WO2013083488A1

WO2013083488A1 - Sulphur-comprising, fluorinated and sulphonated aromatic alkane monomer

Info

Publication number: WO2013083488A1
Application number: PCT/EP2012/074102
Authority: WO
Inventors: Milan Fedurco; Marco Ribezzo
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2011-12-06
Filing date: 2012-11-30
Publication date: 2013-06-13
Also published as: FR2983480A1; JP6112676B2; FR2983480B1; EP2788320A1; CN103974933B; JP2015505871A; CN103974933A

Abstract

A sulphur-comprising, fluorinated and sulphonated aromatic alkane monomer which can be used for the manufacture of a polymer membrane intended, for example, for a PEM (Polymer Electrolyte Membrane) fuel cell, said functionalized monomer corresponding to formula: (I) F-Ar₁-X₁-(CH₂)n-X₂-Ar₂-F in which: -n is included in a range from 1 to 20; -the symbols X₁ and X₂, which may be identical or different, are S, SO or SO₂; -the symbols Ar and Ar₂, which may be identical or different, are a phenylene group, at least one of which bears a sulphonic group -SO₃H or a sulphonate group -SO₃M, wherein M is an alkali metal cation.

Description

- -

ALOMANIC AROMATIC ALOMANE MONOMER, FLUORINATED AND SULFONATED I. FIELD OF THE INVENTION

The present invention relates to the monomers that can be used for the synthesis of polymers intended in particular, in sulphonated form, to constitute a solid electrolyte or membrane in a fuel cell.

It relates more particularly to the above monomers of the aromatic type and comprising a central structural unit of the alkylene type, as well as polymers derived from such monomers.

IT STATE OF THE ART

Recent interest in fuel cells comes from their ability to convert chemical energy into electricity with relatively high efficiency and low emissions of environmental pollutants. Today, the use of such electrochemical devices extends from the automotive industry to laptops, cell phones, stationary generation of electrical energy, and other applications including the exploration of sea and space. It will be recalled first of all that a fuel cell is an electrochemical energy generator in which a chemical reaction is maintained under control between hydrogen and oxygen which will produce water (reverse reaction of electrolysis). ). It produces electrical energy and heat. The electrolyte typically consists of a polymer membrane PEM (abbreviation for "Polymer Electrolyte Membrane") proton-conducting and capable of separating the reactive species, consisting of two distinct nanophases: on the one hand a hydrophobic part ensuring the mechanical integrity, waterproof and gas (¾ and 0 ₂ ), on the other hand a sulfonated portion consisting of narrow hydrophilic channels allowing the passage of protons and thus ensuring the ionic conductivity of the battery. This polymer membrane is disposed between the anode and the cathode of the cell, such an assembly being commonly called "ME A" (Membrane Electrode Assembly).

Such fuel cells and MEA assemblies, as well as their general operating principles, are well known. They have been described in a very large number of documents; one can cite for example the general article entitled "Functional fluoropolymers or fuel cell membranes" Renaud Souzy & Bruno Ameduri, Prog. Polymer Sci. 30 (2005), - -

644-687, as well as patent applications WO 2005/006472, WO 2006/012953, WO 2006/012954, WO 2006/100029, WO 2008/125174.

A good candidate polymeric material for a PEM fuel cell must meet very high requirements with respect to its mechanical, physical and chemical properties. Ideally, the MEA assembly is expected to operate for thousands of hours at relatively high temperatures (60 to 100 ° C in the case of PEM batteries, up to 160 ° C in the case of DMFC methanol) while being exposed to particularly high humidity and acid pH values close to zero. Most of the known polymers undergo decomposition under such conditions, whether of aliphatic or aromatic type.

Aliphatic copolymers derived from perfluorosulfonic acid, commercialized for example under the name Nafion ^® or Flemion ^®, have been used extensively as conductive membranes in fuel cells such as hydrogen / air, hydrogen / oxygen or methanol / air.

Despite a very good ionic conductivity and a high intrinsic chemical stability, the use of Nafion ^® type polymers is firstly not suitable for use in fuel cells methanol type, this due to a performance reduced for the highest use temperatures, due to a significant increase in permeability of the membrane to methanol.

Another drawback of the known type polymer Nafion ^® in use in the battery, is their chemical mechanical stability relatively limited. Indeed, perfluorinated polymers are known to absorb significant amounts of water responsible for swelling and repeated dimensional changes of the membrane: repeated cycles of drying and humidification, during successive stops and starts of the fuel cell, result in increased gas permeability (H ₂ and O ₂ ); this increased permeability is responsible for the formation of oxygenated water and free radicals (OH), mechanisms that can lead to rapid degradation of the membrane and premature end of life of the fuel cell. In order to limit these dimensional changes and thus improve the endurance of the membranes, it has notably been proposed to add, as reinforcing polymer, a second fluorinated polymer, especially a PTFE (polytetrafluoroethylene) of the expanded microporous type (or "ePTFE"). ), and thus constitute more enduring composite membranes (see for example US 6,495,209).

