Solid-state C-13-NMR analyses of the structure and chain conformation of thermotropic liquid crystalline polyether crystallized from the melt throughthe liquid crystalline state

Solid-stare C-13-NMR analyses of the structure and chain conformation have been carried out for a main-chain thermotropic liquid crystalline polyether which was polymerized with 4,4'-dihydroxy-alpha-methylstilbene and 1,9-dib romononane. This sample was crystallized by cooling from the isotropic melt through the nematic liquid crystalline stare. Differential scanning calori metry measurements and polarizing optical microscopic observation have conf irmed that the nematic liquid crystalline phase clearly exists in the wide range of temperature in both heating and cooling scans. T-1C analyses have revealed that each resonance line of the methylene sequence contains three components with different T-1C values and these values become significantly longer with decreasing temperature. The evaluation of C-13 chemical shifts considering the gamma-gauche effect indicates that methylene sequences for the two components with the longer T-1C values adopt the specific overall conformation, in which successive trans-gauche exchange and isolated trans conformations coexist. in contrast, all the C-C bonds of the methylene sequ ence for the component with the shortest T-1C value, which corresponds to t he supercooled liquid crystalline component, is in the rapid trans-gauche e xchange conformation, reflecting the conformation in the liquid crystalline state. (C) 1999 Elsevier Science Ltd. All rights reserved.