Isobutenyl-telechelic polyisobutylenes (PIBs) were synthesized by reacting telt-chlorine-telechelic and living PIBs with isobutenyltrimethylsilane (IBTMS) in the presence of TiCl4 in CH2Cl2/hexane (40/60 v/v) solvent mixtures at -78 degrees C. In order to obtain PIE oligomers, living polymerization of isobutylene was induced by the di-(2-hydroxy-2-propyl)-5-tert-butylbenzene (tBuDiCumOH)/BCl3 combination in CH2Cl2 followed by addition of required amounts of hexane and TiCl4 to avoid polymer precipitation and permanent termination. Although quantitative end-quenching of living PIE was achieved with IBTMS, chain coupling between the living PIE chains and isobutenyl-ended polymers also occurred. This side reaction was avoided by isobutenylation of tert-chlorine-telechelic PIE with IBTMS in the presence of TiCl4. The resulting isobutenyltelechelic PIE contains exclusively exo-CH2-C(CH3)=CH2 endgroups, and is free from -CH=C(CH3)(2) endo olefins usually obtained in small quantities (similar to 3-8% of total double bonds) as a side product of other methods used in the past.