Rheological characterization of block copolymer systems in organic solvents

Abstract Block copolymers (BCPs) are macromolecules composed of distinct blocks of repeating units, offering hybrid properties that make them useful in various industrial fields. In solution, BCPs can self-assemble into ordered structures via micro-phase separation, driven by the incompatibility of their blocks and the solvent. This phase behaviour is influenced by temperature, often transitioning from an isotropic state to micro- and eventually macro-phase separation as temperature decreases. Key factors affecting this behaviour include degree of polymerization, chain composition and topology, block interactions and solvent selectivity. This study examines how polydispersity, solvent selectivity, temperature and polymer concentration impact the phase behaviour of styrene-butadiene BCP solutions. Two similar types of BCPs were analyzed: one with a near-monodisperse molar mass distribution ( M ) and another with a polydisperse distribution ( P ). In the latter, polydispersity affects both the overall molecular size and the relative block fractions. Solutions of these BCPs have been investigated using two model solvent systems: one consisting of an acetonitrile/ethylbenzene (ACTN/EB) mixture and the other composed of squalene/xylene (SQ/XY). Solvent-polymer compatibility was evaluated using Hildebrand solubility parameters. To assess phase separation, temperature and frequency sweep analyses were conducted to derive viscosity changes with temperature and Van Gurp-Palmen plots, with further validation provided by optical analysis, through visual inspection using crossed polarizers. The results show that P copolymer exhibits an earlier phase separation with respect to M, and it occurs in a wider range of temperatures for all the solutions of the two model solvent systems. Graphical Abstract Created in BioRender. Perna, I. (2025) https://BioRender.com/vx4iedp