Background

Copolymers of tetrafluoroethylene (TFE) and monomers having sulfonic acid pendant groups are known for making membranes for electrical cells and fuel cells. Typically, such membranes are prepared by first generating a copolymer of TFE and a monomer having pendent sulfonyl fluoride groups (also referred to as “sulfonyl fluoride polymer” or “precursor polymer”) and subsequently hydrolyzing the sulfonyl groups. The resulting sulfonate groups are then converted into sulfonic acid groups, for example by treatment with acids or by ion exchange with cation exchange resins, to produce a perfluorosulfonic acid polymer, also referred to as “PFSA ionomer”. Compositions containing the resulting PFSA ionomer, can be used to make membranes, as described for example in W02004/062019 A1 (Hamrock et al.).

There is a need to provide PFSA ionomers in a dried form rather than as solutions or dispersions. The dried PFSA ionomer particles are more stable upon storage and easier to handle during storage than the respective liquid compositions. The dried PFSA ionomer particles are re-dispersed in a liquid to make dispersions which can be used, for example, to make membranes, catalyst inks or binder materials for batteries and electrodes. In United States Patent No. 10,189,927 (Ino et al.) a sulfonyl fluoride precursor polymer was hydrolyzed by an aqueous base and then treated with hydrochloric acid to provide a perfluorosulfonic acid polymer and the resulting composition was dried. For making a membrane the dried composition was re-dispersed in a liquid by subjecting the mixture to elevated pressure and temperature in an autoclave before processing it for making a membrane. However, it has been found that dried PFSA ionomer compositions may be difficult to re-disperse in water or water-solvent mixtures at ambient conditions or only rather viscous compositions could be obtained. For coating applications, for example for making catalyst inks or binder materials for batteries and electrodes and for making thin membranes, liquid compositions of low viscosity typically are easier to apply than viscous compositions. However, diluting viscous PFSA ionomer compositions would reduce the PFSA ionomer content, which is typically undesired. Processing diluted compositions leads to increased costs because more solvent would have to be removed, recycled or discarded.

Summary

It has now been found that PFSA ionomer particles can be prepared that can be dispersed in a liquid to form PFSA ionomer dispersions of low viscosity. Advantageously, the particles can be dispersed to provide dispersions having substantially constant viscosities over a wide range of shear rates, for example the ratio of the viscosity of the dispersion determined at a shear rate of 1/s to the viscosity of the dispersion measured at a shear rate of 1000/s is from about 0.9 to 1.20, preferably between 0.9 to 1.1.

Such dispersions can be processed at a wide processing window and may be useful, for example, for producing membranes, catalyst inks or binder materials for electrodes or batteries.

Therefore, in one aspect, there is provided particles comprising a PFSA ionomer, wherein the composition has a BET surface area of at least 0.1 g/m~. wherein the PFSA ionomer comprises (i) divalent units derived from tetrafluoroethene (TFE) and represented by formula -[CF2-CF2]- and (ii) divalent units represented by formula (I), wherein a represents 0 or 1, b is an integer from 2 to 8, c is an integer from 0 to 2, and e is an integer from 1 to 8 and X represents an OH (hydroxyl) group or a group OZ wherein O is an oxygen anion and Z represents a counter cation other than a hydrogen cation.

In another aspect there is provided a dispersion obtained by combining the particles with a liquid.

In a further aspect there is provided a method of making a dispersion comprising combining the particles with a liquid, preferably a liquid comprising water or an aliphatic alcohol having from 1 to 5 C- atoms or a combination thereof.

Further, there is provided a method of making the composition, said method comprising subjecting an aqueous PFSA ionomer composition to a process comprising a drying step selected from freeze-drying, freeze-granulation, spray-drying or a combination thereof to provide PFSA ionomer composition comprising particles having a BET surface area of at least 0.1 g/mT

Description of the Figure

Figure 1 is an electron microscope picture of PFSA particles according to the present disclosure obtained by a freeze-granulation process.

Detailed Description

When the amounts of ingredients of a composition are indicated by weight percentages, (also referred to herein as “% by weight” or “% wt” or “wt %”) the weight percentages are based on the total weight of the composition, i.e. the amounts of all ingredients of the composition will give 100 % wt, unless specified otherwise. Likewise, when the amounts of ingredients are identified by % mole (or “% mole” or “mole %”) the amount of all ingredients gives 100% mole unless specified otherwise.

In case the description refers to standards like DIN, ASTM, ISO etc. and in case the year that standard was issued is not indicated, it is referred to the version that was in force in 2018. In case no version was in force in 2018 anymore, for example the standard has expired, the version that was in force at the date closest to 2018 is referred to. PFSA ionomer dispersions

In one aspect perfluorosulfonic acid (PFSA) ionomer particles provided by the present disclosure can be dispersed in a liquid to produce liquid dispersions of low viscosity at both low and high shear rates, for example dispersions having a viscosity at a shear rate of 1/s of less than 400 milliPascabseconds (mPa*s), preferably less than 150 mPa*s and most preferably less than 100 m Pa*s: and having a viscosity at a shear rate of 1000/s of less than 400 mPa*s, preferably less than 150 mPa*s and most preferably less than 100 mPa*s. In some embodiments, the PFSA ionomer particles can be dispersed in a liquid to produce dispersions of low viscosity wherein the viscosity is substantially the same when measured at shear rate of 1/s or at a shear rate of 1000/s. For example, the particles can be dispersed to provide dispersions having a viscosity of less than 400 mPa*s both at a shear rate of 1/s and at a shear rate of 1000/s, preferably having a viscosity of less than 150 mPa _* s both at a shear rate of 1/s and at a shear rate of 1000/s and more preferably having a viscosity of less than 100 mPa _* s both at a shear rate of 1/s and at a shear rate of 1000/s. In some embodiments, the PFSA ionomer particles can be dispersed to provide dispersions having a calculated ratio of the viscosity at 1/s to the viscosity at 1000/s from about 0.9 to 1.20, preferably from about 0.9 to 1.1. This means the viscosity remains constant over a wide range of shear rates which allows for a wide processing window.

Preferably, the liquid is selected from water; a protic solvent having at least one hydroxyl functionality and, preferably, having from 1 to 5 carbon atoms; and combinations thereof. Protic solvents include C i to C5 alkanols, for example methanol, ethanol, isopropanol, n-propanol, tert-butanol, n- butanol, pentanol, and amylalcohol. Preferably, the protic solvent is selected from ethanol, n-propanol, iso-propanol and combinations thereof. The liquid may include mixtures of water and one or more protic solvent, preferably in a ratio of water to protic solvent(s) from about 100 : 1 to 1 : 100 % by weight, preferably from 10 : 1 to 1 : 10 % by weight. The liquid may also be only water or only the protic solvent or a combination of several protic solvents.

It is an advantage of the PFSA particles according to the present disclosure that they can be dispersed at concentrations of at least 5% by weight and up to for example 35% by weight, or for example up to 50% by weight in a liquid that is environmentally safe and easy to handle, for example a liquid as described above containing at least 30% by weight preferably at least 50% by weight or at least 80% by weight or even 95% or even 100% by weight of water. The PFSA ionomer particles according to the present disclosure can be combined with the liquids described above to produce the liquid dispersions of low viscosity by mixing the PFSA ionomer composition and the liquid at room temperature and ambient pressure within a period of 24 hours, for example by agitating the mixture on a roller set at 45 to 65 rpm for a period of 24 hours.

In some embodiments, the PFSA ionomer particles may be dispersed in the liquid in amounts of at least 5, 10, 15, or even 20 percent by weight based on the total weight of the dispersion. In some embodiments, the PFSA ionomer particles may be dispersed in the liquid in amounts of up to 50 percent by weight, e.g., up to 40 percent by weight, based on the total weight of the dispersion. In some embodiments, the dispersion contains 5 to 10 % by weight of the PFSA ionomer particles based on the total weight of the dispersion, e.g., when used to form electrode inks or other compositions with high loadings of other solids. In some embodiments, the dispersion contains 10 to 50 % by weight, e.g., 15 to 40, or even 20 to 30% by weight of the PFSA ionomer particles based on the total weight of the dispersion. For example, these higher concentrations may be useful for making membranes.

The PFSA ionomer particles according to the present disclosure can be obtained by subjecting an aqueous composition comprising the PFSA ionomer to a treatment comprising a drying step selected from spray-drying, freeze-drying, freeze-granulation and a combination thereof. Preferably, the drying is done by a cryo-method, i.e. by freeze-drying or freeze-granulation. More preferably, the drying is done by using freeze-granulation.

Spray-drying is known in the art and produces a dry powder from a liquid or slurry by rapidly drying with a hot gas. Preferably, the spray-drying is done at a temperature below 220 °C. The spray driers use a device, typically an atomizer or spray nozzle, to disperse the liquid or slurry into a controlled drop size spray. Spray-driers are commercially available.

Freeze-drying is a known low temperature dehydration process that involves freezing the composition, lowering the pressure and removing the frozen water by sublimation. Freeze-driers are commercially available.

Freeze-granulation is another low temperature dehydration process. It involves pumping the composition through a device, typically an atomizer or a spray nozzle or combination thereof, to disperse the liquid or slurry into a controlled drop size spray and freezing the spray, for example by exposing the spray to liquid nitrogen. The freezing medium is removed (evaporated) to provide the dried powder. Freeze-granulation equipment is commercially available.

Preferably, the moisture content of the dried ionomer particles is below 15% by weight but residual amounts of moisture may remain in the PFSA ionomer particles. For example, in some embodiments, the particles may have a moisture content of at least 1% by weight, e.g., at least 2 % by weight, at least 3 or even at least 4 % by weight.

