Synthesis and photo‐induced transformation of helical aromatic polyamides consisting of axially dissymmetric biphenylene joints and azobenzene segments in the backbone

Wholly aromatic polyamides having a novel helical structure were prepared by the reaction of axially dissymmetric (R)- or (S)-6,6′-dimethylbiphenyl-2,2′-dicarbonyl chloride with aromatic diamines, which are soluble in common solvents such as tetrahydrofuran and N,N-dimethylformamide. Photo-irradiation of a tetrahydrofuran solution of the polymer obtained with 4,4′-diaminoazobenzene induced a change of the helical conformation because of the trans–cis isomerization of the azobenzene units in the polymer chain. No change in the specific rotation of the polymer was observed on heating at 100°C for 4h, indicating thermal stability of its helical structure. CD spectra showed that the helical conformation was maintained in methanesulphonic acid.