Morphology of semicrystalline block copolymers: polyethylene-b-atactic-polypropylene

Transmission electron microscopy (TEM) and electron diffraction (ED) are used to study the morphology of a semicrystalline polyolefin diblock copolymer polyethylene-b-atactic-polypropylene (PE-b-aPP) and its blend with polyethylene homopolymer. By using RuCl3/NaClO as the staining agent, both the contrast between amorphous PP and amorphous PE regions and the contrast between amorphous PE regions and crystalline PE regions can be obtained. As a result, both the larger lamellar structures due to microphase separation and the smaller crystalline PE lamellae can be resolved on TEM micrographs. Electron diffraction coupled with TEM imaging is used to elucidate the orientation of PE crystallites with respect to the interfaces of the microphase separated block copolymer lamellar domains. Fast quenching from a microphase separated melt-state was found to result in confinement of PE crystallization within the microphase separated PE domains of the block copolymer morphology. The orientation of the PE crystallites thus formed was found to be random.