Deactivation study of zirconocene immobilization into Lewis acid and dual-shell silicas prepared by a nonhydrolytic sol-gel method

Cp2ZrCl2 was entrapped into dual-layered silica by two iterated nonhydrolytic sol-gel steps. Silica was modified by WCl6 and organosilanes, which acted as potential Lewis acid sites and active site spacers, respectively. For comparative reasons, entrapped ((BuCp)-Bu-n)(2)ZrCl2 systems and one-layer W-containing systems were also synthesized. Catalyst activity was evaluated in ethylene polymerization, with methylaluminoxane (MAO) as the cocatalyst. Dual-shell systems have shown greater resistance than grafted ones when exposed to air. The presence of Lewis acid centers (W) on the support improves contaminant tolerance. ATR experiments indicate that tungsten oxides increase acetone adsorption onto the silica surface. GPC measurements show polyethylene low mass fraction reduction, which suggests that ketones preferably deactivate this specific site of polyolefin production. The polymer polydispersity index is broadened in dual-shell systems, such as that containing one silica layer modified with Me-Si, and another with C8-Si moieties containing two different metallocenes (nonsubstituted and alkyl-substituted). (C) 2019 Elsevier Inc. All rights reserved.