DETECTION OF NEMATIC SMECTIC PHASE-TRANSITION IN A SEMIFLEXIBLE MAIN-CHAIN LIQUID-CRYSTALLINE POLYMER

We investigate the low-temperature phase of a semiflexible liquid crys talline polyester that was previously thought to display only a nemati c mesophase. The polymer is the condensation product of 1,10-decanediy ldioxybis(benzoylchloride) and ethoxy-substituted hydroquinone and has a chemical structure that is strictly periodic. Polymers of two diffe rent molecular weights were prepared. For these viscous materials, sta ndard techniques for phase identification are problematic; however, rh eological studies easily reveal a nematic-smectic transition and pinpo int the transition temperature. According to X-ray diffraction on orie nted fibers, both samples exhibit a smectic A mesophase, in which the layer repeat is equal to one-third the molecular repeat. TEM morpholog ical investigation confirms the rheological and X-ray studies and reve als parabolic focal-conic textures, characteristic of smectics. The ut ility of rheology as a simple indication of a transition to a smectic phase is emphasized.