The aqueous ionomer composition to be subjected to the drying treatment can be obtained, for example, by hydrolyzing the corresponding sulfonylfluoride precursor polymer, e.g., with an aqueous composition comprising a base (e.g., an alkali base selected from a Li, Na, or K base or a combination thereof) and converting it into its sulfonic acid form, (e.g., by subjecting it to cation-exchange with at least one cation-exchange resin). In some embodiments, the sulfonyl fluoride precursor polymer has been subjected to a fluorination treatment to reduce the amount of carboxylic acid end groups prior to hydrolysis, preferably to below 150 carboxylic acid end groups per 10 ⁶ carbon atoms. In some embodiments, the sulfonyl fluoride polymer has been obtained by polymerizing tetrafluoroethene (TFE) with the one or more perfluorinated sulfonyl fluoride monomers. In some embodiments, the sulfonyl fluoride precursor polymer has a glass transition temperature (Tg) of up to 25 °C, 20 °C, 15 °C, or 10 °C. In some embodiments, the sulfonyl fluoride precursor polymer has a melt flow index (MFI, e.g., 265 °C/5 kg) of at least 1 gram per 10 minutes and up to 100, preferably up to 80 grams per 10 minutes, for example between 5 and 55 grams per 10 minutes. The PFSA ionomers according to the present disclosure typically exhibit a thermal transition between a state in which the ionic clusters are closely associated and a state in which the interactions between those clusters have been weakened. This transition is described as an alpha transition, and the transition temperature is T(a) or T alpha. In some embodiments, the PFSA ionomers (free acid form) have a T(a) of from 70°C and up to 150°C, for example but not limited to from 75°C to 135°C. In some embodiments, the PFSA ionomers have a T(a) in the range from 75 °C to 125 °C or 80 °C to 120°C.

Preferably, the PFSA ionomers according to the present disclosure have up to 150 carboxylic acid end groups per 10 ⁶ carbon atoms, preferably up to 100 or up to 50, for example between 1 and 45 or between 10 and 90 carboxylic acid end groups per 10 ⁶ carbon atoms.

The PFSA ionomers according to the present disclosure typically have an equivalent weight (EW, or -SO3H equivalent weight) of up to 2000. In some embodiments, the copolymer has an EW in a range from 600 to 1400, preferably, from about 650 to about 1200 and more preferably from about 700 to about 1000

The ionomer particles may be soft or hard. The particles may be friable. The particles may be in the form of, for example, chunks, lumps, flakes, granules. Preferably, the particles are spherical or substantially spherical (i.e. their shape can be best approximated by a sphere). The particles may typically have a size of 2.0 mm or less (i.e. D 100 is less than or equal to 2.0 mm), or a size of 1.0 mm or less (i.e.

D 100 is equal to or less than 1.0 mm). Preferably at least 90% of the particles (D90) have a particle size of 2.0 mm or less or preferably of 1.0 mm or less. In one embodiment the particles have an average particle size (D50) in the range of from about 5 pm to 500 pm or from about 25 pm to 350 pm. The particle size may be determined by image analysis. Sieving can be used to exclude particles above or below a certain threshold value.

The PFSA ionomer particles according to the present disclosure have a high BET surface area, i.e., a BET surface area of at least 0. 1g/m ² . In some embodiments, the BET surface area of the ionomer particles is at least 0.3 g/m ² , e.g., at least 0.5 g/m ² , or even at least 1.0 g/m ² . In some embodiments, the PFSA ionomer particles have a BET surface area of from 0.3 and up to 10 g/m ² , e.g., from 0.5 up to 10 g/m ² or even from 1 g/m ² up to 9 g/m ² .

The PFSA ionomer particles according to the present disclosure contain at least 50% by weight, preferably at least 80% by weight, more preferably at least 85% by weight of PFSA ionomer. In some embodiments, the PFSA ionomer composition has a moisture content from 1 to 15% by weight, preferably from 3 to 13 % and more preferably from 3.9 to 12 % by weight based the total weight of the composition is 100% by weight, preferably based on the weight of the PFSA ionomer.

The PFSA ionomer according to the present disclosure is a copolymer of tetrafluoroethene (TFE) and at least one, preferably at least two comonomers. Consequently, the copolymer contains units derived from TFE. Such units include divalent units represented by formula -[CF2-CF2]-. Typically, the PFSA ionomer according to the present disclosure contains at least 60 mole % of divalent units represented by formula -[CF2-CF2]-, based on the polymer (100 mole %). In some embodiments, the PFSA ionomer comprises at least 65, 70, 75, 80, or 90 mole % of divalent units represented by formula -[CF2-CF2]-, based on the polymer (100%).

The ionomer according to the present disclosure further includes divalent units independently represented by formula (I):

In formula (I), a represents 0 or 1, b is an integer from 2 to 8, c is an integer from 0 to 2, and e is an integer from 1 to 8 and X represents an OH (hydroxyl) group, i.e., the pending ionomer side group terminates a perfluorosulfomc acid group (-SO3H) or X represents a group OZ wherein O represents an oxygen anion and Z represents a counter cation, i.e. the side group terminates as a perfluorosulfomc acid salt group (-SO3Z). Z preferably represents an alkali metal cation or a quaternary ammonium cation. The quaternary ammonium cation can be substituted with any combination of hydrogen and alkyl groups, in some embodiments, alkyl groups independently having from one to four carbon atoms. In some preferred embodiments, Z is an alkali-metal cation, preferably a sodium or lithium cation. Preferably, however, X represents OH.

C _e F2 _e may be linear or branched and preferably is linear. C _b F _2b may be linear or branched and preferably is branched. In some embodiments, b is a number from 2 to 6 or 2 to 4. In a preferred embodiment a is 0. In another preferred embodiment a and c are both 0, and e is 3 to 8, preferably 3 to 6, more preferably 3 to 4, and most preferably 4. Typically, the PFSA ionomer according to the present disclosure contains from 10 to 40 mole % of divalent units represented by formula (I) based on the polymer (100 mole %). In some embodiments, the PFSA ionomer comprises from 15 to 25 mole % of units represented by formula (I) based on the total units of the polymer (100 mole %).

Ionomers having divalent units represented by formula (I) can be most conveniently prepared by copolymerizing the corresponding sulfonyl fluoride, e.g. a compound represented by formula CF2=CF(CF2) _a -(0CbF2b) _c -0-(C _e F2 _e )-S02X’, in which a, b, c, and e are as defined above and X’ is F.

The sulfonylfluoride will then be hydrolyzed to produce the sulfonic acid salt, i.e. a compound represented by formula CF2=CF(CF2) _a -(0CbF2b) _c -0-(C _e F2 _e )-SO2 X”. X” represents OZ and each Z is a cation as described above, preferably an alkali metal cation or a quaternary ammonium cation. The quaternary ammonium cation can be substituted with any combination of hydrogen and alkyl groups, in some embodiments, alkyl groups independently having from one to four carbon atoms. In some preferred embodiments, Z is an alkali-metal cation, preferably a sodium or lithium cation.

Preferred sulfonyl fluoride monomers include CF2=CF-0-(CF2) _e -S02F with e = 1-8,

CF ₂ =CF-0-CF ₂ CF(CF3)0(CF2) _e -S02F with a = 1-8, CF ₂ =CF[0CF ₂ CF(CF ₃ )] _c -S02F with c = 1-5. Particular examples include CF2=CF0CF2CF2S02F, CF2=CF0CF2CF2CF2CF2S02F, CF2CFOCF2CF2CF2SO2F, CF ₂ =CF0CF2CF(CF3)0CF2CF ₂ S02F,

CF ₂ =CF0CF2CF(CF3)0CF2CF2CF ₂ S02F, CF ₂ =CF0CF ₂ CF(CF ₃ )S02F, CF ₂ ^CF-CF ₂ -O-CF ₂ CF ₂ - SO2F. More preferred sulfonyl fluoride monomers include CF2=CF0CF2CF2S02F, CF ₂ =CF0CF2CF2CF2CF ₂ S02F, CF ₂ =CF0CF2CF(CF3)0CF2CF ₂ S02F. Most preferred is CF ₂ =CFOCF ₂ CF ₂ CF ₂ CF ₂ SOgF.

In a preferred embodiment. The PFSA ionomer according to the present disclosure further comprises divalent units independently represented by formula (II):

In formula (II), m’ is 0 or 1, and Rf ₁ is a linear or branched perfluoroalkyl group having from 1 to

12 carbon atoms that can be interrupted once or more than once by an (ether) oxygen atom, in which case Rfl is a perfluoroalkoxyalkyl group. Typically, the PFSA ionomer according to the present disclosure contains from 0 to 15 mole % units represented by formula (II) based on the polymer (100 mole %). In some embodiments, the PFSA ionomer comprises from 3 to 15 mole %, preferably from 5 to 10 mole% of units represented by formula (II).

Ionomers having divalent units represented by formula (II) can be most conveniently prepared by copolymerizing a monomer represented by C F 2=C F -( C F ₂ ) _m · -O-Rf ₁ with m’ and Rf _| being the same as described above. For example, in case m’ is 0, the unit represented by formula (II) is derived from a perfluoroalkyl or perfluoroalkoxy alkyl vinyl ether comonomer. For example, using CF2-CF-O-C3F7 (PPVE-1) as comonomer will lead to a unit according to formula (II) with m’ being 0, and Rfl being C3F7.

In case m’ is 1, the unit is derived from a perfluoroalkyl or perfluoroalkoxyalkyl allyl ether comonomer For example, using CF2=CF-CF2-0-C ₃ F7 (PPAE-1) as comonomer will lead to a unit according to formula (II) wherein m’ is 1 and Rfl is C3F7. Examples of suitable perfluoroalkyl vinyl ether and perfluoroalkyl allyl ethers inclde but are not limited to compounds according to the formula CF2=CFORfl and CF ₂ =CFCF ₂ ORfl with Rfl being methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl. Preferably, Rfl is linear.

