Polyether based side-chain liquid crystalline polymers: Anionic polymerization and phase structures

Side-chain liquid crystalline (SCLC) polyethers with different spacers are successfully synthesized via anionic polymerization for the first time. The molecular weights of the polymers can range up to ∼53 kg/mol with Mw/Mn <1.1. The precise chemical structures including end groups have been characterized by employing Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-TOF) and the polymerization condition free of side reactions is further discussed. The phase behavior and structures of the polyethers have been investigated by combining various techniques including differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS) and polarized light microscopy (PLM). Two phase transformations are generally observed for each type of SCLC polyethers. Based on 2-dimensional (2D) X-ray patterns of oriented fiber and mechanically sheared samples, the low ordered liquid crystalline phase at high temperature is identified as a SmA phase for both SCLC polyethers. It is found that the polyether with a longer spacer exhibits a complex phase which is a mixture of a HexB phase and a frustrated HexB phase in analogy to smectic antiphase, whereas no such effect occurs for the polymer with a shorter spacer. Only HexB phase is observed for the low temperature phase of this polymer. The difference in phase structures is also revealed in the texture changes of PLM.

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