Quantitative Investigation of a Hybrid Ziegler–Natta Catalyst Support Prepared by Grafting Di(n‐butyl)magnesium onto Partially Dehydroxylated Silica

Abstract

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 (nBu(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 nBu(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 nBu(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(nBu)](n). Upon exposure of nBu(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.

Silica-supported Ti chloride tetrahydrofuranates, precursors of Ziegler–Natta catalysts

“…[10][11][12][13][14] Amorphous silica was successively employed as a support also for Ti-based Ziegler-Natta catalysts for ethylene polymerization. 9,15,16 The simple combination of titanium tetrachloride on silica yielded low-reactivity catalysts; however, the combination of a magnesium compound with a porous silica material, followed by reaction with titanium tetrachloride, resulted in a catalyst showing an enhanced reactivity and the excellent handling and polymer particle control characteristic of Phillips' chromium catalysts. 9,15,16 In contrast to chromium-based catalysts, the role of silica surface chemistry in Ziegler-Natta catalysts is often overlooked.…”

Determination of the electronic and structural configuration of coordination compounds by synchrotron-radiation techniques

“…Amorphous silica was successively employed as a support also for Ti-based Ziegler-Natta catalysts for ethylene polymerization [907,915,916]. The simple combination of titanium tetrachloride on silica yielded low-reactivity catalysts; however, the combination of a magnesium compound with a porous silica material, followed by reaction with titanium tetrachloride, resulted in a catalyst showing an enhanced reactivity and the excellent handling and polymer particle control characteristic of Phillips' chromium catalysts [907,915,916].…”

“…Amorphous silica was successively employed as a support also for Ti-based Ziegler-Natta catalysts for ethylene polymerization [907,915,916]. The simple combination of titanium tetrachloride on silica yielded low-reactivity catalysts; however, the combination of a magnesium compound with a porous silica material, followed by reaction with titanium tetrachloride, resulted in a catalyst showing an enhanced reactivity and the excellent handling and polymer particle control characteristic of Phillips' chromium catalysts [907,915,916]. In the frame of a wider work devoted to the physical-chemical characterization of silica-supported Ziegler-Natta catalysts based on tetrahydrofuranates of TiCl 4 and MgCl 2 , Groppo et al performed a detailed spectroscopic investigation on the reactivity of titanium chloride tetrahydrofuranates (TiCl 4 (thf) 2 and TiCl 3 (thf) 3 ) towards a polymer-grade silica and on the structure of the resulting Ti-grafted sites [811,917].…”

Efficient Synthesis of Low-Polydispersity UHMWPE by Elevating Active Sites on Anchored POSS Molecules

“…However, the MWD of the synthesized polymer was only slightly decreased because of the increased complexity of the surface chemical environment. 20,21 Recently, a metal−organic framework-based support was used to anchor the vanadium catalyst in a molecule-like coordination environment, which was able to synthesize the polyethylene with MWD around 3. 22 Over the past decades, polyhedral oligomeric silsesquioxane (POSS) compounds with cage structure and surface silanol groups have been widely used to develop the polyolefin catalysts.…”