IONOMERS WITH IONOGENIC GROUPS IN THE SIDECHAIN

Description

SUMMARY

It is claimed:

• • Ionomer membranes, consisting of a non-fluorinated or partly fluorinated non-, partly or fully-aromatic main chain and a non- or partly-fluorinated side chain with ionic groups or their non-ionic precursors
  • Process for the production of the above mentioned ionomer membranes

STATE-OF-THE-ART

Ionomer membranes containing phosphoric acid or phosphonic acid have received in recent years a growing interest because the phosphoric and phosphonic acid groups show water-free proton conductivity, in that phosphoric acid groups or phosphonic acid groups can act as proton donator as well as as proton acceptor. This water-free proton conductivity of phosphoric acids is especially interesting for fuel cells in the temperature range between 100° C. and 200° C., because in this temperature range in fuel cells the vapour pressure of water is very low so that sulfonic acid containing ionomer membranes do not work anymore, because they need water molecules as proton acceptors. From the literature several membrane types are known, whose proton conductivity is generated from phosphoric acid or phosphonic acids.

There are for example:

• • blend membranes made of polybenzimidazole (PBI) and phosphoric acid with 5 to 6 phosphoric acid molecules per PBI repeating unit¹,². These membranes work at temperatures greater than 100° C. in the fuel cell very well, however phosphoric acid can be transported below 100° C. out of the membrane resulting in a decrease of conductivity and corrosion problems. ¹ Wainright, J. S.; Wang, J.-T.; Weng, D.; Savinell, R. F.; Litt, M. H., J. Electrochem. Soc. 1995, 142, L121² Calundann, G., Sansone, M., Benicewicz, B., Choe, E. W., Uensal, Oe., Kiefer, J., DE 10246459 A1, 2004
  • Phosphonated poly(phosphazene) obtained by reaction of brominated poly(bisphenoxyphosphazene) with t-butyllithium, followed by reaction with chloro-phosphoric acid diphenylester and finally partial hydrolysis of the formed phosphonic acid diphenylester to the free phosphonic acid³. A disadvantage of this reaction is that only a part of the lithiated groups reacts with the chlorophosphoric acid ester, and only a part of the formed phosphonic acid ester groups reacts to the free phosphonic acid group. ³ H. R. Allcock, M. A. Hofmann. R. M. Wood, Macromolecules 2001, 34, 6915-6921
  • Phosphonated poly(ethersulfon)e from brominated poly(ethersulfon)e by the Michaelis-Arbusov reaction⁴. A disadvantage of these polymers is, that the phosphonic acid groups are directly attached to the aromatic main chain, which has a negative impact on the proton conductivity, because the aryl main chain polymers are very stiff polymers and also with this method only a very limited number of phosphonic acid groups can be attached to the aromatic main chain polymer, which results in a great distance between the proton conducting groups and in turn in a low proton conductivity. ⁴ K. Jakoby et al, DE Offen 101 48 131 A1

For sulfonated ionomers it ha been shown, that the arrangement of the sulfonic acid groups in the side chain results in an increase in proton conductivity above 100° C. as compared with sulfonated ionomers with the sulfonic acid groups in the aromatic main chain. In a specific example the proton conductivities of sulfonated PEEK (sPEEK) and of poly(carbonylphenoxy)phenylene (“Poly-X 2000”) at 120° C. have been compared⁵. The Poly-X 2000 polymer was at 120° C. much more proton conducting than sPEEK. Disadvantages of this polymer are the expensive production process and the great stiffness of the polymer main chain and side chain. ⁵N. Ogato, M. Rikukawa, WO 94/24717

Purpose

The aim of the invention is to provide ionomers and ionomer membranes with the ionic group on a flexible side chain which has a positive impact on the proton conductivity of the ionomers. The aim is furthermore to provide processes for the production of these polymeric proton conductors.

Ionomers according to the invention are shown in FIG. 1.

DESCRIPTION

Surprisingly it has been found that ionomers and ionomer membranes with ionic groups or their non-ionic precursors at the end of a flexible side chain can be obtained by method 1 with the following steps:

• 1a: the starting polymer is deprotonated by a metal organic reaction;
• 1b: the deprotonated polymer is reacted with an aliphatic halogen compound, which has preferentially a halogen atom at one end and a non-ionic precursor of the ionic group at the other, wherein the halogen is exchanged nucleophilically;
• 1c: the non-ionic form of the ionic group is hydrolysed, whereby the protonic form of the cation exchange group is liberated.

