Exploring the orthogonal dynamic covalent imine and disulfide bonds in polymer systems

Abstract

In the field of supramolecular systems chemistry the desire of researchers to endow functional macromolecular systems with orthogonal stimuli-responsiveness has fueled interest in the incorporation of multiple orthogonal dynamic covalent chemistries within a single chemical system. Dynamic covalent chemistry involves reversible bond forming processes which can be harnessed in the development of dynamic supramolecular systems providing a mechanism for structural reconfiguration of system components in response to external stimuli. Despite the inspiring gamut of recently brandished studies, there is a still a call on the resourcefulness of chemists to expand the capacity for the introduction of multi-faceted, orthogonal, stimuli-responsive behaviors. Herein, a critical analysis of recently reported landmark studies has been undertaken wherein the utility of orthogonal dynamic covalent bonding motifs in functional systems is highlighted. Furthering the concepts of orthogonality with respect to dynamic covalent chemistry presented therein, a small molecule ‘model system’ was developed with which the orthogonality of imine and disulfide dynamic covalent bonds was demonstrated by its operation. A key focus of this preliminary work was the orthogonal bond forming and bond breaking processes of imine and disulfide dynamic covalent bonds. Upon the establishment of conditions necessary to exploit the orthogonal utility of imine and disulfide bonds, the incorporation of aldehydes, amines and thiols within acrylamide-based copolymers as pendant functional groups was achieved. These pre-formed functional polymer building blocks were shown to undergo stimuli-responsive intermolecular cross-linking in aqueous media yielding disulfide or imine cross-linked nanoparticles or hydrogels. The scope and utility of imine and disulfide bonds in the formation of these nanostructured materials is compared and contrasted. It is reasoned that expanding understanding and availability of dynamic covalent bonding motifs will facilitate evolution of systems of greater sophistication capable of embodying increasingly information-rich processes.