Synthesis, characterization and photo - switching properties of azobenzene mesogen containing poly (ether - ester) s from cashew nut shell liquid

Poly(ether - ester)s containing azobenzene mesogen were prepared from cardanol, a natural renewable resource and waste of the cashew industry. The azobenzene group containing cardanol (HPPP) was synthesized by the coupling reaction between diazotized aminophenol and cardanol. Further, it was alkylated with 3 - bromopropanol by Williamson's etherification process to 3- {4- [4-(3- hydroxy propoxy) phenylazo] -3- pentadecyl phenoxy} propan - 1 - ol(3-HPPP). This dihydroxy compound was characterized by CHN analyzer, UV and H-1 and C-13 - NMR spectroscopies. A series of azobenzene mesogen containing poly (ether - ester)s were synthesized from 3-HPPP and various aliphatic and aromatic diacid chlorides by solution polycondensation technique. The molecular structure of the monomer and polymers was confirmed by FTIR, H-1 and C-13 - NMR spectral analyses. These polymers were studied for their thermal stability and photochemical properties. Thermal properties were evaluated by TGA and DSC. Hot-stage optical polarizing microscopy (HOPM) study showed that most of the polymers exhibit smectic and highly ordered band structure. The photo-switching property of azopolymers was investigated using UV - Vis spectroscopy and noticed that trans to cis isomerization occurs within 35 s in DMF, whereas reverse process takes place in 4 h in DMF solvent.