Initial Particle Morphology Development in Ziegler‐Natta Propylene Polymerization Tracked with Stopped‐Flow Technique

Abstract

In this study, the particle morphology development at the very initial stage of propylene polymerization using a spherical Mg(OEt)2‐based ZN catalyst was precisely tracked by applying stopped‐flow and short‐time slurry polymerizations. Electron microscope observation and mercury porosimetry derived a comprehensive view of the initial particle morphology development. The polymer first filled macropores, which were mainly located in the middle layer of the catalyst particles, then caused the fragmentation of the middle layer, and finally triggered the fragmentation of the particle core in a stepwise manner. Thus, key effects of the layered catalyst architecture and spatial distribution of macropores were discovered on the initial morphology control of catalytic olefin polymerization. magnified image

Kinetics of short‐duration ethylene–propylene copolymerization with MgCl2‐supported Ziegler–Natta catalyst: Differentiation of active centers on the external and internal surfaces of the catalyst particles

“…[1][2][3] However, there are still many unsolved mechanistic problems in this group of important industry catalysts, among them are the formation or initiation of active centers, distribution of multiple active centers, and correlations between polymer chain structure and active center structure. [13][14][15] A high proportion of potential active species cannot be activated at the beginning of polymerization when the primary particles are tightly packed in the particle. 4,[8][9][10] In our previous work, 10 formation of active centers in the induction period of ethylene polymerization with MgCl 2 -supported ZN catalyst was experimentally studied.…”

“…Formation of the active centers in the initial stage of olefin polymerization has been studied by several research groups in the past, [4][5][6][7] but only a few literatures studied the active center formation process by tracing the change of active center concentration in the induction period. 15 Only after complete particle disintegration with help of the polymer phase that these active species can be reached by the cocatalyst and monomer for activation and launching of the polymerization. The number of active centers was found to increase with the polymerization time in two stages, and the polymer-catalyst particles underwent evident disintegration during the second induction period.…”

Development of a Large‐Scale Stopped‐Flow System for Heterogeneous Olefin Polymerization Kinetics

“…They also succeeded to fabricate poly(propylene) ‐block‐ poly(propylene ‐co‐ ethylene) copolymer using a MgCl 2 ‐supported Ziegler‐Natta catalyst through a quasi‐living three‐vessel SF polymerization. In addition, the precise control of the polymerization time at an early stage was exploited to study polymer/catalyst morphology developments, exploring the importance of catalyst macropores in the initial fragmentation process 17…”

Controlling Polyolefin Properties by In‐Reactor Blending: 2. Particle Design

“…Particle morphology development of polyolefins, in particular polyethylene, over a Ziegler–Natta catalyst is a complex matter and is not yet clearly understood 9–11…”

“…Polymer particle development, particularly during the first few (milli)‐seconds is commonly accepted to play the key function in polymer morphology control 11. Nevertheless, this is mainly considered for single‐stage polymerizations and not for multi‐stage processes, taken into account that changing the polymerization conditions can have an effect on the particle morphology, which is particularly important for industry 7, 15.…”