Liquid-crystalline polyesters based on branched propylene spacers

A new promising concept of spacer modification in main chain liquid crystalline polymers is the use of branched alkylene spacers. In this article we give as a first example the polyesters of p,p'-terphenyl-4,4'-dicarboxylic acid as mesogenic unit and disubstituted propylene spacers. The steric restrictions of the spacers lower the melting points compared with the polyesters with linear spacer but they do not flexibilize the main chains as linear alkylspacers do. This leads to a residual stability range of the liquid crystalline state in the homologues of polyesters with disubstituted spacer. The melting and clearing points are lowered to the same extent. Because of the solubility of the higher homologues in common solvents it is possible for the first time to determine molecular masses of this polymer class based on p,p'-terphenyl-4,4'-dicarboxylic acid and aliphatic diols more exactly. X-ray scattering indicates that long side chains are arranged parallel to the main chain and have no longer influence on transition temperatures and intermolecular distances. (C) 1996 John Wiley & Sons, Inc.