Ethylene polymerization with supported bis(triphenylsilyl) chromate catalysts

Abstract

Bis(triphenylsilyl) chromate is an active catalyst for ethylene polymerization without further treatment or additives. Catalytic activity is markedly increased when the compound is deposited on silica–alumina and is further increased if it is deposited on silica and then treated with an aluminum alkyl. Polymer molecular weight can be controlled by reaction temperature, hydrogen addition, support type, and reducing agent structure to give polymers ranging in melt index from essentially zero to > 100. In the supported catalysts the bis(triphenylsilyl) chromate appears to be bound to the support and to undergo a reduction step either by reaction with ethylene or with aluminum alkyl prior to polymerization. The active site is envisioned as chromium alkyl, bound to the support, with propagation occurring by insertion of the monomer into a CrC bond. Chain termination is by chain transfer to monomer.

Switching from ethylene polymerization to nonselective oligomerization over a homogeneous model catalyst: A triphenylsiloxy complex of chromium(VI)

“…In view of the similarity of molecular structural characteristics as well as ethylene polymerization behavior (with or without aluminum alkyl cocatalysts) [8,12], we infer that a similar switching behavior might be also observed over UCC S-2 catalyst activated with MAO. These systematic confirmation experiments over the UCC S-2 catalyst/MAO system are now in progress in our laboratory.…”

“…Traditionally, UCC S-2 catalyst is directly prepared from a triphenylsiloxy complex of chromium(VI) namely bis(triphenylsilyl) chromate (BC) using thermally treated silica gel as support by wet impregnation method as shown in Scheme 1 [8]. As the starting material for UCC S-2 catalyst, BC is a well-defined homogeneous model for UCC S-2 catalyst due to its molecular structural characteristics.…”

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

“…[287][288][289][290][291][292] On contact with ethylene, the Cr VI -containing materials form active species and show behavior similar to that of the Phillips catalyst. Immobilization of CrO 2 Cl 2 or related chromates on silica was investigated to obtain well-defined Cr VI -dioxo surface species.…”

Catalytic Olefin Polymerization

“…Union Carbide has developed a gas phase process for ethylene polymerization [23,29,30] by employing chromocene and bis(triphenylsilyl) chromate supported over silica-alumina, as catalysts. The chromocene-based catalyst is preferably activated by alkyl aluminum alcoholates.…”