Dipolar guest orientation in polymer co-crystals and macroscopic films

The crystal structures of δ-clathrates of syndiotactic polystyrene (s-PS) with highly polar guest molecules (nitrobenzene, NB and p-nitroaniline, NA) have been defined, on the basis of X-ray diffraction and FTIR linear dichroism analyses. The s-PS/NB co-crystal presents a structure very similar to those of the δ-clathrates already described in the literature, i.e. monoclinic and with the guest molecular plane nearly perpendicular to the host helical axes. The s-PS/NA co-crystal presents a definitely different structure, i.e. triclinic and with guest molecular planes inclined with respect to the host helical axes. The definition of the co-crystalline structures has allowed to establish that the a_⊥c_// uniplanar orientation of the co-crystalline phase leads the guest dipoles roughly perpendicular to the film plane, i.e. to a dipole orientation suitable for poling processes. Films presenting a high degree of a_⊥c_// uniplanar orientation of the s-PS/NA co-crystalline phase have been obtained and characterized by X-ray diffraction measurements.