The method 1 is depicted in FIG. 2.

Surprisingly it has been found that also method 2 leads to ionomers and ionomer membranes with a proton conducting group in the side chain:

• 2a: the starting polymer is deprotonated by a metal organic reaction;
• 2b: the deprotonated polymer is reacted with an excess of an aliphatic dihalogen compound or a mixture of different dihalogen compounds (different halogenes and/or different chain lengths of the dihalogen compound(s) are possible), which carry preferentially the halogen compounds at the end of the molecule, whereby a part of the halogen atoms of the dihalogen compound(s) are exchanged nucleophilically: Ar—Li+Hal-((C(R₂)₂)_x-Hal→Ar—((C(R₂)₂)_x-Hal
• 2c: the polymers carrying the nucleophilically exchangable halogens in the side chain are reacted with a compound carrying a nucleophilic group Nu and one or more ionic group(s) or their non-ionic form Y. In doing so the remaining halogens are exchanged nucleophilically;
• 2d: the non-ionic form of the ionic group is hydrolysed, whereby the protonic form of the cation exchange group is liberated.

The method 2 is depicted in FIG. 3.

Surprisingly it has been found that the side chain halogenated polymers can be converted via Michaelis-Arbusov reaction or related reactions and subsequent hydrolysis towards polymers with the phosphonic acid group in the side chain. This reaction is depicted in FIG. 4.

As polymer main chains all kinds of polymers are possible. Preferred as main chains are however:

• • polyolefines like polyethylene, polypropylene, polyisobutylene, polynorbornene, polymethylpentene, poly(1,4-isoprene), poly(3,4-isoprene), poly(1,4-butadiene), poly(1,2-butadiene) and block copolymers, alternating copolymer or statistical copolymers of polydienes polybutadiene and polyisoprene with styrole,
  • styrole(co)polymers like polystyrole, poly(methylstyrole), poly(α,β,β-trifluorstyrole), poly(pentafluorostyrole)
  • perfluorinated ionomers like Nafion® or the SO₂Hal-precursor of Nafion® (Hal=F, Cl, Br, I), Dow®-Membrane, GoreSelect®-Membrane.
  • partly fluorinated polymers like polyvinylidenfluoride, polyvinylfluoride and their copolymers with polyolefines or with aryl main chain polymersfrom FIG. 5 (see below)
  • N-basic polymers like polyvinylcarbazole, polyethylenimine, poly(2-vinylpyridine), poly(3-vinylpyridine), poly(4-vinylpyridine)
  • (Het)aryl main chain polymers, containing the building block depicted in FIG. 5.

Particularly preferred are (Het)aryl main chain polymers like:

• • Polyetherketones like polyetherketone PEK Victrex®, polyetheretherketone
  • PEEK Victrex®, polyetheretherketoneketone PEEKK, polyetherketoneetherketone ketone PEKEKK Ultrapek®
  • Polyethersulfones like polysulfone Udel®, polyphenylsulfone Radel R®, Polyetherethersulfone Radel A®, polyethersulfone PES Victrex®
  • Poly (Benz) imidazole like PBI Celazol® and others the (Benz) imidazole-group containing oligomers and polymer, in which the (Benz) imidazole group can be available in the main chain or in the side chain
  • Polyphenyleneether like poly(2,6-dimethyloxyphenylene), poly(2,6-diphenyloxyphenylene)
  • Polyphenylenesulfide and copolymers
  • Poly(1,4-phenylene) or Poly (1,3-phenylene), which can be modified in the lateral group if necessary with benzoyl, naphtoyl or o-phenyloxy-1,4-benzoyl group, m-phenyloxy-1,4-benzoyl group or p-phenyloxy-1,4-benzoyl group.
  • Poly(benzoxazole) and copolymers
  • Poly(benzthiazole) and copolymers
  • Poly(phtalazinone) and copolymers
  • Polyaniline and copolymers
  • Polythiazole
  • Polypyrrole

Suitable reagents for the deprotonation of the aryl polymer are n-butyllithium, sec-butyllithium, tert. butyllithium, methyllithium, phenyllithium, Grignard compounds like phenylmagnesiumhalide and other Grignard compounds, lithium diisopropylamide, and other lithium amides, sodium naphtalide, potassium naphtalide, zinc organic compounds (“Rieke metals”)

Suitable solvents for the metal organic reaction are ether solvents like THF, diethylether, glyme, diglyme, triglyme, dioxane and other ether solvents as well as hydrocarbon solvents C_nH_2n+2, cyclohexane, benzene, toluene, xylole and other C—H— aromatic solvants and any other mixtures thereof and with ether solvents.

