To investigate the thermally activated structural change of polyetherimide, longitudinal and transverse wave velocity, six kinds of elastic parameters (Young's, shear, and bulk moduli, Lame parameter, Poisson's ratio, and Debye temperature), and dilational and shear internal frictions were simultaneously measured over a temperature range 69-474 K using the ultrasonic pulse method. All elastic moduli decreased with increasing temperature, suggesting a lowering of molecular bonding strength. From shear internal friction, the 190, 314, 371, 395, and 430 K peaks are interpreted as the gamma-[derived from -C(=O)- motion], beta(1)*-(interplane slippage between benzene rings), beta- (softening-glass transition) peaks, and rotational vibration of main benzene rings and a local relaxation of the main chain, respectively. The abrupt increase peak from 449 K in dilational friction would be a low-temperature side shoulder of the alpha-glass-transition peak. (C) 2003 Wiley Periodicals, Inc.