 4940525, EP 1323751 A, EP1172382A. The preparation of a semicrystalline polymer (SP) especially suitable for being used in the present invention is described in WO 2023165912A1.

[0085] The amorphous polymer (AP) and the semicrystalline polymer (SP) may be prepared separately and subsequently blended in desired ratios to form the polymer composition of the invention.

[0086] The polymer composition of the invention comprises from 65.0 wt% to 99.0 wt%, preferably from 70.0 wt% to 97.5 wt% of the amorphous polymer (AP) and from 1 .0 wt% to 35.0 wt%, preferably from 2.5 wt% to 30.0 wt%, of the semicrystalline polymer (SP).

[0087] In a preferred way, the polymer composition may be prepared according to the method of the present invention, which comprises subjecting to a free- radical-initiated polymerization a reaction mixture (RM) comprising TFE, the monomer (A) of any of general formula (I), (II) and (III) and the monomer (B) of general formula (II), namely the building monomers of the amorphous polymer (AP), in the presence of a semicrystalline polymer (SP) asdispersant that has been separately prepared, for example in the way described in WO 2023165912A1 .

[0088] Preferably, the reaction mixture (RM) is polymerized via emulsion polymerization carried out in an aqueous medium in the presence of at least one free-radical initiator.

[0089] The aqueous medium preferably comprises a dispersant to stabilize the dispersion of the particles of amorphous polymer (AP) that form during the reaction. As dispersant, any surfactant known in the art capable of stabilizing fluoropolymer particles may be used; preferably, the dispersant is a high molecular weight polyfunctional fluorinated polymer, more preferably a polyfunctional fluorinated polymer such as the semicrystalline polymer (SP).

[0090] Preferably, the emulsion polymerization is carried out in the absence of non- polymeric surfactants.

[0091] The aqueous emulsion polymerization may be carried out at a temperature within the range from 10°C to 150°C, preferably from 20°C to 130°C. Preferably, the aqueous emulsion polymerization is carried out at a pressure within the range from 2 to 60 bar, more preferably 5 to 45 bar.

[0092] The reaction temperature may be varied during the polymerization, for example to influence the molecular weight distribution of the amorphous polymer (AP), e.g., to obtain a broad molecular weight distribution or to obtain a bimodal or multimodal molecular weight distribution.

[0093] The pH of the polymerization media may be in the range of pH 1 -10, preferably 2-10.

[0094] As said, the emulsion polymerization is carried out in an aqueous medium in the presence of at least one radical initiator. Any known initiators suitable for initiating a free radical polymerization of ethylenically unsaturated monomers may be used without particular limitation.

[0095] Suitable initiators include: (i) inorganic initiators, for example, a persulfate compound such as ammonium persulfate, hydrogen peroxide; (ii) a redox initiator composed of a combination of said persulfate or hydrogen peroxide with a reducing agent such as sodium hydrogen sulfite or sodium thiosulfate; (iii) such inorganic initiator combined with a small amount of iron,a ferrous salt or silver sulfate; (iv) organic initiators, for example, a dibasic acid peroxide such as disuccinic acid peroxide or diglutaric acid peroxide, azobisisobutylamidine dihydrochloride or azobisbutyronitrile.

[0096] The amount of the polymerization initiator may be varied depending upon the type or the emulsion polymerization conditions. Usually, however, the initiator is used in an amount of from 0.01 wt% to 1 .0 wt%, preferably from 0.05 wt% to 0.50 wt%, and more preferably between 0.05 and 0.30% by weight based on the total weight of TFE, monomer (A) and monomer (B).

[0097] Optionally, the aqueous emulsion polymerization can be carried out in the presence of other materials, such as paraffin waxes, buffers, complexformers or chain-transfer agents.

[0098] As per the aqueous medium, water may be used alone or as a mixture with an organic liquid. The organic liquid may be, for example, an alcohol such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, sec-butyl alcohol, pentanol or octyl alcohol, an ether alcohol such as methyl cellosolve, ethyl cellosolve, isopropyl cellosolve, butyl cellosolve or diethylene glycol monobutyl ether or a fluorine-type solvent such as trichlorofluoroethane. Such organic liquids may be used alone or in combination as a mixture of two or more.

