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Abstract Polymer‐brush‐grafted nanoparticles (PGNPs) that can be covalently crosslinked post‐processing enable the fabrication of mechanically robust and chemically stable polymer nanocomposites with high inorganic filler content. Modifying PGNP brushes to append UV‐activated crosslinkers along the polymer chains would permit a modular crosslinking strategy applicable to a diverse range of nanocomposite compositions. Further, light‐activated crosslinking reactions enable spatial control of crosslink density to program intentionally inhomogeneous mechanical responses. Here, a method of synthesizing composites using UV‐crosslinkable brush‐coated nanoparticles (referred to as UV‐XNPs) is introduced that can be applied to various monomer compositions by incorporating photoinitiators into the polymer brushes. UV crosslinking of processed UV‐XNP structures can increase their tensile modulus up to 15‐fold without any noticeable alteration to their appearance or shape. By using photomasks to alter UV intensity across a sample, intentionally designed inhomogeneities in crosslink density result in predetermined anisotropic shape changes under strain. This unique capability of UV‐XNP materials is applied to stiffness‐patterned flexible electronic substrates that prevent the delamination of rigid components under deformation. The potential of UV‐XNPs as functional, soft device components is further demonstrated by wearable devices that can be modified post‐fabrication to customize their performance, permitting the ability to add functionality to existing device architectures. 

In this Account, we describe our recent work in developing polymer brush coatings for nanoparticles, which we use to modulate particle behavior on demand, select specific nanoscopic architectures to form, and bolster traditional bulk polymers to form stronger materials by design. Distinguished by the polymer type and capabilities, three classes of nanoparticles are discussed here: nanocomposite tectons (NCTs), which use synthetic polymers end-functionalized with supramolecular recognition groups capable of directing their assembly; programmable atom equivalents (PAEs) containing brushes of synthetic DNA that employ Watson–Crick base pairing to encode particle binding interactions; and cross-linkable nanoparticles (XNPs) that can both stabilize nanoparticles in solution and polymer matrices and subsequently form multivalent cross-links to strengthen polymer composites. We describe the formation of these brushes through “grafting-from” and “grafting-to” strategies and illustrate aspects that are important for future advancement. We also examine the new capabilities brushes provide, looking closely at dynamic polymer processes that provide control over the assembly state of particles. Finally, we provide a brief overview of the technological applications of nanoparticles with polymer brushes, focusing on the integration of nanoparticles into traditional materials and the processing of nanoparticles into bulk solids.