The living polymerization of isobutylene (IB) by the trans-2,5-diacetoxy-2,5-dimethyl-3-hexene (DiOAcDMH~)/BCla initiating system in 1,2-dichloroethane (DCE) in the -30 to +21~ range has been investigate~. Well-dEfined tert-chlorine terminated polyisobutylenes (--CI-PIB-Cl-) have b-~n obtained at suitably low IB and DiQAcDMH~ concentrations in the -30 ~ to 0~ range. Theoretical CI~ end functionality Fn ~2.0  0.1 was demonstrated by dechlorination with sodium biphenyl coupled with titration using a chlori4e ion selective electrode, and by ZH NMR spectroscopy. The --CI-PIB-CI~ was quantitatively dehydrochlorinated to ~CH2C(CHa )=CH2 capped PIBs which in turn were quantitatively converted by hydroboration/peroxidation to ~CH2CH(CHa)CH2OH ended PIBs. The internal ~C(CHs)2CH=CHC(CHs)2~ initiator fragment in the polymer remains unchanged during end group functionalizatio ns due to steric protection by the gemdimethyl groups and the polymer chain.