Sustainable Design of Reprocessable and Closed-Loop Chemically Recyclable High-Strength Vitrimer-like Polymers via Dynamic Disulfide Bonds

Recyclable thermosets enabled by dynamic covalent chemistry are ideal candidates for next-generation sustainable polymer materials. However, the loss of material properties after multiple reprocessing cycles due to defect accumulation and thermal aging remains challenging. Herein, we report a family of strong, glass-like polymer materials (RHP-Ps) synthesized by Michael addition between N, N ’-bis(acryloyl)cystamine (CBA) and butanediamine (BDA) and p -phenylenediamine (PDA). The high density of disulfide bonds in the network endows these materials with vitrimer-like topological rearrangement capability, while the tunable aromaticity derived from the BDA/PDA ratio allows for fine-tuning of the mechanical properties. The augmentation of the PDA fraction led to an increase in tensile strength from 28 to 82 MPa. However, this increase was accompanied by a decrease in elongation at break from 37% to 3.2%. Dynamic mechanical analysis and stress relaxation demonstrated rapid temperature-activated network exchange with low activation energies (94.5–98.1 kJ/mol) and topological transition temperatures (Tv) well below their respective glass transition temperatures ( T g = 44.0–55.5 °C). RHP-P-3 and RHP- P 4̅ maintained tensile strength above 90% after five cycles of compression molding, but RHP-P-5 demonstrated a loss of mechanical integrity after undergoing repeated processing. We developed a closed-loop chemical recycling route for reprocessing using dithiothreitol (DTT) reduction followed by iodine oxidation. RHP-P-5 was degraded into low-molecular weight species (MW < 1000) and then recross-linked into a polymer. The tensile strength of the recross-linked polymer recovered to 83 MPa, which was similar to the original sample. This work provides a roadmap toward practical routes for engineering repeatable processing with end-of-life closed-loop chemically recyclable recycling that restores material properties in high-performance thermoset-like materials.