Siloxane polymers containing azo moieties synthesized by click chemistry for photo responsive and liquid crystalline applications

Three new types of siloxane-based photoactive liquid crystalline polymers containing azo side groups were synthesized through the click chemistry route. The polymers having molecular weight range of 14,00034,000 g mol-1 were soluble in most of the polar solvents like chloroform, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, and dichloromethane. The photoresponsive transcis photoisomerization under UV radiation and cistrans relaxation process in dark for the polymers were studied. The isomerization rate constants were found to be 0.010.04 sec-1 and 1.16*10-44.67*10-4 sec-1, respectively. It has been noted that the polymers showed high intensity absorption for n-p* in chloroform. Both trans and cis forms of azide monomers having azo moiety exhibited molar extinction coefficient (?max) in the range of 22,00033,000 L mol-1 cm-1. The thermotropic behavior of the polymers was studied by polarizing optical microscope (POM) and differential scanning calorimetry (DSC) experiments. Polymer P1 showed liquid crystalline textures of nematic droplets, whereas P2 showed smectic focal conic texture and nematic droplets. Polymer P1 was also studied for photomechanical bending on exposure to UV radiation. The polymers showed initial degradation temperature in the range of 210275 degrees C. (c) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012