Relaxation Dynamics of Poly(ethylene oxide) Elucidated by the Coupling Model

The relaxation dynamics of poly(ethylene oxide) has been studied repeatedly in the past decades. The study is continued to the present time because the dynamics including the secondary relaxation, the segmental relaxation, and the terminal chain dynamics are determining factors in many different applications of this polymer. Notwithstanding, these relaxation processes found by mostly dielectric experiments vary greatly in their properties, and were interpreted differently and contradictorily in the past. This untenable situation of research in poly(ethylene oxide) is resolved by the results of a detailed investigation of this polymer by dielectric spectroscopy, covering an unprecedented broad frequency and temperature range [Lunkenheimer and Loidl, Macromolecules 2025, 58, 3547]. Three important processes were found and identified by them as (1) a normal mode relaxation of the polymer chains individually with relaxation times τ_α′(T), not considered in previous works; (2) the segmental α relaxation with relaxation times τ_α(T); (3) the slower secondary relaxation with relaxation times τ_β(T), widely overlooked in previous studies. These experimental results challenge theories for explanation of the properties of the processes revealed. In this paper the predictions of the coupling model (CM) are applied quantitatively to prove the observed slower secondary relaxation is the universal Johari–Goldstein β-relaxation, and the normal mode relaxation is from the cooperative relaxation of entangled PEO chains. Rheological data of the terminal relaxation time τ_e(T) of entangled PEO, together with data of PEO tracer diffusion in an entangled PEO matrix, help to confirm the CM predictions. The difference of the temperature dependence of τ_α′(T) or τ_e(T) from that of τ_α(T) is identified and explained quantitatively.