Flow Mechanism and Distinct Rheological Features for Segmented Ionenes

ABSTRACT Segmented ionenes are phase‐separated polymers composed of alternating soft and ionically aggregated hard segments. Although their structure–property relationships have been extensively studied in terms of mechanical properties, their fundamental flow behavior remains unclear. Several studies have proposed that terminal flow originates from dissociation of ionic aggregates or weakening of ionic interactions, usually without direct experimental evidence. In this study, we thus investigate the flow properties of segmented ionenes synthesized from telechelic poly(propylene glycol) bearing pyridine end groups and 1,6‐diiodohexane while systematically varying the molecular weight. Frequency‐sweep rheology combined with time–temperature superposition is employed to evaluate terminal flow behavior and molecular‐weight dependence of viscoelastic properties. Despite the observation of terminal flow in the rheological measurements for samples with different molecular weights, Small‐angle x‐ray scattering (SAXS) at flow temperatures reveal that the ionic aggregates remain stable during flow. These results suggest that terminal flow originates not from aggregate collapse, but from slip‐out or hopping motions of quaternized units. Furthermore, we reveal a non‐universal molecular‐weight dependence of the zero‐shear viscosity. The present study thus highlights the distinct rheological properties of ionenes and provides insights for the design of functional thermoplastics with unique processability.