Studies of molecular relaxation of poly(propylene oxide) solutions by dielectric relaxation and brillouin scattering

Abstract

Dielectric relaxation and Brillouin scattering are jointly used in studying molecular relaxation in poly(propylene oxide) (PPO) and its solutions in methylcyclohexane. The dielectric method was applied to the more concentrated (100%, 80%, 60%, by volume) solutions over a wide temperature and frequency range (30 Hz to 8 GHz) in order that the variation in activation energy characteristic of a glass‐forming substance could be delineated. The present work extends previous work on the undiluted polymer to higher frequencies so that range of 12 decades in the dielectric loss maximum fmax as a function of temperature is now available. The “Antoine” equation is found to represent the behavior of log fmax, of the bulk concentrated solutions very well. The more dilute (40%, 20%) solutions were studied only in the high‐frequency (GHz) region since phase separation occurred at low temperatures. Both the temperature and dilution effects were interpreted in terms of free‐volume theory. Brillouin scattering spectra were obtained at several scattering angles and a wide range of temperatures. A maximum in the curve of hypersonic attenuation versus temperature was observed in each polymer solution. The attenuation maximum shifts toward lower temperature upon dilution, in agreement with the dielectric relaxation result. The Brillouin scattering follows different activation parameters and evidences a more rapid process than does the dielectric relaxation. It is speculated that it monitors a secondary or subglass relaxation, due perhaps, to damped torsional oscillations.

Rayleigh–Brillouin scattering studies of segmental fluctuations in poly(siloxanes)

“…The spectral fit provides the a' and TS values at these temperatures. Similar to that found in alcohols, I3 the TS values obtained at temperatures around the linewidth maximum follows the Arrhenius temperature dependence: with 'To and Ea determined from the spectra around the linewidth maximum, and assuming Ws = w~ (I -bT) (20) determined from the high temperature Brillouin frequency data, one can now simultaneously fit the experimental values of IB and r Busing Eqs. (17) and (18), keeping only Rand r b as free parameters.…”

Physical nature of complex structural relaxation in polysiloxane – PMpTS: α and α′ relaxations

“…In 1976 Yano et al [5] reported new dielectric data on PPO in bulk and solutions in methylcyclohexane. The dielectric relaxation (DR) measurements were performed in a very broad range of frequencies (log f max (Hz) ¼ À3 to 9.5) and were combined with Brillouin scattering.…”

Acoustic Relaxation of Liquid Poly(tetramethylene oxide) with Hydroxyl and Acyl Terminal Groups

“…However, PPO, because of its noncrystallizability and availability in a wide molecular weight range, is acceptable as a model object for close examination of relaxation properties of flexible chain polymers. Its relaxation characteristics, basically those of the corresponding low molecular weight OH-ended analogue, so-called poly(propylene glycol) (PPG), have been intensively studied using dielectric, [1][2][3][4][5][6] optical, 7-10 nuclear magnetic resonance (NMR), [11][12][13] quasi-elastic neutron scattering, 14,15 and ultrasonic, [16][17][18][19][20][21] techniques, as well as various methods for probing viscoelastic properties. [22][23][24] In contrast to PPO, PEO and PTMO are possible to crystallize and they can be closely investigated only in a temperature range above the melting point.…”