Structural characterization of the δ-clathrate forms of syndiotactic polystyrene with n-alkanes

The δ-clathrate forms of syndiotactic polystyrene (s-PS) containing a homologous series of guests characterized by an increasing molecular volume (n-alkanes ranging from n-pentane to n-dodecane) have been investigated. The present analysis allows concluding that the volume of the guest plays a crucial role in the choice of the type of δ-clathrate that can be obtained. As a matter of fact, longer n-alkanes, such as n-octane, n-nonane or n-decane, turned out to give rise triclinic δ-clathrates presenting a guest/monomeric-unit ratio of 1/8, while δ-clathrates containing shorter alkanes, like n-hexane or n-heptane, instead, present a monoclinic or a triclinic structure with a guest/monomeric-unit ratio of 1/4. These results confirm the validity of a simple criterion to predict the type of s-PS δ-clathrate with a certain guest on the basis of the experimental d010, as described in Macromolecules 2010, 43, 8549–8558. Moreover, our analysis confirms previous solid state 13C NMR and Raman spectroscopy data, indicating that shorter n-alkanes molecules, like n-hexane, are hosted in the cavities with an all-trans conformation while longer alkanes, like n-nonane, present bent conformations. The effect of n-alkanes molecules on the crystallization of s-PS amorphous samples has been investigated too.