Macromolecular association creates dispersity of components that determines liquid-liquid phase separation of oppositely charged polyions.

Macromolecular association in homogeneous solutions of oppositely charged polyions creates dispersity that influences liquid-liquid phase separation, forming an open miscibility gap.

• Why it matters: Understanding how phase separation occurs in complex polyelectrolyte mixtures is crucial because it underpins the formation of biomolecular condensates involved in vital biological processes and diseases.
• What they did: The authors revisited previous experimental data on oppositely charged polypeptides, analyzing how intermolecular association affects phase transition and demonstrates dispersity impacts phase behavior.
• The result: Dispersity caused by macromolecular association affects phase separation by creating an open miscibility gap, making phase compositions dependent on initial polymer volume fraction, which may be significant in biological condensate formation.