The Influence of the growing polymer chain on the catalytic complex in homogeneous ziegler-natta polymerization: Density functional calculations on model systems TiCI2R+ and ZrCl2R+

The influence of the growing chain on the electronic structure of soluble Ziegler-Natta catalysts was investigated through quantum-mechanical calculations for model systems MCI₂R⁺ with M = Ti, Zr and R = C_nH_2n+1 where n = 1–7. The theoretical results show an increase in the energy of the Lowest Unoccupied Molecular Orbital (LUMO) of the cation and a decrease of the transition metal charge in the early stages of polymerization. This behaviour could explain the experimentally observed initial acceleration of the monomer insertion rate as reported in literature for ethylene polymerization with TiCp₂CH₃Cl·AlCl₂CH₃ system.