<p>Dilute-solution studies on styrene-acrylonitrile random copolymer (SA2) of molar composition 51% acrylonitrile (AN) in ethyl acetate (EAc) revealed that phase separation occurred in high-molecular-weight fractions as the temperature was raised.' This behavior, known as the lower-critical-solution phenomenon, was originally reported for certain polar systems and attributed to the existence of specific interactions between the polymer and solvent. More recently, Rowlinson and co-worker showed that nonpolar systems also undergo phase separation on elevation of the temperature, but precipitation occurs well above the boiling point of the solvent, in contrast to many polar systems where the polymer usually separates at a temperature below or near the solvent boiling point. From measurements at elevated temperatures, lower-critical-solution temperatures (LCSTs) can be estimated for each fraction, which in the limit of infinite molecular weight is the <em>O</em> temperature.</p>
Dr. Mangalam Ramanathan and Kalpagam, V., “Styrene-acrylonitrile random copolymer in ethyl acetate”, Journal of Polymer Science: Polymer Physics Edition, vol. 20, pp. 773–775, 1982.