Thermotropic polyesters, 6. New approach to the synthesis of segmented liquid-crystalline polymers with an increased with an increased length of mesogenic and flexible elements

A new approach to the synthesis of segmented liquid-crystalline (LC) polymers with an increased length of both mesogenic and flexible moieties is suggested. It consists in the preparation of intermediate polymeric compounds on the basis of aliphatic diols and a “triade” type complex monomer, 4,4′-(oxalyldioxy)dibenzoyl dichloride ( 6 ), whose central oxalyl unit plays the role of a bifunctional protective group and proves to be the structural element of the main chain of the intermediate polymer. The chemodegradation of the latter to bifunctional alkylene bis(4-hydroxybenzoate)s ( 3 ), which differ from the initial complex monomer, is achieved by selective removal of the oxalyl protective group. The desired LC polymers may be synthesized on the basis of such hydroxy-bifunctional compounds 3 and another triade type monomer carrying two acyl chloride functions, 4,4′-(terephthaloyldioxy)dibenzoyl dichloride. The features of each stage of the synthesis are discussed. Special attentional is paid to the selectivity of hydrolysis procedure of the intermediate polymers. A series of segmented LC polyesters containing five or seven 1,4-phenylene units in the mesogenic group are synthesized, their thermal properties are compared with the properties of LC polymers described earlier.