Complete miscibility of ternary aryl polyesters demonstrating a new criterion and horizon for miscibility characterization

A ternary miscible blend system comprising only crystallizable aryl polyesters [poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(butylene terepthalate)] was characterized with the criteria of thermal analyses, microscopy, and X-ray characterizations. The reported ternary miscibility (in the quenched amorphous state of blends of the three aryl polyesters) was truly physical and under the condition of no chemical transesterifications; this justified that transesterification was not a necessary condition for miscibility in polyester blends in this case. This study further proposed and tested a novel concept of a new criterion for miscibility characterization for polymer blends of only crystallizable polymers. A single composition-dependent cold-crystallization-temperature (T_cc) peak in blends of only semicrystalline polymers was taken as an indication of an intimate mixing state of miscibility. The theoretical background for establishing the single composition-dependent T_cc peak as a valid miscibility criterion for crystallizable polymer blends was examined.