Synthesis and Characterization of a Thermotropic, Liquid-Crystalline Polyester Comprising Phenyl Benzoate Groups Connected via a Tris(ethylene oxide) Spacer

A new, thermotropic, liquid-crystalline dimer and high molecular weight polymer in which the rigid, mesogenic unit is connected via a tris(ethylene oxide) spacer have been synthesized. The polymer was fully characterized by IR, NMR, GPC, and dilute solution light scattering and viscometry. Experimental data indicate Mw∼100000 and Mw/Mn = 1.9. The dimer revealed monotropic behavior with a nematic isotropic transition temperature of 125.6 °C and an associated enthalpy of 0.45 kcal/mru, whereas the polymer exhibited a nematic range of approximately 3 °C, with a corresponding nematic → isotropic transition temperature of 141 °C and an associated enthalpy of 0.51 kcal/mru. Comparison of these values with the ones for the corresponding polymer with an even-numbered decamethylene spacer group indicates not only a lower nematic-to-isotropic transition temperature but, more importantly, a much lower (ca. one-third) enthalpy and entropy of the nematic-to-isotropic transition. These findings are consistent with the model of highly extended chain conformations for main-chain, thermotropic polymers with alkylene spacers and indicate little tendency for conformational order and lower orientational order in the polymer with the more flexible ethylene oxide based spacer. © 1989, American Chemical Society. All rights reserved.