Exploring cocatalyst type effect on the Ziegler–Natta catalyzed ethylene polymerizations: experimental and DFT studies
Maryam Masoori, Mehdi Nekoomanesh, Sergio Posada‐Pérez, Reza Rashedi, Naeimeh Bahri‐Laleh
Abstract
Abstract Due to the important role of cocatalyst in the polymerization process employing industrially favored Ziegler–Natta catalysts, its effect on kinetic behavior, catalyst activity, and polymer properties is discussed. In this paper, triethyl aluminum (TEA) and triisobutyl aluminum (TIBA) have been used as the main cocatalyst ingredient with 10–20 mol percent of diethyl aluminum chloride (DEAC) and ethyl aluminum dichloride (EADC) cocatalysts, being neat TEA the cocatalysts with the highest activity. Moreover, TEA-DEAC and TEA-EADC cocatalysts revealed a built-up kinetic profile, while TIBA-DEAC and TIBA-EADC show a decay-type kinetic curve. According to melt flow index results, no considerable change in flowability was detected in the synthesized polyethylenes (PE). On the other hand, the ethylene insertion and chain termination mechanisms were investigated by means of density functional calculations using Ti active center located in (110) and (104) facets of the MgCl 2 surface. To shed light on the bulkiness level of employed cocatalysts, buried volume (V Bur ) together with the two-dimensional map of cocatalyst systems were considered. Higher V Bur of TIBA complex can explain its lower activity and decay type kinetic profile obtained by experimental studies.