In Situ ATR-FTIR Studies on MgCl2-Diisobutyl Phthalate Interactions in Thin Film Ziegler-Natta Catalysts

To study the surface structure of MgCl2 support and its interaction with other active components in Ziegler-Natta catalyst, such as electron donors, we prepared a thin film analogue for Ziegler-Natta ethylene polymerization catalyst support by spin-coating a solution of MgCl2 in ethanol, optionally containing a diester internal donor (diisobutyl-ortho-phthalate, DIBP) on a flat Si crystal surface. The donor content of these films was quantified by applying attenuated total internal reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). Changes in the interaction of DIBP with MgCl2 at various temperatures were monitored by in situ ATR-FTIR. Upon increasing the temperature, a shift in the (C=O) band toward lower wavenumbers was observed together with the depletion of (O-H) stretching band due to the desorption of residual ethanol. We assign this shift to gradual redistribution of adsorbed DIBP from adsorption sites on the MgCl2 (104) surface toward the more acidic MgCl2 (110) surface. The morphologies of MgCl2 and MgCl2/DIBP films were studied by transmission electron microscopy (TEM) revealing a preferential orientation of ClMgCl layers (001) parallel to the lateral film dimensions. This orientation becomes more pronounced upon annealing. In the absence of donor, the MgCl2 grow in to large crystals aligned in large domains upon annealing. Both crystal growth and alignment is impeded by the presence of donor.