Synthesis of side chain liquid crystal-coil diblock copolymers with p-methoxyazobenzene side groups by atom-transfer radical polymerization

The synthesis of two series of liquid crystal-coil (LC-coil) diblock copolymers with narrow molecular weight distributions was achieved by atom-transfer radical polymerization (ATRP), which was designed to have LC conformation of poly[(6-(4-Methoxy-4′-oxy-azobenzene) hexyl methacrylate] and coil-conformation of poly(ethylene oxide) (PEO) (M_n = 5000 or 2000) segment. The LC block in every series was prepared with a wide range of molecular weights from 3.5 × 10³ to 1.7 × 10⁴. The copolymers were characterized by proton nuclear magnetic resonance (¹ NMR), Fourier Transform Infrared (FT-IR) spectra, gel permeation chromatograph (GPC), differential scanning calorimetry (DSC) and polarized optical microscope (POM). The block copolymers exhibited a smectic and nematic mesophase. The phase transition temperatures of the smectic and nematic phase increased and the crystallization temperature of PEO decreased with increasing molecular weight of the LC block.