COMPARISON OF THE VISCOELASTIC PROPERTIES OF SYNDIOTACTIC AND ISOTACTIC POLYPROPYLENES

The viscoelastic properties of fourteen syndio- and isotactic polyprop ylenes (PPs) were measured in the molten slate at several temperatures by means of oscillatory rheometry. Metallocene catalysis allows the c ontrol of molecular mass of both PP families and provides narrow molec ular mass distributions (MMD) with a polydispersity of about 2. The va lidity of the Arrhenius and WLF equations for PP was checked. Syndio- and isotactic PP follow Arrhenius behavior but exhibit different activ ation energies of flow. From the dynamic shear moduli, viscoelastic pa rameters were determined and correlated with molecular mass. The depen dence of the zero shear viscosity on the weight average molar mass exh ibits the well-known scaling relation. Stereoregularity has an importa nt effect on the viscoelestic behavior of PP melts.