Overcoming Fundamental Challenges of Covalent Adaptable Networks (CANs): Aromatic Disulfide Dynamic Cross-Linkers Yield Outstanding High-Temperature Creep Resistance and the First Polypropylene CANs by Radical-Based Reactive Processing

Covalent adaptable networks (CANs) are a promising route to replace unrecyclable thermosets with recyclable polymer networks. Though step-growth methods of CAN production are common, radical-based methods are relatively rarely studied. We developed the aromatic-disulfide-based cross-linker BiPheS methacrylate (BPMA) to enable radical-based CAN synthesis. Our initial study copolymerizing BPMA with n-hexyl methacrylate revealed BPMA’s [2+1] radical-mediated dynamic chemistry (incorporating both associative and dissociative character), as well as a constant cross-link density across the rubbery plateau resulting in outstanding high-temperature creep suppression. Our reactive processing study grafting BPMA to polyethylene (PE) and related copolymers also led to highly creep-resistant CANs while retaining the extrudability of the precursor thermoplastic. Our study grafting BPMA and its resonance-stabilized derivatives to polypropylene (PP) enabled the first-ever production of PP CANs by radical-based processing. In each study, we successfully attained robust and fully reprocessable CANs, indicating the suitability of aromatic disulfides to upcycle and improve the sustainability of PE and PP, which together make up half of global plastic production.