Brillouin, Rayleigh, and depolarized Rayleigh scattering studies of polypropylene glycol. I

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Abstract
A comprehensive light scattering study of an important polymer—polypropylene glycol, HO−[CH(CH3) −CH2O]n−H—having an average molecular weight of about 425 (PPG 425) was carried out. From the polarized spectra, the velocity and attenuation coefficient of the longitudinal hypersound as a function of temperature were determined. Measurements of the velocity and attenuation coefficient indicate the presence of molecular relaxations between 250−390°K. A maximum in the sound attenuation vs temperature curve was observed. The Landau−Placzek ratio over a wide range of temperatures was also measured and compared with the theory of Litovitz and co−workers on the relaxing molecular liquid over a wide temperature range. Depolarized scattering studies were also carried out. The molecular reorientation time and activation energy are determined from the spectral linewidth measurement as a function of temperature. Depolarization ratios (ρv and ρh) were determined. The Krishnan effect was observed at temperatures below 296°K.