Studies on the stress relaxation of polystyrenes in the rubbery‐flow region

Relaxation modulus curves for narrow distribution and broad distribution polystyrenes are compared and the significant effect of molecular weight distribution on these curves is shown. An empirical three‐parameter equation is shown to describe the stress relaxation behavior of narrow distribution polystyrenes. New data for high molecular weight, narrow distribution polystyrenes are presented and used to extend the applicability of previous quantitative relations for higher molecular weights. The stress relaxation technique is shown to be sensitive to the type of plasticizer used at low concentrations.