Drastic Elevation in the Glass Transition Temperatureof Poly(2-vinylpyridine) by the Entanglement-Promoting Palladium Nanoparticles

A favorable interaction between the polymer matrix and nanoparticles (NPs) of a polymer-NP composite (PNC) is computationally predicted to raise a PNC’s glass transition temperature (<i>T</i>_g) and thus enhance its thermal stability. Yet, most PNCs fail the prediction and seldom exhibit >10 °C, if any, elevation in <i>T</i>_g; this <i>T</i>_g invariance is believed to result from the formation of a bound polymer layer on the NP surface. Here, we observe considerable <i>T</i>_g elevations, by as much as 73.7 °C relative to the neat polymer, for the PNCs made of entangled poly(2-vinylpyridine) (P2VP) and ∼3 nm Pd NPs, even though a bound P2VP layer is revealed by X-ray scattering to be present on the NP surface. A rheological and structural analysis suggests that the unprecedented <i>T</i>_g elevations stem from the entanglement-promoting effect of the NPs, which is in turn enabled by the NPs’ nanoscopic size and the strong matrix-NP interaction.