Comparison of ethylene-propylene copolymers obtained with Ti, V and Zr catalyst systems

Ethylene and propylene were copolymerized in n-heptane in the presence of high activity heterogeneous MgCl₂/TiCl₄ catalyst and homogeneous VOCl₃ and Cp₂ZrCl₂ catalysts to study the effect on the catalyst to the microstructure and molecular weight distribution of the copolymer. The copolymer obtained with the zirconium catalyst was much more random in structure than that obtained with the vanadium and titanium catalysts and the molecular weight distribution was very narrow. Ethylene and propylene were also copolymerized in liquid propylene with MgCl₂/TiCl₄ and VOCl₃ catalyst systems. These copolymers were column fractionated and the fractions were analysed by NMR spectroscopy and DSC. The fractions of the copolymer obtained with the titanium catalyst was found to have broader distribution in composition than the copolymer obtained with the vanadium catalyst. This probably explains the traces of crystallinity in the copolymer prepared with the titanium catalyst. However, no effect was seen on the glass transition temperature.