Solid-State 13C NMR Studies of the Structure and Chain Conformation of Thermotropic Liquid Crystalline Polyether Crystallized from the Liquid Crystalline Glassy Phase

The structure and chain conformation of the form β sample newly crystallized from the liquid crystalline (LC) glassy phase have been investigated for a main-chain thermotropic LC polyether, which was polymerized from 3,3′-dimethyl-4,4′-hydroxyl-biphenyl and 1,10-dibromodecane, by solid-state 13C NMR spectroscopy. The 13C spin–lattice relaxation analyses reveal that there exist two components with different T1C values, which correspond to the crystalline and noncrystalline (supercooled liquid crystalline) components. By employing such differences in T1C, the spectra of the respective components are separately recorded, and the conformations of their CH2 sequences are evaluated by considering the γ-gauche effect on the 13C chemical shifts. As a result, the crystalline component is found to adopt the t′xxxtxxxt′ conformation whereas another conformation of t′xxxxxxxt′ is preferably induced in the noncrystalline region, where t, t′, and x indicate trans, trans-rich and trans–gauche exchange conformations, respectively. These conformations are markedly different from txtxtxtxt and xxxxxxxxx in the corresponding components for the form α sample previously reported, probably reflecting the difference in crystallization from different nematic phases Nα and Nβ. Moreover, molecular motion for the mesogen units and the spacer CH2 sequences has been examined by the chemical shift anisotropy (CSA) analysis based on the magic angle turning (MAT) method. The mesogenic phenylene carbons are found to undergo rather restricted flip motion with amplitudes less than 30° around the bond axis in both crystalline and noncrystalline regions, while the flip rates associated with the 13C spin–lattice relaxation may be greatly different in the two regions. The CSA spectrum of the spacer CH2 carbons significantly narrows possibly as a result of the specific change in chain conformation in the crystalline and noncrystalline regions.