Mechanistic Insights into Comonomer Effects on Propylene Polymerization over TiCl3 Catalysts

Incorporating comonomers in propylene polymerization plays a critical role in tuning the physical and chemical properties of the resulting polymers. In this study, the impact of three developed comonomers on propylene polymerization over the triethylaluminum-treated TiCl3 catalyst was investigated in detail by DFT. The results indicate that these comonomers remain highly stable under actual catalytic conditions, with their ions or functional groups showing a low propensity for detachment, which would otherwise poison the catalyst or disrupt the polymerization process. However, the three comonomers on the surface with a strong adsorption capacity may compete with propylene for adsorption, which will affect the polymerization. Among them, Vinyltrimethoxysilane, which exhibits the strongest adsorption ability, tends to form bonds with the ethyl on the catalyst surface, leading to catalyst poisoning and inhibiting the reaction. In contrast, 5-hexenyl methyldichlorosilane demonstrates relatively higher activity due to its balanced properties. The order of reactivity in the polymerization reaction: 5-hexenyl methyldichlorosilane > 5-hexenyldichlorophosphonane > vinyltrimethoxysilane. This work provides fundamental mechanistic insights into how functional comonomers interact with catalytic active sites through adsorption, competitive reactions, and insertion processes. Additional free energy analysis at 333 K confirms that these mechanistic trends remain unchanged under realistic reaction conditions. Rather than directly simulating industrial catalysts, the present study focuses on a model TiCl3 system to elucidate intrinsic structure-reactivity relationships. These findings contribute to a deeper understanding of comonomer effects in olefin polymerization at the molecular level.