Ultrasonic and viscoelastic relaxation in solutions of poly (2,6-dimethyl-p-phenylene oxide)

Abstract

Acoustic relaxation in dilute solutions of poly (2,6-dimethyl-p-phenylene oxide) in toluene is due to conformational change between states which are not exactly isoenergetic, but for which ΔH°= 400 ± 100 J mol^–1 and –6 × 10^–7 < ΔV° < –5 × 10^–8 m³ mol^–1. The relaxation frequencies are rather low, being ∼ 3 MHz at 313 and 333 K, with a temperature dependence less than the experimental error (± 0.3 MHz over 20 K).

Viscoelastic relaxation in the solutions occurs in the frequency range 10⁴–10⁵ Hz, and at 10⁶ Hz normal mode viscous processes make a negligible contribution to the acoustic absorption. The frequency dependence of the viscoelasticity is sharper than expected for very flexible long chains, and indicates that the restricted mobility of chain segments observed in the acoustic, and other, experiments reduces the number of normal modes contributing to the high frequency end of the viscoelastic loss spectrum.