Synthesis and characterization of metal-chelate bridged quasi-ladder main chain discotic liquid crystal polymer

摘要

Columnar discotic liquid crystals have been established as a new materials for rapid charge transference since 1993. A variety of metal-coordinated square-planar complexes, for example, a series of p-diketone-copper(Ⅱ) complexes exhibit columnar or lamellar mesophases. In recent report we also first stated low dimentional conductive behavior of columnar bis(p-diketonato)copper(Ⅱ) complexes with oligo(ethylene oxide) side groups doped with LiClO_4 and iodine, compared with original state, the conductivity increased by about three orders of magnitude and reached 10~(-5) Scm~(-1) when heated to the columnar mesophase. For technical application the liquid crystalline polymers with rodelike(calamitic) units in the main or side chains have been investigated extensively, however, polymers based on discotic mesogenic units have been relatively seldom explored. The titled metal-chelate bridged quasi-ladder discotic liquid crystal polymer(LCP) has been first prepared by a controlled chelation reaction of cupric-ions(Cu~(++)) with p-diketone groups of two adjacent polymer chains(Poly(AADK-HMM)), which was synthesized by hydrosilylation from bis-allyl-group terminated P-diketone monomer and 1,1,3,3-tetramethylhydrodisiloxane (HMM). Molecular weight(Mw) measured by VPO indicates that the quasi-ladder double chain polymer is a predominant product. The LC behavior of the polymer was investigated by polarizing optical microscopy, DSC and X-ray diffraction(XRD). The later shows a sharp reflection peak with spacing around 3.1 A for the moderately annealed samples, which corresponds to the spacing of intermolecular stacking aromatic cores within a column. Furthermore, after annealing at high temperature for long time two strong and sharp reflections with 20: 4.4 and 4.8 degree in small-angle region can be observed, which demonstrate the existence of an ordered columnar rectangular superstructure.