Relating glassy dynamics to fracture behavior in model covalent adaptable networks (CANs)

Covalent adaptable networks (CANs) have emerged as a promising new platform for high performance polymers and composites because they combine the mechanical and environmental robustness of thermosets with the reprocessability of thermoplastics. While numerous dynamic chemistries have been formulated and adapted for various thermoset substrates, detailed characterization of how dynamic covalent bonds affect network scale properties is still needed for deeper understanding of how these chemical changes translate to differences in thermomechanical behavior on the macroscale. To this end, a model system of epoxy-amine networks with varying concentration of dynamic, aromatic disulfide bonds in both epoxide and amine crosslinker components was synthesized and characterized with a variety of techniques. By correlating measurements of local properties like excess free volume and sub-T_g relaxations with structural performance like strength and fracture toughness, greater insight is gained for how network-scale engineering and design can be used to optimize this new class of materials for a range of demanding applications. One example is for using these materials to fabricate reprocessable epoxy concretes for structural applications in the extreme environment of the lunar surface.