Understanding the Chemical and Physical Transformations of a Ziegler–Natta Catalyst at the Initial Stage of Polymerization Kinetics: The Key Role of Alkylaluminum in the Catalyst Activation Process

Abstract

An improved stopped‐flow (SF) technique is employed to clarify the origin of kinetics in propylene polymerization with a Mg(OEt)2‐based Ziegler–Natta catalyst. Polymerization in the range of 0.1–5 s exhibits a kinetic transition from a linear development to a build‐up‐type development of the yield. It is found that a lower alkylaluminum concentration leads to a lower activity in the linear regime, whereas the extent of the activation becomes greater in the build‐up regime. The origin of these kinetic behaviors is studied using scanning electron microscopy (SEM) for catalyst/polymer particles and cross‐fractionation analyses for polymer structures. It is found that the kinetic transition mainly arises from the fragmentation of the catalyst particles and resultant increase in the active site concentration. The fragmentation manner strongly depends on the alkylaluminum concentration, which affects not only the amount, but also the placement of initial polymer formation. The nature of the active sites varies as a result of an aging effect with alkylaluminum: their stereospecificity, propagation rate constant, and tolerance for chain transfer reaction increase as the polymerization progresses.

The 60th Birthday of Prof. Minoru Terano

“…The 60th Birthday of Prof. Minoru Terano www.mcp-journal.de over conventional Ziegler-Natta [1] and newly developed single-site catalytic systems, [2] further development of the Phillips system, [3] and fi nely tuned metallocence systems. [4] Moreover, late-transition-metal complexes are promising for industrial processes producing novel advanced polyolefi n materials, [5] while computation simulation is promising for the design and prediction of effective catalysts, along with the production of advanced polyolefi ns.…”

Kinetics of short‐duration ethylene polymerization with MgCl2‐supported Ziegler–Natta catalyst: Two‐stage initiation evidenced by changes in active center concentration

“…Among these problems, the formation or initiation of catalytic centers in the first few minutes of olefin polymerization is especially important, as it will profoundly influence the kinetics, particle morphology, and polymer chain structure of the whole polymerization process. Many researchers have reported the kinetics and particle morphology of ZN‐catalyzed olefin polymerization in the initial stage . In a recent work, Busico et al .…”

Heterogeneous Ziegler–Natta catalysts with various sizes of MgCl2 crystallites: synthesis and characterization

“…SEM pictures allow the size of the nanoparticles in a Ziegler-Natta catalyst to be estimated [14,16,27]. For example, Busico et al [28].…”

“…SEM pictures were used to find out whether a correlation exists between the size of the nanoparticles [16] in the produced material and the crystal thickness measured by X-ray at 50° 2θ. With the help of IR spectroscopy the positions of the chlorine and the alchoholate groups on Mg, Al and Ti were determined.…”