Atomic force microscopy of polymer crystals: 7. Chain packing, disorder and imaging of methyl groups in oriented isotactic polypropylene

Atomic force microscopy (AFM) was used to study the morphology and nanostructure of mechanically oriented, isotactic polypropylene (i-PP). AFM images of cleaved samples on the micrometre scale unveiled microfibrils with a diameter of 100-150 nm. Chain orientation and imperfections of chain packing were visualized in the (1 1 0) crystal facet at the surface of the microfibrils. Paracrystalline disorder and twisting of macromolecules were observed. Resolution of individual methyl groups with unprecedented quality allowed us to identify the handedness of the helices in the crystalline i-PP matrix. The packing of the methyl groups, visualized by AFM, was compared with the computer-visualized structure. The agreement between the expected and the experimentally determined parameters of the crystal structure was perfect within experimental accuracy.