[0099] The aqueous emulsion polymerization according to the method of the invention results in an aqueous dispersion of polymer particles (latex) of the amorphous polymer (AP) and the semicrystalline polymer (SP). The particle size of both the amorphous polymer (AP) particles and the semicrystalline polymer (SP) particles, expressed as volume average diameter, is typically within the range from 40 nm to 400 nm.

[0100] The amount of polymer solids in the dispersion may vary within a wide range, for example between 20 wt.% and 70 wt.%, and can be adjusted as needed or desired to an amount. Any of the known concentration techniques may be used including ultrafiltration and thermal concentration.

[0101] The polymer composition comprising the amorphous polymer (AP) and the semicrystalline polymer (SP) may be isolated from the latex dispersion by coagulation or any other suitable technique if a polymer in solid form is desired. Processes for the recovery of the polymer in powder form from anemulsion polymerization latex are described in WO 2020094563A1 and WO 2022 / 224105A1.

[0102] The polymer composition may be a powdery material in which the amorphous polymer (AP) and the semicrystalline polymer (SP), each independently, are in their neutral form or ionic form as detailed above.

[0103] The hydrolysis and protonation treatments to convert the polymers from their non-ionic form to their ionic form may be carried out separately on the amorphous polymer (AP) and the semicrystalline polymer (SP) before they are blended to form the polymer composition or they can be carried out after that the two types of polymers have been combined together to form the polymer composition of the invention.

[0104] Depending on the requirements of the application in which the polymer composition is to be used, the amorphous polymer (AP), the semicrystalline polymer (SP) or the polymer composition comprising both polymer may be fluorinated so as to convert any chemically unstable end groups into stable -CF3 end groups.

[0105] The polymer composition of the invention has a relatively high gas permeability, especially to oxygen gas, and high ionic conductivity.

[0106] The oxygen permeability of the polymer composition, measured as described in the examples on a membrane of thickness 50 micrometers, at 80 °C, relative humidity of 100%, is greater than 1 *1 O’14mol / cm / s / KPa, preferably greater than 1 *1 O’13mol / cm / s / KPa, more preferably within the range from 1 *1 O’13to 1 *1 O’12mol / cm / s / KPa.

[0107] The in-plane ionic conductivity of the polymer composition, measured as described in the examples on a membrane at 80 °C, relative humidity of 100%, is greater than 100 mS / cm, preferably greater than 120 mS / cm, more preferably within the range from 120 mS / cm to 400 mS / cm.

[0108] The polymer composition of the invention is suitable for use in the manufacturing of components of an electrochemical device, such as electrolysis cells and fuel cells. Notably, the polymer composition of the invention is suitable for use as proton exchange membrane (PEM) or binder material in a catalyst layer, particularly the cathode for fuel cells and the anode for electrolyzers.

[0109] The polymer composition of the invention can be formed into membranes using any conventional method such as but not limited to extrusion and solution or dispersion film casting techniques. After forming, the membrane may be annealed, typically at a temperature of 120 degrees Celsius (0 C.) or higher, more typically 130° C or higher, most typically 150°C or higher. The membrane thickness can be varied as desired for a particular application. Typically, the membrane thickness is less than about 350 pm, more typically in the range of about 10 pm to about 175 pm.

[0110] As a binder material, the polymer composition may be used in the fabrication of membrane electrode assemblies (MEA's) of fuel cells and electrolyzers. Typical MEA's comprise a PEM, which functions as a solid electrolyte. One face of the PEM is in contact with an anode electrode layer and the opposite face is in contact with a cathode electrode layer. Each electrode layer includes catalyst particles. The catalyst layer also generally comprises a proton conducting material, such as a proton conducting polymer, which can be made of or comprise the polymer composition of the present invention. The anode and cathode electrode layers may be applied to the PEM in the form of a catalyst ink to form a catalyst coated membrane (CCM). The MEA may also contain a porous electrically conductive sheet material that is in electrical contact with each of the electrodes and permits diffusion of the reactants to the electrodes (gas diffusion layer - GDL). In an alternate manufacturing method, the anode and cathode electrode layers may be applied to the GDL in the form of a catalyst ink, rather than to the PEM, and the coated GDL's sandwiched with a PEM to form an MEA.

