Thermodynamic Modeling of the Polydispersity Influence on the Solubility of Ternary Semicrystalline Polymer-Solvent Systems

The understanding and prediction of the solid-liquid phase transition of semicrystalline polymers dissolved in particular solvents are of crucial relevance for several fields. One example is the thermally induced phase separation in which a membrane formation is induced by cooling a respective polymer solution [1]. Besides the solvent species, the molecular architecture, i.e. molecular weight distribution and chemical composition of the polymer, influences the solid-liquid transition strongly. Hence, thermodynamic models are required which are able to consider molecular architecture and predict the polymer solubility behavior. Recently, a thermodynamic model [2] was developed based on continuous thermodynamics [3,4] and lattice cluster theory [5] which considers besides chemical composition also the polydisperse nature of the polymer and predicts the coexistence region of the solid-liquid transition in binary polymer/solvent systems. In this work, the thermodynamic model is extended to ternary semicrystalline polymer-solvent mixtures. This is of particular relevance for, e.g., tailored membrane formation and for the development of solid-liquid phase change materials. Herein the solid-liquid transition of polyethylene/liquid paraffin mixtures is investigated. It turned out that especially the low-molecular weight fractions of the polymers have a significant impact on the shape and broadness of the solid-liquid coexistence region of the polyethylene/liquid paraffin systems.