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

Abstract

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 ( M w ) of PE prepared with dicyclopentadienyltitanium dichloride/aluminoxane (Cp 2 TiCl 2 /MAO) was about 4,0 · 10 5 , while that of PE obtained with dicyclopentadienylzirconium dichloride/aluminoxane (Cp 2 ZrCl 2 /MAO) is about 1,0 · 10 5 . PE of bimodal MWD was obtained with the mixed catalyst Cp 2 TiCl 2 /Cp 2 ZrCl 2 . Narrow MWD PE was obtained with the mixed catalyst Cp 2 ZrCl 2 /Et(ind) 2 ZrCl 2 , because each catalyst produced an M w of 1,0 · 10 5 . However, the change of temperature during the polymerization with the mixture Cp 2 ZrCl 2 /Et(ind) 2 ZrCl 2 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.