Thermodynamic and Kinetic Effects on the Phase States of Amorphous Polymer and Organic Crystal Mixtures

We characterized the phase behavior of polystyrene and pyrene mixtures as a model binary system of amorphous polymer and crystallizing organic compound mixtures using the differential scanning calorimetry (DSC) technique. By employing various thermal processing procedures, we located the binodal temperatures (melting temperatures of pyrene crystals) and effective stability limit temperatures of pyrene crystallizations in the liquid–crystal two-phase domain. We observed that the binodal and effective stability limit temperatures are nearly insensitive to thermal processing procedures which indicates strong thermodynamic origins of these thermodynamic points. Remarkably, the effective stability limit curve shows the signature of an upper critical solution temperature which suggests that the pyrene crystallizations occur via liquid prenuclei domains signaling a hidden liquid–liquid phase domain in the liquid–crystal phase domain. We extracted the chemical compositions of polystyrene phases that have precipitated pyrene crystals using glass transition temperatures and found that the stability limit temperatures are critical in controlling the compositions of the polystyrene phases. Pyrene was solubilized and kinetically arrested up to ∼35 vol % in the glassy polystyrene