Substituted poly(benzobisoxazole)s and poly(biphenylbisoxazole)s were synthesized by polycondensation of silylated diaminohydroquinone or 3,3’-dihydroxybenzidine with substituted terephthaloyl chlorides. Hexadecylthio-, 2,5-bis(hexadecylthio)- and 2,5-bis(hexadecyloxy)terephthaloyl chloride were used as reaction partners. A reaction temperature of 300 degrees C was required for the final cyclization step of the reaction sequence. At this high temperature partial crosslinking occurred in most cases. The poly(biphenylbisoxazole)s melt in the temperature range of 310-350 degrees C, but the characterization of the melt was affected by rapid thermal degradation. By means of wide-angle X-ray scattering powder patterns and C-13 nuclear magnetic resonance cross-polarization/magic-angle spinning spectroscopy, two kinds of sanidic layer structures were found for the solid state. The hexadecyl side chains form reversibly melting quasicrystalline paraffin domains between the layers of the main chain The molar fraction of these ordered paraffin domains is significantly higher for bis(hexadecylthio)-substituted chains than for bis(hexadecyloxy)-substituted ones.