In order to learn the influence of entanglements and other factors on the structural changes of atactic polystyrene, freeze-dried single-chain samples were prepared from dilute solutions of atactic polystyrene (a-PS) in benzene at different concentrations (1×10^－4 and 2×10^－5 g/mL). In this study, the annealing process of the above-mentioned samples at various temperatures for different periods of time has been investigated using Fourier transform infrared (FTIR). According to the IR spectroscopy, when annealing at the temperature of 210 ℃, the peak area of δ(CH₂) bands first decreased gradually and did not change any more till some certain moment. That is because during annealing, the a-PS chains got together and their entanglements increased gradually and finally approach to a stable configuration like the bulk sample. The concentration and temperature dependent of the entanglements are also discussed in this study. The results of FTIR spectra were further analyzed by two-dimensional (2D) correlation method to study the intra- and inter-chain entanglements of the a-PS samples. The asynchronism of the bands assigned to the vibration of benzene ring and CH₂ bending bands indicates that during the annealing process the accumulation of chain structure occurs earlier than the intra- and inter-chain entanglements of the above-mentioned a-PS samples.

Key words: atactic polystyrene, freeze-dried, infrared spectroscopy, entanglement, two-dimensional correlation analysis