MISCIBILITY OF A POLYARYLATE WITH A LIQUID-CRYSTALLINE COPOLYESTER

The miscibility has been investigated for binary blends of a polyarylate (PAr) with a liquid crystalline copolyester of p-hydroxybenzoate and ethylene terephthalate units in a 6/4 molar ratio (PET/PHB). The binary blends were prepared by solution precipitation. The transitions of the PET/PHB have been measured with a rheometrics dynamic spectrometer. The phases in blends have been studied with a differential scanning calorimeter, by thermogravimetry and with a polarizing optical microscope. The blends exhibit two glass transitions (T(g)s) over the composition range 10-90 wt %. The amorphous PET phase from the PET-PHB is found to be partially miscible with PAr, which leads to a decrease of the PAr T(g). The amount of this partially miscible portion of PET has been estimated by the Couchman equation. On heat treatment of the blends at 250 to 300-degrees-C, transesterification takes place, as judged by the shift of the higher of the two T(g)s. (C) 1993 John Wiley & Sons, Inc.