Although the catalyst-free dynamic thia-Michael (tM)
reaction has
been leveraged for a range of significant applications in materials
science and pharmaceutical development, exploiting its full potential
has been limited by relatively low equilibrium constants. To address
this shortcoming, a new series of catalyst-free, room-temperature
dynamic thia-Michael acceptors bearing an isoxazolone motif were developed
and utilized to access both dynamic covalent networks and linear polymers.
By leveraging the generation of aromaticity upon thiol addition and
tuning the electronic-withdrawing/donating nature of the acceptor
at two different sites, a wide range of equilibrium constants (Keq∼1000 to ∼100,000 M–1) were obtained, constituting a 2 orders of magnitude increase compared
to their noncyclic benzalcyanoacetate analogues. Integration into
a ditopic isoxazolone-based Michael acceptor allowed access to both
bulk dynamic networks and linear polymers; these materials not only
exhibited tailorable thermomechanical properties based on thia-Michael
acceptor composition, but the higherKeqtM bonds resulted in more mechanically robust materials relative
to past designs. Furthermore, solution-state formation of linear polymers
was achieved thanks to the increasedKeqof the isoxazolone-based acceptors.