Topology-Driven Interfacial Behavior in Polymer-Grafted Nanoparticles: Loop versus Linear Architectures

The performance of polymer nanocomposites is strongly influenced by polymer–nanoparticle compatibility and dispersion quality, as the interfacial dynamics often deviate significantly from bulk behavior. Motivated by the enhanced miscibility observed in ring–linear polymer blends, we designed and synthesized loop poly(methyl methacrylate) (PMMA)-grafted chains on silica nanoparticles (NPs) to investigate the effect of topological architecture on interfacial properties. Loop-grafted NPs were fabricated from linear-grafted precursors by replacing the chain transfer agent with a thiol functional group, enabling intramolecular “click” reactions between proximal chain ends and an alkene functional linker. Differential scanning calorimetry revealed an increase of approximately 28 °C in the glass transition temperature (T_g) of loop-grafted PMMA relative to its linear-grafted precursor, suggesting more restricted chain mobility at the interface. To elucidate the topological effects on interfacial behavior, we prepared athermal PMMA nanocomposites with identical nanoparticle core loadings, dispersing both loop- and linear-grafted NPs in PMMA matrices. Thermal and dielectric analyses consistently revealed a significant increase in T_g for the loop-grafted composite driven by enhanced interfacial friction and improved mixing arising from its complex interfacial architecture. These findings suggest that the interfacial chain topology in the form of loops can improve phase compatibility and could inform the design of polymer nanocomposites with tunable mechanical and dynamic properties.