Elastomeric properties of ethylene/propylene copolymers prepared by zirconocene/methylaluminoxane catalysts

Ethylene/propylene copolymers (EPM) have been prepared by a liquid propylene suspension process, using homogeneous catalysts based on nonbridged zirconocenes and methylaluminoxane (MAO). When bis(η⁵-cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂), bis(η⁵-cyclopentadienyl) dimethyl zirconium (Cp₂ZrMe₂) and bis(η⁵-cyclopentadienyl), dibenzyl zirconium (Cp₂ZrBz₂) were used as catalyst components, EPM having low average molecular weight (MW) were in general obtained in low yield. On the contrary, a very large improvement of productivity and MW was observed when bis(η⁵-indenyl)zirconium dichloride (Ind₂ZrCl₂) and bis(η⁵-indenyl) dimethyl zirconium (Ind₂ZrMe₂) as well as bis(η⁵-tetrahydroindenyl)zirconium dichloride [(IndH₄)₂ZrCI₂] were employed in combination with MAO. In particular, this last catalytic system allowed one to obtain EPM with a narrower distribution of MW in addition to the above characteristics. Better performances, in terms of rheological and elastomeric properties, were also found for the crude and vulcanized samples prepared by (IndH₄)₂ZrCl₂/MAO catalyst.