On Alternative Thermal Methods for Discerning the Miscibility in Blends of Isotactic Polystyrene and Poly(cyclohexyl methacrylate) with Closely-Spaced Glass Transitions

Abstract

Summary: Thermal characterizations were performed to further discern the miscibility and qualitative interactions in blends of isotactic polystyrene (iPS) and poly(cyclohexyl methacrylate) (PCHMA). A method based on the enthalpy relaxation of the blends was used to overcome the difficulty or ambiguity in resolving closely-spaced glass transitions of these two constituent polymers. Interactions between the blend components were further estimated by two additional methods: the blend's glass transition temperature (Tg) and the melting point depression. The blend's Tg method yielded a χ12 value ranging from −0.0016 (i.e., almost 0) to −1.98 (with the values depending on the amorphous PCHMA contents in the blends) in the temperature range of 95–110 °C, whereas the melting point depression led to χ12 = −0.039 at 240 °C. The interaction parameters obtained from these two methods are negative, confirming the miscibility with weak interactions. The results of these alternative thermal characterizations further clarified that the iPS/PCHMA blends, whose Tg's are too close to allow the use of conventional Tg criteria, are indeed completely miscible. Specific heat increment (ΔCP) at Tg for the iPS/PCHMA blends.