Characterization of molecular mobility in covalent adaptable networks

Covalent adaptable networks (CANs) are crosslinked polymer networks that contain molecular moieties capable of covalent bond rearrangement upon exposure to a specific stimulus. This molecular restructuring imparts greater rheological control over traditional thermosets, allowing the creation in recent years of materials with superior stress relaxation, fatigue resistance, shape memory, and actuation properties. While molecular scale mobility is a key characteristic of CANs, very little work exists explicitly examining the phenomenon of transport through these networks. In this work, diffusion of small molecules and macromolecules in a dynamic network is characterized. Fluorescence recovery after photo-bleaching (FRAP) is used to evaluate differences in diffusivities of fluorescent molecules within a nucleophile-catalyzed thiol-thioester exchange CAN compared to a traditional thermoset of similar composition and crosslinking density. The effects of fluorophore size compared to network mesh size (crosslinking density) are evaluated for both the CAN and traditional thermoset. This work provides insights into the molecular underpinnings of CANs’ rheological behavior, with applications in membranes, drug delivery, and separations.