Observation on inhibition of Ti3+ reduction by fumed silica addition in Ziegler-Natta catalyst with in situ ESR

This study focused on elucidation of effect of fumed silica added in the commercial Ziegler-Natta catalysts by physical solid–solid stirring. The added fumed silica seemed to cover around the catalyst revealed by SEM-EDX and apparently resulted in decreased activity of ethylene polymerization, but increased molecular weight of polyethylene as measured by GPC. Based on the in situ ESR measurement, it can be concluded that fumed silica can inhibit the reduction of Ti3+ by triethylaluminum (TEA). It is suggested that the delay reduction of Ti3+ may be beneficial for propylene polymerization.