Premium
Quantitative Investigation of a Hybrid Ziegler–Natta Catalyst Support Prepared by Grafting Di( n ‐butyl)magnesium onto Partially Dehydroxylated Silica
Author(s) -
Lee MingYung,
Scott Susannah L.
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201002576
Subject(s) - chemistry , protonolysis , catalysis , magnesium , siloxane , polymer chemistry , infrared spectroscopy , ligand (biochemistry) , inorganic chemistry , anhydrous , organic chemistry , polymer , biochemistry , receptor
MgCl 2 ‐modified silica is an important component of some Ziegler–Natta catalysts used in the manufacture of polyethylene. Information about the structure of the dispersed magnesium sites formed by the reaction of di‐ n ‐butylmagnesium ( n Bu 2 Mg) with silica was sought to provide a basis for understanding their subsequent interactions with transition‐metal or co‐catalyst components. From infrared spectra and elemental analysis, we deduced that n Bu 2 Mg reacts with porous silica in two ways: about half (47 %, 0.99 mmol g −1 ) is grafted through protonolysis by surface hydroxyl groups (SiOH), whereas the other half (53 %, 1.11 mmol g −1 ) reacts directly with siloxane bonds (SiOSi). In the 29 Si and 13 C CP/MAS NMR spectra of Sylopol‐2100 silica pretreated at 500 °C then modified with n Bu 2 Mg at room temperature, both alkylsilicon and alkylmagnesium sites are evident. The alkylmagnesium‐modified silica surface is proposed to contain dimers and/or tetramers with the empirical formula [SiOMg( n Bu)] n . Upon exposure of n Bu 2 Mg‐modified silica to anhydrous HCl, alkanes are liberated, hydroxyl groups are regenerated, and water is formed. The appearance of water suggests condensation of hydroxyl group pairs, induced by the coordinatively unsaturated nanoclusters (MgCl 2 ) n that arise by ligand exchange on the silica‐supported n ‐butylmagnesium oligomers.