Magnesium chloride-supported catalysts for Ziegler-Natta propene polymerization: ethyl formate as internal base

MgCl2-supports for Ziegler-Natta polymerization processes were prepared by an activation method based on the thermal removal of ethyl formate (EF) from adducts between EF and MgCl2. The various steps of activation were investigated by X-ray diffraction (XRD) and infrared spectroscopy (FT-IR) of MgCl2(EF)x adducts having 0 less-than-or-equal-to x less-than-or-equal-to 2. A subsequent titanation process of the above supports gives rise to a decrease of the EF content in the obtained products. By XRD on polycrystalline powders, the effects were investigated of the EF concentration in the titanated adducts used in Ziegler-Natta polymerization processes and having a composition [MgCl2(EF)k(TiCl4)m]. Moreover, the relationships were investigated between yield and stereospecificity in the propene polymerization tests; a maximum of isospecificity was observed for the mole ratios Ti/Mg = 0,065, EF/Mg = 0,47 and Ti/EF = 0,15. It was also demonstrated that a progressive removal of EF from the adducts gives rise to supports showing a different structural disorder in dependence on the removal time.