Guest-Induced Syndiotactic Polystyrene Cocrystal Formation from γ and α Phases

Guest-induced transitions from α and γ phases of syndiotactic polystyrene (s-PS) toward cocrystalline and nanoporous phases, and related guest-induced orientation phenomena, have been investigated by X-ray diffraction. Guests, being able to induce cocrystal formation in amorphous s-PS samples, are able to induce room-temperature cocrystal formation from γ and α form films, only if their vapor pressure is higher than 20 and 60 Torr, respectively. Guest-induced recrystallizations of unoriented γ form films generally lead to unoriented cocrystalline and δ form films, while chloroform-induced recrystallization leads to cocrystalline and ε form films with perpendicular orientation of chain axes. On the other hand, guest-induced recrystallizations of unoriented α form films generally lead to oriented cocrystalline and derived δ form films. In particular, recrystallizations of unoriented α form films by room-temperature sorption of trichloroethylene and CHCl 3 lead to films with (002) uniplanar and (2̅10) uniplanar orientations, i.e., with chain axes perpendicular and parallel to the film plane, respectively. The new procedures to prepare nanoporous films with different uniplanar orientations present substantial advantages with respect to the procedures already described in the literature.