Metallocene catalysis was employed to prepare model polypropylenes (PP) with very high molecular weights and narrow molecular weight distributions (MWDs) of M w/M n ≈ 2, typical for “single site” metallocene catalysts. The viscoelastic properties of PP melts were investigated by means of oscillatory rheometry. Arrhenius and WLF equations were applied to model the influence of temperature on PP rheology. With very high molecular weight polypropylene samples it became possible to determine the onset of the plateau zone, reflecting the rubber-like properties of PP. For the first time plateau moduli and entanglement molecular weights M es were determined and found to be depend upon stereoregularity. The entanglement molecular weights were found to be 6900 g/mol for isotactic PP, 7050 g/mol for atactic PP, and 2170 g/mol for syndiotactic PP. This influence of stereoregularity was attributed to the different conformations of syndiotactic PP with respect to isotactic and atactic PP in PP melts.

++The viscoelastic properties of fourteen syndio-and isotactic polypropylenes (PPs) were measured in the molten state at several temperatures by means of oscillatory rheometry. Metallocene catalysis allows the control of molecular mass of both PP families and provides narrow molecular mass distributions (MMD) with a polydispersity of about 2. The validity of the Arrhenius and WLF equations for PP was checked. Syndio-and isotactic PP follow Arrhenius behavior but exhibit different activation energies of flow. From the dynamic shear moduli, viscoelastic parameters were determined and correlated with molecular mass. The dependence of the zero shear viscosity on the weight average molar mass exhibits the well-known scaling relation. Stereoregularity has an important effect on the viscoelestic behavior of PP melts.

The aim of this article is to test and to improve existing models combining rheological data with the molecular weight distribution (MWD). This process of testing and improving was separated into two distinct steps: First, the mixing behavior of the relaxation modulus obtained from a polymer blend was investigated and compared with the proposed mixing behavior derived from the linear and the quadratic mixing rules with a mixing parameter equal to 1 and 2. Second, for the rst time, kernel functions weighted with the MWD are estimated directly from experimental data and compared to the weighted kernel functions published in the literature.

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