Molecular engineering in four dimensions: a mechanistic approach to reprocessable elastomers

In dynamic covalent polymer networks known as vitrimers, the topology is reconfigured through associative exchange reactions. These materials hold promise as repairable and recyclable thermosets and elastomers. The Kalow Lab combines physical organic approaches and mechanical characterization to interrogate the relationship between the molecular exchange chemistry and flow in reprocessable elastomers. These studies are enabled by the use of crosslinks that exchange via a catalyst-free conjugate addition/elimination pathway. We find that stiffness and stress relaxation rate can be decoupled and independently modulated by synthetically tuning the cross-linker and prepolymer backbone, respectively. Our studies reveal the importance of internal catalysis in accelerating exchange reactions, which has inspired our design of switchable cross-linkers.