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

Solid-state C-13 NMR analyses of the structure and chain conformation have been performed for a thermotropic liquid crystalline polyurethane that was polymerized from 3,3'-dimethyl-4,4'-biphenyldiyl diisocyanate, 1,10-decanediol, and 1-hexanol with a mole ratio of 25/24/2. This sample was crystallized by cooling from the isotropic melt through the liquid crystalline state at a rate of 1 degrees C/min. DSC thermograms of the cooling scan exhibit only one endothermic peak, whereas two exothermic peaks corresponding to the melting and isotropic points appear in the heating scan. However, the polarizing optical microscopic observation confirms that the crystallization occurs almost at the same time after the appearance of the liquid crystalline phase, although some part of the liquid crystalline phase is frozen without crystallization. Tie analyses reveal that the sample contains three components with different Tie values, which correspond to the crystalline, medium, and noncrystalline regions. From the line shape analyses of these three components, spacer methylene sequences for the crystalline and medium components are found to be in the same all trans conformation. In contrast, the methylene sequence for the noncrystalline component, which is ascribed to the frozen liquid crystalline component,is in the alternate trans and trans-gauche exchange conformation, probably reflecting the conformation that exists in the liquid crystalline state.