A series of multi-arm star-branched polyisobutylenes was synthesized via living carbocationic polymerization. Arms with molecular weights ranging from 10,000 to 30,000 g/mol were prepared using the cumyl chloride/TiCl4/pyridine initiation system in 60/40 (v/v) hexane/methyl chloride at -80 degrees C and linked by sequential addition of divinylbenzene. The weight average number of arms per star polymer, (N) over bar(w), scaled inversely with arm molecular weight and ranged from 32 to 5. Star-telechelic ionomers were produced by sulfonation of the aromatic initiator residue at the end of each arm, followed by neutralization. Sulfonation was quantitative as indicated by acid-base titration. Potassium ionomers were elastic solids which were marginally soluble in THF; the precursors were tacky and freely soluble in THF. Ionic modification did not alter the glass transition temperature (-66 degrees C), but the thermal decomposition temperature in Nz was increased from 375 to 400 degrees C.