[0111] According to the present invention, the catalyst ink is a liquid dispersion comprising: (i) catalyst particles, (ii) polymer particles comprising or consisting of the polymer composition of the present invention and (iii) an aqueous medium.

[0112] The catalyst particles are particles comprising any active compound capable to catalyze, under the pressure and temperature conditions of a fuel cell, the electro reduction of the oxygen or the electro oxidation of hydrogen or another suitable fuel. Any suitable catalyst may be used in the practice of the present invention. The catalyst is typically a highly dispersed platinumcatalyst, preferably having a specific surface area (BET) of greater than 100 m2 / g, more preferably greater than 500 m2 / g, and most preferably greater than 900 m2 / g. Typically, carbon-supported catalyst particles are used. Typical carbon-supported catalyst particles are 50-90% carbon and 10-50% catalyst metal by weight.

[0113] The polymer particles of the catalyst ink, once incorporated in the electrode layers, behave notably as a binder having high gas permeability, improving the adhesion of the catalyst particles between themselves and of the electrode layers to the support membrane. Once the sulfonyl fluoride -SO2F groups within the binder are transformed into the corresponding sulfonate or sulfonic acid groups, the binder can also improve the ionic conductivity and / or the hydrophilicity of the electrode layers.

[0114] Preferably, the amorphous polymer (AP) and the semicrystalline polymer (SP) in the catalyst ink are in ionic form, more preferably in Na- or H-form; most preferably, they contain the sulfonyl groups in the form of SO3H.

[0115] The aqueous medium comprises water and optionally an organic solvent (e.g. an alcohol). Advantageously, the aqueous medium comprises the aqueous dispersion of polymer particles of the amorphous polymer (AP) and the semicrystalline polymer (SP) as obtained with the method of preparation of the polymer composition of the present invention.

[0116] The catalyst ink typically comprises 25-95% aqueous medium, more typically 50-80% and more typically 60-75%. The catalyst ink typically comprises 1 -50% catalyst particles, more typically 3-40% catalyst particles, and more typically 5-30% catalyst particles. The catalyst ink typically comprises 1 -30% polymer particles, more typically 1 -20% polymer particles, and more typically 1 -10% polymer particles. The catalyst ink may also comprises 1 -50% of a second solvent such as monofunctional alcohols (methanol, ethanol, normal and iso-propanol, diacetone alcohol), bifunctional alcohols (1 ,2-butanediol and 1 ,4-butanediol), acetone, glycols (ethylene glycol, ethylene glycol dimethylether, ethylene diethylether). The above percentages are weight percentages referred to the total weight of the catalyst ink.

[0117] The ink may be applied to a PEM or GDL by any suitable means, including both hand and machine methods, including hand brushing, notch bar coating, fluid bearing die coating, wire-wound rod coating, fluid bearing coating, slot-fed knife coating, three-roll coating, or decal transfer. In the case of decal transfer, the ink is first applied to a transfer substrate and dried, and thereafter applied as a decal to a PEM or GDL. Coating may be achieved in one application or in multiple applications. After coating, the ink may be dried in an oven or the like, in air, at temperatures of about 80 °C, more preferably of about 110 °C and even more preferably of about 140 °C. The GDL may, for example, be carbon paper, carbon cloth, carbon felt or the like. The GDL is preferably treated for water-repellency with polytetrafluoroethylene or the like. The MEA may also comprise a carbon layer between the catalyst layer and the gas diffusion layer.

[0118] The invention will be now explained in more detail with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

[0119] Examples

[0120] Example 1 - Preparation of the semicrystalline polymer (SP)

[0121] An aqueous solution containing a semicrystalline polymer (SP) (25 wt%) was prepared according to WO 20231659121 as described below by polymerizing tetrafluoroethylene (TFE) and perfluoro-5-sulfonylfluoride-3- oxa-1 -pentene (SFVE).

