PHASE-BEHAVIOR OF POLY(P-OXYBENZOATE-CO-ETHYLENE TEREPHTHALATE) (POBET) - EXISTENCE OF 2 ET-RICH PHASES

Two glass transitions (T-g) located at ca. 55 and 85 degrees C, respec tively, were identified using differential scanning calorimetry for a poly(p-oxybenzoate-co-ethylene terephthalate) (POBET) material contain ing ca. 55 mol % OB. The higher T-g was related to the large ET-rich i sotropic particles typically observed via polarized light microscopy. The lower T-g was attributed to ET-rich microdomains within the contin uous nematic phase, which were more fully developed after repeated the rmal treatment at 300 degrees C. The existence of this low-T-g, ET-ric h microphase, as confirmed by transmission electron microscopic observ ations, was explained in terms of precipitation of short ET-rich chain s formed via transesterification within the OB-rich nematic matrix at elevated temperatures.