fvSynchronous TiCl4 immobilization and tetrahydrofuran migration in modified Ziegler-Natta catalysts.

The Ti immobilization process is directly modulated by the THF migration, which reduces the aggregation of TiCl 4 and enhances the formation of active species. [Display omitted] • Formation mechanism of the active species are traced by the in-situ spectra. • Active species distribution of the Ziegler-Natta catalyst is modulated by the THF migration. • The polyethylene with a narrow distribution is synthesized with a high activity owing to the synchronous migration of THF and immobilization of TiCl 4. Manipulating the interplay between electron donor and catalytic species is a major approach of optimizing Ziegler-Natta catalysts. To this end, it is essential to reveal the correlation between the involved dynamic processes. In this work, a greatly enhanced mobility of the internal donor tetrahydrofuran (THF) is realized even at room temperature in the MgCl 2 substrate modified with MgCl functionalized polyhedral oligomeric silsesquioxane (POSS-MgCl). A series of spectroscopic characterizations evidence that, thanks to the high mobility of THF, the immobilization of catalytic Ti species and the migration of THF occurs synchronously and leads to a nearly homogenous distribution of Ti sites. In addition, the incorporation of POSS-MgCl promotes the formation of 4-coordinated Mg sites in the substrate. The modified Ziegler-Natta catalyst shows the remarkable performance toward ethylene polymerization, featured by the high catalytic activity (21.6 × 106 g PE(mol Ti·h)−1) as well as a narrow polydiversity index (3.1) of the synthesized polyethylene. Based on these results, we propose that the Ti immobilization process is directly modulated by the THF migration in this system, which reduces the aggregation of TiCl 4 and enhances the formation of active species. [ABSTRACT FROM AUTHOR]