PHASE-TRANSITIONS IN MESOPHASE MACROMOLECULES .3. THE TRANSITIONS IN POLY(ETHYLENE TEREPHTHALATE-CO-P-OXYBENZOATE)

In the reported experiments, the glass and melting transitions of poly(ethylene terephthalate-co-p-oxybenzoate)s have been studied by differential scanning calorimetry. Despite the higher glass transition expected for polyoxybenzoate, there is almost no change in the glass transition temperature up to 63 mol% oxybenzoate (353 plus or minus 4 K). At high oxybenzoate concentration there seems to be a discontinuous jump to a glass transition of 450 K. This high glass transition has been observed in two-phase materials down to 30 mol% oxybenzoate. The melting transition shows signs of isodimorphism with a minimum in melting temperature at about 60-70 mol% oxybenzoate, 60 K below the melting temperature of poly(ethylene terephthalate). The thermal properties are little affected by the change of the noncrystalline parts of the molecules to a mesophase structure. The transition to the isotropic phase could not be analyzed because of prior decomposition.