Dynamic Covalent Crosslinking Delays Phase Separation in Networks of Incompatible Polymers

Plastic recycling remains both a societal and technological challenge, in part due to the requirement that mixed-stream polymer waste must be separated before being reprocessed into new materials. The long-chain nature of polymers leads to thermodynamic demixing for most commercial plastics, giving rise to poor material properties. This limitation is typically addressed via compatibilization, where copolymers bridge the interface between components and arrest bulk phase separation. This still results in small domains with interfaces that can adversely affect material properties. Strategies that instead facilitate mixing at the molecular level are needed to prevent the formation of these interfaces and allow for intermediate properties between the original blended components. Here we show that the introduction of dynamic covalent bonds, which connect telechelic chains of different polymers via a trifunctional crosslinker during solution synthesis, can create homogeneous dry blends that are slow to phase separate, depending on the bond exchange kinetics. Simulations explore the role of segregation strength, fraction of free ends, and exchange rate on the phase separation kinetics of symmetric vitrimer blends, demonstrating qualitative agreement with experimental observations regarding both the exchange rate and the fraction of free ends. This finding expands the ability to engineer polymer blends from otherwise immiscible components while still allowing for reprocessing or reversion to the starting polymers, unlike permanent network blends.