Ethene/propene copolymerization from metallocene-based catalytic systems: Role of the alumoxane

Ethene/propene copolymerizations were performed with a catalytic system com posed of a metallocene and an alumoxane. The role played by the alumoxane w as investigated by comparing the effects of three different compounds: poly (methylalumoxane) (MAO), tetraisobutylalumoxane (TIBAO), and tetraisooctyla lumoxane (TIOAO). A thorough comparison was performed using rac-ethylenebis (tetrahydroindenyl)zirconium dichloride (r-EBTHIZrCl2) as the metallocene. Further data were obtained with isopropylidenebis(3-tert-butyl-cyclopentadi enyl)zirconium dichloride (r-Me2C(3-t-BuCp)(2)ZrCl2) and dimethylsilylenebi sfluorenylzirconium dichloride (Me(2)SiFlu(2)ZrCl(2)). Main parameters of c opolymerization and copolymers were determined. MAO gives rise to higher po lymerization activities and lower molecular masses of the copolymers. A hig her productivity is obtained with TIOAO than with TIBAO, whereas these two alumoxanes behave very similarly in determining the copolymer properties. A statistical elaboration allowed to derive the reactivity ratios of the com onomers. The copolymer microstructure is essentially due to the metallocene , even though a MAO-based catalytic system shows a slightly higher reactivi ty for propene.