Hydrogen-bonded liquid-crystalline complexes of polyester containing a pyridyl moiety with 4-(alkoxy)benzoic acid

Novel hydrogen-bonded polyester complexes from mesogenic 4-(butyloxy)benzoic acid (2a), 4-(octyloxy)benzoic acid (2b), 4-(dodecyloxy)benzoic acid (2c) and 4-(tetradecyloxy)benzoic acid (2d) as the hydrogen bond donors and a polyester (3) based on 2,6-pyridine dicarboxylic acid as the hydrogen bond acceptor were prepared by the melt method. The association by hydrogen bonding was confirmed by means of FTIR. The components were miscible up to 0.1 mole ratio of 2d and 2c versus the polyester repeat unit. The limiting mole ratio for 2b and 2a to 3 were 0.2 and 0.4, respectively. Phase separation in the supramolecular complexes occurred above these limiting values and a two phase system consisting of a polyester supramolecular complex and 4-(alkyloxy)benzoic acid was formed. This was due to weak hydrogen bonding between the low molecular acid (especially the acid with longer terminal alkoxy group) and pyridyl unit of polyester in comparison with thermodynamically more favorable dimerization of acid molecules. The liquid crystalline behavior of these supramolecular polymeric complexes was confirmed by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). It was found that 2a exhibits no mesomorphism when mixed with polyester. However, among the other acid derivatives, 2b exhibited stable mesogenic complexes.