The βa anomaly shifts to higher temperatures with in-creasing frequency, reflecting the speeding up of polymer chain motions with temperature. Its temperature-frequency relationship is usually modeled with the Vogel-Fulcher (VF) law fm=f0×exp [−U/k(T−T0)] (inset in Fig. 6)[31], where fm represents the average relaxation frequency,Uisaconstant,andT0 is the Vogel temperature at which the relaxation process becomes frozen. Fitting the data in Fig. 6 leads to the following fitting parameters: f0 = 253 MHz, U = 5.55 kJ/mol = 0.0575 eV, and
T0=209.0 K. It should be emphasized that to precisely determine the parameters in the VF equation, very reliable fm data at temperatures close to T0, or at least close to the glass transition temperature Tg (Tg ≈ T0 + 30 ∼ 50◦C)
are required, which necessitate long time data acquisi-tion (i.e., the dielectric constant measured at near static conditions). Fitting the VF law without sufficient exper-imental data can generate significantly different f0, U,