Investigation of the molecular architecture influence on the solid-liquid transition of ethylene/1-octene copolymers in butylal

• Molecular architecture influence in ethylene/1-octene copolymer butylal systems. • Lattice Cluster Theory predicted solid-liquid transitions of polymer-solvent systems. • Thermal and caloric properties of ethylene/1-octene copolymer butylal mixtures. The molecular architecture, in terms of molecular weight and branching, linked with the semi-crystallinity of the polymer, plays a key role in solid-liquid equilibria in polyethylene-solvent systems. Lattice Cluster Theory, in combination with continuous thermodynamics, captures these molecular features and has been successfully applied in the past to predict solid-liquid equilibria of polymer solvent systems. While the solubility of linear low-density polyethylenes in chlorinated solvents has been studied in depth in the past, few investigations have addressed their solubility in less toxic and environmentally more friendly solvents, particularly in relation to the influence of molecular architecture. This study aims to fill this gap by investigating the relationship between molecular architecture of ethylene/1-octene copolymers, covering a wide range of branching levels from 3.5 to 54.6 CH/1000 C, and their solid-liquid phase transitions in butylal. By combining cross-fractionation chromatography, preparative crystallisation fractionation and Lattice Cluster Theory, the solid-liquid transitions of these material systems are elucidated and an architecture-solubility relationship is established. This approach provides detailed insights into how molecular architecture influences crystallisation behaviour, provides a basis for the design of ethylene/1-octene copolymer fractions with tailored microstructural features, and demonstrates the predictive power of Lattice Cluster Theory.