Oriented Gamma Phase in Isotactic Polypropylene Homopolymer

The presence of gamma-phase in isotactic polypropylene is well-known but, up until now, could only be induced by specific processing conditions or material modifications. Typically, for Ziegler-Natta (ZN) iPPs pressures of 2000 bar are required, otherwise, metallocene (M) iPPs and copolymerization using olefin-type counits should be used. Here we show that crystallization under the unique combination of moderate pressure (p >= 900 bar) and strong shear flow oriented specimens with high contents of gamma-phase are created in ZN-iPPs. The oriented morphology is qualified as a shish-kebab structure that templates densely branched gamma-lamellae on parent alpha-lamellae as well as directly to the shish backbone.