Chemically and Mechanically Recyclable Polyolefins Incorporating Covalent Adaptable Networks

ABSTRACT

We report on the synthesis and characterization of mechanically and chemically recyclable polypropylene‐based crosslinked polyolefins (CR‐POs) incorporating ester‐containing covalent adaptable networks (CANs). To obtain the material, polypropylene (PP, Mn ≈ 3900 g/mol) modified with maleic anhydride (MA) is crosslinked via epoxy–anhydride polymerization using 1,4‐butanediol diglycidyl ether (BDE) in the presence of ZnCl ₂ catalyst. Variation of the anhydride‐to‐epoxy (A/E) ratio shows that A/E ≈ 0.5 is the most effective formulation. The resulting crosslinked networks have a gel‐fraction of ∼75% yet remain melt‐processable through extrusion and compression molding due to CANs. CR‐POs are semicrystalline materials with Tm ≈ 140°C and crystallinity of ∼25%. The first‐generation material's flexural modulus (520 MPa) and stress at 5% strain (22 MPa) were intermediate between HDPE and LDPE. The CR‐PO materials can be mechanically reprocessed for at least five compression‐molding cycles without significant degradation of thermal or mechanical properties. CR‐POs can be depolymerized via transesterification to a low‐molecular‐weight polyolefin and repolymerized using BDE after modification with MA. The second‐generation chemically recycled networks exhibited a flexural modulus of 390 MPa and stress at 5% strain of 13 MPa. This work shows a practical route to mechanically and chemically recyclable polyolefin thermosets, advancing circular design for polyolefins.