Mechanical Properties of Epoxy Networks with Metal\nCoordination Bonds: Insights from Temperature and Molar Mass Variation

We investigate the\nthermal and mechanical properties of poly(ethylene\nglycol), PEG, networks with either solely covalent epoxy bonds (single\nnetworks, SNs) or coexisting epoxy and iron–catecholate bonds\n(dual networks, DNs). The latter has recently been shown to be a promising\nmaterial that combines mechanical strength with significant deformability.\nHere, we address the previously unexplored effects of the temperature\nand PEG precursor molar mass on the mechanical properties of the networks.\nWe focus on PEG molar masses of 500 g/mol, where crystallization is\nsuppressed, and 1000 g/mol, where some weak crystals are formed. SNs\nsoften with an increasing PEG molar mass. Heating reversibly softens\nthe DN, but it has a minimal effect on SNs. Nonlinear shear deformation\nof the DN breaks iron–catecholate bonds, and subsequent recovery\nupon shear cessation occurs to a long-time steady-state modulus whose\nvalue is almost triple the original one, likely due to the formation\nof tris-complexes versus initial sterically or kinetically trapped\nbis-complexation. The response under elongation indicates that the\nDN with sacrificial bonds is stiffer and more extensible than the\nother networks. These results may provide guidelines for designing\ndual networks with tunable mechanics at the molecular level.