Finally, another major disadvantage of Nafion ^® type polymers is their cost of synthesis, not to mention a basic chemistry which no longer meets the latest requirements in terms of environment, hygiene and security. - -

Also, much research has been conducted in the past to try to reduce the cost of PEM membranes. It has been proposed in particular to replace the above aliphatic polymers with aromatic polymers, of lower cost and which also have the advantage of having a gas permeability (H ₂ and O ₂ ) which is reduced.

Examples of such polymers are for example poly (arylene-ether-sulfone), sold in particular under the names "Udel", "Radel" or poly (ether-ether-ketone) marketed for example under the name "PEEK". The aromatic polymers above, once sulfonated, do not allow today to reach the compromise of performance and cost offered with the fluorinated aliphatic polymers like Nafion ^®. In addition, these aromatic polymers are generally poorly mixed with an ePTFE-type polymer and the resulting membranes can not therefore be easily reinforced by an ePTFE polymer, such reinforcement requiring a prior surface treatment of the ePTFE polymer by plasma or by in a very aggressive chemical environment (see, for example, article entitled "Challenging reinforced composite polymer electrolyte membranes based on disulfonated poly (arylene-ether-sulfone) -impregnated expanded PTFE for fuel cell applications", Xiaobing Zhu et al., J. Mat. Chem., 2007, 386-397).

Other examples of aromatic type polymers have been described more recently in the documents US2005 / 0221135 and US 7037614. These are sulfonated triazine polymers whose monomers are connected by ether bridges (-O-). The syntheses described in these documents are complex, expensive and difficult to reproduce. It has further been found that their stability, chemical and dimensional, is insufficient even after a final treatment of crosslinking membranes, which treatment also requires another complex and expensive chemistry.

III. BRIEF DESCRIPTION OF THE INVENTION

During the course of their research, the Applicants have found a new aromatic monomer, more specifically a specific aromatic alkane monomer, of the sulfur, fluorinated and sulphonated type, which has proved useful for the synthesis of a polymer membrane making it possible to overcome less in part, the aforementioned disadvantages.

This aromatic alkane compound of the invention corresponds to formula (I): - -

F - An - Xi - (CH ₂ ) _n - X ₂ - Ar ₂ - F in which: n is in a range from 1 to 20;

the symbols Xi and X ₂ , which are identical or different, represent S, SO or S0 ₂ ;

the symbols Ari and Ar ₂ , which are identical or different, represent a phenylene group at least one of which carries a sulphonic group -SO ₃ H or a sulphonate group -SO ₃ M, M representing an alkali metal cation.

The invention also relates to any sulfurized, fluorinated and sulfonated aromatic alkane polymer derived from a monomer according to the invention, that is to say comprising recurring units resulting from the polycondensation of the monomer of the invention with at least one (i.e. one or more) other monomer carrying at least two nucleophilic functions.

The invention also relates to a method for synthesizing a polymer by poly condensation of at least one aromatic alkane monomer according to the invention, with another monomer carrying at least two nucleophilic functions. The invention also relates to the use of an aromatic alkane monomer according to the invention for the manufacture of a polymer membrane that can be used in a PEM type fuel cell.

From the monomer according to the invention, it has proved indeed possible to synthesize a polymer usable for producing PEM membranes unexpectedly compared to commercial membranes including Nafion ^® non-reinforced type, have an ionic conductivity higher. Finally, which is not its least advantage, the polymer resulting from the monomer of the invention can be made compatible with a microporous polymer ePTFE for an optimal reinforcement of the membrane.

The invention as well as its advantages will be readily understood in the light of the detailed description and the following exemplary embodiments, as well as figures relating to these examples which represent or schematize: examples of monomers according to the invention of formula (I), of the respective general formulas (1-1), (1-2) and (1-3) (Figs 1A, 1B and 1C);

examples of monomers according to the invention of formula (II), of particular formulas (II-1), (Π-2) and (Π-3) respectively (Fig. 2A, 2B and 2C);

an example of a polymer according to the invention (Polymer 1), in blocked benzophenone form, as well as a scheme for the possible synthesis of this polymer by - - poly condensation of a monomer Al according to the invention with a second monomer B1 not according to the invention (Figure 3);

another example of a polymer according to the invention (Polymer 2), in blocked benzophenone form, as well as a possible synthesis scheme of this polymer by oxidation of the above Polymer 1 (FIG.

a possible synthesis scheme, in three successive steps, of a monomer Al (or compound 3) according to the invention (FIG.

the 1 H NMR spectrum (500 MHz) of Compound 3 (Al monomer) dissolved in OMSO-d ₆ (Fig. 6);

a possible synthesis scheme, in two successive stages, of a monomer B

(or compound 5) not according to the invention (Fig. 7);

the 1H NMR spectrum (500 MHz) of Polymer 2 dissolved in DMSO- ¾ (FIG 8).

IV. DETAILED DESCRIPTION OF THE INVENTION

The alkane aromatic monomer of the invention, sulfur, fluorinated and sulfonated, therefore has the essential characteristic of responding to formula (I):

F - An - Xi - (CH ₂ ) _n - X ₂ - Ar ₂ - F in which (F representing, of course, fluorine):

n is in a range from 1 to 20;

the symbols Ari and Ar ₂ , which are identical or different, represent a phenylene group at least one of which carries a sulphonic group -SO ₃ H or a sulphonate group -SO ₃ M, M representing an alkali metal cation .

