| This research was focused on the synthesis and polymerization of two series of α,ω-carboxylic acid-hydroxyl-terminated polyester monomers. The monomers were designed with a kink in their structure to partially imitate the shapes of banana-shaped molecules. The first series, 4 ′-[x-3-hydroxyphenoxy)alkyloxy]biphenyl-4-carboxylic acids was x = 6-10, was prepared from resorcinol by a 4-step synthetic route. DSC cooling scans of the C6/monomer (x = 6) showed a broad liquid crystalline region below an isotropization transition at 228°C. Immediately below this transition, PLM observations revealed a thread-like phase on an isotropic background. On further cooling a small transition occurred at 216°C where the threads assumed a twisted helical conformation. Although there is a known link between helical conformations and ferroelectricity, the monomer did not display ferroelectric behavior in this state.; The second series of monomers, 4′-[x-(3-hydroxy-2-methylphenoxy)alkyloxy]-biphenyl-4-carboxylic acids where x = 6-10, was prepared from 2-methylresorcinol by a synthetic route similar to that used for the first series. The methyl substituent was introduced to break up the crystallinity and decrease the phase transition temperatures of the monomer and polymer series. The DSC thermograms of the monomers showed that the isotropization and melting temperatures were approximately 7°C and 19°C, respectively, lower than those of the corresponding monomers without a methyl group present. Helical conformations were also observed in a liquid crystalline phase of these monomers. However, these molecules also did not display ferroelectricity.; Each set of monomers was self-polymerized using a carbodiimide coupling agent. The polyesters obtained from each series had varying solubility and molecular weights. The polyesters prepared from the resorcinol-based monomers with short spacer lengths precipitated during their polymerization and had low intrinsic viscosities. The polyesters obtained from the methyl resorcinol-based monomers were more soluble and stayed in solution, which led to higher intrinsic viscosities, i.e. molecular weights. 2D-WAXD of the polymers showed that the mesogenic groups were tilted with respect to the layer normal, while the average chain axis lay perpendicular to the layer planes. It was postulated that the kink in the monomer structure leads to an overall zig-zag structure. |
