LIQUID-CRYSTAL BEHAVIOR OF SOME LATERALLY SUBSTITUTED STIFFCHAIN POLYESTERS CONTAINING 2-PHENYLBENZOXAZOLE UNITS

The synthesis and the phase behaviour of three laterally substituted stiff-chain polymers containing 2-phenylbenzoxazole units is reported. Polymers were obtained by reaction of 2-(4-acetoxyphenyl)-6-acetoxybenzoxazole with 2-phenoxyterephthalic acid (polymer 2a), 2-phenyl-thioterephthalic acid (polymer 2 b) and 2-hexadecylthioterephthalic acid (polymer 2 c). Polymers 2a and 2b are virtually non-crystalline. 2a is nematogenic, while for 2b a smectic-like liquid-crystal phase is observed, whose structural periodicity is probably connected with the intercalated stacking of the lateral phenyl groups along the direction of the chain axes. The solid phase of 2c is of the sanidic type. On melting, a liquid-crystal phase with equatorial periodicity is observed. This periodicity is probably related to the segregation of the stiff chains between the paraffinic layers.