Thermodynamics and Stereochemistry of Diels–Alder Polymer Networks: Role of Crosslinker Flexibility and Crosslinking Density

Dynamic covalent polymer networks crosslinked through Diels–Alder (DA) reactions are promising self-healing, 3D-printable materials that have the unique ability to reshuffle their dynamic bonds in the solid state. Here, we identify main parameters that control furan/maleimide-based DA network reactions and relate them to shape reconfigurability. Thermodynamics of DA reactions were dominated by entropic effects, with more flexible crosslinkers leading to higher DA bond dissociation temperatures. Furthermore, the fraction of endo vs exo adducts increased with crosslinking density. Less thermally stable endo-attached crosslinks were exploited for shape reconfiguration via conversion to more stable exo adducts by thermal annealing between T_g and the dissociation temperature of the network. Moreover, repeatable network re-arrangements and material shape reconfiguration of more thermodynamically stable all-exo networks were achieved at a more elevated temperature.