Elastic behavior of polymers: Anharmonic and relaxational effects

The behavior with temperature of the dynamic elastic modulus E' in pure poly(ethylene) oxide and poly(ethylene) oxide-potassium thiocyanate solid blends in the region below and at the glass-to-rubber transition is explained in terms of two physical contributions: the first is due to the anharmonicity of vibrational modes; the second to the ?a or primary relaxation that arises from the cooperative segmental motions of the polymeric chains in the amorphous phase of the polymer. The strengths of both contributions show a strong dependence on the degree of crystallinity of the polymer, which has been varied over a wide range by altering the composition. The highest values of the parameters characterizing the two mechanisms are observed when the addition of the potassium salt makes the system completely amorphous. An average relaxation time ??? is obtained by the evaluation of the ?a relaxation in terms of the stretched exponential or Kolrausch-Williams-Watts function ?(t)=exp{-(t/?)?}, where 0