Layers of Close-Packed Alternated Enantiomorphous Helices and the Three Different Uniplanar Orientations of Syndiotactic Polystyrene

Thorough analyses of X-ray diffraction patterns of syndiotactic polystyrene (s-PS) films, exhibiting different crystalline and co-crystalline phases, and related evaluations of degrees of orientation have allowed to give a more accurate as well as simpler description of the three known uniplanar orientations. This new description involves the three simplest orientations of the high density ac layers (i.e. of the layers of close-packed alternated enantiomorphous s-PS helices) with respect to the film plane. On this basis it is proposed that the three uniplanar orientations should be named a|c|, a|c⊥ and a⊥c|, i.e., by a nomenclature which also presents the advantage to be independent of the helical crystalline or co-crystalline s-PS phase.