Chain dynamics of ethylene oxide oligomer melts. An ultrasonic spectroscopy study

Between 0.2 and 2000 MHz, the ultrasonic attenuation spectra of oligomer melts have been measured at 25 °C. The oligomers comprise ethylene glycols with eight different mean degrees [Formula: see text]of polymerization (1 ≤ [Formula: see text] ≤ 13.2), a poly(propylene glycol) ([Formula: see text] = 16.9) and three poly(ethylene glycol) dimethyl ethers (3 ≤ [Formula: see text] ≤ 10.3). The complexity of the ultrasonic spectra increases with [Formula: see text]. The spectra have been analyzed assuming up to four discrete relaxation terms. The relaxation times of these terms are assigned to the first odd modes in the oligomer conformational dynamics and are discussed in the light of the Rouse spring-and-dashpot and the Tobolsky torsional oscillator models of chain variations. The relaxation amplitudes indicate that not only the shear viscosity but also the volume viscosity is involved in ultrasonic relaxation processes. Comparison of relaxation times and shear viscosities for the ethylene glycols with the corresponding data for dimethyl ethers and also n-alkanes reveals significant effects of association.