Broadband Dielectric Spectroscopy of Polymers with Hidden β Relaxation

Gustavo Dominguez-Espinosa , Ricardo Díaz-Calleja and Evaristo Riande
Macromolecules 2006, 39, 5043 -5051

This work reports the relaxation behavior of amorphous polymers the spectra of which do not explicitly present the secondary β relaxation. Poly(2,4-difluorobenzyl methacrylate), a polymer with complex motions in the side groups, was chosen to carry out this study. The apparent distribution of retardation times of the polymer calculated from dielectric loss isotherms in a wide range of temperatures (T > Tg) presents two peaks which do not merge into a single absorption at moderate temperatures. The β absorption appearing as a shoulder of the α relaxation in global thermal stimulated depolarization current experiments is not at first sight detected in the retardation spectra. Separation of the hidden β absorption from the longest time peak in the retardation spectra was carried out by fitting the inverse of the Havriliak−Negami equation to the peak using b = 1 and b