Synthesis of a main-chain liquid crystalline azo-polymer via “click” chemistry

A main-chain liquid crystalline azo-polymer (BPHCHA) was prepared through the copper-catalyzed “click” reaction between the alkyne group on 4,4′-bis((6-(propargyloxy)hexyl)oxy) biphenyl (BPH) and the azide group on 4-(6-azidohexyloxy)carbonyl-4′-(6′-azidohexyloxy) azobenzene (AHCHA). The “click” reaction was confirmed by FT-IR, 1 H NMR, and GPC studies. The phase transition behavior of BPH, AHCHA, and the resulting azo-polymer BPHCHA was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). AHCHA and BPHCHA exhibited mesomorphic behavior, while BPH is a crystalline compound. A liquid crystalline phase from 39 to 69 °C for AHCHA upon heating was observed under POM. Schlieren texture was observed at 130 °C for BPHCHA on cooling from 150 °C and annealed at 130 °C for 15 min. Moreover, DSC and POM studies showed that BPHCHA exhibited monotropic mesomorphic behavior.