Segmental Dynamics of Ethylene Oxide-Containing Polymers with Diverse Backbone Chemistries

The dielectric response of seven nonionic ethylene oxide-containing polymers are investigated. Four different backbone chemistries are considered, including polymethacrylate, polyester ether, polyphosphazene, and polysiloxane. The chemistry of the backbone and the linking chemistry to incorporate ether oxygen (EO) groups dramatically affect polymer segmental dynamics. The T_g of the inorganic backbone polymers is ∼15 °C lower than that of the PEO homopolymer. Polysiloxanes exhibit the lowest T_g of -86 °C when attached with pendent -(CH₂-CH₂-O)₄-CH₃ groups. The strength of the alpha relaxation is the same for the hydrocarbon backbone polymers (Δε = 10), whereas the dielectric constants of inorganic polymers with short pendent groups is lower (Δε = 3). The difference in relaxation strengths is due to restricted motion of ether oxygens close to the backbone. This effect diminishes as the relative backbone concentration is decreased by increasing the pendent EO length. As pendent EO chain length is increased, the segmental relaxation broadens due to ether oxygens experiencing different local environments.