Chain conformation of spacer methylene sequences for a liquid crystalline polyether as revealed by solid-state C-13 NMR spectroscopy

Solid-state C-13 NMR analyses of the structure and chain conformation have been carried out mainly at room temperature for a main-chain thermotropic l iquid crystalline polyether which was newly polymerized from 3,3'-dimethyl- 4,4'-dihydroxybiphenyl and 1,10-dibromodecane by using a phase transfer cat alyst. This sample was crystallized by cooling from the melt through the ne matic liquid crystalline state. Differential scanning calorimetry measureme nts and polarizing optical microscopic observations have confirmed that the nematic liquid crystalline phase appears in both heating and cooling proce sses. C-13 spin-lattice relaxation analyses have revealed that there exist three components with different T-IC values, which correspond to the crysta lline, medium, and noncrystalline (supercooled liquid crystalline) componen ts. By employing the difference in T-IC, the spectrum of each component is separately recorded, and the conformation of the CH2 sequence is evaluated by considering the y-gauche effect on the C-13 chemical shifts. As a result , the crystalline component is found to adopt the alternate trans W and tra ns-gauche exchange W conformation (txtxtxtxt), in good accord with the resu lt separately obtained by the molecular dynamics simulation. In contrast, a ll the C-C bonds of the CH2 sequence for the noncrystalline component are i n the rapid trans-gauche exchange conformation (xxxxxxxxx), reflecting the same conformation in the liquid crystalline phase or at the melt.