PHASE IDENTIFICATION IN A SERIES OF LIQUID CRYSTALLINE TPP POLYETHERS AND COPOLYETHERS HAVING HIGHLY ORDERED MESOPHASE STRUCTURES .1. PHASE DIAGRAMS OF ODD-NUMBERED TPP POLYETHERS

摘要

A series of liquid crystalline polyethers has been synthesized from 1-(4-hydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)propane and alpha,omega-dibromoalkanes [TPP(n)]. From the differential scanning calorimetry experiments, the TPP(n=odd)s show multiple phase transitions during cooling and heating. For each TPP(n=odd) the supercooling dependence of these transitions is found to be smalt A phase diagram of the transition temperatures and the enthalpy and entropy changes of the transitions with respect to the number of methylene units (n) for TPP(n=odd)s have been obtained. Analyses have been conducted regarding the contributions of both the mesogenic groups and the methylene units to the differently ordered structures. Identification of the ordered structures in each phase has been carried out by combining wide angle X-ray powder and fiber diffraction experiments at different temperatures with polarized light and transmission electron microscopy experiments on the liquid crystal morphology and defects. It is found that for TPP(n less than or equal to 13)s the highest temperature transition is from the isotropic melt to a nematic phase. However, for TPP(n greater than or equal to 15)s, the isotropic melt directly converts to a smectic F phase having a monoclinic unit cell (a pseudohexagonal packing tilted toward a side). The WAXD fiber patterns for this phase show that the chain orientation is parallel to the fiber direction. For TPP(n less than or equal to 13)s formation of a smectic F phase with a monoclinic unit cell from the nematic phase can also be determined and the WAXD fiber pattern shows that the chain orientation is at an angle ranging between 0 and 20 degrees with respect to the fiber direction. With an increase in the number of methylene units, this angle gradually decreases until n=15, where this angle becomes zero. Further cooling leads to a smectic crystal G phase for all TPP(n=odd)s, and the different chain orientations with respect to the fiber direction in the WAXD fiber patterns still exist. TPP(n less than or equal to 9)s remain in the smectic crystal G phase down to their glass transition temperatures, while TPP(n greater than or equal to 11)s form a smectic crystal H phase (a tilted herringbone, orthorhombic packing tilted toward the b-axis side, and a > b) in a low temperature range. [References: 29]