Two Different Uniplanar-Axial Orientations of Syndiotactic Polystyrene Films

Two different kinds of uniplanar axial orientations, exhibiting the polymer chain axis parallel to the main draw direction (c(ax)) and the ac plane parallel or perpendicular with respect to the film plane (a(parallel to)c(ax) and a(perpendicular to)c(ax), respectively) have been achieved for several cocrystalline s-PS phases. The preparation procedures involve an unbalanced biaxial stretching, leading to mesomorphic trans-planar phases, followed by cocrystallization procedures induced by suitable guest molecules. In particular, cocrystalline films with a(parallel to)c(ax) and a(perpendicular to)c(ax) orientations have been obtained by using more (e.g., carbon disulfide) and less volatile (e.g., 1,4-dimethylnaphthalene) guest molecules. These uniplanar axial orientations can be maintained after guest removal 6 procedures leading to the 6 phase (i.e., the crystalline phase exhibiting nanoporous cavities), after thermal treatments, leading to the orthorhombic dense gamma phase. These uniplanar axial orientations after chloroform sorption-desorption procedures lead to a(perpendicular to)c(ax) and b(perpendicular to)c(ax) orientations of the orthorhombic nanoporous e phase (i.e., the crystalline phase exhibiting channel-shaped porosity). High degrees of uniplanar axial orientations can lead to a complete 3-D orientational order among the crystallites and as a consequence maximize the anisotropy of the physical properties.