Consequences of Monomer Impurities on Network Characteristics and Dynamic Mechanical Behavior of an Eugenol-Based Covalent Adaptable Network

Abstract

Covalent adaptable networks are an emerging class of polymer networks that exhibit high potential for recyclability. For industrial applications, the robustness of material properties and predictable dynamic behavior are highly desirable. In this study, diepoxides of varying purity were used to prepare hybrid CANs. Hybrid CANs are based on dynamic vinylogous urethane bonds and permanent bonds formed by the reaction of amines and epoxides. The robustness of the materials dynamic exchange behavior against impurities that impair or modify the network characteristics was specifically investigated. Stress relaxation experiments reveal that the dynamic behavior remains relatively stable up to ca. 23% monomer impurity. At higher impurity levels, we observe pronounced changes of the exchange dynamics. All materials, regardless of purity, exhibit incomplete stress relaxation because of the significant fraction of permanent bonds. As a consequence, visible defects (old fragment boundaries) remain visible after reprocessing of the nominally purest materials. We found that the network density and glass transition temperature decrease with increasing impurity, while overall the thermal stability remains largely unaffected. The results demonstrate that hybrid CANs based on vinylogous urethane exchange chemistry can tolerate moderate monomer impurities without losing key dynamic properties, offering insights for industrial-scale processing and material design.