Synthesis of Customizable Macromolecular Conjugates as Building Blocks for Engineering Metal–Phenolic Network Capsules with Tailorable Properties

Abstract

Metal–phenolic networks (MPNs), formed through coordination bonding between phenolic molecules and metal ions, are a promising class of materials for engineering particle systems for diverse applications. However, the properties of such MPNs are inherently restricted due to the finite properties of naturally occurring phenolic molecules. Herein, we report a simple and robust approach to incorporate phenolic moieties into polymers, thereby providing customizable phenolic ligand building blocks that can be used to assemble capsules with a range of tailorable properties. The phenolic ligand building blocks were synthesized via carbonic anhydride coupling to terminal amines, a conjugation approach typically used for peptide coupling but applied herein for functionalizing polymers. The chemistry enabled optimized end-group purity, thus affording a robust and efficient strategy to generate a library of macromolecular poly(ethylene glycol) (PEG) catechol building blocks with different architectures (i.e., 2-, 4-, and 8-arm) and molecular weights (from 2.5 to 20 kDa). The resulting phenolic building blocks were applied to fabricate capsules with shell thickness, permeability, and cell association properties that were controlled via the variation of the macromolecular catechol architecture and molecular weight. Specifically, the shell thickness was varied more than 19-fold (i.e., between ∼9 and 169 nm) by judicious selection of the polymer molecular weight, arm number, and template. Similarly, the permeability of the resulting MPN capsules to 500 kDa dextran was tuned from >90 to <5% by varying the number of arms in the polymer structure while maintaining a constant PEG Mn-to-catechol group ratio. Furthermore, the cell association was reduced by a factor of 2.5 by employing 20 kDa 8-arm PEG instead of 2.5 kDa 2-arm PEG during film assembly. These results demonstrate that the applied macromolecular conjugation approach can be used to customize particle properties, potentially facilitating applications in therapeutic delivery, imaging, separations, and catalysis.