Self-Assembly of Liquid-Crystalline Polyamide Complexes through the Formation of Double Hydrogen Bonds between a 2,6-Bis(amino)pyridine Moiety and Benzoic Acids

Abstract

Supramolecular liquid-crystalline polymeric complexes derived from polyamides containing 2,6-bis(amino)pyridyl units in their main chains and benzoic acid derivatives have been obtained by the formation of intermolecular double hydrogen bonds. The polymeric complexes behave as single liquid-crystalline polymers and exhibit stable and enantiotropic mesophases. The hydrogen-bonded mesogens laterally connected by flexible spacers form a polymeric structure that is not simply classified as a main-chain or a side-chain type.

Functional liquid-crystalline polymers and supramolecular liquid crystals

“…A main-chain polyamide incorporating 2,6-bis(amino)pyridine units can form supramolecular complexes with a biphenylcarboxylic acid. [61][62][63] The direct attachment of supramolecular mesogens to the polymer backbone results in stabilization of the induced smectic A phase over 350°C.…”

Supramolecular Liquid-Crystalline Polyamides. Polymeric Complexes Formed through Hydrogen Bonding between Benzoic Acid Derivatives and a 2,6-Diaminopyridine Moiety in the Polymer Backbone.

“…Polyamide The syntheses of benzoic acid derivatives used in the paper were reported in a previous paper [6] except for Me-80BA. Me-80BA was synthesized from o-cresol by etherification with octyl bromide and regioselective bromination of aromatic ring [12] followed by the 275…”

“…Polyamide P8APy containing a 2,6-diaminopyridine moiety was prepared as previously reported [6]. The inherent viscosity of P8APy was 0.21 dL/g in DMF at 30'C.…”

“…Thermotropic mesomorphic behavior was observed for a number of aromatic polyamides [3 ,4]. Recently, supramolecular thermotropic liquid-crystalline polyamides were obtained by the self-assembly of polymers and small molecules through hydrogen bonding, which is a non-covalent interaction [ 5,6]. A wide variety of well-defined mesogenic polymeric structures such as side-chain [7], main-chain [8], and network [9] polymers as well as low-molecular-weight complexes [10] have also been prepared by the formation of hydrogen-bonded complexes .…”

“…For supramolecular polyamides , we have reported that aromatic nylons containing a 2 ,6-diaminopyridine moiety in their backbones are able to form mesogenic complexes with a 4-(4-alkyloxyphenyl)benzoic acid and 3-substituted 4-alkyloxybenzoic acids through the double hydrogen bonds [5 ,6]. Although the mesogen of the polymeric complexes consists of only two benzene rings, they show stable mesophases up to high temperatures around 200 °C [6]. This high thermal stability can be attributed to the network formation of the interaction between the amide groups in the polyamide backbone [5,11].…”