Dynamic viscoelastic properties of Vulcan XC 72 (excess conductive carbon black)-reinforced solid- and closed-cell microcellular controlled long chain branching grade oil-extended EPDM (Keltan 7341A) rubber vulcanizates were studied at four frequencies of 3.5, 11, 35, and 110 Hz, and at a temperature range of -100 to 160 degrees C. The effect of blowing agent (ADC 21) loading on storage modulus (E') and loss tangent (tan 5) was studied. The log of storage modulus bears a linear relationship with the log of density for both solid and microcellular rubber. Relative storage modulus (E-f'/E-s') decreases with decrease in relative density (rho(f)/rho(s)). Both E' and tan delta were found to be dependent on frequency and temperature. The master curves of the storage modulus versus log temperature-reduced frequency were formed by superimposing E' results and by using shift factors calculated by Arrhenius equation. Strain-dependent isothermal dynamic viscoelastic properties were carried out for dynamic strain amplitude of 0.08-7%. Cole-Cole plots of microcellular vulcanizates show a circular arc with blowing agent (density). Empirical relationship between tan delta versus E' is found to be linear, whose slope is independent of blowing agent loading or density. (c) 2006 Wiley Periodicals, Inc.