Polystyrene-Grafted Silica Nanoparticles: Investigating the Molecular Weight Dependence of Glass Transition and Fragility Behavior

Abstract

Polymer-tethered nanoparticles provide a strategy to improve particle dispersion in polymer nanocomposites and as materials themselves can exhibit self-healing behavior and enhanced mechanical properties. The few studies that previously characterized the glass transition temperature (Tg) behavior of neat polymer-grafted nanoparticles in the absence of a polymer matrix largely focused on average Tg response. We synthesized polystyrene-grafted silica nanoparticles (Si-PS) via ARGET ATRP, achieving the densely grafted state. Using differential scanning calorimetry, we investigated the brush molecular weight (MW) dependence of Tg, Tg breadth, heat capacity jump (ΔCp), and fragility from 12 to 98 kg/mol. Compared with free PS chains of the same MW, brush Tg increases by 1–2 °C, brush Tg breadth remains unchanged within error down to 36 kg/mol and increases by 3–4 °C at brush MWs of 12 and 13 kg/mol, and brush ΔCp and fragility remain unchanged within error down to 52 kg/mol and then decrease with decreasing MW...