POLYANHYDRIDES .5. THERMOTROPIC POLY(ESTER ANHYDRIDES) DERIVED FROM MONOALKYL-THIOTEREPHTHALIC ACIDS, HYDROQUINONE AND 4-HYDROXYBENZOIC ACID

Monoalkylthioterephthalic acids and their acyl chlorides were prepared via nucleophilic substitution of diethylbromo- or diethyl chloroterephthalate with thiols. Various poly(ester anhydrides) were synthesized by polycondensation of alkylthioterephthaloyl chloride with silylated 4-hydroxy-benzoic acid and silylated hydroquinone. The resulting poly(ester anhydrides) were characterized by elemental analyses, inherent viscosities, IR spectroscopy, differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) measurements, optical microscopy and C-13 NMR cross polarization/magic angle spinning (CP/MAS) spectroscopy. For the chain packing of these monosubstituted poly(ester anhydrides) a sanidic type of layer structure with a ''back-to-back array'' of the main chains is proposed. The alkyl side chains form ordered domains with predominantly all-trans conformations. In most cases, three endotherms are observable in the DSC heating traces corresponding to the melting of the side chains and to reversible transitions into two different liquid-crystalline phases.