PHYSICAL AGING OF AMORPHOUS LINEAR POLYESTERS

The physical aging of a series of linear amorphous polyesters (poly(pr opylene isophthalate), poly(propylene terephthalate), poly(ethylene te rephthalate), poly(dipropylene terephthalate) and poly(diethylene tere phthalate)) has been studied by differential scanning calorimetry. The se polyesters have been submitted to comparable aging temperatures bel ow the glass transition temperature, T-g:T-g - 27, T-g - 15 and T-g - 9(degrees C), for a period from 15 min to 480 h. The excess enthalpy o f aged samples, the relaxation time and the activation energy were cal culated. It was found that the polyesters with an ether group have bro ader peaks and a higher relaxation rate, that the methyl group seems t o increase the relaxation rate and that ring substitution can affect t he structural relaxation.