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. Here we develop a library of condensate-amphiphilic block polymers that can efficiently form a polymeric layer on the droplet interface for a wide spectrum of synthetic coacervates and biomolecular condensates. Condensate-amphiphilic block polymers 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 condensate-amphiphilic block polymer membranes render the droplets mechanically robust against fusion, regulate interfacial properties such as permeability and stiffness, and substantially improve droplet tolerance to challenging conditions of temperature, salinity, pH and organic solvents.