Preparation and characterization of liquid crystalline ionic complexes and their macromolecular analogues

The aim of this work was to explore the structures of novel ionic complexes that can be polymerized in the liquid crystalline (LC) state. A homologous series of ionic LC monomer salts has been prepared by complexation of 4-vinylbenzoate (VB) with quaternary ammonium surfactants containing dialkyl dimethylammonium cations (Dn). This DnVB series consisted of the didecyl-, didodecyl-, ditetradecyl- and dioctadecylcompounds (n = 10, 12, 14 and 18). We also prepared the VB complex with the trioctylmethyl cation (T8) for comparison. Their chemical structures were confirmed by 1H NMR and their thermal stability was studied by TGA. Their physical structures at different temperatures were investigated by hot-stage polarizing microscopy and by x-ray scattering.; Cooling the D14VB complex from the isotropic melt led to successive formation of hexagonal columnar, smectic B, a second smectic (probably G or H), and finally smectic A phases. The second smectic form was not seen for D10VB and D12VB, and for D18VB, which has the longest side chain, we only observed the smectic A structure. UV irradiation of monomeric films of the DnVB complexes in the hexagonal and the uniformly orientated (mosaic) smectic B phases led to formation of polymers that formed smectic A structures, with layer spacings dependent on the alkyl chain length. These smectic phases were stable up to their degradation temperatures. The smectic-isotropic transition temperature for T8VB was too low to allow polymerization in the LC phase, but polymerization in the isotropic phase led to a cubic phase. Polymerization of the DnVB monomers was almost complete after 5 hrs; for T8VB about 20 hrs was necessary, probably due to steric effects. Texture evolution during in situ polymerization was followed by polarizing microscopy. For D10VB, D12VB and D14VB, stripe textures were observed during polymerization of the hexagonal phases, due to volume changes. Polymerization in the lower temperature smectic B phase did not yield the stripe texture, probably due to lower thermal mobility and also the fact that the LC monomer in the uniformly oriented texture had a higher packing density compared to the hexagonal phase, such that there was no volume contraction during polymerization.