An investigation of the effect of chain length on stereo-regulation with C2 symmetric metallocene catalysts

[摘要] This study concerns the polymerization of propylene both in the presence and absence ofmolecular hydrogen. The percentage of hydrogen used as a terminating agent in thepolymerization reactions was varied from 0.1 wt% to 15.0 wt% in order to compare avariety of polymers with different percentages of hydrogen incorporated. Two ansametallocene catalysts were used: (A) rac-[ethylene bis(indenyl)] zirconium dichloride(rac-Et(Ind)2ZrCl2) and (B) dimethylsilyl-bis(2-methyl benzoindenyl) zirconiumdichloride (rac-Me2Si(2-MeBenz[e]Ind)2ZrCl2). Methylaluminoxane (MAO) was used ascocatalyst for both of the two catalysts.Characterization of the polymers included using nuclear magnetic resonancespectroscopy (NMR) for information concerning the microstructure of the polymers, hightemperature gel permeation chromatography (HT-GPC) for molecular weight andmolecular weight distributions and differential scanning calorimetry (DSC) to investigatethe melting point and crystallization behaviour of the polymers.The polypropylenes prepared with the dimethylsilyl-bis(2-methyl benzoindenyl)zirconium dichloride catalyst system were compared to the polypropylenes synthesizedwith ethylene-bis(indenyl) zirconium dichloride. In particular, the effects of hydrogen onthe microstructure, molecular weight, molecular weight distribution, melting point andcrystallization behaviour were investigated.

[发布机构] Stellenbosch University