Dielectric Investigations of Poly(Propylene oxide) in the Liquid Region Above T _g

Abstract

Transitions and relaxations in poly(propylene oxide) (PPO) have been extensively studied by dynamic mechanical^1–3 and dielectric^4–7 methods. The molecular weight range of poly(propylene oxide) investigated by dynamic mechanical methods is much larger (400–1,000,000) than the range studied by dielectric methods (400–4,000). Both the dynamic mechanical and dielectric data have always been presented as a function of frequency or reduced frequency. Dielectric studies on poly(propylene oxide) oligomers by Baur and Stockmayer⁷ showed two dispersions in ε′ and ε″. The high frequency process corresponds to the segmental motion at the glass transition and the low frequency process corresponds to the motion of the entire polymer molecule. The maximum in ε″ for the glass transition temperature dispersion is invariant with the molecular weight of PPO, whereas the maximum in ε″ corresponding to the “slow process” moves to lower frequencies and becomes more diffuse with increasing molecular weight. Although Yano et al.⁸ reported the dielectric loss as a function of temperature, they were only interested in the T _g loss peak and not the T >T _g peak. McCammon and Work⁵ were also interested only in the T _g and T>T _g peaks in their dielectric studies. In addition, they used a high molecular weight, partially crystalline PPO in their investigations. Creep, creep recovery, and dynamic mechanical measurements as a function of frequency by Cochrane et al.⁹ and Barlow and Erginsav¹⁰ in the 10³–10⁸ Hz region and dielectric data of Alper et al.¹¹ for PPO of nominal molecular weight 4,000, showed the existence of a slow process attributed to the motion of the entire polymer molecule.