Examples of suitable perfluoroalkoxyalkyl vinyl ethers include but are not limited to

CF ₂ =CFOCF ₂ OCF ₃ , CF ₂ =CFOCF ₂ OCF ₂ CF ₃ , CF ₂ =CFOCF ₂ CF ₂ OCF ₃ , CF ₂ =CFOCF ₂ CF ₂ CF ₂ OCF ₃ ,

CF ₂ =CFOCF ₂ CF ₂ CF ₂ CF ₂ OCF ₃ , CF2=CF0CF ₂ CF20CF ₂ CF ₃ , CF ₂ =CF0CF2CF2CF20CF ₂ CF3, CF ₂ =CF0CF2CF2CF2CF20CF ₂ CF ₃ , CF2=CF0CF ₂ CF20CF ₂ 0CF ₃ , CF ₂ =CFOCF ₂ CF ₂ OCF ₂ CF ₂ OCF ₃ , CF ₂ =CF0CF ₂ CF ₂ 0CF ₂ CF2CF ₂ 0CF ₃ , CF2=CF0CF2CF20CF2CF2CF2CF20CF ₃ , CF2=CF0CF2CF20CF2CF2CF2CF2CF ₂ 0CF ₃ , CF ₂ =CFOCF ₂ CF ₂ (OCF ₂ ) ₃ OCF ₃ , CF ₂ =CFOCF ₂ CF ₂ (OCF ₂ ) ₄ OCF ₃ , CF ₂ =CF0CF2CF20CF20CF ₂ 0CF ₃ , CF ₂ =CF0CF2CF20CF2CF ₂ CF3 CF2=CF0CF2CF20CF2CF20CF2CF ₂ CF ₃ , CF2=CF0CF ₂ CF(CF ₃ )-0-C ₃ F ₇ (PPVE-2), CF2=CF(0CF ₂ CF(CF ₃ )) ₂ -0-C ₃ F ₇ (PPVE-3), and CF ₂ = CF(0CF ₂ CF(CF ₃ )) ₃ -0-C ₃ F ₇ (PPVE-4). Such vinyl ethers can be prepared according to the methods described in U.S. Pat. Nos. 6,255,536 (Worm et al.) and 6,294,627 (Worm et al.) or other methods known in the art and some of these ethers are commercially available. Also the corresponding allyl ethers are useful. Such allyl ethers can be prepared, for example, according to the methods described in U.S. Pat. No. 4,349,650 (Krespan) or other methods known in the art. Some of these ethers are also commercially available.

Particular examples of suitable comonomers leading to a unit according to formula (II) include but are not limited to

(i) perfluoroalkyl vinyl ethers including: CF ₂ =CF-0-CF ₃ (PMYE), CF ₂ =CF-0-CF ₂ CF ₃ (PEVE), CF ₂ =CF-0-CF ₂ CF ₂ CF ₃ (PPVE-1), CF ₂ =CF-0-CF(CF ₃ )CF ₃ ;

(ii) perfluoroalkyl allyl ethers including: F ₂ C=CF-CF ₂ -0-CF ₃ (MAI), F ₂ C=CF-CF2-0-CF ₂ CF ₃ (MA2), F ₂ C=CF-CF ₂ -0-CF ₂ CF ₂ CF ₃ (MA3), F ₂ C=CF-CF ₂ -0-CF ₂ CF ₂ CF ₂ CF ₃ (MA4);

(iii) perfluoroalkoxy alkyl vinyl ethers including: CF ₂ =CF-(0-CF2-CF(CF ₃ ))-0-CF2CF2CF ₃ (PPVE-2), CF ₂ =CF-(0-CF2-CF(CF ₃ )) ₂ -0-CF2CF ₂ CF ₃ (PPVE-3), CF ₂ =CF(0CF ₂ CF(CF ₃ )) ₃ -0-C ₃ F ₇ (PPVE-4); CF2=CF-0-(CF ₂ )3-0CF ₃ (MV31), CF ₂ =CF-0-(CF2)2-OCF ₃ (MV21), CF ₂ =CF-0-(CF ₂ )4-0CF ₃ (MV41), CF ₂ =CF-0-CF ₂ -0CF ₃ (MV11);

(IV) perfluoroalkoxy alkyl allyl ethers including F ₂ OCF-CF ₂ -0-(CF ₂ ) ₃ -0-CF ₃ (MA31), F ₂ OCF-CF ₂ - 0-CF ₂ )2-0-CF ₃ (MA21), F ₂ C=CF-CF2-0-CF ₂ -0-CF3 (MA11), F ₂ C=CF-CF2-0-(CF ₂ )4-0-CF3 (MA41).

Particular examples also include combination of one or more of the monomers within each group (i), (ii), (iii) and (iv). Particular examples also include combinations of one or more of (i) with (ii), (i) with (iii), (i) with (iv), (ii) with (iii), (ii) with (iv) and (iii) with (iv). Other optional comonomers

Although not necessary and less preferred the PFSA ionomers according to the present disclosure may also include units derived from other optional comonomers, in addition to or as alternative to the optional comonomers above providing units according to formula (II). Such other optional comonomers include, for example, fluorinated olefins, non-fluorinated olefins and modifiers and cross-linkers, typically bisolefins. Typically, the ionomers according to the present disclosure contain less than 20% by weight of units derived from optional comonomers and, preferably less than 5% and more preferably 0% by weight based on the total weight of the ionomer.

Fluorinated olefins

In some, less preferred, embodiments the PFSA ionomer according to the present disclosure contain divalent units derived from at least one other fluorinated olefin independently represented by formula C(R)2=CF-Rf2- These fluorinated divalent units are represented by formula -[CR2-CFRf ₂ ]-. In formulas C(R)2=CF-Rf2 and -[CR ₂ -CFRf ₂ ]-, Rf ₂ is fluorine or a perfluoroalkyl having from 1 to 8, in some embodiments 1 to 3, carbon atoms, and each R is independently hydrogen, fluorine, or chlorine. Some examples of fluorinated olefins useful as components of the polymerization include, hexafluoropropylene (HFP), trifluorochloroethylene (CTFE), and partially fluorinated olefins (e g., vinylidene fluoride (VDF), tetrafluoropropylene (R1234yf), pentafluoropropylene, and trifluoroethylene). Preferably, however, the PFSA ionomers according to the present disclosure do not contain any units derived from any other fluorinated olefin.

Bisolefins

The PFSA ionomers of the present disclosure can also include units derived from one or more bisolefins represented by formula X ₂ C=CY-(CW2) _m -(0) _n -RF-(0) ₀ -(CW ₂ )p-CY=CX2. In this formula, each of X, Y, and W is independently fluoro, hydrogen, alkyl, alkoxy, polyoxyalkyl, perfluoroalkyl, perfluoroalkoxy or perfluoropolyoxyalkyl, m and p are independently an integer from 0 to 15, and n, o are independently 0 or 1. In some embodiments, X, Y, and W are each independently fluoro, CF3, C2F5, C3F7, C4F9, hydrogen, CH3, C2H5, C3H7, C4H9. In some embodiments, X, Y, and W are each fluoro (e.g., as in CF ₂ =CF-0-R _F -0-CF=CF ₂ and CF ₂ =CF-CF ₂ -0-R _F -0-CF ₂ -CF=CF ₂ ). In some embodiments, n and o are 1, and the bisolefins are divinyl ethers, diallyl ethers, or vinyl-allyl ethers. Rp represents linear or branched perfluoroalkylene or perfluoropolyoxyalkylene or arylene, which may be non-fluorinated or fluorinated. In some embodiments, Rp is perfluoroalkylene having from 1 to 12, from

2 to 10, or from 3 to 8 carbon atoms. The arylene may have from 5 to 14, 5 to 12, or 6 to 10 carbon atoms and may be non-substituted or substituted with one or more halogens other than fluoro, perfluoroalkyl (e g. -CF3 and -CF2CF3), perfluoroalkoxy (e g. -O-CF3, -OCF ₂ CF3), perfluoropolyoxyalkyl (e g., - OCF2OCF3; -CF ₂ OCF ₂ OCF3), fluorinated, perfluorinated, or non-fluorinated phenyl or phenoxy, which may be substituted with one or more perfluoroalkyl, perfluoroalkoxy, perfluoropolyoxyalkyl groups, one or more halogens other than fluoro, or combinations thereof. In some embodiments, Rp is phenylene or mono-, di-, tri- or tetrafluoro-phenylene, with the ether groups linked in the ortho, para or meta position.

In some embodiments, Rp is CF2; (CF2)q wherein q is 2, 3, 4, 5, 6, 7 or 8; CF2-O-CF2; CF2-O-CF2- CF ₂ ; CF(CF ₃ )CF ₂ ; (CF ₂ )2-0-CF(CF ₃ )-CF ₂ ; CF(CF ₃ )-CF ₂ -0-CF(CF ₃ )CF ₂ ; or (CF ₂ )2-0-CF(CF ₃ )-CF2-0-CF(CF ₃ )-CF2-0-CF _2.

When used in low amounts, for example less than 2% by weight, preferably less than 1% by weight the bisolefms can introduce long chain branches as described in U.S. Pat. Appl. Pub. No.

2010/0311906 (Lavallee et al.). When used in greater amounts the bisolefms can cross-link the ionomer. The bisolefms, described above in any of their embodiments, may be present in the components to be polymerized in any useful amount. In a preferred embodiment, the ionomers do not contain any units derived from bisolefms or contain such units in amounts of from about 0% by weight to about 5% by weight.

The PSFA-ionomer according to the present disclosure is preferably not cross-linked.

Non-fluorinated comonomers

The PFSA ionomers of the present disclosure can also include units derived from non-fluorinated monomers. Examples of suitable non-fluorinated monomers include ethylene, propylene, isobutylene, ethyl vinyl ether, vinyl benzoate, ethyl allyl ether, cyclohexyl allyl ether, norbomadiene, crotonic acid, an alkyl crotonate, acrylic acid, an alkyl acrylate, methacrylic acid, an alkyl methacrylate, and hydroxybutyl vinyl ether. Any combination of these non-fluorinated monomers may be useful. In some embodiments, the components to be polymerized further include acrylic acid or methacrylic acid, and the copolymer of the present disclosure includes units derived from acrylic acid or methacrylic acid. Preferably, the PFSA ionomers according to the present disclosure do not contain units derived from a non-fluorinated comonomer or contains units derived from a non-fluorinated comonomer in an amount of from 0 to 10% by weight (based on the total weight of the ionomer which is 100% by weight).

