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

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Abstract
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 (Mw) 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 Mw 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 Mw/Mn = 4.