Synthesis and characterization of novel side-chain liquid crystalline polycarbonates, 2: Polycondensation of mesogenic diols and diphosgene

摘要

A series of new side-chain liquid crystalline polymers was prepared with a polycarbonate backbone, bearing (E)4′-nitrostllbene mesogenic groups, connected to the backbone by spacers of different length. The polymers were synthesized in 1,4-dioxane by polycondensa-tion of diphosgene and diol monomers with the general structure 2-[ω-(4′-nitrostilben-4-yloxy)alkyloxy]-1,3-propanediol in the presence of pyridine as a proton trap and catalyst. The mesomorphic properties of all monomers, polymers and intermediates were studied by polarized optical microscopy and differential scanning calorimetry (DSC). The polymers were also studied by X-ray diffraction of non-oriented and oriented samples (fibres). All monomers were liquid crystalline with nematic and/or smectic phases. For the polymers a clear relation was found between spacer length and glass transition temperature (T_g), which decreases with increasing spacer length and between spacer length and clearing temperature, which increases with increasing spacer length. X-ray diffraction measurements indicated the presence of a smectic A double layer structure (S_(Ad)) for all polymers at room temperature, with an antiparallel alignment of overlapping mesogenic groups. A distinct difference in the orientation of the mesogens was found when fibres were drawn from the smectic phase or from the nematic or isotropic phase. In the first case the mesogenic groups were oriented perpendicular to the fibre axis and in the second case the mesogenic groups were oriented parallel to the fibre axis. By gel-permeation chromatography (GPC) measurements of heated samples and by thermogravimetric analysis (TGA) and DSC the polymers were found to be thermally stable up to temperatures well above their clearing point.