Liquid crystalline polymorphism in a new class of semiflexible polyesters containing a 2-phenyl-benzoxazole group

The synthesis and phase behaviour of a new class of semiflexible polyesters based on aliphatic dicarboxylic acids (from octanedioic to tetradecanedioic acid) and 2-(4-hydroxy-phenyl)-6-hydroxy benzoxazole are described. All the polymers synthesized are mesogenic and show a nematic or a smectic A phase (or both) depending on the length of the flexible spacer, the smectic mesomorphism being favoured for longer spacers. For the smectogenic polymers, the observed layer periodicity is equal to about half the length of the monomeric unit. A possible explanation is the occurrence of a regularly intercalated packing of the chains, with lateral matching of aliphatic and aromatic molecular sections