Meso- and Rac-[bis(3-phenyl-6-tert-butylinden-1-yl)dimethylsilyl]zirconium Dichloride: Precatalysts for the Production of Differentiated Polyethylene Products with Enhanced Properties

Abstract

Ansa-zirconocene complexes are widely employed as precatalysts for olefin polymerization. Their synthesis generally leads to mixtures of their rac and meso isomers, whose separation is often problematic. In this contribution, we report on the synthesis of a novel silyl-bridged bis(indenyl)-based metallocene, and on the separation of its rac and meso isomers by simple recrystallization from toluene. The two complexes, activated by methylaluminoxane (MAO), have been used as precatalysts in ethylene/1-hexene copolymerization. Regardless of the reaction conditions, the meso complex outperformed its rac congener. A similar trend was observed by performing the process in the presence of the silica-supported versions of the complexes. This is remarkable, since meso metallocenes generally display lower activities than their rac analogues. Furthermore, the meso isomer generates polymer products that are more in line with the targets for the preparation of a bimodal PE grade made of a lower-MW high-density (HDPE) fraction and a higher-MW linear low-density (LLDPE) fraction.

Comonomer-controlled synthesis of long-chain branched (LCB)-polyethylene

“…In order to assess the industrial viability of the process, polymerization tests catalyzed by heterogeneous supp-Zr-1 and supp-Zr-2, synthesized from Zr-1 and Zr-2 according to reported procedures [42,43], were conducted in the presence of 1,7-octadiene [44] as the LCB/cross-linking-promoter and by using triisobutylaluminum (TIBAL) as the scavenger 9 (Table 2) [45]. The productivity of the supp-Zr-1-based system proved only slightly dependent on the diene concentration.…”