Dynamic Ethylene Propylene Rubber (EPR) Network via Multi-Arm Boronic Ester Crosslinkers

Dynamic crosslinked elastomers derived from synthetic rubbers represent a promising strategy to combine the reprocessability of thermoplastics with the mechanical robustness of vulcanized rubbers. However, the development of dynamic networks in saturated polyolefin elastomers like ethylene propylene rubber (EPR) is intrinsically constrained by low reactive density and inefficient dynamic crosslinking kinetics. Herein, we present a topology-engineered dynamic crosslinked EPR elastomer constructed via a trifunctional boronic ester crosslinking strategy which enhances crosslinking efficiency despite the limited reactive density. Hydroxyl-functionalized EPR was first synthesized via a controlled epoxidation-hydrolysis route, followed by dynamic network formation using a tri-functional boronic ester crosslinker. In contrast to conventional dynamic crosslinked systems employing di-functional crosslinkers, such network based on tri-functional crosslinker exhibits significantly improved crosslinking density, improved tensile strength (3.5 MPa), and elongation at break (312%), as well as faster stress relaxation without increased activation energy. The multi-functional junctions effectively suppress the formation of dangling chains with promoted network rearrangement, enabling efficient reprocessing with up to 75% retention of tensile strength. This work highlights the functional numbers of junctions as a critical design parameter to overcome the crosslinking limitations in low-functionality elastomers, offering a generalizable approach to fabricating high-performance, recyclable EPR-based materials.