In this work, an attempt has been made to define a unique relaxation time spectrum for different types of polymeric materials. Empirical models for the relaxation spectrum, proposed for linear flexible polymers in the literature, have been used. A systematic determination of the parameters defining the relaxation time spectrum has been made from dynamic mechanical data. It has been shown that the resulted expression for the relaxation modulus could then be used to calculate the stress response of the materials to various deformations. The strain rate dependence of yield behavior could also be predicted.