Process for the preparation of cross-linked fluorinated polymers

A process for the preparation of a cross-linked fluorinated polymer (XLP) comprising sulfonic acid functional groups, the process comprising the steps of:

• a) providing a liquid composition comprising at least one fluorinated polymer (P) in a liquid medium comprising water, wherein fluorinated polymer (P) comprises at least one —SO3M functional group, wherein each M is selected from the group consisting of H and alkaline metals, said fluorinated polymer (P) containing less than 2% of —SO2F functional groups with respect to the total number of —SO3M and —SO2F functional groups;
• and
• b) reacting said fluorinated polymer (P) with at least one cross-linking agent (XL) of formula R(X)n wherein:
• R is selected from a bond, O, S, N, an aromatic group and an aliphatic group, wherein the aliphatic group may be linear, cyclic, or branched, wherein one or more carbons on the aromatic group or the aliphatic group may be further substituted and/or fluorinated, and wherein carbons in the aromatic group or the aliphatic group may be interrupted by one or more heteroatoms;
• n is an integer ≧2;
• and
• X is a functional group selected from the group consisting of —NH2, —NHRa, —Si(Rb)3, —OH, and —SO2W, wherein
• Ra is a C1-C20 alkyl, Rb is a C1-C5 alkyl, and W is selected from OH, F, Cl, Br, and I;
• said reaction being carried out under conditions that promote the formation of covalent bonds between the at least one functional group —SO3M of the fluorinated polymer (P) and at least one functional group X in the cross-linking agent (XL).