Functional star-branched polyisobutylenes (PIBs) were prepared in high yield based on living cationic polymerization via haloboration initiation. First, living PIBs carrying Cl2B- head groups were prepared via haloboration initiation. Subsequently, the living ends were reacted with a small amount of divinylbenzene (DVB). The products were completely soluble and consisted of a cross-linked core of poly(DVB) to which almost-monodisperse PIB chains were radially attached. The star-branched PIBs were characterized by solution and solid-state NMR spectroscopy and size-exclusion chromatography using triple detection, RI, UV, and light scattering detectors.