Time dependent-measurements of the dynamic shear modulus in the splitting region a,--,~ + fl of poly(n-butyl methacrylate) (PnBMA) and poly(ethyl methacrylate) (PEMA) are reported. Non-equilibrium effects in the frequency-temperature region around the onset of the ct transition are discussed. Physical ageing effects on the intensity, shape and position of the ~ and fl peaks of the shear loss modulus are reported. For the relaxation a shift of the mean relaxation frequency to lower values, a peak sharpening, and an increase in intensity during ageing are observed, whereas the fl intensity decreases significantly. Long times are necessary to reach the equilibrium state a few kelvins below the onset temperature (~ glass transition temperature for PnBMA). A small amplitude fine structure was found in the frequency sweeps at temperatures below the onset temperature, which is discussed in terms of McCrum's sequential ageing.
Посилання на статтю:
Ageing effects on dynamic shear moduli at the onset of the dynamic glass transition in two poly(alkyl methacrylate)s / M. Beiner, F. Garwe, K. Schr6ter and E. Donth // Polymer. – 1994. – Vol 35. – P. 4127-4132.