CRYSTALLINE ORIENTATION IN SYNDIOTACTIC POLYSTYRENE CAST FILMS

The kind and degree of crystalline phase orientation for clathrate s-PS films, obtained by solution-casting procedures, and for semicrystalline films, obtained by suitable treatments on these cast films, are analyzed. Clathrate as well as nanoporous form films can present high degrees of uniplanar orientation, corresponding to the tendency of the ac crystallographic planes, to be parallel to the film plane. The driving force for this kind of orientation is the tendency of rows of parallel s(2/1)2 helices with minimum interchain and maximum interplanar distances to be parallel to the film plane. A high degree of uniplanar orientation is also maintained after annealing procedures leading to gamma form, that is the other crystalline form which presents the same helical conformation. A tentative indexing of the gamma form reflections, based on an orthorhombic unit cell, again indicates the presence of parallelism of ac planes with respect to the film surface. A substantial planar orientation, corresponding to the placement of the chain axes parallel to the film plane can also be maintained after annealing procedures at higher temperatures (220-230 °C) leading to alfa and beta crystalline forms, where trans-planar rather than helical chains are included.