INFLUENCE OF STATIC STRAIN ON THE DYNAMIC MECHANICAL-PROPERTIES OF POLY(DIETHYLENEGLYCOL ISOPHTHALATE) NETWORKS

Time-dependent mechanical properties of small amplitude were superimposed on strained poly(diethyleneglycol isophthalate) networks. The tan δ loss peak associated with the glass-rubber relaxation shifts to lower temperatures as the static strain increases for values of the elongation ratio λ lower than 4, suggesting that volume effects overcome entropic effects in this region. However, for values λ>4, the opposite occurs. The activation enthalpy is a linear function of the activation entropy, but the compensation law does not hold in the present system. Information on network topology is obtained by analyzing the experimental results using theories that predict the value of the loss modulus as a function of the generalized momenta of the elastic chains.