TEMPERATURE-DEPENDENCE OF THE INTERACTION PARAMETER BETWEEN POLYSTYRENE AND POLY(METHYL METHACRYLATE)

The temperature dependence of the interaction parameter X between poly styrene and poly(methyl methacrylate) was studied by means of cloud po int and PVT measurements. With these data the phase diagrams and the t emperature dependence of chi were calculated using the classical Flory -Huggins theory, the equation-of-state theory of Flory, Orwoll, and Vr ij, and a modified cell model by Dee and Walsh. The results obtained f rom all three theories are very similar, suggesting that the free volu me contributions in the system under investigation are of minor influe nce. The comparison between obtained data and literature data of absol ute values of chi is very difficult because a number of model-dependen t quantities, such as segment length or segment volume, influence the results. Thus it is always better to compare the temperature dependenc e of chi. However, also in this case model parameters can lead to diff erent chi(T) functions as shown for the examples of the determination of chi(T) from interfacial thickness data and from phase diagrams usin g equation-of-state theories.