Enhancing hydrolytic stability of dynamic imine bonds and polymers in acidic media with internal protecting groups

Abstract

Imine bonds are among the most explored building motifs in dynamic chemistry, polymers, and materials, and yet, their acid-resistance remains a longstanding issue. Herein we demonstrate a concept of internal protecting groups for improving the kinetic stability of dynamic imine bonds and polymers. Systematic examination of structure-reactivity relationship of a series of aldehydes/imines bearing a neighboring carboxyl allowed uncovering of required structural features for dynamically masking imine bonds with cyclic structures. Mechanistic studies indicated that noncovalent interactions along with sterics control the ring-chain equilibrium and the stability of imine bonds. The incorporation of internal protecting groups into imine polymers further enabled their controlled stability in acidic media. Moreover, a combination of dynamic covalent network and coordination supramolecular network provided a facile means for the modulation of luminescent and mechanical properties of polymers. The strategies and results reported should be beneficial to molecular assemblies, dynamic polymers, biological delivery, and intelligent materials.