Ethylene homo‐ and copolymerization over MgCl₂‐TiCl₄ catalysts: Polymerization kinetics and polymer particle morphology

Abstract

Three procatalysts of the MgCl 2 /TiCl 4 type, differing mainly in their morphological characteristics, were investigated in ethylene polymerization and ethylene-1-butene copolymerization. Apparently, hydrogen has an intrinsic and general deactivating effect but it can also play an activating effect in homopolymerization. This peculiarity was found to be related to a catastrophic breakage of the polymer/catalyst particles during growth and thus to the exposure of new active centers. In this case the kinetic profiles are irregular and characterized by one or more secondary peaks which reflect the moment when this morphology-driven rate-enhancement effect takes place. In general, the prepolymerization of the procatalysts with propylene tends to slightly enhance homopolymerization rate, to slow down copolymerization rate and to stabilize the morphology of the growing polymer particles, thus preventing the occurrence of the irregular kinetic profiles observed during homopolymerization in the presence of hydrogen. The behavior of the procatalysts investigated was found to depend on the distribution of their pore size rather than the absolute values of their porosity. Likely this is due to an easier diffusion of the monomer and a more regular and homogeneous growth of the polymer within larger as opposed to smaller pores.

Effects of MgCl2 Crystallographic Structure on Active Centre Formation in Immobilized Single‐Centre and Ziegler–Natta Catalysts for Ethylene Polymerization

“…High porosity of the support generally leads to relatively easy diffusion of the monomer, and recent studies have demonstrated that pore size is more important than overall porosity in this respect. [19] In the present work, the pore size distributions of MgCl 2 /AlR n (OEt) 3Àn supports were determined by mercury porosimetry, giving the results shown in Figure 3. Further data are given in the Supporting Information, along with pore size distributions of the MgCl 2 Á nEtOH support precursors.…”

A Novel (SiO2/MgO/MgCl2)·TiClx Ziegler–Natta Catalyst for Ethylene and Ethylene/1‐Hexene Polymerization

“…2015, 216, 1472−1482 Table 2 ); B) with Cat1 at different cocatalyst concentration (corresponding to Run 1,3,8,9 in Table 2 ). Table 2 ); B) with Cat3 at different cocatalyst concentration (corresponding to Run 17,18,23 in Table 2 ).…”

“…[ 18,19 ] Further investigation is still needed in order to elucidate the comonomer effects for Ziegler-Natta catalysts.…”

Alternation of Pore Architecture of Ziegler–Natta Catalysts through Modification of Magnesium Ethoxide

“…The obtained polymer was recovered by re-precipitation in acetone/ methanol mixture at 0 8C. The content of butyl branches as a result of 1-hexene incorporation was determined by 13 C NMR (Bruker 400 MHz). [19] …”