Crystalline-crystalline isotactic polypropylene-based block copolymers prepared by Pyridylamidohafnium Catalyst

A structural and morphological characterization at different length scales of cystalline-crystalline block copolymers (BCPs) formed by isotactic polypropylene (iPP) block linked to polyethylene (PE) block1 obtained through metallorganic2 catalysis is reported. These systems allow studying of the effect of confinement on the crystallization behavior under different crystallization conditions. The final morphology of these systems is path dependent, being affected by the competition between crystallization and phase separation. The properties of this class of materials can be tailored by combining the wide range of morphologies that develop in crystalline BCPs with the polymorphism of iPP, and choosing the proper crystallization conditions. To this aim, a detailed structural characterization has been performed for samples crystallized in the bulk, thin films and stretched fibers and stress-induced phase transformations have been also analyzed. Moreover, simultaneous time and temperature-resolved WAXS and SAXS experiments have been performed with synchrotron radiation to clarify the melting and crystallization behavior. Finally, thin films of iPP-block-PE have been epitaxially crystallized onto crystals of organic substrates to achieve a control over the crystallization of both crystalline blocks. The final morphology depends on which polymer block crystallizes first, a sequence that depends on the block copolymer composition and block lengths.