Perpendicular Chain Axis Orientation in s-PS Films:  Achievement by Guest-Induced Clathrate Formation and Maintenance after Transitions toward Helical and Trans-Planar Polymorphic Forms

Guest-induced crystallization of amorphous unoriented syndiotactic polystyrene (s-PS) films can generate oriented clathrate phases with the chain axis of <b>s</b>(2/1)2 helicies nearly perpendicular to the film plane. This perpendicular crystalline phase orientation can be maintained after lower temperature annealing procedures leading to the γ form, where the same helical conformation is present, as well as after higher temperatures annealing procedures leading to α and β crystalline forms (where trans-planar rather than helical chains are present). A high degree of orientation can be also maintained after extraction procedures leading to helical nanoporous δ crystalline form. Also guest diffusion procedures producing guest replacements into clathrate phases of s-PS films can leave substantially unaltered their possible orientation. To our knowledge, the achievement of crystalline phase orientation by simple solvent diffusion crystallization into amorphous unoriented thick films is unprecedented.