Orientation Dynamics of Main-Chain Liquid Crystal Polymers. 1. Synthesis and Characterization of the Mesogen

We have synthesized and characterized a family of liquid crystal copolyesters for a study of orientation kinetics described in the second paper of this series. The difference among members of this homologous series of main-chain liquid crystal polymers is molecular weight. Their backbones are formed by the condensation of pimelic acid and 4-acetoxyphenyl 4-acetoxybenzoate at temperatures in the range 180-285 °C. The polymers were characterized by ¹³C and ¹H high-resolution NMR, differential scanning calorimetry, vapor pressure osmometry, optical microscopy, and solution viscometry. The NMR data indicate that random terpolymers are formed during the polymerization reaction, presumably as the result of transesterification of the central ester bond in the diacetoxy monomer. The family of random liquid crystal polymers synthesized covers the molecular weight range 3900-15800. A major endotherm is observed for all molecular weights within 3°C of 142°C, and optical evidence for a nematic structure is definitely observed above 185°C. An optically visible biphasic structure is not observed below 220°C. Calculations using a chemical model designed from experimental data predict insignificant changes in polydispersity within the molecular weight range of the polymers studied. The detailed chemical characterization is critical to our understanding of liquid crystal microstructure and dynamics. This connection is discussed in the next paper of the series.