SynopsisThe nonsteady flow behavior of a Characterized commercial polystyrene has been examined in a compressed-nitrogen-gas piston viscometer. Nonst,eady flow data were erratic with virgin polymer at 173.9"C. Pretreatment of the polystyrene by subjecting the melt to a higher temperature, with or without shear, changed the nature of the time-dependent flow to that which is generally characteristic of polymers in experiments of this type. The pretreatment had no significant effect on the equilibrium flow curve a t the same temperature nor on the molecular weight of the polystyrene. The results are interpreted in terms of changes in the size or nature of snpermoler\ilar flow units.
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