Characterization of Zirconocene Catalysts and of Polyethylenes Produced Using Them

Our work of the last two years concerning the use of zirconocene catalysts in the production of polyethylene (PE) is reviewed. In earlier studies, using Cp2ZrCl2, the metal loading capacity of different commercial silicas, namely Grace 948, 952 and 956 was determined by Rutherford backscattering spectrometry (RBS). The adsorption isotherms of Al from methylaluminoxane (MAO) and trimethylaluminium (TMA) cocatalysts were determined using the 27Al(p, γ)28Si nuclear reaction at 1.6 MeV. In the present work we could determine the Al/Si ratio with the simultaneous induction of nuclear reactions with 27Al and 28Si using protons of 1.7 MeV. After replacing Cp2ZrCl2 by (nBuCp)2ZrCl2, an exhaustive search of activation, grafting and polymerization conditions (monitored by RBS, infrared spectroscopy, differential scanning calorimetry, and gel permeation chromatography) allowed us to set an optimized protocol that yielded polyethylene with thermal, molecular weight and composition characteristics typical of high-density PE.