Abstract
We report ultrasonic relaxation measurements of amorphous bulk polybutadiene (\( \bar M_w = 13000 \) , T g =222 K) and poly(phenyl methyl siloxane) (\( \bar M = 5000 \) , T g =235 K) in the temperature range 280 K–360 K and frequency range 0.1–100 MHz. Complementary polarized photon correlation studies were performed on the same polybutadine sample.The acoustic parameters of longitudinal and shear wave experiments were interpreted in terms of localized segmental motions of the polymer chain, coherent subchain motion (“Rouse”-like chain modes) and effects of chain entanglements. The mean relaxation times of segmental motions in polybutadiene obtained from light scattering and ultrasonic data over nine decades in time conform to a single WLF equation.At temperature higher than T g , photon correlation spectroscopy detects slower relaxation modes, which based on the ultrasonic results seem to be related to subchain motions and/or entanglement effects.Key wordsPolybutadienepoly(phenyl methyl siloxane)viscoelastic functionultrasoundphoton correlationsegmental motionssubchain motionsentanglement
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