Synthesis of side group liquid crystal-coil triblock copolymers with cyanobiphenyl moieties and PEG as coil segments by atom-transfer radical polymerization and their thermotropic phase behavior

A series of side group liquid crystal-coil(SGLC-coil) triblock copolymers with narrow, polydispersity was synthesized by atom transfer radical polymerization (ATRP), which was designed to have LC conformation of poly(11-(4'-cyanophenyl-4"-phenoxy)undecyl methacrylate) and coil-conformation of polyethylene glycol (PEG) (Mn=6000) segment. The SGLC block was prepared with a rang of molecular weights from 3.5 x 10(3) to 1.4 x 10(4). The macro-initiator PEG6000-Br was synthesized with PEG and 2-Bromo-2-methylpropionyl bromide by reaction of acid bromide. Their characterization was investigated using proton nuclear magnetic resonance (H-1 NMR), Fourier Transform Infrared (FT-IR) spectra, gel permeation chromatograph (GPC), differential scanning calorimetry (DSC) and polarized optical microscope (POM). All the block polymers exhibited a smectic A mesophase. The phase transition temperatures of the smectic to isotropic (T-S-T-I) phase increased and the crystallizability of PEG depressed With increasing of the molecular weight of the LC block.