Evaluation of the Binary Interaction Energy Density between Styrene and Acrylonitrile Units and Its Temperature Dependence

Abstract

The miscibility behavior in blends of monodisperse poly(styrene) (PS) of varying molecular weight and polydisperse styrene/acrylonitrile copolymers (SAN) of varying AN contents was studied at three different temperatures: 120, 200, and 250 °C. An accurate quantitative evaluation of the binary interaction energy density between S and AN, BS/AN, was made at each temperature by analyzing the miscibility data using the copolymer/critical molecular weight method. The values of BS/AN determined by this powerful method show that the Flory−Huggins based interaction energy BS/AN decreases as temperature increases. An equation-of-state analysis using the Sanchez−Lacombe lattice fluid theory was performed to interpret the temperature dependence of BS/AN. An empirical scheme was introduced to account for the temperature dependence of the Sanchez−Lacombe characteristic parameters for PS. With this modification the temperature dependence of the experimental BS/AN is well described by the Sanchez−Lacombe lattice fluid theory using a constant bare interaction energy Δ