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Abstract
The dynamic properties of amorphous polymers were investigated during long-term ageing by means of high resolution low-frequency mechanical spectroscopy. Two polymers are considered in this work, namely atactic polystyrene and quenched amorphous poly(ethylene naphthalate). It is shown that during ageing at temperatures higher than that of secondary relaxation, but lower than that of the primary one (if tested at 1 Hz), the strength of the secondary relaxation first increases and then decreases for long ageing times. This phenomenon is explained on the basis of the concepts of the heterogeneous cohesion of the amorphous network at the nanometric scale and the cooperation of molecular motions responsible for the secondary relaxations.
