Preparation of Ethylene/1-Hexene Copolymers from Ethylene Using a Fully Silica-Supported Tandem Catalyst System

A silica-supported tandem catalyst system, capable of producing ethylene/1-hexene copolymers from ethylene being the single monomer, has been investigated. As tandem couple a phenoxyimine titanium catalyst for ethylene trimerization was combined with a metallocene catalyst for α-olefin polymerization. Two different approaches were pursued to combine the two catalysts as silica-supported tandem partners. The co-immobilization of the catalysts on the same support particles led to low polymerization activities and yielded products with low comonomer content due to interference of the two catalysts on the support. Immobilization of the two catalysts on separate supports prevented this interaction and led to high polymerization activities while the comonomer content of the product was controlled by the employed catalyst ratio. The copolymers obtained via the latter method were thoroughly analyzed with respect to their chemical composition distribution (CCD) by DSC-SSA, Crystaf, and HT-HPLC. The obtained data indicate a broad and in some cases bimodal CCD, which was explained by the synergy of composition drift during the polymerization and increasing diffusion limitation within the expanding polymer particle.