Some of the suitable compounds with nucleophilically substitutable halogens and ionogenic groups or their non-ionic precursors for the reaction with the deprotonated polymers are depicted in FIG. 2. Particularly preferred are compounds of the typ Hal-(CH₂)_x—Y (Y see FIG. 2, x=1−20).

The compounds with nucleophilically substitutable halogens and ionogenic groups may contain as halogene F, Cl, Br, or I. Preferred are Cl, Br and I. Also mixtures of organic compounds with different halgenes and different alkyl chain lengths can be used.

Suitable dihalogene compounds for the reaction with the deprotonated polymers are: Hal-(C(R₁)₂)_x-Hal Cl, Br, I; R₁=H, F, C_nH_2n+1, aryl). The dihalogen alcanes according to the invention method 2 can be also mixed dihalogen alcanes, that is compounds like Br—(C(R₁)₂)_x—I, where both halogen atoms have different reactivity to assure that no cross-linking takes place during method 2. If for example the compound I—(CH₂)—Cl is reacted with lithiated PSU, I is preferred to be exchanged nucleophilically. Thereby Cl, Br and I are preferred. Also mixtures of dihalogene compounds with different halgenes and different alkyl chain lengths can be used. Also compounds like Hal-(C(R₁)₂)_x-Aryl-Hal are possible. According to the invention also Hal-(C(R₁)₂)_x—Z-Aryl-Hal are possible.

Also in another embodiment of the invention halogenated hetaromates can be used. Some of these hetaromates are shown in FIG. 6. The hetaromates may contain in addition organic rests which do not react with the reactands of the process according to the invention.

Suitable nucleophilic groups for the reaction with the side chain halogenated polymers are shown in FIG. 7.

Hereby sulfinate groups SO₂M are especially preferred. There the sulfinates react with the halogenes preferred by S-Alkylation, as depicted in FIG. 8 for the reaction of a side-chain halogenated polymer with lithium sulfinatophenylphosphonic acid dialkylester.

Surprisingly it has been found, that membranes with a proton conducting functional group at the end of an alkyl-, aryl- or alkylaryl side chain can be made according to the following process:

In a suitable solvent (see below), whereby dipolar-aprotic solvents are preferred, the following components are mixed:

• • (1) polymer containing at least sulfinate groups SO₂M;
  • (2) low molecular di- or oligohalogenalcane (Hal-(C(R₁)₂)_x-Hal (Hal=F, Cl, Br, I; R₁=H, F, C_nH_2n+1, Aryl), Hal-(C(R₁)₂)_x-Aryl-Hal or Hal-(C(R₁)₂)_x—Z-Aryl-Hal)
  • (3) low molecular aromatic, aliphatic or aromatic-aliphatic compound, containing at least a sulfinate group and the non-ionic form of a cation exchange group.

If from the solution of these components a thin film is casted and then the solvent at increased temperature and if necessary reduced pressure is evaporated, covalently cross-linked membranes are formed, which contain the non-ionic form of the cation exchange group in the polymer side chain.

Suitable solvents for the reaction of the side-chain halogenated polymers with compounds containing a nucleophilic group and the ionic group or their non-ionic precursor are ether solvents as described above, hydrocarbon solvents (aliphatic or aromatic, as described above), dipolar-aprotic solvents such as NMP, DMAc, DMF, DMSO, Sulfolan, protic solvents such as alcoholes C_nH_2n+1, water or any other mixtures of these solvents with each other.

The reaction temperature for the metal organic reaction is from −100° C. to +100° C. Preferred is the temperature range from −80 to 0° C.

The reaction temperature for the reaction of the deprotonated polymer with the organic compound containing a halogen atom and one or more ionic groups or their non-ionic precursors is from −100° C. to +100° C. Preferred is the temperature range from −80 to 0° C.

The reaction temperature for the reaction of the deprotonated polymer with the dihalogen compounds is from −100° C. to +100° C. Preferred is the temperature range from −80 to 0° C.

The reaction temperature for the reaction of the side-chain halogenated polymer with nucleophilic groups and ionic groups or their non-ionic precursors is from −100° C. to +200° C. Preferred is the temperature range from −80 to +150° C.

