Solid-State 13C NMR Analysis of the Crystalline–Noncrystalline Structure and Chain Conformation of Thermotropic Liquid Crystalline Polyester

Abstract

ABSTRACT:The crystalline-noncrystalline structure and chain conformation of thermotropic liquid crystalline polyester (BB-8), composed of mesogenic biphenyl and spacer CH 2 sequence units, have been characterized by highresolution solid-state 13 C NMR spectroscopy. The sample was crystallized by cooling from the melt through the smectic A phase.13 C spin-lattice relaxation measurements reveal that all resonance lines contain three components with different T 1 C values of 200-430, 9-38, and 0.4-5.5 s, which correspond to the crystalline, medium, and noncrystalline components, respectively. The high-resolution 13 C NMR spectrum for each component is selectively recorded by utilizing the difference in T 1 C and conformation of the spacer CH 2 sequences of each component is evaluated by considering the -gauche effect on 13 C chemical shift values. The noncrystalline component is found to adopt a characteristic conformation xttttttx in which the trans-gauche exchange conformations (x) are introduced at both ends of the CH 2 sequence, whereas the all-trans conformation tttttttt is allowable for the crystalline and medium components. 13 C chemical shift anisotropy spectra of the respective carbons are obtained by the two-dimensional magic angle turning method to examine molecular motion of the mesogen and spacer units. The mesogenic phenylene units undergo rapid fluctuation around the bond axis of the units in the medium and noncrystalline components while the crystalline component is highly restricted in such molecular motion. On the basis of these results, a molecular motion model is proposed for the noncrystalline component, which corresponds to the supercooled smectic A phase, for the BB-8 sample. [DOI 10.1295/polymj.36.830] KEY WORDS Liquid Crystalline Polymer / Polyester / Solid-State 13 C NMR / Conformation / Co-planarity / Molecular Motion / Many different main-chain thermotropic liquid crystalline (LC) polymers have been developed and their phase transition behavior and structures in different levels have extensively been investigated by calorimetry, microscopy, diffractometry, spectroscopy, and so on. [1][2][3][4][5] We have systematically investigated the phase transition behavior and the crystalline-noncrystalline structure, particularly focusing attention on the conformation and dynamics of the mesogen and spacer units, for main-chain thermotropic LC polyurethane (UDMB-10) and polyether (EDMB-10) (Scheme 1) mainly by solid-state 13 C NMR spectroscopy.6,7 These LC polymers have similar chemical structures composed of 3,3 0 -dimethyl-4,4 0 -biphenyl units as mesogen and 10 CH 2 sequences as spacer. The thermal analysis and optical polarizing microscopic observation of the polymers revealed that the nematic phase appears in a somewhat narrow temperature region when cooled from the melt or heated from the crystalline phase.6-10 13 C spin-lattice relaxation measurements for the samples crystallized by cooling from the melt through the nematic phase indicated three components with different molecular mobiliti...

Formation of the Liquid Crystalline Glassy Phase and Cold Crystallization of a New Crystal Form from the Glassy Phase for Thermotropic Liquid Crystalline Polyether

“…However, such a conformational change may hardly affect the three-dimensional crystal lattices basically formed by the mesogen units because there is no appreciable difference in WAXD profiles in the two stages. The detailed conformational characterization of form β and the LC glassy phase is now in progress 21 in relation to form α previously reported. 7,8 …”

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“…To reveal the conformational properties of crystalline as well as non-crystalline samples, highresolution solid-state 13 C NMR spectroscopy has recently proven to be very useful for various types of molecular systems. [25] Analyses were taken under room temperature using a standard 5 mm NMR tube at the JEOL ECZ 500 R NMR device. The sample was dissolved in D 2 O.…”

“…The data obtained were similar to those described in the literature. [25] Based on the results obtained, it was concluded that the water-soluble glucan macromolecule has a branched structure, the basis of which consists of D-glucopyranose residues linked by β-(1→3)-glucoside bonds. Lateral branches, built from β-glucopyranose monomer units, were attached to the O-6 positions of monosaccharide residues.…”