Cationic polymerization of styrene initiated by the CO+ClO4- group on the surface of expanded graphite (EG) was carried out for modifying the surface properties of graphite. The initiating sites were achieved by the reaction of EG with SOCl2 and followed by AgClO4. Subsequently, the cationic polymerization of styrene was conducted to afford polystyrene brush on EG. The influence factors, such as polymerization time and temperature, on the polymerization including the grafting ratio and efficiency were investigated. (C) 2003 Wiley Periodicals, Inc.