Supramolecular side chain liquid crystalline polymers assembled via hydrogen bonding between carboxylic acid-containing polysiloxane and azobenzene derivatives

Supramolecular side chain liquid crystalline polymers were prepared from po ly(3-carboxypropylmethylsiloxane) (PSI100) and azobenzene derivatives throu gh intermolecular hydrogen bonding (H-bonding) between the carboxylic acid groups in the PSI100 and the imidazole rings in the azobenzene derivatives. The existence of H-bonding has been confirmed using FTIR spectroscopy. The polymeric complexes behave as liquid crystalline (LC) polymers and exhibit stable mesophases. The LC behaviour of these H-bonded polymeric complexes was investigated by differential scanning calorimetry, polarizing optical m icroscopy and X-ray diffraction. The complexes exhibit nematic LC phases id entified on the basis of Schlieren optical textures. On increasing spacer l ength or the concentration of the H-bonded mesogenic unit in the complex. t he clearing temperature and the temperature range of the LC phase of the po lymeric complex increase. The terminal group plays a critical role in deter mining the LC properties of the polymeric complexes. A terminal methoxy gro up is more efficient than a nitro group in increasing the clearing temperat ure. The electron donor-acceptor interactions between the H-bonded mesogeni c units containing methoxy and nitro terminal groups in supramolecular 'cop olymeric' complexes lead to an increase in the clearing temperature and a w ider temperature range for the LC phase.