Dielectric relaxation of amorphous random copolymers of poly(ethylene terephthalate) and poly(ethylene‐2,6‐naphthalene dicarboxylate)

The dielectric constant and dielectric loss values have been determined in the 103‐106 Hz frequency range for amorphous random copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene‐2,6‐naphthalene dicarboxylate) (PEN). The dielectric behaviour has been interpreted in terms of the Havriliak‐Negami formulation. On this basis the variation of the dielectric properties with temperature has been qualitatively related mainly to two processes: The α process which is associated to the glass transition of the polymer and depends on the molar ratio of PET and PEN. The β process which is assigned to a local motion of the ‐COO groups attached to the aromatic rings. The existence of a β* process in between the α and the β processes has been observed in PEN at low frequencies. The relaxation time spectrum has been discussed in terms of molecular structure alterations. Finally, the temperature variation of the relaxation time is analyzed in the light of various predictions.