AbstractThe presence of a high temperature (>Tg) relaxation in amorphous polystyrene has been investigated further. In the previous work,1the techniques of differential thermal analysis (DTA) and torsional braid analysis (TBA) were employed to study polystyrene as a function of “monodisperse” molecular weight. The occurrence of theTlltransition appeared to be associated with the attainment of a critical viscosity level with also corresponded with a free volume level. An entanglement network developed at a critical value of molecular weight,Mc, giving a break in theTll‐versus‐Mplots. The present work deals with the influence of dispersity on theTlltransition, below and aboveMc. A series of binary blends of “monodisperse” anionically polymerized polystyrenes with systematic changes in M̄nand heterogeneity index (M̄w/M̄n) was tested by TBA. The results show that when both components have molecular weights belowMc, single and average values ofTgandTllare observed which are linearly related to M̄n−1, as predicted by free volume arguments. Although a singleTgis observed when one component has a molecular weight above and the other has a molecular weight belowMc, the components appear to undergo theTllrelaxation independently. The results indicate that both the glass transition and theTlltransition are basically governed by the same type of molecular motion but at differ
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