Linear polydienes differing in molecular weight as well as in konstitution (vinyl, cis-1,4-butadiene, styrene units) show significant changes in the dynamic mechanical storage and loss moduli. For a given constitution, the reptation time T rep is related to the molecular weight by a characteristic power law. The universal exponent 3.4 is understandable on basis of molecular models. With higher side group density, the plateau modulus G(N) decreases due to lower entanglement density. The plateau modulus was found to be proportional to the inverse-square of the chain cross-sectional area and also to the inverse-cubic of the packing length.