Suitable solvents for the Michaelis-Arbusov-reaction of the side-chain halogenated polymers are ether solvents as described above, hydrocarbon solvents (aliphatic or aromatic, as described above), dipolar-aprotic solvents such as NMP, DMAc, DMF, DMSO, Sulfolan, protic solvents such as alcoholes C_nH_2n+1, water or any other mixture of these solvents with each other. Preferred are dipolar-aprotic solvents, especially preferred is DMSO.

Suitable catalyst systems for the Michaelis-Arbusov-reaction are NiCl₂ (with use of Triethylphosphite as phosphonation agent) or Pd(PPh₃)₄/triethylamine (with use of (EtO)₂POH as phosphonation agent). Preferred is Pd(PPh₃)₄/triethylamine as catalyst system.

Possible is also the use of sodium dialkylphosphite in THF as phosphonation agent. Also other processes known from the literature for this reaction are possible.

The reaction temperature for the Michaelis-Arbusov-reaction of the side-chain halogenated polymer with nucleophilic groups and ionic groups or their non-ionic precursors is from −100° C. to +200° C. Preferred is the temperature range from 0 to +150° C.

Suitable conditions for hydrolysis of the proton-conducting groups are:

• Acid ester:
• —PO(OR₂)₂, —COOR₂, —SO(OR₂)₂: Me₃SiBr/CCl₄, 48% HBr, BBr₃, NaOH, HCl
• Acid halides:
• —POHal₂, COHal, SO₂Hal: 10% NaOH/90° C., 10% HCl/90° C., H₂O/90° C.
• Acid amides:
  concentrated aqueous acids or bases

EXAMPLES

Reaction of Lithiated PSU with Diethyl-2-Bromethylphosphonate

Chemicals:

11.05 g PSU Udel P 1800 (0.025 mol) dried
1000 ml THF anhydrous
5 ml n-BuLi 10 N (0.05 mol)
24.51 g (0.1 mol) Diethyl-2-Bromethylphosphonate (M=245.06 g/mol, δ=1.348 g/cm³)≈18.2 ml

Procedure:

The reaction flask is loaded with THF under inert gas. Subsequently, the dried polymer powder is added under stirring and vigorous flushing with Argon. After the polymer is dissolved, it is cooled down to −60° C., under vigorous flushing with Argon. Then the polymer solution is titrated with n-BuLi (14 ml 2.5N n-BuLi, drum), until a slight yellow/orange colour indicates that the polymer solution is water-free from now on.

Then within 10 min the 10N n-BuLi is syringed in.

The stirring is continued for 2 hours. Then the solution of diethylbromethylphosphonate is added into the reaction mixture as fast as possible. Subsequently, the reaction mixture is stirred for 6 h at −60° C. Then, 100 ml solution is removed from the reaction mixture, which is hydrolyzed in methanol (EA and NMR), the temperature is increased to −40° C./24 h, subsequently to −20° C. and 0° C., under respective hydrolysis of 100 ml solution. Methanol is used as precipitant.

The precipitated polymer is dried at 60° C. From the product, the following analyses are prepared: ¹H—, ¹³C and ³¹P-NMR, elemental analysis.

• Addendum: The methanol-dissolved fractions from −60 to −20° C. are precipitated in methanol>very fine, mucous>not filterable: salting out with saturated table salt solution.
  • The biggest fraction at 0° C. is precipitated in water and filtered over 3 days (G2), washed with water and dried.

Relating to phosphorus content 1.37 groups per repeat unit are bound.

Reaction of Dilithiated PSU with Cl—CH₂—POCl₂

Chemicals:

• 11.05 g PSU Udel P 1800 (0.025 mol) dried
• 1000 ml THF anhydrous
• 5 ml n-BuLi 10 N (0.05 mol)
• 16.7 g (0.1 mol) Chlormethanphosphonsäuredichlorid (M=167.36 g/mol, δ=1.638 g/cm³)≈
• 10.2 ml, SdP.: 78° C./10 mm

Procedure:

The reaction flask is loaded with THF under inert gas. Subsequently, the dried polymer powder is added under stirring and vigorous flushing with Argon. After the polymer is dissolved, it is cooled down to −60° C., under vigorous flushing with Argon. Then the polymer solution is titrated with n-BuLi (14 ml 2.5N n-BuLi, drum), until a slight yellow/orange colour indicates that the polymer solution is water-free from now on. Then within 10 min the 10N n-BuLi is syringed in. The stirring is continued for 2 hours. Then the solution of Chlormethanphosphonsäuredichloride (2-fold excess) is added into the reaction mixture as fast as possible. The solution changes colour at once to black and in a few minutes back to yellow-orange. Subsequently, the reaction mixture is stirred for 6 h at −40° C., increases the temperature for 24 h to −20° C., then for 12 h to 0° C. The polymer is precipitated from the solution with 4 l demineralised water. The polymer soon forms a yellow cake in the upper THF layer, which is separated and digested with methanol for 12 h.

