Samples of melt‐quenched, amorphous poly(ethylene terephthalate), APET, annealed for up to four successive 30‐min intervals at 50°C, were analyzed by Fourier transform IR (FTIR) spectroscopy at room temperature. Results confirm earlier observations that the fraction of the gauche conformation of the ethylene glycol moiety increases upon annealing. This suggests a change toward a more random structure during the concomitant process of volume recovery. Spectra obtained after annealing for times to and beyond the onset of embrittlement, as judged from mechanical response, indicated that several distinct changes in band intensities occur during this time interval. Spectroscopic results for times longer than that required for embrittlement suggest an increase in motions associated with in‐plane vibrations located in and near the aromatic portions of the chains, as well as a decrease in out‐of‐plane vibrations. The overall results suggest that this method has potential for evaluating fast as well as slow recovery processes.
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Moore et al. (1981) studied this question.