A Theoretical Study of a Methylaluminoxane‒Modified Neodymium Ziegler–Natta Catalyst System for the Polymerization of 1,3‒Butadiene. Part 2. Formation Active Sites of Polymerization

Abstract

In this study, quantum chemistry calculations were used to perform comparative theoretical modeling of the active sites formation in 1,3‒butadiene polymerization using neodymium Ziegler‒Natta catalysts. The effect of chloride ion content and methylaluminoxane (MAO) as a modifier on their activity was examined. It was found that the use of MAO leads to an increase in the positive charge on the neodymium atom and a strengthening of the coordination interaction between the active site and the monomer. Thermodynamic analysis revealed that the formation of MAO‒modified active sites is energetically more favorable for less chlorinated structures. It was also found that the effect of MAO leads to the formation of complexes capable of exhibiting catalytic activity even in the absence of chlorides, while an excess of chloride ions, conversely, leads to the displacement of MAO from the active sites.