Propriétés diélectriques de polysiloxanes cristaux liquides à groupements mésogènes diphényles et espaceurs de type thioéther. Dielectric properties of liquid crystalline polysiloxanes with mesogenic diphenyl groups and thioether spacers

Abstract

A series of nine liquid crystalline polysiloxanes was studied by means of dielectric spectroscopy. These polymers contain thioether spacers with different length, a diphenyl unit as mesogenic group and end-groups with cyano, nitro or one or two chiral centers. Another liquid crystalline polymer, without sulfur atom in the spacer, was studied in the same conditions. The dynamics of these polymers shows four molecular relaxation (α, β, γ 1 and δ) processes, and a collective (Goldstone mode) relaxation process for chiral polymers. The α relaxation temperature decreases with increasing spacer length due to the sulfur atom. On the other hand, the thioether spacer prevents cristallinity.