Phase Behavior of Ternary Blends of Tactic Poly(methyl methacrylate)s and Poly(styrene-co-acrylonitrile)

Abstract

Previously, atactic and syndiotactic poly(methyl methacrylate)s (PMMAS) were found to be miscible with poly(styrene-co-acrylonitrile) (PSAN) because all the prepared films were transparent and showed composition dependent glass transition temperatures (Tgs). However, the isotactic PMMA/PSAN blend was immiscible because most of the cast films were translucent and had two glass transition temperatures. Isotactic PMMA is known to be miscible with atactic PMMA according to literature. Atactic PMMA is miscible with both PSAN and isotactic PMMA but PSAN and isotactic PMMA are immiscible. It will be interesting to study the miscibility of ternary blends of isotactic and atactic PMMAs and PSAN. An investigation based on this is reported in this article. Calorimetry was used as the principal tool to study miscibility. A blend composed of isotactic and atactic PMMAs was also prepared and confirmed to be miscible. Tg of this blend seemed to vary linearly with composition. An approximate phase diagram of the ternary blends was established based on differential scanning calorimetry data. The results indicated that the ternary blends rich in isotactic PMMA and with a low PSAN concentration were found to be immiscible. One possible cause is attributed to more repulsive MMA-styrene interaction and/or MMA-acrylonitrile (AN) interaction between isotactic PMMA and PSAN.