Chain Conformation of Spacer Methylene Sequences for a Liquid Crystalline Polyether As Revealed by Solid-State 13C NMR Spectroscopy

Abstract

Solid-state 13C NMR analyses of the structure and chain conformation have been carried out mainly at room temperature for a main-chain thermotropic liquid crystalline polyether which was newly polymerized from 3,3‘-dimethyl-4,4‘-dihydroxybiphenyl and 1,10-dibromodecane by using a phase transfer catalyst. This sample was crystallized by cooling from the melt through the nematic liquid crystalline state. Differential scanning calorimetry measurements and polarizing optical microscopic observations have confirmed that the nematic liquid crystalline phase appears in both heating and cooling processes. 13C spin−lattice relaxation analyses have revealed that there exist three components with different T1C values, which correspond to the crystalline, medium, and noncrystalline (supercooled liquid crystalline) components. By employing the difference in T1C, the spectrum of each component is separately recorded, and the conformation of the CH2 sequence is evaluated by considering the γ-gauche effect on the 13C chemical shifts. As a result, the crystalline component is found to adopt the alternate trans (t) and trans−gauche exchange (x) conformation (txtxtxtxt), in good accord with the result separately obtained by the molecular dynamics simulation. In contrast, all the C−C bonds of the CH2 sequence for the noncrystalline component are in the rapid trans−gauche exchange conformation (xxxxxxxxx), reflecting the same conformation in the liquid crystalline phase or at the melt.