The Thermally Stimulated Currents Spectrum of Side-Chain Liquid Crystalline Polymers. A Further Contribution for the Attribution of the Different Discharges at the Molecular Level

Abstract

The dipolar relaxation mechanisms in two side-chain liquid crystalline polyacrylates with very similar chemical structures have been studied by Thermally Stimulated Discharge Currents (t.s.d.c.). The only structural difference between the two polymers is in the terminal group of the mesogenic moiety: a cyano group for one polymer and a methoxy group for the other. This structural difference gives rise to differences in the t.s.d.c. thermogram of the two polymers which have been interpreted in terms of the attribution of the observed discharges to molecular motions in the liquid crystalline phase. It was also shown that the distribution of the energies of activation and of the relaxation times of the glass transition relaxation is influenced by the motions in the liquid crystalline phase. Finally, it was observed that the shorteness of the spacer which links the main-chain to the mesogenic moiety has an influence on the t.s.d.c. signature of the studied polymers.

Key Words:

• Thermally stimulated depolarization
• dielectric relaxation
• TSC TSDC
• liquid crystal polymer
• phase transition
• compensation.