Dialkylzinc Compounds as Chain Transfer Agents in Ethylene and Propylene Polymerizations Catalyzed by Metallocene Catalysts

Dialkylzinc compounds (ZnR₂) with the alkyl groups of different steric hindrance were used as chain transfer agents in ethylene and propylene polymerizations catalyzed by two conventional metallocene catalysts including rac-Et(Ind)₂ZrCl₂ and rac-Me₂Si[2-Me-4-Ph-Ind]₂ZrCl₂. In general, catalyst activities for ethylene polymerizations are barely affected by chain transfer agents, regardless of the R type; however, there are significant activity reductions in propylene polymerizations when the R in ZnR₂ is less hindered, and as R becomes bulkier, catalyst activities are gradually restored. ZnR₂ and metallocene catalyst active site tend to form a reversible and catalytically inactive complex, thus the geometry congested ZnR₂ would reduce complex formation tendency and hence decreased its negative effect on catalyst activities.