The application of dynamic covalent chemistries in network polymers has resulted in the development of a broad variety of stiumuli-responsive materials that rearrange their molecular bonds to accommodate physical stress.  These covalent adaptable networks (CANs) take advantage of two general bond rearrangement mechanisms.  Dissociative chemistries (e.g. reversible Diels Alder reactions) rely on the equilibrium between coupled, complementary reactive moieties and their unreacted counterparts. That equilibrium can be shifted by application of appropriate stimulus to modify the physical properties of the material.  The dynamic nature of associative chemistries (e.g. thiol-thioester exchange, addition fragmentation chain transfer reactions) results from existing bonds undergoing exchange with complementary unreacted functional groups, without which the network is functionally static.  A variety of dynamic chemistries have been employed in the design of CANs.  In our group, we have focused on those that can be triggered exogenously via exposure to light and, to a lesser extent, to heat.  The former is achieved via radical photoinitiation of those exchange reactions relying on a radical mechanism (e.g. addition fragmentation chain transfer and disulfide exchange reactions) and via employment of photolatent base catalysts for those exchange reactions employing an anionic-mediated mechanism (e.g. thiol-thioester exchange).  The differences in mechanism, both general and specific, as well as the diversity of potential stimuli, make the concept of covalent adaptable networks broadly applicable in the development of functional materials across a wide array of research and potential commercial materials interests.

Covalent adaptable networks in the design of functional materials

ACS Fall 2021

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