[0122] Step 1 - Polymerization

[0123] In a 5 L autoclave the following reagents were charged:1 .8 L of demineralized water;533 g of the monomer with formula: CF2=CF-O-CF2CF2-SO2F (SFVE);89 g of a 46 wt% aqueous solution of the ammonium salt of the fluorocompound of formula:with Xa being NF .The autoclave, stirred at 650 rpm, was heated at 58°C. A water based solution with 16 g / L of ammonium persulfate was added in a quantity of 90 mL. The pressure was maintained at a value of 8.5 bar (abs.) by 8.2 bar of feeding tetrafluoroethylene (TFE). After the initial addition of 83 g, SFVE was added portionwise (23 g) each 5 wt% of TFE 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 into the autoclave. Overall, 0.12 grams of surfactant for each gram of converted TFE were used.The latex thus obtained was degassed for 48 h with air flow to remove monomer’s residuals and then coagulated through freeze-thawing. The powder was washed with deionized water (4 x 1 L) for 30 min and dried in a vent oven at 120°C overnight.A copolymer was obtained, said copolymer having an equivalent weight (EW) of 720 g / mol (corresponding to 1.39 meq / g) and possessing the following composition: TFE: 81.5 mol%; SFVE: 18.5 mol% as determined by FT-IR measurements.

[0124] Step 2 - Hydrolysis and Dissolution in water

[0125] 250 g of the powder obtained in Step 1 was treated at 70°C with a mixture of 10 L / h of fluorine and 4 L / h of nitrogen for 3 h end-capping the backbone with -CF3functional groups and removing the undesired carboxylic acid groups. The powder was treated under stirring with a 1.5 L solution of NaOH / H2O (20 wt.%) and heated at 80°C. Complete conversion of the originally comprised -SO2F groups to ionic -SOsNa 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 under stirring with deionized water (4x 1 L) for 30 min, treated with a stirred solution of HNO3 in water (20 wt%, 1 L) at room temperature for 1 h and washed with deionized water (2x1 L) at room temperature and under stirring. The acidification and washing steps were repeated twice and then the powder, after drying in a vent oven (overnight, 120°C), was dissolved in deionized water in a pressurized vessel heated at 250°C.The dry powder was subjected to DMA analysis to determine the glass transition temperature (Tg) according to ASTM D4065 and to DSC analysis to determine the enthalpy of fusion according to ASTM D3418-08. The copolymer exhibited a glass transition temperature Tg of 138°C and a crystalline melting point (heat of fusion of 1 .9 J / g).The polymer had a number-average molecular weight (Mn) of 93000 and a weight-average molecular weight (Mw) of 241000. Substantially no fraction having a molecular weight Mw below 3000 was detected by GPC.

[0126] Example 2 - Preparation of a polymer composition according to the invention

[0127] Step 1 - Polymerization

[0128] In a 22 L autoclave the following reagents were charged:- 8.6 L of demineralized water;- 750 g of a 20 wt% aqueous dispersion of the semicrystalline polymer (SP) described in Example 1 (dispersing agent).The autoclave, stirred at 540 rpm, was heated at 58°C. A water based solution with 16 g / L of ammonium persulfate was added in a quantity of 90 mL. The pressure was maintained at a value of 9.8 bar (abs.) by feeding tetrafluoroethylene (TFE).760 g of SFVE and 145 g of 2,2,4-trifluoro-5-trifluoromethoxy-1 ,3-dioxole (MDO) were fed in the reactor and the pressure of the autoclave was maintained at constant value of 9.8 bar by feeding TFE while feeding SFVE (140 g) and MDO (76 g) portion wise. After 630 minutes, when a quantity of 2640 g of TFE, 2860 g of SFVE and 1285 g of MDO were fed, the TFE feeding was stopped. By keeping constant stirring of 540 rpm the autoclave was cooled to ambient temperature the latex was discharged after being kept under air bubbling for 48 hours to strip away residual monomers from the polymerization, and then stored in a plastic tank.The latex so produced was characterized by ss-NMR to check the polymer composition, which resulted to be: TFE =77,8 mol%, VEFS= 12,8 mol%, MDO = 9,4 mol% with a resulting EW = 1042 g / mol (corresponding to 0.96 meq / g).The weight ratio of the semicrystalline polymer (SP) in the polymer composition was 5.0 wt.%.The latex was then cooled at -26°C for 72 h to let the powder coagulate. Once the coagulum was formed, the tank was heated up to room temperature and the obtained powder (3 kg) washed in a 100 I stirred reactor. 3 kg of powder were placed in a reactor stirred at 90 rpm at room temperature and the empty space left in the tank was filled with water for 15 minutes to wash the polymer from residual impurities. This step was repeated 4 times for a better washing efficiency, and the obtained powder was dried in an oven at 80°C for 40h.

