Molecular dynamics of polystyrene model molecules. Conformational energy and ultrasonic relaxation of 2,4,6-triphenylheptane

Abstract

Conformational energies have been calculated for isotactic, syndiotactic and heterotactic 2,4,6-triphenylheptane, giving the most likely states and the conformational paths between them. The ultrasonic attenuation of these compounds has been investigated as a function of temperature and frequency. A single relaxation is observed for isotactic and syndiotactic isomers and has been assigned to isomerism between the helix tg⁺tg⁺(or g^–tg^–t) and the transition form g^–ttg⁺ for the isotactic, and between tttt and ttg⁺g⁺(or g^–g^–tt) conformations for the syndiotactic isomer. Two relaxation processes were needed for the heterotactic isomer, each involving one part of the molecule; the rotational isomerism of the meso diad is between g^–ttt (or tg⁺tt) and tttt conformations, while the racemic diad involves a relaxation between g^–ttt and g^–tg⁺g⁺ conformations.