The thus purified polymer is dried at 60° C. From the product, the following analyses are prepared: ¹H—, ¹³C and ³¹P-NMR, elemental analysis.

Relating to phosphorus content 0.31 groups per repeat unit are bound.

Because the reaction at −60° C. is very fast, cool after addition of butyl lithium to −80° C., keep 12 h at −80° C., then follow the instructions as above from −60° C. to room temperature.

Reaction of Dilithiated PSU with Dibromhexane

Chemicals:

• 4.42 g PSU Udel P 1800 (0.01 mol) dried
• 300 ml THF anhydrous
• 2 ml n-BuLi 10 N (0.02 mol)
• 19.52 g Dibromhexane (0.08 mol, 243.98 g/mol)

Procedure:

The reaction flask is loaded with THF under inert gas. Subsequently, the dried polymer powder is added under stirring and vigorous flushing with Argon. After the polymer is dissolved, it is cooled down to −60° C., under vigorous flushing with Argon. Then the polymer solution is titrated with n-BuLi (14 ml 2.5N n-BuLi, drum), until a slight yellow/orange colour indicates that the polymer solution is water-free from now on. Then within 10 min the 10N n-BuLi is syringed in. The stirring is continued for 2 hours. Then the solution of dibromhexane is added into the reaction mixture as fast as possible. Subsequently, the reaction mixture is stirred for 12 h at −20° C., the temperature is increased to 0° C. for 4 h. The solution is hydrolysed with 10 ml MeOH, precipitated in 2 l MeOH, digested in MeOH and washed on the filter twice.

The thus purified polymer is dried at 25° C. under vacuum.

Relating to bromine content 0.87 groups per repeat unit are bound.

Reaction of Dilithiated PSU with Dibrombutane

Chemicals:

• 4.42 g PSU Udel P 1800 (0.01 mol) dried
• 300 ml THF anhydrous
• 2 ml n-BuLi 10 N (0.02 mol)
• 21.59 g Dibrombutane (0.1 mol, 215.9 g/mol)

Procedure:

The reaction flask is loaded with THF under inert gas. Subsequently, the dried polymer powder is added under stirring and vigorous flushing with Argon. After the polymer is dissolved, it is cooled down to −60° C., under vigorous flushing with Argon. Then the polymer solution is titrated with n-BuLi (14 ml 2.5N n-BuLi, drum), until a slight yellow/orange colour indicates that the polymer solution is water-free from now on. Then within 10 min the 10N n-BuLi is syringed in. The stirring is continued for 2 hours. Then the solution of dibrombutane is added into the reaction mixture as fast as possible. Subsequently, the reaction mixture is stirred for 12 h at −20° C., the temperature is increased to 0° C. for 4 h. The solution is hydrolysed with 10 ml MeOH, precipitated in 2 l MeOH, digested in MeOH and washed on the filter twice.

The thus purified polymer is dried at 25° C. under vacuum.

Relating to bromine content 0.98 groups per repeat unit are bound.

Reaction of Dilithiated PSU with Dibromdodecane

Chemicals:

• 4.42 g PSU Udel P 1800 (0.01 mol) dried
• 300 ml THF anhydrous
• 2 ml n-BuLi 10 N (0.02 mol)
• 23.4 g Dibromdodecane (0.071 mol, 328.14 g/mol)

Procedure.

The reaction flask is loaded with THF under inert gas. Subsequently, the dried polymer powder is added under stirring and vigorous flushing with Argon. After the polymer is dissolved, it is cooled down to −60° C., under vigorous flushing with Argon. Then the polymer solution is titrated with n-BuLi (14 ml 2.5N n-BuLi, drum), until a slight yellow/orange colour indicates that the polymer solution is water-free from now on. Then within 10 min the 10N n-BuLi is syringed in. The stirring is continued for 2 hours. Then the solution of dibromdodecane is added into the reaction mixture as fast as possible. Subsequently, the reaction mixture is stirred for 12 h at −20° C., the temperature is increased to 0° C. for 4 h. The solution is hydrolysed with 10 ml MeOH, precipitated in 2 l MeOH, digested in MeOH and washed on the filter twice.

