Neighboring Group Participation in Ionic Covalent Adaptable Networks

Covalent adaptable networks (CANs) typically require external catalysts for efficient cross-linker exchange, which can limit network reprocessability due to catalyst leaching and degradation. In this study, catalysts were avoided by using a bicyclo[3.3.1]nonane bis-alkyl halide cross-linker with sulfur-atom neighboring group participation (NGP) to increase the rate of bond exchange. Stress relaxation analyses demonstrate that the resultant pyridine-based network has an Arrhenius dependence on viscous flow at elevated temperatures (130-170 °C), which arises from S_N1 transalkylation exchange. This thermally mediated cross-link interchange and associated flow behavior enabled reprocessing of the ionic networks over multiple damage and repair cycles. Additionally, these NGP-based CANs are chemically recyclable, allowing for recovery of the pyridyl-based polymer starting material, which comprises >90 wt % of the parent network. The dual thermal and chemical recycling potential of this catalyst-free CAN platform addresses key criteria for designing thermosets with extended lifecycles.