Liquid‐crystalline and photo‐induced properties of P 4 VP quaternized with bromo derivative of dialkyloxy‐phenyleneazobenzene groups

Poly(4‐vinylpyridine) was partially (20% and 50%) and fully (100%) quaternized with a bromo‐terminated 4,4′‐dialkyloxy‐substituted cyanophenyleneazobenzene group (Azo‐Br). The resulting liquid crystal azopolymers were studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X‐ray diffraction (XRD) to determine their thermotropic behavior. They showed only a smectic phase that extends over a broad temperature range. The smectic period was found to correspond to a double layer stacking where the pendant groups (mesogens) are partially interpenetrated. On the other hand, the azopolymers were irradiated (UV‐vis wavelengths) to induce trans‐ to‐ cis conversion (photoisomerization), molecular alignment (birefringence), and mass migration (surface relief gratings). Results showed the lowest trans ‐to‐ cis photo conversion for the polymer with the highest content (100%) of chromophore units, and it was simply attributed to constrains arising from their close packing. On the contrary, this polymer showed the highest birefringence value suggesting a coordinated motion of the tightly held chromophore units at the smectic domains, as it was indeed reported for other photo‐active liquid crystal azopolymers. Finally, surface relief gratings, having a sinusoidal profile with regular periodicity, were registered. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44819.