[0129] Step 2 - Hydrolysis and Dissolution in water

[0130] At this point a basification of the SO2F pendant group into SOsNa group was performed. The washed powder from Step 1 was placed in a 100 I reactor stirred at 45 rpm and 75 I of NaOH aqueous solution (20 wt.%) were added. The temperature was raised to 80°C and the reaction was conducted at this temperature for at least 8 h. After 8 h, the reactor was cooled down to room temperature and the NaOH solution was removed from the reactor, and then the powder washed 5 times with 90 L of distilled water for 30 min at 45 rpm for each step until reaching a pH = 7,5. In order to transform the -SOsNa group to the corresponding -SO3H, the powder was further treated with a HNO3 / H2O solution (75 L) at room temperature for 1 h and then extensively washed with demineralized water (25 L x 4) for 20 min. The acidification / washing procedure was repeated twice.

[0131] For the dissolution step, 2,9 kg of the powder were placed in a 19 L reactor together with 11 ,4 kg of distilled water. The mixture was stirred at 450 rpm at 250°C for 3h and autogenic pressure of 40 bar was generated into the reactor.

[0132] The dry powder, before dissolution, was subjected to DMA analysis to determine the glass transition temperature (Tg) according to ASTM D4065and to DSC analysis to determine the enthalpy of fusion according to ASTM D3418-08. The polymer composition exhibited a glass transition temperature Tg of 123°C and a crystalline melting point (heat of fusion of 0.4 J / g.

[0133] Example 3 - Comparative material - Preparation of the amorphous polymer (AP)

[0134] Step 1 - Polymerization

[0135] In a 22 L autoclave the following reagents were charged:- 8.6 L of demineralized water;- 743 g of a 42.6 wt% aqueous solution of the ammonium salt of the fluorocompound of formula:with Xa being NFkThe autoclave, stirred at 540 rpm, was heated to 58°C. A water based solution with 16 g / L of ammonium persulfate was added in a quantity of 90 mL. The pressure was maintained at a value of 9.8 bar (abs.) by feeding tetrafluoroethylene (TFE).760 g of SFVE and 145 g of MDO were fed in the reactor and the pressure of the autoclave was maintained at constant value of 9.8 bar by feeding TFE while feeding SFVE (140 g) and MDO (76 g) portion wise. After 630 minutes, when a quantity of 2640 g of TFE, 2860 g of SFVE and 1285 g of MDO were fed, the TFE feeding was stopped. By keeping constant stirring of 540 rpm the autoclave was cooled to ambient temperature the latex was discharged after being kept under air bubbling for 48 hours to strip away residual monomers from the polymerization, and then stored in a plastic tank.The latex produced was characterized by ss-NMR to check the polymer composition, which results to be: TFE =79.9 mol%, VEFS= 12.2 mol%, MDO = 7.9 mol% with a resulting EW = 1069 g / mol (corresponding to 0.94 meq / g).The latex was then cooled at -26°C for 72 h to let the powder coagulate.Once the coagulum was formed, the tank was heated up to room temperature and the obtained powder (3 kg) washed in a 100 L stirred reactor. 3 kg of powder were placed in a reactor stirred at 90 rpm at room temperature and the empty space left in the tank was filled with water for 15 minutes to wash the polymer from residual impurities. This step was repeated 4 times for a better washing efficiency, and the obtained powder was dried in an oven at 80°C for 40h.

