Poly(isobutylene-b-epsilon-caprolactone) diblock and poly(epsilon-caprolactone-b-isobutylene-b-epsilon-caprolactone) triblock copolymers have been prepared and characterized. The synthesis involved the living cationic polymerization of IB, followed by capping with 1,1-diphenylethylene or 1,1-p-ditolylethylene and end-quenching with 1-methoxy-1-trimethylsiloxy-2-methyl-propene to yield methoxycarbonyl functional PIB. Hydroxyl end-functional PIB polymers were quantitatively obtained by the subsequent reduction of methoxycarbonyl end-functional PIB with LiAlH4. The structure of hydroxyl end-functional PIBs was confirmed by H-1 NMR and IR spectroscopy. Poly(epsilon-caprolactone-b-isobutylene) diblock copolymers and poly(epsilon-caprolactone-b-isobutylene-b-epsilon-caprolactone) triblock copolymers were synthesized by the living cationic ring-opening polymerization of E-caprolactone with hydroxyl end-functional PIB as macroinitiator in the presence of HCl.Et2O via the "activated monomer mechanism". The block copolymers exhibited close to theoretical M(n)s and narrow molecular weight distributions.