Induced vibrational circular dichroism and polymorphism of syndiotactic polystyrene

The intense circular dichroism (CD) phenomena, as induced in amorphous samples of syndiotactic polystyrene (s-PS) by cocrystallization with nonracemic volatile guest molecules (carvone and limonene), have been investigated by Vibrational Circular Dichroism (VCD) measurements and X-ray diffraction characterizations. Moreover, the stability of these CD phenomena after thermal and solvent treatments, leading to different polymorphic crystalline phases of s-PS, has been studied. The CD phenomena remain stable not only after guest extraction but also after thermal annealing procedures leading to the helical γ phase or to the transplanar α phase. The CD phenomena are instead reduced for the solvent treatments involving at least partial dissolution and crystallization that lead to the helical ε phases and even lost for thermal treatments involving melting and crystallization that lead to the β phase. The reported results indicate that the intense CD phenomena observed for s-PS films are due to a supramolecular chirality associated with the native cocrystal morphology.