In other words, the fluorinated alkane monomer of the invention of formula (I) has the structural formula:

wherein R is hydrogen or a substituent for hydrogen. - -

Thus, by way of example, in the preferred case where X ₁ and X ₂ are identical and R is hydrogen, then the monomer of the invention of formula (I) corresponds to one of the three formulas. , 1-2 and 1-3 respectively shown in Figures 1A, 1B and 1C appended. According to an essential embodiment of the invention, at least one of the phenylene groups carries a sulphonic group -SO ₃ H or a sulphonate group -SO ₃ M, M representing an alkali metal cation.

By phenylene group carrier, it is understood in the present application that the phenylene group itself or one of the possible substituents of its hydrogen atoms is carrying a sulfonic or sulfonate group.

In other words, by way of example, in the particular case where each phenylene group carries a sulphonic group or a sulphonate group, the fluorinated alkane monomer of the invention of formula (I) therefore has the structural formula:

In other words, by way of example, in the preferred case where n is equal to 4, where X ₁ and X ₂ are identical and where only one sulphonate group is present on each phenylene group, the monomer of the invention of formula (I) corresponds to one of the three formulas II-1, II-2 and II-3 respectively represented in FIGS. 2A, 2B and 2C appended hereto.

In the formula (I) above and all the preferred variants of the invention described in the present application, n preferably ranges from 2 to 20, more preferably from 2 to 8; more particularly still, the alkane monomer of the invention is a butane monomer, that is to say that n is equal to 4. - -

A preferred characteristic of the monomer of the invention is that at least one of the phenylene groups carries a sulphonate group (-SO ₃ M), M representing an alkali metal cation, preferably Na ⁺ or K ⁺ . Preferably, Xi and X ₂ , which are identical or different, represent SO or SO ₂ , more preferably S0 ₂ .

The phenylene groups Ari and Ar ₂ may be substituted or unsubstituted by optional substituents other than sulfonic or sulfonated groups on the one hand, other than fluorine on the other hand. When this is the case, the invention applies in particular to cases where only one phenylene group per monomer of formula (I) is substituted, as in the case where several phenylene groups per monomer are substituted, a single substituent or several substituents, identical or different. different, which may be present on the same phenylene group (s).

As examples of possible optional substituents aromatic rings (that is to say more exactly hydrogen atoms of these phenylene groups) include the following substituents: o - Cl; - Br; - CN; - CF ₃ ; - N0 ₂ ; N (CH ₃ ) ₂ ; even - F;

o - COOH; - COOM; - P0 ₃ H; - P0 ₃ M; -S0 ₃ H; - S0 ₃ M (the symbol M

representing an alkali metal cation, preferentially Na ⁺ or K ⁺ );

the hydroxyl, alkyl, cycloalkyl, perfluoroalkyl, sulphoalkyl, sulphoaryl, aryl, alkylcarbonyl, arylcarbonyl, alkoxy and aryloxy radicals.

These optional substituents are preferably selected from the group consisting of the substituents - CN, - CF ₃ , - PO ₃ H, - PO ₃ M, - F and the mixtures of these substituents.

In the particular case where R is hydrogen, that is to say where none of the phenylene groups is substituted with an optional substituent, then the aromatic alkane monomer of the invention corresponds to one of the formulas (I ) as shown in Figures 1A, 1B and 1C appended hereto.

The two fluorine atoms confers its polymerizable character on the monomer of the invention, thanks to their electrophilic character well known to those skilled in the art: as a reminder, an electrophilic function or group (atom or group of atoms) (also called Lewis acid or electron acceptor) has a missing pair of electrons and is therefore capable of covalently bonding with a Lewis base; reciprocally, a nucleophilic function or group (atom or group of atoms) (also called Lewis base or donor - - of electrons) has a pair of free electrons and is therefore able to create a covalent bond with a Lewis acid.

Thus, in the particularly preferential case where the alkylene central block (CH ₂ ) _n is a butylene (n equal to 4) and in which the phenylene groups Ari and Ar ₂ both carry a sulphonate group -SO ₃ M, the The alkane aromatic monomer of the invention is an alkali metal salt of 3,3'-bis (4-fluorophenylthio) butane disulfonate, 3,3'-bis (4-fluorophenylsulfoxy) butane disulfonate, or 3,3'-bis (4-fluorophenylthio) butane disulfonate. bis (4-fluorophenylsulfonyl) butane disulfonate, respectively corresponding to the formulas (II-1), (Π-2) and (Π-3) shown in Figures 2A, 2B and 2C appended, these phenylene groups Ari and / or Ar ₂ may in addition optionally include optional substituents such as those described above.

The aromatic alkane monomer according to the invention described above is advantageously usable for the synthesis of polymers which may constitute, in sulphonated form, an electrolyte (or membrane, which is equivalent) in a fuel cell. By polymer is meant any homopolymer or copolymer, especially a block copolymer, comprising at least structural units derived from the monomer of the invention.

The term "sulfonated monomer" or "sulfonated polymer", by definition in the present application and in known manner, respectively a monomer or polymer bearing one or more sulfonic groups (-SO3H), sulfonates (-SO3M), or mixtures such groups, M representing an alkali metal cation; M is preferably selected from lithium (Li), cesium (Cs), sodium (Na) and potassium (K), more preferably from sodium (Na) and potassium (K). It will be briefly recalled here that it is the sulfonic groups which in a PEM cell ensure the proton conductivity of the polymer used as a membrane.

