Study of the catalytic species metallocene/MAO and metallocene/TMA by cyclic voltammetry

Abstract

In this paper, an electrochemical study of the metallocene/methylaluminoxane (MAO) and metallocene/trimethylaluminium (TMA) species is presented. The metallocenes used were [(CH3)2Si(Cp)2ZrCl2] and [(Cp)2ZrCl2]. The evaluation of the Metallocene/MAO and Metallocene/TMA systems was based on the analysis of the redox potentials of the solutions with different Al/Zr molar ratios using acetonitrile as solvent. The results obtained for Al/Zr ratios lower than 30, suggested that in presence of TMA or MAO, the formed monomethylated species are [(L)ZrIV(CH3)Cl], L = cyclopentadienyl (Cp)2 or (CH3)2Si(Cp)2. For Al/Zr molar ratios higher than 30, the results obtained in TMA presence are in agreement with the formation of the species [(L)ZrIV(CH3)( -CH3)Al(CH3)2]+, while in MAO presence the ionic pair,[(L)ZrIVCH3]+[MAOCl]−, is formed. There’s a general agreement that these are active species in olefin polymerization.