DYNAMIC SHEAR MEASUREMENTS OF PHYSICAL AGING AND THE MEMORY EFFECT IN A POLYMER GLASS

the real and imaginary parts of the dynamic shear modulus, G prime and G double prime , respectively, of 10% and 30% poly(2,6-dimethyl-1,4-phenylene oxide)-polystyrene (PPO-PS) blends were measured from 10** minus **3 to 1 Hz during physical ageing up to 10**6 s. In the first experiment, isothermal ageing after cooling the samples from the rubbery to the glassy state, G prime increased and G double prime decreased monotonically with time at a rate that increased with decreasing frequency. In the second experiment, isothermal ageing of samples that had undergone densification during their previous ageing at a lower temperature, G prime first decreased then increased and G double prime first increased and then decresed, showing a minimum and maximum, respectively. The occurrence of minima and maxima is a reflection of the 'memory effect' observed earlier by others in the volume and refractive index studies of glasses.