Fluorinated polymer particles with grafting sulfonate chains, which showed high dispersion stability in aqueous media, were synthesized by the crosslinking of block copolymer micelles. A crosslinkable block copolymer, poly[(2,3,4,5,6-pentafluorostyrene)-co-4-(1-methylsilacyclobutyl)styrene l-b-poly(neopentyl 4-styrenesulfonate), composed of a statistical copolymer segment of 2,3,4,5,6-pentafluorostyrene with 4-(1-methylsilacyclobutyl)styrene and a neopentyl 4-styrenesulfonate segment, was prepared by the nitroxy-mediated living radical polymerization of a 2,3,4,5,6-pentafluorostyrene/4-(1-methylsilacyclobutyl)styrene mixture and neopentyl 4-styrenesulfonate. The block copolymer formed micelles with a poly[(2,3,4,5,6-pentafluorostyrene)-co-4-(1-methylsilacyclobutyl)styrene ] core in acetonitrile, which were crosslinked via the ring-opening reaction of silacyclobutyl groups in the core by a treatment with a platinum catalyst. The deprotection of sulfonate groups in the micelle corona by exposure to trimethylsilyl iodide and a treatment with aqueous HCl, followed by neutralization with aqueous NaOH, provided a polymer particle with polymer chains of sodium 4-styrenesulfonate grafted on its surface. (c) 2007 Wiley Periodicals, Inc.