AbstractA new route for the preparation of cation exchange membranes from polystyrene–polyisoprene–polystyrene (SIS) block copolymers has been studied, using N‐chlorosulfonyl isocyanate. At temperatures of 0° to 20°C, N‐chlorosulfonyl isocyanate reacts readily with the olefin group in polyisoprenes, resulting in a β‐lactam‐N‐sulfonyl chloride group. Films of this product can be cast which are hydrolyzed afterwards with aqueous ammonia at room temperature to give a membrane with ionic sulfonate and neutral carbamoyl groups. Homogeneous membranes are prepared with an SIS block copolymer as starting material and with mole ratios of N‐chlorosulfonyl isocyanate/isoprene between 15 and 45. In hyperfiltration experiments at 40 atmospheres, both NaCl and Na2SO4are rejected up to 82, while fluxes of 0.25 to 0.30 cm3/cm2·hr are obtained. From permeation and hyperfiltration experiments, it is concluded that the weight fraction of membrane water has a large influence on the flux. The water content in the membrane during the hyperfiltration process is primarily determined by the applied pressure, the type of salt, an
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