Miscibility and phase behaviour of binary and ternary homoblends of poly(styrene-co-acrylic acid), poly(styrene-co-N,N-dimethylacrylamide) and poly(styrene-co-4-vinylpyridine)

The miscibility and phase behaviour of binary and ternary homoblends prepared from poly(styrene-co-acrylic acid) (SAA14), poly(styrene-co-N,N-dimethylacrylamide) (SAD25) and poly(styrene-co-4-vinylpyridine) (S4VP15) were investigated by DSC. SAA14 is miscible with both S4VP15 and SAD25 and interacts more strongly with S4VP15 than with SAD25 as evidenced by comparing their compositional variation of glass transition temperatures (Tg). Positive and negative deviations from linear average line were respectively observed with the SAA14/S4VP15 and SAA14/SAD25 blends. Several conventional theoretical approaches were used to describe these Tg-composition behaviours. The one parameter Gordon–Taylor equation or the two parameters Kwei equation describe very well the behaviour of SAA14/S4VP15 system. However, the recent three parameters Brostow equation was needed to reproduce experimental Tg-composition for the SAA14/SAD25 system. Reasonable agreement with the experimental values are obtained for both systems when the fitting parameter free method developed by Coleman et al. is applied to predict the composition dependence of the glass transition temperature. The experimental phase diagram of the SAA14/S4VP15/SAD25 ternary polymer blend system presents an immiscibility region due to the unbalanced interactions among the three polymer pairs.