Density functional study on the role of electronic factors in variation of polymerization activity for Ziegler-Natta catalyst

Abstract

The role of electronic factors in the variation of activity of Ziegler-Natta (ZN) catalysts having chloride, alkoxy and other ligands for ethylene and propylene polymerization has been investigated using density functional calculations at B3LYP/LANL2DZ level. The barriers for olefin insertion into [TiCl₂CH₃]⁺ for ethylene and propylene are comparable whereas for catalysts with alkoxy and non-alkoxy ligands having varying heteroatoms, the insertion barriers for propylene are about 3-6 kcal/mol higher than the corresponding ethylene insertion barriers. This supports the experimental observation that the propylene polymerization with ZN catalyst having alkoxy and non-alkoxy ligands has very low catalytic activity as compared to that for ethylene polymerization whereas [TiCl₂CH₃]⁺ polymerizes both ethylene and propylene.