Detection of Nematic-Smectic Phase Transition in a Semiflexible Main-Chain Liquid Crystalline Polymer

HUDSON, S. D.; LOVINGER, A. J.; LARSON, R. G.; DAVIS, D. D.; GARAY, R. O.; FUJISHIRO, K.

MACROMOLECULES

AMER CHEMICAL SOC

Lugar: Washington; Año: 1993 vol. 26 p. 5643 - 5650

0024-9297

We investigate the low-temperature phase of a semiflexible liquid crystalline polyester that was previously thought to display only a nematic mesophase. The polymer is the condensation product of 1,10-decanediyldioxybis(benzoylchloride) and ethoxy-substituted hydroquinone and has a chemical structure that is strictly periodic. Polymers of two different molecular weights were prepared. For these viscous materials, standard techniques for phase identification are problematic; however, rheological studies easily reveal a nematic-smectic transition and pinpoint the transition temperature. According to X-ray diffraction on oriented fibers, both samples exhibit a smectic A mesophase, in which the layer repeat is equal to one-third the molecular repeat. TEM morphological investigation confirms the rheological and X-ray studies and reveals parabolic focal-conic textures, characteristic of smectics. The utility of rheology as a simple indication of a transition to a smectic phase is emphasized.