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Low-Temperature Elastic Moduli and Dilational and Shear Internal Friction of Polycarbonate

Longitudinal and transverse wave velocity, and five kinds of elastic parameters (Young's, shear and bulk moduli, Lamè parameter, Poisson's ratio) for polycarbonate were simultaneously measured over a temperature range of 68 to 434 K, using the ultrasonic pulse method. All elastic moduli decrease with increasing temperature, suggesting the lowering of molecular bonding strength, accompanied by fluctuation of density due to loosely packed chains. From dilational and shear internal frictions, the 201, 313, 359 K peaks, an abrupt increase from 421 K and a decrease to 148 K are interpreted as free motion of carbonate group in the main chain (γ dispersion), motion of molecular chains between weak intermolecular bonds (β dispersion), dipole-dipole association between ester side chains (β' dispersion), glass transition (α dispersion) and a δ peak, respectively.