MESOPHASE IDENTIFICATIONS IN A SERIES OF LIQUID-CRYSTALLINE TPP POLYETHERS AND COPOLYETHERS HAVING HIGHLY ORDERED MESOPHASE STRUCTURES .2. PHASE-DIAGRAM OF EVEN-NUMBERED POLYETHERS

Liquid crystalline polyethers have been synthesized from -hydroxy-4'-b iphenylyl)-2-(4-hydroxyphenyl)propane and alpha,omega-dibromoalkanes w ith even-numbers of methylene units [TPP(n = even)s]. Multiple phase t ransitions are found during cooling and heating via differential scann ing calorimetry (DSC), and they show little undercooling dependence. O rdered structure identifications are based on experimental observation s of wide angle X-ray powder and fiber diffraction experiments at diff erent temperatures. Polarized light and transmission electron microsco py observations on mesophase morphology combined with DSC results on t hermodynamic transition properties also provide additional evidence fo r these phase assignments. Moreover, the contributions of the mesogeni c groups and the methylene units to each ordering process are obtained based on the changes of transition enthalpy and entropy. In TPP(n les s than or equal to 8)s the highest temperature transition is from the isotropic melt to a nematic phase. This nematic phase is only stable i n a narrow temperature range. For instance, it is 12 degrees C for TPP (n = 4) and 6 degrees C for TPP(n = 8). When the number of methylene u nits n greater than or equal to 10, the isotropic melt directly enters a smectic F phase. The second transition in TPP(n less than or equal to 8)s is from the nematic to the smectic F phase. As a result, the sm ectic F phase exists for all TPP(n = even)s. Decreasing the temperatur e further leads to another transition in TPP(n = even)s to form a smec tic crystal G phase which is followed by a transition to a smectic cry stal H phase. This smectic crystal H phase remains for TPP(n less than or equal to 8)s down to their glass transition temperatures, while in TPP(n greater than or equal to 10)s further ordering processes occur and crystal phases are observed. A phase diagram of TPP(n = even)s is constructed.