Branched azobenzene side-chain liquid-crystalline copolymers obtained by self-condensing ATR copolymerization

The one step synthesis of a series of branched azobenzene side-chain liquid-crystalline copolymers by the self-condensing vinyl copolymerization (SCVCP) of a methyl acrylic AB* inimer, 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM), with the monomer 6-(4-methoxy-azobenzene-4'-oxy)hexyl methacrylate (M), by atom transfer radical polymerization (ATRP) in the presence of CuBr/N,N,N',N',N'-pentamethyldiethylenetriamine as a catalyst system, and in chlorobenzene solvent, is reported. The degree of branching (1313), and the molecular weights and polydispersities of the resultant polymers were determined by NMR spectroscopy and size exclusion chromatography, respectively. The phase behaviors of the branched copolymers were characterized by differential scanning calorimetry (DSC) and thermal polarized optical microscopy (POM). The degree of branching of the branched copolymers could be controlled by the comonomer ratio in the feed and influenced their liquid-crystal properties. Liquid-crystal properties were not exhibited when the comonomer ratio was low. Comonomer ratios greater than 8 gave polymers with a lower number of branches, which exhibited both a smectic and a nematic phase.