CALCULATIONS OF THE PHASE-DIAGRAMS OF POLYETHYLENE DISSOLVED IN SUPERCRITICAL SOLVENTS

Calculations have been made, using the equation of state theory of P.J. Flory and coworkers, of the phase diagrams of high density polyethylene and low density polyethylene dissolved in ethylene, and of high density polyethylene dissolved in fluorotrichloromethane. This was done using reduction parameters obtained by fittting the equation of state to data from the literature for ethylene and fluorotrichloromethane and to measured PVT data for the polyethylenes. The theory correctly describes the experimental LCST and UCST (lower and upper critical solution temperature) phase diagrams within the uncertainties of the reduction parameters. This was achieved assuming a zero value for the interaction parameters which do not contribute significantly within a realistic range of possible values. The main uncertainties arose from the high sensitivity of the predicted phase diagrams to the values of the reduction parameters of the pure components.