Two sets of styrene-based semifluorinated block copolymers, one with a perfluoroether pendant group and another with a perfluoroalkyl group, were synthesized by atom transfer radical polymerization. Microphase separation of the block copolymers was established by small-angle X-ray scattering and differential scanning calorimetry (DSC). DSC measurements also showed that the perfluoroether-based polymer had a low glass-transition temperature (- 44 degreesC). Contact-angle measurements indicated that the semifluorinated block copolymers had low surface-energies (ca. 13 mJ/m(2)). These materials hold promise as low-surface-energy additives or surfactants for supercritical CO2 applications. (C) 2004 Wiley Periodicals, Inc.