Supporting materials for Nature Chemistry article. Article title: Universal membranization of synthetic coacervates and biomolecular condensates towards ultrastability and spontaneous emulsification. DOI : 10.1038/s41557-025-01800-4

Membranization of membraneless coacervates and condensates is emerging as a promising strategy to resolve their inherent susceptibility to fusion, ripening, and environmental variations. Yet current membranization agents by design are largely limited to a subclass or a specific kind of coacervate or condensate systems. Herein, we develop a library of Condensate-Amphiphilic block Polymers (CAPs) that can efficiently form a polymeric layer on the droplet interface for a wide spectrum of synthetic coacervates and biomolecular condensates. CAPs are designed with a condenophilic block firmly anchored to the condensed phase, a condenophobic block extended to the dilute phase, and a self-association block to promote membrane formation. Critical to our design is the condenophilic block of phenylboronic acid and amidoamine that target the disparate chemistry of condensed droplets via multivalent affinities. The CAP membranes render the droplets mechanically robust against fusion, can regulate interfacial properties such as permeability and stiffness and they significantly improve droplet tolerance to challenging conditions of temperature, salinity, pH, and organic solvents.