The homopolymerization of styrene and its copolymerization with ethylene in the presence of a vanadium-based supported catalyst, (VCI?, 1 AICI,], associated to triethylaluminium is examined. As indicated by means of ''C nuclear magnetic resoance and differential scanning calorimetry analysis, the homopolystyrenes obtained present a highly isotactic microstructure and are semicrystalline (melting temperature 220°C).In the case of styrenelethylene random copolymerization, the formation of both, polyethylene blocks and isotactic polystyrene sequences was identified by analysis of the crude polymer. Solubility characteristics and structural characteristics from nuclear magnetic resonance spectra of these products support the formation of copolymers with ethylene and isotactic styrene blocks rather than that of two distinct homopolymers.