New polymer syntheses, 30. Thermotropic polyesters of 2‐(2‐naphthylthio)terephthalic acid

2-(2-Naphthylthio)terephthalic acid (3 b) was synthesized from 2-naphthalenethiol and dimethyl 2-nitroterephthalate. Homopolyesters of this diacid were prepared by thermal condensation with the diacetates of hydroquinone or 4,4′-biphenyldiol. Copolyesters were obtained by concondensation with 4-acetoxybenzoic acid. For comparison a homopolyester was prepared from 2-(2-naphthyloxy)terephthalic acid and hydroquinone. DSC measurements and microscopic observation under polarized light revealed that the homopolyesters are semicrystalline and form a nematic mesophase above their melting points. The polyester from 3 b and hydroquinone crystallizes significantly more rapidly than the polyester of 2-(2-naphthyloxy)terephthalic acid. All copolyesters are amorphous and form a nematic phase between the glass-transition temperature (130 –140°C) and the temperature at which rapid thermal decomposition takes place (470 ± 10°C). The polyesters were also characterized by elemental analyses, viscosity measurements, thermomechanical analyses and thermogravimetry.