Oriented gamma phase in isotactic polypropylene homopolymer

The presence of ¿-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 ¿-phase are created in ZN-iPPs. The oriented morphology is qualified as a shish-kebab structure that templates densely branched ¿-lamellae on parent a-lamellae as well as directly to the shish backbone.