Planar model system for olefin polymerization: the Phillips CrOx/SiO2 catalyst

A planar CrOx/SiO2/Si(100) model for the Phillips ethylene polymerization catalyst has been prepared by spincoat impregnation from an aqueous solution of CrO3. The model catalyst polymerizes ethylene from the gas phase at 160°C with a constant activity and forms a 400 nm thick layer of polyethylene in 1 h. The superior definition of the polymer films produced on this catalyst and the control over the distribution of active sites on its flat surface make this model catalyst an ideal substrate for kinetic studies on catalytic polymerization and for morphologic studies of the polymer product by scanning force microscopy. At extremely low catalyst loading we observe isolated polymer islands formed on single chromium sites. The work also opens attractive opportunities for future studies of nascent morphology of catalytically formed polymers.