The attached FIG. 3 represents an example of a polymer according to the invention, synthesizable from an aromatic alkane monomer according to the invention, as well as a possible synthetic scheme for this polymer from such a monomer.

The polymer (hereinafter referred to as "Polymer 1") as represented in FIG. 3, in sulphonated form, consists of two types of structural units connected to each other by ether bridges (-O-). This Polymer 1 can be prepared by poly condensation of a monomer according to the invention denoted Al (here, in disulfonated form) with a second monomer (monomer of the triazine type) not according to the invention denoted Bl in FIG. 3, in the presence of a base and an organic solvent, according to a procedure which will be described in detail below. Al monomer corresponds to the aromatic alkane monomer of formula (Π-3) previously described (FIG 2C). - -

The attached FIG. 4 represents another example of a polymer (hereinafter referred to as "Polymer 2") synthesizable from an aromatic alkane monomer according to the invention, as well as a possible synthetic scheme for this polymer 2 by oxidation of the Polymer 1 above, according to a procedure which will be described in detail later.

V. EXAMPLES OF CARRYING OUT THE INVENTION

The following tests first describe in detail the synthesis of the monomers Al (according to the invention) and B 1 (not in accordance with the invention) and that of Polymer 1 and Polymer 2.

Then, Polymer 1 is characterized and tested as a proton conducting membrane in a PEM type fuel cell. Here, Polymer 1 and Polymer 2 comprise chain ends blocked by hydrophobic and sterically hindered benzophenone blocking groups (denoted by B in FIGS. 3 and 4) intended to reduce the solubility of the polymer in water.

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are% by weight.

V-1. Synthesis of Al monomer

The monomer Al is 3,3 'bis (4-fluorophenylsulphonyl) butane disulfonated, whose formula (reproduced for example in Figure 3, M being here sodium Na) is as follows:

This Al monomer (or Compound 3 in Figure 5) was prepared according to the procedure shown diagrammatically in Figure 5, in three successive steps, as detailed below.

V-1-A) Step 1

In a first step, Compound 1 or 1,4-bis- (4-fluorophenylthio) -butane is prepared according to the procedure which follows and shown schematically in FIG. 5A. - -

Sodium methanolate (8.72 g or 161.6 mmol) is placed in a three-necked flask of 500 ml under a stream of nitrogen; 200 ml of anhydrous methanol are added and the mixture is stirred until the salt is dissolved. Then 4-fluorothiophenol (20.68 g or 161.6 mmol) is introduced and the reaction mixture is refluxed for 60 minutes. After distillation of the methanol (150 mm / Hg), the sodium fluorothiophenol (white solid) obtained is stored under a stream of nitrogen in the apparatus, at room temperature. 170 ml of dimethylformamide (DMF) are then introduced into the flask under an inert atmosphere, and the mixture is stirred until the salt is dissolved. The solution is then cooled with an ice bath (temperature between 0 ° C. and 5 ° C.), still under a stream of nitrogen, and 1,4-diiodobutane (25.0) is added dropwise. 0.81 mmol). The temperature is allowed to rise to room temperature (25 ° C) and then heated overnight (about 12 hours) at 40 ° C. The next day, the temperature is raised to 60 ° C for one hour, then the solution is poured into a 3.0 liter beaker and 2.5 liters of deionized water are added. The white precipitate thus obtained is stirred at ambient temperature (23 ° C.) for 30 minutes; it is then isolated by filtration on filter paper. The isolated white solid is washed with three 600 ml portions of demineralized water and then finally oven-dried overnight (70 ° C., 1 mbar, about 12 hours). 18 g of white solid are thus obtained (reaction yield equal to 72%), whose melting point, measured by DSC, is equal to 94.4 ° C., and having the formula:

Its NMR analysis gives the following results:

¹ H NMR, 500 MHz (DMSO-d ₆ ): 7.14 - 7.17 (m, 4H), 7.35 - 7.38 (m, 4H), 2.93 - 2.95 (m, 4H), 1.63 - 1.65 (m, 4H).

V-l-B) Step 2

Then, in a second step, Compound 2 or 1,4-bis- (4-fluorophenylsulfonyl) -butane is prepared, according to the following procedure and diagrammatically in FIG. 5B.

