Copolymers comprising crosslinkable protogenic groups which can be used to constitute fuel cell membranes

Abstract

The invention relates to copolymers comprising: at least one recurrent unit of the following formula (I): ##STR00001## at least one recurrent unit of the following formula (II): ##STR00002## and at least one recurrent unit of the following formula (III): ##STR00003## wherein: R.sup.1 and R.sup.2 represent, independently of each other, an alkylene group; Z.sup.1 is a group of formula PO.sub.3R.sub.3R.sub.4, R.sub.3 and R.sub.4 representing, independently of each other, a hydrogen atom, an alkyl group or a cation; Z.sup.2 is a group of formula SO.sub.2R.sub.5, R.sub.5 representing an alkyl group or an aryl group; X and Y represent, independently of each other, a halogen atom or a perfluorocarbon group.

Claims

1. A copolymer comprising: at least one recurrent unit of the following formula (I): ##STR00018## at least one recurrent unit of the following formula (II): ##STR00019## and at least one recurrent unit of the following formula (III): ##STR00020## wherein: R.sup.1 and R.sup.2 represent, independently of each other, an alkylene group; Z.sup.1 is a group of formula PO.sub.3R.sub.3R.sub.4, R.sub.3 and R.sub.4 representing, independently of each other, a hydrogen atom, an alkyl group or a cation; Z.sup.2 is a group of formula SO.sub.2R.sub.5, R.sub.5 representing an alkyl group or an aryl group; X and Y represent, independently of each other, a halogen atom or a perfluorocarbon group.

2. The copolymer according to claim 1, wherein R.sup.1 is a group of formula CH.sub.2CH.sub.2.

3. The copolymer according to claim 1, wherein R.sup.2 is a group of formula CH.sub.2CH.sub.2CH.sub.2CH.sub.2.

4. The copolymer according to claim 1, wherein X and Y each represent a halogen atom, at least one of the groups X or Y being a fluorine atom.

5. The copolymer according to claim 1, wherein X represents a perfluoroalkyl group, while Y represents a halogen atom.

6. The copolymer according to claim 1, further comprising at least one recurrent unit of the following formula (IV): ##STR00021## wherein R.sup.6 is an alkyl group.

7. The copolymer according to claim 1, selected from among the following copolymers: copolymers comprising as a recurrent unit compliant with formula (I), a recurrent unit of the following formula (Ia): ##STR00022## wherein Z.sup.1 is a group of formula PO.sub.3R.sub.3R.sub.4, with R.sub.3 and R.sub.4 as defined in claim 1; as a unit compliant with formula (II), a recurrent unit of the following formula (IIa): ##STR00023## and as a unit compliant with formula (III), a recurrent unit of the following formula (IIIa): ##STR00024## copolymers comprising as a recurrent unit compliant with formula (I), a recurrent unit of the following formula (Ia): ##STR00025## wherein Z.sup.1 is a group of formula PO.sub.3R.sub.3R.sub.4, with R.sub.3 and R.sub.4 as defined in claim 1; as a unit compliant with formula (II), a recurrent unit of the following formula (IIb): ##STR00026## and as a unit compliant with formula (III), a recurrent unit of the following formula (IIIa): ##STR00027##

8. A method for preparing a copolymer as defined in claim 1 comprising the following steps: a copolymerization step, in the presence of at least one free radical initiator, of at least one monomer of formula (V), of at least one monomer of formula (VI), of at least one monomer of formula (VII) and optionally at least one monomer of formula (VIII): ##STR00028## wherein R.sup.1, Z.sup.1, R.sup.2, Z.sup.2, X, and Y are as defined in claim 1 and R.sup.6 is an alkyl group; optionally, a step for hydrolysis of the PO.sub.3R.sub.3R.sub.4 group (when R.sub.3 and R.sub.4 represent an alkyl group), in return for which said group is transformed into a PO.sub.3R.sub.3R.sub.4 group, with R.sub.3 and R.sub.4 representing a hydrogen atom or a cation.

9. A cross-linked material obtained by a method comprising a heat cross-linking step of at least one copolymer as defined according to claim 1.

