Liquid-crystalline main-chain polyesters with lateral aromatic substituents

Varying the structure of common main-chain polymers, a series of new mostly liquid-crystalline polyesters with y-shaped mesogens derived from hydroquinone diacetate with different lateral aromatic substituents (4-methoxyphenyi, 4-biphenyl) and 4,4'-alkylenedioxydibenzoic acids was synthesized. At given lateral group, the number of methylene units separating the aromatic ester triade mesogens ranges up to ten. First structure-property relationships could be determined using optical microscopy, differential scanning calorimetry and X-ray diffraction techniques. Corresponding to other types of liquid-crystalline polymers with laterally stressed mesogenic units, the anisotropic melts of our polyesters are nematic phases. Furthermore, X-ray investigations give hints to the existence of cybotactic groups. With increasing lateral substituents the lowering of the isotropization temperatures is accompanied by an enhanced tendency to form anisotropic glasses. Therefore, also polymers consisting of highly branched mesogenic building stones can form mesophases within a wide temperature interva