Typical PFSA ionomers

Preferred embodiments of PFSA ionomers according to the present disclosure contain at least 60 mole %, preferably from 65 to 90 mole %, of units derived from TFE, i.e., units represented by formula - [CF2-CF2]- and from 10 to 40 mole %, preferably from 15 to 25 % by mole of units represented by formula (I). The PFSA ionomer according to the present disclosure may contain from 0 to 15 mole %, preferably 5 to 10 mole% of units represented by formula (II) and from 0 to 30% by mole of units derived from other comonomers including the other optional comonomers described above.

The PFSA ionomer according to the present disclosure may contain from 5 to 50 % by weight, for example from 10 to 40 % by weight of units according to formula (I). The PFSA ionomer according to the present disclosure may contain from 30 to 95 % by weight, for example from 45 to 90 % by weight of units represented by formula -[CF2-CF2]- and units represented by formula (II). Preferably, the PFSA ionomer according to the present disclosure may contain from 30 to 95 % by weight, for example from 45 to 90 % by weight, of units represented by formula -[CF ₂ -CF ₂ ]- and units represented by formula (II) and the molar ratio of units represented by formula -[CF ₂ -CF ₂ ]- derived to units according to formula (II) is from 90 : 1 to 4 : 1. The total weight of the polymer is 100 % by weight.

Preferably, the PFSA ionomer is perfluorinated which means it is obtained by using only perfluorinated monomers and no partially or non-fluorinated polymers. A partially fluorinated monomer contains C-F bonds and C-H bonds, a perfluorinated monomer contains C-F bonds but does not contain C-H bonds and a non-fluorinated monomer contains no C-F bonds but C-H bonds.

In a preferred embodiment the PFSA ionomer is as described above, wherein in formula (I) a is 1 or 0, c is 0, C _e F _2e is linear and e is 2, 3 or 4, more preferably in formula (I) a is 1 or 0, c is 0, C _e F _2e is linear and e is 4.

In another preferred embodiment the PFSA ionomer is described above wherein the PFSA ionomer comprises units according to formula (II) and wherein in formula (II) rri is 0 and Rf is selected from CF3, C2F5, C3F7, preferably CF2CF2CF3.

In another preferred embodiment the PFSA ionomer is described above wherein the PFSA ionomer comprises units according to formula (II) and wherein in formula (II) rri is 1 and Rf is selected from CF3, C2F5, C3F7, preferably CF2CF2CF3.

In another preferred embodiment the PFSA ionomer is described above wherein the PFSA ionomer comprises units according to formula (II) and wherein in formula (II) rri is 1 and Rf is selected from (CF2) _n OCF3 and n is 1, 2, 3, or 4, preferably n is 3.

In another preferred embodiment the PFSA ionomer is described above wherein the PFSA ionomer comprises units according to formula (II) and wherein in (I) iri is 0 and Rf is selected from (CF2) _n OCF3 and n is 1, 2, 3, or 4, preferably n is 3.

In another preferred embodiment the PFSA ionomer is described above wherein the PFSA ionomer wherein in formula (I) a is 0, c is 0, C _e F _2e is linear and e is 4 and the PFSA ionomer comprises units according to formula (II) and in formula (II) rri is 0 and Rf is selected from CF3, C2F5, C3F7, preferably CF2CF2CF3.

In another preferred embodiment the PFSA ionomer cis described as above wherein in formula (I) a is 0, c is 0, C _e F _2e is linear and e is 4 and in formula (II) rri is 1 and Rf is selected from CF3, C2F5, C3F7, preferably CF2CF2CF3.

In another preferred embodiment the PFSA ionomer is as described above and wherein in formula (I) a is 0, c is 0, C _e F _2e is linear and e is 4 and in formula (II) rri is 0 and Rf is selected from (CF2) _n OCF3 and n is 1, 2, 3, or 4, preferably n is 3.

In yet another preferred embodiment the PFSA ionomer is as described above wherein in formula (I) a is 0, c is 0, C _e F _2e is linear and e is 4 and in formula (II) rri is 1 and Rf is selected from (CF2) _n OCF3 and n is 1, 2, 3, or 4, preferably n is 3. Preparation of the PFSA ionomers

The PFSA ionomers of the present disclosure can be prepared by copolymerizing the comonomers, i.e. TFE, and comonomers giving the divalent units of formula (I) and, optionally, the comonomers giving the units of formula (II) and, optionally, copolymerizing optional comonomers for example the optional comonomers described above.

The monomers are charged to the reaction in proportions and amounts to give the final polymer with the desired comonomer units in the desired amounts. Differing incorporation speeds have to be taken into account when selecting the monomer feed. The monomers may be charged continuously or intermittently, for example as a batch polymerization. They may be charged continuously with the same amounts and speed or with varying amounts and feeding speeds depending on the polymer architecture to be created, i.e. core-shell polymers, random polymers or heterogenous polymers, for example bimodal or polymodal polymers.

The polymerization can be carried out by free-radical polymerization. Reaction equipment is used that is appropriate for handling corrosive substances including exposure to HF. The reaction equipment may allow handling under inert gases or purging with inert gases. Typically, stainless steel vessels are used but if appropriate the vessels can be made of other materials or may contain an inert protective lining, for example a PTFE lining. Samples or materials may be stored in stainless steel containers or in HDPE containers or other appropriate containers. The vessels and other equipment, for example stirring equipment, may vary in dimensions and design depending on the polymers to be produced.

Concentrations of ingredients may be determined on line, for example, by using pressure, pH, or other appropriate indicators, or samples may be taken intermittently and actual amounts of ingredients may be measured offline, for example, by gas chromatography, mass spectrometry, pH electrodes, F-electrodes or other appropriate analytical devices and methods. Free radical polymerization includes radical aqueous emulsion polymerization, which is preferred, suspension polymerization and solvent polymerization. Aqueous emulsion polymerization typically produces polymer particles of about 50 to 500 nm dispersed in the aqueous phase, also referred to in the art as “polymer latex”. Suspension polymerization will typically produce particle sizes up to several millimeters. Solvents for solvent polymerization include chlorofluorocarbon, hydrochlorofluorocarbon, hydrofluorocarbon, hydro fluoroether or the like, more preferably hydrofluorocarbon or hydrofluoroether which will not damage the ozone layer. Suitable hydrofluorocarbons may have from 4 to 10 carbon atoms. The hydrofluorocarbon preferably has a ratio of the number of hydrogen atoms/the number of fluorine atoms (hereinafter referred to as H/F) on a molar basis from 0.05 to 20. The hydrofluorocarbon may be linear or branched. Examples of suitable hydrofluoroethers CF3CH2OCF2CF2H, CHF2CF2CH2OCF2CF2H, CF3CF2CH2OCF2CF2H and CF3CH2OCF2CF2H.

The polymerization initiator to start the polymerization may, for example, be a diacyl peroxide (such as disuccinic acid peroxide, benzoyl peroxide, perfluoro-benzoyl peroxide, lauroyl peroxide or bis(pentafluoropropionyl) peroxide), an azo compound (such as 2,2'-azobis(2-amidinopropane) hydrochloride, 4,4'-azobis(4-cyanovalerianic acid), dimethyl 2,2'-azobisisobutyrate or azobisisobutyronitrile), aperoxyester (such as t-butyl peroxyisobutyrate or t-butyl peroxypivalate), a peroxydicarbonate (such as diisopropyl peroxydicarbonate or bis(2-ethylhexyl)peroxydicarbonate), a hydroperoxide (such as diisopropylbenzene hydroperoxide or t-butyl hydroperoxide), or a dialkyl peroxide (such as di-t-butyl peroxide or perfluoro-di-t-butyl peroxide). Also a water-soluble initiator (for example inorganic initiators, e g., potassium permanganate or a peroxy sulfuric acid salt) can be useful to start the polymerization process. Salts of peroxy sulfuric acid, such as ammonium persulfate or potassium persulfate, can be applied either alone or in the presence of a reducing agent, such as bisulfites or sulfinates (e.g., fluorinated sulfmates disclosed in U.S. Pat. Nos. 5,285,002 and 5,378,782, both to Grootaert) or the sodium salt of hydroxy methane sulfuric acid (sold under the trade designation “RONGALIT”, BASF Chemical Company, New Jersey, USA). The concentration range for the initiators and reducing agent can vary from 0.001% to 5% by weight based on the polymerization medium.

Most of the initiators described above and any emulsifiers that may be used in the polymerization have an optimum pH-range where they show most efficiency. For these reasons, buffers may be useful. Buffers include phosphate, acetate, oxalate or carbonate (e.g., (NH4)2COg or NaHCOg) buffers or any other acid or base, such as ammonia or alkali-metal hydroxides. In some embodiments, the copolymerizing is carried out at a pH of lower than pH 9. The concentration range for the initiators and buffers can vary from 0.01% to 5% by weight based on the aqueous polymerization medium. In some embodiments, ammonia is added to the reaction mixture in an amount to adjust the pH if the pH is too acidic.

Typical chain-transfer agents like Hg, lower alkanes (e.g. n-pentane, n-hexane or cyclohexane), alcohols (e.g. such as methanol, ethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoropropanol, 1,1, 1,3, 3, 3- hexafluoroisopropanol or 2,2,3,3,3-pentafluoropropanol), ethers (e.g. diethyl ether or methyl ethyl ether), esters (e.g. methyl acetate or ethyl acetate), and CHgClg may be useful in the preparation of the polymers according to the present disclosure. Termination primarily via chain-transfer results in a polydispersity of about 2.5 or less. In some embodiments of the method according to the present disclosure, the polymerization is carried out without any chain-transfer agents. A lower polydispersity can sometimes be achieved in the absence of chain-transfer agents. Recombination typically leads to a polydispersity of about 1.5 for small conversions. The amount of the molecular weight-controlling agent if used may be from 0.0001 to 50, or from 0.001 to 10 parts per 100 parts of monomers.

