Toward Stimuli‐Responsive Dynamic Thermosets through Continuous Development and Improvements in Covalent Adaptable Networks (CANs)

Abstract

Covalent adaptable networks (CANs), unlike typical thermosets or other covalently crosslinked networks, possess a unique, often dormant ability to activate one or more forms of stimuli‐responsive, dynamic covalent chemistries as a means to transition their behavior from that of a viscoelastic solid to a material with fluid‐like plastic flow. Upon application of a stimulus, such as light or other irradiation, temperature, or even a distinct chemical signal, the CAN responds by transforming to a state of temporal plasticity through activation of either reversible addition or reversible bond exchange, either of which allows the material to essentially re‐equilibrate to an altered set of conditions that are distinct from those in which the original covalently crosslinked network is formed, often simultaneously enabling a new and distinct shape, function, and characteristics. As such, CANs span the divide between thermosets and thermoplastics, thus offering unprecedented possibilities for innovation in polymer and materials science. Without attempting to comprehensively review the literature, recent developments in CANs are discussed here with an emphasis on the most effective dynamic chemistries that render these materials to be stimuli responsive, enabling features that make CANs more broadly applicable.

Vitrimers: directing chemical reactivity to control material properties

“…A selection of chemistries is provided in our original mini-review and other related overviews and perspectives that recently appeared. [18][19][20][21] Very recently, Winne, Leibler and Du Prez also published a mechanistic perspective on the chemistry underlying vitrimers and dynamic covalent networks in general, with the attempt to clarify the sense and nonsense of distinguishing different types of bond exchange mechanisms, and their relation to mechanical properties. 22 Having established a broad toolbox of building blocks and chemistries that can be used to design vitrimers, researchers are now facing the challenge of gaining control over the reactivity prole, in order to rationally design materials with desired properties in terms of processability and recyclability.…”

Enhanced polymer mechanical degradation through mechanochemically unveiled lactonization

“…Strategies for dealing with this challenge include biodegradable/degradable polymers 1,2 , recyclable/reprocessable polymers [3][4][5][6] , and polymers made from renewable sources 7 . The advance of degradable polymers has been facilitated by the tactical introduction of a rich range of biodegradable or stimuli-degradable motifs into the backbone of linear polymers and/or the cross-linkers of polymer networks 2,[8][9][10][11][12][13] , the degradation of which often occurs in the presence of an external stimulus (e.g., heat, light, chemical, electricity).…”

The Use of Click-Type Reactions in the Preparation of Thermosets

“…However, to summarize them exhaustively is beyond the scope of this paper. Excellent reviews were published by Bowman's group [167,231,232], Du Prez's group [233] and, more recently, by Jin et al [234] and Scheutz et al [235]; the reader is encouraged to consult these publications for more in-depth information.…”