A one-liter, one-liter round flask equipped with a condenser, magnetic bar, and nitrogen inlet is charged with 20.4 g (65.7 mmol) of Compound 1 and 500 ml of glacial acetic acid. After stirring for 5 minutes at room temperature (23 ° C.), the suspension is cooled by an ice bath (between 0 ° and 5 ° C.) and 61.27 g (388 mmol) of KMnO _{4 are then added} ; after stirring for 15 minutes, 35 ml of concentrated (98%) sulfuric acid are added dropwise. - -

After stirring for 30 minutes at 0 ° C to 5 ° C, the reaction mixture is stirred overnight (about 12 hours) at room temperature (23 ° C). The reaction mixture is poured into a 3.0 liter beaker and 1.5 liters of deionized water are added. The mixture is stirred for 15 minutes at room temperature (23 ° C.) and then cooled with an ice bath (0 to 5 ° C.). With stirring, NaOH (solid) is gradually added until a pH of 7 is reached. To the half of the reaction mixture previously prepared, 1 liter of dichloromethane is added and, after stirring for 30 min, the organic phase is separated. of the aqueous phase in a separatory funnel. A solid part (hydrolysed Mn0 ₂ ) is separated from the organic phase by filtering through a microporous silica ("HyFlo Super Elemental Cylinder" Sigma-Aldrich). The organic phase is dried over anhydrous Na ₂ SO ₄ , filtered and the dichloromethane is removed on a rotary evaporator at 40 ° C. The crude solid product (22.8 g) thus obtained is dissolved in acetone (in 3 parts of 8.0 g of product for 1.250 liters of acetone) and refluxed with activated charcoal for one hour. The activated carbon is removed by filtration on filter paper and the filtrate is cooled to room temperature until the product is recrystallized. The white crystals obtained are isolated by filtration and dried in the oven (60 ° C., 1 mbar) overnight (about 12 hours).

This gives 19.8 g of Compound 2 (reaction yield equal to 80.5%), whose melting point measured by DSC is equal to 182.3 ° C., and corresponding to the formula:

Its NMR analysis gives the following results:

¹ H NMR 500 MHz (DMSO-d _6): 7.49 - 7.52 (m, 4H), 7.92 - 7.94 (m, 4H), 1.59 - 1.62 (m, 4H), 3.35 - 3.38 (m, 4H).

V-l-C) Step 3

Finally, during a third and last step, Compound 3 or monomer Al (3,3'-bis (4-fluorophenylsulphonyl) butane disulfonated) is prepared according to the following procedure and diagrammatically in FIG. 5C.

Compound 2 (8.0 g, 21.36 mmol) is placed in a 250 ml three-neck flask equipped with a condenser and a magnetic bar coated with glass. The apparatus is purged with nitrogen and left under an inert atmosphere. 20 ml H ₂ SO ₄ (98%) and then 20 ml (37.3 g) of oleum containing 65% of SO _{3 are added} . The reaction medium is heated at 120 ° C. for 4 hours under a gentle stream of nitrogen. Once the sulfonation is complete, the reaction mixture is cooled to 90 ° C and then poured still hot into 250 g of ice. Always under agitation, once the whole Melted ice, 30 g of NaCl are added to precipitate the disulfonated monomer. The precipitate is then filtered on sintered glass and then dried at 80 ° C. under vacuum overnight (about 12 hours). The dry product obtained is then mixed with 100 ml of distilled water and heated to 50 ° C. After all the product has dissolved, the pH is adjusted to 7.0 by adding 10% NaOH (aqueous). The solution is cooled to room temperature. The product is precipitated by adding 6 g of NaCl. The product is filtered and dried overnight (12 hours) at 150 ° C under vacuum.

There is thus obtained 10.5 g (85% reaction yield) of Al monomer, of which FIG. 6 reproduces the 1 H NMR spectrum (500 MHz) once dissolved in DMSO-¾.

Its NMR analysis gives the following results:

NMR, 500 MHz (DMSO-d ₆ ): 8.11 - 8.13 (m, 2H), 7.84 - 7.87 (m, 2H), 7.41 - 7.45 (m, 2H), 3.36 - 3.39 (m, 4H), 1.62 - 1.65 (m, 4H).

Finally, the molecular weight of the product as measured by mass spectrometry "ESI" (Electrospray Ionization) (negative mode (M - Na ⁺ ); water / acetonitrile mixture (1: 1) is equal to 555.0 (calculated theoretical value equal to 555.5).

V-2. Synthesis of monomer B1

The monomer B1, for a booster not according to the present invention, is 2,4 - [(4-hydroxyphenylsulfanyl phenyl)] - 6- (phenyl) - [l, 3,5] -triazine, whose formula ( already reproduced in Figure 3) is as follows:

This B1 monomer (or Compound 5 in Fig. 7) was prepared according to the procedure shown schematically in Fig. 7, in two successive steps, as detailed below.

V-2-A) Step 1

In a first step, Compound 4 or 2,4-bis- (p -fluorophenyl) -6-phenyl- [l, 3,5] -triazine is prepared, according to the procedure which follows and schematized in FIG. 7A.

This procedure, although different, is inspired by the process for the synthesis of chlorinated triphenyltriazines as described in Spencer RD & Beggs BH, "Determination of - -

Four Closely Related Triaryl-s-Triazines by Infrared Spectroscopy, Anal Chem 1963, 31 (11), 1633-1636.

A 500 ml three-neck round balloon equipped with a magnetic bar, a condenser, a thermometer, is dried using a hot-air gun (apparatus is evacuated). 67.8 g of p-fluorobenzonitrile (ie 0.56 mol) (Fluorochem 99%), 36.0 g of ammonium chloride (ie 0.68 mol), 34.0 g of aluminum chloride (that is 0 26 mol) and 32.0 g of benzoyl chloride (ie 0.22 mol) are placed in the flask under a stream of nitrogen. The flask is immersed in an oil bath heated to 158 ° C and left overnight (about 12 hours) at 150 ° C (temperature inside the reaction flask), a slight stream of nitrogen being above the reaction mixture. The reaction product is then cooled to room temperature (23 ° C.) and hydrolysed by adding 300 g of ice and 60 g of 36% HCl. The solid is filtered, then dispersed in water and washed until a neutral pH is obtained. The white solid is stirred in 500 ml of methanol, refluxed for 30 minutes and then allowed to cool to room temperature (23 ° C.). Finally, the product is filtered and dried at 60 ° C. under vacuum.

