Dielectric relaxation spectroscopy of reactively blended amorphous poly(ethylene terephthalate)-poly(ethylene naphthalate) films

Reactively blended poly(ethylene terephthalate)-poly(ethylene naphthalate) films of different compositions and degrees of ester exchange reaction have been investigated by dielectric relaxation spectroscopy. The alpha -relaxa tion peaks associated with the glass transition have been fitted by the sem i-empirical Havriliak-Negami relaxation function to frequency scans. The pa rameter relating to relaxation broadness, beta, and the relaxation strength , Delta epsilon, were quantified and were found to be a parameter sensitive to processing conditions. Both values were affected on a molecular level b y concentration fluctuation and the molecular chain architecture (such as p olymer chain blockiness). Molecular coupling of the blends was determined f rom the slope of log frequency maxima vs. reduced temperature T-g/T, as com monly done in coupling theory analysis. It was found that the initial mater ials, PET and PEN show very similar coupling behaviour. Molecular coupling of the blends was little affected by the blend composition or the degree of transesterification. Activation energies of molecular motions have also be en determined and show a positive deviation from the rule-of-mixtures avera ges of the homopolymers which indicates greater chain hindrance to motion o f both blocky or the random copolymers formed by the transesterification pr ocess. (C) 2000 Elsevier Science Ltd, All rights reserved.