Nature of Molecular Mobility Through the Glass Transition in Poly(n‐Alkyl Methacrylates): A Study by Dielectric Spectroscopies

For improving the understanding of molecular mobility through the glass transition, we compare results obtained by two dielectric techniques, dynamic dielectric spectroscopy (DDS) and thermo‐stimulated currents (TSC), for a series of amorphous model polymers, the poly(n‐alkyl methacrylates). This permits us to determine the effect of chain structure on relaxations appearing in the glass transition temperature range. This study confirms that the secondary relaxation is not influenced by the alkyl chain length. Contrarily, with increasing alkyl group length, the glass relaxation is subject to internal plasticization and its activation enthalpy decreases. The liquid–liquid relaxation is also shifted to lower temperatures, and we note a crossover of its behavior law. From these results, we then propose a phenomenological model describing the nature of molecular mobility through the glass transition.