How to Characterize Covalent Adaptable Networks: A User Guide.

Since the seminal works on thermoreversible covalent networks followed by the discovery of vitrimers by L. Leibler and co-workers in 2011, numerous chemistries and strategies have flourished to design covalent adaptable networks (CANs) thus opening a novel research field. Using reversible covalent bonds that have been known for decades in molecular chemistry, CANs combine both the rheological characteristics of thermosets (chemically cross-linked networks, insoluble and infusible) and those of thermoplastics (entangled polymer chains able to be dissolved and to flow above their glass transition temperature). The aim of this tutorial review is to provide polymer chemists with guidelines to precisely and properly characterize CANs. Depending on the nature of the exchange mechanism (dissociative, associative, or a combination of both), on the kinetics of exchange, and on the cross-link density, characteristic relaxation times can vary from less than a second to a few hours. The time scale and distribution of relaxation times influence the rheological experiments and models that should be used. The present didactic review provides, from the rich recent literature, a guideline for adequate material characterizations and rheological measurements (and theoretical models applicable) that have been used to study CAN viscoelastic and thermomechanical properties.