MODE-COUPLING ANALYSIS OF AMORPHOUS PET

Dielectric relaxation data on amorphous poly(ethylene terephthalate) ( PET) from the literature have been analysed within the framework of th e mode-coupling theory (MCT). The critical temperature, T-c, was deter mined to be 355 +/- 2 K, in agreement with earlier studies. The spectr a give evidence for a dependence on temperature that differs above and below T-c; for T > T-c, the beta-minimum is well described by the ide alised A(2)-version of the MCT, yielding an exponent parameter, lambda = 0.82. Below T-c, the lower frequency part of the beta-peak shows a crossover between two different power laws, in qualitative agreement w ith MCT predictions. In this temperature range both the idealized and extended A(2)-MCT fail to fit the data. We argue that the dielectric s pectrum is distorted by an A(3) singularity, and by applying the MCT w ith the A(3) scenario, quantitative agreement between theory and exper iment is found over a wide frequency range for all temperatures availa ble. (C) 1998 Elsevier Science B.V. All rights reserved.