<scp>LCST</scp>‐<scp>UCST</scp> Hybrid Phase Diagram of Poly(ɛ‐Caprolactone)/Poly(Styrene‐<i>co</i>‐Acrylonitrile) Blends Through Thermal and Rheological Approaches: Effects of <scp>PCL</scp> Molecular Weight and Cooling Ramp Rate

ABSTRACT The lower critical solution temperature (LCST) phase diagram of poly(ɛ‐caprolactone)/poly(styrene‐ co ‐acrylonitrile) (PCL/SAN) blend was obtained through temperature sweep rheological tests. The effect of the cooling rate of the temperature sweep test and the increased molecular weight of PCL on the phase separation points of PCL/SAN blends was studied. The phase transition boundary of PCL/SAN blends was investigated using the changes in the slope of the storage modulus curve in terms of temperature as well as the spinodal temperatures based on Ajji and Choplin's theory. The LCST diagram obtained through the temperature sweep test for PCL/SAN blends moved to higher points with the increase in the molecular weight of PCL, and the phase diagram was moved to lower points by increasing the cooling rate of the temperature sweep tests. With the increase in the molecular weight of faster PCL phase in the blend, the viscoelastic difference of the two phases decreased and the compatibility window expanded.