The preparation of poly(isobutylene) (PIB) nanoparticles via cationic emulsion polymerization is presented. As a requirement, an oil-in-perfl uoroalkane nonaqueous emulsion is developed, which is inert under the carbocationic polymerization conditions. To stabilize the dichloromethane/ hexane droplets in the fl uorinated, continuous phase, an amphiphilic block copolymer emulsifi er is prepared containing PIB and 1H,1H -perfl uoroalkylated poly(pentafl uorostyrene) blocks. This system allows for the polymerization of isobutylene with number-average molecular weights ((M) over bar (n)) up to 27 000 g mol(-1). The particle morphologies are characterized via dynamic light scattering and electron microscopy. For (M) over bar (n) >20 000 g mol(-1), the particles exhibit shape-persistence at room temperature and are approximate to 100 nm in diameter.