Structure and Properties of Crystalline-Crystalline Block Copolymers Prepared by Living Organometallic Catalysts

The structure, the morphology and mechanical properties of crystalline block copolymers formed by polyethylene (PE) block linked to isotactic polypropylene (iPP) or syndiotactic polypropylene (sPP) blocks are presented. Samples of polyethylene-block-syndiotactic polypropylene (PE-block-sPP) and polyethylene-block-isotactic polypropylene (PE-block-iPP) crystalline-crystalline block copolymers with different block lengths have been synthesized by using living, stereoselective polymerization catalysts (Figure 1). A detailed structural characterization has been performed on both block copolymers for samples crystallized in the bulk, thin films and stretched fibers and stress-induced phase transformations have been analysed. PE-block-sPP samples have been epitaxially crystallized onto crystals of p-terphenyl (3Ph) to achieve a control over the crystallization of both blocks and study the dependence of the thin film morphology on the sequential crystallization of the two blocks by cooling from the melt. Ordered nanostructures where the two blocks are organized in separated alternating lamellar domains guided by the orientation of the crystalline lamellae are obtained. We demonstrate that, tuning the block length and using a specific substrate, it is possible to control the crystallization process and obtain large-sized, well-oriented lamellar microstructures with long range order achieved over the area in contact with the crystalline substrate.