Structural and dynamical properties of n-alkane molecules in clathrate phase of syndiotactic polystyrene

Abstract

Syndiotactic polystyrene (sPS) forms a clathrate phase with a variety of compounds. Not only rigid molecules but also flexible molecules can be stored in the cavities of the clathrate phase. To clarify the adjustment mechanism of a flexible guest molecule to the sPS clathrate system, the host and guest structures were investigated by means of solid-state 13C NMR and Raman spectroscopy, and X-ray diffractometry for the sPS clathrates with a series of n-alkanes from n-hexane to n-decane. Although the 010 spacing of the host sPS lattice expanded slightly on going from n-hexane to n-heptane, it decreased markedly at n-octane and then increased gradually with the chain length of guest n-alkane. The conformational change of guest n-alkane molecules was involved in this anomalous change in the 010 spacing. Majority of the n-hexane and n-heptane molecules took extended chain structures in the clathrates, whereas all longer n-alkanes took bent chain structures. The means-quare displacement of hydrogen atoms in the clathrates was estimated by quasielastic neutron scattering experiments. It was confirmed that the host lattice contraction suppressed thermal motion of the clathrate system. Copyright © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.