Factors affecting the role of SiO2 in MgCl2‐supported Ziegler‐Natta copolymerization catalysts

This paper describes the roles of silica (SiO2), the butoxy ligand (OBu) and ethyl benzoate (EB) on ethylene/1‐butene copolymerization with MgCl2/SiO2‐supported titanium catalysts. The distribution of SiO2 and of the elements Mg and Ti was observed by means of an energy‐dispersed X‐ray micronalyzer on a scanning electron microscope (SEM). An inversed Si/Mg ratio results, at invariant Ti/Mg ratio andOBu content, in higher catalyst efficiency and higher comonomer incorporation, with a correspondingly decreased crystallinity of the copolymers. Thus, the inert carrier SiO2 favors copolymerizability, as seen from the values of the reactivity ratios. The copolymer compositional distribution is also affected by the SiO2 content, as seen from the DSC curves of the copolymers. As to the copolymer morphology, addition of SiO2 makes the copolymer particles larger and more uniform.