Upcycling Polyethylene to Reprocessable Dynamic Covalent Networks via Free-Radical Grafting of Dialkylamino Disulfide Bonds

Current methods for recycling polyolefins result in property degradation over time and downcycling to lower value use. Thermoplastic polyethylene (PE) can be permanently cross-linked into thermoset PE, but permanent cross-links prevent the thermosets from being melt-state reprocessed. An emerging avenue to mitigate such sustainability issues involves enriching waste plastic with dynamic covalent bonds as cross-links. By modifying thermoplastics with dynamic covalent cross-links, the resulting covalent adaptable networks (CANs) exhibit robust mechanical properties characteristic of thermosets yet maintain reprocessability. Using melt-state, free-radical reactive processing, we upcycled polyethylene (PE) into covalent adaptable networks (CANs) using a dynamic cross-linker containing dialkylamino disulfide bonds. Importantly, the PE CANs recover their thermomechanical properties after reprocessing. We demonstrated that creep behavior of the PE CANs above their melt transition is dominated by the exclusively dissociative reversible dynamic chemistry of the cross-linker. We also demonstrated the utility of the high activation energy of the dissociative dynamic chemistry for predicting creep in CANs with different viscoelastic behavior.