[0136] Step 2 - Hydrolysis and Dissolution in water

[0137] At this point a basification of the SO2F pendant group into SOsNa group was performed. The washed powder from Step 1 was placed in a 100 L reactor stirred at 45 rpm and 75 L of NaOH aqueous solution (20 wt.%) were added. The temperature was raised to 80°C and the reaction was conducted at this temperature for at least 8 h. After 8 h, the reactor was cooled down to room temperature and the NaOH solution was removed from the reactor, and then the powder washed 5 times with 90 L of distilled water for 30 min at 45 rpm for each step until reaching a pH = 7,5. In order to transform the -SOsNa group to the corresponding -SO3H, the powder was treated with a HNO3 / H2O solution (75 L) at room temperature for 1 h and then extensively washed with demineralized water (25 L x 4) for 20 min. The acidification / washing procedure was repeated twice.

[0138] The obtained powder was dried at 80°C for 20 h in an oven.

[0139] For the dissolution step, 2,9 kg of the powder were placed in a 19 L reactor together with 11 ,4 kg of distilled water. The mixture was stirred at 450 rpm at 250°C for 3h and an autogenic pressure of 40 bar was generated into the reactor.

[0140] The dry powder, before dissolution, was subjected to DMA analysis to determine the glass transition temperature (Tg) according to ASTM D4065 and to DSC analysis to determine the enthalpy of fusion according to ASTM D3418-08. The polymer exhibited a glass transition temperature Tg of 122°C and no crystalline melting point was detected indicating that the material is amorphous.

[0141] Example 4 - Preparation of membrane M2 (from polymer composition of Example 2) and M3 (from the amorphous polymer of Example 3)

[0142] The polymer composition of the Example 2 and the comparative polymer of the Example 3 were used to prepare respective membranes M2 and M3 as follows.

[0143] The dispersions obtained at the end of Step 2 in Example 2 and Example 3 were formulated with n-propanol and dimethyl sulfone. The formulated dispersions had the following composition: polymer material: 20 wt%, water: 40.5 wt%, n-propanol: 35 wt% and dimethyl sulfone; 4.5 wt%. Dispersion casting was carried out using a doctor blade and an automatic film applicator on a tempered glass support. After deposition, the film underwent a 3 steps heating cycle in a vent oven: 1 h at 65 °C, 1 h at 90 °C and 1 h at 190 °C. The membrane was then peeled off from the glass using demineralized water and dried in a vent oven at 80 °C overnight. Membrane thickness was 54 ± 1 micrometers.

[0144] Example 5 - Measurement of oxygen crossover

[0145] Step 1 - MEA preparation

[0146] Membrane Electrode Assemblies (MEA) were produced using membrane M2 and M3 described in Example 4. For the cathode layer a commercial Pt / C with a loading of 0.45 mgPt / cm2was used as a catalyst. The anode catalyst layer was made in-house with IrOx loading of 0.1 mglrOx / cm2. The latter was produced using 5.5 g of a commercial Aquivion D87-25BS dispersion (EW: 870 g / mol) and 4 g of IrOx, stirred with a magnetic bar for 30 min in a round-bottom flask and 1 h in an ultrasonic bath. The anode layer was then produced using a film depositor and then heated at 90 °C for 2 h. The electrode was obtained by hot pressing the catalyst layer with wet- proofed carbon fiber paper (SGL 25BC) with microporous layer (MPL) as gas diffusion layer (GDL) at 200°C and 8 barA.

[0147] Step 2 - Electrochemical measurement

[0148] The electrochemical measurement procedure consists in a first step of conditioning the cell for 4 h in Fh / air at a temperature of 75 °C and a relative humidity of 65%; after that, the system is purged in N2 at the same temperature. In a second step, the measure is carried out in a 25 cm2active area single cell at 60°C, feeding N2 (cathode) and O2 (anode) at a pressure of 120 kPa. O2 flow rate is 1000 seem, N2 flow rate is 500 seem and thepotential of 1V was imposed using an AutoLab PGSTAT30 potentiostat / galvanostat equipped with the program Nova 2.1. The system records the oxygen reduction reaction current (iORR) and the membrane permeability to oxygen (P02) is calculated through the following equation:where 5mem is the membrane thickness, F is the Faraday’s constant and P02 is the oxygen pressure at the anode side.

