Synthesis and photoresponsive properties of two liquid crystalline polymers bearing branched azobenzene-containing side chains

We synthesized two photoresponsive liquid crystalline polymers bearing branched azobenzene-containing side-chains. The side-chain liquid crystal polymers (SCLCPs) were designed to contain two and three azobenzene moieties in each monomeric unit, which were attached to the backbones via a linkage of biphenylene and flexible spacers. The SCLCPs were synthesized by radical polymerization of corresponding methacrylate-based monomers. The polymers were characterized by FT-IR, H-1 NMR, UV-vis, GPC and small angle X-ray scattering (SAXS). Both polymers formed the smectic-A mesophase in the LC states, whilst the polymer containing three azobenzene-containing branches in each repeat unit showed a high order mesophase in the lower temperature range. The polymers exhibited trans-cis photoisomerization and photoinduced orientation under light irradiation at suitable wavelengths.