Polymer Bulletin, Vol.46, No.2-3, 205-213, 2001
Influence of zirconocene structure and propene content on melt rheology of polyethene and ethene/propene copolymers
Ethene was homo- and copolymerized in the presence of methylaluminoxane (MAO)-activated zirconocenes comprising (Me5Cp)(2)ZrCl2 (Cp*) and racemic dimethylsilylene-bis[-2-methyl-indenyl]-bridged zirconocene dichloride where the ligand framework was varied by benzannelation (MBI), LC-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 much greater than 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 (delta 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.