Aspen Polymers User Guide Volume 2:Physical Property Methods&Models

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These regions are characterized by the upper critical solution temperature
(UCST) and the lower critical solution temperature (LCST). UCST
characterizes the temperature below which a homogeneous liquid mixture
splits into two distinct phases of different composition. This phase behavior is
rather common, and it is observed in many kinds of mixtures of conventional
molecules and polymers. LCST represents the temperature above which a
formerly homogeneous liquid mixture splits into two separate liquid phases.
This thermally induced phase separation phenomenon is observed in mixtures
of conventional molecules only when strong polar interactions exist (such as
aqueous solutions). However, for polymer-solvent mixtures the existence of a
LCST is the rule, not the exception (Sanchez, 1992).