Reversible covalent bonding has historically been used in the field of dynamic covalent chemistry to template receptors to various targets analytes. Recently, these thermodynamically strong bonding interactions, albeit kinetically labile, have been used in a large number of polymeric architectures, imparting self-healing and adaptable structures. Our group has shown that five pairings of Tunable Orthogonal Reversible Covalent (TORC) bonds can be used in a variety of chemical assembly projects. For example, in collaborations within our four research groups, reversible covalent bonds involving aldehydes and hydrazides have been shown to drive tin-doped indium oxide nanocrystals (NCs) assemblies, imparting gel structures that affect infrared optical properties arising from localized surface plasmon resonance of the NCs. Further, the use of reversible thia-Michael conjugate acceptors can be used to control poly(ethylene glycol) based hydrogel backbones.  The tunability of the conjugate acceptor via alternation of substituents controls the on- and off-rates of the thiol, thereby altering the rheology, stress-relaxation, and hydrogel stiffness.  Moreover, using a bis-thia-Michael acceptor “click” unit,  a series of polymers and gels can adapt new morphologies in-situ simply by addition of new cross-linkers, monomers, or oxidants, as well as lead to complete degradation of the polymer by adding a “declicking” agent.  Lastly, these responsive polymers and gels can be applied to sensing applications, wherein the addition of various analytes lead to auto-inductive cascades that result not only in optical responses, but also degradation of physical barriers that facilitate mixing of solutions. The design of TORC bonding units, their use in controlling NC assemblies, polymers, and gels, as well as applications to sensing, will all be covered.

Use of tunable orthogonal reversible covalent (TORC) bonding to control polymer morphology and nanocrystal assembly

ACS Spring 2022

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