Phase stability of hydrogen-bonded polymer mixtures. III. Spinodal diagrams

Relations derived on the basis of the Barker-Guggenheim quasichemical theor y were used for construction of spinodal diagrams (temperature versus compo sition) of a mixture of two polymers in which hydrogen bonds and other stro ng interactions exist. A function dependence of parameters of quasichemical equilibrium, eta, was proposed, which has the form of the Boltzmann functi on at lower temperatures, but at higher temperatures corresponds to random mixing. The spinodal diagrams were constructed for several sets of dependen ces of eta on temperature in a wide temperature range for different chain l engths, r, or for different values of the content of polar groups in one of the polymers. According to circumstances, the phase diagram shows one or t wo temperature regions of phase instability or the phase instability occurs in a certain range of composition at any temperature. Though the chain len gth was chosen equal for both polymers, the phase diagrams are asymmetric i n the sense that the critical points are shifted towards that border of the diagram which corresponds to the component with a larger relative content of the polar group. The temperature range of phase instability is strongly influenced by small changes in the relative surface area of polar groups in the molecules.