[0149] Example 6 - Measurement of the in-plane membrane conductivity

[0150] In-plane membrane conductivity was measured through a Bekktech BT-112 (Scribner, LLC) four-electrodes conductivity cell powered by a potentiostat (Autolab PGSTAT30 from Metrohm). The system was heated at 80°C and fed with hydrogen humidified with water (1000 seem, RH: 100%). Gas provision and humidification was managed by a fuel cell stand station provided by Greenlight Power Technologies. The system measures the resistance (R) and conductivity (o) is calculated accordingly with the equation:where L is the distance between the two inner electrodes (4.25 mm), W is the sample width and T is the membrane thickness.

[0151] In the Table 1 below a comparison of the properties of the polymer composition according to the invention and the comparative material is reported.Table 1*comparative

[0152] The experimental data of Table 1 show that the polymer composition of the present invention has a higher crystallinity compared to the comparative material and substantially the same oxygen permeability and ionic conductivity.

Claims

Claims1 . A polymer composition comprising:- from 65.0 wt% to 99.0 wt% of an amorphous polymer (AP) comprising: a. recurring units deriving from tetrafluoroethylene (TFE); b. recurring units deriving from one or more than one monomer (A) of general formula (I)CF2=CF - (CF2)m - (OCF2CF(RFI ))n - 0 - (CF2)P- SO2X (I) wherein:- m and n are integers each equal to 0 or 1 , p is an integer within the range from 1 to 10, with the proviso that when m is 1 then n is 0;- RFI is F or a C1-C3 perfluoroalkyl group;- X is a halogen atom or a -OZ group, Z being H, NF or alkali metal; c. recurring units deriving from one or more than one monomer (B) of formula (II)CZ1■ cz20 0wherein: Z1and Z2, equal or different from each other, are F, Cl, H or OR1T where R1is a perfluoroalkylene radical having from 1 to 5 carbon atoms, and T is F or Cl, with the proviso that Z1and Z2cannot be both Cl or OR1T; Y1and Y2, equal or different from each other, are F or CF3;- from 1.0 wt% to 35.0 wt% of a semicrystalline copolymer (SP) comprising:(i) recurring units deriving from tetrafluoroethylene, and(ii) recurring units deriving from one or more than one ethylenically unsaturated fluorinated monomer (C) containing at least one ionic group selected from -SO3X, -PO3X, -COOX and a combination thereof, wherein X is H, NH4 or alkali metal; wherein the above weight percentages (wt%) refer to the total weight of the amorphous polymer (AP) and the semicrystalline polymer (SP).

2. The polymer composition according to claim 1 , wherein the monomer (B) is a monomer of formula (II) in which: Z1is F; Z2is F or OR1F where R1is aperfluoroalkylene radical having from 1 to 5 carbon atoms; Y1and Y2, equal or different from each other, are F or CF3.

3. The polymer composition according to claim 1 , wherein the monomer (B) is a monomer of formula (II) in which: Z1is F; Z2is OR1F where R1is a perfluoroalkylene radical having from 1 to 3 carbon atoms, preferably 1 carbon atom; Y1and Y2are F.

4. The polymer composition according to claim 1 , wherein the monomer (B) is selected from 2,2,4-trifluoro-5-trifluoromethoxy-1 ,3-dioxole (MDO) and 4,5- difluoro-bis-2,2 (trifluoromethyl)-l ,3-dioxole (PDD),(MDO) (PDD), preferably the monomer (B) is MDO.

