THERMODYNAMIC TRANSITION PROPERTIES OF HIGHLY ORDERED SMECTIC PHASES - SERIES OF MAIN-CHAIN LIQUID-CRYSTALLINE POLYETHERS

A series of polyethers have been synthesized from (4-hydroxy-4'-biphen yl)-2-(4-hydroxyphenyl)propane and alpha, omega-dibromoalkanes having different numbers of methylene units [TPPs]. Both odd- and even-number ed TPPs [TPP(n = odd)s and TPP(n = even)s) exhibit multiple transition s during cooling and heating and they show little supercooling depende nce, indicating close-to-equilibrium nature of these transitions. Comb ining the structural characterization obtained via wide angle X-ray di ffraction powder and fiber patterns at different temperatures and the morphological observations from microscopy techniques, not only the ne matic liquid crystalline phase but also highly ordered smectic F, smec tic crystal G and H phases have been identified. The phase diagrams fo r both TPP(n = odd)s and TPP(n = even)s have been constructed [1-3]. T hermodynamic properties (enthalpy and entropy changes) during these tr ansitions are studied based on differential scanning calorimetry exper iments. The contributions of the mesogenic groups and methylene units to each ordering process can be separated and they indicate the charac teristics of these processes thereby providing estimations of the tran sition types.