Measurements of complex dielectric constant c*, shear viscosity , and complex shear modulus G* were carried out on narrow molecular weight distribution cis-polyisoprenes (cts-PI) to determine their dielectric relaxation, g(r), and viscoelastic relaxation, H(t), spectra. For each sample the spectra were compared over a wide range of time scale covering the wedge-type to the box-type region of the viscoelastic spectrum. The viscoelastic relaxation time, tv, agreed with the dielectric normal-mode relaxation time, , while the relaxation time at the maximum of the wedge-type spectrum agreed with the dielectric segmental-mode relaxation time, t8. In the wedge-type region, the slope of the log H(t) vs log plot changed at the time scale of the transition from the Rouse-like motions to the segmental motions as decreased.For unentangled cts-PIs with a molecular weight, Mw, less than the characteristic molecular weight, Mc, the observed agreed with the longest Rouse relaxation time calculated with i?o. For entangled cts-PIs with Mw > Mc, the shape of the spectra H(t) and g(r) differed in the terminal region.

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