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A series of azomethine dimers were prepared by condensation reactions of benzaldehyde, biphenylcarboxaldehyde and 9-anthraldehyde with various aromatic diamines of varying flexibility in ethanol in the presence of tosic acid. Their chemical structures were determined by Fourier transform infrared and 1H and 13C nuclear magnetic resonance (NMR) spectroscopies, as well as elemental analysis. Their thermal properties were also examined by using a number of experimental techniques, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarising optical microscopy (POM) and variable temperature X-ray diffraction (VTXRD). Azomethine dimer, prepared from benzaldehyde and 1,9-bis(4-aminophenoxy)nonane, exhibited a monotropic, nematic liquid-crystalline (LC) phase. The majority of the azomethine dimers containing biphenyl moieties exhibited enantiotropic, nematic LC phase on melting at relatively low temperatures, since they developed typical Schlieren, threaded or marbled textures in their LC phase. They also had accessible isotropisation temperatures well below their decomposition temperatures. Azomethine dimers containing anthracene moieties did not exhibit LC properties, but exhibited polymorphism as determined by POM and VTXRD in two cases. All of these azomethine dimers in the series had excellent thermal stability that was in the broad range of temperatures of 307-400°C depending on their degrees of aromaticity index. [ABSTRACT FROM AUTHOR]

Several anthracene derivatives were prepared by a single-step reaction and characterized their thermal properties by differential scanning calorimetry (DSC) and thermogravimetric analyses. Their photoluminescence properties were examined in a large number of organic solvents of increased polarity that included toluene, chloroform, tetrahydrofuran, acetone, methanol, acetonitrile, and dimethyl sulfoxide. Some compounds exhibited emission spectra with vibrational fine structures in organic solvents; and other compounds exhibited structureless emission spectra in organic solvents. [ABSTRACT FROM AUTHOR]

A series of main chain, thermotropic, liquid crystalline (LC) hydrogen-bonded polymers based on 4,4'-bipyridyl as a hydrogen bond acceptor and 4,4'-dicarboxy-α,ω-diphenoxyalkanes as hydrogen bond donors were prepared by a slow evaporation technique from a pyridine solution and characterized for their thermotropic LC properties using a variety of experimental techniques. The homopolymer of 4,4'-bipyridyl with 4,4'-dicarboxy-1,9-diphenoxynonane exhibited relatively low T m at 205°C and low T i at 230°C, giving an LC phase range of 25°C. The other two homopolymers with 4,4'-dicarboxy-1,6-diphenoxyhexane and 4,4'-dicarboxy-1,9-diphenoxydecane exhibited relative low T m values, above which each of them formed high-order smectic phases. With further heating at higher temperature they transformed into low-order smectic phases that persisted up to their decomposition temperatures. Several copolymers also had relatively low T m values as well as low T i values and, therefore, had a broad LC phase range (22-77°C). All of the polymers including copolymers exhibited high-order and low-order smectic phases, since they developed usually mosaic and schlieren (or bâtonnets) textures. Generally, copolymerization increased the temperature range of the LC phases for these polymers. The thermal transitions of all of the polymers were well below their decomposition temperatures, which were in the ranges of 254-329°C. [ABSTRACT FROM AUTHOR]

Several viologen bis{tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate} salts were prepared by metathesis reaction of the corresponding viologen dibromides (diiodide) with sodium bis{tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate} salt in a polar organic solvent. They were characterized for their physical and thermal properties by experimental techniques including variable temperature X‐ray diffraction. All exhibited low T g and T m , and their T g / T m (K) ratios were in the range 0.66–0.79. Several exhibited polymorphism and formed isotropic ionic melts at [ABSTRACT FROM AUTHOR]

This study examines purposes of code switching (CS) and how CS is used as a communicative strategy between Korean–English bilinguals. Data were collected through videotaping of conversations between a first-generation Korean–English bilingual adult and two Korean–English bilingual children. Qualitative data analysis indicated that CS could be brought about and shaped by the dynamics of the relationship of the speaker–addressee and by cultural features embedded in the Korean language. The analysis also posited that CS functions as a communicative strategy for facilitating family communication by lowering language barriers as well as by consolidating cultural identity. Results raise further awareness that CS is a versatile strategy to meet the complex communicative demands between or within generations of an immigrant family. [ABSTRACT FROM PUBLISHER]