10. The cross-linked material according to claim 9, wherein the heat cross-linking step consists of heating the copolymer(s) to a temperature ranging from 100 to 200 C., wherein the copolymer may be shaped as a membrane prior to heating.

11. A membrane comprising at least one copolymer as defined according to claim 1 and/or a cross-linked material obtained by a method comprising a heat cross-linking step of at least one copolymer as defined according to claim 1.

12. A fuel cell device comprising at least one cell comprising two electrodes positioned on either side of a membrane as defined in claim 11.

13. The cross-linked material according to claim 9, wherein the heat cross-linking step consists of heating the copolymer(s) to a temperature ranging from 140 to 170 C.

Description

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

Example 1

(1) This example relates to the preparation of a copolymer according to the invention by copolymerization of chlorotrifluoroethylene (symbolized by the acronym CTFE), of a specific ethylvinylether (symbolized by the acronym DEVEP) and a specific butylvinylether (symbolized by the acronym BVEMs). In order to obtain an ultimate 10% cross-linking level (cf. Example 3), the following molar proportions (CTFE)/(DEVEP)/(BVEMs) 50/40/10 are used.

(2) The aforementioned monomers CTFE, DEVEP and BVEMs respectively fit the following formulae: For CTFE:
F.sub.2CCFCl For DEVEP:

(3) ##STR00015## For BVEMs:

(4) ##STR00016##

(5) CTFE appears in a gaseous form, which requires the use of an autoclave for applying the preparation of the copolymer.

(6) The autoclave is provided with a mechanical stirrer, with two valves (an input valve and a gas output valve), with a safety disc and an accurate manometer.

(7) In a first phase, K.sub.2CO.sub.3, as a powder is introduced into an autoclave, in an amount of 3% molar relatively to BVEMs and DEVEP. The autoclave is then placed in vacuo for about 40 minutes. The DEVEP (13.3 g), the BVEMs (3.3 g), tertiobutyl perpivalate (0.8 g) (in an amount of 1% molar relatively to BVEMs and EVE) and CTFE (10 g) are then introduced.

(8) The autoclave is then placed with stirring and gradually heated up to 75 C. for about 15 hours. The product of the reaction is dissolved in acetone and then precipitated from methanol and placed in vacuo at 50 C. with view to drying.

(9) The yield of the reaction is 72%.

(10) The structure of the copolymer is controlled by NMR (.sup.1H and .sup.19F NMR), differential scanning calorimetry (subsequently entitled DSC), thermogravimetry analysis (subsequently entitled ATG) and by elementary analysis.

Example 2

(11) The operating procedure for obtaining the crosslinkable copolymers of this example remain similar to the one followed in Example 1, except that BVEMs is replaced with tosylated butylvinylether of the following formula:

(12) ##STR00017##

(13) subsequently entitled BVETs.

(14) In order to obtain subsequently a 10% cross-linking level (cf. Example 3), the molar proportions (CTFE)/(DEVEP)/(BVETs): 50/40/10 are used.

(15) The structure of the copolymer is controlled by NMR (.sup.1H and .sup.19F NMR), DSC, ATG.

Example 3

(16) This example illustrates the method for applying the cross-linking and the shaping of the crosslinkable copolymers prepared according to Examples 1 and 2 explained above.

(17) To do this, in a first phase, it is proceeded with putting into solution the copolymer in an organic solvent, dimethylformamide (DMF), the solvent representing 69% based on the mass of the copolymer.

(18) In a second phase, the obtained viscous mixture is deposited on a glass plate by means of a hand applicator placed under a hood with lamina flow. Next, slow evaporation of the solvent is ensured by placing the glass plate in an oven, the temperature of which is set to 80 C. for 12 hours. And the cross-linking reaction is then conducted by placing the glass plate in an oven, the temperature of which is set to 150 C. for 12 hours.

(19) Finally fluorophosphonated membranes insoluble in aqueous and organic solvents such as water, methanol, acetone, methylethylketone, tetrahydrofurane, dimethylsulfoxide and dimethylformamide are finally obtained.