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

A series of liquid crystalline polyethers has been synthesized from -h ydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)propane and alpha,omega-dibro moalkanes [TPP(n)]. From the differential scanning calorimetry experim ents, the TPP(n=odd)s show multiple phase transitions during cooling a nd heating. For each TPP(n=odd) the supercooling dependence of these t ransitions is found to be smalt A phase diagram of the transition temp eratures 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 p hase has been carried out by combining wide angle X-ray powder and fib er diffraction experiments at different temperatures with polarized li ght and transmission electron microscopy experiments on the liquid cry stal morphology and defects. It is found that for TPP(n less than or e qual 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 1 5)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 orientat ion is parallel to the fiber direction. For TPP(n less than or equal t o 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 s hows that the chain orientation is at an angle ranging between 0 and 2 0 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 cry stal 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 greate r than or equal to 11)s form a smectic crystal H phase (a tilted herri ngbone, orthorhombic packing tilted toward the b-axis side, and a > b) in a low temperature range.