The effect of various new electron donors (EDs), specifically esters (dimethyl phthalate, di-t-octyl phthalate, methyl benzoate, ethyl isobutyrate, dimethyl 3,3-dimethylglutarate, dimethyl terephthalate, dimethyl 5-t-butylisophthalate, trimethyl 1,3,5-benzenetricarboxylate) and ketones (acetophenone and benzophenone), on the living cationic polymerization (LC ○+ Pzn) of isobutylene (IB) under various experimental conditions was investigated. The polymerization was effected by the dicumyl chloride (DCC)/BCl 3 initiating system in CH 3 Cl at -80°C. It was found that the nature and concentration of the ED strongly influence the molecular weight distribution of the polymer