Recyclable and Refoamable Zinc-Catalyzed Polyolefin Vitrimer Foams Modified by Epoxidized Soybean Oil with Tailorable Cellular Structure and Robust Mechanical Property

The development of high-performance recyclable polyolefin elastomer foams remains a challenge due to the inherent trade-off between melt strength and foamability. In this work, a zinc-catalyzed transesterification network was constructed in olefin block copolymer (OBC) elastomer through reactive melt-grafting of maleic anhydride (MAH) and subsequent cross-linking with epoxidized soybean oil (ESO), and the supercritical carbon dioxide (scCO 2 ) foaming technology was successfully implemented to prepare sustainable vitrimer foams due to the improved melt strength. The resultant OBC vitrimer shows a stable dynamic-covalent-bonded network with high cross-linking density (gel content of ∼80%). As estimated by Arrhenius-type stress relaxation behavior, the OBC-V elastomer has a delayed dynamic feature with E a ranging from 101.4 to 127.2 kJ/mol, which is favorable for its improved thermomechanical properties and broadened service temperature up to 120 °C. Interestingly, this vitrimer design presents a unique combination of enhanced melt strength for foam stabilization and active stress relaxation for eliminating local stress concentration during cell growth. Consequently, the OBC-V foams exhibited uniform and finely tuned microcellular structures (∼20 μm) under scCO 2 foaming in comparison with the unstable foaming behaviors in both pure OBC and chemically cross-linked OBC samples. Additionally, the OBC-V foams show a high specific strength of 2.7 MPa/(g/cm 3 ), good recyclability, and refoamability. This work provides a promising technique route through vitrimer chemistry toward sustainable and elastomeric polyolefin foams with lightweight and excellent mechanical performance.