Useful polymerization temperatures can range from 20 °C to 150 °C. Typically, polymerization is carried out in a temperature range from 30 °C to 120 °C, 40 °C to 100 °C, or 50 °C to 90 °C. The polymerization pressure is usually in the range of 0.4 MPa to 2.5 MPa, 0.6 to 1.8 MPa, 0.8 MPa to 1.5 MPa, and in some embodiments is in the range from 1.0 MPa to 2.0 MPa.

Perfluorinated or partially fluorinated emulsifiers may be used in the polymerization. Generally, these fluorinated emulsifiers may be present in a range from about 0.02% to about 3% by weight with respect to the polymer. Polymer particles produced with a fluorinated emulsifier typically have an average diameter, as determined by dynamic light scattering techniques, in range of about 10 nanometers (nm) to about 500 nm, and in some embodiments in range of about 50 nm to about 300 nm. Examples of suitable emulsifiers include perfluorinated and partially fluorinated emulsifier having the formula

[Rf-O-L-COO"] _i X ⁱ⁺ wherein L represents a linear partially or fully fluorinated alkylene group or an aliphatic hydrocarbon group, Rf represents a linear partially or fully fluorinated aliphatic group or a linear partially or fully fluorinated aliphatic group interrupted with one or more oxygen atoms, χ ⁱ⁺ represents a cation having the valence i and i is 1, 2 or 3. (See, e.g., U.S. Pat. No. 7,671,112 to Hintzer et al.). Additional examples of suitable emulsifiers also include perfluorinated polyether emulsifiers having the formula CF3-(OCF2)x- O-CF2-X’, wherein x has a value of 1 to 6 and X’ represents a carboxylic acid group or salt thereof, and the formula CF3-0-(CF2)3-(0CF(CF3)-CF2)y-0-L-Y’ wherein y has a value of 0, 1, 2 or 3, L represents a divalent linking group selected from -CF(CF3)-, -CF2-, and-CF2CF2-, and Y’ represents a carboxylic acid group or salt thereof (See, e.g., U.S. Pat. Publ. No. 2007/0015865 to Hintzer et al.). Other suitable emulsifiers include those described in U.S. Pat. Publ. No. 2006/0199898 to Funaki et al.), U.S. Pat. Publ. No. 2007/0117915 to Funaki et al., U.S. Pat. No. 6,429,258 to Morgan et al., U.S. Pat. No. 4,621,116 to Morgan, U.S. Pat. Publ. No. 2007/0142541 to Hintzer et al., U.S. Pat. Publ. Nos. 2006/0223924, 2007/0060699, and 2007/0142513 each to Tsuda et al. and 2006/0281946 to Moritaetal. and U.S. Pat. No. 2,559,752 to Berry). However, conveniently, in some embodiments, the polymerization may be conducted in the absence of any of these emulsifiers or with no fluorinated emulsifier.

The monomers may be charged all at once, or they may be charged continuously or intermittently. Perfluoroalkoxy alkyl vinyl ethers and perfluoroalkoxy alkyl allyl ethers are typically liquids and may be sprayed into tire reactor or added directly, as liquid or vaporized, or atomized. It can be useful to feed the compound represented by formula CF2=CF(CF2) _a -(OCbF2b)c-O-(CeF ^, 2e)-SO2X” and the other comonomers leading to units according to formula (II) as a homogenous mixture or emulsion to the polymerization. It may be useful to use one or more of the emulsifiers described above to prepare such pre-emulsion. It may also be useful to hydrolyze some of the CF2=CF(CF2) _a -(OCbF2b)c-O- (C _e F2 _e )-SO2F by an aqueous base to obtain an “in situ”-emulsifier as for example described in W02005/044878 (Thaler et al).

If fluorinated emulsifiers are used, tire emulsifiers can be removed or recycled from the fluoropolymer latex, if desired, as described in U.S. Pat. Nos. 5,442,097 to Obermeier et al., 6,613,941 to Felix et al., 6,794,550 to Hintzer et al., 6,706,193 to Burkard et al., and 7,018,541 to Hintzer et al. Alternatively, the emulsifiers may also be removed by heat-treatment (for example evaporation or treatment with carrier gas streams or steam) and subsequently be thermally degraded or recovered and recycled. Preferably, the sulfonyl fluoride precursor polymer has a glass transition temperature (Tg) of up to 25 °C, 20 °C, 15 °C, or 10 °C. The Tg of the polymer can be influenced by the monomer compositions. Typically, side chains with perfluoralkoxy groups reduce the Tg of the polymer. Preferably, the sulfonyl fluoride precursor polymer has a melt flow index (MFI, e.g., 265 °C/5 kg) of at least 0.1 gram per 10 minutes and up to 100, preferably up to 80 grams per 10 minutes, for example an MFI between 5 and 55 grams per 10 minutes. The MFI of the copolymer can be adjusted by adjusting the amount of the initiator and/or chain-transfer agent used during polymerization, both of which affect the molecular weight and molecular-weight distribution of the copolymer. MFI can also be controlled by the rate of addition of initiator to the polymerization. Variations in the monomer composition can also affect the MFI.

The SO ₂ F-comonomers may be less reactive than the other comonomers. Therefore, it can be useful to feed these monomers to the polymerization system in excess (for example in an amount greater than 30% than the expected final amount in the polymer) to obtain the desired incorporation into the polymer. To remove and recover excess SO ₂ F -monomer, the reaction mixture can be coagulated and unreacted monomer can be recovered from the coagulate, for example by evaporation. The reaction mixture may or may not be diluted prior to the coagulation or solvents or other liquids that allow recovery of the unreacted monomer may be added prior to the coagulation. The coagulation and monomer recovery can be done in the same reaction vessel or the reaction mixture can be transferred to a different reaction vessel. The reaction mixture can be transferred all at once and then be subjected to an evaporation treatment, or it can be transferred continuously or intermittently in portions. Evaporation may be carried out by heat-treatment, for example in a reactor with an external heating jacket or by using a carrier medium, for example steam, or both. The carrier medium may also be used to heat the reactor, for example when steam is used as carrier medium or a heated carrier gas is used. In case of using a carrier medium the reactor may contain one or more nozzles through which the carrier medium can enter and exit. The reactor may contain one or more stirrer, for example an impeller stirrer or a helical ribbon stirrer, or the reactor can be a fluidized bed reactor. The unreacted monomer can be recovered by condensation and/or other separation from the carrier medium. To coagulate the obtained copolymer latex, any coagulant which is commonly used for coagulation of a fluoropolymer latex may be used, and it may, for example, be a water-soluble salt (e g., calcium chloride, magnesium chloride, aluminum chloride or aluminum nitrate), an acid (e.g., nitric acid, hydrochloric acid or sulfuric acid), or a water- soluble organic liquid (e.g., alcohol or acetone. The amount of the coagulant to be added may be in a range of 0.001 to 20 parts by mass, for example, in a range of 0.01 to 10 parts by mass per 100 parts by mass of the latex. For example, 341 kg of a polymer dispersion with a solid content of 29 % to which 200 kg deionized water is added can be charged into a stainless steel reactor having an internal capacity of 800 1 equipped with a stirrer, a high speed agitator “TURRAX” and steam nozzles for heating up the reactor. While the stirrer of the reactor was rotated at 100 rpm and the high-speed agitator at 600 rpm 65 wt-% nitric acid (28,2 kg) can be fed continuously in the reactor to precipitate the polymer at room temperature and agitation can be continued for lh. This can lead to almost complete coagulation with a solid content of less than 1% in the resulting water phase. Alternatively, or additionally, the latex may be frozen for coagulation or mechanically coagulated, for example, with a homogenizer as described in U.S. Pat. No. 5,463,021 (Beyer et al.). Alternatively, or additionally, the latex may be coagulated by adding polycations. It may be useful to avoid using salts as coagulants to avoid introducing metal contaminants. To avoid coagulation altogether and any contaminants from coagulants, spray drying the latex after polymerization and optional ion-exchange purification may be useful to provide solid precursor polymer.

The coagulated precursor polymer can be collected by filtration and washed with water. The washing water may, for example, be ion-exchanged water, pure water, or ultrapure water. The amount of the washing water may be from 1 to 5 times by mass to the precursor polymer, whereby the amount of the emulsifier attached to the polymer can be sufficiently reduced by one washing. The precursor polymer can be dried with drying equipment as known in the art, for example by a fluidized bed dryer or a tumble drier or simply an oven, to a water content of for example 0.1% by weight or less, preferably less than 0.05%wt. Depending on the nature of the polymerization initiator (e.g. KMnO4) a cation-exchange process might be beneficial prior to the comonomer recovery process. Useful cation exchange resins include polymers (typically cross-linked) that have a plurality of pendant anionic or acidic groups such as, for example, polysulfonates or polysulfonic acids, polycarboxylates or polycarboxylic acids. Examples of useful sulfonic acid cation exchange resins include sulfonated styrene-divinylbenzene copolymers, sulfonated crosslinked styrene polymers, phenol-formaldehyde -sulfonic acid resins, and benzene- formaldehyde-sulfonic acid resins. Preferably, the cation exchange resin is an organic acid cation exchange resin, such as carboxylic acid cation exchange resin. Cation exchange resins are available commercially from a variety of sources. Cation exchange resins are commonly supplied commercially in either their acid or their sodium form. If the cation exchange resin is not in the acid form (i.e., protonated form) it may be at least partially or fully converted to the acid form in order to avoid the generally undesired introduction of other cations into the dispersion. This conversion to the acid form may be accomplished by means well known in the art, for example by treatment with any adequately strong acid The ion-exchange process may be carried out in a continuous mode using fixed bed columns, for example a column with a length to diameter ratio of 20 : 1 to 7 : 1 at a flow rate of 1 bed volume/h. The process can be monitored on line or offline by pH-meter, metal -analyzer (for example if the hydrolyzation is carried out Li -salts, the lithium content can be measured) or other techniques (e.g. conductivity etc.). The ion-exchange resin can be a multimodal resin or a monomodal resin and it can have a broad or narrow particle size distribution. Commercially available cation exchange resins include but are not limited to those available under the trade designation LEWATIT MONO PLUS S 100, AMBERLITE IR-120(Plus) or PUROLITE 150C TLH.

