Synthesis And Characterization Of An ABC Triblock Copolymer With An Azobenzene Block

Liquid crystalline polymers and block copolymers are two classes of materials that can self-assemble. Block copolymer, consisting of different polymers which link to each other with chemical bonds can form micro-phase separation because of the incompatibility among the blocks. However, owing to the chemical linkage between the incompatible polymers, phase separation is limited to a microscopic scale. Combining the properties of both polymer classes by connecting a liquid crystalline polymer (LC) to an isotropic polymer (I) to form an LC/I block copolymer is one of the scientific focuses nowadays, for the obtained polymer system has both the micro-phase separation of block copolymers and the ordered structure of liquid crystalline polymers which may give birth to materials with special properties.Compared with the AB and ABA block copolymers that have been studied widely recent years, ABC triblock copolymers have more complicated morphological structure and properties and show several distinct characters. It attracts much attention these years. Much literature is reported about ABC triblock copolymers, but hardly any on the system combining liquid crystalline polymers with ABC triblock copolymers. In this paper, a nover ABC triblcok copolymer with narrow molecular weight distribution and an azobenzene liquid crystalline polymer block was synthesized using atom transfer radical polymerization (ATRP). The structure of these ABC triblock copolymers was characterized and the liquid crystalline behavior was studied and compared with that of the homopolymer of azobenzene.1. A series of azobenzene homopolymer poly [6-(4′-methoxy-4-oxy-azobenzene) hexyl methacrylate] (PMMAZO) were synthesized via ATRP using ethyl 2-bromoiso butyrate as initiator and CuBr/bpy as catalyst in the solvent chlorobenzene. The structure was characterized by Fourier Transform Infrared Spectroscopy (FTIR), gel permeation chromatograph (GPC) and proton nuclear resonance (1H NMR). The liquid crystalline behavior was studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results showed that PMMAZO had a glass transition temperature Tg, the phase transition temperatures from smectic phase to nematic phase (TS-N) and the phase transition temperatures from nematic phase to isotopic phase (TN-I). POM was used to identify the mesophases ulteriorly. On cooling from the isotropicphase, the typical nematic Schlieren texture was observed and then a focal conic-fan-shaped texture suggesting a smectic phase. The phase transition...