This work presents a study on the cationic polymerization of styrene in different reaction media, super-critical CO2 (scCO(2)), [bmim][PF6], dichloromethane, and scCO(2) plus [bmim][PF6] using AlCh(3) as initiator at temperatures from 273 to 333 K. The reactions were analyzed in relation to the monomer conversion rate, polymer structures, average molecular weights and molecular weight distribution. The polymerization reaction product was characterized by H-1 and C-13 nuclear magnetic resonance (NMR) and by gel permeation chromatography (GPC). In all cases, the styrene polymerization produced oligomers. Reactions using ionic liquid as a solvent led to higher molecular weight and monomer conversion rate. Monomer conversion rates of about 100% and weight average molecular weight (M-w) of 2400 at 298 K were obtained. Reactions with scCO(2) as a solvent yielded low monomer conversion rates (around 50%) and a M-w = 2000 at 298 K. The oligolystyrenes presented rr syndiotatic-rich sequences in the microstructure in all reaction conditions. The use of ionic liquid and scCO(2) results in better yields than the use of the other organic solvents solvents. (C) 2008 Elsevier B.V. All rights reserved.