Dynamic Bonding Enhances Polymer Miscibility in Binary Polymer Blends

Plastic recycling remains both a societal and technological challenge, especially due to the requirement that mixed-stream polymer waste must be separated before being re-processed into new materials. Bulk phase separation occurs for most commercial plastics, giving rise to poor material properties. The fundamental physical limitation is due to the long-chain nature of polymers, which lead to a negligible entropic driving force for mixing. Here, a combined theory and experimental approach demonstrates that the introduction of dynamic covalent bonds to connect the ends of two immiscible polymers can dramatically increase the miscibility criteria compared to the case of blends. This is distinct from compatibilization, where copolymers or crosslinks arrest phase separation of two species. The enhanced miscibility for polymers with dynamic connections is due to the combinatoric entropy of the trifunctional dynamic bond junctions, which can be connected to three chains of the same type or a combinations of both polymers. This junction entropy favors mixing and shifts the thermodynamic criteria for phase separation. Further, predictions indicate that higher functionality dynamic crosslink points can exhibit a factor of seven increase in the critical (χN)_c that sets the criteria for phase separation. Theory and experiments demonstrate that an immiscible blend can be rendered miscible in the presence of these dynamic bonds.