In order to control molecular weight distribution(MWD) of polyolefin(polyethylene, polystyrene), several kinds of silica supported metallocene catalysts were prepared with various metallocene and different preparation conditon.
MWDs of polyethylene prepared by $SiO_2$-supported $Cp_2ZrCl_2$ and $Cp_2HfCl_2$ catalysts were narrow($M_w/M_n=2.5~3.7$), while those by $SiO_2$-supported titanocene catalyst were very broad($M_w/M_n=5~13$). Polymerizations of ethylene were performed over various $SiO_2$-supported titanocene catalysts under different polymerization conditions to correlate MWD of polyethylene with polymerization condition and preparation condition of catalyst. As Al/Ti mole ratio in ethylene polymerization increase, polydispersity of polyethylene increase. Moreover, as increasing the Al/Ti mole ratio in the prepared catalyst, MWD of polyethylene is broader. Therefore, it is speculated that new active sites were generated via interaction of titanium and Al compound.
MWD of syndiotactic polystyrene could be controlled by using hybrid catalyst(homogeneous or heterogeneous type) or varying polymerization temperature. Hybrid catalyst is consist of two metallocene compounds which have different propagation rate and termination rate. MWDs of syndiotactic polystyrenes prepared with hybrid catalysts were somewhat broader($M_w/M_n=2~4$) than prepared over homogeneous metallocene catalysts($M_w/M_n ＜ 2.0$).
