PHASE IDENTIFICATION IN A SERIES OF LIQUID-CRYSTALLINE TPP POLYETHERSAND COPOLYETHERS HAVING HIGHLY ORDERED MESOPHASE STRUCTURE .5. SOLID-STATE C-13 NMR CHARACTERIZATION OF MOTION AND CONFORMATIONS OF METHYLENE AND MESOGEN GROUPS IN DIFFERENT MESOPHASES OF TPP (N=12 AND 15)

Two liquid crystalline polyethers based on hydroxy-4'-biphenylyl)-2-(4 -hydroxyphenyl)-propane and 1,12-dibromododecane and 1,15-dibromopenta decane [TPP(n = 12 and 15)1 have been characterized to examine the mol ecular motion and conformations of the methylene units and mesogenic g roups using solid state C-13 NMR. The methylene conformations were stu died as a function of temperature by the gamma-gauche effect in the C- 13 NMR chemical shift, which depends largely on the C-C conformation u nder the condition of magic angle spinning. The variable-temperature N MR results on the conformational order of the methylene units may be c orrelated with the entropy changes in the methylene units that are ass ociated with phase transitions measured by differential scanning calor imetry experiments. Both the entropy change of the methylene units and C-13 NMR chemical shift show that in the highly ordered liquid crysta lline phases of this series of polyethers, the methylene units play an important role in maintaining the order of these phases.