Influence of zirconocene structure and propene intent on melt rheology of polyethene and ethene/propene copolymers

Summary

Ethene was homo- and copolymerized in the presence of methylaluminoxane (MAO)-activated zirconocenes comprising (Me₅CP)₂ZrCl₂ (Cp^*) and racemic dimethylsilylene-bis[-2-methyl-indenyl]-bridged zirconocene dichloride where the ligand framework was varied by benzannelation (MBI), 4-phenyl (MPI), and 4- naphthyl (MNI) substitution. Zero shear viscosity and shear thinning of the ethene homopolymers increased as a function of the catalyst system with MNI • MPI > MBI >> Cp^* and were correlated with the presence of long chain branches formed via reinsertion of vinyl-terminated polymer chains. The ranking was confirmed using the reduced vanGurp Palmen plot (δ vs. ?G^*?/G_N ⁰) being less sensitive on molecular weight for polyolefin materials. Poly(ethene-co-propene)s (EP) containing 17 and 30 wt.-% propene were long chain branched as reflected by pronounced viscosity build- up at low angular frequency and increased shear thinning at higher angular frequency, whereas with propene comonomer content exceeding 46 wt.-% EP was essentially linear.