Origin of broad molecular weight distribution of polyethylene produced by Phillips-type silica-supported chromium catalyst

The origin of the broad molecular weight distribution of polyethylene produced by Phillips-type silica-supported chromium (Cr/SiO2) catalysts was studied by density functional calculations using active site models with various coordination environments. Difference of the coordination environment of chromium showed remarkable variations for both of the insertion and the chain transfer energies, resulting in a broad range of molecular weight from 10(2) to 10(10) g/mol at 350K. The results clarified that the special catalytic property of Cr/SiO2 for broad molecular weight distribution is attributed to the heterogeneity of the coordination environment of the chromium species. (C) 2011 Elsevier B.V. All rights reserved.