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

Abstract

Solid-state 13C-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- α-methylstilbene and 1,9-dibromononane. This sample was crystallized by cooling from the isotropic melt through the nematic liquid crystalline state. Differential scanning calorimetry measurements and polarizing optical microscopic observation have confirmed 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 13C chemical shifts considering the γ- 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 sequence for the component with the shortest T 1C value, which corresponds to the supercooled liquid crystalline component, is in the rapid trans-gauche exchange conformation, reflecting the conformation in the liquid crystalline state.