The thermally induced phase separation thermodynamics of the ternary solution consisting of isotactic polypropylene (iPP)

di-n-butyl phthalate (DBP) and dioctyl phthalate (DOP) was studied by pseudo-binary approach

considering the co-solvents of DBP and DOP as one component.The mathematical model to calculate pseudo-binary temperature-concentration phase diagrams was proposed. The cloud point curves of iPP-co-solvents systems were obtained with optical microscopy at a cooling rate of 1K8226;min-1.The melting point curves and dynamic crystallization lines of iPP-co-solvents systems were determined with differential scanning calorimetry(DSC) at several cooling rates.The interaction parameter χ between iPP and co-solvents was a function of temperature and co-solvents composition，and was determined from cloud point curves of iPP-co-solvents systems.Good agreement was obtained between the pseudo-binary phase diagrams calculated from the mathematical model and the ones generated from experiments. With increasing DBP fraction in co-solvents

the phase separation of the ternary solution changed from solid-liquid to liquid-liquid with subsequent solid-liquid.By varying the co-solvents composition systematically

the pseudo-binary phase diagrams could be controlled successfully.The thermodynamics of thermally induced phase separation of iPP-DBP-DOP ternary solution could be obtained by only measuring the cloud point curves of pseudo-binary systems of several co-solvents compositions at a lower cooling rate and dynamic crystallization lines of iPP-DOP system at several cooling rates.In the end

it was illustrated that the resulting membrane morphology could be explained successfully with the thermodynamics of iPP-DBP-DOP solution studied via the pseudo-binary approach.