(EP848702-A1)      A sulphonyl fluoride substd. monomer isomer of formula (I) is claimed.    Also claimed are: (i) a cpd. of formula (Ia); (ii) a homopolymer of cpd. (I); (iii) a polymeric compsn. of formula (II), in which m &gt; 0; (iv) a polymeric compsn. of formula (III), in which m &gt; 0, at least one of n, p and q &gt; 0, and A1, A2 and A3 = H, halogens, alkyls, perfluoroalkyls, CF=CF2, CN, NO2, OH, O-R (where R = alkyls, perfluoroalkyls and aryls); (v) a polymeric compsn. of formula (IV) in which m, n and p &gt; 0, and A1 and A2 = H, F, CF3 and paraphenoxy.    USE -   Used as a polymeric membrane of a compsn., an ion exchange membrane, or an electrochemical fuel cell comprising the ion exchange membrane (claimed).    ADVANTAGE -   The membranes can be hydrolysed to give sulphonated membranes. Extrusion, a method for large- scale membrane prodn., is further facilitated by the lower glass transition temps. (Tg) typical of monomeric copolymers. The compsn. is at least partially crosslinked (claimed). Prepd. copolymers have favourable properties such as thermal stability, chemical resistance and mechanical properties such as tensile strength, compared to homopolymeric material formed from , , -trifluorostyrene alone.    (JP11506149-W)      A sulphonyl fluoride substd. monomer isomer of formula (I) is claimed.    Also claimed are: (i) a cpd. of formula (Ia); (ii) a homopolymer of cpd. (I); (iii) a polymeric compsn. of formula (II), in which m &gt; 0; (iv) a polymeric compsn. of formula (III), in which m &gt; 0, at least one of n, p and q &gt; 0, and A1, A2 and A3 = H, halogens, alkyls, perfluoroalkyls, CF=CF2, CN, NO2, OH, O-R (where R = alkyls, perfluoroalkyls and aryls); (v) a polymeric compsn. of formula (IV) in which m, n and p &gt; 0, and A1 and A2 = H, F, CF3 and paraphenoxy.    USE -   Used as a polymeric membrane of a compsn., an ion exchange membrane, or an electrochemical fuel cell comprising the ion exchange membrane (claimed).    ADVANTAGE -   The membranes can be hydrolysed to give sulphonated membranes. Extrusion, a method for large- scale membrane prodn., is further facilitated by the lower glass transition temps. (Tg) typical of monomeric copolymers. The compsn. is at least partially crosslinked (claimed). Prepd. copolymers have favourable properties such as thermal stability, chemical resistance and mechanical properties such as tensile strength, compared to homopolymeric material formed from , , -trifluorostyrene alone.    (EP848702-B1)      A sulphonyl fluoride substd. monomer isomer of formula (I) is claimed.    Also claimed are: (i) a cpd. of formula (Ia); (ii) a homopolymer of cpd. (I); (iii) a polymeric compsn. of formula (II), in which m &gt; 0; (iv) a polymeric compsn. of formula (III), in which m &gt; 0, at least one of n, p and q &gt; 0, and A1, A2 and A3 = H, halogens, alkyls, perfluoroalkyls, CF=CF2, CN, NO2, OH, O-R (where R = alkyls, perfluoroalkyls and aryls); (v) a polymeric compsn. of formula (IV) in which m, n and p &gt; 0, and A1 and A2 = H, F, CF3 and paraphenoxy.    USE -   Used as a polymeric membrane of a compsn., an ion exchange membrane, or an electrochemical fuel cell comprising the ion exchange membrane (claimed).    ADVANTAGE -   The membranes can be hydrolysed to give sulphonated membranes. Extrusion, a method for large- scale membrane prodn., is further facilitated by the lower glass transition temps. (Tg) typical of monomeric copolymers. The compsn. is at least partially crosslinked (claimed). Prepd. copolymers have favourable properties such as thermal stability, chemical resistance and mechanical properties such as tensile strength, compared to homopolymeric material formed from , , -trifluorostyrene alone.