5. The polymer composition according to any one of claims 1 to 4, wherein the amorphous polymer (AP) has the following composition: a. from 0.5 mol% to 40.0 mol%, preferably from 3.0 mol% to 20.0 mol%, of recurring units deriving from one or more than one monomer (A) of formula (I); b. from 0.5 mol% to 40.0 mol%, preferably from 1 .0 mol% to 15.0 mol% of recurring units deriving from one or more than one monomer (B) of formula (II); c. recurring units deriving from tetrafluoroethylene (TFE) in an amount up to 100 mol%; wherein the formulae (I) and (II) are as described in any one of claims 1 to 4; wherein the above molar percentages (mol%) are based on the total number of moles of units constituting the amorphous polymer (AP).

6. The polymer composition according to any one of claims 1 to 5, wherein the monomer (A) and / or the monomer (C) are monomers of formula (III)CF2=CF-O-(CF2)qSO2X (III)wherein:- X is a halogen atom or a -OZ group, Z being H, NH4 or alkali metal;- q is an integer within the range from 1 to 10, preferably from 1 to 6, more preferably from 2 to 4.

7. The polymer composition according to any one of claims 1 to 5, wherein the monomer (A) and / or the monomer (C) are CF2=CF-O-CF2CF2-SO2F (perfluoro-5-sulfonylfluoride-3-oxa-1 -pentene).

8. The polymer composition according to any one of claims 1 to 5, wherein the monomer (A) and / or the monomer (C) are monomers of formula (IV)CF2=CF- OCF2CF(RFi)-O-(CF2)r-SO2X (IV) wherein:- X is a halogen atom or an -OZ group, Z being H, NH4 or alkali metal;- RFI is F or a C1-C10 fluoroalkyl group, optionally substituted with one or more ether oxygen atoms;- r is an integer within the range from 1 to 10.

9. The polymer composition according to any one of claims 1 to 8, wherein the monomer (A) and / or the monomer (C) is CF2=CF-O-CF2CF2-SO2X, wherein X is a halogen atom, preferably F, or an -OZ group, Z being H, NF or alkali metal.

10. The polymer composition according to any one of claims 1 to 9, wherein the amorphous polymer (AP) and the semicrystalline polymer (SP) are in their -SO3H form.11 . A method of preparation of a polymer composition according to claim 1 , which comprises polymerizing a reaction mixture (RM) comprising: a. tetrafluoroethylene (TFE); b. at least one monomer (A) of general formula (I)CF2=CF - (CF2)m - (OCF2CF(RFI ))n - 0 - (CF2)P- SO2X (I) wherein:- m and n are integers each equal to 0 or 1 , p is an integer within the range from 1 to 10, with the proviso that when m is 1 then n is 0;- RFI is F or a C1-C3 perfluoroalkyl group;- X is a halogen atom or an -OZ group, Z being H, NF or alkali metal;c. at least one monomer (B) of formula (II)wherein: Z1and Z2, equal or different from each other, are F, Cl, H or OR1T where R1is a perfluoroalkylene radical having from 1 to 5 carbon atoms, and T is F or Cl, with the proviso that Z1and Z2cannot be both Cl or OR1T; Y1and Y2, equal or different from each other, are F or CF3; in the presence of a semicrystalline polymer (SP) comprising:(i) recurring units deriving from tetrafluoroethylene, and(ii) recurring units deriving from one or more than one ethylenically unsaturated fluorinated monomer (C) containing at least one ionic group selected from -SO3X, -PO3X, -COOX and a combination thereof, wherein X is H, NH4 or alkali metal; wherein the polymer composition comprises from 65.0 wt.% to 99.0 wt.% of the amorphous polymer (AP) and from 1.0 wt.% to 35.0 wt.% of the semicrystalline polymer (SP), the weight percentages (wt.%) being referred to the total weight of the amorphous polymer (AP) and the semicrystalline polymer (SP).

12. The method of claim 11 , wherein the polymerization of the reaction mixture (RM) in the presence of the semicrystalline polymer (SP) is carried out in the absence of a non-polymeric surfactant.

13. A catalyst ink comprising: (i) catalyst particles, (ii) polymer particles comprising the polymer composition according to any one of claims 1 to 10, and (iii) an aqueous medium.

14. A catalyst coated membrane comprising a proton exchange membrane and a catalyst layer in contact with the membrane, wherein the catalyst layer comprises catalyst particles and a polymer composition according to any one of claims 1 to 10.

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