THE ROLE OF TRANSESTERIFICATION ON THE MISCIBILITY IN BLENDS OF POLYCARBONATE AND LIQUID-CRYSTALLINE COPOLYESTER

Transesterification mechanisms and rate in blends of polycarbonate (PC ) and random liquid crystalline polyester copoly(oxybenzoate-p-terepht halate) at molar ratio 40/60 (P46) were studied through a five-compone nt diad analysis and with C-13 and H-1-C-13 nuclear magnetic resonance spectroscopy. It was found that the ester-ester interchange in the tw o polymers took place within 15 min when the blend was annealed at 260 degrees C in vacuum. In the annealed blend, the Bisphenol A unit in p olycarbonate reacted first with the terephthalate unit and then with t he oxybenzoate unit in copoly(oxybenzoate-p-terephthalate). As the tra nsesterification in the blend continued for about 1 h, the forming of dad Bisphenol A-oxybenzoate exceeded that of diad Bisphenol A-terephth alate. This large loss (57%) of the diad oxybenzoate-oxybenzoate cause d the disappearance of the liquid crystalline phase in the blend. In s harp contrast to the originally immiscible blend of PC and P46 (two di stinctive glass transition temperatures), the large loss of the liquid crystalline diad resulted in complete miscibility in the annealed ble nd, as evidenced by the appearance of a single glass transition temper ature in the differential scanning calorimetry measurement.