Synthesis and evaluation of mono(phenoxy-imine) titanium complexes attached to a single polystyrene chain end for ethylene polymerization

Abstract

Monodisperse polystyrene (PS) chains with different lengths are synthesized by atom transfer radical polymerization (ATRP), serving as soluble supports for attaching mono(phenoxy-imine) metal complexes in the chain end. For ethylene polymerization, the PS chain-supported titanium (Ti) complexes exhibit unique catalytic features such as higher activity. Their performance in ethylene polymerization and kinetic examination is extensively investigated to uncover the influence mechanism of support chain length. Initially, the catalytic activity of the supported catalysts increases with the support chain length, but then decreases. Effective preservation by the support prevents catalyst deactivation and enhances the concentration of active sites [C*], leading to increased activity. However, the decline in activity is attributed to the exceptionally long support chain, impeding ethylene diffusion and leading to a reduction in ethylene concentration [M] around active sites. As the support chain length increases, the molecular weight (Mw) of the produced polyethylene (PE) decreases. The nascent polyethylene obtained from supported catalysts displays a uniform petal-like and shish-kebab morphology. The well-defined nature of these PS chain-supported catalysts provides a powerful tool for studying interactions between active centers and supports, offering insights that can guide the design of catalysts.