Enhancing the Equilibrium of Dynamic Thia-Michael Reactions through Heterocyclic Design

Although the catalyst-free dynamic thia-Michael (tM)reaction hasbeen leveraged for a range of significant applications in materialsscience and pharmaceutical development, exploiting its full potentialhas been limited by relatively low equilibrium constants. To addressthis shortcoming, a new series of catalyst-free, room-temperaturedynamic thia-Michael acceptors bearing an isoxazolone motif were developedand utilized to access both dynamic covalent networks and linear polymers.By leveraging the generation of aromaticity upon thiol addition andtuning the electronic-withdrawing/donating nature of the acceptorat two different sites, a wide range of equilibrium constants (K (eq) & SIM;1000 to & SIM;100,000 M-1) were obtained, constituting a 2 orders of magnitude increase comparedto their noncyclic benzalcyanoacetate analogues. Integration intoa ditopic isoxazolone-based Michael acceptor allowed access to bothbulk dynamic networks and linear polymers; these materials not onlyexhibited tailorable thermomechanical properties based on thia-Michaelacceptor composition, but the higher K (eq) tM bonds resulted in more mechanically robust materials relativeto past designs. Furthermore, solution-state formation of linear polymerswas achieved thanks to the increased K (eq) of the isoxazolone-based acceptors.