26.6 g (35% yield) of Compound 4, having a melting point (according to DSC) of 254.5 ° C. are thus obtained. NMR analysis gives the following results:

¹ H NMR, 500 MHz (CD ₂ CI ₂ ): 7.30 - 7.34 (m, 4H), 7.62 - 7.65 (m, 2H), 7.68 - 7.70 (m, 1H), 8.79 - 8.80 (d, 2H), 8.82 - 8.85 (m, 4H).

V-2-B) Step 2

In a second step, Compound 5 or 2,4 - [(4-hydroxyphenylsulfanyl phenyl)] - 6- (phenyl) - [l, 3,5] -triazine is prepared according to the following procedure. and schematized in Figure 7B. 4-hydroxythiophenol (or 4-HTP) (99%, Acros) is stored under nitrogen and in solid form. Compound 4 and K ₂ CO ₃ are dried separately overnight at 150 ° C under vacuum. A magnetic bar is placed in a 2 1 round flask (equipped with a condenser, a thermometer and a nitrogen inlet / outlet). The apparatus is placed under vacuum and dried. A two-way valve is used to replace the vacuum with nitrogen and continuously purge with the inert gas during addition of reagents.

Compound 4 (9.13 g or 26.44 mmol) and anhydrous K ₂ CO ₃ powder (9.69 g or 1.2 eq., Relative to 4-HTP) are added while they are still hot. (drying output), in the equipment purged with nitrogen. Then 750 ml of anhydrous DMSO are added. The suspension obtained is then purged for at least 15 minutes with a stream of nitrogen inside the solution. - -

The required amount of 4-HTP (7.45 g or 58.42 mmol, 2.2 eq.), In liquid form, is transferred using a 10 ml plastic syringe, weighed directly to the patient. inside the syringe and injected into the reaction mixture. Once all the reagents are added, the nitrogen is purged continuously over the solution. The mixture is heated at 100 ° C with constant stirring overnight (20 hours) and then allowed to cool to room temperature.

The purification of the product can not be done in a single step: about 250 ml of aliquot of the reaction are collected and poured into an extraction bulb (3 liters) containing 2.6 liters of ethyl acetate / water (ratio 1/1). The rest of the product is kept under a constant stream of nitrogen. The mixture placed in the extraction funnel is shaken (the color changes from orange to lemon yellow) and the desired product is extracted into the ethyl acetate phase (the DMSO / H ₂ O phase contains only traces of the desired product ). The organic phase is washed with 100 ml of NaHCO ₃ solution, followed by washing with 100 ml of H ₂ O; the organic phase is then dried with anhydrous MgSO ₄ . The process is repeated twice with the other two remaining 250 ml aliquots of the reaction mixture. The ethyl acetate phase is evaporated using the rotary evaporator, there remains a viscous slightly orange liquid having the appearance of honey (containing a small amount of DMSO). DMSO residues are removed at 100 ° C under reduced pressure. A small amount of acetone (10 ml) is added followed by 40 ml of diethyl ether. The solid becomes immediately creamy white, it is filtered on a ceramic filter. The residual thiol is removed from the reaction product by column chromatography using hexane / CH ₂ Cl ₂ / ethyl acetate / methanol (4/2/1/1 weight ratios) as the mobile phase.

This gives 13.1 g (ie a yield of about 89%) of Compound 5. The NMR analysis gives the following results:

¹ H NMR (500 MHz) DMSO-d ₆ : 6.93-6.95 (d, 4H), 7.17-719 (d, 4H), 7.42-7.44 (d, 4H), 7.58-7.60 (m, 2H), 7.65- 7.68 (m, 1H), 8.49-8.50 (d, 4H), 8.61-8.63 (d, 2H), 10.04 (s, 2H).

The molecular weight of the product as measured by "Matrix-assisted Laser Desorption / Ionization" mass spectrometry (positive mode, dithranol matrix) is equal to 558.1 (calculated theoretical value equal to 557.7).

V-3. Synthesis of Polymer 1 This example describes in detail the synthesis, from Al monomers according to the invention and Bl not according to the invention described above, Polymer 1 under - - sulfonated form, blocked by benzophenone groups, as shown in Figure 3.

Monomer B1 is dried at 60 ° C under vacuum overnight. Al monomer and base (Na ₂ CO 3) are dried separately at 150 ° C under vacuum overnight. Then the three compounds are mixed and dried at 160 ° C under vacuum for one hour. The copolymerization of the monomers A1 and B1 is carried out in a 100 ml three-neck round-bottomed flask. The flask is equipped with a nitrogen inlet, a thermometer, a magnetic stirrer and a "Dean Stark" separator surmounted by a coolant. The glass parts of the apparatus are dried under vacuum using a hot air gun to reach a temperature of at least 100 ° C in the reaction flask.