If purification of the fluoropolymer dispersion is carried out using both anion and cation exchange processes, the anion exchange resin and cation exchange resin may be used individually or in combination as, for example, in the case of a mixed resin bed having both anion and cation exchange resins.

Fluoropolymers obtained by aqueous emulsion polymerization typically have a high number of carboxylic acid end groups (more than 200 carboxylic acid end groups per 10 ⁶ carbon atoms created, for example, by a side reaction of the polymerization initiator. Preferably, the copolymer has less than 150 carboxylic acid end groups per lO^ carbon atoms, preferably less than 100 or even less than 50, for example between 1 and 45 or between 10 and 90 carboxylic acid end groups per 10 ⁶ carbon atoms. Reducing the number of carboxylic acid end groups can be accomplished by a fluorination treatment. Fluorination of the fluoropolymer converts unstable end groups to -CF3 end groups. The fluorination may be carried out in any convenient manner. The fluorination can be conveniently carried out with nitrogen/fluorine gas mixtures in ratios of 75 - 90 : 25 - 10 at temperatures between 20 °C and 250 °C, in some embodiments in a range of 150 °C to 250 °C or 70 °C to 120 °C, and pressures from 10 kPa to 1000 kPa. Reaction times can range from about four hours to about 16 hours. The fluorination can be carried out continuously or intermittently, for example by a sequence of fluorination and purging steps, and at the same temperature or at different temperature intervals. Purging is conveniently carried out by using nitrogen gas. Under these conditions, most unstable carbon-based end groups are removed, whereas the- SO2F groups survive. After completion of the reaction the reactor vessel is purged with nitrogen to remove the fluorine gas. The fluorination can be carried out, for example, in an appropriately equipped autoclave, tumble reactor or fluidized bed reactor or a combination thereof.

The S02F-copolymer is hydrolyzed to convert the SC2F-groups into -SO2OX” groups, “sulfonate groups”. X” represents OZ and each Z is a cation, preferably an alkali metal cation or a quaternary ammonium cation. The quaternary ammonium cation can be substituted with any combination of hydrogen and alkyl groups, in some embodiments, alkyl groups independently having from one to four carbon atoms. In some preferred embodiments, Z is an alkali-metal cation, preferably a sodium or lithium cation. The hydrolysis can be done by subjecting the SC^F-polymer to a treatment with an aqueous base. The reaction can be done under pressure, for example in an autoclave, fluidized bed reactor or a stirred vessel. Typically, the hydrolysis is carried out at elevated temperature, for example at a temperature between 150°C -300°C. Reaction times may be from 0.5 to 10 hours. Preferably an alkaline base (for example but not limited to lithium hydroxide or lithium carbonate, an earth-alkali base or ammonia (NR4OH) or a combination thereof are used as base. The water amount may be chosen to give a solid content of 5 to 40% by weight. After the reaction is completed further salts forming poorly soluble fluoride salts (Al(OH)3, Ca(OH)2) or flocculants may be added to reduce the fluorine levels in the water phase. After the fluoride salts have been removed (for example by filtration, centrifugation or sedimentation) the -SO2OX” groups of the polymer are converted into the perfluorosulfonic acid form (- S031T form) by acid treatment or ion-exchange with a cation exchange resin. Cation exchange resins as described above may be used. The ion-exchange process may be carried out as described above, for example, in a continuous mode using fixed bed columns, for example a column with a length to diameter ratio of 20 : 1 to 7 : 1 at a flow rate of 1 bed volume/h. The process can be monitored on line or offline, for example, by pH-meter, metal-analyzer (for example if the hydrolyzation is carried out Li-salts, the lithium content can be measured) or other techniques (e.g. conductivity etc.) including those described above. To create dispersible PFSA ionomer particles, an aqueous PFSA ionomer composition is subjected to drying. Preferably, the drying is carried out at a temperature and for an effective time to reduce the moisture content of the aqueous PFSA ionomer composition to a moisture content of less than 25 weight %, preferably less than 15 weight %, more preferably less than 12 weight % based on the weight of the composition. The drying preferably is carried out such that the moisture content does not decrease below the content described above and below, for example not below 2 weight %, preferably not below 3.1 weight % more preferably below 3.9 wt % (based on the weight of the composition).

Preferably the drying process is carried out such that the temperature of the composition does not exceed 220°C or 200°C or even 100°C. More preferably, the drying is carried out by a cryo process, i.e. a process comprising freezing the dispersion.

In some embodiments, the aqueous PFSA-composition is obtained by a process comprising spray-drying. Typically, the spray-drying process leads to particles having a particle size of from about 10 to 300 pm. These particle sizes may be the D50 value or may be the maximum particle sizes. Using sieves can make sure that particles with diameters in excess of the above sizes are removed from the compositions. The particles are typically spherical or substantially spherical which means the particles are not of a perfectly spherical shape but their geometric shape can be best approximated by a spherical shape.

In other embodiments, the PFSA-composition according to the present disclosure is dried by a process comprising freeze drying. Freeze-drying results in a flaky material, typically of a maximum dimension between 5 pm to 1000 pm. The flakes can be crushed into smaller particles. In some embodiments, a foam is created from the aqueous composition and the foam is freeze-dned. A foam can be created, for example, by subjecting the aqueous composition to ultra sound irradiation, by injecting a gas into the dispersion, for example CO2, or by mechanical forces, for example by subjecting the aqueous composition to one or more high speed agitators. A combination of the above steps may be used, also.

In other embodiments, the PFSA ionomer particles are obtained by a process comprising freeze- granulation, preferably freeze-granulation with liquid nitrogen. Typically, freeze-granulation leads to spherical particles having a particle size between 10 pm and 500 pm. These particle sizes may be the D50 value or may be the maximum particle sizes. Using sieves can make sure that particles with diameters in excess of the above sizes are removed from the compositions. The particles obtained by freeze- granulation are typically porous. They are typically spherical or substantially spherical which means the particles are not perfectly spherical, but their geometric shape can be best approximated by a spherical shape.

The solid PFSA ionomer particles typically have a total content of Na, K and Li ions of less than 100 ppm, preferably less than 50 ppm, or even less than 20 ppm, and one or more of all of these ions may actually be absent. The dispersible PFSA ionomer particles typically have a heavy metal content (total content of Fe, Ni, Cu and Cr ions) of not greater than 100 ppm, preferably less than 20 ppm and more preferably the Fe content is below 5 ppm. The PFSA ionomer particles can typically be directly dispersed at a concentration of at least 10, 15, 20, or 25 percent by weight in a liquid, preferably the liquid selected from water and an organic protic solvent containing at least one hydroxyl functionality and from 1 to 5 carbon atoms as described above and below. In some embodiments, the ionomer particles can be directly dispersed at a concentration of up to and including 30, preferably up to and including 40 or even 50 percent by weight. The PFSA ionomer particles can be dispersed in the liquid to provide a liquid composition having a viscosity of less than 300 mPas, preferably less than 100 mPas at a shear rate 1/s and at a shear rate at 1000/s, or even lower viscosities as described above and below.

The PFSA ionomer particles can be dispersed easily in water or water- miscible solvents to make liquid compositions having low viscosities at low and high shear rates, and, preferably even at rather high concentration of PFSA ionomer, for example at concentrations of up to at least 20 % by weight of PFSA ionomer, or at least up to at least 30% by weight of PFSA ionomer or even up to 40% by weight of PFSA ionomer or more. A further advantage of the PFSA ionomer particles is that they can be used to make dispersions having a low viscosity that remains substantially constant over a wide range of shear rates.

For example, the ratio of the viscosity of such PFSA dispersion measured at a low shear rate, for example 1/s and a high shear rate, for example 1000/s, is equal or close to 1, for example between and including 0.9 and 1.20. This allows for a wide processing window of the dispersions obtained from the PFSA ionomers and ionomer compositions provided in the present disclosure.

A useful method for making such dispersions includes combining the components and mixing the components at ambient temperature and pressure to make the liquid dispersion of ionomer particles. Mixing can be carried out by agitating the composition. Mild agitation conditions may be sufficient, for example placing the mixture on a roller that is set at 45 to 65 rpm for a period of 24 hours at room temperature and ambient pressure. Although the liquid compositions can be prepared at ambient conditions, they may also be prepared in other ways, for example by adding other solvents or operating at elevated temperatures or pressures, but in many cases this is disadvantageous and unnecessary.

The PFSA ionomer dispersions of the present disclosure may be used, for example, in the manufacture of membranes, for example polymer electrolyte membranes for use in fuel cells or electrolyte membranes in an electrochemical cell, for example in a chlor-alkali membrane cell. The PFSA ionomer dispersions are particularly suitable for making thin membranes, i.e. membranes having a thickness of less than 50 micrometer, preferably less than 30 micrometers, for example between 20 and 40 micrometers, or between 10 to 28 micrometers. The membranes are typically extended sheets and may have a length of greater than 12 cm. Typically, the membrane is cast from a liquid composition or a dispersion and then dried, annealed, or both. The membrane may be cast on a support. Typically, the supporting matrix is electrically non-conductive. Typically, the supporting matrix is composed of a fluoropolymer, which is more typically perfluorinated. Typical matrices include porous polytetrafluoroethylene (PTFE), such as biaxially stretched PTFE webs. In another embodiment fillers (e.g. fibers) might be added to the PFSA ionomer composition to reinforce the membrane. After forming, the membrane may be annealed, typically at a temperature of 120 °C or higher, more typically 130 °C or higher, most typically 150 °C or higher.

