Fractionation of ultradisperse polytetrafluoroethylene in supercritical carbon dioxide and the chemical structures of the fractions

With the use of the pressure-temperature phase diagram, the solubility of ultradisperse polytet-rafluoroethylene in liquid and supercritical carbon dioxide has been experimentally studied. The quantitative dependence of the solubility of the polymer in supercritical carbon dioxide on pressure and temperature in the isothermal and isobaric modes, respectively, has been examined through gravimetric measurements. At 75°C and 30 MPa, the polymer was separated into a soluble fraction and an insoluble fraction. The chemical structures of the pristine polymer sample and of both fractions have been compared with the chemical structure of the classical polytetrafluoroethylene Fluoroplast-4 via the methods of FTIR and Raman spectroscopy.