Attempts made to heterogenize MAO via encapsulation within silica through a non-hydrolytic sol–gel process

Methylaluminoxane, tetraethylaluminum and trimethylaluminum were encapsulated within a silica-based material using a non-hydrolytic sol–gel process. Mixed oxides were also produced by combining silica precursors with Mg(OEt)2, MgCl2 and MgCl2·6H2O. The resulting xerogels were characterized by a series of complementary techniques to determine the elemental, the structural, the textural and the morphological characteristics of the encapsulated cocatalysts. The nature of the alkyl aluminum strongly affects the gelification time. The amount of encapsulated cocatalyst did not appear to be affected by the alkylaluminum volume, but the silica network and the xerogel organization were, according to infrared and X-ray diffraction measurements. There was a large surface reduction for the encapsulated systems compared with the silica that was synthesized under the same conditions. The resulting supported alkylaluminum was evaluated in the polymerization of ethylene using Cp2ZrCl2 as the catalyst in the presence and the absence of external MAO. The encapsulated cocatalysts were not shown to be active in the Al/Zr range of 250–500. For the mixed systems that combined homogeneous MAO with encapsulated MAO, the addition of the encapsulated cocatalyst did not appear to affect the catalyst activity. The molecular weight of the polymers that were obtained by using the encapsulated cocatalyst was lower than the molecular weight of the polymers that were obtained by using the homogeneous catalyst. Nevertheless, the polydispersity of the polymers that were obtained in the presence of the encapsulated cocatalyst was greater than the polydispersity of the polymers that were produced with the homogeneous catalyst or the impregnated MAO.