Ethene/Propene Copolymerization from Metallocene-Based Catalytic Systems:  Role of the Alumoxane

Ethene/propene copolymerizations were performed with a catalytic system composed of a metallocene and an alumoxane. The role played by the alumoxane was investigated by comparing the effects of three different compounds: poly(methylalumoxane) (MAO), tetraisobutylalumoxane (TIBAO), and tetraisooctylalumoxane (TIOAO). A thorough comparison was performed using rac -ethylenebis(tetrahydroindenyl)zirconium dichloride ( r -EBTHIZrCl 2 ) as the metallocene. Further data were obtained with isopropylidenebis(3- tert -butyl-cyclopentadienyl)zirconium dichloride ( r- Me 2 C(3- t- BuCp) 2 ZrCl 2 ) and dimethylsilylenebisfluorenylzirconium dichloride (Me 2 SiFlu 2 ZrCl 2 ). Main parameters of copolymerization and copolymers were determined. MAO gives rise to higher polymerization activities and lower molecular masses of the copolymers. A higher 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 comonomers. The copolymer microstructure is essentially due to the metallocene, even though a MAO-based catalytic system shows a slightly higher reactivity for propene.