The reaction flask is loaded with the monomer Al (1.76 g, 3.04 mmol), the monomer B1 (1.7 g, 3.04 mmol), the anhydrous sodium carbonate (0.97 g, ie 9 g, 13 mmol), anhydrous N, N-dimethylacetamide (20 ml) and 4 ml of organic solvent (toluene) as an azeotropic agent. The reaction flask is heated at 100 ° C in an oil bath for 90 min (azeotropic distillation). The toluene circulation valve is then closed and the toluene is distilled at 110 ° C for 90 minutes. The temperature of the oil bath is then increased by 10 degrees every 30 minutes, up to 148 ° C. The toluene is removed from the apparatus ("Dean Stark") by the hatch, then the temperature of the oil bath is increased to about 160 ° C and maintained at this value all night (20 hours in total). Then the temperature dropped to about 90 ° C inside the flask, removing the flask from the oil bath. 8 mg of 4-fluorobenzophenone dissolved in 5 ml of anhydrous Ν, Ν-dimethylacetamide are then added to the reaction using a syringe. The flask is returned to the oil bath at 160 ° C for an additional 1 hour. The reaction mixture is then allowed to cool to room temperature (23 ° C); then the polymer is poured dropwise into 500 ml of 2-propanol with stirring. The fibrous precipitate is recovered by filtration and washed with 2-propanol and then dried in an oven (80 ° C., 1 mbar) overnight (12 hours). 4.1 g of solid material are thus obtained. The polymer is washed with 100 ml of distilled water for 30 minutes. The pH is adjusted to about 4 with 10% aqueous HCI. The product is isolated by filtration, washed with distilled water and dried in an oven overnight (12 hours at 80 ° C., under 1 mbar).

2.7 g of Polymer 1 (reaction yield 81%), in sulphonated form and blocked benzophenone, as shown in FIG. 3 are finally obtained.

Its NMR analysis gives the following results:

¹ H NMR (500 MHz) in DMSO-d ₆ : 7. 12-7.18 (m, 6H), 7.37-7.38 (d, 4H), 7.60-7.62 (d, 6H), 7.66-7.70 (m, 1H) 7.82-7.84 (d, 2H), 8.29 (s, 2H), 8.62-8.64 (d, 4H), 8.67-8.69 (d, 2H), 1.71 (m, 4H), 3.38 (m, 4H). - -

V-4. Synthesis of Polymer 2

This example describes in a detailed manner the synthesis of Polymer 2, by oxidation of Polymer 1, according to the process shown diagrammatically in FIG.

Polymer 1 (1.0 g) is placed in a 50 ml two-neck flask equipped with a condenser, then 12 ml of glacial acetic acid are added and the dispersion obtained is stirred at room temperature (23 ° C.) for 30 minutes. min. 500 μl of concentrated H ₂ SO _{4 are} then added and, after stirring for 3 minutes, 2 ml of H ₂ 0 ₂ (50% aqueous solution). The dispersion is then stirred at room temperature overnight (12 hours). Platinum (2 cm ² plate) is placed in the flask for destruction of the oxygen peroxide, and the reaction mixture is then stirred for 2 hours at room temperature. The acetic acid is evaporated in an oil bath of 50 ° C and in a strong stream of nitrogen. The solid (pale yellow color) obtained is then washed with successive portions of 25 ml of distilled water until a pH of 6 is obtained. The gelatinous solid is isolated by filtration and dried overnight at room temperature. oven (80 ° C, under 1 mbar).

620 mg, in the form of a pale yellow solid, of polymer 2, in sulphonated form and blocked with benzophenone groups as shown in FIG. 5, are thus obtained. FIG. 9 reproduces the 1 H NMR spectrum (360 MHz ) Polymer 2 thus obtained, dissolved in DMSO- <¾.

NMR analysis gives the following results:

¹ H NMR (500 MHz) in DMSO-d ₆ : 7. 11-7.14 (d, 4H), 7.24-7.21 (d, 2H), 7.59-7.70 (m, 3H), 7.81-7.84 (m, 2H) , 8.00-8.03 (d, 4H), 8.17-8.20 (d, 4H), 8.26-8.27 (s, 2H), 8.65-8.67 (d, 2H), 8.82-8.85 (d, 4H), 4.57 (s, -SO ₃ HH ₂ O), 3.38 (m, 4H), 1.68 (m, 4H).

V-5. Manufacture of PEM Membranes In this test, Polymer 1 membranes are prepared according to the so-called "solvent casting" technique as described below.

The polymer (650 mg) previously dissolved in 10 ml of Ν, Ν-dimethylacetamide is filtered in two stages, firstly through a microfilter (company "Millipore") made of PTFE (polytetrafluoroethylene) having a pore size of 5. , 0 μιη, then through a second microfilter of about 0.45 μιη. Then the polymer solution thus filtered is poured into a mold consisting of two superimposed glass plates, the upper plate having a recess (dimensions 9 cm × 9 cm) of depth equal to 1 mm; it is then heated at 50 ° C for 12 h, then 12 h at 60 ° C. Then traces of organic solvent are removed from the membrane thus formed by immersing the latter in a distilled water bath for about 4 hours. - -

After final drying at 60 ° C. for 2 hours under vacuum, a robust and transparent membrane, of thickness equal to approximately 60-65 μιη, is thus obtained, ready for characterization.

