Effects of physical aging on the submicroscopic structure and dynamic mechanical properties of amorphous poly(ether sulfone) copolymer film were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and electron-microscopy measurements. Heat flow responses were measured after annealing the amorphous samples obtained, by quenching the melt into an ice-water bath close to but below the glass transition temperature. The extent of aging is related to the supercooling from the glass transition temperature and to the aging time. The activation energy of the aging process was estimated by the Williams-Watt expression (Williams and Watts, Trans Faraday Soc 1970, 66, 80). A systematic study of the influence of aging on the dynamic mechanical properties of poly(ether sulfone) copolymer has also been made. During isothermal annealing, the increase of the temperature of tan delta peak for the alpha and beta' relaxation with aging time has been observed. The aging in the zone of the delta peak has also been investigated and an interpretation of the results was proposed on the basis of foregone theories. The result of electron-microscopy investigation indicates that poly(ether sulfone) copolymer has formed a local order structure during the physical aging. (c) 2006 Wiley Periodicals, Inc.