For making a membrane a liquid PFSA ionomer dispersion obtained by dispersing the dispersible PFSA ionomer composition in the liquid as described above to produce a liquid composition of low viscosity. However, the dispersible PFSA ionomer particles may also be combined with other liquids to provide a dispersion or a solution. Additives may be added before the membrane is cast. The additives may be added to a composition obtained by combining the dispersible PFSA ionomer particles with a liquid, preferably the liquid described above for producing the liquid PFSA ionomer dispersions of low viscosity or with a different liquid. The additives may be added as solid materials or dissolved or dispersed in a liquid. The additives may also be combined directly with the dispersible PFSA ionomer particles according to the present disclosure and may be added as solids, for examples as powders, or they may be added as solution or dispersion in a liquid, which may be water or the protic organic solvent having at least one functional hydroxyl group as described above, or it may be a different liquid.

In some embodiments, the additive includes a salt of at least one of cerium, manganese or ruthenium or one or more cerium oxide or zirconium oxide compounds and is added to the PFSA ionomer before membrane formation. The salt of cerium, manganese, or ruthenium may comprise any suitable anion, including chloride, bromide, hydroxide, nitrate, sulfonate, acetate, phosphate, and carbonate. More than one anion may be present. Other salts may be present, including salts that include other metal cations or ammonium cations. Once cation exchange occurs between the transition metal salt and the acid form of the ionomer, it may be desirable for the acid formed by combination of the liberated proton and the original salt anion to be removed. Thus, it may be useful to use anions that generate volatile or soluble acids, for example chloride or nitrate. Manganese cations may be in any suitable oxidation state, including Mn2+. Mn3+. and Mn4+, but are most typically Mh^+, Ruthenium cations may be in any suitable oxidation state, including Ru3+ and Ru4+ , but are most typically Ru3+ . Cerium cations may be in any suitable oxidation state, including Ce3 ⁺ and Ce4 ⁺ . Without wishing to be bound by theory, it is believed that the cerium, manganese, or ruthenium cations persist in the polymer electrolyte because they are exchanged with H ⁺ ions from the anion groups of the polymer electrolyte and become associated with those anion groups. Furthermore, it is believed that polyvalent cerium, manganese, or ruthenium cations may form crosslinks between anion groups of the polymer electrolyte, further adding to the stability of the polymer. In some embodiments, the salt may be present in solid form. The cations may be present in a combination of two or more forms including solvated cation, cation associated with bound anion groups of the polymer electrolyte membrane, and cation bound in a salt precipitate. The amount of salt added is typically between 0.001 and 0.5 charge equivalents based on the molar amount of acid functional groups present in the polymer electrolyte, more typically between 0.005 and 0.2, more typically between 0.01 and 0.1, and more typically between 0.02 and 0.05. Further details for combining an anionic copolymer with cerium, manganese, or ruthenium cations can be found in U.S. Pat. Nos. 7,575,534 and 8,628,871, each to Frey et al. The cerium oxide compound may contain cerium in the (IV) oxidation state, the (III) oxidation state, or both and may be crystalline or amorphous. The cerium oxide may be, for example, Ce02 or Ce203. The cerium oxide may be substantially free of metallic cerium or may contain metallic cerium. The cerium oxide may be, for example, a thin oxidation reaction product on a metallic cerium particle. The cerium oxide compound may or may not contain other metal elements. Examples of mixed metal oxide compounds comprising cerium oxide include solid solutions such as zirconia-ceria and multicomponent oxide compounds such as barium cerate. Without wishing to be bound by theory, it is believed that the cerium oxide may strengthen the polymer by chelating and forming crosslinks between bound anionic groups. The amount of cerium oxide compound added is typically between 0.01 and 5 weight percent based on the total weight of the PFSA ionomer, more typically between 0.1 and 2 weight percent, and more typically between 0.2 and 0.3 weight percent. The cerium oxide compound is typically present in an amount of less than 1% by volume relative to the total volume of the polymer electrolyte membrane, more typically less than 0.8% by volume, and more typically less than 0.5% by volume. Cerium oxide may be in particles of any suitable size, in some embodiments, between 1 nm and 5000 nm, 200 nm to 5000 nm, or 500 nm to 1000 nm. Further details regarding polymer electrolyte membranes including cerium oxide compounds can be found in U.S. Pat. No. 8,367,267 (Frey et al.).

The PFSA ionomer particles and dispersions of the present disclosure may also be used for making a catalyst ink composition. For making a catalyst ink, the dispersible PFSA ionomer particles may be used to make the liquid composition of low viscosity according to the present disclosure and combining it with catalyst particles (e.g., metal particles or carbon-supported metal particles). However, the dispersible PFSA ionomer particles may also be combined with other liquids to provide a dispersion or a solution to which catalyst particles may be added. The catalyst particles may also be added directly to the dispersible PFSA ionomer particles and combined with them. The catalyst particles may be added as solid materials or dissolved or dispersed in a liquid, preferably water or the protic solvent having at least one hydroxyl functionality as described above. A variety of catalysts may be useful. Typically, carbon- supported catalyst particles are used. Typical carbon-supported catalyst particles are 50% to 90% carbon and 10% to 50% catalyst metal by weight, the catalyst metal typically comprising platinum for the cathode and platinum and ruthenium in a weight ratio of 2: 1 for the anode. However, other metals may be useful, for example, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, vanadium, and alloys thereof. The ink may then be applied to a substrate, for example a membrane or an electrode. In one embodiment the catalyst particles or at least a part thereof is added to the dispersible PFSA ionomer composition prior to adding the liquid to form a liquid composition. Details concerning the preparation of catalyst inks and their use in membrane assemblies can be found, for example, in U.S. Pat. Publ. No. 2004/0107869 (Velamakanni et al.).

The PFSA ionomer particles and dispersions according to the present disclosure may also be used for making a binder for an electrode or a battery (for example, lithium ion batteries). To make electrodes, powdered active ingredients can be dispersed with a solvent and added as solids, for example as powders, to the dispersible PFSA ionomer dispersion according to the present disclosure or to a composition obtained by combining the dispersible PFSA ionomer composition with a liquid. Preferably the liquid is water or the protic organic solvent having at least one functional hydroxyl group as described above. The binder composition may then be coated onto a substrate, for example a metal foil or a current collector. The resulting composite electrode contains the powdered active ingredient in the polymer binder adhered to the metal substrate. Useful active materials for making negative electrodes include alloys of main group elements and conductive powders such as graphite. Examples of useful active materials for making a negative electrode include oxides (tin oxide), carbon compounds (e.g., artificial graphite, natural graphite, soil black lead, expanded graphite, and scaly graphite), silicon carbide compounds, silicon-oxide compounds, titanium sulfides, and boron carbide compounds. Useful active materials for making positive electrodes include lithium compounds, such as The electrodes can also include electrically conductive diluents and adhesion promoters.

In order that this disclosure can be more fully understood, the following examples are set forth. It should be understood that these examples are for illustrative purposes only and are not to be construed as limiting this disclosure in any manner.

EXAMPLES

Moisture Content Method:

The moisture content of the solid ionomer compositions was determined with a Mettler- Thermowaage HR73, HR83 (Halogen) by thermogravimetric analysis. 3 g of the product was weighed into the thermobalance. The thermobalance was run at 120°C for 30 minutes. The resulting solid content (%) was determined by the ratio of final weight/initial weight times 100. The moisture content (%) was calculated by: 100% - solid content (%).

Viscosity Method:

The viscosities at a shear rate of 1/s and 1000/s were determined by rotational viscometry (rotational viscometer MCR 102 / cylinder system CC 27; Anton Paar Germany GmbH, Ostfildem- Schamhausen, Germany) at 20 °C. The solid samples were milled if necessary before the liquid was added. The liquid was added to the ionomer in amounts to give ionomer dispersion with the desired ionomer content. Unless stated otherwise 6 g of ionomer sample were used. The resulting mixture was placed on a roller box and was rolled for 24 hours at room temperature.

Solid Content Method:

Solid content was usually calculated by the weight of the ingredient. It can be determined gravimetrically by placing samples of the dispersions on a heated balance and recording the mass before and after evaporation of solvent. The solid content is the ratio of the initial mass of the sample and the mass of the sample when the mass did not decrease further with continued heating. A thermobalance (Mettler-Thermowaage HR73, HR83 (Halogen)) was used for thermogravimetric analysis. Typically, 3 g of product was weighed into the thermobalance and the thermobalance was run at 120°C. Equivalent Weight (EW) Method:

The EW of the ionomer was calculated by the formula: wherein M2 is the sulfonyl fluoride monomer and M3 is the optional vinyl ether or allyl ether monomer and M3 is 0 is the optional monomer is not present. ¹⁹ F-NMR spectra can be used to determine the composition of the polymers. An NMR spectrometer available under the trade designation AYANCE II 300 from Bruker, Billerica, MA, USA with a 5 mm Broadband probe can be used. Samples of about 13 weight percent polymer dispersion should be measured at 60 °C. The SO3H-EW is the EW of the free acid form (SC^H-form).

Determination of amount of carboxyl end groups:

A Fourier transform infrared spectroscopy (FT-IR) measurement was used to determine the number of carboxyl endgroups per 10 ⁶ C-atoms in the copolymer. The measurement was performed by FT-IR in a transmission technique. The measured sample had a film thickness of 100 pm. The wave numbers of the COOH peaks of interest are 1775 cm ^-1 and 1808 cm ^-1 . To quantify the amount of carboxyl endgroups of the polymer two IR spectra are taken. One from the carboxyl containing sample and one from a reference sample (without carboxyl groups). The reference material was a TFE/MV4S-copolymer that was subjected to a fluorination treatment for such a period of time that peaks at 1775 and 1808 cm ^-1 were no longer observed.

