Thermoresponsive Simple Coacervation of Copolymers of LCST-type and Hydrophilic Monomers

Coacervates have emerged as promising systems for achieving dynamic compartmentalization. In particular, synthetic polymeric complex coacervates represent a well-established class. However, they often disassemble at high ionic strength condition due to charge screening effects. In contrast, simple coacervates, which form via phase separation of a single polymer species, serve as complementary systems that can exist under such conditions. Despite this advantage, the design and understanding of synthetic simple coacervates remains limited. Here, we report the thermoresponsive simple coacervation behavior of synthetic copolymers compose of lower critical solution temperature (LCST)-type and hydrophilic monomers. Through systematic investigations, we revealed that a wide variety of combinations of LCST-type monomers and hydrophilic monomers enables thermoresponsive simple coacervation in water in the presence of salts. In addition, the phase separation mode of most copolymers switches from simple coacervation to solid-like polymer aggregation at low salt concentrations. Our findings provide a guideline for designing thermoresponsive simple coacervate systems based on synthetic LCST-type copolymers. We also highlight the importance of carefully characterizing the microphases that emerge upon phase separation of thermoresponsive copolymers under each specific usage condition.