BRILLOUIN-SCATTERING FROM OLIGOMERS OF POLYDIMETHYLSILOXANE AND THE ASSIGNMENT OF THE HYPERSONIC A LOSS PEAK IN POLYMERS

Hypersonic sound speed and loss have been measured in poly(dimethylsiloxane) fluids of viscosities 0.65 to 3.5 × 104 centistoke. Both rise to a plateau level for viscosity values in excess of ∼10 centistokes. Loss measurements as a function of temperature indicate that the α loss temperature (Tα) in the dimer is depressed below 180K compared to 230K in the high molecular weight materials. This molecular weight dependence of Tα is used to account for the hypersonic loss as a function of molecular weight in polystyrene and polypropylene glycol in addition to the assignment of the α loss peak in polydimethylsiloxane. © 1979.