SALT-FREE FLLUOROPOLYMER MEMBRANE FOR ELECTROCHEMICAL DEVICES

1 . A process for manufacturing a polymer membrane based on a fluoropolymer hybrid organic/inorganic composite, said process comprising the following steps:

(i) providing a mixture that comprises:

a metal compound of formula (I)

X 4-m AY m   (I)

wherein m is an integer from 1 to 4, A is a metal selected from the group consisting of Si, Ti and Zr, Y is a hydrolysable group selected from the group consisting of an alkoxy group, an acyloxy group and a hydroxyl group, X is a hydrocarbon group, optionally comprising one or more functional groups,

a liquid medium [medium (L)];

optionally, at least one acid catalyst; and

optionally, an aqueous liquid medium [medium (A)];

(ii) partially hydrolysing and/or polycondensing the metal compound of formula (I) by stirring the mixture provided in step (i) until the obtainment of a solid mixture (SM) that comprises a metal compound including one or more inorganic domains consisting of ≡A-O-A≡ bonds and one or more residual hydrolysable groups Y [metal compound (M)], wherein A and Y are as above defined;

and

(iii) mixing the solid mixture (SM) provided in step (ii) with at least one fluoropolymer [polymer (F)] comprising recurring units derived from at least one fluorinated monomer [monomer (FM)] and at least one monomer comprising at least one hydroxyl group [monomer (OH)], so as to provide a solid composition (SC);

and

(iv) processing the solid composition (SC) provided in step (iii) in the molten state, so that at least a fraction of hydroxyl groups of the monomer (OH) of polymer (F) reacts with at least a fraction of residual hydrolysable groups Y of said compound (M),

so as to obtain a polymer membrane comprising a fluoropolymer hybrid organic/inorganic composite including the liquid medium (L).

2 . The process according to claim 3 , wherein in step (ii) the mixture provided in step (i) is subjected to a vigorous stirring at a temperature of at least 30° C. for a time comprised in the range of from 24 to 48 hours.

3 . The process according to claim 1 , wherein step (ii) further comprises a step (ii bis ) of drying the solid mixture (SM) obtained in step (ii) at a temperature of at least 50° C.

4 . The process according to claim 1 , wherein step (ii) further includes a step (ii ter ) of comminuting the solid mixture obtained in step (ii) or in step (ii bis ) so as to provide the solid mixture (SM) in the form of fine powder.

5 . A process for manufacturing a polymer electrolyte based on a fluoropolymer hybrid organic/inorganic composite, said process comprising the following steps:

(a) providing a mixture that comprises:

a metal compound of formula (I)

X 4-m AY m   (I)

wherein m is an integer from 1 to 4, A is a metal selected from the group consisting of Si, Ti and Zr, Y is a hydrolysable group selected from the group consisting of an alkoxy group, an acyloxy group and a hydroxyl group, X is a hydrocarbon group, optionally comprising one or more functional groups,

a liquid medium [medium (L)];

optionally, at least one acid catalyst; and

optionally, an aqueous liquid medium [medium (A)]; and

at least one fluoropolymer [polymer (F)] comprising recurring units derived from at least one fluorinated monomer [monomer (FM)] and at least one monomer comprising at least one hydroxyl group [monomer (OH)];

and

(b) partially hydrolysing and/or polycondensing the metal compound of formula (I) by stirring the mixture provided in step (a) until the obtainment of a solid composition (SCP) that comprises a metal compound including one or more inorganic domains consisting of ≡A-O-A≡ bonds and one or more residual hydrolysable groups Y [metal compound (M)], wherein A and Y are as above defined and at least one polymer (F) as above defined;

and

(c) processing the solid composition (SCP) provided in step (b) in the molten state at least a fraction of hydroxyl groups of the monomer (OH) of polymer (F) reacts with at least a fraction of residual hydrolysable groups Y of said compound (M),

so as to obtain a polymer membrane comprising a fluoropolymer hybrid organic/inorganic composite including the liquid medium (L).

6 . The process according to claim 5 , wherein step (b) includes a further step (b bis ) of drying the composition obtained in step (b) at a temperature of at least 50° C.

7 . The process according to claim 5 , wherein step (b) further includes a step (b ter ) of comminuting the solid mixture obtained in step (b) or in step (b bis ), so as to provide the solid mixture in the form of fine powder.

8 . The process according to claim 1 , wherein the metal compound of formula (I) is a non-functional compound selected from the group consisting of triethoxysilane, trimethoxysilane, tetramethyltitanate, tetraethyltitanate, tetra-n-propyltitanate, tetraisopropyltitanate, tetra-n-butyltitanate, tetra-isobutyl titanate, tetra-tert-butyl titanate, tetra-n-pentyltitanate, tetra-n-hexyltitanate, tetraisooctyltitanate, tetra-n-lauryl titanate, tetraethylzirconate, tetra-n-propylzirconate, tetraisopropylzirconate, tetra-n-butyl zirconate, tetra-sec-butyl zirconate, tetra-tert-butyl zirconate, tetra-n-pentyl zirconate, tetra-tert-pentyl zirconate, tetra-tert-hexyl zirconate, tetra-n-heptyl zirconate, tetra-n-octyl zirconate, tetra-n-stearyl zirconate.

9 . The process according to claim 1 , wherein the acid catalyst is an organic acid, preferably is citric acid or formic acid.

10 . The process according to claim 1 , wherein the medium (A) consists of water and ethanol.

11 . The process according to claim 1 , wherein the monomer (OH) is selected from the group consisting of (meth)acrylic monomers of formula (V) or vinylether monomers of formula (VI)

wherein each of R 1 , R 2 and R 3 , equal to or different from each other, is independently a hydrogen atom or a C 1 -C 3 hydrocarbon group, and R OH is a hydrogen atom or a C 1 -C 5 hydrocarbon moiety comprising at least one hydroxyl group.

12 . The process according to claim 1 , wherein the polymer (F) comprises:

(a) at least 60% by moles of vinylidene fluoride (VDF);

(b) optionally, from 0.1% to 15% by moles of a fluorinated comonomer selected from chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), perfluoromethylvinylether (PMVE) and mixtures therefrom; and

(c) from 0.050% to 10% by moles of monomer (OH) of formula (V)

wherein each of R 1 , R 2 , R 3 , equal to or different from each other, is independently a hydrogen atom or a C 1 -C 3 hydrocarbon group and R OH is a C 1 -C 5 hydrocarbon moiety comprising at least one hydroxyl group.

13 . A solid composition (SC) obtained according to step (iii) of the process of claim 1 .

14 . A solid composition (SCP) obtained according to step (b) of the process of claim 5 .

15 . A polymer membrane obtained by the processes according to claim 1 .

16 . The process of claim 12 , wherein polymer (F) comprises:

(a) at least 85% by moles of vinylidene fluoride (VDF);

(b) optionally, from 0.1% to 10% by moles of a fluorinated comonomer selected from chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), perfluoromethylvinylether (PMVE) and mixtures therefrom; and

(c) from 0.2 to 3.0% by moles of monomer (OH) of formula (V).