V-6. Characterization of PEM membranes

For the acidification of the membrane (as a reminder, exchange of the cation M ⁺ by H ⁺ ), Polymer 1 is initially immersed in 200 ml of H ₂ SO ₄ (aqueous, 3.8M) for 2 h. Double-distilled H ₂ SO ₄ (Sigma Aldrich) is used to avoid traces of metals. Distilled water is then added in several stages (total time about 12 hours) to reach a pH close to 7; the membrane is then stored in distilled water overnight (about 12 hours).

The proton conductivity of the membrane expressed in S / cm (Siemens per centimeter) is determined as indicated below.

Disc-shaped membranes 2 cm in diameter (thickness 60 to 65 μπι) are cut using a punch. The proton conductivity of the membrane is determined by the measurement of the real part (Ohmic) and the imaginary part (Capacitance) of the complex impedance, in the frequency range between 100 kHz and 10 Hz (with amplitude of 100 mV AC). Measurements are made with an impedance / AC potentiostat (Zahner, Germany). Nyquist plots are generated by the measurements of a successive stack of one, two, three and up to six membranes (totally moistened) sandwiched between two platinum electrodes of the same circular shape as the membranes.

For each measurement, the value intercepting the real axis of Nyquist graph is reported, that is to say a value of the imaginary component of the impedance at zero. In general these points are aligned on an affine line whose slope directly determines the value of the resistance of the membrane. Its ordinate at the origin determines the contact resistance between the membranes and the platinum electrodes. These last values and the knowledge of the thickness make it possible to calculate in a known manner the resistivity of the membrane; the inverse of this value is the conductivity.

Thus tested, the membranes derived from Polymer 1 showed remarkable proton conductivity values, equal to about 95 mS / cm at 25 ° C, higher than the conductivity value (about 70 mS / cm) measured on the commercial membrane (" Nafion ^® 112 "), unreinforced, of the same thickness and rigorously tested under the same conditions.

V-7. Other comparative tests - -

Finally, it should be noted that a polymer of the poly (arylene-ether-sulphone) type, such as those mentioned in the introduction of the present disclosure, was synthesized as indicated previously for Polymer 1, starting on the one hand with the monomer Bl previously described and a second monomer not according to the invention.

This second monomer not in accordance with the invention was certainly also a sulfur-type monomer, fluorinated and sulfonated, therefore structurally close to the monomer according to the invention, but not alkane type unlike the latter.

It was more precisely 3,3'-disulfo-4,4'-diflurorophenylsulfone (abbreviated as "SFPS"), as a reminder of the formula:

The above sulfonated monomers as well as their use for the synthesis of poly (arylene-ether-sulfone) polymers and fuel cell membranes have been described in numerous documents, for example by Wang et al in "Direct polymerization". sulfonated poly (arylene ether sulfone) random (statistical) copolymers: candidates for new proton exchange membranes ", Journal of Membrane Science 197 (2002), 231-242, or by Bae et al in" Sulfonated poly (arylene ether sulfone) " ionomers containing fluorenyl groups for fuel cell applications ", Journal of Membrane Science 310 (2008), 110-118.

Membranes were then prepared from this polymer not according to the invention, as described in paragraph V-5 above. They have been found to be relatively brittle, with high rigidity, and significantly reduced mechanical endurance compared to membranes prepared from the alkane monomer according to the invention.

In conclusion, the monomers of the invention make it possible to manufacture PEM polymers and membranes which, unexpectedly, have, on the one hand, an ionic conductivity which may be greater than those of commercial membranes of the Nafion® non-reinforced type, and of on the other hand a mechanical endurance which can be improved over that available with other polymers known for this type of application, poly (arylene ether sulphone) type.

Claims

1. Sulfurated, fluorinated and sulfonated aromatic alkane monomer corresponding to formula (I)

F - An - Xi - (CH ₂ ) _n - X ₂ - Ar ₂ - F in which:

n is in a range from 1 to 20;

2. The monomer of claim 1, wherein n is within a range of 2 to 20.

The monomer of claim 2, wherein n is within a range of 2 to 8.

Monomer according to claim 3, wherein n is 4.

5. Monomer according to any one of claims 1 to 4, wherein at least one phenylene group carries a sulfonate group -SO ₃ M, M representing sodium or potassium.

6. Monomer according to any one of claims 1 to 5, wherein Xi and X ₂ , identical or different, represent SO or SO ₂ , preferably S0 ₂ .

Monomer according to claims 4, 5 and 6, corresponding to the formula:

8. Process for synthesizing a sulfur-containing aromatic alkane polymer, by polycondensation of at least one monomer according to any one of claims 1 to 7, with another monomer bearing at least two nucleophilic functions.

9. Sulfurated aromatic alkane polymer derived from at least one monomer according to any one of claims 1 to 7, and another monomer bearing at least two nucleophilic functions.

10. Use of an alkane monomer according to any one of claims 1 to 7, for the manufacture of a polymer membrane for use in a PEM type fuel cell.