Toughening Polymer Networks Via Topology Regulation: A Strategy Based on Restricted Reconfiguration of Dual Hindrance Urea Bonds

The effective reconfiguration ability of dynamic covalent bonds has raised wide interest in the reprocessing and recycling of thermosets. This study alternatively utilized a polymer network to restrict the reconfiguration of dual hindrance urea bonds (DHUBs) and developed a versatile strategy for toughening. The stepwise dissociation of DHUB was controlled by utilizing the specific reactivity of two secondary amino groups of 4,4′-bis( sec -butylamino)-dicyclohexylmethane (MDHA) as it reacted with aliphatic isocyanates. By constructing a cross-linking network with MDHA and HDI-trimer, the reconfiguration of the DHUB was restricted through thermal treatment of the network above the topology freezing transition temperature ( T V ), followed by quenching to well below the glass transition temperature ( T g ). Both the dual steric hindrance of MDHA and the frozen polymer segments trapped a fraction of the dissociated groups, preventing their rebonding, resulting in dangling chains and increased free volume. These features effectively enhanced energy dissipation, leading to a ca . 110–270% increase of the tensile toughness while retaining the original tensile strength and modulus. The toughened material offers excellent environmental stability along with well-preserved transparency. The effectiveness of this strategy was further demonstrated in multiple dynamic cross-linking networks, highlighting its broad applicability. This work offers a straightforward yet powerful methodology, grounded in rational molecular design, for fabricating high-performance thermosets with a balance of strength and toughness.