Dielectric spectroscopy of the characterization of the structure of amorphous polymeric materials

Thermally stimulated current spectroscopy has been applied to the characterization of the structure of amorphous polymers such as polycarbonate. The existence of a sub-T_g mode that is very sensitive to local order, induced by thermal treatment, has been shown. The dielectric manifestation of the glass transition has been resolved into two components. The lower-temperature one (α₁ ) is always observed, independently of the thermodynamic history of the polycarbonate. The corresponding relaxation times follow a compensation law with a compensation temperature given for the reference state by the empirical relationship found for semicrystalline polymers. On the other hand, the upper temperature one (α_u) is only observed after annealing above T_g. It is also characterized by a compensation law indicative of the existence of a segregated phase. It has been assigned to ordered nodules of some 20 to 40 Å, previously observed by electron microscopy and X-ray diffraction