SINGLE-CRYSTALS OF GAMMA-PHASE ISOTACTIC POLYPROPYLENE - COMBINED DIFFRACTION AND MORPHOLOGICAL SUPPORT FOR A STRUCTURE WITH NONPARALLEL CHAINS

Single crystals of the unusual gamma-phase of isotactic polypropylene have been produced by thin film growth. Their examination by selected area electron diffraction using a tilting stage enables the exploration of nearly the full reciprocal space of this crystal modification. The results fully support and provide an absolute test for a crystal structure proposed recently by Bruckner and Meille characterized by the coexistence in the unit cell of two sets of 3(1) helices with non-parallel axes. The structural relationship between alpha and gamma-phases makes it possible to determine the left- or right-handed chirality of all helices in the single crystals. The surface structure is investigated by the polymer decoration technique, and occasional alpha-growth on gamma-crystals is described and analysed.