Viscoelastic properties of polymers. 4. Thermorheological complexity of the softening dispersion in polyisobutylene

The viscoelastic behavior of a high molecular weight polyisobutylene has been revisited to investigate the unique high-frequency peak (or shoulder) seen in the loss tangent behavior in the glass to rubber softening dispersion. Creep measurements made in the temperature range -74 to +27 °C were initially reduced to a curve, which, upon transformation from the time to the frequency domains, yielded a loss tangent peak with no hint of any shoulder. The original creep compliance curves were rescrutinized independently, and slight variations in the derivatives of the curves revealed the elusive high-frequency loss peak. Additional dynamic measurements were made to connect the transformed creep data to some of the original Fitzgerald, Grandine, and Ferry data [J.Appl.Phys. 1953, 24, 911]. The combined results cover over 9 decades of frequency. This extensive range revealed that the mechanisms contributing to the high-frequency peak have a different temperature dependence than that of those contributing to the main loss peak.