With mononuclear half-titanocenes such as CpTiCl3, IndTiCl(3), and Me5CpTiCl3, as well as the constrained geometry catalyst (CGC) and a new dinuclear hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride) (TSDT), the copolymerization of styrene and ethylene was examined. The thermal properties and structure of copolymerization products were investigated with differential scanning calorimetry and C-13-nuclear magnetic resonance. In addition, the raw polymer was separated into homopolymer and copolymer with an extraction method and cross fractionation chromatography. With the above analysis, it was concluded that the raw polymer obtained with CpTiCl3 and IndTiCl(3) was a mixture of syndiotactic polystyrene and polyethylene homopolymers with 10-30 wt % copolymer, whereas that produced by Me5CpTiCl3 and TSDT was a homopolymer mixture with a negligible amount of copolymer. Only CGC produced the copolymer of styrene and ethylene perfectly.