Creep Resistant and Reprocessable Polyamide Networks Based on Reversible Lactone Ring‐Opening

Amides are robust chemical linkages of interest in the field of dynamic covalent polymer networks (DCPNs), but their activation towards dynamic exchange remains an outstanding challenge. Herein, we introduce γ-hydroxy amides as a versatile motif for the design of creep resistant, yet fully reprocessable crosslinked polyamide-based materials. This was achieved by the reversible ring-opening of γ-lactones with primary amines. Small molecule kinetic studies showed that temperatures exceeding 120 °C are required for the ring-closure to occur at a significant rate. Thus, efficient exchange of the γ-hydroxy amide bonds was expected upon heating, while essentially non-dynamic covalent amide bonds should prevail at lower temperatures. γ-Hydroxy amides were then introduced into DCPNs, for which a newly prepared bifunctional γ-lactone monomer was cured with amine hardeners. A marked thermal response was observed in the rheological behavior, while creep resistance comparable to that of a non-dynamic epoxy-amine network was maintained up to 120 °C. Finally, we could also demonstrate the thermal resilience of γ-hydroxy amides after multiple compression molding cycles for a material with a glass transition temperature above 80 °C. Consequently, we expect that this simple chemistry platform has high potential for application in reprocessable thermoset materials.