Abstract
Two glass transitions (T,) located at ca. 55 and 85 C, respectively, were identified using differential scanning calorimetry for a poly(p-oxybenzoate-co-ethylene terephthalate) (POBET) material containing ca. 55 mol % OB. The higher T, was related to the large ET-rich isotropic particles typically observed via polarized light microscopy. The lower T, was attributed to ET-rich microdomains within the continuous nematic phase, which were more fully developed after repeated thermal treatment at 300 C. The existence of this low-T,, ET-rich microphase, as confirmed by transmission electron microscopic observations, was explained in terms of precipitation of short ET-rich chains formed via transesterification within the OB-rich nematic matrix at elevated temperatures.
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