UV VISIBLE SPECTROSCOPIC STUDY OF THE RAC-ET(IND)(2)ZRCL2/MAO OLEFIN POLYMERIZATION CATALYTIC-SYSTEM, 1 - INVESTIGATION IN TOLUENE/

The U.V./visible spectrum of the rac-Et(Ind)(2)ZrCl2/methylaluminoxane (MAO) catalytic system in toluene at 20 degrees C, which is related t o the 'ligand to metal charge transfer' bands (LMCT), varies greatly w ith the MAO/Zr ratio (mole ratio Al/Zr). Indeed, for MAO/Zr ratios <30 , a hypsochromic shift of the absorption band is observed and is expla ined by monomethylation of the metallocene dichloride. Conversely, a p rogressive bathochromic shift of the absorption band is observed for M AO/Zr ratios ranging from 30 to 2000. This behavior is interpreted by the formation of an increasing proportion of dissociated to associated zirconocenium species [L2ZrX](+) [MAOCl](-). The lambda(max) changes of the U.V./visible spectrum of the rac-Et(Ind)(2)ZrCl2/MAO system wer e correlated with its catalytic activity for the hex-l-ene polymerizat ion. Moreover, a conductimetric study performed on the rac-Et(Ind)(2)Z rCl2/MAO system for different MAO/Zr ratios is also in agreement with the formation of ionic species with different nature and ionization de grees.