The cationic polymerizations of indene (Ind) and styrene (Sty) initiated by iodine (I-2) in liquid sulfur dioxide (SO2) were investigated. Reactions involving Ind were characterized by termination by neutralization between the growing carbocationic species and the nucleophilic counteranion, at low temperature. Sty polymerization is also termination-dominate and gives low conversion at -20 degrees C. High resolution gas chromatography coupled with mass spectrometry (HGC-MS) analysis of non polymeric material in the Sty polymerization suggested that initiation of Sty polymerization involves the formation of 1,2 diiodide adduct prior to initiation with HI.