a separation process has been found in which a polymer - solvent solution separates into phases of highly different composition which are in equilibrium over a broad temperature range . upon addition of the phase separating agent , which is near or above its supercritical conditions , rapid disengagement into two phases occurs . the relative volume of solvent rich phase is substantially larger than the polymer rich phase . the process can be practiced at relatively low temperatures such as those employed in polymerization or post - polymerization processes . the separation is accomplished by adding or elevating the concentration of a phase separation agent to or above a minimum effective concentration , which causes the ucst and lcst lines to merge . suitable phase separating agents are organic and inorganic compounds that are gases at 1 atm pressure and 25 ° c . due to the gaseous nature of the phase separating agent , it is easily removed from the solvent phase for reuse in the process .