1 H and 13 C NMR studies of the reactions between two b-alkyl-substituted aluminoxanes obtained from the in situ Ž . Ž . ) Ž reaction between Al i-Bu , Al i-Oct and H O with two metallocenes Cp ZrCl and Cp ZrCl Cp s cyclopentadienyl, 3 3 2 2 2 2 2 ) . and Cp s pentamethylcyclopentadienyl have been performed. The b-branched aluminoxanes were obtained from the in Ž . Ž Ž . Ž .. situ reaction between Al i-R and H O at AlrH O molar ratio of 2 R s i-Bu TIBAO , R s i-Oct TIOAO . A 3 2 2 comparison of the Cp ZrCl and Cp ) ZrCl reactivity with MAO, as the reference point for aluminoxanes, as well as with 2 2 2 2 Ž . Ž . Ž . Ž . Ž . ) their parent aluminum alkyls AlMe TMA , Al i-Bu TIBA , and Al i-Oct TIOA has been made. Cp ZrCl , because 3 3 3 2 2 of steric hindrance, is less reactive than Cp ZrCl towards all aluminium compounds considered. The Cp ) Zr-i-BuCl and 2 2 2
Cp ) Zr-i-OctCl produced appear to be more stable than Cp Zr-i-BuCl and Cp Zr-i-OctCl due to the Cp ) steric hindrance, 2 2 2 which inhibits b-hydrogen eliminations. The lower reactivity of Cp ) ZrCl along with the higher stability of the zirconium 2 2 alkyls produced has allowed us to produce evidence of the greater capacity of TIOAO with respect to TIBAO for yielding alkylated ion pairs. These results explain the polymerization activities yielded by metallocenes when combined with the above aluminoxanes, that is, the Cp ZrCl activity only with MAO, and the high polymerization activities of substituted 2 2 metallocenes when b-alkyl-substituted aluminoxanes are used as cocatalysts.