Depolarized Rayleigh scattering and backbone motion of polypropylene glycol

The depolarized Rayleigh scattering spectra of polypropylene glycol in optically isotropic cyclohexane were studied as a function of polymer molecular weight, concentration, and temperature. The relaxation times were obtained by curve fitting the observed spectra to Lorentzian functions convoluted with the instrumental spectra. By studying the dependence of relaxation times on viscosity, temperature, and concentration and also comparing the results with theoretical predictions of molecular and sidegroup reorientations, we have associated the depolarized Rayleigh scattering spectra of polypropylene glycol with the segmental motion of polymer backbone. The relaxation times for dilute solutions were found to be larger than those for concentrated solutions. The relaxation times were also found to be independent of the molecular weights of the polymer. The depolarized Rayleigh scattering results were also compared with other types of relaxation studies.