Experimental analysis and modeling of the molecular architecture influence on the solid-liquid transition of ethylene/1-octene copolymer solvent systems

Abstract

The knowledge of solid-liquid equilibria of polymer-solvent systems is particularly important for further clarifying and understanding polymer crystallization. The molecular architecture in terms of molecular weight and branching related to the semicrystallinity of the polymer plays a key role in solid-liquid equilibria in polyethylene-solvent systems. Recently, a new thermodynamic model based on the Lattice Cluster Theory and continuous thermodynamics was developed, which can capture the influence of molecular weight distribution and degree of branching on solid-liquid equilibria. The model was applied to ethylene/1-hexene copolymer-solvent systems. However, the experimental database for solid-liquid equilibria of polymer solvent systems, where comprehensive molecular information of the polymer is connected with morphological quantities, e.g., semicrystallinity, and solid-liquid phase equilibria, is scarcely available in the literature. Therefore, herein a concept for this structure-property relationship is developed for ethylene/1-octene copolymer-solvent systems. The experimentally determined structure-property relationships are then used for determining the parameters of the statistical thermodynamics model and for model validation. The thermodynamic model allows the investigation of the transition zone from branching to molecular weight-induced solid-liquid equilibrium in dependence on the polydisperse nature of ethylene/1-octene copolymers.