AbstractThe volatile‐component evaporation mechanism proposed by Chen et al. to explain molecular‐weight‐dependent endothermic peaks found at temperatures aboveTgin anionically prepared polystyrenes (PSs) on first heating in open DSC pans is inconsistent with several bodies of literature data which were overlooked, including similar data with closed DSC pans. Moreover, this mechanism appears deficient in explaining details of the dependence of the endothermic peak temperature on M̄nboth below and above the entanglement molecular weightMc, with a sharp increase in slope atMc. The original fusion–flow mechanism of Stadnicki et al. is compatible with all other known literature data including results on thermal PS and PMMA fractions. Hot‐stage microscope examination of powdered anionic PSs supports the Stadnicki mechanism from M̄n= 1900 to at least M̄n= 350,000. Addition of small amounts (ca. 1 wt %) of benzene or ethylbenzene to PS results in open‐pan DSC traces without endothermic peaks but with an endothermic slope change indicating gradual loss of diluent at decreasing rate as the temperature is increased from belowTgup throug