NOVELTY - Preparing a crosslinked fluorinated polymer comprising sulfonic acid functional groups comprises: providing at least one fluorinated polymer comprising at least one functional group of sulfate compound; and reacting the fluorinated polymer with at least one crosslinking agent, where the reaction is carried out under conditions that promote the formation of covalent bonds between the functional group of fluorinated polymer and at least one functional group X in crosslinking agent.    USE - The crosslinked fluorinated polymer is useful in an article including a fabric, a fiber, a film, or a membrane, where the article is useful in a fuel cell or a filtration device (all claimed).    ADVANTAGE - The process has reduced number of steps. The articles have improved physical and mechanical resistance.    DETAILED DESCRIPTION - Preparing a crosslinked fluorinated polymer comprising sulfonic acid functional groups comprises: (a) providing at least one fluorinated polymer comprising at least one functional group of sulfate compound of formula (-SO3M), where the fluorinated polymer contains less than 2% of functional group of sulfate compound; and (b) reacting the fluorinated polymer with at least one crosslinking agent of formula (R(X)n), where the reaction is carried out under conditions that promote the formation of covalent bonds between the functional group of sulfate compound of fluorinated polymer and at least one functional group X in crosslinking agent.    M = H or alkaline metals, preferably H;    R = bond, O, S, or N;    R = aryl or aliphatic group (optionally substituted and/or fluorinated with heteroatoms);    n = more than 2; and    X = a functional group of -NH2, or -NHRa1;    Ra1 = 1-20C alkyl, or -Si(Rb1)3;    Rb1 = 1-5C alkyl, -OH, -SO2W1; and    W1 = OH, F, Cl, Br, or I.    INDEPENDENT CLAIMS are included for:    (1) a liquid composition comprising a liquid medium, at least one fluorinated polymer (P) dispersed or dissolved in the liquid medium, and at least one crosslinking agent, and    (2) an article comprising a crosslinked fluorinated polymer obtainable from the process, where the polymer comprises covalent crosslinks comprising moiety -R- moieties deriving from the reaction between functional group of sulfate compound and functional group X.