Effect of entanglements on the glass transition behavior of polymer chains in a melt

In the present work, we study the effect of entanglements on the glass transition behavior of high molecular weight polymers, by comparing disentangled and entangeled melts of high molecular weight polystyrene of identical molecular weight. Single-chain-nanoparticles (SCNPs) were used to prepare the disentangled melt. The SCNPs were prepared by electrospraying technique and characterized using scanning electron microscope and atomic force microscope techniques. Glass transition temeprature (T_g) of disentangled and entangled polymer melts were measured using three different techniques: differential scanning calorimetry, Brillouin light spectroscopy and rheological experiments. We also performed bead-spring polymer model based molecular dynamics simulations. A recently developed approach was used to compare entangled and disentangled polymer melts under cooling. While our experiments suggest a small decrease in the glass transition temperature of films of nanoparticles in comparison to entangled melts, simulations do not observe any significant difference, despite rather different chain conformations.

We acknowledge active collaboration with Geroge Fytas and Heloise Therien-Aubin for this study.