Phase Identification in a Series of Liquid Crystalline TPP Polyethers and Copolyethers Having Highly Ordered Mesophase Structure. 5. Solid State 13C NMR Characterization of Motion and Conformations of Methylene and Mesogen Groups in Different Mesophases of TPP(n = 12 and 15)

Abstract

Two liquid crystalline polyethers based on 1-(4-hydroxy-4‘-biphenylyl)-2-(4-hydroxyphenyl)propane and 1,12-dibromododecane and 1,15-dibromopentadecane [TPP(n = 12 and 15)] have been characterized to examine the molecular motion and conformations of the methylene units and mesogenic groups using solid state 13C NMR. The methylene conformations were studied as a function of temperature by the γ-gauche effect in the 13C NMR chemical shift, which depends largely on the C−C conformation under the condition of magic angle spinning. The variable-temperature NMR results on the conformational order of the methylene units may be correlated with the entropy changes in the methylene units that are associated with phase transitions measured by differential scanning calorimetry experiments. Both the entropy change of the methylene units and 13C NMR chemical shift show that in the highly ordered liquid crystalline phases of this series of polyethers, the methylene units play an important role in maintaining the order of these phases.