New linear triblock copolymers consisting of a rubbery polyisobutylene (PIE) midsegment bonded both sides by glassy cyclized poly(1,3-pentadiene) (cy-PPD) blocks were synthesized by carbocationic polymerization using sequential monomer addition. First, the living polymerization of isobutylene (IB) was induced by bifunctional dicumylmethylether (DiCumOMe)/TiCl4 as initiating system in n-hexanel CH2Cl2 (1/1 v/v) as solvent mixture at -60 degrees C in the presence of DMSO as electron donor (ED). After the living PIE sequences had reached the desired number average molar weight (<(M)over bar(n)>) in the range of 5000 to 25 000 g mol(-1), 1,3-pentadiene (PD) was added to produce the hard cy-PPD outer blocks with <(M)over bar(n)> close to 6000 g mol(-1). The crude copolymers were purified by CH2Cl2 extraction at -60 degrees C and characterized by size exclusion chromatography (s.e.c.) and nuclear magnetic resonance (n.m.r.) spectroscopy.