A new synthetic route for the preparation of polyisobutylene (PIB)-based linear and starshaped block copolymers was developed by combining living carbocationic and anionic polymerizations. Living PIB chains were quantitatively endcapped with 1,1-diphenylethylene, leading to 1,1-diphenyl-1-methoxy (DPOMe) or 2,2-diphenylvinyl (DPV) termini, or both. Both the DPOMe- and DPV-terminated PIBs, and the mixtures of both endgroups were quantitatively metalated with K/Na alloy, Cs metal, or Li dispersion in THF at room temperature. The resulting stable macrocarbanion obtained by metalation with K/Na alloy was used to initiate living anionic polymerization of tert-butyl methacrylate (tBMA) yielding PIB-b-PtBMA block copolymers with nearly quantitative blocking efficiency. Hydrolysis of the ester groups by HCl in dioxane resulted in amphiphilic polyisobutylene-bloch-poly(methacrylic acid) block copolymers. Replacing K+ with Li+ by excess LiCl gave a PIB macroinitiator suitable for anionic polymerization of methyl methacrylate (MMA). A series of linear PMMA-b-PIB-b-PMMA block copolymers and of star-shaped PIB-b-(PMMA)(3) block copolymers were successfully synthesized by telechelic PIB macroanions with high blocking efficiencies. Characterizations of these new thermoplastic elastomers were carried out by SEC, DSC, dynamic-mechanical, and stress-strain measurements.