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 gamma phase or to the transplanar alpha phase. The CD phenomena are instead reduced for the solvent treatments involving at least partial dissolution and crystallization that lead to the helical epsilon phases and even lost for thermal treatments involving melting and crystallization that lead to the beta 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. Chirality 22:E67-E73, 2010. (c) 2010 Wiley-Liss, Inc.