Active Sites in a Heterogeneous Organometallic Catalyst for the Polymerization of Ethylene

Abstract

Heterogeneous derivatives of catalysts discovered by Ziegler and Natta are important for the industrial production of polyolefin plastics. However, the interaction between precatalysts, alkylaluminum activators, and oxide supports to form catalytically active materials is poorly understood. This is in contrast to homogeneous or model heterogeneous catalysts that contain resolved molecular structures that relate to activity and selectivity in polymerization reactions. This study describes the reactivity of triisobutylaluminum with high surface area aluminum oxide and a zirconocene precatalyst. Triisobutylaluminum reacts with the zirconocene precatalyst to form hydrides and passivates −OH sites on the alumina surface. The combination of passivated alumina and zirconium hydrides formed in this mixture generates ion pairs that polymerize ethylene.

A general strategy for heterogenizing olefin polymerization catalysts and the synthesis of polyolefins and composites

“…For example, a large amount of expensive and sensitive aluminum cocatalyst is usually required, which poses the additional issue of side reactions with polar comonomers. The interactions of the active site with the support play important roles in determining the properties of the catalysts 29 . However, these interactions may be significantly weakened or altered by Lewis basic polar-functional groups.…”

A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R3Si+ Species

“…[4] These mixtures can evolve into well-defined surface species that produce narrow molecular weight distributions of polyolefin. [5] Ni-or Pd-catalysts for olefin polymerization incorporate monomers containing heteroatoms, [6] but are generally incompatible with this heterogeneous work-flow. A small family of (α-diimine)NiBr 2 pre-catalysts are active in the presence of alkylaluminum activators and SiO 2 or MgCl 2 , but produce broad molecular weight polymers; incorporation of polar monomers was not reported.…”

“…[21] Therefore, reactions of 1 with vinyl chloride should result in the formation of [(N^N)PdÀ Cl][(R F O) 3 AlÀ OSi�)] (2) and propene, Equation (2), and quantification of propene would correlate with the quantity of PdÀ Me + in 1 capable of inserting an olefin. A similar method was used to quantify active ZrÀ H + sites in a ternary heterogeneous catalyst, [5] and is complementary to other quantification methods that involve contacting an active catalyst with an olefin that inhibits chain growth or quenching an active catalyst with a substrate containing a label. [22] Contacting 1 or 1-13 C with vinyl chloride ( � 100 equiv per Pd) and heating to 60 °C reproducibly results in the formation of 0.050 � 0.003 mmol propene g À 1 .…”

The coordination chemistry of oxide and nanocarbon materials

“…12. 154 Typical mixtures containing 12 : 1 Cp b 2 ZrCl 2 :Al i Bu 3 ([Zr] = 150 μmol g Al 2 O 3 −1 ) evolve under the reaction conditions to give very active catalysts (8.4 × 10 7 g PE mol Zr −1 h −1 ), but only 0.65 μmol Zr g cat −1 is adsorbed on the Al i Bu 3 /Al 2 O 3 support. Contacting Al i Bu 3 and Al 2 O 3 results in the formation Al i Bu 3 /Al 2 O 3 containing a distribution of Al– i Bu sites on the alumina surface, but the organoaluminum sites are not effective activators of Cp b 2 ZrCl 2 in the absence of exogenous Al i Bu 3 in solution.…”