Layer Structures 8. Poly(benzoxazole-ester)s with a Four-Layer or a Six-Layer Repeat Unit

Abstract

Two isomeric polyesters (3a and 3b) were synthesized from 2-(4-hydroxyphenyl)benzoxazolecarboxylic acid, 1,12-dodecanediol, and tetraethylene glycol, so that an alternating sequence of four subunits was obtained. Both polyesters differ in their internal orientation of the benzoxazole units with the consequence that only one of them (3a) is liquid-crystalline forming an enantiotropic smectic-C phase. Furthermore, a third polyester (4) was prepared with an alternating sequence of six subunits using 4,4‘-dimercaptobiphenyl as a third stiff building block. Both DSC and X-ray measurements confirm that all three polyesters form a crystalline solid state with a smectic type layer structure. Fiber pattern indicate that in the case of 3a and 3b the chains are tilted with an angle of about 45° relative to the layer planes, and the solid state corresponds to a smectic-H structure. In the case of 4 the chains are in upright position, although four subunits are identical with the repeat unit of 3b. Therefore, the soli...