A Thermodynamic Approach to Phase Equilibria Investigation of Polyethylene-Ethylene System at High Pressure

A study of phase equilibria of Polyethylene-Ethylene system at high pressure has been carried out using the Flory-Huggins polymer solution theory. The influences of temperature, molecular weight and branching of polymer chain on the equilibrium pressures were so defined. The trends of the boundary curves have been located in the (P, c) and (T, c) diagrams and ourresults determine part of the critical locus in (P, Tcomposition) space. The ethylene exhibits a poor solvent behavior and therefore the system presents an UCST (upper critical solution temperature) as well as a LCST (lower critical solution temperature) which decreases as the pressure rises, shifting towards lower polymer concentrations.