Unraveling the Reactivity of SiO2-Supported Nickel Catalyst in Ethylene Copolymerization with Polar Monomers: A Theoretical Study

Understanding the catalytic behavior of heterogeneous systems for the copolymerization of ethylene with polar monomers is essential for developing advanced functional polyolefins. In this study, we conducted a quantum chemical investigation of the SiO₂-supported Ni-allyl-α-imine ketone catalyst (Ni-OH@SiO₂) to uncover the factors governing monomer insertion, selectivity, and reactivity. Using DFT calculations and energy decomposition analysis (ALMO-EDA), we evaluated the coordination and insertion of six industrially relevant polar monomers, comparing their behavior to ethylene homopolymerization. Our results show that special polar monomers (SPMs) with aliphatic spacers, such as vinyltrimethoxysilane (vTMS) and 5-hexenyl acetate (AMA), exhibit favorable insertion profiles due to enhanced electrostatic and orbital interactions with minimal steric hindrance. In contrast, fundamental polar monomers (FPMs), including methyl acrylate (MA) and vinyl chloride (vCl), show higher activation barriers and increased Pauli repulsion due to strong electron-withdrawing effects and conjugation with the vinyl group. AMA displayed the lowest activation barrier (7.4 kcal/mol) and highest insertion thermodynamic stability (-17.6 kcal/mol). These findings provide molecular-level insight into insertion mechanisms and comonomer selectivity in Ni-allyl catalysts supported on silica, extending experimental understanding. This work establishes key structure-reactivity relationships and offers design principles for developing efficient Ni-based heterogeneous catalysts for polar monomer copolymerization.