PHYSICAL AGING OF AMORPHOUS LINEAR POLYESTERS

The physical aging of a series of linear amorphous polyesters (poly(propylene isophthalate), poly(propylene terephthalate), poly(ethylene terephthalate), poly(dipropylene terephthalate) and poly(diethylene terephthalate)) has been studied by differential scanning calorimetry. These polyesters have been submitted to comparable aging temperatures below 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 of aged samples, the relaxation time and the activation energy were calculated. It was found that the polyesters with an ether group have broader peaks and a higher relaxation rate, that the methyl group seems to increase the relaxation rate and that ring substitution can affect the structural relaxation.