Material PropertiesDetermination of plateau moduli and entanglement molecular weights of ultra-high molecular weight isotactic polypropylene synthesized by Ziegler-Natta catalyst

Ziegler-Natta catalysis was employed to prepare isotactic polypropylenes (iPPs) with various viscosity average molecular weight Mη, where Mη exceeds 1 000 000 g/mol. The viscoelastic properties of the synthesized ultra-high molecular weight iPPs (UHMWiPPs) were investigated by means of oscillatory rheometry. Due to the polydispersity of these polymers that derived from multi-sites catalyst, the UHMWiPPs rheological parameters, including Arrhenius activation energy Ea, plateau modulus GN0, as well as the molecular weight between entanglements Me, were compared with that of the reported monodisperse iPPs. We critically evaluated the typical methods for the experimental determination of GN0 for polydisperse UHMWiPPs with linear architecture and concluded that the preferred method for UHMWiPP was the extrapolation integration method, which gave an average value of GN0 = (4.9 ± 0.3) × 105 Pa and Me = (6300 ± 400) g/mol. The polydipersity was proved to be acceptable for the UHMWiPP system in this research. However, the rheological measurements should be operated with caution because the temperature window was very narrow and the UHMWiPPs were extremely sensitive to thermal oxidative degradation during the tests.