Novel features of the rheological behaviour of metallocene catalysed atactic polypropylene

This study was designed to determine the linear viscoelastic properties of a family of metallocene-catalysed propylene homopolymers in the ‘plateau’ and terminal regions. A low value of the plateau modulus, around 4.8×105 Pa, was obtained. Our results differ from those reported for conventional amorphous polypropylene in several recent studies. As previously undertaken for metallocene-catalysed polyethylenes, the rheological behaviour observed was discussed in terms of a possible decrease in the entanglement density and/or an increase in chain flexibility with respect to other polymers of similar chemical composition. We subsequently applied an existing model, based on simplified molecular dynamics, that provided a correct description of the dynamic modulus from knowledge of the form of the molecular weight distribution and the materialsʹ rheological constants GN0 and η0. This method has been successfully applied to several types of polymer.