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 (scCO2) 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 Ea 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 scCO2 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/cm3), 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.
Ma et al. (Wed,) studied this question.