In situ absorbance of syndiotactic polystyrene (sPS) at elevated temperatures is investigated. The irradiation environments of air, vacuum and oxygen are considered. The decreasing loss in transmittance after irradiation follows the sequence: oxygen, air and vacuum. The UV cutoff and shoulder wavelengths of sPS irradiated in an air atmosphere are greater than those in vacuum. Two types of color centers are responsible for the reduction of transmittance in the irradiated specimen. They are annealable and permanent. A first order annihilation model is proposed to analyze the annealable color centers. The results show that the annealable color center of sPS irradiated in vacuum required to overcome less energy barrier to annihilate than that in air, but the permanent color centers in the former is less than those in the latter after annealing. No annealable color center is observed in sPS irradiated in an oxygen atmosphere. The EPR spectra and FTIR spectra were also studied to enhance the understanding of kinetics of color center. (c) 2005 Elsevier Ltd. All rights reserved.