Macromol. React. Eng. 8/2009

Macro Chemistry & Physics

Terano

2014

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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.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Dwivedi

Macro Chemistry & Physics

Terano

2014

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“…The morphology of obtained polymer/catalyst particles was observed by scanning electron microscopy (Hitachi S‐4100) based on a previously developed procedure 19. The number‐average molecular weight ($\overline {M} _{{\rm n}} $ ) and molecular weight distribution (MWD) were determined with gel permeation chromatography (Waters Associates, ALC/GPC 150C) operated at 140 °C using o ‐dichlorobenzene as the medium.…”

Section: Methodsmentioning

confidence: 99%

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

Macro Reaction Engineering

Sano

Ikeya

et al. 2012

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Stopped‐flow (SF) polymerization is a powerful tool to investigate the nature of the active site of heterogeneous Ziegler‐Natta catalysts, but poor polymer yields due to short polymerization times limit detailed structural analyses of the obtained polymer. A new large‐scale SF polymerization system is described in which an arbitrary volume of slurry can be transferred to obtain a polymer yield sufficient for a variety of analytic purposes. The developed LSF system is proven to be highly scalable and stable, leading to reproducible polymerization in an expanded time range from 0.03 s to a few seconds. The accurate polymerization below 0.1 s is promising for future studies to evaluate accurate kinetics as well as dormant processes in Ziegler‐Natta olefin polymerization.

“…The effectiveness of this quenching and stabilization procedure was well established for morphological study, especially at a low polymer yield, in our previous paper. [21] After several washings, the particles were dried in vacuo and kept in a vial under inert atmosphere.…”

Section: Propylene Polymerizationmentioning

confidence: 99%

“…In this study, the living morphology development at the very initial stage including the pore filling, first fragmentation, and further development, was continuously captured for propylene polymerization by means of the stopped-flow technique, combined with the previously established quenching technique. [20,21] A spherical Mg(OEt) 2 -based ZN catalyst was employed, which shows the highest performance in propylene polymerization and random copolymerization with ethylene. Although Mg(OEt) 2 -based ZN catalysts possess the greatest flexibility in tuning the catalyst particle size, i.e., the final polymer particle size, particle morphology development is poorly understood.…”

Section: Introductionmentioning

confidence: 99%

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

Macro Chemistry & Physics

Thang

Binh

et al. 2011

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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