Control of molecular weight and molecular weight distribution in ethylene polymerization with metallocene catalysts

The molecular weight (MW) and the molecular weight distribution (MWD) of polyethylene (PE) prepared with various metallocene catalysts were investigated. The weight-average molecular weight (M _w) of PE prepared with dicyclopentadienyltitanium dichloride/aluminoxane (Cp₂TiCl₂/MAO) was about 4,0 · 10⁵, while that of PE obtained with dicyclopentadienylzirconium dichloride/aluminoxane (Cp₂ZrCl₂/MAO) is about 1,0 · 10⁵. PE of bimodal MWD was obtained with the mixed catalyst Cp₂TiCl₂/Cp₂ZrCl₂. Narrow MWD PE was obtained with the mixed catalyst Cp₂ZrCl₂/Et(ind)₂ZrCl₂, because each catalyst produced an M _w of 1,0 · 10⁵. However, the change of temperature during the polymerization with the mixture Cp₂ZrCl₂/Et(ind)₂ZrCl₂ produced PE with a bimodal MWD and a value of the ratio of weight- to number-average molecular weights of M _w/M _n = 4.