Effect of temperature on the isospecific propylene polymerization catalyzed by rac-dimethylsilylbis(2,4,6-trimethyl-1-indenyl)zirconium dichloride/methyl aluminoxane

Abstract

A new chiral ansa-metallocene catalyst, namely rac-dimethylsilyl-bis(2,4,6- trimethyl-1-indenyl)zirconium dichloride (1), has been synthesized and used as a catalyst for isospecific polymerization of propylene, with methyl aluminoxane (MAO) as the cocatalyst. The influences of polymerization temperature (T p) on the polymerization activity, polypropylene (PP) microstructure and polymer properties are investigated, and the results are compared with rac-dimethylsilyl-bis(indenyl)zirconium dichloride congener (2) under identical conditions. 1/MAO has a very high activity for propylene polymerization at 50-70°C and 1 atm propylene pressure. A beneficial feature of catalyst 1 is its higher stability at elevated temperature than 2. At Tp = 50°C, the novel catalyst shows a great improvement in terms of stereoregularity, with [mmmm] = 92% and Tm = 146°C, while 2 displays [mmmm] of 82% and Tm of 134°C under the same conditions. The regiospecificity of 1/MAO is also better than 2/MAO. © 2005 Elsevier Ltd. All rights reserved.