Dynamics of Six Generations of PAMAM Dendrimers As Studied by Dielectric Relaxation Spectroscopy

Broadband dielectric relaxation spectroscopy (DRS) was employed to study molecular dynamics of the first six generations of poly(amidoamine) (PAMAM) dendrimers with ethylenediamine core and amino surface groups. DRS was performed over a wide range of frequency and temperature. Dendrimers show distinctly different relaxation behavior below and above the temperature of −30 °C, which roughly corresponds to their calorimetric Tg. Three relaxation processes are observed below −30 °C, and an explanation of their molecular origin is provided. The interplay between molecular architecture and hydrogen bonding was found to have an effect on dielectric relaxation that is not found for dynamic mechanical relaxation. All those processes are characterized by Arrhenius-like temperature dependence. Above −30 °C, the spectra are dominated by conductivity and are analyzed using the dielectric modulus and conductivity formalisms. The average relaxation time for the segmental process was calculated from the dielectric loss m...