Liquid Crystal Polymers Containing Macroheterocyclic Ligands. 5.^† Structure of the Liquid Crystal Phases of Poly [4- [(11-methacryloylundecan-l-yl)oxy] −4′-(4′-carboxybenzo-15-crown-5)biphenyl]

The liquid crystalline phases displayed by poly[4-[(11-methacryloylundecan-l-yl)oxy]-4′-(4′-carboxybenzo-15-crown-5)biphenyl] were characterized by a combination of DSC, thermal optical polarized microscopy and X-ray scattering (WAXS and SAXS) techniques. All three techniques demonstrate that the polymer exhibits a nematic mesophase between 129 and 166 °C. DSC and thermal optical microscopy experiments suggest a single smectic phase below 129 °C. However, X-ray scattering experiments have demonstrated that three different smectic phases appear below the nematic phase: a high-temperature interdigitated monolayer S_a phase, which is stable between 132 °C and about 125 °C (layer periodicity L = 41 Å); a lower temperature unindentified smectic phase with layer periodicity L = 57 Å (probably a double-layer tilted phase that is stable up to 125 °C); and a metastable smectic C phase (layer periodicity L = 32 A). The smectic C phase is kinetically favored over the phase with L = 57 A. The bulkiness of the crown ether group and its specific interactions cause a series of unusual behaviors as, for example, a very low rate of transformation of the smectic A and of the smectic phase with L = 57Å and a highly discontinuous smectic C to smectic A phase transition. The influence of sample history on the interconversion of these phases is presented. Two possible molecular models for the smectic A phase are discussed.