The number of endgroups per 10 ⁶ carbon atoms can be calculated via equation 1 and 2 for Fi and

(peak height x F ₁ ) / film thickness [mm] (1)

(peak height x F ₂ ) / film thickness [mm] (2) with the peak height being the difference of the peak height of the sample and the peak height of the reference sample at 1775 and 1808 cm ^-1 ;

F ₁ : calculated factor (= 320) related to u = 1775 cm ^-1 f _rom us patent No. 4,675,380 (Buckmaster et al) incorporated herein by reference;

F2: calculated factor (= 335) related to u = 1808 cm ^-1 f _rom us patent No. 4,675,380 (Buckmaster et al) incorporated herein by reference.

The sum of the results from the equations 1 and 2 yield the number of carboxyl end groups per 10 ⁶ carbon atoms. Particle Size Method of solid compositions:

The particle sizes of solids compositions were determined by optical methods using a scanning electron microscope taken on a Phenom G2 Pure SEM from ThermoFischer Scientific. The dimensions of the particles were measured manually using the imaging software from the Phenom SEM. DIO, D50, D90 (i.e the diameters of spherical particles or the maximum dimensions of flake like particles at which 10%, 50% and 90% respectively of the particles were smaller than this respective value) were determined. Preferably, the sample size comprises 100 particles.

Melt Flow Index Method:

The melt flow index (MFI), reported in g/10 min, can be measured with a GOETTFERT MPD, MI- Robo, MI4 melt indexer (Buchen, Germany) following a similar procedure to that described in DIN EN ISO 1133-1 at a support weight of 5.0 kg and a temperature of 265 °C. The MFI can be obtained with a standardized extrusion die of 2.1 mm in diameter and a length of 8.0 mm.

T(α) Measurement Method:

A TA Instruments AR2000 EX rheometer can be used to measure the T(a) of the polymer samples. Samples were heated on a temperature ramp from -100 °C to about 125 °C at 2 °C per minute. Measurements were made at a frequency of one hertz.

Glass Transition Temperature Method:

A TA Instruments Q2000 DSC can be used to measure the glass transition temperature (Tg) of the polymer samples. Samples were heated on a temperature ramp from -50 °C to about 200 °C at 10 °C per minute. Transition temperatures were analyzed on the second heats.

Metal Content Method:

The metal ion content of the ionomer can be measured by Inductively coupled plasma optical emission spectrometry (ICP-OES, also known as ICP-AES, ICP atomic spectrometry) in a Thermo Scientific ICP-OES-ICAP 7400; CCD-detector according to DIN EN ISO 11885. For the quantitative determination the sample can be incinerated (for example in a quartz glass container at a temperature of 550°C for 30 minutes in an electric oven) and the residue is taken up in an acid solution (for example in aqueous HC1 solution (35% HC1); ultra pure grade) and analyzed with ICP-OES.

BET Surface Area Method:

The determination of the specific surface according to the BET method per nitrogen adsorption was carried out using the Surface Area Analyzer SA 3100 from Beckman Coulter according to DIN 9277:2010 (dynamic volumetric method, using polytetrafluoroethene (PTFE) TF2071Z available from 3M Company, St. Paul, MN, USA as reference substance. TF2071 Z has a surface area of 9.9 m ² /g +/- 0.4 m ² /g). The sample vessel unit (consisting of a sample container with a volume of 12 ml, slide-in tube and lid) was first weighed at room temperature on an analytical balance. Then 2-3 g of dry ionomer sample was introduced into the sample vessel and the slide-in tube was inserted and the lid was closed. The sample vessel unit containing the ionomer sample was heated for 180 minutes at 80 °C in the analyzer and was then weighed again to obtain the exact mass of degassed ionomer. The specific surface area analysis was performed by nitrogen adsorption (99.99% pure nitrogen) at -196 °C in the Surface Area Analyzer SA 3100 using multiple point determination. Each sample was subjected to a duplicate determination.

Example 1 (freeze granulation); EX1:

An aqueous PFS A ionomer dispersion (solid content 11.1 % by weight) was subjected to freeze granulation.

The dispersion was obtained in general by polymerizing TFE and F2C=F-O-CF ₂ CF ₂ CF ₂ CF ₂ SO ₂ F in aqueous emulsion polymerization and subsequent hydrolyzation of the sulfonyl polymer to provide the free sulfonic acid polymer. The monomers were used in amounts to create an equivalent weight (EW) of 950. The PFSA ionomer had less than 100 unstable end groups per 10 ⁶ carbon atoms (postfhiorination). The SO2F precursor polymer had an MFI at 265°C/5kg load (MFI 265/5) of 0.2 g/10 min.

Freeze granulation was carried out using a POWDERPRO Freeze granulator LS-2, from PowderPro AB, Sweden. A IL beaker was filled with liquid nitrogen and stirred by a magnetic stirrer at 400 rpm. The ionomer suspension was atomized in a two-substance nozzle into a fine spray with a flow rate of 2 liters/hour and at 0.2 bar nitrogen and sprayed into stirred liquid nitrogen where the droplets instantaneously froze. In a subsequent freeze-drying step, the frozen granules were dried by sublimation of ice in an ALPHA 2-4 LSCplus freeze dryer from Martin Christ Gefriertrocknungsanlagen GmbH, Germany, under a 1.5 bar vacuum. Within 24h temperature was raised to 18°C while maintaining the vacuum of 1.5 mbar. In a post drying step temperature was raised from 18 to 22°C within 6 hours while the pressure was further reduced from 1.5 mbar to 0.5 mbar. After in total 30h drying the vacuum was released. The properties of the resulting material are shown in table 1. The resulting powder was suspended in n-propanol/water (60% wt / 40% wt) in a concentration to give 20% wt of ionomer content and the viscosity of the resulting dispersion was measured. The results are shown in table 1.

Example 2 (freeze granulation); EX2:

An aqueous PFSA ionomer dispersion (solid content 8.5 % by weight) was subjected to the same treatment as described in Example 1. The PFSA ionomer was obtained as described in example 1 except that TFE was copolymerized with a different comonomer: C F 2 - C F - O - C F 2 C F ( C F 3 ) - O - C F 2 C F 2 S O 2 F . The monomers were used in amounts to give an EW of 1070. The resulting powder were suspended in n- propanol/water (60% wt / 40% wt) in a concentration to give 20% wt of ionomer content and the viscosity of the resulting dispersion was measured. The results are shown in table 1.

Example 3 (spray drying); EX3: An aqueous PFSA ionomer dispersion was obtained as described in Example 1 except that the monomers were used in amounts to provide an equivalent weight (EW) of 800. The PFSA ionomer had less than 100 unstable end groups per 10 ⁶ carbon atoms. The sulfonyl fluoride precursor had an MFI (265/5) of 18 g/10 min. The PFSA dispersion (solid content 13 % by weight) was subjected to spray-drying. Spray drying was carried out using a co-current spray drying equipment out of glass from ProCepT n.v., Zelzate, Belgium. The ionomer dispersion was dosed into the spray dryer with a rate of 5 g/min. A bi-fluid nozzle with 0.8 mm inner diameter and a nozzle gas (air) velocity of 4.2 1/min was used. The fed dispersion was heated by hot air. The air was dosed with a velocity of 0.4 m3/min, the air inlet temperature was set to a temperature of 160°C. Outlet temperature was 80°C. The resulting powder was dispersed in n- propanol/water (60% wt / 40% wt) in a concentration to give 20% wt of ionomer content and the viscosity of the resulting dispersion was measured at different shear rates. The results are shown in table 1.

Example 4 (freeze drying); EX4:

The ionomer dispersion of example 3 was subjected to freeze-drying. Freeze drying was carried out using an ALPHA 2-4 LSCplus freeze dryer from Martin Christ Gefriertrocknungsanlagen GmbH, Germany. A sample pan was filled with ionomer dispersion to a liquid level of about 10 mm and placed in the freeze dryer to freeze the ionomer dispersion for 19 h at a set shelf temperature of -65 °C. The frozen ionomer dispersion was dried by sublimation of ice under vacuum. 1.5 mbar vacuum was applied with a pressure reduction from 1 bar to 0.2 mbar within 10 min at -65°C set shelf temperature. Within 2 hours the temperature was raised to 40°C while maintaining the vacuum of 0.2 mbar. The temperature was held at 40°C at 0.2 mbar for 25h. After 27h of drying the vacuum was released. The resulting powder was dispersed in n-propanol/water (60% wt / 40% wt) in a concentration to give 20% wt of ionomer content and the viscosity of the resulting dispersion was measured at different shear rates. The results are shown in table 1. Table 1: Results of Examples. Comparative Example 1 (oven-drying)

A perfluorosulfonic acid (PFSA) ionomer composition obtained in essence by polymerizing TFE and F2C=CF-0-CF2CF2CF2CF2S02F in aqueous emulsion polymerization and subsequent and hydrolyzation of the sulfonyl polymer to provide the free sulfonic acid polymer (EW of 800, T alpha of 118°C, less than 100 instable end groups per 10 ⁶ carbon atoms (postfluorination)). The solution was kept in open HDPE bottles and was dried at different temperatures and periods to different moisture levels as indicated in table 2. The resulting friable PFSA solids (chunks of about 5 mm particle size in average; BET surface area was less than 0.001 m^/g) were re-dispersed in n-propanol/water (60% wt / 40% wt) in a concentration to give 20% wt of ionomer content and the viscosity of the resulting dispersion was measured. The results are also shown in table 2.

Table 2: Results of comparative example 1 n.d. = not determined

The examples demonstrate that the PFSA ionomers according to the present disclosure can be easily resuspended and provide low viscosity suspension over a wide range of different shear rates (1/s to 1000/s). The viscosity does not change much over different shear rates (calculated ratio of viscosity at 1/s to 1000/s is from about 0.9 to about 1.20.) Easily dispersible PFSA-ionomer compositions can also be prepared by a very specific and carefully controlled drying regime as demonstrated in comparative example 1 but the viscosities appear to be higher and the viscosity ratio at 1/s to 1000/s is 1.24 or greater. All methods recited in the following claims refer to the methods described in the example section of the present disclosure.