Nanocomposite tectons (NCTs) are a recently developed building block for polymer–nanoparticle composite synthesis, consisting of nanoparticle cores functionalized with dense monolayers of polymer chains that terminate in supramolecular recognition groups capable of linking NCTs into hierarchical structures. In principle, the use of molecular binding to guide particle assembly allows NCTs to be highly modular in design, with independent control over the composition of the particle core and polymer brush. However, a major challenge to realize an array of compositionally and structurally varied NCT-based materials is the development of different supramolecular bonding interactions to control NCT assembly, as well as an understanding of how the organization of multiple supramolecular groups around a nanoparticle scaffold affects their collective binding interactions. Here, we present a suite of rationally designed NCT systems, where multiple types of supramolecular interactions (hydrogen bonding, metal complexation, and dynamic covalent bond formation) are used to tune NCT assembly as a function of multiple external stimuli including temperature, small molecules, pH, and light. Furthermore, the incorporation of multiple orthogonal supramolecular chemistries in a single NCT system makes it possible to dictate the morphologies of the assembled NCTs in a pathway-dependent fashion. Finally, multistimuli responsive NCTs enable the modification of composite properties by postassembly functionalization, where NCTs linked by covalent bonds with significantly enhanced stability are obtained in a fast and efficient manner. The designs presented here therefore provide major advancement for the field of composite synthesis by establishing a framework for synthesizing hierarchically ordered composites capable of complicated assembly behaviors.

Summary:The governing parameters controlling the glass transition temperature of polymer-grafted particle systems are analyzed for the particular case of polystyrene (PS)-grafted silica colloids in the dense grafting limit. At a given degree of polymerization of surface-grafted chains the glass transition temperature is found to increase as compared to linear chain polymers of equivalent degree of polymerization. The difference in the glass transition temperature between polymer-grafted particle systems and their respective linear polymer analogs increases with decreasing degree of polymerization of surface-grafted chains and levels off at similar plateau values for particle brushes of distinct particle core size. The trend toward increased glass transition temperature is interpreted as a consequence of the increased steric hindrance in polymer-grafted particles that counteracts the relaxation of surface-grafted polymer chains. The increase in glass transition temperature is shown to be approximately consistent with the chain conformational regimes that are predicted on the basis of a Daoud-Cotton type scaling model.

Filler aggregation in polymer matrix nanocomposites leads to inhomogeneity in particle distribution and deterioration of mechanical properties. The use of polymer grafted nanoparticles (PGNPs) with polymers directly attached to the particle surfaces precludes aggregation of the filler. However, solids composed of PGNPs are mechanically weak unless the grafted chains are long enough to form entanglements between particles, and requiring long grafts limits the achievable filler density of the nanocomposite. In this work, long, entangled grafts are replaced with short reactive polymers that form covalent crosslinks between particles. Crosslinkable PGNPs, referred to as XNPs, can be easily processed from solution and subsequently cured to yield a highly filled yet mechanically robust composite. In this specific instance, silica nanoparticles are grafted with poly(glycidyl methacrylate), cast into films, and crosslinked with multifunctional amines at elevated temperatures. Indentation and scratch experiments show significant enhancement of hardness, modulus, and scratch resistance compared to non-crosslinked PGNPs and to crosslinked polymer films without nanoparticle reinforcement. Loadings of up to 57 wt% are achieved while yielding uniform films that deform locally in a predominantly elastic manner. XNPs therefore potentially allow for the formulation of robust nanocomposites with a high level of functionality imparted by the selected filler particles.

Nanocomposite filler particles provide multiple routes to mechanically reinforce pressure-sensitive adhesives (PSAs), as their large surface area to volume ratios provide a means of effectively crosslinking multiple polymer chains. A major advancement could therefore be enabled by the design of a particle architecture that forms multiple physical and chemical interactions with the surrounding polymer matrix, while simultaneously ensuring particle dispersion and preventing particle aggregation. Understanding how such multivalent interactions between a nanoparticle crosslinking point and the PSA polymer affect material mechanical performance would provide both useful scientific knowledge on the mechanical structure−property relationships in polymer composites, as well as a new route to synthesizing useful PSA materials. Herein, we report the use of polymer-grafted nanoparticles (PGNPs) composed of poly(nbutyl acrylate-co-acrylic acid) chains grafted to SiO 2 nanoparticle (NP) surfaces to cohesively reinforce PSA films against shear stress without compromising their adhesive properties. The use of acrylic acid-decorated PGNPs allows for ionic crosslinking via metal salt coordination to be used in conjunction with physical entanglement, yielding 33% greater shear resistance and up to 3-fold longer holding times under static load. In addition, the effects of material parameters such as PGNP/crosslinker loading, polymer graft length, and core nanoparticle size on mechanical properties are also explored, providing insights into the use of PGNPs for the rational design of polymer composite-based PSAs.

Polymer‐grafted nanoparticles (PGNPs) are ideal additives to enhance the mechanical properties and functionality of a polymer matrix and can even potentially serve as single‐component building blocks for highly filled composites if the polymer content is kept low. The major challenge facing such syntheses is that PGNP‐based solids with short polymer brushes often have low mechanical strength and limited processability. It therefore remains difficult to form robust architectures with a variety of 3D macroscopic shapes from single‐component PGNP composites. Forming covalent bonds between cross‐linkable PGNPs is a promising route for overcoming this limitation in processability and functionality, but cross‐linking strategies often require careful blending of components or slow assembly methods. Here, a transformative aging strategy is presented that uses anhydride cross‐linking to enable facile processing of single‐component PGNP solids via thermoforming into arbitrary shapes. The use of low Tg polymer brushes enables the production of macroscopic composites with >30 vol% homogeneously distributed filler, and aging increases stiffness by 1–2 orders of magnitude. This strategy can be adapted to a variety of polymer and nanofiller compositions and is therefore a potentially versatile approach to synthesize nanocomposites that are functional, mechanically robust, and easily processable.