Molecular Control over Vitrimer-like Mechanics – Tuneable Dynamic Motifs based on the Hammett Equation in Polyimine Materials

We report the quantitative control over macroscopic dynamic material properties using the Hammett equation in dynamic (imine-based) polymer networks. Via this established physical-organic principle, operating on the molecular level, one can fine-tune and control dynamic material properties on the macroscopic level, by systematic variation of dynamic (covalent) bond dynamics through selection of the appropriate substituent of the aromatic imine building blocks.
Five tuneable, crosslinked polyimine network materials, derived from dianiline monomers with varying Hammett parameter (σ) were studied by rheology. We found a distinct, often linear correlation between the σ value and a range of dynamic material properties, including the kinetic activation energy for the imine bond exchange, the creep behaviour, the glass transition and topology freezing temperature. As a result, it was possible to tune the dynamic mechanical and thermal properties of dynamic covalent polyimines via the electronic effect of dianiline monomers based on the Hammett equation.
Lastly, the dynamic nature of the imine bond enabled recycling and intrinsic self-healing of the materials over multiple cycles without any external input.