The thus purified polymer is dried at 25° C. under vacuum.

Relating to bromine content 0.3 groups per repeat unit are bound.

Reaction of Dilithiated PSU with Diiodbutane

Ansatz:

• 4.42 g PSU Udel P 1800 (0.01 mol) dried
• 300 ml THF anhydrous
• 2 ml n-BuLi 10 N (0.02 mol)
• 62 g Diiodbutane (0.2 mol, 309.92 g/mol)

Procedure:

The reaction flask is loaded with THF under inert gas. Subsequently, the dried polymer powder is added under stirring and vigorous flushing with Argon. After the polymer is dissolved, it is cooled down to −60° C., under vigorous flushing with Argon. Then the polymer solution is titrated with n-BuLi (14 ml 2.5N n-BuLi, drum), until a slight yellow/orange colour indicates that the polymer solution is water-free from now on. Then within 10 min the 10N n-BuLi is syringed in. The stirring is continued for 2 hours. Then the solution of diiodbutane is added into the reaction mixture as fast as possible. Subsequently, the reaction mixture is stirred for 12 h at −20° C., the temperature is increased to 0° C. for 4 h. The solution is hydrolysed with 10 ml MeOH, precipitated in 2 l MeOH, digested in MeOH and washed on the filter twice.

The thus purified polymer is dried at 25° C. under vacuum.

Relating to iodine content 1.51 groups per repeat unit are bound.

Reaction of Dilithiated PSU with Diioddecane

Chemicals:

• 4.42 g PSU Udel P 1800 (0.01 mol) dried
• 300 ml THF anhydrous
• 2 ml n-BuLi 10 N (0.02 mol)
• 38 g diioddecane (0.096 mol, 394.08 g/mol)

Procedure:

The reaction flask is loaded with THF under inert gas. Subsequently, the dried polymer powder is added under stirring and vigorous flushing with Argon. After the polymer is dissolved, it is cooled down to −60° C., under vigorous flushing with Argon. Then the polymer solution is titrated with n-BuLi (14 ml 2.5N n-BuLi, drum), until a slight yellow/orange colour indicates that the polymer solution is water-free from now on. Then within 10 min the 10N n-BuLi is syringed in. The stirring is continued for 2 hours. Then the solution of diioddecane is added into the reaction mixture as fast as possible. Subsequently, the reaction mixture is stirred for 12 h at −20° C., the temperature is increased to 0° C. for 4 h. The solution is hydrolysed with 10 ml MeOH, precipitated in 2 l MeOH, digested in MeOH and washed on the filter twice.

The thus purified polymer is dried at 25° C. under vacuum.

Relating to iodine content 0.56 groups per repeat unit are bound.

Production of a Covalently Cross-Linked Ionomomer Membrane

3 g PSU(SO₂Li)₂ (2 sulfinate groups per PSU repeating unit, sulfinate-IEC=3.4 meq SO₂Li/g polymer) are dissolved in 17 g NMP. 2.7 mmol meta-LiO₂S-benzolphosphonic acid dioctylester (obtained by lithiation of benzolphosphonic acid dioctylester under Argon in THF and subsequent reaction with SO2) and 0.4 mmol 1,4-Diiodbutan are added to the solution and let to homogenise. Then the polymer solution is casted on a support (glas plate or metal plate and/or cloth/vlies/mocroporous membrane). The solvent is evaporated in a ventilated or vacuum drying ovenat increased temperature of 50 to 140° C. Hereby the sulfinate-S-alkylation of the sulfinato-benzolphosphonic acid ester and the diiodbutane takes place and the membrane cross-links. After solvent evaporation the membrane is posttreated to saponificate the phosphonic acid ester with 48% HBr or concentrated HCl under reflux.

CITED NON-PATENT LITERATURE

• ¹ Wainright, J. S.; Wang, J.-T.; Weng, D.; Savinell, R. F.; Lift, M. H., J. Electrochem. Soc. 1995, 142, L121
• ³ H. R. Allcock, M. A. Hofmann, R. M. Wood, Macromolecules 2001, 34, 6915-6921