Novel polyisobutylene-polyisoprene (PIB-PIP) multiblock polymers have been synthesized and used for the preparation of UV-cured transparent flexible coatings. The block polymers were tailor-made by bidirectional living carbocationic polymerization of isobutylene (IB) followed by sequential isoprene (IP) addition. PIB-PIP multiblocks containing highly cyclizedtr-1,4-PIP sequences were mixed with a bisazide and photocrosslinked. Epoxidized PIB-PIP blocks were blended with a cationic photoinitiator and UV-cured. Blocks having 23 mol% total PIP content and PIB segments ofMn= 16,600 and 18,800, respectively, gave transparent flexible coatings with 45 kg/cm2tensile strength and 450% elongation. The coatings exhibited good adhesion to aluminum and are expected to have excellent barrier properties due to the presence of PIB sequences.