Cation exchange membranes prepared from random and multiblock side-chain sulfonated poly(ether sulfone)s have been characterised to evaluate their suitability for electrodialysis and membrane capacitive deionization applications. The side chain sulfonation of the copolymers resulted in membranes with a high degree of sulfonation and ion exchange capacities (IEC) in the range of 1.44-2.05 mmol/g, which is comparable to commercially available membranes. The multiblock copolymer, which can be considered as having a microheterogeneous structure, exhibited a high IEC and water uptake due to large, hydrophilic domains, while the random copolymers had lower swelling rates. Membrane conductivity in the Na+ form reached as high as 15.13 mS/cm for the random copolymers and 16.74 mS/cm for the block copolymer. Transport numbers were found to be as high as 0.99 for random copolymers, but as low as 0.84 for the block copolymer. Based on these results, these side-chain sulfonated random copolymers are potential candidates for use in electro-driven desalination systems. (C) 2013 Elsevier B.V. All rights reserved.