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Specific Roles of Al‐Alkyl Cocatalyst in the Origin of Isospecificity of Active Sites on Donor‐Free TiCl 4 /MgCl 2 Ziegler‐Natta Catalyst
Author(s) -
Liu Boping,
Nitta Takashi,
Nakatani Hisayuki,
Terano Minoru
Publication year - 2003
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.200290022
Subject(s) - stereospecificity , chemistry , alkyl , active site , catalysis , active center , polymer chemistry , ziegler–natta catalyst , polymerization , fractionation , substrate (aquarium) , natta , medicinal chemistry , organic chemistry , polymer , ethylene , oceanography , geology
The formation, deactivation and transformation of stereospecific active sites on the donor‐free TiCl 4 /MgCl 2 catalyst induced by short time reaction with triethylaluminium (TEA) cocatalyst (pretreatment time: 0 ∼ 60 s) were investigated by stopped‐flow propylene polymerization combined with temperature rising elution fractionation (TREF) and gel permeation chromatography (GPC) methods. We got the first report that the origin of isospecificity of active sites derived from the catalyst substrate and cocatalyst were individually observed without and with TEA pretreatment, respectively. Based on the three‐sites model of Corradini and Busico et al., a plausible mechanism of the formation and transformation of stereospecific active sites was proposed using active sites models in terms of specified roles of Al‐alkyl cocatalyst. It was demonstrated that the introduction of bulky alkyl groups instead of chlorine atoms into the neighborhood of active sites seems to be crucial for the generation of active sites with the highest isospecificity.