Fiber Forming Poly(Urethane Acylsemicarbazides) with Photochromic Behavior

Segmented poly(urethane acylsemicarbazides) (PUS) containing azobenzene groups in the main chain were synthesized by a two‐step polymerization process from polymeric polyol, diisocyanate, and 4,4′‐azobis(benzoylhydrazide). The hard segment content was varied by altering the NCO/OH ratio in order to study the effect of the variation on the properties. IR studies were carried out to confirm the structures and the polymers were characterized by TGA, DSC, DMA, and stress–strain analysis. Both the DSC and DMA measurements showed that T g of the soft segment shifted with variation in the hard segment content. UV/VIS spectroscopy of solutions and creep recovery studies of the films were carried out to confirm the photoisomerization behavior of polymers. Isomerization upon irradiation of polymer solutions with UV light was observed as decrease in intensity of absorbance corresponding to trans‐form and increase in the absorbance of cis‐form. A decrease in the deformation of films subjected to irradiation as revealed by creep studies further confirmed the photochromic nature. The influence of polymer structure and chromophore concentration on the photoisomerization rates were determined from UV/VIS spectroscopic studies which showed that the rates were independent of the structure of polymer backbone and concentration of chromophores.